The Simulation And The FPGA Design Of π/4-DQPSK Modulation And Demodulation

Software defined radio(SDR)technology is put forward in resent years as a new system structure applied to wireless communication. The appearance of software radio technology has played an important role in promoting the development of communication.It is flexible to realize the functions of modem that using software radio technology, which can meet the requirements of different communication systems by downloading different softwares and can make communication systems expand and upgrade easily.π/4-DQPSK is a modification of QPSK modulation. It is a linear narrowband technology which has been widely employed in mobile communication system, satellite communication system. It is of properties of high spectrum utilization ratio,better spectrum specification, stronger anti-fading performance and applicability to non-coherent detection.The modem based on the idea of Software Radio has been designed.Signal can be transmitted byπ/4-DQPSK in this modem. The modulator can be implemented easily in this method with better performance. The FPGA architecture has been used in the digital correlator,by which the signal can be demodulated at the intermediate frequency.A communication system ofπ/4DQPSK based on FPGA has been researched and designed in this dissertation. Firstly, the principle of a FPGA-Basedπ/4DQPSK modem is introduced in the dissertation. After that, BER of system is simulsted. Secondly, under the ISE10.1 of XILINX, VHDL has been adopted for designing and implementing the system. The designs mainly included differential demodulation at the intermediate frequency, correlator and bit synchronization and so on.The functional simulation of system is completed with FPGA simulation software. Finally the PCB board is designed based on FPGA chip and circuit debug is finished. The modulation and demodulation system ofπ/4DQPSK is proved to be correct.In this dissertation,there are two methods forπ/4-DQPSK demodulation, coherent detection and non-coherent detection. Non-coherent detection is difference detection. In the moving communication, the performance of coherent detection is not as good as non-coherent detection. So intermediate frequency differential detection is used in this dissertation. The parallel correlator base on the D-trigger is designed, it not only just save resource but also convenient for parameter designs. The basic module of Virtex is logic cell (LC),each LC consists of four inputs function production, one carry logic module and one memory location. The function production is a look up table(LUT) in nature. One LUT can make up of 16 bit shift register, the structure is SRL16. It can realize by macro transfer,and also can be carry out by ISE auto-synthesis according to language criterion. Therefore, the design of correlator mainly use parallel correlator base on the SRL16.Take into account about the require of BER and SNR and realizing difficulty, the direct square method to realize the bit synchronization is chosen.Theπ/4DQPSK modem based on FPGA is designed with high integration, great flexibility and upgrade in software. The design in this dissertation will provide for the further design with more high integration and more great flexibility in the modern communication system in the future.