Transcript Dynamic TDMA Slot Assignment in Ad Hoc Network

Dynamic TDMA Slot
Assignment in Ad Hoc
Network
CN EE CCU
Speaker: 游千冊
2005/11/29
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Outline
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Introduction
USAP
USAP-MA
Dynamic TDMA Slot Assignment
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Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclusion
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Outline
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Introduction
USAP
USAP-MA
Dynamic TDMA Slot Assignment
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
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

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Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution
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Introduction(1/3)
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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.
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Introduction(2/3)
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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.
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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.
collision
R: 傳輸範圍
: host
R
R
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Mobile hosts within two hops from the host.
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Outline
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Introduction
USAP
USAP-MA
Dynamic TDMA Slot Assignment
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
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
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Frame Format
Packet Format
Slot Assignment
Detection of Conflict and its solution
Releasing Slot Assignment
Performance Evaluation
Conclution
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Unifying Slot Assignment Protocol
(USAP) (1/3)
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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)
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Unifying Slot Assignment Protocol
(USAP) (2/3)
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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
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Unifying Slot Assignment Protocol
(USAP) (3/3)
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When a new node joins the network, it is not
assigned any slots and does not have
information about neighbors.
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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.
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Outline
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

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
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USAP Multiple Access (USAP-MA)
(1/2)
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USAP-MA is an extension of USAP,
introduces ABC (Adaptive Broadcast Cycle)
In ABC, frame length and frame cycle can
change dynamically.
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USAP Multiple Access (USAP-MA)
(2/2)
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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.
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Outline
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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
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Dynamic TDMA Slot AssignmentFrame Format
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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.
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Outline
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
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
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Dynamic TDMA Slot AssignmentPacket Format (1/2)
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There are two modes, transmit mode and
control mode.
Transmit mode:
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Data packet (DAT)
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Frame length、slots assigned to the sender、maximum
frame length of the sender and its neighbor、data.
Control mode:
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Request packet (REQ)
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The new node requests the information on the frame
length and assigned slots of all nodes in its contention
area.
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Dynamic TDMA Slot AssignmentPacket Format (2/2)
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Information packet (INF)
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Suggestion packet (SUG)
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Frame length of the sender、slots assigned to the sender
and its neighbors.
The new node announces the frame length and its
assigned slot.
Reply packet (REP)
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Confirmation of a receiving SUG.
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Outline
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
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
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Dynamic TDMA Slot AssignmentSlot Assignment
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Four steps.
1.
2.
3.
4.
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.
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Slot Assignment (step 1)
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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.
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Slot Assignment (step 2)
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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.
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Slot Assignment (step 3)
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The new node selects a slot assigned to itself
by following three procedures.
1.
2.
3.
Getting an unassigned slot (GU)
Releasing multiple assigned slots (RMA)
Doubling the frame (DF)
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Slot Assignment (step 3) –
GU、RMA
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Slot Assignment (step 3) –
DF
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After doubling the frame length, the first slot
in the latter half becomes an unassigned slot.
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Slot Assignment (step 4)
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Send SUG to its neighbors.
Neighbor updates its slot assignment information.
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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.
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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.
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Outline
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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
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Dynamic TDMA Slot AssignmentDetection of Conflict and its solution
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A conflict of slot assignment occurs when a
new node connects two or more nodes to
which the same slot are assigned.
Solutions
1.
2.
3.
Deleting a conflicting slot.
Dividing the assignment.
Doubling the frame and dividing the assignment.
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Solution 1 and 2
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Solution 3
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Outline
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
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
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Releasing Slot Assignment
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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.
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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
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Performance EvaluationSimulation Environment
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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.
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Performance EvaluationEvaluation Criteria
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The channel utilization of node i = i
the number of slots assigned to node i
i 
the frame length of node i
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The average channel utilization is the average of
channel utilization in whole network.
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Performance EvaluationSimulation Results
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Outline
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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
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Conclusion
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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.
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