Survey of Land Mobile Radio use in VHF High Band in London

CONTENTS

SUMMARY

COMPOSITION OF VHF HIGH BAND

LICENCE CHECK

MONITORING SURVEY

Introduction

Background

Closure of VHF High Band in London in 1990

0.1 In 1988 the Agency frequency assignment computer became unable to automatically assign shared use channels in VHF high band in London within the M25 area. At that time assignments were made manually by reference to monitoring data and a list of potentially suitable channels. However, it became increasingly difficult to find suitable channels as the separation between base stations became reduced in some areas to 2 kms or less. The Agency was also receiving increasing numbers of applications for VHF high band assignments particularly from taxis and private car hire and courier firms. As the Band became congested the Agency began to receive co-channel interference complaints from users and it was apparent that the quality of radiocommunication was deteriorating to an unacceptable extent. In the context of the increasing flood of applications; the growing number of co-channel interference complaints; the alternative public access systems that were becoming available in Band III; the proposed public mobile data networks and the expected arrival of new technologies such as Narrow Band technology, the decision was taken to "close" VHF high band in London. Ministers approved the closure and it was announced at a Civil Land Mobile Radio Committee meeting in January 1990.

0.2 In approving the closure Ministers stated that reopening will be conditional upon use of new, more spectrum efficient means of communication.

0.3 Although the decision is referred to as closure it was not a complete closure of all high band channels. Those who had bought equipment prior to the announcement were assigned channels, were allowed to continue operating and amendments to licences were allowed (but not significant moves of base station or additional base stations or large numbers of new mobiles ie. no change that would increase congestion). Licensees with exclusive channels in London were unaffected in respect of their continued use of those channels.

0.4 In order to assist future decision making in VHF high band in London the Agency decided to carry out a check of its licensing records, together with a parallel monitoring exercise and under took to publish the information gained as a result of enquiries. The Civil Land Mobile Radio Committee (CLMRC) and members of the Land Mobile Radio Industry Group were informed of the progress of this exercise, in their meetings with the Agency.

0.5 The objectives of the licence check and associated monitoring exercise were to:

(a) establish the accuracy of the licence data-base, currently existing within the Agency, in the following areas:

(i) identity and location of licensee;

(ii) number of mobiles in use;

(iii) characteristics of radio use;

(b) monitor radio use within the affected band so as to establish the current loading of channels;

(c) to analyze the data obtained from (a) and (b) above, in order to draw conclusions on the current loading in VHF high band London.

0.6 The Agency contacted all VHF High Band licensees, with Base Station addresses inside the M25, asking them to complete an RA questionnaire (copy at Annex A (As this report is very large it is not available on-line, copies can be obtained by contacting)); also to confirm that details of enclosed licence schedules were correct. The results of the Licence Record check is at Section 3.1.1 of this report.

0.7 Licensees who did not reply, were visited by the District Offices. For this group District staff assisted Licensees in the completion of the RA questionnaire.

0.8 RA questionnaires returned to the Agency as 'gone away' were passed to the relevant District in an attempt to trace the service or else establish that use has ceased.

0.9 In order that some confidence might be given to the findings London Districts were asked to sample some of the replies received by means of a visit. Results of the validation check are given at Section 3.2.1 of the report.

0.10 The Agency through its Mobile Monitoring Group at Baldock obtained current and historic channel utilisation data, and details of the busy period for each PMR base transmit channel and each mobile transmit channel. Information was gathered through the installation of 6 unattended monitoring systems (UMS), located around Greater London. In addition to the unattended monitoring, two 4 week periods of attended monitoring from Hyde Park were undertaken. Results obtained from the monitoring exercise are summarised at Section 4 of this report.

0.11 The strategy enabled a vast amount of traffic data to be collected. Regular review meetings were held within the Agency throughout the data acquisition and evaluation stages held so that maximum benefit accrued from the monitoring exercise. An analysis of overall channel loadings based on the full range of channels surveyed, is at Section 5 of this report (As this report is very large it is not available on-line, copies can be obtained by contacting) ; together with a sample of individual channel analyses. A full individual analysis for each of the 309 channels is contained in Part II of this report; together with associated licensing information.

0.12 The Agency would welcome any views or comments on the contents of this report. You are, therefore, invited to send your comments to

David Thomas RA2/ Private Business Systems Section
Wyndham House
189 Marsh Wall
London E14 9SX

Tel: 020 7211 0182

SECTION 1

Summary

1.1 Within areas of information relating specifically to identity and location of radio operation of licensee, the survey found that the Agency's records were 95% accurate. However, records relating to contact names within companies were less accurate.

1.2 Accuracy of records relating to the perimeters surrounding the operation of radio services ( e.g. power levels, aerial height ) were largely correct and when the survey excluded minor data-base entry errors; were better than 97% accurate.

1.3 Confidence in the Survey findings was re-enforced by the validation sample visits performed by District Offices; findings relating to identity and location of licensee were in the main, consistent with the main survey. However, greater disparity with the main survey was found in the perimeters relating to radio operation.

1.4 A significant number of licensee cancellations was uncovered during the survey amounting to 11% of total licensees.

1.5 The total number of mobiles reported through the survey was just over 5% greater than the number originally recorded on Agency records.

1.6 Occupancy levels obtained over the 13 week monitoring period, showed that for the total number of channels contained within the survey, over half were occupied at peak levels 0.5 to 1 Erlang.

1.7 The rates of occupancy varied according to the usage assigned to the channels. Within the occupancy ranges of 0.5 to 1 Erlang, peak occupancy levels, were as follows:

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SECTION 2

Composition of VHF High Band

Description

2.01 Private Mobile Radio and Common Base Station use within VHF High Band is contained within the range 165.04375 to 173.09375 MHz band edges; giving a total of 309 channels.

Channel allocation

2.2 There are 257 dual frequency 12.5 kHz channels and 52 single frequency 12.5 kHz channels designated for PMR use as shown in Table 2.1 below:

Total (MHz) 566 x 12.5 kHz = 7.075

2.3 Common Base Stations are mobile communications services offered by service providers on a commercial basis and are typically single channel dual frequency base station services where channel access is shared by a number of independent users on a first-come, first-served basis.

On-Site Channels

2.4 On-site channels are used for communication between base and mobile stations or mobile to mobile communication within a limited area up to 3 kms in radius from a specified location. Typical users include shopping centres and industrial complexes. Both single and dual frequency channels can be used. The maximum base and mobile ERP is 5 watts. The use of radiating cables and aerials inside buildings is recommended where possible. If an outside aerial has to be used it should be less than 10 metres in height above ground level. Where an aerial exceeds 10 metres the base ERP may have to be lowered and a certain type of aerial fitted to limit transmission to the service area. For hand portables the aerial height and mobile ERP constitute a limiting factor in range.

PMR National Channel Users

2.5 The Agency classifies users in this category as licensees who have nationally exclusive channels allocated to their radio services; licensee groups such as local authorities and medical services operating on channels which are only assigned to similarly categorised users; also licensees who operate a UK General type of service but because of the nature of their radio traffic, require a higher level of protection from co-channel sharing than is available on the standard UK General channels.

Wide Area Shared Channels

2.6 Wide area shared channels are for communication between base and mobile stations over an area up to 30 kms from a specified fixed base station location. These are the most common type of assignment and typical users include taxis and couriers. Only dual frequency channels can be used. The maximum base ERP for aerials up to 30 metres above ground level is 25 watts although assignments within London have shown that most operators can operate at much lower power levels. The maximum base ERP for aerials more than 30 metres above ground level is 10 watts and for 100 metres 5 watts. The maximum mobile ERP is 25 watts.

Parking and Demonstration

2.7 Intended primarily for suppliers of radio equipment. Licensing arrangements applying in this category enable radio suppliers to demonstrate PMR equipment to prospective customers and at exhibitions. They also allow the installation of PMR systems for customers awaiting permanent licence frequency assignments or licence issue.

2.8 The Agency formulated a new licence regime for short term hire use in the early 1990s, in order to authorise dealer hire to end user, where required. Use is often at at sporting events and in industry when short-term additional communication needs require separation from normal radio operations. These channels are also, in some cases, allocated to standard Private Mobile Radio users.

Road Construction

2.9 Principally intended for companies on the Department of Transport list of approved contractors to facilitate the quick issue of radio frequencies for major construction projects. However, within London the channel is allocated for Central Government use.

2.10 UK General channels can be used for mobile to mobile communication anywhere in the United Kingdom provided that the Agency District Office is informed in advance. They are used for short range communication at fixed sites or over larger areas where the coverage area is determined by the size of the aerial and the mobile ERR Typically, users have requirements that mean they move about the country or within a large geographical area on a regular basis. Such users include exhibition contractors, builders and motor rally organisers. Only single frequency channels can be used and base station operation is not allowed. The maximum mobile ERP is 5 watts. Licences which operate at fixed sites for more than 12 months must apply for on-site channels.

SECTION 3

LICENCE CHECK

Survey Cancellations

3.1.1 Survey replies were amended in the light of validation checks by London District Offices and follow-up visits [see Section 3.2.1] and survey questionaires returned as "gone- away". The total number of licences held within VHF High Band totalled 1160.

Cancellations reported during the survey accounted for over 11% of the total.

Table 3.1

3.1.2 A Table outlining the business categories affected by cancellations is given in Table 3.1.1 below:

Survey: Names

3.1.3 An evaluation of records held on current licensees, showed that 95% of licensee names were accurate; and that of the 5% inaccuracies only 3.4% related to an actual change of licensee name; the remainder related to spelling or minor data base entry errors.

Amended Replies

Table 3.2

Survey: Addresses

3.1.4 Addresses were 90.2% accurate; with actual changes of address in 3.4% of the total; the remainder of the inaccuracies relating to spelling and minor data base entry errors.

See Tables 3.3 below:

Table 3.3

Survey: Contact Names

3.1.5 Change of contact name from that originally recorded with the Agency accounted for 21.8% of the total survey.

See Table 3.4 below:

Survey: Evaluation of the Operation of Radio Services

3.1.6 The total number of radio services in operation after cancellation uncovered during the survey totalled 1655. An evaluation of Agency records relating to these areas is as follows:

See Table 3.5 below:

Table 3.5

3.1.7 Survey Grid References, were 97.9% correct, see Table 3.6 below:

Table 3.6

3.1.8 Survey: Channel Allocations, were in 99.8% of cases, those originally assigned, see Table 3. 7 below:

Table 3.7

3.1.9 Survey: ERP Levels, were 99.5% correct for base transmissions and 98.6% correct for mobile transmission. See Tables 3 8.1 and 3.8.2 below:

Base ERP

Table 3.8.1

Mobile ERP

Table 3.8.2

3.1.10 Survey: Base Station, locations were 92.7% correct; and where incorrect 2.9% of the changes related to actual change in base station location; the remainder consisting of minor data base entry errors.

See Table 3.9 below:

Table 3.9

3.1.11 Survey: Aerial Height Changes. Aerial heights were 98.4% correct

Table 3.10

3.1.12 Survey: Number of Mobiles

The total number of licensed mobiles recorded within the Agency at the outset of the Survey, as being available for use within VHF High Band in London totalled 64,159. The total number of mobiles given on Survey returns totalled 67,534 an increase of just over 5%.

Sample: Validation of Licence Information

3.2.1 The District Offices conducted a series of visits, selected on a random basis to validate a sample of replies received from licensees. The visits were used by the Districts as part of the rolling programme of formal inspections. A total of 101 licensees were visited, across the range of small to large users.

The findings of the validation sample check was as follows:

Table3.11

The District Office visits showed that licensee names were 90.3% accurate and that of these inaccurate 4.3% of the changes related to an actual change of name. See tables 3.1 2 below:

Licensee Name  Changes

Sample: Licensee Contact Details

3.2.3 Change of contact details from that originally recorded within the Agency accounted for 38.7% of the total.

See Table 3.13 below:

Table 3.13

Sample: Operation of Radio Services

A total of 103 radio services, were in operation by the 93 licensees, visited (following cancellation).

3.2.4 Call Signs in operation were 97. 1% correct.

See Table 3.14 below:

Table 3.14

Sample: Grid References were 86.4% correct.

See Table 3.15 below:

3.2.6 Sample: Channels in operation were in 98.1% of the cases those allocated by the Agency.

See Table 3 16 below:

Channel Number Changes

Table3.16

3.2.7 Sample: ERP Levels were 96.1% correct for base transmission and 97.1% correct for mobile transmission.

See Tables 3. 17. 1 and 3. 17.2 below:

Table3.17.1

Table3.17.2

3.2.8 Sample: Base Station Locations were 85.4% correct and of those incorrect 40% of the changes related to an actual base station move.

See Table 3.18 below:

Table 3.18

3.2.9 Sample: Aerial Heights were 95.1 % correct

Original number of mobiles recorded prior to the sample check of visits by the District Offices totalled 5,949. The amended total was 4,786; a decrease in the number of mobiles of just under 20% .

3.3.1 CTCSS is an abbreviation for Continuous Tone Controlled Signalling System. This transmits a sub-audio tone which operates the squelch circuit of receivers which have the same sub-audio tone assigned to them.

3.3.2 The District Offices used the validity sample (and 'non-returnees') inspections to gather statistics on the use of CTCSS tones by radio users. For example to establish whether those users with CTCSS tones assigned were using tones and if so whether they were using the correct tones. The following details apply only to the active users that were visited . There were, in total, 544 users checked for the use of CTCSS tones.

3.3.3 Users with CTCSS tones assigned

There were a total of 425 (78.1 %) users with CTCSS tones originally assigned. Of those with CTCSS tones assigned 61 (14.4%) did not have the CTCSS tone in use and a further 29 (6.8%) were using an incorrect tone.

There were a total of 119 (21.8%) users that did not originally have a CTCSS tone assigned. Of these 9 were using a non allocated tone.

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SECTION 4

4.1 Monitoring has taken place from 7 sites selected to represent the majority of London, within the M25. One site was monitored by the Spectrum Surveillance System installed within a Mobile Monitoring vehicle and the other locations monitored by unattended monitoring systems. Hyde Park was selected for the central location, data was collected over 6 weeks from a Mobile Monitoring vehicle scanning around 300 channels per second from 8.00 am Monday to 6.00 pm Friday.

Equipment

4.2 The monitoring vehicle contains automatic spectrum monitoring equipment and manual measuring receivers (As shown in Figure 1 at the end of this section). The Surveillance receiver is programmed with the start and stop frequencies in a range, expected channel spacing, measurement bandwidth and signal level threshold. Once all channels have been scanned the sequence repeats. The receiver is capable of scanning approximately 300 channels per second. If the receiver identifies a busy channel it stops briefly and establishes that the signal is not transient. Once an active channel has been identified a signal strength measurement is made, together with any frequency offset from the expected channel. These details are reported back to the controller.

4.3 In practice this method of operation checks over 100 active channels per second. The number of channels selected for monitoring in the sequence is determined to ensure each channel is re-visited every few seconds. This time varies slightly as the number of active channels vary, the general principle is shown in Figure 2 (As shown at the end of this section).

4.4 The monitoring techniques used for the unattended monitoring systems (UMS) is similar, however they captured data over 24 hours per day and 7 days per week.

4.5 The UMS contains a programmable receiver which is fitted with a tracking pre-selector 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 Group based at Baldock.

4.6 The UMS units measure field strength, by applying cable loss and antenna factors to the voltage measured by the receiver (As shown in Figure 2 at the end of this section). 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 maximum, minimum and average field strengths, together with occupancy is created for each frequency monitored. Results are reported for every 15 minute 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.

4.7 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.

4.8 Each Unattended Monitoring System contained a programmable receiver fitted with a tracking preselector and switchable RF attenuators enabling system performance to be verified. Receiver control was effected through a dedicated computer that programmed locally or else by remote modem link.

4.9 Hyde Park was selected for the vehicle based monitoring as the Royal Parks provided reasonable security, power and a quiet site, away from man made electrical noise.

4.10 The unattended systems were installed at suitable sites that provide security, power and telephone line access. The sites had been chosen to cover areas of London minimising the overlap, site details are given in Table 1 (As shown at the end of this section)and the colour prediction chart shows the theoretical coverage of each site. Table 1 also gives the population count within each area.

4.11 The prediction was based on a minimum field strength of 18 dBuV/m at the monitoring site. This was considered to be representative of 1 uV at the receiver input at a typical PMR installation. However, it was clear that some users would be operating with signals below this threshold.

4.12 It can be seen from the coverage chart that a few pockets within London were 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.

4.13 All VHF high band channels were monitored covering both base and mobile legs where appropriate. On-Site channels have also been monitored although the monitoring locations are not necessarily suited to monitoring On-Site activity. The CLMRC were invited to nominate typical areas for On-Site activity, once the RA receive the site details a short monitoring exercise from a van can provide data. The detail for On-Site monitoring is beyond the scope of the current survey.

4.14 Each high band channel has been monitored from each location, and detailed plots of activity have been produced. To keep the report manageable, the decision was taken at the 'emerging findings' meeting with representatives from the Land Mobile Radio Industry sector to include detailed plots of the channel with the highest peak loading and also the channel with the lowest loading. The latter was predominantly Sydenham as this site has the smallest coverage area, but this was not always the case. The plots from each location, where monitoring took place, are available for future inspection, from,Baldock Mobile Monitoring Group if required. These can be obtained from Paul Jarvis, Mobile Monitoring Group, Baldock Radio Station, Royston Road, Baldock, Herts. SG7 6SH. (Tel: 01462 420428). A sample of monitoring results combined with licence information is at Section 5 of this report.

4.15 Careful comparison of the detailed plots and the licence statistics build up identifiable profiles matched to particular user groups. The profiles will become of particular interest, and represent an important measure of activity, as the Agency works towards defining quality of service expectations for PMR channels.

4.16 Hyde Park results are available for 8.00 am Monday morning through to 6.00 pm on Friday. The vehicles were not able to monitor through the weekend.

4.17 Channel analysis given through samples in this report and for all channels in Part II is based on the following categories of loading:

4.18 The bar charts given in Part II of this report depict the busiest period of the week of the monitoring sites for that channel. These charts give a clear overview of the channel loadings that can occur. In most cases each day was loaded to a similar level, but the maximum day and period is depicted.

4.19 The individual graphs for each site give a much more detailed picture, showing the variation of traffic over the whole week. In some cases the weekends are busier than the weekdays. By combining the, licence data with these charts a profile for the particular category can be established. When taking into account the type of business, number of mobiles etc. it is possible to correlate the traffic with the other data. Some channels reveal that further investigation is required, because there is a discrepancy of the expected use compared with the data revealed by the licence check. These channels will be given further attention by the mobile monitoring team and the local District Offices. The second graph depicts the quietest monitoring sites results. Remaining graphs are available for other sites should they be required.

4.20 The monitoring system gathered data on all mobil~e transmit channels, however the occupancy levels revealed are lower :than the associated base transmit channels. A random selection of charts for 5 channels is included in Annex B of Part 11.

4.21 The position of mobiles is clearly unknown and they may be moving in and out of the area being monitored by each monitoring system. The clutter and shielding at ground level does not permit a reliable measurement to be made but the; data is included for completeness. All other mobile channel data is available for inspection from Baldock Monitoring Group if required.

This report is available in two parts:

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

Part 2: Individual analysis of licensing information relating to the occupancy of all channels.

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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RA 267 (0n-line introduction) March 1995