APPENDIX D: TECHNICAL ISSUES REGARDING THE 1761-1842 MHZ BAND SEGMENT

INTRODUCTION

Expanding the reallocation of the 1710-1755 MHz band to include the 1755-1760 MHz and 1845-1850 MHz band segments is addressed for several reasons. The general consensus among the public-safety organizations responding to the Preliminary Report and the FCC NOI is that the 1710-1755 MHz band is the only band identified for reallocation below 3 GHz that is feasible to support the development of the wide-area emerging technology systems specified in the Coalition of Emerging Multimedia Technologies (COPE) Petition for Rule Making. Thirty-seven commenters on the FCC NOI supported the recommendations made in the COPE petition. Commercial entities believe that the reallocation of a larger portion of the band would greatly enhance their ability to provide new and advanced telecommunications technologies to benefit the needs of the public. In the FCC Report, the FCC supports the reallocation of a larger portion of the 1710-1850 MHz band and specifically recommends that the 1755-1760 MHz and 1845-1850 MHz band segments be reallocated for public-safety and commercial applications. The FCC report states that reallocation of the 1755-1760 MHz band segment would provide a contiguous 50-MHz block of spectrum located in a band for which equipment could be quickly developed. Moreover, the 1845-1850 MHz band segment is immediately adjacent to spectrum currently allocated for PCS and could serve as an adjunct to this service.[EN 1]

The NTIA Preliminary Report discussed the 1710-1850 MHz band as four separate band segments: 1710-1755, 1755-1761, 1761-1842, and 1842-1850 MHz. The 1710-1755 MHz band segment was proposed for reallocation to the private sector on a mixed use basis. The 1761-1842 MHz band segment was excluded from reallocation because it is used by Air Force to operate the Space-Ground Link Subsystem (SGLS). The SGLS has 20 discrete factory preset uplink frequencies throughout the 1761-1842 MHz band segment that provide tracking, telemetry, and control for all military satellites.[EN 2] Over 90 satellites, both geostationary and non-geostationary, are supported by SGLS. In addition to the five fixed SGLS site locations, DOD has transportable SGLS-compatible earth stations that are used to provide additional coverage for launch and on-orbit operations.[EN 3]

In addition to SGLS, DOD also uses this band segment for Air Combat Training Systems (ACTS) such as, Air Force's Air Combat Maneuvering Instrumentation (ACMI) and Navy's Air Combat Maneuvering Range (ACMR) and Tactical Aircrew Combat Training System (TACTS). The ACMI, ACMR, and TACTS all employ factory preset frequencies in 1761-1842 MHz that are used to transmit information to and from training aircraft. Training support systems such as these are key elements in the military's efforts to provide realistic simulation and pilot training in a peacetime environment.[EN 4] As stated in Section 4, NTIA reaffirms its decision not to include the 1761-1842 MHz band segment in the reallocated spectrum.

As shown in Figure D-1, two band segments remain for consideration: 1755-1761 MHz (6 MHz) and 1842-1850 MHz (8 MHz). The Preliminary Report states that a guard band must exist around the 1761-1842 MHz band segment to provide adequate interference protection for both Federal satellite command and control and combat training systems; and PCS (or other adjacent-band users).[EN 5] The question remains as to how wide the guard band should be to protect Federal and non-Federal operations. Transmitter and receiver characteristics (power, antenna gain, emission spectrum, and receiver selectivity) as well as projected PCS transmitter and receiver characteristics will be used to estimate the guard band requirements around the 1761-1842 MHz band segment.

FIGURE D-1: 1710-1850 MHz Band Breakdown.

FIXED MICROWAVE SYSTEMS IN THE 1755-1850 MHZ BAND

Since fixed microwave systems currently operate in the 1710-1850 MHz band with SGLS uplink transmitters it is reasonable to characterize the impact of this existing radio service. From the Government Master File it can be found that in each 5 MHz band segment from 1755-1850 MHz there are an average 492 fixed assignments with typical parameters given in TABLE D-1.
   
============================================================================
TABLE D-1: Caracteristics of Fixed Microwave Systems in 1755-1850 MHz Band
============================================================================
  
  Transmitter Bandwidth   1-8 MHz
      Transmitter Power   3 Watts
           Antenna Gain   28 dBi
============================================================================           
 
Interference from Fixed Microwave Transmitters to Low-Orbiting SGLS Satellite Receivers In this analysis a 1.8 meter parabolic antenna with a mainbeam gain of 28 dBi and a beamwidth of 8 degrees will be used to represent the fixed microwave transmitter in the 1755-1850 MHz band. Since an omnidirectional antenna is assumed for the SGLS satellite receiver, coupling will depend on the mainbeam and sidelobe characteristics of the fixed microwave antenna.

If the fixed microwave transmitters are randomly distributed regarding geographic position as well as azimuth pointing angle, then the number of mainbeam couplings that can occur will be the number of emitters contained in the annular ring of the SGLS low-orbiting satellite footprint where it can be viewed at elevation angles between 0 and 4 degrees. The percent of the area that the annular ring occupies, of the entire footprint, times the number of fixed transmitters, will give the number of mainbeam couplings that can occur. The area of the annular ring and the area of the SGLS low-orbiting satellite footprint are calculated as follows:

Area of annulus = 2R^2(cos(Theta1)-cos(Theta))

A of footprint = 2R^2(cos(Theta))

where

Theta = 90-arcsin(R/(R+H)) (0 degree elevation)

Theta1 = 90-4-arcsin((R/(R+H))cos4) (4 degree elevation)

R is the radius of the earth, and H is the satellite altitude.

The ratio of the area of the annular ring and the satellite footprint is calculated as follows:

Area of annulus/Area of footprint= (cos(Theta1)-cos(Theta))/cos(Theta)

From the above calculation, two percent of the 492 transmitters can intersect the SGLS low-orbiting satellite with their mainbeam. Because of the random azimuth pointing angles, only

(8 degrees/360 degrees)(.02)(492) = .21

will be likely to do so. Therefore, the probability of intersecting the SGLS low-orbiting satellite receiver with a single fixed microwave transmitter antenna mainbeam is low; the probability of multiple intersections is very low. Consequently, for analysis purposes, a single mainbeam coupling will be considered.

In the mainbeam case the elevation angle is near zero degrees, and the slant range to the satellite (250 km orbit) is 1,979 km. For the remaining 491 fixed microwave transmitters, coupling will be in the sidelobe region of the fixed microwave antenna pattern. If the representative elevation angle to the satellite from these transmitters is 45 degrees, the slant range is 415 km. The total interference power density at the SGLS low-orbiting satellite receiver is calculated by

Io= SPD + GT + 10log(n) - LFS - GR
  
  where

   Io is the interference power density at the SGLS low-orbit satellite receiver (dBW/Hz);
   SPD is the fixed microwave power spectral density (dBW/Hz);
   GT is the fixed microwave transmitter antenna gain (dBi);
   n is the number of fixed microwave transmitters;
   LFS is the free space path loss (dB);
   GR is the SGLS receiver antenna gain (dBi). 

  
For a 5 MHz emission bandwidth, the spectral power density is -62.2 dBW/Hz. Using the parameters in TABLE D-1 and the previous calculations, the interference power density at the SGLS low-orbit satellite receiver from fixed microwave transmitters is

Io= -185 dBW/Hz

It should be noted that a Monte Carlo simulation of the interference to low-orbiting satellites in the 2025-2110 MHz band from fixed microwave emissions reaches a very similar estimate of the interference power density.[EN 6]

Interference from Fixed Microwave Transmitters to Geostationary SGLS Satellite Receivers Elevation angles to the SGLS geostationary satellites from fixed microwave transmitters range from 15 to 45 degrees. Using the sidelobe pattern for fixed microwave antennas, the gain in the direction of the SGLS geostationary satellite receiver for this range of elevation angles is

G(Theta)= 52-10log(D/lambda) - 25log(Theta)
  where 
   G(Theta) is the off-axis antenna gain (dBi);
   Theta is the fixed microwave elevation angle (degrees);
   D is the diameter of the fixed microwave antenna (m);
   Lambda is the wavelength (m). 
Using an antenna diameter of 1.8 meters and a frequency of 1755 MHz, the off-axis antenna gains for elevation angles of 15 and 45 degrees are:

G(15) = 12.3 dB
G(45) = .4 dB

The slant range to a geostationary SGLS satellite at elevation angles of 15 and 45 degrees is 40,277 km and 37,627 km respectively. These slant ranges correspond to a free space path loss of approximately 189 dB. For analysis purposes it is assumed that half of the 492 fixed microwave transmitters are at each extreme of elevation angle to the SGLS geostationary satellite. Using the equation stated earlier, the interference power density at the SGLS geostationay satellite receiver from fixed microwave transmitters is given below:

Io= -215 dBW/Hz

Impact to SGLS Satellite Receiver from Fixed Microwave Transmitters Since fixed microwave systems operated by the FPAs and certain safety-of-life stations will continue to operate indefinitely in the 1755-1850 MHz band segment, their contribution must be included in the total interference power density calculation for the SGLS satellite receivers. From the preceding discussion the interference levels from the existing fixed microwave transmitters are: -185 dBW/Hz (low-orbiting satellites) and -215 dBW/Hz (geostationary satellites). When interference from the proposed terrestrial mobile service are on this order, the total interference power density at the SGLS satellite receiver will be increased by 3 dB to take into account the existing interference from fixed microwave transmitters.[EN 7]

TERRESTRIAL MOBILE SERVICES

The mobile telecommunications service industry continues to change as technologies continue to evolve. Because of the volatility, it is difficult to predict what the industry will look like in 5, 10, or 15 years. Different proponents have different perspectives on the future of mobile services, and how the pieces will fit together is not clear. Among the fastest-growing segments of the mobile telecommunications industry are terrestrially-based radio systems serving mobile users in cars (mobile) and on foot (personal). Although clear service definitions and specifications have not yet been developed, the Future Public Land Mobile Telecommunications System (FPLMTS) is currently conceived as a terrestrially-based system located throughout a region to provide an array of voice, data, and video services to mobile users.[EN 8] These characteristics will also be true for Personal Communications Services (PCS), to be allocated in the 1850-1990 MHz band. Estimated characteristics for these terrestrially based mobile and personal stations are given in TABLE D-2.[EN 9]
====================================================================================
TABLE D-2: Estimated Parameters For Terrestrial Mobile And Personal Stations
====================================================================================

                            Base and Mobile Stations         Personal Stations
------------------------------------------------------------------------------------
                                                 Transmitter
------------------------------------------------------------------------------------
Transmitter e.i.r.p.         10 W base, 1 W mobile       3 mW indoor, 20 mW outdoor
Bandwidth per Channel               25 kHz                         50 kHz
Traffic Density                   582 E/km^2                     25000 E/km^2
Assumed Bandwidth                  140 MHz                         140MHz
Estimated e.i.r.p. Density     -104 dBW/m^2/Hz                -123 dBW/m^2/Hz
------------------------------------------------------------------------------------
                                                  Receiver
------------------------------------------------------------------------------------
  Interference Threshold                  -117 dBm indoor stations             
                                          -119 dBm outdoor stations
====================================================================================
The parameters shown in TABLE D-2 were taken from ITU-R Rec. 687-1. The e.i.r.p. densities given in TABLE D-2 represent a worst-case scenario insofar as they correspond to a mature system in an urban environment operating at its peak traffic load. The e.i.r.p densities for rural areas will be much less than those given in TABLE D-2. The e.i.r.p. densities are derived from the number of terminals per km^2 area and the power for each category of station (e.g., mobile or personal).

To facilitate sharing, an allocation of 10% of the total interference budget to external interference sources is used. ITU-R Rec. 687-1 specifies a level of -117 dBm for indoor personal stations and a level of -119 dBm for outdoor personal stations.[EN 10] These values are shown in TABLE D-2 and represent maximum permissible interference levels that can be received by personal stations without significantly degrading the quality of the service provided. ITU-R Rec. 687-1 did not specify an interference threshold for the base stations.

INTERFERENCE TO SGLS SATELLITE RECEIVERS FROM TERRESTRIAL MOBILE SERVICES

Interference to the SGLS satellite receiver will be assessed in terms of carrier-to-interference (C/I) ratio. The C/I ratio represents the number of dB by which the power level of the desired signal "C" at the input of the SGLS receiver exceeds the power level of the undesired signal "I" at the same point in the receiver. The C/I ratios calculated in this analysis will not include the effects of signal processing performed by the SGLS receivers.

SGLS Parameters Used in the Analysis

The nominal SGLS transmitter, receiver, and antenna characteristics used in this analysis are given in TABLE D-3.[EN 11]
  
=========================================================== 
TABLE D-3: Nominal SGLS Characteristics
===========================================================
       Earth Station Transmitter
-----------------------------------------------------------
   Frequency    1763.721 - 1839.795 MHz
Output Power    Fixed SGLS Stations: 2 - 7 kW
                Transportable SGLS Stations: 250W - 1 kW
   Bandwidth    4 MHz with subcarriers
Antenna Gain
  Mainbeam      41 dBi
  Sidelobe      23 dBi
-----------------------------------------------------------
       Satellite Receiver
-----------------------------------------------------------                            
 Selectivity
     -3 dB      3.9 MHz
    -20 dB      7.1 MHz
    -60 dB      14.2 MHz
Antenna Gain    0 dBi
===========================================================
The sidelobe antenna gain given in TABLE D-3 is calculated based on the procedures specified in the International Telecommunication Union (ITU) Radio Regulations Appendix 29 for an elevation angle of 3 degrees.

C/I Analysis for SGLS Low-Orbiting Satellite Receivers

The amount of interference received by a low-orbiting satellite is a function of the altitude of the satellite, the area over which the terrestrial mobile stations are deployed, their radiation characteristics, their population density and other factors.[EN 12] Ignoring the effects of atmospheric refraction, the total area on the Earth visible from a satellite is given by:
 
                                A0 = 2(re)^2 (Beta-1)/  and  Beta = 1+h/re 
  where
   re is the radius of the Earth (6378 km);
   h is the altitude of the satellite.
  
For example, the total area visible from a low-orbiting satellite at an altitude of 250 km is 9.6x106 km^2. The mobile and personal stations are assumed to be uniformly distributed over the field-of-view of the satellite. The amount of interference power received at the satellite due to stations within a spherical area bounded by 1 and 2 elevation angles is proportional to the e.i.r.p., station density, the spherical area, the transmitter antenna gain, the square of the range to the satellite, and the gain of the satellite receiving antenna.[EN 13] The ratio of the station distribution to the total visibility area is given by:
 
                  A/A0 = (Beta/(Beta-1))(cos(Theta2)-cos(Theta1)) and  Thetai = cos-1((1/Beta)cos(i))-i
 
The range to the satellite Rs is given by
  
                                   Rs= re(Beta)(sin(Thetai)/cos(i))
  
Using the above equations it was determined that approximately 14% of the total-visibility interference will be caused by terrestrial stations located between 0 and 5 degrees elevation angle and radiating isotropically (). The area of the spherical region bounded by elevation angles between 0 and 5 degrees is 44% of the total visibility area(A).[EN 14] These values will be used to calculate the aggregate interference power density.

The aggregate interference power density at the output of the satellite receiving antenna caused by the emissions from the terrestrial mobile and portable stations operating in the field-of-view of a low-orbiting satellite is given by [EN 15]

 
             Io = Rho + 10LogA + 10Log(Lambda^2/4) + GR - 10Log - 10Log(4) - 20LogRs - FDR - L 
        
  where
  
   Io is the total interference power density from a given spherical area (dBW/Hz);
  
   Rho is the aggregate e.i.r.p. density (dBW/m^2/Hz);
  
   A is the field of view within the range of elevation angles (0 to 5 degrees);
   
   Lanbda is the wavelength (m);
   
   GR is the antenna gain of the satellite receiving antenna (dBi);
   
     is the fraction of the total-visibility interference contributed by mobile and portable stations      
      operating within the range of elevation angles (e.g.,  0 to  5 degrees);
   
   Rs is the range to the satellite (km);
   
   FDR is the frequency dependent rejection (dB);
  
   L is the building penetration, shadow loss, and urban/rural loss (dB).
  
A document used in the development of ITU-R Rec. 687-1 specifies that building penetration loss, shadowing loss, the relative deployment of urban systems compared to suburban and rural systems, and the relative maturity of the systems will reduce the total interference power density by 20 to 40 dB.[EN 16] A conservative value of 20 dB will be used in this analysis.

The FDR value used in the calculation of the interference power density is the attenuation of an undesired signal power by the SGLS receiver because of on-tune and off-frequency rejection. The on-tune rejection occurs because of the limited bandwidth of a receiver with respect to the undesired terrestrial emission bandwidth. The off-frequency rejection is the rejection provided by detuning of the SGLS receiver with respect to the terrestrial transmitters. From the SGLS receiver selectivity given in TABLE D-3, a value of 23 dB corresponding to a 3.7 MHz frequency separation for the lower SGLS channel (1763.721 MHz) and approximately 40 dB corresponding to a 5 MHz frequency separation on the upper SGLS channel (1839.795 MHz) will be used in this analysis.

Using the parameters given above and a satellite altitude of 250 km, the aggregate interference power density resulting from personal and mobile terrestrial stations to a SGLS low-orbiting satellite receiver is given in TABLE D-4.

  
=================================================================
TABLE D-4: Aggregate Interference Power Density From Terrestrial
           Stations to SGLS Low-orbiting Satellite Receivers
=================================================================          
           
SGLS Channel    Mobile Stations         Personal Stations
                 Io (dBW/Hz)               Io (dBW/Hz)
------------------------------------------------------------------
   Lower           -171                       -190
   Upper           -188                       -207
==================================================================                               
It should be noted that the values of FDR used in the calculation of Io represents a worst-case scenario insofar that it locates all of the mobile and personal stations in the first adjacent channel (minimum frequency separation) from the SGLS receiver. In a more realistic scenario, these stations will be distributed across the entire band, which will result in further reduction of the interference levels at the SGLS receiver. The FDR is one of the parameters in the determination of Io that is not already determined and is significant in determining compatibility.

The carrier power density at the SGLS receiver is given by:

  
                   Co = PT + GT + GR - 10 Log(BW) - LFS
                               
where
   Co is the carrier power density at the SGLS receiver (dBW/Hz);
   PT is the SGLS earth station transmitter power (dBm);
   GT is the  SGLS earth station transmitter antenna gain (dBi);
   GR  is the SGLS satellite receiver antenna gain (dBi);
   BW is the SGLS earth station transmitter bandwidth (Hz);
   LFS is the free-space path loss (dB).
To compute the carrier power density at the SGLS receiver, a transmitter power of 2 kW will be used for fixed SGLS stations and a value of 250 W will be used for transportable SGLS stations. In addition, during approximately half of the time low-orbiting satellites are within range of the earth station at elevation angles of less than 10 degrees above the horizon. To compute the range, an elevation angle of between 0 and 5 degrees will be used, resulting in a range of 1720 km. This value will be used to compute the free-space path loss.

Using the equation above and the parameters in TABLE D-2, the carrier power density at the SGLS low-orbiting satellite receiver for fixed and transportable SGLS stations is given below:

  
                  Co = -155 dBW/Hz    (fixed SGLS stations)
  
                  Co = -165 dBW/Hz    (transportable SGLS stations)
The C/I ratios can now be evaluated for the fixed and transportable SGLS station receivers as follows:
  
                        C/I = Co - Io
The calculated C/I ratios for the upper and lower channels of fixed and transportable SGLS station receivers are given in TABLE D-5.
  
====================================================================================  
TABLE D-5: Calculated C/I Ratios for Fixed and Transportable SGLS Station Receivers
====================================================================================

                             Mobile Stations  Personal Stations
 SGLS Channel                   C/I (dB)          C/I (dB)
------------------------------------------------------------------------------------
   Lower
Fixed SGLS Station                16                35
Transportable SGLS Station         6                25
                               
   Upper
Fixed SGLS Station                33                52
Transportable SGLS Station        23                42
====================================================================================
 

C/I Analysis For SGLS Geostationary Satellite Receivers

As in the case of low-orbiting satellites the amount of interference received by a geostationary satellite receiver is a function of the altitude of the satellite, the area over which the terrestrial mobile stations are deployed, their radiation characteristics, the area visible by the satellite and the density of the mobile and portable stations. The total area on the Earth visible from a geostationary satellite excluding atmospheric effects is 2.2x108 km^2.

As stated earlier, the terrestrial mobile and personal stations are uniformly distributed over the field-of-view of the satellite. Using the previous equations, and a satellite altitude of 36,000 km, it was determined that approximately 0.57% of the total-visibility interference will be caused by terrestrial stations located between 0 and 1 degrees elevation angles and radiating isotropically. The area of the spherical region bounded by the elevation angles between 0 and 1 degrees is 2% of the total visibility area.[EN 17] The aggregate interference power density at the output of the SGLS geostationary satellite receiver caused by the emissions from mobile and personal stations is then given in TABLE D-6.

  
=================================================================
TABLE D-6: Aggregate Interference Power Density From Terrestrial
           Stations to SGLS Geostationary Satellite Receivers
=================================================================

SGLS Channel   Mobile Stations    Personal Stations
                 Io (dBW/Hz)         Io (dBW/Hz)
-----------------------------------------------------------------
 Lower              -184                -204
 Upper              -201                -221
=================================================================
Using the equation stated earlier and the parameters in TABLE D-3, the carrier power density at the SGLS geostationary satellite receiver for fixed and transportable SGLS stations is given below:
  
                         Co = -180 dBW/Hz    (fixed SGLS stations)
  
                         Co = -190 dBW/Hz    (transportable SGLS stations)
  
The calculated C/I ratios for the upper and lower channels of fixed and transportable SGLS stations are given in TABLE D-7.
  
=============================================================================
TABLE D-7: Calculated C/I Ratios For Fixed And Transportable SGLS Stations
=============================================================================

                                   Mobile Stations   Personal Stations
     SGLS Channel                      C/I (dB)           C/I (dB)
-----------------------------------------------------------------------------
  Lower
     Fixed SGLS Station                  4                 24
     Transportable SGLS Station         -6                 14

  Upper
     Fixed SGLS Station                 21                 41
     Transportable SGLS Station         11                 31
=============================================================================

Protection Margin For SGLS Satellite Receivers

In general the C/I threshold levels required for acceptable performance will vary with the modulation specifications. The input C/I thresholds are determined from the output performance requirements on the baseband information extracted (e.g., telephony pW0p, video SNR, digital BER), by including the receiver processing gain as a function of the modulation parameters. ITU-R Rec. 363-3 specifies a C/I protection ratio of 20 dB for spacecraft receivers. An overview of the calculated C/I values is given in TABLE D-8.
  
================================================== 
TABLE D-8: Overview of Calculated C/I Values
==================================================

                  Lower Channel    Upper Channel
--------------------------------------------------
     Low-Orbiting SGLS Satellites
--------------------------------------------------
        Fixed        16 dB             33 dB
Transportable         6 dB             23 dB
--------------------------------------------------
     Geostationary SGLS Satellites
--------------------------------------------------
        Fixed         4 dB             21 dB
Transportable        -6 dB             11 dB
==================================================
The C/I values shown in TABLE D-8 are based on a 5 MHz guard band. Given this guard band constraint, the calculated C/I values for the lower SGLS channel are below the established threshold. Hence, reallocation of the 1755-1760 MHz band segment is not possible without degrading the SGLS uplink transmissions.

The calculated C/I values for the upper SGLS channel for low-orbiting satellites exceed the threshold of 20 dB. However, for geostationary SGLS satellites, the calculated C/I for the upper channel of transportable SGLS earth stations is below the established threshold. Hence, reallocation of the 1845-1850 MHz band segment with a 5 MHz guard band would degrade uplink transmissions of transportable SGLS earth stations.

It should be noted that the actual C/I values may be greater than those shown in TABLE D-8 when factors such as receiver signal processing are taken into consideration.

Interference to SGLS Satellite Receivers from Aeronautical and Satellite Uplinks

Air Force indicates that aeronautical and satellite uplink transmissions in the 1845-1850 MHz band segment will have a high probability of causing interference to low-orbiting and geostationary SGLS satellite receivers. If such interference occurs during critical maneuvers, it could cause satellite contact losses, resulting in auto-track breaks, telemetry stream interference, and probable commanding errors.[EN 18] Air Force urges that aeronautical and Earth-to-space links should be avoided in the 1845-1850 MHz band segment.

INTERFERENCE TO TERRESTRIAL MOBILE SERVICE FROM SGLS EARTH STATIONS

The interference impact on terrestrial mobile and personal stations from SGLS earth stations will be assessed under interference-limited conditions.[EN 19] An interference-limited condition exists when the signal-to-noise ratio at the victim receiver is somewhat greater than the minimum required value, so that the interference level might be allowed to exceed the receiver noise. The maximum permissible interference levels that can be received by personal stations without significantly degrading the quality of the service provided are given in TABLE D-2.

The interference level at a mobile service receiver from SGLS earth station transmissions can be determined using the following equation:

 
                  I = PI + GI + GR - Lreq - FDR
  
  where
   I is the interference power at the terrestrial receiver (dBm);
   PI is the SGLS earth station transmitter power (dBm);
   GI is the SGLS earth station transmitter antenna gain in the direction of the terrestrial mobile receiver (dBi);
        GR is the antenna gain of the terrestrial mobile receiver (dBi);
   Lreq is the propagation loss required to preclude interference to the terrestrial receivers (dB);
   FDR is the frequency dependent rejection (dB).
  
To compute the interference level at a mobile service receiver, a transmitter power of 7 kW will be used for fixed SGLS earth stations and a value of 1 kW will be used for transportable SGLS earth stations. The term GI is a function of the antenna elevation of the earth station. For the purpose of this analysis GI will be calculated using both the mainbeam and sidelobe antenna gains shown in TABLE D-3. The mainbeam gain represents the worst-case condition and will result in the maximum required distance separation to preclude interference to mobile and personal terrestrial receivers. The sidelobe antenna gain was calculated using an earth station elevation angle of 3 degrees and procedures specified in Appendix 29 of the ITU Radio Regulations.[EN 20]

As stated earlier, the FDR term used in the interference calculation is the summation of two terms. The first term takes into account the rejection provided by specific detuning of the terrestrial receivers with respect to the SGLS earth station transmitters. As shown in TABLE D-3, the SGLS earth station uplink transmission bandwidth is 4 MHz with subcarriers.[EN 21] The subcarriers extend beyond 1845 MHz, and cannot be filtered without impacting vital satellite command and control functions. A value of 30 dB will be used in this analysis for the off-frequency rejection based on a 5 MHz guard band. The second term is the power attenuation provided by the terrestrial receiver to the SGLS earth station uplink transmission when the terrestrial receiver bandwidth is narrower than the SGLS uplink transmission bandwidth. Although the channel bandwidth is 4 MHz, the SGLS uplink transmission is not always spread over the entire channel. Air Force states that the worst-case for producing possible interference is a 1 kHz transmission modulating each of the subcarriers.[EN 22] Since a large portion of the signal energy is often concentrated within 1 to 2 kHz on one or more subcarriers, there is no attenuation resulting from the bandwidth mismatch.

Using the above equation and the parameters specified in TABLE D-3, the path loss required for terrestrial receiver protection is given in TABLE D-9.

  
=============================================================================== 
TABLE D-9: Required Path Loss to Preclude Interference to Terrestrial Stations
===============================================================================

                 Indoor Station   Outdoor Station
SGLS Station        Lreq(dB)          Lreq(dB)
-------------------------------------------------------------------------------
Fixed
  Mainbeam Gain       196               198
  Sidelobe Gain       178               180
Transportable
  Mainbeam Gain       188               190
  Sidelobe Gain       170               172
===============================================================================
The values shown in TABLE D-9 represent the path loss that is required to protect the indoor and outdoor personal stations from interference resulting from fixed and transportable SGLS earth station transmissions. In order to determine the required distance separation, the Egli propagation model for ground-to-ground propagation shown below will be used.[EN 23]
  
             Lreq = 48 + 20 LogF + 40LogDsep + (10-10Logh1) + (10-10Logh2)
  where
   Dsep is the required distance separation (km);
   h1 is the height of the personal or mobile receiver antenna (m);
   h2 is the height of the SGLS earth station transmitter antenna (m);
   F is the frequency (MHz).
  
Antenna heights of 1 meter (terrestrial) and 15 meters (SGLS earth station) will be used to determine the required distance separation. Using the above equation, the required distance separations necessary to preclude interference between SGLS earth stations and terrestrial receivers are given in TABLE D-10.
  
============================================================================= 
TABLE D-10: Required Distance Separations to Preclude Interference Between
            SGLS Earth Stations And Terrestrial Receivers
=============================================================================

                   Indoor Station    Outdoor Station
SGLS Station          Dsep (km)         Dsep (km)
-----------------------------------------------------------------------------
Fixed
   Mainbeam Gain         73                 82
   Sidelobe Gain         26                 29
Transportable
   Mainbeam Gain         46                 52
   Sidelobe Gain         16                 18
=============================================================================
Provided that the calculated distance separations given in TABLE D-10 can be maintained, the impact on terrestrial stations from fixed SGLS earth station transmitters is expected to be manageable. However, the transportable SGLS earth stations present a more difficult problem, since their exact locations are not always known, hence making coordination difficult.

Interference to Aeronautical and Satellite Receivers from SGLS Earth Stations

Air Force indicates that the 1845-1850 MHz band segment may be authorized for either aeronautical or satellite operations. As a result, aeronautical and satellite receivers may experience interference when operating within the mainbeam of the SGLS earth station uplink transmitter. Air Force believes that the lack of non-Federal receiver standards coupled with the high-power transmissions of the adjacent band SGLS earth stations would most likely cause numerous interference problems to aeronautical and satellite receivers.[EN 24] Therefore, Air Force urges that aeronautical and space-to-Earth links should be avoided in the 1845-1850 MHz band segment.

INTERFERENCE TO ACTS AIRBORNE RECEIVERS FROM MOBILE SERVICE STATIONS

This section assesses aggregate interference from terrestrial mobile and personal stations into the ACTS receiver. The personal and mobile stations are assumed to be uniformly distributed over the earth's surface, and have the same emission levels and frequency. The aircraft is assumed to have an isotropic antenna pattern (unit gain) over the visibility region determined by the aircraft altitude. The aggregate interference is derived by modeling the emitter distribution and deriving their power-sum level into the victim receiver under free-space propagation conditions.

The ACTS airborne receivers are most susceptible to interference in the Frequency Shift Key (FSK) demodulation stage. This FSK detection, which is accomplished by mark and space filters, uses a selectable FSK data rate of 62 kHz or 198 kHz. It is assumed that the mark and space filter bandwidths are equal to the data rate.[EN 25]

ACTS Interference Threshold

The acceptable level of noise-like interference signals at the ACTS receiver is defined by the signal-to-interference (S/I) ratio threshold of 15 dB in the detection filter bandwidth. This threshold is sufficient to ensure an acceptable 10 E-5 bit error probability.[EN 26]

ACTS Parameters Used in the Analysis

The nominal ACTS transmitter, receiver, and antenna parameters used in this analysis are given in TABLE D-11.[EN 27]
  
=========================================
TABLE D-11: Nominal ACTS Characteristics
=========================================

        ACTS Ground Station Transmitter
-----------------------------------------
Frequency        1840 MHz
Output Power        5 W
Bandwidth         600 kHz
Antenna Gain        0 dBi
-----------------------------------------                            
       ACTS Airborne Station Receiver
-----------------------------------------
 Selectivity
       -3 dB     1.2 MHz
      -60 dB      12 MHz
Antenna Gain       0 dBi
=========================================
Aggregate Interference at ACTS Aircraft Receivers The net interference power at the ACTS receiver can be determined using the following equation:
  
                             I = PR + GR - FDR - L
  
  where
   I is the interference power at the ACTS receiver (dBm);
   PR is the aggregate interference power into the receiver antenna under free-space propagation  (dBm);
   GR is the ACTS airborne receiver antenna gain (dBi);
   FDR is the frequency dependent rejection (dB);
   L is the building penetration, shadow loss, and urban/rural field-of-view loss (dB).
  
The aggregate interference power PR can be derived from a computer program (PDOME), developed by NTIA for this purpose.[EN 28] PDOME computes the power-sum aggregate interference at an airborne receiver by modeling the emitter distribution and integrating their collective effect under free-space propagation. The user specifies the aircraft altitude, the emitter density, the emission level and the emission frequency. Using these values, PDOME determines the number of emitters in the field-of-view of the aircraft and computes the aggregate power-sum into the aircraft receiver.

Using PDOME and the parameters for the mobile and personal stations given in TABLE D-2, the aggregate received power levels into an aircraft receiver at 30,000 feet were determined to be

 
                                      PR = -16.3 dBm (mobile stations)
  
                                      PR = -27.3 dBm (personal stations)
  
The FDR value used in the calculation of the interference power is the attenuation of an undesired signal power by the ACTS receiver because of off-frequency rejection. The off-frequency rejection is the rejection provided by detuning of the ACTS receiver with respect to the terrestrial transmitters. A value of 62 dB corresponding to a 7 MHz frequency separation for the lower ACTS channel (1768 MHz) and 56 dB corresponding to a 5 MHz frequency separation on the upper ACTS channel (1840 MHz) will be used in this analysis. The other values used in the calculation of I were defined earlier.

Using the above results, the net interference power at the ACTS receiver from the terrestrial station emitters is given in TABLE D-12.

  
==================================================================================
TABLE D-12: Net Interference Power at The ACTS Receiver From Terrestrial Stations
==================================================================================

                  Mobile Station   Personal Station 
 ACTS Channel        I (dB)           I (dB)
----------------------------------------------------------------------------------
       Lower          -98             -109
       Upper          -92             -103
==================================================================================
The values of FDR used in the calculation of I represents a worst-case scenario insofar that it locates all of the mobile and personal stations in the first adjacent channel (minimum frequency separation) from the ACTS receiver. In a more realistic scenario, the terrestrial stations will be distributed across the entire band, which will result in further reduction of interference levels at the ACTS receiver.

The minimum desired signal level in the detection filter of the ACTS receiver is given by:

 
                                      S = PT + GT + GR - LFS
  
  where
   S is the minimum desired signal in the detection filter of the ACTS receiver (dBm);
   PT is the ACTS ground station transmitter power (dBm);
   GT is the ACTS ground station transmitter antenna gain (dBi);
   GR is the ACTS airborne station receiver antenna gain (dBi);
   LFS is the free-space propagation loss between the ACTS ground and airborne stations at a 
   maximum altitude of 30,000 feet (dB).
  
Using the equation above, the minimum desired signal level in the detection filter of the ACTS receiver is given below:
 
                                            S = -80 dBm
  
The S/I ratios can now be evaluated for the personal and mobile terrestrial stations as follows:
                                              S/I = S - I
The calculated S/I ratios for the lower and upper channels of the ACTS receiver are given in TABLE D-13.
 
======================================================
TABLE D-13: Calculated S/I Ratios for ACTS Receivers
======================================================

               Mobile Station   Personal Station
ACTS Channel     S/I (dB)          S/I (dB)
------------------------------------------------------
       Lower      18                 29
       Upper      12                 23
------------------------------------------------------
The calculated S/I ratios for the lower ACTS receiver channels exceed the protection threshold. However, the calculated S/I for the upper channel is below the protection threshold of 15 dB. Hence, reallocation of the 1845-1850 MHz band segment will degrade the ACT uplink transmission.

INTERFERENCE TO TERRESTRIAL STATIONS FROM ACTS GROUND STATION TRANSMITTERS

As stated earlier it will be assumed that the personal and mobile systems are interference-limited. To facilitate sharing, an allocation of 10% of the total interference budget to external interference sources is used. ITU-R Rec. 687-1 specifies a level of -117 dBm for indoor personal stations and -119 dBm for outdoor personal stations. These values represent maximum permissible interference power levels that can be received by personal stations without significantly degrading the quality of the service provided.

The interference power at a victim receiver can be determined using the following equation:

  
                                      I = PI + GI + GR - Lreq - FDR
  
  where
   I is the interference power at the terrestrial receiver (dBm);
   PI is the ACTS ground station transmitter power (dBm);
   GI is the ACTS ground station transmitter antenna gain in the direction of the terrestrial
     receiver (dBi);
   GR is the antenna gain of the terrestrial receiver (dBi);
   Lreq is the propagation loss required to preclude interference to the terrestrial receivers (dB);
   FDR is the frequency dependent rejection (dB).
  
As stated earlier, the FDR term used in the interference calculation is the summation of two components. The first term takes into account the rejection provided by specific detuning of the terrestrial receivers with respect to the ACTS ground station transmitters. A conservative value of 50 dB will be used in this analysis, based on the assumption that the adjacent channel selectivity characteristics of the mobile and portable receivers will be similar to the current Federal land mobile receivers.[EN 29] The second term is the power attenuation provided by the terrestrial receiver to the ACTS ground station transmitter signal when the terrestrial receiver bandwidth is narrower than the ACTS emission bandwidth. As shown in TABLE D-11, the ACTS ground station transmitter bandwidth is 600 kHz. The bandwidth of terrestrial personal stations is 50 kHz as given in TABLE D-2. This bandwidth mismatch between the terrestrial receivers and the ACTS uplink transmitter will reduce the interfering signal by an additional 11 dB.

Using the above parameters, the required path loss to preclude interference can be determined and is given below:

  
                  Lreq= 93 dB         (indoor personal stations)
  
                  Lreq = 95 dB        (outdoor personal stations)
  
The values shown above represent the path loss required to protect the indoor and outdoor personal stations from the interference resulting from ACTS ground station transmitters. As stated earlier, the Egli propagation model was used to determine that the required distance separation to preclude interference is less than 1 km. Provided that the calculated distance separation can be maintained, the impact on terrestrial mobile and personal stations from ACTS ground station transmitters is expected to be manageable.

CONCLUSIONS

Based on a 5 MHz guard band, the calculated C/I values for the lower SGLS channel are below the established threshold. Therefore, reallocation of the 1755-1760 MHz band segment for terrestrial mobile and personal stations is not possible without degradation of the SGLS uplink transmission.

Reallocation of the 1845-1850 MHz band segment for terrestrial mobile and personal stations with a 5 MHz guard band will degrade uplink transmissions of transportable SGLS earth stations.

A maximum distance separation of 82 km between fixed SGLS earth stations and terrestrial mobile personal stations is needed to preclude interference. Provided the calculated distance separations can be maintained, the impact on terrestrial mobile and personal stations from fixed SGLS earth stations is expected to be manageable.

A maximum distance separation of 52 km between transportable SGLS earth stations and terrestrial mobile and personal stations is needed to preclude interference. However, because of the highly mobile nature of the proposed terrestrial service and the unknown location of the transportable SGLS earth stations, these distance separartions may be difficult to maintain.

Reallocation of the 1845-1850 MHz band segment for terrestrial mobile and personal stations with a 5 MHz guard band will degrade uplink ACTS transmissions.

To reduce the impact to and from Federal satellite command and control and combat training systems operating in the 1761-1842 MHz band segment, reallocation of the 1845-1850 MHz band segment for aeronautical or satellite links must be avoided.

  
=================================================================================================
ENDNOTES FOR APPENDIX D

      
       Requests for copies of references from Federal departments and agencies should
       be referred to the originating organization. Parts of the reference material
       may be exempt from public release.
 
 

 


1. REPORT FROM THE FEDERAL COMMUNICATIONS COMM'N, to Ronald H. Brown, Secretary, U.S. Dep't of Commerce, 
   Regarding the NTIA PRELIMINARY REPORT, FCC 94-213, at 27 (Aug. 9, 1994) [hereinafter FCC REPORT]. 

2. NAT'L TELECOMMUNICATIONS AND INFO. ADMIN. (NTIA), U.S. DEP'T OF COMMERCE, SPECIAL PUBLICATION 94-27, 
   PRELIMINARY REPORT, at 4-30, (Feb. 1994) [hereinafter NTIA PRELIMINARY REPORT and all comments cited refer 
   to this report, unless otherwise stated].

3. NTIA, U.S. Dep't of Commerce, NTIA Report 92-285, "Federal Spectrum Usage of the 1710-1850 and 2200-2290 MHz
   Bands", at 5-10 (March 1992).

4. NTIA PRELIMINARY REPORT, supra note 2, at 2-27.

5. Id. at 4-30.

6. Int'l Telecommunication Union Radiocommunication Sector (ITU-R) Document, U.S. Working Party (USWP) 7B/4, 
   at 1 (Aug. 12, 1994).

7. Memorandum from the U.S. Dep't of the Air Force, to Chairman of IRAC, Subject: Comments on Draft Final Reallocation 
   Report Executive Summary and App. D, at 2 (Jan. 6, 1995).  

8. The 1992 World Administrative Radio Conference: Technology and Policy Implications, at 77 (May 1993).

9. Int'l Radio Consultative Comm. (CCIR) Recommendation 687-1, "Future Public Land Mobile
   Telecommunication System (FPLMTS), Annex 1, at 16 (Sept. 22, 1992).

10. Id.

11. NTIA, U.S. Dep't of Commerce, NTIA Report 80-47, "Spectrum Resource Assessment in the 1710-1850 MHz Band", at 55 
   (Sept. 1980); Spectrum Planning Subcommittee (SPS) Submission SPS-9082, Loral Model CXS-800 SGLS Transponder; Int'l 
   Telecommunications Union Radio Regulations, Appendix 29, Annex III, at AP29-14 (1990 Edition).  

12. Document U.S. Study Group (USSG) 8A/39 (Rev. 1), "Criteria for Sharing Between the Mobile Services and Space Research, 
    Space Operations and Earth Exploriation-Satellite Service Space Stations in the
    2025-2110 and 2200-2290 MHz Bands", at 6 (Nov. 12, 1991) [hereinafter USSG Sharing Study].  

13. Id. at 7.

14. Id. at 9.

15. Id. at 11.

16. Id. at 12-13.

17. Id. at 16.

18. B.B. Pottorff and N.A. Wilett, Allied Signal Bendix Field Engineering Corp.,
    "Analysis of the Air Force Satellite Control Network Spectrum Usage in the
    1760-1850 MHz and 2200-2300 MHz Bands", at 31 (June 11, 1991).

19. CCIR, supra note 9, at 17.

20. Id. at 8.

21. Air Force Memorandum, supra note 7, at 2.

22. Id. at 5.

23. W.G. Duff, Don White Consultants, Inc., MOBILE COMMUNICATIONS, at 24 (1976).

24. Memorandum from the Dep't of the Air Force, to Chairman of IRAC, Subject: Air Force Comments on 
    Title VI of the Omnibus Budget Reconciliation Act (OBRA) of 1993, at 2-3 (Jan. 5, 1995).

25. Electromagnetic Compatibility Analysis Center, "Electromagnetic Compatibility (EMC) of the Proposed
    Fallon NAS TACTS Expansion", ECAC-CR-87-098, at 3-10 (Oct. 1987); Electromagnetic Compatibility 
    Analysis Center, "EMC Analyis of the Proposed Cherry Point MCAS TACTS and the Dare County Expansion",
    ECAC-CR-86-066, at 3-8 (June 1986); Electromagnetic Compatibility Center, "EMC of Air Combat Maneuvering 
    Instrumentation (ACMI) System at Nellis Range", ESD-TR-75-020, at 48 (Oct. 1975).

26. EMC Analysis of the Proposed Fallon NAS TACTS Expansion, supra note 25, at 3-8.

27. Id.; Spectrum Planning Subcommittee (SPS) Submission SPS-10045, Technical Data Information
    of the TACTS ACMI Aircraft Instrumentation 
    Subsystem (AIS) Pods, at 2 (Aug. 31, 1994).

28. NTIA, U.S. Dep't of Commerce, NTIA-TM-89-139, "Single and Aggregate Emission Level
    Models for Interference Analysis", at 4-1 (March 1989).

29. NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management,
    at Sec. 5.6, 5-27-5-28 (June 6, 1994).


Return to Report Table of Contents.

Proceed to Appendix E, Federal Government Fixed Microwave Stations in the 1710 - 1755 MHz Band Exempted from Reallocation.