Joint optimisation of outer-loop power control and rate adaptation over fading channels

This work examines the joint optimisation of outer-loop power control and transmission rate adaptation, to maximise the spectral efficiency, subject to a long-term transmit power constraint. The method is analyzed and simulated for the MQAM scheme over flat fading channels. We propose an adaptive transmission scheme in which the ´SNR target´ and ´data rate´ are adapted to the estimated bit error rate (BER) or frame error rate (FER), whilst a constant short-term received signal-to-noise ratio (SNR) is maintained by exploiting total or truncated channel inversion strategy in the (fast) inner-loop power control. We show that our adaptive rate and SNR target scheme provides higher spectral efficiency, compared to variable-rate and fixed SNR target scheme of Goldsmith. and Chua (1997) in the cases where the BER becomes worse than the desired BER.