On the bandwidth efficiency of CDMA systems

Compares the bandwidth efficiency of microcellular CDMA wireless access systems with bandwidths of 1.25 to 10 MHz. The authors define the bandwidth efficiency as the simultaneous number of users that can be supported per cell per MHz of bandwidth while achieving the specified grade of service. Variable rate voice sources are considered for all four systems with a peak rate of 9.6 kb/sec. The processing gain increases from 128 for the narrowband system to 1024 for the wideband. The uplink of the CDMA system under consideration uses convolutional codes, orthogonal signaling, fast closed-loop power control and multipath and antenna diversity with noncoherent combining. On the downlink, convolutional codes, BPSK modulation with pilot-assisted coherent reception, fast closed-loop power control and multipath diversity are employed. The downlink bandwidth efficiency of the 2.5, 5 and 10 MHz systems are higher than that of the 1.25 MHz system by about 30%, 60% and 90% for path loss exponent of 4. The bandwidth efficiency of the wideband systems is more pronounced for small path loss exponents. The same channel model was assumed in evaluating the bandwidth efficiency of the four systems. In other words, the effect of channel models is not taken into account in computing the bandwidth efficiencies