energy efficient wireless network (2)

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1 SEMINAR ON LOW ENERGY EFFICIENT WIRELESS SENSOR NETWORK PRESENTED BY-DEEPAK KUMAR DHAL REGD. NO-0901304038 ELECTRONICS AND COMMUNICATION ENGINEERING GANDHI INSTITUTE OF TECHNOLOGY AND MANAGEMENT

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CONTENTS: Introduction. Power Consumption in WSNs. Sleep-wake Scheduling. MAC Protocol for WSN. In-network Processing. Network Coding. Communication Protocol . 2

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What is Wireless Sensor Network? A wireless sensor network is a collection of nodes “ s ensors” organized into a cooperative network. The nodes communicate wirelessly and often self-organize after being deployed in an ad-hoc fashion . Introduction 3

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What is the goal of the sensor node? The goal from the sensor node is to collect the data at regular intervals, then transform the data into an electrical signal and finally send the signal to the sink or the base node. 4 What are the components of the wireless sensor? Processor. Memory. RF transceiver. Power source. Sensor.

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5 TYPES OF SENSORS

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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. Power Consumption in WSNs 6

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How to minimize the energy consumption of sensor nodes while meeting the application requirements? Sleep-wake Scheduling. In-network Processing. Network Coding. Communication Protocol. Sources of power consumption: Useful power consumption: Transmitting or resceiving data. Processing query requests. Forwarding queries and data to the neighbors. 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 ready”. 7

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Sleep-Awake scheduling Goal: reduce the time where the sensor is being idle. Wake State Sleep State Drawback: Additional delay because of waiting for the next-hop node to wake up. 8

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MAC Protocol for WSN 9

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Stand for: S ensors M edium A ccess C ontrol. Strategy: All node follow a periodic sleep/wake cycle, where the waking time is about 10% of the sleeping time, and the nodes that are close to each other synchronize their active cycles together. Advantages: Periodic Listen. Collision Avoidance. Overhearing Avoidance. Message passing. Disadvantages: Latency will be increase. S-MAC Protocol: 10

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T-MAC Protocol: Stand for: T imeout M edium A ccess C ontrol. Strategy: It adaptively adjusts the sleep and wake periods based on the estimated traffic flow. 11

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In-network Processing After the sensors detect phenomena or change, they generate an event to the user and by that we will have a huge number of transmissions which will consume the power of the sensors. Strategy: Reduce the number of transmissions by aggregating several events into a single event. Aggregation takes place if the data arriving to the common node have same attributes of the phenomenon being sensed. 12 Advantages: Reduce the number of transmissions “which will help to reduce the consumption of power”. Disadvantages: There is a potential of having greater delay. Can’t be used in case if all the original packets are needed to be delivered to the destination nodes

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Network Coding Goal: improve the throughput and save the bandwidth. Strategy: allow to mix the data at the intermediate nodes. Advantages: Reduce the number of transmissions by mixing two packets together. Improves throughput and saves bandwidth. 13

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Communication Protocol The goal from adjusting the communication protocol “Medium Access Control” is to avoid the collisions by scheduling nodes onto different sub-channels that are divided either by time “TDMA”, frequency “FDMA” or orthogonal codes “CDMA”. 14

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Scheduled Protocol: Strategy: Prevent the collisions by reserving and scheduling the resources. Example: The best protocol considered as scheduled protocol is the TDMA “Time Division Multiple Access”, where the time is divided into N slots and each slot can be used by only one sensor. Advantages: TDMA supports low-duty-cycle operations on sensors. Saving the power from being wasted by turning off the radio out the allocated time slot. Eliminating the possibility of collisions due contention and eliminating the possibility of overhearing. Disadvantages: Not flexible to changes in sensor density or movements. All sensors should be well synchronized. 15

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Contention Protocol: Strategy: Before sending a message, a sensor listens to the medium. If it is busy, wait a random time then retry again and if it is free then it will send the message. Advantages: It can adapt for changes “in the node density, traffic load or the topology” better than the Scheduled protocol. Support peer-to-peer communications. The sensors don’t have to be synchronized together. Disadvantages: It is the worst protocol among all the previous protocol from the power saving perspective, since all sensors listen to the channel all the time. 16

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Thank you for your attention 18

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