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Delay Aware Link Scheduling for Multi-Hop TDMA Wireless Networks

Petar Djukic* and Shahrokh Valaee+

*University of California+University of Toronto, Toronto, ON, Canada

IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 17, NO. 3, JUNE 2009

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Outline

Introduction Network and transmission model TDMA scheduling Minimum length TDMA scheduling TDMA delay aware scheduling Simulation Conclusion

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Introduction

An important goal for TDMA scheduling algorithms is to find the minimum number of slots required to schedule requested end-to-end rates.

Although previous TDMA scheduling approaches can find minimum length schedules, they do not account for TDMA scheduling delay.

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Introduction

Scheduling delay occurs when packets arriving on an inbound link must wait for the subsequent frame to be transmitted on the outbound link.

Scheduling delay accumulates at every hop in the network, so end-to-end delay experienced on a path can be large.

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Introduction_ goal

Given an assignment of link bandwidths, what is the minimum length TDMA schedule that also minimizes end-to-end scheduling delay?

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Network and transmission model

TDMA network can be represented with a directed connectivity graph

is the set of nodes is the set of directed links

Network and transmission model

Notation:Ts is the duration of each slot.Nc slots reserved for the control traffic.Nd slots reserved for data traffic.

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Network and transmission model

Notation: rj is link rateP is the set of all paths found by the routing algorithmI(.) is the indicator functiongl is the requested end-to-end rate of connection

Notation:cj is capacity.h is the spacing between transmissions of different links.

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Network and transmission model

Notation: nj is the number of times the link transmits in the frame.

The actual rate

The request rate

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Wireless interfere model

Appear in 802.11

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Introduction

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Collision-free scheduling over N slots

Collision-free scheduling over N slots

Collision-free scheduling

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TDMA SCHEDULING

Conflict-Free Scheduling for Fixed Transmission Orders

Even though the general scheduling problem is NP-complete,if the transmission order is fixed, the scheduling problem haspolynomial complexity.

Conflict-Free Scheduling for Fixed Transmission Orders

ei ej

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9

4

-2

9 – 4 = 5

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Bellman-Ford Algorithm

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Multiple Link Transmissions in a Frame

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1

4

2

9

4

2

9

1

1

1

1

eiej

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-1

1

ek

4

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MINIMUM LENGTH TDMA SCHEDULING

The request rate

MINIMUM LENGTH TDMA SCHEDULING_ Linear Search Algorithm

Input : the number of slots in the data sub-frametopology information, link durations, slot duration

MINIMUM LENGTH TDMA SCHEDULING_ Linear Search Algorithm

[e1,e2,e3,…,em]

TDMA DELAY AWARE SCHEDULING_ End-to-End Scheduling Delay

if the conflict is traversed in the opposite direction

TDMA DELAY AWARE SCHEDULING_ End-to-End Scheduling Delay

TDMA DELAY AWARE SCHEDULING_ Min-Max TDMA Delay Scheduling

TDMA DELAY AWARE SCHEDULING_ Algorithm TH

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Simulation

802.16 frame duration is 10ms giving a total of 800 Orthogonal Frequency Division

Multiplexing(OFDM) symbols in each frame. 70 OFDM symbols are for the control sub-frame, 730

symbols for the data sub-frame. Each link transmission has an overhead of h=3 slots. the percentage of the frame used for centralized

scheduling to

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Simulation

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Algorithm-MM

Algorithm-TH

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802.16

Graph coloring

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Simulation

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Simulation

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Simulation

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Simulation

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Conclusions

This paper introduces TDMA delay aware scheduling for multi-hop wireless networks.

The proposed polynomial time algorithm that finds one-frame scheduling delay transmission orders on overlay tree topologies.

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Thank you~

TDMA DELAY AWARE SCHEDULING_ Modulo Operation Preserves Delay Properties

is the final transmission order