Diversity selection combining to enhance the coding gain

Traditional diversity selection combining techniques are designed to minimize the probability of hard decision error (symbol-by-symbol) prior to channel decoding. When the diversity selection combining technique is employed in conjunction with the channel decoding, the traditional diversity selection combining technique does not necessarily minimize the post-decoding error probability because the decoder takes the soft decision of several different symbols in making a decision on a particular symbol. In this paper, we propose diversity combining techniques based on the log-likelihood ratio (LLR) that provide a higher coding gain than the traditional SNR- or LLR-based combining technique does. Simulation results are provided for the turbo and low-density parity-check (LDPC) codes in Rayleigh flat fading channels.