# RF Wireless World

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## Correlation-Auto,Cross MATLAB source code

This section of MATLAB source code covers correlation matlab code. correlation types auto and cross correlation basics including matlab function is covered.

Correlation determines how much two signals or vectors are similar or different in phase and magnitude. There are two types auto correlation and cross correlation. correlation is maximum when two signals are similar. correlation is equivalent to multiplying the complex conjugate of frequency spectrum of one signal by the frequency spectrum of the other.

In auto correlation same signal is correlated to itself or with shifted version of it. In cross correlation two different time series signals are correlated.The example below is for cross correlation. If one set both in1 and in2 as same vectors ( or append zeros initially in one) then it becomes auto correlation.

correlation output z[n] = ∑X[k] * Y[n+k]

### Setting up input parameters

in1=[0 1 2 3 4 5 6 7 8 9];
in2=[9 11 12 13 4 5 16 17 18 19];

### Cross correlation MATLAB Code

if length(in1)>length(in2)
in2 = [in2 zeros(1,pad)];
elseif length(in1)<length(in2)
in1 = [in1 zeros(1,pad)];
end

out_len = length(in1);
out = zeros(1,out_len);

tmp = in2;
for k = 1:out_len
out(k) = in1*tmp';
tmp = [0 tmp(1:end-1)];
end

figure;plot(out);title('Our code CORRELATION OUTPUT'); % output plot as per RF Wireless world design of corr function
[m,n]=max(out) % max value in the correlation and its index

### MATLAB Built in function-xcorr

y=xcorr(in1,in2); % matlab built in function
len=length(y);
index=len/2;
z=y(index:1:end); %extacting one side of the result
figure;plot(z);title('MATLAB xcorr function OUTPUT'); % output plot as per matlab function
[m1,n1]=max(z) % max value in the correlation and its index

### Useful Links to MATLAB codes

Refer following as well as links mentioned on left side panel for useful MATLAB codes.
OFDM Preamble generation  Time off estimation corr  Freq off estimation corr  channel estimation  11a WLAN channel  PN sequence generation  OFDMA Tx Rx  AES DES  carrier aggregation  CCDF  FIR Filter  IIR Filter  Low Pass FIR  Viterbi decoder  CRC8 CRC32