The Burst Mode Gmsk Spread-spectrum Signal Despreading And Demodulation

GMSK modulation has some advantages of continuous phase at the code transiton,constant envelope,rapid power spectrum roll-off,low sidelobe level,etc,which can reduce inter-channel interference and has narrow intermediate frequency bandwidth. So it has been widely used in mobile communications system ,multi-hopping military communication system,etc. Frequency-extended communication has the superiority of low probability of intercept,low probability of detection,efficient utilization rate of spectrum and good anti-multipath performance,etc. So it has been widely used in public communication system and military communication system. The thesis analyzed the GMSK spread spectrum modulation and introduced the principle of GMSK modulation, spread spectrum technique, despread spectrum technique,GMSK demodulation.The thesis focuses on hardware design of digital IF and the main works involved as following:1. Introduce and analyze the principle and implement of msk/gmsk modulation;2. Analyze the principle and implement of direct spread spectrum, despread spectrum;3. Analyze the principle and method for GMSK demodulation based on CORDIC algorithm and differential demodulation;4. Introduce the principle of tamed spread spectrum, focuses on the two ways to implement of demodulation and despread for tamed spread spectrum GMSK: baseband demodulation correlator and IF direct correlator,Then compared one with the other;5. Hardware demodulation and despread of GMSK signal are implemented by way of digital IF instead of SAWTDL matched filter.At the same time,a method is presented to save FPGA resources.The paper is carried out by the method of theoretical analysis,arithmetic simulations and comparison of performance,and then selected implement arithmetic. Then the arithmetic is implemented in FPGA and verified by hardware.Results shows that the digital IF scheme designed is feasible and can be replaced SAW Matched Filter with it.