Antitheft device for a motor vehicle and method for operating the antitheft device
First Claim
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1. A motor vehicle antitheft device, comprising:
- a motor vehicle mounted transceiver unit for transmitting a challenge signal and for receiving a response signal;
a motor vehicle mounted security device connected to said transceiver unit;
an evaluation unit in said transceiver unit for evaluating the response signal and for comparing an item of code information contained in the response signal with an item of expected reference code information and for controlling said security device in dependence on a result of the comparison;
a portable code transmitter for receiving the challenge signal and for transmitting a coded response signal in response to the challenge signal; and
a measuring device in said code transmitter for detecting a received power of the challenge signal and for adding a value representing the received power to the response signal.
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Abstract
A first challenge signal whose reception power is measured in a portable code transmitter is transmitted by a vehicle-mounted transmission unit. Subsequently, a second challenge signal is transmitted under changed transmission conditions, and the reception power of the second challenge signal is also measured. Doors are unlocked, or the internal combustion engine is started only if the received power levels are also different. Otherwise, one or more challenge signals are transmitted once more under changed transmission conditions.
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Citations
8 Claims
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1. A motor vehicle antitheft device, comprising:
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a motor vehicle mounted transceiver unit for transmitting a challenge signal and for receiving a response signal;
a motor vehicle mounted security device connected to said transceiver unit;
an evaluation unit in said transceiver unit for evaluating the response signal and for comparing an item of code information contained in the response signal with an item of expected reference code information and for controlling said security device in dependence on a result of the comparison;
a portable code transmitter for receiving the challenge signal and for transmitting a coded response signal in response to the challenge signal; and
a measuring device in said code transmitter for detecting a received power of the challenge signal and for adding a value representing the received power to the response signal. - View Dependent Claims (2, 3, 4)
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5. A method of operating a motor vehicle antitheft device, which comprises:
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transmitting a first challenge signal with a motor vehicle mounted transceiver unit;
receiving the first challenge signal with a portable code transmitter, measuring a reception power of the challenge signal in the code transmitter, and transmitting a response signal to the transceiver unit with a value representing the first challenge signal reception power;
transmitting a second challenge signal with the transceiver unit under changed conditions as compared to the first transmitting step;
receiving the second challenge signal with the code transmitter, measuring a reception power of the second challenge signal in the code transmitter, and transmitting a response signal to the transceiver unit with a value representing the second challenge signal reception power; and
comparing the challenge signal power level with the second challenge signal power level in the transceiver unit and controlling a vehicle mounted security device in dependence on the comparison and if an item of code information contained in the response signal corresponds to an expected item of reference code information. - View Dependent Claims (6, 7, 8)
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Specification