| As an important part of specialized mobile communication, the digitalization ofanalog two-way radio is the inevitable trend of development of communicationtechnology. In Europe, DPMR and DMR standards have been launched by ETSI. AndChina also released an RF regulation for digital two-way radio. The bright marketprospect of digital two-way radio is the background of my thesis.Digital two-way radio is composed of two parts: RF circuits and basebandprocessing units. Because digital two-way radio is mainly used in a narrowbandchannel, its modulation rate is low. As a result of low modulation rate, its basebandprocessing requirement isn’t high. So using software for baseband processing istotally achievable. Software also has the advantage of flexibility and scalability.My thesis systematically describes the design and implementation of thealgorithms for modulation and demodulation, channel encoding and decoding, whichare essential parts in the digital two-way radio baseband software. In the end of thethesis, the whole software architecture is given.In the aspect of modulation and demodulation, the mathematic model of4-levelFSK is analyzed. A new method for shaping filter design and FM modulation isproposed. Simulation results show that the power spectrum density of modulatedwave meets the requirement of Chinese RF regulation. According to thecharacteristics that shaping filter of4-level FSK has a small roll-off factor, I proposeda new timing recovery scheme. Simulation show that mean square estimating error islower than tradition scheme. In my thesis, I also simulate the different discriminatorsfor FM signal, results of which show that PLL discriminator has the bestperformance.In the aspect of Channel encode and decode, the implementations of codes inDPMR and DMR standards are given. The coding gain of different codes is given bysimulation.In the aspect of software architecture, this thesis presents a hierarchicalframework which can flexibly adapt to different standards... |
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