Modeling and the Congestion Relief in WLANs using Ad hoc Networks

We consider usage of campus wireless LANs (WLANs) consisting of access points (AP) with potentially noncontiguous coverage. Through surveys on mobility patterns and wireless network usage on the college campus, we find that mobility and usage patterns exhibit significant differences across various types of locations on campus. Using the collected data we build a realistic mobility model that we call Weighted-Way Point (WWP), to better simulate wireless network user behavior in a university campus environment. Using WWP, we show that unbalanced wireless network usage and hotspots are likely to occur on campus. We further propose a mechanism to alleviate the local hotspot congestion by using multi-hop ad hoc networks. When a MN determines the local AP is unable to provide satisfactory bandwidth to an on-going flow, it requests the flow to be switched to a neighboring access point (NAP). Our mechanism differs from other schemes by allowing MNs to make the decision of initiating the flow-switching procedure and using bi-directional route-discovery from both the switching MN and NAP to reduce the route discovery delay. We use simulations to show that with this flow-switching mechanism, flows are more evenly distributed across APs. We also show that our mechanism reduces congestion time for popular APs and improves the user-perceived quality.