120-0062 epop 500 Operational Description ZBD Displays

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1.1 V3Protocol

1.1.1 Summary

Thisprotocolutilisesaperiodicseriesofsynchronisationpulsestransmittedbyabase

stationtoenabletimedivisionmultiplexingofthedatatobesenttothetargetdisplays.



Thesyncpulsealsocontainsinformationonwhichdisplaysthebase‐stationwishesto

communicatewithinthattimeslotaswellasameasureofexactlywhereinthetimeslot

thedisplayhaswokenup.



Duringtheperiodbetweenthesyncpulsesthedisplayswillbeinadeepsleepmode

runningoffalow‐powerRCoscillator.Thisisthefeaturethatextendsbatterylife

considerably.



Datapacketsarebroadcastaftereachsyncpulsewiththemaximumcombinedtimeof

eachsyncpulse/datapacketburstbeingnomorethan1s.Thisistocomplywiththe

relevantEuropeanradioregulations.LBT(listen‐before‐talk)isimplementedbetween

timeslotstoreducetheeffectofdutycyclerestrictions.Datapacketsareacknowledged

ingroupstoincreasetheprotocolefficiency.AllpacketshaveauniqueIDandare

repeatediftheyfailtogetthroughduetointerference.



DisplaysarealsoplacedintodistincttimeslotsbasedontheLSBoftheiraddress,

allowingthepollingperiodtobefurtherextended.Thisistoensureaneven

distributionofdisplaysinastore.



1.1.2 USSpectrumRegulations



TheUSregulationsallowustousetheentire902‐928MHzbandaslongasweuseonly

0.75mWERP.



IfmorepowerisrequiredeitherFrequencyHoppinghastobeused(withadwelltime

of0.4s)orwidebandmodulation(e.gDSSS).



TheUSversionoftheprotocoltransmitsatapowerlevelof0.75mW.Thismaximises

compatibilitywiththeEuropeanversionofthesystem.Tocompensateforthereduced

ERPandthereforerangethesystemisdesignedtohandlemultiplebase‐stations.Larger

areascanbecoveredbythissystembyincreasingthenumberoftransmitters.



902.0 928.0

50mV/m@3m =

0.75mW

26MHz

0.25Watts

(Frequency hopping)