Research Of MAC Access Technology And QoS Guarantee In Broadband Wireless Networks

As broadband wireless networks are being used in more and more areas, some new kinds of services have come out. The aim of modern network study is to provide quality of service (QoS) guarantee to different kinds of services and improve the network efficiency as much as possible. Since the medium access technology implemented in medium access control (MAC) sublayer is very important to QoS guarantee, the study of medium access technology in broadband wireless networks is of high significance.In this paper, we studied the medium access technology of broadband wireless access networks, that is, wireless local area networks (WLAN) baesd on the IEEE 802.11 standard and the IEEE 802.11e draft, and wireless metropolitan area networks (WMAN) based on the IEEE 802.16 standard.There are mainly two kinds of medium access functions, contention access function and center controlled scheduling function. As to contention access function, our research focused on the distributed coordination function (DCF) and enhanced distributed channel access (EDCA) of WLAN. After analyzing the IEEE 802.11 standard and 802.11e draft deeply, we proposed a new analytic model for EDCA. It is a Markov model taking inside collision resolution, retry limit and error-prone channel condition into consideration. After that, simulations were carried out to evaluate the accuracy of the analytic model. Using this model, we analyzed the influence of some important parameters, such as packet size, forward error correction coding scheme and contention window size, to the system performance. At last, we pointed out the characteristics of DCF and EDCA in providing QoS guarantee.As to center controlled scheduling function, our research focused on the two systems of WLAN and WMAN. In WLAN, there are two scheduling functions, the point coordination function (PCF) and hybrid coordination function controlled channel access (HCCA). We discussed the scheduling algorithms belonging to these two functions, and provided the analytic method for calculating polling efficiency of HCCA. The formulae of polling efficiency using singlepoll and multipoll are derived and evaluated by simulation. We proposed a new multipoll algorithm called SA-Multipoll. Its polling efficiency is analyzed and compared with other existing polling algorithms. It is proved that the proposed algorithm has higher polling efficiency. Finally this algorithm is used to support conversational voice services while connecting WLAN with Ethernet and other backbone networks.As to WMAN, IEEE 802.16 standard is deeply analyzed in this paper. Based on the service classes proposed in the standard, we gave out the two-level scheduling model and analyzed the scheduling algorithms on the two levels. Besides, the scheme jointly considering uplink and downlink was introduceded. At last, we explained the MAC scheduling architecture in TDMA mode, and proposed a scheduling scheme in OFDMA mode.