Joint bit and power loading with user and stream selection in OSDM MU-MIMO broadcast channels

Under a given modulation scheme and a target BER (bit error rate) requirement, it is difficult to increase the number of bits transmitted in each symbol (i.e., the rate), since this generally requires a significant increase of transmit power. In this paper, we study how to increase the rate in multiuser multiple-input multiple-output (MU-MIMO) broadcast channels using only bit and power loading, without requiring additional transmit power. To solve this challenging problem, our approach is to carry out a joint design of bit loading and power allocation over all streams, and meanwhile take user and stream selection into account. Specifically, we maximize the total number of bits per symbol (rather than the Shannon capacity) over all selected streams, under a target BER constraint for each stream and a constant total transmit power constraint. To enable flexible user and stream selection as well as achieving a high total rate, we consider OSDM (orthogonal space division multiplexing) rather than BD (block diagonalization) based MU-MIMO broadcast channels. Numerical results show that our proposed joint bit and power loading with OSDM user and stream selection is effective in increasing the total transmission rate without consuming additional resources.