Self Organization and Energy Efficient TDMA MAC Protocol by Wake Up for Wireless Sensor Networks

2005/8/2 NTU NSLAB 1

Self Organization and Energy Efficient TDMA MAC Protocol by Wake Up for

Wireless Sensor Networks

Zhihui Chen and Ashfag KhokharECE/CS University of Illinois at Chicago

IEEE SECON 2004

Presented by Jeffrey


Outline

• Introduction• Channel and Traffic Assumption• TDMA-W: Details

– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W

• Simulation Results• Conclusion


Outline





Wireless Sensor Networks (WSNs) Are Unique

• Traffic rate is very low– Typical communication frequency is at

minutes or hours level• Sensor networks are battery powered and

recharging is usually unavailable– Energy is an extremely expensive resource


Wireless Sensor Networks (WSNs) Are Unique

• Sensor nodes are generally stationary after their deployment

• Sensor nodes coordinate with each other to implement a certain function– Traffic is not randomly generated as those in

mobile ad hoc networks


Previous Energy-Efficient MAC Protocols for WSNs

• “An Energy-Efficient MAC Protocol for Wireless Sensor Networks”– W. Ye, J. Heidemann and D. Estrin– IEEE INFOCOM ’02– S-MAC (10% S-MAC)



• “An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks”– T. Dam and K. Langendoen– ACM SENSYS ’03“– T-MAC


Concentrate traffic to fixed periods?

• Increases contention probability• Incurs unnecessary retransmissions• S-MAC proposes to perform RTS/CTS

handshake procedure• Duty rate or portion of listening period of

S-MAC should be carefully chosen• T-MAC adapts duty cycle to the traffic rate



• “Energy-Efficient, Collision-Free Medium Access Control for Wireless Sensor Networks”– V. Rajendran, K. Obraczka and J.J. Garcia-Luna-Aceves– ACM SENSYS ’03– TRAMA

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Scheduling

• Data transmissions are scheduled in advance to avoid contention

• TDMA-W– TDMA-Wakeup– Each node is assigned two slots– Transmission/Send slot (s-slot)– Wakeup slot (w-slot)

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5 6 7 8 1 2 3 4 5 6 7 8 1 2

1 ZZZ ZZZ ListenWake

up Nd3

Send ZZZ ZZZ ZZZ ZZZ ZZZ Listen ZZZ ZZZ ZZZ

2 ZZZ ZZZ ZZZ

Wakeup

Nd3ZZZ Send ZZZ ZZZ ZZZ ZZZ ZZZ Listen ZZZ ZZZ

3 ZZZ ZZZ

Wakeup

Nd4Listen Listen Listen Send ZZZ ZZZ ZZZ ZZZ Listen ZZZ ZZZ


up Nd6

ZZZ ZZZ Listen Send ZZZ ZZZ Listen ZZZ ZZZ ZZZ


up Nd6

ZZZ ZZZ ZZZ ZZZ Send ZZZ Listen ZZZ ZZZ ZZZ

6 ZZZ ZZZ ZZZ Listen ZZZ ZZZ ZZZ Listen Listen ZZZ ZZZ Listen ZZZ ZZZ

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Outline




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Channel and Traffic Assumption

• Ideal physical layer– The only reason for packet loss is

transmission contention– No packet loss due to noise

• Three types of traffic pattern– One-to-all broadcast– All-to-one reduction– One-hop random traffic

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Channel and Traffic Assumption

• A TDMA-W frame lasts for Tframe seconds

• Tframe is known to all nodes and is preset before deployment

• A TDMA-W frame is divided into slots• Each node is assigned one slot for

transmission and one slot for wakeup• Networks are synchronized

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Outline




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Self-Organization• Assign time slots to the sensors within each

TDMA-W frame• Assume sensor networks has data rate of 1

Mbps• Transmission of a 512 byte packet occupies the

channel for about 3.9 ms• Assume a TDMA-W frame of 1 second divided

into 256 slots– Each slot is of 3.9 ms– Capable of communicating 512 bytes

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Self-Organization Scheme

1. Each node randomly selects a slot with uniform probability among all slots to be its s-slot

2. During its selected s-slot, each node broadcasts– Its node ID– Its s-slot number– Its one-hop neighbors’ IDs and their s-slot

assignments– Slot number of any s-slot during which this node has

identified a collision

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3. When a node is not transmitting, it turns on its receiver circuit and listens to the traffic from neighbors

• The node should record all the information being broadcast by all its neighbors• Their s-slot assignments and their node IDs• The slot number of any slot being broadcast as a

collision-prone slot

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4. If a node determines that – it is involved in a collision – or finds out that one of its two-hop neighbors

has the same s-slot– It then randomly selects an unused slot and

go to step 2

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5. If – no new nodes are joining in– or s-slot assignments are not changing– or no collisions are detected for a certain

period– It implies all neighbor nodes are found and

all the s-slots are final

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6. Each node broadcasts the s-slot selections of their two-hop neighbors.

• Each node identifies an unused slot or any s-slot being used by the nodes beyond its two-hop neighbors and declares it as its w-slot

• Note that w-slots need not be unique

7. Each node broadcasts its w-slot and the self-organization is complete

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Can Detect Any Two-hop Collisions

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Undetectable One Hop Collision

• To solve this problem– Let a node go to the listening mode in its

assigned s-slot with a probability

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Deadlock

• To listen during s-slot with a probability• To set a collision counter

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Outline




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TDMA-W Channel Access Protocol

1. Each node maintains a pair of counters for every neighbors

– Outgoing counters – Incoming counters– These counters are preset to an initial value

2. If no outgoing data is sent to a node in a TDMA-W frame

– The node decrements the corresponding outgoing counter by one

– Otherwise it resets the counter to the initial value

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3. If no incoming data is received from a neighboring node in a TDMA-W frame

– The node decrements the corresponding incoming counter by one

– If the counter is less than or equal to zero, the node stop listening to that slot starting from next TDMA-W frame

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4. If a outgoing data transmission request arrives

– The node first checks the outgoing counter– If the counter is greater than zero, then the

link is considered active and the packet can be sent out during the s-slot

– If the counter is less than or equal to zero, a wakeup packet is sent out during the w-slot of the destination node prior to the data transmission

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5. If a node receives a wakeup packet in its w-slot

– It turns itself on during the s-slot corresponding to the source node ID contained in the wakeup packet

– If a collision is detected in the w-slot• More than one node intends to send data• The node then searches all its neighbors for

incoming traffic

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Packet Content

• Wakeup packet contains only the source and the destination information

• Data packet may only contain the destination information– Omit source ID since the source ID is

determined by the s-slot

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Broadcast

• If a data packet is to be broadcast to multiple nodes– The destination address contains a special

identifier to mark it as a broadcast message– Before sending a broadcast data packet

• The node should wakeup all its neighbors that intend to receive this packet

• In the case when multiple users share the same w-slot

– The destination field of the wakeup message should also be set to a broadcast address

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Outline




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Performance Analysis of TDMA-W

• Let us fix the position of the w-slot

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Average Delay

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Outline




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Deployment of Sensor Nodes

• Nodes are deployed randomly in a 500x500 sq. ft. area

• Communication range is 100 feet for all nodes• Assume an IEEE 802.11 basic rate of 1 Mbps as

the physical layer transmission rate• Slot length is set to be 4 ms

– Long enough for transmitting a 512-byte packet

• Tframe is set to one second– A TDMA-W frame has 250 slots

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Simulation Results of Self-Organization Protocol

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Power Consumption

• Power consumption– Transmission : Receiving/Listening : Sleeping = 1.83 : 1 : 0.001

• 10% S-MAC– Use RTS/CTS frames to reserve channel for node-to-

node traffic – Use ACK packet to acknowledge the successful

transmission– If data or ACK packet is corrupted by collision, the

data packet is retransmitted

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Power Consumption

• The network is synchronized– All the nodes become active at the same time

• All data packets are fixed to be 256 bytes in length

• Control packets (RTS, CTS, ACK in S-MAC and Wakeup packet in TDMA-W) are about 20 bytes in length

• Assume energy consumption for a control packet is 1/10 of a data packet

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Power Consumption

• Initial value for counters is set to 3• Transmission buffer length is set to 50

packets• Both TDMA-W and S-MAC are run for 10

minutes

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Power Consumption of One-Hop Random Traffic

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Delay of Random One-Hop Traffic

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Delay of All to One Reduction Operation Traffic

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Outline




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Conclusion

• Efficient protocols TDMA-W for self-organization and channel access control in wireless sensor networks are proposed

• Proposed protocols were verified using extensive simulations

• Proposed protocols only consume 1.5% to 15% power of 10% S-MAC– 6 to 67 times better than 10% S-MAC

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Conclusion

• Proposed scheme responds to the event with a delay comparable to S-MAC for one-hop traffic

• Proposed protocol is collision free for data traffic so reliable transmission is guaranteed for all types of traffic

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Comments

• Strength – Great improvement in the power consumption

• Weakness– Verify results by using simulation (MATLAB)

with not so practical assumptions – Delay could be significant– Scalability would be poor

• Large overhead in memory

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Thank you very much for your attention!

Self Organization and Energy Efficient TDMA MAC Protocol by Wake Up for Wireless Sensor Networks

Documents

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deploymenta tdmaw frame

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uniquesensor nodes

deploymentsensor nodes

hours levelsensor networks