A Survey of Wireless Communications

NATO-ARW, Suceava, Romania, September 4-8, 2006 11

A Survey of Wireless Communications

Professor S. Olariu

Department of Computer ScienceOld Dominion University

Norfolk, VA 23529U.S.A.

[email protected]://www.cs.odu.edu/~olariu


In case you haven’t 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??


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.


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!


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


The vision: an integrated global communication system

Portable terminals

Stationary terminals

Mobile terminals Nomadic business users

Individual multimedia communication

Local and group multicast services

High speed provider link


Hybrid wireless networks


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

Major issues (1)


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

Major issues (2)


Cellular networks

• A Mobile Host (MH) communicates with

• A Base Station (BS) that controls

• A Cell - the BS’s area of coverage


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


Increasing system capacity

B: Channels used at reduced power

A3

B

A1

BA2

B

A: Channels used at full power


Handoff

A B


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


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


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


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


The HALO network


Multi-hop self-organized networks

Peer to peer networks Ad hoc networks Sensor networks

Rapidly deployable networks (1)


Wireless mesh


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


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


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

Characteristics of MANET


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


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


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


Carrier-sensing in MANET

Problems Hidden terminal problem Exposed terminal problem

Possible solution: Busy tone


Hidden terminal problem

A

B

XNode X finds that the mediumis free, and transmits a packet

No carrier does not imply OK to transmit!

A is transmitting a packet to B


Exposed terminal problem

A is transmitting a packet to B

X will not transmit to Y, eventhough it will not interfere at B

A

B

XY

Presence of carrier does not imply to hold off transmission!


Busy tone

A

B

XA

B

XY

X OK to transmit X not OK to transmit

1. Receiver transmits busy tone when receiving data2. All nodes hearing busy tone keep silent3. Requires a separate channel for busy tone

B is receiving a packet from A


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

Topology control


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

Data communication


MANET – Effect of dynamic topology

S

X

Y

D

S

D

Z

X


Dominating sets


Wireless Sensor Networks


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


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


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

What are sensors?


Typical sensor diagram

Transceiver

Embedded

Processor

Sensor

Battery

Memory

Transceiver

Embedded

Processor

Sensor

Battery

Memory

1Kbps-10Kbs-transmission

range3-10m

4bit, 5-10 MHz

Slow processor

Non-renewable

4-8Kb

-Limited storage

Low-power special-purpose


Types of sensors

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

Sensors you can buy off-the-shelf


Distance to an object Direction of object Ambient temperature Presence of

chemicals Light intensity Vibrations Motion Seismic tremors Noise (acoustic data)

Thus, sensors can measure…


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

Sensors – modus operandi


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


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

Homeland security applications


Early warning systems

Networked sensors make monitoring and early warning systems more accurate and affordable


Traffic control

Can networked sensors control traffic flow better than a loose network of people?


Securing US ports

Only 2% of the containers entering our ports are checked!


Securing container transit


… and handling


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


Centrally-controlled network

Sink

End user

Internet

EventSatellite


Autonomous sensor network

Command Node

Command Node

Command Node

Remote security monitoring station

Sensor nodes


Conquering scale: the virtual infrastructure


How do we conquer scale?

Golden Rule: Divide and Conquer!

Graft a virtual infrastructure on top of physical network

Infrastructure leveraged by many protocols!


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


The dynamic coordinate system

Components:Components: coronascoronas wedgeswedges

Individual sensors Individual sensors

acquireacquire corona numbercorona number wedge numberwedge number

Coordinate system is Coordinate system is

dynamic and does not dynamic and does not

require sensor IDsrequire sensor IDs

Works perfectly well in Works perfectly well in

autonomous settingautonomous setting

My My coordinates coordinates are (4,2)are (4,2)

Mine too!Mine too!


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!


A multi-sink sensor network


Routing to closest sink


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


Providing mission-oriented security

Patrol Search and Rescue (PSAR) vehicle


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

AFN

AFN

AFN

AFN

AFN

AFN

AFN

AFN

AFN

AFN

AFN

PSAR

AFNAggregate & forward node

Patrol, search, rescue vehicle

Miniaturized sensor node

PSAR

B

A

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

Routing aggregated data to PSAR

AFN

AFN

AFN

AFN

AFN

AFN

AFN

AFN

AFN

AFN

AFN

PSAR

AFNAggregate & forward node

Patrol, search, rescue vehicle

Miniaturized sensor node

PSAR

B

AAFN

PSAR


Biomedical applications


Habitat monitoring


Ecosystem monitoring

Primary node

Secondary nodes

•Dense network of physical, chemical sensors in soil and

canopy

•Measure and characterize previously unobservable

ecosystem processes


Supply chain management


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)

Homeland security applications

Documents

A Survey of Wireless Communications