Wi-Fi enabled hand-held devices quickly occupied the consumer market as a result of the remarkable customer acceptance of IEEE 802.11 standard. But the widely used contention based medium access mechanism is unable to meet the increasing traffic demand of today's home users. Especially, delay sensitive multimedia contents suffer heavily from quality degradation under high traffic load. However, the time synchronized medium access mechanism of 802.11 called PCF offers lower delay and loss, and holds true potential in supporting high traffic load. For design and planning of such networks, a thorough performance analysis of PCF based 802.11 WLANs is of profound importance. But existing studies on this lack proper and accurate mathematical modeling considering realistic assumptions, which is investigated in this paper. We develop a Markov chain to analyze the time synchronized PCF based medium access mechanism considering error prone channels, and determine throughput, delay, and packet loss in a WLAN. The impact of traffic load and retry limit is also analyzed. We use our model to analyze performance of PCF mechanism in supporting both data and multimedia traffic.
Voice capacity over IEEE 802.11 networks can be increased with time synchronized medium access, but it is restricted to single hop networks only. We propose a collaborative mechanism that enables client nodes to carry out the time synchronization on ad hoc basis, thereby extends the time synchronized access mechanism over multiple hops, and increases voice capacity considerably. To model real scenario closely, we consider the impact of channel error and employ a Markov chain to determine delay and loss in both medium access and in queue which is then used to derive user perceived voice quality using ITU-T E-model. Our model is then used to determine voice capacity of multichannel, multihop networks. The impact of data rate, interference range, and multiple channels are also analyzed