Patent Publication Number: US-2010128636-A1

Title: Sensor network with rapid, intuitive configuration

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority from U.S. Provisional Patent Application Ser. No. 61/117,817 filed on Nov. 25, 2008. 
    
    
     BACKGROUND 
     The present disclosure generally relates to wireless networks of sensors and in particular to a method of configuring such a network that is procedurally simple and that works with sensors having reduced hardware configurations. 
     Significant progress has been made monitoring patients in a bedside setting using electronic sensors. Such sensors, by providing continuous monitoring of the patient, in contrast to periodic monitoring by a nurse or physician, can greatly improve the outcomes of medical treatment by providing better and faster data in response to potentially serious medical conditions. 
     Using electronic sensors to monitor ambulatory patients either within a hospital or a home setting has proven to be much more difficult. While generally the sensors can be sufficiently compact and lightweight to move with the patient, the wiring harness necessary to collect the data from the sensors and to communicate the collected data to a remote monitoring station is cumbersome and unacceptably reduces the freedom of movement of the patient. 
     For this reason, it has been proposed to use wireless transmission to connect electronic medical sensors to a remote monitoring station. One attractive protocol for such a system is the ZigBee IEEE 802.15.4 network standard which provides for end devices having extremely simple hardware requirements with a protocol designed for long battery life. Such end devices could potentially be used to provide wireless communication not only between the patient and a remote station but also between the individual sensors themselves. This latter approach would allow each sensor to be freely and individually attached or removed from the patient without the need for a wiring harness or the like. 
     While such a wireless network provides great freedom in using biosensors attached to a mobile patient, wireless networks are not without drawbacks, most notably of which is the complexity of configuring a network where connections are not defined by physical wires. While the ZigBee protocol allows for a nearly automatic connection of end devices to other devices by seeking out strong connections providing the least network depth, this approach of automatic connection may not be practical in a hospital environment where multiple devices and multiple similar networks in close proximity are associated with different patients and where strict network communication boundaries must be enforced between patients. That is, in a typical hospital environment, a given ZigBee end device should not be free to connect across patient clusters, since such a connection might confusingly associate medical data for one patient with another patient. 
     One method of enforcing network topologies is to preconfigure the router or coordinator device with the hardware addresses (MAC addresses) of the other devices to which they should connect. In this way the network connections, being predefined, insure integrity of the transmitted data. However, such preconfiguration is time consuming and rather inflexible. 
     SUMMARY 
     Although such a wireless network of independent biosensors is currently possible, its acceptance may be severely curtailed by the difficulties of network configuration by an inexperienced home user or a busy healthcare practitioner. As one possible solution, the present disclosure provides a simplified network configuration using an intuitive paradigm of touching devices together to make a connection. A button pressed on the devices when they are in proximity completes the connections so that the devices may be withdrawn while retaining the connection and ignoring potential connections with other devices. To the user, the touching process connects an invisible string between the devices that holds them in communication regardless of how they are separated. As well as providing an understandable connection metaphor (physical touching), this connection method can be performed with extremely rudimentary hardware devices that do not have keypads or display screens for the entry and confirmation of numeric data. 
     In one embodiment, the touching of the devices may be detected by monitoring the carrier signal between the devices thus eliminating the need for additional hardware for proximity sensing and making use of native instructions available in the ZigBee standard. A variety of other proximity sensing techniques and implementation of a button pressing also may be used. 
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate the best mode presently contemplated of carrying out the disclosure. In the drawings: 
         FIG. 1  is a simplified representation of an ambulatory patient having a variety of ZigBee end devices independently attached to the patient and communicating wirelessly with a router and or coordinator device to connect with a remote station; 
         FIG. 2  is a block diagram of two inter-communicating ZigBee devices having external buttons used for establishing a network connection when the devices are in proximity; 
         FIG. 3  is a graph showing a carrier signal strength as a function of distance and showing transmission range, proximity range, and defined transmitter peak power; 
         FIG. 4  is a pair of flow charts implementing the present disclosure on a ZigBee parent and child device to create a network connection between the two devices; and 
         FIGS. 5-7  are fragmentary portions of the block diagram of  FIG. 2  showing other proximity sensing techniques including bar codes, RFID tags, and an acoustic contact sensing using an accelerometer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , an ambulatory patient  10  may have a variety of directly attached nodes (DANs)  12  that each include a ZigBee end device including one or more biosensors that monitor biosignals from the patient  10 . The DANs  12  communicate with a personal area coordinator (PAC)  14 , for example, incorporating a ZigBee router. The PAC  14  may also communicate with one or more personal environmental nodes (PENs)  12 ′, that each include a ZigBee end device having a sensor or sensors to sense the environment around the patient but not attached to the patient  10 . 
     The DANs  12  may include, for example, end devices having sensors of body temperature, heart rate, ECG values, or blood oxygen levels. The PENs  12 ′ may, for example, include end devices that provide sensors associated with equipment such as scales, blood pressure cuffs, or blood glucose meters, that also provide information about the patient  10  but which are not physically attached to the patient for an extended period of time. The PENs  12 ′ may alternatively or in addition provide general environmental sensors detecting light level, humidity level, ambient temperature, or environmental noise in the area near the patient  10 . 
     In the embodiment shown in  FIG. 1 , the PAC  14  creates a network within the personal area  15  generally surrounding the patient  10 . The PAC  14  generally gathers information from the DANs  12  and PENs  12 ′ that are members of the PAC created network within the personal area  15 . The PAC  14  is configured to receive information from the DANs  12  as well as send out a network signal that can be received by the DANs  12 . 
     If a home monitoring application scenario is considered with respect to  FIG. 1 , the separation between personal and environmental monitoring becomes more obvious. While environmental data can be sent without encryption, patient-sensitive health data should not be transmitted from the PAC  14  without encryption. Thus, when the network of  FIG. 1  is utilized with a home monitoring application, the PAC  14  must allow for encrypted storage, analysis, and forwarding of patient data to a home healthcare provider. 
     In addition, in such a home monitoring application, it is desirable to allow for the ad-hoc association of individual end devices (DAN  12  and PEN  12 ′) to allow for easy setup of a network. In a general application scenario, the users of the network must be assumed to have no detailed knowledge of the network functionalities or extended technical knowledge. It is thus desirable to allow for easy association between the end devices of the DANs  12  and the personal area coordinator  14 . This will enable users to be monitored in their own home and to add and remove devices in the monitoring network. 
     Note that it is important that the particular DANs  12  and PENs  12 ′ be associated with a particular PAC  14  and thus be topologically locked to the patient&#39;s network created by the PAC  14  to prevent cross sharing of information between patients. 
     The PAC  14  may in turn be connected to a general area gateway (GAG)  16  incorporating a ZigBee coordinator and having substantially greater computational powers for preprocessing of the data for a given patient, for example, to format it with a patient identification number or the like. The GAG  16  may, for example, provide for a conventional terminal connection allowing the inputting of data or the like and may provide a non-ZigBee connection to a local network  18  and thus access to a remote monitoring station  20 . The GAG  16  can be configured to collect and process data from different PACs  14 . As an example, in a hospital environment, the GAG  16  could be at the nurses&#39; station and could be connected to the network  18  either wirelessly or through a wired connection. The GAG  16  would receive patient information from multiple PACs  14  as shown. The remote monitoring station  20  may monitor data from multiple patients  10  and may provide for an internal rules engine or the like establishing automatic rules to alert a nurse or other caregiver with respect to information obtained from sensors associated with one or more of the DANs  12 . 
     Referring now to  FIG. 2 , a parent device and child device, for example a DAN  12  and PAC  14  that may be connected together on a wireless network, provide similar architectures including, for example, a processor  22  communicating with a memory  24  containing stored programs ( 40 ,  42 ) implementing the network connection process of the present disclosure as well as general features of the device including the ZigBee stack. Generally each DAN  12  will have a battery  27  such that the end device of the DAN  12  can be completely untethered from electrical power cords or the like while the PACs  14  and GAGs  16  may have dedicated connections to a power line. The DANs  12  include a biomonitoring electronic sensor  21  of the type described above. 
     The processor  22  of the ZigBee devices may communicate with a wireless transceiver  26  having an antenna  28  for providing radio communications according to the ZigBee standard. In the present disclosure, processor  22  may also connect with an input device  30 , such as an electrical switch or push button, providing an extremely simplified user interface on the DAN  12 , PAC  14 , and GAG  16  used in the present disclosure. A signaling device  31  such as an LED indicator or audio transducer may also be provided. In a typical commercial implementation of the DANs  12 , the processor  22 , transceiver  26  and memory  24  will be a single integrated circuit providing a lightweight and compact hardware implementation. 
     Referring now to  FIG. 3 , the ZigBee standard follows an underlying IEEE 802.15.4 specification and provides the ability of software monitoring of radio carrier signal strength  32  received at the antenna  28  of each of the nodes  12 . In other words, the processor  22  running the stored program  40 ,  42  may query the signal strength of any carrier received from the transceiver  26 . The peak power level  36  of the carrier signal  32  at a predetermined distance from the device is well-defined by the standard. Generally, as long as carrier signal strength is above a transmission threshold  34 , the devices  12 ,  14 , and  16  may communicate with each other. 
     The strength of the carrier signal  32  will generally rise in a power-law relationship as distance between two communicating devices  12 ,  14 , or  16  is decreased. Thus, a proximity threshold  38  may be established such that when the strength of the carrier signal  32  exceeds the proximity threshold  38 , the strength of the carrier signal indicates an extremely close proximity of the devices, for example less than 10 cm. This close proximity is much less than the 10 to 75 m transmission range of the devices. It is possible to define a single proximity threshold  38  that indicates close proximity for devices  12 ,  14 ,  16  even operating at different peak powers, as a result of this power-law relationship. 
     Referring now to  FIG. 4 , two devices, for example a DAN  12  as a child device and a PAC  14  as a parent device, may be logically connected together in the network according to a protocol implemented by programs  40  running on the DAN  12  and programs  42  running on the PAC  14 , for example. Although  FIG. 4  is described as the protocol between one of the DANs  12  and the PAC  14 , a similar protocol may be performed between PAC  14  as a child device and GAG  16  as a parent device. Logical connection means that the devices are in fact capable of exchanging data and are independent of whether they can in fact receive each other&#39;s radio transmissions. 
     In order to implement the connection, the parent and child devices are initially brought together to touch and preferably so as to be within approximately 10 cm of each other. Once in this close proximity, the input devices  30  on each of the devices, such as the push buttons shown in  FIG. 2 , are pressed as indicated by process blocks  44  and  46 . Prior to the button on the end device of the PAC  14  being depressed, the device of the PAC  14  is operating in a state that prevents joining of new nodes to the network. The button pressing on the parent PAC  14  places it in a condition to receive join requests within a predetermined period of time, for example, one minute. 
     The button press  44  on the child DAN  12  triggers the ZigBee stack to execute a scan to find networks in the neighborhood of the DAN  12  having a carrier signal strength exceeding the proximity threshold  38 , as indicated by process block  48 . If at decision block  50  no network (n) or more than one network meeting this criterion are found, then the program  40  waits for a random time  52 . During this delay, the end device of the DAN  12  optionally signals the user by means of the signaling device  31 . The user is then prompted to actuate the input device  30  again if desired. 
     If at decision block  50  only one network is found having a network carrier signal that exceeds the proximity threshold, a request to join is made by the child DAN  12 , as indicated by process block  54 . The request to join is received on the parent PAC  14 , as indicated by process block  56 . If the request to join is received by the parent PAC  14  within the predetermined time, as determined by decision block  58 , the MAC addresses of the child DAN  12  is recorded by the parent PAC  14  and stored as indicated by process block  60  creating a persistent connection that survives as the devices are separated and the carrier signal strength  32  drops below the proximity threshold  38 . 
     If in decision block  50  the DAN  12  determines that more than one suitable network was located, the system also proceeds to block  52  where a random time is allowed to expire before the program again returns to step  44  to determine whether the input device on the child device has been actuated. When the child DAN  12  senses more than one network in the immediate vicinity, the end device of the DAN  12  returns to monitoring for activation of the input device which should allow simultaneous ongoing association procedures in the vicinity of the node under consideration. Preferably, the DAN  12  will provide an indication to the user of this state, such as through an LED, so that the user can repeat the association procedure by depressing the button in step  44 . 
     The process, from the point of view of the user, requires only a simple holding together of the devices to be connected while actuating the input device  30  on each device at approximately the same time. 
     Referring now to  FIG. 5 , the above embodiment provides an extremely simple hardware configuration, however it will be appreciated that the button pressing function and proximity sensing function may be accomplished in a variety of other ways. For example, the child DAN  12  may include an RFID tag  64  such as may be read by a reader  66  on the parent PAC  14 . The local operation of such readers  66  can provide both a proximity signal and an effective button pressing or maybe augmented by a separate button press. 
     Referring to  FIG. 6 , in an alternative embodiment, the child DAN  12  may have a barcode  68  and a barcode reader  70  may be on the parent PAC  14  to provide proximity sensing and a button pressing or to be used with independent button pressing. A similar approach (not shown) may make use of an electrical connector which physically connects the two devices providing both indication of proximity and the desire to connect the devices normally provided by the button pressings. 
     Referring to  FIG. 7 , an acoustic transducer or accelerometer  72  in the child DAN  12  and the parent PAC  14  may sense a proximity inferred from high-frequency signals from the accelerometer  72  caused by a tapping of the two devices together. These proximity signals in conjunction with the button pressing may establish the connection of the present invention. 
     Alternatively, other proximity sensing techniques may be used including, for example, the direct electrical connection of two external metal parts on the housings of the devices (to be distinguished from the electrical connector described above). With either of these electrical connection techniques, the fact of connection may signal proximity and promote the connection process like a button-press, but may also communicate a signal between the devices for other purposes. In an alternative embodiment, the proximity sensing may be an LED, for example, producing a predetermined coded or frequency-modulated signal to be detected by a sensor on the other unit. Again identification of the signal may indicate proximity but the signal may also communicate data. 
     An alternative proximity sensor may be provided through a low-frequency magnetic field transmission, or standard low powered RF transmissions through-body from a dedicated transmitter used solely for proximity detection. This latter technique, may use the patient&#39;s body as an antenna, allowing a network to be configured by proximity, per the present invention, where the proximity is defined by the personal space of the patient for an extremely intuitive association of network devices related to a patient. None of these proximity detecting techniques should be considered to exclude others known in the art. 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.