Time-of-Flight Ranging Systems

• US 20080284564A1
• Filed: 07/06/2005
• Published: 11/20/2008
• Est. Priority Date: 07/07/2004
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Leitch, Adam S.
• Granted Patent: US 7,978,049 B2
• Time in Patent Office: Days
• US Class Current: 340/5.61
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user
• CPC Class Codes: G01S 13/76 wherein pulse-type signals are transmitted
• CPC Class Codes: G07C 2009/0038 whereby the wake-up circuit is situated in the keyless data carrier
• CPC Class Codes: G07C 2009/00555 comprising means to detect or avoid relay attacks
• CPC Class Codes: G07C 2009/00793 by Hertzian waves
• CPC Class Codes: G07C 2209/63 Comprising locating means for detecting the position of the data carrier, i.e. within the vehicle or within a certain distance from the vehicle
• CPC Class Codes: G07C 9/00309 operated with bidirectional data transmission between data carrier and locks

Abstract

A time-of-flight ranging system, such as a keyless access control system, comprises a first part (10) and a second part (12), which may implemented as a portable device such as a key fob. Both parts have signal transmitting and receiving means (14, 22 and 26, 32) for effecting communication with each other. At least the first part comprises means for determining the distance between the first and second parts based on time-offlight. In order to save power, when that first and second parts are a relatively great distance apart, the time-of-flight measuring means computes the time based on a relatively coarse algorithm, and when the parts are relatively close, the computation is carried-out using a more precise algorithm. In variants and refinements of the system the clock frequency may be reduced when the first and second parts are a relatively great distance apart and increased when they are closer and the transmitter power may be reduced when the first and second parts are relatively close together and increased when they are a relatively great distance apart. The time-of-flight ranging system may be applied to not only entry security systems but also to tracking systems such as systems for tracking toddlers, personnel and equipment.

Claims

1. A method of operating a time-of-flight ranging system comprising first and second stations (10, 12) having transmitting and receiving means, the method comprising the first station measuring the time-of-flight of a signal between the first and second stations, calculating the time-of-flight using a relatively coarse algorithm when the second station is relatively far from the first station and calculating the time-of-flight in accordance with a relatively precise algorithm when the second station is relatively close to the first station.

2. A method as claimed in claim 1, characterised by reducing a clock frequency when the second station is relatively far from the first station.

3. A method as claimed in claim 1, characterised by reducing the transmitting power of at least the first station when the second station is relatively close to the first station.

4. A time-of-flight ranging system comprising first and second stations (10, 12), each of the first and second stations having transmitting and receiving means (22, 32) for communicating with each other, and control means (18, 30), characterised by the first station further comprising time-of-flight measuring means (18, 72) for determining the distance between itself and the second station, the measuring means being adapted to calculate time-of-flight in accordance with a relatively coarse algorithm when the second station is relatively far from the first station and to calculate time-of-flight in accordance with a relatively precise algorithm when the second station is relatively close to the first station.

5. A system as claimed in claim 4, characterised in that at least the first station comprises a clock generating means (66) for generating relatively low and relatively high clock frequencies and in that the control means (18) in the first station is responsive to the selected coarse or precise algorithm for selecting respectively the low or high frequency.

6. A system as claimed in claim 5, characterised by means (22) for producing a transmission frequency from the clock generating means.

7. A system as claimed in claim 4, characterised by at least the first station (10) having transmitting power management means (74) for adjusting the transmitting power between at least a first, high level when the relatively coarse algorithm is being used to calculate time-of-flight and a second, low level when the relatively precise algorithm is being used to calculate time-of-flight.

8. A system as claimed in claim 7, characterised by the second station (10) having transmitting power management means (90) for adjusting the transmitting power between at least a first, high level when the relatively coarse algorithm is being used to calculate time-of-flight and a second, low level when the relatively precise algorithm is being used to calculate time-of-flight.

9. A system as claimed in claim 4, characterised in that at least the first station (10) comprises a clock generating means (66) for generating relatively low and relatively high clock frequencies, in that the control means (18) in the first station is responsive to the selected coarse or precise algorithm for selecting respectively the low or high frequency, in that at least the first station has transmitting power management means (74) for adjusting the transmitting power between at least a first, high level when the relatively coarse algorithm is being used to calculate time-of-flight and a second, low level when the relatively precise algorithm is being used to calculate time-of-flight.

10. A system as claimed in claim 9, characterised by the second station (12) having transmitting power management means (90) for adjusting the transmitting power between at least a first, high level when the relatively coarse algorithm is being used to calculate time-of-flight and a second, low level when the relatively precise algorithm is being used to calculate time-of-flight.

11. A keyless access control system comprising first and second stations (10, 12), each of the first and second stations having transmitting and receiving means (22, 32) for communicating with each other, and control means (18, 30), characterised by the first station further comprising time-of-flight measuring means (18, 72) for determining the distance between itself and the second station, the measuring means being adapted to calculate time-of-flight in accordance with a relatively coarse algorithm when the second station is relatively far from the first station and to calculate time-of-flight in accordance with a relatively precise algorithm when the second station is relatively close to the first station.

12. A vehicle security system comprising lockable security means responsive to locally generated signals and a keyless access control system comprising a fixed first part (10) to be mounted in a vehicle and a portable second part (12) to be carried by a vehicle user, both said parts having signal transmitting and receiving means (22, 32) for effecting communication with each other, and control means (18, 30), characterised by the fixed first part further comprising time-of-flight measuring means (18, 72) for determining the distance between itself and the second station, the measuring means being adapted to calculate time-of-flight in accordance with a relatively coarse algorithm when the second station is relatively far from the first station and to calculate time-of-flight in accordance with a relatively precise algorithm when the second station is relatively close to the first station.