Frequency Offset Estimation And Channel Estimation Research Of OFDMA And The Application In IEEE 802.11ax System

Since people’s requirements for the WLAN is improving., study on WLAN standard has never stopped. From the very first 802.11a standard,802.11b standard and the 802.11g, and the most widely used standard 802.11n, to the recently 802.11ac work in the 5GHz band, the data transmission rate is going faster and the WLAN is more and more reliable. When the 802.11ac is getting started, the Wi-Fi association and the IEEE announce the research on the next generation WLAN standard together, which is called IEEE 802.11ax. It is not like the previous standards which treat the throughput capacity as the most important goal, IEEE 802.1 lax pay more and more attention to the overall productivity and the users’experience about the network, and also introduce a new technology OFDMA which is the key technology of 802.11ax.In this article, we concentrate on the next generation WLAN IEEE 802.1 lax uplink OFDMA multiuser system, analyzing the channel estimation, channel equalization and the frequency estimation technology based on the design of the pilot in the data field.Firstly, we introduce the standard frame structure of the IEEE 802.11ax, and then describe the basic principle of the OFDM system and the uplink OFDMA system. And considering the demand of the IEEE 802.11ax,a brief analysis about the key technology OFDMA is given.Secondly, after the study about the pilot pattern of the IEEE 802.11 ax standard, we analyze the channel estimation for the uplink data field. Channel estimation for the pilot subcarrier is the first issue we need to solve, there are three algorithm, LS channel estimation, LMMSE channel estimation and the SVD-LMMSE channel estimation. With the channel values of the pilot field, the channel interpolation estimation is used to estimate the channel values of the data subcarriers. The simulation results indicate that the performance of the LS channel estimation is worse than the other algorithm, since it doesn’t consider the influence of noise, and the DFT channel interpolation algorithm is the most practical considering its performance and complexity. And the results also indicate that, for the IEEE 80.11ax uplink multiuser system, the user which allocated more RU has a better performance.Finally, combine the pilot pattern of the IEEE 802.11ax and a more efficient frequency offset estimation algorithm which is based on the difference of phase frequency offset, we simulate it in the uplink OFDMA multiuser scenario. The results show that with a superior algorithm, only a few pilots subcarriers is needed which reduce the storage overhead of the receiver, we get an excellent frequency offset estimation performance. And then two linear channel equalization algorithms are introduced. For the IEEE 802.11ax uplink multiuser system, no matter which user, MMSE channel equalization has a better BER and PER performance than ZF channel equalization.