The FAT is Dead: Long Live the FAT

Digital Dividend Spectrum AllocationsThe Frequency Allocation Table is the central pillar of Article 5 of the ITU Radio Regulations. It’s a record of the allocation of one of the five main services[1] and their sub-services[2] to a frequency band.

The three Regional FATs in Article 5 are subsequently managed and modified by World and Regional Radiocommunications Conferences of the one hundred and ninety four ITU member states.   At the national level, local National Regulatory Authorities (NRAs) then adopt the FAT and develop and amend it to fit local conditions.  The national FAT and its series of footnotes is therefore the central policy making and policy development instrument.

But this is the historic state.  Things are changing.   We all recognise that enhanced flexibility adds value to the spectrum.  And we’ve now all grasped the principle of technology and service neutrality.  So what future is there now for a rigid or stove-pipe[3] FAT?  It is consigned to the dustbin of history as progress takes over from order?

The FAT – Made by Regulators

The FAT is a human construct.  It was made by conferences of regulators because it brought order and order was good.  Order meant that compatible services shared and generally this afforded protection to services – numerous studies have shown that whenever incompatible services share a band (even if separated in frequency in sub-bands), problems occur[4].  But steadily, over the years, more and more services have been declared ‘co-primary’ until in the latest band to be re-farmed in Region 1, the 790-862MHz digital dividend band, fixed, broadcasting and mobile have been declared co-primary.  In Region 3, radionavigation, a sub-service of radiodetermination, has also been added.  So where does this leave order?   The FAT is a rigid stove-pipe structure but modern spectrum management demands freedom.  And where will it end?  Will it simply be that all bands will be open to all services in a blended FAT?  Is that what will yield ultimate value?

Principles of Modern Spectrum ManagementInfluence Diagram Covering Key Issues in Modern Spectrum Management

For an answer we need to look at some of the key principles of modern spectrum management.  First we need to be able to assure protection between services such that interference is controlled[5] – this need perseveres.  Second we need to get under-utilised or unutilised spectrum used.  Third we need to re-farm to allow new, more efficient technologies to be adopted.  And fourth we need the freedoms that service and technology neutrality will bring.  At first glance these are all opposing demands.  Looking at the influence diagram (right) does however show a different picture.

In the influence diagram, green lines indicate a positive influence between the entities.  Re-farming by an NRA positively influences getting underutilised or unutilised spectrum used.  Indeed much unused spectrum is caused by the historical rigid FAT[6].  Orange lines suggest a neutral state exemplified by the neutral linkage between re-farming and the degree of protection afforded to licensees.  Just because an NRA re-farms does not mean that the protection is reduced.

Red lines indicate a negative influence.  Demanding service and technology neutrality for all licensees must by definition degrade the degree of protection available.  Allowing high power broadcasting in a band also used by mobile or used over the border by mobile will degrade the protection afforded to the mobile services over that existing if all were using mobile.  Technology and service neutrality requires a blended FAT.  But a stove-pipe FAT with ‘one service, one band’ allocation, affords planned protection.  Service and technology neutrality and protection oppose.  Unless that is, something replaces the stove-pipe FAT.

Development of Licence Constraints

That activity is the modelling of interference and the development of a series of licence constraints including spectrum masks or spectrum usage rights.  Calculation of the constraints must be done per band and per country (or region where sharing is proposed within a country).  It must be done every time a spectrum band is to be released to the market, confirming that it will neither be victim to nor generate undue interference to existing licensees.

Stove-pipes As Containers for Allocated ServicesSo there we have it; the stove-pipe FAT is dead.  But from its demise comes the blended FAT and with that, the development of specific licence constraints which, if met, permit service and technology neutrality.  That neutrality is conditional.  Neutrality can be granted within the scope of the current allocations, allotments and assignments in both the local nation-state and in its neighbours.  The 790-862MHz band can indeed be used for mobile, broadcasting, fixed or indeed radiodetermination but only if a determined set of constraints are met.  It may be that the only way these conditions can be met is to preclude high power broadcasting, replacing it instead with multiplexed low power transmitters.  And it may be that radiodetermination is not in reality permissible.  But the FAT can indeed show allocation of all four services on a co-primary basis.  It’s just that this is subject to conditions.

A Priori Makes Way

So in the future a priori allocation of services to bands will make way for a posteriori development of country specific licence constraints, pushing responsibility from the ITU and its conference structure to the local NRA.  This places a huge burden on the NRA for technical competence and tools but it does meet our modern needs to make sure spectrum maximises its contribution to our economic and social welfare.

The stove-pipe FAT is dead – long live the blended FAT.

Post note

The author acknowledges that some bands have been shared for many years (such as by fixed and satellite) thereby breaking the stove-pipe concept but even then conditions were implemented to assure protection.  Also whilst this article may imply that all bands will go ‘service and technology’ neutral, there will always likely be a need to afford protection to some services in some bands (such as GPS/ Glonass, or Radioastronomy, or SOLAS) in the historic stove-pipe way.  Finally, there is of course significant scope for de facto standards to emerge causing a diminished interest in neutrality in any band.  IMT is a good example in the UHF region.


[1] Mobile, broadcasting, fixed, radiodetermination and space.

[2] Typically structured into sub-services for each service like the mobile example: land mobile, aeronautical mobile and maritime mobile.

[3] ‘Stove-pipe’ describes the way in which each band in the FAT forms a rigid container for one allocated service.

[4] The Ofcom Autonomy project was one such example.  The overview is available at  http://www.atdi.co.uk/PaperDocument/overview(1).pdf  accessed on 5 May 2011.

[5] Section VII of Article 1 of the ITU Radio Regulations usefully defines interference, permissible interference, accepted interference, harmful interference and protection.

[6] The spectrum in the 800MHz band in Region 1 was allocated to mobile and is specifically intended for TETRA even though TETRA was never likely to use this band.  In Europe, the spectrum around 169MHz was allocated to mobile and was intended for ERMES, the paging standard, even though no-one was likely to use paging.

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