Efficient User, Bit and Power Allocation for Adaptive Multiuser MIMO-OFDM with Low Signalling Overhead

Block diagonalization (BD) of multiple users combined with coordinated transmitter-receiver processing and scheduling between users is a simple and straightforward method to utilize the available spatial degrees of freedom in downlink multi-user (MU) multiple-input multiple-output (MIMO) channel for increasing the system throughput. In this paper, an efficient user, bit and power allocation algorithm with low signalling overhead (LSO) is proposed for maximizing the downlink spectral efficiency of the adaptive multiuser MIMO-OFDM system with BD decomposition. A greedy allocation algorithm with Hughes-Hartogs loading is also proposed and used as a reference for LSO algorithm. For a small number of users, the performance of LSO algorithm is shown to be very close to the greedy algorithm. Iterative BD decomposition with a single reiteration is shown to provide significant gains to the non-iterative solution. Linear minimum mean square error (LMMSE) filter is applied at the receiver to suppress the remaining multi access interference from incomplete orthogonalization together with a simple compensation algorithm with low rate scalar feedback to the transmitter. The proposed MU MIMO-OFDM system is also shown to be robust against imperfect channel state information at the transmitter, providing always superior performance to a time switched single user MIMO-OFDM solution.