Vehicular Communication
Technology
17.07.2016
Vehicular Communication Technology
1
Motivation


Safety and transport efficiency
 In Europe around 40,000 people die and more than 1.5 millions
are injured every year on the roads
 Traffic jams generate a tremendous waste of time and of fuel
Most of these problems can be solved by providing appropriate
information to the driver or to the vehicle
17.07.2016
Vehicular Communication Technology
2
Vehicle Communication (VC)

VC promises safer roads,

… more efficient driving,
17.07.2016
Vehicular Communication Technology
3
Vehicle Communication (VC)

… more fun,

… and easier maintenance.
17.07.2016
Vehicular Communication Technology
4
Smart Vehicle
Event data recorder (EDR)
Forward radar
Positioning system
Communication
facility
Rear radar
Display
17.07.2016
Computing platform
Vehicular Communication Technology
5
Approaches to vehicular communication
Communication using
dedicated infrastructures
Communication using
cellular systems
Direct Communication
17.07.2016
Vehicular Communication Technology
9
Vehicular Ad Hoc Network (VANET)

Ad-Hoc Network:




A network with minimal or no infrastructure
Self-organizing
Each node can act as the source of data, the
destination for data and a network router
Vehicular Ad Hoc network (VANET)


17.07.2016
Uses equipped vehicles as the network nodes
Nodes move at will relative to each other but
within the constraints of the road infrastructure
Vehicular Communication Technology
11
Differences VANETs from MANETs

Rapid Topology Changes


Frequent Fragmentation


Chunks of the net are unable to reach nodes in nearby regions
Small Effective Network Diameter


High relative speed of vehicles => short link life
A path may cease to exist almost as quickly as it was discovered
(reactive routing)
Limited Redundancy


17.07.2016
The redundancy in MANETs is critical to providing additional
bandwidth
In VANETs the redundancy is limited both in time and in function
Vehicular Communication Technology
12
Vehicular Ad Hoc Network (VANET)

Message propagates to destination using a
number of intermediate links
17.07.2016
Vehicular Communication Technology
13
Vehicular Ad Hoc Network (VANET)

If vehicle mobility causes links to break,
message rerouted using a different path
17.07.2016
Vehicular Communication Technology
14
Why use VANETS?

Easier deployment




Decreased dependency on fixed infrastructure
Sparse network of roadside beacons
Permit gradual introduction of technology
Location-oriented services can be provided
with little or no running costs to the users
17.07.2016
Vehicular Communication Technology
15
Lot of Involved Parties
17.07.2016
Vehicular Communication Technology
16
Major problems in this area

Communication / Networking

Localization
17.07.2016
Vehicular Communication Technology
17
Requirements on vehicular communication







Mobility
Delay bounded (real-time)
Scalability
Bandwidth efficiency
Cost
Fairness
Any time, any place, any hosts (GPS
unequipped vehicles, standardization
between cars’ manufactures)
17.07.2016
Vehicular Communication Technology
18
Addressing the challenges

Physical Layer


Link Layer


limited bandwidth
congestion control, latency, throughput, fairness
and scalability
Network (Routing) Layer

17.07.2016
rapid topology changes and network
fragmentation
Vehicular Communication Technology
19
Dedicated Short Range Communications
(DSRC)

DSRC operates at 5.9 GHz
17.07.2016
Vehicular Communication Technology
20
DSRC – Operating Characteristics






IEEE 802.11p protocol (802.11a modification
for VC)
Maximum range: 1000 m
Vehicle speeds up to 100 mph
Low latency: 50 ms
Application priority: 8 levels
Channel 172: vehicle safety only
17.07.2016
Vehicular Communication Technology
21
How does DSRC work?

Road-Side Unit (RSU)


Announces to OBUs 10 times per second
applications it supports on which channel
On-Board Unit (OBU)





17.07.2016
Listens on Channel 172
Executes safety applications first
Then switches channels
Executes non-safety applications
Returns to Channel 172 and listens
Vehicular Communication Technology
22
Channel allocation (MAC)


Existing MAC protocols (CSMA/CA, MACA,
MACA-BI) are contention-based => not delay
bounded
Proposed MCS/CDMA


17.07.2016
Each vehicle senses all the spreading codes,
finds a code that is not used by nearby vehicles,
and transmits data using the selected code
Search for free code, contention for free code (if
vehicles > codes) => large delays
Vehicular Communication Technology
23
Channel allocation (MAC)

Location-based Channel Access (LCA)





17.07.2016
The geographical area is divided into a cellular structure
Each cell has a unique channel associated with it
Multiple access scheme, such as CSMA/CA and
MCS/CDMA, can be used within each cell
Main design parameters: cell size and channel reuse
distance
Advantages: no central station for channel assignment,
no wait before transmit, no contention for free channels,
reuse of channels => delay bounded, fairness,
bandwidth efficiency, scalability and mobility
Vehicular Communication Technology
24
Routing Schemes

Proactive (table-driven)




Reactive (source-driven, on-demand)




Each node attempts to maintain a current representation of the
network topology
Advantage: lower message latency (routes are immediately
available)
Disadvantage: bandwidth overhead (to maintain routes),
restricted scalability
Routes are requested by source nodes only when needed
Advantage: bandwidth economy (no control messages for nonactive routes)
Disadvantage: latency (establishing a route)
Hybrid

17.07.2016
ZRP – proactive within zone, reactive outside zone
Vehicular Communication Technology
25
Major problems in this area

Communication / Networking

Localization
17.07.2016
Vehicular Communication Technology
27
GPS
17.07.2016
Vehicular Communication Technology
28
Space Segment
17.07.2016
Vehicular Communication Technology
29
How does GPS work?
17.07.2016
Vehicular Communication Technology
33
How do we compute Position?







GPS is a Distance (Range) Measuring System
Stable Frequency Standards in the Satellites and
Receivers
Able to compute a Clock Offset
Velocity of Radiowave is known
Thus Distance = V x T
Since the coordinates of the Satellites are known at
any point of time, with 4 ranges the position of the
GPS Antenna can be computed
3-D Trilateration: Distance, Distance, Distance and
Distance Intersection
17.07.2016
Vehicular Communication Technology
34
DGPS

Differential GPS can improve accuracy from several
meters to a few centimeters
17.07.2016
Vehicular Communication Technology
35
However…


Vehicles may be unequipped with GPS or sometimes
cannot obtain line-of-sight access to satellites (in
tunnels)
In order to discover their position (or at least driving
direction), GPS-U vehicles can use communication with
GPS-E vehicles




17.07.2016
GPS-U periodically broadcasts PREQ message to its one-hop
neighbors
When GPS-E receives PREQ, it sends back PREP message
including its current position
The knowledge of the exact position depends on the number of
neighbors sending PREP messages
GPS-U can compute its exact position if it receives at least three
PREP from three different vehicles (by triangulation)
Vehicular Communication Technology
36
Thank You!
17.07.2016
Vehicular Communication Technology
37