The Realization Of Multi-Channel TETRA Demodulator Based On Undersampling

With the development of technology, the era of digital communication is coming, therefore the digital trunking communication system, which belongs to private mobile communication system, has attracted more attentions. TETRA is one of the industrial recommended standards of digital trunking system, and it is used extensively in the private mobile communication system of China.With the development of software radio in the 1990s, undersampling technique is used in many wireless products based on software radio. Traditional TETRA receiver is only digitalized traditional analog communication equipments, and no multi-channel TETRA receiver using software radio approved. The main topic of this thesis is how to realize the direct sampling of multi-channel TETRA signals, whose intermediate frequency is 70 MHz, using undersampling. There are three parts in this thesis:Firstly, the background of this topic is introduced briefly. The theory ofπ/4-DQPSK modulation is introduced simply, and the development process of trunking system is reviewed and the direction of future development is analyzed.At that, the whole design is obtained from the system demand point of view, and the IF sampling theory as well as digital down converter technique is discussed. The detailed parameters of devices are decided based on the analyzing of system requirement. In the part of hardware design, the applications of Protel DXP software as well as the design process is introduced in detail, and the SCH PCB documents of all the parts of the system is given. In the part of software design, the characteristics of VHDL language as well as the design process of ISE software is introduced, and the theory of distributed FIR filter and differential demodulator in the IF is presented, which are used to realize separation filter and demodulation ofπ/4-DQPSK signals respectively, the simulation results are also drawn in this part.Finally, the debug process of software and hardware is shown, and the problems associated with solutions are also given. The problems in the debug process, which more attentions should be focused on, are pointed out. Moreover, the experience obtained from the debug process is summarized in detail. The design theory of this system is in accord with the development of the theory and realization of software radio, and demodulation of multi-channel TETRA signals can be realized in one processor. Furthermore, the designed system can be used as an experiment platform of all digital signal processing, and therefore, it has high value of actual hardware realization.