QPSK信号的调制解调过程，内容包括带通滤波，脉冲成形，以及硬判决译码过程-QPSK modulation and demodulation process of the signal, including a band-pass filtering, pulse shaping, and a hard-decision decoding process

实现QPSK调制，并实现了QPSK的硬判决。(To achieve QPSK modulation, hard decision.)