3 ms·
The car manufacturers are going to need to incorporate a time of flight measurement into the key system. Obviously amplitude can be faked.
by cameldrv 8y ago
The car manufacturers are going to need to incorporate a time of flight measurement into the key system. Obviously amplitude can be faked.
- wglb 8y agoSo the test for amplitude is aided by the fact that the signal strength received at the car increases by a factor of four if the distance is cut in half. Thus, you have a nice margin for setting your threshold. With measuring the time, however, presuming that radio signal will travel on the order of one foot per nanosecond, you have much less of a threshold tolerance. If the unlock takes place within two feet of the car, that is two nanoseconds. If the key sits 20 feet away, that is a 20-nanosecond one-way travel. So this solution would need to be able to distinguish between a four nanosecond gap (round trip time) and a 40-nanosecond round-trip time. Add to that the turnaround time in the car CPU which I would imagine to be some number of milliseconds, would 10 ms be reasonable? Thus, the electronics in the car needs to distinguish between 10ms + 4 ns vs 10ms + 40ms. And given jitter in any modern CPU/memory/OS/electronics device, I would bet that the jitter totally swamps that. (Keep in mind that this is a BOEC https://en.wikipedia.org/wiki/Back-of-the-envelope_calculation https://en.wikipedia.org/wiki/Back-of-the-envelope_calculati...)
- deleted 8y ago[deleted]
- kevin_thibedeau 8y agoOr just use physical contacts on a real key.
- izacus 8y agoNot having to drag keys out of your pockets is a feature.
- bas 8y agoYou meant a solution in search of a problem.
- teddyfrozevelt 8y agoNot really, for some people it saves very little time, for most it's a small convenience, and for others it saves a lot of time, especially women who have their keys in their purse and don't have to search for them. Just because it's not useful to you doesn't mean that it isn't for others. Car manufacturers aren't going to change something for no reason unless people actually want it.
- asdff 8y agoYeah, for the thief, maybe. This is a classic example of tech attempting to eliminate a mild inconvenience that no one really complained about before, and clumsily engineering a 'solution' that causes a dozen other novel and catastrophic problems in the process.