Vehicle Networks V2X communication protocols - STI Innsbruck

Vehicle Networks 

V2X communication protocols 

Univ.-Prof. Dr. Thomas Strang, Dipl.-Inform. Matthias Röckl

Lecture Vehicle Networks, Thomas Strang and Matthias Röckl, WS 2008/2009 

Outline 

Wireless Access for Vehicular Environments (WAVE) 

IEEE 802.11p 

IEEE 1609.1-4 

SAE 2735 

Car-2-Car Communication Consortium & ETSI TC ITS


Wireless Access for Vehicular Environments 

Rationale 

What was the motivation behind a vehicle specific WLAN? What 

prevented the existing IEEE 802.11-family from being adopted as is? 

[Source: Daimler/C2C-CC]


Wireless Access for Vehicular Environments (WAVE) 

IEEE 802.11p + 1609.x + SAE 2735


Higher 

Layers 

Network 

Services 

Lower 

Layers 

Wireless Access for Vehicular Environments 

Overview 

SAE J2735 

IEEE 1609.1 

IEEE 1609.2 

IEEE 1609.3 

IEEE 1609.4 

IEEE 802.11p 

No. of 

layer 

ISO/OSI 

ref model 

1609.1 Resource Manager 

1609.2 Security Services 

1609.3 Networking Services 

1609.4 Multi-channel operations 

7 Application e.g. HTTP 

4 Transport TCP/UDP 

3 Network IPv6 

Data Plane Management Plane 

WAVE 

Application 

(Resource Manager) 

WSMP 

2b 

802.2 LLC 

2a 

Data Link 

WAVE MAC 

MAC 

Management 

1b 

1a 

Physical 

WAVE Physical Layer 

Convergence Protocol (PLCP) 

WAVE Physical Medium 

Dependent (PMD) 

PHY 

Management 

Management 

WAVE WAVE Station Station Management Entity Entity 

WSME WSME


IEEE 802.11p 

Requirements 

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 max excess)), 

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 Channel 

Impairments in DSRC Vehicular Communications


IEEE 802.11p 

Overview 

IEEE 802.11p is based on: 

IEEE 802.11a PHY: OFDM modulation 

IEEE 802.11 MAC: CSMA/CA 

IEEE 802.11e MAC enhancement: message prioritization


IEEE 802.11p 

Communication entities 

Communication between: 

roadside units and mobile radio units (Vehicle-2-Infrastructure), 

mobile units (Vehicle-2-Vehicle), or 

portable 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) 

Denso DSRC platform 

Based on IEEE 802.11p


IEEE 802.11p 

Vehicle-2-Pedestrian 

[Source: 

www.OKI.com]


IEEE 802.11p 

Pedestrian? 

IEEE 802.11p DSRC module 

GPS receiver 

Regular GSM phone


V2X frequency bands


IEEE 802.11p 

Frequency band 

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

5.825 

Power Limit 

Power Limit 

Power Limit 

5.830 

5.835 

5.845 

5.850 

Shared Public Safety/Private Dedicated Public Safety 

Control Medium Rng 

Service 

Short Rng 

Service 

High 

Availability 

Intersections 

5.855 

5.860 

33 dBm 

5.865 

5.870 

5.875 

44.8 dBm 

5.880 

5.885 

Uplink 

Downlink 

Public 

Safety 

Veh-Veh 

Public 

Safety/ 

Private 

Public 

Safety/ 

Private 

Public 

Control 

Safety/ 

Channel 

Private 

Public 

Safety/ 

Private 

Public Safety 

Intersections 

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

5.890 

5.895 

5.900 

5.905 

40 dBm 

23 dBm 

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

5.910 

5.915 

5.920 

5.925


IEEE 802.11p 

Multi-channel 

Control Channel (CCH): 

Broadcast communication 

Dedicated to short, high-priority, data and management frames: 

Safety-critical communication with low latencies 

Initialization of two-way communication on SCH 

Service Channel (SCH): 

Two-way communication between RSU and OBU or between 

OBUs 

For specific applications, e.g. tolling, internet access 

Different kinds of applications can be executed in parallel on 

different service channels 

Requires the setup of a WAVE Basic Service Set 

(WBSS – “Ad-hoc group”) prior to usage of the SCH


IEEE 802.11p 

Operation modes 

Without WAVE Basic 

Service Set (WBSS) 

Safety-critical, low latency 

messages and control messages 

Mainly broadcast 

Only on CCH 

Operation modes 

With WAVE Basic 

Service Set (WBSS) 

Two-way transactions (e.g. 

tolling, internet access) 

Required to use a SCH 

Requires initiation on CCH 

In contrast to the Independent 

Basic Service Set (IBSS), 

WBSS does not require 

authentication and association 

procedures


IEEE 802.11p 

PHY 

OFDM-based modulation similar to 

IEEE 802.11a 

Halved channel bandwidth of IEEE 

802.11a: � 10 MHz channels 

� half data rate: 3-27 Mbps 

� doubled symbol duration: 8.0 μs 

10 MHz 

156.25 kHz


IEEE 802.11p 

PHY: Comparison to IEEE 802.11a 

Data rate 6, 9, 12, 18, 24, 

36, 48, 54 Mbps 

Modulation BPSK OFDM 

QPSK OFDM 

16-QAM OFDM 

64-QAM OFDM 

Error Correction Coding Convolutional 

Coding with K=7 

IEEE 802.11a IEEE 802.11p 

3, 4.5, 6, 9, 12, 

18, 24, 27 Mbps 

BPSK OFDM 

QPSK OFDM 

16-QAM OFDM 

64-QAM OFDM 

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 GHz 

Longer guard period 

� Less Inter-symbol Interference 

� Better resistance against multipath error 

Re-order of sub-carriers 

� Better multipath mitigation 

Dedicated frequency band 

� Less Co-Channel Interference


IEEE 802.11p 

MAC 

Based on Distributed Control Function (DCF) with CSMA/CA 

MAC-level acknowledgements for unicast communication, 

but no acknowledgements for broadcast communication 

� unreliable broadcast communication 

RTS/CTS is only used on SCH 

Because of higher range, slot time and SIFS should be longer 

Addressing: 

RSUs have a fixed 48-bit MAC address 

OBUs generate a random MAC address 

upon start-up of the device 

If 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 μs 

SIFS time 16 μs 32 μs 

CW min 15 15 

CW max 1023 1023 

SIFS – Short Inter-Frame Space


IEEE 1609.4 

Extension for multi-channel coordination 

IEEE 1609.4 is a functional extension to IEEE 802.11e MAC to enable 

multi-channel coordination 

Functions: 

Channel routing 

Data buffers (queues) 

Prioritization 

Channel coordination


IEEE 1609.4 

Channel Coordination 

Each Universal Time Coordinated (UTC) second is split 

into 10 Sync Intervals 

Every Sync Interval is composed of alternating: 

CCH Intervals: Every node monitors the CCH and 

SCH Intervals: Nodes can monitor one of the SCHs 

All WAVE devices have to monitor the CCH during the CCH Interval 

During the SCH Interval nodes may switch to a SCH (RX or TX) 

At the start of each UTC second the first Sync Interval begins 

Synchronization is performed via GPS


IEEE 1609.3 

Networking Services 

IP-based communication: 

IPv6-based with optional: 

Mobile IPv6 (MIPv6) and 

Network Mobility (NEMO) 

enhancements 

UDP or TCP on transport layer 

Transmission on SCH only 

Non-IP-based communication: 

Based on 

WAVE Short Message Protocol 

(WSMP) 

Transmission on CCH or SCH 

No. 

of 

layer 

Data Plane 

4 

3 

TCP/UDP 

IPv6 

WSMP 

2b 802.2 LLC 

2a WAVE MAC 

1b WAVE PLCP 

1a WAVE PMD 

SCH 

CCH/SCH


IEEE 1609.3 

WAVE Short Message Protocol (WSMP) 

Networking protocol specifically designed for V2X communications 

WAVE Short Message (WSM) 

structure: 

WSMP can use CCH and SCH 

During 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 

Interval 

In order to access a SCH, the nodes have to be member of the WBSS 

WBSS roles: 

Provider: Initiates a WBSS by sending a WAVE Announcement 

User: Joins a WBSS based on the receipt of the WAVE 

Announcement


SAE J2735 

Message Dispatcher 

Implementation specific common 

Implementation specific 

Based on: Robinson et al. (2006): Efficient Coordination and 

Transmission of Data for Cooperative Vehicular Safety Applications


SAE J2735 

Basic message set definition 

SAE J2735: Dedicated Short Range Communication (DSRC) Message 

Set Dictionary 

ASN.1 representation of message structures 

Hierarchical definition of messages and substructures 

Basic message set is not so basic any more, i.e. comprehensive: 

16 different message frames, which use 

54 different data frames, which are parametrized through 

162 different data elements


Car-2-Car Communication Consortium 

(C2C-CC) 

& 

ETSI TC ITS


Car-to-Car Communication Consortium 

Partners 

Partners 

Associate 

Members 

Dev. 

Members



Protocol stack


Objectives 

Car-to-Car Communication Consortium 

Objectives of the First Demonstration (October 2008) 

Demonstrate the 

functionality of CAR 2 CAR Communication Consortium system 

with 5 selected use cases 

Warning of road works 

Emergency vehicle 

Broken down vehicle 

Motorcycle use case / intersection scenario 

Situation Monitor 

interoperability between different communication platforms 

9 vehicle manufacturers 

(Opel, BMW, Daimler, Volvo, Renault, Fiat, 

Volkswagen, Audi, Honda, …) 

4 communication supplies 

(NEC, Hitachi / Renesas, Delphi, Denso) 

1 after market supplier 

(Alpine) 

impact of vehicle-to-x communication 

[Slide by M. Kranz]


Demonstration self-restricted 

to just two message types: CAM and DEN 

Demonstration of technology although not 

fully specified yet. Thus, as compromise, 

mask layer 3..6 (i.e. APP on top of LLC) 

Cooperative Awareness Message (CAM) 

Type of Vehicle, Position, Speed, Heading 

Broadcasted by all vehicles with 1 Hz 

Decentralized Environment Notification Message (DEN) 

Type of Event, Region of Event 

Broadcasted by RSU or Vehicle 

No. of 

layer 

7 

6 

5 

4 

3 

Data Plane 

Demo-APP 

2b 802.2 LLC 

2a WAVE MAC 

1b WAVE PLCP 

1a WAVE PMD


Use Case 1 

Use Cases – Warning of Road Works 

Construction sites and temporary maintenance working areas are 

accident black spots: 

Changed traffic flow 

More traffic signs 

Lane width changes, lane merging, “stress”, and other factors 

The CAR 2 CAR system informs the driver on the details of the 

situation well before entering the potentially dangerous area 

Geographic extent and affected area 

Duration of road works 

Reason of road works 

… 

[Slide by M. Kranz]


Use Case 2 

Use Cases – Emergency Vehicle (EV) 

When it comes to situations affecting the safety of lives every minute 

and every second is crucial. Road users are obliged to make way for 

Emergency vehicles (EVs) like ambulances or police cars. Potential 

problems are: 

Source of siren 

Crossing emergency vehicles at “green” lights 

Destination of emergency vehicle 

The CAR 2 CAR system informs the driver 

about the location of the source of the siren 

where the emergency vehicle is heading 

on what lane the emergency vehicle will be overtaking 

only if the emergency vehicle is expected to cross his route 

[Slide by M. Kranz]


Use Case 3 

Use Cases – Broken Down Vehicle / 

Post Crash Warning 

Accidents and break downs are dangerous for any involved or 

assisting person as well as for approaching vehicles. Problems are: 

Line of sight obstruction, e.g. behind a curve or hill top or due to 

weather conditions 

Timely warning of affected traffic participants 

If a vehicle detects a incident based on emergency flasher status, 

crash sensors, or onboard diagnosis, it can use the CAR 2 CAR 

system to 

inform about the type and location of the incident 

raise awareness and alertness to the traffic situation 

act as “modern warning vest” 

[Slide by M. Kranz]


Use Case 4 

Use Cases – Motorcycle Warning / 

Intersection Assistance 

European In-depth motorcycle accident analyses highlights that 

human error, and more specifically not seeing the motorcycle coming 

or misinterpreting distance and speed is the primary cause of 

accidents involving motorcycles. Reasons are: 

Motorcycles have a smaller silhouette and are easier to “overlook” 

Motorcycles do not have a crumble zone 

The CAR 2 CAR system informs the drivers of the involved vehicles 

about the presence of other traffic participants 

by sending a respective warning message if a crash is predicted 

[Slide by M. Kranz]



Focus and on-going discussions 

Focus on vehicle-to-vehicle communication (well, focus get’s blurred 

more and more …) 

Multi-hop 

Geo-based addressing and routing 

Dual-receiver concept: 

Parallel reception on 2 channels 

Optional: dual-transmitter 

Simulation scenarios and scalability 

… 

If you are looking 

for an interesting 

thesis topic in this 

area, contact me!


Car-2-Car Communication Consortium / ETSI TC ITS 

Relationship 

European industrial development of V2X communication by C2C-CC 

Created the European derivative of IEEE 802.11p 

Standardization by the European Telecommunications Standards 

Institute (ETSI) Technical Committee ITS 

ETSI is the relevant European standardization body for 

telecommunication protocols 

Transferring the standardization process from C2C-CC to ETSI TC ITS 

C2C-CC WGs act as preparatory platforms & discussion fora for ETSI 

TC ITS WGs. 

One critical issue with the transfer of standardization to ETSI are the 

ETSI voting rules, which may add a strong bias to the whole process

Vehicle Networks V2X communication protocols - STI Innsbruck

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