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
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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
M. Röckl and T. Strang, 2010
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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
M. Röckl and T. Strang, 2010
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Vehicle-2-Pedestrian
[Source: www.OKI.com]
M. Röckl and T. Strang, 2010
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IEEE 802.11p DSRC module
GPS receiver
Regular GSM phone
M. Röckl and T. Strang, 2010
Vehicle-2-Pedestrian
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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
M. Röckl and T. Strang, 2010
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
M. Röckl and T. Strang, 2009
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V2X frequency bands
M. Röckl and T. Strang, 2009
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IEEE 802.11pFrequency band
U.S. FCC allocated 75 MHz band in 1999 for ITS
5.85
0
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5
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5
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Uplink
Downlink
Ch 172 Ch 174 Ch 176 Ch 180 Ch 184Ch 182Ch 178
PublicSafety/Private
Public SafetyIntersectionsControl
Channel
PublicSafety/Private
PublicSafety/Private
Inter-sections
Control High Availability
Dedicated Public SafetyShort Rng
ServiceMedium Rng
Service
Shared Public Safety/Private
PublicSafety/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
M. Röckl and T. Strang, 2010
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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
M. Röckl and T. Strang, 2009
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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
M. Röckl and T. Strang, 2009
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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
M. Röckl and T. Strang, 2009
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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
M. Röckl and T. Strang, 2009
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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
M. Röckl and T. Strang, 2009
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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
M. Röckl and T. Strang, 2009
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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
M. Röckl and T. Strang, 2010
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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
M. Röckl and T. Strang, 2009
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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
M. Röckl and T. Strang, 2009
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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
M. Röckl and T. Strang, 2010
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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
M. Röckl and T. Strang, 2009