T.-M. Lin and W.-T. Chen (Taiwan)
VoIP, 802.11, WLAN, Low Power, Multicast
Energy efficiency is one of the critical issues of a mobile device supporting real-time services over wireless networks. This paper addresses the power consumption problems of Voice-over-IP (VoIP) services in the IEEE 802.11 networks, and proposes a low power medium access control (MAC) enhancement, called Unicast-to Multicast (UtoM) scheme, for mobile stations (MSs) accessing VoIP services. The proposed scheme employs the MAC multicast transmission technique together with a frame aggregation method to eliminate the acknowledgement (ACK) frames and redundant inter frame spacing (IFS) that introduce extra power consumption for voice packet transmission. To avoid packet lost due to unreliable delivery of MAC multicast frames, a collision feedback and a piggyback acknowledgement method are thus implemented to reduce packet loss rate, i.e. to guarantee voice qualities, for the proposed UtoM scheme. The performance in terms of power consumption of MSs, packet loss rates, and packet delays are evaluated and analyzed in this paper. The results demonstrate that the UtoM scheme performs superior over the traditional 802.11 protocol in saving energy and permits an adequate packet delay and voice quality for VoIP over WLANs.
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