Koninklijke Philips Corporation N.V.

Adam Leitch

Martin S Wilcox

Neil Christopher Bird

Paul M Fulton

A device and method corrects time data based on a clock signal affected by jitter. The error due to jitter in a time measurement of an event in the clock signal is determined at the time of the event or as an average over a number of events. A measurement is made of a time dependent reference variable associated with a long-time constant device, such as a capacitor, which is relatively immune to localized jitter. The measurement may be a reading of the voltage across a charging capacitor. The measured value is compared to an expected value, and the time error is based on the result. The expected value may be stored or calculated from known charging rates of the capacitor. The error due to jitter of a time measurement is approximately linearly proportional to the difference in voltage between the measured and the expected values of the capacitor.

Measuring clock jitter

First and second devices having clocks which may have different clock rates. Obtaining a measure of the distance of propagation of a signal passing between the devices involves transmitting a first signalfrom the first device to the second device. After a turnaround time TAT, a second signalis transmitted from the second device to the first device. Any error in the clocks may lead to an error in the measurement of the turnaround time TAT. One device contains circuitry to calculate the ratio of the clock rates of the first and second devices, either by adjusting frequency divider ratios until there is LO frequency match, or by determining the offset frequency of an envelope of a mixed signal. The ratio of the clock rates is used to compensate the turnaround time TAT, to mitigate error. The accurate distance measurement can be used to determine if a relay attack has taken place in a vehicle security system.

Measuring the distance between devices

A time-of-flight ranging system, such as a keyless access Control system, comprises a first part and a second part, e.g., a portable device such as a key fob. Both parts have a transceiver for effecting communication with each other. At least the first part includes a device, e.g., a processor, for determining the distance between the two parts based on time-off-light. To save power, when the two parts are a relatively great distance apart, a time-of-flight measuring device 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. The clock frequency may be reduced when the two parts are a relatively great distance apart, and increased when they are closer. Further the transmitter power may be reduced when the two parts are relatively close together and increased when they are a relatively great distance apart.

Time-of-flight ranging systems using coarse and fine measurements

A network for locating a wireless tag comprises a plurality of wireless nodes. The nodes are not connected together by a wired network. Each node is included in a floor tile for installation inside a building and configured to be wirelessly connectable to at least one other node. When the floor tiles are installed, the plurality of nodes form a mesh or grid and provide overlapping wireless coverage for locating the tag by reference to the mesh.

Network for locating a wireless tag

Method for obtaining range and/or positional information of electronic devices typically rely on a device (A) re-questing that another device (B) supplies a reply message (), which contains some timing information (T, T) on the signals received and sent. Problems that arise in such networks comprise: firstly, some devices (C) may be out of range of the device (A) that initiates the ranging measurements, and secondly, some devices (B, C) may not be allowed to communicate with each other and thus, the distance between these devices cannot be found. This invention discloses that in these cases, eavesdropping on messages () passing between other devices (A, B, C) in the system can result in that distances between additional devices are found. Furthermore, by using eavesdropping the number of transmissions, and therefore the potential for collisions, is reduced. Thus, the power consumption of the nodes in the network can be lowered.

Making time-of-flight measurements in master/slave and ad hoc networks by eaves-dropping on messages

A method of determining the relative position of a secondary station (SS) in a radio system including at least one master station (MS) and a plurality of secondary stations (SS), comprises the master station establishing a master log of the time stamp of signals transmitted by active stations and their identities and active secondary stations (SS) establishing a log of the time stamp of signals transmitted by other stations and their respective measured received quality. One of the active secondary stations forwards its log to the master station and the master station correlates the time stamps in the received log with the time stamps in the master log in order to determine the identities of the transmitters and utilizes the measured signal quality indications in the received log to determine the relative position of the secondary station with respect to the locations of the transmitters identified.

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Brighton, United Kingdom

Adam Leitch