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Sogang University ICC Lab A Survey on Sensor Networks.

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1 Sogang University ICC Lab A Survey on Sensor Networks

2 Sogang University ICC Lab. 2 Reading Materials  Reference book and papers : 무선센서네트워크기술 : 저자 : 이상학, 정태충 경희대학교출판국 ( 구 ) 경희서적센터  Related papers sensor-survey.pdf  Reference book and papers : 무선센서네트워크기술 : 저자 : 이상학, 정태충 경희대학교출판국 ( 구 ) 경희서적센터  Related papers sensor-survey.pdf

3 Sogang University ICC Lab. 3 Agenda  Introduction to Sensor Networks  Sensor Network Vs Fixed and Ad-Hoc Networks  Routing Protocols for Sensor Networks  Proposed Routing Protocol  Performance Metrics  Introduction to Sensor Networks  Sensor Network Vs Fixed and Ad-Hoc Networks  Routing Protocols for Sensor Networks  Proposed Routing Protocol  Performance Metrics

4 Sogang University ICC Lab. 4 Introduction to Sensor Networks  What is a Sensor? A sensor is a device the produces a measurable response to a change in physical condition such as temperature or chemical condition such as concentration Types of Sensors - Temperature, Pressure, Humidity, Image etc  What is a Sensor? A sensor is a device the produces a measurable response to a change in physical condition such as temperature or chemical condition such as concentration Types of Sensors - Temperature, Pressure, Humidity, Image etc

5 Sogang University ICC Lab. 5 Sensor Network Architecture Sensor Nodes Sink Internet/Satellite Task Manager User

6 Sogang University ICC Lab. 6 Sensors Berkeley Mote EmbedSense - Wireless Sensor and Data Acquisition System

7 Sogang University ICC Lab. 7  A sensor network is composed of a large number of sensor nodes, - which are densely deployed either inside the phenomenon or very close to it.  A large number of low-cost, low-power, multifunctional, and small sensor nodes  Sensor node consists of sensing, data processing, and communicating components  The position of sensor nodes need not be engineered or pre-determined. - sensor network protocols and algorithms must possess self-organizing capabilities.  A sensor network is composed of a large number of sensor nodes, - which are densely deployed either inside the phenomenon or very close to it.  A large number of low-cost, low-power, multifunctional, and small sensor nodes  Sensor node consists of sensing, data processing, and communicating components  The position of sensor nodes need not be engineered or pre-determined. - sensor network protocols and algorithms must possess self-organizing capabilities. Sensors

8 Sogang University ICC Lab. 8 Applications of Sensor Networks  Monitoring Applications  Military  Security  Intrusion Detection  Habitat Monitoring  Environment Observation and Forecasting  Monitoring Applications  Military  Security  Intrusion Detection  Habitat Monitoring  Environment Observation and Forecasting

9 Sogang University ICC Lab. 9 Sensor Vs Ad-Hoc Networks  Network topology is not fixed  Power is an expensive resource in these networks  Nodes are connected by wireless links  The number of sensor nodes in a sensor network is much more than the nodes in an ad hoc network.  Sensor nodes are densely deployed.  Sensor nodes are prone to failures.  The topology of a sensor network changes very frequently.  Network topology is not fixed  Power is an expensive resource in these networks  Nodes are connected by wireless links  The number of sensor nodes in a sensor network is much more than the nodes in an ad hoc network.  Sensor nodes are densely deployed.  Sensor nodes are prone to failures.  The topology of a sensor network changes very frequently.

10 Sogang University ICC Lab. 10 Sensor Vs Ad-Hoc Networks  Large number of sensors  Addressing scheme for sensor nodes  Sensor network used for data gathering  Ad - Hoc network used for distributed computing  Data flows from multiple sources to a single destination  Redundancy in data traffic  Large number of sensors  Addressing scheme for sensor nodes  Sensor network used for data gathering  Ad - Hoc network used for distributed computing  Data flows from multiple sources to a single destination  Redundancy in data traffic

11 Sogang University ICC Lab. 11 Sensor Vs Ad - Hoc Networks  Sensor nodes are prone to failure  Sensor nodes mainly use broadcast communication paradigm whereas most ad hoc networks are based on point-to-point communications.  Sensor nodes are limited in power, computational capacities, and memory.  Sensor nodes may not have global ID because of the large amount of overhead and large number of sensors.  Sensor nodes are prone to failure  Sensor nodes mainly use broadcast communication paradigm whereas most ad hoc networks are based on point-to-point communications.  Sensor nodes are limited in power, computational capacities, and memory.  Sensor nodes may not have global ID because of the large amount of overhead and large number of sensors.

12 Sogang University ICC Lab. 12 Sensor networks communication The sensor nodes are usually scattered in a sensor field Each of these scattered sensor nodes has the capabilities to collect data and route data back to the sink The sink may communicate with the task manager node via Internet or Satellite.

13 Sogang University ICC Lab. 13 Hardware constraints  A sensor node is made up of four basic components  a sensing unit  usually composed of two subunits: sensors and analog to digital converters (ADCs).  processing unit,  Manages the procedures that make the sensor node collaborate with the other nodes to carry out the assigned sensing tasks.  A transceiver unit  Connects the node to the network.  Power units (the most important unit)  A sensor node is made up of four basic components  a sensing unit  usually composed of two subunits: sensors and analog to digital converters (ADCs).  processing unit,  Manages the procedures that make the sensor node collaborate with the other nodes to carry out the assigned sensing tasks.  A transceiver unit  Connects the node to the network.  Power units (the most important unit)

14 Sogang University ICC Lab. 14 Hardware constraints

15 Sogang University ICC Lab. 15 Sensor network topology  Pre-deployment and deployment phase  Sensor nodes can be either thrown in mass or placed one by one in the sensor field.  Post-deployment phase  Sensor network topologies are prone to frequent changes after deployment.  Re-deployment of additional nodes phase  Addition of new nodes poses a need to re-organize the network.  Pre-deployment and deployment phase  Sensor nodes can be either thrown in mass or placed one by one in the sensor field.  Post-deployment phase  Sensor network topologies are prone to frequent changes after deployment.  Re-deployment of additional nodes phase  Addition of new nodes poses a need to re-organize the network.

16 Sogang University ICC Lab. 16 Power consumption  Only be equipped with limited power source(<0.5 Ah 1.2V)  Node lifetime strong dependent on battery lifetime  Power consumption can be divided into three domains:  sensing, communication, and data processing.  Only be equipped with limited power source(<0.5 Ah 1.2V)  Node lifetime strong dependent on battery lifetime  Power consumption can be divided into three domains:  sensing, communication, and data processing.

17 Sogang University ICC Lab. 17 Sensor networks communication

18 Sogang University ICC Lab. 18 Management Planes  These management planes make sensor nodes work together in a power efficient way, route data in a mobile sensor network, and share resources between sensor nodes.  Power management plane  manages how a sensor node uses its power.  For example, the sensor node may turn off its receiver after receiving a message.  When the power level of the sensor node is low, the sensor node broadcasts to its neighbors that it is low in power and cannot participate in routing messages.  These management planes make sensor nodes work together in a power efficient way, route data in a mobile sensor network, and share resources between sensor nodes.  Power management plane  manages how a sensor node uses its power.  For example, the sensor node may turn off its receiver after receiving a message.  When the power level of the sensor node is low, the sensor node broadcasts to its neighbors that it is low in power and cannot participate in routing messages.

19 Sogang University ICC Lab. 19 Management Planes  Mobility management plane  detects and registers the movement of sensor nodes  So a route back to the user is always maintained  the sensor nodes can keep track of who are their neighbor sensor nodes.  Task management plane  Balances and schedules the sensing tasks given to a specific region.  Not all sensor nodes in that region are required to perform the sensing task at the same time.  Mobility management plane  detects and registers the movement of sensor nodes  So a route back to the user is always maintained  the sensor nodes can keep track of who are their neighbor sensor nodes.  Task management plane  Balances and schedules the sensing tasks given to a specific region.  Not all sensor nodes in that region are required to perform the sensing task at the same time.

20 Sogang University ICC Lab. 20 Physical Layer  Frequency selection, carrier frequency generation, signal detection, modulation, and data encryption.  915 MHz ISM band has been widely suggested for sensor networks.  Open research issues  Modulation schemes  Strategies to overcome signal propagation effects  Hardware design  Frequency selection, carrier frequency generation, signal detection, modulation, and data encryption.  915 MHz ISM band has been widely suggested for sensor networks.  Open research issues  Modulation schemes  Strategies to overcome signal propagation effects  Hardware design

21 Sogang University ICC Lab. 21 Data link layer  The data link layer is responsible for the multiplexing of data stream, data frame detection, medium access and error control  MAC protocol for sensor network must have built- in power conservation, mobility management and failure recovery strategies  The data link layer is responsible for the multiplexing of data stream, data frame detection, medium access and error control  MAC protocol for sensor network must have built- in power conservation, mobility management and failure recovery strategies

22 Sogang University ICC Lab. 22 Power saving modes of operation  turn the transceiver off when it is not required.  Not exactly  There can be a number of such useful modes of operation for the wireless sensor node  depending on the number of states of the micro- processor, memory, A/D convertor and the transceiver.  turn the transceiver off when it is not required.  Not exactly  There can be a number of such useful modes of operation for the wireless sensor node  depending on the number of states of the micro- processor, memory, A/D convertor and the transceiver.

23 Sogang University ICC Lab. 23 Network layer  The networking layer of sensor networks is usually designed according to the following principles:  Power efficiency is always an important consideration.  Sensor networks are mostly data centric.  Data aggregation is useful only when it does not hinder the collaborative effort of the sensor nodes.  An ideal sensor network has attribute-based addressing and location awareness.  The networking layer of sensor networks is usually designed according to the following principles:  Power efficiency is always an important consideration.  Sensor networks are mostly data centric.  Data aggregation is useful only when it does not hinder the collaborative effort of the sensor nodes.  An ideal sensor network has attribute-based addressing and location awareness.

24 Sogang University ICC Lab. 24 Transport layer  The transport layer is needed when the system is planned to be accessed through Internet or other external networks.  Not any scheme related to the transport layer of a sensor network has been proposed in literature.  The transport layer is needed when the system is planned to be accessed through Internet or other external networks.  Not any scheme related to the transport layer of a sensor network has been proposed in literature.

25 Sogang University ICC Lab. 25 Data-centric Routing  Interest dissemination is performed to assign the sensing tasks to the sensor nodes.  Two approaches used for interest dissemination:  Sinks broadcast the interest  Sensor nodes broadcast an advertisement for the available data and wait for a request from the interested sinks.  Interest dissemination is performed to assign the sensing tasks to the sensor nodes.  Two approaches used for interest dissemination:  Sinks broadcast the interest  Sensor nodes broadcast an advertisement for the available data and wait for a request from the interested sinks.

26 Sogang University ICC Lab. 26 Data-centric Routing  Requires attribute-based naming  Querying an attribute of the phenomenon, rather than querying an individual node.  Ex: “the areas where the temperature is over 70°F” is a more common query than “the temperature read by a certain node”  Requires attribute-based naming  Querying an attribute of the phenomenon, rather than querying an individual node.  Ex: “the areas where the temperature is over 70°F” is a more common query than “the temperature read by a certain node”

27 Sogang University ICC Lab. 27 Data aggregation  A technique used to solve the implosion and overlap problems in data-centric routing  Data coming from multiple sensor nodes with the same attribute of phenomenon are aggregated  A technique used to solve the implosion and overlap problems in data-centric routing  Data coming from multiple sensor nodes with the same attribute of phenomenon are aggregated

28 Sogang University ICC Lab. 28 Data aggregation - continue Sensor network is usually perceived as a reverse multicast tree.

29 Sogang University ICC Lab. 29 Data aggregation - continue  can be perceived as a set of automated methods of combining the data the comes from many sensor nodes into a set of meaningful information  With this respect, data aggregation is known as data fusion  can be perceived as a set of automated methods of combining the data the comes from many sensor nodes into a set of meaningful information  With this respect, data aggregation is known as data fusion

30 Sogang University ICC Lab. 30 Internetworking  Sink nodes can be used as a gateway to other network  Create a backbone by connecting sink nodes together and make it access other network via a gateway  Sink nodes can be used as a gateway to other network  Create a backbone by connecting sink nodes together and make it access other network via a gateway

31 Sogang University ICC Lab. 31 Network layer  Open research issues  Improved or new protocols to address higher topology changes and higher scalability.  Open research issues  Improved or new protocols to address higher topology changes and higher scalability.

32 Sogang University ICC Lab. 32 Transport layer  The transport layer is needed when the system is planned to be accessed through Internet or other external networks.  Not any scheme related to the transport layer of a sensor network has been proposed in literature.  The transport layer is needed when the system is planned to be accessed through Internet or other external networks.  Not any scheme related to the transport layer of a sensor network has been proposed in literature.

33 Sogang University ICC Lab. 33 Transport layer  An approach such as TCP splitting may be needed to make sensor networks interact with other networks such as Internet. TCP/UDP ?

34 Sogang University ICC Lab. 34 Transport layer  Open research issues  Hardware constraints such as limited power and memory. Each sensor node cannot store large amounts of data like a server in the internet.  Acknowledgments are too costly.  may be needed where UDP-type protocols are used in the sensor network and TCP/UDP protocols in the internet or satellite network.  Open research issues  Hardware constraints such as limited power and memory. Each sensor node cannot store large amounts of data like a server in the internet.  Acknowledgments are too costly.  may be needed where UDP-type protocols are used in the sensor network and TCP/UDP protocols in the internet or satellite network.

35 Sogang University ICC Lab. 35 Application layer  Potential application layer protocols for sensor networks remains a largely unexplored region.

36 Sogang University ICC Lab. 36 Routing issues  Node deployment  Manual deployment  Sensors are manually deployed  Data is routed through predetermined path  Random deployment  Optimal clustering is necessary to allow connectivity & energy-efficiency  Multi-hop routing  Node deployment  Manual deployment  Sensors are manually deployed  Data is routed through predetermined path  Random deployment  Optimal clustering is necessary to allow connectivity & energy-efficiency  Multi-hop routing

37 Sogang University ICC Lab. 37 Routing issues  Data routing methods  Application-specific  Time-driven: Periodic monitoring  Event-driven: Respond to sudden changes  Query-driven: Respond to queries  Hybrid  Data routing methods  Application-specific  Time-driven: Periodic monitoring  Event-driven: Respond to sudden changes  Query-driven: Respond to queries  Hybrid

38 Sogang University ICC Lab. 38 Routing issues  Node/link heterogeneity  Homogeneous sensors  Heterogeneous nodes with different roles & capabilities  Diverse modalities  If cluster heads may have more energy & computational capability, they take care of transmissions to the base station (BS)  Node/link heterogeneity  Homogeneous sensors  Heterogeneous nodes with different roles & capabilities  Diverse modalities  If cluster heads may have more energy & computational capability, they take care of transmissions to the base station (BS)

39 Sogang University ICC Lab. 39 Routing issues  Fault tolerance  Some sensors may fail due to lack of power, physical damage, or environmental interference  Adjust transmission power, change sensing rate, reroute packets through regions with more power  Fault tolerance  Some sensors may fail due to lack of power, physical damage, or environmental interference  Adjust transmission power, change sensing rate, reroute packets through regions with more power

40 Sogang University ICC Lab. 40 Routing issues  Network dynamics  Mobile nodes  Mobile events, e.g., target tracking  If WSN is to sense a fixed event, networks can work in a reactive manner  A lot of applications require periodic reporting  Network dynamics  Mobile nodes  Mobile events, e.g., target tracking  If WSN is to sense a fixed event, networks can work in a reactive manner  A lot of applications require periodic reporting

41 Sogang University ICC Lab. 41 Routing issues  Transmission media  Wireless channel  Limited bandwidth: 1 – 100Kbps  MAC  Contention-free, e.g., TDMA or CDMA  Contention-based, e.g., CSMA, MACA, or 802.11  Transmission media  Wireless channel  Limited bandwidth: 1 – 100Kbps  MAC  Contention-free, e.g., TDMA or CDMA  Contention-based, e.g., CSMA, MACA, or 802.11

42 Sogang University ICC Lab. 42 Routing issues  Connectivity  High density  high connectivity  Some sensors may die after consuming their battery power  Connectivity depends on possibly random deployment  Connectivity  High density  high connectivity  Some sensors may die after consuming their battery power  Connectivity depends on possibly random deployment

43 Sogang University ICC Lab. 43 Routing issues  Coverage  An individual sensor’s view is limited  Area coverage is an important design factor  Data aggregation  Quality of Service  Bounded delay  Energy efficiency for longer network lifetime  Coverage  An individual sensor’s view is limited  Area coverage is an important design factor  Data aggregation  Quality of Service  Bounded delay  Energy efficiency for longer network lifetime

44 Sogang University ICC Lab. 44 Classification of Routing Protocols  Data-centric protocols  naming 과 query-based 로 중복된 전송제거  Hierarchical protocols  data 를 집적하고 축소 하기 위해 클러스터링을 이용  Location-based protocols  전체 네트워크 보다는 요구된지역에 data 를 전달하기 위하여 위치 정보를 이용  Data-centric protocols  naming 과 query-based 로 중복된 전송제거  Hierarchical protocols  data 를 집적하고 축소 하기 위해 클러스터링을 이용  Location-based protocols  전체 네트워크 보다는 요구된지역에 data 를 전달하기 위하여 위치 정보를 이용

45 Sogang University ICC Lab. 45 Data Centric Routing  Address Centric Routing  Finding short routes between pairs of addressable end nodes  Data Centric Routing  Perform in-network consolidation of redundant data while routing from source to the sink  Address Centric Routing  Finding short routes between pairs of addressable end nodes  Data Centric Routing  Perform in-network consolidation of redundant data while routing from source to the sink

46 Sogang University ICC Lab. 46  Flooding  Each node receiving a data or management packet repeats it by broadcasting  Does not require costly topology maintenance and complex route discovery algorithms.  Implosion: a situation where duplicated messages are sent to the same node.  Overlap: If two nodes share the same obserying region, both of them may sense the same stimuli at the same time. As a result, neighbor nodes receive duplicated messages.  Resource blindness: flooding does not take into account the available energy resources.  Flooding  Each node receiving a data or management packet repeats it by broadcasting  Does not require costly topology maintenance and complex route discovery algorithms.  Implosion: a situation where duplicated messages are sent to the same node.  Overlap: If two nodes share the same obserying region, both of them may sense the same stimuli at the same time. As a result, neighbor nodes receive duplicated messages.  Resource blindness: flooding does not take into account the available energy resources. Flooding

47 Sogang University ICC Lab. 47  Gossiping  A derivation of flooding  Nodes send the incoming packets to a randomly selected neighbor.  Avoids the implosion problem  It takes a long time to propagate the message to all sensor nodes.  Gossiping  A derivation of flooding  Nodes send the incoming packets to a randomly selected neighbor.  Avoids the implosion problem  It takes a long time to propagate the message to all sensor nodes. Gossiping

48 Sogang University ICC Lab. 48  Sensor protocols for information via negotiation (SPIN):  Designed to address the deficiencies of classic flooding by negotiation and resource adaptation.  sending data that describe the sensor data instead of sending the whole data  As a result, the sensor nodes in the entire sensor network that are interested in the data will get a copy. Note that SPIN is based on data-centric routing.  Sensor protocols for information via negotiation (SPIN):  Designed to address the deficiencies of classic flooding by negotiation and resource adaptation.  sending data that describe the sensor data instead of sending the whole data  As a result, the sensor nodes in the entire sensor network that are interested in the data will get a copy. Note that SPIN is based on data-centric routing. The SPIN protocol

49 Sogang University ICC Lab. 49  Sequential assignment routing (SAR)  A set of algorithms, which perform organization, management and mobility management operations in sensor networks  Creates multiple trees where the root of each tree is one hop neighbor from the sink  Most nodes belong to multiple trees, allows a sensor node to choose a tree to relay its information back to the sink.  select a tree for data to be routed back to the sink according to the energy resources and additive QoS metric  Sequential assignment routing (SAR)  A set of algorithms, which perform organization, management and mobility management operations in sensor networks  Creates multiple trees where the root of each tree is one hop neighbor from the sink  Most nodes belong to multiple trees, allows a sensor node to choose a tree to relay its information back to the sink.  select a tree for data to be routed back to the sink according to the energy resources and additive QoS metric sink SAR( Sequential assignment routing )

50 Sogang University ICC Lab. 50 Hierarchical Protocols  When sensor density increases single tier networks cause  Gateway overloading  Increased latency  Large energy consumption  Clustered Network allow coverage of large area of interest and additional load without degrading the performance  When sensor density increases single tier networks cause  Gateway overloading  Increased latency  Large energy consumption  Clustered Network allow coverage of large area of interest and additional load without degrading the performance

51 Sogang University ICC Lab. 51 Hierarchical Protocols  Hierarchical routing  Uses Multi - hop communication within a cluster  Performs data aggregation and fusion on data to reduce number of transmitted messages to the sink  Maintain the energy reserves of nodes efficiently  Example - LEACH, PEGASIS  Hierarchical routing  Uses Multi - hop communication within a cluster  Performs data aggregation and fusion on data to reduce number of transmitted messages to the sink  Maintain the energy reserves of nodes efficiently  Example - LEACH, PEGASIS

52 Sogang University ICC Lab. 52  Low-energy adaptive clustering hierarchy (LEACH)  Randomly select sensor nodes as cluster-heads, so the high energy dissipation in communicating with the base station is spread to all sensor nodes in the sensor network.  Set-up phase  each sensor node chooses a random number between 0 and 1  If this random number is less than the threshold T(n), the sensor node is a cluster-head.  Low-energy adaptive clustering hierarchy (LEACH)  Randomly select sensor nodes as cluster-heads, so the high energy dissipation in communicating with the base station is spread to all sensor nodes in the sensor network.  Set-up phase  each sensor node chooses a random number between 0 and 1  If this random number is less than the threshold T(n), the sensor node is a cluster-head. P,the desired percentage to become a cluster-head; r,the current round G, the set of nodes that have not being selected as a cluster- head in the last 1/P rounds. LEACH

53 Sogang University ICC Lab. 53  Set-up phase (cont’d)  The cluster-heads advertise to all sensor nodes in the network  The sensor nodes inform the appropriate cluster-heads that they will be a member of the cluster. (base on signal strength)  Afterwards, the cluster-heads assign the time on which the sensor nodes can send data to the cluster-heads based on a TDMA approach.  Set-up phase (cont’d)  The cluster-heads advertise to all sensor nodes in the network  The sensor nodes inform the appropriate cluster-heads that they will be a member of the cluster. (base on signal strength)  Afterwards, the cluster-heads assign the time on which the sensor nodes can send data to the cluster-heads based on a TDMA approach. LEACH

54 Sogang University ICC Lab. 54  steady phase (cont’d)  the sensor nodes can begin sensing and transmitting data to the cluster-heads.  The cluster-heads also aggregate data from the nodes in their cluster before sending these data to the base station.  After a certain period of time spent on the steady phase, the network  goes into the set-up phase again and  enters into another round of selecting the cluster-heads.  steady phase (cont’d)  the sensor nodes can begin sensing and transmitting data to the cluster-heads.  The cluster-heads also aggregate data from the nodes in their cluster before sending these data to the base station.  After a certain period of time spent on the steady phase, the network  goes into the set-up phase again and  enters into another round of selecting the cluster-heads. LEACH

55 Sogang University ICC Lab. 55 Directed Diffusion the sink sends out interest to sensors As the interest is propagated throughout the sensor network, the gradients from the source back to the sink are set up When the source has data for the interest, the source sends the data along the interest ’ s gradient path

56 Sogang University ICC Lab. 56 Location Based Protocols  Location information can be used to  Find shortest path to the sink  Form a virtual grid and keep only few nodes active at a time  Example  GAF  GEAR  Location information can be used to  Find shortest path to the sink  Form a virtual grid and keep only few nodes active at a time  Example  GAF  GEAR

57 Sogang University ICC Lab. 57 Determining Location  Location of a node can be determined using  Global Positioning System  Ultrasonic Systems  Beacons  Location based protocols assume that each node knows its location in the network  Location of a node can be determined using  Global Positioning System  Ultrasonic Systems  Beacons  Location based protocols assume that each node knows its location in the network

58 Sogang University ICC Lab. 58 GAF(Geographic Adaptive Fidelity)  Forms a virtual grid of the covered area  Each node associates itself with a point in the grid based on its location  Nodes associated with same point in grid are considered equivalent  Some nodes in an area are kept sleeping to conserve energy  Nodes change state from sleeping to active for load balancing  Forms a virtual grid of the covered area  Each node associates itself with a point in the grid based on its location  Nodes associated with same point in grid are considered equivalent  Some nodes in an area are kept sleeping to conserve energy  Nodes change state from sleeping to active for load balancing

59 Sogang University ICC Lab. 59 GAF  A node remains active for time Ta  Ta of a node in the grid is broadcasted to other equivalent nodes  The sleeping time of a node is adjusted depending on Ta  In the discovery state each node broadcasts discovery messages periodically (Td)  A node remains active for time Ta  Ta of a node in the grid is broadcasted to other equivalent nodes  The sleeping time of a node is adjusted depending on Ta  In the discovery state each node broadcasts discovery messages periodically (Td)

60 Sogang University ICC Lab. 60 Sleeping Discovery Active After Ts After Td State Transition for GAF

61 Sogang University ICC Lab. 61 Routing in GAF Base Station

62 Sogang University ICC Lab. 62 GAF  Not very scalable. As the network size increases distance to the base station increases  Only the active nodes sense and report data. Hence data accuracy is not very high.  Not very scalable. As the network size increases distance to the base station increases  Only the active nodes sense and report data. Hence data accuracy is not very high.

63 Sogang University ICC Lab. 63 GEAR ( Geographically and Energy Aware Routing )  Queries  Contain location information  Disseminated to only the specified region of the network  Neighbors are selected probabilistically to forward the query to the target location  Query is flooded only in the target region  Queries  Contain location information  Disseminated to only the specified region of the network  Neighbors are selected probabilistically to forward the query to the target location  Query is flooded only in the target region

64 Sogang University ICC Lab. 64 GEAR  Each node maintains a neighbor table  Energy levels and locations of each neighbor  Cost to transmit to each neighbor  Packet is forwarded to neighbor with smallest cost  Each node maintains a neighbor table  Energy levels and locations of each neighbor  Cost to transmit to each neighbor  Packet is forwarded to neighbor with smallest cost

65 Sogang University ICC Lab. 65 Base Station Region of Interest GEAR

66 Sogang University ICC Lab. 66 GEAR  Not Scalable  All nodes are active even though only a part of the network is queried  Not Scalable  All nodes are active even though only a part of the network is queried

67 Sogang University ICC Lab. 67 Performance Metrics  Average Energy Consumption  Impact of localization errors  Energy and time expended for cluster formation  Network lifetime  Average Energy Consumption  Impact of localization errors  Energy and time expended for cluster formation  Network lifetime

68 Sogang University ICC Lab. 68 Conclusion  In the future, this wide range of application areas will make sensor networks an integral part of our lives.  However, realization of sensor networks needs to satisfy the constraints introduced by factors such as fault tolerance, scalability, hardware, topology change, environment and power consumption.  Many researchers are currently engaged in developing the technologies needed for different layers of the sensor networks protocol stack  In the future, this wide range of application areas will make sensor networks an integral part of our lives.  However, realization of sensor networks needs to satisfy the constraints introduced by factors such as fault tolerance, scalability, hardware, topology change, environment and power consumption.  Many researchers are currently engaged in developing the technologies needed for different layers of the sensor networks protocol stack


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