Baseband Algorithms Of Digital Trunking Handheld And Implementation

Digital trunking communication system is a dedicated dispatching communication system. Because this system can use the spectrum effectively as well as provide better call quality and rich communication services, it has attracted attention of scholars domestic and abroad in recent years. But our country is still relatively backward in the research field of digital trunking communications technology comparing to foreign countries. In this paper, the baseband algorithm of the digital trunking communication system Mobile Telephone Service (MTS) handset are analyzed and researched, and the author has implement various baseband algorithm modules in an hardware environment based on TI OMAP5912 dual-core chipMTS digital trunking communication system is developed in accordance with the needs of China's public security departments. In this paper, an overview of the background and the technology developing history of digital trunking communications is first discussed, then the protocol standards which is relative to the analysis of the baseband algorithm module latter is given.The encoding and decoding module in our system includes: Cyclic Redundancy Checks (CRC) check code, Reed-Muller error-correcting codes, convolutional codes, interleaving , scrammber code and so on. In the third chapter we explore the coding and decoding theory of each module, and then carryout one proper way to realize these modules.Chapter four discussed the Gaussian Minimum Shift Keying (GMSK) modulation and demodulation techniques.In this chapter we propose two method to implement the modulation of GMSK signal. Method one uses a number of look-up tables which is really fast, while method two apploys an recursiveness of GMSK modulation which avoid the lose of accuracy when float data change into fix-point data. In our system we use method one to realize GMSK modulation.Besides 3 different Differential Phase Detector (DPD) structure is discussed in Chapter four. One is the regular DPD receiver. And type two is a feedback Differential Phase Detector (FDPD) which utilize the the previous evaluated data to cancel partly Inter-symbole interference (ISI). And type 3 is a new type of GMSK demodulation which employs a combination of differential phase detector (DPD) combined Maximum A Posteriori (MAP) decoding algorithm. Simulation results show that at the bit error rate of 10-5 DPD combined MAP structure using joint iterative demodulation and decoding algorithm is better than the other two receivers. It can cut down 6dB compare to the simply DPD structure, while FDPD can only outperformance 1dB at the same BER rate. But because type 3 receiver orders a large memory storage, cost a long time to compute and need to estimate the noise SNR, our system cann't implement the DPD combined MAP algorithm (DPD-MAP) structure. But this paper give out the realization of FDPD receiver.In the fifth chapter, the paper analyzes the principle and implementation of frame synchronization. Besides, we analyzed the state transition and the processing flow chart of decoding the burst according to the protocol in simplified application scenery of digital handset trunking system.Chapter six gives out the experimental test results of the part of algorithm modules of this system, such like various channel coding modules, GMSK modulation and demodulation modules and so on. These results also show that the implementation scheme we achieved is effective in our system.Finally, in Chapter seven, the author sum up the principal ideas of the whole dissertation and the directions of the further research.