Signal Processing with GNURadio and SDRs WORKSHOP...•Space generates a lot of Radio waves too •Radio waves are EM waves too •Most of the space discoveries are the result of some

Signal Processing with

GNURadio and SDRs

Ateet Kumar

Senior Security Researcher, Xen1thLabs

Digital14 LLC

About me

• The Signals Guy• Electronics and Communication Engineer• Former DRDO Research Fellow

Ateet Kumar | Senior Security Researcher

Ateet KumarSenior Security ResearcherXen1thLabs, Digital 14 LLC

@HyperS0nik [email protected]

Content

• Basics of EM and RF

• Important DSP Techniques

• GNURadio hands-on

• SDRs Hands-on


PART 1Basics of EM and RF


If you want to find secrets of the universe, think in terms of

energy, frequency and vibration.~Nikola Tesla


EM Spectrum

• EM waves are composed of oscillating magnetic and electric fields

Image Source: https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html, https://science.nasa.gov/ems/05_radiowaves


https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html

https://science.nasa.gov/ems/05_radiowaves

• EM waves with wavelength longer than infrared.

• 30Hz to 300GHz

• Either in terms of frequency or wavelength

• Generated by accelerating electric charges. ( e.g.current)

• Space generates a lot of Radio waves too

• Radio waves are EM waves too

• Most of the space discoveries are the result of someRadio signal from the space.

Image Source: https://science.nasa.gov/ems/05_radiowaves, http://www.ni.com/tutorial/3541/en/


Radio Waves

https://science.nasa.gov/ems/05_radiowaves

http://www.ni.com/tutorial/3541/en/

RF Communication Systems

Image Source: https://commons.wikimedia.org/wiki/


Simplex

Full Duplex Half Duplex

https://commons.wikimedia.org/wiki/

Wireless Communication System


Modulation


1. Analog Modulation

2. Digital Modulation

Types of Modulation


1. Amplitude Modulation (AM): the amplitude of the carrier varies in accordance tothe message signal

2. Frequency Modulation (FM): the frequency of the carrier varies in accordance tothe message signal

3. Phase Modulation (PM): the phase of the carrier varies in accordance to themessage signal

• Carrier signal: c(t) = Ac sin(ωc + φ)

• Message Signal: m(t) = Am sin(ωm + φ)

• Modulated O/P signal: x(t) = [Ac + m(t)].c(t)

Amplitude Shift Keying


• ASK

• FSK

• PSK

1 0 1 0 1

Frequency Shift Keying


• ASK

• FSK

• PSK

1 0 1 0 1

Phase Shift Keying


• ASK

• FSK

• PSK

1 0 1 0 1


PART 2Important DSP Techniques

Frequency Domain Anlaysis Vs Time Domian Analysis


Time domain and frequency domain plots of a Sine Wave

Image Source: Data Communications and Networking, Fourth Edition, Forouzan


Decomposition of a composite periodic signal in the time andfrequency domains

Image Source: Data Communications and Networking, Fourth Edition, Forouzan


CT DT

Sampling

Image Source: https://en.wikipedia.org/wiki/Sampling_(signal_processing)


• Reducing sampling rate

• Simply Low pass filtering

• Also called Downsampling

• The decimation factor is simply the ratio of the input rate to the output rate. It is usually symbolized by “M”, so input rate / output rate=M.

• Why decimate? to reduce the cost of processing

• You can only decimate by integer factors; you cannot decimate by fractional factors.

• A signal can be down-sampled (without doing any filtering) whenever it is “oversampled”, that is, when a sampling rate was used that was greater than the Nyquist criteria required.

Decimation

Image Source: https://dspguru.com/dsp/faqs/multirate/decimation)


• Inserting zero-valued samples between original samples to increase the sampling rate.

• Zero Stuffing

• Upsampling

• Increase the sampling rate at the output of one system so that another system operating at a higher sampling rate can input the signal.

• The interpolation factor is simply the ratio of the output rate to the input rate. It is usually symbolized by “L”, so output rate / input rate=L.

Interpolation

Image Source: https://dspguru.com/dsp/faqs/multirate/decimation)


A BREAK IS ALWAYS GOOD


PART 3GNURadio Practical

• Free and open source SDK

• Signal Processing modules for SDRs

• Source: www.gnuradio.org

Let’s use it to learn it ….



PART 4Software Defined Radios

Image source: https://en.wikipedia.org/wiki/Software-defined_radio

Software Defined Radios


BladeRF from Nuand HackRf one – Great Scott Gadgets

RTL-SDR DongleLime SDR

Ettus Research USRP B210

Some popular SDRs


• SDR#

• GQRX

• SDR Console

• GNURadio

• HDSDR

• Sigdigger

There are many. You just have to look for the appropriate one.


Some popular SDRs


How to Start looking into Signals

Choose the region of

Frequency

Know the legal rules and

regulations in your region/

country

Select the appropriate SDR

device

Prepare the system – OS,

SDR tools, Signal

Processing tools

Start Signal Analysis

Region Specific

Spectrum

Region Specific

Cheap or Costly

Lots of guidance

online

Avoid interfering

Let’s start Signal Hunting …


You can download the GNUradio examples from below:

https://github.com/AteetKumar/GNUradio_examples

Note:

• You may require to change the values in some blocks to make them work according to your system.

• Also, you can follow from the recording of the workshop all the GNURadio and SDR examples that were covered in this workshop.

Please feel free to contact me for any queries on RF Research, I will be happy to help.

Thank YouAteet Kumar, [email protected]

See you at HITB's Discord channel for questions & answers!

Documents

Signal Processing with GNURadio and SDRs WORKSHOP...•Space generates a lot of Radio waves too •Radio waves are EM waves too •Most of the space discoveries are the result of some