文档介绍：CHAPTER1SignalsandSystems :physicalphenomenaorphysicalquantities,:x(t).  Continuous-timeandDiscrete-timeSignals(连续时间和离散时间信号)continuous-timesignals’independentvariableiscontinuous:x(t)discrete-timesignalsaredefinedonlyatdiscretetimes:x[n]RepresentingSignalsGraphically0X(t)(a)continuous-timeand(b)discrete-timesignals(a)-2X[-1]X[0]X[4]-4-3-1012345X[n]n(b)(周期和非周期信号)Foracontinuous-timesignalx(t)x(t)=x(t+T)-timesignalx[n]x[n]=x[n+N],wesaythatx(t)(x[n])isperiodicwithperiodT(N).(t)=2cos(10πt+1)-sin(4πt-1).Fromtrigonometry,weknowthatthefundamentalperiodofcos(10πt+1)isT1=1/5,andsin(4πt-1)isT2=1/(t)?TheanswerisifthereisarationalT,monmultiple(最小公倍数)ofT1andT2,thenwesaythatx(t)isperiodicwithfundamentalperiodT,orelse,x(t)(t)inthisexample,,anditisrational,sothatthefundamentalperiodofx(t)(确定性信号和随机信号)Adeterminatesignal——x(t)Arandomsignal——(能量信号和功率信号)TheinstantaneouspowerisThetotalenergyisTheaveragepowerisGenerally,thetotalenergyoverthetimeintervalinacontinuous-timesignal:Similarly,thetotalenergyinadiscrete-timesignalx[n]overthetimeinterval:Thetotalenergyoveraninfiniteintervalis,incontinuoustime,indiscretetime,Thetime-averagepoweroveraninfiniteinterval:incontinuoustimeanddiscretetime,,wecanidentifythreeimportantclassesofsignals:EnergysignalsPowersignalsSignalswithneitherfinitetotalenergynorfiniteaveragepower