This thesis first studied the communication system with detailed theories so that to choose the appropriate method of modulation and demodulation . n / 4dqpsk is a kind of modulation method which is appropriate to transfer in the attenuated channel / 4dqpsk是一种比较适合在衰落信道中传输的调制方式，它不需要提取相干载波，因而不存在相位模糊、环路跳周等问题。
