外文资料翻译---信号与系统精选.docVIP

外文资料 Signals and System Signals are scalar-valued functions of one or more independent variables. Often for convenience, when the signals are one-dimensional, the independent variable is referred to as “time” The independent variable may be continues or discrete. Signals that are continuous in both amplitude and time (often referred to as continuous -time or analog signals) are the most commonly encountered in signal processing contexts. Discrete-time signals are typically associated with sampling of continuous-time signals. In a digital implementation of signal processing system, quantization of signal amplitude is also required . Although not precisely Correct in every context, discrete-time signal processing is often referred to as digital signal processing. Discrete-time signals, also referred to as sequences, are denoted by functions whose arguments are integers. For example , x(n) represents a sequence that is defined for integer values of n and undefined for non-integer value of n . The notation x(n) refers to the discrete time function x or to the value of function x at a specific value of n .The distinction between these two will be obvious from the contest . Some sequences and classes of sequences play a particularly important role in discrete-time signal processing .These are summarized below. The unit sample sequence, denoted by δ(n)=1 ,n=0 ，δ(n)=0,otherwise (1) The sequence δ(n) play a role similar to an impulse function in analog analysis . The unit step sequence ,denoted by u(n), is defined as U(n)=1 , n≧0 u(n)=0 ,otherwise (2) Exponential sequences of the form X(n)= (3) Play a role in discrete time signal processing similar to the role played by exponential functions in continuous time signal processing .Specifically, they are eigenfunctions of discrete time linear system and for that reason form the basis for transform analysis techniques. When ︳α ︳=1, x(n) t