Research And Implementation On Chain-type Wireless Mesh Networks Based On STDMA

The characteristic of self-organization of wireless mesh networks meets the requirements of the node of the Internet of things with independent management capability.The performance of the MAC layer access mechanism can directly affect the performance of the network,and the CSMA and TDMA are often used as the MAC layer access mechanism in wireless mesh networks.The Related researches show that TDMA access mechanism is more suitable than CSMA access mechanism for long-distance network scenarios,such as rivers,coastal lines,highways,national land borders and underground mine tunnels.The geographical nature of these premises demands that mesh routers deployments should be restricted to the long stretches of narrow and elongated corridors.These scenarios are called as chain-type wireless mesh networks.Although the TDMA mechanism can improve the performance of the wireless mesh network,the way to allocate different time slots for each node is the waste of channel.Therefore,improving the channel utilization ratio of TDMA is the core and key point of this thesis.First of all,this thesis summarizes the concept of CSMA and TDMA access mechanism in wireless mesh network,and introduces that the TDMA access mechanism is more suitable for long-distance wireless mesh network than the CSMA.Since end-to-end delay is often used to evaluate the performance of wireless mesh networks,this thesis compares the end-to-end delay between CSMA and TDMA access mechanism in wireless mesh networks with mathematical formulas and simulation.Among them,the mathematical formula about end-to-end delay is based on the queuing theory.The theoretical formulas have reflected that the packet collision and the packet waiting time are the main reason that affects the end-to-end delay of CSMA and TDMA respectively.By comparing the end to end delay,it is proved that the TDMA access mechanism is more suitable for long-distance chain-type wireless mesh network.Secondly,this thesis uses spatial re-use technology to solve the problem of the waste of channel of conventional TDMA,and it is proved that spatial re-use TDMA precedes conventional TDMA in term of end-to-end delay by using mathematical formulas and simulation,and points out that the data packet waiting time is the main reason to have less end-to-end delay.To solve the problem that researches and methods about spatial re-use TDMA are not suitable for the chain network structure,this thesis combines hello message of AODV routing protocol with spatial re-use technology to design a self-adapting STDMA access mechanism.The mechanism does not need to allocate time slots for each node in advance,and can automatically complete the allocation of time slots by exchanging Hello messages.Finally,the proposed self-adapting STDMA access mechanism is implemented and can successfully run in the NS2 simulation tool,and it is proved that the self-adapting STDMA access mechanism is more suitable for long-distance chain-type wireless mesh network by using the myEvalvid video quality assessment tools.