Study On Automatic Detection And Time Delay Estimation Of TDMA Signals

TDMA (Time Division Multiple Access) is one of the key technologies of ground and satellite mobile communications. Research on TDE (Time Delay Estimation) of TDMA signals has a very important practical significance for mobile targets positioning. TDMA is a multiplexing method of multi-users. Different users have different locations, which leads to different time delay values. So how to extract the slot signals of different users is a key problem. Bursty traffic is another significant feature of TDMA system, so the occurrence moment of TDMA signals has a large uncertainty. Thus, achieving the automatically signal detection technology can greatly improve the efficiency of practical spectrum monitoring.Oriented to the wireless positioning technology, automatic detection, time slot extraction and time delay estimation methods of synchronized TDMA signals are systematically studied in this paper. Specific research results are as follows:(1) The cyclic autocorrelation characteristic of TDMA signals with modulation type of BPSK is derived and analyzed. Then a sliding window based cyclic autocorrelation detection of TDMA signals is proposed, and experiments have demonstrated its effectiveness comparing with the direct cyclic autocorrelation detection method. Meanwhile, in order to overcome the defect that the method above requires experiments to identify the threshold, the asymptotic optimality theory is applied to the TDMA signals detection. And a cyclic autocorrelation based CFAR detection method of TDMA signal is proposed. The paper experimentally validated its feasibility.(2) Time slot extraction problem of TDMA signals under both protocol unknown and protocol known conditions is discussed in this paper. Base on the analysis of TDMA signal in the time domain, a blind time slot extraction algorithm is proposed with protocol unknown. Although this method has limitations, for the TDMA signals which meet the requirements, it can serve the function of blind slot extraction pretty well, which increase the system’s ability to handle unknown TDMA signals; As for the protocol known condition, take the disclosed protocol of GSM system as example, we propose a GSM frame synchronization method and a non-cooperative time slot extraction scheme, providing a solution idea for other protocols.(3) Considering the fractional time delay and frequency difference problems, different interpolation methods and frequency difference estimation methods are studied. On the study of ambiguity function, an improved time delay estimation method based on fourth-power spectrum and MCZT for the TDMA signals is proposed, and the experimental results show that the improved method has better estimation effect. Finally, the automatically detection and time delay estimation solution of TDMA signals is proposed, and experimental simulation is given to test the TDE performance of TDMA signals, which demonstrates the validity and accuracy of the system.