Adaptive SIMO and SDMA transmission mode for single carrier FDMA uplink

This paper is dedicated to better understanding of the achievable sum rate in the single carrier FDMA (SC-FDMA) system. We investigate the achievable sum rate in a two-user SC-FDMA system, where a mix of SIMO (single input multiple output) and SDMA (space division multiple access) transmission mode is assumed for the wideband communication. The problem is formulated which appears to be non-convex. Relation to the conventional waterfilling solution is pointed out for single mode (SIMO or SDMA) transmission. We show that a mix of SIMO and SDMA transmission mode in the wideband is not favorable for any pair of the user equipments. A better strategy would be to switch to SIMO mode or SDMA mode adaptively. We also propose a simple algorithm to find the group of users for SDMA mode based on the wideband average spatial correlation. Performance improvement is shown by combining adaptive SIMO mode and SDMA mode selection with our proposed user grouping algorithm.