Fast forced symbol method for distributed space-time turbo codes using complex orthogonal design

The idea of Distributed Space-Time Codes (DSTCs) was proposed to achieve spatial and temporal diversity without having channel information at the relays in wireless networks. In that scheme, distributive relays cooperate with each other to generate a Space-Time Code (STC) at the receiver. However, DSTCs have poor error rate performances at low signal to noise ratios (SNRs) that may disqualify them from being used in next generation mobile communications systems. To overcome this issue, this paper proposes a novel scheme based on the joint use of DSTCs and turbo codes, which we call “Distributed Space-Time Turbo Codes (DST-TCs)”. We also propose a Fast Forced Symbol Method (FFSM) which significantly improves the coding gain of the proposed DST-TCs. The FFSM is based on repeated decoding operations and does not require any significant change in the design of encoder and decoder of DST-TC. The FFSM provides 0.9 dB of coding gain over simple DST-TC at frame error rate (FER) of 10^-5.