Authors
Joseph W, Verloock L. (2010). Influence of mobile phone traffic on base station exposure of the general public. Health Phys. 99(5):631-8.

Introduction
Radiofrequency (RF) signals from mobile phone base stations (BS) vary in time. Available data about temporal variation of these signals are very limited. There is an increasing interest in characterizing RF exposures from base stations over longer periods, in particular, in obtaining accurate estimates of average and maximum exposures. For a variety of reasons, it is difficult to perform measurements over a long time. Therefore, it is important to find out whether such estimates can be based on short-term measurements.

Objective
The objectives were: 1) to study the influence of mobile phone traffic on temporal RF exposure from base stations over a 7-day period at five different sites and to compare these data with Erlang data representing the average traffic intensity over a period of time; 2) to determine minimum required measurement periods to obtain accurate estimates of maximum and average exposure over a longer period (7 days).

Methods
Temporal electric field strength measurements were performed for FM, GSM900, GSM1800 and UMTS during 7 days at 5 sites that differ in terms of environment, population density and mobile phone traffic: 1) residential area, 2) rural terrain, 3) office environment, 4) urban environment, 5) industrial environment. The Erlang traffic intensity values were obtained from wireless telecom operators. Minimum required measurement periods were determined for different RF signals.

Results and Interpretation
It was shown that the minimum required measurement periods were long (several hours or even days). Only for FM signal that is relatively constant in time maximum and average exposures over a 7-day period could be estimated from measurements during periods shorter than 3 minutes. Therefore, new methodologies are needed to estimate maximum and average exposure over a long time. It was shown that the time periods of high exposure and time periods of high traffic intensity (Erlang data) were in good agreement. The authors proposed a method to estimate electric fields at a time instant using Erlang data and short-term measurements.

Conclusion
The proposed method makes it possible to estimate maximum and average exposures over a week from short-term measurements using Erlang data and avoiding long-term measurements. This method can be used by control agencies to check maximum exposure values for compliance with exposure limits.


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