CA2128107A1

CA2128107A1 - Radio coverage in closed environments

Info

Publication number: CA2128107A1
Application number: CA002128107A
Authority: CA
Inventors: Stefan Erik Paulus Kallander; Philippe Charas
Original assignee: Individual
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1992-11-23
Filing date: 1993-11-19
Publication date: 1994-06-09
Also published as: EP0623261A1; JPH07507189A; JP3386811B2; CN1092571A; SG49242A1; DE69331572D1; US5603080A; AU668798B2; FI943476A0; AU5581894A; FI943476A; WO1994013067A1; KR950700644A; TW255080B; US5404570A; EP0623261B1; NZ258262A; MY130078A

Abstract

ABSTRACT OF THE DISCLOSURE

A repeater system in a communication system including a base station and a mobile unit provides a communications link between the base station and the mobile unit when the mobile unit is located in an environment that is substantially closed off to high radio frequency communication between the base station and the mobile unit. The repeater system has a first linear two-way frequency converter including a high frequency port for two-way coupling to the base station and a low frequency port for two-way coupling to a low frequency signal that is capable of distributing radio frequency power through the closed environment. The low frequency port is connected to a cable which propagates and receives low radio frequency power within the closed environment. The repeater system also includes a first antenna for wireless coupling to the cable, and a second linear two-way frequency converter having a low frequency port connected to the first antenna for two-way coupling to a low frequency signal and a high frequency port for two-way coupling to a signal that is compatible with the high radio frequency signal used by the communications system. A second antenna is connected to the high frequency port of the second linear two-way frequency converter for wireless coupling of the second linear two-way frequency converter to a nearby mobile unit.

Description

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WO g~/13067 PcT/sE93/oos92 RADIO COVERAGE IN CLOSED E~ IRONMENTS

BACKGROUND OE: I HE ll~II!;2 1. Field of the Invention The presen~ invention relates to ~dio coverage in envi~nments that are othervise closed off to such coverage, and more particularly to cellular radio S communications coverage in such closed off eslYironments by means of repcaters, :~
and even more particularly to a repeater system which c~nv~s communications system high radio fiequency signals into low ~adio frequency signals for propagation in the closed offenvh~nment, and then baclcinto high radio frequency signals.

2. Related Art In a c~llular telephone system, each portable tdephone, refes~ed to here as a mobile unit, is able to function only to the e~tent that it is a~le to send and rcceive radio signals to and &om a base station associa~ed with the s3tstem. : -However, in thc ~eal world en~ nmcnt th~e arc impediments to normal radio conununication. For e~amplc, at fre~uencies of a~o:cimatdy 1 GHz or higher, obs~ctions such as tunnels can ar~umatc the radio signal 50 dBlhn up to total cut~f The a nount of attenuadon will dcpcnd on ci:cums~c~s such as the shape of thc hmnd~ and the presencc of obst~uctio~ lil~c t~ains. This attesluation mal~s the ~adio propagation environment ~a8c and un~iabk.
~ior a~empts to sadiate sadio frequency (RP) power into problematic isolated struch~Ies, rcfer~d So bac as c~osed envimn nents, include the use of -leaky coa~ial cable in the struchme, and also the b~ute f~rce approach of di~cting a large RF power levd into the stru~ However, such approaches have p~ven to be both e~pensive and prohibitivdy complicated. , ;

2S SUMMARY QE TEIE INYE~r.nON ~ ~
It is therefore one object of the present imrention to p~nride a simple and ~ :
cost effecdvc approach to providing ~adio cov~agc in closed ~vironments.
Another object of thc u vention is to e~end a celluiar telephone architec~re ~ -into a closed environment so that the closed a~nment is subdivided into sev~al ~ -:

1~, L ~ 3 7 WO 94/L~067 PCrlSE93/1~0992 _ ~ _ cells, and to provide for the hand off of frequencies between them as a mobiie unit moves fmm one oell to another.
A further object of the inven~on is to offer a simple and cost effective solution which can be implemented as an ~add-on kit~ to present radio hardware S without substan~al change or e~t~a cost to this hard~vare.
According to the presen~ invention, the foregoing and other objccts are attained in a repcater system for use in a communication system tha~ includcs a base st, tion and a mobile unit, both openting at a high radio f~quency. The r~peater system provides a communications link between thc base stadon and the 10 mobile unit when ~e mobilc unit is located in an environment that is substantially closed off to high Iadio frequency communication between the base station and the mobile unit. The repeater tystem compriset a first linear two-way fre~uency conv~r~r including a high frequency port for two-way coupling to the base stafion, and a low frequency port for two-way coupling lo a low frequency tignal that is 15 capable of distributing frequency powe~ through the closed en~ronmént. The repeater system also includes cable ~ansmission means coMec~d to the low frequency port of the first linear two-way f~quency convertcr. The cable tran~s~on means is located within the closed en~ironment for radiating the low *equeney conver~d ~gnals within the closed en~ironment. The r~peater system 20 also ineludes a fi~t antenna for wireless coupling to the cable tIansmission means, and a socond linear two-way fi~uency conver~ r ineluding a low frequency port conneeted to the firs~ antenna for two-way coupling to a low ~equency signal, and a high *~quency port for tw~way coupling to a signal that is compa~ible with thehigh ~io frequen~y signal used by the communiea~ions system. The repcater 25 system also has a second antenna eoMected to the high fiequency port of the' second line~r two-way frequa~cy converter.
With the above~escribed structure, a mobil unit in the viciniq of ~he second antenna can communica~e with the base s~tion in a nonnal fashion. ~he convcs~on of the high frequency signal into a low ~quency signal and thesl bac~
30 again into a high frequency signal is complctely tIansparent to both the mobile unit and the base station.

~ j 7 WO ~1113067 PCrlSE93/00~92 In another embodiment of the a~ove~escribed repcater svstem, the firs~
antonna, second linear tw~way fre~uency convener, and se~ond antenna are located within a ~rchicle, and the cable t~ansmission means is distnbuted along an andcipated path of the v~,icle through the closed environment. As used S throughout this specificadon, the term ~vehicle~ is used to represent a conveyance within which a mobile unit is to be able to opaate. For ~ample, the vehicle may be a train car t~avelling through a hmnd as part of a subw~y systes~. In this e~ample, a passenger on the ~ is able to use a mobil unit to communicate with the base s~tion by means of the rcpeater system. This is because a train car so 10 equi~ped becomes a mobile base s~ion that ser~ s a moving cell that is defined by the confines of ~e t~ain itself. A passeng on the t;ain may use a mobile unit the same as hc or she would outside of the subway system.
Besides pro~iding normal communications service to a mobile unit lo~ated on a vehicle that is ~a~dling within a closed en~ironment, a furthcr advantage of IS thc dcscribed mobile base station is that the high radio frequcncy power Icvel need only bc s~ong cnough bo pr~e through thc train car l.e., the moving cell).
This lceeps the total radiated power in the closot cnvironme~t at a low levd compared to ~e high levd of ou~ut powcr that would be rcquired to p~paga~e the high ~adio frequency signal ~roughout the nmnel for dir~ re~pdon by a 20 mobile unit on a tlain. Oth en~nsomnental benefits are achieved by not having to subject passcngas and oth equ~pmcnt to high levels of ra~io wavc energy.
Instead, passengers are only subjec~d to ~he low power signal transmitted by the second anta~na on boa~d the tlain.
Anoth feature of thc r~peater system is useful, for e~ample, when a 2S communication sys~n has a base station located in each of adjac~nt subway:
slations. Here, the cable transn~ission means is associated with a fi~t ~e station, and a tamin~ p~ion of the cable transmission means overiaps a c~re~onding te2min~ portion of a cable ~ransmission means tha~ is associated with a sccond basc station. The rcgion of o~e lap should bc sufficient to permit thc vehicle, in 3Q this OEse a t~ain car, to simultaneously pass by the t~minal por~ons of both cable t~ansmission mcans for at lcast sievaal seconds whcn the ~ehiclei is t~avelling at a S A) ~
WO 94/L3067 h L ~ '~ PCI'tSE93/00992 typical speed away from the first base sta~on and toward the second basc station.
This avoids the problem of having all mobilc uni~ on b~ the t~ain, travelling away from the first base station and toward the second base sta~on, handed off ~om the f~rst basc sta~on to the second base sta~on at the s~une time.
A150, in the e~ample of a mobil unit loca~d on a moving vehiclc, the above-desc~ibed rep~ater system may fi~ther include a seslsor ooupled to the second linear two- vay f~quency a~nve~er for alten~a~vely tula~ing the se~ond lincar tw~way frequency conver~ on and off i~ response to respectivdy sensing the vehicle entering and e~iting the closed en~ironmcnt.
In another embodimcnt of the r~es s3~stem, the high ~adio frequency is in a range of 900 to 2000 megahertz, and the low frequency is in a range of 30 to 300 megahe~z.
In yet another embodiment of the repea~ system, the cable ~ansmis~on means is a bifilar cable.
1~ still anoth cmbodiment of the r~peater system, the cablc t~ansmis~on means comprises a c~a~ial cable connec~ed to the f~rst lin~r two-way f~queacy converter, an amplifier ha~ing an input connec~d to the coa~ial cable, and a third antenna connected to an output of the amplifier.
~ another cmbodiment of the ~er system, thc f~st and second linear tw~way f~quency conver~s are synchroniz~ to a system cloclc BRI~ DESC~E~
Pigure 1 is a bloclc diag~am of one cmbodiment of the systun in accordance witk thc present invention.
Figures 2a and 2b are morc deta~ed block dia~ams showiDg two prefa~
embodimcnts of thc cablc t~ansmissioQ means for use in tbe prescnt invention.
Figure 3 is a block dia~am showing another cmbodiment of ~^ p~s~nt invcntion.
Figures 4a 4c show altu~ative embodiments of anotber feanlre of the psesent in~ention which pro~ides continuous mobile telecommunications scn~ice as a subscriber moves back and forth be~ween op~ and ~closed en~nmnments.

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WO 941L~067 pcr/sE93lo~992 DESCRIPI7ON OF THE P~
The present invention pro~ides ~io coveIage to closed envi~onments by recognizing that the radio fre~quency en~romncnt consists of two parts: a fi~st en~ironmcnt in which thc rddio signal is propagated u~ to, bu~ not within, the S doset en~ronment; and a second cnvironmem coDsisting of thc ar~d located within the closed environment. Methods for pmpagating a ~a~io sigDal in the first en~ron;nent, which does not presl~ the abave~escri~ed signal obstruction problems, are well blown to thosc of ordinary sl~ll in the art, and need not be described here. Cellular telcphone systems functioning in this first en~rironment ~pically Iadiate R~: power in the 900 2000 megahertz (MHz) ~ange. Both the mobile units and the base stations of such a system are a~ted to ~ansmit and receive in this fre~uency Iange.
Pr~paga~on of thc signal within the second, dosed en~ironmcnt can be accomplished by propagating a low ~adio frequeslcy signal, prefeably in the ~ange lS 3~300 ~, through either a coa~ial or a bifilar conductor located within theclosed em~imnment. ~Iowev, it should be r~dily a~rcnt that a ~ypical mooile unit is not ca~able of operadng in this frequcncy ~ange, and cannot direc~y takeadvantageof such a signal~
Refer~ing to Flgure 1, a psefesred embodiment of a system 100 for enabling a snobilc unit 102 to continue to apaate within a closed en~ronmcnt 104 is shown. The s3rsbem 100 includes a multi~b~n:l Base Transceiver S~ion (BIS) 106 asso~a~d with a cellular td~phone syslem (not shown). The BTS 106 opaates on a fIequeDcy that is compatible with the cellular telephcnc ~cm. For the p~pose~ of this tcsc~tion, it will be }ncsumed tha~ the BTS 106 t~ansmits ant re~ives R~ power m the lSOO M~ ba~t with ~ 45 ME~ tuple~
bawecn ~linlc ant downlinlc *equatcies. ;
The closed e~imnment 104 may bc a tunnd that is part of a subway s3rstem. In such a GUe, a BTS lQ~ is p~e~ably placed in ea~ch under~gund ~ , with BTS-s 106 located at adjaceDt undcr~rwnd st~ons apating at diffcrcnt *equçncies in a~rtanc~ with ~cy alloca~on ~irements for o~a~ cell planning. ;

~ i 2 v ~ ~ 7 wo 94113067 PcrlsEs3/ooss2 In order to communicau with the mobile unit 102 located in the closed en~ironment 104, the BTS 106 is connected to the high-frequency port of a first linear two-way ~equency converter 108. The low frequency port of the first frequenoy conveater 108 is coMected to cable t~nsmission means 110. The S fi~nction of the first frequency converter 108 is to conver~ the lS00 MHz signal that is output by the BTS 106 into a low f~quency RF signal which can be propaga~ into the closed en~ironment 104 by mcans of the cable ~ansmission means 110 which is distributed throughout the closed environment 104, preferablyalong an anticipated path of the vehicle 114 containing a mobile unit 102. For 10 purposes of discussion, it will be assumed that this low frequency RF signal is 200 MHz. , The fi~t frequenc,v converter 108 also converts low ~i~quency RF signals, whicll may ~e reccived from another source and p~agated by the cable tsansmission mcans 110, into high f~ ncy signals for recep~on by thc BTS 106.
15Thus, in the illus~ativc e:tample, a 200 M~ signal pmpagated by the cable t~smission means 110 would be converted to a 1500 ME~ signal for use by the BTS 106.
It has been men~oned that the function of thc cablc transmission means 110 is to pr~pagate a low *equency R~ signal ~roughout the closed em~ironment 104.
20Figur~ 2a and 2b illus~atc two diffe~ent embodiment~ for accomplishing this.
Figure 2a shows the cable t~ansmission mean~ 110 implemented as a simple bifilarcable 202 coone~ted to simple ~adi~ors 204, suc~ as dipole antennas, that ar~
located th~ughout ~e dosed en~ironment 104. Power *om the low fr~quency RF signal is then radia~d into the closed en~ronme~t 104 tl~ugh the simple 25r= 204 as we~l as thrwgh the bifi~r cable 202 itself. The same bifilar cabl:
. 202 may be used to p~pagate a low frequency RP signal ~at is r~ceived, as described below, within the closed c~ment 104, for ~c~ption by the low frequency port of the first frequency convert~ 108.
An altcmative embodiment of the cable t~ansmission means 110 is shown 30in Figurc 2b. Hcre, an ine~cpensive coaxial cable 2oe disaibuSes the low ~equency RF signal to a se~ics of simplc` low cost amplificrs 208, eac}~ connected to an , J ~ ;~ 7 W~, 94l13067 Pt~lSE93/00992 ante~na 210. The amplifier 208/antenna 210 comibina~ons can be placed at every 100 m along the closed environmeslt. Output power can be maintained at a very low levd that i5 arnplified by each successive arnplifier 208. Each amplifier 208 should be capable of amplifying signals travelling in two directions, that is, into and out of the first frequency conver~r 108. The pulpose of this two way signal propagation is to pennit bidirectional communication between a mobile unit 102 and the BTS 106. This is descnbed in greater detail below.
Another alternative cmbodiment of the cable ~ansm~ion means 110 is to use ~vo cables in parallel, each dedicated to prcpaga~ng a signal in only one direc~on. For c~ample, the cable ~ans~ion means 110 may ~e embodied by ~;
h,~ro bifilar cable 20Q/radiator 204 combinasions which are ~oth distributed along ~`
thc same path in the closed environment 104. ~ this case, cach bifilar ca~le 202is dedica~d to propagation of a low frequency RF sign~l in only one di~ tion, eith into or out of the first *~quency convcr~er 108.
IS Refe~ing baclc to Figure l, the mobile unit lOQ i~ located inside a vehicle ~ -114, which may bc a train car. Associ~ed vrith the vdlicle 114 is a second linear - -two-~vay fIequency converter 116. The second f~quency conver~:r 116 is connec~d at its low ~cquency po~t to a first antenna 118. The f~rst antenna 118 is located on the outside of the Yehicle 114 as closc as possible to the xadia~ng cable t ion meaDs llO, to enable it to ~rccive and transmit the low ;frequencyRF sigDal.
The second frequency converter 116 is COMa:S~!i;d at its high frequenc3r po~t to a second a~tenna 120, which t~ansmits and ~ecei es the high RF signal inside the vehicle 114. -The first and second &~quency conYer~s 108, 116 are phasc loc3~ed to the, - :~
system cloc3c so that thar output ~equcncie.~ will `be ~ynch~nized to opaate at fi~ed offsets from onc anothe~. This will gal~e a moving hding patt~n fo~ ube mobile radio stations ~ied by the subscnbers, as explained bdow. ~ :
Wlth the configu~ation described above, c~ch ~ dlicIe 114 i~ treated as an acteinded BTS aill, allowing hand held cellular ~phonc~ to be usod in thc ordinaryway. ~:

WOg4/130C7 ~ t .~i ! Pcr/sEs3/oos92 The above~esc~ibed system 100, i~volving the use of frequency conversion, is preferably part of a digital communicaions system thal utilizes aFrequency Division Multiple Access (FDMA), Time Division Mul~plc Access (I~MA), or Cod~ Division Multiplc Access (CDMA) me~hod of ~ smission.
5 However, it could also be used in an analog commwucations system.
Refcmng now to Figure 3, an e~arnple is shown in which the vehicle 114 is one car in a trai~l 314 in a subway system. A first BTS 302 is located at a first subway station, and a second BTS 308 is locatet at a secondlsubway ssation that is adjacent the first. The first BTS 302 communi~tes with a mobilc unit 322 located on the ~ain 314 by propaga~ing its low R~ frequency signal ~10ng the first cable t~ansmission means 306, which may p~fably be either of the embodiments des~ibed above with respect to Figures 2a and 2b. As ~he t~ain 314 moves away ~rom the first station toward the second station, it will be neeessary for the first BTS 302 to band off the call to the second BTS 308. In ord to prevent all mobile u~its 3æ ~om mal~ng hand offs at thc same time, tesminal portions of the fi2~t and second cable transmission mcans 306, 312 should ov~ap one another.
The a nount of ovcrla,p 324 should be tc~gnet to pcrmit the second antcnna 320, mounted o~ th- vchicle, to be n~r both the Srst and secont cable transn~is~on means 30~, 312 for scve~al seeonds when the train 314 is travclling at a typicalspeed. For a~ample, thc system may be designed to pennit the second antenna 320 to be near both the first and second cable t~ansn~ission means 306 for aboutS seconds when the tlain 314 is travclling at a ~peed of 20 meters per sçcond byallow~ng terminal por~ons of the first ant seco~d cable t~on m~s 306, 312 ~o overLap one another for a length of about 100 mcters. Thi3 will allow ~e 2S secont antenna 320 to a~pesicnce a gIatual decrcase in ~ceived power as it lea~/es the co~re.-age ara of the first BTS 302 while a~ the same time e~piencing a g~adual incrcase in receivcd pow as it a~proacbes the co~vesage arca of the socond BTS 308.
In another ~eature of the prescnt imention, the two-way freqDcy convertcr 316 loGItcd inside the tIain 314 is switched offwhcn the ~ain 314 leaves the tu~md 326 and com undcr ~c coveragc of anothe~ BTS cdl that does not Wo94113067 PCTISE93/00992 ~ g provide ses~ice to the closed environment (not shown). Similarly, the frequcncy con~e~er 316 located inside the tlain 314 is switched on when thc train 314 enters a tunnel 326. Thc switching on and off of the frequency converter 316 is activated by a magnetic scnsor 324, or the li3~e, in the t~ain that senses the emerging ` S cntranc~ into ant e~it from ~he tunnel 326, and sends a~pr~riate signals to the frequ~ncy converter 316.
It is impo~nt to note that wher. the t~in 314 leaves the tur~nd 326, causang the two-way f~quency conver~er 316 to be su~itched off, a mobile unit 3æin usc at the dme must quiclcly be handed off to an outside BTS cell that does not 10 provide sc~nnce bo the closed en~rimnment Snot shown). Thus, the outside BTS cell should pro~ride good c~vaage to ~hc area just outside the tunnd. To achieve this, an outsidc BTS cell may prefaably be pla~ed at the ~it of the tunnd 326.
In`anoth~ feature of the prcsent im~n~on, ~h BTS 302, 308 has a third antenna 328 which eDables it to directly sve any moi~ile uDit bdng opesated at IS the subway s~ion. Thus, a passenger who is utilizing a mobilc unit 322 at a subway s~ion may continue to be serviced by the same BTS 302, 308 as he or she moves fn~m thc s~on platfonn to the ~ain 322. Ihe samc is true when a passeng~ who is using a mobile unit 322 lca~a the tra~ 322 and stcps onoo a station platfo~
It is not always possible or desi~able in a tdeeommunicllions systcm to ha~e a base sta~on locaset at a ~ubway stasion for t = ion to mobilc units that are ~a~ on ~e sta¢ioQ pla~fa¢m or elsewhe~ within the sta~ion. This is ~rue, as wdl, in many other enclosed ~QS, such a~ in me~l :slcysaapQ~, building dev~ and basallcnts, mina and a~ . None~cl~, it is in~x;rtant 2S for mobilc tde~honc ~ubscri~e~s to be able to continue ~Ising thdr mobilc units as, they move, for e~le9 ~om a location out~de a t~ain station to loca~o&s S~t within the station and then inside the t~ain itsdf. Alt~ve embodirnents of ~c prcsent invention will now be descnoed, wi~h rcfercnce to Figm~ 4a~i, which present solutions to this problem.
Figure 4a is a block tia~am of an enclosed environment ~04 into which an alte~ive embodiment of the present inv~n~on bas b~ installed. A base .

wo g4/l3067 PcrlsEs3looss2 - 10- , transcuv statdon 402, located outside of the enclosed environment 404, broadcasts and receives high frequency signals by means of a bæ stadon antenna 428. Such high f~quency signals are normally received and transmitted by mobile units (not shown) which are located outside of thc enclosed environment 4~4. In S order to pern~it one or more mobile units 422, 422', which ar~ located within the enclosed environment 404, to continue communicadng with the base t~anscciver stadon 402, an outside antenna 412 is couplcd to a high f~qu~cy port of a first t~o-way ~equency converter 408. Ihe outside antenna is disposed at a location which permits it to receive high frequency signals from, and ~ansmit high frequency signals to one or more base station transceivers 402, 452. Thc low &equency port of the first ~v~way frequency converter 408 is coupled to cable ~ansmission means 410 as descnbed above with respect to other embadiments of the invention. This low fre~uency port t~ansmits and/or ~ceives signak in a *~quency range suitable for transm~on on the cable transmission means 41û
15 vithin the enclosed en~nronment 404.
The cable t~ansm~on mc~ 410 is tispos~d within the eslclosed en~nronmcnt so as to travcrse ar~as in which mobile communica8ons are to be pro~nded. Connected to the cable t~ansmission means 410, at vanous loca~ons within thc enclosed environmcnt 4û4, are the low f~eauency ports of ~i~e 20 ~ird two-way ~equency convcr~rs 418. Ea~:h of the third two-way f~qu~cy conver~ 418 reca~es a low-*~quency signal at its low-f~equency port, ~d conYerts that signal into high-frequ~ncy signal which is made a~railable at its high-f~equency port. An antenna 420 is coupled to the high-frequency port of each third two-way frequency comerter 418, so th~t a high frcquency signal will be 25 transmitted within the endosed enn~nent for reception by ~e mobile unit 4æ.
The third two-way f~quency conY~ 418, which arc all connec2Od to the samc cable ~ansmission means 410, are disposed within the 0closet en~ onment 404 at loc~ons such that as a subscn~ using a mobile unit 4æ bcgins to leaYe an area senred by onc of the third t~v~way frequcncy conYer~s 418, he vvill 30 simultaneously enter an ar~a scn~ed by an adjacent ~hird tw~way frequ~cy conver~er, so that no handoff is necessary. ~ :

WO s4tL~ PCT/SE93/00992 Similarly when the mobile unit 4æ transmits a high-f~equency signal, this high-frequency signal is received by a nearby antenna 420 coupled to the high-frequency port of a corresponding third tw~way frequency conve~er 418. The ~irt f~quency converter 418 converts this to a low-frequcncy signal that is S suitable for t~ansmission on the cable tIansmission means 410 which is coupled to the low-Sequency por~ of that third tw~way f~uency converter 418. That signal is subsequcntly converted into a high frequency signal by the first n~o-way frequency converter 408. That high-frequency signal is then broadcast bac~ to one of the c~rIe~onL~ng base station lIansceiv~ 402, 4S2 by mcans of thc antenna 410.
As mentioned above, thc embodiment of the im.rendon as depicted in Figure 4a is usefi~l for pro~iding condnuous mobile telecommunicadons service as a subscriber maves bacl~ and for~ between ~pen and enclosed en~rironments. When the enclosed en~ronmalt is, for c~amplc, a subway sy~m, ~e embodiment lS shown in Figure 4a may be combined with any of the prcviously described ernbodimens, so that a subscnbcr may rcce~ve a~ntinuous mobile tdecommurlications senrice not only upon en~ring and lcaYing the enclosed isonment, such as ha~ens ~vhe~ that subsa~er walh from a street lcvd location to a subway pla~form, but also whe~ tha~ subscnber leav~ the subway 20 platform by baarding a t~ain. In such a situadon, ~e platform may be equippedwith third two-way *equ~g con~er~s 418 in the manner depicted in Pigure 4a Under these cira~nces, the third tw~way frequcncy conYer~ 418 are coupled to thc same cable t~on m~ans which also pro~idc the low-*eguency ~i~ that may be leal~d ot othen~nse broadcast to the second 2S ~equcncy convertcr 116 which ~s located h the train. The ~equency con~rters in the t~ and thc ones fi~edly mounted on ~he pla~form should be c~ntrolled so fflat thar t~ansmitting ~equencies are offset by a p~determinod arnount, such asS0-100 IIz from the synchronous com~erter freque~cy, in ord~r to produce a mo~ing f~ding pattan. This will prwent radio waves from OEncelling one ano~er 30 at ~ised 1ocations at which a non-moving subscIi~er's ability to communicate WO 94/13a67 PCT/SE93l00992 would otherwise be hindered, while maintaining a contiguous cell created:by the *equency converers 418.
When a subscnber who is ta~ng by mcans of his mobile unit 422 enters or leaves a t~ain, no handoff is ~equired because thc high frequency antennas ofS the conver~ in the ~ain and on ~e platfonn handle the samc signals asso~ated with the same base transcuver station 402. The sasne is truc when a subscri~er who is wal~ng through a corndor of the subway sta~on leaves the vianity of one fLsedly mounted tw~way frequcncy con-~cr~ 418 and a~pr~es another: no handoff is r~uir~d because the two fr~ucncy convcrters are deriving signals ~om IQ the sarnc cable.
The arrangemcnt of Figure 4a, in which the first two-way frequency conver~er 408 reccives high frequency signals from the basc transceiver s~ation 40.2 by means of a Iadio coupling has the ad~rantage that a subsystem for closed cn~rironments is entirdy freestanding, and may be ins~lled in a closed 0~i~nmentin ordcr to ~t~nd thc scTvice p~vided by scvaal competing opaators. Because it may ~e shared by thcse o~abors~ ~e cost of ~is subsystem may be shared among opesators. ~ this case, one or more addiS;onal base stations 4S2, as well as the bæe station 402, communicate ~ria radio with the fi~st frequency a3n~rcr~r 408, whereby the air-int~cc is such that the first fr~quency conva~r 408 emulatcs the mobile s~ions hidden by thc closcd eDDnrnent to this diIect ~adio :
pa~. Each of the base mtions 402, 4S2 may use different frequency Sands, such as ~ the casc of baso stadons belonging to comp~ing ~ators. For ~ample, one basc station 402 may usc the ~A~ band of the A~S standard, and the othcr base station 452 may use the ~B~ band of ~at standard. Altesna~vely, if the two neighb~ing basc s~ons 402, 4S2 belong to thc samc op~ator, thc same~, &equency band may be used with the control a~d t~c c~annds of re:ipecdve base sta~ons using different frequeacies acco~ding to thc frequency pl~n of the cellular system. ~:
l~he Tadio path as shown in Figure 4a betwecn the base statio~s 402, 4~2 and thc first fr~quency converter 408 may also be used in ~e embodiments of ;~

: ~ :

,~i2 J ~ 7 wo g4~l3067 PcrlSE93/0~992 Figures 1 and 3, between the BTS lOo and the first frequency convelter 1-OB, well as between tne BTS 302 and thc &t fre~luency converter 304.
However, an alternati~e embodiment is depicted in Figure 4'o which may aLso be used in appropriate situatior.s. The bloc3~ diag~am of Figure 4b is identical S to that of Figure 4a, e~cept that base transceiver stations 402', 452' and a high *equency por: of the fi~t t v~way ~equency converter 408' are directly coupled via r~pective ooupling means 406, 406', ~ather than bcing coupled by a radio lisk. ~: -E~cept for this difference, the operation of the system shown in Figure 4b is idcntical to that descnbed a~ove with ~spect to Figure 4a.
The alternative embodiments descn~ed with reference to Figures 4a and 4b may be arIanged to provide additional ad-~antages. One e~ccmplary embodiment of such an a~angement is shown in Figure 4c. In Figure 4c, two systems of the tgpe. depi-cted in Figure 4b are both installed within one enclosed environment 404. -In a fi~ system, a base transceiver station 402' is di2~c~y coupled to a high fn quency port of ~e f~rst tw~way fIequency con~ter 408' by the c~upling means 406. It will be recognized, howcver, that an air-interface such as thc oneshown in Figu;r~ 4a may alternativcly be used. The low frequency port of thc first t~vo-way frequency convater 408' is coupled to the cable transmission mcans 410,which in turn is coupled to the two-way frequency convaters 418 exactly s dess~ibed above with reference to Figure 4b. The a~Tangemlt of these ;
~ynch~onous *equency a~nvcrters 418 effec~vdy forms a first cdl 461, such that no handoff is requir~d so long ;~s the mobile unit 4æ is located within the service area of one of ~e corIe~onding an~nnas 420.
A second sys~m, comp~ising ~e base t~ansceivcr s~on 462, coupling means 466, f~Ist hvo-way frequency convertcr 468, cable tran~ission means 460,'.and third tvo-~vay fre~uency c~n~er~rs 418 coupled to cos~onding antennas 420 is similarly ar~anged within the enclosed environmellt to form a second c~
462. , , ~, Each of the first and socond cells 461, 462 can, for ~ample, bc a celli TDMA, CD~A, oranalog cdl.

wO 94113067 PcIlsE93/oos92 The antennas 420 of the first and second ce31s 461, 462 may be d~sposed to create an area of overla~, so tha~ when a subscriber who is using his mobile unit 422 is about to leave, for e~arnple, the first cell 461, he will at the same time start to enter a region that is also se~ved by the second cell 462. This will be detected, S and a handoff of the call from the first cell 461 to the second cell 462 can be effected in accordance with ~sinciples that ax well Icnown to those of ordinary sldll in the ar~ Thus, this embodiment of the present invennon perrnits a plurali~y of cells to be formed within one enclosed en~ironment.
The invention has been described with reference to particular embodiment.
10 HoweYer, it will be readily apparent to those slcilled in the art that it is possible to embody the invention in specific forms other than those of the preferred embodiment described a~ove. This may be done without depamng from the spirit of the invention. For e~ampk, if only one-way communication is required, then the two linear frequency c~nver~s ne~d only be capable of converting signaLs in 15 one direction. Also, thc inventire conccpts are wt limited to a~plication in subway systems, but are equally a~plicable to other situations where it is advanlageous to prwidc mobile subsaibers vvith a means for continuing normal operation of their mobile units as they leave open envir~nents ard enter enclosed environments, such as metal slcysc~apers, building devators and basements, mines20 and culverts.
The prefa~d embodimcnt is merely illus~ative and should not ~e considexd rcs~icti~c in any way. The scope of the invcntion is given by ~e -a~p~ded claims, ~ather than the preceding tes~iption, and all ~aria~ions and equivalents which fall within ~e ~ange of thc claims are int~nded to be embra 25 thaein.

~ ~ . . . ~ . .

Claims

WHAT IS CLAIMED IS:

1. In a communication system including at least one base station and at least one mobile unit, both operating at a high radio frequency, a repeater system forproviding a communications link between the base station and the mobile unit when the mobile unit is located in an environment that is substantially closed off to high radio frequency communication between the base station and the mobile unit, the repeater system comprising:
a first linear two-way frequency converter including:
a high frequency port for two-way coupling to a base station; and a low frequency port for two-way coupling to a low frequency signal that is capable of radiating radio frequency power through the closed environment;
cable transmission means connected to the low frequency port of the first linear two-way frequency converter, and located within the closed environment for radiating and receiving the low frequency signal within the closed environment;
a first antenna for wireless coupling to the cable transmission means;
a second linear two-way frequency converter including:
a low frequency port connected to the first antenna for two-way coupling to a low frequency signal; and a high frequency port for two-way coupling to a signal that is compatible with the high radio frequency signal used by the communication system; and a second antenna connected to the high frequency port of the second linear two-way frequency converter.

2. The repeater system of claim 1 wherein the first antenna, second linear two-way frequency converter, and second antenna are disposed on a vehicle, and the cable transmission means is distributed along an anticipated path of the vehicle through the closed environment.

3. The repeater system of claim 2 wherein the cable transmission means is associated with a first base station, and a terminal portion of the cable transmission means overlaps a corresponding terminal portion of a cable transmission means associated with a second base station, the region of overlap being sufficient topermit the vehicle to simultaneously pass by the terminal portions of both cabletransmission means for at least several seconds when the vehicle is travelling at a typical speed away from the first base station and toward the second base station.

4. The repeater system of claim 2 wherein the vehicle further includes a sensor coupled to the second linear two-way frequency converter for alternatively turning the second linear two-way frequency converter on and off in response to respectively sensing the vehicle entering and exiting the closed environment.

5. The repeater system of claim 2 wherein the high radio frequency is in a range of 900 to 2000 megahertz, and the low frequency is in a range of 30 to 300megahertz.

6. The repeater system of claim 2 wherein the cable transmission means is a bifilar cable.

7. The repeater system of claim 2 wherein the cable transmission means comprises:
a coaxial cable, connected to the first linear two-way frequency converter;
an amplifier having an input connected to the coaxial cable; and a third antenna connected to an output of the amplifier.

8. The repeater system of claim 2 wherein the first and second linear two-way frequency converters are synchronized to a system clock

9. The repeater system of claim 2 further comprising:
a base station, located at a station along an anticipated path of the vehicle and coupled to the high frequency port of the first linear two-way frequency converter, the base station including a fourth antenna for wireless, high radio frequency coupling to a mobile unit.

10. The repeater system of claim 1 wherein the high radio frequency is in a range of 900 to 2000 megahertz, and the low frequency is in a range of 30 to 300 megahertz.

11. The repeater system of claim 1 wherein the cable transmission means is a bifilar cable.

12. The repeater system of claim 1 wherein the cable transmission means comprises:
a coaxial cable, connected to the first linear two-way frequency converter;
an amplifier having an input connected to the coaxial cable; and a third antenna connected to any output of the amplifier.

13. The repeater system of claim 1 wherein the first and second linear two-way frequency converters are synchronized to a system clock.

14. In a communication system including at least one base station and at least one mobile unit, both operating at a high radio frequency, a method for communicating between the base station and the mobile unit when the mobile unit is located in an environment that is substantially closed off to high radio frequency communication between the base station and the mobile unit, comprising the stepsof:
linearly converting a base station high radio frequency signal into a low frequency signal that is capable of radiating radio frequency power into the closed environment;

using cable transmission means to distribute the low frequency signal within the closed environment;
receiving the distributed low frequency signal in a first antenna;
linearly converting the received low frequency signal into a reconverted high radio frequency signal; and using a second antenna to transmit the reconverted high radio frequency signal to a nearby mobile unit.

15. The method of claim 14 wherein the steps of receiving, linearly converting the received low frequency signal, and using a second antenna to transmit are performed on a vehicle.

16. In a communication system including a base station and a mobile unit, both operating at a high radio frequency, a method for communicating between the basestation and the mobile unit when the mobile unit is located in an environment that is substantially closed off to high radio frequency communication between the base station and the mobile unit, comprising the steps of:
using a second antenna to receive a high radio frequency signal from a mobile unit;
linearly converting the received high radio frequency signal into a low frequency signal that is capable of radiating radio frequency power into the closed environment;
radiating the low frequency signal from a first antenna;
using cable transmission means to receive the low frequency signal within the closed environment;
linearly converting the received low frequency signal into a base station high radio frequency signal; and outputting the base station high radio frequency signal to a base station.

17. The method of claim 16 wherein the steps of using a second antenna to receive, linearly converting the received high radio frequency signal, and radiating are performed on a vehicle.

18. In a communication system including at least one stationary base station and at least one mobile unit, both operating at a high radio frequency, a mobile base station for providing communication system service to a mobile unit when the mobile unit is located in a vehicle that is travelling in an environment that issubstantially closed off to high radio frequency communication between the stationary base station and the mobile unit, the mobile base station comprising:first means, disposed on the vehicle, for wireless coupling to a cable transmission means, coupled to a stationary base station, for two-way, low frequency signal propagation within the closed environment;
a linear two-way frequency converter, disposed on the vehicle, including:
a low frequency port connected to the first wireless coupling means for two-way coupling to a low frequency signal; and a high frequency port for tow-way coupling to a signal that is compatible with the high radio frequency signal used by the communications system; and second means, disposed on the vehicle and connected to the high frequency port of the linear two-way frequency converter, for wireless high radio frequency coupling to a mobile unit located in the vehicle.

19. The mobile base station of claim 18 wherein the first wireless coupling means and second wireless coupling means are, respectively, first and second antennas.

20. The repeater system of claim 1, further comprising:
a third linear two-way frequency converter, located within the closed environment, including:

a low frequency port connected to the cable transmission means for two-way coupling to the low frequency signal; and a high frequency port for two-way coupling to the signal that is compatible with the high radio frequency signal used by the communication system; and a third antenna connected to the high frequency port of the third linear two-way frequency converter.

21. The repeater system of claim 20, wherein the closed environment is a subway station.

22. The repeater system of claim 20, wherein the closed environment is a building.

23. The repeater system of claim 20, wherein the closed environment is a mine.

24. The repeater system of claim 20, wherein the closed environment is a culvert:

25. The repeater system of claim 20, wherein the first antenna, second linear two-way frequency converter, and second antenna are disposed on a vehicle, and placement of the cable transmission means within the closed environment includesdistribution along an anticipated path of the vehicle through the closed environment.

26. The repeater system of claim 20, further comprising:
a fourth linear two-way frequency converter, located within the closed environment, including:
a low frequency port connected to the cable transmission means for two-way coupling to the low frequency signal; and a high frequency port for two-way coupling to the signal that is compatible with the high radio frequency signal used by the communication system; and a fourth antenna connected to the high frequency port of the fourth linear two-way frequency converter, wherein the fourth linear two-way frequency converter operates at a frequency that is synchronized to have a fixed offset from a frequency being used by the third linear two-way frequency converter, and wherein the third and fourth antennas are disposed within the enclosed environment so as to form a first contiguous cell within the enclosed environment.

27. The repeater system of claim 25, wherein placement of the cable transmission means within the closed environment further includes distribution in location where the mobile unit is expected to be carried.

28. The repeater system of claim 25, wherein the closed environment is a building, and wherein the vehicle is an elevator in the building.

29. The repeater system of claim 25, wherein the closed environment is a subway system comprising station platforms interconnected by train tunnels, and wherein the vehicle is a train car in the subway system.

30. The repeater system of claim 25, wherein the second and third linear two-way frequency converters are synchronized to a system clock.

31. The repeater system of claim 29, wherein signals carried by the cable transmission means are associated with a first base station, and wherein a terminal portion of the cable transmission means overlaps a corresponding terminal portion of a cable transmission means that is associated with a second base station, theregion of overlap being sufficient to permit the vehicle to simultaneously pass by the terminal portions of both cable transmission means for at least several seconds when the vehicle is travelling at a predetermined speed away from the cable transmission means associated with the first base station, and toward the cable transmission means associated with the second base station, in order to permit ahandoff of service from the first base station to the second base station.

32. The repeater system of claim 1, further comprising a third antenna, connected to the high frequency port of the first linear two-way frequency converter, for wireless coupling to the at least one base station.

33. The repeater system of claim 1, further comprising second cable transmission means, coupled to the high frequency port of the first linear two-way frequency converter, for coupling to the at least one base station.

34. The method of claim 14, further comprising the initial step of receiving the base station high radio frequency signal from an air-interface.

35. The method of claim 14, further comprising the initial step of receiving the base station high radio frequency signal from a wire interface.

36. The method of claim 16, wherein the step of outputting the base station high radio frequency signal to a base station comprises transmitting the base station high frequency signal to the base station via an air-interface.

37. The method of claim 16, wherein the step of outputting the base station high radio frequency signal to a base station comprises transmitting the base station high frequency signal to the base station via a wire interface.

38. In a communication system including at least one base station and at least one mobile unit, both operating at a high radio frequency, a repeater system forproviding a communications link between the base station and the mobile unit when the mobile unit is located in an environment that is substantially closed off to high radio frequency communication between the base station and the mobile unit, the repeater system comprising:
a first linear two-way frequency converter including:
a high frequency port for two-way coupling to a signal that is compatible with the high frequency signal used by the communication system; and a low frequency port for two-way coupling to a low frequency signal having a frequency that is capable of radiating radio frequency power through the closed environment;
a first antenna, coupled to the high frequency port of the first linear two-way frequency converter, for receiving and transmitting the high frequency signal;
cable transmission means connected to the low frequency port of the first linear two-way frequency converter, and located within the closed environment for distributing the low frequency signal within the closed environment;
a second linear two-way frequency converter, located within the closed environment, including:
a low frequency port connected to the cable transmission means for two-way coupling to a low frequency signal; and a high frequency port for two-way coupling to a signal that is compatible with the high radio frequency signal used by the communication system; and a second antenna connected to the high frequency port of the second linear two-way frequency converter.

39. In a communication system including at least one base station and at least one mobile unit, both operating at a high radio frequency, a repeater system forproviding a communication link between the base station and the mobile unit when the mobile unit is located in an environment that is substantially closed off to high radio frequency communication between the base station and the mobile unit, the repeater system comprising:
a first linear two-way frequency converter including:

a high frequency port for two-way coupling to a signal having a frequency that is compatible with the high frequency signal used by the communication system; and a low frequency port for two-way coupling to a low frequency signal having a frequency that is capable of radiating radio frequency power through the closed environment;
first cable transmission means connected to the low frequency port of the first linear two-way frequency converter, and located within the closed environment for distributing the low frequency signal within the closed environment;
a second linear two-way frequency converter, located within the closed environment, including:
a low frequency port connected to the cable transmission means for two-way coupling to a low frequency signal; and a high frequency port for two-way coupling to a signal that is compatible with the high radio frequency signal used by the communication system;
a first antenna connected to the high frequency port of the second linear two-way frequency converter, and disposed within the closed environment to servea first cell in the communication system;
a third linear two-way frequency converter including:
a high frequency port for two-way coupling to a signal having a frequency that is compatible with the high frequency signal used by the communication system; and a low frequency port for two-way coupling to a low frequency signal having a frequency that is capable of radiating radio frequency power through the closed environment;
second cable transmission means connected to the low frequency port of the third linear two-way frequency converter, and located within the closed environment for distributing the low frequency signal within the closed environment;

a fourth linear two-way frequency converter, located within the closed environment, including:
a low frequency port connected to the second cable transmission means for two-way coupling to a low frequency signal; and a high frequency port for two-way coupling to a signal that is compatible with the high radio frequency signal used by the communication system; and a second antenna connected to the high frequency port of the fourth linear two-way frequency converter and disposed within the closed environment to serve a second cell, wherein the second antenna is disposed within the enclosed environment at a location which causes a portion of the second cell to overlap a portion of the first cell, whereby a handoff of service between first and second base stations serving, respectively, the first and second cells can be effected when a mobile unit moves between the first and second cells.