Research Of Digital Transformation Of Police350M Analog Relay Station

Police350M trunking system is a special communication system used by police department, which has some special functionalities, such as group calling, scheduling, fast personal calling, and plays an important role in police communications. With the development of information digitalization, the original350M analog police trucking system which can offer speech communication only can’t meet the processing needs of current daily affairs any more. And it’s necessary to develop a new digital communication system for police department, which can both offer speech service and data service, and is also complied with Chinese Police Digital Trunking (PDT) standard. So it’s valuable to research the digitalization technologies of the original analog police trucking system.This thesis focuses on the digitalization technologies of the analog relay station of the analog police trunking system. Firstly, the PDT-related physical layer and data-link layer protocols are introduced. Then the general technology scheme for the digitalization of the analog relay station is presented and illustrated. The hardware design and signal processing of the digital relay station is illustrated in detail. The designed digital relay station includes control module, interface module, analog signal processing module, and digital signal processing module, and so on. A91SAM9XE128is selected as the processing core of the control module, which is in charge of system control, system survey, responding to the requests, processing exceptions. Interface module is designed to achieve the seamless connection between the digital relay station and the original analog channel machine. Low passing filtering circuit in the receiving path and modulating circuit in the transmitting path are implemented in the analog signal processing module. Digital signal processing module is the key module in the digital relay station, which implements FM demodulating algorithm, matched filter, and correlator when keeping the analog interface unchanged. The hardware and software of the main board is implemented in this thesis, which is installed in the existing analog relay station MX800. Testing is conducted to evaluate the speech quality under the same preconditions and environment. The results show that the digitalized relay station can offer better speech quality than that of original analog relay station, but has less communication distance.