The coding-Spreading Tradeoff Problem in Finite-Sized Synchronous DS-CDMA Systems

This dissertation provides a comprehensive analysis of the coding-spreading tradeoff problem in finite-sized synchronous direct-sequence code-division multipleaccess (DS-CDMA) systems. In contrast to the large system which has a large number of users, the finite-sized system refers to a system with a small number of users. Much work has been performed in the past on the analysis of the spectral efficiency of synchronous DS-CDMA systems and the associated coding-spreading tradeoff problem. However, most of the analysis is based on the large-system assumptions. In this dissertation, we focused on finite-sized systems with the help of numerical methods and Monte-Carlo simulations. Binary-input achievable information rates for finite-sized synchronous DS-CDMA systems with different detection/decoding schemes on additive white Gaussian noise (AWGN) channel are numerically calculated for various coding/spreading apportionments. We use these results to determine the existence and value of an optimal code rate for a number of different multiuser receivers, where optimality is in the sense of minimizing the SNR required for reliable multiuser communication. Our results are consistent with the well-known fact that all coding (no spreading) is optimal for the maximum a posteriori (MAP) receiver.