Handovers in wireless overlay networks

Abstract

Wireless Overlay Networks (WONs) are multi-layer networks in which mobile nodes (MNs) move freely within cells of the same overlay or between cells of different overlays. Such a structure provides global access to MNs regardless of time and location. In spite of their advantages, WONs pose many challenges due to the simultaneous existence of horizontal handovers between cells of the same wireless network and vertical handovers between different overlay networks. Minimizing power drain, handover latency, overhead due to extra messaging during handovers, eliminating the number of unnecessary handovers and maximizing throughput are some of these challenges. While dealing with all this, end users should be isolated from making additional configurations and handovers should be performed seamlessly. Thus, an efficient mobility management system achieving all these goals needs to be built for the WON architecture. Currently, there are many efforts in dealing with the problems mentioned above. Related work in this area focuses on the development of new mobility management architectures as well as improving the handover decision phase to quickly and accurately trigger handovers without triggering any unnecessary ones. The thesis includes a survey of present handover schemes proposed forWONs and points out their drawbacks. Then, by taking into consideration the drawbacks and incompleteness of the current schemes in literature, this thesis proposes a new mobility management scheme for WONs. The proposed scheme divides into two main parts. The first part covers the problem of horizontal handovers and presents a solution which reduces latency as much as possible. The proposed model also deals with oscillations as MNs moves back and forth between two Access Routers (ARs). The simulation results show that the proposed horizontal handover model reduces latency significantly especially in highly crowded subnets at the expense of slightly increased overhead. The second part covers the problem of vertical handovers. This scheme integrates a Handover Decision Manager (HDM) to detect network condition changes in a timely and accurate manner, and a Subnet Agent (SA) to maintain the connection and manage handovers. The proposed HDM algorithm considers many factors such as the candidate networks’ cost, coverage, data rate and traffic load. The algorithm gives accurate and timely decisions and considerably decreases MNs’ power consumption at the expense of slightly increased complexity. The simulations, which compare the proposed HDM scheme with two-level thresholding and utility-based schemes, show that the number of unnecessary handovers and MNs’ power consumption are decreased considerably while MNs’ throughput is not significantly affected by the proposed algorithm. Meanwhile, the novel SA-based architecture brings a new signaling flow for downward and upward vertical handovers. The performance of the architecture is evaluated by comparing its signaling flow with that of the two latest architectures in literature. The analytical work done for this evaluation shows that the proposed SA-based architecture has a significantly lower overhead and an acceptable latency.