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Health aspects of wireless communication: health and safety associated with exposure to wireless radiation from personal telecommunication base stations

While there are new next-generation network roll-outs due this year, projected cellular mobile phone shipments from major makers continue to show a slowdown in growth. The personal wireless communication business probably will not soon pick up from where its growth left off. When they do, more wireless systems are likely to come on line, each with its own network of base stations. This would extend the trends for the future that look much the same as before the stall in the current product cycle, except that economic, public relations, and regulatory interests would likely lead to co-location of towers and antennas (i.e., locate base stations from different services on the same site or structure.) The geographic region served by a base station is called a cell. A cellular base station or cell site refers to the antennas and their associated electronic equipment. Each base station is the equivalent of a radio station. Co-location of a greater number of base stations would undoubtedly result in increased levels of public exposure to microwave energy over time, Cellular mobile communication systems make use of many base stations (or cells) located throughout a service area. When a user places a call, the handset communicates with a nearby base station. The base station then relays the call to a switching office and then to another cell phone handset, or to the conventional wired telephone network. As the user moves about, from one cell to another, the system automatically hands-off the call, seamlessly, to the next base station. Base stations and antennas are essential for cellular telephone and other wireless communications services. Microwave radiation is used to carry telephone messages and data between the mobile unit and base-station antenna at a fixed cellular site. Together, they make mobile telephony and wireless communication a reality, so that user can communicate, and access data and information, while on the go. While the message or data handling processes and computational capability are all necessary aspects of a wireless communication system, the form and intensity of the transmitted microwave energy is of the greatest interest to biological responses. There are considerable public concerns regarding the biological effects and safety of microwave exposure from wireless base stations. There have been repeated calls for measures and tools that would reduce the exposure to microwave radiation from cellular mobile telephone operations. In fact, at any given time, there are always one or two or maybe a dozen communities trying to stop a proposed base-station site. The radiated power from a base station antenna can vary from less than a watt to as high as 500 watts per channel (or transmitter), depending on the location and type of the antenna used for a cellular communication system. A typical base station antenna is mounted on a tower, on the roof, or on the sides of a building, or on another structure that provides the required height. It may also be mounted indoors, on the ceilings of offices, homes, or airport terminals. These antennas provide tether-less access, with short distances between the transmitter and receiver to enhance and supplant existing wired networks. Higher power antennas are used at rural base stations to relay calls between the user and the wireless telephone system base stations, which are spaced far apart. The distribution of base stations and antenna powers are determined by two related factors of the wireless communication system: Coverage and capacity. An adequate signal strength is necessary to cover the entire service area, and a sufficient capacity is needed to provide enough free channels to accommodate any user within the cell who might wish to use the system. As the number of users grows, more base stations are installed closer together to increase capacity. However, they are operated at lower power levels to provide comparable signal strength and to prevent interference among neighboring base stations. Thus, in urban areas, base stations (or cells) are closer together, but are operated at lower power levels than in rural areas, where the cells tend to be larger. The amount of microwave power radiated from a base station is limited by national and international regulations. For example, in the U.S. Federal Communications Commission (FCC) permits an effective radiated power (ERP) of up to 500 W per channel. A cellular base station may transmit using as many as 21 channels per sector in a sectorial arrangement, typically with three sets of directional transmitting and receiving antennas to cover 360 degrees. Thus, the total ERP can be as high as 10.5 kW per sector. An ERP of 500 watts corresponds to an actual radiated power of 25-50 watts, depending on the type of antenna used. The ERP is higher than the power that is radiated because it takes the directional characteristics of the antenna into account. In rural or less-populated areas, a cellular base station may use several omnidirectional antennas, 3 to 5 m (10 to 15 ft) in length. The antennas may be from 30 to 100 m (100 to 300 ft) above ground. When omnidirectional antennas are used, up to 96 channels could be implemented at a cell site with a maximum radiated power of 48 kW. An omnidirectional antenna radiates uniformly in all directions in the horizontal plane. Its radiation pattern might be visualized as a thin doughnut, centered on the antenna. Base station antennas are frequently located on freestanding, tall, tapered poles, much like lamp standards, or