# I/Q samples treatment with Matlab

I collected Iridium (satcom) I/Q samples (5120 x 100000 complex double) and I would like to plot the range-Doppler response map by using the matlab tool (https://www.mathworks.com/help/phased/ref/phased.rangedopplerscope-system-object.html)

scope = phased.RangeDopplerScope( ... 'IQDataInput',true,'RangeMethod','Matched filter', ... 'Name','Range-Doppler Scope', ... 'Position',[560 375 560 420],'ResponseUnits','db', ... 'RangeUnits','m','DopplerFFTLength',1024, ... 'DopplerOutput','Speed','OperatingFrequency',fc, ... 'SampleRate',fs,'PropagationSpeed',c);

scope(( my 5120 x 100000 complex double),mfcoeffs);

How can I get my mfcoeffs? During my researches I found What is matched filter in QPSK signal?. But It does not answer my question. Also, I found https://www.mathworks.com/help/phased/ref/phased.phasecodedwaveform.getmatchedfilter.html ('getMatchedFilter' that uses a phase-coded waveform ) to get my mfcoeffs.

But according to https://www.mathworks.com/help/phased/ug/phase-coded-waveforms.html it is recommended to use another waveform instead of a phase-coded waveform when you need to detect or track high-speed targets or Phase-coded waveforms tend to perform poorly when signals have Doppler shifts. it is my case.

So How can I get mfcoeffs?

Iridium uses an SRRC PSF. So, you will need an SRRC match filter. In MATLAB you will use:

mfcoeffs = rcosdesign(beta,span,sps)

Where,

-beta is the excess bandwidth (rolloff) of the waveform.

-span is the number of symbols the filter will use. Just use the default value. I have only seen this matter when processing needs to be performed in real-time.

-sps is the samples per symbol of the waveform. It's calculated using $$\frac{f_s}{R_s}$$, where $$R_s$$ is the symbol rate.

So, you'll need to figure out the symbol rate and rolloff of the waveform you are trying to receive. Once you have those just plug them into the MATLAB function and you should be good to go.

• Thanks Lennon and djg! -beta: In case it is stated "0.4 root raised cosine filter". Does that mean the rolloff is 0.4? -The Rs of Iridum burst is 25 Ksymbol/s, so I can have my sps.
– nov
Nov 5, 2021 at 3:41
• Yes, nov. That is exactly right.
– user58975
Nov 6, 2021 at 16:11