Multimedia Wireless Communication Networks

Architecture and resource management

Multimedia Wireless Networks and Applications

High data transmission rateAdapt to high mobilityWide coverage area and seamless roaming among different systemsHigh capacity and low bit costEfficient resource control to provide QoS for Multimedia ApplicationsDynamic spectrum assignmentSoftware radio and smart radio that can accommodate multiple systems

Access Technology for Multimedia Support

LAN access: Ethernet, Fast EthernetFor home user to have high Internet connection: solve the “last mile” problem.Digital Subscriber Line (DSL)

Use regular phone line to achieve high speeds (e.g 1.5Mbps)Cable modem

Use TV cable to achieve high speeds. 3G wireless cellular network

144k-384 kbps for high mobility users with wide coverage and, 2Mbps for low mobility users with local coverage.Support of multimedia services a requirement

High data transmission rate: 10-20Mbit/s for 4G cellular system and higher rate for WLAN (IEEE 802.11b, IEEE 802.11a)

Interworking Between Different Access Systems

Software Radio and Smart Radio

Software radio is the solution to realize the convergence of multiple wireless access technologies.Corresponding software programs can be download into the mobile station in accordance with the user’s wireless system.Problems still exist

Large volume of software depends on the required system.The confidential techniques may leak out when software programs are downloaded.

Issues of QoS

User’s expectations and challengesSpeed (throughput, bit rate) : Variable link bandwidth due to statistical multiplexing and changing channel conditions.Accuracy (error rate, loss rate): Packet losses due to RF environment and buffer overflow.Latency : Variable queueing delay due to scheduling and RF condition.Availability (blocking, setup time): Control plane signaling and mobile processor capacity.Reliability (call dropping, out rage): Mobility management and network restoration strategy.

QoS Engineering for Multimedia Wireless Network

Traffic characterization – voice, web-browsing, WAP, streaming videoAdmission control and network resource allocationServer/link scheduling and traffic policing/shapingQoS mapping between networks and between layersService level agreements and policy managementRadio channel selection and bandwidth allocationRF power control and rate control among usersRF resource set-up and tear-down strategiesTraffic engineering and network design

Traffic Management

What is traffic management?It is a set of policies and mechanisms that allow a network to efficiently satisfy a diverse range of service requests.It includes admission control, scheduling, buffer management and flow control, which are important to provide QoS.

Admission Control

To adapt to the multimedia applications in the wireless environment, the admission control must own following attributes:

Stability of the provided QoS (blocking/BER/delay)Adaptability in the varying wireless channel conditionAbility to be reconfigured and extended for new servicesSimplicity and minimization of processing time

Parameter-Based Admission Control (PBAC)

PBAC schemes use a priori traffic specification to determine the parameters of deterministic or stochastic models.Deterministic models, including the peak-rate and worst-case models, reserve bandwidth to meet even the most critical conditions, which results in low bandwidth utilization.Stochastic models utilize the concept of equivalent bandwidth that is based on the statistic approximation of incoming traffic, and ensure that the outrage probability is below the defined threshold. Stochastic models can achieve high bandwidth utilization.

Measurement-Based Admission Control (MBAC)

MBAC relies on the measurement of actual traffic load and QoS performance in making admission decisions.MBAC provides higher bandwidth utilization and is more suitable to support real-time applicationsAdmission decisions are made by

Measuring the actual traffic load of existing flowsUsing a priori admission policy to determine whether the new flow is admitted or rejected

Scheduling Schemes

Why do we need scheduler in networks?Various multimedia applications emerge with diverse QoS requirements, e.g. the voice and web browsing have different throughput and delay requirements.To support different QoS requirements, scheduler operates among sessions to ensure that proper resource is allocated for sessions with their QoS requirements.

Fair Scheduling

Scheduling discipline allocates a resourceIntuitively

each connection gets no more than what it wantsthe excess, if any, is equally shared

provides protectiontraffic hogs cannot overrun othersautomatically builds firewalls around heavy users

Scheduling in Wireless Multimedia Networks

Various multimedia applications have diverse QoS requirements, e.g. the voice and web browsing have different throughput and delay requirements.The existing wireline scheduling schemes may not be applied to the wireless networks due to the time-varying and location-dependent wireless channelsExtra information must be exchanged between mobile station and base station to make the scheduling possibleThe scheduling scheme must be effective to save the limited battery life of mobile stationHandoff and bursty errors could result in unfairnessThe interference must be considered in CDMA system to meet the required SIR when multiple users are scheduled

Components of Scheduler

Scheduler

Channel StateMonitor/Predictor

IdealModel

Compensation

Transceiver

Session 1

Session 2

Session N

Components of Scheduler

An error free ideal model that describe how the algorithm provides service with error-free channels.A compensation model that provide “fairness” among sessions depending on their class and requirements (e.g. delay-sensitive interactive applications).Separate packet queues for different sessions that can support, e.g. delay-sensitive or error-sensitive.Channel state predictor that detects the channel conditions of all backlogged sessions.

Scheduler of TDMA Wireless System

Session 1

Session 2

Session 3

Scheduler

Time Slot

Only a single user is scheduled for transmission in a time-slot.

Scheduler of CDMA Wireless System

Session 1

Session 2

Session 3

Scheduler

ScheduledTransmit Rate

Time Slot

Multiple users are scheduled for transmission at a time-slot.

CDMA Scheduling Algorithms-- Compensation procedure

C

Assigned

Power Index

C

Power IndexCapacity

AssignedPower Index

Compensated

Power IndexGiven up

rate

lagging leading lagginglaggingleading leading

The error-free ideal system Iteratively distribute the system power index to obtain high resource utilization

Make the adjustment to achieve fairness

Example: Influence of Wireless Environment on Video

Unreliability: Unlike wired links, wireless channels are more noisy and have fades, making the BER very high, which can have devastating effect on video quality.Bandwidth Fluctuation: Bandwidth fluctuation may be caused when

User moves from WLAN to WWAN (Corresponding bandwidth changes from Mb/s to kb/s)Handoff happens, the new cell may not have enough resource to support the previous service qualityinterference variesThe distance to the base station changes

Heterogeneity:In the multicast case, all receivers are forced to receive the same content despite their channel qualities, processing power etc. That means multicast service loses the flexibility of QoS negotiation.

Adaptive Wireless Video Transmission Framework

The adaptive framework consists of three basic components:Scalable video codingNetwork-aware end systemAdaptive service

Sender Side

Network-awareEnd System

Receiver Side

Network-awareEnd System

Adaptive Service(Application-aware Networks)

Scalable Video RepresentationsScablable

Video EncoderScablable

Video Encoder

Scalable Video Coding

Following example encodes the raw video sequence into three layers: one base layer and two enhancement layer.The base layer can be can be independently decoded and it provides basic video quality.The enhancement layers can only be decoded together with the base layer and they further refine the quality of the base layer.

Layered Codec

+

+

Decoder

Decoder

Decoder

Layer 0

Layer 1

Layer 2

64k/s

256k/s

1Mb/s

Network-aware End System and Adaptive Service

Network-aware end system consists of two elements: network monitoring and adaptation.Network monitoring

Network monitoring aims to collect information about network status, like the available bandwidth and BER. This information could be sent to the end system from the base station.

AdaptationBy the known network information, the end system may choose what layers video is to be transmitted since multiple enhancement layers in the high BER condition can only result in worse video quality.The objective of adaptive services is to achieve smooth change of perceptual quality in the presence of bandwidth fluctuations in wireless channels.Reserve a minimum bandwidth to meet the demand of the base layer. As a result, the perceptual quality can always be achieved at an acceptable level.Adapt the enhancement layers based on the available bandwidth and the fairness policy. In other words, it scales the video streams based on resource availability and the fairness policy.