proposed l-band interference scenarios...tx-rx spacing between two systems) and frequency planning...

Proposed L-Band Interference Scenarios

DOCUMENT IDENTIFIER: D1

ISSUE: 1.0

ISSUE DATE: 04.02.2008

AUTHOR: DEUTSCHES ZENTRUM FÜR LUFT- UND

RAUMFAHRT E.V. (DLR)

DISSEMINATION STATUS: CO

DOCUMENT REF: CIEA15_EN511.10

Report number: D1 Issue: 1.0

File: D1_Interference_Scenarios_10.doc Author: DLR

Page: I

History Chart

Issue Date Changed Page (s) Cause of Change Implemented by

DRAFT A 14.12.2007 All sections New document DLR

1.0 01.02.2008 All sections Finalisation and incorporation of review comments received by ECTL

DLR

Authorisation

No. Action Name Signature Date

1 Prepared S. Brandes, M. Schnell (DLR)

2008-02-01

2 Approved M. Schnell (DLR) 2008-02-01

3 Released C. Rihacek (FRQ) 2008-02-05

The information in this document is subject to change without notice.

All rights reserved. No part of the document may be reproduced or transmitted in any form or by any means, electronic or mechanical, for any purpose, without the written permission of FREQUENTIS AG.

Company or product names mentioned in this document may be trademarks or registered trademarks of their respective companies.

CCMU

Freigabe



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Contents

1. Executive Summary.......................................................1-1

2. Introduction .................................................................2-1

3. Modelling of DME Interference.........................................3-1 3.1.1. Implementation of DME interference................................................. 3-2 3.1.2. Consideration of duty cycle ............................................................. 3-3

4. DME Interference Scenarios Involving DME GSs.................4-1 4.1. Static victim receiver...................................................................... 4-4 4.2. Example: B-AMC forward link scenario with static victim RX................. 4-7 4.3. Moving Victim Receiver................................................................... 4-9 4.4. Example: B-AMC forward link scenario with moving victim RX ............ 4-10

5. DME Interference Scenarios Involving Airborne DME Interrogators................................................................5-1

5.1. NAVSIM Procedure ......................................................................... 5-1 5.2. Determination of Interference Power Distribution................................ 5-3 5.3. Determination of Duty Cycle............................................................ 5-5 5.4. Example: B-AMC Reverse Link Scenario ............................................ 5-8

6. Consideration of Other Interference Sources .....................6-1 6.1. JTIDS/MIDS Interference ................................................................ 6-1 6.2. SSR Mode S Interference ................................................................ 6-4 6.3. UAT Interference ........................................................................... 6-8

7. Conclusions ..................................................................7-1

8. References ...................................................................8-1

9. Abbreviations ...............................................................9-1



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Illustrations

Figure 3-1: Block diagram of interference simulator ............................................ 3-1 Figure 3-2: Example of parameter file for DME interference.................................. 3-2 Figure 3-3: Generation of DME pulse pairs assuming 3600 ppps duty cycle............. 3-4 Figure 4-1: DME stations at Paris CDG, observed from FL450 ............................... 4-2 Figure 4-2: Position of DME/TACAN stations around CDG, 995 MHz ....................... 4-3 Figure 4-3: Position of DME/TACAN stations around CDG, 997 MHz ....................... 4-4 Figure 4-4: DME and TACAN ground antenna vertical pattern GTx (φ) [D4] ............ 4-6 Figure 4-5: Vertical patterns of airborne DME and MIDS antennas GRx (α) [D4] ...... 4-6 Figure 4-6: PDF for four DME/TACAN stations at 994 MHz .................................. 4-11 Figure 4-7: PDF for three DME/TACAN stations at 995 MHz ................................ 4-12 Figure 4-8: PDF for two DME/TACAN stations at 996 MHz................................... 4-12 Figure 4-9: PDF for DME/TACAN stations at 997 MHz......................................... 4-13 Figure 5-1: Snapshot of air traffic possibly interrogating DME stations at channel

35X/Y and corresponding interference power at victim ground station ... 5-2 Figure 5-2: Topology of DME stations round CDG, 35X/Y...................................... 5-3 Figure 5-3: Interference power PDFs originating from interrogations of DME

stations at 1059 MHz located around Paris, CDG................................. 5-5 Figure 5-4: Topology of DME/TACAN stations at Paris CDG, 1059 MHz ................... 5-7 Figure 5-5: Cross section of relevant fraction of operational range within

overlapping area............................................................................ 5-8 Figure 5-6: Interference power PDFs originating from interrogations of DME

stations at 1058 MHz located around Paris CDG.................................. 5-9 Figure 6-1: Measured JTIDS/MIDS TX Spectrum ................................................. 6-1 Figure 6-2: JTIDS/MIDS TX Spectral Mask ......................................................... 6-2 Figure 6-3: Distribution of interference power from JTIDS .................................... 6-4 Figure 6-4: Required spectrum limits for transponder transmitter [Annex10] .......... 6-6 Figure 6-5: Required spectrum limits for interrogator transmitter [Annex10] .......... 6-7

Tables

Table 4-1: NAVSIM data extraction, victim receiver in 45000 feet (rH = 261 nm) at CDG............................................................................................. 4-7



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Table 4-2: Example: DME/TACAN stations for B-AMC forward link scenario at FL 450 assuming frequency planning, static B-AMC victim RX................... 4-8

Table 4-3: B-AMC forward link scenario with moving victim RX .......................... 4-11 Table 5-1: DME/TACAN stations for RL scenario with frequency planning............... 5-9 Table 6-1: Pulse shapes of Mode S replies [Annex10, Tab.3-2] ............................ 6-5 Table 6-2: Pulse shapes of Mode S and interrogations ........................................ 6-6



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1. Executive Summary

In this deliverable, procedures for generating interference scenarios are described that model interference from existing L-band systems towards new candidate L-band systems. The candidate L-band systems intend to use different frequency ranges and therefore they have to cope with significantly different interference conditions. Hence, it is difficult to define detailed, universally applicable interference scenarios, which can be used for investigating any arbitrary L-band system. However, the general procedures outlined in this deliverable can be applied to any frequency range and any L-band system for generating appropriate interference scenarios.

As DME is the main source of interference in the aeronautical L-band, particular emphasis is put on modelling of DME interference and defining appropriate interference scenarios.

In Chapter 3, an interference simulator is described that generates the DME signal in time domain. Different interference conditions can be set by varying the power, the duty cycle, the distance between the two pulses of a pulse pair, the centre frequency of the DME signal as well as the number of different independent interferers having the same or different centre frequencies.

In Chapter 4, the methodology for generating interference scenarios taking into account DME ground stations is described. With the NAVSIM tool, the interference power received from any DME ground station operating in a certain area can be determined based on actual DME channel assignments. The interference power is determined at the input of the victim receiver, taking into account elevation angle dependent antenna patterns of typical L-band devices, cable losses and free space loss due to the spatial separation between the interference source and the victim receiver. Thereby, the victim receiver can be considered either static resulting in fixed interference power values or mobile (moving in a certain range) resulting in a varying interference power described by a power probability density function (PDF). From these data, interference scenarios for any L-band system can be derived by simply considering those channels relevant for the victim system under investigation. As an example, an interference scenario has been defined for the B-AMC forward link (FL).

In Chapter 5, interference originating from aircraft interrogating DME ground stations is investigated. The victim receiver is on ground. With the NAVSIM tool, the DME ground stations, which are interrogated by aircraft in the considered area, are identified and the resulting interference power received at the victim receiver on ground is determined. For each ground station in the considered area, an interference power PDF is obtained that represents the interference caused by interrogations of different aircraft at different distances to the respective DME station and to the victim ground station. Moreover, a procedure for determining the corresponding aggregate duty cycle is described. Interference scenarios are determined by generating the required data, i.e. interference power PDF and duty cycle for all relevant DME stations in the considered channels and in the considered area. As an example, an interference scenario for the B-AMC reverse link (RL) is given.

Finally, interference from other L-band systems is addressed. In the time domain, the pulses of JTIDS, UAT and SSR can be modelled in a simplified way avoiding the detailed implementation of the signal generation of the considered systems. For the duration of the pulses, noise with a power level corresponding to the received interference power is added to the desired signal. Pulse duration and duty cycles are given in the specifications; the received power level can be derived from the distance in space and in frequency between the interfering and the victim system.



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With the described procedures, all building blocks are available that are required to generate interference scenarios for any arbitrary L-band system. Depending on the position in the L-band, different interference sources may be relevant and thus are requiring a combined application of different procedures for generating an overall interference scenario reflecting the interference situation for the considered L-band system.

----------- END OF SECTION -----------



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2. Introduction

In this report, interference scenarios for simulating interference from existing L-band systems towards any candidate L-band radio system are defined.

The L-band systems to be considered are:

! DME,

! JTIDS/MIDS,

! SSR Mode S, and

! UAT.

In the first stage of the B-AMC study, the impact of these systems onto the B-AMC system has already been investigated. Based on these results summarized in the B-AMC Deliverable D5 [D5], the procedure for generating interference scenarios is generalized such that it can be applied to any candidate L-band system independent of its frequency offset to DME channels. In addition, the influence of JTIDS/MIDS, SSR Mode S, and UAT is considered and included into the interference scenarios.

The proposed scenarios aim at enabling comparative investigations of typical performance/capacity of different candidate L-band systems in a typical environment comprising multiple interferers. Therefore, location, power, duty-cycle and other parameters of interfering sources are generally based on statistics (distributions). The exact laboratory assessment of the worst-case impact of interference (e.g. at closest TX-RX spacing between two systems) and frequency planning may require different kind of deterministic scenarios (one desired signal source, one undesired signal source, one victim receiver).

Note: As the candidate L-band systems are intended to be operated in different parts of the aeronautical L-band each exhibiting significantly different interference conditions, in this document only the rationale for taking into account different interfering L-band systems and determining interference scenarios is described. It is difficult to define a detailed common interference scenario that can be used for each candidate L-band system.

This deliverable is organized as follows. As DME is considered to be the main source of interference, emphasis is put on its accurate modelling. In Chapter 3, the methodology for modelling DME interference is described. In Chapters 4 and 5, interference scenarios with DME ground and airborne stations as interference source are defined taking into account real DME channel assignment and real air traffic. The impact of other L-band systems such as JTIDS/MIDS, SSR Mode S and UAT is addressed in Chapter 6.

----------- END OF SECTION -----------



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3. Modelling of DME Interference

A simulator for modelling DME interference has to be designed to simulate the impact of DME interference on the victim receiver as realistically as possible. Hence, a realistic representation of the interference signals and their processing at the victim receiver is considered by means of this simulator.

Therefore, pulse pairs with a Gaussian shape characteristic for DME signals are generated in time domain. At the input of the victim receiver, this signal is superimposed with the desired signal. Afterwards, it is filtered by the RF filter and processed in the same way as the desired signal.

In the first part of the B-AMC study, it has been shown that it is important to consider B-AMC receiver processing (right part of Figure 3-1) as it may have several effects on the spectral shape of the DME signal as experienced by the victim B-AMC receiver. The same applies to any victim receiver. However, the task of modelling a particular victim receiver is technology-specific and must be done individually for each candidate victim receiver, which is out of the scope of this work.

Figure 3-1: Block diagram of interference simulator

The interference simulator is designed flexibly. Therefore, it is be able to simulate an arbitrary number of DME interferers each operating in an arbitrary channel within the L-band. The parameters for each interferer can be adjusted in a parameter file serving as input to the interference simulator. In the parameter file, the following values can be set:

! TYPE DME

! FREQ absolute DME transmitting frequency in MHz. The victim receiver centre frequency is given in the parameter file for the complete simulation chain. Hence, the DME interferer frequency relative to the victim system can be adjusted in the interference simulator.

! DELTAT interval between two pulses of a pulse pair in µs, chosen according to operational mode of interferer

! POWER received total power of DME interferer in dBW, measured at the input of the victim RX, i.e. after the RX antenna. The procedure for determining the received interference power is addressed in the next chapter. Instead of a constant interference power, a probability density function (PDF) of the power (that produces the corresponding dBW value) can be used in order



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to model a movement of the victim RX or the interfering airborne DME stations.

! DUTY duty cycle of DME interferer in ppps

Note: The parameters TYPE, FREQ and POWER apply to any type of L-band interferers; the parameters DUTY and DELTAT are DME-specific and are used for generating a time domain representation of the interfering DME signal. In case of other L-band systems, similar or different parameters can be used for describing the time behaviour of these signals.

In Figure 3-2, an extraction from such a DME interference parameter file is shown. If multiple DME interferers occur in the same channel, e.g. two interferers at 992 MHz and four interferers at 995 MHz, a statistically independent interference signal for each interferer is generated. Finally, all interference signals are summed up and processed in the victim receiver as depicted in Figure 3-1. This is repeated for each simulation run. If the parameter "POWER" is not set to a fixed value as shown in Figure 3-2, but a power PDF will be chosen instead, in each simulation run, a new power value is generated from the power PDF of the corresponding interferer.

TYPE=DME FREQ=992 DELTAT=12 POWER=-106.38 DUTY=3600 TYPE=DME FREQ=992 DELTAT=12 POWER=-104.78 DUTY=3600 TYPE=DME FREQ=994 DELTAT=12 POWER=-106.40 DUTY=3600 TYPE=DME FREQ=995 DELTAT=12 POWER=-114.00 DUTY=2700 TYPE=DME FREQ=995 DELTAT=12 POWER=-118.91 DUTY=2700 TYPE=DME FREQ=995 DELTAT=12 POWER=-118.11 DUTY=3600 TYPE=DME FREQ=995 DELTAT=12 POWER=-114.81 DUTY=2700

Figure 3-2: Example of parameter file for DME interference

3.1.1. Implementation of DME interference

During the simulation run, an interference DME signal is generated according to the input from the parameter file. A pair of two Gaussian-shaped pulses with a distance of t∆ (given by DELTAT) can be represented in time domain as

2 2/ 2 / 2( ) 11 2( ) with 4.5 10t t td t e e sα α α− − −∆ −= + = ⋅

The factor α is chosen such as to obtain DME pulses with the correct width and rise time as defined in [Annex 10, I]. The baseband Gaussian DME pulses are used to amplitude-modulate the DME carrier. The DME carrier frequency (defining the relative offset nf∆ to

the centre frequency of the victim receiver) is set as a simulation parameter (FREQ).

Note: The above model does not include any impact of the DME TX radiated broadband noise or spurious signals and is therefore applicable only for larger TX-RX distances where these contributions can be neglected. This is assumed to be well applicable to "typical" scenarios, however close or co-located systems must be investigated by using other methods.



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Finally, DN DME signals with different powers nP , different carrier frequency offsets nf∆ ,

different phase nϕ , and different start time nt are summed up. Power and frequency are

given in the interference parameter file by "POWER" and "FREQ", respectively. The phase

nϕ is determined randomly for each interferer assuming a uniform distribution for nϕ

between 0 and 2π. The selection of the start time nt is explained in the next subsection.

The resulting interference signal is given by

( )2

1( ) ( )

Dn n

Nj f t

n nn

x t P d t t e π ϕ∆ +

=

= ⋅ − ⋅∑.

3.1.2. Consideration of duty cycle

When considering the duty cycle in the simulations, it has to be taken into account that the DME/TACAN stations do not generate pulse pairs in absolutely regular intervals. At the same time, the pulse pairs are not completely randomly distributed such that several pulse pairs never occur in a short period of time followed by a longer period of silence.

In the simulations, the DME duty cycle is considered as follows: At first, the duration of one transmit frame of the interfered system is cut into segments of equal length according to the duty cycle such that one pulse pair occurs in each segment. Assuming e.g. a duty cycle of 3600 ppps and a frame duration of 6.48 ms as in B-AMC, 23 pulse pairs can occur within the duration of one transmit frame. Hence, the transmit frame is cut into 23 segments of 281.7 µs. In each segment, one pulse pair is generated starting at a random time within this segment. The random start time is constrained to the length of the segment shortened by the total duration of the pulse pair. That way, it is guaranteed that always complete pulse pairs are generated in each segment. In doing so, certain regularity as well as certain randomness of the interference signals is simulated with this approach which is illustrated in Figure 3-3.

Alternatively, the inter-arrival time between DME pulse pairs can be assumed to be exponentially distributed. Hence, the number N of pulse pairs started in a certain time interval can be modelled as a Poisson process. This has also been proposed in [DO-292].

The probability that k DME pulse pairs have started before time instance t is then

( )( )!

kttP N k e

kλλ −= =

with parameterλ corresponding to the average number of pulses per time interval. In the considered example 23/ 6.48msλ = .



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Figure 3-3: Generation of DME pulse pairs assuming 3600 ppps duty cycle

----------- END OF SECTION -----------



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4. DME Interference Scenarios Involving DME GSs

In this interference scenario, DME ground stations are considered as interference source for the airborne receiver of the L-band communications system. All DME ground stations within the radio horizon of the considered aircraft are taken into account.

First, interference scenarios for three different environments characterized by different flight phases and flight levels (FL) have been defined:

! Airport (APT) scenario (FL 0-50),

! TMA scenario (FL 50-245), and

! ENR scenario (FL 245-450).

For determining the radio horizon of the victim receiver, in each interference scenario, the maximum flight level is assumed in order to obtain a worst case scenario with respect to the number of interfering DME GSs. The flight level ranges are chosen in accordance to [COCR].

For determining interference scenarios, a realistic topology of DME and TACAN stations operating in Europe is considered. The relevant data of each DME or TACAN ground station including e.g. geographical position, EIRP, and reply frequency are taken from the COM3 data base [COM3].

Interference conditions are investigated in that area with the highest density of DME stations in Europe in order to simulate worst case conditions. The NAVSIM tool, which is based on realistic DME channel assignment [COM3], has identified the area around Paris, Airport Charles de Gaulle (CDG), as that area with highest density of DME/TACAN stations seen within the radio horizon (261 nm) from an aircraft flying at high altitude (FL 450). In the screenshot from the NAVSIM tool shown in Figure 4-1, all 675 DME and TACAN stations deployed within 261 nm from CDG are plotted, regardless of the DME channel they use.

In addition, mobile TACAN stations used by the military have been considered in the NAVSIM tool. For each "ALL country_x" entry (e.g. "ALL FRANCE") in the COM3 data base one mobile TACAN station has been placed at the closest possible distance to the victim RX. For example, in Belgium mobile TACAN stations may be operated at 995 and 997 MHz, respectively. They are positioned on Belgium territory as close as possible to the victim receiver located at Paris, CDG1. Screenshots from the NAVSIM tool depicted in Figure 4-2 and Figure 4-3 show the worst case position of the Belgian mobile TACAN station and all other stations operating in those channels around CDG.

For each interference scenario, interference arising from DME ground stations in DME channels adjacent to the centre frequency of the victim receiver located in the considered area (see sections 4.1 and 4.3, respectively) is determined by means of the NAVSIM tool. As data about all DME channels used in Europe is available [COM3], the NAVSIM tool allows the same procedure to be applied to any DME channel.

In the lower part of Figure 4-1, the power density produced by these GSs within the entire L-band from 962-1213 MHz is illustrated, as seen by an airborne receiver at FL450

1 B-AMC system investigations used CDG as the reference point. But, any other reference area and the observation point within that area may be selected, as well.



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above Paris, CDG. For each DME channel the power density received at the victim receiver antenna is given in dBW/m2, based on known EIRP values of DME/TACAN GS transmitters.

In the following, the procedure for determining the interference power at the input of the victim receiver is described for two different cases: First, the victim receiver is assumed to be at a fixed position in the centre of the considered area. Therefore, fixed values for interference power in each considered DME channel are obtained (see section 4.1). Second, the victim receiver is assumed to move within the considered area, which results in a probability density function (PDF) for interference power in each considered DME channel (see section 4.3). Both possibilities can serve as input to the interference simulator as described in the previous chapter.

Figure 4-1: DME stations at Paris CDG, observed from FL450



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Figure 4-2: Position of DME/TACAN stations around CDG, 995 MHz



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Figure 4-3: Position of DME/TACAN stations around CDG, 997 MHz

4.1. Static victim receiver

The victim airborne receiver is positioned in the centre of the European area with most dense DME population, i.e. at Paris Airport CDG. The actual position of the victim receiver is at a MLS/DME station at CDG (N49°01�19.45 / E002°31�02.69). For FL 245 and FL 450, the victim aircraft is positioned exactly above the interfering GS, i.e. the aircraft altitude is assumed as the minimum vertical distance between DME GS and victim RX in order to simulate the worst case situation when the aircraft with the victim B-AMC RX on board flies over the DME GS. For the ground scenario (FL 0 - FL 50), a minimum horizontal distance of 600 m to the MLS/DME station at Paris CDG has been assumed.

The radius of the area of interest is set according to the radio horizon seen at a certain flight level, namely:

! Airport (APT) scenario (FL50): rH =28 nm

! TMA scenario (FL245): rH = 192 nm

! ENR scenario (FL450): rH = 261 nm



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Assuming an airborne victim receiver at a fixed position in the centre of the most dense area around Paris CDG, the NAVSIM tool provides data about all currently operated and planned DME and TACAN GSs in the surrounding area, including:

! DME station name and ID,

! distance and slant range between victim RX and interfering DME/TACAN station,

! DME/TACAN GS channel/operating mode and reply frequency,

! type and duty-cycle of DME/TACAN GS,

! GS EIRP (dBW),

! ground/airborne elevation angles at DME/TACAN ground station and victim RX including corresponding antenna gain [D4], and

! interference power (dBW) received at input of victim receiver.

The interference power interfP received at the input of the victim receiver is calculated as

interf [ ] ( ) ( ) ( )Tx Rx RxfreeP dBW EIRP G L d G G Cϕ α= + − + + − .

The known EIRP of the interfering GS is assumed to contain the maximum peak ground antenna gain. In [DO-292], the maximum antenna gain of L-band ground equipment is specified as 8 dBi. In addition, the antenna pattern from Figure 4-4 (label: DME_G

composed) [D4] is considered and an antenna gain ( )TxG ϕ dependent on the elevation angle ϕ between the interfering GS and the victim receiver is added to the transmitter

EIRP. The spatial distance d between the interfering GS and the victim receiver is taken into account by means of a simple propagation model. Within the radio horizon, the free space loss is defined as

( ) 37.8 20 log 20 logfreeL d d f= + ⋅ + ⋅

where

Lfree(d): transmission loss (dB) between transmitter and receiver as a function of distance,

d: distance between transmitter and receiver (nm),

f: frequency (MHz).

At the antenna of the victim receiver, the maximum peak ground antenna gain

5.4 dBiRxG = and an elevation angle dependent antenna gain ( )RxG α is added. The antenna of the victim receiver is assumed to have the same antenna pattern as conventional airborne L-band antennas. A representative antenna pattern, that is also used here, is depicted in Figure 4-5 [D4]. In addition, cable losses 3 dBC = are taken into account.



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Figure 4-4: DME and TACAN ground antenna vertical pattern GTx (φ) [D4]

Figure 4-5: Vertical patterns of airborne DME and MIDS antennas GRx (α) [D4]



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Note: Please refer to [D4, Chap. 5.1] for a detailed definition of the elevation angles α and ϕ.

From the available data, the total interference power within each DME channel and the data/constellation of all visible ground DME/TACAN stations contributing to this power can be derived. An example of an available data set is given in Table 4-1 for Paris CDG at FL 450. For reasons of clarity, the data set is reduced to its relevant columns, e.g. ground and airborne antenna gains are omitted.

ID DME Station Name Distance

in nm

Slant Range in nm

DME channel

Reply Frequency

in MHz Type

EIRP in

dBW

Received power at RX input in dBW

TST METZ/FRESCATY 141 141 23X 984 TACAN 30 -110.9

LRE LURE 178 178 23X 984 TACAN 40 -103.5

WOL WOLVERHAMPTON 279 279 23X 984 DME 29 -147.6

MAS MAASTRICHT 176 176 23X 984 VOR/DME 37 -106.2

DIJON/LONGVIC 146 146 24X 985 MLS/DME 29 -112.2

MAM MARHAM 230 230 24X 985 TACAN 37 -109.2

COL COLA/KOLN 222 222 25X 986 TACAN/VOR 40 -105.5

BLM BALE/MULHOUSE 214 214 25X 986 VOR/DME 26 -119.1

BT PARIS/LE BOURGET 5 9 25X 986 VOR/DME 37 -99.3

IBR BRUXELLES/NATIONAL 135 135 26X 987 ILS/DME 29 -111.5

KSL KASSEL-CALDEN 299 299 26X 987 MLS/DME 29 -179.6

AS ANGERS 155 155 26X 987 ILS/DME 29 -112.7

AT ANNECY-MEYTHET 234 234 26X 987 ILS/DME 29 -117.3

GSI GUISCRIFF 255 255 26X 987 ILS/DME 29 -118.1

SDI SAINT-DIZIER 95 95 26X 987 MLS/DME 29 -107.4

Table 4-1: NAVSIM data extraction, victim receiver in 45000 feet (rH = 261 nm) at CDG

For generating interference scenarios, the victim receiver is adjusted to a certain frequency and the interference in all relevant DME channels can be determined from the available NAVSIM data. In each relevant DME channel, all DME stations within the radio horizon are considered with interference power calculated by NAVSIM. The duty cycle for each considered GS is assumed to be maximum, i.e. 2700 ppps for DME and 3600 ppps for TACAN stations. If more than one DME/TACAN station is active per channel, the contributions of all individual stations are considered with their respective received powers and duty-cycles. The individually generated interference signals are summed up, resulting in the total interference signal in the respective channel.

4.2. Example: B-AMC forward link scenario with static victim RX

As an example, an interference scenario specific for the B-AMC system is derived in the following. The B-AMC channels are placed at 0.5 MHz offset from the DME channel grid (1 MHz). Investigations in the first stage of the B-AMC study have shown that for TX-RX distances of 600 m or more only two adjacent DME channels (at +/-0.5 MHz and +/-1.5



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MHz offset from the selected B-AMC channel) at each side of the B-AMC channel effectively contribute to the interference situation. It is assumed that frequency planning was applied for selecting the B-AMC centre frequency, i.e. the "most appropriate" B-AMC channel is selected such as to minimize interference from DME systems operating in the two adjacent channels.

Note: For other victim receivers with broader reception bandwidth/lower selectivity, additional DME channels may become relevant (this fact would have to be included in interference investigations).

For the considered scenario at FL 450, 995.5 MHz has been selected (evaluation the data from NAVSIM) as B-AMC centre frequency when assuming 985-1009 MHz as the frequency range available for the B-AMC GSs.

According to the NAVSIM data shown in Table 4-2, in the channels next to 995.5 MHz, i.e. 994-997 MHz, only relatively small interference powers occur. Therefore, 995.5 MHz has been selected as B-AMC operating frequency. In the channel with -0.5 MHz offset to the B-AMC centre frequency one TACAN interferer occurs. In the channel with +0.5 MHz offset, two DME/TACAN stations occur, one with a peak interference power of -76.41 dBm, and another one with a peak interference power of -92.6 dBm. Interference in the channels at +/-1.5 MHz offset from the B-AMC centre frequency listed in Table 4-2 is composed of the contributions of several DME/TACAN stations that also can be derived from the NAVSIM data (see Table 4-1). Each interferer is modelled separately with its respective power shown in Table 4-2. For the duty cycle, the maximum pulse rate is taken into account for each station. In reality, the duty cycle of some stations may be lower when stations operate in variable mode with a duty cycle ranging from 700 to 2700 ppps for DME stations.

Frequency relative to B-AMC system

Distance to B-AMC victim RX [nm]

Type of station

Pulse rate [ppps]

Mode Interference power at input of victim RX considering antenna patterns [dBm]

-1.5 171 TACAN 3600 X -74.0

-1.5 148 TACAN 3600 X -72.4

-1.5 190 TACAN 3600 X -88.2

-0.5 112 TACAN 3600 X -67.9

0 B-AMC

0.5 171 TACAN 3600 X -74.0

0.5 230 TACAN 3600 X -90.3

1.5 136 MLS/DME 2700 X -81.6

1.5 220 DME/ILS 2700 X -86.5

1.5 201 DME 2700 X -85.7

1.5 254 DME 2700 X -88.1

1.5 149 DME 2700 X -82.5

1.5 106 TACAN 3600 X -68.9

Table 4-2: Example: DME/TACAN stations for B-AMC forward link scenario at FL 450 assuming frequency planning, static B-AMC victim RX



Page: 4-9

The procedure for deriving interference scenarios for DME GSs described above can be extended and applied to any arbitrary system operating in the L-band. After determining the interference power at a certain location for the victim RX received from all ground stations in the frequency range of interest (for that victim RX), interference scenarios can be derived with known

! offset to DME channels,

! centre frequency of victim L-band RF channel, and

! number of relevant DME channels around that RF channel causing harmful interference.

That way, all relevant parameters required as input to the DME interference simulator can be determined.

4.3. Moving Victim Receiver

Within this study, interference scenarios are refined such as to model the interference situation occurring during a flight through an entire cell, i.e. an area rather than just a selected point in space has to be considered.

Note: This scenario is offered as an option � it should be agreed which kind of scenarios (static - or moving victim RX) would be finally used for testing new aeronautical systems.

For each interference scenario, a circular area is defined, in which the GS of the victim system communicates with the victim airborne receiver. The centre of this area can e.g. be at CDG (as in the first version of the interference scenarios) or at any other arbitrary position. In contrast to the first version of the interference scenarios, the location of the victim receiver is no longer considered to be fixed but varies within a service volume (ENR, TMA, or APT) as the victim receiver moves. The position is assumed to be equally distributed within the highest flight level of the considered service volume (worst case regarding the radio horizon).

Due to the random locations of the victim receiver, the received interference power coming from a particular DME station varies and can be modelled by means of a PDF. The power PDF is generated for each DME channel by positioning the victim receiver at many different locations within the cell and determining the interference power received from each DME station in all relevant DME channels. For the link budget calculations, elevation angle dependent antenna characteristics of both the victim receiver and the interfering ground station have to be considered as described in the previous section.

In order to simplify the interference simulator, for each DME channel and all DME stations within each channel, all determined values of the interference power in a certain channel can be collected and the probability of their occurrence can be determined. For each DME channel, all relevant DME ground stations can be summarized and a compound received power PDF is then produced for each DME channel.

The duty cycle in each channel can be determined by summing up the duty cycles of all contributing DME/TACAN stations. Again, the duty cycle of any particular DME and TACAN station is assumed to correspond to 2700 ppps and 3600 ppps, respectively.



Page: 4-10

4.4. Example: B-AMC forward link scenario with moving victim RX

The generation of interference scenarios is explained in the following by using the B-AMC forward link as an example. Again, the B-AMC centre frequency is assumed to be set at 995.5 MHz. DME stations in the channels at 994, 995, 996, and 997 MHz are considered as potential interferers. The area of interest is located around Paris CDG. For the ENR scenario, the interference occurring at the victim receiver moving within a radius of 120 nm around Paris CDG, is observed. In the NAVSIM tool, the interference situation has been monitored at FL 450 at 72 discrete positions equally distributed within the observation area. DME/TACAN stations identified to be relevant are listed in Table 4-3. Comparing Table 4-3 with the version for a static victim receiver (Table 4-2), obviously more DME/TACAN stations per channel have to be taken into account when considering an entire observation area. The power PDFs corresponding to each involved DME/TACAN station and each DME channel are depicted in Figure 4-6 to Figure 4-9. According to simulation results from [D3], interferers with powers smaller than -130 dBW have no impact on the B-AMC system. Hence, if the interference power originating from a certain DME/TACAN station at a certain position is below a threshold of -130 dBW = -100 dBm, the power of the interferer is assumed to be -135 dBW. If the values below the threshold are just skipped, the power valued above the threshold become more probable hence falsely increasing the average interference power. This explains the peaks at -135 dBW in the PDFs in Figure 4-6 to Figure 4-9. The average power of the contributing DME/TACAN stations is slightly increased by a few dB when considering the entire observation area as compared to the situation with a single observation point.


Location Type of station

Duty cycle [ppps]


-1.5 Kempten DME 2700 X

-1.5 Kleine Brogel TACAN 3600 X

-1.5 Odiham TACAN 3600 X

-1.5 Sint-Truide TACAN 3600 X

Power PDFs from Figure 4-6

-0.5 All Belgium TACAN 3600 X

-0.5 All Italy TACAN 3600 X

-0.5 Wunstorf DME 2700 X


0 B-AMC

0.5 Kleine Brogel TACAN 3600 X

0.5 Lyneham TACAN 3600 X


1.5 All Belgium TACAN 3600 X

1.5 Brest DME 2700 X

1.5 Brussels DME 2700 X

1.5 Exeter DME 2700 X

1.5 Friedrichshafen DME 2700 X




Page: 4-11


Location Type of station

Duty cycle [ppps]


1.5 Geneva DME 2700 X

1.5 Groningen DME 2700 X

1.5 Luxembourg DME 2700 X

1.5 Nantes DME 2700 X

1.5 Remaining stations

DME 2700 X

Table 4-3: B-AMC forward link scenario with moving victim RX

Note: At 997 MHz, many different DME stations occur at only a few discrete locations within the observation area. For reasons of simplicity all these stations have been summarized to one station with a representative power PDF, shown in Figure 4-9 with the label "remaining stations". Since these stations occur only seldom and their powers are very small, the total duty cycle is assumed to correspond to 2700 ppps.

In a similar way, all other stations occurring in the same channel can be summarized to one representative station with a composite power PDF. The duty cycles of all stations sum up.

-135 -130 -125 -120 -115 -110 -105 -100 -95 -900

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

power (dBW)

norm

aliz

ed p

roba

bilit

y

KemptenKleine BrogelOdihamSint-Truiden

Figure 4-6: PDF for four DME/TACAN stations at 994 MHz



Page: 4-12

-135 -130 -125 -120 -115 -110 -105 -100 -95 -900

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

power (dBW)

norm

aliz

ed p

roba

bilit

y

all Italyall BelgiumWunstorf

Figure 4-7: PDF for three DME/TACAN stations at 995 MHz

-135 -130 -125 -120 -115 -110 -105 -100 -95 -900

0.05

0.1

0.15

0.2

0.25

0.3

0.35

power (dBW)

norm

aliz

ed p

roba

bilit

y

Kleine BrogelLyneham

Figure 4-8: PDF for two DME/TACAN stations at 996 MHz



Page: 4-13

-135 -130 -125 -120 -115 -110 -105 -100 -95 -900

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

power (dBW)

norm

aliz

ed p

roba

bilit

y

all BelgiumBrestBruxellesExeterFriedrichshafenGeneveGroningenLuxembourgNantesremaining stations

Figure 4-9: PDF for DME/TACAN stations at 997 MHz

----------- END OF SECTION ---------



Page: 5-1

5. DME Interference Scenarios Involving Airborne DME Interrogators

In these interference scenarios, the victim receiver is the ground station of the future L-band communications system. Thus, interference arising from airborne DME stations has to be considered. All aircraft within the radio horizon of the considered victim receiver on ground are taken into account. Interference from DME ground stations is neglected as only a few DME ground stations are within the limited radio horizon and their interference contribution is small compared to interference from aircraft flying over the victim ground station.

The interference situation at the victim ground station only depends on the spatial distribution of all aircraft using relevant DME channels for their DME interrogations, regardless of their flight level. Therefore, no distinction between different scenarios for different flight levels - as for the scenarios involving DME ground stations - is required.

DME interference scenarios involving airborne DME stations are only relevant for L-band systems operating in the ranges 1035-1085 MHz and 1095-1164 MHz as DME airborne stations are only active at these frequencies.

5.1. NAVSIM Procedure

For NAVSIM simulations, the same area as that used for the investigation of the forward link is considered, namely Paris CDG, which is the area with the highest density of DME/TACAN stations. In the airspace above this area aircraft are flying and interrogating DME/TACAN ground stations. At the same time they cause interference at the victim ground station, which is assumed to be in the centre of the considered area at Paris CDG (N49°01�19.45 / E002°31�02.69).

Air traffic is simulated according to Eurocontrol data of real aircraft movements monitored on July 7, 2000. The data are relatively old, but they still represent current worst case conditions as a day with high air traffic load has been considered. At first, the DME/TACAN ground stations an aircraft can communicate with are identified. This is done by checking if the signal from a certain ground station is received at least with a certain power density. If the received power level exceeds the sensitivity threshold of a DME/TACAN airborne receiver, i.e. the signal strength is above -89 dBW/m2, as specified in [D1], an aircraft can theoretically interrogate that ground station. At a certain time instance, the aircraft interrogates only that ground station from which it has received the strongest signal. NAVSIM simulations are based on the assumption that at each time instance each aircraft is interrogating one DME/TACAN ground station, namely the one from which it has received the strongest signal. Depending on the distance of the aircraft to the victim ground station, the interference power received by the victim ground station is determined by means of the free space propagation model described in the previous chapter. Moreover, elevation angles of the aircraft with respect to the victim ground stations are determined and the corresponding antenna patterns are considered in the same way as in the scenarios with DME ground stations involved.

That way, the interference power received by the B-AMC victim ground station from each aircraft in the surrounding airspace is obtained. Thereby, the individual contributing DME/TACAN stations as well as the DME channels including X and Y mode are distinguished. Moreover, a time-variant distribution of air traffic is taken into account by



Page: 5-2

taking snapshots at different time instances. In order to simulate worst-case conditions, air traffic is simulated during "rush hour", i.e. between 4 and 5 p.m.

A snapshot of the air traffic including the interference power caused at the victim ground station is shown in Figure 5-1 for the DME channel at 1059 MHz. In this channel, all aircraft that interrogate DME ground stations on channels 35X and 35Y, i.e. on 1059 MHz, and receive responses at 996 MHz and 1122 MHz, have to be considered. For reasons of clarity, the topology of interrogated DME/TACAN ground stations is shown in Figure 5-2.

With the NAVSIM tool, all possible interrogations from aircraft in the airspace above the victim ground station are simulated. From the obtained data, conclusions about the distribution of interference power can be drawn. However, real interrogations taking into account different modes of DME devices (i.e. scan mode or track mode) and different duty cycles have not been considered.

Figure 5-1: Snapshot of air traffic possibly interrogating DME stations at channel 35X/Y and corresponding interference power at victim ground station

Note: In Figure 5-1 yellow dots indicate aircraft and green lines indicate the communication with a DME/TACAN ground station. The colour of the



Page: 5-3

interconnecting lines indicates the interference power received by the victim B-AMC ground station. A red line corresponds to the interference power exceeding -75 dBW, an orange line stands for an interference power level between -105 dBW and -75 dBW, and a yellow line indicates a received interference power level between -135 and -105 dBW.

Figure 5-2: Topology of DME stations round CDG, 35X/Y

Note: In Figure 5-2, ground stations with green labelling are DME TMA stations, yellow labelling indicates DME en-route stations and TACAN stations are labelled in red.

5.2. Determination of Interference Power Distribution

From NAVSIM data, the distribution of interference power in a certain DME channel can be derived.

Similar as for the scenarios with DME ground stations the interference power interfP at the

receiver input is determined according to

interf [ ] ( ) ( ) ( )Tx Rx RxfreeP dBW EIRP G L d G G Cα ϕ= + − + + − .



Page: 5-4

According to [D4], the EIRP of an airborne DME unit is assumed to be 33 dBW= 63 dBm.

The maximum peak antenna gain TxG of L-band airborne equipment is specified as

5.4 dBiTxG = in [DO-292] and is already included in EIRP. In addition, the antenna

pattern from [D4] (see Figure 4-5) is assumed and an antenna gain ( )TxG α dependent on the elevation angle α between the interfering airborne unit and the victim ground receiver is added to the EIRP. The antenna of the victim ground receiver is assumed to have the same antenna pattern as conventional ground L-band antennas. The maximum

peak antenna gain RxG of L-band airborne equipment is specified as 8 dBiRxG = . In

addition, an elevation angle dependent antenna pattern defining ( )RxG ϕ is considered. A representative antenna pattern is given in [D4] and is shown in Figure 4-4. Moreover, cable losses 2 dBC = are taken into account.

The values of interference power received at the input of the victim receiver and measured at different points in time are collected. Interference power in different DME channels and originating from interrogations of different DME stations in that channel are distinguished. The interference power PDF for each DME channel and each DME station within that channel is generated by evaluating the probability of each power value.

In the considered area around Paris CDG all aircraft up to FL450 that are in the radio horizon (261 nm) of the victim ground station cause interference at the victim ground receiver. These aircraft may interrogate DME ground stations within the considered area and even beyond. Taking into account an operational range of 200 nm for a DME en-route or a TACAN station, all DME/TACAN stations within an area of 461 nm have to be considered. However, not all interrogations of remote DME/TACAN stations cause significant interference power levels. Hence, the actual number of DME/TACAN stations to be considered reduces.

As an example, the interference power PDF for the channel at 1059 MHz is derived in the following. According to the topology of DME/TACAN stations interrogated at 1059 MHz (Figure 5-2), seven DME stations and one TACAN station are within the area of interest and can be interrogated by aircraft within the radio horizon as seen from the victim receiver at Paris CDG. Due to very small interference power caused by aircraft interrogating the DME station at Milan in a distance of 309 nm and at Schleswig in a distance of 438 nm from the victim receiver, these DME stations are omitted. For all other stations, the resulting power PDF is shown in Figure 5-3. The shape of the PDFs is as expected: There are few aircraft close to the victim ground station causing high interference power levels. With increasing distance to the victim ground station interference power decreases, but the number of aircraft causing interference grows. Nevertheless, it can be distinguished between two different shapes of power PDFs. DME/TACAN stations "Koksijde" and "Kleine Brogel" cause interference power levels up to -62 dBm. Their peak is at -82 dBm. All other stations cause interference power levels up to only -78 dBm and their peak is also slightly lower at about -84 dBm. This can be explained by the spatial distance between the interrogated ground stations and the victim receiver. "Koksijde" and "Kleine Brogel" are relatively close to the victim receiver such that aircraft in the proximity of the victim station interrogate these two stations and hence cause high interference levels. All other stations are farer away, such that an aircraft interrogating these stations never is in the direct proximity and hence does not cause maximum interference.

All considered DME/TACAN stations can either be simulated separately with their respective power PDFs or alternatively, one compound power PDF can be generated



Page: 5-5

which represents interference power received from all aircraft independent of which ground station they interrogate. The compound power PDF is shown in Figure 5-3, as well.

-100 -95 -90 -85 -80 -75 -70 -65 -600

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

power (dBm)

norm

aliz

ed p

roba

bilit

y

FairoaksKleine BrogelKoksijdeLa RochelleLynehamDortmundcompound pdf

Figure 5-3: Interference power PDFs originating from interrogations of DME stations at 1059 MHz located around Paris, CDG

Note: Interference power values below -100 dBm have been neglected as they are considered to provide only very minor contributions to the overall interference situation. It can be seen from the power PDFs that even values up to -90 dBm occur only seldom and hence can be omitted as well.

5.3. Determination of Duty Cycle

Since no real interrogations were simulated in NAVSIM, the duty cycle for the aircraft interrogating each DME or TACAN ground station had to be estimated. Therefore, it is assumed that each ground station receives exactly that number of interrogations it can reply to at maximum duty cycle, i.e. full load is assumed for each ground station. For a DME and TACAN station it is assumed that the interrogations from all aircraft in the operational range give 2700 ppps and 3600 ppps, respectively.

Moreover, it is assumed that all aircraft are equally distributed within the operational range. Consequently, if parts of the operational range are beyond the radio horizon, the number of aircraft to be considered reduces by that fraction which is beyond the radio horizon. At the same time, this translates into a reduction of the duty cycle.



Page: 5-6

For determining that part of the operational range of the considered ground stations in which aircraft have impact on the victim ground station, the distance between the victim ground station and the DME or TACAN ground stations interrogated on DME channels close to the B-AMC RL centre frequency has to be known. The topology of DME and TACAN stations that are interrogated at 1058 MHz is shown in Figure 5-2 and redrawn in Figure 5-4, respectively.

For evaluating the number of contributing DME and TACAN stations in the considered area, it has been assumed that the service volume of a DME TMA station is 130 nm in radius at a height of 18,000 ft [ED54]. Hence, all interrogating aircraft within a radio horizon of 177 nm, corresponding to FL180, have to be taken into account as they are seen from the B-AMC victim ground station. These aircraft can communicate with DME TMA ground stations up to 130 nm beyond the radio horizon. Hence, all DME TMA stations within a range of 130 nm + 177 nm = 307 nm have to be considered.

For DME ENR and TACAN stations an operational range of 200 nm has been considered [ED54]. Assuming a maximum flight level at 45,000 ft, all aircraft within the radio horizon of 261 nm have a line of sight connection to the victim ground station. Consequently, all DME ENR and TACAN stations within a range of 261 nm + 200 nm = 461 nm have to be considered.

In Figure 5-4, the victim ground station is located in the centre of the considered area around Paris CDG. When considering all DME TMA stations in a radius of 307 nm as explained above, five DME TMA stations at 1059 MHz have to be considered (these are the same as the ones considered for determining the power PDF). The aircraft interrogating these ground stations are assumed to be equally distributed within the operational range of 130 nm. However, due to the limited flight level of 18,000 ft, only that fraction of aircraft in a maximum distance of 177 nm, i.e. within the radio horizon corresponding to FL180, causes interference in the victim system. The overlapping area between the operational range of the DME TMA station and the radio horizon of the B-AMC victim ground station is determined by simple geometric calculations. The ratio of the overlapping area to the total operational area indicates which fraction of the duty cycle has to be considered. For the DME TMA station at a distance of 247 nm to the B-AMC victim ground station (highlighted in Figure 5-4), 13.8% of the operational range are within the radio horizon of the victim ground station. Hence, a pulse rate of 0.138 * 2700 ppps = 373 ppps applies.

However, not all aircraft in the overlapping area are visible within the radio horizon of the B-AMC ground station. Considering a DME TMA station, all aircraft in a distance of 177 nm which are below FL 180 can not be "seen" by the victim ground station. Hence, in a second step the fraction of aircraft in the overlapping area, which is visible within radio horizon of the victim ground station, is determined. As illustrated in Figure 5-5 the area that is visible within the radio horizon of the victim ground station is approximated by a cone. The operational range of a DME/TACAN station is also represented by a cone since, in particular for a DME TMA station, it can not be assumed that aircraft on the ground or at low altitudes in the outer area of the operational range interrogate the DME ground station. Again, the aircraft are assumed to be equally distributed in the operational range.

For the DME TMA station at a distance of 247 nm to the victim ground station considered above, 42.35% of the aircraft within the overlapping area are within the radio horizon of the victim ground station. Hence, the duty cycle further reduces to 0.4235 * 0.138 * 2700 ppps = 158 ppps.



Page: 5-7

This procedure is repeated for all relevant DME TMA stations in the considered channels. In addition, as shown in Figure 5-4, the relevant duty cycle of the TACAN station interrogated at 1059 MHz is determined as an example. The overlapping area is determined based on a radio horizon of 261 nm, a maximum flight level of 45,000 ft, an operational range of 200 nm and a maximum pulse rate of 3600 ppps. For these parameters, a pulse rate of 2368 ppps is obtained.

Figure 5-4: Topology of DME/TACAN stations at Paris CDG, 1059 MHz



Page: 5-8

Figure 5-5: Cross section of relevant fraction of operational range within overlapping area

5.4. Example: B-AMC Reverse Link Scenario

As another example, the generation of an interference scenario for the B-AMC reverse link is considered. The B-AMC victim receiver is again located at Paris CDG. The B-AMC centre frequency is set between the two DME channels with the smallest total interference power and the smallest number of contributing DME/TACAN stations. Within the frequency range 1048-1072 MHz, assumed for the B-AMC reverse link [D4], 1058.5 MHz seems to be the best choice for the B-AMC centre frequency. However, this approach is very simple and needs further refinement. Hence, the selection of the B-AMC centre frequency may not be optimal.

Form the available NAVSIM data, interference power PDFs and corresponding duty cycles have to be derived for the channels 1058 and 1059 MHz. For 1059 MHz, interference power PDFs as well as corresponding duty cycles have already been derived in the example considered above. For all DME stations at 1059 MHz this procedure has to be repeated. As already seen in [D5], interferers in the channels at 1057 and 1060 MHz, i.e. at +/- 1.5 MHz offset from the B-AMC centre frequency, have no impact on the B-AMC system and can be need not to be considered.

The parameters for the RL interference scenario with frequency planning derived from NAVSIM data are listed in Table 5-1.



Type of station Duty cycle [ppps]

Mode Interference power at input of victim RX considering antenna patterns [dBW]

-0.5 62 DME TMA 1962 Y Power PDF from Figure 5-6








-0.5 107 TACAN 3223 X Power PDF from Figure 5-6



Page: 5-9



Type of station Duty cycle [ppps]

Mode Interference power at input of victim RX considering antenna patterns [dBW]



0 B-AMC

0.5 127 DME TMA 1061 Y Power PDF from Figure 5-3



0.5 210 DME TMA 317 X Power PDF from Figure 5-3

0.5 247 DME TMA 158 Z Power PDF from Figure 5-3

0.5 183 TACAN 2368 X Power PDF from Figure 5-3

Table 5-1: DME/TACAN stations for RL scenario with frequency planning

-100 -95 -90 -85 -80 -75 -70 -65 -60 -550

0.05

0.1

0.15

0.2

0.25

0.3

power (dBm)

norm

aliz

ed p

roba

bilit

y

ReimsAll BelgiumLe MansEinhovenDüsseldorfFrankfurtCoventryZürichLeeuwardenall Italyall Spaincompound pdf

Figure 5-6: Interference power PDFs originating from interrogations of DME stations at 1058 MHz located around Paris CDG

----------- END OF SECTION ---------



Page: 6-1

6. Consideration of Other Interference Sources

6.1. JTIDS/MIDS Interference

As a basis for investigating the impact of JTIDS/MIDS interference on the victim receiver, the basic characteristics of the JTIDS signal are modelled by means of a model developed during the previous stages of the B-AMC study [D5].

The spectrum of a JTIDS signal has a 3 dB bandwidth of about 3 MHz when considering measured spectra (Figure 6-1) and of 6 MHz when assuming the spectral mask (Figure 6-2). In the L-band, i.e. in the 969 to 1008 MHz, 1053 to 1065 MHz and 1113 to 1206 MHz bands, the JTIDS system uses 51 frequencies with a spacing of 3 MHz for pseudo-random frequency hopping.

Figure 6-1: Measured JTIDS/MIDS TX Spectrum



Page: 6-2

Figure 6-2: JTIDS/MIDS TX Spectral Mask

For a victim system that is operating at only a small offset to any JTIDS hopping frequency and having a bandwidth smaller than the JTIDS/MIDS system, this would mean that the victim system is completely hit by JTIDS interference. In an OFDM based system such as B-AMC all sub-carriers are affected.

In time domain, the JTIDS signal consists of trapezoidal pulses with a width of 6.4 µs plus 800 ns rise and fall time. In the interference simulator, the actual signal pattern of a JTIDS pulse, e.g. Continuous Phase-Shift Modulation (CPSM) at a rate of 5 megabits per second to produce a 32 bit message symbol, is not emulated in detail. It is sufficient to model the JTIDS time domain signal by noise with a certain power during the pulse duration. Hence, the time domain interference signal consists of zeros interrupted by 8 µs periods of a noise signal.

After generating the time domain interference signal, it is processed in the same way as the desired signal would be processed in the victim receiver. This is important in order to take into account effects occurring during receiver processing that may affect the spectral shape of the JTIDS/MIDS interference signal.

Similar to the DME interference simulator, the number of JTIDS pulses occurring per time unit is set in a parameter file by means of the variable "DUTY". The power "POWER" is also set in the parameter file either in form of a fixed value or a power probability density function.

Note, the parameters "DELTAT" and "FREQ" are not required for the generation of the JTIDS interference signal.

JTIDS airborne and ground stations access the channel based on a time-division multiple-access (TDMA) scheme. Hence, in the forward link, the victim receiver is disturbed by JTIDS ground stations as well as by aircraft with JTIDS equipment. In the reverse link, the victim ground station is also disturbed by some ground stations in the proximity as well as by aircraft with JTIDS equipment. Since the interference power is varying with air traffic movement and movement of the own aircraft (in the FL), the interference power is modelled by means of a power probability density function. The maximum received interference power is determined by the JTIDS TX power and the minimum spatial



Page: 6-3

distance between the victim RX and the interfering ground station or airborne unit. According to [JTIDS], the maximum received signal level is -33 dBm. This value is based on 53 dBm JTIDS TX power and about 900m minimum spatial distance. Starting with this value and assuming an equally distributed aircraft population, a power PDF can be determined. Therefore, it is assumed that aircraft are distributed within a circle of 261 nm radius which corresponds to the radio horizon at FL450. With respect to received interference power, this area is relevant for both victim ground and airborne stations. The victim receiver is positioned at the centre of this area.

For the entire range, i.e. from 900m to 261 nm in steps of 0.5 nm, the received interference power is determined by subtracting free space loss from the maximum JTIDS TX power of 53 dBm. At the moment, effects of TX and RX antennas and cable losses are not taken into account. The minimum received interference power originates from a JTIDS unit in the maximum distance to the victim receiver and equals -92.94 dBm = -122.94 dBW. In between the maximum and the minimum, interference power decays with the square of the distance from the victim receiver to the interfering JTIDS unit.

From the assumed aircraft population, the probability, that a certain interference power occurs, can be determined without knowledge of the actual number of interfering aircraft. (The number of aircraft affects only the duty cycle, but not the distribution of interference power). The probability, that a certain interference power occurs, is directly related to the ratio of aircraft located at a certain distance from the victim receiver and the amount of aircraft in the entire considered area. The considered area is subdivided into concentric rings each having a width of 0.5 nm. Assuming equally distributed aircraft, the percentage of aircraft in such a ring described by the inner and outer radius r1 and r2 equals

2 22 1

2

r rd−

,

where d is the radius of the entire considered area, i.e. d =261 nm.

Hence, the corresponding interference power determined for distances ranging from r1

and r2 occurs with probability 2 2

2 12

r rd−

. The resulting power PDF is shown in Figure 6-3.

Note: The obtained power PDF shows a good agreement with the power PDFs obtained with the NAVSIM tool.



Page: 6-4

-100 -90 -80 -70 -60 -50 -40 -300

0.02

0.04

0.06

0.08

0.1

0.12

power (dBm)

norm

aliz

ed p

roba

bilit

y

Figure 6-3: Distribution of interference power from JTIDS

For determining the duty cycle it is assumed that all timeslots are used, i.e. 1536 timeslots per frame, equivalent to 128 timeslots per second. In the standard JTIDS message packing structure 258 pulses per timeslot are created. Therefore, the maximum number of pulses transmitted per second is 33,024 assuming 100% time slot duty factor (TSDF). Since JTIDS employs pseudo-random frequency hopping across 51 frequencies, in the worst case there would be 648 pulses per second per frequency. Although JTIDS is capable of operating more than one JTIDS net simultaneously in the same geographic region through using a different frequency hopping pattern, it is currently not permitted by any State. Therefore, the maximum number of pulses per time slot and frequency is 648.

This interference scenario represents a worst-case interference environment as the worst case is assumed for the power as well as for the duty cycle.

6.2. SSR Mode S Interference

SSR Mode S interference can be modelled similar to JTIDS/MIDS interference. Interference pulse duration and duty cycle are chosen according to SSR Mode S specifications recapitulated in the following.

RTCA DO-292 states the following:

Onboard Mode S/TCAS/1090ES TXs operate between 1085 and 1095 MHz with maximum 27 dBW EIRP, maximum pulse width of 1 µs and maximum duty-cycle of 6.25%. Out-of-band emissions (at larger offsets) are constrained to at most -60 dBc.

The ground Mode S station has been characterised as operating between 1025 and 1035 MHz with 52.5 dBW maximum EIRP, maximum pulse width of 30.25 µs and maximum duty-cycle of 9.55%. Out-of-band emissions (at larger offsets) are constrained to at most -60 dBc.



Page: 6-5

Note: As out-of-band emissions are given as absolute power (dBc) rather than noise density, it should here represent discrete spurious signals rather than broadband noise.

B-AMC D4 states the following:

Onboard Mode S/TCAS/1090ES TX operates on 1090 ±3 MHz with maximum 27 dBW at the antenna port.

Ground Mode S TX operates on 1030 ±0.2 MHz. The power at the antenna port or EIRP are not limited, but [DO-292] suggests 52.5 dBW (82.5 dBm) as a maximum EIRP.

ICAO Annex 10 Vol. IV, Sect. 3.1.2, states the following:

Onboard Mode S TX operates on 1090 ±1 MHz. The reply consists of a preamble and a data block. The preamble is a sequence of 4 pulses and data block is binary pulse-position modulated at 1 MBps rate. The pulse shapes are as indicated in Table 6-1. The interference power received at the victim receiver depends on the frequency offset between the Mode S transmitter and the victim receiver and can be derived from the EIRP and the spectral mask shown in Figure 6-4.

Table 6-1: Pulse shapes of Mode S replies [Annex10, Tab.3-2]



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Figure 6-4: Required spectrum limits for transponder transmitter [Annex10]

Ground Mode S TX operates on 1030 ±0.1 MHz. Mode S interrogations consist of a sequence of pulses. Pulse durations are between 0.8 µs and 30.25 µs with rise times between 0.05 and 0.1 µs.

Detailed information about pulse parameters can be found in Table 3-1 in Vol. IV Sect. 3.1.2 which is inserted below (Table 6-2).

Table 6-2: Pulse shapes of Mode S and interrogations



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Short (16.25 µs) and long (30.25 µs) P6 pulses use internal binary differential phase modulation of the carrier with 180° phase reversal and 4 MBps modulation rate. The duration of the phase reversal shall be less than 0.8 µs. The interrogator�s spectrum is data dependent. The broadest spectrum is generated when the interrogation contains pattern with all binary "1"s.

Note: In D4 and ICAO Annex 10, slightly different values for the accuracy of the Mode S centre frequency are found. In the following, the values from Annex 10 are assumed, i.e. the onboard Mode S TX operates on 1090 ±1 MHz and the ground Mode S TX operates on 1030 ±0.1 MHz.

The interference power is determined taking into account the distance between the SSR Mode S transmitter and the victim receiver. In addition, the frequency distance between the SSR Mode S transmitter and the frequency band under investigation is considered. Spectral limits for the Mode S interrogator are given in Figure 3-2 in Vol. IV Sect. 3.1.2 and re-inserted below in Figure 6-5.

Figure 6-5: Required spectrum limits for interrogator transmitter [Annex10]

At relatively large frequency offsets and short TX-RX distances SSR Mode S interference is considered to just increase the RX effective AWGN level during its pulse duration.



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6.3. UAT Interference

UAT interference can be modelled similar to JTIDS/MIDS interference.

Interference burst duration and duty cycle are chosen according to UAT specifications.

RTCA DO-292 states the following (referring to RTCA DO-282):

Onboard UAT TXs operate on 978 MHz with maximum 16 dBW EIRP, maximum burst width of 420 µs and maximum duty-cycle of 0.042 %. Out-of-band emissions (at larger offsets) are constrained to at most -60 dBc.

B-AMC D4 states the following:

Maximum UAT airborne transmitter power is 250 W (54 dBm) measured at the antenna port. The maximum EIRP for a UAT aircraft shall not exceed +58 dBm (including antenna gain).

The maximum EIRP specification (+58 dBm) for an airborne UAT TX is also valid for the ground UAT TX.

UAT SARPs state the following:

The spectrum of an UAT ADS-B message modulated with pseudorandom message data blocks shall fall within the limits specified in SARPS Table 2 when measured in 100 kHz bandwidth.

The time-amplitude profile of UAT message transmissions shall be as in Section 12.1.2.6 of UAT SARPs.

The carrier is modulated by using CPFSK (Continuous Phase Frequency Shift Keying) with the modulation index h not less than 0.6. The modulation rate is 1.041667 MBps.

Note: At relatively large frequency offsets and short TX-RX distances UAT interference is considered to just increase the RX effective AWGN level during its burst duration.

The interference power is determined taking into account the distance between the UAT transmitter and the victim receiver.

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7. Conclusions

In this deliverable, procedures for generating interference scenarios have been described, that model interference from existing L-band systems onto new candidate L-band systems. The candidate L-band systems differ with respect to the frequency range they intend to use and consequently are confronted with significantly different interference conditions. Hence, it is difficult to define detailed universally valid interference scenarios, with which any arbitrary L-band system can be investigated. However, the general procedures provided in this deliverable can be applied to any frequency range and any L-band system for generating appropriate interference scenarios.

As DME is the main source of interference in the aeronautical L-band, special emphasis is put on the modelling of DME interference and defining appropriate interference scenarios.

In Chapter 3, an interference simulator is described that generates the DME signal in time domain. Different interference conditions can be set by varying the power, the duty cycle, the distance between the two pulses of a pulse pair, the centre frequency of the DME signal as well as the number of different independent interferers having the same or different centre frequencies.

In Chapter 4, the methodology for generating interference scenarios taking into account DME ground stations is described. With the NAVSIM tool, the interference power received from any DME ground station operating in a certain area can be determined based on actual DME channel assignments. The interference power is determined at the input of the victim receiver, taking into account elevation angle dependent antenna patterns of typical L-band devices, cable losses and free space loss due to the spatial separation between the interference source and the victim receiver. Thereby, the victim receiver can be considered either static resulting in fixed interference power values or mobile (moving in a certain range) resulting in a varying interference power described by a power probability density function (PDF). From these data, interference scenarios for any L-band system can be derived by simply considering those channels relevant for the considered victim system. As an example, an interference scenario has been defined for the B-AMC forward link.

In Chapter 5, interference originating from aircraft interrogating DME ground stations is investigated. The victim receiver is on ground. With the NAVSIM tool, the DME ground stations which are interrogated by aircraft in the considered area are identified and the resulting interference power received at the victim receiver on ground is determined. For each ground station in the considered area, an interference power PDF is obtained that represents the interference caused by interrogations of different aircraft at different distances to the respective DME station and to the victim ground station. Moreover, a procedure for determining the corresponding aggregate duty cycle is described. Interference scenarios are determined by generating the required data, i.e. interference power PDF and duty cycle for all relevant DME stations in the considered channels and in the considered area. As an example, an interference scenario for the B-AMC reverse link is given.

Finally, interference from other L-band systems is addressed. In the time domain, the pulses of JTIDS, UAT and SSR can be modelled in a simplified way avoiding the detailed implementation of the signal generation of the considered systems. For the duration of the pulses, noise with a power level corresponding to the received interference power is added to the desired signal. Pulse duration and duty cycles are given in the



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specifications; the received power level can be derived from the distance in space and in frequency between the interfering and the victim system.

With the described procedures, all building blocks are available which are required to generate interference scenarios for any arbitrary L-band system. Depending on the position in the L-band, different interference sources may be relevant and thus are requiring a combined application of different procedures for generating an overall interference scenario reflecting the interference situation for the considered L-band system.

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8. References

Reference Description

D1 B-AMC Project Deliverable D1, �DME Spectrum Characterisation and L-band Spectrum Availability for an OFDM-like System�, Draft C, 08 May 2007

D4 B-AMC Project Deliverable D4, �B-AMC Interference Analysis and Spectrum Requirements�, Issue 1.1, October 22, 2007

D5 B-AMC Project Deliverable D5, �Expected B-AMC System Performance�, Issue 1.1, 24 September 2007

D3 B-AMC 2 Project Deliverable D3, �WP3-Systematic Interference Investigations�, Issue 1.0, January 31, 2008.

COCR EUROCONTROL/FAA Future Communications Study, Operational Concepts and Requirements Team, Communications Operating Concept and Requirements for the Future Radio System, Ver. 2, May 2007

COM3 COM3 data base, March 2007

RTCA/DO-292 RTCA/DO-292, Assessment of Radio Frequency Interference Relevant to the GNSS L5/E5A Frequency Band, July 29, 2004

Annex 10, I ICAO, �International Standards and Recommended Practices, Aeronautical Telecommunications, Annex 10 to the Convention on International Civil Aviation�, Volume I (Radio Navigation Aids), Sixth Edition, July 2006

Annex 10, IV ICAO, �International Standards and Recommended Practices, Aeronautical Telecommunications, Annex 10 to the Convention on International Civil Aviation�, Volume IV (Surveillance Radar and Collision Avoidance Systems), Third Edition, July 2002.

JTIDS JTIDS / MIDS MULTINATIONAL AD HOC SPECTRUM SUPPORT WORKING GROUP NOTEBOOK, May 2006

ED54 European Organization for Civil Aviation Electronics (EUROCAE), Minimum Operational Performance Requirements for Distance Measuring Equipment Interrogator (DME/N and DME/P) operating within the radio frequency range 960 to 1215 MHz (Airborne Equipment), ED-54, Jan. 1987

DO-292 RTCA DO-292 Assessment of Radio Frequency Interference Relevant to the GNSS L5-E5A Frequency Band

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9. Abbreviations

Abbreviation Meaning

APT Airport

AWGN Additive White Gaussian Noise

CDG Charles-de-Gaulle airport

COCR Communications Operating Concept and Requirements

CPFSK Continuous Phase Frequency Shift Keying

CPSM Continuous Phase-Shift Modulation

DME Distance Measuring Equipment

EIRP Equivalent Isotropic Radiated Power

ENR En-Route

ES Extended Squitter

FL Forward Link, Flight Level

GS Ground station

ICAO International Civil Aviation Organization

JTIDS Joint Tactical Information Distribution System

MIDS Multifunctional Information Distribution System

nm Nautical mile (1 nm = 1.852 km)

OFDM Orthogonal Frequency Division Multiplex

PDF Probability density function

ppps Pulse pairs per second

RL Reverse Link

RTCA Radio Technical Commission for Aeronautics

SARP Standard and Recommended Practice

SSR Secondary Surveillance Radar

TACAN Tactical Air Navigation

TCAS Traffic Alert and Collision Avoidance System

TDMA Time-Division Multiple-Access

TMA Terminal Mane Area

TSDF Time Slot Duty Factor

UAT Universal Access Transceiver

proposed l-band interference scenarios...tx-rx spacing between two systems) and frequency planning...

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