an overview of sdr and enabling technologies · 2019. 2. 6. · jeff wepman institute for...
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An Overview of SDR and Enabling Technologies
Jeff WepmanInstitute for Telecommunication Sciences
National Telecommunications and Information AdministrationU.S. Department of Commerce
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Introduction
� What is an SDR?� Advantages of SDR� Why so much interest in SDR?� Design of SDR�s� Key enabling technologies for SDR� SDR Forum
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Definition of SDR� Differing opinions on definition
� Many different ways to design SDR� SDR design represents merging of
different fields:
Computer Science RF System Design
Digital Signal Processing
Analog & Digital Circuit Design
SDR
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Definition of SDR
� Definition adopted in American Nat�l Standard Telecom Glossary 2000
� SDR consists of RCVR and/or XMTR where:� Received signal digitized� Processed with software programmable DSP
techniques� Digitization may occur at RF, IF, or baseband
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Definition of SDR
� Modulated signal to be transmitted generated as digital signal using software programmable DSP techniques
� Digital signal converted to analog for transmission
� Conversion to analog may occur at RF, IF, or baseband
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SDR Programmability
� Key factor in SDR�s: � Programmability allows easy changes of
radio�s fundamental characteristics� Operating frequencies, bandwidths, modulation
types� Multiple access schemes, source & channel
coding/decoding� Frequency spreading/despreading,
encryption/decryption� Traditional radios - hardware changes
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SDR Programmability
� Different ways to provide programmability� Over-the-air download� Internet download� From software on a PC using standard external
port (PC serial port)� Keypad on radio� Remove & reprogram PROM� Proprietary internal or external port
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Advantages of SDR
� Programmability� Advantages result replacing analog
implementations radio functions w/ software or digital hardware
� Radio functions can be implemented not possible in analog hardware� Example: FIR filter, sharp rolloff & linear
phase
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Advantages of SDR
� Radio functions implemented w/ DSP offer performance closer to ideal
� Repeatability and temp stability much better
� Radio functions implemented w/ DSP don�t require tuning or tweaking
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Interest in SDR
� Military, Public Safety/Law Enforcement, & Commercial Sectors great interest in SDR
� SDR potential aid for interoperability problems� Military: Many different types of legacy radios and
new radios � Within same service� Between services� Between allies
� Need to communicate between these different radios
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Interest in SDR
� Large Joint Services SDR program� JTRS (Joint Tactical Radio System)� Requirements state JTRS should be
compatible with over 30 different air interfaces!
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Interest in SDR
� Public Safety/Law Enforcement� Equipment operates over 10 distinct frequency
bands 30 � 869 MHz� New 700 MHz band being proposed� Equipment uses different air
interfaces/protocols� Proj 25, analog FM, proprietary trunked, etc.
� Need to communicate between these different radios
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Interest in SDR
� Commercial Sector� Many different existing air interfaces
� AMPS, TDMA, GSM, CDMA, etc.� New air interfaces being developed (3G)� Different frequency bands for different services
& different world regions� Cellular, PCS, 3G
� Need to have equipment that can be used universally
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The SDR Solution
� Replace many radios with 1 SDR� Just change software to change radio type� Minimizes cost of procurement, spare
parts, & logistics� Can reduce size & weight of required radio
equipment� Aircraft may need only 1 radio not 6 or 7
� Eventually achieve cost savings by economy of scale
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SDR Designs
� Primary differences in SDR designs� DSP platform used
� ASIC�s, DSP chips, FPGA�s, general purpose processors, or combination of these
� Platform affects software that needs to be developed
� Where digitization in RCVR & conversion to analog in XMTR occurs (RF, IF, or baseband)
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SDR Designs
� Digitization in RCVR & conversion to analog in XMTR� Ideal goal: occurs at RF
� Many radio applications: current ADC�s & DAC�s do not have high enough speed with required performance
� OK for some radios with low SFDR requirements� Typically occurs at IF in current designs� Occurs at baseband in some designs
� Some new RCVR designs downconvert directly from RF to baseband
� Some new XMTR designs upconvert directly from baseband to RF
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Key SDR Enabling Technologies
� High sampling rate, high performance data converters (ADC�s & DAC�s)
� Wideband Tunable Analog RF Transceiver Front-Ends
� Digital signal processing hardware� Flash Memory� Wideband Linear RF Power Amplifiers
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Data Converters
� For given radio RCVR application � ADC sample rate, max analog input frequency &
performance determine whether digitization can occur at RF, IF, or baseband
� For given radio XMTR application� DAC update rate & performance determine whether
conversion to analog can occur at baseband, IF, or RF
� SFDR & SNR (or SINAD): useful performance measures
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Data Converters
� SFDR� Ratio signal power & power largest spur within
given BW� Input signal: single tone or multitone� SFDR important
� RCVR: detect small signal in presence of large signal
� XMTR: ensure out-of-band spurs below spectral mask before transmission
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Data Converters
� Be careful with SFDR specs� Must know details of test
� Type of input, frequencies & amplitude of input� Sample rate� BW of measurement
� Example ADC�s� High SFDR, moderate sample rate
� 14-bit, 80 Msample/sec, ~90 dB SFDR� Moderate SFDR, high sample rate
� 8-bit, 1.5 Gsample/sec, ~50 dB SFDR
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Wideband Tunable Analog RF Transceiver Front-Ends
� Important since data converters currently can�t be used at RF for many applications
� Convert received RF to IF or baseband for digitization
� Convert baseband or IF signal (at output of DAC) to RF for transmission
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Wideband Tunable Analog RF Transceiver Front-Ends
� Example: DARPA Miniature Radio Codec� Direct conversion RF to baseband� Operates from 20-2500 MHz� 10 MHz BW� 1 Watt transmitter output power
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Digital Signal Processing Hardware
� Programmable digital downconverter & upconverter ASIC�s
� Larger, faster FPGA�s� FPGA�s reconfigurable digital hardware� Up to 10 million gates, > 400 MHz internal
clock� FPGA�s were used just for digital logic � Now gate count & speed permit FPGA use
in digital signal processing
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Digital Signal Processing Hardware
� New, high-speed DSP chips� 16-bit fixed point, 6 GOPS� 32-bit floating point, up to 1.5 GFLOPS
� DSP chip vs. FPGA� FPGA: architecture tailored to the
algorithm to be implemented� DSP chip: algorithm must be tailored to the
architecture
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Digital Signal Processing Hardware
� General purpose processors� Very flexible� Probably easiest to program (can use high
level languages)� Speed has increased dramatically
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SDR Enabling Technologies
� Flash memory� Erasable, reprogrammable ROM� Enables download of new radio configuration
� Wideband linear power amplifiers� Class A amplifiers: linear but consume too much
power� Alternative: use linearization techniques on more
power efficient, nonlinear amplifiers� Example: Feed forward & feedback techniques
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Challenges in SDR
� SDR�s currently available for cellular/ PCS base stations & fixed military applications
� Big challenge: developing practical handheld devices� Need to reduce power consumption, size, weight,
and cost of SDR� Mobile (Vehicular) applications: more doable
� Constraints of power consumption, size, weight less critical
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SDR Forum
� Non-profit org dedicated to promotion� Development, deployment, & use of open
architecture for advanced wireless systems� Established in 1996� Membership:
� More than 100 organizations worldwide� Commercial, government, & academic
sectors
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SDR Forum
� Comprised of 3 core committees� Markets, Technical, Regulatory
� Markets committee key outputs:� Predictions of SDR market size & business
revenue� Identification of primary market
characteristics & drivers (commercial, military, civil government sectors)
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SDR Forum
� Technical Committee� Developing open architecture specs of SDR
hardware & software structures� Separate working groups for handheld, base
station, & mobile SDR�s� Regulatory Committee
� Addresses international regulatory issues for SDR�s
� For more info: www.sdrforum.org
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Conclusion
� Gave broad definition of SDR� Advantages of SDR
� Programmability� Benefits of digital vs. analog
implementation� Interest in SDR�s
� Potential to aid interoperability problem� Replace many radios with one SDR
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Conclusion
� Design of SDR�s driven by enabling technologies � In particular� Data converters� Digital signal processing hardware
� SDR Forum