Based on Matlab / Simulink for QDPSK study of modulation and demodulation system

According to the defects of the XCTD (Expendable Conductivity, Temperature, and Depth) Profiler low data transmission rate and reliability, a modem underwater data transmission system is introduced. The absolute phase-shift demodulated signal of the phase ambiguity problem is overcome by π/4-QDPSK, which is a linear narrow-band digital modulation technique and has high bandwidth efficiency, low bit error rate advantage. On the basic principles of modulation and demodulation QDPSK as well as the design model of each module is focused paper. And finally in the SIMULINK environment, the system for each sub-module completes the functional simulation. The results show that the design of π/4-QDPSK communication system to meet the basic requirements of communication systems, the simulation waveforms with the conventional analysis of the results obtained are consistent.