Image Processing Reference
In-Depth Information
In today's luxury cars, up to signals (i.e., elementary information such as the speed of the vehi-
cle) are exchanged by up to ECUs []. Until the beginning of the s, data were exchanged
through point-to-point links between ECUs. However this strategy, which required an amount of
communication channels of the order of
n
where
n
isthenumberofECUs(i.e.,ifeachnodeis
interconnected with all the others, the number of links grows in the square of
n
), was unable to
cope with the increasing use of ECUs due to the problems of weight, cost, complexity, and relia-
bility induced by the wires and the connectors. These issues motivated the use of networks where
the communications are multiplexed over a shared medium, which consequently required defining
rules—protocols—for managing communications and, in particular, for granting bus access. It was
mentionedinapressrelease(quotedinRef.[])thatthereplacementofa“wiringharnesswith
LANs in the four doors of a BMW reduced the weight by kg.” In the mid-s, the third part
supplier Bosch developed controller area network (CAN), which was first integrated in Mercedes
production cars in the early s. Today, it has become the most widely used network in automotive
systems and it is estimated [] that the number of CAN nodes sold per year is currently around
millions (all application fields). Other communication networks, providing different services,
are now being integrated in automotive applications. A description of the major networks is given in
Section ..
13.1.2 Car Domains and Their Evolution
As all the functions embedded in cars do not have the same performance or safety needs, different
quality of services (QoS) (e.g., response time, jitter, bandwidth, redundant communication channels
for tolerating transmission errors, efficiency of the error detection mechanisms, etc.) are expected
from the communication systems. Typically, an in-car embedded system is divided into several func-
tional domains that correspond to different features and constraints. Two of them are concerned
specifically with real-time control and safety of the vehicle's behavior: the “powertrain” (i.e., con-
trol of engine and transmission) and the “chassis” (i.e., control of suspension, steering, and braking)
domains. he third, the “body,” mostly implements comfort functions. he “telematics” (i.e., integra-
tion of wireless communications, vehicle monitoring systems, and location devices), “multimedia,”
and “human machine interface” (HMI) domains take advantage of the continuous progress in the
field of multimedia and mobile communications. Finally, an emerging domain is concerned with the
safety of the occupant.
he main function of the powertrain domain is controlling the engine. It is realized through several
complex control laws with sampling periods of a magnitude of some milliseconds (due to the rotation
speed of the engine) and implemented in microcontrollers with high computing power. To cope with
the diversity of critical tasks to be treated, multitasking is required and stringent time constraints
are imposed on the scheduling of the tasks. Furthermore, frequent data exchanges with other car
domains, such as the chassis (e.g., ESP, ABS) and the body (e.g., dashboard, climate control), are
required.
The chassis domain gathers functions such as ABS, ESP, Automatic Stability Control, Wheel
Drive, which control the chassis components according to steering/braking solicitations and driv-
ing conditions (ground surface, wind, etc.). Communication requirements for this domain are quite
similar to those for the powertrain but, because they have a stronger impact on the vehicle's stability,
agility, and dynamics, the chassis functions are more critical from a safety standpoint. Furthermore,
the “X-by-Wire” technology, currently used for avionic systems, is now slowly being introduced to
execute steering or braking functions. X-by-Wire is a generic term referring to the replacement of
mechanical or hydraulic systems by fully electrical/electronic ones, which led and still leads to new
design methods for developing them safely [] and, in particular, for mastering the interferences
between functions []. Chassis and powertrain functions operate mainly as closed-loop control sys-
tems and their implementation is moving toward a time-triggered (TT) approach [,,,],
