1. Software Defined Radio
Let our software handle the complexity…
Devesh Samaiya
M.Tech. VIPES, 11EC65R10
IIT Kharagpur
2. Agenda
SDR??
?
What? When? How? Why?
Techniques All Important :
Introduction Brief History behind & How Applications &
to Significance
“Do It Yourself”
2
3. What ???
Some related Terms…
I&Q
Softwar
e Radio
FFT
OS/Linu
DSP x
ADC
Samplin Sky waves
g
3
4. So how are they related ?
Someone said RADIO ???
We all know, A Radio is something which can catch/release
energy ripples or Waves…
Base
Band
Processin
g
Our RADIO
DSP
Front
ADC
DAC
RF
FFT
Filters
4
5. How is it related to software???
Which is the
device, where we
have all of these
blocks??
DSP
ADC
DAC
FFT
Filtering
What about the Sound card of our PC, which has all the needed
stuff ?
And which is software controllable too…
Our OS provides drivers and platform to handle working of Sound
Card 5
6. Now we can formulate a „Easy To Understand‟ definition for SDR…
“A communication equipment/technique/architecture
which involves minimal of hardware complexities and
at the same time is reconfigurable for wide range of
communication related technologies and practices, By
using general purpose hardware.”
6
8. Brief History
Like many other breakthrough
technologies SDR is also initiated by
Military.
Again related terms are DARPA, NSA,
Navy etc.
DARPA with NSA started a
Communication reform project in 1992
named “SpeakEasy I - II - III” with aims…
1. Interoperability of different radio signals.
2. Responsive to incorporation of future developments.
3. Cost reduction potential for Radio deployment.
8
9. How ???
There can be many ways to
implement a SDR transceiver but the
idea is same.
Building blocks are…
1. RF Front
2. ADC
3. DSP
4. DAC
9
10. Lets get the idea following a
sample design…
Design Issues
1. Receiver Architecture Sampling
Methods
2. Sampling Device
3. DSP Engine
4. SDR Control
10
11. Receiver Architecture
Two Possible Solutions
Direct
Superheterodyne Conversion
Working with IF Receivers
11
13. Why Not IF ???
We need faster ADC.
The whole purpose of SDR is to keep
Hardware as simple as possible.
Generally sound cards can‟t sample
signals even at IF range.
Sampling frequency of 16-bit sound card
is 44,100 Hz. (Nyquist ???)
13
14. DC Receivers
Sampling using
Inbuilt ADC
+
Baseband
Processing
Image Source – “A Software Defined Radio for the Masses “, By Gerald Youngblood, QEX Magazine, Pg15,
Jul / Aug 2002
What about Image Frequencies
????
14
15. An elegant solution…
Someone said “Give me „I‟ and „Q‟ and I can demodulate
anything”. [Ref 1]
The idea of „I‟ and „Q‟ Processing in fundamental to the
operation of SDR.
I + jQ are shown on complex
In Phase Signal „I‟ on the real plane. The vector rotates
plane. The magnitude, m(t) is counterclockwise at rate 2πF.
easily measured as the Both magnitude and phase
instantaneous peak voltage , but can be detected
no Phase Information. Can work
for AM detector Q
mt q(t)
0
In Phase I
I(t)
mt
15
16. Quadrature
Mixing
Image Courtesy- Article “Watch your „I‟s and „Q‟s “, Steve Ireland, RadCom Magazine, Pg54-55-56,
Jan 2007
16
17. Now only Hardware we require is a “Tayloe
Detector”… 6 dB of
Noise free
Gain !!!
Image Source – “A Software Defined Radio for the Masses “, By Gerald Youngblood, QEX Magazine, Pg18,
Jul / Aug 2002
US Patent Document No 6230000
The switch rotates at the carrier frequency so that each capacitor
samples the signal once each revolution. The 0˚ and 180˚ capacitors
differentially sum to provide the in-phase „I‟ signal and the 90˚ and 270˚
capacitor sum to provide the Quadrature „Q‟ signal.
17
18. Commercial SDR‟s Hardware
Architecture (Rx)
What‟s
Inside?
??
Image Source – “A Software Defined Radio for the Masses “, By Gerald Youngblood, QEX Magazine, Pg20,
Jul / Aug 2002
18
19. Now its time to look –
What‟s there inside PC Sound Card, that‟s helps doing
SDR ???
AntiAliasing Filter + ADC
Giving Sampled „I‟ and
„Q‟
Have you got Fmax = Fs/2
?
If Yes Welcome! Else
Sorry!
19
20. Block level abstraction for Software Architecture
Brick
Wall
Filter
Image Source – “A Software Defined Radio for the Masses “, By Gerald Youngblood, QEX Magazine, Pg18,
20
Jul / Aug 2002
21. Writing the actual software…
1. Writing each block of code by scratch.
2. Using precompiled Open Source Libraries like Intel‟s
DSP Library or DttSP library by MIT.
3. Using Precompiled API‟s for development of software
of our Purpose. Microsoft is currently providing one
DirectX API.
4. Use Freely available SDR control software's like GNU
Radio, LinRAD & PowerSDR.
Using a Library and writing our own software seems to be an obvious
choice because it saves our time of writing all low level details like
managing Captured circular buffers and secondly it gives us flexibility to do
it our own way.
(2nd one is really important )
21
22. • Microsoft‟s API allows direct access to the PC sound card
under
C++ and VB.
• DirectX internally manages all low level buffers and there
interface to
sound card.
• It gives the stored digital data from stereo in an circular buffer
called
„DirectSoundCaptureBuffer()‟ .
• It is also responsible for low level operation of storing the
processed
I
digital data ADC circularDirectSoundCaptureBuffe
to a buffer called „DirectSoundBuffer()‟
Q r
DSP Engine
DAC DirectSoundBuffer
AF/Dat
a
22
23. Functions to perform in Software…(lots of things !!!)
• Split the stereo sound buffers into I and Q channels.
• Converting to frequency domain using FFT.
• Cartesian to polar conversion of signal vectors.
• Frequency translation if necessary. If there is any signal offset.
• Sideband Selection.
• BPF coefficients selection
• FFT fast convolution filtering.
• Back to time domain using IFFT.
• Doing Digital AGC.
• Transferring the processed buffer for Transmit or Receive.
23
24. A sample algorithm between DSP…
Algorithm for Side Band Selection-
Image Source – “A Software Defined Radio for the Masses “, By Gerald Youngblood, QEX Magazine, Pg30, 24
25. Some free SDR control and processing
Software‟s…
1. PowerSDR (Open Source)
2. Rocky (Free)
3. LinRAD (Open Source)
4. WinRAD (Free)
5. GNU Radio (Open Source)
6. M0KGK SDR
7. EasyPC
25
26. GNU Radio
Its all about connecting DSP blocks using a glue called GNU Radio…
Source http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html 26
28. Applications and Advantages…
1. Military Radio
2. Cellular Service Providers
3. Competition grade HF transceivers
4. All Present and Future Modes can be demodulated or
generated.
5. As Little hardware as possible.
6. Ability to adapt to Requirements.
7. Hardware never become obsolete, every new piece of
software creates a whole new device on the fly.
8. Reduced deployment cost.
28
29. Future…
Software Based
Radio
Software
Defined Radio
Software Radio
All these things are leading the Cognitive Radio &
way of technology to intelligent Universal
radio or Cognitive Radio, where Communication
future of wireless Devices
Communications lies
29
30. References…
1. “A Software Defined Radio For Masses”, Part 1-4, Gerald
Youngblood, Jul/Aug, Sep/Oct, Nov/Dec- 2002, Mar/Apr – 2003, QEX
Magazine , ARRL
2. “Software Defined Radio – Enabling Technologies” , John Wiley &
Sons Ltd, Edited by “Walter Tuttlebee”, 2002 edition
3. “Signals, Samples & Stuff – A DSP Tutorial”, Part 1-4, By Doug
Smith, QEX Magazine , Mar/Apr, Jul/Aug, Sept/Oct, May/June 1998
4. “Watch Your Is and Qs” , By Steve Ireland, RadCom Magazine, Pg
54-55-56, Jan 2007
5. “Software Defined Radio – Facets of a Developing technology” , By
Walter H.W. Tuttlebee, IEEE Personal Communications, April 1999
6. “Elektor Software Defined Radio” , By Burkhard Kainka, Elektor
Electronics UK Magazine, May 2007
7. White Paper on “SDR – A Technology Review”, Wipro Technologies,
August 2002
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