The use of a magnetic field from the basestation to the tag, combined with an UHF link from the tag to the car receiver unit, provides the advantage of a well defined range of operation, avoiding interference with other systems. Communication with the tag is triggered as soon as the door lever is pulled. The tag also features a backup mode to allow the system to operate, even in the case of a battery low condition. However, in this case, the operating range is reduced to 10 cm. The tag provides a high level of integration, and tags are available in the shape of a card or keyfob.
First prototypes are available for system demonstration purposes.
Introducing passive entry immediately raises a lot of system issues. The key point is to detect the location of a tag outside or inside the vehicle, with sufficient accuracy to initiate vehicle locking. A number of basestation antennas have to be installed in the vehicle to detect and collect information about tags in the vicinity of the driver's door, passenger's door or trunk. Our basestation concept relies on the active antennas being placed close to the antenna coil in the desired operating range. The active antennas are wired, via a serial link, to the main access controller, which collects information about tags present and initiates the proper vehicle body function.