说明：  1.单位抽样序列是指在单位时间内的抽样所产生的序列； 2.单位阶跃序列是单位样值序列的求和运算； 3.离散傅里叶变换（DFT），是傅里叶变换在时域和频域上都呈现离散的形式，将时域信号的采样变换为在离散时间傅里叶变换（DTFT）频域的采样； 4.正余弦序列是对正余弦信号进行采样； 5.周期序列具有周期特性的序列。
(1.Unit sampling sequence refers to the sequence generated by sampling in unit time; 2.Unit step sequence is the sum operation of unit sample value sequence; 3.Discrete Fourier transform (DFT) is a discrete form of Fourier transform in both time domain and frequency domain. It transforms the sampling of time domain signals into the sampling of discrete time Fourier transform (DTFT) in frequency domain; 4.The sine cosine sequence is to sample the sine cosine signal; 5.A sequence with periodic characteristics.)