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Defending Our Spectrum:

What Do You Mean When You Say

You’ve “Used” Spectrum

Air Force Flight Test Center

Charles H. Jones, PhD

812TSS/ENTI

chjones@edwards.af.mil

I n t e g r i t y - S e r v i c e - E x c e l l e n c e

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Outline

• Spectrum

– Overviewed

– Example Propagation

– Two Definitions of “Use”

• Legal Allocation

– Licensed and Scheduled

• Dimensional Separation

• On-Demand Buffering

• Misc Comments

• Summary and Conclusion

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Defending Our Spectrum

• Over the last several years the T&E

community has been asked to provide

spectrum “usage” data

• Part of the response has been based on data

from the Interrange Frequency Deconfliction

System (IFDS)

– This data captures when data was “scheduled”

– We’ve been asked what our “real” usage is

• This presentation discusses why “scheduled”

usage is “real” usage

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Spectrum

• Radio Frequencies (RF)

– Electromagnetic waves from about 3 Hz to 300

GHz propagating through time and space.

– Commonly called “wireless communication”

• Dimensions of Spectrum

– Three of Space

– Time

– Frequency

– Power

– Polarization

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First Definition of “Use”

“Spectrum is used if there are

electromagnetic waves propagating

through a particular geographic

location at a particular time.”

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First Definition of “Use”

“Spectrum is used if there are

electromagnetic waves propagating

through a particular geographic

location at a particular time.”

It is the intent of this presentation to convince

people that this is a naïve definition.

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Omnidirectional Propagation

• Consider a standard FM Radio

Station with a dipole antenna

– Ideal radiation pattern emits

energy in all horizontal

directions

• Consider a standard airborne

telemetry dual antenna

transmission pattern

– Ideal radiation pattern is

spherical about the moving

platform

Antenna Patterns

Antenna Pattern “slice” in the azimuth plane

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Non-Ideal Propagation

• The “porcupine” composite antenna shape is

due to difference in amplitude and phase of

the signals being transmitted between the top

and bottom antennas

• The edge of a radio station pattern is

amorphous due to geography and multipath

that interfere with the radial propagation

• Transmission power and receiver sensitivity

affect distance

• The “frequency” is actually the center

frequency in a band of contiguous

frequencies

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What Spectrum is “Used”?

• Do the non-lobe portions of the antenna

pattern represent spectrum use?

– There is no, or little, electromagnetic energy

propagating through those portions of space.

• At what distance do we say that a radio

station is no longer using the spectrum in its

geographic vicinity?

The point here is that even when doing a simple

spatial analysis, it is not clear what “use” is in

terms of RF transmission.

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Second Definition of “Use”

“Use” is “Denial to Others”

But there are many legitimate reasons for

denying use to others even when no energy is

being propagated.

Propagating energy through portions of

the spectrum is a primary method of

denying use to others

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Legal Allocation

• Spectrum is legally allocated for use to

individuals or organizations through a

complex, often political, process.

• The U.N. Treaty created Radio Bureau of the International Telecommunications Union (ITU-R) establishes international radio regulations which are then used as the basis for national level allocations

– Meets at the World Radiocommunication Conference (WRC) every 3 years.

The International Process

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United

Nations

International

Telecommunications

Union

DoD FAA Non-Federal

Users

etc National

Telecommunications

Delegates

US State

Department

FCC US DOC

Federal Users

Regional Organizations

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National Level Allocation

• After the ITU-R process is over, then the

individual nations make more detailed

allocations.

The National Process

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Federal Communications Commission

FCC Commissioners (5)

Congress

Asstnt Sctry of Commerce for Comm and Information

(Administrator, NTIA)

Department of Commerce

National Telecommunications &

Information Administration

Interdepartment Radio Advisory Committee

President

FCC Bureaus

•Non-Federal Users •Commercial •State & local government •NGOs •Private individuals

Participation/ License Applications

Licenses

President appoints

All Federal Users

A

s

s

i

g

n

m

e

n

t

s

Coordination

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U.S. Spectrum Allocation

• Which leads to the following chart

• (Ovals added to point out some of the Mobile

Telemetry Bands)

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L-Band S-Band

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Assignments and Licenses

• This trickles down to assignments of use of

particular frequencies at particular times by

particular organizations.

– This assignment is what T&E Frequency

Managers do.

– Commercial users get licenses. The spectrum

auctioned off in recent years is via licenses.

• When spectrum is auctioned off and

“repurposed” it changes the words on the

previous chart.

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No Obligation

• Many licenses and assignments contain no

legal obligation to transmit.

Legal ownership is denial to

others without necessarily

transmitting.

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Business

• In 2006, SpectrumCo LLC, (Comcast, Time

Warner, Cox, Advance/Newhouse and Sprint

Nextel), won 137 wireless spectrum licenses

for $2.37 billion in the FCC’s auction

– Verizon is trying to buy these for $3.6 billion.

– For 6 years there’s been no transmission.

• TV broadcasters “white space” is another

example of spectrum with no transmission

over a long period of time.

Business decisions can lead to denial to

others without necessarily transmitting.

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Scheduling

• At the bottom of this legal process, T&E

Frequency Managers schedule spectrum by

assigning contiguous blocks of spectrum to

particular test programs.

• These assignments can be thought of as

rectangles in the time/frequency grid.

• Due to logistical reasons it is not always

possible to transmit during the entire time

scheduled.

Scheduling is denial to others.

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Time/Frequency Grid

2200

2205

2210

2215

2220

2225

2230

2235

2240

2245 Scheduled Mission

2250

2255

2260

2265

2270

2275

2280

2285

2290

0:0

0

1:0

0

2:0

0

3:0

0

4:0

0

5:0

0

6:0

0

7:0

0

8:0

0

9:0

0

10:0

0

11:0

0

12:0

0

13:0

0

Time (Hours)

Fre

qu

en

cy (

MH

z)

X

Y

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Dimensional Separation

• To avoid interference, transmission signals

are separated in one or more dimensions.

– This evolves from the physics of transmission

techniques

• This separation includes purposely not

transmitting in portions of the spectrum

between the separated signals.

– In some cases there may be RF “leakage” or

spurious transmissions into the separation

zones, which is why the zones are created

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PCM/FM Separation

-70

-60

-50

-40

-30

-20

-10

0

1435 1455 1475 1495 1515 1535

dBc

Frequency (MHz)

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TDMA Separation

• Time Division Multiple Access (TDMA)

provides time slots dedicated to particular

users.

– Because of timing inaccuracies, guard bands

(small time slices) are created between the

assigned time slots

– iNET will be using TDMA

User

1

G

B

User

2

G

B

User

1

G

B

User

2

…

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Dimensions

• Spatial separation is near universal

• Frequency separation is common

– There are no even decimals on the FM dial

• Scheduled telemetry separates in space,

frequency, and time

• Separation via polarization is rare, but is used

• Spread spectrum techniques, such as CDMA

used by cell phone companies, separate in

the dimension of power

Use of separation zones is denial to others.

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Spread Spectrum and CDMA

• In a CDMA system the same frequency can be

used in every cell, because channelization is

done using pseudo-random codes

– The power is spread out over more frequencies

than necessary

– This allows multiple people to use the same

frequency at the same time and location

• This could be considered Power Division

Multiple Access since each user is allowed a

certain amount of power on a common

frequency

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CDMA and Pseudorandom Codes

• XOR Data Signal and Pseudorandom Code to

Transmission Signal.

• XOR Transmitted Signal and Pseudorandom

Code to get the Data Signal.

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On-Demand Buffering

• Cell phones use spectrum on an on-demand

basis, coming and going on individual whim.

– CDMA lends itself to this type of access

– WiFi and garage door openers are also

examples

• There must be a constant surplus of spectrum

in order to accommodate on-demand service

• Cell phone frequencies are used almost

continuously but rarely, if ever, at full capacity

– There is transmission over frequencies but not

to a maximal power limit

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T&E and Cell Phones

A Comparison

• Scheduled spectrum for T&E is a form of on-

demand buffering.

– A best effort is made to schedule exactly when

spectrum will be used

– The logistical difficulties of coordinating all

assets for a test make it virtually impossible to

be transmitting exactly when scheduled

T&E buffers in the dimension of time

Cell Phones buffer in the dimension of power

On-demand buffering is denial to others.

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Efficiency

• Every method and application of RF

transmission can be questioned as to their

efficiency.

– 4G is more efficient than 3G

– SOQPSK is more efficient than PCM/FM

– Probably even SpectrumCo would not claim

they made efficient use of their spectrum

Inefficient transmission is denial to others.

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Other Examples

• The National Radio Quiet Zone around Green

Bank National Observatory (NTIA Manual

8.3.9).

– Any transmission in any frequency in this area

interferes with Radio Astronomy

• Some national borders have frequency buffer

zones for cross border non-interference

– There is one along the U.S. – Mexican border

• Radar is not a continuous transmission

• Spectrum can be fragmented due to

difficulties of scheduling

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Standardization Effort

• The Range Commander’s Council (RCC)

Frequency Manager’s Group (FMG) has

established a formal Task to develop a

standard on frequency management metrics.

• Part of this will include formally defining

spectrum “use” within the context of T&E.

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Summary

• Just because there is no electromagnetic

energy flowing through time and space, does

not mean that that spectrum is not being

“used”

– Legal authority to use

– Impacts of business decisions

– Dimensional separation

– On-demand buffering

– Other reasons

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Conclusion

• In order to define and quantify spectrum

“use” it is necessary to look at many factors

– Functional requirements

– Physics and technology used

– Business incentives

– Legal realities

• A one-size-fits-all definition is not practical

• It seems reasonable to start with

then develop application specific refinements

“Use” is “Denial to Others”