1. SOFTWARE
DEFINED
RADIO

2. PRESENTATION OVERVIEW
Definition
History
SDR advantages
Motivation toward SDR
Technical overview
Architecture
Software Overview

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. 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. 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. 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.

7. TECHNICAL OVERVIEW
• IDEAL SDR
• IDEAL RECEIVER
• IDEAL TRANSMITTER
• PRACTICAL RECEIVERS
• TYPICAL COMPONENTS

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. 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. 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. 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. Architectures of SDR
DUC: Digital
upconverter
DDC: Digital
downconverter
CFR: Crest factor
reduction DPD:
Digital
predistortion
PA: Power
amplifier
LNA: Low noise
amplifier

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. 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. 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. 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. 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. 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. 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. 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. 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. QUESTIONS