KOBA MIRESASHVILI  Chief of Environmental and Sanitary Control Service of MagtiCom

Our readers have shown a keen interest in the publications dealing with cellular communication and the related sanitary safety issues. Numerous letters addressed to the MagtiCom Sanitary Service is a proof of this interest.
   The majority of questions we receive from our readers concern cellular base stations. This is a broad topic exploring a number of problems. To make this article simple and concrete, we decided to present it in the form of questions and answers.

Q: Is there any hazard related to cellular base stations? What do scientists think?
 
   Scientists from many different countries (Petersen, Thasandott, Maulder, Hant, etc.) have worked out a common approach to the question and believe that the operation of a base station is absolutely safe, provided all the necessary requirements are met. These requirements are as follows:

· modeling the level of electromagnetic field prior to the installation of a base station;
· measuring the intensity of the electromagnetic field at the moment of phasing in and throughout the operation of a base station;
· compatibility of the intensity of the electromagnetic field to the statutory sanitary norms at any stage of operation.
 
   We should note here that the Georgian legislation (Decree #297/n of 16 August, 2001 by the Minister of Labor, Health Care and Social Protection of Georgia “Of the Approving of the Norms of the Qualitative State of the Environment”) sets forth all the required measures to be taken. Moreover, in Georgia the maximum acceptable level of intensity of the electromagnetic field is 10 mW/cm², which is much lower than the corresponding parameter in the United States and the EU countries (470 mW/cm²).

Q: What is a cellular base station? Does the “base station” mean the main station?

   First, let us differentiate the terms: mobile phone - also referred to as a mobile radio station, a cellular phone or a portable phone - is a low-power one-channel transceiving radio. “Mobile” means that such a transceiver can move in space together with its user or be built into a vehicle, a train or an aircraft and used when those means of transportation are in motion.
   A base station  also known as a cellular communications station, a cellular radio station, or a cellular radio knot) is a low-power multi-channel radio transceiver. The name “base” means that such a transceiver does not move in space. It is located in a specially chosen place to create the so-called “coverage area”. To better understand the meaning of a base station let us discuss its place in the system of cellular communication (Draw. 1).
   As is seen from the drawing, when the number of a mobile addressee (B) is dialed on a mobile handset (A), the latter uses a radio signal to establish connection with the base station (I) in the coverage of which it presently is. The signal from the base station is transferred to the Main Switching Center (MSC), which establishes the location of subscriber B and sends a signal to the appropriate base station (II). The addressee receives a radio signal directly from base station II.

   During a telephone conversation the radio signal passes this track in a two-way direction. Thus, a base station is a connecting link between the mobile user and the MSC. The quality of cellular communication greatly depends on the coverage and the capacity of a base station.

Q: What are the main criteria in selecting the location for a base station? What should be the shortest distance between a base station and a residential house?

   When choosing a place for a base station, special attention is paid to the altitude at which the antenna is mounted. That is why in populated areas a sufficiently tall building or other high installations are chosen, and special towers are mounted in non-populated areas to achieve optimum coverage and low indices of intensity of the electromagnetic field.
   As for the distance between base stations and residential houses, in the US, EU and CIS it is determined by the demand placed on any base station operating within the range of radio frequency that the intensity of electromagnetic field generated by radio antennae must not exceed the maximum acceptable level. That level is 10 mW/cm² in Georgia. The sanitary safety of the population is contingent on this parameter and not by the actual distance between a base station and a residential home.

Q: Are there any limitations placed on locating base stations in “the most vulnurable areas”?
(These include residential homes, schools, nursery gardens, hospitals, etc.)

   No. The sanitary norms for base stations operating within the radio frequency range do not set any limitations regarding to the location of an antenna unless the intensity of electromagnetic field exceeds the maximum acceptable level. As for the idea that a base station should be as far as possible from sensitive areas, it is entirely unfounded. The matter is that the intensity of electromagnetic field generated by the base station antenna is decreased much more rapidly when moving away from the antenna in a vertical direction (either up or down) than in the horizontal plane along the axes of electromagnetic field (Draw. 2a and 2b).

   This is confirmed by instrumental measurements. The influence of the electromagnetic field on people (residents, employees, students, etc.) in a building with a BS antenna on the roof is much weaker than it is on people several hundred meters away. However, in both cases the intensity of electromagnetic field does not exceed the maximum acceptable level.

Q: How is the compatibility of the intensity of electromagnetic field generated by a BS with the statutory  norms determined?

   This can be determined either by calculation or by measurement. Both methods are based on the physics of RF radiation.
   Calculation requires knowledge of such technical characteristics of BS transmitters and antennae as the frequency range, transmission power, diagram of antenna direction, altitude of antenna location, inclination, etc.
   Measurement requires expensive state of the art equipment.
   The State Sanitary Inspection carries out instrumental measurements of the intensity of electromagnetic field with such equipment in order to constantly monitor the sources of electromagnetic field. When making these calculations or measurements, one should take into consideration the possible existence of other sources of RF band, because their signal will be added to that of a base station, thus increasing the total intensity of the electromagnetic field.

Q: What permits are needed to construct and operate a base station?

   When a site for a base station is chosen, the area is either rented or purchased in accordance with the relevant regulations, an estimation of construction and sanitary parameters is elaborated.
   These estimates are submitted to the competent agency for review, following which permission for construction is granted.
    The Inspectorate of State Supervision over Sanitary Norms and Rules at the Ministry of Labor, Health Care and Social Protection of Georgia is responsible for setting the necessary sanitary-safety and construction limitations.
   When the construction is completed and the BS is put into operation, the Inspectorate of Sanitary Supervision conducts an instrumental measurement of the electromagnetic field. If the results of the measurement fully satisfy the sanitary norms and rules, a relevant document is issued. If the results of the measurement are not satisfactory, the characteristics of the BS antenna are changed or the antenna is dismantled.