Software defined radio
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Software defined radio uses software to control radio functions like modulation and demodulation rather than using dedicated hardware components. It allows a software radio to function as different types of radios through software changes alone. This reduces costs compared to hardware radios and makes radios more flexible and upgradable. Software defined radios achieve this by sampling radio signals digitally and performing signal processing using software on a general purpose processor or computer rather than dedicated circuits.
![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](https://image.slidesharecdn.com/softwaredefinedradio-120908233536-phpapp01/85/Software-defined-radio-15-320.jpg)
Software defined radio
- 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
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- 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
- 12. Superheterodyne Type Receiver Architecture Source- “A technology review on SDR”, Wipro Technologies, White Paper, Aug 2002 12
- 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
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- 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 30
- 31. Thank You 31
- 32. Q? 32