Research On TETRA Release 2 Multi-carrier FMT Technique

To satisfy the needs of broadband services,ETSI began to introduce TETRA Release 2 in 2005.TETRA has a wide market and application prospects in China,but the core technology has always been monopolized by foreign manufacturers.Therefore,studying TETRA can not only bring huge economic benefits,but also an inevitable requirement of national security.TETRA Release 2 achieves data rates much higher than TETRA through a series of new technologies at the physical layer,the most prominent of which is multi-carrier FMT.This paper researched the synchronization algorithm of FMT system based on FCB frame structure in TETRA version 2,designed a hardware implementation based on SDR and finally,designed an adaptive subcarrier bandwidth system and a variable number of subcarriers system based on FMT technology as recommendations for TETRA release 2.By using the timing synchronization sequence S in the FCB frame together with the redundant data of the prototype filtering as a new synchronization sequence,a stronger autocorrelation than S can be obtained.Based on this characteristic,a timing synchronization algorithm of peak detection was designed.After being modulated,frequency synchronization sequence in the FCB frame will generate a peek at the fixed position,and because of this feature,a new frequency offset estimation algorithm utilizing frequency domain characteristic of synchronous training sequences was proposed.After simulating above algorithm using Matlab,the results show that the proposed synchronization algorithm has smaller timing bias and larger frequency estimation range.Considering the feature for TETRA release 2 system,a hardware implementation based on software-defined radio was designed on CPU/ARM general hardware platform.To reduce the time spent by the synchronization algorithm,a new timing synchronization algorithm was designed.The algorithm divided timing into two steps: coarse synchronization and fine synchronization.Coarse one only did a threshold judgment to find the approximate range of the received signal,and then fine one was responsible for finding the exact position of the frame header.This scheme eliminates the shift-related calculation of the noise signal and ensures timely processing of the data.At the same time,the system is optimized by multi-threading technology.Finally,the hardware platform was built,and then the system is tested in the actual environment to verify that the system meets the design requirements.The reason why any subcarrier system can improve the bandwidth utilization of TETRA release 2 and achieve multi-user shared bandwidth is described,and then an adaptive subcarrier bandwidth system and a variable subcarrier number system are proposed.Utilizing the feature of the dependence of each subcarrier in FMT system,the modulation and demodulation structure of FMT-based adaptive subcarrier bandwidth system and variable subcarrier number system were designed respectively,and the calculation formula of system parameters was derived.Finally,the two systems were simulated by Matlab,and the feasibility of the algorithm was verified.