On adaptive modulation when the received signal is corrected with imperfect channel estimates

This paper investigates an adaptive M-QAM modulation scheme with constant peak power for which the received signal is divided by the estimated channel gain. Generally, for adaptive modulation schemes, the transmitter adjusts its modulation parameters based on the received power. The receiver estimates channel conditions and sends feedback information via a return channel to the transmitter. In this paper, we consider Rayleigh flat fading channels. At the receiver the fading is estimated using pilot symbols. To cancel the channel impact, we correct the received signal by dividing it by the estimated value of the fading. So, we propose to adjust the modulation level by examining the statistics of the corrected signal. The modulation switching protocol take into account the channel estimation error variance. Since linear region of practical amplifiers is limited, when switching from one modulation scheme to an other, the peak power is kept constant.