Research On Acknowledgement Mechanism Of Medium Access Control In Wireless Mesh Networks

For the past few years, with the improvement of the wireless communication andchip technology, the convenient mobile device has been rapidly developed. Our demandfor the Internet access in mobile environment is growing. Nowadays the cellularnetwork (such as GPRS,3G and LTE) has been widely developed to provide wide rangenetwork access, but the cost is relatively high. In addition, the cellular network isdifficult to meet the explosive growth need of mobile terminal equipment in dataquantity. Wireless Mesh network, which can provide high speed, low cost and highstability network acces, is considered to be a substitute of cellular network for mobiledevice to provide network access service. IEEE802.11, with the advantages ofsimpleness and efficience, is widely applied in the wireless Mesh networks.In IEEE802.11, the MAC protocol is an important factor for the work performance and has beenwidely studied.Due to the vulnerability to multipath effect, noise and interference, the quality ofwireless link is not stable. IEEE802.11uses frame acknowledgement mechanism toimprove the reliability of data transmission. Frame acknowledgement mechanism canimprove the network transmission reliability but the acknowledgement frames willoccupy part of the channel resources at the same time, which limits the networkthroughput. In order to overcome the disadvantage of IEEE802.11in movingenvironments, researchers proposed a mutiple association scheme to provide seamlessnetwork access in recent years. In theory, mutiple association scheme can effectivelysolve the frequently re-association problem, but existing MAC layer acknowledgementmacanism is not suitable.In order to solve the above problems, this paper studied the details of MAC layeracknowledgement mechanism, and proposed a cross-layer scheme to combile the MAClayer acknowledgement frame with TCP protocol’s acknowledgement message toimprove network performance.This cross-layer scheme is applicable to unidirectionalTCP flows, which is universal in wireless Mesh networks. We put the TCP protocol’sacknowledgement information into the MAC frame to reduce the acknowledgementframes and packets, which improvs the utilization ratio of network bandwidth. It canalso guarantee data transmission reliability to some extent as the traditional way. Inaddition, in view of the problems of recently proposed multiple association mechanismin MAC layer acknowledgement mechanism, this paper analyses the possible ACKcollision problem and conducts sufficient experiments to verify our analysis. Throughtheoretical analysis and actual tests, this paper concluds the conditions where the ACKcollision will occur. To solve the ACK collision problem, this paper proposes an ACK detection scheme. ACK detection scheme just tests the signal length of collided ACKswhen ACK collision problem occurs. The ACK detection scheme does not need to makeany modification of existing hardware, and can effectively solve the ACK collisionproblem, which makes multiple association scheme into practical application.The simulation and actual system test results show that the proposed optimizationsof the MAC layer acknowledgement mechanism can solve the defects of traditionaltechnology and effectively improve the network performance.