Impact of reporting-channel coding on the performance of distributed sequential sensing

This paper compares the impact of using an error detection code and an error correction code for cooperative sequential sensing in cognitive radios. The analyzed system model is a distributed parallel detection network in which each secondary user (SU) sends a soft decision in the form of quantized local log-likelihood ratio (LLR) to the fusion center (FC), which makes the final decision in a sequential manner. At each SU, the quantized LLRs are converted to bits using Gray mapping. These bits are then channel coded and transmitted using binary phase shift keying (BPSK) to the FC. The reporting-channels between the SUs and the FC may cause errors in the decision statistics. In case of an error detecting code, the decision statistics detected in error are dropped while in case of an error correcting code, the decision statistics are used anyway. The performances of these two schemes are also compared to the case where no channel coding is used. It is shown that even a simple error correcting code gives huge improvement in the performance of sequential sensing while error detecting code may even perform worse than the case where no channel coding scheme is used.