Uplink sumrate maximization with different types of channel state information at the transmitters

We study the multiple access channel (MAC) with perfect channel state information (CSI) at the base station and different types of CSI at the mobiles, i.e. without CSI, with long-term CSI and with perfect CSI. The average sumrate of the MAC depends on the statistics of the channel realizations and on the transmission strategy and CSI at the mobiles. In this work, we analyse the impact of the fading distributions on the achievable average sumrate. We show for the case in which the mobiles have no CSI, that the maximum sumrate is obtained for fading channels which have second order moments equally distributed. For the case in which the mobiles have information about the long-term statistics of the fading channels in terms of the fading variances, we derive the optimum power allocation and show that in this case the sumrate is maximised if one user has largest second order moment. Finally, in the case in which the mobiles have perfect CSI, only the best user is allowed to transmit. For this type of CSI, the average sumrate is maximal if one user has large fading variance and all other users have very low fading variances. We illustrate these results by numerical simulations.