RTCG Laboratory Report CDMA / CAD & CT2 Compatibility Spectrum for Asset Tracking Mobile Data Networks

Spectrum suitable for CDMA spread-spectrum asset tracking 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 asset 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 asset 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.

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