Alamouti-coded decode-and-forward protocol with optimum relay selection and power allocation for cooperative communications

Wanakorn Swasdio,Gerd Ascheid,Somchai Jitapunkul,Chaiyod Pirak

doi:10.1186/1687-1499-2014-112

Abstract

Abstract In this paper, an Alamouti-coded decode-and-forward protocol with optimum relay selection for three-user one destination cooperative communications is investigated. Particularly, we design the new protocol that allows the source node retransmitting the signal to the destination node at the same time as the relay node forwarding the received signal to the destination node with an Alamouti coding scheme. We exploit the cooperative maximum ratio combining technique (C-MRC) at the destination for combining a multiple copy of received signals. Therefore, the proposed scheme achieves the maximum diversity gain and lower probability of error in comparison with the existing decode and forward protocol. We also analyze a symbol error rate (SER) upper bound of the single relay system, and exploit a result of this analysis to select the optimum relay in a multiple-relay cooperation scheme based on the minimum SER selection strategy. Moreover, the optimum power allocation for the proposed protocol is derived, and it is able to provide the optimum transmission power strategy to the source and the relay nodes in order to achieve the minimum probability of error. In the performance analysis, the theoretical error probability is studied and compared with the simulation results. Simulation results indicate that the proposed protocol significantly outperforms the existing protocols, and the theoretical error probability curve is relatively close to the simulated SER curve.

Highlights

In the future multimedia communications, broadband wireless communications will play a major role in personal voice and data communications that support fixed, nomadic, portable, and mobile accesses
The results show that the diversity factor depends on the number of relays, and a 10-dB signal-to-noise ratio (SNR) improvement compared with the single relay system is achieved
We introduce a weighting factor w in phase 2 based on a concept of cooperative maximum ratio combining (C-maximum ratio combining (MRC)) signal combining, yd1 in which w = γeq/γrd, where γeq = min, and γsr and γrd are the instantaneous SNR between the source-to-relay link and the relayto-destination link, respectively

Summary

Introduction

In the future multimedia communications, broadband wireless communications will play a major role in personal voice and data communications that support fixed, nomadic, portable, and mobile accesses. Referring to the existing Alamouti-based decode-andforward protocol in [3], it is obvious that the degree-offreedom of the system, i.e., a possible opportunity of signal transmission in all available time slots, is not fully used Such system performance could be enhanced by the cooperative maximum ratio combining (C-MRC) technique, and the bandwidth efficiency could be increased by using the optimum relay selection technique. We analyze a symbol error rate upper-bound for the Alamouti-coded decode-and-forward protocol with the C-MRC signal combining, and evaluate the analysis results by comparing with the simulation results. Based on this analysis, we can select the optimum relay that provides the lower probability of error for cooperative communications.

System and received signal models

D: Receive S1 from S D

Performance analysis

The optimum power allocation

Conclusion