Inter-operator Co-existence and Co-ordination Guidelines for BFWA Systems Operating in the Band 27.5 - 29.5GHz

1

Introduction

Licences for Broadband Fixed Wireless Access (BFWA) in the 28GHz band cover operation in three paired-spectrum blocks as indicated in Section 3. Additionally these three paired-blocks have been assigned in a number of geographical regions throughout the UK. The close location of co-frequency and adjacent frequency systems requires that certain measures are required in order to enable substantially interference free operation for the licensees.

The Radiocommunications Agency (the Agency) is not anticipating playing a major role in the co-ordination process. However, to facilitate the minimum of difficulties, the guidelines detailed in this document are set out to provide a basis for co-ordination. If any cases of difficulty arise, which are ultimately referred back to the Agency, the guidelines will be used as a basis to examine whether adequate steps have been taken to avoid problems. Where possible, these guidelines are based upon work carried out not only by the Agency but also by other international regulatory and standardisation bodies involved in this field.

It may not be possible to provide an environment that is completely interference free, where co-existence without some degree of constraint does not arise. Therefore, operators are encouraged to both take into account the range of possibilities set out in this document and to take their own steps to examine further enhancements that might take advantage of their particular deployment situations.

A degree of co-operation between operators would be beneficial to make the most of specific radio equipment parameters or deployment scenarios that may lead to "closer" co-existence.

These guidelines have been developed in consultation with BFWA industry partners through the Agency consultation groups and should be enhanced as operational experience is gathered.

2

Scope

These guidelines cover two scenarios for inter-operator co-existence and co-ordination:

• Scenario 1 - Operators using the same frequency blocks in neighbouring geographical regions.
• Scenario 2 - Operators in the same geographical region using adjacent frequency blocks.

The guidelines cannot anticipate every deployment situation. For scenario 1, maximum levels of expected interference are detailed as a trigger for "inter-operator" action. For scenario 2, reference is made to analysis methods and results from other bodies. Specifically, reference is made to ideas developed, or under development, within CEPT, ETSI and IEEE as well as work carried out directly by the Agency.

3

Frequency band and BFWA spectrum packages

3.1

Frequency band

The 27.5GHz to 29.5GHz band is shared on a co-primary basis between the Fixed Service (FS), the Fixed Satellite Service (FSS) [Earth to space] and the Mobile Service (MS). The BFWA spectrum has been planned in accordance with the CEPT T/R 13-02 recommended channel plan. Two frequency blocks of 392MHz are available and are given by 28.0525GHz to 28.4445GHz paired with 29.0605GHz to 29.4525GHz. The layout of frequency band, showing the BFWA spectrum, is given in Figure 1.

Notes:
1) The use of the band 29.1 GHz to 29.5 GHz [Earth to space] by the fixed satellite service is limited to geostationary satellite systems and feeder links to non geostationary satellite systems in the mobile satellite service.
2) Currently no planned use with the UK.

Figure 1 - 27.5GHz to 29.5GHz frequency band

The allocation of parts of the band in Europe to either the Fixed Service or Fixed Satellite Service is detailed in ERC Decision ERC/DEC(00)09.

3.2

BFWA spectrum packages

BFWA licences cover 11 English regions, Scotland, Wales and Northern Ireland with up to three licensees per region. The Agency has applied 28MHz guard bands between the three licensed frequency blocks in a region. The resulting three spectrum packages are detailed here and shown in Figure 2.

• Package 1 28.0525 - 28.1645GHz (BFWA 1) paired with 29.0605 - 29.1725GHz (BFWA 1')
• Package 2 28.1925 - 28.3045GHz (BFWA 2) paired with 29.2005 - 29.3125GHz (BFWA 2')
• Package 3 28.3325 - 28.4445GHz (BFWA 3) paired with 29.3405 - 29.4525GHz (BFWA 3')

Figure 2 - BFWA spectrum packages

4

The Role of the Agency

4.1

General

The Agency will undertake to support the BFWA licence holders within the band 27.5GHz to 29.5GHz by:

• providing advice and guidance on best practices and co-ordination processes to facilitate inter-operator co-existence;
• protecting assignments by the registration of BFWA deployments through the UK national and international ITU procedures;
• registering deployments on the Radiocommunications Agency Unified Licensing Executive System (RULES) database;
• acting as arbitrator in co-existence issues if co-operation between operators fails; and
• protecting the assignments and acting on behalf of BFWA operators in addressing both national and inter-national co-ordination and policy issues.
  

4.2

Arbitration

The Agency, through the guidelines set out in this document, encourages operators to resolve co-existence difficulties themselves. However, if either party encounters difficulties, bi-lateral negotiation may, at any time, be requested by the Agency to resolve the issue.

Evidence of application of the guidelines in this document will be viewed by the Agency as an indication of the will of operators to resolve any issues.

4.3

Inter-operator co-operation

The BFWA Licence states:

"The Radio Equipment shall be operated in accordance with any co-ordination procedure notified to the Licensee in writing by the Radiocommunications Agency to ensure that operation does not cause undue interference to equipment in adjacent areas or frequency bands."

Therefore the BFWA operators have a duty of care to the operators in adjacent areas or frequency blocks, not to cause harmful interference.

Guidelines and measures are detailed to help minimise inter-operator co-existence difficulties and their consequent effect on deployment of BFWA. However, these guidelines and measures cannot cope with every variation in equipment and deployment characteristic but are put forward as a baseline having made assumptions about anticipated typical parameters.

Therefore, it is entirely possible that more detailed co-ordination between neighbouring operators (by area or frequency block) can reduce the impact of co-existence difficulties. To carry this out it may be necessary for operators to co-operate to some degree including exchanging technical information relevant to resolving co-existence difficulties.

At a minimum this information should be sufficient to enable any neighbouring operator to assess the impact of any potentially interfering deployment on his ability to serve his customers. Account should be taken also of customer base expansion.

In cases of difficulty, evidence of negotiation will be requested by the Agency.

5

Technical basis for co-existence limits

The scenario 1 co-ordination trigger and "acceptable" co-existence limit is based on an agreed degradation of the receiver thermal noise floor (interference to noise (I/N) ratio) and consequent impact on link budget. Scenario 2 co-existence guidelines are based upon frequency separation (and spatial separation if appropriate) justified by statistical analysis of the likelihood of interference degrading link performance below a given level.

6

Frequency band planning

It is important to note that the guidelines detailed in this document make no assumption about FDD/TDD or harmonisation of the frequency plan.

The CEPT/ERC Recommendation on 27.5-29.5GHz band [1] recommends the following harmonised arrangement:

"that in the case of deployment of FDD systems the upper subband should be used for the transmission from the terminals to the central station (hub) and the lower for the transmission from the central station to the terminals;"

Therefore the following is recommended for FDD systems only:

• The lower sub-band 28.0525 - 28.4445GHz is to be used for central station to terminal station transmission;
• The upper sub-band 29.0605 - 29.4525GHz is to be used for terminal station to central station transmission.

7

Maximum recommended EIRP levels

In order to ensure the adequacy of the co-existence guidelines the following maximum EIRP levels are strongly recommended:

An Automatic Transmitter Power Control (ATPC) range of at least 15dB is assumed for all P-MP terminal station transmitters and for all MP-MP and P-P transmitters.

Any major departures from these recommended maximum EIRP values would require re-evaluation of the inter-operator guidelines.

8

Methods for Inter-operator co-existence and co-ordination

There are two scenarios to consider:

• Scenario 1 - Operators using the same frequency blocks in neighbouring geographical regions.
• Scenario 2 - Operators in the same geographical region using adjacent frequency blocks.

The following methods proposed apply to all types of Fixed Service system deployed in the BFWA frequency ranges identified in Section 3.2 irrespective of network architecture. However, certain assumptions have been made in developing the guidelines so care is required when considering systems that have system parameters/characteristics that depart substantially from those assumed (see Annex B).

8.1

Scenario 1

For each station deployed within the licensed area, the operator shall carry out a calculation of the PFD level at or beyond the licensed area boundary which shall be compared to the boundary PFD trigger level.

If the boundary PFD trigger level is exceeded there are two routes to resolve this:

1. The "preferred route" is negotiation between operators in adjacent regions to investigate whether the exceeded PFD trigger level could be acceptable. For example it may be possible that the threshold evaluation location can be moved by negotiation.
2. The "secondary route" is to take the necessary steps to reduce the PFD to be less than or equal to the PFD trigger level.

The overall process is illustrated in the flow diagram at Annex A.

The boundary PFD trigger level = -102.5 dBW/MHz/m².

The derivation of this figure is given in Annex B. Additionally there is a report [2] that provides a full examination of these calculations that is available from the Agency website.

When stations are deployed along or near a coastline, and the coastline of another licensed area is less than 60km away from the deployed station, then the remote coastline should also be considered as part of the licence area boundary for the purposes of checking the boundary PFD level.

8.1.1

Calculating the boundary PFD

In carrying out the calculation of the boundary PFD resulting from the deployment of any transmitting station (i.e. central, terminal, repeater or in-band P-P link) the operator should advantageously make use of the appropriate propagation tools and terrain as opposed to a worst case free space loss calculation.

It is recommended that the operator employs methods consistent with ITU-R P.452-9 [3]. To assess the excess loss due to time varying effects a figure for percentage time equal to 50% is recommended.

Sample calculations are given in Annex C.

8.1.2

Adequacy of the PFD trigger level

The value has been set having considered a balance between minimising the constraints on deployment against the probability of unacceptable interference in a neighbouring area. Meeting the PFD trigger level does not in itself guarantee interference free operation in the neighbouring area. However, statistical modelling [2] has demonstrated that when allowance is made for the limited line of sight between interferer and victim stations and the realistic deployment of antennas that application of this limit will ensure substantially interference free co-existence.

Annex B lists the typical parameters used for deriving the trigger value and testing its adequacy in multiple interferer scenarios.

8.2

Scenario 2

Referencing work that considers this interference scenario, it is generally concluded that some frequency separation between operator deployments in adjacent frequency blocks is required for reasonably interference free operation and unco-ordinated deployment. (Ref: [2], [4], [5] and [6]) Additionally, when considering the deployment of P-P systems it is recommended [6] that angular discrimination will require consideration possibly in conjunction with higher performance antennas.

8.2.1

Guard band/spatial separation guidelines

Between FDD system assignments operating in a harmonised sub-band plan detailed in Section 6 and employing channelisation schemes up to 28MHz, one guard band equal to 28MHz is recommended ([1] and [4]).

Systems that are not operating in accordance with any harmonised sub-band plan should ensure adequate spatial separation between central stations when deploying P-MP systems. CEPT [1] recommends a minimum of 500m in conjunction with one guard band. In circumstances where spatial separation is not possible, a larger guard band may be required and operators should co-operate to fairly apportion the increased guard band requirement.

For network architectures that do not employ central stations, guidance suggests again that a single channel guard band is adequate for acceptable performance [5].

It is recognised that further study of these issues is required for the consideration of mixed system type deployments.

8.2.2

Guard band adequacy

The guidelines detailed in 8.2.1 above are based on the conclusions of ERC Report 99 [4]. The executive summary of that report highlights the limitations of the work which has not considered systems employing modulation schemes more complex than 4 level, channel spacings other than 28MHz or the sensitivity of the conclusions to radio system performance.

However, one 28MHz single channel guard band between licensed frequency blocks is included in the BFWA assignment plan detailed in Section 3. Therefore, as suggested by report [2], there should be sufficient protection inherent in the assignment plan, under most circumstances detailed above, to minimise the inter-operator co-ordination and co-operation required.

However, operators in the same area must accept that no reasonable guard band can guarantee complete interference free operation. There will always be a likelihood that a small part of their coverage area will be subject to an unacceptable level of interference. As a benchmark an area of around 1% (so-called interfered area [4] or %KO [6]) is reasonable and has been assumed in verifying guard band widths in these references. Operators should therefore co-operate to some extent to minimise the impact on their deployments.

Testing the adequacy of a particular guard band size is complicated and dependent upon many specific operational and deployment characteristics. The references cited above detail a variety of analysis methods which may be used to verify the adequacy of any specific guard band size.

9

References

-111 dBW (QPSK)
-125.5 dBW/MHz

Base station to base station