Research On Key MAC Technologies Of High Throughput In Wireless Local Area Network IEEE802.11n

IEEE802.11n whose main feature is high throughput, is the standard of next generation of wireless local area network. The work group of IEEE802.11 added some new MAC protocols to overcome the throughput constraint due to the large overhead of legacy MAC protocols. This thesis will study the MAC key technologies of high throughput: packet aggregation, reverse direction, central scheduling.As to packet aggregation, this thesis compared the transmission efficiency and reliability of four main aggregation methods. Then chose the A-MPDU with good transmission efficiency and reliablity as the research object. Derived the mathematical expressions of saturation throughput of DCF, EDCA and Multipolling syetem with A-MPDU. Analysed the relation of the system throughput and the aggregation number. The derived expressions can be a theoretical guide for practical application.In order to improve the system throughput of IEEE802.11n under delay constraint, an in-depth analysis is presented on the average delay of system and each backoff stage of distributed coordination function (DCF) with aggregation scheme. The average data quantity of one transmission with aggregation under non-ideal channel condition (transmission error exists) is derived. We get the calculating formula of saturation throughput of DCF system in non-ideal channel condition by inlaying the average data quantity into the mathematical expression of saturation throughput in Markov model which describe the DCF system in ideal channel condition. To maximize the saturation throughput, we propose an algorithm of dynamically adjusting the packet size and aggregation number according to the variable channel conditions, under delay constraint. The simulation results show that system throughput by using the proposed algorithm is obviously higher than using fixed packet size and aggregation number.As to bi-direction transmission protocol, this thesis derived the mathematical expression of saturation throughput of EDCA system with bi-direction transmission and A-MPDU, using the modified Markov model. Analysed the relation of bi-direction saturation throughput with the station number and aggregation number. The derived expressions can be reference for practical application.As to central scheduling, this thesis estimated the improving scale to system throughput with modifying central scheduling methods. Proposed a new central scheduling method to resolving the throughput degrading with hidden terminals. Compared the scheduling efficicncy of new method with other methods when existing various proportions of hidden terminals.