Unlocking the demo

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Unlocking the demo.

• Jason Hill

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Data Aggregation

• Reduce network bandwidth requirements by
  aggregating data close to the source.
• Two types aggregation
• Strongest magnetometer data
• Shortest time-of-flight distance measurements
• High value data transported to base station

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Aggregation Protocol

• All nodes announce to their neighbors strong
  sensor readings
• All nodes collect local readings
• Leader is chosen as the node with the highest
  quality data
• Leader is responsible for sending a collection
  of the best readings to base stations

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Data Transport

• Aggregation results in high value data
• Packet loss becomes significant
• Aggregated data must be send over a reliable
  transport mechanism
• Added
• Per link acknowledgements
• REL_DEL geographic based reliable delivery
  mechanism

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Reliable Transport

• X, Y grid of nodes
• Up to 6 retransmissions
• First try last parent 3 times
• Then try other neighbors
• Base station at (0,0)

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Per-link Acknowledgements

• Packets sent to TOS_BCAST or TOS_LOCAL_ADDRSS
  automatically acknowledged
• TOS_MsgPtr-gtack set to 1 when returned in
  MSG_SEND_DONE event
• Acknowledgement signals packet received and
  passed CRC by at least 1 node.

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Acknowledgement Costs

• Acknowledgement immediately follows signal
  strength pulse.

Start Symbol
Length Field
Strength Pulse
CRC
Data Payload
4-byte Header
Preamble
Phase Shift
ACK
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Breakdown of Time

• 30-byte packet (1/40th of a second)

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System Buffering

• Reliable delivery required in-network buffering
• REL_DEL networking layer provides multi-hop
  reliability
• Up to 16 local messages and 16 transient messages
  can be stored
• Local node can have 16 sends pending
• Local messages serviced first (use
  MSG_REL_SEND_MSG)

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Other networking pieces

• All packets acknowledged upon reception
• Variable length packets added to improve
  bandwidth utilization
• CRC calculation performed in parallel with
  transmission and data encoding
• CRC calculation must be completed in time for
  acknowledgement
• Signal strength detection added to high-speed
  stack
• All packets have CRC field (1 passed CRC
  check, 0 failed)