Combined turbo-code and modulation for CDMA wireless communications

This paper investigates a system of combined turbo-code and M-ary orthogonal signaling for CDMA wireless communications. The performance of the system is studied over an AWGN channel with coherent and noncoherent detection for short frame lengths, with emphasis on the effect of noise correlation between the coded bits. It is shown that eliminating this correlation is important in improving the transmission performance of the system. When a 64-Hadamard signaling is employed, the performance of the system is improved by approximately 0.8 dB at a signal-to-noise ratio (SNR) per information bit of 4 dB, and the improvement increases as the SNR increases. It is also shown that for the bit error rate (BER) of interest in voice communication systems, 8-Hadamard mapping performs almost as well as 64-Hadamard mapping, with less complexity and delay.