**Before the**

**FEDERAL COMMUNICATIONS COMMISSION**

**Washington, DC 20554**

+-------------------------------------+---+----------------------------+
| In the Matter of                    | ) | ET Docket No. 03-237       |
|                                     |   |                            |
| Establishment of an Interference    | ) |                            |
| Temperature                         |   |                            |
|                                     | ) |                            |
| Metric to Quantify and Manage       |   |                            |
| Interference and                    | ) |                            |
|                                     |   |                            |
| to Expand Available Unlicensed      | ) |                            |
| Operation in Certain Fixed, Mobile  |   |                            |
| and Satellite Frequency Bands       | ) |                            |
|                                     |   |                            |
|                                     | ) |                            |
+-------------------------------------+---+----------------------------+

**[COMMENTS OF THE NATIONAL TELECOMMUNICATIONS]{.underline}**

**[AND INFORMATION ADMINISTRATION]{.underline}**

Michael D. Gallagher Kathy D. Smith

Assistant Secretary for Chief Counsel

Communications and Information

Fredrick R. Wentland

Associate Administrator

Office of Spectrum Management

Mark Settle

Edward Drocella

Electronics Engineers

Office of Spectrum Management National Telecommunications and

Information Administration

U.S. Department of Commerce

Room 4713

1401 Constitution Avenue, N.W.

Washington, DC 20230

\(202\) 482-1816

August 13, 2004

**TABLE OF CONTENTS**

**[Section]{.underline}** **[Page]{.underline}**

[EXECUTIVE SUMMARY v](#executive-summary)

[I. INTRODUCTION 2](#introduction)

[II. INTERFERENCE TEMPERATURE LIMITS COULD BE USED AS A MEASURE FOR
DETERMINING APPROPRIATE DEVICE CHARACTERISTICS FOR OPPORTUNISTIC USE OF
THE SPECTRUM, BUT SHOULD NOT BE CONSIDERED A BASIS FOR DETERMINING
NON-INTERFERENCE FROM AN UNLICENSED DEVICE.
5](#interference-temperature-limits-could-be-used-as-a-measure-for-determining-appropriate-device-characteristics-for-opportunistic-use-of-the-spectrum-but-should-not-be-considered-a-basis-for-determining-non-interference-from-an-unlicensed-device.)

[III. THE INTERFERENCE TEMPERATURE MODEL SHOULD NOT BE USED TO
FACILITATE UNDERLAYING UNLICENSED DEVICE OPERATIONS IN FREQUENCY BANDS
LISTED IN SECTION 15.205 OF THE COMMISSION'S RULES.
6](#the-interference-temperature-model-should-not-be-used-to-facilitate-underlaying-unlicensed-device-operations-in-frequency-bands-listed-in-section-15.205-of-the-commissions-rules.)

[IV. THE FREQUENCY BANDS TRANSFERRED FROM THE FEDERAL GOVERNMENT SHOULD
BE CONSIDERED FOR THE INITIAL IMPLEMENTATION OF THE INTERFERENCE
TEMPERATURE MODEL.
11](#the-frequency-bands-transferred-from-the-federal-government-should-be-considered-for-the-initial-implementation-of-the-interference-temperature-model.)

[V. HIGHER-POWERED UNLICENSED DEVICES EMPLOYING DYNAMIC FREQUENCY
SELECTION MAY BE DIFFICULT TO IMPLEMENT IN THE FIXED SERVICE FREQUENCY
BANDS, HOWEVER, EMPLOYING GEO-LOCATION TECHNOLOGY MAY PERMIT SHARING
OPPORTUNITIES.
14](#higher-powered-unlicensed-devices-employing-dynamic-frequency-selection-may-be-difficult-to-implement-in-the-fixed-service-frequency-bands-however-employing-geo-location-technology-may-permit-sharing-opportunities.)

[VI. OPERATIONAL PARAMETERS THAT ARE UNIQUE TO INDIVIDUAL RADIO SERVICES
MUST BE CONSIDERED IN DEVELOPING INTERFERENCE TEMPERATURE LIMITS.
17](#operational-parameters-that-are-unique-to-individual-radio-services-must-be-considered-in-developing-interference-temperature-limits.)

[VII. A THRESHOLD BASED ON A ΔT/T OF ONE PERCENT SHOULD BE EMPLOYED FOR
SITUATIONS WHERE UNLICENSED DEVICES ARE SHARING WITH FIXED-SATELLITE
SERVICE UPLINK RECEIVERS.
20](#a-threshold-based-on-a-δtt-of-one-percent-should-be-employed-for-situations-where-unlicensed-devices-are-sharing-with-fixed-satellite-service-uplink-receivers.)

[VIII. GEO-LOCATION TECHNOLOGY CAN BE USED TO FACILITATE SHARING BETWEEN
UNLICENSED DEVICES AND RADIO ASTRONOMY OPERATIONS IN THE 6650-6675.2 MHz
FREQUENCY BAND.
24](#geo-location-technology-can-be-used-to-facilitate-sharing-between-unlicensed-devices-and-radio-astronomy-operations-in-the-6650-6675.2-mhz-frequency-band.)

[IX. GEO-LOCATION TECHNOLOGY CAN BE USED TO PREVENT UNCOORDINATED USE OF
SPECTRUM WITHIN RADIO QUIET ZONES, AND COORDINATION ZONES.
26](#geo-location-technology-can-be-used-to-prevent-uncoordinated-use-of-spectrum-within-radio-quiet-zones-and-coordination-zones.)

[X. THE PARAMETERS OF THE REFERENCE RECEIVER USED TO ESTABLISH THE
INTERFERENCE TEMPERATURE LIMITS COULD BE DEVELOPED IN THE COMMISSION'S
RULEMAKING PROCEEDING ON RECEIVER STANDARDS.
30](#the-parameters-of-the-reference-receiver-used-to-establish-the-interference-temperature-limits-could-be-developed-in-the-commissions-rulemaking-proceeding-on-receiver-standards.)

[XI. SPATIAL, ANGULAR, TEMPORAL, AND FREQUENCY FACTORS MUST BE
CONSIDERED IN ACCURATELY MEASURING THE INTERFERENCE TEMPERATURE LIMITS.
33](#spatial-angular-temporal-and-frequency-factors-must-be-considered-in-accurately-measuring-the-interference-temperature-limits.)

[XII. DOMESTICALLY AND INTERNATIONALLY DEVELOPED STANDARDS COULD BE USED
FOR DEFINING THE PERMISSIBLE INTERFERENCE LEVELS FOR EACH RADIO SERVICE.
38](#domestically-and-internationally-developed-standards-could-be-used-for-defining-the-permissible-interference-levels-for-each-radio-service.)

[XIII. DEFINING INTERFERENCE TEMPERATURE IN TERMS OF SIGNAL-TO-NOISE
RATIO COULD PROVIDE GREATER FLEXIBILITY AND CERTAINTY THAT BOTH
INCUMBENT AND FUTURE SPECTRUM USERS DESIRE.
42](#defining-interference-temperature-in-terms-of-signal-to-noise-ratio-could-provide-greater-flexibility-and-certainty-that-both-incumbent-and-future-spectrum-users-desire.)

[XIV. IN ORDER TO MAXIMIZE THE USEFULNESS OF MEASURED INTERFERENCE
TEMPERATURE LEVELS, THE PARAMETERS OF THE MEASUREMENT SYSTEM SHOULD BE
STANDARDIZED.
44](#in-order-to-maximize-the-usefulness-of-measured-interference-temperature-levels-the-parameters-of-the-measurement-system-should-be-standardized.)

[XV. BEFORE IMPLEMENTING THE INTERFERENCE TEMPERATURE MODEL, THE RIGHTS
AND RESPONSIBILITIES OF BOTH LICENSED AND UNLICENSED SPECTRUM USERS MUST
BE DEFINED.
47](#before-implementing-the-interference-temperature-model-the-rights-and-responsibilities-of-both-licensed-and-unlicensed-spectrum-users-must-be-defined.)

[XVI. TO EFFECTIVELY IMPLEMENT THE INTERFERENCE TEMPERATURE MODEL,
REPRESENTATIVE OPERATIONAL SCENARIOS MUST BE DEVELOPED FOR EACH RADIO
SERVICE.
49](#to-effectively-implement-the-interference-temperature-model-representative-operational-scenarios-must-be-developed-for-each-radio-service.)

[XVII. THE INTERFERENCE TEMPERATURE LIMITS MUST PROTECT BOTH IN-BAND AND
ADJACENT BAND SPECTRUM USERS.
53](#the-interference-temperature-limits-must-protect-both-in-band-and-adjacent-band-spectrum-users.)

[XVIII. ADDITIONAL PROVISIONS ARE NOT NECESSARY TO PROTECT DEEP SPACE
NETWORK RECEIVERS IN THE 12.75-13.25 GHz BAND LOCATED AT THE GOLDSTONE
COMPLEX.
55](#additional-provisions-are-not-necessary-to-protect-deep-space-network-receivers-in-the-12.75-13.25-ghz-band-located-at-the-goldstone-complex.)

[XIX. TECHNICAL ISSUES RELATED TO THE COMPLIANCE MEASUREMENTS OF
UNLICENSED DEVICES THAT EMPLOY THE INTERFERENCE TEMPERATURE MODEL MUST
BE ADDRESSED.
56](#technical-issues-related-to-the-compliance-measurements-of-unlicensed-devices-that-employ-the-interference-temperature-model-must-be-addressed.)

[XX. THE INTERFERENCE TEMPERATURE LIMITS IN A FREQUENCY BAND SHOULD BE
BASED ON THE MOST SENSITIVE RADIO SERVICE OPERATING IN A BAND.
59](#the-interference-temperature-limits-in-a-frequency-band-should-be-based-on-the-most-sensitive-radio-service-operating-in-a-band.)

[XXI. INTERFERENCE TEMPERATURE MEASUREMENTS MADE BY A SATELLITE RECEIVER
CANNOT BE USED TO PROTECT GROUND-BASED RECEIVERS.
60](#interference-temperature-measurements-made-by-a-satellite-receiver-cannot-be-used-to-protect-ground-based-receivers.)

[XXII. BASELINE MEASUREMENTS IN SELECTED LICENSED AND UNLICENSED
FREQUENCY BANDS SHOULD BE PERFORMED BEFORE DECIDING WHETHER OR NOT THE
INTERFERENCE TEMPERATURE MODEL CAN BE IMPLEMENTED.
63](#baseline-measurements-in-selected-licensed-and-unlicensed-frequency-bands-should-be-performed-before-deciding-whether-or-not-the-interference-temperature-model-can-be-implemented.)

[XXIII. CONCLUSION 65](#conclusion)

> ASSESSMENT OF PROPOSED POWER LEVEL AND DETECTION THRESHOLD IN THE 6
> GHz AND 13 GHz FIXED SERVICE FREQUENCY
>
> BANDS...........................................................................APPENDIX
> A
>
> ASSESSMENT OF POTENTIAL INTERFERENCE TO GOLDSTONE
>
> DEEP SPACE NETWORK OPERATIONS IN THE 12.75-13.25 GHz
>
> BAND...\..........................................................................APPENDIX
> B
>
> DISCUSSION OF THE CRITICAL PARAMETERS OF THE INTERFERENCE
>
> TEMPERATURE MEASUREMENT SYSTEM ...........................APPENDIX C
>
> Discussion of opportunities that can exist for unlicensed DEVICE use
> in certain areas, while protecting the
>
> locations that are potentially more sensitive to
> interference...\............................................................APPENDIX
> d

ASSESSMENT OF THE POTENTIAL IMPACT OF INCREASING THE

NOISE
FLOOR..................................................................APPENDIX
E

# EXECUTIVE SUMMARY {#executive-summary .unnumbered}

The National Telecommunications and Information Administration (NTIA)
commends the Federal Communications Commission (Commission) for
initiating this proceeding that will examine a more quantitative
approach to spectrum management with the goals of providing radio
service licensees with greater certainty regarding the maximum
permissible interference present in the frequency bands in which they
operate and possibly allowing more opportunistic access to the spectrum
by unlicensed devices. NTIA believes that properly developed
quantitative permissible interference standards could assist the
Commission in assessing the degree of potential harm from interference
caused by undesired signals. NTIA believes that the interference
temperature metric, which quantifies the levels of interference at the
licensed user's receiver, should be examined to assess whether it can be
used to allow greater access to the radio frequency spectrum. However,
NTIA believes that opportunistic use of frequency bands by means of the
interference temperature limit is not appropriate for all frequency
bands. NTIA offers the following comments in response to the specific
issues raised in the Commission's Notice of Inquiry and Notice of
Proposed Rulemaking (NOI/NPRM) on the establishment of the interference
temperature metric.

NTIA recommends the following:

-   Any device authorized to make opportunistic use of spectrum within
    the interference temperature limits must still be subject to the
    general conditions of unlicensed device operation.

-   Unlicensed devices using the interference temperature model should
    not be employed in the frequency bands listed in Section 15.205 of
    the Commission's Rules.

-   Initially, the Commission should consider implementing the
    interference temperature model in the frequency bands that have been
    transferred from federal government to private sector use in
    accordance with the requirements of Title VI of the Omnibus Budget
    Reconciliation Act of 1993 and the Balanced Budget Act of 1997.

-   The Commission should not adopt the power levels and dynamic
    frequency selection (DFS) detection thresholds developed for sharing
    with radar systems without performing a further analysis that takes
    into account specific technical factors unique to fixed service (FS)
    systems.

-   Geo-location technology that unlicensed devices can employ to
    facilitate sharing with the FS can also be employed to protect the
    radio astronomy observatories monitoring the methanol spectral line
    in the 6650-6675.2 MHz band.

-   The Commission should not adopt interference temperature limits
    without performing the appropriate supporting technical studies.

-   A change in the receiver temperature divided by the receiver
    temperature (ΔT/T) threshold of 1 percent is appropriate for sharing
    between unlicensed devices and fixed-satellite service uplink
    receivers.

-   The Commission should issue a follow-on NPRM that builds upon the
    existing public record established in the NOI on receiver
    performance requirements to determine the reference receiver
    performance parameters to be used in establishing interference
    temperature limits.

-   The results of the first phase of NTIA's study on interference
    protection criteria values for specific radio services be included
    as part of an NOI to establish maximum permissible interference
    levels applicable to the various radio services.

-   The parameters of the interference temperature measurement system
    should be identified for each frequency band and standardized to
    maximize the usefulness of the measurements.

-   Before the interference temperature model is implemented, the rights
    and responsibilities of spectrum users should be addressed.

-   Operational scenarios and maximum permissible interference limits
    should be developed for each radio service to be used in determining
    the interference temperature limits.

-   When establishing the interference temperature limits, the emissions
    from licensed and unlicensed systems operating in adjacent or
    harmonically related frequency bands should be taken into
    consideration.

-   Prior to implementing the interference temperature model, technical
    issues related to performing the compliance measurements should be
    resolved.

-   The interference temperature limit for unlicensed devices should be
    established to protect both primary and secondary allocated services
    within the frequency band.

-   The Commission should not use the ΔT/T levels measured by a
    satellite receiver to control the operating characteristics of
    unlicensed devices.

-   NTIA and the Commission should identify a list of candidate licensed
    and unlicensed frequency bands where the emission or noise levels
    can be measured using standardized measurement systems, and these
    measurements should serve as a baseline for characterizing the
    existing emission environment in those bands.

NTIA commends the Commission for initiating this proceeding examining
possibilities to expand the options for unlicensed device use while
providing certainty and predictability desired by licensed spectrum
users. NTIA agrees with the Commission regarding the benefits that could
be gained by increasing spectrum access opportunities for unlicensed
devices. Implementation of the interference temperature model and the
use of interference mitigation techniques such as DFS and geo-location
represent a shift in interference management from the transmitter to the
receiver. The NOI identifies many technically challenging issues that
must be addressed before the interference temperature model can be
implemented in a frequency band. These technical issues, include but are
not limited to: development of radio service specific reference receiver
parameters; development of radio service specific maximum permissible
interference limits and operational scenarios; and measurement of the
existing radio frequency signal environment in order to establish a
proper baseline. Until these technical issues, as well as the rights and
responsibilities of spectrum users have been resolved, wide-spread
implementation of the interference temperature model will not possible.
Because of the sensitive nature of the operations in many of the
restricted frequency bands, implementing the interference temperature
model would be difficult, if not impossible. However, if the initial
implementation of the interference temperature model were limited to
specific bands, for example, bands transferred from the federal
government, many of the technical issues listed above could be addressed
and possibly resolved with minimal impact to incumbent spectrum users.
NTIA believes interference mitigation techniques, such as DFS and
geo-location, hold great promise for facilitating sharing between
licensed and unlicensed spectrum users. However, these techniques should
not be employed until the supporting studies examining the specific
characteristics of the licensed services and unlicensed device
applications have been completed.

**Before the**

**FEDERAL COMMUNICATIONS COMMISSION**

**Washington, DC 20554**

+-------------------------------------+---+----------------------------+
| In the Matter of                    | ) | ET Docket No. 03-237       |
|                                     |   |                            |
| Establishment of an Interference    | ) |                            |
| Temperature                         |   |                            |
|                                     | ) |                            |
| Metric to Quantify and Manage       |   |                            |
| Interference and                    | ) |                            |
|                                     |   |                            |
| to Expand Available Unlicensed      | ) |                            |
| Operation in Certain Fixed, Mobile  |   |                            |
| and satellite Frequency Bands       | ) |                            |
|                                     |   |                            |
|                                     | ) |                            |
+-------------------------------------+---+----------------------------+

**[COMMENTS OF THE NATIONAL TELECOMMUNICATIONS]{.underline}**

**[AND INFORMATION ADMINISTRATION]{.underline}**

The National Telecommunications and Information Administration (NTIA),
an Executive Branch agency within the Department of Commerce, is the
President's principal adviser on domestic and international
telecommunications policy, including policies relating to the Nation's
economic and technological advancement in telecommunications.
Accordingly, NTIA makes recommendations regarding telecommunications
policies and presents Executive Branch views on telecommunications
matters to the Congress, the Federal Communications Commission
(Commission), and the public. NTIA, through the Office of Spectrum
Management (OSM), is also responsible for managing the federal
government's use of the radio frequency spectrum. NTIA respectfully
submits the following comments in response to the Commission's Notice of
Inquiry and Notice of Proposed Rulemaking (NOI/NPRM) in the
above-captioned proceeding.[^1]

# INTRODUCTION

In this NOI/NPRM the Commission seeks comments on a new interference
temperature metric for quantifying and managing interference. The
Commission believes that this metric could shift the current method for
assessing interference, which is based on the emissions generated by the
transmitter, to an approach that is based on the actual radio frequency
(RF) environment, taking into account the interactions between
transmitters and receivers. As envisioned, the Commission believes that
the interference temperature metric could allow non-licensed device
operations within licensed frequency bands based on the unlicensed
user(s) not exceeding the interference temperature limit.

The Commission, in the NOI portion of this proceeding, requests comment
on a number of issues relating to the development and use of the
interference temperature metric for managing a possible transition from
the current transmitter-based approach for interference management to
the new interference temperature metric. The Commission poses questions
concerning the development of the interference temperature metric,
including the determination of interference temperature limits for
specific frequency bands, and an assessment of the cumulative noise and
interference environment in RF bands, including standard methodologies
for making assessments to support the selection of those limits. In the
NPRM portion of this proceeding, the Commission seeks comment on
technical rules that would permit higher-powered unlicensed device
operation in specific frequency bands used primarily by fixed-satellite
uplinks and terrestrial fixed point-to-point links.

The interference temperature metric in and of itself is not a new
concept, and has been used extensively in the satellite and radio
astronomy services, where the distances from the receiver to RF sources
are very large.[^2] For example in the fixed-satellite service a change
in receiver temperature divided by receiver temperature (ΔT/T) criterion
has been used by the International Telecommunication Union (ITU) as a
trigger for coordination of co-primary satellite systems. However, the
Commission's proposals to establish and codify interference temperature
limits: based on actual measurements of the RF environment and using the
RF environment measurements to permit underlaying higher-powered
unlicensed devices in bands used by licensed radio services are new
concepts that must be evaluated very carefully.

There are several ongoing Federal programs that could benefit from
establishing interference temperature limits in some frequency bands.
The Department of Defense (DoD) is developing the neXt Generation (XG)
program through the Defense Advanced Research Projects Agency
(DARPA).[^3] Like DARPA's early work on the Internet, XG-based
technology is applicable to both military and civilian applications. The
National Science Foundation (NSF) is also exploring the technology
developments needed for enhancing spectral efficiencies of wireless
networks in support of expanding opportunities for new services in the
wireless industry. NSF's Networking Technology Systems (NeTS) program is
addressing the challenges associated with these networks.[^4]

NTIA agrees with recommendations made in the Spectrum Policy Task Force
(SPTF) Report that the Commission should explore adopting a more
quantitative approach to spectrum (interference) management.[^5] Many of
the issues raised in the SPTF report were also addressed in NTIA's
Spectrum Summit.[^6] NTIA believes that properly developed quantitative
permissible interference standards could assist the Commission in
assessing the degree of potential harm from interference caused by
undesired signals. NTIA understands that the interference temperature
metric as proposed is to quantify and manage the permissible levels of
interference at the licensed user's receivers. NTIA believes that the
interference temperature metric should be examined to assess whether it
can be used to allow greater access to the RF spectrum. However,
opportunistic use of frequency bands by means of an interference
temperature metric is not appropriate for all frequency bands. NTIA also
believes that the determination of the level of interference that a
non-licensed user can or will cause is difficult to ascertain. This
level of interference is a function of many factors that include, but
are not limited to, the transmit power of the non-licensed user, the
propagation loss between the non-licensed and licensed users, the
antenna pattern and gain of the licensed and non-licensed users, and
possibly the aggregation of interference resulting from multiple users
(non-licensed and licensed).

NTIA supports the Commission in its investigation of the interference
temperature metric to quantify and manage interference in a more precise
fashion and to expand the opportunities for new services in the wireless
industry, while at the same time to provide licensed operations with
greater certainty regarding the maximum permissible interference level
and greater protection against interference. NTIA offers the following
comments in response to the specific issues raised in the Commission's
NOI/NPRM.

# INTERFERENCE TEMPERATURE LIMITS COULD BE USED AS A MEASURE FOR DETERMINING APPROPRIATE DEVICE CHARACTERISTICS FOR OPPORTUNISTIC USE OF THE SPECTRUM, BUT SHOULD NOT BE CONSIDERED A BASIS FOR DETERMINING NON-INTERFERENCE FROM AN UNLICENSED DEVICE.

In the NOI, the Commission seeks comment on the feasibility of using
interference temperature as a general approach to spectrum management.
The Commission specifically seeks comment on whether a general metric
can be used to gauge the success of the introduction of the interference
temperature into a new frequency band. Comments are also sought on
whether there is a simple metric that can be used to gauge the effect of
these unlicensed devices upon the incumbent services.[^7]

The interference temperature model has merit as a measure of received
undesired energy, and potentially as a means to determine how a device
should or should not operate in order to minimize the potential for
interference. However, any device authorized to make opportunistic use
of spectrum within the interference temperature limits must still be
subject to the general conditions of unlicensed operation. Specifically,
persons operating intentional or unintentional radiators shall not be
deemed to have any vested right to continued use of any given frequency
by virtue of prior registration or certification of equipment, and also
these devices may not cause harmful interference, and must accept
interference from authorized users of the spectrum.[^8] No "safe harbor"
approach should be utilized, since an objective of this proceeding is to
provide radio service licensees with greater certainty regarding the
maximum permissible interference, and greater protections against
harmful interference that could be present in the frequency bands in
which they operate.[^9] Additionally, the interference temperature model
should not impact the definition of harmful interference, which is
defined as "\[i\]nterference 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."[^10]

# THE INTERFERENCE TEMPERATURE MODEL SHOULD NOT BE USED TO FACILITATE UNDERLAYING UNLICENSED DEVICE OPERATIONS IN FREQUENCY BANDS LISTED IN SECTION 15.205 OF THE COMMISSION'S RULES.

In the NOI, the Commission acknowledges that licensees would prefer to
see the interference temperature limits in the bands they use set low,
while the manufacturers and users of unlicensed devices would prefer to
see these limits set high. The Commission requests comment on whether
there are some services or frequency bands for which the Commission
should continue to use the current interference protection
procedures.[^11]

Unlicensed devices that would operate under the Commission's proposed
interference temperature model would still have to comply with the
fundamental conditions of operating under Part 15 of the Commission's
Rules. For example, unlicensed devices operating under the interference
temperature model would still be required to accept whatever
interference is received and must correct whatever interference is
caused to licensed services, even if this means ceasing operation.[^12]
Also, unlicensed devices may not operate in the designated restricted
frequency bands listed in Section 15.205 of the Commission's Rules.[^13]
The restricted frequency bands include bands used to support
safety-of-life functions such as aeronautical radionavigation and bands
employed by radio services that must function, as a nature of their
operation, using extremely low received signal levels. The systems that
operate in these frequency bands may be passive, such as radio
astronomy, or active, such as satellite downlinks. In these restricted
frequency bands, only spurious and unintentional emissions are
permitted. The only exception to this prohibition is for devices
employing ultrawideband (UWB) technology operating under SubPart F of
Part 15 of the Commission's Rules. Unlicensed devices that employ UWB
technology, by their very nature, have wide transmit bandwidths and
cannot avoid operation in many of the restricted frequency bands.
Operation in the restricted frequency bands has also been permitted
under specific circumstances.[^14]

It is difficult to envision how the interference temperature model as
described in the NOI can be implemented to manage interference in the
restricted frequency bands without establishing interference temperature
limits that are so low that any commercial wireless device would be
rendered useless. For example, it does not appear possible to allow
opportunistic use of radio astronomy bands and still protect radio
astronomy observatories and other passive sensing applications by
employing the interference temperature model, due to the nature and
extremely low power of the cosmic signals the radio astronomers need to
study. The permissible interference levels for primary radio astronomy
frequency bands are given in ITU-Radiocommunications Sector (ITU-R)
Recommendation RA.769.[^15] Table 1 gives the permissible interference
levels, and the corresponding interference temperature limits in several
radio astronomy frequency bands.

Table 1.

+--------------------+-------------------------+-----------------------+
| **Frequency        | **Permissible           | **Interference        |
| Range**            | Interference Level**    | Temperature**         |
|                    |                         |                       |
| **(MHz)**          | **(dB(W/m^2^Hz))**      | **(K)**               |
+--------------------+-------------------------+-----------------------+
| 608-614            | -253                    | 7 x 10^-5^            |
+--------------------+-------------------------+-----------------------+
| 1400-1427          | -255                    | 8 x 10^-6^            |
+--------------------+-------------------------+-----------------------+
| 4990-5000          | -241                    | 1.7 x 10^-5^          |
+--------------------+-------------------------+-----------------------+

The interference temperature levels shown in Table 1 were calculated
using the power flux density for the maximum permissible interference
level specified in ITU-R Recommendation RA.769, assuming that the radio
telescope receives interference through the sidelobe of the antenna
(assuming 0 dBi gain). A 2000 second integration time is used in the
calculation of the permissible interference levels in ITU-R
Recommendation RA.769. If a longer integration time is used, as
frequently occurs in sensitive radio astronomy observations, the
tolerable interference temperature levels would be further reduced.

NTIA does not believe that wireless consumer devices, on a real-time
basis, will be able to measure such low levels of interference
temperature, and such measurements are believed to be outside of the
range of any practical monitoring station. Therefore, it would not be
practical to monitor such low interference temperatures by any of the
methods described in the NOI.[^16] Even if someday such monitoring
capabilities were to become feasible, because of the low interference
temperature required to protect radio astronomy and passive operations,
few if any new opportunities could be expected to become available to
other spectrum users.

Figure 1 of the NOI illustrates the interference temperature model by
showing a "service range" that decreases with distance from the
transmitter.[^17] This may be applicable to communication systems.
However, there is no equivalent service range for radio astronomers and
the passive services. The power at the radio astronomy receiver is a
line that is parallel to the original noise floor shown in Figure 1 of
the NOI, and in fact, may lie well below that noise floor. Communication
signals and those that radio astronomers and passive services seek to
detect are very different, providing another reason why the interference
temperature model should not be applied in the restricted frequency
bands. For example, celestial signals are 1x10^6^ to 10^12^ times weaker
than typical communication signals and consist of Gaussian noise with
little or no modulation.[^18] When observing a celestial source, radio
astronomers detect small increases in the noise power over the ambient
noise at the output of the receiver by performing long integrations
(often lasting several hours and even days) by accurately pointing at
and tracking the celestial source. By a combination of increased
integration time and increased bandwidth, noise fluctuations at the
celestial source are reduced by a large factor. By contrast, interfering
signals due to communication systems vary in time, either intrinsically,
or because they are seen drifting through the sidelobe structure of the
telescope, as it tracks the celestial source being observed, and these
signals are not likely to average out with time.

In addition to the gains in scientific knowledge that results from radio
astronomy and passive sensing, related research spawns technological
developments that are of direct and tangible benefit to the public have
emerged. For example, radio astronomy techniques have

contributed significantly to major advances in the following areas:
computerized tomography as well as other technologies for studying and
creating images of tissue inside the human body; increasing the ability
to forecast earthquakes using very-long-baseline-interferometric (VLBI)
measurements of fault motion; and use of VLBI techniques in the
development of wireless telephone geographic location technologies that
can be used in connection with the Commission's Enhanced-911
requirements.[^19] The continued development of new critical
technologies by passive scientific observers of the spectrum depends on
researchers having continued access to interference-free spectrum.

NTIA believes that there are several technical problems associated with
employing the interference temperature model in the restricted frequency
bands, such as the limitations in the monitoring systems and the limited
commercial viability for unlicensed devices operating at the permissible
interference levels required in many of the restricted frequency bands.
The prohibition on unlicensed device operations in the restricted
frequency bands is the only practical method to protect sensitive
operations that must measure extremely low signal levels. Therefore,
NTIA does not support employing the interference temperature model to
allow unlicensed use in the frequency bands listed in Section 15.205 of
the Commission's Rules. NTIA believes that this should not impact the
Commission's ability to examine the feasibility of the interference
temperature model, since there is sufficient spectrum available outside
of the restricted frequency bands.

# THE FREQUENCY BANDS TRANSFERRED FROM THE FEDERAL GOVERNMENT SHOULD BE CONSIDERED FOR THE INITIAL IMPLEMENTATION OF THE INTERFERENCE TEMPERATURE MODEL.

In the NOI, the Commission seeks comment on whether the introduction of
devices employing the interference temperature model should be done in
stages to ensure that incumbent radio services do not suffer undue
interference. For example, the Commission asks how it should limit the
initial introduction of the devices to protect the incumbent systems if
the interference temperature were implemented in stages.[^20]

Many of the parties that submitted comments in response to the
Commission's SPTF Report believe that there are potential problems with
the interference temperature model as proposed in the report.[^21] These
commenters represent a broad class of commercial terrestrial and
satellite service providers, equipment manufacturers, and industry
associations. Several commenters believe that the adoption of the
interference temperature model, to allow the underlaying of unlicensed
devices, will degrade the performance of currently deployed systems and
may make future systems more costly, or inhibit the deployment of new
technologies by

incumbent service providers.[^22] The incumbent service operators also
believe that since the

interference temperature model analyzes the "worst case" under current
technology and spectrum usage conditions, it could possibly preclude
implementing new technologies that may improve spectral efficiency and
provide communications at levels that may not be possible today.[^23]
Even the commenters that support the interference temperature approach
believe that more work is needed in defining the noise environment and
recommend that the Commission proceed cautiously.[^24]

In the NPRM, the Commission proposes to allow underlaying higher-powered
unlicensed device operation in selected frequency bands used for
commercial fixed service (FS) and fixed-satellite service (FSS)
operations in the 6525-6700 MHz band and broadcast auxiliary and cable
television relay services in the 12.75-13.25 GHz band (excluding mobile
operations in the 13.15-13.2125 GHz band).[^25] The 6650-6675.2 MHz band
segment is used by the radio astronomy service and the 12.75-13.25 GHz
band is used for government and non-government space research downlink
operations on a secondary basis. Although the NPRM addresses underlaying
higher-powered unlicensed devices in these bands, the Commission's
proposals do not address any of the technical issues raised in the NOI
for implementing the interference temperature model.

Many of the concerns raised by the commenters to the SPTF report are
similar to those raised by the federal agencies. However, NTIA believes
that it is possible to study and develop the interference temperature
model on a limited basis before the more general implementation has
begun. NTIA recommends that initially the Commission should consider
implementing the interference temperature model in the frequency bands
that have been transferred from federal government to private sector use
in accordance with the requirements of Title VI of the Omnibus Budget
Reconciliation Act of 1993 and the Balanced Budget Act of 1997. The
transferred frequency bands represent spectrum that at this time has
limited commercial usage or has not been transferred for private sector
use. Therefore, limiting the initial introduction of the interference
temperature model to the transferred bands will allow the Commission to
address the many technical issues raised in the NOI while minimizing the
impact on incumbent service providers and their customers.

An example of a transferred frequency band where the interference
temperature model could be initially employed is the 3650-3700 MHz band.
The Commission has an ongoing rulemaking proceeding in which it is
considering both licensed and higher-powered unlicensed device
operations.[^26] Since there are no service rules in place for the
licensed or unlicensed users, this band would give the Commission an
opportunity to employ some of the techniques proposed in the NOI (e.g.,
measurement of the RF signal environment).

# HIGHER-POWERED UNLICENSED DEVICES EMPLOYING DYNAMIC FREQUENCY SELECTION MAY BE DIFFICULT TO IMPLEMENT IN THE FIXED SERVICE FREQUENCY BANDS, HOWEVER, EMPLOYING GEO-LOCATION TECHNOLOGY MAY PERMIT SHARING OPPORTUNITIES.

The Commission is seeking comment on employing Dynamic Frequency
Selection (DFS) to permit higher-powered unlicensed device operation in
the 6525-6700 MHz (6 GHz band) and 12.75-13.25 GHz (13 GHz band) FS
frequency bands.[^27] Specifically, the Commission proposes to require a
minimum detection threshold of -64 dBm for unlicensed devices operating
at power levels above 23 dBm and -62 dBm for unlicensed devices
operating at power levels below 23 dBm.[^28] The Commission tentatively
concludes that equivalent isotropically radiated power (EIRP) levels of
between 30 dBm to 36 dBm are possible in the FS frequency bands.[^29]
The 6525-6700 MHz band is used to support public safety and railroad,
water, and energy services that are vital to the nation's
infrastructure.[^30] NTIA believes that there are several areas of the
Commission's proposals that require further examination before this
approach can applied in the FS frequency bands.

The DFS detection thresholds proposed by the Commission are based on a
technical analysis performed to ensure compatibility between unlicensed
devices and high-powered federal radar systems. The DFS technique
studied in that analysis is applicable to radar systems where the
transmitter and receiver are at the same location, and where the
propagation path from the DFS equipped unlicensed device back to the
radar receiver is the same as the path from the radar transmitter to the
DFS equipped unlicensed device. In this situation, any shielding (e.g.,
terrain, foliage, building) that attenuates the signal from the radar to
the DFS-equipped unlicensed device would similarly attenuate the
unlicensed device transmitter signal that is received at the radar.
However, in the FS, the transmitter and receiver are typically separated
by tens of kilometers. Since the FS transmitter and receiver are at
different locations, the problem of the "hidden transmitter" exists. In
the hidden transmitter problem, if the DFS-equipped unlicensed device is
blocked from receiving the transmitted FS signal it will be permitted to
transmit. When the unlicensed device is permitted to transmit and is
close to a FS receiver, it may preclude the FS receiver from detecting
the desired signal. It is also possible for the DFS equipped unlicensed
device to be located outside of the FS transmitting antenna beam, which
would greatly reduce the signal level at the unlicensed device making
detection for DFS difficult. In its proposal the Commission does not
address the hidden transmitter problem. Before DFS techniques can be
employed in the FS frequency bands, the hidden transmitter problem must
be addressed.

The DFS detection thresholds proposed by the Commission are based on
assessing aggregate interference to radar systems in the 5250-5350 MHz
and the 5470-5725 MHz bands from a specific number of unlicensed devices
all of which were assumed to be operating well below the EIRP level of
36 dBm proposed by the Commission for operation in the 6525-6700 MHz
band.[^31] Thus, it is unclear whether these detection thresholds can be
applied to sharing with FS receivers without further study. In Appendix
A, the results of a link budget analysis are presented that determined
whether: the proposed DFS detection threshold is adequate for protection
of FS receivers based on the proposed power level for unlicensed
devices. The analysis in Appendix A also determines the EIRP of an
unlicensed device that is necessary to preclude potential interference
to FS receivers. Based on the results of the analysis in Appendix A, the
detection threshold for the 6 GHz band is -110 dBm and -95 dBm for the
13 GHz band. These detection thresholds are well below the -64 dBm
proposed by the Commission. In order to eliminate potential interference
to FS receivers, the EIRP levels of the unlicensed devices must be
limited to -28dBm/MHz (6 GHz band) and -9 dBm/MHz (13 GHz band). These
EIRP levels are lower than the Commission's proposal of 36 dBm for
unlicensed device operation in these bands. If the unlicensed device
operates at the proposed EIRP level of 36 dBm, separation distances of
28 km (6 GHz band) and 14 km (13 GHz band) are necessary to avoid
potential interference.

NTIA recommends that the Commission not adopt the power levels and
detection thresholds developed for sharing with radars systems without
performing a further analysis that takes into account specific technical
factors unique to FS systems. There are several fundamental differences
between radar and FS system operations that could make the effective
implementation of DFS difficult in bands used by the FS. For example, it
is unclear whether a DFS-equipped unlicensed device can be designed with
sufficient sensitivity to detect FS signals. There are also technical
issues related to the hidden transmitter problem for FS systems, but not
for radar systems, that need to be addressed. NTIA believes that
higher-powered unlicensed device operation is feasible in the FS bands
if the unlicensed device is equipped with geo-location technology. In
comments in another Commission rulemaking proceeding, the Institute of
Electrical and Electronics Engineers 802.18 Radio Regulatory Technical
Advisory Group stated that embedding global positioning system (GPS)
technology in unlicensed devices is technically feasible and could be
used to limit the device so it does not transmit when located in or near
an area where interference to a satellite receive earth station is
likely.[^32] This approach could also apply to FS locations, where
exclusion zones can be established around each site. Unlicensed devices
that employ geo-location technology in conjunction with an online
database of the FS site locations can then be prohibited from operating
in those areas.[^33] The Commission, in another rulemaking, also noted
that one of the benefits of cognitive radio would be the ability to
determine its location and the location of other transmitters, and then
select the appropriate operating parameters such as the power and
frequency allowed at its location.[^34] This could also be true for the
use of the interference temperature model.

# OPERATIONAL PARAMETERS THAT ARE UNIQUE TO INDIVIDUAL RADIO SERVICES MUST BE CONSIDERED IN DEVELOPING INTERFERENCE TEMPERATURE LIMITS.

Operational parameters of both licensed services and proposed unlicensed
uses are required in order to adequately determine the technical
characteristics needed for successful implementation of any interference
temperature limits. An example of an appropriate methodology for
conducting interference analyses that can be used in setting
interference temperature limits appears in the recent 5-GHz Unlicensed
National Information Infrastructure (U-NII) proceeding.[^35] The
analyses used to determine appropriate thresholds for use by U-NII
devices employing DFS took into account the appropriate technical
characteristics of the radiolocation transmitter and receiver (e.g.,
antenna pattern, bandwidth, scan rate), as well as the appropriate
technical characteristics of the proposed unlicensed use of the band by
Radio Local Area Network (RLAN) devices. The results of these analyses
indicated combinations of transmit power, antenna gain, RF bandwidth,
and measurement integration time that would allow successful sharing
between the unlicensed RLANs and the radiolocation systems. Similar
analyses would need to be conducted for each frequency band being
considered for setting of interference temperature limits. Each
analysis, however, would be unique due to differing technical
characteristics of various licensed services and various unlicensed
device applications, as well as differing propagation characteristics in
each frequency band.

The Satellite Link Budget Analysis contained in Appendix B of the
NOI/NPRM contains a collection of assumptions that were made in
performing the analysis. While it is necessary to make certain
assumptions in order to conduct the analysis, some of the assumptions
could prove to be incorrect. In particular, the assumptions shown in
Table 1 of Appendix B of the NOI/NPRM that were made for the
distribution of power levels in unlicensed devices is highly dependent
on the type of applications being offered in the unlicensed spectrum.
The assumptions made in this instance appear to follow closely the
methodology used in determining power distribution in the 5 GHz U-NII
R&O.[^36] These assumptions, however, were made with

the input of the incumbent users of the band, and with the input of
unlicensed manufacturers as

to how they intended to use the band (i.e., RLANs). The lower output
levels were based on use

of wireless access cards in laptop computers. In such an application, RF
personal exposure

limits and laptop battery life limit the use of transmit power. The same
assumptions would not hold true for other services, such as Wireless
Internet Service Providers (WISPs) where maximum coverage would be
accomplished by higher power levels from outdoor antennas mounted on
towers or rooftops. This is an example where greater flexibility for the
unlicensed user could result in less certainty for the licensed user.

The NOI/NPRM also proposes to use the same DFS detection thresholds
determined for U-NII devices in the 5250-5350 MHz and 5470-5725 MHz
bands.[^37] While the methodology used to determine these thresholds
could be applied to other radiocommunication services, these particular
thresholds were determined through extensive modeling efforts undertaken
by industry, the Department of Defense, and NTIA for the specific
sharing scenarios between the radiolocation service and RLANs. The
individual thresholds are not necessarily applicable to other radio
services operating in other frequency bands.

NTIA believes that there are many radio service dependent operational
factors that must be considered in the technical studies used to
establish interference temperature limits. NTIA strongly recommends that
the Commission not adopt interference temperature limits without
performing the appropriate supporting technical studies.

# A THRESHOLD BASED ON A ΔT/T OF ONE PERCENT SHOULD BE EMPLOYED FOR SITUATIONS WHERE UNLICENSED DEVICES ARE SHARING WITH FIXED-SATELLITE SERVICE UPLINK RECEIVERS.

The Commission proposes to permit unlicensed devices operating at higher
power levels to underlay in the 6525-6700 MHz and 12.75-13.25 GHz FSS
uplink frequency bands. The Commission proposes that a ΔT/T threshold of
5 percent for the aggregation of unlicensed devices be used to assess
whether or not sharing is possible. The Commission also performed a link
budget analysis using an assumed unlicensed device distribution for the
power levels and duty cycles of the individual devices. The analysis
computes the number of aggregate co-channel unlicensed devices that are
needed to exceed the ΔT/T threshold. The Commission seeks comment on the
appropriate level for the ΔT/T threshold to be used and the various
assumptions included in their link budget analysis.[^38]

Inmarsat is currently procuring its next generation of satellites for
launch in 2004 and 2005, one of which will be visible from the United
States. These satellites operate in frequency bands that include the
6525-6700 MHz band and are used for a number of mission critical
purposes. This band is used to support feeder links for Inmarsat mobile
satellite services, as part of the Global Maritime Distress and Safety
System (GMDSS), which provides safety-of-life services to the maritime
community throughout the world.[^39] This band is also used for feeder
links to support the Satellite Based Augmentation System (SBAS) signals,
which are part of the radio navigation satellite service (RNSS).[^40]
The SBAS is used to enhance GPS capability (integrity as well as
improved accuracy and availability), used for aircraft navigation
purposes. These feeder links are used in the United States to support
the Federal Aviation Administration's (FAA's) Wide Area Augmentation
System (WAAS).

NTIA agrees with the Commission that a ΔT/T threshold is appropriate to
use when assessing potential aggregate interference to satellite
receivers. The ΔT/T concept uses interference allotments to apportion
interference to different types of sources and is used in assessing
potential interference to FS and FSS systems. The Commission proposes a
ΔT/T of 5 percent which is slightly more conservative than the value of
6 percent used as a coordination trigger between co-primary satellite
systems. The interference margin in the FSS system is intended to
accommodate external sources, such as other mobile satellite service
(MSS) systems, downlink interference to earth station from RNSS systems,
other FSS systems, and fixed and mobile services. Since there are
numerous possible sources of external interference in the FSS band,
their available margin is already reduced. NTIA believes that it may be
more appropriate to use a ΔT/T value of 1 percent for sharing with
unlicensed devices. This would be consistent with the interference
allotment approach that the FSS and FS uses for the totality of
non-primary (unlicensed) interference sources.[^41]

In general, NTIA agrees with the factors included in the Commission's
link budget analysis. The assumptions that have the greatest bearing on
the results of the analysis are the distribution of unlicensed device
EIRP levels and duty cycles, which are used to determine the EIRP level
of a single "representative" unlicensed device. The distribution of EIRP
levels and duty cycles will be directly related to the type of
unlicensed device application that will be operating in the frequency
band. Based on the past analysis of U-NII devices and radar systems, the
distribution of EIRP levels and duty cycles assumed in the Commission's
link budget analysis appear to be representative of unlicensed devices
that are predominantly used for lap-top Wireless Access Systems. These
EIRP level and duty cycle distributions may not be representative for
higher-powered unlicensed device applications that employ
omni-directional antennas. For example, devices that would provide
wireless broadband connectivity by WISPs, would employ omni-directional
antennas to achieve uniform coverage of a particular geographic
area.[^42] Using higher EIRP levels without the significant antenna gain
reduction in the direction of the satellite that the Commission used in
their analysis would greatly increase the interference seen by the
satellite receiver. In this situation, the increased interference level
would reduce the total number of unlicensed devices that could operate
before the ΔT/T threshold is exceeded.

With regard to the link budget, NTIA agrees with the calculations up to
the point where the "Allowable Emitters per Beam in RLAN BW" is
computed. The numbers computed in the Commission's analysis are 171,544
for the 6 GHz band and 739,832 for the 13 GHz band. The remaining
portion of the link budget in question is given in Table 2.

Table 2.

  ------------------------------------------ -------------- --------------
  **Parameter**                              **6 GHz Band** **13 GHz
                                                            Band**

  Allowable Number of Emitters per Satellite 171,544        739,832
  Beam                                                      

  Available Bandwidth                        175            500

  Part 15 Reuse Bandwidth in FSS Band        11.67          25

  Alternative Polarizations                  2              2

  Total Number of Unlicensed Systems within  53,369,095     369,916,129
  CONUS                                                     
  ------------------------------------------ -------------- --------------

The "Part 15 Reuse Bandwidth in the FSS Band" factor (third entry in
Table 2) is determined by dividing the "Available Bandwidth" factor
(second entry in Table 2) by an assumed 20 MHz channel bandwidth of the
unlicensed devices considered in this analysis. This indicates the total
number of unlicensed channels that would be sharing the FSS band. The
total number of unlicensed systems in the United States (fifth entry in
Table 2) is determined by multiplying the "Allowable Number of Emitters
per Satellite Beam" (first entry in Table 2), the "Part 15 Reuse
Bandwidth in the FSS Band" factor, and the "Alternative Polarizations"
factor (fourth entry in Table 2). For the 6 GHz band case there appears
to be an error in the third row entry because 175/20 equals 8.75 not
11.67. Furthermore, it appears that the total number of unlicensed
systems for both the 6 GHz and 13 GHz bands is also incorrect.

Table 3 provides what NTIA believes to be the correct calculation of the
total number of unlicensed systems.

Table 3.

  ------------------------------------------ -------------- --------------
  **Parameter**                              **6 GHz Band** **13 GHz
                                                            Band**

  Allowable Number of Emitters per Satellite 171,544        739,832
  Beam                                                      

  Available Bandwidth                        175            500

  Part 15 Reuse Bandwidth in FSS Band        8.75           25

  Alternative Polarizations                  2              2

  Total Number of Unlicensed Systems within  3,002,020      36,991,600
  CONUS                                                     
  ------------------------------------------ -------------- --------------

The values shown in Table 3 are based on an interference allotment of 5
percent for unlicensed device interference. If a 1 percent interference
allotment were used, the number of unlicensed devices that could be
permitted would be 606,835 for the 6 GHz band and 7,062,700 for the 13
GHz band.

NTIA agrees with the Commission that a ΔT/T threshold is appropriate to
use when assessing potential aggregate interference to satellite
receivers. The ΔT/T model uses interference allotments to apportion
interference to different types of sources, which is an established
spectrum management technique for sharing between licensed and
unlicensed radio services. NTIA believes that a ΔT/T threshold of 1
percent is appropriate for sharing between unlicensed devices and FSS
uplink receivers.

# GEO-LOCATION TECHNOLOGY CAN BE USED TO FACILITATE SHARING BETWEEN UNLICENSED DEVICES AND RADIO ASTRONOMY OPERATIONS IN THE 6650-6675.2 MHz FREQUENCY BAND.

As part of the Commission's proposal to allow higher-powered unlicensed
device operations in the 6525-6700 MHz band, it requests comment
regarding protection of radio astronomy observations in the 6650-6675.2
MHz portion of the band. The Commission specifically requests comment on
whether it is necessary to preclude unlicensed device operations in the
6650-6675.2 MHz portion of the band or can suitable technical standards
be developed to ensure that harmful interference is not caused to radio
astronomy observations.[^43]

The 6650-6675.2 MHz band is used for observations of the 6668.518 MHz
methanol spectral line. The methanol line is an important tracer of star
formation activity. Although there is no allocation for radio astronomy
in this segment of the band, this spectral line is listed in ITU-R
Recommendation RA.314 among the lines of greatest importance to radio
astronomy.[^44] International footnote 5.149 also specifically
recognizes that administrations are urged to take all practicable steps
to protect radio astronomy operations from harmful interference.
Emissions from spaceborne and airborne stations can be particularly
serious sources of interference to radio astronomy observations.

The U.S. radio astronomy observatories that are observing the methanol
spectral line are given in Table 4.

Table 4.

  --------------------------- ----------------- --------------- ---------------
  **Radio Astronomy           **Latitude**      **Longitude**   **Elevation**
  Observatory**                                                 

  Allen Telescope Array       40º  49' 04'' N   121º  28' 24''  1043 m
                                                W               

  Arecibo Observatory         18º  20' 46'' N   066º  45' 11''  496 m
                                                W               

  Green Bank Telescope        38º  25' 59'' N   079º  50' 24''  825 m
                                                W               

  Very Large Array            34º  04' 44'' N   107º  37' 04''  2126 m
                                                W               

  Very Long Baseline Array                                      
  Stations                                                      

  Pie Town, AZ                34º  18' 04'' N   108º  07' 07''  2371 m
                                                W               

  Kitt Peak, AZ               31º  57' 22'' N   111º  36' 42''  1916 m
                                                W               

  Los Alamos, NM              35º  46' 30'' N   106º  14' 42''  1967 m
                                                W               

  Ft. Davis, TX               30º  38' 06'' N   103º  56' 39''  1615 m
                                                W               

  N. Liberty, IA              41º  46' 17'' N   091º  34' 26''  241 m
                                                W               

  Brewster, WA                48º  07' 53'' N   119º  40' 55''  255 m
                                                W               

  Owens Valley, CA            37º  13' 54'' N   118º  16' 34''  1207 m
                                                W               

  St. Croix, VI               17º  45' 31'' N   064º  35' 03''  16 m
                                                W               

  Hancock, NH                 42º  56' 01'' N   071º  59' 12''  309 m
                                                W               

  Mauna Kea, HI               19º  48' 16'' N   155º  27' 29''  3720 m
                                                W               
  --------------------------- ----------------- --------------- ---------------

Table 5 lists the major cities in proximity to observatories and their
distances from the radio astronomy sites that are observing the methanol
spectral line.

Table 5.

  -------------------- --------------------------------------------------
  **Observatory**      **Distance to Major U.S. Cities**

  Allen Telescope      Sacramento 250 km; San Francisco 350 km
  Array                

  Green Bank Telescope Pittsburgh 230 km; Washington DC 250 km; Richmond
                       240 km

  Very Large Array     Albuquerque 150 km; EL Paso 270 km; Tucson 270 km;
                       Phoenix 410 km

  Very Long Baseline   
  Array Stations       

  Pie Town, AZ         Albuquerque 160 km; EL Paso 320 km; Tucson 350 km;
                       Phoenix 360 km

  Kitt Peak, AZ        Tucson 70 km; Phoenix 180 km; Los Angeles 630 km

  Los Alamos, NM       Albuquerque 80 km; EL Paso 440 km; Amarillo 410 km

  Ft. Davis, TX        EL Paso 270 km

  N. Liberty, IA       Chicago 320 km; Milwaukee 330 km; Des Moines 170
                       km

  Brewster, WA         Seattle 210 km; Tacoma 250 km; Spokane 180 km

  Owens Valley, CA     San Bernardino 350 km; Sacramento 320 km; Fresno
                       140 km; Bakersfield 220 km; Las Vegas 290 km

  Hancock, NH          Boston 110 km; New York 300 km

  Mauna Kea, HI        Honolulu 290 km
  -------------------- --------------------------------------------------

As shown in Table 5, many of the radio astronomy observatories observing
the methanol spectral line are located in remote areas, in radio quiet
zones, or in the mountains where they are afforded a great deal of
protection from ground-based interfering sources. NTIA believes the
geo-location technology that unlicensed devices can employ to facilitate
sharing with the FS can also be employed to protect the radio astronomy
observatories listed in Table 4.

# GEO-LOCATION TECHNOLOGY CAN BE USED TO PREVENT UNCOORDINATED USE OF SPECTRUM WITHIN RADIO QUIET ZONES, AND COORDINATION ZONES.

Radio quiet zones and coordination zones are intended to provide
protection to passive sensing of the electromagnetic spectrum. The
nature and intent of these zones are directly in conflict with the
notion of opportunistic use of spectrum using the interference
temperature model. These zones were created to minimize potential
interference to radio astronomy or other facilities that require
low-noise environments and are highly sensitive to RF interference. The
low-noise environments that are created to protect these facilities are
the same environments that opportunistic use of spectrum under the
interference temperature model could attempt to exploit. Higher-powered
unlicensed use under the interference temperature model could present
difficulty in protecting these locations from interference. Because
there is no transmitted signal from these stations, real-time sensing of
the RF environment cannot indicate the need for protecting these
services. Geo-location technologies could provide a basis for protecting
these sensitive facilities from harmful interference, while still
allowing opportunistic use of the spectrum in areas that are
sufficiently distant from the facilities.

The National Radio Quiet Zone (NRQZ) was established to protect the
National Radio Astronomy Observatory in Green Bank, West Virginia and
the Naval Radio Research Observatory in Sugar Grove, West Virginia from
possible harmful interference. The NRQZ is the area bounded by 39°15' N
on the north, 78°30' W on the east, 37°15' N on the south, and 80°30' W
on the west. The reference point that is used for calculating the
potential for interference is the prime focus of the Green Bank
Telescope (GBT). The location (NAD83) of the GBT prime focus is
38°25'59.2" N latitude, 79°50'23.4" W longitude. The ground elevation is
776 m, and the height is 139.6 m above ground level. For successful
coordination in the NRQZ, the calculated power density of the
transmitter at the reference point should be less than:

-   1 x 10^-8^ W/m^2^ for frequencies below 54 MHz

-   1 x 10^-12^ W/m^2^ for frequencies from 54 MHz to 108 MHz

-   1 x 10^-14^ W/m^2^ for frequencies from 108 MHz to 470 MHz

-   1 x 10^-17^ W/m^2^ for frequencies from 470 MHz to 1000 MHz

-   f^2^ (in GHz) x 10^-17^ W/m^2^ for frequencies above 1000 MHz

In frequency bands that are allocated to the radio astronomy service,
the criteria of ITU-R Recommendation RA.769-1 are applied.[^45]

The Table Mountain Radio Receiving Zone (TMRZ) of the Research
Laboratories of the Department of Commerce is used for research
concerned with low signal levels, such as from deep-space,
extraterrestrial low-signal satellites, or very sensitive receiver
techniques, to be conducted without the potential for interference found
in most areas of the nation. NTIA's Institute for Telecommunication
Sciences (ITS) has maintained oversight of the TMRZ to ensure the levels
of unwanted RF energy within the site conform with federal regulations
and the site remains a valuable national research asset. The TMRZ
facility is essential to research in the area of very wideband receiver
technology and radio wave propagation. The federal government has a
number of permanent facilities used for ongoing research projects at the
TMRZ. In addition to ITS, the facilities at the TMRZ support research
and development activities being performed by the National Institute of
Standards and Technology, the National Atmospheric and Oceanic
Administration, the United States Geological Survey, as well as other
federal agencies, research universities, and telecommunication and
technology industries. To ensure that the capabilities of the site (1800
acres in the vicinity of 40°07'50" N latitude, 105°15'40" W longitude)
remain conducive to this type of research, the field strengths received
from radiated signals should be limited to the values shown in Table
6.[^46]

Table 6.

  ----------------------- ----------------------- -----------------------
  **Frequency Range**     **Field Strength (mV/m) **Power flux density\*
                          in authorized bandwidth (dBW/m^2^) in
                          of service**            authorized bandwidth of
                                                  service**

  Below 540 kHz           10                      -65.8

  540 to 1600 kHz         20                      -59.8

  1.6 to 470 MHz          10                      -65.8

  470 to 890 MHz          30                      -54.2\*\*

  Above 890 MHz           1                       -85.8\*\*
  ----------------------- ----------------------- -----------------------

\* Equivalent values of power flux density are calculated assuming free
space characteristic impedance of 376.7=120π ohms.

\*\* Space stations shall conform to the power flux density limits at
the earth's surface specified in appropriate parts of the Commission's
rules, but in no case should exceed the above levels in any 4 kHz band
for all angles of arrival.

Additionally, the following guidelines are given for determining whether
coordination is necessary:

-   All stations within 2.4 km (1.5 miles).

-   Stations within 4.8 km (3 miles) with 50 watts or more average
    effective radiated power (ERP) in the primary plane of polarization
    in the azimuthal direction of the TMRZ.

-   Stations within 16.1 km (10 miles) with 1 kW or more average ERP in
    the primary plane of polarization in the azimuthal direction of the
    TMRZ.

-   Stations within 80.5 km (50 miles) with 25 kW or more average ERP in
    the primary plane of polarization in the azimuthal direction of the
    TMRZ.[^47]

The Arecibo Coordination Zone was created to protect the radio astronomy
operations at the Arecibo Observatory. The coordination zone consists of
the islands of Puerto Rico, Desecheo, Mona, Vieques, and Culebra. The
interference guidelines shown in Table 7 are used in coordination
efforts within the Arecibo Coordination Zone.

**Table 7.**

  ----------------------- ----------------------- -----------------------
  **Frequency (MHz)**     **Bandwidth (MHz)**     **Threshold level of
                                                  spectral power flux
                                                  density (dBW/m^2^/Hz)**

  13.36-13.41             0.05                    -248

  25.55-25.67             0.12                    -249

  73.0-74.6               1.6                     -258

  322.0-328.6             6.6                     -258

  406.1-410.0             3.9                     -255

  425.0-435.0             10.0                    -255

  608.0-614.0             6.0                     -253

  1332-1400               70.0                    -255

  1400-1427               27.0                    -255

  1610.6-1613.8           3.2                     -238

  1660-1670               10                      -251

  2370-2390               20.0                    -247

  2690-2700               10.0                    -247

  4800-4990               190.0                   -241

  4990-5000               10.0                    -241

  10600-10700             100.0                   -240
  ----------------------- ----------------------- -----------------------

The radio quiet zones and radio receiving zones are currently protected
by coordination requirements and maximum allowable field strength
requirements. These coordination and analyses efforts are performed on a
case-by-case basis by personnel from the affected facility and the
applicant desiring to make use of the spectrum in these areas. NTIA
believes that new technologies could allow this analysis to take place
on a real-time basis within a device (whether licensed or unlicensed)
and that coordination with the affected facility might not be necessary
for unlicensed devices employing geo-location technologies.

# THE PARAMETERS OF THE REFERENCE RECEIVER USED TO ESTABLISH THE INTERFERENCE TEMPERATURE LIMITS COULD BE DEVELOPED IN THE COMMISSION'S RULEMAKING PROCEEDING ON RECEIVER STANDARDS.

In the NOI, the Commission requests comment on the receiver performance
parameters that should be considered in setting the interference
temperature limits.[^48] Specifically, the Commission requests
information on whether there are minimum receiver performance criteria
that should be considered as a reference in setting interference
temperature limits and how should the specifications for such a receiver
should be developed. The Commission also seeks comment on whether a
worst receiver available for a service, or an average receiver should be
used in determining the interference temperature limits.[^49]

A receiver used for a specific radio service is required to receive and
process a wide range of signal powers, but in most cases it is important
that they be capable of receiving distant signals whose power has been
attenuated during transmission. There are several parameters that can be
used to define the minimum performance of a reference receiver for the
purpose of establishing interference temperature limits: sensitivity,
noise figure, and selectivity. The sensitivity is one of the most
important receiver characteristics and defines the weakest signal power
that may be processed satisfactorily. The noise figure is the amount of
noise (in decibels) that the receiver adds to the input noise within its
noise bandwidth.[^50] The selectivity is the property of the receiver
that allows it to separate a signal or signals at one frequency from
those at all other frequencies. These parameters are related, and
changes in one will likely result in changes to the others. For example,
selectivity can be enhanced by adding greater filtering to the RF input
of the receiver. This will also result in greater loss at the desired
frequency, causing a reduction in sensitivity.

Although the parameters discussed above are applicable to all receivers,
the actual values of these parameters will vary dramatically for each
authorized radio service. For example, receivers operating in the RNSS
have noise figures on the order of 2 to 3 dB and are capable of
receiving signals below their thermal noise floor, whereas, land mobile
receivers typically have noise figures of 8 to 10 dB and a sensitivity
at or above their thermal noise floor. Thus, it is clear that the
performance parameters used in determining the reference receiver to
establish the interference temperature limit will vary depending upon
the radio service(s) operating in a specific frequency band.

To establish the interference temperature limits, a reference receiver
model must be developed for each radio service. It is difficult to
determine whether the reference receiver should be based on parameters
representing an "average" or "worst" receiver until these terms are
defined. It is also important to realize that what one group would
consider to be a worst receiver (e.g., low immunity to interference)
another group would consider to be a "best" receiver due to its greater
sensitivity. For this discussion, a reference receiver based on the
average receiver has parameters that are in between the minimum and
maximum values of receivers operating in a radio service. For example,
if the noise figure of receivers operating in a frequency band varies
from 4 to 8 dB, a value of 6 dB is used to define the noise figure of
the average reference receiver. A reference receiver based on a worst
receiver would use parameters representing the most sensitive (e.g.,
lowest measured noise levels) values of a receiver operating in a radio
service. Using the previous example, a reference receiver based on a
worst receiver would use a value of 4 dB to define noise figure of the
reference receiver. Based on these definitions, it is clear that if the
reference receiver is defined based on average parameters, the measured
noise levels will be higher and there is a risk that all of the
receivers in a given radio service will not be adequately protected.
Therefore, NTIA recommends that the parameters for the reference
receiver to be used in establishing the interference temperature limits
should be based on the most sensitive parameters of the receivers
operating in the authorized radio services.

There are many national and international standards bodies that have
been involved in developing receiver standards that the Commission
should take into consideration in defining the parameters for the
reference receivers. These standards bodies, include but are not limited
to, the Telecommunications Industry Association (TIA), the Consumer
Electronics Association (CEA), RTCA, Inc.,[^51] the ITU-R, the
International Civil Aviation Organization (ICAO), the European
Telecommunications Standard Institute (ETSI), and the International
Electrotechnical Commission (IEC). NTIA has recently published a study
on receiver standards, documenting currently existing domestic and
international receiver standards.[^52] NTIA recommends that the
Commission consider the information contained in this report in
developing the reference receiver performance parameters.

In response to the SPTF recommendation to consider applying receiver
performance requirements, the Commission issued a NOI seeking public
comments on the following areas: current receiver environment;
performance and standards; possibilities of improving receiver immunity;
potential approaches to achieving desired levels of performance;
considerations that should guide the Commission's approach; and issues
relating to the possible incorporation of receiver immunity performance
incentives, guidelines, or standards.[^53] Based on the results of this
NOI, the Commission has started developing a public record of the
technical issues related to receiver performance standards. NTIA
recommends that the Commission issue a follow-on NPRM that builds upon
the existing public record to determine the receiver performance
parameters to be used in establishing interference temperature limits.

# SPATIAL, ANGULAR, TEMPORAL, AND FREQUENCY FACTORS MUST BE CONSIDERED IN ACCURATELY MEASURING THE INTERFERENCE TEMPERATURE LIMITS.

One of the goals of the interference temperature limits is to protect a
licensed user's receiver from an unlicensed user that is transmitting on
the same frequency. As discussed in the NOI, the Commission requests
comment on two approaches that could be used in measuring the
interference temperature levels: real-time measurements, and
measurements from multiple fixed monitoring (reference) sites.[^54]

In order to provide a meaningful measurement of the interference
temperature, the signal levels measured by the real-time (i.e.,
integrated within the unlicensed device) or fixed (i.e., dedicated
reference equipment) monitoring site receivers must be representative of
the signal levels that a licensed user's receiver operating within the
frequency band of interest would encounter. Several technical factors
can have a significant impact on the signal levels measured by real-time
or fixed monitoring station receivers: antenna height, antenna gain
pattern, antenna polarization, and bandwidth.

Using an improper antenna height for the real-time or monitoring network
receivers could result in either an under estimation or over estimation
of the received signal levels used to determine the interference
temperature levels. For example, if the monitoring network receivers are
at ground-level but the licensed user's receiver is elevated (e.g., a
base station tower), then the propagation loss between the potential
interferer and an elevated user will be different than the loss between
two ground-level users. In this situation, the monitored and reported
interference temperature levels would differ significantly from the
interference temperature observed by the licensed user, making
compliance with the established limits difficult if not impossible to
enforce. This problem could be addressed by assuming a worst-case, from
an interference perspective, propagation loss environment such as free
space. However, this brings up the fundamental issue of range estimation
between a potentially unlicensed interferer and a licensed user, which
will vary for different licensed services and unlicensed device
applications.

When the licensed user and the monitoring receiver have antennas with
similar gain patterns, the reported measured interference temperature
levels would be an adequate representation of the RF environment. If the
licensed user's antenna has a different antenna gain pattern than the
monitoring antenna, the interference temperature measurements obtained
using the monitoring antenna would not reflect the actual interference
experienced by the licensed user. For example, when the interference
temperature monitoring device is equipped with an omni-directional
antenna, the resulting reported interference temperature level would
appear to be uniform, and any directional variations would tend to be
smoothed out. However, if the licensed user has a directional or higher
gain receive antenna, then the interference temperature experienced by
the licensed user would be lower than the level measured by the
monitoring receiver in some directions.[^55] The potential for such
variations would need to be considered when establishing an interference
temperature limit to ensure that the limit appropriately represents the
worst case (from an interference perspective) operating environment of
the licensed receivers.

Similar to the antenna gain variations, problems would be created if the
licensed user's receiver and the monitoring receiver operate with
different intermediate frequency (IF) bandwidths. For example, if the
licensed user's receiver IF bandwidth is narrow (e.g., 25 kHz) and the
bandwidth of the interference temperature monitoring receiver is wide
(e.g., 5 MHz), there is a 23 dB difference in the noise floor between
these two bandwidths. If there are discrete spurious sources that are
contributing to the interference temperature, this would be averaged and
reported over the wider bandwidth of the monitoring receiver. Over most
of the band, the actual interference temperature would be somewhat lower
than the reported (average) interference temperature. However, on the
particular channel that contains the spurious sources, the interference
temperature could be considerably worse than the reported average level.
The problem of taking the bandwidth into account when measuring the
interference temperature is further complicated by systems that employ
adaptive bandwidth technology to increase the throughput.[^56] If the
interference temperature is to accurately represent the interference
encountered by a licensed receiver, it should take into account the
impact of bandwidth disparities.

The polarization of the interference temperature monitoring system is
another factor that could greatly underestimate the measured signal
levels. The most common polarizations are linear (horizontal or
vertical), circular (left hand and right hand) or elliptical. If the
polarization of the monitoring system's receive antenna is different
from the polarization of the transmitted signals in the environment a
polarization mismatch loss is encountered.[^57] Table 8 provides a
summary of the mismatch losses for different combinations of antenna
polarizations.[^58]

Table 8.

  ----------------------- ----------------------- -----------------------
  **Polarization**                                **Polarization Mismatch
                                                  Loss**

  **Monitoring Antenna**  **Transmitted Signal**  

  Horizontal              Vertical                Greater than 20 dB

  Horizontal              Circular                3 dB

  Vertical                Horizontal              Greater than 20 dB

  Vertical                Circular                3 dB

  Circular                Horizontal              3 dB

  Circular                Vertical                3 dB

  Circular (Left Hand)    Circular (Right Hand)   Greater than 25 dB

  Circular (Right Hand)   Circular (Left Hand)    Greater than 25 dB
  ----------------------- ----------------------- -----------------------

As it can be seen from Table 8, the error resulting from using different
polarizations for the monitoring system can result in a significant
underestimation of the measured signal. It should also be pointed out
that the polarization of an antenna remains relatively constant
throughout the main lobe of the antenna pattern, but can vary
considerably in the minor lobes, which could result in additional
measurement errors.[^59]

Taking the above factors into consideration, achieving finer resolution
to account for minimum receiver bandwidths or minimum receive antenna
beamwidths would appear to be necessary to ensure that an interference
temperature limit is established that provides adequate protection to
all licensed user's receivers. However, if an interference temperature
monitoring receiver utilizes narrow bandwidths and beamwidths, the
increases in the number of observation points, both in frequency and
azimuth sweeps, would greatly increase the total sweep time and would
introduce latency in the update rate for unlicensed transmitters
depending on real-time information from the monitoring stations. For
example, increasing the total sweep time would increase the likelihood
that maximum actual interference temperature values are not measured in
a time-varying environment, such as for packet data systems, systems
using antennas employing

beam forming techniques, or frequency hopping systems. This would
further extend the time delay before interference above the interference
temperature limit is detected and action is taken by the unlicensed
device.

Real-time or fixed interference temperature monitoring receivers could
encounter spatial, angular, temporal, and frequency limitations. Some of
these limitations can be addressed by establishing antenna heights,
bandwidths, and antenna gain patterns and polarizations for the
monitoring receivers that are representative of the licensed user's
receiver. However, if frequency and angular increments are too small, a
time delay in measured interference temperature levels may be
introduced, where the licensed user would not be adequately protected on
a real-time basis. For mobile real-time monitoring systems and mobile
licensed users, it is not clear how the technical limitations raised
above can be addressed. However, NTIA believes that it is possible to
resolve many of these technical issues if the locations of both the
monitoring system and licensed user are fixed.

# DOMESTICALLY AND INTERNATIONALLY DEVELOPED STANDARDS COULD BE USED FOR DEFINING THE PERMISSIBLE INTERFERENCE LEVELS FOR EACH RADIO SERVICE.

In the NOI, the Commission requests comment on whether a modest rise in
the noise floor of a receiver as envisioned by the interference
temperature model, would generally not cause harmful interference as
defined under their definition of harmful interference.[^60] Comments
are sought on how much interference can be tolerated before it is
considered harmful for a given radio service in a given frequency band.
If the determination of harmful interference is based on a specific
quality of service level, the Commission seeks comment on the rationale
used to justify this level. The Commission also requests that commenting
parties identify the specific frequency bands and services associated
with these levels.[^61]

The interference temperature metric as defined in the NOI is merely a
measuring tool. It could be used to identify how much interference
exists in a particular band at a particular time in a given geographical
area. However, it does not determine whether the measured level of
interference is too high, too low, or just right. In order to use the
interference temperature metric, this determination will have to be made
in many frequency bands across the RF spectrum. To accomplish this in a
way that promotes spectrum efficiency, provides protection to
incumbents, and that is predictable and non-arbitrary, a permissible
interference standard is needed, not just a new technical metric. The
need for a permissible interference standard is discussed in an article
submitted as part of the public record for the SPTF.[^62] This article
identifies the lack of permissible interference standards in the
Commission's Rules as a problem and proposes that such standards be
developed, and suggests a framework to accomplish this objective. This
is consistent with the Commission's stated objective of providing radio
service licensees with greater certainty regarding the maximum
permissible interference in the frequency bands in which they
operate.[^63]

One of the key steps in any interference, electromagnetic compatibility,
or sharing assessment is identifying an appropriate level of permissible
interference. The identification of the appropriate level is often
confusing, time consuming, with no single reference source from which to
draw. Complications arise because of the divergent needs of incumbents
and proposed entrants into any frequency band. The complexity of this
process is further complicated by the numerous terms used regarding
interference. For example, various fora including the NTIA, the
Commission, and the ITU-R define five terms relative to interference:
Interference, Permissible Interference, Accepted Interference, Harmful
Interference, and Protection Ratios. Other terms that are commonly used,
but not specifically defined are Allowable Performance Degradation,
Interference Protection Criteria, and Spectrum Sharing Criteria. Since
the spectrum sharing criteria normally depend upon specifics of the
interfering and interfered-with systems, as well as

the types of interfering signals, a very large number of combinations
are possible.

Permissible interference levels can be specified for aggregate (e.g.,
total from all sources of interference) or single-entry interference.
For a given radio service and type of system (e.g., communications,
radar), the parameters listed in Table 9 should be considered in
developing the aggregate and single-entry permissible interference
levels. The parameters listed in Table 9 will vary depending on the
radio service operating in a given frequency band. For example, in
developing permissible interference levels in the frequency bands used
by the aeronautical radio navigation service, the power thresholds would
not be permitted to vary based upon time duration of the interference,
due to the safety-of-life functions of this service. On the other hand,
in the frequency bands used by the FS, power thresholds can be based on
long-term and short-term time percentages of interference.

Table 9.

+----------+---------+------------------------------------------------+
| **Par    | **      | Description                                    |
| ameter** | Typical |                                                |
|          | Units** |                                                |
+----------+---------+------------------------------------------------+
| Power    | dBm,    | Two or more levels of interfering signal power |
| T        |         | (I), interference-to-noise-ratio power ratios  |
| hreshold | dBW,    | (I/N), or signal -- or carrier-to interference |
|          |         | power ratios (S/I or C/I)                      |
|          | dB      |                                                |
+----------+---------+------------------------------------------------+
| R        | Hz,     | Bandwidth in which interfering signal power    |
| eference |         | should be calculated or measured.              |
| B        | kHz,    |                                                |
| andwidth |         |                                                |
|          | MHz     |                                                |
+----------+---------+------------------------------------------------+
| Pe       | Percent | For each power threshold, the percentage of    |
| rcentage |         | time during which the threshold should in the  |
| of Time  |         | case of S/I or C/I or should not in the case   |
|          |         | of I or I/N, be exceeded.                      |
+----------+---------+------------------------------------------------+
| Pe       | Percent | For each power threshold, the percentage of    |
| rcentage |         | locations at which the threshold should in the |
| of       |         | case of S/I or C/I or should not in the case   |
| L        |         | of I or I/N, be exceeded. Used in some radio   |
| ocations |         | services to protect operations within a        |
|          |         | service area.                                  |
+----------+---------+------------------------------------------------+
| Special  | Various | Information needed for interpretation or       |
| Co       |         | application of the thresholds, including as a  |
| nditions |         | minimum whether the permissible interference   |
|          |         | is for aggregate or single-entry interference. |
|          |         | The type of interfering signal for which the   |
|          |         | permissible interference level pertains to the |
|          |         | I/N, S/I, or C/I thresholds the definition of  |
|          |         | the N, S, C reference levels. This may include |
|          |         | the duration for which permissible             |
|          |         | interference can be exceeded; specific         |
|          |         | category of victim or interfering stations;    |
|          |         | and frequency off-tuning associated with the   |
|          |         | power thresholds.                              |
+----------+---------+------------------------------------------------+

It is possible to describe potentially interfering signals using a
number of generic categories. Table 10 provides a list of the generic
categories that can be used to describe potentially interfering signals.
The permissible interference levels for a system operating in a given
radio service can vary depending on the types of interfering signal
being received. For example, GPS receivers operating in the RNSS are
more susceptible to continuous wave (CW) signals compared to noise-like
signals and are less susceptible to interference from low-duty cycle
pulsed signals. This susceptibility to CW and robustness to pulsed
interfering signals is directly related to the signal structure of the
GPS navigation signal.

Table 10.

  ---------------- ------------------------------------------------------
  **Type of        **Definition**
  Interfering      
  Signal**         

  Continuous Wave  A continuous signal with a bandwidth much smaller than
                   the receiver baseband (output bandwidth).

  Noise-Like       A continuous signal that resembles Gaussian white
                   noise over the radio frequency bandwidth of the
                   receiver (uniform power spectral density) or produces
                   the same effect as such a signal.

  Pulsed           A signal that is turned on and off over time defined
                   by the time on (pulse width) and the repetition rate
                   of the pulses. The pulses may occur at a constant or
                   changing repetition rate.

  Impulse          A signal with very short duration pulses, generally
                   less than 0.1 -2 nanoseconds in duration and occurring
                   at constant or changing repetition rates.

  Same as Desired  A signal with modulation parameters that are the same
  Signal           as the desired signal except the baseband information
                   content (carrier frequencies may differ).
  ---------------- ------------------------------------------------------

NTIA recently completed the first phase of a study that reviewed
existing standards and identified available interference protection
criteria (IPC) for the various radio services in the 30 MHz to 30 GHz
frequency range.[^64] The study considered national and international
standards from the following organizations: ITU-R, TIA, RTCA, ICAO,
ETSI, IEC, International Maritime Organization, World Meteorological
Organization, European Radiocommunications Organization, Radio Technical
Commission Maritime, Aerospace and Flight Test Telemetry Coordination
Committee, Institute for Electronic and Electrical Engineers, United
Kingdom Radiocommunications Agency, and Eurocontrol. Based on its
review, NTIA determined that for many of the radio services, the IPC
values contained in the various publications were incomplete and varied
due to the specific type of interfering signal being received. During
the second phase of the NTIA study, emphasis will be placed on
developing IPC or other criteria for frequency sharing situations of
practical importance. NTIA expects to publish these findings as well.

The Margie Article identified the need to establish consistent
permissible interference standards, and recommended that the Commission
initiate a NOI on the subject.[^65] NTIA agrees with this suggestion and
recommends that the results of the first phase of the NTIA study on IPC
values for specific radio services be included as part of the NOI. The
first phase of the NTIA study represents a comprehensive review of
existing national and international standards and can serve as a solid
basis for the Commission to begin building a public record with the goal
of establishing maximum permissible interference levels to promote
predictability and certainty for both licensed and unlicensed spectrum
users.

# DEFINING INTERFERENCE TEMPERATURE IN TERMS OF SIGNAL-TO-NOISE RATIO COULD PROVIDE GREATER FLEXIBILITY AND CERTAINTY THAT BOTH INCUMBENT AND FUTURE SPECTRUM USERS DESIRE.

In the NOI, the Commission requests comment on what elements should be
considered in setting interference temperature limits for different
bands and locations.[^66] The Commission suggests several factors such
as type and criticality of service, its susceptibility to interference,
types of licensees, state of the development of technology, and
propagation characteristics of the frequency band that could be
considered in setting interference temperature limits for a band. The
Commission seeks comment on whether these factors are appropriate as
well as whether other criteria should be addressed.[^67]

For many active services, such as the broadcast service, existence (or
lack thereof) of a desired signal at some level above the measured noise
floor can be used as an indication of spectrum utilization. Desired
signal strengths that are well in excess of maximum noise levels (high
S/N) might allow opportunistic underlay by unlicensed devices with a
lower potential of causing harmful interference to the licensed user.
Non-existence of a desired signal above the noise floor indicates that
the spectrum is not currently being used in the location of the
measurement. Therefore no harmful interference could occur and
opportunistic use could be permitted. The geographic area in between
these two extremes, however, is the area where receivers are most
vulnerable to interference (marginal S/N). Passive services, services
using low received signal strengths, such as satellite downlinks, and
mobile services which do not always operate in the same geographic
region are not likely to lend themselves to this approach.

Appendix D investigates opportunities that can exist for unlicensed use
in certain areas, while protecting the locations that are potentially
more sensitive to interference. These areas of opportunity could be
utilized by unlicensed devices that are capable of measuring the RF
environment, and making a determination to transmit based on whether
excess margin or insufficient desired signal exists, or a determination
to not transmit if the desired signal level is such that an increase in
noise could potentially disrupt communications. NTIA believes that
defining the interference temperature in terms of the available S/N
could provide greater flexibility and certainty for both incumbent and
future spectrum users.

# IN ORDER TO MAXIMIZE THE USEFULNESS OF MEASURED INTERFERENCE TEMPERATURE LEVELS, THE PARAMETERS OF THE MEASUREMENT SYSTEM SHOULD BE STANDARDIZED.

In the NOI, the Commission requests comment on the approaches to be used
for measuring the interference temperature on a real-time basis, and in
the case of interference temperature derived from measurements at
multiple fixed sites, communicating that information to unlicensed
devices that are required to protect the limit.[^68] The Commission also
seeks comment on the measurement system(s) and procedures to be employed
in measuring the interference temperature.[^69]

In the NOI, the Commission describes how they envision that the measured
interference temperature levels can be used in underlaying unlicensed
device operations. For example, the interference temperature
measurements performed by multiple fixed monitoring stations can be
combined at a central location. The combined data can then be
distributed to unlicensed devices that in turn could modify their
operating characteristics (e.g., frequency, power) in response to the RF
environment that is represented by the interference temperature. Since
the measured interference temperature levels can be used to modify, on a
real-time basis, the characteristics of an unlicensed device that could
have a direct effect on its compatibility with licensed users, the
properties of the measurement system must be defined in sufficient
detail to ensure that the appropriate interference temperature limits
are applied to protect all licensed receivers.

The Naval Postgraduate School performed a literature and research study
for the Commission on the impact of noise on wireless
communications.[^70] As part of this study, different approaches to
perform noise measurements were examined. Based on their assessment, it
is clear that in the design of a measurement system there are a number
of diverse factors that must be considered.

NTIA believes that the interference temperature measurement system
should be a spectrum analyzer (SA) based system that is computer
controlled. A specialized front-end should be implemented before the SA
that includes an effective bandpass filter and a low noise preamplifier.
The low noise preamplifier is used to increase the dynamic range of the
measurement system and the bandpass filter is used to protect the low
noise preamplifier from being saturated by strong out-of-band signals.
The critical parameters of the interference temperature measurement
system include detector function, measurement bandwidth, noise figure,
sensitivity, measurement time, and the measurement antenna.

A detailed discussion of each of the critical parameters of the
interference temperature measurement system is provided in Appendix C.
NTIA recommends that the interference temperature measurements be made
using both peak and root-mean-square (RMS) detector functions. As
discussed in Appendix C, the RMS detector provides a true representation
of the average power and the interference impact to most licensed
receivers can be quantified in terms of average power. The resolution
bandwidth (RBW) of the measurement system should be consistent with the
IF bandwidth(s) of the licensed receiver(s) operating in the frequency
band being monitored. The video bandwidth employed should be as wide or
wider than the RBW to avoid the problems associated with video averaging
that are discussed in Appendix C. The preamplifier used in the front-end
of the SA based interference temperature measurement system establishes
the measurement system's noise figure, sensitivity, and dynamic range.
As with the bandwidth, the noise figure of the measurement system used
to perform the interference temperature measurements should be
representative of that used by the licensed receivers operating in the
measured frequency band. In frequency bands where the signal activity is
highly dynamic (e.g., land mobile bands), a swept frequency approach can
be used to monitor the band. However, in frequency bands where the
signals occur on a periodic basis (e.g., radiolocation bands), a stepped
frequency approach may be more appropriate. The measurement interval to
be used in either the stepped or swept frequency approach is difficult
to estimate without prior knowledge of the RF signal environment that is
being monitored or the receivers that are to be protected. For example,
it may be possible to estimate the measurement interval based on the
characteristics of the licensed signals (e.g., symbol length in a
digital system), but in general it will be necessary to perform
preliminary measurements in a frequency band to determine the
appropriate measurement interval to be employed. The antenna to be used
to measure the interference temperature levels should have a gain
pattern that is consistent with the antennas employed by the licensed
user operating in the frequency band being monitored. A discussion of
the different types of commercially available measurement antennas is
provided in Appendix C. Since noise measurements are statistical in
nature, first order statistics such as amplitude probability
distributions (APDs) could be used to characterize and understand the
effect of the measured signals on the licensed receivers. Higher order
statistics can also be used to further characterize the RF signal
environment. This would require use of a spectrum analyzer capable of
sampling the time waveform of the received signal(s), and possibly other
more specialized equipment.

NTIA believes that the criticality of defining the measurement system
parameters is directly related to how the interference temperature
measurements are going to be used. For example, if the measured
interference temperature levels are to be used to gain a gross
understanding of the signal occupancy in a frequency band, then some of
the measurement system parameters may be less important. However, the
Commission indicates in the NOI that the measured interference
temperature levels can be used by unlicensed devices to control their
operating characteristics. In this situation, the parameters of the
measurement system become more critical and must be considered very
carefully to ensure that interference temperature measurements
adequately protect the licensed receivers. Therefore, NTIA recommends
that the parameters of the interference temperature measurement system
that are discussed above be identified for each frequency band and
standardized. NTIA believes that standardizing the measurement system
will maximize the usefulness of the measurements.

# BEFORE IMPLEMENTING THE INTERFERENCE TEMPERATURE MODEL, THE RIGHTS AND RESPONSIBILITIES OF BOTH LICENSED AND UNLICENSED SPECTRUM USERS MUST BE DEFINED.

The SPTF Report addresses the subject of spectrum rights and
responsibilities and recommends that the Commission define these rights
and responsibilities for all spectrum users, particularly with respect
to interference and interference protection, and those rights and
responsibilities should be considered and established to the extent
possible and practical.[^71] In the NOI, the Commission seeks comment as
to how this objective can be accomplished and avoid long, drawn out
interference disputes without detrimentally affecting reasonable
expectations of all interested parties, including expectations regarding
the Commission's use of its authority to impose conditions, modify
licenses and take other steps to promote greater access to, and more
efficient use of the spectrum.[^72]

Throughout the Commission's SPTF and NTIA's Spectrum Summit, providing
predictability and certainty for licensed and unlicensed, as well as
incumbent and new users of the spectrum, was identified as a critical
goal to effectively manage the RF spectrum. Providing predictability and
certainty to all spectrum users can only be accomplished if the rights
and responsibilities of spectrum users are clearly defined. Several
examples exist where the lack of definition in the rights and
responsibilities of the incumbent and new spectrum users appear to have
resulted in problems with deployment of new commercial services,
including the General Wireless Communications Service (GWCS), the
Wireless Communications Service (WCS), and the 700 MHz Commercial Mobile
Radio Service (CMRS). For GWCS and WCS, flexibility of use was stressed
over clearly defined service rules, which resulted in spectrum below 5
GHz where little or no commercial applications have been deployed.[^73]
In the case of 700 MHz CMRS, the uncertainty regarding when and how the
broadcasters were to vacate the spectrum has resulted in delays of the
auction and deployment of commercial services.

One of the major findings and recommendations of the SPTF was that
regulatory models must be based on clear definitions of the rights and
responsibilities of both licensed and unlicensed spectrum users,
particularly with respect to interference and interference
protection.[^74] The SPTF also concluded that there are certain common
elements that the Commission should incorporate into its spectrum policy
regardless of the regulatory model that is used, including clear and
exhaustive definition of spectrum users' rights and
responsibilities.[^75] It is expected that clear definitions of rights
and responsibilities of spectrum users would simplify the rulemaking
process, and could prevent heated public disputes over potential
interference.[^76] In addition to these recommendations of the SPTF,
spectrum rights were also a major point of discussion in the NTIA
Spectrum Summit.[^77]

NTIA believes that a clear definition of both spectrum rights and
responsibilities would facilitate a simplified technical process for
considering new services, whether licensed or unlicensed, in many
frequency bands. Clearly defined rights and responsibilities will also
simplify the analysis of whether new unlicensed services can and should
be introduced in licensed bands. NTIA recommends that before the
interference temperature model is implemented, the rights and
responsibilities of spectrum users be addressed. This could be
accomplished as part of the ongoing interference temperature rulemaking
proceeding or as part of the recommended NOI to identify permissible
interference levels.

# TO EFFECTIVELY IMPLEMENT THE INTERFERENCE TEMPERATURE MODEL, REPRESENTATIVE OPERATIONAL SCENARIOS MUST BE DEVELOPED FOR EACH RADIO SERVICE.

In the NOI, the Commission seeks comment on what assumptions should be
made regarding operating scenarios to be used when performing
interference studies assessing how much interference can be tolerated
before it is considered harmful. The Commission also seeks comment on
whether a statistical approach can be developed to arrive at the
interference temperature limits. If a statistical approach can be
developed, commenters should identify what parameters need to be
developed. The commenters should also explain how such a statistical

approach would be applied.[^78]

In assessing potential interference to receivers from transmitters, a
source-path-receiver analysis is often performed. The basic parameters
that must be defined for this type of analysis include the maximum
permissible interference level, the output power and antenna gain of the
potentially interfering transmitter, the propagation path defined by a
minimum separation distance between the transmitter and receiver, and
the gain of the receive antenna in the direction of the potentially
interfering transmitter. Collectively, this information defines an
operational scenario, which establishes how close the transmitter and
receiver may come to one another under actual operating conditions, and
likely orientation of the antennas. This information is used to
determine the appropriate model to use in computing the propagation
loss. The operational scenario can also be used to determine the
applicability of other factors such as building attenuation, allowance
for multiple transmitters, and safety margins.

The operational scenarios considered using the source-path-receiver
approach typically assume that the parameters (e.g., transmitter power,
antenna gain) are represented by a single fixed value. However, a
probabilistic approach can also be employed, in which the analysis
treats the parameters as statistical quantities, each defined by a mean
and deviation around the mean. This analysis method could be employed by
choosing or deriving a Probability Distribution Function (PDF) for each
parameter. The joint PDF can be computed by convolving the individual
PDFs with one another. The main difficulty with this approach is
collecting a sufficient amount of data to accurately develop the PDFs
for the parameters in the analysis. For radio services that require a
high degree of confidence in the analysis results, such as the
aeronautical radionavigation service, there is little benefit in
employing this approach since the higher probabilities as defined by the
PDF (*e.g.*, 99.99999%) must be used to develop the statistics for the
analysis parameters.

Analyzing operational scenarios with consideration of locations of
licensed receivers and unlicensed transmitters has been a major
difficulty in past rulemaking proceedings.[^79] In particular, analyses
considering mobile services (licensed and unlicensed), where the
locations of the transmitters are unknown, rely upon assumptions
concerning separation distances that might or might not be appropriate.
Such radiocommunication services might be better analyzed by considering
interference scenarios, and the probability that harmful interference
will occur, by employing Monte Carlo analysis techniques.[^80] Using
Monte Carlo analysis techniques, the worst-case scenarios, as well as
less conservative scenarios, can be taken into account in assessing
potential interference to a receiver. This approach was used in the 5
GHz U-NII R&O, where the location of the radar receiver, unlicensed
device transmitter locations, and shielding losses were treated as
random variables. Using this approach, propagation effects for locations
that accounted for nearly free-space propagation, as well as other
locations that warranted greater propagation losses due to terrain and
shielding effects, were taken into consideration in assessing potential
interference to radar receivers.

In assessing potential interference to receivers using the interference
temperature model, it will be necessary to develop radio service
specific operational scenarios. Currently most of the efforts in
developing documented operational scenarios for assessing potential
interference to receivers have been limited to the aviation industry.
For example, RTCA Special Committee 159 (SC-159) Working Group 6 (WG 6)
developed an operational scenario used to assess potential interference
to aviation GPS receivers used for a Category I precision approach from
MSS mobile earth terminals (METs).[^81] In this operational scenario, a
minimum separation distance of 100 feet was established and the free
space model was determined to be appropriate to compute the propagation
loss. The GPS receive antenna was assumed to be located on top of the
aircraft and the antenna gain in the direction of the MET taking into
account shielding from the aircraft was established. The maximum
permissible interference level was based on a GPS receiver operating in
the tracking mode, receiving a signal from a low elevation satellite,
and a noise-like interfering signal. A safety margin was also included
in the analysis to account for uncertainties such as multipath, receiver
implementation losses, and variations in the antenna gain. This
operational scenario only considered interference from a single
interfering transmitter and did not consider interference from multiple
transmitters of the same radio service or transmitters from multiple
radio services. RTCA SC-159 WG 6 has expanded the scope of their work to
include additional aviation scenarios as well as potential interference
from multiple interfering transmitters within the same radio service and
from transmitters in multiple radio services.[^82] In order to develop
interference temperature limits for each radio service, the operational
scenarios and appropriate assumptions for each will need to be
developed. These operational scenarios will be different for each radio
service and must include information regarding transmitter and receiver
parameters such as locations, transmitter power, transmit and receive
antenna gains and any other radio service specific parameters (e.g.,
safety margin for aviation). NTIA believes that operational scenarios
employing statistical techniques can be used for considering aggregate
interference especially when the number and location of the transmitters
are unknown. However, it must be realized that if a licensed service is
to provide consumers with robust, reliable services, the probability of
interference occurring must be kept low. NTIA recommends that
operational scenarios be developed for each radio service to be used in
determining the interference temperature limits. NTIA believes that
adoption of radio specific operational scenarios in conjunction with
maximum permissible interference levels will provide the certainty and
predictability that incumbent and new users of the spectrum desire and
is consistent with the recommendations of the Commission's SPTF.

# THE INTERFERENCE TEMPERATURE LIMITS MUST PROTECT BOTH IN-BAND AND ADJACENT BAND SPECTRUM USERS.

In the NOI, the Commission's request for comments only addresses
interference to in-band spectrum users and does not specifically address
issues related to users operating in the adjacent bands. In the NPRM,
the Commission does address the issue of out-of-band emissions.
Specifically, the Commission recognizes the need to assure that
increased operation of unlicensed devices enabled under the interference
temperature model will not result in harmful out-of-band
interference.[^83]

Currently, adjacent band operations are protected by unwanted (i.e.,
out-of-band and spurious) emission limits that are either described as
an absolute power or EIRP level, or as a reduction in power level as the
frequency becomes farther removed from the fundamental

frequency of the emission. Adequate measures of adjacent band energy
must be included in the

interference temperature model if the adjacent band users are to benefit
from the same levels of protection that they are afforded under the
current rules. This protection could arise from specifying the frequency
roll-off, as is done in current regulations, or by defining the
temperature

limit that unwanted emissions must meet to successfully operate under
the interference temperature model.

A separate but equally important issue with respect to adjacent band
emissions is how to

take them into account when establishing the interference temperature
limit within a frequency

band. Because, even if the interference temperature limit in a
particular band is well below the permissible limit, an unlicensed
device's unwanted emissions could cause the interference temperature
limit in an adjacent band to be exceeded, particularly if the
interference temperature in the adjacent band is very close to the
permissible limit and reflects the cumulative effect of many unlicensed
devices. For example, in the RNSS frequency bands used by GPS there are
no in-band, ground-based transmitters permitted. However, there is a
concern that the cumulative effect from transmitters operating outside
the RNSS bands can impact the GPS receiver noise floor. The potential
sources of interference to GPS receivers include adjacent band emissions
from MSS METs; harmonic emissions from television transmitters; spurious
and harmonic emissions from 700 MHz commercial base, mobile, and
portable transmitters; and unwanted emissions from unlicensed devices.
These multiple sources of potential interference, which might
individually be tolerated by a GPS receiver, could combine under certain
circumstances (e.g., close separation distances, operating at the
maximum allowable out-of-band emission level) to create an aggregate
interference level that could prevent the reliable reception of the GPS
signal.

NTIA believes that if implemented properly, the interference temperature
model can be used to protect adjacent band licensed systems. NTIA
recommends that when establishing the interference temperature limits
the emissions from licensed and unlicensed systems operating in adjacent
or harmonically related frequency bands be taken into consideration.

# ADDITIONAL PROVISIONS ARE NOT NECESSARY TO PROTECT DEEP SPACE NETWORK RECEIVERS IN THE 12.75-13.25 GHz BAND LOCATED AT THE GOLDSTONE COMPLEX.

In the NPRM, the Commission proposes to permit unlicensed devices
operating at a maximum EIRP of 36 dBm in the 12.75-13.25 GHz frequency
band. This band is allocated to the federal and non-federal space
research service for reception at Goldstone, California. The Commission
does not believe that its proposal will be detrimental to space research
operations. The Commission tentatively concluded that since Goldstone is
located in a rural location with natural shielding by virtue of its
location in a valley, very few, if any, unlicensed devices would be
operated in locations that could impact its operations. The Commission
requests comment on this tentative conclusion.[^84]

Every U.S. deep space mission is designed to allow continuous radio
communications with the spacecraft. Continuous 24-hour coverage for
several spacecraft requires several earth-based stations at locations
that compensate for the earth's daily rotation. The locations in Spain,
Australia, and California are approximately 120 degrees apart in
longitude, which enables continuous observation and suitable overlap for
transferring the spacecraft radio link from one complex to the next.

The National Aeronautics and Space Administration (NASA) Goldstone
complex is located on the U.S. Army's Fort Irwin Military Reservation,
approximately 72 kilometers (45 miles) northeast from the nearest
populated city. The Goldstone complex is situated in semi-mountainous,
bowl shaped terrain to shield against radio frequency interference. The
70 meter antenna is the largest, and therefore the most sensitive, Deep
Space Network (DSN) antenna, and is capable of tracking a spacecraft
traveling more than 16 billion kilometers (10 billion miles) from the
Earth. Given the importance and the sensitivity of the DSN antenna an
analysis was performed to determine the impact on DSN receivers based on
the Commission's proposed EIRP level for unlicensed devices operating in
the 12.75-13.25 GHz frequency band. The results of the analysis provided
in Appendix B indicate that an unlicensed device operating at an EIRP
density of 36 dBm/MHz would have to be within approximately 16 km of a
DSN antenna before potential interference occurs. At an EIRP density of
36 dBm/20 MHz the separation distance reduces to approximately 8 km.

Protection of the spectrum used by the DSN receivers is essential for
safeguarding data communications capabilities between spacecraft and the
Goldstone tracking antennas. The remote location of the Goldstone
complex provides protection for the sensitive DSN receivers from local
interference. Given the geographically remote location of the Goldstone
complex, interference to DSN receivers will only be encountered when the
unlicensed devices are operated on the Goldstone complex by NASA or
Department of Defense personnel. It is believed that the existing
spectrum coordination and monitoring activities will ensure that DSN
receivers are protected from interference caused by unlicensed device
operations. Thus, NTIA agrees with the Commission's tentative
conclusion, and no additional provisions are necessary to protect the
DSN receivers at the Goldstone complex.

# TECHNICAL ISSUES RELATED TO THE COMPLIANCE MEASUREMENTS OF UNLICENSED DEVICES THAT EMPLOY THE INTERFERENCE TEMPERATURE MODEL MUST BE ADDRESSED.

Transmitters must be tested to show compliance with the applicable
requirements before they can be certified. For unlicensed transmitters,
both the technical requirements and the test procedures are specified in
Part 15 of the Commission's Rules. In the NOI, the Commission discusses
several actions that may be taken by an unlicensed device when its
emissions cause the interference temperature limits to be exceeded at
the licensed receiver. For example, the unlicensed device could select a
different transmitting frequency; cease transmitting for a period of
time; decrease its power using automatic transmitter power control; or
electrically re-shape its antenna pattern.[^85] The NOI does not address
technical issues related to compliance measurements of unlicensed
devices that employ the interference temperature model.

The technologies contemplated in this NOI reach far beyond the
traditional methodologies employed in device certification. For example,
measurement of transmitter power across a given frequency range is
insufficient to ensure that dynamic systems are functioning properly.
Telecommunication Certification Bodies (TCB) are responsible for
performing the compliance measurements, including those of unlicensed
devices operating under Part 15 of the Commission's Rules. The
introduction of unlicensed devices employing the interference
temperature model will raise technical issues that need to be addressed
specifically with respect to the TCBs. In the Commission's NPRM on
cognitive radio technology, many of the compliance measurement issues
that will be encountered by devices employing interference temperature
are also being addressed.[^86] As indicated in the Commission's NPRM on
cognitive radio technologies, many new technical issues must be resolved
to show that a device is compliant with the Commission's Rules. Many of
the same compliance measurement issues must be resolved for devices
employing the interference temperature model. For example, for devices
employing DFS, these technical issues can include determining the
frequency bands that are to be monitored, the monitoring bandwidth, the
sensitivity of the monitoring receiver, the ability of the device to
select an operating frequency and power level based on the presence of
various standardized test input signals, the monitoring period and
revisit time, and the time required to move off of a frequency once the
interference temperature limit is exceeded. For devices employing
geo-location techniques, compliance measurement issues related to the
ability to correctly identify their location based on geo-location
technology and the ability to access a database and correctly determine
the location of authorized transmitters must be addressed. TCBs must be
required to develop new capabilities in both the test equipment
available, and the expertise of their technical staff in order to
certify devices utilizing these new technologies.[^87]

In the past, because of their simplicity, the compliance measurement
procedures were typically considered after the development of the
service rules. However, given the complexity of the devices that employ
technologies capable of modifying operating characteristics that can
change their electromagnetic compatibility with other devices, the
compliance measurement procedures must be addressed at the same time the
service rules are developed. The TCBs are the experts in the area of
performing the compliance measurements and need to be actively engaged
in providing guidance on the technical issues related to device
certification. NTIA believes that technological approaches that cannot
be verified in the TCB laboratories should not be relied upon for
successful spectrum sharing using the interference temperature model.
NTIA recommends that the Commission resolve the technical issues related
to performing the compliance measurements prior to implementing the
interference temperature model.

# THE INTERFERENCE TEMPERATURE LIMITS IN A FREQUENCY BAND SHOULD BE BASED ON THE MOST SENSITIVE RADIO SERVICE OPERATING IN A BAND.

There are many instances where several radio services share the same
frequency band on a primary and secondary basis. In the frequency bands
where several radio services share the spectrum on a primary or
secondary basis, the Commission requests comment on whether the
interference temperature limit should be based on all the licensed
services or only on the service that is most susceptible to
interference.[^88]

In frequency bands where several radio services share the spectrum on a
primary or secondary basis, the interference temperature limit for
unlicensed devices should be established to protect all licensed
services. If this approach is not used, unlicensed devices would enjoy a
higher status than the secondary services operating in the band. This
would result in less, not more regulatory certainty for the incumbent
services than under the current regulatory framework. The primary
service in a frequency band is not always the most susceptible to
interference. In the particular case of radio astronomy, observations
are carried out successfully in several bands where the radio astronomy
service has a secondary allocation, and is the most sensitive service.
For example, the 14.47-14.7145 GHz band is shared between the fixed,
mobile, and fixed satellite services on a primary basis with radio
astronomy operations on a secondary basis. In this band, extensive
coordination agreements or other regulatory approaches can be used such
that the secondary radio astronomy operations can co-exist with the
other primary services, which is not possible with unlicensed devices.
If the interference temperature in the 14.47-14.7145 GHz band were based
on only the primary services, the permissible level of interference
could be approximately 72 dB higher than the level necessary to protect
the radio astronomy observations.[^89] If an interference temperature
limit is established in a band in which both primary and secondary
allocated services operate, NTIA recommends the limit should be based on
the most sensitive radio service operating in the frequency band.

# INTERFERENCE TEMPERATURE MEASUREMENTS MADE BY A SATELLITE RECEIVER CANNOT BE USED TO PROTECT GROUND-BASED RECEIVERS.

In the NOI, the Commission describes a number of approaches to perform
adaptive or real-time interference temperature measurements by which
monitored information regarding spectrum occupancy could be transmitted
back to individual unlicensed devices.[^90] For example, the Commission
believes that satellites could monitor the ΔT/T and make the measured
data available to individual devices, which in turn could adjust their
operation to ensure that they do not interfere with licensed operations.
The Commission requests comment on the utility and potential benefits of
such a real-time monitoring approach in the 6525-6700 MHz and
12.75-13.25 GHz bands, as well as other frequency bands. Comments are
also requested on how the monitored information could be acquired by the
unlicensed devices.[^91]

The interference level at a satellite receiver that results from a large
number of ground-based unlicensed devices operating within the footprint
of the satellite will cause an increase in the ΔT/T level in the
satellite receiver. The effective interference at the satellite receiver
would be an aggregate from a large number of unlicensed devices. This
aggregate signal results from ground-based devices where each device is
essentially the same distance from the satellite receiver, thus there
cannot be a single dominant device. However, the measured ΔT/T level at
the satellite receiver is only applicable for assessing potential
interference to a satellite receiver. In the case of the ground-based
radio services (e.g*.*, fixed, mobile), the potential interfering
unlicensed devices can operate in close proximity to the ground-based
receiver. Unlike interference to a satellite uplink receiver, a single
unlicensed device could be the dominant factor in establishing the
effective interference power level at a ground-based receiver. The
interference interactions between satellite and ground-based receivers
and ground-based unlicensed devices are completely different. Thus, it
does not appear possible to use the interference levels measured by a
satellite receiver to control the operating characteristics of
unlicensed devices to the extent necessary to protect licensed
ground-based receivers.

Using satellites to make measurements of the noise within a frequency
band has been ongoing for years. Government and commercial satellite
systems monitor geophysical, metrological, and environmental conditions
on the Earth. These satellite systems are capable of measuring small
changes in the noise, and the data is downloaded (not on a real-time
basis) for use in long-term weather prediction models. However, using
this measured data on a real-time basis to control the operating
characteristics of a ground-based transmitter has not been attempted.
Recently, a system has been proposed by Mobile Satellite Ventures (MSV)
that will monitor ancillary terrestrial component (ATC) emissions within
the footprint of their satellite.[^92] The purpose of this monitoring is
to provide assurance that the level of ground-based co-channel
interference (e.g., ΔT/T) as seen by other satellite systems remains
below acceptable levels. In the MSV proposal the aggregate signal level
at a particular co-channel frequency generated by ATC operations within
each satellite cell will be monitored. By combining the co-channel
contributions from all satellite cells containing ATC components, the
total (aggregate) co-channel signal generated by the entire ATC network
can be measured and recorded. Using a closed-loop feedback control, a
centralized controller can set the appropriate limits on ATC emissions
if interference begins to approach a specified level. The proposed
monitoring system will use logarithmic amplification to detect
relatively small changes in the noise floor.[^93] The proposed
monitoring system will also have the means to self calibrate to noise
levels in the absence of ATC emissions. MSV specifically states that the
monitoring and control of ATC emissions can only work in a satellite
system that is completely integrated and coordinated between the space
and ground-based segments with the real time control of information
between the two.[^94] The approach being proposed by MSV appears to be
similar to that envisioned by the Commission. MSV plans to use this
approach to ensure that their ATC system does not interfere with in-band
Inmarsat operations. NTIA recommends that the Commission monitor the MSV
system as it is implemented, and possibly establish a limited test
program in the 6 or 13 GHz frequency bands based on this approach.

It appears there are possible approaches that can be used to make
measurements of ΔT/T levels in frequency bands used by satellite
uplinks. However, it is unknown if the measured ΔT/T levels can be used
to prevent unlicensed ground-based transmitters from interfering with a
satellite receiver, especially if the satellite and ground-based
transmitters are not operating under a central controller. For example,
if the ΔT/T limit is exceeded, it is unclear what factors would be used
to determine which devices would modify their operating characteristics
(e.g., turn off all or some percentage of devices, incrementally reduce
power for all devices). NTIA believes that the interference interactions
between satellite and ground-based receivers and ground-based unlicensed
devices are completely different. Thus, NTIA does not believe it is
possible to use the ΔT/T levels measured by a satellite receiver to
control the operating characteristics of unlicensed devices to the
extent necessary to protect licensed receivers operating in frequency
bands used by the ground-based radio services (e.g., fixed, land mobile,
radiolocation).

# BASELINE MEASUREMENTS IN SELECTED LICENSED AND UNLICENSED FREQUENCY BANDS SHOULD BE PERFORMED BEFORE DECIDING WHETHER OR NOT THE INTERFERENCE TEMPERATURE MODEL CAN BE IMPLEMENTED.

The Commission states that the noise floor has increased at various
points, which are indicated by peaks above the original noise floor
shown on Figure 1 in the NOI.[^95] In between the peaks, the level is
close to the original noise floor. The Commission believes that by
allowing the entire noise floor in a band to increase to the levels
represented by the peaks, greater access by higher-powered unlicensed
devices is possible. The Commission proposes that the interference
temperature limit should be set at this elevated noise level.[^96]

There are two problems with the interference temperature model as
proposed by the Commission. First, increasing the overall noise level in
a frequency band will not necessarily permit more opportunistic use of
the spectrum by higher-powered unlicensed devices. As shown in Appendix
E, an elevated noise level will impact both licensed and unlicensed
users equally. Therefore, if the noise is elevated, a higher transmitter
power is necessary to achieve the same range that was obtainable in a
lower noise environment. The study performed by the Naval Postgraduate
School reviewed a limited set of measured data in the 2.4 GHz unlicensed
band and stated that there is a serious concern about saturation of the
present unlicensed bands and the degradation in system performance that
accompanies spectrum saturation.[^97] The Commission's Technical
Advisory Council (TAC) also raised Concerns regarding the degradation of
the noise environment.[^98]

The second problem encountered is the lack of measured data supporting
the "original noise level" or the "elevated peak levels" shown in Figure
1 of the NOI. As pointed out in the Naval Postgraduate School Report,
the largest body of environmental noise measurements was developed by
NTIA's ITS.[^99] Although the ITS spectrum surveys provide an excellent
database of noise at the time the measurements were performed, the
measurements were conducted prior to the widespread deployment of many
of the wireless radio services in operation today.[^100] As the Naval
Postgraduate School report points out, a similar set of measurements has
not been performed by the ITS in a number of years, and it is believed
that the existing data is only of limited historical interest.[^101] The
Commission's Interference Protection Working Group and TAC also
indicated that a better understanding of the existing noise environment
is necessary.[^102]

Although based on a limited set of measured data, in one frequency band,
the Naval Postgraduate School Report does raise the issue of spectrum
saturation and the possible interference problems that could arise if
the noise level is permitted to increase across a frequency band. NTIA
believes that the lack of basic information of the existing noise
environment greatly limits the ability of licensed and unlicensed system
designers to conduct practical and useful system performance analysis.
To begin addressing these problems, NTIA and the Commission should
identify a list of candidate licensed and unlicensed frequency bands in
which the emission or noise levels can be measured using standardized
measurement systems. NTIA believes that these measurements can serve as
a baseline for characterizing the existing emission environment in those
bands, which can be used to determine whether the interference
temperature model can be implemented in such a way as to achieve the
Commission's longer term spectrum management objectives.

# CONCLUSION

NTIA commends the Commission for initiating this proceeding to examine
possibilities to expand the options for unlicensed device use while also
providing certainty and predictability desired by licensed spectrum
users. NTIA agrees with the Commission regarding the significant
benefits that could be gained by increasing the spectrum access
opportunities for unlicensed devices. The implementation of the
interference temperature model and the use of interference mitigation
techniques such as DFS and geo-location represent a shift in
interference management from the transmitter to the receiver. The NOI
identifies many technically challenging issues that must be addressed
before the interference temperature model can be implemented in a
frequency band. These technical issues include, but are not limited to,
the development of radio service specific reference receiver parameters,
the development of radio service specific maximum permissible
interference limits and operational scenarios, and measurement of the
existing RF signal environment in order to establish a proper baseline.
Until these technical issues and the rights and responsibilities of
licensed and unlicensed spectrum users have been resolved, wide spread
implementation of the interference temperature model will not possible.
Because of the sensitive nature of the operations in the restricted
frequency bands, implementing the interference temperature model would
be difficult if not impossible. However, if the initial implementation
of the interference temperature model were limited to specific bands,
for example, bands which have been transferred from the federal
government, many of the technical issues listed above could be addressed
and possibly resolved with minimal impact to incumbent commercial and
federal government users. NTIA believes that active interference
mitigation techniques such as DFS and geo-location hold great promise
for facilitating sharing between licensed and unlicensed spectrum users.
However, these techniques should not be employed until the supporting
technical studies examining the specific characteristics of the licensed
radio services and the unlicensed device applications have been
completed.

For the foregoing reasons, NTIA submits these comments

Respectfully submitted,

Michael D. Gallagher Kathy D. Smith

Assistant Secretary for Chief Counsel

Communications and Information

Fredrick R. Wentland

Associate Administrator

Office of Spectrum Management

Mark Settle National Telecommunications

Edward Drocella and Information Administration

Electronics Engineers U.S. Department of Commerce

Office of Spectrum Management Room 4713

1401 Constitution Avenue, N.W.

Washington, DC 20230

> \(202\) 482-1816

August 13, 2004

**APPENDIX A**

ASSESSMENT OF PROPOSED POWER LEVEL AND DETECTION THRESHOLD IN THE 6 GHz
AND 13 GHz FIXED SERVICE FREQUENCY BANDS

**INTRODUCTION**

This appendix assesses the feasibility of the Commission's proposal for
sharing between higher-powered unlicensed devices and fixed service (FS)
systems in the 6 GHz and 13 GHz bands. The analysis considers an
unlicensed device operating at an equivalent isotropically radiated
power level (EIRP) of 36 dBm located 100 meters from the FS
receiver.[^103] The unlicensed device employs Dynamic Frequency
Selection (DFS) and has a detection threshold of -64 dBm.[^104] The DFS
detection threshold of --64 dBm is based on technical studies assessing
compatibility between 5 GHz radar systems and Unlicensed National
Information Infrastructure (U-NII) devices.[^105] The FS transmitter
power received at the unlicensed device is computed based on typical
parameters for the FS link and compared to the proposed detection
threshold. The transmitted signal from the unlicensed transmitter at the
FS receiver is computed and compared to the interference-to-noise (I/N)
threshold of --13 dB, which corresponds to a 5 percent increase in
system noise in the receiver.[^106]

**FS SYSTEM PARAMETERS**

The parameters for the FS systems considered in this assessment are
given in Table A-1.

Table A-.

  -------------------------- ---------------------- ----------------------
  **Parameter**              **Value**              

                             6 GHz                  **13 GHz**

  Frequency                  6600 MHz               13000 MHz

  Transmitter Power          30 dBm                 30 dBm

  Mainbeam Antenna Gain      44 dBi                 44 dBi

  Line Loss                  2 dB                   2 dB

  Antenna Height             50 m                   50 m

  Transmitter/Receiver       40 MHz                 40 MHz
  Bandwidth                                         

  Noise Figure               4 dB                   4 dB

  Path Length                40 km                  20 km

  Antenna Mask               32-25 Log(Off-Axis     32-25 Log(Off-Axis
                             Angle)                 Angle)

  Minimum Carrier-to-Noise   28 dB                  28 dB
  Ratio                                             
  -------------------------- ---------------------- ----------------------

**UNLICENSED DEVICE PARAMETERS**

The parameters for the unlicensed device considered in this analysis are
provided in Table A-2.

Table A-.

  ----------------------------------- -----------------------------------
  **Parameter**                       **Value**

  EIRP                                36 dBm

  Antenna Gain                        0 dBi

  Antenna Height                      2 m

  Transmitter Bandwidth               20 MHz

  DFS Detection Bandwidth[^107]       1 MHz
  ----------------------------------- -----------------------------------

**ASSESSMENT OF PROPOSED DFS DETECTION THRESHOLD**

The level of the FS transmitted signal received by the unlicensed device
is computed using the following equation:

> P~U~ = P~FS~ + G~FS~ - L~T~ - L~P~ - L~Clutter~ - BWCF + G~U~ (A-1)

where:

P~U~ is the FS transmitted power received by the unlicensed device
(dBm);

P~FS~ is the transmitted power of the FS (dBm);

G~FS~ is the mainbeam antenna gain of the FS (dBi);

L~T~ is the insertion loss for the FS transmitter (dB);

L~P~ is the propagation loss (dB);

L~Clutter~ is the clutter loss (dB);

> BWCF is the loss due to the difference between the FS transmit and
> detection measurement bandwidths (dB);

G~U~ is the antenna gain of the unlicensed device (dBi).

In this assessment, the Irregular Terrain Model (ITM) is used to compute
the propagation loss. [^108] The parameters used in the ITM propagation
model are shown in Table A-3.

Table A-.

  ----------------------------------- -----------------------------------
  **Parameter**                       **Value**

  Frequency                           6600 MHz, 13000 MHz

  Polarization                        Vertical

  FS Transmitter Site Criteria        Careful

  Unlicensed Device Receiver Site     Random
  Criteria                            

  Delta H                             10 meters

  Dielectric Constant                 15

  Surface Refractivity                301 N-Units

  Conductivity                        0.005 S/m

  Radio Climate                       Continental Temperate

  Percent Time                        10%

  Percent Location                    50%

  Confidence Level                    50%

  Mode of Variability                 Mobile
  ----------------------------------- -----------------------------------

In the development of the -64 dBm detection threshold, the 5 GHz studies
included a clutter factor that was randomly varied between 0 dB and 20
dB. In this assessment, a value of 13 dB is used for the clutter factor.

The level of the received signal from the FS transmitter will be reduced
due to the mismatch in bandwidth between the FS transmitter of 40 MHz
and the detection bandwidth of 1 MHz used in this assessment. The
bandwidth correction factor is given by:

BWCF = 10 Log (1/40) = -16 dB

Using Equation A-1, the power level of the received FS transmitted
signal at the unlicensed device is shown in Table A-4 for the 6 GHz and
13 GHz links.

Table A-.

  ----------------------- ----------------------- -----------------------
  **Parameter**           **Value**               

                          **6 GHz**               **13 GHz**

  P~FS~                   30 dBm                  30 dBm

  G~FS~                   44 dBi                  44 dBi

  L~T~                    -2 dB                   -2 dB

  L~P~                    -153 dB                 -138 dB

  L~Clutter~              -13 dB                  -13 dB

  BWCF                    -16 dB                  -16 dB

  G~U~                    0 dBi                   0 dBi

  P~U~                    -110 dBm                -95 dBm
  ----------------------- ----------------------- -----------------------

As shown in Table A-4, the computed FS transmitted signal power levels
received by the unlicensed device are well below the proposed detection
threshold of -64 dBm. Since the received FS transmitted power levels are
below the detection threshold, a DFS equipped unlicensed device would
sense that the channel is not being used and would be permitted to
transmit.

**ASSSESSMENT OF INTERFERNCE TO FS RECEIVERS FROM UNLICENSED DEVICES
OPERATING AT THE PROPOSED POWER LEVEL**

The power level of the unlicensed device transmitter at the FS receiver
is computed using the following equation:

> P~R~ = EIRP~U~ -- L~R~ - L~FS~ - L~Clutter~ - BWCF + G~FS~ (A-2)

where:

P~R~ is the unlicensed device transmitted power received by the FS
receiver (dBm);

EIRP~U~ is the EIRP of the unlicensed device (dBm);

L~R~ is the insertion loss for the FS receiver (dB);

L~P~ is the propagation loss (dB);

L~Clutter~ is the clutter loss (dB);

> BWCF is the loss due to the difference between the FS receiver and the
> unlicensed device bandwidths (dB);

G~FS~ is the gain of the FS receive antenna in the direction of the
unlicensed device (dBi).

Since the unlicensed device is assumed to be operating 100 meters
horizontally from the FS receiver, the free space propagation model
given by the following equation applies:[^109]

L~P~ = 20 Log F + 20 Log D -27.55 (A-3)

where

L~P~ is the free space propagation loss (dB);

F is the frequency (MHz);

D is the distance separation between the unlicensed device and the FS
receiver (m).

Since there is a difference between the antenna heights of the
unlicensed device and the FS receiver the slant range is used to compute
the separation distance. The slant range is computed as follows:

D = (100^2^ + (50-2)^2^)^1/2^ = 111 meters

Since the separation distance is only 111 meters it is not appropriate
to include a clutter factor.

The 40 MHz bandwidth of the FS receiver is larger than the 20 MHz
unlicensed device transmitter bandwidth so the bandwidth correction
factor is 0 dB.

The FS receive antenna gain in the direction of the unlicensed device is
a function of the off-axis angle which is computed as follows:

Off-Axis Angle = Tan^-1^ ((50-2)/100) = 25.6 degrees

Using the antenna gain mask from Table A-1, the FS receive antenna gain
in the direction of the unlicensed device is:

G~FS~ = 32 -- 25 Log (25.6) = -3.2 dBi

Using Equation A-2, the power levels received at the FS receiver from
the unlicensed device transmitter are shown in Table A-5.

Table A-.

  ----------------------- ----------------------- -----------------------
  **Parameter**           **Value**               

                          **6 GHz**               **13 GHz**

  EIRP~U~                 36 dBm                  36 dBm

  L~T~                    -2 dB                   -2 dB

  L~P~                    -89.7 dB                -95.6 dB

  L~Clutter~              0 dB                    0 dB

  BWCF                    0 dB                    0 dB

  G~FS~                   -3.2 dBi                -3.2 dBi

  P~R~                    -58.9 dBm               -64.8 dBm
  ----------------------- ----------------------- -----------------------

The noise power of the FS receiver is computed using the following
equation:

N = -114 + 10 Log (RBW) + NF (A-4)

Where:

N is the receiver noise power (dBm);

RBW is the receiver bandwidth (MHz);

NF is the receiver noise figure (dB).

Using the values of FS receiver bandwidth of 40 MHz and noise figure of
4 dB, the FS receiver noise power is -94 dBm.

The I/N is the difference between the power level of the unlicensed
device transmitter at the FS receiver and the receiver noise power:

I/N = -58.9 - (-94) = 35.1 dB (6 GHz)

I/N = -64.8 - (-94) = 29.2 dB (13 GHz)

The computed I/N values exceed the -13 dB threshold by 48 dB (6 GHz) and
42 dB (13 GHz). In order to reduce the interference received from the
unlicensed device transmitter to meet the interference threshold of -107
dBm (-94 dBm - 13 dB), either the EIRP level of the unlicensed device
must be reduced or the separation distance between the unlicensed device
and FS receiver must be increased.

The maximum allowable EIRP levels referenced to a 1 MHz bandwidth that
the unlicensed device can have and still meet the interference threshold
are:

36 - 48 + 10 Log (1/40) = -28 dBm/MHz (6 GHz)

36 - 29.2 + 10 Log (1/40) = -9.2 dBm/MHz (13 GHz)

These EIRP levels are below the proposal made by the Commission, but
they are still higher than the general emission EIRP limit of -41.3
dBm/MHz currently permitted in this band under Part 15 of the Commission
Rules.

If the unlicensed device has an EIRP level of 36 dBm, the separation
distances from the FS receiver must be increased from 100 meters to 28
kilometers (6 GHz) and 14 kilometers (13 GHz).

In addition to an I/N, the carrier-to-interference (C/I) can also be
used to assess potential interference to the FS receiver. The minimum
carrier power level can be computed as follows:

C~min~ = C/N + N = 28 + (-94) = -66 dBm (A-5)

The nominal carrier power at the FS receiver is computed using the
following equation:

> C~nom~ = P~FS~ + G~FS~ - L~T~ - L~P~ - L~T~ + G~FS~ (A-6)

where:

C~nom~ is the nominal carrier power level at the FS receiver (dBm);

P~FS~ is the transmitted power of the FS (dBm);

G~FS~ is the mainbeam gain of the FS transmit antenna (dBi);

L~T~ is the insertion loss of the FS transmitter (dB);

L~P~ is the propagation loss (dB);

G~FS~ is the mainbeam gain of the FS receive antenna (dBi).

To compute the nominal carrier levels the parameters from Table A-1 and
the ITM propagation model are used. The nominal carrier power levels and
the available fade margins for the link considered in this assessment
are shown in Table A-6.

Table A-.

  ----------------------- ----------------------- -----------------------
  **Parameter**           **Value**               

                          **6 GHz**               **13 GHz**

  P~FS~                   30 dBm                  30 dBm

  G~FS~                   44 dBi                  44 dBi

  L~T~                    -4 dB                   -4 dB

  L~P~                    -140 dB                 -137 dB

  G~FS~                   44 dBi                  44 dBi

  C~nom~                  -26 dBm                 -23 dBm

  C~min~                  -66 dBm                 -66 dBm

  Fade Margin             40 dB                   43 dB
  ----------------------- ----------------------- -----------------------

As shown in Table A-6, the fade margins for the links considered in this
analysis are not excessive.

The minimum carrier power computed using Equation A-5 and the
interference power levels given in Table A-5 can be used to compute the
available C/I ratio using the following equation:

C/I = C~min~ - P~FS~ = -66 - (-58.9) = -7.1 dB

C/I = C~min~ - P~FS~ = -66 - (-64.8) = -1.2 dB

These computed C/I values are much lower than the values necessary to
provide reliable performance on any FS link.

**CONCLUSION**

The combination of DFS detection threshold and EIRP level proposed for
unlicensed devices operating in the 6 and 13 GHz frequency bands are not
adequate to protect FS receivers from potential interference.

**APPENDIX B**

**ASSESSMENT OF POTENTIAL INTERFERENCE TO GOLDSTONE DEEP SPACE NETWORK
OPERATIONS IN THE 12.75-13.25 GHz BAND**

**INTRODUCTION**

This appendix assesses the potential interference from unlicensed
devices operating at the maximum equivalent isotropically radiated power
(EIRP) level of 36 dBm as proposed by the Commission to Deep Space
Network (DSN) receivers in the 12.75-13.25 GHz frequency band.

**INTERFERENCE CRITERIA**

The interference criteria used in this analysis to assess whether the
unlicensed device causes interference to the DSN receiver is based on
ITU-R Recommendation SA.1157.[^110] In the 12.75-13.25 GHz band, a
maximum allowable power spectral density of -220.5 dBW/Hz is specified.
This interference criterion for the deep-space receiver is specified at
the receiver input terminals.

**ASSESSMENT OF INTERFERENCE TO DSN RECEIVERS**

In this assessment, the distance separation required to preclude
potential interference is computed based on the maximum EIRP level of 36
dBm proposed by the Commission and interference criteria specified in
ITU-R Recommendation SA.1157.

The Commission's proposal does not specify a bandwidth for the
unlicensed device. Unlicensed device bandwidths of 1 MHz and 20 MHz are
used to compute the EIRP density used in this analysis.

EIRP~U~ = 36 dBm/MHz - 60 - 30 = -54 dBW/Hz (1 MHz)

EIRP~U~ = 36 dBm/20 MHz - 73 - 30 = -67 dBW/Hz (20 MHz)

The required propagation loss to preclude potential interference is
calculated using the following equation:

L~P~ = EIRP~U~ - I~T~ (B-1)

where:

> L~P~ is the required propagation loss necessary to preclude potential
> interference to the DSN receiver (dB);

I~T~ is the DSN receiver interference criteria (dBW/Hz);

EIRP~U~ is the EIRP density of the unlicensed device (dBW/Hz).

Using Equation B-1 the values of required propagation loss are:

L~P~ = 166.5 dB (1 MHz)

L~P~ = 153.5 dB (20 MHz)

Using the required propagation loss, the Irregular Terrain Model (ITM)
propagation model is used to determine the separation distance necessary
to preclude potential interference to DSN receivers.[^111] The
parameters used in the ITM propagation model are given in Table B-1.

Table B-1.

  ----------------------------------- -----------------------------------
  **Parameter**                       **Value**

  Frequency                           13000 MHz

  Polarization                        Vertical

  Unlicensed Device Antenna Height    2 meters

  DSN Receiver Antenna Height         10 meters

  Unlicensed Device Transmitter Site  Random
  Criteria                            

  DSN Receiver Site Criteria          Careful

  Delta H                             100 meters

  Dielectric Constant                 15

  Surface Refractivity                280 N-Units

  Conductivity                        0.005 S/m

  Radio Climate                       Desert

  Percent Time                        10%

  Percent Location                    50%

  Confidence Level                    50%

  Mode of Variability                 Mobile
  ----------------------------------- -----------------------------------

Based on the ITM propagation model, the following approximate separation
distances are necessary to preclude potential interference to the DSN
receivers:

D~Req~ = 16 km (1 MHz)

D~Req~ = 8 km (20 MHz)

Since the nearest populated town is approximately 72 km away, the
computed approximate separation distances are small enough where an
unlicensed device would have to be operated by Department of Defense
(DoD) or National Aeronautics and Space Administration (NASA) personnel
at the Goldstone complex to result in potential interference to DSN
receivers.

Protection of the Goldstone radio frequency spectrum is essential for
safeguarding data communication capabilities between spacecraft and the
Goldstone tracking antennas. This spectrum protection is being
successfully accomplished through mutual coordination between DoD and
NASA. It is believed that this coordination and the existing spectrum
monitoring activities will ensure that the DSN receivers are protected
from unlicensed devices operating on the Goldstone facility.

**APPENDIX C**

**DISCUSSION OF THE CRITICAL PARAMETERS OF THE INTERFERENCE TEMPERATURE
MEASUREMENT SYSTEM**

**INTRODUCTION**

This appendix discusses the different parameters that define the
interference temperature measurement system. In general the interference
temperature measurement system should be a spectrum analyzer (SA) based
system that is computer controlled. A specialized front-end should be
implemented before the SA that includes an effective bandpass filter and
a low noise preamplifier. The low noise preamplifier is used to increase
the dynamic range of the measurement system and the bandpass filter is
used to protect the low noise preamplifier from being saturated by
strong signals outside the passband. The critical parameters of the
interference temperature measurement system include detector function,
measurement bandwidth, noise figure, sensitivity, measurement time, and
the measurement antenna. Statistical measurements of the signal
environment are also discussed.

**DETECTOR FUNCTION**

Interference temperature measurements should be made using both peak and
average detector functions. The peak detector function is used to
measure the peak power level of a signal in a specified measurement
interval. The average detector is a little more complicated, since
"average" is a mathematically defined quantity, and many different
averaging functions exist. These include, but are not limited to, linear
average, logarithmic average, and root-mean-square (RMS) average.[^112]
The different average detector functions tend to emphasize particular
parts of the time waveform that is being measured. The logarithmic
detector function gives greatest weight to the relatively lower values
in the time waveform and thus discounts voltage peaks or spikes. The
linear average detector tends to be more affected equally by the whole
range of signal values. The RMS detector function is related to the
"voltage-squared" values of the time waveform, and as such tends to be
more affected by the highest signal levels of the waveform. However,
this voltage-squared aspect is a measurement of the true average power
of the signal. A study performed by NTIA's Institute for
Telecommunication Sciences (ITS) examined the effect of using different
detector functions on measuring noise-like, pulse-like, and continuous
wave signals.[^113] The ITS study generally concluded that the
divergence in measured values for the various average detector functions
are different for the three average detector functions, but they would
be even greater for signals that contain spikes, such as out-of-band
emissions from low-duty cycle pulsed or impulse signals. The study also
concluded that the RMS detector gave the most accurate measure of the
average power.[^114]

Another type of averaging, often referred to as "video averaging" is
performed by using a relatively wide resolution bandwidth (typically
about 1 MHz) and a narrow video bandwidth (as narrow as a few hertz).
The idea behind this technique is to utilize a resolution bandwidth that
is sufficiently wide to follow fluctuations of the signal in the
pre-detection stages, and then to obtain an average value by smoothing
the measured signal with a narrow post-detection low pass filter (the
video bandwidth). In effect, this average suppresses the broadband
content of the measured signal, allowing measurement of its narrowband,
continuous-wave component, if any exists. To illustrate the potential
problem with using the video averaging technique, measurements of
emissions from microwave oven measured using video averaging indicated
levels which were tens of decibels lower than the value that would have
been indicated by wide bandwidth, peak detected measurements.[^115]

**MEASUREMENT BANDWIDTH**

In the SA based measurement system, there are two bandwidths of concern:
the resolution bandwidth (RBW) also referred to as the IF bandwidth and
the video bandwidth (VBW) which is referred to as the post-detection
bandwidth. To perform interference temperature measurements that are
representative of the signal levels that a licensed receiver would
experience, the measurements should be performed in a bandwidth that
matches the licensed receiver IF bandwidth. This may be difficult since
most SAs have a limited set of fixed RBWs.[^116] When the IF bandwidth
of the licensed receiver does not match the available SA RBW, the RBW
that is closest to matching the licensed receiver bandwidth should be
employed. For example, if the licensed receiver has a IF bandwidth of 25
kHz it is appropriate to perform the interference temperature
measurement using a RBW of 30 kHz. Performing the interference
temperature measurement in a much wider RBW will reduce the sensitivity
of the measurement.[^117] If narrower RBWs are employed it will take
longer to measure across a given frequency range and time delays in the
reported interference temperature measurements will exist. If there are
multiple radio services operating in a frequency band or if adaptive
bandwidth technology is employed it may be necessary to perform the
interference temperature measurements in several RBWs. The VBW employed
in the interference temperature measurement should be as wide or wider
than the RBW.[^118] If the VBW is narrower than the RBW, the problems
associated with the video averaging technique discussed earlier could be
encountered.

**NOISE FIGURE AND SENSITIVITY**

The preamplifier used in the front-end of the SA based interference
temperature measurement system establishes the measurement system's
noise figure, sensitivity, and dynamic range.[^119] Since the noise
figure of a SA is typically high (on the order of 20 to 30 dB), the
overall noise figure of the measurement system is dominated by the noise
figure of the first stage, which in this case is the preamplifier placed
in front of the SA. By reducing the preamplifier's noise figure and or
increasing its gain the sensitivity of the measurement system will
improve. In an optimized measurement system, the sum of the preamplifier
gain and noise figure should be nearly equal to the noise figure of the
SA across the frequency range to be measured.[^120] As with the
bandwidth, the noise figure of the measurement system used to perform
the interference temperature measurement should be representative of
that used by the licensed receivers operating in the frequency band
being monitored.

**MEASUREMENT TIME**

The measurement time includes both measurement interval on a specific
frequency in a band and the time required to measure all of the
frequencies in a segment of the spectrum. There are two approaches that
can be used to measure the interference temperature across a band of
frequencies: stepped frequency measurements and swept frequency
measurements. In the stepped frequency approach the measurement consists
of a series of individual measurements made at predetermined (fixed
tuned) frequencies across a spectrum band of interest. The measurement
system remains tuned to each frequency for a specified measurement
interval referred to as the time step or dwell. The frequency interval
for each step is typically set equal to the RBW of the measurement
system. For each specified time interval the highest signal level
occurring in that interval would be reported as the peak and the RMS is
calculated based on the samples that occur during that interval. In the
swept frequency approach the measurement system sweeps across the
spectrum in individual segments that are referred to as spans. The
frequency range of each span is then broken into individual frequency
bins.[^121] As the SA sweeps across a selected span, it spends a finite
amount of time measuring the received power in each of the bins.[^122]
Within each measurement bin a single peak power level or RMS level is
reported. The stepped frequency approach is typically used to capture
peak signals occurring on an intermittent basis, such as a periodically
scanning radar. The swept frequency measurement approach can be used to
measure the peak and RMS levels in highly dynamic frequency bands, such
as the land mobile bands.

The measurement interval to be used in either the stepped or swept
frequency approach is difficult to estimate without prior knowledge of
the signal environment that is being monitored or the receivers that are
to be protected. If the measurement interval is too short then reported
values may not be accurate representations of the peak and RMS levels
and the receiver may not be adequately protected. On the other hand, if
the measurement interval is too long it will increase the time required
to monitor a frequency band, introducing time delays in the reported
interference temperature measurement levels. It may be possible to
estimate the measurement interval based on the characteristics of the
licensed signals. For example, if the licensed signal employs digital
modulation with symbol or bit durations of 20 milliseconds, a
measurement interval on the order of 20 milliseconds should be adequate
to measure the RMS level and have a level that accurately represents the
interference potential to that receiver. However, in general it will be
necessary to perform preliminary measurements in a frequency band in
order to determine the appropriate measurement interval to be employed.

**MEASUREMENT ANTENNA**

The antenna used to measure the interference temperature levels should
have a gain pattern (e.g., omni-directional or directional) that is
consistent with the antennas employed by the licensed user operating in
the frequency band being monitored. Omni-directional, slant polarized,
biconical antennas provide a good response to circular, vertical, and
horizontal polarizations and are commercially available in the 0.1 to 20
GHz frequency range. A slanted-polarized log periodic antenna may also
be employed if most of the radio activity is confined to an area
subtending 180 degrees or less, relative to the measurement system. A
variety of broadband cavity-backed spiral antennas have gain patterns
that are most useful for directional measurements and are commercially
available in the 1 to 18 GHz frequency range. Parabolic reflector
antennas with a choice of feeds (linear, cross-polarized, and circular)
are also an option for performing directional measurements.

**STATISTICAL MEASUREMENTS**

Receiver noise, which is stationary and Gaussian, can be characterized
by one statistic, the mean temperature, and how it affects receiver
performance, thus it is easy to define a noise temperature. For
non-Gaussian noise such as impulsive processes, the mean temperature is
not sufficient to adequately characterize the noise process and how it
will affect receiver performance. In a study performed by ITS, using a
simple matched filter receiver and Binary Phase Shift Keying modulation,
it was found that receiver performance can be more severely degraded by
non-Gaussian impulsive noise when compared to Gaussian noise, given the
same mean temperature for both noise sources.[^123] This result
emphasizes that mean interference temperature may not be sufficient to
characterize the interference process and its effects on a particular
receiver.

In addition to the peak and RMS measurements discussed earlier,
amplitude probability distribution (APD) measurements should also be
considered to characterize the signal environment.[^124] APD
measurements represent first order statistics that have proven to be a
valuable technique used to characterize white Gaussian noise
processes.[^125] Interference from man-made noise processes are often
more complex than white Gaussian noise processes, and may also require
the use of higher order statistics for complete characterization to
understand their effect on victim receivers.[^126] Measurements made
with the peak and RMS detector functions represent two points on the APD
curve. This would require use of a spectrum analyzer capable of sampling
the time waveform of the received signal(s), and possibly other more
specialized equipment.

Appendix D

**Discussion of opportunities that can exist for unlicensed DEVICE use
in certain areas, while protecting the locations that are potentially
more sensitive to interference**

**INTRODUCTION**

This appendix provides an alternative to the method of implementing the
interference temperature model as proposed by the Federal Communications
Commission in the Notice of Inquiry (NOI) portion of the interference
temperature rulemaking.[^127] The alternative method is based on
real-time measurement of desired (i.e. licensed) signal levels, and
baseline measurements of noise levels existent in the frequency bands of
interest. Existence (or lack thereof) of a desired signal at some level
above the measured noise floor can be used as an indication of spectrum
utilization. Licensed signal strengths that are well in excess of
maximum noise levels (high signal-to-noise ratio (S/N)) could allow
opportunistic use by unlicensed devices with a lower probability of
causing harmful interference to licensed users. However, the high
licensed signal level could present a challenge for the operation of the
unlicensed service (i.e. operations in the presence of a high
interfering signal level). Non-existence of a desired signal above the
noise floor indicates that the spectrum is not currently being used in
the location of the measurement. Therefore no harmful interference could
occur and opportunistic use could be permitted. The geographic area in
between these two extremes, however, is the area where receivers are
most vulnerable to interference because the S/N is approaching the
minimum usable value.

**GENERIC COMMUNICATIONS SYSTEM STRUCTURE**

Figure D-1 shows a block diagram that is typical of any
radiocommunications link. This diagram is generic in that it does not
show characteristics that are specific to a particular service, such as
antenna type or pattern, antenna heights, and distance.

Figure D-1. Generic Communications Link Block Diagram

The generic equation that can be used to analyze the communications link
in Figure D-1 is shown in Equation D-1 below:

$P_{R} = P_{T} + G_{T} - L_{P} + G_{R} + G_{\text{OTHER}}$$$ (D-1)

Where: *P~R\ ~*is the usable power at the receiver;

*P~T~* is the transmitter output power;

*G~T~* is the transmit antenna gain in the direction of the receiver;

*L~P~* is propagation losses (including terrain, vegetation, buildings,
etc.);

*G~R~* is the receive antenna gain in the direction of the transmitter;

> *G~OTHER~* is the gains or losses unique to the design of the system,
> such as processing gain or fading losses.

The S/N in the receiver is then determined by comparing the usable
received power level (*P~R~*) to the level of system noise (N). System
noise is made up of thermal noise, as well as any undesired signal
present in the receiver.

The bottom line in determining if a communication link is viable is
determined by the S/N level within the receiver. Licensees must optimize
the link equation to enable the particular type of service they wish to
provide. That is, there must be sufficient S/N to use the received
signal. Tradeoffs must be considered when optimizing the link equation
to provide adequate service within acceptable costs.

*P~T~*: Increasing *P~T~* results in a corresponding increase in *P~R~*.
The tradeoffs are greater cost, reducing frequency re-use, increasing
radiation hazards, reducing battery life, and increasing equipment size.

*G~T~*: Increasing *G~T~* results in a corresponding increase in *P~R~*.
The tradeoffs are greater cost, reduced gain in other directions, since
increasing gain in one direction must result in decreasing gain in other
directions (this could also be a benefit, depending on the type of
service, since there would be more isolation toward off-axis receivers),
and the physical size of directional antennas is typically larger than
that of omni-directional antennas.

*L~P~*: Decreasing *L~P~* results in a corresponding increase in *P~R~*.
This can be accomplished by increasing the antenna height (e.g. on a
tower), reducing the amount of obstructions in the path (e.g., use an
outside antenna), or by reducing the distance between the transmitter
and receiver.

*G~R~*: Increasing *G~R~* results in a corresponding increase in *P~R~*.
The tradeoffs are greater cost, reduced gain in other directions, since
increasing gain in one direction must result in decreasing gain in other
directions (this could also be a benefit, depending on the type of
service, since there would be more isolation from off-axis
interference), and the physical size of directional antennas is
typically larger than that of omni-directional antennas.

*G~OTHER~*: Increasing *G~OTHER~* results in a corresponding increase in
*P~R~*. Increasing other system gains, such as processing gains, can
allow reception of signals that are not usable without this gain. The
tradeoffs are greater cost, and greater complexity of systems employing
these gain factors.

**ALTERNATIVE METHOD FOR IMPLEMENTING THE INTERFERENCE TEMPERATURE
MODEL**

Because licensees have built their systems to operate in the level of
noise currently present and provide service to customers within a
certain coverage contour, any increase in noise will likely require
compensation by an increase in one of the factors in the link equation
or else system performance will be degraded. However, in areas where
excess margin exists, or where insufficient signal exists for a usable
communications link, opportunities for unlicensed use could more easily
be exploited. This can be seen in Figure D-2.

![](media/image1.jpeg){width="6.5in" height="4.875in"}

Figure D-2. Opportunities for Spectrum Access in Areas With Excess
Margin or Lacking Sufficient Signal-to-Noise (S/N) for Licensed Service.

As shown in Figure D-2, opportunities can exist for unlicensed use in
certain areas, while protecting the locations that are potentially more
sensitive to interference. These areas of opportunity (the shaded areas
in Figure D-2) could be utilized by unlicensed devices that are capable
of measuring the radio frequency (RF) environment, and making a
determination to transmit based on whether excess margin or insufficient
desired signal exist, or a determination to not transmit if the desired
signal level is such that an increase in noise could potentially disrupt
communications.

**MEASUREMENT CHALLENGES**

Interference temperature is proposed within the NOI to be defined as a
measure of the RF power generated by undesired emitters plus noise
sources that is present in a receiver system (I+N) per unit of
bandwidth.[^128] Difficulty in measuring this quantity arises for
several reasons.

First, the desired signal of the licensed service will be received along
with any undesired signals. Hardware and/or software algorithms may be
developed that are able to distinguish between a licensed desired signal
and noise. Such a measurement process, however, would be very dependent
on a detailed knowledge of the licensed signal. Requirement of such an
in-depth knowledge of licensed signal structure could have a detrimental
effect on the flexibility of a licensee, since any change in signal
structure would potentially nullify any measurements made with the
expectation of a different signal structure to be present.

Second, if interference temperature is to be referenced at the receiver,
knowledge about the licensed receive antenna is required. This would
include antenna location and main-lobe gain, as well as the shape of the
antenna pattern, so that off-axis properties can be taken into
consideration.

Finally, measurement of interference temperature at any location other
than that of the licensed receiver location makes the assumption that
the undesired signals and man-made noise are homogeneous in nature. This
is not necessarily the case.

These challenges will likely exist no matter how the interference
temperature model is implemented, and must be resolved to successfully
allow unlicensed use without endangering licensed services.

**APPENDIX E**

**ASSESSMENT OF THE POTENTIAL IMPACT OF INCREASING**

**THE NOISE FLOOR**

This appendix provides an assessment of the potential impact the
increased noise, as discussed in the Federal Communication Commission
(Commission) proposal of the interference temperature model, will have
on licensed and unlicensed spectrum users. This assessment considers the
link budget for interference from an unlicensed transmitter to a
licensed user receiver and the link budget for an unlicensed link. It is
assumed that the unlicensed transmitter is constrained to a relatively
low equivalent isotropically radiated power level and thus would have to
be close to the licensed user receiver to cause interference. The
unlicensed transmitter would also have to be close to the unlicensed
receiver to establish a communications link. Under this transmitter
power constraint the elevated, background noise (N~e~) shown in Figure 1
of the Commission's Notice of Inquiry can be considered constant over
the area of concern.[^129]

In order for the unlicensed transmitter not to interfere with the
licensed service the following link budget constraint must be satisfied:

P~TU~ - C~U-L~ - N~e~ = (I/N)~L~ + L~ML~ (E-1)

where:

P~TU~ is the transmitter power of the unlicensed device;

C~U-L~ is the coupling loss from the unlicensed transmitter to the
licensed receiver;

N~e~ is the elevated background noise;

(I/N)~L~ is the required interference-to-noise ratio for satisfactory
performance of the licensed link;

L~ML~ is the available link margin for the licensed service.

The coupling loss includes antenna gains of the licensed and unlicensed
transmitters and receivers, propagation losses, and any other additional
losses (e.g., foliage, insertion). The link margin includes gains that
are unique to the system, such as processing gain and represents the
desired signal in excess of the minimum required signal.

Equation E-1 can be rearranged to determine the maximum allowable power
level of the unlicensed device:

P~TU~ = (I/N)~L~+ C~U-L~ + L~ML~ + N~e~ (E-2)

If the unlicensed link is to satisfy the performance requirement, then
the following link budget must be satisfied:

(P~R~/N)~U~ = P~TU~ - C~U-U~ - L~MU~ - N~e~ (E-3)

where:

(P~R~/N)~U~ is the required signal-to-noise ratio for satisfactory
performance of the unlicensed link;

C~U-U~ is the coupling loss from the unlicensed transmitter to the
unlicensed receiver;

L~MU~ is the available link margin for the unlicensed service.

Substituting Equation E-2 into Equation E-3 results in:

(P~R~/N)~U~ = (I/N)~L~ + C~U-L~ + L~ML~ + N~e~ - C~U-U~ - L~MU~ - N~e~
(E-4)

The elevated, background noise level cancels out in Equation E-4.
Therefore, the performance capabilities of the unlicensed device link
are not impacted by an increasing noise floor. This is not an unexpected
result. The increase in the noise floor does allow higher transmitter
power as shown in Equation E-2; however, this higher transmitter power
does not improve the performance of the unlicensed link as this
unlicensed signal has to compete with the same increased noise level for
satisfactory reception as shown in Equation E-3. The result is shown in
Equation E-4 as performance that is independent of the elevated noise
floor. This phenomenon needs further study before unlicensed devices are
permitted to operate at higher-power levels based on consideration of an
elevated noise level.

[^1]: . *Establishment of an Interference Temperature Metric to Quantify
    and Manage Interference and to Expand Available Unlicensed Operation
    in Certain Fixed, Mobile and Satellite Frequency Bands*, Notice of
    Inquiry and Notice of Proposed Rulemaking, ET Docket No. 03-237, 18
    F.C.C. Rcd. 25309 (2003) ("NOI/NPRM").

[^2]: . The distance between the source in the sky and the receiving
    antenna on the surface of the earth varies little, and a single
    temperature can be used to adequately describe the amount of energy
    coming from the source.

[^3]: . XG Working Group, *The XG Vision*, Request for Comments Version
    2.0, BBN Technologies, Cambridge, Massachusetts. This document and
    other information about the DARPA XG program are available at
    http://www.darpa.mil/ato/programs/XG/rfcs.htm.

[^4]: . National Science Foundation, Directorate for Computer and
    Information Science Engineering, Division of Computer and Network
    Systems, Research in Networking Technology and Systems (NeTS). More
    information on the NeTS program is available at http://www.cise.nsf.

[^5]: . Federal Communications Commission, *Spectrum Policy Task Force
    Report*, ET Docket No. 02-135, at 5 (November 15, 2002) ("SPTF
    Report").

[^6]: . NTIA hosted a summit on April 4-5, 2002, to help identify the
    best solutions to challenges posed by management of the nation's
    airwaves.

[^7]: . NOI/NPRM at ¶ 21.

[^8]: . *See* 47 C.F.R. § 15.5.

[^9]: . NOI/NPRM at ¶ 1.

[^10]: . *See* 47 C.F.R. § 2.1.

[^11]: . NOI/NPRM at ¶ 21*.*

[^12]: . *See* 47 C.F.R. § 15.5.

[^13]: . *See* 47 C.F.R. § 15.205.

[^14]: . In the 608-614 MHz frequency band used by radio astronomers for
    Very Long Baseline Interferometry, the Wireless Medical Telemetry
    Service is permitted, but operation is limited to health care
    facilities and frequency coordination is necessary.

[^15]: . ITU-R Recommendation RA.769-1, *Protection Criteria Used for
    Radioastronomical Measurements* (1992-1995).

[^16]: . NOI/NPRM at ¶ 10.

[^17]: . NOI/NPRM at ¶ 15.

[^18]: . A few sources such as pulsars, show rapid, periodic variations
    in time, others show slow variability on the scale of weeks or
    months.

[^19]: . Reply Comments of Cornell University, ET Docket No. 02-135, at
    4 (July 23, 2002).

[^20]: . NOI/NPRM at ¶ 20.

[^21]: . V-COMM L.L.C. Reply Comments, ET Docket No. 02-135, at 7
    (February 28, 2003); Cellular Telecommunications and Internet
    Association Comments, ET Docket No. 02-135, at 10 (January 27,
    2003); Cingular Comments, ET Docket No. 02-135, at 17 ( January 27,
    2003 ) ("Cingular Comments"); AT&T Wireless Services, Inc. Comments,
    ET Docket No. 02-135, at 9 (January 27, 2003) ("AT&T Comments");
    Telecommunications Industry Association Comments, ET Docket No.
    02-135, at 8 (January 27, 2003); Lucent Technologies Inc. Comments,
    ET Docket No. 02-135, at 2 ( January 27, 2003 ); Motorola Comments,
    ET Docket No. 02-135, at 13 (January 27, 2003); United Telecom
    Council Comments, ET Docket No. 02-135, at 5 (January 27, 2003); The
    Boeing Company Comments, ET Docket No. 02-135, at 8 (January 27,
    2003); Lockheed Martin Corporation Comments, ET Docket No. 02-135,
    at 6 (January 27, 2003) ("Lockheed Martin Comments"); Industrial
    Telecommunications Association, Inc. Comments, ET Docket No. 02-135,
    at 11 (January 27, 2003); Verizon Wireless Reply Comments, ET Docket
    No. 02-135, at 9 (February 28, 2003) ("Verizon Wireless Reply
    Comments").

[^22]: . Verizon Wireless Reply Comments at 12; Cingular Comments at 25.

[^23]: . Verizon Wireless Reply Comments at 14; Lockheed Martin Comments
    at 7; AT&T Comments at 15; Cingular Comments at 20.

[^24]: . WiFi Alliance Comments, ET Docket No. 02-135, at 5 (January 27,
    2003); Wireless Communications Association International, Inc.
    Comments, ET Docket No. 02-135, at 9 (February 27, 2003).

[^25]: . NOI/NPRM at ¶ 31.

[^26]: . *Unlicensed Operations in the Band 3650-3700 MHz*; *Additional
    Spectrum for Unlicensed Services Below 900 MHz and in the 3 GHz
    Band; Amendment of the Commission's Rules with Regard to the
    3650-3700 MHz Government Transfer Band*, Notice of Proposed
    Rulemaking, ET Docket Nos. 04-151, 02-380, 98-237, 19 F.C.C. Rcd.
    7545 (2004) ("3650-3700 MHz NPRM"); *see also* 69 Fed. Reg. 26790
    (2004).

[^27]: . DFS is a mechanism that dynamically detects signals that are
    received above a specified threshold level and avoids co-channel
    operation with these systems.

[^28]: . NOI/NPRM at ¶ 44.

[^29]: . *Id.* at ¶ 47.

[^30]: . National Telecommunications and Information Administration,
    NTIA Special Publication 01-49, *Current and Future Spectrum Use by
    the Energy, Water, and Railroad Industries* (January 2002).

[^31]: . ITU-R Recommendation M.1652, *Dynamic Frequency Selection (DFS)
    in Wireless Service Systems Including Radio Local Area Networks for
    the Purpose of Protecting the Radiodetermination Service in the 5
    GHz Band* (2003) ("ITU-R M.1652").

[^32]: . The Institute of Electrical and Electronics Engineers, Inc.
    Comments, ET Docket No. 02-380, at 10 (April 17, 2003).

[^33]: . One method could be for the unlicensed device to connect to the
    internet to receive updated FS site location information. Such
    updates could be done over the air or through a computer with a
    wired connection (attaching to a universal serial bus port through a
    cradle as currently done for personal data assistants and cell
    phones).

[^34]: . *Facilitating Opportunities for Flexible, Efficient, and
    Reliable Spectrum Use Employing Cognitive Radio Technologies*,
    Notice of Proposed Rulemaking, ET Docket No. 03-108, 18 F.C.C. Rcd.
    26859, at ¶ 47 (2003) ("Cognitive Radio NPRM").

[^35]: . *Revision of Parts 2 and 15 of the Commission's Rules to Permit
    Unlicensed National Information Infrastructure (U-NII) Devices in
    the 5-GHz Band*, Report and Order, ET Docket No. 03-122, 18 F.C.C.
    Rcd. 24484 (2003) ("5 GHz U-NII R&O").

[^36]: . Although the Commission did not indicate its use of the
    methodology in ITU-R Recommendation M.1652 in the 5 GHz U-NII R&O,
    it is clear from the DFS parameters adopted in that order that this
    methodology was used. *See* 5 GHz U-NII R&O at ¶ 29.

[^37]: . NOI/NPRM at ¶ 44.

[^38]: . NOI/NPRM at ¶ 38.

[^39]: . The GMDSS is required by international treaty resulting from
    Safety of Life at Sea (SOLAS) convention.

[^40]: . The SBAS is part of the Global Satellite Navigation Satellite
    System (GNSS) which will be used for aviation, maritime, and
    terrestrial navigation.

[^41]: . ITU-R Recommendation F.1094-1, *Maximum Allowable Error
    Performance and Availability Degradations to Digital Radio-Relay
    Systems Arising from Interference from Emissions and Radiations from
    Other Sources*; ITU-R Recommendation S.1432, *Apportionment of the
    Allowable Error Performance Degradations to Fixed-Satellite Service
    (FSS) Hypothetical Reference Digital Paths Arising from Time
    Invariant Interference for Systems Operating Below 15 GHz.*

[^42]: . 3650-3700 MHz NPRM at ¶ 42.

[^43]: . NOI/NPRM at ¶ 48.

[^44]: . ITU-R Recommendation RA.314-8, *Preferred Frequency Bands for
    Radioastronomical Measurements*.

[^45]: . *See* <http://www.gb.nrao.edu/nrqz/nrqz.html> for additional
    information.

[^46]: . *See* 47 C.F.R. § 21.113(b).

[^47]: . *See* 47 C.F.R. § 21.113(b)(1).

[^48]: . NOI/NPRM at ¶ 21.

[^49]: . *Id.*

[^50]: . In practice, the 3 dB bandwidth of the filter used to determine
    the receiver selectivity is assumed to be the receiver's noise
    bandwidth.

[^51]: . Formerly the Radio Technical Commission for Aeronautics (RTCA).

[^52]: . National Telecommunications and Information Administration,
    NTIA Report 03-404, *Receiver Spectrum Standards Phase 1 -- Summary
    of Research into Existing Standard*s (November 2003).

[^53]: . *Interference Immunity Performance Specifications for Radio
    Receivers*, ET Docket No. 03-65, Notice of Inquiry, 18 F.C.C. Rcd.
    6039 (2003).

[^54]: . NOI/NPRM at ¶ 22.

[^55]: . The problem encountered with the antenna pattern is made more
    difficult when steerable or adaptive antennas are employed.

[^56]: . A variable bandwidth radio system monitors the frequency band
    and automatically increases the bandwidth and the corresponding
    throughput when the channels become available.

[^57]: . Polarization mismatch loss is the ratio at a receiving point
    between received power in the expected polarization and received
    power in a polarization orthogonal to it from a wave transmitted
    with a different polarization.

[^58]: . American National Standard, ANSI C95.3-1973, *Techniques and
    Instrumentation for the Measurement of Potentially Hazardous
    Electromagnetic Radiation at Microwave Frequencies*, at 12 (April
    20, 1973).

[^59]: . *Antenna Analysis*, E. A. Wolff, at 17 (1966).

[^60]: . NOI/NPRM at ¶ 27.

[^61]: . *Id.* at ¶ 28.

[^62]: . R. Paul Margie, *Efficiency, Predictability, and the Need for
    an Approved Interference Standard at the FCC*, 2003
    Telecommunications Policy Research Conference (September 2003) (This
    article is available at
    <http://stlr.stanford/stlr/articles/03_stlr_5/index.htm>) ("Margie
    Article").

[^63]: . NOI/NPRM at ¶ 1.

[^64]: . NTIA expects to publish the results of this study later this
    summer.

[^65]: . Margie Article at 38.

[^66]: . NOI/NPRM at ¶ 21.

[^67]: . *Id.*

[^68]: . *Id.* at ¶ 22.

[^69]: . *Id.*

[^70]: . Naval Postgraduate School, NPS-EC-02-004, *Literature* *Search
    and Review of the Impact of Noise on Wireless Communications* (March
    2002) ("Naval Postgraduate School Report").

[^71]: . SPTF Report at 18.

[^72]: . NOI/NPRM at ¶ 19.

[^73]: . The GWCS auction was indefinitely postponed due to lack of
    interest and the WCS auction generated minor interest and licenses
    were awarded for as low as \$1.

[^74]: . SPTF Report at 3.

[^75]: . *Id.* at 4.

[^76]: . *See* Testimony of Dr. Paul Kolodzy, Former Director of the
    Spectrum Policy Task Force, Federal Communications Commission,
    Before the U.S. Senate Committee on Commerce, Science and
    Transportation, Thursday, March 6, 2003.

[^77]: . *See* Keynote Address of Assistant Secretary Nancy J. Victory,
    Before the Federal Communications Bar Association (FCBA), Spectrum
    Policy Summit & CLE, Washington, DC, April 16, 2002.

[^78]: . NOI/NPRM at ¶ 28.

[^79]: . The Margie Article contains a discussion of how vagueness and
    inconsistency in the rulemaking process affected the Multichannel
    Video Distribution and Data Service and Ultrawideband technologies
    rulemaking proceedings. *See* Margie Article at 20.

[^80]: . The Monte Carlo method has been used for the simulation of
    random processes and is based upon the principle of taking samples
    of random variables from their defined probability density
    functions.

[^81]: . Document No. RTCA/DO-235, *Assessment of Radio Frequency
    Interference Relevant to the GNSS* (January 27, 1997).

[^82]: . Document No. RTCA/DO-235A, *Assessment of Radio Frequency
    Interference Relevant to the GNSS* (December 5, 2002).

[^83]: . NOI/NPRM at ¶ 49.

[^84]: . NOI/NPRM at ¶ 39.

[^85]: . NOI/NPRM at ¶ 13.

[^86]: . Cognitive Radio NPRM at ¶¶ 99-107.

[^87]: . *See* 47 C.F.R. § 2.962 (b). Under the Commission's Rules, to
    be designated as a TCB, the TCB is required to demonstrate expert
    knowledge of the regulations for each product with respect to which
    the body seeks designation. Such expertise includes familiarity with
    all applicable technical regulations, administrative provisions or
    requirements, as well as, the policies and procedures used in the
    application thereof. The TCB is required to have the technical
    expertise and capability to test the equipment it will certify.

[^88]: . NOI/NPRM at ¶ 21.

[^89]: . The permissible interference level for land mobile operations
    is approximately -146 dBW, whereas the maximum permissible
    interference level to protect radio astronomy operations, based on
    Recommendation ITU-R Recommendation RA.769 in the 14.44-14.5 GHz
    band, is -218 dBW.

[^90]: . NOI/NPRM at ¶ 37.

[^91]: . *Id.* at ¶ 51.

[^92]: . Mobile Satellite Ventures *Ex Parte* Presentation, IB Docket
    No. 01-185*, Monitoring and Control of Ancillary Terrestrial
    Emissions by MSV's Space Segment* (March 28, 2002).

[^93]: . *Id.* at 3, 13.

[^94]: . *Id.* at 3.

[^95]: . NOI/NPRM at ¶ 15.

[^96]: . *Id.*

[^97]: . Naval Postgraduate School Study at 380.

[^98]: . Federal Communications Commission, Technical Advisory Council,
    Fourth Meeting Report, at 23, Annex 4 (March 24, 2000).

[^99]: . National Telecommunications and Information Administration,
    Institute for Telecommunication Sciences, NTIA Report 97-334,
    *Broadband Spectrum Survey at San Diego, California* (December
    1996); National Telecommunications and Information Administration,
    Institute for Telecommunication Sciences, NTIA Report 97-336,
    *Broadband Spectrum Survey at Los Angeles, California* (May 1997);
    National Telecommunications and Information Administration,
    Institute for Telecommunication Sciences, NTIA Report 99-367,
    *Broadband Spectrum Survey at San Francisco, California* May-June
    1995 (July 1999); National Telecommunications and Information
    Administration, Institute for Telecommunication Sciences, NTIA
    Report 95-321, *Broadband Spectrum Survey at Denver, Colorado*
    (September 1995).

[^100]: . Naval Postgraduate School Report at 380.

[^101]: . *Id.*

[^102]: . Federal Communications Commission, Spectrum Policy Task Force,
    Report of the Interference Temperature Working Group, at 28
    (November 15, 2002); Federal Communications Commission, Technical
    Advisory Council, Sixth Meeting Report, at 9 (September 27, 2000).

[^103]: . *Establishment of an Interference Temperature Metric to
    Quantify and Manage Interference and to Expand Available Unlicensed
    Operation in Certain Fixed, Mobile and Satellite Frequency Bands*,
    Notice of Inquiry and Notice of Proposed Rulemaking, ET Docket No.
    03-237, 18 F.C.C. Rcd. 25309, at ¶ 47 (2003).

[^104]: . *Id.*

[^105]: . *Revision of Parts 2 and 15 of the Commission's Rules to
    Permit Unlicensed National Information Infrastructure (U-NII)
    Devices in the 5-GHz Band*, Report and Order, ET Docket No. 03-122,
    18 F.C.C. Rcd. 24484 (2003).

[^106]: . ITU-R Recommendation F.1094 permits a 1 percent increase in
    system noise attributable to non-primary (unlicensed) interference
    sources, which corresponds to an I/N = -20 dB.

[^107]: . The Commission's proposal did not include a measurement
    bandwidth for the detection threshold. A bandwidth of 1 MHz is used
    consistent with the value used in the U-NII DFS device and radar
    analysis that determined the --64 dBm threshold.

[^108]: . National Telecommunications and Information Administration,
    Institute for Telecommunication Sciences, NTIA Report 82-100, *A
    Guide to the Use of the ITS Irregular Terrain Model in the Area
    Prediction Mode* (April 1982).

[^109]: . For separation distances of less than 1 kilometer, the ITM
    propagation model defaults to the free space model.

[^110]: . ITU-R Recommendation SA.1157, *Protection Criteria for
    Deep-Space Research* (1995).

[^111]: . National Telecommunications and Information Administration,
    Institute for Telecommunication Sciences, NTIA Report 82-100, *A
    Guide to the Use of the ITS Irregular Terrain Model in the Area
    Prediction Mode* (April 1982).

[^112]: . The RMS detector determines the average power based on the RMS
    voltage levels that are measured.

[^113]: . National Telecommunications and Information Administration,
    Institute for Telecommunication Sciences, NTIA Report 01-383, *The
    Temporal and Spectral Characteristics of Ultrawideband Signals*
    (January 2001).

[^114]: . *Id.* at 8-13.

[^115]: . National Telecommunications and Information Administration,
    NTIA Report 94-303-1, *Radio Spectrum Measurements of Individual
    Microwave Ovens Volume I*, at 9 (March 1994).

[^116]: . SA RBWs may be selected from 0.01 to 3000 kHz, in a 1,3,10
    progression. Modern SAs have RBWs as wide as 8 MHz.

[^117]: . Wider RBWs have higher noise levels which reduces the
    signal-to-noise ratio and the achievable sensitivity.

[^118]: . The rule-of-thumb is that the VBW should be three times wider
    than then RBW.

[^119]: . The dynamic range is the difference, in dB, between the
    maximum and minimum acceptable signal level in a measurement system.

[^120]: . A higher noise figure results in loss of sensitivity; gain
    that is too low will fail to overdrive the measurement system noise,
    while gain that is too high will reduce the available dynamic range
    of the measurement system. The desirable gain of the preamplifier
    can be estimated as follows: G~PA~ = NF + L + 5 dB; where NF is the
    noise figure in dB of the SA and L is the loss in dB in the cable
    connecting the preamplifier to the SA.

[^121]: . The number of bins is dependent on the SA. For example,
    Hewlett Packard SAs have 1001 frequency bins, whereas Agilent SAs
    have 601 bins.

[^122]: . For example, a 20 millisecond sweep time divided by 1001
    measurement bins per sweep yields a 20 microsecond measurement time
    in each frequency bin.

[^123]: . National Telecommunications and Information Administration,
    Institute for Telecommunication Sciences, NTIA Report 82-95,
    *Digital System Performance Software Utilizing Noise Measurement
    Data* (February 1982).

[^124]: . APDs show the percentage of time that measured emissions
    exceed a given power threshold.

[^125]: . First order statistics accurately characterize variables that
    are independent and identically distributed.

[^126]: . Second order statistics measure the correlation between random
    variables.

[^127]: . *Establishment of an Interference Temperature Metric to
    Quantify and Manage Interference and to Expand Available Unlicensed
    Operation in Certain Fixed, Mobile and Satellite Frequency Bands*,
    Notice of Inquiry and Notice of Proposed Rulemaking, ET Docket No.
    03-237, 18 F.C.C. Rcd. 25309 (2003).

[^128]: . *Id.* at ¶ 10.

[^129]: . *Establishment of an Interference Temperature Metric to
    Quantify and Manage Interference and to Expand Available Unlicensed
    Operation in Certain Fixed, Mobile and Satellite Frequency Bands*,
    Notice of Inquiry and Notice of Proposed Rulemaking, ET Docket No.
    03-237, 18 F.C.C. Rcd. 25309 (2003).