ECE/MAE 7750: Distributed Control Systems FISP: Focused Independent Study and Presentation TMAC - An Adaptive Energy-Efficient MAC Protocol for Wireless.

ECE/MAE 7750: Distributed Control SystemsFISP: Focused Independent Study and Presentation

TMAC - An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks

Presenter: Abhishek Gupta

Dept. of Electrical and Computer Engineering Utah State University

Email: [email protected]: February 23, 2005

OutlineOutline

Overview Issues related to Wireless Sensor networks Current approaches and their shortcomings T-Mac protocol design Performance Analysis Conclusion

Introduction to Ad-hoc Wireless Sensor Introduction to Ad-hoc Wireless Sensor NetworksNetworks

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

Introduction MAC protocolsIntroduction MAC protocols

MAC stands for Medium Access Control. The main purpose of MAC protocol is to ensure that

no two nodes interfere with each others transmission.

Primary

Secondary

Essential attributes of MAC are

Collision Avoidance Energy Efficiency Scalability and adaptivity Channel Utilization Latency Throughput Fairness

Secondary

Energy Efficiency in Wireless Sensor Energy Efficiency in Wireless Sensor NetworksNetworks

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

Causes of energy waste Collisions

Takes place at the receiver Increases Latency

Overhearing Happens when the nodes pick up data destined

to other nodes Idle Listening

Listening to traffic that is not sent

MAC ProtocolsMAC ProtocolsExisting Solution

Traditional schedule based protocols are not appropriate for sensor networks.

TDMA Disadvantage: Very difficult to maintain

synchronization. IEEE 802.11 with power save mode

Disadvantage: Not designed for multi-hop networks SMAC protocol with fixed duty cycle

Existing SolutionsExisting SolutionsSMAC protocol

SMAC stands for Sensor Medium Access Control (protocol).

Time is divided into fairly large frames.

The ratio of the listen time to Sleep time is called as the duty cycle.

Existing SolutionsExisting SolutionsSMAC protocol

During the Sleep time, node turns off its radio. During the active time, nodes can communicate with each other.

Drawback of SMAC approach

Difficult to optimally tune it under static traffic condition.

Energy waste due to idle listening in active state when the load is low and traffic is dynamic

Increases the latency of the network

TMAC EvolutionTMAC Evolution(TMAC – Timeout Medium Access Control)(TMAC – Timeout Medium Access Control)

CSMA/CD CSMA/CA SMAC TMAC

IEEE 802.11IEEE 802.3

Carrier Sense Multiple Access with Collision

Avoidance

Fixed duty cycle

Adaptive duty cycle

ARC

Adaptive Rate

Control

DMAC/MMAC

Directional

Antennas

Carrier Sense Multiple Access with Collision

Detection

TMAC designTMAC designBasic Communication Scheme

Nodes can communicate in active time and turn off radio at sleep time

TMAC uses RTS- CTS-ACK scheme

TMAC designTMAC designBasic Communication Scheme

The active period can be dynamically ended if no activation event is detected.

Activation events include Firing of periodic frame timer Reception of any data Sensing of any communication on the radio The knowledge that the data exchange of the neighbors have

ended This scheme moves all the communication to a burst at the

beginning of the frame

TMAC DesignTMAC DesignClustering and Synchronization

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 2Schedule 1 Border nodes with

2 schedule broadcast twice

TMAC DesignTMAC DesignAdditional Features of TMAC: Fixed Contention interval

In traditional protocols, back off scheme is used Back-Off scheme reduces the probability of

collisions when the load is high TMAC transmits its queued message in burst at the

start of the frame. TMAC uses fixed contention interval Contention time is always used, even if no collision

has occurred yet.

TMAC DesignTMAC DesignAdditional Features of TMAC: RTS retries

When a node sends a RTS but does not receive CTS, there are 3 possible reasons

The receiving node has not heard RTS

The receiver is prohibited from replying

The receiver node is sleeping

TMAC retries by sending additional RTS before giving up on the node

TMAC DesignTMAC DesignOverhearing Avoidance

SMAC have introduced overhearing avoidance by putting nodes to sleep after hearing RTS\CTS packets destined for other nodes

Main Advantage: Energy is saved

Disadvantage: Higher Collision overhead.

TMAC has kept overhearing avoidance feature of SMAC as an optional feature.

TMAC DesignTMAC DesignEarly Sleeping Problem

This problem is seen in unidirectional traffic, like in node to sink communication.

Early sleeping problem reduces the maximum throughput of the network.

TMAC Design Early Sleeping ProblemTMAC Design Early Sleeping Problem Proposed Solution: Future-Request-To-Send (FRTS)

The idea is to let other node know that we still have a message for it, but are ourselves prohibited from using the medium.

The FRTS packet contains the length of time for which communication is blocked.

The node that receives the FRTS packet knows that it will be the future target of an RTS packet and must be awake by that time.

TMAC Design Early Sleeping ProblemTMAC Design Early Sleeping Problem Proposed Solution: Full Buffer Priority

When node’s transmit/routing buffer are almost full, it may prefer sending to receiving.

Advantages: Probability of early sleeping problem is reduced. The scheme introduces limited flow control in the

network.

TMAC DesignTMAC DesignSimulation set up and parameters

For protocol design simulations and implementations, EYES wireless sensing nodes were used.

EYES nodes have TI MSP430F149 processor, 60Kb flash memory and the processor runs on variable clock rate

The capabilities and power consumption of EYES nodes are quite similar to other prototype sensor nodes, for example, popular Berkeley motes

Carrier Sense Multiple Access SMAC with varying active time from 75 ms to 915 ms TMAC protocol with frame length of 610 ms and TA of 15 ms

3 Protocols were used and compared.

TMAC DesignTMAC DesignPerformance: Homogenous Local Unicast

Homogenous unicast is the best case for SMAC since the load is constant

TMAC DesignTMAC DesignPerformance: Event based local unicast

Figure shows an event based unicast scenario

x axis- message frequency

y axis- average energy consumption

TMAC DesignTMAC DesignConclusion

TMAC offers a novel way of dynamically adapting the duty cycle and thus obtaining optimal performance.

TMAC offers significant energy efficiency over always listening MAC protocols.

References: 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 )

An Adaptive Energy Efficient MAC Protocol for Wireless Sensor Networks by Tijs van Dam, Koen Langendoen (SenSys’03, November 5–7, 2003, Los Angeles, California, USA.)

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