Digital Modulation And Demodulation Technology Research QDPSK

Digital modulation and demodulation technology is one of the key technologies of digital communication systems, while limit the research on digital communication systems. The research on digital modulation and demodulation technology is significant for further improving the performance of digital communication systems. Simultaneously, it provides broad application prospects in future communication systems. Therefore, the research on all-digital QDPSK modulation and demodulation technology has important significance.This basic theories of modulation and demodulation systems are introduced. An in-depth study of all-digital QDPSK modulation and demodulation technology is researched and the design block diagram of the systems is finished. The QDPSK modulation mainly includes data scrambling, convolutional encoding, differential coding, baseband shaping filter, interpolation filter and quadrature modulation. And the demodulation mainly includes DDC, matched filtering, differential decoding, Viterbi decoding, data descrambling and synchronization technology. MATLAB simulations results based on the analysis of principles of each module are analyzed. The synchronization thechnology is especially focused on and the carrier frequency offset estimation, carrier recovery loop and symbol synchronization loop are expounded in detail. Based on the analysis and comparison of various synchronization algorithms, the paper applies frequency offset estimation algorithm using FFT for the large frequency offset correction, Costas cross ring for carrier phase tracking and Gardner algorithm for symbol synchronization. Then the theoretical analysis and MATLAB simulations are performed for these algorithms. Finally, the performance of the whole system is simulated, then the bit error rate performance of the system is shown.