MIMO downlink spatial multiplexing algorithms applied to channel measurements

Several algorithms have recently been proposed for multiplexing multiple users in multiple-input, multiple-output (MIMO) downlinks. The ability of a transmitter to accomplish this using spatial methods is generally dependent on whether the users´ channels are linearly independent. Until now, most multiplexing algorithms have been tested on uncorrelated Gaussian channels, a best-case scenario. We examine the performance of multiplexing multiple users using actual channel measurements. We impose the constraint that all inter-user interference must be zero, and optimize the transmit vectors to maximize total throughput under this constraint. The maximum throughput was calculated for different user separation distances, and the results show that for this particular set of measurement data, a separation of five wavelengths is enough to achieve close to the maximum available performance for two users.