RA285 - Audit of Land Mobile Radio use in VHF Mid Band in the London Area

0.1 In July 1992 a review was commissioned by the President of the Board of Trade and the Secretaries of State for Defence, Home Affairs and Scotland with the aim of 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 submitted to the President and his colleagues in January 1994 (report of the Radio Spectrum Review Committee Stage 3: 28-470 MHz; published March 1994, ISBN 1 85569 172 8). The Government Response to the Report was published in April 1995 (ISBN 1 85569 172 8). Copies of the Report and the Government Response are available from:

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 This recommendation was accepted in the Government Response and the Radiocommunications Agency is responding by carrying out audits of the land mobile radio bands on a band by band basis. A Report on VHF High Band was published in March 1995 "Survey of Land Mobile Radio use in VHF High Band in London, ISBN 1 85569 198 1". Future audits will cover the UHF Bands, VHF Low Band and Band III.

0.5 This Report covers the audit of VHF Mid Band and provides details of land mobile radio services operating on Mid Band frequencies (139.51250-165.04375MHz) and channel utilisation data gathered by the Agency's Mobile Monitoring Group.

0.7 The Agency contacted all VHF Mid Band 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) (As this report is very large it is not available on-line, copies can be obtained by contacting) and to confirm that the details recorded on their licence schedule(s) were correct.

0.8 Licensees who did not reply were visited by staff from the Agency's District Offices. The District staff assisted these licensees in the completion of the questionnaire and verification of the schedule details.

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

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

0.11 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. Results obtained from the monitoring exercise are summarised at Section 3 of this Report.

0.12 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 272 channels in VHF Mid Band is contained in Part 2 of this Report; together with information on the services which operate on these channels.

0.13 The Agency would welcome any views or comments on the contents of this Report. Please send your comments to Ray Wilson, Radiocommunications Agency, Branch 2, Spectrum Planning and Engineering Section, 11th Floor North, Desk 20.3, New King's Beam House, 22 Upper Ground, London SE1 9SA (Tel: 0171211 0253).

SECTION 1

SUMMARY

1.1 The audit established that there were 422 radio services operating on Mid Band channels in the London area (an average of 1.6 services per channel). It should be noted that these figures exclude the transient services on Short Term Hire, Road Construction, UK General, and Parking & Demonstration channels.

Note: the total of 422 radio services is made up of sites which use a base station and those which operate mobile radios only (a base station which has been allocated more than one radio channel will have been counted more than once).

1.2 The average number of services per channel (excluding transient services) for the various channel categories in Mid Band is as follows:

Common Base Station channels	0.7
National channels	1.9
National Mobile Data channels	1.6
On-site services channels	15.4
Wide area shared channels	0.4

1.3 Monitoring of the 272 Mid Band channels indicated that 16.9% achieved a peak occupancy level of between 0.5 and 1 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:

Common Base Station channels	29.3%
National channels	2.2%
National Mobile Data channels	69.2%
On-site services channels	10.0%
Wide area shared channels	11.1%
Miscellaneous channels	11.1%

2.1 Private Mobile Radio, Common Base Station, and Mobile Data Network use of VHF Mid Band is contained within the range 139.51250-165.04375 MHz (band edges) providing a total of 272 channels.

2.2 There are 248 dual and 24 single frequency channels in Mid Band. These use 12.5 kHz channel spacing. However, five of the duals and three of the singles are currently taken up by a national channel user who operates a radio system requiring 25 kHz channels (providing 2 x 25 kHz dual and 1 x 25 kHz single frequency channels). Mid Band channels are designated for use by PMR, Common Base Station, and National Mobile Data Network services as shown in the Table below:

Description of Channels	Single	Dual
Common Base Stations	-	75
National channels	7	84
National mobile data networks	1	25
On-site services	10	-
Wide Area Shared	-	9
Miscellaneous
Short Term Hire	-	10
Road Construction	-	5
Parking & Demonstration	-	1
UK General	2	-
Reserved for particular purposes	-	25
Unallocated	4	14
Total	24	248

2.3 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.

2.4 Mid Band users in this category are either licensees who have channels allocated for their sole use in the United Kingdom or licensee groups, such as the utilities, who operate on channels which are only assigned to similarly categorised users.

2.5 National Mobile Data Networks are mobile data only, communications services offered by service providers on a commercial basis. Uses include despatch operations, credit card verifications, and vehicle location/status messages.

2.6 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. Typical users include shopping centres and industrial complexes. 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. The maximum permitted base and mobile ERP is 5 watts.

2.7 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. In Mid Band only dual frequency channels are available for wide area use and these are assigned, in the main, to courier services. Of the nine wide area shared channels in Mid Band seven are used by other service categories outside of the London area.

The maximum permitted base ERP for wide area shared services with aerials not exceeding 30 metres above ground level is 25 watts. The maximum base ERP for services with aerial heights exceeding 30 metres is 10 watts and is 5 watts if the height exceeds 100 metres. The maximum permitted mobile ERP is 25 watts.

2.8 Short Term Hire (STH) allows a radio dealer 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.

The Agency, in conjunction with representatives of the mobile radio trade, introduced a new STH licensing regime in the early 1990s. This was designed to deal with abuses of STH and to relieve congestion on the channels allocated to the service. A number of new channels was made available, mainly in VHF Mid Band.

Three of the ten STH channels in Mid Band are for use on construction projects only. Although the STH channels are designated as dual frequency the base and mobile transmit legs of these channels are mainly used as single frequency channels.

2.9 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. Most of the channels used by the scheme are in VHF Mid Band.

2.10 The Parking and Demonstration licence is intended primarily for suppliers of radio equipment and permits temporary uses of certain designated frequencies. The licence enables suppliers to demonstrate radio equipment to prospective customers and to install systems for customers who are awaiting a permanent frequency assignment. The licence also permits the demonstration of PMR equipment at exhibitions.

2.11 UK General channels can be used for communications between mobile radios any~vhere in the United Kingdom provided that

the appropriate Agency District Office is informed in advance. The service operates only on single frequency channels and use of base stations is not permitted.

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.

2.12 These channels have been reserved for future growth of specific services such as Common Base Stations and for the introduction of data-dominant radio services.

2.13 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.

3.1 Monitoring has taken place from 7 sites selected to represent the majority of London, within the M25. The monitoring has been undertaken by unattended monitoring systems located in 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 10.

3.2 The monitoring techniques used for the unattended monitoring systems capture data over 24 hours per day and 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.

3.4 The units measure field strength, by applying cable loss and antenna factors 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 strengths, together with occupancy is created for each frequency monitored. Results can be 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 UMS systems were left in place for 13 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 unattended systems are installed at suitable sites that provide security, power, and telephone line access. The sites have been chosen to cover areas of London, minimising overlap. Site details are given in Table 1 and the colour prediction chart on Page 11 shows the theoretical coverage of each site.

Site No.	Site Name
1	Stanmore
2	Lippitts Hill
3	Romford
4	Sydenham
5	Banstead
6	Heathrow
7	Holborn

3.7 The prediction is based on a minimum field strength of 18dBuV/m at the monitoring site. This is considered to be representative of 1uV at the receiver input at a typical PMR installation. 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 in band transmitters, which would raise the noise floor to unacceptable levels. All VHF Mid Band channels have been monitored covering both base and mobile legs where appropriate.

3.9 Each Mid 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 the 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.

Part 1: Overview of findings obtained from licensing and monitoring information relating to occupancy of channels.

Part 2: Analysis of licensing and monitoring information relating to the occupancy of each channel in VHF mid band.

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

Audit of Land Mobile Radio use in VHF Mid Band in the London Area

CONTENTS

INTRODUCTION

SECTION 1

SUMMARY

SECTION 2

COMPOSITION OF VHF MID BAND

Miscellaneous

Short Term Hire

SECTION 3

MONITORING SURVEY