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 using NCTUns simulation tools. The 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 signaling 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 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 nontransparent relay shows that the throughput degradation between low mobility MS (30m/s) and high mobility MS (50m/s) is only about 2.0%. The proposed relay selection mechanisms can be applied in any high mobility multi-tier cellular network.