Abstract:
Systems, methods and computer program products for accurately determining the location of people or objects are disclosed. The location of people or objects is calculated based on a received signal strength indication (RSSI). The distance between a transmitter and a receiver is calculated in a manner that can reduce or eliminate the effect of multiple paths of a signal between the transmitter and the receiver. Therefore, the location system provides a mechanism for determining the RSSI value accurately regardless of the multiple paths between a transmitter and receiver.

Description:
REFERENCE TO RELATED APPLICATIONS 
   The present invention claims priority to U.S. Provisional Patent Application Ser. No. 60/512,935, filed Oct. 20, 2003, entitled Peak Picking Time Diversity Used in Location Systems, the contents of which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to location systems, in particular to methods, systems and computer program products for determining object locations in the location systems. 
   BACKGROUND OF THE INVENTION 
   It is useful to know the location of people or objects for several reasons. The location of people or objects allows another party to find lost people or objects, such as a child or expensive equipments. Location information can also be used as a piece of data in conjunction with other information. For example, knowledge about the location of a portable laptop computer combined with knowledge about the location of all the printers in a building can allow a system to automatically route a print job from the laptop computer to the nearest printer, thus saving time and aggravation. Additionally, the knowledge of who is in a particular room in a building can also allow a system to adjust the temperature or lighting of that room to the individual&#39;s preferences or route that person&#39;s telephone calls to the phone in that room. These applications are examples illustrating the utility of a system that allows the location of people or objects to be known. 
   Conventional location systems are generally based on one of two methods. In the first method, the amount of time is measured for a signal to travel from point A to point B, and then the distance between the two points A and B is calculated. In the second method, the conventional location systems calculate the distance between a transmitter and a receiver based on a received signal strength indication (RSSI). The RSSI is a function of distance and a path-loss factor:
 
 RSSI= 1/ d   −f 
 
where d is distance and f is the factor.
 
   While the second method is conceptually simpler than the first method, the signal wave travels over many paths between the transmitter and the receiver, especially in indoor space. Sometimes these multiple path signals arrive at the receiver in-phase (constructively) and sometimes they arrive at the receiver out-of-phase (destructively). This means that the RSSI can be 3 dB higher than the actual value or as much as 30 dB lower than the true value. This multiple path fading makes it extremely difficult to determine the RSSI value accurately in the location systems that are based on the second method. 
   SUMMARY OF THE INVENTION 
   There is a need for location systems that accurately determine the location of people or objects using a received signal strength indication (RSSI). The present invention provides such location systems that are able to accurately calculate the distance between a transmitter and a receiver based on the RSSI. In the present invention, the distance between the transmitter and the receiver is calculated in a manner that reduces or eliminates the effect of multiple paths of a signal between the transmitter and the receiver. Therefore, the present invention provides a mechanism for determining the RSSI value accurately regardless of the multiple paths of a signal between the transmitter and the receiver. 
   In accordance with one aspect of the present invention, a system is provided that includes a transmitter for transmitting a signal. The system also includes a receiver for receiving the signal transmitted from the transmitter. The receiver determines the strength of the signal based on a highest peak value of the signal within a sampling window defined with respect to time. 
   In accordance with another aspect of the present invention, a method is provided for determining signal strength in a computing device. The method includes the step of receiving a signal transmitted from a transmitter. The method also includes the step of determining the strength of the signal based on a highest peak value of the signal within a sampling window defined with respect to time. 
   In another aspect of the invention, a computer program product is provided for holding instructions executable in a computer for determining a signal strength. The instructions are executed to receive a signal transmitted from a transmitter. The instructions are also executed to determine the strength of the signal based on a highest peak value of the signal within a sampling window defined with respect to time. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned features and advantages, and other features and aspects of the present invention, will become better understood with regard to the following description and accompanying drawings, wherein: 
       FIG. 1  illustrates an exemplary location system having an object identifier and a location determining module according to an embodiment of the invention; 
       FIG. 2  illustrates the location system in more detail that includes a network connection element, one or more object identifiers, a location resolver, and an optional fixed location identifier; 
       FIG. 3  illustrates an object identifier according to an embodiment of the invention; 
       FIG. 4  is a perspective view of an object identifier according to an embodiment of the invention; 
       FIGS. 5A-5C  illustrate various methods of operation of an object identifier according to various embodiments of the invention; 
       FIG. 6  illustrates a network connection element according to an embodiment of the invention; 
       FIG. 7  illustrates a fixed location identifier according to an embodiment of the invention; 
       FIG. 8  illustrates a location resolver according to an embodiment of the invention; 
       FIG. 9A  provides a method of operation of a location resolver according to an embodiment of the invention; 
       FIG. 9B  is flow chart showing an exemplary operation of the location resolver to determine the strength of the received signal according to an embodiment of the invention; 
       FIG. 9C  is a flow chart illustrating that the peak picking method of the present invention is used in conjunction with space diversity; 
       FIG. 9D  is a flow chart illustrating that the peak picking method of the present invention is used in conjunction with time diversity; 
       FIG. 9E  is a flow chart illustrating that the peak picking method of the present invention is used in conjunction with polarization diversity; 
       FIG. 10A  depicts an example of the received signal; 
       FIG. 10B  depicts an example of the received signal with a sampling window superimposed on it; 
       FIG. 10C  depicts an example of the received signal in which peak values are selected with the sampling window; 
       FIG. 11  illustrates a location system according to a further embodiment of the invention; 
       FIG. 12  provides a perspective view of a location system installed at a location according to a further embodiment of the invention; and 
       FIG. 13  illustrates a network interface for use in a network connection element or a location resolver according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   Certain embodiments of the present invention are described below. It is, however, expressly noted that the present invention is not limited to these embodiments, but rather the intention is that additions and modifications to what is expressly described herein also are included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein, without departing from the spirit and scope of the invention. 
   The illustrative embodiment of the present invention provides a location system that can be used to locate people or objects in a space, primarily indoors. In the illustrative embodiment, an array of sensors or receivers pick up energy transmitted from a device (tag), such as an object identifier and a transmitter, coupled to the people or objects. The examples of types of this energy may include infrared ( 1 R), radio-frequency (RF) and ultrasonic (US). The location system processes the data obtained from the sensors and/or their supporting equipments using one or more computational techniques to determine the location of the people or objects. These computational techniques include, but are not limited to, triangulation, multilateration, received signal strength and time-of-arrival calculations, which will be described below in more detail with reference to  FIG. 9A . The illustrative embodiment provides a technique that utilizes RF signal strength to accurately determine the location of the people or objects. In particular, the illustrative embodiment accurately determines the RF signal strength based on a highest peak value of the RF signal within a given sampling window, which is subsequently used in the location computation process. One of ordinary skill in the art will appreciate that although the illustrative embodiment will be described relative to RF signals, the present invention may apply to other types of signals, such as US signals. 
     FIG. 1  is an exemplary location system  100  provided in the illustrative embodiment of the present invention. The exemplary location system  100  includes an object identifier  800  and a location determining module  14 . The object identifier  800  may be coupled to an object such that a location of the object corresponds to the location of the object identifier  800 . The object identifier  800  may be any device capable of transmitting a signal for use in identifying a location of an object. In the illustrative embodiment of the present invention, the object identifier  800  can be implemented in an electronic device. The electronic device may take many forms of, for example, a processor, a portable computer, a personal digital assistant, a communication device, such as a cellular phone, a network and any device capable of manipulating information, a receiver, a transmitter, an interface or any combination of these devices. A network may be a local area network (LAN), a wide area network (WAN), the Internet, an intranet, or a metropolitan network. The network may be a wireless network such as a Bluetooth network, a cellular network, a GSM based network, a hard wired network, or some other type of network. 
   According to various embodiments of the invention, the object identifier  800  transmits two identifiers, one identifier corresponding to the particular object identifier  800  and a second identifier which is a group designator. While the identifiers may be in many forms, some examples, according to various embodiments of the invention, include numbers, letters, URLs, MAC addresses and IP addresses. The object identifier  800  will be described below in more detail with reference to  FIGS. 3-5C . 
   According to an embodiment of the invention, the location determining module  14  may include any structure suitable for determining location. Examples include any device with intelligence to determine the location of one or more object identifiers. According to various embodiments of the invention, the location determining module  14  may include one or more, or combinations, of each of the following: a network connection element, a fixed location identifier, a location resolver, a database, topology data, an electronic device, a web interface, a network interface, a specialized network interface, an implementation interface, a database interface, a network and/or a specialized network, a receiver and/or a transmitter. According to various embodiments of the invention, the location determining module  14  may have only a receiver, only a transmitter, both a receiver and a transmitter, and additional hardware if desired. It will be apparent to one of ordinary skill in the art that one or more components may be distributed in a wide variety of configurations. 
   According to various embodiments of the present invention, the present invention may be used to determine a location of an object with the location determining module  14 , or of the module  14  itself. In such an embodiment, the location determining module  14  may be a mobile module, capable of determining its own location relative to one or more object identifiers. In such an embodiment, the object identifiers may be fixed. Optionally, the object identifiers may be moving. One example of the use of a mobile location determining module  14  involves a location system configured to determine locations within a large area. If such a large area is populated by a small number of objects, the components of such a location system may be more efficiently configured by providing functionality of a location determining module  14  with each object. In such a case, object identifiers could be distributed throughout the large area. The location determining module  14  could then be adapted to receive location signals from the object identifiers and thereby determine a location of the location determining module  14 . In this embodiment, the location of the objects is determined relative to the location of one or more object identifiers, although the locations of the object identifiers may be known, allowing locations of objects to be determined relative to other references or by name, such as a location on a map or a specific room. 
   The configuration above is contrasted with another embodiment of the invention, better suited to environments with a greater number of objects in a smaller area. In such an embodiment, each object may be provided with an object identifier. One or more location determining modules may then be located within the area to receive location signals transmitted by the object identifiers. In this embodiment, the location of the objects is determined by determining the location of the object identifiers. 
   According to various embodiments of the invention, the location determining module  14  may be capable of performing additional functionality, such as receiving requests for information, providing information, storing information, commanding actions in response to location information, associating objects with other objects or with locations, establishing privacy conditions regarding availability of location information, interfacing directly with various network types, and the like. According to further embodiments of the invention, the location determining module  14  includes multiple, distributed receivers, some of which may be connected to a network, and others not connected to a network. According to various embodiments of the invention, the object identifier  800  and location determining module  14  utilize both RF signals and IR signals for the determination of location. 
   According to an embodiment of the invention, the location determining module  14  may include one or more databases. The databases may store information relating to current location of object identifiers, fixed location identifiers and network connection elements. The databases will be described below in more detail with reference to  FIG. 7 . 
   According to various embodiments of the invention, the location system  100  may be employed within an enclosed structure and hence can be applied to as an indoor positioning system. Enclosed structures include buildings, such as office buildings, exhibition halls, health care institutions, homes or other structures. According to other embodiments, the invention may be used outside of enclosed structures or may be used both concurrently within and outside enclosed structures. 
     FIG. 2  is a detailed block diagram of the location system  100  according to an illustrative embodiment of the present invention. The location system  100  is illustrated by way of example having an object identifier  800  in communication with a location determining module that include at least a network connection element  900 . According to an embodiment of the invention, the object identifier  800  is physically coupled to an object so that the location of the object identifier  800  is considered to be the location of the object. According to another embodiment of the invention, the location of the object may be determined by locating one or more object identifiers  800  in an area and coupling a network connection element  900  to an object. In such an embodiment, the location of the network connection element  900 , and hence the object, is determined relative to the one or more object identifiers  800 . The network connection element  900  is configured to be coupled to a network  400 . According to an optional embodiment of the invention, the network may be a wireless network. As illustrated in  FIG. 2 , one or more object identifiers  800  communicate to the network connection element  900 . According to another embodiment of the invention, the network connection element  900  may communicate back to the object identifier  800 . 
   According to a further embodiment of the invention, the location determining module  14  can include a fixed location identifier  1000 . Those of ordinary skill in the art will recognize that the fixed location identifier  1000  can be separate from the module  14 . The fixed location identifier  1000  is configured to receive signals from one or more object identifiers  800  and to retransmit that information. The retransmitted information may be received by the network connection element  900 . According to one embodiment of the invention the retransmitted information includes the information provided by the object identifier  800 , coupled with additional information to identify the fixed location identifier  1000  that is re-transmitting the information. According to an embodiment of the invention, a plurality of network connection elements  900 , fixed location identifiers  1000  and object identifiers  800  may be provided in the location system  100 . In such a case, the network  400  may provide communication among the network connection elements  900  in order to determine the location of one or more object identifiers  800  by one or more network connection elements  900  or by the use of other devices coupled to the network  400 . 
   As shown by way of example, a location determining module  14 , according to an embodiment of the invention, is illustrated, by way of example, as including the network connection element  900 , the fixed location identifier  1000  and the network  400 . One or ordinary skill in the art will appreciate that the location determining module  14  may not include one or more of these elements in other embodiments. 
   According to an embodiment of the invention, the object identifier  800  and/or fixed location identifier  1000  transmits various information. According to an embodiment of the invention, this information is transmitted over both RF and IR signals. Optionally, the information may be transmitted over only one signal. According to an embodiment of the invention, examples of the information transmitted may include one or all of the following: RF power level; IR power level; battery level; input device status; transmission frequency, e.g. repetition rate, for any or all types of transmissions, such as IR and/or RF; an identifier corresponding to the transmitting device; an identifier corresponding to a group to which the transmitting device is associated; any information received from another system component; status or condition information; or the like. According to an embodiment of the invention, some information may be repeated over multiple signal transmissions. Examples include transmitting input device status over ten transmissions to increase the likelihood of receipt by other components of the location system. 
   According to another embodiment of the present invention, the location system  100  can include a location resolver  1100  provided for communication with the network connection element  900 . In this embodiment, the location resolver  1100  communicates with one or more network connection elements  900 , or if desired other system components, to obtain information pertaining to the location of one or more object identifiers  800  and one or more optional fixed location identifiers  1000 . The location resolver  1100  may be provided in the form of software or hardware or a combination of both. The location resolver  1100  may communicate with one or more network connection elements  900  over a network  400 . The location resolver  1100  may directly be coupled to one or more network connection elements  900  in other embodiments. 
   As shown by way of example, the location determining module  14 , according to an embodiment of the invention, is illustrated, by way of example, as including the network connection element  900 , the location resolver  1100  and the fixed location identifier  1000 . In this embodiment, the network  400  is included in the location determining module  14 , although this need not be the case, and the location resolver  1100  may communicate with the location determining module  14  directly or over the network  400 . The location resolver  1100  will be described below in more detail with reference to  FIGS. 8-10C . 
     FIG. 3  is an exemplary object identifier  800  used in the illustrative embodiment of the present invention. The object identifier  800  is provided with a controller  810  and controller support  820 . The controller support  820  may include various items such as a power supply, such as a battery or other apparatus to provide electrical power, memory and/or various time keeping circuitry such as an oscillator. Controller support  820  may optionally include non-volatile memory. Various components of the controller support  820  may optionally be incorporated into the controller  810  or may be provided from an external source, outside the object identifier  800 . 
   According to an embodiment of the invention, the object identifier  800  may be provided with an RF transmitter  830 . According to a further embodiment of the invention the object identifier  800  may be provided with an IR transmitter  840 . According to an further embodiment of the invention the object identifier  800  is provided with both an RF transmitter  830  and an IR transmitter  840 . 
   According to another embodiment of the invention, the object identifier  800  is provided with an RF receiver  850 . According to another embodiment of the invention the object identifier may be provided with an IR receiver  860 . 
   The object identifier  800  may also be provided with an input device  870 . Examples of input devices include buttons, switches, keypads, ports for electrical or optical communication with other devices, sensors, such as photocell cameras or microphones. Other types of input devices  870  may be apparent to one of ordinary skill in the art upon reading this disclosure and are to be considered within the scope of the invention. One or more input devices  870  are configured to provide input to the controller  810  in order to allow the controller  810  to take an action, not take an action, or to forward information outside the object identifier  800  by way of an RF transmitter  830  and/or an IR transmitter  840 . 
   According to a further embodiment of the invention an indicator  880  may be provided to enable the controller  810  to output information in the proximity of the object identifier  800 . Examples of indicators  880  include visual, audio and vibrational devices. Examples of these include buzzers, bells, horns, LEDs, other forms of lights and/or displays. The indicator  880  may be configured to display or output information determined by the controller  810  or received by the controller  810  through the input device  870 , RF receiver  850  and/or the IR receiver  860 . 
   An object identifier  800  is illustrated by way of example according to an embodiment of the invention, in  FIG. 4 . The object identifier  800  is illustrated with two indicators  880  in the form of two LEDs. Three input devices  870  are also illustrated in the form of switches. Two switches are illustrated so as to correspond to the two indicators  880 , while the third switch  870  is illustrated on an opposing surface of the object identifier  800 . According to this illustrative embodiment, the input device  870  on the lower surface of the object identifier  800  is normally pushed in when the object identifier  800  is attached to an object. Upon removal from the object, the input device  870  extends, resulting in a change of position of the input device  870 . This embodiment allows the controller  810  to be alerted when the object identifier  800  is removed from an object. Each of the indicators  880  may be configured to illuminate upon the activation of the corresponding switches, input devices  870 , so as to allow visual confirmation of the activation of one of the switches. Various uses of these switches will become apparent to one of ordinary skill in the art. Several examples, by way of illustration, include panic alerts, causing the processor  810  to emit a specialized signal through at least one of the RF transmitter  830  and the IR transmitter  840 . A further example may involve an ability to configure a portion of the location system  100  remotely by the activation of the input devices  870 . 
     FIGS. 5A ,  5 B and  5 C illustrate, according to various embodiments of the invention, various examples of a transmission of signals from the object identifier  800 . A first method  802  is illustrated in  FIG. 5A  according to an embodiment of the invention. An RF power level is set to Pn (step  804 ). An IR signal is transmitted (step  806 ). The delay of m seconds then occurs (step  808 ). An RF signal is transmitted (step  812 ). A further delay of x seconds occurs (step  814 ). Pn is then incremented (step  816 ). This method  802  provides a substantially consistent IR power level, while varying an RF power level. Varying the RF power level may assist in determining a location of the object identifier  800  by enabling the location determining module  14 , and in particular the network connection element  900  or location determining module  14  to receive less than all of the RF signals. According to an embodiment of the invention, one or both of the IR and RF signals are also transmitting information. Examples of this information may include the signal strength being transmitted, the period between transmissions, the length of time of the transmissions, various identifiers, corresponding to the object identifier  800 , information received from one or more input devices  870  and/or various status information, such as those pertaining to the controller  810  controller sport  820  or other components of the object identifier  800 . According to one embodiment of the invention the RF signal is transmitted every ten seconds and the IR signal is transmitted every twenty seconds. 
   Determination of the frequency and length of the transmissions involves considerations including battery life precision of location, frequency of updates to location, interference among signal transmissions and network traffic. 
   A further method  822  of an embodiment of the invention is illustrated in  FIG. 5B . According to this embodiment, an RF signal is transmitted (step  824 ) and a delay (step  826 ) occurs before the next transmission of an RF signal (step  824 ). Independently of the RF transmission, an IR signal is transmitted (step  828 ). The IR transmission (step  828 ) may occur simultaneously with the transmission of the RF signal (step  824 ) but this embodiment of the invention is not so limited. The transmission of the RF signal (step  828 ) may occur at any time relative to the transmission of the RF signal step  824 . A delay of c seconds step  832 , occurs before the next transmission of the RF signal,  828 . 
   According to a further embodiment of the invention, a further method  842  is illustrated by way of example in  FIG. 5C . According to this embodiment, an RF signal is transmitted (step  844 ) and an IR signal is transmitted (step  846 ). According to an alternative embodiment, a transmission in another medium may also occur (step  848 ). Examples of other mediums include ultra-sonic (US), visual light, or audible sound. According to the method  842  of  FIG. 5C , transmissions may be continuous, variable or occur at regular intervals. The transmissions among various mediums may be synchronized or random relative to transmissions in other mediums. 
   An example of a network connection element  900  according to an embodiment of the invention is illustrated in  FIG. 6 . A network connection element  900  can include one or more components similar to those of the object identifier  800  illustrated by way of example in  FIG. 3 . A network connection element  900  is provided with a controller  910  and a controller support  920 . Controller support  920  may optionally include non-volatile memory. Optionally, various embodiments of the invention may include one or more of the following in the network connection element  900 : an RF receiver  930 , an IR receiver  940 , an RF transmitter  950 , an IR transmitter  960 , an input device  970  and/or an indicator  980 . 
   The network connection element  900  is adapted to receive signals from the object identifier  800 . According to an embodiment of the invention, the network connection element  900  contains hardware and software capable of receiving signals from other components of the location system, such as an object identifier  800 , other network connection elements  900 . According to an embodiment of the invention, the network connection element  900  may have network connectivity software, a local web server, object identifier analysis software, software to transmit the results of an object identifier analysis to a remote server, DHCP software and local permanent storage. According to an embodiment of the invention, the network connection element  900  may also include configuration, service and debug applets to be used in the maintenance and configuration of the object identifier  800 . 
   The network connection element  900 , according to an embodiment of the invention, may further be provided with a web server  990 . As with the web server  340  of the receiver  300  of location system  100 , web server  990  of network connection element  900  is able to provide or receive information or commands. In various embodiments of the invention, the web server  990  may allow for control and configuration of any component of the location system. 
   According to a further embodiment of the invention, the network connection element  900  may be provided with a network interface  992 . The network interface  992 , as with the network interface  330  of location system  100 , is configured to couple the controller to a network  400 . According to an embodiment of the invention, the network interface  992  is adapted to packetize buffered information received and send this information as a group, thereby providing more efficient network usage in some applications. 
   A further embodiment of the invention provides a database  996  in communication with then controller  910  of the network connection element  900 . The database  996  may be provided within the network connection element  900  or may be provided on a network  400 . According to alternative embodiment of the invention, the database  996  may be provided within the network connection element  900  and also in direct communication with the network  400 . 
   The fixed location identifier  1000 , according to an embodiment of the invention is illustrated by way of example in  FIG. 7 . The fixed location identifier  1000  is similar to the object identifier- 800  illustrated and described in relation to  FIG. 3 . A controller  1010  is provided in communication with controller support  1020 . RF and IR transmitters and receivers  1030 ,  1040 ,  1050 ,  1060  may be provided individually or in combination according to various embodiments of the invention. An input device  1070  and indicator  1080  may also each or both be included in various embodiments of the invention. The fixed location identifier  1000  is configured to receive signals from one or more object identifiers  800 , and/or other fixed location identifiers  1000 , and retransmit these signals to a network connection element  900  along with identifying information to designate which of the fixed location identifiers  1000  is retransmitting the information. Additional information relating to the retransmitting fixed location identifier  1000  may also be appended, such as battery information or other status information allowing remote monitoring of the fixed location identifier  1000 . 
   According to various embodiments of the invention, the fixed location identifier  1000  may be provided with input devices  1070  or indicators  1080  to enable input information or various signaling functionality. Fixed location identifiers  1000  do not need to be coupled to other components by the use of wiring or other infrastructure. Therefore, the use of fixed location identifiers  1000  enable a location system to be implemented with fewer network connection elements, as fixed location identifiers can provide additional information as to the location of object identifiers  800 . Furthermore, fixed location identifiers  1000 , can extend the range of network connection elements  900  by providing an optional higher power transmission signal to reach network connection elements  900  at ranges that object identifiers  800  may be incapable of reaching. 
   The network connection element  900  is adapted to receive signals from the fixed location identifier  1000  as described above in relation to signals from the object identifier  800 . According to an embodiment of the invention, the network connection element  900  contains hardware and software capable of receiving signals from the fixed location identifier  1000 . According to an embodiment of the invention, the network connection element  900  may have network connectivity software, a local web server, fixed location identifier software, software to transmit the results of a fixed location identifier analysis to a remote server, DHCP software and local permanent storage. According to an embodiment of the invention, the network connection element  900  may also include configuration, service and debug applets to be used in the maintenance and configuration of the fixed location identifier  1000 . 
   The location resolver  1100 , according to an embodiment of the invention, is illustrated by way of example in  FIG. 8 . As shown in  FIG. 8 , a controller  1110  is provided in communication with a network interface  1120 . The network interface  1120  is adapted to be coupled to the network  400 . Controller support may also be optionally provided. A web server  1130  is provided in communication with a controller  1110 . The web server  1130  of the location resolver  1100  is similar to the web server  990  of the network connection element  900 , discussed herein. 
   According to an embodiment of the invention, the location resolver  1100  may be provided with a configuration capability to configure other components of the location system. For example, an embodiment of the location resolver  1100  may perform some or all of the following functions: reset system time; reset communications; disable all or selected input devices of all or selected components, such as object identifiers, fixed location identifiers, network connection elements; establish and/or cancel associations between all or selected components; establish and/or cancel privacy settings for specific location information; configure network communication protocols; configure receiver and/or transmitter configurations, altering or eliminating signals, signal types, such as RF, IR, ultrasonic, or the like, or transmission frequencies and the frequencies at which transmissions are expected; receive information on the location of the object identifier; determine or calculate the location of the object identifier  800 . 
   An implementation interface  1140  is also provided in communication with controller  1110 . The implementation interface  1140  is provided to communicate with other devices in order to allow for the communication of location information and/or initiation or response to commands as described herein. Various examples of implementation interfaces  1140  include XML and SMTP protocols, other examples may be apparent to those of ordinary skill in the art. 
   A database  1150  is also provided either within the location resolver  1100  or external the location resolver  1100 . The database  1150  is adapted to store information relating to the location of one or more object identifiers  800  and/or optional fixed location identifiers  1000  and/or network connection elements  900 . According to various embodiments of the invention, the database  1150  may store current and/or previous location and status information of location system components, associations of location system components with each other or locations, privacy protocols and status, topology data indicating locations of some or all location system components relative to each other, or in other descriptive terms, such as room or location names or by a coordinate system. 
   A database interface  1155  may be provided in another embodiment of the invention in order to facilitate interaction between the database  1150  and the controller  1110 . The database interface  1155  may be a network or other hardware or software to controller  1110  to enable the controller  1110  to access the database  1150 . Various examples of database interfaces  1155  include JDBC and ODBC, other examples may be apparent to those of ordinary skill in the art. 
   A method  1102  of operation of the location resolver  1100 , according to an embodiment of the invention is illustrated in  FIG. 9A . The location resolver  1100  initially waits for input from a receiver, such as the network connection element  900  (step  1104 ). The location resolver  1100  then determines whether an IR signal is received (step  1106 ). If an IR signal is received, data received from the transmitter and receiver&#39;s location is made available (step  1108 ). If an IR signal is not received, the location resolver  1100  checks to see if an RF signal is received (step  1112 ). Location resolver  1100  also checks to see if an RF signal is received after making any data available from the reception of an IR signal available. If an RF signal is not received, the location resolver  1100  according to an embodiment of the invention returns again to wait for further input from the network connection element  900 . If an RF signal is received, the location resolver  1100  determines the strength of the received RF signal using the peak picking method provided in the illustrative embodiment of the present invention (step  1113 ). The peak picking method will be described below in more detail with reference to  FIGS. 9B-10C . If the strength of the received RF signal is determined, the location resolver  1100  determines whether the RF signal power is high (step  1114 ). If so, data received from the transmitter is made available with a message indicating that the object identifier is within a large radius of the network connection element  900  (step  1116 ). If the RF signal power is not high, the location resolver  1100  determines whether the RF signal power is medium (step  1118 ). If so, data received from the object identifier is made available with a message that the object identifier is within a smaller radius of the network connection element  900  (step  1122 ). If the RF signal power is not medium, the location resolver  1100  determines whether the RF signal power is low (step  1124 ). If so, data from the object identifier  800  is made available with an indication that the object identifier is within a smaller radius of the network connection element  900  (step  1126 ). The location resolver  1100  then returns to await further input from one or more of the network connection elements  900  (step  1104 ). 
   It is understood that the method of  FIG. 9  may be accomplished by using transmitters or object identifiers that vary in output power or by constant power output transmitters. In using constant power output transmitters, received signal strength is categorized according to signal strength, such as by the use of a histogram. According to an embodiment of the invention, the network connection element  900  classifies signal strength within specific ranges and may pass an indication of the appropriate range to other location system components. According to another embodiment of the invention, the network connection element  900  provides a signal strength value that may be passed to other location system components, such as the location resolver  1100 , allowing more precise analysis of received signal strength information. 
   According to one embodiment of the invention, RF and IR signal strength are adjusted to a range of approximately 20 feet. Other embodiments of the invention may involve adjusting signal strength of RF and/or IR and/or other signal types, such as ultrasonic, ranges to a few inches, feet, thousands of feet, or miles. Another embodiment of the invention involves varying signal strength among various types of object identifiers. 
   A method of operation of the location resolver  1100  involves multilateration. Multilateration determines location by determining range from a relative location. Multilateration can be performed by a single receiver, but is best accomplished by multiple receivers. An object can infer the location of another object by calculating its range from one or more beacons with known locations using some type of signal measurement. According to an embodiment of the invention RF signal strength is used to determine location. According to a further embodiment both RF and IR are used to determine location. It is understood that an absence of a signal that is expected is considered a signal for purposes of determining location. For example, receipt of an RF signal but not an IR signal may indicate a transmitter is out of IR range but within RF range, or just out of line-of-sight if required for lower-powered IR transmissions. The receiver may be configured to expect both RF and IR transmissions at specific intervals generally or for a specific transmitter. This is one example of the use of both RF and IR for determination of location. 
   In addition to current signal information, other information may be used in determining location. Previous location information may also be used in determining current location. Locations of other location system components may also be used in determining location. For example, locations of one or more network connection elements  900 , one or more fixed location identifiers  1000  and other object identifiers  800  may be used in determining location of a particular location system component. According to one embodiment, establishing relative distances between additional nearby components and the component for which location information is desired assist in establishing a location with greater particularity. 
   According to an embodiment of the invention, transmission rates may vary among different types of object identifiers. Transmission rates may be adjusted in relation to the type of object for which location information is desired. Examples include low transmission rates for objects typically stationary, such as equipment typically found in a particular room. Whereas people, or mobile equipment may be better tracked by more frequent signal transmissions. 
   Another method of determining location involves at least one Bayesian network. A further method of determining location involves triangulation. An example of one or more of the foregoing methodologies are described, for example, in U.S. Pat. No. 5,774,876, which is incorporated herein by reference. Bayesian networks are also described in Castro, Paul et al. “A Probabilistic Room Location Service for Wireless Networked Environments” In:  Ubicomp  2001 : Ubiquitous Computing, Third International Conference, Atlanta, Ga., USA, Sep.  30- Oct.  2, 2001  Proceedings . Edited by G. D. Abowd, et al. Heidelberg, Germany: Springer-Verlag, 2001, LNCS 2201, p. 18 ff. This publication is incorporated herein by reference. Combinations of these methods or other methods of location determination may be apparent to one of ordinary skill in the art and are included within the scope of the invention. 
   Privacy conditions may be established regarding location information for one or more location system components. Privacy may be accomplished in a variety of ways. For example, privacy may be accomplished by not making location information available or by not determining location information. Privacy may be managed by an opt-out protocol, requiring an action to establish privacy. Privacy may be managed by an opt-in protocol, requiring an action to cancel privacy. A not-opt-out protocol may also be used, preventing action from establishing privacy. Various protocols may be used in combination within a location system. Different location system components may subject to different protocols. Examples include various groups of object identifiers being subject to different protocols, such as some people able to select a privacy protocol or a privacy status, such as privacy or no privacy, while object identifiers used to locate equipment may be subject to a not-opt-out protocol. According to an embodiment of the invention, protocols or privacy status may be assigned through a batch-processing capability in a user interface. According to another embodiment, privacy status for opt-in or opt-out protocols may be accomplished by an input device incorporated in the location system component. Optionally, privacy status may be confirmed by an indicator incorporated in the location system component. 
   Associations associating objects with other objects or with locations may be established. Examples of the use of associations include: determining procedure times, room utilization, proximity alerts that may be used to alert a fall of a person, regulatory compliance, person &amp; equipment associations, location &amp; equipment associations, friend &amp; foe associations, and automatic billing. According to an embodiment of the invention, association information may be stored in a database. Associations may be performed through a batch-processing capability in a user interface. According to another embodiment, associations may be accomplished by an input device incorporated in the location system component. Optionally, association status may be confirmed by an indicator incorporated in the location system component. One example involves activating an input device on an object identifier, fixed location identifier or network connection element. An indicator indicates, such as by an LED or sound, that association can be performed. An input device may then be activated within a limited time on another location system component, such as an object identifier, to establish an association between the components. 
   Events or actions may be initiated based on location information association information or input device status, or changes in any of these. One example involves sending information in response to an object identifier being within a range of locations or a specific location. An example includes paging a doctor when a specific patient enters a treatment area. Other examples of actions include entering information in a database, sending XML data containing the current location data and status of a location system component onto the network. An example is the use of a cardiac monitoring application typically used in a health care institution for receiving a report of a cardiac arrest. The term health care institution, as used herein, includes a wide variety of facilities associated with providing health care or services. Examples include hospitals, managed care facilities, assisted care facilities and clinics. The location system according to an embodiment of the invention may be configured to receive a request for the location of a particular patient, or the cardiac monitoring equipment sounding the alarm. The location system can then automatically reply with location information to assist health care institution staff in locating the patient in need. A similar example could use the activation of an input device on an object identifier as a distress call by a patient, with the alert and location information forwarded to a health care institution communication system for prompt attention by health care institution staff. One embodiment of the invention may interface with a Winegard interface to unlock a door, or activate other security equipment, in response to location information or input device status. Other examples include pages, WAP messages, sending e-mails and activating or canceling alarms. 
   According to an embodiment of the invention, the components of the location system do not retransmit signals if they are not received. By waiting until the next scheduled transmission, transmissions throughout the location system area are reduced and interference difficulties are reduced. 
     FIG. 9B  is a flow cart showing an exemplary operation of the location resolver  1100  to determine the strength of the received RF signal. In the illustrative embodiment of the present invention, the location of the object identifier  800  is calculated based on a received signal strength indication (RSSI). The RSSI is a function of distance and a path-loss factor:
   RSSI= 1/ d   −f   
where d is distance and f is the factor.
 
   If the location resolver  1100  receives the signal, it may include multiple paths fading of the signal (step  1132 ). Fading refers to the variation (with respect to time) of the amplitude or relative phase, or both, of one or more of the frequency components of the received signal.  FIG. 10A  depicts an exemplary received signal that reflects the multiple paths fading of the signal. The multiple paths fading may occur because the same signal wave travels over multiple paths between the object identifier  800  and the network connection element  900 , especially indoors. The exemplary signal depicted in  FIG. 10A  shows that the multiple paths wave sometimes arrives at the network connection element  900  in-phase (constructively) and sometimes out-of-phase (destructively). 
     FIG. 10B  depicts the exemplary received signal on which a sampling window  1001  is placed, as illustrated by step  1134  of  FIG. 9B . The sampling window  1001  may be selected to be small relative to the length of the time interval by which the object identifier transmits the RF signals in the illustrative embodiment. In the illustrative embodiment, the RF signals are received every ten seconds as described above with reference to  FIGS. 5A-5C . In the example depicted in  FIG. 10B , the sampling window  1001  is selected to have a 0.5 millisecond (msec) width. One of skill in the art will appreciate that the sampling window  1001  is illustrative and the width of the sampling window  1001  can be different in other embodiments depending on the time that the received signal lasts. 
   Referring back to  FIG. 9B , the location resolver  1100  then determines the peak value of the RSSI as a function of time within the sampling window  1001  (step  1136 ). The peak values can be determined, for example, by taking the derivative of the RSSI.  FIG. 10C  depicts the exemplary received signals in which peak values  1003 ,  1005  and  1007  of the received RF signal are determined with the sampling window  1001 . The peak values  1003 ,  1005  and  1007  in  FIG. 10C  indicate that the object identifier  800  to be located is moving. The highest peak value  1007  within the sampling window  1001  is then used in subsequent location calculations, such as multilateration and triangulation, that are described above with reference to  FIG. 9A  (step  1138 ). Although the highest peak value of the received RF signal is not the true RSSI, it has a slight offset that can be easily calculated out. For example,  FIG. 10C  show that the maximum RSSI value within the sample window is approximately +7 dBm. Within the same sampling window  1007 , the instantaneous RSSI varied between −38 dBm and +7 dBm. This +7 dBm value is used in subsequent location calculations. 
   An advantage of the present invention is that the illustrated location system reduces or eliminates the variability of the RSSI when the highest peak value is used in a subsequent location calculation than when an instantaneous value is used. Another advantage of the illustrative embodiment of the present invention is that the illustrative embodiment of the present invention can work with existing RSSI-based location systems. Also, the location system of the illustrative embodiment of the present invention is simple and easy to implement. 
   One of ordinary skill in the art will appreciate that the peak picking method of the present invention may apply to a single packet data and across multiple packet data in different embodiments. One of ordinary skill in the art will also appreciate that the peak picking method of the present invention may apply to continuous signals as well as discrete signals. 
   The peak picking method or technique of the present invention can be used in conjunction with various transmission and/or reception schemes, such as one or more of a space diversity technique, a time diversity technique and a polarization diversity technique.  FIG. 9C  is a flow chart illustrating that the peak picking method or technique of the present invention is used in conjunction with a space diversity technique. In this example, the location determining module  14  can receive the signal transmitted from the object identifier  800  in a space diversity technique (step  1142 ). The space diversity is a method of transmission or reception, or both, in which the effects of fading are minimized by the simultaneous use of two or more physically separated antennas, ideally separated by one or more wavelengths. If the signal is received using the space diversity technique, the strength of the signal is determined using the peak picking method or technique of the present invention described above in step  1113  of  FIG. 9A . For example, in the space diversity technique, the peak picking method or technique can be applied to the signals received by each of the antennas. The peak picking method compares these two signals, and selects a better signal, for example, a signal having a higher peak value. 
     FIG. 9D  is a flow chart illustrating that the peak picking method or technique of the present invention is used in conjunction with a time diversity technique. In this example, the location determining module  14  can receive the signal transmitted from the object identifier  800  in a time diversity technique (step  1144 ). In the time diversity technique, signals representing the same information are sent over the same channel at different times. The time diversity is often used over systems subject to burst error conditions, and at intervals adjusted to be longer than an error burst. If the signal is received using the time diversity technique, the strength of the signal is determined using the peak picking method or technique of the present invention described above in step  1113  of  FIG. 9A . 
     FIG. 9E  is a flow chart illustrating that the peak picking method or technique of the present invention is used in conjunction with a polarization diversity technique. In this example, the location determining module  14  can receive the signal transmitted from the object identifier  800  in a polarization diversity technique (step  1146 ). The polarization diversity is a diversity transmission and reception wherein the same information signal is transmitted and received simultaneously on orthogonally polarized waves with fade-independent propagation characteristics. If the signal is received using the time diversity technique, the strength of the signal is determined using the peak picking method of the present invention described above in step  1113  of  FIG. 9A . 
   One of skill in the art will appreciate that the peak peaking method or technique of the present invention can be used in conjunction with the combination of two or more diversity techniques described above. 
   A location system  720 , according to a further embodiment of the invention, is illustrated by way of example in  FIG. 11 . The location system  720  includes various object identifiers  800 , network connection elements  900  and fixed location identifiers  1000 . A network  400  is illustrated along with a database  1150  and location resolver  1100 . According to the present embodiment, a topology database  1152  is separately provided from the database  1150 . The topology database  1152  may be provided with information pertaining to the locations of network connection elements  900  and fixed location elements  900  and fixed location identifiers  1000 . Such topology information allows for more descriptive data to be provided regarding the location of object identifiers  800 . For example, the location of a fixed location identifier  1000  or network connection element  900  may be specified as a particular office, hallway or area. Therefore, if an object identifier  800  is identified as within a small radius of a fixed location identifier  1000  or network connection element  900 , the object identifier  800  may be identified as being within a specific room, office or area. 
   An electronic device  1101  is provided to host the location resolver  1100 . According to this embodiment the location resolver  1100  is in the form of software operating on the electronic device  1101 . Examples of electronic devices  1101  include computers, processors or other devices capable of implementing the functionality of the location resolver  1100 . 
   As shown by way of example, a location determining module  14 , according to an embodiment of the invention, is illustrated, by way of example, as including one of the fixed location identifiers  1000 , the network  400 , the electronic device  1101 , the location resolver  1100 , the database  1150  and topology database  1152 . 
   An example of a location system in use in a health care institution setting is illustrated in  FIG. 12 . As shown by way of example in  FIG. 12 , a network  400  is provided to allow for communication among multiple network connection elements  900 . A location resolver  1100  is also provided in communication with the network  400 . It is noted that the network is not limited to a wired network, as the network may be a wireless network. A fixed location identifier  1000  is illustrated and is in communication with the network connection elements  900 . Various object identifiers  800  are illustrated as a fixed to various pieces of equipment within the health care institution setting. The object identifiers  800  may be in communication with one or more of each of the network connection elements  900  and the fixed location identifier  1000 . 
   As illustrated in  FIG. 13 , a network interface  992 ,  1120  is shown by way of example according to an embodiment of the invention. The network interface  992 ,  1120  may be used in one or more of the network connection elements  900  and/or location resolver  1100  or other components adapted for communication with a network. A network interface  992 ,  1120  is adapted to be directly coupled to a network. The network interface  992 ,  1120  may be configured with one or more of the appropriate configurations for the corresponding networks. For example, it is illustrated by way of example in  FIG. 13 , the network interface  992 ,  1120  may be configured to be directly to an Ethernet network by way of Ethernet circuitry  994 . According to a further embodiment, the network interface  992 ,  1120  may be coupled to a telephone system to a modem  996 . According to another embodiment of the invention, the network interface  992 ,  1120  may be provided with one or more of a cable television modulator  998  to allow communication with a cable T.V. network, a UTP network card  1002 , to allow communication with a UTP network, or a universal serial bus (USB) card  1004  and/or a medical telemetry transmitter  1006  for communication with a medical telemetry network. 
   The present invention has been described by way of example, and modifications and variations of the described embodiments will suggest themselves to skilled artisans in this field without departing from the spirit of the invention. Aspects and characteristics of the above-described embodiments may be used in combination. The described embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is to be measured by the appended claims, rather than the preceding description, and all variations and equivalents that fall within the range of the claims are intended to be embraced therein.