Research And Implementation Of Carrier Synchronization Technique In SOQPSK Short Burst Systems Of Xidian University

The short burst communication systems are widely used for many fields of communications, such as military communications, satellite communications, deep space exploration,high-speed mobile communications and so on. As the channels of these systems are limited in power and bandwidth, it is the primary problem to communicate more efficiently with the limited power and frequency. The shaped offset quadrature phase-shift keying(SOQPSK) signal is a special form of CPM modulation, which is based on OQPSK. It has become the most common mode of modulation in above areas because of its characteristic of constant envelope, and its advantages of high frequency spectrum utilization, high power utilization and so on, which is inherited from CPM and OQPSK. In addition, the received signal has a relatively large frequency offset due to the rapid relative movement between the communicating parties. Therefore, in order to be received reliably for the signal, we should consider how to realize accurate carrier synchronization in the environment of large frequency offset.In order to solve the above mentioned problem, we firstly study the carrier synchronization algorithms based on the time domain correlation function, including Kay algorithm, Fitz algorithm, L&R algorithm, M&M algorithm and CC algorithm. And the frequency-domain carrier synchronization algorithms based on FFT are also studied, including FFT algorithm, R&O algorithm, AVG algorithm, R&A algorithm and RPA algorithm. Through the research and analysis of these two kinds of algorithms, it is obvious that the time domain algorithms have higher estimation accuracy and the frequency domain algorithms have larger estimation range. And the cross correlation(CC) algorithm and the rotational periodogram averaging(RPA) algorithm are the best algorithms of these two kinds of carrier synchronization algorithms, respectively. Especially the CC algorithm, its estimation range and estimation accuracy can be adjusted according to the distance between two pilot used for cross correlation operation. Secondly, considering their own advantages and disadvantages of time domain and frequency domain carrier synchronization algorithms, a novel distributed joint time-frequency domain(DJTFD) carrier synchronization algorithm is proposed. The main idea is that it first takes advantage of RPA algorithm to get a coarse frequency offset value, and then the CC algorithm to obtain a fine residual frequency value. However the frequency domain estimation has a larger residual offset with a limited pilot overhead. So we need the distributed time domain estimation to assure both larger estimation range and higher accuracy. Simulation results show that the proposed algorithm has both low complexity and high accuracy in the estimation range of ±50% symbol rate. Finally, the modulation and demodulation technique of SOQPSK and the DJTFD carrier synchronization algorithm are finished in FPGA chips based on the Verilog program language and the software of Quartus II 9.0. Then we analyze the resource occupancy and information processing speed of this FPGA project. And the correctness of this scheme is verified by simulation.