In-band Full-Duplex (FD) Multiple-Input Multiple-Output (MIMO) systems present a major opportunity for Integrated Sensing and Communication (ISAC) by enabling simultaneous signal transmission and reception. In this paper, we study the performance and implementation of FD-ISAC for vehicle-to-infrastructure (V2I) communications using a more precise sensing model. A common assumption in ISAC performance analysis has been that all targets can be represented by asingle pointcoordinate - named single ray sensing model (SRSM). This assumption simplifies performance analysis and algorithm implementation for ISAC, but it overlooks the shape and size of the sensing targets. Thus, we model each sensing target as acluster of rayswith certain angular characteristics associated with its geometry - named cluster ray sensing model (CRSM). Then, we derive the Cramer-Rao Bound (CRB) for angular direction and the variance of cluster-modeled targets. We also provide an (easy to optimize) lower bound of CRB for angular direction in terms of eigenvalues of the covariance matrix and its derivative, which approaches the original value in the low signal-to-noise (SNR) and low angular spread regime. Our analysis shows that a more accurate model (with large angular variance) improves the estimation of the direction of arrival of targets. Based on the CRB expressions, we design a partially connected hybrid beamforming (HBF) algorithm for millimeter wave (mmWave) OFDM FD-ISAC systems. The simulation results show that assuming CRSM together with a proposed HBF increases the data rate of the system by 25% as compared to assuming SRSM and a max signal to interference plus noise ratio (SINR) scheme.

This paper explores a bistatic Integrated Sensing and Communication (ISAC) framework, where a base station transmits communication signal that serve both direct communication with a user and multi-target parameter estimation through reflections captured by a separate sensing receiver. We assume that the instantaneous knowledge of the transmit signal at the sensing receiver is not available, and the sensing receiver only has knowledge of the statistical properties of the received signal. Unlike prior research that focuses on power allocation or optimal beamforming design for ISAC, we emphasize the inadequacy of the Cramér-Rao Bound (and its variant) in low Signal-to-Noise Ratio (SNR) regimes, particularly in passive sensing scenarios. Due to severe path loss and other impairments, the received sensing SNR is often significantly lower than that of direct Line-of-Sight communication, making CRB-based performance evaluation unreliable. To address this, we adopt the Ziv-Zakai Bound (ZZB) for Angle of Arrival estimation, which provides a more meaningful lower bound on estimation error. We derive analytical expressions for the ZZB and the achievable ergodic communication rate as functions of SNR. Through numerical simulations, we analyze the pareto-front between communication and sensing performance, demonstrating why ZZB serves as a better metric in low sensing SNR ISAC where traditional CRB-based approaches fail.

The majority in existing energy harvesting (EH) models utilize complex analysis and often overlook the memory effects of the system’s low-pass filter (LPF). In this work, we aim to fill this gap and propose a simple yet effective approach to model the receiver’s output and capture the LPF’s memory. Specifically, we analyze two fundamental circuits: the half-wave rectifier (HWR) and the diplexer-based receiver (DBR). By using circuit analysis, we derive mathematical models for each receiver’s output, validated through circuit simulations. We then investigate these models in the context of integrated simultaneous wireless information and power transfer (SWIPT) receivers. For the HWR, we consider amplitude modulation and, using communication theory tools, we evaluate the performance in terms of bit error rate (BER) for both maximum likelihood (ML) and ML sequence detection (MLSD) schemes. Our results reveal the impact of memory-induced intersymbol interference on the BER and indicate that MLSD is necessary towards achieving higher data rates. For the DBR, we show that its LPF exhibits similar characteristics to the HWR yet is able to achieve better EH performance due to the lack of signal splitting. Finally, we explore the DBR’s band-pass filter output for information decoding, highlighting its capability to also use phase modulation. Clearly the DBR stands out as a more flexible receiver, while the HWR’s simple design makes it ideal for devices with limited resources.

Wireless power transfer has been proposed as a key technology for the foreseen machine type networks. A main challenge in the research community lies in acquiring a simple yet accurate model to capture the energy harvesting performance. In this work, we focus on a half-wave rectifier and based on circuit analysis we provide the actual output of the circuit which accounts for the memory introduced by the capacitor. The provided expressions are also validated through circuit simulations on ADS. Then, the half-wave rectifier is used as an integrated simultaneous wireless information and power transfer receiver where the circuit's output is used for decoding information based on amplitude modulation. We investigate the bit error rate performance based on two detection schemes: (i) symbol-by-symbol maximum likelihood (ML); and (ii) ML sequence detection (MLSD). We show that the symbol period is critical due to the intersymbol interference induced by circuit. Our results reveal that MLSD is necessary towards improving the error probability and achieving higher data rates.

In classical capacity analysis for point-to-point (P2P) channels, all transmitted data is equally protected. Transmitted data will be recovered if and only if transmitted at a rate below the channel's capacity. When a P2P channel is studied in the Finite Blocklength (FBL) regime the inclusion of a reliability term suggests the possibility of constructing codes that protect portions of the data differently. In this paper, we present an FBL achievable bound for the utilization of superposition (SUP) coding with successive interference cancellation (SIC) in the realization of Unequal Bit Protection (UBP) in transmission over a static, scalar additive white Gaussian noise (AWGN) channel. We also present a converse bound for the problem. Through our numerical analysis we show that in cases where data to be transmitted has known and differing reliability requirements, the use of superposition coding can increase the achievable sum rate of transmission of all classes of data protection over a uniform protection coding scheme and orthogonalization over time. However, the (SUP-SIC) achievable region and converse are not tight, and the FBL UBP capacity remains an open problem.

The global wireless industry works like clockwork. Every decade, the global community ratifies a new generation of cellular standards relying on advances from the past decades; a similar rhythm drives Wi-Fi standardization. In all standards, cellular and Wi-Fi, a core design principle is that wireless nodescan either transmit or receive in a given frequency band. However, a node cannot simultaneously transmit and receive in the same frequency band due to high self-interference from its own transmitted signal that can drown out the receive signal. As a result, to enable bidirectional communications between nodes, network designs have relied on partitioning time and frequency using a mix of time-division duplex and frequency-division duplex. In short, wireless designs have not considered in-band full duplex (IBFD) as a building block.

In this article, we review the key concepts and the progress in the design of physical-layer aspects of in-band full-duplex (IBFD) communications. One of the fundamental challenges in realizing IBFD is self-interference that can be up to 100 dB stronger than signals of interest. Thus, we start by reviewing state-of-the-art research in self-interference cancellation, addressing both model-based and emerging machine learning-based methods. Then, we turn our attention to new wireless systems with many degrees of freedom for which the traditional IBFD designs do not gracefully scale and, hence, require many innovations to enable IBFD. We provide an extensive review of basic concepts and state of the art in massive multiple-input–multiple-output IBFD. Then, we consider the mmWave band IBFD and review advanced physical-layer architectures. The above review provides the proper context to discuss IBFD innovations and new challenges for sixth-generation networks and beyond, where wireless networks are envisioned to be multifunctional, combining communications with functions such as sensing, cognitive radios, physical-layer security, and wireless power transfer. We conclude this article with a status update on the adoption of IBFD in communication standards.

The capability of nodes to transmit and receive data simultaneously within the same frequency band, referred to as in-band FD, disrupts the conventional assumptions underlying wireless network design. This new feature enhances spectral efficiency and reduces latency, which are essential drivers in advancing next-generation networks. In the past few years, full-duplex (FD) has evolved from being a laboratory idea to being incorporated into telecommunications standards and proof of concepts. From 2010 to 2020, considerable research and development efforts were devoted to advancing FD wireless communications. By 2015, the cable modem industry had already implemented in-band FD technology to establish the DOCSIS 4.0 standard, enabling next-generation cable modems to operate in FD mode. By 2020, FD wireless products started to emerge in the market.

The use of in-band full-duplex (FD) enables nodes to simultaneously transmit and receive on the same frequency band, which challenges the traditional assumption in wireless network design. The full-duplex capability enhances spectral efficiency and decreases latency, which are two key drivers pushing the performance expectations of next-generation mobile networks. In less than ten years, in-band FD has advanced from being demonstrated in research labs to being implemented in standards, presenting new opportunities to utilize its foundational concepts. Some of the most significant opportunities include using FD to enable wireless networks to sense the physical environment, integrate sensing and communication applications, develop integrated access and backhaul solutions, and work with smart signal propagation environments powered by reconfigurable intelligent surfaces. However, these new opportunities also come with new challenges for large-scale commercial deployment of FD technology, such as managing self-interference, combating cross-link interference in multi-cell networks, and coexistence of dynamic time division duplex, subband FD and FD networks.

This paper considers the single antenna, static, scalar Gaussian broadcast channel in the finite blocklength regime. Second order achievable and converse rate regions are presented. Both a global reliability and per-user reliability requirements are considered. The two-user case is analyzed in detail, and generalizations to the$K$-user case are also discussed. The largest second order achievable regions presented here require both superposition and rate splitting in the code construction, as opposed to the (infinite blocklength, first order) capacity region which does not require rate splitting. Indeed, the finite blocklength penalty causes superposition alone to under-perform other coding techniques in some parts of the region. In addition, the proposed scheme uses joint simultaneous decoding as opposed to successive interference cancellation. Interestingly, in the two-user case with per-user reliability requirements, the capacity achieving superposition encoding order (with the codeword intended for the user with the smallest received SNR as cloud center) does not necessarily give the largest second order region. Instead, the message of the user with the smallest point-to-point second order capacity should be encoded in the cloud center in order to obtain the largest second order region for the proposed scheme.

Integrated Sensing and Communication (ISAC) has attracted substantial attraction in recent years for spectral efficiency improvement, enabling hardware and spectrum sharing for simultaneous sensing and signaling operations. In-band Full Duplex (FD) is being considered as a key enabling technology for ISAC applications due to its simultaneous transmission and reception capability. In this paper, we present an FD-based ISAC system operating at millimeter Wave (mmWave) frequencies, where a massive Multiple-Input Multiple-Output (MIMO) Base Station (BS) node employing hybrid Analog and Digital (A/D) beamforming is communicating with a DownLink (DL) multi-antenna user and the same waveform is utilized at the BS receiver for sensing the radar targets in its coverage environment. We develop a sensing algorithm that is capable of estimating Direction of Arrival (DoA), range, and relative velocity of the radar targets. A joint optimization framework for designing the A/D transmit and receive beamformers as well as the Self-Interference (SI) cancellation is presented with the objective to maximize the achievable DL rate and the accuracy of the radar target sensing performance. Our simulation results, considering fifth Generation (5G) Orthogonal Frequency Division Multiplexing (OFDM) waveforms, verify our approach’s high precision in estimating DoA, range, and velocity of multiple radar targets while maximizing the DL communication rate.

In this paper, we propose a wideband Full Duplex (FD) Multiple-Input Multiple-Output (MIMO) communication system comprising of an FD MIMO node simultaneously communicating with two multi-antenna UpLink (UL) and DownLink (DL) nodes utilizing the same time and frequency resources. To suppress the strong Self-Interference (SI) signal due to simultaneous transmission and reception in FD MIMO systems, we propose a joint design of Analog and Digital (A/D) cancellation as well as transmit and receive beamforming capitalizing on baseband Orthogonal Frequency-Division Multiplexing (OFDM) signal modeling. Considering practical transmitter impairments, we present a multi-tap wideband analog canceller architecture whose number of taps does not scale with the number of transceiver antennas and multipath SI components. We also propose a novel adaptive digital cancellation based on truncated singular value decomposition that reduces the residual SI signal estimation parameters. To maximize the FD sum rate, a joint optimization framework is presented for A/D cancellation and digital beamforming. Finally, our extensive waveform simulation results demonstrate that the proposed wideband FD MIMO design exhibits higher SI cancellation capability with reduced complexity compared to existing cancellation techniques, resulting in improved achievable rate performance.

Recent applications of the Full Duplex (FD) technology focus on enabling simultaneous control communication and data transmission to reduce the control information exchange overhead, which impacts end-to-end latency and spectral efficiency. In this paper, we present a simultaneous direction estimation and data transmission scheme for millimeter Wave (mmWave) massive Multiple-Input Multiple-Output (MIMO) systems, enabled by a recent FD MIMO technology with reduced hardware complexity Self-Interference (SI) cancellation. We apply the proposed framework in the mmWave analog beam management problem, considering a base station equipped with a large transmit antenna array realizing downlink analog beamforming and few digitally controlled receive antenna elements used for uplink Direction-of-Arrival (DoA) estimation. A joint optimization framework for designing the DoA-assisted analog beamformer and the analog as well as digital SI cancellation is presented with the objective to maximize the achievable downlink rate. Our simulation results showcase that the proposed scheme outperforms its conventional half-duplex counterpart, yielding reduced DoA estimation error and superior downlink data rate.

Despite the recent interest in Wireless Information and Power Transmission (WIPT) - in which information and energy flow together through the wireless medium - there remains key challenges for practical implementations. So far, it is assumed that it is not possible to perform Wireless Power Transfer (WPT) and Wireless Information Transmission (WIT) operations on the same received signal using one antenna. In this paper, we propose a receiver circuit implementation that extract both RF power and data from the same signal. The key to our implementation is the use of RF diplexers that implements frequency-domain multiplexing. The proposed sustainable unified receiver use low-power components and can hence be entirely powered by RF wave. We also establish a theoretical performance foundation for the proposed receiver by deriving achievable rate to serve as guideline for the optimization of energy-rate bi-objective function. The simulation results prove that the proposed sustainable unified architecture always out performs the existing low-complexity integrated receiver architecture.

Recent push for low-latency and high-reliability systems requires derivation of fundamental trade-offs between reliability and rates in multi-user systems with hard deadlines and reliability constraints. Towards this goal, this paper provides a second-order analysis of superposition coding and other orthogonal access schemes for the two-user static Gaussian broadcast channel. Numerical evaluations show that, since reliability and rates are intertwined when a hard-deadline is imposed, the scheduling of resources among users, including the level of reliability for each user, must be done jointly at the physical layer in order to optimize the overall system performance.

We investigate the feasibility of second-order statistics-based blind channel estimation in the context of two-hop full-duplex relay systems. To that end, the performance of blind and traditional pilot-based (training sequence based) channel estimation approaches are compared. This is accomplished by deriving the Cramer-Rao Lower Bound (CRLB) expressions for both blind and pilot-based schemes, and comparing them to each other and to the mean-squared error (MSE) values measured via simulation. Post-equalization SINR expressions are also derived for both blind and pilot-based methods. Furthermore, a modified post-equalization SINR expression, where the channel estimation error is replaced by the inverse of the Fisher information matrix (FIM) is proposed, providing an upper bound for the post-equalization SINR. These analytically-predicted SINR values for the blind approach are compared to the SINR measured via link simulation. The performance of the two channel estimation methods is analyzed by comparing the CRLB, post-equalization SINR, and BER performance for two significantly different transmission packet sizes. All of the above metrics indicate that blind estimation provides clear performance advantages relative to the pilot-based counterpart. Additionally, the blind approach eliminates the overhead associated with the pilot-based method, where a portion of the system resources is allocated to the pilot sequence. To quantify this, the spectral efficiency of the FD relay system employing blind and pilot-based channel estimation methods are compared, indicating that at high SNR, the blind approach provides around 2-bps/Hz spectral efficiency gain relative to a typical pilot-based method. Finally, the computational complexity of the two channel estimation techniques are evaluated and compared. The blind approach has a clear computational advantage for larger packet sizes.

To account for the ever-increasing demand for wireless broadband, it is critical to develop new techniques that can increase throughput. Network-coded (NCed) hybrid automatic repeat request (HARQ) has previously been shown to hold much potential for increasing network throughput by utilizing the retransmissions and side-information. However, the previous performance analysis did not take into account that the implementation of NCed HARQ requires additional control information that indicates which packets are included in one network coded packet and additional ARQ acknowledgements for the packets overheard by the unintended users. In this paper, we analyze the resources required for additional overhead and derive the outage probability and throughput for both downlink and uplink. With the analytical expressions and Monte Carlo simulation results, we study the trade-off between the maximum number of users (MNU) for NCed HARQ system and the overall throughput. Finally, we numerically show the existence of the optimal MNU and derive an approximate closed-form expression for the optimal value.

Single-antenna full-duplex communication technology has the potential to substantially increase spectral efficiency. However, limited propagation domain cancellation of single-antenna system results in a higher impact of receiver chain nonlinearities on the residual self-interference (SI) signal. In this paper, we offer a comprehensive SI model for single-antenna full-duplex systems based on direct-conversion transceiver structure considering nonlinearities of all the transceiver radio frequency (RF) components, in-phase/quadrature (IQ) imbalances, phase noise effect, and receiver noise figure. To validate our model, we also propose a more appropriate digital SI cancellation approach considering receiver chain RF and baseband nonlinearities. The proposed technique employs orthogonalization of the design matrix using QR decomposition to alleviate the estimation and cancellation error. Finally, through circuit-level waveform simulation, the performance of the digital cancellation strategy is investigated, which achieves 20 dB more cancellation compared to existing methods.

In this paper, we focus on reduced complexity full duplex Multiple-Input Multiple-Output (MIMO) systems and present a joint design of digital transmit and receive beamforming with Analog and Digital (A/D) self-interference cancellation. We capitalize on a recently proposed multi-tap analog canceller architecture, whose number of taps does not scale with the number of transceiver antennas, and consider practical transmitter impairments for the full duplex operation. Particularly, transmitter IQ imbalance and nonlinear power amplification are assumed via relevant realistic models. Aiming at suppressing the residual linear and nonlinear self-interference signal below the noise floor, we propose a novel digital self-interference cancellation technique that is jointly designed with the configuration of the analog taps and digital beamformers. Differently from the state of the art, we design pilot-assisted estimation of all involved wireless channels. Our representative Monte Carlo simulation results demonstrate that our unified full duplex MIMO design exhibits higher self-interference cancellation capability with less analog taps compared to available techniques, which results in improved achievable rate and bit error performance.

In this paper, we focuse on mitigating the damage due to a seismic event in a mid-size building using wireless structure control (WSC). We consider the nature of wireless communication channels and integrates it into a structural control system that minimizes the building response to external excitation - earthquake events. The control and communication constraints in terms of delay and channel reliability are analyzed and incorporated into the regulator model, which incorporates both estimator and feedback command. The short packet formulation provides the ability to link latency and channel reliability, i.e. error rates. This error-delay coupling allows us to analyze the performance of the control system for several scenarios and channel variation models. The simulations show that measurement error harmfully impacts the system performances more than delayed measurements. On the other hand, it is demonstrated that delayed control commands have more impact on the structural response than lost command packets.

Backscatter modulation (BM), usually used for radio frequency identifications, has the potential to be exploited in a wider range of applications such as the Internet of Things and wireless sensor networks. In this paper, we leverage the BM by increasing its down-link (from reader to tag) and up-link (from tag to reader) ranges. We propose two active two-way BM tag configurations, named parallel and series. For both configurations, we use active loads in the tag modulators to maximize the BM range and implement the desired backscattered constellation, subject to no data loss in the down-link path. Contrary to most existing BM studies, we use Thevenin/Norton equivalent circuit, only to calculate the received power at tag, while we derive the tag backscattered power using the antenna scatterer theorem. Moreover, we obtain a closed-form expression of the average bit error probability (BEP) at the reader in Rician fading channel environment for both tag configurations. We compare the proposed active BM tags with the conventional passive BM tags. The simulation results prove that for an average BEP equal to 10-4, an SNR improvement of up to 19 and 24 dB can be achieved for parallel and series configurations, respectively.

This paper, motivated by mission-critical and latency-constrained traffic, focuses on delivering different messages to various end-users within hard deadlines on the downlink of a wireless system. A novel deadline outage performance criterion is introduced, which accounts for both the violation of the hard deadline by any of the messages as well as for channel decoding errors due to finite block-length. This formulation allows for the study of scheduling policies under a more refined model of the physical layer channel than is usually assumed in the networking literature. Different scheduling polices under hard deadline constraints are proposed, and the corresponding deadline outage probabilities evaluated. The main result is that, to reduce the deadline outage probability, a scheduling policy should cleverly combine time-sharing and concatenate-and- code.

The Mobile Internet connects billions of smart phones and laptops. With this global connectivity, the stage is set for the emergence of: (a)Tactile Internetto deliver haptic experiences to remote users, and (b) flexible and integratedBackhaul/Fronthaulnetworks to support demands of such applications.

In this paper we optimize the pilot overhead for ultra-reliable short-packet transmission and investigate the dependence of this overhead on packet size and error probability. In particular, we consider a point-to-point communication in which one sensor sends messages to a central node, or base-station, over AWGN with Rayleigh fading channel. We formalize the optimization in terms of approximate achievable rates at a given block length, pilot length, and error probability. This leads to more accurate pilot overhead optimization. Simulation results show that it is important to take into account the packet size and the error probability when optimizing the pilot overhead.

In this paper we analyze the performance of a full-duplex relay system in the presence of residual self-interference (SI) and frequency-selective fading. In particular, the residual SI channel estimation performance is evaluated both analytically and via simulation. The bit error rate (BER) performance at the destination is also characterized via simulation. Two schemes are considered for the equalization of the source-to-relay (SR) and relay-to-destination (RD) channels: end-point equalization and distributed equalization. In the first approach, channel equalization is performed only at the destination and is similar to an amplify-and-forward model. In the second approach, equalization of the SR channel is performed at the relay, while the RD channel equalization is performed at the destination. We show that at the cost of a modest complexity increase at the relay, the distributed scheme provides more robust performance than its end-point counterpart.

Network-coded (NCed) automatic repeat request (ARQ) techniques have been shown to provide significant throughput improvements over basic ARQ systems in two-way wireless systems. Most results derived so far, however, used the assumption of no extra overhead. In practical systems, NCed-ARQ requires more information exchange between base-station and end-nodes, and therefore it is crucial to study the impact of the extra-overhead on such systems. In this paper, we analyze the performance of a practical NCed-ARQ system. We assume M end-users wish to exchange information with a base-station. We derive first the average number of extra acknowledgments required to facilitate NCed-ARQ scheme. Then, we derive both downlink and uplink throughput expressions and study the tradeoff between feedback and re-transmission. Finally, we numerically optimize the throughput with respect to the number of end-users.

In a wireless structural control system, a linear quadratic Gaussian regulator, under measurements loss, is used to limit the RMS structural response to natural hazards. The analysis shows the dependence of the state estimation error, and corresponding control performance, to the packet error probability and transmission delay. These metrics are studied for two communication access techniques: code-division multiple-access (CDMA) and time-division multiple-access (TDMA). By simulating a 9-story benchmark building with real earthquake inputs, it is shown that CDMA scheme performs better with few sensors scenario due to the low latency, however, more sensors may decrease the closed-loop performance due to high delay (TDMA) or high lost rate (CDMA).

In this paper, we introduce a new full-duplex wireless communication system, named ReflectFX, that relies on backscatter modulation. This paper offers a new concept for two-way wireless communication: rather than avoiding self-interference as in half-duplex, or combatting self-interference as in conventional full-duplex, nodes will re-use the received interfering radio-carrier waves to transfer information. The electromagnetic waves are modulated and reflected by the same antenna that receives them. We consider two nodes, a base-station and an end-user, that wish to exchange data over a wireless Rayleigh fading channel with additive white Gaussian noise. With ReflectFX, the end-user receives a self-interference free signal. We improve the transmission range of ReflectFX by adding negative resistance to the end-user load. We derive an expression for the overall achievable throughput and ergodic capacity of ReflectFX. Simulation results show that ReflectFX outperforms both conventional full-duplex and half-duplex.

In this paper, we consider a multiple-access broadcast channel (MABC) with ARQ feedback, in which M endusers wish to exchange messages with a central node or basestation. In this scenario, an end-user may overhear other endusers' messages prior to the re-transmission phase. We propose a new network coded (NCed)-ARQ scheme with reverse-link-assistance (RLA) that exploits this overheard information in uplink transmission to increase the downlink throughput. We derive throughput expressions for the new NCed-ARQ scheme in wireless additive white Gaussian noise with Rayleigh fading channel, which we numerically evaluate. For low/moderate SNRs, NCed-ARQ with RLA greatly improves the performance of downlink throughput.

In this paper, we consider two nodes that wish to communicate through wireless channels simultaneously at the same frequency. Our concept is based on backscatter modulation (BM), where electromagnetic waves are modulated and reflected by the same antenna that receives them. The base-station transmits a signal by varying amplitude and phase of the carrier wave. The end-user reflects the same signal with a new message modulated onto the received waveform. In this paper, we investigate different backscatter modulation constellations adequate for the full-duplex wireless communication system. Formulation for ASK, PSK and QAM 16 modulation, backscatter modulation and demodulation will be explored.

In this paper, we study the role of combined CSI and ARQ feedback in the context of two-way wireless communications. We consider two nodes that wish to exchange data over, a frequency division duplex, wireless additive white Gaussian noise with Rayleigh fading channel. In two-way scenarios the data and resources allocated to feedback and channel estimation share the same link, leading to interesting tradeoffs. To analyze these, we present a generalized framework for feedback, which combines limited CSI feedback and ARQ. All resources in the two-way communication, that is, 1) training (estimating channel state), 2) feedback (ARQ and CSI), and 3) data are taken into account, and share the same noisy fading channel. We obtain an expression that captures the tradeoffs between allocating resources for these different tasks on the overall achievable throughput in each direction, which we numerically evaluate. In particular, we obtain the optimal resource allocations corresponding to different channel conditions, SNR regimes, transmitter protocols, and receiver feedback protocols.

In this paper, we study ARQ feedback in the context of two-way wireless communications. In particular, we consider two nodes which wish to exchange data over a frequency division duplex, time-varying wireless additive white Gaussian noise with Rayleigh fading, channel. In two-way scenarios, unlike the more well studied one-way data scenarios, the data and resources allocated to feedback and channel estimation may share the same link, leading to interesting tradeoffs. To analyze these, we present a two-way framework in which 1) training (estimation of channel state), 2) feedback (in the form of ARQ), and 3) data are taken into account, and share the same noisy fading channel. We obtain an expression which captures the tradeoffs between allocating resources for these three tasks on the overall throughput achievable in each direction, which we numerically evaluate. In particular, we obtain the optimal resource allocations corresponding to different channel conditions, SNR regimes, and receiver feedback protocols under fast and slow fading conditions.

In this paper, we consider network coded (NCed) Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of throughput expressions for NCed HARQ with arbitrary number of users in identical i.i.d. channels amid packets for all users. We apply the result to Rayleigh fading channels and two packet combining schemes: incremental redundancy (IR) and chase combining (CC). We verify the analytical results with simulations and observe substantial SNR improvements over NCed ARQ and HARQ. The SNR gains in the moderate/high and low throughput regimes are mainly due to network coding and packet combining, respectively. For low/moderate SNRs, NCed HARQ with IR surpasses the CC performance. In addition, we introduce a novel re-transmission strategy that makes the network coding more efficient at low SNR.

In this work, we propose a QPSK OFDM code that has both low peak to average power ratio and good bit error rate performance. We consider a Time-frequency Turbo Block code. This code is composed of the cosets of the first-order binary Reed-Muller (RM) code in the frequency domain, and Bose-Chaudhuri-Hocquenghem (BCH) code in the time domain. Our contributions are two-fold: 1) we introduce two encoding schemes that guarantee a PAPR of 3 dB for QPSK constellation, 2) we propose moderate complexity decoding procedures for these schemes. We evaluate the performance of the proposed schemes for the additive white Gaussian noise channel. Our code performs only slightly worse than the best known Turbo codes but has significantly lower PAPR. This gives a significant total power gain over the best known Turbo codes.

In this paper, we provide a geometric interpretation of the Peak Interference to Carrier Ratio (PICR) of OFDM signals. Based on this interpretation, we propose a simple approach to reduce the sensitivity of OFMA system to carrier frequency offset (CFO). The main idea is to choose a well understood code and to rotate each coordinate of the code by a fixed phase shift such that the maximum inter-carrier interference (ICI) taken over all sub-carriers is minimized. This approach enjoys the twin benefits of interference reduction and error correction and is easy to implement in practice. Simulation results show that a reduction of 7 dB can freely be obtained.

We consider a cellular network inspired channel model which consists of the bi-directional exchange of information between a base-station and M terminal nodes with the help of a relay. The base-station has a message for each of M terminals, and conversely, each terminal node has a message for the base-station. A single relay assists the bi-directional communication endeavor. We assume an AWGN channel model with direct links (omitted in previous studies) between the base-station, relay, and half-duplex nodes. In this scenario, we derive achievable rate regions for two temporal protocols - needed in half-duplex networks - which indicate which users transmit when. These achievable rate regions are based on a novel lattice encoding and decoding strategy which outperforms previously derived regions using random-coding based decode-and-forward strategies under certain channel conditions. The terminal nodes employ nested lattice codes, and the relay decodes a series of codeword combinations - one of the main novelties of our scheme - from which it deduce the sum-codewords of the base-station to terminal node i, which it then broadcasts. This scheme differs markedly from previously considered successive-decoding based lattice strategies and provides a more general framework for the joint decoding of lattice codewords in a MAC. Numerical evaluations of our lattice-based inner bounds are shown to improve upon previous random-coding based schemes under certain channel conditions, and are compared to half-duplex cut-set outer bounds. We further demonstrate a constant sum-rate gap result using this lattice-based scheme for symmetric channels for one of the two protocols.

In this paper, we present an advanced solution for the long standing problem of large peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. Although the design of low PAPR codewords has been extensively studied and the existence of asymptotically good codes with low PAPR is also proven, still no code has been constructed to satisfy all requirements. The main goal of the paper is to develop a coding scheme that not only generates low PAPR codewords, but it also performs relatively close to the Shannon limit. We achieve this goal by implementing a time-frequency turbo block coded OFDM. In this scheme, we design the frequency domain component to have a tightly bounded PAPR. The time domain component code is designed to obtain good performance while the decoding algorithm has reasonable complexity. Through comparative performance evaluation we show that utilizing the proposed method, we achieve considerable improvement in terms of PAPR while we slightly loose the performance compared to capacity achieving codes with similar overall block length.

In this paper, we study the air-to-ground cellular systems with no frequency reuse. We provide an analysis of the inter-cell interference under idealized assumptions: 3D hexagonal cell planning, a line of sight channel model with no shadowing and idealized antenna patterns. Based on this model, we derive approximate bounds for the inter to intra-cell interference ratio for the air-to-ground link. In addition, we provide upper bounds on the interference and the outage probability for the ground-to-air link. Simulation results are provided to validate the accuracy of the analytical results.

In this paper, we consider network coded (NCed) Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of a throughput expression for NCed HARQ with arbitrary number of users in i.i.d. channels. We apply the result to Rayleigh fading channels for incremental redundancy (IR) and chase combining (CC) based NCed HARQ. We verify the analytical approach with simulations and observe substantial SNR (or energy) improvements over regular ARQ with network coding as well as classical (H)ARQ. The SNR gains in the high and low throughput regimes are mainly due to the network coding and HARQ aspects, respectively. For low SNRs, NCed HARQ with IR surpass the CC performance.

The multi-pair bi-directional relay network under consideration consists of one base-station, multiple (say m) terminal nodes and one relay, all of which are half-duplex, in which, contrary to prior work, each node has a direct link with every other node. Each of the m terminal nodes exchanges messages with the base-station in a bi-directional fashion, leading to 2m total messages to be communicated with the (possible) help of the relay. Our contributions are: 1) the introduction of three new temporal protocols which fully exploit the two-way nature of the data, over-heard side-information through network coding, random binning, and compress-and-forward terminal node cooperation, 2) derivations of achievable rate regions and 3) cut-set based outer bounds for the multi-pair network, and 4) a numerical evaluation of the derived regions in Gaussian noise which illustrate the performance of the proposed protocols.

In this contribution an accurate average Bit Error Rate (BER) formula is derived for MC-DS-CDMA in the context of asynchronous transmissions and random spreading sequences. We consider a flat Nakagami-m fading channel for each subcarrier. Our analysis is based on the Characteristic Function (CF) and does not rely on any assumption concerning the statistical behavior of the interference. We develop a new closed-form expression for the conditional CF of the inter-carrier interference and provide a procedure for calculating the exact BER expressed in the form of a single numerical integration. The accuracy of the Standard Gaussian Approximation (SGA) technique is also evaluated. Link-level results confirm the accuracy of the SGA for most practical conditions.

We consider on the move satellite systems with geostationary satellites. Using the antenna pointing distribution of Weerackody and Gonzalez, we derive tight upper and lower bounds of the interference between adjacent satellites from/to the on-the-move platforms. We then compute the distribution of the interference and the outage probability of the system. Simulation results are provided demonstrating that the analytical estimates are accurate.

Abstract In this paper, we address the issue of multi‐user receiver design in realistic multi‐cellular and multi‐rate CDMA systems based on performance analysis. We consider the multi‐user detection (MUD) technique, denoted interference subspace rejection (ISR), because it offers a wide range of canonic suppression modes that range in performance and complexity between interference cancellers and linear receivers. To further broaden our study, we propose a modified ISR scheme called hybrid ISR to cope better with multi‐rate transmissions. The performance analysis, which is based on the Gaussian assumption (GA) and validated by simulations, takes into account data estimation errors, carrier frequency mismatch, imperfect power control, identification errors of time‐varying multipath Rayleigh channels and intercell interference. This analysis enables us to optimize the selection of the MUD mode for multi‐rate transmissions in different operating conditions. The effectiveness of interference cancellation is indeed investigated under different mobile speeds, numbers of receiving antennas, near‐far situations, channel estimation errors, and out‐cell to in‐cell interference ratios. This investigation suggests that the out‐of‐cell interference, the residual in‐cell interference, the noise enhancement as well as low mobility favor the simplest MUD modes as they offer the best performance/complexity tradeoffs. Copyright © 2008 John Wiley & Sons, Ltd.

Interference in cellular terrestrial systems has been extensively studied in the literature mainly through the use of simulations. The interference for CDMA cellular air-to-ground systems has been similarly evaluated through extensive simulations. However, the air-to-ground systems are simpler to analyze than terrestrial systems. In this note, we provide analytic bounds for inter-cell interference in air-to-ground cellular systems with no frequency reuse. We consider the standard 3D hexagonal cell plan and a line of sight channel model with no shadowing and no fading. Simulation results demonstrate that our approximations are extremely tight.

In this contribution an accurate average bit error rate (BER) formula is derived for Nakagami-faded MC-DS-CDMA in the context of asynchronous transmissions and random spreading sequences. Our analysis is based on the Characteristic Function (CF) and does not rely on any assumption concerning the statistical behavior of the interference. We develop a new closed-form expression for the conditional CF of the inter-carrier interference and provide a procedure for calculating the exact BER expressed in the form of a single numerical integration. The accuracy of the standard Gaussian approximation (SGA) technique is also evaluated. Link-level results confirm the accuracy of the SGA for most practical conditions.

This paper proposes a spectrum-efficient spatio-temporal array-receiver for multi-carrier CDMA systems named MC-STAR. First, we derive a new post-correlation model for MC-CDMA that characterizes the structure of the channel in space, time and frequency. Based on this model, we introduce a new multi-carrier array-receiver with rapid and accurate joint synchronization in time and frequency. There, we exploit jointly the spatial, temporal and frequency diversities as well as the intrinsic inter-carrier correlation (termed hereafter frequency gain) to improve the channel identification and the synchronization operations. In addition, based on a new link/system-level performance analysis, with a band-limited chip waveform assumption, we provide a comparative performance study of MC-STAR over two multi-carrier CDMA air-interface configurations, namely MT-CDMA and MC-DS-CDMA, in the most realistic operating conditions. Link/system-level results confirm the advantages of MT-CDMA in increasing throughput and bandwidth efficiency. The current trend is to design radio air-interfaces with flat fading subcarriers. In contrast, with MC-STAR we show that the positive effects of multipath diversity and frequency gain over large strongly-overlapping subcarriers is more significant than the negative effects of multipath and multi-carrier interference.

The spatio-temporal array-receiver (STAR) decomposes generic wideband CDMA channel responses across various parameter dimensions (e.g., time-delays, multipath components, etc...) and extracts the associated time-varying parameters (i.e., analysis) before reconstructing the channel (i.e., synthesis) with increased accuracy. This work verifies the performance of STAR by comparing the results achieved with generic and measured channels for an average multipath power profile of [0, -4, -8] dB and a vehicular speed below 30 Km/h. The results suggest that losses due to operations with real 5 MHz channels are only 1 dB in SNR and 20-30% in capacity with DBPSK and single transmit and receive antennas. The corresponding SNR threshold for operation with real channels is about 5 dB.

In this paper, we extend the investigation of the generalized MC-CDMA system by considering a practical band- limited chip waveform, namely, a square-root raised cosine waveform. The analysis is based on the standard Gaussian approximation. The effects of the chip waveform and the spacing between two adjacent subcarriers on the interference level and on the average BER have been evaluated. The results show that for a given subcarrier spacing between two adjacent subcarriers, there exists a corresponding best choice of the chip waveform. In addition, they suggest that MT-CDMA has the optimum spacing between subcarriers and achieves the best BER performance.

This paper proposes a spectrum-efficient spatio-temporal array-receiver (STAR) for multi-carrier CDMA systems named MC-STAR. First, we derive a new post-correlation model for MC-CDMA that supports both the MT-CDMA and MC-DS-CDMA air-interfaces. Based on this model, we introduce a new multi-carrier receiver with rapid and accurate joint synchronization in time and frequency. We also exploit the intrinsic subcarrier correlation to improve the channel identification and the synchronization operations. We analyze the performance of MC-STAR in an unknown time-varying Rayleigh channel with multipath, carrier offset and cross-correlation between subcarrier channels. Simulation results confirm the accuracy of the joint time/frequency synchronization. They also confirm that for each MC-STAR configuration there exists an optimum number of subcarriers which results in maximum throughput. A higher number of subcarriers increases the inter-carrier interference while a lower number of subcarriers reduces the frequency gain. With four receiving antennas and five MT-CDMA subcarriers in 5 MHz bandwidth, MC-STAR provides about 1.2 bps/Hz at low mobility for DBPSK, i.e., an increase of 30% in spectrum efficiency over DS-CDMA.

This paper evaluates the capacity degradation due to the coexistence of a 3G/WCDMA system with second-generation systems in the North American PCS band. The performance impact of deploying 3G FDD and 2G systems on adjacent frequency bands (not overlapping) in the same block with the same FDD directionality is studied. The methodology is based on the elaboration of a multi-cell system-level simulation tool that allows a quantitative assessment of the change of capacity due to the presence of another wireless system operating in an adjacent band. This simulation tool follows generally agreed principles and assumptions as proposed by 3GPP with some additional assumptions related to the North American second-generation system (GSM, IS-136 and IS-95). The main results of this study are that in most cases, the 2G system is found to be the aggressor and the 3G system the victim, and that the worst-case deployment is an un-coordinated one, which requires improvement in power budget of 30 dB (assuming no guard-band).

This letter presents an efficient and accurate performance evaluation method for binary MC-CDMA systems with deterministic signature sequences. This method is based on a formulation of the characteristic function, and does not resort to any assumption on the statistical or spectral behavior of the interference. The accuracy of the Gaussian approximation method is also considered.