DESIGN AND IMPLEMENTATION OF A SOFTWARE RADIO TESTSET FOR

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DESIGN AND IMPLEMENTATION OF A SOFTWARE RADIO
TESTSET FOR RESEARCH AND LABORATORY INSTRUCTION

• Fraidun Akhi
• 10/30/03

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CONTENTS..

• Statement of Purpose
• Introduction to Software Radios
• The Software Radio Concept
• The Wireless Communications Industry
• Potential Benefits
• Potential Applications
• Technological Hurdles to Ideal Software Radio
  Design
• Practical Software Radio Designs
• RF Front-Ends
• Data Converters
• Signal Processors

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...CONTENTS

• Data Converters Circuits
• Digital to Analog Converter
• RF Measurements
• Transmitter measurements
• Project Status and Future Development
• What has been accomplished
• What remains to be done
• The potential benefits of this project to AU

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CONTENTS

• RF Front-End Design and Implementation
• The RFMD WLAN Chipset

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STATEMENT OF PURPOSE

• To explore the design and implementation of a
  software radio testset that could be used for an
  undergraduate teaching lab, or as the foundation
  for a graduate-level research lab
• Emphasize on
• RF design and measurement capability
• DSP algorithm design and implementation
• Integration of the RF and DSP sections through
  the use of data converter circuits
• Evaluation Modules and Circuit Assembly
• Shielding and Grounding Issues
• DSP Starter Kits
• Serial Ports
• Code Composer Studio

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SOFTWARE RADIO, THE CONCEPT

• Transfer transceiver functionality from the
  hardware to the software domain, eliminate RF
  front-end
• Filtering
• Equalization
• Encoding/decoding
• Modulation/demodulation
• ..All done by software in DSP

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THE WIRELESS PHONE INDUSTRY

• More than 1.3 billion cellular phone users in
  2003

2001 PCS Market
2005 PCS Market
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GSM v.s. CDMA

• GSM
• Time Division Multiplexing
• 200 KHz wide channels
• GMSK Modulation

• CDMA
• DSSS
• 1.25 MHz wide channels
• QPSK Modulation

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THE WLAN INDUSTRY

• More than 4 million Wireless Local Area Network
  (WLAN) users in North America, and growing
• Many different standards competing for the market
• IEEE 802.11b DSSS, 2.4 GHz, 11 Mbps
• Bluetooth FHSS, 2.4 GHz, 1 Mbps
• IEEE 802.11a OFDM, 5.8 GHz, 54 Mbps
• IEEE 802.11g OFDM, 2.4-2.483 GHz, 54 Mbps
• Backward compatible with 802.11b
• IEEE 802.15.3a UWB, 3.1 GHz 7.1 GHz, 110 Mbps
• Still in development

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POTENTIAL BENEFITS OF SOFTWARE RADIO

• Real-time Configuration
• Download new features into handsets
• All phone features can become adaptive to
  environment
• Adaptive control of power emissions
• Adaptive signal processing
• Multi-Standard Operation
• Cellular basestations and handsets no longer
  becomes obsolete with changing standards
• Interoperability between standards

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MORE POTENTIAL BENEFITS

• Power Efficiency
• Some 70 of wireless transceiver power
  consumption is due to RF front-end, which
  software radio eliminates
• Digital Performance Advantage
• Digital technology is more predictable, reliable,
  and immune to environmental factors
• Fewer Components, no RF-Front-End
• Cost savings
• More compact designs

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POTENTIAL SOFTWARE RADIO APPLICATIONS

• Cellular Phone Systems
• Can help reduce migration costs in basestations
• Can improve the performance and price of handsets
• Military / Law Enforcement
• Interoperability between different units radios
• An effective intelligence gathering device
• Academia
• Real-world implementation and analysis of signal
  processing algorithms

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TECHNOLOGICAL HURDLES TO IDEAL SOFTWARE RADIO
DESIGN

• Analog to Digital Conversion
• Fastest low power ADCs with reasonable
  bit-resolution sample at 300 Msamples/s
• The Ideal software radio requires at least 10
  Gsamples/s
• Processing Power
• If the ADC problem was solved, could the
  transceiver process so many samples?
• Multi-processor units can handle large processing
  loads, but these are only possible in static
  units such as basestations, not in handsets where
  low power consumption is key

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PRACTICAL SOFTWARE RADIO DESIGN

• Include an RF front end to ease the requirements
  placed on the data converters and thus ease the
  processing load
• The drawbacks are bandwidth limitations of the
  front-end, and the loss of control over
  modulation/demodulation

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SUPER-HETERODYNE RF FRONT-END

• Modulate/demodulate in more than one stage
• Low Power, high performance, no DC offset, very
  few high-performance parts needed
• Drawbacks include the high chip count, bulkier
  design, narrower bandwidth

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DIRECT CONVERSION RF FRONT-END

• Low chip count, less cost, more compact design
• No image rejection problem
• Drawbacks include DC offset caused by LO
  self-mixing, I/Q balancing issues at RF

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LOW-IF RF FRONT-END

• Fewer components than Super-heterodyne, no DC
  offset problem, design is partly digital
• Currently the best option for software radios
• Drawbacks are that a higher performance ADC is
  needed, I/Q imbalance problem at RF

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DATA CONVERTERS

• Low power digital to analog converters available
  at speeds of 800 MHz, DACs lead ADCs in speed
• The lack of fast, low-power, high-resolution ADCs
  is holding up the realization of software radios
• Most software radios include a low-IF RF
  front-end, usually with an IF less than 100 MHz
• Subsampling, whereby under-sampling of the IF (or
  potentially RF) carrier leads to the sampling of
  its image near baseband, is a potential solution
  to the shortfall in ADC performance

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SIGNAL PROCESSORS

• ASIC (Application Specific Integrated Circuit)
• Highest performance, lowest programmability
• FPGA (Field Programmable Gate Array)
• Very high performance, programmability
• Ideal for semi
• DSP (Digital Signal Processor)
• High performance, real-time programmability
• The ideal engine for a software radio because of
  its real-time configurable features

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RF FRONT-END CHIPSET
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RF TRANSMITTER ASSEMBLY
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RF RECEIVER ASSEMBLY
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SHIELDING AND GROUNDING
RF Transmitter
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SHIELDING AND GROUNDING
RF Receiver
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DSP STARTER KITS
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DSP TESTING
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CODE COMPOSER STUDIO
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MCBSP CABABILITIES

• Transfer serial data stream as fast as 35 Mbps
• Implement a number of standard or custom serial
  port interfaces
• Can be used to send data and sync channels
  through RF link, in DSSS implementation

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DSSS IMPLEMENTATION
Figure 4.4 Data processing at the transmitter
  Figure 4.5 Data processing at the receiver
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MULTI-CHANNEL BUFFERED SERIAL PORTS
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DIGITAL TO ANALOG CONVERTER
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DAC PERFORMANCE
Output at 1.25 MHz
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RF TESTING
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RF MEASUREMENTS
Direct Sequence Spread Spectrum Processing Gain
Data Signal Spectrum
Spread Signal Spectrum
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PROCESSING GAIN

• Processing (PG) is a comparison of the bandwidth
  of the symbol stream to that of the spread chip
  stream
• In the previous slide, a 16-bit PN sequence was
  used to spread the data sequence so

• Measured Processing gain is 7.83 dB (17.33 -
  9.5), from spectrum analyzer measurements

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ACCOMPLISHMENTS

• Successfully wrote and tested the DSSS programs
  on the MCBSPs in wired mode
• Successfully built and tested the DAC circuit
  with the DSK and the RF transmitter
• Successfully built and tested the RF transmitter
  and receiver units

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LESSONS LEARNED

• The initial reason that the RFMD chipset was
  chosen, was that its super-heterodyne structure
  offered many test points for RF measurements
• EVMs were very sensitive to static and voltage
  surges, and thus many chips were accidentally
  destroyed
• Debugging of the RF circuitry took up most of the
  time spent on the project, and limited further
  software development
• If a suitable RF front end is not commercially
  available, perhaps a more compact chipset such as
  the MAX2822 single-chip direct conversion
  transceiver should be looked into

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REMAINING WORK

• Test the ADC circuit that is currently under
  construction this will close the loop
• Build a rigid single-board RF front-end in a
  chassis
• Use ADC and DAC daughter-cards as data
  converters, improve performance
• Add processing power by adding FPGAs into the
  mix

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WHY THE SOFTWARE RADIO PROJECT SHOULD BE CONTINUED

• Software radio is the future of the wireless
  industry and thus should be a focus of the
  Wireless Engineering program at Auburn University
• An active software radio project or lab at AU
  would put the it at the forefront of wireless
  research and development with the likes of MIT
  and GA Tech, both of whom put lots of research
  emphasis into software radio
• It would provide an educational/research setting
  for undergraduate/graduate students who seek to
  study design and implementation of wireless
  systems with DSPs, FPGAs, RF front-ends,
  antennas, and data converters