Experiments of In-Vehicle Power Line Communications [chapter]

Fabienne Nouvel, Philippe Tanguy, S. Pillement, H.M. Pham
2011 Advances in Vehicular Networking Technologies  
The omnipresence of ECU (electronic control units) in vehicles has lead the automotive industry to face a great challenge in its transition from mechanical engineering towards mechatronical products. The X-by-wire and X-tainment applications involve efficient networks that allow bus sharing while reducing both cabling costs, number of wires and connectors. This chapter deals with the embedded in-vehicle networks and the use of emerging technologies combining different communication systems like
more » ... power line communications (PLC) and/or wireless communications and pushing to a dynamic configuration of both networks and ECU. The ECUs that replace mechanical or hydraulic systems require secure and specific bus for communication. In order to exchange information between sensors and actuators, different networks have been proposed, from low data rate up to high data rate namely LIN, CAN, FlexRay. In section 2, these networks are presented identifying their strengths and possible drawbacks. As a result of using these fieldbuses, the cost of advanced systems should plummet. Furthermore, X-by-wire systems do not depend on conventional mechanical or hydraulic mechanisms. In (Len & Hefferman, 2001), the authors demonstrate the advantages of X-by-wire and embedded networks. Considering these specific domain embedded networks, we can observe that each solution uses its specific wires and communication system. The growth of the complexity leads to the necessity to commit to a limited set of networks which answers to these multiple applications. An attractive solution to reduce the wires is the power line communication (PLC) using the power lines (12/42V) to transmit both the power and the messages without functional barriers domain. It can answer the vehicles requirements namely cost, decrease of the amount of wires, flexibility and bandwidth. Section 3 is dedicated to PLC systems. Nowadays, this technique is already proposed for domestic uses (Ribeiro et al., 2006) . In vehicle PLC seems to be a promising technology and has numerous advantages; it could reduce the weight of wires, the amount of splicing, and simplify cables bundle and the networks between ECU. The background and current studies are first addressed in Section 3. Although high data rate and flexibility obtained for indoor domestic PLC are proven, it is not possible to apply them directly to cars because the geometrical characteristics and wires www.intechopen.com Advances in Vehicular Networking Technologies 256 topologies are totally different. Moreover, the in-vehicle PLC channels are affected by the variable activation schedules of electrical functions, such as brakes, indicators, etc, which produce sharp modifications in the circuit's load impedances over brief time intervals, as presented in (Lienard et al., 2008) . To optimize high bit-rate communication, the PLC channel transfer function must be carefully studied because it is frequency selective. Previous studies show that the promising techniques are based on wide bandwidth transmission, such a spread spectrum or orthogonal frequency division multiplex (OFDM). Section 4 provides a description of the experimentations using the existing DC electrical wires. The discussion is framed by describing in particular the area of PLC applications. Results for different cars configurations are presented and demonstrate the feasibility of PLC for automotive. Section 5 will complete the chapter by describing other alternative solutions for in-vehicle communication based on wireless communications such as ZigBee, Wireless USB, Wifi .... These technologies have been adopted for V2V, R2V and can be extended to in-vehicle communication. Different solutions are proposed, giving a new perspective for ECU communications, both for cars to cars and/or intra-cars communications. In order to propose more flexibility with these different communication networks, new electronic architecture need to be adopted to reduce the size of ECU. One solution is based on dynamic reconfiguration. Section 6 will analyze this new concept for our embedded system. Reconfigurable systems are already proposed for video driver assistance (Claus & Stechele, 2010) . The reconfiguration can increase both safety and flexibility. An ECU can migrate tasks from one node to another. Furthermore, this functionality can be extended to network architecture: according to the channel, the ECU loads, the modem can be dynamically reconfigured to offer seamless communication between ECUs. www.intechopen.com Experiments of In-Vehicle Power Line Communications 257 Fig. 1. Network architecture (from http:// www.freescale.com) Conceived in 1998, the LIN network (LIN, 2003 is an inexpensive slow and serial bus used for distributed body control electronic systems in vehicle. It enables effective communication for sensors and actuators where bandwidth, speed and versality are not required (i.e. inside mechatronic based subsystems generally made of an ECU and its set of sensors and actuators). LIN is commonly used as a sub bus for CAN and FlexRay. A LIN network is based on one master node and LIN slaves (up to 16 over 40 meters line length). The master node decides when and which frame shall be transmitted according to the schedule table containing the transmission order. At the moment a frame is scheduled for transmission, the master sends the header inviting a slave node to send its data in response. Any node interested can read a data frame transmitted on the bus. The reliability of LIN is high but it does not have to meet the same levels as CAN. The LIN can be implemented using just a single wire, while CAN needs two. The physical layer (PHY) supports a data rate equal to 20 Kbps (due to electromagnetic limitations) but other transmission supports enabling higher data rates are possible. LIN is widely used in middle range cars but it can not support high data rate as required by devices like portable DVD players or multimedia applications. The Local Interconnect Network: LIN
doi:10.5772/14258 fatcat:cihh5engbfhshe2il22sgapioq