Book Description

Wireless networks provide flexible and ubiquitous access to the telephone networks or the Internet. Multiple technologies have been developed to provide wireless access including cellular/3G/LTE, WiFi, and WiMAX. The cellular network is the most popular network, which provides the stable and constant service under most types of mobility. Its future version, LTE Advanced, is the most advanced wireless access technology, and supports the current or future bandwidth-sensitive and/or delay-sensitive applications, such as Voice over IP and real-time video streaming. The WiFi network has been aggressively deployed in many areas and provide access to laptops, PDAs and smartphones. These are referred to as WiFi hotspots. The basic WiFi infrastructure usually offers flexible and easy to deploy wireless access inside a small area at a low cost. The WiMAX network has its own advantages to provide higher transmission speed for a point-to-point communication over longer transmission distances. In many areas, these wireless networks co-exist, overlap and interlace with one another to create a heterogeneous wireless network. Instead of functioning independently, significant benefits can be accrued through cooperation and coordination among these networks by leveraging their unique advantages. This is possible as user devices come with multiple network interfaces to connect to each of these networks. In order to exploit the advantages of these heterogeneous networks, it is important to implement an efficient resource allocation algorithm to coordinate the resources of multiple wireless networks and also have a good design of the heterogeneous network. The dissertation makes contributions in both the above areas. In current WiFi networks, the overall spectrum is divided among multiple overlapping channels. The adjacent access points need to operate on orthogonal channels to avoid the interference. In Chapter II, we give a precise analysis of the interference among different channels and discuss the potential possibility of utilizing partially overlapping channels in the multi-hop mesh networks. It is possible to optimize different network performance metric, such as throughput, by balancing parallel transmissions and partially received transmission power offers the best system performance, such as throughput. In the multi-hop mesh networks, some mesh nodes are highly congested either due to the interferences from multiple neighbors, or when they are located at the intersection of multiple routing paths. These highly congested mesh nodes significantly degrade the network performance, since the throughput of a path is limited by the node with minimum capacity. In Chapter III, we discuss the efficient cooperation between a WiFi-based mesh network and a WiMAX network to mitigate the impact of congested nodes. The WiMAX network, with its longer transmission range, can be leveraged to bypass the traffic from some highly congested mesh nodes. The load balancing makes the throughput of the heterogeneous network higher than the sum of the throughput from the WiFi and WiMAX networks if they operate independently. In the widely deployed wireless networks, the infrastructure mode is used, where customer devices only communicate with the base stations. This mode is suitable for normal Internet access. However, some emerging applications, such as P2P file sharing, teleconferencing, network games, require frequent communications among terminals that may be in the coverage of the same base station. The exiting infrastructure mode of the network architecture results in high resource waste due to the unnecessary transmissions via the base station even when both the user could directly communicate. In Chapter IV, we propose a novel network architecture, Local-Interest-Group (LIG), in which all nodes can communicate in any ways according to the application requirements. The real-time algorithm and protocol minimize the interferences among co-existing LIGs and maximize the bandwidth utilization, which greatly improves the overall system performance under multiple performance metrics. In network planning, it is difficult to efficiently locate base stations due to the inaccuracies in the prediction of the traffic density. The movement of traffic to different parts in the city during different times of a day makes fixed base stations either operate at very low load or become highly congested at different time periods. Fortunately, the detailed analysis based on network measurement shows that the movement of traffic density is predicable. In Chapter V, we propose a new network component, Traffic-Tracing Gateway (TTG), which works as the base station but traces the traffic movement taking the advantage of the heterogeneous wireless networks. By following the optimal trajectories, TTGs cover the maximum traffic and provide much better system performance in both single-hop or multi-hop networks. This dissertation proposes efficient resource allocation methods in heterogenous wireless access network with partially overlapping channels and the cooperation between WiFi and WiMAX networks. In the dissertation, we also propose the novel network designs based on local-interest-groups and traffic-tracing gateways, to augment existing wireless access networks and making them more resource efficient while providing higher end-to-end performance.