An Adaptive TDMA Slot Assignment Protocol in Ad Hoc Sensor Networks Akimitsu Kanzaki, Takahiro Hara and Shojiro Nishio ACM Symposium on Applied Computing, 2005 (ACM SAC’05)

2 Outline Introduction Related Work  USAP(Unifying Slot Assignment Protocol)  USAP-MA(USAP-Multiple Access)  ASAP(Asaptive Slot Assignment Protocol) E-ASAP (Extend ASAP) Simulation Results Conclusion

3 Introduction Motivation  E-ASAP prevents the excessive increase of unassigned slots By minimizing each node’s frame length.

4 Related Work- USAP(Unifying Slot Assignment Protocol) MILCOM’96 N frames=Cycle M slots The first slot in each frame is reserved to transmit control packet

5 Related Work- USAP(Unifying Slot Assignment Protocol) When a new node joins the network  It firstly collects NMOPs by listening the network channel for a cycle  It recognizes the slot assignments in its contention area. Disadvantage of USAP  N(frame) and M(slot) should be large enough  The channel utilization usually becomes low Due to a large number of unassigned slots. MILCOM’96

6 Related Work- USAP-MA(USAP-Multiple Access) MILCOM’99 Frame Length= 8 Frame Length= 4 Frame Length= 8 Frame Length= 4 Double frame length

7 Related Work- USAP-MA(USAP-Multiple Access) Advantage of USAP-MA  USAP-MA improves the channel utilization By reducing unassigned slots with consideration of the number of nodes and the network topology. Disadvantage of USAP-MA  The channel utilization is still low Unassigned slots in the later part if frame when frame length is double  USAP-MA does not offer When and how to change the frame length How to select a slot assigned to a new node MILCOM’99 Frame Length= 8 Frame Length= 4

8 Related Work- ASAP(Asaptive Slot Assignment Protocol) Set the frame length for a new node  Base on the number of nodes in its contention area  Minimize the number of unassigned slots to improve the channel utilization Packet Format  Transmit mode Data packet (DAT)  Contain the information on the frame length and slots assigned to the sender  Maximum frame length of the sender and its neighbor AINA 2003

9 Related Work- ASAP(Asaptive Slot Assignment Protocol) Packet Format  Control mode Request packet (REQ)  A requests the information on the frame length and assigned slots of all nodes in its contention area. Information packet (INF)  Contain the information on the frame length of B and slots assigned to the sender and C Suggestion packet (SUG)  A sends to its neighbors to announce the frame length and its assigned slot. Reply packet (REP)  B transmits to confirm of receiving SUG AINA 2003 A C B New node 1 3 REQ INF

10 Related Work- ASAP(Asaptive Slot Assignment Protocol) Packet Format  Control mode Request packet (REQ)  A requests the information on the frame length and assigned slots of all nodes in its contention area. Information packet (INF)  Contain the information on the frame length of B and slots assigned to the sender and C Suggestion packet (SUG)  A sends to its neighbors to announce the frame length and its assigned slot. Reply packet (REP)  B transmits to confirm of receiving SUG AINA 2003 A C B New node 1 3 SUG REP

11 Related Work- ASAP(Asaptive Slot Assignment Protocol) Setting the frame length and grasping slot assignment  After collecting INFs from all neighbors, new node sets its frame length. New node adopts the maximum frame length among all nodes in the contention area AINA 2003 Frame Length= 8 Frame Length= 4

12 Related Work- ASAP(Asaptive Slot Assignment Protocol) Selecting an assigned slot  Getting an unassigned slot (GU)  Releasing multiple assigned slots (RMA)  Doubling the frame (DF) 1a 2b 3d 4c 5a 6b 7e Double

13 Related Work- ASAP(Asaptive Slot Assignment Protocol) Disadvantage of ASAP  Frame length in the whole network tends to increase Frame length of a new node is set as the maximum frame length among nodes in its contention area.

14 E-ASAP (Extend ASAP) Each node assigns a slot to itself in the frame of the minimum length Frame Length= 8 Frame Length= 4 h c f d g i 1 j

15 E-ASAP (Extend ASAP) Information held by node h in E-ASAP h 1 hop2 hop

16 Slot Assignment E-ASAP (Extend ASAP)- Slot Assignment Steps:  New node collects INFs transmitted by its neighbors Try to assign a slot to itself in the minimum frame length of 4 slots  New node searches a slot  Getting an unassigned slot (GU)  If the first slot is not assigned to any neighbors, and some unassigned slots are found.  Releasing multiple assigned slots (RMA)  If the first slot is not assigned to any neighbors and all the other slots are assigned to other nodes in its contention area  Doubling the frame (DF)  If no slot is available in the current frame length, new node doubles the frame and tries again to assign a slot  RMA and GU ab Unassigned slot abcdabe Multiple slots

17 E-ASAP (Extend ASAP) New node 1/8 3/4 0/4 2/4 1/4 a b cd e Double 2/8, 6/8RMA b New node GU

18 Detecting of conflict E-ASAP (Extend ASAP)- Detecting of conflict a b c d e fg New node conflict

19 Solution to solve conflict E-ASAP (Extend ASAP)- Solution to solve conflict Deleting a conflicting slot Divide the assignment Delete slot 3 of a Divide slots

20 Frame Length= 8 Solution to solve conflict E-ASAP (Extend ASAP)- Solution to solve conflict Doubling the frame and dividing the assignment Frame Length= 8 Frame Length= 4 Double

21 Releasing Slot Assignment E-ASAP (Extend ASAP)- Releasing Slot Assignment When a node exits from the network  It releases slots assigned to itself, and its neighbors detect the exit  After reconfiguring the slot assignment information The neighbors of the exiting node temporarily release their own assigned slots And search for slots that can be assigned to themselves by Getting an unassigned slot (GU)  If a neighbor finds a slot which can assign to itself in the shorter frame than the current one It updates its own assignment  Each neighbor updates its own assignment transmits in its contention area.

22 Simulation E-ASAP (Extend ASAP)- Simulation Simulation Environment  Each node in the network does not move.  Initially 2 nodes, and this number increases one by one until 50 nodes are present. The number of nodes then decreases one by one in the reverse order  ASAP and E-ASAP New node listens to the channel for 128 slots for collecting information  USAP: frame length 50 slots

23 Simulation E-ASAP (Extend ASAP)- Simulation Average channel utilization

24 Simulation E-ASAP (Extend ASAP)- Simulation Control traffic

25 Simulation E-ASAP (Extend ASAP)- Simulation Setting delay (control mode changes to transmit mode)

26 Conclusion E-ASAP (Extend ASAP)- Conclusion E-ASAP is a TDMA slot assignment protocol  To improve the channel utilization.  To decreases the number of unassigned slots  Efficiently assign slots to nodes When a node appears and disappears from the network Future Work  To consider a frame format to accommodate the movement of nodes.  To extend E-ASAP to adapt the change of network environment Such as traffic load

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