Research And Implementation On Synchronization Agorithm For SC-FDE Systems In Low SNR Environment

With the rapid development of the wireless communication technology in the past few decades, people have more stringent requirement on the performance of wireless communication. In order to meet requirements of long-distance transmission in low SNR environment, microwave communication technologies have emerged over the horizon. OTH microwave troposcatter communications mainly include troposphenc scatter communications and meteor burst communications. Tropospheric scatter communications systems with anti-interference ability, long non-relay transmission distance, high security, good mobility and other characteristics, have been widely used in not only military communications systems but also civilian communications systems. However, in order to achieve the advantages above, Synchronization technology, as the prerequisite of demodulation and decoding, has played a vital role in these communication systems.In this paper, we study the design and implementation of synchronization algorithm in the single-carrier frequency domain equalization (SC-FDE) system in tropospheric scatter communications. Firstly, we analyze the transmission characteristics "of tropospheric scatter channel and study the basic principles of SC-FDE system, multiple-input-multiple-output(MIMO) technology and common synchronous training sequence, etc. Secondly, we have designed the key modules and three different frame structures, including synchronizing frame, non-synchronizing frame and channel-adaptive frame, in the SC-FDE system. Finally, according to the system programs and different frame structures, we have made a detailed design of the synchronization system, improved the capturing algorithm in time domain to that in frequency domain, and implement the synchronization scheme on the FPGA hardware platform. Additionally, we have analyzed the autocorrelation properties of Golay complementary sequences and its change under different noise interference and designed the frame structure based on Golay complementary sequences, in which string time domain, parallel hybrid autocorrelation detection methods have been used in capturing. In order to further achieve the requirements of fast and accurate synchronization, fast Fourier transform has been used in the frequency domain correlation; sooner or later the door has been used in a combination of sample values to adjust tracking; multipath search and sample has been in the adjustment of tracking strongest path.This paper focuses on the following three aspects. Firstly, we combine the symbol tracking and strong path tracking together for the purpose of adjusting the sample. Secondly, based on the improvements of the synchronous frame synchronization, the direct use of the improved frame structure has been used in fast synchronization. Thirdly, based on this synchronization system, we have designed the channel-testing program, which not only verifies the feasibility of synchronous systems, but also tests the basic features of the actual channel. The results show that the frequency difference between the sending and receiving end is less than2Hz, and the SINR threshold is low to-32dB when the Doppler shift is less than lOHz. In addition, the tracking robustness of this system is very good.