Optimal transmit covariance matrices for MIMO high speed uplink packet access

The increasing importance of uplink scheduling in the future wireless systems is mirrored in the work on the high speed uplink packet access (HSUPA) radio link design. The nature of the optimization problems associated with uplink scheduling [H. Bosche et al., 2003; E.M. Yeh, 2002] has shown the importance of geometrical knowledge in the capacity and stability region. This knowledge can significantly facilitate the design of delay scheduling routines. We provide the geometrical analysis of the capacity and stability region in the multi-antenna uplink. We give an insight in the general structure and state general properties of the capacity and stability region. Concentrating on the MIMO-MAC with individual power constraints, we identify and interpret specific points and regions at the boundary and characterise transmit strategies in achieving them. We state a general and sufficient condition for emerging of rate-sum optimal corner points in the capacity and stability region. Finally, we analyse the behaviour of the capacity and stability region in terms of power constraint variation.