a_filter_design.m

几个有延时的FIR滤波器的设计

% Design filter by specifying delay in units and
% looking at mag and phase response
		% Good default values for fft_size = 128 and num_carriers = 32
delay_1 = 6;				%		6
attenuation_1 = 0.35;		%		0.35
delay_2 = 10;				%		10
attenuation_2 = 0.30;		%		0.30

num = [1, zeros(1, delay_1-1), attenuation_1, zeros(1, delay_2-delay_1-1), attenuation_2];
[H, W] = freqz(num, 1, 512);	% compute frequency response
mag = 20*log10(abs(H));		% magnitude in dB
phase = angle(H) * 180/pi;	% phase angle in degrees
figure(9), clf
subplot(211), plot(W/(2*pi),mag)
title('Magnitude response of multipath channel')
xlabel('Digital Frequency'), ylabel('Magnitude in dB')
subplot(212), plot(W/(2*pi),phase)
title('Phase response of multipath channel')
xlabel('Digital Frequency'), ylabel('Phase in Degrees')

break




% Design filter using MATLAB command 'fir2'
nn = 40;	% order of filter
f = [0, 0.212, 0.253, 0.293, 0.5];
m =[1, 1, 0.5, 1, 1];
num = fir2(nn, 2*f, m);
den = 1;

[H, W] = freqz(num, den, 256);	% Compute freq response
mag = 20*log10(abs(H));	% Get mag in dB
phase = angle(H)*180/pi;	% Get phase in degrees

clf
subplot(211), plot(W/(2*pi),mag)
subplot(212), plot(W/(2*pi),phase)

break
% Design filter using MATLAB command 'fir1'

% These coeffs work well for OFDM vs. QAM!!!
% nn = 4;	% order of filter
% wl = 0.134;	% low cutoff of stopband
% wh = 0.378;	% high cutoff of stopband
% nn = 4;	% order of filter
% wl = 0.195;	% low cutoff of stopband
% wh = 0.309;	% high cutoff of stopband

nn = 8;	% order of filter
wl = 0.134;	% low cutoff of stopband
wh = 0.378;	% high cutoff of stopband
num = fir1(nn, 2*[wl, wh], 'stop');
den = 1;

[H, W] = freqz(num, den, 256);	% Compute freq response
mag = 20*log10(abs(H));	% Get mag in dB
phase = angle(H)*180/pi;	% Get phase in degrees

clf
subplot(211), plot(W,mag), hold on, plot(wl*2*pi,0,'o'), plot(wh*2*pi,0,'o')
subplot(212), plot(W,phase), hold on, plot(wl*2*pi,0,'o'), plot(wh*2*pi,0,'o')
hold off

break
% Design filter by specifying delay in units and looking at mag and phase response
n = 512;

d1 =4;
a1 = 0.2;
d2 = 5;
a2 = 0.3;

num = [1, zeros(1, d1-1), a1, zeros(1, d2-d1-1), a2]
den = [1];

[H, W] = freqz(num, den, n);
% F = 0:.1:pi;
% H = freqz(num, den, F*180/pi, 11025);

mag = 20*log10(abs(H));
% phase = angle(H * 180/pi);
phase = angle(H);

clf
subplot(211), plot(W,mag), hold on, plot(0.17*pi,0,'o'), plot(0.34*pi,0,'o')
subplot(212), plot(W,phase), hold on, plot(pi/2,0,'o')
hold off

break
% Design filter by specifying mag response at particular frequencies

n = 2;
f = [0, 0.25, 0.5];
mag = [1, .05, 1];

[num, den] = yulewalk(n,2*f,mag);

[H, W] = freqz(num, den);

mag = 20*log10(abs(H));
phase = angle(H * 180/pi);

clf
subplot(211), plot(W,mag)
subplot(212), plot(W,phase)