Analytical Model for an IEEE 802.11 WLAN using DCF with Two Types of VoIP Calls

We formulate an analytical model for capacity evaluation of an infrastructure IEEE 802.11 based network carrying full-duplex packet telephone calls when different types of codecs are used for voice calls. The analysis of the model utilizes the attempt rate results from a well known fixed-point based saturation analysis. The performance estimates obtained match very well with ns2 simulations. The network comprises wireless STAs establishing voice calls with wired STAs on a high speed local area network to which the access point is connected. We consider packet voice calls from two different types of coders, with N1 calls of Type 1 and N2 calls of Type 2, from a high speed local area network, terminating at N1 and N2 wireless STAs through an AP. We model the number of STAs that have an up-link voice packet as a Markov renewal process embedded at so called channel slot boundaries. Analysis of the evolution over the channel slot is done using saturation analysis. We find that the AP is the bottleneck, and the system can support (in the sense of a bound on the probability of delay exceeding a given value) a number of calls less than that at which the arrival rate into the AP exceeds the average service rate applied to a saturated AP.