This paper introduces a novel method to minimize the peak-to-average power ratio (PAPR) and at the same time enhance the data rates of orthogonal frequency-division multiplexing (OFDM) systems by combining tone reservation (TR) and index modulation (IM). Unlike conventional TR methods, in which a number of tones (or subcarriers) with fixed positions are reserved for canceling the peaks in OFDM signals, the TR-IM method treats the positions of the reserved tones (TR tones) as random and embeds extra information in their positions using IM. In the proposed system, the amplitudes of the TR tones are quantized with a novel quantization method, which not only helps the receiver distinguish between data tones and TR tones, but also enables the TR tones to carry data on their amplitudes. Based on that, we propose a novel forward error correction (FEC) structure to increase the reliability of detection without requiring extra overhead. The proposed FEC design encodes the IM activation pattern rather than the index data bits, and carries the resulting parity bits with a novel mechanism that exploits the extra bits carried on the amplitudes of the TR tones. Simulation results show that, not only does our proposed system have significantly higher data rates, but it can also achieve remarkable PAPR reduction performance as well as a lower bit error rate than the original OFDM systems under the influence of the non-linear distortion caused by power amplifiers.

In this article, we present a device-to-device (D2D) transmission scheme for aiding long-range frequency-hopping spread spectrum (LR-FHSS) LoRaWAN protocol with application in direct-to-satellite Internet of Things (IoT) networks. We consider a practical ground-to-satellite fading model, i.e., shadowed-Rice channel, and derive the outage performance of the LR-FHSS network. With the help of network coding, a D2D-aided LR-FHSS transmission scheme is proposed to improve the network capacity for which a closed-form outage probability expression is also derived. The obtained analytical expressions for both LR-FHSS and D2D-aided LR-FHSS outage probabilities are validated by computer simulations for different parts of the analysis capturing the effects of noise, fading, unslotted ALOHA-based time scheduling, the receiver’s capture effect, IoT device distributions, and distance from node to satellite. The total outage probability for the D2D-aided LR-FHSS shows a considerable increase of 249.9% and 150.1% in network capacity at a typical outage of 10−2 for the data rates of DR6 (325 bps) and DR5 (162 bps), respectively, when compared to LR-FHSS. This is obtained at the cost of a minimum of one and a maximum of two additional transmissions per IoT end device imposed by the D2D scheme in each time slot.

This article investigates the effect of uncertainty in the positions of a set of spatially separated receivers (gateways) that are used to localize a device (target) that transmits a burst signal intermittently. Such systems have applications in radar, sonar, and wireless sensor networks, and have been extensively studied, at least in the context of point estimation. This article extends the limited work on region estimation to include the effect of uncertainty in the locations of the gateways on the probability that the target is in a specified region. Specifically, this article extends previous work that found the a posteriori probability density function (pdf) of the target’s coordinates from estimates of the times the transmitted message arrives at the receivers [Time of Arrivals (ToA)] under the assumption the positions of the gateways were known exactly. The expression for the a posteriori pdf is redeveloped to include the uncertainty in the measurement of the receivers’ positions. Three practical scenarios are considered: 1) the target transmits a single message and the gateways measure the ToAs as well as their own positions; 2) the target transmits multiple messages and the gateways measure the ToAs as well as their own positions upon each reception; and 3) the target transmits multiple messages and the gateways measure the ToAs upon each reception, but the positions of the gateways are measured once, at the time of installation. Various numerical examples are given to corroborate, provide insights, and illustrate the utility of the obtained results.

This paper proposes a novel design of multi-symbol unitary constellation for non-coherent single-input multiple-output (SIMO) communications over block Rayleigh fading channels. To facilitate the design and the detection of large unitary constellations at reduced complexity, the proposed constellations are constructed as the Cartesian product of independent amplitude and phase-shift-keying (PSK) vectors, and hence, can be iteratively detected. The amplitude vector is detected by exhaustive search, whose complexity is sufficiently low in short packet transmission scenarios. To detect the PSK vector, we use the posterior probability as a reliability criterion in the sorted decision-feedback differential detection (sort-DFDD), which results in near-optimal error performance for PSK symbols with equal modulation orders. This detector is called posteriori-based-reliability-sort-DFDD (PR-sort-DFDD) and has polynomial complexity. We also propose an improved detector called improved-PR-sort-DFDD to detect a more generalized PSK structure, i.e., PSK symbols with unequal modulation orders. This detector also approaches the optimal error performance with polynomial complexity. Simulation results show the merits of our proposed multi-symbol unitary constellation when compared to competing low-complexity unitary constellations.

This paper proposes a non-coherent communication scheme for short packet communications (SPCs), called spectrally-efficient modulation on conjugate reciprocal zeros (SE-MOCZ). The proposed SE-MOCZ scheme is realized by combining the recently-proposed MOCZ and faster-than-Nyquist (FTN) signaling. Specifically, the pulses carrying the polynomial coefficients of MOCZ are accelerated beyond the Nyquist limit to enhance the spectral efficiency. The spectral efficiency enhancement, however, comes at the expense of inter-polynomial-coefficient interference (IPCI), which increases the number of received complex zeros in the$z$-domain of the polynomial representing the received signal. We design a partial-complex-zeros-removal filter at the receiver to partially remove the pre-defined zeros due to the FTN signaling. Furthermore, we also optimize the radius of the transmit complex zeros in SE-MOCZ to improve the bit error rate (BER) performance. We propose a maximum likelihood (ML) detector for the proposed SE-MOCZ scheme. To strike a balance between the BER performance and computational complexity, we adopt a root-finding minimum distance (RFMD)-based detector. Simulation results clearly show the performance advantage of the proposed SE-MOCZ when compared to MOCZ for a wide range of operating parameters.

In this paper, we propose a novel multi-symbol unitary constellation structure for non-coherent single-input multiple-output (SIMO) communications over block Rayleigh fading channels. To facilitate the design of large unitary constellations at reduced complexity, the proposed constellations are constructed as the Cartesian product of independent amplitude and phase-shift-keying (PSK) vectors. We exploit this structure to formulate an optimization problem to maximize the minimum distance, which has low complexity compared to optimal unitary constellations. Simulation results show that our proposed multi-symbol unitary constellation has higher minimum distance and better error performance than other low-complexity unitary constellations when using maximum likelihood (ML) detector.

This article investigates a new model to improve the scalability of low-power long-range (LoRa) networks by allowing a group of multiple end devices (EDs) to communicate with multiple multi-antenna gateways simultaneously (i.e., in the same time slot) on the same frequency band and using the same spreading factor. The maximum-likelihood (ML) decision rule is first derived for noncoherent detection of information bits transmitted by multiple devices in a group. To overcome the high complexity of the ML detection, we propose a suboptimal two-stage detection algorithm to balance the computational complexity and error performance. In the first stage, we identify transmitted chirps (without knowing which EDs transmit them). In the second stage, we determine the EDs that transmit the specific chirps identified from the first stage. To improve the detection performance in the second stage, we also optimize the transmit powers of EDs to minimize the similarity, measured by the Jaccard coefficient, between the received powers of any pair of EDs in the same group. As the power control optimization problem is nonconvex, we use concepts from successive convex approximation to transform it to an approximate convex optimization problem that can be solved iteratively and guaranteed to reach a suboptimal solution. Simulation results demonstrate and justify the tradeoff between transmit power penalties and network scalability of the proposed LoRa network model. In particular, by grouping two or three EDs in each group for concurrent transmission, the uplink capacity of the proposed network can be doubled or tripled over that of a conventional LoRa network, albeit at the expense of additional 3.0 or 4.7 dB transmit power.

This paper develops a low-complexity suboptimal non-coherent receiver for a multi-level energy-based coded modulation system. Inspired by the turbo processing principle, we incorporate the fundamentals of bit-interleaved coded modulation with iterative decoding (BICM-ID) into the proposed receiver design. The resulting system is called bit-interleaved coded energy-based modulation with iterative decoding (BICEM-ID) and its error performance is analytically studied. Specifically, we derive upper bounds on the average pairwise error probability (PEP) of the non-coherent BICEM-ID system in the feedback-free (FF) and error-free feedback (EFF) scenarios. It is revealed that the definition of the nearest neighbors, which is important in the performance analysis in the FF scenario, is very different from that in the coherent BICM-ID counterpart. The analysis also reveals how the mapping from coded bits to energy levels influences the diversity order and coding gain of the BICEM-ID systems. A design criterion for good mappings is then formulated, and an algorithm is proposed to find a set of best mappings for BICEM-ID. Finally, simulation results corroborate the main analytical findings.

Maintaining freshness of data collection in Internet-of-Things (IoT) networks has attracted increasing attention. By taking into account age-of-information (AoI), we investigate the trajectory planning problem of an unmanned aerial vehicle (UAV) that is used to aid a cluster-based IoT network. An optimization problem is formulated to minimize the total AoI of the collected data by the UAV from the ground IoT network. Since the total AoI of the IoT network depends on the flight time of the UAV and the data collection time at hovering points, we jointly optimize the selection of hovering points and the visiting order to these points. We exploit the state-of-the-art transformer and the weighted A*, which is a path search algorithm, to design a machine learning algorithm to solve the formulated problem. The whole UAV-IoT system is fed into the encoder network of the proposed algorithm, and the algorithm’s decoder network outputs the visiting order to ground clusters. Then, the weighted A* is used to find the hovering point for each cluster in the ground IoT network. Simulation results show that the trained model by the proposed algorithm has a good generalization ability to generate solutions for IoT networks with different numbers of ground clusters, without the need to retrain the model. Furthermore, results show that our proposed algorithm can find better UAV trajectories with the minimum total AoI when compared to other algorithms.

In this paper, frequency diversity (FD) schemes to improve the bit error rate (BER) performance of orthogonal frequency-division multiplexing with index modulation (OFDMIM) and OFDM with subcarrier number modulation (OFDMSNM) are proposed. In addition, subcarrier-level interleaving is incorporated to enhance the error performance of OFDMIM-FD and OFDM-SNM-FD. A tight upper bound on the BER and diversity order of the proposed schemes are found and corroborated with simulation results. The obtained results show that the proposed OFDM-IM-FD and OFDM-SNM-FD significantly outperform the conventional OFDM-IM, OFDMSNM, and OFDM-IM with transmit diversity.

Abstract In this paper, a downlink multi‐user communication of an intelligent reflecting surface (IRS)‐assisted multiple‐input single‐output (MISO) power‐domain non‐orthogonal multiple access (NOMA) system is investigated. Considering multi‐carrier (MC) transmission and to enhance user fairness, two users are assigned to the same subcarrier. For such a system, the authors optimize active beamforming at the base station (BS), subcarrier allocation policy, and phase shifts at the IRS to maximize the system throughput. A semi‐definite relaxation (SDR) is applied to tackle the non‐convex optimization problem, and an alternating optimization (AO) algorithm is proposed to obtain a suboptimal solution. Numerical results illustrate the higher throughput of the proposed MC multi‐user IRS‐aided MISO‐NOMA system as compared to the conventional IRS‐assisted orthogonal multiple access (OMA) system.

LoRaWAN is a prominent communication standard to enable reliable low-power, long-range communications for the Internet of Things (IoT). The modulation technique used in LoRaWAN, commonly known as LoRa modulation, is based on the principle of chirp spread spectrum (CSS). The main objective of this article is to design a practical, low-complexity coherent receiver for a recently proposed CSS-based modulation scheme, called phase-shift keying CSS (PSK-CSS), that embeds extra information bits in the starting phases of conventional CSS symbols. To this end, a novel method is proposed to perform coarse timing and frequency synchronization that makes use of a preamble consisting of both up and down chirps and the shape of the pulse shaping and/or receive (matched) filters. Furthermore, to enable fine synchronization, timing, and phase loop filters are designed as simple first-order and second-order phase-locked loop (PLL) circuits with dynamic gain control. A natural outcome of our design is a practical noncoherent receiver that can be used for the conventional LoRa/CSS system and has better performance and/or lower computational complexity as compared to other existing designs. Extensive simulation results are presented to demonstrate the excellent performance and merits of the proposed design. In particular, the bit-error-rate (BER) performance of the higher-rate PSK-CSS system obtained with the proposed coherent receiver is only 0.25 dB worse than that obtained with the ideal co-coherent receiver, whereas it enjoys about 0.75-dB power gain over the noncoherent detection performance of the conventional CSS system. Thanks to the extra information bits carried by the phases of CSS symbols, the PSK-CSS system implemented with quadrature phase-shift keying (QPSK) delivers additional 23.44% and 18.75% data rate as compared to the conventional CSS system for the spreading factors (SFs) of 8 and 10, respectively.

This article proposes a novel approach to improve the energy efficiency (EE) of an energy-harvesting (EH)-enabled IoT network supported by simultaneous wireless information and power transfer (SWIPT). More specifically, the device-to-device (D2D) users harvest ambient energy throughout their communication with the time switching (TS) technique, while the Internet of Things (IoT) users harvest energy from the base station (BS) based on the power splitting (PS) method. We study the EE optimization problem that takes into account transmit power feasibility conditions for D2D users and IoT users, the minimum data rate requirements for D2D and IoT users, joint spectrum sharing block, and time allocation for the D2D links. The underlying problem is a highly nonconvex mixed-integer nonlinear problem (MINLP) and the global optimal solution is intractable. To handle it, we decompose the original problem into three subproblems: 1) joint subchannel allocation and PS; 2) power control; and 3) time allocation. Since it is difficult to find an exact state model approach in a dynamic environment with a large state space, we exploit a$Q$-learning method based on reinforcement learning (RL) to solve the first subproblem. To solve the second subproblem, we apply a conventional convex optimization technique based on the majorization–minimization (MM) approach and Dinkelbach method. Simulation results not only demonstrate the superiority of our proposed algorithm as compared to other methods in the literature but also confirm impressive EE gains through spectrum sharing and harvested energy from D2D and IoT users.

Employing unmanned aerial vehicles (UAVs) has attracted growing interests and emerged as the state-of-the-art technology for data collection in Internet of Things (IoT) networks. In this article, with the objective of minimizing the total energy consumption of the UAV-IoT system, we formulate the problem of jointly designing the UAV’s trajectory and selecting cluster heads in the IoT network as a constrained combinatorial optimization problem, which is classified as NP-hard, and challenging to solve. We propose a novel deep reinforcement learning (DRL) with a sequential model strategy that can effectively learn the policy represented by a sequence-to-sequence neural network for the UAV’s trajectory design in an unsupervised manner. Through extensive simulations, the obtained results show that the proposed DRL method can find the UAV’s trajectory that requires much less energy consumption when compared to other baseline algorithms and achieves close-to-optimal performance. In addition, simulation results show that the trained model by our proposed DRL algorithm has an excellent generalization ability to larger problem sizes without the need to retrain the model.

This paper develops a non-coherent index modulation (IM) system in which activation patterns are characterized by multi-level block codes. We analyze performance of such a system under the maximum-likelihood (ML) receiver and when the set of activation patterns follows a multi-level code generated from asymptotically optimal alphabets. An asymptotic analysis of the pair-wise error probability (PEP) shows that the system can exploit a diversity order that is determined by the distance of the worst codeword pair in the$l_{1}$metric, known as the Manhattan norm. We then explore the rate-diversity tradeoff for the developed non-coherent IM system as a function of the code length. Specifically, Gilbert-style bounds on the data rates for systems based on binary and ternary codes are obtained that can ensure a given diversity order. We approach the problem of packing in the$l_{1}$metric by partitioning codes into permutation modulation codes (PMCs) and obtaining Gilbert-style bounds on PMCs. Several achievable rates for non-coherent binary and ternary IM systems, as well as a tradeoff between the information rate and codeword error probability (CEP) are also derived. Finally, simulation results are provided to corroborate the theoretical analysis.

LoRa, a low-power long-range physical-layer communication method, is one of the emerging technologies in low-power wide-area networks (LPWANs). In LoRa, a linearly varying-frequency up chirp and its cyclic shifts act as an orthonormal basis set for message representation. The number of orthonormal basis functions dictates the achievable bit rate of a LoRa system. This article aims to increase the achievable data rate of a conventional LoRa system by adding a set of new orthonormal basis functions to the existing set. Specifically, we use a linearly varying-frequency down chirp and its cyclic shifts to generate the second set of orthonormal basis functions in the proposed scheme, named slope-shift-keying LoRa (SSK-LoRa) modulation. We also develop both low-complexity optimum coherent and noncoherent detection algorithms for the proposed SSK-LoRa modulation. We then obtain closed-form analytical and tight approximations for the bit and symbol error probabilities of noncoherent detection in a Rayleigh fading environment. Our proposed SSK-LoRa scheme is shown to outperform the state-of-the-art LoRa-based modulation schemes.

This article introduces a novel frequency-shift chirp spread spectrum (FSCSS) system with index modulation (IM). By using combinations of orthogonal chirp signals for message representation, the proposed FSCSS with index modulation (FSCSS-IM) system is very flexible to design and can achieve much higher data rates than the conventional FSCSS system under the same bandwidth. The article presents optimal detection algorithms, both coherently and noncoherently, for the proposed FSCSS-IM system. Furthermore, a low-complexity noncoherent detection algorithm is also developed to reduce the computational complexity of the receiver, which is shown to achieve near-optimal performance. The results are presented to demonstrate that the proposed system, while enabling much higher data rates, enjoys similar bit-error performance as that of the conventional FSCSS system.

This article was motivated by the need to localize a sensor (signal source) in an Internet-of-Things (IoT) network to an area with a predetermined probability (credibility). The source is assumed to transmit a short time duration (burst) signal in a homogeneous line-of-sight environment. The source's signal is known to an array of spatially separated receivers, which can measure the times of arrival of the source's signal subject to Gaussian measurement errors. The time that the signal leaves the source (i.e., the transmit time) is, however, unknown. The authors develop a method for computing the exact a posteriori probability density functions (pdfs) of the coordinates of the source's in both 2-D and 3-D spaces. The obtained a posteriori pdfs incorporate arbitrary a priori densities, which makes them very useful in many practical scenarios. Unlike existing point-estimate methods, the probabilistic method does not simultaneously solve a set of equations so there is neither a lower nor upper limit on the number of receivers. Various examples are provided to demonstrate the superiority and usefulness of the proposed method. In particular, it is shown that the joint a posteriori pdf of the target's location is not always approximately jointly Gaussian, especially when the target is in close proximity to one of the gateways, or when the gateways are located in close proximity to each other.

Energy load balancing is an essential issue in designing wireless sensor networks (WSNs). Clustering techniques are utilized as energy-efficient methods to balance the network energy and prolong its lifetime. In this article, we propose an improved soft-k-means (IS-k-means) clustering algorithm to balance the energy consumption of nodes in WSNs. First, we use the idea of clustering by fast search and find of density peaks (CFSFDPs) and kernel density estimation (KDE) to improve the selection of the initial cluster centers of the soft k-means clustering algorithm. Then, we utilize the flexibility of the soft-k-means and reassign member nodes considering their membership probabilities at the boundary of clusters to balance the number of nodes per cluster. Furthermore, the concept of multicluster heads is employed to balance the energy consumption within clusters. Extensive simulation results under different network scenarios demonstrate that for small-scale WSNs with single-hop transmission, the proposed algorithm can postpone the first node death, the half of nodes death, and the last node death on average when compared to various clustering algorithms from the literature.

Providing ultra reliable and low-latency communication (URLLC) is considered one of the major challenges for wireless communication networks. This article considers a downlink URLLC system in which a base station (BS) serves multiple single-antenna users in the short blocklength regime. With the objective of maximizing the users' minimum rate, three different optimization problems are considered: (i) joint design of bandwidth and power allocation for the case of a single-antenna BS; (ii) beamforming design for the case of a multiple-antenna BS; and (iii) design of power allocation with regularized zero-forcing beamforming for the case of a multiple-antenna BS. In the short blocklength regime, the achievable rate is a complicated function of bandwidth and power allocation coefficients or beamforming vectors, which makes these max-min rate optimization problems challenging to solve. This work develops path-following algorithms, which generate a sequence of improved feasible points and converge at least to a locally optimal solution, to solve these three optimization problems. Performance of the proposed algorithms is analyzed through extensive simulations under various settings of transmit power budget, number of users, total bandwidth, transmission time, and number of transmit antennas at the BS. Simulation results clearly demonstrate the merits of the proposed algorithms.

This paper proposes a novel successive interference cancellation method to enhance the ergodic spectral efficiency of a cell-free massive multiple-input multiple-output (MIMO) system with non-orthogonal multiple-access (NOMA). Unlike the majority of existing research works on performance evaluation of NOMA, which assume perfect channel state information and perfect data detection for successive interference cancellation, we take into account the effect of practical (hence imperfect) successive interference cancellation (SIC). We show that the received signal at the backhaul network of a cell-free massive MIMO-NOMA system can be effectively treated as a signal received over an AWGN channel. As a result, a discrete joint distribution between the interfering signal and its detected version can be analytically found, from which an adaptive SIC scheme is proposed to improve performance of interference cancellation.

In this study, the authors investigate the intra‐physical functional splits of 5G new radio protocol stack proposed by different groups. Based on the location of the digital beamforming block, the radio units (RUs) are divided into two categories: Category A and Category B. Two implementation modes of hybrid beamforming at the physical layer are considered, in which digital beamforming is performed either at the distributed unit (DU), as in the Category A RU based hybrid beamforming (HBF‐A) scheme, or at the RUs, as in the Category B RU based hybrid beamforming (HBF‐B) scheme. To maximise the weighted sum rate, the authors formulate the problems of jointly designing hybrid beamforming, analogue combining and fronthaul compression strategies for both HBF‐A and HBF‐B. The formulated problems are simplified by adopting the codebook‐based design, and further tackled by leveraging the majorisation–minimisation algorithm. Finally, numerical results confirm that the HBF‐A scheme outperforms the HBF‐B scheme in the large power regime. Compared with the HBF‐A method, the HBF‐B method is more sensitive to changes in system parameters, such as the compression noise and the number of receive antennas, in the large power regime, while it is less sensitive in the small power regime.

Recent studies of single-cell two-user networks have shown that a higher network throughput is achieved by using a common message to be decoded by both users and conveying partial information for both users, rather than using the common message to convey the entire information for one of the two users. The latter is essentially the conventional non-orthogonal multiple access (NOMA), which performs better than orthogonal multiple access (OMA) only under users' dissimilar channel conditions. Unlike NOMA, the former performs consistently better than OMA. This paper generalizes such a signaling strategy to a general multi-cell multiuser network, which leads to a new NOMA approach (called n-NOMA) in which each pair of users decodes a message that conveys partial information for one of them only. Unlike the conventional NOMA, whose performance is dependent on the users' pairing strategy, the proposed n-NOMA consistently outperforms both NOMA and OMA schemes. Both proper and improper Gaussian signaling is considered for all the concerned schemes and it is shown that the latter is clearly more advantageous than the former.

Recent technology advancement has resulted in optimistic view toward the practicability of wireless sensor networks (WSNs) in the context of Internet of Things (IoT) and Cyber Physical Systems (CPS). However, to realize their full benefits in a broad range of commercial applications, there are still many technical hitches that need to be overcome. In this paper, we address three vital technical issues in a WSN: (1) distributed event detection, (2) distributed parameter estimation, and (3) network's robustness. We make use of a recent development in social networks called small world characteristics and propose novel fault-resilient distributed detection and estimation methods over a small world WSN (SW-WSN). In particular, a small world WSN has been developed by mounting antenna arrays on sensor nodes for the purpose of beamforming. A low-complexity optimization problem for beamforming is formulated by introducing a new parameter Flow between node pairs. Additionally, a new beamforming algorithm is also proposed which optimizes this flow, leading to optimal beam parameters. The proposed method yields a lower average path length and a higher average clustering coefficient of the network. Experiments are conducted using simulations and real node deployments over a WSN testbed. Analysis and experimental results obtained demonstrate that the proposed SW-WSN model achieves faster convergence rates for both distributed detection and distributed estimation while being resilient to node failures when compared to results obtained using state-of-the-art methods.

This paper generalizes the conventional noncoherent OFDM-IM systems by allowing selection of different numbers of active subcarriers for message representation. We then present the maximum-likelihood (ML) detection rule for frequency-selective block fading channels. The performance of the ML receiver is analyzed in terms of pairwise-error probability as well as diversity order. Asymptotic analysis of the proposed system reveals the role of partial Hamming distance in designing diversity-exploiting activation patterns. Practical issues including low-complexity receiver, and code (activation pattern) design techniques are discussed. Furthermore, the effect of inter-carrier interference in fast fading scenarios, and generalization of the technique to multiple-antenna scenarios are studied. Finally, we present simulation results to illustrate performance benefits of the generalized OFDM-IM systems over the conventional noncoherent OFDM-IM systems.

This paper proposes and investigates an overlay spectrum sharing system in conjunction with the simultaneous wireless information and power transfer to enable communications for the Internet of Things (IoT) applications. Considered is a cooperative cognitive radio network, where two IoT devices (IoDs) exchange their information and also provide relay assistance to a pair of primary users (PUs). Different from most existing works, in this paper, both IoDs can harvest energy from the radio-frequency signals received from the PUs. By utilizing the harvested energy, they provide relay cooperation to PUs and realize their own communications. For harvesting energy, a time-switching-based approach is adopted at both IoDs. With the proposed scheme, one round of bidirectional information exchange for both primary and IoT systems is performed in four phases, i.e., one energy harvesting phase and three information processing phases. Both IoDs rely on the decode-and-forward operation to facilitate relaying, whereas the PUs employ selection combining technique. For investigating the performance of the considered network, this paper first provides exact expressions of user outage probability (OP) for the primary and IoT systems under Nakagami-m fading. Then, by utilizing the expressions of user OP, the system throughput and energy efficiency are quantified together with the average end-to-end transmission time. Numerical and simulation results are provided to give useful insights into the system behavior and to highlight the impact of various system/channel parameters.

LoRa is an abbreviation for low power and long range and it refers to a communication technology developed for low-power wide-area networks (LPWANs). Based on the principle of chirp spread spectrum (CSS), LoRa technology is very attractive to provide low bit-rate wireless connections over an extended communication range and under very low power consumption. While the medium access control (MAC) layer of LoRa specifications is open for developers, the physical layer is not. In particular, LoRa modulation and demodulation techniques are patented by Semtech and have not been mathematically described in detail. This paper presents novel approaches to modulate and demodulate LoRa signals with very high implementation efficiency, great flexibility, and excellent performance. In particular, compared to the commercially available receiver made by Semtech, the proposed design is shown to yield a saving of transmitted power from 0.9 to 2.5 dB over the spreading factor (SF) range of 6-12. Moreover, this paper suggests a method to exploit the phase information of CSS signals to encode extra information bits, leading to throughput improvement over the conventional CSS system, for example, by 33%, 25%, 20%, and 17% for SFs of 6, 8, 10, and 12, respectively.

This paper considers a cooperative cognitive radio system that enables bidirectional primary and secondary transmissions along with simultaneous wireless information and power transfer (SWIPT). In the considered scheme, two secondary users (SUs) provide relay assistance to a pair of primary users (PUs), and in return, they are allowed to exploit the licensed spectrum for realizing their communications. With such a scheme, two end-to-end transmissions can be accomplished in four phases including the phase for energy harvesting (EH). Different from most previous works, a hybrid-SWIPT is adopted in this paper, whereby the SUs can adaptively utilize both EH techniques, i.e., time switching and power splitting. Both SUs perform amplify-and-forward operation to facilitate relay cooperation. On the other hand, PUs employ a selection combining technique to make use of multiple intended signal copies broadcasted from a pair of SUs. For evaluating the performance of the considered network, the exact outage probability expressions for both primary and secondary systems under Nakagami-m fading are provided. Numerical and simulation results illustrate the accuracy of derived expressions and give useful insights into the system behavior, especially with respect to the spectrum sharing factor and hybrid SWIPT parameters.

Among many proposed multi-carrier systems, circular filter bank multi-carrier offset quadrature amplitude modulation (CFBMC-OQAM) is one of promising candidates for future wireless networks. This paper studies the impacts of the intrinsic interferences, namely inter-symbol interference (ISI) and inter-carrier interference (ICI), and phase noise (PN) on the performance of CFBMC-OQAM systems. Two types of PN are considered: one is based on a free-running oscillator and the other is based on a phase-locked loop oscillator. Sources of performance degradation are quantified and a closed-form expression is derived for the signal-to-interference ratio (SIR). An algorithm is then applied to mitigate the PN impacts which takes into account the intrinsic interferences. It is observed that while the impact of the self interference can be negligible when there is no PN, the presence of PN significantly degrades performance of CFBMC-OQAM systems. The applied algorithm is shown to effectively remove the PN impacts.

Quadrature spatial modulation (QSM) exploits the in-phase and quadrature antenna dimensions to increase the number of spatial constellation points. In this paper, an improved version of QSM, which is naturally called improved quadrature spatial modulation (IQSM), is proposed. The main feature of the proposed scheme is to send a second constellation symbol over the in-phase and quadrature antenna dimensions. A significant performance advantage of the proposed scheme is realized at the cost of a slight increase in the number of radio-frequency (RF) chains. Performance comparisons with the most recent spatial modulation schemes confirm the advantage of the proposed IQSM. A theoretical upper bound of the bit error rate is also given and shown to be very tight at high signal-to-noise ratios.

This paper considers constellation design for quadrature spatial modulation (QSM) to minimize the average probability of error. Different than the constellation design previously obtained for spatial modulation (SM), it is shown that, the error performance of QSM not only depends on the Euclidean distances between the amplitude-phase modulation (APM) symbols and the energies of APM symbols, but also on the in-phase and quadrature components of the QSM symbols. The analysis of the union bound of the average error probability reveals that at a very large number of transmit antennas, the optimal constellations for QSM converge to a quadrature phase-shift keying (QPSK) constellation. Simulation results demonstrate the performance superiority of the obtained constellations over the standard PSK and QAM constellations, as well as the constellations specifically designed for SM.

It is known that superposition signaling in Gaussian interference networks is capable of improving the achievable rate region. However, the problem of maximizing the rate gain offered by superposition signaling is computationally prohibitive, even in the simplest case of two-user single-input single-output interference networks. This paper examines superposition signaling for the general multiple-input multiple-output broadcast Gaussian interference networks. The problem of maximizing either the sum rate or the minimal user's rate under superposition signaling and dirty paper coding is solved by a computationally efficient path-following procedure, which requires only a convex quadratic program for each iteration but ensures convergence at least to a locally optimal solution. Numerical results demonstrate the substantial performance advantage of the proposed approach.

This paper presents an OFDMA channel estimation technique that jointly considers the effects of coarse timing error and multipath propagation. Many conventional approaches only consider an optimistic scenario where timing synchronization is perfect and each of the channel delays is an integer number of system samples. In realistic scenarios, timing offsets and echo delays are not integer multiples of the system's sampling period. This threatens sub-carrier orthogonality and causes leakage in the discrete Fourier transform (DFT)-based channel estimation method. Such leakage leads to poor estimation and consequently reduces the system's overall performance. Proposed in this paper is a novel iterative channel estimation technique that considers the practical scenario of fractional timing error and non sample-spaced echo delays. The proposed method does not require channel state information (e.g. second-order statistics of the channel impulse responses or the noise power). Simulation shows that, when comparing OFDMA channel estimation techniques under DOCSIS 3.1 realistic channel conditions, the proposed algorithm significantly outperforms all conventional methods known to the authors.

This paper studies the technique of bit-interleaved coded modulation with iterative decoding (BICM-ID) in a two-way relaying communication system. Iterative decoding based on the quaternary code representation is adopted at the relay for the multiple access (MA) phase. An upper-bound of the bit error probability (BEP) under the error-free (EF) feedback assumption for BICM-ID in the MA phase is obtained. Based on the obtained EF bound of the BEP, it is found that the multiple-access interference (MAI) is successfully eliminated by performing the iterative decoding and XOR based network coding at the relay. Simulation results are provided to corroborate the analysis and demonstrate the performance superiority of the proposed framework.

This paper proposes a design of distributed space-time coding (DSTC) for the multiple access (MA) phase of a two-way relaying communication system. Bit-interleaved coded modulation (BICM) is used by the two terminal nodes and decoding based on the quaternary code representation is adopted at the relay. Based on an upper bound of the error probability, the impact of DSTC on the error performance is analyzed by considering three error types in the MA phase. Specifically, it is shown that type-3 errors need to be carefully taken into account in the design of a DSTC scheme. By developing a performance metric related to type-3 errors, a single parameter can be searched and its optimal value is obtained. To corroborate the analysis and optimization, simulation results are provided to show the advantage of the proposed DSTC scheme over other schemes under both Rayleigh and Rician fading channels.

Motivated by the work of Dahrouj and Yu in applying the Han-Kobayashi transmission strategy for mitigating the intercell interference in a multi-cell multi-user multiple-input single-output interference network (MISO IN), this paper considers splitting messages into private and common parts in a multi-cell multi-user MIMO IN. Specifically, the covariances of the private messages and common messages are designed to optimize either the sum rate or the minimal rate. The common messages and private messages are decoded in sequence using successive decoding. This paper shows how these difficult optimization problems can be adequately solved by means of d.c. (difference ofconcave functions) optimization over a simple convex set. Numerical and simulation results also reveal the great advantage of our proposed solutions for various types of INs. In particular, the proposed solutions are shown to outperform the algorithm developed by Dahrouj and Yu for the simpler case of the MISO IN.

This paper is concerned with distributed estimation of a scalar parameter using a wireless sensor network (WSN) that employs a large number of sensors operating under limited bandwidth resource. A semi-orthogonal multiple-access channel (MAC), which provides transmission of observations from K sensors to a fusion center (FC) via N (N ≤ N) orthogonal channels, is studied. The K sensors are divided into N groups, where the sensors in each group simultaneously transmit on one orthogonal channel (and hence the transmitted signals are directly superimposed at the FC as opposed to being coherently combined). Two versions of the semi-orthogonal MAC are developed and analyzed in detail: fixed sensor grouping and adaptive sensor grouping. Both versions are shown to outperform the orthogonal MAC, especially the one with adaptive sensor grouping. In fact, the semi-orthogonal MAC with adaptive sensor grouping is shown to perform very close to that of the hybrid MAC, while requiring much smaller amount of feedback.

This paper is concerned with the design of distributed precoding in the multiple access (MA) phase for two-way relaying communication (TWRC) systems using OFDM. The error probability analysis is conducted to establish the diversity and coding gains for three error types in the MA phase. Then the design criteria of distributed precoding to achieve the maximum diversity and coding gains are given. The frequency-grouped linear constellation precoding (F-GLCP) is first investigated and shown not to be able to achieve the maximum diversity gain under type-3 errors. Then a novel frequency-time GLCP (FT-GLCP) which performs precoding in both frequency and time domains is proposed. It is proved that the proposed FT-GLCP is able to achieve the maximum diversity gain under type-3 errors, while maintaining the maximum diversity and coding gains under type-1 and type-2 errors. To corroborate the theoretical analysis, simulation results are provided to show the advantage of the proposed FT-GLCP over other schemes in both Rayleigh and Rician fading channels.

An improved iterative receiver is developed for multiuser communications using fast frequency-hopping modulation. Each user employs a channel encoder to protect its information and facilitate interference cancellation at the receiver. At the destination, in order to reliably extract signals from all users, the detection algorithm employs double iteration process: an outer iteration between the interference canceler and soft-input soft-output (SISO) decoder, and an inner iteration between the soft demapper and the SISO decoder. The proposed detection algorithm works with direct as well as relay-aided transmissions. Two relay scenarios are investigated, which are amplify-and-forward and partial-decode-and-forward relaying. Under the same spectral efficiency, simulation results demonstrate the excellent performance of the proposed receiver when compared to the performance of single iterative receiver and other previously-proposed interference cancellation schemes.

This study studies dual‐hop amplify‐and‐forward relaying system employing differential encoding and decoding over time‐varying Rayleigh‐fading channels. First, the convectional ‘two‐symbol’ differential detection (CDD) is theoretically analysed in terms of the bit error rate. The obtained analysis clearly shows that performance of two‐symbol differential detection severely degrades in fast‐fading channels and reaches an irreducible error floor at high signal‐to‐noise ratio region. To overcome the error floor experienced with fast‐fading, a practical suboptimal ‘multiple‐symbol’ detection (MSD) is designed and its performance is theoretically analysed. The analyses of CDD and MSD are verified and illustrated with simulation results under different fading scenarios. Specifically, the obtained results show that the proposed MSD can significantly improve the system performance in fast‐fading channels.

A novel iterative receiver is proposed for relay‐assisted multiuser communications in which multiple users transmit to a destination with the help of a relay and using fast frequency‐hopping modulation. Each user employs a channel encoder to protect its information and facilitate interference cancellation at the receiver. The signal received at the relay is either amplified, or partially decoded with a simple energy detector, before being forwarded to the destination. The proposed iterative receiver exploits the soft outputs of a channel decoder to successively extract the maximum‐likelihood symbols of the users and perform interference cancellation. Under the same spectral efficiency, simulation results demonstrate superior performance of the proposed receiver when compared to the performance of an interference cancellation scheme that was previously proposed for multiuser communications and is extended to multiuser amplify‐and‐forward relaying considered in this study, as well as performance of the maximum‐likelihood multiuser detection for uncoded transmission.

This paper considers joint linear processing at multi-antenna sources and one multiple-input multiple-output (MIMO) relay station for both one-way and two-way relay-assisted wireless communications. The one-way relaying is applicable in the scenario of downlink transmission by a multi-antenna base station to multiple single-antenna users with the help of one MIMO relay. In such a scenario, the objective of join linear processing is to maximize the information throughput to users. The design problem is equivalently formulated as the maximization of the worst signal-to-interference-plus-noise ratio (SINR) among all users subject to various transmission power constraints. Such a program of nonconvex objective minimization under nonconvex constraints is transformed to a canonical d.c. (difference of convex functions/sets) program of d.c. function optimization under convex constraints through nonconvex duality with zero duality gap. An efficient iterative algorithm is then applied to solve this canonical d.c program. For the scenario of using one MIMO relay to assist two sources exchanging their information in two-way relying manner, the joint linear processing aims at either minimizing the maximum mean square error (MSE) or maximizing the total information throughput of the two sources. By applying tractable optimization for the linear minimum MSE estimator and d.c. programming, an iterative algorithm is developed to solve these two optimization problems. Extensive simulation results demonstrate that the proposed methods substantially outperform previously-known joint optimization methods.

Selection combining (SC) at the destination for differential amplify-and-forward (AF) relaying is attractive as it does not require channel state information as compared to the semi maximum-ratio-combining (semi-MRC) while delivering close performance. Performance analysis of the SC scheme was recently reported but only for the case of slow-fading channels. This paper provides an exact average bit-error-rate (BER) of the SC scheme over a general case of time-varying Rayleigh fading channels and when the DBPSK modulation is used together with the non-coherent detection at the destination. The presented analysis is thoroughly verified with simulation results in various fading scenarios. It is shown that the performance of the system is related to the auto-correlation values of the channels. It is also shown that the performance of the SC method is very close to that of the semi-MRC method and the existence of an error floor at high signal-to-noise ratio region is inevitable in both methods. The obtained BER analysis for the SC method can also be used to approximate the BER performance of the MRC method, whose exact analytical evaluation in time-varying channels appears to be difficult.

This paper considers joint optimization of cooperative beamforming and relay assignment for multi-user multi-relay wireless networks to maximize the minimum of the received signal-to-interference-plus-noise ratios (SINR). Separated continuous optimization of beamforming and binary optimization of relay assignment already pose very challenging programs. Certainly, their joint optimization, which involves nonconvex objectives and coupled constraints in continuous and binary variables, is among the most challenging optimization problems. Even the conventional relaxation of binary constraints by continuous box constraints is still computationally intractable because the relaxed program is still highly nonconvex. However, it is shown in this paper that the joint programs fit well in the d.c. (difference of two convex functions/sets) optimization framework. Efficient optimization algorithms are then developed for both cases of orthogonal and nonorthogonal transmission by multiple users. Simulation results show that the jointly optimized beamforming and relay assignment not only save transmission bandwidth but can also maintain well the network SINRs.

A novel iterative receiver is proposed for relay-aided multiuser communications in which multiple users transmit to a destination with the help of a relay and using fast frequency-hopping modulation. Each user employs a channel encoder to protect its information data and to help interference cancellation at the receiver. The received signal at the relay is partially decoded with a simple energy detector. At the destination, the iterative receiver exploits the soft outputs of the channel decoders to successively extract the maximum likelihood symbols of the users and perform interference cancellation. Under the same spectral efficiency, simulation results demonstrate the excellent performance of the proposed receiver when compared to the performance of decoding without interference cancellation as well as performance of the maximum likelihood multiuser detection previously developed for uncoded transmission.

Adaptive physical layer network coding (PNC) has been shown to be effective in two-way relay communications (TWRC). Given that the existing PNC methods were developed for frequency-flat fading channels, this paper studies adaptive PNC in OFDM systems operating over frequency-selective fading channels. Proposed and investigated are three methods to determine a common clustering for all subcarriers in order to reduce the overhead information required in the broadcast phase. The “Min-SER” method is given based on the analysis of the error event in the multiple access phase, while the “Max-fade-SER” and “Min-fade-distance” methods are recommended to further reduce the computational complexity in determining the common clustering. Considering the trade-off among performance, overhead and complexity, the “Max-fade-SER” method is the most attractive clustering method for applying adaptive PNC in OFDM systems.

This paper considers the performance of differential amplify-and-forward (D-AF) relaying over time-varying Rayleigh fading channels. Using the auto-regressive time-series model to characterize the time-varying nature of the wireless channels, new weights for the maximum ratio combining (MRC) of the received signals at the destination are proposed. Expression for the pair-wise error probability (PEP) is provided and used to obtain an approximation of the total average bit error probability (BEP). The obtained BEP approximation clearly shows how the system performance depends on the auto-correlation of the direct and the cascaded channels and an irreducible error floor exists at high signal-to-noise ratio (SNR). Simulation results also demonstrate that, for fast-fading channels, the new MRC weights lead to a better performance when compared to the classical combining scheme. Our analysis is verified with simulation results in different fading scenarios.

This letter proposes and analyses selection combining (SC) at the destination for differential amplify-and-forward (D-AF) relaying over slow Rayleigh-fading channels. The selection combiner chooses the link with the maximum magnitude of the decision variable to be used for non-coherent detection of the transmitted symbols. Therefore, in contrast to the maximum ratio combining (MRC), no channel information is needed at the destination. The exact average bit-error-rate (BER) of the proposed SC is derived and verified with simulation results. It is also shown that the performance of the SC method is very close to that of the MRC method, albeit with lower complexity.

This paper is concerned with design problems of joint source power allocation and relay beamforming in multi-user multi-relay networks that use single-carrier frequency division multiple access (SC-FDMA) and amplify-and-forward relaying. Examined are the joint programs of (i) maximizing the minimum signal-to-interference-plus-noise ratio (SINR) under various transmitted power constraints, and (ii) minimizing the total transmitted power subject to prescribed SINR thresholds of users. Although these optimization problems are highly nonconvex and have large dimensions, by exploiting their partial convexities and making elegant nonlinear variable changes, they are recast as d.c. (difference of two convex) programs. Efficient d.c. iterative procedures are then developed to find the solutions. Simplified joint programs under the two cases of equal source power and equal relay beamforming weights, respectively, are also considered. Branch-and-bound algorithms of deterministic global optimization are then proposed for solving the simplified joint programs. Simulation results confirm the excellent performance and computational efficiency of all the proposed solutions.

Beamforming design for multi-user wireless relay networks under the criterion of maximin information throughput is an important but also very hard optimization problem due to its nonconvex nature. The existing approach to reformulate the design as a matrix rank-one constrained optimization problem is highly inefficient. This paper exploits the d.c. (difference of two convex functions) structure of the objective function and the convex structure of the constraints in such a global optimization problem to develop efficient iterative algorithms of very low complexity to find the solutions. Both cases of concurrent and orthogonal transmissions from sources to relays are considered. Numerical results indicate that the proposed algorithms provide solutions that are very close to the upper bound on the solution of the non-orthogonal source transmissions case and are almost equal to the optimal solution of the orthogonal source transmissions case. This demonstrates the ability of the developed algorithms to locate approximations close to the global optimal solutions in a few iterations. Moreover, the proposed methods are superior to other methods in both performance and computation complexity.

Optimizations of precoding matrices in precode-and-forward (PF) MIMO relaying are nonconvex programs in precoding matrix variables. The semidefinite relaxation (SDR) technique, which relaxes the concerned nonconvex quadratic constraints by (convex) semi-definite ones, can locate the optimal solutions, provided that the numbers of relaying antennas and users are very small. The computational complexity of the SDR grows explosively even with a very moderate increase in the numbers of relaying antennas and/or users, making the existing semidefinite programming (SDP) solvers incapable. In this paper, much more efficient problem formulations of precoding matrix design that exploit the spectral matrix optimization are developed. Such formulations have a low dimensionality and are computationally-tractable nonconvex matrix programs. Furthermore, by exploiting their partial convex structures in the d.c. (difference of two convex functions) framework, new effective iterative solutions are obtained. Extensive simulation results are presented to support the computational advantage of the proposed approach and show that the proposed approach can effectively handle all three considered optimization problems of precoding matrices in MIMO PF relaying, while the SDR approach either is computationally impractical or fails.

We are concerned with a cooperative beamforming design for multi-user multi-relay wireless networks in which the single-carrier frequency division multiple access (SC-FDMA) technique is employed at the terminals. The problem of interest is to find the beamforming weights across relays to maximize the minimum signal-to-interference-plus-noise ratio (SINR) among users subject to individual power constraints at each relay. Such a beamforming design is shown to be a hard nonconvex program and therefore it is mathematically challenging to find the optimal solution. By exploring its partial convex structures, we recast the design problem as minimization of a d.c. (difference of two convex) objective function subject to convex constraints and develop an effective iterative algorithm of low complexity to solve it. Simulation results show that our optimal cooperative beamforming scheme realizes the inherent diversity order of the relay network and it performs significantly better than the equal-power beamforming weights.

For multi-user (MU) amplify-and-forward (AF) cooperative networks, their spectral efficiency can be upgraded within the orthogonal transmission of each source node to an assigned subset of all available relays while their information throughput can be improved through optimized power allocation. We consider the joint optimization in both relay assignment for each source-destination pair and power allocation, which is in fact among the hardest problems in optimization. This is the minimization of a nonconvex objective function subject to mixed integer constraints. The existing numerical algorithms could rarely address to its solutions through computationally affordable procedures. Even the conventional relaxation of the integer constraints by linear constraints does not lead to convex optimization, so the standard convexification does not work either. Nevertheless, we show that it can be effectively solved in the d.c. (difference of two convex) programming context. Numerical simulation confirms the effectiveness of our setting.

In this paper, the asymptotic performance of a precoded bit-interleaved coded modulation with multiple-input multiple-output (BICM-MIMO) system in a block-fading environment is first evaluated. Specifically, the asymptotic pairwise error probability is derived for imperfect channel state information (CSI) and of the minimum mean squared-error (MMSE) detector. The analysis is then used to evaluate the impact of two different training schemes. It is shown that inserting training symbols before precoder is a better option than multiplexing training symbols with data symbols after the precoder. The theoretical result is verified by simulation.

The problem of decision fusion for cooperative spectrum sensing in cognitive radio networks is studied when noisy fading channels are present between the cognitive radios (CRs) and the fusion center (FC). The CRs perform spectrum sensing using energy detection and transmit their binary decisions to the FC for a final decision on the absence or presence of the primary user activity. Considering the limited resources in cognitive radio networks, which makes it difficult to acquire the instantaneous channel state information, noncoherent transmission schemes with on-off keying (OOK) and binary frequency shift keying (BFSK) are employed to transmit the binary decisions to the fusion center. The aim is to optimize the detection performance in terms of the achievable secondary throughput in the cognitive radio network. Toward this end, for each of the transmission schemes considered, first a weighted energy-detector is obtained. Then the detection threshold at the CR nodes as well as at the FC, the sensing weights and the sensing time are optimized to maximize the secondary throughput.

Two designs of un-uniformed constellations for wireless relay networks are considered. The first design is concerned with the unequal error protection issue, in which two data streams to be transmitted from a source to a destination are protected at two different levels. Based on a simple approximation of the average bit-error-rate (BER), a design parameter is obtained in a closed form. The second design focuses on minimizing the average BER of the combined data stream at the destination. Developed are two near optimal designs for 4/16-QAM and 4/64-QAM hierarchical modulation schemes. Simulation results confirm the superiority of the proposed designs as well as the advantages of the relay-assisted transmission with a hierarchical modulation over the conventional point-to-point transmission.

This paper considers beamforming problem in relay-assisted multi-user communication and presents an efficient algorithm to solve Min-max optimization of information throughput under limited power resources. We use DC programming and penalty function method to handle the inherent non-convexity of the associated objective function and follow an iterative procedure to solve for the global optimal beamforming vector. Extensive simulations are performed to establish the effectiveness and superiority of the proposed algorithm over conventional techniques based on randomization.

The performance of bit-interleaved coded modulation in multiple-input multiple-output (BICM-MIMO) systems using an iterative channel estimator is analysed. In a conventional iterative channel estimator, after initialisation with the training phase, the channel estimator switches to the data phase. However, such a conventional iterative channel estimator does not always improve the performance of the receiver. In order to guarantee the performance improvement, a condition on when the output of the decoder should be used by the estimator is determined. Such a condition is related to the reliability of the soft information utilised by the channel estimator. The key in establishing this relationship is to use the mutual information (MI) that the observation vector has about the channel gains given the output of the decoder at each iteration. In this switch-augmented conventional iterative channel estimator, referred to as SAICE, the condition is theoretically found and indicates the needed reliability of the soft information for the channel estimator at the switching time. The switch-augmented scheme guarantees performance improvement of the iterative receiver with each iteration, however, it might need many iterations to converge for moderate to low signal-to-noise ratios (SNRs). A less computationally intensive approach is to use both the training and data segments of the observation. This approach produces a combined iterative channel estimator (CICE) for BICM-MIMO systems. The performance behaviour of the BICM-MIMO system is illustrated through the extrinsic information transfer (EXIT) chart with imperfect channel state information (CSI). Analytical results are verified with computer simulations.

Optimal training design and channel estimation for spatially correlated multi-user multi-input multi-output with orthogonal frequency-division multiplexing (MIMO-OFDM) systems is still an open research topic of great interest. This study first applies tractable semi-definite programming (SDP) to obtain the optimal training signal for the general case of spatial channel correlations for multi-user MIMO-OFDM. In order to reduce the computational complexity of the SDP-based solution, an approximate solution in closed-form is then presented. For a special case of transmit correlations, an optimal solution in closed-form expression is also derived. Analytical and simulation results demonstrate the excellent performance of the proposed designs and their performance advantage over the existing equi-powered training designs.

This paper develops a detection scheme based on the implicit pilot-symbol-assisted architecture of M-ary frequency-shift-keying (FSK) modulation in amplify-and-forward (AF) multiple-relay networks. It is shown that, at the expense of the low spectral efficiency inherent in FSK modulation, every transmitted symbol from the source to the destination can be used as a pilot symbol. In the proposed detection scheme, the destination combines the signals from the source and the relays to perform detection by using the estimated channels obtained from the implicit pilot symbols. Using the Gaussian approximation for the effective noise at the destination, an upper bound of the approximated bit-error-rate (BER) is provided. Simulation results reveal that the proposed scheme can significantly improve the BER performance when compared to previously proposed schemes in a temporally-correlated fading environment. The simulation results also verify the obtained upper bound on the approximated BER.

Power allocations in an interference-limited wireless network for global maximization of the weighted sum throughput or global optimization of the minimum weighted rate among network links are not only important but also very hard optimization problems due to their nonconvexity nature. Recently developed methods are either unable to locate the global optimal solutions or prohibitively complex for practical applications. This paper exploits the d.c. (difference of two convex functions/sets) structure of either the objective function or constraints of these global optimization problems to develop efficient iterative algorithms with very low complexity. Numerical results demonstrate that the developed algorithms are able to locate the global optimal solutions by only a few iterations and they are superior to the previously-proposed methods in both performance and computation complexity.

Optimization problems of beamforming in multi-user amplify-and-forward (AF) wireless relay networks are indefinite (nonconvex) quadratic programs, which require effective computational solutions. Solutions to these problems have often been obtained by relaxing the original problems to semi-definite programs (SDPs) of convex optimization. Most existing works have claimed that these relaxed SDPs actually provide the optimal beamforming solutions. This paper, however, shows that this is not the case in many practical scenarios where SDPs fail to provide even a feasible beamforming solution. To fill this gap, we develop in this paper a nonsmooth optimization algorithm, which provides the optimal solution at low computational complexity.

In order to improve bandwidth efficiency and bit error rate (BER) performance, a new training scheme is proposed for bit-interleaved coded modulation in multiple-input multiple-output (BICM-MIMO) systems. Typically, in a block fading channel, the training overhead used for obtaining channel knowledge is proportional to a power of two of the number of transmit antennas. However, this overhead can be reduced by embedding pilot symbols within data symbols before precoding. The values and positions of pilot symbols are theoretically found by minimizing the Cramer-Rao bound (CRB) on channel estimation error. Computer simulations are presented to demonstrate the advantage of the proposed scheme over other training methods, in terms of both the mean square error (MSE) of the channel estimation and the system's BER.

Power allocations in an interference-limited wireless network for global maximization of the weighted sum throughput or global maximization of the minimum rate among network links are not only important but also very hard optimization problems due to their nonconvexity nature. Recently developed methods are either unable to locate the global optimal solutions or prohibitively complex for practical applications. This paper exploits the d.c. (difference of two convex functions/sets) structure of either the objective function or constraint of the these global optimization problems to develop efficient iterative algorithms with very low complexity. Numerical results demonstrate that the developed algorithms are able to locate the global optimal solutions by only a few iterations and they are superior to the previously-proposed methods in both performance and computation complexity.

This paper develops a detection scheme based on implicit pilot-symbol-assisted architecture for non-coherent amplify-and-forward (AF) relay networks. The networks use M-ary frequency-shift-keying (FSK) modulation and multiple relays to assist communication from a source to a destination. Built on the fact that every transmitted symbol from the source to the destination can be considered as a pilot symbol, the destination combines the signals from the source and the relays to perform detection by using the estimated channels obtained from the implicit pilot symbols. A tight upper bound on the bit-error-rate (BER) of the developed scheme is obtained and used to show that the proposed scheme achieves a full diversity order. Moreover, simulation results reveal that the proposed scheme can significantly improve the BER performance when compared to previously proposed schemes in a temporally-correlated fading environment.

This paper discusses dynamic state estimation for nonlinear measurement model through distributed multisensor network under power constraints. For this scenario, we propose an optimized power allocation strategy based on semidefinite programming, that achieves minimum mean-squared error for the estimate subject to constraints on total transmit power. System nonlinearity is handled effectively with the help of distributed unscented Kalman filtering and linear fractional transformation. Furthermore, advantage of using multiple sensors over a single independent sensor is established through simulation results for tracking a maneuvering target.

This paper deals with optimized training sequences to estimate multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) channel states in the presence of spatial fading correlations. The optimization criterion is the entropy minimization of the error between the high multi-dimensional and correlated channel state and its estimator. The globally optimized training sequences are exactly solved by a semi-definite programming (SDP) of tractable computational complexity O((Mt(Mt+ 1)/2)2.5), where Mtis the transmit antenna number. With new tight two-sided bounds for the objective function, the optimal value of the generic SDP can be approximately solved by the standard water-filling algorithm. Intensive simulation results are provided to illustrate the performance of our methods.

The optimum multiuser detection (OMD) is a discrete (binary) optimization. The previously developed approaches often relax it by a semi-definite program (SDP) and then employ randomization for searching the optimal solution around the solution of this relaxed SDP. In this paper, we show the limited capacity of this SDP program, which at the end cannot give a better solution than the simple linear minimum mean square error detector (LMMSE). Our departure point is to express the problem as quadratic minimization over quadratic equality constraint (QMQE) or concave quadratic minimization over a box of continuous optimization (CQOB). The QMQE allows us to develop a nonsmooth optimization algorithm to locate the global optimal solution of OMD, while CQOB facilities effective confirmation of the solutions found by QMQE. Our intensive simulation clearly shows that the algorithm outperforms all previously developed algorithms while the computational burden is essentially reduced.

Optimal training design and channel estimation for spatially correlated multi-user multi-input multi-output with orthogonal frequency-division multiplexing (MIMO-OFDM) systems is still an open research topic of great interest. This paper applies tractable semi-definite programming to obtain the optimal training signal for the general case of spatial channel correlations for multi-user MIMO-OFDM. The optimal solution in closed-form expression is also derived for a special case of transmit correlations. Analytical and simulation results demonstrate the excellent performance of the proposed designs and their performance advantage over the equi-powered training designs.

This article studies optimal power allocation schemes in a multi-relay cooperating network employing amplify-and-forward (AF) protocol with multiple source–destination pairs. It is assumed that full channel state information is available at the relays. As such, distributed beamforming is employed in forwarding signals to the destinations. In this context, the authors extend recent works on distributed beamforming for a single source–destination pair to the scenario where multiple source–destination pairs are competing for the power resource at the relays. Under orthogonal transmissions of each source–destination pair, considered are the two following power allocation problems: (i) minimise the sum relay power with guaranteed quality of service (QoS) in terms of signal-to-noise ratio (SNR) at the destinations, and (ii) jointly maximise the SNR margin at the destinations subject to individual power constraints at the relays. Although these optimisation problems can be formulated as second-order conic programs (SOCP), the main contribution of this work are proposals of simple and fast converging numerical algorithms, based on the fixed point iteration framework, to efficiently solve these two problems.

An incremental relaying protocol based on the adaptive decode-and-forward relaying scheme is presented for a cooperative wireless network with binary frequency-shift keying modulation. To reduce error propagation and satisfy bit-error-rate (BER) requirement, the proposed protocol employs two thresholds. One threshold is used to select reliable relays: if a relay is requested to re-trnsmit, it will do so if its decision variable is larger than the threshold; otherwise, it remains silent. The other threshold is used at the destination as follows: the destination sends a request to re-transmit if the decision variable corresponding to a received signal is smaller than the threshold, otherwise, the destination sends a request to stop re-transmissions. The destination combines the signals from the requested relays and from the source to make the final decision. Very-tight closed-form upper bounds for both the average BER and throughput are derived for the proposed protocol. Based on the obtained BER and throughput expressions, the problem of choosing optimal thresholds to maximise the throughput while the BER meets a given constraint is investigated. Simulation results show that our proposed protocol leads to a considerable improvement in the performence of cooperative diversity systems.

A relaying technique based on single relay selection is studied for multiple-relay networks using hierarchical modulation for unequal error protection. A single relay selection scheme achieves a higher bandwidth efficiency while maintaining the same diversity order as when all the relays are selected in a multiple-relay network. Specifically, a cooperative network with one source, K relays, and one destination is considered in which two different protection information classes are modulated by a hierarchical 2/4-amplitude shift keying (ASK) constellation at the source. After selecting a relay to cooperate with the source, based on the instantaneous received SNR, the selected relay decides to retransmit both classes by using a hierarchical 2/4-ASK constellation, or the more protection class by using a 2-ASK constellation, or remains silent. The approximated bit error rate (BER) of each information class is derived. Optimal thresholds are chosen to minimize the BER of one class while satisfying the BER constraint of the other. Analytical and simulation results show that the optimal thresholds can improve the error performance significantly.

Abstract-Given the ever growing demand for radio spectrum,cognitive radio has recently emerged as an attractive wireless technology. Since orthogonal frequency division multiplexing (OFDM) is one of the major wideband transmission techniques, detection of OFDM signals in low signal-to-noise-ratio (SNR)scenario is an important research problem. In this paper, it is shown that the cyclic prefix correlation coefficient (CPCC) algorithm, which has been introduced as a simple and computationally efficient spectrum sensing test for OFDM signals, is a special case of the constrained generalized likelihood ratio test(GLRT) in the absence of multipath. As such, the performance of this algorithm degrades in a multipath scenario where OFDM is usually implemented. Moreover, by considering the multipath correlation in the GLRT algorithm and employing the inherent structure of OFDM signals, a simple and low complexity algorithm, called multipath-based constrained-GLRT (MP-based CGLRT)algorithm is obtained. The MP-based C-GLRT algorithm is shown to outperform the CPCC-based algorithm in a rich multipath environment. Further performance improvement can be achieved by simply combining both the CPCC-based and MPbased C-GLRT algorithms.

This paper considers a cooperative network in which binary frequency-shift-keying (BFSK) modulation is employed to facilitate noncoherent communications between a source and a destination with the help of K relays. Proposed is an adaptive cooperative scheme that employs two thresholds as follows. One threshold is used to select retransmitting relays: a relay retransmits to the destination if its decision variable is larger than the threshold, otherwise it remains silent. The other threshold is used at the destination for detection: the destination marks a relay as a retransmitting relay if the decision variable corresponding to the relay is larger than the threshold, otherwise, the destination marks it as a silent relay. Then the destination combines the signals from the retransmitting relays and from the source to make the final decision. The average end-to-end (e2e) bit-error-rate (BER) is derived in a closed-form expression for single-relay and two-relay networks. The problems of selecting optimal thresholds or jointly optimal thresholds and power allocation to minimize the average BER are investigated. Simulation results are provided to validate our analysis. Compared to the previously proposed piecewise-linear (PL) detection scheme, our proposed scheme yields a superior performance under a wide range of channel conditions when optimal thresholds or jointly optimal thresholds and power allocation are employed.

Wireless amplify-and-forward relay networks in which the source communicates with the relays and destination in the first phase and the relays simultaneously forward signals to the destination in the second phase over uncorrelated Rayleigh fading channels are considered. We examine the scenario in which each relay only knows the perfect information of its source-relay channel while the destination knows the exact information of the relay-destination channels and the statistics of the source-relay channels. Based on a combiner developed at the destination, we propose an efficient beamforming scheme at the relays and develop its quantized version using Lloyd's algorithm to work with a limited-rate feedback channel. Simulation results show that the non-orthogonal relaying with the proposed beamforming scheme outperforms the orthogonal relaying with power allocation in terms of the ergodic capacity. In terms of the signal-to-noise ratio, the non-orthogonal scheme also becomes superior to the orthogonal scheme when the number of quantization regions increases.

This study improves the fading channel estimation in bit-interleaved coded modulation systems with iterative decoding (BICM-ID) and signal space diversity (SSD) by embedding a training sequence. Existing training schemes work well at high signal-to-noise ratio (SNR) or slowly time-varying channels whereas the applications of BICM-ID are beneficial at low SNR and fast time-varying fading channels. Motivated by the power/bandwidth efficiency of the SSD technique and the fact that superimposed training outperforms pilot symbol-assisted modulation (PSAM) training over relatively fast time-varying channels, a new superimposed training sequence is explored. The proposed training sequence inserts pilot bits into the coded bits prior constellation mapping and signal rotation. This becomes a superimposed training sequence in the rotated symbols and helps the estimator to track fast variation of the channel gains. A soft iterative channel estimator is developed to work with the superimposed training sequence. The performance of the proposed scheme, namely SSD-pilot, is shown to be superior to PSAM scheme. To gauge the performance improvement achieved with the proposed channel estimation, an analytical bound on the asymptotic bit error probability for BICM-ID using SSD over correlated fading channels is provided. The Cramer–Rao bound on the mean-square error of the channel estimator is also derived to evaluate the performance of the iterative channel estimator.

A relaying technique based on single-relay selection is studied for multiple-relay networks when hierarchical modulation is employed for unequal error protection. A single-relay selection scheme achieves a higher bandwidth efficiency while maintaining the same diversity order as when all the relays are selected in a multiple-relay network. Specifically, a cooperative network with one source, K relays, and one destination is considered in which two different protection information classes are modulated by a hierarchical 2/4-amplitude shift keying (ASK) constellation at the source. After selecting a relay to cooperate with the source, based on the instantaneous received signal-to-noise ratio, the selected relay decides to retransmit both classes by using a hierarchical 2/4-ASK constellation, or the more protection class by using a 2-ASK constellation, or remains silent. The approximated bit error rate (BER) of each information class is derived. Optimal thresholds are chosen to minimise the BER of one class while the BER of the other class satisfies a requirement. Numerical and simulation results are provided to validate the analysis. The results also show that the optimal thresholds can improve the error performance significantly.

Decorrelate-and-forward relaying scheme for wireless synchronous code division multiple access (CDMA) networks where multiple sources communicate with a destination supported by multiple relays in flat Rayleigh fading channels is considered. By exploiting equicorrelated spreading sequences, a simple near–far resistant decorrelator together with a beamforming scheme at each relay and the maximal ratio combiner (MRC) at the destination are developed in order to achieve the full cooperative diversity for every source. Different from the case with a single source, the beamforming design in multiple-source networks needs to take into account the amount of transmit power each relay spends to forward the signals from the sources. As such, the authors also propose a novel power allocation scheme to improve the fairness among the sources in terms of the instantaneous signal-to-noise ratio. Simulation results demonstrate the effectiveness of the proposed solution.

Turbo (iterative) decoding can be implemented with a large family of soft-input soft-output (SISO) algorithms, including suboptimal but practical algorithms such as the soft-output Viterbi algorithm (SOVA) and max-log-MAP algorithm. The performance with these practical algorithms can be improved with simple scaling factor methods. However, their theoretical analysis was mainly based on the relaxed assumption proposed by Papke et al. that the extrinsic information is Gaussian distributed. This study proposes a novel scaling factor approach for reducing both the overestimation of reliability values and the correlation between the intrinsic and extrinsic information. Explicit formulae for computing the scaling factors are derived based on mathematical statistics. A key difference compared to the scaling factor method of Papke et al. is that the proposed scaling factors can be computed off-line. The numerical results show that when implemented in the decoding algorithm of block component codes, the proposed scaling factor approach improves the performance of turbo decoding over additive white Gaussian noise and Rayleigh fading channels. It is superior than the method by Papke et al. in both performance and complexity.

This paper develops an amplify-and-forward relaying scheme for multiuser wireless cooperative networks under frequency-selective block-fading. Single-carrier frequency division multiple-access with frequency-domain equalization technique is employed at both the relay and destination to combat the inter-block and inter-symbol interference caused by multipath propagation. With the assumption that the full channel state information (CSI) is available at the destination, the relay only knows the uplink channels while no CSI is available at the sources, two power allocation schemes are developed for the relay: (i) to minimize the total transmit power at the relay while maintaining the signal-to-interference-plus-noise ratio (SINR) for each user at the destination above a certain level, and (ii) to maximize the worst SINR among all the users subject to a constraint on total relay power. In the first problem, it is shown that SINR adaptation is needed not only to guarantee a feasible solution but also to significantly reduce the transmit power at the relay for certain channel conditions. In the second problem, a flexible multi-level water-filling scheme is developed, which can be easily modified to adapt to the different channel conditions as well as different quality-of-service provision strategies.

This paper proposes a capacity-approaching, yet simple scheme for multi-input multiple-output (MIMO) channels. The proposed scheme is based on a concatenation of a mixture of short memory-length convolutional codes or repetition codes and a short, and simple rate-1 linear block code, followed by either 1-dimensional (1-D) anti-Gray or Gray mapping of quadrature phase-shift keying (QPSK) modulation. By interpreting the rate-1 code and the 1-D mapping as a multi-D mapping performed over multiple transmit antennas, the error performance is analyzed in two regions. In the error-floor region, a tight union bound and the corresponding design criterion on the asymptotic performance are derived. The bound provides a useful tool to predict the error performance at relatively low bit error rate (BER) values. Based on the obtained design criterion, an optimal rate-1 code for each 1-D mapping is then constructed to achieve the best asymptotic performance. In the turbo pinch-off region, by using extrinsic information transfer (EXIT) charts, the most suitable mixed codes are selected for both symmetric and asymmetric antenna configurations. It is demonstrated that the simple concatenation scheme can achieve a near-capacity performance over the MIMO channels. Furthermore, its error performance is shown to be comparable to that obtained by using well-designed irregular LDPC and RA codes, and therefore, the proposed scheme significantly outperforms a scheme employing a parallel concatenated turbo code. Simulation results in various cases are provided to verify the analysis.

Only one asymptotic training design for a special case of channel correlation was proposed in the literature for spatially correlated multiple-input multiple-output with orthogonal frequency-division multiplexing (MIMO-OFDM) systems. To fill this gap, this letter applies tractable semi-definite programming (SDP) to obtain the optimal superimposed training signals for the general case of channel correlation. For a more efficient computation, two approximate designs are also proposed. Simulation results demonstrate the efficiency of our approach and its advantage over the asymptotic design.

In this paper, the training sequence design for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems under the minimum mean square error (MMSE) criterion is addressed. The optimal training sequence for channel estimation in spatially correlated MIMO-OFDM systems was not known for an arbitrary signal-to-noise ratio (SNR). Only one class of training sequences was proposed in the literature in which the power allocation is given only for the extreme conditions of low and high SNRs. The current paper presents a necessary and sufficient condition for the optimal training sequence, and reformulates the training design problem as a convex optimization problem whose optimal solution is efficiently solved. In addition, tight upper bounds for MMSE and resulting low complexity iterative algorithms with the closed-form expression in iterations to find the optimum training sequence are derived. Simulation results confirm the superiority of the proposed design over the existing one in terms of both MSE estimation and BER performance. The proposed methods are also shown to be robust with respect to the spatial correlation mismatch at the transmitter.

This paper proposes a capacity-approaching, yet simple scheme over a multiple-input single-output (MISO) wireless fading channel, which is very common in the downlink of a cellular system. The proposed scheme is based on a concatenation of a mixture of short memory-length convolutional codes or repe

This paper studies optimal distributed beamforming designs to jointly maximize the signal-to-noise (SNR) margin in a multiuser multi-relay network. Considered are optimization problems with two different types of power constraints: sum relay power constraint and per-relay power constraints. Although these two problems can be readily solved by the bisection method via a sequence of second-order conic feasibility programs, we propose simple and fast converging iterative algorithms to directly solve the two optimization problems under consideration.

This paper studies a relaying technique in cooperative networks using hierarchical modulation. Hierarchical modulation is useful in applications that require different protection classes of the information. In particular, a cooperative network with one source, one relay, and one destination is considered. Two different protection classes are modulated by a hierarchical 2/4-amplitude shift keying (ASK) constellation at the source. Based on the instantaneous received signal-to-noise ratio (SNR) at the relay, the relay decides to retransmit both classes by using a hierarchical 2/4-ASK constellation, or the more protection class by using a 2-ASK constellation, or remains silent. Optimal thresholds are chosen to minimize the bit-error-rate (BER) of the less protection class while the BER of the more protection class meets a given requirement. Numerical and simulation results are provided to verify the analysis. The results show that the optimal thresholds improve the performance significantly.

This paper considers optimal distributed beamforming designs in a multi-relay network with multiple sources and multiple destinations. It is assumed that all source-destination pairs operate in orthogonal channels to avoid inter-user interference at the destinations. The distributed beamforming designs are carried out to minimize the sum relay power with guaranteed quality of service (QoS) in terms of signal-to-noise-ratio (SNR) at the destinations. Considered are optimization problems with and without per-relay power constraints. Although the two optimization problems can be readily transformed into convex second-order conic programs (SOCPs), the paper proposes simple and fast iterative algorithms to efficiently solve them.

This paper develops an amplify-and-forward relaying technique for multiuser wireless cooperative networks under frequency-selective block-fading. Single-carrier frequency division multiple-access with frequency-domain equalization technique is employed at both the relay and destination to combat the inter-block and inter-symbol interference caused by multipath propagation. With the assumption that the full channel state information (CSI) is available at the destination, the relay only knows the uplink channels while no CSI is available at the sources, two power allocation schemes are obtained: (i) to minimize the total transmit power at the relay while maintaining the signal-to-interference-plus-noise ratio (SINR) for each user at the destination above a certain level, and (ii) to maximize the worst SINR among all the users subject to a constraint on total relay transmit power. Analysis and simulation results are provided to illustrate the effectiveness of the proposed schemes.

This paper proposes a simple yet capacity-approaching concatenation of a mixture of short memory length convolutional codes and simple rate-1 block code followed by either complex 1-dimensional (1-D) anti-Gray or Gray mapping over multiple antenna channels with quadrature phase-shift keying (QPSK). By interpreting rate-1 code together with 1-D mapping as a multi-D mapping employed over multiple transmit antennas, the error performance is analyzed in two regions, the error-floor and turbo pinch-off regions. In the former one, a tight union bound and design criterion on the asymptotic performance are first derived, which provide an useful tool to predict the error performance. Based on the design criterion, an optimal rate-1 code for each 1-D mapping is then constructed to achieve the best asymptotic performance. In the turbo pinch-off area, by using extrinsic information transfer (EXIT) chart, the most suitable mixed codes are selected for both symmetric and asymmetric antenna setups. It is demonstrated that the simple concatenation scheme can achieve near-capacity. Furthermore, its error performance is comparable to that obtained by using well-designed irregular low-density parity-check (LDPC) and repeat accumulate (RA) codes, and thereby, outperforms a scheme employing a parallel concatenated turbo code.

This paper investigates the diversity performance of wireless relay networks with multiple parallel relays communicating with the destination over orthogonal channels. The networks under consideration employ two signal-to-noise ratio (SNR) thresholds and multiple hard-decision detections (HDD) at the destination. One SNR threshold is used to select transmitting relays in the second phase: a relay retransmits to the destination if its received SNR is larger than the threshold, otherwise, it remains silent. The other threshold is used at the destination for detection: the destination makes a hard decision on the received signal from a relay if its SNR is higher than the threshold, otherwise, the destination makes an erasure decision. Then the destination simply combines all the hard-decision results and makes the final binary decision based on majority voting. Focusing on the decode-and-forward (DF) relaying protocol, the paper derives the end-to-end bit error and outage probabilities, and presents the diversity analysis of the proposed method. It is shown that the full diversity order can be achieved by setting appropriate thresholds even when the destination does not know the exact or average SNRs of the source-relay links. The diversity analysis is further extended to multi-hop cooperation and/or with the presence of a direct link where multiple thresholds are needed.

The optimal training sequence for channel estimation in spatially correlated multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems has not been found for an arbitrary signal-to-noise ratio (SNR). Only one class of training sequences was proposed in the literature in which the power allocation is given only for the extreme conditions of low and high SNR. Provided in this paper are (i) a necessary and sufficient condition for the optimal training sequence together with a convex programming to find the solution, and (ii) efficient procedures to find the optimal training sequence. Simulation results confirms the superiority of the proposed design over the existing one.

This paper proposes a novel power allocation among the source and relays of wireless relay networks to minimize the mean-square error of the channel estimation when distributed space-time coding (DSTC) is applied. Both the maximum likelihood (ML) and minimum mean-square error (MMSE) estimations are considered. The impact of imperfect channel estimation on the error performance of DSTC is also analyzed, where it is proved that the mismatched decoding of DSTC is able to achieve the same diversity order as the coherent decoding of DSTC. Furthermore, when the optimal power allocation obtained in the training phase is applied to the transmission phase, the mismatched decoding is able to achieve the maximum diversity order as the coherent decoding.

This paper considers a communication network with multiple pairs of source and destination, assisted by multiple relays. It is assumed that perfect channel state information (CSI) is available at the relays. In a two-stage AF protocol, all the sources broadcast their signals to all the relays in the first stage. The received signal at each relay is processed by a beamforming weight and then re-broadcasted to all the destinations at the same time with other relays in the second stage. The focus is to find the optimal beamforming weights to meet a given set of target signal-to-interference-and-noise ratio (SINR) at the destinations, while minimizing the total transmitted power at the relays. We show that this problem can be formulated as a nonconvex quadratically constrained quadratic program (QCQP). Through relaxations, the problem can be solved efficiently by convex programming.

This paper derives an optimal power allocation (PA) to maximize the effective average signal-to-noise ratio (SNR) of distributed space-time coding (DSTC) in wireless relay networks, where the locations of the relays can be anywhere between the source and destination. It is first shown that in maximizing the average SNR, not all the relays might be active, and hence the code performance might be compromised. The amount of fading is then introduced for the relay networks and used as a constraint to derive a novel PA scheme. This new PA is shown to obtain the maximum diversity order of both noncoherent and coherent DSTC systems at high SNR.

Amplify-and-forward (AF) wireless relay networks in which the source communicates with the relays and destination in the first phase and the relays forward signals to the destination in the second phase over orthogonal and uncorrelated Rayleigh fading channels are considered. Convex programming is used to obtain optimal and approximately optimal power allocation (OPA) schemes to maximize the average signal-to-noise ratios(SNRs) at the output of the receiver filters under two different assumptions of partial channel state information (CSI). Analysis and simulation results demonstrate the superiority of the proposed power allocation schemes over the equal-power allocation scheme. Performance comparison to the extreme cases of (i) direct transmission between the source and destination and (ii) having full CSI is made to illustrate the gain and loss, respectively, of the proposed schemes. The impact of power allocation between the source and the relays is also investigated by computer simulation.

Signal space diversity (SSD) has been recently applied to improve the error performance of bit-interleaved coded modulation with iterative decoding (BICM-ID) systems over wireless fading channels. Previous works, however, only consider perfect channel estimation at the iterative receiver of the system. Performing channel estimation is an important task in a practical BICM-ID system and is the focus of this paper. To exploit the technique of SSD for improving channel estimation, a new method of using training sequences is presented. The proposed method inserts pilot bits between the coded bits, i.e., before constellation mapping and signal rotation. It is therefore can be considered as superimposed training. Developed is a soft iterative channel estimator to work with the new arrangement of the training signal. The performance of the system with the proposed training and channel estimation is shown to be superior that with pilot symbol assisted modulation (PSAM). To benchmark the achievable error performance of the system with channel estimation, an analytical bound of the asymptotic bit error probability for BICM-ID using SSD over correlated fading channels and perfect channel state information (CSI) is also derived.

This paper considers power allocation and distributed beam-forming optimization in a multiuser multi-relay network. Under the constraint on the total relay power, we investigate two resource allocation problems, namely the sum-rate maximization and minimum-rate maximization. Although both problems are not readily expressed in a convex form, a change in variables transforms the problems into standard optimization problems, which then can be solved efficiently. In addition, via dual decomposition, two algorithms are proposed to solve the two problems in a distributed fashion.

Decorrelate-and-forward (DCF) relaying for multiuser wireless CDMA networks with equicorrelated spreading sequences is developed and analyzed. By employing a simple near-far resistant decorrelator together with a precoding technique at each relay and the maximal-ratio-combiner (MRC) at the destination, it is shown that the full cooperative diversity order can be obtained for every user. Furthermore, the fairness among the users in terms of the instantaneous signal-to-noise ratio is significantly improved by exercising a power allocation scheme obtained with geometric programming (GP).

For the decode-and-forward (DF) strategy, smart relaying has been shown to achieve the maximal spatial diversity order over Rayleigh fading channels even when erroneous detection is committed at the relays. Due to the importance of Nakagami and Hoyt statistical models in describing channel fading in land, mobile and satellite communications, this paper performs diversity analysis of the smart relaying systems under Nakagami and Hoyt generalized fading channels. Performance analysis proves that, at high signal-to-noise ratio (SNR), the maximal diversity order of the smart relaying system under the Nakagami channel is mSD+ min{mSR, mRD}, where mSR, mRDand mSDare the fading figures of the source-relay (S-R), relay-destination (R-D) and source-destination (S-D) links. Under the Hoyt fading channel, the diversity order is 2.

In cognitive radio networks with the coexistence of primary and secondary users, the problem of how to optimally allocate available resources (e.g., bandwidth and power) to multicast groups of secondary users that use orthogonal frequency division multiplexing (OFDM) is important. Taking the maximization of the weighted sum rate of such groups as the design objective, we propose a practically optimal subcarrier and power allocation scheme under constraints on the tolerable interference thresholds at individual primary user's frequency bands. Specifically, the optimization problem is solved via the dual method, where subcarriers are assigned in a per-tone basis and power is distributed in a water-filling fashion. As the number of subcarriers becomes large, the dual-domain solution becomes the global optimum of the primal problem with the duality gap vanishing to zero. The proposed design is valid for both unicast and multicast transmissions, and its computational complexity is only linear in the number of subcarriers. The effects of adjacent subcarrier nulling technique, which is to reduce mutual interference between primary and secondary frequency bands, on the proposed scheme are also examined. The superiority of the dual approach is confirmed by numerical results.

Signal transmission with the help of relay(s) in wireless networks can achieve spatial diversity without the need of having multiple attennas at the source and/or destination. Among various signal processing techniques proposed for the relays, the adaptive decode-and-forward (DF) relaying strategy, recently proposed by Wang et al. and generally referred to as smart relaying, has been shown to achieve the maximal spatial diversity even when imperfect detection is committed at the relays. The work by Wang et al., however, only considers Rayleigh fading channels. This paper extends the diversity analysis of the smart relaying technique to the important Nakagami and Hoyt generalised fading channels. Performance analysis proves that, at high signal-to-noise ratio, the maximal diversity order achieved by the smart relaying system under the Nakagami channel is mSD+min{mSR, mRD}, where mSR, mRD and mSD are the fading figures of the source–relay (S–R), relay–destination (R–D) and source–destination (S–D) links. Under the Hoyt fading channel, the diversity order is 2. The obtained results on the diversity order are shown to be insensitive to the quality of the R–D feedback channel.

A design method is introduced for linear dispersion (LD) space-time codes in wireless relay networks under Rayleigh fading channels. The codes are designed with a stochastic quasi-gradient algorithm to minimize the upper bound of the average pairwise error probability. Simulation results show that the optimized codes achieve a coding gain of about 2 dB over codes that are randomly generated based on the isotropic distribution.

This letter generalizes the application of signal space diversity (SSD) over multiplicative fading channels, where fading is represented by the product ofKstatistically independent Nakagami-mrandom variables. The pairwise error probability (PEP) for the systems is first obtained in a closed-form using generalized hypergeometric functions. Based on the obtained PEP expression, it is shown that the error performance over multiplicative fading channels can be significantly improved by using high diversity constellations. Furthermore, by employing SSD with a sufficiently large dimension, it is observed that the adverse effects of multiplicative fading can be practically eliminated without any power nor bandwidth expansion. Simulation results for both uncoded and coded systems are provided to show the agreement with the analysis.

This paper generalizes the application bit-interleaved coded modulation with iterative decoding (BICM-ID) using signal space diversity (SSD) overkeyholeNakagami-mfading channels. The tight union bound on the asymptotic error performance is first analytically derived. The near-optimal rotation matrix with respect to both the asymptotic performance and the convergence behavior is then determined. In particular, it is demonstrated that the suitable rotation matrix is the one that has 1) all entries equal in magnitude, 2) a high diversity order, and 3) a large minimum product of the ratios between squared distances to the powermand log-squared distances to the powermof the rotated constellation scaled by factors of signal-to-noise ratio (SNR) and the parameterm. Various analytical and simulation results show that by employing SSD with a sufficiently large dimension, the error performance can closely approach that over an additive white Gaussian noise (AWGN) channel, even in the worst case of keyhole fading.

In this letter, the use of adaptive source transmission with amplify-and-forward relaying is proposed. Three different adaptive techniques are considered: (i) optimal simultaneous power and rate adaptation; (ii) constant power with optimal rate adaptation; (iii) channel inversion with fixed rate. The capacity upper bounds of these adaptive protocols are derived for the amplify-and-forward cooperative system over both independent and identically distributed (i.i.d.) Rayleigh fading and non-i.i.d. Rayleigh fading environments. The capacity analysis is based on an upper bound on the effective received signal-to-noise ratio (SNR). The tightness of the upper bound is validated by the use of a lower bound and by Monte Carlo simulation. It is shown that at high SNR the optimal simultaneous power and rate adaptation and the optimal rate adaptation with constant power provide roughly the same capacity. Channel inversion is shown to suffer from a deterioration in capacity relative to the other adaptive techniques.

Optimal training design and channel estimation for spatially correlated multiple-input multiple-output systems with orthogonal frequency-division multiplexing (MIMO-OFDM) is still an open research topic of great interest. Only one asymptotic design for a special case of channel correlations was proposed in the literature. To fill this gap, this paper applies tractable semi- definite programming (SDP) to obtain the optimal superimposed training signals for the general case of channel correlations. To improve computational efficiency, an approximate design in closed-form is also proposed. This approximate design is formed by minimizing an upper bound of the channel estimation mean-square error. Since the superimposed training approach is taken, the derivation of an optimal non-redundancy precoder for data detection enhancement is also given. Analytical and simulation results demonstrate the excellent performance of the proposed designs and their superior performance compared to the previously proposed design.

For a decode-and-forward (DF) relaying system with maximal-ratio combining (MRC) at the destination, spatial diversity is lost except when the source-relay link is reliable. This paper considers and analyzes a smart relaying scheme, in which the relay scales its transmitted power adaptively to the channel conditions without exceeding the total power used in the conventional relaying system. Performance analysis proves that a diversity order of two is always achieved with binary- phase-shift-keying (BPSK) and quadrature-phase-shift-keying (QPSK) constellations. The order-2 diversity is also observed from numerical results for rectangular quadrature amplitude modulation (QAM).

The use of constant-power, rate-adaptive M-QAM transmission with an amplify-and-forward cooperative system is proposed. The upper bound expressions are derived for the outage probability, achievable spectral efficiency, and error rate performance for the amplify-and-forward cooperative system over both independent and identically distributed (i.i.d.) and non-i.i.d. Rayleigh fading environments. The analysis is based on an accurate upper bound on the total effective signal-to- noise ratio SNR at the destination. Adaptive continuous rate M-QAM achieves a capacity that comes within a constant gap of the Shannon capacity of the channel, but adaptive discrete rate M-QAM suffers additional performance penalties.

The symbol error rate (SER) and the bit error rate (BER) of orthogonal space-time block codes (OSTBCs) with antenna selection over keyhole fading channels are examined. Considered are receive antenna selection, transmit antenna selection, and joint antenna selection at both the transmitter and the receiver. The exact SER of OSTBCs for M-PSK and square M-QAM constellations is obtained using the technique of moment generating function. By applying the Bonferroni-type bounds, tight lower and upper bounds for both the SER and BER are provided in closed-form expressions with finite-range single integrals. The bounds can be applied to arbitrary constellations and mappings. Numerical results show that the bounds can be used to provide practically the exact SER and BER over a wide range of the signal-to-noise ratio.

Space-time-frequency (STF) coding for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) over frequency-selective Rayleigh fading channels is considered. The maximum diversity order and coding gain of the system are derived when linear constellation preceding (LCP) is applied to OFDM symbols. It is also shown that with a proper subcarrier grouping of the OFDM symbols, the system implementation can be greatly simplified while maintaining the diversity order and coding gain. In particular, as long as the group size F is not less the number of effective resolvable channel taps L, the maximum diversity order can always be achieved. Moreover, if F ges L, and F is an Euler number or an integer power of 2, the maximum coding gain can be achieved. Otherwise, the achievable coding gain approximates 70% of the maximum one.

This paper applies the sigma mapping of M-QAM in linear diversity-embedded space-time block codes (LDE-STBC) to achieve different diversity levels and various coding gains for unequal error protection (UEP). By controlling the basis vectors of sigma mapping, the bit error rate (BER) performance of each bit in a layer can be made to satisfy its quality-of-service (QoS) requirement. Moreover, with the low decoding complexity offered by sigma mapping, highly-flexible codes can be designed.

It has been shown that relaying systems can offer spatial and multipath diversity in amplify-and-forward (AF) relay-assisted transmission over frequency-selective fading channels when trellis coded modulation (TCM) is applied as an outer code. However, the price for such advantages is the high decoding complexity. To overcome this disadvantage, the technique of subcarrier grouping is applied for orthogonal frequency division multiplexing (OFDM)-based relaying systems. If there exists a strong line-of-sight path in the relay-to-destination link, it is shown that the system can achieve both maximal spatial and multipath diversity gains. When all the underlying channels are frequency-selective, simulation results indicate that the full spatial and multipath diversity gains can also be realized.

Bit-interleaved coded modulation with iterative decoding (BICM-ID) using signal space diversity (SSD) is considered for cascaded Rayleigh fading channels. A tight bound on the asymptotic error probability is derived to determine the optimal rotation matrix for SSD design and to identify the key parameters that influence the system performance. It is shown that, for small modulation constellation, a cascaded Rayleigh fading causes a much more severe performance degradation than a conventional Rayleigh fading. However, BICM-ID employing SSD with a sufficiently large constellation can close the performance gap between the conventional and cascaded Rayleigh fading channels, and their performance can closely approach that over an AWGN channel. Illustrative simulation results for various scenarios are in a good agreement with analytical derivations.

The problems of designing signature sequences and power allocation policy for code-division multiple access (CDMA) are important and have been the subject of intensive research in recent years. Taking the maximization of the system information theoretic sum capacity as the design criterion, most of the previous works only consider the optimizations of signature sequences and power allocation separately. In contrast, this letter presents a jointly optimal design of signature sequences and power allocation for a CDMA system with fixed, but unequal channel gains and under the sum power constraint. The proposed design is of closed-form, and applicable for the general case of correlated signals and colored noise. Numerical results verify the superiority of the proposed design over the existing ones.

The problem of channel estimation for spatially correlated fading multiple-input multiple-output (MIMO) systems is considered. Based on the channel's second order statistic, the minimum mean-square error (MMSE) channel estimator that works with the superimposed training signal is first developed. The problem of designing the optimal superimposed signal is then addressed and solved with an iterative optimization algorithm. Results show that under the constraint of equal training power and bandwidth efficiency, our optimal design of the superimposed training signal leads to a significant reduction in channel estimation error when compared to the conventional design of time-multiplexing training, especially for slowly time-varying channels with a large coherence time. The issue of power allocation between the information-bearing and training signals for detection enhancement is also investigated. Simulation results demonstrate excellent bit-error-rate performance of orthogonal space-time block codes with our proposed channel estimation.

The symbol error rate (SER) and the bit error rate (BER) of orthogonal space-time block codes (OSTBCs) with antenna selection over keyhole fading channels are examined. Considered are receive antenna selection, transmit antenna selection, and joint antenna selection at both the transmitter and the receiver. The exact SERs of OSTBCs for M-PSK and square MQAM constellations are obtained using the technique of moment generating function (MGF). By applying the Bonferroni-type bounds, tight lower and upper bounds for both the SER and BER are provided in closed-form expressions with finite-range single integrals. The bounds can be applied to arbitrary constellations and mappings. Numerical results show that the bounds can be used to provide practically the exact SER and BER over a wide range of the signal-to-noise ratio.

The problems of designing signature sequences and power allocation policy for code-division multiple access (CDMA) are important and have been the subject of intensive research in recent years. Two different criteria adopted in such design problems are the user capacity and the information-theoretic capacity. Regarding the maximization of the information-theoretic capacity, most of the previous works only consider the optimizations of signature sequences and power allocation separately. In contrast, this paper presents a jointly optimal design of signature sequences and power allocation under the sum power constraint. The proposed design is of closed-form and applicable for the general case of correlated signals and colored noise. Numerical results verify the superiority of the proposed design over the existing ones.

Exploiting signal space diversity (SSD) to improve the error performance of communications systems over fading channels has been shown to be a very effective technique. The application of SSD in bit-interleaved coded modulation with iterative decoding (BICM-ID) is considered for cascaded Rayleigh fading channels, which are suitable for mobile-to-mobile communications. A tight bound on the asymptotic error performance is first derived. The bound is then used to find the optimal rotation matrix. It is shown that employing SSD in a sufficiently large constellation can close the performance gap between a conventional Rayleigh fading channel and a cascaded Rayleigh fading channel. In fact, similar to the case of conventional Rayleigh fading, it is demonstrated that the error performance of BICM-ID with SSD over a cascaded Rayleigh fading channel can also closely approach the performance of BICM-ID over an AWGN channel. Various analytical and simulation results are provided to confirm the analysis.

This paper generalizes the application of bit interleaved coded modulation with iterative decoding (BICM-ID) using signal space diversity (SSD) over keyhole Nakagami-m fading channels. The tight union bound on the asymptotic error performance is first analytically derived. The optimal rotation matrix with respect to both the asymptotic performance and the convergence behavior is then determined. In particular, it is demonstrated that the most suitable rotation matrix is the one that has i) all entries equal in magnitude, ii) high diversity order, and iii) large minimum product of the ratios between squared distances and log-squared-distances of the rotated constellation scaled by factors of SNR and the parameter m. Various analytical and simulation results show that by employing SSD with a sufficiently large dimension, the error performance can closely approach that over an AWGN channel, even in the worst case of keyhole fading.

Based on convex programming, this paper presents the optimal training signal design for orthogonal frequency-division multiplexing (OFDM) under colored noise. An effective method for OFDM symbol detection with the use of preceding is also described. Both analytical and simulation results show that the proposed design and method can effectively estimate the channel and reliably detect the OFDM symbols. By working in the frequency domain rather than the time domain, the computation complexity of the proposed estimation algorithm is significantly reduced.

Clipping and filtering (CF) is a simple but effective technique for peak-to-average ratio (PAR) reduction of orthogonal frequency division multiplexing (OFDM) signals. This paper determines the optimal clipping value for the CF method in order to maximize the power efficiency of the high power amplifier (HPA). A transmission spectral mask is placed on the output of the HPA as a design constraint in determining the optimal clipping value. The optimal clipping value is obtained for each specified bit error rate (BER) level. Results show that the optimal clipping value maximizes the efficiency of the HPA modelled as a travelling wave tube amplifier (TWTA), without causing a deterioration in BER performance.

Multi-dimensional mapping over groups of subcarriers, called subcarrier mapping, is proposed and investigated for bit-interleaved coded in OFDM with iterative decoding (BI-COFDM-ID) over correlated frequency-selective Rayleigh fading channels. A tight bound on the asymptotic error performance is first presented and used to establish the design criterion. It is then shown that one could choose an optimal subcarrier grouping scheme and an optimal multi-dimensional mapping independently to achieve the best overall error performance. Analytical and simulation results show that it is not necessary to implement linear constellation precoding (LCP) in the proposed system while still achieving the full diversity offered by frequency-selective fading channels, and at the same time providing significant coding gains compared to the previously studied BI-COFDM-ID. Such coding gains are obtained without any power nor bandwidth expansion and with the same receiver complexity.

This paper is concerned with the bit error probability (BEP) of coded unitary space-time modulation systems based on finite-length low density parity check (LDPC) codes. The union bound on the BEP is derived for any code rate, unitary space-time constellation and mapping. The tightness of the bound is verified with simulation results of the ordered statistic decoding (OSD). Numerical and simulation results show that the union bound is also close to the error performance of the sum-product decoding at the low bit error probability (BEP) levels when Gray mapping is employed. The derived bound is useful to benchmark the error performance of LDPC coded unitary space-time modulation systems.

The problem of joint source–channel and multiuser decoding for code division multiple access channels is considered. The block source–channel encoder is defined by a vector quantiser (VQ). The jointly optimum solution to such a problem has been considered before, but its extremely high complexity makes it impractical for systems with medium to large number of users and/or medium to large size of VQ codebook. Instead, the optimum linear decoder with a much lower complexity that minimises the mean-squared error is introduced. The optimum linear decoder is soft in the sense that it utilises all the soft information available at the receiver. Analytical and simulation results show that at low channel signal-to-noise ratio region, the proposed decoder's performance is almost the same as that of the jointly optimum decoder and significantly better than that of the tandem approaches that use separate multiuser detection and table-lookup decoding.

The application of Bonferroni-type bounds is investigated for orthogonal space-time block codes over a keyhole Nakagami-m fading channel, which includes a cascaded Rayleigh fading channel as a special case. In particular, upper and lower bounds on the symbol error rate and bit error rate are derived and shown to be very tight at any signal-to-noise ratio. The developed bounds are applicable for arbitrary signal constellations and mappings and can be accurately computed with single finite-range integrals.

This paper studies the bit error probability of coded unitary space-time modulation with iterative decoding where neither the transmitter nor the receiver knows the channel fading coefficients. The tight error bound with respect to the asymptotic performance is first analytically derived for any given unitary constellation and mapping rule. Design criteria regarding the choice of unitary constellation and mapping are then established. Furthermore, using the unitary constellation obtained from orthogonal design with quadrature phase-shift keying (QPSK or 4-PSK) and 8-PSK, two different mapping rules are proposed. The first mapping rule gives the most suitable mapping for systems that do not implement iterative processing, which is similar to a Gray mapping in coherent channels. The second mapping rule yields the best mapping for systems with iterative decoding. In particular, analytical and simulation results show that with the proposed mappings of the unitary constellations obtained from orthogonal designs, the asymptotic error performance of the iterative systems can closely approach a lower bound which is applicable to any unitary constellation and mapping

Employing multi-dimensional constellation and mapping to improve the error performance of the bit-interleaved coded modulation with iterative decoding (BICM-ID) has recently received a lot of attention, both in single-antenna and multiple-antenna systems. To date, except for the cases of BPSK and QPSK constellations, good multi-dimensional mappings have only been found by computer searching techniques. This paper introduces an explicit algorithm to construct a good multidimensional mapping of 8-PSK for improving the asymptotic performance of BICM-ID systems. By comparing the performance of the proposed mapping with an unachievable lower bound, it is conjectured that the proposed mapping is the global optimal mapping. The superiority of the proposed mapping over the best conventional (two-dimensional) mapping and the multidimensional mapping found previously by computer search is also thoroughly demonstrated

This paper presents a performance analysis of bit-interleaved coded-modulation with iterative decoding (BICM-ID) and complex N-dimensional signal space diversity in fading channels to investigate its performance limitation, the choice of the rotation matrix and the design of a low-complexity receiver. The tight error bound is first analytically derived. Based on the design criterion obtained from the error bound, the optimality of the rotation matrix is then established. It is shown that using the class of the optimal rotation matrices, the performance of BICM-ID systems over a Rayleigh fading channel approaches that of the BICM-ID systems over an AWGN channel when the dimension of the signal constellation increases. Furthermore, by exploiting the sigma mapping for any M-ary QAM constellation, a very simple sub-optimal, but yet effective iterative receiver structure suitable for signal constellations with large dimensions is proposed. Simulation results in various cases and conditions indicate that the proposed receiver can achieve the analytical performance bounds with low complexity

Employing multi-dimensional constellation and mapping to improve the error performance of bit-interleaved coded modulation with iterative decoding (BICM-ID) has recently received a lot of attention, both in single-antenna and multiple-antenna systems. To date, except for the cases of BPSK and QPSK constellations, good multi-dimensional mappings have only been found by computer searching techniques. This paper introduces an explicit algorithm to construct a good multi-dimensional mapping of 8-PSK for improving the asymptotic performance of BICM-ID systems. By comparing the performance of the proposed mapping with an unachievable lower bound, it is conjectured that the proposed mapping is the globally optimal mapping. The superiority of the proposed mapping over the best conventional (two-dimensional) mapping and the multi-dimensional mapping found previously by computer search is also demonstrated.

This paper presents a performance analysis of bit-interleaved coded-modulation with iterative decoding (BICM-ID) and complex N-dimensional signal space diversity in fading channels to investigate its performance limitation, the choice of the rotation matrix and the design of a low-complexity receiver. The tight error bound is first analytically derived. Based on the design criterion obtained from the error bound, the optimality of the rotation matrix is then established. It is shown that using the class of the optimal rotation matrices, the performance of BICM-ID systems over a Rayleigh fading channel approaches that of the BICM-ID systems over an AWGN channel when the dimension of the signal constellation increases. Furthermore, by exploiting the sigma mappings for M-QAM constellations, a very simple suboptimal, but yet effective iterative receiver structure suitable for signal constellations with large dimensions is proposed. Simulation results in various cases and conditions indicate that the proposed receiver can achieve the analytical performance bounds with low complexity.

The application of bit-interleaved coded modulation and iterative decoding (BICM-ID) in OFDM systems with modulation diversity over frequency selective Rayleigh fading channels is considered. A tight bound on the asymptotic error performance is first derived for general preceding over all N subcarriers and used to establish the best achievable performance with modulation diversity. It is then shown that preceding over subgroups of at least L subcarriers per group, where L is the number of channel taps, is sufficient to achieve this best performance while keeping the receiver complexity at minimum. The jointly optimum subcarrier grouping and rotation matrix are derived by solving the Vandermonde linear system

A cooperative coding scheme using M-ary modulation for high spectral efficiency and repetitive information transmission for diversity improvement is proposed. The encoder is a parallel concatenation of two bit-interleaved coded M-ary modulators (BICM) with scalable repetition of information symbols. As a result, the fraction of repeated information and the spectral efficiency of M-ary modulation can be used for bandwidth-performance tradeoff. Simulation results for different M-PSK and M-QAM systems in various block fading scenarios show that for a given bandwidth efficiency, a proper selection of the fraction of repeated information and the spectral efficiency of M-ary modulation can provide a large performance improvement.

This paper examines the bit error probability (BEP) of bit-interleaved coded modulation and iterative decoding (BICM-ID) in OFDM systems with modulation diversity (MD) over correlated frequency selective Rayleigh fading channels. A tight bound on the asymptotic error performance is derived for the general preceding over all the N subcarriers, which includes preceding over subcarrier groups as a special case. A design parameter that characterizes the effects of signal constellation, mapping and modulation diversity on the asymptotic performance is then established. Various analytical and simulation results are provided to confirm the tightness of the derived error bound.

This paper studies the bit error probability (BEP) of coded unitary space-time modulation with iterative decoding where neither the transmitter nor the receiver knows the channel fading coefficients. The tight error bound on the asymptotic performance is first analytically derived for given unitary constellation and mapping rule. Design criterion regarding the choice of unitary constellation and mapping is then established to achieve the best asymptotic performance. Furthermore, using the unitary constellation obtained from orthogonal design and 4-PSK, two mapping rules are proposed. In particular, one mapping is the best mapping for systems with iterative decoding, whereas the other mapping is most suitable for systems that do not implement iteration process. The latter mapping is similar to Gray mapping considered for coherent channels. Analytical and simulation results show that with the proposed mapping of the unitary constellation obtained from orthogonal design, the error performance of the iterative systems can approach very near the performance of the ideal unitary constellation and mapping

This paper introduces new mappings of QPSK symbols, viewed as a multi-dimensional hypercube, to improve the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID). By evaluating the upper bound of the bit error rate performance of BICM-ID, a condition to find the best mapping of a hypercube constellation in terms of the asymptotic performance under different channel models is established. A general and simple algorithm to construct the best mapping of a hypercube is then proposed. Analytical and simulation results show that the use of the proposed mappings together with very simple convolutional codes can offer significant coding gains over the conventional BICM-ID systems for all the channel models considered. Such coding gains are achieved without bandwidth or power expansion and with a very small increase in the system complexity.

The optimal decoding of vector quantization (VQ) over a code-division multiple-access (CDMA) channel is too complicated for systems with a medium-to-large number of users. This paper presents a low-complexity, suboptimal decoder for VQ over a CDMA channel. The proposed decoder is built from a soft-output multiuser detector, a soft bit estimator, and the optimal soft VQ decoding of an individual user. Simulation results obtained over both additive white Gaussian noise and flat Rayleigh fading channels show that with a lower complexity and good performance, the proposed decoding scheme is an attractive alternative to the more complicated optimal decoder.

In burst mode communication, the beginning of a burst is often estimated by comparing the power in a sliding window to a threshold. The simplicity of the algorithm makes it very attractive. The probability density function of the detection variable for this simple algorithm is the subject of (H. H. Nguyen et al., April 2003) where it is shown to be approximately Gamma distributed. This paper provides further analysis of this low complexity edge/burst detection DSP algorithm. The analysis yields two equations that relate "the probability of false detection" and "the probability of missing a detection" to window size and the decision threshold.

Synchronous CDMA systems whose transmission bandwidth is quantified through the fractional out-of-band energy (FOBE) constraint are considered. Either a conventional matched filter (MF) receiver or a minimum mean-square error (MMSE) receiver is employed for users' data detection. The total squared correlation (TSC) and the total mean-square error (TMSE) are proposed as the performance parameters for the MF and MMSE receivers respectively. These parameters need to be minimized in order to maximize the signal-to-interference ratios (SIRs) at the receivers' outputs. For a given FOBE bandwidth constraint, the sets of signature waveforms that minimize either TSC or TMSE are obtained from the prolate spheroidal wave functions (PSWFs). Furthermore, if the number of users is the size of a Hadamard matrix, then optimal signature waveforms can be obtained to maximize the individual SIR for every user. Due to the complicated nature of the PSWFs, simplified MF and MMSE receivers based on the Walsh signal space are developed.

Synchronous code-division multiple-access systems where each receiver is a minimum mean-squared-error receiver and each user has the same received power, signaling rate, and required signal-to-interference ratio are considered. Based on the results Viswanath, Anantharam and Tse (see IEEE Trans. Inform. Theory, vol.45, p.1968-83, 1999), the optimal signature waveforms under both fractional out-of-band energy and root-mean-square bandwidth constraints that maximize the network capacity are determined. Comparison to various suboptimal signature waveforms, including the ones constructed from rectangular pulses, is also made to quantify the gain achieved by the optimal signature waveforms.

Turbo trellis-coded modulation (T-TCM) is one of several techniques for combining turbo codes with multilevel modulation in order to save the bandwidth of the transmission systems. T-TCM was shown to perform very well on AWGN channels, but its performance over frequency-selective fading channels is unknown. In this paper, a system model to investigate the performance of T-TCM schemes over frequency-selective fading channels is proposed. Simulation results show that when an appropriate receiver is available, T-TCM also performs well on frequency-selective fading channels. T-TCM performance is much better than any other coded-modulation scheme for this type of channel.

Various turbo codes together with /spl pi//4 DQPSK modulation are investigated for frequency-selective Rayleigh fading channels. The soft output Viterbi algorithm (SOVA) is selected for equalising multipath fading channels so that both reliability information can be available for turbo decoding and the channel impulse response can be effectively estimated. To keep the receiver's complexity low, turbo codes are, built from a simple recursive systematic convolutional code with constraint length K=3. The number of channel estimators in the SOVA and the number of iterations to be performed in turbo decoders are also kept small. Simulation results for different mobile speeds and different frame lengths are obtained and it is shown that when the frame size is long enough, turbo codes can significantly outperform a convolutional code of constraint length K=6.