Feedback Delay Effect on the CDMA Closed loop Power Control

Abstract

This paper is aimed to evaluate the effect of feedback delay on the performance of closed loop power control in CDMA System. Even though power control can mitigate the problem fluctuation due to fading, however due to the feedback delay, that advantage is invisible if this parameter is not decreased. Feedback delay is the total time that is taken by the power control from the mobile transmit signal is estimated at base station until power update command is received again at the mobile to do the transmission power update. Feedback delay worsens the performance of closed loop power control. To see this effect of feedback delay, in this study we evaluated the system of closed loop at three delay interval, i.e. 1Tp (Tp=power control interval), 2Tp and 3Tp. Performance of power control subject to feedback delay would be evaluated in term of bit error rate (BER) as a function of bit energy Eb to interference power spectral density I0 (Eb/I0). The simulation results have shown that the feedback delay cause the performance of system is degraded even at feedback delay of 3Tp, the performance is drop until the system performance without power control. By joining analysis between feedback delay and selecting step size, we have found the tradeoff between step size=1 dB and 2 dB in specific feedback delay.