A Pre-BSC Model for Distributed Turbo Codes

A model that effectively captures the relay decoding error is proposed for a distributed turbo code (DTC) over a cooperative relay channel. The model consists of a memoryless binary symmetric channel (BSC) placed before the relay encoder, hence called pre-BSC. Accordingly the required iterative decoder is derived that consists of an extra update function to be applied on extrinsic information before their exchange. The derived update function is in form of a smooth clipping and therefore the overall decoder is called clipped iterative decoder (clipped ED). Clipped ID is robust to the relay decoding error and is able to significantly improve the final performance, especially when source-to-relay link becomes erroneous.