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2005/8/2NTU NSLAB3 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion
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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
2005/8/2 NTU NSLAB 2
Outline
• Introduction• Channel and Traffic Assumption• TDMA-W: Details
– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W
• Simulation Results• Conclusion
2005/8/2 NTU NSLAB 3
Outline
• Introduction• Channel and Traffic Assumption• TDMA-W: Details
– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W
• Simulation Results• Conclusion
2005/8/2 NTU NSLAB 4
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
2005/8/2 NTU NSLAB 5
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
2005/8/2 NTU NSLAB 6
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)
2005/8/2 NTU NSLAB 7
Previous Energy-Efficient MAC Protocols for WSNs
• “An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks”– T. Dam and K. Langendoen– ACM SENSYS ’03“– T-MAC
2005/8/2 NTU NSLAB 8
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
2005/8/2 NTU NSLAB 9
Previous Energy-Efficient MAC Protocols for WSNs
• “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
2005/8/2 NTU NSLAB 10
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)
2005/8/2 NTU NSLAB 11
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
4 ZZZ ZZZ ListenWake
up Nd6
ZZZ ZZZ Listen Send ZZZ ZZZ Listen ZZZ ZZZ ZZZ
5 ZZZ ZZZ ListenWake
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
2005/8/2 NTU NSLAB 12
Outline
• Introduction• Channel and Traffic Assumption• TDMA-W: Details
– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W
• Simulation Results• Conclusion
2005/8/2 NTU NSLAB 13
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
2005/8/2 NTU NSLAB 14
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
2005/8/2 NTU NSLAB 15
Outline
• Introduction• Channel and Traffic Assumption• TDMA-W: Details
– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W
• Simulation Results• Conclusion
2005/8/2 NTU NSLAB 16
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
2005/8/2 NTU NSLAB 17
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
2005/8/2 NTU NSLAB 18
Self-Organization Scheme
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
2005/8/2 NTU NSLAB 19
Self-Organization Scheme
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
2005/8/2 NTU NSLAB 20
Self-Organization Scheme
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
2005/8/2 NTU NSLAB 21
Self-Organization Scheme
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
2005/8/2 NTU NSLAB 22
Can Detect Any Two-hop Collisions
2005/8/2 NTU NSLAB 23
Undetectable One Hop Collision
• To solve this problem– Let a node go to the listening mode in its
assigned s-slot with a probability
2005/8/2 NTU NSLAB 24
Deadlock
• To listen during s-slot with a probability• To set a collision counter
2005/8/2 NTU NSLAB 25
Outline
• Introduction• Channel and Traffic Assumption• TDMA-W: Details
– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W
• Simulation Results• Conclusion
2005/8/2 NTU NSLAB 26
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
2005/8/2 NTU NSLAB 27
TDMA-W Channel Access Protocol
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
2005/8/2 NTU NSLAB 28
TDMA-W Channel Access Protocol
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
2005/8/2 NTU NSLAB 29
TDMA-W Channel Access Protocol
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
2005/8/2 NTU NSLAB 30
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
2005/8/2 NTU NSLAB 31
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
2005/8/2 NTU NSLAB 32
Outline
• Introduction• Channel and Traffic Assumption• TDMA-W: Details
– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W
• Simulation Results• Conclusion
2005/8/2 NTU NSLAB 33
Performance Analysis of TDMA-W
• Let us fix the position of the w-slot
2005/8/2 NTU NSLAB 34
Average Delay
2005/8/2 NTU NSLAB 35
Outline
• Introduction• Channel and Traffic Assumption• TDMA-W: Details
– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W
• Simulation Results• Conclusion
2005/8/2 NTU NSLAB 36
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
2005/8/2 NTU NSLAB 37
Simulation Results of Self-Organization Protocol
2005/8/2 NTU NSLAB 38
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
2005/8/2 NTU NSLAB 39
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
2005/8/2 NTU NSLAB 40
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
2005/8/2 NTU NSLAB 41
Power Consumption of One-Hop Random Traffic
2005/8/2 NTU NSLAB 42
Delay of Random One-Hop Traffic
2005/8/2 NTU NSLAB 43
Delay of All to One Reduction Operation Traffic
2005/8/2 NTU NSLAB 44
Outline
• Introduction• Channel and Traffic Assumption• TDMA-W: Details
– Self-Organization– TDMA-W Channel Access Protocol– Performance Analysis of TDMA-W
• Simulation Results• Conclusion
2005/8/2 NTU NSLAB 45
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
2005/8/2 NTU NSLAB 46
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
2005/8/2 NTU NSLAB 47
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
2005/8/2 NTU NSLAB 48
Thank you very much for your attention!