Effect of fast transmit power control on forward link capacity of ds-cdma cellular mobile radio

This paper proposes applying fast transmit power control (TPC) to the forward link of a direct sequencecode division multi-access (DS-CDMA) cellular system. Orthogonal spreading is assumed at a base station transmitter and coherent RAKE combining is assumed at a mobile station receiver. In DS-CDMA cellular mobile radio, the multiple access interference (MAI) from other cells and background noise limit the forward link capacity. Therefore, to increase the link capacity, fast transmit power control (TPC) can be introduced, which is similar to that developed for the reverse link, i.e., the transmit powers of forward link channels are independently raised or lowered according to the instantaneous signal-to-background noise plus interference ratios (SIR's) measured at mobile stations. Fast TPC is fast enough to track the multipath fading as well as slow variations in the distance-dependence path loss and shadowing. On the average, the transmit power is increased to a user closer to the cell edge so that the effects of both other-cell MAI and background noise can be reduced while it is decreased to a user closer to the cell center. The effect of the TPC parameters (TPC interval, TPC target value, TPC step size, etc) on the forward link capacity in single- and multi-cell environments is evaluated by computer simulation. It is shown that fast TPC can almost double the forward link capacity in a multi-cell environment.