Research On Resource Allocation And Congestion Control In Wireless Mesh Networks

With the development of wireless communication technologies and the prevalence of mobile equipments, to provide high quality services of wireless broadband access has become people's daily increasing demand. However, the relatively mature techniques of WLAN can't satisfy people's requirement for large coverage of wireless network since it can only realize single-hop wireless access. As a new next generation network, the wireless mesh network provides more extensive coverage of wireless access networks, and it has become a key wireless broadband technique according to its various advantages such as large coverage and low cost.Because the wireless mesh network uses multi-hop wireless technology, the performance of flows will decrease rapidly when they traverse through the network by multiple hops. So how to reduce the interference and improve the network performance are the key issues of wireless mesh networks. This paper aims to resolve these problems by researching on the channel assignment, multi-channel routing and congestion control for the IEEE 802.11-based wireless mesh networks. The major works and innovations of this paper are described as below:Firstly, the principle of wireless mesh networks is summarized. Some key problems for current wireless mesh networks are proposed and the shortages of existing researches are analyzed. The hiberarchy of node in IEEE 802.11-based wireless mesh networks and the related hot research issues are introduced. Meanwhile, the well-known international research programs and existing solutions are also summarized.Secondly, the problems of intra-flow and inter-flow contentions are analyzed. The principles and characteristics of realizing cross-channel communication in single-radio mesh networks and multi-radio mesh networks are introduced respectively. Three kinds of current channel assignment schemes are classified which are dynamic assignment, static (or quasi-static) assignment and mixed assignment. According to the characters of backbone mesh networks, a centralized quasi-static channel assignment scheme is presented which is able to provide flexible and efficient ways for utilizing the channel resources. Simulation results show that after using the proposed channel assignment algorithm, both the network throughput and stability get effectively improved.Thirdly, related ad hoc routing protocols and existing wireless mesh network routing protocols are summarized. The principle of existing multi-channel mesh routing protocols is introduced which realize channel-diverse and high-throughput routing by establish path metric which can evaluate path qualities. Via analyzing the interactions between channel assignment and routing and combining with the load-balancing function of multi-path routing technique, a load-balancing multi-channel routing scheme is proposed to provide high-throughput paths for the backbone traffics in wireless mesh networks. Simulation results validate that with the load-balancing routing algorithm, the aggregate network throughput surpasses those of the single-channel routing as well as the common multi-channel routing.Then, the problems for traditional TCP and UDP protocols to be faced in wireless multi-hop networks are proposed and two kinds of existing congestion control schemes for wireless multi-hop networks are classified, which are respectively the window-based schemes and the rate-based schemes. Through studies on the spatial channel reuse of single-channel mesh networks, a link-layer packet drop model for multi-hop transmission is established. Meanwhile, considering the high processing capacity and the traffic aggregate character of the mesh gateway, a rate-adaptive gateway congestion control scheme is proposed, aiming at improving the spatial channel reuse and avoiding congestion for single-channel mesh networks. Performance evaluations prove that the proposed scheme outperforms existing control scheme in both the network throughput and fairness.Finally, the paper studies the multi-hop transmission differences between multi-channel networks and single-channel networks, and presents dual channel reuse characteristic in spatial and spectral aspects for multi-channel networks. Existing congestion control schemes suffer MAC-layer transmission coordination problems due to this characteristic. So a new contention-aware congestion control scheme is proposed, which introduces the way of dispatching multiple packets at each transmission interval instead of single packet in traditional rate-based control scheme. The proposed scheme computes a proper transmission interval according to node's available bandwidth. As a result, it's able to relieve the MAC-layer contention as well as improve the channel utilization. Simulations prove that the proposed scheme has quite good effects in improving the network throughput and fairness as well as reducing the network delay.