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Effective link layer retransmission mechanisms in wireless networks are important as they can reduce packet loss due to bit errors. For wireless voice over IP (VoIP), a key question that needs to be addressed in order to provide the best possible perceived speech quality is how to utilize retransmission schemes to recover corrupted packets whilst avoiding excessive retransmission delays. The contributions of this paper are twofold. First, we use an objective measure of perceived conversational speech quality (MOSc) as a metric to evaluate the performance of three current retransmission schemes (i.e. no retransmission, speech property-based retransmission and full retransmission), while considering the impact of retransmission jitters. Our findings indicate that the performance of the retransmission mechanisms is a function of both wireless link quality and delay introduced in the wireline network. Second, we propose a new perceived speech quality driven retransmission mechanism which may be used to achieve optimum perceived speech quality for wireless VoIP (in terms of the objective mean opinion score) by switching to the most suitable retransmission schemes under different communication conditions.
Date of Conference: 25-27 June 2003