Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 3775

e) for areas/regions of frequency congestion, a precise determination of separation may be required using the appropriate criteria. 7.2.1.1.2 The nominal link budget for VDB is shown in Table D-3. The figures in the table assume a receiver height of 3 000 m (10 000 ft) MSL and a transmit antenna designed to suppress ground illumination in order to limit the fading losses to a maximum of 10 dB at coverage edge. In the case of GBAS/E equipment, the 10 dB also includes any effects of signal loss due to interference between the horizontal and vertical components. 7.2.1.2 FM immunity 7.2.1.2.1 Once a candidate frequency is identified for which the GBAS and VOR separation criteria are satisfied, compatibility with FM transmissions must be determined. This is to be accomplished using the methodology applied when determining FM compatibility with VOR. If FM broadcast violates this criterion, an alternative candidate frequency has to be considered. Table D-2. Assumed D/U required signal ratios to protect VOR from GBAS VDB Frequency offset [D/U]required ratio to protect VOR receivers (dB) Co-channel | fVOR – fVDB | = 25 kHz | fVOR – fVDB | = 50 kHz –34 | fVOR – fVDB | = 75 kHz –46 | fVOR – fVDB | = 100 kHz –65 Table D-3. Nominal VDB link budget VDB link elements Vertical component link budget at coverage edge Horizontal component link budget at coverage edge Required receiver sensitivity (dBm) –87 –87 Maximum aircraft implementation loss (dB) Power level after aircraft antenna (dBm) –76 –72 Operating margin (dB) Fade margin (dB) Free space path loss (dB) at 43 km (23 NM) Nominal effective radiated power (dBm) 23/11/06 ATT D-18 2007/70/II. szám Attac ment Annex 10 — Aeronautical Communications 7.2.1.2.2 The desensitization is not applied for FM carriers above 107.7 MHz and VDB channels at 108.050 MHz because the off-channel component of such high-level emissions from FM stations above 107.7 MHz will interfere with GBAS VDB operations on 108.025 and 108.050 MHz, hence those assignments will be precluded except for special assignments in geographic areas where the number of FM broadcast stations in operation is small and would unlikely generate interference in the VDB receiver. 7.2.1.2.3 The FM intermodulation immunity requirements are not applied to a VDB channel operating below 108.1 MHz, hence assignments below 108.1 MHz will be precluded except for special assignments in geographic areas where the number of FM broadcast stations in operation is small and would unlikely generate intermodulation products in the VDB receiver. 7.2.1.3 Geographic separation methodologies 7.2.1.3.1 The methodologies below may be used to determine the required GBAS-to-GBAS and GBAS-to-VOR geographical separation. They rely on preserving the minimum desired-to-undesired signal ratio. [D/U]required is defined as the signal ratio intended to protect the desired signal from co-channel or adjacent channel interference from an undesired transmission. [D/U]required values required for protection of a GBAS receiver from undesired GBAS or VOR signals are defined in Appendix B, 3.6.8.2.2.5 and 3.6.8.2.2.6. [D/U]required values intended for protection of a VOR receiver from GBAS VDB transmissions as shown in Table D-2 are not defined in SARPs and represent the assumed values based on test results. 7.2.1.3.2 Geographic separation is constrained by preserving [D/U]required at the edge of the desired signal coverage where the desired signal power is derived from the minimum field strength requirements in Chapter 3. This desired signal level, converted to dBm, is denoted PD,min. The allowed signal power of the undesired signal (PU,allowed) is: PUallowed(dBm) = (PD,min (dBm) – [D/U]required (dB)) The undesired signal power PU converted to dBm is: PU(dBm) = (TxU (dBm) – L (dB)) where TxU is the effective radiated power of the undesired transmitter; and L is the transmission loss of the undesired transmitter, including free-space path loss, atmospheric and ground effects. This loss depends upon the distance between the undesired transmitter and the edge of the desired signal coverage. To ensure D/Urequired is satisfied, Pu  DUallowed. The constraint for assigning a channel is therefore: L(dB)  ([D/U]required (dB) + TxU(dBm) – PD,min (dBm)) 7.2.1.3.3 The transmission loss can be obtained from standard propagation models published in ITU-R Recommendation P.528-2 or from free-space attenuation until the radio horizon and then a constant 0.5 dB/NM attenuation factor. These two methodologies result in slightly different geographical separation for co-channel and first adjacent channels, and identical separation as soon as the second adjacent channel is considered. The free-space propagation approximation is applied in this guidance material. 7.2.1.4 Example of GBAS/GBAS geographical separation criteria 7.2.1.4.1 For GBAS VDB co-channel transmissions assigned to the same time slot, the parameters for horizontal polarization are: ATT D-19 23/11/06 2007/70/II. szám Annex 10 — Aeronautical Communications Volume I D/U = 26 dB (Appendix B, 3.6.8.2.2.5.1); PD,min = –72 dBm (equivalent to 215 microvolts per metre, Chapter 3, 3.7.3.5.4.4); and TxU = 47 dBm (example link budget, Table D-3); so L  (47 + 26 – (–72)) = 145 dB. 7.2.1.4.2 The geographic separation for co-channel, co-slot GBAS VDB assignments is obtained by determining the distance at which the transmission loss equals 145 dB for receiver altitude of 3 000 m (10 000 ft) above that of the GBAS VDB transmitter antenna. This distance is 318 km (172 NM) using the free-space attenuation approximation and assuming a negligible transmitter antenna height. The minimum required geographical separation can then be determined by adding this distance to the nominal distance between the edge of coverage and the GBAS transmitter 43 km (23 NM). This results in a co-channel, co-slot reuse distance of 361 km (195 NM). 7.2.1.5 Guidelines on GBAS/GBAS geographical separation criteria. Using the methodology described above, typical geographic separation criteria can be defined for GBAS to GBAS and GBAS to VOR. The resulting GBAS/GBAS minimum required geographical separation criteria are summarized in Table D-4. Note.— Geographical separation criteria between the GBAS transmitters providing the GBAS positioning service are under development. A conservative value corresponding to the radiohorizon may be used as an interim value for separation between co-frequency, ad acent time slot transmitters to ensure time slots do not overlap. 7.2.1.6 Guidelines on GBAS/VOR geographical separation criteria. The GBAS/VOR minimum geographical separation criteria are summarized in Table D-5 based upon the same methodology and the nominal VOR coverage volumes in Attachment C. Note 1.— hen determining the geographical separation between VOR and GBAS, VOR as the desired signal is generally the constraining case due to the greater protected altitude of the VOR coverage region. Note 2.— Reduced geographical separation requirements can be obtained using standard propagation models defined in IT -R Recommendation P.52 -2. Table D-4. Typical GBAS/GBAS frequency assignment criteria Channel of undesired VDB in the same time slots Path loss (dB) Minimum required geographical separation for TxU = 47 dBm and PD,min = –72 dBm in km (NM) Cochannel 361 (195) 1st adjacent channel (±25 kHz) 67 (36) 2nd adjacent channel (±50 kHz) 44 (24) 3rd adjacent channel (±75 kHz) No restriction 4th adjacent channel (±100 kHz) No restriction Note.— No geographic transmitter restrictions are expected between co-frequency, ad acent time slots provided the undesired V B transmitting antenna is located at least 200 m from areas where the desired signal is at minimum field strength. 23/11/06 ATT D-20 2007/70/II. szám Attac ment Annex 10 — Aeronautical Communications Table D-5. Minimum required geographical separation for a VOR coverage (12 000 m (40 000 ft) level) VOR coverage radius Channel of undesired GBAS VDB Path loss (dB) 342 km (185 NM) 300 km (162 NM) 167 km (90 NM) Co-channel 892 km (481 NM) 850 km (458 NM) 717 km (386 NM) | fDesired – fUndesired | = 25 kHz 774 km (418 NM) 732 km (395 NM) 599 km (323 NM) | fDesired – fUndesired | = 50 kHz 351 km (189 NM) 309 km (166 NM) 176 km (94 NM) | fDesired – fUndesired | = 75 kHz 344 km (186 NM) 302 km (163 NM) 169 km (91 NM) | fDesired – fUndesired | = 100 kHz No restriction No restriction No restriction Note.— Calculations are based on reference frequency of 112 M z and assume GBAS Tx 47 dBm and VOR P ,min 79 dBm. 7.2.2 The geographical separation criteria for GBAS/ILS and GBAS/VHF communications are under development. 7.2.3 Compatibility with ILS. Until compatibility criteria are developed for GBAS VDB and ILS, VDB cannot be assigned to channels below 112.025 MHz. If there is an ILS with a high assigned frequency at the same airport as a VDB with a frequency near 112 MHz, it is necessary to consider ILS and VDB compatibility. Considerations for assignment of VDB channels include the frequency separation between the ILS and the VDB, the distance separation between the ILS coverage area and the VDB, the VDB and ILS field strengths, and the VDB and ILS sensitivity. For GBAS equipment with transmitter power of up to 150 W (GBAS/E, 100 W for horizontal component and 50 W for vertical component) or 100 W (GBAS/H), the 16th channel (and beyond) will be below –106 dBm at a distance of 200 m from the VDB transmitter, including allowing for a +5 dB positive reflection. This –106 dBm figure assumes a –86 dBm localizer signal at the ILS receiver input and a minimum 20 dB signal-to-noise ratio. 7.2.4 Compatibility with V F communications. For GBAS VDB assignments above 116.400 MHz, it is necessary to consider VHF communications and GBAS VDB compatibility. Considerations for assignment of these VDB channels include the frequency separation between the VHF communication and the VDB, the distance separation between the transmitters and coverage areas, the field strengths, the polarization of the VDB signal, and the VDB and VHF sensitivity. Both aircraft and ground VHF communication equipment are to be considered. For GBAS/E equipment with a transmitter maximum power of up to 150 W (100 W for horizontal component and 50 W for vertical component), the 64th channel (and beyond) will be below –120 dBm at a distance of 200 m from the VDB transmitter including allowing for a +5 dB positive reflection. For GBAS/H equipment with a transmitter maximum power of 100 W, the 32nd channel (and beyond) will be below –120 dBm at a distance of 200 m from the VDB transmitter including allowing for a +5 dB positive reflection, and a 10 dB polarization isolation. It must be noted that due to differences in the VDB and VDL transmitter masks, separate analysis must be performed to ensure VDL does not interfere with the VDB. 7.2.5 For a GBAS ground subsystem that only transmits a horizontally-polarized signal, the requirement to achieve the power associated with the minimum sensitivity is directly satisfied through the field strength requirement. For a GBAS ground subsystem that transmits an elliptically-polarized component, the ideal phase offset between HPOL and VPOL components is 90 degrees. In order to ensure that an appropriate received power is maintained throughout the GBAS coverage volume during normal aircraft manoeuvres, transmitting equipment should be designed to radiate HPOL and VPOL signal components with an RF phase offset of 90 degrees. This phase offset should be consistent over time and environmental conditions. Deviations from the nominal 90 degrees must be accounted for in the system design and link budget, so that any fading due to polarization loss does not jeopardize the minimum receiver sensitivity. System qualification and flight inspection procedures will take into account an allowable variation in phase offset consistent with maintaining the appropriate signal level throughout the GBAS coverage volume. One method of ensuring both horizontal and vertical field strength is to use a single VDB antenna that transmits an elliptically-polarized signal, and flight inspect the effective field strength of the vertical and horizontal signals in the coverage volume. ATT D-21 23/11/06 2007/70/II. szám Annex 10 — Aeronautical Communications Volume I 7.3 Coverage 7.3.1 The GBAS coverage to support approach services is depicted in Figure D-4. When the additional ephemeris error position bound parameters are broadcast, differential corrections may only be used within the Maximum Use Distance (Dmax) defined in the Type 2 message. Where practical, it is operationally advantageous to provide valid guidance along the visual segment of an approach. 7.3.2 The coverage required to support the GBAS positioning service is dependent upon the specific operations intended. The optimal coverage for this service is intended to be omnidirectional in order to support operations using the GBAS positioning service that are performed outside of the precision approach coverage volume. Each State is responsible for defining a service area for the GBAS positioning service and ensuring that the requirements of Chapter 3, 3.7.2.4 are satisfied. When making this determination, the characteristics of the fault-free GNSS receiver should be considered, including the reversion to ABAS-based integrity in the event of loss of GBAS positioning service. 7.3.3 The limit on the use of the GBAS positioning service information is given by the Maximum Use Distance (Dmax), which defines the range within which the required integrity is assured and differential corrections can be used for either the positioning service or precision approach. Dmax however does not delineate the coverage area where field strength requirements specified in Chapter 3, 3.7.3.5.4.4 are met nor matches this area. Accordingly, operations based on the GBAS positioning service can be predicated only in the coverage area(s) (where the field strength requirements are satisfied) within the Dmax range. 7.3.4 As the desired coverage area of a GBAS positioning service may be greater than that which can be provided by a single GBAS broadcast station, a network of GBAS broadcast stations can be used to provide the coverage. These stations can broadcast on a single frequency and use different time slots (8 available) in neighbouring stations to avoid interference or they can broadcast on different frequencies. Figure D-4A details how the use of different time slots will allow a single frequency to be used without interference subject to guard time considerations noted under Table B-59. For a network based on different VHF frequencies, guidance material in 7.17 should be considered. 7.4 Data structure A bit scrambler/descrambler is shown in Figure D-5. Note.— Additional information on the data structure of the V F data broadcast is given in RTCA/ O-246B, GNSS Based Precision Approach Local Area Augmentation System (LAAS)—Signal-in-Space Interface Control Document (ICD). 7.5 Integrity 7.5.1 Different levels of integrity are specified for precision approach operations and operations based on the GBAS positioning service. The signal-in-space integrity risk for Category I is 2 × 10-7 per approach. GBAS ground subsystems that are also intended to support other operations through the use of the GBAS positioning service have to also meet the signal-inspace integrity risk requirement specified for terminal area operations, which is 1 × 10-7/hour (Chapter 3, Table 3.7.2.4-1). Therefore additional measures are necessary to support these more stringent requirements for positioning service. The signalin-space integrity risk is allocated between the ground subsystem integrity risk and the protection level integrity risk. The ground subsystem integrity risk allocation covers failures in the ground subsystem as well as core constellation and SBAS failures such as signal quality failures and ephemeris failures. The protection level integrity risk allocation covers rare faultfree performance risks and the case of failures in one of the reference receiver measurements. In both cases the protection level equations ensure that the effects of the satellite geometry used by the aircraft receiver are taken into account. This is described in more detail in the following paragraphs. 7.5.2 The GBAS ground subsystem defines a corrected pseudo-range error uncertainty for the error relative to the GBAS reference point (ıpr_gnd) and the errors resulting from vertical (ıtropo) and horizontal (ıiono) spatial decorrelation. These 23/11/06 ATT D-22 2007/70/II. szám Attac ment Annex 10 — Aeronautical Communications uncertainties are modelled by the variances of zero-mean, normal distributions which describe these errors for each ranging source. 7.5.3 The individual error uncertainties described above are used by the receiver to compute an error model of the navigation solution. This is done by projecting the pseudo-range error models to the position domain. General methods for determining that the model variance is adequate to guarantee the protection level integrity risk are described in Section 14. The lateral protection level (LPL) provides a bound on the lateral position error with a probability derived from the integrity requirement. Similarly, the vertical protection level (VPL) provides a bound on the vertical position. For Category I precision approach and APV, if the computed LPL exceeds the lateral alert limit (LAL) or the VPL exceeds the vertical alert limit (VAL), integrity is not adequate to support the operation. For the positioning service the alert limits are not defined in the standards, with only the horizontal protection level and ephemeris error position bounds required to be computed and applied. The alert limits will be determined based on the operation being conducted. The aircraft will apply the computed protection level and ephemeris bounds by verifying they are smaller than the alert limits. Two protection levels are defined, one to address the condition when all reference receivers are fault-free (H0 – Normal Measurement Conditions), and one to address the condition when one of the reference receivers contains failed measurements (H1 – Faulted Measurement Conditions). Additionally an ephemeris error position bound provides a bound on the position error due to failures in ranging source ephemeris. For Category I precision approach and APV, a lateral error bound (LEB) and a vertical error bound (VEB) are defined. For the positioning service a horizontal ephemeris error bound (HEB) is defined. 7.5.4 Ground system contribution to corrected pseudo-range error (ıpr gnd). Error sources that contribute to this error include receiver noise, multipath, and errors in the calibration of the antenna phase centre. Receiver noise has a zero-mean, normally distributed error, while the multipath and antenna phase centre calibration can result in a small mean error. 7.5.5 Residual tropospheric errors. Tropospheric parameters are broadcast in Type 2 messages to model the effects of the troposphere, when the aircraft is at a different height than the GBAS reference point. This error can be well-characterized by a zero-mean, normal distribution. 7.5.6 Residual ionospheric errors. An ionospheric parameter is broadcast in Type 2 messages to model the effects of the ionosphere between the GBAS reference point and the aircraft. This error can be well-characterized by a zero-mean, normal distribution. 7.5.7 Aircraft receiver contribution to corrected pseudo-range error. The receiver contribution is bounded as described in Section 14. The maximum contribution, used for analysis by the GBAS provider, can be taken from the accuracy requirement, where it is assumed that ıreceiver equals RMSpr_air for GBAS Airborne Accuracy Designator A equipment. 7.5.8 Airframe multipath error. The error contribution from airframe multipath is defined in Appendix B, 3.6.5.5.1. Multipath errors resulting from reflections from other objects are not included. If experience indicates that these errors are not negligible, they must be accounted for operationally or through inflation of the parameters broadcast by the ground (e.g. ıpr_gnd). 7.5.9 Ephemeris error uncertainty. Pseudo-range errors resulting from ephemeris errors (defined as a discrepancy between the true satellite position and the satellite position determined from the broadcast data) are spatially decorrelated and will therefore be different for receivers in different locations. When users are relatively close to the GBAS reference point, the residual differential error due to ephemeris errors will be small and both the corrections and uncertainty parameters ıpr_gnd sent by the ground subsystem will be valid to correct the raw measurements and compute the protection levels. For users further away from the GBAS reference point, protection against ephemeris failures can be ensured in two different ways:

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