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Note.— The DPSK signal requires more protection than the scanning beam so that by limiting the undesired co-channel
signal to minus 120 dBm, interference from the scanning beam is negligible.
9.3 Adjacent frequency requirements
9.3.1 Considering the absence of requirements on transmitter spectrum characteristics for the first and second adjacent
channels, the ground stations operating at these frequencies should be placed at a geographical separation that exceeds the
radio horizon distance at any point in the promulgated coverage sector of the desired facility.
Note.— Where for specific reasons (for example, ILS/MLS/DME pairing channels) the first or second adjacent channels
need to be assigned, a less conservative method to assure receiver protection is to guarantee that the minimum SNR values as
quoted in 3.11.6.1.4 are available at any point in the promulgated coverage sector of the desired facility while the undesired
facility is transmitting.
9.3.2 For the third and subsequent adjacent channels, the ground stations operating at these frequencies should be
placed at a geographical separation which guarantees that the minimum SNR values as quoted in Chapter 3, 3.11.6.1.4 are
available at any point in the promulgated coverage sector of the desired facility while undesired facilities are transmitting.
9.3.2.1 If there is no undesired MLS transmission situated at less than 4 800 m from any point of the promulgated
coverage, the –94.5 dBW/m² maximum power of Chapter 3, 3.11.4.1.4.2 compared to the minimum power density of
Chapter 3, 3.11.4.10.1 assures that the SNR minimum values will be met. No constraints are anticipated.
9.3.2.2 If there is an undesired MLS transmission situated at less than 4 800 m from a point of the promulgated
coverage, the maximum power produced by this transmission and measured, during transmission time for angle and data
signals, in a 150 kHz band centred on the desired nominal frequency has to be assessed taking into account the frequency
separation, spectrum performances and antenna pattern of the transmitter and the appropriate propagation losses. This
maximum power has then to be compared to the desired angle and data level to check that the minimum SNR values defined
in 3.11.6.1.4 are met. If not, another channel offering a larger frequency separation has to be assigned in order to reduce this
maximum undesired power taking benefit of the spectrum characteristic of the transmitter.
ATT G-29 23/11/06
Annex 10 — Aeronautical Communications Volume I
9.4 Development of frequency planning criteria
9.4.1 The controlling factor when developing adjacent channel frequency planning criteria is the radiated spectrum
from the MLS ground station. When developing frequency planning criteria for the third adjacent channel and above, ideally,
the radiated spectrum output of individual MLS ground stations should be considered. However it may be possible in a
eographic region g to use a generic MLS transmitter mark which meets the requirements of that region.
10. Material concerning MLS installations at special locations
10.1 MLS facility performance throughout the coverage volume
10.1.1 It is recognized that at some locations the requirements for MLS specified in Chapter 3, 3.11 cannot be met
throughout the whole volume of coverage due to environmental effects on the signal. It is expected that at such locations the
requirements of Chapter 3, 3.11 are to be met at least in the guidance sector for all published instrument procedures to a
defined point beyond which the MLS guidance is not used for intended operations. To assist appropriate authorities with the
initial appraisal of the suitability of such individual MLS installations for the intended operations, relevant coverage
restrictions need to be promulgated.
11. Integrity and continuity of service — MLS ground equipment
11.1 Introduction
11.1.1 This material is intended to provide description of the integrity and continuity of service objectives of MLS
ground equipment and to provide guidance on engineering design and system characteristics of this equipment. The integrity
and continuity of service must of necessity be known from an operational viewpoint in order to decide the operational
application which an MLS could support.
11.1.2 It is generally accepted, irrespective of the operational objective, that the average rate of a fatal accident during
landing, due to failures or shortcomings in the whole system, comprising the ground equipment, the aircraft and the pilot,
should not exceed 1 × 10–7. This criterion is frequently referred to as the global risk factor.
11.1.3 In the case of Category I operations, while minimum standards of accuracy and integrity are required during the
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