Advanced Mobile WiMAX OFDMA System using the combination of MIMO with Adaptive Beamforming

Abstract

Multiple antenna technologies are known to improve wireless link quality and/or increase throughput. Each technology supports different type of performance improvement by its own gain where diversity gain can be obtained from STC (Space Time Coding), multiplexing gain from SM-MIMO (Spatial Multiplexing – Multiple Input Multiple Output), and beamforming gain from ABF (Adaptive Beamforming), respectively.. The first part of this thesis studies various multiple antennas technologies defined in IEEE 802.16e OFDMA (Orthogonal Frequency Division Multiple Access) standard. Basic principles and performances are described throughout the first part following Mobile WiMAX system. The essential algorithm, “the combination of MIMO with ABF technology (ABF-MIMO)” is described at the second part. From the simulation results, it is shown that the BER performance can be dramatically improved when ABF technology is applied to the conventional MIMO system under Mobile WiMAX signal environment. To verify its performance improvement by the proposed combination, practical ABF-MIMO OFDMA system is designed and implemented. Expeimental results show that the practical ABF-MIMO OFDMA system outperforms conventional MIMO OFDMA system in a real wireless channel environment in terms of both throughput and BER. We provide theoretical analysis for the performance difference between ABF-MIMO OFDMA and onventional MIMO OFDMA system. It is verified that creating a beam toward a target antenna at the receiver improves the performance by reducing fading correlation between antennas.