Research Of Modulation And Demodulation Technology Based On Software Radio

Far distance, large communication capability and high transmission quality are required in modern communication system. Software Radio has been proposed as the new communication architecture in recent years. As it is flexible and re-configurable, and it records with the current thought of the communication development, it has become the focus of the research on the design of communication systems. Modulation and demodulation, which is one of the most key techniques in communications, has always been an important aspect of researching field. Thus, it is very significant making a thorough and careful study of modulation and demodulation technology based on software radio, especially in the more rapid development of modern communication systems.The modulation and demodulation techniques ofπ/4-DQPSK and 16QAM are mainly studied in this paper. First, the methods and basic principles ofπ/4-DQPSK and 16QAM are introduced, and a systematic scheme is given. Then, the algorithm of frame synchronization, frequency-offset estimation, which is related to the digital quadrature modulation and demodulation, is described in detail. A rapid synchronization algorithm that achieves rapid symbol timing and slight time jitter is proposed for differential demodulation in this paper. Based on the software radio, a narrowband and high-speed modem is implemented on the hardware platform with the intermediate frequency of 36MHz. The bandwidth of the modem is 200KHz and the bit rates are 256Kbps and 512Kbps. Finally, a design of the RF circuit is proposed.