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 forwa rd link of a direct sequence-code division multi-access (DS-CDMA) cellular system. Orthogonal spreading is assumed at a base station transmitter and c oherent RAKE combining is assumed at a mobile station receiver. In DS-CDMA cellular mobile radio, the multiple access interference (MAI) from other ce lls and background noise limit the forward link capacity. Therefore, to inc rease the link capacity, fast transmit power control (TPC) can be introduce d, which is similar to that developed for the reverse link, i.e., the trans mit powers of forward link channels are independently raised or lowered acc ording to the instantaneous signal-to-background noise plus interference ra tios (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 ta rget value, TPC step size, etc) on the forward link capacity in single- and multi-cell environments is evaluated by computer simulation. It is shown t hat fast TPC can almost double the forward link capacity in a multi-cell en vironment.