You Can’t Stop Noise – But You Can Stop it Affecting a Car’s Network. Here’s How.

View from car dashboard

How frightening would it be for the driver of a car if turning up the air-conditioning fan to full power stopped the brakes from working? Or if sounding the horn made the headlights switch off?

These might sound far-fetched, but they are conceivable scenarios. Car makers have to be sure this could never happen in the real world.

One potential cause of such hair-raising events is automotive ‘impairment noise’. This occurs when one system in a car which generates a lot of electro-magnetic emissions interferes with another system in the car. Many parts of a car generate emissions – in electrical terms, cars are extremely noisy environments! Any kind of motor, solenoid or switch might be guilty of interfering with other systems.

Today’s cars generally handle this problem just fine: they use components that are hardened – they can cope with whatever emissions the automotive environment throws at them.

But many cars in development now are set to include a ‘new’ networking technology: Ethernet. Ethernet is, of course, not really new – it has been used to connect computers and servers in offices and data centers for decades. In cars, however, the use of Ethernet is new. Because of the nature of Ethernet’s signals and modulation scheme, it is more sensitive to external electro-magnetic noise than well-known automotive network technologies such as CAN and MOST.

In the worst-case scenario – electrical noise could be coupled or radiated onto wire harnesses causing safety critical systems to become temporarily disabled a situation no car driver would like to experience. Ethernet is attractive to car makers for many good reasons, and most of all because of its ability to carry huge amounts of data at very high speed. The IEEE industry is working on a new set of standards for time-sensitive networks (TSN) with a cleaver approach to increase the robustness of Ethernet to noise for usage in safety critical systems.

If not implemented and tested correctly noise would be able to impair and block these safety-critical signals from arriving to their destination, resulting in a loss of control for the driver, passengers and other road users could be put at risk.

By properly implementing an Ethernet network design, a car maker can ensure that it poses no threat to safety. But in its development phase, a network design has to take account of all the potential sources of noise, and their effect on it.

There are various ways to model noise sources such as fans, pumps, motors and power supplies, and to test their effect on network components and systems. Car makers often use drive testing to find out how prototypes of other types of systems behave in real-world conditions.

But for testing designs for Ethernet network equipment and components, by far the best way to test the effects of noise is in the lab, with a dedicated impairment noise generator. This specialized type of test equipment – Spirent’s AING-5000 is a good example – can replay automotive noise sources, and enables engineers to precisely measure the effect of noise on network devices.

Screenshot of the AING-5000 illustrating a continuous impulse noise event

If they want to find out how strong the emissions from a fan’s motor have to be before they impair the network signal, test engineers can gradually amplify the noise more… and a bit more… and a bit more… until they find the point at which the network fails.

If they want to find out the effect of multiple noise sources, with an AING-5000 they can virtually ‘turn on’ the air-conditioning, then start the engine running, then play the car radio, then turn on the headlights, then beep the horn, and so on and so on, and measure exactly how many transmitted data packets reach their destination, and how many are lost, with each combination of noise sources.

And they can keep repeating the tests indefinitely, and modify them in any way they like – all in the tightly controlled lab environment.

As the scenarios described at the start of this piece suggest, there is a lot – safety, quality and the car manufacturer’s reputation – hanging on the effect of noise on the new automotive Ethernet networks. The proper testing of noise effects is an extremely important issue for car makers and their suppliers.

Automotive noise white paper coverYou can find out much more about this topic by reading the new Spirent white paper on noise in automotive Ethernet networks. In the white paper, you’ll learn all about the causes of noise in the car, its effect on sensitive network devices and equipment, and the many varieties of test that a dedicated impairment noise generator can support. Download it today to find out about the best and most configurable way to test for the effect of noise on automotive Ethernet systems.

Download 'Verifying the effect of electro-magnetic noise on an in-vehicle Ethernet network'.

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