Cross-Layer Schemes for Optimization of VoIP Over 802.11e WLAN

Voice over Internet Protocol (VoIP) over wireless local area network (WLAN) is becoming a widely used technique. However, several technical problems exist in this application: First, voice delay is unacceptable in the presence of coexisting with other applications. Second, the inherent characteristic of WLAN causes low voice capacity. To address the problems, in this paper we propose and analyze two schemes, slotted TXOP and time-slot reuse scheme, that can significantly advance the voice capacity in WLAN. In the proposed scheme, with interaction with application layer, the delay of voice packets can reach its minimum value. In addition, with the help of time-slot reuse, the network capacity is significantly advanced. We also show the performance analysis and simulation of our proposed schemes in various PHY rates and over various voice codecs. The simulation results show that the proposed schemes greatly enhance the system capacity for VoIP compared with HCCA of 802. lie.