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GNU Radio
CENG - 5931
Signal Sources
By:-
Surendra Babu Donepudi
UHCL ID : 1004771
Contents
1
GNU Radio
2
Programming Languages
3
Signal Sources
4
Types of Signal Sources
5
Conclusion
What is GNU Radio ?
•
•
•
GNU radio is a free/open-source software toolkit for
building software radios, in which software defines the
transmitted waveforms and demodulates the received
waveforms.
It turns radio hardware problems into software
problems.
GNU Radio provides the signal processing runtime and
processing blocks to implement software radios using
readily-available, low-cost external RF hardware and
commodity processors.
Architecture of GNU Radio
Programming Languages in GNU Radio
There are two programming languages used in
GNU Radio, C++ and Python
C++

Extensive library of signal processing blocks

Performance-critical modules
Python



Environment for composing blocks
Glue to connect modules
Non performance-critical modules
Signal Processing Blocks
Signal sources
gnuradio.gr.glfsr_source_b Galois LFSR pseudo-random
source.
gnuradio.gr.glfsr_source_f Galois LFSR pseudo-random source
generating float outputs -1.0 - 1.0.
gnuradio.gr.lfsr_32k_source_s LFSR pseudo-random source with
period of 2^15 bits (2^11 shorts)
gnuradio.gr.null_source A source of zeros.
gnuradio.gr.noise_source_c random number source
gnuradio.gr.noise_source_f random number source
gnuradio.gr.noise_source_i random number source
gnuradio.gr.noise_source_s random number source
gnuradio.gr.sig_source_c signal generator with gr_complex output.
gnuradio.gr.sig_source_f signal generator with float output.
gnuradio.gr.sig_source_i signal generator with int output.
gnuradio.gr.sig_source_s signal generator with short output.
Signal sources
gnuradio.gr.vector_source_b source of unsigned char’s that gets its data
from a vector
gnuradio.gr.vector_source_c source of gr_complex’s that gets its data
from a vector
gnuradio.gr.vector_source_f source of float’s that gets its data from a
vector
gnuradio.gr.vector_source_i source of int’s that gets its data from a
vector
gnuradio.gr.vector_source_s source of short’s that gets its data from a
vector
gnuradio.gr.file_descriptor_source Read stream from file descriptor.
gnuradio.gr.file_source Read stream from file.
gnuradio.gr.message_source Turn received messages into a stream.
gnuradio.gr.udp_source Read stream from an UDP socket.
gnuradio.gr.wavfile_source Read stream from a Microsoft PCM (.wav)
file, output floats.
Types of signal sources
Signal sources can be divided into 7
sub groups they are:
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•
•
•
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Sinusoidal and constant sources
Noise sources
Null sources
Vector sources
File sources
Audio source
USRP source
Sinusoidal and constant sources
Block : gr.sig_source_X.
Usage:
gr.sig_source_c [f, i, s] ( double sampling_freq,
gr_waveform_t waveform,
double frequency,
double amplitude,
gr_complex [float, integer,
short] offset )
The suffix X indicates the data type of the signal
source. It can be ‘c’ (complex), ‘f’ (float), ’i’ (4 byte
integer) or ‘s’ (2 byte short integer).
Contd…..
The waveform argument indicates the type of the
wave form. gr_waveform_t is an enumeration type
defned in gr_sig_source_waveform.h. Its value can
be:
gr.GR_CONST_WAVE
gr.GR_COS_WAVE
gr.GR_SIN_WAVE
When you use gr.GR_CONST_WAVE, the output will
be a constant voltage, which is the amplitude plus
the offset.
Noise sources
Block : gr.noise_source_X.
Usage:
gr.noise_source_c [f, i, s] ( gr_noise_type_t type,
float amplitude,
long seed )
The suffix ‘X’ indicates the data type of the signal source.
It can be ‘c’ (complex), ‘f’ (float), ‘i’ (4 byte integer) or ‘s’
(2 byte short integer).
Contd…..
The type argument indicates the type of the noise. gr_noise_type_t is
an enumeration type defined in gr_noise_type.h. Its value can be:
GR_UNIFORM
GR_GAUSSIAN
GR_LAPLACIAN
GR_IMPULSE
Choosing GR_UNIFORM generates uniformly distributed signal
between [-amplitude, amplitude].
GR_GAUSSIAN gives us normally distributed deviate with zero mean
and variance amplitude2.
GR_LAPLACIAN and GR_IMPLUSE represent a Laplacian distribution
and a impulse distribution respectively.
All these noise source blocks are based on the pseudo random number
generator block gr.random.
Null sources
Block: gr.null_source.
Usage:
gr.null_source ( size_t sizeof_stream_item )
gr.null_source produces constant zeros. The
argument sizeof_stream_item specifies the data type
of the zero stream, such as gr_complex, float, integer
and so on.
Vector sources
Block: gr.vector_source_X.
Usage:
gr.vector_source_c [f, i, s, b] ( const std::vector< gr_complex > & data,
bool repeat = false )
(gr_complex can be replaced by float, integer, short, unsigned char)
The suffix ‘X’ indicates the data type of the signal source. It can be ‘c’
(complex), ‘f’ (float), ‘i’ (4 byte integer), ‘s’ (2 byte short integer), or ‘b’ (1
byte unsigned char).
These sources get their data from a vector. The argument repeat decides
whether the data in the vector is sent repeatedly. As an example, we can use
the block in this way in Python:
src_data = (-3, 4, -5.5, 2, 3)
src = gr.vector_source_f (src_data)
File sources
Block: gr.file_source
Usage:
gr.file_source ( size_t itemsize,
const char * filename, bool repeat )
gr.file_source reads the data stream from a file. The name of the file is
specified by filename. The first argument item size determines the data
type of the stream, such as gr_complex, float, unsigned char. The argument
repeat decides whether the data in the file is sent repeatedly.
As an example, we can use the block in this way in Python:
src = gr.file_source (gr.sizeof_char, "/home/dshen/payload.dat", TRUE)
Audio source
Block: gr.audio_source
Usage:
gr.audio_source (int sampling_rate)
audio_source reads data from the audio line-in. The
argument sampling_rate specifies the data rate of the
source, in samples per second.
USRP source
Block: usrp.source_c [s]
Usage:
usrp.source_c (s) ( int
unsigned int
int ncha
int mux
int mode
which_board,
decim_rate,
= 1,
= -1,
=0)
when we design a receiver using GNU Radio, i.e. working on the RX
path, probably we need the USRP as the data source. The suffix ‘c’
(complex), or ‘s’ (short) specifies the data type of the stream from
USRP.
which_board specifies which USRP to open, which is probably ‘0’ if
there is only one USRP board.
decim_rate tells the digital down converter (DDC) the decimation
factor D.
Contd…..
• Mux sets input MUX configuration, which determines which
ADC(or constant zero) is connected to each DDC input .
`-1' means we preserve the default settings.
• Mode sets the FPGA mode, which we seldom touch. The default
value is 0,representing the normal mode.
• Quite often we only specify the first two arguments, using the
default values for the others. For example:
usrp_decim = 250
src = usrp.source_c (0, usrp_decim)
Conclusion
• Signal sources are used to generate the
required signals in the program.
• Software radio is a revolution in radio design
due to its ability to create radios that change
on the fly, creating new choices for users.
• GNU Radio is widely used in hobbyist, academic
and commercial environments to support
wireless communications research as well as to
implement real-world radio systems.
References
• http://gnuradio.org/redmine/wiki/gnuradio
• http://gnu.ist.utl.pt/software/gnuradio/doc/group__block.html
• http://www.snowymtn.ca/GNURadio/GNURAdioDoc-9.pdf
• http://www.reynwar.net/gnuradio/sphinx/gr/index.html
• http://www.wu.ece.ufl.edu/projects/softwareRadio/documents
/Project%20Report_James%20Chen.pdf
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Thank You !