i Performance Evaluation of Vehicle to Vehicle (IEEE 802.11p) Communication Systems Charles Joseph OGALA Submitted toInstitute of Sciencesin partial fulfillment of the requirements for the Degree of Masters of Science InInformation Systems Engineering Cyprus International University January 2012 Nicosia, North Cyprus ii Approval of the Institute of Graduate Studies and Research Prof. Dr. Hikmet Secim Director I certify that this thesis satisfies the requirements as a thesis for the degree of Master of Sciences in Information Systems Engineering. Asst. Prof. Dr. Mehmet Toycan Supervisor Wecertifythatwehavereadthisthesisandthatinouropinionitisfullyadequatein scopeandqualityasathesisforthedegreeofMasterofSciencesinInformation Systems Engineering. Examining Committee 1.Asst. Prof. Dr. Hseyin ADEMGIL 2.Asst. Prof. Dr. Mehmet TOYCAN 3.Asst. Prof. Dr. Devrim SERAL iii ABSTRACT This research is fundamentally built on IEEE 802.11p which is the official standard for Vehicle to Vehicle (V2V) and Vehicle to Infrastructure (V2I) Wireless communication. The vehicular standard is an improvement of IEEE 802.11a which is a member of IEEE 802.11 family. It uses Orthogonal Frequency Division Multiplexing (OFDM) carrier for thetransmissionofdatafromthetransmitterdownto thereceiver.However,vehicular standardalsousesahalfclockmodewhichhavepositiveeffectonthebandwidth, symbol length by making the signal more robust against fading during transmission. InthisresearchAgilentsAdvancedDesignSystems(ADS)simulatorisusedto measure performance of the Physical layer (PHY) with regards to Bite Error rate (BER)and Packet Error Rate (PER) for different fadingchannel whichinclude; Typical urban environment,RuralenvironmentandFreespaceenvironment.ADS,isflexibleduring usage and it also provides accurate measurement for the different modulation technique for Line of Sight (LOS) and Non Line of Sight (NLOS). iv To my parents; Mr. Joseph Adeyi OGALA and Mrs. Mary OGALA v ACKNOWLEDGEMENTS Firstly,IwillliketoexpressmyheartfeltthankstomysupervisorAsst.Prof.Dr. Mehmet TOYCAN for suggesting my thesis topic and guiding me through this research analysis.FurthermoreIwillliketoappreciatetheopportunitygiventomebyhimto presentmyresearchworktotheCyprusInternationalUniversityResearchgroupand also to advice the undergraduate student on the importance of carrying out research. I would gratefully like to acknowledge the support of Asst.Prof.Dr.Devrim SERAL and Assoc.Prof.Dr.ValiBASHIRYforprovidingmewithpatientguidance,greatkindness and friendly assistance during the preparation and completion of this research work. IamparticularlyindebtedtomybrothersDr.WilliamsJosephandDr.Armstrong JosephandmybelovedsisterDr.Mrs.ComfortEkeleforfinancingmystudiesand providingmewiththegreatopportunitytogrowasastudentandasanEngineerin Cyprus International University. Finally,IwillliketoappreciatetheeffortofmyunclesProf.BissallahAhmedEkele andDr.WilsonOkpekefor theirprayersandsupportduringthecauseofmyprogram.vi TABLE OF CONTENTS ABSTRACT ................................................................iiError! Bookmark not defined. Dedication ..................................................................................................................... i ACKNOWLEDGEMENTS ...........................................................................................v TABLE OF CONTENTS ............................................................................................. vi List of Tables .............................................................................................................. xii List of Figures .......................................................................................................... xiiiii List of Acronyms ........................................................................................................xvi Chapter 1 .......................................................................................................................1 INTRODUCTION .........................................................................................................1 1.1THESIS OVERVIEW .........................................................................................2 Chapter 2 .......................................................................................................................4 EVOLUTION OF 802.11p TECHNOLOGY..................................................................4 2.1 WLAN ARCHITECTURE .......................................................................................4 2.1.1 Station .................................................................................................................5 2.1.2 Access Points (APs) ............................................................................................5 vii 2.1.3 Wireless Medium ................................................................................................5 2.1.4 Basic Service Set (BSS) ......................................................................................5 2.1.5 Extended Service Set (ESS) .................................................................................6 2.1.6 Distribution System (DS) ....................................................................................7 2.2 The IEEE 802.11 Standards ....................................................................................7 2.2.1 Frequency Hopping Spread Spectrum (FHSS) .....................................................8 2.2.2 Direct Sequence Spread Spectrum (DSSS) ..........................................................8 2.2.3 Orthogonal Frequency Division Multiplexing (OFDM) .......................................9 2.3 IEEE 802.11a .........................................................................................................9 2.4 IEEE 802.11b .........................................................................................................9 2.5 IEEE 802.11g ....................................................................................................... 10 2.6 IEEE 802.11n ......................................................................................................... 10 2.7 THE IEEE 802.11 PROTOCOL ........................................................................... 11 2.8 PHYSICAL LAYER (PHY) ................................................................................. 12 2.9 MEDIUM ACCESS CONTROL (MAC) LAYER ................................................ 12 2.10 DISCUSSION ...................................................................................................... 13 Chapter 3 ..................................................................................................................... 15 viii VEHICULAR COMMUNICATION AT A GLANCE ................................................. 15 3.1 WHY OFDM ......................................................................................................... 16 3.2 OFDM PRINCIPLE FOR VEHICLE TO VEHICLE COMMUNICATION ........... 17 3.3 PHYSICAL LAYER (PHY) OF IEEE 802.11p ...................................................... 19 3.3.1 IEEE 1609 Wireless Access in Vehicular Environment (WAVE) ........................ 20 3.3.1.1 IEEE 1609.1 ..................................................................................................... 20 3.3.1.2 IEEE 1609.2 ..................................................................................................... 21 3.3.1.3 IEEE 1609.3 ..................................................................................................... 21 3.3.1.4 IEEE 1609.4 ................................................................................................... 21 3.3.2 IEEE 802.11p Channel and Protocol .................................................................. 22 3.3.2.1 WAVE Short Message Protocol (WSMP) ......................................................... 22 3.3.2.2 Standard Internet Protocol Version 6 (IPv6) ..................................................... 23 3.3.3 WAVE Multi-Channel and Medium Access Control ........................................... 23 3.4 VEHICULAR PROPAGATION CHANNELS ....................................................... 23 3.4.1 Path loss .............................................................................................................. 24 3.4.2 Signal Fading .................................................................................................... 24 3.4.2.1 Rayleigh Fading ............................................................................................... 25 ix 3.4.2.2 Rician Fading ................................................................................................... 25 3.5 PROPAGATION ENVIRONMENTS .................................................................... 26 3.6 VEHICULAR ANTENNA ..................................................................................... 26 3.7 ANTENNAS FOR MOBILE TERMINALS ........................................................... 27 3.8 VEHICLE TO INFRASTRUCTURE CHANNELS AND SCENARIO .................. 29 3.9 DISCUSSION ........................................................................................................ 30 Chapter 4 ..................................................................................................................... 32 SIMULATION MODEL .............................................................................................. 32 4.1 TRANSMITTER SIDE .......................................................................................... 33 4.1.1 WLAN Data ........................................................................................................ 34 4.1.2 Scrambler ............................................................................................................ 35 4.1.4 Data interleaving ................................................................................................. 36 4.1.5 Modulation & Mapping ....................................................................................... 37 4.1.6 Preamble ............................................................................................................. 39 4.1.7: IFFT and FFT ..................................................................................................... 40 4.1.8 Multiplexing process of OFDM Frames............................................................... 41 4.1.9: Finite Impulse Response (RF Mod FIR) ............................................................. 42 x 4.1.10 Error Vector Magnitude (EVM)......................................................................... 42 4.2 CHANNEL MODEL ............................................................................................ 43 4.3 BASE STATION ANTENNA ................................................................................ 45 4.4 VEHICULAR ANTENNA ................................................................................... 45 4.5.1 Frequency Domain Equalizer ............................................................................ 46 4.5.2 OFDM symbol de-multiplexer ............................................................................. 47 4.5.3 Remove cyclic prefix ......................................................................................... 47 4.5.4 Demodulator Bank (De-mapping)........................................................................ 48 4.5.5 Evaluation of the Reliability Modules.................................................................. 48 4.6 DISCUSSION ........................................................................................................ 49 Chapter 5 ..................................................................................................................... 52 SIMULATED RESULTS FOR FADING CHANNEL ................................................. 52 5.1GENERATING AN OFDM CODE ..................................................................... 53 5.2 PERFORMANCE ON A TYPICAL URBAN FADING CHANNEL ..................... 55 5.3 PERFORMANCE ON FREE SPACE .................................................................... 59 5.4 PERFORMANCE OF PACKET ERROR RATE IN FREE SPACE ENVIRONMENT ........................................................................................................ 64 xi 5.5 PERFORMANCE ON A RURAL FADING CHANNEL ....................................... 66 5.6 DISCUSSION ........................................................................................................ 68 Chapter 6 ..................................................................................................................... 69 CONCLUSION............................................................................................................ 69 6.1 FUTURE WORK ................................................................................................... 70xii LIST OF TABLES Table 2.1: Summaries of the IEEE 802.11 Standards .................................................... 14 Table3.1:Physical layer implementation comparison of IEEE 802.11a and IEEE 802.11p .................................................................................................................................... 21 Table 4.1: Different modulation schemes and date rate................................................. 41 Table 4.2: Environment & Power Classes 802.11p ....................................................... 46 Table 5.1: Simulation parameters ................................................................................. 58 Table 5.2: Comparing BER against SNR for LOS and NLOS in Urban Environment ... 61 Table 5.3: Simulations parameters................................................................................ 63 Table 5.4: Comparing BER against SNR for LOS and NLOS in Free Space Environment .................................................................................................................................... 67 Table 5.5: Simulation Parameter .................................................................................. 68 xiii LIST OF FIGURES Figure 2.1: Basic services set ...................................................................................................... 9 Figure 2.2: Independent Basic services ........................................................................................ 9 Figure 2.3: Extended Service set ............................................................................................... 10 Figure 2.4: Layers of 802.11.................................................................................................... 15 Figure 3.1: WLAN block diagram for IEEE 802.11p scenario ................................................... 17 Figure 3.2: Comparing FDM and OFDM methodologies ........................................................... 19 Figure: 3.3: OFDM block diagram ............................................................................................ 20 Figure 3.4: IEEE 802.11p channel allocation. ............................................................................ 21 Figure 3.5: Wireless vehicular communication standards for WAVE family. ............................ 23 Figure 4.1: Block diagram of a simulated model. ...................................................................... 34 Figure 4.2: Transmitter block diagram model ............................................................................ 35 Figure 4.3: Scrambler functionality ........................................................................................... 37 Figure 4.4: Interleaving Process ................................................................................................ 38 Figure 4.5: Modulation mapping, (a) BPSK, (b) QPSK, (c) 16 QAM, (d) 64 QAM. .................. 40 Figure 4.6: IFFT and FFT processing ........................................................................................ 43 Figure 4.7: Radio frequency and finite impulse responses ......................................................... 44 xiv Figure 4.8: Base station ............................................................................................................. 47 Figure 4.9: IEEE 802.11p receiver block diagram ..................................................................... 48 Figure 4.10: OFDM symbol de-multiplexing process ................................................................ 49 Figure 4.11: Removal of cyclic prefix on an 802.11p symbol .................................................... 50 Figure 4.12: BER and PER schematic ....................................................................................... 51 Figure 5.1: IEEE 802.11p OFDM block diagram ...................................................................... 55 Figure 5.2: Generating an OFDM Signal ................................................................................... 56 Figure 5.3: A typical urban scenario .......................................................................................... 57 Figure5.4:ComparingtheBERoffadingchannelinatypicalurbanareaforBPSK, QPSK and 16 QAM with regards to LOS. ................................................................................. 59 Figure5.5:ComparingtheBERoffadingchannelinatypicalurbanareaforBPSK, QPSK and 16 QAM with regards to NLOS. .............................................................................. 60 Figure 5.6: A free space scenario .............................................................................................. 62 Figure 5.7: Comparing the BER of fading channel in a free space for BPSK, QPSK and 16 QAM with regards to LOS ................................................................................................... 64 Figure 5.8: Comparing the BER of fading channel in a free space for BPSK, QPSK and 16 QAM with regards to NLOS................................................................................................. 65 xv Figure5.9:ComparingthePERofBPSK,QPSKand16QAMinafreespace environment .............................................................................................................................. 66 Figure 5.10: Comparing the BER of fading channel in a rural scenario for BPSK, QPSK and 16 QAM with regards to LOS. ............................................................................................ 69 Figure 6.1: An antenna mounted on a roof top of a car .............................................................. 74 xvi List of Acronyms AP APP AWGN BER BPSK BS BSS CCK CHs CSI DS DSL ER EWM FDM FFT FIR GI ICI IFFT ISI Access Point A-Posteriori Probability Additive White Gaussian Noise Bit Error Rate Binary Phase Shift Keying Base Station Basic service set Complementary Code Keying Channels Channel State Information Delay Spread Delay Spread Length Error Ratio Emergency Warning Message Frequency Division Multiple Fast Fourier Transformation Finite-length Impulse Response Guard Interval Inter Carrier Interference Inverse Fast Fourier Transformation Inter Symbol Interference xvii ISM ITS I2V LOS LLC LLRs LS LTI LTV MAC NLOS OFDM OSI PDF PDP PDF PER PHY PLCP PMD PSDU PPDU RMS SCHs Industrial, Scientific and Medical Intelligent Transport Systems Infrastructure-to-Vehicle Line-of-Sight Logical Link Control Log-Likelihood Ratios Least Squares Linear Time Invariant Linear Time Variant Medium Access Control Non-Line-of-Sight Orthogonal Frequency Division Multiplexing Open Systems Interconnection Probability Density Function Power-Delay Profile Probability Density Functions Packet Error Rate Physical Layer Physical Layer Convergence Protocol Physical Medium Dependent PLCP Service Data Unit PLCP Protocol Data Unit Root Mean Square Service Channel xviii SNR S/P TCP QAM QPSK UDP V2IV2VWi-FiWAVEWLANWSMPZF Signal-to-Noise-Ratio Serial-to-Parallel Transmission Control Protocol Quadrature Amplitude modulation Quadrate Phase Shift Keying User Datagram Protocol Vehicle-to-Infrastructure Vehicle-to-Vehicle Wireless Fidelity Wireless Access in Vehicular Environments Wireless Local Area Network WAVE Short Messages Protocol Zero-Forcing 1 Chapter 1 INTRODUCTION Overthepastyears,therehasbeenanincreasinglyhighusagerateofmobileservices andend-devices. Thisisinversely phasing out the traditionalmeans ofnetworking and communicating.Tomeetupwiththefutureglobalizedstandardofroadtransport,a convenient way of communicating which confirm with the wireless nomenclature has to be adopted for road transportation user to enable the road transport system met up with future safety standard. In 2009 the American Federal communication commission (FCC) dedicated75MHzbandwidthof5.850-5.925GHzforVehicletoVehicle(V2V) wireless communication. The vehicular band is located right above Unlicensed National Information Infrastructure (U-NII) radio band. In 2004 a task group under IEEE and OSI committeedevelopedaninitiativethatwillenhancecommonPhysical(PHY)forV2V andVehicletoInfrastructure(V2I)communicationat5.9GHz.Afterthattheytryto initiateawaytoincludePHYandMediumAccessControl(MAC)layerwhich eventually became the IEEE 802.11p. VehicularcommunicationisapartofIntelligentTransportSystems(ITS)thatenables communicationbetweenvehicle to vehicle andalso vehicle to infrastructure. Themain motivebehindthisresearchistoimprovesafetyofhumanlivesonthehighwayby creatingalessharmfulenvironmentforthevehiclessuchthatroadtrafficwillbe minimized. To be able to build a road worthy of Vehicle-to-Vehicle (V2V) and Vehicle-2 to-Infrastructure(V2I)wirelesscommunication,weneedtocarryoutasimulationthat significantlyrelatestotherealtimeenvironment.Thesimulationmustconfirmwith IEEE802.11pstandardwhichistheofficialstandardforthevehicularenvironment. However,theV2VandV2Ialsoaffectwiderangeofapplicationsuchastraffic management with real time data in order to respond to road congestion.1.1 THESIS OVERVIEWThe thesis is composed of six chapters.Chapter 2 constitutes the general architecture of a WLAN technology and its important toIEEE802.11andalsoagenerallookat802.11familystandardsanditsessentialto wireless communication with regards to its Physical (PHY) and Medium Access Control (MAC) Layer.Chapter3discussesWLANaccordingtoIEEE802.11p,whichisthestandardfor vehicular communication. However, the standard comprises of sub-standards which are: IEEE1609.1,IEEE1609.2,IEEE1609.3andIEEE1609.4whichwillbeanalyzed includingabrieflookatpathlossandfadingwithrespecttoLineOfSight(LOS)and Non-LOS (NLOS). Chapter 4focuses on thesimulationmodel using AgilentsAdvanced Design Systems Update1(ADS2008U1)simulatorwhichcomprisesofthefollowingcomponent; WLANsSource(TheTransmitter),BaseStationAntenna,WLANChannel,Antenna for Mobile Terminal, andWLAN Receiver. The aim of this research work is to analyze the LOS and NLOS on a fading channel. 3 Chapter5explainsthesimulationresultswithtechnicalcommentsbasedonthe analysisandperformancemeasurementscarriedoutwithregardstoIEEE802.11p fading channel. Chapter 6 summarizes the conclusion and suggests possible future work. 1.2 ORIGINAL CONTRIBUTIONS ThisresearchworkpresentIEEE802.11pWirelessCommunicationaccordingtothe Vehicular standardLiteraturereviewofIEEE1609WirelessAccessinVehicular Environment. Modeling Agilents Advanced Design Systems (ADS) according to IEEE 802.11p for the vehicular environment.StudyingandmodelingOFDMtransmitteraccordingto802.11p standards.Simulatingthetransmissionfordifferentenvironmentsuchas: performanceinatypicalurbanenvironment,performanceofafading channel in a rural environment, performance on a free space environment andperformanceinanAWGNchanneltodetermineBitErrorRate (BER), against Signal to Noise Ratio (SNR). 4 Chapter 2 EVOLUTION OF 802.11p TECHNOLOGY 2.1 WLAN ARCHITECTURE WirelessLocalAreaNetwork(WLAN)technologyisoneofthebestformsof networkingthatprovidesmobilitytousersandenablesconnectiontoalreadyexisting network. The technology supports roaming in manufacturing and warehouse facilities in ordertosavecost.ItalsofocusedonPHYandMACfunctionalitywhichis predominately found on laptops, PC cards, wireless router, access points and many more makingitmoreeconomicaltodeploycomparedtoitwiredversionchangesrapidly with increasing number wireless devices such as phones, PDAs, consumer electronically device and many more TheWLANArchitectureis created to support network wheremobile station determine mostofitsdecision.HoweverthestandardIEEE802.11aconsistofdifferentnetworking componentwhich are:station, Access Point (APs), wireless medium, Basic ServiceSet(BSS),DistributionSystem(DS)andExtendedServiceSet(ESS),these componentaredividedintotwogroupwhich:stationserviceanddistributionservice [1]. 5 2.1.1 Station Stationisessentialwirelessnetworkcomponentsthatprovidewirelessconnectionand serveaccesstodistributingcomponent,thecomponentaredevicesthatconfirmto 802.11 MAC and PHY standard function like hardware and software. 2.1.2 Access Points (APs) APsenableframesfrom 802.11networks to be convertedfor it to be delivered outside the network. It also bridges the gap between wireless to wireless networks. 2.1.3 Wireless Medium Wireless medium is the channel used for transferring frame from one station to another. ThearchitectureenablesseveralPHYlayerstobedevelopedtosupportthe802.11 MAC. 2.1.4 Basic Service Set (BSS) BasicServiceSetconsistsoftwo, orset ofstationsthatcommunicatewitheachother. They made up of two types which are: Independent BSS (also referred to as IBSS), and infrastructureBSS.However,whenaBSScontainsnoaccesspoints,itimpliesthatit cantconnecttoanyotherbasicserviceset.SuchaBSSisreferredtoasindependent BSS(IBSS),IBSSstationcommunicatedirectlywithoneanother(peartopear)but unable to communicate with BSS [2].

6 Figure2.1: Basic services set [3] Figure2.2: Independent Basic services [4] 2.1.5 Extended Service Set (ESS) Thisconsistoftwoormultiple802.11BSSwhichareconnectedusingwirelessor wired LAN, figure 2.3 is an illustrationofa Extended Service Set (ESS) , theBSS cellare connectionto one anotherviadistribution system. 7 Figure 2.3: Extended Service set [5]. 2.1.6 Distribution System (DS) The wired or wireless linkage between this set of BSS is what is referred Distribution System (DS) as shown in the above Figure2.3. It has great benefits of enabling free roaming among the ESS. 2.2 The IEEE 802.11 Standards The IEEE 802.11 was originally first publishedin 1997, the standard state that WLAN canbetransmittedviaairusingopticalorradiotechnology,thestandardhasgrown sincethenwithdifferentadjustmentbeenmadetoimproveitfunctionalityintermsof networksecurity,qualityandservice.Atfirsttheoriginalstandardsdefinedratesof1 Mbpsthenlatersupport2MbpswitharadiotechnologyknownasSpreadspectrum modulation,thisspreadspectrummodulationtechniquesisoftwotypeswhichare: FrequencyHoppingSpreadSpectrum(FHSS)andDirectSequenceSpreadSpectrum (DSSS)Themajorconstrainofthestandardistheinabilitytotransmithighdatain business environment.8 IEEE802.11hasa2.4-2.4835GHzradiofrequencyrangewith11dividedpartially overlappingchannelswiththreenon-overlappingwhichare:1mbps,6mbps,and11 Mbps The 802.11 standard uses different spread spectrum wireless exchange techniques for it physicallayer.Thesetechniquesare:Frequencyhoppingspreadspectrum(FHSS), DirectSequenceSpreadSpectrum(DSSS)andOrthogonalFrequencyDivision Multiplexing (OFDM). 2.2.1 Frequency Hopping Spread Spectrum (FHSS) FHSSdividestheassignedfrequencyintochannels.Fordatatobetransmittedthe technologyusesnarrowbandcarrierwhichoperateinarandombutpredictable sequencefromonefrequencytoanotherasafunctionoftimeoverawidebandof frequencies.Itschannelhasthesamesizeofbandwidthwhichisdeterminedbythe modulationtechniqueandthedatarate.TheFHSSisoftwotypesandthey;theslow frequency hopping and the fast frequency hopping. 2.2.2 Direct Sequence Spread Spectrum (DSSS)Thisis one of themost recognizedform of the spread spectrum,it modulatedit signals by spreading the message over the band width which is typically much greater than that required for reliable communications. However, the technology PHY layer function 2.4 GHzfrequencybandwithdatatransmissionwhichrunthroughtheDSSSPMDsub layer [6]. 9 2.2.3 Orthogonal Frequency Division Multiplexing (OFDM)This is the multi-carrier modulation technique that is used in the cause of this research, thetechniquesisveryessentialintransmissionhigh-ratewirelesslocalareanetworks (WLANs). OFDM is very important to IEEE 802.11 standard as a result of it robustness against frequency selective fading and narrow interference. 2.3 IEEE 802.11a Thisis a wireless standard that specify the requirementforthe PHY anda MAClayer. The standard made available two PHYs - IEEE 802.11b of 2.4-GHz operation andIEEE 802.11aforhighdatarate operation,thedesigntargetedapplicationthatrequiredhigh datathan11Mbpsin5GHzfrequencybandusingorthogonalfrequencydivision multiplexing (OFDM) as it multi carrier.2.4 IEEE 802.11b This is the most popular member IEEE 802.11 family; one of the reasons is that 802.11b better serves at home market while 802.11a is mostly found on business networks. Thestandardutilizes2.4GHzlicensefreebandwhichincludes:microwaveovens, Bluetoothdevices,babymonitorsandcordlesstelephones.Anditalsorelatewiththe PHY by provide 11mbps transmission for the WLAN channel model. IEEE 802.11b use Direct Sequence Spread Spectrum (DSSS),as it modulation techniquewhich combinethe sent databyspread code , generatedby complementary code keying (CCK), which allows higher data speeds and is less susceptible to multipath-propagation interference. 10 IEEE 802.11b handle the case interference to it barest minimum due to fragmentation. It a MAClayerfeature that enable the breaking down of data frameinto smallin order to increase the probability of packet delivered without errorintroduce by interference . 2.5 IEEE 802.11g In2003theamendmentfor802.11gwasproposed,thestandardofferswireless transmissionoverrelativelyshortdistancesat20-54Mbpsin2.4GHzband.The 802.11gstandardusesDSSSandOFDMencodingschemewhichusesOrthogonal Frequency Division Multiplexing (OFDM) that guild against multipath component. The standards operate at the MAC layer. 2.6 IEEE 802.11n TheIEEE802.11nStandardswasbuiltuponprevious802.11,tofunctionbetterthan 802.11aand802.11g.ItoperatesattheMAClayerwithamaximumincreaseof54 mbps to 600 mbps with a more resistance to signal interference from outside Table: 2.1 is the summary of the whole standards [7] 11 Table 2.1: Summaries of the IEEE 802.11 Standards YearsStandardsSpeedFrequency Range Frequency Band Approximate indoor Range Approximate outdoor Range 1997802.11-97 1Mbps 2 Mbps 2401-2420 MHz 2.4GHz band 20 Meter100 Meter 1999802.11aUpto54 mbps 5001-5.020 MHz 5GHzband 35 Meter120 Meter 1999802.11b5.5Mbps 11Mbps 2401-2420 MHz 2.4GHz band 38 Meter140 Meter 2003802.11g54Mbps 108Mbps 2401-2420 MHz 2.4GHz band 38 Meter140 Meter 2007802.11n100 Mbps2400-2440 MHz 2.4GHz band 70 Meter250 Meter 2.7 THE IEEE 802.11 PROTOCOL The 802.11 protocol is made up of two (2) layers which are MAC andPHY layer , the PHYlaterisdividedintotwosublayerwhicharePhysicalLayerConvergence Procedure (PLCP) and Physical Medium Dependent (PMD) sub layers 12 2.8 PHYSICAL LAYER The PHY is a layer that work hand in hand with the data link layer which operate on 2.4 GHzISMband,thislayerisassociatedwith802.11gstandardandithasaspectral spreading,channelcodingandmodulationwhichenableittogenerateadatarates 1mbps, 2 mbps, 5 mbps, 6 mbps, 11 mbps, 12 mbps and 24 Mbps However,it has additional data rate of 9mbps, 18mbps, 22mbps, 33mbps, 36mbps, 48mbpsand54MbpswhichisdefinedatthePhysicalLayerConvergenceProtocol(PLCP)payload as stated in Figure 2.4 below [8]. Figure 2.4: Layers of 802.11 [6] 2.9 MEDIUM ACCESS CONTROL LAYER The MAC is very essential to 802.11 specifications. It enables transmission user data to the air and is also a key to 802.11 specifications. It provides the core framing operation andenableinteractionwithwirednetworkbackbone.Moresothestandardprovide Ethernet way ofcommunicating using carrier sensemultipleaccess (CSMA) to control accesstothetransmissionmedium.RatherthanCarrierSenseMultipleAccess/ CollisionDetection(CSMA/CD)usedbyEthernetitusesCarrierSenseMultiple 13 Access/CollisionAvoidance(CSMA/CA)todistributeschemewithnocentralized controller [9]. 2.10 DISCUSSIONIn this chapter we highlighted on the essential of wireless fidelity to the communication inindustry.Thetechnologyusesradiofrequencytotransmitdataintheair,whichis more economical compared to its wired version. However the architecture of a wireless networkisaimedtosupportnetworkwheremostofthedecisionsaredeterminedby mobile stations. The standard is made of different network component which perform different function. Theseare:AccessPoint(AP),wirelessmedium,andBasicServiceSet(BSS), Distribution System (DS) and Extended Service Set (ESS) The IEEE 802.11 standard was originally first published in 1997, the standard state that WLAN can be transmitted via air using optics or radio technology, it has four different wireless exchange techniques for it physical layer.IEEE 802.11 standard comprises of different version for instance; the 8O2.11a standard was designed for higher scalability and higher bandwidth which enables transmission of high data rate via OFDM technique. While the 802.11b operate on 2.4 GHz license free band which includes:microwave ovens, Bluetooth devices, baby monitors and cordless telephones. It also uses Direct Sequence Spread Spectrum (DSSS). 14 The 802.11g standard offers wireless transmission over relatively short distances at 20- 54Mbpsin2.4GHzbandandwhiletheoperatesat theMAClayerwithamaximum increase of 54 mbps to 600 mbps. 15 Chapter 3 VEHICULAR COMMUNICATION AT A GLANCE TheFigure3.1isablockdiagramshowingIEEE802.11pscenario.Thesescenarios illustrate a case of Line of sight, Non line of sight (NLOS) and traffic in a typical urban environment.

Figure 3.1: WLAN block diagram for IEEE 802.11p scenario [10]. InthecaseofLOS,thereisnoobstaclebetweenthetransmittingantennaandthe receiving antenna of both vehicles , these obstacles can be in form of a moving vehicle, buildingoranyobjectthat obstruct thetransmissionpathofthetwoormorevehicles. The LOS scenariois a situationwhere we have two vehiclesmoving on the same path, 16 both vehicle can identify the presence of each otherand also know when the other step on a break or tries to change direction via WLAN channel. For NLOS scenario, without visual contact between the vehicles both vehicles can detect the presence of each other.3.1 WHY OFDM Orthogonalfrequencydivisionmultiplexing(OFDM)isabroadbandmulticarrier modulationmethodthatprovidesefficiencyandsuperiorperformanceoverits predecessorslikesinglecarriersystemandfrequencydivisionmultiplexing(FDM) multicarrier.OFDMsignalcanwithstandmultipathcomponentduringtransmission using an equalizer. In single carrier systems, theinformationis representedby abit or combination ofbits calledsymbolsandalargeamountofbandwidthisusedtotransmiteventiny information.Thisisinefficientandtheinformationisalsovulnerabletosignal reflection, impulse noise and other impairments. TheFrequencyDivisionmultiplexing(FDM)isanimprovementoversinglecarrier modulation;itinvolves the use ofmultiplesub-carriers within the same single channel. This implies that the whole amount of data rate to be sent is divided between the various subcarriers.ItisadvantageoustouseFDMoversinglecarriermodulationbecause interferenceonlyaffectsoneofthefrequencysub-bands,whiletheothersare unaffected. If FDM system is able to use a set of subcarriers that are orthogonal to each other,ahigherlevelofspectralefficiencycouldhavebeenachieved.Orthogonality enablessubcarrierspectraltooverlapeachother,increasestheefficiencyofthe spectrum.Asfarastheorthogonalityismaintained,thetransmittedsignalcanbe 17 recoveredinspitetheiroverlappingspectrums.Figure3.2showstheorthogonalityand difference between FDM and OFDM methodologies [11]. Figure 3.2: Comparing FDM and OFDM methodologies. [8] 3.2 OFDM PRINCIPLE FOR VEHICLE TO VEHICLE COMMUNICATION OFDM is useful in the wireless access in vehicular environment (WAVE) system; it is a goodandefficientmultiplexerthatisusedtoachievehighdataspeedsovertime, frequency andselectivefading channel. Thebasic principleis to break downhigh data rate stream into a number of low rate streams which are then transmitted simultaneously overanumberofsubcarrierswhichhelpinreducestheamountofdispersionintime caused by multipath delay spread. The use of guard time solves the issue of inter-symbol interference in every symbol and inter carrier interference. Figure: 3.3 illustrates OFDM block diagram with the transmission and the receiving processes [12]. 18 Figure 3.3: OFDM block diagram [13]. In the figure 3.3 above, the serial to parallel converter enable the symbol that is in serial formtobeconvertedtoparallelform.However,datainparallelformindividually occupyonlysmallpart ofavailablebandwidth.Thedataisthenmappedandmodulate using a particularmodulating technique. InverseFast FourierTransform (IFFT)is used totransmitdatafromfrequencydomaintotimedomain.Afterthat,cyclicprefixis added for the signal to be transmitted across fading channel.Atthereceiver,thecyclicprefixisremovedandthesignalisconvertedbacktoserial formusingtheserialtoparallelconverter.ThesignalisthenpassedthroughtheFast Fourier Transform (FFT) in order to be transformed back to frequency domainDemodulatorconvertsdatabacktoitsoriginalformwhichisfinallyconvertedtoits original serial form. The IEEE 802.11p is the standard for vehicle to vehicle (V2V) communication has a lot ofsimilaritieswiththeIEEE802.11astandard.Themajordifferencebetweenboth standards is the uses of half clocked mode. The half clocked mode affects the following; bandwidth, subcarrier spacing, symbol length and frequency as stated in Table 3.1. The IEEE 802.11p OFDM has 64 sub-carriers and 52 out of the 64 are used.48 sub-carriers represent the actual data while 4 represent the pilot carriers [14].19 Table3.1: PHY layer implementation comparison of IEEE 802.11a and IEEE 802.11p. ParameterIEEE 802.11a IEEE 802.11p Half Clocked Mode Differences Bit rate (Mbit /s)6, 9, 12, 18, 24, 36, 48, 54 3, 4.5, 6, 9, 12, 18, 24, 27 Half Modulation modeBPSK, QPSK, 16QAM, 64QAM BPSK, QPSK, 16QAM, 64QAM No change Code rate1/2, 2/3, 3/41/2, 2/3, 3/4No change Number of subcarriers 5252No Change Symbol duration4 s8 sDouble Guard time0.8 s1.6 sDouble FFT period3.2 s6.4 sDouble Preamble duration16 s32 sDouble Subcarrier spacing0.3125 MHz0.15625 MHzHalf 3.3 PHYSICAL LAYER (PHY) OF IEEE 802.11p TheIEEE802.11pchannel(CHs)bandisdividedintoseven;10MHzbandwidth channels (CHs 172 to 184), of which CHs 178 located at the middle is referred to as the controlchannel(CCH)anditisrestrictedtosafetyrelateddatatransmission.Thetwo channels at both ends of the spectrumband are reservedfor special use. The remaining channelsareServiceChannels(SCHs)andtheyareavailableforsafety,non-safety 20 relateddatatransmissionthatincludesgeneralInternetservice.Figure3.4depictsthe channel allocation for IEEE 802.11p [15]. Figure 3.4: IEEE 802.11p channel allocation [11]. 3.3.1 IEEE 1609 Wireless Access in Vehicular Environment (WAVE) WAVEisstandardthatdefineswirelessaccessinavehicularenvironment.This transmissionexistsbetweenV2V,vehicletoroadside,andV2Icommunication.The WLANcommunicationsystemguaranteesafetytothoseonboardbyintegratesthe information of engine, gearing, brake and roadside unit. The main WAVE standard comprises of four sub-standards, which are listed below -IEEE 1609.1 -IEEE 1609.2 -IEEE 1609.3 -IEEE 1609.4 3.3.1.1 IEEE 1609.1This sub-standard enables the resource manager to access to the WAVE environment. It createsapathforremotemanagertoestablishcontactwithresourcecommandonan onboard unit which is the vehicle. 21 3.3.1.2 IEEE 1609.2IEEE1609.2presentsseveralsecurewaysofsendingandreceivingmessageina WAVEsystem.ThisincludestheprotectionofWAVEmanagementmessagesand applicationmessages.Italsokeepsthemessagessecurefromattackssuchas eavesdropping,spoofing,alteration,replay,andlinkableinformationtounauthorized parties. 3.3.1.3 IEEE 1609.3ThisisthenetworkserviceslayerofaWAVEsystemandusuallylocatedonthe network and transport layers of the OSImodel. It supports a high data rate, with alow latency, communication between devices. The WAVE system supports both IP and non-IPapplications.FortheIPapplications,itsupportsIPv6trafficsandsupportsWAVE short message services for the non-IP applications. The WAVE Short Message Protocol (WSMP)ensuresproperaddressingandroutingservicesystemswhileenhancinghigh priority and time sensitive communication to vehicles. Logical line control (LLC), User DatagramProtocol(UDP)/TransmissionControlProtocol(TCP)andWAVEshort message protocol all have a particular function according the WAVE standard.3.3.1.4 IEEE 1609.4 The 1609.4 standard deals with the WAVE multichannel operations. It helps in defining thefunctionsofMACsubLayerManagementEntity(MLME)andWAVEMACwith channelcoordination.Figure3.5showsthefamilystandardofWAVE,comprisedof different sub-standard and their respective layers as earlier discoursed [16].22

Figure 3.5: Wireless vehicular communication standards for WAVE family. 3.3.2 IEEE 802.11p Channel and Protocol WAVE system is made up of two channels; the control channel (CCH) and the service channel(SCH).WAVEhasoneCCHandmultipleSCHs.Thecontrolchannelisused for system controlmessages andhigh-priority applications while theservice channelis usedforgeneralpurposedatatransferapplications.Channelstimingaredividedinto synchronization timingintervalmade up of control channel (CCH)intervaland service channel (SCH) interval 3.3.2.1 WAVE Short Message Protocol (WSMP) WSMPisusedtoincreasemessagetransmissionandservicesonWAVEsystem. WAVEshortmessagescanbesentbothoncontrolchannelsandservicechannels.It allowsphysicallayerparametersliketransmitterpowertobecontrolledbythis application. 23 3.3.2.2 Standard Internet Protocol Version 6 (IPv6) InthiscasetransmissionbasedonthestandardIPv6canonlybeusedontheservice channels(SCH).IPv6protocolislocatedonthenetworklayeroftheopensystem interconnection (OSI), its main function is to enables data communications (sending and receiving of packet) over a packet switched network. 3.3.3 WAVE Multi-Channel and Medium Access ControlMultichannelpropertyenhancesanefficientwaytocontroltheoperationofupper layers.WAVEdevices(on-boardunits)createanenvironmentwhichsupportsasingle controlchannel(CCH)andmultipleservicechannels(SCHs).Thecontrolchannelis usedfortransmittingofWAVEshortmessages.Theservicechannelsareutilizedfor communicationandtransmissionbetweenapplications.WAVEusesthePHY specificationinIEEE802.11aandrevisestoIEEE802.11p.IEEE1609.4standard coordinates and manages the channel [17]. 3.4 VEHICULAR PROPAGATION CHANNELS There is a great difference between V2V and V2I when it comes to the channel systems invehicularenvironment.V2Vhasnoaccesspointorbasestationsunlikethecellular environment that have a fixed base station; it has a mobile transmitter and receiver with manyscattersalongthecommunicationpath.Thenumberofscatererdependsonthe environmentandmorescattersareassociatedwithurbanandruralenvironment compared to an open space environment [18]. 24 TheV2Iisrelatedtocellularsystemsofcommunication.Itworkslikeabasestation tryingtocommunicatewithmultiplecarsusingmicrocell.Theinformationabouta particularvehicle canbe transferredfrom one antennabasestation to another,justlike hand over in cellular environments [19]. 3.4.1 Path loss Thisisreferredasagraduallossinpowerdensityofasignalasitpropagatesthrough space which is the ratio of a transmitted power to that of the receiving power. Equation below shows the calculation for path loss and it is usually measured in decibels [20]. Y X d d n P d P + + =o) / ( log 10 ) (0 10 0 Eq 3.1 Inthisequation,nispathlossexponentthatisusedtoindicatetherateofincreaseof pathlosswithrespecttodistance.d=Representdistance, OP =poweratreference distance Od and while oX =large scale fading, Y= Small scale fading [21]. 3.4.2 Signal Fading Therearetwomaintypesofsignalfading,largescalefadingandsmallscalefading. SmallscalefadinghastodowithDopplerspreadanddependencyonmovementof vehicular scatters. While the large scale fading is determine by the environment, such as the building infrastructures, moving cars etc.25 3.4.2.1 Rayleigh FadingRayleighfadingisafadingtypethatoccurswhenthesignalencounterscattererin betweenthetransmitterandreceiverwhichcreatesanonLineofSight(NLOS) communication.Thisfadingisusuallynoticedwhenmultipathcomponentexistalong transmissionandreceivingpath.TheRayleighdistributionshaveaProbabilityDensity Functions (PDF) given by: =||.|

\|2222exp0) (o or rr p) 0 () 0 ( > r A) 0 ( < r Eq 3.3 IntheaboveEq3.3,Arepresenttheamplitudeofthedominantcomponent, o represent the root mean squarevoltagea received signal , the time average power of a received signal is denoted by 2o , 0Irepresent Bessel function and zero function [22]. 26 3.5 PROPAGATION ENVIRONMENTS Vehicularpropagationchannelisassociatedwiththeenvironmentwherethe transmissionoccurs.Forthisreason,measurementsarecompletedfordifferent propagatingenvironment,suchasV2Vinanurbanenvironment,V2Vinafreespace environment, V2Vina rural environment etc. Urban Streets are usually wide with one or multiple lanes in each direction. Region also has significant effect on urban street. For instance,AmericanstreetsarewiderandstraightwhilethoseofEuropeancitiesare narrow and winding.Theruralenvironmentstreetusuallyhavesinglelaneineachdirectionwithfeworno buildingalongthestreet.Thesetypesofenvironmentsareusuallyassociatedwith vegetation and hill that creates a lot of multipath component with a light traffic.3.6 VEHICULAR ANTENNA Vehicletovehicle(V2V)andVehicletoInfrastructure(V2I)wirelesscommunication bothsharethesameantenna.Thisisbecausebothantennasareslightlydifferentfrom each other. Antennas,whicharedesignedforvehicles,havecertainfeatures:light,miniaturized, mechanicalstrengthandeasyintegrationtovehicles.Basedontheindustryanalysis, present and further systems utilizing the geosynchronoussatellites, the L-band (1.6/1.5 GHz)isusedincommunicationlinksbetweenthesatelliteandmobiles.TheL-band communicationsystemsrequiresaboutonly8%ofitsfrequencybandwidthtocover transmitting and receiving channels. The planar type antenna is becoming more rampant 27 invehicles;howeverthisantennaisfundamentallynarrowband.Thereforevarious techniques must be utilized to widen the bandwidth. The required gain for vehicular antenna is realized using the link budget analysis, which is generated by taking into account the required channel quality (expressed as the C/No. whichisdefinedasthecarrier-to-noisepowerdensityratio)andsatellitecapability. Sinceantennaisrequiredtocover00to900inelevationand00to3600inazimuth direction, the designers would require an antenna with Omni-directional properties[23]. 3.7 ANTENNAS FOR MOBILE TERMINALSThemobileantennaisthefinalpartofradioterminal.Logically,mobileantennasare expected to be omni-directional since the signals can come from any direction at various randompointsintime,duetothespontaneity.Fastandrelentlessadjustmentsneedto properlyachieve omnidirectional coverage. It is obvious that the portable terminals are unlikelytousemulti-elementadaptivearraybecauseofthesizerestrictionimposed. Thus,smallinsize,havingreasonablegainandpreferablyomnidirectionalradiating pattern are the desirable characteristics of mobile antennas. Thewell-knownwhipcarantennaisquarterwaveunitygainantennawhichdisplays broad radiation patterns.In the case of vehicle antennas, there are various additionalfactors that tend to affect its performance,suchastheterminalmobility,orientationwithrespectto thebasestation electricfieldpolarization,proximitytobodyandchangesinthesurrounding environment. 28 The car antenna can be placed on various parts of the car depending on the perception in termsofdesignandefficiency.Generally,theantennarelatetothepositionofthe antenna on a certain part of a vehicle, e.g. roof, wind-screen, or window.Theantennastandingwaveratio(SWR)orrelatedreflectioncoefficientisessentialin determiningtransmitterpoweroutput.IntheIdealcase,theantennaSWRshouldbe unity, however this is rarely the case and a range between 1.5-2.0 is acceptable, anything higher,causesantennainefficiencies.Thesamevariablestendtoaffectthepower handling or voltage rating of the antenna. The size of the antenna ground plane to a large extentdeterminestheantennasradiationpattern.However,invehicularantennathe ground plane has been recommended to be equal to one hold wavelength at 30 MHz and onewavelengthatfrequenciesbetween100and1250MHz.Choosinganantennatype depends on the environment where mobile is most likely to operate. The terrain changes fromurbantorural.Inurbanareaswheresignalsarrivefromdifferentdirectionswith similarstrengths,unitygainantennaisprobablythebestchoice.Insub-urbanareas wherecellseparationislargerandthesignalisexpectedfromlowerangles,3dB collinearmaybe a better choicehighergain antennas are good in rural areasbecauseit helps increase the coverage area. Basedonrecentresearch,resultsshowthatforextremelyhighfrequencies(>20GHz), adaptive antenna array with fast beam steering may be the answer to large variability in the received signal to interference levels. The adaptive algorithm in general is unable to track the swift changes in the direction of the signal arrival. The major limitation of the adaptive antenna is the large number of antenna elements forming an array. It is usually 29 difficulttoconfinethemintosmallspaces.Thecoveragerequirementsdependsonthe typeofapplication;forvehicletovehiclecommunicationscoverageintheazimuth planesufficeswhereasawideanglecoveragebothinelevationandinazimuthare required for system that use higher base station antenna[24]. 3.8VEHICLETOINFRASTRUCTURECHANNELSAND SCENARIO V2I is classified into two different types; the conventional cellular infrastructure and the dedicatedinfrastructureofIntelligentTransportSystem(ITS)forIEEE802.11p standard. In either case, the communication occurs between a devicein avehicle and a highinfrastructurepoint,microcellscancoverurban/ruralareasbyconventional microcellularbasestation(BS),orWAVEinfrastructure.Thepropagation characteristicsassociatedwiththesetwocasesarequitesimilar.BSsorAccessPoints (APs)areplacedlowtoaheightofatrafficlight,mostlyinaT-junctioninorderto coverthestreetandallsurroundingbuildings.Thecoverageareasincludetunnelsand high ways. Intheurbanenvironmentmacrocellsisusuallydominatedbythreepropagation phenomenatheseincludescatteringaroundtheMobileStation(MS),rooftop propagationbetweentheMSsurroundingsandBaseStation;waveguidinginstreet canyons; andreflection by remote objects. Themacrocellsintheruralenvironmentahavefewpropagatingobstacles,withfew scattering around mobile station area [25,26]. 30 3.9 DISCUSSION This chapter talks about WLAN channel according to the IEEE 802.11p standard which comprises of different mode signal transmission LOS and NLOS. However, Orthogonal FrequencyDivisionMultiplexingisusedbyVehicletoVehiclecommunicationto guildagainstmultipathcomponent.Itincreasetherateofdatabeentransmittedasa resultof52subcarriersofdifferentfrequency.TheIEEE802.11aisrelatedtoIEEE 802.11p, the major difference between both standards is the uses of half clocked mode. Thehalfclockedmodeaffectsthefollowing;bandwidth,subcarrierspacing,symbol lengthandfrequency.Thestandardhasabandwidthof5.850-5.925GHzforV2V wireless communication In other for data to be transmitted efficiently and more secured, the IEEE 1609 Wireless AccessinVehicularEnvironmentwascreated,thisstandardcomprisesofsubstandard (1609.1,1609.2,1609.3and1609.4).IEEE1609.1enablescommunicationbetween remotemanagersandonboardunit,theIEEE1609.2createseveralsecurewaysof sending and receivingmessagein aWAVE system, thenetwork and servicelayer uses IEEE1609.3itsupportsbothIPandnon-IPapplications.FortheIPapplications,it supportsIPv6andsupportsWAVEshortmessageprotocol.WhiletheIEEE1609.4 standard handles theWAVEmultichannel operations. It helpsin defining thefunctions ofMACsubLayerManagementEntityandWAVEMACwithchannelcoordination. For vehicles to communicate there must be a propagating channel, this include V2V and V2I. 31 V2V hasno access point or base stations unlikeVehicle to Infrastructure are related to cellular systems of communication, this channels uses antenna that confirmed with the vehicular standard. 32 Chapter 4 SIMULATION MODEL The block diagram of an Agilents Advanced Design Systems (ADS) simulated model is showintheFigure4.1below.Itillustratesthesimulationmodelfortheproposed scenario. Figure 4.1: Block diagram of a simulated mode [27]. 802.11psignalisgeneratedatthewirelesslocalareanetwork(WLAN)IEEE802.11p source.Then,thesignalisconvertedfromfrequencydomaintotimedomainand connectedtobasestationsinputport.Theoutputportofthebasestationisusedfor receivingthesignalfromthemobileterminals.Theantennalocatedat thebasestation hasOmni-directionalcharacteristicsandpriorityforreceivingisgiventoemergency related cases. TheWLANChannelsimulatesdifferentenvironmentswithpropertiesofmultipath component,LineOfSightandNoneLineOfSight.Forinstance,theenvironmentis WLAN IEEE802.11p Source Antenna BaseStation WLAN Channel Antenna for Mobile Terminal WLAN Measurements BER, PER etc Add Noise Density WLAN IEEE 802.11p Receiver 33 quite critical for a car to communicate with other cars or base station. The on board unit forthemobileterminalhasareceiverthatconvertsasignalfromtimedomainto frequency domain to enhance communication. 4.1 TRANSMITTER SIDE TheWLANsignalsourceisthepointwhereIEEE802.11pOFDMRFsignalis generated.Inordertoactivatethesignalsource,theRFcarrierfrequency(Cf )and powerhavetobeadjustedaccordingtoIEEE802.11pstandards.Multipathcomponent can be introduced by setting the resistance, temperature, noise etc. Figure 4.2 illustrates the block diagram for the transmitter model [28]

Figure 4.2: Transmitter block diagram model [29]. ThetransmitterbeginswiththeWLANData.Itisusedtogeneratephysicallayer convergence protocol (PLCP). Protocol Data Unit (PPDU) is aframe thatiscreated by PLCPbyusingtheMACsub-layerforthetransmission.ThePPDUismadeupofthe synchronization, service field, PSDU, pad bit, tail bit, signal and etc. This data frame is WLAN Data WLAN Scrambler IFFTOFDM SYMWLAN Mapping WLAN Interleaver WLAN Tail Punch-Coder Preamble Logic Gate XOR 34 sent to the XOR gate; only one frame goes through the XOR gate either the PSDU frame or the matrix class frame.Afterthat,itmovetotheWLANtailwheresixnonscramblezeroisaddedtothe scrambled PPDU, the essence of the zeros is to increase the length of the signal without havingeffectonthesignalitself.Then,WLANpuncturecoder(PuncCoder)isused wheredifferentcoderateisbeengeneratedfromthemothercoderate()of convolutional encoder. After that, the signal is interleaved in order to combat the effect of burst error in code word. It would be quite difficult to decode if there are many errors on the code. Mappingprocessofdatahastodowithdifferentmodulationtechniques,each modulationtechniquehavedifferentdata rate. IEEE802.11puse orthogonalfrequency divisionmultiplexing (OFDM) with 64sub carriers. 52 sub-carriers are utilized and 12 are reserved. 4 sub-carriers represent the pilot tones while 48 are the actual data. Finally, inversefastFouriertransform(IFFT)convertsthesymbolsfromfrequencydomainto time domain. 4.1.1 WLAN Data ThePPDUisgeneratedattheWLANData;theframeformatconsistsof16bits.The first 6 bits (0 to 6) is set to zero, these bits are used for synchronizing the descrambler at the receiver. The remaining bits (7 to 15) reserved for future use. The PPDU tail bit field comprisesof6bitsof0,whichisusedtoreturntheconvolutionalencoderto thezero state. The PLCP tail bit field is generated by replacing 6 scrambled 0 bits following the 35 end of message with 6 unscrambled 0 bits. Note that the number of bits in the data field is a multiple of the number of coded bits in an OFDM symbol. 4.1.2 Scrambler Thepurposeofscrambleristosecuredataduringtransmissionandalsodatasare randomizetoavoidlongstringofzeros(0)and ones(1). Thescramblerperformsdual function,scramblingtransmitteddataanddescramblingthetransmitteddataatthe receiverend.Thismodelhasalengthof127framessynchronousscramblerwith generator polynomial 1 ) (4 7+ + = x x x S . The scrambler generates 127 bits repeatedly for theinitial1011101.Theblockdiagramofascramblerthatshowsthefunctionalityis depicted in Figure 4.3. Figure 4.3: Scrambler functionality. 4.1.3 Encoder Convolutional encoder is used for coding of the transmitted bits. The codes are made of threemainparameters;numberofinputbits(k),numberofoutputbits(n)andthe numberofmemoryregister.Thescrambleddataistransferredtotheconvolutional encoderbyusinglinearshiftregisters.Someredundancybitstreamisintroducedina controlled way. Its main aim is to correct errors in coding which enables the receiver to 36 combattheimpairmentsofthechanneland,hence,achievereliablecommunication. Thisis done through puncturing andit has a standard rate of for coding at each time index.Theencodertakessingleinformationandproducesadoublecodebitsatthe output.Convolutioncodecanbetransformedintoablockbyusingtwodifferent standardmodifications,knownastruncationandtermination.Withaterminated convolutioncode,theinputisgivenbyNinformationbitsfollowedbymzerosbits, where m is encoders memory order. 4.1.4 Data interleaving Indigitaltransmission,datainterleavingprocessisusedtoreducetheeffectofburst errors.Whenacodewordcontainstoomanyerrors,decodingsuchacodewordat the receiver is always very difficult. To combat such an effect, the bits in one code word are interleavedbeforebeingtransmitted.Wheninterleavingoccurstheplaceofbitswill change,itrearrangestheinputdatasuchthatconsecutivedataaredividedamong differentblocks;thisenablesthecodewordtocopewithchannelnoiseandfading. Figure 4.4 shows the effect of interleaver at a transmitter. Figure 4.4: Interleaving Process [30]. 37 One of the major classes of interleaving is the block interleaving process. Encoded data can easilybeinterleaved withit.In this case, the block sizehas to correspond with the number bits in a single OFDM symbol.Thematrixinputvectorcanbeinterleavedaccordingto thegivennumberofrowsand columns. In this system, the number of rows and columns is given by: Interleaver Rows = 16. The Advance Design System (ADS) interleaver is defined by a two permutations. Thefirstpermutationenablestheadjacentcodedbitstobemappedintononadjacent subcarrierswhilethesecondpermutationenablesadjacentcodedbitstobemapped alternatelyinto less significant bits of the constellation [31]. This preventslong runs of low reliability bits. 4.1.5 Modulation & Mapping Modulationcandefinedastheprocessofvaryingoneormorepropertiesofahigh-frequency periodic waveform, known as the carrier signal, with a modulating signal that contains information to be transmitted.In the course of research, different modulation techniques are considered and simulated accordingly,suchasbinaryphaseshiftkeying(BPSK),quadraturephaseshiftkeying (QPSK), and quadrature amplitude modulation (QAM), etc.ForBPSKmodulation,thecarrierhastwodifferentphases(0and180degrees).It comprisesofonedimensionwhichrepresentabinaryoneorzero.Themodulation techniqueisassociatedwithdifferentdatarates.Forexample,rate6or9Mbps represents BPSK, is mapped with one input bit to produce complex output data.When it comes to QPSK, the carrier can assume one offour phase states, which are 0, 90, 180, 38 and270degrees.Itrepresentsthesymbols00,01,11,and10.Intheliterature,QPSK modulator is considered as two BPSK modulators that are out of phase by 90 degree. Ithasarateof12or18Mbpswhenitcomestomapping,itconsistsoftwodimensionswithaninputdatabitsof2-bitandmappedtocomplexdataaftermapping,theoutput signalisnormalizedbynormalizationfactora. On the other hand, 16 QAMhasa data rate of 24, 27 Mbps, with an input bits of 4-bit groups and mapped to complex data. Symbolsaremappedtoasubcarrieramplitudeandphaseonacomplexplane.Signal constellationis the geometricalconstellation of the symbolsin the complex plane. The purposeistoreducethemeansignalpowerwithoutreducingtheminimumdistance between symbols and to ensure that potential symbol errors result in as few bit errors as possible. Different modulation constellations are shown in Figure 4.5. (a) (b) (c)(d) Figure 4.5: Modulation mapping, (a) BPSK, (b) QPSK, (c) 16 QAM, (d) 64 QAM. 39 Table4.1illustratesdifferentmodulationschemesandtheirassociateddataandcode rates.Thisimpliesthateverydataratehasadifferentmodulationtechniqueand modulation parameters dependent on the data rate used Table4.1: Different modulation schemes and date rate DataRate (Mbps) ModulationCode Rate (R) 6BPSK1/2 9BPSK3/4 12QPSK1/2 18QPSK3/4 2416-QAM1/2 2716-QAM9/16 4.1.6 Preamble PhysicalLayerConvergenceProtocolServiceDataUnit(PSDU)isusedwithaPLCP headerinordertoformaframewhilethedateistransmitted.Theframecontains transmissionrateinformationandthenumberofoctetsinthePSDU.IEEE802.11p 40 PLCPfieldiscomposedoffourparts:shortpreamble,longpreamble,signalanddata fields. The short preamblefield consists of 10 repetitions of a short preamble with 8s time duration.Thelongpreamblefieldconsistsof2repetitionsofalongpreamble(8stime duration).PLCPPreambleisthecombinationofthetwopreambles(longandshort preamble) with constant time duration (16 s) for all the source parameter settings. The signal field for 802.11p comprise of data rate, payload data, and length). Data field containsthepayloaddata.Channelcoding,interleaving,mappingandIFFTprocesses are also included in Signal and Data parts generation.4.1.7: IFFT and FFT AnOFDMsystemprocessesthesourcesymbolsatthetransmittersectioninthe frequency-domain.ThesesymbolsareusedastheinputstoanInverseFastFourier Transform(IFFT)blocktobringthesignalintotimedomain,theparalleltoserial converterisusedtotransmittimedomainsamplesofonesymbol.WhiletheFast Fouriertransform(FFT)convertsthesignalbacktofrequencydomainatthereceiver side.OFDMsystemisacombinationofFFTandIFFT,withtheIFFTallocating differentsubcarrierfortransmittedbits.Orthogonalityenablessubcarrierspectralto overlapeachother,therebyincreasingtheefficiencyofthespectrum.Aslongasthe orthogonalityismaintained,thetransmittedsignalcanberecoveredatthereceiver. Figure 4.6 is a block diagram of IFFT and FFT. 41 Figure 4.6: IFFT and FFT processing [32]. 4.1.8 Multiplexing process of OFDM FramesIEEE 802.11p standard specifies an Orthogonal Frequency Division MultiplexingPHY that employs 64 sub-carriers which 52 of the 64 are utilized. 48 contains the actual data andtheremaining4subcarriersisreferredtoasthepilot,thepilotsubcarrierstransmitafixedpattern,usedintracingfrequencyoffsetandphasenoise.The4pilot and48sub-carriersprovidetransmissionofdataatrates3,4.5,6,9,12,18,24or27 Mbps. The system uses pilot sub-carriers as a reference to disregard frequency or phase shifts of the signal during transmission and while the 12 zero-subcarrier in the complex value represent the different modulation technique constellation point which are BPSK, QPSK, 16QAM or 64QAM. In order for an OFDM complex data to be transmitted through a modulating channel, it hastobesplitinto48differentcomplexnumbersinlinewiththedatasubcarrier.The logical subcarrier numbers are then mapped into frequency offset index -26 to 26, while 42 skipping subcarriers -21, -7, 0, 7 and 21. After that, the assembler block enables the pilot subcarriers to be inserted into the positions of -21, -7, 7 and 21, which includes the zero DCsubcarrierbetweenthedatasubcarriersbymeansofverticalconcatenation. Subcarrier -32 to -27 and 28 to 32 are set to 0 to serve as guard bands which are used for reducing out of band power. 4.1.9: Finite Impulse Response (RF Mod FIR) Figure4.8depictstheFiniteImpulseResponse(FIR)filterwhichisatypeofasignal processing filter whose impulse response is of finite duration. Figure 4.7: Radio frequency and finite impulse responses. The RF Mod FIR is a hierarchical model that have different components which include I and Q signal. The input is made up of baseband I and Q signals with only 1 sample per symbol.Theinputsignalsareupsampled,filteredandthenusedtomodulatethein-phaseandquadraturephasecarriersofaQAMmodulator.Foreachinputsample consumed, sample per symbol output samples are produced.4.1.10 Error Vector Magnitude (EVM) EVM,alsocalledasconstellationerror,isawayofdeterminingtheperformanceand function of a digital radio receiver or transmitter. When a signalis sent from a reliable transmitterorreceiver,thesignalhasitsidealconstellationpointattherightlocation 43 before being transmitted. In order to demodulate the incoming data, one must accurately determine the exact magnitude and phase of the received signal for each clock transition. However, transmitted signals are usually affected by various multipathcomponents e.g. phase noise etc. This has a crucial effect on the constellation point causing it to deviate. EVM is a measure of how far the points shift from the ideal locations [33,34]. 4.2 CHANNEL MODEL Vehicularchannelmodelrepresentanalysisoftheradiochannelinputandoutputof vehicularpropagationbysimulation,theseincludepathloss,delayspread,Doppler spreadandfadingstatistic.InthisresearchRay-basedmodelisusedasthechannel model.Ray-basedmodelisawayofmappingdifferentpropagatingenvironmenton software;itincludesobstacles,environmentandscattererbehaviorthataffectwave propagation [35]TheAdvanceDesignSystemsimulatorwithregardstovehicletovehicle,ithasfour basicenvironmentalmodelsofdifferentpowerclass.ModelAdescribestypicalurban environmentsandmodelBforTypicalRuralSuburbanEnvironments.Inaddition, modelCreflectsruralareaenvironmentsandmodelDdescribesFreeSpaces.These modelshavesomecharacteristics,suchasmultipathcomponent,LineofSightAnd Non Line of Sight, etc.Theurbanenvironmentisassociatedwithhighpopulationdensity,scattered,lineof sightandnonlineofsightproperties.Suburbanenvironmentisaresidentialareaofa city associated withLine of Sight and NonLineof Sight. Rural environment describes 44 not an urbanize area and associated with vegetation, large and small cities with and Line of Sight. TheV2VEnvironmentisassociatedwithdifferentmodelclassandthismodelhasits own power class as stated in Table 4.2. For instance, ModelA corresponds to a typical office environment. Model B corresponds to a typical large Open-Space Environment with NLOS conditions or an office environment with a large delay spread. Model C and E correspond to typical largeopen-spaceindoorandoutdoorenvironmentsrespectively,withalargedelay spread.ModelDexpressesLOSconditionsinalargeOpen-Spaceindoororoutdoor environment. Table 4.2: Environment & Power Classes 802.11p V2V EnvironmentsModel TypePower Class Typical urban environmentA1-10 Typicalruralsuburban environment B10-20 Rural areaC20-28.8 Free spaceD28.8 The multipath delay profile determines the frequency selective nature of the channel and the delay profile is specified by the ADS designer [36,37]. 45 4.3 BASE STATION ANTENNA Inthisresearch,abase(orfixed)stationantennasofEIA/TIA-329-B,specificationis used. The base station uses a half dipole antenna that is linearly polarized. It is isotropic in nature and is made up of multiple input pin to receive and transmit signal to multiple cars along the channels. However, the frequency of these cars has to confirm with IEEE 802.11pstandardwhichis5.85-5.925GHz.Figure4.8illustratesbasestationdiagram from ADS simulator.

Figure 4.8: Base station [38] 4.4 VEHICULAR ANTENNAA mobile antenna of "EIA/TIA-329-B-1 specification is used in this vehicular research. This antenna is omnidirectional in nature, which mean it receive signal in all directions and transmit in all directions. This antenna has a multi-input pin to receive and transmit multiplechannelssimultaneously.ThegainunitismeasuredindBwithanisotropic source and the antenna is a half wave dipole antenna. [39] 4.5 RECEIVER SIDEThe receiver block diagram of IEEE 802.11p is shown in the Figure 4.9. Figure 4.9: IEEE 802.11p receiver block diagram.

FFT OFDM SYM WLAN PSDU WLAN Demappiing

OFDM Equalizer WLAN Deinterleaver WLAN Descrambler 46 Whenthesignalarrivesatthetransmitter, theFastFourierTransforms(FFT)converts thesignalfromtimedomaintofrequencydomainsynchronizationaccordingtothe IEEE 802.11p standard. This enables the signal to be filtered and un-sampled for it to be convertedfromrealandimaginaryformtoacomplexsignal.Afterthat,thecomplex signal is equalized in order to split the signal into data and training symbols. The OFDM symbolde-multiplexincomingsymbolintopilotsub-carrieranddatasubcarrierwhich willhavetobede-interleaved,whichisaprocessofrearrangingthebitsbacktoits original form. PuncturingDecoderisusedfordecodingcoderatetoitsoriginalform1/2sinceeach modulationtechniquehasdifferentcoderate.Finally,descrambleprocessisusedto achieve the signal as its original form. 4.5.1 Frequency Domain EqualizerFrequencydomainequalizerisusedtoeliminateorpreventtheeffectofmultipath componentonthereceivedsignal.Whenreceiverrealizesadistortion,anequalizer combats the distortion introduced by the channel. The OFDM channel equalization algorithm is: ) () () (i hi xi = o Eq4.1 Whereh(i)isthechannelestimation,x(i)isthereceivedsignalinactivecarriers and ) (i o istheequalizedoutputsignal.Receiverusuallyknowsthechannelcoefficient ofthesystemwhichmakesitpossibleformultipathcomponenttobereducedtothe 47 barestminimumvalues.Equalizerintroducesacoefficientwhichisinversely proportionaltothechannelcoefficient.Thechannelisestimatedbydividingthe received training symbol. The equalizer at the receiver is a zero forcing equalizer with a frequency input block of training symbol and data symbol [40] 4.5.2 OFDM symbol de-multiplexer ThissectionenablestheOFDMsymboltobede-multiplexed(e.g.BPSK,QPSK,and 16-QAMmodulation)into data and pilot forms.The complex signalis converted to 48 data and 4 pilots as show in Figure 4.10.

Figure 4.10: OFDM symbol de-multiplexing process. 4.5.3 Remove cyclic prefix The essence of cyclic prefix is to prevent inter symbol interference (ISI) and inter carrier interference (ICI) during transmission; the cyclic prefixis removed at the receiver ends togettheoriginalsignalback.Figure4.11depictstheplaceofthecyclicprefixona symbol [41]. 48 Figure 4.11: Removal of cyclic prefix on an 802.11p symbol [36]. 4.5.4 Demodulator Bank (De-mapping) Mappedsignal,aredemappedatthedemodulationbank.Signalsaremappedwith respecttodifferentdatarates.Forexample,whenaRateissetto6or9Mbps,BPSK signalisdemappedaccordingtoBPSKmappingconstellationstandard.Thesame methodology applies to QPSK which has a Rate of 12 or 18 Mbps, and 16-QAM with a Rate is set to 24, 27, or 36 Mbps. After that, the equalized output is converted into a symbol. Thissymbolis expected be the same as the transmitted symbol. When no error occurs during demapping, it signifies thatthetransmittedcodewordissameasthecodeworddemapped.Inthisresearch, soft demapping is used to demapp the complex value.[42] Soft demapping decrease the probability of residual decoding error which makes it better then hard demapping which isbasedonminimumEuclidiandistancebetweenthereceivedsymbols.Soft demapping is base on APosteriori probability [43,44]. 4.5.5 Evaluation of the Reliability ModulesThissectionisusedtomeasuretheBitErrorRateandPacketErrorRateofthe transmittedsignal.BERissaidtobetherateoferrorinatransmissionsystem.The definition of bit error rate can be translated into a simple formula: BER = Number of Errors Found / Whole Number of Bits Transmitted49 Thebiterrorratefunctionofeachmodulationtechniqueisdifferentsinceeach modulationtechniquebehavesdifferentwhenitcomesincontactwithnoise.For instance, the one withhigher data rate, like 64 QAM, are not as robust as the one with lower date rate, e.g. BPSK. PERisoneofthemajorqualitiesofIEEE802.11pwirelessnetwork.Itisaswell derivedfrom BER whichindicates the number of errors in a transmitted packet.Figure 4.12 illustrates the BER and PER schematic whichis asnap-shot fromADS simulator. This where the reference signal of IEEE 802.11p is received, saved and displayed at the end of each simulation [45]. Figure 4.12: BER and PER schematic [40]. 4.6 DISCUSSIONThischapteremphasizedontheessentialoftheAgilentsAdvanceDesignSystems (ADS)simulationmodel.Thesimulationcomprisesofseven(7)stageswhichareWLANsource,Basestationantenna,WLANchannel,Antennaformobileterminal,AddnoiseDensity,WLANreceiverandWLANmeasurementforBERand PER . Signal source (Transmitter) is the point where the RF carrier frequency (fc) and power is generated.The transmitter where the RF signal is generated , comprises 50 often sub stageswhich are WLAN data source , WLAN data scrambler , Logic XOR gate,WLANtail,Punch-Coder,WLANInterleaver,WLANmapping,Preamble,OFDMsymbol , and IFFT However ,the PPDU data frameis generatedWLAN data , a six zero digitis addedtotheframetoincreasethelengthofframeafterthatframeispuncturedusingconvolutionalencoderforittobeinterleaved.Interleavertocombattheeffectof multipath component, for data t o be modulated it has to be mapped. Mappingis carried outinrespectofthemodulatingtechniqueforexamplebinaryphaseshiftkeying (BPSK),quadraturephaseshiftkeying(QPSK),andquadratureamplitudemodulation (QAM),etc.theIEEE802.11pstandarduseorthogonalfrequencydivision multiplexing (OFDM) , themultiplexercomprisesof64 essentialsub carriers which 12arereserved,while4sub-carriersrepresentthepilottones.Finally,inversefast Fourier transform (IFFT) converts the symbols from frequency domain to time domain. Channelmodelisreferredto thewirelessmediumwhichthissignalsaretransferred, this research Ray-based model is used as the channel model. Ray-based model is a way ofmappingdifferentpropagatingenvironmentonsoftware;itincludesobstacles, environmentandscattererbehaviorthataffectwavepropagation.Thebasestation antenna used in this research is of EIA/TIA-329-B specification. This base station uses ahalfdipoleantennathatislinearlypolarized,likewisethevehicularantennawhich uses a half wave dipole of EIA/TIA-329-B-1 specification TheWLANreceivercomprisesofsevensubstandardswhichFFT,OFDM,OFDM symbol,WLANDemapping,WLANDeinterleaver,DescramblerandWLAN51 PSDU. The arriving signal at the receiver is converted by fast Fourier transforms (FFT) from time domain to frequency domain synchronization according to the IEEE 802.11p standard. However the signal is filtered and un-sampled then, converted from real and imaginary form to a complex signal. After that, the complex signal is equalized in order tosplitintodataandtrainingsymbols.OFDMsymbolde-multiplexincomingsymbol into pilot sub-carrier and data subcarrier which will have to be de-interleaved. 52 Chapter 5 SIMULATED RESULTS FOR FADING CHANNEL Inthisresearch,abasebandsimulationperformanceiscarriedoutwithregardstoBiteErrorRate (BER) against Energy per bit to noise power spectral density ratio (Eb/N0) BERhastodowiththeamountoferrordividedbythetotalnumberoftransferredbitsduringthe period. The Eb /No can be represented mathematically as: bSR Guard FFTSizeFFTSizeP Eb1+ = Eq5.1 SP=Receivesignalpower, bR=datarate,FFTSize=thesizeofFastFourier Transform and Guard represent Guard interval

S OT N * * 22o = Eq 5.2 In the above equation ON =Noise power per power bits, ST = sample rate and 2ois the Noise variance 53

SbSO bTR Guard FFTSIZEFFTSizePN E* * 21* */2o +=Eq 5.3 Atransmissionpathexperiencesfadingwhenthereismulti-pathpropagationbetweenthe transmitter and the receiver, this in turn causes differences in time delay and gain in arrival of signals [46] [47]. In the cause of this research, we considered three scenarios which are: Typical urban scenario, free space scenario and rural area. 5.1GENERATING AN OFDM CODE TheOFDMblockdiagramgenerationalcodeforIEEE802.11pisgeneratedusingmat labasstatedinFigure:5.1.ThecodeforthegenerationofOFDMcanbefindin Appendix A. Figure 5.1: IEEE 802.11p OFDM block diagram [48] IntheaboveOFDMblock,theinputteddataareinserialformwhichisconvertedto parallelformbyserialtoparallelconverter.Themappingofasignaldependsonthe actualmodulation technique usesin order to map the signalinto the right constellation after whichis transferred to pilot sequenceinsertion.The pilot contain signals that are known to receiverand it use by the receiver to make coherent detectionand while theOFDM Signal X-bits Serial data Input Serial to Parallel Converter Signal Mapping Pilot Sequence Insertion Guard Bit Insertion IFFTD/AUp-sampling 54 guardinsertionprotectagainstintersymbolandintercarrierinterference.However,in thenextblockisanIFFTitenabletheconvertingofsignalfromfrequency domaintotimedomainwhichisthenpassedtodigitaltoanalogconverter,therethe signal is transform from it digital formto analogform for it transmitted. Figure5.2 is an illustration of how the OFDM symbolafter the generation process. [49] Figure5.2: Generating an OFDM Signal 55 5.2 PERFORMANCE ON A TYPICAL URBAN FADING CHANNELA typical urban environment area is associated with high population density whichmaybe informofacityortownwithsomanytallbuildingsindicatinganenvironmentwith scaterers and multi path component. In this scenario we have three vehicles moving in the same direction within a typical urban area, two of thevehicular antennasare at a point of viewtoeachotherindicatingLineofSight(LOS)whichisassociatedwithRician distribution as shown in the Figure 5.3.

Figure 5.3: A typical urban scenario. Whilethirdcarhastodowithnonelineofsight(NLOS)whichindicatesRayleigh distribution.The tablebelowstate the parameters usedfor LOS andNLOS. Table 5.1 illustrates the parameter used in the simulation. 56

Table 5.1: Simulation parameters. ParametersLOSNLOS Central Frequency5.9 GHz5.9 GHz Bandwidth1010 Data Rate9 Mbps , 18 Mbps and 24 Mbps 9 Mbps , 18 Mbps and 24 Mbps Height of Vehicular Antenna 1.5 m1.5 m Height of Base station20 m20 m EnvironmentTypical UrbanTypical Urban Fading TypeRicianRayleigh Model TypeCC Transmitting Power20dBm20dBm FFT Size6464 Modulation TechniqueBPSK ,QPSK and 16 QAM BPSK ,QPSK and 16 QAM In the scenario, simulation is carried out for Binary Phase Shift Key (BPSK) at 9 mbps, Quadrate Phase ShiftKey (QPSK)modulation techniqueis carried out at 18 mbps and 16QuadratureAmplitudeModulations(QAM)at24mbpsisusedtosimulatingfor BER against Signal to Noise Ratio (SNR). The figure 5.4 and figure: 5.4 shows that the 57 simulatedresultcurveissimilarto thetheoreticalcurveandtheonesimulatedonMat lab this imply that the result is good. [50]. In both Figure , a coding rateof is used forthesimulationwithregards toLOS and NLOS forBPSK scenario , while acoding rate is used for QPSKanda coding rate of is used for the 16 QAM [51], [52]

Figure 5.4: Comparing the BER of fading channel in a typical urban area for BPSK, QPSK and 16 QAM with regards to LOS. The result indicates the higher the SNR, the lower the BER. It also shows a quick drop as a result of signal fading due to multi path component on the transmission path. At the starting point of the simulated result in Figure 5.2 for BPSK BER against SNR the result was 0.493 at -2.000 and 2.954E-5 at 4.750 at the ending. For QPSK the result was 0.486 at -2.000 for the starting point and 4.844E-4 at 4.750 and while for the 16 QAM it has a starting point of 0.481 at -2.000 with an ending point of 0.004 at 4.750 which shows that BPSK has the least BER for a distance of 100m. 58 The resultinFigure 5.4indicates that QPSK and 16 QAMis result significantly poor comparetothatofBPSK.ThisbecausetheconstellationQPSKand16QAMare denselyspaced than the symbol compareto BPSK whichjust havetwo constellation pointwith a very low error probability . More so, it is visible that QPSK and 16 QAM are very close, this is an indication that 16 QPSK is not a good modulation technique for the fading channel. -1 0 1 2 3 4 5 6 7 -2 81E-51E-41E-31E-21E-11E-66E-1Eb/No (dB)BER802.11p BER In A Typical Urban Area For NLOS Fading ChannelBPSK 3/4QPSK 3/416 QAM 1/2 Figure 5.5: Comparing the BER of fading channel in a typical urban area for BPSK, QPSK and 16 QAM with regards to NLOS. However in Figure 5.5 the BER against SNR for BPSK indicates 0.493 at -2.000 for the starting point and 1.018E-4 at 4.429 at the ending. For the QPSK the result is 0.486 at -2.000forthestartingpointand0.001at4.429.Andforthe16QAMithasastarting point of 0.481 at -2.000 with an ending point of 0.006 at 4.429. 59 TheperformanceofFigure5.5resultisobservedtodegradeasaresultofmultipath componentandNLOSbetweenthetransmitterandthereceiver.Inadditiontheresult indicates that the environment is associated with a lot building and Doppler component thatwillhindertheeffectivetransmissionofsignalalongthechannel[53].The comparison can be seen in Table 5.2. Table 5.2 Comparing BER against SNR for LOS and NLOS in Urban Environment ModulationandCoding RateBER/SNRinanUrban Scenario for LOS BER/SNRinanUrban Scenario for NLOS BPSK 3/42.954E-51.018E-4 QPSK 3/44.844E-40.001 16 QAM 1/20.0040.006 5.3 PERFORMANCE ON FREE SPACEIn the case of free space scenario it has to do with an open environment where we have two or multiple carsmovingin thesame direction ona singlelane where thereisLine Of Sight (LOS) and Non Line Of Sight as illustrated in Figure 5.6. 60 Figure 5.6: A free space scenario [54]. Theabovescenarioisdefinedbythefollowingparametersintable:5.3inasituation where both transmitter and receiver are at a point of view and situat ion where there is no point of view between both components. Table 5.3 Simulations parameters. 61 In the above scenario, a simulation is also carried out with regards to LOS.During the simulation, a 9mbps data rate of coderate is usedfor the BPSK simulation, while a with a data transmission of 18mbps is usedfor that of QPSKand also a coding rate ofwith a data transmission of 24 mbps is used for the 16 QAM. From the whole result,itisconspicuousthatFigure5.7hasthelowestBERcomparetotheresultin Figure 5.5 and Figure 5.6. This is because the free space performance has less multi path component and Doppler spreads compare the performance in rural fading channel.ParametersLOSNLOS Central Frequency5.9 GHz5.9 GHz Bandwidth1010 Data Rate9 Mbps , 18 Mbps and 24 Mbps 9 Mbps , 18 Mbps and 24 Mbps Height of Vehicular Antenna 1.5 m1.5 m Height of Base station20 m20 m EnvironmentFree SpaceFree Space Fading TypeRicianRayleigh Model TypeCC Transmitting Power20dBm20dBm FFT Size6464 Modulation TechniqueBPSK ,QPSK and 16 QAMBPSK ,QPSK and 16 QAM 62 -1 0 1 2 3 4 5 6 7 8 9 -2 101E-51E-31E-11E-75E-1Eb/No(dB)BER802.11p BER In A Free SpaceFor LOS Fading ChannelBPSK 3/4QPSK 3/416 QAM 1/2Figure 5.7: Comparing the BER of fading channel in a free space for BPSK, QPSK and 16 QAM with regards to LOS TheFigure5.7showstherepresentationofLOSresultforBERagainstSNRindicate 0.492 at -2.000 at starting point and 9.766E-7 at 7.000 at the ending point for BPSK. In QPSK the result indicate 0.488 at -2.000 for the starting point and 1.733E-5 at 7.000 for the ending point. And for the 16 QAMit has a starting point of 0.480 at -2.000 with an ending point of 1.074E-5 at 10.000. 63 -1 0 1 2 3 4 5 6 7 8 9 -2 101E-51E-41E-31E-21E-11E-65E-1Eb/No(dB)BER802.11p BER In A Free Space For NLOS Fading ChannelBPSK 3/4QPSK 3/416QAM 1/2 Figure 5.8: Comparing the BER of fading channel in a free space for BPSK, QPSK and 16 QAM with regards to NLOS. TheFigure5.8isarepresentationofNLOSforperformanceinfreespace,theresult states that BPSK has a BER of 1.416E-5 at 6.250 but it is also glaring that QPSK and 16QAMarealmostthesameindicatingthatitnotagoodchoicetouseQPSK. However,theresultindicatesthefigure5.7resultshasthelowestBERcompareto figure 5.8. Due to LOS that exist between the two car antennas 64 5.4 PERFORMANCE OF PACKET ERROR RATE IN FREE SPACE ENVIRONMENT Toknowtherateoferrorinatransmittedsignal,simulationisbeencarriedoutfor different modulation technique. For BPSK a coding rate of is used for the simulation, coding rate is used for the simulation of QPSK and coding rate is used for 16 QAM as stated in Figure 5.9. The simulation result recorded a PER of 0.001 at 7.000 for BPSK, a record of 0.007 at 7.000 for QPSKand a record of 0.168 at6.571for 16 QAM The simulated result in theFigurealsoindicatedthatBPSKhasthelowestPERdueto theconstellation pointonBPSK.16QAMhasthehighesterrorratebecauseitconstellationpointare densely packed to each other [55]. Figure 5.9: Comparing the PER of BPSK, QPSK and 16 QAM in a free space environment 65 Table5.4isusedtocomparethemodulationtechniquewhichhasthelowestBER against SNR for LOS and NLOS in free SpaceTable 5.4: Comparing BER against SNR for LOS and NLOS in Free Space Environment Modulationand Coding Rate BER/SNRinFree SpaceScenariofor LOS BER/SNRinFree SpaceScenario for NLOS PER/SNRinan SpaceScenario for LOS BPSK 1/29.766E-71.416E-50.001 QPSK 3/41.733E-50.0010.007 16 QAM 1/21.074E-50.0061.168 66 5.5 PERFORMANCE ON A RURAL FADING CHANNEL The performance of signal in a rural fading channel has to do with a country side that is not urbanized. These areas consist of trees and open field. However, rural area has less multipathcomponentcompareto theruralarea.Thetable5.5istheparameterusedin the LOS simulation of Figure 5.10. Table 5.5 Simulations parameters. ParametersLOS Central Frequency5.9 GHz Bandwidth10 Data Rate9Mbps,18 Mbps and 24 Mbps Height of Vehicular Antenna1.5 m Height of Base station20 m EnvironmentRural Area Fading TypeRician Model TypeC Transmitting Power20dBm FFT Size64 Modulation TechniqueBPSK ,QPSK and 16 QAM The simulated resulted below indicate that BPSK has a BER of 4.844E-5at 6.000 Eb/No with a code rate of , QPSK has BER of 2.844E-5 at 6.000with a code rate of and67 while 16QAM has a BER of 1.636E-5 at 7.000 with a code rate of . Figure 5.10 has a consistentlylower BER compareFigure 5.4 thisbecause performance of a ruralfading channel has less signal obstacle compare to urban scenario. -1 0 1 2 3 4 5 6 -2 71E-51E-41E-31E-21E-11E-65E-1Eb/No(dB)BER802.11p BER In A RuralArea For LOS Fading ChannelBPSK 3/4QPSK 3/416QAM 1/2 Figure 5.10 Comparing the BER of fading channel in a rural scenario for BPSK, QPSK and 16 QAM with regards to LOS. 68 5.6 DISCUSSIONIn this chapter the simulation result is been discussed with regard to performance of BER against SNRonafadingandnonfading.However,wecomparetheeffectofsignaltransmissionindifferent environment with respect to LOS and NLOS which indicates the performance on a free space LOS has the lowest BER compare to that of NLOS this is because free space performance has less multi path component due to thepoint of view that exist between the transmitter and receiver. The performance in a typical urban area indicate environment area is associated with high population density which may beinformofacityortownwithsomanytallbuildingsresultingtoscaterersandmultipath component. This implies that the signal performance is not as good as that free space performance. And fortheperformanceofsignalinaruralfadingchannelhastodowithacountrysidethatisnot urbanized. These areas consist of trees and open field but in this case Figure5.9 indicate a lower BER compare Figure 5.4 this because performance of a rural fading channel has less signal obstacle compare to urban scenario. 69 Chapter 6 CONCLUSION The vehicle to vehicle (V2V) and vehicle to Infrastructure (V2I) is gradually becoming a realityinplacesliketheunitedstateandotherdevelopedcountrieswithmostcar companiesandtransportauthoritiesarebeginningtoinvestintheresearch.However, OrthogonalFrequencyDivisionMultiplexing(OFDM)isusedasthefrequencycarrier forVehicletoVehiclewirelesscommunicationtoguildagainstmultipathcomponent and to enable data to be transmitted more efficiently in a secured manner. ThethirdchapterdiscussesIEEE1609WirelessAccessinVehicularEnvironment (WAVE)anditssubstandard(1609.1,1609.2,1609.3and1609.4).Inthefirstsub standard whichis IEEE 1609.1enables communicationbetween remotemanagers and onboardunit,thesecondsubstandardIEEE1609.2createseveralsecurewaysof sending and receivingmessagein aWAVE system, thenetwork and servicelayer uses IEEE1609.3itsupportsbothIPandnon-IPapplications.FortheIPapplications,it supportsIPv6andsupportsWAVEshortmessageprotocol.WhiletheIEEE1609.4 standard handles theWAVEmultichannel operations. It helpsin defining thefunctions ofMACsubLayerManagementEntity(MLME)andWAVEMACwithchannel coordination. 70 ThechapterFourofthisresearchcenteredonAgilentsAdvanceDesignSystemssimulation model whichcomprises of a WLANTransmitter , Base stationantenna, WLAN channel ,Antenna formobileterminal , Add noise Density , WLAN receiverandWLAN measurementforBER. The Signal source is the point where the Radio Frequency,Carrierfrequencyandpowerisgenerated. ThetransmitterwheretheRF signalisgenerated,comprisesoftensubstageswhichareWLANdatasource, WLANdatascrambler,LogicXORgate,WLANtail,Punch-Coder,WLANInterleaver,WLANmapping,Preamble,OFDMsymbol,andIFFT.Howeverthe antennas used is of EIA/TIA-329-B, specification for the base station and"EIA/TIA-329-B-1 specification for the car antenna The resultchapter comparetheperformance ofBite error rate (BER) againstSignal to Noise Ratio(SNR) ondifferent environmentwhich are; typical urban environment, free space environment and rural environment. Theresults indicate that performance on freespacehasthelowestBERcomparetotypicalurbanenvironmentandrural environment. This is because free space environment has less multi path component and Doppler spreads compare the performance in rural and the typical urban environment.6.1 FUTURE WORK Inthefutu