Current Trends in Vehicular Ad Hoc Networks

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					     Current Trends in Vehicular Ad Hoc Networks
                               ∗                                  ∗
 Ghassan M. T. Abdalla , Mosa Ali Abu-Rgheff                          and Sidi Mohammed Senouci ∗∗
              ∗
                     University of Plymouth – School of Computing, Communications & Electronics
                                                Mosa Ali Abu-Rgheff
                                      Mobile Communications Network Research
                                           Portland Square Building A206
                                                     Drake Circus
                                             Plymouth Devon PL4 8AA
                                                         UK
                                               Tel (+44) 1752 23 35 13
                                           Email : mosa @plymouth.ac.uk
                ∗∗
                     France Telecom – R & D Lannion Cedex - France




Abstract
Vehicular Networks are receiving a lot of attention due to the wide variety of services they can
provide. Their applications range from safety and crash avoidance to Internet access and
multimedia. A lot of work and research around the globe is being conducted to define the
standards for vehicular communications. These include frequency allocation, standards for
physical and link layers, routing algorithms, as well as security issues and new applications. In
this paper we review the standardization work and researches related to vehicular networks and
discuss the challenges facing future vehicular networks.

Index Terms−− DSRC, IEEE 802.11, MAC, Routing, Security, UTRA-TDD, Vehicular
           −
communications, WAVE.
      Current Trends in Vehicular Ad Hoc Networks
     Ghassan M. T. Abdalla, Mosa Ali Abu-Rgheff and Sidi Mohammed Senouci

Abstract                                            reliability and scalability are of concern. VANET
Vehicular Networks are receiving a lot of           therefore is not an architectural network and not
attention due to the wide variety of services       an ad hoc network but a combination of both; this
they can provide. Their applications range          unique characteristic combined with high speed
from safety and crash avoidance to Internet         nodes complicates the design of the network.
access and multimedia. A lot of work and                 In this paper we provide an overview of the
research around the globe is being conducted        technologies and ongoing research related to
to define the standards for vehicular               VANET. The history and the first generation
communications. These include frequency             VANET systems around the world are reviewed
allocation, standards for physical and link         in the next section. Current frequency allocation
layers, routing algorithms, as well as security     and physical layer standards are presented in
issues and new applications. In this paper we       section three. In section four the WAVE and
review the standardization work and                 IEEE 802.11p standards for vehicular
researches related to vehicular networks and        communications are discussed. The fifth part
discuss the challenges facing future vehicular      presents link layer, routing and broadcasting
networks.                                           algorithms designed and studied in the European
                                                    project FleetNet. An overview of VANET
Index Terms−− DSRC, IEEE 802.11, MAC,
           −                                        applications is provided in section six along with
Routing, Security, UTRA-TDD, Vehicular              some current prototypes of these applications. A
communications, WAVE.                               discussion about security issues followed by
                                                    open research problems are presented in sections
1. Introduction                                     seven and eight, and then finally the paper is

M      illions of people around the world die
       every year because of car accidents and
many more are injured. Implementations of
                                                    concluded.

                                                    2. Background of Vehicular Communications
safety information such as speed limits and road         The original motives behind vehicular
conditions are used in many parts of the world      communications were safety on the road, many
but still more work is required. Vehicular Ad       lives were lost and much more injuries have been
Hoc Networks (VANET) should, upon                   incurred due to car crashes. A driver realising the
implementation, collect and distribute safety       brake lights of the car in front of him has only a
information to massively reduce the number of       few seconds to respond, and even if he has
accidents by warning drivers about the danger       responded in time cars behind him could crash
before they actually face it. Such networks         since they are unaware of what is going at the
comprise of sensors and On Board Units (OBU)        front. This has motivated one of the first
installed in the car as well as Road Side Units     applications for vehicular communications,
(RSU). The data collected from the sensors on       namely cooperative collision warning which uses
the vehicles can be displayed to the driver, sent   vehicle to vehicle communication [1]. Other
to the RSU or even broadcasted to other vehicles    safety applications soon emerged as well as
depending on its nature and importance. The         applications for more efficient use of the
RSU distributes this data, along with data from     transportation network, less congestion and faster
road sensors, weather centres, traffic control      and safer routes for drivers. These applications
centres, etc to the vehicles and also provides      cannot function efficiently using only vehicle to
commercial services such as parking space           vehicle      communications        therefore     an
booking, Internet access and gas payment. The       infrastructure is needed in the form of RSU.
network makes extensive use of wireless             Although safety applications are important for
communications to achieve its goals but although    governments to allocate frequencies for vehicular
wireless communications reached a level of          communications, non-safety applications are as
maturity, a lot more is required to implement       important for Intelligent Transportation Systems
such a complex system. Most available wireless      (ITS) for three reasons [2]:
systems rely on a basestation for synchronization   1) ITS systems rely on essential equipment
and other services; however using this approach          which should be installed in every car and is
means covering all roads with such infrastructure        widely available to the users. However, it is
which is impractically too expensive. Ad hoc             unlikely that individuals can afford such
networks have been studied for some time but             expensive equipment.
VANET will form the biggest ad hoc network          2) Safety applications generally require limited
ever implemented, therefore issues of stability,         bandwidth for short intervals of time. Since
     bandwidth efficiency is an important factor,
     non-safety applications are important to                                         Optional                      Optional
     increase bandwidth efficiency.                                                   20MHz                         20MHz
                                                                                                    Control
3) The availability of RSU provides an
                                                                        Ch            Ch        Ch Ch           Ch            Ch            Ch
     infrastructure which can be used to provide a                      172           174       176 178         180           182           184
     lot of services with only a little increase in
     cost.




                                                            5.850
                                                                    5.855

                                                                              5.865

                                                                                            5.875

                                                                                                    5.885

                                                                                                            5.895

                                                                                                                      5.905

                                                                                                                                    5.915

                                                                                                                                                  5.925
                                                                                                                                                          GHz
     Besides road safety, new applications are
proposed for vehicular networks, among these
are Electronic Toll Collection (ETC), car to                Fig (1): DSRC bands in North America.
home communications, travel and tourism
information distribution, multimedia and game               OFDM is a multi-carrier modulation scheme.
applications just to name a few. However these         Data is split into multiple lower rate streams and
applications need reliable communication               each stream is used to modulate one of the
equipment which is capable of achieving high           subcarriers. Since the data rate is reduced, lower
data rates and stable connectivity between the         bandwidth is required for each carrier. The
transmitter and the receiver under high mobility       carriers are spaced at intervals of 1/T, where T is
conditions and different surroundings.                 the symbol duration; therefore they are
     Different frequencies for VANET were              orthogonal to each other. Although high data
allocated in different parts of the world. In North    rates can be achieved using OFDM, the
America       the     Dedicated     Short     Range    performance of OFDM can degrade rapidly if
Communications (DSRC) band 902-928 MHz                 careful considerations for synchronization and
was allocated. It provided short range                 channel variations are not taken. OFDM is
communications (<30m) and low data rates (500          sensitive to frequency and phase errors [6, 7].
kbps). It is still used for some types of electronic   Because the subcarriers are very close to each
toll collection systems but its performance is too     other, any drift in the frequency causes Inter
limited to satisfy the demanding requirements of       Carrier Interference (ICI). In VANET the high
ITS applications.                                      relative speeds between vehicles on opposite
     In Japan the bands 5835-5840 and 5845-            sides or between the vehicle and the RSU cause
5850 MHz were allocated for uplink and 5790-           an increase in the received frequency as the
5795 and 5800-5805 MHz for downlink for the            vehicles move towards each other and a decrease
Association of Radio Industries and Businesses         as vehicles move away due to the Doppler effect.
standard ARIB STD-T55. The system relies on            This must be taken into account during the
road architecture, as with DSRC, and provides          design of the receiver as it destroys the
ETC service. The standard uses ASK modulation          orthogonality of the carriers and increases ICI [8].
for a data rate of 1Mbps with 8 slot- TDMA/FDD              IEEE 802.11a standard uses 64 carriers, 48
to provide service for a maximum of 8 cars             are dedicated for data, 4 are pilot carriers and the
within a range of 30m. Currently a new standard        other carriers are not used to reduce interference
(ARIB STD-T75) is being developed [3].                 to other bands. Training sequences are used at the
     These systems can be regarded as the first        beginning of the packet for training and the pilot
generation for vehicular communications. The           carriers channel response is extrapolated to
different standards and frequencies have hindered      estimate the channel response for the other
the implementation of ITS systems since each           carriers [9]. This scheme performed well with
country has its own specifications and operating       WLAN since the terminals had limited mobility,
system. Moreover the low data rates and short          however with VANET the terminals can move in
distances were only suitable for a limited number      speeds of 100 km/hr or more. To illustrate this
of applications.                                       consider two cars moving in opposite directions
                                                       each with speed of 150 km/hr. At 5.9 GHz this
3. Physical Layer                                      results in a Doppler Shift of 2 kHz, yielding a
In    1999     the    Federal    Communications        channel coherence time of 250 µs. The maximum
Commission (FCC) allocated a new 75 MHz                length of an IEEE 802.11 packet is 18768 bits
band DSRC at the 5.9 GHz frequency for ITS             and at 54 Mbps this takes 348 µs to be
applications in North America. The band is             transmitted. Note that 54 Mbps is the maximum
divided into 7 channels as shown in Fig. (1) [4].      data rate, if the nodes are using a lower data rate
     A physical layer standard is being developed      (e.g. 6 Mbps) this will take much longer.
by the American Society for Testing and Material       Therefore the training sequence at the start of the
(ASTM) known as the ASTM E2213 standard. It            frame will lose its significance at the end of the
uses      Orthogonal      Frequency      Division      packet and whether the 4 pilot carriers are
Multiplexing (OFDM) as its modulation scheme           significant to estimate the channel or not is a
and covers distances up to 1 km [5].                   matter of concern.
     In Europe a spectrum aligned with the                                   Wireless Access for Vehicular Environment
DSRC spectrum in North America is being                                      (WAVE) Resource Manager. It defines the
considered as shown in Fig (2) [10]. The band                                services and interfaces of the WAVE resource
5.885 to 5.905 GHz in the form of two 10 MHz                                 manager application as well as the message and
channels is expected to be allocated first                                   data formats. It provides access for applications
followed by the rest of the spectrum [11]. The                               to the other architecture. P1609.2 defines security,
adaptation of UTRA-TDD for VANET                                             secure message formatting, processing, and
communications was studied in the FleetNet                                   message exchange. P1609.3 defines routing and
project but this is still an open area and some                              transport services. It provides an alternative for
projects adapt IEEE 802.11 for their studies.                                IPv6. It also defines the management information
UTRA-TDD standard, however, can provide a                                    base for the protocol stack. P1609.4 covers
maximum data rate of 2 Mbps for still nodes and                              mainly how the multiple channels specified in the
384kbps for mobile nodes [3].                                                DSRC standard should be used. The WAVE
                                                                             stack uses a modified version of IEEE 802.11a
              Part 2                  Part 1              Part 2             for its Medium Access Control (MAC) known as
                        Road                                                 IEEE 802.11p [12, 13]. The protocol architecture
           Non-                        Critical              Road
                        safety                                               defined by IEEE is shown in Fig (4) and the
          safety-                       road              safety and
                         and
          related
                       traffic
                                       safety               traffic          WAVE standards in Fig (5) [13].
                                      IVC and             efficiency
                       efficie-
                                        R2V
                         ncy
         IVC and                      Focus on            IVC and                                Applications
           R2V                          IVC                 R2V
                       IVC and
                         R2V
                                  Channel
                                  Control




                                                          Focus on
                      Focus on
                                                            R2V                 Management Plane            Data Plane
                        R2V

5.850     5.865     5.875     5.885               5.905              5.925             WME           UDP         WAVE Short
                               GHz
                                                                                                                  Message
        Fig (2): Frequency Proposal in Europe.                                                       IPv6

                                                                                                      Logic Link Control
     In Japan the new ARIB STD-T75 standard
                                                                                             MLME   Medium Access Control
uses 14, 4.4 MHz channels, 7 for downlink and 7
for uplink as shown in Fig (3). The standard uses                                            PLME            Physical
ASK to provide a data rate of 1Mbps and QPSK
to provide 1 or 4 Mbps. It also makes use of 8
slots TDMA/FDD to provide service to a                                                                        Medium
maximum of 56 cars within a range of 30m. The                                            Fig (4): IEEE architecture
system provides ETC service as well as
information shower [3]. For Inter-Vehicle
Communication (IVC) cars need to communicate                                    P1609.1      Upper Layers
in an ad hoc manner. Since no infrastructure is                                 and others
                                                                                                                           P1609.2




present, cars in the road form a temporary group                                              Networking        WAVE
in order to use the standard to exchange                                          P1609.3                       Security
                                                                                               Services
information.
                                                                                 P1609.4     Lower Layers
          4.4MHz
                        Downlink                                                 802.11p


                                                                                               Medium
   5.775 5.780 5.785 5.790 5.795 5.800 5.805 5.810 GHz

                            Uplink
                                                                                         Fig (5): WAVE standards

   5.810 5.815 5.820 5.825 5.830 5.835 5.840 5.845 GHz                           IEEE 802.11p is still under development.
                                                                             The draft specifies data rates from 3 to 27 Mbps
                                                                             for 10 MHz channels and 6 to 54 Mbps for 20
      Fig (3): ARIB STD-T75 frequencies.
                                                                             MHz channels. Nodes communicate with each
4. IEEE Standards
                                                                             other in an ad hoc fashion known as Wireless
     While ASTM E2213 standard is being
                                                                             Access for Vehicular Environment (WAVE)
developed, the IEEE standards IEEE P1609.1,
                                                                             mode. RSU form a Basic Service Set with the
P1609.2, P1609.2 and P1609.4 were prepared for
                                                                             vehicles, known as WAVE BSS (WBSS) in order
vehicular networks. P 1609.3 is still under further
                                                                             to    communicate.      RSU       sends    WBSS
development but the other three were recently
                                                                             announcement frames and vehicles can
released for trial use. P1609.1 is the standard for
optionally join the WBSS. Authentication and         VANET changes frequently, the signalling
association routines are not performed in WBSS       messages of proactive protocols can result in a
and the Point Coordination Function (PCF) will       large overhead load. PBF and CBF use location
not be used in this standard. Data priorities are    service algorithms to find the position of the
handled using Enhanced Distributed Channel           destination, based on this position PBF selects
Access (EDCA) as defined in the IEEE 802.11e         one of the surrounding nodes to forward the
standard. The protocol can operate in the            message. This process is repeated till the
European and Japanese frequencies [12, 14].          message reaches it destination. In CBF the source
     The use of Request To Send/Clear To Send        transmits the message with the position of the
(RTS/CTS) packets and windows in IEEE                destination; every node receiving the message
802.11p does not solve the hidden/exposed            sets a timer inversely proportional to the
terminals in the ad-hoc Vehicle-to-Vehicle (V2V)     difference between its position and the
communications mode due to the high mobility         destination. If the timer expires and no other
of the terminals. A packet between two stationary,   node has broadcasted the message, the node
or slowly moving, vehicles passing all the           forwards the message to the destination. In
Distributed Coordination Function (DCF)              AODV the source floods the network with a
constraints can still collide with another packet    route request for the destination. Nodes receiving
sent from a fast moving (or in the opposite lane)    the request calculate a distance vector and
vehicle unaware of the RTS/CTS handshake.            forward the message, this process is repeated till
This scenario can occur rapidly in V2V networks      the destination is reached which sends a route
causing very low throughput.                         reply. Once the reply is received the route is
                                                     ready for sending the data. To reduce the
5. FleetNet Project                                  flooding effects maximum hop count and Time
     In Europe the FleetNet project studied the      To Live (TTL) fields are used in route messages.
extension of the UTRA-TDD standard for               Simulations show that CBF performs better than
decentralised vehicular networks. An ad-hoc          the other algorithms and it adapts to changes in
mode of UTRA-TDD known as Opportunity                the topology which interrupt routes in the other
Driven Multiple Access (ODMA) can provide            two protocols. CBF, however, requires the
access to approximately five nodes within            assistance of maps in cities when multiple roads
coverage range but relies on a basestation for       intersect and run in parallel, its performance in
synchronization. Since a basestation is not          congested areas also requires more investigation
always available to provide synchronization, a       since several cars might have the same distance
new ad-hoc proposal based on UTRA-TDD was            to the destination which might cause collisions
introduced [15]. The new modified UTRA-TDD           [21, 22].
achieves synchronization in two steps, first using         A broadcasting algorithm based on CBF has
GPS to achieve coarse synchronization between        also been suggested for safety applications. A car
nodes, then using a midample to achieve fine         encountering an accident broadcasts a safety
synchronization [16, 17]. The standard uses          message and its current position. Other cars
TDMA slots with 16 CDMA codes for every slot.        receiving this message set a retransmission timer
Reserve slots are used by the nodes to reserve a     inversely proportional to their distance from the
slot prior to communication while high priority      source and re-broadcast the message if no other
data are transmitted via separate dedicated slots    node broadcasts first and keeps re-broadcasting
[18]. Simulations showed that the modified           till it receives a message from another node or
UTRA-TDD outperformed the IEEE 802.11b               the message is no longer relevant [23].
[19]. The proposed access mode was extended
afterwards to work with several frequencies [20].    6. Applications of VANET
     Broadcasting and routing algorithms for              A large number of applications have been
VANET were also studied in FleetNet project.         specified by governments for DSRC applications,
Their focus was on using the positioning             we cover here a few of them. Traffic control is a
information provided by GPS for routing and          major factor for efficient use of the network.
broadcasting. Three routing protocols were           Currently traffic lights organize the flow of
considered, Position Based Forwarding (PBF),         traffic at junctions. With DSRC traffic lights
Contention Based Forwarding (CBF) and Ad hoc         become adaptive to the traffic and can provide
On-Demand Distance Vector (AODV). All these          priority to emergency vehicles as well as safety
protocols are reactive protocols. Reactive           to pedestrians and cyclists. Moreover information
protocols discover the route to a destination only   about the status of the road can be distributed to
when a message is to be delivered counter to         cars to warn them of problems ahead such as ice
proactive protocols which tend to store routing      or maintenance work on the road. This system
tables for every destination and update these        will also be very efficient in the case of accidents,
routing tables continuously. As the topology of      automatically notifying the nearest ambulance
and other emergency vehicles to approach the          the best two routes. The routes are compiled from
accident if needed and even provide telemedicine      a 9 months survey as well as simulations. In its
services if the patient requires immediate            final version the system should be able to collect
attention, especially when there are no nearby        data from the sensors installed in cars and
hospitals. Crash prevention is the main motive        provide the routes to the OBU [25].
behind ITS, therefore a number of applications             The       Vehicle      Information       and
have been specified. Crash prevention                 Communication System (VICS) is another
applications that rely on an infrastructure include   Japanese implementation of roadside to vehicle
road geometry warning to help drivers at steep or     communications. Subscribers to the system get
curved roads and warn overweight or overheight        an onboard navigation system that receives
vehicles, highway-rail crossing and intersection      weather, road conditions, traffic information and
collision systems to help drivers cross safely,       any other related data from road side units and
pedestrian, cyclist and animal warning systems to     displays them to the user [26].
inform drivers of possible collisions, these               In Europe the eSafety initiative was
systems become of vital importance at night or        launched in April 2002. Currently it has 14
under low visibility conditions [1].                  workgroups working in the areas of accident
     Safety applications which do not rely on an      causation analysis, communications, digital maps,
infrastructure include an emergency brake             Emergency Call (eCall), heavy duty vehicles,
announcement which is the most important              Human-Machine Interaction (HMI), information
application for crash prevention. The first two       and communication technologies for clean
cars might not benefit from the emergency brake       mobility, implementation road map, international
system but further cars can avoid the crash. Lane     cooperation, Real-time Traffic and Travel
change assistance, road obstacle detection, road      Information (RTTI), research and development,
departure warning as well as forward and rear         security, service-oriented architectures and user
collision warning are all examples of safety V2V      outreach. The eSafety forum aims to accelerate
applications. Vehicles can also automatically         the development, deployment and use of eSafety
send help requests in case of accidents which can     systems to reduce the number of fatalities in
be vital when no other cars are around [1]. An        Europe to 50% by 2010 [24].
ongoing European project, eCall, aims at
providing this automatic call service by 2009         7. Security issues
using existing cellular infrastructure [24]. The           The ongoing Network On Wheels (NOW)
OBU system can also help the driver in other          project addresses a number of issues in vehicular
different ways such as vision enhancement via         networks with a focus on security. The project
image processing techniques, lane keeping             adopts an IEEE 802.11 standard for wireless
assistance and monitoring of onboard systems as       access and aim at implementing a reference
well as any cargo or trailers connected to the        system. The project addresses a number of
vehicle. Such systems are generalised as              security issues for VANET [27]. VANET
Advanced Driver Assistance Systems (ADAS)             security should satisfy four goals, it should
[24].                                                 ensure that the information received is correct
     The commercial applications of the system        (information authenticity), the source is who he
cover a wide range of innovative ideas aiding         claims to be (message integrity and source
individuals and tourists such as booking a            authentication), the node sending the message
parking place, downloading tourism information        cannot be identified and tracked (privacy) and the
and maps for restaurants and gas stations,            system is robust. Several attacks can be identified
navigation and route guidance, payment at toll        and these can be generalized depending on the
plazas, Internet access and connection to home        layer the attacker uses. At the physical and link
computers. Other devices within the vehicle can       layers the attacker can either disturb the system
also be connected to the On Board Units (OBU)         by jamming or overloading the channel with
to access any services provided by the network or     messages. Injecting false messages or re-
through the Internet. These applications are not      broadcasting an old message is also a possible
required by the government but they encourage         attack. The attacker can also steal or tamper with
people to install the system.                         a car system or destroy a RSU. At the network
     A Japanese project called P-DRGS                 layer the attacker can inject false routing
(Dynamic Route Guidance System) is one                messages or overload the system with routing
possible implementation of the navigation and         messages. The attacker can also compromise the
route service. This project is currently developing   privacy of drivers by revealing and tracking the
a system know as PRONAVI that consists of a           positions of the nodes. The same attacks can also
server accessible through the Internet. Users         be achieved using the application layer [28].
enter their start position, destination and time to        In the IEEE WAVE standard vehicles can
start their journey and the server responds with      change their IP addresses and use random MAC
addresses to achieve security [12]. Vehicles also     TDD is 2Mbps which is lower than the minimum
keep the message exchange to a minimum at the         data rate specified for IEEE 802.11p.
start of the journey for some time so that the             Efficient broadcasting algorithms are
messages can not be tied to the vehicle.              essential for delivery of safety and routing
     A number of security algorithms have been        messages. Routing protocols that rely on GPS
developed in France Telecom R&D department.           were introduced in section 5. However these
The security proposal provides security at the        protocols still require further investigations to
link layer for vehicle safety and commercial          attain their stability and capabilities to work
applications, higher layer security protocols can     when few cars are on the road as well as in
also be used to further enhance the security or       congested areas are of concern.
provide end to end security in a multihop link.             IP version 6 has been proposed for use in
     The proposal makes use of four types of          vehicular networks. Cars should be able to
certificates, two long term and two short term.       change their IP addresses so that they are not
One long term and one short term certificates are     traceable, however it is not clear how this will be
used for ITS services while the others are for        achieved. Moreover this can cause inefficiency in
non-ITS applications. Long term certificates are      address usage since when a new address is
used for authentication while short term              assigned the old address cannot be reused
certificates are used for data transmission using     immediately. Delayed packets will be dropped
public/private key cryptography.                      when the car changes its IP address which causes
     Safety messages are not encrypted as they        unnecessary retransmissions.
are intended for broadcasting, but their validity          Vehicular networks rely on distributed
must be checked; therefore a source signs a           untrustworthy nodes which should cooperate
message and sends it without encryption with its      with each other and with RSU. Issues of security
certificate, other nodes receiving the message        are a major concern for safety applications as
validate it using the certificate and signature and   well as for commercial applications. Any
may forward it without modification if it is a        developed security solution should meet the
valid message. Non-ITS data can rely on higher        diverse needs of the applications while taking
layer protocols to provide end-to-end security        into consideration the processing capabilities of
especially over a multihop link [29].                 the OBU. The network should also work with
                                                      minimum human interaction since otherwise it
8. Open Research Issues                               will divert the driver’s attention from the road.
     Vehicular networks introduce a new                    Other related research areas of great
challenging environment for communication             importance include sensor design, antenna design,
engineers. The communication channel can vary         OBU specifications, driver-OBU interface, RSU
from a simple point to point microwave link for       design, RSU to RSU communication network
cars in open areas, to rich Rayleigh fading within    specifications and VANET servers’ requirements
the cities. Moreover the channel varies               and software platform just to name a few. These
considerably every few seconds and line of sight      systems should cooperate in an efficient manner
blockage occurs frequently. Therefore the             to reach the ultimate goal of faster, safer and
physical layer commonly operates under various        information rich journeys on the road.
channel conditions and is expected to provide
high data rates even though the communication         9. Conclusion
time can be limited to a few seconds. Adaptive        In this paper we have provided an overview of
and efficient channel estimation algorithms are       the development of the communication standards
needed, diversity techniques to overcome fading       and ongoing research for vehicular networks.
effects should be examined and Doppler effects        Frequencies have already been allocated in North
should be carefully considered especially when        America and Japan and are expected soon in
using OFDM signalling.                                Europe. The IEEE 802.11p and WAVE suite
     The link layer is expected to provide various    were recently released for trial use. Routing
delay needs and QoS classes to satisfy the            protocols, broadcasting algorithms and security
different requirements of the applications. It        algorithms are being developed for vehicular
should also organize the access to the medium         networks as well as safety and commercial
and resolve collisions under high mobility            applications. Vehicular networks will not only
conditions. The RTS/CTS mechanism of IEEE             provide safety and life saving applications, but
802.11 will perform poorly in V2V                     they will become a powerful communication tool
communications because the nodes move very            for their users.
fast. UTRA-TDD provides a number of elegant
solutions but how it will perform under different     Acknowledgement
load conditions is a matter that requires further
investigation. The maximum data rate for UTRA-
The authors would like to thank France Telecom                    Evaluation of Computer and Telecommunication
and the University of Plymouth for supporting                     Systems SPECTS 2002 San Diego, CA, USA, July
this work.                                                        2002.
                                                           [19]   A. Ebner, H. Rohling, L. Wischhof, R. Halfmann,
                                                                  and M. Lott, "Performance of UTRA TDD Ad
References                                                        Hoc and IEEE 802.11b in Vehicular
[1] "ITS             Applications           Overview,"
                                                                  Environments," in IEEE Vehicular Technology
     http://itsdeployment2.ed.ornl.gov/technology_ove
                                                                  Conference. vol. 2 Jeju, South Korea, April 2003,
     rview/.
                                                                  pp. 960-964.
[2] K. Matheus, R. Morich, and A. Lübke,
                                                           [20]   M. Lott, R. Halfmann, and M. Meincke, "A
     "Economic        Background       of    Car-to-Car
                                                                  Frequency Agile Air-Interface for Inter-Vehicle
     Communication,"           http://www.network–on–
                                                                  Communication," in ICT 2003 Tahiti, Feb 23 -
     wheels.de/documents.html, 2004.
                                                                  March 1, 2003.
[3] K. Tokuda, "DSRC-Type Communication System
                                                           [21]   M. Torrent-Moreno, A. Festag, and H.
     for Realizing Telematics Services," Oki Technical
                                                                  Hartenstein, "System Design for Information
     Review, vol. 71, No.2, pp. 64-67, April 2004.
                                                                  Dissemination in VANETs," in 3rd International
[4] L. Armstrong, "Dedicated Short Range
                                                                  Workshop on Intelligent Transportation(WIT),
     Communications (DSRC) at 5.9 GHZ,"
                                                                  Hamburg, Germany, March 2006, pp. 27-33.
     Presentation,
                                                           [22]   M. Torrent-Moreno, F. Schmidt-Eisenlohr, H.
     http://www.leearmstrong.com/DSRC%20Home/St
                                                                  Füßler, and H. Hartenstein, "Packet Forwarding
     andards%20Programs/North%20American/DSR
                                                                  in VANETs, the Complete Set of Results," Dept.
     C%20Summary.ppt.
                                                                  of Computer Science Universität Karlsruhe (TH)
[5] "American Society for Testing and Materials
                                                                  2006.
     (ASTM)," www.astm.org.
                                                           [23]   M. Meincke, P. Tondl, M. Dolores, P. Guirao,
[6] M. C. D. Maddocks, "An Introduction to Digital
                                                                  and K. Jobmann, "Wireless Adhoc Networks for
     Modulation and OFDM Techniques," BBC
                                                                  Inter-Vehicle Communication," in Zukunft der
     Research Department Report No RD 1993/10
                                                                  Netze - Die Verlezbarkeit meistern, 16. DFN-
     1993.
                                                                  Arbeitstagung \über Kommunikationsnetze: GI,
[7] J. A. Stott, "The Effects of Frequency Errors in
                                                                  2002.
     OFDM," BBC Reseearch Department Report No
                                                           [24]   "eSafety Forum," http://www.escope.info/.
     RD 1995/15 1995.
                                                           [25]   T. Yamamoto, "Transportation and Safety In
[8] T. Wang, J. G. Proakis, E. Masry, and J. R.
                                                                  Japan," IATSS Research, vol. 29, pp. 110-113,
     Zeidler, "Performance Degradation of OFDM
                                                                  2005.
     Systems Due to Doppler Spreading," IEEE
                                                           [26]   J. Njord, J. Peters, M. Freitas, Bruce Warner, K.
     Transactions On Wireless Communications, vol.
                                                                  C. Allred, R. Bertini, R. Bryant, Robert Callan, M.
     5, pp. 1422-1432, June 2006.
                                                                  Knopp, L. Knowlton, C. Lopez, and T. Warne,
[9] B. O'Hara and A. Petrick, IEEE 802.11 Handbook
                                                                  "Safety Applications of Intelligent Transportation
     A Designer's Companion. New York: Institute of
                                                                  Systems in Europe and Japan," American Trade
     Electrical and Electronics Engineers Inc., 1999.
                                                                  Initiatives Jan. 2006.
[10] S. Hess, "Frequency spectrum for ITS,"
                                                           [27]   "Network On Wheels," http://www.network-on-
     COMeSafety July 2006.
                                                                  wheels.de/.
[11] "COMeSafety                                Forum,"
                                                           [28]   A. Aijaz, B. Bochow, F. D¨otzer, A. Festag, M.
     http://www.comesafety.org.
                                                                  Gerlach, R. Kroh, and T. Leinm¨uller, "Attacks
[12] "IEEE Draft P802.11p/D2.0, November 2006."
                                                                  on Inter Vehicle Communication Systems - an
[13] "IEEE Draft P1609.0/D01, February 2007."
                                                                  Analysis,"                        www.network-on-
[14] "IEEE Draft P802.11p/D0.25, November 2005."
                                                                  wheels.de/downloads/NOW_TechReport_Attacks_
[15] M. Lott, "Performance of a Medium Access
                                                                  on_Inter_Vehicle_Communications.pdf.
     Scheme for Inter-vehicle Communication," in
                                                           [29] C. Tchepnda, H. Moustafa, H. Labiod, and G.
     Proc.      of   International     Symposium      on
     Performance Evaluation of Computer and                       Bourdon,         "Securing       Vehicular
     Telecommunication Systems (SPECTS'02), San                   Communications An Architectural Solution
     Diego, California, July 2002.                                Providing     a     Trust   Infrastructure,
[16] A. Ebner, H. Rohling, R. Halfmann, and M. Lott,              Authentication, Access Control and Secure
     "Synchronization in Ad Hoc Networks Based on                 Data Transfer," IEEE Workshop AutoNet'2006,
     UTRA TDD," in Proceedings of the 13th IEEE                   San Francisco, USA, 27 November-1
     International Symposium on Personal, Indoor                  December 2006.
     and Mobile Radio Communications (PIMRC
     2002), Lisbon, Portugal, 2002.
[17] A. Ebner, H. Rohling, M. Lott, and R. Halfmann,
     "Decentralized Slot Synchronization In Highly
     Dynamic Ad Hoc Networks," in Proceedings of
     the 5th International Symposium on Wireless
     Personal        Multimedia         Communications
     (WPMC'02), Honolulu, Hawaii, 2002.
[18] M. Lott, "Performance of a Medium Access
     Scheme for Inter-Vehicle Communication," in
     International Symposium on Performance

				
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Description: Current Trends in Vehicular Ad Hoc Networks