Downlink Scheduling for Multimedia Multicast/Broadcast over Mobile WiMAX Connection-oriented Multi-state Adaptation

Source:IEEE Wireless Communications Magazine ,2009/8Authors:Hongfei Du, Jiangchuan Liu, Jie Liang

Reporter: M9856020 陳煥文 M9856023 吳政霖 M9856026 陳鴻斌 M9856029 林佳彥 M9856031 蔡人喆 M9856034 施鎰升

Outline• ABSTRACT• Introduction• Background• MAC and QoS Scheduling in WiMAX• Connection-Oriented Multi-State

Optimization• Performance Analysis• Conclusion

ABSTRACT

• This article systematically examines the design issues and the state of the art of multimedia downlink scheduling in the multicast/broadcast-based WiMAX system.

• We propose a viable end-to-end framework, connection-oriented multistate adaptation, by considering cross-layer adaptations in source coding, queue prioritization, flow queuing, and scheduling.

Introduction

• WiMAX lie in its cost-competitive deployment and comprehensive quality of service support for large numbers of heterogeneous mobile devices with high-data rate wireless access.

• Digital multimedia broadcasting (DMB) have offered the network operator a platform to deliver multimedia services to a mass market.

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Introduction A novel concept of connection-oriented service

flow, supporting QoS for both uplink and downlink on a per service flow basis.

A viable end-to-end cross-layer framework, connection-oriented multistate adaptation(CMA), which adopts the service-oriented design on per-service-flow connections carrying multisession MBS.

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Background-Overview

6Multicast/broadcast WiMAX system architecture for MBS service delivery

Background-Overview

• The 802.16e radio interface adopts orthogonal frequency-division multiple access(OFDMA).

• WiMAX system in point-to-multipoint (PMP) mode, where the QoS is mainly enforced by the MAC and APP layers.

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Medium access control"Medium access control "is also called

Media access control.

The MAC include three sublayers. There are ：• Convergence sublayer• Common part sublayer• Security sublayer

WiMAX support two types of scheduling in MAC1.Downlink scheduling2.Uplink request/grant scheduling

e.g. Downlink scheduling procedures from Base station (BS)

We’ll describe MAC sublayer with two diagrams

The scheduling between SS and BS

SS ： Subscriber station- From the user sideBS ： Base stationCS ： Convergence sublayerCPS ： Common part sublayerUL-MAP ： Uplink-MAP

The scheduling of Uplink Channel

• Uplink request/grant scheduling was denoted the process that CS recieve a service request from SS and deliver the packets to CS.

• In the uplink channel it will build a scheduling for service classify when the connection was linked.

• The incoming Packet classified in different service classes when the packet pass through Convergence Sublayer (CS), and service data unit(SDUs) are assigned to appropriate connection in Common part sublayer (CPS).

The scheduling between SS and BS

SS ： Subscriber stationBS ： Base stationCS ： Convergence sublayerCPS ： Common part sublayerDL-MAP ： Downlink-MAP

The scheduling of Downlink Channel

Three sublayers in MACConvergence sublayer

For packet classification with incoming packet from Upper layer.

Common part sublayerConnection assignment base on the different service request, and assigned to appropriate connection base on the priority.

Security sublayerProvide security functions, such as secure key exchange and encryption on the receive PDUs

Qos-Based Scheduling in WiMAX Qos Mechanism

• The success of WiMAX lies in its comprehensive supports for a variety of dominant broadband services in a suite of QoS scheduling types.

1.Unsolicited grant service – (UGS)2. Extended real-time polling service – (ertPS)3. Real-time polling service – (rtPS)4. Non-real-time polling service – (nrtPS)5. Best effort – (BE)

Unsolicited grant service (UGS): UGS transmit periodic real-time character of the fixed data. It requires reserved traffic rate, maximum latency, and tolerated jitter.Such as T1/E1 transport.

Extended real-time polling service (ertPS):It’s built on the efficiency of both UGS and rtPS, reduces overhead and access delay of rtPS, and improves uplink resource utilization of the UGS. Such as voice of IP (VoIP).

UGS scheduling service uplink grants allocation mechanism

Real-time polling service (rtPS): It supports variable bit rate (VBR) traffic via minimum reserved and maximum sustained traffic rates, and requires tolerable stringent latency constraints. Such as MPEG audio/video streaming and video conferencing.

rtPS scheduling service uplink grants allocation and request mechanism

Non-real-time polling service (nrtPS): Delay-tolerant streams with variable-sized packets, for which only minimum reserved and maximum sustained traffic rates are required.Such as FTP.

Best effort (BE) service: BE services" are handled on a space available basis and do not require tight latency/ jitter constraints, with upper limited bandwidth consumption via maximum sustained traffic rate. Such as HTTP and email.

WIMAX SCHEDULING: STATE OF THE ART

• Weighted Round Robin(WRR)• Deficit Round Robin (DRR)• Weighted Fair Queue(WFQ)• Earliest Deadline First (EDF) • Max C/I

Weighted Round Robin(WRR)

Weighted Fair Queue(WFQ)

Deficit Round Robin (DRR)

Earliest Deadline First (EDF)

Max C/I (carrier-to-interference)

The main drawbacks of this scheduler are mainly its inherent unfairness and coverage limitations. This scheduler essentially ranks all the users according to their instantaneous carrier-to-interference (C/I) ratios. This scheduler is optimal in obtaining the maximum network throughput

Scheduling problem in WIMAX

• QoS differentiation:class,herterogeneous service

• Connection-oriented:scheduling and flow diff- erentiation• Guarantee:monitor instaneous perfomance• Scheduling:chanel vibrations,queuing dynamic• Adapt transmitter side settings

Connection-OrientedMultistate Optimization

Optimization Criteria

QoS profile (PQoS)

• It jointly considers end-to end delay factor ,packet loss rate (PLR) factor (FEP), and E2E throughput factor for the ith session and is defined as

PQoS(i) = FED(i) FEP(i) FET(i)⋅ ⋅ where each factor reflects the difference

between the instantaneous performance and its application-specific target

Queuing state profile (PQS)

It considers multiple dynamic queuing metrics in terms of queuing delay, buffer occupancy, and overflow probability.

Channel state profile (PCS)

It reflects the overall reception condition for each session based on the reception conditions for all subscriber stations (SSs) within the MC/BC group.

Problem Formulation

Possible state element

• Dynamic metric

• Threshold metric

• Distortion metric

• Adaptation metric

Queuing State

• Queuing delay factor (FQD)

• Buffer occupancy factor (FBO)

• Overflow probability factor (FOP)

Effective Reception

The SS performs the following two important tasks:

1. Monitors the CSI in terms of received SINR continuously, and sends this information to the BS 。2. Measures the instantaneous E2E performance in terms of delay, PLR, and throughput

The instantaneous E2E performance is thencompared with QoS constraints, and the followingmeasures are determined:

1. E2E delay factor

2. E2E throughput factor

3. E2E PLR factor

PCS(i) = Prob{PCS(i,j) | PCS(i,j) > PCS*(i,j)}

Adaptive Queue Prioritization

Packet Classification

• in MC/BC-based WiMAX, the packets received by the BS and destined to the downlink are sorted by the packet classification before being buffered into one of the per class queues in the BS.

• Video streams are encoded via an H.264/SVC encoder before transmission together with other download services.

CMA

• Multiple connections/queues are then subject to scheduling functions based on the serving orders derived from the CMA module.

• The CMA considers multiple important metrics.

Two important performanceindices

• Demanding index (DI):– how much resource the flow is demanding

• Satisfaction index (SI):– how much resource allowance the flow has for

sharing with other flows

Source Coding Adaptation• Scalable Video Coding (SVC) extension of

H.264/AVC for cross-layer optimization.• To deliver video stream in wireless network is

very difficult .• SVC can overcome the signal fading, bit error

and packet loss in wireless network.

SVC

• With SVC, a MBS video stream is split into a base layer (BL) and multiple enhancement layers (ELs) that refine the video quality.

• All MC/BC connections to be originated from a single BS with no connection sharing or handoff events.

H.264/SVC

• Temporal Scalability

H.264/SVC

• Spatial Scalability

H.264/SVC

• SNR Scalability

Adjustment

• We assume the BL is successfully obtained by all users by applying robust modulation and coding or FEC/automatic repeat request (ARQ).

• We associate different Real-Time Transport Protocol (RTP)payload types to the BL and the ELs.

Suggestion

• Performing BL/EL rate control based on the QoS satisfaction of each SS, rather than unified treatment on all SSs.

• The SSs with undersatisfied QoS will be assigned more important streams.

Performance Analysis

• Simulation consists of two parts ：– H.264/MPEG-4 AVC JM reference software– System-level simulation model in NS-2

• An indicative simulation scenario is set to ：a total of 20 SSs located randomly within 5 × 5 km2, with the BS located at the center of the area.

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Performance Analysis• CID-SFID mapping settings to ：

• CID 1-SFID 1: （ e.g., MPEG video ）BL video stream at 360 kb/s, in VBR rtPS with 1.08 Mb/s sum stream rate• CID 2-SFID 1: （ e.g., MPEG video ）EL video stream at 720 kb/s, in VBR rtPS with 1.08 Mb/s sum stream rate• CID 3-SFID 2: （ e.g., FTP ）CBR nrtPS services at 360 kb/s• CID 4-SFID 3: （ e.g., e-mail ）CBR BE services at 360 kb/s

Performance Analysis

• Four schemes and CMA scheme ：– Weighted Round Robin(WRR):

proportion, weight– Weighted Fair Queue(WFQ):

regulating, weight– Earliest Deadline First (EDF):

deadline, packet– Max C/I: upper bound of system capacity

Performance Analysis

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The 95th percentile CDF of E2E delay for rtPS services under different downlink scheduling schemes

Performance Analysis

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Variance of overall throughput ratios under different downlink scheduling schemes

Conclusion• The framework performs simultaneous

adaptations across protocol stacks on source coding, queue prioritization, flow queuing, and scheduling.

• The heterogeneity in wireless link variations, queue fluctuations, and reception diversities are incorporated.

• Simulation studies on the proposed framework showed improved performance on delay, throughput, and fairness.

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Thanks for your listening