Performance analysis of the reliability based direct decoding algorithm for Turbo codes with QPSK modulation and different interleavers

Achieving ultra reliable and low latency communication with short length information blocks has been an open research problem in the recent years. The bit error rate performance of turbo codes deteriorates when compared with the convolutional codes for short block lengths. This constrains the usage of turbo codes for short block length communication applications. A reliability based direct soft decision decoding algorithm for short block length turbo codes with improved performance has been proposed and developed recently. The new algorithm uses the actual reliability of the bits as probability density values. This together with a check equation that characterises the turbo encoder, processes the decoding through levels. The proposed decoding algorithm has shown significant BER performance improvement and varying time complexity with channel conditions. As an extension to the previous work, performance analysis of the proposed algorithm with QPSK modulation and different interleavers to provide a generalization of the algorithm has been presented in this paper. Detailed simulation has been performed to examine the decoding algorithm’s performance with QPSK modulation and different interleavers. Simulation results show that the decoding algorithm has improved BER and time complexity performance with QPSK modulation when compared to log-MAP based turbo decoder. This performance holds good with different interleaving patterns also.