Seminar by Dr. Pavan S. Nuggehalli
Online Association Policies in IEEE 802.11 WLANs
Dr. Pavan S. Nuggehalli
Assistant Professor, Centre for Electronics Design and Technology
Indian Institute of Science
Bangalore
Date: Tue, Nov 18, 2005
Time: 1200
Venue: CS 101 Abstract:
In many IEEE 802.11 WLAN deployments, wireless clients have a choice of access points to connect to. In current systems, clients associate with the access point with the strongest signal to noise ratio. However, such an association mechanism can lead to unequal load sharing resulting in diminished system performance. In this talk, we describe an analytical approach based on stochastic dynamic programming to find the optimal client-AP association algorithm. For a simple topology consisting of two access points, we numerically determine the optimal association rule. By studying the nature of the optimal rule, we propose a near-optimal heuristic and study its efficacy for more complicated arrival patterns and larger topologies. We then study the stability of different association policies as a function of the spatial distribution of arriving clients. We find for each policy the range of client arrival rates for which the system is stable. For small networks, we use Lyapunov function methods to formally establish the stability or instability of certain policies in specific scenarios. Our heuristic policy is shown to have very good stability properties when compared to several other natural policies. We also validate our analytical results by detailed simulation employing the IEEE 802.11 MAC and provide pointers on implementation.