Sdr seminar


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Sdr seminar

  2. 2. PRESENTATION OVERVIEW Definition History SDR advantages Motivation toward SDR Technical overview Architecture Software Overview
  3. 3. DEFINITION What’s SDR Software-defined radio (SDR) is a radio communication system where components that have been typically implemented in hardware (e.g. mixers ,filters , amplifiers , modulators /demodulators , detectors , etc.) are instead implemented by means of software on a personal computer or embedded system.
  4. 4. HISTORY OF SDR • The term "Software Defined Radio" was coined in 1991 by Joseph Mitola, who published the first paper on the topic in 1992 • One of the first public software radio initiatives was a U.S. military project named SpeakEasy. • The primary goal of the SpeakEasy project was to use programmable processing to emulate more than 10 existing military radios, operating in frequency bands between 2 and 2000 MHz.
  5. 5. Complete Base band processing digital – Reconfigurable Software upgrading of commercial radios – Future proof Generic hardware can be used for a variety of applications – Inventory Software prototyping faster and cheaper than hardware prototyping – Time to market Libraries of software radio components are easily created and shared – Reuse Digital processing of signals is ideal, unencumbered by the non- linearities that plague analog hardware-Reliability SDR ADVANTAGES
  6. 6. MOTIVATION TOWARDS SDR • Commercial wireless communication industry is currently facing problems due to constant evolution of link-layer protocol standards (2G, 3G, and 4G) • existence of incompatible wireless network technologies in different countries inhibiting deployment of global roaming facilities • problems in rolling-out new services/features due to wide- spread presence of legacy subscriber handsets.
  8. 8. IDEAL SDR • The ideal SDR will cover all frequencies from 9kHz to 300GHz. • •It will receive/transmit and modulate/demodulate all modulation modes and bandwidths • •It will configure itself automatically. •
  9. 9. IDEAL TRANSMITTER AND RECEIVER • The ideal receiver scheme would be to attach an analog-to- digital converter to an antenna to directly convert RF to digital. • A digital signal processor would read the converter, and then its software would transform the stream of data from the converter to any other form the application requires. • An ideal transmitter would be similar. • A digital signal processor would generate a stream of numbers. These would be sent to a digital-to-analog converter connected to a radio antenna.
  10. 10. PRACTICAL RECEIVERS Current digital electronics are too slow to receive typical radio signals that range from 10 kHz to 2 GHz Problem solved by using a mixer and a reference oscillator to heterodyne the radio signal to a lower frequency. Digital IQ modulator used. Real analog-to-digital converters lack the discrimination to pick up sub-microvolt, nanowatt radio signals. A low noise amplifier must precede the conversion step.
  11. 11. Typical Components of SDR  Analog Radio Frequency (RF) receiver/transmitter in the 200 MHz to multi-gigahertz range.  High-speed A/D and D/A converters to digitize a wide portion of the spectrum at 25 to 210 Msamples/sec.  High-speed front-end signal processing including Digital Down Conversion (DDC) consisting of one or more chains of mix + filter + decimate or up conversion.  Spread spectrum and ultra wideband techniques allow several transmitters to transmit in the same place on the same frequency with very little interference  PC equipped with sound card
  12. 12. Architectures of SDR DUC: Digital upconverter DDC: Digital downconverter CFR: Crest factor reduction DPD: Digital predistortion PA: Power amplifier LNA: Low noise amplifier
  13. 13. RF Front End  The principle of operation depends on the use of heterodyning or frequency mixing.  The signal from the antenna is filtered sufficiently at least to reject the image frequency and possibly amplified.  A local oscillator in the receiver produces a sine wave which mixes with that signal, shifting it to a specific intermediate frequency (IF), usually a lower frequency.  The IF signal is itself filtered and amplified and possibly processed in additional ways
  14. 14. DIGITAL IQ modulator  Two carriers of same frequency but 90 deg out of phase are used, which are combined at transmission.  Message too is modified to consist of two separate signals 90 deg phase shifted version original 90 deg phase shifted version
  15. 15. ADC & DAC  ADC- Sampling ( Nyquist theorem) Quantisation Flash ADC is the fastest of all.  DAC- weighted resistor R-2R ladder V(out)= V( ref)* (D/2^N) The main problem in both directions is the difficulty of conversion between the digital and the analog domains at a high enough rate and a high enough accuracy
  16. 16. DDC- Digital Down Conversion Digital radio receivers often have fast ADC converters delivering vast amounts of data; but in many cases, the signal of interest represents a small proportion of that bandwidth. A DDC allows the rest of that data to be discarded. When performed in a field programmable gate array (FPGA), simple digital down conversion is broken up into three distinct steps: frequency shifting, filtering, and decimation
  17. 17. DUC-Digital Up Conversion  Digital radio transmitters use DAC, A DUC is used to generate an IF signal and increase the sampling rate. The DUC process is the exact inverse of the DDC process. Instead of down conversion and decimation, a DUC uses interpolation and up conversion.  Interpolation, or up sampling, translates a low sample rate modulated signal into a much higher sample rate signal that is ready for up conversion. This step, often performed in software, can multiply the overall waveform size by any factor.  Finally, the modulated, interpolated data mixes with a carrier that upconverts the baseband signal to the required carrier frequency.
  18. 18. Crest factor REDUCTION (CFR)  Crest factor is a measure of a waveform, such as alternating current or sound, showing the ratio of peak values to the average value. In other words, crest factor indicates how extreme the peaks are in a waveform  modulation techniques that have smaller crest factors usually transmit more bits per second than modulation techniques that have higher crest factors.  Crest factor reduction (CFR) reduces the output peak-to-average ratio by clipping . We can operate closer to the amplifier compression point, therefore it is more efficient.
  19. 19. DIGITAL PREDISTORTION (DPD)  DPD is an active linearisation technique used to compensation for amplifier’s non- linearity  Allows the signal to operate close to or even below P sat.  Correction signal is injected at PA’s input in order to reduce the overall distortion at output.
  20. 20. FPGA  SDR system uses a generic hardware platform with programmable modules (DSPs, FPGAs, microprocessors) and analog RF modules  FPGAs (Field Programmable Gate Arrays) are amazing devices that now allow the average person to create their very own digital circuits.  It is an IC that could contain million of logic gates that can be electrically configured to perform a certain task using HDL ( Hardware Description Languages)  More flexible than microcontroller.
  21. 21. Software Overview  Digital Signal Processing (DSP) software applications employ the math of Fourier Transforms..  FT describes which frequencies are present in the original function.  An open architecture  Allows third party waveform/component development  Standardised procedure for Loading and Control of software modules  Should be one relying on proven technologies – shorter development time
  22. 22. QUESTIONS