Communications: electrical – Condition responsive indicating system – With particular coupling link
Reexamination Certificate
1998-08-18
2001-03-27
Crosland, Donnie L. (Department: 2736)
Communications: electrical
Condition responsive indicating system
With particular coupling link
C340S854600, C340S870160, C340S870210, C340S511000, C340S531000, C340S870030, C340S870030, C340S870030
Reexamination Certificate
active
06208247
ABSTRACT:
BACKGROKUND OF THE INVENTION
1. Field of the Invention
The invention relates to wireless telemetry, security networks, or monitoring of physical conditions. In particular, the invention relates to the remote detection, monitoring or tracking of vehicles, personnel, or other physical conditions, for example in industrial equipment monitoring and control systems.
2. Description of the Related Art
Sensor networks have numerous applications, such as security, industrial monitoring, military reconnaissance and biomedical monitoring. In many such applications it is either inconvenient or impossible to connect the sensors by wire or cable; a wireless network is preferable.
Seismic sensors, for example, can be used to detect intrusion or movement of vehicles, personnel or large earth masses. For example, U.S. Pat. No. 4,649,524 to Vance (1987) describes an integrated acoustic network which provides warning of impending groundfall in underground mines. The system includes a plurality of geophones which derive acoustic signals from which the source of seismic disturbances is located, and an array of high frequency piezoelectric sensors which pick up signals from small ground disturbances which precede groundfall.
The detection of vehicles and personnel is more difficult than detecting large signals, as from earthquakes or movement of earth masses. Quiet vehicles and personnel movement produce seismic signals which may not be detectable by geophones at ranges of more than tens of meters, particularly in the presence of background noise. The reliable detection or tracking over large areas thus requires very large numbers of sensitive detectors, spaced closely. The placement of such large numbers of conventional detectors is generally inconvenient, expensive and time consuming if they must be wired for communication or power supply. A wireless network of numerous sensitive, low cost, low powered sensor stations would be more desirable.
Wireless networks of sensor stations, however, present several technical challenges. Wireless communication generally requires higher power than wired communication over the same distance; but an individual wireless sensor station requires a limited, self- contained power supply, which usually dictates that it conserve energy. The resulting low power constraint severely limits the range of wireless transmission by an individual sensor station. There are other drawbacks: wireless communication is vulnerable to jamming or unintentional interference. It is also overt in that the source of a transmission can be located by a hostile agent. If control or data processing occurs at a central location, then the entire network is vulnerable to failure of the central processor. Such an architecture has low reliability and cannot easily survive in a hostile environment. Wireless communication among large numbers of densely placed sensor stations requires sophisticated multiplexing or scheduling to avoid cross-interference. If the stations are placed randomly or some have initially unknown locations, it is difficult to learn the topology of the network so that multi-hop communications (communications relayed among multiple stations) may be scheduled.
Wireless security devices, such as wireless alarms, are widely available. Such systems generally employ only one-way wireless communication. For example, Brunius, U.S. Pat. No. 4,855,713 describes a system in which one-way alarm transmitters report to a central processing unit (CPU). The system even permits the CPU to detect new alarm transmitters and add them to the programmed system. Such systems are limited by one-way communication from the alarms to the central control. This limits their flexibility and utility, because it is impossible to remotely reprogram or adapt the network of sensors to a changing environment or a new purpose. An additional problem in the patented system is that the alarm transmitters must each have sufficient power to be received by the central receivers, or a repeater must be provided. This requires relatively high power to cover a significant area. The number of possible transmitters is also limited to the number of communication channels available; otherwise, simultaneous transmissions on the same channel will interfere with one another and be unintelligible. This system cannot be extended to permit a truly distributed, multihop network containing very high numbers of densely placed, low power sensor stations.
Another shortcoming of prior detection and alarm systems is that very little signal processing of the alarm condition is available at the sensor station, especially with wireless systems. This makes it difficult to distinguish among relevant, urgent or irrelevant signals unless the entire signal is transmitted, which would require a large expenditure of energy.
SUMMARY OF THE INVENTION
The invention is a miniature electronic sensing station, adaptable for two-way wireless communication in a network with other similar sensing devices, for sensing events such as an intrusion, vehicle movement, a change in status of some industrial process, or any physical change that can be detected by the sensors. Deployment in a network allows monitoring of the spatial extent and distribution of the sensed condition. Each sensing station in the network includes one or more sensors; a digital signal processor for analyzing the data from the sensors; a programmable microprocessor for making decisions based upon the analyzed data, and for controlling communication functions; a power supply; and a wireless transceiver, for communicating with other sensing devices in the network and with users. All of the components of the sensing station are enclosed in a single package and collectively constitute a “node” of the network. In a typical application a network of such nodes may contain large numbers of such sensing nodes (more than 100), spaced fairly closely together (typically within less than 100 yards). The nodes can be placed randomly. They could, for example, be dropped from an aircraft or a ship; they could be placed manually. It is not necessary for each node to have a known location before startup; the nodes are programmable to organize themselves in a distributed fashion. Control of the network is distributed among the nodes; no indispensable central controller is necessary.
The invention preferably is used in a large network of wireless nodes, each of which is very compact and has a very limited power supply. The limitation on available power makes low power consumption an objective at every level of the invention. The practical implementation of this network architecture depends on several features which cooperate in a synergistic manner to allow effective, low powered sensing and wireless communication. At the node level the invention uses low powered sensors, low powered digital signal processing, a micropower programmable microprocessor, and a low powered RF transceiver, all cooperating in an architecture well adapted to conserve energy. At the network level, the design also conserves energy by fully utilizing the large number of nodes and low powered short range multi-hop communication in a web-like network.
Two techniques are used at the node level as energy conserving motifs: (1) circuits which are not required to be active during a time window are held in an inactive “sleep mode” so as to conserve energy, and (2) whenever possible, data is processed, compressed or summarized before transmission. This latter technique is effective because wireless transmission consumes vastly more energy than computation, especially where low power complementary metal oxide semiconductor (CMOS) circuitry can be used for computation.
The sensor or sensors may be of several types, such as seismic, acoustic, infrared, thermal, optical, magnetic or mechanical (for example, an accelerometer). The invention includes realizations of micro-seismic and micro-infrared sensors, but other sensors could also be used, as long as they consume low power and are small.
The sensor may include a sensing device that produces an an
Agre Jonathan R.
Clare Loren P.
Engdahl Jonathan R.
Kaiser William
Loeffelholz Christian J.
Crosland Donnie L.
Koppel & Jacobs
Rockwell Science Center LLC
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