Proposal to IEEE 802'15'4

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Proposal to IEEE 802.15.4
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Outline

• 802.15.4b
• Two kind of solutions for multi-hop beacon enable
  networks
• Beacon conflict problems

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Support of Multi-hop Beacon Enabled Networks

• Approach 1
• - Each coordinator selects a contention-free
  time-slot for its active period.
• It includes the Beacon_Tx_Offset (between its
  beacon and its parents
• beacon) in its beacon payload.
• Every new coordinator obtains its neighbors and
  their parents time-slots
• from the neighbors beacons.

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Support of Multi-hop Beacon Enabled Networks

• Approach 2
• Every coordinator selects a contention-free
  time-slot within the beacon-only-
• period to transmit its own beacon
• A postBeaconDelay has to be added to the MAC PIB
  to delay the data
• transmissions to the end of the
  Beacon-only-Period

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Support of Multi-hop Beacon Enabled Networks

• Problems of approach 1
• Assumption very low duty cycle and very short
  active period
• Shall we limit the beacon-enabled mode only to
  low duty cycle applications?
• Every coordinator has to wake up in both its own
  active period and its parents active period
• Benefits of approach 2
• Without the limitation of low duty-cycle
• Every node only needs to wake up once within one
  beacon interval
• Approach 2 Backward compatibility
• For 15.4 device, the NWK layer has to prevent the
  MAC layer from sending packets before the end of
  the Beacon-only-Period

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Direct and Indirect Beacon conflict Problems

• Change the superframe structure as starting with
  a Beacon period
• However, if two coordinators within the same POS
  join the WPAN almost at the same time, it is
  still possible that the two coordinators choose
  the conflicted beacon transmission time

• Direct conflict
• Multiple coordinators within the same POS
• Example Two coordinators with parent-child
  relationship

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Three Cases for Indirect Beacon Conflicts

• D1 has been associated to c1
• C2 joins the WPAN by associating to coordinator c3

• Two coordinators c1 and c2 have been in WPAN
• D wants to join the WPAN

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Solutions to Indirect Beacon conflict

• Base on the beacon period solution
• Two kinds of methods
• Reactive approach
• perform 2 ?orphan scan?,?? beacon conflict
  notification
• Proactive approach
• Suggest that all devices respond to the beacon
  request command actively or passively
• After receiving a beacon request command, if a
  device is a coordinator, besides its beacons sent
  periodically, it will also reply with a beacon
  time notification command to report its parent
  coordinators beacon time information
• If a device who received the beacon request
  command is not a coordinator, it will reply with
  a beacon time notification command to report its
  parent coordinators beacon time information