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Building Efficient Spectrum-Agile Devices for Dummies

Building Efficient Spectrum-Agile Devices for Dummies

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Building Efficient Spectrum-Agile Devices for Dummies

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  1. Building Efficient Spectrum-Agile Devices for Dummies Eugene Chai, Kang G. Shin University of Michigan – Ann Arbor Jeongkeun “JK” Lee, Sung-Ju Lee, Raul Etkin Hewlett Packard Labs – Palo Alto

  2. Why Fast Spectrum Shaping? ~1GHz 300MHz What about allocation over time? Using measurement traces from RWTH Aachen University: Median Channel Availability = 3 seconds, approx

  3. How Can We Do This? Option 1: Commercial Off-The Shelf (COTS) Devices MAC: Incompatible preambles PHY: Monolithic spectrum Option 2: Software Defined Radios FPGA: Complex Software: Slow

  4. Our Solution: Rodin APP Hybrid Architecture TRANS COTS NET Per-Frame Spectrum Shaping Rodin MAC MAC Spectrum-Agile Preamble SDR PHY

  5. Rodin: Spectrum Shaping Rodin detects interference and reshapes next frame Empty Empty Empty Empty Empty Frequency Time

  6. Rodin: Spectrum Shaping Rodin splits a monolithic spectrum into two subbands: From COTS To Channel

  7. Rodin: Filter Design Problem: Frequency offset between devices

  8. Our Solution: Rodin APP Hybrid Architecture TRANS COTS NET Per-Frame Spectrum Shaping Rodin MAC MAC Spectrum-Agile Preamble SDR PHY

  9. Rodin: Spectrum Agreement Why is spectrum agreement hard? This is the actual spectrum allocation This is what the receiver sees A Occupied Empty Empty B Occupied Frequency Frequency Empty Empty B Occupied A Occupied The receiver does not know which subbands are assigned to each transmitter If a transmitter uses M out of N total subbands, the number of possible combinations is

  10. Rodin: Spectrum Agreement Solution: I-FOP (In-Front Of Preamble) Composite Rodin Frame I-FOP COTS Preamble Data Transmitter P1 Empty P2 Frequency Empty P3 P4

  11. Rodin: Spectrum Agreement Solution: I-FOP (In-Front Of Preamble) Composite Rodin Frame I-FOP COTS Preamble Data P1 PN Sequences P1,…,P4 Receiver X P2 Frequency Order X P3 Arrival Time P4 Time

  12. Rodin: Spectrum Agreement Receiver searches for P1,…, P4 in each subband simultaneously P1 P2 P1 P3 P4 X Receiver … P2 Frequency X P3 P1 P4 P2 P3 Time P4

  13. Rodin: Spectrum Agreement Device Addressing Association frame with an association preamble address Preamble Collision Same PN sequences; same order; same transmit instant Receiver Complexity Parallel search over multiple subbands in hardware

  14. Our Solution: Rodin APP Hybrid Architecture TRANS COTS NET Per-Frame Spectrum Shaping Rodin MAC MAC Spectrum-Agile Preamble SDR PHY

  15. How Does Rodin Compare? Picasso (SIGCOMM 2012) WiFi-NC (NSDI 2012) • Concurrent operations over sub-channels Spectrum Virtualization Layer (DySpan 2012) • Software layer between standard PHY and channel Jello (NSDI 2010) • Flow-based spectrum allocation

  16. Evaluation Spectrum Shaping I-FOP Throughput

  17. Implementation & Evaluation Spectrum Shaping Parameters • FPGA and Matlab implementations • 10MHz COTS signal split into two 5MHz subbands separated by 10MHz • Interference BW is 2.5, 5 and 10MHz

  18. Evaluation: Spectrum Shaping Experiment 1: Spectrum shaping vs no spectrum shaping. No interference. Spectrum shaping does not distort the signal

  19. Evaluation: Spectrum Shaping Experiment 2: Spectrum shaping with interference Error Vector Magnitude Without shaping With shaping Rodin can avoid interference effectively

  20. Implementation & Evaluation I-FOP • Implemented using WARPLab and Matlab • 5 WARP devices placed throughout an office • 20MHz channel with 8 subbands • Preamble consists of 4 sequences transmitted over 4 subbands

  21. Evaluation: I-FOP Experiment 3: I-FOP under varying SIR levels We randomly select 3 devices as transmitter, receiver and interferer Detection ratio increases with increasing preamble sequence length

  22. Simulations Experiment 4: Transmission opportunities in 1.5GHz spectrum band centered at 5.25GHz More transmit opportunities with smaller subband bandwidth

  23. Where do we go from here? Spectrum Agile Networks How well do current protocols work under spectrum agility? Whitespace Networks What happens if we change the operating frequency? Integrated Hybrid Platform Can we build a more integrated device?

  24. Conclusions Hybrid Architecture Per-Frame Spectrum Shaping Spectrum-Agile Preamble Rodin is the key to enabling large scale spectrum agile networks

  25. Questions?