Cooperative diversity using message passing in wireless sensor networks

Cooperative diversity schemes have been introduced in earlier works to achieve diversity in a block fading channel. However, most of these schemes ignore the quality of the source-relay (S-R) channel in the decoding process, even though it is this channel that limits the performance of cooperation schemes. This paper introduces a simple yet robust scheme for cooperative diversity based on message passing in the decoding process, which accounts for the quality of the S-R channel. In our scheme, the relay decodes the source symbols and forms parity bits, which are in turn used by the destination (D) to decode the source message. By accounting for the reliability of the parity bits, performance measures, such as bit error rate, are not limited by the S-R channel quality and improve with increasing signal-to-noise ratio on the S-D and R-D channels. With our scheme, feedback signals to the source node are not required, with only simple decoding and encoding required at the relay.