Research Of The Iterative Synchronization Algorithm For BVR Wireless Communication System

The over-the-horizon wireless communication achieves reliable communication using the inhomogeneous in the air to scatter the electromagnetic signals. The scattering object scatters a part of the electromagnetic signals to the direction of the receiver. Then the receiver with a high sensitivity receives this week signal, achieving long-distance communication with its ultra-high performance. BVR scatter communication systems have shown a clear advantage both in the military and civilian communications, and they are increasingly being used. In order to ensure that the wireless communication systems can have high quality of demodulation and decoding with weak received signals, high accuracy is required for synchronization algorithm.To achieve high accuracy synchronization algorithm in the BVR wireless communication systems, the thesis first discourse BVR scatter communication channel model, development process, and synchronization technology, then research the key technologies in the system in depth, such as the symbol timing estimation, MIMO and Golay sequence. On this basis, the thesis built a communication model of transmitter and receiver, designed pilot sequence, realized the entire synchronization function of the receiver. The thesis put emphasis on analysis of the anti-noise performance of Golay sequence, definition of adaptive threshold using "early-late-mid gate" and the design of loop filter. Ultimately, the thesis simulated the variance of relevant results in different lengths and the output of the loop filter values. The result proved the reliability of the program. At last, a precise synchronization was achieved. This thesis has three innovations. The first one is the use of relative threshold value and absolute threshold value during capture process, the relative threshold value is used to extracting the maximum correlation, and the absolute threshold value is used to prevent the false caused by noise. The second one is the "early-late-middle gate" algorithm which is based on the "early-late gate" algorithm, the "middle gate" is used to provide different threshold value in different SNR case. The third one is the use of "cubic spline" method to adjust the samples, in order to achieve high-precision adjustment of samples.At last, the synchronization method was implemented on the FPGA. Validation results show that system can achieve accurate capture under-30dB SNR case, and the tracking loop can ensure that the deviation of samples kept within1/8samples, which reached the system communication requirements.