cbtc radios.pdf

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CBTC Radios What to Do? Which Way to Go?

Industry Standard? Commercial off the Shelf? Or Custom designs? About

the only thing the transit industry is able to agree upon is that it cannot.

By Tom Sullivan

Continuous bi-directionalcommunications forms the heart ofCBTC technology. By using two-waycommunications instead of traditionalfixed block track circuits some transitoperators have been able to realizesignificant performance improvementswhile at the same time increasing safetyand lowering operating costs.

Consider San rancisco!s "uni "etro.#ith CBTC technology it has been ableto double the number of trains$hr in its"arket Street Subway. But "uni!s%lcatel Seltrac CBTC& like '(B its)*+,!s erman predecessor & is basedupon a near-field inductive loop/operating on a 01 k2z carrier. Today&most new 3 CBTC/ systems areoperating in the 2z range& or about amillion times faster.

Photo1. Inductive Loop CBTC such as this one

at SF Municipal Railway have thirty years of

service proven history.

Loop Benefits & Liabilities

There are a lot of advantages toinductive loop CBTC. The technologyhas been service-proven for threedecades& it!s easy to install& and usesinexpensive unshielded stranded wirethat is easy to repair in the field.

Today& transmit and receive interfacecircuitry for inductive loop systems iseasy to design& build& and maintain.Technology obsolescence is of littleconcern because there are so many waysto design replacement subsystems usingreadily available Commercial 4ff TheShelf 5C4TS6 components.

So why are so many new CBTC systems

using 3 technology7 %nswers are manyand varied but primarily it seems mosttransit operators& i.e.& those who have noprior experience with CBTC& simplydon!t like the idea of a wire loop that canbe easily vandalized or perhaps evenresold for scrap.

But while 3-CBTC systems largelyeliminate these two concerns& they havetheir own problems. %nd while these

problems are significant they were notwidely understood when the transitindustry& and especially "T% 8ew 9orkCity Transit& first began to take a hardlook at 3-CBTC systems in the early)**,!s.

:raft ;ersion of %rticle published in 3ailway %geS Buyer


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The RF Bandwagon Begins

eneral 3ailway Signal 5now %lstom6was perhaps the first signal company towork with a specialty radio manufacturer5in this case #atkins ?ohnson6 to design

and build a custom transit radio for 3-CBTC.

Photo2.Stillborn:Watkins ohnson!s CBTC

radio developed for "RS circa #$$% never saw

revenue service.

@ndependently& but at about the sametime& S B%3T saw value in anadvanced radio ranging/ from 2ughes%ircraft Company developed for the AS%rmy and "arines. nown as D'3S&B%3T hoped to leverage theapproximately E0,,&,,,&,,, in sunkengineering costs the A.S. governmentpaid to develop D'3S and believed it

could easily adapt this radio for itsCBTC train system that B%3T called%dvanced %utomatic Train Control5%%TC6.

% #estinghouse 5now Bombardier6also got into the act by teaming with%ndrew Corporation another specialtyradio manufacturer. Anlike other signaland radio suppliers& however&Bombardier and %ndrew believed that alossy line was the only way to ensurereliable communications in the subways.

% lossy line& sometimes called a leakyfeeder/ is a coaxial cable with periodicopenings in the outer shield to permit 3

energy to leak out or radiate in. @t!s beenused for decades in subways for voiceradio but Bombardier!s leaky feederCBTC design is uniFue.

Today& %ndrew!s "odel =G,, directseFuence spread spectrum radio is insuccessful revenue service at the Sanrancisco %irport& soon SDT%& andelsewhere.

Photo 3. &ndrew!s Model '%(( radios is used in

a nu)*er of initial Bo)*ardier CBTC

installations in the #$$(!s.

Troble in RF!CBTC City

But there!s a problem with the %ndrew"odel =G,, radioH %fter only a fewyears& it was discontinued due to poor



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sales. 4ne of the alleged reasons for itspoor sales is that it was designed to workclosely with Bombardier!s lexiblok5now CityloI 10,6 CBTC. Thus& whileother firms might be interested& its close

connection with Bombardier makes itharder to interface with other systems.

"eanwhile& back on the #est Coast2" 5a Joint venture of 2ughes and"6 after spending all of the availablefederal research funds decided it wantedout. 2ughes then sold its D'3Stechnology to 3aytheon and ultimately 5which bought 2armon6 whichbegan to build a lower cost version of

the original 2ughes D'3S radio.

@nstallation of %%TC at B%3T continuesand radios are installed on virtually all ofits cab cars and approximately )$K of thesystem.

Photo 4. GE's CBTC radio network installed at SFBART is based upon advanced technolog originalldeveloped !or the "S #ilitar

4ne of the challenges with any newtechnology is not the overall concept and

design. %ctually& that!s where all the funis for engineers. The challenge is in thedetails which is usually where many ofthe hidden costs begin to appear.

or example& CBTC radios are relativelysmall and light weight. So are theantennae. But B%3T and 89CT havebeen surprised to discover that there issignificantly additional costs to ensure

that these system can be maintainedsafely.

Consider the significant CBTC andantennae structures installed by B%3T inits elevated sections. %n 4S2%approved ladder and appropriateprotections were provided to ensureworker safety.

Photo 5. BART train nearing a waside CBTC antennacantilevered o!! an elevated track section.

Radio Technology "arches #long

@n %pril of =,,K& Bombardier won yet aanother CBTC Job& this time in Taiwan.But because Bombardier was no longerable to purchase custom %ndrew CBTCradios it needed to find a new radio.

Derhaps based upon its unfortunateexperience with %ndrew this time

Bombardier elected to go with aninexpensive commercial off the shelf5C4TS6 radio made by Safetran.

%t less than )$), the cost of %ndrews!custom radio 5E)1,, ;s E==&,,,6&



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Safetran!s C4TS thernet SpreadSpectrum 3adio also occupies only 1Lof the volume.

%ndrew!s discontinued "odel =G,, has

a @% 3S-0K, interface. The Safetranthernet 3adio has a standard& andinfinitely more popular& ),$),, BaseTthernet port.

Photo 6. Commercial off the Shelf. Bo$bardier nowuses a co$pact and ine%pensive Ethernet SpreadSpectru$ radio b Sa!etran Sste$s

4n ?uly )0& =,,G the 'as ;egasmonorail went into full revenue service.Controlled by a Seltrac 3 CBTCsystem& the data radio technology%lcatel selected was not a custom dataradio& nor was it a C4TS data radio.3ather %lcatel elected to use @ Std.M,=.)) data radios.

9es& that!s right. The same very popularindustry standard data radio protocol&also called #ii&/ that you probablynow have operating in your notebook

computer and palm pilot is now safetyand reliably controlling trains in 'as;egas.

#hile %lcatel says it will continue to

support and provide inductive loopSeltrac systems when reFuested& %lcatelalso says that it has decided tostandardize on @ Standard data radiotechnology for its 3-Seltrac systems.

% look under the hood of a typical%lcatel wayside radio location helpsexplain why. %t Denny!s Bay& 2ongong& most of the space in the cabinet isempty. @n the top left hand corner you

can make out the @ M,=.)).

#hile many had doubts that M,=.))could be used reliably for train controlsystems 5and some still do6 'as ;egas isproving them wrong. Clearly& theadvantages to using @ industrystandard data radios are many andprofound.

To begin with& the cost of M,=.)) radiosis approximately )$), that of a C4TSradio and less than )$),, the cost of acustom CBTC radio.

@nteroperability among multiple radiosuppliers is ensured by an industry tradegroup know as the #ii %lliance./

@ M,=.)) technology andinteroperability continues to evolve at adizzying rate. 3ecently %therosCommunications announced that is nowsampling a single integrated circuit thatsupports M,=.))a$b$g as well as the newstandard for security M,=.))i and theFuality of service extensions associatedwith M,=))e.



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Photo 7. Alcatel's Radio CBTC sste$s !or &ong ong()as *egas and +aris #etro use $ulti,sourced -EEEStd. /0.11 radios 2top le!t corner3

Thus& it appears the only thing we can

really be sure about @ standard dataradios is that they will continue to evolveand improve and continue to besupported for a long time.

Bt What #bot $%C Transit?

Back on the ast Coast 89CT!s CBTCtechnology leader Siemens 5formerly"%T3% Transport6 is moving aheadwith the installation of its custom

Siemens CBTC radio on 89CT!sCanarsie Dilot CBTC 'ine./

Photo 8. Sie$ens proprietar 0.4 Gh5 CBTC Radiowill be used onl on 67CT8s Canarsie )ine

The original plan for 8ew 9ork you mayhave heard was to develop a standardCBTC design by selecting onetechnology leader and two followerswho would provide CBTC eFuipmentcompatible with the leader!s.

Anfortunately& things have not yetworked out as planned. %lstom& one ofthe followers has dropped out and%lcatel the other follower is stillworking to build a CBTC Systemcompatible with Siemens!.

But what about the radio7 %nd whatabout compatibility and interoperabilityand competition on future 89CT lines7

Things remain murky. %s of 8ovember=,,G the specific procurement strategyfor the second CBTC line& lushing& isnot resolved. Dartly this is because thereis only one firm who can provide the



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radio. But this is not the radio that isgoing to be used on lushing.

Senior "T% and 89CT managementdesire a total of four suppliers of

compatible& interoperable CBTCeFuipment. But currently& 89CT ishaving trouble getting two compatiblesystems let alone three or four. 8o smallpart of the problem is custom proprietaryradios.

o where are we going?

Clearly& there are a lot changes in dataradio technology today. 8ext generationsoftware radios/ will allow their

personalities to change by downloadingnew code. %nd beyond that cognitive

radios/ that have the ability to adapt to awireless spectrum or networkenvironment automatically toaccomplish some task are coming.

To help put these radio types/ inperspective and better understand theseissues and recent radio history& Table )lists some key attributes associated withCustom& C4TS& and @ industrystandard radios.

or additional information and toparticipate in a discussion forum onCBTC radios please go towww.tsd.org$cbtc.

RadioAttribute

IEEEStandard

CommercialOff The Shelf

CustomRadio

ProductEam!le

"Radio # C$TC%

IEEE Std& 8'(&))9Alcatel Seltrac

In*ens+s,Safetran9Bo$bardier CitFlo

:;/

-at.ins /ohnson9GRS Atlas

Andre09Adtran5 Fle%iblok

Siemens9#atra #eteor

Si1e,-ei2ht S$allest Co$pact )argest

Relati*e Cost 1 1/< 1//iFi Alliance3

6one 6one

Radio C$TCIntero!erabilit+

6one 6one 6one

Radio C$TCin Ser*ice

7es2Alcatel )as *egas3

6o 7es2Bo$bardier ? SF@3

et0or.Interface

Co$$unications-ndustrStandard

-+ over Ethernet

-ndustr Standard2ATCS( Ethernet

)on>orks3

Tpicall(custo$ or e%ternal to radio

Table ) C$TC Radio T+!es Com!ared


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