Performance of low-rate orthogonal convolutional codes in DS-CDMA applications

Low-rate orthogonal convolutional codes (LROCC), originally proposed by A.J. Viterbi (1971), can be used in a direct-sequence code-division multiple access (DS-CDMA) system to achieve both spreading of the data and providing coding gain. The implementation of this type of multiplexing in a practical DS-CDMA system is presented, and the theoretical performance of the proposed system under "other-user" noise, additive white Gaussian noise (AWGN), intercell interference, and thermal noise is established using a computer simulation. The improvement in system performance, gained through the use of a nonspreading randomizing sequence on the encoded output symbols, is also studied. Performance curves for a rate 1/64 orthogonal convolutional code are shown, and the impact of code rate, quantization methods, and constraint length on the overall system performance are discussed.