Report on test procedures and measurements results for the ...



AMCP WGB/11-WP4 Rev.1

Report on test procedures and measurement results for the development of frequency planning criteria for VDL Mode 4

Author: Dr. Armin Schlereth, DFS

Date: 5th September 2001

Abstract

This document provides an overview on test procedures as agreed in ICAO/AMCP-WG-B and test results of measurement exercises conducted in DFS labs 6th of November to 1st of December 2000 and from 7th of May to 16th of August 2001. Further test results are from a measurement exercise at EUROCONTROL Experimental Centre in Bretigny, which took place from 12th to 14th of December 2000.

This report contains test data related to:

• VDL Mode 4 power spectrum measurements

• VDL Mode 4 receiver sensitivity

• VDL Mode 4 interference on VDL Mode 4

• VDL Mode 4 interference on analog voice DSB-AM radios and vice versa

This includes also a validation of the so called S/P 6 dB criteria. Comprehensive voice samples have been recorded in that context.

• VDL Mode 4 interference on VDL Mode 2

• VDL Mode 2 interference on VDL Mode 4, but only for –82 dBm input power value. Measurements for –88 dBm input power value are still missing.

• VDL Mode 4 interference on VOR

• VDL Mode 4 interference on ILS

No data on impact of VDL Mode 4 on GBAS and vice versa could be gathered due to lack of GBAS equipment.

As VDL Mode 4 units two radios from one manufacturer have been investigated in detail.

References:

|[1] |Voice-Interference Tests for VDL Mode 4; Dr. Armin Schlereth; AMCP/WG-D12-WP12; Jan. 2000 |

|[2] |Report to AMCP/WG-B: Frequency Planning Criteria for VDL Mode 4; VDL Mode 4 VSG; Sept. 1999 |

|[3] |AMCP/WG-B 8th Meeting Report; Jan. 2000 |

|[4] |AMCP/WG-B 9th Meeting Report; July 2000 |

|[5] |Preliminary general interference assessment results in VHF band; EUROCONTROL; AMCP/WG-B/WP 8-4; Jan. 2000 |

|[6] |A proposal for VDL Mode 2 to DSB-AM interference criteria definition; EUROCONTROL; AMCP/WG-B/WP 8-6; Jan 2000 |

|[7] |Some further explanations on EUROCONTROL proposed method to assess frequency planning criteria; EUROCONTROL; AMCP/WG-B/IP 8-2; |

| |Jan. 2000 |

|[8] |Test Results of the Aviation Data System Innovations LLC (ADSI) VDL Mode 4 Equipment for ADS-B Applications in the Upper VOR |

| |Band; Trent A. Skidmore and Aaron A. Wilson; Ohio University Avionics Engineering Center; July 1999 |

|[9] |VDL2/ACARS/Voice to AM-DSB Interference, Technical Report, Thomson-CSF Communications, B. Bourcier, Dec. 1999 |

|[10] |Minimum Operational Performance Specification for an Airborne VDL Mode 2 Transceiver, EUROCAE Document ED-92; March 2000 |

|[11] |Compatibility Between The Sound-Broadcasting Service In The Band Of About 87-108 MHz And The Aeronautical Services Band 108-137|

| |MHz, Rec. ITU-R IS.1009-1 |

|[12] |Test Procedures For Measuring Aeronautical Receiver Characteristics Used For Determining Compatibility Between The |

| |Sound-Broadcasting Service In The Band Of About 87-108 MHz And The Aeronautical Services In The Band 108-118 MHz, Rec. ITU-R |

| |IS.1140 |

|[13] |Test procedures and results for the development of frequency planning criteria for VDL Mode4; WP of AMCP-WG-B meeting in San |

| |Diego, January 2001. |

1. Introduction

This document provides an overview on test procedures as agreed in ICAO/AMCP-WG-B and test results of measurement exercises conducted in DFS labs 6th of November to 1st of December 2000 and from 7th of May to 16th of August 2001. Further test results are from a measurement exercise at EUROCONTROL Experimental Centre in Bretigny, which took place from 12th to 14th of December 2000.

This report contains test data related to:

• VDL Mode 4 power spectrum measurements

• VDL Mode 4 receiver sensitivity

• VDL Mode 4 interference on VDL Mode 4

• VDL Mode 4 interference on analog voice DSB-AM radios and vice versa

This includes also a validation of the so called S/P 6 dB criteria. Comprehensive voice samples have been recorded in that context.

• VDL Mode 4 interference on VDL Mode 2

• VDL mode 2 interference on VDL Mode 4, but only for –82 dBm input power value. Measurements for –88 dBm input power value are still missing.

• VDL Mode 4 interference on VOR

• VDL Mode 4 interference on ILS

No data on impact of VDL Mode 4 on GBAS and vice versa could be gathered due to lack of GBAS equipment.

As VDL Mode 4 units two radios from one manufacturer have been investigated in detail.

In section 2 a short introduction of the different test cases used is outlined.

In the appendices A to G different test cases are described in more detail.

In appendix I measurement results are outlined. These results cover the grey shaded cases in table 1-1 below.

Table 1-1: Overview on test cases conducted (grey shaded)

| |Interference Source |

|vs. | |

| |DSB-AM |VDL-2 |VDL-3 |VDL-4 |GBAS |VOR |ILS |FM |

| |DSB-AM |

| | |

| | |

|Victim | |

| |DSB-AM |VDL-2 |VDL-3 |VDL-4 |GBAS |VOR |ILS |FM |

| |DSB-AM |- |

| | | |

| | | |

|Victim | | |

|Power output |= 44 dBm |MOPS |

|Feeder loss |= 3 dB |Assumed figure (used in RTCA172) |

|Antenna gain |= 0 dB |Assumed |

| | | |

|Receiver | | |

|Minimum expected signal at the antenna |= 75(V/m |Annex 10 Volume III, Part II, Para 2.3.2.2.1 |

| |( -82dBm (isotropic Antenna) | |

|Feeder loss |= 3 dB |Assumed figure (used in RTCA172) |

|Antenna gain |= 0 dB |Assumed |

Ground

|Transmitter | | |

|Power output |= 50 dBm |Annex 10 Volume V, Attachment A, Para 2.4 |

|Feeder loss |= 3 dB |Assumed figure (used in RTCA172) |

|Antenna gain |= 2 dB |Assumed |

| | | |

|Receiver | | |

|Minimum expected signal at the antenna |= 20(V/m |Annex 10 Volume III, Part II, Para 2.2.2.2. |

| |( -93dBm (isotropic Antenna) | |

|Feeder loss |= 3 dB |Assumed figure (used in RTCA172) |

|Antenna gain |= 2 dB |Assumed |

VDL MODE 2/3

AIRBORNE & GROUND

|Transmitter | | |

|Power output |= 42 dBm (on channel VDL Mode 2) |MOPS |

| |44 dBm (on channel VDL Mode 3) |MOPS |

| | | |

| |-18 dBm (1st Adjacent, 16kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| |-28 dBm (2nd Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| |-38 dBm (4th Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| |-43 dBm (8th Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| |-48 dBm (16th Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| |-53 dBm (32nd Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

|Feeder loss |= 3 dB |Assumed figure (used in RTCA 172) |

|Antenna gain |= 0 dB (airborne) |Assumed |

| |2 dB (ground) |Assumed |

| | | |

|Receiver | | |

|Minimum expected signal at the |= 20(V/m |Annex 10 Volume 3, Part II, Para 6.3.5.1 |

|antenna |(-93dBm (isotropic Antenna) | |

|Undesired signal rejection |= 40 dB (1st Adjacent channel) | |

| |60 dB (3rd Adjacent channel) | |

|Feeder loss |= 3 dB |Assumed figure (used in RTCA 172) |

|Antenna gain |= 0 dB (airborne) |Assumed |

| |2 dB (ground) |Assumed |

VDL MODE 4

AIRBORNE & GROUND

|Transmitter | | |

|Power output |= 40 dBm (airborne at the antenna VDL Mode 4) |MOPS |

| |44 dBm (ground at the antenna VDL Mode 4) | |

| |-18 dBm (1st Adjacent, 16kHz BW) |MOPS |

| |-28 dBm (2nd Adjacent, 25kHz BW) | |

| |-38 dBm (4th Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| |-43 dBm (8th Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| |-48 dBm (16th Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| |-53 dBm (32nd Adjacent, 25kHz BW) |Annex 10 Volume 3, Part I, Para 6.3.4 |

| | |Annex 10 Volume 3, Part I, Para 6.3.4 |

| | |Annex 10 Volume 3, Part I, Para 6.3.4 |

|Feeder loss |= 3 dB |Assumed figure (used in RTCA 172) |

|Antenna gain |= 0 dB (airborne) |Assumed |

| |2 dB (ground) |Assumed |

| | | |

|Receiver | | |

|Minimum expected signal at the |= 35(V/m |Annex 10 Volume 3, Part II, Para 6.9.5.1.1.1 |

|antenna |(-88dBm (isotropic Antenna) | |

|Undesired signal rejection |= 40 dB (1st Adjacent channel) | |

| |60 dB (3rd Adjacent channel) | |

|Feeder loss |= 3 dB |Assumed figure (used in RTCA 172) |

|Antenna gain |= 0 dB (airborne) |Assumed |

| |2 dB (ground) |Assumed |

APPENDIX C

TEST METHOD 1

INTRODUCTION

This test method can be used to assess the impact of VDL signals on a DSB-AM (25 kHz and 8,33 kHz) victim receiver and is based on the ratio of power of the desired and undesired signals in the passband of the receiver. This method was used as the basis for the work which lead to a change in the VDL transmitter mask adopted by AMCP 6

SQUELCH BREAK

Test Setup

Test Procedure

• The undesired VDR is tuned to the centre frequency of the AM receiver under test and the signal level increased until the squelch is broken and the level recorded.

• The undesired VDR is then tuned to the adjacent channel and the signal level increased until the squelch is broken and the level recorded.

• The undesired VDR is then tuned to the next adjacent channel in a given set of N adjacent channels and the signal level increased until the squelch is broken and the level recorded. This is repeated until the last channel in the reference set is tested.

• AM test frequencies are 119, 128 and 136 MHz.

• Adjacent channels be used are 1st, 2nd, 3rd, 4th, 5th, 10th, 20th, 40th (25 kHz spacing) as far as possible.

• Desired AM source is turned off.

Remark: This tests are also covered within test method 2 and therefore not required.

ON CHANNEL D/U RATIO

Test Setup

Test Procedure

• The desired AM signal is set so as to produce a –82dBm or –93 dBm, 30% modulated with ATC phrases at the input of the victim receiver

Remark: -93 dBm simulates a worst case scenario for a ground receiver.

• The undesired VDL signal is then set to give a W dB D/U in the passband of the receiver on the first and subsequent adjacent channels and a recording made of the audio output from the receiver for each adjacent channel. W is determined by subjective testing for each VDL mode.

• A listening panel then assess the quality of the audio results recorded scoring each.

Remark: Tests regarding a –82 dBm value have already been made and results are outlined in Ref. [1] with a recommendation for 20 dB D/U in case of VDL Mode 4.

APPENDIX D

TEST METHOD 2

INTRODUCTION

This test method investigates separately the effects of the pulse and continuous modulation of a digital signal on a DSM-AM (25 kHz and 8,33 kHz) victim receiver. By separating the effects of the pulse and modulation two objective parameters can be defined which can therefore be tested for and measurements made. To assess the impact of a digital signal on a DSB-AM receiver in the presence of a wanted signal two criteria are proposed a Signal + Noise to Noise ratio (S+N/N) and a signal to pulse (S/P) ratio.

SQUELCH BREAK

Test Setup

Test Procedure

• The undesired VDR is tuned to the centre frequency of the AM receiver under test and the signal level increased until the squelch is broken and the level recorded.

• The undesired VDR is then tuned to the adjacent channel and the signal level increased until the squelch is broken and the level recorded.

• The undesired VDR is then tuned to the next adjacent channel in a given set of N adjacent channels and the signal level increased until the squelch is broken and the level recorded. This is repeated until the last channel in the reference set is tested

• AM test frequencies are 119, 128 and 136 MHz.

• Adjacent channels be used are 1st, 2nd, 3rd, 4th, 5th, 10th, 20th, 40th (25 kHz spacing) as far as possible.

• Impact of short (one slot) and long transmissions from the undesired VDR (VDL Mode 4) for different duty cycles shall be investigated.

Note: The following interference scenarios for VDL Mode 4 shall be considered:

➢ 1.3 % duty cycle (one Sync burst transmission in one slot every second) simulating worst case cosite scenario

➢ 2.7 % duty cycle (two slot burst transmission every second) simulating worst case cosite scenario for transmitting e.g. TCP-information

➢ 50 % duty cycle (Sync burst transmissions in every other slot) simulating a medium dense scenario of interferers at equal distance

➢ 50 % duty cycle (two slot burst transmissions in every other two slots) simulating a medium dense scenario of interferers at equal distance

• Desired AM source is turned off.

S+N/N RATIO DEGRADATION

Test Setup

Test Procedure

• The wanted signal is set so as to produce a –82 dBm or –93 dBm, 30% modulated 1 kHz tone (30 % modulation depth) at the input of the victim receiver.

Note: Also 90% modulation depth might be investigated due to the fact, that this refers to an average modulation depth of 30% for real speech signals.

• The undesired VDR is set in bursted mode with a centre frequency offset from the desired AM signal by one channel and the level of signal at the input of the victim AM receiver varied until a S+N/N degradation on the audio output of 6 dB is measured and the level noted.

Note 1: The S+N/N measurement is conducted with an output power meter as „audio test equipment“. The S+N values are derived with a desired signal with modulation present, whereas the N value is derived with the modulation removed. In fact the procedure gives the (S+D+N)/N ratio in case additional harmonic distortion D is present.

• When the (S+N)/N ratio reduction of 6 dB is reached, the audio level is measured to check that it is more than the nominal level minus 6 dB. If it were not the case, so the unwanted signal level to get the nominal audio level minus 6 dB would be noted.

Note 3: The receiver degradation could also appear to be an audio „blocking“ (audio level reduction). The tolerance generally considered for this audio reduction is 6 dB.

• The audio distortion is then checked to ensure that it is less than 10%, which is equivalent to (S+D)/D or better than 20 dB. If this is not the case then the unwanted VDR signal level required to get a 20 dB (S+D+N/N) value is noted.

Note 4: Audio distortion will be measured with a distortiometer as „audio test equipment“. The measurement principle is to reject the audio tone of 1 kHz (modulation signal). The audio fundamental at 1 kHz is suppressed and the remaining energy is due to the audio harmonics, hence to the distortion (in %). However the measurement is correct only if the noise energy is low enough. In fact the measurement gives the (S+D+N)/(D+N) ratio.

• This is repeated for the next adjacent channel for the undesired VDR in a given set of N adjacent channels.

• Adjacent channels be used are 1st, 2nd, 3rd, 4th, 5th, 10th, 20th, 40th (25 kHz spacing) as far as possible.

• AM test frequencies are 119, 128 and 136 MHz.

SIGNAL TO PULSE RATIO LEVEL

Test Setup

Test Procedure

• The wanted signal is set so as to produce a –82dBm or –93 dBm, 30% modulated 1kHz tone (30 % modulation depth) at the input of the victim receiver

Note: Also 90% modulation depth might be investigated due to the fact, that this refers to an average modulation depth of 30% for real speech signals.

• The undesired VDR is set in burst mode with a centre frequency offset from the desired AM signal by one channel and the level of signal at the input of the victim AM receiver varied until level of the audio pulses is 6 dB below the nominal audio peak level (the audio pulse level is half of the nominal audio peak level)

•

Note: The measurement procedure is as follows; Modulate the wanted signal with a 1 kHz tone. Note the audio peak level (1 kHz) at the receiver audio output with the unwanted transmitter off. Then suppress the wanted signal modulation and increase the unwanted signal level to get spurious audio pulses half of the nominal audio peak level, which means that S/P is now equal to 6 dB.

• The undesired VDR is then set to the next adjacent channel and the level of signal at the input of the victim AM receiver varied until the audio pulse level is 6 dB below the nominal audio peak level and the level noted.

• This is repeated for the next channel in a given set of N adjacent channels.

• AM test frequencies are 119, 128 and 136 MHz.

• Adjacent channels be used are 1st, 2nd, 3rd, 4th, 5th, 10th, 20th, 40th (25 kHz spacing) as far as possible.

APPENDIX E

TEST METHOD 3

INTRODUCTION

This test method can be used to assess the impact of either a DSB-AM or VDL signal on a VDL victim receiver and is based on the bit error rate performance of the radio

Note: In case of VDL Mode 4 as an alternative the evaluation of message error rate performance is proposed.

BIT ERROR RATE TEST

Test Setup

Test Procedure

• The desired VDR signal is set such that the level at the input to the VDR receiver under test is –82dBm or –93 dBm.

• The undesired signal source is tuned to the centre frequency of the VDR receiver under test and the signal level increased until the bit error rate of the desired signal falls below the required level and the undesired signal level at the input to the victim receiver recorded.

• The undesired signal source is then tuned to the adjacent channel and the signal level increased until the bit error rate of the desired signal falls below the required level and the undesired signal level at the input to the victim receiver recorded.

• The undesired signal source is then tuned to the next adjacent channel in a given set of N adjacent channels and the signal level increased until the bit error rate of the desired signal falls below the required level and the undesired signal level at the input to the victim receiver recorded. This is repeated until the last channel in the reference set is tested.

• Desired source test frequencies are 119, 128 and 136 MHz.

• Adjacent channels be used are 0th (co-channel), 1st, 2nd, 3rd, 4th, 5th, 10th, 20th, 40th (25 kHz spacing) as far as possible.

APPENDIX F

TEST METHOD 4

INTRODUCTION

This test method can be used to assess the impact of a VDL Mode 4 signal on a VOR victim receiver and is based on the changes in selected VOR bearing or VOR flag indication.

VOR BEARING CHANGE TEST

Test Setup

Test Procedure

• Channel spacing for VOR equipment is 50 kHz.

• VDL interference source shall be channelled in 25 kHz steps.

• For VDL Mode 4 the following duty cycles shall be investigated:

➢ 1.3 % duty cycle (one Sync burst transmission in one slot every second) simulating worst case co-site scenario

➢ 2.7 % duty cycle (two slot burst transmission every second) simulating worst case co-site scenario for transmitting e.g. TCP-information

➢ 50 % duty cycle (Sync burst transmissions in every other slot) simulating a medium dense scenario of interferers at equal distance

➢ 50 % duty cycle (two slot burst transmissions in every other two slots) simulating a medium dense scenario of interferers at equal distance

Note: 50 % duty cycle leads to a beat frequency of 37 Hz. VORs are rather sensitive against low beat frequencies on the order of 30 Hz. This scenario could be considered as a medium dense scenario with interferers at equal distance.

• VOR test frequencies are fVOR,i = 112 MHz, or 115 MHz, or 117.95 MHz.

• Both co- and adjacent channel interference shall be investigated using the following VDL frequencies: fVDL,i = fVOR,i ( 25 (,or 50, or 75, or 100) kHz

• Interference criteria shall be the changes in selected VOR bearing of ( 0,3° (Rec. ITU-R IS.1140) or appearance of flag, which ever comes first.

Note:

A 0.3° course indicator deflection equates to a deviation bar drive current of 4.5 µA.

• For each series of tests the output power level on the VOR Signal Generator will be set to provide –79 dBm RF input level (ICAO and RTCA/DO-196 reference signal level) at the VOR receiver under test.

APPENDIX G

TEST METHOD 5

INTRODUCTION

This test method can be used to assess the impact of a VDL Mode 4 signal on a ILS victim receiver and is based on ITU-R IS.1140 [12] recommendations.

Test Setup

Test setup is equal to test method 5, but with ILS Signal Generator and ILS Receiver under test.

Test Procedure

• VDL interference source shall be channelled in 25 kHz steps.

• For VDL Mode 4 the following duty cycles shall be investigated:

➢ 1.3 % duty cycle (one Sync burst transmission in one slot every second) simulating worst case co-site scenario

➢ 2.7 % duty cycle (two slot burst transmission every second) simulating worst case co-site scenario for transmitting e.g. TCP-information

➢ 50 % duty cycle (Sync burst transmissions in every other slot) simulating a medium dense scenario of interferers at equal distance

➢ 50 % duty cycle (two slot burst transmissions in every other two slots) simulating a medium dense scenario of interferers at equal distance

• ILS test frequency is fVOR,i = 111.95 MHz.

• Both co- and adjacent channel interference shall be investigated using the following VDL frequencies: fVDL,i = fVOR,i ( 25 (,or 50, or 75, or 100) kHz

The interference thresholds for a wanted signal with a difference in depth of modulation (DDM) of 0.093 are:

• a change in course deflection current of 4,5 (A, or

• the appearance of the flag, whichever occurs first

• For each series of tests the output power level on the ILS Signal Generator will be set to provide –86 dBm RF input level (ICAO and RTCA/DO-195 reference signal level) at the ILS receiver under test.

APPENDIX H

SAMPLE LINK BUDGET FOR THE PROTECTION OF GNSS

|Sample link budget for the protection of GNSS receivers on board the same aircraft as a VDL transceiver |

|GPS Interference Threshold (dBm) |-110.5 |

|Expected Antenna Isolation (dB) |-30* |

|GPS antenna gain, dBi |-4.5 |

|Reqd VDL Spurious and Harmonic Emission Limit, eirp (dBm) |-76** |

|* Antenna isolations will vary from airframe to airframe. |

|** One administration is planning to require that newly certified VHF A/G radios control their spurious |

|emissions and harmonics in the GNSS (L1) frequency band (1559-1610 MHz) to an eirp of –80 dBm. |

-----------------------

AM Receiver Under Test

RF Combiner

Variable RF Attenuator

Variable RF Attenuator

Undesired VDR Signal Source

Desired AM Signal Source

Audio Recorder

AM Receiver Under Test

RF Combiner

RF Attenuator

RF Attenuator

Undesired VDR Signal Source

Desired AM Signal Source

AM Receiver Under Test

RF Combiner

RF Attenuator

RF Attenuator

Undesired VDR Signal Source

Desired AM Signal Source

Audio Test Equipment

AM Receiver Under Test

RF Combiner

RF Attenuator

RF Attenuator

Undesired VDR Signal Source

Desired AM Signal Source

Audio Test Equipment

AM Receiver Under Test

RF Combiner

RF Attenuator

RF Attenuator

Undesired VDR Signal Source

Desired AM Signal Source

VDR Receiver Under Test

RF Combiner

Variable RF Attenuator

Variable RF Attenuator

Undesired AM/VDR Signal Source

Desired VDR Signal Source

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