UBC Theses and Dissertations
Power allocation schemes for cooperative communication system using weighted sum approach Devarajan, Rajiv
This thesis investigates power allocation schemes for an amplify-and-forward dual-hop relay based cooperative communication system with perfect and imperfect channel state information (CSI). We define cost functions and propose power allocation schemes such that the cost functions are minimized. We analyze a multiuser system, where we select the best user for transmission, who incurs the least cost of transmission. In a practical system, estimated CSI is often imperfect. We assume the estimated CSI is affected by estimation errors, which are modeled as zero mean complex Gaussian. First we propose an optimization scheme where the objective is to minimize the weighted sum of source and relay powers. Then we propose a more general multi-objective optimization scheme which jointly optimizes sum power and signal-to-noise ratio (SNR). In our proposed schemes, source and relay nodes share a fixed total power, and transmission is allowed only if the minimum required SNR at the destination can be achieved with the available power budget. These schemes are analyzed under both perfect and imperfect CSI assumptions. In addition to proving the convexity of these problems, we propose analytical solutions for sum power minimization and SNR maximization schemes in the presence of imperfect CSI. Performance of the systems under the proposed schemes are investigated in terms of energy efficiency, throughput and outage. Simulation results show that proposed schemes reduce wastage of power by avoiding unsuccessful transmissions.
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