Analysis of transmit beamforming and fair OFDMA scheduling
Alex, Leith (2008) Analysis of transmit beamforming and fair OFDMA scheduling. Masters thesis, Iowa State University.
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Wireless Communication systems have been steadily evolving in order to improve performance for users. Two promising candidates for beyond 3rd generation (B3G) and 4G communication standards are multiple input multiple output (MIMO) and orthogonal frequency division multiple access (OFDMA) systems. MIMO systems use antenna arrays at both the transmitter and the receiver. By using multiple antennas different multiplexing, coding, or diversity gains can be achieved. One such MIMO technique which increases performance in wireless systems is called transmit beamforming (TB). The advantages of TB is by measuring the channel, one can use adaptive modulation techniques to achieve a coding gain over other MIMO schemes. In the considered model we assume delayed feedback, along with imperfect channel estimation (ICE) at the receiver. We will analyze how detrimental these effects can be to TB's performance. These analytical results will help in designing more robust TB schemes to be used in practical systems. OFDMA is a multicarrier, multiuser technique which through joint resource allocation can increase capacity and decrease transmission power. Dynamic OFDMA uses adaptive modulation based on instantaneous channel conditions, where even higher gains in terms of throughput and power savings can be achieved compared to time division multiple access (TDMA) or code division multiple access (CDMA). The second part of this thesis will propose a multiuser diversity scheme using weighted SNR (w-SNR) based ranking with adaptive rate tracking to achieve long term rate proportional fairness (RPF) for downlink OFDMA. This method has many advantages over traditional schemes, including low complexity, providing a higher data rate with fairness, and allowing for distributed scheduling.
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