Multicast Polling and Efficient VoIP Connections in IEEE 802.16 Networks

Olli AlanenTelecommunication LaboratoryDepartment of Mathematical Information Technology University of Jyvaskyla, FINLAND

ACM MSWiM 2007

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Outline

Introduction Contention resolution process Multicast polling Simulation Conclusions

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Introduction

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Introduction

UGS rtPS ertPS nrtPS BE

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Contention resolution process

802.16-2004 and 802.16eBEnrtPSertPS

Contention resolution mechanism when the connections have some packets in the uplin

k buffers, and no slots are allocated for them

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Contention resolution process

The worst case MAC delayno downlink part

C1

Tf

2 T‧ f

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Contention resolution process

The worst case MAC delay

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Contention resolution process

The worst case MAC delay for the packet is:

Where i equals the last possible frame where contentionresolution can occur.

FPS is the Frames per second value and it isstatically set at the base station.

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Contention resolution process

In a particular case where backoff start and backoff end are set to equal

where B is the value of the backoff start and end.

the number of request opportunities per frame (N)

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Multicast polling

Each SS can belong to one or zero polling groups

The memberships are managed dynamically

Two management messages MCA-REQ and MCA-RSP

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Multicast polling

When there is insufficient bandwidth for unicast polling multicast polling

Multicast polling is only allowed to be used with nrtPS ertPS BE

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Multicast polling

The decision about the sizes of the polling groups is also important when setting them up

the probability p for successful transmission for an SS:

N: the number of connectionsW: the size of the backoff window

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Simulation

NS-2 simulator Packing Fragmentation management signalling ARQ initial ranging 5 service classe Scheduling dynamic service flow management contention resolution process PHY layer

• OFDM and OFDMa PHY layers

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Simulation

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Simulation scenario 1

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Simulation scenario 1

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Simulation scenario 1

I: VoIP connections:10BE connections:0Unicast polling

How much bandwidth do the VoIP connections take

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Simulation scenario 1

II:BE connections:50VoIP connections: unicast polling with

1 polling slot in ertPS

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Simulation scenario 1

III: VoIP connections: exclude ertPS polling

regular broadcast contention mechanism

The backoff parameters are adjusted to minimize the packet loss, with the price of lost delay guarantees

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Simulation scenario 1

IV: Backoff parameters are changed to serve sm

aller MAC delays with the cost of decreased utilization

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Simulation scenario 1

V:VoIP connections:

broadcast Multicast Polling

backoff parameters are now adjusted to guarantee 15ms MAC delays

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Simulation scenario 1

VI:MAC delay of 20ms is now guaranteed

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Simulation scenario 1

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Simulation scenario 2

24 VoIP users

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Simulation scenario 2

smaller group equals tolesser collisionsless packet lossthe size of the UL-MAP↓

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Simulation scenario 2

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Simulation scenario 3

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Simulation scenario 3

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Simulation scenario 3

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Conclusions

How multicast polling groups can be used to achieve a better quality of service

This paper proposition is to use separate multicast polling groups for service classes with different QoS requirements set the backoff parameters based on the delay and lo

ss targets Different delay requirements can also be guara

nteed with multicast polling

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