Electronic tether

Details Electronic tether Electronic tether

2001-06-13

2003-03-04

Wu, Daniel J. (Department: 2632)

Communications: electrical

Condition responsive indicating system

Specific condition

C340S990000

Reexamination Certificate

active

06529131

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to positioning determining devices, and in particular to devices that enable the position of a person to be determined relative to another person wherein a global positioning system receiver is used to determine the distance, direction and possible elevation distance between another global position receiver with the two devices interacting directly with each other not requiring a monitoring station.
2. Description of the Related Art
There have been many attempts in the past to construct and market an electronic tether. The most common forms of these products have used radio frequency (RF) transmitters and receivers. In this prior art, an individual (subordinate) would carry a portable RF transmitter that would periodically emit an RF signal that would be received by a master unit. The master unit relied upon the signal strength of the RF transmission to determine the proximity of the subordinate unit. If the received signal strength was less than a predefined level, an alert was sounded. These devices lacked the sophistication necessary to accurately determine distance between the subordinate unit and master unit or where the subordinate unit was in relation to the master unit. It is to be understood that a typical master unit would be a parent and a subordinate unit would be a child. A typical environment would be in the wilderness, theme park, shopping mall or in a crowded city.
Recent technology developments permit the monitoring of an individual's location by incorporating a Global Positioning System (GPS). Global positioning uses satellites that are able to accurately fix an individual's location within a few feet in distance. However, the use of this technology has, in the past, required the user to subscribe to monthly monitoring services. Such a method does not and cannot address the need for a parent, guardian or caregiver to be notified immediately if the individual under their supervision has traveled beyond a safe predetermined distance. Further, this method does not facilitate the use of location identification as a portable, use as needed, monitoring device. Another use of the GPS is to use two portable devices, master and subordinate, each equipped with a GPS receiver and the capability of the subordinate unit to transmit its location as defined by signals it receives from the GPS. In this implementation, the ability to locate an individual is dependent upon the fact that both the caregiver and the supervised individual's device must be receiving GPS signals.
The prior art systems have many disadvantages. First, with reference to a device that relies solely on signal strength to determine range, these devices cannot compensate for signal strength variations that occur in one's surroundings. That is to say, RF signals do not always arrive at a receiver with predictable strength in all locations. We know, for example, that signal strength at a particular distance in open space will be significantly different from the same transmitter when it is moved from open space to compartmentalized spaces of buildings. Therefore, an individual, such as a child, moving from an open play area within his safe zone to a playground maze or other type of structure, also within his safe zone, may cause nuisance type alarms because of signal attenuation. Secondly, devices that rely solely on data received from GPS satellites are subject to the availability of the GPS signal. However, depending upon the terrain and other obstructions, a temporary loss of signal can and does occur. In this situation, there would be an inactive period until the GPS receiver reacquires position information. During this temporary interruption of signal, the whereabouts of the child would be unavailable.
SUMMARY OF THE INVENTION
The system of this invention uses GPS receivers combined with RF transceivers and proprietary software. Both master and subordinate portable units are composed of a GPS receiver, RF transceiver, power supply, electronic compass, user interface and microprocessor. The units of this invention may be packaged as user wearable compact devices. In another embodiment, the master unit of this invention is capable of being connected to a fixed position base unit that is interfaced with a personal computer.
The operation of the system of this invention begins with the programming of the master unit and its associated subordinate unit(s). By utilizing the user interface, the units are placed in a program mode. This program mode facilitates the identifying of subordinate unit(s) by the master unit, and the identification of the master unit by the subordinate unit(s). Unique identification information contained in each master and subordinate unit are exchanged during the set-up stage of the user program. The information exchanged is kept in memory of the master and subordinate units. The exchange and storage of this information is to assure that when multiple users of the invention are in close proximity to each other that only those units programmed to be a “family” will communicate with each other. While in the programming mode, the master unit will identify each subordinate's unique identification number and will place in memory the identification number for each subordinate unit in its family. Subsequent to programming the master and subordinate unit(s) as a family, the master unit is programmed through the user interface to alert the master if the subordinate unit(s) has traveled beyond a selected distance. The user selected distances, of pre-established values have been optimized for system accuracy. In some embodiments of the subordinate unit(s), it is possible to program similar distance monitoring, measurement and notification as that of the master unit.
Once placed in service, the master and subordinate unit(s) will acquire information from the available GPS satellites. This data is placed in temporary memory. Upon completion of the acquisition process, the master unit will begin polling or interrogating the subordinate unit(s) by means of the RF transceiver. The subordinate unit(s) receiving the request from the master unit will respond by means of the RF transceiver, with the current or stored GPS coordinates. Included in this transmission will be the time that those coordinates were stored in temporary memory and the time of the response (transmission) to the polling request. Upon receipt of the polling response from the subordinate unit(s) by means of its RF transceiver, the master unit will calculate the distance to the subordinate unit(s) based upon the coordinates of the subordinate(s) with regard to the current coordinates of the master unit, compare that distance to the selected allowable range, and immediately display, and continuously display, the distance to and direction of travel to each subordinate unit. This process continues as long as the devices are in service. The continuing process of polling, receiving and calculating distance provides constant visual indication of the distance to a subordinate unit with regard to the position of the master unit. Depending upon the type of display used in a master unit, the location information of each subordinate unit may scroll automatically or manually at the discretion of the master user. As an important part of this invention, the proprietary software not only references the calculated distance to each subordinate unit against the user selected allowable range, but will reference the time associated with the coordinates that were transmitted by the subordinate unit(s) response.
The time associated with the received coordinates of a subordinate unit may be critical in determining the validity of the calculated distance to the subordinate unit(s). Whereas GPS signal availability could become temporarily unavailable, system design provides for alternate methods of determining distance that can be used in redundancy with valid GPS data or can determine distance independently of the availability of the GPS data. As previously

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