This document summarizes a student project on signal processing using a Pluto-SDR hardware platform and GNU Radio Companion software. It introduces software defined radio (SDR) and discusses implementing basic digital modulation schemes like AM and FM. Experiments were conducted transmitting test signals, taking FFTs and waterfall plots of received signals, and building an FM receiver flowgraph. The document concludes SDR concepts were demonstrated practically using the Pluto-SDR and GRC helps learn communication system theories.

1. Project report on
Signal Processing using
Pluto-SDR
LAB BASED PROJECT (ECN-300)
​Under the Guidance Of
Dr. Meenakshi Rawat
Assistant Professor
Department of Electronics and Communication Engineering
Submitted By
Bhavna Singh Rohit Raushan
15116012 14116058

2. Contents
1) Abstract and Introduction
2) Software Defined Radio
3) Hardware Platform( Pluto-SDR)
4) GNU Radio Companion
5) IIO-Oscilloscope
6) SDR Working Model
A) Transmit Test
B) FFT & Waterfall Sink Test
C) IIO Oscilloscope
7) GRC Implementation
A) Cyclic Sine Wave
B) Amplitude Modulation
C) FM Receiver
8) Conclusion
9) Reference

3. ABSTRACT
Here we represent the basic idea about the Software Defined Radio (SDR) and have
demonstrated the fundamental digital modulation schemes.
SDR is a technique which can be used to replace the current hardware.
Implementation of simple modulation schemes like AM,FM and tested different
modulation circuits to test our Pluto-SDR connectivity with GNU Radio signals and
IIO-Oscilloscope..
​Software Used: GNU Radio Companion, IIO-Oscilloscope.
INTRODUCTION
We illustrated here a simple and easily interpretable demonstration of basic
communication systems using the SDR. This paper is divided into different sections.
First section deals with introduction to software defined radio. Second section deals with
a brief introduction to commonly used blocks in GNU radio companion. Third section
gives the implementation procedure and final section gives the conclusion and future
work.
Software Defined Radio
In today’s world all the communication processes are done on hardware but the
assembly of the proper hardware can many times cause errors in the processing of
signals. The hardware is very costly moreover it is many times used only for a specific
process. The hardware is also not easily portable, as a result to get away with all this
problems researchers have come up with Software Defined Radio or SDR.a complete
software implementation of hardware processes. SDR with its dynamic nature of
modifying the system parameters without actually changing the hardware part is very
effectively used today. So, SDR proves to be an effective solution to the very high cost
and limited flexibility of hardware based radios.
Software defined radio is a radio communication systems wherein which the hardware
like filters, amplifiers, modulators etc are implemented in the personal computers or
some embedding devices. By doing so, hardware complexity can be widely reduced. In
addition to software part there is a RF front end preceding this software section. By using
such a design one can transmit and receive variety of signals based on the applications.
In SDR, signal is captured by an antenna which is further converted into digital samples
with regular intervals.These digital values are then processed in software, where the

4. required application is written. The resulting output can be then converted back into
audio, video or required form. The next section describes the hardware and software
platform used for this project.
​GNU Radio Companion:
GNU Radio​ is a free & open-source software development toolkit that provides signal
processing blocks to implement software radios. It ​can​ be used with readily-available
low-cost external RF hardware to create software-defined radios, or without hardware in
a simulation-like environment.It ​is a graphical tool for creating signal flow graphs and
generating flow-graph source code.
Digital signal processing :
Use of ​digital processing, such as by computers or more specialized digital signal
processors, to perform a wide variety of ​signal operations. The signals processed in this
manner are a sequence of numbers that represent ​samples of a ​continuous variable in a
domain such as time, space, or frequency
Signal processing concerns the analysis, synthesis, and modification of ​signals, which
are broadly defined as functions conveying "information about the behavior or attributes
of some phenomenon”, such as sound ,images and biological measurements.For
example, signal processing techniques are used to improve signal transmission fidelity,
storage efficiency, and subjective quality, and to emphasize or detect components of
interest in a measured signal.
Analog to digital conversion:
(​ADC​, ​A/D​, or ​A-to-D​) is a system that converts an ANALOG signal, such as a sound
picked up by a microphone or light entering a digital camera into a digital signal an ADC
converts a continuous-time and continuous-amplitude analog signal to a discrete-time
and discrete-amplitude digital signal.
Three processes are involved in A/D conversion are ​sampling ,Quantization and Binary
coding.

5. (analog signal) (converted digital signal)
SDR HARDWARE
In this section, a theoretical review of hardware differences between traditional and SDR
receivers is performed at first, explaining also how the software defined transmission
takes place.
SDR Working Model:
In SDR, signal is captured by an antenna which is further converted into digital samples
with regular intervals. These digital values are then processed in software.The resulting
output can be then converted back into audio, video or required form.

6. SDR Receiver:
At first, the RF tuner converts the analog signal to IF, performing the same operation that
the first three blocks of the superheterodyne receiver. Up to this point the two schemes
converge. Next, the IF signal is passed to the ADC converter in charge of changing the
signal’s domain, offering digital samples at its output. The samples are feed to the
following stage’s input which is a Digital Down Converter (DDC). The DDC is commonly
a monolithic chip and it stands as the key part of the SDR system.
It consists of three main components:
(1) A digital mixer,
(2) A digital local oscillator, and
(3) A Finite Impulse Response (FIR) low-pass filter.
The components operation is similar to their analog counterparts. The digital mixer and
the local oscillator shift the IF digital samples to baseband, while the FIR low-pass filter
limits the bandwidth of the final signal. For the implementation of each of its parts, the
DDC includes a high number of multipliers, adders and shift registers. Observe that the
signals are transferred to their baseband equivalent at the digital mixer’s output by the
disintegration into the I and Q counter phase components [20]. If the tuning of the digital
local oscillator is modified, the desired signal can be shifted away or towards the point
where it reaches 0Hz. This variation, together with the bandwidth adjustment of the
low-pass filter, defines which part of the reception is treated as a useful signal. Another
procedure, known as decimation, is commonly performed for reducing the sampling
frequency or sample rate. Thus, the new sampling frequency in baseband results from

7. the division of the original sampling frequency by an N factor, called decimation factor.
The final sample rate can be as little as twice the highest frequency component of the
useful signal, as proposed by the well-known Nyquist theorem. Furthermore, practical
approaches have shown that reduction can be applied up to an extra 20% without
significantly affecting the quality of the result [19]. This can be expressed numerically as
is done in equation 1.
f b2=0.8fb=fs/N (1)...
where
fb is the frequency at baseband,
fs is the sampling frequency,
N is the decimator factor and
f b2 is the new calculated baseband frequency after the decimation is applied.
Finally, the baseband samples are passed to the Digital Signal Processing (DSP) block,
where task such as demodulating and decoding are performed, among others. SDR
Transmitter Although the most common SDR devices are receivers, the technology also
includes transmission schemes. The price of a SDR receiver can be as low as 20 USD
[16], while the cost of SDR transmitters/ receivers typically exceeds 300 USD [23].
The SDR transmitter structure is explained below.
SDR transmitters receive a baseband signal as an input, typically generated by a DSP
step as it is shown in Fig. 3. The first block is a Digital Up Converter (DUC) which
transfers the baseband signal to IF. The DAC that follows transform the samples to the
analog domain. Next, the RF converter shifts the signal towards higher frequencies.
Finally, the signal is amplified and directed to the antenna.

8. Within the DUC, the Interpolation Filter is responsible for raising the baseband signal’s
sample rate to match the operating frequency of the components that follow. Therefore,
it performs the Decimator’s opposite operation in the receiver’s architecture. Then, the
digital mixer and the local oscillator shift the samples to IF, the shift being controlled by
the local oscillator.
Overview of Adalm-pluto SDR:
ADALM-PLUTO active learning module (Pluto-SDR) helps introduction to the
fundamentals of software-defined radio (SDR), radio frequency (RF), and wireless
communications.the module can be used for and self directed learning to help students
develop a foundation in real-world RF and communications that they can build . The
PlutoSDR works as a portable lab that, when used with a host, can augment classroom
learning. MATLAB® and Simulink® are two of the many software packages supported
by PlutoSDR, and it provides an intuitive graphical user interface (GUI).

9. Features of Pluto SDR:
● The PlutoSDR features independent receive and transmit channels that can be
operated in full duplex .
● The active learning module can generate or acquire RF analog signals from 325
MHz to 3800 MHz at up to 61.44 megasamples per second (MSPS).
● Small enough to fit in a shirt pocket, the PlutoSDR is completely self-contained
and entirely USB powered with the default firmware.
● As Pluto SDR is enabled by libiio drivers, it supports OS X® , Windows® , and
Linux® , which allows to learn and explore on a variety of devices.
● PlutoSDR can be used to generate and capture RF waveforms.
Pluto SDR as hardware:--​Working on Adalm-PLUTO
General Testing:
1. Transmit Test
Next we tried adapting a simple transmit test by creating a flowgraph sending and
receiving signal via Pluto-SDR.
Transmit Performance:
Output Power (how far can I transmit)
Output Fidelity (how accurate is the transmission)

10. 2. ​FFT and Waterfall SInk Test
We tested a simple FFT and Waterfall sink using the Pluto SDR source. We set the
sample rate to the maximum of 61.44 MSPS, and the RF bandwidth to 60M. we were
able to see the 900 MHz GSM band. It seemed the max sample rate is not used as the
output is only 30 MHz, or perhaps it’s only one ADC.
3. ​IIO-Oscilloscope Testing:
We tested using the PlutoSDR IIO-OSCILLOSCOPE software and were able to
generate a FFT spectrum of the GSM band.

11. FFT(Fast Fourier Transform) Plots:
Fourier analysis of a periodic function refers to the extraction of the series of sines and
cosines which when superimposed will reproduce the function. This analysis can be
expressed as a Fourier Series. The Fast Fourier transform is a mathematical method for
transforming a function of time into a function of frequency. Sometimes it is described as
transforming from the time-domain to the frequency domain. It is very useful for analysis
of time-dependent phenomena.
Waterfall Plots:
A ​waterfall plot​ is a three-dimensional ​plot​ in which multiple curves of data,
typically spectra, are displayed simultaneously. ... The ​waterfall plot​ is often
used to show how two-dimensional information changes over time or some other
variable such as rpm.

12. EXPERIMENTS & RESULTS:
Cyclic Sine Wave:
Output Plots in GNU Radio:

13. Waterfall Plot:
Amplitude modulation:
Amplitude modulation (AM) is a modulation technique used in electronic communication,
most commonly for transmitting information via a radio carrier wave. In amplitude
modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to that
of the message signal being transmitted. The message signal is, for example, a function of
the sound to be reproduced by a loudspeaker, or the light intensity of pixels of a television
screen. This technique contrasts with frequency modulation, in which the frequency of the
carrier signal is varied, and phase modulation, in which its phase is varied.
AM was the earliest modulation method used to transmit voice by radio.

14. Output Plots:
FM Receiver:
A radio receiver is an electronic device that receives radio waves and converts the
information carried by them to a usable form. An antenna is used to catch the desired
frequency waves. The receiver uses electronic filters to separate the desired radio
frequency signal from all the other signals picked up by the antenna, an electronic

15. amplifier to increase the power of the signal for further processing, and finally recovers
the desired information through demodulation.
Of the radio waves, FM is the most popular one. Frequency modulation is widely used
for FM radio broadcasting. It is also used in telemetry, radar, seismic prospecting, and
monitoring newborns for seizures via EEG, two-way radio systems, music synthesis,
magnetic tape-recording systems and some video-transmission systems. An advantage
of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects
radio frequency interference better than an equal power amplitude modulation (AM)
signal.
CONCLUSION:
We have implemented simple modulation schemes and tested different modulation
circuits to test our Pluto-SDR connectivity with GNU Radio signals and
IIO-Oscilloscope.This concept of SDR using GNU Radio helps us to learn the concepts
practically.Our work is to get familiar with GRC open source software tool. The basic
demonstrations are done using the basic theories of communication systems. One
single Universal Software Radio Peripheral (USRP) can implement all the modulations
and multiplexing techniques in real time.

16. References:
1. https://www.mouser.in/new/Analog-Devices/adi-adalm-pluto/
2. http://www.csun.edu/~skatz/katzpage/sdr_project/sdr/grc_tutorial.pdf
3. https://www.sciencedirect.com/science/article/pii/S187770581200985X
4. http://oz9aec.net/radios/gnu-radio/grc-examples
5. Analog and Digital Modulation Toolkit for Software Defined Radio-paper published by
R.Gandhiraja , Ranjini Ramb , K.P.Somanb
6. Bard, John and Kovarik, Vincent, “Software Defined Radio: The Software
Communications Architecture,” Wiley Series in Software Radio, 2007