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Seminar On Low Energy Efficient Wireless Sensor

Network

PRESENTED BY-DEEPAK KUMAR DHALREGD. NO-0901304038

ELECTRONICS AND COMMUNICATION ENGINEERINGGANDHI INSTITUTE OF TECHNOLOGY AND MANAGEMENT

NOVEMBER 2012

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CONTENT

What is WSN?Power consumption in WSNSources of energy wasteGeneral approaches to energy savingMAC protocol for WSNConclusionReference

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What is WSN?

A wireless sensor network is a collection of nodes “sensors” organized into a cooperative network. Wireless sensor network consists of sensor nodes deployed over a geographical area for monitoring physical phenomena like temperature, humidity, vibrations, seismic events, and so on.

SENSOR NODES COMPONENTS

•Sensing Subsystem•Processing Subsystem•Wireless communication subsystem•Power source

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Power consumption in WSNs

The power issue in the wireless sensor network is one of the biggest challenges, because the sensor has a limited source of power which is also hard to replace or recharge “e.g. sensors in the battle field, sensors in a large forest … etc”.

Why limited source of power? Inexpensive nature. Limited size and weight. Redundant nature.

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Major Sources of Energy Waste in WSNs

1. Useful power consumption:Transmitting or receiving data.Processing query requests.Forwarding queries and data to the neighbors.

2. Wasteful power consumption: Idle listening to the channel “waiting for possible traffic”. Retransmitting because of collisions “e.g. two packets arrived

at the same time at the same sensor”. Overhearing “when a sensor received a packet doesn’t belong

to it”. Generating and handling control packets. Over-emitting “when a sensor received a packet while it is not

rea

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GENERAL APPROACHES TO ENERGY SAVING

Duty CyclingData DrivenDuty cycle Duty cycle is defined as the fraction of time nodes

which are active during their lifetime.

Data Driven Data driven approaches can be used to improve

the energy efficiency even more.

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SENSOR MODES

TRANSMISSION RECEPTION IDLE SLEEP

DUTY CYCLING

It can be achieved through two different approaches:

it is possible to exploit node redundancy which is typical in sensor networks and adaptively select only a minimum subset of nodes to remain active for maintaining

connectivity. Nodes that are not currently needed for ensuring

connectivity can go to sleep and save energy.

WAKE UP

SLEEP

Goal: reduce the time where the sensor is being idle.Drawback: Additional delay because of waiting for the next-hop node to wake up

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ON-DEMAND PROTOCOL The basic idea is that a node should wake up only when

another node wants to communicate with it. The main problem associated with on-demand schemes is how

to inform the sleeping node that some other nodes are willing to communicate with it.

SCHEDULED RENDEZVOUS APPROACH The basic idea behind scheduled rendezvous schemes is that

each node should wake up at the same time as its neighbours. Typically, nodes wake up according to a wakeup schedule and

remain active for a short time interval to communicate with their neighbours. Then, they go to sleep until the next rendezvous time.

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MAC PROTOCOL FOR WSN

MAC ( medium access control)

Contension based

S(sensor)-MAC

TDMA basedHybrid

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Stand for:Sensors Medium Access Control.

Strategy: All node follow a periodic sleep/wake cycle, When a node is idle, it is more likely to be asleep instead of continuously listening to the channel. S-MAC reduces the listen time by letting the node go into periodic sleep mode.

Advantages: Periodic Listen. Collision Avoidance. Overhearing Avoidance. Message passing.

Disadvantages:S-MAC fixed duty cycle i.e. active time is fixed• if message rate is less energy is still wasted in idle-listening.

S-MAC

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Stand for:Timeout Medium Access Control.

Strategy: It adaptively adjusts the sleep and wake periods based on the estimated traffic flow.

AdvantageTimes out on hearing nothing.

DisadvantageEarly sleeping problemi.e. node goes to sleep when aneighbor still has message for it.

T-MAC

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U-MAC

Stand forUtilization Medium Access ControlStrategy

U-MAC is based on the S-MAC protocol and provides three main improvements on SMAC:

various duty cycles, utilization based tuning of duty-cycle, and selective sleeping after transmission.

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μ- MAC

Stand forEnergy-Efficient Medium Access ControlStrategy μ-MAC assumes a single time slotted channel as shown in

Figure. Protocol operation alternates between a contention and a

contention-free period. The contention period is used to build a network topology and

to initialize transmission sub channels.

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DEE-MAC

Stand forDynamic Energy Efficient Medium Access ControlStrategy DEE-MAC is an approach to reduce energy consumption, which lets the idle listening nodes go into sleep using synchronization

performed at the cluster head DEE-MAC operation comprise of two phase:

1) Cluster formation phase

2) Transmission phase

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SPARE-MAC

Stand forSlot Periodic Assignment for Reception Medium Access ControlStrategy save energy through limiting the impact of idle listening and traffic

overhearing. It utilizes a distributed scheduling solution, which assigns specific

time slots to each sensor node for reception.

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Z-MAC

Stand forZebra Medium Access ControlStrategy guaranteed access to its owner slot (TDMA style) a contention-based access to other slots (CSMA style)Advantage• collisions and energy consumptions are reduced.

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A-MAC

Stands forAdvertisement-based Medium Access Control

Strategynode is active only when it is the sender or the receiver, during other time it just goes to sleep.

Advantageenergy waste is avoided on overhearing and idle listening.

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Data Driven Approach

Data-driven approaches can be used to improve the energy efficiency even more.

Data-driven approaches can be divided to data reduction schemes address the case of unneeded samples, while energy-efficient data acquisition schemes are

mainly aimed at reducing the energy spent by the sensing subsystem. Data reduction can be divided two parts

1) in-network processing

2) Dataprediction In-network processing consists in performing data aggregation (e.g., computing

average of some values) at intermediate nodes between the sources and the sink. In this way, the amount of data is reduced while traversing the network towards the sink.

Data prediction consists in building an abstraction of a sensed phenomenon

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CONCLUSION

Energy is one of the most critical resources for WSNs. Extensive research has been conducted to address these limitations by developing schemes that can improve resource efficiency.

In this paper, we have summarized some research results which have been presented in the literature on energy saving methods in sensor networks.

Although many of these energy saving techniques look promising, there are still many challenges that need to be solved in the sensor networks.

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REFERENCE

Energy Saving in Wireless Sensor Networks, Zahra Rezaei, Shima Mobininejad, Department of Computer Engineering Islamic Azad University, Arak Branch , Arak , Iran.

I.Demirkol,C.Ersoy,F.Alagöz, "MAC Protocols for Wireless Sensor Networks: A Survey", IEEE Communications Magazine.

A.Bachir, Mischa Dohler,T.Watteyne,K.Leung, "MAC Essentials for Wireless Sensor Networks", IEEE COMMUNICATIONS SURVEYS & TUTORIALS.