Requirements for designing next-generation key fobs.
Both systems are based on a preprogrammed key fob device ID and authentication protocols which include an encryption stage for authorizing the issue of key fob commands to the vehicle. In this way the key can be identified by the vehicle and vice versa before any action is executed. All RKE-based systems require key fobs to support RF links which fall into Industrial, Scientific and Medical (ISM) frequency bands (i.e., 0- 135 kHz, 13.56 MHz, 315/433 MHz, 869 MHz, and 915 MHz). However, for a PE system the LF downlink is used by the key fob to compute a Received Signal Strength Indicator (RSSI) value and thus the fob's physical coordinates in relation to the vehicle while the RF link is used to execute the authentication protocol with the vehicle. RKE and PE system fobs are designed to be powered by a small coin battery intended to last for the life of the vehicle.
Moreover, all key fobs support engine immobilizer system authentication. To prevent theft, every automobile uses an immobilizer system which authenticates engine starts. In this case, the key fob acts as a passive authentication tag similar to the RFID tag but with a larger feature set. Most automotive key fobs use Near Field Communication (NFC) transponders which communicate with the engine controller. The transponder is integrated into the key and is a passive device. It does not need a battery for operation, but instead uses a magnetic field generated by the LF vehicle coil. It also transmits the device ID and executes a special immobilizer protocol for its authentication, but all communication takes place via an LF field generated by the vehicle.
Physical Interface (3) (Button, Touch, etc.) Class Immobilizer Battlery/ Remote Remote Accessories (1) Recharge (2) Start Entry Basic x - - - - RKE (std.) x x/ x - - RKE (ext.) x x/x x - x PE (std.) x x/x x x x PE (ext.) x x/x x x x Class Passive Personalization Settings Time/Data Logging (Entry/Go) In Fob (4) Basic - x x RKE (std.) - x RKE (ext.) - x x PE (std.) x/x x PE (ext.) x/x x x (1) Immobilizer support includes secure fob and vehicle authentication via the LF Field using an integrated LF transponder. (2) The fob includes a built-in battery with the option of recharging the battery via the LF field. (3) Remote Start and Remote Entry are controlled via RF uni- or bidirectional link. Control of accessories can either be done using RF or IrDA links. (4) Data can be logged such as time stamp data, last device ID, last vehicle service date, and much more either via LF or RF links.
Expanding Fob Applications
Originally key fobs were designed for only one purpose: to unlock the door and start the engine with the metal key. Later, remote keyless entry was used to remotely (HF field) unlock the door. The integrated con-tactless passive transponder (LF field) then unlocked the steering column and enabled the engine start.
To view the expanded online versions of these articles with footnote/reference info, visit www.ecnm
By Paul Lepek, Atmel Corporation, www.atmel.com
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|Publication:||ECN-Electronic Component News|
|Date:||Jan 1, 2011|
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