Chapter 8. Vehicle to Vehicle interactions (V2V)

Since the topology of the network is constantly changing, the issue of routing packets between any pair of nodes becomes a challenging task. In a MANET routers (i.e. hosts) can be mobile and inter -router connectivity can change frequently during normal operation. In contrast the Internet (like most of the telecom networks) possesses a quasi-fixed infrastructure consisting of routers or switches that forward data over hardwired links. Traditionally end-user devices, such as host computers or telephones, attach to these networks at fixed locations. As a consequence they are assigned addresses based on their location in a fixed network-addressing hierarchy. It simplifies routing in these systems, as a user’s location does not change.

The end devices are increasingly mobile, meaning that they can change their point of attachment to the fixed infrastructure. This is the paradigm of cellular telephony and its Internet equivalent, mobile data network. In this approach a user’s identity depends upon whether the user adopts a location-dependent (temporary) or location-independent (permanent) identifier. Users with temporary identifiers are sometimes referred to as nomadic, whereas users with permanent identifiers are referred to as mobile. The distinction is that although nomadic users may move, they carry out most network related functions in a fixed location. Mobile users must work “on the go” changing points of attachment as necessary. In either case additional networking support may be required to track a user’s location in the network so that information can be forwarded to its current location using the routing support within the more traditional fixed hierarchy.

Figure 8.4. Multi-hop routing (Source: http://sar.informatik.hu-berlin.de)

Internet is hardly tuned to allow mobility during the data transfers because protocols are not conceived for devices that frequently change their point of attachment in the topology. There is typically a change of the physical IP address each time a mobile node changes its point of attachment and thus its reachability to the Internet topology. This results in losing packets in transit and breaking transport protocols connections if mobility is not handled by specific services. The protocol stack must therefore be upgraded with the ability to cross networks during data transfers, without breaking the communication session and with minimum transmission delays and signalling overhead. This is commonly referred to as mobility support. Host mobility support is handled by Mobile IPv6.

In contrast, the goal of mobile ad hoc networking is to extend mobility into the field of autonomous, mobile, wireless domains, where a set of nodes, which may be combined routers and hosts, themselves form the network routing infrastructure in an ad hoc way. With Mobile Ad Hoc Networking, the routing infrastructure can move along with the end devices. Thus the infrastructure’s routing topology can change, and the addressing within the topology can change. In this paradigm an end-user’s association with a mobile router (its point of attachment) determines its location in the MANET. As mentioned above a user’s identity may be temporary or permanent. The fundamental differences in the composition of the routing infrastructure (fixed, hardwired, and bandwidth-rich opposite to dynamic, wireless, and bandwidth-constrained) causes that much of the fixed infrastructure’s control technology is no longer useful. The infrastructure’s routing algorithms and much of the networking suite must be reworked to function efficiently and effectively in mobile environment.

Figure 8.5. Multicast communication (Source: http://en.wikipedia.org/wiki/File:Multicast.svg)

Multicast routing (delivery of information to a group of destination devices simultaneously in a single transmission) is another challenge because the multicast tree is no longer static due to the random movement of nodes within the network. Routes between nodes may potentially contain multiple hops, which is more complex than the single hop communication.

In addition to the common vulnerabilities of wireless connection an ad hoc network has its particular security problems. Mobile hosts join in on the fly and create a network on their own. With the network topology changing dynamically and the lack of a centralized network management functionality, these networks tend to be vulnerable to a number of attacks. If such networks are to succeed in the transportation, the security aspect naturally assumes importance. The unreliability of wireless links between nodes, constantly changing topology owing to the movement of nodes in and out of the network and lack of incorporation of security features in statically configured wireless routing protocols not meant for ad hoc environments all lead to increased vulnerability and exposure to attacks.

Security in wireless ad hoc networks is particularly difficult to achieve, because of the vulnerability of the links, the limited physical protection of each of the nodes, the sporadic nature of connectivity, the dynamically changing topology, and the absence of a certification authority and the lack of a centralized monitoring or management point. This underscores the need for intrusion detection, intrusion prevention, and related countermeasures. The wireless links between nodes are highly susceptible to link attacks, which include the following threats (See [111]).

Eavesdropping might give an adversary access to secret information, violating confidentiality. Active attacks might allow the adversary to delete messages, to inject erroneous messages, to modify messages, and to impersonate a node, thus violating availability, integrity, authentication, and non-repudiation (these and other security needs are discussed in the next section). Ad hoc networks do not have a centralized piece of machinery such as a name server, which could lead to a single point of failure and thus, make the network that much more vulnerable.

An additional problem related to the compromised nodes is the potential byzantine failures encountered within Mobile Ad hoc Network (MANET) routing protocols wherein a set of the nodes could be compromised in such a way that the incorrect and malicious behaviour cannot be directly noted at all. The compromised nodes may seemingly operate correctly, but, at the same time, they may make use of the flaws and inconsistencies in the routing protocol to undetectably distort the routing fabric of the network. In addition such malicious nodes can also create new routing messages and advertise non-existent links, provide incorrect link state information and flood other nodes with routing traffic, thus inflicting byzantine failures on the system. Such failures are severe, because they may come from seemingly trusted nodes. Even if the compromised nodes were noticed and prevented from performing incorrect actions, the erroneous information generated by the byzantine failures might have already been propagated through the network.

Finally scalability is another issue that has to be addressed when security solutions are being devised, for the simple reason that an ad hoc network may consist of hundreds or even thousands of nodes. The scalability requirements directly affect the scalability requirements targeted to various security services such as key management. Standard security solutions would not be good enough since they are essentially for statically configured systems. This gives rise to the need for security solutions that adapt to the dynamically changing topology and movement of nodes in and out of the network.

These vulnerabilities allow a lot of special attacks in the vehicular networks including but not limited to the following examples:

Figure 8.6. Bogus information attack

As apparent from the above the security aspects are the most critical challenges before the wide spreading of the vehicular networks.

The goal of QoS support is to achieve a more deterministic communication behaviour, so that information carried by the network can be better prioritized and network resources can be better utilized. The notion of QoS is an agreement or a guarantee by the network to provide a set of measurable pre-specified service attributes to the user in terms of network delay, delay variance (jitter), available bandwidth, probability of packet loss (loss rate), etc. The IETF RFC 2386 characterizes QoS as a set of service requirements to be met by the network while transporting a packet stream from source to destination. A network’s ability to provide a specific QoS depends upon the properties of the network itself, which span over all the elements in the network. For the transmission link, the properties include link delay, throughput, loss rate, and error rate. For the nodes, the properties include hardware capability, such as processing speed and memory size. Above the physical qualities of nodes and transmission links, the QoS control algorithms operating at different layers of the network also contribute to the QoS support in networks. Unfortunately the features of MANETs show weak support for QoS. The wireless link has low, time-varying raw transmission capacity with relatively high error rate and loss rate. In addition, the possible various wireless physical technologies that nodes may use simultaneously to communicate make MANETs heterogeneous in nature. Each technology will require a MAC layer protocol to support QoS. Therefore the QoS mechanisms above the MAC layer should be flexible to fit the heterogeneous underlying wireless technologies. Providing different quality of service levels in a constantly changing environment will be a challenge. The inherent stochastic feature of communications quality in a MANET makes it difficult to offer fixed guarantees on the services offered to a device.

In addition to the communication within an ad hoc network, internetworking between MANET and fixed networks (mainly IP based) is often expected in many cases. The coexistence of routing protocols in such a mobile device is a challenge for the harmonious mobility management.

For most of the light-weight (handheld) mobile terminals and also the built-in automotive ECUs, the communication-related functions should be optimised for low power consumption. Conservation of power and power-aware routing must be taken into account.

The IEEE 802.11p WAVE standardization process originates from the allocation of the Dedicated Short Range Communications (DSRC) spectrum band in the United States and the effort to define the technology for usage in the DSRC band. The evolutions and the basics are explained in the following chapters from [112].

In 1999 the U.S. Federal Communication Commission allocated 75MHz of Dedicated Short Range Communications (DSRC) spectrum at 5.9 GHz to be used exclusively for vehicle-to-vehicle and infrastructure-to-vehicle communications. The primary goal is to enable public safety applications that can save lives and improve traffic flow. Private services are also permitted in order to spread the deployment costs and to encourage the quick development and adoption of DSRC technologies and applications.

As shown in Figure 126 the DSRC [113] spectrum is structured into seven 10 MHz wide channels. Channel 178 is the control channel (CCH), which is restricted to safety communications only. The two channels at the ends of the spectrum band are reserved for special uses. The rest are service channels (SCH) available for both safety and non-safety usage.

Figure 8.8. DSRC spectrum band and channels in the U.S.

The DSRC band is a free but licensed spectrum. It is free because the Federal Communications Commission (FCC) does not charge a fee for the spectrum usage. Yet it should not be confused with the unlicensed bands in 900 MHz, 2.4 GHz and 5 GHz that are also free in usage. These unlicensed bands, which are increasingly populated with WiFi, Bluetooth and other devices, place no restrictions on the technologies other than some emission and co-existence rules. The DSRC band, on the other hand, is more restricted in terms of the usages and technologies. FCC rulings regulate usage within certain channels and limit all radios to be compliant to a standard. In other words one cannot develop a different radio technology (e.g. that uses all 75 MHz of spectrum) for usage in the DSRC band even if it is limited in transmission power as related to the unlicensed band.

Similar efforts are occurring in Europe to set spectrum aside for vehicular usage. Since 2008 European Commission’s decision provides a single EU-wide frequency band that can be used for immediate and reliable communication between cars, and between cars and roadside infrastructure. It is 30 MHz of spectrum in the 5.9 Gigahertz (GHz) band which is allocated by national authorities across Europe to road safety applications, without barring other services already in place (such as radio amateur services). The intention is that compatibility with the USA will be ensured even if the allocation is not exactly the same; frequencies will be sufficiently close to enable the use of the same antenna and radio transmitter/receiver. (Source: [114])

The worldwide DSRC spectrum allocation is shown in Figure 127 [113].

Figure 8.9. DSRC spectrum allocation worldwide

In the U.S. the initial effort at standardizing DSRC radio technology took place in an American Society for Testing and Materials (ASTM) working group. In particular the FCC rule and order specifically referenced this document for DSRC spectrum usage rules. In 2004 this effort migrated to the IEEE 802.11 standard group as DSRC radio technology is essentially IEEE 802.11a adjusted for low overhead operations in the DSRC spectrum. Within IEEE 802.11 DSRC is known as IEEE 802.11p WAVE. IEEE 802.11p is not a standalone standard. It is intended to amend the overall IEEE 802.11 standard.

One particular implication of moving the DSRC radio technology standard into the IEEE 802.11 space is that now WAVE is fully intended to serve as an international standard applicable in other parts of the world as well as in the U.S. The IEEE 802.11p standard is meant to:

The IEEE 1609 family of standards defines the following parts (see [113]):

The primary architectural components defined by these standards are the On Board Unit (OBU), Road Side Unit (RSU) and WAVE interface.

The IEEE 1609.3 standard covers the WAVE connection setup and management. The IEEE 1609.4 standard sits right on top of the IEEE 802.11p and enables operation of upper layers across multiple channels, without requiring knowledge of PHY parameters. The standards also define how applications that utilize WAVE will function in WAVE environment. They provide extensions to the physical channel access defined in WAVE.

The third important standard related to vehicle communication is the J2735, Dedicated Short Range Communications (DSRC) Message Set Dictionary, maintained by the Society of Automotive Engineershttp://www.sae.org). This SAE Standard specifies a message set, its data frames and data elements specifically for use by applications intended to utilize the (DSRC/WAVE) communications systems. Although the scope of this Standard is focused on the message set and data frames of DSRC. This standard therefore specifies the definitive message structure and provides sufficient background information for the proper interpretation of the message definitions from the point of view of an application developer implementing the messages according to the DSRC standards.

It supports interoperability among DSRC applications through the use of standardized message sets, data frames and data elements. The message sets specified in J2735 define the message content delivered by the communication system at the application layer and thus defines the message payload at the physical layer. The J2735 message sets depend on the lower layers of the DSRC protocol stack to deliver the messages from applications at one end of the communication system (OBU of the vehicle) to the other end (a roadside unit). The lower layers are addressed by IEEE 802.11p, and the upper layer protocols are covered in the IEEE 1609.x series of standards.

The message set dictionary contains:

The most important message type is the basic safety message (often informally called “heartbeat” message because it is constantly being exchanged with nearby vehicles). Frequent transmission of “heartbeat” messages extends the vehicle’s information about the nearby vehicles complementing autonomous vehicle sensors. Its major attributes are the following [115]:

The other kinds of messages are the following (See [113]):

Safety use cases are those where a safety benefit exists when the vehicle enters into a scenario applicable to the use case. The following safety applications can be relevant with the help of V2V communication.

Figure 8.11. Hazardous location warning (source: http://car-to-car.org)

Figure 8.12. Privileging fire truck (source: http://car-to-car.org)

Figure 8.13. Reporting accidents (source: http://car-to-car.org)

Traffic Efficiency use cases are those meant to improve efficiency of the transportation network by providing information either to the owners of the transportation network or to the drivers on the network.

Figure 8.14. Intelligent intersection (source: http://car-to-car.org)

This category does not contain direct traffic related applications, rather comfort services. Many of these use cases interact more directly with the vehicle owner on daily basis providing entertainment or information on a regular basis. Others are transparent to the driver but still perform a valuable function such as increasing fuel economy.

The electronic payment applications result in convenient payments and avoiding congestions caused by toll collection and makes pricing more manageable and flexible.

The V2V communication system can support the currently available driver assistance systems. With help of the broadcasted vehicle parameters the adaptive cruise control and park pilot functions can be improved.

Figure 8.15. V2V based Cooperative-adaptive Cruise Control test vehicle. (Source: Toyota)

With special low-cost roadside units (RSU) the road sign recognition function can be supported and the reliability can be improved. In special cases it could offer safety functions in case of bridge or tunnel height or gate width.

Another important field of usage could be the policing and enforcement. Police could use the V2V communication in several ways especially checking the traffic rules such as: