Research On OFDMA Access Technology In The Next Generation WLAN

With the rapid development of Internet and mobile Internet,WLAN terminals are facing with the indoor and outdoor dense deployment scenarios,which are featured by high communication speed,ubiquitous devices coverage,massive access user number and higher requirements of user experience.Traditional WLAN based on CSMA / CA random access protocol will lead to more serious conflicts and backwards.As a result,the current WLAN is faced with low channel utilization,low throughput,poor user experience and other major issues.Since the present WLAN is inefficient in terms of these challenges,IEEE Standard Committee has launched a new task group for 802.11 ax,which considered OFDMA as the key technology of physical layer,and adopted enhanced multiple access mechanism based on OFDMA as the key technology of MAC layer.Following the research status of the next generation WLAN,we regards the research of OFDMA based multiple access and the design of prototype system as the focus in this paper,and try to solve the problem of channel access and transmission in dense deployment scenarios to achieve higher spectral efficiency and betterregional throughput.The specific research contents and innovations are as follows.Firstly,the next-generation WLAN scenes and requirements the traditional multi-channel transmission mechanism leads to the rapid decline of channel utilization in the access point-intensive,user-intensive wireless environment,which can prove the necessity of introducing OFDMA key technology.Additionally,the existing problems of the traditional multi-channel transmission mechanisms as well as OFDMA multiple users access procedures are discussed deeply,which can prove the necessity of adopting OFDMA key technology and proposing new access mechanisms.Secondly,an enhanced OFDMA multiple access scheme is propsoed in this paper.In this scheme,making full use the multi user parallel transmission in multiple sub-channels,the traditional single channel competition backoff mechanism can be transformed into the competition of multiple subchannels,which can improve the spectrum access flexibility of OFDMA.In order to meet the uplink synchronization requirements of OFDMA,we design a random access mechanism for two-dimensional time-frequency resource blocks,which ensures that all access terminals can receive multiple users' access requests.Moreover,a new frame structure for enhanced OFDMA multiple access technology is designed.For performance analysis,the G-S network throughput delay analysis model is adopted to establish theoretical formulas to evaluate the upper bounds for throughput and delay for the enhanced OFDMA multiple access scheme.After that,we use simulation results to analyze the influence of the competition parameters on the performance,under saturated network load condition and actual network load condition.Theoretical analysis and simulation results can provide strong support and guidence to the breakthrough of the OFDMA multiple access technology and the application of the OFDMA multiple access in the next generation WLAN.Finally,to verify the key technology feasibility and practical performance of OFDMA random access,a prototype system applied to ultra-high-speed links and ultra-dense high-speed cells is designed and implemented.In the overall architecture design,the original system architecture of WLAN is inherited and the special requirements of future dense deployment scenarios are taken full account of.In the prototype system,the ZC706 FPGA board with embedded dual cores ARM Structure is adopted,the architecture and interfaces of the proposed enhanced OFDMA multiple access scheme are designed,and the detailed design of the software and hardware modules is given.On the basis of the prototype system,the advantages of enhanced OFDMA multiple access technology,the efficiency and the practical feasibility of platform design are analyzed in this paper.