Research On MAC And Routing Technology In Wireless Ad Hoc Networks

Compared with traditional Internet and wireless networks, wireless ad hoc networks havegreat challenges. Wireless ad hoc networks are typically characterized by infrastructureless ,self-organizing, multi-hop routing, dynamic topology, wireless channels with limitedbandwidth and nodes' limited capability. To be adapted to these special network characters, thecorresponding protocols must be designed. The medium access control technology andmulti-hop routing technology are the most distinguishing core technologies in wireless ad hocnetworks. Mobile ad hoc networks and wireless sensor networks are two important directionsof wireless ad hoc networks with different application fields and different features. Mobile adhoc networks are faced to the mobile communication of "people to people ''. The nodes aremobile and the topology changes rapidly, which is the main challenge of mobile ad hocnetwork design. Wireless sensor networks are faced to the information interchanging of"machine to machine and machine to people". The battery exhaustion is the dominant factorcausing node's failure. How to prolong the network lifetime with low power schemes is themain challenge of wireless sensor networks.This dissertation mainly focuses on important problems of medium access control layer andnetwork lay within the main application fields of wireless ad hoc networks. The channel accessfairness in wireless ad hoc networks, the low power MAC address coding in wireless sensornetworks, and the routing's dynamic topology adaptivity in mobile ad hoc networks etc., areresearched in detail .The main creativities of this thesis are summarized as follows:(1) The active relinquishment fairness algorithm is proposed for improving the channelaccess fairness in wireless ad hoc networks.The node's channel access fairness is an important metric of MAC protocol performance.IEEE802.11 MAC protocol is the fact standard of MAC layer in wireless ad hoc networks,which use the binary exponential backoff algorithm to control node's channel random access.The binary exponential backoff algorithm exists the channel access fairness problem inwireless ad hoc networks for the affection of hidden terminal and position competition. Thispaper presents the active relinquishment fairness algorithm. In order to improve the fairness, ituses the active relinquishment method to prevent node from occupying channel consecutively.In order to increase the throughput, it uses the data burst method to reduce the backoff waitingtime of channel access. The analysis and simulation results show that the active relinquishmentfairness algorithm can effectively improve the fairness and maintain the throughput whencompared to the binary exponential backoff algorithm. The new algorithm is simple to carryout and compatible with IEEE802.11.(2) A mixing address coding method is proposed for the design of the low power MACaddress coding in wireless sensor networks.The communication energy consumption is the dominant factor causing the energyexhaustion of wireless sensor. When the low power MAC address coding in wireless sensornetworks is designed, not only the energy consumption of address transmission must beconsidered, but also the following factors , such as the capacity of address codes, the support ofdifferent address types, and the address fairness etc, must be considered. In this dissertation theadvantages and disadvantages of current methods, such as the fixed size address coding and theHuffman address coding in wireless sensor networks, are analyzed. A mixing address coding ispresented and the performance parameters of address coding are put forward. The simulationresults show that the new method has merged the advantages of two kinds of address codingmethods, satisfied the design requirements of low power MAC address coding in wirelesssensor networks.(3) A new method of selecting stable paths based on the neighbor change ratio is proposedfor improving the routing's adaptability to dynamic topology in mobile ad hoc networks.The dominant feature of mobile ad hoc networks is dynamic topology, which causes theroutes break frequently, decreases the network performance and restricts the networkscalability further. Selecting stable paths is an effective way to reduce the routes break andimprove the routing's adaptability to dynamic topology. Current methods of selecting stablepaths in mobile ad hoc networks suffer from several shortcomings. They may need a hardwarefunction support for geographical position location or cross-layer function support for sendingsignal strength information to upper layers. In this thesis a new simple method for selectingstable paths is proposed. This method uses a Neighbor Change Ratio metric and does notrequire any special hardware support or cross layer support. The method selects path which hassmall hop counts and stable local topologies. NCR-AODV routing protocol is an extension ofthe AODV on-demand route protocol with the new method. The simulation results show thatcompared to the AODV protocol, the NCR-AODV protocol has reduced the long-paths' breakprobability and improved the network performance. It means that the new method can improvethe routing's adaptability to dynamic topology.