A new amplify and forward relay based OFDM cooperative communication system

Abstract

In this paper, we present a new amplify and forward (AF) based orthogonal frequency division multiplexing (OFDM) cooperative system with 2 relays. Most of the cooperative systems use distributed space time coding (DSTC) for achieving cooperative diversity, which results in rate-loss. The proposed system achieves full rate and full diversity by utilizing the existing signal space diversity technique. Protocols with round robin relaying do not consider the communication link between the relays, whereas the proposed protocol forgoes such assumption. Further we describe the preamble and header forwarding technique at the relays. The preamble forwarding technique aims at reducing the complexity of channel estimation at the destination. The header forwarding technique is intended to aid the destination in retrieving the operating time slot information. The impact of carrier frequency offset (CFO) on the cooperative system at destination is also addressed. Maximum a posteriori probability (MAP) based multiple input and multiple output (MIMO) detection is used at the destination. Pairwise error probability (PEP) analysis shows that the proposed system achieves 3 ^rd order diversity. The proposed system provides a gain of 18 dB for uncoded scenario and 4 dB with 1/2 rate convolutional code at a bit error rate (BER) of 10 ^-5 , compared with the non-cooperative system under frequency selective Rayleigh channel conditions and in the presence of carrier frequency offsets.