| Public communication is mainly based on the fixed base station, in the case of public facilities destroyed, communication will be interrupted immediately, it recovers for a long time, and it is also a great need to invest. The special radio stations are widely utilized by the virtue of their unique advantages: low cost, easy to open, efficient and convenient features.LTE, as the main modern communications technology, has been used and implemented by the major carriers, it has some advantages: high-capacity, high-bandwidth, multi-service, wide coverage. The design draws on the LTE baseband protocol, and the key parts of which are modified and designed in order to develop a set of baseband system suitable for emergency communications.Firstly, for the baseband processing section, this paper does the research of 512-606 MHz high-speed transmission system of the special radio stations, combining architecture of the special radio stations and requirements that related companies proposed to design a development program.Secondly, this paper analyzes the channel equalization technology and the digital intermediate frequency technology of the baseband processing, simulating the key technology of the channel equalization and the digital intermediate frequency. At the same time, this paper puts forward equalization algorithm and IF signal processing that suitable for the system, which brings good accuracy and performance. It is proved that the idea of the design is right and highly efficient by the theoretical analysis and MATLAB simulation. It not only meets the design requirement of the system, but also provides a effective guidance of the development of baseband system based on FPGA for special radio station.At last, this paper completes the implementation of the program in the hardware. The main chip of development is the XC7A200T-3FBG676 chip of Xilinx, and this paper implements the baseband system by using VHDL language, include the following modules: clock management module, rate conversion module, frame count module, 8PSK modulation, OFDM sub-carrier mapping, IFFT, insert pilot and synchronization as well as CP, IF part of the transmitter(DUC buffer, DUC, IF carrier modulation), etc. It also includes the corresponding demodulation part of the receiver.Co-simulating and improving in Modelsim simulation software, and spectrum test and certification by downloading code to actual board. The transmitter and receiver of the baseband system have reached the design requirements by testing. |
