Gaussian Frequency-shift Keying With GNU Radio

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2015

Author: Rakesh

Email id: [email protected]

Gaussian frequency-shift keying With GNU Radio


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 licensed under the GNU General Public License (GPL) version 3. All of the

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.

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.

Idea behind GNU Radio:

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 ways to use it.

Why GNU Radio?

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

implemented using gnu radio software and with support of minimal hardware.


Blocks explanation:

Every flow graph should contain atleast one source and destination blocks. Signal Source block is used to generate an analog waveform (e.g. sine) in the host machine. This block acts like signal generator

The Throttle block is used limit the processing power of the system. It avoids number of CPU cycles eating up to execute the flow graph. Set the sample rate accordingly

The process of efficiently converting the output of either analog or digital source into a sequence of binary digits is known as source encoding. Packet encoder is a type of source encoder in digital communication. Samples/Symbol parameter should be greater than or equal to two and Bits/Symbol represents the how many 1s or 0s are carried over a symbol.

A GFSK, Gaussian frequency shift keying 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.

Gaussian filtering is a standard way for reducing spectral width; it is

called "pulse shaping" in this application.

In ordinary non-filtered FSK, at a jump from 1 to +1 or +1 to 1, the

modulated waveform changes rapidly, which introduces large out-of-

band spectrum. If we change the pulse going from 1 to +1 as 1, .98,

.93, +.93, +.98, +1, and we use this smoother pulse to determine the

carrier frequency, the out-of-band spectrum will be reduced. The input is

a byte stream (unsigned char) and the output is the complex modulated

signal at baseband


The input is the complex modulated signal at baseband and the output is a stream of bits packed 1 bit per byte (the LSB). The GFSK Demodulator demodulates the modulated signal.

The quadrature Demodulation derive the in-phase (I) and quadrature (Q) components by demodulation to baseband by two oscillator signals separated by 90 radians (i.e. in quadrature)

The packet Decoder decodes the packet information coming from the demodulated signal

The WX GUI Scope sink is the destination block of the flow chart. This block is used to view the time domain representation of the output. The simulation output of the received signal is seen with this block.


Final view of the flow graph

Gaussian Frequency-shift Keying With GNU Radio

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