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Agenda Item 1.d.i:Review of ICAO Position for WRC-07; Agenda Item 1.6; Resolution 414

Analysis of 960-1215 Mhz band

(Presented by Mike Biggs)

Summary

As part of aviation studies in support of the 2007 World Radiocommunication Conference (WRC-07), aeronautical frequency bands are being considered for co-primary aeronautical mobile (route) service (AM(R)S) allocations. This paper analyzes the 960-1215 MHz aeronautical radionavigation service (ARNS) band, and concludes that a portion of that band would also be suitable for AM(R)S.

1.0 Introduction

1.1 The 960-1215 MHz band is allocated in all Regions for the aeronautical radionavigation service (ARNS), and is heavily utilized worldwide for distance measuring equipment (DME), tactical air navigation (TACAN), secondary surveillance radar (SSR), military identification friend or foe (IFF), and in some States the military Joint Tactical Information Distribution System/Multifunctional Information Distribution System (JTIDS/MIDS)[1]. The frequency 978 MHz is also planned for the Universal Access Transceiver (UAT) currently being standardized by ICAO. Because of its good propagation characteristics, this band would be suitable for both air-air and air-ground communications.

2.0 Analysis of Current Usage

2.1 DME/TACAN use of the band is strictly governed through a channel plan contained in Annex 10. This plan results in different portions of the band having different characteristics, and provides further guidance as to the suitability of specific frequencies for AM(R)S. In particular, the following sub-bands can be defined:

  • 960-977 MHz
  • Termed national allotment channels, these frequencies are not part of the ICAO DME channel plan. These channels are used in some States for military mobile TACAN.
  • JTIDS/MIDS starting at 969 MHz
  • 978 MHz
  • DME “emergency channel”, only 8 operational ground-based assignments worldwide.
  • Used in some States for DME ramp testers
  • Planned for use by UAT
  • JTIDS/MIDS channel
  • 979-1024 MHz
  • DME/TACAN use limited to fixed ground-based transponders
  • 1021-1024 MHz generally not assigned in order to protect SSR
  • JTIDS/MIDS
  • 1025-1150 MHz
  • Heavily utilized by both airborne and ground-based DME/TACAN transmitters
  • Includes 1030 MHz and 1090 MHz SSR/IFF channels with their high-density/wide-band emissions.
  • JTIDS/MIDS
  • 1151-1163 MHz
  • DME/TACAN use limited to fixed ground-based transponders
  • 1151-1156 MHz generally not assigned in order to protect SSR
  • JTIDS/MIDS
  • Adjacent to sensitive GNSS band 1164-1215 MHz
  • 1164-1215 MHz
  • DME/TACAN use limited to fixed ground-based transponders
  • Next generation GNSS systems in development
  • JTIDS/MIDS

3.0 960-1215 MHz Band Conclusions

3.1 Reviewing the defined sub-bands, the following conclusions regarding new AM(R)S allocations can be drawn:

a) 960-977 MHz offers a good opportunity for aviation use with minimal impact on existing aviation infrastructure;

b) 978 MHz should be included to facilitate UAT development. Compatibility of UAT and DME has already been decided;

c) 979-1024 MHz provides good potential for sharing with AM(R)S. Existing users are fairly narrowband and generate pulsed emissions with pulse lengths on the order of 10 microseconds. In addition the expected interference environment is analyzable and manageable due to the predominance of fixed ground-based emitters.

d) 1025-1150 MHz should be avoided by AM(R)S. The band is heavily utilized for both ground-based and airborne emitters, and it includes the wideband air traffic control 1030/1090 MHz systems. Aircraft cosite problems are likely to be an issue.

e) 1151-1163 MHz offers potential for AM(R)S, though care must be taken to protect the upper-adjacent GNSS band. Best potential might be the currently little-used 1151-1156 MHz band, which would then preserve a guard band around the GNSS. Cosite issue would probably restrict such AM(R)S use to short, low duty-cycle burst transmissions. An alternative might be to use those channels for any military mobile TACANs that are currently accommodated in 960-977 MHz, thereby freeing those lower channels for AM(R)S.

f) 1164-1215 MHz is heavily used by DME/TACAN, including powerful enroute systems. In addition, while the GNSS in development for that band has been designed to be compatible with that DME/TACAN interference, little margin remains to accommodate additional sources, especially on-board transmitters such as a new aeronautical communications system. As a result, this sub-band should be avoided for AM(R)S.

4.0 960-1215 MHz Band Recommendations

4.1 AM(R)S allocation should be sought for the 960-1024 MHz band.

4.2 Proposed AM(R)S systems should be designed to be highly tolerant of narrowband pulsed emissions (e.g., digital systems employing error-correction coding and messages (or bits) that are long compared to 10 microsecond pulses).

4.3 Due to the structured DME/TACAN ground system environment, proposed AM(R)S systems and aircraft cosite integration issues may benefit from a design with strict front-end filtering of adjacent channel emissions. Frequency hopping or multi-frequency techniques making use of published ground station databases may also prove useful. Appendix A contains additional band characteristics and considerations that may facilitate compatibility.

APPENDIX A

Design of the new communications system (CS) should take account of the incumbent users of the band to maximize its acceptance. From an initial examination, two characteristics of the ICAO standard distance measuring equipment (DME) could provide opportunity for CS implementation.

Characteristic #1: The DME band is assigned on 1 MHz channels, with the interrogation and reply channels separated by 63 MHz. In addition, in the 979-1024 MHz portion of the band all the transmitters are on the ground in fixed locations.

Possible Exploitations:

a. Since the DME are at fixed locations, the DME environment in each part of the new CS service volume is calculable. The CS could be designed to use a pre-selected (based on the published DME database) subset of CS channels depending on geographic location, ensuring compatibility within the service volume without the “hidden terminal” risks inherent in systems that “listen” for clear channels on which to broadcast.

b. Though the airborne portion of the DME system would have a receiver at the ground frequency (i.e., in the 960-1024 MHz band), the airborne transmitter will be above 1042 MHz (ground system freq plus 63 MHz). Once tracking, that on-board DME component (termed the interrogator) would only need to transmit a few times a second, and would know (within a small time window) when to expect a reply. As a result, it is possible the DME interrogation and CS transmissions could be coordinated such that the CS is not transmitting when the DME reply is expected. For example, if the new CS utilizes time division multiple access (TDMA), perhaps the expected DME reply could be scheduled for the end of the guardtime interval so that even if there was step-on from off-board CS transmissions, it was from a CS transmitter that was distant/weak. From testing accomplished during the Global Navigation Satellite System (GNSS) integration studies, the DME signal is relatively robust and tends to "ride" on noise-like signals.

Characteristic #2: The transmitted DME signal is quite narrowband (order of 300 kHz), though the DME receiver bandwidth is closer to 650 kHz to account for slight mistuning.

Possible Exploitation:

a. Current voice communication channels can be accommodated in less than the ICAO standard 8.33 kHz, though with the data requirements it is expected the CS channels would be wider. As a result however, it is possible that relatively narrow communication channels could be fitted between the DME channels to minimize impact. For example, 100 kHz communication channels could be defined in the band 960-1024 MHz (about 640 of them). Given the widespread deployment of DME, it is likely only certain channels could be used in certain areas. In the unlikely situation that all channels are utilized by DME in a given sector, one still might be able to use the xxx.4; xxx.5 and xxx.6 channels without impacting the adjacent xxx.0 and xxx+1.0 DME channels. In areas without large-scale DME presence, more of the defined channels could be used.

[1]In at least one State, next-generation JTIDS/MIDS equipment will be capable of remapping frequencies below 1030 MHz to the sub-band above 1030 MHz. That may offer the opportunity to move, as needed, JTIDS/MIDS signals from below 1030 MHz.