Wireless Personal Area Networks (WPAN): Lowrate amd High Rate
1. Wireless Personal Area Networks (WPAN):
Lowrate amd High Rate
Chapter 20.1-20.5
Donavon M. Norwood
CS286 Dr. Moh
SJSU
08/11/2009
2. Introduction – 20.1
Wired sensor networks have been around for a very long time and contain an
array of gauges measuring temperature, fluid levels, humidity, and other
attributes on pipelines, pumps, generators, and manufacturing lines. Many of
these are connected to separate wired networks sometimes linked to a
computer but often to a control panel that flashes a light or sounds an alarm
when the temperature rises too high or a machine vibrates too much. Mesh
networks topologies will allow a node to route around a node failure or who's
signal is degraded by interference from heavy equipment. Gateways will
create a two link with legacy control systems, hosts, wired local area
networks (WLAN) or the Internet. Wireless sensor networks can use several
wireless technologies including 802.11 WLAN's, Bluetooth, and radio
frequency identification (RFID). In this chapter we will focus on 802.15.3
(WPAN-LR) and 802.15.13a (WPAN-HR).
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3. Wireless Sensor Networks - 20.2
Wireless sensor networks contain a large number of sensor nodes that are
densely deployed either inside the phenomenon to be sensed or very close
to it. Sensor nodes contain sensing, data processing, and communication
components. The position of the sensor nodes does not to be engineered or
predetermined, which allows the random deployment in inaccessible or
disaster relief operations. Another feature of sensor networks is the
cooperative effort of sensor nodes. Sensor nodes are fitted with an inboard
processor, and instead of sending raw data to nodes responsible for the
fusion, they compute simple computations with their own processors and
transmit required and partially processed data. Wireless sensor networks
applications require ad hoc networking techniques. Many protocols and
algorithms have been proposed for traditional ad hoc wireless networks, but
they are not well suited for wireless sensor network features and application
requirements. Also one of the most important constraints of wireless sensor
nodes is low power consumption.
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4. Figure 20.1 A summary of IEEE 802.15 WPAN statndards
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5. Usage of Wireless Sensor Networks - 20.3
Wireless sensor networks are primarily deployed in the following areas:
Environmental observations: used to monitor environmental changes
with an example of water detection in a lake that is located near a
chemical factory. Other examples include air pollution, forest fire
detection and rainfall observation.
Military monitoring: used for battlefield surveillance. Sensor nodes
monitor vehicle traffic, track the position/movement of the enemy, etc.
Building monitoring: used in building/factories to measure the change
in the climate.
Health care: used in biomedical applications to improve the quality of
care.
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6. Wireless Sensor Network Model - 20.4
Wireless sensor networks consists of hundreds or even thousands of low cost nodes which
could have either a fixed location or be randomly deployed to monitor the environment.
Sensors communicate with each other using multihop approach. The flow of data ends at
special nodes called base stations sometimes referred as sinks. Base stations links the
sensor network to other networks to disseminate the data sensed for further processing
and they have enhanced capabilities over simple sensor nodes because they must do
complex data processing. Base stations have workstation/laptop class processors, enough
memory, energy, storage, and computational power to perform their tasks well.
Communication between base stations is usually down over high speed links. One of the
biggest problems of sensor networks is power consumption which is greatly affected by
communication between nodes. Aggregation points are introduced into the network to
solve this problem which reduces the total number messages exchanged between nodes
and saves some energy. Sensor nodes are also organized into clusters each having a
cluster head as the leader. Communication in the cluster goes through the cluster head
which is forwarded to a neighboring cluster until it reaches it destination the base station.
Another method to save energy is for nodes to go into sleep mode when not needed and
wake up from sleep mode when needed.
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8. Wireless Sensor Network Model – 20.4 (Continued)
The design factors of Sensor Networks
The design of Sensor Networks is influenced by the following factors:
Fault tolerance: the ability to sustain network functionality without
interruption due to a sensor node failure. The reliability Rk t of a sensor
node is usually modeled using Poisson's distribution:
R k t =e t
−
k
k =the failure rate of the sensor
t =the time period
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9. Wireless Sensor Network Model – 20.4 (Continued)
The design factors of Sensor Networks
Scalability: the number of nodes used to study a phenomenon maybe
from hundreds to thousands. Depending on the application this number
may reach in the value of millions. New schemes must must be able to
work with this number of nodes and most utilize the high density of the
sensor network which could be from a few sensor nodes to a few hundred
sensor nodes in the region. The density can be calculated as:
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N R
R=
A
N =number of scattered sensor nodes region A
R=radiotransmission range
R=number of nodes within the transmission radius of each node region A
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10. Wireless Sensor Network Model – 20.4 (Continued)
The design factors of Sensor Networks
Production cost: since sensor networks consists of many sensor nodes
the cost of each sensor node is important to justify the overall cost of the
network. The cost of each sensor node has to be kept very low and must
be less than US$1 for this to be possible.
Hardware constraints: a sensor node is made up of four basic
components which are the sensing unit, processing unit, transceiver
unit, and power unit. There are other additional components such as
the location finding system, power generator, and mobilizer. Sensors
are also composed of two subunits: sensors and analog-to-digital
convertors (ADC). The analog signal of the sensor are converted into
digital signals by the ADC and fed into the procession unit. The
processing unit allows the sensor node to collaborate with other nodes
and the transceiver connects the node to the network. The power unit
may be supported by power scavenging units such as solar cells.
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12. Wireless Sensor Network Model – 20.4 (Continued)
The design factors of Sensor Networks
Sensor network topology: hundreds to several thousands of nodes are
deployed throughout the sensor field and deploying a high number of
nodes densely requires a careful handling of topology maintenance.
Operating environment: sensor nodes are densely deployed either very
close to or directly inside the phenomenon to be observed which usually
work unattended in remote geographic areas. They also may work in the
interior of large machinery at the bottom of the ocean, in a biological or
chemical contaminated field, in a battlefield beyond enemy lines or in a
home or large building.
Transmission media: in a multihop sensor network, communication
nodes are linked together by a wireless medium which are formed by
radio, infrared, or optical media. Infrared and optical media require a line
of sight between sender and receiver.
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13. Wireless Sensor Network Model – 20.4 (Continued)
The design factors of Sensor Networks
Power consumption: wireless sensor nodes can only be equipped with
a limited power source (<0.5 Ah, 1.2 V). Sensor node lifetime is
dependent on battery lifetime. The energy in data communication
involves both data transmission and reception. Formulation for radio
power consumption P c :
P c =N T [ P T T on T st P out T on ] N R [ P R R on Rst ]
P T = power consumed by transmitter , P R= power consumed by receiver
P out =output power of transmitter , T on =transmitter on time
Ron =receiver ontime , T st =transmitter start−uptime
N T , N R=transmitter / reciver switched on per unit time which depends on MAC scheme
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14. Wireless Sensor Network Model – 20.4 (Continued)
The design factors of Sensor Networks
The power consumption in data processing P p :
P p=CV 2 f power loss by leakage current
dd
C =total sitching capacitance
V dd =voltage swing
f = switching frequency
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15. Sensor Network Protocol Stack - 20.5
The Sensor Network Protocol Stack combines the power of and routing
awareness, integrates data with networking protocols, communicates power
efficiently through the wireless medium and promotes cooperative efforts of
sensor nodes. The Sensor Network Protocol Stack consists of the physical
layer, data link layer, network layer, transport layer, application layer,
application layer, power management plane, mobility management and
task management plane.
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17. Physical Layer - 20.5.1
The physical layer addresses the needs of simple but robust
modulation,transmission and receiving techniques. The physical layer is
responsible for:
• Frequency selection
• Carrier frequency generation
• Signal detection
• Modulation
• Data encryption
Modulation depends on the transceiver and hardware design, which aim for
simplicity, low power consumption and low cost per unit.
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18. Data Link Layer - 20.5.2
The data link layer is responsible for:
• Multiplexing data streams
• Data frame detection
• Medium access
• Error control
The MAC protocol in a wireless multihop network achieve two goals:
• The creation of a network infrastructure for MAC to establish
Communication links for data transfer.
• To be able to share communication resources between sensor nodes.
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19. Network Layer - 20.5.3
The network layer is responsible for routing the data supplied by the
transport layer. The network layer of a sensor network is designed according
to the following principles:
• Power efficiency is always an important consideration.
• Sensor networks are data centric which is when dissemination is
performed to assign the sensing task to the sensing nodes.
• Data aggregation which combines data from many sensor nodes into a
more compact form before forwarding to a location for processing.
• Attribute-based routing which is used to carry out queries by using the
attributes of the phenomenon.
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20. Transport Layer - 20.5.4
The transport layer is responsible for maintaining the flow of data if the
sensor network node requires it. The transport layer is needed when a
system is planned to be accessed through the Internet or other external
networks. TCP splitting may be needed to make sensor networks interact
with other networks like the Internet. With this approach TCP connections
are ended at the sink nodes, and a special transport layer protocol can
handle the communication between the end user and the sink nodes.
Communication between the user and sink nodes is down by UDP or TCP via
the Internet or satellite or just by UDP type protocols. Event-to-sink reliable
transport (ESRT) has been proposed to to achieve reliable event detection
(at sink node) with a protocol that is energy aware and has congestion
control mechanisms.
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21. Application Layer - 20.5.5
Depending on the sensing tasks, there are different types of applications
software that can be built an used at the application layer. Three possible
applications for sensor networks are:
• Sensor management protocol (SMP)
• Task assignment and data advertisement protocol (TADAP)
• Sensor query and data dissemination protocol (SQDPP)
The application layer management protocol makes the hardware and
software at the lower layers transparent to the sensor network management
applications.
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22. Power, Mobility, and Task Management Planes - 20.5.6
The Power, Mobility, and Task Management Planes monitor the power,
movement and task distribution among sensor nodes. These planes help the
sensor nodes coordinate the sensing task which help lower power
consumption. The power management plane manages how a sensor
node uses its power and when power of a sensor node is low it will broadcast
to its neighbors that is low in power and can not participate in participate in
routing messages and remaining power is used for sensing. The mobility
management plane detects and records the movement of sensor nodes so a
route back to the user is always maintained, for sensor nodes to maintain
who their neighbors are, and so the sensor node can balance its power and
and task using. The task management plane balances and schedules the
sensing tasks given in a specific region or area.
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