Energy efficient user grouping algorithm for multi-user MIMO systems

A multi-user MIMO (MU-MIMO) system configures orthogonal MIMO channels for active mobile users by use of multiple antennas of the base station (BS). Because different grouping of users can introduce different channel properties in MU-MIMO, user groupinging can minimize BS transmit power in order to satisfy an essential requirement for BS energy savings. In this paper, we discuss how such user groupinging can vary transmit power consumption in a hybrid spatial and time diversity access (SDMA/TDMA) downstream. Then, we proposed an energy efficient user grouping algorithm for applications in MU-MIMO systems which finds a solution close to optimal by swapping users between different groups and comparing the transmit powers. The proposed greedy-swapping algorithm achieves 37% transmit power saving, which is close to the optimal for the exhaustive search, compared to the traditional capacity optimal scheduling algorithm PU2RC with 6% of the computational time for the optimal exhaustive search.