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 single-user 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 single-user 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.