Http://www.mathworks.it/it/help/phased/ug/matched-filtering.html

And I think for energy detection you can use sum(abs(x).^2) if u are considering a voltage kind of signal.

if ur signal is complex

Step-1 collect N samples (using some window).

Step-2 Take N point FFT of that frame consisting of N complex samples.

Step-3 Find the absolute value of every sample and take square of each of them. Say it is a vector X of length N.

Step-4 Assuming your sampling rate is Fs hence frequency resolution will be Fs/N Hz. Say it a "step"

Step-5 Assuming your center frequency of the collected data as Fc the output from the step-3 can be mapped as

Step-6 If you used fft function of matlab then shift then circular shift the output by N/2

Step-7 Now X[0] is the energy content of Fc-N/2*step

X[1] is the energy content of Fc-(N/2-1)*step

.

.

.

X[N-1] is the energy content of Fc+N/2

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Let us assume that we have 1024 (I and Q) samples gathered using a tuner

centered at 20MHz. And let us assume that the sampling frequency was

8MHz.

Doing 1024 points complex FFT means:

1) FFT Frequency resolution is : 8MHz / 1024 = 7812.5 KHz

2) The output of the FFT X[0] represents the spectrum at 20MHz.

3) The output of the FFT X[1] to X[511] represents the frequencies from

20.0078125 MHz to 23.9921875 MHz (about 4MHz above center frequency).

4) The output of the FFT X[512] to X[1023] represents the frequencies

from

16.0078125 MHz to 19.9921875 MHz (about 4MHz bellow center frequency).

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Now you can compare the energy with some threshold (to determine the threshold is another big challenge) to find out which channel is free and which is busy.

Give me your mail id. I will give you the correct code.