Multiple Access Relay Channel Research Articles

Effects of relay (source) side information on the coverage region in wireless Rayleigh and Rician fading multiple access relay channel

In this paper, we analyze the side information (SI) effect on the coverage region of the wireless multiple-access relay channel (MARC) in two different communications scenarios: SI only at one source and SI only at the relay. Aiming at this work, (I) a general achievable rate region is proved for wireless MARC with SI at one source and SI at the relay in two fading models (Rayleigh model, which has been widely studied in the literature; and Rician model the rate region of which for MARC has not been obtained before); (II) This obtained region, while including previous regions as its special cases, (a) shows the advantage of the SI known at the relay compared to the SI known at one encoder in removing the SI interference at the receiver (as seen in Theorem 2.2, Remark 2.1), and on the related coverage regions, too; and (b) can be exploited to prove corresponding coverage regions; (III) Then, the SI effect on the coverage region is scrutinized in different situations (SI only at one source and SI only at the relay), and also the differences between two fading models (Rayleigh and Rician) are investigated. (IV) Finally, theoretical findings are evaluated numerically.

Uplink-Downlink Duality Between Multiple-Access and Broadcast Channels With Compressing Relays

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.

Inner and outer bounding capacity region for multiple-access relay channel with non-causal side information at one encoder

Inner and outer bounding capacity region for multiple-access relay channel with non-causal side information at one encoder

On the capacity region of the multiple access half‐duplex relay channel

SummaryIn this paper, we consider the transmission over multiple access relay channel (MARC) in which the relay operates in half‐duplex mode. The main contribution of this paper is establishing the capacity of the multiple access half‐duplex relay channel (MAHRC). Toward achieving this goal, we first derive a new achievable rate region. While deriving the achievable rate region, well‐known encoding and decoding schemes, which are used for transmission and reception over the degraded broadcast channel and the multiple access channel, are used. In this transmission scheme, the transmission from the two sources via the half‐duplex relay, to the destination, is split into two phases. Afterwards, an outer bound to the transmission over the discrete memoryless MAHRC is developed. Consequently, we show that the achievable rate region matches the outer bound and therefore the capacity region is formed. Further, the capacity region is extended to the case of Gaussian channel. Additionally, many numerical examples are shown to validate our theoretical derivations. In particular, these numerical examples show that the achievable rate region, and then the capacity, that we derive is larger than the well‐known results in the literature.

Effects of relay and side information at one encoder on the coverage regions in Gaussian multiple‐access channel

AbstractThe 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 discrete alphabet and memoryless MARC with common and private messages, partial decode and forward strategy at the relay and fixed locations of the nodes, a general achievable rate region is obtained. The SI effect is seen and can be analyzed. Second, we extend the discrete result to a practical communications model: Gaussian multiple‐access relay channel (GMARC), showing previous works as its special cases. Third, the effect of (perfect and nonperfect) SI on the maximum coverage region of GMARC for a fixed rate of the transmitters and a fixed distance between relay and destination is analyzed. It is shown that the SI increases the coverage region of encoders, and consequently, it can improve communication energy efficiency. Finally, mathematical findings are validated numerically by using Matlab.

Finite Blocklength Analysis of Multiple Access Channels With/Without Cooperation

Motivated by the demand of reliable and finite blocklength communications, we employ tools from information theory, stochastic processes and queueing theory, in order to provide a comprehensive framework regarding the analysis of a Time Division Multiple Access (TDMA) network with bursty traffic, in the finite blocklength regime. Specifically, we reexamine the stability conditions of a non-cooperative TDMA multiple access channel, evaluate the optimal throughput, and identify the optimal data packet size, k, for fixed codeword of blocklength, n. The evaluation is performed both numerically and via the proposed approximations, which result in closed form expressions and provide insight on how the optimal data size, k*, relates to the information metrics of channel capacity and channel dispersion in the finite blocklength regime. Then, we examine the stability conditions and the performance of the Multiple Access Relay Channel with TDMA scheduling, subject to finite blocklength constraints, by applying a cognitive cooperation protocol that assumes relaying is enabled when sources are idle. Finally, we propose the novel Batch-And-Forward (BAF) strategy, a mechanism that allows terminals to send batches of data packets instead on individual data packets, and evaluate the stability conditions and the optimal throughput. Numerical evaluation of the proposed strategy indicates that the performance of the cooperative network in the finite blocklength regime, in terms of throughput, can be significantly enhanced. Moreover, it reduces the requirement in control signals (metadata) [3], since, it avoids the unnecessary repetition of metadata (e.g. address of the source terminal and the destination). The BAF strategy is quite versatile, thus, it can be embedded in existing cooperative protocols, without imposing additional complexity on the overall scheme.

Dual-Band Fading Multiple Access Relay Channels

Relay cooperation and integrated microwave and millimeter-wave (mm-wave) dual-band communication are likely to play key roles in 5G. In this paper, we study a two-user uplink scenario in such dual-bands, modeled as a multiple-access relay channel (MARC), where two sources communicate to a destination assisted by a relay. However, unlike the microwave band, transmitters in the mm-wave band must employ highly directional antenna arrays to combat the ill effects of severe path-loss and small wavelength. The resulting mm-wave links are point-to-point and highly directional, and thus used to complement the microwave band by transmitting to a specific receiver. For such MARCs, the capacity is partially characterized for sources that are near the relay in a joint sense over both bands. We then study the impact of the mm-wave spectrum on the performance of such MARCs by characterizing the transmit power allocation scheme for phase faded mm-wave links that maximizes the sum-rate under a total power budget. The resulting scheme adapts the link transmission powers to channel conditions by transmitting in different modes , and all such modes and corresponding conditions are characterized. Finally, we study the properties of the optimal link powers and derive practical insights.

Multiple access relay channel: Achievable rates over orthogonal channels

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.

Performance analysis of multiple access relay channels for non-coherent modulations

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.

Transmission of Analog Information Over the Multiple Access Relay Channel Using Zero-Delay Non-Linear Mappings

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.

A Tutorial on Lossy Forwarding Cooperative Relaying

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.

Limited Feedback Assisted Dynamic Decode-and-Forward Relaying for Multiple Access Relay Channel

Feedback about the channel state information (CSI) enables the transmitter nodes to exploit channel conditions to yield large improvements in almost any performance metric. However, in practice, channel adaptive techniques based on full CSI have been deemed impractical due to the finite capacity of the feedback links. This work considers a multiple-access relay channel (MARC) where two source nodes communicate with one destination node assisted by one half-duplex dynamic decode-and forward (DDF) relay. Using the diversity-multiplexing tradeoff as a figure-of-merit, we propose a practical limited-feedback (LF) mechanism for MARC and show that a small number of information bits about the channel conditions leads to near optimal performance. With no CSI, this system incurs diversity-gain loss at higher multiplexing gains. However, by using an LF scheme where the destination sends an ACK or NACK to the relay, we show that the optimal diversity gain can be achieved across all the multiplexing gains for the considered DDF based MARC system.

Performance Analysis of Lossy Decode-and-Forward for Non-Orthogonal MARCs

Non-orthogonal transmission is considered to be one of the promising techniques for improving the throughput of the existing and future wireless communication networks. We concentrate on the transmission of both independent and correlated binary sources over a non-orthogonal multiple access relay channel (MARC), which consists of two sources, one relay, and one destination. The lossy decode-and-forward (DF), developed from the conventional DF, is adopted at the relay. Two time slots are required with non-orthogonal transmission over such network setup, while three time slots are required with the conventional orthogonal transmission. We analyze the outage probability of transmission of independent binary sources over the non-orthogonal MARC based on the theorem of multiple access channel (MAC) with a helper, which combines the Slepian-Wolf rate region and the MAC capacity region. For the performance verification, we implement a practical coding-decoding chain, which is applicable to the transmission of both independent and correlated binary sources. Exclusive-OR based multi-user complete decoding is introduced at the relay node, and iterative joint decoding is utilized at the destination by taking into consideration the estimated intra-link error probability and correlation information between the sources. The practical simulation results are well matched with the theoretical analyses.

Multiple Access Relay Channel With Relay-Sources Feedback

Feedback analysis on the rate region of multi-user channels is a problem of great importance in information and communication theory. In this paper, the Slepian-Wolf multiple access relay channel (SW-MARC) with relay-sources feedback is studied as a more general model of MARC where feedback outputs are taken into consideration. First, an inner bound on the capacity region of the discret alphabet and memoryless (DM) model of this channel (DM-SW-MARC) is obtained using partial decode and forward strategy. Second, an outer bound on the capacity region is derived by applying Fano’s inequality. Third, the DM results are extended to the continuous alphabet version, where an inner bound on the capacity region of the Gaussian MARC (GMARC) with relay-sources feedback is derived. Fourth, it is shown that our results include the important previous works on multiple-access channel with feedback (Cover-Leung rate region) and without feedback (Slepian-Wolf (SW) rate region, etc.) as special cases. Finally, we investigate the effect of feedback and show that the presence of feedback enables the sources to understand each other’s messages, which in turn allows the sources to cooperate to resolve the residual uncertainty at the receiver in an efficient way and at the same time, independent fresh information from the sources is superimposed upon the resolution information.

Joint Source-Channel Coding for Asymmetric Slepian-Wolf Multiple Access Relay Channel

This letter considers a code design for an asymmetric Slepian-Wolf multiple-access relay channel, in which the users and relay have different channel conditions. In this case, the conventional parity approach distributed source coding is no longer applicable. Hence, a new distributed joint source-channel superposition coding (DJSC-SC) is proposed. The proposed DJSC-SC matches the asymmetric channels, and makes full use of the good channel to obtain a better performance. Simulation results show that, compared with the conventional PA, the performance of the DJSC-SC scheme has a significant improvement and is within 1.4 dB from the capacity limit.

A novel scheme inspired by the compute-and-forward relaying strategy for the multiple access relay channel

This paper proposes a novel scheme for the slow block fading Gaussian multiple access relay channel inspired by the compute-and-forward (CoF) relaying strategy. The CoF relaying strategy exploits interference to obtain significantly higher rates between users in a network by decoding linear functions of the transmitted messages. Unlike other approaches in the literature, our approach is valid for any number of transmitters and, most importantly, it only requires channel state information at the receiver side, while it still attains similar or higher rates than the other approaches found in the literature.

Energy‐efficient communications over multiple access relay channels

SummaryRecently, due to the importance of green communications and power‐limited systems, energy efficiency in vehicular technologies has become a hot research topic. In this paper, we analyze energy‐efficient coding schemes in multiple access relay channels. First, the coding scheme in the multiple access relay channel is introduced. At the desired source rates, 3 optimal sets of resource allocation (the total power consumption, the relay power consumption, and the source power consumption) are given in the closed form. The analysis shows that the proposed energy‐efficient schemes achieve higher data rates and significantly outperform especially by reducing the relay energy consumption, which is useful for the shared relays. Moreover, the results allow a comprehensive description of the power consumption systems and give a detailed understanding of the desired message coding and the resource dedication for every desired sum rate.

Channel capacity of the distributed MIMO relay in visible light communication systems

Visible light communication (VLC) is a novel paradigm that uses light-emitting diode (LED) light as an information carrier and has several advantages over radio-frequency communication in terms of the bandwidth, security and multi-path fading. When the VLC system is considered in an indoor environment, LED lamps, which are placed at the ceiling to provide ambient light, can offer rich spatial resources for VLC as distributed intermediate relaying terminals. This paper introduces a novel distributed multiple-input multiple-output (D-MIMO)-relaying VLC scheme and analyzes its communication performance. Using the sum rate of the broadcasting and multiple access relay channels, a tight upper bound on the channel capacity was derived. The numerical results showed that the D-MIMO-relaying VLC scheme outperformed the direct-path-based scheme in terms of the channel capacity. For a given indoor environment, the capacity of D-MIMO-relaying VLC can be improved further by selecting the appropriate relay parameters, such as the number of LED–PD pairs in a relay, distance between relays and height of relays.

On Buffer-Aided Multiple-Access Relay Channel

The paper treats uplink scenario where M user equipments (UEs) send to a Base Station (BS), possibly via a common Relay Station (RS) that is equipped with a buffer. This is a multiple-access relay channel (MARC) aided by a buffer. We devise a protocol in which the transmission mode is selected adaptively, using the buffer at the RS in order to maximize the average system throughput. We consider the general case in which the RS and the BS can have limits on the maximal number of transmitters that can be received over the multiple access channel. In each slot there are three type possible actions: (A1) multiple UEs transmit at rates that enable BS to decode them (A2) multiple UEs transmit, the BS can only decode the messages partially, while the RS completely; (A3) RS forwards the side information to BS about the partially decoded messages, which are going to be combined and decoded entirely at the BS, while simultaneously a number of UEs sends new messages to the BS. The results show that the adaptive selection of direct and buffer-aided relay transmissions leads to significant average throughput gains.

다중 접속 릴레이 채널에서 비대칭 데이터 전송을 위한 계층 변조 및 네트워크 코딩 결합 기법

다중 접속 릴레이 채널에서 비대칭 데이터 전송을 위한 계층 변조 및 네트워크 코딩 결합 기법