Analytical Modelling and Performability Evaluation of Multi-Channel WLANs with Global Failures

Abstract

Wireless local area networks (WLANs) which are based on IEEE 802.11 standard are used widely in existing local area network configurations. IEEE 802.11 offers multiple non-overlapping channels to increase the capacity of the network. There are strong evidences that WLANs are prone to impairments. In order to improve the quality of service (QoS) and to evaluate the performance of WLANs realistically, the availability of the systems should be considered. This paper studies performability evaluation of a multi-channel WLAN using analytical modelling approach. Unlike the existing studies, the failures of the overall system, where a critical function unit fails making all the channels unavailable are considered. A new term is introduced as global failures. It is possible to solve the models considered using matrix geometric method where system parameters and minimal non negative solution R is computed by an iterative method. However spectral expansion method is a well-known alternative where the iterative calculations for solving R is avoided using eigenvalues and eigenvectors. The exact spectral expansion method is employed to obtain performability measures such as mean queue length and blocking probability. Iterative refinements are employed in solution of simultaneous equations.

Analytical Modelling of a New Handover Algorithm to Improve Allocation of Resources in Highly Mobile Environments

“…Figure 1 shows the handover process in such environments. The traditional handover approach introduces two types of threshold circles in the coverage area of the system [3,8,9,17]. The handover threshold and the exit threshold circles are shown in Figure 1 for the traditional handover approach.…”

“…Hence, the maximum number of calls in the system is given by L where L = S + Q. The traditional handover queueing model is given in Figure 2 [3,8,9]. The originating calls and handover calls are two kinds of arrival rates defined in the system, with mean arrival rates given as λ O and λ H , respectively.…”

“…If the channels are available and idle in the system, both call's arrival can be assigned to any channel. Otherwise, the incoming call request is added to the queue if the channels are busy [3,8,9]. In addition, if the queue is full, the incoming call is blocked.…”

“…This is also assumed to be exponentially distributed with a mean rate of µ dwell . The equation 1 is used in the literature for the dwell time in wireless and mobile systems [3,8,9] for traditional handover queuing model. Thus, µ dwell can be calculated and described as follows:…”

“…cell [3,8,9]. The total channel holding time of a call is exponentially distributed with mean 1/µ where, µ = µ C +µ dwell .…”