Open Spectrum
Physics, Engineering, Commerce and Politics
Brough Turner
http://www.broughturner.com

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

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

How could this work?
Noise
Interference
Chaos … !
4

How could this work?
Noise
Interference
Chaos … !
Receiver performance is the
critical issue…
5

Visible light analogy
Our vision system
(eyes + visual cortex)
= extremely efficient
400-790 THz receiver
6

Visible light analogy
Our vision system
(eyes + visual cortex)
= extremely efficient
400-790 THz receiver
The product of years
of evolution!
7

Spatial discrimination
For Humans:
~ 1/60th of a degree
8

Enormous knowledge base
Detailed catalog of the characteristics of most
potential visible light sources
9

Leveraging source motion
to increase received information …
10

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

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

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

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

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

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

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

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

New York City
Unusually heavy communications during Republican National Convention
August 30 to September 3, 2004 brought spectrum occupancy up to 13%.
19

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

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

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

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

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

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

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

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

OFDM
Many closely-spaced sub-carriers, chosen to be
orthogonal, thus eliminating inter-carrier
interference
28

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

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

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

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

4G Technology - MIMO
Multiple paths improve link reliability and
increase spectral efficiency (bps per Hz),
range and directionality
33

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

Municipal Multipath Environment
Source: Fanny Mlinarsky, Octoscope 35

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

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

The Ultimate Metric:
bps per Hertz per acre per watt
30–50 mi.
38

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

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

Other myths
Auctions drive efficient use of spectrum
41

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

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

Other myths
Utilization requires massive investments
E.g. spectrum purchase; network buildout
44

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Thank You
Brough Turner
broughturner@gmail.com
rbt@ashtonbrooke.com