Research On 4CPFSK Baseband Signal Processing And IC Design Based On DMR Protocol

DMR (Digital Mobile Radio) is the latest digital trunking communication system protocol proposed by the international organization ETSI. This protocol transferring from analog to digital system is first applied to digital interphone. The modulation method of DMR is 4CPFSK, but there is little research on 4CPFSK in this system, even no basic modulation & demodulation structures. So the research about 4CPFSK baseband signal processing based on DMR protocol is a significant subject.Firstly we introduced digital trunking communication system and continuous phase modulation technology. Then we further described DMR digital trunking protocol, both included physical layer, data link layer and call control layer. Also based on CPM signal model, we analyzed the relationship between power spectrum and modulation index, and used Euclidean distance to evaluate the ideal receiver.Secondly, we focused on 4CPFSK modulation & demodulation algorithm based on DMR protocol, both included design plan and realization principles about transmitter and receiver. The transmitter is consisted of slot control, mapping, shaping filter and frequency modulator. And the receiver include differential phase discrimination, signal detecting, frequency estimates and timing tracking loop. And we mainly introduced timing tracking loop applied in 4CPFSK demodulation. It estimates the timing error based on differential phase discrimination. Simulation results showed that this algorithm can estimate the timing error accurately.Finally, we analyzed two problems existed in actual DMR communication system. For nonlinear distortion, we measured the actual AM-AM and AM-PM character curves based on amplify model, and proposed a frequency compensation method which can eliminate the influence by nonlinear distortion. In order to improve the detect correct rate, we applied time diversity and space diversity, due to difference application on mobile station and base station. And then we introduced dedicated communication chip based on DMR and gave the test results about the chip.