sensor networks - unina.it
TRANSCRIPT
Forest Fire Detection
Body Networks for healthcare applications
Tracking of robots, vehicles in closed areas
…
APPLICATIONS
Amount of Data Generated by Nodes: nodes can send few Bytes per hour, or many KBytes per second….
Event Triggered Reporting Event Detection / Control
Loose Reporting Estimation of Spatial and
Temporal Processes / Control
Frequent Periodic Reporting Monitoring / Tracking / Control
TYPE OF REPORTING
APPLICATIONS
Taxonomy
Event Triggered Reporting delay
Loose Reporting data losses
Frequent Periodic Reporting network throughput
TYPE OF REPORTING
PERFORMANCE REQUIREMENT
Taxonomy
Event Detection
Density of nodes: the event is detected with given probability;
Coverage, related to sensing range of nodes and event type, distributed localisation algorithms
connectivity, related to transmission range of nodes
The samples can be received by the sink(s) with given probability;
communication protocols
responsiveness, related to event type: the report timely reaches the sink(s)
TYPE OF REPORTING SN ISSUSES
Estimation of Processes
Density of nodes: the process is accurately estimated;
Connectivity, related to transmission range of nodes
Coverage, related to sensing range of nodes
The samples can be received by the sink(s) with given probability;
Data processing, related to process type
communication protocols
The sampling frequency must ensure the process evolution is tracked;
Responsiveness, related to process type, the report timely reaches the sink(s)
Tracking: Estimation of Processes Event Detection
TYPE OF REPORTING SN ISSUSES
Probability of false alarm < 0.1 – 0.001
Probability of missed detection < 0.1 – 0.001
Localization precision < 100 – 1 m Latency < 0.1 – 10 s
Network lifetime > months - years
The different types of requirements make SN features very application-dependent.
REQUIREMENT EXAMPLES
TAXONOMY
Wireless Ad Hoc Networks
MANETs (Mobile Ad Hoc Networks) are formed dynamically by anautonomous system of nodes connected via wireless links without using anexisting network infrastructure or centralized administration.
Nodes are connected through “ad hoc” topologies, set up and clearedaccording to user needs and temporary conditions.
MANETS (1/3)
Main Features
Fixed infrastructure is not needed
Unplanned and highly dynamical
Nodes are “smart” terminals (laptops, …)
Real-time or non real-time data, multimedia, voice, …
Every node can be either source or destination of information
Every node can be a router toward other nodes
Energy is not the most relevant matter
Capacity is the most relevant matter
MANETS (2/3)
Applications
Emergency Services – nodes are mobile over large areas
Home and Enterprise Networks – nodes are laptops
Attendees in a conference room sharing documents and other information via their laptops and handheld computer;
Armed forces creating a tactical network in unfamiliar territory for communications and distribution of situational awareness information;
Small sensor devices located in animals and other strategic locations that collectively, monitor habitats and environmental conditions;
Emergency services communicating in a disaster area and sharing video updates of specific locations among workers in the field, and back to headquarters.
IEEE 802.11/Wi-fi
MANETS (3/3)
Nodes are “smart” terminals (laptops, …)
Real-time or non real-time data, multimedia, voice, …
Every node can be either source or destination ofinformation
Every node can be a router toward other nodes
Energy is not the most relevant matter
Capacity is the most relevant matter
WSNS VS MANETS (1/2)
WSNS VS MANETS (2/2)
HETEROGENEOUS NETWORKS
PROTOCOL STACK FOR SNS (1/2)
Rb : The channel capacity (bit rate)
PROTOCOL STACK FOR SNS (2/2)
SINGLE-SINK SINGLE-HOP (1/3)
N : The number of nodes Rb : The channel bit rate
αA : Factor taking into account of the overhead introduced by all protocol
stack layers SA : Maximum data throughput measured at the application layer
We consider a WSN where nodes are requested to
send their samples (composed of D bytes each) taken
from the monitored space every TR seconds.
Let us give a simple and approximate evaluation of the capacity of a single-
sink WSN, defined in terms of maximum number of nodes that can be
attached to the sink.
N ?
SINGLE-SINK SINGLE-HOP (2/3)
N : The number of nodes Rb : The channel bit rate
αA : Factor taking into account of the overhead introduced by all protocol
stack layers SA : Maximum data throughput measured at the application layer
SINGLE-SINK SINGLE-HOP (3/3)
To give a numerical example, assume Rb = 250 Kbit/s, TR = 1 s, αA=0.1,
D=3; then the maximum number of nodes is approximately 1000.
On the other hand, if TR=10 ms, then N can not exceed 10.
It is clear that the requirements set by the application scenario play a very
relevant role when defining the capacity of a single-sink WSN.
In the case discussed above, the N nodes are all within range of the sink.
If the transmis- sion range of links between sink and nodes is R, then the
density of nodes is
SINGLE-SINK MULTI-HOP
N : The number of nodes Rb : The channel bit rate
αA : Factor taking into account of the overhead introduced by all protocol
stack layers SA : Maximum data throughput measured at the application layer hm : Average number of hops per data sample
If a node can send its sample to the sink through h hops, then the delivery
of the data sample requires h transmissions. Let us denote by hm the
average number of hops per data sample taken from the field and if no
smart reuse of radio resources is introduced, then we have for a single-sink
multi-hop WSN:
The capacity of the network is reduced by a factor of hm.