《DSP using MATLAB》Problem 5.11
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代码:
%% ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ %% Output Info about this m-file fprintf(‘ *********************************************************** ‘); fprintf(‘ <DSP using MATLAB> Problem 5.11 ‘); banner(); %% ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ % -------------------------------------------------------------- % 1 h(n) = [0.9^n] n=[0:5] % -------------------------------------------------------------- nn1 = [0:5]; hh1 = 0.9 .^ nn1; NN1 = length(hh1); % length is 6 %m = mod_1(nn1, NN1); h = [hh1 zeros(1, 2)]; % padding zeros n = [nn1 max(nn1)+1:max(nn1)+2]; figure(‘NumberTitle‘, ‘off‘, ‘Name‘, ‘P5.11.1 Causal Real LSI h(n)‘) set(gcf,‘Color‘,‘white‘); subplot(2,1,1); stem(nn1, hh1); xlabel(‘n‘); ylabel(‘h(n)‘); title(‘h(n)=0.9^n ori sequence‘); grid on; subplot(2,1,2); stem(n, h); xlabel(‘n‘); ylabel(‘h(n)‘); title(‘h(n) padding zeros‘); grid on; %% ============================================================================= %% DTFT H(w) of hn sequence, w=[0:2pi], %% ============================================================================= MM = 500; [Hw_DTFT, w] = dtft1(h, n, MM); magHw_DTFT = abs(Hw_DTFT); angHw_DTFT = angle(Hw_DTFT)/pi; realHw_DTFT = real(Hw_DTFT); imagHw_DTFT = imag(Hw_DTFT); %% -------------------------------------------------------------- %% START H_DTFT‘s mag ang real imag %% -------------------------------------------------------------- figure(‘NumberTitle‘, ‘off‘, ‘Name‘, ‘P5.11.1 H(w) DTFT of h(n)‘); set(gcf,‘Color‘,‘white‘); subplot(2,2,1); plot(w/pi,magHw_DTFT); grid on; % axis([-2,2,0,15]); title(‘Magnitude Part‘); xlabel(‘frequency in pi units‘); ylabel(‘Magnitude |H\\_DTFT|‘); subplot(2,2,3); plot(w/pi, angHw_DTFT); grid on; % axis([-2,2,-1,1]); title(‘Angle Part‘); xlabel(‘frequency in pi units‘); ylabel(‘Rad pi‘); %axis([-200,200,0,2]); subplot(‘2,2,2‘); plot(w/pi, realHw_DTFT); grid on; title(‘Real Part‘); xlabel(‘frequency in pi units‘); ylabel(‘Real‘); subplot(‘2,2,4‘); plot(w/pi, imagHw_DTFT); grid on; title(‘Imaginary Part‘); xlabel(‘frequency in pi units‘); ylabel(‘Imaginary‘); %% -------------------------------------------------------------- %% END H_DTFT‘s mag ang real imag %% -------------------------------------------------------------- %% ------------------------------------------------------------------ %% DFT(k) of hn sequence, k=[0:N-1] %% w=2pi*k/N k=Nw/(2pi) %% ------------------------------------------------------------------ N1 = length(h); k1 = [0 : N1-1]; %k2 = [-N : N-1]; %k3 = [-N/2 : N/2]; Hk_DFT = dft(h, N1); % DFT magHk_DFT = abs( Hk_DFT ) % DFT magnitude angHk_DFT = angle( Hk_DFT )/pi % DFT angle realHk_DFT = real(Hk_DFT); imagHk_DFT = imag(Hk_DFT); figure(‘NumberTitle‘, ‘off‘, ‘Name‘, ‘P5.11.1 DFT(k) of h(n)‘) set(gcf,‘Color‘,‘white‘); subplot(2,1,1); stem(k1, magHk_DFT); hold on; plot(N1*w/(2*pi), magHw_DTFT,‘r--‘); hold off; %axis([-N/2, N/2, -0.5, 50.5]); xlabel(‘k‘); ylabel(‘magnitude(k)‘); title(‘DFT magnitude of h(n), N=8‘); grid on; subplot(2,1,2); stem(k1, angHk_DFT); hold on; plot(N1*w/(2*pi), angHw_DTFT,‘r--‘); hold off; %axis([-N/2, N/2, -0.5, 50.5]); xlabel(‘k‘); ylabel(‘angle(k)‘); title(‘DFT angle of h(n), N=8‘); grid on;
运行结果:
只会第1小题。
8点DFT基本能反映DTFT的幅度谱,但相位谱感觉稍有欠缺。
第2小题不会做。
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