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University of Messina - DIECII

The gr-bertool

Supervisors

Prof. Salvatore Serrano

Prof. Giuseppe Campobello

Candidate

Arturo Rinaldi

Department of Electronics Engineering, Chemistry and Electrical EngineeringBEST School - Messina, September 2013

mailto:[email protected]








Goal of the thesis work

• The making of a learning tool for the analysis of the digital modulationsin different communication channels

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Arturo Rinaldi - The gr-bertool







• The simulated channels were :

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◦ Wired : AWGN

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◦ Wired : AWGN◦

Wireless : Rayleigh and Rician

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◦ Wired : AWGN◦

Wireless : Rayleigh and Rician• Verify the correspondence between the theoretical and experimental

results of the BER (Bit Error Rate)

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◦ Wired : AWGN◦



• Provide complementary tools to show how audio and video files aremodified under the effect of the transmission channels

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◦ Wired : AWGN◦



• Provide complementary tools to show how audio and video files aremodified under the effect of the transmission channels

• The gr-bertool was built by using the open-source DSP platform GNURadio

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GNU Radio

• GNU Radio is an open-source softwaretoolkit providing a huge library of blocks for Digital Signal Processing

(DSP) written in C++ which can becombined together in order to build anddevelop radio applications

Python Flow Graph

(Created using the processing blocks)

USB Interface / Gigabit Ethernet

Generic RF Front End

SWIG (Port C++ blocks to Python)

GNU Radio Signal Processing Blocks

( USRP / USRP 2 )

Gnu Radio Companion (GRC), XML

(C++)

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GNU Radio

• GNU Radio is an open-source softwaretoolkit providing a huge library of blocks for Digital Signal Processing

(DSP) written in C++ which can becombined together in order to build anddevelop radio applications

• It is provided with a graphical interfaceto ease its learning curve (GRC : GNU

Radio Companion)

Python Flow Graph

(Created using the processing blocks)

USB Interface / Gigabit Ethernet

Generic RF Front End

SWIG (Port C++ blocks to Python)

GNU Radio Signal Processing Blocks

( USRP / USRP 2 )

Gnu Radio Companion (GRC), XML

(C++)

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Software-Defined Radio : an introduction

• GNU Radio was developed to be in use of Software-Defined Radio(SDR), a new “paradigm” of communication systems

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• A receiver is an SDR device if its communication functions are made asreconfigurable software working on ad hoc hardware

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•

So it’s possible to implement different software transmission standardsby using only one device

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•

So it’s possible to implement different software transmission standardsby using only one device

• An SDR sytem is also able to recognize and avoid possible interferenceswith other transmission channels

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A general overview on the mainGNU Radio blocks

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Signal Source

The block generates different kind of waveforms tobe used as the main signal to transmit or as areference one.

The block is only not able to generate Sinusoidal or

Costant kind of waveforms but also Square,Triangle and Saw Tooth ones.

Type : complex, float, int, short

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Noise Source

The block is able to generate noise according to theUniform, Gaussian, Laplacian and Impulsemodels.

Please also note that the Amplitude parameter fed

to the Gaussian kind of noise is the standarddeviation σ of the Gaussian Noise, given by :

σ =

N 0

2

where N 0/2 is the power spectral density of whitenoise (i.e. its variance).

Type : complex, float, int, short7 of 66






Operators

These blocks perform the four basic arithmeticalfunctions over the signal sources they are fed with(sum, subtraction, multiplication and division).

Please also note that they perform the operationelement by element (i.e. first element of the row -first element of the column) so the rule of thumb isto feed the inputs with equal amounts of data.

Type : complex, float, int, short

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Random Source 2

The block generates a random array of unsignedinteger data with values spanning from 0 to 255 (weare working with 1-byte elements !).

We use it because is a more reliable source of

random data compared to the one provided with theGNU Radio platform.

The only parameter fed to the block is the numberof samples (i.e. the length of the generated list of

elements).

Type : complex, float, byte

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Random Source 2

1 from g n u r a d i o i m p o r t g r23 i m p o r t random45 d e f OnD a ta S ource ra ndom ( sa m pl es ) :6 s r c 1 = [ ]7 f o r i i n r a ng e ( sa mpl e s ) :8 d a t a = random . r a n d i n t ( 0 , 2 5 5 )9 s r c 1 . append ( d a t a )

10 r e t u r n s r c 11112 c l a s s r a n d o m s o u r c e b ( g r . h i e r b l o c k 2 ) :1314 d e f i n i t ( s e l f , n u m be r s a m pl e s ) :1516 g r . h i e r b l o c k 2 . i n i t ( s e l f , ” r a n d o m s o u r c e b ” ,17 g r . i o s i g n a t u r e ( 0 , 0 , 0 ) ,18 g r . i o s i g n a t u r e ( 1 , 1 , g r . s i z e o f c h a r ) )1920 d a t a s a m p l e s = OnData Source ra ndom ( n u m b e r s a m p l e s )

2122 s e l f . v e c t o r = g r . v e c t o r s o u r c e b ( d a t a s a m p l e s , True , 1 )2324 s e l f . c o n n e c t ( s e l f . v e c t o r , s e l f )

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Random Source - The easy way

The block generates a random array of unsignedinteger data.

It is a more direct implementation compared to theone we have just seen.

We feed it with the data list (of unsigned integer of course) and we also set to Yes the repeat optionsince we need a constant stream of data.

Let’s see how to build the data array this time....

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Random Source - The easy way

1 f ro m g n u r a d i o i m p o r t g r23 i m p o r t numpy45 d a t a = map ( i n t , numpy . r an do m . r a n d i n t ( 0 , 2 5 6 , 6 e 5 ) )67 v e c t o r = g r . v e c t o r s o u r c e b ( d at a , True , 1 )

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Packed to Unpacked

The block returns sequences of packed bytesaccording to the integer number we set to the Bitsper Chunk argument.

It is possible to set the Endianness of the outputsequences according to Big (MSB) or Little (LSB)a.

So let’s assume we have this binary sequence11100001. If we feed it to the block we’ll get fourbinary sequences, specifically :• 00000011

• 00000010

• 00000000

• 00000001

Type : int, short, byte

aJohathan Swift, “Gulliver’s Travels”13 of 66


http://en.wikipedia.org/wiki/Gulliver's_Travels#Cultural_influences



http://en.wikipedia.org/wiki/Gulliver's_Travels#Cultural_influences



Map

We usually exploit this block every time we want toperform Gray Coding on the symbols of a digitalmodulation.

For a 2-bit symbols modulation :• Binary to Gray sequence : [0,1,3,2]

• Gray to Binary sequence : [0,1,3,2]

For a 3-bit symbols modulation :• Binary to Gray sequence : [0,1,3,2,7,6,4,5]

• Gray to Binary sequence : [0,1,3,2,6,7,5,4]

Type : byte

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Constellation Decoder - 1

It could be seem strange feeding the same codingnumeric sequence when un-gray a constellation.However, this is due to how GNU Radio works and inparticular how the Constellation Decoder blockoperates over the signal points.

So, once you have assigned the correct SymbolValue Out (i.e. for a QPSK constellation is[0,1,2,3]), you have to scramble the SymbolPosition values again to perform a correct decoding.

You can take care of this by using a cascading link tothe Map block again and feeding it with theoriginary coding sequence.

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Constellation Decoder - 2

Please also note that all our work is based on the ”old” version of thegr constellation decoder block. In fact, the version we have just dealtwith is the one taken from the GNU Radio 3.4.2 tarball and built again as acustom block with the cmake custom wrapper you can usually find inside atarball1.

This however is nowadays considered an old-school method since the latesttarballs provide the “Swiss-army knife” tool called gr-modtool, which willgenerate the skeleton of your new custom package.

1This is true for tarball version ranging from 3.5.0 to 3.6.5.1

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Chunks to Symbols

Once we have set the coding on our binary sequences(the ones from the Packed to Unpacked block) wecan assign the points of the constellation to them.

So for example, if we want to build a BPSKconstellation we will assign the points [-1,1] to theSymbols Table.

Otherwise if we want to build a QPSK constellationwe will assign these other points :

[1+1j,-1+1j,-1-1j,1-1j]Input type : int, short, byteOutput type : complex, float

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Throttle

We usually use this block to limit the cpu load whenoperating with non-audio or non-usrp sources/sinks.

This means that our system won’t freeze or beoverloaded by the GNU Radio engine.

If by any chance we forget it to put it in our flowgraph, we will be warned about it runtime.

Type : complex, float, int, short, byte

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WX GUI Slider

It’s a simple slider making part of the GNU RadioGUIs. We can use to vary at runtime the value of certain variable we have previously set.

We will mostly use this slider to set the E b /N 0 value

in our simulations.

We are also able to set the Default Value (it isusually a float one), and the number of stepsbetween the Maximum and Minimum value of the

variable itself.

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WX GUI Scope Sink

The WX GUI Scope Sink is a simple graphical sinkto show our generated waveforms or digitalconstellations as well.

At runtime, you will notice that is provided withbuttons to set the X and Y axis divisions and theiroffset as well.

Be sure to set XY Mode to On when working withdigital constellations or any complex stream of datato show both the orthogonal components in the

correct way.

Type : complex, float

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Unpacked to Packed

Basically, this block exactly works in the reverse wayof the Packed to Unpacked block we saw a coupleof slides ago.

Remembering the four binary sequences, which were“splitted” from the original one :• 00000011

• 00000010

• 00000000

• 00000001

they will be reverted to the original transmitted

binary sequence 11100001.

Type : int, short, byte

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Import

The Import block allows us to import the installedpython libraries or even some custom code residingin your PYTHONPATH(s).

Some common examples of imports into the block

are :• Import: numpy

• Import: scipy

• Import: <my-code>

and so on.

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WX GUI Number Sink

The WX GUI Number Sink is a simple graphicalsink to display the result of a numeric calculation of a GNU Radio flow graph.

We also might feed it,for example, with a constant

source (depending on a variable) to have a numericreference to compare with a real-time result.

You can also set the number of the decimal digits soto get more accuracy in the displayed result.

Type : complex, float

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BER and SER calculation

These ones are the blocks for the BER and SERcalculation of the digital modulation. We usuallyfeed their inputs with the reference and the decodedstream of data.

Please note that we have only to specify the numberof Bits per Symbol only in the BER block.

It is also recommended to set number of samples of Window Size to 600k or 1M (and of the input datastreams as well) to get an accurate measure of the

error rates.

Input type : byteOutput Type : float

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Now let’s build a QPSKconstellation together ! ! !

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Click on the GRC icon in your menu bar

or just type from your local shell :

$ gnuradio-companion &

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map(int, numpy.random.randint(0, 256, 6e5))

1+1j, -1+1j, -1-1j, 1-1j27 of 66






The developed tool :gr-bertool

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The developed tool : gr-bertool

• The tool main GUI

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• BER experimental verification

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• Real-Time BER experimental verification

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• Complementary tools

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The BER Calculation

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BER experimental verification

• The Bit Error Rate (BER) of a digital modulation, is the number of biterrors divided by the total number of transferred bits during a studiedtime interval

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• Let’s verify the BER theoretical values with the experimental ones byvarying the signal-to-noise ratio E b /N 0

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• Let’s verify the BER theoretical values with the experimental ones byvarying the signal-to-noise ratio E b /N 0

• From digital communications theory is well known that for a Q-PSKmodulation the Bit Error Rate is given by :

P b = Q

2E b

N 0

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• This set of tools calculates the BER ina range of E b /N 0 values given by min

and max with the opportunity tochoose the increase step size

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• We can enable or disable the GrayCoding

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• We can enable or disable the GrayCoding

• By clicking on the Plot button the BERcurves are showed in a simple BER vsE b /N 0 diagram

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We can see a perfect agreement between the theoretical results and theexperimental ones :

(a) BER AWGN BPSK (b) BER AWGN Q-PSK (c) BER AWGN 8-PSK

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Let’s try it together ! ! !

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The Real-Time BER Calculation

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Real-Time BER and signal constellation evolution

• This tool allow us to show the real-timeBER and signal constellation evolutionin the three different types of examinated transmission channels

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• In the following example we’ll show the

BER evolution in the Rician Channel inthe range of E b /N 0 values going from−15 dB to 0 dB

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• Once started the BER value settles tothe BER value corresponding to

E b /N 0 = 0 dB about equal to ≈ 0.11

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E b /N 0 = 0 dB about equal to ≈ 0.11• Ch1 Experimental Value ; Ch2

Theoretical Value

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E b /N 0 = 0 dB about equal to ≈ 0.11• Ch1 Experimental Value ; Ch2

Theoretical Value

• Let’s see the evolution.... 39 of 66






Real-Time BER evolution

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R l T BER l






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R l Ti BER l i






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Th i l ll i





The signal constellation

• Let’s consider a generic transmission scheme for a TLC system.Tx RxTx Channel

m(t) s(t) r(t) d(t)

S D

Figure : Generic block diagram for a TLC system

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Th i l t ll ti






• Let’s consider a generic transmission scheme for a TLC system.Tx RxTx Channel

m(t) s(t) r(t) d(t)

S D

Figure : Generic block diagram for a TLC system

• In the absence fo any noise in the channel the generci transmittedsymbol s̄ i will be correctly received. The plot of the received symbols isknows as “Constellation” of the digital modulation.

ℜ

ℑ

s̄0 (‘11’)

s̄3 (‘01’)

s̄2 (‘00’)

s̄1 (‘10’)

Figure : Constellation of a QPSK modulation46 of 66


Th i l t ll ti






• The presence of noise in the channel modifies phase and amplitude of the transmitted symbols and so the received symbol r̄ i is not onebelonging to the constellation showed before

ℜ

ℑ

s̄0 (‘11’)

s̄3 (‘01’)

s̄2 (‘00’)

s̄1 (‘10’)

r̄i

The transmitted s̄i symbol is not

correctly received

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E ol tion of the Signal Constellation





Evolution of the Signal Constellation

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Real-Time BER Evolution





Real-Time BER Evolution


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Image Transmission

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Image Transmission





Image Transmission

• This tool allow us to observe how themost common image formats areaffected by digital modulations

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Image Transmission





Image Transmission


• We studied the effects over the

simulated channels (AWGN, Rayleigh eRician) for a fixed value of E b /N 0 = 0 dB and Q-PSK digitalmodulation for a Jpeg image

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Image Transmission





Image Transmission


• We studied the effects over the

simulated channels (AWGN, Rayleigh eRician) for a fixed value of E b /N 0 = 0 dB and Q-PSK digitalmodulation for a Jpeg image

• Let’s see the results......

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Image Transmission : AWGN Channel





g

(a) Original (b) AWGN

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Image Transmission : Rician Channel





g

(c) Original (d) Rician

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Image Transmission : Rayleigh Channel





g y g

(e) Original (f) Rayleigh

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Image Transmission





g


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Audio Transmission





• This tool allow us to observe how themost common audio formats areaffected by digital modulations

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Audio Transmission






• We studied the effects over thesimulated channels (AWGN, Rayleigh e

Rician) for a fixed value of E b /N 0 = 10 dB and Q-PSK digitalmodulation

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Audio Transmission






• We studied the effects over thesimulated channels (AWGN, Rayleigh e

Rician) for a fixed value of E b /N 0 = 10 dB and Q-PSK digitalmodulation

• We took as sample the wav fileplay it sam.wav with the following

specifications :

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Audio Transmission





Specifications of the sample file

play_it_sam.wav :

File Size: 1.76M

Bit Rate: 1.41M

Encoding: Signed PCM

Channels: 2 @ 16-bit

Samplerate: 44100Hz

Replaygain: off

Duration: 00:00:10.00

• Let’s see the results....

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Audio Transmission





(g) Original (h) AWGN Channel

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Audio Transmission





(i)Rician

(j)Rayleigh

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Conclusions

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Conclusions





Why using gr-bertool ? Advantages It’s an helpful tool for the teacher to use in TLC courses

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Conclusions






The student can find a quick verification with the learnt notions duringclasses

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Conclusions







It has an ”user-friendly” GUI

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Conclusions







It has an ”user-friendly” GUI

It’s open-source !

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Contact Information





Arturo RinaldiFreelance Collaborator @ DIECIIAddress : Dep. of Electronics Engineering (DIECII) C.da di Dio, 98166 Messina (Italy)E-mail : [email protected] : +39-090-3977376 ; Mobile : +39-340-5795584 (Whatsapp)Skype : arty.net ; Facebook : arty.netTwitter : artynet2 ; LinkedIn : Arturo Rinaldi

Prof. Giuseppe Campobello, Ph.D.Researcher in TelecommmunicationsAddress : Dep. of Electronics Engineering (DIECII) C.da di Dio, 98166 Messina (Italy) - Room: 636(block B, 6th floor)E-mail : [email protected] : +39-090-3977378

Prof. Salvatore Serrano, Ph.D.Researcher in Telecommmunications

Address : Dep. of Electronics Engineering (DIECII) C.da di Dio, 98166 Messina (Italy)E-mail : [email protected] : +39-090-3977522

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