ANNEX D Approved June 4, 2020 Terrestrial-Satellite Coexistence During and After the C-Band Transition Technical Work Group #1

Scope of Work

1. Preventing Interference

1.1. Emphasize the need for the FCC to complete its review of the pending C-Band incumbent earth station registration and modification applications in IBFS.

1.2. Agree on relevant data necessary for protection of Earth stations. (All 3.7 GHz Service licensees need to work from a common list of Earth stations.)

1.3. Understand best practices that 3.7 GHz Service licensees use to predict whether the FCC- specified power flux density (PFD) limits will be exceeded at earth station locations.

1.4. Agree on a common method for converting between PFD and power spectral density (PSD) at the Earth station.

1.5. Understand the nature of the Earth station receive filters to ensure that they will be adequate to reject 3.7 GHz Service signals below 3.98 GHz over a range of environmental conditions in order to ensure that the FCC-specified blocking PFD limit is met.

2. Interference Detection

2.1. Develop a procedure for earth stations to positively identify or exclude sources of interference. This procedure should rapidly eliminate non-3.7 GHz Service causes and initiate the inter-service interference resolution process. Consider whether a detection and alerting mechanism could be automated, particularly for major Earth station facilities.

2.2. Develop estimates of distances between 3.7 GHz facilities and earth stations beyond which interference is unlikely.

2.3. Develop a process for positively identifying or excluding sources of 3.7 GHz interference. (This could be based on identification of the base stations belonging to the 3.7 GHz operator and may involve in-band (3.7 GHz) measurements to identify the strongest source(s). This may also involve consideration of transmitter manufacturer data on OOBE characteristics and may require a process to share manufacturer’s confidential proprietary data on a need to know basis such as using neutral third party for information exchange.)

2.4. Develop a mechanism and process for Earth station and satellite operators experiencing interference to contact 3.7 GHz Service licensees with interference concerns. The mechanism should provide documentation of complaints and actions taken to diagnose and resolve them.

2.5. Develop a method for measuring PFD levels at earth stations.

1 Approved June 4, 2020 3. Interference Mitigation

3.1. Create a toolbox for 3.7 GHz Service licensees to mitigate the impact of 5G base stations on earth stations, including potential interference mitigation strategies that can be implemented by 3.7 GHz Service licensees at the earth stations to assist in interference mitigation.

3.2. Consider whether there are Phase I-specific issues that should be addressed and whether there are minimum processes that can be defined solely for Phase I.

3.3. Develop a process to address situations where the PFD limits are determined to be compliant by measurement or calculation but earth station characteristics, such as look angle, are such that interference nonetheless arises or is likely to arise. See Item 1.4.

4. Interference Enforcement

4.1. Define a process for earth station operators seeking resolution of situations where measurements indicate the PFD at their earth station exceeds the protection limits.

4.2. Consider whether a process should be defined locally or centralized and how to ensure that the appropriate contacts are available to earth station licensees (and updated). Develop a list of points of contact of 3.7 GHz Service licensees for interference reporting and technical questions.

4.3. Consider whether the enforcement process can be expedited through the use of approved third-party firms that can determine compliance with PFD limits or identify interference source by cell/sector.

5. Clarification Needed

5.1. Does there need to be an agreement to allow the 3.7 GHz and Earth Station operators reciprocal site access to conduct their own measurements?

5.2. Is the FCC willing to compile and publish in a convenient format a database of Earth stations eligible for protection? If so, will it be available before the auction? If not, how do we handle pending applications?

5.3. Is the -124 dBW/m2/MHz PFD limit per 3.7 GHz site, per operator, or aggregate?

2 ANNEX E Use of Power Flux Density and Power Spectral Density in Interference Prediction Models by Terrestrial Licensees

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-003 Authors: Neeti Tandon July 16, 2020 Navid Motamed

Summary: This submission discusses the use of Power Flux Density (“PFD”) and Power Spectral Density (“PSD”) in the prediction of potential interference to C-band earth stations resulting from 3.7 GHz Service operations. This submission is intended to clarify the real-world use of PFD and PSD to inform further discussions regarding terrestrial-satellite coexistence. This discussion relates entirely to interference modeling and prediction and does not discuss the use or utility of PFD or PSD with respect to earth station operators’ interference detection.

PFD Compliance Testing. The C-Band Order states that the FCC will use PFD measurements to determine compliance with the requirement to protect C-band earth stations from out-of-band emissions from terrestrial broadband networks deployed by 3.7 GHz Service licensees. The FCC adopted a PFD limit because compliance with a PFD limit can be measured independently using readily available test equipment (e.g., spectrum analyzer or scanner) without the requiring specific knowledge of either the design and engineering specifications of the terrestrial broadband network or the Fixed Satellite Service (“FSS”) equipment and antenna characteristics.

TWG-1 is developing a set of processes and procedures—including, among other things, parameters for test equipment setup, recommendations on the type of measurement antenna, definitions for locations of measurements and corresponding antenna orientation—to ensure uniform and repeatable testing results.

The linear relationship for PFD in Watts/m2 is

PFD = = (1) which is represented in logarithmic form using corresponding lower-case subscripts (as opposed to upper-case subscripts for the linear equivalents) as

= + 20 log ( ) + /MHz) (2) − − 38.55 dB(W/m where:

Pr is measured channel power (PSD) in dBW/MHz f is the measurement frequency in MHz

1 TWG1-003 Ref. TWG1-003

Gr is antenna gain of the measurement antenna in dBi

Lc is cable (and other) losses in dB

A constant of 68.55 can be used if Pr is in dBm rather than dBW, yielding:

= ( ) + 20 log ( ) + 68.55 dB(W/m /MHz) (3) − − Similar protocols will be needed for purposes of C-band coordination activities and in the validation of interference claims by earth station operators.

FCC PFD Requirements. The C-Band Order authorizing the 3.7 GHz Service requires that, “[t]o protect incumbent earth stations from out-of-band emissions from fixed stations, base stations and mobiles, the power flux density (PFD) of any emissions within the 4000-4200 MHz band must not exceed -124 dBW/m2/MHz as measured at the earth station antenna,” 47 C.F.R. §27.1423(a). The C-Band Order explains that “3.7 GHz Service licensees will be obligated to ensure that the PFD limit at FSS earth stations is not exceeded by base and mobile station emissions, which may require them to limit mobile operations when in the vicinity of an earth station receiver,” ¶ 361. The FCC adopted a PFD limit, rather than a PSD limit, because “[u]sing PFD avoids the complexity of registering complex antenna gain patterns for more than twenty thousand earth stations, and it avoids multiple angular calculations that would be necessary to predict PSD within each satellite receiver,” ¶363.

The PFD limit adopted in the C-Band Order is -124 dBW/m2/MHz per licensee at the earth station antenna, which translates to a power spectral density of -128 dBm/MHz in aggregate for each licensee. This PFD “is based on a reference FSS antenna gain of 0 dBi, interference-to- noise (I/N) protection threshold of -6 dB, a 142.8K FSS earth station receiver noise temperature, and results in a calculated PFD of -120 dBW/m2/MHz,” ¶ 363.

Thermal noise is calculated from

= (4) where k is Boltzman’s constant (1.3810-23 J/K), T is system noise temperature in Kelvin, and B is bandwidth in Hertz.

In decibel terms for the FCC’s assumed system noise temperature,1 the earth station receiver input noise power density, Nt, is -147.05 dBW/MHz (-117.05 dBm/MHz). Limiting the interference power density to 6 dB below Nt (i.e., I/N = -6 dB) gives -153.05 dBW/MHz (-123.05 dBm/MHz) as the interference PSD objective.

1 T = 142.8K 2 Ref. TWG1-003

The PFD that corresponds to this interference limit is determined by subtracting the effective area of the receiving antenna, which the FCC assumes to be an isotropic antenna (Gr = 0 dBi):

= or Ae = 10log10( ) + 10log10(Gr) 2 2 which is -33.5 dB(m ) at 4000 MHz. Thus, the interference4 PFD limit is -119.55 dBW/m /MHz at 4000 MHz, which the FCC rounds to -120 dBW/m2/MHz. An adjustment of 4 dB is made to allow for multiple interference sources to arrive at an aggregate interference PFD limit of -124 dBW/m2/MHz per licensee.2

All things being equal an I/N of -6 dB means there will be 1.0 dB of link margin degradation. The FCC also stated that “the PFD limit we are adopting accounts for the potential of aggregate interference and will protect FSS earth stations from harmful interference,” ¶ 364. Accordingly, each 3.7 GHz Service licensee should determine if its operations, in aggregate, would result in a PFD in excess of -124 dBW/m2/MHz at the location of the receive antenna of any registered C- band earth station.

PFD to PSD Conversion for Interference Prediction.

Figure 1. Calculation of aggregate In-Band and Out-of-Band 3.7 GHz PSD levels at the input to an Earth station LNB.

The following formula calculates the aggregate PSD level (in dBm/MHz) at the LNB input of the antenna corresponding to the PFD limit per 47 C.F.R. §27.1423(a).

] (5) where: = ∑[ + − + + GES is the gain of the earth station antenna above an isotropic in the direction of the 3.7 GHz facility (i.e., assumed to be 0 dBi in the FCC Order) 2 PFD i is the maximum PFD per licensee (i.e., -124 dBW/m /MHz for out-of-band emissions)

2 Recognizing that interference “will be dominated by a single interferer,” the FCC adjusted its calculated PFD by -4 dB, which “assum[es] the dominant interferer is 40% of the aggregate power,” and “results in [a PFD of] -120 dBW/m2/MHz - 4 dB = -124 dBW/m2/MHz,” ¶ 363. 3 Ref. TWG1-003

LF is the loss from the antenna feed to the LNA input, including filter, in dB (i.e., 0.5 dB) 2 Ae is the effective area of isotropic antenna in dB m (i.e., for a 0 dBi antenna at 4 GHz, 10 log ( /4 ) » 33.5 dB(m ) ∙ is the conversion from dBW/MHz to dBm/MHz (i.e., 30 dB) C λ −

Thus, for the assumed conditions, the maximum out-of-band emissions PSD per 3.7 GHz Service licensee is (–124 – 0 – 0.5 – 33.5 + 30) = –128 dBm/MHz referenced at the LNB input.

Calculation of PFD by 3.7 GHz Service Licensees. From the 3.7 GHz Service licensee perspective for network design, the following best practices should be used for predicting PFD at an Earth station site. For the purpose predicting out-of-band emissions from 3.7 GHz Service networks, the interference power into a potential victim FSS receiver location is dependent upon the out-of-band emissions of the 3.7 GHz Service equipment, the path loss between the network and the FSS receiver location, and the gain of the 3.7 GHz Service antenna in the direction of the FSS location:

= ( , , + , ) (6) where: ∑ − is the aggregated received interference power spectral density I [RW] in dBm/MHz 3

PTX is the radiated OOBE PSD from each of a 3.7 GHz Service licensees’ transmitters

is the propagation loss, including clutter losses as appropriate, LP between each of a 3.7 GHz Service licensees’ transmitters and the FSS receiver in dB

is the 3.7 GHz Service transmitter antenna gain in the direction GTX of the FSS site in dBi (Note: OOB antenna gain/pattern may be different from In-Band gain/pattern)

3 Submissions in the C-band docket show that the OOBE level corresponding to -40 dBm/MHz can be achieved by 3.7 GHz service equipment with a 20 MHz offset from the band edge into the FSS band. See, e.g., https://ecfsapi.fcc.gov/file/1081482808988/C-Band%20Reply%20Comments-Final.pdf; https://ecfsapi.fcc.gov/file/10807668903645/Nokia%20Comments%20on%203.7.pdf; https://ecfsapi.fcc.gov/file/12110329723187/Ericsson%203.7%20to%204.2%20GHz%20Reply%20Comments% 20(12-11-2018).pdf. 4 Ref. TWG1-003

The predicted aggregate out-of-band power spectral density from all 3.7 GHz Service transmissions of an operator received in the FSS band (4.0 to 4.2 GHz) must remain below -128 dBm/MHz.

Equations (3) and (6) can also be applied to predict the aggregate in-band power spectral density from all 3.7 GHz Service transmissions of an operator in the 3.7 GHz band (3.7 to 3.98 GHz). The aggregate PFD limit (“blocking limit”) is -16 dBW/m2/MHz measured at the earth station antenna location. ¶366.

5 ANNEX F Estimated Separation Distances Between 3.7 GHz Facilities and Earth Stations to Minimize Potential Interference

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-004 Author: Robert Weller July 16, 2020

Purpose: The intention of this contribution is to provide reasonable worst-case [and typical] estimates of distance separation beyond which interference to Earth stations from 3.7 GHz base station facilities is unlikely.

1. Out-of-Band Emissions from 3.7 GHz Base Stations

Assumed 3.7 GHz Transmitter OOBE. FCC Rule 27.53(l)(1) states, “For base station operations in the 3700-3980 MHz band, the conducted power of any emission outside the licensee’s authorized bandwidth shall not exceed -13 dBm/MHz.” For this analysis, it is assumed that the 3.7 GHz base station transmitter meets this requirement and any out-of-band emissions (OOBE) above 4.0 GHz will equal -13 dBm/MHz on a conducted basis. This level is taken as a likely worst-case value.

Alternative levels of OOBE may be considered with appropriate support. Based upon filings with the FCC by Ericsson,1 Nokia,2 and Samsung,3 a conducted OOBE level of -40 dBm/MHz should be achievable at the lower portion of the satellite band, 4000–4020 MHz (i.e., 20–40 MHz above the upper 3.7 GHz band edge at 3980 MHz). With more than 20 MHz frequency separation (i.e., above 4020 MHz), lower OOBE levels might be expected based upon the same filings. (Note: It is unclear whether those levels have been demonstrated in practice or whether manufacturers and 3.7 GHz operators will commit to those levels.)

Assumed Radiated OOBE. Commercially available base station antennas in the 3.7 GHz frequency range may have gains of 18.5 dBi or more.4 While antenna gain outside of the intended in-band operating frequency range (3.7 to 3.98 GHz) is uncertain, it seems reasonable to assume that the gain above 4.0 GHz will be no greater than the in-band gain. For this analysis, a gain of 18.5 dBi is assumed. Taken together with the conducted OOBE, an equivalent isotropically-radiated power (EIRP) of +5.5 dBm/MHz is assumed as the likely worst-case.

1 See comments of Ericsson, December 11, 2018, https://ecfsapi.fcc.gov/file/12110329723187/Ericsson%203.7%20to%204.2%20GHz%20Reply%20Comments%20(12 -11-2018).pdf 2 See comments of Nokia, August 7, 2019, https://ecfsapi.fcc.gov/file/10807668903645/Nokia%20Comments%20on%203.7.pdf 3 See comments of Samsung, August 14, 2019, https://ecfsapi.fcc.gov/file/1081482808988/C-Band%20Reply%20Comments-Final.pdf 4 See, e.g., PCTel FP base station antenna at https://www.pctel.com/wp-content/uploads/2018/11/VenU-FP-Series.pdf Alternative antenna gain and EIRP figures may be considered with appropriate support. Lesser antenna gains, as low as -45 dBi, have been suggested for situations where the 3.7 GHz sector radiates in the direction opposite the Earth station.

Likely Worst-Case Separation Distance Based on Radiated OOBE. It is desired to determine the likely worst-case distance separation required between a compliant 3.7 GHz installation having an OOBE EIRP of +5.5 dBm/MHz and an Earth station such that a power flux density (PFD) of -124 dBW/m2/MHz is obtained at the Earth station site under free space conditions. Because power spectral density (PSD) is the quantity typically measured, this analysis first derives a relationship between PFD and PSD.

For the same bandwidth (1 MHz in this case), the PSD available at the receive antenna terminals is equal to the PFD times the effective area, Ae, of the receiving antenna:

PSD = PFD × Ae (1)

The maximum effective area of any antenna is given by:

= (2) where G is the antenna gain and  is the free-space wavelength.

Combining (1) and (2), we obtain: = (3) or, in decibel terms: PSD = PFD + 10× log ( ) + 20× log ( ) – 10× log (4 ) (4)

For an isotropic receiving antenna (Gr = 0 dBi) operating at 4000 MHz ( = 0.075 m), equation (4) reduces to PSD = PFD + 0 – 22.50 – 10.99 = PFD – 33.49 (5)

Thus, a PFD of -124 dB(W/m2/MHz) is equivalent to a PSD at the Earth station’s antenna terminals of -157.49 dBW/MHz or -127.49 dBm/MHz. The FCC rounds this value to -128 dBm/MHz in its Order. Allowing for a Earth station filter loss of 0.5 dB, the -128 dBm/MHz PSD seems reasonable at the low-noise block downconverter (LNB) or low-noise amplifier (LNA) of the Earth station.

In the far-field of an antenna under free-space conditions, PFD varies with distance according to the inverse square law, and the resulting PSD can be determined using the Friis transmission equation:

= = (6) or in decibel terms: PSD = 10× log ( ) + 10× log ( ) + 10× log ( ) – 20× log ( ) – 20× log ( ) – 27.56 (7)

2 Rearranging terms in (7), we obtain

20× log ( ) = 10× log ( ) + 10× log ( ) + 10× log ( ) – 20× log ( ) – 27.56 – PSD (8a)

Solving for d, we obtain:

× ( ) × ( ) × ( ) – × ( ) – . – d = 10 (8b) For the likely worst-case values assumed, we obtain:

. – × ( ) – . . . – . – . . d = 10 = 10 = 26,629 m (9) Thus, beyond 26.6 kilometers (16.5 miles), it is unlikely that the OOBE PFD from a single 3.7 GHz facility would exceed -124 dBW/m2/MHz, or that the PSD at the Earth station LNB would exceed -128 dBm/MHz, assuming an Earth station receive antenna gain of 0 dBi and a filter loss of 0.5 dB.

Equation 8b may be used to determine separation distances for other values of receive antenna gain and PSD. For a conducted OOBE level of -40 dBm/MHz and base station antenna gain of 18.5 dBi, d = 1,189 meters.

Note that free-space calculations do not include the practical effects of terrain, clutter, etc. For example, the range of distances predicted using an implementation of the ITS Irregular Terrain Model is 8.6 to 20.2 kilometers with corresponding situational variabilities (confidence) of 90% and 10%.5 [Navid]

2. In-Band (Blocking) Emissions from 3.7 GHz Base Stations

Required Blocking Level. FCC Rule 27.1423(b) states, “To protect incumbent earth stations from blocking, the power flux density (PFD) of any emissions within the 3700–3980 MHz band must not exceed -16 dBW/m2/MHz as measured at the earth station antenna.”

Assumed 3.7 GHz Transmitter In-Band Power Levels. FCC Rule 27.50(j)(1) states, “The power of each fixed or base station transmitting in the 3700–3980 MHz band and located in any county with population density of 100 or fewer persons per square mile, based upon the most recently available population statistics from the Bureau of the Census, is limited to an equivalent isotropically radiated power (EIRP) of 3280 Watts/MHz. This limit applies to the aggregate power of all antenna elements in any given sector of a base station.”

Similarly, FCC Rule 27.50(j)(2) states, “The power of each fixed or base station transmitting in the 3700-3980 MHz band and situated in any geographic location other than that described in paragraph

5 ITM v.1.5.5, Area mode, Careful siting, TX and RX heights 15 m, Terrain roughness h = 12 m, Continental Temperate climate, Horizontal polarization, atmospheric refractivity 301 N-units. 3 (j)(1) of this section is limited to an EIRP of 1640 Watts/MHz. This limit applies to the aggregate power of all antenna elements in any given sector of a base station.”

For this analysis, it is assumed as a worst-case that the 3.7 GHz base station will radiate at EIRP PSD of either 3280 W/MHz or 1640 W/MHz, depending upon whether the 3.7 GHz base station is located in a “rural” county or not. Alternative EIRP figures may be considered with appropriate support.

Worst-Case Calculation of Separation Distance Based on Radiated In-Band Emissions (Blocking). It is desired to determine the distance separation required between a compliant 3.7 GHz installation having an EIRP of 3280 or 1640 W/MHz and an Earth station site, such that a power flux density (PFD) of -16 dBW/m2/MHz is obtained at the site under free-space conditions.

In the far-field of an antenna under free-space conditions, PFD varies with distance from the source according to the inverse square law:

= (10) Or in decibel terms,

PFDr = 10× log ( ) – 10× log (4 ) – 20× log ( ) (11)

For the assumed conditions, we obtain:

-16 dBW/m2 = 10× log (3280 ) – 10.99 – 20× log ( ) (12)

Rearranging (11), we obtain:

20× log ( ) = 35.16 dBW – 10.99 + 16 dBW/m2 = 40.17 dB(m2) (13)

Solving (12) for d,

. = 10 = 102 meters for 3280 watts EIRP (14) Similarly, d = 73.2 meters for 1,640 watts EIRP.

[Consider adding a generalized expression that includes variables for Earth station filter rejection, filter insertion loss, receive antenna gain, I/N, receiver Noise Factor, etc.]

4 ANNEX G Earth Station Interference and Tracking Process

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-005 Authors: Andy Scott August 27, 2020 Mike Beach Objective

 Create interference and tracking processes that address the following sections from the TWG-1 scope of work:

 2.4 - Develop a mechanism and process for Earth station and satellite operators experiencing interference to contact 3.7 GHz Service licensees with interference concerns. The mechanism should provide documentation of complaints and actions taken to diagnose and resolve them.

 4.1 - Define a process for earth station operators seeking resolution of situations where measurements indicate the PFD at their earth station exceeds the protection limits.

 4.2 - Consider whether a process should be defined locally or centralized and how to ensure that the appropriate contacts are available to earth station licensees (and updated). Develop a list of points of contact of 3.7 GHz Service licensees for interference reporting and technical questions.

Assumptions

 Apply a business to business approach; parties will initially attempt to resolve interference in a timely manner without FCC intervention.

 Earth station operators desire a rapid resolution to any interference from 3.7 GHz licensees upon detection. A single point of contact for every 3.7 GHz licensee will enhance communication.

 Earth station operators will likely not have test equipment necessary to make power flux density (PFD) measurements at earth station location(s) initially. They may have this capability in the future. Contracting out the measurements to a third-party is an option but would likely be ineffective in identifying interferer(s) quickly, which may be necessary in severe interference cases.

 Initially, interference concerns will be treated the same in terms of response, regardless of severity. However, the process should evolve to a sliding schedule for urgent versus nuanced interference problems.

1 TWG1-005  The Earth station operator has installed a bandpass filter meeting the specifications of TWG1- 009 and paragraphs 367–370 of the C-Band Report and Order.1

 The FCC’s IBFS will be used by the 3.7 GHz licensee as the primary means to obtain incumbent earth station information (including location and height), except contact data, which will be superseded by the POC.

 Incumbent earth stations are defined as those earth stations described in paragraph 116 of the C-Band Report and Order,2 and set forth on the list published by the FCC’s International Bureau on August 3, 2020, as well as any subsequent modifications to that list that may be authorized or directed by the FCC.3 It is noted that the list includes both authorized and pending earth station data and that specific location information on 41 earth stations, including transportable earth stations (TES), is not reflected in IBFS or on the published list. [A request is pending with FCC staff for its opinion on whether certain other earth stations (not on the August 3 list) are required to be protected with respect to PFD limits.]

 Differences between IBFS data and actual deployments should be reconciled by the Earth Station operator.

 Earth station operators should feel free to contact the FCC’s Enforcement Bureau if interference from 3.7 GHz Service licensee facilities is not resolved in a timely manner.

1 – Process during initial 3.7 GHz network site builds

The initial process is intended to specify procedures that would be followed as 3.7 GHz Service licensees are engaged in the initial deployment of terrestrial networks in a region, as opposed to the more steady-state, and routine expansion and reconfiguration of established 3.7 GHz networks. The intent of the initial process is to recognize that initial network deployments may illuminate immediate issues that may be more likely to be the result of 3.7 GHz Service activity.

 [By YYYY/MM/DD] [As soon as possible] 3.7 GHz licensees and Earth station operators will exchange point of contact (POC) information for all earth stations located inside or within [n] kilometers of the boundary of each PEA (“local market area”) where the 3.7 licensee is operating.

 If the earth station(s) experience interference, the earth station operator will take steps to determine whether the interference is coming from a 3.7 GHz Service licensee or another source as discussed in the Ongoing Process section.

 If the earth station(s) experience interference that appears to be from a 3.7 GHz facility the earth station POC will contact the 3.7 GHz licensee nationwide PoC with the following minimum information and any available supporting material on the nature of the interference observed.

1 Report and Order and Order of Proposed Modification, GN Docket 18-122, adopted February 28, 2020, released March 3, 2020, FCC 20-22. 2 Ibid. 3 FCC Public Notice DA 20-823, IB Docket 20-205 and associated spreadsheet. See: https://docs.fcc.gov/public/attachments/DA-20-823A1.pdf downloaded August 26, 2020 2 TWG1-005 1. Service Impact

. Outage: satellite(s) and transponder(s) affected

. Degradation: satellite(s) and transponder(s) affected

2. Earth Station Antenna(s) Impacted

. IBFS registration/callsign

. Latitude and Longitude of Earth Station

. Earth station azimuth/elevation angles to affected satellites

. Height above ground

3. Time when interference was observed and duration, if applicable (date/time in UTC)

4. Any supporting information, as available, that would help resolve interference

. Pre and post interference spectrum plots at earth station location (3.7–4.2 GHz)

5. SNR or Eb/No change at the receiver with respect to reference baseline (with respect to normal operating conditions), if available.

 The 3.7 GHz licensees identified as the likely sources of the interference according to the measurement procedure [outlined in the TWG1 best practices document] shall demonstrate compliance with the -124 dBW/m2/MHz PFD per licensee aggregate limit.

 3.7 GHz licensees will respond to the earth station POC within [n] hours and will work in good faith with the earth station operator to resolve the interference issue within [n] [hours][days]. This includes situations in which measured or predicted PFD levels at the earth station location specified in §27.1423(a) and §27.1423(b) are compliant, yet the earth station continues to experience interference from a 3.7 GHz Service licensee(s).

o In cases where the Earth station experiences a complete outage that is coincident in time with the commissioning of a new 3.7 GHz facility, the identified 3.7 GHz operator shall make prompt adjustments to determine the root cause and eliminate the interference in the fastest possible manner.

o In cases where the Earth stations experiences degradation (e.g., increased error rate) that is coincident in time with the commissioning of a new 3.7 GHz facility but is nonetheless usable, the 3.7 GHz operator shall make appropriate adjustments to determine the sensitivity and interference impact.

 Parties will be notified within [n] days if there any changes to POC information.

3 TWG1-005 2 – Ongoing process following initial network site builds.

After 3.7 GHz Service networks are initially deployed, the ongoing process will be used to resolve potential interference issues between terrestrial operators and earth stations.

If the earth station(s) experience interference, the earth station operator will take steps to determine whether the interference is coming from a 3.7 GHz Service licensee or another source. Interference sources can be thought of in three segments, noise or other unwanted emissions generated by the earth station equipment, unwanted emissions generated or retransmitted through the satellite being accessed or another satellite, and emissions radiated from other terrestrially based sources. Although this document addresses potential interference from new 3.7 GHz Service licensees within the 3.7–3.98 GHz band, this section could be used to consider any source of interfering RF energy affecting system performance. The assumption in this recommended troubleshooting process (including the use of available monitoring equipment) is to follow the process of elimination, with the easiest to identify potential interference source first, then work to increasingly difficult to clear sources.

Note that this section addresses only interference within the updated satellite C-band (4.0–4.2 GHz) from 3.7 GHz sources. If interference from an adjacent frequency source above or below this definition is identified, some version of filtering should be considered.

 Look for signs of terrestrial interference by monitoring 3.7–4.2 GHz

o By monitoring the 3.7–4.2 GHz spectrum at the site/facility where interference is observed, earth station operators can compare pre- and post-incident spectrum captures to determine if significant changes occurred coincident with interference observations.

A) A spare earth station antenna at site with no 5G rejection filter (legacy 3.7–4.2 filter/LNB), if available, as shown in Figure 1.

Figure 1. C-Band earth station without 5G rejection filter to facilitate interference detection and resolution. This configuration allows for monitoring across 500 MHz (3.7–4.2 GHz) at the earth station for interference resolution.

4 TWG1-005 B) Install a modified earth station filter with coupled port to monitor 3.7–4.2 GHz (one per site), if available, as shown in Figure 2.

Figure 2. Modified C-Band earth station 5G rejection filter to facilitate interference detection and resolution. This configuration allows for full-band (3.7–4.2 GHz) monitoring through a -30 dB coupling port at the earth station for interference resolution, as well as out-of-band (4.0–4.2 GHz) monitoring through the 5G rejection filter.

If monitoring indicates changes to terrestrial emissions in the 3.7–3.98 GHz band that coincide with the interference event then the earth station operator should notify all 3.7 GHz Service POCs and provide pre- and post-event monitoring data. If monitoring does not indicate any changes to the terrestrial emissions, earth station operators should proceed to next troubleshooting step.

 Check earth station equipment

o When the signal degradation started were there any maintenance or operational changes in process? If so, reverse the change and confirm fault clearance.

o When the signal degradation started were there alarms that would indicate equipment failure as opposed to only signal failure? If so, take action with the alarming equipment.

o Looking at the in-house signal flow with a tool such as a spectrum analyzer or network analyzer can help to understand where the distortion is and is not.

 Check the satellite link

o If it seems the damage isn’t self-generated, or if an earth station does not have the proper testing tools to know, begin coordinated efforts with the satellite operator.

o Looking at the signal with a tool such as a spectrum analyzer may confirm any signal distortion on the inbound and/or outbound signal.

o Satellite issues can include equipment failure in the spacecraft, adjacent satellite interference (ASI), or in linearly-polarized systems energy can be coming from the opposite polarization (cross-pol).

. Satellite equipment failure – in this case the satellite operator will be well aware of the issue and will be busily responding to the problem when you call them.

5 TWG1-005 . ASI – The two possibilities in this case are either your receiving antenna is off peak and needs adjustment, or someone else is uplinking using a mispointed antenna. If an uplink is off peak the satellite operator will be able to tell, and will begin to track down the offending earth station to get them to correct the issue.

. Cross-Pol – The two possibilities in this case are either the polarization of your antenna is off peak and needs adjustment, or someone else is uplinking on a misadjusted polarity. If an uplink is not optimally polarized the satellite operator will be able to tell and will begin to track down the offending earth station to get them to correct the issue.

. A note of caution: it is entirely possible that if your antenna is an uplink, the satellite operator may find your system to be the offender in which case you may be interfering with someone else as well as degrading your own signal.

o Check for other potential source of interference

. Interference from another earthbound emitter is referred to as Terrestrial Inference (TI). If you are able to clear both your facility and the satellite link, then it is reasonable to assume some emitter in relatively close proximity to your satellite antenna is causing the interference. A look at an FCC license database to discover licensed emitters physically near your location operating within, or close to, C- band could offer a list of potential interference sources. It is possible the emitter is not individually licensed, which is the case with the 3.7 GHz Service systems, in which case a database will not help.

. Use of a spectrum analyzer and directional antenna ‘sniffer’ could help determine the direction between the satellite antenna and the interfering emitter. Sometimes that’s enough to visually see the likely emitter. Other times taking bearings from more than one location and plotting the lines on a map is needed to find it. One complicating factor is the three-dimensional propagation property of the RF energy: if either the earth station and/or the interfering emitter are in an urban area with many flat reflective buildings it may be challenging to locate the source. If this testing capability is not on hand, a 3rd party technical resource may be available to help track down the offender.

If after taking these steps the earth station operator believes that the interference is coming from a 3.7 GHz Service licensee, the earth station operator, to the extent technically feasible and consistent with good engineering practice, will make measurements to determine compliance with the PFD limits specified in FCC Rules §27.1423(a) and §27.1423(b). [Reference TWG-1 PFD measurement contributions and other methods]

The earth station POC will contact the 3.7 GHz Service licensee POCs. The earth station(s) POC should be prepared to provide the following information:

Entity Information Earth station operator (Comcast, Fox, etc.) Earth station type (Cable, TV Broadcast, etc.) 6 TWG1-005 Call Sign Street address, city, state, zip Contact information (name, phone number, e-mail, as appropriate)

Interference location Location(s) where interference is being received, including latitude and longitude.

Interference description Service(s) affected (e.g., video, audio, one transponder, all transponders, frequency range, etc.)

Severity Service down, service intermittent, more/less than 50% degradation, etc.)

Additional Information Steps taken to diagnose the problem, results of test and measurements conducted, other remedial action taken, etc. Monitoring data of emissions in 3.7–4.2 GHz (if available) PFD measurements (if available)

Resolving Interference

 3.7 GHz Service licensees will respond to any inference complaint within [n] hours. [Resolution time may depend on severity of interference and information provided.]

 3.7 GHz Service licensees will work in good faith with the earth station operator to resolve any interference complaint within [n] [hours][days]. This includes situations in which the PFD levels at the earth station location meet or exceed (comply with) the limits specified in §27.1423(a) and §27.1423(b), yet the earth station continues to experience interference from a 3.7 GHz licensee(s).

7 ANNEX H Development of a Methodology for Measuring PFD Levels at Earth Stations

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-006 Author: Kevin Murray August 15, 2020

Summary: This submission defines a methodology and test plan to measure the out-of-band emission (“OOBE”) Power Flux Density (“PFD”) of new 3.7 GHz Service licensees operating in the 3.7–3.98 GHz frequency band impacting Fixed Satellite Service (“FSS”) incumbents in the 4.0–4.2 GHz band. The methodology will result in a determination of compliance with the current protocol that states a maximum per licensee aggregate PFD of -124 dBW/m2/MHz. The methodology is defined assuming no knowledge of the specific site locations of any 3.7 GHz Service licensee.

General Approach

1. Perform FSS in-band PSD (so-called Received Signal Strength Indication or “RSSI” in this document) measurement to assess impact of 3.7 GHz Service transmissions.

2. If the results of (1) show PFD levels above -124 dBW/m2/MHz, then identify 3.7 GHz Service licensees with sites deployed within 26.6 km.1

3. Perform in-band 3.7 GHz service measurements for each licensee utilizing a 5G-NR capable scanner to measure cell/beam-specific 5G-NR Synchronization Sub Block (SSB) Reference Signal Received Power (“RSRP”). This step enables the generation of a priority list of the strongest cell/beam contributors to enable licensee mitigation (possibly executed prior to (4)). It is expected that there will be some correlation between the cells with the strongest measured SSB RSRP and those with the largest contribution to the OOBE interference in the FSS band.

4. Assess PFD compliance utilizing the following:

a. Perform in-band 3.7 GHz Service RSSI measurements for each licensee identified in (2). Estimate the aggregate, per licensee PFD through application of a transmitter signal emission mask. Based upon filings with the FCC by three equipment manufacturers,2 it is believed that conducted OOB levels of -40 dBm/MHz or below will be achieved 20 MHz

1 Distance agreed October 15, 2020 2 See: Comments of Ericsson, December 11, 2018, https://ecfsapi.fcc.gov/file/12110329723187/Ericsson%203.7%20to%204.2%20GHz%20Reply%20Comments%20( 12-11-2018).pdf Comments of Nokia, August 7, 2019, https://ecfsapi.fcc.gov/file/10807668903645/Nokia%20Comments%20on%203.7.pdf Comments of Samsung, August 14, 2019, https://ecfsapi.fcc.gov/file/1081482808988/C-Band%20Reply%20Comments-Final.pdf

1 TWG1-006 August 15, 2020

above the 3.7 GHz channel edge (i.e., at 4.0 GHz for the highest 3.7 GHz channel) and beyond. This conducted PSD value can be used to determine a reference (assumed) mask if the actual transmitter OOBE performance is not available. The actual OOBE performance information may be provided by the licensee and may vary depending upon the deployed infrastructure. For a licensee’s outdoor network deployments, however, it is likely that a common radio infrastructure and associated emission mask will be deployed within each geographic area. [OOBE performance information may also be available from transmitter manufacturer filings with the FCC.] Per licensee compliance is determined by assessing adherence to a maximum PFD of -124 dBW/m2/MHz.

b. If a 5G-NR scanner is available, information transmitted by the Sync Sub Block (SSB) and System Information Blocks (SIBs) can be used to determine an SSB reference signal conducted power level in the 3.7 GHz channel. For example, in 5G-NR standalone mode, if SIB1 shows +20 dBm for a 30 kHz subcarrier spacing system, this would correspond to a 3.7 GHz PSD of 35.2 dBm/MHz (20 dBm + ). Assuming -40 dBm/MHz as the OOB PSD gives a rejection of 75.2 dBr (35.2 – (-40) dBm/MHz), relative to the SSB power). 10

c. The ratio of a PSD or PFD measurement taken in a 3.7 GHz channel can thus be used to infer the OOBE PSD or PFD in the 4.0–4.2 GHz satellite band. [Note that not all 3.7 GHz systems may use 30 kHz subcarrier spacing and there may be differences in the radiated power level of the SSB and traffic channels.]

Step 1: In-Band FSS PFD Based on Observed RSSI.

In this step, the RSSI is measured in-band to the FSS as shown in figure 1.

Figure 1. FSS In-band RSSI measurement setup

The setup shows the utilization of a vertically polarized receive antenna that exhibits relatively wide horizontal and narrower vertical beamwidths attached to a receiver (or spectrum analyzer), with the use of a band-pass filter and LNA as required. The choice of the specific measurement antenna is driven by the overall goal of the PFD measurement: namely the assessment of

2 TWG1-006 August 15, 2020 potential interference from the 3.7 GHz licensees. The choice of antenna characteristics is therefore twofold:

I. Limit energy from the FSS satellite downlinks such that their contribution to the overall PFD measurement is negligible. If this is not possible, a baseline PFD measurement without the influence of these transmissions will be required.

II. Use an antenna having sufficient gain such that the interfering signal can be detected at least 6 dB the noise floor of the spectrum analyzer or measurement receiver considering all other aspects of the receive chain (an example measurement setup is described later in this document).

Given the relatively low OOB PFD limit, the measurement setup should ensure that the minimum target signal is at least 6 dB above the sensitivity of the instrument. Table I shows the calculation of minimum required signal level with the receiver noise figure required as input. Table II then shows the link budget to determine the minimum required antenna gain of the measurement antenna.

RSSI measured using this method will capture OOBE from all sources including all mobile operators within the 3.7–3.98 GHz band. It should also be noted that all 3.7 GHz service licensees will utilize 5G-NR, which continuously transmits several control signals and channels, but only transmits power associated with traffic channels when there is subscriber activity. Measured RSSI will therefore vary depending on the time of day, and the specific activity of the subscribers utilizing each gNB base station. Loading levels at each gNB base station are not correlated, varying independently and could result in highly changeable and unrepeatable RSSI measurements.

Table I. Minimum Required Signal Level Determination

Parameter Value Units Comments a Thermal Noise -173.98 dBm/Hz kT (T = 290K) b Receiver Noise Figure 4 dB Input c Measurement Bandwidth 1 MHz 106 Hz d Minimum level above noise floor 6 dB e Minimum Signal Level -103.98 dBm e = a + b + d + 10log(c)

3 TWG1-006 August 15, 2020

Table II. Measurement Setup Link Budget

Parameter Value Units Comments a Frequency 4000 MHz Input b Wavelength 0.075 m c Ae -33.49 dB(m2) Unity gain antenna aperture d Maximum aggregate PFD -124.00 dBW/m2/MHz PFD Limit e Minimum Signal Level -103.98 dBm Input from Table I Minimum required measurement system gain (antenna gain - component f losses) 23.51 dB f = e - (d + c +30) g Component Losses 4 dB Input h Minimum Antenna Gain 27.51 dBi h = f + h

Measurement Considerations

 All equipment to be calibrated prior to measurement execution

 Measurement antenna to be located such that is clear of obstructions within at least 2d2/λ where d is the maximum dimension of the measurement antenna.

 Absolute measurement accuracy (uncertainty) of the receiver to be considered and incorporated into the calculations shown in Table I and II.

 Individual measurements to carried out in the azimuth plane at a resolution of rotation defined by the measurement antenna horizontal beamwidth.

 Each individual measurement to consist of at least 100 sweeps of a 1 MHz bandwidth centered on the center frequency of the FSS.

 The result will be based on the 95th percentile maximum PFD of all measured values

Step 3: Utilization of 5G-NR Physical Cell ID (PCI) Beam SSB Reference Signal Received Power (RSRP) measurements to enable interference mitigation

In this step, individual base station sectors of each service licensee are assessed for their likely contribution to that licensee’s composite interference in the FSS band. Here, the Reference Signal Received Power (RSRP) of each Synchronization Signal Block (SSB) of the observed 5G-NR signals are measured. In 5G-NR, the SSB is transmitted periodically with a fixed power level that does not change as the traffic load on the cell varies. SSB RSRP measurements are therefore repeatable and have no dependence on system loading. Maximum potential total received power (RSSI) from any base station can be determined based on the known SSB RSRP, its configuration, and the potential beamforming methodology utilized for traffic carried on the

4 TWG1-006 August 15, 2020 data channel (Physical Downlink Shared Channel (PDSCH)). An additional advantage of this approach is that interference assessment will only include contributions from the specific licensee that operates on the channel being measured.

The use of this approach also enables 3.7 GHz service licensees to proactively monitor and mitigate changes in RSSI without repeating measurements. Provided there are no physical base station adjustments or beamforming configuration changes, the RSSI contribution of a base station can estimated based on maximum load or any load (present or future).

To assess the likely contribution of each site/sector to the measured PFD, a number of 5G-NR configuration details must be known as shown in Table III. Both Beamforming Gain and out-of- band suppression (emission mask) typically require information from the licensee, whilst sub- carrier spacing (SCS) and licensee center frequency of operation (defined by the New Radio Absolute Radio Frequency Channel Number, NR-ARFCN), can be easily determined through external measurement if necessary.

Table III. 5G-NR required configuration details for PFD determination

Licensee input or determined through 5G-NR Sub-Carrier Spacing (SCS) measurement Licensee input or determined through 5G-NR Center Frequency (NR-ARFCN) measurement Licensee input (based on network Spectrum OOBE Mask configuration - cannot be easily measured) Maximum 5G-NR Beamforming Gain Licensee input (based on network (PDSCH over SSB) configuration - cannot be easily measured)

The PDSCH beamforming gain over an SSB reflects the likely implementation of 5G-NR in the 3.7 GHz spectrum whereby a base station will transmit a number of relatively wide SSB beams for synchronization but will assign narrower, more refined (higher gain) traffic beams for user data transfer. Assessment of likely contribution to aggregate PFD should therefore consider this potential gain differential between the measured SSB beams and traffic beams. In the worst case, a traffic beam within an SSB beam could be aligned directly with the FSS. In this case, the impact would be increased by the maximum beamforming gain.

The calculation methodology used to determine individual PFD contribution based on an assumed transmission mask and beamforming gain is shown in Table IV.

5 TWG1-006 August 15, 2020

Table IV. Calculation of cell/beam potential contribution to PFD

Parameter Value Units Comments a Frequency 3800 MHz Input b Wavelength 0.079 m c Antenna Gain 5.00 dBi Input d Gain - linear 3.16 e Effective antenna aperture 0.00157 m2 f Measured RSRP -68.10 dBm Input g RSRP in dBW -98.10 dBW g = f - 30

h Transmission mask attenuation 75.2 dB Input (example, see text)

i Beamforming Gain 6.00 dB Input j RX Power in FSS band -167.30 dBW j = g - h + i k SSB BW 0.03 MHz Input Rx Power Flux Density (100% l load) -124.03 dBW/m2/MHz l = j - 10log(e) - 10log(k)

Considerations for this approach are:

- Determination of an appropriate OOBE transmission mask: Ideally, it would be provided by the licensee and may vary with the deployed infrastructure. - In this case, an antenna with an omnidirectional pattern in the azimuth plane can be utilized without impacting the ability of the procedure to detect potentially interfering licensee signals. - The OOB PFD contribution for a given 5G-NR site, calculated as illustrated in Table IV, is the worst case, assuming 100% load at the service licensee 5G-NR site with alignment of SSB and traffic beams in the direction of the FSS. An additional assumption is that there is correlation between the antenna pattern and gains at the defined frequency of operation (3.7–3.98 MHz).

Step 4: PFD Utilizing 5G-NR Licensee In-band RSSI Measurements

In this step the RSSI in-band to each 3.7 GHz service licensee is assessed at the FSS location. OOB PFD compliance in the FSS band is determined by applying an appropriate transmission mask to the measured values. The calculation methodology used to determine PFD compliance is shown in Table V.

6 TWG1-006 August 15, 2020

Table V. PFD determination utilizing in-band 3.7 GHz licensee measurements

Parameter Value Units Comments a Frequency 3800 MHz Input b Wavelength 0.079 m c Antenna Gain 5.00 dBi Input d Gain - linear 3.16

2 = e Antenna Aperture 0.00157 m f Measured RSSI -46.85 dBm Input g RSSI in dBW -76.85 dBW g = f - 30

h Transmission mask attenuation 75.2 dB Input (example, see text)

i RX Power in FSS band -152.05 dBW i = g - h j Rx BW 1.00 MHz Input k Rx Power Flux Density -124.00 dBW/m2/MHz k = i - 10log(e) - 10log(j)

Considerations for this approach are:

- Determination of appropriate OOBE transmission mask: Ideally, it would be provided by the licensee and may vary with the deployed infrastructure. - The measured RSSI includes contributions from all sources associated with the 3.7 GHz service licensee’s band of operation that are within the measurement receiver’s bandwidth. As stated earlier, this measurement will vary depending upon the loading of the service licensee network (assuming 5G-NR is deployed). - In this case, an antenna with an omnidirectional pattern in the horizontal plane can be utilized without impacting the ability of the procedure to detect potentially interfering 3.7 GHz licensee signals.

7 TWG1-006 ANNEX I 3.7 GHz Service Operating Parameters

(CTIA/Wireless Industry Response to RTCA Questions, Submitted to TWG3 on July 1, 2020)

Technical Working Group #1

Ref.: TWG1-007 Author: CTIA July 2, 2020 Note: Some items highlighted during July 16 TWG1 call

In the interests of advancing the discussion within Working Group #3—5G/Aeronautical Coexistence, the wireless and aviation industries agreed to exchange questions and provide information regarding the general operating parameters for 5G networks to be deployed in the 3.7 GHz Service and altimeter and other aeronautical operations in the 4.2-4.4 GHz band, respectively. The information that the wireless industry provides here is in response to questions from RTCA on behalf of the aeronautical industry. This information is provided solely for the purposes of the work of Working Group #3 in response to Federal Communications Commission GN Docket No. 18-122, and reflects the unique environment and network characteristics within the United States. Neither the information nor studies or analyses thereof may be used for any other purposes or made available in any other fora. By making this information available, the wireless industry does not endorse or support any analyses or studies that the aeronautical industry may perform.

1 What is an appropriate signal waveform to use in interference tolerance bench testing of radar altimeters that will be reasonably representative of potential 5G emissions in the 3.7-3.98 GHz band?

Clarifying points and follow-on questions:

Are there any additional frequency-dependent characteristics of the transmission path (e.g. bandpass filters) which should also be accounted for in the interference signals to be injected into the receiver input of each radar altimeter under test? If yes, could you assist with obtaining relevant equipment to account for these frequency-dependent characteristics?

How do the waveforms and/or frequency-dependent characteristics differ between base station emissions and user equipment emissions? It would be helpful in creating our tests to have additional details in support of the same.

For the representative 5G waveforms indicated above, is there guidance on the peak-to-average power ratio (PAPR) characteristics, such that these may be considered in statistical analysis of the interference power received by radar altimeters in various operational scenarios?

Any additional guidance relative to simulating potential 5G emissions for these testing efforts, as appropriate, would be helpful.

Context on previous efforts:

Previous testing conducted by AVSI has used a single OFDM signal with 52 BPSK-modulated subcarriers (using random baseband data). The modulation clock rate (and thus the subcarrier spacing) was adjusted to produce each desired total signal bandwidth (ranging from 20 MHz to 280 MHz). While AVSI is confident in the previous test results which have been submitted to the FCC, there admittedly may be room for improvement in representing the potential 5G emissions as accurately as possible.

5G transmission signals:  Baseline assumption: 100 MHz.  Upper bound: 160 MHz, assumes licensees are co-located.  Factors reducing energy density include various network factors such as scheduling, network loading, etc.  To simplify modeling and testing, the worst-case maximum EIRP can be used with the baseline and upper bound bandwidths above, to account for network factors. In practice the signal will be beamformed to the users, and the in-band emissions in the direction of the radio altimeter can vary based on the antenna patterns.  Maximum base station EIRP per FCC is 1640 W/MHz for non-rural and 3280 W/MHz for rural.  The waveform should use QPSK. BPSK modulation is not included in the 5G NR air interface forward link.  The OFDM test signal will capture an appropriate PAPR as part of the testing. For statistical analysis, we should discuss how that would be applied to better understand how best to answer.  The FCC rule for conducted emissions above 3980 MHz is -13 dBm/MHz for the base station and user equipment. Generally, equipment emissions roll off significantly as a function of frequency separation. Therefore, a base station emissions sensitivity analysis could be performed with values other than -13 dBm/MHz, such as -20 to -40 dBm/MHz. For the user equipment, 3GPP further defines a spurious emissions requirement of -30 dBm/MHz.1

2 What are the possible signal bandwidths, for both base station downlink emissions and user equipment uplink emissions, which will be reasonably representative of potential 5G emissions in the 3.7-3.98 GHz band?

Clarifying points and follow-on questions:

What would a reasonable spectrum utilization layout (including spectrum reuse), possibly including multiple network operators, look like for: a) Densely populated regions? b) Rural and suburban regions? c) In and around airports?

It is assumed that all 280 MHz of available spectrum can be used simultaneously in a given geographical area. Details of representative spectrum segmentation across network operators (downlink/uplink and slot scheduling as applicable) throughout the 3.7-3.98 GHz band are requested.

Context on previous efforts:

1 3GPP TS 38.101 “User Equipment (UE) radio transmission and reception”, Table 6.5.3.1-2 Requirement for general spurious emission limits. 2 Previous testing conducted by AVSI has considered 20 MHz and 100 MHz interference signal bandwidths (under guidance from the FCC’s Office of Engineering and Technology), as well as a full 280 MHz bandwidth as a worst case. Further, it is acknowledged that the FCC R&O defines fourteen 20 MHz sub- blocks throughout the 3.7-3.98 GHz band which may be individually licensed, and thus the final contiguous bandwidths for each network operator will ultimately depend on the auction results. However, reasonable assumptions must be established such that various scenarios may be evaluated, and worst-case conditions relevant to aircraft operations can be identified.

From a practical perspective given tower space and loading constraints, it is reasonable to assume that no more than 100 to 160 MHz will be in use at a single location. Question 1 provided further details on the bandwidth.

For TDD asymmetry, typical DL:UL split is 2:1 in time. This means that within a 5G NR radio frame, the base station transmits for approximately two-thirds of the time, and the devices transmit for approximately one-third of the time. It is important to note that the base stations and devices do not transmit at the same time.

Base stations do not transmit at maximum power all of the time. This is captured in network simulations by network loading. A network loading value of 20% would normally represent a typical/average value for the loading of base stations across a network (or part thereof).

UEs are subject to transmit power control. Guidance on UE power control is provided in Recommendation ITU-R M.2101-0 “Modelling and simulation of IMT networks and systems for use in sharing and compatibility studies,” February 2017.

Typical inter-site distance is 0.7 km for urban, 1.7 km for suburban, and 6 km for rural.

Sites in and around airports typically mount antennas in the clutter to avoid FAA lighting and marking requirements.

3 3 What are the possible base station antenna radiation patterns or models, specifying absolute directivity, which will be reasonably representative of what will be deployed in the 3.7-3.98 GHz band?

Clarifying points and follow-on questions:

If multiple different types of antennas with different radiation patterns will be used for different purposes (e.g. rural, suburban, urban macro-cells, urban micro-cells etc.), one or more examples of each type will be needed to allow for the characterization of various scenarios such that worst-case conditions relevant to aircraft operations may be identified. Details on variations in base station deployments across geographic areas in support of the same are requested.

Ranges of possible mast heights and downtilts (electrical/mechanical as applicable) which may be utilized for each antenna type are requested.

If multiple types of antenna technologies will be utilized (e.g. passive/fixed antennas, active antenna systems/beamforming, MIMO, etc.) in the 3.7-3.98 GHz band, specify which technologies are applicable to which applications/deployment scenarios, and how this may impact the overall radiation patterns. Relevant antenna polarization pattern information in support of the same is requested.

If active antenna systems will be utilized, will there be any limitations (regulatory, operational, or practical) on the beamsteering capabilities in the elevation plane? Supporting details are requested.

Context on previous efforts:

Previous analysis conducted by AVSI has considered a base station antenna pattern calculated in accordance with Recommendation ITU-R F.1336-5, with assumptions of a 7-degree elevation beamwidth, 3-degree downtilt, no beamforming, and 90 ft mast height, meant to represent a single base station in a rural deployment scenario.

Assume all base stations will use an active antenna array system with beamforming – this enhances the coverage range of the base station to better match the existing cell site footprint. The larger array size below is close to the maximum FCC EIRP. The smaller array size results in a lower EIRP.

Antenna height: 35 m for rural, 25 m for suburban areas, 20 m for urban.

4 Representative configurations of AAS BS are given below.

Option 1 Option 2 Units Environment Type Urban Suburban Rural Urban Suburban Rural Base station antenna AAS AAS Antenna array size 8x8 16x16 Front-to-back ratio 30 30 dB Conducted power per element 25 25 dBm Antenna polarization Linear +/- 45 Degrees Antenna peak gain 24.5 25.2 30.5 31.2 dBi Vertical scan (below horizon) 0 to -30 0 to -10 0 to -30 0 to -10 Degrees Antenna element gain 6.4 7.1 6.4 7.1 dBi Horizontal/vertical radiating H: 0.5λ H: 0.5λ H: 0.5λ H: 0.5λ element spacing V: 0.7λ V: 0.9λ V: 0.7λ V: 0.9λ Horizontal/vertical 3 dB H: 90 H: 90 H: 90 H: 90 Degrees beamwidth of single element V: 65 V: 54 V: 65 V: 54 Mechanical downtilt 10 6 3 10 6 3 Degrees Antenna beam patterns ITU-R M.2101 Technology 3GPP 5G NR

Array losses are included in the element gain.

4 Are there any general comments which can be provided on the following approach to propagation modeling, or suggestions for alternative propagation models which should be considered, noting that the strongest possible interference coupling must be evaluated for relevant aircraft operational scenarios?

Clarifying points:

To evaluate the interference coupling from 5G emission sources in the 3.7-3.98 GHz band (both base stations and user equipment located on the ground), the primary consideration will be direct line-of-sight propagation, i.e. free-space path loss only from 5G terrestrial emission sources to an airborne radar altimeter, as this direct path will lead to the strongest coupling under most conditions. Further, for certain terrain conditions and interference geometries, ground-bounce propagation will also be considered to evaluate additional non-line-of-sight paths that may direct higher power levels into a radar altimeter receiver onboard an aircraft.

Recommendation ITU-R P.528 provides propagation modeling guidance for aeronautical paths. ITU-R P.528 should be used in conjunction with ITU-R P.2108, which provides a slant path clutter loss model, and ITU-R P.2109 provides building entry loss guidance for indoor UEs. The percentage of UEs operating indoors is assumed to be 70%.

5 5 What are the possible reasonably representative timing patterns of uplink emissions in the 3.7-3.98 GHz band from multiple simultaneously operating UEs (e.g. passenger-carried devices) that could be located onboard an airborne platform?

Clarifying points:

Any details considering different subcarriers/resource blocks and different network operator cells, as applicable, are appreciated to assist in creating an accurate model.

Context on previous efforts:

The worst case being considered currently is that 100% of UEs located onboard an airborne platform may transmit simultaneously in the same time slot. It is also considered that UEs may emit at full power (+30 dBm) when they are located on an airborne platform, since the path losses to base stations on the ground will be significant when accounting for fuselage attenuation, propagation distance, and possibly low directivity of the base station antennas at elevation angles above the horizon. Feedback on these assumptions is requested.

Handheld cellular devices must be in airplane mode when in flight, per FCC title 47 part 22.925, which includes this notice: “The use of cellular telephones while this aircraft is airborne is prohibited by FCC rules, and the violation of this rule could result in suspension of service and/or a fine. The use of cellular telephones while this aircraft is on the ground is subject to FAA regulations.”

Since all handheld devices that support C Band will also support the cellular band, the FCC effectively prohibits airborne operation of these devices. Of further note, the C Band spectrum in 3700-3980 MHz is designated as “mobile except aeronautical mobile” which precludes use of the band for airborne devices. Since the FCC rules prohibit use of devices while airborne, the expected operating environment is that no devices would be transmitting in the C-Band onboard an aircraft.

6 ANNEX J Determination of Separation Distance Between FSS and a Single 3.7 GHz Service Transmitter Based on AAS (5G) Antenna Pattern and FCC OOBE PFD Rules

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-008 Authors: Neeti Tandon September 10, 2020 Navid Motamed

Executive Summary: This submission discusses the derivation of separation distances between a single 3.7 GHz Service transmitter using an Advanced Antenna System (AAS) typical in 5G networks and Fixed Satellite Service (FSS) earth stations, using the FCC’s out-of-band emissions (OOBE) protection rules. This document utilizes the basic formulas set forth in TWG1-003 for determination of Power Spectral Density (PSD).1

Background. In order to understand typical separation distances required between 3.7 GHz Service transmitters and FSS earth stations, this submission considers a single AAS transmitter and a random distribution of FSS earth station locations around a single AAS. In addition to the interference power calculation set forth in TWG1-003, the submission also relies upon typical 5G antenna characteristics, as set forth in TWG1-007 (from TWG3), supplemented with data from ITU-R M.2101, section 5.1.

AAS Antenna Assumptions. As set forth in TWG1-003, the total interference power from n 3.7 GHz Service transmitters is given by: n

I = å(PTX - LP +GTX ) j=1 where:

I is the total received Interference power in dBm/MHz

is the OOBE from each of a 3.7 GHz Service licensees’ PTX transmitters

is the propagation loss, including clutter losses, between each of LP a 3.7 GHz Service licensees’ transmitters and the FSS receiver in dB

is the 3.7 GHz Service transmitter antenna gain in the direction GTX of the FSS receiver in dBi

1 The gain of the earth station antenna above an isotropic in the direction of the 3.7 GHz facility is assumed in this document to be 0 dBi. 1 TWG1-008 September 10, 2020

Thus, the required separation between a single 3.7 GHz Service transmitter and an FSS earth station depends upon the OOBE from the 3.7 GHz equipment, path loss, and 3.7 GHz Service antenna gain oriented towards the FSS location. TWG1-007 provides antenna pattern and default input parameters to model active antenna systems with beamforming as shown in Table 1:

Option 1 Option 2 Units Environment Type Urban Suburban Rural Urban Suburban Rural Base station antenna AAS AAS Antenna array size 8x8 16x16 Front-to-back ratio 30 30 dB Conducted power per element 25 25 dBm Antenna polarization Linear +/- 45 Degrees Antenna peak gain 24.5 25.2 30.5 31.2 dBi Vertical scan (below horizon) 0 to -30 0 to -10 0 to -30 0 to -10 Degrees Antenna element gain 6.4 7.1 6.4 7.1 dBi Horizontal/vertical radiating H: 0.5λ H: 0.5λ H: 0.5λ H: 0.5λ element spacing V: 0.7λ V: 0.9λ V: 0.7λ V: 0.9λ Horizontal/vertical 3 dB H: 90 H: 90 H: 90 H: 90 Degrees beamwidth of single element V: 65 V: 54 V: 65 V: 54 Mechanical downtilt 10 6 3 10 6 3 Degrees Antenna beam patterns ITU-R M.2101 Technology 3GPP 5G NR Table 1. AAS parameters.

The antenna beam pattern is derived from Section 5.1 of ITU-R M.2101.2 This analysis uses Option 2, a 1616 antenna array size with a 6.4 dBi single antenna element gain.3 The antenna pattern for each element of the antenna array is defined in Table 2:

2      Horizontal Radiation Pattern A   min12  , A dB E,H    m   3dB   Horizontal 3dB bandwidth of Input parameter single element / deg ( 3dB )

Front-to-back ratio: Am and SLAv Input parameter 2    90  Vertical Radiation Pattern A   min12  ,SLA  dB E,V    v   3dB   Vertical 3dB bandwidth of Input parameter single element / deg ( 3dB ) Single element pattern AE ,   G E ,max  min  AE , H   AE ,v , Am 

Element gain (dBi), GE,max Input parameter Table 2. Element pattern for antenna array (from ITU-R M.2101).

2 ITU-R Recommendation M.2101 (02/2017), “Modelling and simulation of IMT networks and systems for use in sharing and compatibility studies”

3 Note that the antenna array pattern is not employed in this analysis. Only the element pattern, which is applicable to OOBE, is used. 2 TWG1-008 September 10, 2020

Modeling OOBE radiated from a Single 3.7 GHz Sector: This analysis hypothesizes a single 120-degree AAS antenna sector, with 1000 FSS earth stations randomly placed within a radius of 2.5 km. as shown in Figure 1:

Single 5G Antenna with 1,000 FSS Randomly Distributed Points 3

FSS Points

2.5

2 G 5

m o r f

m K

1.5 n i

e c n t a s i D

1

0.5

0 -2.5 -2 -1.5 -1 -0.5Distance in 0Km from 5G 0.5 1 1.5 2 2.5 Figure 1. Random placement of earth stations within 2.5 kilometers of a single sector 3.7 GHz base station

Utilizing the random placement of Figure 1 and the formulas provided above, the distribution of AAS antenna gains shown in Figure 2 was derived:

3 TWG1-008 September 10, 2020

5G Antenna Gain Distribution FSS =100 ft; 5G =100 ft Distance = 5km

160 120%

100% 140 96% 100% 120 83% s t 80% n 73% i

o 100 P

65% S S

F 56%

f 80 60% o 49% r

e 44% 138 Freq b

m 60 38% Cumulative % u 33% 40% N 97 27% Individual % 40 24% 83 83 68 19% 74 14% 55 59 20% 10% 48 50 51 53 20 7% 35 34 35 14% 37 7% 8% 8% 10% 4% 3% 5% 5% 4% 6% 6% 5% 5% 4% 0 0%

5G Ant Gain (dBi) Figure 2. Distribution of 3.7 GHz base station out-of-band antenna gains over 2.5-kilometer radius shown in Figure 1. Note: 5 km should read 2.5 km

PTX values can range from -13 dBm/MHz to -40 dBm/MHz. Using the 7%, 49% and 96% cumulative values above, Table 3 shows the path loss required to meet the -124 dBW/m2/MHz compliance limit, which is -128 dBm/MHz in PSD units.4

AAS Antenna Gain (Expected Fraction of Cases) OOBE Conducted Level -23.6 dBi (7% ) -5.6 dBi (49%) 4.4 dBi (96%) -13 dBm/MHz -91.4 dB -109.4 dB -119.4 dB -40 dBm/MHz -64.4 -82.4 -92.4 Table 3: Required Path loss as a function of 3.7 GHz transmitter OOBE and AAS antenna gain.

Table 4 converts the path losses from Table 3 into separation distances assuming free-space propagation. For information, free-space values are tabulated in Appendix 1.

AAS Antenna Gain (Expected Fraction of Cases) OOBE Conducted Level -23.6 dBi (7%) -5.6 dBi (49%) 4.4 dBi (96%) -13 dBm/MHz 0.2 km 1.5–2.0 km 5.5 km -40 dBm/MHz < 0.2 < 0.2 < 0.3 Table 4. Required separation distance between AAS antenna and FSS site based on free-space conditions.

The gain distribution of Figure 2 was based on the use of the same height for both the AAS and FSS antennas. To test the sensitivity of antenna height and separation distance, the distribution of Figure 3 was derived, which assumes an FSS antenna height of 5 ft and AAS antennas at 500 ft with 1,000 FSS antennas located within a radius of 2.5 kilometers.

4 See TWG1-004. 4 TWG1-008 September 10, 2020

5G Antenna Gain Distribution FSS =5 ft; 5G =500 ft Distance = 5km

160 120%

100% 140 97% 100% 120 83% s t

n 73% 80% i

o 100 P

65% S S

F 57%

f 80 60% o

r 49%

e 44% 136 Freq b

m 60 39% Cumulative % u 33% 40% N 98 28% Individual % 40 24% 81 77 84 68 19% 14% 57 20% 10% 48 51 53 53 51 20 7% 36 34 38 14% 35 10% 7% 8% 8% 8% 4% 3% 5% 5% 4% 6% 5% 5% 5% 4% 0 0%

5G Ant Gain (dBi)

Figure 3. Distribution of 3.7 GHz base station out-of-band antenna gains with AAS height 500 feet and FSS antenna height 5 feet. Note: 5 km should read 2.5 km

Compared with the first scenario that assumed same FSS and AAS heights, this scenario assumes a significant height difference (5 feet and 500 feet). The differences in the distributions indicates that antenna height differential between FSS and AAS antennas may have a limited role in defining the out-of-band gain from the AAS antenna towards FSS locations. It is expected that a majority of the cases will resemble the geometry in the first scenario.

5 TWG1-008 September 10, 2020

Appendix 1 Free-Space path loss at corresponding distances at 4.0 GHz

Distance Path Loss 11 125.3 0.2 km 90.5 dB 11.5 125.7 0.3 94 12 126.1 0.4 96.5 12.5 126.4 0.5 98.5 13 126.8 0.6 100.1 13.5 127.1 0.7 101.4 14 127.4 0.8 102.6 14.5 127.7 0.9 103.6 15 128 1 104.5 15.5 128.3 1 104.5 16 128.6 1.5 108 16.5 128.8 2 110.5 17 129.1 2.5 112.5 17.5 129.4 3 114 18 129.6 3.5 115.4 18.5 129.8 4 116.5 19 130.1 4.5 117.6 19.5 130.3 5 118.5 20 130.5 5.5 119.3 20.5 130.7 6 120.1 21 130.9 6.5 120.7 21.5 131.1 7 121.4 22 131.3 7.5 122 22.5 131.5 8 122.6 23 131.7 8.5 123.1 23.5 131.9 9 123.6 24 132.1 9.5 124 24.5 132.3 10 124.5 25 132.5 10.5 124.9 25.5 132.6

6 TWG1-008 ANNEX K Earth Station Passband Filter Requirements

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-009 Author: Steve Corda July 22, 2020

A. 100 + 20 MHz “Red” Filter (Phase 1):

1 TWG1-009 2 TWG1-009 B. 280 + 20 MHz “Blue” Filter:

280+20 MHz “Blue” Filter

Passband 4000 - 4200 MHz

Group delay variation within +/- 0.5 MHz 1.45 nSec max

Insertion Loss in Pass Band 1.3 dB max

Return Loss 20 dB min Electrical Rejection from 3700 MHz to 3900 MHz 70 dB min Characteristics Rejection from 3900 MHz to 3980 MHz 60 dB min

Rejection from 3980 MHz to 3985 MHz 30 dB min

Rejection from 3985 MHz to 4000 MHz 0 dB min

Rejection above 4230 MHz 25 dB min

CPR-229G & CPR-229F Interfaces Through holes both ends

Size (L x W x H) Mechanical Length inclusive of flanges Characteristics Width and height exclusive of flanges 6.75'' x 3.00'' x 2.00'' Width and height inclusive of flanges 6.75'' x 3.00'' x 2.96''

Operating Temperature -40º C to +50º C

Finish Matte white light textured paint

3 TWG1-009 4 TWG1-009 ANNEX L Power Flux Density Measurement Concept and Identification of the Source of Interference

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-010 Author: Marian Angheluta August 20, 2020

Summary

This submission defines a methodology to measure the Power Spectral Density (PSD) generated by the new 3.7 GHz IMT2020 network in the vicinity of a victim FSS Earth station within the FSS band, to calculate the Power Flux Density (PFD) equivalent to the measured PSD and to identify the source(s) (Base Station) of the most significant emission(s) contributing to the measured PSD.

The described methodology is technology neutral, oriented toward maximizing the accuracy of the measurements, and does not need information about the IMT2020 Base Station characteristics (antenna height, power levels, spectral mask, location).

The methodology evaluates the PFD of the received signals in any one MHz in the 4000 MHz to 4200 MHz FSS band. The results of the interference measurement and identification procedure are the PFD value, the geolocated area, and the list of 5G-NR Physical Cell ID (PCI) Synchronization and Signal Block (SSB) beams received from the geolocated area.

High-level description of the concept

The PFD of the received signals is calculated from the measured PSD using a Real Time Spectrum Analyzer (RTSA). The RTSA is fed by a very directive, high-gain, passive antenna that is directly connected to a Bandpass Filter (BPF) and a Low Noise Amplifier (LNA).

Considering the very low levels to be measured, it is mandatory to directly connect the filter and the LNA to the antenna, since any supplementary attenuation on the RF chain between the antenna and LNA decreases the signal to noise ratio.

The directive antenna is installed on a Controlled Antenna Rotator (CAR).

The signal from the LNA output is split two ways with one output connected to RTSA and the second output to an IMT scanner.

The IMT scanner will identify the list of 5G-NR PCI SSB Beams. It is important that the signal received from the antenna be split only after the LNA, so the splitter attenuation does not affect the OOB Signal to Noise Ratio.

TWG1-010 LS telcom, Inc. Page 1 Due to BPF rejection, the list of identified PCIs will be limited to the strongest base stations at the measurement location.

A Command and Control Unit (built using a laptop and special software) will be used to:

1. Control the Antenna Rotator;

2. Control the RTSA measurement;

3. Synchronize the RTSA result with the position of Antenna Rotator and the list of 5G-NR PCI Beam SSB;

4. Generate the results as an open street map with the indication of the geolocated area (as the azimuth of the antenna when the maximum result was achieved and the 1 dB antenna beamwidth span centered on the measured azimuth) and the list of the 5G-NR PCI Beam SSB.

The generated Report is sent to Mobile Operator contact points. The high-level measurement concept is described in Figure 1:

Fig. 1 High-level concept measurement description

TWG1-010 LS telcom, Inc. Page 2 Notes:

1. Other relevant information from IMT scanner (e.g., SSB index or SSRe) can be included if the 5G licensees will find it helpful in more rapidly identifying cell sites. 2. Interference hunting procedures may be necessary starting from this point. In some particular cases, such as when line-of-sight between Base Station and Earth Station is obstructed or if the Base Station antenna sector is oriented in the opposite direction, the interfering signal can be received from a reflection point, further investigations should be conducted. The directive identification of the PCI on the same direction as the direction of arrival of the interference (if this procedure is possible) will increase the efficiency in identification of the relevant Base Station.

Detailed description of the methodology:

The 5G PFD will be evaluated through the measured Channel Power level in 1 MHz bandwidth in the vicinity of the affected Earth Station;

Considering the fact that the level of the 5G interference may be below the thermal noise and the need to perform the measurement with the highest accuracy possible, the RF testbed will include:

1.1 passive high gain antenna; 1.2 Band Pass filter; 1.3 LNA; 1.4 Controlled switch; 1.5 Controlled antenna rotator; 1.6 2-way Splitter; 1.7 Measurement receiver 1.8 IMT scanner.

Recommended criteria for the selection of the measurement equipment:

 Passive antenna: calibrated, passive high-gain (25 dBi) antenna;  Band Pass filter: 3.7 GHz interference filter rejection – as specified by regulator or TWG document;  LNA: lowest possible noise temperature; if LNA models including integrated filters can be identified, these models should be preferred;

Considering the fact that the maximum 1 dB beamwidth of around 23–25 dBi passive directive antenna is about 4 degrees, 90 measurements will be necessary to cover 360 degrees in azimuth.

To decrease the measurement time without decreasing the accuracy, a system with 4 receiving paths (antenna, filter and LNA) should be used; the system will be rotated with 4-degree steps. 60 seconds will be necessary for the antenna rotator to complete a full 360 degrees rotation, so the revisit time will be in the range of 15–20 seconds.

 Antenna switch: a controllable 4 inputs/1-output antenna switch must be used.

TWG1-010 LS telcom, Inc. Page 3  Measurement receiver: RTSA with 40 MHz real time bandwidth; Using this type of receiver, a 40 MHz band can be quasi-instantaneously analyzed, the 1 MHz PFD evaluation can be performed in the entire band of each FSS transponder. A five-step sweep is necessary to cover the 4.000 – 4.200 MHz band, considering the actual specifications of RTSA the measurement is almost instantaneous.  IMT scanner: the main role of the IMT receiver is to provide a list of received 5G-NR Physical Cell ID (PCI) Beam SSB from the same direction of arrival of the interference.  2-way splitter: a high frequency (min. 4.2 GHz) -3.5 dB splitter should be used.

The measurement setup is described in Figure 2:

Fig. 2 Full measurement setup

A simplified measurement setup can be also used as illustrated in Figure 3.

TWG1-010 LS telcom, Inc. Page 4 Fig. 3. Simplified measurement setup

Fig. 4. RF components

The measurement system will be installed in the immediate vicinity of the ES antenna, 1 m above the ES antenna. If this is not possible, two measurements can be performed in the vicinity of the Earth Station antenna as shown in Figure 5. The measurement points will be diametrically opposed, considering as reference point the Earth Station antenna.

TWG1-010 LS telcom, Inc. Page 5 Fig 5. Two measurement options depending on the measurement antenna height

 Option 1: Measurement antenna higher than Earth Station antenna;  Option 2: Earth Station antenna higher than Measurement antenna.

If the interference persists long enough, a simplified measurement setup consisting of a single antenna, filter and LNA (with no antenna switch) can be used.

Measurements results evaluation

The PFD will be calculated using the general formula:

2 PFD[dBW/m /MHz] = PSD[dBm/MHz] + 20*log10(f) – G[dBi] – 68.2

The above formula is derived from:

PFD[dBW/m2] = E[dBuV/m2] – 145.8

E[dBuV/m2]= P[dBm] + AF [dB(m-1)] + 107

-1 AF dB(m ) = 20*log10(f) – G[dBi] – 29.7 where:

 E= field strength [dBuV/m]  G= Antenna gain [dBi]  AF = Antenna Factor [dB(m-1)]

TWG1-010 LS telcom, Inc. Page 6  F = frequency [MHz]  Antenna impedance = 50 ohms

Considering the contribution of every element in the RF chain, the PSD is calculated as:

PSD[dBm/MHz] = PR[dBm/MHz] + System Attenuation + BPF attenuation – LNA Gain where:

 PR[dBm] represents the channel power in 1 MHz as displayed by the measurement receiver;  System Attenuation = Connection attenuation = Antenna to BP Filter attenuation + BP Filter to LNA attenuation + LNA to Feeder Attenuation + Feeder Attenuation + Feeder to Measurement Receiver Attenuation

Link Budget verification a. PFD limit -124 dBW/m2/MHz b. Frequency 4000 MHz c. Antenna gain 25 dBi d. PSD limit -102.84 dBm/MHz e. BPF in-band attenuation 0.2 dB f. LNA noise temperature 15 K g. LNA noise factor (290 K) 0.22 dB h. Connection attenuation 0.4 dB i. PSD limit before LNA -103.67 i = d – e – g - h dBm/MHz amplification j. Thermal noise -113.98 dBm/MHz

The LNA amplification, with a minimum of 50 dB, will increase the measured signal to a value of about -54 dBm/MHz, which is about 50 dB higher than the Displayed Average Noise Level (DANL) of a typical spectrum analyzer, even after a 3.5 dB attenuation due to the 2-way splitter. The splitter attenuation will not decrease the Signal to Noise ratio, because the noise level as seen by the measurement is not the RTSA noise level, but the thermal noise from the input of the LNA, amplified by it.

The RTSA is centered on 4020 MHz, with an instantaneous acquisition bandwidth of 40 MHz and calculates the Channel Power in 1 MHz channels.

It is necessary to use a Command and Control Unit (CCU), a portable computer with dedicated software, to synchronize the RTSA measurements with the Antenna Rotor position change, also to calculate the PFD value corresponding to each measured sector and to generate alarms when the calculated PFD exceeds the PFD threshold.

TWG1-010 LS telcom, Inc. Page 7 Identification of interference source(s) (Base Stations) with the most significant emission(s) contributing to the measured PSD.

The IMT scanner will decode the 5G-NR PCI Beam SSB, as synchronously commanded by the CCU. As the signal received by the IMT scanner is coming from a very directive antenna and attenuated by the rejection of the BP Filter, the list of PCIs will be limited to the strongest received signals from the same direction, presumably also with the highest potential for interference. Also, the detection distance will generally be limited to the nearest base stations.

If practice proves that the signals are too attenuated to be decoded, alternative solutions for IMT antenna should be considered (like using a separate omnidirectional antenna). The disadvantage of using a separate omnidirectional antenna is that the list of decoded PCIs will no longer be correlated with the measurement antenna direction. In that case, the LNA can then be replaced with an LNB and the 2-way switch is no longer necessary.

If the calculated PFD limit is exceed, the CCU will automatically issue a PFD limit “violation report” including general data (time and location of the measurement), measurement setup specific data (1 dB antenna beamwidth), the calculated value of PFD, the list of 5G-NR Physical Cell ID (PCI) Beam SSB as reported by IMT scanner at the time of violation detection and the map (for example open street map) with the geolocated area semi-transparent superposed on it.

The Report will be used by the Mobile Operators to identify the BS or a short list of BSs most likely to create interference.

A measurement antenna having a 3 dB beamwidth of 10 degrees would be expected to have a 1 dB beamwidth of about 4 degrees.

The geolocated area, considering a maximum interference distance of 10 km, will be in a range of 3.5 km2. If a cell radius of 200 meters is considered, the average number of Base Stations in the geolocated area is 27.5 Base Stations, as shown in Figure 6. The number of the considered Base Stations is much lower than the number of available PCI.

TWG1-010 LS telcom, Inc. Page 8 Figure 6.

TWG1-010 LS telcom, Inc. Page 9 ANNEX M Earth Station Interference from 3.7 GHz Facilities and Low Elevation Angles

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-011 Author: Robert Weller September 10, 2020 (updated November 3, 2020 to reflect updated incumbent earth station list published by FCC)

Purpose: The intention of this contribution is to provide guidance to Earth Station operators and 3.7 GHz licensees concerning certain situations where interference to satellite reception is possible regardless of compliance with FCC requirements concerning PFD.

1. FCC PFD Requirements FCC Rules Section 27.1423(a) limits the power flux density (PFD) of 3.7 facilities in the satellite receive band (4.0–4.2 GHz) to -124 dBW/m2/MHz per licensee measured at the location of the Earth station antenna. This PFD limit is the aggregate of emissions from all base station and user equipment from a single licensee. Similarly, Section 27.1423(b) limits the power flux density (PFD) of 3.7 facilities in the 3.7 GHz band (3.7–3.98 GHz) to -16 dBW/m2/MHz as measured at the location of the Earth station antenna.

These PFD limits were derived by the FCC, based on a defined interference to noise (I/N) protection criteria and reference receive parameters for the Earth station’s antenna. Specifically, the reference system noise temperature was 142.8 K and the reference gain of the Earth station antenna was 0 dBi. In addition, the Earth stations are required to have a bandpass filter installed, having a rejection of that meets the mask of Table 1.1 This integrated rejection is equivalent to 60 dB in 1 MHz.

Frequency Range Attenuation From 3.7 GHz to 100 megahertz below FSS band edge -70 dB From 100 megahertz below lower FSS band edge to -60 20 megahertz below lower FSS band edge From 20 megahertz below lower FSS band edge to -30 15 megahertz below lower FSS band edge Table 1. FSS 5G-rejection filter mask.

2. Satellite Interference When PFD Limits are Compliant The FCC made clear in its Order that incumbent earth stations operating in 4–4.2 GHz “will be able to continue receiving uninterrupted service both during and after the transition.”2

1 See, e.g., FCC Report and Order, GN Docket 18-122, Adopted February 28, 2020, ¶367 and 371. 2 47 CFR §27.1411(b)(3)

1 TWG1-011 While the FCC also clarifies the PFD limits “will adequately protect FSS earth station receivers from out-of-band emissions from fixed and mobile operations,”3 there may be earth station and base station configurations where interference can nonetheless occur.

A. 3.7 GHz OOBE Interference (4.0 to 4.2 GHz) A possible scenario where interference can occur despite compliance with the PFD limits is in situations where the Earth station antenna is oriented such that the gain is not 0 dBi in the direction of the 3.7 GHz facilities. This situation may arise particularly when an Earth station in the eastern Contiguous United States (CONUS) is receiving signals from a geosynchronous satellite stationed toward the Western end of the U.S. Domestic satellite (US Domsat) arc. Such Earth stations will have lower elevation angles above the horizon, which may place one or more 3.7 GHz facilities nearer to the main beam of the Earth station antenna resulting in a gain in excess of the reference 0 dBi.4

For purposes of determining the geographic areas in CONUS where antenna gain above 0 dBi can occur, it should be assumed that the antenna pattern of the Earth station is circularly symmetric and has the performance specified in Section 25.209(a)(1) of the FCC Rules, copied below in Table 2: Gain, dBi Angle from Boresight,  29 – 25log10() for 1.5° ≤  ≤ 7° 8 for 7° ≤  ≤ 9.2° 32 – 25log10() for 9.2° ≤  ≤ 48° -10 for 48° ≤  ≤ 180° Table 2. Earth station performance requirements as specified in 47 CFR §25.209(a)(1) Graphically, a portion of the Earth station performance requirements (gain envelope) from Table 2 is shown in Figure 1.

25

20

15

10 ) i B d ( 5 n i a G

0

-5

-10

-15 2 7 12 17 22 27 32 37 42 Off axis angle (deg) Figure 1. Assumed Earth Station Gain from Table 2.

3 See, e.g., FCC Report and Order, GN Docket 18-122, adopted February 28, 2020, at ¶363 4 Similarly, Earth stations located in some southern CONUS regions might have higher elevation angles to satellites, which might result in gain below 0 dBi in the direction of 3.7 GHz facilities and would afford the Earth station with added margin. See FCC Report and Order, at ¶359. 2 TWG1-011 From Table 2, it is calculated that gain of the Earth station antenna is 0 dBi or less when the angle from boresight is approximately 19° or greater. Because 3.7 GHz base stations are expected to be uniformly distributed around Earth station sites, the gain of the Earth station antenna in the direction of the 3.7 GHz base station is likely to exceed 0 dBi when the Earth station antenna is accessing a satellite having a local elevation angle of 19° or less.

[The western most orbital slot serving incumbent earth stations in CONUS) is 135° West Longitude.5] Additionally, interference protection of Earth stations applies at any orbital location across the full U.S. Domsat arc (“ALSAT”), irrespective of whether a particular orbital slot is currently in use.6 A number of satellites in the Western portion of the US Domsat arc are known to be commonly accessed or provisioned for broadcast use, however. These include Galaxy 12 (129°W) and Galaxy 14 (125°W).7 The map of Figure 2 shows the areas of CONUS where the elevation angle of an Earth station antenna would be 19° or less when pointed at the 135°W and 123°W orbital slots.

Figure 2. Map showing areas where Earth Station elevation angles may be 19° or less or satellite orbital slots of 135°W and 123°W.

Based upon the current list of incumbent Earth stations published by the FCC, there are approximately 129 Earth station sites in the area east of the 123°W line and approximately 1813 Earth station antennas in the area east of the 135°W line.8 The list of incumbent earth stations in the 3.7–4.2 GHz may change. Earth station operators and 3.7 GHz licensees in these areas should consider the recommendations in section 3 to mitigate potential interference and to resolve interference.

5 [See Final Satellite Transition Plans rec’d Aug 14, 2020 (SES, Intelsat, Eutelsat, Telesat, Claro).] 6 FCC Order ¶372. 7 Intelsat launched Galaxy 30 in August 2020, which is expected to commence operation at 125°W in 2021. 8 FCC Public Notice, “International Bureau Releases Updated List of Incumbent Earth Stations in the 3.7–4.2 GHz Band in the Contiguous United States,” IB Docket 20-205, DA 20-1260, October 23, 2020. 3 TWG1-011 Protection Criteria. OOBE emissions from 3.7 GHz licensees should not exceed the protection threshold (I/N) of -6 dB (equivalent to a 1 dB increase in the system noise level). This I/N value is measured at the Earth station receiver input.

B. 3.7 GHz In-Band Blocking Interference (3.7 to 3.98 GHz) The rejection performance specification of the Earth station filter described in TWG1- 009 appears adequate to prevent gain compression (“blocking”) in most low-noise amplifier systems (LNAs, LNBs).9 However, the gain of the Earth station antenna towards 3.7 GHz facilities at low elevation angles may be greater than 0 dBi such that the filter is not adequate to prevent blocking. As described in the previous section, this condition has higher chance of occurrence in areas where Earth station antennas are at lower elevation angles.10

3. Recommendations

A. To avoid possible interference for earth stations with low elevation angles (and associated azimuth angles), a list of earth station locations can be developed and used to help avoid the 3.7 GHz site orientations corresponding to FSS sites with low elevation angles. This list can be used by 3.7 GHz licensee in the network designs to identify specific orientations that may result in interference in excess of the I/N protection criteria of -6 dB (or increase the likelihood of blocking). An illustrative list of Earth stations that have calculated elevation angles less than 19° toward the 135°W orbital slot is provided in Appendix 1.

B. In the event interference from a 3.7 GHz facility (or facilities) is observed at an earth station and PFD levels are determined to be compliant, the 3.7 GHz licensee should check if the FSS is on the list of incumbent earth stations corresponding to low look angles. If so, a possible resolution to eliminate the interference could be to re-calculate the required PFD at the earth station and make appropriate adjustments in order to comply with protection criteria, using the actual earth station orientation (azimuth and elevation angles).

C. Case-specific negotiations between 3.7 GHz licensees and FSS operators may be appropriate.11

9 See also FCC Order, ¶367. 10 Earth stations positioned in regions with high elevation angles, conversely, may have added margin from interference due to 3.7 GHz sources. 11 See FCC Order, ¶359. 4 TWG1-011 Appendix 1

Illustrative List of Earth Stations Having Calculated Elevation Angles Less than 19° Toward the 135°W Orbital Slot

Final CBand ES list 135 below 19deg (no dups).xlsx

5 TWG1-011 ANNEX N Potential Mitigation Techniques to Resolve Interference Between a 3.7 GHz Service Transmitter and a Fixed Satellite Service Earth Station

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-012 Authors: Neeti Tandon (AT&T) August 27, 2020 Navid Motamed (AT&T)

Summary: This submission discusses a variety of techniques that could be employed to mitigate interference at a Fixed Satellite Service (FSS) earth station due to a 3.7 GHz Service base station. This document offers a number of potential remediation mechanisms that might be undertaken by a 3.7 GHz Service license at its base station or, in some cases, at the earth station facility, to mitigate out-of-band emissions (OOBE) shown to cause interference at the earth station.

Interference Mitigation Techniques. In the TWG-001 Scope of Work, the Working Group stated it would “[c]reate a toolbox for 3.7 GHz Service licensees to mitigate the impact of 5G base stations on earth stations, including potential interference mitigation strategies that can be implemented by 3.7 GHz Service licensees at the earth stations to assist in interference mitigation.” A non-exclusive list of some options for such remediation are provided below.

Mitigation Techniques at 3.7 GHz Service Base Stations

 Reduce Base Station Power. OOBE should be directly related to base station power, so reduction of the operating power of a base station should reduce OOBE interference.

 Improved Base Station Filter Rejection. In some cases, OOBE levels could be decreased by using/adding filters to achieve better performance than the minimum FCC requirement for 3.7 GHz transmitters and increase the suppression of power outside the occupied channel.

 Reorienting Base Station Antennas. Most 3.7 GHz Service antennas are likely to be directional, so it should be possible to adjust the main beam orientation to minimize the power directed at the FSS earth station location. To the extent a site does not already employ a directional antenna, sectorized antennas can be deployed.

 Implementation of 5G Active Antenna Systems. 5G systems deployed in the 3.7 GHz Service band are expected to be able to take advantage of new, high-performance Active Antenna Systems (AAS). Better OOBE performance in the direction of the earth station receiver may be possible by deploying an AAS at the offending base station if not already so equipped.

 Engineering Increased Path Loss By Taking Advantage of Clutter and Terrain. In certain cases, 3.7 GHz Service base stations may be able to be modified (e.g., side-mounting an antenna on a building rather than top mounting, decreasing base station height) to take

1 TWG1-012 August 27, 2020

advantage of natural and man-made clutter to attenuate transmissions in the direction of the FSS earth station.

 Beam Nulling. For 5G base stations that employ AAS, modification of the Pre-Coder Matrix Index may be possible to create antenna “nulls” toward FSS earth stations.

Mitigation Techniques at the FSS Earth Station

 Transponder/Satellite Change. Consider changing the transponder or serving satellite used to avoid use of a channel that is close to the 3.7 GHz Service band, creating additional frequency separation and greater attenuation, or avoiding a satellite with a look angle that places the base station close to the main beam of the earth station antenna.

 Shielding FSS Antennas. Depending upon the earth station site location and azimuth/elevation to the satellite in use, it may be possible to add additional shielding (such as a berm) at the earth station site between the 3.7 GHz Service transmitter and the facility.

 Improve FSS Link Margin. In some cases, it may be possible to improve the link margin at an earth station facility by, for example, deploying a larger antenna with a narrower operating beamwidth, or replacing other equipment.

 Improved 5G Rejection Filter.

2 TWG1-012 ANNEX O WRC229 C-band Filter-Coupler Assembly Preliminary Specification Report

Submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-013 Authors: Navid Motamed (AT&T) July 30, 2020 (on behalf of Milad Sharifi, Apollo Microwaves) WR229 C-band Filter-Coupler Assembly Preliminary Specification Report

Milad Sharifi

Apollo Microwaves

July 24, 2020 July 30, 2020

3 TWG1-013 July 30, 2020

4 TWG1-013 July 30, 2020

5 TWG1-013 July 30, 2020

6 TWG1-013 July 30, 2020

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7 TWG1-013 ANNEX P Temporary Fixed and Transportable Earth Stations

submission to

Terrestrial-Satellite Coexistence During and After the C-Band Transition

Technical Working Group #1

Ref.: TWG1-014 Author: Rob Lamb October 1, 2020

Purpose: The purpose of this contribution is to present the unique operational characteristics of Temporary Fixed and Transportable Earth Station (“TES”) facilities and suggest how these stations can co-exist with 3.7 GHz wireless operations. This contribution focuses on three issues:

1. The geographic coordinates of TES facilities are not included in IBFS or in the FCC’s published list of incumbent Earth station sites, and some procedure is needed so that 3.7 GHz licensees are aware of TES locations and TES licensees have contact information for the 3.7 GHz licensees operating at any given location.1

2. 3.7 GHz sites and TES are likely to be located in close proximity, leading to inherently strong 3.7 GHz signals as well as an increased possibility of anomalous propagation (building reflections, etc.) that would not be considered by traditional propagation modeling by 3.7 GHz licensees during network design. Contemporaneous coordination and response may be needed to resolve interference issues.

3. 3.7 GHz Service licensees and TES operators should work cooperatively and in good faith to incorporate interference management solutions that allow both systems to operate simultaneously.

1. Preventing Interference

1.1 Temporary Fixed and Transportable Earth Station facilities (“TES”) do not operate permanently at a fixed location (latitude and longitude) but instead can operate anywhere within the contiguous United States.2

1.2 Locations for TES antennas are determined in consultation with the owner of the venue and others, and include consideration of many location-specific factors including satellite line-of-sight, prime power availability, connections to video/audio/data feeds, local traffic laws, etc. The locations may not be the same

1 FCC Public Notice and attachment, IB Docket 20-205, “International Bureau Releases List of Incumbent Earth Stations in the 3.7–4.2 GHz Band in the Contiguous United States,” released August 3, 2020, DA 20-823. https://docs.fcc.gov/public/attachments/DA-20-823A2.pdf 2 See Report and Order and Order of Proposed Modification, GN Docket 18-122, adopted February 28, 2020, released March 3, 2020, FCC 20-22 (“C-Band Order”) at 122. “…the classes of earth stations entitled to protection and transition are those registered as fixed or temporary fixed (i.e., transportable) earth stations in IBFS.” The Commission also stated that “[t]o maintain the status quo during the transition, we decline at this time to authorize additional registrations for occasional use of transportable earth stations. That decision, however, does not preclude the Commission from considering other methods of responding to temporary, targeted spectral needs on a negotiated, non-interfering basis, such as through the use of Special Temporary Authority.” See also C-Band Order at fn. 421. TWG1-014 from event to event at some venues, while other venues may have one or more specific locations designated for TES to locate. Both TES and 3.7 GHz Service licensees should work in good faith prior to the commencement of any TES operation to make use of all interference mitigation tools available for both networks to coexist.

1.3 TES licensees should develop a web-based database of common operating venues, including specific location(s) of TES sites at those venues, if known. The database should include the PEA associated with each venue. 3.7 GHz Service licensees are encouraged to make use of the TES siting database for venues in their licensed markets to limit interference to TES sites at the locations identified in that database during initial network design. TES and 3.7 GHz Service licensees should work together in good faith during the network design stage to resolve any potential interference issues by using all mitigation tools available [including limiting PFD at specific locations] for both systems to coexist.

1.4 Generally, once a TES deployment is planned for a specific event at a venue, the 3.7 GHz licensee(s) should be notified of the date and times of the deployment, as well as the specific operating location and additional technical details, including satellite and transponder, if known. This notification could be done by a third-party, such as a frequency coordinator. When possible, TES operators should attempt to coordinate their siting at the venue with 3.7 GHz Service Licensees and venue owners to minimize the potential for interference. Consideration should be given to selecting higher satellite transponders and frequencies, where possible, to minimize the potential impact of OOBE from 3.7 GHz Service operations. Where flexibility exists with respect to locating the TES antenna, measurements [of PFD, multipath conditions, error rates, and other appropriate factors] should be conducted to minimize the potential for interference.

1.5 The close proximity of 3.7 GHz operations to TES sites may increase the likelihood of both LNA/LNB saturation (“blocking”) and out-of-band interference. Consideration should be given to the use of 5G rejection filters at the TES having performance better than required by the FCC, recognizing that increased insertion loss and other factors may limit such options. Similarly, consideration should be given to the use of transmitter low-pass filters or other measures to reduce OOBE levels, recognizing that increased insertion loss and other factors may limit such options.

2. Interference Detection

2.1 At many venues, the precise location and operational characteristics of TES are often determined with little advance notice and the duration of transmission is often limited to hours, such as the duration of a football game. Because of the limited duration of the events, TES and 3.7 GHz Service licensees should work together in good faith prior to the commencement of and during any TES operation to resolve

2 TWG1-014 any potential interference as rapidly as possible by using all interference mitigation tools available for both systems to coexist.

2.2 A process for Earth station and satellite operators experiencing interference to contact 3.7 GHz Service licensees with interference concerns is described in TWG1-005. The outcome of that process for specific TES venues should also document interference history by location, past complaints, actions taken to diagnose and mitigate the interference, and the final outcome of the interference case. This information can be used for mitigating future interactions between TES and 3.7 GHz facilities, but additional measures may be needed by both TES and 3.7 GHz licensees. TES operators are encouraged to include site-specific mitigation and interference resolution measures in the TES venue database that were previously successful.

2.3 [To facilitate relocation with comparable facilities,3] TES vehicles may require a spectrum analyzer, Mobile Network Scanner and other specialized equipment (including engineer training and specialized antennas) to rapidly identify 3.7 GHz operators and specific sites (i.e., capture PLMN identifier, System Information Blocks, Physical Cell Identifiers, etc.) that may be causing interference problems.

3. Interference Mitigation

3.1 Due to the likely close proximity of 3.7 GHz sites to TES facilities at major venues, mitigation performed solely by TES operators may not be adequate to eliminate the interference. Certain mitigation options (such as change of satellite, change of transponder frequency and/or polarization, use of terrestrial facilities, improvised interference shielding techniques, frequency band changes, and location moves) will not be available in many cases, due to restrictions described in Section 1.2, as well as restrictions due to the associated TES uplink frequency coordination requirement, which protects terrestrial fixed wireless licensees. Additionally, the close proximity of 3.7 GHz sites to TES increases the likelihood of multipath interference as described in Section 4.1 and may make some TES mitigation options ineffective. Relocation of the TES, even by a few feet when possible, may help reduce interference levels.

Additionally, event venues during major events are also locations where 5G coverage is critically needed and will likely be densely deployed, because such venues involve high densities of users anticipated to be engaged in a variety of multimedia activities (including AR/VR/video) and communications in support of public safety and welfare. Wireless providers during an event may have a limited ability to engage in ad hoc network changes to mitigate interference concerns. Physical mitigations such as downtilting, reorienting sectors, or filter installation may be infeasible given the timing. The ability to perform 3.7 GHz network modifications during an event may be similarly restricted.

3 See C-Band Order at 183. 3 TWG1-014

3.2 Both TES and 3.7 GHz Service licensees should work in good faith prior to the commencement of and during any TES operation to make use of all interference mitigation tools available for both networks to coexist. However, contemporaneous coordination and rapid response may be needed to mutually resolve interference issues not detected or mitigated prior to TES operation.

3.3 Consider whether a mitigation process for TES at specific venues as well as at itinerant locations should be defined locally or by a centralized authority (NOC) and define that process. If a local contact is needed for 3.7 GHz licensees, consider how to ensure that the appropriate contacts are made available to TES licensees (and continually updated). Such contact information could be exchanged as part of the notification process described in Section 1.4.

4. Multipath Interference

4.1. The effects of interference received via an indirect path (multipath interference) occurs when an RF signal from a transmitter arrives at the receiver after reflection off the ground, a building, or some other object. It is possible such interference can involve reflection from multiple objects as illustrated in Figure 2.

Figure 2. lllustration of multipath interference.

Such anomalous propagation paths were observed during joint 5G testing in August 2019.4 Engineers from the CBA and PSSI documented such interference.

4 See PSSI Ex Parte Presentation to FCC 10/18/2019 https://www.fcc.gov/ecfs/filing/101801726144

4 TWG1-014 Multipath or reflections present unique concerns for TES since they are often surrounded by vehicles, street signs, buildings and the like at a live entertainment or sporting event. This phenomenon is especially troublesome for TES operations near downtown urban locations and where 3.7 GHz nodes may be very close. When possible, prior to the event, measurements should be conducted to select the best possible location for TES to minimize potential interference, directly or indirectly, from 3.7 GHz services.

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