WLAN Systems for Communication in Transportation Systems

Vehicular Ad-Hoc Networks (VANETs) are wireless networks primarily meant to enforce vehicular safety. The incumbent international VANET solution is based on an adaptation of WLAN to the 5.9 GHz band and to the vehicular environment: it is universally known as IEEE 802.11p. One of the main reasons for the success of IEEE 802.11p lies on the functional requirement of a decentralized solution, that is, one able to work in the absence of infrastructure. While Filed-Operational Tests are being developed world-wide and new VANET applications, not restricted to safety, are being developed, new requisites are emerging. Some limitations of the IEEE 802.11p are coming to light as well: stakeholders must be aware of them to prevent misleading conclusions on reliability and, most importantly, improper solutions for the safety which the protocol is aimed at.

Modeling of Polymer Optical Fibers

The idea of this chapter is to give a complete overview on a matrix approach to describe light propagation in strongly multimode fibers such as 1-mm diameter plastic optical fibers. These large core fibers accept such a huge number of travelling modes that they can be viewed as a continuum. Thus, light propagation can be described as a power flow by a differential equation that can be more easily solved using matrices. Thus, the key of this method is the propagation matrix that is calculated from the diffusion and attenuation functions characteristic for a given fiber type. The propagation matrix has temporal frequency dependence and can be used to obtain not only angular power distributions but also temporal parameters such as pulse spread or bandwidth. This approach is flexible to introduce localized perturbations of power distribution provided they can be modeled as matrices. Thus, the effect of devices such as scramblers or connectors and also of disturbances such as curvatures and tensions can be introduced at different points in the fiber path to assess their impact on transmission properties. One of the most critical parameters when designing a network is its bandwidth and how it decreases when increasing the link reach. This dependence has been assumed to be linear when both bandwidth and length are represented in logarithms with a slope whose value provides information of the processes underlying propagation. Thus, the authors apply the model to calculate the bandwidth versus length dependence under different conditions analyzing the value of the slope and explaining previous experimental findings.

Communication Systems in Automotive Systems

Communication networks in general, can be divided into 4 different classes: Ring (one directional or bidirectional), Star (active or passive), Tree, and Bus (passive). These 4 classes of communication networks are also used in transport systems. The main properties of these networks are overviewed. Then, the most important automotive networks are discussed: LIN, CAN, MOST, Ethernet, and Flexray, as well as their implementations in cars. For the MOST and Ethernet networks, different physical layer implementations are possible. The different factors determining the choice of a network are discussed. Cost is a major driver for automotive networks. For avionics networks, different standards for the network protocols and the physical layer implementations exist. In most cases physical layer implementations are proprietary, although, due to cost reduction pressure, more and more standardization is ongoing, and a tendency exist to adapt automotive network standards, and for the pressurized part of the airplane, also automotive physical layer implementations.

Optical Wireless Communications in Vehicular Systems

This chapter reviews some of the network topologies and technologies within current vehicular systems. This is then followed by a proposal from the authors with initial viability results, into the possibility of implementing optical wireless links to either replace or complement these existing ideas. The initial motivation for this work (Green, 2010) is that there exist multiple pathways within a vehicle such as the engine compartment, within the frame of the chassis, or the internal cockpit that all lend themselves nicely to free space optical propagation. The first specialised study on the viability of optical wireless communications within the vehicles cabin was then published in (Higgins et al, 2012) which provided a further impetus to the concept. It is hoped that through the original results presented here, the reader can gain a basic understanding of the concepts compared to the current technologies, and are then able instigate their own research ideas.

Transmission Lines for Serial Communication

Automotive bus systems like e.g. LIN, CAN, and FlexRay™ distribute their serial data streams NRZ1 coded in the base band among the communication nodes. The nodes are interconnected by passive nets. Depending on the type of application some of these nets may consist of up to one hundred meters of different bus cables arranged in various topologies. The individual pieces of information inside the data streams are represented by voltage steps and current steps. They have to be passed among all connected nodes via the bus cables. The succeeding sections introduce the commonly known transmission line theory focused of the physical effects being relevant for automotive serial bus communication in the time domain.

FlexRay™ Electrical Physical Layer

Modern medium and high end vehicles are no longer imaginable without using technologies to broadcast local available data. The speed information for example is used by many well known functions: the anti blocking system, the radio, the dashboard, the cruise control, the electronic stability program, etc. Usually, this data is distributed among vehicle’s electronic control units by various serial bus systems. The succeeding sections introduce the automotive communication system named FlexRay™. The development of FlexRay™ had been initialized by requirements expected for drive-by-wire systems. The content is focused on its electrical physical layer beginning with active components like bus interfaces as well as passive components like common mode filters and bus-cables. Comparisons to the state of the art systems CAN and LIN are used to support the comprehensibility.

Communication Networks to Connect Moving Vehicles to Transportation Systems to Infrastructure

Communication in transportation systems not only involves the communication inside a vehicle, train, or airplane but it also includes the transfer of data to and from the transportation system or between devices belonging to that system. This will be done using different types of wireless communication. Therefore in this chapter, first, the fundamentals of mobile communication networks are shortly described. Thereafter, possible candidate networks are discussed. Their suitability for a certain transportation system can be evaluated taking into consideration the system’s requirements. Among the most prominent are the influence of speed and mobility, data rate and bit error rate constraints, reliability of the system and on-going connections. As in most of the cases, there will be no single best wireless communication network to fulfil all requirements, and in this chapter also hybrid networks are discussed. These are networks consisting of different (wireless) access networks. The devices may use the best suited network for a given situation but also change to another network while continuing the on-going connection or data transfer. Here the design of the handover or relocation plays a critical role as well as localization.

Physical Layer Implementations of Communication Standards in Automotive Systems

This chapter is divided into three sections. The first section gives an overview of the different cables used in automotive communication systems. Although 6 different kind of cables and their corresponding connector systems have been qualified for use in automotive applications (3 electrical cable types and 3 optical cable types), up to now, only three types are commonly used: Unshielded Twisted Pairs (UTP), Coax cable, and 1 mm PMMA POF. GOF and multimode PCS up to now are not used for mass volume production. The second section overviews the optical connectors used in automotive communication systems. The electrical connectors used in LIN and CAN networks. The optical connectors standardized by MOST. In the early phase of MOST implementation, the number of MOST connectors has been large: long pigtails, short pigtails, micro pigtails, and these connectors are combined with electrical connections with a wide range of pin sizes. The number of connectors used in MOST – mainly under cost pressureis now drastically reducing. The third section overviews the different fiber optic transceivers used for MOST. The different packages for MOST25 and MOST150 transceivers are discussed. The most difficult step was the conversion of the fiber optic transceivers to be compatible with reflow SMD processes. This step is now taken. Also the evolution towards higher data rates is shown.

Short-Range Ultrasonic Communications in Air

The idea of this chapter is to give an overview of a relatively new technology – that of using ultrasound to transmit data at short ranges, within a room say. The advances that have made this a useful technology include the ability to utilize a sufficiently wide bandwidth, and the availability of instrumentation that can send and receive ultrasonic signals in air. The chapter describes this instrumentation, and also covers the various aspects of ultrasonic propagation that need to be discussed, such as attenuation, spatial characteristics, and the most suitable forms of modulation. Provided such details are considered carefully, it is demonstrated that ultrasonic systems are a practical possibility for in-room communications.

Radiometric Speed Sensor for Vehicles

One of the main parameters for providing traffic safety of vehicles is the knowledge of their speed. In this chapter results of research activities on a microwave radiometric sensor for the measurement of the velocity of land vehicles are presented. The work concentrates on a Radiometric Speed Sensor of Correlation Type (RM SSCT). For the analysis of design principles of the RM SSCT, the main parameters of radiometers are defined. The nature and statistical characteristics of radio thermal radiation of a terrestrial surface and objects are considered. For an estimation of the influence of parameters of the antenna system and the linear path of the receiver on parameters of the signal formed at the output of the correlator, a statistical analysis of the radiometric system of correlation type is carried out. Using a statistical model of the RM SSCT, the parameters of the antenna system were optimized as well as the radiometric receivers for various types of objects present on a terrestrial surface. Statistical results of the performance of the RM SSCT and an analysis of the basic characteristics of the SSCT for various types of objects are finally presented.