A Survey of Wireless Communications

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A Survey of Wireless Communications

• Professor S. Olariu
• Department of Computer Science
• Old Dominion University
• Norfolk, VA 23529
• U.S.A.
• olariu_at_cs.odu.edu
• http//www.cs.odu.edu/olariu

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In case you havent noticed

• Tethered communication does not scale
• End-user mobility is becoming the norm rather
  than the exception
• Anytime/anywhere communication is here to stay
• Paradigm shift the way we view communication
  and computation must change if we want to remain
  competitive
• Are we ready for it??

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Recent trends

• One billion wireless communication devices in use
  worldwide (2005)
• 400 million wireless telephone handsets
  (purchased annually)
• Users want (need?) anytime/anywhere
• communications
• Emerging PCS services, multimedia, mobile
  commerce, etc.

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Networks 101

• Wired networks
• static no mobility
• e.g. LAN, MAN, WAN, and Internet
• Wireless networks
• mobility is becoming the norm
• name of the game
• Hide mobility from the application!

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Wireless networks 101

• Infrastructure-based networks
• cellular networks
• satellite networks
• HALO-type networks
• Infrastructure-free networks
• Mobile Ad hoc Networks (MANET)
• wireless sensor networks
• other rapidly-deployable networks
• Hybrid networks
• Wireless Internet

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The vision an integrated global communication
system
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Hybrid wireless networks
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Major issues (1)

• Mobility management
• addressing and routing
• location tracking GPS, E-911
• Network management
• virtual infrastructure
• Resource management
• network resource allocation
• energy management
• QoS management
• dynamic resource reservation and adaptive error
  control techniques

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Major issues (2)

• MAC protocols
• contention control and resolution
• Middleware
• measurement and experimentation
• Security
• authentication, encryption, anonymity, and
  intrusion detection
• Error control and fault tolerance
• error correction and retransmission management
• deployment of back-up systems

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Cellular networks

• A Mobile Host (MH) communicates with
• A Base Station (BS) that controls
• A Cell - the BSs area of coverage

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Channel assignment

• Co-channel interference between frequencies used
  in neighboring cells
• Fixed assignment
• poor for hotspots
• good in uniformly high loads
• Dynamic assignment
• complex
• Hybrid assignment
• fixed assignment plus dynamic pool

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Increasing system capacity
A Channels used at full power
B Channels used at reduced power
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Handoff
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Wireless QoS

• QoS in wireless networks difficult due to user
  mobility, limited bandwidth, various impairments,
  etc.
• Demand for new services yields multi-class
  traffic with different resource and QoS
  requirements
• telephony
• web
• e-mail
• video

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Classification of QoS parameters

• Packet level
• packet delay
• jitter
• packet dropping probability
• Call level
• call dropping probability (CDP)
• call blocking probability (CBP)
• supplied bandwidth
• Session level

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LEO satellites

• Description
• Low Earth Orbit 500km-2000km
• high, constant, velocity
• deployed in constellations of multiple satellites
• Benefits
• low power requirements at the end-user level
• low signal propagation delay
• global coverage

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LEO satellites

• Satellite footprint
• coverage area on the surface of the surface of
  the Earth
• Footprint
• divided into spotbeams, forming a pattern of
  overlapping circles, similar to a cellular network

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The HALO network
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Rapidly deployable networks (1)

• Multi-hop self-organized networks
• Peer to peer networks
• Ad hoc networks
• Sensor networks

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Wireless mesh
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Brief history of rapid deployment

• The concept of rapidly-deployable networks dated
  back to 1970s
• DARPA packet radio networks
• Development languished in 1980s
• due to the lack of low cost CPU and memory for ad
  hoc routing
• Rekindled about 1995
• DARPA vision late 1990s Smart Dust consisting
  of mm3 devices

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MANET an intro

• MANET consist of mobile nodes that form a network
  in an ad hoc manner
• The nodes intercommunicate using single or
  multi-hop wireless links
• Each node in MANET can operate as a host as well
  as a router
• The topology, locations, connectivity,
  transmission quality are variable

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Characteristics of MANET

• Self-organizing no central control
• Scarce resources bandwidth and batteries
• Dynamic network topology

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MANET applications

• Civilian
• Wireless LANs/WANs mobile and stationary
• Remote data collection and analysis
• Taxi cabs
• Disaster recovery
• Vehicular ad hoc network (VANET)
• Defense
• Battlefield communications and data transfer
• Surveillance
• Early warning systems

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MANET issues and challenges

• Operating in presence of unpredictable mobility
• Operating in an error-prone media
• Low bandwidth channels
• Low power devices with limited resources
• Maintaining and retaining connectivity and state
  info
• Security infrastructure and communication

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MAC for MANET

• Special requirements
• Avoid interferences among simultaneous
  transmissions
• Yet, enable as many non-interfering transmissions
  as possible
• Fairness among transmissions
• No centralized coordinators, should function in
  full distributed manner
• No clock synchronization, asynchronous operations

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Carrier-sensing in MANET

• Problems
• Hidden terminal problem
• Exposed terminal problem
• Possible solution Busy tone

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Hidden terminal problem
A is transmitting a packet to B
Node X finds that the medium is free, and
transmits a packet
No carrier does not imply OK to transmit!
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Exposed terminal problem
A is transmitting a packet to B
X will not transmit to Y, even though it will not
interfere at B
Presence of carrier does not imply to hold off
transmission!
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Busy tone
B is receiving a packet from A
X OK to transmit
X not OK to transmit

1. Receiver transmits busy tone when receiving data
2. All nodes hearing busy tone keep silent
3. Requires a separate channel for busy tone

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Topology control

• Neighbor discovery
• Network organization
• choosing transmission radii
• choosing neighbors
• Scheduling node activity
• Clustering
• Select cluster-heads
• assign nodes to clusters
• Dominating sets each node in set or neighbor
• of some node in the set
• Bluetooth scatternet formation

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Data communication

• Routing find a path from source to destination
• Location update maintain destination information
• Broadcasting send from source to all nodes
• Multicasting send from source to some nodes
• Geocasting send from source to all nodes
• inside a region
• Network partitioning data/service replication
• IP-based addressing and routing

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MANET Effect of dynamic topology
D
Y
X
S
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Dominating sets
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• Wireless Sensor Networks

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How it all started

• SmartDust program sponsored by DARPA defined
  sensor networks as

A sensor network is a deployment of massive
numbers of small, inexpensive, self-powered
devices that can sense, compute, and communicate
with other devices for the purpose of gathering
local information to make global decisions about
a physical environment
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SmartDust the vision

• An airplane traverses a battlefield and deploys
  massive numbers of tiny sensors
• The sensors randomly scatter spatially as they
  land
• They self-organize into an ad hoc network such
  that information can be transmitted multi-hop to
  a collection point
• The sensors monitor and report on troop
  movements, armaments, mine fields, etc

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What are sensors?

• Miniature devices with modest capabilities linked
  by some wireless medium (e.g. radio, ultrasound,
  laser)
• Non-renewable energy budget
• Disposable tiny, mass-produced, dust cheap!
• Mass production implies
• testing is not an option
• anonymity no fabrication-time IDs

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Typical sensor diagram
-
1Kbps-10Kbs
transmission range 3-10m
Transceiver
Transceiver
-
Limited storage
4-8Kb
Memory
Memory
Embedded
Slow processor
Embedded
4bit, 5-10 MHz
Processor
Processor
Sensor
Sensor
Low-power special-purpose
Battery
Non-renewable
Battery
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Types of sensors

• Pressure
• Temperature
• Light
• Biological
• Chemical
• Strain, fatigue
• Tilt
• Acceleration
• Seismic
• Metal detectors

Sensors you can buy off-the-shelf
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Thus, sensors can measure

• Distance to an object
• Direction of object
• Ambient temperature
• Presence of chemicals
• Light intensity
• Vibrations
• Motion
• Seismic tremors
• Noise (acoustic data)

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Sensors modus operandi

• Must work unattended
• Modest non-renewable energy budget
• Name of the game prolong longevity of network
• sleep a lot, wake up periodically
• work locally, communicate sparingly
• optimize transmission radius when communicating!
• Supplement modest energy budget by scavenging
• Hopefully, energy will not be a major problem

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Sensor networks

• Distributed systems with no central control
• Massive number of tiny sensors densely deployed
  in the area of interest
• Random deployment individual sensor positions
  cannot be engineered
• Main goal produce globally-meaningful
  information from locally-collected data
• Only as good as the information produced
• information quality
• information security

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Homeland security applications

• Battlefield surveillance - monitoring critical
  terrain, routes, bridges and straits for enemy
  activity
• Battle damage assessment - field reports from
  attached sensors afford real-time assessment
• Early detection of biological, chemical, or
  nuclear attack
• Early warning systems
• Containment of terrorist attacks - in
  metropolitan areas guide public and first aid
  providers

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Early warning systems
Networked sensors make monitoring and early
warning systems more accurate and affordable
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Traffic control
Can networked sensors control traffic flow better
than a loose network of people?
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Securing US ports
Only 2 of the containers entering our ports are
checked!
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Securing container transit
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and handling
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Two views of sensor networks

• Centrally controlled
• the user pushes queries/interests
• sensor network provides answers
• does not scale well
• prone to creation of energy holes
• Autonomous
• assumes a pervasive instrumentation
• organized ad hoc in service-centric fashion
• scales well
• less prone to the creation of energy holes

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Centrally-controlled network
Satellite
Event
Internet
Sink
End user
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Autonomous sensor network
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• Conquering scale
• the virtual infrastructure

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How do we conquer scale?

• Golden Rule Divide and Conquer!
• Graft a virtual infrastructure on top of physical
  network
• Infrastructure leveraged by many protocols!

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Components of the virtual infrastructure

• Dynamic coordinate system
• location-based identifiers
• coarse-grain location awareness
• Clustering scheme
• cheap scalability
• Work model
• hierarchical specification of work and QoS
• Task-based management model
• low-level implementation of work model

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The dynamic coordinate system

• Components
• coronas
• wedges
• Individual sensors acquire
• corona number
• wedge number
• Coordinate system is dynamic and does not require
  sensor IDs
• Works perfectly well in autonomous setting

My coordinates are (4,2)
Mine too!
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The cluster structure

• Cluster locus of all sensors having the same
  coordinates
• Clustering -- free once coordinate system
  available
• Accommodates sensors w/o IDs
• In our model, smallest unit of work!

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A multi-sink sensor network
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Routing to closest sink
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ANSWER

• AutoNomouS Wireless sEnsor netwoRk
• capable of performing sophisticated analyses
• detecting trends and
• identifying unexpected, coherent and emergent
  behavior
• Primary goal of ANSWER provide in-situ users
  with information services, for example enhancing
  their location awareness
• ANSWER finds immediate applications to tactical
  battlefield surveillance, crisis management and
  homeland security

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Providing mission-oriented security

• Patrol Search and Rescue (PSAR) vehicle

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Initiating interaction

• Authenticate PSAR before entering ANSWER
• Establishment of trust relationship
• PSAR is issued seeds from PCC passed on to
  sensors
• Upon entering, PSAR organizes sensors in its
  vicinity

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Routing aggregated data to PSAR

• When the task has been completed the aggregated
  data will be routed to the specified cluster in
  order to be available to the PSAR in a timely
  fashion
• As the PSAR reaches the cluster, it will interact
  with the sensors in its immediate neighborhood
  and collect the aggregated data

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Biomedical applications
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Habitat monitoring
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Ecosystem monitoring
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Supply chain management
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Homeland security applications

• Homeland security applications
• monitoring friendly forces equipment and
  ammunition (via attached sensors)
• battlefield surveillance (monitoring critical
  terrain, routes, and straits for enemy activity)
• battle damage assessment (field reports from
  attached sensors give reports in real-time)
• biological, chemical, or nuclear attack detection
  and containment (sensors deployed across
  metropolitan areas to guide public and first
  responders)