Study And Realization On Digital Modulation And Demodulation Of CPM Waveforms In Physical Layer Of Data Link

The informationization level of modern wars is getting higher and higher. Systems are built into a cohesive whole unit with data link, to maximize the power of the combat units as much as possible. It is self-evident that the role of data link system is very important, whose the foundation is the physical layer waveforms. Simple and efficient modulation and demodulation techniques for physical layer waveforms have a great influence on the performance for the data-link system. With the high spectrum and power efficiencies, continuous phase modulation(CPM) has attracted great attention in the military communication and tactical data link. For instance, the MSK is employed by Link-16, the GMSK is adopted in the TTNT, and the SOQPSK, FQPSK-JR, ARTM-CPM and PCM/FM are used in IRIG106 standard, etc. Therefore, the study of simple and efficient modulation and demodulation techniques for CPM signals are greatly significant to promote the development of data link.Hence, the CPM modulation and demodulation techniques are discussed in the dissertation. Low complexity CPM modulator and detector scheme are proposed for data link system. Finally, the whole scheme is also designed and realized on the FPGA hardware platform. The mainly contents are as follows:(1) The principle of modulation and the formation process of phase for CPM are researched. Two schemes of modulator for CPM, one based on phase generation and the other based on waveform storage, are given. The two schemes have their own advantage and disadvantages, where the former needs lower memory resources and the latter requires less computational logic resources. Then the output phase, waveform and spectrum of two schemes are simulated to show the correctness of the proposed schemes. The result of simulation also shows that the CPM signal has better spectral and power efficiencies than the traditional PSK signal, which can meet the demand of the data link.(2)The demodulation algorithm for CPM signals is studied, including MLSD optimal demodulation, Laurent optimal detection and Laurent suboptimal detection, etc. Moreover, the detailed steps and specific structure of realization on the above three algorithms are given. The construction method of the phase state transition trellis of CPM signals is proposed, according to the phase state transition rule. The trellis, which includes the information of phase state transition, is the core of demodulator. Performance simulation and complexity analyses indicate that Laurent suboptimal demodulator which is suitable for data link system can reduce the complexity greatly with an extremely low performance loss.(3)The CPM signal modulator based on phase generator has been realized in the hardware platform. The baseband modulation and digital up conversion(DUC) for CPM signals are completed in FPGA and AD9957, respectively. The content of this specific design includes quantitative standards, phase generator, NCO waveform generator based on dual port ROM look-up table, AD9957 chip configuration and so on. The test verifies the correctness of CPM signal transmitter.(4)The low complexity demodulator of CPM signals based on Laurent suboptimal detection is implemented on FPGA platforms, including matched filter design with four parallel pipeline, dedicated complex multiplier design based on operation combination of the look-up table, calculator of metric path and state design based on look-up table, the Viterbi backtracking design based on shift register, etc. The test result shows the correctness of the CPM signal demodulator.