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AD HOC SENSOR NETWORKS

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					            SENSOR NETWORK
             ARCHITECTURE


                     By
              Shweta Shrivastava
               Manali Joglekar
               Gaurav Rajguru




4/23/2004                          1
                  Outline

 Introduction to sensor networks
 Evolution
 Applications
 Architecture
 Some commercial sensor networks
 The ZigBee Alliance

4/23/2004                           2
                   Introduction

 Wireless sensor networks have been identified as
  one of the most important technologies for the 21st
  century.
 Advances in hardware and wireless network
  technologies have created low-cost, low-power
  multi-functional miniature sensor devices.
 These networks are revolutionizing sensing in a
  wide range of applications.

4/23/2004                                               3
         Evolution Of Sensor Networks

 Early Research on Military Sensor Networks
           During the Cold War, the Sound Surveillance system
            (SOSUS), a system of acoustic sensors was deployed on
            the ocean bottom to detect and track Soviet submarines.
           National Oceanographic and Atmospheric
            Administration (NOAA) now uses SOSUS for
            monitoring oceanic events, e.g., animal activity.
           The air defense system with sensors has also evolved
            over the years.


4/23/2004                                                             4
         Evolution Of Sensor Networks
                   ( Contd.)
 Distributed Sensor Networks Program at the
  Defense Advanced Research Projects Agency
           Network of many spatially distributed low-cost sensing
            nodes that collaborate with each other but operate
            autonomously, with information routed to the nodes that
            can best use it.




4/23/2004                                                             5
            Technology Trends




4/23/2004                       6
                   Applications

   Infrastructure Security
   Environment and Habitat Monitoring
   Industrial Sensing
   Traffic Surveillance
   Military sensing
   Parking lot sensor networks



4/23/2004                                7
            Ad Hoc Sensor Networks

 A collection of sensor nodes forming a temporary
  network in the absence of any stationary
  infrastructure.
 A group of sensors form a clusters.
 Each cluster appoints a cluster head to manage its
  sensors.




4/23/2004                                              8
            Hierarchical Sensor Network
                    Architecture




4/23/2004                                 9
            Sensor Network Architecture




4/23/2004                                 10
            Sensor Networks Architecture
                      (contd)
         Three layers :
     1.     Services layer
     2.     Data Layer
     3.     Physical Layer
         Services include routing protocol, data
          dissemination and data aggregation.
         Data layer models all the messages.
         Physical layer consists of nodes that are
          sinks,children nodes,cluster heads and parents.

4/23/2004                                                   11
              Sensor Network
             Architecture(contd)
 The sink nodes broadcast a query.
 Sensor nodes close to the sensed object broadcast
  the sensed data to their neighboring sensor nodes.
 Cluster heads receive this data from their children
  nodes and are responsible for processing and
  aggregating it .
 Cluster heads then broadcast the response to the
  sink nodes through the neighboring nodes.

4/23/2004                                               12
            Sensor Network Challenges

 Low Energy Use
 Ad Hoc Network Discovery
 Network Control and Routing
 Collaborative Information Processing
 Tasking and Querying



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               Low Energy Use

 Sensor nodes are deployed in remote areas in many
  applications.
 Servicing of such nodes is a very difficult task.
 Hence,lifetime of the node depends on its battery
  life. This requires very low energy expenditure.
 Recharging so many sensor batteries would be
  expensive as well as time consuming.


4/23/2004                                         14
            Ad Hoc Network Discovery

 Network topology frequently changes due to the
  failure or deployment of new sensors.
 Nodes need to know the identity and location of
  their neighbors for processing and collaboration of
  information.
 Since each sensor node interacts only with its
  neighbors,global knowledge is not needed.
 Hence relative-positioning algorithms can be used.

4/23/2004                                               15
            Network Control And Routing

 Network must be able to re-organize itself
  dynamically in case of node failures or addition of
  new nodes.
 Alternatives to traditional Internet methods e.g., IP
  is required.
           Sensors are deployed in large number
           Routes are built using geo-information as and when
            needed due to data-specific purposes.
           IP needs to maintain routing tables and updating it would incur
            heavy overhead in terms of time, money and energy


4/23/2004                                                                     16
            Network Control And Routing

 Routing algorithms that can adapt to the changes are
  required.
           e.g., Diffusion routing methods that depend only on the information
            at the neighboring nodes.
 A comparison of multicast, flooding and diffusion based
  routing algorithms was performed and the results showed
  that multicast protocols require less than half the energy
  required for flooding and diffusion requires only 60% of the
  energy needed for even multicast.



4/23/2004                                                                     17
         Collaborative Information Processing

 Nodes collaborate to collect and process data to
  generate useful information.
 Tradeoffs between performance and resource
  utilization.
           Better performance is achieved by processing data from
            more sensors, but requires more communication
            resources.(e.g., energy)
           Communication of information at low-level(e.g.,raw
            signals) results in lesser information loss, but requires
            more bandwidth.

4/23/2004                                                               18
         Collaborative Information Processing
                        (contd)

 FUSION
           Information from multiple sensors has to be fused with
            the local information.
           Information arriving at a node might have traveled
            multiple paths.
           Fusion algorithm should recognize the dependency in the
            information to be fused and also avoid double counting.




4/23/2004                                                         19
         Collaborative Information Processing
                        (contd.)

 DATA ASSOCIATION
           This problem arises in the presence of multiple targets.
           Every node must associate the measured information
            with individual targets.
           Also to avoid duplication and enable fusion, targets
            detected by different nodes have to associate with each
            other.
           Hence, distributed data association algorithms are
            required.

4/23/2004                                                              20
                    Tasking And Quering

 Two types of addressing in sensor networks:
           Data-centric
            A query is sent to a specific region.
           Address-centric
            A query is sent to an individual node.
 Sensor networks should be data-centric.
           Giving unique address to each node is costly.
           Limited memory and computational power.


4/23/2004                                                   21
            Tasking And Quering(contd)

 A sensor field is just like a database in which data is
  dynamically collected.
 The data is distributed across the geographically
  dispersed nodes.
 Hence the need for simple user interface.
     e.g., handheld unit which accepts speech input from user.




4/23/2004                                                        22
                      Security

 The network should be protected against intrusion
  and spoofing.
 Network techniques need to provide low-latency,
  survivable and secure networks.




4/23/2004                                             23
                Sensor Networks
            Communication Architecture.




4/23/2004                                 24
                Sensor Networks
            Communication Architecture.
 The sensor nodes are usually scattered in a sensor field as
  shown in the earlier slide.
 Each of these scattered sensors nodes are capable to collect
  data and route data back to the sink.
 Data are routed back to sink by multi hop infrastructureless
  architecture thru the sink.
 The sink may communicate with the task manager node via
  Internet or Satellite.
 The design of sensor networks is influenced by many factors
  like fault tolerance, scalability, production costs, operating
  environment, power consumption etc.

4/23/2004                                                     25
            Protocol Stack




4/23/2004                    26
                The Physical layer

 Responsible for frequency selection, carrier frequency
  generation, signal detection, modulation and data
  encryption.
 So far, the 915 MHz ISM band has been widely suggested
  for sensor networks.
 Energy minimization assumes significant importance in
  designing the physical layer for sensor networks.
 The physical layer is a largely unexplored area in sensor
  networks.
 The open research issues are power-efficient transceiver
  design and modulation schemes.

4/23/2004                                                     27
                     The Data Link Layer

 The data link layer is responsible for multiplexing of data
  streams, data frame detection, medium access and error
  control.
 It ensures reliable point-to-point and point-to-multipoint
  connections in a multi point connections in communication
  network.
 Issues to be considered for the data link layer are:
            (1) Medium Access Control
            (2) Error control



4/23/2004                                                       28
            Medium Access Control

 The MAC protocol in a wireless multihop self-organizing
  sensor network must achieve the following goals:
  (1) Creation of network infrastructure
  (2) Fair and efficient sharing of communication resources
       between sensor nodes.
 Some of the proposed MAC protocols are:
  (1) Self-Organizing MAC for sensor networks (SMACS)
  (2) CSMA-Based MAC
  (3) Hybrid TDMA/FDMA-Based MAC.

4/23/2004                                                     29
       Medium Access Control(contd)

 The following table shows the qualitative overview of MAC protocols
  for sensor networks:




4/23/2004                                                               30
                        Error Control

 Another important function of data link layer.
 Two important modes of error control are:
     (1) Forward Error Correction (FEC)
    (2) Automatic Repeat Request (ARQ)
 The usefulness of ARQ in multihop sensor network
  environment is limited by the additional retransmission, energy
  cost and overhead. On the other hand, the decoding complexity
  is greater in FEC since error correction capabilities need to be
  built in.
 So, simple error control codes with low complexity encoding
  and decoding present the best solutions for sensor networks.

4/23/2004                                                     31
            Open Research Issues in Data
                    Link Layer
 The key research issues pertaining to the data link layer are:
   (1) MAC for mobile sensor networks
   (2) Determination of lower bounds on the energy required
       for sensor network self-organization.
   (3) Error control coding schemes
   (4) Power-saving modes of operation




4/23/2004                                                      32
                   The Network Layer

 The networking layer of the sensor networks is usually
  designed according to the following principles:
   (1) Power efficiency is always an important consideration
   (2) Sensor networks are mostly data centric
   (3) Data aggregation is useful only when it does not hinder the
       collaborative effort of the sensor nodes.
   (4) Attribute based addressing and location based awareness
 One important function of the network layer is to provide
  internetworking with external networks, command and
  control systems and the Internet.


4/23/2004                                                            33
            The Network Layer(contd)

 Energy efficient routes can be found based on the available
  power (PA) in the nodes or the energy required ( ) for
  transmission in the links along the routes.
 Next slide shows the power efficiency of the routes.
 An energy efficient route is then selected based on various
  approaches which are discussed later.




4/23/2004                                                       34
            Power Efficiency of Routes.




4/23/2004                                 35
            Power Efficiency of Routes.

 In the earlier figure, T is the source node that senses the
  phenomena. It has the following routes to communicate with
  the sink.
   (1) Route 1: Sink A-B-T, total PA = 4, total  = 3
   (2) Route 2: Sink A-B-C-T, total PA = 6, total  = 6
   (3) Route 3: Sink D-T, total PA = 3, total  = 4
   (4) Route 4: Sink E-F-T, total PA = 5, total  = 6


 We can select an energy efficient route based on various
  criteria as discussed in the next slides.


4/23/2004                                                    36
            Power Efficiency of Routes.

 Maximum PA route: The route having maximum PA is
  preferred. The total PA is calculated by summing PA’s of
  each node along the route. Accordingly, route 2 is selected.
  However, we do not select route 2 as it is not power efficient
  as it only extends route 1 by adding an extra node to it. So
  we select route 4.

 Minimum Energy (ME) route: The route that consumes
  minimum energy to transmit data packets between the sink
  and sensor node is ME route. Thus, we see that rout 1 is ME
  route.

4/23/2004                                                     37
            Power Efficiency of Routes.

 Minimum hop (MH) route: The route that makes the minimum hops to
  reach the sink is preferred.. Thus, route 3 is preferred.

 Maximum minimum PA node route: The route along which the
  minimum PA is larger than the minimum PA’s of the other routes is
  preferred. Thus, route 3 is most efficient.




4/23/2004                                                             38
                  Current research on
                  Networking Layer.
 The various schemes proposed for sensor networks are:
  (1) Small Minimum Energy Communication Network (SMECN)
  (2) Flooding
  (3) Gossiping
  (4) Sensor Protocols for Information Via Negotiations (SPIN)
  (5) Sequential Assignment Routing
  (6) Low Energy Adaptive Clustering Hierarchy (LEACH)
  (7) Directed Diffusion
 The next slide gives an overview of the protocols described above.




4/23/2004                                                              39
            Network Layer




4/23/2004                   40
                  Transport Layer

 Transport layer is needed when system is planned to be
  accessed through the Internet or other external networks.
 Transport layer protocols are still unexplored.
 The protocols may be purely UDP-type protocols, because
  each sensor node has limited memory and power.




4/23/2004                                                     41
                 Application Layer

 Although many applications of sensor networks are found,
  the potential application layer protocols for sensor networks
  remain a largely unexplored region.
 It is one of the hottest research issues at present.




4/23/2004                                                     42
            Other issues of the protocol
                       stack
 The power management plane manages how a sensor node
  uses its power.
 The mobility management plane detects and registers the
  movement of sensor nodes, so a route back to the user is
  always maintained and the sensor nodes can always keep a
  track of who the neighboring sensor nodes are.
 The task management plane balances and schedules the
  sensing tasks given to a specific region.



4/23/2004                                                    43
            Current Research Projects




4/23/2004                               44
            Current Research
             Projects(contd)




4/23/2004                      45
                      Conclusions

 The flexibility, fault tolerance, high sensing fidelity, low
  cost and rapid deployment characteristics of sensor networks
  create many new and exciting areas for remote sensing.
 In the future, the wide applications of sensor networks will
  make it an integral part of our lives.




4/23/2004                                                   46
            Some Currently Available
                   Sensors
 Smart dust (mote)
 Sensor network by Millenial Net
 Sensor Network by Ember Corporation




4/23/2004                               47
                         Smart Dust
     Developed at UC, Berkeley and now commercialized by
      Dust Inc., Crossbow etc.
     A self-contained sensing and communication platform for
      a massively distributed sensor network.
     Size ~ millimeter scale – around the size of a grain of sand.
     Contains sensors, computational ability, bi-directional
      wireless communications, and a power supply.
     Inexpensive enough to deploy by the hundreds.
     Have self-organizing capabilities.
     TinyOS – An open source OS for motes.

4/23/2004                                                       48
            Smart Dust (contd.)




4/23/2004                         49
        Some Example Applications of
                Smart Dust
 Can be scattered around battlefields to track troop
  movements.
 Can be embedded in roads to collect traffic data.
 Used for detecting climatic conditions.
 Monitoring energy use in buildings (offices, supermarkets
  etc.)
 Environmental and habitat monitoring (air quality, soil
  moisture, animal tracking etc.)
 Industrial monitoring.




4/23/2004                                                     50
                     Millenial Net

 Provides self organizing sensor network technology.
 Provides endpoints, routers and gateway hardware and
  software.
 Is reliable and scalable.
 Low data rates
 Low power consumption (long battery life).
 Fault tolerant.
 Supports multiple topologies including star-mesh, simple
  mesh, simple star and linear.
 Uses IEEE 802.15.4 WPAN components.


4/23/2004                                                    51
            A Typical Topology




4/23/2004                        52
            Millenial Net’s Protocol Stack




4/23/2004                                    53
                               Application Areas
   Functions
           Monitor environmental conditions and process-control variables
           Monitor machine activity and status
           Track assets, work in progress (WIP), inventory, and goods in transit
           Conserve energy and resources
           Monitor and protect personnel
   Industries and Markets
           Industrial automation and process control
           Building automation and facilities management systems
           Security and access control systems
           Defense, homeland security, and crisis management
           Automatic meter reading
           Home automation and appliance control
           Supply-chain management
           Telemetry and remote sensing
           Medical and athletic performance monitoring




4/23/2004                                                                           54
            Ember’s Sensor Network

 A self-organizing, self-healing wireless sensor networking
  platform.
 Secure, scalable and reliable.
 Easy to use and install.
 Supports mesh-, star-, and hybrid-network topologies.
 Consumes low power.
 No separate hardware/software for endpoints, routers and
  gateways.




4/23/2004                                                      55
            Ember net Topology




4/23/2004                        56
            Protocol Stack




4/23/2004                    57
                Application Areas

 Industrial Automation:
  Process Temperature Control - Continuous delivery

 Defense:
  Unattended Ground Sensors - Real-time monitoring

 Utilities:
  Automated Meter Reading - Accurate billing

 Building Automation:
  HVAC Controllers - Energy and cost savings

4/23/2004                                             58
                What about Interoperability?
     Different vendors have their own designs of sensor
      hardware and software.
     A multitude of wireless standards already exist.
     The existing standards are only suitable for high data rate
      applications like voice, video, PC LANs etc. and not for
      sensors, which do not require high bandwidth, but require
      low latency and very low power consumption.
     Thus, it was realized that a standard for sensor networks
      was needed, which would
               provide interoperability between sensor networks from different
                vendors
               meet the unique needs of sensors (and other low data rate
                equipments like control devices)

4/23/2004                                                                         59
               The ZigBee Alliance
     The ZigBee Alliance emerged in order to address the
      issues just discussed.

     The ZigBee Alliance is an association of companies
      working together to enable reliable, cost-effective, low-
      power, simple to implement, wirelessly networked
      monitoring and control products based on an open global
      standard.

     Members include Motorola, Philips, Samsung, Dust
      Incorporation, NEC and many others.

     Their technology is based on IEEE 802.15.4 standard.
4/23/2004                                                     60
                         Target Applications
 Traffic Types
           Periodic data, low data rate
           Application defined rate (e.g., sensors)
           Intermittent data
           Application/external stimulus defined rate (e.g., light switch)
           Repetitive low latency data
 Applications
           Sensor Networks
           Industrial Monitors and Automation Control
           Consumer Electronics
           PC Peripherals – mouse, keyboard, joystick
           Home Automation – Security, lighting
           Personal healthcare – monitors, sensors



4/23/2004                                                                     61
            Introduction to IEEE 802.15

 This is the IEEE standard for Wireless Personal Area
  Networks (WPAN).

 WPANs are short range wireless networks used for
  networking of portable and mobile computing devices PCs,
  PDAs, peripherals, cell phones, pagers and consumer
  electronics.




4/23/2004                                                    62
                  IEEE 802.15 Subgroups

 802.15.1 – WPAN standards based on Bluetooth.
 802.15.2 – Standards for coexistence of Wireless Personal
  Area Networks™ (802.15) and Wireless Local Area
  Networks (802.11).
 802.15.3 - Standard for high-rate (20Mbit/s or greater)
  WPANs. Focus on digital imaging and multimedia
  applications on portable devices.
 802.15.4 - A low data rate solution with multi-month to
  multi-year battery life and very low complexity.
           Approved in May, 2003



4/23/2004                                                     63
            Overview of IEEE 802.15.4

   Low data rates.
   Very low power consumption; hence long battery life.
   Operates in unlicensed, international frequency bands.
   Fully handshaked protocol for reliability.
   Support for critical latency devices.

 ZigBee takes full advantage of a powerful physical radio
  specified by IEEE 802.15.4.
 ZigBee adds logical network, security and application
  software.


4/23/2004                                                    64
            Where does IEEE 802.15.4/
                   ZigBee fit?




4/23/2004                               65
             Characteristics of ZigBee
                   Technology
   Data rates of 250 kbps and 20 kbps
   255 devices per network
   CSMA-CA channel access
   Optional Guaranteed Time Slot
   Fully handshaked protocol for transfer reliability
   Low power (battery life multi-month to nearly infinite)
   Dual PHY (2.4GHz and 868/915 MHz)
   Extremely low duty-cycle (<0.1%)
   Range: 10m nominal (1-100m based on settings)
   Location Aware: Yes, but optional
   Multiple topologies: star, peer-to-peer, mesh



4/23/2004                                                     66
            The ZigBee Protocol Stack




4/23/2004                               67
                 ZigBee vs Bluetooth

 Good for static network             Works with mobile ad hoc
  (master-slave conf)                  networks
 Applications with small             Screen graphics, pictures,
  data packets                         file transfer
 Uses DSSS PHY layer                 Uses FHSS PHY layer
 Peak Information Rate ~             Peak Information Rate ~
  128 Kbit / second                    720 Kbit / second
 2+ years of battery life            Power model as mobile
  from normal batteries                phone (regular recharging)
     The two technologies are two solutions for two different application
     areas. They are complementary rather than competitive.

4/23/2004                                                            68
        Wireless Networking Standards
Market Name        GPRS/GSM             Wi-Fi™        Bluetooth™      ZigBee™
Standard          1xRTT/CDMA            802.11b         802.15.1      802.15.4
Application       Wide Area        Web, Email,    Cable            Monitoring &
Focus             Voice & Data     Video          Replacement      Control
System
                  16MB+            1MB+           250KB+           4KB - 32KB
Resources
Battery Life
                  1-7              .5 - 5         1-7              100 - 1,000+
(days)
Network Size      1                32             7                255 / 65,000
Bandwidth
                  64 - 128+        11,000+        720              20 - 250
(KB/s)
Transmission
                  1,000+           1 - 100        1 - 10+          1 - 100+
Range (m)
                                   Speed,         Cost,            Reliability,
Success Metrics   Reach, Quality
                                   Flexibility    Convenience      Power, Cost

4/23/2004                                                                     69
                     Conclusions
 Recent technological trends have resulted in more reliable
  wireless communication and low-cost manufacturing of
  small and powerful sensors with embedded processing and
  wireless networking capabilities.
 Sensor networks can be used in many new applications
  ranging from environmental monitoring to industrial sensing
  as well as traditional military applications.
 Since sensor networks have special requirements, many new
  protocols for these are being developed, but no common
  standard exists.
 The ZigBee Alliance was formed with the aim of coming up
  with a common standard for sensor networks.

4/23/2004                                                   70
                       References

 Sensor networks: an overview
  Tubaishat, M.; Madria, S.; Potentials, IEEE , Volume: 22 ,
  Issue: 2 , April-May 2003
 A survey on sensor networks
  Akyildiz, I.F.; Weilian Su; Sankarasubramaniam, Y.;
  Cayirci, E.;
  Communications Magazine, IEEE , Volume: 40 , Issue: 8 ,
  Aug. 2002, Pages:102 - 114
 Sensor networks: evolution, opportunities, and challenges
  Chee-Yee Chong; Kumar, S.P.; Proceedings of the IEEE ,
  Volume: 91 , Issue: 8 , Aug. 2003
  Pages:1247 - 1256

4/23/2004                                                      71
              References (contd.)

 Smart dust project –
  http://robotics.eecs.berkeley.edu/~pister/SmartDust/
 Smart dust training –
  http://www.xbow.com/Support/Support_pdf_files/Motetrain
  ing/IntroSmartDust.pdf
 IEEE 802.15 working group website –
  http://grouper.ieee.org/groups/802/15/
 The ZigBee Alliance – http://www.zigbee.org/
 ZigBee and IEEE 802.15.4 Resource Center –
  http://www.palowireless.com/zigbee/


4/23/2004                                               72
                       References (contd.)

 Sensor Network Companies
           Millenial net – http://www.millennial.net/index.cfm
           Ember Corporation –
            http://www.ember.com/products/solutions/index.html
           Dust Incorporated – http://www.dust-inc.com
           Crossbow Technology – http://www.xbow.com/index.htm
           Sensoria – http://www.sensoria.com/index.htm
           Sensicast Systems –
            http://www.sensicast.com/products_services/h900.php
           Microstrain – http://www.microstrain.com/wireless_sensors.htm




4/23/2004                                                                   73

				
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