Mobile WiMAX: Downlink Performance Analysis with Adaptive MIMO Switching

The WiMAX standard has emerged to harmonise the wide variety of Broadband Wireless Access (BWA) technologies. The recent mobile WiMAX standard (802.16e) supports broadband applications to mobile terminals and laptops in urban environments. Mobile WiMAX supports a full range of multiple-input multiple-output (MIMO) techniques including space time block coding (STBC), spatial multiplexing (SM) and eigen-beamforming (EB). This paper compares the performance of the above schemes in terms of achievable throughput and operating range. Simulated packet error rate (PER) and throughput results are presented for each MIMO technique, and for a range of modulation and coding rates. Based on a typical link-budget, the expected throughput for each scheme is computed as a function of the basestation-terminal separation distance. The paper highlights the use of Adaptive MIMO Switching (AMS) in mobile WiMAX. The SNR switching points between each MIMO mode is determined and their dependency on channel spatial correlation is demonstrated. Finally the operating range of the different MIMO schemes is determined (based on a 10% PER) for a mobile WiMAX system. The use of eigen-beamforming together with AMS is shown to offer significant performance benefits in terms of robustness, capacity and operating range. For the scenario under test, the use of eigen-beamforming (based on the dominant eigen-mode) extends the operating range by 16%, and doubles the received data rate for 65% of locations.