Effects of additive noise on the throughput of CDMA data communications

We analyze the optimum transmitter power levels and the optimum number of active terminals sending data to a CDMA base station. The objective is to maximize the aggregate throughput of the base station. We find that in the presence of additive noise, received power balancing is suboptimal mathematically. We consider N terminals transmitting at the same data rate, with the power of the most distant terminal (terminal N), fixed at its maximum value, and the power of the other N-1 terminals varying. We conclude that the aggregate throughput at the base station is maximized or minimized (depending on the spreading gain G) when the receiver powers for the N-1 terminals operate at an identical receiver power, which is larger than that of the power-limited terminal. This finding reduces the complexity of the analysis to a univariate optimization problem. A numerical analysis indicates the extent to which additive noise reduces the optimum number of active terminals and the maximum base station throughput.