The report has main part as Results, which is divided into two parts "Radio" and "System" The radio part discusses the Modulation technique (OFDM), the second part Radio Definition explains the number of channels, channel bandwidth, and the purpose of the channels, and the finally the Existing Traffic System in detail. The system part elaborates the Intelligent Transport System and the most important issue in communication is the Security of the network and the information. Finally conclusion part makes the final words about the discussion. .
802.11p extention is one of the extentions under development for the 802.11 protocol. Being implemented in the traffic systems in vehicles and along the roads. The protocol is an extention to 802.11 and also extension to 802.11a/g as these protocols serves as basis for the development of 802.11p. Different services can be provided in the form of information about nearby traffic, the toll collection and the parking fee etc.
802.11p project is the part of ITS Intelligent Transport System, vision of an intelligent traffic system, possibly leading towards self driven vehicles in normal traffic.
Scope
This report explores 802.11p extention what it can provide. The already in place traffic systems which are providing help to vehicles and drivers (RDS) traffic information system will also be brought up and compared with 802.11p. As 802.11p is a public network so the security aspects has also been examined.
Results
We have divided the results in to two parts. The "Radio Part" which deals primly with the radio specifications for 802.11p extention, which includes the basic comparison to GPS / RDS, based traffic information systems.
The "System Part" deals with the intelligent systems in general, introducing the concepts of ITS and security of vehicular communications.
Radio
OFDM
OFDM is the combination of modulation and multiplexing to utilize the channel more effectively and increases the spectral efficiency. Which makes it the most used modulation Technology today. The basic working of OFDM in a channel is subdivided into multiple small narrow band channels and symbols are then transmitted through these sub channels. The orthogonality between the channels makes it possible that no one channel interferes the other. These are the modulation techniques for OFDM: BPSK.QPSK, 16QAM and 64QAM.
Radio Definition
802.11p is not like other 802.11 radio definitions, which operates on unlicensed radio band, on the other hand it operates on the licensed Dedicated Short Range Communication (DSRC) bands. It uses 5.9 GHz and 5.8 GHz in US and Europe / Japan respectively. It uses the OFDM modulation which uses seven 10 MHz wide sub channels with a 5MHz wide guard band.
There is a center sub channel which is used as control channel, and the upper and lower sub channels are dedicated for special uses, such as for emergency vehicles to signal traffic.
In order to cover larger area, four different classes for transmission power are defined where the highest one is 44dbm (30watts), allocated for emergency vehicles. This can be compared to the 802.11a amendment, for which North American channels are restricted to 40mw, 200mw or 800 mw depends on category. The maximum range of about 1km allows for the wider placement of access points.
When 802.11a / g were developed it was assumed that the channels would be static, but not the case regarding traffic. Due to the movement of vehicles, not only the channel varies over time, but Doppler shifts will also be considered as vehicles can reach high speeds in opposing directions.
Symbol rate is 8.0µsec for DSRC with 1.6µsec guard band interval with a signal bandwidth of 10MHz. DSRC uses 64 sub carriers with only 52 sub carriers used for transmission. Out of 52, 4 are pilots used for phase tracking, while rests of the 48 are used for data.
3.1.3 Existing Traffic System
The 802.11p protocol is designed to provide traffic information. There are also the similar systems for these services majority of the GPS receivers can receive data via RDS and already covers almost (98%) of Sweden. The traffic message channel (TMC) information is sent with a regular radio program, in Swedish case with P3.
The benefit of using TMC 802.11p for information transmission is that it uses already existing infrastructure, with a considerable transmission range. The car GPS receivers that utilize TMC data are common today; many motorists already have access to reliable traffic information.
With the technology scope of TMC with 802.11p, it can provide information about car crash, blocked roads or even bull fights, it is limited to providing traffic information from a centralized source. The fire truck or ambulances equipped with 802.11p could signal nearby traffic in more effective manner then a horn and flashing light.
One of the aspects of the TMC is security. TMC data is transmitted in plain text with least one application developed in 2007, is capable of injecting false traffic information using cheap electronics. This false message could be about roads closed, that a bomb attack had occurred few of the examples. This would be discussed thoroughly latter on.
System
3.2.1 Intelligent Transport Systems
ITS is a wider concept of Engineering improvements to transportation systems using information and communication technology. The Improvements aim to fuel efficiency, time efficiency, risk efficiency, load efficiency etc. As with all information systems, surveillance and monitoring is another aspect where ITS, can provide additional enhancements.
Under ITS, there includes systems that have been in existence for many years. Some of them includes old sensor nodes placed over roads either temporarily, or built-in into the roads permanently, often installed at traffic light controlled intersections, with the purpose of counting vehicles, which can be used for traffic planning during rush hours etc.
ITS is divided into three stages.
1. Data Collection
Sensors, learning of data, cell phone positions, electrical traffic accounting, automated radio based traffic toll systems, video based traffic toll systems etc.
2. Data Communication
Collected data generally has to be communicated somewhere.
3. Data Calculations
Then data is processed i-e possible actions are taken (and possibly communicated to actors).
802.11p is concerned with the communication stage within a subset of all ITS communication, which concerns communication between vehicles and other vehicles, or vehicles and infrastructure.
3.2.2 Security
Security is the most important aspect, vehicles communication can be used, but at the same time the applications which are going to serve might make tempting targets for cyber criminals. Examples of potential targets may include automatic toll system, parking system and traffic safety messages.
There are papers and work available regarding the issue of security in vehicular communication which discussed the data types, flags and structure of messages that are passed across wireless networks. The messages can be protected against different kinds of attacks such as eavesdropping, spoofing, alteration and message reuse, other concerns include different types of system models, communication models, adversary models and design principles.
Two of the most concerned security aspects are Non-Repudiation and Confidentiality, Integrity and Availability (CIA).
Non- Repudiation means if any entity takes an action, it can not deny it. A basic example would be prevention of the spreading of false messages or denial of service attacks, as source of information can always be tracked.
Confidentiality, Integrity and Availability (CIA)
Confidentiality means that the identity of the users should be protected against an unauthorized party, so that they cannot use other user's profiles. Integrity means authentication is required to stop unauthorized messages. A timing system can be employed to maintain the freshness of messages and avoid repeating messages. Availability is achieved through the routing protocol.
Conclusion
The possibilities introduced might lead to a safer and smoother traffic flow, due to information provided to motorists regarding emergency vehicles and traffic conditions, as well as the possibilities of collecting toll and parking fees transparently. The usage of vehicular communication might also beg a few questions with regards to privacy, and the possibilities of tracking unwilling motorists. This is however far outside the scope of this report.
802.11p based technologies has two interesting improvements over existing technology however, decentralization and reliability. With Ad-hoc networks formed on the roads, motorists are no longer limited to information distributed by a central bureaucracy or business, but can exchange information directly over relatively large distances. Increased reliability is associated with decentralization in the increased number of sources of information.
Implementing 802.11p requires huge investment as access points will have to be established every few kilometers on roads. Which makes it unlikely that any deployment of 802.11p technology will be seen in the next few years?
Documentation is mostly limited to IEEE articles and a few articles published by car manufacturers, making information on the project more scare, as the motivations for making publications is lacking, due to the pure industry interest in the field.
Review Question
Which 802.11 technology 802.11p based on and why was the previous technology not enough for wireless vehicular communications?
