1. Dynamic TDMA Slot Assignment in Ad Hoc Network
CN EE CCU
Speaker: 游千冊
2005/11/29

2. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclusion

3. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

4. Introduction(1/3)
Ad hoc network are temporarily constructed by only mobile hosts.
TDMA provide the collision-free packet transmission regardless of the traffic load.
Traditional TDMA technique do not take into consideration autonomous behaviors of mobile host , and thus they cannot assign time slots for new coming mobile hosts.

5. Introduction(2/3)
A few conventional protocols [7,8] that assign time slots for new coming mobile hosts , but the channel utilization is low.
Our proposed protocol to improve the channel utilization by changing the frame length dynamically according to the number of mobile hosts in the contention area.

6. Introduction(3/3)
Contention area is defined for each mobile host as the set of mobile hosts that can cause collisions of sending packets with each other.

7. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

8. Unifying Slot Assignment Protocol (USAP) (1/3)
The TDMA format in USAP , which consists of N frames and a frame consists of M slots.
N and M are fixed number.
NMOP (Net Manager Operational Packet)

9. Unifying Slot Assignment Protocol (USAP) (2/3)
NMOP contains the following information.
STi(s) : 1: if node i transmits a data packet to its
neighbors in slot s, 0: otherwise.
SRi(s) : 1: if node i receives a data packet from one of its neighbors in slot s, 0: otherwise.
NTi(s) : 1: if node i has neighbors which transmit data packets to their neighbors in slot s, 0: otherwise.
i: the node that transmits the NMOP
s: a slot in the frame

10. Unifying Slot Assignment Protocol (USAP) (3/3)
When a new node joins the network, it is not assigned any slots and does not have information about neighbors.
First. Listen the channel => recognizes the slot assignments in its contention area.
Second. Select an unassigned slot.
Third. Announce the selected slot to its neighbor.
Channel utilization is low.

11. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

12. USAP Multiple Access (USAP-MA) (1/2)
USAP-MA is an extension of USAP, introduces ABC (Adaptive Broadcast Cycle)
In ABC, frame length and frame cycle can change dynamically.

13. USAP Multiple Access (USAP-MA) (2/2)
USAP-MA improves the channel utilization by reducing unassigned slots with consideration of the number of nodes and the network topology.
When and how to change the frame length??
How to select a slot assigned to a new node??
When the frame length is doubled, the channel utilization is still low.

14. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

15. Dynamic TDMA Slot Assignment- Frame Format
The frame length is set as a power of 2.
The first slot is reserved for new nodes to transmit control packets for requesting a slot assignment.

16. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

17. Dynamic TDMA Slot Assignment- Packet Format (1/2)
There are two modes, transmit mode and control mode.
Transmit mode:
Data packet (DAT)
Frame length、slots assigned to the sender、maximum frame length of the sender and its neighbor、data.
Control mode:
Request packet (REQ)
The new node requests the information on the frame length and assigned slots of all nodes in its contention area.

18. Dynamic TDMA Slot Assignment- Packet Format (2/2)
Information packet (INF)
Frame length of the sender、slots assigned to the sender and its neighbors.
Suggestion packet (SUG)
The new node announces the frame length and its assigned slot.
Reply packet (REP)
Confirmation of a receiving SUG.

19. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

20. Dynamic TDMA Slot Assignment- Slot Assignment
Four steps.
Requesting the information on slot assignment in the contention area.
Setting the frame length and grasping slot assignment.
Selecting an assigned slot.
Announcement and Confirmation.

21. Slot Assignment (step 1)
Listen the DAT packet. => gets the position of the first slot in a frame and maximum frame length among all nodes in its contention area.
Send REQ in the first slot of the next frame.
=> neighbors transit to the control mode.
Neighbors transmit an INF in its assigned slot.
=> declare to its neighbors that the node has transited to the control mode.

22. Slot Assignment (step 2)
Collect INFs from all neighbors => set its frame length. (select the maximum frame length among all nodes in the contention area.
Create its own slot assignment information.

23. Slot Assignment (step 3)
The new node selects a slot assigned to itself by following three procedures.
Getting an unassigned slot (GU)
Releasing multiple assigned slots (RMA)
Doubling the frame (DF)

24. Slot Assignment (step 3) – GU、RMA

25. Slot Assignment (step 3) – DF
After doubling the frame length, the first slot in the latter half becomes an unassigned slot.

26. Slot Assignment (step 4)
Send SUG to its neighbors.
Neighbor updates its slot assignment information.
If its frame length is different from the SUG
=> change in the same way in “step 2”
Each neighbor sends a REP to its neighbors.
Confirmation of the SUG for the new node.
Announcement of updating the slot assignment information.
Exiting from the control mode for all neighbors of the sender.
Adopt the new slot assignment and restart data transmission.

27. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

28. Dynamic TDMA Slot Assignment- Detection of Conflict and its solution
A conflict of slot assignment occurs when a new node connects two or more nodes to which the same slot are assigned.
Solutions
Deleting a conflicting slot.
Dividing the assignment.
Doubling the frame and dividing the assignment.

29. Solution 1 and 2

30. Solution 3

31. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

32. Releasing Slot Assignment
When a node exits from the network, it releases slots assigned to it self and stops transmitting DATs.
Neighbor nodes release the slots assigned to the exited node from their slot assignment information.
Neighbor nodes release the slots assigned to nodes that have gone out of their contention areas due to the node’s exit.
Reconfiguring the slot assignment and send the updated information to their neighbors.

33. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

34. Performance Evaluation- Simulation Environment
Each node does not move.
A new node appears at a random position.
The number of nodes is initially 2, and increases one by one until the whole number of nodes in the network becomes 50.
For USAP => set frame length 50.
The new node is assigned the slot with the smallest slot number among all unassigned slots.

35. Performance Evaluation- Evaluation Criteria
The channel utilization of node i =
The average channel utilization is the average of channel utilization in whole network.

36. Performance Evaluation- Simulation Results

37. Outline Introduction USAP USAP-MA Dynamic TDMA Slot Assignment
Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution

38. Conclusion
In this paper, we have proposed a TDMA slot assignment protocol to improve the channel utililation.
Our protocol can enlarge the frame length, but cannot minify it.
The unfairness of the channel utilization.
How to accommodate the movement of nodes.