**Federal Communications Commission**

**Spectrum Policy Task Force**

**Report of the Interference**

**Protection Working Group**

November 15, 2002

**Interference Protection**

**Working Group**

Keith Larson, Chair

Lisa Cacciatore Susan Crawford

Thomas Eng Ed Jacobs

Jay Jackson Joe Levin

Bill Luther Mike Marcus

Tim Maguire Bob Nelson

Sankar Persaud Ron Repasi

Bruce Romano Tom Stanley

John Williams John Wong

[Disclaimer]{.underline}

The findings and recommendations contained in this Report are those of
the Interference Protection Working Group members, and do not
necessarily reflect the views of the Commission, Commission management,
or the Spectrum Policy Task Force.

[Table of Contents]{.underline}

Page

I.  Introduction 1

II. Future Challenges Warranting Consideration of New

    Interference Protection Paradigms 2

III. Nature of Recommendations 6

IV. Quantification of Acceptable Interference Levels 6

    A.  Current regulations and statutes 6

    B.  Views expressed in the public record 8

    C.  Conclusions 11

        1\. There is a need to quantify acceptable levels of actual

        interference 11

        2\. As a long-term strategy, the Commission should consider

        use of the "Interference Temperature" metric as a means of

        quantifying and managing interference 12

    D.  Recommendations 15

V.  Transmitter Enhancement for Interference Control 15

    A.  Current regulations 15

    B.  Views expressed in the public record 16

    C.  Conclusions 17

        1\. The Commission should make clear that its spectrum

        policies are based on "interference-limited" rather than

        "ambient noise-limited" environments 17

        2\. The Commission should consider extended use of

        environmental sensing and control technology,

        including technology that could be used in conjunction with the
        interference temperature metric 17

        3\. Interference management could be enhanced to the extent

        the strengths of emitter-generated signals are spatially

        uniform over nominal signal ranges 19

        4\. Effective interference mitigation could also be advanced

        through use of modern transmitter output filtering and

        related digital signal processing capabilities 19

        D. Recommendations 20

        VI\. Allocating Spectrum to Radiocommunications Services that
        are

        Grouped Together by Their Similar Technical Characteristics 20

        A. International Telecommunications Union (ITU) and FCC

        Spectrum Allocations Processes 20

        1\. International approach to spectrum allocations 21

        2\. Domestic approach to spectrum allocations 22

        B. Findings and Conclusions 23

        C. Recommendations 24

        VII\. Receiver Standards/Guidelines 24

        A. Background 24

        B. Discussion 25

        C. Recommendations 27

        VIII\. Communications with the Public on Interference Issues 29

        A. Introduction 29

        B. Discussion 29

        1\. Harmonizing Interference Language (Technical Terms and
        Units) 29

        2\. Ensuring Consistent and Appropriate Use of Interference

        Language (Non-Technical Qualifiers) 31

        3\. Facilitating Access to the FCC's Rules on Interference 33

        4\. Facilitating Access to Successful Practices for Interference

        Resolution 35

        C. Recommendations 37

        IX\. Acknowledgements 38

        Appendix A -- Allocating Spectrum to Radiocommunication Services
        that

        are Grouped Together by Their Similar Technical Characteristics
        39

        **I.** **Introduction**

The Interference Protection Working Group ("Working Group") of the
Commission's Spectrum Policy Task Force is pleased to present its
findings and recommendations.[^1] The Working Group was established to
assist the Task Force identify and address spectrum policy issues and
challenges involving interference protection. To that end, it reviewed
comments filed by parties responding to the Task Force's Public Notice
of June 6, 2002, particularly comments relating to interference
protection (ET-Docket No. 02-135). On August 2, 2002, it participated in
a public workshop on Interference Protection ("Interference Protection
Workshop") that addressed "Interference Challenges, Advanced Technology
and A Better Process." [^2] This report summarizes the Working Group's
analyses and presents its findings and recommendations. Some
recommendations are intended to enhance interference management in the
near-term, while others address longer-term challenges.

Interference protection is central to effective spectrum management.
Electromagnetic interference plays a pivotal role in the design and
operation of telecommunications equipment and systems, and related
costs. In today's radio frequency environment, interference generally
limits the useable range or technical effectiveness of communications
signals. Its effects on spectrum users and service providers range from
annoyance, to economic harm, to threats to the safety of life and
property. Interference protection is fundamentally related to spectrum
rights and obligations. It also affects the efficiency of spectrum use.
Regulatory interference protection standards that are too lax could
prove detrimental to existing or planned services. Conversely, standards
that are overly protective could prevent or impede the introduction of
new services and technologies.

Interference protection has always been a core responsibility of the
Commission. Section 303(f) of the Communications Act of 1934 as Amended
directs the Commission to make regulations it deems necessary to prevent
interference between stations, as the public interest shall require.[^3]
The Commission's strategic plan for the years 2003-2008 includes as a
spectrum-related objective the "vigorous protection against harmful
interference\..."[^4]

Interference protection is addressed in virtually all of the
Commission-regulated services that use the radio spectrum. Historically,
various approaches have evolved for managing interference. Typically,
FCC rules and policies have been tailored to the expected uses and
technical characteristics of particular services at the time of their
creation. Most services have common elements aimed at interference
protection such as limits on in-band power and out-of-band emissions.
For many wireless and satellite services, the potential for interference
is evaluated by outside frequency coordinators. Negotiated interference
agreements among affected parties are also permitted in numerous
services.

The record in this proceeding indicates that many of the Commission's
rules and processes for managing interference have been generally
successful. In recent years, few instances of systemic interference have
been directly linked to Commission allocation or licensing
processes.[^5] Industry sources suggest that formal and informal
frequency coordination processes have been effective.[^6] The Commission
has implemented new services by means of a variety of *ad hoc*
approaches. Existing services have been able to grow and add new
features resulting from the flexibility for licensees to make technical
and operational changes.

**II.** **Future Challenges Warranting Consideration of New Interference
Protection Paradigms**

As reflected by commenters and workshop participants, there are rising
concerns that future spectrum demands will challenge current
interference management paradigms. First, many radio communications
services have grown substantially in recent years. For instance, Stratex
Networks, Inc. comments that the 6, 11, 18 & 23 GHz bands in the Common
Carrier and Operational Fixed Services in New York City, Los Angeles,
Chicago, San Francisco, Philadelphia, Boston and Washington, D.C. have
exhibited growth rates ranging from 15 percent to 900 percent.[^7] The
median growth rate for these cities and bands is 150%. Sprint comments
that in the six years since they and other PCS licensees entered the
market, "The number of mobile customers has nearly quadrupled, from 33.8
million in December 1995 to 128.4 million in December 2001.[^8]
According to Sprint, 58 percent of all Americans 12 and older now
subscribe to a mobile service.

A second challenge is presented by the explosive consumer demand for RF
devices. The comments of the Consumer Electronics Association ("CEA")
illustrate the large variety of very low power small-range RF devices in
common use, including garage and car door openers, baby monitors, family
radios, wireless headphones, and wireless Internet access devices using
Wi-Fi™ or Bluetooth™ technologies.[^9] According to CEA, the most common
wireless device is the cordless phone, with 2001 sales of almost 36
million units.[^10] By the end of the year more than 10 million
computers are expected to use wireless networking technology and the
wireless LAN industry is expected to reach a value of \$5.2 billion by
2005.[^11] CEA forecasts that, "As people become more mobile, moving
from the office to the home, to the coffee shop, or to the airport,
wireless networking application will become increasingly
pervasive."[^12]

The cumulative impact of the increasing volume and density of radio
devices on the RF environment will challenge the Commission's current
approaches to interference management.[^13] Dr. Paul Steffes of Georgia
Tech University, who is the past Chair of the Committee on Radio
Frequencies, represented the interests of radio astronomy at the FCC's
Interference Protection Workshop. He indicated that the radio astronomy
community, which pays attention to the growth of spectrum use, has
observed an explosion in spectrum use around the passive services.
According to Dr. Steffes, "Just because we know the rate of growth is so
significant, the minimal pressures now will become major pressures
within the next four years."[^14]

The National Aeronautics and Space Administration ("NASA") also comments
on the burdens placed on the ability to manage the spectrum, due in part
to the "tremendous" growth in personal communications devices and the
increased congestion over the past ten years or so.[^15] According to
NASA, "All the best allocation and assignment processes which maximize
the use of the RF spectrum are to no avail if the RF environment becomes
corrupted and interference becomes 'harmful' to radio services depending
on that spectrum for fulfillment of mission goals."[^16]

Cingular Wireless LLC reports on some of the activities and findings of
the FCC's Technological Advisory Council ("TAC")[^17] that relate to the
state of the RF noise environment.[^18] Among the TAC findings cited by
Cingular are the following:[^19]

> \[There\] "could be a very serious emerging problem caused by the
> explosive growth of both intentional and unintentional radio sources.
> The future could be very different from what we might expect from past
> experience. The key to getting our hands around this issue will be a
> good set of models for both intentional and unintentional radiators
> which can then be used to predict the evolution of the noise
> background." *Second Meeting Report of the TAC at 1, 9.*
>
> "\[W\]e could potentially be entering a period of rapid degradation of
> the noise environment. Such degradation would reduce our ability to
> meet the communications needs of the country. The principal negative
> impacts are likely to be reductions in the performance or reliability
> of wireless systems or increases in their costs." *Fourth Meeting
> Report of the TAC at 23 (Annex 4).*

Cingular Wireless comments that the Commission accepted TAC
recommendation to undertake a multi-part study of the noise floor. Two
of the seven findings of the first step of this study are given below:
[^20]

> "Until \[noise floor\] information is organized and analyzed, the FCC
> will not have a firm basis for deciding whether current noise
> standards are too tight, too loose, or maybe even just right." *Sixth
> Meeting Report of the TAC at 9.*
>
> "As we enter the new millennium, new noise sources are being developed
> (e.g., ultrawideband devices), and other electronic devices continue
> to proliferate as fast as the technology and the regulatory process
> will allow. Many of these other individual sources of "noise" may meet
> the current Federal Communications Commission (FCC) rules, but in
> great numbers they may negatively affect the overall electromagnetic
> noise environment. *Sixth Meeting Report of the TAC at 25.*

A third interference management challenge is presented by the migration
from a relatively small number of waveforms to widely varying signal
architectures and modulation types for voice, video, data and
interactive services. Even single classes of users are now using a wide
variety of digital technologies. Cingular Wireless notes that CMRS
licensees "commonly use analog AMPS technology and four different
digital technologies (TDMA, CDMA, GSM and iDEN)" and that other more
advanced technologies will follow.[^21]

Under the current interference management approaches, tension is likely
to arise between the competing Commission objectives of flexible service
offering and well-defined protection rights.[^22] If flexible use is to
be fully realized, it will become increasingly difficult to
pre-determine interference ranges. Worst-case propagation analysis may
not always be applicable. Laboratory testing to demonstrate the spectrum
sharing compatibility of two or more waveforms will become increasing
complicated, time consuming and costly. [^23] In Dr. Steffe's view:

> "The problem, of course, for the future is complexity. Obviously, the
> number of users and the management of the problem becomes dramatically
> enhanced...we were saying that it's \[consideration of interference\]
> at least a six dimensional problem, meaning spatial, x-y-z, frequency,
> time and waveform, and of course since the wave form can be infinitely
> complicated, you can make it an n-fold problem, which basically has
> more variables than you have numbers."[^24]

Due to the complexity of interference issues and the RF environment,
interference protection solutions may largely be technology driven. As a
fourth challenge, the Commission will need to keep abreast of the
rapidly advancing technology, in order to promote and empower its use.
Due to advances in digital signal processing and antenna technology,
communications systems and devices are becoming more tolerant of
interference through their ability to sense and adapt to the RF
environment. According to Dr. Raymond Pickhotz of George Washington
University, it is important to recognize the impact of different kinds
of interference, "not all of which are bad," on a particular
technology.[^25] Sources of signal impairment in wireless systems
include internal (or self-generated interference), external interference
and various sources of noise. Dr. Pickholtz indicated that in some
systems of cooperative users (e.g., systems that use Code Division
Multiple Access technology), "you can actually exploit the fact that
there's a lot of *a priori* knowledge about the nature of the
interference and either eliminate it or minimize it the point where it's
not very important...\[T\]he concept here is that to the extent that you
can avoid interference and not treat it as it if was noise you can
increase the \[system\] capacity and therefore get more revenue...CDMA
handsets use intersymbol interference to improve performance." [^26] Dr.
Pickholtz added that other types of interference, for example from
external sources, may be similar to thermal noise, which cannot be
mitigated by digital signal processing.

Thus, the Commission will be challenged to understand the rapidly
changing communications technologies and the interactions of diverse
signals. The Commission will also need to keep abreast of advances in
spectrum monitoring and measurement technologies.

### **III.** **Nature of Recommendations**

### 

The Interference Protection Working Group recommends consideration of
the following paradigms to supplement current interference management
approaches, which the Working Group believes will significantly help the
Commission meet its future challenges: Quantification of Acceptable
Interference Levels, Transmitter Enhancement for Interference Control,
Allocating Spectrum to Radiocommunications Services that are Grouped
Together by Their Similar Technical Characteristics, Inclusion of
Receiver Standards/Guidelines (through incentives, mandates, or a
combination of these), and Improved Communications on Interference
Issues with the Public. The Working Group submits it analyses,
conclusions and recommendations for each of these.

**IV.** **Quantification of Acceptable Interference Levels**

**A.** **Current regulations and statutes**

Two key questions raised in the June 6, 2002, Public Notice are whether
the Commission's current definitions of interference need to be changed
and whether more explicit protection from harmful interference should be
provided to incumbent spectrum users.[^27] The Commission's Rules define
four levels of interference:

> *Interference*. The effect of unwanted energy due to one or a
> combination of emissions, radiations, or inductions upon reception in
> a radiocommunication system, manifested by any performance
> degradation, misinterpretation, or loss of information which could be
> extracted in the absence of such unwanted energy.[^28]
>
> *Harmful Interference*. Interference which endangers the functioning
> of a radionavigation service or of other safety services or seriously
> degrades, obstructs, or repeatedly interrupts a radiocommunication
> service operating in accordance with these \[International\] Radio
> Regulations.[^29]
>
> *Permissible Interference*.*  *Observed or predicted *interference*
> which complies with quantitative interference and sharing criteria
> contained in these \[International (FCC)\] Regulations or in ITU-R
> Recommendations or in special agreements as provided for in these
> Regulations.[^30]
>
> *Accepted Interference*. Interference at a higher level than defined
> as permissible interference and which has been agreed upon between two
> or more administrations without prejudice to other
> administrations.[^31]

These definitions of interference, which are decades old, are also found
in the international radio regulations. The terms *permissible
interference* and *accepted interference* are used in the international
coordination of frequency assignments between administrations.[^32] The
Commission's service rules for a number of radio services include the
definition of harmful interference given in § 2.1(c).[^33]

The terms *interference* and *harmful interference* also are found in
the Communications Act of 1934 as Amended:

· **Sec. 302 \[47 U.S.C. 302(a)\] Devices which interfere with radio
reception.**

> "(a) The Commission may, consistent with the public interest,
> convenience, and necessity, make reasonable regulations, (1) governing
> the interference potential of devices which in their operation are
> capable of emitting radio frequency energy by radiation, conduction,
> or other means in sufficient degree to cause **harmful interference**
> to radio communications; and (2)..." (emphasis supplied).
>
> · **Sec. 303 \[47 U.S.C. 303\] General powers of the Commission.**
>
> "Except as otherwise provided in this Act, the Commission from time to
> time, as public convenience, interest or necessity requires shall ---
>
> \* \* \* \* \*
>
> \(f\) Make such regulations not inconsistent with law as it may deem
> necessary to prevent **interference** between stations and to carry
> out provisions of the Act: *Provided, however*,... (emphasis
> supplied).
>
> \* \* \* \* \*
>
> \(y\) Have authority to allocate electromagnetic spectrum so as to
> provide flexibility of use, if --
>
> \(1\) such use is consistent with international agreements to which
> the United States is a party;
>
> and

(2) the Commission finds, after notice and an opportunity for public
    comment, that --

> \(A\) such an allocation would be in the public interest;
>
> \(B\) such use would not deter investment in communications services,
> or technology development; and
>
> \(C\) such use would not result in **harmful interference** among
> users." (emphasis supplied).

The means of interference protection vary for different radio services.
The most common elements are limits on transmitted in-band power and
out-of-band emissions. Outside frequency coordination is employed in
many wireless telecommunication and satellite services and in the
broadcast auxiliary services. Negotiated interference agreements are
permitted in many services.

The service rules vary considerably regarding how interference is
quantified, predicted or otherwise managed. Several examples illustrate
the different approaches. Licensees in the PCS and some Private Land
Mobile Services must limit their signal strength to prescribed values
along their geographic boundaries to protect licensees in adjacent
areas. Some land mobile services use minimum station separations
corresponding to different power and antenna height combinations. The
extent of interference protection afforded to analog television
broadcast stations is defined by minimum station separations between
stations assumed to be operating with the maximum allowable combination
of antenna height and power. Power flux density limits are commonly used
as a means of protection in many Satellite services.

The rules for some services prescribe detailed criteria for predicting
interference at protected service locations. For example, the service
populations of digital television stations are protected on the basis of
calculations of desired-to-undesired signal strength ratios at locations
where service is predicted to occur in the absence of interference. The
Multipoint Distribution Service rules prescribe a rigorous interference
methodology for two-way communications systems, based in part on an
assumed statistical distribution of the subscriber locations. The
frequency coordination process for some point-to-point microwave
operations considers harmful interference to occur if a transmitter
would "degrade the threshold of a victim receiver by no more than 1
dB."[^34]

**B.** **Views expressed in the public record**

[Definitions of "interference" and "harmful interference"]{.underline}:
Commenters are divided on the need for new definitions of *interference*
and *harmful interference*. Some favor retaining the current
definitions. The comments of Nortel Networks reflect several of the
reasons given by commenters supporting this position:

> \[the\] "current definitions are generic, and allow appropriate
> interpretation on a case-by-case basis ...More rigid definitions may
> inhibit the industry and stifle innovation... 'Harmful interference'
> is interpreted relative to past performance, and since performance is
> constantly changing, any technical definition would have to change
> constantly, as well"... and "Nortel urges that the Commission maintain
> consistency with international definitions." [^35]

Several commenters point out that the generic definition of "harmful
interference" allows the Commission to interpret its meaning differently
for particular radio services. According to Verizon Wireless, "It is not
the definition of 'harmful interference' that is in need of change but
the way in which the Commission enforces its rules or establishes
policies regarding interference."[^36]

Other commenters urge the Commission to clarify or change the current
definition of *harmful interference*. Sprint contends the current
definition has several weaknesses: it is highly subjective - the terms
"serious degradation" and "repeated interruptions" are not defined and
are open to *ad hoc* interpretation; it does not sufficiently address
the current RF environment and modern technology (i.e., adaptive
capabilities of modern communications systems); and that the definition
is too general.[^37] According to Sprint, "The specific definition of
'harmful interference' should depend on the nature of the victim service
and the function it is intended to serve."[^38] Xtreme Spectrum contends
that the current definition of *harmful interference* causes uncertainty
and suggests that the definition's subjective nature accounted for much
of the controversy in the ultra-wideband proceeding.[^39] As a better
approach, it recommends a system of interference protection based on
quantitative measures of harmful interference (degradation or
interruption) a given service can tolerate.

The Satellite Industry Association ("SIA") comments that harmful
interference is an extreme level and that just because interference does
not rise to this level, it cannot be concluded that the interference is
acceptable to the victim.[^40] According to SIA, attempts to quantify
the level of harmful interference would not be useful. Rather, efforts
should be made to ensure that levels of interference will not result in
service interruption or degradation, a level characterized as
"acceptable" interference -- the level operators would coordinate among
themselves. SIA suggests that, when adopting spectrum sharing criteria,
the Commission use the terms "permissible or acceptable"
interference.[^41]

Steve Baruch expressed a somewhat similar view at the Commission's
Interference Protection Workshop. He indicated that a level of
interference could be harmful or not harmful depending on the victim and
that attempts to quantify *harmful interference* amount to identifying
acceptable or tolerable levels of interference to parties sharing the
spectrum. According to Mr. Baruch, "You can identify objective limits of
what would be tolerable, but not would be harmful."

[Need for more explicit interference protections]{.underline}: As noted,
some parties recommend that more explicit protections be built into the
definitions of interference. Others urge the Commission to give careful
consideration to the condition of the RF noise floor.[^42] According to
Cingular Wireless:

> "...increasing the noise floor by even a few dB may adversely impact
> existing licensed systems and their customers in a number of ways,
> such as: (1) coverage, (2) system capacity, (3) reliability of data
> throughput, and (4) quality of voice service. To overcome these
> effects, licensees may have to reconfigure previously optimized
> systems and deploy additional facilities to regain what the noise
> floor increase erased. Thus, the incumbent's service should be
> considered 'seriously degraded, obstructed, or repeatedly
> interrupted,' constituting harmful interference, as a result of the
> newly authorized spectrum assignment."[^43]

Cingular Wireless also notes that the Commission could set signal
strength limits that would "establish a rebuttable presumption against
interference or noninterference with respect to particular technologies
and services, taking into account industry standards, prevailing noise
levels, receiver characteristics and other factors."[^44]

At the Interference Protection Workshop David Hageman urged a common
approach for measuring interference compliance:

> "I think that if you're going to do something that way, you need to
> have clearly defined measurements. You need to come up with some way
> that the common person out there, the small carrier, can take a
> spectrum analyzer or some common piece of equipment with some standard
> things that they have and say I'll stick this antenna up and I'll make
> this measurement and I'll turn this knob and set that switch and,
> bang, here's my level. And it meets it or it doesn't. And it needs to
> be the same for every one." [^45]

Several commenters recommend that the Commission pay attention to the
cumulative or aggregate effects of interference from multiple RF
emitters.[^46] For example, according to the Association for Maximum
Service Television and the National Association of Broadcasters:

> "The Commission typically conducts an *ad hoc,* case-by-case
> interference analysis and considers the harmful interference caused on
> an incremental basis. Thus, even if each new spectrum use does not
> cause significant interference to existing spectrum users, the
> *cumulative* effect of all the new spectrum uses authorized in recent
> years has degraded the quality of the spectrum for all users."[^47]

As another means of more explicit protection, a commenter suggests that
as spectrum demand increases, incumbent users be required or provided
incentives to migrate to the use of more robust and spectrally efficient
technologies, accompanied by required use interference avoidance and
mitigation techniques.[^48]

Finally, some commenters discuss the need for more explicit protection
in terms of "interference rights"; contending, for example, that
incumbent users should not be subjected to additional unwanted
interference.[^49]

**C.** **Conclusions**

1\. [There is a need to quantify acceptable levels of actual
interference:]{.underline}

The previous section highlighted future challenges to the effectiveness
of the current interference management paradigms, as the Commission
seeks to accommodate the high demand for spectrum-based services and
devices for both licensed and unlicensed services. Approaches such as
predictive modeling, laboratory compatibility testing of signal
waveforms and spectrum use decisions based on knowledge of the local
environment -- standing alone -- will be increasingly strained by the
increasing intensity of spectrum use and the changing nature of the RF
environment, especially in urban areas of the country. The radio
environment will be increasingly characterized by flexible service
offerings with a multitude of signal waveforms and by higher densities
of low power RF emitters with small signal ranges. The cumulative
effects of these devices and other sources of RF energy will raise the
noise floor and could threaten the reliability of existing communication
services.

As a result of these factors, it will not always be possible to
guarantee well-defined interference protection rights based on
comprehensive predictive analyses. Nor will current interference
management approaches inform the Commission of the intensity of spectrum
use or the condition of the RF noise floor as it considers spectrum for
new technologies or to accommodate the growth of existing services.[^50]

The Working Group concludes that the current definitions of interference
in Part 2 of the Commission's Rules adequately address the broad and
changing technical and operational characteristics of the many radio
services. [^51] Rather than change the definitions, the Working Group
recommends that the Commission consider addressing its long-term
interference management and spectrum policy challenges by supplementing
its transmitter-centric approach with a new paradigm based on (1)
real-time measurements of spectrum use and the RF environment and (2)
adaptive responses of transmitters and receivers to these measurements.
As set forth below, maximum acceptable levels of interference could be
established to provide well-defined protection rights to incumbents.
Such threshold levels could also be used as a basis for permitting
additional spectrum access to new RF-based technologies and services.

Commenters and workshop participants indicate that technology for
sensing and reacting to the interference environment is now
available.[^52] For example, according to Sprint, "the IS-95
code-division multiple access ("CDMA") air interface used in PCS and
cellular networks uses transmit power control on both uplink and
downlink transmissions...If the interference at the receiver is
increased, the transmitter will increase its power output to compensate
-- up to a limit." Personal Telecom Tech, Inc. comments that
"Frequency-agile technology via software-defined radio technology can be
used to monitor power in spectrum bands and thus determine where
channels might not be used or not available for licensed services due to
buildout and deployment or environmental or topological considerations."
The next section of the Working Group report discusses how interference
measurements could be combined with adaptive transmitter control
technology to limit interference to within established levels.

2\. [As a long-term strategy, the Commission should consider use of the
"Interference Temperature" metric as a means of quantifying and managing
interference]{.underline}:

As introduced in this report, "interference temperature" is a measure of
the RF power available at a receiving antenna to be delivered to a
receiver -- power generated by other emitters and noise sources. [^53]
More specifically, it is the temperature equivalent of the RF power
available at a receiving antenna per unit bandwidth, measured in units
of ºKelvin.[^54] As conceptualized by the Working Group, the terms
"interference temperature" and "antenna temperature" are
synonymous.[^55] The term "interference temperature" is more descriptive
for interference management. [^56]

Use of the interference temperature concept would be more amenable to an
RF environment having the properties of additive Gaussian white noise;
*i.e.*, with signals having uniform power spectral density over their
frequency bandwidth. For such signals, the received power at the output
terminals of the antenna could be calculated as the product of the
interference temperature, the bandwidth and Boltzman's Constant.[^57]

As illustrated in Figure 1, interference temperature measurements could
be taken at receiver locations throughout the service areas of protected
communications systems, thus estimating the real-time conditions of the
RF environment.

![](media/image1.wmf){width="5.532638888888889in"
height="2.703472222222222in"}

**Figure 1**

Like other representations of radio signals, instantaneous values of
interference temperature would vary with time and, thus, would need to
be treated statistically. The Working Group envisions that interference
"thermometers" could continuously monitor particular frequency bands,
measure and record interference temperature values and compute
appropriate aggregate value(s). These real-time values could govern the
operation of nearby RF emitters. Measurement devices could be designed
with the option to include or exclude the on-channel energy
contributions of particular signals with known characteristics; *e.g.,*
the emissions of users in geographic areas and bands where spectrum is
assigned to licensees for exclusive use.[^58]

The Commission could use the interference temperature metric to set
maximum acceptable levels of interference, thus establishing a "worst
case" environment in which a receiver would operate. Interference
temperature thresholds could thus be used, where appropriate, to define
interference protection rights. Several commenters support capping
interference levels.[^59] Threshold levels could be set for different
bands, geographic regions or services after the Commission has reviewed
the condition of the RF environment.[^60] These levels could serve as
benchmarks to guide engineering tradeoffs for radio equipment and system
designers.[^61]

**D.** **Recommendations**

> · The Working Group recommends that, as a long-term strategy, the
> Commission consider the interference temperature metric for
> quantifying and managing interference, together with established
> "acceptable" levels of interference.
>
> · The Working Group recommends that the Commission promote and hasten
> the transition from analog to digital transmission techniques and, if
> necessary, effect this transition by rule. Digital operations are
> generally more resistant to interference and would enhance use of the
> interference temperature metric.

**V.** **Transmitter Enhancement for Interference Control**

A.  **Current regulations**

The Commission's Rules prescribe upper limits for in-band transmitter
power and out-of-band emissions for the majority of spectrum uses.
Automatic transmitter power control ("ATPC") to ensure transmission of
the minimum power necessary for reliable communications is generally not
required. The rules do provide that all satellite earth stations in the
20/30 GHz band "shall employ uplink adaptive power control or other
methods of fade compensation such that the earth station transmissions
shall be conducted at the power level required to meet the desired link
performance while reducing the level of mutual interference between
networks."[^62] Earth stations in the Fixed Satellite Service operating
in the 13.77 to 13.78 GHz band may use ATPC to increase power to
compensate for rain attenuation.[^63] Additionally, the Commission
recently adopted rules to permit licensees in the radio and television
broadcast auxiliary and cable relay services to use ATPC.[^64]

B.  **Views expressed in the public record**

The record in this proceeding indicates that ATPC and other adaptive
technologies are now in use. At the Interference Protection Workshop,
Dr. Andrew Clegg stated that his company, Cingular Wireless, has
"already deployed power control as tightly as we can..." Sprint comments
that its CDMA PCS and cellular systems use transmitter power control for
uplink and downlink transmissions. [^65] As an alternative to power
control, it comments that wireless local area network standards IEEE
802.11(a) and (b) provide for data rate adaptation, whereby reductions
in the signal to interference ratio due to interference can be
compensated by a reduction in the transmitted data rate.[^66]

Commenters and workshop participants report that advances in cognitive
radios, antennas and signal processing and coding are evolving and may
soon become practical and without the high costs usually associated with
implementing new technologies.[^67] According to Vanu, Inc., a soft-ware
defined radio ("SDR") proponent:

> "SDR will permit devices to alter the signal processing they are
> performing in order to get the best performance for the current
> conditions. For example, under poor signal to noise conditions,
> aggressive forward error correction may be called for. As conditions
> improve, the error correction could be modified in order to get
> improved data rates. Without the flexibility to make these changes
> quickly and inexpensively, the benefits of adaptation for the current
> operating environment could not be realized....SDR will at times be
> helpful in addressing harmful interference issues as quickly and
> efficiently as possible"[^68]

Dr. David Reed offers further perspective on emerging technology:

"\[W\]e must recognize that in the not-too-distant future, all radio
systems will

> be based on digital signal processing, and thus will approach
> 'Cognitive Radio' capability. By cooperatively sensing and
> manipulating their electromagnetic environment, a network of software
> defined radio transceivers can adapt to their physical environment to
> match demand much closer to the capacity achievable by joint action of
> a group of radios."[^69]

HYPRES, Inc., another SDR proponent, describes an automated system to
dynamically monitor broad areas of spectrum and to "pass details of
observed signal characteristics to central controllers for
evaluation."[^70] HYPRES suggests that the Commission consider
implementing a monitoring capability to provide data for spectrum
management. It notes that among the techniques made possible by the
related technology is the "spotting \[of\] interfering emitters to
support adaptive cancellation and/or null steering of adaptive
antennas."[^71]

C.  **Conclusions**

    The Working Group believes that signal sensing and adaptive
    technology, such as that now used for ATPC, will become increasing
    sophisticated and could play a major role in the self-regulation of
    interference. Such technology could be used in conjunction with the
    interference temperature metric to ensure that the condition of the
    RF environment does not exceed permissible levels.

    1\. [The Commission should make clear that its spectrum policies are
    based on "interference-limited" rather than "ambient noise-limited"
    environments.]{.underline}[^72]

    An interference-limited policy reflects typical RF environments,
    enhances frequency re-use, and would facilitate use of the
    interference temperature metric and established acceptable
    interference limits.

    2\. [The Commission should consider extended use of environmental
    sensing and control technology, including technology that could be
    used in conjunction with the interference temperature
    metric.]{.underline}

    The comments of Dr. David Reed in this regard are insightful:

> "As long as the regulatory process (including litigation and lobbing,
> and even secondary markets) focuses on defining interference without
> reference to the actual dynamics of systems, there will be no means in
> the reduction of 'actual' interference (as opposed to the current
> measure of 'imaginary' interference)."[^73]

The Working Group describes an approach in which transmitters and
receivers using advancing technologies could interact with the RF
environment. In addition to the interference temperature metric, there
are three major elements: (1) the information an emitter would need to
adapt to the environment to ensure that a maximum acceptable
interference threshold is not exceeded, (2) the manner of acquiring
interference temperature data and delivering this data to the emitter,
and (3) the responses of the emitter to the data.

An RF emitter would need to know the interference temperature (or,
alternatively, the interference temperature density) at locations within
its nominal signal range. This data could be acquired in several ways.
It could be measured directly by the emitter; *e.g.,* for low power
devices with very small signal ranges. More generally, a grid of
spectrum monitoring stations could be established that would
continuously scan the RF environment for particular frequency bands,
process the data and broadcast packetized interference temperature data
from omni-directional antennas transmitting on dedicated frequencies.
Data packets could also include the geographic location of the
interference temperature measurement, the associated frequency or
frequency band and the measurement bandwidth. As another means of data
delivery, transmitters and receivers operating in the environment -- for
example, in "an adaptive *ad hoc* wireless network" -- could be equipped
with interference temperature "thermometers" and GPS sensors to
determine measurement locations. The devices in the network would
constantly measure interference temperature and route real-time data
packets through the network. RF devices not in the network could also be
equipped to measure and send this information.

For devices required to conform to interference temperature thresholds,
responses could include a reduction in transmitter power, antenna beam
re-shaping, selection of a different transmitting frequency or a "stand
down" decision to wait until the environment adjusted to permit a
transmission that would not cause an acceptable interference level to be
exceeded within the emitter's nominal signal range. The sensory/control
system could thus provide a self-enforcing mechanism to ensure the
integrity of the interference temperature limit for that frequency band,
service and geographic area. As an additional benefit, such an approach
could provide data to update a Commission data base on the condition of
the RF noise floor.

Potentially significant benefits of using the interference temperature
metric with sensory/control devices are illustrated in Figures 2 and 3.

![](media/image2.wmf){width="5.799305555555556in"
height="2.4569444444444444in"}

**Figure 2**

Figure 2 depicts a communications system designed to operate within a
signal range at which the received power level approaches the noise
floor that existed when the system was established. As additional
interfering signals are added -- for example, due to further aggregation
of unlicensed devices or out of band emissions from new users -- the
noise floor can rise unpredictably. As a result, service reliability and
signal coverage could be increasingly worsened without warning to the
system licensee.

![](media/image3.wmf){width="5.780555555555556in"
height="2.7715277777777776in"}

**Figure 3**

In Figure 3, the evisceration of service is capped by an "acceptable"
interference temperature. In those portions of the signal path for which
the temperature limit has not been exceeded, opportunities would exist
for additional spectrum use; *e.g.*, by low power "underlay" emitters
equipped with interference temperature "thermometers" and transmission
"controlling" devices. In the long-term, this approach could also
possibly be used as an alternate means of regulating out-of-band
transmitter emissions; *i.e.*, in lieu of more expensive transmitter
filtering.

3\. [Interference management could be enhanced to the extent the
strengths of emitter-generated signals are spatially uniform over
nominal signal ranges.]{.underline}

The Working Group believes that signal strength uniformity could enhance
interference management and, in particular, the accuracy of the
environmental sensory/control approach; for example, by avoiding
complications caused by RF "hot spots." Antenna technology now exists to
facilitate signal strength uniformity. Use of low power distributed
transmission networks, in combination with beam shaping antennas, could
also serve this purpose.

4\. [Effective interference mitigation could also be advanced through
use of modern transmitter output filtering and related digital signal
processing capabilities.]{.underline}

Use of such technologies could increase the "purity" of transmitted
signals and reduce interference caused by adjacent channel "splatter".
In this regard, the Working Group concludes that it would be appropriate
for the Commission to consider the gradual tightening of out-of-band
emission limits in its rules for the various radio services.

D.  **Recommendations**

· The Working recommends that the Commission affirm that its
interference management policies will be generally based on
interference-limited RF environments.

· The Working Group recommends that the Commission promote transmitter
enhancements as a means of interference management; for example,
increased use of automatic transmitter power control.

> · As a long-term strategy, the Working Group recommends that
> Commission consider augmenting existing interference management
> approaches by promoting the use of self-enforcing environmental
> sensing and adaptive transmitter control technology, in conjunction
> with use of the interference temperature metric.
>
> · The Working Group recommends that the Commission promote the use of
> technologies that enhance the spatial uniformity of signal levels.
>
> · The Working Group recommends that the Commission begin to examine
> the out-of-band emission limits in its rules in light of modern
> technology and related costs, with a view toward gradually tightening
> existing limits.

**VI.** **Allocating Spectrum to Radiocommunications Services that are
Grouped Together by Their Similar Technical Characteristics**

The Commission's mission is "to promote the public interest through a
fully competitive marketplace \-- with access for all Americans to
communications services \-- in a cost-effective, efficient, and
transparent regulatory environment." To realize this mission, spectrum
managers should allocate spectrum to radiocommunication services within
the same frequency band or to services in adjacent frequency bands in a
way that places the fewest technical and regulatory constraints on all
of the services in that spectrum. With fewer constraints, licensees will
have the flexibility to deploy equipment in a cost-effective manner that
has the greatest promise of consumer acceptance of new and innovative
communication services. The Commission can foster spectrum efficiency
and flexibility by allocating spectrum to radiocommunication services
that are grouped together by their similar technical characteristics.

**A.** **International Telecommunication Union (ITU) and FCC Spectrum
Allocation Processes**

Implementation of a new radiocommunications system requires substantial
lead time for design and implementation particularly if the system
requires a new service allocation and interference protection.
Protection from interfering sources, both in-band and adjacent band,
requires that service allocations are made whereby the systems operating
in the spectrum are technically compatible. Technical compatibility
among the radiocommunication systems leads to more efficient use of the
spectrum and less constraints on the systems operating within a
particular service allocation. This portion of the report summarizes the
current international and domestic service allocation processes, finds
that the Commission does already promote the "zoning" approach to
spectrum allocations internationally, and concludes that a similar
approach should be considered domestically in order to promote its goals
of placing the fewest operating constraints on new systems without
disrupting the operating environment that currently operating
radiocommunication systems rely on.

**1. [International approach to spectrum allocations]{.underline}**.

International spectrum allocations are made to radiocommunication
services such as Broadcasting or Fixed-Satellite, not to systems.
Service allocations are broad in scope. The Commission participates in
the ITU spectrum allocation process with other U.S. Government agencies,
the U.S. industry, and foreign administrations. The Commission considers
industry proposals and positions that focus on future spectrum uses and
it tries to reconcile the many competing interests associated with a new
spectrum allocation keeping in mind the practicality of the operating
constraints on the systems operating in the allocations.

Article 5 of the International Radio Regulations contains the
International Table of Frequency Allocations. This table has been
developed over the past century[^74] under the auspices of the ITU. Over
the years a multi-step technical approach has evolved to determine which
radiocommunication services are able to share spectrum with other
services. Generally, the steps are as follows:

i\) [Technical description of service]{.underline}. A detailed
description of the technical parameters of the new service are developed
and introduced into the appropriate ITU technical study group. These
parameters include, but are not limited to, items such as the expected
transmit power, antenna gain, geographic service area, receiver
sensitivity, types of modulation employed and the types of applications
proposed. This information is necessary to introduce the technical
concepts of the new service to other members of the study group.

ii\) [Selecting applicable frequency range]{.underline}. Some wireless
systems can only be implemented at a specific frequency or range of
frequencies.[^75] Other systems, due to atmospheric propagation affects
and/or the current state of technology, can be implemented over a fairly
wide frequency range such as 1-3 GHz. Generally, two frequency ranges
are considered. One in which the system is capable of being implemented
and, two, a preferred frequency range within which the future system
operators would realize fewer constraints on system implementation.

iii\) [Spectrum sharing studies]{.underline}. Much of the frequency
spectrum that is technically suitable for the implementation of a new
communication system is already occupied by existing systems in a
service allocation. Ideally, all of the currently operating or proposed
systems within the preferred frequency range of the new application will
be studied to see if co-frequency sharing is technically feasible. These
studies result in the development of sharing constraints that would have
to be placed upon both the existing and the new services in order for
all of them to operate in the same frequency band. In almost all cases,
co-frequency operation of two different radio services will result in
constraints being placed upon both services.

iv\) [Allocation changes]{.underline}. When the constraints are
acceptable to all services involved in the spectrum sharing study, and
the technical studies are completed, an ITU Recommendation is adopted by
the administrations that describes the sharing constraints placed on the
new and existing systems. ITU Recommendations are used by the ITU World
Radiocommunication Conferences (WRC) as technical input to effect
changes to the International Table of Frequency Allocations and by
administrations to coordinate the operations of their
radiocommunications systems.

One of the positive aspects of the ITU process for new and modified
spectrum allocations is the amount of detailed analysis that is
conducted to evaluate the system sharing possibilities prior to
allocation. The studies are carried out by technical experts from a
number of administrations and the resulting ITU Recommendation has a
high probability of being correct in its conclusions and having
international acceptance of the technology and constraints before new
systems are implemented. The trade-off is that the ITU allocation
process can take years to complete which creates a delay for
international or regional deployment of new systems.

**2. [Domestic approach to spectrum allocations]{.underline}**.

The Commission's allocation process also allocates spectrum to services,
not to systems. Since its allocation process is not system or technology
specific, a competitive marketplace is fostered by the Commission.
Either on its own, or in response to a petition from the public, the
Commission issues a rulemaking proceeding to allocate spectrum, it
studies the technical aspects of the proposed services competing for new
allocations and, through a transparent regulatory process, it strikes a
balance among the services in allocating spectrum. In many instances,
the domestic spectrum allocations are similar to, if not the same as,
those that are internationally or regionally allocated. In those
instances, the Commission takes full advantage of the technical studies
conducted in the ITU process that led to the international frequency
allocations. To a great extent, therefore, the Commission does already
group service allocations based on technical characteristics of in-band
and adjacent band services.

In some instances, however, the domestic allocations are significantly
different than the international or regional frequency allocations. In
some cases, too, the international process has not been completed but
the time is ripe to implement a new service in the U.S. In other cases,
the desire to sell new equipment outside of the U.S. may not exist or
there may not be a requirement for international protection from
interference. In these cases, the time associated with the domestic
allocation process is the driving factor in the amount of lead-time that
a new system would need for design and implementation. The lead-time
includes the technical compatibility studies necessary to support the
service allocation.

During the domestic allocation process, the technical specifics of a new
system or technology usually are provided to the Commission in the form
of a petition for service rulemaking or in the form of a system license
application. In deciding which competing systems will operate in a
particular allocation, the Commission evaluates the technical
characteristics of the systems that propose to operate in the service
allocation from a potential inter-service and inter-system interference
standpoint. After it adopts the technical rules for a service, the
operating constraints that would need to be accepted by all services in
the allocation (and at times, in the adjacent allocation) are defined.
At this stage, the Commission essentially determines the amount of
technical flexibility a particular system or systems will have within
the service allocation. The Commission also develops license conditions
and operating provisions that are placed on the system authorization
consistent with the service rules for the allocation. The sharing
arrangements in several frequency allocations are described in Appendix
A to provide examples of how grouping like users in certain allocations
has led to competition within a service, technical flexibility and
efficient use of the spectrum.

**B. Findings and Conclusions**

Interference control is complicated by the mismatch between technical
characteristics of systems close in frequency. Authorization of
technically compatible systems within international and domestic
spectrum allocations will promote the systems' technical flexibility,
efficient spectrum usage, and provide radiocommunication system
manufacturers an opportunity to more readily deploy equipment throughout
the U.S. and abroad. For services that are global in nature, where U.S.
manufacturers desire to deploy equipment abroad, or where cross-border
coordination of a system is necessary, the Commission has promoted the
"zoning" approach to spectrum allocations internationally. Commission
staff participates in the international allocations processes and study
group activities. A review of several services in various exclusive and
shared allocations in Appendix A reveals that the Commission, to a great
extent, does already take a "zoning" approach to domestic spectrum
allocations as well.

The zoning approach leads to fewer constraints on the systems operating
in the exclusive or shared allocations which provides greater technical
flexibility for the services to develop, grow and evolve. In some cases
(e.g. fixed-satellite) coordinated approaches to spectrum access have
been developed whereby a system may operate without coordination if it
operates below an established interference threshold. In a few other
instances, the Commission has taken an ad hoc approach to spectrum
allocations. The tradeoff made by the Commission in order to provide for
a new service was to add more constraints to the existing and new
services in the allocation. As more radiocommunication systems serve end
users directly, and as the density of the user population increases, it
will become even more important for the Commission to group spectrum
allocations based on mutually-compatible technical characteristics of
the services.

**C. Recommendations**

The Commission has had success in its "zoning" approach to grouping
together systems with similar technical characteristics. In this regard,
the Commission has, to a significant extent, grouped allocations based
on mutually-compatible technical characteristics. It should continue
this policy with respect to allocation of spectrum for new uses and also
consider creating incentives to evolve dissimilar uses to compatible
groupings. In this vein, the Working Group recommends that the
Commission:

**\[1\]** continue to foster the "zoning" approach to spectrum
allocations internationally and regionally. The Commission should
continue to participate in the international spectrum allocation
processes, working with other U.S. Government agencies, U.S. industry,
and foreign administrations, to develop technical criteria for
intra-system and inter-system interference mitigation and spectrum
sharing;

**\[2\]** develop service rules for systems and authorize those systems
to use the frequency allocations in a way that least constrains all
users of the spectrum \[domestic and international\] thereby increasing
system technical flexibility and spectrum efficiency; and

**\[3\]** use its spectrum rulemakings and service rules findings and
conclusions, where appropriate, to support additional or modified
international or regional frequency allocations in the ITU process.

**VII. Receiver Standards/Guidelines**

**A.** **Background**

> For more than six decades, the Commission's general policy for
> managing or eliminating interference has been to control transmission
> parameters, mostly power and height, but sometimes antennas. For the
> most part, the earlier state of spectrum use and receivers allowed for
> such a general spectrum policy. Receiver quality, oftentimes, became
> an afterthought. When the need to evaluate interference at the
> receiver level does arise, the Commission either applies a set of
> worst case receiver parameters or uses general receiver
> characteristics for its determinations. This policy is reasonable for
> a spectrum environment that processes numerous fixed and high power
> services and a limited number of mobile and low power services.
>
> The transformation of the spectrum environment to more cellular-like
> usage, with lower power levels and mobile use, necessitates that the
> Commission revisit its general policy requirements. As interference
> issues become more complex and the number of users and emitters
> proliferates, the Working Group believes the Commission will need to
> address receiver interference concerns and specific receiver
> evaluation criteria. Further, consideration should be given to new and
> more novel approaches to spectrum access, usage, and management to
> include adaptive receivers and future advanced receivers capable of
> monitoring interference temperature as a spectrum policy.
>
> As part of its assigned tasks, the Working Group considered the
> following receiver-related questions:

-   Should the Commission promulgate rules on receiver standards or
    request that the telecommunications industries voluntarily establish
    receiver standards and/or guidelines?

-   Should the Commission adopt minimum receiver performance standards
    and encourage the markets to build and deploy higher quality
    receivers above our minimum threshold?

-   Should the Commission define a quality of service threshold based on
    operational requirements for each service?

-   Should the Commission promote the development of receivers to foster
    the concept of interference temperature?

    **B.** **Discussion**

> From a simplistic and physical standpoint, any transmission facility
> requires a transmitter, a medium for transmission, and a receiver.
> Focus on receiver characteristics has not been high in past spectrum
> use concerns, hence, a shift in focus is in order. The Working Group
> believes that receiver reception factors, including sensitivity,
> selectivity, and interference tolerance, need to play a prominent role
> in spectrum policy.
>
> The record, including a number of commenters to the Task Force's
> public notice (PN commenters)[^76] and participants in the Working
> Group's public workshop supported the need for receiver standards,
> guidelines, or incentives to evaluate harmful interference. Both the
> PN commenters and the workshop participants assert that from a
> technical standpoint, interference acceptability and susceptibility,
> as well as increased spectrum efficiency, are highly dependent on the
> quality and sensitivity of the receiver used. Spectrum sharing
> feasibility studies are made easier if, at least, the minimum
> performance characteristics of receivers operating in a band are
> known. They noted, however, that unless the characteristics of the
> receiver can be dictated by the service provider (e.g. cellular
> telephones), the provider has no control over the quality of the
> receiver (e.g. broadcasters). The commenters further noted that
> rapidly advancing technology such as software-defined radio and
> adaptive receivers that can filter and excise interference effectively
> should be factored in spectrum policy considerations.[^77]
>
> The PN commenters also generally favored the development, adoption,
> and implementation of receiver standards/guidelines/incentives
> (receiver standards), or, in the alternative, minimum receiver
> performance requirements. Their views are buttressed by those of the
> workshop participants held by the other three Spectrum Policy Task
> Force Working Groups.
>
> On receiver standards, participating parties, both those favoring and
> those opposing Commission adoption of receiver standards or minimum
> receiver performance requirements, acknowledged that receiver
> performance characteristics are essential to interference evaluation,
> feasibility studies, and the design of new and improved systems.[^78]
> The parties supporting Commission adoption of receiver standards or
> minimum receiver performance requirements indicated that receiver
> standards would promote spectrum sharing and system interoperability,
> and provide common performance values that all equipment manufacturers
> must meet.[^79]
>
> The opposing parties stated that receiver standards would stifle
> innovation and negate the natural progression of technology, could
> eliminate lowest cost receivers from the marketplace, and could force
> consumers to purchase higher priced receivers.[^80] They also pointed
> out that the rapidly changing technology landscape would result in
> receiver standards that would require constant Commission monitoring
> and maintenance.[^81] Even those parties opposing receiver standards,
> however, did support, in varying degrees, the adoption of minimum
> receiver performance requirements.
>
> If adoption of either receiver standards or minimum receiver
> performance requirements is contemplated, working group participants
> suggested consideration of the following parameters. They include
> selectivity, susceptibility, dynamic range, local oscillator phase
> noise, data throughput, unwanted emissions, various carrier-to-noise
> or carrier-to-interference metrics, equipment performance labeling,
> tuned filtering, and interference suppression and rejection.[^82]
>
> Parties supporting receiver standards believe that long-term
> protection of legacy receivers stifles innovation and delays public
> acceptance and purchase of new technology, and that legacy receivers
> should not receive long-term or indefinite protection.[^83] A few
> commenters suggested that a date-certain protection sunset for legacy
> receivers, based on equipment life cycles and amortization schedules,
> should be imposed.[^84] Others suggested that receiver certifications
> be time-limited (perhaps five to seven years), and that at the end of
> the certification period, the receiver manufacturer should be required
> to cease manufacture of the obsolete equipment.[^85] Virtually all
> public participants agreed that there should be differing receiver
> standards among various radio services, and that services could be
> grouped by spectral characteristics, the application using the
> service, the bandwidth required by the application, and the
> application's potential for spectrum efficiency and sharing.[^86]

In addition to the above, commenters specifically recommended the
following:

-   The Commission should initiate an evaluation of the performance
    characteristics of current receivers, particularly interference
    immunity, in order to provide an accurate assessment of the current
    operating environment on which to base new
    standards/guidelines/incentives or minimum receiver performance
    requirements.[^87]

-   The Commission should convene an industry panel to devise a plan for
    the resale, trade-in, and recycling of legacy receivers to stimulate
    public acceptance of new technologies.[^88]

-   The Commission should require product labeling that contains
    evaluation of product performance against objective performance
    benchmarks.[^89]

    **C. Recommendations**

> The public record voiced a need for further action on receiver
> standards by the Commission. As discussed above, the Working Group has
> been considering the concept of interference temperature as another
> means of improving spectrum access and the creation of receivers
> capable of monitoring interference temperature needs to follow.
>
> 1\. The Working Group recommends that the Commission initiate a
> *Notice of Inquiry* (NOI) addressing the adoption and implementation
> of either receiver standards/guidelines/incentives or minimum receiver
> performance requirements in the very near future. It suggests that the
> NOI seek comments on: how to characterize the current receiver
> environment; whether the Commission has the authority to issue
> receiver standards; what minimum performance parameters need to be
> considered; how to group differing receiver standards for different
> radio services; how recent receiver developments such as
> software-defined radios could decrease current interference
> constraints; the level of protection and the length of time protection
> is afforded to legacy receivers, particularly those deployed by Public
> Safety and rural users; how receiver standards, if adopted, might
> stifle innovation; and how to contend with the possible potential
> negative effect of eliminating the lowest cost receivers from the
> marketplace.
>
> 2\. The Working Group also recommends that the Commission pursue a
> detailed study of the advantages and disadvantages of using
> interference temperature as a means of addressing spectrum access and
> interference acceptance in the future. Future studies should include a
> comprehensive assessment of the interference(noise) temperature for
> all regions of the country. This assessment necessarily would be time
> consuming and expensive. While resource intensive, such an assessment
> could reap enormous spectrum access benefits and improvements for the
> telecom industry. As such, the telecom industry may consider funding
> or assisting in the funding of the assessment. If this interference
> temperature assessment is successful, the Commission should take
> prompt regulatory action to incorporate the use of interference
> temperature as part of its future spectrum policy. In this regard, for
> those receivers that the Commission might choose to be subjected to
> interference temperature limits, the Working Group recommends that the
> Commission either propose performance requirements for interference
> temperature capable receivers or request that the industry adopt and
> implement such standards.
>
> 3\. Aside from the NOI and unrelated to interference temperature, the
> Working Group recommends that the FCC either commission a study group
> or issue a contracting proposal for an evaluation of the performance
> characteristics of current receivers to provide a better assessment of
> the current interference environment. This assessment could be used to
> improve the Commission's spectrum allotment policies or assist in the
> future development of receiver standards.
>
> 4\. The Working Group also suggests that parallel to the NOI, the
> Commission convene industry committees to seek the creation of
> voluntary industry standards, guidelines or labeling for advancing
> receiver standards. If consensus is reached, the Commission could
> initiate a rulemaking to embrace the standards, either through a
> labeling or certification program or as part of the Commission's
> Rules.
>
> 5\. The Working Group further suggests that the Commission urge the
> telecommunications industries to devise a plan to expedite legacy
> receiver replacement, perhaps by implementing the
> resale/trade-in/recycle plan suggested by the public. In the
> alternative, as an incentive to the deployment of more advanced
> receivers and the replacement of legacy receivers, the Commission
> could allow additional flexibility or increased power for those
> services or users deploying more advanced receivers.
>
> In short, the time for intensive study and review of both current and
> future receivers is now.

### **VIII.** **Communications with the Public on Interference Issues**

**A.** **Introduction**

The ability of the new radio-based technologies to become realities in
the marketplace depends to an important extent on the terms and
descriptions of interference. Disputes as to what may or may not
constitute an effect of one service on another has been made at times
more difficult to resolve because of informal and inconsistent language
describing interference and its impact. In addition, entrepreneurs and
others seeking to implement new systems or improvements to existing
systems have found it difficult to determine which rules are appropriate
candidates for revision and what the changes would be. Beyond the
regulatory language and rules addressing interference, the actual
experience of licensees and others engaged in the process of fielding
new or changed communications systems constitutes an important asset
that should be more easily available to others seeking to establish
radio-based services.

**B.** **Discussion**

The Working Group sees a need to consider several focused efforts to
make the Commission's interference rules, policies, processes and
available tools more transparent, that is, more comprehensible,
consistent, and easy to use.

**1. Harmonizing Interference Language (Technical Terms and Units)**

The rules governing interference for the wide variety of radio-based
communications regulated by the FCC today are the result of a process
that has evolved over time and that addresses the specific services
involved and circumstances of the potential interference situations.
Historically, the Commission has developed the technical interference
criteria contained in the various parts of its rules on an industry by
industry and service by service basis, responding to the particular
situation presented by those seeking to establish new services and
reacting to the concerns of potentially affected existing services. Each
industry and to some extent each service within an industry has its own
engineering "culture," that is, a body of conventional technical
practices and terminology widely used by planners and licensees within
that particular service.

The resulting treatment of interference for the *ad hoc* situations
presented to the FCC has led to the successful implementation of a wide
variety of radio-based systems in operation today. The existing
language, however, addressing interference is highly diverse and not
always consistent. This resulting body of interference language has
become a daunting challenge for those seeking to learn how they should
consider the lessons of the past in order to plan for the future.

The interference management rules governing a particular radio service
have been adopted in a public proceeding based on a record containing
technical material submitted by stakeholders of the pertinent industry
and other potentially affected parties. The specific criteria are often
the result a compromise between competing goals of a satisfactory level
of performance for the licensees and an acceptable level of impact on
others in nearby frequency bands or geographic locations. The
circumstances for the determination of each new service are frequently
unique to the situation brought to the FCC by petitioners seeking to
alter the status quo in order to permit them to operate under the
revised rules. The language addressing interference differs from service
to service and reflects the nature of the service, the sharing
situation, and the expectations of the community.

The technical interference criteria contained in the Commission's rules
are fundamentally based on considerations of power and propagation in
broad frequency classifications (*i.e.* high frequency (HF), very high
frequency (VHF), ultra high frequency (UHF), *etc*.) The criteria in the
rules also reflect operating considerations, such as whether the service
is a fixed or mobile service. For example, interference criteria for
mobile units generally incorporate an additional margin to account for
signal fading resulting from the motion of the mobile unit. The
technical criteria also reflect an expectation of the quality of service
that will be demanded by licensees. Some services can be completely
functional in the presence of a low level of interference, whereas users
of other services, particularly public safety services, subscriber
services, and broadcast services, have an expectation of a greater
freedom from interference.

Even within a particular service the language describing interference
may be variable and inconsistent. For example, rules defining
interference levels may have initially been established for analog
systems and not comparably revised for the advent of digital systems.
Over time estimated propagation distances and hence expectations of
impact may have changed due to the wide-spread availability of more
accurate propagation models. In addition newly implemented services
similar to an earlier generation of systems may have the expectation of
more technical freedom and flexibility and hence have simpler
interference rules.

The wide differences in approaches to interference management in the
FCC's rules also shows up in the technical parameters that are used to
describe performance and impact. The differences in units, methods and
metrics for interference management that exist between the various
services can be categorized as major differences, minor differences and
inconsistencies. The major differences arise when the service quality or
reliability goals for the services differ, or when concerns for
administrative efficiency outweigh those for more accurate technical
assignment (*e.g.,* if a large number of license application filings is
expected). A different approach may also be appropriate where a service
is presumed to be interference-limited rather than noise-limited under
the expected operating radio frequency environment. Another factor
resulting in major differences is whether the service is structured as a
broadband or narrowband service. Broadband services must rely far more
heavily on frequency use coordination between licensees to manage
interference than do narrowband services. As a result, FCC technical
rules for broadband services focus on signal coverage parameters rather
than desired-to-undesired signal ratios. Broadband services also
incorporate technical flexibility as well as service flexibility, which
may limit the usefulness of such ratios.

Minor differences arise when services utilize a similar approach
(*e.g.,* minimum D/U ratio), but employ different propagation models for
the same general frequency range. In the UHF range, the Commission has
approved or required the use of methods derived from three somewhat
different sets of empirically derived field strength curves---R6602,
Carey (ITU) and Okimura---for essentially similar services. For example,
the historical and current practice is to use Carey-based tools for CMRS
systems licensed under Part 22 and methods based on R6602 for similar
CMRS licensed under Part 90. Furthermore, Okimura based criteria are
used for other service types of stations, such as for paging systems as
opposed to two-way radios for both Part 22 and Part 90. Finally,
inconsistencies may appear to exist where the FCC's rules contain
different expressions of engineering units that have been derived from
different considerations of power, relative power, or electric field.
These differences reflect the different approaches to describing and
characterizing interference and its impact that are peculiar to the
specific situation such as for broadcast or mobile services, for
example, D/U and C/I, or dBμ and dBμV/m.

When the FCC makes a determination to implement a new or changed
service, it correctly focuses on the interference situations presented
by the parties and also on the context of the existing rules and
services for impacted services. The resulting record of interference
language in the rules today, however, for the many FCC-regulated
services has become unnecessarily varied and is not always
consistent---service to service. It has not been a focused goal of the
FCC to treat its own rules objectively as a source of information on
approaches to interference---its definition, management and control.
Although the record stands as an authoritative body of rules on
interference, it appears that these interference rules could be made
more user-friendly; and it may be an appropriate and useful expenditure
of the FCC's resources to review its rules on interference with the
objective of harmonizing the language of interference to the extent
possible. While important distinctions should always be made, there is a
benefit to using more uniform language when describing interference and
its impact. It is noted that the process of biennially reviewing and
streamlining the FCC's rules is an existing process that could be tasked
with an additional goal of harmonizing the interference rules. Where
possible, consistencies and inconsistencies in the technical parameters
and units could be highlighted and explained. In addition the FCC should
be conscious of the international environment for the language
describing interference and seek to harmonize our descriptions with
those of other administrations.

**2.** **Ensuring Consistent and Appropriate Use of Interference
Language (Non-Technical Qualifiers)**

The same variability in language on interference that pervades the FCC's
rulemaking proceedings and the resulting rules also gives rise to
inconsistent discussion of the impact of interference from a
non-technical perspective. While in principle technical terminology may
be made more objectively uniform, where possible, especially if the
technical assumptions and conditions are specified, the terminology
addressing the resulting impact of signal degradation on a user or
subscriber may be regarded as subjective.

In its June 2002 public notice, the SPTF signaled its openness on the
interest in, or need for, new definitions of "interference" and "harmful
interference." In response, the majority of parties commenting on this
issue argue that no change in the definitions is needed. Those arguing
that the current definitions are too subjective and open to
interpretation are outnumbered by those who believe that formal revision
of the definitions would lead to constraints on technical innovation and
to more interference disputes. However, a consensus among both sets of
commenters is that the *usage* of these terms by the FCC is unclear.

Commenters on both sides raise issues with the current definitions and
their use in the FCC's rules. They argue that the use of the terms
"interference" and "harmful interference" is too informal and
inconsistent. Sprint asserts that "there can be no serious dispute over
the need for the Commission to confirm and clarify the scope of harmful
interference, if not codify those clarifications in the rules or in
notes to the rules."[^90] The Information Technology Industry Council
recommends, "in order for the Commission to be able to solve actual
harmful interference situations, the Commission needs to better define
the distinction between interference and harmful interference."[^91]
PanAmSat's comments propose an alternative to redefining the terms: "The
Commission should not redefine the terms "interference" and "harmful
interference," or attempt to quantify what constitutes harmful
interference, but should clarify the use of those terms in its
rules."[^92]

Bringing in the international perspective, the Satellite Industry
Association (SIA) elaborates on the appropriate use of the terms
"harmful," "accepted," and "permissible" interference in the context of
adopting sharing criteria:

> "The definitions for 'interference' and 'harmful interference' have
> been established and agreed to within the ITU for some time. In
> addition, there are also established definitions for 'permissible
> interference' and 'accepted interference.'... It is not clear what
> purpose would be served by redefining any of these terms. Instead the
> Commission should make clear the use of these terms in its
> regulations. Harmful interference is an extreme level of interference
> that is rarely seen when properly functioning radio equipment is used
> in a frequency band by services or systems that operate on a
> co-primary basis. At the same time, it is clear that just because
> interference between such services or systems in a band does not rise
> to the high level of 'harmful interference' it cannot be reasonably
> concluded that the interference is subjectively acceptable or
> tolerable to the victim service or users. As a result, the
> Commission's, and even the ITU's, attempts to quantify the level that
> constitutes harmful interference are really not a useful exercise. The
> key is to find ways to ensure that the level of interference \... is
> not and will not be at a level that will result in the interruption or
> degradation of one of the services using the band. Therefore, the
> level of interference that is appropriate for allowance from one
> service into another is always less than harmful interference. That is
> where the term acceptable interference should be used ... For the
> Commission's purposes, the object of most spectrum sharing rulemaking
> proceedings -- at least those not involving assessment of interference
> to a safety service -- should be to identify the level of permissible
> interference... \[T\]he Commission should, when adopting sharing
> criteria, use the terms permissible or acceptable interference."[^93]

Although distinctions between of levels of interference will continue to
be discussed, the Working Group believes that the qualifiers describing
the impact of the interference should be more consistent and
appropriate, as the FCC discusses its interference decisions and
describes its interference rules.

A systematic review of the interference rules and definitions would be
required to ensure such consistency. The interference definitions
scattered throughout the rule parts may be standardized to reflect the
language of the definitions from Section 2.1 of the FCC's rules or the
ITU Radio Regulations. In addition, undefined qualifiers such as
"objectionable" may be replaced with standard qualifiers or re-defined
to remove ambiguity and subjectivity. Instances of the terms "harmful,"
"accepted," and "permissible" interference could be reviewed to ensure
that their use matches the meanings of their respective definitions. The
FCC may also seek to add qualifiers where such an addition may usefully
clarify the meaning.

Short of redefining interference broadly, the consistent and appropriate
use of qualifiers would remove some ambiguity for licensees, applicants,
industry, and the general public who are trying to comply with
interference rules. The Working Group believes that clarifying the use
of interference qualifiers and ensuring consistency is a suitable
compromise between the extremes of redefining interference and taking no
action with the definitions.

**3. Facilitating Access to the FCC's Rules on Interference**

Title 47 of the Code of Federal Regulations contains the rules governing
interference for FCC-regulated services. These rules however are spread
throughout a number of different rule parts comprising five volumes and
over 3600 pages. Beyond the problems cited in the preceding paragraphs
on the technical and non-technical language on the definition and
management of interference, the body of regulations governing
interference for all services is vast in scope and voluminous in size.
Moreover, the actual interference rules themselves are not easily
identified and isolated in the context of all the rules governing a
particular service. For example, for certain services interference may
be indirectly governed by specifying minimum separation distances or
limitations on transmitter power and antenna height---without ever
mentioning the word "interference" or referring to levels of
interference.

In order to assist those seeking to understand the interference
determinations for the existing services, it seems appropriate for the
FCC to provide a roadmap or directed guide that would facilitate access
to rules governing interference for any regulated service. Providing the
interference rules for all services in all frequency bands regulated by
the FCC in *a consolidated summary* may be helpful to licensees when
evaluating actual interference from other users or determining their own
requirements.

Rules governing interference protection may include, depending on the
service, a combination of service contours, interference contours,
emission masks, transient frequency behavior, directional antennas,
out-of-band emission limits, power limit, antenna height restrictions,
and other criteria. Procedures to measure interference-related
parameters may also be contained in the rules. For example, certain
rules may specify technical relationships and limitations by means of
equations, propagation models, or measurement procedures. The direct
availability of the rules governing interference may help to more
quickly resolve interference disputes or determine the potential for
interference and could service as an aid to frequency coordination. A
consolidated summary may also prove useful to licensees who may not know
exactly which services are in shared or adjacent bands or the
corresponding FCC rules that regulate these services.

There are also additional interference requirements that may not be
contained in the section of 47 CFR that contain a given service's
technical rules. In 47 CFR Parts 1 and 2 certain requirements and
procedures are specified that pertain to a number of services in various
rule parts. For example, Section 1.924 of the rules contains procedures
and associated field strength limits licensees should be aware of to
protect radio astronomy sites, FCC field offices and sensitive
Government facilities. Licensees may not be aware of such requirements
because the governing rules are not directly included in their services'
rule parts. In addition, Section 1.923 states that some channel
assignments and/or usage may be subject to provisions and requirements
of treaties and other international agreements between the United States
and Canada and Mexico. This general requirement is more typically
contained in 47 CFR Part 1 rather than in the applicable rule part. (The
treaties and agreements are not actually contained in the rules. Certain
agreements with Canada and Mexico are contained within the International
Bureau's web site http://www.fcc.gov/ib/sand/agree/. This is not an
inclusive list however, as many agreements were approved decades
ago[^94].)

An analogy to a consolidated summary of rules governing interference may
be made to OET Bulletin 65, which contains the general rules on limits
for the absorption of electromagnetic radiation by humans. This
bulletin, and its many supplements and annexes, may be analogous to a
summary of interference rules, but on a much smaller scale, in that it
addresses all FCC-regulated services in specifying acceptable
measurement procedures for compliance with the standard for absorption
of radiation.

A single document containing the consolidated summary of interference
rules would be physically large, and maintaining its currency could
require a considerable expenditure of time and other resources. The FCC
is necessarily continually in the process of revising its existing rules
and establishing new ones, and the potential exists for differences to
develop between the rules as contained in 47 CFR and those as summarized
in a separate document. Therefore, a practical means to maintain a
consolidated summary of the interference rules may be to establish a web
site that provides links to the appropriate sections of the most recent
version 47 CFR and other useful information such as access to
propagation models in current use. An electronic implementation of the
consolidated summary of the interference rules comprising a series of
links to the most recent version of the Rules may be the most efficient
way to keep the summary up to date. For instance, the United States
Government Printing Office periodically updates 47 CFR and houses the
single source the FCC rules at its web site,
http://www.access.gpo.gov/ecfr/.

**4.** **Facilitating Access to Successful Practices for Interference
Resolution**

In an ideal world new services following the technical specifications
and the service rules developed through the FCC's processes and
promulgated in 47 Code of Federal Regulations (Telecommunications) would
be designed, licensed, and implemented, without interference to existing
licensees in neighboring frequency bands and geographic areas. In
reality, however, practical systems are developed and fielded with an
appreciation of the fact that transmissions from actual equipment in
operation may be received by neighboring licensees for a variety of
reasons including the non-ideal nature of transmitters, antennas, and
receivers, the details of their relative positioning, and the
statistical nature of electromagnetic propagation. Increasingly, the FCC
has come to depend on the efforts of new and existing licensees and even
third parties to make practical systems function together without
improperly affecting each other, especially in shared bands. Indeed, the
FCC has long depended on the efforts of third parties such as frequency
coordinators for certain bands to assist new entrants by selecting
appropriate frequencies and locations using detailed and complete data
bases of licensee information including the technical specifications and
actual locations of the transmitters and receivers. Fixed microwave
facilities, private mobile radio services, and satellite earth-stations
are examples. Importantly, the FCC in permitting increasingly flexible
services such as Personal Communications Services has come to assume
that licensees or their agents will seek to coordinate their system
implementations and subsequent changes directly with each other rather
than seek FCC intervention. PCS licensees have strongly supported this
approach and have made it work.

Realizing the importance of the efforts of licensees themselves and of
third parties to supplement the effectiveness of defined interference
limitations and the technical and operational service rules, the
Spectrum Policy Task Force raised the question of the desirability of
facilitating privately negotiated solutions to interference problems.
Such an approach could bring to the process of resolution of
interference---from both a planning and an operational
perspective---economic considerations of the impact of interference.
Many commenters viewed positively efforts by the Commission to support
such direct negotiated solutions. A general sense from the comments is
that if private parties have sufficient information at their disposal,
and if the Commission's rules regarding licensee rights with respect to
possible interference are clear, the preferred approach is to try to
resolve interference problems directly among the affected parties. Only
if such efforts fail should the interference problem be referred to the
Commission for resolution. Parties feel that private negotiations will
lead, in most cases, to a much faster and more acceptable resolution of
interference problems than using the Commission's regulatory processes.

In view of the fact that the total compendium of the FCC's rules in 47
CFR is not a complete handbook on how to implement practical
communications systems, the experience of licensees and third parties
across the several communications communities regulated by the FCC
should be viewed as a valuable asset that could be used more widely.
Accordingly, a "handbook" identifying successful practices, standards
associations, key technical bulletins from the industry associations,
and other aids in the resolution of interference could supplement the
effectiveness of 47 CFR for interference management. Such a gathering of
successful practices, a "best practices handbook," would be especially
useful to those outside the existing communications communities seeking
access to the electromagnetic spectrum for the first time with
potentially innovative technologies. A "best practices handbook" for
interference management would be a compendium of available information
broadly related to the subject of interference management. Such a
compendium need not be an actual physical document and could be realized
as a web site containing important documents and standards addressing
interference and links to other sites with relevant information on
interference management for specific licensee communities. In this way,
the information could be continuously and efficiently updated, and users
could be assured that they were accessing the latest available
information. Included in such a handbook could be such material as
current industry guidelines used to coordinate spectrum use and manage
co-channel and adjacent-channel interference problems for each service
or group of services, examples of successful interference management
negotiations, a list of steps parties should take to resolve
interference problems; a list of steps parties could take to demonstrate
that a proposed service will not pose undue interference on incumbent
licensees, relevant technical bulletins issued by the FCC or technical
standards bodies, a list of frequency coordination organizations,
including links to their web sites, and a discussion of the FCC's
licensee databases, including general instructions on how to conduct
searches for co-channel licensees, for example, within a specified
geographic area.

The handbook could be a vehicle to assemble and organize relevant
interference management information in one virtual location to assist
parties to help themselves to resolve problems independently, without
direct FCC involvement. An example of the successful use of an actual
best practices guide is a document developed in 2000 by several trade
associations, an equipment manufacturer, and a wireless service provider
to suggest ways to reduce or eliminate interference between public
safety and CMRS radio systems. Subsequently, the Commission issued a
News Release describing the guide and providing a copy of the full
publication by means of a link to an electronic version. It is
anticipated that a best practice handbook for interference management
would include a link to this guide as well as any similar guides that
may be relevant to interference management.

**C. Recommendations**

The Working Group recognizes the importance of the public's access to
comprehensible and useful information and practices on interference
management and has the following recommendations that address broadly
(1) the language of interference and (2) the rules and practices
governing interference management:

-   Initiate a review and revision of the FCC's rules, possibly in
    conjunction with the existing biennial reviews, with the goals of

    -   Harmonizing interference language, focusing on technical terms
        and units, and

    -   Ensuring consistent and appropriate use of interference
        language, focusing on non-technical qualifiers.

-   Organize and make public in documentation or at a web site, for the
    purpose of facilitating public access, a comprehensive and
    authoritative gathering of

    -   The rules on interference for all the FCC's radio-based services
        and

    -   The practices and procedures for interference resolution.

        **IX. Acknowledgements**

The members of the Interference Protection Working Group wish to thank
the participants in the public workshop on Interference Protection held
on August 2, 2002. The wide-ranging views of these professionals reflect
the deep experience of a diversity of communications communities and
disciplines and have significantly informed the public discussion on the
subject of interference.

# APPENDIX A

**Allocating Spectrum to Radiocommunication Services that are Grouped
Together by their Similar Technical Characteristics**

***Exclusive Use of Service Allocations Based on Technical
Characteristics***

Radiocommunication services are able to operate in adjacent frequency
bands through the use of power limits, out-of-band emission limits, and
use of receivers that are able to filter out unacceptable interference
from systems operating in adjacent frequency allocations. Other portions
of this report focus on the specific technical characteristics that can
be used for groupings or "zoning" based on a system's sensitivity to
interference and how in-band signals are transmitted.[^95] We focus here
on the services that are allocated the same spectrum and have regulatory
status in that spectrum.

***Terrestrial Broadcasting Services***

AM radio stations operate in the Broadcasting Service allocations from
535 kHz - 1705 kHz. AM stations are assigned frequencies on a
non-interfering basis using desired-to-undesired signal ratios and power
limits. There are four classes of AM stations with permissible powers
between 0.25 kW and 50 kW. FM radio stations operate in the Broadcasting
Service allocation from 88 -108 MHz. The Commission authorizes
commercial and noncommercial educational (NCE) full-service stations,
and low power FM (LPFM), FM translator, and FM booster secondary
stations in this exclusive spectrum. Only commercial FM stations (92.1
MHZ to 107.9 MHZ) are assigned channels based on geographic allotments.
Commercial FM stations are assigned these channels using minimum
distance separation requirements that are based on desired-to-undesired
signal ratios. There are seven classes of commercial FM stations (Class
A, B1,B, C3, C2, C1, C) that are based on power (maximum permissible ERP
is 100 kW) and antenna height (maximum permissible antenna HAAT is 600
meters) requirements. NCE FM stations are assigned channels on a
non-interfering basis using desired-to-undesired signal ratios and power
and antenna height limits. Based on power and antenna height authorized,
NCE FM stations are assigned the same classes as commercial FM stations.
There are two classes of LPFM stations (LP100 - 100 watts max ERP and 30
meters max antenna HAAT, LP10 - 10 watts max ERP and 30 meters max
antenna HAAT) which are assigned channels using minimum distance
separation requirements that are based on desired-to-undesired signal
ratios. FM translator and FM booster stations are assigned channels on a
non-interfering basis using desired-to-undesired signal ratios. AM and
FM radio technology has substantially evolved over several decades. The
exclusive Broadcasting allocations have provided this service the
opportunity to explore ways to overlay digital radio technology in the
same allocations (e.g. In-band, On Channel (IBOC) and In-band, Adjacent
Channel (IBAC)). The constraints on the development of the digital
systems have been inter-system related, not inter-service related. The
addition of inter-service constraints would likely have resulted in
further difficulties in developing the digital overlay techniques that
are now being evaluated.

Broadcast television is allocated spectrum from 54 MHz to 806 MHz. The
Commission authorizes full-service commercial and noncommercial TV
broadcast stations, and low power TV (LPTV), TV translator, and TV
booster secondary stations throughout the allocation. Only full-service
commercial and noncommercial FM stations are assigned based on
geographic allotments made to communities using minimum distance
separation requirements that are based on desired-to-undesired signal
ratios. Secondary LPTV, TV translator, and TV booster stations are
assigned, for the most part, on a non-interfering basis using
desired-to-undesired signal ratios. Broadcast TV has exclusive use of
the Broadcasting Service allocation on channels 2 through 13 (54 MHZ to
216 MHZ) and channels 21 to 69 (512 MHZ to 806 MHZ), but must share
spectrum on channels 14 through 20 (470 MHZ to 512 MHZ) with Public
Mobile Services (Part 22) and Private Land Mobile Radio Services (Part
90). Broadcast auxiliary services also operate in the shared spectrum
and are assigned frequencies on a non-interfering basis. The Commission
continues to encourage Digital Television implementation in the
exclusive Broadcasting Service allocation. The exclusive allocation has
provided for digital television service rules that are less constrained
than if the allocation were shared with other services.

***Terrestrial Mobile Services***

Mobile services are provided terrestrially in a wide variety of
frequency bands, predominantly less than 2 GHz, allocated to the Mobile
(and frequently Fixed) Services, for a wide variety of private and
commercial purposes. The earliest mobile services were in support of
public safety purposes and eventually evolved into the larger class of
non-commercial, land mobile radio services, which today are usually not
inter-connected to the public switched telephone network. This larger
class is dominated by private land mobile services (Part 90), but also
includes aviation (Part 80) and maritime (Part 87) services. Private
land mobile radio services, which support the radio needs of private
companies, as opposed to companies that offer communications services to
the public, and other organizations such as state and local governments,
generally share the frequencies that they occupy below 470 MHz. They
have non-exclusive access to the channels through coordinators and may
be assigned to time-share certain channels that are being used by other
private users. For private services that use bands generally above 800
MHz, access to the spectrum is on an exclusive, "first come, first
served" basis. Licenses for these services are generally site-based,
that is, an applicant is granted the exclusive right to use the certain
frequencies within an area determined by a base station location and a
radius of operations for the mobile units. Other channels in the same
geographic area may be assigned to other applicants through a
coordinator for the services who maintains a database of the
assignments. The same channel may be re-used by another licensee, if it
is determined that the inter-site distance is sufficiently large so that
the services would not interfere with each other; for example, 70 miles
separation is required for private services at 800 MHz, because of the
high power of the base station transmitters.

Commercial mobile radio services, on the other hand, are generally
provided on a for-profit basis and offer inter-connection to the public
switched telephone network (PSTN). The commercial mobile services of
today have evolved from efforts to extend the PSTN to people in moving
vehicles allowing them to talk to land-based telephone subscribers. The
cellular concept evolved in a major movement away from the large
separation distances required by private mobile services, which serve
their mobiles with a single, high-powered transmitter. This concept
involved the re-use of the same channels through smaller radius cells
with lower-powered base stations and mobiles. The first important
commercial radio service was cellular radiotelephone service. Starting
in the 1980s, the FCC assigned equal amounts of spectrum on an exclusive
basis to two cellular systems in each geographic area. These early
assignments established a duopoly of carriers and involved licensing the
single wireline common carrier in each area, but then making another
license available, through administrative hearings and, later,
lotteries. The two cellular providers were to compete in their offerings
of cellular service to the public and initially used the same mandated
analog technical standard developed by the industry and placed into the
rules by the FCC. The rules for the exclusive use by the licensees
included the identification of separate bands for the two competing
entities, power and height standards, and emission limitations for the
base station and mobile unit transmitters. These limitations were
largely to assure that the cellular concept was implemented rather than
the earlier concept of higher power base stations serving large areas.
In order to protect other cellular licensees on the same bands, but in
adjacent geographic areas, the licensees were permitted direct
coordination with their neighbors in order to assure that the channels
selected by the neighboring cellular licensees would not cause
interference.

In its first major move to establish technical flexibility, the FCC in
the late 1980s relaxed the rules for the cellular radiotelephone service
and permitted the licensees the use of technologies alternative to the
analog standard. (Although alternative technologies such as digital
transmission techniques were permitted, the carriers were required to
maintain a level of analog service in order to keep open the option of a
nation-wide common standard. The FCC is currently considering the
removal of this analog requirement.) By giving the cellular licensees
the flexibility to use alternative transmission standards, the FCC
enabled the move to digital mobile services. The FCC encouraged the
cellular industry to act on its own and declined to participate in the
industry standard-setting process to develop alternative digital
standards, allowing the industry to determine its own best standards to
best serve its business concept of service to the public. Out of this
process digital mobile systems were developed and fielded for
next-generation Time Division Multiple Access (TDMA) and Frequency
Division Multiple Access (CDMA) systems. The CDMA standards developed in
this process have evolved become the basis for the advanced
communications services being considered for much of the world today. In
addition to this technical flexibility for the cellular service, the FCC
also granted service flexibility by facilitating other uses of the
cellular frequencies than for the mobile service. Fixed services may be
offered by the licensee. Data services, permitting early access to
computer networks, were also enabled for the mobile user through the use
of cellular-delivered, packet-data (CDPD) service. The freedom given to
the exclusive licensees of the cellular frequency bands for flexible use
of alternative digital technical systems and of alternative service
offerings is limited by the requirement that other cellular operators
not experience interference to their services.

In contrast to the cellular service, which started out with a detailed
technical standard for a specific and well-defined concept of mobile
service, the Personal Communications Services (PCS) at 1850-1990 MHz was
conceived from its beginning on the basis of technical flexibility to
the licensee to choose the transmission standard that would best achieve
the licensee's own concept of service. The purpose of the service was
left to the licensee and was not specified in the minimal regulations,
but only had to be consistent with the frequency allocation of Mobile or
Fixed Services. The sizes of the spectrum blocks were sufficiently large
to permit the licensees to subdivide the frequencies in order to offer
alternative services. PCS licenses were assigned by competitive bidding,
which was authorized by Congress in 1993. Accordingly, the licenses went
to the highest bidder, thus allowing exclusive use of the spectrum under
a flexible regime that would allow the licensee to respond to the market
demands for service. Changes in the marketplace for communications
services could in principle be undertaken without going to the FCC to
initiate a rulemaking to implement new technical or service rules. The
PCS technical rules specified no standard for channelization or for
transmission and only gave height and power and emission limitations for
the base stations and a maximum field strength to be maintained at the
boundary of the service area. This field strength level could be
re-negotiated by the neighboring licensees. Within the licensee's
service area, the licensee is free to use the technology of its choice
to offer the service it deems appropriate, consistent with the few
limitations that were imposed. Fewer constraints on the terrestrial
mobile (and fixed) services led to greater technical flexibility within
the service. The Commission is now considering how to implement 3^rd^
Generation mobile services where even more technical flexibility is
envisioned.

***Satellite Services***

Satellite systems are used to provide fixed, mobile, broadcasting and
other types of commercial services. The antenna patterns of satellites
(international and domestic) generally overlap each other in the same
geographic service area. The isolation among the satellite systems comes
from orbital location separation, antenna beam separation, frequency
assignment separation, or a combination of these. We evaluate these
concepts and how they have been applied by the Commission to services
that have similar technical characteristics. In many instances,
satellite services are grouped together based on their similar technical
characteristics. Many of the intra-service coordination mechanisms
described below result from such groupings.

***Fixed Satellite Service (FSS) - Geostationary(GSO/ FSS) sharing*.**
GSO/GSO FSS sharing has been accomplished through orbital arc separation
and the management of noise temperature (noise power) contributions from
other GSO FSS networks. First, the amount of orbital arc separation
between GSO FSS satellites was derived from extensive studies based on
analysis of management of noise temperature from contributions of
adjacent systems in the GSO arc. The Commission has adopted rules
requiring an orbital separation of 2 degrees (2-degree spacing) for GSO
FSS systems sharing the same spectrum and serving the U.S. This has
provided for closer orbital spacing than generally used internationally
and "packed" the GSO arc over the U.S. more densely. This has led to a
rather competitive GSO FSS marketplace in the U.S. However, under this
condition GSO systems are required to meet certain technical
requirements including antenna directivity, off axis performance, EIRP
limits and power levels at the GSO arc in order to minimize interference
to adjacent GSO systems. This sharing orbital arc sharing mechanism
provides an efficient way for utilizing the orbital arc and spectrum
while providing sufficient system flexibility to GSO FSS operators.

The Commission's 2-degree spacing policy is based on the management of
noise temperature among GSO FSS systems sharing the same spectrum. This
concept is based on the premise that the noise temperature of a system
is subject to increase as the level of interfering emissions from other
systems increases. It is, therefore, applied irrespective of the
modulation characteristics. Additionally, the ITU has relied on this
concept for administrations, including the US administration, to follow
to determine the potential for interference among GSO networks.
Specifically, the ratio of the apparent increase in the equivalent
satellite link noise temperature resulting from interfering emissions to
the equivalent satellite link noise temperature (ΔT/T) is determined. If
the ratio exceeds 6 percent, as determined by the ITU, then there exist
the potential for interference and coordination is required between the
GSO FSS systems. The equivalent satellite link noise temperature is
referred at the output of the receiving antenna. For a bent pipe
transponder (non-processing transponder) system the analysis encompasses
both the uplink and downlink noise contributions. For a base-band
transponder (signal processing transponder) system each portion of the
link (i.e. uplink and downlink) is treated independently. This ΔT/T
approach to satellite coordination is made possible through grouping FSS
systems with similar technical characteristics in the same service
allocation.

*Very Small Aperture Terminals (VSATs).* In 1986 the Commission
established rules for the licensing of very small aperture (VSAT)
satellite earth stations in the 12/14 GHz bands.[^96] Since then, VSAT
operations have been widely deployed across the United States. VSAT
systems are private networks that use a large main antenna to
communicate by satellite link to a large number of smaller remote earth
stations. The hub station controls all remote transmissions. The
Commission provided for \"blanket\" licensing of VSATs by creating an
exclusive allocation for the GSO FSS and VSAT operations. The FSS
allocations that are used for VSAT operations have no terrestrial
operations in them and, therefore, coordination among the operations is
not necessary. This has led to much technical flexibility and growth in
the service. The Ku-band FSS satellite networks are used for voice,
data, facsimile and video transmission, satellite control signals and,
also, broadcasting to consumers in what is called the
"Direct-to-Home"[^97] (DTH) GSO/Fixed Satellite Service. This should not
be confused with the BSS described below. The allocations are now used
to provide internet and video services directly to end users via smaller
antennas than originally envisioned that are more marketable to
consumers.

***Broadcasting Satellite Service (BSS).*** In the 1980's, satellite
technology advanced to the point where the direct to home Broadcast
Satellite Services (BSS) could become a reality. The member states of
the ITU realized that the ability to broadcast to the people of their
countries could be extremely important and, in-order to ensure that all
countries had access to this service, ordered the ITU to draft a
technical plan whereby every administration could receive BSS TV
services. The BSS plans took into account the requirements of all of the
member states and, based upon assumed technical parameters and agreed
upon interference allotments, attempted to fulfill everyone's BSS
requirements. The ITU first developed a BSS plan for Regions 1 and
3[^98]. Later, a Region 2[^99] plan was developed that included the US
requirements. In the ITU Region 2 the BSS Plan used 12.2 -- 12.7 GHz for
the satellite-to-user frequency band. At the same time the ITU
recommended that the 12.2-12.7 GHz band be cleared of the existing fixed
services because it was expected that fixed service systems would give
interference to the ubiquitously deployed home BSS receivers. The
exclusive BSS allocation allows satellite systems to share the spectrum
through a geographic and orbital separation allotment plan that provides
administrations access to particular orbital slots and channels in the
plan. By limiting the operating constraints to inter-system sharing,
U.S. BSS networks have adapted to the plan and use higher powered
satellites to serve small antennas (i.e. smaller than 1.2 m VSAT
antennas) that have much less gain but are more marketable to consumers.

*Mobile Satellite Service (MSS).* Exclusive spectrum and exclusive
frequency assignments within the spectrum have been made by the
Commission to provide for the implementation of MSS systems. In order to
use omnidirectional antennas on the mobile satellite handsets, frequency
separation among the satellite systems is necessary. Separate frequency
assignments allow for higher power satellites to deliver signals to
handsets with low antenna gain (e.g. omnidirectional antennas) and
higher gain antennas on the satellites to receive weaker signals from
the handsets. Like PCS and other emerging technologies, the exclusive
MSS frequency assignments allow for smaller, less power consuming end
user equipment that is marketable to consumers. The size of the mobile
earth terminals (METs) must be small enough to have consumer acceptance.
This could not be accomplished by PCS or MSS with directional antennas
on the mobile terminals. The frequency and geographic isolation tradeoff
in order to implement these services, therefore, leads to exclusive
spectrum for the services whereby the systems have technically similar
and compatible characteristics and the constraints are limited to
intra-service sharing of the spectrum. Specifically, the Commission has
allocated the 1525-1559 MHz/1626.5-1660.5 MHz (L-band), 1610-1626.5
MHz/2483.5-2500 MHz (Big LEO band), and 1990-2025 MHz and 2165-2200 MHz
(2 GHz MSS) bands for MSS system implementation.

*L-band MSS*. The L-band allocation was made by the Commission in 1986
and it concluded that, because of the difficulties in sharing the
spectrum, the spectrum available in the L-band could support only one
U.S. space station licensee. Currently, that U.S. MSS system is
operating in portions of the L-band spectrum. Spectrum sharing problems
arose because of the combined use of regional coverage antennas on the
L-Band satellites and near-omni-directional antennas on the user
terminals. The use of near omni-directional antenna was required to
reduce the size of the user terminal but the lack of antenna
discrimination prevented the isolation among the different L-Band MSS
systems thereby reducing the total number of systems that could be
implemented in the spectrum. For these same reasons, L-band MSS systems
do not share the L-band service allocation with other services.

*Big LEO MSS*. The 1992 World Administrative Radio Conference (WARC-92)
allocated the 1610-1626.5 MHz band on a co-primary basis with other
satellite services for MSS operations in the Earth-to-space direction.
WARC-92 also allocated the 2483.5-2500 MHz band on a co-primary basis
for MSS operations in the space-to-Earth direction (the "Big LEO"
bands). On a secondary basis, WARC-92 further allocated the
1613.8-1626.5 MHz band for MSS operations in the space-to-Earth
direction. In 1994, the Commission allocated exclusive spectrum (with
the exception of Radioastronomy in the 1610.6-1613.8 MHz band) and
issued service rules for Big LEO MSS. Furthermore, the Commission
designated the 1621.35-1626.5 MHz band exclusively to time division
multiple access/frequency division multiple access (TDMA/FDMA)
operations and the 1610-1621.35 MHz and 2483.5-2500 MHz bands for code
division multiple access (CDMA) operations because of the inability of
CDMA systems and TDMA/FDMA systems to share the same frequencies.
Nonetheless, these constraints were intra-service related and were much
less constraining on the deployment of the two MSS systems in operation
today than inter-service constraints may have been on these systems.

*2 GHz MSS*. WRC-92 also allocated 1980-2010 MHz and 2170-2200 MHz bands
to MSS on a global basis. Additionally, WRC-95 adjusted the allocations
to include the 2010-2025 MHz and 2160-2170 MHz bands for MSS in ITU
Region 2, effective January 1, 2005 in the United States and Canada
effective January 1, 2000. In 1997, the Commission allocated the
1990-2025 MHz (uplink) and 2165-2200 MHz (downlink) bands to MSS in
United States, it adopted 2 GHz MSS service rules in August, 2000, and
issued MSS licenses in June, 2001. The 2 GHz MSS allocations are shared
with terrestrial systems, however, and exclusive MSS use of the
allocations is premised on the MSS licensees, according to service rule
requirements, relocating the incumbent terrestrial systems.

***Fixed Satellite Service (FSS) - Non-Geostationary Fixed Satellite
Service (NGSO/ FSS) sharing***. Service allocations typically do not
distinguish among the different service delivery options available to
the operators.[^100] In the 1990s, a variation in the use of the FSS
spectrum was initiated. It was proposed that constellations of
Non-Geostationary (NGSO) satellites in the Ku-band frequencies (11 and
12 GHz band downlink, 14 GHz band uplink), under certain conditions,
could share the same spectrum with the GSO FSS and the DBS systems.
These systems now have international and domestic allocations in the
11.7-12.7 GHz range. NGSO FSS systems had a high potential to cause
unacceptable interference to operational and planned GSO FSS systems.
Initial sharing proposals from the NGSO community were based on non
operation of NGSO systems within a defined orbital separation from the
GSO arc. This was intended to limit the potential for in-line event
interference. The initial proposals indicated that the NGSO systems
could share without impact on the GSO networks and that the GSO networks
would not be aware of the NGSO systems operations. However, the
potential interference increases with the implementation of additional
NGSO systems.

Previously, the GSO FSS interference environment was defined by the
characteristics of the particular satellite networks in the GSO arc (GSO
satellite sharing was based on orbital position, knowledge of antenna
directivity and off axis gain characteristics, as well as power density
levels -- See earlier discussion of ΔT/T). Now after more than 6 years
of technical studies, a sharing solution was reached that provides for
NGSO system operations without overly constraining incumbent GSO FSS
systems.[^101] The solution defined for the GSO community an aggregate
interference that could be designed around by their future systems to
accept the anticipated level of interference. Furthermore, the GSO FSS
would have to limit its antenna off axis EIRP levels for future
networks. The NGSO community as a result has a defined interference
environment that is produced by the operational GSO FSS systems that it
can design around.

Constraints were placed on the GSO FSS operations (and FS operations in
the shared allocations) in the Ku-bands in the U.S. in order to increase
in spectrum utilization within the FSS by NGSO systems. The price paid
to maximize the use of the "white space" in the spectrum was that the
incumbent GSO FSS operations (and terrestrial system operations in the
shared bands) are more constrained in that they must take measures to
protect the NGSO systems and accept more interfering power from them.
The flexibility lost by the GSO FSS is that a possible reduction in
antenna size or use of higher power levels in the future (which may be
needed for higher level modulation to support new applications) were
sacrificed to accommodate the new use of the FSS and FS allocations. The
interactions between GSO and NGSO systems are being further considered
in higher frequency bands such as 20/30 GHz (Ka-band) and 30/40 GHz
(V-band).

***Shared Use of Service Allocations***

*The C-band and Ku-band Fixed Satellite and Fixed Service Allocations.*
It is possible, too, for various services to share the same spectrum
when their technical characteristics are different but compatible. For
instance, in the United States, the 4/6 GHz spectrum (C-band) and 11/14
GHz spectrum (Ku-band) is allocated on a co-primary basis to the
terrestrial Fixed Service (FS) and the Fixed-Satellite Service (FSS).
Since 1974, thousands of terrestrial microwave stations and satellite
earth stations have been coordinated and licensed by the Commission in
the C-band alone. Within the FS, the bands are used for both commercial
and private microwave communications. In the FSS, the 4 GHz and 11 GHz
portions of the C-band and Ku-band are used for space-to-Earth
(downlink) applications including direct-to-home video programming. The
6 GHz and 14 GHz portions of the bands are used for Earth-to-space
(uplink) communications. International allocations are similar to the
U.S. allocations. The stations of the two services use directional
antennas which can be coordinated to use the same frequency assignments
through geographic separation. Both services continue to coordinate the
use of the "white space" in the C-band and Ku-band to maximize the use
of the frequencies.

Indeed, the service rules for FS and FSS systems in the shared frequency
bands require advanced (prior to license application) frequency
coordination between the fixed earth stations and microwave stations.
The constraints are limited, however, to those that are necessary to
complete the coordination of the systems (i.e. the constraints placed on
the stations are limited to those necessary to resolve mutually
unacceptable interference and the constraints may be more or less for
different stations).

More recently, the Commission has adopted service rules and a licensing
approach for C-band Small Aperture Terminals (CSATs). CSATs are similar
to Ku-band VSATs (described earlier) in that they consist of networks of
smaller remote earth stations that communicate via satellite to a large
main antenna or hub. The hub station controls all remote transmissions.
Because the C-band is used heavily by the Fixed Service, unlike the
exclusive Ku-band FSS allocations for VSATs, technical constraints and
coordination procedures were placed on CSAT operations. CSATs are
limited to a portion of the shared allocation and to communications over
a limited number of satellites. By adopting these limits, a streamlined
licensing approach was made possible for CSAT licensees to more readily
deploy networks of CSAT remote antennas while protecting the FS from
unacceptable interference and preserving the C-band for future
terrestrial FS growth.

*Ku-band BSS, NGSO FSS and FS sharing*. Use among systems in a shared
allocation will become more and more constrained as system requirements
call for complex sharing arrangements for all of the allocated services
to have access to the spectrum. As more services are delivered directly
to end users (the users can be anywhere in the geographic service area
and the user density in the geographic area is high) the demand for
uncoordinated access to the spectrum increases for ubiquitous deployment
of systems. Furthermore, the licensing method used for ubiquitous
terrestrial services authorizes the service provider on an 'area wide'
basis the flexibility to install systems within a given geographic area.
Any interference generated within the system is under control of the
single operating entity. By the same token, ubiquitous space services
that meet certain criteria can be provided 'blanket' licenses where the
criteria applied to the space system prevents interference from
occurring and allows the earth terminals to be placed at any location
within the satellite service area. If transmitters of one system are
randomly placed among the receivers of another system through wide-area
or blanket licensing, interference will occur. Therefore, sharing
between two ubiquitous services in the same geographic areas is, in
general, not feasible.

Furthermore, it is costly for ubiquitous services to have constraints on
the placement of terminals because of the needed ability to serve
customers that may be anywhere within the licensed geographic service
area. Operating constraints such as transmitter power or placement limit
the operators' flexibility to provide true ubiquitous service. For
example, the Direct Broadcast Service (DBS) is a BSS service in the U.S.
which is ubiquitous. Geostationary (GSO) DBS satellites deliver
broadcast signals to users through out the U.S. The DBS receivers all
use high gain antennas that generally point in a southerly direction and
can be located anywhere in the country. The NGSO/FSS proposed to take
advantage of these operating characteristics and limit the interference
power that it would produce at a DBS receiver from a constellation of
satellites delivering broadband data in the same frequency band. This
sharing situation results in power constraints on the NGSO/FSS and an
increase in the interference normally received by a DBS user.

Recently, another service, MVDDS, proposed to operate in the FSS and BSS
frequency bands. MVDDS is a terrestrial point-to-multipoint service. In
this case, the Commission adopted rules that will permit the three
ubiquitous services to exist in the same band by placing constraints on
the MVDDS transmitters and defining areas where NGSO/FSS stations are
not permitted to operate. It also adopted a "first-in" arrangement
whereby the MVDDS operator must not operate within 10 km of an NGSO
receiver and the NGSO operator must accept interference from preexisting
MVDDS transmitters. Additionally, the MVDDS operator must notify the
NGSO operator of the location of the MVDDS transmitters so that the NGSO
operators can avoid them. In sum, the introduction of MVDDS resulted in
power constraints on the MVDDS to protect both the DBS and NGSO FSS
systems, the possible exclusion of the NGSO/FSS from areas near an MVDDS
antenna, and DBS receivers will need to accept additional interference.

In general, the tradeoff for introducing more services into an
allocation is to limit some of the technical flexibilities of all the
systems in the allocation. As the sharing situation becomes more
complex, more constraints must be placed on newly introduced services
and on the existing services as well. Wide-area and blanket licensing is
also constrained due to the need to accommodate the "first-in" stations
of the other service. At this stage, the services are no longer truly
ubiquitous.

Sharing possibilities in the Ku-band among ubiquitous services have been
explored but in the Ka-band and V-band, the Commission has taken a
different approach. The approach has led to fewer technical and
regulatory constraints on the services but the cost associated with the
flexibility to have blanket licensing and wide area licensing comes at
the price of exclusive service allocations. In the Ka-band and V-band,
it is proposed that ubiquitous point to multipoint services with small
antennas with little or no sidelobe attenuation would have highly dense
deployment of transmitters and receivers. If both services are to
operate in same frequency band, many more constraints on both services
would have to be in place to avoid mutually unacceptable interference.
An alternative would be to allocate spectrum exclusively to each of the
particular services and limit constraints to intra-service operations.
This provides certainty to licensee and provides for more technical
flexibility within the service.

*Ka-band FSS and FS sharing*. From 1997 to the present, the Commission
has modified the frequency allocations and developed service rules
(including rules for relocation of incumbent systems) throughout the
17-20 GHz range of frequencies. The allocation changes and service rules
adopted by the Commission define the sharing possibilities among the
various satellite services and terrestrial services. The following
figure shows how the service allocations have changed in recent years.

The main reason for the band arrangement is that both the satellite and
the fixed services had requirements for ubiquitous deployment of
end-user stations. There is great difficulty in having two truly
ubiquitous services sharing the same spectrum as discussed earlier. In
this case the ubiquitous services included the BSS, NGSO/FSS and
GSO/FSS. The FSS proposed to provide service to businesses and
households from low-orbit and geostationary satellites. The FS
allocation is mainly used to provide wireless cable distribution. The
BSS proposals are to transmit to the satellites from feeder-link earth
stations and downlink to ubiquitous home receivers in the 17.3-17.7 GHz
band.

18 GHz Order

The amount of spectrum that is shared among the terrestrial and
satellite services has been significantly reduced. By separating the
band into allocations to services that have similar technical
characteristics, blanket licensing and wide-area licensing for the FSS
and FS, respectively, is made possible for the services over most of the
spectrum.[^102] This permits the service operators to deploy user
terminals without having to coordinate with each other. This can only be
done without interference constraints relating to inter-service sharing
(i.e. in bands free of other services). This required the Commission to
adopt rules for relocation of incumbent systems at the expense of the
new system operators.

*V-band FSS and FS sharing*. Prior to 1994, most of the millimeter wave
technology in the V-band was funded by the U.S. Government for military
and scientific purposes. There was little commercial use of the band,
but as technology has evolved, the Commission has initiated several
proceedings to make portions of the V-band available for commercial use.
Proposals for new technologies increased the demand for spectrum
allocations in the 36-51 GHz band and led to complicated spectrum
sharing arrangements. The Commission proceedings addressed the potential
interference problems between terrestrial wireless systems and satellite
services recognizing the limited possibilities of high-density
terrestrial wireless systems and high-density satellite systems sharing
the same frequency bands.

The Commission recognized, too, that sharing between services intended
for communications with ubiquitous consumer terminals, would likely
result in undue technical constraints on one or both of the services.
These technical constraints would not permit terrestrial fixed wireless
systems (FS) or FSS to achieve their full potentials. After several
years of domestic proceedings and World Radiocommunication Conferences
(WRCs), the Commission released a Further Notice of Proposed Rulemaking
in May 2001 that proposes to re-designate portions of the V-band
spectrum for FS and FSS, and it creates and shifts allocations of the
services. The proposed changes reflect the "soft segmentation approach"
developed by the U.S. delegation to the WRC-2000 and adopted by the
WRC-2000. The "soft-segmentation" sharing arrangement was also
incorporated in the International Radio Regulations. The soft
segmentation approach generally favors wireless services in the spectrum
below 40 GHz and favors satellite services in the spectrum above 40 GHz
by requiring more stringent satellite power limits in the spectrum below
40 GHz. The U.S. is attempting to harmonize its spectrum allocations
with the international and regional allocations in order to promote
cross-border arrangements that would enhance the delivery of all V-band
services to consumers.

[^1]: The Interference Protection Working Group is an interdisciplinary
    group of staff from across the Commission's Bureaus and Offices.

[^2]: A transcript of the public workshop is available at the Task
    Force's web site, <http://www.fcc.gov/spft>.

[^3]: 47 U.S.C. § 303 (f).

[^4]: *See Federal Communications Commission Strategic Plan FY 2003 --
    FY 2008*, available at
    <http://www.fcc.gov/omd/strategicplan2003-2008.pfd>.

[^5]: An example is the on-going conflict in the 800 MHz band, involving
    high power commercial radio transmitters and vulnerable mobile
    public safety receivers operating in close proximity on adjacent
    frequencies. The potential for interference between these services
    worsened as commercial licensees evolved the nature of their
    operations from SMR service (with relatively few stations serving
    wide areas) to a cellular service (with many stations serving
    smaller areas). The rules for interference that were established to
    manage interference in this band were developed years ago and
    currently do not appear to be sufficient. This conflict underscores
    the tension that can arise between flexible service offerings and
    the certainty of interference protection. *See* In the Matter of
    Improving Public Safety Communications in the 800 MHz Band and
    Consolidating the 900 MHz Industrial/Land Transportation and
    Business Pool Channels, *Notice of Proposed Rule Making* in WT
    Docket 02-55, 17 FCC Rcd 4873 (2001) (800 MHz Proceeding).

[^6]: For example, while acknowledging the interference conflict at 800
    MHz, Glen Nash, past President of the APCO, Int., stated at the
    August 2, 2002, Interference Protection Workshop: "We really don't
    have a problem. Where we've gotten into trouble is when people don't
    want to play the game." Dr. Andrew Clegg of Cingular Wireless LLC
    added that interference provisions for the PCS service (power limit,
    boundary field strength limit and informal licensee coordination)
    work well and, in his opinion, could serve as a model for the
    future. Other participants at that workshop indicated that many
    interference problems are solved through cooperation among the
    parties through facilities adjustments. According to David Hageman
    of Poka Lambro Telcom, interference is not a major issue in rural
    areas.

[^7]: Comments of Ronald D. Coles on behalf of Stratex Networks, Inc. at
    5. According to Stratex, anecdotal evidence indicates "that in major
    metropolitan areas it is becoming more difficult to coordinate
    frequency pairs in the preferred bands of 11 & 18 GHz."

[^8]: Comments of Sprint Corporation at 2.

[^9]: Comments of CEA at 2-4.

[^10]: *Id.*

[^11]: *Id.*

[^12]: *Id.*

[^13]: At the Interference Protection Workshop, Dr. Clegg made the
    following statement about interference: "I think I can predict the
    future fairly confidently that we're going to see the same that we
    see today, but we're going to see a lot more of it...and it's going
    to be a gradual thing. It may not be so obvious on a day to day
    basis, but the interference will increase."

[^14]: Interference Protection Workshop remarks of Dr. Paul Steffes.

[^15]: Comments of NASA at 6.

[^16]: *Id.*

[^17]: The TAC was created for the purpose of advising the Commission on
    the impact of emerging technologies and other spectrum management
    issues.

[^18]: Comments of Cingular Wireless LLC at 37-38.

[^19]: *Id.*

[^20]: *Id.*

[^21]: *Id.* at 12.

[^22]: The potential for mutual interference among different waveforms
    sharing the same or adjacent spectrum has not been fully quantified.
    It is easier to design rules to protect transmissions with the same
    known waveforms than to protect a waveform of one type from many
    (possibly variable) waveforms.

[^23]: The compatibility of new technologies with those used by
    incumbents is often demonstrated by subjective and objective
    laboratory and/or field-testing. Separate tests are conducted to
    determine the impact of a new waveform on each existing waveform
    that will share the same or adjacent spectrum. As the number of
    available signal waveforms (and combinations thereof) continues to
    rise, the compatibility testing process will become increasingly
    unwieldy and, unless the process is streamlined in some fashion, it
    could jeopardize the ability of technologists to bring their
    products to market with their economic window of opportunity.

[^24]: Interference Protection Workshop remarks of Dr. Paul Steffes.

[^25]: Interference Protection Workshop remarks of Raymond Pickholtz.

[^26]: *Id.*

[^27]: *See* Public Notice, "Spectrum Policy Task Force Seeks Public
    Comment on Issues Related to Commission's Spectrum Policies,"
    Questions 7 and 9, DA 02-1311 (June 6, 2002).

[^28]: 47 C.F.R. § 2.1(c); ITU RR 1.166.

[^29]: 47 C.F.R. § 2.1(c); ITU RR 1.169.

[^30]: 47 C.F.R. § 2.1(c); ITU RR 1.167.

[^31]: 47 C.F.R. § 2.1(c); ITU RR 1.168.

[^32]: *See* Comments of the Satellite Industry Association at 10, which
    note that the term "acceptable interference" can be used in the
    coordination process to define limits to protect against
    unacceptable interference.

[^33]: *See*, for example, 47 C.F.R. §§ 21.2, 90.7 and 101.3, which give
    the definition for *harmful interference* for the Domestic Public
    Fixed Service (Multipoint Distribution Service), Private Land
    Mobile, and Fixed Microwave Services, respectively. Means of
    applying this definition vary with the nature of the service; for
    example, the definition is applied differently depending on whether
    a particular spectrum band is available for exclusive or shared use.
    Note also that 47 C.F.R. § 15.5(b) conditions the operation of
    unlicensed intentional and unintentional radiators on not causing
    *harmful interference* to an authorized radio station.

[^34]: Comment of Comsearch at 7-8.

[^35]: Comments of Nortel Networks at 1. *See also*, for example, the
    Comments of Wayne Longman at 15-16, who contends that a quantified
    definition would "cause more disputes than it resolves"; Comments of
    NASA at 7, which state that "considering new definitions could be
    detrimental to commercial as well as Federal agencies that rely on
    such technical criteria for design and development of new radio
    systems;" and the Comments of Telesat Canada at 3.

[^36]: Comments of Verizon Wireless at 7. *See* *also* Comments of the
    Satellite Industry Association at 10; and Comments of Cingular
    Wireless LLC at 40.

[^37]: Comments of Sprint at 13-17. *See* *also* Comments of National
    Public Radio at 14.

[^38]: *Id.* at 15.

[^39]: Comments of Xtreme Spectrum, Inc. at 6-9. According to Xtreme
    Spectrum, "In the ultra-wide band proceeding the parties generally
    concurred on the appropriate techniques for predicting interference,
    but differed greatly on what assumptions to use -- and consequently
    differed on whether interference would or would not occur in
    practice." *Id.* at 8.

[^40]: Comments of the Satellite Industry Association at 10-11.

[^41]: *Id.*

[^42]: *See*, for example, Comments of Cingular Wireless LLC at 41;
    Comments of Dominion Resources, Inc. at 5-6; Comments of NASA at 7;
    and AT&T Wireless Service at 15.

[^43]: Comments of Cingular Wireless LLC at 41.

[^44]: *Id.* at 43. *See also* the Comments of Motorola, Inc. at 17
    ("The level of interference that can be tolerated may vary depending
    on the nature of the service involved."); and the Comments of Dr.
    Charles L. Jackson at 2 ("If licenses contained clauses stating that
    licensees would have to accept up to some specific level of
    co-channel and adjacent channel energy, then some such disputes
    would be easier to resolve, or might not be disputes at all.")

[^45]: In this context, Mr. Hageman reflected on a past experience in
    which he was informed that there are multiple formulas for
    calculating a field strength limit at a service area boundary.

[^46]: Comments of Telesat Canada at 2; Comments of Bell South at 7.

[^47]: Comments of MSTV/NAB at 12-13.

[^48]: Comments of Carl Stevenson.

[^49]: *See,* for example, the Comments of AT&T Wireless Service at 14;
    Comments of SIA at 13-14; and the Comments of Wayne Longman at 16.

[^50]: Since most of the favored spectrum bands are already in use, much
    of the future demand may be in the form of requests to share
    spectrum with incumbent licensees, for example, by placing very low
    power RF devices "underneath" the much higher emission levels of
    incumbent users.

[^51]: The definitions in Section 2.1(c) of the Commission's Rules are
    sufficient for their intended purpose, provided they clearly state
    that means of interference protection may be tailored to specific
    services. We agree with commenters that any efforts to effect
    significant changes to these definitions should be well coordinated
    with all affected stake holders. The Commission may wish to consider
    a larger role domestically for the definitions of "permissible" and
    "acceptable" interference, in the manner in which these are used in
    the Satellite services.

[^52]: Comments of Personal Telecom Tech, Inc. at 2. Further, Jack Rosa
    of HYPRES, Inc. stated the following at the Interference Protection
    Workshop: "If you had a fast enough machine you could monitor the
    spectrum continuously. You could put in intelligent controllers,
    so-called bandwidth on demand. That technology can be accomplished
    now." A variety of devices are now commonly used to measure RF
    energy. The key is to integrate these devices with high speed
    frequency monitoring technology.

[^53]: The related term "noise temperature" is used by radio astronomers
    as a measure of the intensity of radiations from space. The noise
    temperature concept is also used in the satellite industry in
    connection with determinations of the need for international
    frequency coordination.

[^54]: Interference temperature can be calculated as the power received
    by an antenna (watts) divided by the associated RF bandwidth (hertz)
    and a term known as Boltzman's Constant (equal to 1.3807
    watt-sec/ºKelvin). Alternatively, it can be calculated as the power
    flux density available at a receiving antenna (watts per meter
    squared), multiplied by the effective capture area of the antenna
    (meter squared), with this quantity divided by the associated RF
    bandwidth (hertz) and Boltzman's Constant. An "interference
    temperature density" could also be defined as the interference
    temperature per unit area, expressed in units of ºKelvin per meter
    squared and calculated as the interference temperature divided by
    the effective capture area of the receiving antenna \-- determined
    by the antenna gain and the received frequency. Interference
    temperature density could be measured for particular frequencies
    using a reference antenna with known gain. Thereafter, it could be
    treated as a signal propagation variable independent of receiving
    antenna characteristics.

[^55]: The idea of an interference temperature as a measure of the
    antenna "noise" power in a particular band and location is well
    established. *See*, for example, Wolfram Research at
    <http://scienceworld.wolfram.com/physics/AntennaTemperature.html>.

[^56]: Interference temperature is a component of the total noise
    temperature of a receiving system, which also includes the thermal
    noise generated within the receiver. The publication,
    "Telecommunications: Glossary of Telecommunications Terms," prepared
    by the National Communications System's Technology & Standards
    Division and Published by the General Services Administration
    defines "noise temperature" as follows: "At a pair of terminals, the
    temperature of a passive [system]{.underline} having an available
    [noise power]{.underline} per unit [bandwidth]{.underline} at a
    specified [frequency]{.underline} equal to that of the actual
    terminals of a [network]{.underline} (the underlined terms are, in
    turn, also defined; for example, noise power is the "Interfering and
    unwanted power in an electrical device or system"). *See*
    <http://www.its.bldrdoc.gov/fs-1037/dir-024/_3565.htm>.

[^57]: The spectral characteristics of non-Gaussian signals generally
    are not scalable; *e.g.,* the total power in a frequency bandwidth
    cannot readily be extrapolated from the power level for a sub
    interval of that bandwidth. Thus, if an interference temperature
    "thermometer" measured the temperature of a portion of the bandwidth
    of such a communications system, that value could not be assumed to
    be constant over the entire bandwidth. The thermometer would need to
    measure frequency intervals comprising the whole bandwidth and use
    the largest measured temperature value to characterize the
    environment for the particular receiver.

[^58]: It may be technically complex to estimate the interference
    temperature excluding the licensed desired users. A simple
    measurement in this case would overestimate the actual interference
    temperature, but may be adequate in many cases because it would err
    on the side of preventing unwanted interference.

[^59]: *See*, for example, the Comments of Sky Tower; Comments of CTIA
    at 12 (suggesting a "zoning-like" model for determining what is
    acceptable interference); Comments of Sprint at 17 (suggesting a
    "harmful interference" threshold to cap the "total interference
    effect from all overlaid or coexisting systems. Once the
    interference effect reaches the cap, no more secondary devices or
    systems would be authorized to share the affected band.").

[^60]: In considering candidate bands for interference temperature
    thresholds, the Commission should take into account such other
    factors as the nature and extent of incumbency and the nature of the
    spectrum use. For example, it may not be appropriate to use the
    concept for certain public safety services.

[^61]: Acceptable "interference temperature" limits could, in effect,
    provide implicit receiver standards, because equipment manufacturers
    would have the option of designing receivers to operate in "worst
    case" RF environments.

[^62]: 47 C.F.R. § 25.204 (g). In ATPC systems, when a receiver detects
    a decrease in the necessary signal strength, it sends a control
    signal to the transmitter to increase power.

[^63]: 47 C.F.R. § 25.204 (f).

[^64]: *See* Revisions to Broadcast Auxiliary Service Rules in Part 74
    and Conforming Technical Rules for Broadcast Auxiliary Service,
    Cable Television Relay Service and Fixed Services in Parts 74, 78
    and 101 of the Commission's Rules, FCC 02-298, *Report and Order* in
    ET Docket No. 01-75, adopted October 30, 2002.

[^65]: Comments of Sprint at 14.

[^66]: *Id.* at 15.

[^67]: According to remarks made by Jack Rosa of HYPRES, Inc. at the
    Interference Protection Workshop, indications are that the next
    generation of technology will cost "dramatically less" than current
    systems based on current technology.

[^68]: Comments of Vanu, Inc. at 4-5.

[^69]: Comments of David Reed at 8-9.

[^70]: Comments of HYPRES, Inc. at 2-3.

[^71]: *Id*. at 3.

[^72]: In a noise-limited environment, the range of a signal is
    determined in the assumed absence of interfering signals. In an
    interference-limited environment, the range is determined in the
    presence of interfering signals.

[^73]: Comments of David Reed at 16-19.

[^74]: As an example of the progress in radio technology, the Final Acts
    of the 1949 ITU Radio Conference contain, in Article 5, a Table of
    Frequency Allocations from 10 kHz to 10.5 MHz. The current Article 5
    extends from 9 kHz to 275 GHz.

[^75]: Some types of earth-resource and radio astronomy sensing detect
    the emissions of atoms or molecules that only occur at specific
    frequencies. Other types of sensing, such as sea surface wave height
    are best accomplished over fairly narrow bands of frequencies.

[^76]:
    > *See Public Notice,* "Spectrum Policy Task Force Seeks Public
    > Comment on Issues Related to Commission's Spectrum Policies," DA
    > 02-1311 (June 6, 2002) (PN).

[^77]:
    > Comments of HYPRES, Inc. at 5.

[^78]:
    > Comments of Aeronautical Radio, Inc. at 4; Comments of Cingular
    > Wireless LLC at 52; and, Comments of National Public Radio at 17.

[^79]: Late-Filed Comments of IEEE 802.18 Radio Regulatory Technical
    Advisory Group, IEEE 802.11, 802.15, and 802.16 Working Groups, and
    the IEEE 802 Metropolitan Network Standards Committee at 10; and
    Comments of Public Safety Wireless Network Program at 11.

[^80]:
    > Comments of BellSouth Corporation at 12; Comments of Charles L.
    > Jackson at 3; Comments of Nortel Networks at 6; and Comments of
    > Wayne Longman at 19.

[^81]: Comments of BellSouth Corporation at 12.

[^82]:
    > Late-Filed Comments of IEEE 802.18 Radio Regulatory Technical
    > Advisory Group, IEEE 802.11, 802.15, and 802.16 Working Groups,
    > and the IEEE 802 Metropolitan Network Standards Committee at 10;
    > Comments of Dr. William C. Y. Lee, LinkAir Communications, Inc. at
    > 4; and Comments of Nortel Networks at 8.

[^83]:
    > Reply Comments of American Mobile Telecommunications Association
    > at 8; and Comments of Marlon K. Schafer at 5.

[^84]:
    > Late-Filed Comments of IEEE 802.18 Radio Regulatory Technical
    > Advisory Group, IEEE 802.11, 802.15, and 802.16 Working Groups,
    > and the IEEE 802 Metropolitan Network Standards Committee
    >
    > at 11.

[^85]:
    > Comments of David R. Hughes, Old Colorado City Communications
    > Company at 3.

[^86]:
    > Comments of Ericsson Inc. at 7; Late-Filed Comments of IEEE 802.18
    > Radio Regulatory Technical Advisory Group, IEEE 802.11, 802.15,
    > and 802.16 Working Groups, and the IEEE 802 Metropolitan Network
    > Standards Committee at 11; Comments of Dr. William C. Y. Lee,
    > LinkAir Communications, Inc. at 4; Comments of Marlon K. Schafer
    > at 5; and Comments of Public Safety Wireless Network Program
    >
    > at 11.

[^87]:
    > Comments of National Public Radio at 21.

[^88]:
    > Comments of Citizens Media Corp/Allston-Brighton Free Radio at 13.

[^89]:
    > Comments of National Public Radio at 19.

[^90]: Sprint Comments at 12.

[^91]: Information Technology Industry Council Comments at 9.

[^92]: PanAmSat Reply Comments at 2.

[^93]: Satellite Industry Association Comments at 10-11.

[^94]: For example, *see* *Agreement Concerning the Coordination and Use
    of Radio Frequencies Above Thirty Megacycles per Second, with Annex,
    as amended*, Exchange of Notes at Ottawa, Canada, October 24, 1962,
    Entered into force October 24, 1962. See *also* USA: T*reaties and
    Other International Acts Series* (TIAS) 5205; CAN: *Canada Treaty
    Series* (CTS) 1962 No. 15; *Agreement Revision Technical Annex to
    the Agreement of October 24, 1962* (TIAS 5205/CTS 1962 No. 15)
    Effected by Exchange of Notes at Ottawa, Canada, June 16 and 24,
    1965, Entered into force June 24, 1965. USA:TIAS 5833/CAN: CTS 1962
    No. 15, as amended June 24, 1965.

[^95]: These two areas are evaluated in other sections of this report on
    "Including receiver tolerances in the regulations" and "Enhancing
    transmitter interference control," respectively.

[^96]: *In the Matter of Routine Licensing of Large Networks of Small
    Antenna Earth Stations Operating in the 12/14 GHz Frequency Bands*,
    Declaratory Ruling (rel. April 9, 1986) (VSAT Order). The 11.7-12.2
    GHz Ku-band Fixed Satellite Service (FSS) downlink is associated
    with uplink spectrum at 14.0-14.5 GHz.

[^97]: DTH-FSS originated in the 4/6 GHz, C-band frequencies and was
    later deployed in the Ku-band frequencies. Millions of home
    subscribers still receive programming in these frequency bands.

[^98]: ITU-R Region 1 is comprised of Europe, Russia and Africa. ITU-R
    Region 3 is comprised of Asia and Australia.

[^99]: ITU-R Region 2 comprises North and South America.

[^100]: The service allocation is technology neutral. For example, the
    allocation does not limit the frequency band to a particular
    modulation or orbital altitude.

[^101]: The sharing criteria resulted in limits to aggregate and single
    entry Equivalent Power Flux Density (EPFD) both in the uplink and
    downlink directions from the NGSO systems. This was a defined value
    which represents the combined radiation levels from the NGSO systems
    into any GSO receive antenna either at an Earth station or
    satellite.

[^102]: The MSS/FL allocation from 19.3-19.7 GHz does not involve
    ubiquitous services and therefore sharing with the FS is possible.
    Mobile satellite service Feeder-links only involve a few earth
    stations that use large, highly directive, antennas. These earth
    stations can share with the FS via standard a frequency coordination
    approach and wide FS station deployment is still possible.