Decimation With GNU Radio

8/9/2019 Decimation With GNU Radio

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2015

Author: Rakesh

Email id: [email protected]

Decimation using FIR Filter


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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 do you mean by Decimation?

In digital signal processing, decimation is the process of reducing the sampling rate of

a signal.

Complementary to interpolation, which increases sampling rate, it is a specific case

of sample rate conversion in a multi-rate digital signal processing system. Decimation

utilizes filtering to mitigate aliasing distortion, which can occur when simply down

sampling a signal.[3] A system component that performs decimation is called a decimator.

Decimation reduces the data rate or the size of the data. The decimation factor is usually

an integer or a rational fraction greater than one. This factor multiplies the sampling time

or, equivalently, divides the sampling rate. For example, if 16-bit compact disc

audio (sampled at 44,100 Hz) is decimated to 22,050 Hz, the audio is said to be

decimated by a factor of 2. The bit rate is also reduced in half, from 1,411,200 bit/s to

705,600 bit/s, assuming that each sample retains its bit depth of 16 bits.

Decimation by an integer factor, M, can be explained as a 2-step process, with an

equivalent implementation that is more efficient:

1. Reduce high-frequency signal components with a digital low-pass filter.

2. Down sample the filtered signal by M; that is, keep only every Mth sample.

Down sampling alone causes high-frequency signal components to be misinterpreted by

subsequent users of the data, which is a form of distortion called aliasing. The first step,

if necessary, is to suppress aliasing to an acceptable level. In this application, the filter is

called an anti-aliasing filter, and its design is discussed below. Also see under

sampling for information about down sampling band-pass functions and signals.

http://www.tenettech.com/http://www.tenettech.com/http://www.tenettech.com/mailto:[email protected]://en.wikipedia.org/wiki/Digital_signal_processinghttp://en.wikipedia.org/wiki/Sampling_(information_theory)http://en.wikipedia.org/wiki/Sampling_ratehttp://en.wikipedia.org/wiki/Signal_(information_theory)http://en.wikipedia.org/wiki/Interpolationhttp://en.wikipedia.org/wiki/Sample_rate_conversionhttp://en.wikipedia.org/wiki/Multi-rate_digital_signal_processinghttp://en.wikipedia.org/wiki/Aliasinghttp://en.wikipedia.org/wiki/Decimation_(signal_processing)#cite_note-milic-3http://en.wikipedia.org/wiki/Decimation_(signal_processing)#cite_note-milic-3http://en.wikipedia.org/wiki/Decimation_(signal_processing)#cite_note-milic-3http://en.wikipedia.org/wiki/Data_signaling_ratehttp://en.wikipedia.org/wiki/CD-DAhttp://en.wikipedia.org/wiki/CD-DAhttp://en.wikipedia.org/wiki/Hzhttp://en.wikipedia.org/wiki/Bit_ratehttp://en.wikipedia.org/wiki/Lowpass_filterhttp://en.wikipedia.org/wiki/Undersamplinghttp://en.wikipedia.org/wiki/Undersamplinghttp://en.wikipedia.org/wiki/Bandpasshttp://en.wikipedia.org/wiki/Bandpasshttp://en.wikipedia.org/wiki/Undersamplinghttp://en.wikipedia.org/wiki/Undersamplinghttp://en.wikipedia.org/wiki/Lowpass_filterhttp://en.wikipedia.org/wiki/Bit_ratehttp://en.wikipedia.org/wiki/Hzhttp://en.wikipedia.org/wiki/CD-DAhttp://en.wikipedia.org/wiki/CD-DAhttp://en.wikipedia.org/wiki/Data_signaling_ratehttp://en.wikipedia.org/wiki/Decimation_(signal_processing)#cite_note-milic-3http://en.wikipedia.org/wiki/Aliasinghttp://en.wikipedia.org/wiki/Multi-rate_digital_signal_processinghttp://en.wikipedia.org/wiki/Sample_rate_conversionhttp://en.wikipedia.org/wiki/Interpolationhttp://en.wikipedia.org/wiki/Signal_(information_theory)http://en.wikipedia.org/wiki/Sampling_ratehttp://en.wikipedia.org/wiki/Sampling_(information_theory)http://en.wikipedia.org/wiki/Digital_signal_processingmailto:[email protected]://www.tenettech.com/


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1) Decimation

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 unique

variable. This variable block has no graphical representation. The variable can be referenced

(by ID) from other blocks in the flowgraph.

o ID = samp_rate

o Value = 32000Hz

Signal source is a wave form genrator. Very first block genrates the sine wave, second block

genrates the square wave, third block genrates triangler wave and finaly fourth block genrates the

sawtooth waveform.



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o ID:analog_sig_source_x_0

o Output type: float

o Freq: 100Hz

o Amplitude: 1V

Decimating FIR filter: this filter decrease the sampling rate of signal by a decimating factor.

ID: fir_filter_xxx_0

Type: float

Decimation: 10

Taps:1



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Throttel block : Throttel is a device that control the flow of samples such that average rate does

not exceeds samples/sec. Throttle is used because no hardware interface has done.

o ID: blocks_throttel

o Type: float

o Vec length: 1



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WX GUI scope sink: 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.

o ID: wxgui_scopesink2_0

o Type: float



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The Complete block representation

Genrated output

Decimation With GNU Radio

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