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Adaptation based on channel information in advanced wireless communication systems

Authors Cheung, Chun
Issue Date 2011
Summary The tremendous growth in wireless access for internet and multimedia applications in recent years increases the demand for more reliable and high speed wireless communication capability. To face this challenge, we need to explore new wireless radio technologies and utilize the present network resources more efficiently. While new wireless communication technologies including multi-band orthogonal frequency division multiplexing (MB-OFDM) in ultra-wideband (UWB) system, network coding, Hybrid ARQ (HARQ), and cooperative communications, are introduced and developed, it is important to make use of these new technologies efficiently. Adaptive and dynamic schemes based on communication channel state information or statistics had been shown to improve efficiency significantly. In this thesis, we study how dynamic adaptation using these technologies can further benefit new advance communication systems. In a point-to-point short range UWB system where power spectral density level instead of the total power is the limitation, traditional power allocation scheme cannot be used. We proposed a new adaptive symbol interleaved coded modulation and frequency spreading technique and showed how it can dynamically combine and utilize the otherwise unused power in weak subcarriers to increase the overall system performance. In an uplink cellular communication system with cooperative relay, we proposed two adaptive multiuser cooperative HARQ retransmission strategies, one for network-coded retransmission and one for superposition modulated retransmission. The network-coded HARQ retransmission dynamically determines the group of packets from multiple users that should be combined in the HARQ retransmission at the relay station. We optimized the grouping in this strategy and evaluated via simulation the performance improvement under various channel conditions. For the superposition modulated retransmission scheme, we used the information-theoretic approach to derive the outage probability and derived the superposition weighting factor to minimize this outage probability in a two-user system. We derived analytically the system throughput and investigated the improvement achieved by the proposed optimized scheme under channels with various diversity orders. The adaptation concept is extended to the interference channel modeling a two-cell scenario with two mobiles accessing two base stations in a cellular network. Assuming the presence of a backhaul connection between the base stations, we proposed a scheme that uses the base station as a relay to adaptively forward either the signal or the interference or nothing at all over the backhaul connection. We derived the analytical characterizations of the condition for each forwarding schemes and the resulted system throughputs. Results were compared to non-cooperative scheme. Detail analyses of the influences of the backhaul channel capacity and the ratio of two transmitters information bit rates on the system throughput gains of the cooperative schemes over the non-cooperative scheme were also given. Simulation results in fading channels showed that our proposed dynamic cooperation scheme outperforms the individual non-dynamic cooperative schemes significantly.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2011
Language English
Format Thesis
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