Research On Techniques Of Multiple Access And Routing For Wireless Multihop Networks

Wireless multihop network is the self-organized network architecture, which is composed of mobile nodes. Wireless multihop network can be deployed instantly and provides network communications for highly mobile users, without the need of any pre-established infrastructures. This dissertation is dedicated to researches on some key techniques of multiple access and routing for wireless multihop networks.In wireless multihop networks, the effects of hidden terminals on the single common channel can be greatly reduced by using CDMA techniques. In chapter 2, we presented two families of nonlinear multiple access sequences, namely BPC sequence (Balanced Phase Controlled sequence) and NPC sequence (No-based Phase Controlled sequence). NPC sequence is a generalization of construction of BPC sequence. On the base of a No sequence family of period 2n-l and the cyclic shift of a phase sequence of period 2n/2+1, a family of 2n/2(2n/2+1) NPC sequences can be constructed. Compared with some typical nonlinear sequences, NPC families can provide much more sequences, with 0-1 balance and good correlation. Their correlation bound is similar to Gold sequences of the same period. With the use of NPC families, much more mobile nodes can be contained in wireless multihop networks, for the static allocation strategy of multiple access sequences; and requirement of topology control can be reduced for the dynamic strategy, so that better connectivity is permitted.Transmission schedule to ensure good system performance is an important and complex issue for TDMA wireless multihop networks. The purpose of the transmission schedule is to allocate the transmission slots for mobile nodes to provide the contention-free packet transmission and maximize the spatial reuse of time slots. In charpter3, a new transmission scheduling algorithm, so called as CA-PRS (Collision Avoidance Proper Robust Schedule) algorithm, is presented. A distinguished difference from traditional PRS is that, CA-PRS algorithm specifies a unique transmission schedule for each link, and adjusts the slot assignments in response to dynamic topology changes, to avoid contention for packet transmissionover the shared wireless medium. The problem of head-of-line blocking in CA-PRS algorithm is also analyzed, and the degradation of performance caused by head-of-line blocking can be eliminated by using virtual queuing policies with certain packet scheduling. The algorithm proposed has some properties, such as low protocol overhead, simple and easy to implement, and eliminate the requirement of the maximum nodal degree in C-PRS algorithm, and all these make it suitable for the network environment of highly mobility.The limitation bandwidth is a basic characteristic for wireless multihop networks. How to make the optimal use of wireless resource is always an attractive topic for such network architectures. In chapter 4, we developed a novel dynamic slot scheduling algorithm, referred as M-PRS (Migratory Proper Robust Schedule) algorithm. In this method, nodes in the network are divided into three categories by using the threshold strategy, such as light-load, middle-load and heavy-load nodes. By using the distributed message communication mechanism, mobile nodes in the network can dynamically reallocate transmission slots, so that some certain slots assigned to light-load nodes can be transferred to heavy-load nodes, to alleviate the congestion on them. A judgment criterion of the migration slots is also given to reduce the collision in packet transmission. Simulation results reveal that, M-PRS algorithm has the advantages over non-migratory CA-PRS algorithm with more flexible sharing of channel resources, and effective improvement of the system throughput.Routing is an actively research area related to wireless multihop networks. The development of the efficient routing protocol is essential if wireless multihop networks need to meet the demands for higher data rates within the limited amount of the available radio bandwidth. In chapter 5, a novel multiple-path table-driven routing protocol for wireless multihop networks, referred as M-WRP (Multipath Wireless Routing Protocol) is presented. M-WRP protocol introduces the multiple-path routing mechanism to WRP, and establishes multiple paths with equal distance between source and destination pairs, so as to provide the possibility of routing optimization. A criterion of selection in forwarding paths, based on the metric of "Minimum Path Average Hop" is also given, to achieve load balance and...