Author: Peter
Date:2020-10-09
Location:FZU
∵ ω = 2 π N T = 3 π 7 \omega=\dfrac{2\pi N}{T}=\dfrac{3\pi}{7} ω=T2πN=73π
∴ T = 14 N 3 T=\dfrac{14N}{3} T=314N
∵当N=3时,T=14为x(n)的最小周期
∵ x ( n ) = c o s ( n 8 − π ) − j s i n ( n 8 − π ) x(n)=cos(\dfrac{n}{8}-\pi)-jsin(\dfrac{n}{8}-\pi) x(n)=cos(8n−π)−jsin(8n−π)
∵ ω = 2 π N T = 1 8 \omega=\dfrac{2\pi N}{T}=\dfrac{1}{8} ω=T2πN=81
∴ T = 16 π N T=16\pi N T=16πN
∵T中含有 π \pi π,T不能为整数
∴x(n)不是周期序列
∵ x ( n ) = G 5 ( n ) = u ( n ) − u ( n − 5 ) x(n)=G_5(n)=u(n)-u(n-5) x(n)=G5(n)=u(n)−u(n−5)
∵由(1)知 h ( n ) = ( 1 3 ) n u ( n ) h(n)=(\dfrac{1}{3})^nu(n) h(n)=(31)nu(n)
∴ y ( n ) = h ( n ) ∗ x ( n ) = ∑ m = − ∞ + ∞ h ( m ) x ( n − m ) y(n)=h(n)*x(n)=\sum\limits_{m=-∞}^{+∞}h(m)x(n-m) y(n)=h(n)∗x(n)=m=−∞∑+∞h(m)x(n−m)
= ∑ m = − ∞ + ∞ ( 1 3 ) m u ( m ) [ u ( n − m ) − u ( n − m − 5 ) ] \ \ \ \ \ \ \ \ \ \ \ =\sum\limits_{m=-∞}^{+∞}(\dfrac{1}{3})^mu(m)[u(n-m)-u(n-m-5)] =m=−∞∑+∞(31)mu(m)[u(n−m)−u(n−m−5)]
= ∑ m = 0 n ( 1 3 ) m − ∑ m = 0 n − 5 ( 1 3 ) m \ \ \ \ \ \ \ \ \ \ \ =\sum\limits_{m=0}^{n}(\dfrac{1}{3})^m-\sum\limits_{m=0}^{n-5}(\dfrac{1}{3})^m =m=0∑n(31)m−m=0∑n−5(31)m
= ∑ m = n − 4 n ( 1 3 ) m 其 中 n − 4 ≥ 0 \ \ \ \ \ \ \ \ \ \ \ =\sum\limits_{m=n-4}^{n}(\dfrac{1}{3})^m \ \ \ \ 其中n-4\geq0 =m=n−4∑n(31)m 其中n−4≥0
= ( 1 3 ) n − 4 [ 1 − ( 1 3 ) 5 ] 1 − 1 3 u ( n − 4 ) \ \ \ \ \ \ \ \ \ \ \ =\dfrac{(\dfrac{1}{3})^{n-4}[1-(\dfrac{1}{3})^5]}{1-\dfrac{1}{3}}u(n-4) =1−31(31)n−4[1−(31)5]u(n−4)
= 121 3 n n = 4 , 5... \ \ \ \ \ \ \ \ \ \ \ =\dfrac{121}{3^n} \ \ \ \ \ n=4,5... =3n121 n=4,5...
∵ y ( n ) = h ( n ) ∗ [ u ( n ) − u ( n − 5 ) ] , 当 n = 0 , 1 , 2 , 3 , 4 时 y ( n ) = h ( n ) ∗ u ( n ) 既 ( 2 ) 中 的 解 y(n)=h(n)*[u(n)-u(n-5)],当n=0,1,2,3,4时y(n)=h(n)*u(n)既(2)中的解 y(n)=h(n)∗[u(n)−u(n−5)],当n=0,1,2,3,4时y(n)=h(n)∗u(n)既(2)中的解
∴ y ( n ) = [ 3 2 − 1 2 ( 1 3 ) n ] [ u ( n ) − u ( n − 5 ) ] + 121 3 n u ( n − 5 ) y(n)=\bigg[\dfrac{3}{2}-\dfrac{1}{2}\big(\dfrac{1}{3}\big)^n\bigg][u(n)-u(n-5)]+\dfrac{121}{3^n}u(n-5) y(n)=[23−21(31)n][u(n)−u(n−5)]+3n121u(n−5)
∵ h ( n ) = x ( n ) = u ( n ) − u ( n − 4 ) h(n)=x(n)=u(n)-u(n-4) h(n)=x(n)=u(n)−u(n−4)
∴ h ( n ) = x ( n ) = { 1 , 1 , 1 , 1 } n = 0 , 1 , 2 , 3 h(n)=x(n)=\{1,1,1,1\} \ \ \ \ \ n=0,1,2,3 h(n)=x(n)={ 1,1,1,1} n=0,1,2,3
∴根据不进位乘法可得 y ( n ) = { 1 , 2 , 3 , 4 , 3 , 2 , 1 } n = 0 , 1...6 y(n)=\{1,2,3,4,3,2,1\} \ \ \ \ n=0,1...6 y(n)={ 1,2,3,4,3,2,1} n=0,1...6
∵ h ( n ) = 2 n [ u ( n ) − u ( n − 4 ) ] h(n)=2^n[u(n)-u(n-4)] h(n)=2n[u(n)−u(n−4)]
∴ h ( n ) = { 1 , 2 , 4 , 8 } n = 0 , 1 , 2 , 3 h(n)=\{1,2,4,8\} \ \ \ \ \ \ n=0,1,2,3 h(n)={ 1,2,4,8} n=0,1,2,3
∵ x ( n ) = { 1 , 0 , − 1 } n = 0 , 1 , 2 x(n)=\{1,0,-1\} \ \ \ \ \ \ \ n=0,1,2 x(n)={ 1,0,−1} n=0,1,2
∴根据不进位乘法可得 y ( n ) = { 1 , 2 , 3 , 6 , − 4 , − 8 } n = 0 , 1...5 y(n)=\{1,2,3,6,-4,-8\} \ \ \ \ n=0,1...5 y(n)={ 1,2,3,6,−4,−8} n=0,1...5
∵ y ( n ) = x ( n ) ∗ h ( n ) = 0. 5 n u ( n ) ∗ [ u ( n ) − u ( n − 5 ) ] y(n)=x(n)*h(n)=0.5^nu(n)*[u(n)-u(n-5)] y(n)=x(n)∗h(n)=0.5nu(n)∗[u(n)−u(n−5)]
= ∑ m = − ∞ + ∞ x ( m ) h ( n − m ) \ \ \ \ \ \ \ \ \ \ \ =\sum\limits_{m=-∞}^{+∞}x(m)h(n-m) =m=−∞∑+∞x(m)h(n−m)
= ∑ m = − ∞ + ∞ 0. 5 m u ( m ) [ u ( n − m ) − u ( n − m − 5 ) ] \ \ \ \ \ \ \ \ \ \ \ =\sum\limits_{m=-∞}^{+∞}0.5^mu(m)[u(n-m)-u(n-m-5)] =m=−∞∑+∞0.5mu(m)[u(n−m)−u(n−m−5)]
= ∑ m = 0 n ( 1 2 ) m − ∑ m = 0 n − 5 ( 1 2 ) m \ \ \ \ \ \ \ \ \ \ \ =\sum\limits_{m=0}^{n}(\dfrac{1}{2})^m-\sum\limits_{m=0}^{n-5}(\dfrac{1}{2})^m =m=0∑n(21)m−m=0∑n−5(21)m
= ∑ m = n − 4 n ( 1 2 ) m 其 中 n − 4 ≥ 0 \ \ \ \ \ \ \ \ \ \ \ =\sum\limits_{m=n-4}^{n}(\dfrac{1}{2})^m \ \ \ \ \ 其中n-4\geq0 =m=n−4∑n(21)m 其中n−4≥0
= ( 1 2 ) n − 4 [ 1 − ( 1 2 ) 5 ] 1 − 1 2 \ \ \ \ \ \ \ \ \ \ \ =\dfrac{(\dfrac{1}{2})^{n-4}[1-(\dfrac{1}{2})^5]}{1-\dfrac{1}{2}} =1−21(21)n−4[1−(21)5]
= 31 2 n u ( n − 4 ) \ \ \ \ \ \ \ \ \ \ \ =\dfrac{31}{2^n}u(n-4) =2n31u(n−4)
∵ 当 n = 0 , 1 , 2 , 3 , 4 时 y ( n ) = 0. 5 n u ( n ) ∗ u ( n ) 当n=0,1,2,3,4时y(n)=0.5^nu(n)*u(n) 当n=0,1,2,3,4时y(n)=0.5nu(n)∗u(n)
∵ Y ( z ) = 2 z z − 1 − z z − 1 2 Y(z)=\dfrac{2z}{z-1}-\dfrac{z}{z-\dfrac{1}{2}} Y(z)=z−12z−z−21z
∴ y ( n ) = 2 − ( 1 2 ) n n = 0 , 1 , 2 , 3 , 4 y(n)=2-(\dfrac{1}{2})^n \ \ \ \ \ n=0,1,2,3,4 y(n)=2−(21)n n=0,1,2,3,4
∴ y ( n ) = [ 2 − ( 1 2 ) n ] [ u ( n ) − u ( n − 5 ) ] + 31 2 n u ( n − 5 ) y(n)=[2-(\dfrac{1}{2})^n][u(n)-u(n-5)]+\dfrac{31}{2^n}u(n-5) y(n)=[2−(21)n][u(n)−u(n−5)]+2n31u(n−5)
∵ T [ C 1 x 1 ( n ) + C 2 x 2 ( n ) ] = [ C 1 x 1 ( n ) + C 2 x 2 ( n ) ] s i n ( 2 π 7 n + π 6 ) T[C_1x_1(n)+C_2x_2(n)]=[C_1x_1(n)+C_2x_2(n)]sin(\dfrac{2\pi}{7}n+\dfrac{\pi}{6}) T[C1x1(n)+C2x2(n)]=[C1x1(n)+C2x2(n)]sin(72πn+6π)
∵ [ C 1 y 1 ( n ) + C 2 y 2 ( n ) ] = [ C 1 x 1 ( n ) + C 2 x 2 ( n ) ] s i n ( 2 π 7 n + π 6 ) [C_1y_1(n)+C_2y_2(n)]=[C_1x_1(n)+C_2x_2(n)]sin(\dfrac{2\pi}{7}n+\dfrac{\pi}{6}) [C1y1(n)+C2y2(n)]=[C1x1(n)+C2x2(n)]sin(72πn+6π)
∴ T [ C 1 x 1 ( n ) + C 2 x 2 ( n ) ] = [ C 1 y 1 ( n ) + C 2 y 2 ( n ) ] T[C_1x_1(n)+C_2x_2(n)]={[C_1y_1(n)+C_2y_2(n)]} T[C1x1(n)+C2x2(n)]=[C1y1(n)+C2y2(n)]
∵ T [ x ( n − m ) ] = x ( n − m ) s i n ( 2 π 7 n + π 6 ) T[x(n-m)]=x(n-m)sin(\dfrac{2\pi}{7}n+\dfrac{\pi}{6}) T[x(n−m)]=x(n−m)sin(72πn+6π)
∵ y ( n − m ) = x ( n − m ) s i n [ 2 π 7 ( n − m ) + π 6 ] y(n-m)=x(n-m)sin[\dfrac{2\pi}{7}(n-m)+\dfrac{\pi}{6}] y(n−m)=x(n−m)sin[72π(n−m)+6π]
∵ T [ x ( n − m ) ] ≠ y ( n − m ) T[x(n-m)]\not ={y(n-m)} T[x(n−m)]=y(n−m)
∴系统为线性时变
∵ T [ C 1 x 1 ( n ) + C 2 x 2 ( n ) ] = [ C 1 x 1 ( n ) + C 2 x 2 ( n ) ] 2 T[C_1x_1(n)+C_2x_2(n)]=[C_1x_1(n)+C_2x_2(n)]^2 T[C1x1(n)+C2x2(n)]=[C1x1(n)+C2x2(n)]2
∵ [ C 1 y 1 ( n ) + C 2 y 2 ( n ) ] = [ C 1 x 1 ( n ) ] 2 + [ C 2 x 2 ( n ) ] 2 [C_1y_1(n)+C_2y_2(n)]=[C_1x_1(n)]^2+[C_2x_2(n)]^2 [C1y1(n)+C2y2(n)]=[C1x1(n)]2+[C2x2(n)]2
∴ T [ C 1 x 1 ( n ) + C 2 x 2 ( n ) ] ≠ [ C 1 y 1 ( n ) + C 2 y 2 ( n ) ] T[C_1x_1(n)+C_2x_2(n)]\not={[C_1y_1(n)+C_2y_2(n)]} T[C1x1(n)+C2x2(n)]=[C1y1(n)+C2y2(n)]
∵ T [ x ( n − m ) ] = [ x ( n − m ) ] 2 T[x(n-m)]=[x(n-m)]^2 T[x(n−m)]=[x(n−m)]2
∵ y ( n − m ) = [ x ( n − m ) ] 2 y(n-m)=[x(n-m)]^2 y(n−m)=[x(n−m)]2
∵ T [ x ( n − m ) ] = y ( n − m ) T[x(n-m)]={y(n-m)} T[x(n−m)]=y(n−m)
∴系统为非线性时不变
∵ y ( n ) = x ( n ) ∗ h ( n ) = ∑ m = − ∞ + ∞ x ( m ) h ( n − m ) y(n)=x(n)*h(n)=\sum\limits_{m=-∞}^{+∞}x(m)h(n-m) y(n)=x(n)∗h(n)=m=−∞∑+∞x(m)h(n−m)
∴ y ( n ) = ∑ m = − ∞ + ∞ α m u ( m ) β ( n − m ) u ( n − m ) y(n)=\sum\limits_{m=-∞}^{+∞}\alpha^mu(m)\beta^{(n-m)}u(n-m) y(n)=m=−∞∑+∞αmu(m)β(n−m)u(n−m)
= ∑ m = 0 n α m β ( n − m ) \ \ \ \ \ \ \ \ \ \ \ =\sum\limits_{m=0}^{n}\alpha^m\beta^{(n-m)} =m=0∑nαmβ(n−m)
= β n ∑ m = 0 n ( α β ) m \ \ \ \ \ \ \ \ \ \ \ =\beta^n\sum\limits_{m=0}^{n}\big(\dfrac{\alpha}{\beta}\big)^m =βnm=0∑n(βα)m
= β n ⋅ 1 − ( α β ) n + 1 1 − α β \ \ \ \ \ \ \ \ \ \ \ =\beta^n\cdot\dfrac{1-\big(\dfrac{\alpha}{\beta}\big)^{n+1}}{1-\dfrac{\alpha}{\beta}} =βn⋅1−βα1−(βα)n+1
= β n + 1 − α n + 1 β − α u ( n ) \ \ \ \ \ \ \ \ \ \ \ =\dfrac{\beta^{n+1}-\alpha^{n+1}}{\beta-\alpha}u(n) =β−αβn+1−αn+1u(n)
∵ y ( n ) = x ( n ) ∗ h ( n ) y(n)=x(n)*h(n) y(n)=x(n)∗h(n)
∵ x ( n ) ∗ δ ( n − m ) = x ( n − m ) x(n)*\delta(n-m)=x(n-m) x(n)∗δ(n−m)=x(n−m)
∴ y ( n ) = u ( n − 2 ) − u ( n − 3 ) = δ ( n − 2 ) y(n)=u(n-2)-u(n-3)=\delta(n-2) y(n)=u(n−2)−u(n−3)=δ(n−2)