Audit of Land Mobile Radio Use in VHF Low Band in the London Area

CONTENTS

INTRODUCTION

Background

Audit of Mobile Radio Bands in London

0.1 In July 1992 a review was commissioned aimed at examining current use of the radio frequency spectrum from 28-470 MHz and making recommendations in the light of developments.

0.2 The Report of the Review Committee was published in March 1994 (Report of the Radio Spectrum Review Committee Stage 3: 28-470 MHz; ISBN 185569 172 8). A response to the Report was published in April 1995 (ISBN 1 85569 172 8). Copies of the Report and the Response are available from:

Library & Information Service Radiocommunications Agency
Wyndham House
189 Marsh Wall
LONDON
E14 9SX

0.3 One of the recommendations of the Review Committee was that "The existing mobile radio allocations in London should be the subject of a detailed "spectrum audit" to establish whether they are adequate to cope with current demands".

0.4 The Radiocommunications Agency is responding to this recommendation by carrying out audits of the land mobile radio bands on a band by band basis. Reports have been completed on VHF High Band, VHF Mid Band, UHF 2, and UHF 1 :

"Survey of Land Mobile Radio use in VHF High Band in London" (ISBN 185569 1981) published in March 1995;

"Audit of Land Mobile Radio use in VHF Mid Band in the London area" (ISBN 185569 2333) published in September 1996;

"Audit of Land Mobile Radio use in UHF 2 Band in the London area" (ISBN 185569 2694) published in March 1998;

"Audit of Land Mobile Radio use in the UHF 1 Band in the London area" published in December 1998.

0.5 This Report covers the audit of VHF Low Band and provides details of land mobile radio services operating on VHF Low Band frequencies (68.08125 - 87.49375 MHz) and channel utilisation data gathered by the Agency's Mobile Monitoring Group.

0.6 The final audit in the series will cover Sub Bands I and 2 of Band III.

Objectives

0.7 The objectives of the audit were to:

(a) establish the accuracy of the Agency's licensing data, in particular data relating to the technical characteristics of Low Band radio services, numbers of mobiles in use, and location of services;

(b) monitor radio traffic on Low Band channels so as to establish current loadings;

(c) analyse the data obtained from (a) and (b) above in order to draw conclusions on the current loading of Low Band channels in the London area.

Methodology

Licensing Data Check

0.8 The Agency contacted all LowBand licensees operating radio services from sites located within a radius of 30 kilometres from Central London (NOR: TQ 300 800). They were asked to complete a questionnaire (copy at Annex A) and to confirm that the details recorded on their licence schedule(s) were correct.

0.9 Licensees who did not reply were contacted by staff from the Agency's Local Office. The Local Office staff assisted these licensees in the completion of the questionnaire and verification of the schedule details.

0.10 Questionnaires returned to the Agency undelivered were passed to the Local Office so that an attempt could be made to trace the licensee. Appropriate action was taken where services had ceased to operate.

0.11 In order that a degree of confidence might be given to the findings the Local Office made a random sample check of some of the replies received. This involved a visit to the licensee and examination of the radio system.

0.12 The Agency's Mobile Monitoring Group at Baldock obtained radio traffic data, including details of the busy period for each base transmit frequency and each mobile transmit frequency. Information was gathered through the installation of 7 unattended monitoring systems (UMS), located around Greater London. Details of the methodology employed are set out in Section 3 of this Report.

0.13 An analysis of overall channel loadings, based on the full range of channels surveyed, is at Section 4 of this Report; together with a sample of individual channel analyses. A full individual analysis for each of the 373 channels in Low Band is contained in Part 2 of this Report; together with information on the services which operate on these channels.

0.14 The Agency would welcome any views or comments on the contents of this Report. Please send your comments to:

Ray Wilson
Radiocommunications Agency
Private Business Systems Unit
Wyndham House
189 Marsh Wall
LONDON E14 9SX

Tel: 01712110253
Fax: 01712110252

E-Mail: ray.wilson@ra.gsi.gov.uk

SECTION 1

SUMMARY

Number of Services

1.1 The audit established that there were 794 radio services operating on Low Band channels in the London area (an average of 2.1 services per channel). It should be noted that these figures exclude the transient services on the Short Term Hire, Parking & Demonstration, Road Construction, and UK General channels.

The average number of services per channel (excluding the transient services referred to in pare 1.1 above) for the various channel categories in Low Band is as follows:

Channel Occupancy

1.3 Monitoring of the 373 Low Band channels indicated that 23.9% achieved a peak occupancy level of between 0.5 and 1I Erlang.

1.4 The rates of occupancy varied according to the types of radio service operating on the channels. For each of the channel categories covered by the audit the percentage of channels in the 0.5 to 1 Erlang range was as follows:

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SECTION 2

COMPOSITION OF VHF LOW BAND

Description

2.1 Private Business Radio (PBR) and Common Base Station (CBS) use of VHF Low Band is contained within the range 68.08125 - 87.49375 MHz (band edges) providing a total of 373 channels.

2.2 There are 339 dual and 34 single frequency channels in Low Band. These use 12.5 kHz channel spacing and are designated for use by PBR and CBS services as shown in the Table below.

National Channel Users

2.3 Low Band users in this category are either:

a) licensees such as the Automobile Association and the Royal Automobile Club who have channels allocated for their sole use in the United Kingdom;
or
b) licensee groups such as water industry companies and local government who operate on channels which are only assigned to similarly categorised users.

On-site channels are used for communications between base and mobile stations, or for mobile to mobile communications. Mobile operation is restricted to within an area of 3 kms radius from a specified location. To ensure maximum reuse of channels, and to reduce to a minimum the potential for interference, the Agency imposes tight engineering constraints on on-site users. On-site systems normally have a maximum permitted base ERP of 2 watts. The maximum permitted mobile ERP is 5 watts.

2.5 The technical characteristics of Low Band mean that the band is not as well suited to handportable radio operations, or to use in urban areas, as the higher VHF and UHF land mobile radio bands. The Low Band on-site channels are, therefore, very lightly loaded, particularly in city areas.

2.5 Wide area shared channels are for communications between base and mobile stations over an area up to 30 kms from a specified fixed base station location.

2.6 The maximum permitted base ERP for wide area shared services is normally 10 watts. The maximum permitted mobile ERP is 25 watts.

2.7 Exclusive users channels support radio services which are given a high degree of protection from co-channel interference. The users in this category operate over large regional areas.

2.8 Short Term Hire (STH) and Parking and Demonstration uses are now licensed under the Private Business Radio Suppliers Licence. Formerly separate licences were required for these categories.

2.9 STH allows a radio supplier to hire equipment to his customers for periods of up to one year. It is used for many short term purposes, including communications at sporting events. STH is also used by organisations which have a permanent radio service but have a short term requirement for additional, or separate, radio capacity.

2.10 Parking and Demonstration enables suppliers to demonstrate radio equipment to prospective customers and to install systems for customers who are awaiting a permanent frequency assignment. It can also be used for demonstrations of PMR equipment at exhibitions.

Road Construction

2.11 The Road Construction scheme is principally intended for companies on the Department of Transport list of approved contractors to facilitate the quick assignment of radio frequencies for major road construction projects.

UK General

2.12 UK General channels can be used for communications between mobile radios anywhere in the United Kingdom provided that the appropriate Agency Local Office is informed in advance. The service operates only on single frequency channels and use of base stations is not permitted.

2.13 The most common users are those who move about the country, or within a large geographical area, on a regular basis i.e. they do not have a requirement to use radio long term from a fixed location (fixed site users who require to use radio for more than 12 months are assigned on-site channels). UK General users include exhibition contractors, sporting event organisers, and construction companies. The maximum permitted mobile ERP is 5 watts.

2.14 These channels have been reserved for future growth of specific services or licensees, and for spectrally efficient services such as those which use data dominant technology.

2.15 The unallocated channels are a resource which has yet to be earmarked for any particular purpose but which could be used for future growth of existing services, for new services, or for future exceptional circumstances.

2.16 The base receive legs of these dual frequency channels are not yet available for private business radio use. They are due to be relinquished by their current users over the next five years.

2.17 Common Base Stations are mobile communications services offered by service providers on a commercial basis. A typical Common Base Station employs a single dual frequency channel, though some service providers offer a multi-channel service. Channel access is shared by a number of independent users on a first-come, first served, basis.

SECTION 3

MONITORING SURVEY

3.1 Monitoring was performed at 7 sites selected to represent the majority of London, within the M25. The monitoring was undertaken by unattended monitoring systems (UMSs) located at secure sites. Computed predictions have been made to indicate the area in which contributions from mobiles would be accounted for within the monitoring results. The general principle is shown in Figure 1 on Page l0. (As this report is very large it is not available on-line, copies can be obtained by contacting):

3.2 The monitoring techniques used for the unattended monitoring systems capture data over 24 hours, 7 days per week.

3.3 The UMS contains a programmable receiver which is fitted with a tracking preselector and switchable RF attenuators, the latter enables system performance to be verified. The system is controlled by a dedicated computer that can be programmed locally or by remote modem link. The complete system can be configured, programmed and data extracted by the Agency's Mobile Monitoring facility based at Baldock in Hertfordshire.

3.4 The UMSs measure field strength, by applying cable loss and antenna factor to the voltage measured by the receiver. This level is then compared to the threshold set in the set up file. Values above the threshold increment the occupancy register. The field strength is also recorded and a report detailing max, min and average field strength, together with occupancy is created for each channel monitored. Results are reported for every 15 min period. Both peak and average detectors can be selected, however the average detector is used for this type of monitoring exercise. Scan rate is a fixed 20 channels per second.

3.5 As the scan rate is relatively slow, the UMSs were left in place for l0 weeks and the results aggregated for the corresponding 15 minute period for each day. This approach has resulted in approximately 360 samples contributing to each 15 minute period.

3.6 The UMSs are installed at suitable sites to provide security, power, and telephone line access. UMS field strength thresholds were chosen to provide coverage of London whilst minimising overlap. Site details are given in Table1and the colour prediction chart on Page 11 shows the theoretical coverage of each site (As this report is very large it is not available on-line, copies can be obtained by contacting):

Table1. Monitoring Locations

3.7 Non - overlapping coverage is based on a minimum field strength of 30dBuV/m at each monitoring site. It is clear that some users will be operating with signals below this threshold.

3.8 It can be seen from the coverage chart that a few pockets within London have not been monitored; alternative sites that offered the security and other necessary facilities could not improve the situation. The sites chosen were generally free of inband transmitters, which would raise the noise floor to unacceptable levels. All VHF Low Band channels were monitored covering both base and mobile legs where appropriate.

3.9 Each Low Band channel has been monitored from each location, and detailed plots of activity have been produced. To keep this Report manageable, plots for two locations only are included - the one with the highest peak loading and the one with the lowest loading. The plots for each location are available for inspection, if required.

3.10 Careful comparison of the detailed plots and the licence statistics build up identifiable profiles matched to particular user groups. The profiles have become an important measure in the Agency's work towards defining quality of service expectations for a channel.

3.11 The occupancy categories have been chosen to indicate the variation of occupancy levels across channels in a particular group.

This report is available in two parts:

Part 1: Audit of Land Mobile Radio Use in VHF Low Band in the London Area (An Overview)

Part 2: Audit of Land Mobile Radio use in VHF Low Band in the London area (Individual Channel Analysis)

As this report is very large it is not available on-line, copies can be obtained by contacting:

The Information and Library Service
Radiocommunications Agency
Wyndham House
189 Marsh Wall
London E14 9SX

Tel: 020 7211 0502 or 0505
Fax: 020 7211 0507
e-mail: library@ra.gsi.gov.uk

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