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In this article, we consider the downlink of a cellular communication network, where dual-connectivity at the end-users is enabled with the assistance of a full-duplex (FD) massive-multiple-input-multiple-output (mMIMO) relay. In particular, the base station transmits separate data streams through the cochannel direct link as well as the FD relay channel, utilizing the successive-interference-cancellation (SuIC) capability at the receiver. As a result, the downlink communication data can be interchangeably loaded to separate subcarriers, employing an orthogonal multicarrier strategy, or to different available links, i.e., direct or FD relay link, employing the nonorthogonal SuIC at the receiver. In order to reliably model the SuIC operation at the receiver, the collective sources of impairments, including the nonlinear transmit and receiver chain distortions as well as the channel state information inaccuracy are incorporated. An optimization problem for joint subcarrier and power allocation is then devised in order to maximize system sum-rate, which belongs to the class of smooth difference-of-convex problems. An iterative optimization solution is then proposed, utilizing successive inner approximation framework, which converges to the point that satisfies Karush–Kuhn–Tucker optimality conditions. Numerical results show performance and robustness gain of proposed SuIC scheme in terms of sum-rate compared to previously proposed single-connectivity and half-duplex relaying schemes.

In this paper, we analyze inner and outer bounding capacity region of two-user multiple-access relay channel (MARC) with side information (SI) non-causally known at one encoder in different scenarios. First, we obtain a general capacity inner bound including various previous results as its special cases, where, the informed encoder transmits two-layer individual description of side information to the relay and destination, and block Markov, superposition, Marton and Gel’fand-Pinsker coding at the encoders and sliding-window decoding at the receiver are exploited. This individual side information can be considered as the partial SI at the relay and destination, which can potentially increase the transmission rates, especially for the uninformed encoder. Second, to show practical importance of the obtained inner bound, we extend it to the Gaussian version, which can be used in studying the coverage region and energy efficiency. Third, we study outer bounding the capacity region, aiming at outer bounds less than cut set bounds, by considering a general MARC with partial decode and forward (PDF) strategy at the relay. Finally, the obtained Gaussian inner bound is evaluated numerically, and we showed that our capacity inner bound results in more sum-rate in comparison with the previous studies.

Uplink-downlink duality refers to the fact that under a sum-power constraint, the capacity regions of a Gaussian multiple-access channel and a Gaussian broadcast channel with Hermitian transposed channel matrices are identical. This paper generalizes this result to a cooperative cellular network, in which remote access-points are deployed as relays in serving the users under the coordination of a central processor (CP). In this model, the users and the relays are connected over noisy wireless links, while the relays and the CP are connected over noiseless but rate-limited fronthaul links. Based on a Lagrangian technique, this paper establishes a duality relationship between such a multiple-access relay channel and broadcast relay channel, under the assumption that the relays use compression-based strategies. Specifically, we show that under the same total transmit power constraint and individual fronthaul rate constraints, the achievable rate regions of the Gaussian multiple-access and broadcast relay channels are identical, when either independent compression or Wyner-Ziv and multivariate compression strategies are used. The key observations are that if the beamforming vectors at the relays are fixed, the sum-power minimization problems under the achievable rate and fronthaul constraints in both the uplink and the downlink can be transformed into either a linear programming or a semidefinite programming problem depending on the compression technique, and that the uplink and downlink problems are Lagrangian duals of each other. Moreover, the dual variables corresponding to the downlink rate constraints become the uplink powers; the dual variables corresponding to the downlink fronthaul constraints become the uplink quantization noises. This duality relationship enables an efficient algorithm for optimizing the downlink transmission and relaying strategies based on the uplink., Comment: Accepted in IEEE Transactions on Information Theory; 34 pages

Minimizing the average achievable distortion (AAD) of a Gaussian source at the destination of a two-hop block fading relay channel is studied in this paper. The communication is carried out through the use of a Decode and Forward (DF) relay with no source-destination direct links. The associated receivers of both hops are assumed to be aware of the corresponding channel state information (CSI), while the transmitters are unaware of their corresponding CSI. The current paper explores the effectiveness of incorporating the successive refinement source coding together with multi-layer channel coding in minimizing the AAD. In this regard, the closed form and optimal power allocation policy across code layers of the second hop is derived, and using a proper curve fitting approach, a close-to-optimal power allocation policy associated with the first hop is devised. It is numerically shown that the DF strategy closely follows the Amplify and Forward (AF) relaying, while there is a sizable gap between the AAD of multi-layer coding and single-layer source coding.

In recent years, considerable studies have been devoted to physical-layer network coding (PLNC) in a two-way relay channel (TWRC) network with the symmetric channel. However, it may not be appropriate for the asymmetric channel in which the source-to-relay channels are not equally strong and the two sources may utilise different modulation. In this study, the authors studied the heterogeneous PLNC design in the asymmetric TWRC network with high-order modulation and proposed a relay denoising mapping approach to reduce the decoding error probability. Firstly, they put forward a cluster maximisation algorithm to enlarge one cluster by sucking the neighbour points, which satisfy the exclusive law. Then, based on this algorithm, they designed the heuristic nearest-neighbour denoising mapping (HNDM) approach. The HNDM algorithm divides the nearest neighbour superimposed constellation points into the same cluster as far as possible. Points in the same cluster are coded into a new symbol by a specific mapping that achieves a many-to-one mapping. Performance results are provided in terms of symbol error rate. Under diversity channel conditions, the performances of 16-quadrature amplitude modulator (16-QAM)-8-phase-shift keying and 16-QAM-quadrature phase-shift keying are evaluated.

This paper investigates coherent detection for physical-layer network coding (PNC) with short packet transmissions in a two-way relay channel (TWRC). PNC turns superimposed EM waves into network-coded messages to improve throughput in a relay system. To achieve this, accurate channel information at the relay is a necessity. Much prior work applies preambles to estimate the channel. For long packets , the preamble overhead is low because of the large data payload. For short packets , that is not the case. To avoid excessive overhead, we consider a set-up in which short packets do not have preambles. A key challenge is how the relay can estimate the channel and detect the network-coded messages jointly based on the received signals from the two end users. We design a coherent detector that makes use of a belief propagation (BP) algorithm to do so. For concreteness, we focus on binary frequency-shift-keying (FSK) modulation. We show how the BP algorithm can be simplified and made practical with Gaussian-mixture passing. In addition, we demonstrate that prior knowledge on the channel distribution is not needed with our framework. Benchmarked against the detector with prior knowledge of the channel distribution, numerical results show that our detector can have nearly the same performance without such prior knowledge.

This paper studies the transceiver design of the Gaussian two-pair two-way relay channel (TWRC), where two pairs of users exchange information through a common relay in a pairwise manner. Our main contribution is to show that the capacity of the Gaussian two-pair TWRC is achievable to within $\frac{1}{ 2}$ bit for arbitrary channel conditions. For the outer bound, we derive a genie-aided bound of the Gaussian two-pair TWRC, which is tighter than the cut-set bound. For the inner bound, we develop a hybrid coding scheme involving Gaussian random coding, nested lattice coding, superposition coding, and network-coded decoding. We further present a message-reassembling strategy to decouple the coding design for the user-to-relay and relay-to-user links, so as to provide flexibility to fully exploit the channel randomness. We show that judicious power allocation at the users and at the relay is necessary to approach the channel capacity under various channel conditions.

In this paper, we propose a link adaptation algorithm for slow-fading half-duplex orthogonal multiple access multiple relay channel under a centralized node scheduling approach. During the first phase, the sources transmit in turn. During the second phase, a scheduled node (relay or source) transmits incremental redundancies on its correctly decoded source messages. The proposed algorithm aims at maximizing the average spectral efficiency under individual QoS targets for a given modulation and coding scheme family. The main principle of the algorithm is to reduce the complexity, and this is achieved using Best-Response Dynamics (BRD) tools. The rates are first initialized and then an iterative rate correction is applied. The resulting scheduling offers a tractable complexity under practical knowledge of channel states and yields performance close to the corresponding exhaustive search approaches as demonstrated by Monte-Carlo simulations.

We establish a new upper bound on the capacity of the relay channel which is tighter than all previous bounds. The upper bound uses traditional weak converse techniques involving mutual information inequalities and identification of auxiliary random variables via past and future channel random variable sequences. We show that the new bound is strictly tighter than all previous bounds for the Gaussian relay channel for every set of non-zero channel gains. When specialized to the class of relay channels with orthogonal receiver components, the bound resolves a conjecture by Kim on a class of deterministic relay channels. When further specialized to the class of product-form relay channels with orthogonal receiver components, the bound resolves a generalized version of Cover's relay channel problem, recovers the recent upper bound for the Gaussian case by Wu et al. and also improves upon the recent bounds for the binary symmetric case by Wu et al. and Barnes et al., which were all obtained using non-traditional geometric proof techniques.

The two‐user multiple‐access relay channel (MARC) is investigated in the presence of side information (SI) available only at the informed transmitter in the present article. First, for the...

In this paper, we consider the multiple access relay channel (MARC) in which two users want to communicate with a destination in the presence of a common intermediate node, the relay. This paper considers the case in which the relay can partially listen to both the users until it can estimate their signals. Specifically, a two-phase transmission scheme, (i) listening phase, and (ii) forwarding phase, is designed toward deriving the achievable rate region. In particular, the achievable rate region is basically derived in the cases of additive Gaussian channel and Rayleigh fading channel. Our numerical results show that (i) the derived achievable rate region contains the available rate region in the literature, and (ii) the sum rate has a concave relation with the number of channel uses in the listening phase.

This paper investigates the performance analysis of a selection combining scheme, which utilizes a variable gain amplify and forward relay over a Nakagami- $m$ fading channel. A selection combiner at a destination node chooses the better link between a relay channel and a direct channel. We derived exact closed-form expressions for moments of signal to noise ratio (SNR), ergodic capacity, and average symbol error probability. Simulation examples confirm that our exact formulas offer a more accurate analysis tool for selection combining than other prevailing approximations without extra complexity. The derived expressions serve as a useful tool for system design due to their validity for any SNR and arbitrary system parameters.

Both polar codes and physical network coding (PNC) are promising techniques to achieve low-latency and high-rate transmission in 5G communications. In this letter, we investigate a joint polar-coded PNC system over a wireless two-way relay channel (TWRC). By exploiting the nature of PNC, we then propose two successive cancellation list (SCL) decoding schemes for the polar-coded PNC system, XOR-based conventional SCL (XOR-SCL) and joint decoding of PNC and SCL decoding (JPSCL), where message update rules are derived for odd and even channels. Simulation results demonstrate that JPSCL outperforms XOR-SCL over both AWGN and Rayleigh fading channels. In particular, JPSCL achieves a small bit error rate gap, i.e., within 1 dB at rate of 2/5, from SCL in the polar-coded point-to-point system at BER of $10^{-5}$ .

One of the most important applications of network coding is the Multiple Access Relay Channel (MARC) technique in which source terminals transmit independent data blocks over one or more relay terminals to a common destination terminal. In recent years, MARC has become one of the vital network coding applications in the area of innovative wireless cooperative communications for enhancing spectral efficiency. In this paper, non-coherent binary frequency shift keying (BFSK) modulation and differential binary phase shift keying (DPSK) modulation techniques are applied to the decode-and-forward (DF)-based MARC model and the average bit error rate (BER) of the proposed system is derived theoretically by using the maximum likelihood (ML) decision rule. The simulation results show that the BER performance of DPSK modulation is better than the non-coherent BFSK and full diversity gain is achieved in both modulation techniques. We also propose a power allocation scheme for the proposed system model which optimizes the power allocated to the source and relay transmissions. Depending on the location of the relay, performance gains up to 1.25 dB are achieved with the proposed optimum power allocation (OPA) scheme. Also, the mathematical derivations are verified through Monte-Carlo simulations and the superior performance of the OPA over equal power allocation (EPA) is observed.

In this paper, we use self-adaptive dynamic differential evolution (SADDE) to search for multi-input/multi-output (MIMO) relay locations and transmitter locations to reduce the outage probability in the indoor ultra-wideband (UWB) environment. Amplify-and-forward (AF) MIMO relay is chosen to improve the performance of the environment. We use the shooting and bouncing ray/image (SBR/image) method to compute the frequency response, which is used to compute capacity. The channel capacities for the linear antenna with 1 × 1 antenna, 3 3 spaced linear antennas, and 3 × 3 tri-polarized antennas are compared. First, we deploy the relay and transmitter at the equipartition area. It is found that there are some outage receiving points. Thus, the SADDE is employed to optimize the position of the relay and transmitter in order to reduce the outage probability. Numerical results show that the outage probability for the relay and transmitter location is reduced by SADDE. Moreover, it is found that the channel capacity for the tri-polarized antennas has increased when comparing to 3 × 3 spaced linear antennas. For the zero outage probability requirement, the signal to noise for the tri-polarized antennas is lower 6 dB than that for 3 × 3 spaced linear antennas.

This paper discusses the two-stage single-relay channel model for in-home broadband power line communication links with up to two hops. This channel model consists of the concatenation of two single-relay channels that can result in eight configurations; however, only five of them are analyzed in this work since they cover up to one relay availability. In this context, a discussion addressing both amplify-and-forward and decode-and-forward cooperative protocols at relay node and maximal ratio combining at destination node is carried out. As the power line channels are frequency selective, the attenuation profile increases along with both distance and frequency, and the additive noise is colored, we discuss achievable data rate analyses using a data set covering the frequency band from 1.7 to 100 MHz, under sum power constraint. Based on the attained results, we state that the two-stage single-relay channel model is the best option for in-home broadband power line communication systems when the source-to-destination link is severely degraded (e.g., high signal attenuation and/or high-power noise presence), while the two-hop channel model is more appropriate when the channel degradation is not severe. Moreover, we show that the single-relay channel model may be remarkably outperformed by the two-stage single-relay channel model.

This paper focuses on the hybrid power line/wireless single-relay channel (HSRC) model, which is constituted by parallel power line and wireless single-relay channel (SRC) models, for data communication purposes. Closed-form expressions for ergodic achievable data rates and outage probabilities are presented. These expressions are based on the fact that both power line and wireless are frequency-selective block-fading channels corrupted by additive random noise with a definite power spectral density. Moreover, comparisons among HSRC, power line SRC, and wireless SRC under the sum power constraint with optimal and uniform power allocations, the use of amplify-and-forward and decode-and-forward cooperative protocols, and different relay positions are discussed. Based on asymptotic, analytical, and numerical results, we show that HSRC outperforms both power line and wireless SRCs in all considered scenarios. Furthermore, a performance comparison between HSRC and the so-called two wireless SRC shows that the former surpasses the latter when the sum power constraint with optimal power allocation is adopted.

Recently, WLANs using multiple frequency bands (e.g., 5 GHz, 2.4 GHz, and 920 MHz) have become popular as a means to increase spectral efficiency. However, during multi-hop transmissions in such multi-band WLANs, the relay node experiences a significant increase in delay and loss of data frames. This happens because of the difference of link rates between the receiving and sending sides of the relay node. In order to address this problem, we consider the channel conditions of each band on either side of the relay. Accordingly, the receiving and sending rates at the relay node are measured and calculated, respectively. Based on the measured receiving rate and calculated sending rate, we propose an algorithm for the relay node to determine the optimal coding rate and modulation method so as to dynamically control the best band and channel selection for the sending side. Simulation results demonstrate the effectiveness of our proposed algorithm in terms of improvement of delay and transmission failure probability.

We study a multihop “virtual” full-duplex relay channel as a special case of a general multiple multicast relay network. For such a channel, quantize-map-and-forward (QMF) [and its generalization of noisy network coding (NNC) and short message NNC] achieves the cut-set upper bound within a constant additive gap, where the gap grows linearly with the number of relay stages $K$ . This gap, however, may not be acceptable for practical communication systems with multihop transmissions (e.g., a wireless backhaul operating at high frequencies). Recently, we improved the capacity scaling by using a forward sliding-window (SW) decoding and by optimizing the quantization level at each relay, obtaining the gap that grows logarithmically as $\log {K}$ . Furthermore, the improved scheme has lower decoding complexity and delay than the general QMF and NNC approaches. In this paper, we further improve the performance by presenting a mixed scheme in which each relay can perform either decode-and-forward (DF) or the improved QMF (with SW decoding) and can choose to perform rate-splitting to enable partial interference cancellation. In general, the optimization of the relay DF/QMF configuration is combinatorial. Nevertheless, we provide that a simple greedy algorithm finds an optimal configuration under some practically reasonable assumptions. We derive an achievable rate that is easily computable and show that the proposed mixed scheme outperforms the QMF-only schemes. We demonstrate that the performance improvement increases with $K$ , which indicates that the mixed scheme is indeed beneficial for multihop transmission.

Lossy decode-and-forward (DF) relaying, also referred to as lossy forwarding (LF), can significantly enhance the transmission reliability and expand the communication coverage at the cost of a small increase in computational effort compared to its DF counterpart. Furthermore, it can further simplify the operations at the relay nodes by removing the error-detecting operation, e.g., cyclic redundancy check, which is used in the conventional DF systems. Due to these advantages, LF has been intensively investigated with the aim of its applications to various cooperative communication networks with different topologies. This paper offers a comprehensive literature review on the LF relaying strategy and makes comparisons between LF and DF. Five basic exemplifying scenarios are taken into consideration. These are the three-node network, the single-source multi-relay network with direct source-to-destination link, the multiple access relay channel, the two-way relay network, and the general multi-source multi-relay network. The paper includes not only theoretical performance limit analyses, but also performance evaluation by employing low-complexity accumulator aided turbo codes at the sources and relays as well as joint decoding at the destination. As expected, the performance enhancement in terms of outage probability, frame error rate, and $ {\epsilon }$ -outage achievable rate by LF over DF is significant, which is demonstrated in all the exemplifying scenarios in the literatures. Hence LF has a great potential to be applied to future 5G wireless communication networks, e.g., device-to-device, vehicle-to-vehicle, and machine-type communications, which are composed of the aforementioned exemplifying scenarios.

Consider a two-hop half-duplex relay channel (source–relay–destination) with a Markovian-constrained relay. The capacity of such channel is shown to be equal to the well-known cut-set upper bound. For the case where the relay-to-destination link is noise-free, the optimal state transition probabilities that give rise to the capacity are determined. This result links the relay channel to Shannon’s entropy maximization by introducing a relay adjacency matrix . For the case where both source-to-relay and relay-to-destination links are noisy, lower bounds on the achievable information rates for various constrained sequences are computed. We conjecture that our numerical bounds are tight. The numerically computed capacities and optimized information rates are significantly higher than the rate achieved by the traditional predetermined time-sharing scheme.

The use of existing network devices as relays has a potential to improve the overall network performance. In this work, we consider a two-hop wireless relay setting, where the channels between the source and relay nodes to the destination node are time varying. The relay nodes are able to overhear the transmissions of the source node which may have a weak connection to the destination, and they help the source node by forwarding its messages to the destination on its behalf, whenever this is needed. We develop a distributed scheme for relay selection and channel access that is suitable for time-varying channels, and prove that this scheme is throughput optimal. We obtain the achievable rate region of our proposed scheme analytically for a relay network with a single source and a single relay node. Meanwhile, for a more general network with more than one relay nodes, we perform Monte-Carlo simulations to obtain the achievable rate region. In both cases, we demonstrate that the achievable rate region attained with our distributed scheme is the same as the one attained with centralized optimal scheme.

We consider the zero-delay encoding of discrete-time analog information over the Multiple Access Relay Channel (MARC) using non-linear mapping functions. On the one hand, zero-delay non-linear mappings are capable to deal with the multiple access interference (MAI) caused by the simultaneous transmission of the information. On the other, the relaying operation is a Decode-and-Forward (DF) strategy where the decoded messages are merged into a single message using a specific continuous mapping depending on the correlation level of the source information. At the receiver, an approximated Minimum Mean Squared Error (MMSE) decoder is developed to obtain an estimate of the transmitted source symbols which exploits the information received from the relay node in combination with the messages received from the transmitters through the direct links. The resulting system provides better performance than the other alternative encoding strategies for the MARC with similar complexity and delay and also approaches the performance of theoretical strategies which require a significantly higher delay and computational cost.

We consider a signal detection problem by using deep learning techniques in a multiple-input multiple-output (MIMO) decode-forward (DF) relay channel. There exist some suboptimal detectors such as the near maximum likelihood (NML) detector and the NML with two-level pair-wise error probability (NMLw2PEP) detector in the channel. However, the NML detectors require an exponentially increasing complexity as the number of transmit antennas increases. More seriously, without the channel state information (CSI) of the source-relay (SR) link, there is no detector that can achieve good performance even at high complexity. In this paper, we propose a deep learning approach to the NML (DL-NML) detector that achieves good performance with low complexity regardless of whether the CSI of the SR link is known or not at the destination. The DL-NML detector can detect signals in changing channels after a single training by using randomly generated channels. Furthermore, we propose a linear detector and a semidefinite relaxation approach to the NML detector to compare with the DL-NML detector in performance and complexity. The complexity analysis and simulation results validate the superiority of the proposed DL-NML detector.

This chapter considers the design of wireless communication systems with multiple transmission nodes powered by energy harvesters. Different from the point‐to‐point channel case, it is not optimal anymore for the multi‐node scenarios to separately optimize the transmission of each energy harvesting (EH) communication link with only local energy state information (ESI). The chapter investigates the multiple‐access channels with conferencing links and shared energy harvesters and discusses the transmission cooperation among the transmitters. It considers a three‐node relay channel with energy harvesting (EH) sources, where it is shown that the proposed cooperative transmission scheme can exploit a new form of diversity arising from the independent source and relay energy availability over time, termed "energy diversity," even over time‐invariant channels. The chapter turns to a large relay network, where multiple relays are powered by energy harvesters, and shows that the power allocation for each EH relay should be determined by the overall energy distribution among these relays.

In this paper, the causal cognitive interference relay channel (CCIRC) is considered. The CCIRC is obtained from the classic cognitive interference channel by introducing a full-duplex relay that has causal and noisy access to the transmitted signals and aids the communication between the two users. For this channel model, a simple upper bound on the capacity is initially established. Then, we derive an achievable rate region that jointly applies cooperative Han–Kobayashi rate splitting, block Markov encoding, superposition coding, Marton’s binning encoding, and backward decoding. In particular, these bounds are derived for both discrete memoryless model and Gaussian channel. Further, both our theoretical and numerical results indicate that the derived achievable rate region encompasses all known available results in the literature.

In this paper, we investigate the performance of an underlay cognitive two-way relay system with direct link using time division broadcast protocol in the presence of primary user's interference. Herein, relying on the practicability and low complexity of statistical channel state information, the secondary transmissions are in compliance with the fading-averaged interference constraints imposed by the primary receiver. For this setup, we study an adaptive link utilization scheme (ALUS) that can exploit both direct and relay links with appropriate diversity combining methods to improve the performance of secondary users. Based on ALUS, we evaluate and compare the performance of two decode-and-forward based relaying strategies viz., fixed relaying and incremental relaying. We derive the tight closed-form expressions of outage probability of the secondary communications for both the strategies over Nakagami- m fading channels. We further conduct asymptotic high signal-to-interference-plus-noise ratio analysis to examine the achievable diversity order of the considered system. In addition, we quantify the expected spectral efficiency and average transmission time for both relaying strategies. Our results illustrate that the incremental relaying strategy can significantly improve the system performance in comparison with fixed relaying. Numerical and simulation results are provided to attest our theoretical studies.

In this paper, we study a diamond-relay channel where the source is connected to $M$ relays through orthogonal links and the relays transmit to the destination over a wireless multiple-access channel in the presence of an eavesdropper. The eavesdropper not only observes the relay transmissions through another multiple-access channel, but also observes a certain number of source-relay links. The legitimate terminals know neither the eavesdropper's channel state information nor the location of source-relay links revealed to the eavesdropper except the total number of such links. For this wiretapped diamond-relay channel, we establish the optimal secure degrees of freedom. In the achievability part, our proposed scheme uses the source-relay links to transmit a judiciously constructed combination of message symbols, artificial noise symbols as well as fictitious message symbols associated with secure network coding. The relays use a combination of beamforming and interference alignment in their transmission scheme. For the converse part, we take a genie-aided approach assuming that the location of wiretapped links is known., Comment: 30 pages, 4 figures, Submitted to IEEE Transactions on Information Theory

Cooperative communication is a promising technique to mitigate channel impairment and improve spectral efficiency. Due to the mobility of relay nodes (RNs) and the unfavourable effects of wireless channels, channel conditions may change as time passes. Therefore, how to design proper long-term incentive mechanisms for RNs in such dynamic communication environments is an essential issue. This paper investigates the contract incentive method under asymmetric information scenario, where the relay channel condition and cost are the RNs’ private information. To capture the dynamic characteristic of the RNs’ cooperative information during the long-term cooperation, two dynamic contract mechanisms are introduced into long-term relay incentive with different RNs’ relay information structures. The optimal contract is derived to maximize the source's expected utility for both independent asymmetric information and correlated asymmetric information . Numerical results are presented to evaluate the effectiveness of the proposed dynamic contract-based incentive mechanism.

In this paper, for a two-way relay channel comprising two multi-antenna transceivers and $L$ single-antenna potential relay nodes, we propose three network-coded cooperative spatial multiplexing (CSM) schemes that effectively overcome the rate loss incurred due to the half-duplex limitation of the transceivers and the relay nodes and achieve high spectral efficiency. In the following, these three schemes are referred to as time-division broadcast (TDBC)-CSM , incremental (I)-TDBC-CSM and multiple-access broadcast (MABC)-CSM . We investigate these schemes in terms of the outage probability, the average transmission rate, the asymptotic behavior, and the diversity-multiplexing tradeoff. The analysis of the paper shows that, first, the I-TDBC-CSM scheme achieves the full diversity of order $L\min (M_1,M_2)+M_1M_2$ , where $M_1$ and $M_2$ are the numbers of antennas employed by the two transceivers; second, the TDBC-CSM and MABC-CSM schemes achieve the diversity of order $L\min (M_1,M_2)$ , where this quantity is the maximum achievable diversity gain in the absence of the direct link between the transceivers; third, the TDBC-CSM and I-TDBC-CSM schemes effectively overcome the rate loss incurred due to the half-duplex limitation of the relay nodes; fourth, the MABC-CSM scheme not only overcomes the half-duplex limitation of the relay nodes but also mitigates the spectral efficiency loss incurred due to the half-duplex limitation of the transceivers; and fifth, if one or both of the transceivers are equipped with a massive antenna array, the asymptotic average rate of the CSM-based schemes scales linearly with the number of potential relay nodes, as opposed to the conventional relaying schemes, in which the average rate is not scalable with $L$ . We provide extensive simulation results to confirm the theoretical analysis of the paper. The simulation results show that for a given outage probability, the proposed schemes outperform the conventional relaying schemes in terms of the average transmission rate.

Relay selection is considered to enhance the secrecy of a dual-hop regenerative multi-relay system with an eavesdropper. Without assuming perfect decoding at the relays, the secrecy outage probability of a single relay system is obtained first. Secrecy outage of optimal, traditional, and suboptimal relay selection schemes is then evaluated. To reduce the power consumption, partial relay selection schemes based only on either of the source-relay or relay-destination instantaneous channel state information (ICSI) are introduced. The secrecy outage is evaluated and compared with the other schemes. Secrecy outage of all the selection schemes are obtained in closed-form. An optimal relay selection scheme is proposed using secrecy outage, which does not require any ICSI. Asymptotic and diversity gain analysis of the secrecy outage is presented when source-relay and relay-destination average SNRs are the same or different. We observe that the improvement in eavesdropper link quality affects the secrecy outage more when required secrecy rate is low as compared to the case when rate is high. We also observe that relay selection improves performance more when number of relays are more. It is important to note that either of the source-relay or the relay-destination link quality can equally limit the secrecy outage performance even if the other link quality is infinitely good.

In the following paper, we will analyze and study over a subset of channels including relay with channel side information. First, it has been derived an upper bound on the capacity for this AWGN relay channel when the channel side information is non-causally accessible at both, the transmitter and the relay. In the following, a minimization problem for the energy-per-bit for this type of channel has been presented. After that, by using derived results for the capacity of this channel, we evaluate a lower bound for the problem of the minimum energy-per-bit. We investigate that this bound could be less than the bound founded of the classical AWGN relay channels.

This paper will propose a policy and show how our approach works by utilizing a threshold. The threshold is a proper measure for evaluating the amount of freshness of the information. Finding the threshold is a time-consuming and challenging task, and we propose an algorithm to find it based on the Nested Interval Theorem. We have also solved it for some initial points by the Bisection method. Examples and simulation results prove all of our claims as well. Finding the average age for the policy is another innovative task in this paper. We also extend our findings for a network with one relay and show how the relay reduces the average age. All of our works are compared by utilizing the simulation results.

In this paper, we mathematically analyze the performance of an energy harvesting (EH) full-duplex (FD) decode-and-forward (DF) relay system. Unlike previous works on EH-FD relay systems, we consider the case of source is static while both relay and destination are mobile. Thus, the relay - destination channel is cascade (double) Rayleigh fading while the source - relay channel is Rayleigh fading. We derive the exact closed-form expression of symbol error rate (SER) of the considered EH-FD relay system under the impacts of the cascade Rayleigh fading channels and the residual self-interference (RSI) due to FD mode. Numerical results show a significant performance degradation because of the cascade Rayleigh fading channels. Furthermore, the SER goes to error floor due to the impact of the RSI at high signal-to-noise ratio (SNR) region. We see that there is an optimal value of the EH time duration that minimizes the SER of the considered EH-FD relay system. Monte Carlo simulations are given to validate all analysis results.

In order to solve the problem of millimeter-wave massive MIMO channel estimation in a relay environment, this paper proposes a single-path channel model of a downstream millimeter-wave massive MIMO relay system. After that, based on the Compressive Sensing (CS) algorithm, an adaptive compressed sensing channel estimation scheme is proposed. Simulation experiments prove the applicability of the compressed sensing algorithm under the relay channel model. Finally, this paper compares the adaptive compressed sensing algorithm with the traditional orthogonal matching tracking (OMP) compressed sensing algorithm, and proves that the proposed adaptive compressed sensing algorithm improves the channel estimation accuracy.

The incessant increase in service needs and the number of subscribers is a major subject of concern to operators of mobile communication networks. Cooperative systems are one of the solutions proposed by the communities to meet these needs. In this proposal, we focus on the successive cancellation list (SCL) decoder for polar codes on cooperative communication which is composed of three blocks: the transmission module, a relay block and a reception node. The transmission on the channel is divided into two times. Data coded with a polar code is transmitted simultaneously by the source to the reception system and to the relay bloc. The relay processes its version with an SCL protocol before proceeding to polar coding then transmits them to the destination. After a SCL decoding, the reception uses the MRC (Maximum Ratio Combining) combination method to compare the two versions of the signals and extracts the useful information. We propose a protocol for the construction of polar codes to reach the theoretical capacity in the half-duplex relay channel. We also demonstrate that the polar code (1024, 512) is decoded by the decoder. SC-List of the proposed model with a very large size of the list ( $\mathrm{L}=32$ ) can reach a bit rate of 10−4 to 2dB. The simulation results obtained show proven performance compared to other existing codes such as the turbo code and the low-density parity check) codes.

This paper studies Physical-layer Network Coding (PNC) in a two-way relay channel (TWRC) operated based on OFDM and QPSK modulation but with the presence of carrier frequency offset (CFO). CFO, induced by node motion and/or oscillator mismatch, causes inter-carrier interference (ICI) that impairs received signals in PNC. Our ultimate goal is to empower the relay in TWRC to decode network-coded information of the end users at a low bit error rate (BER) under CFO, as it is impossible to eliminate the CFO of both end users. For that, we first put forth two signal detection and channel decoding schemes at the relay in PNC. For signal detection, both schemes exploit the signal structure introduced by ICI, but they aim for different output, thus differing in the subsequent channel decoding. We then consider CFO compensation that adjusts the CFO values of the end nodes simultaneously and find that an optimal choice is to yield opposite CFO values in PNC. Particularly, we reveal that pilot insertion could play an important role against the CFO effect, indicating that we may trade more pilots for not just a better channel estimation but also a lower BER at the relay in PNC. With our proposed measures, we conduct simulation using repeat-accumulate (RA) codes and QPSK modulation to show that PNC can achieve a BER at the relay comparable to that of point-to-point transmissions for low to medium CFO levels.

Network coding is a new and promising paradigm for modern communication networks by allowing intermediate nodes to mix messages received from multiple sources. Compute-and-forward strategy is one category of network coding in which a relay will decode and forward a linear combination of source messages according to the observed channel coefficients, based on the algebraic structure of lattice codes. The destination will recover all transmitted messages if enough linear equations are received. In this work, we design in a system level, the compute-and-forward network coding coefficients by Fincke-Pohst based candidate set searching algorithm and network coding system matrix constructing algorithm, such that by those proposed algorithms, the transmission rate of the multi-source multi-relay system is maximized. Numerical results demonstrate the effectiveness of our proposed algorithms.

In this paper we propose a novel power adaptive network coding (PANC) for a non-orthogonal multiple-access relay channel (MARC), where two sources transmit their information simultaneously to the destination with the help of a relay. In contrast to the conventional XOR-based network coding (CXNC), the relay in PANC generates network coded symbols by considering the coefficients of the source-to-relay channels, and forwards each symbol with a pre-optimized power level. Specifically, by defining a symbol pair as two symbols from the two sources, we first derive the expression of symbol pair error rate (SPER) for the system. Noting that deriving the exact SPER are complex due to the irregularity of the decision regions caused by random channel coefficients, we propose a coordinate transform (CT) method on the received constellation to simplify the derivations of the SPER. Next, we obtain the optimal power level by decomposing it as a multiplication of a power scaling factor and a power adaptation factor. We prove that with the power scaling factor at the relay, our PANC scheme can achieve a full diversity gain, i.e., an order of two diversity gain, while the CXNC can achieve only an order of one diversity gain. In addition, we optimize the power adaptation factor at the relay to minimize the SPER at the destination by considering of the relationship between SPER and minimum Euclidean distance of the received constellation, resulting in an improved coding gain. Simulation results show that (1) the SPER derived based on our CT method can well approximate the exact SPER with a much lower complexity; (2) the PANC scheme with power adaptation optimizations and power scaling factor design can achieve a full diversity, and obtain a much higher coding gain than other network coding schemes.

This paper deals with joint source and relay beam- forming (BF) design for an amplify-and-forward (AF) multi- antenna multirelay network. Considering that the channel state information (CSI) from relays to a destination is imperfect, we aim to maximize the worst-case received signal-to-noise ratio (SNR). The associated optimization problem is then solved in two steps. In the first step, by fixing the source BF vector, a semi-closed-form solution of the relay BF matrices is obtained, up to a power- allocation factor. In the second step, the global optimal source BF vector is obtained based on the polyblock outer approximation (PA) algorithm. We also propose two low-complexity methods for obtaining the source BF vector, which differ in their complexity and performances. The optimal joint source and relay BF solution obtained by the proposed algorithms serves as the benchmark for evaluating the existing schemes and the proposed low-complexity methods. Simulation results show that the proposed robust design can significantly reduce the sensitivity of the channel uncertainty to the system performance. Index Terms—Amplify and forward (AF), beamforming (BF), global optimal, multiantenna multirelay system.

This paper deals with joint source-relay-destination beamforming (BF) design for an amplify-and-forward (AF) relay network. Considering the channel state information (CSI) from the relay to the destination is imperfect, we first aim to maximize the worst case received SNR under per-antenna power constraints. The associated optimization problem is then solved in two steps. In the first step, by revealing the rank-one property of the optimal relay BF matrix, we establish the semi-closed form solution of the joint optimal BF design that only depends on a vector variable. Based on this result, in the second step, we propose a low-complexity iterative algorithm to obtain the remaining unknown variable. We also study the problem for minimizing the maximum per-antenna power at the relay while ensuring a received signal-to-noise ratio (SNR) target, and show that it reduces to the SNR maximization problem. Thus the same methods can be applied to solve it. The differences between our result and the existing related work are also discussed in details. In particular, we show that in the perfect CSI case, our algorithm has the same performance but with much lower cost of computational complexity than the existing method. Finally, in the simulation part, we investigate the impact of imperfect CSI on the system performance to verify our analysis.

In this letter, we study relay-aided networks with presence of single eavesdropper. We provide joint beamforming design of the source and relay that can minimize the overall power consumption while satisfying our predefined quality-of-service (QoS) requirements. Additionally, we investigate the case that the channel between relay and eavesdropper suffers from channel uncertainty. Finally, simulation results are provided to verify the effectiveness of our algorithm., Comment: CL

The full duplex (FD) two-way relay channel (TWRC) has recently been shown to be a feasible way to improve the network throughput in practical communications. In this correspondence, we consider the convolutionally coded physical-layer network coding over the TWRC in which two sources work in the FD mode and there exists a direct link between them. Every source receives two packets, one packet from the other source and one network coded packet from the relay. A near-maximum-likelihood decoding algorithm for the sources is proposed. A salient feature of the proposed algorithm is that it exploits the code structure to mitigate the error propagation induced by the relay. Furthermore, we derive the near maximum-likelihood decoding bound on end-to-end BER for the system. Simulation results indicate that the performance of the proposed algorithm matches well the bound.

The feasibility of enabling massive wireless connectivity to cell-edge users is investigated by means of multiple relay-aided massive multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA). The key challenge of channel state information (CSI) acquisition is overcome by estimating the cascaded relay channel at the base-station via pilots sent by users. The achievable rates are derived by assuming that the users rely on statistical channel knowledge for signal decoding. Our analysis is useful to quantify the joint adverse effects of intra-cluster pilot contamination, imperfect CSI, precoding uncertainty, and imperfect successive interference cancellation. The achievable rates of the proposed relay-aided massive MIMO NOMA are compared against the orthogonal multiple access (OMA) counterpart. We reveal that although multiple relayaided massive MIMO NOMA is able to support overloaded case, massive MIMO OMA outperforms NOMA counterpart in terms of the achievable sum rate in the underloaded cases.

This paper presents multiple turbo coded cooperative orthogonal frequency division multiplexing (MTCC-OFDM) scheme over a quasi-static frequency selective Rayleigh fading channel. The MTCC-OFDM scheme is composed of multiple input and multiple output antennas. As, in practical coded cooperative scenario, the relay terminal is mostly in outage due to noisy source to relay channel which causes an erroneous transmission towards the destination terminal that eventually results in a very low bit-error rate (BER) performance of the communication system. Therefore, in the proposed scheme, a turbo iterative decoding is being performed at the relay terminal that considerably improves the BER performance of the communication system. The numerical simulated results confirm that the proposed scheme not only out-performs its related coded non-cooperative scheme i.e., turbo coded OFDM scheme under a similar conditions in terms of bit error-correction performance but also offers robustness in a noisy (practical) source to relay channel scenario.

This paper proposes an adaptive relay selection method that exploits the social network and establishes a physical domain and social domain-based model named the Social-based device-to-device (D2D) relay selection model to address relay selection failure caused by the diversity of users cooperation willingness and the instability of communication links due to human mobility. Under the premise of tolerable interference caused to cellular users, the proposed approach synthetically considers the desired physical-relation factor and the social-interaction factor for the relay user. In particular, the reliability of the D2D link is obtained by considering the transmission stability of the link, assessed by the user encounter history and cooperation willingness characterized by user social distance, which is set as the criterion of relay selection, combined with the physical channel condition. Simulation results show that compared with the traditional socially blind method, the proposed method can increase the probability of relay selection success and reduce the burden of the cellular network to improve the system performance.

In this paper, we investigate secure communication for a dual-hop relay channel in the presence of an eavesdropper. A novel independent randomize-and-forward (IRF) strategy is proposed to enhance the secrecy performance, where the relay maps the decoded message to an independent message set then encodes the message by random-coding argument. For the discrete model, we establish the achievable rate-equivocation for the IRF strategy. For the Gaussian model, we derive the perfect secrecy rate of IRF strategy and compare it with decode-and-forward (DF), amplify-and-forward (AF) and noise-forwarding (NF) strategies. Theoretical analysis indicates that the relay's engagement of independent secure coding enhances the security of transmission. Numerical results also show the proposed IRF strategy can significantly improve the secrecy performance of the dual-hop relay channel in some cases.

We examine the frequency-selective Gaussian primitive diamond relay channel, where the signal received at both relays is described by identical frequency-selective Gaussian channels, and where the relays are connected to the destination via noiseless fronthaul links of a given capacity. The frequency response of the filters are available to all system components. We characterize analytically the Gaussian input frequency power distribution that maximizes the optimal information rate of the oblivious (code independent) relay operation achieved by joint decompression-decoding (or optimized Wyner-Ziv) procedure.

The integration of wireless power transfer (WPT) with the low-power backscatter communications provides a promising way to sustain battery-less wireless networks. In this paper, we consider a backscatter communication network wirelessly powered by a power beacon station (PBS). Each backscatter radio uses the harvested energy to power its data transmissions, in which some other radios can help as the wireless relays with an aim to improve throughput performance by cooperative transmission. Under this setting, we formulate a throughput maximization problem to jointly optimize WPT and the relay strategy of the backscatter radios. An iterative algorithm with reduced complexity and communication overhead is proposed to decompose the original problem into two sub-problems distributed at the PBS and the backscatter receiver. Moreover, we take uncertain channel information into consideration and formulate robust counter-parts of the throughput maximization problem when either the backscatter or relay channel is subject to estimation errors. The difficulty of the robust counter-part lies in the coupling of the PBS’ power allocation and relay strategy in matrix inequalities, which is addressed by alternating optimization with guaranteed convergence. Numerical results reveal that the cooperative relay strategy of the backscatter radios significantly improves the throughput performance.

This paper considers the use of polar codes to enable secure transmission over parallel relay channels. By exploiting the properties of polar codes over parallel channels, a polar encoding algorithm is designed based on Channel State Information (CSI) between the legitimate transmitter (Alice) and the legitimate receiver (Bob). Different from existing secure transmission schemes, the proposed scheme does not require CSI between Alice and the eavesdropper (Eve). The proposed scheme is proven to be reliable and shown to be capable of transmitting information securely under Amplify-and-Forward (AF) relay protocol, thereby providing security against passive and active attackers.