Performance Comparison of Optimal and Suboptimal Forward-Link Channel-Sharing Schemes

In this paper, we evaluate the performance of various channel-sharing schemes in the forward link from a base station (BS) to several mobile stations (MSs). Simultaneous transmission (broadcasting) to all mobile stations using the entire available bandwidth is known to yield rates dominating any other channel-sharing technique for Gaussian channels. However, broadcasting is very complicated from an implementation point of view. We analyze and compare different channel-sharing techniques on the basis of the asymptotic minimum signal-to-noise ratio (SNR) per MS necessary at the BS to transmit to a certain set of MSs in a single cell at a common data rate. From our results we conclude that suboptimal but practical methods like two- or three-level superposition coding when used in conjunction with frequency division multiplexing perform sufficiently close to the optimum and hence, are good alternatives to the optimal broadcasting scheme.