Interference from cloud-to-ground and cloud flashes in wireless communication system.

(1)

ContentslistsavailableatScienceDirect

Electric

Power

Systems

Research

jou rn al h om e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / e p s r

Interference

from

cloud-to-ground

and

cloud

flashes

in

wireless

communication

system

Mohd

Riduan

Ahmad

a,b,∗

,

Mona

Riza

Mohd

Esa

a,c

,

Vernon

Cooray

a

,

Eryk

Dutkiewicz

d

a_Ångström_Laboratory,_Division_for_Electricity,_Department_of_Engineering_Sciences,_Uppsala_University,_Box_534,_S-75121,_Sweden b_Universiti_Teknikal_Malaysia_Melaka,_Hang_Tuah_Jaya,₇₆₁₀₀_Durian_Tunggal,_Malacca,_Malaysia

c_Universiti_Teknologi_Malaysia,₈₁₃₁₀_Skudai,_Johor_Bahru,_Johor,_Malaysia

d_Wireless_{Communications}_and_Networking_Lab,_Department_of_Electronic_Engineering,_Macquarie_University,_Sydney,_Australia

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received30July2013

Receivedinrevisedform17February2014 Accepted11March2014

Availableonline13April2014

Keywords:

Biterrorrate Cloudflash Cloud-to-groundflash Interference Microwaveradiation Wirelesssystem

a

b

s

t

r

a

c

t

Inthisstudy,cloud-to-ground(CG)flashandintra-cloud(IC)flasheventsthatinterferewiththe trans-missionofbitsinwirelesscommunicationsystemoperatingat2.4GHzwereanalyzed.Biterrorrate (BER)andconsecutivelostdatagram(CLD)measurementmethodswereusedtoevaluateBERandburst errorfrom3tropicalthunderstormsonNovember27,28,and29during2012northeasternmonsoonin Malaysia.Atotalof850waveformsfromtheelectricfieldchangerecordingsystemwererecordedand examined.Outofthese,94waveformsofveryfinestructurewereselectedwhichmatchedperfectlywith thetiminginformationoftherecordedBER.WefoundthatbothCGandICflashesinterferedsignificantly withthetransmissionofbitsinwirelesscommunicationsystem.Theseverityoftheinterferencedepends mainlyontwofactorsnamelythenumberofpulsesandtheamplitudeintensityoftheflash.The inter-ferencelevelbecomesworstwhenthenumberofpulsesinaflashincreasesandtheamplitudeintensity ofpulsesinaflashintensifies.Duringthunderstorms,wirelesscommunicationsystemhasexperienced mostlyintermittentinterferenceduetobursterror.Occasionally,inthepresenceofveryintenseNBP event,wirelesscommunicationsystemcouldexperiencetotalcommunicationlost.InCGflash,itcanbe concludedthatPBPisthemajorsourceofinterferencethatinterferedwiththebitstransmissionand causedthelargestbursterror.InICflash,wefoundthatthetypicalICpulsesinterferedthebits transmis-sioninthesamewayasPBPandmixedeventsinCGflashandproducedcomparableandinsomecases higheramountofbursterror.NBPhasbeenobservedtointerferethebitstransmissionmoreseverely thantypicalICandCGflashesandcausedthemostseverebursterrortowirelesscommunicationsystem.

1. Introduction

Wirelesscommunicationsystemhasevolvedrapidlyfromthe lastdecadeandutilizedwiderangeoffrequencybandsfortheir operationparticularlyinthemicrowaveregion.Currently, broad-bandwirelesssystems(e.g.WiFi,WiMAX)areoperatingbetween 2and6GHzfrequencybands.Recentobservationsofmicrowave radiationfromlightningflashesin[1,2]havetriggeredinterestto

∗_{Corresponding}_author_at:_Ångström_Laboratory,_Division_for_Electricity,

Depart-mentofEngineeringSciences,UppsalaUniversity,Box534,S-75121,Sweden. Tel.:+46184715849;fax:+46184715810.

E-mailaddresses:riduan.ahmad@angstrom.uu.se,riduan@utem.edu.my

(M.R.Ahmad),monariza.esa@angstrom.uu.se(M.R.M.Esa),

Vernon.cooray@angstrom.uu.se(V.Cooray),eryk.dutkiewicz@mq.edu.au

(E.Dutkiewicz).

studyitseffectsonwirelesscommunicationsystem.Theworkin [1]hasobservedstrongmicrowaveradiationat1.63GHz associ-atedwithcloud-to-ground(CG)flasheventssuchaspreliminary breakdownprocess(PBP),steppedleaders(SLs),dartleaders(DLs), andreturnstrokes(RSs).Moreover,similarmicrowaveradiation at2.4GHzassociatedwithcloud(IC)flasheventssuchasnarrow bipolarpulses(NBPs)wereobservedin[2].

Work donein[3] pioneeredthe investigationontheeffects of interferencefrom naturallightning flashes onwireless com-municationlinksat2.4GHz.Areceivedsignalstrengthindicator (RSSI)measurementmethodhadbeenusedwith1mlineofsight (LOS)separation.ThemeasuredRSSIvalueswereusedtosimulate biterrorrate(BER)fordata,audioandvideotransmissions.The measurementwasconductedinMalacca,Malaysiaduringarainy dayinSeptember 2010.Itwasconcludedthat lightningflashes reducethereceivedpowerandleadtounreliablecommunication links.

http://dx.doi.org/10.1016/j.epsr.2014.03.022

(2)

In[4,5]theeffectsofinterferencefromnaturallightningflashes onBERof anaudiotransmission wererecordedat 2.4GHz and 5.8GHz.Themeasurement wasconductedin Malacca,Malaysia betweenJanuaryandMarch2011.ThehighestrecordedBERwas 9.9×10−1withthemeanBERwas2.07×10−2.Thereference mea-surements under fair weather conditions give a baseline mean BERvalueat1.75×10−5.BERvaluesduringthunderstormsthat higherthan1.75×10−5wereinterpretedasbeinginterferedbythe lightningflashes.Thereforeitwasconcludedthatwireless commu-nicationsystemoperatingat2.4GHzwassignificantlyinterferedby lightningflashes.Howeverduetothelackoflightningflashevents information,thetypeofCGandICeventsthathaveinterferedwith thebitstransmissioncouldnotbeidentified.

Furtherworkin[6]evaluatedpossiblebursterroreventtooccur duringthebitstransmissionofanaudiostreamingapplicationat 2.4GHz.Aconsecutivelostdatagram(CLD)measurementmethod wasusedtoevaluatethebursterroreventduring3heavy thunder-stormsbetweenJanuaryandMarch2011inMalaysia.Itwasfound thatthenumberoflostpacketsperburstforallthunderstormswas rangingfrom8to40lostpackets.Howeverduetothelackof light-ningeventsinformation,whichCGandICeventscontributedtothe bursterroreventcouldnotbeidentified.

Inthispaper,wearemotivatedtoinvestigatewhattypeofCG andICeventsthatpossiblyhaveinterferedthebitstransmission ofawirelesscommunicationsystemoperatingat2.4GHz,which couldnotbeidentifiedby[3–6].Moreover,itisinterestingtostudy whichtypeofCGandICeventswouldinterferemoreseverelythan theothersandcontributetothehighBERandbursterrorevents. RecordingfromtheBERmeasurementsystemandtheelectricfield changerecordingsystemhavebeensynchronizedtoprovide com-montimestampinformation.Lightningwaveformstogetherwith theBER and maximum CLD from3 tropical thunderstormson November27,28,and29during2012northeasternmonsoonin Malaysiawereexaminedandanalyzed.

2. Measurementcampaign

Themeasurements wereconducted betweenNovember and December2012duringthenortheastmonsoon periodat Obser-vatory Station in Universiti Teknologi Malaysia (UTM), Johor, Malaysia,locatedatsouthernpartofpeninsularMalaysia(1◦ _N,

103◦_E)._The_measuring_system_was_situated_on_a_top_of_a_hill_that

is132mabovesealevelandabout30kmawayfromTebraustrait. AverticallypolarizedwhipantennawasconnectedthroughRF coaxialcabletoaLeveloneWUA-0614wirelessnetworkcard[7] attachedtoalaptopactingasaserver.Thesamelaptopactedas aclientand wasconnectedtoaCiscoWUSB600Nwireless net-workcard[8]throughaUSBcable.Atthesametime,thelaptop actedasa GPS-basedtime synchronizationserverand hasbeen synchronizedwithdigitalstorageoscilloscope(DSO)oftheelectric fieldchangerecordingsystem.Thelaptopwasbattery-powered andlocatedinsidetheobservatorystationbuilding.

Boththetransmitting(whipantenna)andreceivingantennas werepositionedonaplasticstructure(polyvinylchlorideorPVC) 1mabove ground and 3mfrom the observatory building. The ‘ground’referstotheEarth’ssurface.A5mdistanceseparatedthe transmittingantennafromthereceivingsystem.Fig.1illustrates theseconfigurations.Boththetransmitterandthereceiverwere operatingat2.4GHz.Adaptivemodulationswerechosen.Taking 5mofLOSrangeintoconsideration,mostprobably64-quadrature amplitudemodulation(QAM)wasfullyutilized.

Theapplicationlayerattheserverofthetransmittingsystem emulatedaRealAudioapplicationbroadcastingaudiocontentfrom amultimediaCD-ROM.Theaveragesendingdataratewas80Kbps. Thesizeoftheaudiodatawas1MB.Thisdatawastransmittedusing

Fig.1.BERandCLDrecordingsystemlocated3mfromtheobservatorystation building.Thetransmittingantenna(verticallypolarizedwhipantenna)was con-nectedtoaserverlaptopthroughthecoaxialcable.Thereceivingsystemwas connectedtoaclientlaptopthroughtheUSBcable.Boththetransmittingand receiv-ingantennaswerepositionedontopofaplasticstructure(PVC)1mfromground andseparatedby5mdistance.

realtimeprotocol(RTP)[9]overuserdatagramprotocol/Internet protocol(UDP/IP)asillustratedbyFig.2in[5].Thepayloadtype oftheRTPwasG.729[10,11].Thetotaloverheadaddedtoasingle audiodatapacketwas40bytes(fromRTP,UDPandIPheaders). HoweverdatagramsegmentationattheUDPlayerandpacket frag-mentationattheIPlayercouldincreasemorethetotaloverhead addedtotheaudiodatapacket.Thusthetotalnumberofbytessent fromtheserverwas1MBaudiodataincludingthetotaloverhead dependingonhowmanydatagramswasgenerated.

(3)

TheLevelonewirelessnetworkcardforwardedthesepackets tothereceivingsystemoverthewirelesscommunicationlinkby using802.11nradiointerface[12]withamaximumsendingrateof 150Mbps.Distributedcoordinatedfunction(DCF)protocol with-outtherequest-to-send/clear-to-send(RTS/CTS)mechanismwas chosenfortheoperationof802.11nradio.Thehandshaking mech-anismwasdisabledafterthehiddennodeproblemwaseliminated completely.Alsoothermeasurestoeliminatehiddennode prob-lemhadbeentaken suchasproviding strongLOSpath,shorter Transmitter–Receiverseparationandtheusageofomni-directional antenna.

The802.11nradiointerfaceatthereceivingsystemreceived thetransmittedbytes andforwarded themto theclientlaptop throughUSBinterfacewithamaximumdatarateof480Mbps. For-warderrorcorrection(FEC)mechanismwasusedinthe802.11n radiointerfacetocorrectanydetectederrorinthereceivedbytes. Theframechecksequence(FCS)attheendofeachframedetects most of the errors that are not corrected by the FEC scheme. TheseerrorsarecorrectedbyretransmissionsattheMAC layer. AnybitthatcannotbecorrectedbytheFECandFCSwascounted as an error at the IP layer.At the UDP layer, a packet with a certainnumberoferrorbyteswasconsidereddamagedand dis-carded. The report of the total number of bytes and packets in error was transmittedto the serverafter the run time was completed.

Theelectricfieldchangerecordingsystemconsistedofa paral-lelflatplateantennaplacedonametalstand1.5maboveground connectedviaashort60cmshieldedcoaxialcabletoa battery-poweredbuffercircuit. Theparallelflatplateantennastogether withthebuffercircuit(shieldedinametalcaseasshowninFig.2) were positioned about 9m away from the observatory station building.Thetopplateoftheantennawasconnectedtotheinner conductorofthecoaxialcablewhilethebottomplatewas con-nectedtothescreening conductorofthecoaxialcable.Alsothe bottomplatewasconnecteddirectlytothesinglepoint ground-ingsystem.Thebuffercircuitwasconnected toa LeCroyWave Runner44Xi-ADSOvia10mlongshieldedcoaxialcable.The con-figurationsofparallelflatplateantennaandbuffercircuitwere similartotheconfigurationsusedin[13].TheDSOdigitizedthe outputofthebuffercircuitat25MegaSamples/s(20nstime reso-lutionwith500msfullwindowsize)and8-bitverticalresolution witha100MHzbandwidth(10nsimpulsewidthresolution).The DSO wastriggered byeither positive edge or negative edge of incomingsignalwithtriggerlevelwasvariedbetween0.1Vand 1V.

3. Resultsandanalysis

Atotalof850waveformsfromtheelectricfieldchange recor-dingsystemwererecordedandexaminedduringthismeasurement campaign.Outofthese,94waveformsofveryfinestructurewere selectedwhichmatchedperfectlywiththetiminginformationof therecordedBER.78outof94arenegativeCG(-CG)flash wave-formsandtherestareICflashwaveforms.5outof16ICwaveforms areNBPevent.

EachBERpointcorrespondstothenumberoferrorbits mea-suredatthereceiverforacompletetransmissionofa1MBtrain ofbitsfromthetransmitter.Thetransmissiontimeforacomplete 1MBtrainofbitsis800ms.EachmaximumCLDpointcorresponds tothenumberofconsecutivelostdatagramobservedatUDPlayer. Itisanindicatorofhowseveretheoccurrenceofbursterrorin wirelesscommunicationsystem.Aslightningflashconsistsevents withimpulsiveactivities,itismorelikelythenatureofinterference willbeintheformofbursterror.

Thereferencemeasurementsunderfairweatherconditionsgive abaselineaverageBERvalueataround1×10−5.ThusBERvalues duringthunderstormsthathigherthan1×10−5areinterpretedas beinginterferedbylightningflashes.Ingeneral,acommunication linkforbroadcastaudiostreamsisrecommendedtomaintainBER below1×10−3[14].Inordertoincreasetheaccuracyofthe anal-ysisandfollowingtherecommendationoutlinedby[14],wehave chosenhigherbaselineBERvalueataround1×10−3.Therefore, lightningwaveformswhichhaveassociatedBERvalueshigherthan 1×10−3_are_regarded_as_the_source_of_interference_to_the_wireless

communicationsystem.Atfrequenciesbelow10GHz,attenuation byatmosphericgasesand rainmaynormallybeneglected[15]. Thus,weareconvincedthatthewirelesscommunicationsystem wasaffectedbythethunderstormalone.

3.1. Interferencefromcloud-to-groundflashes

ThreecategoriesofnegativeCG flashhave beenobserved to interfere the wireless communication systemsignificantly. The firstcategoryofCGflash(Category1)consistsoftypicalground flashwithoutPBPandcomeswithorwithoutchaoticpulses(CP). Fig.3 shows anexampleof 4 RSs(withassociated SLand dart steppedleader)withoutCP.Atotalof20waveformsarefallunder thiscategorywith8waveformsconsistCP.WeobservedthatallCP wereoccurredpriortosubsequentRSorinbetweenRS.Inaddition toRSandCP,thesecondcategoryofCG(Category2)consistsPBP

(4)

Fig.4.Activityrecordedon27November2012,tracenumber230at16:22:47,thetimewindowduringthismeasurementwas500mswithpre-triggerdelayof150ms.This typeofactivityisfallunderCategory2ofCGflash.

asillustratedinFig.4.Atotalof38waveformsarefallunderthis categorywith16waveformsconsistCP.

ThethirdcategoryofCGflash(Category3)consistsofmixed eventsoflargebipolarpulses(Fig.5a),trainofunipolarand bipo-larpulses(Fig.5b),andNBP(Fig.5c)thatweredetectedtogether withearliercategories.Atotalof20waveformsarefallunderthis category.AscanbeobservedfromFig.5,thelargebipolarpulses, NBPandtrainofpulseswerefoundtooccurbetweenand follow-ingRS.AlltheNBPeventswereobservedtohavelowerintensity comparedtothelargestRSbutcomparabletothelowestintensity RS.

Thepulseduration of thelargebipolarpulses and NBPwas observedtobelessthan100␮s.Thepulsedurationofthelarge bipolarpulsesisintherangebetween80and100␮swhileNBP

pulsedurationisintherangebetween5and20␮s.Incontrast,the durationofthetrainofunipolarandbipolarpulseswasobservedto exceed100␮s.Furthermore,wedetectedonlynegativepolarityof largebipolarpulsesandNBPcorrespondstotheBERvaluehigher than1×10−3.Ontheotherhand,thetrainsofpulsesweredetected withbothpolarities.

CorrelationofBERandCLDwiththenumberofRSisshownin Figs.6and7,and10forallnegativeCGflashcategoriestabulatedin Table1.KnowingthecorrelationofBERandCLDwiththenumber ofRS,onewillbeabletounderstandhowsignificantmicrowave radiationfromtheRSinterferingthetransmissionofbitsin wire-lesscommunicationsystem.Furthermore,oneisabletoidentify whichcategoryofCGinterferesmoreseverelythetransmissionof bitsandproduceshigherbursterror.Thebest-fitcorrelationlines

(5)

95% conﬁdence limits Linear least sq. ﬁt

Measured data Bit Error Rate

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

−0.2

1 2 3 4 5 6

Number of return strokes

r2_{= 0.85}

y = mx + c m = 0.06

Fig.6.LinearcorrelationbetweenBERandthenumberofRSforCategory1ofCG flash.TheBERvaluehasbeengiveninpercentagescale,e.g.1×10−2_corresponds_to

1.

Measured data

1 2 3 4 5 6

0 6

4

2

0

r2_{= 0.93} y = mx + c m = 0.3

1 2 3 4 5 6

0 (A)

7

7 8 9

10

8

6

4

2

0 (B)

r2_{= 0.89} y = mx + c m = 0.13 Bit Error Rate

Fig.7. LinearcorrelationbetweenBERandthenumberofRSfor(A)Category4a and(B)Category4b.TheBERvaluehasbeengiveninpercentagescale,e.g.1×10−2

correspondsto1.

Fig.8.Statisticaldistributionof(A)BERand(B)maximumCLDvaluesforCategories 1to3ofCGflash.TheBERvaluehasbeengiveninpercentagescale,e.g.1×10−2

correspondsto1.

Fig.9.Statisticaldistributionof(A)BERand(B)maximumCLDvaluesfor Cate-gory4ofCGflash.TheBERvaluehasbeengiveninpercentagescale,e.g.1×10−2

correspondsto1.

Table1

Definitionsandexplanationsofthecategoriesof-CGandICflashes.

Flash Category Events

-CG 1₂ RSs_Categoryaccompanied₁_event_accompaniedbysteppedleader,_by_PBPdart_event(stepped)_prior_theleaders,_first_RSandchaoticpulses.

3a Category1eventaccompaniedbymixedeventsconsistslargebipolarpulses,trainofunipolarandbipolarpulses,andNBP. 3b Category2eventaccompaniedbymixedeventsconsistslargebipolarpulses,trainofunipolarandbipolarpulses,andNBP. 4a CombinationofCategory1andCategory3aevents,wherePBPeventisabsent.

4b CombinationofCategory2andCategory3bevents,wherePBPeventispresent.

IC 1 TypicalICpulses

(6)

Measured data

1 2 3 4 5 6

Fig.10.LinearcorrelationbetweenmaximumCLDandthenumberofRSfor(A) Category4aand(B)Category4bofCGflash.

wereobtainedbyusingthemethodofleastsquaresregression.In thecasewhenlinearbest-fitlinecouldnotbeobtainedandthe cor-relationcoefficientrequirementcannotbesatisfied(r2_≥_0.7),_the

methodofnonlinearleastsquareswithGauss–Newton

optimiza-tionalgorithmwasappliedtoobtainthenonlinearbest-fit line. Thegradientvalue,mandinterceptvalue,cofthelinearbest-fit correlationlinescanbeobtaineddirectlyfromthefirstorderof polynomialequation,y(x)=mx+c.Ontheotherhand,thegradient value,bandinterceptvalue,aofthenonlinearbest-fitcorrelation linescanbeobtaineddirectlyfromtheequationofanexponential function,y(x)=aebx_.

ForCategory1ofCGflash,theBERandthenumberofRSshows linearcorrelationwithr2₌_0.85_and_m₌_0.06_as_shown_in_Fig.₆_._As thenumberofRSincreasesfrom1to6,theBERvalueincreases linearlyfrom1.5×10−3 to4.5×10−3.We can seeclearly from thefigurethat95%ofthemeasuredBERvaluesareliewithinthe range of confidence limitsof thefit line. Moreover,linear cor-relationisalsoobservedforCategory4aand Category4b ofCG flashinFig.7AandB,respectively.ThegradientofCategory4ais muchsmallerthanCategory4bwithm=0.13comparedtom=0.30, respectively,butmuchhigherthanthegradientofCategory1of CGflash,m=0.06.AsthenumberofRSincreasesfrom1to6,the BERvalueofCategory4bhasincreaseddrasticallyfrom1×10−2 to2.5×10−2,muchhigherthanCategory4aandCategory1with linearincrementfrom2×10−3_to₈_×₁₀−3_and_from_1.5_×₁₀−3_to

4.5×10−3,respectively.

Apparently, the BER performance of all CG flash categories becomesworstasthenumberofRSincreases.Further,this obser-vationmaysuggest that PBPin Category4b hasradiatedmore significantmicrowavepulsesthatinterferedwiththebits trans-mission,asareflectiontothemuchhighergradientandBERvalues thanCategory1andCategory4aofCGflash.Also,itcanbe sug-gestedthatthemixedeventsinCategory3ofCGflashradiated significantmicrowavepulsesinterferedwiththebitstransmission

95% conﬁdence limits Nonlinear least sq. ﬁt

Measured data (A) Bit Error Rate

(B) Maximum CLD

Intensity (Digizer volt) 10

Fig.11.Nonlinearcorrelationbetween(A)BERandthelargestintensity,and(B) maximumCLDandthelargestintensity,forCategory2ofCGflash.TheBERvalue hasbeengiveninpercentagescale,e.g.1×10−2_corresponds_to_1.

Measured data (A) Bit Error Rate

(B) Maximum CLD

(7)

Fig.13.Activityrecordedon27November2012,tracenumber257at16:51:26,thetimewindowduringthismeasurementwas500mswithpre-triggerdelayof150ms. ThistypeofactivityisfallunderCategory1ofIC.

butnotasmuchasPBP,asareflectiontolowerBERvaluesandsmall differenceingradientvaluesbetweenCategory1andCategory4a ofCGflash.

The statistical distribution of BER values in Fig. 8 supports thereflectionsofthecorrelationanalysis.Category1ofCGflash recordedthesmallestBER rangeandalsothelowestmeanBER valueat3.8×10−3whencomparedtoothercategoriesasevidenced inFig.8A.ThePBPinterferedthebitstransmissioninthemost sig-nificantwaycausesgreaterBERrangeandalsohighermeanBER valuesat1.77×10−2and3.58×10−2forCategory2andCategory 3bofCGflash,respectively.Category3arecordedonlyaslightly increaseinthemeanBERvaluewhencomparedtoCategory2of CGflash,2.25×10−2comparedto1.77×10−2,whichsuggeststhat theinterferencefromthemixedeventsisalmostcomparableto PBP.However,itisimportanttonoticethattherangeofBERvalues forCategory3aismuchsmallerthantherangeofbothCategory2

andCategory3bofCGflash.Moreover,therangeandmeanBERof Category4aaremuchsmallerthantherangeandmeanBERof Cat-egory4basevidencedinFig.9A.Therefore,itcanbesuggestedthat themixedeventshaveinterferedthebitstransmissionsignificantly butnotasmuchasPBPevent.Consequently,thismayexplainwhy themixedeventsinCategory3ofCGflasharesuggestedtoradiate significantmicrowavepulsesbutnotasmuchasPBPasrevealed fromthecorrelationanalysis.Further,wecouldobservethatallthe BERvalues(outliersexcluded)ofCategory1ofCGflashand Cate-gory4aarebelow1.5×10−2whilemorethan50%oftheBERvalues ofCategory2ofCGflashandCategory4barehigherthan1×10−2as evidencefromthemedianvaluesinFigs.8Aand9A.MostlikelyPBP eventisthestrongestsourceofmicrowaveradiationinCGflash.

AlinearcorrelationbetweenmaximumCLDandthenumberof RScanbeseenclearlyfromFig.10Awithr2₌_0.91_and_from_Fig.₁₀_B withr2₌_0.94_for_Category_4a_and_Category_4b,_{respectively.}_As_the

(8)

(A)

(B)

Intensity (Digizer volt) 10 Nonlinear least sq. ﬁt

Measured data

Fig.15.NonlinearcorrelationbetweenBERandthelargestintensityfor(A)Overall CGflash,(B)TypicalICflash,and(C)NBP.TheBERvaluehasbeengiveninpercentage scale,e.g.1×10−2_corresponds_to_1.

numberofRSincreasesfrom1to6,thenumberoflostdatagram forCategory4ahasincreasedfrom5to20datagrams.ForCategory 4b,thenumberoflostdatagramhasincreasedmoredrasticallyand higherthanCategory4a,from20to60datagrams.Moreover,the gradientofCategory4bisestimatedtobe7.8,muchhigherthanthe gradientofCategory4aat2.7.Therefore,itcouldbesuggestedthat Category4bradiatedthemostsignificantmicrowavepulses,which interferedwiththebitstransmissionandcausedthehighestburst error.Apparently,correlationanalysisrevealsthatthebursterror ismoreprevalentasthenumberofRSincreasesandPBPinterfered thebitstransmissioninthemostsignificantway.

Further,statisticaldistributionofCLDvaluesinFig.8Bsupports therevelationofcorrelationanalysiswherewecanobservethat Category3brecordedthehighestmeanCLDvalueat73.78when comparedtoCategory3aandCategory1with42.09and7.15mean CLDvalues,respectively.EvidencefromFig.9Brevealsthemean CLDofCategory4bisdoublethemeanCLDofCategory4a.Also, therangeandmedianvaluesoftheformercategoryaremuchlarger thanthelattercategory.Inaddition,wealsoobservethatalltheCLD values(outliersexcluded)ofCategory4aarebelow20datagrams whilemorethan50%oftheCLDvaluesofCategory4barehigher

Measured data (A) Maximum CLD

(B)

Fig.16.NonlinearcorrelationbetweenmaximumCLDandthelargestintensityfor (A)OverallCGflash,(B)TypicalICflash,and(C)NBP.

than20datagramsandupto190datagrams.Evidently,PBPisthe strongestsourceofmicrowaveradiationinCGflashthatinterfered thebitstransmissionandconsequentlyincreasestheBERandCLD values.

CorrelationofBERandmaximumCLDwiththelargestintensity is shown in Figs. 11 and 12. The largest intensity here corre-spondstothelargestamplitudeofRSandreflectsthedistanceto thesourceofradiation.ThelargestRSintensityisassumedtobe inverselyproportionaltothedistancefromthesourceofradiation. Consequently,closeradiationsourcewouldrecordsmuchhigher intensityRSthanthedistantradiationsource.ForCategory2ofCG flashandCategory4b,theBERandthelargestintensityshowsvery goodexponentialcorrelationwithr2₌_0.91₍_Fig.₁₁_A)_and_r2₌_0.93 (Fig.12A),respectively.Also,themaximumCLDandthelargest intensityshowsverygoodexponentialcorrelationwithr2₌_0.91 (Fig.11B)fortheformercategoryandr2₌_0.91₍_Fig.₁₂_B)_for_the lattercategory.ThegradientofCategory2ofCGflashisestimated tobe0.4forbothBERandmaximumCLD,thesameasthe gradi-entestimatedforCategory4b.Astheintensityincreasesfrom1 to5volts,theBERandmaximumCLDvaluesofbothcategories increasesfrom1×10−2_to₄_×₁₀−2_and_from₂₀_to₈₀_datagrams,

(9)

Fig.17.Statisticaldistributionof(A)BERand(B)maximumCLDvaluesforoverallCG,IC,andNBPflashes.TheBERvaluehasbeengiveninpercentagescale,e.g.1×10−2

correspondsto1.

severelywiththebitstransmission.Alsothebursterrorismore prevalentastheintensityincreases.

3.2. Interferencefromcloudflashes

TwocategoriesofIChavebeenobservedtointerferethe wire-lesscommunicationsystemsignificantly.ThefirstcategoryofIC consiststypicalcouldflashpulsesasshowninFig.13.Atotalof 11waveformsfallunderthiscategory.ThesecondcategoryofIC isaspecialtypeofICknownasNBP.Atotalof5waveformsfall underthiscategory.Outofthese,4areisolatedNBPand1isin thecategoryofmultipleNBP(showninFig.14).AlltheNBPinthis categorywereobservedwithlargeintensitycomparableandeven largerthanthelargestRS,unliketheNBPfoundtooccuraspartof negativeCGflash.Further,wedetected2positivepolarityisolated NBPcorrespondingtotheBERvaluehigherthan1×10−3andthe othershavetheoppositepolarity.

CorrelationofBERandmaximumCLDwiththelargestintensity isshowninFigs.15and16.Thelargestintensityherecorresponds totheamplitudesofthelargestICpulseandNBPandreflectsthe distancetothesourceofradiation.ThelargestICandNBP intensi-tiesareassumedtobeinverselyproportionaltothedistancefrom thesourceofradiation.Consequently,closeradiationsourcewould recordmuchhigherintensitythanthedistantradiationsource.The BERandthelargestintensityshowsverygoodexponential correla-tionwithr2₌_0.70₍_Fig.₁₅_B)_and_r2₌_0.99₍_Fig.₁₅_C)_for_the_first_and secondcategoriesofIC,respectively.Also,themaximumCLDand thelargestintensityshowsverygoodexponentialcorrelationwith

r2₌_0.71₍_Fig.₁₆_B)_and_r2₌_0.99₍_Fig.₁₆_C)_for_the_first_and_second categoriesofIC,respectively.ForbothBERandmaximumCLD,the gradientofthesecondcategoryofICismuchhigherthanthefirst categoryofICandoverallCGflashcategory(Figs.15Aand16A),2.0 comparedto1.3and0.4,respectively.

Thisresultmaysuggestthat,astheimpulsiveactivityofICgets moreintense,itwouldinterferemoreseverelywiththebits trans-mission.Alsothebursterror ismoreprevalentas theintensity increases.Further,thegradientvaluestellusthattheNBPradiated themostintenseimpulsivemicrowavepulses,evenwhen com-paredtoallcategoriesofCGflash.Thestatisticaldistributionsof BERandCLDvaluesinFig.17AandBaresupportingthisfinding

wheretheNBPrecordedthehighestmeanBERandCLDvaluesat 4×10−2and91.60,respectively.Ontheotherhand,thefirst cat-egoryofICrecordedmeanBERandCLDvaluesat2.54×10−2_and

53.36,respectively,whicharefoundtobehigherthanthe over-allCGcategorywithmeanBERandCLDvaluesat1.69×10−2and 31.92,respectively.

4. Discussionandconclusion

(10)

However,asdiscussedin[17],thedatapointsofspectral ampli-tudeabove10MHzfrequencyregionsweremostlyscattered.Thus, itwasrecommendedthatmoremeasurementsshouldbedonefor individualeventathigherfrequenciestoobtainreliableresultsto resolvetheambiguitiesinthespectralshape.

Inthelightofveryrecentfrequencyspectrumstudyin[1],PBP, SLandDLfromanegativeCGflashhavebeenobservedto gener-atetrainsofindividuallyresolvablemicrowavepulsesat1.63GHz band.TheamplitudeofthemicrowavepulsesproducedbyPBPwas observedtobemoreintensethanSLandDL.Ontheotherhand, thenegativeRSwasobservedtogeneratenoise-likemicrowave burstinsteadofindividualpulsesbutwithmoreintenseamplitude whencomparedtoPBP.However,themicrowaveburstofRSlasted onlyforafewhundredsofmicrosecondswhilemicrowavepulses ofPBPlastedlongerforseveralmillisecondsduration. Thismay explainwhytheinterferencelevelfromCGflashissignificantly higherduringthepresenceofPBPasevidencedinFigs.8and9.The typicalPBPtraindurationisbetweenafewmillisecondandtens ofmillisecondsandthus,mostlikelythateachpulsesinthePBP trainradiatesmicrowavepulsesandinterfereswiththebits trans-missionfordurationlongerthanotherCGflasheventssuchasRS. Therefore,inCGflash,itcanbeconcludedthatPBPisthemajor sourceofinterferencethatinterferedwiththebitstransmission andcausedthelargestbursterror.

InICflash,wefoundthatthetypicalICpulsesinterferedthe bitstransmissioninthesamewayasPBPandmixedeventsinCG flashandproducedcomparableandinsomecaseshigheramount ofbursterror.Ontheotherhand,NBPhasbeenobservedto inter-ferethebitstransmissionmoreseverelythantypicalICand CG flashesasevidencedinFigs.15–17.Recentworkin[2]revealed thatNBPhasproducednoise-likemicrowaveburstlastedfor sev-eralmicrosecondsat2.4GHzband.Itisinterestingtowonderhow asingleNBPpulsecouldproduceveryintensemicrowave radi-ationpulses that couldinterferethebitstransmission severely. Ifwe considerthe very recentproposal putforwardin [19] to betrue that NBPdischarge is the result of relativisticelectron avalanchesmechanismratherthanconventionalleaderdischarge. Then,thespectralamplitudeoftheresultantradiationfieldwould bepeakedataround1GHzasestimatedin[20].Thismayexplain ourfindingand provide logical reason whya single NBPpulse couldproduceveryintensemicrowaveburstat2.4GHzbandand caused themost severeburst errorto wireless communication system.

Acknowledgements

Thispaperisarevisedandextendedversionofcontribution[4] kindlypresentedbythefirstauthoratthe2012International Con-ferenceonLightningProtection(ICLP).Wewouldliketothankthe participantsfortheirhelpfulcommentsandsuggestions.Research workinthis paperwasfundedbyMinistryofHigherEducation MalaysiaandAnnaMaria LundinFoundation(Småland Nation). ParticipationofVernonCooraywasfundedbythefundfromthe B.JohnF.andSveaAnderssondonationatUppsalaUniversity.We wouldlike tothankAssoc.Prof. Dr.Zulkurnain Abd.Malek,Dr.

Azlinda,Ms.Zaini,Mr.KamyarandMr.Behnam,fromIVAT,UTM, Malaysiaforthesupportsduringthemeasurementcampaign.

References

[1]D. Petersen,W.Beasley,Microwaveradioemissionsofnegative cloud-to-groundlightningflashes,Atmos.Res.135–136(2014)314–321.

[2]M.R.Ahmad,M.R.M.Esa,V.Cooray,Narrowbipolarpulsesandassociated microwaveradiation,in:Proc.ofProgressInElectromagneticsResearch Sym-posium(PIERS),Stockholm,Sweden,August12–15,2013,pp.1087–1090.

[3]M.R.Ahmad, M.Rashid,M.H.A.Aziz,M.M.Esa,V.Cooray,M.Rahman,E. Dutkiewicz,Analysisoflightning-inducedtransientin2.4GHzwireless com-municationsystem,in:Proc.ofIEEEInternationalConferenceonSpaceScience and Communication(IconSpace),Penang,Malaysia,July12–13,2011, pp. 225–230.

[4]M.R.Ahmad,M.R.M.Esa,M.Rahman,V.Cooray,Measurementofbiterrorrate at2.4GHzduetolightninginterference,in:Proc.ofInternationalConference onLightningProtection(ICLP),Vienna,Austria,September2–7,2012,pp.1–4.

[5]M.R.Ahmad,M.R.M.Esa,M.Rahman,V.Cooray,E.Dutkiewicz,Lightning inter-ferenceinmultipleantennaswirelesscommunicationsystems,J.Light.Res.4 (2012)155–165.

[6]M.R.Ahmad,M.R.M.Esa,V.Cooray,E.Dutkiewicz,Performanceanalysisof audiostreamingoverlightning-interferedMIMOchannels,in:Proc.of Interna-tionalSymposiumonCommunicationsandInformationTechnologies(ISCIT), GoldCoast,Australia,October2–5,2012,pp.513–518.

[7]LeveloneWirelessNanoUSBNetworkAdapterWUA-0614Datasheet. Avail-able:http://global.level1.com/datasheet/WUA-0614-V2SPECEN.pdf

[8]Linksys Ultra Rangeplus Dual-band Wireless-N USB Network Adapter WUSB600N Specifications (Network Adapter), CNET Review Web Site. Available: http://reviews.cnet.com/adapters-nics/linksys-ultra-rangeplus-dual/4507-33807-32816737.html

[9]H.Schulzrinne,S.Casner,R.Frederick,V.Jacobson,RTP:ATransport Pro-tocolforReal-TimeApplications,IETFRFC3550Standard2003.Available:

http://tools.ietf.org/html/rfc3550

[10]Implementors’GuideforITU-TRec.G.729(2007):CodingofSpeechat8kbit/s UsingCS-ACELP,TelecommunicationStandardizationSectorofITUSeriesG: TransmissionSystemsandMedia,DigitalSystemsandNetworks2009. Avail-able:http://www.itu.int/rec/T-REC-G.Imp729-200911-I/en

[11]IEEEstandardforinformationtechnology:Telecommunicationsand infor-mationexchangebetweensystems:Localandmetropolitanareanetworks: Specificrequirements,Supplementtocarriersensemultipleaccesswith col-lisiondetection(CSMA/CD)accessmethodandphysicallayerspecifications: Physicallayerparametersandspecificationsfor1000Mb/soperationover 4-pairofcategory5balancedcoppercablingtype1000BASE-T,IEEEstandard 802.3ab1999.

[12]IEEE standard for information technology: Local and metropolitan area networks:Specificrequirements:Part11:WirelessLANmediumaccesscontrol (MAC)andphysicallayer(PHY)specificationsamendment5:Enhancementsfor higherthroughput,IEEEstandard802.11n2009.

[13]M.R.M.Esa,M.R.Ahmad,V.Cooray,Waveletanalysisofthefirstelectricfield pulseoflightningflashesinSweden,Atmos.Res.138(2014)253–267.

[14]Y.Chen,T.Farley,N.Ye,QoSrequirementsofnetworkapplicationsonthe Internet,J.Inform.Knowl.Syst.Manage.4(2004)55–76.

[15]RecommendationITU-RP.618-9:PropagationDataandPredictionMethods RequiredfortheDesignofEarth-SpaceTelecommunicationSystems, Radio-communicationSectorofITUSeriesP:RadiowavePropagation2009.Available:

http://www.itu.int/rec/R-REC-P.618-10-200910-I/en

[16]C.D.Weidman,E.P.Krider,M.A.Uman,Lightningamplitudespectrainthe inter-valfrom100kHzto20MHz,Geophys.Res.Lett.8(1981)931–934.

[17]D.M.LeVine,ReviewmeasurementsoftheRFspectraofradiationfrom light-ning,Meteorol.Atmos.Phys.37(1987)195–204.

[18]U.Sonnadara,V.Cooray,M.Fernando,Thelightningradiationfieldspectraof cloudflashesintheintervalfrom20kHzto20MHz,IEEETrans.Electromagn. Compat.48(1)(2006)234–239.

[19]V.Cooray,G.Cooray,T.Marshall,S.Arabshahi,J.Dwyer,H.Rassoul, Electro-magneticfieldsofarelativisticelectronavalanchewithspecialattentionto theoriginoflightningsignaturesknownasnarrowbipolarpulses,Atmos.Res. (2014)(inpress).