intelligent transportation systems - sti innsbruck · pdf file ·...

Intelligent Transportation Systems

Wireless Access for Vehicular Environments (WAVE)

Prof. Dr. Thomas Strang

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Outline

Wireless Access for Vehicular Environments (WAVE)

IEEE 802.11p

IEEE 1609.1-4

SAE 2735

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Wireless Access for Vehicular EnvironmentsRationale

What was the motivation behind a vehicle specific WLAN? What prevented the existing IEEE 802.11-family from being adopted as is?

[Sou

rce:

Dai

mle

r/C2C

-CC

]

M. Röckl and T. Strang, 2009

http://www.car-2-car.org/index.php?id=138

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IEEE 802.11 in C2CRequirements to be used for C2C

Changes in baseline 802.11 standards are required to:support longer ranges of operation (up to ~1000 meters), the high speed of the vehicles (up ~500 km/h relative velocities), the extreme multipath environment (many reflections with long delays (up to ~5 μs)), the need for multiple overlapping ad-hoc networks to operate with extremely high quality of service, and the nature of the automotive applications (e.g. reliable broadcast) to be supported.

Based on: IEEE 802.11p & Tan (2008): Measurement and Analysis of Wireless ChannelImpairments in DSRC Vehicular Communications


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IEEE 802.11 in C2CVANET communication entities – not only cars

Communication between:roadside units and mobile radio units (Vehicle-2-Infrastructure),mobile units (Vehicle-2-Vehicle), orportable units and mobile units (Vehicle-2-Pedestrian)

Infrastructure:Roadside Units (RSUs)Gantries (e.g. tolling gantries)Poles, traffic lights, etc.

Mobile/Portable equipment:On-board Unit (OBU)

Based on IEEE 802.11p

Denso DSRC platform


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Vehicle-2-Pedestrian

[Source: www.OKI.com]


http://www.oki.com/en/press/2007/z07023e.html

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IEEE 802.11p DSRC module

GPS receiver

Regular GSM phone


Vehicle-2-Pedestrian

http://www.i4u.com/article9192.html

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0 Wireless Access for Vehicular Environments (WAVE)

IEEE 802.11p + 1609.x + SAE 2735

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Wireless Access for Vehicular EnvironmentsOverview

No. of layer

ISO/OSI ref model Data Plane Management Plane

7 Application e.g. HTTPWAVE

Application (Resource Manager)

4 Transport TCP/UDPWSMP

WAV

E S

tation Managem

ent Entity

WS

ME

3 Network IPv6

2bData Link

802.2 LLC

2a WAVE MAC MACManagement

1bPhysical

WAVE Physical Layer Convergence Protocol (PLCP) PHY

Management1a WAVE Physical Medium

Dependent (PMD)

IEEE 1609.4IEEE 802.11pLo

wer

Laye

rsN

etw

ork

Serv

ices

1609.1 Resource Manager1609.2 Security Services1609.3 Networking Services1609.4 Multi-channel operations

IEEE 1609.3IEEE 1609.2

Hig

her

Laye

rs

IEEE 1609.1

WAVE Station M

anagement Entity

WSM

EMAC Management

PHYManagement

SAE J2735


IEEE 802.11p

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IEEE 802.11pOverview

IEEE 802.11p is based on:IEEE 802.11a PHY: OFDM modulationIEEE 802.11 MAC: CSMA/CAIEEE 802.11e MAC enhancement: message prioritization


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V2X frequency bands


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IEEE 802.11pFrequency band

U.S. FCC allocated 75 MHz band in 1999 for ITS

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Uplink

Downlink

Ch 172 Ch 174 Ch 176 Ch 180 Ch 184Ch 182Ch 178

PublicSafety/Private

Public SafetyIntersectionsControl

Channel



Inter-sections

Control High Availability

Dedicated Public SafetyShort Rng

ServiceMedium Rng

Service

Shared Public Safety/Private


PublicSafety

Veh-Veh

40 dBm

33 dBm

23 dBm

Power Limit

Power Limit

Power Limit

44.8 dBm

Based on B. Cash (2008): North American 5.9 GHz DSRC Operational Concept / Band Plan


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IEEE 802.11p Multi-channel

Control Channel (CCH):Broadcast communicationDedicated to short, high-priority, data and management frames:

Safety-critical communication with low latenciesInitialization of two-way communication on SCH

Service Channel (SCH):Two-way communication between RSU and OBU or between OBUsFor specific applications, e.g. tolling, internet accessDifferent kinds of applications can be executed in parallel on different service channelsRequires the setup of a WAVE Basic Service Set (WBSS – “Ad-hoc group”) prior to usage of the SCH


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IEEE 802.11pFrequency band

European ITS-G5 Frequency Allocation

ITS

road

saf

ety

(ITS

-G5A

)

Futu

re IT

S a

pplic

atio

ns

ITS

non-

safe

ty a

pplic

atio

ns (I

TS-G

5B)

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IEEE 802.11pOperation modes

Without WAVE Basic Service Set (WBSS)

Operation modes

Safety-critical, low latency messages and control messages

Mainly broadcastOnly on CCH

With WAVE Basic Service Set (WBSS)

Two-way transactions (e.g. tolling, internet access)Required to use a SCHRequires initiation on CCHIn contrast to the Independent Basic Service Set (IBSS), WBSS does not require authentication and association procedures


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IEEE 802.11pPHY

OFDM-based modulation similar to IEEE 802.11aHalved channel bandwidth of IEEE 802.11a: 10 MHz channels

half data rate: 3-27 Mbpsdoubled symbol duration: 8.0 μs 10 MHz

156.25 kHz


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IEEE 802.11pPHY: Comparison to IEEE 802.11a

Longer guard period Less Inter-symbol InterferenceBetter resistance against multipath error

IEEE 802.11a IEEE 802.11pData rate 6, 9, 12, 18, 24,

36, 48, 54 Mbps3, 4.5, 6, 9, 12, 18, 24, 27 Mbps

Modulation BPSK OFDMQPSK OFDM16-QAM OFDM64-QAM OFDM

BPSK OFDMQPSK OFDM16-QAM OFDM64-QAM OFDM

Error Correction Coding Convolutional Coding with K=7

Convolutional Coding with K=7

Coding Rate 1/2, 2/3, 3/4 1/2, 2/3, 3/4

# of subcarriers 52 net 52 net

OFDM Symbol Duration 4.0 μs 8.0 μs

Guard Period 0.8 μs 1.6 μs

Occupied bandwidth 20 MHz 10 MHz

Frequency 5 GHz ISM band 5.850-5.925 GHzDedicated frequency band

Less Co-Channel Interference

Re-order of sub-carriersBetter multipath mitigation


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IEEE 802.11pMAC

Based on Distributed Control Function (DCF) with CSMA/CAMAC-level acknowledgements for unicast communication, but no acknowledgements for broadcast communication

unreliable broadcast communicationRTS/CTS is only used on SCHBecause of higher range, slot time and SIFS should be longer

Addressing:RSUs have a fixed 48-bit MAC addressOBUs generate a random MAC address upon start-up of the deviceIf a MAC address collision occurs the OBU automatically changes its MAC address

Prioritization based on IEEE 802.11e EDCA (Enhanced Distributed Channel Access), defined in IEEE 1609.4

IEEE 802.11a

IEEE 802.11p

Slot time 9 μs 13 μsSIFS time 16 μs 32 μsCWmin 15 15

CWmax 1023 1023

SIFS – Short Inter-Frame Space


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IEEE 1609.4Extension for multi-channel coordination

IEEE 1609.4 is a functional extension to IEEE 802.11e MAC to enable multi-channel coordinationFunctions:

Channel routingData buffers (queues)PrioritizationChannel coordination


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Priorization

B. Kloiber and T. Strang, 2010

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IEEE 1609.4 Channel Coordination

Each Universal Time Coordinated (UTC) second is split into 10 Sync IntervalsEvery Sync Interval is composed of alternating:

CCH Intervals: Every node monitors the CCH andSCH Intervals: Nodes can monitor one of the SCHs

All WAVE devices have to monitor the CCH during the CCH IntervalDuring the SCH Interval nodes may switch to a SCH (RX or TX)At the start of each UTC second the first Sync Interval beginsSynchronization is performed via GPS time base


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IEEE 1609.3Networking Services

IP-based communication:IPv6-based with optional:

Mobile IPv6 (MIPv6) andNetwork Mobility (NEMO)enhancements

UDP or TCP on transport layerTransmission on SCH only

Non-IP-based communication:Based on WAVE Short Message Protocol (WSMP)Transmission on CCH or SCH

No. of

layerData Plane

4 TCP/UDPWSMP

3 IPv6

2b 802.2 LLC

2a WAVE MAC

1b WAVE PLCP

1a WAVE PMD

CCH/SCHSCH


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IEEE 1609.3WAVE Short Message Protocol (WSMP)

Networking protocol specifically designed for V2X communicationsWAVE Short Message (WSM)structure:

WSMP can use CCH and SCHDuring the SCH Interval low priority messages can be transmitted on CCH for stations that do not switch to a SCH, high priority frames and WAVE Announcement frames shall be transmitted during the CCH IntervalIn order to access a SCH, the nodes have to be member of the WBSSWBSS roles:

Provider: Initiates a WBSS by sending a WAVE AnnouncementUser: Joins a WBSS based on the receipt of the WAVE Announcement


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SAE J2735Message Dispatcher

Based on: Robinson et al. (2006): Efficient Coordination and Transmission of Data for Cooperative Vehicular Safety Applications

Implementation specific Implementation specificcommon


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SAE J2735Basic message set definition

SAE J2735: Dedicated Short Range Communication (DSRC) Message Set Dictionary

ASN.1 representation of message structuresHierarchical definition of messages and substructuresBasic message set is not so basic any more, i.e. comprehensive:

16 different message frames, which use54 different data frames, which are parametrized through 162 different data elements


intelligent transportation systems - sti innsbruck · pdf file ·...

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