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

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

• Zhihui Chen and Ashfag Khokhar
• ECE/CS University of Illinois at Chicago
• IEEE SECON 2004
• Presented by Jeffrey

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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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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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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

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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

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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)

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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

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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

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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

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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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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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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

• 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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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

• Each node randomly selects a slot with uniform
  probability among all slots to be its s-slot
• 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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Self-Organization Scheme

• 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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Self-Organization Scheme

• 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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Self-Organization Scheme

• 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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Self-Organization Scheme

• 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
• 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

• 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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TDMA-W Channel Access Protocol

• Each node maintains a pair of counters for every
  neighbors
• Outgoing counters
• Incoming counters
• These counters are preset to an initial value
• 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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TDMA-W Channel Access Protocol

• 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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TDMA-W Channel Access Protocol

• 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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TDMA-W Channel Access Protocol

• 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

• 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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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

• 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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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

• 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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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!