ACP-WG-F30/WP-16
International Civil Aviation Organization
WORKING PAPER
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
30TH MEETING OF THE WORKING GROUP F (WG F)
Pattaya, Thailand 13 – 19 March 2014
Agenda Item X: XXXXXXXX
AFC response to US Harm Claim Threshold Concept
(Presented by Andrew Roy)
SUMMARY
This paper details the US Aeronautical Frequency Committee’s response to a
harm claim threshold whitepaper being consider by the US regulator,
explaining the early concept as proposed, and the current status of the work.
ACTION
The Working Group is invited to note the results of the study
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INTRODUCTION
1.
The US Aeronautical Frequency Committee (AFC1) consists of US airlines, associations and
ANSPs, collaborating on common spectrum management issues in the VHF spectrum and other areas. In
Feb 2013, the AFC filed comments on the US Federal Communication Commission’s (FCC) whitepaper
‘Interference Limits Policy - The use of harm claim thresholds to improve the interference tolerance of
wireless systems’2. The whitepaper investigated options to integrate receivers into the federal spectrum
management process, and therefore enabling greater sharing of the RF spectrum for new broadband
applications while attempting to minimize uncertainty for new and existing operators. This information
paper details the AFC’s public comment to the concept.
AIM
2.
To inform ICAO WG-F of the AFC’s comments on potential receiver standards in the US.
BACKGROUND
3.
Although several attempts have been made in the US to integrate receivers into the spectrum
management process, no standards - have been fully implemented except for specific applications under
set conditions. However, the combination of the recent LightSquared/GPS events, and requirement to
release spectrum for wireless broadband in the US, has provided renewed impetus to consider the concept
in the US again. Therefore, the FCC tasked its Technical Advisory Council3 (TAC) to investigate other
options that may be considered, incorporating the lessons learnt from previous work. This could then be
discussed in public to determine its feasibility and how it could be applied. Released for comment on 22
April 2013, a range of comments were received4, including the AFC’s.
THE HARM CLAIM THRESHOLD CONCEPT
4.
The harm claim threshold concept defines a signal strength profile that a receiver must be capable
of rejecting before a claim of interference can be made (i.e. an interference limit). Intended to be more of
a target than traditional standard, the setting of the threshold would allow manufacturers to make their
own choices while not mandating specific receiver standards. Applied on a case-by-case basis to both in
band and Out-Of-Band (OOB) emissions that a receiver would be subject to, this method was seen as a
more flexible approach than traditional receiver standardization, allowing several potential benefits:
a. Enabling industry to find the solutions without complex federal mandates increasing costs and
stifling innovation.
1
http://www.asri.aero/afc-membership/
http://transition.fcc.gov/bureaus/oet/tac/tacdocs/WhitePaperTACInterferenceLimitsv1.0.pdf
3
The FCC’s Technological Advisory Council (TAC) provides technical advice to the FCC. The TAC is organized
under the authority of the Federal Advisory Committee Act. The current TAC, which is the FCC’s 5th
Technological Advisory Council, was formed on October 21, 2010. The TAC is comprised of a diverse array of
leading experts that helps the FCC identify important areas of innovation and develop informed technology policies
supporting America’s competitiveness and job creation in the global economy.
4
http://apps.fcc.gov/ecfs/comment_search/execute?proceeding=13101&applicant=&lawfirm=&author=&disseminated.minDate=&disseminated.maxDate=&recieved.minDate=6%2F
10%2F12&recieved.maxDate=&dateCommentPeriod.minDate=&dateCommentPeriod.maxDate=&dateReplyComm
ent.minDate=&dateReplyComment.maxDate=&address.city=&address.state.stateCd=&address.zip=&daNumber=&
fileNumber=&bureauIdentificationNumber=&reportNumber=&submissionTypeId=&__checkbox_exParte=true
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b. Clearly define the RF environment of transmitters and receivers, providing certainty for new and
existing users.
c. Indirectly incorporates receivers into the regulatory framework, partially bypassing previous legal
issues.
d. Allow for better system design with a known receiver performance criteria that could be met.
5.
These thresholds would be defined as the aggregate Field Strength Density (FSD) (or equivalent
Power Flux Density (PFD)) for a percentage of time and/or locations. Defined for both in-band and OOB
received signals, the process attempts to keep parameters manageable by using constant profiles for each
of the in-band, lower and upper adjacent spectrum areas. Transitioning between the frequency bands at
the band edge is an instantaneous step function with no roll off, with the upper and lower adjacent
spectrum limits incorporating the worst case of systems operating in nearby adjacent bands. Annex A
contains an excerpt from the whitepaper, graphically explaining the application of the threshold.
6.
To declare interference, a receiver must first be able to meet the required interference rejection
threshold. Any signal received over this limit for the required percentage of time and/or locations would
then be subject to restrictions as its transmitter would be operating outside of its agreed license. If the
interfering signal degraded a receiver that did not meet the required interference rejection limits, then no
claim of interference could be made5. The whitepaper recognized that special circumstances may need to
be applied to safety service such as aviation; however, how this may implemented within the concept was
not discussed at this early stage.
7.
Although the thresholds will be decided by a multi-stakeholder industry group, receivers would
not be mandated to meet these interference limits. The paper highlights opportunities where a
manufacturer may offset cost by not meeting the published levels when operating in a relatively quiet
environment, as implemented in several satellite allocations where signals from adjacent satellite
allocations are known to be low power and at distance. Additionally, the paper recognizes that the
thresholds should reflect the future interference environment, potentially applying higher levels in order
to accommodate a wider range of future services, or provide an extra margin for uncontrolled transmitters
such as unlicensed devices. Should this not be feasible or predictable at the time, then future
renegotiation of limits would be possible to ensure the best use of the spectrum.
8.
The whitepaper proposes a three step process to decide on and implement the harm claim
thresholds, conducted as a separate process for each frequency band:
a. Identify frequency bands and boundaries where there would be benefits. The whitepaper
proposed a gradual implementation process, identifying an initial set of frequency bands where the
benefit would be greatest or the agreement of values would be simple to decide. Although no detailed
criteria were stated, several suggestions are discussed that may provide more immediate benefits,
including: 2.4 GHz unlicensed, 3.4 – 3.6 GHz FSS and mobile satellite earth stations. The whitepaper
did recognize that not all bands may be suitable due to operational or technical reasons.
b. Encourage multi-stakeholder involvement to define the thresholds. Once a frequency band
was deemed appropriate, a multi-stakeholder committee of all interested parties would convene to
agree on a set of suitable limits, or at least a set of parameters that could ultimately define such limits.
The paper does not clarify if it would still be classified as interference if an ‘out of spec’ receiver received a signal
higher than even an ‘in spec’ receiver would be able to tolerate.
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3
This would primarily be based on suitable modeling to provide a prediction of the RF environment,
although physical monitoring and testing remains an option should modeling be unsuitable for some
reason. If agreement on an interference limit cannot be reached, then the FCC would itself make a
decision based on any agreed parameters defining the environment and proceed to the next stage for
approval. Should no agreement be found even at the parameters level, then it is proposed that the
FCC would take the decision in consideration of the public interest, decided by the net social gain of
any recommendation.
c. Issue rulemaking notice for public consideration and comment. Once the multi-stakeholder
process has reached an agreed decision, a Notice of Proposed Rulemaking on the thresholds would be
issued for comment before implementation at licensing or renewal. The FCC would then follow
normal procedure in addressing comments before making a rulemaking.
COMMENTS PROVIDED BY THE US AERONAUTICAL FREQUENCY COMMITTEE (AFC)
9.
The AFC reviewed the whitepaper at its June 2013 meeting, and although the membership
recognized that it was an early concept paper, several comments and recommendations were noted.
These were publically filed6, and included the following recommendations:
a. Aviation operates within a unique setting, combining a ubiquitous airborne environment used by
international users, with a high level of safety. Extensive work and coordination would be
required, both domestically and internationally, to ensure all factors and impacts are considered.
The AFC recommended that these factors must be considered in any standard, should this even be
feasible given the concept proposed.
b. Given the large number of existing international standards within the aviation industry, the AFC
recommended that these regulations should be adopted if any aviation systems come under
consideration7. This would ensure the continued protection of safety-of-life systems,
compatibility with international regulations, and minimal disruption to the aviation industry.
c. The AFC noted that not all the required information on an RF environment may be known by the
users, or even be practical to measure with any accuracy, in certain environments. Therefore
notification timelines for frequency bands under consideration should take into account the
possible need for testing and measurement, if this is even possible for airborne environments.
d. On the possibility of renegotiation set interference limits, the AFC noted that these thresholds
should not be totally inflexible for changes to the future RF environment. However, all limits
should be given a minimum period of validity before being subject to possible renegotiation.
This will prevent uncertainty and additional expense by existing users in the frequency bands,
especially for systems with 20-30 year lifecycles such as aircraft avionics, where retrofitting costs
can be exceptionally high.
e. Given the potential complexities of base lining and investigating any aviation RF environment,
the AFC recommended that the procedures in these scenarios and certification should be clarified.
This was recognized by the whitepaper, and is intended for further work into the practicalities of
such a process.
6
http://apps.fcc.gov/ecfs/document/view?id=7520932706
The AFC did note that not all aviation standards would be immediately compatible with the harm claim threshold
concept, or even be in existence for certain systems due to commercially confidential information.
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f.
The whitepaper proposal included an additional margin for unknown elements in an RF
environment that might not be observable given locations or availability. The AFC recommended
that these should be adopted if the concept were to be developed further, and even enhanced for
safety services such as aviation as recommend by ICAO.
REACTION AND ACTIVITY POST COMMENTS
10.
The filing attracted a range on mixed comments from multiple industry sectors and companies.
As reported in a follow up meeting of the TAC on 23 September 2013, the majority of comments
welcomed some type of clarification of the RF environment. However, the implementation methods
would have to be carefully planned to minimize disruption. It was also noted that not many industries
favored implementing the process in frequency bands used by their own sector.
11.
Given the somewhat positive reaction, the TAC felt there was enough support for the FCC to
create a pilot project. Consequently, the TAC recommended the formation of a multi-stakeholder group
to investigate interference limits and pilot the use of harm claim thresholds in the 3.5 GHz band. This is
due to be discussed at the next TAC meeting scheduled for 10 March 2014.
CONCLUSION
12.
The AFC was broadly supportive of the intention to protect existing services and define the RF
environment; however it felt the current proposal was too simplistic in its method for a mobile aviation
environment requiring high levels of safety. Should the concept be considered for aviation services, the
AFC made several recommendations for the future development to ensure the unique aspects of aviation
where taken into account. It proposed this as a minimum before any further work be considered for
aviation services.
13.
As it is still a concept under review, the whitepaper itself recognizes that it does not address all
issues in a detailed manner, and it hopes the pilot program will identify any deficiencies that may require
further work and define its applicability.
RECOMMENDED ACTION BY THE MEETING
14. The meeting is invited to:a. note the content of this paper;
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ANNEX A – EXCERPT OF GRAPHICAL EXPLANATION OF HARM
CLAIM THRESHOLDS FROM WHITEPAPER
In order not to change the rights of neighboring incumbents, harm claim thresholds would be no lower
than the interference caused by existing operations; thus, transmissions by incumbent neighbors would
not exceed the harm claim threshold and could not trigger a harmful interference claim . Conversely, if
an incumbent neighbor’s assignment includes harm claim thresholds, the transmission permissions
assigned to a new operator in block (1) would be chosen so that the resulting signals will not exceed
those thresholds.
If harm claim thresholds are in place for bands adjoining a new allocation, they enable the regulator to
derive allowable transmission permissions rapidly and formulaically. The regulator can choose out-ofblock levels that are above extant signal levels in adjacent bands, indicated by the dotted green lines (2),
so that legacy operation in neighboring bands isn’t newly categorized as interference. The harm claim
threshold is greater than the current generated signal level, with a margin to allow for uncertainty and
cases where signals from two operators in the adjacent band combine (3). This yields the protection level
(4). The dot on the end of the protection limit line indicates that the block (1) will be given no protection
against interfering signals beyond this point.
In new allocations where a currently quiet adjacent band (5) has the potential for transition to more
intensive use, i.e. there is likely to be an increase in the aggregate signal level in the future due to new
services, the regulator should define harm claim thresholds that reflect the anticipated future interference
environment (6). This is a way to implement the proposal of Kwerel & Williams (2011) that future
allocations should self-protect against projected adjacent band interference, and puts the new licensees
on notice that they could not depend on the absence of adjacent channel interference to continue into the
future.
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