We introduce a deep learning-based hybrid beamforming (HBF) strategy for millimeter-wave transmission systems, specifically addressing the challenges posed by phase noise of local oscillators. Our approach utilizes a deep neural network to optimize precoding and combining matrices based on channel state information. We incorporate the symbol index through an adaptive attention mechanism and employ a self-supervised learning approach with a phase-noise-aware loss function to mitigate the effects of phase noise. While primarily focused on phase noise, our method also accommodates other practical constraints, such as limited-resolution phase shifter and imperfect channel estimation. Simulation results demonstrate that our design outperforms traditional and deep-learning based HBF methods in terms of data rate both in scenarios impacted only by phase noise and compounded distortion scenarios including low-resolution phase shifters and channel estimation errors.

Rate-splitting multiple access (RSMA) has been proposed as a flexible multiple access scheme for improving interference management in sixth-generation (6G) networks. In particular, the low latency facilitated by RSMA and its robustness against user mobility and imperfect channel state information make it an ideal candidate for the ultra-reliable and low-latency (URLLC) use case in 6G networks. However, since the common message in RSMA needs to be decoded by all the users, the achievable rate of the common message is determined by the user with the poorest channel quality. To overcome this bottleneck, an active intelligent reflecting surface (IRS) can be deployed to enhance the achievable rate of the common stream. However, this comes at the expense of additional power consumption due to the active IRS. In this paper, we consider an active IRS-aided RSMA-based downlink URLLC system and study the resource allocation design for minimization of the power consumption of the base station and the active IRS under quality-of-service constraints for the URLLC users. Our simulation results reveal that active IRSs yield a lower overall power consumption and require a smaller surface size compared to passive IRSs in RSMA-based URLLC systems. Moreover, we show that active IRS-aided RSMA systems consume less power than active IRS-aided space division multiple access (SDMA) systems.

Nonterrestrial networks (NTNs) complement the terrestrial cellular networks by extending coverage to the user equipments (UEs) located in unserved and underserved areas. One of the most critical problems faced by NTN UEs is the lack of uplink (UL) synchronization and the associated initial access failure resulting from the high Doppler frequency offset caused by satellite velocity. While NTN new radio (NR) UEs rely on the global navigation satellite system (GNSS) to resolve the UL synchronization problem, it is not always feasible for power-critical NTN Internet of Things (IoT) UEs. To this end, we design synchronization signal-based positioning in IoT NTNs (SPIN) which enables the IoT UEs to tackle the UL synchronization problem. SPIN estimates position and velocity of the UE using time difference of arrival (TDOA) and frequency difference of arrival (FDOA) measurements on the downlink synchronization signals. Consequently, the UEs can use the position and velocity estimates to compute and compensate for the residual time and frequency offsets, thereby successfully synchronizing to the NTN UL. We conduct physical layer and system-level simulations to show the effectiveness of our solution. SPIN positioning accuracy achieves the Cramér-Rao lower bound and meets the target accuracy required for UL synchronization. We also compare the battery life of an NTN IoT UE which uses SPIN for UL synchronization with that of a UE using GNSS-based solution. Our numerical results show that SPIN has significant battery life savings over GNSS-based solution while also maintaining a low computational complexity.

The spectrum scarcity in the radio frequency (RF) communication in indoor environments motivates the integration of an alternative technology like visible light communication (VLC) with the existing RF architecture that results in a hybrid RF/VLC network. While VLC helps offloading the congested RF spectrum by offering capacity-per-area improvements, the resulting heterogeneity and narrow coverage areas of optical base stations (BSs) impose several challenges for user mobility such as unnecessary handovers. To help addressing these challenges, in this paper, we derive the mean and the distribution of sojourn time in RF/VLC hybrid networks. The mathematical analysis conducted in this paper makes use of the tools from stochastic geometry and abstracting the BSs’ locations via two independent homogeneous Poisson point processes (PPPs). Since PPP modeling is yet to be well established for RF/VLC hybrid networks, we compare the PPP based analytical results to those obtained for an actual deployment, a Matérn hard-core point process (MHCPP) based deployment, and a deterministic square lattice deployment of VLC luminaries. Furthermore, we utilize the sojourn time distribution to calculate the unnecessary handover probability. Our numerical results show the interplay between the sojourn time and the receiver field of view as a function of BS density and they highlight the cost of BS densification in terms of unnecessary handovers.

This paper considers the downlink of a cloud radio access network (C-RAN) consisting of a central processor (CP) and a network of connected radio units (RUs). We propose a novel resource allocation solution for the scenario with full-duplex (FD) self-backhauling RUs connected through hybrid radio-frequency (RF)/free-space optical (FSO) links to the CP for improved network throughput. This enables us to study the feasibility of the FD mode in terms of required self-interference cancellation to outperform the benchmark half-duplex hybrid RF/FSO transmission. Since the derived optimization problem for the design of the linear precoders and quantizers subject to the fronthaul capacity, zero-forcing, and power constraints, is non-convex and intractable, we develop an algorithm to solve it via an alternating optimization approach. In the simulation results, the proposed hybrid RF/FSO policy is assessed in terms of achievable rate, and we highlight the parameter range for which FD transmission is more rewarding than the time-division approach, under different weather conditions and selected RF bandwidth.

Massive machine-type communication (mMTC) is one of the most rewarding and at the same time challenging components in the fifth-generation (5G) cellular solutions supporting the Internet of Things (IoT). The 5G mMTC is considering the use of a combination of two key mMTC enabling technologies-grant-free (GF) transmission and nonorthogonal multiple-access (NOMA), called GF-NOMA, which can potentially exploit the advantages of both schemes. A primary challenge in GF-NOMA is to reduce the packet drop rate. Owing to the decentralized nature of the GF schemes and the lack of control over user equipment, only hybrid automatic repeat request (HARQ) Type I has been employed for enhancing the reliability of GF-NOMA so far. In this article, uplink GF-NOMA transmission schemes using HARQ Type III are proposed. Two types of packet combining-1) chase combining and 2) incremental redundancy combining are considered. Moreover, we introduce a GF single-transmission (GFST) scheme where all redundancy versions of the packet are transmitted in one shot. We present a comprehensive evaluation of both the GF and the conventional grant-based methods in mMTC scenarios and demonstrate the superiority of our proposed methods over the existing ones.

Device-to-device communication (D2D) is a key enabler for connecting devices together to form the Internet of Things (IoT)[1]. A growing issue with IoT networks is the increasing number of IoT devices congesting the spectral resources of the cellular bands. Operating D2D in unlicensed band alleviates this issue by offloading network traffic from the licensed bands, while also reducing the associated licensing costs. To this end, we present a new low-cost radio access technology (RAT) protocol, called sidelink communications on unlicensed bands (SCUBA), which can be implemented on cellular devices such that it coexists with the legacy cellular protocol by operating as a secondary RAT in a time division multiplexed manner using the existing radio hardware. SCUBA is compatible on different types of cellular devices including the low-complexity half-duplex frequency-division duplex machine type communication (MTC) user equipments. SCUBA provides flexible sidelink (SL) latency and battery life tradeoff using a discontinuous reception procedure, which ensures that it is applicable across a wide range of use cases. We prove the effectiveness of our protocol with analyses and simulation results of the medium access control layer of SCUBA using different types of MTC traffic for both SL and the underlying cellular communication.

Microwave backhaul links are characterized by high signal-to-noise ratios permitting spectrally-efficient transmission. The used signal constellation sizes and achievable data rates are typically limited by transceiver impairments, predominantly by phase noise from non-ideal carrier generation. In this article, we propose a new method to improve the data rate over such microwave links. We make use of the fact that adjacent frequency channels are inactive in many deployment scenarios. We argue that additional data can be transmitted in the skirts of the spectral mask imposed on the transmission signal by regulation. To accomplish this task, we present a shaped wideband single-carrier transmission using non-Nyquist pulse shapes. In particular, we design spectrum-skirt filling (SSF) pulse shaping filters that follow the spectral mask response, and perform detection using an accordingly increased sampling frequency at the receiver. We evaluate the achievable information rates of the SSF-based transmission considering practical dispersive channels and non-ideal transmitter and receiver processing. To compensate for phase noise impairments, we derive carrier phase tracking and estimation techniques, and utilize them in tandem with nonlinear precoding which mitigates the intersymbol interference introduced by the non-Nyquist SSF shaping filter. Quantitative performance evaluations show that the proposed system design achieves higher data rates in a dispersive microwave propagation environment with respect to the conventional transmission with Nyquist pulse shaping.

This paper considers the application of widely linear (WL) receivers in an uplink multi-user system using real-valued modulation schemes, where the cellular base station (BS) with multiple antennas provides connectivity for randomly deployed single-antenna users. The targeted use case is massive machine type communication (mMTC) with grant-free access in the uplink, where the network is required to host a large number of low data rate devices transmitting in an uncoordinated fashion. Four types of WL receivers are investigated, namely the WL zero-forcing (ZF) and the WL minimum mean-squared error (MMSE) receivers, along with their enhanced versions employing successive interference cancellation (SIC) with channel-dependent ordering, i.e., the WL-ZF-SIC and WL-MMSE-SIC receivers. The outage performances of these receivers are analytically characterized in the high signal-to-noise ratio (SNR) regime and compared to those of conventional linear (CL) receivers using complex-valued modulation schemes. For the non-SIC receivers, we show that, when compared to the CL counterparts, the WL receivers yield a higher diversity gain when decoding the same number of users and have the same diversity gain but a decreased coding gain when the number of users is nearly doubled. The outage performance analysis of WL-SIC receivers is facilitated by the marginal distribution of ordered eigenvalues of a real-valued Wishart matrix. It is shown that the SIC operation with channel-dependent ordering brings no additional diversity gain to the WL receivers but instead increases the coding gain. Moreover, the coding gain of WL-SIC receivers grows as the number of users increases and even exceeds that of CL-SIC receivers under suitable conditions. For the mMTC scenario with grant-free transmission, it is demonstrated that the WL receivers outperform their CL counterparts in terms of offering a lower outage (and packet drop) probability and a higher system throughput for a given packet drop probability.

The integration of visible light communication (VLC) with existing radio frequency (RF) networks has emerged as a new network architecture to meet the rapidly growing traffic demand. The resulting RF/VLC hybrid network structures offer capacity-per-area improvements due to the use of two technologies operating at different frequency bands and the relatively higher base station (BS) density. However, the reduced BS coverage footprints and the heterogeneous BS types result in challenges for user mobility such as frequent handovers and the need for suitable BS association policies. To help addressing these challenges, in this paper, we conduct a user mobility analysis for RF/VLC hybrid networks by deriving the user-to-BS association probabilities and handover rates. The analysis makes use of stochastic geometry and modeling BSs’ locations via a Poisson point process (PPP). Since PPP modeling has not yet been well established for hybrid RF/VLC networks, we support the applicability of our approach by comparing the user mobility performance to those obtained for an actual deployment, a Matérn hard-core point process (MHCPP) based deployment, and a deterministic square lattice deployment of VLC luminaries. Furthermore, since the handover rates directly depend on the association policies, we consider two popular association policies. Our numerical results show that the PPP, the MHCPP, the square lattice, and the actual deployments have comparable performance in terms of handover rates regardless of the association policy, and they highlight the tradeoff between balancing network load and handover rates achieved by the association policies.

Faster-than-Nyquist (FTN) transmission employs non-orthogonal signaling to improve spectral efficiency over conventional orthogonal transmission at the Nyquist rate. However, FTN signaling also introduces inter-symbol interference (ISI), which must be mitigated through additional signal processing.In this paper, we present a scalable FPGA-based architecture for a turbo maximum-a-posteriori (MAP) equalizer based on the Bahl-Cock-Jelinek-Raviv (BCJR) algorithm to mitigate the ISI. In contrast to many existing hardware implementations of BCJR, where the algorithm performs turbo decoding over a binary alphabet for an already-equalized channel, our FPGA design applies BCJR to non-binary signal constellations and for the task of equalization. To the best of our knowledge, this is the first published FPGA-based BCJR equalizer implementation suitable for FTN applications, where a binary forward-error-correction decoder is employed in tandem with the equalizer.Through careful tradeoff selection and optimization of the design space, our implementation achieves a maximum per-PE throughput of 602 Mbps, and a total of 15.4 Gbps within the constraints of a Xilinx UltraScale+(xcvu13p) device.

Minimizing the resynchronization time in Long-Term Evolution for Machine Type Communications (LTE-M) is highly desirable to enhance the battery lifetime of low-power and possibly deep-coverage user equipments (UEs) targeting Internet-of-Things (IoT) applications. This has led the 3rd Generation Partnership Project (3GPP) to initiate a work item in Re1-15 LTE-M to improve cell search and/or system information acquisition time. This has been accomplished by developing a new resynchronization signal (RSS) that can be detected during relatively short device wake-up times and with low computational effort. In this paper, we review the design aspects that have been considered while deriving the new RSS signal and describe the RSS design that has been adopted by 3GPP. Moreover, we propose another RSS design and show the differences between the proposed design and the one adopted by 3GPP in terms of the detection performance and the computational and memory complexity. Finally, we highlight the gains resulting from employing the new RSS design compared to the legacy synchronization signals.

Device-to-device (D2D) communication finds widespread applicability in enabling connectivity for the Internet of Things. Leveraging the unlicensed frequency bands for D2D communication reduces the spectrum licensing costs, and offloads network traffic from the limited licensed spectral resources. Towards achieving a cost-efficient solution, we study the feasibility of integrating such a D2D operation in the unlicensed band (D2D-U) within legacy cellular devices as a secondary radio access technology in a time division multiplexed manner. To this end, we evaluate the constraints faced in incorporating D2D-U in various challenging environments, such as within devices that use a single radio architecture and a half-duplex with frequency division duplexed cellular operation. We propose time instances that can be exploited to multiplex D2D-U without violating regulatory restrictions imposed on using different unlicensed frequency bands. Based on our analyses and simulation results, we suggest guidelines for a prospective D2D-U protocol that can achieve efficient sidelink communications while also ensuring coexistence with legacy cellular operation.

Future wireless cellular communication networks are expected to provide connectivity for massive machine-type communication (mMTC) devices. The main challenge of supporting mMTC traffic for a cellular network lies in the high density of these devices, which individually have relatively little data to transmit. This suggests the use of low overhead, grant-free access scheme for uplink data transmission, which, however, suffers from packet collisions when devices attempt to access the channel. In this article, we suggest the use of real-valued transmission together with widely linear (WL) reception for improving resource access and thus data throughput in the uplink of mMTC traffic scenarios. We show that not surprisingly, the WL scheme can virtually double the number of receive antennas at the base station (BS). We analyze the effect of this on the supported user density and data throughput for grant-free uplink transmission. As a specific example, we consider the narrowband Internet-of-Things (NB-IoT) cellular communication system, which already includes real-valued modulation modes. Our numerical results show that the supported user density and data throughput of grant-free NB-IoT systems can be significantly improved due to the use of WL receivers. For example, considering an NB-IoT system with 1% packet drop probability, we obtain a tenfold (for single-antenna BS) and a sixfold (for dual-antenna BS) increase in the supported user density by using WL receivers instead of their conventional linear counterparts.

We investigate the problem of coded caching for nonuniform demands when the structured clique cover algorithm proposed by Maddah-Ali and Niesen for decentralized caching is used for delivery. We apply this algorithm to all user demands regardless of their request probabilities. This allows for coding among the files that have different request probabilities but makes the allocation of memory to different files challenging during the content placement phase. As our main contribution, we analytically characterize the optimal placement strategy that minimizes the expected delivery rate under a storage capacity constraint. It is shown that the optimal placement follows either a two or a three group strategy, where a set of less popular files are not cached at all and the files within each of the other sets are allocated identical amounts of storage as if they had the same request probabilities. We show that for a finite set of storage capacities, that we call the base-cases of the problem, the two group strategy is always optimal. For other storage capacities, optimal placement is achieved by memory sharing between certain base-cases and the resulting placement either follows a two or a three group strategy depending on the corresponding base-cases used. We derive a polynomial time algorithm that determines the base-cases of the problem given the number of caches and popularity distribution of files. Given the base-cases of the problem, the optimal memory allocation parameters for any storage capacity are derived analytically.

Narrowband Internet of Things (NB-IoT) is one of the most prominent low power wide area (LPWA) technologies to support massive connections among low-cost devices with enhanced coverage. Addressing the further increase in the number of supported connections in IoT applications, we investigate the use of real-valued modulated signals together with widely linear detection (WLD) to NB-IoT. In this paper, we show that the use of WLD to resolve collisions of two simultaneously transmitted real- valued signals generated from two user equipments (UEs) enhances the capability of NB-IoT systems to facilitate massive connectivity. More specifically, to demonstrate the performance improvements, we analyze the uplink transmission reliability and the device density supported in NB-IoT systems with WLD in a grant-free scenario. The numerical results show that, for a 1% probability of decoding failure, the supported device density can be increased by one order of magnitude compared to that of conventional complex-valued signalling schemes.

The power line is inherently a broadcast medium when used for data transmission, since the electricity grid has no well defined boundaries for communication signals. This broadcast nature of the channel leads to mutual interference of communication signals emitted in relative proximity. To overcome the rate-limiting effect of this interference, recently the concept of interference alignment (IA) has been applied to power line communications (PLC). In particular, the benefits of IA have been shown for transmission in multi-input multi-output (MIMO) PLC systems. However, the results were obtained under the assumption of independent noise at the different ports of the PLC receiver. Unlike for most wireless communications scenarios for which IA has usually been studied, this assumption is often not valid for MIMO PLC. In particular, due to the dominance of noise signals induced and broadcast from grid-connected devices as well as the signal cross-coupling in PLC networks, noise is often found to be spatially correlated. Therefore, in this paper we explore the performance of IA for MIMO PLC in the presence of correlated noise obtained from indoor measurements. To this end, we adopt the maximum signal- to-interference-plus-noise ratio IA algorithm, whose formulation includes the noise statistics. Numerical results quantify the effect of noise correlation on the achievable sum-rate for MIMO PLC with IA.

Coded caching is an effective technique to reduce the redundant traffic in wireless networks. The existing coded caching schemes require the splitting of files into a possibly large number of subfiles, i.e., they perform coded subfile caching. Keeping the files intact during the caching process would actually be appealing, broadly speaking because of its simpler implementation. However, little is known about the effectiveness of this coded file caching in reducing the data delivery rate. In this paper, we propose such a file caching scheme that uses a decentralized algorithm for content placement and either a greedy clique cover or an online matching algorithm for the delivery of missing data. We derive approximations to the expected delivery rates of both schemes using the differential equations method, and show them to be tight through concentration analysis and computer simulations. Our numerical results demonstrate that the proposed coded file caching is significantly more effective than uncoded caching in reducing the delivery rate. We, furthermore, show the additional improvement in the performance of the proposed scheme when its application is extended to subfile caching with a small number of subfiles.

In this work, joint design of fronthaul compression and precoding in cloud radio access networks (C-RANs) is studied for full-duplex (FD) multiple-input multiple-output (MIMO) underlay cognitive radio networks. In this system, multiple secondary uplink (UL) and downlink (DL) users equipped with multiple antennas communicate with a control unit (CU) in the “cloud” through a set of multi-antenna secondary FD radio units (RU) which are connected to the CU through limited capacity links. We address the sum-rate maximization problem subject to UL and DL fronthaul rate constraints at each RU, power constraints at each RU and UL users, and maximum allowed interference at the primary users. Casting this non-convex problem as a difference of convex (DC) problem, an iterative algorithm based on the Majorization Minimization (MM) approach that guarantees convergence to a stationary point is proposed. Numerical results demonstrate the advantage of the proposed algorithm.

The Internet of Things (IoT) extends network connectivity and computing capability to physical devices. However, data from IoT devices may increase the risk of privacy violations. In this paper, we consider smart meters as a prominent early instance of the IoT, and we investigate their privacy protection solutions at customer premises. In particular, we design a load hiding approach that obscures household consumption with the help of energy storage units. For this purpose, we leverage the opportunistic use of existing household energy storage units to render load hiding less costly. We propose combining the use of electric vehicles (EVs) and heating, ventilating, and air conditioning (HVAC) systems to reduce or eliminate the reliance on local rechargeable batteries for load hiding. To this end, we formulate a Markov decision process to account for the stochastic nature of customer demand and use a Q-learning algorithm to adapt the control policies for the energy storage units. We also provide an idealized benchmark system by formulating a deterministic optimization problem and deriving its equivalent convex form. We evaluate the performance of our approach for different combinations of storage units and with different benchmark methods. Our results show that the opportunistic joint use of EV and HVAC units can reduce the need of dedicated large-capacity or fast-charging-cycle batteries for load hiding.

We are at the dawn of an era in information and communication technology with unprecedented demand for connected and automated everything. Both Shannon theories and industrial advances have clearly evidenced that more densely packed networks and a much wider operating bandwidth are key drivers for meeting the escalating wireless network demands. Recently, there have been substantial research efforts on the exploitation of higher frequency bands, in particular the millimetre wave and optical wireless bands. After a decade of active research and development, and along with the maturity of device technology, Visible Light Communications (VLC) has emerged as a very promising technology to enable next generation digital innovations and support wide range of applications. This special issue on VLC focuses on three core thrusts of the discipline:Localisation, CommunicationandNetworking. The overall aim of the special issue is to inspire multi-disciplinary international communities to work together in order to achieve further research advances. Indeed, a total of 96 high quality papers were received from both academia and industry. After a careful peer-reviewing process, 17 papers were selected based on their combined novelty, rigour, and impact. Owing to the highly selective nature of JSAC, many other interesting papers were not selected for the special issue, but we hope that these papers might appear elsewhere.

In an advanced metering infrastructure (AMI), data acquisition points (DAPs) are responsible for collecting traffic from several smart meters and automated devices and transmitting them to the utility control center. Although the problem of optimized data collector placement has already been addressed for wireless broadband and sensor networks, the DAP placement is quite a new research area for AMIs. In this paper, we investigate the minimum required number of DAPs and their optimized locations on top of the existing utility poles in a distribution grid, such that the smart grid quality of service requirements can best be provided. In order to solve the problem for large-scale AMIs, we devise a novel heuristic algorithm using a greedy approach for identifying potential pole locations for the DAP placement and the Dijkstra's shortest path algorithm for constructing reliable routes. We employ the characteristics of medium access schemes from the IEEE 802.15.4g smart utility network (SUN) standard and consider mission-critical and non-critical smart grid traffic. The performance and the time complexity of our algorithm are compared with those obtained by the IBM CPLEX software for small scenarios. Finally, we apply our devised DAP placement algorithm to examples of realistic smart grid AMI topologies.

We consider optimal linear precoder and decoder designs in a multi-cell multiple-input multiple-output system, where base stations and mobile users are both operating in full-duplex (FD) mode. Existing works on FD cellular systems focus on the maximization of overall throughput, which can result in unfairness between uplink and downlink channels depending on the self-interference power and inter-user interference levels. Therefore, to introduce fairness, in this paper, we consider the transmit and receive beamforming designs that maximize the harmonic-sum of signal-to-interference-plus-noise ratios (SINRs) in the uplink and downlink channels. We propose a low-complexity alternating optimization algorithm which converges to a stationary point. Moreover, in order to address practical system design aspects, we consider the transceiver design that enforces robustness against imperfect channel state information (CSI) while providing fair performance among the users. To this end, we formulate an optimization problem that maximizes the worst case SINR among all users under norm-bounded CSI errors. We devise a low-complexity iterative algorithm based on alternating optimization and semidefinite relaxation techniques. Numerical results verify the advantages of incorporating FD mode into cellular systems, and practical issues, such as CSI uncertainty and fairness performance.

In this paper, we address the problem of improving the medium access control (MAC) layer efficiency in indoor broadband power line communication networks. Several overheads in the MAC layer, like random back-offs and collision recovery, degrade the MAC efficiency. To reduce these overheads, we apply in-band full-duplexing (IBFD), which enables medium-aware transmission at all the network nodes. Specifically, we propose two new schemes called contention-free pre-sensing and mutual preamble detection to minimize the time spent during contentions and collisions. Considering the non-idealities of IBFD, we analytically show the feasibility of our solutions. We further design a comprehensive simulation model with multiple priority data frames and Poisson network traffic arrival to emulate a real in-home network traffic. We then present numerical results for both the classical saturated network model and the comprehensive traffic model, to show through OMNeT++ simulations that our presented solutions achieve over 95% of the optimum MAC efficiency that can only be attained in the idealized case of no contentions or collisions.

Faster-than-Nyquist (FTN) transmission employing antenna polarization multiplexing and higher order modulation (HoM) schemes can significantly increase the spectral efficiency (SE) of the existing wireless backhaul links. However, the benefits of each of these SE enhancement techniques come with a price. While FTN introduces inter-symbol interference, a dual-polarized (DP) transmission suffers from cross-polarization interference (XPI), and HoM makes a communication system vulnerable to phase-noise (PN) distortions. In this paper, we investigate, for the first time, a DP-FTN HoM transmission system. We propose a XPI cancellation and PN mitigation structure, coupled with adaptive decision-feedback equalization or linear precoding, to jointly mitigate interference and accomplish carrier-phase tracking. The DP systems combined with the FTN signaling presented in this paper offer more than 150% increase in SE compared with a single-polarized Nyquist transmission. The effectiveness of the proposed algorithms is demonstrated through computer simulations of a coded DP-FTN microwave communication system in the presence of PN. Numerical results suggest that with the proposed interference cancellation methods, a DP-FTN transmission can yield a 3-5.5-dB performance improvement over an equivalent DP-Nyquist system that employs a higher modulation order to achieve the same data rate.

Visible light communication (VLC) is an emerging short-range optical wireless communication technology that is driven by the widespread deployment of light-emitting diodes (LEDs). Indoor VLC users may experience noticeable interference when independent transmitters utilizing wide-beam luminaires are closely located. In this paper, a coordinated beamforming (CB) scheme is proposed for downlink interference mitigation among the coexisting VLC attocells utilizing multi-luminaire transmitters. Compared to joint transmission (JT) schemes, wherein the data and channel state information are shared among transmitters of different attocells, the proposed CB scheme places lower requirements on the network in terms of backbone traffic, and is easier to implement in a practical deployment, though at the cost of compromised performance. In this paper, we investigate the downlink transmission of coordinated VLC attocells and focus on its transmitter design. The weighted sum mean square error (WSMSE) is adopted as the performance metric to take into consideration interference, noise, and fairness among users in system optimization. The WSMSE minimization problem is considered with linear beamforming restricted by amplitude constraints. Such constraints arise from the dynamic range limitations in typical LEDs. Moreover, we extend our design method to take into account possible mismatches in channel information available to the transmitters. Numerical examples are provided to illustrate the performance of the proposed CB scheme in typical VLC scenarios. We also quantify the performance gap among several coordination schemes including JT and CB.

The fifth-generation (5G) wireless communication systems envision the deployment of massive multiple-input multiple-output (MIMO) technology for enhanced network coverage and capacity. With frequency division duplex (FDD) being the prominent mode of operation, addressing the challenges for massive MIMO systems in FDD is extremely important. One such challenge is the downlink channel estimation, which should be accomplished with minimal pilot overhead. To address this challenge, we propose a compressive sensing (CS) algorithm based on alternating direction method of multipliers (ADMM). We demonstrate how our proposed algorithm fully exploits the block sparsity inherent in the spatial correlations of MIMO channels to provide improved performance than the conventional CS based algorithms used for massive MIMO FDD systems.

In this work, we consider a joint grouping and scheduling algorithm for fair user scheduling in massive multiple-input multiple-output (MIMO) systems that support Internet of Things (IoT) application scenarios. Our proposed method serves the users consecutively in groups, where the group sizes are derived from the optimal number of active users in the zero-forcing downlink channel. To select the best group members we adopt a version of the popular semi-orthogonal user selection (SUS) algorithm. Specifically, we identify the drawbacks of the original SUS algorithm when operating in a massive MIMO system and present a modified SUS strategy (SUS-M) for user selection. Simulation results demonstrate that our proposed method outperforms the conventional SUS strategy and provides improved fairness in terms of the individual user rates.

In this paper we address the linear precoding and decoding design problem for a bidirectional orthogonal-frequency-division-multiplexing (OFDM) communication system, between two multiple-input-multiple-output (MIMO) full-duplex (FD) nodes. The effects of hardware distortions, leading to residual self-interference and inter-carrier leakage, are taken into account. In the first step, the operation of a FD MIMO OFDM transceiver is modeled under the impact of known hardware impairments. An alternating quadratic convex program (AltQCP) is then provided to obtain a minimum-mean-squared-error (MMSE) design for the defined system. The proposed design is then extended to maximize the system sum rate, applying the weighted-MMSE (WMMSE) method. The proposed AltQCP methods result in a monotonic improvement, leading to a necessary convergence to a stationary point. Finally, the performance of the defined system is evaluated under various system conditions, and in comparison to the other approaches in the literature. A significant gain is observed via the application of the proposed method as the hardware inaccuracy, and consequently inter-carrier leakage, increases.

Faster-than-Nyquist (FTN) transmission applies non-orthogonal linear modulation to increase spectral efficiency compared with the well-known orthogonal transmission at Nyquist rate. This comes at a price of inter-symbol interference (ISI), which usually is equalized through receiver processing. In this paper, we investigate the alternative approach of pre-equalization at the transmitter. First, we consider Tomlinson-Harashima precoding (THP) for FTN and propose two novel soft demapping algorithms to generate the soft-input for the error-correction decoder. The developed demappers effectively compensate the modulo-loss associated with conventional THP transmission. Second, we propose a linear pre-filtering strategy to pre-equalize the ISI induced by FTN. We show that the linear pre-equalization approach is equivalent to an orthogonal transmission with a modified pulse shape. It thus yields the optimal error-rate performance while affording higher spectral efficiency. We validate our proposed precoding algorithms through computer simulations of a coded coherent optical communication system as a practical application example for FTN.

Although in-band full-duplexing (IBFD) has long been implemented in various communication media, it was only recently that an IBFD solution was presented for broadband power line communications (BB-PLCs). The maximum attainable echo suppression using this solution is, however, limited by the dynamic range of the analog-to-digital converter (ADC). To counter this critical constraint, we propose echo cancellation in the analog domain, while persisting with a low-complexity frequency domain digital echo estimation. By formulating an expression for the number of ADC bits lost in IBFD over a conventional half-duplex operation, we show that the ADC dynamic range is no longer a limiting factor for our solution. We further extend our solution to present an analog cancellation method for multiple-input multiple-output IBFD BB-PLC systems. Finally, we present simulation results of echo cancellation and data rate gains obtained under realistic in-home BB-PLC settings, to demonstrate that our solution is capable of doubling bidirectional transfer rates in a large number of the tested network conditions.

Machine Type Communications (MTC) is one of the major drivers for the future growth of the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE)/LTE-Advanced (LTE-A) standards. A primary challenge associated with MTC using LTE/LTE-A is to cater to varied requirements of the User Equipment (UE) like coverage enhancement, low complexity, low power consumption, etc. The current LTE/LTE-A standards incorporate the Discontinuous Reception (DRX) mechanism for reduced energy consumption where the UE wakes up periodically to check for a paging message from the base-station. On each wake-up occasion, the UE has to decode the paging information, which requires accurate timing resynchronization. In the case of the MTC UEs, especially when the devices are deployed in low coverage areas, the resynchronization consumes a significant amount of time which increases the ON time of the UE leading to higher energy consumption. In this paper, we introduce the Enhanced Primary Synchronization Signal (ePSS) within the LTE/LTE-A standardization framework and propose a novel DRX mechanism which uses our ePSS for faster resynchronization and reduced energy consumption. We demonstrate that our mechanisms are more energy efficient than the legacy DRX mechanism for the MTC UEs with coverage enhancement.

In this paper, we introduce a new scheme called Mutual Preamble Detection (MPD) to reduce the collision recovery time in broadband power line communication (BB-PLC) networks. Although latest BB- PLC products deliver a physical layer data rate of over 1000 Mbps, this is not efficiently translated into the medium access control (MAC) layer throughput due to several factors, including the long time intervals taken to recover from collisions. To address this, we use in-band full duplex operation to enable network nodes to transmit and simultaneously detect preambles, making them aware of a potential frame collision. With the detection of such a potential collision, we compel the network nodes to refrain from frame transmission in order to avoid the lengthy collision recovery time. The near-zero values of detection error and false alarm probabilities ensure the feasibility of our scheme in typical in-home BB-PLC networks. We present OMNeT++ simulation results to demonstrate the considerable increase in MAC efficiency obtained by using our proposed MPD scheme, over a traditional BB-PLC protocol.

This paper studies an indoor communication system that integrates visible light communication (VLC) and power line communication (PLC) technologies. We exploit the application of the same orthogonal multicarrier modulation format for both PLC and LC link and present the framework for the capacity analysis of the hybrid VLC-PLC (HVP) system. In addition, several computationally efficient subcarrier allocation schemes are proposed to maximize the system capacity. The results demonstrate that the proposed subcarrier allocation in the HVP system can provide an improvement in the system capacity over random subcarrier allocation.

Energy consumption in wireless communication systems is exponentially increasing due to growing wireless traffic. Combating adverse effects of excessive energy consumption calls for energy- aware system design, leading to a new research paradigm, green communications. To achieve energy awareness in a full-duplex (FD) bi-directional multiple antenna system, in this paper, we study a Quality-of-Service (QoS) problem, where the total transmit power is minimized subject to minimum rate constraints at each node, and propose two algorithms. We first apply a penalty-based method in order to obtain an efficient optimization strategy. Afterwards, in the second algorithm, we generalize the well-known relationship between Weighted-Sum-Rate (WSR) andWeightedMinimum-Mean- Squared-Error (WMMSE) problems, originally used to solve the sum-rate maximization problem, to tackle the sum-power minimization problem.

We consider a single cell multiple-input multiple-output (MIMO) system, where a base-station (BS) operating in full-duplex (FD) mode serves multiple uplink (UL) and downlink (DL) mobile users operating in half-duplex (HD) mode, simultaneously. The self-interference at the BS, and co-channel interference (CCI) from UL users to DL users are both taken into account. We consider the transmit and receive filter design for sum- rate maximization subject to a sum-power constraint at the BS and individual power constraints at each UL user of the system under the limited dynamic range considerations at the transmitters and receivers. By reformulating this non-convex problem as an equivalent component-wise convex optimization problem with the addition of two auxiliary variables, we propose a low complexity algorithm which converges to a stationary point.

Sustaining high data rates over an indoor broadband power line communication (PLC) link is a challenging task due to the significant attenuation of high frequency signals transmitted over power cables. Repeaters are often used to alleviate the problem of signal attenuation, however, this comes at a loss of multiplexing gain. On the other hand, modern relaying concepts, as used in wireless systems, are not as effective in PLC setups due to the absence of diversity improvement. In this study, the authors address this issue and propose a new approach to improve the multiplexing gain of relay‐aided PLC systems. The authors consider a multi‐user indoor PLC scenario where all users want to share their data. For this setup, the authors then advocate the application of amplify‐and‐forward (AF) multi‐way relaying (MWR). Considering the practical constraints of an indoor PLC system, the authors study the achievable data rates of AF MWR, and compare them to those achievable with direct (non‐cooperative) transmission and conventional relaying schemes. The simulations demonstrate that depending on the network topology, MWR can result in significant performance improvement. The authors further discuss how their rate analysis can be exploited to decrease the energy consumption in the system.

The Third Generation Partnership Project (3GPP) has recognized machine-type communications (MTCs) as a vital medium to drive the Internet of Things (IoT). One of the key challenges in MTC is to reduce the energy consumption of the MTC user equipment (UE). Currently, the 3GPP Long Term Evolution (LTE)/LTE-advanced (LTE-A) standards incorporate discontinuous reception (DRX) mechanism for this purpose. In this paper, we propose a modified DRX mechanism incorporating the quick sleeping indication (QSI) as a novel, simple, and energy-efficient solution for low-complexity, low-mobility MTC UEs. We demonstrate our QSI transmission mechanisms using the broadcast and synchronization channels of LTE/LTE-A for MTC UEs in normal coverage and using the data channel for MTC UEs operating in “coverage enhancement” (CE) mode. For MTC UEs in normal coverage, our simulation results and analysis show that our DRX with QSI mechanisms result in 45% improvement in the energy efficiency and 66% reduction in the computational complexity at the UE receiver, when compared to the current DRX mechanism. For MTC UEs with CE, the energy and computational efficiency increase to 63% and 68%, respectively.

In recent decades, power line communication (PLC) has attracted considerable attention from the research community and industry, as well as from regulatory and standardization bodies. In this paper, we provide an overview of both narrowband and broadband systems, covering potential applications, regulatory and standardization efforts, and recent research advancements in channel characterization, physical layer performance, medium access, and higher layer specifications and evaluations. We also identify the areas of current and further study that will enable the continued success of PLC technology.

Welcome to the IEEE JSAC special issue on Power Line Communications and its Integration with the Networking Ecosystem. This special issue was motivated by the growth in maturity of power line communications (PLC) over the last ten years since the last JSAC special issue focusing on PLC in 2006. For this special issue, we hoped to receive papers showing the growth of PLC technology itself, and works showing applications and integration with the technology ecosystem.

We introduce in-band full duplexing (IBFD) for broadband power line communication (BB-PLC) systems. Inspired by the use of IBFD in digital subscriber lines, Ethernet, cable communication, and recently in wireless communication, we investigate the constraints and requirements for a successful IBFD implementation in BB-PLC. We propose a two-stage IBFD structure consisting of an initial analog isolation using an active hybrid circuit, and a simplified mixed-domain digital echo cancellation procedure to suppress the self-interference. Furthermore, we enhance the digital cancellation filter to better adapt to linear periodically time-varying channel conditions, commonly encountered in PLC scenarios. We evaluate our solution under diverse power line channel and noise conditions to examine the overall data rate gains that can be achieved. Last, we extend IBFD to multiple-input multiple-output (MIMO) BB-PLC systems that enable faster and/or more robust data transmission.

A wideband spectrum sensing method for cognitive radios is presented which is based on compressed measurements. The proposed detector does not require signal reconstruction from the compressed measurements. A fusion centre collects the measurements from different sensing nodes and then makes a sensing decision based on a simplified maximum likelihood criterion which does not require prior signal information. This results in an efficient and low complexity spectrum detector especially for dynamic spectrum occupancy scenarios. The performance of the proposed detector is exhibited by means of numerical simulations for probability of erroneous detection and receiver operating characteristic curves.

In this paper, we consider mean squared error (MSE)-based robust transceiver optimization for multi-user multi-input multi-out (MU-MIMO) cellular network that exploits interference alignment (IA) for its downlink communication. First, we consider the conventional sum-MSE minimization problem, where the MSE is calculated at user equipments (UEs). Second, we consider a different approach where the MSE can be calculated at base stations (BSs) i.e., leakage-based MSE from each BS. Different from conventional per-base station power constraint (PBPC), we assume practical per-antenna power constraint (PAPC) due to linearity of the power amplifier that feeds each transmit antenna at the BSs. To this end, we derive robust precoders and receive filters for these two design objectives under statistical channel state information (CSI) uncertainty. Simulation results suggest that our robust designs offer a good performance, showing resilience against CSI uncertainty. In addition, the sum-rate performances for designs with PAPC and PBPC are compared. It is observed that the sum-rate loss due to PAPC is relatively small for the robust designs.

In this paper, we study robust transceiver optimization for device-to-device (D2D) communications that aims for signal-to-interference-plus-noise-ratio (SINR) fairness among D2D users. We assume that the multi-antenna D2D users in the cellular network employ interference alignment (IA) for their communication. In addition to an interference power constraint that is set by the primary network (i.e., macrocell) in the underlay cognitive transmission, we also consider channel state information (CSI) imperfectness to obtain a robust transceiver design for the D2D users. Due to the non-convexity of the design problem, we resort to an alternating minimization technique. Numerical simulations demonstrate the performance of the proposed transceiver compared to the benchmark case of an IA system without primary network/macrocell (non-cognitive). It is observed that at low SNR and high CSI error with relaxed interference power constraint, the worst-case stream data rate of the D2D users are close to that of the users in non-cognitive IA system but performance degrades significantly with stringent interference power constraint.

In a multi-input multi-output (MIMO) interference network, the maximum achievable signal-to-interference-plus-noise ratio (SINR) determines the level of quality of service (QoS) that can be supported by each stream. In this paper, we study the problem of maximizing the minimum SINR of independent parallel data streams across all users in a MIMO interference network that employs interference alignment (IA) in the presence of channel state information (CSI) uncertainty. To this end, we propose a low-complexity robust SINR fairness algorithm based on the power allocation across data streams. Building on the conventional IA design, we provide a closed-form solution for the power allocation problem. It is observed that the proposed power allocation (PA)-based robust design outperforms the conventional robust design, when the channel changes drastically and the CSI uncertainty cannot be reliably bounded. Furthermore, the PA-based robust design provides significant performance gain over the benchmark Max-SINR algorithm.

This paper considers improving the confidentiality of visible light communication (VLC) links within the framework of physical-layer security. We study a VLC scenario with one transmitter, one legitimate receiver, and one eavesdropper. The transmitter has multiple light sources, while the legitimate and unauthorized receivers have a single photodetector, each. We characterize secrecy rates achievable via transmit beamforming over the multiple-input, single-output (MISO) VLC wiretap channel. For VLC systems, intensity modulation (IM) via light-emitting diodes (LEDs) is the most practical transmission scheme. Because of the limited dynamic range of typical LEDs, the modulating signal must satisfy certain amplitude constraints. Hence, we begin with deriving lower and upper bounds on the secrecy capacity of the scalar Gaussian wiretap channel subject to amplitude constraints. Then, we utilize beamforming to obtain a closed-form secrecy rate expression for the MISO wiretap channel. Finally, we propose a robust beamforming scheme to consider the scenario wherein information about the eavesdropper's channel is imperfect due to location uncertainty. A typical application of the proposed scheme is to secure the communication link when the eavesdropper is expected to exist within a specified area. The performance is measured in terms of the worst-case secrecy rate guaranteed under all admissible realizations of the eavesdropper's channel.

Visible light communication (VLC) reuses illumination devices, particularly light-emitting diodes (LEDs), for communication purposes. It has great potential to alleviate the strain on radio-frequency spectrum in indoor environments. VLC-enabled LED luminaries form VLC attocells that carry downlink data traffic to indoor mobile or stationary terminals. While one of the advantages of indoor VLC is low interference due to natural cell boundaries such as walls, multiple VLC attocells within a room would interfere. This is because illumination requirements often mandate a rich overlap of emissions of luminaries in a room. In this paper, we suggest the coordination of multiple VLC attocells (i.e., VLC-enabled LED luminaries) to turn the problem of overlap and thus interference into an advantage. We stipulate that this coordination can be accomplished through power line communication, which has been considered before as a means to transport data to VLC transmitters. Borrowing from concepts developed for radio-frequency wireless communications, we develop several precoding schemes for the new coordinated VLC broadcasting architecture. These include designs for the case of imperfect channel knowledge at the VLC transmitter, since channel information is usually provided through a low-rate feedback channel. The performance advantages for VLC transmission due to the proposed coordination and precoding designs are demonstrated based on a set of numerical results.

Visible-light communication (VLC) systems leverage solid-state illumination devices to create high-speed communication links. Orthogonal frequency-division multiplexing (OFDM) has been considered for these intensity-modulated/direct-detection (IM/DD) optical channels, however, it suffers from high peak-to-average power ratio (PAPR). Moreover, the implementation of linear, power-efficient, high-current, wideband drivers is challenging. In this paper, the concept of spatial summing is developed where wideband, high PAPR OFDM signals are partitioned into many low-PAPR narrowband signals that are transmitted from multiple LEDs. The signals from different LEDs are allowed to sum in space before being detected by a conventional OFDM receiver. Spatial optical-OFDM (SO-OFDM) is proposed in which filtered subsets of carriers are emitted by each LED. In addition, low-PAPR optical single-carrier FDMA (OSC-FDMA) is developed where different collections of LEDs act as virtual users in a multiple-access scheme. The different variations of SO-OFDM and OSC-FDMA are compared to conventional DC-biased optical (DCO) OFDM and are shown to achieve lower PAPR and more robustness to LED nonlinearities leading to error rate performance gains at high signal-to-noise ratios.

The simultaneous use of wireless and power line communications (PLC) channels provides a convenient method for increasing the coverage and throughput of indoor networks. In this paper, we compare coding diversity and modulation diversity schemes that both utilize parallel wireless and PLC links. The signal to noise ratio (SNR) values used in this analysis are determined by conducting a series of average link gain measurements in an office environment. Measurement results show that both wireless and PLC SNRs have a wide range, but neither type of media is guaranteed to dominate performance for a given link. The empirical SNR values are used in a Monte Carlo simulation to evaluate the possible throughput advantages of coding and modulation wireless-PLC media diversity.

This paper considers secure transmission over the visible light communication (VLC) channel by the means of physical-layer security techniques. In particular, we consider achievable secrecy rates of the multiple-input, single-output (MISO) wiretap VLC channel. The VLC channel is modeled as a deterministic and real-valued Gaussian channel subject to amplitude constraints. We utilize null-steering and artificial noise strategies to achieve positive secrecy rates when the eavesdropper's channel state information (CSI) is perfectly known and entirely unknown to the transmitter, respectively. In both scenarios, the legitimate receiver's CSI is available to the transmitter. We numerically evaluate achievable secrecy rates under typical VLC scenarios and show that simple precoding techniques can significantly improve the confidentiality of VLC links.

In this paper, a multiuser two-way filter-and- forward relaying scheme for wireless communication over wideband channels is considered. We propose pre/post-rake processing in conjunction with optimized filtering at the relay to reduce the signal processing burden at the source and destination nodes. Two relay filter design problem formulations are introduced, namely (a) a convex optimization problem formulation with closed-form solutions and (b) the more general case, which is a non-convex problem solvable via an alternating optimization algorithm. For both design alternatives widely linear formulations are devised. The presented numerical results demonstrate the capability of the proposed designs to establish reliable two-way communication links between nodes with limited signal processing power and in the absence of a direct link.

The low sound speed in water makes propagation delay (PD)-based range estimation attractive for underwater acoustic localization (UWAL). However, due to the long channel impulse response and the existence of reflectors, PD-based UWAL suffers from significant degradation when PD measurements of nonline-of-sight (NLOS) communication links are falsely identified as line-of-sight (LOS). In this paper, we utilize expected variation of PD measurements due to mobility of nodes and present an algorithm to classify the former into LOS and NLOS links. First, by comparing signal strength-based and PD-based range measurements, we identify object-related NLOS (ONLOS) links, where signals are reflected from objects with high reflection loss, for example, ships hull, docks, rocks and so on. In the second step, excluding PD measurements related to ONLOS links, we use a constrained expectation-maximization algorithm to classify PD measurements into two classes: LOS and sea-related NLOS (SNLOS), and to estimate the statistical parameters of each class. Since our classifier relies on models for the underwater acoustic channel, which are often simplified, alongside simulation results, we validate the performance of our classifier based on measurements from three sea trials. Both our simulation and sea trial results demonstrate a high detection rate of ONLOS links, and accurate classification of PD measurements into LOS and SNLOS.

In this paper, we propose multiuser two-way relaying strategies for pairwise internode communication in a network consisting of ultrawideband transceivers with limited signal processing capability, via a central relay unit. We propose reducing the complexity associated with the design of filters at the relay by using pre/post-rake processing in conjunction with optimized filtering at the relay. Two relaying strategies relevant to multipath fading channels, namely, detect-and-forward and filter-and-forward with self-interference cancelation, are considered. For both methods, we start with a convex optimization problem formulation with closed-form solutions, then extend the design to the more general case, which is a nonconvex problem, and use an alternating optimization algorithm to solve the design problems. Furthermore, for both design schemes, widely linear design formulations are devised. The presented numerical results demonstrate the capability of the proposed design schemes in establishing a reliable communication link between nodes with limited signal processing power and in the absence of a direct link.

Node localization is a difficult task in sensor networks in which the ranging measurements are subject to errors and anchor positions are subject to uncertainty. In this paper, the robust localization problem is formulated using the maximum likelihood criterion under an unbounded uncertainty model for the anchor positions. To overcome the non-convexity of the resulting optimization problem, a convex relaxation leading to second order cone programming (SOCP) is devised. Furthermore, an analysis is performed in order to identify the set of nodes which are accurately positioned using robust SOCP, and to establish a relation between the solution of the proposed robust SOCP optimization and the existing robust optimization using semidefinite programming (SDP). Based on this analysis, a mixed robust SDP-SOCP localization framework is proposed which benefits from the better accuracy of SDP and the lower complexity of SOCP. Since the centralized optimization involves a high computational complexity in large networks, we also derive the distributed implementation of the proposed robust SOCP convex relaxation. Finally, we propose an iterative optimization based on the expectation maximization (EM) algorithm for the cases where anchor uncertainty parameters are unavailable. Simulations confirm that the robust SOCP and mixed robust SDP-SOCP provide tradeoffs between localization accuracy and computational complexity that render them attractive solutions, especially in networks with a large number of nodes.

Power line communications (PLC) plays an important role in the blend of communication technologies considered for enabling the smart grid vision. However, different from, e.g., wireless communications, for which ready-to-use modules are included in several simulation packages, there are no freely available software tools to simulate PLC networks. In particular, software modules which emulate the PLC channel are needed to capture the specifics of PLC in a communication network simulation. In this paper, we aim at closing this gap and present a PLC channel simulator written using the network simulator-3 (ns-3) library and made available for free use.

Power line communication (PLC) provides a reliable and inexpensive solution to enable high data rate services for indoor environments. In this work, we consider an indoor PLC network where several devices (or users) want to exchange data. To prevent severe signal attenuation and thus performance degradation over relatively long PLC links, we consider the use of a relay at a central location to assist the users in their data communication. For this scenario, we suggest the application of amplify-and-forward (AF) multi-way relaying (MWR) based on physical-layer network coding at the relay. To evaluate the performance of this scheme, its achievable data rate is studied with practical assumptions applicable to PLC systems. Our study shows that the employed AF MWR improves the system performance and increases the achievable common data rate at the users.

The presence of time-varying frequency-selective channels and impulsive noises renders the design of MAC protocols for in-vehicle power line networks challenging. It is then important to understand the impact of carrier sensing errors, i.e., false alarm and miss detection on the performance of the MAC layer. This paper attempts to model the effect of carrier sensing errors on the performance of a contention-based MAC protocol, called selective tournaments, well suited for in-vehicle power line communication. We start with addressing the problem of detection of unknown signals in impulsive noise by using a robust detector, which first removes the impulses from the signal and then performs energy detection on the cleaned samples. We then obtain the network throughput and delay as a function of carrier sensing errors. Finally, numerical results are presented to demonstrate the sensitivity of the network throughput and delay with respect to the sensing threshold.

The papers in this special issue explore advances in communication technologies that have the potential for improving energy efficiency and realizing the smart grid vision.

Pre-rake ultra-wideband (UWB) systems are appealing for UWB communications applications which include devices with different processing capabilities so that signal processing complexity need to be shifted from the receiver of one or more devices to the transmitter of another. Recently, basic pre-rake schemes have been extended to include full pre-equalization, multiple-antenna, and multi-user interference processing. All these design approaches for pre-rake UWB systems have relied on the availability of accurate channel state information (CSI) at the transmitter. However, uncertainties in the acquisition of CSI can drastically affect the overall system performance. Therefore, in this paper, we present robust design methods for pre-equalization filters (PEFs) for pre-rake UWB systems that take CSI uncertainties into account. We treat the general case of a broadcast (i.e., multiuser) pre-rake UWB system, which includes single-user communication often considered in literature as a special case. For this general setting, we derive new PEF designs that improve system performance with imperfect CSI. Similar to the literature on robust filter designs for multiple-input multiple output (MIMO) systems, we consider two uncertainty models, namely stochastic and bounded uncertainty, which correspond to different performance optimization paradigms, and we adjust these according to channel estimation of UWB channels. As most of previous work on (pre-rake) UWB, we focus on binary transmission. We argue that widely linear filter design should be applied in this case and thus extend the robust filter design methodology accordingly. Our numerical results for typically UWB test channels demonstrate the efficacy of the proposed design procedures to achieve reliable communication in multiuser pre-rake UWB systems.

Power line communications (PLC) has attracted considerable attention for supporting smart grid applications. Since it reuses the existing grid infrastructure, it offers cost advantages over alternative communications methods and gives electric utilities control over the communications medium. Furthermore, the "through-the-grid" property of PLC extends its possible use beyond mere communications. Since the PLC signals are bound to travel through the power grid, they can also be used for inference tasks, such as online diagnostics of power line integrity. In this paper, we consider such an inference application of PLC, enabled by modern signal processing. We assume a power grid at whose edges PLC devices are deployed to form a PLC network for purposes such as advanced meter reading. We are interested in retrieving the physical power-grid topology, i.e., the connections and lengths of power lines reaching to the locations of the PLC devices. To this end, we propose the combination of PLC-based ranging with inference based on end-to-end measurements. In the context of communication networks, the latter is known as tomography and hence, we refer to the developed method as power grid tomography. For the purpose of ranging we formulate a new super-resolution ranging algorithm specifically tailored for signal propagation through power lines. Numerical results for low-voltage distribution grid examples demonstrate the successful reconstruction of the grid topology by the proposed power grid tomography method.

This paper focuses on the problem of optimal bit and power allocation in linear periodically time varying (LPTV) channels in broadband (BB) power line communication (PLC). Previous work has demonstrated that improvements in bit loading can be achieved with LPTV channel adaptation via so-called microslots in time for an orthogonal frequency division multiplexing (OFDM) system. In this paper, we present that the application of a power constraint that is averaged over many microslots can be exploited for further performance improvements through loading. Due to the matroid structure of the optimization problem, greedy-type algorithms are proven to be optimal for the new LPTV-aware bit and power loading. Significant gains are attained especially at reduced transmit-power levels, where the energy per bit-transmission is also low, and for poor (i.e. high attenuation) channel conditions. Furthermore, two mechanisms are utilized to reduce the complexity of the optimal LPTV-aware bit loading and peak microslot power levels: (i) employing representative values from microslot transfer functions, and (ii) power clipping. Our results indicate that the reduced complexity LPTV-aware bit loading with power clipping performs very close to the optimal LPTV-aware bit loading, which makes it an attractive option in a practical setting.

Underwater acoustic localization (UWAL) is a key element in most underwater communication applications. The absence of GPS as well as the signal propagation environment makes UWAL similar to indoor localization. However, UWAL poses additional challenges. The propagation speed varies with depth, temperature, and salinity, anchor and unlocalized (UL) nodes cannot be assumed time-synchronized, and nodes are constantly moving due to ocean currents or self-motion. Taking these specific features of UWAL into account, in this paper, we describe a new sequential algorithm for joint time-synchronization and localization for underwater networks. The algorithm is based on packet exchanges between anchor and UL nodes, makes use of directional navigation systems employed in nodes to obtain accurate short-term motion estimates, and exploits the permanent motion of nodes. Our solution also allows self-evaluation of the localization accuracy. Using simulations, we compare our algorithm to two benchmark localization methods as well as to the Cramér-Rao bound (CBR). The results demonstrate that our algorithm achieves accurate localization using only two anchor nodes and outperforms the benchmark schemes when node synchronization and knowledge of propagation speed are not available. Moreover, we report results of a sea trial where we validated our algorithm in open sea.

In this paper we study the effect of channel uncertainty on the performance of pre-equalized pre-rake UWB systems. We consider a bounded uncertainty model and propose a pre-rake design that enables the system to satisfy the required performance in absence of ideal channel state information. Furthermore, we integrate spectral mask constraints into the proposed robust design and investigate the performance of the resulting robust pre-equalized pre-rake UWB system. Our numerical results show the efficacy of the proposed robust design in retaining the required quality of service also in the presence of channel estimation errors while satisfying the spectral mask constraints.

Frequency Domain Reflectometry (FDR) is a technique that was proposed for fault detection in Digital Subscriber Line (DSL) cables. In this paper, we describe how FDR can be used to determine the topology of power line networks. To this end, we first infer distance information from the multiple signal reflections measured and processed with FDR. Then, we present an algorithm that uses these distance measurements to reconstruct the topology step by step operating on a network graph. Numerical results for sets of sample networks demonstrate the effectiveness of the proposed topology-inference approach.

Tone reservation (TR) has been proposed to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiple access (OFDMA) uplink communication systems. However, it introduces multiple-access interference (MAI) at the receiver. To reduce the effects of MAI, TR was proposed which uses all unused subcarriers at the OFDMA transmitter to generate a peak reduction signal under power spectral density constraints. However, the accumulated MAI at the receiver can be significant, which leads to performance degradation. To address this problem, we consider both PAPR and MAI reduction using TR and propose ordering the subcarriers before allocating the peak reduction tones. In so doing, we are able to achieve PAPR reduction with causing only minimal MAI.

We propose a buffer-aided relaying protocol for a three node relay network comprised of a source, a half-duplex relay with buffer, and a destination. We assume a direct source-destination link is available and all links undergo fading. The proposed protocol enables the half-duplex relay to choose its reception and transmission time slots adaptively and based on the quality of the involved links. We derive the achievable ergodic rate of the considered three-node network for the proposed protocol. Our results show that this achievable ergodic rate exceeds existing unachievable ergodic capacity upper bounds for the three-node half-duplex relay channel with the relay always alternating between reception and transmission in successive time slots.

"Smart Grid" refers to the modernization of electric grid to allow for more efficient generation, transmission, distribution, and usage of energy. This is becoming necessary in order to transition to a more sustainable energy generation and consumption and to reduce any adverse effects on the environment. While more advances in areas like renewable energies and network control are necessary, advances in communication technologies, data fusion and mining, as well as scheduling and optimization are also critical in order to achieve this vision. It is anticipated that the same communication technologies that have revolutionized our way of life in the past decades, ranging from sensor networks, mobile Internet, cloud computing, smart phones and many others, will have direct applicability to Smart Grid. Our objectives for this series of IEEE JSAC are focused on identifying the numerous communication challenges posed by the various aspects and functionalities of the Smart Grid and exploring research avenues for addressing them. We have received 67 papers, and after thorough review and careful deliberations, we have accepted 10 papers in this first issue. The articles in this issue can be grouped into 4 main sub-topic areas, namely, scheduling and load balancing, energy pricing, routing, and security.

We consider the design of ultra-wideband (UWB) systems that enable high data rate communications for short-range wireless applications. In particular, we consider the downlink of a direct sequence UWB (DS-UWB) system in which the base station is equipped with multiple antennas and employs pre-rake combining, while each user employs a simple single antenna receiver. We propose the use of multiuser filters for the purpose of pre-equalization at the transmitter in order to mitigate the combined effects of intersymbol interference (ISI) and multiuser interference (MUI) that are generated at the receivers as a result of the wideband nature of the users' channels. For this system, we study the joint design of the transmitter's pre-equalization filters and each receiver's scalar gain under two design criteria. The first design minimizes the total transmitted power from the base station subject to achieving physical layer quality of service requirements of different users. For this design, we show that the calculation of the pre-equalization filters and the receiver gains can be formulated as an efficiently solvable convex optimization problem. In the second design, we consider the minimization of a weighted sum of each user's mean-square error. In order to obtain a computationally tractable solution for this design criterion, we exploit the dual DS-UWB uplink that employs rake combining and post-equalization filters at a central receiver. The numerical studies for each design criterion under realistic models of UWB channel propagation demonstrate the effectiveness of the proposed multiuser pre-equalization filter designs in mitigating ISI and MUI, and thus their ability to enable reliable pre-rake DS-UWB downlink transmission.

We consider the problem of designing multipulse pulse-position modulation (MPPM) constellations whose sizes are powers of two. This problem amounts to selecting a subset from the collection of all (wn) possible signal points of MPPM with w pulses in n time slots. In a previous work, we have tackled this selection using combinatorial heuristics. In this letter, we further explore two new continuous optimization approaches. The first one is a modified Blahut-Arimoto algorithm. The second one is inspired from compressed sensing. Using the constellation-constrained channel capacity as the figure of merit, numerical results from a relevant free-space optical communication example suggest that simple combinatorial heuristics yield practically the best designs.

High peak to average power ratio is a major drawback in orthogonal frequency division multiplexing (OFDM) systems. A high PAPR can lead to saturation in the power amplifier and consequently increase spectral spreading, distorts the signal, and reduces power amplifier efficiency. In this paper, we propose a method based on compressed sensing (CS) to recover nonlinearly distorted OFDM signals. The method exploits pilot tones inserted in the OFDM signal for channel estimation. The key steps are a CS-based estimation of clipping noise and its removal from the received OFDM signal. In our work, we also include the effect of nonlinear distortion on channel estimation. Numerical results show that the proposed CS-based method significantly improves the bit error rate (BER) performance over previously proposed techniques which iteratively estimate the clipping noise and cancel it from the received signal.

A programmable-gain amplifier (PGA) for in- vehicle power-line communication (PLC) is implemented in 0.13-μm CMOS. The PGA robustly operates over the extended automotive temperature range of -55°C to +125°C. A transconductance boosting technique is employed to improve the linearity of the amplifier. Post-layout simulation results confirm that the amplifier achieves a gain range of 0 to 60 dB, while the variation of each gain setting is less than 0.3 dB when the temperature changes from -30°C to +80°C, and is less than 0.9 dB when the temperature changes from -55°C to +125°C. The P1dBof the PGA at its minimum gain is 2.5 dBm, and the -3-dB bandwidth of the circuit at its maximum gain is 90 MHz. The PGA consumes less than 9.0 mW from a 1.2 V supply.

In this paper we address the problem of spatialreuse scheduling for underwater acoustic communication (UWAC) networks that support high traffic broadcast communication and require robustness to inaccurate topology information. To this end, we derive a broadcast scheduling algorithm that combines topology-transparent and topology-dependent scheduling methodologies to achieve high-throughput in static and dynamic topology scenarios. While we focus on scheduling in UWAC networks, our approach can also be adopted for broadcast scheduling for radio ad-hoc network if robustness to topology uncertainties is desired. Simulation results for typical UWAC scenarios demonstrate that our protocol achieves high throughput and provides robustness to outdated topology information in dynamic topologies.

Bit-interleaved coded modulation (BICM) has become the de facto coding standard for communication systems. Recently, BICM has been cast as a mismatched decoding scheme due to the assumption of independent bit metrics. In addition to this inherent mismatch, practical demodulators may produce mismatched decoding metrics because of implementation constraints, such as clipping and metric approximation to reduce computational complexity. In this paper, we investigate BICM with such metrics. In line with recent works on this topic, we adopt the generalized mutual information (GMI) as the pertinent performance measure. First, we show that level-dependent scaling of logarithmic bit metrics can improve the BICM GMI. Second, we propose a uniform metric scaling which can lead to an improved performance of mismatched sum-product symbol-by-symbol decoding, even if the GMI is not changed. Third, we investigate general metric-mismatch correction methods and analyze their effects in terms of the GMI. By means of three application examples, we illustrate that metric-mismatch correction, including metric scaling, can significantly increase BICM rates.

Multilevel coding (MLC) is the main contender to the celebrated bit-interleaved coded modulation (BICM) technique for combining binary error-control codes with multilevel constellations. Although MLC has a more complex encoding-decoding structure, it can achieve a larger rate in a number of important scenarios such as multiple-input multiple-output (MIMO) and orthogonal modulation transmission. In this paper, we consider two issues related to the application of MLC. First, we examine the use of general decoding metrics in MLC, including mismatched metrics that arise from approximations to reduce detection complexity. We make use of recent advances in the analysis of BICM and apply those techniques to individual MLC transmission layers. Our contributions include rate analysis and metric-mismatch correction to improve throughput performance of MLC. Second, we consider the combination of MLC with binary rateless codes. Such a combination eliminates the need to carefully design code rate for each MLC layer. In slow fading environments, rateless coding can also seamlessly adapt to the instantaneous channel quality and achieve an increased average throughput compared to a fixed-rate MLC transmission. However, due to the MLC structure, we show that a naive combination of MLC and rateless coding can cause a significant rate loss. Thus, we propose a novel rotation rateless scheme which preserves the rate advantage of MLC over BICM. We provide relevant examples with MIMO, frequency-shift keying (FSK), and pulse-position modulation (PPM) signaling to demonstrate that our scheme can achieve throughput gains compared to BICM in a variety of transmission scenarios.

In this paper, we study the problem of resource allocation and optimization for multiple-input multiple-output (MIMO) cognitive radio (CR) systems under the assumption of imperfect channel state information (CSI) of the channels between the secondary users (SUs) and the primary users (PUs) at the SUs. We formulate robust design optimization problems for CR systems with one or more SUs communicating over a single or multiple frequency carriers in the presence of multiple PUs. We propose a linear matrix inequality (LMI) transformation that facilitates proper treatment of channel uncertainty at the SU transmitter and we provide solutions to the design problems based on convex optimization and Lagrange dual decomposition techniques. Finally, we demonstrate the importance of the proposed formulations and the implications of ignoring channel uncertainties when designing for CR systems.

Regulation in Europe and Japan requires the implementation of detect-and-avoid (DAA) techniques in some bands for the coexistence of licensed primary systems and secondary ultra wideband (UWB) systems. In a typical coexistence scenario, a primary system may have potentially interdependent uplink-downlink communication channels (e.g., simultaneous uplink-downlink communications in a frequency division duplex system) overlapping with the frequency band of a UWB system. If such interdependencies of primary systems' activities are known, the UWB system's ability to detect primary systems can be improved. In this study, we are interested in determining the possible gains in the detection performance when taking interdependencies into account for practically implementable detection methods. Contrary to selecting the detection thresholds individually for each band as in a conventional detection approach, the bands are jointly processed. To this end, maximum a posteriori (MAP) decision variables are generated at the receiver, and bias terms are introduced to achieve a desired trade-off between the probabilities of detection and false alarm. In addition to finding the optimal detection results based on the Neyman-Pearson (NP) test, a suboptimal but practically implementable approach is also considered, and the gain compared to conventional independent detection is quantified for various practical scenarios. The results obtained from this study can be used for improving the primary system detection performance of UWB systems, as well as for cognitive radios that perform spectrum sensing in multiple bands.

Dynamic decode-and-forward (DDF) is a version of decode-and-forward relaying in which the duration of the listening phase at relays is not fixed. In this paper, we investigate half-duplex DDF relaying based on rateless codes. The use of rateless codes allows relays to autonomously switch from listening to the source node to transmitting to the destination node. We first revisit different signal combining strategies applied at the destination node, namely energy and information combining known from literature, and propose a new combining method which we refer to as mixed combining. The different combining methods give rise to different achievable rates, i.e., constrained channel capacities, for which we provide analytical expressions. The capacity analysis reveals the conditions under which mixed combining is superior and how it can be optimized. We then consider Raptor codes as a specific implementation of rateless codes and develop a density-evolution approximation to predict the data-rate performance of these codes in DDF relaying. Furthermore, we devise an optimization of the output symbol degree distribution of Raptor codes that is mainly used to benchmark the performance of Raptor codes with a fixed degree distribution. Numerical results for exemplary three-node and four-node relay networks show that the proposed mixed combining provides significant gains in achievable data rate and that Raptor codes with a fixed degree distribution are able to realize these gains and to approach closely the constrained-capacity limits.

We consider the design of ultra-wideband (UWB) systems that provide high capacity communication for short-range wireless applications. The design configuration is a multiuser pre-rake UWB broadcast communication system in which the base station is equipped with multiple antennas to achieve high data rates while each user is equipped with a simple and cost-efficient single antenna receiver. We assume the use of multiuser pre-equalization filters at the base station to mitigate the effect of inter-symbol interference (ISI) and multiuser interference (MUI) at the receivers. For the optimization of these filters we develop an analytical framework that minimizes the total transmission power while satisfying (physical layer) users' quality of service for reliable communications. In particular, the quality of service constraints are expressed in terms of the mean square error (MSE) for each user. We show that the design problem is equivalent to a convex optimization problem that can be solved efficiently. The numerical studies confirm that the proposed design strategy for multiuser pre-equalization filters enables the reduction of the total transmission power to achieve a given set of requested MSE targets.

In this paper, we study design problems for single and multiple-carrier Multiple-Input Multiple-Output (MIMO) Cognitive Radio (CR) systems. We assume imperfect Channel State Information (CSI) of the channels between the Secondary Users (SUs) and the Primary Users (PUs) at the SUs and propose solutions based on a Linear Matrix Inequality transformation that facilitates proper treatment of channel uncertainty at the SU transmitter. We employ convex optimization tools and use a Lagrange dual decomposition approach to solve the optimization problems efficiently. We also present a number of numerical results which clearly demonstrate the robustness and importance of the proposed algorithms.

Bit-interleaved coded modulation (BICM) has established itself as the prevalent coded modulation scheme for wireless communication systems. There are a number of semi-analytical approaches for BICM performance analysis, all of which have limitations in terms of applicability and/or complexity. In this paper, we present a novel analytical approach to approximate the bit error rate (BER) of BICM. Our approach is unified in the sense that a (i) large class of fading channels, (ii) arbitrary labeling rules, and (iii) all common signal constellations are encompassed, and it is preferable over previous work in that we provide closed-form expressions. We also derive expressions for the asymptotic BER, which reveals the diversity order and coding gain of BICM transmission over fading channels. The accuracy of proposed analytical approximations is validated through comparison with selective simulation results.

Ultra wideband (UWB) technology is well suited for communication in wireless sensor networks, in which low power consumption for data transmission and the availability of precise ranging information are highly desirable. In this paper, we consider the application of UWB in an event-detection sensor network, and we are interested in maximizing the network operational lifetime while satisfying requirements on the detection and false alarm probabilities. Towards the goal of lifetime maximization we (i) jointly find the optimal routes from multiple events to the sink, to avoid the bottleneck-node phenomenon which often limits lifetime, and (ii) allow adjustment of the data rate that each sensor generates to contribute to event detection, in order to balance the energy consumption among the nodes in the network. Using the UWB signal characteristics, we present a convex optimization model to solve the lifetime maximization problem. The numerical results show that the proposed framework leads to significant improvements in network operational lifetime compared to benchmark approaches.

Impulse-radio ultra-wideband (IR-UWB) radios are slated to be the next generation of transceivers that can support power-constrained applications such as wireless sensor and body area networks. However, despite inherent advantages of UWB transmission due its large signal bandwidth, adoption of IR-UWB radios is hampered by relatively complex receiver structures. In this overview paper, we will first provide a brief description of the challenges for IR-UWB receiver design. Then, we will discuss two recently presented promising UWB receiver concepts, which are based on compressed sensing and multichannel autocorrelation, respectively, and which are apt to overcome current limitations.

Non-contiguous orthogonal frequency division multiplexing (NC-OFDM) is an effective transmission method for cognitive radio systems. It can provide high bandwidth utilization and robustness against time dispersive channels. However, NC-OFDM inherits the problems of high sidelobes and peak-to-average power ratio (PAPR) of the OFDM signal. If not accounted for, this introduces leakage into a primary user (PU) band and distorts the signal of the secondary user (SU). This paper proposes a joint sidelobe and PAPR reduction method that can simultaneously reduce the inherent OFDM out-of-band (OOB) radiation and the OOB radiation caused by a nonlinear power amplifier. In this method, selected mapping (SLM) sequences, which are generated from sequences with a low average sidelobe power, are used to improve the PAPR performance. The key idea is to generate multiple representations of the transmit signal and select a sequence with low OOB radiation and PAPR. We examine the performance of the proposed method taking into account the effects of non-ideal (i.e. non-linear) power amplification. The simulation results show that the proposed technique can significantly reduce OOB radiation while improving the PAPR and bit error rate (BER) for NC-OFDM signals.

Wireless Sensor Networks are well suited for tracking targets carrying RFID tags in indoor environments. Tracking based on the received signal strength indication (RSSI) is by far the cheapest and simplest option, but suffers from secular biases due to effects of multi-path, occlusions and decalibration, as well as large unbiased errors due to measurement noise. We propose a novel algorithm that solves these problems in a distributed, scalable and power-efficient manner. Firstly, our proposal includes a tandem incremental estimator that learns and tracks the radio environment of the network, and provides this knowledge for the use of the tracking algorithm, which eliminates the secular biases due to radio occlusions etc. Secondly, we reduce the unbiased tracking error by exploiting the co-dependencies in the motion of several targets (as in crowds or herds) via a fully distributed and tractable particle filter. We thereby extract a significant 'diversity gain' while still allowing the network to scale seamlessly to a large tracking area. In particular, we avoid the pitfalls of network congestion and severely shortened battery lifetimes that plague procedures based on the joint multi-target probability density.

Bit-interleaved coded modulation (BICM) has established itself as a quasi-standard for bandwidth- and power-efficient wireless communication. In this paper, we present an analytical approach to evaluate the performance of BICM transmission over frequency-flat fading additive white Gaussian noise channels. The statistic of the fading envelope is modeled as Nakagami-m distributed, which spans a wide range of practical multipath fading scenarios through adjustment of the m-parameter. For this setup, we derive approximations for the bit-error rate (BER) and cutoff rate of BICM. Different from previously proposed methods, our analysis is valid for general quadrature amplitude modulation and phase shift keying signal constellations and arbitrary bit-to-symbol mapping rules, and it results in simple closed-form expressions. The key idea is to use well-chosen subsets of signal points to approximate the probability density function of reliability metrics used for decoding. This approximation is accurate for signal-to-noise ratio regions of interest for BICM systems with moderate coding complexity such as, e.g., convolutional coded BICM systems. Based on this approximation we also derive an asymptotic BER expression, which reveals the diversity order and coding gain of BICM. The usefulness of the proposed analytical approach is validated through numerical and simulation results for a number of BICM transmission examples.

Bit-interleaved coded modulation (BICM) is often the method of choice for multilevel transmission over fading channels. If relatively simple forward error-correction (FEC) codes such as convolutional codes are employed, iterative decoding between demapper and FEC decoder can provide significant performance improvements over non-iterative decoding. To keep the complexity of iterative decoding low, the use of hard-decision feedback from FEC decoder to demapper is appealing. However, the price to be paid is a performance degradation due to feedback errors. In this letter, two new demapper designs are developed which are able to strongly mitigate the effect of erroneous feedback. The key ideas are (a) the use of an estimate of the average error rate for the hard-decision feedback and (b) the interpretation of feedback errors as additive impulsive noise. Simulation results show that the proposed designs achieve error rates close to those for iterative decoding with soft feedback, while they maintain the complexity advantage of using hard decision feedback.

Bit-interleaved coded modulation (BICM) has been adopted in many systems and standards for spectrally efficient coded transmission. The analytical evaluation of BICM performance parameters, in particular bit-error rate (BER), has received considerable attention in the recent past. In this paper, we derive BER approximations for BICM transmission over general fading channels impaired by Gaussian mixture noise (GMN). To this end, we build upon the saddlepoint approximation of the pairwise error probability (PEP) and a recently established approximation for the probability density function (PDF) of bit-wise reliability metrics for nonfading additive white Gaussian noise (AWGN) channels. We extend this PDF approximation to the case of GMN, and obtain closed-form expressions for its Laplace transform for fading GMN channels. The latter allows us to express the PEP and thus BER via the saddlepoint approximation. For the special case of fading AWGN channels the presented approximations are closed form, since the saddlepoint is well approximated by 1/2 for BICM decoding. Furthermore, we derive closed-form PEP expressions also for GMN channels in the high signal-to-noise ratio regime and establish the diversity and coding gain for BICM transmission over fading GMN channels. Selected numerical results for the BER of convolutional coded BICM highlight the usefulness of the proposed approximations and the differences between AWGN and GMN channels.

It has been widely acknowledged that the aggregate interference at the receiver for various practical communication channels can often deviate markedly from the classical additive white Gaussian noise (AWGN) assumption due to various ambient phenomena. Moreover, the physical nature of the underlying interference generating process in such cases can lead to a bursty behaviour of the interfering signal, implying that it is highly likely that consecutive symbols are affected by similar noise levels. In this paper, we devise and analyze detection techniques, in conjunction with a convolution code, for such interference channels that possess non-negligible memory by considering optimum and sub-optimum decoding metrics. In particular the inherent memory in the noise process is modeled as a first-order Markov chain, whose state selects the variance of the instantaneous Gaussian noise, leading to a Markov-Gaussian channel model. Analytical expressions are obtained for the cut-off rate, which is an ensemble code parameter, and the bit error rate for a convolutionally coded system, that are subsequently employed for an extensive evaluation of the various metrics considered. Furthermore, the interleaving depth is considered as a design parameter and its effect on performance is analyzed over a range of noise scenarios.

In this letter, we address two questions concerning the application of multipulse pulse-position modulation (MPPM) for free-space optical (FSO) communications: (1) under what condition would MPPM offer a notable advantage over conventional pulse-position modulation (PPM), and (2) what practical coding scheme should be used to realize that advantage. Focusing on bandwidth-efficient FSO transmission, we find decimated MPPM constellations which are suitable for combining with binary codes and offer significant gains in terms of constellation-constrained capacity over PPM under simultaneous peak-power, average-power, and bandwidth constraints. We then consider labeling design for the popular bit-interleaved coded modulation (BICM) and devise a new multilevel coding (MLC) architecture for MPPM, which we refer to as reduced-layer MLC (RLMLC). Considering the Poisson FSO channel model as a relevant example, we provide simulative evidence that RL-MLC MPPM with off-the-shelf low-density parity-check codes can outperform any PPM scheme under the same transmission constraints.

The usual approach when designing an orthogonal frequency division multiplexing (OFDM) system, is to dimension the length of the cyclic prefix (CP) equal to the length of a typical "bad" (i.e., long) channel impulse response, so that both inter-symbol and inter-carrier interference are avoided for almost all channel realizations. However, such an approach does not maximize system capacity. It (a) wastes channel resources for relatively short channel impulse response realizations and (b) it is not necessarily optimal to completely eliminate interference. In this paper, we study the problem of designing the CP length for OFDM systems in a capacity-optimal way. To this end, we first present optimal and simplified metrics suitable to maximize capacity. Then, we apply those metrics and propose practical resource (bit-loading and OFDM sub-channel assignment) algorithms that include CP-length adaptation. We present numerical results for the example of a power line communication (PLC) OFDM system with typical indoor PLC channels that confirm the gains achievable with the proposed CP-length adaptation.

Free-space optical (FSO) transmission systems enable high-speed communication with relatively small deployment costs. However, FSO suffers a critical disadvantage, namely susceptibility to fog, smoke, and conditions alike. A possible solution to this dilemma is the use of hybrid systems employing FSO and radio frequency (RF) transmission. In this paper we propose the application of a rateless coded automatic repeatrequest scheme for such hybrid FSO/RF systems. The advantages of our approach are (a) the full utilization of available FSO and RF channel resources at any time, regardless of FSO or RF channel conditions and temporal variations, and (b) no need for a-priori rate selection at the transmitter. In order to substantiate these claims, we establish the pertinent capacity limits for hybrid FSO/RF transmission and present simulation results for transmission with off-the-shelf Raptor codes, which achieve realized rates close to these limits under a wide range of channel conditions. We also show that in conditions of strong atmospheric turbulence, rateless coding is advantageous over fixed-rate coding with rate adaptation at the transmitter.

We propose a novel communication scheme that combines rateless transmission and multilevel coding (MLC). The scheme is able to attain a throughput that is equal to the constellation-constrained channel capacity. It is particularly useful in cases where the celebrated bit-interleaved coded modulation (BICM) would leave significant gaps to the channel capacity and therefore, MLC is necessary for efficient transmission. We illustrate the application of this scheme to pulse-position modulation (PPM) in free-space optical and multiple-input multiple-output (MIMO) transmission in radio-frequency communication systems. Our numerical results show that, employing an off-the-shelf Raptor code, the proposed scheme achieves a throughput that exceeds the BICM capacity limit in a wide range of signal power.

We have recently proposed a novel receiver for Ultra-Wide-band Impulse-Radio communication in bursty applications like Wireless Sensor Networks. The receiver, based on the principle of Compressed Sensing (CS), exploits the sparsity of the transmitted signal to achieve reliable demodulation. It acquires a modest number of projections of the received signal using analog correlators, and performs a joint decoding of the time of arrival and the data bits from these under-sampled measurements via an efficient quadratic program. In this paper we examine the robustness of this receiver to strong narrow-band interference (NBI) from primary licensed systems like WiMAX. First, by choosing frequency selective test functions in the front-end correlators, we ensure that the interferer can corrupt only a small fraction of the CS measurements. Then we implement a 'digital notch' by identifying and dropping those affected measurements during the quadratic programming reconstruction. The method is easily extended to multiple interferers without additional cost or complexity. We show that by implementing such a 'digital notch' the receiver becomes extremely robust to NBIs. For example its performance is negligibly affected even when the WiMAX customer premise equipment is at a distance comparable to that of the UWB transmitter and the base station is only ten times farther off, both very practical scenarios.

In this paper we present an alternative separable implementation of L2-orthogonal space-time codes (STC) for continuous phase modulation (CPM). In this approach, we split the STC CPM transmitter into a single conventional CPM modulator and a correction filter bank. While the CPM modulator is common to all transmit antennas, the correction filter bank applies different correction units to each antenna. Thereby desirable code properties as orthogonality and full diversity are achievable with just a slightly larger bandwidth demand. This new representation has three main advantages. First, it allows to easily generalize the orthogonality condition to any arbitrary number of transmit antennas. Second, for a quite general set of correction functions that we detail, it can be proved that full diversity is achieved. Third, by separating the modulation and correction steps inside the receiver, a simpler receiver can be designed as a bank of data independent inverse correction filters followed by a single CPM demodulator. Therefore, in this implementation, only one correlation filter bank for the detection of all transmitted signals is necessary. The decoding effort grows only linearly with the number of transmit antennas.

We present an analytical approach to determine the performance of bit-interleaved coded modulation (BICM) transmission over unfaded Gaussian channels. In particular, we derive expressions for bit-error rate and cutoff rate assuming general quadrature amplitude modulation (QAM) constellations. Different from previously proposed methods, our analysis is valid for arbitrary labeling rules and results in simple closed-form expressions. The key idea is to utilize a simplification to estimate the probability density function of reliability metrics, which is tight for signal-to-noise ratio regions of interest for BICM systems with moderate coding complexity such as, e.g., convolutional coded BICM systems. The usefulness of the proposed analytical approach is validated through numerical and simulation results for a number of BICM transmission examples.

Multilevel (Q-ary, Q > 2) pulse-position modulation (Q-PPM) with direct detection is a very popular transmission method for power-efficient free-space optical communication systems. The combination of Q-PPM with error-control coding is an effective means to further improve power efficiency. In this paper, we study the application of the multilevel coding (MLC) paradigm to Q-PPM transmission. In particular, we devise a powerful coded Q-PPM scheme which is a simplified version of MLC and which we refer to as reduced-level MLC (RL-MLC). We show how to design and optimize RL-MLC for Q-PPM when using constellation-constrained capacity as the pertinent figure of merit. Furthermore, we provide simulative evidence that RL- MLC with off-the-shelf low-density parity-check codes (LDPC) closely approaches its corresponding capacity limit. For 64-PPM, RL-MLC with only two levels achieves practically the same performance as that of bit-interleaved coded modulation with iterative decoding (BICM-ID), which involves a more difficult design procedure.

We propose a novel technique for tracking multiple co-dependently maneuvering targets using a wireless sensor network. We consider the scenario where the targets carry radio frequency identification (RFID) tags and the sensors in the network measure some metric of the radio transmissions from these tags, like the received signal strength, the time of arrival or the angle of arrival. These measurements are then processed by a sampling importance re-sampling particle filter for tracking. While such a set-up is now fairly standard in literature, the novel aspect of our algorithm is that it exploits the co-dependencies in the motion of the targets via a fully distributed and tractable particle filter bank. We thereby extract a significant "diversity gain", while allowing the network to scale seamlessly to a large tracking region. In particular, we avoid the pitfalls of network congestion and severely shortened battery lifetimes that plague currently used procedures that implement the filter on the joint multi-target probability density.

The invention of practical rate-less codes in the form of Luby transform and Raptor codes has facilitated the implementation of decode-and-forward relaying schemes which permit the relay to autonomously switch between listening and collaboration phase. Considering the classical three-node relay network employing such a flexible decode-and-forward mechanism, in this paper we investigate signal combining strategies for the destination node. In particular, we compare information and energy combining considered previously in the literature and introduce a new, so-called mixed combining scheme, which is a hybrid of the two former strategies. Assuming general finite-size signal constellations we show that mixed combining is advantageous over the pure combining schemes in terms of achievable rate given the same total transmit energy. A comparison of the associated constellation-constrained capacities with simulated rates achieved for relay transmission with moderate-length Raptor codes underscores (i) the relevance of the capacity-based analysis and (ii) the suitability of rate-less codes for relay transmission.

In this paper, we introduce a new Differentiated Successive Interference Cancellation (DiffSIC) ordering technique for up-link multi-user Multiple-Input Multiple-Output (MIMO) systems. Unlike classical SIC, DiffSIC is capable of differentiating users according to their priority or class of service by selecting a detection order that best fits the users' service profiles. In addition, DiffSIC is able to achieve the optimal SIC detection order that results in the best overall system performance. In order to develop DiffSIC, we introduce analytical methods towards finding instantaneous symbol error rates (SER) for the Zero Forcing SIC (ZF-SIC) and Minimum Mean Square Error SIC (MMSESIC) detectors. We present a number of numerical results which clearly demonstrate the ability of DiffSIC to accomplish service differentiation and overall performance improvement in general.

The recently approved IEEE 802.15.4a standard defines an ultra-wideband (UWB) based physical layer using concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM) and direct-sequence spreading with time hopping. The concatenated code consists of an outer Reed-Solomon (RS) and an inner convolutional code, and the coding and modulation are combined such that both coherent and noncoherent receiver architectures are supported. In this paper, the error-rate performance of IEEE 802.15.4a compliant UWB radios is investigated. To this end, semi-analytical expressions for the bit-error rate (BER) and frame-error rate (FER) of the coded UWB system are derived. The presented framework is comprehensive in that (i) different methods for generating reliability information (i.e., decoding metrics), (ii) the effects of suboptimal multipath combining, and (iii) coherent and noncoherent reception methods are included. Furthermore, a particularly suited errors-and-erasures RS decoding scheme is devised. The evaluation of the error-rate expressions together with simulation results for realistic UWB channels show that (i) the error-rate approximations are tight over wide ranges of BER and FER, (ii) symbol-wise metrics are clearly advantageous over bit-wise metrics for decoding of the convolutional code, (iii) combining the 5 to 10 strongest multipath components approaches the performance of full combining within 1-2 dB for residential and 3-5 dB for outdoor UWB environments, and (iv) the simplicity of noncoherent detection comes at loss of more than 10 dB in signal-to-noise ratio compared to coherent detection.

In this letter, we design and analyze the performance of single-user-type non-linear detectors that are able to cope with the impulsive nature of multiuser interference (MUI) in timehopping impulse-radio ultra-wideband (TH IR-UWB) systems. We collectively refer to these detectors as "robust" detectors. We first propose two novel detectors and then derive semi-analytical expressions for the bit-error rate (BER) of TH IR-UWB with general robust detection. The evaluation of these expressions greatly facilitates the optimization of detector parameters and provides insight into the effects of MUI. A performance comparison shows that (1) robust detection significantly improves performance over conventional detection in the presence of MUI, (2) the parameters for various parametric robust detectors can be chosen to be constant over many transmission scenarios with only little performance degradation compared to using the optimal parameter value, and (3) the proposed two-term detector, which requires a modest amount of parameter estimation, achieves consistently the best performance.

A Wireless Sensor Network (WSN) observes a natural field and aims to recreate it with sufficient fidelity at a, perhaps distant, Fusion Center (FC) using a wireless communication channel of arbitrary capacity. We propose a universal and power efficient method for such data extraction, based on Digital Fountain Codes (DFCs) and joint-source channel decoding. Our method implements a distributed `rate-lessiquest DFC which automatically tunes the number of transmissions to the channel capacity. Furthermore, instead of directly compressing the WSN data, we achieve rate reduction by treating the spatiotemporal dependencies in the field as an outer code, and jointly decoding this concatenation at the FC using a multi-stage iterative decoder. We demonstrate that a power efficiency close to the capacity-rate-distortion limit is achieved at moderate distortion levels, irrespective of the channel capacity or field dependencies. As compared to the traditional approach of source-channel separation, the proposed data extraction scheme is particularly attractive for WSN applications due its computationally simple encoding procedure, low latency and the ability to seamlessly trade-off fidelity of reconstruction for power consumption.

In this paper, we investigate noncoherent detection, i.e. detection assuming the absence of channel state information at the receiver, of on-off keying in an intensity modulation and direct detection (IM/DD) free-space optical (FSO) system. To partially recover the performance loss associated with symbol- by-symbol noncoherent detection, we consider the application of multiple-symbol detection (MSD), in which block-wise decisions are made using an observation window of several bit intervals. Specifically, we develop a fast search algorithm for optimal MSD and propose a reduced-complexity decision metric suitable for suboptimal MSD; performance results confirm that the optimal and suboptimal metrics perform comparably well. Significantly, the complexity of our receiver, on a per bit-decision basis, is only logarithmically dependent on the observation window size. We also present the framework for a decision-feedback receiver and obtain performance expressions for the ideal case of error-free feedback; these expressions serve as an upper bound to the performance of MSD. Analytical and simulation results indicate that as the observation window size increases, the performance of the MSD receiver approaches that of detection with channel state information. The conclusion is reached that the proposed implementation provides an attractive low-complexity mechanism for performing noncoherent MSD in FSO systems.

This paper presents an analysis of the performance of the multiband orthogonal frequency division multiplexing (MB-OFDM) system for ultra wideband (UWB) communication in the presence of interference from IEEE 802.16 WiMAX systems operating in the 3.5 GHz band. We present an exact analysis of the uncoded bit error rate (BER) of the MB-OFDM system, based on Laplace transform techniques. We also present a simple Gaussian approximation for the WiMAX interference, and establish its relative accuracy and usefulness by means of comparison with the exact analysis and simulations. Such a Gaussian approximation is especially useful for simplified performance analysis, as well as for the design of interference mitigation techniques. Motivated by the Gaussian approximation, we propose a simple two-stage interference mitigation technique for coded MB-OFDM transmissions, consisting of interference spectrum estimation during silent periods followed by appropriate bit metric weighting during Viterbi decoding. We compare parametric and non-parametric spectrum estimation techniques for various scenarios of interest. In the presence of WiMAX interference, the two-stage interference mitigation provides substantial gains in performance in return for modest increases in complexity and without requiring any modifications to the MB-OFDM transmitter or signal structure.

In this paper, we consider a relay-assisted wideband cognitive-radio (CR) system under the assumption that the frequency band chosen by the CR relay network for unlicensed spectrum usage overlaps with one or more bands dedicated to primary (e.g., licensed) narrowband links. Our objective is to optimize the performance of the CR system while limiting the interference in direction of the primary receivers, without requiring any adaptation of the transmitted signal spectra at the cognitive nodes. To this end, we study appropriate transmit power allocation (TPA) strategies among the cognitive relays. We first investigate the optimal centralized (OC) TPA solution and show that it can be formulated as a linear program. Since the OC-TPA solution requires a considerable amount of information exchange between the cognitive nodes, we develop two distributed TPA schemes, namely (i) a fully decentralized (FD) TPA scheme and (ii) a distributed feedback-assisted (DFA) TPA scheme. The FD-TPA scheme aims at maximizing the output signal-to-interference- plus-noise ratio (SINR) at the destination node of the CR network according to a best-effort strategy. It requires neither feedback information from the destination node nor an exchange of channel state information between the cognitive relays. The DFA-TPA scheme, on the other hand, utilizes feedback information from the destination node, in order to achieve a predefined target output SINR value, while minimizing the overall transmit power spent by the relays. Analytical and simulation-based performance results illustrate that notable performance improvements compared to non-cooperative transmission (i.e., without relay assistance) are achieved by the proposed schemes, especially when more than two hops are considered. In particular, the proposed distributed TPA schemes typically perform close to the OC-TPA solution.

In this paper, we develop an analytical framework for performance analysis of generic bit-interleaved coded modulation orthogonal frequency-division multiplexing (BICMOFDM) systems impaired by ultra-wideband (UWB) interference. For practical relevance we consider multi-band OFDM (MB-OFDM), direct-sequence UWB (DS-UWB), and impulseradio UWB (IR-UWB) interference formats following recent IEEE/ECMA standards or standard proposals. Besides the exact analysis we calculate the bit error rate (BER) for the case when the UWB interference is modeled as additional Gaussian noise. Our results show that in general the BER of the BICM-OFDM system strongly depends on the UWB format and the OFDM sub-carrier spacing. While the Gaussian approximation is very accurate for DS-UWB, it may severely overor underestimate the true BER for MB-OFDM and IR-UWB interference. Our analysis is applicable to e.g. IEEE 802.11 wireless local area networks (WLANs), IEEE 802.16 wireless access systems (WiMAX), and 4th generation mobile communication systems. Furthermore, since the ECMA MB-OFDM standard is also based on the BICM-OFDM concept, our analysis can also be used to evaluate the impact of other UWB signals on ECMA MB-OFDM UWB systems.

We analyze the performance of a fully decentralized (FD) transmit power allocation (TPA) scheme for relay-assisted cognitive-radio (CR) systems. In particular, we assume that the frequency band chosen by the CR relay network for unlicensed spectrum usage overlaps with an active primary narrowband link. The considered FD-TPA scheme maximizes the signal-to-noise-plus-interference ratio at the destination node of the CR network according to a best-effort strategy, while limiting the interference experienced by the primary receiver. Numerical performance results show substantial improvements compared to non-cooperative transmission. Moreover, the performance of the FD-TPA scheme is close to that of the optimal centralized power allocation solution.

In this paper, we propose a theoretical framework for the analysis of the impact of ultra-wideband (UWB) interference on systems that use the popular combination of bit- interleaved coded modulation (BICM) and orthogonal frequency- division multiplexing (OFDM). For the UWB interference we consider multi-band OFDM (MB-OFDM), direct-sequence UWB (DS-UWB), and impulse-radio UWB (IR-UWB) formats following recent IEEE/ECMA standards and standard proposals. Our analysis is applicable to generic BICM-OFDM victim systems including IEEE 802.11 wireless local area networks (WLANs), IEEE 802.16 wireless access systems (WiMAX), and 4th generation mobile communication systems. Besides the exact analysis we also calculate the bit-error rate for the case when the UWB interference is modeled as additional Gaussian noise. Our results show that in general the BER of the BICM-OFDM system strongly depends on the type of the UWB interference and the sub-carrier spacing. While the Gaussian approximation is very accurate for DS-UWB, it may severely over- or underestimate the true BER for MB-OFDM and IR-UWB interference.

We propose a hybrid non-orthogonal amplify- decode and forward (NADF) transmission protocol for two half- duplex relay nodes. This strategy allows simple amplify and forward (AF) nodes and more complex decode and forward (DF) nodes to participate jointly in the transmission of information. Such a strategy is useful in networks with heterogeneous devices. Analysis of the diversity-multiplexing trade-off (DMT) shows our protocol to be better than the dynamic decode and forward (DDF) protocol for rates between 1/2 and 2/3. Our technique demonstrates that the DDF protocol is not an upper bound and that protocols exist which perform closer to the DMT limit. The NADF protocol has equal performance to the DDF protocol for rates between 2/3 and one. It has a DMT performance below the DDF protocol and identical to or better than the slotted amplify and forward (SAF) protocol and non-orthogonal amplify and forward (NAF) schemes for rates from zero to 1/2.

In this paper, we introduce distributed generalized cyclic delay diversity (DGCDD) for cooperative signaling in orthogonal frequency division multiplexing (OFDM) wireless relay networks. We assume that the set of cooperating nodes is a priori unknown and assign each node in the network a fixed cyclic filter (CF). Assuming bit-interleaved coded modulation (BICM) for forward error correction, we derive an optimization criterion for the CFs and show that DGCDD can exploit the full diversity of the wireless channel. A numerical method for CF design is provided and compared with randomly generated filters. Simulation results confirm the excellent performance of the proposed scheme and show that the performance loss of DGCDD compared to GCDD with co-located antennas is small for sufficiently long CFs.

Fountain codes have recently gained wide attention in communications due to their capacity-approaching performance and rateless properties that allow them to seamlessly adapt to unknown channel statistics. In this paper, we consider the problem of low complexity decoding of Luby transform codes, which are a class of linear fountain codes. We adapt the recently proposed technique of informed dynamic scheduling to the rateless regime, and combine it with the method of incremental decoding to obtain a decoder that has a significantly reduced computational load compared to the commonly used alternative of message-reset decoding with a flooding schedule. This reduction in complexity, in some cases as large as a factor of sixty, is obtained without affecting the error rate performance of the code.

Bit-loaded orthogonal frequency division multiplexing (OFDM) with convolutional coding is a powerful technique for transmission over quasi-static frequency-selective fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we develop a novel analytical method for bit error rate (BER) estimation of bit-loaded coded OFDM systems operating over frequency-selective quasi-static channels with non- ideal interleaving. To illustrate the application of the proposed analysis, we compare the performance of a number of OFDM bit-loading schemes applied to Multiband OFDM (MB-OFDM) for Ultra-Wideband (UWB) radio, and to IEEE 802.11a/g systems for wireless local area networks (WLANs). We also propose and evaluate a hybrid loading scheme which selects the best loading for each channel realization from amongst a number of candidates.

In this paper, the application of combinatorial geometry to noncoherent multiple-symbol differential detection (MSDD) is considered. The resulting algorithm is referred to as CG-MSDD. Analytical expressions for the complexity of CG-MSDD are derived and it is shown that it is polynomial in the length N of the MSDD observation window if the rank of the N times N channel autocorrelation matrix is fixed, but in fact exponential in N if standard fading models are considered. Compared to popular sphere-decoder based MSDD, CG-MSDD is superior (i) in low-signal-to-noise power ratio (SNR) slow-fading channels as its complexity is independent of the SNR, (ii) as its complexity is constant, i.e., independent of the particular channel and noise realization, and (iii) asymptotically, as its complexity exponent only scales linearly with the bandwidth of the fading process.

In this paper, a unified framework for the analysis of differential detection (DD) schemes in time-variant multiple-input multiple-output Rayleigh fading channels is provided. The present results are very general in that they apply to transmission with differential phase-shift keying, unitary differential space-time modulation (DSTM), and block DSTM and reception with conventional DD (CDD), multiple-symbol DD (MSDD), decision-feedback DD (DFDD), and (differentially) coherent detection (CD). New result for general quadratic forms of Gaussian random variables are derived which allows us to obtain elegant closed-form expressions for the pairwise error probabilities (PEPs) of the dominant error events of the considered detectors. Furthermore, it is shown that a unified treatment of all considered detectors is possible with a properly defined effective signal-to-noise ratio (ESNR) and a useful connection between MSDD and minimum-mean-squared-error (MMSE) interpolation is established. Interesting novel results obtained from this analysis include: (i) DSTM constellations designed for CDD and CD are also optimum for MSDD and DFDD; (ii) the error floor entailed by MSDD and DFDD in time-variant fading decreases exponentially with the observation window size N; and (iii) in time-variant fading with effective normalized fading bandwidth Bh,effT MSDD with N → ∞ suffers only from an SNR loss of (1 -2Bh,effT) compared to CD, whereas DFDD suffers from a diversity loss of (1 - 2Bh,effT).

In this paper, binary linear block codes with very low encoding and decoding complexity (therefore, "simple" codes) are introduced as outer codes in a serially concatenated coding scheme employing multilevel differential phase-shift keying, i.e., differential modulations, as inner codes. Such a concatenated coding scheme is particularly suitable for power- and bandwidth-efficient transmission over channels with phase ambiguities or completely unknown phase at the receiver. Using extrinsic information transfer chart based analysis and optimization, the performance of the new concatenated codes is found to be within less than 1 dB of the pertinent capacity limit for the additive white Gaussian noise channel. This compares favorably with more complex benchmark schemes using e.g. outer low-density parity-check codes proposed recently in the literature. Simulation results confirm the predicted performance advantages for the proposed simple codes.

Partial transmit sequences (PTS) is a popular technique to reduce the peak-to-average power ratio (PAR) in orthogonal frequency division multiplexing (OFDM) systems. PTS is highly successful in PAR reduction and efficient redundancy utilization, but the considerable computational complexity for the required search through a high-dimensional vector space and the necessary transmission of side information (SI) to the receiver are potential problems for a practical implementation. In this paper, we revisit PTS for PAR reduction and tackle these two problems. To address the complexity issue, we formulate the search problem of PTS as a combinatorial optimization (CO) problem. This enables us to (i) unify various search strategies proposed earlier in the PTS literature and (ii) adapt efficient search algorithms known from the CO literature to PTS. We also propose a modified PTS objective function, which reduces the number of multiplications required for PTS. Numerical results show that, perhaps surprisingly, simple random search yields the best performance-complexity tradeoff for moderate PAR reduction, whereas two novel CO-based methods excel if close-to-optimum PAR reduction is desired. The SI transmission problem is solved by a simple preprocessing of the data stream before PAR reduction. This preprocessing introduces the minimal possible redundancy and allows SI embedding without affecting the PAR reduction capability of PTS or causing peak regrowth.

We employ a photon-counting signal model of a multiple-input multiple-output (MIMO) free-space optical (FSO) system and investigate detection assuming the absence of channel state information (CSI) at the receiver, in moderate to strong atmospheric turbulence. The considered modulation format is on-off keying with repetition coding across the transmitters. To partially recover the performance loss associated with symbol-by-symbol detection without CSI, we consider the application of multiple-symbol detection (MSD) to equal gain combined (EGC) statistics. We develop a fast search algorithm for EGC-MSD and propose a suboptimal closed-form decision metric suitable for reduced-complexity implementation; performance results confirm that the true and suboptimal metrics perform comparably well. Significantly, the complexity of our receiver, on a per bit-decision basis, is only logarithmically dependent on the observation window length N, and is effectively independent of the size of the MIMO array. We also present the framework for a decision-feedback receiver and obtain performance expressions for the ideal case of error-free feedback; these expressions serve as an upper bound to the performance of EGC-MSD. Analytical and simulation results indicate that the system effectively realizes the diversity gains expected from a MIMO configuration and that the performance of the EGC-MSD receiver approaches the EGC with CSI lower bound with increasing N.

The combination of space-time (ST) coding and continuous-phase modulation (CPM) is attractive for power- efficient transmission over fading channels. In this paper, we propose a diagonal block-based ST-CPM (DBST-CPM) scheme, which in addition to its high power efficiency facilitates noncoherent detection at the receiver. DBST-CPM can be regarded as a non-trivial extension of well-known differential ST modulation (DSTM) with diagonal signal matrices for linear modulation formats. For optimization of the code parameters of DBST-CPM we derive an upper bound on the frame-error rate of DBST-CPM in the quasi-static fading channel (QSFC) and we present an efficient optimization algorithm. Additionally, we derive decision rules for low-complexity non-coherent detection of DBST-CPM in various fading environments. Numerical and simulation results show that (a) the derived upper bound accurately predicts the performance of DBST-CPM in the QSFC, (b) the proposed code optimization yields highly power-efficient designs, and (c) the non-coherent detectors approach the performances of their coherent counterparts for various fading channel models.

In this paper, distributed space-time (ST) codes for continuous-phase modulation (CPM) are introduced. The distributed ST codes are designed to operate in wireless networks containing a large set of nodes N, of which only a small a priori unknown subset S sub N will be active at any time. Under the proposed scheme, a relay node transmits a signal which is the product of a diagonal block-based ST code (optimized specifically for ST-CPM transmission) and a signature vector of length Ncuniquely assigned to each node in the network. An efficient method is presented for the design and optimization of appropriate signature vector sets, assuming a quasi-static, frequency nonselective fading channel model. If a properly designed signature vector set is employed it is shown that a diversity order of d = min{Ns,Nc} can be achieved, where Nsis the number of active relay nodes. The decoding complexity of the proposed scheme is shown to be independent of the number of active relay nodes, and non-coherent receiver implementations, which do not require channel estimation, are applicable. Compared to distributed ST transmission with linear modulation, distributed ST-CPM can considerably reduce the energy consumption at the transmitter due to the constant envelope of the transmit signal. At the same time, the additional energy consumption due to more complex receiver processing can be kept low. Therefore, the proposed distributed ST-CPM scheme is particularly apt for energy-efficient cooperative transmission in wireless networks.

We investigate an 'inference first' (IF) approach to information retrieval from a wireless sensor network (WSN). In this method, statistical estimation pertinent to the user's application is implemented within the network (in-situ) and only the relevant sufficient statistics are exported. We formulate this procedure as a delay-free filtering problem on a spatio-temporal hidden Markov model (HMM), and propose a scalable approximate distributed filter. The algorithm is a novel application of the idea of iterated decoding, where we iteratively marginalize the joint distribution of the state of the HMM at two consecutive time epochs. We compare and contrast algorithms like the Gibbs sampler (GS), mean field decoding (MFD) and broadcast belief propagation (BBP), and discuss their suitability for in-situ marginalization. A simplified analysis of the energy gain achievable by the IF approach, relative to centralized processing, is provided.

In many lifetime enhancement strategies for wireless sensor networks (WSNs) it is often necessary to identify the statistical model of the underlying physical field. We consider the problem of in-situ inference as an exemplary application and propose an in-situ model estimation algorithm that works in tandem with a parametric distributed filtering procedure. We demonstrate, via averaged-gradient analysis and simulations, that the resulting adaptive filter is stable, robust and, importantly, fully scalable. It compares favorably with kernel-regression inference, and typically significantly outperforms the latter when the spatio-temporal variations in the natural field are relatively rapid.

In this paper, we investigate noncoherent detection, i.e. detection assuming the absence of channel state information at the receiver, of on-off keying in a free-space optical system. To partially recover the performance loss associated with symbol- by-symbol noncoherent detection, we consider the application ofmultiple-symboldetection(MSD), in which block-wise decisions are made using an observation window ofNbit intervals. Specifically, we develop a fast search algorithm for optimal MSD and propose a reduced-complexity decision metric suitable for suboptimal MSD; performance results confirm that the optimal and suboptimal MSD metrics perform equally well. Significantly, the complexity of our MSD receiver, on a per bit-decision basis, is effectively independent of the length of the observation window. Furthermore, bit-error-rate results clearly indicate that the performance of the MSD receiver approaches the coherent detection lower bound with increasingN.

In this paper, a class of distributed space-time (ST) codes for continuous-phase modulation (CPM) is introduced. The distributed ST codes are designed to operate in wireless networks containing a large set of nodes N , of which only a small a priori unknown subset S sub N will be active at any time. Under the proposed scheme, a relay node transmits a signal which is the product of a diagonal block-based ST (DBST) code (optimized specifically for ST-CPM transmission) and a signature vector of length Nc uniquely assigned to each node in the network. Two efficient methods are presented for the design and optimization of signature vector sets. If a properly designed signature vector set is employed it is shown that a diversity d = min{Ns,Nc} can be obtained, where Nsis the number of active users. Further, the decoding complexity of the proposed scheme is shown to be independent of the number of active relay nodes. Through the combination of DBST-CPM codes and signature vector sets the proposed distributed DBST-CPM codes allow for power-efficient cooperative transmission, and low complexity coherent and noncoherent receiver implementations.

In this paper differential space-frequency frequency division multiplexing (MIMO-OFDM) and multiple-symbol differential detection (MSDD) without channel state information (CSI) at the receiver is considered. Inspired by previous work presented in the literature, a novel DSFM scheme is devised, which makes use of spatial and/or spectral (multipath) diversity and is particularly suited for MIMO-OFDM and power-efficient, low-delay MSDD. Furthermore, the application of a two-dimensional (2D) observation window to MSDD (2D-MSDD) in order to exploit channel correlations in both time and frequency direction, is investigated and tree-search decoding is applied to solve the detection problem efficiently. An analytical approximation of the symbol-error rate of 2D-MSDD for MIMO-OFDM under spatially correlated fading is derived, which enables quick and accurate performance evaluations. Numerical and simulation results corroborate the efficacy of our approach and show that power efficiency close to that of coherent detection with perfect CSI is feasible in all standard fading scenarios at reasonable decoder complexity.

In this paper, the application of combinatorial geometry to noncoherent multiple-symbol differential detection (MSDD) is considered. The resulting algorithm is referred to as CG-MSDD. Analytical expressions for both the complexity and the error-rate performance of CG-MSDD are derived and it is shown that its complexity is polynomial in the length N of the MSDD observation window if the rank of the N times N channel autocorrelation matrix is fixed, but in fact exponential in N if standard fading models are considered. Compared to popular sphere-decoder based MSDD, CG-MSDD is superior (i) in low-signal-to-noise power ratio (SNR) slow-fading channels as its complexity is independent of the SNR, (ii) as its complexity is constant, i.e., independent of the particular channel and noise realization, and (iii) asymptotically, as its complexity exponent only scales linearly with the bandwidth of the fading process.

Orthogonal frequency-division multiplexing (OFDM) with multiple transmit and receive antennas (MIMO-OFDM) and adaptive bit-loading (ABL) offers reliable high-data rate communication for systems with moderate mobility as considered in e.g. IEEE 802.16e. In this paper, we propose and optimize wrapped space-time coding (WSTC) for bit-loaded MIMO-OFDM. We further optimize V-BLAST with ABL by mitigating error propagation inherent in its detection process. We compare their performances with benchmark schemes known from the literature. Simulation results show that WSTC-based MIMO-OFDM achieves excellent error rate performances while feedback requirements for loading are low.

Free-space optics (FSO) have received increased attention recently for last-mile, line-of-sight wireless links. In this paper, we employ a photon-counting signal model of an FSO system and investigate noncoherent detection, i.e. detection assuming the absence of channel state information at the receiver, of on-off keying (OOK). To partially recover the performance loss associated with symbol-by-symbol noncoherent detection, we consider the application of multiple-symbol detection (MSD), in which block-wise decisions are made using an observation window of N bit intervals. We develop a fast search algorithm for optimal MSD, which corresponds to a fixed bit-wise implementation complexity effectively independent of N. Furthermore, we obtain performance expressions for an ideal decision-feedback receiver, which serve as an upper bound to the performance of the MSD receiver. Analytical and simulation results indicate that the performance of the MSD receiver approaches the coherent detection lower bound with increasing N.

In this paper, we propose a generalized version of cyclic delay diversity (CDD) which is a popular form of space-frequency coding for multi-antenna orthogonal frequency division multiplexing (OFDM) systems. In this generalized CDD (GCDD) the cyclic delays of CDD are replaced with cyclic diversity filters. Assuming bit-interleaved coded modulation (BICM) for forward error correction, we derive an optimization criterion for the GCDD filters and a gradient algorithm for finding the optimum filters. For certain special cases we also provide a closed-form solution for the optimum filters. Simulation results confirm that GCDD can achieve significant performance gains for conventional CDD, especially in spatially correlated fading.

Free-space optics (FSO) have received increased attention recently for last-mile wireless links. In this paper, we investigate noncoherent detection, i.e. detection assuming the absence of channel state information at the receiver, of on-off keying (OOK) in an FSO system. To partially recover the performance loss associated with conventional symbol-by- symbol noncoherent detection, we consider the application of decision-feedback detection (DFD), in which symbol-by-symbol decisions are made using previous decisions and an observation window of N received statistics. Analytical and simulation results indicate that the performance of a DFD receiver approaches the coherent detection lower bound with increasing window length. Consequently, as the proposed receiver exhibits a complexity independent of N, the conclusion is reached that DFD is an effective approach for noncoherent detection in an FSO system.

Two new Bluetooth receiver designs, the so-called modified limiter-discriminator detector with integrate and dump filtering (LDI) and noncoherent sequence detection (NSD), have recently been proposed in the literature. These receivers have been shown to improve the Bluetooth system performance in terms of physical-layer measures like bit-error rate (BER) and packet-error rate (PER) compared to the conventional LDI receiver. In this paper, we present a more comprehensive performance comparison for these receivers, which includes consideration of the spatial distribution of Bluetooth devices, channel propagation, data traffic, scheduling, automatic repeat request (ARQ), and baseband packet selection. The performance is measured in terms of practically relevant metrics such as end-to-end delay and throughput. Our numerical and simulation results verify that incorporating the new receivers into Bluetooth devices can considerably improve data-rate and quality-of-service performance compared to employing state-of-the-art LDI receivers.

Recently, Rankin, Taylor, and Martin (RTM) (Rankin, 2006) have proposed a simple channel augmentation scheme for multiple input multiple output (MIMO) systems. They have shown that the virtual receive antennas created by repeating the same transmit symbols several times can improve the outage rate of slow MIMO fading channels, especially if the number of transmit antennas is smaller than the number of receive antennas. Inspired by (Rankin, 2006) we propose in this paper two novel channel augmentation schemes which have the same complexity as the RTM scheme. In the first scheme, the transmitted symbols are not only repeated but also complex conjugated leading to the conjugate virtual antenna (CVA) scheme. In the second scheme, the transmitted symbols are constrained to be real-valued leading to the real virtual antenna (RVA) scheme. We show that the RTM, CVA, and RVA schemes can achieve a higher outage rate than the baseline scheme without augmentation for both V-BLAST and D-BLAST. Thereby, the novel RVA and CVA schemes are more robust to channel correlations than the RTM scheme.

The paper considers the single relay orthogonal cooperative diversity decode and forward scenario as a block fading channel model. A closed form expression for the pairwise error probability is derived which leads to design criteria for full diversity and coding gain. Furthermore, the power distribution between the source and relay units is introduced as a design parameter. Fixed power distribution allocation has the potential of improving performance with no increase in the system complexity. Several techniques for improving the coding gain are given based on the power distribution during the cooperation phase of the transmission. As an example, the (1,7/5) convolutional code was considered. Simulation results for this example show that a 1 dB performance gain can be achieved by modifying the power distribution of the source and relay. For the code considered, the equal power allocation method most commonly used gave the worst performance. The best performance was achieved when the source was silent during the cooperation phase. This observation simplifies protocol design.

Recently, Rankin, Taylor, and Martin (RTM) have proposed a simple channel-augmentation scheme for multiple-input multiple-output (MIMO) systems. They have shown that the virtual receive antennas created by repeating the same transmit symbols several times can improve the outage rate of slow MIMO fading channels, especially if the number of transmit antennas is smaller than the number of receive antennas. Inspired by the RTM paper, we propose in this paper two channel-augmentation schemes having the same low complexity as the RTM scheme. In the first, the transmitted symbols are both repeated and complex conjugated leading to the conjugate virtual antenna (CVA) scheme. In the second, the transmitted symbols are constrained to be real-valued leading to the real virtual antenna (RVA) scheme. We show that the RTM, CVA, and RVA schemes can achieve a higher outage rate than the baseline scheme without augmentation for both V-BLAST and D-BLAST. The novel RVA and CVA schemes are seen to be more robust to channel correlation than the RTM scheme.

The application of trellis shaping was proposed to reduce the peak-to-average power ratio (PAR) of orthogonal frequency division multiplexing (OFDM) signals. In this letter, we review the trellis-shaping schemes presented in the literature, and we introduce modifications such as a new decoding metric and the use of sequential decoding. We conduct comprehensive complexity and performance comparisons for the different schemes, and one interesting result of this work is that, in terms of PAR-reduction capability, trellis shaping with time-domain metrics is generally superior to trellis shaping with frequency-domain metrics. Furthermore, the proposed modifications enable trellis shaping for PAR reduction with a flexible performance-complexity tradeoff.

Ultra-wideband wireless transmission has attracted considerable attention both in academia and industry. For high-rate and short-range transmission, direct sequence based ultra-wideband (DS-UWB) systems are a strong contender for consumer market applications. Due to the large transmission bandwidth, the UWB channel is characterized by a long root-mean-square delay spread and the RAKE receiver cannot always overcome the resulting intersymbol interference. We therefore study equalization for DS-UWB systems. This paper is comprised of two parts. In this first part, we consider DS-UWB with binary phase-shift keying (BPSK) modulation, which is the mandatory transmission mode for DS-UWB systems promoted by the UWB Forum industry alliance. We derive matched filter bounds for optimum equalization taking into account practical constraints like receiver filtering, sampling, and the number of RAKE fingers when RAKE preprocessing is applied at the receiver. Our results show that chip-rate sampling is sufficient for close-to-optimum performance. For analysis of suboptimum equalization strategies we further study the distribution of the zeros of the channel transfer function including RAKE combining. Our findings suggest that linear equalization is well suited for the lower data rate modes of DS-UWB systems, whereas nonlinear equalization is preferable for high-data rate modes. Moreover, we devise equalization schemes with widely linear processing, which improve performance while not increasing equalizer complexity. Simulation and numerical results confirm the significance of our analysis and equalizer designs and show that low-complexity (widely) linear and nonlinear equalizers perform close to the pertinent matched filter bound limit.

Direct-sequence ultra wideband (DS-UWB) transmission is a strong contender for the physical layer of high data-rate short-range UWB systems. Since long delay spreads in UWB channels cause significant intersymbol interference, DS-UWB systems require equalization. In this second part of two papers, we investigate equalization for DS-UWB with 4-ary biorthogonal keying (4BOK), which is one of the two modulation formats that was proposed for standardization by the IEEE 802.15.3a task group. To this end, we first derive expressions for the bit error rate (BER) according to the matched-filter bound for 4BOK DS-UWB, which serve as theoretical performance limits for equalization. We then devise structures and methods for filter optimization for low-complexity linear and nonlinear equalization schemes. In this context, we develop a new equivalent multiple-input multiple-output (MIMO) description of 4BOK DS-UWB, which facilitates the design of efficient equalizers using MIMO filter optimization techniques. Furthermore, we propose the application of widely linear processing to these equalizers. Simulation and semianalytical results show that MIMO equalization is greatly advantageous over more obvious non-MIMO schemes and that the proposed MIMO equalizers allow for power-efficient 4BOK DS-UWB transmission close to the theoretical limits with moderate computational complexity.

Differential space-time modulation (DSTM) using unitary-matrix signal constellations is an attractive solution for transmission over multiple-input multiple-output (MIMO) fading channels without requiring channel state information (CSI) at the receiver. To avoid a high error floor for DSTM in relatively fast MIMO fading channels, multiple-symbol differential detection (MSDD) has to be applied at the receiver. MSDD jointly processes blocks of several received matrix-symbols, and power efficiency improves as the blocksize increases. But since the search space of MSDD grows exponentially with the blocksize and also with the number of transmit antennas and the data rate, the complexity of MSDD quickly becomes prohibitive. In this paper, we investigate the application of tree-search algorithms to overcome the complexity limitation of MSDD. We devise a nested MSDD structure consisting of an outer and a number of inner tree-search decoders, which renders MSDD feasible for wide ranges of system parameters. Decoder designs tailored for diagonal and orthogonal DSTM codes are given, and a more power-efficient variant of MSDD, so-called subset MSDD, is proposed. Furthermore, we derive a tight symbol-error rate approximation for MSDD, which lends itself to efficient numerical evaluation. Numerical and simulation results for different DSTM constellations and fading channel scenarios show that the new tree-search MSDD achieves a significantly better performance-complexity tradeoff than benchmark decoders.

Several recent standards such as IEEE 802.11a/g, IEEE 802.16, and European Computer Manufacturers Association (ECMA) multiband orthogonal frequency division multiplexing (MB-OFDM) for high data-rate ultra-wideband (UWB), employ bit-interleaved convolutionally coded multicarrier modulation over quasi-static fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we present two novel analytical methods for bit error rate (BER) estimation of coded multicarrier systems operating over frequency-selective quasi-static channels with nonideal interleaving. In the first method, the approximate performance of the system is calculated for each realization of the channel, which is suitable for obtaining the outage BER performance (a common performance measure, for e.g., MB-OFDM systems). The second method assumes Rayleigh distributed frequency-domain subcarrier channel gains and knowledge of their correlation matrix, and can be used to directly obtain the average BER performance. Both methods are applicable to convolutionally coded interleaved multicarrier systems employing quadrature amplitude modulation (QAM), and are also able to account for narrowband interference (modeled as a sum of tone interferers). To illustrate the application of the proposed analysis, both methods are used to study the performance of a tone-interference-impaired MB-OFDM system.

Several standards such as IEEE 802.11a/g, IEEE 802.16, and the European Computer Manufacturers Association (ECMA) multiband orthogonal frequency division multiplexing (MB-OFDM) for high data-rate ultra-wideband employ bit-interleaved convolutionally coded multicarrier modulation over quasi-static fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we present two novel analytical methods for bit error rate (BER) estimation of coded multicarrier systems operating over frequency-selective quasi-static channels with nonideal interleaving. In the first method, the approximate performance of the system is calculated for each realization of the channel, which is suitable for obtaining the outage BER performance (a common performance measure for, e.g., MB-OFDM systems). The second method assumes Rayleigh distributed frequency-domain subcarrier channel gains and knowledge of their correlation matrix, and can be used to directly obtain the average BER performance. Both methods are applicable to convolutionally coded interleaved multicarrier systems employing quadrature amplitude modulation, and are also able to account for narrowband interference (modeled as a sum of tone interferers). To illustrate the application of the proposed analysis, both methods are used to study the performance of a tone-interference-impaired MB-OFDM system.

Multiple-symbol differential detection (MSDD) for multiple-input-multiple-output Rayleigh-fading channels is considered. MSDD, which jointly processes blocks of N received symbols to detect N-1 data symbols, allows for power-efficient transmission without requiring channel state information at the receiver. In previous work, the authors showed that computational efficient sphere decoding algorithms can be used to accomplish MSDD. In this correspondence, the computational complexity of this sphere-decoding based MSDD is analyzed. In particular, it is proven by means of a lower bound that the complexity of the Fincke-Pohst multiple-symbol differential sphere decoder (FP-MSDSD), while being very low over wide ranges of N and signal-to-noise ratios, is exponential in N in principle. Furthermore, both exact and simple approximate expressions for the complexity of FP-MSDSD are derived, which allow for quick assessment of ranges of useful window sizes N of FP-MSDSD and show that the exponential rate of growth of the complexity of FP-MSDSD is asymptotically equal to that of brute-force MSDD

In this paper, we investigate the effect of multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) interference on narrowband (NB) receivers. For this purpose, we first derive the exact moment generating function of MB-OFDM UWB interference. Based on this result, we develop analytical expressions for the amplitude probability distribution (APD) and the bit error rate (BER) of a binary phase-shift keying NB receiver. These expressions can be efficiently numerically evaluated and the presented analysis is general enough to encompass non-fading and various fading NB channels. We show that for NB signals with, respectively, much smaller and much larger bandwidths than the MB-OFDM sub-carrier spacing a Gaussian approximation (GA) and an impulsive GA (IGA) of the MB-OFDM UWB interference lead to accurate performance predictions. However, for most NB channel models and signal bandwidths the exact BER analysis has to be used to obtain meaningful results. An exception is the Rayleigh fading NB channel where both GA and IGA yield tight approximations of the exact BER regardless of the NB signal bandwidth.

In this paper, we propose a simple orthogonal space-time block coding (OSTBC) technique for continuous-phase modulation (CPM). Although the straightforward combination of orthogonal designs (ODs) and CPM was deemed impossible in X. Zhang and M.P. Fitz (2003) G. Wang and X-G Xia (2004) we show that this is easily accomplished with a burst-based approach. In fact, using the proposed technique ODs can be combined with any CPM scheme. After an appropriate ST combining at the receiver, the same detection techniques as in case of single-antenna transmission can be applied. This is a significant advantage over previously proposed ST coding schemes for CPM. We also derive accurate approximations for the bit error rate and the frame error rate of CPM with OSTBC. Both analysis and simulations show in good agreement the excellent performance of the proposed scheme

In this paper, we analyze the frequency-hopping orthogonal frequency-division multiplexing (OFDM) system known as Multiband OFDM for high-rate wireless personal area networks (WPANs) based on ultra-wideband (UWB) transmission. Besides considering the standard, we also propose and study system performance enhancements through the application of Turbo and Repeat-Accumulate (RA) codes, as well as OFDM bit-loading. Our methodology consists of (a) a study of the channel model developed under IEEE 802.15 for UWB from a frequency-domain perspective suited for OFDM transmission, (b) development and quantification of appropriate information-theoretic performance measures, (c) comparison of these measures with simulation results for the Multiband OFDM standard proposal as well as our proposed extensions, and (d) the consideration of the influence of practical, imperfect channel estimation on the performance. We find that the current Multiband OFDM standard sufficiently exploits the frequency selectivity of the UWB channel, and that the system performs in the vicinity of the channel cutoff rate. Turbo codes and a reduced-complexity clustered bit-loading algorithm improve the system power efficiency by over 6 dB at a data rate of 480 Mbps.

In this paper, we introduce a new class of distributed space-time trellis codes (DSTTCs) for wireless networks with a large set of decode-and-forward relay nodes N. We consider the general case where each relay node is equipped with NTantennas and the destination node is equipped with NRantennas. It is assumed that at any given time only a small, a priori unknown subset of nodes S ∈ N is active and neither the relay nodes nor the destination node know which relay nodes are active. In the proposed scheme, each node is assigned a signature matrix and the signal transmitted by an active node is the product of the signature matrix and a space-time trellis code (STTC) matrix originally designed for Ncco-located antennas. It is shown that existing full-rank STTCs designed for Nc⩾ 2 co-located antennas are a favorable choice for the code matrix. Two practical designs for good deterministic signature matrix sets are provided and compared with random signature matrices. If the signature matrices are properly optimized, the proposed DSTTCs achieve a diversity order of d = min{NcNR, NTNSNR} if NSnodes are active. Simulation results confirm that DSTTCs yield significant performance gains over distributed space-time block codes and distributed space-time filtering. Furthermore, equipping relay nodes with a second antenna can be highly beneficial especially if only few nodes can be active at any given time.

In this paper, binary linear block codes with very low encoding and decoding complexity are introduced for the use as outer codes in a serial concatenated coding scheme employing differential modulations as inner codes. Using extrinsic information transfer chart based analysis and optimization the performance of the new concatenated codes is found to be within less than 1 dB of the pertinent capacity limit for the additive white Gaussian noise channel. This compares favorably with more complex benchmark schemes using e.g. outer low density parity check codes proposed recently. For decoding without channel phase estimation a low-complexity noncoherent decoder is presented, which achieves performance close to that of a coherent decoder in channels with moderate phase noise.

Data transmission over power lines is an attractive alternative to well-established wireline and wireless communication technologies. One of the main challenges in accomplishing reliable power-line communication (PLC) is channel impairment through electromagnetic interferences, or so-called impulse noise. In this paper, we consider transmission over impulse-noise channels for a typical narrowband system architecture employing convolutional codes and Viterbi decoding. We present different decoding metrics, including new designs adopted from the multiuser detection literature, and we derive expressions for cutoff rate and bit-error rate (BER) performances of the corresponding decoders. These expressions are amenable for quick numerical evaluation and thus, constitute a valuable tool for decoder optimization and performance comparison. Our numerical and BER simulation results show that one of the proposed metrics enables robust decoding without knowledge of the statistic of the impulse noise with a performance close to that of optimum decoding, which relies on the noise statistic. It is further highlighted that, different from transmission over the Gaussian-noise channel, quadrature detection is beneficial in case of real-valued modulation and passband transmission over impulse-noise channels.

This paper takes a fresh look at peak-to-average power ratio (PAR) reduction for orthogonal frequency-division multiplexing (OFDM) using partial transmit sequences (PTS). In particular, the two major drawbacks of PTS, its high complexity when searching for a "good" solution and the need to transfer side information (SI) to the receiver are addressed. Reformulating PTS as a combinatorial optimization (CO) problem enables us to apply various efficient search strategies from the CO literature to PTS. We also incorporate an approximation of the PTS objective function to further reduce the overall complexity. Finally, we propose an implicit SI embedding scheme. This low-complexity scheme requires minimal redundancy and has minimal effect on the overall performance of the OFDM system.

The combination of space-time (ST) coding and continuous-phase modulation (CPM) is attractive for power-efficient transmission over fading channels. In this paper, we propose a diagonal block based ST-CPM (DBST-CPM) scheme, which in addition to high power efficiency facilitates detection without channel state information at the receiver. DBST-CPM can be regarded as a non-trivial extension of well-known differential ST modulation (DSTM) with diagonal signal matrices for linear modulation formats. We derive an upper bound on the frame- error rate of DBST-CPM and we present an efficient algorithm for optimization of the code parameters of DBST-CPM. Numerical and simulation results show that the upper bound accurately predicts the performance of DBST-CPM and that the proposed code optimization yields highly power-efficient designs.

Several recent standards such as IEEE 802.11a/g, IEEE 802.16, and ECMA multiband orthogonal frequency division multiplexing (MB-OFDM) for high data-rate ultra-wideband (UWB), employ bit-interleaved convolutionally-coded multicarrier modulation over quasi-static fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we present two novel analytical methods for bit error rate (BER) estimation of coded multicarrier systems operating over frequency-selective quasi-static channels with non-ideal interleaving. In the first method, the approximate performance of the system is calculated for each realization of the channel, which is suitable for obtaining the outage BER performance (a common performance measure for e.g. MB-OFDM systems). The second method assumes Rayleigh distributed frequency-domain subcarrier channel gains and knowledge of their correlation matrix, and can be used to directly obtain the average BER performance. Both methods are applicable to convolutionally-coded interleaved multicarrier systems employing quadrature amplitude modulation (QAM). To illustrate the application of the proposed analysis, both methods are used to study the performance of the MB-OFDM system.

The application of trellis shaping was recently proposed to reduce the peak-to-average power ratio (PAR) of orthogonal frequency division multiplexing signals. In this paper, we review the trellis shaping schemes presented in the literature and we introduce modifications such as a new decoding metric and the use of sequential decoding, which improve PAR reduction and/or reduce complexity of trellis shaping. Based on implementation onisuggestions, we conduct a complexity and performance comparison for the different schemes. One interesting result of this work is that trellis shaping with time-domain metrics is superior to trellis shaping with frequency-domain metrics.

In this paper, we present a receiver design for Bluetooth transmission based on Laurent's decomposition of the Bluetooth transmit signal. The main features of this receiver are (a) its low complexity compared to alternative solutions, (b) its excellent performance close to the theoretical limit, and (c) its high robustness against frequency offsets, phase noise, and modulation index variations, which are characteristic for low-cost Bluetooth devices. In particular, we show that the devised noncoherent decision-feedback equalization receiver achieves a similar performance as a recently proposed 2-state noncoherent sequence detector, while it is advantageous in terms of complexity. The new receiver design is therefore highly attractive for a practical implementation.

In this paper, we evaluate the effect of multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wide-band (UWB) interference on a narrowband (NB) receiver. For this purpose, we first derive an analytical expression for the exact moment generating function (MGF) of MB-OFDM UWB interference. Subsequently the bit error rate (BER) of a binary phase-shift keying (BPSK) NB receiver impaired by MB-OFDM UWB interference and additive white Gaussian noise is analyzed. We show that for NB signal bandwidths much smaller and much larger than the OFDM sub-carrier spacing a Gaussian approximation (GA ) and an impulsive GA of the MB-OFDM UWB interference leads to accurate performance predictions, respectively. However, for most NB signal bandwidths of practical interest the exact BER analysis has to be used to obtain meaningful results.

Direct-sequence spreading ultra-wideband (DS-UWB) is a strong contender for the standardization of the physical layer of wireless personal area networks (WPANs) by the IEEE 802.15.3a committee. Since long delay spreads in UWB channels cause significant intersymbol interference, equalization is required at the receiver of DS-UWB systems. In this paper, we investigate equalization for DS-UWB with 4-ary bi-orthogonal keying (4BOK), which is one of the two proposed modulation formats. We first derive the corresponding matched-filter bound (MFB), which is the theoretical performance limit. Considering a new equivalent multiple-input multiple-output (MIMO) description of 4BOK DS-UWB, we then devise linear and nonlinear MIMO equalizers. Furthermore, we propose the application of widely linear (WL) processing to these equalizers. Simulation and semi-analytical results show that the proposed MIMO equalizers allow for power-efficient 4BOK DS-UWB transmission close to the theoretical limits with moderate computational complexity.

In this paper, we introduce a new class of distributed space-time trellis codes (DSTTCs) for wireless networks with a large set of decode-and-forward relay nodes N. It is assumed that at any given time only a small, a priori unknown subset of nodes S - N is active. We consider the general case where each relay node is equipped with NT antennas and the destination node has NR antennas. In the novel distributed space-time trellis coding scheme each relay node is assigned a unique signature matrix but all active nodes use the same trellis for encoding. Efficient methods for the optimization of the set of signature matrices are provided and it is shown that existing full-rank STTCs designed for Nc - 2 co-located antennas are a favorable choice for the trelis encoding. If properly designed, the proposed DSTTCs achieve a diversity order of d = min{NcNR, NTNSNR} if NS nodes are active. Simulation results show the superior performance of the novel DSTTCs compared to distributed space-time filtering and distributed space-time block coding.

Recently, a new noncoherent sequence detection receiver for Bluetooth systems has been developed. The receiver is based on Rimoldi's decomposition of the Bluetooth transmit signal and its power efficiency was shown by software simulations. In this paper, a hardware implementation of the decoder for this receiver is presented. In particular, we describe a low-complexity Viterbi decoder that performs noncoherent sequence detection in a two-state trellis using per-survivor processing. The prototype decoder is implemented in a field programmable gate array (FPGA). The bit-error-rate performance of the implemented decoder is compared with that of the reference software simulations.

We consider multiple-symbol differential detection (MSDD) for multiple-input multiple-output Rayleigh-fading channels. MSDD, which jointly processes blocks of N received symbols to detect N - 1 data symbols, allows for power-efficient transmission without requiring channel state information at the receiver. In previous work, we showed that computationally efficient sphere decoding algorithms can be used to accomplish MSDD. In this paper, we analyze the computational complexity of this sphere-decoding based MSDD. In particular, we prove by means of a lower bound that the complexity of the Fincke-Pohst multiple-symbol differential sphere decoder (FP-MSDSD), while being very low over wide ranges of N and signal-to-noise ratios, is exponential in N in principle. We further derive expressions for the exact complete of FP-MSDSD, which allow for quick assessment of ranges of useful window sizes N

The random coding exponent for differential modulation with finite signal sets over block-fading channels and multiple-symbol differential detection with an observation window size of N symbols is considered. Different from and in extension to previous work, the channel coherence interval is independent of N and the case of spatial transmit diversity is included. In this context, we also devise bounds and approximations of the random coding exponent, which allow for efficient numerical evaluation. The presented numerical results provide useful information on the performance of coded differential transmission with short to moderate code lengths

In this paper, we introduce a new channel allocation scheme for up-link code division multiple access (CDMA)-based multi-user multiple-input multiple-output (MIMO) systems. In such a system, different users are treated as multiple antennas and space-time multi-user detection algorithms are used at the receiver to separate users sharing the same channel. In our allocation scheme, users are allowed to share multiple up-link codes simultaneously. This improves the overall up-link system capacity and fairly equalizes the bit error rate (BER) performance of different users

In this paper, we evaluate the effect of multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) interference in fading narrowband (NB) channels. We derive the exact bit error rate (BER) of a binary phase-shift keying (BPSK) NB receiver impaired by fading, MB-OFDM UWB interference, and additive white Gaussian noise. We show that for NB signal bandwidths much smaller and much larger than the OFDM sub-carrier spacing a Gaussian approximation (GA) and an impulsive GA (IGA) of the MB-OFDM UWB interference lead to accurate performance predictions, respectively. While for general fading distributions and most NB signal bandwidths of practical interest the exact BER analysis has to be used to obtain meaningful results, both the GA and the IGA are very accurate for Rayleigh fading and arbitrary NB signal bandwidths

In this paper, we consider transmission in relatively wide-stretched power line communication (PLC) networks, where repeaters are required to bridge the source-to-destination distance. In particular, it is assumed that each network node is a potential repeater and that multihop transmission is accomplished in an ad hoc fashion without the need for complex routing protocols. In such a scenario, due to the broadcasting nature of the power line channel, multiple repeater nodes may receive and retransmit the source message simultaneously. It is shown that, if no further signal processing is applied at the transmitter, simultaneous retransmission often deteriorates performance compared with single-node retransmission. We therefore advocate the application of distributed space-time block codes (DSTBCs) to the problem at hand. More specifically, we propose that each network node is assigned a unique signature sequence, which allows efficient combining at the receiver. Most notably, DSTBC-based retransmission does not require explicit collaboration among network nodes for multihop transmission and detection complexity is not increased compared with single-node retransmission. Numerical results for multihop transmission over PLC networks show that DSTBC-based retransmission achieves a considerably improved performance in terms of required transmit power and multihop delay compared with alternative retransmission strategies.

In this paper, a new class of distributed space-time block codes (DSTBCs) is introduced. These DSTBCs are designed for wireless networks which have a large set of single-antenna relay nodes Nscr, but at any given time only a small, a priori unknown subset of nodes SsubeNscr can be active. In the proposed scheme, the signal transmitted by an active relay node is the product of an information-carrying code matrix and a unique node signature vector of length Nc. It is shown that existing STBCs designed for Nc2 co-located antennas are favorable choices for the code matrix, guaranteeing a diversity order of d=min{NS,Nc} if NSnodes are active. For the most interesting case, NSgesNc, the performance loss entailed by the distributed implementation is analytically characterized. Furthermore, efficient methods for the optimization of the set of signature vectors are provided. Depending on the chosen design, the proposed DSTBCs allow for low-complexity coherent, differential, and noncoherent detection, respectively. Possible applications include ad hoc and sensor networks employing decode-and-forward relaying

Coded interleaved differential M-ary phase-shift keying (M-DPSK) with iterative decoding, the so-called "Turbo DPSK," is known as a power-efficient transmission format. Due to the rotational invariance of DPSK, it particularly enables detection without channel state information (CSI). However, the soft-input soft-output (SISO) component decoder for DPSK is the computational bottleneck if performance close to the ideal case of perfect CSI is desired. In this paper, we take a fresh look at SISO decoding without CSI and apply sphere decoding (SD) to reduce complexity. In particular, we devise a maximum a posteriori probability (MAP) multiple-symbol differential sphere decoder (MSDSD) which efficiently solves the high-dimensional search problem inherent to detection without CSI. Together with a soft-output generation device the MAP-MSDSD algorithm forms a new SISO-MSDSD module for iterative decoding. We analyze the extrinsic information transfer (EXIT) characteristic of the novel module, by means of which we are able to design powerful encoder and decoder structures. For, respectively, the additive white Gaussian noise (AWGN) and the continuously time-varying Rayleigh-fading channel without CSI these designs operate within 1.7-1.9 and 2.3-2.5 dB of channel capacity assuming perfect CSI. These figures compare favorably with results available in the literature, especially for reasonably high data rates of 1-2 bit/channel use. Simulation studies of the average and the maximum complexity required by SISO-MSDSD demonstrate the advantageous performance versus complexity tradeoff of our approach.

Several approaches have recently been proposed for the efficient optimum or approximate solution of the detection problem in multiple-input multiple-output transmission systems. These are, however, difficult to compare. In the present work we briefly summarize the most popular and promising of these approaches and offer a way to visualize the tradeoff between complexity of the detection and the achievable power efficiency using "complexity-power diagrams". We conclude that the so-called sphere decoder algorithm is very attractive in terms of average complexity, while for low and constant processing delay lattice reduction with subsequent simple linear or nonlinear detection is more favorable

We consider multiple-symbol differential detection (MSDD) for multiple-input multiple-output (MIMO) Rayleigh-fading channels. MSDD, which jointly processes blocks of N received symbols to detect N - 1 data symbols, allows for power-efficient transmission over rapid-fading channels. However, the complexity of the straightforward approach to find the maximum-likelihood (ML) MSDD solution is exponential in N, the number of transmit antennas N/sub T/ and the rate R. In this paper, we introduce an MSDD algorithm based on sphere decoding whose average complexity is not exponential in N for interesting ranges of signal-to-noise ratio (SNR) and arbitrary unitary signal constellations. For the interesting special cases of diagonal and orthogonal constellations we achieve a similar complexity reduction in N/sub T/ and R. Based on an error-rate analysis for MSDD we also propose a variant of MSDD that considerably improves power efficiency in relatively fast fading at a very moderate increase in complexity.

In this paper, we propose a simple orthogonal space-time block coding (OSTBC) technique for continuous-phase modulation (CPM). Although the straightforward combination of orthogonal designs (ODs) and CPM was deemed impossible in [(X. Zhang and M.P. Flitz, 2003) and (G. Wang and X-G. Xia, 2004)], we show that this is easily accomplished with a burst-based approach. In fact, using the proposed technique ODs can be combined with any CPM scheme. After an appropriate ST combining at the receiver, the same detection techniques as in case of single-antenna transmission can be applied. This is a significant advantage over previously proposed ST coding schemes for CPM. We also derive accurate approximations for the bit error rate and the frame error rate of CPM with OSTBC. Both analysis and simulations show in good agreement the excellent performance of the proposed scheme

In this paper, a new class of distributed space-time block codes (DSTBCs) is introduced. These DSTBCs are designed for wireless networks which have a large set of nodes N but at any given time only a small, a priori unknown subset of nodes S /spl sub/ N can be active. In the proposed scheme, the signal transmitted by an active node is the product of an information-carrying code matrix and a unique node signature vector. It is shown that existing STBCs designed for N/sub c/ /spl ges/ 2 co-located antennas are favorable choices for the code matrix guaranteeing a diversity order of d = min{N/sub S/, N/sub c/} if n/sub S/ nodes are active. For the most interesting case N/sub S/ /spl ges/ N/sub c/ the performance loss entailed by the distributed implementation is analytically characterized. Furthermore, efficient methods for the optimization of the set of signature vectors are provided. Possible applications of the proposed DSTBCs include ad hoc and sensor networks employing decode-and-forward relaying.

This paper presents an improved error-correction decoder for Bluetooth systems employing the expurgated (15,10) binary Hamming code to protect the payload of data medium rate packets. For detection prior to error-correction decoding we consider the application of the limiter-discriminator detector with integrate and dump filter (LDI detector) and a two-state sequence detector (SD), respectively. The proposed decoder exploits the error statistic of the respective detector output and makes use of the single-error-correcting-double-adjacent-error-correcting (SEC-DAEC) capability of the expurgated (15,10) code. As a result, notable improvements in data throughput and/or transmission range are achieved. Since the performance gains come at no additional cost in implementation, the proposed decoder is highly attractive for application in low-cost Bluetooth devices.

In this paper, we revisit multiple-bit differential detection (MBDD) of differential offset quadrature phase-shift keying (DOQPSK) with conventional bit-wise differential encoding (DE). We introduce two novel MBDD schemes that outperform Simon's MBDD and approach the performance of coherent detection (CD) as the observation window size N increases. The proposed full-size (F-MBDD) and improved (I-MBDD) MBDD schemes use the full available (N - 1 bit intervals) and a reduced (N - 3 bit intervals) detection window, respectively. For both MBDD schemes accurate BER approximations are derived. Our results show that I-MBDD of DOQPSK with bit-wise DE achieves a performance similar to that of Phoel's MBDD of DOQPSK with more complex symbol-wise DE. Since the complexity per bit decision of brute force decoding of MBDD of DOQPSK grows exponentially with N, we develop a fast decoding algorithm with a complexity per bit decision of order log(N + 1).

The frequency-hopping orthogonal frequency-division multiplexing (OFDM) proposal, known as multiband OFDM, is a strong contender for the physical layer IEEE standard for high-rate wireless personal area networks (WPANs) bused on ultra-wideband (UWB) transmission. In this paper we analyze the performance of the multiband OFDM proposal. To this end, we (a) study the channel model developed under IEEE 802.15 for UWB radio from a frequency-domain perspective suited for OFDM transmission, (b) develop and quantify the appropriate information-theoretic performance measures, (c) compare these measures with simulation results for multiband OFDM systems, and (d) consider the influence of practical, imperfect channel estimation on the performance.

The design of power efficient receivers for Bluetooth systems is a challenging task due to stringent complexity constraints. In this paper, we tackle this problem and present a receiver design consisting of a single filter and a subsequent noncoherent sequence detector. This receiver outperforms the conventional discriminator detector by more than 4 dB for typical Bluetooth channels. Thereby, the proposed noncoherent sequence detection (NSD) algorithm is both favorably low complex as it operates on a two-state trellis and highly robust against channel phase variations caused by low-cost local oscillators. The particular filter design accomplishes effective out-of-band interference suppression. Different from previous work on sequence detector receivers published in the literature, we take possible variations of the Bluetooth modulation parameters into account, and we also devise efficient methods for combined NSD and forward error correction decoding. Hence, the presented receiver design is an attractive solution for practical Bluetooth devices.

This letter presents an improved error-correction decoder for Bluetooth systems, employing the limiter-discriminator detector with integrate and dump filter (LDI detector) and the expurgated (15,10) binary Hamming code, which is used to protect the payload of data medium-rate packets. The proposed decoder exploits the error statistic of the LDI detector output and makes use of the single-error-correcting double-adjacent-error-correcting (SEC-DAEC) capability of the expurgated (15,10) code. As a result, notable improvements in data throughput and/or transmission range are achieved. Since the performance gains come at no additional cost in implementation, the proposed decoder is highly attractive for application in low-cost Bluetooth devices.

In this letter, we consider iterative decision-feedback differential demodulation (iterative DFDM), which was proposed previously as a low-complexity solution for power-efficient transmission over flat fading channels without channel state information at the receiver. We devise a modified demodulator (inner decoder), which improves both the achievable bit-error rate performance and the convergence of iterative DFDM without increasing complexity. We also establish an equivalent decoder model for iterative DFDM which enables a convergence analysis by means of extrinsic information transfer charts.

In multiple-symbol differential detection (MSDD) for power-efficient transmission over Rayleigh fading channels without channel state information, blocks of N received symbols are jointly processed to decide on N-1 data symbols. The search space for the maximum-likelihood (ML) estimate is therefore (complex) (N-1)-dimensional, and maximum-likelihood MSDD (ML-MSDD) quickly becomes computationally intractable as N grows. Mackenthun's low-complexity MSDD algorithm finds the ML estimate only for Rayleigh fading channels that are time-invariant over an N symbol period. For the general time-varying fading case, however, low-complexity ML-MSDD is an unsolved problem. In this letter, we solve this problem by applying sphere decoding (SD) to ML-MSDD for time-varying Rayleigh fading channels. The resulting technique is referred to as multiple-symbol differential sphere decoding (MSDSD).

In this paper, we consider multiple-bit differential detection (MBDD) of differential offset quadrature phase-shift keying (DOQPSK) with conventional bit-wise differential encoding (DE). We propose two novel MBDD schemes that outperform Simon's MBDD and approach the performance of coherent detection (CD) as the observation window size N increases. The first scheme uses the full available detection window spanning N-1 bit intervals, and is referred to as F-MBDD. A careful bit-error rate (BER) analysis shows that a significant performance improvement can be realized by reducing the detection window size to N-3 bit intervals. The resulting improved MBDD (I-MBDD) of DOQPSK with bit-wise DE achieves a similar performance as Phoel's MBDD of DOQPSK with more complex symbol-wise DE. For both F-MBDD and I-MBDD, tight upper bounds and accurate BER approximations are derived. In addition, since the complexity per bit decision of brute-force decoding of MBDD of DOQPSK grows exponentially with N, we develop optimum and suboptimum fast decoding algorithms with complexities per bit decision of orders log(N+1) and N, respectively.

In this paper, we propose a novel differentially coherent (DC) parallel interference cancellation (PIC) scheme for direct-sequence code-division multiple access (DS-CDMA) employing differential phase-shift keying (DPSK). The proposed scheme combines decision-feedback differential detection (DF-DD) and PIC. For optimization of the DF-DD and interference cancellation (IC) filters three different criteria are adopted. The first (DC-PIC I) and the second (DC-PIC II) criteria assume a constant channel and a channel with a small constant frequency offset, respectively, whereas the third criterion (DC-PIC III) optimizes the filters in the minimum mean-squared error (MMSE) sense taking into account the statistical properties of the underlying channel. Simulations show the high achievable performance and the robustness of the novel DC-PIC receiver. A comparison with linear DC receivers and a previously proposed DC-PIC scheme show the superiority of the proposed approach.

In this paper, optimum and suboptimum diversity combining schemes for coherent and differential M-ary phase-shift keying (M-PSK) transmission impaired by general Ricean fading and impulsive Class-A noise are derived and analyzed. The proposed suboptimum coherent combining (SCC) and suboptimum noncoherent combining (SNC) schemes yield similar performance as the corresponding optimum combining schemes but require a lower computational complexity. In addition, the novel SCC and SNC strategies achieve large performance gains over conventional maximum ratio combining (MRC) and equal gain combining (EGC), respectively. For MRC and EGC, respectively, we also provide a performance analysis for coherent and differential M-PSK transmissions over general Ricean fading channels with Class-A noise. Furthermore, tight performance upper bounds for the proposed optimum and suboptimum combining schemes are derived.

The design of power efficient receivers for Bluetooth systems is a challenging task due to stringent complexity constraints. We tackle this problem and present a novel receiver consisting of a single filter and a subsequent sequence detector. This receiver outperforms the conventional discriminator detector by more than 4 dB for typical Bluetooth channels. Thereby, the proposed sequence detection (SD) algorithm is of favorable low complexity, as it operates on a two-state trellis, and is highly robust against channel phase variations caused by low-cost local oscillators. Different from previously published work on SD, we take possible variations of the Bluetooth modulation parameters into account. Hence, the presented receiver design is an attractive solution for practical Bluetooth devices.

In this paper, optimum (ONC) and suboptimum (SNC) noncoherent diversity combining schemes for M-ary differential phase-shift keying (MDPSK) transmission over general Rician fading channels with impulsive class-A noise are derived and analyzed. The proposed SNC scheme yields a similar performance to ONC, but requires a lower computational complexity, and achieves a large performance gain over conventional equal gain combining (EGC). We provide a performance analysis for MDPSK transmission with EGC over general Rician fading channels with class-A noise, and derive a tight lower bound on the bit error rate of ONC.

In multiple-symbol differential detection (MSDD) for power-efficient transmission over fading channels without channel state information, blocks of N received symbols are jointly processed to decide on N - 1 data symbols. The search space for the maximum-likelihood (ML) estimate is therefore (complex) (N - 1)-dimensional, and MSDD quickly becomes computationally intractable as N grows. Sphere decoding (SD) is a widely used approach to find the ML estimate in such high-dimensional spaces. In this paper, we devise the application of SD to accomplish MSDD, and we refer to the resulting technique as multiple-symbol differential sphere decoding (MSDSD). We present an efficient algorithm for MSDSD, whose excellent performance versus complexity trade-off is verified by various simulation results and by comparisons with other, suboptimum approaches known from the literature.

Algorithms for the detection problem in multiple-input multiple-output (MIMO) transmission systems are compared, and the tradeoff between detection complexity and the achieved power-efficiency is visualized using "power-complexity" diagrams.

Iterative decision-feedback (DFB) differential demodulation (DFDM) has recently been introduced for low-complexity noncoherent detection. The convergence analysis of this iterative decoding scheme is complicated since hard-decision decoding is involved. We develop an equivalent iterative decoder model which lends itself to a convergence study and as such constitutes a powerful tool for system design and analysis. Furthermore, we propose a modification of iterative DFDM which significantly improves convergence and hence power efficiency.

In this paper, sequence detection and channel estimation for frequency-selective, intersymbol interference (ISI)-producing channels under Class-A impulsive noise are considered. We introduce a novel suboptimum sequence detection (SSD) scheme and show that although SSD employs a simplified metric, it achieves practically the same performance as maximum-likelihood sequence detection (MLSD). For both SSD and MLSD, a lower bound on the achievable performance is derived, which is similar to the classical matched-filter bound for frequency-selective (fading) channels under Gaussian noise. For channel estimation, we adopt a minimum entropy criterion and derive efficient least-mean-entropy and recursive least-entropy algorithms. For both adaptive algorithms, we analyze the steady-state channel-estimation error variance. Theoretical considerations and simulation results show that in Class-A impulsive noise, the proposed sequence detection and adaptive channel-estimation schemes yield significant performance gains over their respective conventional counterparts (designed for Gaussian noise). Although the novel algorithms require knowledge of the Class-A noise-model parameters, their computational complexity is comparable to that of the corresponding conventional algorithms.

The application of powerful coding for transmission over multiple-input/multiple-output channels is discussed. The authors emphasize that as an immediate consequence of the mutual information chain rule, multilevel coding (MLC) constitutes the optimum coded modulation scheme. On the other hand, simple bit-interleaved coded modulation (BICM) is only a convenient alternative for the case of two transmit and one receive antennas when combined with orthogonal space-time block codes. Starting from MLC, the authors further propose a hybrid coded modulation scheme, which favorably combines the advantages of MLC and BICM.

In this paper, space-time block-coded transmission over frequency-selective fading channels is investigated. A lower bound for the pairwise error probability for optimum detection is given. Also, an approximation for the bit-error rate is derived and compared with simulation results for maximum-likelihood sequence estimation (MLSE) for the GSM/EDGE (Enhanced Data Rates for GSM Evolution) system. Furthermore, a novel design rule for space-time block codes (STBCs) for frequency-selective fading channels is provided. A corresponding code is designed and shown to yield higher performance than Alamouti's code. It is demonstrated that for fading channels with L independent impulse response coefficients, STBCs designed for the flat fading channel can achieve at most a diversity order of (N/sub T/+L-1)N/sub R/ if N/sub T/ transmit antennas and N/sub R/ receive antennas are used. On the other hand, the maximum diversity order employing the proposed code design rule is LN/sub T/N/sub R/.

We design and analyze novel noncoherent receivers for direct-sequence code-division multiple access (DS-CDMA) with multi-chip (MC) differential encoding (DE). The proposed receivers for MC-DE are based on multiple-symbol detection and decision-feedback differential detection, which have been previously applied for symbol-level DE. While the complexity of the proposed receivers is moderate, it is shown that they enable large performance gains over conventional differential detection for various channel environments, such as additive white Gaussian noise (AGWN) channels, Rayleigh and Ricean fading channels, and channels with frequency offset and phase noise. Furthermore, we show that in most cases MC-DE outperforms single-chip differential encoding and, in addition, decreases receiver complexity. Another result of this paper is that quaternary differential phase-shift keying (QDPSK) is more suitable for chip-level DE than binary DPSK.

In this paper, we propose a widely linear (WL) decision-feedback (DF) minimum mean-squared error (MMSE) receiver for direct-sequence code-division multiple access (DS-CDMA) with binary phase-shift keying (BPSK) modulation. Both theoretical considerations and simulations show that the novel receiver yields significant performance gains over both WL receivers without feedback and conventional DF receivers. In particular, the proposed WL DF-MMSE receiver achieves a high performance even in overloaded systems. For efficient adaptation of the filter coefficients a WL least-mean-square (LMS) algorithm and a WL recursive least-squares (RLS) algorithm are devised.

We propose decision-feedback differential detection (DF-DD) for direct-sequence code-division multiple access (DS-CDMA) with multi-chip (MC) differential encoding (DE). While the complexity of the novel receiver is moderate, it enables large performance gains over conventional differential detection for various channel environments. Furthermore, we show that, in most cases, MC-DE outperforms single-chip differential encoding and, in addition, decreases receiver complexity. Another result of the paper is that quaternary differential phase-shift keying (QDPSK) is more suitable for chip-level DE than binary DPSK (BDPSK).

In this paper, powerful coding techniques for differential space-time modulation (DSTM) over Rayleigh flat fading channels and noncoherent demodulation without channel state information at the receiver are investigated. In particular, multilevel coding (MLC), bit-interleaved coded modulation (BICM), and so-called hybrid coded modulation (HCM) are devised and compared using capacity arguments. For improved noncoherent reception multiple-symbol differential detection (MSDD) and a low-complexity version of MSDD are adapted to DSTM.

The combination of continuous phase modulation (CPM) with direct-sequence code-division multiple access (DS-CDMA) for multiuser transmission over the additive white Gaussian noise channel is discussed. Concentrating on the important special case of generalized minimum-shift keying, particularly simple receiver structures are obtained. To emphasize on low complexity, noncoherent reception is proposed and appropriate transmitter and receiver designs are provided. The application of reduced-state noncoherent sequence detection and noncoherent filter adaptation ensures high power efficiency and robustness against channel phase variations. Simulation results confirm that the chosen approach of CPM for DS-CDMA achieves high performance with very moderate complexity.

In this paper, a novel data-aided stochastic gradient algorithm for adjustment of the widely linear (WL) minimum mean-squared error (MMSE) filter for multiple access interference (MAI) suppression for direct-sequence code-division multiple access (DS-CDMA) is introduced and analyzed. We give analytical expressions for the steady-state signal-to-interference-plus-noise ratio (SINR) of the proposed WL least-mean-square (LMS) algorithm, and we also investigate its speed of convergence. Both analytical considerations and simulations show in good agreement the superiority of the novel WL adaptive algorithm. Nevertheless, the computational complexity of the proposed algorithm is lower than that of the linear LMS algorithm.

In this paper, we design decision-feedback differential detection (DF-DD) schemes for channels with phase noise. If the DF-DD feedback filter is properly optimized, a performance similar to that of more complex, some reported schemes based on multiple-symbol detection [K. Kiasaleh (December 1997)] and expectation maximization (EM) [E. Chiavaccini and G.M. Vitetta (December 2001)] can be achieved. However, it is also shown that an error floor is unavoidable. In contrast to previously proposed receivers for channels with phase noise, the DF-DD receiver can be made robust against unknown frequency offsets by introducing a simple linear constraint.

A bit-interleaved concatenated coding scheme consisting of an outer convolutional code and an inner space-time modulation together with an iterative decoding-demapping method is analyzed. As a result, two parameters based on bitwise pairwise error probabilities (b-PEP) for the cases with and without a-priori knowledge are proposed as new measures for a labeling of signal points suited to iterative decoding-demapping. In particular, we demonstrate that the two parameters are closely related to the transfer characteristic (TC) of the demapper and accordingly lead to the same design guideline as a TC analysis. By optimizing these two analytical parameters for an orthogonal space-time block code (oSTBC) employing 16QAM constituent symbols w.r.t. an outer simple 4-states rate 1/2 convolutional code, a highly power efficient concatenated scheme with rate of 2 bits per channel use is proposed, which offers an excellent trade off between power efficiency and complexity.

In this paper, a power-efficient low-complexity iterative receiver structure for noncoherent transmission over Rayleigh flat fading channels without channel state information (CSI) is presented. As the main contribution, several novel decision-feedback assisted differential demodulators are derived, which are well-suited implementation. Thereby, the general case of multiple transmit and multiple receive antennas is considered. We further provide analytical expressions for the achievable bit-error rate, which in good accordance with simulation results highlight the advantageous properties of the proposed receiver structure. Despite its simple components, the noncoherent iterative receiver without CSI can outperform a coherent scheme assuming perfect CSI.

In this paper, a novel blind minimum-output-energy (MOE) algorithm for adjustment of the unbiased widely linear (WL) minimum mean-squared error (MMSE) filters for multiple access interference (MAI) suppression for direct-sequence code-division multiple access (DS-CDMA) is introduced and analyzed. We analyze the steady-state signal-to-interference-plus-noise ratio (SINR) and the convergence of the proposed blind WL stochastic gradient algorithm. Wherever possible comparisons with the linear blind MOE algorithm are made. Both analytical considerations and simulations show in good agreement the superiority of the novel WL adaptive algorithm. Nevertheless, it requires a lower computational complexity than its linear counterpart.

In this letter, we design decision-feedback differential detection (DF-DD) schemes for channels with phase noise. If the DF-DD feedback filter is properly optimized, a performance similar to that of a more complex scheme, recently reported by Chiavaccini and Vitetta, based on expectation maximization, can be achieved. However, it is also shown that an error floor is unavoidable for channels with phase noise. If a constraint is introduced, the DF-DD receiver can be made robust against unknown frequency offsets.

In this article, modulation diversity (MD) for frequency-selective fading channels is proposed. The achievable performance with MD is analyzed and a simple design criterion for MD codes for Rayleigh-fading channels is deduced from an upper bound on the pairwise error probability (PEP) for single-symbol transmission. This design rule is similar to the well-known design rule for MD codes for flat fading and does not depend on the power-delay profile of the fading channel. Several examples for MD codes with prescribed properties are given and compared. Besides the computationally costly optimum receiver, efficient low-complexity linear equalization (LE) and decision-feedback equalization (DFE) schemes for MD codes are also introduced. Simulations for the widely accepted COST fading models show that performance gains of several decibels can be achieved by MD combined with LE or DFE at bit-error rates (BERs) of practical interest. In addition, MD also enables the suppression of cochannel interference.

In this paper, powerful coding techniques for differential space-time modulation (DSTM) over Rayleigh flat fading channels and noncoherent detection without channel state information at the receiver are investigated. In particular, multilevel coding, bit-interleaved coded modulation, and so-called hybrid coded modulation (HCM) are devised and compared. For improved noncoherent reception multiple-symbol differential detection (MSDD) is adapted to DSTM. In order to reduce the computational effort required for MSDD, a low-complexity version of MSDD is applied. Evaluating the ergodic channel capacity for the different schemes as appropriate performance measure, HCM with simplified MSDD is shown to offer a favorable tradeoff between complexity and achievable power efficiency. Simulation results employing turbo codes in properly designed HCM schemes confirm the predictions from information theory.

Bit-interleaved coded differential space-time modulation (DSTM) for transmission over flat Rayleigh fading channels is discussed. For improved noncoherent detection without channel state information at the receiver, iterative decoding employing hard-decision feedback and prediction-based metric computation are applied. The performance is assessed based on analytical expressions for the bit-error rate and simulations. For the most relevant case of two transmit antennas, it is shown that the proposed scheme offers high power efficiency exploiting both space and time diversity, while computational complexity is kept at a low level.

Space-time block-coded transmission over fading intersymbol interference (ISI) channels is investigated. A lower bound on the pairwise error probability for optimum detection is given. Also, an approximation for the bit error rate is derived and compared with simulation results for maximum-likelihood sequence estimation (MLSE) for the GSM/EDGE (enhanced data rates for GSM evolution) system. Furthermore, a novel design rule for space-time block codes (STBC) with arbitrary rate for fading ISI channels is provided. A corresponding full-rate code is designed and shown to yield higher performance than Alamouti's code. It is demonstrated that for fading channels with L independent impulse response coefficients, full-rate STBCs designed for the flat fading channel can achieve at most a diversity order of (N/sub T/+L-1)N/sub R/ if N/sub T/ transmit antennas and N/sub R/ receive antennas are used. On the other hand, the maximum diversity order employing the proposed code design rule is LN/sub T/N/sub R/.

A well-known receiver strategy for a linearly modulated signal transmitted over a frequency-selective channel is channel equalization. Recently it was proposed to employ a minimum mean-squared error (MMSE) channel equalizer for the downlink of CDMA. In this paper, we introduce a new receiver concept using MMSE channel equalization as a first stage and MMSE decision-feedback equalization (DFE) utilizing soft feedback from the decoding unit as a second stage. Both schemes are compared for the downlink of CDMA. It turns out, that after channel decoding we gain about 1 dB compared to conventional MMSE channel equalization.

Bit-interleaved coded differential space-time modulation for transmission over spatially correlated Ricean flat fading channels is discussed. For improved noncoherent detection without channel state information at the receiver, iterative decoding employing hard-decision feedback and prediction-based metric computation is applied. The performance is assessed based on the associated cutoff rate, analytical expressions for the bit error rate and the outage probability, respectively and simulations. It is shown that the proposed scheme offers high power efficiency exploiting both space and time diversity, while the computational complexity is kept at a relatively low level.

Coded continuous phase modulation based on a feedback-free modulator with noncoherent detection is discussed. Low-complexity receiver processing is achieved by using only two or three linear filters for demodulation and applying noncoherent sequence estimation with reduced-state Viterbi decoding and simple branch metric calculation. Overall, the proposed noncoherent receiver provides significant advantages over previously presented approaches.

In this paper, noncoherent receivers for differential space-time modulation (DSTM) are investigated. It is shown that the performance of the previously proposed conventional differential detection (DD) receiver is satisfactory only for very slow flat fading channels. However, conventional DD suffers from a considerable loss in performance even for moderately fast fading, especially if more than one transmit antenna is used. In order to overcome this problem, two improved noncoherent receivers are considered. The first one is the multiple-symbol detection (MSD) receiver. Because of the high computational complexity of MSD, also a low-complexity decision-feedback differential detection (DF-DD) receiver is derived. Analytical and simulation results confirm that both receivers perform equally well and can take full advantage of the enhanced diversity provided by multiple transmit antennas even for fast fading.

Bit-interleaved coded phase and amplitude modulation over frequency-non-selective Ricean fading channels without channel state information at the receiver is studied. We propose a low-complexity noncoherent receiver structure which is very well suited to time-variant fading transmission scenarios, and which provides gains of several dBs in power efficiency compared to conventional differential detection.

In this paper, noncoherent receivers for differential space-time modulation (DSTM) are investigated. It is shown that the performance of the previously proposed conventional differential detection (DD) receiver is satisfactory only for very slow flat fading channels. However, conventional DD suffers from a considerable loss in performance even for moderately fast fading. In order to overcome this problem, multiple-symbol detection (MSD) and low-complexity decision-feedback differential detection (DF-DD) receivers are derived.

Continuous phase modulation (CPM) systems for noncoherent coded transmission are proposed and analyzed. Specifically, the application of a feedback-free modulator is regarded. For demodulation, a receiver structure which requires only two or three linear filters is considered. For decoding, noncoherent sequence estimation (NSE) with Viterbi decoding and per-survivor processing is applied. Noteworthy, in our approach the problems of low-complexity filtering and reduced-state decoding can be treated separately. Since we give a recursive formula for the phase reference symbol necessary for NSE metric calculation, computational effort is further decreased. Overall, in terms of complexity, the proposed noncoherent receiver provides significant advantages over approaches in the literature. The high performance of the novel noncoherent CPM system is confirmed by simulation results.

A simple receiver structure previously proposed by the authors for convolutional coded M-ary differential phase-shift keying transmission over flat Rayleigh fading channels without channel state information is analyzed in detail. We present a thorough discussion of the iterative decoding procedure, which is referred to as iterative decision-feedback differential demodulation (iterative DF-DM). The convergence behavior of iterative DF-DM is theoretically examined. The analysis supports the observation that the iterative decoding scheme works well for target bit-error rates which are usually of interest. Furthermore, the associated cut-off rate for error-free decision feedback is studied. Judging from this performance parameter, remarkable gains in power efficiency compared to conventional differential demodulation are indicated, while the computational complexity of the decoding remains low. The results from information theory are in good agreement with the given simulation results.

A novel simple receiver structure for M-ary differential phase-shift keying (MDPSK) transmission over flat Rayleigh fading channels without channel state information is proposed. We apply convolutional codes for error correction and bit-interleaving as appropriate means to combat the effects of fading. In the decoding the hard decisions of the Viterbi algorithm are fed back to enable a more reliable estimation of the current channel state. A theoretical analysis of the associated cutoff rate for error-free feedback shows remarkable gains in power efficiency compared to conventional differential demodulation, while the computational complexity of the decoding remains low. The results from information theory are in good agreement with the obtained simulation results. The proposed scheme works remarkably well for target bit error rates which are usually of interest.