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Copyright © 2010 Agilent Technologies
A Design-to-Test Methodology for SDR and Cognitive Radio
Authors: Greg Jue & Bob Cutler, Agilent Technologies
Copyright © 2010 Agilent Technologies
Agenda
• SDR Waveform Challenges• SDR Waveform Design• SDR Hardware Testing• Cognitive Radio Algorithm Development Challenges• Cognitive Radio Testbed
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Copyright © 2010 Agilent Technologies
Software Defined Radios
Flexibility• Radio can support multiple waveforms: Different formats, different
revisions of a format, backwards compatibility, future-proofing• Combination of DSP/FPGA/GPP C++/HDL• Flexibility increases demands on RF HW performance• HW may be flexible or reconfigurable to more efficiently support
waveforms with significantly different characteristics (e.g. OFDM vs MSK)
Portability• Across single vendors platforms (usually proprietary)• Across multiple vendors platforms (based on standards such as SCA)• Portability of waveform components (e.g. Viterbi decoder)
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Copyright © 2010 Agilent Technologies
Portability and Flexibility
Challenges and opportunities
• RF performance determined by both hardware and software. Performance could change with “bug fix”.
• Hardware platforms may come from different vendors and have different capabilities. Not quite “write-once, run anywhere”.
• Probe points in the signal path are now digital, as well as analog. Need a consistent way to measure.
• Component implementations in C++, HDL, possibly also from different vendors.
• Need to design and test hardware to support waveforms that have yet to be invented.
• Can use test waveforms for development, diagnostics and manufacturing test.
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Copyright © 2010 Agilent Technologies
Impacts of SDR Technology on Test
RF performance is a combination of baseband processing, radioconfiguration, and RF hardware performance• Hard to isolate root causes of performance problems. Finger pointing
between hardware and software teams and/or suppliers• Need consistent way to quantify “RF Performance” in the both the hardware
and in the soft-bits.• Abstraction layers help with portability, but can introduce performance and
optimization issues (e.g. timing, or optimal hardware configuration for a waveform) as well as organizational issues (hardware and software from different vendors)
Baseband Processing RF
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Copyright © 2010 Agilent Technologies
Example: High TX ACPSeveral Potential Sources of Error
• Insufficient stop band rejection on baseband DSP filter• Poor design• Truncated filter coefficients
• Insufficient numeric resolution (adds digital noise)• Insufficient numeric range (non-linear over/under flow)• Improper timing (PA enable, frequency settling, glitches, etc)• Improperly programmed hardware (excess gain, misconfigured parts)• Distortion in D/A• Poor analog baseband/IF filtering• IF Distortion due to improper levels• Spurious signals• Excessive phase noise• PA Distortion
D/A PAFPGA/DSP
A 2 dB problem is usually a combination of several sub-1dB problems.
Need to accurately characterize performance in both the digital and analog signal paths
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Copyright © 2010 Agilent Technologies
SimulationDesignSignal analysisSpectrum analysisBit-accurateAlgorithmCode generation
Code Generation
Baseband/IF/RF (scope)Signal analysis Spectrum analysisHardware configTiming
RF/IF (VSA)Signal analysisSpectrum analysisPhase noiseLevelsDistortion
D/AFPGA/DSP
Digital (logic analyzer)Signal analysisSpectrum analysisHardware configTimingPacket inspectionRTOS scheduling
A Consistent Way To Measure
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Copyright © 2010 Agilent Technologies
Impacts of SDR Technology on TestFuture Proofing
Need a different test strategy when goal is to support future waveforms• Can’t just test supported waveforms, need to test radio configurations
that might be used with future waveforms• When deployed, will Waveform C have adequate RF performance?
(ACP, BER, EVM, spurious, noise figure, etc)
Baseband Processing
FPGA/DSP/GPP
Converters and Flexible RF
Waveform A 2009
Waveform B 2009
Waveform C 2013
How do we ensure that Waveform C will have adequate performance when installed in radios
deployed in 2009?Configure
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Copyright © 2010 Agilent Technologies
SDR Technology Usually Implies Flexible Hardware
TEST APPROACHES
1. Test with real waveforms and their configurations
2. Test broad selection of representative waveforms
3. Test with custom waveforms to exercise different hardware configurations
Signal bandwidthdynamic range
Low phase noise (NB, OFDM)Fast tuning (FHSS, duplex)
Phase coherent (MIMO)
High efficiency (FM)High linearity(OFDM)Pulsed, continuous
Signal power stats(Distortion req’s)Signal BW
Tunable or broadband antennafor frequency coverage
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Copyright © 2010 Agilent Technologies
Use Simulation to Design Test Waveforms, Introduce Defects, and Verify Test Coverage
Noise only DC offset Quadrature error
Delay mismatch
Distortion
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Copyright © 2010 Agilent Technologies
Agenda
• SDR Waveform Challenges• SDR Waveform Design• SDR Hardware Testing• Cognitive Radio Algorithm Development Challenges• Cognitive Radio Testbed
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Copyright © 2010 Agilent Technologies
Design SDR RF Using Various Types of Waveform Formats
Use waveform sources to design SDR RF
Waveform Sources• HDL code• FPGA hardware • Simulation models• Algorithm code
Waveformsignal source
Simulated RF transmitter design
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Copyright © 2010 Agilent Technologies
Example 1: Use HDL-Based WiMAX™ Waveform to Design SDR RF Transmitter
EVM = 8.4%
Simulated SDR transmitter output
Simulated RF transmitter designVSA
measurement
Waveform sources• HDL code• FPGA hardware • Simulation models• Algorithm code
“Mobile WiMAXtm” is a registeredtrademark of the WiMAX Forum.
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Copyright © 2010 Agilent Technologies
EVM = 9.1%
Simulated SDR transmitter output
Simulated RF transmitter designVSA
measurement
Waveform sources• HDL code• FPGA hardware• Simulation models• Algorithm code
Example 2a: Use FPGA-Based Legacy Waveform toDesign SDR RF Transmitter
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Copyright © 2010 Agilent Technologies
EVM=10.5%
Reconfigure legacy FPGA waveform for a new
waveform (LTE)
Simulated RF transmitter designVSA
measurement
Simulated SDR transmitter output
Example 2b: Re-Configure FPGA-Based Waveform toEvaluate SDR RF Transmitter Design Interoperability
Waveform sources• HDL code• FPGA hardware• Simulation models• Algorithm code
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Copyright © 2010 Agilent Technologies
Example 2c: Probing an FPGA Waveform with Dynamic Probe
Simulated RF transmitter design
Waveform sources• HDL code• FPGA hardware• Simulation models• Algorithm code
Preliminary work-in-progress16
Copyright © 2010 Agilent Technologies
Simulated RF receiver design
Waveform simulationreceiver
Waveform simulation
source
Pre-configured algorithm models (customizable) Select ADC model…
Waveform sources• HDL code• FPGA hardware • Simulation models• Algorithm code
Example 3a: Use Simulation-Based WiMAX Waveform to Design SDR RF Receiver
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QPSK BER vs. ADC Jitter vs. EbNo
Red: 4% ADC JitterBlue: 6% ADC JitterGreen: 8% ADC Jitter
16 QAM BER vs. ADC Jitter vs. EbNo 64 QAM BER vs. ADC Jitter vs. EbNo
Example 3a Results: WiMAX BER vs. ADC Jitter
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Copyright © 2010 Agilent Technologies
Simulated RF receiver design
New waveform simulationreceiver New waveform
simulationsource
Replace WiMAX waveform source & receiver with LTE
New BER results
Example 3b: Replace Waveform to Evaluate SDR Receiver Design Interoperability
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Waveform sources• HDL code• FPGA hardware • Simulation models• Algorithm code
Customize OFDMA algorithms
Example 4: Use Algorithm Code Waveforms
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Copyright © 2010 Agilent Technologies
*Please note: this next section of the presentation contains “Preliminary” product information that is part of new product development (next 3 slides)
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Copyright © 2010 Agilent Technologies
SCA Waveform Rapid Prototyping Concept
Waveform Components/
BlocksRF Tx RF Channel/ RF
Interferers/Jammers RF RxWaveform
Components/Blocks
Physical-layer environment for waveform development/verification
SCA compliant environment For component design,
implementation, and deploymentFunctional Componentwrapper
Deployablecomponent
ExportImport “OE in the loop”Component
Model
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Preliminary
Copyright © 2010 Agilent Technologies
Example 5: SCA Waveform DesignExport C++ and XML
PHY
Link
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Preliminary
Copyright © 2010 Agilent Technologies
Example 5: Verify End-to-End System with OE In the Simulation Loop
QPSK Transmitter(OE-in-the-loop)
RF Channel
BER Sink
ADI ADC
RF Transmitter RF Receiver
PA Output Receiver Digital Output
QPSK Receiver(OE-in-the-loop)
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Preliminary
Copyright © 2010 Agilent Technologies
Agenda
• SDR Waveform Challenges• SDR Waveform Design• SDR Hardware Testing• Cognitive Radio Algorithm Development Challenges• Cognitive Radio Testbed
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Copyright © 2010 Agilent Technologies
SDR Hardware Testing
SDR testing challenges:• Custom/proprietary waveforms not supported by COTS test
equipment• Flexible SDR test platforms are needed for today’s and tomorrow’s
waveforms• Different tools used between design and test- makes it difficult to
debug issues • Solution- Combine the flexibility of simulation with test equipment
for flexible SDR testing
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Copyright © 2010 Agilent Technologies
16822A Logic Analyzer with Agilent SystemVue*
14 Bit A/D board DUT
* Note: SystemVue does not ship with logic analyzer
• Test waveform coding/decoding SW-defined• Customizable algorithms• Customizable test waveforms
Adding Flexibility to SDR Testing with Simulation
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Copyright © 2010 Agilent Technologies
OFDMA BER Hardware Test Results
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Copyright © 2010 Agilent Technologies
Simulate an SDR Receiver with a Hardware Front End (N6841 RF sensor)
Wideband RF sensor
HW DUT test signal
Simulated RF receiver design
VSAmeasurement
Simulated SDR receiver output
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Copyright © 2010 Agilent Technologies
Agenda
• SDR Waveform Challenges• SDR Waveform Design• SDR Hardware Testing• Cognitive Radio Algorithm Development Challenges• Cognitive Radio Testbed
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Copyright © 2010 Agilent Technologies
Cognitive Radio
• Many definitions of CR.• A radio that is aware of its environment and adjusts its behavior accordingly.
• Key application for CR is Dynamic Spectrum Access(DSA)
• Radio adjusts frequency, power, modulation based on sensed spectrum, location, policy and databases
• Complimentary to SDR in this application
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Copyright © 2010 Agilent Technologies
Filling the Whitespace
Goal: Increase spectrum utilization without causing interference
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Copyright © 2010 Agilent Technologies
CR Design and Measurement Considerations
• Interference (actual, or potential for)
• Radio system performance (capacity, link establishment and reliability)
• Radio physical layer performance (e.g. adjacent channel power)
• Environment sensing performance (spectrum sensing, location sensing)
• Policy performance (does the policy over, or under protect)
• Radio environment (channel, noise, occupancy)
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Copyright © 2010 Agilent Technologies
Challenges of Spectrum Sensing
Performance of various spectrum sensing algorithms– False positives, false negatives– Response to real-world signal environment (dynamic, many
signals)– Radio design
• Spurious• Amplitude accuracy• Intermod distortion• Sensitivity• Selectivity• Frequency accuracy
– Speed/complexity/cost tradeoffs
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Copyright © 2010 Agilent Technologies
CR Development Needs
• Need to characterize, capture, and replicate real-world spectral environments.
• Needs to be done over time, frequency and location.• Need to use captured environments to evaluate CR algorithms and
radio link performance. • Need to evaluate performance using non-ideal radios.
• Need a flexible and comprehensive CR R&D Testbed!
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Copyright © 2010 Agilent Technologies
Agenda
• SDR Waveform Challenges• SDR Waveform Design• SDR Hardware Testing• Cognitive Radio Algorithm Development Challenges• Cognitive Radio Testbed
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Copyright © 2010 Agilent Technologies
Cognitive Radio R&D Testbed
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Copyright © 2010 Agilent Technologies
CR Algorithm Development and Testing Environment
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Copyright © 2010 Agilent Technologies
Mobile WiMAX Case Study
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Copyright © 2010 Agilent Technologies
Step 1: Capture Signal and Bring into SystemVue
Captured CR environment
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Copyright © 2010 Agilent Technologies
Step 2: Whitespace Math Algorithms Determine Valid Whitespace
Frequency Rules Policy
Valid whitespace determined within
the policy
Rising/falling edgesdetected to determine
whitespace
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Copyright © 2010 Agilent Technologies
Debugging Whitespace Algorithms
Add/remove breakpointSingle-step through code
Code variable values aredisplayed as code is
single-stepped
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Copyright © 2010 Agilent Technologies
Step 3: Whitespace Math Algorithms Determine Valid Whitespace
WiMAX spectrum (scaled and centered
in the valid whitespace)
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Copyright © 2010 Agilent Technologies
Analyze Detect-and-Avoid Interferer Scenarios
Sweep narrowbandinterferer vs. frequency to evaluate impact on OFDMA BER
Narrowbandinterferer
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Copyright © 2010 Agilent Technologies
Sensed spectrum
Step 4: Identify Detected Signals in Simulation or with Test Equipment
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Copyright © 2010 Agilent Technologies
Remotely located N6841A RF sensor
www.agilent.com/find/eesof-cognitive-whitepaper
Video Demo with SystemVue + N6841A N6841A is Remotely Located Across Washington State
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Copyright © 2010 Agilent Technologies
New Whitepaper Available: www.agilent.com/find/eesof-cognitive-whitepaper
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Copyright © 2010 Agilent Technologies
Summary
• Use waveforms sources in various formats (HDL, FPGA hardware,simulation models, math algorithms) to design SDR transmitters andreceiver and evaluate interoperability
• Use improved SCA waveform flow for SDR waveform design and test
• Seamless integration between design and test capability • creates flexible SDR testing platform • enables R&D engineers to develop and test algorithms and hardware
with real field signals
• Evaluate Cognitive Radio link performance, perform ‘what-if’ detect-and-avoid interference scenarios
Explore a Cognitive Radio simulation example in the SystemVue 2009.08 example set – request a free evaluation at:
www.agilent.com/find/eesof-systemvue-latest-downloadsOr, contact your local Agilent representative
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Copyright © 2010 Agilent Technologies
Additional Resources
Product Web sites:
SystemVue http://www.agilent.com/find/systemvue
RF sensors http://www.agilent.com/find/rfsensor
Whitepapers and application notes:
Cognitive Radio Algorithm Development and Testing:http://www.agilent.com/find/eesof-cognitive-whitepaper
Software Defined Radio Measurement Solutions:http://cp.literature.agilent.com/litweb/pdf/5990-4146EN.pdf
Solutions for Addressing SDR Design and Measurement Challengeshttp://www.agilent.com/find/sdrhttp://www.agilent.com/find/powerofx
Videos:
Web video of CR Testbed discussed in this paper:http://www.agilent.com/find/eesof-cognitive-whitepaper
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Copyright © 2010 Agilent Technologies
Thank You!
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Copyright © 2010 Agilent Technologies
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© Agilent Technologies, Inc. 2010Printed in USA, October 29, 20105990-6694EN
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