Resource Allocation And Performance Analysis For Wireless Relay Systems

Relay technology has won intensive attentions of industry and academia due to the improvement of reliability and robustness in wireless link transmission. It is one of the core areas in future wireless commu-nications. Therefore, this dissertation discusses several key technologies in detail from physical layer and presents some theoretical results for wireless relay systems, by resorting to optimization theory, graph theory and probability theory. The main contents and contributions include:1. For two user pairs in an OFDM (frequency division multiplexing orthogonal) AF (amplify and for-ward) two-way relay system, the primal user pair and the secondary counterpart coexist. For rational utiliza-tion of resources, a dual method is used to design a joint optimization algorithm of power allocation, subcarrier assignment and subcarrier pairing. This joint algorithm can meet the target rate requirement of the primal user pair and maximize the sum rate of the secondary user pair at the same time.2. For OFDM AF multi-relay systems, a mathematical model is built to reduce BER (bit error rate) of this system as the objective function under the total power constraint and the individual power constraints of the source node and the relay nodes. A joint algorithm of power allocation, relay selection and subcarrier pairing is proposed to achieve resource optimization. Compared with existing methods, the proposed algorithm can significantly reduce the BER and improve system performance.3. We analyze capacity and moments of SNR (signal to noise ratio) in an OFDM relay system over Rayleigh fading environment. Two common relaying protocols are investigated:DF (decode and forward) protocol and AF protocol. With aid of order statistics, we obtain closed-form formulas of capacity and mo-ments of SNR in three subcarrier pairing cases:ordered subcarrier pairing, reversely ordered subcarrier pairing and non-subcarrier pairing. Simulation results substantiate the accuracy and effectiveness of our formulas.4. Finally, the performance of an AF relay system is analyzed over Nakagami-m fading channel. Whether this AF relay system adopts fixed power allocation or water-filling power allocation, we harvest closed-form expressions of performances, including outage probability, moments of SNR, capacity and av-erage SER (symbol error rate). Similarly, the simulation results are in exact agreement with the numerical solution of theoretical analysis, which provides an important theoretical suggestion to evaluate the actual performance of an AF relay system.