This work describes a detailed simulation-based study of the performance of an IEEE 802.11e  Medium Access Control  (MAC) layer over an IEEE 802.11g  Physical  (PHY) layer. The study focuses on the number of simultaneous bidirectional G.711  Voice over IP  (VoIP) calls that can be supported by a  Wireless Local Area Network  (WLAN) using the  Extended Rate PHY - Orthogonal Frequency Division Modulation  (ERP-OFDM) mode of 802.11g.A new scheme for adapting the WLAN MAC parameters is proposed in this work. The new scheme dynamically adapts the  Contention Window  (CW) based on the retransmission rate of the system. In addition, an adaptive  Transmission Opportunity  (TXOP) mechanism aids in balancing the uplink and downlink traffic levels and so provides the equality in uplink and downlink performance that is required for bidirectional VoIP traffic. The proposed scheme can thus maintain acceptable levels of QoS for higher call capacities, increasing the overall VoIP capacity of the system.
['Gráinne Hanley', 'Sean Murphy', 'Liam Murphy']
Adapting WLAN MAC parameters to enhance VoIP call capacity