Power control in feedback communications over a fading channel

Power control using noiseless and delayless feedback over a slowly Rayleigh fading channel is considered. Pilot symbol assisted modulation and a MMSE channel estimator are used to employ feedback MMSE power control. The performance difference between optimal and feedback power control is shown to be less when employing the MMSE estimator than when using the previously presented one-shot MAP estimator. The lag error is, however, noticed to cause severe performance degradation even when the channel is very slowly fading. The operating strategy of feedback MMSE power control is shown by simulations to be such that during deep fadings the power control algorithm gives up and elsewhere it tries to stabilize the received SNR to a constant level.