Parallel Relay Network Research Articles

On the Symbol Error Probability of Multihop Parallel Relay Networks

In this paper we analyze the symbol error probability (SEP) of a cooperative multihop parallel relay network in Rayleigh fading channels for M-ary Phase-shift keying (M-PSK) modulation. The general closed form expression of the SEP is derived. We present numerical results on the performance of the network.

A Novel Soft Forwarding Technique for Memoryless Relay Channels Based on Symbol-Wise Mutual Information

In this letter, we propose a mutual information based soft forwarding scheme for memoryless parallel relay networks. The relay forwarding function of the proposed scheme consists of the hard decisions of the symbol estimates and a reliability measure. The reliability measure is determined by the symbol-wise mutual information computed from the absolute value of the log-likelihood ratio at the relay. The superiority of the proposed scheme to the existing relay forwarding schemes is demonstrated through bit error rate performance and average mutual information at the destination. Simulation results show that for a parallel relay network with two relay nodes and BPSK modulation, the proposed mutual information based soft forwarding scheme yields signal-to-noise ratio gains of about 0.5-1 dB compared to various existing memoryless relay forwarding schemes.

The Effect of Noise Correlation in Amplify-and-Forward Relay Networks

In wireless relay networks, noise at the relays can be correlated possibly due to common interference or noise propagation from preceding hops. A parallel relay network with noise correlation is considered in this network. For the relay strategy of amplify and forward (AF), the optimal rate maximizing relay gains when correlation knowledge is available at the relays are determined. Interestingly, it is shown that, on average, noise correlation is beneficial regardless of whether the relays know the noise covariance matrix. However, the knowledge of correlation can greatly improve the performance. Typically, the performance improvement from correlation knowledge increases with the relay power and the number of relays. With perfect correlation knowledge the system is capable of canceling interference if the number of interferers is less than the number of relays. For a two-hop multiple-access parallel network, closed-form expressions for the maximum sum rate and the optimal relay strategy are determined. Relay optimization for networks with three hops is also considered. Based on the result of two-hop network with noise correlation, an iterative algorithm is proposed for solving the relay optimization problem for three-hop networks.

Flow optimization in parallel relay networks with cooperative relaying

We investigate the relaying problem in parallel relay networks consisting of a source sending information to a destination via multiple relays. To exploit the broadcasting nature of the wireless channel, the source broadcasts to the relays and the relays forward the decoded information to the destination. The flow rates on all links in the network are selected to minimize the average transmit power required. We consider two optimal protocols, respectively in which the relays forward the decoded information phase-synchronously and phase-asynchronously. It turns out that not all relays forward information in the optimal phase-asynchronous protocol. Using this fact, we propose a sub-optimal protocol employing at most two relays. In phase-synchronous relaying, the optimal protocol gives around 1dB and over 3 dB improvements compared at the outage probability of 10-4 with respect to the single-relay optimal protocol at low-rate and high-rate requirements, respectively. Again, we propose a two-relay sub-optimal protocol for phase-synchronous transmission. Simulation results indicate that these sub-optimal protocols give performances that are close to the performances of the optimal protocols and superior to that of the single-relay optimal protocol.

Distributed power allocation strategies for parallel relay networks

We consider a source-destination pair assisted by parallel regenerative decode-and-forward relays operating in orthogonal channels. We investigate distributed power allocation strategies for this system with limited channel state information at the source and the relay nodes. We first propose a distributed decision mechanism for each relay to individually make its decision on whether to forward the source data. The decision mechanism calls for each relay that is able to decode the information from the source to compare its relay-to-destination channel gain with a given threshold. We identify the optimum distributed power allocation strategy that minimizes the total transmit power while providing a target signal-to-noise ratio at the destination with a target outage probability. The strategy dictates the optimum choices for the source power as well as the threshold value at the relays. Next, we consider two simpler distributed power allocation strategies, namely the passive source model where the source power and the relay threshold are fixed, and the single relay model where only one relay is allowed to forward the source data. These models are motivated by limitations on the available channel state information as well as ease of implementation as compared to the optimum distributed strategy. Simulation results are presented to demonstrate the performance of the proposed distributed power allocation schemes. Specifically, we observe significant power savings with proposed methods as compared to random relay selection.

Throughput Optimal Control of Cooperative Relay Networks

In cooperative relaying, multiple nodes cooperate to forward a packet within a network. To date, such schemes have been primarily investigated at the physical layer with the focus on communication of a single end-to-end flow. This paper considers cooperative relay networks with multiple stochastically varying flows, which may be queued within the network. Throughput optimal network control policies are studied that take into account queue dynamics to jointly optimize routing, scheduling and resource allocation. To this end, a generalization of the maximum differential backlog algorithm is given, which takes into account the cooperative gains in the network. Several structural characteristics of this policy are discussed for the special case of parallel relay networks.