• As part of the comprehensive spending review in 2010, the Government announced a target of 500 MHz of public sector spectrum below 5 GHz to be released by 2020. This was updated in the 2016 Budgetannouncement to a new government commitment that 750MHz of valuable public sector spectrum in bands under 10GHz will be made available by 2022, of which 500MHz will be made available by 2020.

    Within this initiative, the part of the spectrum (2.7-2.9 GHz) used by aviation stakeholders for civil and military primary surveillance radars (PSR) was identified as a potential candidate to contribute to the overall release. Therefore, the CAA, at the request of the Department for Transport, undertook a research programme to examine the feasibility of releasing around 100 MHz of spectrum in the lower part of 2.7-2.9 GHz.

    Background

    There were two separate strands to the feasibility studies. The first, on PSR planning, was seeking to confirm viability of spectrum release through band re-farming. The aim was to develop new frequency planning criteria for this band by engaging with the main radar suppliers in the UK to carry out the necessary evidence-based engineering work. The first step was to address the technical impact of planning PSRs closer in frequency and then to translate the technical impact into an operational impact by identifying operationally acceptable emission limits and levels of interference for PSR in a multi-radar environment. The intent was to test a frequency allocation plan that has an overall occupation of about 100 MHz if applied across the entire UK radar population.

    The second strand is on emerging technologies. We sought industry input on evidence of feasibility of three emerging independent non-cooperative surveillance technologies, such as multi-static primary surveillance radar (MSPSR), including Passive Coherent Location system (PCL) and netted low power radar (LPR) operating at other, less congested, frequencies. Several trials were undertaken at airports.

    During the programme, the MoD awarded its Project Marshall contract, which included the implementation of new PSR at MoD aerodromes using commercial-off-the-shelf products. These need to be accommodated within the 2.7-2.9 GHz frequency plan.

    Activity was also undertaken internationally to seek a change to the way in which the 2.7-2.9 GHz band was allocated by the International Telecommunications Union. However, the most recent World Radiocommunications Conference (November 2015), which provides the highest level of spectrum management, concluded that there would be no change in the current status of the 2.7-2.9GHz band.

    Outcome of the programme

    he PSR planning and spectrum sharing programme developed three options to contribute towards the Public Sector Spectrum Release target. We describe them simply as shift, squash and share. Shift is the possibility of using alternative bands for radar. Squash is the possibility to improve the efficiency in the use of spectrum. Share is the option to share the radar band with other users either through geographical, frequency or temporal separation.

    Radar Planning Findings (shift and squash)

    We can squash

    The programme has delivered a frequency probe tool with the ability to predict the degradation in radar performance when the radar is the victim of interference from one or more adjacent radars. By setting an acceptable threshold for the predicted interference, radar frequencies can be re-planned to make more efficient use of the radar spectrum.

    • Based on our feasibility studies, the 100 MHz of spectrum previously identified for ‘release’ remains a valid, although ambitious target. It has not been determined the most cost efficient way to realise this target, the likely timings and whether it is ultimately seen as affordable. There is a fixed cost element to the re-planning of all radars that is predicted to not exceed £9M (based on costing from the previous radar remediation programme). The most cost efficient way to realise the target is likely to be through a combination of re-planning and targeted use of new technology
    • An acceptable threshold for interference from adjacent radar has been determined that, in turn, has led to revised re-planning criteria.

    We can safely accommodate the MoD Marshall programme – the frequency probe tool has shown that the implementation of new PSR at MoD aerodromes can be met through re-planning of current frequency assignments.

    With remediation/improvements in performance, or consolidation of existing radar, we could squash further

    One option for shift is close to delivery-
    New ‘X-band’ radars are being installed at several airports, primarily operating as an “infill” radar, as a means of mitigating wind turbine impacts on primary radar. As these radars are being run in parallel with existing S-Band radars, there is an opportunity to gather in-service evidence of suitability for more general primary surveillance radar use, particularly around the performance of the X-band radar in precipitation and fog.

    Other options for shift are emerging -
    Manufacturers have indicated that civil MSPSR is likely to become a commercial offering in UK over the next 3-5 years. This has the potential to release spectrum in both the S-band and the L-band.

    Potential future work

    Further studies will be required into the planning of radar when the spectrum use and characteristics of the devices that are being planned to be introduced into the band are known.

    There is a natural upgrade path from enhanced planning to the planning for sharing. Enhanced planning is based on the frequency probe tool (see above). The frequency probe tool could be extended to enable the prediction of the degradation in radar performance when the radar is subject to interference from one or more adjacent ‘other’ systems (and vice-versa). This would enable planning for sharing.

    Developments in waveform technology, such as reduced bandwidth signals and low probability of interference, have the potential to leverage the freeing up of parts of the L and S-band spectrum in the medium term through further squashing; it may also be possible to reduce the number of radars, while retaining the right level of coverage. However, industry is not currently incentivised towards either of these approaches, for example because they do not pay for the use of S-Band spectrum. The level of demand in the civil sector for both the refinement of radar technology and the consolidation of radar provision could increase if incentives were acting upon industry to use spectrum more efficiently. Therefore there is a need to determine the appropriate balance of further remediation of existing radar against incentivising industry to consolidate radar assets and/or invest in new technology.

    There is a national strategic and policy aspect to consider – for example at present PSR are located on or close to each aerodrome, which will fund the capital and operational expenditure of the radar. It may be possible to consolidate radar without compromising coverage but potentially may result in a monopoly surveillance service provider and/or equipment manufacturer. Equally the system(s) that will share the band may have a significant bearing on the type of radar remediation required; this is also likely to have an effect on the cost effectiveness of sharing in this band. The MoD’s use of the band needs to be taken into account and any impact on its capability thoroughly assessed. There is also the international harmonisation aspect to consider, as although there is presently little support for allocating this spectrum for other uses, the risks of making any national allocation in the near term should be considered against the potential for longer term global harmonisation.

    Conclusions and recommendations

    The research has shown that the 2.7-2.9 GHz spectrum used by aviation stakeholders for civil and military PSR would be a viable option to contribute to the overall public sector spectrum release programme.

    • The release may be realised through a combination of shift, squash and share. Shift through use of alternative bands for radar; squash through improvements to the spectral efficiency of radar without detrimental impact to the output; share is the option to share the radar band with other users, either through geographical, frequency or temporal separation.
    • Although the basic principles of PSR remain the same, there is new technology under development that could potentially result in a step change in the efficient use of spectrum, should the systems become operational. However, with a radar having an operational lifespan of 15-20 years, there may need to be some form of incentives on industry to drive through change.
    • There is presently little support internationally for changing the way in which the 2.7-2.9 GHz band is allocated by the International Telecommunications Union. It is recommended that support is sought to keep this on the agenda of the World Radio Conference and to report the outcome of current and future studies with the aim of securing a globally harmonised allocation.