Why DSRC?
by Radovan Miucic, PhD
Changan US R&D Center, Inc.
Motivation For Vehicle Safety Communication
1) 2014 Motor Vehicle Crashes (US) 1
• 32,675 fatalities
• 2,338,000 injured
2) 2011 yearly national (US) travel delay 5.5 billion hours2
1 https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/812246
2 http://www.huffingtonpost.com/2014/06/10/worst-places-to-commute_n_5454130.html
Why DSRC for V2X?
• DSRC uses 802.11 chipset (or 802.11p), commodity -> low cost.
• Data rate 6Mbps – can a accommodate hundreds (or more than thousand with CC
protocol engaged) of vehicles in communication range
• DSRC uses CSMS/CA ->
• no need for additional infrastructure for wireless resource scheduling, not optimal but
decentralized simple scheme that works
• DSRC prototype devices have been available to OEMs/Tier 1 for many years -> OEMs are
familiar with DSRC, many years of testing:
• Range, Latency, Cooperative Applications, Interoperability, Scalability, Security, Plug-test…
• Applications: V2V, V2I, V2P
• Proven DSRC large scale model deployment (Ann Arbor Safety Pilot, Scalability Tests…)
• DSRC is well standardized -> physical layer, security, application layer
• Standards have been developed with strong support from Automotive Industry
• Frequency is already allocated for ITS licensed usage-> 75MHz in 5.9 GHz range of
licensed spectrum
• Low latency (no handshake no association), broadcast, scalable
• High availability – e.g. V2V is on a dedicated channel (no need to be on channels
competing for service)
Why DSRC for V2X? Complete Solution
Basic Safety Message
WAVE protocol stack
SAE J2735
Transport
layer
Network
layer
PART I
LLC (802.2)
WAVE upper MAC
(IEEE 1609.4)
WAVE lower MAC
(IEEE 802.11p)
WAVE PHY
(IEEE 802.11p)
Data link
layer
Physical
layer
PART II
Security Services is specified
on IEEE 1609.2
WSMP
(IEEE 1609.3)
Application
layer
Element
MsgCount
TemporaryID
DSecond
Latitude
Longitude
Elevation
PositionalAccuracy
TransmissionAndSpeed
Heading
SteeringWheelAngle
AccelerationSet4Way
BrakeSystemStatus
VehicleSize
PathHistory
PathPrediction
EventFlags
Why DSRC for V2X? Application Design
http://www.nhtsa.gov/DOT/NHTSA/NVS/Crash%20Avoidance/Technical%20Publications/2011/811492B.pdf
Why DSRC for V2X? Cooperative Applications
Emergency Electronic Brake Lights (EEBL)
Intersection Movement Assist (IMA)
HV warns driver when in danger of rear-end collision
Forward Collision Warning (FCW)
Obstruction
HV warns driver when in danger of rear-end collision
Blind Spot Warning (BSW)
HV warns driver when it is not safe to enter intersection.
Control Loss Warning (CLW)
HV warns driver when vehicle ahead lost control
HV warns driver when there is a vehicle in blind zone
Why DSRC for V2X? Real World Tested
200 Vehicle Tests
http://www.its.dot.gov/presentations/CV_PublicMeeting2013/PDF/Day1_LukucInteroperability.pdf
Sample DSRC Performance (NLOS)
http://papers.sae.org/2012-01-0491/
What about Cellular for V2X?
• Infrastructure dependent (not all roads are covered with cellular infr.)
• Additional Investments needed to support broadcast/multicast function
• Current Broadcast/Multicast Service (eMBMS) designed to support static
scenarios (such as the crowd in a stadium) not dynamic scenarios.
• Unclear how handovers between mobile network operators (MNOs) and
cooperation between application service providers will be managed.
• Automotive Safety Integrity Level (ASIL) conformance will make the modem
hardware more expensive
• V2V traffic is to be supported for free, MNOs will have to develop
alternative business models to justify any investments.
http://www.automotive-eetimes.com/design-center/why-80211p-beats-lte-and-5g-v2x/
What about Cellular for V2X?
• Cellular systems are capable of low latency, but not in all conditions: if
resources are not pre-allocated to V2X services., such as when
operating across multiple MNOs, across borders, or across cells.
• To make D2D profile suitable for V2V communication will lead to new
hardware solutions, and the associated time and costs for their
development.
• V2X services based on 802.11p have already been standardized and
available to all.
• Today’s cellular infrastructure isn’t equipped to support the many V2x
use cases that require short latency in situations of high mobility or
congestion.
http://www.automotive-eetimes.com/design-center/why-80211p-beats-lte-and-5g-v2x/
What about
Cellular for V2X?
IEEE 802.11p
IEEE 802.11p
Msgs
2015
Technology ready for large
scale deployment
2009
Standards ready
• Cellular community
will find a technical
solution for V2X.
The question is not
if, but when.
Cellular
LTE-release 8
2015 Technology deployed on a large scale
2009
Standard ready
LTE-release 10
2017
2011
Standard ready
Control
Msgs
LTE-release 13
2016
Standards ready
2022
LTE-release 14
Msgs
2017
Standards ready
http://www.automotive-eetimes.com/design-center/why-80211p-beats-lte-and-5g-v2x/
2023
Conclusion
• Yes there are issues with DSRC such hidden node, channel switching,
and protocol not being optimal, but it is currently the only system
that offers complete solution that meet requirements of being on a
free spectrum, is low latency and high availability, infrastructure
independent, for which applications are developed and real-world
tested.
• If we are to deploy V2X (V2V) today, DSRC is the only complete
technology as of now.
Appendix
Simulation Approach for Scalability
Communication
Congestion
Physical Layer Challenges
• Vehicular environment communication channels have
• Time selective fading due to mobility
• Frequency selective fading due to multi-path and delay spread.
• The interspacing between two pilot subcarriers are much larger than the
coherence bandwidth
• The packet transmission time can be longer than the channel coherence time.
• Channel switching is wasteful
• Hidden node