One of the most effective techniques to mitigate multipath fading and inter-cell interference at a downlink wireless channel in WCDMA systems for achieving high capacity is transmitter power control. In this case, system increases the power of the subscriber when its interference increases in order to satisfy the requested signal qualities. However, when the requested signal qualities are infeasible, the power control algorithms might diverge as a result of power limitation. Another way to mitigate multipath problems is using diversity techniques. Space-time diversity offers an advantage in the forward link of the WCDMA system. In this paper, three environments for forward link power control, together with space-time diversity, are examined. These are indoor office, indoor-outdoor pedestrian and vehicular environments. The simulator takes into account 19 hexagonal cells with spatially uniform user distribution and a propagation channel characterized by distance attenuation, fast Rayleigh fading and inter-cell interference. Computer simulations are given to evaluate the effect of space-time diversity on convergence of downlink power control algorithms. Simulation results show that space-time diversity together with downlink power control have very good performance, especially in the vehicular environments with high mobile speed.