Channel reliability metric for Nakagami-m fading without channel state information

An exact channel reliability metric for Nakagami-m fading when no channel state information (CSI) is available at the receiver is developed. The proposed metric is suitable for combination with iterative decoding schemes to ensure optimum performance. A low complexity cubic approximation to the exact metric, which offers almost identical performance and significantly outperforms the conventional linear approximation, is presented. The numerical results obtained using a single parity check (SPC) block turbo code (BTC), show that the conventional linear approach can result in up to a 27.5 dB penalty at BER of 10^-5, compared to the case where perfect CSI is available. On the other hand, the use of the proposed exact reliability metric results in only a 1.1 dB performance loss at the same BER