Performance Of Closed-loop Power Control Research Articles

Performance analysis of imperfect closed-loop power control over Rayleigh fading

The performance of closed-loop power control in code division multiple access systems considering several non-ideal conditions such as multiple power control, group delays, channel estimation error, and power control command bit error probability is investigated.

Error probability analysis for CDMA systems with closed-loop power control

Fast closed-loop-power-control (CLPC) plays a key role in direct-sequence (DS) code division multiple access (CDMA) systems, aiming at achieving acceptable carrier-to-interference (C/I) ratios in all active links. Assuming a terrestrial mobile access, where the round-trip delay may be smaller than the channel time-coherence, fast CLPC can compensate for fading and reduce the error burstiness, as well. This paper provides analytical expressions for the bit error probability given: the CLPC algorithm specified in terms of loop delay and updating rate, the propagation power delay-profile and the terminal speed. A binary PSK DS spread spectrum radio interface, with RAKE processing of multipath or diversity, is considered. Our link-level analysis, being conditioned to a specified average value of C/I, is focused on the inverse update algorithm, which is aimed at keeping the received power at a constant level. Applications of the derived method, aimed at getting insight about CLPC performance in 3rd generation radio interfaces, is also provided and discussed.

Performance of closed-loop power control in DS-CDMA cellular systems

In situations where the round-trip delay between the mobile and the base 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. We study 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 power 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-varying channel. To study more complex update strategies, detailed simulations that estimate the channel bit-error performance are carried out. Simulation results are combined with coding bounds to obtain quasi-analytic estimates of the reverse link capacity in a direct-sequence code-division multiple-access (DS-CDMA) cellular system. The quasi-analytic approach quantifies the performance improvements due to effective power control in both single-cell and multicell DS-CDMA systems operating over both frequency-nonselective and frequency-selective fading channels. The effect of nonstationary base stations on the system performance is also presented.