phase-shift keying with gnu radio

8/9/2019 Phase-shift Keying With GNU Radio

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2015

Author: Rakesh

Email id: [email protected]

PSK Modulation with GNU Radio


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#9/3, Shree Lakshmi Complex, 2nd Floor, Opp. To Vivekananda Park, Girinagar, Bangalore - 560085.Ph. No: 080-26722726, Website: www.tenettech.com , Email: [email protected]

What is Gnu radio?

GNU Radio is a software library, which can be used to develop complete applications for

radio engineering and signal processing.

Introduction

GNU Radio is a free and 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.

GNU Radio is licensed under the GNU General Public License (GPL) version 3. All ofthe code is copyright of the Free Software Foundation. While all the applications are

implemented using python language while critical signal processing path is done using

C++ language.

Idea behind GNURADIO

The goal is to give ordinary software people the ability to 'hack' the electromagnetic

spectrum, i.e. to understand the radio spectrum and think of clever ways to use it.

Why GNURADIO

Instead of purchasing multiple expensive radios, a single generic radio can be

implemented using gnu radio software and with support of minimal hardware to receive

and transmit processed signal at required frequencies and any data type can be passed

from one block to another i.e.it can be in bits, bytes, vectors, bursts or more complex data

types

Since the performance critical blocks are implemented in C++ using processor floating

point extensions the developers are able to implement real-time, high-throughput radio

systems in a simple-to-use, rapid-application-development environment.

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One can use it to write applications to receive data out of digital streams or to send data

into digital streams, which is then transmitted using hardware. GNU Radio has filters,

channel codes, synchronisation elements, equalizers, demodulators, vocoders, decoders,

and many other elements which are called as blocks that are typically found in radio

systems.

Features

The main features of gnu radio are flexibility and configurability.

Extending GNU Radio is also quite easy, if you find a specific block that is missing you

can quickly create and add it.



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What is PSK modulation?

Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing,

or modulating, the phase of a reference signal (the carrier wave).

Any digital modulation scheme uses a finite number of distinct signals to represent

digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary

digits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms

the symbol that is represented by the particular phase. The demodulator, which is

designed specifically for the symbol-set used by the modulator, determines the phase of

the received signal and maps it back to the symbol it represents, thus recovering the

original data. This requires the receiver to be able to compare the phase of the received

signal to a reference signal — such a system is termed coherent (and referred to as

CPSK).

Alternatively, instead of operating with respect to a constant reference wave, the

broadcast can operate with respect to itself. Changes in phase of a single broadcast

waveform can be considered the significant items. In this system, the demodulator

determines the changes in the phase of the received signal rather than the phase (relative

to a reference wave) itself. Since this scheme depends on the difference between

successive phases, it is termed differential phase-shift keying (DPSK). DPSK can be

significantly simpler to implement than ordinary PSK since there is no need for the

demodulator to have a copy of the reference signal to determine the exact phase of the

received signal (it is a non-coherent scheme). In exchange, it produces more erroneous

demodulation.



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Implementation of PSK modulation

The GNUradio Companion with basic blocks (Options block and Variable block)

Options block defines the ID, Title and Description of the experiment.



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Variable Block defines to declare variables globally. This block maps a value to a uniquevariable. This variable block has no graphical representation. The variable can be referenced(by ID) from other blocks in the flowgraph.

o ID = samp_rateo Value = 32000Hz

Random source: Generates samples of random number of [min,max) repeat samples ifspecified.

o ID:analog_random_source_x_0o Output type: Byteo Number of samples: 10000



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PSK Mod : Hierarchical bock for RRC-filtered modulation. The input is a byte stream treatedas series of packed symbols. Symbols are groued from MSB to LSB.

o ID: digital_psk_mod_0

Throttel block : Throttel is a device that control the flow of samples such that average rate doesnot exceeds samples/sec. Throttle is used because no hardware interface has done.

o ID: blocks_throttel_0o Type: complexo Vec length: 1



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QT GUI Frequency sink: the GUI hint can be used to position the widget within theapplication. A graphical sink to display multiple signal in frequency.

o ID: qtgui_freq_sink_X_0o Type: complexo FFT size: 1024

QT GUI time sink: A graphical sink to display multiple signals in time. This is a QT-basedgraphical sink the takes set of a complex streams and plot them in the time domain.ID: qtgui_time_sink_X_0TYPE: complex

Number of points: 200



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QT GUI constellation sink: A graphical sink to display the IQ constellation of multiple signals.This is a QT-based graphical sink takes set of a complex streams and plots them on an IQconstellation plot.ID: qtgui_const_sink_x_0Type: complex

Number of points: 4096



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The Complete block representation

phase-shift keying with gnu radio

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