International Civil Aviation Organization

WORKING PAPER

ACP-WGF21/WP-12

AERONAUTICAL COMMUNICATIONS PANEL (ACP)

NINETEENTH MEETING OF WORKING GROUP F

Bangkok, Thailand 10 – 18 December 2009

Subject : Working paper on UAS SPECS

TITLE

(Presented by Gerlof Osinga)

SUMMARYThis paper presents analyses of proposed bands for UAS utilisation.

ACTIONWGF is invited to discuss possible bands for the UAS utilisation. It would help the aeronautical community if ICAO could show their preference to particular bands or to exclude bands for these applications.

(22 pages)

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Introduction

Resolution 421 (WRC-2007) calls to consider the spectrum requirements and possible regulatory actions, including additional allocations, to support the safe flight operation of UAS.

The objective of the study in this working paper, is to identify spectral bands in which the control and non-payload communications (CNPC) links of future UAS can operate reliably without causing harmful interference to incumbent services and systems.

This working paper provides the latest status of the frequency band study to support control links for unmanned aircraft systems within the ITU-R WP 5B as of 4th of December 2009.

Action to be takenWGF is invited to discuss possible bands for the UAS utilisation. It would help the aeronautical community if ICAO could show their preference to particular bands or to exclude bands for these applications.

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Radiocommunication Study Groups

Source: Documents 5B/147, 5B/296A14, 5B/361, 5B/377, 5B/388 and 5B/390

Document 5B/TEMP/187-E1 December 2009English only

Working Party 5B

PRELIMINARY DRAFT NEW REPORT ITU-R M.[UAS-BANDS]

Frequency band study to support control links for unmanned aircraft systems (UAS)

[Editorial Note: it is desirable to have one single ITU-R Report dealing with this subject, however should the circumstances necessitate that separate reports be prepared that approach would be followed. In case that WP 5B opts for a single report material from 5B/147 and 5B/377 5B/388 need to be included into this report]

1 Introduction

Significant growth is forecast in the unmanned aircraft (UA) systems (UAS) sector of aviation. The current state of the art in UAS design and operation is leading to the rapid development of UAS applications to fill many diverse requirements. [Current and future UAS operations may include scientific research, search and rescue operations, hurricane and tornado tracking, volcanic activity monitoring and measurement, mapping, forest fire suppression, weather modification (e.g. cloud seeding), surveillance, communications relays, agricultural applications, environmental monitoring, emergency management, and law enforcement applications.]

Though UA have traditionally been used in segregated airspace where separation from other air traffic can be assured, some administrations expect broad deployment of UA in nonsegregated airspace shared with manned aircraft. If UA operate in nonsegregated civil airspace, they must be integrated safely and adhere to operational practices that provide an acceptable level of safety comparable to that of a conventional manned aircraft. In some cases, those practices will be identical to those of manned aircraft. Thus it is envisioned that UA will operate alongside manned aircraft in nonsegregated airspace using methods of control that could make the location of the pilot transparent to air traffic control (ATC) authorities and airspace regulators.

Because the pilot is located remotely from the UA, bandwidth will be required to support, among other things, UA telemetry data, telecommand messages, and the relay of ATC communications. Since this bandwidth will be used to ensure the safety of life and property,

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the service using it is therefore a safety service. It is also expected that the characteristiUACS of the information and associated safety considerations will necessitate user authentication, and interference resilience. Even for autonomous UAS operations, some bandwidth will be required for emergencies as well as for selected operating conditions. If the spectrum requirements of UAS operations cannot be accommodated within existing aviation spectrum allocations, additional safety communication links such as aeronautical mobile (route) service (AM(R)S), aeronautical mobile satellite (route) service (AMS(R)S), or both may be necessary to support UAS operations.

The goal of airspace access for appropriately equipped UAS requires a level of safety similar to that of an aircraft with a pilot onboard. The safe operation of UAS outside segregated airspace requires addressing the same issues as manned aircraft, namely integration into the air traffic control system. Because some UAS may not have the same capabilities as manned aircraft to safely and efficiently integrate into nonsegregated airspace, they may require communications link performance that exceeds that which is required for manned aircraft. In the near term, the most critical component of UAS safety is the communication link between the remote pilot’s control station (UACS) and the UA.

Radiocommunication is the primary method for remote control of the unmanned aircraft. Seamless operation of unmanned and manned aircraft in nonsegregated airspace requires high-availability communication links between the UA vehicle and the UA control station (UACS). In addition, radio spectrum is required for various sensor applications that are integral to UAS operations including on-board radar systems used to track nearby aircraft, terrain, and obstacles to navigation.

The objective of this study is to identify spectral bands in which the control and non-payload communications (CNPC) links of future UAS can operate reliably without causing harmful interference to incumbent services and systems.

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2 Terminology

2.1 Radiocommunication definitions

Control and non-payload communications (CNPC): The radio links, used to exchange information between the UA and UACS, that ensure safe, reliable, and effective UA flight operation. The functions of CNPC can be related to different types of information such as : telecommand messages, non-payload telemetry data, support for navigation aids, air traffic control voice relay, air traffic services data relay, target track data, airborne weather radar downlink data, non-payload video downlink data.

Control and non-payload communications (CNPC): The radio links, used to exchange information between the UA and UACS, that ensure safe, reliable, and effective UA flight operation. The functions of CNPC can be related to the following types of information that are exchanged:

UA-control station (UACS): facilities from which a UA is controlled remotely.

Sense and avoid (S&A): S&A corresponds to the piloting principle “see and avoid” used in all air space volumes where the pilot is responsible for ensuring separation from nearby aircraft, terrain and obstacles.

Unmanned aircraft (UA): designates all types of aircraft remotely controlled

Unmanned aircraft system (UAS): consists of the following subsystems:• Unmanned aircraft (UA) subsystem (i.e. the aircraft itself);• Control station (UACS) subsystem;• Air traffic control (ATC) communication subsystem (not necessarily relayed through the UA);• Sense and avoid (S&A) subsystem; and• Payload subsystem (e.g. video camera…)1

1 UAS payload communications are not covered by WRC-12 agenda item 1.3.

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3 Review of radiocommunication spectrum requirements

In order to ascertain the amount of spectrum needed for UAS control links, it is necessary to estimate the non-payload UAS control link bandwidth requirements for safe, reliable, and routine operation of UAS. The estimated throughput requirements of a single generic UA and long-term bandwidth requirements for UAS non-payload control link operations through 2030 have previously been studied and can be found in ITU-R Report M.[UAS-SPEC].

The report provides the analyses for determining the amount of spectrum required for the operation of a prospected number of UAS sharing non-segregated airspace with manned air vehicles as required by Resolution 421(WRC-07) and in response to Agenda item 1.3 (WRC-12).

The Report estimates the total spectrum requirements covering both terrestrial and satellite requirements in a separate manner. Deployment of UAS will require access to both terrestrial and satellite spectrum.

The maximum amount of spectrum required for UAS are:– 34 MHz for terrestrial systems,– 56 MHz for satellite systems.

[Note: new text need to be developed to introduce the figures 3-1 and 3-2]

FIGURE 3-1

Links involved in LOS (line-of-sight) communications

For LOS links:– the remote pilot stations satisfy the definition No. 1.81 (aeronautical station) of the Radio Regulations (RR);– the UA corresponds to definition No. 1.83 (aircraft station) of the RR.

Therefore AM(R)S, the aeronautical-mobile service (AMS) and the mobile service (MS) could be considered for links 1 and 2.

ATC Control Station

Remote Pilot to UA

1. Remote Pilot to UA

UA to Remote Pilot

2. UA to Remote Pilot

12

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[Editorial Note: The following principles summarize the discussion during the debate at the November 10 Meeting. The Text below may need to be revised. Contributions to the May 10 Meeting of WP 5B are invited.]

The following principles apply to service allocations and the use of frequencies for the satellite component of UAS radiocommunications within the scope of WRC-12 Agenda item 1.3:1) Under No. 191 of the ITU Constitution, international telecommunications must give absolute priority to all telecommunications concerning safety of life. 2) All UAS radiocommunications within the scope of WRC-12 Agenda Item 1.3 are radiocommunications concerning safety of life. 3) No. 1.59 of the RR states that any radiocommunication service used permanently or temporarily for the safeguarding of human life and property is a safety service.4) No. 4.10 of the RR states that Member States recognize that the safety aspects of radionavigation and other safety services require special measures to ensure their freedom from harmful interference and that it is necessary therefore to take this factor into account in the assignment and use of frequencies. 5) It is recognized that the aeronautical safety of life aspects need to be treated within ICAO through the development of new standards and recommended practices (SARPs)6) Any special measures as referred to above must be clear, implementable in practice and designed to avoid creating difficult regulatory situations.7) Taking No. 1.59 of RR into account, provided existing allocations to services described hereafter and in frequency bands listed in section 5 can support safety of life UAS radiocommunications, existing allocations should be considered before considering the need for new allocations.

FIGURE 3-2

Links involved in BLOS (beyond line-of-sight) communications via satellite

For BLOS links, three cases need to be considered.

ATC

UA

UAControl Station see section 2(mobile or fixed)or Gateway station (to which remote pilots are connected)

14

32

SatelliteForward link :

1. Remote Pilot to satellite

2: satellite to UA

Return link :

3: UA to satellite

4.: satellite to

Remote Control Station

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Case 1: Mobile control station– The UA corresponds to definition No. 1.84 (aircraft Earth station) of the RR;– the satellite corresponds to definition No. 1.64 (space station) of the RR;– the UAUACS (case of mobile remote pilot station) corresponds to definition No. 1.68 (mobile Earth station) of the RR.

Therefore, from the Radio Regulations point of view, the services AMS(R)S, AMSS and MSS for links 2 and 3 could be considered. The service MSS for links 1 and 4 could be considered. In the case of remote pilot station located on the Earth’s surface, MSS except aeronautical for links 1 and 4 could be considered.

Case 2: Fixed control station– The UA corresponds to definition No. 1.84 (aircraft Earth station) of the RR;– the satellite corresponds to definition No. 1.64 (space station) of the RR;– the remote pilot station (case of fixed remote pilot station) or the gateway station corresponds to definition No. 1.63 (Earth station) of the RR.

Therefore, from the Radio Regulations point of view, the services AMS(R)S, AMSS and MSS for links 2 and 3 could be considered. The service FSS for links 1 and 4 could be considered.

Case 3: Control station providing feeder link station functions– The UA corresponds to definition No. 1.84 (aircraft Earth station) of the RR;– the satellite corresponds to definition No. 1.64 (space station) of the RR;– the remote pilot station or the gateway station corresponds to definition No. 1.82 (aeronautical Earth station) of the RR.

Therefore, from the Radio Regulations point of view, the services AMS(R)S, AMSS and MSS for links 2 and 3 could be considered. The services FSS, AMSS, AMS(R)S for links 1 and 4 could be considered.

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4 Criteria for evaluating candidate frequency bands

Current UAS use a wide range of frequency bands for control of the UA in segregated airspace. Systems operate on frequencies ranging from VHF (72 MHz) up to Ku-Band (15 GHz) for both line-of-sight (LOS) and beyond line-of-sight (BLOS). None of these bands currently have the safety aspect required to enable UA flight in non-segregated airspace. In certain situations, the UA communications are carried via satellite services within FSS frequency bands. This has proven to be very effective, due to the availability of wideband FSS spectrum, in promoting advancement of UAS technology. In choosing bands for reallocation as UAS safety spectrum, the following criteria should be considered:

Controlled-access spectrum: Each of the potential solutions should be evaluated on whether they will operate in spectrum that has some type of controlled access to enable the limitation and prediction of levels of interference.

International Civil Aviation Organization (ICAO) position on AM(R)S and AMS(R)S spectrum: To date, the ICAO position is to ensure that allocations used for UAS command and control, ATC relay and S&A in non-segregated airspace are in the AM(R)S, AMS(R)S and/or ARNS.

There are four levels for AM(R)S and AMS(R)S allocations:1) Spectrum that is or could be explicitly and exclusively allocated to AM(R)S or AMS(R)S;2) Spectrum that is or could be explicitly allocated to AM(R)S or AMS(R)S but shared with other “aviation services” managed by civil aviation authorities;3) Spectrum that is or could be allocated explicitly to AM(R)S or AMS(R)S but shared with other services than those managed by civil aviation authorities;4) Spectrum that is or could be allocated to AM(R)S or AMS(R)S through an MS, MSS, AMS or AMSS allocations and shared with other services than those managed by civil aviation authorities.

The first two levels identified above concern frequency bands managed exclusively by civil aviation authorities, while the last three concern those whose management is shared with other entities.

Spectrum obtainability: The essence is the ease or difficulty of gaining access to certain bands based on compatibility with incumbent services, the amount of negotiation required in individual countries, or the number of regulatory bodies involved in the decision on allowing UAS to use the particular spectrum. Therefore, each potential solution should be evaluated on whether the spectrum would be obtained through the WRC process and how much coordination would be needed relative to the host nations to allocate UAS operations in the frequency range.

Worldwide spectrum allocation: It will be advantageous if global harmonization is achieved and the equipment needed by a UA could thus be the same for operation anywhere in the world.

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Potentially available bandwidth: Under this criterion a favourable rating is more likely to be awarded to a candidate band whose incumbent RF systems currently leave a substantial amount of spectrum unoccupied, and have technical or operational characteristics UACS that appear to suit them for coexistence with future in-band UAS control systems. Many BLOS systems share the control link and the payload return link on one common carrier so the wide bandwidth needs of the payload return link may drive this choice more than the lower data rate needs of the control link.

Link range: This criterion evaluates the distance in which the unmanned aircraft can fly away from its control station without the support of additional control stations.

Link availability: Weather-dependent availability of the link is also a very important evaluation criterion. Therefore, each candidate band should be evaluated according to the approximate availability associated with the frequency of operation. Higher frequency ranges are more susceptible to signal degradation due to rainfall and therefore receive less favorable ratings. The markedly different transmission characteristics of terrestrial and satellite paths must be taken into account when performing comparative analyses of LOS and BLOS systems (see “Satellite transmission characteristics,” below.).

Satellite transmission characteristics: In order to determine whether satellite systems can provide the integrity and reliability needed to satisfy the link availability required for communications through satellite platforms to and from the UAS certain transmission characteristics need to be defined in sufficient detail. The following is a list of such information that is needed to make this determination. 1. Minimum antenna sizes and corresponding transmit gains of the Earth station and of the airborne station.2. Maximum effective isotropically radiated power (EIRP) capability of the Earth station and of the airborne station.3. Minimum ratio of receiving-antenna gain to receiver thermal noise temperature in Kelvins (G/T) of the receiving Earth station and of the airborne station.4. The rain conditions (i.e. rain rates) in which the link must operate. Any other propagation conditions that need to be considered.5. Minimum required availability for the total (up and down) link ( both outbound and inbound). Alternatively, the minimum required availability in the uplink and the minimum required availability in the downlink. Note should be also taken of certain double-hop links (e.g. ATC-UA communications relayed through UACS link).6. Carrier characteristics

a. Information ratesb. Occupied bandwidthc. Allocated bandwidthd. Modulation typee. Forward Error Correction ratef. Minimum required C/(N+I) for the satellite to UA link and the Satellite to control station link.g. The minimum and maximum acceptable latency in the transmission to and from the UA and UACS

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Co-site compatibility: This metric evaluates the relative feasibility of operating future UAS control-link radios in the band under consideration, without causing unacceptable interference to the collocated receivers of incumbent systems in the same UA or UACS.

Airborne equipment size, weight, and power: The driving factor for applying this criterion is the size of the antennas on board the unmanned aircraft. Credit should be given to frequency bands in which control links could operate using omnidirectional antennas.

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5 Frequency bands under consideration

The frequency bands listed below are considered for the use of UAS provided the safety aspects are ensured. In the context of the criteria outlined in section 4 these bands have been suggested for further detailed analyses. • 960 –1 164 MHz• 1 545–1 555 (space-to-Earth) and 1646.5–1656.5 MHz (Earth-to-space)• 1610-1626.5 MHz (space-to-Earth and Earth-to-space)• 5 000–5 150 MHz• Other frequency bands may also be added

These bands are evaluated separately in the following subsections.

[Editors Note: In this section only short descriptions of the usage of the bands under consideration are expected. Sharing studies shall be presented in annexes. Studies need to be performed to determine whether sufficient spectrum would be available for UAS applications in the bands under consideration]

5.1 960-1 164 MHz

Figure 4-1 depicts frequency use in the 960-1 164 MHz band. The ARNS has a worldwide primary allocation throughout the band, which is heavily utilized by distance measuring equipment (DME) and tactical air navigation (TACAN). WRC 2007 gave the 960-1 164 MHz sub-band an additional AM(R)S allocation. Portions of the 960-1 164 MHz band could be considered to support UAS control links as well as other communications with manned aircraft. It is to be noted that the Global Navigation Satellite System (GNSS) in the band 1164 – 1215 MHz need to be protected. The incumbent ARNS still has the right to operate throughout the 960-1 164 MHz frequency range, so sharing criteria will be required for any AM(R)S or UAS control link operation in that range.

FIGURE 5-1

Aeronautical frequency use in the 960-1 164 MHz band

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960MHz 1164MHz

AERONAUTICAL RADIONAVIGATION

AERONAUTICAL MOBILE (ROUTE)

978MHz 1030MHz 1090MHz

UAT RX TRANSPONDER TX

DME AND TACAN

JTIDS JTIDS JTIDS

POTENTIAL UAS SPECTRUM

SERVICES

SYSTEMS

Non-ICAO ARNS in CIS countries

Secondary surveillance radar (SSR), the Traffic Alert and Collision Avoidance System (TCAS), and Identification Friend or Foe (IFF) nominally operate at 1 030 and 1 090 MHz but generally require interference protection throughout the 1 020-1 040 and 1 080-1 100 MHz sub-bands. Even larger guardbands may be needed to protect against airborne co-site interference to or from those systems.

Two Automatic Dependent Surveillance – Broadcast (ADS-B) systems also use the band. The Universal Access Transceiver (UAT) system2 operates on a single frequency, 978 MHz. Compatibility may be addresses by avoiding this frequency. The other ADS-B system in the band is called 1090 Extended Squitter (1090ES)3. It is designed to coexist with other systems using 1090 MHz. It is assumed that systems that are compatible with other users of this frequency will also be compatible with 1090ES.

The Joint Tactical Information Distribution System (JTIDS) operates within this band on 51 hopping channels, each 3 MHz wide. Their centre frequencies lie in three separate sub-bands (969-1 008, 1 053-1 065, and 1 113-1 206 MHz)4.

There are also ongoing research programs to study the possibility of using the 960–1 164 MHz to support future ATC data communications. Two separate approaches are being considered. L-band Digital Aeronautical Communications System 1 (L-DACS1) is a frequency-division duplex (FDD) system using OFDM, and L-DACS2 is a time-division duplex (TDD) system using a single carrier, constant envelope modulation. It is anticipated that these two choices will eventually be reduced to one as a result of further research. Because of the anticipated difficulty of fitting two new systems into the already-congested band, it might make sense to consider one integrated system to support both LDACS and CNPC—sharing capacity in a flexible way to support localized needs. Another approach that might be possible, if both L-DACS candidates can be shown to be viable, is to use one for LDCS and the other for CNPC.

2 Minimum Operational Performance Standards for Universal Access Transceiver (UAT) Automatic Dependent Surveillance – Broadcast (ADS-B), DO-282A, RTCA.

3 Minimum Operational Performance Standards for 1090 MHz Extended Squitter Automatic Dependent Surveillance – Broadcast (ADS-B) and Traffic Information Service – Broadcast (TIS-B), DO-260A, RTCA.4 Suitability of Civil Aviation Bands for the Future Communication Infrastructure, 14th meeting of ACP Working Group F, Malmo, Sweden, 22-26 August 2005.

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The remainder of this section covers relevant characteristics of existing and potential in-band and adjacent-band systems, and uses this information to develop various considerations that may constrain the design of future L-band CNPC links.

5.1.1 Existing in-band systems

Appendix A summarizes the publicly available RF characteristics of airborne systems currently occupying the 960–1164 MHz band.

All of the aeronautical systems now using the band are pulsed systems with short pulses and low transmitter duty factors. They are also tolerant to relatively low success rates for individual signalling elements. In the case of information-bearing signals such as JTIDS or UAT, this is so because the systems employ strong forward error correction (FEC) techniques. Systems that rely primarily on the signal timing (e.g. DME) are designed to operate when the success rate for individual messages is significantly less than 100%. DME interrogators can operate even when the ground reply efficiency is substantially less than 100%. This means that the systems can successfully coexist, provided that the number of individual users is kept under control.

Thus, from a historical standpoint, a very low transmitter duty factor might seem to be a desirable characteristic for a UAS CNPC system operating in this band. On the other hand, a low duty factor implies a sacrifice in system throughput. In order to support data throughput rates that are acceptable for CNPC applications, the instantaneous bandwidth of any such candidate might have to be very large.

5.1.1.1 DME and TACAN

DME and TACAN are very similar in their properties, so they will be discussed together. The discussion will focus on DME. Differences associated with TACAN will be pointed out when relevant. The relevant RF parameters are found in Appendix A.

The DME system allows an airborne user to determine its distance from a ground site through a process of round trip timing. An airborne radio transmits a sequence of “pulse pairs” in which the gaps between the pairs are chosen pseudo-randomly. Ground stations reply to the received interrogations by transmitting their pulse pairs with a fixed time delay. The airborne receiver then searches for a sequence of replies with the same pseudorandom gaps that it used for transmission. This pseudorandom process allows a particular airborne unit to separate its own information from replies to interrogations from other airborne units by correlating over a number of pulse pairs. After the fixed delay is subtracted from the round trip time difference, the distance is determined using the speed of light.

Two modes of DME are commonly used: X-Mode and Y-Mode. They differ by their pulse-pair separations and by the frequencies used for interrogations and replies. (There are also definitions for a W-Mode and a Z-Mode, but these are not used.) For X-Mode the spacing for both interrogations and replies is 12 µs. For Y-Mode the spacing for interrogations is 36 µs and the spacing for replies is 30 µs. For each mode there are 126 potential channels whose interrogation and reply frequencies are on integer megahertz centers from 962 to 1213 MHz. For a given channel the interrogation and reply frequencies are always separated by exactly 63 MHz; however, the reply frequency plan depends on the mode as shown in Fig. 5-2.

FIGURE 5-2

DME frequency plan

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1213 (126X)

X)

962 (1X)

X)

1024 (63X)

X)

1151 (64X)

X)

1088 (1Y)

X)

1050 (63Y)

X)

1025 (64Y)

X)

1087 (126Y)

X)

Reply Frequencies Interrogation Frequencies Frequencies

Figure 5-3 depicts current actual usage of the DME reply frequencies in the US and Canada. By comparing with Fig. 2-2, it can be observed that the X-Mode is more heavily used. It can also be seen that there are gaps in the assignments surrounding 1030 and 1090 MHz for the protection of SSR/TCAS (see below). There are also related gaps 63 MHz above and below these bands that are due to the DME frequency-pairing approach. For example, channels 1X through 16X are seldom assigned to fixed ground stations, and the corresponding band (up to 977 MHz) is not subject to international agreement and is relegated to national assignment status. Channels 17X and 18X (978 and 979 MHz reply frequency) are supposed to be reserved for ramp testing, which is one of the reasons that 978 MHz was the frequency selected for UAT (see below). However, DME does use those two channels in some locations.

FIGURE 5-3

Spectral occupancy of DME and TACAN ground assignments

0

5

10

15

20

25

30

35

40

960

966

972

978

984

990

996

1002

1008

1014

1020

1026

1032

1038

1044

1050

1056

1062

1068

1074

1080

1086

1092

1098

1104

1110

1116

1122

1128

1134

1140

1146

1152

1158

1164

1170

1176

1182

1188

1194

1200

1206

1212

Num

ber o

f Ass

ignm

ents

Frequency (MHz)

960 - 1215 MHz DME/TACAN Assignments in U.S. and Canada

In the time domain, an X-Mode pulse pair looks like Fig. 5-4. The two pulses are separated by 12 µs, and each pulse has a raised cosine shape with a half-amplitude width of 3.5 µs. This shaping results in a compact spectrum, as shown in Fig. 5-5. The overall shape is due to the individual pulse shape and the finer details are due to the 12 µs spacing between pulses (assuming coherence between the two pulses. The occupied bandwidth of the signal is on the order of 400 kHz.

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FIGURE 5-4

X-Mode DME pulse pair description

0

0.25

0.5

0.75

1

1.25

-4 -2 0 2 4 6 8 10 12 14 16 18 20

Ampl

itude

Time (microseconds)

DME Pulse-Pair Shape

FIGURE 5-5

X-Mode DME spectrum

-80

-70

-60

-50

-40

-30

-20

-10

0

0 0.2 0.4 0.6 0.8 1 1.2 1.4Frequency Offset (MHz)

DME Spectrum

Even though the power of the DME signal is mostly contained within 300 kHz, DME receivers typically have bandwidths on the order of 1 MHz. This large bandwidth allows for accurate measurement of the timing of the rising edges of the pulses, and therefore an accurate measurement of the separation between pulses. Robust measurement of time is critical to accurate distance estimation.

Because the spacing of DME assignments is 1 MHz and the receiver bandwidths are also about 1 MHz, there are no “natural” frequency gaps between DME channels for other systems to occupy. This limits the options for new systems in the band, such as CNPC, to the following:1) Use a part of the band not occupied by DMEs.2) Use a waveform with a low duty factor.

Coordinate with the spatial distribution of DME frequency usage to reduce co-channel interference.

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5.1.1.2 Secondary surveillance radar and TCAS (1030/1090 MHz)

Two types of aeronautical systems operate at 1030 and 1090 MHz: SSR (which includes air traffic control radar beacon system (ATCRBS) and Mode S), and TCAS. 5

SSR provides cooperative surveillance information from appropriately equipped aircraft. An SSR can function either as a stand-alone system, or in conjunction with primary long range and terminal surveillance radars. SSR operation requires an uplink interrogation, a reception and response by a cooperative airborne transponder, and reception of the transponder's downlink reply. The transponder's response identifies the aircraft and is ordinarily much stronger than the reflection that would be received by a primary surveillance radar. A side-lobe suppression system is used to prevent false triggering of transponders by radiation emitted from the interrogator’s antenna side lobes. All SSR systems use 1030 MHz as the uplink frequency, and 1090 MHz as the downlink frequency.

ATCRBS provides identification and other flight information about an aircraft for tracking and management by air traffic controllers. It is the means for obtaining altitude information from aircraft equipped with altitude-reporting (Mode C) transponders. ATCRBS uses a ground-based interrogator that transmits pulses via a 1030-MHz uplink to airborne transponders, which reply via a 1090-MHz downlink. ATCRBS interrogations are transmitted from a directional SSR antenna beam that rotates along with the primary radar antenna (if one is present). As the beam rotates toward the azimuth at which the aircraft is located, the airborne transponder begins to receive interrogations which result in transponder replies. ATCRBS is an “all-call” system in which every transponder that is within the beamwidth of the interrogator antenna, and is capable of responding, does so.

Mode S is a discrete-address beacon system that selectively interrogates aircraft. As in ATCRBS, the ground-based interrogators in Mode S transmit at 1030 MHz and receive the transponders' replies at 1090 MHz. Mode S has two principal modes of operation, which are interleaved in time: the all-call mode that ATCRBS also uses, and a roll-call mode. Mode S transponders will not respond with ATCRBS replies to the modified ATCRBS interrogations transmitted by a Mode S interrogator, but they will reply to all-call interrogations. The response to an all-call interrogation is a Mode S reply that contains the aircraft’s 24-bit address.

TCAS provides pilots with traffic alerts of potential threats, and resolution advisories that supply manoeuvre guidance in the vertical plane to help pilots achieve separation from a threat. To ensure that the recommended maneuvers of two TCAS-equipped aircraft do not conflict, the resolution advisories are coordinated using air-to-air Mode S data link communications. TCAS operates at 1030 and 1090 MHz and is independent of any ground system. TCAS employs a low-gain directional antenna array on top of the aircraft, along with an omnidirectional antenna on the bottom of the aircraft.

TCAS interrogates and tracks aircraft equipped with Mode S transponders by means of discrete interrogation and reply. Such aircraft are initially acquired by TCAS via unsolicited "squitter" reply transmissions that announce the transponder's identity. Interrogation and tracking of aircraft with ATCRBS transponders is via a "whisper-shout" technique. This consists of a total of 84 modified Mode C interrogations spaced 1 ms apart, each preceded by a lower-power suppression pulse followed by another suppression pulse. Four sequences of interrogations are contained in the 84; from the top directional antenna the first 24 are radiated forward, the following 40 are radiated sequentially to both sides, the next 15 are radiated aft, and the last 5 are radiated downward by the bottom antenna. Power is lowered progressively

5 RTCA Special Committee 185, Aeronautical Spectrum Planning for 1997–2010, RTCA/DO-237, 27 January 1997.

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through the sequence, so ideally each aircraft will respond only once per sequence, to the first reply for which the initial suppression pulse falls below the threshold. Preceding stronger interrogations should all cause transponder suppression, and following weaker interrogations should fall below receiver threshold. In practice, on about 10% of the whisper-shout sequences, an additional reply is elicited.

RF interference to the transponders used by SSR and TCAS can degrade their performance in several ways. These include: • Generation of undesired replies to nonexistent interrogations• Overlooking and thus failing to reply to actual interrogations• Garbling of replies.

Transponder selectivity curves of SSR and TCAS receivers have wide skirts, as noted in Appendix A. This makes it difficult for them to coexist with other systems in the band unless large frequency separations (up to 25 MHz) are maintained. A suppression bus can be used to protect them from airborne co-site in-band interference, but unless the collocated potentially interfering transmitter has a low duty cycle (preferably 1% or less), transponder performance will suffer because interrogations will be missed during pulse-blanking intervals.

5.1.1.3 JTIDS and MIDS

The Joint Tactical Information Distribution System (JTIDS) and the Multifunctional Information Distribution System (MIDS) are identical at the RF level, and they are treated together. (They are both also referred to as Link 16.) They are systems that were initially designed to provide situation awareness in a hostile (i.e., jammed) environment by using frequency hopping and strong error correction. JTIDS is permitted to operate in the band on a non-interfering basis, subject to nation-by-nation agreements.

Many of the RF parameters of JTIDS were carefully chosen to achieve compatibility with the aeronautical systems then existing in the same band (DME/TACAN and SSR, at the time). These parameters can be found in Appendix A. As an example of how the JTIDS design was influenced by compatibility with DME, the pulse length was chosen to be 6.4 µs and the spacing between pulses was chosen to be 13 µs. Furthermore, the frequency-hopping algorithm ensures that successive pulses will always be separated by at least 30 MHz. Taken together, these factors make it highly unlikely that a single JTIDS terminal could generate a signal that mimics UACS a DME pulse pair.

Compatibility with 1030/1090 MHz operation is addressed by strictly limiting the power that a JTIDS terminal is allowed to radiate in the neighbourhoods of these frequencies. Every JTIDS terminal is required to have an autonomous receiving capability to monitor its emissions in these bands. If strict thresholds are exceeded, the terminal automatically shuts down. This is called the Interference Protection Function (IPF).

Additionally, the total number of JTIDS pulses that can be transmitted per second in any given geographic location is limited to 33024. This corresponds to a maximum system duty factor of 21% in any given region. Since JTIDS hops over 51 frequencies, the system duty factor on any given carrier frequency is only about 0.4%. On the other hand, it must be borne in mind that the instantaneous bandwidth of JTIDS is about 3 MHz, so more than one DME channel is affected by each hop.

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Proving that JTIDS can operate on a non-interfering basis has been the subject of much analysis and testing spread out over several years6, 7, 8. In the US, at least, the FAA continues to monitor the number of JTIDS pulses transmitted per second.

5.1.1.4 UAT

The Universal Access Transceiver (UAT) operates at a single frequency, 978 MHz. Other relevant characteristics UACS are listed in Appendix A. UAT provides a number of aeronautical services including Automatic Dependent Surveillance – Broadcast (ADS-B), Traffic Information Service – Broadcast (TIS-B), Automatic Dependent Surveillance – Rebroadcast (ADS-R), and Flight Information Service – Broadcast (FIS-B). The transmissions of the first three types comprise short bursts of either 265 µs or 403 µs. Airborne users transmit one ADS-B burst each second. The FIS-B bursts are longer (4.27 ms), but they are transmitted by only ground stations. ADS-R and TIS-B bursts are also transmitted by only ground stations. ADS-B, TIS-B and ADS-R messages are sent at pseudorandom times chosen in a common time interval, so there can be non-negligible self-interference in dense aircraft environments. The deleterious effects of this self-interference are limited due to the very low duty factor of each airborne transmitter (0.0265% or 0.0403%) and the frequency modulation (FM) capture effect. On the other hand, the longer FIS-B message transmissions are separated in time from the other types and their mutual timing is tightly controlled in order to minimize self-interference.

Each ADS-B message contains either 144 or 272 bits of user information, so the bit rate for individual airborne users is very low. Nevertheless, the messages are sufficient to convey all the necessary surveillance information at the required update rates. Each FIS-B burst carries 3456 bits of user information, which may comprise weather maps, text messages etc.

During the development of UAT Minimum Operational Performance Standards (MOPS) under the purview of RTCA SC-186 WG 5, there was extensive analysis, simulation and testing of the effects of interference between UAT and DME9 and between UAT and JTIDS10. There were also studies of UAT with both DME and JTIDS11, 12. The scenarios were based on future traffic densities at LAX and Core Europe, plus a prescribed JTIDS environment provided by the US DoD13. As a result of all this research, the FEC selected for the different UAT message types was strengthened to allow them to meet requirements in worst-case scenarios. Also, it was verified that the level of interference from UAT was acceptable.

Many of the studies mentioned in the previous paragraph were focused on interference between transmitters and receivers on separate platforms; however, some of them considered

6 NTIA Spectrum Planning Subcommittee (SPS) WG-1, JTIDS EMC Features Guidelines (and Addendum), TR-91-001 Revision A.7 NTIA Spectrum Planning Subcommittee (SPS) WG-1, Effects of JTIDS on the ATCRBS Interrogator Receiver System, TR-92-001 (including Appendix E parts 1 and 2).8 NTIA Spectrum Planning Subcommittee (SPS) WG-1, MIDS/JTIDS Spectrum Supportability Documaentation: Mode S Sensor System, TR-98-002.9 RTCA Working Papers generated by Special Committee 186, Working Group 5: UAT WP2-05, 3-02, 3-10, 3-11, 4-13, 5-09A, 5-16, 6-12, 6-13, 6-14, 7-11, 7-12, 7-14, 7-15, 8-05, 8-09,10-6 and 11-12. These are available at http://adsb.tc.faa.gov/WG5.htm10 RTCA Working Papers generated by Special Committee 186, Working Group 5: UAT WP1-04, 3-12, 4-04, 4-05, 4-16, 5-07, 6-02 and 6-03. These are available at http://adsb.tc.faa.gov/WG5.htm11 RTCA Working Papers generated by Special Committee 186, Working Group 5: UAT WP3-07, 5-14, 8-10, 9-05, 9-06, 9-09, 11-16 and 11-19. These are available at http://adsb.tc.faa.gov/WG5.htm12 Also, see Appendix O of the UAT MOPS (see footnote 3)13 Appendix G of RTCA DO282A, UAT MOPS (see footnote 3)

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co-site interference. Although the effect of UAT airborne co-site interference on other systems is limited by its low duty factor, it was considered prudent to limit the effects even further; so it was agreed that a UAT transmitter would be able to provide an appropriate signal to an installed suppression bus to allow for receiver blanking if deemed necessary.

Note that subsequent to the publication of the UAT MOPS (DO-282) by RTCA, UAT was also addressed by ICAO. ICAO has published Standards and Recommended Practices (SARPs) for UAT14.

5.1.1.5 Non ICAO standardized aeronautical Radionavigation System

National radionavigation systems refer to non-ICAO standard ARNS systems. Specifically the countries referred to in RR No. 5.312 of the RR operate the ARNS systems of the following three types:• the ARNS systems of the first type refer to direction-finding and ranging systems. The systems are designed for finding an azimuth and a slant range of an aircraft as well as for area surveillance and inter-aircraft navigation. They are composed of air-borne and ground-based stations. The air-borne stations generate requesting signals transmitted via omnidirectional antennae and received at ARNS ground stations which also operate in an omnidirectional mode. The ground stations generate and transmit response signals containing azimuth/ranging information. Those signals are received and decoded at the ARNS air-borne stations. The first type stations transmit the signals requesting the azimuth/ranging data outside the 960-1 164 MHz frequency band. After receiving a requesting signal the ARNS ground stations use the 960-1 164 MHz frequency band only for transmitting the ranging data to be received at the ARNS air-borne stations. Thus the ARNS systems of the first type use the 960-1 164 MHz frequency band only for transmitting the signals in the surface-to-air direction. The maximum operation range for the first type ARNS systems is 400 km. It is expected that in some of the countries mentioned in RR No. 5.312 the usage of type 1 of ARNS mentioned above may be discontinued.• the ARNS direction-finding and ranging systems of the second type are designed for the same missions as the first type ARNS systems. The primary difference of the second type stations refers to the fact that requesting signals are transmitted by the air-borne stations in the same frequency band as responding signals transmitted from the ground stations. Moreover the ground-based ARNS stations of the second type can operate in both directional and omnidirectional modes. Directional mode provides increased number of operational channels at the ARNS stations. The maximum operation range for the first type ARNS systems is 400 km. It is planned to use the overall frequency band 960-1 164 MHz allocated to ARNS in order to increase flexibility of operation of the second type ARNS systems. Application of the wideband tuning filter on the ARNS receiver front end is the design peculiarity of the second type ARNS systems which is stipulated by the necessity to receive signals on several channels simultaneously. The passband of this filter is 22 MHz and it allows receiving simultaneously up to 5 channels among 30 overlapping channels of 4.3 MHz each. The simultaneous usage of wideband filter and correlator allows to increase the accuracy of aircraft position data measurement and C/N ratio at the receiver front end as well. Type 2 of ARNS system can operate in a limited number of countries mentioned in RR No. 5.312.• the ARNS systems of the third type are designed for operating at the approach and landing stages of flight. The system provides control functions of heading, range and glide path at aircraft approach and landing. The ARNS ground stations of the third type operate in both directional and omnidirectional modes. Operation range of the third type ARNS systems

14 ICAO Document 9861, UAT Technical and Implementation Manuals.

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does not exceed 60 km. The 960-1 164 MHz frequency band is used for operation of the channels designed for control of the glide path and range between air-borne and ground ARNS stations. Type 3 of ARNS system can operate in a limited number of countries mentioned in RR No. 5.312.

Table below provides brief technical description of the ARNS stations.

Thus the stations of the non-ICAO systems operate using the air-to-surface and surface-to-air links and are made up of ground and airborne receivers and transmitters. Technical parameters of these systems are presented in Table A-2 of Appendix A.

5.1.2 Potential in-band systems

Unlike the existing systems, the potential L-DACS systems do not employ pulsed, low-duty-factor signals-in-space. Thus, they must use other strategies to minimize interference. The basic idea is to use frequencies that are not locally used by the existing systems. Note that even if the frequency separations are sufficient to control interference between different, separated platforms, co-site interference between the systems must also be considered. This will be discussed further below.

Since L-DACS1 is an FDD system, its terminals must use two frequencies sufficiently separated to allow simultaneous transmission and reception. Although the design of L-DACS1 has not been finalized, a preliminary plan is to use the band from 985 to 1009 MHz for ground transmissions and the band from 1048 to 1072 MHz for airborne transmissions. Frequency pairs are separated by 63 MHz, just as they are for DMEs. Because L-DACS1 overlaps X-Mode channels 24X through 48X, it would appear that there is a large potential for interference. The proposal by the L-DACS1 designers is to use gaps in the geographical distribution of DME frequency usage to find acceptable operating locations. This is explained in more detail below.

For L-DACS2, frequency separation is achieved by using carrier frequencies from 960.5 to 975 MHz. The band is well-separated from 1030 and 1090 MHz, and it is just below the UAT allocation (978 MHz). It is contained within a band (960 to 977 MHz) that is not governed internationally, and its usage is controlled on a nation-by-nation basis. It has this special status because it is approximately 63 MHz below the protected region around 1030 MHz, so up link DME frequencies cannot be paired with usable down link frequencies. Thus, it is not commonly used for DME/TACAN. However, frequencies in this band are known to be sometimes allocated to ship-borne TACAN units.

Note that L-DACS1 uses a combination of FDD and orthogonal frequency-division multiplexing (OFDM), while L-DACS2 employs a combination of TDD and a constant-envelope waveform. It is also possible to use other combinations such as FDD with constant-envelope or TDD with OFDM. For historical reasons, these other combinations did not become L-DACS candidates. The discussion of the two existing candidates should be sufficient to cover all the relevant issues.

5.1.2.1 L-DACS1

OFDM was selected as the modulation for L-DACS1 because it is expected to have high spectral efficiency combined with good multipath resistance. It is also attractive because of the possibility of using modern cellular telephone technology, which also uses OFDM. One disadvantage of OFDM is that it is not a constant envelope waveform, so that it requires a rather linear channel (including amplifiers) in which to operate. Linear amplifiers are less

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efficient than nonlinear ones. Whether this point is important for aeronautical applications needs to be studied.

FDD operation has the potential to provide double the throughput of a TDD system using the same signal-in-space (at the expense of using twice as much spectrum). It also simplifies the issue of frequency reuse since airborne transmissions do not interfere with the reception of ground transmissions. (In the current definition of L-DACS115, communication is strictly air-to-ground and ground-to-air. There are no air-to-air links.) In order to succeed, a FDD system must be able to transmit and receive simultaneously on a single platform. To make this possible, the forward and return link frequencies must be separated by a gap that is a significant fraction of either carrier frequency. For L-DACS1 the gap is always 63 MHz. If a typical frequency is taken to be 1028.5 (average of the highest and lowest frequencies) then the frequency differences are about 6% of the carrier frequencies. Although this is a reasonably substantial gap, it will be a technical challenge to provide enough receive/transmit isolation using filtering and/or diplexing.

The L-DACS1 OFDM structure is based on subcarriers spaced by 9.765625 kHz (which is exactly (102.4 µs)-1). Fifty of these are modulated, so the total occupied bandwidth is approximately 500 kHz. The signals are centered on channels situated between the DME frequencies, i.e., on XXX.5 MHz. This “inlay” approach may help provide some degree of compatibility between L-DACS1 and DME. The individual subcarriers can be modulated in various ways ranging from QPSK to 64 QAM. When all overhead deductions are accounted for, the data rates that can be sustained vary from about 300 kbps to 1.4 Mbps in the ground-to-air direction and from about 200 kbps to 1.0 Mbps in the air-to-ground direction. As might be expected, the higher-rate modes are less robust and have smaller ranges.

The L-DACS1 approach to frequency compatibility16 is to identify gaps in the geographical distribution of DME frequencies. For example, if in some region it can be shown that reply frequencies 981 and 982 MHz are not used, then there is a possibility that 981.5 MHz could be used for the L-DACS1 ground-to-air link. This is particularly true if the neighbouring frequencies - 980 and 983 MHz - are also not used very close-by. The L-DACS1 designers have done a preliminary study to determine if they could assign L-DACS1 frequencies in a cellular pattern throughout Europe. Although success was not completely achieved when the most conservative protection rules were applied, the overall results were encouraging. This study focused on protecting the reply (uplink) frequencies, because that was considered the worst case scenario for inter-site compatibility; however, interrogation (downlink) compatibility may be an issue in cases where co-site interference is important.

5.1.2.2 L-DACS2

L-DACS217 is a TDD system, and so does not need to use two well-separated frequency bands. Thus, it is able to postulate using a single band within the little-used 960 -977 MHz region. Also, the spectrum of its single-carrier, constant-envelope signal-in-space is easier to control, even with nonlinear amplification. This may simplify the problem of controlling interference with nearby systems. (The highest proposed L-DACS2 frequency is 975 MHz, which is only 3 MHz from the UAT frequency.)

The modulation chosen for L-DACS2 is Gaussian Minimum Shift Keying (GMSK) with a modulation rate of 270.833 kbps and with BT = 0.3. The bit rate cited is the raw channel bit rate and does not include any deductions for such overhead factors as error correction, guard

15 EUROCONTROL, L-DACS1 System Definition Proposal v0.1, 29 December 2008.16 EUROCONTROL, Draft B-AMC Frequency Plan: Report D2, 27 April 2008.17 EUROCONTROL, L-DACS2 System Definition Proposal: Deliverable D1 v0.34, 11 March 2009.

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times or net management; so all that can be said at this point is that the user data rate per channel will be considerably less than 270 kbps. The channels used by L-DACS2 are separated by 200 kHz. Note that the channel spacing is smaller than the modulation rate; this is possible because of the spectral properties of GMSK. The designers of L-DACS2 state that 2 or more channels can be combined if some link has a throughput requirement larger than what can be provided by a single channel.

The development of the L-DACS2 is not as far along as that of L-DACS1 due to the sequencing of contractual arrangements. Therefore, various compatibility issues that will eventually need to be addressed have thus far remained unstudied. Of particular interest will be co-site interference issues. For example, it may be difficult for a high duty factor transmission at 975 MHz to avoid causing unacceptable interference to a nearby (in frequency) victim such as a UAT receiver at 978 MHz or an airborne DME receiver at 980 MHz. If the top frequency of L-DACS2 needs to be lower than 975 MHz, there will be a corresponding decrease in overall system throughput.

5.1.3 Existing adjacent-band systems

Due to time constraints the requirements related to compatibility with systems occupying bands just above and just below the band under study have not been closely examined. Clearly, these requirements would need to be addressed at some point. A few general characteristics of neighbouring systems are listed below.

5.1.3.1 Cellular systems below 960 MHz

P-GSM-900 uses 890-915 MHz for uplink (mobile-to-base) and 935-960 MHz for downlink (base-to-mobile). For E-GSM-900, the bands are 880-915 MHz and 925-960 MHz. In either case there is potential interference, particularly between the GSM base station transmissions and the L-DACS2 transmissions. So this would be an issue that any CNPC system similar (or identical) to L-DACS2 would have to consider. This could possibly be addressed by careful frequency planning.

5.1.3.2 GNSS systems above 1 164 MHz

The center frequency of the GPS L5 and Galileo E5a signal is 1 176.45 MHz. The center frequency for Galileo E5b is 1207.14 MHz.

5.1.4 Design considerations

From the discussion above, it seems clear that any viable L-band solution will not use frequencies near 978 MHz (UAT) or 1 030 and 1 090 MHz (SSR/TCAS etc.). The effort it would take to provide backward compatibility would far outweigh the extra throughput using these (relatively) narrow bands would provide. On the other hand, the remainder of the 960 to 1 164 band is occupied by DME/TACAN [and by JTIDS/MIDS]. Dealing directly with the issue of compatibility with those systems cannot be avoided. It may be of considerable interest to monitor the progress of the L-DACS designers in confronting these issues, since they will encounter nearly the same set of technical challenges.

5.1.4.1 Inter-site compatibility

Two approaches for achieving compatibility have been identified. Historically, all the current systems use relatively low duty factor signals-in-space. This type of approach has been shown to be suitable for providing navigation information. In the case of JTIDS/MIDS, the signal-in-space provides a robust data capability, at the expense of inefficient use of frequency

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resources. A single, completely utilized JTIDS net provides about 115.2 kbps of data throughput using 153 MHz of spectrum - less than 0.001 bps/Hz. (In peacetime, only one net is normally allowed to operate in any given area. If not for this restriction, JTIDS potential efficiency would be higher, but still far less than 1.) Such inefficiency is acceptable in a military system, but might not provide enough system throughput to support CNPC requirements.

If it is necessary to use a high duty factor signal-in-space to support CNPC throughput requirements, then a new type of compatibility study will have to be undertaken. Strategies for frequency assignments based on existing DME frequency usage will need to be devised (as has been preliminarily done for L-DACS1). Because JTIDS/MIDS installations are mobile, geographical usage scenarios will need to be agreed upon (as was done in the UAT MOPS development). Detailed studies (and eventually testing) will need to be performed to assess any proposed CNPC system - considering interference to and from all current band users.

5.1.4.2 Co-site compatibility

Even if a particular CNPC solution appears to be promising in terms of inter-site interference, it is quite possible that co-site interference will be a problem. Therefore, co-site compatibility will need to be addressed as a separate issue. The reason why co-site interference is special is that there is typically limited isolation between transmitters and victim receivers on the same platform. For example, noise floor effects that would be negligible for inter-site geometries might be significant on platforms with only 20 to 30 dB of antenna isolation.

It is certainly possible that such interference issues can be overcome. For example, the L-DACS1 system proposes to transmit and receive simultaneously on a single platform. The two frequencies are separated by 63 MHz, which may allow for diplexers and/or filters to provide adequate isolation. In this case it may also be possible, using the same techniques, to protect DME receivers because of the way the L-DACS1 frequency plan is aligned with that of the DMEs. (The frequency assignment rules necessary to implement this idea were not considered in the frequency planning exercise described in Section 5.1.2.1.)

On the other hand, it may be too difficult (or uneconomical) to provide enough isolation to protect legacy systems from L-band transmissions of a new CNPC system. In such a case, it may be possible to have a hybrid system in which the ground-to-air communications link is in the L-band and the air-to-ground link is in some other band where co-site interference is less of an issue.

5.1.5 Summary of sub-band advantages and disadvantages

The advantages and disadvantages of various parts of the 960-1 164 MHz band for UAS control links are briefly summarized below. Many of the points in this summary have been adapted from those in a 2005 ICAO paper18 on the suitability of this band for AM(R)S.– The 960-977 MHz sub-band is used by TACAN but not DME, and appears suitable for UAS control links, at least in areas where TACAN is not in use.– 978 MHz is the only frequency used by the Universal Access Transceiver (UAT) and thus does not seem suitable for use by a new UAS control link service.

18 M. Biggs, Analysis of 960–1215 MHz Band, RPG/ACP/NSP WP-12, ICAO ACP Working Groups B and F, Bangkok, Thailand, 21-25 February 2005.

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– The 979-1 010 MHz sub-band appears relatively attractive for UAS control link because its DME and TACAN emitters are limited to fixed ground-based transponders, creating a relatively manageable and predictable RFI environment.– The 1 010-1 050 MHz sub-band (especially the 1 020-1 040 portion) could be problematic for UAS control link use, particularly for UA equipped with 1 030-1 090 MHz transponders, since co-site RFI could result.– The 1 050-1 070 MHz sub-band is heavily used by airborne as well as ground-based DME and TACAN transmitters and thus presents a less predictable RFI environment than that of 979-1 010 MHz, but should still be considered for potential UAS control link use.– The 1 070-1 110 MHz sub-band is less attractive than 1 050–1 070 MHz for UAS control link use, because of the threat of co-site RFI aboard UA equipped with 1 030-1 090 MHz transponders.– The 1 110-1 150 MHz sub-band appears as suitable for UAS control links as the 1 050-1 070 MHz band.– The 1 150-1 164 MHz sub-band should be considered for UAS control link use because, as with the 979-1 010 MHz band, its DME/TACAN use is limited to fixed ground-based transponders. (Also, some of the 1 151-1 156 MHz part of the sub-band may be relatively unused by DME and TACAN to avoid undesired interactions with transponders at 1 090 MHz5.) However, this sub-band is adjacent to the 1 164-1 215 MHz RNSS sub-band, so co-site issues might restrict its use by UA transmitters, especially at frequencies close to 1 164 MHz.– The frequency band 960-1164 is also used by non-ICAO radionavigation systems in countries listed in RR No. 5.312. – The results of studies, conducted under WRC-12 AI 1.4, show that sharing between ARNS and AM(R)S systems operating in the 960-1 164 MHz frequency band would be feasible only subject to geographical and frequency separation since their shared co-frequency operation could be implemented only at beyond line-of-sight distances. [Since it will be impossible to use the same frequencies for AM(R)S and ARNS in the same geographical area there are might be no available spectrum for UAS.]– Opportunities for geographical separation of ARNS and AM(R)S systems are limited in certain areas in particular in those with high density of ARNS stations.

5.2 1 545-1 555 MHz (space-to-Earth), 1 610-1 626.5 MHz (space-to-Earth and Earth-to-space), and 1 646.5-1 656.5 MHz (Earth-to-space)

These bands are attractive for UAS control links because they are already allocated for mobile-satellite use and are currently operational over a number of MSS networks worldwide. The bands could be utilized without much delay or start-up cost. Radio Regulations No. 5.357A indicates that the bands 1 545-1 555 and 1 646.5-1 656.5 MHz are allocated to the MSS but that in applying the provisions of Section II of Article 9 the MSS shall give priority to the AMS(R)S. These bands are currently a subject of studies under WRC-12 Agenda Item 1.7. . Nos. 5. 351A 5.149, 5. 5.341, 5.364, 5.365, 5.366, 5.367, 5.368, and 5.372 also apply in the 1 610-1 626.5 MHz band.

Geostationary MSS satellites currently operate worldwide in the 1 545-1 555 MHz (space-to-Earth) and 1 646.5-1 656.5 MHz bands with provisions for AMS(R)S priority use and in addition in one Administration in the 1 555-1 559 MHz space-to-Earth and 1 656.5-1 660.5 MHz Earth-to-space bands pursuant to 5.362A (note that aircraft stations are aircraft Earth stations using the mobile satellite service). In addition, non-geostationary low Earth orbit

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(LEO) MSS satellites currently operate in the 1 610-1 626.5 MHz band (Earth-to-space) and 1 613.8-1 626.5 MHz (space-to-Earth) in spectrum that is also allocated on a primary basis to AMS(R)S in RR 5.367.

Since launching a new satellite system is probably beyond the scope of the UAS industry at the moment, several global satellite systems (HIBLEO-2, HIBLEO-4, and Inmarsat) and regional systems (MSV-1A/CANSAT-23/CANSAT(107.3W)-L) in these bands could form the basis of the discussion on use of this spectrum19,20. Inmarsat currently operates globally in parts of the 1 525.0-1 559.0 MHz band (space-to-Earth) and 1 626.5-1 660.5 MHz band (Earth-to-space), shared with a number of other MSS operators and subject to licensing and coordination agreements. These bands are used extensively by various MSS systems worldwide providing many different types of satellite applications. HIBLEO-2 currently operates in the 1 617.775-1 626.5 MHz band (both space-to-Earth and Earth-to-space) and HIBLEO-4 currently operates globally in the 1 610-1 618.725 MHz band (Earth-to-space) and 2 483.5-2 500 MHz (space-to-Earth) band.

It may be necessary to ask these providers to ensure the integrity of their systems for UAS control link communication use by appropriate means. However, the integrity of UAS control link communications needs to be specified, taking into account the transmission characteristics UACS of operating satellite systems and the associated UAS terminals.

Figure 5-6 depicts existing and potential frequency allocations and use in these bands. The figure also shows the frequency ranges that are filed with the ITU for some operational MSS systems, although the operational bands are subject to licensing and coordination agreements.

19 International Telecommunication Union, Draft New Recommendation ITU-R M.[MOBDIS], Use of mobile-satellite service (MSS) in disaster response and relief, 25 September 2009. http://www.itu.int/md/R07-SG04-C-0094/en20 International Telecommunication Union, Draft New Report ITU-R M.[REP-MOBDIS], Use and examples of mobile-satellite service systems for relief operation in the event of natural disasters and similar emergencies, 9 September 2009, http://www.itu.int/md/R07-SG04-C-0095/en

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FIGURE 5-6

Aeronautical and satellite frequency use in 1 525-1 559 and 1 610-1 660.5 MHz bands

________________________________________________________________________

5.2.1 Radio astronomy considerations in the 1 610-1 660.5 MHz band

Radio astronomy (RA) observatories use frequencies near 1.6 GHz for observations of the hydroxyl (OH) molecule, which provides extensive information on the processes by which stars are born and evolve.

The frequencies at which the OH molecule emits or absorbs are fixed by physics. The radio astronomy service has the following allocations in and near the 1 614-1 660.5 MHz band:

SERVICES

SYSTEMS

1525 MHz 1559 MHz 1614 MHz 1660.5 MHz

SPACE OPS MOBILE - SATELLITE

MOBILE - SATELLITE AERONAUT. RADIONAV

GEO SATELLITE

LEO E-s and s-E

HIBLEO-2

POTENTIAL UAS SPECTRUM(using HIBLEO-4, Inmarsat, and/or HIBLEO-2)

GEO SATELLITE

1535 MHz 1545 MHz 1610 MHz 1626.5 MHz 1646.5 MHz

AMS(R)S

Inmarsat

HIBLEO-4 -

Earth-to-spaceSpace-to-Earth

NOTE: This chart does not completely depict all systems or allocations in these bands.

AMS(R)S

1555 MHz

AMS(R)S

1656.5 MHz

RA

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1 610.6-1 613.8 MHz: Primary, shared with active services, and potentially susceptible to RFI from emitters in the 1 614-1 660.5 MHz band. In the US, protection of radio astronomy in this band is covered in Title 47 Code of Federal Regulations, Part 25, Section 25.213;21 coordination for airborne use of portions of this band are specifically covered in paragraph 25.213(a)(1)(iv). The US National Science Foundation has also executed coordination agreements with HIBLEO-2 and HIBLEO-4 covering aeronautical use of MSS terminals in portions of this band.22 International footnote 5.372 prohibits stations operating in the radiodetermination-satellite service and MSS from causing harmful interference to radio astronomy stations operating in the 1 610.6-1 613.8 MHz band. Administrations are urged to give all practicable protection to radio astronomy stations conducting research in the 1 660.5-1 668.4 MHz.

1 613.8-1 660 MHz: No radio astronomy allocation, but used in the search for extraterrestrial intelligence, as noted in RR No. 5.341.

1 660-1 660.5 MHz: Primary radio astronomy allocation, shared with active services; must be protected against emissions from users of the adjacent 1 614-1 660 MHz band.

1 660.5-1 668.4 MHz: In the U.S., this is a primary exclusive passive band. Worldwide, the 1 660.5–1 668 MHz range is a primary passive band, shared with secondary active services; while in the 1 668-1 668.4 MHz range, passive services are primary and shared with active services. The 1 660.5-1 668.4 MHz band must be protected against emissions from users of the nearby 1 614-1 660 MHz band.

The advantages and disadvantages of various parts of the 1 545-1 555 MHz, 1 610-1626.5 MHz and 1 646.5-1 656.5 MHz frequency range for UAS control links are briefly summarized below. • The bands 1 545-1 555 MHz, 1 610-1 626.5 MHz and 1 646.5-1 656.5 MHz are heavily congested by incumbent services and systems, and any additional allocations in this band could cause serious difficulties and worse interference situation for incumbent systems• Current allocations to AMS(R)S in the bands 1 545-1 555 MHz, 1 610-1 626.5 MHz and 1 646.5-1 656.5 MHz could be used for UAS operation subject to not imposing additional restrictions on operation of other incumbent systems in these bands.

[5.3 5 000-5 150 MHz

[Editorial Note: Section 5.3 was not reviewed during the November 09 5B meeting since a general revision is expected to be propose at the May 10 Meeting due the decision to include material from Doc 5B/temp 169, 5B/147 and additional material]

The Table of Frequency Allocations of the Radio Regulations lists the ARNS and the AMS(R)S as primary services from 5 000 to 5 150 MHz. Figure 5-7 provides an overview of services in throughout this band, with examples of systems using those services. The band comprises three principal sub-bands:– The 5 000-5 030 MHz sub-band, which is currently allocated to the radionavigation-satellite service (RNSS) and is also being considered, under WRC-12 Agenda item 1.4, for an additional allocation for AM(R)S on the airport surface. Due to the existing allocations in this sub-band, coordinating the use of UAS control link spectrum in this sub-band will not be an easy task.

21 Available at http://edocket.access.gpo.gov/cfr_2008/octqtr/pdf/47cfr25.213.pdf.22 An example agreement is available at http://www.astro. caltech.edu/USNC-URSI- J/nsffrequencyagreements.pdf (PDF pp. 1-10).

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– The 5 030-5 091 MHz sub-band currently used (although not heavily) by the Microwave Landing System (MLS).– The 5 091-5 150 MHz sub-band, which was originally reserved as an expansion band for MLS but now is also allocated to the fixed-satellite service (FSS) for use by MSS Earth-to-space feeder links, and has an AM(R)S airport-surface allocation as well as an allocation for AMS. Existing and planned systems in the band include LEO satellite feeder uplinks, the Airport Network and Location Equipment (ANLE), aeronautical flight telemetry, and aeronautical security systems. Because of the existing allocations and users in this sub-band, coordinating the use of UAS control link spectrum in this sub-band would not be an easy task.

FIGURE 5-7

Aeronautical, RNSS, and satellite frequency use in the 5 000-5 150 MHz band

The 5 000-5 010 MHz band is allocated to RNSS (Earth-to-space) and the 5 010-5 030 MHz band is allocated to RNSS space-to-Earth) for systems such as GPS and Galileo, and so they would not be suited for UAS control link use. RR No. 5.444 gives precedence to the MLS from 5 030 to 5 091 MHz The 5 091-5 150 MHz band is designated as the MLS expansion band, although MLS is unlikely ever to need the 5 091–5 150 MHz band, and MLS no longer has precedence in this band. Feeder links of mobile-satellite systems in non-geostationary orbits – e.g.  LEO systems—are also primary in the 5 091–5 150 MHz band until 2018 and under Resolution 114, this allocation must be reviewed prior to 2018 and could continue beyond 2018.

In the U.S., radio astronomy has an exclusive passive primary allocation in the adjacent 4 990-5 000 MHz band, and a primary worldwide ITU allocation shared with active services. That band is extensively used by Radio Astronomy observatories throughout the world.

FIXED-SATELLITE SERVICE (Earth-to-space)*- - *

AERONAUTICAL RADIONAVIGATION

SERVICE

WRC-2012 Agenda Iitem 1.4

FUTURE RNSS LINKS

MICROWAVE LANDING SYSTEM (MLS)

LEO SATELLITE FEEDS SYSTEMS

AIRPORT NETWORK AND LOCATION EQUIPMENT (ANLE) AERONAUTICAL FLIGHT TELEMETRY AERONAUTICAL SECURITY SYSTEM

POTENTIAL UAS

SPECTRUM

AERONAUTICAL MOBILE SATELLITE (ROUTE)–

CURRENT AM(R)S

MLS (EXPANSION BAND)

AMS

* This allocation is limited to MSS feeder links.

5000 MHz 5030 MHz 5091 MHz 5150 MHz

NOTE: This chart does not completely depict all systems or allocations in this band.

Proposed ANLE

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The US is moving forward with the use of the 5 091–5 150 MHz sub-band (and possibly the 5 000-5 030 MHz sub-band depending on the outcome of WRC-12 Agenda Item 1.4) for the future ANLE system. ANLE is visualized as a high-integrity, high-data-rate wireless LAN for the airport surface, with terminals on the ground and on taxiing aircraft. The IEEE 802.16e WiMAX standard is the candidate architecture for ANLE. Other applications now being considered for the 5 091-5 150 sub-band include aeronautical flight telemetry and a new aeronautical security system. An AM(R)S designation for the 5 091-5 150 MHz sub-band was secured at WRC-07, and WRC-12 Agenda item 1.4 calls for consideration of a similar designation for the 5 000-5 030 MHz sub-band. The AM(R)S designations are prerequisites for the use of those sub-bands for ANLE.

The compatibility of a US-wide 802.16e-based ANLE system, with HIBLEO-4FL and [LEO-F] feeder links in the 5 091-5 150 MHz band, has been analysed. ANLE was assumed to be using a single 20 MHz channel at all 497 towered civilian airports in the US.

Each ANLE transmitter was assumed to have an omnidirectional antenna radiating the minimum power (1.66 W) necessary to close the link at an assumed maximum distance of 3 km. The 497 ANLE transmitters’ aggregate interference power in the passbands of HIBLEO-4FL and [LEO-F] satellite feeder-link receivers was computed at 2° latitude and longitude increments at orbital altitudes. The maximum aggregate interference power was found to be 0.9 and 2.8 dB below the interference threshold for HIBLEO-4FL and [LEO-F], respectively. These interference margins could be improved by perhaps 4 dB if three 20 MHz channels were made available to ANLE, so that no satellite receiver would need to be exposed to co-channel interference from more than one-third of the total population of ANLE transmitters. These results indicate that if ANLE is implemented throughout the US in the 5 091-5 150 MHz band, it will be compatible with LEO satellites, but relatively little interference margin would remain to accommodate an additional nationwide system of UAS control links in the channel(s) used by ANLE. The proposed telemetry and security applications, if implemented, would probably use up the entire remaining margin.

Even if UAS control links operated in a 20 MHz channel separate from ANLE and the telemetry/security applications, UA control link implementation beyond the near vicinity of the control station would still be problematic, since links longer than 3 km would require far more power (e.g. about 30 dB greater for 100 km links) and potentially pose a much greater threat to the LEO receivers. Reducing the control link bandwidth would help. A reduction to 1.25 MHz (the minimum for 802.16e) would reduce the power requirement by only about 12 dB, but a control link bandwidth of 20 kHz could reduce it by 30 dB. Still, the need to protect the incumbent satellite service in the 5 091–5 150 MHz band, with or without the potential introduction of ANLE and other proposed services into the same band, might impose unacceptable constraints on the introduction and subsequent growth of any future UAS control link system placed in the same band. The downlink power requirements at long ranges might also be impracticably large for some classes of UA. Moreover, airframe shadowing is more intense in this band than at lower frequencies and might necessitate the use of multiple antennas on the UA to provide the required diversity.

The only UAS control link applications for which 5 091–5 150 MHz might be a viable candidate band are those requiring short-range, high-bandwidth communication at short ranges - e.g., pilot control of a low-autonomy UA during takeoff and landing. During those crucial phases of flight, a short-range system using this band might be useful as a backup for a “primary” control link operating in a less encumbered band such as 960–1 164 MHz. At ranges less than 3 km, the power levels necessary for the 5 091–5 150 MHz link would probably be consistent with the need to protect incumbent satellite services and with UA power constraints. It is likely that relatively few UA would be taking off or landing at any

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given time within the NAS, thus minimizing the interference threat to satellite uplinks. The guard times necessary at such short ranges would be small enough that the UAS control links might be able to employ the IEEE 802.16e standard, whose growing acceptance for vehicular applications may eventually drive down the unit costs of lightweight IEEE 802.16e devices that would be suitable for UA use. However, it is not yet clear that 802.16e links will perform well at UA takeoff and landing speeds. Some degradation of 802.16e’s higher-order modulations might result, adversely affecting link capacities. Measurement and/or analysis would be needed to quantify this effect, as well as compatibility with other services and systems allocated to the band.

It may also be feasible, at least from a regulatory standpoint, to develop a satellite based system for the UAS control link in the 5 030-5 091 MHz part of this band, which is currently used exclusively by MLS. Radio Regulations footnote 5.367 says AMS(R)S has a primary allocation from 5 000 to 5 150 MHz. Since RR No. 5.444 states that the requirements of MLS take precedence over other uses of the 5 030-5 091 MHz frequency range, any 5 030-5 091 MHz AMS(R)S system would have to operate to give precedence to MLS, which can mean operation on a non-interference basis with respect to MLS. Moreover, the (R) designation might limit the use of any such system to controlled airspace.

A proposal to develop a satellite-based UAS control link within the 5 000-5 150 MHz band was recently introduced in the European Organization for Civil Aviation Equipment (EUROCAE) and other forums. 23

The technical feasibility of a 5 030-5 091 MHz AMS(R)S UAS control link is less clear than the regulatory feasibility. In the three decades since its adoption by ICAO as an international standard, the growth of MLS has been stunted (especially in the US) by competition from GPS and the well-established ILS, and has never needed more than a small fraction of its exclusive 5 030-5 091 MHz frequency allocation. Complete abandonment of MLS would greatly facilitate establishment of an AMS(R)S system in its place. However, many aircraft are MLS-equipped, and some CAAs (especially in Europe) are reluctant to abandon a system that is technically far superior to ILS and less vulnerable than a satellite navigation system to widespread outages. The disappearance of MLS cannot be taken for granted.

Alternatively, it might be possible to partition the 5 030-5 091 MHz band into separate MLS and AMS(R)S segments, with the MLS portion sized to reflect realistic estimates of future MLS growth. However, subsequent MLS frequency assignments and reassignments might then be seriously impeded by the need to observe standard rules of frequency pairing with collocated DME, VOR, and ILS stations. A better approach would be for the AMS(R)S system to share spectrum locally with MLS. Frequency-assignment criteria could be developed that would ensure sufficient frequency separation between each satellite spot beam and each MLS in or near that spot beam.

A terrestrial LOS UAS CNPC system could also be developed to operate in the 5 030-5 091 MHz band. A new AM(R)S allocation for the band would be necessary to enable this. Like its proposed AMS(R)S counterpart, an AM(R)S UAS CNPC system in this band would need to follow appropriate frequency-assignment criteria, to prevent the UAS CNPC links from interfering with nearby MLS receivers. Electromagnetic compatibility (EMC) analyses of MLS and future UAS CNPC systems in the 5 030-5 091 MHz band appear in the following subsections.

23 A. Klaeyle, The 5 GHz “Safety Satcom” Infrastructure, UAS_305.1, EUROCAE WG-73, 31 December 2008.

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5.3.1 EMC analysis of MLS and in-band AM(R)S UAS CNPC system

5.3.1.1 MLS characteristics

MLS is a precision approach and landing guidance system that provides position information and various ground-to-air data from ground transmitters to airborne receivers at altitudes up to 20 000 feet and ranges out to 22.5 nmi. The system’s functions may be divided as follows: approach azimuth, back azimuth (missed approach and departure), approach elevation, range, and data communications. All the functions except ranging use the 5030–5091 MHz band.

Azimuth guidance equipment is normally located at each end of the runway. The azimuth antenna facing the approaching aircraft is configured as the approach azimuth transmitting antenna, while the opposite antenna becomes the back azimuth transmitting antenna. The approach azimuth transmitter is used to guide the aircraft during an instrument (non-visual) approach to the runway. The azimuth coverage extends to 62 degrees (normally 40 degrees) on either side of the runway.

As viewed by the pilot of an aircraft on final approach to the runway, the azimuth beam is swept from the rightmost coverage angle to the leftmost in the "to" scan and is then returned from the left to right coverage angle in the "fro" scan after a specified delay at the leftmost limit. The time difference between receptions of the signals during the to and fro scans is determined. Information derived from the data words transmitted to the aircraft by the MLS gives the aircraft MLS receiver specific information with regard to site geometry. This information is used along with beam timing to determine accurately the azimuth angle of the aircraft.

The elevation station transmits signals on the same frequency as the azimuth station. The elevation beam originates at an angle near horizontal (minimum elevation angle), scans to the upper elevation angle limit of 29.5 degrees (normally 15 degrees) in an upward direction (the to scan), and then returns (the fro scan). The time interval between the to and fro scans is measured in the receiver and based on the data transmitted from the ground (concerning site geometry and configuration) the elevation angle of the aircraft is determined.

The range signal is produced by the distance measuring equipment (DME), which operates in the 960–1215 MHz band. The DME is the MLS ranging element, and is responsible for providing the aircraft's slant range to a specified ground position. Precision distance measuring equipment (DME/P) provides for two modes of operation for approaching aircraft. The initial approach (IA) mode is active in the region from 7 nmi to 22 nmi from the DME/P transponder. The final approach (FA) region is from the transponder to a range of 7 nmi. The FA mode has enhanced precision and tolerances when compared to the IA mode. The narrow-spectrum distance measuring equipment (DME/N) is compatible with the IA mode. DME transponders operate on assigned frequencies that are paired with specific frequencies of the MLS angle transmitters.

MLS data communications include station identification and location, DME channel and status, waypoint coordinates, runway conditions, and weather.

A preamble is transmitted using differential phase shift keying (DPSK) modulation. It is followed by azimuth, elevation, and back azimuth unmodulated continuous wave (CW) signals and data (DPSK) as depicted in Fig. 5-8 24.

24 Unwanted Emission Characteristics in the 5010-5030 MHz Band from the ICAO Standard MLS, ICAO Working Paper, Montreal, Canada, 24 March - 3 April, 2009.

ACP-WGF21/WP-12

FIGURE 5-8

MLS transmission sequence

The MLS angle and data functions operate on any one of the 200 channels that are spaced 300 kHz apart between 5031 and 5090.7 MHz. (The expansion band up to 5150 MHz is not currently used.) Each MLS channel is paired with a DME channel. Forty MLS channels paired with DME X and DME W operate between 5031 and 5042.7 MHz. One hundred sixty MLS channels paired with DME Y and DME Z operate between 5043 and 5090.7 MHz. MLS channels paired with DME W and DME Z are currently not used.

The distance between co-channel MLS stations must be at least 205 nmi, and the desired/undesired (D/U) received-signal ratios must be at least +26.5 dB. The ground stations operating on the first and second adjacent channels are sited beyond the radio horizon distance from the coverage volume to avoid ground/air intra-MLS interference.

The emission attenuation of a DPSK-modulated MLS transmitter is plotted in Fig. 5-9 and described by1 10*log(∆f2/Bfd), where:

fd = modulation rate = 15.625 kHzB = bandwidth = 150 kHz

∆f = frequency offset (kHz); 75 kHz or more from centre frequency

ACP-WGF21/WP-12

FIGURE 5-9

MLS/DPSK emission mask

0

10

20

30

40

50

60

70

-60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60

Atten

uatio

n (d

Bc)

Frequency Offset (MHz)

Essential MLS parameters25, 26, 27 appear in Table 5-1. The conservative assumption, also stated in the table, of a 6-dBi MLS receiving-antenna gain in the direction of the potential interferer is taken from a related ITU Recommendation 28.

25 International Civil Aviation Organization, Annex 10, Aeronautical Telecommunications, Volume 1: Radio Navigation Aids, International Standards and Recommended Practices, Sixth Edition, July 2006.26 Aeronautical Communications Panel, Fifteenth Meeting of Working Group F, ACP-WGF15/IP03 Rev.1, June 2006.27 Federal Aviation Administration, Spectrum Management Regulations and Procedures Manual, Order 6050.32B, November 2005.28 International Telecommunication Union, Method for determining the necessary geographical separation distances, in the 5 GHz band, between the international standard microwave landing system (MLS) stations operating in the aeronautical radionavigation service and transmitters operating in the aeronautical mobile service (AMS) to support telemetry, Rec. ITU-R M.1829, 2007.

ACP-WGF21/WP-12

TABLE 5-1

MLS characteristics

Frequency range (MHz) for non-DME functions 5 030-5 091

Frequency range (MHz) for DME functions 960-1 215

Power (dBm) 43 (all signals)

Preamble and data antenna gain (dBi) 2 to 8; 0 outside coverage region

Azimuth and elevation antenna gain (dBi) up to 23; 0 outside coverage region

Airborne antenna gain (dBi) toward MLS ground station 0

Airborne antenna gain (dBi) assumed toward potential

interferer6

Azimuth antenna beamwidth (degrees) Less than 4

Azimuth scan limits (degrees)−40 to +40 (typical), −62 to 62

(max)

Azimuth scan duration (ms) 15.9

Elevation antenna beamwidth (degrees) Less than 2.5

Elevation scan limits (degrees) 0.9 to 15 (typical), 0.9 to 29.5 (max)

Elevation scan duration (ms) 5.6

Polarization vertical

Longest continuous DPSK data sequence (ms) 9.3 - 15

Duty factor 25% (DPSK)

DPSK emission bandwidth (kHz) 150

Max unwanted emissions PFD at 840 kHz offset (dBW/

m²)−94.5 (DPSK)

Receiver bandwidth (kHz) 150

Receiver sensitivity (dBm) −112

Interference threshold at MLS receiver input

(dBm/150 kHz)−130

5.3.1.2 Interference analysis

Figure 5-10 shows potential mutual interference between MLS and a UAS terrestrial CNPC uplink (UL) and downlink (DL) operating in the 5 030-5 091 MHz range. The MLS receiver and the UA links operate within specific service volumes (SVs). The UAS ground radio (GR) operates from the UAS control station.

ACP-WGF21/WP-12

FIGURE 5-10

Potential interference between MLS and UAS CNPC terrestrial links

Four potential interference cases exist:1) UAS downlink CNPC transmitter to MLS receiver2) MLS transmitter to UAS uplink CNPC receiver3) UAS uplink CNPC transmitter to MLS receiver4) MLS transmitter to UAS downlink CNPC receiver.

Only cases 1 and 2 are explicitly considered here. Since the altitudes involved in cases 3 and 4 are generally lower than in the cases 1 and 2, the distance constraints derived below for the first two cases are likely to suffice to cover cases 3 and 4 as well.

Case 1: Potential RFI from UA terrestrial downlink transmitter to MLS receiver

In order to avoid harmful interference, the undesired UA signal at MLS receiver should not exceed MLS interference threshold TMLS. This can be described by the following (in which the UAS DL is assumed to be horizontally polarized):

Puas + GMLS − 20log(f dmin) − 38 − FDR − LPOL = TMLS (5-1)

where:Puas = UA transmitter EIRP (dBm)

GMLS = MLS Rx antenna gain (dBi) toward the UA = 6 dBif = frequency (MHz) = 5 060 MHz

dmin = minimum required distance separation (nmi)FDR = frequency-dependent rejection (dB)LPOL = cross-polarization loss (dB) = 10 dBTMLS = MLS interference threshold = -−130 dBm

On the basis of the maximum 320-kbps single-UA throughput requirement of the CNPC downlink in the manual mode during the terminal arrival phase 29, we can assume a 300-kHz channel will suffice for the UAS downlink (DL) just as it does for MLS. (Data rates would be much lower with the video downlink not in use, but then multiple UA could share a single downlink channel.) The UA EIRP (Puas) can be estimated as follows:

Puas + Grx – 20 log (f dmax) – 38 = Sr + M (5-2)29 Characteristics of unmanned aircraft systems (UAS) and spectrum requirements to support their safe operation in non-segregated airspaces, USWP5B09-25, September 2009.

Desired UL Signal

Undesired MLS Signal

Undesired UA DL Signal

UA

MLS Tx

GR

Desired MLS SignalCNPC SV

MLS SV

Desired DL Signal

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where:Grx = receiving antenna gain = 0 dBi

f = 5060 MHzdmax = maximum UA downlink distance (nmi)

Sr = receiver sensitivity (dBm) = −114 + 10 log R + NR = maximum data rate (0.32 Mbps)N = receiver noise figure (10 dB)M = fading margin (10 dB)

If we assume maximum UAS link distance to be 50 nmi, Puas = 47 dBm.

The UA CNPC downlink emission spectrum postulated for this analysis is based on an ACP UA telemetry spectrum model 30 and is shown in Fig. 5-11. FDR can be expressed as follows:

FDR (f) = 10 log10 (5-3)

where:S (f) is the transmitter power spectral densityR (f) is the receiver selectivity with the receiver tuned to the transmitter

frequencyf is the difference between tuned transmitter and receiver frequencies.

Calculated FDR values of the postulated UAS DL emission spectrum convolved with an assumed MLS receiver “boxcar” 150-kHz-bandwidth selectivity curve having a floor of −60 dB are shown in Table 5-2.

30 International Civil Aviation Organization, Considerations and propositions to answer to the future telecommunication needs related to WRC 07 A.I. 1.5 and 1.6, ACP-WGF14/WP-21, Annex 1, August 2005.

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FIGURE 5-11

Postulated UA CNPC transmitter emission mask

0

10

20

30

40

50

60

70-1200 -1050 -900 -750 -600 -450 -300 -150 0 150 300 450 600 750 900 1050 1200

Atten

uatio

n (d

Bc)

Frequency Offset from UAS Carrier (kHz)

TABLE 5-2

FDR of UA CNPC transmitter and MLS receiver

∆ Channels 0 1 2 3 ≥ 4

∆ f (kHz) 0 300 600 900 ≥ 1 200

FDR (dB) 3 30 44 56 58

Based on the specified assumptions, the calculated values of the minimum distance separation between the UA and the MLS receiver can be obtained from the formula below and are shown in Table 5-3.

= 1111 × 10–FDR/20 (5-4)

TABLE 5-3

Minimum distance between UA terrestrial downlink transmitter and MLS receiver

∆ Channels 0 1 2 3 ≥ 4

∆ f (kHz) 0 300 600 900 ≥ 1 200

dmin (nmi) BLOS 35 7 1.8 1.4

Case 2: Potential RFI from MLS into UA terrestrial uplink receiver

The maximum UAS uplink data rate (during the terminal arrival phase) is about 10 kbps, so that a UL bandwidth of 10 kHz is possible.

A potential worst-case interference situation would seem to arise when the UA is within the coverage angle of the unmodulated MLS azimuth and elevation transmissions that have antenna gains of up to 23 dBi. However, those high-gain antennas scan continuously

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throughout the coverage volume and so will appear as brief pulses ( 0.5 ms) with repetition intervals of 5.6–15.9 ms to any UA receivers they illuminate; the average received power would be 10–15 dB less, affording protection to UA receivers with sufficiently long integration times. Moreover, the emission spectrum of the unmodulated signal is much narrower and falls to –60 dB referred to the carrier (dBc) much faster than the MLS/DPSK emission mask shown in Figure 5-9. Accordingly, this analysis instead considers the DPSK-modulated signal, whose antenna gain is only 8 dBi, as the actual worst-case interferer.

PMLS + Gt(MLS) + Gr(UAS) – 20 log(fdmin) – 38 – FDR – LPOL = Prd – Rdu, (5-5)

where:PMLS = MLS transmitter power = 43 dBm

Gt(MLS) = MLS transmitter antenna gain (dBi) = 8 dBiGr(UAS) = UAS UL receiver antenna gain (dBi) = 0 dBi

f = frequency (MHz) = 5060 MHzdmin = minimum required distance separation (nmi)

FDR = frequency-dependent rejection (dB) based on the MLS emission maskLPOL = cross-polarization loss (dB) = 10 dB

Prd = UAS UL signal at UA receiver (dBm)Rdu = minimum allowable D/U ratio of UAS UL (10 dB assumed)

If the EIRP of the UAS UL transmitter is equal to 47 dBm and the UA is 50 nmi away from that transmitter, the desired signal at the UA receiver is:

Prd = 47 − 20 log (5060*50) − 38 = −99 dBm.

Assuming a UA terrestrial uplink-receiver selectivity floor of -60 dB, and a postulated D/U requirement of 10 dB for interference-free operation of the UA uplink, the UA and MLS ground transmitter need to be separated by approximately the distances obtained from the following formula and tabulated in Table 5-4.

(5-6)

TABLE 5-4

Minimum distance between MLS transmitter and UA terrestrial uplink receiver

∆ Channels 0 1 2 3 9 50∆ f (kHz) 0 300 600 900 2 700 15 000FDR (dB) 12 28 34 37 47 58dmin (nmi) 20 3 1.6 1.1 0.4 0.1

Case 3: Potential interference from UA terrestrial CNPC transmitter to MLS receiver

[Analysis still needed]

Case 4: Potential interference from MLS to UAS terrestrial downlink receiver

[Analysis still needed]

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5.3.2 EMC Analysis of MLS and In-Band AMS(R)S UAS CNPC System

The possible coexistence of MLS and a satellite-based UAS CNPC system in the 5030–5091 MHz band is currently being studied. 31 The satellite segment of the proposed system would utilize several geostationary (GEO) satellites, each of which would create a global-coverage beam and several spot beams. The service (satellite–UA) links would operate in the 5030–5091 MHz band. The feeder links between the earth station (ES) and the satellite might operate in the same band, or might operate in other bands (e.g., FSS bands). Figure 5-12 illustrates the UAS and MLS links that might be subject to mutual interference within the 5030–5091 MHz band.

FIGURE 5-12

Potential interference between MLS and UAS CNPC satellite links

Table 5-5 lists service-link parameters, taken from the CEPT/ECC reference cited in the preceding paragraph, that are relevant to an interference analysis.

31 European Conference of Postal and Telecommunications Administrations (CEPT) Electronic Communications Committee (ECC), MLS & AMS(R)S Coexistence Studies,, ECC/CPG11/PTC(2009)117, Geneva, September 16–18, 2009.

MLS UPLINK

GEO SATELLITE

MLS Rx

SERVICE UPLINK

SERVICE DOWNLINK

FEEDER UPLINK

FEEDER DOWNLINK UA

MLS TxES

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TABLE 5-5

AMS(R)S service link parameters

Frequency range 5030–5091 MHzChannel width 75 kHzTotal path loss between UA and satellite 201.8 dBPolarization CircularSatellite antenna diameter 6 mSatellite antenna gain (spot beam) 45.1 dBiUA antenna gain (20–78 from zenith) 0–3 dBiUplink EIRP (per carrier) 47 dBmDownlink EIRP (per carrier) 80.9 dBm

Table 5-6 lists eight potential interference cases involving MLS and the satellite links, together with possible separation criteria for achieving the necessary interference protection.

TABLE 5-6

Potential interference cases involving MLS and AMS(R)S links

Case Interference source Interference victim Separation criterion(dependent on source-victim

frequency offset)1 Service uplink’s UA

transmitter MLS receiver Minimum distance between UA and

MLS receiver2 MLS transmitter Service downlink’s UA

receiverMinimum distance between UA and MLS transmitter

3 Service downlink’s satellite transmitter

MLS receiver Minimum angular separation of MLS receiver from satellite spot-beam boresight

4 MLS transmitter Service uplink’s satellite receiver

Minimum angular separation of MLS transmitter from satellite spot-beam boresight

5 Feeder uplink’s Earth station transmitter

MLS receiver Minimum distance between Earth station and MLS receiver

6 MLS transmitter Feeder downlink’s Earth station receiver

Minimum distance between Earth station and MLS transmitter

7 Feeder downlink’s satellite transmitter

MLS receiver TBD

8 MLS transmitter Feeder uplink’s satellite receiver

TBD

Each of these potential interference cases is examined below.

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Case 1: Potential RFI from service uplink’s UA transmitter to MLS receiver

Equation (5-1), which was developed in section 5.3.1.2 for terrestrial interference case 1, applies to this case as well. However, two parameters have different values here. First, the UA transmitter EIRP (Puas) is construed here as the combined EIRP of four service uplink carriers, each in a 75-kHz channel, within a single 300-kHz MLS channel. Since each carrier has an EIRP of 47 dBm, Puas is four times as large: 53 dBm. Second, since the satellite link is circularly polarized while MLS uses vertical polarization, cross-polarization loss LPOL now is only 3 dB instead of 10 dB. All other relevant parameters (including the postulated emission mask of the UA transmitter, and hence the calculated FDR values of Table 5-2) are assumed to be the same as before. The resulting expression for minimum allowable distance is

dmin = 5 012 × 10–FDR/20 (5-7)

Table 5-7 shows the results for various frequency offsets between the service uplink and the MLS signal. These distance constraints are considerably more severe than those previously calculated for terrestrial case 1.

TABLE 5-7

Minimum distance between UA AMS(R)S uplink transmitter and MLS receiver

∆ Channels 0 1 2 3 ≥ 4∆ f (kHz) 0 300 600 900 ≥ 1 200dmin (nmi) BLOS 158 32 8 6

Case 2: Potential RFI from MLS transmitter to service downlink’s UA receiver

Equation (5-5), developed in section 5.3.1.2 for terrestrial interference case 2, also applies here. All of the relevant parameters are the same as in that terrestrial case, with the following exceptions. First, Gr(UAS), the gain of the UAS receiving antenna in the direction of the interfering transmitter, is assumed to be 3 dBi. Second, cross-polarization loss LPOL again becomes 3 dB. Third, the received desired signal Prd now is the downlink signal arriving from the satellite and is calculated as follows:

Prd = Pse + Grd(UAS) – Lpd (5-8)

wherePse = satellite downlink transmitter EIRP per carrier (rounded off) = 81 dBm

Grd(UAS) = UAS receiving-antenna gain in direction of the satellite = 0 dBiLpd = total path loss between satellite and UA (rounded off) = 202 dB.

This yields a Prd value of –121 dBm (much smaller than in the terrestrial case). The resulting expression for minimum allowable distance thus becomes

dmin = 3 132 ×10–FDR/20 (5-9)

Approximate FDR values are shown in Table 5-8. (The service downlink’s UA receiver is modelled here with a “boxcar” 75-kHz-bandwidth IF filter and a selectivity floor of −60 dB.)

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TABLE 5-8

FDR of MLS transmitter and UA service downlink receiver

∆ Channels 0 1 2 3 9 50 150∆ f (kHz) 0 300 600 900 2 700 15 000 45 000FDR (dB) 3 19 25 28 38 52 58

Table 5-9 shows the results for various frequency offsets between the service downlink and the MLS signal.

TABLE 5-9

Minimum distance between MLS transmitter and UA AMS(R)S downlink receiver

∆ Channels 0 1 2 3 9 50 150

∆ f (kHz) 0 300 600 900 2 700 15 000 45 000

dmin (nmi) BLOS 351 176 125 39 8 4

These distance constraints are much more severe than those calculated for terrestrial case 2. The reasons for this are the satellite service downlink’s wider passband (75 kHz vs. the 10 kHz assumed for the terrestrial uplink), weaker desired signal (–121 vs. –99 dBm), and reduced cross-polarization protection (3 vs. 10 dB). All of those factors combine to make the satellite downlink more vulnerable than the terrestrial uplink to MLS interference, requiring more stringent distance constraints than in the terrestrial case to provide adequate protection.

Case 3: Potential RFI from service downlink’s satellite transmitter to MLS receiver

[Analysis still needed]

Case 4: Potential RFI from MLS transmitter to service uplink’s satellite receiver

[Analysis still needed]

Case 5: Potential RFI from feeder uplink’s Earth station transmitter to MLS receiver

[Analysis still needed]

Case 6: Potential RFI from MLS transmitter to feeder downlink’s Earth station receiver

[Analysis still needed]

Case 7: Potential RFI from feeder downlink’s satellite transmitter to MLS receiver

[Analysis still needed]

Case 8: Potential RFI from MLS transmitter to feeder uplink’s satellite receiver

[Analysis still needed]

ACP-WGF21/WP-12

5.3.3 Hybrid AM(R)S/AMS(R)S UAS CNPC System

A hybrid system comprising both AM(R)S and AMS(R)S elements is also possible in the 5030–5091 MHz band. The satellite part of the system could be reserved largely for UA overflying remote areas not served by terrestrial CNPC links. In that event, another EMC analysis will be needed to determine criteria for avoiding RFI between the system’s terrestrial and satellite links.

The advantages and disadvantages of various parts of the 5000-5150 MHz frequency range for UAS control links are briefly summarized below. • The studies conducted under WRC-07 Agenda Item 1.5 indicated that it is may not be feasible to operate AM(R)S with MLS in the same frequency band. Since the band 5030-5091 MHz is primary MLS band the access of MLS to this band should be safeguarded.• With respect to possible UAS - AMS(R)S usage in this band current provisions of 5.367A and 5.444A provide regulatory solution to share the band 5030-5150 MHz between AMS(R)S and ARNS. It is important that these provisions will be maintained in order to keep MLS priority in this band.]

ACP-WGF21/WP-12

6 Conclusions

7.1 960-1 164 MHz

Initial studies indicate that it may be difficult to use this Band for UAS Application since the band is heavily congested.

7.2 1 545-1 555 MHz (space-to-Earth), 1 610-1 626.5 MHz (space-to-Earth and Earth-to-space), and 1 646.5-1 656.5 MHz (Earth-to-space)10-1 660 MHz (Earth-to-space) [TBD]

7.3 [5 030-5091 or 5150] MHz

[TBDThe use and development of this band by the MLS System should not be constrained

]

Appendix A

Parameters of airborne 960–1164 MHz transmitters and receivers

The known parameters of relevant systems are presented in tabular form in Tables A-1 and A-2, which list the airborne transmitter and receiver characteristics, respectively. The footnotes and references shown after Table A-2 apply to both tables. In both tables, values in cells with footnotes have been verified against the cited reference documentation.

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TABLE A-1

Airborne transmitters in the 960–1 164 MHz band

Incumbent System

Airborne Transmitter Characteristics UACS

Freq. (MHz) Power (dBm)

Emis. BW

(MHz)

PW (s)

PRF (pps)

Duty Factor

Spur. Emis. (dBc)

SSR Trans-

ponder

(ATCRBS

Replies)

1 090 1 48–57 1 4.5 20 15 200 18 0.40% 76

SSR Trans-

ponder (Mode

S Replies)

1 090 1 48–57 1 2.6 64 15 4.5 15 0.03% 76

TCAS

(Mode S

Interrogations)

1 030 2 56 19 2.6 20 15 5 15 0.01% 76

TCAS

(Whisper-

Shout

Interrogations)

1 030 2 29–52 2.6 25 15 80 15 0.20% 76

DME 1 041–1 150 7 47–54 3 0.4 19 15 70 15 0.13% 50

ADS-B

(Extended

Squitter)

1 090 5 57 5 2.6 120 5 6 0.07% 76

UAT 978 4 43–54 4 0.9 400 1 0.04% 70 16

JTIDS/MIDS

969–1 008,

1 053–1 065,

1 113–1 206 8

53–60 10 3 10 6.4 6 648 21 0.41% 21

70 16

TACAN 1 025-1 150 7  57 12   3.5 17 7 200 17     

ACP-WGF21/WP-12

TABLE A-2

Typical characteristics UACS of the ARNS stations operating in the countries referred to in 5.312 RR

ARNS system characteristics UACS

Type 1 Type 2 Type 3

PurposeRadio systems of short-range

navigation

Radio systems of short-range navigation

Radio systems of approach and landing

Operating frequency range

960-1 000.5 MHz

960-1164 MHz

Radioline direction “Earth-aircraft”

“Earth-aircraft”

“aircraft-Earth”

“Earth-aircraft”

“aircraft-Earth”

Operation range, km up to 400 up to 400 up to 400 up to 45 up to 45

Transmitted information

Transmission of azimuthal signals, range

response signals and request to indication

Transmission of

azimuthal signals, range

response signals and request to indication

Transmission of range

request signal and indication response signal

Transmission of signals in glide path and course

channels and range

response signals

Transmission of range request

Transmitter characteristics UACS

Station name

Airport and en-route path

ground stations

Airport and en-route path

ground stations

Aircraft station Airport ground station

Aircraft station

Signal type Pulsed pulsed pulsed pulsed pulsed

Class of emission 700KРХХ 4M30P1N 4M30P1D 700KP0X; 4M30P1N

700KP0X; 4M30P1N

Channel spacing 0.7 MHz 0.7 MHz 0.7 MHz 0,7 MHz 2 MHzType of modulation Pulsed pulsed pulsed pulsed pulsedTransmitter power (pulsed), dBW 20-45 29-39 27-33 3-30 5-33

Mean output power(min/max), dBW 7.6 / 13.2 7.1/13.8 −8.2 −4/−6 −7.5

Pulse length, s 1.5; 5.5 1.25; 1.5; 5.5 1.5 1,7 1,7Duty factor (%) 0.018; 0.066 0.064-0.3 0.00765 0.04; 0.025 0.009

Antenna type omnidirectional

array antenna

omnidirectional

array antenna

omnidirectional

Max/min antenna gain, dB 6/0 15.6 −10/3 10/0 1.5/−3

Height above the ground, m 10 10 up to 12 000 10 up to 12 000

Receiver

ACP-WGF21/WP-12

ARNS system characteristics UACS

Type 1 Type 2 Type 3

PurposeRadio systems of short-range

navigation

Radio systems of short-range navigation

Radio systems of approach and landing

characteristics UACS

Receiving station Aircraft station Aircraft station

Airport and en-route path

ground stations

Aircraft station

Airport ground station

Height above the ground, m up to 12 000 up to 12 000 10 up to 12 000 10

Receiver passband, MHz 1.5 22 22 7 7

Receiver noise temperature, K 400 1 060 550 400 400

Max/min antenna gain, dB 1.5/−3 3/−10 14 1.5/−3 10/0

Polarization horizontal horizontal horizontal horizontal horizontalReal receiver sensitivity, dBW −120 −118 −125 −110…−120 −113

Protection ratio C/I, dB 25 17 20 25 25

ACP-WGF21/WP-12

TABLE A-3

Airborne receivers in the 960–1164 MHz band

Incumbent System

Airborne receiver characteristics

Freq. (MHz)Sensi-tivity

(dBm)

RF BW (MHz) Recov. Time (s)

Adj. Chan. Rejec. (dB)

Image Rejec. (dB)

Spur. Rejec. (dB)3 dB 6 dB 10 dB 20

dB 23 dB 40 dB

50 dB

55 dB

60 dB

70 dB

SSR Trans-ponder (ATCRBS Replies)

1030 1 –73±4 dB1 6 1 30 1 15 1 80 70

SSR Trans-ponder (Mode S Replies)

1030 1 –74±3 dB1 6 1 30 1 50 1 45 1

TCAS (Mode S Interroga-tions)

1090 2 –74±2 dB 19 11 19 20 19 30 19 50 19 80 70

TCAS (Whisper-Shout Interroga-tions)

DME 978–1215 7 –83 3 1.8 11 2.1 11

2.6 11

3.0 11

6.0 11 8 50 3 80 80

ADS-B (Extended Squitter)

1090 5 –84 5 11 20

UAT 978 4 –93 4 1.2 4 4 20 4 15 40 18

JTIDS/MIDS

969–1008, 1 053–1065, 1113–1206 8

–95 10

TACAN 962–10241151–1213 7 -92 12

References for Tables A-1 and A-2:1. RTCA DO-181C, Minimum Operational Performance Standards (MOPS) for Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment.

2. RTCA DO-300, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System II (TCAS II) Hybrid Surveillance.

3. RTCA DO-189, Minimum Operational Performance Standards for Airborne Distance Measuring Equipment (DME) Operating within the Frequency Range of 960 - 1215 Megahertz.

4. RTCA DO-282A, Vol. 1, Minimum Operational Performance Standards for Universal Access Transceiver (UAT) Automatic Dependent Surveillance - Broadcast (ADS-B).

5. RTCA DO-260A, Vol. 1, Minimum Operational Performance Standards for 1090 MHz Extended Squitter Automatic Dependent Surveillance - Broadcast (ADS-B) and Traffic Information Services - Broadcast (TIS-B).

6. CFR 47 Part 87.479.

7. ICAO Annex 10 Volume I.

ACP-WGF21/WP-12

8. Suitability of Civil Aviation Bands for the Future Communication Infrastructure, 14th meeting of ICAO ACP Working Group F, Malmo, Sweden, 22–26 August 2005.

9. JTIDS Key Features, http://www.rockwellcollins.com/ecat/gs/JTIDS.html.

10. R. Echevarria and L. Taylor, “Co-Site Interference Tests of JTIDS, EPLRS, SINCGARS, and MSE (MSRT),” Proc. 1992 Tactical Communications Conf., Vol. 1, pp. 31–39, April 1, 1992.

11. Compatibility between UMTS 900/1800 and Systems Operating in Adjacent Bands, Electronic Communications Committee (ECC) Report 96, Krakow, March 2007.

12. www.rockwellcollins.com/ecat/gs/AN_ARN-153V.html

13. ICAO Annex 10 Volume IV

14. http://www.fas.org/man/dod-101/sys/ship/weaps/an-wlr-1.htm

15. RTCA SC-186 WG5, UAT-WP-11-12, ADS-B UAT MOPS, 4 March, 2002

16. ICAO ACP-WGF14/WP-11

17. www.globalsecurity.org/military/library/policy/navy/nrtc/14090_ch2.pdf

18. RTCA DO-282A, Vol. 2, Minimum Operational Performance Standards for Universal Access Transceiver (UAT) Automatic Dependent Surveillance - Broadcast (ADS-B).

19. RTCA DO-185B, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System II (TCAS II), Volume I.

20. RTCA DO-260A, Vol. 2, Minimum Operational Performance Standards for 1090 MHz Extended Squitter Automatic Dependent Surveillance - Broadcast (ADS-B) and Traffic Information Services - Broadcast (TIS-B).

21. Heuristic Assessment of the Compatibility Issues between the Aeronautical FRS (Future Radio System) and Radionavigation DME/TACAN System in the Band 960-1164 MHz, ICAO ACP-WGF18/WP-13, Montreal, Canada, May 2008.

Glossary ACP Aeronautical Communications PanelADS Automatic Dependent SurveillanceADS-B ADS – BroadcastADS-C ADS – ContractADS-R ADS – RebroadcastAM(R)S aeronautical-mobile (route) serviceAMS aeronautical-mobile serviceAMS(R)S aeronautical-mobile satellite (route) serviceAMSS aeronautical-mobile satellite serviceANLE Airport Network and Location Equipment (a highly integrated, high-data-rate, wireless local-area network for airport surface areas)ARNS aeronautical radionavigation serviceATC air traffic controlATCRBS air traffic control radar beacon systemATS air traffic servicesBLOS beyond line-of-sight BW bandwidth

ACP-WGF21/WP-12

CAA Civil Aviation AuthorityCEPT European Conference of Postal and Telecommunications AdministrationsCNPC control and non-payload communicationsCPM conference preparatory meetingUACS UA control stationdB decibel(s)dBc dB relative to the carrierdBi dB referred to the gain of an isotropic antennadBm dB referred to one milliwattdBW dB referred to one wattDL downlinkDME distance measuring equipmentECC Electronic Communications CommitteeE-GSM-900 Extended Global System for Mobile CommunicationsEIRP effective isotropically radiated powerES Earth stationEUROCAE European Organization for Civil Aviation EquipmentFAA Federal Aviation AdministrationFCC Federal Communications CommissionFDD frequency-division duplexFDR frequency-dependent rejectionFEC forward error correctionFIS-B Flight Information Service – BroadcastFM frequency modulationFSS fixed-satellite serviceGEO geostationaryGNSS Global Navigation Satellite SystemGPS Global Positioning System (U.S.)GR ground radioG/T ratio of receiving-antenna gain to receiver thermal noise temperature in KelvinsHIBLEO-2 non-geostationary orbit satellite networkHIBLEO-4 non-geostationary orbit satellite networkICAO International Civil Aviation OrganizationIEEE Institute of Electrical and Electronics UACS EngineersIEEE 802.16e IEEE standard for mobile broadband wireless access systems)IFF Identification Friend or FoeIFR instrument flight rulesILS Instrument Landing SystemIPF interference protection function

ACP-WGF21/WP-12

ITU International Telecommunication UnionITU-R ITU Radiocommunication SectorJTIDS Joint Tactical Information Distribution SystemkHz kilohertzLAN local area networkLAX Los Angeles, California international airportLEO low Earth orbit (or a satellite in that orbit) L-DACS L-band digital aeronautical communications systemL-DACS1 L-band digital aeronautical communications system 1 (FDD-based)L-DACS2 L-band digital aeronautical communications system 2 (TDD-based)LOS line-of-sightMHz megahertzMIDS Multifunctional Information Distribution SystemMLS Microwave Landing SystemMOPS minimum operational performance standardsMS mobile serviceMSS mobile-satellite serviceNAS National Airspace SystemOFDM orthogonal frequency-division multiple accessOH hydroxylP-GSM-900 primary global system for mobile communicationspps pulses per secondPRF pulse repetition frequencyPW pulse widthRA radio astronomyRF radio frequencyRFI radio frequency interference RNSS radionavigation-satellite serviceRR Radio RegulationsRTCA Radio Technical Commission for Aeronautics UACSRx receiverS&A sense and avoidSAT satelliteSATCOM telecommunication satelliteSARPs standards and recommended practicesSSR secondary surveillance radarSV service volumeSWAP airborne equipment size, weight, and powerTACAN tactical air navigation

ACP-WGF21/WP-12

TCAS Traffic Alert and Collision Avoidance SystemTDD time-division duplexTIS-B Traffic Information Services – BroadcastTx transmitterUA unmanned aircraftUAS UA system(s)UAT Universal Access TransceiverUL uplinkUS United StatesVHF very high frequencyVOR VHF omnidirectional rangeW wattWiMAX Worldwide Interoperability for Microwave AccessWP working partyWRC World Radiocommunication ConferenceWRC-07 WRC 2007WRC-12 WRC 2012µs microsecond

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