Tdd Microwave Communication System Research And Implementation Of Modem Module

In modern wireless communication systems, modulation and demodulation module occupies a very important position in the wireless communication system, Its function directly affect the performance of the entire communication system. with the concept of software radios being put forward, we will digitize directly from IF signal or RF signal in the future communications systems, all-digital modulation and demodulation system is the direction for future development.In the article, we first briefly described the transceiver system which is based on the software defined radio, focusing on the modulation and demodulation techniques. Among the many type of modulation, QPSK has the advantages of faster transfer rate、 high spectral efficiency, strong anti-interference ability, etc, so we use the QPSK modulation mode, the paper focusing on the basic principles of digital modulation and demodulation of QPSK, we carry out a brief analysis and comparison between the traditional modulation and demodulation technology in analog domain and the modern IF modulation and demodulation technology in digital domain, summarizes the respective advantages and disadvantages. According to the indicators in the project requirements we have determined the program for the carrier synchronization in the burst communications as well as the modulation and demodulation. we use differential encoding to resolve phase ambiguity problem in digital baseband signal processing, we choose crystal and PLL to generate the305MHz local oscillator signal. Because the paper is a module which is based on TDD communication system design, so we made a brief introduction to the data processing flow in FPGA and DSP.The initial Program of the modulation and carrier synchronization module in this paper is made by the Matlab-Simulink simulation, in addition, this paper has also completed the selection of the related chip and hardware circuit board production eventually we achieve a success on QPSK modulation and demodulation, the baseband information rate is120Mbps,bandwidth is60MHz, the center frequency of the IF signal is305MHz, bandwidth is120MHz. Finally, we made a introduction on the test method and results related to the Key performance indicators of QPSK modems.