Quality of Service Schedulingfor 802.16

Broadband Wireless Access Systems

Sih-Han Chen Department of Computer Science and Information EngineeringNational Taipei University of Technology2006.11.21

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Outline Overview IEEE 802.16 IEEE 802.16 MAC and QoS Proposed QoS strategy Simulation result Summary and Reference

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Wireless TechnologiesBandwidth

1 Gbps

100 Mbps

10 Mbps

1 Mbps

PAN LAN MAN WAN<1m 10m 100m Up to 50Km Up to 80Km

802.15.1Bluetooth

Wi-Fi802.11a/g

Wi-Fi802.11b

802.15.3High Speed

WirelessPAN

Wi-MAX802.16

(802.16-2004 & 802.16e)

4G

3G

2.5G

IEEE 802.15 IEEE 802.11 IEEE 802.16 3GPP

PAN: Personal area networksMAN: Metropolitan area networks

LAN: Local area networks Wide area networks

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IEEE 802.16 Operation Mode

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IEEE 802.16 TDD frame structure

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DL-MAP and UL-MAP

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Downlink Subframe

Broadcast

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Uplink Subframe

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Outline Overview IEEE 802.16 IEEE 802.16 MAC and QoS Proposed QoS strategy Simulation result Summary and Reference

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IEEE Std 802.16 MAC Protocol Layering

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Service Specific Convergence Sublayer

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MAC Convergence Sublayer Functions:

Classification processing of higher-layer PDUs

Delivery to proper MAC SAP Receives CS PDUs from peer

Two sublayers specified: ATM convergence sublayer Packet convergence sublayer

Service Specific Convergence Sublayer

(CS)

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ATM Convergence Sublayer ATM cells mapped to MAC frames Differentiates Virtual Path switched / Virtual

Channel switched ATM connections Assigns channel ID (CID) Can perform Payload Header Suppression

(PHS)

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Packet Convergence Sublayer Used for all packet-based protocols,

such as IPv4, IPv6, Ethernet, and VLAN Similar functions as ATM convergence

sublayer, including PHS

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MAC Common Part Sublayer Defines multiple-access

mechanism Functions ：

connection establishment connection maintenance Call admission control bandwidth request bandwidth allocation

MAC Common Part Sublayer

(MPC)

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Security Sublayer Two component protocols

Encapsulation protocol for data encryption

Privacy key management (PKM)

describes how the BS distributes keys to client SS

Security Sublayer

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Media Acces Control (MAC) Connection orienteded

Service Flow(SF) Connection ID (CID)

Channel access: UL-MAP

Defines uplink channel access Defines uplink data burst profiles

DL-MAP Defines downlink data burst profiles

UL-MAP and DL-MAP are both transmitted in the beginning of each downlink subframe (FDD and TDD).

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Bandwidth Request SSs may request bandwidth in 3 ways:

Use the ”contention request opportunities” interval upon being polled by the BS (unicast, multicast or broadcast poll)

Send a standalone MAC message called ”BW request” in an already granted slot

Piggyback a BW request message on a data packet

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Bandwidth Allocation BS grants/allocates bandwidth in one of

two modes Grant Per Subscriber Station (GPSS) Grant Per Connection (GPC)

Decision based on requested BW, QoS parameters and available resources

Grants are realized through the UL-MAP

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Service Classes Unsolicited Grant Services (UGS):

Constant Bit Rate (CBR) services, T1/E1 emulation, and Voice Over IP (VoIP)

Real-Time Polling Services (rtPS): real-time services variable size data packets MPEG video or VoIP with silence suppression.

Non-Real-Time Polling Services (nrtPS): Used for delay tolerant traffic requiring some minimum data rate FTP

Best Effort Services (BE) : Used for streams with no rate guarantees. WEB , HTTP

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QoS mechanisms Classification

Mapping from MAC SDU fields (e.g destination IP address or TOS field to CID and SFID

Call admission Control Scheduling

Downlink scheduling module Uplink scheduling module

No algorithms defined in standard

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IEEE 802.16 QoS Architecture

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Call Admission Control in IEEE 802.16 Admission control

To ensure required QoS is guaranteed while admit a new connection

Assessment of admission connection Usually use traffic descriptor and effective bandwidth

But… Traffic descriptors may not reflect the real traffic Traffic descriptors is very simple (peak rate, avg. rate, etc…) Users may overestimate their requirements QoS is uneasy to guarantee

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Outline Overview IEEE 802.16 IEEE 802.16 MAC and QoS Proposed QoS strategy Simulation result Summary and Reference

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Hierarchical and Distributed QoS Architecture

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Scheduling Algorithm at BS Define two types of queue

Type (I) queue Type (I I) queue

Admission Control

Scheduling Algorithm

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At BS Scheduling for Type I queue Type I queue Use for

UGS Dedicated request opportunities for rtps and nrtp

s

Guarantee grants to be scheduled without interrupt

First-in First-out (FIFO) ， is employed

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At BS Scheduling for Type II queue Type II queue Use for

rtPS ， nrtPS ， and BE

To Guarantee Minimum bandwidth for each service flow Fairness to distributing excess bandwidth

To propose a fair queuing algorithm

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Type II QueueBandwidth Allocation

Grant Per Connection (GPC) BiMIN ： the minimum reserved bandwidth

for connection i BRi ： bandwidth currently demanded by th

e connection

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Call Admission Control (CAC) The sum of minimum reserved bandwidth

for all the connection should not exceed the available bandwidth B

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Fairness to distributing excess bandwidth

i queue connection of weightthe :

i queue connection to allcated bandwidth excess of amount the :

bandwidth excess the :

bandwidth available total the :

wbBB

i

EX

i

EX

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A Extended Issue It also can be wasted when ：

Certain of connections don’t need so much bandwidth

Solution ： It allows the empty connection queue to contribut

e its unused portion to the next round of excess bandwidth allocation

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Scheduling Algorithm at SS WHY ?

Due to the large Round Trip Delay (RTD) Possible collision occurred in the uplink channel

So…BS has only limited or even outdated information about each uplink connection

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At SS Priority of scheduling service

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At SS UGS Queue Scheduling Properties

Critical delay Critical delay jitter

Firstly guarantee the bandwidth

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At SS rpPS Queue Scheduling Properties

Should meet tight delay bound Each packet of rtPS should be mark a deline

t ： arrival time tolerated delay ： Maximum Latency for each service flow

Schedule base on the deadline stamp

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At SS nrtPS Queue Scheduling Properties

Target at maintaining throughput Each packed with a virtual time stamp When a new packer arrives in ， the virtual time

must be calculated at first

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Virtual Time Stamp

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At SS BE Queue Scheduling Properties

There is no QoS guarantee required

A simple FIFO mechanisms is applied

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Outline Overview IEEE 802.16 IEEE 802.16 MAC and QoS Proposed QoS strategy Simulation result Summary and Reference

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Simulation Environment Used NS2 PMP MAC opera

tion TDD-OFDM One BS and 20

SSs

SS UGS rtPS nrtPS BE

First 1 1 1 1

Second 1 1 1 1

Third 2

Fourth 2

Fifth 2

Other v

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PHY layer parameters

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The End-to-End Delay

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The End-to-End Delay (for UGS_1)

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Compare Delay of rtPS_1 service

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For rtPSDifferent number of background SS

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Throughput of nrtPS

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Outline Overview IEEE 802.16 IEEE 802.16 MAC and QoS Proposed QoS strategy Simulation result Summary and Reference

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Summary Introduced a hierarchical distributed QoS At BS

Guarantee the minimum bandwidth Fairness distributing excess bandwidth

At SS Flexible QoS support four service flow Reduce the delay of real-time application Guarantee the throughput of non-real-time applicati

on

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References[1] Sun, J.; Yanling Yao; Hongfei Zhu,“Quality of Service Sched

uling for 802.16 Broadband Wireless Access Systems” Vehicular Technology Conference, 2006. VTC 2006-Spring. IEEE 63rd Volume 3, 2006 Page(s):1221 - 1225

[2] Jayaparvathy, R.; Sureshkumar, G.; Kanakasabapathy, P., “Performance evaluation of scheduling schemes for fixed broadband wireless access systems”,2005 13th IEEE International Conference on Volume 2, 16-18 Nov. 2005 Page(s):6 pp.

[3] IEEE 802.16 Standard (2004), "IEEE Standard For Local and Metropolitan Area Networks - Part 16:Air Interface for Fixed Broadband Wireless Access Systems".

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OFDM Frame Structure with TDD:PMP mode

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Service Specific Convergence Sublayer

The service specific convergence sublayer (CS) provides any transformation or mapping of external network data, received through the CS service access point (SAP)

Object : classifying external network service data units (SDU) and associating them to the proper service flow identified by the connection identifier (CID)

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IEEE 802.16 Scope :

Specifies the air interface, MAC (Medium Access Control), PHY(Physical layer)

Purpose : Enable rapid worldwide deployment of cost-effective

broadband wireless access products Facilitate competition in broadband access by providi

ng alternatives to wireline broadband access Main advantage :

Fast deployment, dynamic sharing of radio resources and low cost

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IEEE 802.16 Deployment