| With the development of digital communication,the traditional digital communication system has a fixed transmission rate,which greatly increases the difficulty and complexity of communication between systems at different rates.The universal digital communication system based on software radio solves the problem of multirate signal processing and has become a hot research topic for scholars at home and abroad.Therefore,this paper combines the research project and software radio technology of a research institute to design and implement a variable rate QPSK modulation and demodulation system.In terms of modulation,the shaping filter is mainly studied.In order to solve the problem that the symbol rate and the system clock are not integral multiples,the original implementation method is improved,and an asynchronous forming filter that can satisfy any symbol rate is designed.In the aspect of demodulation,the principle of resampling is first studied.In order to solve the problem of multirate signal processing,a high-efficiency decimation filter bank cascaded by CIC filter,HB filter and FIR filter is designed.Secondly,for carrier synchronization,in order to improve the phase-detection performance,the arc-cut phase-detection method based on CORDIC algorithm is adopted to study the synchronization performance under different noise bandwidth and signal-to-noise ratio.Finally,the timing synchronization method based on interpolation filter is analyzed.In order to achieve both capture and tracking performance,a structure combining AND_filter and second-order loop filter is designed to achieve fast capture speed and small timing error jitter.Good performance.Based on the above research and MATLAB simulation,the FPGA program of each module is written,the design scheme of the hardware platform is given,and the hardware test is carried out by the host computer.The test results show that the system can complete the modulation and demodulation with variable symbol rate from 20 kbps to 20.48 Mbps,which has good demodulation performance and verifies the feasibility and correctness of the system. |
