FSK and Adalm-Pluto

I am getting some errors in the following code;

clc;
%Creating transmission object
txPluto = sdrtx('Pluto','RadioID','usb:0','CenterFrequency',2.4e9, ...
               'BasebandSampleRate',1e6,'ChannelMapping',1);
           
%creating receiver object
rx = sdrrx('Pluto','RadioID','usb:0','CenterFrequency',2.4e9, ...
               'BasebandSampleRate',1e6,'ChannelMapping',1);
           
%Creating fsk modulator and demodulator objects
fskMod = comm.FSKModulator(2,1000,100);
fskDemod = comm.FSKDemodulator(2,1000,100);

%Creating array of data
data = randi([0 1],5,1);

%Modulating the data using FSK scheme
modSignal = step(fskMod,data)

%Transmitting singal
txPluto(modSignal);

%Releasing the transmitter
release(txPluto);

%Capturing the data from the receiver
[data,mdata]=capture(rx,length(modSignal))

%Demodulating the signal to attain the original data
%demodSignal=step(fskDemod,data);
demodSignal=fskDemod(data)

At the moment the final line is not working. I get the following error message: "The input data type must be double precision or single precision."

In addition, when the arrays modSignal and data are not the same. Does anyone know why this is?

--Cheers, A

Answer 1

[Sriram Tadavarty]

Hi Andrea,

The error can be solved when the variable data passed to fskDemod is type casted to double. Update the following in the code:

demodSignal=fskDemod(double(data))

The purpose of this update is due the different type provided by capture, based on the input length. Here are more details about what the data type of data would be while using the capture function of Pluto. https://www.mathworks.com/help/supportpkg/plutoradio/ref/plutoradio.sdrrxpluto.capture.html#mw_2dd7d96d-66cc-4e3d-a19a-8bcf004cf4c2 (Go through output arguments sections)

Regarding the dimensions of modSignals and data. The property 'SamplesPerSymbol' of FSKModulator decides it. The defult value is 17. So, the output length is the product of SamplesPerSymbol and length of input, i.e. 17*5 = 85. For more derails on the usage of object, go through https://www.mathworks.com/help/comm/ref/comm.fskmodulator-system-object.html

Hope this helps.

Regards,

Sriram

[Andrea Carroll]

Thank you Sriram, that defintely helped. Would you know how to synchronise the reciever so that it only records the data that has been sent by the transmitter and not random transmissions in the environment?

--Cheers A

[Sriram Tadavarty]

Hi Andrea,

Please do accept the answer if it is helpful. For the next question, here are few examples in MATLAB, which can help to have a quick start on this https://www.mathworks.com/help/supportpkg/plutoradio/examples/qpsk-receiver-with-adalm-pluto-radio.html (This examples addresses the practical issues in the receiver using ADALM-PLUTO)

https://www.mathworks.com/help/comm/synchronization-and-receiver-design.html (This page indicates lot of details of receiver aspects)

Hope this helps.

Regards,

Sriram

[Andrea Carroll]

Thanks, I will have a look into those links and if there are any further problems, I'll get back to you!

--cheers, A

[Andrea Carroll]

Hi Sriram,

Would you know how to implement a simple FSK transmission model using the Adalm-Puto SDR on simulink? The example of QPSK you sent above is still quite complex and not intuitive to understand.

thanks, A