Open Spectrum - Physics, Engineering, Commerce and Politics

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The Open Spectrum Potential for Evolutionary and Revolutionary Technology and Business Solutions
by
Brough Turner; Founder and CTO at Ashtonbrooke and Chief Strategy Officer at Dialogic

Presented to the Boston chapter of the IEEE Communications Society, May 14, 2009.

In November 2008, the FCC voted unanimously to permit unlicensed wireless devices that operate in the empty "white space" between TV channels. Their “TV White Spaces” decision was the culmination of many years of proceedings, but it's just one step in a much larger discussion, commonly referred to as “Open Spectrum.”

Our use of radio spectrum is regulated under principles that were established in the 1920s, when radio spectrum appeared to be a scarce resource and frequency was the only reasonable basis for allocation. Today’s wireless technology vastly exceeds anything imagined in the 1920s and from physical principles we know that many, many orders of magnitude further improvement are possible. Already the application of new approaches in just a few slivers of spectrum has fostered new industries – WiFi, Bluetooth and more.

The presentation discusses the predecessors, potentiality, and directions for Open Spectrum. This will include:

A brief history spectrum regulation from before the Radio Act of 1925 to today.

Results from measurements of actual spectrum utilization in New York and Washington DC.

An overview of "Open Spectrum" experiments to date, including “license exempt sharing” in the 900 MHz, 2.4 GHz and 5 GHz bands and different forms of "secondary use" including UWB, 3650 MHz and now TV White Spaces.

The physics of propagation and its impact on the range of White Spaces services vs. WiFi, WiMAX, 3GSM and LTE.

IEEE 802.11y protocols and the prospects for expanding secondary use beyond TV White Spaces.

Brough Turner is founder and CTO at Ashtonbrooke and Chief Strategy Officer at Dialogic. Formerly he was founder and CTO at Natural MicroSystems and NMS Communications. He speaks and writes on a variety of communications topics including 3G and 4G wireless tutorials. He presented most recently at the 4G Wireless Evolution conference in February. Brough is an electrical engineering graduate of MIT and has 25 years experience in telecommunications.

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Open Spectrum - Physics, Engineering, Commerce and Politics

  1. 1. Open Spectrum Physics, Engineering, Commerce and Politics Brough Turner http://www.broughturner.com
  2. 2. Open Spectrum 1. Electromagnetic spectrum for which there are no licensing requirements E.g., Visible light, 400-790 THz 2. “A movement to get the government to provide more unlicensed spectrum” (Wikipedia, 5/2009) 2
  3. 3. Open Spectrum 1. Electromagnetic spectrum for which there are no licensing requirements E.g., Visible light, 400-790 THz 2. “A movement to get the government to provide more unlicensed spectrum” (Wikipedia, 5/2009) US regulates 9 KHz – 300 GHz today 3
  4. 4. How could this work? Noise Interference Chaos … ! 4
  5. 5. How could this work? Noise Interference Chaos … ! Receiver performance is the critical issue… 5
  6. 6. Visible light analogy Our vision system (eyes + visual cortex) = extremely efficient 400-790 THz receiver 6
  7. 7. Visible light analogy Our vision system (eyes + visual cortex) = extremely efficient 400-790 THz receiver The product of years of evolution! 7
  8. 8. Spatial discrimination For Humans: ~ 1/60th of a degree 8
  9. 9. Enormous knowledge base Detailed catalog of the characteristics of most potential visible light sources 9
  10. 10. Leveraging source motion to increase received information … 10
  11. 11. Radio receivers today Far from the selectivity and sensitivity of mammalian vision systems Today’s “cognitive radios” can’t match the performance of the visual cortex But far ahead of receivers in use when regulatory schemes were established 11
  12. 12. Origins of Wireless Communications 1864: James Clark Maxwell ● Predicts existence of radio waves 1886: Heinrich Rudolph Hertz ● Demonstrates radio waves 1895-1901: Guglielmo Marconi ● Demonstrates wireless communications over increasing distances Also in the 1890s ● Nikola Tesla, Alexander Stepanovich Popov, Jagdish Chandra Bose and others, demonstrate forms of wireless communications 12
  13. 13. US Radio Spectrum Regulation Radio Act of 1912 Titanic disaster tips the tide to licensing & rules Seafaring vessels to maintain 24-hour radio watch Radio Act of 1927 Rise of broadcasting brings chaos, then restrictive licensing – “in the public interest” Communications Act of 1934 Combines telecom and radio regulation Establishes the FCC 13
  14. 14. 1920s consumer radio receivers Crystal, Regenerative, Tuned RF, Neutradyne, … Low selectivity, sensitivity, stability Super-heterodyne not yet at consumer prices 833 KHz, AM only, until 1922; then 10 KHz spacing ~600 licensed stations by 1930 Tuned RF Crystal 14
  15. 15. 1920s State of the Art Amplitude modulated RF carriers Separated by frequency Receivers with limited selectivity Analog tank circuits Mostly, omni-directional antennas Mostly fixed broadcast locations 15
  16. 16. Regulations made sense In 1927, spectrum was a scarce resource We’ve come a long way since 1927 But Regulation vested interests resistance to change 16
  17. 17. Radio Spectrum Occupancy Urban areas, 30 MHz to 3 GHz. Above 3 GHz mostly vacant. As measured by Shared Spectrum Company and the University of Kansas Center for Research for the NSF National Radio Network Research Testbed (NRNRT) 17
  18. 18. Radio Spectrum Occupancy Urban areas, 30 MHz to 3 GHz. Above 3 GHz mostly vacant. As measured by Shared Spectrum Company and the University of Kansas Center for Research for the NSF National Radio Network Research Testbed (NRNRT) 18
  19. 19. New York City Unusually heavy communications during Republican National Convention August 30 to September 3, 2004 brought spectrum occupancy up to 13%. 19
  20. 20. Most spectrum idle most of the time FCC Regs protect obsolete technology e.g. TV guard bands are to protect pre-1950 receiver technology. You wouldn’t run your business on a 1950s mainframe computer… 20
  21. 21. Most spectrum idle most of the time FCC Regs protect obsolete technology e.g. TV guard bands are to protect pre-1950 receiver technology. You wouldn’t run your business on a 1950s mainframe computer… Rights holders utilizing subset of their rights Governmental entities sitting on spectrum Partial buildouts; financial or tech problems; market changes; incumbents sitting on spectrum. 21
  22. 22. Spectrum Myths Spectrum is scarce 4G is the future of wireless Auctions drive efficient use of spectrum Utilization requires massive investments TV spectrum is “beach front” property 22
  23. 23. Spectrum not so scarce New modulations Multiple users separated by frequency (FDMA), in time (TDMA), by codes (CDMA) OFDMA simultaneously optimizes frequency, time and user data demands Directional antennas & beamforming Multiple Input Multiple Output (MIMO) 23
  24. 24. 1G – Separate Frequencies FDMA - Frequency Division Multiple Access 30 KHz 30 KHz 30 KHz Frequency 30 KHz 30 KHz 30 KHz 30 KHz 30 KHz 24
  25. 25. 2G – Time Division Multiple Access One timeslot = 0.577 ms One TDMA frame = 8 timeslots 200 KHz Frequency 200 KHz 200 KHz 200 KHz Time 25
  26. 26. 3G – Code Division Multiple Access Spread spectrum modulation originally developed for the military resists jamming and many kinds of interference coded modulation hidden from those w/o the code All users share same (large) block of spectrum one for one frequency reuse; soft handoffs possible All 3G cellular standards based on CDMA CDMA2000, W-CDMA and TD-SCDMA 26
  27. 27. 4G Modulation – OFDM/OFDMA Orthogonal Frequency Division Multiplexing Optimization in time, frequency and code OFDM deployed in 802.11a & 802.11g Increasing Wi-Fi capacity from 11 Mbps to 54 Mbps Orthogonal Frequency Division Multiple Access OFDM plus statistical multiplexing of users OFDMA used in both WiMAX & LTE 27
  28. 28. OFDM Many closely-spaced sub-carriers, chosen to be orthogonal, thus eliminating inter-carrier interference 28
  29. 29. OFDM Many closely-spaced sub-carriers, chosen to be orthogonal, thus eliminating inter-carrier interference Varies bits per sub-carrier based on instantaneous received power 29
  30. 30. Statistical Multiplexing (in OFDMA) Dynamically allocate user data to sub-carriers based on instantaneous data rates and varying sub-carrier capacities Highly efficient use of spectrum Robust against fading, e.g. mobile operation 30
  31. 31. 4G Technology – SC-FDMA Single carrier multiple access Used for LTE uplinks Being considered for 802.16m uplink Similar structure and performance to OFDMA Single carrier modulation with DFT-spread orthogonal frequency multiplexing and FD equalization Lower Peak to Average Power Ratio (PAPR) Improves cell-edge performance Transmit efficiency conserves handset battery life 31
  32. 32. 4G Technology - MIMO 2x3 TX RX Multiple Input Multiple Output Spatial Multiplexing: Data is organized in spatial streams that are transmitted simultaneously “N x M MIMO” ( e.g. “4x4”, “2x2”, “2x3”) N transmit antennas M receive antennas N x M paths 32
  33. 33. 4G Technology - MIMO Multiple paths improve link reliability and increase spectral efficiency (bps per Hz), range and directionality 33
  34. 34. Indoor MIMO Multipath Channel Multipath reflections come in “clusters” Reflector Moving reflector Reflections in a cluster Rx arrive at a receiver all from the same general direction Wall Direct ray Statistics of clusters are key to MIMO system Reflector operation Tx 802.11n developed 6 models: A through F Source: Fanny Mlinarsky, Octoscope 34
  35. 35. Municipal Multipath Environment Source: Fanny Mlinarsky, Octoscope 35
  36. 36. Outdoor Multipath Environment Base Station picocell radius: r < 100 m micro: 100 m < r < 1 000 m macro: r > 1 000 m One or two dominant paths in outdoor environments – fewer paths and less scattering than indoors Source: Fanny Mlinarsky, Octoscope 36
  37. 37. Spectrum Abundance Original thinking was wrong More transmitters, alternate paths, motion – all serve to increase capacity More info receiver has about environment the better it can do at extracting the desired signal MIMO key to 3.5G, 4G 4G will be followed by 5G, 6G and so on! New RF, new antenna technology, new networking (meshes), … 37
  38. 38. The Ultimate Metric: bps per Hertz per acre per watt 30–50 mi. 38
  39. 39. The Ultimate Metric: bps per Hertz per acre per watt 30–50 mi. 2 7 3 5 2 1 6 3 4 1 6 2 7 4 5 2 7 3 5 1 6 3 4 1 2 7 5 39
  40. 40. The Ultimate Metric: bps per Hertz per acre per watt 30–50 mi. 2 7 3 5 2 1 6 3 4 1 6 2 7 4 5 2 7 3 5 1 6 3 4 1 2 7 5 40
  41. 41. Other myths Auctions drive efficient use of spectrum 41
  42. 42. Other myths Auctions drive efficient use of spectrum And yet more innovation in WiFi than in all the 2G, 3G, 4G cellular bands OFDM, MIMO – WiFi leads, cellular follows 42
  43. 43. History of IEEE 802.11 1985: FCC authorizes spread spectrum in ISM bands: 900 MHz, 2.4 GHz, 5 GHz 1990: IEEE begins work on 802.11 1994: 2.4 GHz products ship 1997: 802.11 standard approved 1997: FCC authorizes the UNII Band – more @ 5 GHz 1999: 802.11a, b ratified 802.11 pioneered commercial 2002: FCC allows new modulations deployment of OFDM and MIMO – key wireless signaling 2003: 802.11g ratified technologies today 2007: 802.11n draft 2 products certified by the Wi-Fi Alliance Source: Fanny Mlinarsky, Octoscope 43
  44. 44. Other myths Utilization requires massive investments E.g. spectrum purchase; network buildout 44
  45. 45. Other myths Utilization requires massive investments E.g. spectrum purchase; network buildout But in license-exempt bands Access is free Radios are purchased by individuals Arguably, greater economic value per Hz created by commerce in “free spectrum” 45
  46. 46. TVWS – Beach-front Property? Optimum antenna length a multiple of ¼ wavelength 3.3 feet for 70 MHz 4” for 700 MHz 1” for 2.4 GHz Longer antennas gather more energy, but difficult for handheld devices 46
  47. 47. Antenna Fresnel Zone r r = radius in feet D = distance in miles D f = frequency in GHz Fresnel zone is the shape of Example: D = 0.5 mile electromagnetic signal and is a function r = 30 feet for 700 MHz of frequency r = 16 feet for 2.4 GHz r = 10 feet for 5.8 GHz Constricting the Fresnel zone introduces attenuation and signal distortion Source: Fanny Mlinarsky, Octoscope 47
  48. 48. Building façade variations Lower frequencies experience less attenuation through building materials But primary problem is multiple paths! Differential absorption in windows, wall sections Shorter wavelengths refracted at window edge introduce multiple paths Fresnel zone constrictions introduce attenuation 48
  49. 49. MiMO favors higher bands Shorter wavelengths – smaller antennas No significant atmospheric absorption below 10 GHz Water vapor, CO2 an issue above 10 GHz Future “beach front” spectrum may be: 3 GHz – 10 GHz 49
  50. 50. 802.11y and shared use 2005: FCC releases rules for shared use & “lite licensing” in 3650-3700 MHz band No interference with existing users; geographic database; listen-before-talk License-exempt stations under positive control of a licensed station’s beacon 2008: 802.11y standard approved Rich set of standard protocols targets 3650 band, but applicable to any form of shared use or secondary use 50
  51. 51. 802.11y Contention-based protocol Enhances 802.11 carrier sense and energy detection Extended channel switch announcement Access point tells stations to switch channels Dependent station enablement Licensed station handles geographic databases and other rules on behalf of the dependent stations 51
  52. 52. Spectrum policy Today all spectrum is regulated (by the FCC or NTIA), but Regulation limits technology deployment Regulation or policy change takes years Incumbents play policy game very well Startups have limited runways Investors don’t like regulatory uncertainty FCC in the business of regulating “speech” 52
  53. 53. Spectrum vs. printing presses Supreme Court lenient on spectrum regulation because spectrum is “unusually scarce” Prof. Stuart Minor Benjamin, Duke University The Court has never confronted an allegation that government actions resulted in unused or underused spectrum, ... Government limits on the number of printing presses almost assuredly would be subject to heightened scrutiny and would not survive such scrutiny. 53
  54. 54. Prospects for Change Substantial vested interests Broadcasters, cellular operators, many other existing spectrum owners Overwhelming success of WiFi, Bluetooth Commercial successes new interests Intel, Google, Microsoft, Apple Rural wireless ISPs Frequently leverage unlicensed technology Get attention in Congress 54
  55. 55. Gaining access to spectrum “License-exempt” began in “junk” bands ISM (900 MHz, 2.4 GHz) Extended into UNII (5 GHz) and 60 GHz 55
  56. 56. Gaining access to spectrum “License-exempt” began in “junk” bands ISM (900 MHz, 2.4 GHz) Extended into UNII (5 GHz) and 60 GHz Underlays – Low power (below licensees) “Ultra Wideband” in 3.1–10.6 GHz 56
  57. 57. Gaining access to spectrum “License-exempt” began in “junk” bands ISM (900 MHz, 2.4 GHz) Extended into UNII (5 GHz) and 60 GHz Underlays – Low power (below licensees) “Ultra Wideband” in 3.1–10.6 GHz Shared use with “lite-licensing” 3650-3700 MHz ; license-exempt based on listen-before-talk, location & licensed beacon Managed by 802.11y protocols from IEEE 57
  58. 58. Secondary Use TV White Spaces Multi-year battle vs. strong vested interests Favorable FCC decision – Nov. 2008 Tight restrictions may ease over time, based on new technology and actual field experience Prospect for additional bands? More access at 4.9 & 5 GHz? potentially w/802.11y IMT-Advanced candidate bands (2300-2400, 2700- 2900, 3400-4200, and 4400-5000 MHz) will take years to clear but could be used now under 802.11y 58
  59. 59. Secondary Use TV White Spaces Multi-year battle vs. strong vested interests Favorable FCC decision – Nov. 2008 Tight restrictions may ease over time, based on new technology and actual field experience Prospect for additional bands? More access at 4.9 & 5 GHz? potentially w/802.11y IMT-Advanced candidate bands (2300-2400, 2700- 2900, 3400-4200, and 4400-5000 MHz) will take years to clear but could be used now under 802.11y 59
  60. 60. Open spectrum Today’s regulation inhibits innovation Inhibits communication & freedom of speech Technology has outrun today’s regulation Decades of further innovation ahead “Secondary use” the best path forward 60
  61. 61. Thank You Brough Turner broughturner@gmail.com rbt@ashtonbrooke.com

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