An Adaptive TDMA Slot Assignment Protocol

in Ad Hoc Sensor Networks

Akimitsu Kanzaki, Takahiro Hara and Shojiro NishioACM Symposium on Applied Computing, 2005

(ACM SAC’05)

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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

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Introduction

Motivation E-ASAP prevents the excessive increase of

unassigned slots By minimizing each node’s frame length.

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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

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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

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Related Work- USAP-MA(USAP-Multiple Access)

MILCOM’99

Frame Length= 8

Frame Length= 4

Frame Length= 8

Frame Length= 4

Double frame length

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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

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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

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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

CB

New node

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REQ

INF

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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

CB

New node

13

SUG

REP

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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

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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)

1 a2 b3 d4 c5 a6 b7 e

Double

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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.

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E-ASAP (Extend ASAP)

Each node assigns a slot to itself in the frame of the minimum length

Frame Length= 8

Frame Length= 4

hc

f

d

g

i

1j

5

6

4

2

1

3

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E-ASAP (Extend ASAP)

Information held by node h in E-ASAP

h 1 hop 2 hop

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E-ASAP (Extend ASAP)-Slot AssignmentSlot 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 a

re 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

a b

Unassigned slot

a b cd a b e

Multiple slots

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E-ASAP (Extend ASAP)

New node

1/83/4

3/4

0/4

2/4

1/4

a

bc d

eDoubleDouble

2/8 , 6/8

RMARMA

b

New nodeNew nodeGUGU

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E-ASAP (Extend ASAP)- Detecting of conflictDetecting of conflict

a

b

c

d

e

f g

3

1

2

3 5

4

4New node

conflict

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E-ASAP (Extend ASAP)- Solution to solve conflictSolution to solve conflict

Deleting a conflicting slot

Divide the assignment

Delete slot 3 of a

Divide slots

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Frame Length= 8

E-ASAP (Extend ASAP)-Solution to solve conflictSolution to solve conflict

Doubling the frame and dividing the assignment

Frame Length= 8Frame Length= 4 Double

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E-ASAP (Extend ASAP)- Releasing Slot AssignmentReleasing 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.

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E-ASAP (Extend ASAP)-SimulationSimulation

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

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E-ASAP (Extend ASAP)-SimulationSimulation

Average channel utilization

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E-ASAP (Extend ASAP)-SimulationSimulation

Control traffic

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E-ASAP (Extend ASAP)-SimulationSimulation

Setting delay (control mode changes to transmit mode)

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E-ASAP (Extend ASAP)-ConclusionConclusion

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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