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TABLE OF CONTENTS 1. ABSTRACT 2. INTRODUCTION 3. DESIGN STRATEGY 4. ROUTING PHASE 4.1 AVOIDING COLLISIONS 4.2 UPDATING PARENT AND HOP DISTANCE 4.3 TIME SYNCHRONISATION 4.4 ADDING AND DELETING NODES 4.5 LISTENING PHASE 5. EXPERIMENTATION 5.1 SIGNAL STRENGTH AND DISTANCES 5.2 OBTAINING EMPIRICAL RESULTS 5.3 COLLISION RATES 6.USER END PROCESSING 7. CONCLUSION because radio waves from satellites do not penetrate into buildings. Laser-range scanners which can be used in indoors 1.ABSTRACT: The object tracking scheme generally employs estimation. surveillance Surveillance and is location usually cannot cover wide areas because of the cost problem. This paper describes an object tracking scheme that employs sensor fusion approach which is

carried out using video cameras. At present, GPS is the most popular and efficient outdoor location estimation system .It cannot be used indoors

composed of visual information and location information estimated from WiFi signals. Different approaches from which the use

conventional

another kind of sensors, our approach can cover wider areas both indoor and outdoor with lower cost because of characteristics of Wi-Fi signals. Location information is calculated by a set of received signal strength values of beacon packets from Wi-Fi access points around the targets. Sensor nodes are installed at various positions in and around the surveillance camera, where each sensor node will be provided with an IP address. Sensor nodes can be imagined as small computers, extremely basic in terms of their interfaces and their components. Thus a Wi-Fi router detects each sensor node in a unique manner and this in turn communicates with the Client server. There are two types of positioning systems over wireless

send a Wi-fi signal of specified strength. So, when an object is being tracked, depending on the RSSI from each access point, it could be located between specific access points, thus in turn estimating the appropriate location. Thus this approach also overcomes the defect caused by usual camera surveillance that fails to cover the camera handover areas(i.e.)disjoint areas. Thus, through this approach a stable tracking system is provided.

2.INTRODUCTION:

Visual surveillance system is getting more important because of our growing concern about security. So, object

detection and tracking is demanded to get higher performance. But it is difficult to achieve more accurate and stable tracking performance by only using the visual information in the tracking

networks. One is called time difference of arrival (TDOA), the other is called received signal strength identifier (RSSI) model. The former approach needs accurate time synchronization between multiple Wi-Fi APs. RSSI model is easier to use in this approach. In this model, the information sent to the client consists of IP address and received signal strength identifier from each WiFi access point. Each of these access points is initially trained in such a way to

network. To realize this objective, sensor fusion techniques are proposed in many application areas. A location estimation system which can be used easily in wide area is strongly needed for surveillance applications. Recently, city-wide public wireless LAN services have become increasingly popular. Joint tracking

method has two phases: Detecting phase based on conventional methods and Tracking phase based on Wi-Fi location estimation. The tracking method

‡ Low cost of sensor nodes compared to GPRS modems ‡ Minimal energy consumption ‡ Easy expansion & reduction of coverage area

switches these two phases depending on the estimated position of the target. Following section describes our system¶s design strategies, our proposed tracking method and implementation of Wi-Fi in location estimation.

3.DESIGN STRATEGY The sensor network setup consists of a number of nodes that have all been programmed with the same code. These nodes are capable of initially

establishing routing in the network and once this is done, they go into a listening mode during which they relay all packets from the transmitter being tracked to the base station. The transmitter is assumed to be hostile and does not transmit any information in the packet, only its own ID. These raw packets are taken and a time stamp and a received signal strength parameter value is augmented to their data pay load by all listening nodes. The packets are then routed through the network. It is also ensured that during the routing period, time synchronization Wireless Sensor Networks offer distinct advantages over other alternative is achieved in the network. All the data is collated at a base station which then passes all the data onto a processing server.

approaches to solve such an object tracking problem. Some of these are mentioned below. ‡ Nearly zero configurability

4.ROUTING PHASE

When a packet flooding strategy like the To begin with, all the sensor nodes are booted up. The last node to be booted is the base station. The base station on booting broadcasts a route finding message onto the network. This message carries the node ID of the base along with a hop count field as well as the base station¶s time stamp. The hop count is initially set by the base station to 1. All nodes within a single hop distance of the base receive this message and set their Parent to be the base station and their Hop Distance to be 1. These nodes also reset their clocks to synchronise with the base station. All these nodes then rebroadcast the routing message writing inside their own node ID instead of the base¶s, incrementing the hop count by 1 and also update the time stamp of the message. In this manner the route finding messages are flooded through the network and all nodes soon know who their parent node is and also at what hop distance they are residing from the base. All message transmition in the listening period of the node is directed towards the parent node. 4.2 UPDATING PARENT AND HOP DISTANCE 4.1 AVOIDING COLLISIONS Each node receives multiple routing one described above is used to determine routing, it is very likely that due to the large number of broadcast packets in circulation, some nodes may not receive the packet in one go due to interference. Hence it becomes essential to rebroadcast packets for a certain period of time to ensure with a probability that every node has received a routing packet atleast once. To ensure this the base station keeps sending out these broadcast messages for a fixed period of time (around 10 seconds) with a random back-off (of the order of 1 second). Every node will thus receive much more than just a single routing packet and it must make a decision about which of these packets it will further transmit as otherwise there will be excessive packet flooding in the network and functionality may get severely affected. To counter this, a simple heuristic was adopted. A node re-broadcasts only those packets which lead to an updating of its Parent and/or Hop Distance.

packets during the initial working phase of the network. All of these cannot be allowed to change its Parent and/or Hop Distance. The simplest strategy to follow is that both the values are changed only if the new Hop Distance is less than the old one. This simple check also ensures that atleast one path to the base is available to every node in the network. 4.3 TIME SYNCHRONISATION The routing messages that flood the network also carry time stamps.

th processing of received data. The strategy we use to counter this phase difference is that although we increment the node clocks every 128/1024

milliseconds; the basic unit of time is 1 second. Thus, some of this phase difference is just ironed over. However, if n were to become fairly large, this might pose a problem. The second problem is that of clock skew. This is basically the difference in clock times of two nodes that might occur even though they may have started at the same time value. In case of the hardware used clock skew was of the order of 1 millisecond in every 50,000 milliseconds. Clock skew can be completely taken care of by periodically putting the system into the routing phase; thus re-synchronising clocks. 4.4 ADDING AND DELETING

Whenever a node receives a message and decides to change its Parent and Hop Distance, it also updates its clock. In such a manner time synchronisation may achieved in the network. There are however a couple of issues with this strategy. The first problem is that of the clocks of adjacent nodes in the network being slightly out of phase (by an amount ). This will happen due to the delay introduced due to message radio transmission, reception and processing. This delay although not the same in every case will roughly be of the same order of magnitude. Therefore in an nhop network, the worst case delay would be × n. This delay due to phase

NODES

The addition and deletion of nodes to the network can be done as long as rerouting is done. Hence to allow for easy addition and deletion of nodes the routing stage needs to be initiated repeatedly.

shifting is almost unavoidable, unless some correction factors are introduced in 4.5 LISTENING PHASE

After the reception of a routing packet at a node, a short timer is started that signals the end of the routing period and the beginning of the listening period. In this period, the aim of each node is to listen for messages sent out by the transmitter being tracked and then try to route these packets all the way to the base station. Before routing, the nodes augment three pieces of information to the received message :‡ Node ID ‡ Time Stamp ‡ Received Signal Strength (RSSI value) All the augmented data is essential for the front end processing in order to determine the location of the transmitter. A node ID to coordinate mapping is maintained at the processing server. Hence when the messages reach the server, it knows from where what signal strength is being received. This is the data needed for location estimation. The time stamp is necessary to ensure that when the location estimation is being done, signal strengths measured at the same time time points are being used as otherwise irrelevant results may be obtained. 5.EXPERIMENTATION

Experiments were carried out with the intention of either arriving at certain empirical results, or at optimal values of certain parameters to enhance network functionality. In this section, we describe some of the important experiments that were carried out. 5.1 SIGNAL STRENGTH AND

DISTANCES It is essential to have knowledge of a relation between received signal strength and distance of the emitting node, in order to make estimates of location. Hence, experiments were carried out in different field locations to establish the nature of this relation. A signal strength measure is provided by the sensor nodes in the form an RSSI (Reduced Signal Strength Indication) value. This value has a known linear relationship with signal strength. Our aim is to correlate this signal strength indicator with

distance. In order to do so, we conducted experiments in different environmental settings to establish such a relation. The

of an empirical conversion formula; a least square quadratic curve fitting was done using MATLAB.

RSSI to Signal Strength relationship RSSI(dBm) = í51.3 × VRSSI í 49.2 experiments were conducted by placing a node programmed to emit a fixed number of messages, at certain measured distances. These messages were then counted at the base station and their RSSI values on reception noted. These data readings were then used to do a quadratic least square curve fitting to determine an empirical relation between distance and RSSI values. The 5.3 COLLISION RATES The entire design strategy as far as route determination as well as package routing is concerned uses a lot of non-intelligent random back-offs to prevent collisions of data packets. It was therefore

necessary to establish the order of magnitude of these random back-offs in order to ensure that firstly time spent in communication is minimised and

experiment was performed in three environments :1. Building Corridors 2. Forest Type Environment 3. Open Ground 5.2 OBTAINING EMPIRICAL

secondly that packet loss rate or collision rate is minimised. In order to determine these values, a small single hop network was setup using one base station, three listening nodes and a single transmitter. The nodes simply relayed all messages to the base exactly once without waiting for acknowledgements. The main

RESULTS The experimental data is obtained as a set of RSSI values for each distance measurement. This data showed a

conclusions drawn were :‡ Simultaneous transmission from three nodes lead to almost 100% packet loss

roughly quadratic variation. To get hold

‡ With differences of the order of 200+ ms there was nearly 0% packet loss ‡ With decrease in time interval between transmissions, there was increase in packet loss, but this increase was not very dramatic. ‡ Even with small intervals of about 20ms, packet loss was below 10%

lot of cases due to the nature of solution that is being seeked and the unreliable relation between RSSI and distance. The idea is to have a Wireless Sensor Network up and running, this network being in constant communication with a computer on the network. The User End processing is then fed to a Web Based Interface from where the position of the

6. USER END PROCESSING

transmitter can be tracked on screen.

At the user end, the server keeps receiving the signal strength values from base station. These readings are

recovered from the packet and correlated to get distance estimates. These are then used along with a database that lists the locations of all the sensor nodes to get an estimate of the location of the object being tracked. Presently we use a simplistic scheme to determine the location of the object.This is well described by the figure above. We only consider the top three strongest signal values and use them to estimate the location. This sorting of readings and figuring out of top three strongest signal measurements is done at the base station itself and is transparent to the server. This simplistic approach is however not a good idea since it gives no result in a Presently we use a simplistic scheme to determine the location of the object. This is well described by the figure above. We only consider the top three strongest signal values and use them to estimate the location. This sorting of readings and

figuring out of top three strongest signal measurements is done at the base station itself and is transparent to the server. This simplistic approach is however not a good idea since it gives no result in a lot of cases due to the nature of solution that is being seeked and the unreliable relation between RSSI and distance. The idea is to have a Wireless Sensor Network up and running, this network being in constant communication with a computer on the network. The User End processing is then fed to a Web Based Interface from where the position of the transmitter can be tracked on screen. T. Miyaki, T. Yamasaki, and K. Aizawa, ³Visual tracking of pedestrians jointly using wi-fi location system on R. Cucchiara, ³Multimedia surveillance systems,´ in Proc. of ACM VSSN, 2005, pp. 3±10. References: Y.C. Cheng, Y. Chawathe, A. LaMarca, and J. Krumm, ³Accuracy

characterization for metropolitan-scale Wi-Fi localization,´ in Proc. of ACM MobiSys, 2005, pp. 233±245.

distributed camera network,´ in Proc. of 7.CONCLUSION: The architectures of tracking system fusing visual and Wi-Fi localizations is described . With this method for tracking, with two phases we our result has complemental characteristics: 1. It can cover large areas 2. Detection of location of the target with visual information is obtained. The above characteristics effectively co-operate in order to realize continuous object tracking in non over lapping areas between two surveillance cameras used in object detection ICME, 2007.

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