Distributed Turbo Coding Schemes for Receive Diversity: A Modified Matched S-Random Interleaver for Half-Duplex Wireless Relay Channels

Abstract

It is known that one of the essential building blocks of distributed turbo codes is the interleaver and its design uses random, semi-random (S-Random) and deterministic permutations. In this paper, a new modified matched S-random interleaver for turbo code is proposed. Then we extend the effect of this new interleaver to the relay channel to evaluate the interleaving gain in two different distributed turbo-coding schemes: distributed turbo codes and distributed multiple turbo codes for half-duplex relay system. For these schemes with half- duplex constraint, the source node transmits its information with the parity bit sequence(s) to both the relay and the destination nodes during the first phase. The relay receives the data from the source and processes it by using decode and forward protocol. For the second transmission period, the decoded systematic data at relay is interleaved and re-encoded by a recursive systematic convolutional encoder and forwarded to the destination. At destination node, the signals which are received from the source and relay nodes are processed by using turbo log-MAP iterative decoding for retrieving the original information bits. We demonstrate via simulations that the new interleaving gain has a large effect with distributed turbo coding scheme when we use only one recursive systematic convolutional encoder at both the source and relay. Index Terms—Distributed turbo codes, interleaver, semi- random, relay channel