Summary of Oral Evidence presented to IEGMP by Professor P Ramsdale and Ms R Whetstone, One 2 One, on Friday 8 October 1999

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Professor Ramsdale gave a presentation describing existing mobile phone networks and foreseeable future technological developments. At present Global System for Mobiles (GSM) networks are operated at around 900 megahertz (MHz) by Cellnet and Vodafone, and at around 1800 MHz by Orange and One 2 One. Networks consist of a series of hexagonal cells served by tri-sectored base stations. Cells covering densely populated areas tend to be smaller, and when usage within a cell starts to approach the limit of capacity the operator will split the cell, resulting in an increase in the number of base stations, but a decrease in the power radiated from each site. At that time about a third of the UK population used mobile phones (eighteen million).

Base stations

Traditional base stations have six antennas covering the three sectors, although the introduction of flat-panel antennas resulted in a requirement for only three antennas, which can often be packaged into a single tube. It is likely that with continued improvements in design, it will be possible to mount new antennas for third generation phones in existing tubes. Although antennas are often mounted on purpose-built masts, where possible they are mounted on or in existing structures such as tall buildings, churches, or water towers. The process of site selection is influenced by a number of factors. These include the level of coverage required, the potential sites available, and the need to share sites where possible. Operators are required as a condition of their licenses to share sites where possible, and may also need to demonstrate that this is not feasible in order to obtain planning consent for new sites. It is estimated that approximately 65% of antennas are mounted on existing structures, and that about a third of ground-based masts are shared with other operators. However, there are a number of reasons for not sharing masts. For example, existing masts may lack the necessary physical strength or height to take additional antennas, or may be badly located for another operator’s network. In some cases local residents may express a preference for two shorter masts rather than a single tall one. Sharing of antennas is problematic because operators use base station units produced by different manufacturers, and these combine signals in different ways; theoretically, systems can be combined upstream of base stations, but this does not happen in practice. At present, operators share headframes and could share antenna tubes.

Planning issues

The requirements for planning consent are complex and depend on both the nature of the structure to be erected and its location. The operators' licenses have given them powers to roll out their networks. Nevertheless, for masts in excess of 15 m, or located in either a National Park or a Site of Special Scientific Interest, they have to follow full planning procedures. This is generally not necessary for masts less than 15 m high. Where masts are less than 15 m high and located on a green field site, the operator would have to allow a period of 42 days for objections to be lodged. Where the mast is less than 1 m high, but not ground-based, this period is reduced to 27 days. Local authorities do consider health issues during the planning process, but are required by Planning Policy Guidance Note 8 to seek advice from the Health and Safety Executive. In addition, the Department of Health has input into the planning process and the Department of Transport, Environment and the Regions has produced new draft guidance, which is currently at the consultation stage. The Scottish Executive is in the process of developing a system for dealing with these issues and this is likely to be similar to the Whitehall approach.

Exposure from base stations

For a typical base station mounted on a roof top, with an antenna gain of around 17 decibels (dB), the maximum power density within the building is unlikely to exceed 10 microwatts per per square metre (µW/m²) due to attenuation of around 12 dB by the building. Variation in field strength in the street below is likely to be extremely complex. Close to the building the power density decreases according to the inverse square law. However, further away interference with reflected radiation can lead to increased power density, whilst at greater distances from the antenna the power density can decrease according to an approximately inverse cubed relationship. Operators do not routinely measure the fields around their base stations as there is no legal requirement for them to do so, and they do not consider such measurements to be informative. Typically exposures are 50,000 times below the National Radiological Protection Board (NRPB) investigation levels. NRPB has undertaken surveys around a number of base station sites. Whilst the results are usually similar, local residents derive reassurance from such surveys. Power densities around base stations tend to be somewhat lower than those around military and police installations. The Radiocommunications Agency produces an annual summary of frequency bands and their usage.

Exclusion zones

In order to comply with guidance on restricting exposure, exclusion zones are designated around base station antennas. These extend to approximately 0.5 m above and below the antennas. For GSM systems, most operators already define their exclusion zones with reference to the guidance from the International Commission on Non-Ionizing Radiation Protection (ICNIRP); at 1800 MHz, exclusion zones are set to avoid power densities in excess of 9 W/m². The telecommunications industry does not consider compliance with either set of guidelines to be an issue. Industry argues that the public cannot gain access to areas where investigation or reference levels may be exceeded. Most base stations are surrounded by perimeter fences, and exposures at the boundary are approximately 300-fold lower than the ICNIRP reference levels. Masts often also carry line-of-sight microwave communication dishes. These are highly directional low power devices, and the exclusion zones typically do not extend beyond the mouth of the dish.

Microcells

Where additional capacity is required in urban areas, operators often use layered systems involving microcells. These are low power base stations covering a small area, usually less than 50 m in diameter, and suitable only for slow-moving traffic as in a train station or shopping mall. All operators use microcells, although the definition can vary, with the term sometimes applied to equipment that is physically small, and sometimes used to describe installations below rooftop level. In addition, microcells may be used to provide additional capacity or to increase coverage. At present there are probably only around a thousand microcells in operation, but in the future this could well increase to ten or even a hundred thousand units, with a number of microcells being used instead of a single macrocell. Microcell antennas are generally small and are often disguised, in shop signs, for example. Although the antennas are concealed, they may be labelled to indicate the presence of a radio transmitter and its associated exclusion zone. Because microcells operate at low power, exclusion zones are usually around 10 cm from the antennas.

New technology

Handset dosimetry is more complex because exposures occur in the near field. GSM 900 handsets produce SARs in the head of around 1–3 W/kg under worst case conditions, somewhat below the NRPB basic restriction of 10 W/kg in any 10 g mass. Basic restrictions in the trunk would not be exceeded when using hands-free kits. Older analogue handsets may have higher output powers. Third-generation mobile communications will operate at higher powers because this is the only realistic means of achieving the high bit rates required. However, most of the data will be transmitted on the downlink rather than the uplink; the devices will probably operate with one time slot up and four time slots down. As a result, most of the increase in radiated power will be from the base station not the handset and hence exposures would be expected to be low. In addition, as rapid data transfer will be required for functions such as internet access, it is less likely that the handset would be close to the head. In general, operators have an incentive to transmit data as efficiently as possible in order to maximise their profits. In addition, the activities of operators are monitored by the Radiocommunications Agency. Speech transmission does not require high bit rates and so can operate at lower power. Nevertheless, it may be important to engineer third-generation handsets to ensure that they cannot radiate high powers when close to the head. Another possible future development is that slow data transmissions, that do not require high powers, could be handled by microcells, whilst high bit rate, high power transmissions could be handled by macrocells.

The current second-generation GSM system will be developed to give enhanced second-generation systems, which will continue to operate for some time to come and will probably continue to be improved. In time the third-generation UMTS (Universal Mobile Telecommunication Service) system will be introduced, although this will be subject to the sale of new licenses. UMTS will operate using wideband Code Division Multiple Access (CDMA), which is slightly more efficient than the current GSM system which is based on Frequency Division Multiple Access (FDMA). One potentially important difference between the signals used by the two systems is that the amplitude will be more constant with UMTS. The UMTS forum was suggested as a useful source of information.

The introduction of improved technologies that allow more rapid transfer of data will permit the development of new services. These are likely to include e-mail, internet access, video/graphics transmission, teleservices, mobile information services, and customer self-service. In addition, the operators will attempt to use excess off-peak capacity by increasing delay-tolerant applications and machine-machine communication.

At present the mobile phone market is fragmenting, with the youth market a major growth area. Young subscribers tend to be major users of both voice and short message services. Handsets aimed at this market are often sold with free headsets. This is done mainly to satisfy customers' lifestyle requirements, although the operators also wish to minimise concern.

Another new development utilises the 'bluetooth' protocol to provide local radio links to other devices such as cordless headsets, computers, and printers. This effectively creates a personal area network and will be available next year. The cordless headsets will give rise to localised exposures, but are low power devices with power outputs around 10 milliwatts (mW).

Professor Ramsdale was also party to the oral evidence presented to the Group by the Federation of Electronics Industries.

First issued 5 April 2000