Overview of Wireless Networks:
Cellular
Mobile Ad hoc
Sensor
Cellular Architecture
- Infrastructure-based networks
- All units are fixed in location except mobile units
- BS and MSC are connected via wirelines
- Communication between BS and mobile unit is wireless
WIRELINE
Cell
Base Station (BS)
Mobile unit
Wireless Links
Wired Links
Mobile Switching Center (MSC)
NETWORK
Why Mobile Ad hoc Networks?
 Characteristics
- Infrastructure-less
- All nodes are potentially mobile
- Network topology is dynamic
- All nodes act as individual routers
 Examples
- Disaster recovery situations
- Battle field communications
- Law enforcement operations
- Civilian applications
 Objectives
- Maintain connectivity between mobile devices
- Provide congestion-free routing for multimedia traffic
- Support scalability
- Minimize memory, bandwidth and energy consumption
Mobile Ad hoc Networks (MANET)
transmission
range
Hybrid Environments
 Use infrastructure when convenient
 Use ad hoc connectivity when necessary or superior
BS1
infrastructure
A
BS2
E
Z
Ad hoc connectivity
X
© 2001 Nitin Vaidya
Variations
• Symmetric environments
o Nodes having identical capabilities and responsibilities
• Asymmetric capabilities
o Transmission ranges
o Processing power
o Battery lifetime
o Mobility speed
• Asymmetric responsibilities
o Some nodes may forward route packages
o Leaders vs. ordinary nodes
• May co-exist (and collaborate) with an infrastructure-based
network
Variations
• Traffic characteristics
o Bit rate
o Timeliness constraints
o Reliability requirements
• Mobility Patterns
o Students on campus
o Passengers on airports
o Taxi cabs
• Mobility Characteristics
o Speed / Direction / Pattern of movement
Sensor Networks
Wireless sensor networks consists of group of sensor nodes
to perform distributed sensing task using wireless medium.
Characteristics
- low-cost, low-power, lightweight
- densely deployed
- prone to failures
- two ways of deployment: randomly, pre-determined or engineered
Objectives
- Monitor activities
- Gather and fuse information
- Communicate with global data processing unit
Sensor Networks
Application Areas [Akyildiz+ 2002]
1. Military:



Monitoring equipment and ammunition
Battlefield surveillance and damage assessment
Nuclear, biological, chemical attack detection and reconnaissance
2. Environmental:

Forest fire / flood detection
3. Health:


Tracking and monitoring doctors and patients inside a hospital
Drug administration in hospitals
Sensor Networks
Application Areas [Akyildiz+ 2002]
4. Home:


Home automation
Smart environment
5. Other Commercial Applications:




Environmental control in office buildings
Detecting and monitoring car thefts
Managing inventory control
Vehicle tracking and detection
Sensor Networks vs. Traditional
Wireless Networks (Cellular, MANET)
– Higher number of sensor nodes (several orders of magnitude)
– Dense deployment
– Prone to failures
– Limited in power, computation and memory
– May not have global identification (ID) due to high overhead and
the total number of sensors
– Optimization on the energy consumption vs. QoS and high
bandwidth constraints
– Stationary vs. mobile
– Data flow: unidirectional vs. bi-directional
– Date rates
Sensor Networks Preliminaries
– For large scale environment monitoring applications, dense
sensor networks are mainly used
– Sensing capabilities should be distributed and coordinated
amongst the sensor nodes
– Algorithms deployed should be localized since transmissions
between large distances are expensive and lowers networks life
time
– These networks should be self-configuring, scalable, redundant
and robust during topology changes
Current Challenges
 Limited wireless transmission range
 Broadcast nature of the wireless medium
 Packet losses due to transmission errors
 Mobility-induced route changes
 Mobility-induced packet losses
 Battery constraints
 Potentially frequent network partitions
 Ease of snooping on wireless transmissions (security hazard)
Research Problems in Ad hoc and
Sensor Networks
 Clustering
– Partitioning of the network
– Identification of vital nodes (clusterheads)
 Routing
– Discovering routes from source to destination
– Maintaining the routes
– Rediscovery and repair of routes
 Topology management
– Maintain the links
– Minimize the changes in underlying graph
 Security
Research Problems in Ad hoc and
Sensor Networks
 Medium Access Control Protocols
 Sensor data management
 Power conservation/energy consumption
 Data fusion and dissemination of sensor data
 New applications for ad hoc and sensor networks
References
[Akyildiz+ 2002] I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, A Survey
on Sensor Networks, IEEE Communications Magazine, Vol. 40, No. 8, pp. 102-114,
August 2002.