Research And Implement On Baseband Transmission Key Technology Of DMR Digital Trunking

With the development of wireless communication technology, analogcommunication system has been far from being able to meet people’s requirements forcommunication quality, digital communication technology came into being, in whichdigital trunking mobile communication is an important branch of the digitalcommunication technology. Digital trunking mobile communication has goodmomentum of development in recent years, and has been widely used in publicsecurity, airports, government, fire and other departments and group that needscommand and dispatch, including some individual users with special needs. The wideapplication of technology caused concern and attention of research departments athome and abroad, so in2004the International Telecommunications Association ETSIproposes a new digital trunking mobile communication technology standard-DMR(Digital Mobile Radio) standard, compared to mature TETRA and iDEN standards,which is still being improved, technological monopoly has not yet formed, the systemstructure model and the technology is simple, the product cost is not high, DMRdigital communication system’s advantages make it have great value of research anddevelopment. Practical application requires DMR digital trunking communicationsystem with excellent communication performance, and requires the receiving endwith a very low Error Ratio, so as to meet communication quality requirements of thespecific industry and professional sectors.This paper first introduces digital trunking communication system’s developmentand DMR digital interphone protocol, and provides information about the keytechnologies of DMR baseband transmission, including the baseband transmissionand system simulation model, digital filtering technology,4FSK modulation anddemodulation technology, synchronization technology and the hardware platform.The paper use signal generator E4438C and channel machine MX800to build aplatform of collecting test data, achieve the generation and acquisition of DMR signal,and build a Matlab simulation platform on PC. Combined with the actual situation,the paper focuses on original fixed decision threshold defects to propose an improvedscheme for the sampling judgment of4FSK demodulation algorithm, and use adynamic judgment threshold method to optimize demodulation algorithm. After ErrorRatio testing experimental verification on Matlab simulation platform, compared with a fixed decision threshold solution, the improved scheme effectively reduces ErrorRatio to optimize the communication performance of the system, and prove thefeasibility and effectiveness of the scheme.