20^th March 2001, RAL.

Chair: Dr M.J.Willis RAL

Present - See Annex 1.

Cyprien de Cosson - ATDI, Lloyd Lukama - Keble College Oxford, Richard Germon - Nottingham Trent University, Dr Salous - UMIST, Prof. Peter Watson - University of Bath, Brian Mason - One2One, Dave McCole RA.

1. Introductions & apologies for absence

The meeting commenced with a short introduction to the sub group and the purpose of this meeting. Participants described their name and affiliation.

Presentations were made by Prof. Kiddle, on the RRAC, Dr Craig on the Mobile and Terrestrial Task Group, by Mr Eden on the Task Group on Factors Affecting Propagation above 13 GHz and by Mr Nixon on the Broadband Wireless Technical Group.

Mr Hewitt asked Prof. Kiddle what was meant by "Strategic" research. Prof Kiddle replied that there were 3 areas of strategic research requirements, The Short Term, where results were required now, the Medium Term where results would be needed in the next few years and the Long Term where output may be needed in 5 years. Prof. Kiddle emphasised that this covered work where the prime strategy was the efficient utilisation of spectrum and as such, was not limited solely to propagation.

The draft terms of reference and aims were introduced. Some immediate comments were made:

Mr Eden proposed that the frequency range should extend from 2 GHz.

Dr Craig noted that Optical technologies should also be considered.

It was decided to remove the 15km reference distance for services and to replace the reference to interference distance with Inter-operator and Inter Service Interference.

The meeting moved on to more detailed presentations from participants on their interests in BFWA.

Mr Nixon noted that his interests as a regulator were required to be technology neutral where possible. Particular issues were Adjacent Spectrum compatibility and the automatic frequency allocation schemes proposed by TDD operators where the system searches for a clear spectrum with the intention of causing minimal interference to existing users.

Transfinite systems produce the Visualise simulation tool and undertake studies for clients. A recent study of the effect of BFWA at 42.5-43.5 GHz on the Radio Astronomy service was briefly introduced. The key issues relevant to this group that arose from this study are that:

1) Existing models such as ITU-R P.452 do not provide any guidance on the simultaneous occurrence of propagation phenomena over an area. This makes realistic determination of interference difficult, for example could rain be occurring in one area while ducting enhancement is occurring in another, both conceivably leading to interference to a Radio Astronomy facility.

2) There is a very significant difference between taking worst case antenna masks compared to more realistic patterns when considering the interference from a BFWA terminal. It is not efficient to consider that every terminal is the worst case.

3) There is a significant difference between single entry interference and aggregate interference in the case of high-density systems such as BFWA.

The slides from this presentation are attached.

Dr Craig outlined the work of the RCRU in the CRABS and EMBRACE programmes. The new ITU-R recommendation on broadband fixed wireless access systems (ITU-R P.1410) originated from propagation work done under the CRABS programme. Suggested areas for future work were:

• Architectures - cell versus mesh.
• Sharing issues - Heterogeneous networks, Inter- and intra-franchise interference/co-ordination, FDMA/TDMA/CDMA sharing, Backbone fixed link sharing.
• Availability and performance enhancement - Diversity and network quality of service issues.
• Planning tools - Optimisation (coverage, financial, spectrum), Better (inexpensive) databases.

Slides from the presentation are attached.

Dr Gibbins discussed his recent work on sharing studies, in particular the effect of large numbers of HDFS terminals on other spectrum users. A co-ordination procedure based on aggregated radiated power had been developed, together with a model that estimates the Equivalent EIRP of an HDFS system. It was unclear how to treat the contention channels of TDMA systems.

Hughes Networks is a manufacturer of wireless products for HDFS operators. This includes equipment for 3.5 GHz through 26 GHz. Two web addresses were put forward:

These pages are best viewed with Internet Explorer and currently do not display properly with Netscape.

A specific issue is the sharing of the 28 GHz band between the Fixed Service and the Fixed Satellite Service. The ERO proposal splits the band into 3, one each FS/FSS and one shared. The main question is over interference from off-axis radiation from the FSS earth terminal into the HDFS networks.

UMIST are able to make wideband channel measurements over a 90 MHz bandwidth. Their equipment is being upgraded to 300 MHz. The sampling rate is 250 samples/second.

Topics of interest are:

The temporal variation of a channel

Whether multipath is an issue at 28 GHz with narrow antennas

Frequency scaling and time scaling of channel characteristics

Norweb telecom have 4 28 GHz licenses and are currently testing systems ready for a roll out of a 28 GHz BFWA service. They have noted a large variation in the type of equipment available from operators.

Their problems are that currently available equipment is:

DERA have a wideband channel sounder with 120 MHz bandwidth, 76 dB dynamic range and operating at 1.7-2.7 GHz, 30 GHz and 60 GHz. They are also working on wavefront correction techniques in conjunction with St Andrews University.

Issues for broadband high speed links are:

Coherency Bandwidth

Coherency Time

Spatial Coherency

Channel non-linearity

Barry Lewis - Ensemble Communications

Ensemble (www.ensemblecom.com) are a manufacturer of P-MP BFWA equipment for 24-30 GHz. Their system uses TDD and adaptive QAM (4-64 levels). They are concerned about mis-interpretation and incomplete assessment of spectral efficiency leading to artificial technology blocks being imposed by regulators.

Questions are:

website: http://www2.ee.port.ac.uk/~uwavewww

The University of Portsmouth have a channel sounder that can be used to characterise BFWA channels. They also have 6 years data from a network of rainguages that have demonstrated the temporal evolution of rain cells. Future work should include defining what measurement time resolution is required and the development of a model for raincell evolution.

The University of Essex has been studying the effects of rain sleet and the melting layer on microwave links. Sleet and melting snow can cause severe attenuation though traditional rainguage measurements do not predict this. More work needs to be done in this area, especially at higher frequencies. Modelling of sleet attenuation is ongoing. The attenuation and interference effects of melting particles are still not well understood.

Much of this item had already been covered under agenda item 2. Peter Vogan of NORWEB had already identified some issues to do with rolling out a service but much more work was required in this area. In particular, the RA have produced guidelines for planning and co-ordination but these have not yet been tested in practice. The meeting considered that Norweb’s experiences in rolling out their service would be invaluable. Prof. Vilar inquired whether it would be possible to instrument NORWEB test links.

There was a clear feeling expressed by many of the operators present that they would like to see much more data. Mr Hewitt urgently needed more raw data from measurements at BFWA frequencies for testing models.

Mr Eden outlined the work that RA were currently sponsoring in this area:

It was agreed that a revised set of terms be produced and circulated with the minutes of the meeting.

The key themes outlined in the agenda were accepted with the addition of:

• The implications of impairments on system design and performance
• Correlation
• Interference and Sharing
• Antennas
• Mitigation

In a round table discussion the following topics and work areas were identified:

None

There was general support for the continuation of the group, though members were not sure of the form the group should take. Possibilities are as a subgroup reporting to the mobile and terrestrial task group or as a full task group, through a general rearrangement of the two existing task groups. After some discussions with the Task group chairmen it was decided to wait until the group had reported back to the task groups before planning future activities.

Email from Brian Mason - One2One

This subgroup consists of interested members of the Radiocommunications Agency (RA) Task Groups on Mobile and Terrestrial Propagation and Fixed Links Propagation together with the Broadband Fixed Wireless Access Technical Group.

It is intended that this new group concentrate on strategic research applicable to broadband fixed wireless access (BFWA) systems operating at frequencies above 2 GHz.

Fixed wireless access systems give customers an alternative delivery mechanism to wired systems. They differ from broadcasting services as each user is individually addressable and the links are bi-directional. The UK has pioneered BFWA systems. Their anticipated popularity has led to large allocations of bandwidth being made available in the microwave region.

The radiowave propagation characteristics of the new allocations are less well known than at lower frequencies, especially with regard to frequency re-use, sharing and the effects of clutter. New broadband digital services are significantly different from current systems in their channel requirements and in their tolerance to propagation impairments such as fading, multipath and interference. It is clear from discussions in the technical groups within the RA that much uncertainty still exists in the use and value of this spectrum.

The principle aims of the group will be to identify the requirements for efficient spectrum engineering. The group will feed back to the task group on what strategic research should be done. The task group will then forward the proposals to the Radio Research Advisory Committee. Areas under consideration are:

• Propagation Models
• Radio System Planning and Optimisation Tools
• Spectrum Management Tools
• Spectrum Efficiency Optimisation
• New Measurements
• The implications of impairments on system design and performance
• Correlation of propagation phenomena over time and space
• Interference and Sharing
• Antennas & Antenna Masks, Smart Antennas.
• Mitigation

It is also important to highlight co-ordination issues. These may arise from spectrum sharing between services (e.g. Fixed and Satellite) and intra-service issues and compatibility (e.g. FDD and TDD in adjacent areas). For example, current co-ordination criteria are often very conservative, particularly the protection ratios required for sharing at the boundaries between operators and services. Large gains in spectrum efficiency may be realised by more quantitatively based planning. An interference-limited system could be more efficient than a noise limited one if interference mitigation techniques are given similar weight to measures designed to overcome other propagation impairments.

It is important to recognise that the scope of the research funding advised on by the Radio Research Advisory Committee (RRAC) is for strategic radio research that will benefit the UK economy, not just the RA.

It is believed that this activity is timely as a result of the recent 28 GHz auction new BFWA services are about to be deployed.