Digital Modulation And Demodulation Technology Research Based On Software Radio

At present, all-digital receivers have been widely used in digital communication systems. It has become an important technology of modern communication to design the modulator and demodulator of communication system in digitalization method. It is very important to the performance of the communication system selecting suitable and efficient modulation and demodulation methods according to the characteristics of different channels. The emergence of software radio technology has played a significant role in promoting the development of mobile 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.After reading massive domestic and foreign literature about modem and software radio, a comprehensive discussion is made about the significance of this subject, the applications and prospects of software radio and the main technologies used by modern modulation and demodulation. It focuses on using all-digital technology to realize QPSK, MSK, GMSK modem which include the principles, signal power spectrum and bit error rate characteristics of the basic digital modem systems, on the basis of which, the modulation and demodulation processes and performances of QPSK, MSK and GMSK are studied using MATLAB software. After that, a detailed study of the design of pulse shaping filter, signal power spectrum, bit error rate characteristics and constellation that through channels of AWGN and Rayleigh is made. To fit the needs of burst communication systems,one-bit and two-bit differential demodulation methods are studied in the thesis and realizes GMSK modulation and demodulation process using the former. A comparison is made to see the performance differences of the two methods using MATLAB. Further, the realization and performances of the modulation and demodulation algorithms of the above modem styles are studied in DSP and relevant data graphs are given in CCS development software. To sum up, the QPSK, MSK and GMSK modulation and demodulation processes are realized using MATLAB and CCS software and the performances of these modem technologies are analyzed.It deepens my understanding of the software radio technology and the results given by this thesis also have certain reference significance on relevant study.