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International Civil Aviation Organization / ACP-WGF16/WP-11

AERONAUTICAL COMMUNICATIONS PANEL (ACP)

Sixteenth MEETING OF THE WORKING GROUP F

Montreal, Canada 11 – 15December 2006

Agenda Item 7: / Any other business

Developmentof new primay radar technOLOGY

(Presented by the EUROCONTROL Agency)

SUMMARY
Within the context of the ‘Air Traffic Management Strategy for the Years 2000+’, EUROCONTROL is investigating whether new technologies or alternative uses or recent advances in existing technologies could be used to support the provision of surveillance data.
One of these candidate technologies is Multi-Static PSR (also known as Primary Multi-Lateration technique), which was previously employed in a defence type arena. The Eurocontrol Agency sought to investigate further whether recent advances in this technique, or adaptations thereof, could make it suitable for use in civilian applications and, following an open call for tender, THALES Air Defence were awarded a study contract to assess the feasibility of such an approach. Initial indication shows that this alternative surveillance technique could meet the requirements placed upon Primary Surveillance radar. However, the study has identified a significant constraint which could impede further development of this technique - namely the lack of available spectrum for which this approach is dependent.
A executive summary of THALES findings is attached
ACTION
ACP Working Group F is invited
-to note the interest of this new surveillance concept
-to consider the THALES proposal on spectrum allocation(s), in relation with the current debate on “numeric TV dividend”.

Executive Summary on Frequency Allocation Issues

This Executive Summary is prepared by THALES Air Defence for EUROCONTROL in the frame of the Contract N° C06/11267CG relative to the ADT (“Alternative Detection Techniques to Supplement PSR Coverage) study.

This study ([1]) started on the initiative of the EUROCONTROL Surveillance Domain. Indeed, the Surveillance Strategy states that PSR is required during the timeframe of the Strategy = 2020+ until another alternative is available (for non-cooperative targets). Multi-Static PSR (MSPSR) is a potential (cheaper) alternative.

The expected interests for aviation are:

  • an improved detection coverage (in rain thanks to UHF, in any clutter thanks to long integration time, at low altitude and in mountain region thanks to the multiple Transmitters and Receivers configuration…),
  • a more complete (altitude, velocity) and better (thanks to higher data rate) localisation accuracy,
  • a lower cost.

This study deals with the feasibility of a MSPSR Multi-Static PSR system based on a sparse network of low power omni-directional transmitters (Tx) and omni-directional receivers (Rx) interconnected to a Central Unit:

Figure 1: MSPSR Concept (Components)

Figure 2: MSPSR Concept (Principles of Multistatic Detection)

The main principles of this system is that transmitters use different waveforms and that each receiver processes the signal coming from all transmitters after reflection on the target(s).

Receivers process signal on independent channels for each transmitter and extract the target data by “ellipsoid” ([2]) intersection between all transmitters. The “plot” extracted in this way contains 3D information in both position and velocity, this last feature being obtained thanks to multi-perspective Doppler combination.

The system is based on several elementary “cells”, arranged in such a way that they cover the area to be controlled (e.g. Approach/TMA or En-route). An example of both elementary cell and arrangement of cells to control a 20 Nm x 15 Nm area is shown below:

Figure 3: Example of MSPSR elementary cell (left) and 20Nm x 15Nm arrangement (right)

Preliminary assessments show that performance of this system could comply with the requirements for Approach/TMA even on low RCS targets (e.g. UAVs), and also for En-route on targets such as Business Jets and Liners.

An attractive property of this system is that it requires only a very low transmit power (typically 50W per transmitter) and thus it has a limited impact onto the environment.

This can be obtained thanks to recent advances in the technological domains of low frequency bands such as UHF (300 MHz – 1 GHz) , and more precisely thanks to the possibility to apply advanced techniques like real time omnidirectional Digital Beam Forming and Multi-Channel Coherent Range * Doppler processing. This makes these “software radar” techniques now affordable for low frequencies.

Indeed, the complexity of such systems directly depends on the number of receiver antenna elements, which, for the same radar budget, is proportional to F2 (where F is the carrier Radio Frequency). For instance, UHF compared to S-Band requires about 50 times less elements.

UHF also offers advantages compared to higher bands (e.g. L to X) for its specific propagation properties:

  • Reduced atmospheric losses and rain clutter insensitivity,
  • Low altitude detection capability by diffraction effect, as illustrated below for two radars designed with the same operational constraints (detection range and data rate),

Figure 4: Low altitude detection compared capabilities (UHF on the left, X-band on the right)

The early works already conducted in the frame of the “ADT” study give a strong feeling that an alternative detection technique to supplement PSR coverage is feasible in UHF band and has numerous advantages such as:

  • Low transmit power,
  • Redundancy, continuous service (e.g. during maintenance),
  • Robustness (no rotating part),
  • Performance:
  • Detection (multistatic RCS),
  • Localisation (3D capability),
  • Velocity vector from multiple Doppler estimates,
  • High Data Rate (e.g. 100ms),
  • Flexible processing (e.g. integration time adaptable to target range and/or manoeuvre…),
  • Progressive deployment:
  • Additional Rx for improved performance with no impact on transmission,
  • Additional Rx+Tx for coverage extension (e.g. «corridors»),
  • Adaptation to environment:
  • Rx and Tx sitting in an optimal way vs terrain, man-made obstacles…
  • Possible use of existing infrastructures (e.g. masts…),
  • Rx/Tx may be moved afterwards (reconfigurable architecture).

Its main growth potential being, in addition:

  • Non Cooperative Target Recognition (using Doppler signatures and/or ISAR effects),
  • Detection and tracking of (mobile) surface targets,
  • Anti-intrusion,
  • Transmitted signal available for radiolocation (e.g. by on-board receivers)…

Regarding the bandwidth requirement, a preliminary analysis shows that transmission could be made with 1 MHz bandwidths for each transmitter. In order to avoid interferences, each transmitter central frequency would be separated from another one by about 2 MHz, as illustrated below:

Figure 5: A possible MSPSR transmission frequency scheme

On the basis of the elementary cell presented above, and for transmitters and receivers supposed installed on masts 20m above the ground, the number of transmitters which can be “seen” by each receiver is about 20. For taking in account of the terrain and propagation, one should take a margin and consider rather a maximum number of 25 transmitters.

This implies that a 50 MHz band would be required for the system.

The ITU service which corresponds to this application is “Aeronautical Radionavigation”, for which frequency slots are currently allocated, as it is illustrated on the next diagram, covering only UHF, L and S-Band:

Figure 6: Current Frequency allocations (UHF, L and S Bands only)

The only UHF “slot” which could correspond is the 328.6 MHz to 335.4 MHz band, but it is already used by ILS Glide Slope. The other 960 MHz to 1213 MHz band is used by DME, and is too high in frequency for taking benefits of the advantages which are expected (see before).

However, thanks to the Digital Video Broadcasting “Spectrum Dividend” regarding frequencies which could be freed in the UHF band allocated to the Broadcasting service (see purple slots in Figure 6), there is certainly a possibility to negotiate such a 50 MHz (e.g. 470 MHz to 510 MHz) for new applications such as MSPSR.

Table 1: List of acronyms

[1] whose results are foreseen to be presented at the next EUROCONTROL Surveillance team in May 2007.

[2] Ellipsoids results from the geometrical properties between transmitter and receiver, as usually in a bistactic system. In practice ellipsoids are truncated thanks to the receiver antenna directivity, which drastically reduces the number of combinations and the ghosting risk.