Guard Bands Between BFWA Operators In The 28GHz Band

28GHz band BFWA inter-operator guard bands

At the last two Technical Sub Group meetings the issue of guard band requirements has been discussed at some length. Work being carried out within ETSI, CEPT and IEEE has been reviewed as well as work carried out in the UK by industry and work sponsored by the RA. Additionally the group has been the focus for UK contribution to the work of CEPT WG-SE regarding FWA (and therefore BFWA) deployment issues underpinning the draft CEPT Recommendation regarding FWA deployment in the 26GHz band which is expected to form a template for the 28GHz band in the near future.

In its considerations the group has noted the proposals for 3 equal paired 112MHz licences in the band and the fact that this proposal implies inclusion of any inter-operator guard band requirements within these 2*112MHz assignments.

The group has examined the associated issues and has concluded that generally this policy is sound subject to further work on detail needed to ensure that the obligation on operators to co-operate is clear and accountable.

In examining the decision to include guard band requirements within the assigned blocks the following considerations have been taken into account:

	Studies within CEPT and ETSI have shown that the variety of technologies, duplexing and multiple access methods lead to differing requirements for guard band size ranging from zero to at least two equivalent channel widths.
	Different studies conclude differently on the required guard band size.
	Studies recognise that even two equivalent channel widths is not sufficient offer complete adjacent channel protection.
	These studies have also shown that deployment scenarios significantly impact the guard band requirements.
	[Some studies suggest that a single equivalent channel width guard band leads to a negligible and predictable interference impact on a victim cell (around 1-3% of cell area suggested).
	Predictability of interfered area enables operators to plan for this area.]
	The draft ERC Recommendation for FWA in the 26GHz band suggests "that the estimated size of the guard band needed is equal to the greater channel used by the two neighbouring systems;"
	Under certain conditions large guard bands might be unnecessary and lead to wasted spectrum which could otherwise be used under certain conditions.
	Guard bands of two equivalent channel widths represent a significant proportion of the spectrum available for BFWA in the 28GHz band.
	Through limiting the amount of spectrum available, "hard" guard bands would also colour the technology choice for an operator.
	The RA wishes to maximise the spectrum available and used for BFWA services.

However there remain some drawbacks to this approach. These are summarised below:

	It may be difficult for competing operators to co-operate in order to minimise guard band size, interference and deployment constraints on each other.
	An agreement needs to be reached over the acceptable level of potential interference between operators given that complete protection cannot be guaranteed without excessive guard bands.
	The band plan leads to the situation where the centre 2x112MHz assignment has a greater co-operation burden with operators on either side of the assignment. This may lead to limitations on the technology choice for this operator.

Operator co-ordination is cited as an acceptable method of determining the guard band requirements in draft ERC Recommendation covering FWA in the 26GHz band by consideration of the guard band as an "edge band".

In the first instance, care should be exercised when planning use of the outermost channels of an assignment that co-existence issues with the neighbouring frequency assignment are examined. It would seem appropriate that specific licensing conditions and a suitable process are in place to ensure that any operator carries out the necessary co-ordination before deployment in spectrum adjacent to a neighbouring operator.

To enable operators to co-operate and co-ordinate then it will be necessary for the exchange of a minimum set of parameters and characteristics to allow operators to mutually agree co-ordination. This could be as minimal as geographic location of stations along with a "worst case" set of characteristics. More characteristics will allow a greater degree of co-ordination leading to even better use of the guard band regions.

The Technical Sub Group will develop such a list of parameters and characteristics.

Potential operators must understand that the need to protect a neighbouring assignment will lead to some constraint on use of the outermost channels in an assignment and that it is in the interest all concerned that every effort is made to co-operate and deploy in a responsible manner.

¹Draft Recommendation "USE OF THE BAND 24.5-26.5 GHz FOR FIXED WIRELESS ACCESS" See BFWAtg(00)04

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