Study On Modulation And Demodulation Technique Of GMSK

In digital communication systems, all-digital receivers become more popular. It has become an important technology that realizes the modulator and demodulator of communication system in digitalization method. Minimum Gaussian frequency shift keying (GMSK) is a typical continuous phase modulation method, which has the characteristics of constant envelope, compact spectrum, and anti-jamming performance. GMSK can effectively reduce inter-channel interference, improve the efficiency of non-linear power amplifier, and has been widely used in mobile communications system (such as GSM system) and others systems. The modulator and demodulator designed in traditional method can not meet the need of programmable, multi-mode for all digital receivers.The thesis focuses on the study on digitialization of GMSK modem. The main works involved as following:1. It is complex to design a GMSK moderm in traditional method, and the GMSK moderm has the shortage of accumulated phase error. Base on related literatures, an improved quadrature waveform storage GMSK modulation signal generation method was studied in the thesis. The method does not have the shortage of accumulated phase error in traditional method, needn't filter and reduce the device resources significantly. Simulation results and FPGA realization results show that the method has the advantages of small computation, less resources and easy to realize high sidelobe suppressed GMSK signal.2. The demodaltion technologies in digitalization method is studied. To fit the need of burst communication systems, 1-bit and 2-bit differential demodulation method were studied. A 1-bit demodulator is designed and released. Simulation results and FPGA realization results show that scheme designed can demodulate GMSK signal effectively and archieve good BER performance.3. The effect of various GMSK parameters for system transmission performance is studied. Through simulation comparision, selection criteria for parameter BT and BER performance for various modu-demodu scheme were studied.4. The designed GMSK scheme has been realized in FPGA chips. Simulations and online verification results show that designed scheme work well. The study of the thesis is carried out by the method of theoretical analysis, scheme comparisons, simulations and FPGA verifications. Results shows that the scheme designed is feasible anc can be adopted in practice system after futher optimization.