Research On The Frame Aggregation Mechanism Of IEEE802.11n

With the tremendous growth of wireless communication services and rapiddevelopment of intelligent hanheld devices, high speed WLAN becomes more andmore desired. To break the bottleneck in improving the throughpout at MAC layer,frame aggregation is proposed in IEEE802.11n.Frame aggregation could improve the throughput and efficiency of MAC layer bysending several data frames within one transmission opportunity. In this paper, bothA-MSDU (MAC Service Data Unit Aggregation) and A-MPDU (MAC Protocol DataUnit Aggregation) are investigated. Analysis shows that A-MSDU has loweraggregation overhead but it is vulnerable to the error-prone channel. For differentBER, there is a particular A-MSDU length that can maximize the throughput.Compared to A-MSDU, A-MPDU has a higher aggregation overhead but outperformsA-MSDU when the channel is in bad condition.For the sake of combining the advantages of both A-MSDU and A-MPDU,two-level aggregation is analyzed in this paper. Theoretical saturated throughput andaverage delay of two-level aggregation are derived by extending the Markov chainmodel. Baesd on the extended model, an algorithm of dynamically adjusting theA-MSDU frame length in two-level aggregation (TA-DAAL) is proposed. TA-DAALcould adjust the A-MSDU frame length according to the BER of channel and theservice delay limit so as to meet the delay requirement and improve the throughput atthe same time. Simulation results show that the proposed algorithm has a stable delayperformance within the whole BER range and could achieve a higher throughputcompared to the traditional fixed length two-level aggregation scheme and A-MPDU.In addition, TA-DAAL can also adjust the number of aggregated MSDUs according tothe MSDU size. Thus the throughput can keep stable when the size of MSDUchanges.