Polyphase signature sequences for DS/CDMA systems

Abstract

In this dissertation, we propose four classes of multi-valued signature sequences and consider their applications to the performance improvement of the direct sequence code division multiple access (DS/CDMA) systems. We propose a class of polyphase sequences which can be generated using a simple index calculation with the points equally spaced on the unit circle in the complex plane. We examine the correlation properties of the proposed sequence: the magnitudes of the even crosscorrelation function are always zero and the magnitudes of the odd crosscorrelation function are smaller than those of the other sequences with high probability. The performance of the proposed sequence in DS/CDMA systems is investigated and shown to be better than that of other sequences for asynchronous additive white Gaussian noise channel environment with and without Rayleigh multipath fading. We then propose three classes of multi-valued signature sequences. The pro-posed classes are obtained based on the perfect reconstruction quadrature mirror filter (PR-QMF) banks. The first class has perfect correlation properties when the number of users is two in the DS/CDMA system. To accommodate more users in the DS/CDMA system, the second and third classes of signature sequences are proposed based on the multi-band PR-QMF banks. The second and third classes have perfect correlation properties when used in synchronous DS/CDMA systems. In addition, the third class in general has better correlation properties compared to other well-known sequences when used in asynchronous DS/CDMA systems. Some numerical results for the performance of the DS/CDMA systems with several sequences including the third class of sequences are obtained.