HowCellTowersWork - Unison Site

1 How Cell Towers WorkBY MICHAEL HARRISAs acel ltowe rsite leaseholder, yo uare famil iar with the income and expen sesof the busine ss. But how about the tech nolo gie sinvolve dand their role in thedelivery of wireless communicationsservice sthat we rely on every day?To underst and how cell towers and base stations wor k, star tby taking alook in your own hom you are like 80 %ofyour American nei ghbor s, you own acor dl ess phone system that plugsinto your home teleph one line. As the nam eimpl ies, acordless handset connects wirelessly toasmall base stat ion, allowing you to walk and talk untether ed while maintaining alink to thewire softhe public switched telephone network (PSTN) .In principle, acellular tow er and base st ation that ena ble voice an dda ta service sfor aBlackberryor iPhone aren t much different. Except ,of course ,that the yare bu ilt towiths tand the elements ,cover afar greater geogr aphic area tha nyou rhome, simultan eously sup port hundreds ofhandsets, oper ate in different radio freq uenc ies, an dallo wuse rs tomaintain their connec tionswhile trav el ing from one base station to ano ther ,eve nwhile driv ingat highwa yspe , Cells an dHexesWe re not lau nching int oadiscussion about life in medieval Europe.

2 Rather, towers, cells andhexes are key bu ilding blocks for thedesign and operation of wirelesscommu nication snetw thewireless wor ld,acell is thegeographic coverage areaenab ledby atower. Locat ion sare carefully selected toensure that ind ividual ce lls form atight lyknit mesh wit hout cov erage holes orunnecessa ry overlap, as shown inFigur e1. Engineers use hex sche me sto desi gncell ular ne tworks an dpinpoint towerloca tio ns to me et ser vice demand. Copyri ght 201 rights reser nSi te Manage men ELESS WH ITEP APERFIGURE 1:Towers and Ce llsinaHex Patte rnThe What, Where and HowThe primar yjob of acel ltow er is to elev at ean ten nas tha ttra nsmit an dreceive radio-freq ue ncy(RF) signals from mobile phones and devic es . Wires run from the towe rantenn as to bas estationequipment, typical ly located at ground leve lin se aled telecom eq uipme nt cabinet s. Compon entsof the base stati on include transcei ve rs, which enable the tran smiss ionan dreception ofradiosignals through the antennas, plus sign al amplifiers, co mb ine rs,and asystem controller.

3 To ensure ant ennas are tall enough to cover atargeted cell area, cell towers are typically 50 to 200feet in heigh t. Tow ers ca nbe standalone structures, such as steel poles or lattice frame, or af fixedto other struct ures. In the latter category, cell towers are attached to buildings, water towers,br idges, tun nels, str eet lights, traffic lights, stadium lights, and bi llboards, among other thi ngs. Toaccomm odat eco mmun ityaesth etic concerns, tower sare increasingly camoufl aged to resembletrees or flag poles, or co ncealed in pur pose-built structures, such as church bell tow ers or fac tors affecting cell tower site se lect ionare comp lexand plentifu l. At abasic level, thesite mus tbe adjacent to aroad for physical acc ess ,with ava ilab ility of electrical powe randtelecommunications networ kconnect ivit y. Loca lzon ing ordina nces must acc ommod atetower he ight requirements to ens ure sign al coverage across the terra in.

4 Sourc es ofelectromagneticint er ference need to be avo ided to en su re rad io sig na linteg rity .Env iro nmental and wildli fe impacts must beco nside red, in ad dition toarchitectu ralhist oricpreservati on and avi ation requir eme nts . q ~ ~ ~ K p I ~ ~ ~ K t ~ ~ I ~ ~ ~ ~ ~ ~ ~I ~ I ~ ~ I ~ ~ ~ ~ K -MichaelHarrisThis mix helps carriers und erstand how many potenti al wireless users live or work in the ar eaeach day ,plusthose tha twill bepass ing thr ough on the way to another itionally, wire less carries carefully stud ythe voi ce and data traf fic traver sing their netw or ksin each ce ll area . If utilization be gins to near the capaci ty limits of the antennas on agiventower, they need to eva luate opt ions to incr ease capaci ty.

5 Likewi se, if local population anddemographic da ta is favorable, be fore acar rier begins aggr essi vel ymar keting wireless servicein agiven geog raphic area, the ywant to be sure they have enough capacity in place to servethe new subscrib ers that will be added to the network. Copyri ght 201 rights reser nSi te Manage men TOWERS WORKPAGE ELESS WH ITEP APER Copyri ght 201 rights reser nSi te Manage men TOWERS WORKPAGE ELESS WH ITEP APERLike beverag es, cell towers co me in small ,medium and lar ge sizes (seeTable 1). On thesuper-si ze side of the sca le are macrocell tow er s. These standalone or structure-attachedcellsite sliterally towe rove rthe targe tarea, offering arange of 10 mil es or more in rur al are the mid-sized option, frequently em ployed in ur ban and suburban areas,coveri ng cell areas less than amile in diameter. Tiny picocells typi cal ly cover less than 250yard sand are used in office buildings ,airports and busi ness centers.

6 The newest arrival,femtocells, are personal de vice sintended for hom eor of fice use and offer acoverage rangesimilar to aco rdless phone ba se stati ning the RANTog et her ,the radio fre quency spectrum, towe r, base st atio neq uipme nt and us er mobile devic escrea te aRadio Ac cess Network (RAN), illust ratedinFigu re thefou nd atio nfor the deli ve ryof all mobile services and applications, just like physi cal net works co nst ruct ed of fiber- optic andcop pe rwiring enable telephone, data and TV services tohomes and businesse s. The RANcrea tesareliable and robust communi cat ions network infrastru ctu re, just wi thout the wir the , wireless carrier stypicall yuse one of two st anda rd techno logy pla tform sto offerdigital mobile services Code Divisi on Mul tiple Acces s(CDMA) orGlob al Sy stem for Mo bil eCo mm unic ations (GS M) in arange ofradio freq uencies alloca tedbythe Feder alCo mm unic ations Commission (FC C).

7 CDMA and GSM are co nsid ered digi tal sec ond- gener ati on(2G) technologies,as they supplanted the first- gene ration ofan alog cellul ar techn ologi es. q J ~ EPdF ~ J ~ EQdF `aj^ ~ dpj ~ ~ ~ ~ ~ ~ f ~ ~~ ~ K -MichaelHarrisCDMA is ageneral term fortechnical standards known as cdmaOne (IS- 95), a2G technology,and CDMA2000 (IMT-MC ), a3G platform. CDMA2 000 includes prot ocols for ac celerated da taTOWER TYPEM acrocellsMicrocellsPicocellsFemtocellsME ANINGDESCRIPTION10 milesStandalone or structure attached1mile in diameterUrban and suburban250 yardsOffice buildings, airports, campusesLimited in buildingPersonal devices for home/officeTABL E1:Cel lTower Typ es Copyri ght 201 rights reser nSi te Manage men vi ce s, including 1xEV- DO(Ev olution-Data Optimized) protocol su ccess or to CDMA2000, a4 Gtech nol ogy, iscal led 3 GPP LongTer mEvolution (LT E).

8 Wo rldwide, GSM is the most widelyused 2G wireless com municationstech nology. For 3 GGSM, there aretwo favored tech nical approaches En hanced Data rates forGSME volution (EDGE) and UniversalMob ile Tele communi cationsSystem (UMTS). UM TS requirestha tcarriers comple tely replacethe ir exist ingba se stat ionequipment tooffe r3G service s, while EDGE doe snot. Howeve r, UMTS is also afou ndat ion for LTE 4 Gtechnology. Mobi le WiMAX (al so known as ) is separate 4 Gtech nology now being deployed in the Tech Alphabet SoupFIGUR E2:Wireless Rad io Access NetworkACRONYM1xEV-DO2G, 3G, 4G3 GPPCDMA cdmaOneCDMA2000 EDGEGSMLTEUMTSWiMAXMEANINGE volution-DataOptimized, a3G CDMA technology for boosting data speeds and network capacityThe second-generation,third-generationand fourth-generationof digital wireless technologies3rd Generation Partnership Project, aGSM wireless technology standards consortiumCode Division Multiple Access, afoundational digital wireless technologyThe 2G version of CDMA, also called IS-95 The 3G version of CDMA, which includes 1xEV-DOEnhanced Data rates for GSM Evolution, a3G GSM technologyGlobal System for Mobile Communications,the world s most widely deployed 2G wireless technologyLong Term Evolution, a4G technology platformUniversal Mobile TelecommunicationsSystem, a3G GSM technologyWorldwide Interoperabilityfor Microwave Access.

9 The Mobile version is a4G technology and is alsocalled TOWERS WORKPAGE 4 WIR ELESS WH ITEP APERWhat s the Freq uency?In theU. S., tod ay s 2G and 3G wireless communicati on servi ces are commonly deli ver ed intwo radio-f requen cy spectrum bands the Cellular band and the PCS (PersonalCommunicationsSe rvices) band. Cell towers ar econfigured wi th antennas to support servicesin these freque Cellular band, al so called 80 0 MegaH ertz (MHz) ,incl udes twoblocks of frequencies of25 MHz each, one from 824 -849 MHz and the other from 86 9- 894 MH z. The PCS Ba nd, alsoknown as GigaHert z(which equat es to 190 0 MHz) ,inc ludes six freq uency blocks of 10 to30 MHz auct ionin gthe se Cellular and PCS frequency bl ocks to carri er s, the FCC pl aced strictlimits on theamount of spectrum an indi vidual carri er coul dpurchase in agiven geographicar ea. The int ent was tocreate acompetitive market with mul tipl ewi reless car riers in ever ymaj or metropo lita nservice area (MSA).

10 As aresul t, lim ited wir eless spectrum was avai labl etoeach carrie rto offer services. As mo re customers were added to thei rnetworks ,carri er sneeded to find ways to stret ch the finite RF spectru mthey had avai labl 2006 ,the FCC auctioned additional spectr um for Advanced Wireless Ser vices (AWS)operating in the 1710-1755 MHz and 2110- 2155 MHz bands. The forced transi tion from anal ogto di gital broadcast televisio nservices freed up aswath of additional spectrum in the 700 MHzband, wh ich the FCC au ctioned to wireless car riers in 2008. Verizon Wireless and AT&TMob ility were thebi ggest bu yers and are eyeing the frequencies for 3G and 4G uce and ReuseTwo tech nical approach es frequ ency reuse and sectorization have helped wireless carriersget the most of their Cellular and PCS riers typically configure adjacent cell stouse diff ere nt fre quencies, preventing con fusion among hand sets abo ut whichtower ante nna to connect (se eFig ure 3).