Implementation of pilot symbol assisted rateless codes to mitigate fading in Rayleigh fading channels

摘要

The principal design problem encountered in wireless communications is how to overcome the distortion of received signals by a time-varying and frequency-selective propagation path due to the phenomenon called fading. In this paper, a channel coding method referred as pilot symbol assisted rateless coding (PSAR) is considered to mitigate the effects of fading; where a predetermined fraction of binary pilot symbols are interspersed with the channel-coded bits at the channel coding stage instead of multiplexing the pilots with the data symbols at the modulation stage, as in classic pilot symbol assisted modulation (PSAM). PSAR codes are a specific family of rateless codes that are capable of modifying their code-rate as well as their degree distribution based on the channel state information (CSI), in an attempt to adapt to the time-varying nature of the channel. The performance of pilot symbol assisted code aided system is measured in Raleigh fading channels with the help of two parameters, bit error rate (BER) and latency. Compared with theoretical BER results, PSAM and a fixed rate (7, 4) cyclic code, the introduced PSAR codes are beneficial in terms of significantly reducing the fading effects. The results also suggest that a significant reduction in the BER can be attained by PSAR coding system, when compared to the PSAM scheme having the same pilot overhead.