Research And Design Of Synchronization Technology Based On DPMR Protocol

Private wireless communications has been always used in the GroupCommunication Environment such as traffic control, police communicationsand woekshop scheduling. Analog Radio communication system is a typicalRepresentative of the private wireless communications system, which hastaken over the main market for a long time, but along with the digitization ofcommunication, and it is difficult to adapt to the current special wirelesscommunication environment. Therefore, whether in China or the world isactively proceeding the conversion of analog radio to digital radio. Digitalradio not only achieves point to point communication, but alsopoint-to-multipoint communication function, SMS, text messaging and datatransmission communications to meet the needs of the private wirelesscommunications environment. This paper studied the digital radiocommunication protocol dPMR structure, function mode and the systemworkflow, and analyzed the characteristics of a narrowband channel with6.25kHz and FDMA code.This subject came from the digital radio system based on dPMRAgreement, focused on the design of digital radio terminal receivers and synchronization system, including the RF signal reception and demodulation,IF digital signal carrier synchronization and4FSK modulated digital signaltiming synchronization system.This paper analyzed the RF receiver system works, compared to asuperheterodyne receiver design and choosed direct down conversion receiverdesign. This paper designed RF receiver demodulation system based onCMX994series chips and the dPMR protocol standard,included the designof the external circuit of the voltage-controlled oscillator VCO and PLL design,amplifier, filter and power supply design, the RF receiver system achieved RFsignal demodulation function and narrowband6.25kHz channel selection.After coherent demodulation, the RF signal by the analog to digital conversionchanged into the broadband IF digital signal processing. In this paper, basedon the Costas loop carrier synchronization structure, improved LMS algorithmstructure, and eliminated the interference caused by the difference between theoriginal signal’s initial frequency and carrier’s initial frequency, designed atwo-tier LMS arithmetic operations structure for the estimation of the carrierphase to achieve accurate tracking of the carrier phase of the broadband IFdigital signal. Finally, the broadband IF digital signal demodulated digitallyinto the4FSK modulation signal, this paper based on4FSK modulated signalcharacteristics in dPMR agreement, improved Gardner algorithm, eliminatedthe calculated interference caused by the four level signals to achieve accurateposition of the symbol’s best sampling location. All aboved have been tested, the digital radio terminal synchronizationsystem achieved the reception and demodulation of RF signals, widebanddigital IF signal carrier phase tracking, and accurate position of the4FSKmodulation signal symbol’s best sampling location.