Watch our demo on vehicular
GeoMAC: Geo-backoff Based Co-operative MAC for V2V Networks. Sanjit
Kaul, Marco Gruteser, Ryokichi Onishi, Rama Vuyyuru. IEEE International
Conference on Vehicular Electronics and Safety (ICVES), 2008.
Virtual Trip Lines for Distributed Privacy-Preserving Traffic
Monitoring. Baik Hoh, Marco Gruteser, Ryan Herring, Jeff Ban, Dan Work,
Juan-Carlos Herrera, Alexandre Bayen, Murali Annavaram, Quinn Jacobson.
ACM Mobisys, 2008.
Experimental Analysis of Broadcast Reliability in Dense Vehicular
Networks, Kishore Ramachandran, Marco Gruteser, Ryokichi Onichi, and
Toshiro Hikita. IEEE Vehicular Technology Magazine, 2(4), Dec 2007.
Preserving Privacy in GPS Traces via Density-Aware Path Cloaking. Baik
Hoh, Marco Gruteser, Hui Xiong, Ansaf Alrabady. ACM Conference on
Computer and Communications Security (CCS), 2007.
Effect of Antenna Placement and Diversity on Vehicular Network
Communications. Sanjit Kaul, Kishore Ramachandran, Pravin Shankar,
Sangho Oh, Marco Gruteser, Ivan Seskar, Tamer Nadeem. IEEE Conference on
Sensor, Mesh and Ad Hoc Communications and Networks (SECON), San Diego,
Enhancing Security and Privacy in Traffc-Monitoring Systems. Baik Hoh,
Marco Gruteser, Hui Xiong, Ansaf Alrabady. IEEE Pervasive Computing
Magazine (Special Issue on Intelligent Transportation Systems), 5(4), 2006.
This project seeks to develop networking protocols for reliable and trustworthy communication in automotive ad hoc networks. Automotive ad hoc networks are a challenging application due to high node mobility causing frequent network topology changes, low-latency interaction requirements, and privacy and security concerns. We meet these challenges by developing location-aware ad hoc network protocols, which address network nodes through their geographic position rather than conventional network addresses.
Maturing ad hoc wireless communications
and distributed computing technology enable novel distributed automotive
sensing and control systems with compelling applications, such as
preventing traffic accidents and improving traffic flow. Automotive
vehicle accidents still account for approximately 40,000 fatalities in
the US and are the leading cause of death for people aged 5-45 years.
Accidents are also a primary contributor
to congestion, which overall results in 5.7 billion person-hours of
wasted travel time annually in the US (2002 estimate). Current
technology seeks to address these challenges through in-vehicle sensing,
control systems (e.g., electronic vehicle stability control) and road
side infrastructure (e.g., dynamic traffic signs, ramp metering).
Significant additional potential can be
realized by combining these systems through wireless communications into
distributed sensing and control systems. Applications of such systems
include cars on collision course
warning each other and coordinating an evasive maneuver or cars can
their sensor readings to following vehicles to notify them of hazards
(e.g., slippery road conditions) and congestion levels.
These compelling applications have recently led the US Federal
Communications Commission (FCC) to approve radio spectrum for Dedicated
Short Range Communications, a networking standard for inter-vehicle and
vehicle to roadside communication and innovative uses, from cordless phones and wireless
LANs to meter readers and home entertainment products.
These diverse services will need to coexist with the emergence of a wide
variety of wireless devices, ranging from low bit rate sensors to
high resolution full motion video cameras. The combination of
increasing data rates and the proliferation of devices could easily
lead to inefficiency in the use of unlicensed spectrum due to a
combination of overuse and failure to develop mechanisms for
efficient sharing of this resource.
Realizing this vision requires protocols for highly reliable
communication between vehicles in severe fading channels, protocols that
scale to very high node densities, and addressing privacy concerns. To
this end, we have developed the GeoMAC protocol, conducted scalability
evaluations, and designed the virtual trip line concept, which are
GeoMAC exploits spatial diversity in highly
mobile wireless networks. It aims to achieve low latency and
high reliability, goals that are intrinsic to the success of many
envisioned vehicular safety applications. Conventional MAC
layers address reliability through ARQ mechanisms that retransmit messages from the source, if earlier transmissions were
not acknowledged. These schemes essentially exploit temporal
diversity since retransmissions are only likely to succeed if the
channel has improved. GeoMAC exploits spatial diversity, by
allowing other nearby nodes to opportunistically forward and
retransmit messages. Through a geo-backoff mechanism it uses
geographic distance to the destination as a heuristic to select
the forwarder most likely to succeed. This mechanism does
not require nodes to monitor channel state or position of their
neighbors, except for approximate node density, thus enabling
their use in highly mobile networks with low coordination
overhead. To date we have evaluted the performance of GeoMAC
using trace-driven ns2 simulation using packet error measurements from
a freeway environment. GeoMac leads to lower delay jitter
combined with up to 50% packet delivery rate gains, compared
to the AODV and GPSR routing protocols, which also take
advantage of nearby nodes for packet forwarding. Spatial
diversity is also shown to better utilize available channel
opportunities than ARQ mechanisms.
Dedicated Short Range Communications (DSRC)-
based communications enable novel automotive safety applications
such as an Extended Electronic Brake Light or Intersection
Collision Avoidance. These applications require reliable wireless
communications even in scenarios with very high vehicle density,
where these networks are primarily interference-limited. Given
the uncertainties associated with current simulation models, particularly
their interference models, it is critical to experimentally
validate network performance for such scenarios.
Towards this goal, we present a systematic, large-scale experimental
study of packet delivery rates in a dense environment
of 802.11 transmitters. We show that even with 100 transmitters
in communication range with a frame size of 128 bytes and
a bit-rate of 6Mbps, (a) most receivers can decode over 1500
pps in a saturated network, which corresponds to a packet
delivery rate of 45% and (b) the mean packet delivery rate,
for 10 pps per node workload that emulates vehicular safety
applications, is about 95%. These results demonstrate that a
COTS 802.11 implementation can correctly decode many packets
under collision due to physical layer capture and can serve as a
reference scenario for validation of network simulators.
Virtual Trip Lines:
Automotive traffic monitoring using probe vehicles
Positioning System receivers promises significant improvements in
cost, coverage, and accuracy. Current approaches, however, raise
privacy concerns because they require participants to reveal their
positions to an external traffic monitoring server. To address this
challenge, we propose a system based on virtual trip lines and an
associated cloaking technique. Virtual trip lines are geographic
markers that indicate where vehicles should provide location updates.
These markers can be placed to avoid particularly privacy
sensitive locations. They also allow aggregating and cloaking several
location updates based on trip line identifiers, without knowing
the actual geographic locations of these trip lines. Thus they facilitate
the design of a distributed architecture, where no single entity
has a complete knowledge of probe identities and fine-grained location
information. We have implemented the system with GPS
smartphone clients and conducted a controlled experiment with 20
phone-equipped drivers circling a highway segment. Results show
that even with this low number of probe vehicles, travel time estimates
can be provided with less than 15% error, and applying the
cloaking techniques reduces travel time estimation accuracy by less
than 5% compared to a standard periodic sampling approach.
Results To Date and Future Work
We are continuing the development of GeoMAC and plan to
test it on the vehicular ORBIT outdoor testbed. We are also designing
protocols for steerable antenna array systems on commuter vehicles to
efficiently communicate with roadside access points. Several additional projects on vehicular networks have been carried out or are in progress, including a study on reliable broadcast protocols, vehicular sensing for parking (ParkNet) and geographic content caching (GeoCache).
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