Relay selection and connectivity in mobile multihop relay network

Mobile Multihop Relay (MMR) network is an attractive and low-cost solution for expanding service coverage and enhancing throughput of the conventional single hop network. However, mobility of Mobile Station (MS) in MMR network might lead to performance degradation in terms of Quality of Service (QoS). Selecting an appropriate Relay Station (RS) that can support data transmission for high mobility MS to enhance QoS is one of the challenges in MMR network. The main goal of the work is to develop and enhance relay selection mechanisms that can assure continuous connectivity while ensuring QoS in MMR network. The first approach is to develop and enhance a relay selection for MS with continuous connectivity in non-transparent relay. In this approach, the standard network entry procedure is modified to allow continuous connectivity with reduced signalling messages whenever MS joins RS that is out of Multihop Relay Base Station (MRBS) coverage and the relay selection is based on Signal to Noise Ratio (SNR). The second approach is to develop and enhance relay selection that allows cooperative data transmission in transparent relay that guarantees continuous connectivity. The proposed relay selection defined as Cooperative Relay Selection based on SNR and LET (Co-ReSL) depends on weightage of SNR, a and weightage of Link Expiration Time (LET), B. National Chiao Tung University network simulator (NCTUns) is used in the simulation study. The QoS performances of the proposed relay selections are in terms of throughput and average end-to-end (ETE) delay. The findings for the proposed relay selection in non-transparent relay shows that at heavy traffic load p=0.8, and MS speed of 30 mis, throughput increases by 2.0% and average ETE delay reduces by 9.0% compared to random relay selection due to selection of RS with good link quality and provision of continuous connectivity. In addition, the throughput degradation between low mobility MS (30 mls) and high mobility MS (50 mls) is only about 2.0%. Findings for Co-ReSL show that at heavy traffic load, throughput increases up to 5.7% and average ETE delay reduces by 7.5% compared to Movement Aware Greedy Forwarding (MAGF) due to cooperative data transmission in selective links. By setting a=0.8 for Co-ReSL, the decrement of throughput between low mobility MS and high mobility MS is about 2.3% compared to the rapid decrement of 5.5% and 6.0% experienced by Co-ReSL with a=O.2 and MAGF, respectively. In addition, Co-ReSL improves throughput by 11.9% and reduces average ETE delay by 7.7% compared to non-cooperative method. The proposed relay selection mechanisms can be applied in any high mobility multitier cellular network.