Trends in Automotive Communication Systems NICOLAS NAVET, YEQIONG SONG, FRANÇOISE SIMONOT-LION, AND CÉDRIC WILWERT Invited Paper The use of networks for communications between the electronic windows, and, recently, entertainment and communication control units (ECU) of a vehicle in production cars dates from the equipment (e.g., radio, DVD, hands-free phones, navigation beginning of the 1990s. The specific requirements of the different systems). car domains have led to the development of a large number of auto- motive networks such as Local Interconnect Network, J1850, CAN, In the early days of automotive electronics, each new TTP/C, FlexRay, media-oriented system transport, IDB1394, etc. function was implemented as a stand-alone electronic This paper first introduces the context of in-vehicle embedded sys- control unit (ECU), which is a subsytem composed of a tems and, in particular, the requirements imposed on the commu- microcontroller and a set of sensors and actuators. This nication systems. Then, a comprehensive review of the most widely approach quickly proved to be insufficient with the need for used automotive networks, as well as the emerging ones, is given. Next, the current efforts of the automotive industry on middleware functions to be distributed over several ECUs and the need technologies, which may be of great help in mastering the hetero- for information exchanges among functions. For example, geneity, are reviewed. Finally, we highlight future trends in the de- the vehicle speed estimated by the engine controller or by velopment of automotive communication systems. wheel rotation sensors has to be known in order to adapt Keywords—Car domains, in-vehicle embedded systems, field- the steering effort, to control the suspension, or simply to buses, middlewares (MWs), networks, real-time systems. choose the right wiping speed. In today’s luxury cars, up to 2500 signals (i.e., elementary information such as the speed of the vehicle) are exchanged by up to 70 ECUs [1]. Until I. AUTOMOTIVE COMMUNICATION SYSTEMS: the beginning of the 1990s, data was exchanged through CHARACTERISTICS AND CONSTRAINTS point-to-point links between ECUs. However this strategy, From Point-to-Point to Multiplexed Communica- which required an amount of communication channels of tions: Since the 1970s, one observes an exponential the order of where is the number of ECUs (i.e., if each increase in the number of electronic systems that have node is interconnected with all the others, the number of gradually replaced those that are purely mechanical or links grows in the square of ), was unable to cope with hydraulic. The growing performance and reliability of hard- the increasing use of ECUs due to the problems of weight, ware components and the possibilities brought by software cost, complexity, and reliability induced by the wires and technologies enabled implementing complex functions that the connectors. These issues motivated the use of networks improve the comfort of the vehicle’s occupant as well as their where the communications are multiplexed over a shared safety. In particular, one of the main purposes of electronic medium, which consequently required defining rules—pro- systems is to assist the driver to control the vehicle through tocols—for managing communications and, in particular, functions related to the steering, traction (i.e., control of for granting bus access. It was mentioned in a 1998 press the driving torque) or braking such as the antilock braking release (quoted in [2]) that the replacement of a “wiring system (ABS), electronic stability program (ESP), electric harness with LANs in the four doors of a BMW reduced power steering (EPS), active suspensions, or engine control. the weight by 15 kilograms.” In the mid–1980s, the third Another reason for using electronic systems is to control part supplier Bosch developed the Controller Area Network devices in the body of a vehicle such as lights, wipers, doors, (CAN), which was first integrated in Mercedes production cars in the early 1990s. Today, it has become the most widely used network in automotive systems and it is estimated [3] Manuscript received September 6, 2004; revised March 11, 2005. N. Navet, Y. Song, and F. Simonot-Lion are with the Loria Laboratory, that the number of CAN nodes sold per year is currently Vandoeuvre-lés-Nancy 54506, France (e-mail: [email protected]; around 400 million (all application fields). Other communi- [email protected]; [email protected]). cation networks, providing different services, are now being C. Wilwert is with PSA Peugeot Citröen, La Garenne-Colombes Cedex 92256, France (e-mail: [email protected]). integrated in automotive applications. A description of the Digital Object Identifier 10.1109/JPROC.2005.849725 major networks is given in Section II. 0018-9219/$20.00 © 2005 IEEE 1204 PROCEEDINGS OF THE IEEE, VOL. 93, NO. 6, JUNE 2005 Car Domains and Their Evolution: As all the functions selves. Not all nodes require a large bandwidth, such as the embedded in cars do not have the same performance or one offered by CAN; this lead to the design of low-cost net- safety needs, different QoSs (e.g., response time, jitter, works such as Local Interconnect Network (LIN) and TTP/A bandwidth, redundant communication channels for toler- (see Section II). On these networks, only one node, termed ating transmission errors, efficiency of the error detection the master, possesses an accurate clock and drives the com- mechanisms, etc.) are expected from the communication munication by polling the other nodes—the slaves—period- systems. Typically, an in-car embedded system is divided ically. The mixture of different communication needs inside into several functional domains that correspond to different the body domain lead to a hierarchical network architecture features and constraints [4]. Two of them are concerned where integrated mechatronic subsystems based on low-cost specifically with real-time control and safety of the ve- networks are interconnected through a CAN backbone. The hicle’s behavior: the “powertrain” (i.e., control of engine activation of body functions is mainly triggered according and transmission) and the “chassis” (i.e., control of suspen- to the driver and passengers’ solicitation (e.g., opening a sion, steering, and braking) domains. The third, the “body,” window, locking doors, etc). mostly implements comfort functions. The “telematics” Telematics functions are becoming more and more nu- (i.e., integration of wireless communications, vehicle mon- merous: hands-free phones, car radio, CD, DVD, in-car itoring systems and location devices), “multimedia,” and navigation systems, rear seat entertainment, remote vehicle “human–machine interface” (HMI) domains take advantage diagnostics, etc. These functions require a lot of data to be of the continuous progress in the field of multimedia and exchanged within the vehicle but also with the external world mobile communications. Finally, an emerging domain is through the use of wireless technology (see, for instance, concerned with the safety of the occupant. [10]). Here, the emphasis shifts from messages and tasks The main function of the powertrain domain is control- subject to stringent deadline constraints to multimedia data ling the engine. It is realized through several complex control streams, bandwidth sharing, multimedia QoS where pre- laws with sampling periods of a magnitude of some millisec- serving the integrity (i.e., ensuring that information will not onds (due to the rotation speed of the engine) and imple- be accidentally or maliciously altered) and confidentiality of mented in microcontrollers with high computing power. In information is crucial. HMI aims to provide HMIs that are order to cope with the diversity of critical tasks to be treated, easy to use and that limit the risk of driver inattention [11]. multitasking is required and stringent time constraints are im- Electronic-based systems for ensuring the safety of the oc- posed on the scheduling of the tasks. Furthermore, frequent cupants are increasingly embedded in vehicles. Examples of data exchanges with other car domains, such as the chassis such systems are impact and rollover sensors, deployment (e.g., ESP, ABS) and the body (e.g., dashboard, climate con- of airbags and belt pretensioners, tire pressure monitoring, trol), are required. or adaptive cruise control (ACC) (in which the car’s speed The chassis domain gathers functions such as ABS, is adjusted to maintain a safe distance from the car ahead). ESP, ASC (Automatic Stability Control), 4WD (4 Wheel These functions form an emerging domain usually referred Drive), which control the chassis components according to as “active and passive safety.” to steering/braking solicitations and driving conditions Different Networks for Different Requirements: The (ground surface, wind, etc). Communication requirements steadily increasing need for bandwidth1 and the diversifica- for this domain are quite similar to those for the powertrain tion of performance, costs and dependability2 requirements but, because they have a stronger impact on the vehicle’s lead to a diversification of the networks used throughout stability, agility and dynamics, the chassis functions are the car. In 1994, the Society for Automotive Engineers more critical from a safety standpoint. Furthermore, the (SAE) defined a classification for automotive communica- “x-by-wire” technology, currently used for avionic systems, tion protocols [13]–[15] based on data transmission speed is now being introduced to execute steering or braking and functions that are distributed over the network. Class A functions. “X-by-wire” is a generic term referring to the networks have a data rate lower than 10 kb/s and are used replacement of mechanical or hydraulic systems by fully to transmit simple control data with low-cost technology. electrical/electronic ones, which led and still leads to new They are mainly integrated in the “body” domain (seat design methods for developing them safely [5] and, in control, door lock, lighting, trunk release, rain sensor, etc.). particular, for mastering the interferences between functions Examples of class A networks are LIN [16], [17] and TTP/A [6].