www.gusucode.com > signal 案例源码程序 matlab代码 > signal/AlignSignalsWithDifferentStartTimesUsingXcorrExample.m

    %% Align Signals Using Cross-Correlation
% Many measurements involve data collected asynchronously by multiple
% sensors. If you want to integrate the signals and study them in tandem,
% you have to synchronize them. Use |xcorr| for that purpose.
%
% For example, consider a car crossing a bridge. The vibrations it produces
% are measured by three identical sensors located at different spots. The
% signals have different arrival times.

% Copyright 2015 The MathWorks, Inc.


%%
% Load the signals into the MATLAB(R) workspace and plot them.

load relatedsig

ax(1) = subplot(3,1,1);
plot(s1)
ylabel('s_1')
axis tight

ax(2) = subplot(3,1,2);
plot(s2)
ylabel('s_2')
axis tight

ax(3) = subplot(3,1,3);
plot(s3)
ylabel('s_3')
axis tight
xlabel('Samples')

linkaxes(ax,'x')

%%
% Compute the cross-correlations between the three pairs of signals.
% Normalize them so their maximum value is one.

[C21,lag21] = xcorr(s2,s1);
C21 = C21/max(C21);

[C31,lag31] = xcorr(s3,s1);
C31 = C31/max(C31);

[C32,lag32] = xcorr(s3,s2);
C32 = C32/max(C32);

%%
% The locations of the maximum values of the cross-correlations indicate
% time leads or lags.

[M21,I21] = max(C21);
t21 = lag21(I21);

[M31,I31] = max(C31);
t31 = lag31(I31);

[M32,I32] = max(C32);
t32 = lag31(I32);

%%
% Plot the cross-correlations. In each plot display the location of the
% maximum.

subplot(3,1,1)
plot(lag21,C21,[t21 t21],[-0.5 1],'r:')
text(t21+100,0.5,['Lag: ' int2str(t21)])
ylabel('C_{21}')
axis tight
title('Cross-Correlations')

subplot(3,1,2)
plot(lag31,C31,[t31 t31],[-0.5 1],'r:')
text(t31+100,0.5,['Lag: ' int2str(t31)])
ylabel('C_{31}')
axis tight

subplot(3,1,3)
plot(lag32,C32,[t32 t32],[-0.5 1],'r:')
text(t32+100,0.5,['Lag: ' int2str(t32)])
ylabel('C_{32}')
axis tight
xlabel('Samples')

%%
% |s2| leads |s1| by 350 samples; |s3| lags |s1| by 150 samples. Thus |s2|
% leads |s3| by 500 samples. Line up the signals by clipping the vectors
% with longer delays.

s1 = s1(-t21:end);
s3 = s3(t32:end);

ax(1) = subplot(3,1,1);
plot(s1)
ylabel('s_1')
axis tight

ax(2) = subplot(3,1,2);
plot(s2)
ylabel('s_2')
axis tight

ax(3) = subplot(3,1,3);
plot(s3)
ylabel('s_3')
axis tight
xlabel('Samples')

linkaxes(ax,'x')

%%
% The signals are now synchronized and ready for further processing.