Software defined radio


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Software defined radio

  1. 1. Software Defined Radio Let our software handle the complexity…Devesh SamaiyaM.Tech. VIPES, 11EC65R10IIT Kharagpur
  2. 2. Agenda SDR?? ?What? When? How? Why? Techniques All Important :Introduction Brief History behind & How Applications & to Significance “Do It Yourself” 2
  3. 3. What ??? Some related Terms… I&Q Softwar e Radio FFT OS/LinuDSP x ADC Samplin Sky waves g 3
  4. 4. So how are they related ?Someone said RADIO ???We all know, A Radio is something which can catch/releaseenergy ripples or Waves… Base Band Processin g Our RADIO DSP Front ADC DAC RF FFT Filters 4
  5. 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. 6. Now we can formulate a „Easy To Understand‟ definition for SDR…“A communication equipment/technique/architecturewhich involves minimal of hardware complexities andat the same time is reconfigurable for wide range ofcommunication related technologies and practices, Byusing general purpose hardware.” 6
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  8. 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. 9. How ??? There can be many ways to implement a SDR transceiver but the idea is same. Building blocks are…1. RF Front2. ADC3. DSP4. DAC 9
  10. 10. Lets get the idea following asample design…Design Issues1. Receiver Architecture Sampling Methods2. Sampling Device3. DSP Engine4. SDR Control 10
  11. 11. Receiver Architecture Two Possible Solutions DirectSuperheterodyne Conversion Working with IF Receivers 11
  12. 12. Superheterodyne Type ReceiverArchitectureSource- “A technology review on SDR”, Wipro Technologies, White Paper, Aug 2002 12
  13. 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. 14. DC Receivers Sampling using Inbuilt ADC + Baseband ProcessingImage Source – “A Software Defined Radio for the Masses “, By Gerald Youngblood, QEX Magazine, Pg15,Jul / Aug 2002 What about Image Frequencies ???? 14
  15. 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 phaseinstantaneous peak voltage , but can be detectedno Phase Information. Can work for AM detector Q mt q(t) 0 In Phase I I(t) mt 15
  16. 16. Quadrature MixingImage Courtesy- Article “Watch your „I‟s and „Q‟s “, Steve Ireland, RadCom Magazine, Pg54-55-56,Jan 2007 16
  17. 17. Now only Hardware we require is a “TayloeDetector”… 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 6230000The switch rotates at the carrier frequency so that each capacitorsamples the signal once each revolution. The 0˚ and 180˚ capacitorsdifferentially sum to provide the in-phase „I‟ signal and the 90˚ and 270˚capacitor sum to provide the Quadrature „Q‟ signal. 17
  18. 18. Commercial SDR‟s HardwareArchitecture (Rx) What‟s Inside? ??Image Source – “A Software Defined Radio for the Masses “, By Gerald Youngblood, QEX Magazine, Pg20,Jul / Aug 2002 18
  19. 19. Now its time to look –What‟s there inside PC Sound Card, that‟s helps doingSDR ??? AntiAliasing Filter + ADC Giving Sampled „I‟ and „Q‟ Have you got Fmax = Fs/2 ? If Yes Welcome! Else Sorry! 19
  20. 20. Block level abstraction for Software Architecture Brick Wall FilterImage Source – “A Software Defined Radio for the Masses “, By Gerald Youngblood, QEX Magazine, Pg18, 20Jul / Aug 2002
  21. 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 softwares like GNU Radio, LinRAD & PowerSDR.Using a Library and writing our own software seems to be an obviouschoice because it saves our time of writing all low level details likemanaging Captured circular buffers and secondly it gives us flexibility to doit our own way.(2nd one is really important ) 21
  22. 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 DirectSoundBufferAF/Data 22
  23. 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. 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. 25. Some free SDR control and processingSoftware‟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. 26. GNU Radio Its all about connecting DSP blocks using a glue called GNU Radio…Source 26
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  28. 28. Applications and Advantages…1. Military Radio2. Cellular Service Providers3. Competition grade HF transceivers4. 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. 29. Future… Software Based Radio Software Defined Radio Software Radio All these things are leading the Cognitive Radio & way of technology to intelligent Universalradio or Cognitive Radio, where Communication future of wireless Devices Communications lies 29
  30. 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 , ARRL2. “Software Defined Radio – Enabling Technologies” , John Wiley & Sons Ltd, Edited by “Walter Tuttlebee”, 2002 edition3. “Signals, Samples & Stuff – A DSP Tutorial”, Part 1-4, By Doug Smith, QEX Magazine , Mar/Apr, Jul/Aug, Sept/Oct, May/June 19984. “Watch Your Is and Qs” , By Steve Ireland, RadCom Magazine, Pg 54-55-56, Jan 20075. “Software Defined Radio – Facets of a Developing technology” , By Walter H.W. Tuttlebee, IEEE Personal Communications, April 19996. “Elektor Software Defined Radio” , By Burkhard Kainka, Elektor Electronics UK Magazine, May 20077. White Paper on “SDR – A Technology Review”, Wipro Technologies, August 2002 30
  31. 31. Thank You 31
  32. 32. Q? 32