MIMO processing for WiMAX in challenging radio environment

Wireless communication systems based on multicarrier techniques such as orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) are capable of offering reliable high data-rate transmission by transferring a frequency selective radio channel into a series of parallel frequency-flat channels. This work focuses on the systems based on the IEEE 802.16-2005 standard applying OFDMA technique for both uplink and downlink transmission. While this standard is mainly intended for metropolitan and local area networks, the target environment for these systems lays in the urban and rural areas. In this paper, the extension of these systems to isolated research networks located in remote mountainous areas is studied from the physical layer perspective. Firstly, the channel modelling for mountainous environments is discussed and a novel channel model extension for the WINNER channel model is presented. Secondly, multiple-input multiple-output (MIMO) transmission techniques, such as space-time codes, spatial multiplexing and beamforming, are studied to enhance the system performance in this demanding radio environment. The simulation results indicate that the mountainous environment significantly lengthens the channel impulse response and also affects to the direction-of-arrival of the signal. The simulation results also demonstrate that instead of frequency-flat processing, frequency dependant beamforming techniques are preferred to cope with the distortion caused to the signal by the demanding channel model.