实现了DQPSK下用Gardner算法实现位同步，并对信噪比、余弦滚降因子的影响加以讨论-achieve symbol synchronous by Gardner in the condition of DQPSK

接收端时间同步环仿真，包括插值滤波器、环路滤波器、GARDNER算法以及数字控制振荡器(Receiver time synchronization loop simulation, including interpolation filter, loop filter, GARDNER algorithm and digital controlled oscillator)