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My first aperosentation 9/6/2008 Marios Karagiannis

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Localization

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Problem: Nodes need to know their location

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Localization Problem: Nodes need to know their location so that applications like Target Tracking and Geographic Routing may actually work

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Localization The easy way out: GPS

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Localization The easy way out: GPS Well not quite, because GPS is:

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Localization The easy way out: GPS Well not quite, because GPS is: -expensive

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Localization The easy way out: GPS Well not quite, because GPS is: -expensive -big and heavy

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Localization The easy way out: GPS Well not quite, because GPS is: -expensive -big and heavy -working only outdoors

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Localization The easy way out: GPS Well not quite, because GPS is: -expensive -big and heavy -working only outdoors -working only on Earth

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Localization The easy way out: GPS Well not quite, because GPS is: -expensive -big and heavy -working only outdoors -working only on Earth -controlled by the USA

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Localization The easy way out: GPS Well not quite, because GPS is: -expensive -big and heavy -working only outdoors -working only on Earth -controlled by the USA -energy hungry

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Localization The easy way out: GPS Well not quite, because GPS is: -expensive -big and heavy -working only outdoors -working only on Earth -controlled by the USA -energy hungry -not very accurate

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Localization So what do we do?

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Localization So what do we do? It depends. Is our node capable of detecting its distance from another node?

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Localization So what do we do? It depends. Is our node capable of detecting its distance from another node? Range based approaches YES

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Localization So what do we do? It depends. Is our node capable of detecting its distance from another node? Range based approaches Range free approaches YES NO

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Localization Both approaches assume the existence of special nodes which already know their position

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Localization Both approaches assume the existence of special nodes which already know their position These nodes are called anchors or beacons

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Localization Each other node must use these special nodes to calculate an approximation of its own position

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Localization Distance estimation may be calculated by using:

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Localization Distance estimation may be calculated by using: Time difference of Arrival

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Localization Distance estimation may be calculated by using: Time difference of Arrival By making the anchor send a radio and a sound signal at the same time, the node can calculate the distance by measuring the time difference between reception of the two signals

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Localization Distance estimation may be calculated by using: Time difference of Arrival By making the anchor send a radio and a sound signal at the same time, the node can calculate the distance by measuring the time difference between receptions of the two signals This, of course, requires special equipment like tone generators and microphones

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Localization Distance estimation may be calculated by using: Signal strength attenuation

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Localization Distance estimation may be calculated by using: Signal strength attenuation By measuring the signal strength and compare it with the maximum strength possible, a node can estimate the distance the radio wave travelled

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Localization Distance estimation may be calculated by using: Signal strength attenuation By measuring the signal strength and compare it with the maximum strength possible, a node can estimate the distance the radio wave travelled Of course this requires equipment capable of measuring the signal strength

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Localization Trilateration

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Localization Trilateration A B C n

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Localization Trilateration A B C n n can be on any point of the circles perimeter

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Localization Trilateration A B C n n can be either here or here

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Localization Trilateration A B C n n know its position

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Localization Trilateration A B C n When distance calculations are not precise, we have an approximation of the position

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Localization Trilateration A B C n In this case, more than 3 anchors may help pinpoint the location D

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Localization Range free estimation using hop count A B C n5 n10 n8 n3 n7 n4 n1 n2 n9 n6

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Localization Range free estimation using hop count A B C n5 n10 n8 n3 n7 n4 n1 n2 n9 n6

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Localization Range free estimation using hop count A B C n5 n10 n8 n3 n7 n4 n1 n2 n9 n6 N10 is at position (1,6,5)

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Localization Range free estimation using hop count A B C n5 n10 n8 n3 n7 n4 n1 n2 n9 n6 because it is 1 hop from A, 6 hops from B and 5 hops from C

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Localization Range free estimation using hop count A B C n5 n10 n8 n3 n7 n4 n1 n2 n9 n6 by knowing its communication radius, it has estimate its distances and so its position

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Localization Range free estimation using hop count A B C n5 n10 n8 n3 n7 n4 n1 n2 n9 n6 So if it nodes that its radius is 1m, it may guess that it is 1 meter from A, 6 m from B and 5 m from C which is not that different from its real position

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Localization Range free estimation using hop count A B C n5 n10 n8 n3 n7 n4 n1 n2 n9 n6 In a dense network, this method is more accurate

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Localization Angle estimation n Supposed anchors A and C are equipped with lasers and n is equipped with a laser sensor A C

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Localization Angle estimation Supposed anchors A and C are equipped with lasers and n is equipped with a laser sensor A C n

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Localization Angle estimation n senses C laser at time t1 A C n

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Localization Angle estimation n senses C laser at time t1 A C n

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Localization Angle estimation n senses C laser at time t1 A C n

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Localization Angle estimation n senses C laser at time t1 A C n n senses A laser at time t2

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Localization Angle estimation n senses C laser at time t1 A C n n senses A laser at time t2

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Localization Angle estimation n senses C laser at time t1 A C n n senses A laser at time t2

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Localization Angle estimation n senses C laser at time t1 A C n n senses A laser at time t2

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Localization Angle estimation n senses C laser at time t1 A C n n senses A laser at time t2 n senses A laser again at time t3

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Localization Angle estimation n senses C laser at time t1 A C n n senses A laser at time t2 n senses A laser again at time t3

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Localization Angle estimation n senses C laser at time t1 A C n n senses A laser at time t2 n senses A laser again at time t3

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Localization Angle estimation n senses C laser at time t1 A C n n senses A laser at time t2 n senses A laser again at time t3 n senses C laser again at time t4

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Localization Angle estimation By knowing: As and C laser rotation rate As and C laser maximum and minimum angles n can calculate the angles to A and C based on t1,t2,t3 and t4 A C n

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Localization Angle estimation It takes just 2 anchors for this technique but result is a scale-prone model of the network A C n

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Localization When a node becomes localized it then transforms to a new anchor

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Localization When a node becomes localized it then transforms to a new anchor Because it is an anchor, it will broadcast its own position in order to help other nodes localize as well

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Localization If all nodes which becomes anchors broadcast greedily, we will localize the whole network

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Localization If all nodes which becomes anchors broadcast greedily, we will localize the whole network But should they?

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Localization In this case we will have lots of collisions!

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Localization In this case we will have lots of collisions! Unless we introduce delays randomly or semi-randomly

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Localization

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The network is localized

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Localization Our goal is to introduce a mechanism that will reduce the number of broadcasts in order to:

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Localization Our goal is to introduce a mechanism that will reduce the number of broadcasts in order to: Save energy

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Localization Our goal is to introduce a mechanism that will reduce the number of broadcasts in order to: Save energy Avoid collisions

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Localization Our goal is to introduce a mechanism that will reduce the number of broadcasts in order to: Save energy Avoid collisions Localize the network in a shorter time

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Localization In order to do that, a node that has been recently localized must decide to broadcast its position

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Localization In order to do that, a node that has been recently localized must decide to broadcast its position or not

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As described in Localization algorithm for wireless ad-hoc sensor networks with traffic overhead minimization by emission inhibition Pierre Leone, Luminita Moraru, Olivier Powell, Jose Rolim

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Localization B A C

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B A C 3 covered

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Localization B A C 3 covered 2 covered

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Localization B A C 3 covered 2 covered 1 covered

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Localization B A C 3 covered 2 covered 1 covered Naturally 3 covered will be localized

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Localization B A C 3 covered 2 covered 1 covered If they all broadcast at different times many nodes will receive more than 3 anchors

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Localization B A C 3 covered 2 covered 1 covered This is unnecessary!

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Localization B A C 3 covered 2 covered 1 covered We only need to make sure that nodes that need one more to localize (2 covered)

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Localization B A C 3 covered 2 covered 1 covered will get one more anchor!

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Localization B A C 3 covered 2 covered 1 covered So, we give a timer to each newly localized node depending on its distance from

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Localization B A C 3 covered 2 covered 1 covered a critical point!

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Localization B A C 3 covered 2 covered 1 covered So how do we calculate a critical point?

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Localization B A C We find the intersection points for each pair of circles

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Localization B A C A critical point can be here or here for the circles of A and B

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Localization B A C Which one do we choose?

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Localization B A C We choose the one that is not Inside the circle of C

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Localization B A C We choose the one that is not Inside the circle of C

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Localization B A C

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B A C 3 covered 2 covered 1 covered By repeating this procedure for all 3 pairs we find the 3 critical points

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Localization B A C 3 covered 2 covered 1 covered

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Localization B A C 3 covered 2 covered 1 covered Nodes closer to the critical points will broadcast first

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Localization B A C 3 covered 2 covered 1 covered Nodes closer to the critical points will broadcast first

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Localization B A C 3 covered 2 covered 1 covered This happens by setting a timer for each node in the 3 covered area

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Localization B A C 3 covered 2 covered 1 covered The timer is proportional to the distance d to its closest critical point or to d 2

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Localization B A C 3 covered 2 covered 1 covered Other nodes will wait for their turn, but will not broadcast at all if they hear another node broadcasting which is closer to their critical point

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Localization B A C 2 covered 1 covered Other nodes will wait for their turn, but will not broadcast at all if they hear another node broadcasting which is closer to their critical point

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Localization B A C 2 covered 1 covered In this case we maximize nodes that are in 2 covered areas

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Localization B A C 2 covered 1 covered In this case we maximize nodes that are in 2 covered areas

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Localization Experiments have shown that this technique achieves the goals set before!

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Thank you