Study On GMSK Modulation / Demodulation Based On CMX909B

With a wide range of digital wireless communication technology applications, digital modulation/demodulation technology as an important part of them. Because the GMSK Modulation/Demodulation has better signal spectrum efficiency,low Bit Error Rate, stronger anti-interference performance and smaller-band radiation, it is widely applied to wireless communications.First, the thesis describes the development of the modulation/demodulation technology. Then, on the basis of the GMSK modulation/demodulation, presents GMSK modulation/demodulation module for digital transformation of analog communication equipment. The module can be used on analog communication equipments digital transformed, to meet the requirements of long-distance high-capacity communications, obtain a higher transmission rate and better BER performance.In this paper, we use the CML company's CMX909B chip, as the GMSK modulation/demodulation data pump.It integrates a Gaussian filter for MSK pre-filter. It uses FEC,CRC,interleaving encoding and decoding technology to improve the noise immunity. We can choice the external crystal oscillator with the chip setting, changing the Baseband transmission rate, to meet different analog communication equipments' digital transformed.The main work of this thesis:Firstly, according to digital transforming for analog communication equipments'requirements, design hardware platform for 9.6kbps rate GMSK modulation/demodulation module. Then, we use C8051 MCU as the controller, designing the software for the module, to receiving and sending data. Finally, we test the hardware module in the laboratory. After testing, the modulation/demodulation module can send and transfer data normally, transfer rate adjustable, showing good flexibility, adapt to transform different analog communication equipments, to improve signal transmission quality, reduce loss of information and error rate. Optimized design for the module's circuit board, it can be more compact, used for the hand-held radio or car radio's digital transforming with a high value.