Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2002-03-29
2004-04-13
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S463000, C342S464000
Reexamination Certificate
active
06720922
ABSTRACT:
BACKGROUND
1. Technical Field
The invention is related to location tracking systems, and more particularly to a system and process for determining the location of persons and objects carrying radio frequency (RF) transmitters that transmit data messages to at least one RF receiver connected to a computer in a computer network. The receivers forward data received from the transmitters to the network, along with radio signal strength indicator (RSSI) data, for computation of the location of the person or object carrying each transmitter.
2. Background Art
Knowledge of the location of people and objects is essential to the viability of many current mobile and ubiquitous computing schemes. For example, in a mobile computing environment, a user of a mobile computing device (e.g., notebook computer, handheld PC, palm-size PC, Personal Digital Assistant (PDA) or mobile phone) may wish the device to provide directions to a particular location in a building, such as the nearest printer, snack room, restroom, etc., or perhaps directions to a particular conference room or office within the building. This type of information is dependent on knowing the current location of the user. Mobile computing device users also typically expect messages and other notification information to be provided to them wherever they happen to be. However, some notifications can be dependent upon the user's location. For instance, a user might be notified that he or she is near a printer where a user-submitted document has been printed. Again the user's current location is needed to make such a notification. A mobile computing device user might also want to know the location of other people in the building, in order to find them or obtain information about them. For example, a user might want to get a list of the names of people attending the same meeting. To obtain this information, it is necessary to know what people are at the location of the meeting. The foregoing are just a few examples of the need to know the location of people. It is easy to imagine many other situations where knowledge of the location of people would be useful to a mobile computing device user.
Location information is equally critical in so-called ubiquitous computing. Ubiquitous computing revolves around extending computational activities beyond the current desktop model and into the environment. In future homes and offices, access to computing should be as natural as access to lighting. Users should not be required to go to a special place (i.e., the desktop) to interact with the computer. Rather, the computer should be available to interface with the user anywhere in the home or office (or more generally anywhere in an arbitrarily large environment), through whatever set of devices is available, be they fixed or carried by the user.
It is noted that the term computer is used loosely here in that the user actually would have access to a wide variety of computing and information services, which will likely employ many computers and “smart” devices such as the aforementioned PDA's, mobile phones, etc. For example, computing services such as web browsing, document editing, or video conferencing are envisioned. Thus, it should be understood that when the term computer is used in connection with the concept of ubiquitous computing, in actuality many computers may be involved non-exclusively in a single interactive session.
The usefulness of an ubiquitous computing system hinges on the ability to maintain an awareness of the users, particularly their locations. One goal of such a system would then be to understand the physical and functional relationship between the users and various I/O devices. This knowledge could be employed to allow a user to move from room to room while still maintaining an interactive session with the computer. In addition, knowledge about who and what is in the vicinity of a person can be used to tailor a person's environment or computing session to behave in a context-sensitive manner. For example, knowing the location of a person in a building can be used to infer what activity that person is engaged in and then the environment or computing session can be adjusted appropriately.
There are several current technologies for automatically determining the location of people and objects. For example, one of the first of such location systems uses diffuse infrared technology to determine the location of people and objects in an indoor environment. A small infrared emitting badge (sometimes referred to as a button or tag) is worn by each person, or attached to each object, whose location is to be tracked. The badge automatically emits an infrared signal containing a unique identifier every 10 seconds, or upon request of a central server. These requests are transmitted to the badges via a series of fixed infrared sensors placed throughout the indoor environment—typically mounted to the ceiling. The sensors also receive the infrared emissions from badges within their line-of-sight. The central server, which is hardwired to each sensor, collects the data received by the sensors from the badges and provides it to a location program for processing. These types of systems do not provide the actual 3D location of the person or object carrying the badge. Rather, the person's or object's location is deemed to be within the room or area containing the infrared sensor that received the emission from the badge attached to the person or object. In addition, these systems, being infrared-based, are susceptible to interference from spurious infrared emissions from such sources as fluorescent lighting or direct sunlight. Further, diffuse infrared-based systems have a limited range, typically only several meters. Thus, except in small rooms, multiple sensors are required to cover the area. In addition, since the sensors must be within the line-of-sight of the badges, a sensor must be placed in every space within a room that cannot be seen from other parts of the room. As a result, a considerable number of sensors have to be installed and hardwired to the central server. This infrastructure can be quite expensive and in some cases cost prohibitive.
Other existing indoor location systems attempt to improve the accuracy of the location process using a combination of radio frequency and ultrasonic emission. In these systems, a central controller sends a request for location data via a short range radio transmission to each badge worn by the people, or attached to the objects, whose location is being tracked. In response, the badges emit an ultrasonic pulse to a grid of fixed receivers, which are typically mounted to the ceiling. Each receiver that “hears” the ultrasonic pulse emitted from a badge reports its distance from the badge to the central controller via hardwired connections. Specifically, a synchronized reset signal is sent to each receiver at the same time the location request is transmitted to the badges. This reset signal starts a timing procedure that measures the time between the reset signal and the receipt of a ultrasonic pulse for a badge within range of the receiver. The receiver then computes its distance from the badge emitting the pulse and reports this to the central controller. An ultrasound time-of-flight lateration technique is then used by the controller to accurately determine the locations of the badges. While these types of systems do provide very accurate location information, they again require an expensive infrastructure in form of multiple receivers mounted throughout the environment which must be hardwired to the central controller. In addition, the accuracy of these systems has been found to be adversely affected if the placement of the receivers is less than optimal. Further, there is a concern associated with animals being sensitive to ultrasonic emissions.
A variation of the combined radio frequency and ultrasonic location system requires the badges to determine their own location, presumably to compute directions, and the like, and to provide the information to a person ca
Needham Roger M.
Williams Lyndsay
Lyon Richard T.
Lyon & Harr LLP
Microsoft Corporation
Phan Dao
LandOfFree
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