| Summary: | 碩士 === 國立交通大學 === 電信工程系所 === 96 === Cooperative multi-hop relay networks progress significantly in recent years. Conventionally, relay stations are used to achieve higher diversity gain and improve link reliability. However, how to choose a relay to obtain higher throughput
is rarely discussed in the literature.
This thesis is aiming at proposing the relay selection rules to achieve higher throughput, while maintaining link reliability. We propose two partner selection methods in this thesis. The first one is to calculate throughput corresponding to each relay, and then choose the relay achieving the maximal throughput. Though this method can achieve the highest throughput, its computation cost is quite high. In the second method, we first compare the SNR of the relay link from the source with the SNR of the relay link to the destination, and designate the smaller one as the bottleneck SNR associated with that relay. The bottleneck SNR of each relay is recorded and compared. The relay with the largest bottleneck SNR is selected. Both methods have the similar throughput performance. However, the outage probability of the second method is better than that of the first one. Meanwhile, compared to the conventional signal-based partner selection, the proposed bottleneck SNR approach can achieve higher throughput at the cost of small SNR degradation.
Furthermore, we examine the performance of the considered relay selection rules in the multiple relay case. We find that at the same consumed power level the outage probability and throughput performance in the multi-relay case is indeed worse than those in the one relay case. This is because the multi-relay case yields more power consumption and higher probability in selecting inappropriate relays.
In the traditional method, the transmit power allocated in the relay link from the source is the same as that in the relay link to the destination. Now, we suggest a simple power distribution algorithm to adjust transmit power from the relay as the number of the relays increases. In the suggested power distribution rule, the transmit power of each relay is inversely proportional to the number of relays, and the sum of the total transmit power from the relay is equal to the transmit power from the source. Our results show that at the same consumed power level the proposed power distribution can improve outage probability, while maintaining throughput even in the multi-relay case. The proposed power allocation can eliminate unnecessary power in the second transmission phase with multiple relays.
To summarize, we first propose two throughput-oriented relay selection rules and provide the trade-off analysis between throughput and reliability. Second, we develop a power distribution algorithm and improve the outage probability even in the multi-relay case. Last but not least, we obtain insights of relay selection rule for the design in a multi-hop relay network.
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