Open Spectrum - Physics, Engineering, Commerce and Politics

Open SpectrumPhysics, Engineering, Commerce and Politics

Brough Turner

http://www.broughturner.com

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Open Spectrum

1. Electromagnetic spectrum for which there are no licensing requirementsE.g., Visible light, 400-790 THz

2. “A movement to get the government to provide more unlicensed spectrum”(Wikipedia, 5/2009)

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Open Spectrum

1. Electromagnetic spectrum for which there are no licensing requirementsE.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

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How could this work?

� Noise

� Interference

� Chaos … !

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How could this work?

� Noise

� Interference

� Chaos … !

� Receiver performance is the critical issue…

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Visible light analogy

Our vision system (eyes + visual cortex) = extremely efficient 400-790 THz receiver

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Visible light analogy

Our vision system (eyes + visual cortex) = extremely efficient 400-790 THz receiver

� The product of years of evolution!

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Spatial discrimination

� For Humans:~ 1/60th of a degree

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Enormous knowledge base

� Detailed catalog of the characteristics of most potential visible light sources

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Leveraging source motion

to increase received information …

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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

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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, JagdishChandra Bose and others, demonstrate forms of wireless communications

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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

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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

Crystal

Tuned RF

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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

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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

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Radio Spectrum Occupancy

As measured by Shared Spectrum Company and the

University of Kansas Center for Research for the

NSF National Radio Network Research Testbed (NRNRT)

Urban areas, 30 MHz to 3 GHz. Above 3 GHz mostly vacant.

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Radio Spectrum Occupancy

As measured by Shared Spectrum Company and the

University of Kansas Center for Research for the

NSF National Radio Network Research Testbed (NRNRT)

Urban areas, 30 MHz to 3 GHz. Above 3 GHz mostly vacant.

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New York City

Unusually heavy communications during Republican National Convention

August 30 to September 3, 2004 brought spectrum occupancy up to 13%.

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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…

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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.

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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

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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)

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1G – Separate Frequencies

30 KHz

30 KHz

30 KHz

30 KHz

30 KHz

30 KHz

30 KHz

30 KHz

Frequency

FDMA - Frequency Division Multiple Access

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2G – Time Division Multiple Access

Frequency

Time

200 KHz

200 KHz

200 KHz

200 KHz

One timeslot = 0.577 ms One TDMA frame = 8 timeslots

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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

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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

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OFDM

� Many closely-spaced sub-carriers, chosen to be orthogonal, thus eliminating inter-carrier interference

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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

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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

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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

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4G Technology - MIMO

� 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

TXTX RXRX

2x3

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4G Technology - MIMO

� Multiple paths improve link reliability and increase spectral efficiency (bps per Hz), range and directionality

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Indoor MIMO Multipath Channel

� Multipath reflections come in “clusters”

� Reflections in a cluster arrive at a receiver all from the same general direction

� Statistics of clusters are key to MIMO system operation

� 802.11n developed 6 models: A through F

Wall

Reflector

Moving reflector

Direct ray

Tx

Rx

Reflector

Source: Fanny Mlinarsky, Octoscope

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Municipal Multipath Environment


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Outdoor Multipath Environment

� One or two dominant paths in outdoor environments – fewer paths and less scattering than indoors

Base Station

picocell radius: r < 100 m

micro: 100 m < r < 1 000 m

macro: r > 1 000 m


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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), …

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The Ultimate Metric:bps per Hertz per acre per watt

30–50 mi.

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572

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30–50 mi.

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30–50 mi.

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Other myths


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Other myths


� And yet more innovation in WiFi than in all the 2G, 3G, 4G cellular bands

� OFDM, MIMO – WiFi leads, cellular follows

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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

� 2002: FCC allows new modulations

� 2003: 802.11g ratified

� 2007: 802.11n draft 2 products certified by the Wi-Fi Alliance

802.11 pioneered commercial 802.11 pioneered commercial

deployment of OFDM and deployment of OFDM and

MIMO MIMO –– key wireless signaling key wireless signaling

technologies todaytechnologies today


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Other myths


� E.g. spectrum purchase; network buildout

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Other myths


� 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”

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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

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Antenna Fresnel Zone

� Fresnel zone is the shape of electromagnetic signal and is a function of frequency

� Constricting the Fresnel zone introduces attenuation and signal distortion

r = radius in feet

D = distance in miles

f = frequency in GHzD

Example: D = 0.5 mile

r = 30 feet for 700 MHz

r = 16 feet for 2.4 GHz

r = 10 feet for 5.8 GHz

r


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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

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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

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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

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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

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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”

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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.

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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

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Gaining access to spectrum

� “License-exempt” began in “junk” bands

� ISM (900 MHz, 2.4 GHz)

� Extended into UNII (5 GHz) and 60 GHz

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� “License-exempt” began in “junk” bands

� ISM (900 MHz, 2.4 GHz)


� Underlays – Low power (below licensees)

� “Ultra Wideband” in 3.1–10.6 GHz

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� “License-exempt” began in “junk” bands� ISM (900 MHz, 2.4 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

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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

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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

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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

Thank You

Brough Turner

[email protected]

[email protected]