Research On OFDMA Resource Allocation And Synchronization Technology In IEEE 802.11ax System

WLAN (Wireless Local Area Network) is based on the wireless communication technology. It can satisfy users’ demand for wireless internet access in a certain area, so it has been widely used in many areas. With people’s communication demand changing to multimedia service, the existing WLAN communication system can’t satisfy the users’ requirement of bandwidth and quality of service. IEEE organization and Wi-Fi alliance have been started the standardization of the next generation of WLAN protocol 802.1 lax, which is expected to be completed in 2018. The biggest difference between 802.11 ax and previous ptotocol standards is that it introduces the OFDMA technology, which can support uplink multi-user data parallel transmission based on the OFDM.Moreover, as the expansion of the Internet, the Internet of Things (IoT) can achieve the full range of information perception, reliable transmission and data processing. WLAN is always used as the transmission network of IoT, which is called long range transmission scenario. Because of the high-density network and large scale fading channel, the MAC and PHY layer design of the previous WLAN system can’t be used in the new scenario. In this paper, we study the application of 802.11ax in the long range scenario for the above problems.First of all, we introduce the basic MAC layer and PHY layer protocol of 802.11ac, describing the details of each part of the preamble in the framework and the MAC layer access mechanism. Then explain the principle of OFDMA technology and its implementation in the 802.11ax system.Furthermore, we describe the long range application of WLAN system related to IoT, analyzing the challenges that 802.11ax faced in the high-density network and large scale fading channel conditions. In order to support more users’data transmission,802.11ax divides the time, frequency, space resource into several parts. Therefore, it’s necessary to add resource indication part in the frame structure. In chapter three, we proposed the G-RTS/G-CTS access mechanism based on the grouping concept, which enables 802.1 lax to support the simultaneous access of UL multiple STAs effectively. In addition, we provide the design of the resource indication scheme, which can support both OFDMA and MU-MIMO.Finally, we study the PHY layer design challenges brought by long range transmission scenario, explaining the importance of synchronization in the receiver signal processing. And provide corresponding improved algorithm of normal synchronization algorithms of WLAN system, making 802.11ax more suitable for long range transmission scenario. We use the large scale fading model to simulate the long range scenario, applying the classical time synchronization and frequency synchronization algorithms, but the performance is not good. Therefore, we bring about a new time synchronization algorithm which is based on differential correlation. And put forward to use Golay sequence as the L-STF and L-LTF preamble to synchronize. Simulation results show that the proposed algorithms have better performance than the original algorithm in the long distance transmission scenario.