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What are White Spaces?

Reclaiming the White Spaces: Spectrum Efficient Coexistence with Primary Users George Nychis †, Ranveer Chandra § , Thomas Moscibroda ★ , Ivan Tashev § , Peter Steenkiste † † Carnegie Mellon University, §Microsoft Research, ★ Microsoft Research Asia. What are White Spaces?. -60.

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What are White Spaces?

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  1. Reclaiming the White Spaces:Spectrum Efficient Coexistencewith Primary UsersGeorge Nychis†, RanveerChandra§, Thomas Moscibroda★, IvanTashev§, Peter Steenkiste† †CarnegieMellon University, §Microsoft Research, ★Microsoft Research Asia

  2. What are White Spaces? -60 Wireless Mic TV “White spaces” 0 MHz 54-90 170-216 2400 2500 5180 5300 470 700 7000 MHz } dbm 9 Orthogonal Channels (150Mbps per chan) More Spectrum ISM (Wi-Fi) Proliferation of Wireless & Mobile: ISM Band is Insufficient to Meet Demand Potential Applications Rural wireless broadband City-wide mesh 700 MHz 470 MHz …….. Longer Range -100 …….. Frequency are Unoccupied TV Channels White Spaces at least 3 - 4x of Wi-Fi

  3. Reclaiming the White Spaces White Space Availability • Spectrum availability is critical to adoption and goals • Spectrum is most critical in populated areas • Measure spectrum availability in top 30 U.S. cities [1] • “[to] make a significant amount of spectrum available for new and innovative products and services” – FCC 08-260 Goal: Rescue White Space by Enabling Mic Coexistence single channel Losing aSignificantAmount ofWhite Spaceto Mic Rules Number ofAnalog TVBroadcastsDecreasingOver Time 53% of cities cannot support single 802.11 channel in the white spaces 2 Reserved Channels [1] Geo-location database: http://whitespaces.msresearch.us/

  4. Outline • Background on mic signals • Data transmission impact on mic audio • Critical insight on coexistence • SEISMIC: Spectrum Efficient Interference-Free System for MICs • Regains spectrum with zero audible interference • Evaluation of effectiveness and efficiency

  5. Analog Microphone Background • One-way communication: receiver never transmits • Micalwaystransmitting (even idle) • Signal Components: FM Modulated Audio Signal Mic Receiver Wireless Mic Used By Mic Receiver to Detect Low Signal and Mute

  6. Outline • Background on mic signals • Data transmission impact on mic audio • Critical insight on coexistence • SEISMIC: Spectrum Efficient Interference-Free System for MICs • Regains spectrum with zero audible interference • Evaluation of effectiveness and efficiency

  7. How Do You Coexist to Reclaim Spectrum? • First in-depth analysis RF interference on mic audio quality • 3 Dimensions: time, frequency, and power • Study Impact on 6 Mics: • Audio Technica, Sennheiser (3), Shure, and Electro-Voice • First in-depth analysis RF interference on mic audio quality • 3 Dimensions: time, frequency, and power

  8. Experimental Setup • PESQ worldwide audio evaluation standard • Compare recording to original • 0 (total disruption)  1 (perfect) 1. PC Output to Speakers Mic 2. MIC Recording to Computer Mic Receiver White Space Device

  9. Interference in Frequency • Fix power and duration, vary frequency (25KHz steps) 2. Suppression Req. Varies by Mic 1. Avoid Disruption, Still Use 97% of Channel

  10. Interference in Power • Fix freq. and duration, vary power of WSD (2dB steps) WSNm(dB) WSNs (dB) Despite 25dB of noise! • Record value of WSNm& WSNs when PESQ=1 • No audio disruption when interference is just below the squelch tones! (WSNs = 1dB) “FM receivers exhibit a `capture effect’ in which they respond to only the strongest signal received on a frequency and reject any weaker interfering signals.”- FCC (First Order: 04-113)

  11. Implications of Interference Study • Coexistence in the same channel is possible! • Great! Just suppress bandwidth required at center frequency Not that simple…

  12. The Challenge of Suppression Stronger WSD  More Suppression `Perfect Suppression’ would have sharp edge Actual SuppressionLeaks Power in to the Band Weaker Mic More Suppression

  13. Information Needed to Suppress • Twocomponentsneeded at WSD to suppress properly: 1. WSD Interference Power at the Mic Receiver White Space Device(WSD) Mic Receiver Wireless Mic 2. Mic Signal Power at Mic Receiver

  14. Lack of Information at WSD • No feedback on either required components • Without feedback, the system is open-loop • Mustsuppress “worst-case” to be conservative Given the open-loop state of the system (info available)… Unfortunately, worst-case is vacation! (6MHz) … the FCC made the right decision by requiring vacation.

  15. Need a Closed-Loop to Avoid Vacation Feedback SEISMIC Analysis Measurement White Space Device) Mic Mic Receiver Adaptation

  16. Outline • Background on mic signals • Data transmission impact on mic audio • Critical insight on coexistence • SEISMIC: Spectrum Efficient Interference-Free System for MICs • Regains spectrum with zero audible interference • Evaluation of effectiveness and efficiency

  17. SEISMIC System Overview • Implements closed-loop design to avoid vacation: • Measurement: MicProtector measures key components at receiver • Feedback: “Strobe” signal to notify WSD of impending disruption • Analysis / Adaptation: SEISMIC protocol to adapt frequency Feedback MicProtector Mic White Space Device Mic Receiver

  18. Measurement: MicProtector • Key measurement needed: squelch & interference power • Squelch Measurement: estimated in the mic’s band • Interference Measurement: estimated in control bands Control Control Band Band Power in Mic Band Shifts Interference Level Amplitude Frequency 25KHz 25KHz

  19. Feedback: Strobes • MicProtector needs to convey information to WSD • Strobe is similar to Morse-codes and on/off-keying (OOK) • Allows us to convey necessary information without complex protocol (e.g., 802.11) • Strobe signals convey: • (1) impending disruption,(2) required bandwidth, (3) center frequency Amplitude Frequency

  20. Adaptation / Analysis: SEISMIC Protocol • WSD: sends probe packets with increasing power (exploit capture) • MicProtector: notifies of impending disruption, using strobes Control Control Band Band Interference Level Amplitude Protection Threshold Frequency 25KHz 25KHz

  21. Adaptation: SEISMIC Protocol • WSD: sends probe packets with increasing power (exploit capture) • MicProtector: notifies of impending disruption, using strobes Pkts: Probe Strobe Convergence To Coexistence MicProtector Strobes the WSD for interference near threshold MicProt. 250 WSD 250 Increase in Power 250 150 200 100 50 100 Suppressed Frequency (KHz) Time

  22. Summary of SEISMIC Design • MicProtectorcomponents: • detection of impending audio disruptions • feedback using strobes to WSD enables closed-loop • Note: can be built directly in to future receivers • WSD and MicProtector engage in SEISMIC protocol • converge to optimal suppression around mic • Formalizationshows correctness with multiple WSD • WSDs will converge and never interfere, in paper  SEISMIC

  23. Outline • Background on mic signals • Data transmission impact on mic audio • Critical insight on coexistence • SEISMIC: Spectrum Efficient Interference-Free System for MICs • Regains spectrum with zero audible interference • Evaluation of effectiveness and efficiency

  24. Evaluating SEISMIC • Full MicProtector and SEISMIC WSD prototypes • custom USRP2 builds with UHF front ends • Evaluation on several coexistence points: • Effectiveness: ability to avoid audio disruption • Efficiency: ability to enable high spectrum re-use • Single microphone scenario • Many microphone scenario

  25. Effectiveness of SEISMIC’s Coexistence • Challenge: Low-power & mobile microphone • SEISMIC WSD must never interfere despite mic signal fluctuations WSD vacateschannel whenmic power islow to be safe WSD continuallyand quickly adapts to avoidaudio disruption! Mobility createsquick fluctuations

  26. Efficiency of SEISMIC’s Coexistence • Evaluate efficiency under two mobile mic scenarios • Far mic (low/moderate signal) .. close WSD (high interference) • Mod. mic (moderate signal) .. nearby WSD (moderate interference Mic Signal (dBm) WSD Signal (dBm) Low (-95-75) High (-50-30) Moderate (-70) Moderate (-65) Common scenario: 95% of time >5.7MHz Challenging scenario: 70% of time >5.2MHz

  27. SEISMIC Efficiency with Many Mics • Obtain real micfreq placement from coordinators • Model components: 1) Mic signals, 2)WSDs & interference • Given components, how much spectrum does WSD X have? SEISMIC-enabled Mic System SEISMIC-enabled WSD • Mic signals generated using mobile mic measurements • Adaptrum WSD freq suppression w/ leakage used for WSDs

  28. SEISMIC Spectrum Efficiency • On average, SEISMIC-enabled WSDs: • SEISMIC has 22x, 3.6x, and 1.6x availability compared to channel vacation • SEISMIC near perfect suppression,suppresses only when necessary (closed-loop) • With 150MHz: can support 7 150Mbps channels! (2.5x 2.4GHz, with 4x range)

  29. Summary • Spectrum availability is critical to white spaces • Coexistence possible between WSD and mics • Closed-loop solution required to avoid vacation • SEISMIC enables disruption-free coexistence • Up to 95% of the spectrum can be regained • Demoed to FCC chairman, mic manufacturers, mic coordinators, audio community

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