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.
TopVehicular Subsystems And Network Requirements
In general, a vehicle can be segmented into the five subsystems or domains as shown in Figure 1 (Navet et al., 2005, Nolte et al., 2005, Sangiovanni-Vincentelli & Di Natale, 2007). Within the powertrain subsystem, a highly complex and strictly timed set of mechanisms exist that control the engine and transmission. This occurrence of frequent data transmission requires a highly reliable network that also exhibits a high bandwidth to enable such real-time information to be communicated without error. Similarly, real-time, high bandwidth and safety critical networks exist within the chassis domain that is typically thought of encompassing the suspension, steering and brakes. The body and comfort subsystem comprises electronics such as air-conditioning, lighting, wipers, cruise control and locking mechanism for example. The functionality of these components, although required to be reliable, is not considered safety critical, and would generally not require a high bandwidth network for which many elements might be considered as lower in cost. The safety subsystem is formed by a sensor network attached to impact and rollover zones, airbags and seatbelts. The quality of this network is ultimately a factor into the overall success of a vehicles ability to protect the driver and/or passengers from unpredictable and possibly severe events. Whilst the bandwidth may not be an issue (as some of the sensors and actuators will be comparably simple) it must have a high availability. Finally, the infotainment and telematics subsystem deals with the multimedia and mobile communications devices such as audio-visual units, GPS or computer consoles etc. This subsystem is distinctly different to the chassis subsystem as many devices may be considered by vehicle manufactures as optional, or indeed installed and maintained by third parties. This subsystems network is likely to require a very high bandwidth for video and music streaming whilst also being reliable and possibly upgradable given that entertainment and data requirements are possible evolving faster than the time between vehicle purchases.
Figure 1. The five embedded vehicular subsystems
TopCurrent Vehicular Network Technologies
Historically, within a given vehicle, is was not uncommon to find up to 70 Electronic Control Units (ECUs) which exchange data around the vehicle (Navet et al, 2005). As the functionality within newer vehicles increased, the resultant demand on vehicular networks also increased to the point that an increase in network bandwidth and reliability was desired, but, as was true then as it is now, to obtain it at lower cost. What transpired is that from an engineering point of view, this problem can be solved by reducing the size and complexity of this “network or networks” whilst maintaining or increasing upon the capabilities of the overall network requirements listed above (Sangiovanni-Vincentelli & Di Natale, 2007, Kopetz & Bauer, 2003). Several excellent wired and wireless solutions, or candidate solutions have been proposed in recent years. A course breakdown of each technology can be seen in Figure 2.
Considering Figure 2 for a moment, a striking, if not obvious observation one could make is that the names of the wired networks are all specific, seemingly specialised to the vehicular market, and only to be understood by vehicular engineers. Contrary to this are the names of the wireless networks, seemingly common to every layperson and synonymous in everyday life. This observation is not uncommon and in fact a virtue to the relative maturities wired vs wireless and industrial uptake. Therefore, considering first the more mature, wired technology, a brief description for each is as follows: