GSM Base Station Antennas GSM Technology (cont’) GSM Base Station Antennas Antenna is the Interface between the Radio Networks and the external environment. Radio frequency (RF) energy is coupled from the transmitter to the air and from the air to the receiver. Omni-directional Antennas: Gives 360 degrees radiation pattern. Directional Antenna: Where the energy is focused on one of the directions according to the antenna pattern. Antenna Gain is the ratio of the radiation intensity in the main beam direction to the radiation from isotropic antenna.

Omni-Directional Antenna GSM Technology (cont’) Omni-Directional Antenna

GSM Technology (cont’) Directional Antenna

Types of GSM Base Stations GSM Technology (cont’) Types of GSM Base Stations Macro Cells Constitute the main backbone of most cellular networks Height above roof tops. High output Power: from 25-40 Watts .in addition to the antenna gain (mostly 13 to 21 dBi), which yield to a range of Effective Isotropic Radiated Power EIRP mostly from 500 to 1000 Watt . Commonly sectorized for efficient frequency utilization hence more capacity. Coverage ranges from 500 m to 35 km.

Types of GSM Base Stations (cont’) GSM Technology (cont’) Types of GSM Base Stations (cont’) Micro Cells Height below rooftops. Low output power, generally 2 W in addition to antenna gain (Mostly 13 to 18 dBi) which yields EIRP up to 40 Watt. Usually deployed for capacity (in the hot spots) hence spectrum efficiency Coverage up to few hundred meters.

GSM Technology (cont’) Types of GSM Base Stations (cont’) Pico Cells Mostly Indoors. Operators usually adjust the power levels to low output due to proximity to humans (usually the antennas are fixed on ceilings or wall mounted) Customary used to improve indoor coverage and provide additional capacity.

Effect of Radiations on Humans Non-Ionizing Radiation: Are radiations that do not have sufficient energy to break the chemical Bonds in the body. The main effect is the heating of the body tissues. Source: http://radsafe.berkeley.edu

Effect of Radiations on Humans (cont’) Ionizing Radiation: High-energy radiation, such as X-Ray radiation, where the electromagnetic photons have sufficient energy to break chemical bonds. This energy can remove electrons from the atoms( ionization), which will recombine with other atoms and thereby might cause some damage to biological tissue potentially leading to serious diseases. Source: http://radsafe.berkeley.edu

Effect of Radiations on Humans (cont’) Specific Absorption Rate (SAR) The rate of energy absorption is called Specific Absorption Rate (SAR). It is measured in Watts/Kilograms (W/Kg). SAR is directly proportional to the conductivity and inversely proportional to the density of tissue. SAR=σ* E^2/ρ

International Bodies Guidelines The most widely adopted guidelines are those developed by: American National Standards Institute (ANSI) The Institute of Electrical and Electronics Engineers (IEEE) International Commission on Non-Ionizing Radiation Protection (ICNIRP) National Radiological Protection Board (NRPB) These International bodies are satisfied that below the recommended levels there is no scientific evidence that the exposure poses any health risk.

International Bodies Guidelines (cont’) The ICNIRP guidelines are less than NRPB (National Radiological Protection Board) guidelines and ANSI/IEEE guidelines. The ICNIRP guidelines for the public have been incorporated in European Council Recommendations (1999) which have been agreed In principle by all countries in European Union (EU). Some European countries have incorporated the ICNIRP guidelines into statute.

Exposure levels set by ICNIRP International Bodies Guidelines (cont’) Exposure levels set by ICNIRP ICNIRP (International commission on Non-Ionizing Radiation Protection) restriction on exposure for general public: SAR (Specific Absorption Rate) limit is 0.08 W/kg (average over 6 minutes period). Power density in GSM 900 MHZ is 4.5 W/square meter. Power density in GSM 1800 MHZ is 9 W/square meter.

International bodies Findings and Recommendations Operators can adjust the network settings hence demonstrate compliance with the recommended levels set by ICNIRP. FCC require specific site environmental assessments for roof top base station Antennas with total power greater than 1000W ERP for cellular (800-900 MHz) . Power of Indoor antennas must be adjusted to low levels due to the proximity of humans.

International bodies Findings and Recommendations (cont’) Where the guidelines levels may be exceeded (e.g. next to base stations antenna at a roof top), physical exclusion zones has to be established around the antennas. Each exclusion zone should be defined by a physical barrier and prominent signs with logos. Example1: below are “ the estimated worst case horizontal distances that should be maintained from a single sectorised, cellular base station antenna to meet FCC RF exposure guidelines”* *Source: http://wireless.fcc.gov

International bodies Findings and Recommendations (cont’) Example2: the “estimated worst case horizontal distances that should be maintained from a single sectorised PCS base station antenna to meet FCC RF exposure guidelines”* * Source: http://wireless.fcc.gov

International bodies Findings and Recommendations (cont’) “ The relationship between the RF power density levels required to produce known biological effect, The RF power density levels specified in the safety guidelines , and the RF power density levels actually measured around Mobile Base Stations” Source: http://www.mcw.edu

International bodies Findings and Recommendations (cont) UK NPRB has conducted spot checks in England on the average intensities at some publicly accessible sites around some Base Stations, the maximum was far below the ICNIRP public exposure guidelines. Note: The results might differ if measured in other areas with different circumstances, e.g. different EIRP or number of antennas/operators. Source: http://www.mcw.edu

References U.S. Federal Communications Commission (FCC),“A Local Government Official’s Guide to Transmitting Antenna RF Emission Safety: Rules, Procedures, and Practical Guidance.”27-29:June 2,2000. http://wireless.fcc.gov/siting/FCC_LSGAC_RF_Guide.pdf. Stewart Report

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