View
217
Download
0
Category
Preview:
Citation preview
1
Wireless sensor network
Wireless sensor network: a surveyLF.Akyildiz, W. Su, Y. Sankarasubramanisam, E. Cayirci
Computer Network 38 (2002) 393-422Speaker: 高新傑
Member: 孫明煌 林承毅 陳立明 趙偉成 吳展奇
2
Outline
Introduction Factors influencing sensor network
design Sensor networks communication
architecture Conclusion
3
Introduction A large number of low-cost, low-
power, multifunctional, and small sensor nodes
Sensor node consists of sensing, data processing, and communicating components
Collaborative effort of a large number of nodes
Primarily focus on power consumption
4
The difference between sensor network and ad hoc network
Sensor nodes: Number of sensor nodes is larger Densely deployed, prone to failures The topology of a sensor network
changes very frequently Mainly use broadcast Limited in power No global identification
5
Sensor network applications
Military applications Environmental applications Health applications Home applications Other commercial applications
6
Factors influencing sensor network design Fault tolerance Scalability Production costs Hardware constraints Sensor network topology Environment Transmission media Power consumption
7
Fault tolerance
Fault tolerance is the ability to sustain sensor network functionalities without any interruption due to sensor node failures
The protocols may be designed to address the level of fault tolerance
8
Scalability
The number of sensor nodes may be in the order of hundreds or thousands
The node density depends on the application in which the sensor nodes are deployed
9
Production costs
Since the sensor networks consist of a large number of sensor nodes, the cost of a single node is very important
The cost of a sensor node should be much less than 1$
10
Hardware constraint
Four basic hardware components: Sensing unit Processing unit Transceiver unit Power unit
11
The components of a sensor node
12
Sensor network topology
Sheer numbers of inaccessible and unattended sensor nodes make topology maintenance a challenge
Topology maintenance: Pre-deployment Post-deployment
Mobility Energy depletion or destruction
13
Environment
The sensor nodes usually work unattended in remote geographic areas
They may work in interior of a large machinery, at the bottom of an ocean, inside a twister, in a battlefield, in a home, in a large building, or be attached to animals
14
Transmission media
Radio One option is ISM band The advantages of ISM band are free,
huge spectrum allocation and globally available
The constraints are power limitation and harmful interference from existing applications
15
Transmission media - continue
Infrared The advantages are license-free and
robust to interference from electrical device
The drawback is the requirement of a line of sight between sender and receiver
16
Transmission media - continue
Optical media Smart dust mote Two transmission schemes:
Passive transmission using a corner-cube retroreflector (CCR)
Active communication using a laser diode and steerable mirror
17
Power consumption
Sensor node lifetime shows a strong dependence on battery lifetime
Power consumption can be divided into: Sensing Communication Processing
18
Sensor network communication architecture
The sensor nodes are usually scattered in a sensor field
Sensor nodes can collect data and route data back to sink
The sink may communicate with the task manager node via Internet or Satellite
19
The architecture
20
Protocol stack Application layer Transport layer
Maintain flow of data Network layer
Take care of routing the data supplied by the transport layer
Data link layer Power aware Minimize collision with neighbor’s broadcast
Physical layer Simple but robust modulation, transmission,
and receiving techniques.
21
Protocol stack - continue
22
Management Planes
These planes helps the sensor node coordinate the sensing task and lower the overall power consumption
Power management plane Mobility Management Plane Task Management Plane
23
Application layer
Sensor management protocol (SMP)
Task assignment and data advertisement protocol (TADAP)
Sensor query and data dissemination protocol (SQDDP)
24
Sensor management protocol
It makes the hardware and software of the lower layers transparent to the sensor network management application
SMP needs to access the node by using attribute-based naming and location-based addressing
25
Task assignment and data advertisement management protocol
Task assignment Users send their interest to a sensor
node Data advertisement
Sensor nodes advertise the available data to user
26
Sensor query and data dissemination protocol An interface to issue queries,
respond to queries and collect incoming replies
Attributed-based or location-based naming is preferred Example: The location of the nodes that
sense temperature higher than 70°F Sensor query and tasking language
(SQTL) is proposed
27
Transport layer The layer is especially needed
when the system is planned to be accessed through Internet or other external networks
The communication between the sink and user is by UDP or TCP
The communication between the sink and sensor is by UDP type protocols
28
Network layer
Special multihop wireless routing protocols between the sensor nodes and sink node are needed
Design principles Power efficiency Sensor networks are data centric Data aggregation Attribute-based and location-based nami
ng
29
Energy efficient route
Maximum available power (PA) route
Minimum energy (ME) route Minimum hop (MH) route Maximum minimum PA node route
30
Energy efficient route - continue
PA: Available Powerα: Energy required to transmit a data packet through the related link
31
Data centric routing
Two approach Sinks broadcast the interest Sensor nodes broadcast an
advertisement for available data Attribute-based naming required
32
Data aggregation
A technique used to solve the implosion and overlap problems in data-centric routing
Data coming from multiple sensor nodes with the same attribute of phenomenon are aggregated
33
Data aggregation - continue
34
Internetworking
Sink nodes can be used as a gateway to other network
Create a backbone by connecting sink nodes together and make it access other network via a gateway
35
Some schemes proposed for the sensor network Small minimum energy communication
network (SMECN) Flooding Gossiping Sensor protocols for information via
negotiation (SPIN) Sequential assignment routing (SAR) Low-level adaptive clustering hierarchy
(LEACH) Directed diffusion
36
SPIN
37
Data link layer
The data link layer is responsible for the multiplexing of data stream, data frame detection, medium access and error control
38
Medium access control
Two goals: Creation of the network infrastructure Fairly and efficiently share communicatio
n resources between sensor nodes Why existing MAC protocol can’t be
used? The primary goal of the existing MAC prot
ocol is the provision of high QoS and bandwidth efficiency
39
MAC for sensor networks
MAC protocol for sensor network must have built-in power conservation, mobility management and failure recovery strategies
A variant of TDMA, random medium access, constant listening times and adaptive rate control schemes can help achieve energy efficiency
40
Some MAC protocols proposed for sensor network
SMACS and EAR algorithm CSMA based medium access Hybrid TDMA/FDMA based
41
Power saving modes of operation
The most obvious means of power conservation is to turn the receiver off
Operation in a power saving mode is energy efficient only if the time spent in that mode is greater than a certain threshold because of the short data packets
42
Error Control
Forward error correction (FEC) Encode data before sending
decreases the bit error rate (BER) Additional processing power goes into
encoding and decoding Automatic repeat request (ARQ)
Limited by the additional retransmission cost and overhead
43
Physical layer
The physical layer is responsible for frequency selection, carrier frequency generation, signal detection, modulation and data encryption
The choice of a good modulation scheme is critical for reliable communication in a sensor network
44
Conclusion
The sensor network needs to satisfy the constraint: fault tolerance, scalability, cost, hardware,
topology chance, environment and power consumption
New networking technique for the layers of the sensor networks protocol stack is required
Recommended