Dmr Baseband System Research And Implementation Of The Algorithm

Digital Mobile Radio has been proposed by European TelecommunicationsStandards Institute in April2005. In this paper, baseband algorithms of DMR systemwill be analyzed and researched. Three modules including channel encoding anddecoding, modulation and demodulation, frame synchronization will be simulated inMATLAB and implemented on DSP chip.Cyclic Redundancy checks code, Quadratic Residue Code, Golay Code, Rate3/4Trellis code，and Block Product Turbo Code are used in DMR systems. This paper willexplore the encoding and decoding theory of each module, and then provide theirdetailed implementation processes on DSP chip.In order to meet different hardware requirements, this paper will propose twodifferent methods of4FSK modulation and demodulation based on Orthogonal modeland direct frequency modulation model respectively. In the receiver, the baseband signalobtained from quadrature demodulator is same as the one from frequency discriminator,so this paper will propose two demodulation methods of4FSK baseband signal. Onemethod makes full use of features of four level signal, tries to find the dynamic rangeand three thresholds of the received signal, then does corresponding judgement andfinally changes symbols into dibits. However, in case of low SNR, this method willmake wrong judgements near thresholds. To make up for this deficiency, anothermethod according to maximum-likelihood criterion is proposed. But the second methodis so time-comsuming that it is unacceptable. Therefore, this paper combined the twomethods to solve the above these problems.Finally, this paper has tested all these algorithms in the OMAP5509A platform. Onthe one hand, we give the test results of these channel encoding and decoding modulesand verify the stability of the software design of these modules. On the other hand, wetest the4FSK modulation and demodulation algorithms to prove that they are practical.