The TDMA-based MAC Protocols for WSNs----- EMACs and LMAC

EMACs: IEEE VTC 2004-Spring LMAC: INSS 2004

Wang, Sheng-Shih

Feb. 21, 2005

Advantage of a TDMA based, energy-efficient, self-organizing MAC protocol for WSNs

L. F. W. van Hoesel†, T. Nieberg†, H. J. Kip††, and P. J. M. Havinga†

† Department of Electrical Engineering, Mathematics and Computer Science

University of Twente, The Netherlands††

Nedap N. V., Groenlo, The Netherlands

IEEE Vehicular Technology Conference(VTC2004-Spring)

European Research Project EYES

Website: http://eyes.eu.org

Data Splitting

(Multipath) Routing

Clustering

EMACs

Connected active set formation

TDMA-based

Applications

Dynamic Topology

Overview --- EMACs

frame …

…timeslot

CR TC DATA

frame frame frame frame

• CR: Communication Request Section• TC: Traffic Control Section• DATA: Data Section

time

Overview --- Clustering

Overview --- Clustering (cont’d)

anchor

bridge

• Both the anchor and bridge nodes are regarded as the active nodes• All active nodes comprise the connected dominating subset

nonmember

EMACs Main goal

Minimize energy consumption Operation modes

Active Forward messages to a destination Accept data from passive nodes

Passive Keep track of the active node

Dormant Enter low power states

EMACs --- Frame Structure

frame …

…time slot

TC DATA

frame frame frame frame

• CR: Communication Request Section• TC: Traffic Control Section• DATA: Data Section

An active node autonomously picks its own

time slotCR

EMACs --- Frame Structure (cont’d) Communication Request Section

An active node listens for incoming requests from passive nodes

The passive node sends the request if any data Traffic Control Section

An active node transmits a short control message The possible acknowledgement to the request Control and synchronization messages (e.g., slot

schedule table) The passive node listens the message from its active

node Data Section

Used for the actual transfer of data

EMACs --- Operation

A

…

C…

D

…

B

…

• Node A is an active node, while nodes B, C, and D are all passive nodes • Nodes B, C, and D are node A’s neighbors• Nodes B, C, and D intend to send packets to node A

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• In CR section, nodes B, C, and D send their own requests to node A (via random backoff mechanism)

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• Suppose the transmission of node C is allowed • In TC section, node A broadcasts a control message (w/ ack. of the request, slot schedule table, etc)

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• In DATA section, node C transmits the data to node A (w/o any collision)

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• In CR section, nodes B and D send their own requests to node A (via random backoff mechanism)

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• Suppose the transmission of node B is allowed • In TC section, node A broadcasts a control message (w/ ack. of the request, slot schedule table, etc)

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• In DATA section, node B transmits the data to node A (w/o any collision)

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• In CR section, node D sends its own request to node A (via random backoff mechanism)

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• Suppose the transmission of node D is allowed • In TC section, node A broadcasts a control message (w/ ack. of the request, slot schedule table, etc)

EMACs --- Operation (cont’d)

A

…

C…

D

…

B

…

• In DATA section, node D transmits the data to node A (w/o any collision)

EMACs --- Operation (cont’d) Schedule Challenges

Request collision Time slot selection Node role determination

…

…

…

…

A

B

C

D

transmitting/receiving state

power-saving state

Request Collision

The node will not receive any acknowledgement from the active node

The node sends the request in the next active node’s time slot

Time Slot Selection

The active node sends the time schedule table in the TC

The table contains the assignment of time slots occupied by the active node and its one-hop neighbors

The information is encoded by a number of bits

A node can pick an unused time slot for itself

Time Slot Selection (cont’d)

?

6

3

2

5

1

5

44

0101100…

0111100…

0110110…

1110100… 1101100…

0010110…

1001110…

1001100…

The occupied time slots for?

1111110…

free time slot

? 7

(OR bit sets)

Node Role Determination

Based on passive clustering The anchor (cluster head) and bridge (gateway

node) are regarded as the active nodes The nonmember (ordinary node) is regarded

as the passive node

Simulation

Simulator: OMNet++ Routing protocol: DSR Network environment

Number of nodes: 46 Number of data sources: 5 (5-byte length data) Number of the sink: 1 Size: 5 by 5 times the transmission range of a node

Network types Static Dynamic

Random waypoint model

Simulation --- Static Network

EMACs is able to prolong the lifetime with 30% to 55% compared to SMAC

Simulation --- Dynamic Network

EMACs is able to extend the lifetime with a factor of 2.2 to 2.7 compared to SMAC

Question

Source Frequent transceiver state switch

Results Increase energy consumption Increase latency

Solution LMAC

A Lightweight Medium Access Protocol (LMAC) for Wireless Sensor Networks

L. F. W. van Hoesel and P. J. M. Havinga† Department of Electrical Engineering, Mathematics and Computer Science

University of Twente, The Netherlands

International Workshop on Networked Sensing Systems (INSS 2004)

Frame Structure

frame …

…timeslot

TC DATA

frame frame frame frame

• TC: Traffic Control Section• DATA: Data Section

Operation

All nodes should be awake in all TCs A node always transmits a control message in its o

wn TC, all neighbors should receive the control message

A node is addressed: listen to the data section A node is not addressed: switch off transceiver, and wake

up at the next time slot Control message: 12 bytes

Simulation --- Static Network

LMAC reduces preamble transmissions and transceiver state switches

Summary

EMACs vs. LMAC Active vs. passive

Advantages of EMACs/LAMC (compared to SMAC) Energy conservation (mainly about idle listening) Delivery ratio

Drawbacks of EMACs/LMAC (compared to SMAC) High latency

Energy-Efficient Medium Access Control

Koen Langendoen and Gertjan HalkesDelft University of Technology

Book Chapter in the Embedded Systems HandbookR. Zurawski (editor), CRC press, to appear in Aug. 2005

Simulation Parameters

Simulation Result --- Latency

Average delay for one hop transmission is half the length of a frame

Adaptive listening mechanism(messages can travel about 2 hops during one active period)

Conclusion

EMACs and LMAC are robust in the dynamic network

TDMA-based protocol Less energy consumption due to free of idle listening Incur high latency Overhead of schedule computing and distribution throug

h the network limit the applications