Research On Key Technologies Of Digital Trunking Mobile Communication System Terminals

Digital trunking mobile communication system is a new generation of private mobile radio system, which is widely used in China. Systems which comply with the statdard (A) of digital trunking mobile communitcaion system has occupied more than 60% of digital trunking system market in China for its excellent performance and complete system architecture. Most of the systems, which comply with the statdard (A), are TETRA systems, which have been monopolized by the foreign companies. Information-sensitive departments can not use these systems. There is nearly not any Chinese equipments have independent intellectual property rights. In order to break the situation, the paper does research on key technologies of digital trunking system complies with standard (A) in the background of developing encryption handset mobile station.Firstly,the message related threats, user related threats and system related threats of digital trunking system are analyzed. The security mechanisms, such as air interface authentication, air interface encryption and end-to-end encryption, are described. A new error control scheme is developed to transmit encryption synchronization information without stealing the traffic data. The new method can provide greater data transmission capability. The simulation results show that the packet error rate of the new shceme is much lower than the original one when the SNR is larger than 5dB.Secondly, the requirements of modulation schemes of digital trunking system are analyzed. Orthogonal modulation and differential detection methods ofπ/4-DQPSK signal are discussed. The symbol error performance ofπ/4-DQPSK signal is analyzed. The symbol error rate expressions of three different decision rule for fractional spacedπ/4-DQPSK signal are derived from analyzing the bit error rate of in-phase and quadratrue channels, and the best decision rule is find out through comparison. A new automatic frequency control method is carried out base on the inter-symbol correlation ofπ/4-DQPSK codes. Practical system application testing shows that the method is rapid enough to correct the frequency in a TDMA burst.Thirdly, transmitter’s linearization technologies are analyzed in the paper. The normal linearization methods of power amplifier are enumerated. The influence of loop phase in Cartesian feedback loop is discussed, and a method on calculating and correcting the loop phase is established. The nonlinear distortions of amplitude and phase in the Cartesian feedback loop are analyzed. To compensate the distortion, a digital base band pre-distortion technique is established. The effectiveness of the loop phase calibration and distortion compensation methods is verified by a practical system at last.Finally, a design of underlying protocol stack for mobile station complies with standard (A) of digital trunking mobile communication system is established base on the research of the air interface protocol. The work of underlying protocol stack is divided into 10 tasks, to which priorities are assigned. A new task management and dispatch mechanism for underlying protocol stack is developed. A data acquisition and simulation system is developed to overcome the shortcomings in the procedure of underlying protocol stack developing, such as high speed and strong randomness of signals, and difficult to reproduce and recover, etc. At the end of the paper, the underlying protocol stack is tested in two aspects: receiver and transmitter. The results show that the design of underlying protocol stack satisfies the requirements of standard (A).