PERFORMANCE OF CLOSED-LOOP POWER-CONTROL IN DS-CDMA CELLULAR-SYSTEMS

In situations where the round-trip delay between the mobile and the ba se stations is smaller than the correlation time of the channel, power -control schemes using feedback from the base station can effectively compensate for the fast fading due to multipath. In this paper, we stu dy several closed-loop power-control (CLPC) algorithms by analysis and detailed simulation. We introduce a new loglinear model for analyzing the received power correlation statistics of a CLPC scheme. The model provides analytical expressions for the temporal correlation of the p ower-controlled channel parameterized by the update rate, loop delay, and vehicle speed. The received power correlation statistics quantify the ability of closed-loop power control to compensate for the time-va rying channel. To study more complex update strategies, detailed simul ations that estimate the channel bit-error performance are carried out . Simulation results are combined with coding bounds to obtain quasi-a nalytic estimates of the reverse link capacity in a direct-sequence co de-division multiple-access (DS-CDMA) cellular system. The quasi-analy tic approach quantifies the performance improvements due to effective power control in both single-cell and multicell DS-CDMA systems operat ing over both frequency-nonselective and frequency-selective fading ch annels. The effect of nonstationary base stations on the system perfor mance is also presented.