Working Document Toward a Preliminary Draft New Report on Compatibility Studies Between

- 1 -

1-8/TEMP/71-E

Agenda Item 4:Ultra Wide Band (UWB)

WORKING DOCUMENT TOWARD A PRELIMINARY DRAFT NEW REPORT ON COMPATIBILITY STUDIES BETWEEN UWB DEVICES AND RADIOCOMMUNICATION SERVICES

/ INTERNATIONAL TELECOMMUNICATION UNION
RADIOCOMMUNICATION
STUDY GROUPS / Document 1-8/TEMP/71-E
17 June 2004
English only

Source: Doc. 1-8/81 & 106

Task Group 1/8
WG 2 (Compatibility)

Proposed text for section 3.4.2.2

WORKING DOCUMENT TOWARD A PRELIMINARY DRAFT NEW REPORT ON COMPATIBILITY STUDIES BETWEEN UWB DEVICES AND RADIOCOMMUNICATION SERVICES:

3.4.2.2Aeronautical service

[3.4.2.2.1Introduction

Aeronautical services are recognized internationally to be prime users of radio frequencies without which aircraft operations would not be capable of meeting the global demand for safe, efficient and cost-effective transport. Aeronautical radionavigation service (ARNS) service provides radionavigation relating to safety and regularity of flight. The Aeronautical mobile (R) service (AM(R)S) and aeronautical mobile satellite (R) service (AMS(R)S) provide communications relating to safety and regularity of flight. The prominent safety-of-life element, present during all phases of an aircraft’s flight, is accorded special treatment internationally and is granted protection from harmful interference through agreed measures. Provision No. 4.10 of the Radio Regulations (RR) recognizes that radionavigation and other safety services require special measures to ensure freedom from harmful interference and that it is necessary to take this factor into account in the assignment and use of frequencies.

Aeronautical spectrum use is divided into two main functions: ground-air communications and radionavigation. The future will also see the gradual introduction of more satellite-based services in accordance with the communications, navigation and surveillance/air traffic management (CNS/ATM) policies agreed at Air Navigation Conferences and approved by the ICAO Council.

3.4.2.2.2Aeronautical safety services and UWB

Safety services in general are based on the reception of emissions with higher levels of integrity and availability than is generally required for other radiocommunication services. Ultra-wideband (UWB) devices are intended for operation across numerous frequency bands and may affect, simultaneously, stations of several radiocommunication services identified in Article 5 of the RR, including aeronautical safety services such as the ARNS, AM(R)S and AMS(R)S. Emissions from UWB devices may have the potential to cause harmful interference to aeronautical safety services receivers.

UWB systems are not standardized and different UWB system parameters may have an impact on the transmitted waveform. It is important to note that different interference signal characteristics may affect the operation of aeronautical safety services in different ways.

Annex 10 to the Convention on International Civil Aviation does not specify all receiver interference immunity characteristics necessary to fully evaluate the potential for interference to aeronautical safety services from emissions of UWB devices.

It is therefore of paramount importance to determine the characteristics of typical aeronautical receiver necessary to evaluate the potential for interference to aeronautical safety services from emissions of UWB devices. Therefore, standardized test procedures need to be developed.

ITU-R Recommendation SM.1140 may provide guidance in the development of test procedures for measuring aeronautical receiver characteristics to be used for determining the influence of emissions from UWB devices into ARNS

3.4.2.2.3Interference evaluation model

Parameter / UWB Interference Signal / Comments
a)Measured maximum value of UWB interference signal power that is tolerable when the desired signal is at its minimum required level (dB(W/MHz)) / __dB(W/MHz) / Maximum value of UWB interference signal power that still allows the receiver to meet its performance requirements. To be derived by measurements, and the result may be specific to the UWB waveform tested. For some systems ICAO Annex 10 specifies the minimum required desired signal level.
b)Antenna gain difference (dB) / __dB / The difference in antenna gain towards the desired signal and the interference signal
c)Aeronautical safety factor (dB) / __dB / Additional margin for safety service (see also ITU-R Rec. M.1477 and M.1535)
d)Total tolerable interference level at isotropic antenna port (dB(W/MHz)) / __dB(W/MHz) / Total tolerable interference level for the specific UWB signal tested.
e)Multiple interference source factor (dB) / __dB / If there is a potential for other than UWB interference sources at the same time, an allowance should be made for the aggregate interference
f)Total tolerable UWB interference level at isotropic antenna port (dB(W/MHz)) / __dB(W/MHz)
g)Multiple UWB interference source factor (dB) / __dB / If there is a potential for more than one UWB source of interference at the same time, an allowance should be made for the aggregate interference. This should include free space propagation loss between victim receiver antenna and interference source. It may be necessary to apply a specific model in order to calculate the cumulative interference power of more than one UWB interference source. (see Attachment to Annex 1)
h)Tolerable interference emission of a single UWB device (dB(W/MHz)) / __dB(W/MHz) / If this power density is exceeded interference may occur and further analysis is required

3.4.2.2.4Methodology for calculation of cumulative interference power

In highly populated areas, aircraft in flight may be exposed to interfering signals transmitted from a large number of emitters on the ground at the same time. This leads to the issue of potential aggregate interference. This methodology was developed to estimate aggregate interference power levels.

The methodology makes a number of fundamental assumptions:

a)that all emitters are uniformly distributed in a circular area below the victim receiver;

b)that all emitters radiating on the same frequency, the same power levels and using isotropic antennas with omni-directional radiation pattern;

c)that free space propagation are assumed; and

d)that all single emitters are statistically independent and the power contribution of all single emitters can be added arithmetically.

Figure 1

The cumulative methodology

The power flux density pfd generated by a single isotropic radiator with the power p at distance d and assuming free-space propagation can be derived from the following equation:

/ (1)

where:

pfdpower flux density in W/m2

piisotropically radiated power from a single device in W

ddistance between transmitting and receiving site in m

To begin the derivation the first thing to determine is the differential circular area dA at a distance r. This is defined as:

/ (2)

The total transmitted power from a differential circular area dp is the product of the density of emitters per square-meter n, the isotropically radiated power from a single device and of the differential circular area. It is shown in the following equation:

/ (3)

The determination of the differential power flux density dpfd at a distance d from the victim receiver follows from dividing the total transmitted power from a differential circular area dp by the surface area of a sphere with a radius d. This leads to:

/ (4)

The distance d can also be written as:

/ (5)

After substitution it leads to the expression:

/ (6)

Integrating the differential power flux density over a range from the minimum radius to the maximum radius of the annulus under consideration yields the total power flux density at the victim receiver location:

/ (7)

The received cumulative interference power at the port of an isotropic antenna is the product of the total power flux density at the victim receiver location and the aperture of an isotropic antenna. It is shown in the following equation:

/ (8)

where

pcumreceived cumulative interference power per reference bandwidth in W

awaperture of an isotropic antenna in m2

wavelength in m

ndensity of emitters per m2

piisotropically radiated power from a single emitter per reference bandwidth in W

haircraft height in meters

rmininner radius of the observed zone

rmaxouter radius of the observed zone

This equation provides the foundation for computing the aggregate power level.

Since the model given in Annex 1 requires the determination of the tolerable interference emission of a single emitter the above equation needs to be rearranged. The determination of the tolerable interference emission of a single emitter pi_tol follows from dividing the cumulative interference power (total tolerable UWB interference level at the isotropic antenna port) pcum_tol by the multiple interference source factor.

/ (9)

Rewriting this equation in logarithmic form yields:

/ (10)

3.4.2.2.5Future work program

Test procedures for measuring aeronautical receiver characteristics in the presence of emissions from UWB devices needs to be developed. ITU-R Recommendation SM.1140 may provide guidance in the development of these test procedures for measuring aeronautical receiver characteristics to be used for determining the influence of emissions from UWB devices into ARNS.

3.4.2.2.6Conclusions

The simplified static model, as described in this chapter, should be used for the initial evaluation of the potential for interference to aeronautical safety services from emissions of UWB devices.

The maximum value of UWB interference signal power that still allows the aeronautical receiver to meet its performance requirements need to be derived by measurements. It should be noted that the result may be specific to the UWB waveform tested.

Test procedures for measuring aeronautical receiver characteristics in the presence of emissions from UWB devices needs to be developed.

If the interference evaluation model indicates a potential for interference that would impair the specific aeronautical safety function, then a more detailed and dynamic analysis may be required.]

[3.4.2.2.1Aeronautical mobile (R) service

3.4.2.2.1.1System characteristics

M.441.1 - Signal-to-interference ratios and minimum field strengths required in the aeronautical mobile (R) service above 30MHz

M.1040 - Public mobile telecommunication service with aircraft using the bands 1670-1675MHz and 1800-1805MHz

M1459 - Protection criteria for telemetry systems in the aeronautical mobile service and mitigation techniques to facilitate sharing with geostationary broadcasting-satellite and mobile-satellite services in the frequency bands 1 452-1 525 MHz and 2 310-2 360 MHz

ICAO Annex 10 to the Convention on International Civil Aviation,

• Volume III, Part I – Digital Data Communications Systems
• Volume III, Part II – Voice Communications Systems
• Volume V, Aeronautical Radio Frequency Spectrum Utilisation

ICAO document 9718 – Handbook on Radio Frequency Spectrum Requirements for Civil Aviation

3.4.2.2.1.2System description

Aeronautical Mobile (R) systems (AM(R)S) provide a means of two way communication between an aircraft station and either a ground or another aircraft station. Systems operate in both the HF (various bands between 2.85 – 22 MHz), over the horizon, and the VHF (108 – 137 MHz), radio line of sight, bands. These systems are used to pass both air traffic control and regulatory of flight messages.

Basic analogue receiver characteristics

Frequency Band / 2.85 – 22 MHz / 117.975 – 137 MHz
System / HF Comms / VHF Comms
Receiver Location / Airborne / Ground / Airborne / Ground
Antenna Height Above Ground / 0 – 10,000 metres / 30 metres (typical) / 0 – 10,000 metres / 30 metres (typical)
Minimum Equivalent Receiver Sensitivity at Antenna / [T.B.D] / [T.B.D] / -90 dBm / -94 dBm
Typical Receiver 6dB Bandwidth / 3 kHz / 3 kHz / 16 kHz (25) 5.6 kHz (8.33) / 16 kHz (25) 5.6 kHz (8.33)
Required Signal to Interference Ratio
(Note 1) / [15 dB] / [20 dB]

NOTE 1 - The values are for intra-system protection criteria and not necessarily valid for UWB

Basic digital receiver characteristics

Frequency Band / 108 – 137 MHz / 117.975 – 137 MHz
System / VDL mode 4 / VDL mode 2 & 3
Receiver Location / Airborne / Ground / Airborne / Ground
Antenna Height Above Ground / 0 – 10,000 meters / 30 meters (typical) / 0 – 10,000 meters / 30 meters
(typical)
Minimum Equivalent Receiver Sensitivity at Antenna / -82 dBm / -89 dBm / -82 dBm / -96 dBm
Typical Receiver 6dB Bandwidth / 5.56 kHz / 6 kHz / 16 kHz / 8 kHz
Required Signal to Interference Ratio
(Note 1) / [20 dB]

NOTE 1 - The values are for intra-system protection criteria and not necessarily valid for UWB

3.4.2.2.1.3Methodology

3.4.2.2.1.3.1Overview

In order to assess whether UWB is likely to cause interference to aviation systems an understanding of what is considered harmful interference in respect of aviation systems needs to be determined. Once harmful interference has been defined an aggregate protection level for all interference sources at an appropriate point (e.g. the receive antenna ) within the aviation system can be defined. This aggregate protection level then has to be apportioned since a single interference system/network should not be able to claim the total aggregate protection margin. Knowing the apportioned aggregate protection level, the minimum coupling loss required between a single UWB source and the victim receiver can be calculated. Once the minimum coupling loss is known a minimum separation distance for a single UWB device and the maximum UWB density can be calculated assuming free space path loss

3.4.2.2.1.3.2Definition of harmful interference

Article 1.169 of the Radio Regulations defines “harmful interference” as:-

“Interference which endangers the functioning of a radionavigation service or of other safety services or seriously degrades, obstructs, or repeatedly interrupts a radiocommunication service operating in accordance with Radio Regulations (CS)”.

Within the context of this document harmful interference is taken to occur when the aggregated interference signal level exceeds either (or both):-

a)the minimum desired signal level at the receive antenna minus the required signal to interference ratio,

b)the receiver sensitivity level

3.4.2.2.1.3.3Determination of harmful interference protection level

As described in section 4.2 there are two conditions that define harmful interference within the context of this paper, if either or both conditions are exceeded then harmful interference is deemed to have been caused:-

a)the minimum desired signal level at the receive antenna minus the required signal to interference ratio,

For a majority of systems used in aviation the ICAO Standards And Recommended Practice (SARPs) recommends a minimum wanted signal level at the receive antenna. ICAO also recommend a minimum receiver sensitivity level at the same point which is normally slightly below the recommended minimum wanted signal. In certain circumstances, a service provider can be approved to provide a minimum wanted signal within the facilities service area that is equivalent to the defined minimum receiver sensitivity. The minimum desired signal level is therefore taken as the lower value given by either the minimum wanted signal or the minimum receiver sensitivity. Combining the minimum wanted signal at the receive antenna and the required S/I gives the maximum level of interference at the receive antenna to ensure protection of the wanted signal in terms of dBm. Where figures are not available from ICAO SARPs (e.g. Primary Radar, Radio Altimeters etc) then the information should be sourced from other ICAO Documentation, ITU-R Recommendations or manufacturers data.

b)the receiver sensitivity level

Within ICAO SARPs the only figure quoted is the minimum sensitivity. Practical receivers by definition must equal or exceed this minimum figure and therefore this figure cannot be used for calculating receiver protection figures. For a number of systems, such as radar, there are typical figures quoted in ITU-R Recommendations & Resolutions. Otherwise the only source of information is manufacturer’s information.

Normally a receiver’s sensitivity is quoted at the input to the receiver. In order to ensure that protection requirements are defined at a common point (e.g. input to the antenna) it is therefore necessary to take into account the gain of the antenna system including feeder losses

Since harmful interference is deemed to have occurred when either of the above conditions has been exceeded. Where ICAO SARPs define a minimum wanted signal level then this should take account of the required signal to interference ratio. However where a figure is not defined as is the case for radar based systems then a practical receiver sensitivity figure should be taken preferably from an acknowledged source such as an ITU Recommendation.

Table XXX

System / Receiver Location / Minimum Desired Signal Level
(Note 1) / Practical Receiver Sensitivity / Antenna System Gain / Required S/I / Signal Level to be Protected
(Ground/Air) / (V/m2) / (dBm) / (dBm) / (dB) / (dB) / (dBm)
NDB / Air / A1 / B1=20log(A1)-20log(F)-167.2 (note 2) / F1 / G1=B1-F1
VHF Comms (8.33 kHz) / Ground / A2 / B2=20log(A2)-20log(F)-167.2 (note 2) / F2 / G2=B2-F2

Note 1. The conversion assumes an ideal isotropic receive antenna and that the effects are the same for both the wanted signal and the UWB signal at the frequency under consideration

2. F equals the centre frequency of the band under consideration

3.4.2.2.1..3.4Calculation of the Maximum Level of Aggregate Interference

When considering protection criteria it is normal to express the limit in terms of power spectral density. The figures calculated through the process given above can be converted to power spectral density, provided that the receiver bandwidth is known. This is not always the case.

ICAO SARP’s, for some systems, either directly define the minimum receiver bandwidth or define the wanted signal that a receiver has to capture. Since practical receivers must have a greater bandwidth than this value, using these values for the receiver bandwidth will produce results that are generous to the interference source(s). An alternative would be, where applicable, to use the channel bandwidth. However this will give an over conservative result. The third possibility, and the one taken, is to use worst case actual receiver bandwidths obtained either from manufacturer’s data or ITU recommendations/resolutions.

Additionally in ICAO’s Publication “Handbook on Radio Frequency Spectrum Requirements for civil aviation, including approved ICAO policies” it is recommended that an additional 6 dB safety margin should be added to any protection limit.

Table XXX

System / Receiver Location / Signal Level to be Protected / Receiver Bandwidth / Aviation Safety Margin / Maximum Level of Aggregate Interference
(Ground/Air) / (dBm) / (MHz) / (dB) / (dBm/MHz)
NDB / Air / G1 / H1 / J1 / K1=G1-10log(H1)-J1
VHF Comms (8.33 kHz) / Ground / G2 / H2 / J2 / K2=G2-10log(H2)-J2

3.4.2.2.1.3.5Apportionment of system protection limit

When considering an assessment of compatibility between an interferer (single source or an accumulation of like sources) and a victim, the protection limit for the victim is taken as the maximum aggregate level of interference at the input to the victim receiver. This assumes that there is only either one interference source (e.g. a fixed link) or the accumulation of a number of sources of the same type ( e.g. multiple UWB devices).