GNU Radio based Real Time Data Transmission and Reception

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
p-ISSN: 2395-0072Volume: 04 Issue: 07 | July -2017 www.irjet.net
110
GNU Radio based Real Time Data Transmission and
Reception
Anusha.S1, Lahari.T.N2, G.S.N.Bhavana3 , Pradeep.H.S4
1, 2, 3
B.E Student, Dept. of ECE, Siddaganga Institute of Technology, Tumakuru, Karnataka.
4
Assistant Professor, Dept. Of ECE, Siddaganga Institute of Technology, Tumakuru, Karnataka.
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract – Today the world is using the most advanced
technologies everywhere. From electronic devices used
for household to artificial intelligence there is a need for
communication. Two devices may involve in a
communication where one has to transmit data while the
other needs to receive for the operation. The problem
becomes evident if the systems are at a very larger
distances. So we need to go for wireless communication.
A software defined radio is a reconfigurable radio
whose physical layer functions are mainly or fully defined
by software instead of hardware. Because of their
exibility and cost efficiency, SDRs allow the
implementation of radio communication systems that are
interoperable among different standards, protocols,
frequency bands, user
requirements and functionalities.
In this paper, real time data transmission and
reception using different digital modulation
techniques like GMSK, GFSK and DPSK are
implemented using GNU Waveguru and GNU Octave
tool.
Keywords-software defined radio, GMSK, GFSK,
DPSK, GNU Octave.
I. INTRODUCTION
SDR(Software Defined Radio) is a radio
communication system where components that have been
typically implemented in hardware are instead
implemented by means of software on a personal
computer or an embedded system. SDR are used for its
simplicity and exibility. With the right software, a single
SDR chip could perform the functions such as recording
FM radio and digital television signals, read RFID chips,
track ship locations, or do radio astronomy which makes
SDR versatile.
What is GNU radio? GNU Radio is a free and open-
source software development tool kit 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 widely used in
hobbyist, academic and commercial environments to
support both wireless communications research and real-
world radio systems.
II. LITERATURE REVIEW
Many techniques were developed in recent years.
The main approaches of the techniques was to transmit
and receive data without much hardware needed using
GNU radio. In this section, a brief literature review is
given.
In paper [1], the authors discuss about the emerging
trends of SDR for the applications in modern
communication systems.
In paper [2], the authors focus on SDR from a
discrete-time sampling perspective and discuss the efforts
that are currently being pursued in order to further bridge
the gap between these discrete-time samples. Highlighting
the advantages and current issues with SDR technology,
this paper also presents several examples using a recently
released, commercially available SDR platform.
In paper [3], the authors portray the exibility and
reusability of SDR. SDR designers have turned to FPGAs to
provide a exible and reconfigurable hardware that can
support computationally intensive and complex
algorithms which can be used in a multitude of voice, data,
and multimedia applications.
In paper [4], the authors specify that the Gaussian
Frequency Shift Keying modulation and demodulation is
the most widely used modulation scheme for wireless
communication as this scheme uses a brand new
architecture based on reconfigurable CORDIC is involved
which saves about 640Kbits memory units.
III. SYSTEM OVERVIEW
GNU Radio is a framework that enables users to
design, simulate, and deploy highly capable real-world
radio systems. This signal processing blocks can be linked
together for building and creating the baseband part of the
dedicated radio. The most basic structure of the
constructed radio is as shown in Fig.1.
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 110

111
Fig.1: Basic Structure of GNU Radio Flow Graph.
It consists of three parts; signal source, signal
processing and signal sink. Signal source is where the
signal is generated. There is several signal source blocks
available in GNU Radio for instance USRP, sound card
(microphone), signal source (signal generator) etc.
Signal Processing is where signal source is manipulated
before it is loaded into signal sink block. Most of the
baseband processing for signal manipulation is already
available in GNU Radio for instance FIR filters, IIR filters,
FFT, Multipliers etc. Signal sink is where the signal is
translated into the form that user desired. Examples of
signal sink are sound card (speaker), USRP, data in
integer form, graph etc.
IV. IMPLEMENTATION
WaveGuru is a platform to generate and analyze
baseband I/Q (In phase/Quadrature phase) signals which
are compliant to specific technology standards. The
WaveGuru box is used as the USRP. It is used to implement
GNU Radio.
GNU Octave is mainly used in order to accept the
real-time data from the user. It is one of the major free
alternatives to Matlab. It is primarily intended for
numerical computations. Octave helps in solving linear
and nonlinear problems numerically, and for performing
other numerical experiments using a language that is
mostly compatible with Matlab. It can be also referred as a
clone of Matlab. The octave code helps in taking the real
time text input from the user and is later saved to a file.
Modulation Techniques:
a. GMSK (Gaussian Minimum Shift Keying):
GMSK is derived from MSK. It is unique due to the
relationship between the frequency of a logical zero and
one. The difference between the frequency of a logical zero
and a logical one is always equal to half the data rate. In
other words, the modulation index is 0.5 for MSK. The
fundamental problem with MSK is that the spectrum is not
compact enough to realize data rates approaching the
RF(Radio Frequency) channel Bandwidth(BW). A plot of
the spectrum for MSK reveals side lobes extending well
above the data rate. For wireless data transmission
systems which require more efficient use of the RF
channel BW, it is necessary to reduce the energy of the
MSK upper side lobes. The pre-modulation low pass filter
must have a narrow BW with a sharp cut-off frequency
and very little overshoot in its impulse response. A
Gaussian filter which has an impulse response
characterized by a classical Gaussian distribution (bell
shaped curve) is shown in Fig.2. Notice the absence of
overshoot or ringing.
Fig.2: Gausssian filter impluse response
BT is related to the filters - 3dB BW and data rate by (1)
b. GFSK(Gaussian Frequency Shift Keying):
Rather than directly modulating the frequency
with the digital data symbols, instantaneously changing
the frequency at the beginning of each symbol period,
Gaussian frequency shift keying filters the data pulses with
a Gaussian filter to make the transitions smoother. This
filter has the advantage of reducing sideband power,
reducing interference with neighbouring channels, at the
cost of increasing inter-symbol interference.
A GFSK modulator differs from a simple frequency
shift keying modulator in that before the baseband
waveform (levels 1 and +1) goes into the FSK modulator, it
is passed through a Gaussian filter to make the transitions
smoother so to limit its spectral width. Gaussian filtering is
a standard way for reducing spectral width, called “pulse
shaping” in this application. The Fig.3 shows the
modulation of a particular signal.
Fig.3: GFSK Modulation.

112
c. DPSK (Differential Phase Shift Keying):
In Differential Phase Shift Keying , the phase of the
modulated signal is shifted relative to the previous signal
element. No reference signal is considered. The signal
phase follows the high or low state of the previous
element. Thus DPSK technique does not need a reference
oscillator. The Fig.4 represents the model waveform of
DPSK. It is seen from the below figure that, if the data bit is
Low i.e., 0, then the phase of the signal is not reversed, but
continued as it was. If the data is a High i.e., 1, then the
phase of the signal is reversed, as with NRZI, invert on 1 (a
form of differential encoding).
Fig.4: Waveform of DPSK.
DPSK Modulator: It encodes two distinct signals, i.e., the
carrier and the modulating signal with 1800 phase
shift each. The serial data input is given to the XNOR gate
and the output is again fed back to the other input
through 1- bit delay. The output of the XNOR gate
along with the carrier signal is given to the balance
modulator, to produce the DPSK modulated signal.
DPSK Demodulator: In DPSK demodulator, the phase of
the reversed bit is compared with the phase of the
previous bit. That signal is made to confine to lower
frequencies with the help of low pass filter. Then it is
passed to a shaper circuit, which is a comparator or a
Schmitt trigger circuit, to recover the original binary data
as the output.
Text Transmission
The modulation techniques like GFSK, GMSK and
DPSK are implemented to transmit the text data over a
wireless medium.
a. Transmitter:
The flow graph of the transmitter of a text file is
shown in Fig.5 where GFSK modulation is implemented.
Similarly Fig.6 and Fig.7 shows the flow graph of
transmitter which uses GMSK and DPSK modulator
respectively.
Fig.5: Flow graph of text transmitter using GFSK
modulator.
Fig.6: Flow graph of text transmitter using GMSK
modulator.
Fig.7:Flow graph of text transmitter using DPSK
modulator.
b. Receiver:
The following flow graphs show the
reception of text by using different demodulation
techniques like GFSK, GMSK and DPSK as shown in Fig.8,
Fig.9 and Fig.10 respectively.
Fig.8: Flow graph of text receiver using GFSK
demodulator.
Fig.9: Flow graph of text receiver using GMSK
demodulator.

113
Fig.10: Flow graph of text receiver using DPSK
demodulator.
can be either 2,4,8 or 16 and it can be specified according
to requirements. There is an option for using Gray coding.
As gray coding is more advantageous, it is by default used
while the block is selected. Fig.13 is the transmitter flow
graph created using GNU radio for DPSK modulation.
V. RESULTS
A GFSK modulator is similar to a FSK modulator,
except that before the baseband waveform (levels 1 and
+1) goes into the FSK modulator, it is passed through a
Gaussian filter to make the transitions smoother so to limit
its spectral width. If the pulses are changed from 1 to +1 as
1, .98, .93, +.93, +.98, +1, and this smoother pulse is used
to determine the carrier frequency, thus out-of-band
spectrum will be reduced. The input is a byte stream
(unsigned char) and the output is the complex modulated.
Fig.11 is the transmitter flow graph created using GNU
radio for GFSK modulation.
Fig.11: GFSK text transmitter flow graph.
GMSK Mod block is responsible for the
modulation of the data before transmission. It provides
the advantage of carrying out the modulation while using
the spectrum efficiently. The roll-off factor also called as
excess bandwidth can be specified. It is usually set to 0.35
to achieve minimum EVM(Error Vector Magnitude). Fig.12
is the transmitter flow graph created using GNU radio for
GMSK modulation.
Fig.12: GMSK text transmitter flow graph.
DPSK modulation technique does not have any
absolute carrier phase reference, instead transmitted
signal itself is used as phase reference. Samples/symbol
Fig.13: DPSK text transmitter flow graph.
Fig.14, Fig.15 and Fig.16 are the receiver flow graphs
created using GNU radio for GFSK, GMSK and DPSK
demodulations respectively.
Fig.14: GFSK text receiver flow graph.
Fig.15: GMSK text receiver flow graph.
Fig.16: DPSK text receiver flow graph.

114
For different modulation techniques and
different distances, different sizes of text file is
transmitted and the resulting received power levels
are tabulated in the Table.1.
Table.1: Power levels for different distances and
data sizes.
The inferences that is made from the Table.1 are as
follows:
 The receiver antenna placed at the distance of
3.05m which is in line-of- sight(LOS) of
transmitter antenna has maximum reception
power level.
 The antennas which are in line-of-sight
comparatively have better reception power.
 Irrespective of size, as the distance increases the
received power decreases.
For different modulation techniques, different
data sizes and different distances, the transmitter gain is
varied. The results are presented in the Table.2.
Table.2: Received power levels for different gains.
The inferences that is made from the Table.2 are as
follows:
 For the gain values less than 35, there is no
reception of data irrespective of distance.
 The minimum gain required for successful
reception of data is found to be greater or equal to
35.
 As the distance increases with the same gain for
different modulation techniques, the reception
power level decreases.
 As the gain value increases, the reception power
level also increases comparatively.
 For gain values above 45, reception power level is
saturated.
 The effect of data size when gain is varied for
different distances is very minimal.
VI. CONCLUSION
In this paper, data is successfully transmitted
over wireless media using GNU radio and USRP. Text is
transmitted using different modulation techniques.
Different sizes of text have been transmitted and received
by multisystem simultaneously over different distances.
Receiver system kept at near distances receive faster than
systems at larger distances with different power levels.
REFERENCES
[1] U. L. Rohde, A. K. Poddar and T. K. Sarkar, “Next
generation networks: Software defined radio,
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[2] R. G. Machado and A. M. Wyglinski, “Software Defi
ned Radio: Bridging the Analog Digital Divide", in
Proceedings of the IEEE, vol. 103, no. 3, pp. 409-423,
March 2015.
[3] R. K. Kodali, L. Boppana and G. Gayathri, “FPGAs in
software defined radio", 15th International
Conference on Advanced Computing Technologies
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[4] X. Long et al., “Design of novel digital GFSK
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115
[6] J. Muslimin, A. L. Asnawi, A. F. Ismail and A. Z. Jusoh,
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