The Role of Coding in CDMA Systems With Multiuser Detection

In a direct sequence code division multiple access (CDMA) system, a fixed bandwidth expansion could be allocated to either error correcting coding or modulation signal spreading. The role of coding in CDMA systems that employ multiuser detection is explored here. A comparison is made between the maximum throughputs (in bits/chip or bits/s/Hz) achievable using multiuser detection and singleuser detection, for both "single-cell" and cellular systems. For the single-cell scenario, our results indicate that asynchronous multiuser detection systems employing long (random) spreading sequences and low rate coding, can provide considerable improvements in spectral efficiency over singleuser detection systems. However, for cellular systems with universal frequency reuse, the improvement is spectral efficiency (per cell) offered by multiuser detection may not be as significant. I INTRODUCTION In code-division multiple-access (CDMA) systems, redundancy via bandwidth expansion is used to counter..