Research And Implementation Of Multi-User Access Technology Based On Layered Code In Next Generation WLAN

In recent years, with the rapid development of wireless communication and the rapid growth of the number of high performance intelligent terminal and wireless equipment, there has formed a relatively crowded WLAN environment, especially in wifi hot spot. Therefore, the bandwidth demand is greatly increased. However, the available spectrum resources for WLAN is very limited. Therefor how to maximize the utilization of spectrum resources and improve the transmission capacity and the quality of service as far as possible is an important research direction of the next generation of WLAN standard. The spectral efficiency mainly depends on the MAC protocol, so more and more scholars focus on the study of the optimization of MAC protocol in order to achieve higher efficiency and throughput.The CSMA/CA adopted by IEEE802.11 is firstly analyzed and summarized in this paper. Under CSMA/CA, only one user is allowed to access channel for data transmission at a moment, moreover, there existing the problem of hidden node and the low utilization of channel, especially when the number of users is large. Even if the system adopts the binary backoff mechanism, collisions which seriously affect the performance of the system still occurs frequently. The multiuser access mode based on layered code for WLAN is studied in this paper. In this mode, multiple users can occupy the same time-frequency resource for data transmission to greatly enhance the system throughput. The MAC access procedure of the multiple access scheme is proposed and the frame structure that involved is modifid. Then, the system throughput with different parameters for the proposed access mechanism is simulated. The simulation results show that the system throughput in intensive scenarios can be effectively improved in comparison with the existing CSMA/CA mechanism and the enhancing degrade of throughput is proportionate to the number of used layered code. In addition, the optimal contention window scheme and SD scheme that several papers has proposed are introduced in this paper. Although the performance of SD scheme is worse than the optimal contention window scheme, its implementation complexity is far lower than the optimal window scheme. Therefore, an enhanced SD scheme that can approach the performance of the optimal window scheme is proposed in this paper.The multi-user access scheme based on layered code with the enhanced SD scheme is studied to further improve the performance of system.