The Research On GMSK Modulation And Demodulation And Its Realization Techniques

Proposed in the1980s, the Gaussian Minimum Shift Keying (GMSK) is a typicalcontinuous phase modulation method, which has characteristics of constant envelope,spectrum compact, side lobe roll off fast, small-band radiation, often as an efficientdigital modulation scheme is widely used in many fields, such as GSM, GPRSmobile communication systems, Wireless LAN, TT&C and other system. The thesishave a research on GMSK modem and its implementation techniques based of theprinciples and theory of GMSK modem.In this thesis the modulation section major study focuses on the GMSK waveformstorage orthogonal modulation scheme. To address the amplitude error and phaseimbalances in I/Q channel which can seriously impact on the modulated signal quality,based on the relevant literature, an improved waveform storage GMSK orthogonalmodulation schemes was proposed in this thesis. In the improved scheme has nodigital/analog converter to the baseband signal, and using orthogonal carrier modulewhich has been optimized in terms of speed and consume resources for FM. Finally,the entire implementation of the modulation system has been given. Simulationresults show that the improved scheme has good modulation performance, fastercomputing speed, lesser resource and phase imbalance improvement.In this thesis the demodulation section major focuses on the research ofnon-coherent demodulation differential demodulation scheme and1-bit differentialdemodulation scheme is used there. In order to improve the BER performance ofdifferential demodulation caused by inter-symbol interference from Gaussian filter, animproved1-bit differential demodulation based on Viterbi algorithm was presented.Results from the designed simulation program show that the four orders of magnitudeof bit-error-rate can be obtained and can save about2dB gain than the originalalgorithmon when the signal-to-noise ratio is9dB.This thesis used Matlab/Simulink platform combining DSPBuilder tool to achievethe critical set simulation. Using the powerful interactive capability of DSPBuilder,the algorithm simulation and hardware implementation co-design is utilized; thus the design efficiency is achieved by avoiding the complicated hardware descriptionlanguage design, greatly shorten the development cycle of the communication system.