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摘要：在数字通信中，理想的MDPSK信号在码元切换时会发生相位跳变，旁瓣功率较大，需要经过限带滤波后才能够发射。经过限带滤波后的QDPSK信号的码元波形可分为稳定区与过渡区，根据这一特点可以利用DFT方法来实现信号的解调和位同步。在这种数字化解调器中需要设计一个合适的带通滤波器，以便尽可能地消除信号的旁瓣分量而不影响信号码元稳定区内的波形。本文介绍了QDPSK信号的调制解调，还介绍了上述带通滤波器的方案选择和基于Matlab的滤波器参数设计方法，以及仿真效果。
关键词：QDPSK；DFT；带通滤波器；MATLAB
Design of Band-pass Filter for QDPSK
Abstract: In digital communication, ideal MDPSK signal has the phase jump and larger side beam power in the code switching.It can be sent only after a bandpass filter. After a bandpass filter, QDPSK signal’s symbol can be divided into steady section and transition section, so the demodulation and synchronization for the signal can be realized with DFT. In such a digital demodulator，it is important to design a proper bandpass filter to get rid of side beam power and don’t change the waveform in steady section. This paper introduces the modulation and demodulation for QDPSK signal, and the scheme selection, parameter design method and simulate effect for this filter based on Matlab.
Key words：QDPSK，DFT，band-pass filter，MATLAB
