Power Saving in Wireless Sensor Networks

Power Saving in Wireless Sensor Networks

Eng. Mshari Alabdulkarim

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

Energy Saving in WSNs

Studied Paper Topic:

Energy saving in wireless sensor networks.

By: Hnin Yu Shew, JIANG Xiao-hong, Susumu Horiguchi(Department of Computer Science, Graduate School of Information Science, Tohoku University, Sendai 980-8579, Japan)

Date: May 2009

Type: Survey on the main techniques used for energy saving in WSNs.


Wireless Sensor Network?

A wireless sensor network is a collection of nodes “sensors” organized into a cooperative network. The nodes communicate wirelessly and often self-organize after being deployed in an ad-hoc fashion.

Introduction

Sensor Field

Base StationDetection


What are the components of the wireless sensor?1. Processor.2. Memory.3. RF transceiver.4. Power source.5. Sensor.

Introduction (Cont.)


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.




Sensor Types

TemperatureSensor

LightSensor

SoundSensor

VibrationSensor


Wireless Sensor Network Applications:

• Monitoring Space.environmental and habitat monitoring, precision agriculture, indoor climate control, surveillance, treaty verification, and intelligent alarms.

• Monitoring Objects.structural monitoring, condition-based equipment maintenance, medical diagnostics, and urban terrain mapping.

• Monitoring Interactions of Objects and Space.wildlife habitats, disaster management, emergency response, ubiquitous computing environments, asset tracking, healthcare, and manufacturing process flow.



Wireless Sensor Network Example (1):



Wireless Sensor Network Example (2):



Short Video



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?

1. Inexpensive nature.2. Limited size and weight.3. Redundant nature.

Power Consumption in WSNs


sources of power consumption:

1. Useful power consumption: Transmitting or resaving 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 ready”.


How to minimize the energy consumption of sensor nodes while meeting the application requirements?

Sleep-wake Scheduling. In-network Processing. Network Coding. Communication Protocol.


Sleep-wake schedulingSensor Modes

Transmission Reception Listening Idle

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.


State Idle Sleep Transmit Receive

ProcessorActive X X XSleep X

Radio Board

Transmit XReceive X

Sleep X X

Power consumption model:

Wake WakeSleep SleepSleep

Sleep and Wake Duty Cycle

Time


Sleep-wake schemes

On-demand Scheduled rendezvous Asynchronous


1. On-demand Scheme:

Strategy: Sensor should be awakening just when it receives a packet from neighbors.

Advantages: Minimize the power consumption. The best sleep-wake scheme for the applications with low duty cycle.

Disadvantages: Additional delay incurred when a node has to wait for its next hop node to

wake up. Not suitable for Disruption Tolerant Network (DTN).


2. Scheduled Rendezvous Scheme:

Strategy: All sensors should wake up at the same time.

Sleep

Sleep

Sleep

Sleep

Sleep

Sleep

Wake

Wake

Wake

Wake

Transmitter:

Receiver:

Send Packets

Receive Packets


2. Scheduled Rendezvous Scheme (Cont.):

Advantages: All sensors are awake in the same time “which allowing the broadcast

massages”.

Disadvantages: All sensors should be synchronized in order to wake and work in the same

time.


3. Asynchronous Scheme:

Strategy: All neighbors should have an overlapping between their wake periods.

Sleep

Sleep

Sleep

Sleep

Wake

Wake

Transmitter:

Receiver:

Send Packets

Check the channel

Preamble Data

Check the channel and receive

Data


3. Asynchronous Scheme (Cont.):

Advantages: The sensors don’t have to be synchronized together. Allow each node in the WSN to set its own sleep/wake schedule

independently. The contention is reduced, because nodes wake up at different time

instances.


MAC Protocol for WSNMAC

Medium Access Control

S-MAC T-MAC B-MAC


Stand for:Sensors Medium Access Control.

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.

1. S-MAC Protocol:

Listen ListenSleep Sleep

TimeT


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

Disadvantages: Latency will be increase.

1. S-MAC Protocol (Cont.):


1. T-MAC Protocol:Stand for:Timeout Medium Access Control.

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

Sleep Sleep Sleep

Sleep Sleep Sleep

Normal

S-MAC

T-MAC


Questions?What S-MAC, T-MAC, B-MAC are doing?Trying to minimize idle listen as mush as possible.

Why radio should listen the channel?To minimize collisions.

How can we make collision free without listen the channel?TDMA “Time Division Multiple Access”.


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.


In-network Processing

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.


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.


Network Coding


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”.

Medium Access Control

Scheduled Protocol Contention Protocol


1. 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.

1 2 3 N 1 2 3 N

Frame 1 Frame 2

Time

TDMA MAC Protocol


1. Scheduled Protocol (Cont.):

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.


1. 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.


Thank you for your attention


Technology

Power Saving in Wireless Sensor Networks