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UBC Theses and Dissertations

Improving lifetime in wireless selective relay networks Mousavifar, Seyed Ali


Two novel algorithms based on imposing a soft limit on transmit power are proposed for improving the lifetimes of Amplify and Forward (AF) wireless relay networks. The impact of the algorithms on the network lifetime of four selective relay strategies, Minimum Transmission Power (MPT), Minimum Outage Probability (MOP), Maximum Energy Index (MEI), and Maximal Residual Energy (MRE) are studied. The network lifetime is defined as the number of successfully received messages at the destination while ensuring the system outage probability requirement is met. In the first system model, there are N number of parallel relay paths with only one relay in each path between the source and the destination. The proposed algorithm uses the system outage probability derived in previous studies and a fixed transmit power threshold at the relays. The algorithm increases the lifetime drastically when the number of relays is larger than 3. In the second system model, the destination uses N number of parallel paths with only one relay in each path and the source-destination link to receive messages. A diversity scheme is proposed in which the destination uses the source-destination link to obtain the signal broadcast to the relays by the source. The destination then informs the relays of the SNR deficiency which needs to be made up by the selected relay. The system outage probability is derived for the diversity scheme. The proposed algorithm deploys a dynamic transmit power threshold with the diversity scheme and improves the lifetime drastically. The proposed algorithms are shown to improve the lifetime while ensuring that a target system outage probability is met. However, their features also increase the delay that a message may experience. To address this problem, we propose a delay reduction scheme, which disables the soft transmit power limit, if message delay exceeds a certain threshold. The delay reduction scheme is shown to significantly lower the message delay without much decrease in the lifetime.

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