Comparative evaluation of CDMA and FD-TDMA cellular system capacities with respect to radio link capacity

This paper presents a comparative evaluation of code-division-multiple access (CDMA) and frequency-division time-division-multiple-access (FD-TDMA) system capacities as a function of the radio link capacity (i.e. Shannon bound). This bound is first evaluated over time-varying frequency-selective fading channels by treating this information theoretic value of the capacity as a random variable. The total system sum-of-rates capacity is then evaluated for both multiple-access schemes using a multi-cell simulator and the 99% reliability level of the radio link capacity. System capacity is compared as a function of the number of cells per cluster and the use of power control in the FD-TDMA system, the spreading gain in the CDMA system, the receiver space diversity level, the number of channel multipath components as well as large-scale propagation parameters such as the shadowing standard deviation and the path-loss exponent. According to this methodology, it is observed that CDMA system capacity can be but is not always superior to FD-TDMA capacity. The spectral efficiency advantage (in terms of capacity per unit bandwidth) of CDMA over FD-TDMA systems is however much larger for larger spreading gains.