PEOPLE LOCATING SYSTEM USING ZIGBEE Field of the invention:

This invention relates to a technology which is used to locate and track people in disaster situations or emergency incidents by using short range wireless communication.

Background of the invention:

People locating devices are becoming important during times of natural disasters such as earthquake, tsunami or during other disasters such as war or flight accidents. People locating devices are known to track people or children in such a disastrous situation, when it becomes really tough to locate people trapped under buildings in an earthquake or flight accidents in dense forests or mountains. Most of the locator devices available use GPS (Global Positioning System) which require a clear sky view and in most of the situations such as in thick forest or in building, location retrieval is difficult.

The present invention therefore suggests location retrieval by means of Received Signal Strength Index (RSSI) of the node from the respective router or coordinator. The Coordinator communicates to each node and router in the network via Zigbee communication and issue commands such as to get the RSSI and information of all connected nodes. Zigbee's low power consumption is very suitable and uses low energy transmission techniques which allow continuous use without changing battery for long periods. The technology is also affordable and cheap.

Objectives of the Invention:

The object of the invention is to track the absolute position of a person, especially in disastrous situations, to locate a remote person.

Another object of the invention is to provide location information to rescue teams to track victims during disasters.

Yet another object of the invention is to provide an affordable and cheap technology which can be implemented.

Summary of the Invention:

The system in accordance with this invention envisages means for tracking people using Zigbee network.

The present invention is meant for places such as a war field, thick forest, mountains or valleys where finding a person under a disaster situation is difficult. The person under disaster situation carrying an arm band equipped with Zigbee, in accordance with the said invention will receive and send signals to another Zigbee router or coordinator which is equipped in the arm band of another person participating in locating the person. The coordinator forms the root of the network tree and might bridge to other networks. There is exactly one ZigBee coordinator in each network since it is the device that started the network originally and is able to store information about the network. One and only one coordinator in the network newly formed by all Zigbee devices in the location communicates to each router and nodes to gather the location information of the person(s) under disaster. The router acts as an intermediate router, passing on data from other devices. Each person participating in search carries a Zigbee router equipped with GPS, low power processor, wireless device, power circuit, memory, LCD panel and a rechargeable battery. Zigbee is used to communicate to other nodes, especially the nodes of person(s) under disaster and Bluetooth is used to communicate to the mobile device carried by the search person.

Coordinator communicates to each node and router in the network via Zigbee communication and issue commands such as get the RSSI and information of all connected node. These nodes especially the routers will respond to the coordinator with RSSI with respect to its connected node and Latitude/Longitude and/or magnetic bearing. Latitude Longitude and Magnetic bearing is acquired from the device carried by the search person(s). Since GPS requires a clear sky view, most of the situations such as in a thick forest or in building, location retrieval is difficult. This invention suggests the location retrieval by means of the Received Signal Strength Index (RSSI) of the node from the respective router or coordinator. Each person can see the position of the target node by means of the RSSI from the attached device.

The features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention taken in conjunction with the accompanying drawings.

Brief description of the drawings

Figure 1 is a diagram illustrating a mesh network

Figure 2 is a diagram illustrating a map on the device

Figure 3 is a diagram illustrating programmable transmission power control

Figure 4 is a block diagram illustrating the components used in the arm band of the victim according to the present invention.

Figure 5 is a block diagram illustrating the components used in the arm band of the search person conducting the search according to the present invention.

Figure 6 is a block diagram illustrating the components used in the arm band of the coordinator conducting the search according to the present invention.

Figure 7 is a flow chart illustrating the functionalities of the coordinator

Figure 8 is a flow chart illustrating the functionalities of the search device

Figure 9 is a flow chart illustrating the functionalities of the target device or end device

Detailed description of drawings:

The present invention involves the use of arm bands by the victim and the person conducting the search.

Hardware

There are three types of devices involved in this system.

(1)Arm band for victim (hereafter known as target device, end device or victim's device)

(2) Mobile device for the search person (hereafter known as router or search person's device)

(3) Mobile device for Staff-in-charge (hereafter known as coordinator)

As shown in Figure 4, Badge or arm band of the victim consists of a low power processor, memory, wireless module and a long life primary battery. The power circuit distributes appropriate power to processor, memory and wireless module from the attached battery. Each person in the disastrous area wears this device as an arm band. It behaves as a Zigbee device, by default works as an end device and on request changes its function to a router. The badge is uniquely distinguished by a Node ID assigned to the device.

The software inside the memory turns the device as a Zigbee router or end device and sleeps many of the times to save battery power. Also it accepts commands from the parent and coordinator and sends responses appropriately. It also sends and receives messages from its peers and children when it is act as a router.

Mobile device of the search person consists of Zigbee router so that another search person (router) or victim (end device) can connect to it. The block diagram of this device is shown in Figure 5. It consists of an LCD panel to display the relative position of all search people (router) as well as victims (end device). It is attached with a GPS system to identify its own current position. The power circuit distributes the power to processor, memory, GPS system, wireless module and LCD panel. The power circuit takes electrical power from the rechargeable battery which is charged by the charging circuit. Charging circuit is connected to the mains power supply of any range from 115V to 230 VACwith50Hzor60Hz.

The software inside the memory makes the device to perform as a Zigbee router. It receives the request and responds to the coordinator. It also sends and receives messages to its children and peer devices. Each mobile device of the search person is uniquely identified by their assigned Node IDs.

The Figure 6 shows the block diagram of the coordinator. There is one and only one Zigbee coordinator available, which is carried by the staff-in-charge, to initiate the Zigbee network, consolidate results and update to each search person. It consists of an LCD panel to show the relative position of the coordinator, routers and victims. The coordinator is attached with a GPS system so that to identify its own location. The computer interface helps the device to connect and perform data transfer from a computer (PC). It is powered by rechargeable battery. The power circuit distributes the power to processor, memory, GPS system, wireless module and LCD panel. The power circuit takes electrical power from the rechargeable battery which is charged by the charging circuit. Charging circuit is connected to the mains power supply of any range from 115V to 230 V with 50 Hz or 60 Hz.

The software in the memory performs the device to work as a coordinator. It sends and receives responses from the devices connected to the network. It helps to download the map of the disastrous area from a computer using the computer interface. The coordinator distributes maps to all search devices on request.

Initialization

All persons in the disaster prone areas wear badges/arm bands consisting of Zigbee device which can work as an end device as well as a router. These badges are initialized as end devices and sleeping most of the time to increase the battery life. These devices can also work as routers by giving commands from the coordinator.

When a disaster is reported to the control room, the person in-charge instructs their staff about the operation to be performed in the disaster area. The coordinator downloads the site map from a computer. The site map is a small sketch of the place which contains only minimal information such as the boundaries (latitude/longitude) of the disastrous areas, points representing landmarks and streets. This map will be shared across all search personal via the Zigbee network. Also the coordinator registers the details such as Node ID of all search people's device as an initialization process. The Node ID of the search person's device helps the coordinator to distinguish the search person from the victim.

Each search person will carry a Zigbee router and the staff-in-charge will carry a Zigbee coordinator. The coordinator will initialize the network with a given PANID and channel. Once it is powered up, it will search for a wireless network with a predefined PANID and channel. Since the coordinator is already established the network, the routers in the visibility can join to the Zigbee Mesh network.

Zigbee Mesh Network

In general, Zigbee mesh topology consists of a coordinator, a set of routers and end devices. As shown in Figure 1, a router can be linked to one or more routers and end devices. The communication rules of mesh topology are flexible because the routers that are located within the range of each other can communicate directly. An advantage of mesh network is that there is likely another alternative route in case an existing link fails. Hence, this type of network topology is very reliable. Also this concept is applicable to wireless networks, wired networks and software interaction.

Building of Zigbee network is done automatically by the devices. The coordinator starts a Zigbee network by scanning for existing PANs in that area and for available channels. It then selects an unused PAN ID and a channel. From now on, a router or an end device can join a nearby Coordinator or another router that has already joined the PAN. If the router or end device is not being a part of the network, it performs a PAN scan of the SC channels and looks for the coordinator or router operating with the valid PAN ID. The router or end device scans the SC channel until the valid device is discovered. Then it sends an association request frame to associate device and receives an association response to verify the allowance into the network. The joining router and end device then send a broadcast discovery frame to discover 64 bit address of the coordinator. Each router and coordinator parent can allow up to 8 end device children to join their own device.

Coordinator is a node that has the unique function of forming a network. The Coordinator is responsible for establishing the operating channel and PAN ID for an entire network. Once established, the Coordinator can form a network by allowing Routers and End Devices to join to it. Once the network is formed, the Coordinator functions like a Router (it can participate in routing packets and be a source or destination for data packets).

Router is a node that creates/maintains network information and uses this information to determine the best route for a data packet. A router must join a network before it can allow other Routers and End Devices to join to it. A Router can participate in routing packets and is intended to be a mains-powered node.

End Devices have no routing capacity. End Devices must always interact with their parent node (Router or Coordinator) in order to transmit or receive data. An End Device can be a source or destination for data packets but cannot route packets. End Devices can be battery-powered and offer low-power operation.

All Zigbee devices can be uniquely identified using the Node Identifier. All search persons devices (routers) are registered with the coordinator as a non-victim device. When the wireless network is in the visibility of the victim's end device, it connects to the network. Victim's device can connect to one or more search person's device(s).

Each router will update the node identifier of newly connected devices to the coordinator. Router can verify the associated nodes and update to the coordinator if any new device is found. Since victim's end device is not registered with the coordinator, coordinator identifies it as the victim. Coordinator then informs the respective victim to get the RSSI.
Upon receiving the request from the coordinator, the end device (Victim's device) will send broadcast message to all routers with radius of broadcast equal to 1. The broadcast address is OxFFFC so that it is intended to all routers. Since the radius of broadcast equal to 1, it sends only to the first level of parents. Upon receiving the broadcast message, the respective parent will determine the RSSI of the end device which broadcasted the RSSI message. Each parent then sends the RSSI of the node from which the broadcast is received to the coordinator along with node id of both parent and child node.

Also the coordinator asks for the location of each router from the attached GPS device. The coordination will receive the response of the target device and all connected routers so that location of all routers and RSSI of the device from the connected routers will be known to it. Once the target device is connected to one of the routers coordinator ask the device to change its function from end device to router so that other devices (victims, if any) can connect to the device and extend the range of discovery of victims.

Correction on RSSI calculation (Calibration of RSSI)

In real world, radio propagation patterns exhibits different non-isotropic path loss due to the various transmission mediums and directions. The multi path and non uniformity of the signal is self calibrated dynamically based on the RSSI between routers and their GPS location. After applying the calibration, RSSI is re-calculated to identify the position of the device. The attenuation or multi path of signals will be calculated based on the RSSI between routers and absolute distance calculated based on their GPS locations. The geographical pattern and materials (like snow, water, sand) between the victim and connected nodes are taken into account for the RSSI variations. Raw RSSI values are collected from the search persons devices are used for calibrating the RSSI value in the current place. To get the actual location and distance between the search persons device is determined from the GPS device. The following formula can be used to calibrate the RSSI.

RSSI,-A
n. = -
lOtogtocL
-Equation (1)
where

n: Signal propagation constant or exponent at the given terrain

d: Distance from sender device

A: Received signal strength at 1 meter distance (this is a pre-defined value obtained in a
no-obstacle one-meter distance signal strength measurement from the device).

Coordinator will send frequent request for location and RSSI to all routers available in the network. Based on the set of values collected from routers (RSSI and GPS location for calculation the actual distance) the coordinator can calibrate the RSSI in any location. The coordinator maintains the signal propagation constant of each router. When RSSI is reported by the victim's device, coordinator find the signal propagation constant of its parents and do a correction in the RSSI. Or in other words, for the calculation of distance based on RSSI of the end device from its parent, coordinator uses signal propagation constant of the parent which is already determined from the previous measurements.

Calculation of distance based on RSSI

One possibility to acquire a distance is measuring the received signal strength of the incoming radio signal. The idea behind RSS is that the configured transmission power at the transmitting device (Pyx) directly affects the receiving power at the receiving device (PRX)- According to Friis' free space transmission equation, the detected signal strength decreases quadratic ally with the distance to the sender.

PRX = PTX*GTX*GRX*(A)2 Equation (2) (4 TTd)2
PTx = Transmission power of sender
PRX = Remaining power of wave at receiver
GTX = Gain of transmitter
GRX = Gain of receiver
A = Wave length
d = Distance between sender and receiver
The relationship between RSSI and distance are shown below.
RSSI [dBM] = - (10.n.log10(d)+A) - Equation (3) where
n : Propagation constant or exponent at the given terrain
d: distance from the sender device
A: received signal strength at 1 meter distance

Based on the equation 3, distance of the node can be calculated from RSSI and appropriate propagation constant will be taken for the above equation. For example, to calculate the distance, if RSSI of the node N is taken into account, then the average propagation constant associated with the parent (Node P) of Node N which has determined the RSSI of this node will be taken into account. The average propagation constant of the Node P is calculated based on the equation (4).

[n(P,1)+n(P,2)+...+n(P,N)+..+n(P,M)]/M - Equation (4) where

M: number of children for the node P n(P,1): Calculated propagation constant based on RSSI between the parent node and first child

n(P,2): Calculated propagation constant based on RSSI between the parent node and
second child

n(P,N): Calculated propagation constant based on RSSI between the parent node and
Nlh child

n(P,M): Calculated propagation constant based on RSSI between the parent node and
Mth child

Triangulation

If less than three devices are connected to the device using RSSI, coordinator will find the probable location of the device as a circle. Also this information will be given to each router so that all search persons can see the victim's location in their display. On the display the position of all routers are shown as reference and the target node is shown relative to them.

The nearest router(s) which are not connected to the target device can move to the probable location of the device, ie. into the circle represents the probable location of the victim. Once these router(s) are in the visibility of the target device, the coordinator will send a request to the target node to change its function from end device to router so that it can connect to all routers in the visibility. The router functionality is not for routing the messages in the network but to connect to multiple routers which are in the visibility. The target node then connects to them and information is updated to the coordinator. If three or more than three devices are connected to the target device, trilateral technique will be applied to get more accurate location information.

Self adjusted transmission power of Out-of-coverage of routers When the device is moving away from the network the signal strength (RSSI) as well as LQI will reduce. Once it reached a lower threshold, it will programmatically increase the transmitting power and inform the coordinator about its current position and lower threshold limit of the signal. Coordinator identifies all routers connected to this device and informs them to increase the transmitting power to stay connected with the out-of-coverage device. Dynamically changing the transmitting power based on need basis, extends the life of the battery of all mobile units as well as will give wide range of visibility between modules.
However, the target device(s) will not increase their transmitting power and hence the RSSI from the target device does not require corrections due to the increase in power of the search nodes. For dynamically calculating the environmental effect on RSSI, the transmission power changes are required for the coordinator. So every router informs the current transmitting power to the coordinator along with the other information.

As shown in Figure 3, Programmable gain control adjusts the transmitting power of the Power Amplifier (PA) and receiving sensitivity of the low signal noise amplifier (LNA). This software controlled power control and sensitivity adjustment increase the battery backup time as well as improve the throughput of the wireless network by reducing the interference and cross talk disturbances.

Maps and locations

Each display of the router displays the preloaded map of the search location along with the current location of the router and probable location of the victim. Coordinator periodically updates the positions of all search persons and probable location of the target to all devices and able to see them on their display. Also the coordinator will update the search coverage areas on the map based on locations visited by search persons.

As shown in the Figure 2, coverage area is displayed as a semi transparent shaded area in the map in the coordinator and search persons' devices. The coverage area will be updated along with new position of the nodes in the network. The search persons can coordinate each other to make a combined move to cover all disastrous areas.

More than one victim in the disastrous area

Consider the scenario when more than one victim is there in the disastrous location. When any one of the devices of the victims is connected to the search person's device and more than one router is in its visibility, it will change to the router so that end device of another victim can connect to the device. This will give a chain of actions so that after a few minutes all the victims will be visible to search persons. Since the device of the victim does not have the GPS functionality, it cannot be located accurately. However, using the trilateration, any one of the devices can be located, if at least three routers which can have accurate location determination using their GPS, are connected to the device. If a device of another victim is connected to the newly located device, based on RSSI from the newly connected device, its position can be determined. So after a few iterations all possible victims can be located approximately with help of known positions of search persons and approximate positions of victims.

No GPS for search persons

GPS requires direct view to the GPS satellites and in certain cases there will not be GPS fix due to lack of direct visibility of satellites. In such cases using RSSI and some reference nodes with known position can locate the search position. This procedure is same as that of identifying the victims location based on RSSI to referenced nodes. For accurate location identification of search person's device, at least three devices with known location must be there in its visibility.

Power saving options

Victim's device

Badges wore by the people are powered by small batteries and power consumption must be as low as possible to increase the backup time of the battery. End devices are low power devices and sleeping will increase the backup time. However normal Zigbee end devices will not connect to multiple routers simultaneously and hence RSSI measurement with directly connected nodes is not possible. Once the device is connected to the network, coordinator informs the device to change its function from end device to router. This enables the device to connect to multiple routers as well as allowing other end devices to connect to it. The router will consume more power due to more processing requirements as well as the requirement of "always awake". But the function change will happen only during the discovery process and will not have much impact on the overall power consumption of the device.

Search person's device

Search person's device require more power to operate as it has input and output device and more processing capabilities to display maps. It will be powered by a rechargeable battery and is having more mAH compare to the battery in the victim's device. However, as a mobile unit in a remote location requires more backup time, the power consumption of the device must be as less as possible. To reduce the power consumption the transmission power of the wireless changes with the demand. If the device is out-of-coverage or is connected to one or more devices in out-of coverage, the transmission power will be increased. Other cases the transmission power is less and hence less power consumption which increases the battery life.

Coordinator

This is always on and having good processing capabilities. It will have a GPS and LCD unit. It connects to the search devices, initialize them and configure the network during the search mode. It requires more power compare to other devices and will be powered from a rechargeable battery. It will have all features of a search person's device with additional processing capability.

Procedure

As shown in the flow chart in Figure 7, the coordinator initiates the network by assigning appropriate PAN ID and Channel ID. Once the network is setup, it allows routers and end devices to join. Coordinator receives messages send by routers and end devices. If it receives the node information of device newly joined, it will parse them and store into the node list. If the newly added node is not in the search list, this node will be treated as a target node (victim's device) and send a request for RSSI to the device.

If the coordinator receives the RSSI message, it will parse and collect the RSSI. Then based on RSSI it calculates the appropriate distance from the parent node and update into the list. When the coordinator receives the out-of-coverage warning, it parses and finds the node id of the device. Also it will search in the node list for last updated list of its parent(s). The Coordinator then sends a request to increase the transmission power to all parents of the node which sent the out-of-coverage warning.

If the coordinator receives the location information from a node, it parses and keeps the information along with the node list. If the received message contains the location type as GPS it will extract the latitude/longitude of the position and update into the list. If the location type as RSSI, it will extract the RSSI value from the message format and update into the list.

The coordinator periodically checks the node list and sends location request message to each node if it belongs to the search person's device. Also it sends frequent RSSI request to each search person's device. From the distance calculated from the GPS locations and RSSI received the current signal strength calibration constants are calculated for each and every router in the network.

It updates the map and current position of all nodes in the visibility so that the receiving node can display this information in the LCD panel. If the node selected is a target device (victim's device) and more than one router is in the visibility, coordinator will send a request to change the function of the device from end device to router. However the coordinator will not send this request if the selected node is already connected with more than one router.

As shown in flow chart in Figure 8, the search person's device will have preloaded map of the area for search and function as a router. Also the Node ID of the device is registered with coordinator as search person's device. On power up, the router will connect to the wireless network if PANID and channel matches. If the device is connected to the coordinator, the coordinator will add this node id into its device list. If the device is connected to another router in the network, the parent router will update the node id of this device along with the parent.

If another device (router or end device) joined into this router, this device will update the newly joined device id along with its id to the coordinator. If the router receives the location request from the coordinator, it responds with location response message which consists of the GPS coordinates (if GPS fix) or RSSI. If the router receives the map information, it will parse the message and display with appropriate icons on the map on the LCD panel.

If the device detects that the RSSI or LQI from the parent, lowest value if more than one parent, is less than the lower threshold value, the node will send out-of-coverage warning to the coordinator. Upon receiving this request, the coordinator will send request to all of its parents to increase the transmission power. If the device receives the RSSI request message, it will send a broadcast message to all routers, with a broadcast address of OxFFFC. If the device receive broadcast message, it will determine the RSSI and send to the coordinator along with source node id and its own id.

As shown in flow chart in Figure 9, the target device (Victim's device) is an end device with low power mode. It periodically checks the presence of a wireless network and if it matches the PAN ID and channel, it will connect to the network through one of the routers or directly to the coordinator. The joining information of the newly added device will be updated to the coordinator by the respective parent. If the target device receives the RSSI request from the parent, it broadcasts to all routers with a radius = 1.

As it is an end device, it can connect to only one of the routers in the visibility and hence RSSI can be determined only by that parent. Trilateration requires three or more routers with known position and hence if the coordinator identifies more than one router in the proximity of the target, will send function change request to the target. Upon receiving the function change request, the device will change its function from end device to the router and restart as router. As it is a router, the device will allow other target devices and routers to connect to it. This function change reduces the battery backup time but increases the coverage area of the network. This helps to discover other victims in the disaster area quickly.

Message format between routers and coordinator

1. Number of nodes connected

2. Node identifier of each node connected

3. Time stamp

4. Current transmission power of the router/end device

5. Current location of the router from GPS device Request for map

1. Message Type (request for map)

2. Node ID Map update message

1. Message Type (Map update)

2. Number of nodes

3. Node ID

4. Type of fix (x,y or radius)

5. X, y (radius)

6. Node ID

7. Type of fix (x,y or radius)

8. X,y (radius)

9. Newly joined device message

1. Message Type (Newly joined device)

2. Node ID of the newly joined device

3. Node ID of the parent node

4. Time stamp RSSI request message

1. Message Type (RSSI request) RSSI Response Message

1. Message Type (RSSI response)

2. Node ID of the target (from where the packet received for calculating RSSI)

3. Node ID of this node(device received the packet)

4. RSSI

5. Time stamp Non-Coverage Warning

1. Message Type (Non-coverage warning)

2. Node ID of this node

3. Lowest RSSI/LQN from its parent(s)

Increase transmission power request

1. Message Type(lncrease TX power)

2. Node ID

3. Power value to be increased

Location request message

1. Message Type (location request)

Location response message

1. Message Type (location info)

2. Node ID

3. Location type (GPS/RSSI)

4. Latitude (if location type is GPS)

5. Longitude (if location type is GPS)

6. RSSI (if location type is RSSI)

The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.

We claim

1. A system for determining location of a victim, the system comprising:

a) an arm band attached to a victim desirous of being located, said band comprising a low power processor connected to a Zigbee node; memory;
wireless module, long life primary battery and a power circuit wherein power circuit takes electrical power from the rechargeable battery and provides power to all components at their desired voltage levels;

wherein processor controls and manages the Zigbee and sends the RSSI and connected router ID to the requested coordinator;

wherein software inside the memory turns the device as a Zigbee router or end device; wherein Zigbee is used to communicate to other nodes in the network

b) an arm band attached to one or more search people desiring to locate the victim, said band comprising a low power processor connected to a Zigbee node; memory;

power circuit;

rechargeable battery;

GPS system;

LCD panel and a wireless module wherein power circuit takes electrical power from the rechargeable battery and provides power to all components at their desired voltage levels; wherein processor controls and manages the Zigbee and sends the RSSI and connected router ID to the requested coordinator; wherein Zigbee is used to communicate to other nodes in the network;

wherein software inside the memory turns the device as a Zigbee router;

wherein GPS identifies its own current position;

wherein LCD panel displays the relative position of all search people (router) as well as victims (end device)

c) an arm band attached to the staff-in-charge desiring to locate the victim, said band comprising a low power processor connected to a Zigbee node; memory;

power circuit;
rechargeable battery;
GPS system;
LCD panel;

Computer interface and a wireless module wherein power circuit takes electrical power from the rechargeable battery and provides power to all components at their desired voltage levels;

wherein Zigbee is used to communicate to other nodes in the network;

wherein software inside the memory turns the device as a Zigbee coordinator and
initiates the Zigbee network;

wherein GPS identifies its own current position;

wherein LCD panel displays the relative position of all search people (router) as well as victims (end device);

wherein computer interface helps to download map of the disastrous area from a computer which can then be transmitted to search devices upon request

2. A method for determining location of a victim, the method comprising:

initiating a Zigbee network by the coordinator;

registering all search devices (routers) with the coordinator as a non-victim device;

updating the node identifier of newly connected devices by the router to the coordinator and identifying the new device as the victim or target device;

receiving request from the coordinator by the victim to obtain the RSSI;

identifying proximal router by the target device and connecting to the said router;

computing return signal strength indicator (RSSI) from the connected router to the target
node and reporting RSSI along with node ids and GPS location to the coordinator.

3. The method as claimed in claim 2, wherein the RSSI from the router to the target node is recalculated as and when they are moving towards the target.

4. The method as claimed in claim 2, wherein the target device changes its function as a router upon request by the coordinator to increase the chance of detecting other victims in the disastrous area.

5. The method as claimed in claim 2, comprising receiving a plurality of return signal strength indicator (RSSI) values from connected routers and calculating the actual location of the target using triangulation technique when GPS of target device is not available.

6. The method as claimed in claim 2, wherein RSSI is calibrated dynamically based on the distance calculated using GPS and RSSI between routers and transmission power of each router.

7. The method as claimed in claim 2, wherein if less than three search devices are connected, coordinator will find the probable location of the device as a circle.

8. The method as claimed in claim 2, wherein transmission power of the mobile devices carried by the search person are dynamically adjusted to increase the battery life.

9. The method as claimed in claim 2, wherein transmission power of the mobile devices carried by the search person are dynamically adjusted to stay connected with out-of-coverage devices.

10. The method as claimed in claim 2, wherein an optimized map is used to reduce the network bandwidth requirement for transmitting the map details between devices.