In Code Division Multiple Access (CDMA) systems forward error correction (FEC) is an
important factor in improving system perfonnance. Because of the multiple access
interference observed in asynchronous CDMA, FEC is required to improve system
capacity. Several alternative coding techniques are available, including "trellis codes"
specifically designed for CDMA, very low rate convolutional codes and conventional
convolutional codes.
An analytic approach is developed to compare the perfonnance of different coding
techniques for CDMA on the same basis by extending several improved analysis
techniques which were developed for uncoded CDMA. Analytic results are presented for
additive white Gaussian noise (AWGN) channels and frequency non-selective Rician
Fading (FNRF) channels. The perfonnance of coded CDMA systems in frequency
selective Rayleigh fading channels is also analyzed using simulation techniques.
Both analytic and simulation results show that by using trellis codes or very low rate
convolutional codes significant perfonnance improvement is achieved over conventional
convolutional codes. Trellis codes outperfonn very low rate convolutional codes in
AWGN and FNRF channels while both codes show similar perfonnance in frequency
selective Rayleigh fading channels.
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