CDMA / CAD & CT2 Compatibility (Version 1.2)

RTCG Report No. 485

Contents

1.0 Abstract

2.0 Introduction

3.0 Theoretical Predictions

4.0 Objective Measurements

5.0 Subjective Assessments

6.0 Further Analysis

7.0 Conclusions

1.0 Abstract

Spectrum suitable for a CDMA spread-spectrum vehicle tracking system is being sought in the UK.

The investigation detailed in this report was conducted to assess whether this system could operate within the 863-865 MHz band without causing unacceptable interference to the existing services. These services are (a) Cordless Audio Devices (CAD), 863-864 MHz with possible extension to 865 MHz and (b) second generation Cordless Telephones (CT2), 864-868 MHz.

The sensitivity and protection requirements of typical equipment used by the two existing services were determined from measurements and specifications. Wanted field strengths were calculated using an indoor propagation model, and interfering field strengths (for various percentages of the time) were predicted using an extended Hata propagation model and Monte Carlo analysis. The magnitude of the interference that should be anticipated was assessed for specific scenarios.

A variety of subjective listening tests were also conducted to determine the subjective effect of ‘real’ interference under ‘real’ operating conditions i.e. under conditions where the occurrence and level of the interference is random, and the wanted signal is also suffering other impairments due to fading etc. It was confirmed that the subjective magnitude of the interference present at the lower wanted field strengths was being reduced (masked) by the presence of other impairments such as noise and fading.

The findings were analysed and conclusions drawn.

Summary of conclusions:

	Introducing the proposed vehicle tracking system at 864 MHz will result in some limited interference to CAD’s, but the magnitude of this interference is considered acceptable in all cases, and insignificant or non-existent in most.
	Compatibility with some types of CAD i.e. in-ear monitoring, in-vehicle systems and personal cordless have not been not been specifically investigated, but it is considered that the magnitude of the interference described in this report will be similar for all types of CAD.
	Introducing the proposed vehicle tracking system at 864 MHz will result in some very limited interference to CT2’s, but the magnitude of this interference is considered unlikely to be noticed.
	No problems are envisaged with the upper or lower adjacent band services providing the spurious emissions from the tracking system transponders meet the normal UK and European limits.
	The magnitude of the interference will depend on the number and e.r.p. of the transmissions, and their geographical distribution. It would be prudent for any licence to include a mechanism to ensure that the numbers, e.r.p’s. and population densities specified by the potential system operator, and used in this investigation, are not exceeded.
	No assessment has been made of the tracking systems paging requirements, possible paging frequencies, or the compatibility between the tracking systems paging transmitters and other services.

2.0 Introduction

Details of the proposed vehicle tracking system can be found in the Section 2 (Introduction) of RTCG Report 416, which investigated sharing spectrum with other existing users in the region of 437 MHz.

This report (485) details an investigation conducted to assess whether this system could operate within the 863-865 MHz band, without causing unacceptable interference to the existing services. These services are (a) Cordless Audio Devices (CAD), 863-864 MHz with possible extension to 865 MHz and (b) second generation cordless telephony equipment (CT2), 864-868 MHz.

The magnitude of the interference that CAD and CT2 users will be subjected to will depend the number and e.r.p. of the transmissions, and their geographical distribution. This investigation has used the information provided by the potential system operator regarding the numbers, e.r.p’s. and population densities etc.

3.0 Theoretical Predictions

3.1 The interfering field strength will vary considerably with time. The amount of time that specific field strengths are expected to be exceeded was calculated using Monte Carlo modelling similar to that described in RTCG Report 416. The basic model employed distributes the interfering equipments around the victim in a uniform but random manner, and then calculates the interfering field strength at the victim from the number and location of the active interfering equipments, and their effective radiated power. A factor to account for building loss was also included, but no attempt was made to simulate fading. Each calculation represents a single instant in time. Repeating this calculation for a large number of instants enables the field strength exceeded, for various percentages of the time, to be determined.

3.2 The computer program given in Annex D of RTCG Report 416 was modified to return the effective path loss between the interferers and victim, rather than the total interference power at the victim, for each instant in time. From this data the field strength at the victim was calculated. The results are presented graphically in Figures 1, 2 and 3. The isolated symbols (squares, diamonds, triangles, circles and bold stars) should be ignored at present.

Figure 1

Figure 2

Figure 3

4.0 Objective Measurements

4.1 Victim Equipments

Table 1

Table 2

The co-channel interfering signal was simulated in the manner described in Section 5 (Simulation of Interfering Equipment) of RTCG Report 416.

4.3 Victim Sensitivities

Sensitivities were measured in a G-TEM cell.

4.3.1 Cordless Audio Devices. The CAD transmitter module was placed in a screened enclosure in close proximity to a dipole. The RF output from the dipole was coupled through the enclosure to a variable attenuator that controlled the field strength in the G-TEM cell. A 1 kHz tone was connected to the audio input of the transmitter module, and the level adjusted according to the device's instructions. The CAD receiver was placed in the G-TEM cell and orientated for optimum reception (no marked directivity was noted). The audio output power was then measured and noted as being the reference level (0 dB). The 1 kHz tone was then removed and the field strength adjusted until the audio output power (QP CCIR weighted) fell by 20, 30, 40, 50 or 60 dB (S/N ratio). The 1 kHz tone was then restored, and the reference level checked. If the reference level had changed it was updated and the procedure repeated until no further change occurred. The field strength at the victim was then determined and recorded as the field strength resulting in the specific S/N ratio.

Table 3

4.3.2 Cordless Telephones. The cordless portable part (CPP) was placed in a screened enclosure in close proximity to a dipole. The RF output from the dipole was coupled through the enclosure to a variable attenuator that controlled the field strength in the G-TEM cell. The cordless fixed part (CFP) was placed in the cell and orientated for best reception once a call had been established. The field strength was then adjusted until the link was just interrupted, and then increased slightly to restore communications. The field strength at the victim was then determined and recorded as the minimum for reliable operation.

Table 4

4.4 Victim Co-channel Protection.

Protection requirements were measured in a G-TEM cell.

4.4.1 Cordless Audio Devices. Measurements were conducted in a similar manner to the sensitivity (4.3.1). In this case however, the co-channel simulated interferer was introduced, and its level increased until the desired signal to noise ratio was obtained. The difference between the power (field strength) of the victim and interfering signals was then measured on a spectrum analyser.

Table 5

4.4.2 Cordless Telephones. Measurements were conducted in a similar manner to the sensitivity (4.3.2). In this case however, the co-channel simulated interferer was introduced, and its level increased until the desired effect was obtained. The difference between the power (field strength) of the victim and interfering signals was then measured on a spectrum analyser.

Table 6

4.5 Analysis of Objective Measurements.

4.5.1 Cordless Audio Devices. At the lower wanted field strengths, the signal to noise ratio will be low, and this will tend to mask the interference i.e. the protection requirement will be relatively small. At the high wanted field strengths, the signal to noise ratio will also be much higher, and the protection requirement will be relatively large.

The interfering field strength that needs to be exceeded before interference becomes perceptible can be found by subtracting the protection requirements given in Table 5, from the sensitivities given in Tables 3. As expected, the resulting interfering field strength is not proportional to the wanted field strength. Furthermore, although there is some variation between victim equipments, this is not excessive. On average, an interfering field strength of 35 dBm V/m would have to be exceeded before interference became perceptible.

It should be noted that this does not mean that the interfering field strength should never exceed 35 dBm V/m, it simply means that a continuous interfering field of this strength would be perceptible. The percentage of the time that this and other field strengths can be expected to occur is given in Section 3 of this report, and the percentage of time that interfering fields of various strengths can be permitted to occur, is assessed subjectively in Section 5 of this report.

4.5.2 Cordless Telephones. Being digital devices, the communications link quality tends to be either very good, or non-existent. At the lower wanted field strengths, frequent interruptions in the link can be expected due to fading and shadowing. These interruptions would be indistinguishable from those caused by interference of short duration. With a sensitivity of approximately 40 dBm V/m, and a protection requirement of approximately 0 dB, it is expected that an interfering field strength of 40 dBm V/m would cause a slight reduction in the maximum range of the cordless telephone.

It should be noted that this does not mean that the interfering field strength should never exceed 40 dBm V/m, it simply means that a continuous interfering field of this strength would be expected to reduce the maximum range. The percentage of the time that this and other field strengths can be expected to occur can be found in Section 3 of this report, and the percentage of time that interfering fields of various strengths can be permitted to occur, is assessed subjectively in Section 5 of this report.

It should be noted that the interference will not be precisely co-channel for the majority of the CT2 channels. However, as the interferer is broadband, the improvement due to frequency separation is small initially i.e. » 5 dB at 0.5 MHz separation, » 15 dB at 1 MHz and » 30 dB at >2MHz.

5.0 Subjective Assessments

5.1 Subjective Assessment under Controlled Conditions

The aim was to determine the subjective effect of a burst of interference, at various levels relative to the wanted (protection ratios), under normal operating conditions.

5.1.1 Cordless Audio Devices. Under normal listening conditions, the protection ratio will depend on the music, artist, track and even the precise timing of the occurrence of the burst within a specific track. This means that a very large number of lengthy assessments are required to accurately characterise, in a statistical manner, the subjective effect of the interference. This was impractical in the time-scales available. A less accurate but practical alternative was to subject a listener to a single burst of interference and have them assess how frequent they considered that this could be permitted to occur, before they would deem it unacceptable. This was the approach taken. The listener was permitted to listen to many bursts of interference, with a variety of music, before making an assessment. No time limit was placed on an assessment; the listener was permitted to take as long as they felt necessary. Generally each assessment took 5 to 10 minutes.

The assessments are presented in Table 7 in terms of the percentage of the time that interference could be permitted before it should be deemed unacceptable. It should be noted that these assessments may only be valid for 250 ms bursts of interference.

Table 7a

5.1.2 Cordless Telephones. The protection requirement will remain relatively constant under normal operating conditions i.e., as this is a digital system, variations in the users voice characteristics etc. would not be expected to affect the magnitude of the impairment. This means that only a small number of assessments are required to determine the subjective effect of the interference.

The assessments are presented in Table 8 in terms of the percentage of the time that interference could be permitted before it should be deemed unacceptable. It should be noted that these assessments may only be valid for 250 ms bursts of interference.

Table 8

The aim was to determine the subjective effect of ‘real’ interference under ‘real’ operating conditions i.e. under conditions where the occurrence and level of the interference is random, and the wanted signal is also suffering other impairments due to fading etc. The field strength of the interference at the victim was calculated using Monte Carlo modelling (see Section 3) for each 250 ms instant in time.

This field was then generated by radiating a simulated interfering signal of an appropriate level, from a calibrated dipole antenna 1 m from the victim receiver. The transmitting part of the victim was then placed at various distances from the victim receiver, including in different rooms, to simulate normal usage. The primary benefit of this ‘non-controlled’ assessment was that it introduced other normal impairments, especially those that would be present when operating close to the CAD equipment’s maximum range, which permitted the additional impairment caused by the interference to be assessed in context.

The level of the interfering signal was controlled by an arbitrary waveform generator connected to the envelope input of the interfering signal generator. The waveform was output at a rate of 4 elements per second i.e. each element of the waveform represented one 250 ms instant in time. The voltage output for each element was arranged to be proportional to the field strength required at that instant. The data downloaded to the arbitrary waveform generator was normalised to make maximum use of the instruments dynamic range (» 70 dB). In practice however, the dynamic range of the simulation was limited to just over 30 dB by the signal generators envelope control circuitry i.e. the RF output tracked the waveform voltage to within 1 dB until approximately –33 dB was reached, below which the RF output was zero. This was of little concern however, as any interference below this level would be imperceptible.

As correction and normalising factors had to be applied to determine the correct RF level to set the interfering signal generator to, the field strength at the victim was measured with known (calibration) data downloaded into the arbitrary waveform generator. The median field strength at the victim was found to be within 1 dB of that expected, although spot variations of up to 4 dB were present due to reflections.

Only the worst case urban and rural interference scenarios were assessed. An opinion regarding the acceptability of the interference observed is given in Section 5.3.2.1 of this report.

5.2.1.1 CAD Scenario: Worst Case Urban, i.e. second floor with a weak wanted field strength. Interference was heard at 5, 7½, 13, 21(loud), 26, 29 and 47 minutes during the assessment of DUT C. Additional interference may have occurred at other times, but was not noticed.

5.2.1.2 CAD Scenario: Worst Case Rural, i.e. second floor with a weak wanted field strength. Interference was heard at 2, 6½, 8(just), 12, 15½, 19, 19¼(loud) and 23 minutes during the assessment of DUT C. Interference was heard at 7, 9½, 11, 13, 16½, 19, 25, 25¼, and 31 minutes during the assessment of DUT D. Additional interference probably occurred at other times, but was not noticed.

5.2.2 Cordless Telephones.

Only the worst case interference scenario was assessed i.e. rural, second floor with a weak wanted field strength. Short breaks in communications were noted, but it was only possible to determine that these were due to interference when the user was stationary.

5.3 Analysis of Subjective Assessment.

5.3.1 Analysis of Subjective Assessment under Controlled Conditions.

5.3.1.1 Cordless Audio Devices. The listener was not given any visual indication of when the interference occurred as it was noted at a very early stage that interference which was clearly audible with a visual cue, was often unnoticed without. Furthermore, if every suspected burst of interference was counted, and then compared with the number of bursts known to have occurred within the counting period, considerably more interference was counted than actually occurred. The subjective assessments detailed in Section 5.1 of this report are believed to have been conducted in a manner that largely excluded this type of effect i.e. no visual indication was given and suspected bursts of interference were not counted.

The results given in Tables 7a, 7b, 7c and 7d show the expected trend i.e. in general the rate (%) at which the interference was considered acceptable was lower when the wanted audio quality (and field strength) was high. The lowest rate (%) given in these Tables for any wanted/unwanted field strength combination has been plotted on Figures 1, 2 and 3 (a square symbol represents victim A, a diamond victim B, a triangle victim C and a circle victim D). From these plots it can then be seen that; (a) the listener considered that a 250 ms burst of interference that occurred, on average, no more than once every 15 minutes was always acceptable no matter what the listening conditions; (b) the limit of acceptability is not expected to be exceeded in an urban environment, but may be exceeded in some suburban and rural environments when the wanted field strength is weak.

The lowest rate deemed acceptable with a weak wanted field strength is likely to be pessimistic however, as these subjective assessments took place under static conditions that excluded ‘normal’ impairments that may have masked some of the interference. Section 5.3.2 of this report analyses the findings of a subjective assessment of the worst case urban and rural interference scenarios, conducted in a more realistic manner.

5.3.1.2 Cordless Telephones. The listener was not given any visual indication of when the interference occurred. It was found that a 250 ms burst of interference caused a break in communications (audio muted) but did not cause the cordless telephone to attempt to transfer the call to an alternative channel. When the interfering field strength was significantly greater than the wanted field strength, the break seemed to last longer than 250 ms.

From the results given in Table 8, the lowest rate (%) at which the interference was considered acceptable, for any wanted/unwanted field strength combination, has been plotted on Figures 1, 2 and 3 (a bold star symbol represents victim E). From these it can be seen that the rate considered acceptable is not expected to be exceeded in any environment, under any condition.

Although the above indicates that interference to domestic CT2 usage will not be a problem, Section 5.3.2 of this report analyses the findings of a subjective assessment of the worst case interference scenario, conducted in a more realistic manner, to provide additional confidence.

5.3.2 Analysis of Subjective Assessment under Non-controlled Conditions.

5.3.2.1 Cordless Audio Devices. For the worst case urban scenario, the average time between the recorded bursts of interference was 7 minutes (0.06% for a 250 ms burst), which is not dissimilar from that predicted by Figure 1. Interference of this magnitude would be noticed by most listeners, but it is believed that they would be expecting impairments of this magnitude when operating a CAD close to its maximum useable range.

For the worst case rural scenario, the average time between the recorded bursts of interference was 3¼ minutes (0.13% for a 250 ms burst) for DUT C, and 2½ minutes (0.17% for a 250 ms burst) for DUT D, both of which are considerably lower than that predicted by Figure 3 (» 1%). This suggests that much of the predicted interference was being masked by the presence of other impairments in this more realistic assessment. The interference observed was clearly audible however, and would certainly be noticed by the user i.e. it would reduce the listening pleasure and might in some cases be attributed to interference. Although the project engineer considered the magnitude of the observed interference to be acceptable for this worst case interference scenario, the opinion of other RTCG engineers and the project sponsor were sought. None had difficulty recognising the interference, and approximately 50% expressed concern regarding its magnitude. All however, considered the magnitude acceptable for this worst case interference scenario.

5.3.2.2 Cordless Telephones. Short breaks in communications occurred, but it was only possible to determine that these were due to interference, rather than a loss of the wanted signal, when they occurred whilst the user was stationary.

6. Further Analysis.

6.1 Indoor Propagation.

The wanted field strength of CAD and CT2 systems can be calculated using an indoor propagation path loss model, such as that given in ITU Recommendation P.1238.

L_total = 20 log₁₀f + N log₁₀d + Lf(n) - 28 dB

where:

N: distance power loss coefficient (33 for 900 MHz)
f: frequency (MHz)
d: separation distance (m) between base and portable
Lf: floor penetration loss factor (dB) (4n for residential at 1.8-2.0 GHz)
n: number of floors between base and portable

This model can be used to calculate the wanted field strength for a specific CAD or CT2 scenario. This field strength can then be compared with the interfering field strengths predicted in Figures 1, 2 and 3 of this report and from this, together with knowledge of the protection requirements, it is possible to assess the magnitude of the likely interference. The protection requirements for a particular scenario can be estimated from the data given in Section 4 of this report. It should be noted that the protection requirements are related to the wanted field strength.

Examples (a) and (b) that follow are considered to produce sensible results. Example (c) has been included to demonstrate the danger of using this type of calculation for scenarios where significant masking should be expected (see 6.2 below). The result produced is very pessimistic compared to that obtained from subjective assessment of the same scenario.

1. If the CAD Tx and Rx were in the same room, a wanted field strength of the order of 100 dBm V/m should be expected. Under these conditions, when operated in the worst case scenario (CAD Rx on a second floor, in a rural environment), interference is only predicted for » 0.001% of the time. This equates to one 250 ms burst of interference occurring, on average, once every 7 hours. This result is considered realistic.
   
2. If the CAD Tx and Rx were in different rooms of the same house, a wanted field strength in excess of 70 dBm V/m should still be expected. Under these conditions, when operated in the worst case scenario (CAD Rx on a second floor, in a rural environment), interference is predicted for » 0.07% of the time. This equates to one 250 ms burst of interference occurring, on average, less than once every 6 minutes. This result is considered realistic.
   
3. If the CAD Tx and Rx were separated by a considerable distance and/or substantial obstruction(s), then a wanted field strength as low as 40 dBm V/m might still be useable. Under these conditions, when operated in the worst case scenario (CAD Rx on a second floor, in a rural environment), interference is predicted for » 1% of the time. This equates to one 250 ms burst of interference occurring, on average, once every 30 seconds. This result is pessimistic as the more realistic subjective assessment of this scenario only noted one 250 ms burst of interference occurring, on average, once every 3 minutes.

Similar calculations can be made for CT2 scenarios.

Two effects were observed during the subjective listening sessions that reduce the annoyance of a short burst of interference, or mask it altogether.

1. If the 250 ms burst of interference occurs at the same instant in time as an increase in the wanted audio is anticipated e.g. it coincides with the beat of the music, or a loud syllable of speech, its presence is not always noticed even if it is as loud as the wanted audio.
   
2. If other impairments are present e.g. noise, particularly noise of short duration caused by fading etc., then the additional impairment caused by a 250 ms burst of interference will be less annoying, and may not even be recognised as interference.

6.3 Interference to Other Types of Cordless Audio Device.

The functional characteristics of four types of cordless audio device are detailed in Draft EN 301 357, and can be summarised as follows.

1. Cordless wideband audio equipment encompasses radio linked headphones and loudspeakers that may be installed in a building, fitted in a vehicle or body worn. Stereo can be accommodated. The maximum e.r.p. is 10 mW.
   
2. In-ear monitoring equipment is used by stage and studio performers to receive personal fold back (monitoring) of the performance. The maximum e.r.p. is 10 mW.
   
3. In vehicle systems are used for private listening in automobiles and other methods of transport (where permitted). The maximum e.r.p. is 2 mW.
   
4. Personal cordless transmitters are to enable the body worn personal stereo equipment to be wire free. The maximum e.r.p. is 1 mW.

Only interference to CAD's having the functional characteristics described in (a) above have been investigated, but the magnitude of the likely interference to other types of CAD can be estimated from the interference scenario, and the likely performance of that type of CAD (see 7.1.5).

7.0 Conclusions.

7.1 Interference to Cordless Audio Devices.

7.1.1 Introducing the proposed vehicle tracking system at 864 MHz will result in some limited co-channel interference to CAD’s operating between 863-864 MHz (with possible extension to 865 MHz).

7.1.2 The measurements and subjective assessments detailed in this report suggest that:

1. in the most likely CAD usage scenarios, the short bursts of interference will occur too infrequently to be considered an impairment.
   
2. in the worst case CAD usage scenario, short bursts of interference will occur frequently enough to cause some impairment and this might, in some cases, be attributed to interference. It should be noted however, that interference of this magnitude was assessed subjectively by a number of RTCG engineers and although some concern was expressed, all deemed the interference acceptable for this worst case interference scenario.

7.1.3 It should be noted that the peak period of use of most CAD’s (outside normal working hours) would not coincide with that of the vehicle tracking system (normal working hours).

7.1.4 The magnitude of the interference to CAD’s, from the proposed vehicle tracking system, is considered acceptable in all cases, and non-existent or insignificant in most cases.

7.1.5 Compatibility with some types of CAD i.e. in-ear monitoring, in-vehicle systems and personal cordless have not been not been specifically investigated, but the magnitude of the likely interference can be estimated from the interference scenario, and the likely performance of the CAD. For all interference scenarios the interferer is effectively co-channel, and the sensitivity and co-channel rejection performance of the other types of CAD can be expected to be similar to that investigated. The maximum e.r.p. of some types of CAD is lower than that investigated, but this is offset by the lower range demanded, and the likely lack of obstructions. The interfering field strength at a particular height above ground level can be expected to be approximately 5 dB higher for some interference scenarios due to a lack of building losses, but in these cases this will be offset by a reduction in the likely height of the CAD e.g. in-vehicle systems will seldom be operated at heights equivalent to the first or second floor CAD operational scenarios investigated.

It is considered therefore, that the magnitude of the interference described in this report will be similar for all types of CAD.

7.2 Interference to Cordless Telephones (CT2).

7.2.1 Introducing the proposed vehicle tracking system at 864 MHz will result in some very limited interference to CT2 usage when a channel between 864 and 865 MHz is selected by the CT2 system. It should be noted that 75% of the CT2 channels available i.e. those between 865 and 868 MHz, would be unaffected.

7.2.2 The measurements and subjective assessments detailed in this report suggest that even in the worst case domestic CT2 usage scenario, the impairment will be indistinguishable from that caused by fading and shadowing etc. It is unlikely therefore, that domestic CT2 users would notice the presence of the proposed vehicle tracking system.

7.2.3 Compatibility with cordless (CT2) PABX systems was not investigated but, as the specified performance of these systems is identical to that of domestic CT2’s, certain conclusions can be drawn. Only 25% of the available CT2 channels i.e. those between 864 and 865 MHz, would suffer interference of a similar magnitude to that of domestic users. The cordless (CT2) PABX would not attempt to locate or transfer a call to an alternative channel however, as the interference would only be present for 250 ms i.e. there would be no escalating effects that need more careful consideration. Two other factors are worthy of note:

1. the interfering field strength is likely to be slightly lower, due to the additional building loss offered by commercial premises.
   
2. The wanted field strength is likely to be kept well above the maximum sensitivity to ensure reliable communications and handovers etc.

It is unlikely therefore, that cordless (CT2) PABX users would notice the presence of the proposed vehicle tracking system.

7.2.4 The magnitude of the interference to CT2’s, from the proposed vehicle tracking system, is therefore considered acceptable and unlikely to be noticed.

7.3 Interference to Adjacent Band Systems.

7.3.1 The upper adjacent band extends up to 868 MHz and is occupied by CT2. No problems are envisaged.

7.3.2 The immediate lower adjacent band extends down to 862 MHz. No problems are envisaged providing the spurious emissions from the tracking system transponders meet the normal UK and European limits. MoD systems operate immediately below this. Again, no problems are envisaged providing the spurious emissions from the tracking system transponders meet the normal UK and European limits.

7.4 Tracking System Parameters.

7.4.1 The magnitude of the interference that CAD and CT2 users will be subjected to will depend on the number and e.r.p. of the transmissions, and their geographical distribution. This investigation has used the information provided by the potential system operator regarding the numbers, e.r.p’s. and population densities etc. The conclusions detailed in this report are only valid for a tracking system as described. Should such a system be licensed, it would be prudent to include a mechanism to ensure that the numbers, e.r.p’s. and population densities specified by the potential system operator, and used in this investigation, are not exceeded.

7.4.2 The vehicle transponder etc. should meet the normal UK and European limits with respect to spurious, adjacent channel and out of band emissions etc.

7.5 Tracking System Paging Requirements.

No assessment has been made of the tracking systems paging requirements, possible paging frequencies, or the compatibility between the tracking systems paging transmitters and other services.

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