Orthogonal Multiple-access Relay Channel Research Articles

Outage Probabilities of Orthogonal Multiple-Access Relaying Techniques With Imperfect Source-Relay Links

An outage probability that is independent of signaling schemes is theoretically derived in this paper for an orthogonal multiple-access relay channel (MARC) system, where the estimates of the information sequences sent from source nodes, regardless of whether or not they are correctly decoded at the relay, are exclusive-OR (XOR)-network-coded and forwarded by the relay to the destination. The MARC system described above is referred to as estimates-exploiting MARC (e-MARC) in this paper for convenience. Following the probability derivation of e-MARC, comparisons are then made with the outage probability of the orthogonal MARC with the Select Decode-and-Forward relaying strategy (MARC-SDF). It is found through simulations that when one of the source nodes is far away from both the relay and the destination, the e-MARC system is superior to MARC-SDF in terms of outage performance. We further numerically calculate the outage probabilities for two special cases, and compare them with the probability of e-MARC. Furthermore, the impact of the source correlation on the outage probability of the e-MARC system is also investigated.

Joint Adaptive Network–Channel Coding for Energy-Efficient Multiple-Access Relaying

An energy-efficient orthogonal multiple-access relay channel (MARC) system is developed, where accumulator and differential detection (DD) are used at the source and relay nodes, respectively. However, the weak decoding capability of DD degrades the frame error rate (FER) performance of the orthogonal MARC system if the conventional decode-and-forward relaying strategy is applied. In this paper, a novel joint adaptive network-channel coding (JANCC) technique is proposed to support DD by making efficient use of the erroneous estimates output from DD. In the JANCC technique, the destination constructs a vector identifying the indexes of the source nodes whose information parts contain errors and sends it to the relay to request a retransmission. The relay performs network coding by taking the exclusive-or (xor)-operation only over the stored estimates specified by the identifier vector, which aims to avoid unnecessary erroneous estimates being coded. In addition, a bit-flipping probability p <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nc</sub> is obtained between the two sequences; one is the network-coded sequence sent from the relay, and the other is their corresponding xor-ed information sequence. The decoding algorithm of JANCC exploits probability p <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nc</sub> at the destination to update the log-likelihood ratio during the iterative decoding process. Hence, the information sequences received at the destination are able to be recovered, although the redundancy forwarded from the relay is generated from the erroneous estimates. Compared with the system where iterative decoding is performed at the relay, the utilization of DD significantly reduces the computational complexity, which leads to meaningful power savings with only a small loss in FER performance.

Correlated Sources Transmission in Orthogonal Multiple Access Relay Channel: Theoretical Analysis and Performance Evaluation

In this paper, we consider the problem of transmitting two correlated binary sources over orthogonal multiple access relay channel (MARC), where two sources are communicating with a common destination with the assistance of a single relay. We assume decode-and-forward relaying strategy, and bit-wise exclusive or (XOR) network coding is performed at the relay node. First, a joint source-channel-network (JSCN) decoding technique is proposed to fully exploit the correlation between the sources, as well as the benefit of network coding. Then the achievable compression rate region of this system is derived based on the theorem for source coding with side information. It is found that the region is a 3-dimensional space surrounded by a polyhedron. Furthermore, the performance limit in Additive White Gaussian Noise (AWGN) channels and the outage probability in block Rayleigh fading channels are derived based on the achievable compression rate region. It is shown that the outage probability can be expressed by a set of triple integrals over the achievable compression rate region. The impact of source correlation on the performance of the system is investigated through asymptotic tendency analysis. The effectiveness of the proposed JSCN decoding technique and the accuracy of the theoretical analysis have been verified through a series of computer simulations, assuming practical channel codes. It is also shown that, as long as the source-relay links are perfect, the 2nd order diversity is always achieved with our proposed technique regardless of the strength of the source correlation.

The Capacity of Gaussian Orthogonal Multiple-Access Relay Channel

This paper is concerned with the capacity of Gaussian orthogonal multi-access relay channel (OMARC) where multiple sources communicate with one destination in the presence of one relay. The achievability proof and converse for the capacity of Gaussian OMARC are given by e-entropy-typical sequences and cut-set upper bound, respectively. The capacity of Gaussian OMARC is shown to have a max-flow min-cut interpretation.

Network Code Design for Orthogonal Two-Hop Network with Broadcasting Relay: A Joint Source-Channel-Network Coding Approach

This paper addresses network code design for robust transmission of sources over an orthogonal two-hop wireless network with a broadcasting relay. The network consists of multiple sources and destinations in which each destination, benefiting the relay signal, intends to decode a subset of the sources. Two special instances of this network are orthogonal broadcast relay channel and the orthogonal multiple access relay channel. The focus is on complexity constrained scenarios, e.g., for wireless sensor networks, where channel coding is practically imperfect. Taking a source-channel and network coding approach, we design the network code (mapping) at the relay such that the average reconstruction distortion at the destinations is minimized. To this end, by decomposing the distortion into its components, an efficient design algorithm is proposed. The resulting network code is nonlinear and substantially outperforms the best performing linear network code. A motivating formulation of a family of structured nonlinear network codes is also presented. Numerical results and comparison with linear network coding at the relay and the corresponding distortion-power bound demonstrate the effectiveness of the proposed schemes and a promising research direction.