Executive Summary

Electromagnetic Compatibility Aspects of Radio-based Mobile Telecommunications Systems is a research study conducted under the LINK Personal Communications Programme (PCP).  The aim of this study was to quantify the risk associated with unwanted EM interactions between mobile communications devices,  such as mobile phones, and surrounding electrical/electronic equipment.  In addition to the current situation,  emphasis was placed on considering the perceived future position,  to do this mobile communications technology and market trends were considered along with predicted developments in general electronics technology.

The general approach to this study was to define the EM threat produced by single and multiple mobile communications devices and then determine how this would interact/couple with stand alone and distributed electrical/electronic systems.  The predicted threat generated at/within the victim equipment was then compared with current EMC immunity test techniques and levels to determine if they adequately covered the threat posed by mobile communication devices.  Susceptibility experiments were conducted on a selection of medical equipment using simulated mobile communications EM environments.  To understand and demonstrate typical/realistic situations where mobile communications devices and electronic systems coexist,  three different scenarios were developed.

The EM threat posed by mobile communications devices has been defined in terms of the main parameters that constitute it and these include;  frequency,  power,  range(s),  number of devices and modulation/multiplexing scheme.  The threat itself will obviously have characteristics and these will be related to the parameters that constitute it.  The threat characteristics include;  bandwidth,  repetition frequency,  amplitude and probability.

Coupling models have been developed and validated for the interaction between single and multiple sources and wired/distributed systems.  These models have shown that at mobile phone frequencies considerable common mode current can be induced into interconnecting wiring and this can lead to potential interference signals in the cable loads due to mode conversion.

It has been determined that the EM threat generated by mobile communication devices will,  in many realistic situations,  exceed the immunity test limits currently defined in most EMC standards.  Limited susceptibility experiments were conducted and it was found that some medical equipment failed when exposed to the EM signals that can be generated by mobile communications devices.  Although this highlights potential risks this study has shown that the probability of this situation occurring is relatively small and this is supported by the low number of reported incidences.

When assessing the potential future risk both electronic technology within victim equipment and anticipated future mobile communications techniques need to be addressed.

All the information suggests that the speed of electronics will continue to increase and the power consumption will continue to reduce as will operating voltages.  This advancement in electronics has always been considered as detriment to the EMI performance.  This is because higher speed is associated with greater bandwidth, thus more interference energy (noise) will be seen by the electronics,  and this coincides with lower signal power and voltage levels and both these effects will reduce the signal to noise ratio.  On a more positive note modern electronics is becoming more sophisticated and is likely to be better at handling and/or recovering from transient interference effects.

It is believed that the EM threat produced by future mobile communications systems will be less than that associated with current systems.  This is based on the assumption that future systems will rely more on base-band signal processing techniques and thus use lower transmission power.  This is true for CDMA,  which is widely accepted as being the third generation access scheme and will be used in UMTS.  Compared to TDMA systems,  CDMA will further reduce the EM threat as CDMA transmissions are continuous rather than burst.

This report suggests mitigation techniques that could be employed to reduce the potential risk associated with unwanted EM interactions between mobile communication devices and electronic systems.  Also advice and recommendations have been made for equipment.