Research Of IEEE 802.11ac Channel Estimation Method In View Of RF Conformance Test

With the enactment of IEEE 802.11ac and the rapid development of intelligent mobile terminals, the demand for 802.11ac devices is huge in the market. Therefore, independent development of efficient and reliable WLAN test instruments in production line for next generation Wi-Fi device has become an important field of research. In this background, this paper studys the IEEE 802.11ac protocol and channel estimation algorithm of WLAN test instruments, and the specific tasks of this paper are as follows:Firstly, we not only introduce the research situation of RF test for IEEE 802.11ac protocol and channel estimation technology, but also the key technologies of OFDM system are studied including the basic principles and features of OFDM system applied in the 802.11ac PHY. Then study the protocol specification of 802.1 lac PHY such as VHT PPDU frame structure, the single-user SISO transmitter system and the calculation process of EVM, one of RF conformance test.Secondly, we study the commonly used algorithms in channel estimation, mainly based on the data-aided methods, which include those based on preamble training sequence and pilot symbols estimations, and descibe pilot insertion mode, various interpolation methods. On this basis, we study several channel estimation methods which are suitable for 802.11ac proctol in recent years, including estimation based on LSF criterion, finding co-pilot, deciding on constellation-aware, using decision-directed estimation based on a reliable-symbol selection strategy. We anylaze their principle and implementation steps. Then we propose a variable coefficients iteration method, which is suitable for the channel estimation of 802.11ac WLAN test instruments. This method firstly use preamble training sequence for iniatial channel estimation, and then use the added co-pilot to further estimate, and update the channel response by an iterative way. We describe the principle and implementation steps about this method in detail.Thirdly, we introduce the hardware platform for the RF test system based on Aeroflex RF Tester, build the SISO receiving system for 802.11ac PHY based on Matlab, and analyze the specific implementation procedure of each module, and focus on the test of channel estimation module. We test the fundamental methods based on preamble training sequence and pilot estimation, and then complish the simulation of those methods which are suitable for 802.11ac studied in recent years, and compare their performance. Then we test the channel estimation method which is proposed in this paper. Through simulation, comparing and analyzing the simulation result we can observe that the proposed method has better performance in channel estimation of WLAN test instruments.Finally, we research on the RF conformance test items of IEEE 802.11ac standard, including the spectrum mask, transmit power, EVM, center frequency tolerance, phase error. Demonstrate the software systems for WLAN test, and show the test results at the highest rate in the bandwidth of 80MHz for 802.11ac respectively. Then we make a summary of this paper and discuss a future research.