The Research On Frame Synchronization Detection Technology For OFDM-WLAN

OFDM technology, which is a multi-carrier modulation technique with high spectral efficiency, can effectively combat multipath delay spread and frequency selective fading. As one of the key technologies in IEEE 802.11ac standard, OFDM is very sensitive to synchronization error, especially the timing deviation and the frequency deviation since the strict orthogonal between adjacent subcarriers is required. Therefore, synchronization is crucial in the IEEE 802.11ac standard. In the WLAN system, the synchronizations include frame synchronization (coarse time synchronization), coarse frequency synchronization, symbol synchronization (fine time synchronization), fine frequency synchronization. The purpose of frame synchronization is to determine whether there is one frame which has been detected and obtain the frame starting position. Consequently, it is the most important prerequisite for all other synchronization operations. The better performance of frame synchronization would contribute to subsequent other synchronization algorithms. Only when all synchronization algorithms accurately have been finished, the received data can then be demodulated accurately and successfully. With increasing user demand, it requires that WLAN technology can adapt to a more complex channel environment. Therefore, how to complete accurately frame synchronization in the more complex channel environment is a real problem which is worthy of study.This thesis considers IEEE 802.11ac standard as examples. The legacy short training sequence (L-STF for short) is used to frame synchronization in IEEE 802.11ac standard. Thus, we make a in-depth study from two aspects:one is the sequence itself, the another one is the metric function of frame synchronization, and seek a kind of frame synchronization algorithm which has a low complex and outperforms the conventional frame synchronization algorithm.On the one hand, from the structural characteristics of the sequence itself and autocorrelation, Golay sequences with zero autocorrelation (new short training sequence) is proposed which is instead of L-STF. Not only new sequence has similar almost PAPR with L-STF, and the zero autocorrelation features of the new sequence make that the metric of frame synchronization has more stable amplitude, so the probability of frame detection was obviously increased, in other words, the probability of missed detection is reduced.On the other hand, from the perspective of frame synchronization metric function, two improved metric function of frame synchronization have been proposed, and they were statistically analyzed. Hence, it theoretically explains that the algorithms based on the improved metric functions have a better performance of frame synchronization compared with the traditional algorithms. For WLAN simulation platform, the simulation results indicate that the improved metric functions make that the new algorithms has superior performance of frame synchronization compared with the traditional algorithms of frame synchronization.