Long-term variability of electromagnetic field strength for GSM 900MHz downlink band in Belgrade urban area

The long-term variability of electric field strength, obtained by band selective measurements for GSM 900 MHz DL band in real mobile network environment, is considered in this paper. Intensive measurements were carried out for 7 days at each of 7 different locations in urban area of Belgrade. The measurement results show that each day can be divided in two distinctive periods: one with the higher levels and (9h-23h) and one with the lower ones (23h-9h). Regarding the days of the week, the results show that the weekend days are slightly different from the working days. Having in mind the need for determination of values averaged over the defined time period, additional uncertainty stemming from telecommunication traffic and transmitter functionalities must be taken into account. Mentioned uncertainty was determined for different time intervals of averaging: 10s, 30s, 1min, 6min, 15min, 30min, 1h, 3h, 5h, 10h, 14h and 24h. Results show that the uncertainty is in the range 3.57 - 12.11% for 6 different categories defined with regards to the days of the week and the specific day periods.