A radio communications device (102) that has multiple receive antennas processes received data communications signals to select between space time coding and spatial multiplexing as a selected transmission technique from a base device (104) that has multiple transmit antennas. A channel throughput (402-412, 450-454) for each transmission technique is estimated based on signal to interference and noise ratios (502-512, 550-554) of signals being transmitted through a MIMO channel (140) as measured by a receiver (708). The transmission technique with the higher estimated throughput is determined. If spatial multiplexing is determined to have the higher estimated throughput and the throughput of each layer of the spatially multiplexed signal is greater than a threshold, spatial multiplexing is selected. Otherwise, space time coding is selected.