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Chapter 6: Lessons Learned A summary of the lessons learned from the Federal IN To protect public health, standards-setting Focus Wireless Transmission Base Station Symposium organizations have established limits for expo- follows. The lessons learned reflect Ferleral Focus' sures to radio-frequency fields. There is cur- understanding of and conclusions drawn from the rently no single national exposure standard recognized by all Federal agencies and State Symposium's presentations and discussions. Governments although several Federally and A. Lessons Learned About How Base internationally recognized standards-setting Stations Operate organizations as well as several States have set detailed exposure limits.In the absence of a ■ Base stations are essential for cellular tele- single Federal standard,the Federal Commun- phones.Without a network of cellular tele- ications Commission (FCC) in 1985 adopted a phone base stations,cellular telephone corn- 1982 standard promulgated by the American munications would not be possible. National Standards Institute (ANSI), the preeminent private-sector standards-setting ■ Base stations are low-power radio relay sta- )may.The FCC is in clic process of updating its tions.Cellular telephone base stations are own standard and has proposed to use the radio relay stations which operate in the UHF revised (1992)ANSI standard. portion of the radio spectrum near TV Channel 69. Base stations operate at a small fraction of ■ RF exposure from base stations are vastly the power of most commercial radio and tele- below all exposure standards.Measurements vision stations. at numerous cellular base stations conclusively ■ An increasing number of cellular base demonstrate that the ground-level exposures from such facilities are extremely low,hundreds stations areneeded to increase system capaci- or thousands of times below the levels permitted rY and minimize transmission power.Building by the various standards the FCC is currently additional base stations in an area already coy- considering.One participant who has performed • erect,a technique known as"cell splittif,"per- such measurements called the matter of RF mits the same channels to be reused in an area exposure from cellular base stations as"almost relatively close to the base station.This not only a non-issue in terms of actual exposure levels." increases the network's capacity,it also mini- mizes transmission power and antenna height. ■ R.F.exposure from cellular base stations is ■ Cellular networks are �'different from to electromagnetic beginning to deploy fields from power lines.Power line fields are advanced digital technologies to further much lower in frequency(by a factor of 14 increase system capacity.Digital technologies, million),and interact with the human body by such as Time Division Multiple Access vastly different physical mechanisms of interac- (TDMA)and Code Division Multiple Access tion than do the RF fields from a cellular base (CDMA),permit cellular networks to handle station. greater traffic levels in the same amount of radio spectrum than traditional analog tech- C. Lessons Learned About Base Stations nology allows. and Interference B. Lessons Learned About Base Stations ■ Cel a lar base stations rarely cause electro- and Public Health magnetic interference.The radio waves emitted • Cellular base stations emit radio waves..Each by cellular base stations can theoretically interact with electronic equipment,and theoretically radio wave comprises electric and magnetic cause the affected equipment to exhibit symptoms fields.Those fields can affect the atoms,ions, and molecules that make up living cells.The of interference.However,it usually takes a very most common effect of strong fields is a warm- strong radio signal for such interference to manifestung of tissue.Intense fields can produce enough and interference to electronic equipment rarely involves base stations. heating to cause many significant biological effects.Weaker fields can produce subtle chemi- ■ There are no governmental electromagnetic cal changes with no known adverse health interference standards for consumer electronics. effects. Some manufacturers build certain amounts • shielding and filtering into their equipment based on assumed ambient levels of RF energy; others employ little or no shielding.Inadequate immunity can be remedied after the fact,and if 36