Intelligent Transportation Systems

Wireless Access for Vehicular Environments (WAVE)

Engin Karabulut

Kocaeli Üniversitesi,2014

Outline

Wireless Access for Vehicular Environments (WAVE)

IEEE 802.11p

IEEE 1609.1-4

SAE 2735

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?

IEEE 802.11 in C2C Requirements 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.

IEEE 802.11 in C2C VANET communication entities – not only cars

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)

Based on IEEE 802.11p

DSRC platform

Vehicle to Pedestrian

Wireless Access for Vehicular Environments (WAVE)

IEEE 802.11p + 1609.x + SAE 2735

W A

VE Station

MAC

WSME

Managem

Management

PHY

ent

Management Entity

Wireless Access Overview

for Vehicular Environments

SAE J2735

IEEE 1609.1

IEEE 1609.2 IEEE 1609.3

IEEE 802.11p Management

IEEE 1609.4 IEEE 802.11p

1609.1 Resource Manager

1609.2 Security Services

1609.3 Networking Services

1609.4 Multi-channel operations

WA

VE

Sta

tion

Managem

ent E

ntity

WSM

E

Lo

wer

Lay

ers

Net

wo

rk

Ser

vic

es

Hig

her

Lay

ers

No. of

layer

ISO/OSI

ref model

Data Plane

Management Plane

7

Application

e.g. HTTP

WAVE

Application (Resource Manager)

4

Transport

TCP/UDP

WSMP

WA

VE

Sta

tion

3

Network

IPv6

2b

Data Link

802.2 LLC

2a

WAVE MAC MAC

PHY Management

1b

Physical

WAVE Physical Layer

Convergence Protocol (PLCP)

1a WAVE Physical Medium

Dependent (PMD)

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

V2X frequency bands

IEEE 802.11p Frequency band

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

Shared Public Safety/Private Dedicated Public Safety

Medium Rng Service

Short Rng Service

High Availability

Inter- sections

Control

Power Limit 44.8 dBm 40 dBm

Downlink

Public

Safety

Veh-Veh

Ch 172

Public

Safety/

Private

Ch 174

Public

Safety/

Private

Public

Safety/

Private

Ch 180

Public Public Safety

Safety/ Intersections

Private

Ch 182 Ch 184

Control

Channel

Ch 176 Ch 178

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

5.8

25

5.8

30

5.8

35

5.8

45

5.8

50

5.8

55

5.8

60

5.8

65

5.8

70

5.8

75

5.8

80

5.8

85

5.8

90

5.8

95

5.9

00

5.9

05

5.9

10

5.9

15

5.9

20

5.9

25

Po w er L imit

Po w er L im it

33 dBm

23 dBm Uplink

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 Frequency band

European ITS-G5 Frequency Allocation

ITS

non-s

afe

ty a

pplications (

ITS

-G5B

)

ITS

road s

afe

ty (

ITS

-G5A

)

Futu

re I

TS

applications

5500 5550 5600 5650 5700 5750 5800 5850 5900

IEEE 802.11p

Operation modes

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

Safety-critical, low latency

messages and control messages

Mainly broadcast

Only on CCH

With WAVE Basic

Service Set (WBSS)

Without WAVE Basic

Service Set (WBSS)

Operation modes

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 PHY:

802.11p Comparison to IEEE 802.11a

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 802.11a IEEE 802.11p

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

36, 48, 54 Mbps

3, 4.5, 6, 9, 12,

18, 24, 27 Mbps

Modulation BPSK OFDM

QPSK OFDM 16-QAM OFDM

64-QAM OFDM

BPSK OFDM

QPSK OFDM 16-QAM OFDM

64-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 GHz

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

SIFS – Short Inter-Frame Space

IEEE

802.11a

IEEE

802.11p

Slot time 9 μs 13 μs

SIFS time 16 μs 32 μs

CWmin 15 15

CWmax 1023 1023

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

Priorization

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 time base

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

SCH CCH/SCH

No.

of

layer

Data Plane

4 TCP/UDP WSMP

3 IPv6

2b 802.2 LLC

2a

WAVE MAC

1b WAVE PLCP

1a WAVE PMD

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