Research On Synchronization And Channel Estimation Of IEEE802.11a/b/g/n RF Conformance Test

The products and devices developed for WLAN based on IEEE802.11 Std. have drew much attention owing to the development of WLAN. The RF conformance test for these products is of great significance. The focus of this research is on the algorithms of the synchronization and the channel estimation of WIFI integrated tester. The main contents are listed as follows:Firstly, the physical layer of IEEE802.11b Std. are described, including the basic principle of DSSS, the model of transmitter and receiver, the frame structure and the modulation. Meanwhile, the physical layer of IEEE802.11n Std. are introduced, including the basic principle of OFDM, the transmission structure, the frame structure, and the major parameters.Secondly, the synchronization algorithm and the channel estimation algorithm for the receiver based on IEEE802.11b Std. are studied. Two types of symbol synchronization applicable to 802.11b systems are described. On account of the excessive amount of calculation as well as the characteristics of the received data, coarse synchronization is realized by using signal energy and fine synchronization is then achieved by using SFD. The frequency offset estimation is divided into coarse frequency offset estimation with no data-aided and fine frequency offset estimation with data-aided. Channel estimation is realized by using good correlation of Barker codes. The results of frequency offset and EVM are close to the results of the Aeroflex PXI3000 solutions.Thirdly, the synchronization algorithm and the channel estimation algorithm for the receiver based on IEEE802.11n Std. are studied. The impacts of the timing synchronization error and the frequency synchronization error on the performance of integrated tester are discussed, and three types of timing synchronization applicable to OFDM system are introduced. In order to solve the timing inaccuracy and the phantom problem, timing synchronization is improved by conjugating the long training sequence with the local training sequence and then accumulating the derived energy. A distinct single peak is observed in the simulation result and the peak appears at the initial position of the long training sequence. The time domain method and the frequency domain method of frequency synchronization are derived. In order to solve inaccurate estimation of frequency, experiments are conducted and the results indicate that by taking the midpoint of the cyclic prefix of the long training sequence as the initial position of the fine frequency offset, the experimental results are close to the results of the PXI3000 solutions. The channel estimations based on the training sequence and the pilot are introduced. According to the high SNR of channel in the integrated tester, a new channel estimation method based on the LS algorithm is proposed by fitting the impulse response function, the test results are close to the results of the PXI3000.Finally, the test system and the DUT are introduced briefly. The simulation platform of 802.11b/n receiver is built, and the realization of each module of the receiver is introduced according to the test process. The proposed synchronization and the channel estimation are applied to the receiver and the simulation platform is verified by comparing the mean and variance of the frequency offset as well as the EVM of data which are obtained from DUT and vector signal generation. The results indicate that the synchronization algorithm and the channel estimation algorithm proposed in this paper are of strong stability and high test precision characteristics.