addressing the design-to-test challenges for sdr and ... · addressing the design-to-test...

Addressing the Design-to-Test Challenges for SDR and Cognitive Radio

Bob Cutler and Greg Jue, Agilent Technologies

© Copyright Agilent Technologies 2009 Addressing the Design-to-Test Challenges

for SDR and Cognitive Radio

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)

Copyright Agilent Technologies 2009 Addressing the Design-to-Test Challenges


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)

Portability and Flexibility

Challenges and Opportunities

• RF performance determined by both hardware and software. Performance could change with “bug fix”.

• HW 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



• 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.

SDR Designs: Comprised of Baseband AND RF

Tx RxCoding

Algorithms

D/A

Bits InDecoding

AlgorithmsBits Out

ChannelA/D

Gain

LinearityOutput Power

GainNFPhase Noise

SDR Design:



• RF Transmitter: Upconverts Signal to RF• RF Receiver: Downconverts Received RF Signal to IF or IQ

• Coding/Decoding Algorithms to Achieve System Performance

Baseband Waveforms Come in Many Formats-

Creates Barriers for SDR RF Design & Test

Tx RxCoding

Algorithms

D/A

Bits InDecoding

AlgorithmsBits Out

ChannelA/D

Simulation Models

SDR Transmitter:

• Baseband waveforms needed to design & test RF:

Challenge: How can RF designs be designed &

tested with various baseband waveform sources?



FPGA HDL CodeMath Algorithms

Baseband Hardware

tested with various baseband waveform sources?

SDR Receiver:

• Baseband coding/decoding needed to design & test

RF receivers for coded BER metrics…

Challenge: How can Receiver BER performance be

evaluated independently of baseband waveform HW ?

Agilent SystemVue

Integrated Design Environment to

Bring FPGA and RF Designs Together

• Baseband and RF modeling, simulation

• Open, “model-based design” infrastructure forcontinuous verification of heterogeneous IP

• Math/C++ /GUI� Fixed Pt � VHDL/Verilog



• Math/C++ /GUI� Fixed Pt � VHDL/Verilog

• HDL generation & co-simulation

• IP reference blocksets for Mobile WiMAX™, LTE, other formats

• Customizable, standards-based test vectors

• Interoperable with Agilent test equipment

• Test equipment links, VSA integration, and more

“Mobile WiMAX” is a registered trademark of the WiMAX Forum

Design SDR RF Using Various Types of Waveform Formats

Use Waveform Sources to Design SDR RF

Waveform Sources

• HDL Code

• FPGA Hardware

Waveform

Signal

Source



• FPGA Hardware

• Simulation Models

• Algorithm Code Simulated RF Transmitter Design

Example 1: Use HDL-Based WiMAX Waveform to Design SDR RF Transmitter

EVM = 8.4%

Simulated SDR Transmitter Output

Waveform Sources

• HDL Code

• FPGA Hardware




Simulated RF Transmitter DesignVSA

Measurement

• Algorithm Code

EVM = 9.1%


Waveform Sources

• HDL Code

• FPGA Hardware


• Algorithm Code

Example 2a: Use FPGA-Based Legacy Waveform to Design SDR RF Transmitter




Measurement

EVM=10.5%

Reconfigure legacy FPGA

waveform for a new waveform

(LTE)


Example 2b: Re-Configure FPGA-Based Waveform to Evaluate SDR RF Transmitter Design Interoperability

Waveform Sources

• HDL Code

• FPGA Hardware


• Algorithm Code




Measurement

Example 2c: Probing an FPGA Waveform with Dynamic Probe

Waveform Sources

• HDL Code

• FPGA Hardware


• Algorithm Code



Simulated RF Transmitter Design

preliminary work-in-progress

Waveform

Simulation

Receiver

Waveform

Simulation

Source

Waveform Sources

• HDL Code

• FPGA Hardware


• Algorithm Code

Example 3a: Use Simulation-Based WiMAX Waveform to Design SDR RF Receiver



Simulated RF Receiver Design

Receiver Source

Pre-Configured Algorithm Models (Customizable) Select ADC model…

QPSK BER vs. ADC Jitter vs. EbNo

Red: 4% ADC Jitter

Blue: 6% ADC Jitter

Green: 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



New Waveform

Simulation

Receiver New Waveform

Replace WiMAX Waveform

Source & Receiver with LTE

New BER

Results

Example 3b: Replace Waveform to Evaluate SDR Receiver Design Interoperability




Receiver New Waveform

Simulation

Source

Waveform Sources

• HDL Code

• FPGA Hardware


• Algorithm Code

Example 4: Use Algorithm Code Waveforms



Customize OFDMA Algorithms

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



testing

14 Bit A/D

Board DUT

• Test waveform coding/decoding SW-defined

• Customizable algorithms

• Customizable test waveforms

Adding Flexibility to SDR Testing with Simulation



16822A Logic Analyzer with Agilent SystemVue*

* Note: SystemVue does not ship with Logic Analyzer

OFDMA BER Hardware Test Results



Simulation

Code Generation RF

Design-to-Test Tool Consistency Helps Minimize

Unwanted Surprises and Helps to Debug Issues



D/AFGPA/DSP

Digital Signal Capture Analog Baseband

Simulate an SDR Receiver with a Hardware Front

End (N6841 RF Sensor)

Wideband RF Sensor


Simulated SDR

Receiver Output



HW DUT

Test Signal

VSA

Measurement

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



Radio adjusts frequency, power, modulation

based on sensed spectrum, location, policy and databases

Complimentary to SDR in this application

Filling the Whitespace

Goal: Increase spectrum utilization without causing

interference



interference

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)



• Environment Sensing Performance (spectrum sensing, location sensing)

• Policy Performance (does the policy over, or under protect)

• Radio Environment (channel, noise, occupancy)

Radio Environment

In many applications, such as TVWS, very little is actually known about “real environments”

• Where are the wireless microphones and TV signals?

• What are their power statistics?

• What other signals are present? Are they protected?

• How dynamic are they?



• How dynamic are they?

• How does all of this change from one location to another?

• For joint spectral detection, what does the environment look like from two or more locations at any one instant in time?

Need to design for real environments

• Need to capture and replicate environment in the lab

Challenges of Spectrum Sensing

From this display can you tell me…

1. Is the spectrum occupied?

2. How occupied is it?



2. How occupied is it?

3. What is the potential for interference?

4. What signals are present?

Challenges of Spectrum Sensing (cont)

Performance of various spectrum sensing algorithms

• False positives, False negatives

• Response to real-world signal environment (dynamic, many signals)

• Radio Design

– Spurious

– Amplitude accuracy



– Amplitude accuracy

– Intermod distortion

– Sensitivity

– Selectivity

– Frequency accuracy

• Speed/complexity/Cost tradeoffs

Summary: CR Development Challenges

• Need to characterize, capture, and replicate real-world spectral environments.

• Needs to be done over time, frequency and location.

• Need to capture the environment as signals, not power spectra

• Need to use captured environments to evaluate CR algorithms and radio link performance.



link performance.

• Need to evaluate performance using non-ideal radios.

• Need a flexible and comprehensive CR R&D Testbed!

Cognitive Radio R&D Testbed



CR Algorithm Development & Testing Environment



Mobile WiMAX Case Study



Step 1: Capture Signal & Bring into SystemVue

Captured CR environment



Step 2: Whitespace Math Algorithms Determine

Valid Whitespace Frequency Rules Policy



RF Sensors

Valid whitespace

determined within

the policy

Rising/falling edges

detected to

determine

whitespace

Debugging Whitespace Algorithms

Add/Remove Breakpoint

Single-Step Through Code



Code Variable Values are

Displayed as Code is

Single-Stepped

Step 3: Whitespace Math Algorithms Determine

Valid Whitespace



WiMAX spectrum (scaled and centered

in the valid whitespace)

Analyze Detect-And-Avoid Interferer Scenarios

Sweep

Narrowband

Interferer vs.

Narrowband

Interferer



Interferer vs.

Frequency to

Evaluate

Impact on

OFDMA BER

Sensed spectrum

Step 4: Identify Detected Signals in Simulation or

with Test Equipment



Remotely Located

N6841A RF Sensor

Video Demo with SystemVue + N6841A N6841A is Remotely Located Across Washington State



N6841A RF Sensor

www.agilent.com/find/eesof-cognitive-whitepaper

New Whitepaper Available:

www.agilent.com/find/eesof-cognitive-whitepaper



Summary

• Use waveforms sources in various formats (HDL, FPGA hardware, simulation models, math algorithms) to design SDR transmitters and receiver and evaluate interoperability

• Customizable simulation waveforms (WiMAX and LTE)

• Seamless integration between design and test capability

• creates flexible SDR testing platform

• enables R&D engineers to develop and test algorithms and hardware with



• 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

Additional ResourcesProduct Websites:

http://www.agilent.com/find/systemvue

http://www.agilent.com/find/rfsensor

Whitepapers & 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



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 webcast:http://www.agilent.com/find/eesof-cognitive-whitepaper

Q&A



Thank You!



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