Reliable operation of sensor fusion configurations
As many fusion systems are capable of performing autonomous control of certain car functions (examples include steering, braking, accelerating) without the driver, functional safety considerations need to be included to ensure the safe and reliable system operation under various conditions and over the lifetime of the car. As soon as a decision is made and followed up by an autonomous action, the functional safety requirements increase significantly.
With a distributed approach, each module processing critical data or making decisions will have to meet those increased standards. This adds bill of materials (BOM) cost, size, power and software compared to a module that is just gathering and sending sensor information. In an environment where mounting space is scarce, cooling is difficult, and the risk of damage and needed replacement is high (a simple fender bender could result in replacing the bumper and all attached sensors), this can make up for the benefits of a distributed system with many sensor modules.
Alternatively, a “dumb” sensor module needs to do self-diagnostic and error reporting to allow safe operation of the whole system, but not to the extent of a smart sensor module.
While pure driver information systems can shut down in case their function is compromised and notify the driver, highly autonomous functions do not have that freedom. Imagine a car performing an emergency braking maneuver and suddenly disengaging and releasing the brakes. Or imagine the full system shutting down on a highway while the driver is sleeping on “full auto pilot” (a potential future scenario). A minimum time will be needed during which the system has to continue working until a driver can safely take back control, which can last several seconds up to half a minute.
To which extent the system has to be operational and how to ensure operation under fault conditions, there does not yet seem to be a clear consensus in the industry. Airplanes with autopilot features typically use redundant systems. While these are generally considered safe, they are expensive and space-consuming solutions.
Sensor fusion is a critical step towards the goal of turning on the auto pilot and leaning back to enjoy the ride.
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