Decision on Amendments to SRSP-520, Technical Requirement for Fixed and/or Mobile Systems, Including Flexible Use Broadband Systems, in the Band 3450-3650 MHz

Through the release of this document, Innovation, Science and Economic Development Canada (ISED), on behalf of the Minister of Innovation, Science and Industry (the Minister), announces the decisions resulting from the consultation on proposed amendments to Standard Radio System Plan SRSP-520, Technical Requirements for Fixed and/or Mobile Systems, Including Flexible Use Broadband Systems, in the Band 3450-3650 MHz (the SRSP).

In carefully reviewing the submissions and studies described below, ISED took into account all matters that it considered relevant for ensuring the orderly establishment or modification of radio stations in the 3450-3650 MHz band and the orderly development and efficient operation of radiocommunication in Canada, including radiocommunication used in the aeronautical service.

On August 6, 2021, ISED initiated a Consultation on Amendments to SRSP-520, Technical Requirements for Fixed and/or Mobile Systems, Including Flexible Use Broadband Systems, in the Band 3450-3650 MHz (the Consultation), which included proposed measures to protect radio altimeters operating in the band 4200-4400 MHz from harmful interference from 5G operation in the band 3450-3650 MHz (3500 MHz band). Given that radio altimeters are critical in aeronautical services, the amendments proposed to the SRSP were based on protecting the safety of Canadians while still allowing the deployment of 5G operations in the 3500 MHz band.

The main protection measures included:

• exclusion and protection zones to mitigate interference to aircraft around certain airport runways where automated landing is authorized
• a national antenna down-tilt requirement to protect aircraft used in low altitude military operations, search and rescue operations and medical evacuations all over the country

The initial deadline for submitting comments was August 23, 2021. Several comments requested further time to respond to the Consultation. Furthermore, some comments requested clarification as to which studies ISED had reviewed so that stakeholders could also review them prior to submitting comments. In response, ISED published an Addendum to the Consultation on Amendments to SRSP-520, Technical Requirements for Fixed and/or Mobile Systems, Including Flexible Use Broadband Systems, in the Band 3450-3650 MHz (the Addendum), inviting further comments and extending the deadline to October 15, 2021. The Addendum included additional information on the studies used, including some of the factors that ISED considered in the development of the SRSP and preliminary calculations as shown in annex B.

Comments to the Consultation and the Addendum to the Consultation were received from:

• Bell Canada (BCE)
• Coalition of aviation and aerospace stakeholders (The Boeing Company, AIRBUS, Bombardier Aerospace, Canadian Business Aviation Association (CBAA), Air Line Pilots Association International (ALPA), General Aviation Manufacturers Association, MHI RJ Aviation Group (MHIRJ), International Air Transport Association (IATA), National Air Carrier Association, FreeFlight Systems, Collins Aerospace, Airborne Public Safety Association and the Helicopter Association International)
• Department of National Defence Frequency Spectrum Management (DND)
• Iristel Inc. (Iristel)
• Mobile Interest Group (Bell Mobility, Ericsson, Nokia, Rogers, Samsung, SaskTel and TELUS)
• Radio Advisory Board of Canada (RABC)
• Rogers Communications Canada Inc. (Rogers)
• Saskatchewan Telecommunications (SaskTel)
• TELUS Communications Inc. (TELUS)
• Transport Canada Civil Aviation (Transport Canada)
• Xplornet Communications Inc. (Xplornet)

Comments were received from BCE, Mobile Interest Group (MIG), Rogers, SaskTel, TELUS and Xplornet on the publicly available studies and preliminary calculation performed by ISED.

BCE, MIG, Rogers and TELUS commented that the publicly available reports, including ISED's calculations, do not provide evidence that flexible use operation in the 3500 MHz band will cause harmful interference to radio altimeters, and therefore do not justify the proposed restrictions in the SRSP. Moreover, BCE and TELUS mentioned that some of the publicly available studies showing concerns with interference, such as the Radio Technical Commission for Aeronautics (RTCA) report, used flawed assumptions made by the aviation industry. BCE and TELUS highlighted the CTIA's submission to the Federal Communications Commission (FCC) proceedings on the 3800 MHz band, rebutting some of the findings in the RTCA study.

BCE, MIG, Rogers, SaskTel and TELUS commented that the assumptions made in ISED's calculation based on International Telecommunication Union (ITU) Recommendation ITU-R M.2059-0, Operational and technical characteristics and protection criteria of radio altimeters utilizing the band 4200-4400 MHz and the technical parameters of base stations as defined in RSS-192, Flexible Use Broadband Equipment Operating in the Band 3450-3650 MHz were unrealistic.

In particular, BCE, MIG, Rogers and TELUS mentioned that the spurious emission of -13 dBm/MHz (i.e. spurious emission limit set forth in RSS-192, Flexible Use Broadband Equipment Operating in the Band 3450-3650 MHz) is not representative of actual base stations. In their view, a much more appropriate spurious emission of -30 dBm/MHz is generated by base stations, which would not cause in-band interference to radio altimeters in the 4200-4400 MHz band. BCE, MIG and TELUS mentioned that ISED's assumption that the out-band antenna pattern for base stations is the same as the in-band antenna pattern should not be made. TELUS specified a 0 dBi gain for base station antennas at 4200-4400 MHz. MIG mentioned that the only variable of concern is the out-of-band rejection of radio altimeters rather than 5G spurious emissions.

BCE, SaskTel and MIG indicated that the assumption of extremely poor out-of-band filtering in the radio altimeter receiver described in the ITU-R M.2059.0 is also improbable. MIG mentioned that such a poor performance in out-of-band rejection emissions would be unacceptable due to both the safety-of-life nature of the service and the inefficiency in the use of the spectrum. As such, radio altimeters should be more robust against interference. MIG pointed to the frequency-dependent rejection described by AVSI that could be used instead of the ones in ITU-R M.2059.0. Moreover, MIG and TELUS mentioned that ISED's calculation assumed a peak radio altimeter antenna gain of 8-13 dBi based on ITU-R M.2059.0, however 0 dBi should rather be used in the calculation. 

MIG, Rogers, SaskTel and TELUS recommended that ISED gather information on radio altimeters currently in use, and determine their actual performance associated with market penetration, especially with regards to the out-of-band rejection. MIG, Rogers, SaskTel, TELUS and Xplornet recommended that ISED, in collaboration with other stakeholders, perform lab and/or field testing to determine what interference could potentially occur between flexible use deployments and radio altimeters in Canada in order to develop co-existence rules.

TELUS proposed a staged process to address the co-existence concerns. The first stage would include an interim decision that supports the precautionary principle, in this case maintaining the status quo (i.e. no mitigation measures imposed on 5G operation). The second stage would include continuing to study the issue to gain additional evidence. The last stage would determine the final technical rules in consultation with stakeholders and based on the evidence gathered in the second stage.

Discussion

ISED carefully considered the comments asserting that the publicly available reports, including ISED's calculation, do not provide evidence that flexible use operation in the 3500 MHz band could potentially cause harmful interference to radio altimeters and, as such, do not justify the proposed restrictions.

As indicated in section 2.1 of the Addendum, some studies highlighted the potential for harmful interference to radio altimeters operating in the 4200-4400 MHz band from 5G operations in adjacent and nearby bands, while other studies did not. For instance, the RTCA Assessment of C-Band Mobile Telecommunications Interference Impact on Low Range Radar Altimeter Operations report was one of the studies concluding that 5G base stations presented a risk of harmful interference to radio altimeters, by causing inaccurate or invalid altitude readings resulting in an inability to determine aircraft altitude during flight. In certain scenarios, such as an aircraft landing at an airport, an erroneous reading could have catastrophic consequences (e.g. airplane crash and loss of life). ISED recognizes that the CTIA submission to the FCC raised questions about several assumptions made in the RTCA report. However, the aviation and aerospace rebuttal to this CTIA submission provided reasonable clarifications about these assumptions related to technical aspects of aircraft operations. ISED cannot dismiss the conclusions in the RTCA report until further studies are performed.

With respect to the comments received on ISED's calculation, some views highlighted that base stations have spurious emissions well below the -13 dBm/MHz, which is currently the maximum permissible regulatory limit defined in RSS-192. Given that the regulatory limit represents the maximum spurious emissions that base stations could operate at, ISED notes that even if some base stations operate at lower emission levels, for the purposes of determination of interference, in the current context of ensuring safety to aeronautical services, the maximum permissible regulatory limit should be used to ensure that all permissible cases are taken into consideration. If all base stations were to generate spurious emissions of -30 dBm/MHz with a 0 dBi base station antenna gain, ISED agrees that in-band interference concerns in radio altimeters would be significantly minimized or potentially eliminated. ISED could consider a more stringent spurious emission limit for the 4200-4400 MHz range in a future revision of RSS-192. Until then, in-band interference from base station spurious emissions cannot be ruled out.

MIG and TELUS proposed the use of a 0 dBi value for the radio altimeter antenna gain rather than the 8 to 13 dBi gain proposed in Recommendation ITU-R M.2059.0. Based on ISED's ongoing laboratory measurements, it is of the view that the values provided in the Recommendation ITU-R M.2059.0 should be retained at this time until domestic and international studies are completed.

Based on the comment from MIG, ISED repeated the calculation described in annex B of the Addendum using the frequency-dependant rejection described by AVSI, rather than the radio frequency (RF) selectivity curve from Recommendation ITU-R M.2059.0. The separation distances required to prevent front-end overload of radio altimeters were in the range of 140 m to 3.3 km. As such, the results did not change the overall conclusion that the radio altimeter protection criteria may not be satisfied in certain base station deployment scenarios.

ISED agrees with commenters that more information is required on the performance of radio altimeters in order to ensure that the 3500 MHz band is used in a way that maximizes the economic and social benefits to Canadians while at the same time ensuring that appropriate interference protection measures are in place. ISED has been reviewing and analyzing available information and will continue to gather information and study the potential interference to radio altimeters from deployments in the 3500 MHz band, as set out in Next steps.

With regards to TELUS' proposal for a staged process to address co-existence concerns, ISED considers that the precautionary principle, cited by TELUS would not be best met through the status quo. In order to protect the lives and safety of Canadians at this stage, ISED considers a cautious approach to possible interference is warranted by imposing the proposed mitigation measures until further studies are completed.

ISED remains of the view that, in the context of Canadian technical and spectrum policies for the 3500 MHz band, publicly available studies, including the results of ISED's calculation, demonstrate a potential for harmful interference to radio altimeters from 5G operation and, therefore, a risk to the lives and safety of Canadians. Since ISED cannot rule out the use of worst performing altimeters described by the aviation industry in the RTCA report in Canadian territory at this time, the mitigation measures described in section 4 of this document are warranted on an interim basis, while international and domestic studies continue.

All respondents provided comments on the proposed mitigation measures, namely the exclusion/protection zones and the national antenna down-tilt requirement.

The Coalition of aviation and aerospace stakeholders, DND and Transport Canada supported these mitigation techniques. In particular, the Coalition stated that both interim mitigation techniques are essential and reflect proper prudence towards public safety. The Coalition specifically stated that the national antenna down-tilt requirement is a vital step in protecting radio altimeters on helicopters and general aviation aircraft, such as operations conducted by the RCMP and DND, as well as air ambulance services using heliports at hospitals and medical centers, which by nature do not fly predictable routes into and out of major airports. DND also mentioned that without appropriate mitigation measures, there are significant risks to aviation safety, not just from 5G operation in the 3500 MHz band but also from future 5G operation in the 3800 MHz band. Military aircraft are more susceptible to these risks due to the nature of their operations and subsequent heavy reliance on radio altimeters.

While RABC, Rogers, SaskTel, TELUS and Xplornet agreed that the safety of Canadians is paramount, these commenters, including BCE and Iristel, were of the view that these mitigation measures would have a significant impact on 5G deployments in Canada. Moreover, Bell, Iristel, RABC, Rogers, SaskTel TELUS and Xplornet mentioned that they were not aware of any other jurisdiction globally, that had so far imposed such widespread restrictions. For these reasons, the commenters indicated that ISED should not adopt the proposed mitigation measures in the SRSP.

For the exclusion/protection zones, BCE and TELUS commented that 5G deployments in the 3500 MHz band around the selected airports will be negatively impacted. They added that airports are key international trading gateways and the areas around them are hubs of significant economic and industrial activities.

BCE and TELUS also mentioned that the nationwide antenna down-tilt requirement will limit deployment scenarios such as office towers, residential customers in high-rise multiple-dwelling units, businesses and residences located on mountains that are served from sites at a lower elevation and remote piloted aircraft systems (e.g. drones). Instead of a national antenna down-tilt requirement, RABC and SaskTel proposed that ISED consider allowing for antenna uptilts with a suitable maximum power limit that would protect radio altimeters.

SaskTel recognized that the national antenna down-tilt requirement is meant to protect helicopters used by military and emergency first responders. SaskTel commented that it was not unreasonable to identify the models of radio altimeters in these helicopters and determine whether they could in fact operate safely in the vicinity of 3500 MHz deployments. SaskTel recommended that ISED continue further investigation into the altimeters used by military and emergency service helicopters with the goal to rescind the national antenna down-tilt requirement as soon as possible, as was done in France. On the other hand, MIG and BCE commented that since France already removed this requirement, ISED should not impose a national antenna down-tilt requirement.

Rogers proposed that ISED consider more granular interim protection criteria that accounts for differences in urban, rural, and remote areas to maximize 3500 MHz flexible use while still protecting the aviation sensors.

TELUS recommended that the mitigation measures imposed on the telecommunication stakeholders have a specific sunset date of April 2022 to allow for the aviation industry to find a timely solution addressing the performance of radio altimeters.

Iristel recommended that ISED not rush into implementing these mitigation measures. Iristel added that if these measures are imposed, ISED, in collaboration with Transport Canada, should urgently conduct field trials in order to complete them by October 2022, and to re-evaluate the amendments to the SRSP on an expediated basis.

Discussion

ISED's proposed amendments in the SRSP were based on protecting the safety of Canadians while still allowing the deployment of 5G operations in the 3500 MHz band. ISED carefully considered the comments that the proposed mitigation measures would have a significant impact on 5G deployments in Canada. 

In light of the comments, ISED reviewed its proposal to identify exclusion and protection zones to mitigate interference to domestic and foreign aircraft around 26 airports where automated landing is authorized, similar to the framework adopted in France. In the proposed exclusion zones, outdoor 3500 MHz base stations would not be permitted to operate, in order to protect aircraft in critical and final descent of their flight. These exclusion zones represent less than 1% of the population for most of the impacted Tier 4 service areas. Operators would still be able to utilize the 3500 MHz band to provide outdoor fixed and mobile services within the exclusion zones by directing signals from base stations located outside of the exclusion zones. Furthermore, indoor 3500 MHz operation would be permitted within these exclusion zones. Operators would be able to provide a range of services and deployments, such as indoor networks for clients, serving verticals in indoor industrial areas around airports, and providing coverage inside airport terminals. Most airport foot traffic occurs indoors and this is where most high-speed data use would occur. Moreover, the 3500 MHz band, given its relatively high building attenuation propagation characteristic, is highly beneficial in increasing capacity for indoor systems inside buildings. Thus, ISED is of the view that the proposed exclusion zones should not significantly impede the majority of the deployment scenarios in the 3500 MHz band.

In the protection zones, ISED proposed to permit the deployment of 5G operation in the 3500 MHz band, however operators would be required to attest that they meet the proposed power flux density (pfd) limit at 91.44 m (300 feet) from the ground, as specified in the proposed SRSP. ISED notes that 3500 MHz base stations will most likely be deployed near airports using existing infrastructure and antenna towers. When reviewing existing tower locations in ISED's Spectrum Management System (SMS) database, ISED notes that only a very small percentage (<1%) of existing outdoor towers serving other bands (Advance Wireless Services, AWS and Personal Communications Services, PCS) are currently located in the proposed protection zones, which is not anticipated to change significantly. With respect to the impact of the proposed pfd limit on the ability to deploy 5G systems at these existing sites, the vast majority of active antenna systems should be able to meet the proposed pfd limit without any power reduction given the height of antenna structures and typical base station configurations. ISED is of the view that the proposed protection zones should not significantly impact the deployment of 5G networks in the 3500 MHz band in these areas.

ISED also proposed a national antenna down-tilt requirement for 5G base stations similar to the original requirement in France, given that ISED cannot confirm all types of radio altimeters in use on helicopters in Canada at this time. As indicated above, existing base stations in Canada are predominantly designed to transmit radio waves from a higher elevation to a lower elevation (e.g. from the top of a building or tower towards the ground). The height and tilt of a base station antenna is selected to ensure coverage and capacity requirements are met in the targeted area. The majority of towers are also designed with down-tilted antennas in order to prevent the over-shooting of sectors and to limit radio frequency interference within the operator's own network.

ISED notes that operators, including BCE and TELUS, did not provide any data on the number of sites where up-tilting would be required. However, when reviewing an operator's existing network deployments in ISED's SMS database, it was observed that the vast majority of existing base station deployments are operating with down-tilted antennas in mid-band spectrum (AWS and PCS frequency bands). A similar network design would be expected in the 3500 MHz band. Moreover, ISED notes that some operators highlighted the use of antenna up-tilt for serving office towers and residential customers in high rise multiple-dwelling units. ISED is of the view that using the 3500 MHz band for these antenna up-tilt scenarios would not be a likely and/or optimal use of the band, as it could represent significant challenges in providing deep indoor 5G coverage and high capacity in the band, due to penetration loss. Taking all matters into account, ISED is of the view that the national antenna down-tilt requirement should not significantly impact 5G deployment in Canada in the 3500 MHz band.

ISED will continue to study whether allowing antenna up-tilted base stations at a specific power level could be feasible, while still protecting radio altimeters. Based on further investigation, ISED will also consider whether different mitigation measures could be imposed in urban, rural, and remote areas. At this time, ISED considers that the national antenna down-tilt requirement is necessary until more information is available on the types of radio altimeters in use on helicopters in Canada.

As for the sunset date proposed by TELUS, ISED is of the view that it would be premature to define a sunset date for these mitigation measures before domestic and international studies are completed, particularly considering the global use of radio altimeters.

ISED remains of the view that the amendments proposed to the SRSP are the most reasonable way to allow the immediate deployment of 5G operations in the 3500 MHz band while protecting the safety of Canadians. Therefore, ISED is amending the SRSP as proposed and will release issue 2 of the SRSP, to be effective as of the date of this decision.

Some submissions raised issues beyond the immediate implementation of proposed technical amendments to the current SRSP-520. These submissions were related to the possible effect of the proposed amendments to the SRSP on the value of flexible use licences in the 3500 MHz band, based on potential changes to future deployment plans. Some submissions suggested compensation or changes to the payment schedule or payment amounts based on winning bids in the recent 3500 MHz spectrum auction. ISED notes that all licensees are subject to operating within technical parameters as specified in the conditions of licence, which may be amended from time to time. ISED does not plan to modify the licensing process as set out in the Policy and Licensing Framework for Spectrum in the 3500 MHz Band as a result of this decision. However, ISED will continue to consider the views of all stakeholders as the next steps set out below are taken.

ISED has updated the current SRSP-520, Technical Requirements for Fixed and/or Mobile Systems, Including Flexible Use Broadband Systems, in the Band 3450-3650 MHz in accordance with this decision, which is published as SRSP-520, issue 2.

As indicated previously, ISED anticipates that additional evidence from domestic and international studies, such as the report from the European Union Aviation Safety Agency, will be available throughout the balance of this year and into 2022. Furthermore, work is currently underway in the United States to assess the concerns for potential interference from future 5G operations in the 3800 MHz band, and to ascertain whether mitigations measures are required. ISED will closely monitor these development considering the common 5G equipment ecosystem. Should ISED determine, based on a review of these developments and on ISED's continuing work, that further changes could be proposed to the technical rules, including SRSP-520 and RSS-192,  it will launch a future consultation with stakeholders, including the RABC.

ISED will continue its internal studies, lab testing of radio altimeters, and discussions with other regulators. ISED will also participate in the RABC working group that will be established on this issue.

All spectrum-related documents referred to in this paper are available on ISED's Spectrum Management and Telecommunications website.