Abstract:
A sensor network comprising a first sensor ( 104 ) and a second sensor ( 101, 108 ), characterized in that: the first sensor ( 104 ) and the second sensor ( 101, 108 ) are configured to detect an event and to generate a message (M 1,  M 2,  M 3 ) corresponding to the detected event; and wherein the sensor network is configured to provide an assessment of the message (M 1 ) from the first sensor ( 104 ) based on the message (M 2,  M 3 ) from the second sensor ( 101, 108 ).

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a sensor network and a method for detecting an event in a sensor network. In particular, it relates to a sensor network in a surveillance system. 
       BACKGROUND 
       [0002]    Surveillance or monitoring systems known in the art contain a plurality of devices that monitor activity in respective areas or ranges. These devices are called sensors. The sensors are connected to one or more hubs that process signals provided by those sensors and react upon the activation of a sensor. The reaction may differ, depending on the type of sensor and the type or parameters of the signal sent by the sensor. For example, the hub may activate an audio-visual alarm based on detection of motion by a sensor. 
         [0003]    The existing solutions are based on the assumption that the sensors remain active at all times and that the sensors are at all times ready to send signals to the hub. Although being very sensitive, this solution is significantly power-consuming, as it requires keeping all sensors powered on at all times. 
         [0004]    A patent application GB2379354A presents a system that allows for adjustment of the sensitivity of the sensors depending on the captured signal. In the event that the control unit detects activity within the field of view of one of the cameras, it transmits a signal to that particular camera to switch its mode to high resolution. 
         [0005]    However, the known solutions are still based on a central system entirely and provide no means of adjustment of that system in respect to the changing conditions. 
         [0006]    There is a need for an improved sensor network and a method for detecting an event in a sensor network that would allow for lower energy consumption and operation that is less demanding computationally. 
       SUMMARY 
       [0007]    The present disclosure relates to a sensor network comprising a first sensor ( 104 ) and a second sensor ( 101 ,  108 ), wherein: the first sensor ( 104 ) and the second sensor ( 101 ,  108 ) are configured to detect an event and to generate a message (M 1 , M 2 , M 3 ) corresponding to the detected event; and wherein the sensor network is configured to provide an assessment of the message (M 1 ) from the first sensor ( 104 ) based on the message (M 2 , M 3 ) from the second sensor ( 101 ,  108 ). 
         [0008]    Preferably, the assessment is provided by at least one of the sensors ( 101 ,  104 ,  108 ). 
         [0009]    Preferably, the network further comprises a third sensor ( 111 ) adapted to provide an assessment of the message (M 1 ) from the first sensor ( 104 ). 
         [0010]    Preferably, the assessment comprises a confirmation or a negation of the occurrence of the detected event. 
         [0011]    Preferably, the second sensor ( 101 ,  108 ) is configured to operate in at least a first operation mode ( 103 ,  110 ) and a second operation mode ( 102 ,  109 ), wherein the first sensor ( 104 ) is configured to trigger a change of the second sensor ( 101 ,  108 ) from the first operation mode ( 103 ,  110 ) to the second operation mode ( 102 ,  109 ) upon sensing a predetermined event. 
         [0012]    Preferably, the second sensor ( 101 ,  108 ) is configured to change its operation mode based on the message (M 1 ) from the first sensor ( 104 ). 
         [0013]    Preferably, the first operation mode ( 103 ,  110 ) and the second operation mode ( 102 ,  109 ) are sensitivity modes. 
         [0014]    Preferably, the first operation mode ( 103 ,  110 ) and the second operation mode ( 102 ,  109 ) are power modes. 
         [0015]    Preferably, the second sensor ( 101 ,  108 ) is turned off in the first operation mode ( 103 ,  110 ) and turned on in the second operation mode ( 102 ,  109 ). 
         [0016]    Preferably, the first sensor ( 104 ) is adapted to adjust its trigger threshold in case of negation of the occurrence of the detected event. There is also disclosed a method for sensing an event in a sensor network comprising a first sensor ( 104 ) and a second sensor ( 101 ,  108 ), wherein the method comprises steps of: detecting the event by the first sensor ( 104 ); sending a message (M 1 ) by the first sensor ( 104 ) to the second sensor ( 101 ,  108 ); in response to the received message (M 1 ), triggering a change in the second sensor ( 101 ,  108 ) from a first operation mode ( 103 ,  110 ) to a second operation mode ( 102 ,  109 ); checking whether the second sensor ( 101 ,  108 ) detected the event; and providing a message (M 2 ) with a confirmation or a negation of an occurrence of the event to the sensor network. 
         [0017]    There is also disclosed a computer program comprising program code means for performing all the steps of the method as described above when said program is run on a computer, as well as a computer readable medium storing computer-executable instructions performing all the steps of the method as described above when executed on a computer. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]    These and other objects of the invention presented herein, are accomplished by providing a sensor network and method for detecting an event in a sensor network. Further details and features of the present invention, its nature and various advantages will become more apparent from the following detailed description of the preferred embodiments shown in a drawing, in which: 
           [0019]      FIG. 1  presents an example of a sensor network; 
           [0020]      FIG. 2  presents a diagram of the method according to the present invention; 
           [0021]      FIG. 3  presents a diagram of another method. 
       
    
    
     NOTATION AND NOMENCLATURE 
       [0022]    Some portions of the detailed description which follows are presented in terms of data processing procedures, steps or other symbolic representations of operations on data bits that can be performed on computer memory. Therefore, a computer executes such logical steps thus requiring physical manipulations of physical quantities. 
         [0023]    Usually these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. For reasons of common usage, these signals are referred to as bits, packets, messages, values, elements, symbols, characters, terms, numbers, or the like. 
         [0024]    Additionally, all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Terms such as “processing” or “creating” or “transferring” or “executing” or “determining” or “detecting” or “obtaining” or “selecting” or “calculating” or “generating” or the like, refer to the action and processes of a computer system that manipulates and transforms data represented as physical (electronic) quantities within the computer&#39;s registers and memories into other data similarly represented as physical quantities within the memories or registers or other such information storage. 
       DETAILED DESCRIPTION 
       [0025]      FIG. 1  presents an example of a sensor network. The network  100  comprises a plurality of sensors  101 ,  104 ,  108 ,  111  connected to a transmission medium  107 . Any device connected to the system can be considered a sensor. It is not essential whether the sensor can process input or output signals from other sources than the transmission medium  107 . An example of a sensor able to process input from other media than  107  is an infrared motion sensor. An example of a sensor unable to process input from other media than  107  is a siren. Each sensor may further operate in one or more sensitivity modes  102 ,  103  or power modes or the like. The transmission medium  107  may be a dedicated bus or Ethernet network or Internet network or the like, suitable to provide exchange of data. 
         [0026]    Each sensor is capable of receiving and sending messages. It is not essential how the messages are built or what data is carried by them. Each message may be a source message or a response. The source message is a message that is triggered by a sensor detecting a condition (an event). The response message is a message triggered by another message. Each response message may contain one or more references or copies or the like of the messages that that message is a response to. 
         [0027]    In one embodiment, each response message may contain a full list of previous responses up to the point of the source message, including the source message. In another embodiment, each message can be identified with a substantially unique identifier generated by the sensor sending the message. An example of such substantially unique identifier is a Universally Unique Identifier (UUID). Each response includes a list of UUID of each message preceding that response up to the point of the source message. 
         [0028]    The references or copies or the like of the messages that a message is a response to may be used by a sensor that receives the response to identify whether the response was triggered by this sensor&#39;s source message. This in turn may trigger further actions. An example of further action may be adjustment of the sensor&#39;s sensitivity. Other exemplary actions will become apparent from the descriptions of the exemplary embodiments that follow. 
         [0029]    The sensor network is adapted to provide an assessment of the message from a first sensor based on the message from a second sensor. At least one of the sensors comprised in the network is adapted to provide the assessment. The assessment comprises a confirmation in a form of a positive feedback message or a negation in a form of a negative feedback message. Prior to the assessment, the second sensor may, upon receiving the message from the first sensor, switch its operating mode from a first operation mode to a second operation mode. This can further enhance the reliability of detecting the event, while consuming less energy and computational resources in-between events. 
         [0030]    Each response contains feedback information. The feedback is a piece of information about detection or lack of detection of a particular condition. One example of feedback may comprise information on detection of motion measured by a camera. This feedback, when included in a response to an activation of a motion sensor, can be interpreted by that motion sensor. A positive feedback is a confirmation of the information contained in the original message that this feedback is a response to. The positive feedback can reinforce the mechanism (consider it more reliable, and for example maintain its sensitivity) that triggered the response. The negative feedback is a contradiction of the information contained in the original message that this feedback is a response to and can diminish (e.g. by adjustment) the mechanism that triggered the response. 
         [0031]    Each sensor  101 ,  104  can send a message via the transmission medium  107  upon activation or switching to a different operation mode. Each sensor can also receive messages from other sensors. It is in no way limiting to the present invention whether all messages are broadcasted to all sensors or whether the sensors receive messages in groups or individually or the like. 
         [0032]    Each sensor that sent a message may expect a response message to be generated after sending a source message and therefore may be prepared to receive that response message. The response message contains feedback information according to the present invention and it is only decided by the sensor how to react to that feedback. In one embodiment a positive feedback contained in the response message may reinforce the mechanism that triggered the sending of the source message. In another embodiment the positive feedback may maintain the mechanism that triggered the sending of the source message. This results in adjustment of the reaction of the sensor towards the trigger that caused the sending of the message. 
         [0033]    The sensor network may operate as follows. A motion sensor  104  detects motion. The message is sent and received by all other sensors  101 ,  108  and  111 . This may include a camera  108  that is in the same room and a siren  111 . The siren  111  may use a system for dynamic management of resources (such as the one according to the system described in a European patent application EP14198454) to determine that one message from a motion sensor is not enough to cause an alarm. This information though is put into the history data of the siren. The camera  108  receives the message and in response switches to a high resolution mode and starts analyzing the pictures. Two scenarios are possible. In the first scenario the camera  108  detects motion. The camera  108  sends a reply. The reply contains information of the original message triggering the switch. This reply is received by the motion sensor  104  reinforcing the decision mechanism to send the message upon activation or to increase a weight assigned to the message or the like. The same reply is received by the siren  111 . The siren adds the message that has just been received to the history, which tops the threshold and starts an alarm. In the second scenario, it is assumed that the camera  108  detects no motion. The camera sends a reply. This reply contains information of the original message triggering the switch. This reply is received by the motion sensor  104  and the motion sensor diminishes the mechanism to send a message upon activation or decreases the weights assigned to the message or the like. The same reply is received by the siren  111 . The siren  111  detects the negation of the previous message and clears the history. 
         [0034]    It is clear to one skilled in the art that each device needs to contain information about location or obstacles in its proximity or the like so as to be able to determine whether the message from a particular device should or should not trigger any kind of response. An exemplary situation may include two motion sensors located in the same room. A message from one of the motion sensors may cause an action in the other motion sensor, e.g. switching to a high sensitivity mode. Another exemplary situation may comprise two motion sensors located in two different rooms that are not connected by any passage. A message from one sensor will most likely be ignored by the other sensor, as there is no reason why the motion detected by one sensor would propagate to the area covered by the other sensor. 
         [0035]      FIG. 2  presents an example of a method  200  for detecting an event. The method begins at step  201  by initialization of a first sensor, in this case a motion sensor. This may be in form of powering on or resetting to a factory default state or the like. The motion sensor sets a default value of SST (Signal Strength Threshold) at step  202 . The SST determines the threshold of the received signal strength that causes the sensor to react. Typically, the SST value is selected such that it reflects the highest possible sensitivity. At step  203  the motion sensor detects motion. It determines the strength of the received signal, marked herein as ‘S’. At step  204  the strength ‘S’ of the signal is compared with the SST. If not higher, the motion sensor returns to step  203 . If higher, the motion sensor sends a message at step  205 . The message M 1   206  is information that the motion sensor detected a signal (an event). The message  206  carries data stating that this is a source message  207  and an empty history of messages  208 . The message  206  is received by a second sensor, in this case a camera, at step  209 . The camera interprets that the massage  206  carries a source message and switches to a high resolution mode at step  210 . Next, at step  211  the camera checks whether motion is detected. For example, step  211  can be carried out as described in GB2379354A. If motion is confirmed, then at step  213  the camera sends a positive feedback response  215  to the message  206 . This response contains information  216  that the feedback is positive and a history  217  of previous messages, in this case M 1 . The message  215  is received by the motion sensor at step  214 . Since the message  215  contains a positive feedback, nothing is modified in the motion sensor, so as not to make it over-sensitive to motion. Next, the motion sensor returns to detection of motion at step  203 . If at step  211  the motion is not confirmed by the camera, another response message is sent at step  212 . This response  218  contains negative feedback information  219  indicating that motion was not confirmed and a history  220  of previous messages, in this case M 1 . The message  218  is received by the motion sensor at step  221 . The motion sensor determines the feedback  219  as negative and in order to avoid further false positives increases the value of SST so as to reduce the effective sensitivity of the sensor step  222 . Next, the motion sensor returns to detecting motion at step  203 . In other embodiments, the positive feedback message M 2  can be provided to other, actionable sensors, for example to a siren. Such positive feedback message M 2  may be utilized to activate the siren and raise the alarm. It could be also utilized by other elements of a surveillance system. 
         [0036]    The scheme of increasing or decreasing of the SST, as well as the initial value, can be determined in various ways and may depend on factors such as the size of the system, the purpose of its adaptability, the nature of the operating conditions or the like. The example presented in  FIG. 2  is designed at minimizing false positive notifications of motion done by the system i.e. the motion sensor will increase the SST by a large percentage on a false positive but will not decrease on a confirmed positive. 
         [0037]    Another example may include a sensor network system according to  FIG. 1  where the method of connecting a new sensor to the system according to  FIG. 2  is applied only at the learning stage. After the learning stage, the system may forbid further modifications of the SST value or any other values or a subset of all values or the like. In other words, the adjustment of strength of the threshold is no longer necessary. It is also possible to skip the adjustment steps when using the first and the second sensor, and only utilize predefined values or adjust the threshold by other means. 
         [0038]      FIG. 3  presents another example of a method  300  for detecting an event. The method presents the activities of two motion sensors, cooperating with a siren. The system may function in conjunction with a system for dynamic management of resources, such as known from the European patent application EP14198454. The third sensor in the present example is assigned the role of a resource manager. The change processed by it is the detection of motion by the motion sensors and the significance is constantly equal to  1  (by this the time dependency is dropped as not relevant). The third sensor forms or keeps or the like and processes the history of activation of the motion sensors. Hence the method starts at step  301  with a first sensor, in this case a motion sensor, detecting motion and sending a corresponding message  351  at step  302 . The message contains the type information  352  and an empty message history  353  similarly to the embodiments described above. In parallel, a second sensor, in this case also a motion sensor, detects motion at step  303  and sends a corresponding message  361  at step  304 . The message contains the type information  362  and an empty message history  363  similarly to the embodiments described above. Further steps of the method illustrate the ability of a third sensor, in this case a siren, to accept only confirmed signals. Step  305  illustrates the siren listening to incoming messages. At step  306  the message M 1   351  is received and added to the list of received messages. At step  307  the size of the received message list is checked. If larger than  1 , the flow moves to step  311 . If not larger than  1 , the flow moves to step  308  and then to step  309  where the message M 2   361  is received and added to the received message list. At step  310  the size of the received message list is checked. If not larger than  1 , the siren listens to further messages returning to step  305 . If larger than  1 , the history is cleared or cached or stored in a database or the like at step  311  and the siren emits an audiovisual signal at step  312 . In other words, the third sensor provides an action upon confirming the occurrence of a predetermined event, wherein the event sensed by the first sensor is confirmed by the second sensor. This enhances the reliability of operation of the sensor network. 
         [0039]    Further modification of the presented embodiments may comprise modification of the sensitivity of the siren, i.e. the history size at steps  307  and  309  to allow adapting to certain level of confidence of the received messages. This may be achieved according to method of  FIG. 2 . 
         [0040]    The present invention allows for automatic operation of a sensor network system without the need for a central hub. This makes updates of the system capacity non-intrusive towards its structure and allows for automatic calibration. 
         [0041]    The implementation of the invention is effected by the particular computer systems and computer-executed methods. Thus the machine or transformation test is therefore fulfilled and the idea is not abstract. 
         [0042]    It can be easily recognized, by one skilled in the art, that the aforementioned system and method for detecting an event in a sensor network may be performed and/or controlled by one or more computer programs. Such computer programs are typically executed by utilizing the computing resources of the device. The computer programs can be stored in a non-volatile memory, for example a flash memory or in a volatile memory (or otherwise a non-transitory computer readable medium), for example RAM and are executed by the processing unit. These memories are exemplary recording media for storing computer programs comprising computer-executable instructions performing all the steps of the computer-implemented method according the technical concept presented herein. 
         [0043]    While the invention presented herein has been depicted, described, and has been defined with reference to particular preferred embodiments, such references and examples of implementation in the foregoing specification do not imply any limitation on the invention. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader scope of the technical concept. The presented preferred embodiments are exemplary only, and are not exhaustive of the scope of the technical concept presented herein. 
         [0044]    Accordingly, the scope of protection is not limited to the preferred embodiments described in the specification, but is only limited by the claims that follow. 
         [0045]    In addition, any combination of the appended claims in envisaged in the present application.