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Executive Summary • I. The Purpose of this Publication then routes that half of the phone conversa- TDMA(Time Division Multiple Access) tion into the wired telephone network,or and CDMA(Code Division Multiple According to recent news reports, retransmits it by radio to a second subscriber's Access)manipulate digital words associated Americans are signing up for mobile tele- mobile or portable unit_The second half with a number of conversations so that phone service at the rate of about 28,000 of the conversation reaches the base one radio channel can handle more than per day.For reasons described below,as station by wire or radio link.Then the one call at a time. the ranks of subscribers grow,so must the base station transmits it by radio to the number of the fixed facilities known as TDMA is already in use.As implemented first subscriber unit.To make natural "base stations"that relay such phone calls. in North America,TDMA interleaves conversation possible,subscriber units and sequential samples of a few conversations A typical base station employs a small base stations both transmit and receivein one relatively narrow radio channel.A shed for electronic equipment and a set of radio signals simultaneously. TDMA system employs many such narrow- antennas on a support structure.More Each radiotelephone cull entails use of a band channels.CDMA,now undergoing base stations means that more people end portion of the radio spectrum dedicated to field tests,employs a much wider radio up living or working near them.Some the service.Using one particular frequency channel that carries many uniquely coded have voiced concerns about base stations or span of frequencies (channel)generally signals simultaneously. on the grounds of aesthetics,fear of precludes use of the same and nearby adverse health effects,depression of prop- frequencies or channels by others in the More and more conventional ("analog") ern;values,or interference to electronic cellular systems will likely convert to a devices and systems.To examine these same area.Otherwise, interference will digital format as demand for service result.The spectrum available for radio- issues,the Scientific Advisory Group on continues to increase and the neer-scary telephone communications is limited. digital equipment drops in price through Cellular Telephone Research(SAG), Without the use of special communications predecessor to Wireless Technology technologies,demand quickly outstrips supply. mass production. Research,L.L.C. (WTR),commissioned Federal Focus,Inc.,a nonprofit educa- Cellular radio technology is the key to III. There Is No Scientific • tional organization,to convene a National meeting the public's growing demand for Evidence that Base Stations Symposium on Wireless Transmission mobile telecommunications service.This Pose Public Health Risks Base Station Facilities.Experts in a number technology compensates for the limited of fields from the public and private sectors amount of spectrum available by using Modern radiotelephone systems,like other participated.This publication,Federal base stations with modest service areas. forms of radio communications, employ Focus National Symposium on Wireless This allows the reuse of radio frequencies the transmission and reception of radio Transmission Base Station Facilities:A in nearby areas without interference.The signals.Each radio signal consists of electric Tutorial,funded by WTR,provides a reuse of spectrum, in turn, increases the and magnetic fields whose strengths vary at recap of the experts'presentations at the radiotelephone network's call-handling a certain frequency.The same is true of Symposium and examines the issues asso- capacity.As demand for radiotelephone infrared (heat)rays,visible light,and ciated with construction of base stations service grows,the service areas of base other forms of electromagnetic energy. to meet public demand for mobile stations must shrink through reductions Electric and magnetic fields can interact communications. in transmitter power,antenna height,orwi i living and nonliving matter in various both.This technique,called cell splitting, ways,depending mainly on the fields' II. Base Stations Are a requires construction of more base stations strengths and frequencies.Radio signals Technological Response to the near the people they serve. are called nonionizing electromagnetic Scars' of Radio Spectrum any because they do not upset the elec- p Cell splitting has practical limits.To keep trical balance of positive and negative Mobile and portable telephones are acnially up with the demand for service,a radio- charges within each atom (ionize the specialized radio transceivers(transmitter/ telephone network approaching those atom).Higher-frequency forms of electro- receivers) that employ frequency bands limits can bring additional technologies magnetic energy,such as ultraviolet rays, set aside by the Federal Communications to bear.One is the use of special direr- can upset an atom's electrical balance. Commission (FCC)for that purpose.A tional antennas that cover narrow swaths Individual atoms group together to fuuu subscriber's unit impresses the user's voice of area.Digital signal foiwats are a principal onto a radio signal byvaryingsome basic means of using available radio frequencies molecules,and each living cell is a collec- tion of many molecules.A cell reproduces property of that signal in steptepwith the even more effectively.Digital formats • speech.An antenna affixed to the unit or entail the conversion of sequential samples using a blueprint stored chemically in the to the subscriber's vehicle launches the of each half of a radiotelephone conversa- cell's nucleus.Ionizing electromagnetic radio signal into space.A nearby base tion into digital words,strings of ones and energy is dangerous because it can alter station intercepts the signal and extracts zeroes that describe the samples in mathe- the chemical blueprint and cause the cell the embedded speech.The base station matical terms.Digital formats such as to mutate.Weak nonionizing energy,such as the radio waves at ground level from a lill