Resource allocation for fading multiple-access channels with partial channel state information

Dynamic resource allocation based on the current channel state is a promising strategy to increase the capacity of wireless links. In this paper, the optimum accessing and resource allocation scheme for fading multiple–access channels with partial CSI at the transmitters are found. Partial knowledge of the fading states is a reasonable assumption for systems which provide a low rate feedback channel. Two simple feedback strategies are analysed. A 1–bit quantised feedback informs the users whether the channel gain is above a given threshold and is particularly suited for the low SNR regime. The strongest users transmit simultaneously and exploit the inherent multi–user diversity. A best– user feedback only reveals to the transmitters who currently has the best transmit conditions. The optimum accessing strategy is TDMA with random scheduling based on the channel gains. Both schemes operate surprisingly close to the optimum performance with ideal CSI at significantly reduced feedback rates to the transmitters.