Pilot Feedback Equalization for Time Varying OFDM Systems

It is well known that feedback and power loading can enhance the error rate performance (or link quality) of orthogonal frequency-division multiplexing (OFDM) systems. Conventional power loading algorithms for OFDM are based on forward channel state information (CSI) knowledge in the transmitter provided by a dedicated feedback link from the receiver. In this paper, we propose a feedback scheme where instead of providing the transmitter with forward-link CSI we directly send the received pilots back to the transmitter. The transmitter extracts the forward-link CSI, and compensates both the amplitude and the phase of the channel for each tone before transmitting the OFDM symbol, a process also known as pre-equalization. Although the proposed scheme is sub-optimum in terms of power loading, we show that our feedback technique converts the Rayleigh fading channel into a flat channel and also simplifies the receiver.