Cooperative Relay Channel Research Articles

Positioning of a Wireless Relay Node for Useful Cooperative Communication

<span>Given the exorbitant amount of data transmitted and the increasing demand for data connectivity in the 21st century, it has become imperative to search for pro-active and sustainable solutions to the effectively alleviate the overwhelming burden imposed on wireless networks. In this study a Decode and Forward cooperative relay channel is analyzed, with the employment of Maximal Ratio Combining at the destination node as the method of offering diversity combining. The system framework used is based on a three-node relay channel with a source node, relay node and a destination node. A model for the wireless communications channel is formulated in order for simulation to be carried out to investigate the impact on performance of relaying on a node placed at the edge of cell. Firstly, an AWGN channel is used before the effect of Rayleigh fading is taken into consideration. Result shows that performance of cooperative relaying performance is always superior or similar to conventional relaying. Additionally, relaying is beneficial when the relay is placed closer to the receiver. </span>

An Efficient Procedure for Bilayer-Expurgated LDPC Codes Design in Cooperative Relay Channels

This letter proposes a fast optimization procedure to design bilayer-expurgated low density parity check codes in the relay channel. The code optimization problem aims to maximize the code rate while guaranteeing the convergence of the density evolution relations in upper and lower layer codes. The original problem is linear programming. Nevertheless, it suffers from high computational complexity, as it is semi-infinite programming (SIP) in a 2-D continuous interval. To efficiently solve it, we first approximate the density evolutions by polynomials. Then, leveraging optimization problems over the solution of sum of square multivariate polynomials the problem is transformed to semi-definite programming (SDP), where the global solution can be found efficiently using available SDP solvers. Our simulation shows that our approach results in significantly lower computational complexity with respect to the well-known method of quantization for solving the SIP problem, while both achieve the same performance.

Linear Multi-hop Amplify-and-Forward (AF) Cooperative Relay Channels

Cooperative relaying of channels between base station and user equipment emerged as a great technique to enhance the reliability and throughput of cellular networks. The relay nodes normally exploit amplify-and-forward (AF) scheme to relay the connection. Although there have been many previous works on cooperative issues, none of them have considered the fundamental trade-off between the communication reliability and transmission rate. Instead of considering the performance evaluated separately on the achievable rate or the error probability, the RCEE provide insight into fundamental trade-off between the transmission rate and the communication reliability in cooperative relay channels. It has been shown that multi-hop relay nodes are necessary to compensate the decreasing SNR over the distance. As a trade-off, the communication reliability in terms of RCEE is decreasing over the increase of multi-hop relay nodes with low SNR for a given data rate. Therefore, the optimization for the number of hops is preferable in the cooperative relay channels.Cooperative relaying of channels between base station and user equipment emerged as a great technique to enhance the reliability and throughput of cellular networks. The relay nodes normally exploit amplify-and-forward (AF) scheme to relay the connection. Although there have been many previous works on cooperative issues, none of them have considered the fundamental trade-off between the communication reliability and transmission rate. Instead of considering the performance evaluated separately on the achievable rate or the error probability, the RCEE provide insight into fundamental trade-off between the transmission rate and the communication reliability in cooperative relay channels. It has been shown that multi-hop relay nodes are necessary to compensate the decreasing SNR over the distance. As a trade-off, the communication reliability in terms of RCEE is decreasing over the increase of multi-hop relay nodes with low SNR for a given data rate. Therefore, the optimization for the number of hops is preferable in the cooperative relay channels.

철도 무선통신내에서 협력전송기법의 응용

In recent years, according to improvement of various vehicle instruments, railway also has been developed in various fields. As a result, to transmit accurate information to each railway system, the efficient communication system is required. In railway communication system, mitigation of wireless fading is very important. So, in this paper we introduced the cooperative relay channel model and cooperative relay scheme. Also we analyzed and simulated the cooperative relay scheme which is suitable for railway communication systems.

Generalized Sequential Slotted Amplify and Forward Strategy in Cooperative Communications

This paper proposes a generalized sequential slotted amplify and forward (GSSAF) strategy for single-antenna wireless cooperative networks. The diversity and multiplexing tradeoff (DMT) is analyzed. Applications to cooperative multiple relay channels, cooperative broadcast channels (CBC) and cooperative multiple access channels are considered and the DMT upper bound is proven to be achievable for each case. Other than proposing the best known near-optimal strategy for CBC, another important contribution is to show that GSSAF can be used as a unified strategy to achieve DMT optimality in wireless cooperative networks with unit multiplexing gains.

Power and Channel Allocation for Cooperative Relay in Cognitive Radio Networks

In this paper, we investigate power and channel allocation for cooperative relay in a three-node cognitive radio network. Different from conventional cooperative relay channels, cognitive radio relay channels can be divided into three categories: direct, dual-hop, and relay channels, which provide three types of parallel end-to-end transmission. In the context, those spectrum bands available at all three nodes may either perform relay diversity transmission or assist the transmission in direct or dual-hop channels. On the other hand, the relay node involves both dual-hop and relay diversity transmission. In this paper, we develop power and channel allocation approaches for cooperative relay in cognitive radio networks that can significantly improve the overall end-to-end throughput. We further develop a low complexity approach that can obtain most of the benefits from power and channel allocation with minor performance loss.

Maximum likelihood detection with arbitrary modulations in cooperative relay channels

This paper proposes a simple combining technique with arbitrary modulations for a cooperative relay scheme based on a detect-and-forward relay protocol. Here we present maximum likelihood criterion detection at the destination which considers individual symbol error rate to facilitate the detection in noisy relay networks. In particular, our proposed algorithm is flexible to signals with different modulation formats as detection is done on a symbol-by-symbol basis. If different modulations are used at the source and the relays, we propose that lower modulation constellation is used at the source. By computer simulations, the results show that significant packet error rate performance can be achieved by the proposed scheme and we compare it against cooperative-maximum ratio combining and selection combining.

Throughput-reliability tradeoff in decode-and-forward cooperative relay channels: A network information theory approach

Cooperative transmission protocols are always designed to achieve the largest diversity gain and the network capacity simultaneously. The concept of diversity-multiplexing tradeoff (DMT) in multiple input multiple output (MIMO) systems has been extended to this field. However, DMT constrains a better understanding of the asymptotic interplay between transmission rate, outage probability (OP) and signal-to-noise ratio. Another formulation called the throughput-reliability tradeoff (TRT) was then proposed to avoid such a limitation. By this new rule, Azarian and Gamal well elucidated the asymptotic trends exhibited by the OP curves in block-fading MIMO channels. Meanwhile they doubted whether the new rule can be used in more general channels and protocols. In this paper, we will prove that it does hold true in decode-and-forward cooperative protocols. We deduce the theoretic OP curves predicted by TRT and demonstrate by simulations that the OP curves will asymptotically overlap with the theoretic curves predicted by TRT.

Differential Modulation With Threshold-Based Decision Combining for Cooperative Communications

Differential modulation is widely known as a practical alternative that provides a good tradeoff between receiver complexity and performance. However, the available differential schemes for wireless relay networks require perfect synchronization and/or provide limited transmission rates. This paper proposes a threshold-based differential decode-and-forward cooperative scheme that not only alleviates the problems of synchronization and rate limitation, but also efficiently exploits the cooperative relay channels via the use of a predetermined decision threshold. In the proposed scheme, the source information is forwarded by the relay only if it is correctly decoded. The properly designed threshold enables the destination to decide whether the received signal from the relay contains information such that the received signals from the source and the relay can be efficiently combined and jointly decoded. Bit error rate (BER) performance analysis of the proposed scheme is analyzed in the case of differential M-ary PSK signals. The analysis focuses on the case when the relay is able to judge whether each decoded symbol is corrected or not. The obtained BER performance in this case serves as a performance benchmark, and the proposed differential decode-and-forward scheme can achieve it in an ideal situation that the error propagation at the relay can be negligible. A tight BER approximation is first derived, and then BER upper bound and lower bound are determined. Based on the tight BER approximation, joint optimum decision threshold and power allocation are numerically evaluated. Both analytical and simulation results reveal that the decision threshold and the power allocation depend on qualities of the communication channels. Interestingly, when the link quality between relay and destination is very good, the effect of the threshold dominates the effect of the power allocation at high signal-to-noise ratio. Extensive simulation results are provided to validate the merit of the proposed scheme and confirm the theoretical analysis.