Range-Based Wireless Alarm System
First Claim
1. An alarm system comprised of a controlling device and a plurality of portable and handheld devices in communication with the controlling device over a wireless local area network (WLAN), wherein at each reporting interval, the controlling device computes the distance between itself and the plurality of portable and handheld devices and raises an audible or visual alarm when one of the computed distances exceeds the maximum distance value. The reporting interval and the maximum distance value are set by the user on the controlling device. The controlling device may display in real-time the computed distances on its video display unit if it is available.
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Abstract
A range-based alarm system comprised of a controlling device and a plurality of portable, handheld devices communicating over a wireless local area network (WLAN); wherein the controlling device frequently computes the distance between itself and the plurality of portable, handheld devices and raises an audible or visual alarm when one of the computed distances exceeds its programmed operating range. An audible or visual alarm is also triggered on any of a plurality of portable, handheld devices when it has lost communication with the controlling device or when instructed by the controlling device.
23 Citations
18 Claims
- 1. An alarm system comprised of a controlling device and a plurality of portable and handheld devices in communication with the controlling device over a wireless local area network (WLAN), wherein at each reporting interval, the controlling device computes the distance between itself and the plurality of portable and handheld devices and raises an audible or visual alarm when one of the computed distances exceeds the maximum distance value. The reporting interval and the maximum distance value are set by the user on the controlling device. The controlling device may display in real-time the computed distances on its video display unit if it is available.
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2. A method of synchronizing the clocks between two portable devices operating in a WLAN, wherein the first device is the controlling device and the second device is the tracking device, comprised of the following steps:
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a.) Placing both devices in close proximity, pushing a time-sync button on the controlling device, and then pushing the time-sync button of the tracking device within a few seconds. b.) The tracking device transmits a request for synchronization. The controlling device validates the source address of the tracking device and responds with a number of time-sync data packets. Each time-sync data packet carries the time stamp of when the packet is transmitted. The number of time-sync packets transmitted from the controlling device is varied and the last packet is marked by a special identification code. c.) The tracking device receives a time-sync packet from the controlling device, extracts the time stamp and updates its internal clock time with the received time stamp. d.) After receiving the last time-sync packet from the controlling device, the tracking device transmits a confirmation-packet with a time stamp that indicates the time the packet is transmitted. e.) The controlling device extracts the time stamp from the confirmation packet and subtracts this time stamp from its internal time. If the result is non-zero, the controlling device stores this value (TA) in its memory to be used for adjusting the times of packets transmitted from this tracking device. f.) The controlling device sends an acknowledgement packet to the tracking device indicating that the clock synchronization process is complete. g.) The tracking device receives the acknowledgement packet from the controlling device, displays a visual indication to the user that the synchronization with the controlling device is successful. - View Dependent Claims (3, 4, 5, 6)
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Specification