p1031 compatibility scenarios v10 - eurocontrol.int filep1031d005 helios iii of 49 contents 1...

FCI Technology Investigations: L band Compatibility Criteria and

Interference Scenarios Study

Deliverables S1-S7: L-Band Interference Scenarios

Edition Number 1.0 Edition Date 25/08/2009 Status Final

COOPERATIVE NETWORK DESIGN

P1031D005 HELIOS ii of 49

Document information

Document title L-band interference scenarios characterisation

Authors John Micallef, Richard Womersley, Simon Dunkley, Ian Casewell

Produced by Helios

29 Hercules Way

Aerospace Boulevard - AeroPark

Farnborough

Hampshire

GU14 6UU

UK

Produced for Eurocontrol

Helios contact Richard Womersley

Tel: +44 1252 451 686

Fax: +44 1252 451 652

Email: [email protected]

Produced under contract 08-111428-C

Version 1.0

Date of release 25th August 2009

Document reference P1031D005

P1031D005 HELIOS iii of 49

Contents

1 Introduction ............................................................................................................... 1

1.1 General ....................................................................................................................... 1

1.2 About this document.................................................................................................... 2

2 Identification of scenarios ........................................................................................ 3

2.1 Signal Path Scenarios ................................................................................................. 3

2.2 Path Loss .................................................................................................................... 4

2.2.1 Free Space Path Loss ................................................................................................. 5

2.2.2 Near Field Path Loss ................................................................................................... 5

2.2.3 Obstructed Path Propagation Calculations .................................................................. 6

2.2.4 Summary..................................................................................................................... 7

2.3 Scenario Descriptions.................................................................................................. 8

2.3.1 Scenario 1 (and 2): Airborne Aircraft to Airborne Aircraft ............................................. 8

2.3.2 Scenario 3 (and 4): Airborne Aircraft to Ground Station............................................... 8

2.3.3 Scenario 5: Co-located, same Aircraft ......................................................................... 9

2.3.4 Scenario 6 (and 7): Airborne Aircraft to Aircraft on the Ground.................................... 9

2.3.5 Scenario 8 (and 9): Aircraft on the Ground to Ground Station...................................... 9

2.3.6 Scenario 10: Ground Station to Ground Station......................................................... 10

2.3.7 Scenario 11 (and 12): Aircraft on the Ground to Aircraft on the Ground..................... 10

2.4 Summary................................................................................................................... 10

3 GSM.......................................................................................................................... 12

3.1 GSM 900 ................................................................................................................... 12

3.1.1 GSM On-Board (GSMOB) ......................................................................................... 13

3.2 UMTS 900 ................................................................................................................. 15

3.3 Interference Scenarios .............................................................................................. 16

3.3.1 Context...................................................................................................................... 16

3.3.2 Terrestrial GSM base station to LDACS on an aircraft on the ground ........................ 17

3.3.3 Terrestrial GSM base station to LDACS base station ................................................ 17

3.3.4 NCU to LDACS on an aircraft .................................................................................... 18

3.3.5 NCU to LDACS base station...................................................................................... 19

3.4 Summary................................................................................................................... 20

4 GNSS........................................................................................................................ 21

4.1 Overview ................................................................................................................... 21

4.1.1 Power spectral flux density of the wanted GNSS signals........................................... 21

4.1.2 Power spectral flux density of the unwanted out of band GNSS signals .................... 22


P1031D005 HELIOS iv of 49

4.2.1 MEO satellite into aircraft on the ground.................................................................... 22

4.2.2 MEO satellite into an airborne aircraft........................................................................ 23

4.2.3 MEO satellite into ground station ............................................................................... 24

5 DME .......................................................................................................................... 25

5.1 Overview ................................................................................................................... 25

5.1.1 DME RNAV procedures............................................................................................. 25

5.1.2 Precision approaches................................................................................................ 25

5.1.3 Non precision approaches......................................................................................... 26

5.1.4 DME holding.............................................................................................................. 26

5.1.5 DME ground speed checks........................................................................................ 27

5.1.6 DME arcs .................................................................................................................. 28


5.3 Summary................................................................................................................... 29

6 SSR........................................................................................................................... 31

6.1 Overview ................................................................................................................... 31

6.2 SSR systems transmit power and EIRP levels........................................................... 31


6.3.1 SSR/Mode S transponder to an LDACS receiver on the same aircraft....................... 33

6.3.2 SSR/Mode S airborne transponder to LDACS ground station receiver ...................... 33

6.3.3 SSR/Mode S transponder on the ground to LDACS ground station receiver ............. 34

6.3.4 SSR/Mode S transponder to LDACS receiver on another airborne aircraft ................ 34

6.3.5 SSR/Mode S interrogator to LDACS on an airborne aircraft ...................................... 35

6.3.6 SSR/Mode S transponder on the ground to LDACS airborne receiver....................... 36

6.3.7 SSR/Mode S interrogator to LDACS ground station receiver ..................................... 36

6.4 Summary................................................................................................................... 37

7 UAT........................................................................................................................... 39

7.1 Overview ................................................................................................................... 39

7.2 UAT transmission power and EIPR levels ................................................................. 39



7.4.1 UAT on an aircraft to LDACS on an the same aircraft................................................ 41

7.4.2 UAT on an aircraft to an LDACS ground station ........................................................ 41

7.4.3 A UAT ground station to an LDACS ground station ................................................... 41

7.5 Summary................................................................................................................... 42

8 JTIDS/MIDS .............................................................................................................. 43

8.1 Overview ................................................................................................................... 43

P1031D005 HELIOS v of 49

8.1.1 Technical Parameters................................................................................................ 43


A Abbreviations and acronyms.................................................................................. 47

B References............................................................................................................... 48

P1031D005 HELIOS 1 of 49

1 Introduction

1.1 General

1.1.1 Recognising that there is insufficient spectrum in the standard VHF band to support future aeronautical communications needs, two options for an L-Band Digital Aeronautical Communications System (L-DACS) have been identified by the European and US ICAO ACP members under the joint development activity known as the Future Communications Study (Action Plan 17). The first option for L-DACS is a frequency division duplex (FDD) configuration utilizing OFDM modulation techniques. The second L-DACS option is a time division duplex (TDD) configuration utilising a binary (GMSK) modulation scheme.

1.1.2 One of the key questions with respect to these candidate L-DACS technologies which needs to be addressed is that of its compatibility with other, existing L-Band systems. Not only must the candidate systems be able to operate effectively whilst in the presence of interference from other systems, but they must also cause the minimum possible interference to the legacy systems. These compatibility analyses are required in order to assess the feasibility of using the competing L-DACS systems both in a ground, and in particular in an airborne environment.

1.1.3 This study aims to define the interference scenarios to be investigated for the case in which the LDACS system is the victim system and the other systems in the L band are the interfering systems. The list of potentially interfering systems includes those considered in the Study deliverables C1-C71, with the addition of the military system JTDS/MIDS.

1.1.4 The following diagram outlines the process currently foreseen by EUROCONTROL, showing the steps to be undertaken to complete the L-DACS selection.

Figure 1 – Overall evaluation process currently foreseen

1 DME/TACAN, SSR, UAT, GSM/UMTS and GNSS.

L-DACS1/2

Specifications

Interference Scenarios,

Criteria and Testing Plan

Development of

TX prototype

Development of

RX prototype

Testing and

Evaluation

L-DACS

Selection


1.1.5 This document is a deliverable of the study covering the grey box in Figure 1 addressing the interference criteria, scenarios and testing plan. The overall study addresses two aspects of the current systems. The first one considers the current systems as victims and aims to define the appropriate spectrum compatibility criteria with a new system. The second one considers the current systems as interferers and aims to define the appropriate interference scenarios to be used when evaluating the impact of the current systems to a new system.

1.1.6 For the first part, there are 5 deliverables covering DME, UAT, SSR, GSM/UMTS and GNSS (C1, C2, C3, C4 and C5). For the second part, there is one deliverable consolidating the interference scenarios for all the previously considered systems and JTDS/MIDS in addition. There is also a combined deliverable (C6/S6) covering both the criteria and scenarios for the RSBN system. Finally there is one deliverable C7 providing an analysis of the potential usage of the suppression bus by a new system.

1.2 About this document

1.2.1 This document collects deliverables S1-S72 of the Spectrum Compatibility criteria and Interference Scenarios for existing systems operating in the L band study produced by Helios for Eurocontrol under Contract 08-111428-C as contribution to the Future Communication Study (FCS) activities, and in support of the work to realise one of the recommendations of the FCS to develop an L-band data link.

1.2.2 The development of the L-band data link is identified in the development activities for the SESAR Implementation Package 3 (IP3) in the post 2020 timeframe. Therefore, the outcome of this deliverable will be used as input to the SESAR JU development activities under WP15.2.4.

1.2.3 The scenarios identified in this document are based on the current operating conditions of legacy systems operating in the L-band, As such, issues such as frequency separation and emission masks for L-DACS are based on current standards and specifications and take into consideration specific operating conditions for each of the systems in order to reflect the conditions in practical day to day operations. This paper is thus intended to provide the groundwork for the prototyping and compatibility trials bearing in mind that it will be possible to derive the interference scenarios based on the operation of L-DACS (in the reverse direction) at a later stage when the L-DACS specifications are more mature.

2 S6 on RSBN systems is produced under separate cover.


2 Identification of scenarios

2.1 Signal Path Scenarios

Although there are a number of different deployment possibilities for various radio technologies, the possible signal paths between systems follow a generic pattern. Which interference scenario is the most severe or problematic depends on the systems in question, and the relative levels between wanted and unwanted signals, however the possible signal paths can be generically defined.

The possible signal path scenarios are illustrated in Figure 2.

AB

A B A B

ABAB

1

2

3 4

5

6 7

8

910

11

12

airborne aircraft

aircraft

on the

ground

groundstation

Figure 2 - Interference paths

In each instance, there are two systems under consideration, A and B. The signal paths shown are only from system A into system B, however clearly the arrows can be reversed (or the two systems designations swapped) representing signal paths in the opposite direction. The signal paths between these systems are therefore as follows:

� Scenario 1: Airborne Aircraft to Airborne Aircraft. This scenario represents the situation between two airborne aircraft where emissions from system A on one airborne aircraft are being received by system B on another airborne aircraft.

� Scenario 2: Airborne Aircraft to Airborne Aircraft. This scenario represents the situation between two airborne aircraft where emissions from system A on one airborne aircraft are being received by system B on another airborne aircraft. This scenario is identical to scenario 1 unless the transmission or reception parameters of the two systems somehow differ between aircraft (which is unlikely).

� Scenario 3: Airborne Aircraft to Ground Station. This scenario represents the situation where emissions from system A on an airborne aircraft is being received by a system B ground station.


� Scenario 4: Ground Station to Airborne Aircraft. This scenario represents the situation where emissions from a system A ground station are being received by system B on an airborne aircraft.

� Scenario 5: Co-located, same Aircraft. This scenario represents the situation where emissions from system A on an aircraft are being received by system B on the same aircraft. Note that although the diagram shows the aircraft concerned as being airborne, the same parameters would apply to one on the ground.

� Scenario 6: Airborne Aircraft to Aircraft on the Ground. This scenario represents the situation where emissions from system A on an airborne aircraft are being received by system B on an aircraft situated on the ground.

� Scenario 7: Aircraft on the Ground to Airborne Aircraft. This scenario represents the situation where emissions from system A on an aircraft situated on the ground are being received by system A on an airborne aircraft.

� Scenario 8: Aircraft on the Ground to Ground Station. This scenario represents the situation where emissions from system A on an aircraft situated on the ground are being received by a system B ground station.

� Scenario 9: Ground Station to Aircraft on the Ground. This scenario represents the situation where emissions from a system A ground station are being received by system A on an aircraft situated on the ground.

� Scenario 10: Ground Station to Ground Station. This scenario represents the situation where emissions from a system A ground station are being received by a system B ground station.

� Scenario 11: Aircraft on the Ground to Aircraft on the Ground. This scenario represents the situation where emissions from system A on an aircraft on the ground are being received by system B on another aircraft on the ground.

� Scenario 12: Aircraft on the Ground to Aircraft on the Ground. This scenario represents the situation where emissions from system A on an aircraft on the ground are being received by system B on another aircraft on the ground. This scenario is identical to scenario 11 unless the transmission or reception parameters of the two systems somehow differ between aircraft (which is unlikely).

For each of these scenarios we can therefore define the scenario parameters and hence the range of possible losses between the two systems. These losses will be identical for the reverse situation (ie system B into system A), hence there is no need to define an additional 12 sets of scenarios to represent these. When combined with the other criteria specific to systems A and B (e.g. antenna gains and compatibility criteria), this will therefore allow an analysis of the most problematic situations in order that the most appropriate compatibility tests can be undertaken.

2.2 Path Loss

The key parameters in defining each of the preceding scenarios is the path loss between the two devices under consideration.

Path loss is the reduction in extent to which an electromagnetic wave is attenuated as it propagates through space. Path loss is a major component in the analysis and design of the link budget of radio communication systems. There are a number of mechanisms for calculating path loss. In its simplest form, the loss between two points can be determined using free space path loss. This is


appropriate when the route between two ends of a path is completely unobstructed, not just for the direct path, but for several Fresnel zones either side of it (ie from a ground station to a satellite).

The point at which the wave radiated from an antenna can be considered a plane wave and as such, far-field equations hold, is the generally held to be defined by the equation:

Dmin=2D²/λ

where:

� Dmin is the distance from the antenna (in metres);

� D is the size of the antenna (in metres); and

� λ is the signal wavelength (in metres).

At distances closer than Dmin the fields are complex, there is a lot of stored energy and the wave can not be considered plane. When these conditions are met, far-field equations do not hold true and alternative methods of considering the interaction between systems are required.

2.2.1 Free Space Path Loss

The equations to calculate free space path loss (FSPL) are as follows:

FSPL = ( 4Πd / λ )²

= ( 4Πdf / c )²

where:

� λ is the signal wavelength (in metres);

� f is the signal frequency (in Hertz);

� d is the distance from the transmitter (in metres); and

� c is the speed of light in a vacuum (in metres per second).

This equation can be used in situations where distances are greater than around one wavelength and where paths are unobstructed.

Typically this equation is rearranged such that the result is in dB. It then becomes:

FSPLdB=20log10d + 20log10f - 147.56

or

FSPLdB=20log10d’ + 20log10f’ +32.44

if d’ is in kilometres and f’ in MHz.

The free space path loss equation generally holds valid for situations where the first Fresnel zone of the link is not obscured.

2.2.2 Near Field Path Loss

The wavelength of an LDACS signal is approximately 30cm. If it is assumed that the aircraft antenna will be a quarter-wave whip, of length 7.5 cm, the Fraunhofer point is at 37.5 cm, implying the validity of the free space path loss equation at


distances from the antenna which are roughly greater than one wavelength. It is unlikely that other (L-Band) antennas would be installed closer than this on an aircraft and as such free space path loss applies in the same-aircraft situation. However, often antennas are mounted on opposite sides of the fuselage such that there is additional shielding between antennas, increasing the path loss above that of free space. Coupling between respective antennas on the same side of an aircraft body located no more than a few metres away from each other has been shown3 to be of order 30 dB, corresponding well with the free space loss. Where such figures are available, these will be used for analysis.

For ground stations where antenna sizes may be significantly larger, the situation is more complex. If a 19dBi 120-degree sector antenna were used, this has a size of approximately 1 metre, implying unpredictable near field effects at distances of less than 6.6 metres. There are, however, cases where antennas have been co-sited on the same mast and general approximations as to the coupling between them can be applied based on the measurements taken between these antennas. As such, where figures are available, these will be used for analysis.

2.2.3 Obstructed Path Propagation Calculations

Where the first Fresnel zone of the path between two points is obscured, as is the case when aircraft on the horizon are communicating with a ground station, the free space path loss equation becomes inaccurate.

There are many models which have been developed to provide an improvement in accuracy for propagation predictions however most have been designed with certain characteristics in mind. The most appropriate is that given by ITU-R P.582-24. To a large approximation this model uses the free-space calculation until the free space path is obscured which is determined by the height of the stations at either end of the link.

The path loss for SHF links is given by the graph below:

3 UAT conceptual design lead

4 “Propagation curves for Aeronautical Mobile and Radionavigation services using the VHF, UHF and

SHF Bands.”


Figure 3 - Transmission loss predicted for excess path loss

The various curves are defined by the height of the two ends of the link as follows:

Curve H1 (metres) H2 (metres)

A 15 1000

B 1000 1000

C 15 10000

D 1000 10000

E 15 20000

F 1000 20000

G 10000 10000

H 10000 20000

I 20000 20000

Table 1 - transmission loss for different combinations of antenna heights

2.2.4 Summary

We will use:

� Measured results in situations where antennas are in very close proximity (ie on the same structure);

� Free space path loss equation where the first Fresnel zone of the link is not obstructed;

� The curves of ITU-R P.528 at distances beyond this.


2.3 Scenario Descriptions

For each scenario, a range of losses is possible dependent upon the distance between the two ends of the link. In this section we discuss the practicalities of the situations concerned and produce a range of losses representing the extremes of the scenario under consideration.

In all cases an operational frequency of 1 GHz has been assumed. There is a variance (approximately ± 10%) between the frequencies at the extremities of the band. As, however, most of the use being contemplated is concentrated in the lower portions of the band, the variance is much smaller, in the region of ± 4% which represents a difference in results of only ± 0.35 dB and hence is negligible.

2.3.1 Scenario 1 (and 2): Airborne Aircraft to Airborne Aircraft

In this scenario, the minimum distance likely to be encountered between the two ends of the link is as one aircraft passes above another. In RVSM airspace, this represents a distance of 1000 ft (or 305 m). At this distance, the free space path loss equation applies. The minimum loss is therefore 82 dB.

The maximum operationally relevant distance likely to be encountered between aircraft of two opposite ends of an operational sector using technologies which require air to air reception. Typically such systems (in L-Band) require an operational range of 30 NM (55.6 km), indicating a path loss of 127dB. For long-range ADS-B, the maximum useful operational range extends as far as 200 NM (370.4 km) indicating a path loss of 144 dB.

The range of losses applicable in this scenario is therefore 82 to 144 dB.

2.3.2 Scenario 3 (and 4): Airborne Aircraft to Ground Station

In this scenario, the minimum distance likely to be encountered between the two ends of the link is during the approach or take-off phase of flight when the aircraft is close to the runway. On occasion, radio equipment is mounted just to the side of the runway and thus it is possible that (for a fleeting moment), the closest distance between the two could be as low as 50 metres, indicating a path loss of 66 dB.

The maximum relevant distance likely to be encountered between the two ends of the links is when the aircraft is at the extremities of the operational range of the system in question, and at maximum height. We shall assume a height of 40,000 ft (12.2 km) and a distance from the ground station of 200NM (370.4 km). We shall assume that the height of the ground station antenna above ground is 15 metres. Based on the ITU curves, at this point, the free space path loss equations are still dominant and as such this represents a path loss of approximately 144dB.


Scenario 4 is the reverse path of scenario 3 which, in terms of analysis, will have different parameters, however in terms of the path loss will be the same


2.3.3 Scenario 5: Co-located, same Aircraft

For this scenario, measurements of the coupling between various antennas are by far the best mechanism to arrive at possible ranges of losses. These have been shown to be around 30 dB in a typical installation.

2.3.4 Scenario 6 (and 7): Airborne Aircraft to Aircraft on the Ground

In this scenario, the minimum distance likely to be encountered between the two ends of the link is when aircraft in the take-off run have just become airborne. This is only a temporary situation given the speed of the departing aircraft but in large airports, the time of exposure while the departing aircraft is still in low altitude could last up to a minute. While still above the airport, departing aircraft could be in the region of 500 ft (150 metres) above the airport surface, representing a minimum loss of 76 dB.

The maximum distance is limited by the likely necessity for an aircraft on the ground to need to receive signals from an airborne aircraft. This is likely to be at the point when the airborne aircraft has intercepted the ILS and established on a 3 degree glide slope. In this phase of flight, the approaching aircraft is loosing altitude rapidly and getting closer in horizontal distance as well as in altitude to the airport surface. The final approach fix is the point in space where the final approach begins in an instrument approach. The final approach fix is indicated when the aircraft crosses the outer marker of the airport's marker beacon. The location of the marker beacon varies from airport to airport, usually between 4 to 7 miles from the runway. In this phase of flight, flight crew workload is at a peak and communications load at a minimum, however there is likely to be various data exchanges and telemetry between automated systems. This gives a range of 12,000 to 7,500 metres from a ground station located in or in the vicinity of the airport surface.

Range (km) Loss (dB)

7.5 110

12 114

Table 2 – Estimated path losses in the airport vicinity


2.3.5 Scenario 8 (and 9): Aircraft on the Ground to Ground Station

In this scenario, the minimum distance likely to be encountered between the two ends of the link is when the aircraft is parked in the apron area, or taxiing in the vicinity of the runway. The distance will therefore depend upon the location of the ground station relative to the aircraft. At large airports such as Frankfurt, this may be up to 2,500 m from the aircraft’s location. In other places, the aircraft may be expected to come within 50 metres of a ground station.



2.3.6 Scenario 10: Ground Station to Ground Station

In this scenario, the minimum distance likely to be encountered between the two ends of the link is when both ground stations are co-located (ie at the same physical site) and loss will be at a minimum when the antennas for the two ground stations are mounted on the same mast. In such situations, the loss between two systems can be as low as 30 dB.

The maximum distance likely to be encountered will be when both ground stations are located at the same airport but at opposite extremities5. This will depend upon the size of the airport itself but could be up to 2,500 metres.


2.3.7 Scenario 11 (and 12): Aircraft on the Ground to Aircraft on the Ground

In this scenario, the minimum distance likely to be encountered between the two ends of the link is when both aircraft are parked next to each other. However in this case, the aircraft is largely inactive in terms of operational and ATC data exchanges and any transmissions in this instance will be limited. The most operationally relevant scenario for aircraft on the ground is when aircraft are operating in the vicinity of the active runway when preparing for take-off, or just after landing. In many busy airports the separation between aircraft is at a minimum while queuing for their take-off slot. This will, potentially, be slightly closer for small aircraft than for large aircraft. Typical minimum separation distances between aircraft could be as low as 50 metres.

The maximum operational distance in this scenario would be between an aircraft parked at a remote location within an airport to that at another location on the opposite side of the airport. This could be up to 2,500 metres.


2.4 Summary

For each of the scenarios presented above, we have calculated the minimum path length and hence minimum possible loss between two points, as well as the maximum path and thus maximum loss. These two figures will represent the ‘wanted’ and ‘unwanted’ signal paths for the various systems under consideration.

The table below summarises the minimum and maximum losses applicable in each scenario:

5 Clearly there is a situation wherein one ground station could be outside the airport perimeter, however

such scenarios are unlikely to yield interference problems and though feasible do not form part of this scenario.


Scenario Minimum Loss Maximum Loss

1 (and 2): Airborne Aircraft to Airborne Aircraft 82 dB 144 dB

3 (and 4): Airborne Aircraft to Ground Station 66 dB 144 dB

5: Co-located, same Aircraft 30 dB

6 (and 7): Airborne Aircraft to Aircraft on the Ground

76 dB 114 dB

8 (and 9): Aircraft on the Ground to Ground Station

66 dB 100 dB

10: Ground Station to Ground Station 30 dB 100 dB

11 (and 12): Aircraft on the Ground to Aircraft on the Ground

66 dB 100 dB

Table 3 – Range of losses estimated for each of the identified scenarios


3 GSM

3.1 GSM 900

The context of GSM technology, in particular the receiver characteristics, is explained in deliverable C4. The specifications for the transmission characteristics, required to determine the impact of the GSM system on the candidate LDACS systems, are specified in 3GPP TS 11.21, release 8.10.00, version 1999 for the base station and 3GPP TS 05.05, release 8.20.00, version 1999 for the mobile stations, and are summarised below.

The transmitter maximum output power6 is specified for 8 different classes of equipment, the first having the highest power. The specification is summarised in the following table.

TRX Maximum power class output power

1 320 - (< 640) W 2 160 - (< 320) W 3 80 - (< 160) W 4 40 - (< 80) W 5 20 - (< 40) W 6 10 - (< 20) W 7 5 - (< 10) W 8 2,5 - (< 5) W

Table 4 - GSM900 maximum output power for base station

The transmitter mask for a Class 1 base station (typical maximum power for a GSM BTS transmitter is +43dBm) operating in the 900MHz band is summarised in Table 5. The maximum allowed EIRP for the band is +62dBm [1], equivalent to an antenna gain of +19dBi. Higher gain antennas (up to +25dBi) may be used in some circumstances, however the transmitter power would need to be reduced in order to remain within the +62dBm EIRP limit. The table below assumes a maximum +43dBm transmitter and 19dBi gain antenna, however the same EIRP would result from a +37dBm transmitter and 25dBi antenna.

6 At the input of the BSS Tx combiner.


Figure 4 - GSM transmit mask

Offset from carrier (kHz)

(measurement bandwidth 30kHz)

Relative power (dB)

7

Power for Class 1 BS (dBm)†

EIRP (dBm) (assuming 19dBi

antenna)

100 +0.5 +35.2 +54.2

200 -30 +4.7 +23.7

250 -33 +1.7 +20.7

400 -60 -25.3 -6.3

600-1200 -70 -35.3 -16.3

1200-1800 -73 -38.3 -19.3

1800-6000* -75 -35.0 -16.0

>6000* -80 -40.0 -21.0

Table 5 - Estimated EIRP for GSM900

* measurement bandwidth 100kHz.

† assumes the average power in the carrier is 20W (+43dBm)/200kHz, equivalent to 34.7 dBm in 30kHz and 40.0 dBm in 100 kHz.

3.1.1 GSM On-Board (GSMOB)

Mobile telephone use is currently forbidden on most aircraft, however, in April 2008, the Commission ruled that the use of mobile devices in midair is to be allowed by means of on-board picocells (GSM on-board (GSMOB)) in the 1800MHz band linked back to the fixed infrastructure via satellite.

7 The GSM 05.05 standard provides the transmitter mask relative to a measurement bandwidth of 30

kHz up until 1.8 MHz and of 100 kHz above 1.8 Mhz.


Safe GSMOB operation is achieved by restricting use to above 3000m, constraining the power that the on-board BSs and MSs can transmit (and coordinating the channels used with nearby aircraft) and using an on-board Network Control Unit (NCU) transmitting a low-power signal in the DL band of all mobile technologies, including CDMA-450, GSM-900 and UMTS2000 as well as GSM-1800 to mask any signals that individual MSs might detect from ground-based BSs and thus attempt to ensure that MS only transmit on the frequencies selected for use on the aircraft concerned.

The components of the system are illustrated in the figure below[2]8.

Figure 5: On-Board GSM System Components

The NCU serves a dual purpose of acting as an onboard picocell transmitting to cabin mobile telephones via leaky feeder antennas, and blocking signals to other mobile technologies. The typical signal generated by the NCU is illustrated in the figure below9.

8 A detailed description of the system is contained in ECC report 93, Compatibility between GSM equipment on board aircraft and terrestrial networks, from which this diagram is sourced.

9 From ECC report 93


Table 6 - Typical NCU generated spectrum

The maximum power allowed to be generated by the NCU is altitude dependent and summarised in the table below for the 900-MHz band.

Maximum permitted e.i.r.p. produced by NCU/aircraft-BTS, defined outside the aircraft in dBm / channel, with victim receiver directly

below aircraft

Altitude (m)

(dBm/200 kHz)

3000 -19

4000 -16.5

5000 -14.5

6000 -12.9

7000 -11.6

8000 -10.5

Table 7 - NCU power variation with aircraft altitude

3.2 UMTS 900

The context of UMTS technology, in particular the receiver characteristics, is explained in deliverable C4. The specifications for the transmission characteristics, required to determine the impact of the UMTS system on the candidate LDACS systems, are specified in ETSI TS 115 101, release 8.3.0 for both base and mobile stations, and are summarised below.

The transmitter mask for a UMTS transceiver (User Equipment and Base Station) is summarised in the table below:


Table 8 - UMTS transmitter mask

The maximum power for a Class 3 base station operating in band VIII is +24dBm per carrier (equivalent to +20dBm/MHz or +5dBm/30kHz). Connected to an antenna gain of +19dBi, this produces a maximum EIRP of +43dBm (equivalent to +39dBm/MHz or +24dBm/30kHz).

This translates into an absolute transmitter mask as shown in the table below.

∆f (MHz) Requirement (dBm) Measurement bandwidth

2.5-3.5 -30 - 15.(∆f(MHz)-2.5) 30kHz

3.5-7.5 -30 - 1.(∆f(MHz)-3.5) 1MHz

7.5-8.5 -26 - 10.(∆f(MHz)-7.5) 1MHz

8.5-12.5 -44 1MHz

Table 9 - Absolute UMTS transmitter mask for Class 3 equipment

3.3 Interference Scenarios

3.3.1 Context

Interference could be experienced by either component of the LDACS system from terrestrial GSM and/or UMTS base stations and/or mobile stations, or from components of the GSMOB system, in particular, the NCU.

Realistic potential interference scenarios are therefore:

� GSM/UMTS ground station to LDACS ground station;

� GSM/UMTS ground station to LDACS on an aircraft on the ground;


� GSM NCU to LDACS on-board an aircraft;

� GSM NCU to LDACS ground station.

The severity of interference experienced by the LDACS system from these four scenarios will depend on three factors:

� GSM/UMTS Adjacent Channel Leakage Ratio (ACLR): the extent to which power spills outside the intended band, and documented above;

� LDACS Adjacent Channel Selectivity (ACS): the victim receiver’s vulnerability to strong signals in adjacent bands10;

� Isolation: the extent to which unwanted transmissions are shielded from victim systems, both by physical separation (propagation loss) and antenna (mis)orientation.

These four interference scenarios are discussed below, in order of likely severity (most severe first).

3.3.2 Terrestrial GSM base station to LDACS on an aircraft on the ground

This scenario sees ground-based GSM/UMTS base stations interfering with LDACS on an aircraft on the ground. The terrestrial base station could potentially be transmitting at full power (as indicated in section 2). In the future, it is likely that they will be operating in mixed (GSM/UMTS) mode, especially in rural areas. The ground station operates in the 925-960 MHz band, therefore in order to obtain a representative GSM residual power profile for the LDACS band, it is convenient to consider two ranges for the near band (0.6-1.2 MHz representative for L-DACS/2) and far band (>6.0 MHz representative for L-DACS/1).

This represents scenario 9 above and thus the minimum path loss expected between the ground station and aircraft would be 66 dB. The interference parameters are estimated as per the table below.

Value Parameter

Near band Far band

Units

Base station transmission residual power -35.3 -40.0 dBm

Interferer antenna gain +19 +19 dBi

Minimum Path Loss 66 66 dB

Victim antenna gain 0 0 dBi

Victim interference received (from GSM) -82.3 -87.0 dBm.

Table 10 - Link budget parameters relevant to scenario 9

3.3.3 Terrestrial GSM base station to LDACS base station

This scenario sees ground-based GSM/UMTS base stations interfering with LDACS base stations. The terrestrial base station could potentially be transmitting

10 ACS is dependent on the receiver’s filter characteristics both at the antenna port and internally as

part of frequency translation and de-modulation. In digital receivers, ACS is dependent on the antenna port filtering and the accuracy of any ADC’s used.


at full power (as indicated in section 2). In the future, it is likely that they will be operating in mixed (GSM/UMTS) mode, especially in rural areas.

Two scenarios are foreseen:

� LDACS and terrestrial base stations collocated, with suitable engineering to maximise isolation; and

� base stations separated by 2.5 km (as per path loss scenario 10).

For the purpose of this scenario, the 1.8-6.0 MHz frequency separation case from Table 5 is considered.

Parameter Value Units

Victim-interferer separation 2.5 km Co-sited m

Base station transmissions -35 -35 dBm

Interferer antenna gain +19 -20 dBi

Propagation loss 100 30 dB


Victim interference received (from GSM) -116 -85 dBm


3.3.4 NCU to LDACS on an aircraft

This interference situation is not covered by the general situations identified earlier as it is driven by interference from equipment inside the aircraft to antennas mounted on the outside. The nearest situation is scenario 5 but additional path loss needs to be taken account of the attenuation caused by the hull of the aircraft.

This scenario sees the onboard NCU transmitting in the 900 MHz band interfering with an aircraft’s onboard LDACS equipment whilst flying at an altitude of 8000m (and thus whilst the NCU is radiating the maximum power). The power levels indicated in Table 7 represent on-channel power for the NCU. There is no specific transmit mask specified for the NCU for adjacent channel emissions, therefore the same mask as for the GSM BS have been considered (Table 5). As this scenario involves reception of LDACS on board the aircraft, the same frequency separation cases as those in 3.3.2 are considered.


Value Parameter

Near band Far band

Units

-10.5 dBm/200kHz

-18.76 dBm/30 kHz

NCU transmission on channel power density

11

-13.52 dBm/100 kHz

NCU transmission off-channel power -88.76 -93.52 dBm

Interferer antenna gain 0 0 dBi

Victim-interferer separation 10 10 m

Propagation loss 3512

35 dB


Victim interference received (from NCU) -123.76 -128.52 dBm


3.3.5 NCU to LDACS base station

This scenario sees the onboard NCU transmitting in the 900MHz band interfering with LDACS base stations when aircraft are operating at 3000m (the lowest NCU operating altitude), flying directly over an LDACS base station.

As in 3.3.3, for the purpose of this scenario, the 1.8-6.0 MHz frequency separation case from Table 5 is considered.


-19 dBm/200kHz NCU transmissions power density

-22 dBm/100kHz

NCU transmission power (off-channel) -97 dBm

Victim-interferer separation 3000 m

Propagation loss 101 dB

Interferer antenna gain 0 dBi

Victim antenna gain 0 dBi

Victim interference received (from NCU) -198 dBm

Table 13 - Ground station to ground station link budget

NCU emissions are specified outside of the aircraft and thus there is no need to take account of hull losses.

11 In order to apply the GSM BS transmit mask to derive the off-channel NCU power, the transmission

power density is converted from the 200 kHz reference bandwidth to the 30 kHz and 100 kHz reference bandwidths required by the GSM mask specified in Table 5.

12 This represents the worst case 30 dB coupling between antennas on an aircraft plus an additional 5

dB for hull shielding.


3.4 Summary

The table below summarises the outcomes of the four interference scenarios analysed above.

Scenario Victim (LDACS) interference power (dBm)

Notes

GSM/UMTS base station to LDACS on an aircraft -82.3/-87

Worst-case scenario. Does not appear to offer a significant threat, but further work would need to be carried out to investigate how close aircraft come to terrestrial base stations in reality

GSM/UMTS base station to LDACS base station

-116/-85 No apparent threat. Requires coordination of base stations and/or suitable engineering where base stations are collocated

NCU to LDACS on an aircraft

-124/-129

No apparent threat. Further work needs to be carried out to investigate the extent to which LDACS airborne units can be shielded from NCU transmissions

NCU to LDACS base station

-198 Does not appear to offer any threat

Table 14 - Identification of most relevant GSM interference scenarios


4 GNSS

4.1 Overview

GNSS equipment is passive and so the user navigation equipment installed upon aircraft (and on the ground) has no need to transmit signals; it merely receives and processes signals transmitted by one or more constellations of satellites located in Medium Earth Orbit (MEO).

The radius of a MEO orbit is typically in excess of 20,000 km and as satellite power generation capabilities are limited, transmit powers are also limited. Thus the power spectral flux density of the wanted signal incident on, or near to the surface of the earth is inherently very low. Estimates of power spectral flux density of the wanted signal are presented in section 3.1.1.

Like all transmitters, the GNSS satellite can radiate unwanted signals in bands adjacent to the wanted signals. The characteristics of these signals are discussed and their likely power spectral flux densities are estimated in section 3.1.2.

4.1.1 Power spectral flux density of the wanted GNSS signals

The power of a single GNSS ranging signal is generally specified as the minimum power developed at the terminals of some defined receiving antenna located on or close to the surface of the earth. In reference [6] the nominal powers were all presented at the terminals of a 0dBi RHCP antenna. These powers are repeated in row 1 of Table 1.

Taking account of the effective area of a 0 dBi gain RHCP antenna, the power flux density of each signal at the surface of the earth is shown in shown in row 2 of Table 1.

Using the estimates of the effective bandwidth of each signal, and the estimated dynamic range, it is the possible to estimate the maximum power spectral flux density of each signal at the surface of the earth as shown in rows 3 to 6 of Table 1.

Finally having adjusted for the likely maximum number of signals visible for a given location it is possible to estimate the maximum power spectral flux density present at the surface of the earth for each of the sub-sets of GNSS signals shown in Table 1.

For those signals which illuminate the entire surface of the earth, the maximum power spectral flux densities range from -126 dBW/m²/MHz at 1176 MHz , -128 dBW/m²/MHz at 1207 MHz , -119 dBW/m²/MHz at 1227 MHz -121 dBW/m²/MHz at 1278 MHz and -116 dBW/m²/MHz at 1574 MHz.

In those areas covered by the high power military spot beams, the maximum power spectral flux densities range from -112 dBW/m²/MHz at 1227 MHz and -109 dBW/m²/MHz at 1574 MHz.

In order to protect the ARNS band, paragraph (c) of reference [2] notes that:

“that this Conference revised this provisional limit and decided that the level of -121.5 dB(W/m2) in any 1 MHz for the aggregate equivalent pfd (epfd) applying for all the space stations within all RNSS systems, taking into account the reference worst-case ARNS system antenna characteristics described in Annex 2 of Recommendation ITU R


M.1642, is adequate to ensure the protection of the ARNS in the band 1 164-1 215 MHz;”

Furthermore [7] recommends that the:

“that in the implementation of resolves 5 of Resolution 609 (WRC 03), in the frequency band 1 164-1 215 MHz, the maximum pfd produced at the surface of the Earth by emissions from a space station in the RNSS, for all angles of arrival, should not exceed -129 dB(W/m2) in any 1 MHz band under free space propagation conditions;”

It can be seen that the relevant estimates contained in Table 1 are consistent with the limits recommended by the ITU at WRC-2003.

All of the GNSS satellites considered employ either a CDMA or FDMA multiple access schemes. The GNSS signals are designed to provide a continuous navigation capability and are therefore intended to be transmitted continuously. Thus, for the purpose of this report, all GNSS signals can be considered to be continuous and therefore have a duty cycle of 100%.

4.1.2 Power spectral flux density of the unwanted out of band GNSS signals

The respective ICDs for the various GNSS systems do not specify out of band spurious emissions. The generic limits imposed by the ITU-R on radio transmitters are contained in [8]. However these limits do not apply to stations in the space service, since it states:

“These levels are not applicable to stations in the space services, but the levels of their spurious emissions should be reduced to the lowest possible values compatible with the technical and economic constraints to which the equipment is subject. Values for these systems may be provided by the relevant ITU-R Recommendations, when available (see Recommendation 66 Rev.WRC-2000)*).

*Note by the Secretariat: This Recommendation was abrogated by WRC-03.“

Therefore it is difficult to provide definitive information regarding the levels of the spurious emissions of the various GNSS satellites without obtaining access to the detailed procurement specifications for the individual satellite payloads.


Of those paths being studied as part of this project, only the following are relevant to GNSS since the transmitter is in MEO. The main scenarios are therefore:

� MEO satellite into aircraft on the ground;

� MEO satellite into airborne aircraft; and

� MEO Satellite into ground station.

4.2.1 MEO satellite into aircraft on the ground

In this scenario, the GNSS transmitter is located on a satellite in MEO and the victim LDACS receiver is located on an aircraft on the ground.

The power spectral flux density resulting from the individual GNSS wanted signals have been estimated in section 4.1.1 above. The estimated total power spectral


flux density from all of the GNSS wanted signals are shown diagrammatically in Error! Reference source not found.. The purple and blue curves represent the estimated total power spectral flux density incident at the surface of the earth outside and inside the areas covered by the military spot beam. Whilst the yellow curve indicates the WRC limit.

As the aircraft is located on the ground, the estimated total power spectral flux density from all of the GNSS wanted signals are shown in Error! Reference source not found. is directly applicable to this scenario.

The interfering power received from the GNSS satellite presented to the LDACS receiver will depend upon the effective area of the LDACS antenna in the direction of the sky.

The LDACS receive antenna may be located either on the underside of the aircraft’s fuselage or on the top side of the fuselage. When on the ground the upper antenna is likely to be selected and this will lead to the worst case received interfering power.

-140

-135

-130

-125

-120

-115

-110

-105

-100

1100 1120 1140 1160 1180 1200 1220 1240 1260 1280 1300

Frequency (MHz)

Po

we

r S

pe

ctr

al F

lux

De

ns

ity

(d

BW

/m2/M

Hz) Inside Military Spot Beam

Outside Military Spot Beam

WRC limit

Figure 6 - Received GNSS Signal Levels

4.2.2 MEO satellite into an airborne aircraft

In this scenario, the GNSS transmitter is located on a satellite in MEO and the victim LDACS receiver is located on an aircraft in flight.

Since atmospheric absorption at L-band and the difference in free space path loss is insignificant, the estimated total power spectral flux density from all of the GNSS wanted signals are shown in Error! Reference source not found. is also directly applicable to this scenario.



When the lower antenna is selected, as would be the case for air to ground communications, the gain of the LDACS antenna in the direction of the sky is likely to minimal. The exact gain would depend upon the antenna type and its precise location.

When the upper antenna is selected, as may be the case for air to air communications, the gain of the LDACS antenna in the direction of the sky near is likely to be its nominal value.

4.2.3 MEO satellite into ground station

In this scenario, the GNSS transmitter is located on a satellite in MEO and the victim LDACS receiver is located at the ground station.

The estimated total power spectral flux density from all of the GNSS wanted signals as shown in Error! Reference source not found. is also directly applicable to this scenario.


The gain of the LDACS ground station antenna are not know to the author; however, it is reasonable to assume that the ground antenna will provide a shaped bean with a maximum gain a few degrees above the horizontal. Such a pattern would maximise the range of the system and may provide a small aggregate attenuation to GNSS signals which will be, more or less, evenly distributed over the upper hemisphere.


5 DME

5.1 Overview

Distance measuring equipment (DME) provides pilots with distance information between the aircraft and the ground station, and is used in all phases of flight. A number of such procedures in common operational are described in the following sections. In all cases, the procedure involves reception of ground beacon DME replies on board an aircraft operating in TMA or en route airspace.

5.1.1 DME RNAV procedures

DME/DME RNAV is used for navigation on Area Navigation (RNAV) routes, RNAV Standard Instrument Departures (SIDs), and RNAV Standard Terminal Arrivals (STARs), where DME ranging from at least two DME facilities are used to determine the aircraft’s horizontal position. DME/DME RNAV offers higher accuracy at longer range compared to standard VOR/DME procedures. High Power DMEs13 are usually used to support DME/DME RNAV/RNP En Route operations.

DME/DME RNAV procedures are becoming an increasingly popular means of navigation. Navigation in airspace around some European hub airports, such as Arlanda, are already based on DME/DME procedures. In the US, NextGen has initiated a national program to renew DME infrastructure in support of DME/DME operations in its FY2009 work programme.

The accuracy of DME/DME RNAV14 depends on the accuracy of each DME ranging signals as well as the inclusion angle between the two DMEs used in determining the position. When using ICAO DME accuracy error, DME/DME RNAV (two DMEs with a RVSM baro-altimeter) can achieve RNAV-1 when limiting the inclusion angle between 30 degrees and 150 degrees. RNAV procedures are typically used in upper airspace operations where the distance to the DME beacon can extend to line of sight.

5.1.2 Precision approaches

Instrument landing system marker beacons provide information on distance from the runway by identifying predetermined points along the approach track.

The outer marker, when installed, is located 3.5NM to 6 NM from the threshold, usually within 250 ft of the extended runway centre line. It marks the approximate point at which aircraft normally intercept the glide slope, and designates the beginning of the final approach segment. When geographical constraints prevent marker equipment to be installed (e.g. over sea or mountainous terrain), the outer marker beacon is denominated by a DME fix.

The back course marker (BM), if installed, is normally located on the localizer back course approximately four to six miles from the runway threshold. The BM low pitched tone (400 Hz) is beard as a series of dots. It illuminates the aircraft's white

13 Typically 1000W or greater.

14 DME/DME accuracy study report, Proceedings of the 2008 National Technical Meeting of the Institute of

Navigation, January 2008.


marker beacon light. An NDB or DME fix can also be used and in most locations replace the BM.

5.1.3 Non precision approaches

In airports which are not equipped with ILS or VASI, a VOR/DME approach procedure allows a pilot to judge his glide slope especially in low visibility. Since there is no glide slope information for such an approach, it is classified as a non-precision approach.

The operation requires the aircraft to track the specified VOR radial to the arrival runway. After passing the final approach fix the aircraft descends to a Minimum Descent Altitude (MDA) until reaching the missed approach point. The missed approach point and final approach fix, in most cases, is identified by using DME.

The MDA is the minimum altitude that an aircraft may descend down to until the Missed Approach Point (MAP). For illustration, if the MDA at a particular airport is 400ft, and the MAP is 0.7 DME, this means that the aircraft can not go below 400ft until it reaches 0.7 DME unless the runway has been visually acquired.

The final approach starts at the FAF and ends at the MAP. The optimum length of the final approach is about five miles; the maximum length is about ten miles.

5.1.4 DME holding

A holding procedure involves flying an aircraft in a “racetrack” pattern in order to maintain the current position, referenced to a navigation beacon such as a VOR, until the next segment along the route (typically the approach to an airport) is available. The key steps of a standard holding procedure are as follows:

1. Having entered the holding pattern, on the second and subsequent arrivals over the fix, the aircraft executes a right turn to fly an outbound track that positions the aircraft most appropriately for the turn onto the inbound track;

2. The aircraft then continues outbound for one minute if at or below 14 000 ft, or one and a half minutes if above 14 000 ft . ATC specifies distance, not time, where a DME fix is to be used for holding (see below);

3. The aircraft finally turns right to realign the aircraft on the inbound track.

Figure 7 – Standard holding

DME holding is subject to the same entry and holding procedures described above, except that distances, in NM are used instead of time values. In describing


the direction from the fix on which to hold and the limits of a DME holding pattern, an ATC clearance will specify the DME distance from the navigation aid at which the inbound and outbound legs are to be terminated. The end of each leg is determined by the DME indications.

A typical example of how this procedure is executed is illustrated below. In this case, an aircraft cleared to the 270˚ RADIAL 10 mile DME fix, to hold between 10 and 15 miles, will hold inbound on the 270˚ radial, commence turn to the outbound leg when the DME indicates 10 NM and commence turn to inbound leg when the DME indicates 15 NM.

Figure 8 - DME holding

The distance between the DME navaid and the DME fix can vary considerably, depending on whether the aircraft is operating in dense continental airspace or in remote airspace. The largest expected distance is encountered in the case of upper airspace en route holding. In order to estimate the worst case distance, the en route holding patterns published in the UK AIP are considered. The largest distance noted is for the PLYMO holding fix15 which specifies a DME distance of 130 NM.

5.1.5 DME ground speed checks

An accurate estimate of ground speed is an important part of aircraft navigation. Ground speed is sensitive to local wind aloft conditions. Normally ground speed is available from ATC, but there are instances when the flight crews need to estimate ground speed from their own navigational sources, including DME.

Ground speed checks are typically carried out in en route airspace where wind conditions can change over a large distance. Ground speed checks can be carried out within any distance from a DME station provided the DME distance from the beacon is greater than or equal to the aircraft’s altitude (in thousands of ft) in order to limit the impact of slant range on the calculation below. The aircraft must also be flying either directly to or directly from a station to get an accurate ground speed check. The timing procedure starts when the DME indicator on the aircraft displays a whole number. After a predetermined time (in minutes), the DME distance that has elapsed is recorded. To calculate the ground speed, the distance (in nautical miles) is divided by the elapse time (usually 1 or 2minutes) and the quotient is

15 The holding procedure for the Plymouth fix specifies “Inbound track 077

0 MAG, turning left at 130

DME SAM.”


multiplied by 60, to obtain the ground speed in knots. For example, 12 nm/2 min = 6 X 60 = 360 knots

For aircraft operating at cruising level therefore, the distance to the DME beacon is anywhere between 37 NM and 200 NM.

5.1.6 DME arcs

There are a number of instrument approach procedures that incorporate DME arcs. The operational procedure for intercepting and maintaining such arcs are applicable to any airport that provides DME information16.

The following are the key steps taken as a typical example of an aircraft flying a DME arc:

1. The inbound aircraft tracks a VOR radial, while the pilot checks the DME mileage readout at intervals;

2. A .5 NM lead is usually satisfactory for groundspeeds of 150 knots or less; start the turn to the arc at 10.5 miles. At higher groundspeeds, use a proportionately greater lead.

3. Continue the turn for approximately 90°. The roll-out heading will be 055° in no-wind conditions.

4. During the last part of the intercepting turn, the pilot monitors the DME closely. If the arc is being overshot (more than 1.0 NM), the aircraft continues through the originally-planned roll-out heading. If the arc is being undershot, the aircraft rolls out of the turn early.

Figure 9 – DME arc

In the example illustrated in the figure, the procedure for intercepting the 10 DME when on an outbound route is basically the same, the lead point being 9.5 NM (10 NM minus .5 NM).

16 Such a facility may or may not be collocated with the facility that provides final approach guidance.


The key to intercepting an arc precisely at the desired DME lies in performing an accurate lead point calculation (LPC) to determine the correct lead point DME to initiate the interception turn. For radial to arc intercepts, the lead point is determined in miles (DME) instead of radials. When intercepting an arc, the pilot calculates the lead point at which the aircraft initiates the turn in order to intercept it at the correct distance. To determine the lead point, 1 percent of the ground speed is used as a rule of thumb. For example, whether flying inbound or outbound at a ground speed of 250 knots, your lead point will be 2.5 DME prior to the desired arc17.

DME arcs are normally associated with approaches to airports in the vicinity of the aircraft, at most 20 NM away. Considering the lead point, and the TMA airspeed restriction of 250 knots, the largest distance to the DME beacon in this case is estimated at 22.5 NM.


DME is a terrestrial navigation system with no operational requirement for aircraft to aircraft communication whether airborne or on the ground. As such, the relevant interference scenarios reduce to the following:

� DME interrogator to LDACS receiver on the same aircraft;

� DME interrogator to an LDACS receiver on the ground;

� A DME beacon to LDACS receiver on an aircraft; and

� A DME beacon to an LDACS receiver on the ground.

5.3 Summary

The table below identifies the power levels relevant to the interference scenarios above.

Path loss Maximum incident power

Scenario DME EIRP

Worst Typical Worst Typical

DME on an aircraft to LDACS on the same aircraft

58.5 dBm 35 dB (isolation assumed between antennas on the same side of the fuselage)

70.5 dB (based on a an effective separation of 8m between antennas on opposite ends of a A320 sized aircraft calculated at 1000 MHz)

23.5 dBm -12 dBm

17 When inbound to the arc, 1 percent is added to the arc DME and when outbound, 1percent is

subtracted from the arc DME when calculating the lead point.


A DME ground station to LDACS on an aircraft (en route)

18

70.0 dBm 92.5 dB (assuming an aircraft performing a DME-fix approach at 1000m)

102 dB (assuming an aircraft at a typical cruise altitude of 3000m)

-22 .5 dBm

-32 dBm

A DME ground station to an LDACS ground station.

70.0 dBm 96 dB (assuming a separation distance of 1.5 km between antennas on a medium sized airport)

103.3 dB (assuming a separation distance of 3.5 km between antennas on a large sized airport)

-26 dBm -33.3 dBm

DME on an aircraft to an LDACS ground station;

58.5 dBm 86.4 dB (assuming a separation distance of 500m between the aircraft and ground antenna located near the runway).

102 dB (assuming an aircraft at a typical cruise altitude of 3000m)

-27.9 dBm -43.5 dBm

A DME ground station to LDACS on an aircraft (TMA)19

60.0 dBm 94.7 dB (assuming a slant separation distance of 1.3 km for MAP

20

between the approaching aircraft and ground DME antenna)

113 dB (assuming an aircraft on a typical 6 NM final approach)

-34.7 dBm -53 dBm

Table 15 - Identification of most critical scenarios relevant to DME

18 Assuming the ground beacon is transmitting at a typical peak power of 10 kW EiRP

19 Assuming the ground beacon is transmitting at a typical peak power of 1 kW EiRP.

20 See section 5.1.3


6 SSR

6.1 Overview

The current major users of the 1090 MHz channel include aircraft responding to interrogations (i.e., Mode A/C and Mode S on 1030 MHz.) from ground SSRs and from ACAS. Also, each Mode S-equipped aircraft transmits short squitters once per second that are used to support ACAS target acquisition. Additional users of the 1090 MHz channel will be ADS-B and TISB. A basic 1090ES ADS-B airborne installation would transmit extended squitters at a rate of 4.2 per second. Different classes of aircraft have different transmitter power. There is also a class for ground vehicles.

It is assumed that ground stations will transmit TIS-B messages providing state vector information applicable to those aircraft that are not equipped with 1090ES.21

The levels of 1090 MHz RF mutual interference is generally expected to increase proportionally to the increase in aircraft traffic levels.

Traditional SSR systems use the sliding window format. Newer SSR systems use the monopulse technique. They operate in the same environment and therefore display the same scenarios but the transmission technique and the quality of the beam is different. The differences are summarised in the table below.

Monopulse Sliding window

Rotation period (sec) 4.6 4.7

Time share per interrogator (sec)

0.23 0.235

Beamwidth (degrees) 2.75 7.28

Burst length (msec) 35 95

Interrogation rate (msg/sec) 130 331.5

Table 16 - Monopulse vs sliding window SSR

6.2 SSR systems transmit power and EIRP levels

The ground interrogator operates only on 1030 MHz. SSR replies, Mode S replies, 1090ES ADS-B transmissions and TCAS signalling are all relayed on 1090 MHz.

The transmitter power mask for a SSR based interrogators and transponders operating on the above frequencies band is provided in [4]. This data is summarised in the following two tables.

21 A 1090ESequipped aircraft uses TIS-B messages to supplement ADS-B messages received directly

air-to-air from other 1090ES equipped aircraft.


Offset from carrier (MHz)

Relative power (dB)

Absolute power for interrogator

(dBm)22


antenna)

4 -6 +56 +83

6 -11 +51 +78

8 -15 +47 +74

10 -19 +43 +70

20 -31 +31 +58

30 -38 +24 +51

40 -43 +19 +46

50 -47 +15 +42

60 -50 +12 +39

Table 17 - Estimated off-channel EIRP for SSR interrogator

Offset from carrier (MHz)

Relative power (dB)

Absolute power for interrogator

(dBm)23


antenna)

1.5 -3 +54 +59

7 -20 +37 +42

25 -40 +17 +22

78 -60 -3 +2

Table 18 - Estimated off-channel EIRP for SSR transponder


SSR (and Mode-S) is primarily an air-ground communication system, however there exist operational situations in which the system continues to transmit when the aircraft is on the ground (for example in AS or GCS configurations).

When used as part of TCAS or as an ADS-B data link (1090ES), it does have an aircraft to aircraft component. Such uses, however, do not have a ground component (ie there is no operational requirement for aircraft to aircraft communication when one of the aircraft is on the ground). As such, only the following interference scenarios are relevant:

� SSR on an aircraft to LDACS on an the same aircraft;

� SSR on an airborne aircraft to an LDACS ground station;

� SSR on an aircraft on the ground to an LDACS ground station;

� SSR on an airborne aircraft to LDACS on another airborne aircraft;

� An SSR ground station to LDACS on an airborne aircraft;

22 Assumes an on channel power of 32 dBW (62 dBm) [3].

23 Assumes an on channel power of 32 dBW (62 dBm) [3].


� SSR on an aircraft on the ground to LDACS on an airborne aircraft;

� An SSR ground station to an LDACS ground station.

6.3.1 SSR/Mode S transponder to an LDACS receiver on the same aircraft

This scenario considers the operation of both the avionics SSR transponder and the LDACS receiver on the same aircraft. The transmit mask of the SSR transponder, and consequently the residual power in the LDACS receiver pass band, can differ significantly depending on the frequency separation from the 1090 MHz channel. Since both LDACS options have their closest assignable frequency at a distance greater than 78 MHz, the residual SSR transponder power will be 60 dB below the main carrier power.

The minimum path loss expected between the radios assumes antennas installed on the same side of the fuselage providing 35 dB of special isolation. The interference parameters would therefore be as indicated in the table below.


SSR Xponder maximum peak power 57 dBm

SSR residual off-channel power -3 dBm


Minimum Path Loss 35 dB


Victim interference received -33 dBm

Table 19 - Link budget parameters relevant to cosite scenario

6.3.2 SSR/Mode S airborne transponder to LDACS ground station receiver

This scenario considers the operation the avionics SSR transponder and the LDACS receiver resident in the ground station. Again, the transmit mask of the SSR transponder can differ significantly depending on the frequency separation from the 1090 MHz channel.

In this case, a representative channel offset from (SSR) carrier is 1.5 MHz for L-DACS/1 and 78 MHz for L-DACS/2 (see Table 18).

The minimum path loss expected between the radios is derived from Scenario 3 (see Table 3), hence 66 dB of isolation. The interference parameters would therefore be as indicated in the table below.


Value Parameter

Near band Far band

Units

SSR Xponder maximum peak power 57 57 dBm

SSR residual off-channel power 54 -3 dBm

Interferer antenna gain 5 524

dBi



Victim interference received 1 -56 dBm


6.3.3 SSR/Mode S transponder on the ground to LDACS ground station receiver

This scenario considers an SSR/Mode S equipped aircraft operating on the ground interfering with an LDACS installation on the ground.

In order to estimate the SSR incident off-channel power, a representative worst case frequency separation is considered for LDACS. For LDACS1, the lower end of the RL band is 1048.5 MHz (∆f = 41.5 MHz), and for LDACS2 the upper end of the band is 975 MHz (∆f = 115 MHz). From Table 18, the residual power emanating form the 1030 MHz transmissions have been interpolated at 15 dBm and -3 dBm respectively.

The isolation relevant to this scenario (from Table 3) is 66 dB.

Value Parameter

LDACS1 band LDACS2 band

Units

SSR interrogator maximum peak power

57 57 dBm

SSR residual off-channel power 15 -3 dBm




Victim interference received -38 -56 dBm


6.3.4 SSR/Mode S transponder to LDACS receiver on another airborne aircraft

This scenario is similar to that described in 6.3.1, except that the minimum isolation figure is 82 dB per scenario 1 in Table 3.The interference parameters would therefore be as indicated in the table below.

24 The transponder signal is primarily directed to ground stations, hence the antenna is typically located

on the underside of the fuselage. The position should give the antenna a full 360 degree view of the horizon. The maximum gain of a typical SSR airborne co-polar antenna pattern (NTIA 01-43) when airborne, considering a 30 degree elevation angle on a bottom mounted antenna is 5 dBi.










6.3.5 SSR/Mode S interrogator to LDACS on an airborne aircraft

This scenario considers a ground-based SSR interrogator interfering with an overflying aircraft operating LDACS. The altitude of the aircraft depends on whether the aircraft is:

• an over-flight using the airport as a waypoint,

• an approaching aircraft, or

• a departing aircraft.

Overflights are typically conducted above the TMA, at an altitude of at least FL150 (4.5km). Approaching aircraft commence the final approach at about 10 NM (18.5 km), which is when the final coordination for the flight takes place. After this point, the aircraft is in a stable approach and committed to land, unless an incident occurs which places the flight on a missed-approach path. Aircraft departing from the same airport have the shortest exposure time due to the acceleration of the outbound flight. However it is also the closest distance to the SSR interrogator on the airport surface during take-off when the aircraft enters the main beam of the interrogator at a time when critical data communications may take place. Location of the radar antenna to the active runway depends heavily on the size of the airport and varies from one airport to another. For small sized airports, this distance can be as close as 1000 feet (305 metres). This results in about 82 dBm of isolation, which is consistent with the minimum and maximum bounds specified in Table 5.

The interference parameters (along with the ∆f assumed in 6.3.3) is as indicated in the table below.

Value Parameter


Units


62 62 dBm

SSR residual off-channel power 31 15 dBm




Victim interference received -16 -32 dBm



6.3.6 SSR/Mode S transponder on the ground to LDACS airborne receiver

This scenario sees ground-based SSR equipped aircraft interfering with LDACS equipped aircraft operating n the vicinity of the airport. The closest critical path is when both aircraft are operating in the vicinity of the runway. For single runway operations, we consider an aircraft on the CAT3 holding line (137 metres from runway centreline [4]) while an aircraft lands (205 metres separation considering approaching aircraft at 200 feet above threshold). For dual runway operation, we consider arriving and departing traffic operating at a runway separation distance25 of 3400 feet (1035 metres). Both are highly transient operations due to the speed of the approaching and departing aircraft – the smaller of the two is considered as a worst case as it is reasonable that rotary wing aircraft can also operate at this height above an airport.

The resulting isolation figure (evaluated at 1000 MHz) is 78 dB. This is consistent with the minimum isolation bound for the applicable scenario 7 of 76 dB. The interference parameters would therefore be as indicated in the table below.









6.3.7 SSR/Mode S interrogator to LDACS ground station receiver

This scenario considers SSR/Mode S interrogators interfering with an LDACS installation on the ground. Although the terrestrial base station could potentially be located in the far field for en route communications, LDACS is intended to cover airport and approach communications. Therefore the worst case ground station separation distance is considered with the LDACS and SSR equipment co-located at the same airport. This is equivalent to scenario 10 with an isolation figure of just 30 dB (see Table 5). The interference parameters would therefore be as indicated in the table below.

The same ∆f has been considered as those in 6.3.3. From Table 17, the residual power emanating form the 1030 MHz transmissions have been estimated at 31 dBm and 15 dBm respectively.

25 For independent parallel operations.


Value Parameter


Units


62 62 dBm

SSR residual off-channel power 31 15 dBm




Victim interference received 36 20 dBm


6.4 Summary

The table below summarises the outcomes of the seven interference scenarios identified above.



Notes

SSR/Mode S interrogator to LDACS ground station receiver

20 to 36

This is the largest expected outfall from the SSR to LDACS due to the inherently high interrogator power, high antenna gains, and the close proximity of co-located stations. However the isolation figure can be increased significantly through the use of filtering techniques. In practise, careful site planning will also lead to better isolation between the two antennas.

SSR/Mode S interrogator to LDACS on an airborne aircraft

-32 to -16

SSR/Mode S transponder to an LDACS receiver on the same aircraft

-33

This scenario assumes that the L-DACS transmitter and the victim SSR transponder are isolated by 35 dB and that both antennas are mounted on the same side of the aircraft.

SSR/Mode S airborne transponder to LDACS ground station receiver

-56 to 1

Sensitive to the frequency separation to the 1090 MHz channel.

SSR/Mode S transponder on the ground to LDACS ground station receiver

-56 to -38

Same as above.

SSR/Mode S transponder on the ground to LDACS airborne receiver

-76

Transient scenario resulting in very short exposure time.

SSR/Mode S transponder to LDACS receiver on another airborne aircraft

-80

Table 23 - Identification of most critical scenarios relevant to SSR systems


7 UAT

7.1 Overview

UAT is essentially an air-ground communications link broadcasting ADS-B data in regular and periodic transmissions. Although its time-based usage profile is dissimilar to that of DME and SSR (i.e. service invocation at the user level and burst profile at the physical level), it has a similar usage profile in the operational sense. The UAT system transmits and receives both in the en route and approach phases of flight, the location of radio equipment and isolation is similar to that of other L-band systems, and the systems power budget is of the same order of that of other L-band systems due to similar operational range requirements.

The main difference is that UAT operates on a single global signalling channel at 978 MHz. Therefore all residual power measurements are relative to the location of this channel. Although this document is intended to remain detached from specific LDACS system properties, there is no intention of operating LDACS co-channel with UAT or in the immediate vicinity. This has been taken into consideration below in the power mask requirements of UAT.

7.2 UAT transmission power and EIPR levels

UAT avionics equipment transmission power is summarised in the following table, as derived from the UAT MOPS.

Equipment class Tx power at antenna (dBm)

A0/A1L 38.5 – 42.5

A1H/A2 42.46

A3 50-54

Table 26 - UAT avionics transmit power (MOPS)

The following figure illustrates the UAT transmit mask, as derived from the UAT MOPS. Given the separation of the UAT signalling channel (978 MHz) from the planned LDACS bands, the frequency separation is considered to be greater than 3 MHz, therefore the level of adjacent channel Protection (ACP) offered is considered to be at least 60 dBc i.e. 60 dB below the power level indicated in Table 26.

The UAT SARPs specify an upper bound for the transmitter power of 54 dBm, at the antenna end of the feedline (i.e. including cable loss).


Figure 10 - UAT transmit mask (MOPS)

Considering the aircraft transmitter class of the highest power from Table 26 (54 dBm) and the expected ACP in the LDACS band (minimum 60 dBc), the incident power is -6 dBm at zero isolation26.

Typical airborne installations currently use antennas with a gain of 0 dBi. Experimental work carried out with UAT radios has considered 5.162 dBi gain antennas for aircraft installations and 8 dBi gain antennas for ground installations [5].


UAT is an air-ground communication system with no operational requirement for aircraft to aircraft communication whether airborne or on the ground. As such, only the following interference scenarios are relevant:

� UAT on an aircraft to LDACS on an the same aircraft;

� UAT on an aircraft to an LDACS ground station;

� A UAT ground station to an LDACS ground station.

Note – The UAT signalling channel of 978 MHz is part of the DME band. The results of the previous testing has shown that co-channel operation of DME and UAT is possible in the approach/landing scenario, albeit only at low density UAT operations [3]. However in the majority of the cases, only first-adjacent (DME to UAT) operation was considered in the worst case. Due to the upper and lower limits of the planned LDACS bands, the current scenario considers off-channel interference only (see 7.2).

26 The interference scenarios identified below will determine how much isolation is applicable to each

operational case.



7.4.1 UAT on an aircraft to LDACS on an the same aircraft

The applicable isolation figure is 30 dB per scenario 5. Considering the frequency separation to the uppermost bound of the LDACS2 band (975 MHz) the ACP protection level at 3 MHz separation is -55dBc. Considering the UAT transmission mask, protection levels offered at greater frequency separations typical of LDACS1 are at most 5 dB better (hence similar), therefore -55 dBc is considered as a binding case.


UAT airborne transmitter power 54 dBm

UAT residual off-channel power -1 dBm





Table 27 - Link budget parameters relevant to scenario

7.4.2 UAT on an aircraft to an LDACS ground station

The applicable isolation figure is 66 dB per scenario 3 (see Table 3).








Table 28 - Link budget parameters relevant to scenario

7.4.3 A UAT ground station to an LDACS ground station

The applicable minimum isolation figure is 30 dB per scenario 10 (see Table 3).









Table 29 - Link budget prameters relevant to scenario

7.5 Summary

The table below summarises the outcomes of the three interference scenarios identified above.


Notes

UAT ground station to an LDACS ground station

-15

Due to the vicinitity of co located stations, this is the highest incidence of UAT power on the LDACS victim. However due to the relatively low power of the UAT ground transmitter (when compared to DME beacons and SSR interrogators) the interference spillage is benign. Further isolation can be assured by implementing additional filtering at the ground station sites.

UAT on an aircraft to LDACS on an the same aircraft -31

The limited cosite isolation available leads to a relatively high incidence of UAT power. This can be even higher if LDACS is to be installed on smaller aircraft (such as GA aircraft operating UAT today).

UAT on an aircraft to an LDACS ground station

-67

This is a transient situation involving aircraft passing in proximity to the ground statin antenna while operating on the airport surface. However the interference power is relatively benign and can be controlled by careful siting of the LDACS antenna.

Table 30 - Identification of most critical scenarios relevant to UAT systems


8 JTIDS/MIDS

8.1 Overview

The Joint Tactical Information Distribution System (JTIDS) is an L-band TDMA network radio system used by NATO to support data communications needs, principally in the air and missile defence community. It provides high-jam-resistance, high-speed, crypto-secure connectivity.

JTIDS is one of the family of radio equipment implementing Link 16. Link 16, a highly-survivable radio communications design to meet the most stringent requirements of modern combat, provides reliable situational awareness for fast-moving forces. JTIDS is defined in NATO document STANAG 5516.

The Multifunctional Information Distribution System (MIDS) represents the NATO requirement which can be met by JTIDS/Link 16. Most modern JTIDS systems are actually MIDS systems. At the user level, JTIDS and MIDS can be assumed to be interchangeable. MIDS is defined in NATO document STANAG 4175.

JTIDS provides digital communication of data and voice for command and control, navigation, relative positioning, and identification. It is a time division multiple access (TDMA) communication system which operates over line-of-sight ranges up to 500 nautical miles with automatic relay extension beyond.

The use of the frequency band 960 to 1215 MHz by JTIDS/MIDS equipment is made possible under the provisions of ITU Radio Regulation number S4.4. That is, JTIDS/MIDS transmissions shall not cause harmful interference to either existing or future equipment and systems in the Aeronautical Radionavigation Service and for itself cannot claim protection from harmful interference.

NATO operates JTIDS over 52 frequencies in the frequency band 960 to 1215 MHz. The operation of this system is agreed on a bilateral basis between the military and civil aviation authorities within each country and is normally subjected to some form of frequency clearance agreement. Within some states like the UK, this agreement is designed such that the maximum JTIDS pulse density allowable is approximately 9dB below the point where DME will fail to meet its operation requirement. As it is unlikely that a new frequency clearance agreement restricting the pulse density even further could be agreed with the military, the future communications system will only have approximately 9dB of margin to use.

8.1.1 Technical Parameters

While the system is capable of transmitting on a single frequency at 969 MHz, the normal mode of operation is where individual pulses are transmitted using a pseudorandom hopping sequence across 51 carrier frequencies (3 MHz spacing) in the 969 to 1008 MHz, 1053 to 1065 MHz and 1113 to 1206 MHz bands inclusive.

The system employs a TDMA transmission architecture with a time slot duration of 7.8125 milliseconds (ms). Each terminal transmission within a time slot consists of a sequence of either 72 pulses, 258 pulses or 444 pulses spaced by 6.6 microseconds (µs). Individual pulses are 6.4 µs in duration and the carrier is modulated by Continuous Phase Shift Modulation (CPSM) at a rate of 5 megabits per second to produce a 32 bit message symbol. Pulse rise and fall times are approximately 800 nanoseconds (ns).


The active transmission period for a standard (258 pulses) time slot is 1.6512 ms. The signal format accommodates up to 128 time slots per second giving a maximum pulse rate of 56,832 pulses per second (444 pulse time slots). There are 1536 time slots in a frame of 12 seconds duration. Time Slot Duty Factor (TSDF) is the percentage of time slots occupied in a 12 second frame (based on 258 pulses per time slot).

The pulse spectrum is measured in a 300 kilohertz (kHz) bandwidth.

� At ± 3 MHz from the carrier - at least 10 dB below peak.



� At more than ± 15 MHz from the carrier - at least 60 dB below peak.

Note that emission within ± 7 MHz of 1030 MHz and 1090 MHz are at least 60 dB below peak with reference to the maximum JTIDS/MIDS signal level measured in a 300 kHz bandwidth

Maximum transmitter power is a nominal 200 Watts measured at the terminal output. Transmitter antenna gains is as follows27:

� Ground Station, 4dBi.

� Large Aircraft, 4 dBi.

� Fighter Aircraft, 3 dBi.


JTIDS operates on a non-interference basis, that is to say that it is not permitted to cause interference to existing services an must also be prepared to suffer from any interference caused by the primary users of the band. As such, JTIDS is not afforded any protection from other authorised services, including LDACS; nor is LDACS required to offer any protection to JTIDS.

Nonetheless it is commonplace for systems operating in L-Band to consider the effects of JTIDS operation within the band. JTIDS systems have both airborne and ground transmitter components and interference to LDACS could come from either, however the situation in which JTIDS is used on the same aircraft as LDACS will not be considered. As such, the following interference scenarios are relevant:

� JTIDS on an airborne aircraft to an LDACS ground station;

� JTIDS on an aircraft on the ground to an LDACS ground station;

� JTIDS on an airborne aircraft to LDACS on another airborne aircraft;

� A JTIDS ground station28 to LDACS on an airborne aircraft;

� JTIDS on an aircraft on the ground to LDACS on an airborne aircraft;

27 These figures take into account nominal losses between the transmitter and antenna.

28 Note that a JTIDS ground station could be on a seafaring vessel.


� A JTIDS ground station to an LDACS ground station.

As JTIDS is a frequency hopping technology, the interference presented to LDACS will be varying and transient. As such, JTIDS/MIDS scenarios also need to be defined in terms of source time slot duty factor (TSDF), a measure of number of pulses per second, and source received power level. The TSDF is a two term parameter that specifies the maximum number of JTIDS transmitted pulses allowed within a specified geographic portion of the structure. This representation includes both the total number of pulses from all users in a given region (Total Pulse Density) and the maximum number of pulses for the highest single user (Maximum Single User). These are represented in percentages (%) where 396,288 pulses per 12 seconds (Frame) is 100%. TSDF is not a fraction and is only written with a slash (/) for convenience. For example, a TSDF of 40/20 is not the same as a TSDF of 100/50.

The following table defines the various possible received power levels in the possible scenarios. These signal levels are for an on-frequency hop of the JTIDS system, i.e. when the hop frequency coincides with the frequency on which the LDACS receiver is opeating

Scenario JTIDS EIRP Path Loss Maximum Received Power

29

JTIDS on an airborne aircraft

30 to an LDACS

ground station

57 dBm 66 to 144 dB –9 dBm

JTIDS on an aircraft on the ground to an LDACS ground station

57 dBm 66 to 100 dB –9 dBm

JTIDS on an airborne aircraft to LDACS on another airborne aircraft

57 dBm 82 to 144 dB –25 dBm

A JTIDS ground station to LDACS on an airborne aircraft;

57 dBm 66 to 144 dB –9 dBm

JTIDS on an aircraft on the ground to LDACS on an airborne aircraft;

57 dBm 76 to 114 dB –19 dBm

In the worst case, therefore, the level of interfering signal that an LDACS receiver is likely to encounter from a JTIDS transmitter is -9 dBm. It is worth noting, however, that when on an adjacent 3 MHz channel, the level of interference will still be relatively high at -19 dBm as the pulse spectrum is only reduced by 10 dB at this offset. Given that the system hops in a pseudo-random fashion, there is therefore twice the probability of this 10 dB lower signal being received than a -9 dBm signal.

29 This assumes a receive antenna gain of 0 dBi.

30 In all cases where JTIDS is mounted on an aircraft, the antenna gain figures for a larger aircraft have

been used as this is marginally (by 1 dB) the worst case scenario.


However, the extent to which this will cause interference depends upon the TSDF. For simulation purposes, in similar situations (e.g. for GNSS receiver testing31), the worst case TSDF’s 100/50 has been used with multiple networks in the foreground and background combining to produce the overall interference scenario.

In the case of a 100/50 scenario, and based on random hopping between all 51 channels, emissions from any given unit will be present on-channel for a maximum of just over 1% of overall time. Adjacent channel emissions at -10dB compared to co-channel emissions will be present for a maximum of 2% of overall time. Background network are typically at least 25dB below foreground networks.

The table below therefore gives the probability of the various signal levels (within a 12 second frame) in each of the scenarios listed above.

Scenario JTIDS EIRP Path Loss Maximum Received Power

32

JTIDS on an airborne aircraft to an LDACS ground station

57 dBm 66 to 144 dB –9 dBm

JTIDS on an aircraft on the ground to an LDACS ground station

57 dBm 66 to 100 dB –9 dBm

JTIDS on an airborne aircraft to LDACS on another airborne aircraft

57 dBm 82 to 144 dB –25 dBm

A JTIDS ground station to LDACS on an airborne aircraft;

57 dBm 66 to 144 dB –9 dBm

JTIDS on an aircraft on the ground to LDACS on an airborne aircraft;

57 dBm 76 to 114 dB –19 dBm

31 “Validation of the Feasibility of Coexistence of the New Civil GPS Signal (L5) with Existing Systems”,

MITRE Corporation, 2001

32 This assumes a receive antenna gain of 0 dBi.


A Abbreviations and acronyms

DME Distance Measuring Equipment

GCS Ground Clutter Suppression

GNSS Global Navigation Satellite Service

GSM Global System for Mobile communications

JTIDS Joint Tactical Information Distribution System

LDACS L-Band Digital Aeronautical Communications System

MIDS

NATO North Atlantic Treaty Organisation

STANAG STANdard AGreement

TDMA Time Division Multiple Access

TSDF Time Slot Duty Factor

UAT Universal Access Transceiver


B References

[1] UK Interface Requirement 2014, Public Wireless Networks, Ofcom, August 2005, 98/34/EC notification number 2005/245/UK.

[2] Report from CEPT to the European Commission in response to the EC Mandate on Mobile Communications Services on board Aircraft (MCA), CEPT Report 016, 12 June 2007.

[3] DME Operation in the Presence of UAT Signals, Mike Biggs for the FAA, Navigation Systems Panel, Spectrum Subgroup meeting, May 2004.

[4] ICAO Annex 14 Volume 1.

[5] UAT: A case ofr gain Antennas, RTCA SC 186, Working Group 5 (UAT-WP-6-16), UPS Aviation Technologies, July 2001.

[6] Helios Technology, Compatibility criteria and test specification for GNSS (C5) version B.

[7] ITU, Guidelines for consultation meetings established in Resolution 609, RECOMMENDATION 608 (WRC-03).

[8] ITU, Tables of maximum permitted power levels for spurious or spurious domain emissions, APPENDIX 3 (Rev.WRC-03).

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