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SPECIAL REPORT: EMERGING WIRELESS TECHNOLOGY
by Randy Frank Contributing Editor
EXPLORING VEHICLE-TO-VEHICLE
COMMUNICATIONS AND VEHICLE
INFRASTRUCTURE INTEGRATION
As vehicle-to-vehicle (V2V) and vehicle-to-roadside (V2R) communication
technologies evolve, one of the essential and common elements is the
wireless communication technique. As part of AE’s ongoing reporting of Vehicle
Infrastructure Integration (VII) [1, 2, 3], this report includes the successful
completion of the most recent VII Consortium milestone, the viability assessment
decision, and a controversy that has arisen.
The Michigan VII developmental
test environment or DTE
for proof of concept (POC) of
several applications offi cially started
in November 2007. “However,
prior to that, there was almost two
years of work going on with the
14 AUTO ELECTRONICS | JULY/AUGUST 2008
consortium in cooperation with the
U.S. Department of Transportation,”
Dave Henry, president, VII Consortium
& senior manager, Chrysler
LLC., noted.
Supported by nine major OEMs
(General Motors, Ford, Chrysler,
Mercedes-Benz, BMW, Nissan, Volkswagen,
Honda, and Toyota), the test
fl eet consisted of 25 vehicles with
four different makes. An On-Board
Equipment (OBE) module, a 5.9 GHz
Dedicated Short Range Communication
(DSRC) radio with Linux
Figure 1. Wireless communications between the infrastructure and other vehicles occur in the Dedicated Short Range Communication
(DSRC) network [4] .
807AESR1.indd 14 10/2/2008 4:11:51 PM

Figure 2. Consisting of more than 40 roadside equipment (RSE) units, the Michigan VII
DTE public 5.9 GHz DSRC test bed with VII network has been in operation for OEM testing
since November 2007 [4] .
xprinc th driv
automotiv.tlmatics.snsors.infotainmnt.scurity.
drivers and an antenna were integrated
in each vehicle with CAN
access and a display. Prototype
applications developed to exercise
the network include probe data
collection, off-board navigation,
in-vehicle signage and payment
applications. Figure 1 shows the
VII concept.
“As we were developing the
equipment and then integrating the
equipment into the vehicles, the US
DOT through its contractor Booz
Allen, was also creating the RSUs or
roadside units,” said Henry. “We
now have equipped vehicles as well
as what we call the DTE or the developmental
test environment.” The
DTE is basically a roadway in the
807AESR1.indd 15 10/2/2008 4:11:52 PM

Novi, MI area that is equipped with
roadside units that cover an area
of about 45 square miles and 75
miles of roadway. With the DTE in
Figure 3. In a cooperative collision avoidance (CCA) application, improved delay results
by using a TDMA protocol with an in-band signaling technique [5] .
Michigan and vehicles with the integrated
equipment, in November 2007,
carmakers were ready to start proofof-concept
testing. Figure 2 shows the
location of the RSE units northwest of
Detroit.
The executive leadership team,
the decision-making body of The VII
National Coalition, made up of the VII
consortium that represents the automakers,
the state and local departments
of transportation, as well as the
DOT, met in May to discuss the results
of the testing to date. With results and
16 AUTO ELECTRONICS | JULY/AUGUST 2008
a plan to move forward, Henry presented
the status of the VII testing at
Telematics Update 2008 [4] . “I reported
that the executive leadership team
did agree to continue work on the VII
concept, thus passing through the
fi rst milestone, which was the viability
assessment decision,” he said.
While requesting continued investment
in VII, the team proposed an
accelerated effort in describing the
business deployment, security and
governance alternatives for VII.
“I think we have kind of proven
the technical feasibility, although we
are not done, a lot of scalability work
has to be done, but I think we are
proving that the concept is a viable
one to pursue,” said Henry. “One of
the things that we have to begin a lot
of good work on is the business model
and infrastructure governance framework.”
Next steps from the technology
perspective will be more fi eld
operation testing, some of it
collaborative, some by individual
automakers.
As part of the preliminary conclusions,
the cited observations and
fi ndings include successfully sending
and receiving vehicle “heartbeat”
messages among multiple vehicles.
While early tests indicate that the system
supports transmission of signal
phase and timing and intersection
maps, message priority testing has
not yet been completed. However, the
preliminary conclusion is that V2V
safety applications can be supported.
Also, pending the completion of tests
to determine prioritization of safety
messages, applications such as cooperative
intersection collision avoidance
systems can be supported.
Initial fi ndings in specifi c applications
include [4] :
• Heartbeat messages can be exchanged
between moving vehicles.
• Safety link messages can be wirelessly
communicated to vehicles.
• Probe data can be wirelessly collected
by DSRC and can be subscribed
to through the network.
• Signage messages can be wirelessly
pushed to the vehicles and
displayed.
• Large fi les such as those required
for Off Board Navigation can be
communicated across the non-
contiguous network.
• Electronic payments can be conducted
at speed.
VII’s leadership team came to
the initial conclusion that DSRC
wireless communication together
with the POC network architecture
807AESR1.indd 16 10/2/2008 4:11:53 PM

can serve diverse applications
required for safety, mobility and
commercial applications. However,
some wireless experts believe the
protocol used in the current POC
testing is inadequate for real-time
safety — one of the major applications
unique to DSRC.
Avoiding Collisions
While DSRC was being developed,
a number of parallel efforts
were being pursued by communications
companies seeking to establish
their piece of the navigation services
and entertainment pie. “Purely
from a technical perspective, the
cell phone guys are not there to solve
the safety problems,” said Subir
Biswas, Associate Professor and the
Director of the Networked Embedded
and Wireless Systems Laboratory
at Michigan State University. “If
safety is the main concern with
ultrafast message delivery, you need
different protocols.” For safetyrelated
systems, avoiding message
collisions is key to avoiding vehicle
collisions.
Medium Access Control (MAC)
protocols generally can be classified
in two broad categories. The first is
random access protocols. “The Wi-Fi
protocol, 802.11, fundamentally is a
random access protocol,” said
Biswas. With a random access protocol,
the main problem is delay or
latency. When a vehicle wants to
send a message and when it actually
sends the message is unpredictable.
Message delivery depends on the
behavior of others.
The other protocol is Time Division
Multiple Access (TDMA), where
time slots are allocated so each node
gets a chance to communication in
an assigned slot. This approach is
predictable since they are allocated.
In contrast, in the random access
protocol, the unbounded delay can
occur when all nodes are trying to
send in an uncoordinated manner.
“It is really chaos that can happen,
which is also known as a collision
storm,” explained Biswas.
An ideal solution does not exist
today, so additional development
experience the drive
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Figure 4. Within a time slot, in a self-organizing TDMA-based architecture, a ranging
signal occupies the full bandwidth and following the ranging signal, the band is divided
into sub-bands. Source: ACS.
work is required. In a 2007 IEEE
paper [5] , Biswas discusses a Vehicular
Self-Organizing MAC (VeSOMAC)
with an in-band signaling technique.
As shown in Figure 3, in a cooperative
collision avoidance (CCA) application,
vehicle A sends a message alerting
vehicles to slow down. The message
should be forward by all vehicles
across the platoon with minimum
latency. The regular TDMA scheme in
Figure 3b uses arbitrary slot allocation
and takes three frames to reach
vehicle D. In contrast, with the proposed
VeSOMAC, the slots are allocated
based on the vehicle’s relative
location, signifi cantly reducing the
delivery delay.
The concern goes beyond the
academic world. The DSRC uses carrier
sense multiple access (CSMA) but
the latency of CSMA is undefi ned.
“For a real-time safety system, the
latency of that (CSMA) is too great,”
said Milt Baker president and co-
18 AUTO ELECTRONICS | JULY/AUGUST 2008
founder of Automotive Communications
Systems, a company that has
expertise in wireless communication
systems. The company has a patent
pending for a TDMA scheme that
could solve the problem [6] .
With all the testing performed in
the VII test environment, the delay
problem could have occurred but
apparently did not. “They do not have
a lot of cars running, so it is diffi cult to
determine if there will be channel
interference,” countered Baker. Simply
turning the message rate up will
not provide the confi dence that the
problem will not occur. Since each car
has a different back-off time, two
cars going faster does not simulate
lots of cars.
On a busy highway with six to
eight lanes of traffi c, theoretically several
hundred to a thousand cars could
try to communicate with each other if
they are all connected to the same
access point. If there is an accident or
traffi c fl ow stoppage, all vehicles
may want to transmit at the same
time. Figure 4 shows how an out
of range vehicle can receive
timely input using ACS’s TDMA
architecture.
Besides the contention
problem, there are two other
problems according to Baker. VII
wants to be able to resolve the
position of each car within one
foot. “Without differential GPS,
no one knows how to do that
today,” said Baker. “With different
GPS there is a latency issue
there, too, because you have to
calculate the GPS equations and
the car is moving down the road
and you get positional inaccuracy.”
The third issue is the multipath
problem that can occur due
to the conventional modulation
in today’s DSRC radios that use
Orthogonal Frequency Divisional
Multiplexing (OFDM). Baker noted
that the telecommunications industry
has essentially gone away from
OFDM because it is subject to multipath.
A new standard called Coded
Orthogonal Frequency Division Multiplex
(COFDM) is used in digital video
broadcast to the handhelds in Europe,
real-time video for surveillance and
WiMAX.
ASC believes its patent solves the
contention issue. “Once you solve the
contention issue, we believe that you
can add the one foot position accuracy
by using time of fl ight from the
cars and we believe that with the
COFDM modulation, those three
things together, you have a much better
system and to our mind, it’s lower
in cost than the path the industry is
going down today.”
Knowing how many cars are in
the ring, strictly defi nes the latency in
a TDMA protocol. The problem is a
TDMA system requires a master to
807AESR1.indd 18 10/2/2008 4:11:54 PM

determine who is going to talk. Since a
master does not exist in the automotive
environment, a new approach is
required. ACS’s solution involves cars
self-assigning time slots in a dynamic
situation. The time slot is preserved so
each car has its unique time to talk
and the latency is defi ned. VII has a
latency requirement of 100 ms. Baker
insisted, “It looks to us like the system
can be architected, so even with 400
cars or however many cars, you can
still maintain 100 ms latency and give
each car an access to the channel.”
The need for a time-critical bus
has already been recognized by automakers
for communication in
onboard safety systems. CAN is not a
deterministic bus, so automakers and
tier one suppliers developed FlexRay,
a deterministic bus developed initially
for safety systems. However, to date
the problem has not been observed in
the VII testing.
According to Baker, the process
to get from patent to POC involves
simulation to make sure that they
have a sound basis for proceeding.
This activity is being pursued. The
next step would be to create a fi eldprogrammable
gate array (FPGA) to
build hardware with the software to
provide a drop-in replacement for the
existing radio. Then comparison testing
could be conducted by switching
from the current to the proposed
approach.
Encouraged by the architecture
disclosed in ACS’ patent, STMicroelectronics
has already established a
partnership with ACS. In doing so,
STM supports the possibility of resolving
some of the major challenges facing
the VII initiative such as channel
access, reliability of communications,
and precision vehicle location at a
much lower cost than current solutions.
Based on the result of testing
with an FPGA version, STMicroelectronics
could investigate what it takes
for a chip implementation using their
standard cell library. Figure 5 shows
the circuitry involved to implement
the ACS concept, which is explained
in greater detail in references [6,7] .
ConTEnTion REsolUTion
With all the effort that VII participants
invested in the current 802.11p,
the need for a bounded TDMA protocol
is certainly an unpopular message
— one of contention. Since DSRC is
quite far along in their process, the
change from 802.11p to TDMA can be
considered as a disruptive event, even
though it has technical benefi t
insisted MSU’s Biswas. Until there is
suffi cient testing to verify whether a
bounded protocol is required or not,
the current activity will continue.
With the success experienced so far, if
there is a latency problem, it will be
eventually be uncovered.
References:
1. “1-2-3 Red Light!,” Auto Electronics
Nov/Dec 2007.
2. “Vehicle to Vehicle or Vehicle to
Roadside Communications?,” Auto
Electronics, Nov/Dec 2006.
3. “Making Vehicles and Highways in
Intelligent,” Auto Electronics, Nov/Dec 2005.
4. David Henry, “VIIC Program Progress,”
presentation at Telematics Update
2008, May 21, 2008.
5. Fan Yu and Subir Biswas, “Self-
Confi guring TDMA Protocols for
Enhancing Vehicle Safety With
DSRC Based Vehicle-to-Vehicle
Communications,” IEEE Journal on
Selected Areas in Communications, vol.
25, No. 8, October 2007.
6. International Publication No. WO
2007/133264 A2, “Integrated Vehicular
Positioning and Integrations Scheme.”
7. Milt Baker and Lawrence Hill, “A
Safety Communications Protocol for
V2V and V2I,” Auto Electronics, July/
August 2008.
ABOUT THE AUTHOR
Randy Frank is president of Randy
Frank & Associates Ltd., a technical
marketing consulting fi rm based in
Scottsdale, AZ. He is an SAE and
IEEE Fellow and has been involved
in automotive electronics for more
than 25 years. He can be reached at
r.frank@ieee.org.
Figure 5. The transceiver logic block diagram shows the RF and digital elements in the
TDMA architecture. Source: ACS.
JULY/AUGUST 2008 | AUTO ELECTRONICS
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