Abstract:
Disclosed is a system and method for locating a mobile node in a network. The system comprises a plurality of beacon nodes, at least a router, a location host, and at least a mobile node. Each beacon node broadcasts at least a beacon signal at a first channel. A mobile node receives a plurality of beacon signals, and sends a corresponding packet&#39;s information to the location host at a second channel through a router. According to the packet&#39;s information, the location host may compute the location for the mobile node. This system distributes the communication loading to different groups and channels, which may estimate the locations for lots of mobile nodes at the same time, and gives a high communication quality and a good location estimation result.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to a system and method for location estimation of a mobile node in a network. 
       BACKGROUND OF THE INVENTION 
       [0002]    The Receive Signal Strength Indication (RSSI) is to determine the distance between the transmitting end and the receiving end of a radio signal according to the radio signal strength measured by the detection circuit at the receiving end. When a mobile node receives at least three signal strength information, the signal strength information is sent to a positioning host. Based on the positioning database on the positioning host, such as a database constructed according to the experience or signal decay model, the positioning may compute to obtain the location estimation. Because RSSI is easily affected by the shadow fading in the environment, such as caused by the building absorption and reflection, or multi-path, several enhancement approaches are developed for RSSI. 
         [0003]    For example, by using chaos processing method to generate more RSSI data from the received RSSI samples, more possible locations can be obtained, and one optimal location can be selected. Another example is to compare the RSSI in the mobile device communication and the database to obtain a positioning system suitable for outdoors and indoors. Other examples are to use probabilistic RSSI model to construct the database, to combine the RSSI and time difference of arrival (TDOA) to estimate location, or to combine RSSI and time of flight (TOF) for positioning. 
         [0004]    The data transmission architecture of the RSSI-based positioning system may be divided into two types, as shown in the exemplary diagrams of  FIG. 1  and  FIG. 2 , respectively. 
         [0005]    Referring to  FIG. 1 , in this data transmission architecture, mobile node  101  uses active scan to request beacon from routers  103 , or uses passive scan to receive beacon periodically broadcast by routers  103 , to obtain at least three RSSI, marked as  11   0 . Through the routers, such as routers  105 A,  105 B, of multi-hop mesh network  105 , the packet information, such as mobile node ID, corresponding router node ID, RSSI, and so on, can be transmitted in unicast mode to location server  107  to estimate the location of mobile node  101 . Location server  107  may transmit the location information of mobile node  101  to mobile node  101 . In this architecture, mobile node  101  and all the routers work and transmit packets on the same channel. If NM is the number of mobile nodes, NR is the number of routers, the communication load of packet transmission is O(N R *N M ). If the mobile nodes uses active scan to request beacon from routers  103 , the load may increase to O(N R *N M   2 ). 
         [0006]    Referring to  FIG. 2 , in this data transmission architecture, mobile node  201  periodically broadcasts packets. Router  203  that receives the broadcast packet will obtain RSSI, marked as  215 . Through the routers, such as routers  205 A,  205 B, of multi-hop mesh network  205 , the packet information, such as mobile node ID, corresponding router node ID, RSSI, and so on, can be transmitted in unicast mode to positioning server  207 . For a single mobile node, positioning server  207  must receive at least three RSSI in order to compute the location of mobile node  201 , marked as  210 . Similar to the architecture of  FIG. 1 , mobile node  201  and all the routers of  FIG. 2  also work and transmit packets on the same channel, and the communication load of packet transmission is O(N R *N M ). 
         [0007]    In the aforementioned technologies, it is the same node to transmit beaconing signals and to transfer packets, which may easily lead to delay in positioning for multi-node positioning. Also, when beaconing signal transmission and packet transferring are both on the same channel, it is easy to cause packet collision or packet loss in multi-node positioning, and also increase the communication load. 
       SUMMARY OF THE INVENTION 
       [0008]    The primary object of the present invention may provide a system and method for locating a mobile node in a network. 
         [0009]    In an exemplary embodiment, the disclosed is directed to a system for locating a mobile node in a network, comprising a plurality of beacon nodes, at least a router, a location host, and at least a mobile node. Each beacon node broadcasts at least a beacon signal on a first channel. Each mobile node receives a plurality of beacon signals, and transmits the information of a corresponding packet by a second channel to the location host through the at least a router. According to the corresponding packet information, the location host computes the corresponding location information of the mobile node. 
         [0010]    In another exemplary embodiment, the disclosed is directed to a method for locating a mobile node in a network, comprising: each beacon node of a plurality of beacons nodes broadcasting at least a beacon signal on a first channel; a mobile node receiving a plurality of beacon signals on the first channel and obtaining at least three RSSIs; the mobile node transmitting the information of a corresponding packet by a second channel to a location host through at least one router; and according to the corresponding packet information, the location host computing the corresponding location information of the mobile node. 
         [0011]    The exemplary embodiments of the present invention divide the beacon nodes transmitting location signals and the routers transferring packets into two groups. The beacon nodes transmit the beacon signals on the first channel, and the routers transfer the packets on the second channel. The location host may transmit the location information of the mobile node depending on the needs of positioning applications. 
         [0012]    The foregoing and other features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows a schematic view of an exemplary architecture of data transmission for an RSSI-based location system. 
           [0014]      FIG. 2  shows a schematic view of another exemplary architecture of data transmission for an RSSI-based location system. 
           [0015]      FIG. 3  shows a schematic view of an exemplary system for locating a mobile node in a network, consistent with certain disclosed embodiments. 
           [0016]      FIG. 4  shows an exemplary flowchart illustrating the operation of a method for locating a mobile node in a network, consistent with certain disclosed embodiments. 
           [0017]      FIG. 5  shows a schematic view of an exemplary wireless location system, consistent with certain disclosed embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    The exemplary embodiments of the present invention use RSSI for location estimation for mobile nodes. By dividing the beacon nodes transmitting beacon signals and routers transferring packets into two groups that are working on different channels, for locating multiple mobile nodes at the same time, the communication load may be distributed to different groups and channels to reduce the packet collision delay in transmission as well as the packet loss rate. 
         [0019]      FIG. 3  shows a schematic view of an exemplary system for locating a mobile node in a network, consistent with certain disclosed embodiments. Referring to  FIG. 3 , location system  300  comprises a plurality of beacon nodes, at least a router, a location host, and at least a mobile node; for example, beacon nodes  303 A,  303 B,  303 C, routers  305 A,  305 B,  305 C, location host  307 , and mobile nodes  3011 - 301 n (n≧1). Each beacon node  303 A,  303 B,  303 C broadcasts at least a beacon signal on a first channel. Each mobile node, e.g., mobile node  3011 , receives a plurality of beacon signals, such as  3031 ,  3032 ,  3033 , and through the routers, such as router  305 A, to transmit the information of a corresponding packet to location host  307  through a second channel, for example, using multi-hop short distance communication to achieve long distance communication in a multi-hop mesh-type network. According to the corresponding packet information, location host  307  computes the location information  307   a  of a corresponding mobile node. 
         [0020]    As shown in  FIG. 3 , location system  300  divides beacon nodes  303 A,  303 B,  303 C that transmit beacon signals and routers  305 A,  305 B,  305 C that transfer packets into two groups that work on different channels. For example, beacon nodes  303 A,  303 B,  303 C transmit beacon signals on the first channel, and routers  305 A,  305 B,  305 C transfer packets on the second channel. 
         [0021]    Let N M  be the number of mobile nodes and N B  be the number of beacon nodes. In the exemplary embodiment of  FIG. 3 , because of the design of separate groups and channels, the communication loads on the two separate channels are O(N B ) and O(N M ), respectively. Therefore, when a large number of mobile nodes need to be estimated location at the same time, the disclosed embodiment may effectively reduce the communication load on one channel, and thus reduce the chance of communication overloading as well as packet collision delay and packet loss rate. 
         [0022]    Each mobile node, each beacon node, each router and the location host of location system  300  all have a unique ID. The information in each packet may include its corresponding mobile ID, at least a corresponding beacon ID, and at least three RSSIs. In other words, mobile node  3011  receives at least three RSSIs on the first channel. Depending on the applications, estimated location information  307   a  may be transmitted to the corresponding mobile node through the second channel. For example, if the location system is for the service-based tracking application, the location host does not need to return the location information of the mobile node. On the other hand, if the positioning system is for the client-based location application, the location host needs to return the location information of the mobile node to the mobile node. 
         [0023]    Location host  307  of location system  300  may be combined with a router or a beacon node. The location system may also be applied to a wireless platform, such as ZigBee, wireless fidelity (Wi-Fi), Bluetooth, or ultra wide band (UWB) technologies. The realization of the constituting modules of the location system may be carried in many ways, such as, a microprocessor with a built-in or external memory, short distance radio transmitter and antenna, and main power supply or battery power supply. Also, depending on the applications, a sensor may be included or excluded. Beacon nodes and routers may be either vertically or horizontally distributed and installed on the ceiling, and use the main power. 
         [0024]      FIG. 4  shows an exemplary flowchart illustrating the operation of a method for locating a mobile node in a network, consistent with certain disclosed embodiments. Referring to  FIG. 4 , in step  401 , each beacon node broadcasts at least a beacon packet on the first channel. For example, after each beacon node is activated, the beacon nodes may randomly broadcast beacon packets on the first channel or periodically broadcast beacon packets to reduce the packet collision. In step  402 , a mobile node receives packets that a plurality of beacon nodes broadcast on the first channel and obtains at least three RSSIs. The mobile node will stay on the first channel until least three RSSIs are received. 
         [0025]    In step  403 , the mobile node transfers the information of a corresponding locating packet to the location host on the second channel through at least a router. For example, after the mobile node is activated, the mobile node joins the nearby router and views the router as a parent node to transfer the packet information on the second channel. In step  404 , the location host estimates the location information of the mobile node according to the corresponding packet information. The location host receives the required location information, such as RSSIs, on the second channel from the mobile node, and may estimate the location information of the mobile node. 
         [0026]    In this way, the beacon nodes transmitting beacon signals and the routers transferring the packets are divided into two groups and operate on different channels. In a multi-hop mesh network, in addition to the mesh connection, the packet information may also be transferred through multi-hop short distance communication to achieve long distance communication. Each communication may be limited to at most K hops, such as K=5, to increase the communication reliability. Value of K can determine the range and the number of routers deployed. The beacon nodes and the routers may be installed and deployed in a vertically or horizontally distributed manner. The mobile node may use the nearby routers to transfer the packet information on the second channel in a unicast mode. 
         [0027]      FIG. 5  shows a schematic view of an exemplary wireless location system, consistent with certain disclosed embodiments. Referring to  FIG. 5 , wireless location system  500  includes at least a beacon node. Each beacon node, such as beacon node  503 , broadcasts a beacon packet on the first channel, marked as  511 . A mobile node  501  passively receives the beacon packet, and obtains at least three RSSIs, marked as  512 . Then, through a multi-hop mesh network, a locating packet is transferred on the second channel to location host  307  to estimate the location of mobile node. The locating packet information at least includes the mobile node ID, at least a corresponding beacon node ID, at least three RSSIs, and so on. The transferring of packet information is described as follows. 
         [0028]    After receiving beacon signal, mobile node  501  transmits packet information through the second channel to the router. After the router is activated, the router processes the joining of mobile node on the second channel, and transfers the packet. The packet may be transferred in the multi-hop communication manner. For example, on the second channel, mobile node  501  transmits packet information to router  305 A, marked as  513   a , router  305 A transmits to the next neighboring router  305 B, marked as  513   b , and router  305 B then transmits to next router  305 C, marked as  513   c . Then, router  305 C transmits packet information to location host  307  on the second channel, marked as  514 . The maximum number K of the hops is related to the deployment range and number of the routers. In the above example, K is set as 4. 
         [0029]    Based on the experience-based database or signal decay-based model, the location host may estimate the location of the mobile node by the RSSI. If the estimated location needs to be returned, location host  307  may send the estimated location through routers  305 C,  305 B,  305 A back to mobile node  501  on the second channel, marked as  520 . Mobile node  501  may receive on the second channel periodically. 
         [0030]    Therefore, communication load may be distributed to different groups and channels, and thus the packet collision delay and packet loss rate during transmission can be reduced. Also, the disclosed exemplary embodiments of the present invention may improve the communication quality and locating results when simultaneously locating a large number of mobile nodes. 
         [0031]    Although the present invention has been described with reference to the exemplary embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.