Study On Multiple Access Technology Of Wireless Local Area Network

As one of the most effective wireless access methods, wireless local area network (WLAN) has aroused the interests of more and more users and researchers for its high speed, safety and convenience. Since the radio-frequency (RF) bandwidth allocated for wireless communications is a diminishing resource. WLAN has fundamental limitation on throughput and communication delays. With exponentially growing demand for multimedia application such as voice and video services, this limitation becomes a bottleneck for expanding the wireless network capabilities. As a consequence, next generation of WLAN should adopt other key technologies such as the smart antenna, which has proved to be a valuable add-in feature for communication systems.The research work in this dissertation carries a deep study on new techniques of WLAN and put emphasis on the multiple access protocol to support the integration of smart antennas with WLAN. The major achievements and results are outlined as follows.1. Based on the performance evaluation of the IEEE 802.11 MAC protocol which has the integration of contention and polling, a protocol for integrated data and voice transmission is proposed. Data traffic is transmitted with the Distributed Coordination Function (DCF). while voice with the Point Coordination Function (PCF). By simulation, we evaluate the network throughput and the average MAC Protocol Data Unit (MPDU) delay for various values of the protocol parameters and ascertain the max number of the voice sen ice users on the condition of defined data throughput. Especially, voice traffic is sensitive to delay jitter and here we point out the main factors influencing it. Numerical results show that it is important to choose appropriate protocol parameters and we should make a compromise between the number of the voice stations and the data traffic throughput to get the enhanced performance of IEEE 802.11. Finally, the performance of protocol in theory is derived, which verifies the correctness of the simulation results.2. Considering the change of the voice stations in the network, a self-adaptive transmission protocol to support multi-service over the IEEE 802.11 WLAN is put forward. The simulation results show that, on the premise of satisfying the maximumallowable delay of packet voice, the self-adaptive transmission protocol can improve the data traffic performance and increase the WLAN capacity by the dynamic and appropriate adjustment of the protocol parameters. Especially, the protocol is easy to be realized with no change in the MAC protocol needed.3. We put forward an exact approach to analyze the performance of the spatial signatures detection algorithms in terms of required time so that the access point (AP) becomes aware of user locations and grants access to the system. Through the analysis the optimal protocol parameters are gotten. Four different algorithms of detecting all the users' spatial signatures are compared. The numerical results show that the algorithm which distinguishes the users residing in or out of the broadcasting coverage range of the AP can provide lower detection delay. In addition, the simulation results verify the theoretical approach.4. The use of smart antenna in extending coverage range and capacity of wireless LAN dictates the employment of novel media access control (MAC) protocols, with which the AP provides access to remote users by learning their spatial signatures. A novel and efficient MAC protocol for WLAN with smart antenna is proposed. Employing the hybrid superframe structure of contention-free period and contention period, the protocol distinguishes the users residing in or out of the broadcasting coverage range of the AP. By simulation, we evaluate the average packet delay and the network throughput for the various values of protocol parameters. The performance of the protocol is compared with other different three protocols and the effectiveness and robustness of the novel protocol has proved through simulation. The results show that the protocol can extend the coverage range of WLAN effectively and support the data exchange between the AP and the stations residing out of its broadcast range.