Wireless Personal Area Networks (WPAN):Lowrate amd High Rate

Chapter 20.1-20.5

Donavon M. NorwoodCS286 Dr. Moh

SJSU08/11/2009

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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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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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Figure 20.1 A summary of IEEE 802.15 WPAN statndards

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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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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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Figure 20.2 Wireless Sensor Network

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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 : the ability to sustain network functionality without interruption due to a sensor node failure. The reliability of a sensor interruption due to a sensor node failure. The reliability of a sensor node is usually modeled using Poisson's distribution: node is usually modeled using Poisson's distribution:

Rk t

Rk t =e−k t

k=the failure rate of the sensor

t=the time period

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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:

R=N R2A

N=number of scattered sensor nodes region AR=radiotransmission range

R=number of nodeswithin the transmission radius of eachnode region A

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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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Figure 20.3 The components of a sensor node

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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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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 :

Pc

Pc=N T [PT T onT st Pout T on]N R [PR RonRst ]

PT= power consumed by transmitter , PR= power consumed by receiver

Pout=output power of transmitter ,T on=transmitter ontime

Ron=receiver ontime ,T st=transmitter start−uptime

N T , N R=transmitter /reciver switched on per unit timewhichdependson MAC scheme

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Wireless Sensor Network Model – 20.4 (Continued)The design factors of Sensor Networks

The power consumption in data processing :

P p

P p=CV dd2 f power lossby leakage currentC=total sitching capacitance

V dd=voltage swing

f =switching frequency

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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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Figure 20.4 The sensor network protocol stack

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Physical Layer - 20.5.1

The physical layer addresses the needs of simple but robustmodulation,transmission and receiving techniques. The physical layer isresponsible for:

• Frequency selection• Carrier frequency generation• Signal detection• Modulation• Data encryption

Modulation depends on the transceiver and hardware design, which aim forsimplicity, low power consumption and low cost per unit.

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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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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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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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Application Layer - 20.5.5

Depending on the sensing tasks, there are different types of applicationssoftware that can be built an used at the application layer. Three possibleapplications 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 andsoftware at the lower layers transparent to the sensor network managementapplications.

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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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THANK YOU!

References: Wireless and Data Communications and Networking, Vijay K. Garg