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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