S-MAC Protocol for Ad-hoc ZigBee Wireless Sensor Networks

Presented by:-Pramod KumarM.Tech. (Adv. ECE), SEM-IIRoll No.:- 1309136706

OUTLINEOUTLINE

• Introduction to Ad-hoc Wireless Sensor Networks

• The problem and existing solutions

• Introduction to S-MAC protocol

• S-MAC design

• Performance

• Conclusion

Introduction to Ad-hoc Wireless Sensor NetworksIntroduction to Ad-hoc Wireless Sensor Networks

• An Ad-Hoc wireless sensor network is a network of sensor devices that are deployed in an ad-hoc fashion and coordinate for sensing a physical phenomenon.

• Each wireless sensing node typically includes

– A Sensor

– A processor

– A radio

– A battery

Ad-hoc Wireless Sensor Network Ad-hoc Wireless Sensor Network Applications

Applications include– Traffic Surveillance– Military Applications– Fire Detection– Agricultural management– Structure and Earthquake monitoring– Industrial Control– Rescue Operations

Energy Efficiency in Ad hoc Wireless Sensor NetworksEnergy Efficiency in Ad hoc Wireless Sensor Networks

• Energy efficiency is the primary concern in a wireless sensor networks.

• Causes of energy waste

– Collisions Takes place at the receiverIncreases Latency

– OverhearingHappens when the nodes pick up data destined to other nodes

– Idle ListeningListening to traffic that is not sent

Energy Efficiency in Ad hoc Wireless Sensor NetworksEnergy Efficiency in Ad hoc Wireless Sensor Networks

• Motes, which are used as nodes in wireless sensor networks, work on extremely low energy !!!

Source: http://www.intel.com/research/exploratory/motes.htm

MAC Protocols MAC Protocols Existing Solution

• Stands for Medium Access Control.

• Determine when and how nodes should access the shared medium.

• Two broad categories

– Contention based protocols e.g. IEEE 802.11, CSMA etc.

– Scheduled based protocols e.g. TDMA, FDMA etc

MAC Protocols MAC Protocols Limitations of Existing Solution

• TDMA (Scheduled protocol)

– Each node gets full bandwidth for a pre-allocated time in turns

– Major drawback: Not suitable for networks whose node density changes.

• FDMA (Scheduled protocol)

– Each node gets a permanent share of bandwidth

– Major drawback: Poor bandwidth utilization

• IEEE 802.11 (Contention based protocol)

– Each node contends for the medium as necessary

– Major drawback: Wastes a lot of energy in idle listening

Introduction of SMAC ProtocolSMAC Protocol

• Stands for Sensors Medium Access Control

• Specifically designed for Ad hoc wireless sensor networks

• Primary goal: Energy Efficiency

SMAC design SMAC design FeaturesMain features of SMAC include

– Periodic Listen– Collision Avoidance– Overhearing Avoidance– Message Passing

Tradeoffs

Latency

fairnessEnergy

SMAC Design SMAC Design Periodic Listen and Sleep

• Problem: Idle listening consumes significant energy

• Solution: Put all the nodes to sleep periodically

Turn off radio when sleepingReduce duty cycle to ~10%Preferable, neighboring nodes follow same schedule

Latency Energy

SMAC Design SMAC Design Choosing and Maintaining Schedule

• Nodes exchange their schedule by periodically broadcasting SYNC packet

• Nodes take following 2 steps to choose their schedule

• Listen for SYNC packets for a fixed amount of time

• Case 1: No SYNC packets are received

• Case 2: SYNC packet is received.

• Case 3: Multiple SYNC packets are received.

• Broadcast the chosen schedule by sending out SYNC packet.

Schedule 2

Schedule 1 Border nodes with 2 schedule broadcast twice

SMAC Design Listen and Sleep - SMAC Design Listen and Sleep - Maintaining Synchronization

• The listen time is divided into two parts:

– For sending/receiving SYNC signal.

– For sending/receiving Data.

SMAC Design SMAC Design Adaptive listening

• Used to reduces multi-hop latency due to periodic sleep.

• Neighboring nodes wake up for a short period of time at the end of each transmission.

41 2 3

CTS

RTS

CTS

SMAC Design SMAC Design Overhearing Avoidance

• All immediate neighbors of sender and receiver are put to sleep upon receiving RTS/CTS.

• Neighbors do not overhear data packets and following ACKS.• The duration field in the packet indicates how long to sleep.

SMAC design SMAC design Message Passing

• SMAC reintroduces the concept of Message Passing

• Long messages are converted into small fragment and are transmitted in bursts.

• Receiver acknowledges each received fragment.

DATA/ACK DATA/ACK DATA/ACK DATA/ACK

Contention for mediumUnfairness

Hidden terminal problem solved by ACK

A BDATA

CSYNC

corrupt

SMAC Design SMAC Design Implementation• To demonstrate the effectiveness of SMAC protocol compared to

conventional protocols, they were implemented and tested on Motes.

• Operating System used was TinyOS.

• Three MAC modules were implemented on Rene Motes

UCB mote with whip Antenna

An 802.11 like protocol without sleep SMAC without periodic sleep SMAC with period sleep

SMAC Design SMAC Design Implementation Tests on a two hop network Measures total energy overtime to send messages

The graph shows the mean energy on radios of source nodes

Idle listening rarely happens

Periodic sleep for Idle listening

SMAC Design SMAC Design Implementation• Tests on a ten hop network

The graph shows aggregate energy consumption in a 10-hop network

SMAC Design SMAC Design Conclusion

•SMAC offers significant energy efficiency over always listening MAC protocols.

•SMAC is able to greatly prolong the network life, which is critical for real-world network applications.

References: • Performance Analysis of SMAC Protocol in Wireless Sensor Networks Using Network

Simulator (Ns-2) by Gayatri Sakya, Vidushi Sharma

• Medium Access Control With Coordinated Adaptive Sleeping for Wireless Sensor Networks, by Wei Ye, John Heidemann, and Deborah Estrin (IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 12, NO. 3, JUNE 2004 )

• Presentation by Wei Ye on MAC Layer Design for Wireless Sensor Networks

• Presentation by Ranjith Udayshankar on Medium Access Control With Coordinated Adaptive Sleeping for Wireless Sensor Networks

• Figure of motes power spectrum obtained from http://www.intel.com/research/exploratory/motes.htm