Research On MAC And Load Balancing Technology In Mobile Ad Hoc Networks

Mobile Ad hoc networks (MANET) is one of the research hotspot in mobile communication technology area and it is absolutely the result of the fast development of communication, network technique and requirement to the global information sharing. MANET plays a more and more important role in many aspects of people's daily life depending on its characteristics such as multi-hop, no infrastructure, self-organized and fast deployment. The wide application and development prospect of MANET have driven and stimulated the energetical development of relevant research work. Under this background, this dissertation carries on deep research and study on how to less the influence of the interference in MAC protocol design in MANET, how to choose the more appropriate sending power and the load balancing problem.This dissertation focuses on the research of three aspects in MANET. The first two is based on the Distribution Coordination Function (DCF) in the standard of media access control in IEEE 802.11 and concretely we emphasize on the influence about the interference problem about RTS/CTS mechanism in IEEE 802.11 DCF and search the improvement method. The load balancing problem in MANET is also investigated. The main contents and innovation of this dissertation are listed as following:1. The history, main characteristic, application prospect and research hotspot of MANET are reviewed. The IEEE 802.11 protocol and its media access control method are discussed too. We analyze the distribution coordination function (DCF) of IEEE 802.11 which includes two access mechanisms: one is the tow-way handshake mechanism; the other is the four-way handshake mechanism known as RTS/CTS (Request to Send/ Clear to Send) mechanism. We provide an extensive analysis of the RTS/CTS mechanism and the hidden terminal problem.2. Based on the concept of interference range and transmission range, we deduce the relationship about the distance between the sender and transmitter with interference and transmission range. We point out that it exists that interference range maybe larger than transmission range leading to the effectiveness problem about the RTS/CTS mechanism. Then an improvement named PCR (Probabilistic CTS Reply) method is proposed which considering both the influence of interference range and the opportunity of CTS reply. PCR take the reply power threshold and the reply probability into account and both the theoretical result and simulation can prove that PCR can less the interference probability and improve the network performance.3. According to the power control mechanism using in IEEE 802.11 DCF, the problems and the solution are discussed. Firstly we analyze the mathematics expressing about transmission range and interference range using sending power. Then we discuss the hidden terminal problem in power control mechanism. In order to control the interference range under the transmission range, a new method to choose the more appropriate sending power is proposed which can less the influence about the hidden terminal according to the simulation results.4. The load balancing problem in MANET is discussed. We take the multi-path between the communication nodes, the media usage and the traffic load of the nodes, and the route discovery method into account, and propose a load balancing judgment standard based on ARLR (Average Remained Load Ratio). Then LBS (Load Balancing Strategy) is proposed which can find the appropriate path. The results of the theory analysis and the network simulation give the conclusion that LBS can effectively balance the traffic of the mobile ad hoc networks and improve the performance of the network.