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D ESIGN AND I MPLEMENTATION OF A S OFTWARE R ADIO T ESTSET FOR R ESEARCH AND L ABORATORY I NSTRUCTION. Fraidun Akhi 10/30/03. C ONTENTS…. Statement of Purpose Introduction to Software Radios The Software Radio Concept The Wireless Communications Industry Potential Benefits

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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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STATEMENTOF 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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Analog

TDMA

Analog

CDMA

iDEN

CDMA

4%

10%

1%

12%

4%

20%

TDMA

10%

GSM

iDEN

68%

1%

GSM

70%

THEWIRELESS PHONE INDUSTRY

  • More than 1.3 billion cellular phone users in 2003

2001 PCS Market

2005 PCS Market


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GSM

Time Division Multiplexing

200 KHz – wide channels

GMSK Modulation

CDMA

DSSS

1.25 MHz – wide channels

QPSK Modulation

GSM v.s. CDMA


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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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SHIELDINGAND GROUNDING

RF Transmitter


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SHIELDINGAND 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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DSSSIMPLEMENTATION

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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DIGITALTO 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 FPGA’s into the mix


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WHYTHE SOFTWARE RADIO PROJECT SHOULDBE 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


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