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 (1.3810-23 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.