The Research Of Ultra Narrow Band Communication Technology And Design Of Demodulator

With the development of digitization and intelligence, higher requirement is put forward in therespect of low power consumption and data transfer rate in long distance. Although many kinds oflow power consumption technique such as ZigBee and Enocaen have been widely used, it still can’tmeet the demand of long distance in low power consumption. In addition, radio frequency resourcesbecomes scarcer, it is need to find one kind of high efficient modulation mode to significantlyimprove the spectrum efficiency. Therefore, Ultra Narrow Band(UNB) communication technique isgradually noticed by people, it can provide very high spectrum efficiency and long communicationdistance. UNB technology is mainly consist of two types of modulation modes which called VeryMinimum Shift Keying(VMSK) and Minimum Sideband Modulation(MSB), this paper focuses onMSB type modulation mode, analyze the modulation theory in detail. Based on the theoreticalanalysis, this paper designs a MSB demodulator based on frequency lock and phase lockloop(FPLL), and implement the demodulator with C++language on the computer.The first part of this paper do analysis on present research status of UNB technology, introduceVMSK and MSB’s basic principle and implementation method, and focus on the power spectralcharacteristics of MSB modulation method. The second part put forward the design of MSBdemodulator which is based on FPLL, and analyze and simulate every modules in the system onMATLAB platform, implement the functions of carrier recovery, phase jump extraction based onPFLL and automatic switch between Automatic frequency control(AFC) and PLL. This methodboth expand carrier capture range and capture precision, makes the whole system maintain goodfrequency range with high precious carrier track ability. According to the characteristics of thephase detector output signal, this paper studies appropriate detection method, and the method ofjudge threshold is analyzed.In addition, the method this paper constructed solve the synchronization problem incommunication system. And, synchronous carrier can be extracted directly by phase locked loop;bit synchronization can be implemented by software according to phase discriminator; the framesynchronization can be implemented by inserting a auxiliary code.Finally, the whole MSB type transmission system is implemented on the MATLAB platform,and complete the demodulation algorithm on the computer, it uses full digital processing to makethe structure of whole system become more flexible, open and modular. The software demodulatorimplemented in this paper choice a low carrier frequency, it lowers exploitation difficulty, but it laysthe foundation for using high speed ADC/DAC and CPU to implement high-frequency UNBcommunication.