hamidr. rabiee mostafasalehi, fatemehdabiran...

Wireless Multimedia Networks

Hamid R. RabieeMostafa Salehi, Fatemeh Dabiran, Hoda Ayatollahi

Spring 2011

2

Outlines

²Wireless & Multimedia² Motivations

² Requirements

² Challenges

² Solutions

²Hot topics² Video Streaming over IEEE 802.11

² Video Streaming In Mobile Ad-hoc Networks

² Wireless Multimedia Sensor Networks (WMSN)

² IPTV over WiMAX

Digital Media Lab - Sharif University of Technology

Wireless Networks

² A Wireless revolution is set to transform the world telecommunications

Industry.

² Wireless networks are a class of networks that use infrared or radio

channels as the transmission medium.

² Classification of growth of wireless networks:

² First generation analog voice wireless networks.

² Second generation digital voice/data networks are under development.

² Third generation networks are designed to carry multimedia traffic.

3 Digital Media Lab - Sharif University of Technology

Wireless Classes

² Wide Area Networks (WANs)

² greater mobility, but lower data rates

² Cellular networks

² Local Area Networks (LANs)

² higher bandwidths, but a limited coverage

² Wireless LANs (WLANs) and HiperLANs

² Personal Area Networks (PANs)

² deployed for cable replacement

² Bluetooth and Ultra Wide Bands (UWBs)


Wireless & Multimedia

² Strong trends in using multimedia wireless technologies in

recent years² Wide-spread use of wireless technologies

² Multimedia applications become popular

² new hardware opportunities allow for more efficient use of

energy in mobile devices


Motivations

² Why should we study/research multimedia topics?

² Huge interest and opportunities

² High speed Networks

² Powerful (cheap) computers (Laptops … cell phones)

² Abundance of multimedia capturing devices (cameras, speakers, …)

² Tremendous demand from users (mm content makes life easier, more

productive, and more fun)

² Here are some statistics …


Motivations

² YouTube: fastest growing Internet server in history

² Serves about 300—400 million downloads per day

² Has 40 million videos, most of them (87%) less than 5 min

² Adds 120,000 new videos (uploads) per day

² CBS streamed the NCAA March Madness basketball games in 2007 online

² Had more than 200,000 concurrent clients

² And at peak time there were 150,000 Waiting

² Plus …

² Pretty much all major web sites have multimedia

clips/demos/news/broadcasts/…


Multimedia Requirements

² As mentioned before:²² SynchronizationSynchronization :video and audio should be synchronized to within 20

msec.

² Throughput:Throughput: the minimum video bit-rate to be supported is 32 kbps. Video

rates of 128 kbps, 384 kbps and above should be supported as well.

² DelayDelay: the maximum end-to-end transmission delay is defined to be 400

msec.

² JitterJitter: the maximum delay jitter (maximum difference between the average

delay and the 95th percentile of the delay distribution) is 200 msec.

²² Error RateError Rate: the video conferencing system should be able to tolerate a

frame error rate of 10−2 or bit error rate of 10−3 for circuit switched

transmission.


Multimedia Service Requirements

² Resource sharing

²Multimedia data integration

² Local intelligence and autonomy

² Graphical interfaces

² Vendor independence


Wireless Multimedia Transmission Requirements

² To achieve a high level of acceptability, several key

requirements need to be satisfied by multimedia streaming

solutions

²² easy adaptability easy adaptability to wireless bandwidth fluctuations

²² robustnessrobustness to partial data losses and high packet error rates

²² support for heterogeneous support for heterogeneous wireless clients with regard to

their access bandwidths, computing capabilities, buffer

availabilities, display resolutions, and power limitations.


Challenges in Wireless Multimedia

² Network Challenges² Heterogeneous Networks

² bandwidth, reliability, and receiver device characteristics

² Delay

² queuing, propagation, transmission, and processing delays

² Lost or discarded Packets

² complexity/power limitations or display capabilities of the receiver

² Packet loss up to 10% or more

² Variations in Channel Condition

² different access technologies, multipath fading, , cochannel interference,

noise, mobility, handoff, competing traffic from other wireless users

² Finite BW resources


Challenges in Wireless Multimedia

²Device Challenges²Mobility

² Hand off

² Adaptive Decoding² Optimizing rich digital media for mobile information devices with

limited processing power, limited battery life and varying display

sizes


Solution for the improvement of multimedia communication over wireless Networks

² High performance local and metropolitan area networks

has to be designed including control schemes which

provide high throughput while simultaneously supporting

real time services.

² The topic of multimedia QoS is very broad and there is an

extensive pool of solutions in the literature.

² In this present, we only mention some of these solutions.


QoS on Wireless Networks

² A multitude of protection and adaptation strategies exists

in the different layers of the Open Systems Interconnection

(OSI) stack² Data Link-Layer QoS

² Network-layer QoS

² Application-layer QoS

² End-user QoS


QoS on Different Layers

² Data Link Layer QoS² Concerned with

² Network Layer QoS² Concerned with reliable and fast delivery of multimedia data over the wireless

technologies

² Application Layer QoS² Concerned with the quality of the multimedia encoding, delivery, adaptation, decoding

and play out on the client device

² End-user QoS ² Concerned with the end-user experience in terms of audio and visual quality

² Cross-layer solutions² QoS schemes implemented at each of these layers have an effect on each other


16

QoS Support required at every layer

² Physical Layer

² Robust modulation

² Link adaptation

² MAC Layer

² Offer priorities

² Offer guarantees (bandwidth, delay)

² Network Layer

² Select “good” routes

² Offer priorities

² Reserve resources (for guarantees)

² Transport Layer

² Attempt end-to-end recovery

when possible

² Application Layer

² Negotiate end-to-end and with

lower layers

² Adapt to changes in QoS


17

QoS Flavors

²Similar to RSVP in the Internet

²Has to implement connection admission control

²Difficult in WMNs due to:²Shared medium (see

provisioning section)²Fading and noise

²Similar to diffserv in the Internet

²Offers classes of services²Generalization of

fairness²A possible

implementation on next slide

Guarantees Priorities


Application Layer Solutions

² There are several aspects to application-layer QoS that deal with all stages of

the applications lifecycle:

² Encoding

² The choice of right encoding settings

² Delivery

² Adaptation

² Adaption Capabilities are used to minimize the effects of poor network conditions

² Decoding

² Error Correction & Concealment

² On the client device

² interpolate the missing multimedia data from the received data in order and mask these

errors to improve the end-user perceived quality


End User QoS

² End-user QoS is the primary goal of application-layer QoS schemes and a

somewhat secondary goal of network-layer QoS schemes

² methods for assessing end-user QoS:

² subjective assessment and testing

² objective assessment and testing


HOT TOPICS

Video Streaming over IEEE 802.11

Video Streaming In Mobile Ad-hoc Networks

Wireless Multimedia Sensor Networks (WMSN)

IPTV over WiMAX


Hot Topics

²In this section, we cover some hot topics!² Video streaming over 802.11

² Video Streaming In Mobile Ad-hoc Networks

²Wireless Multimedia Sensor Networks (WMSN)

² IPTV over WiMAX


VIDEO OVER 802.11


Motivation for video over 802.11

² The number of homes with TV is greater than the number

of homes with Internet

² The average US home has 3 TVs

² 802.11 must work when every home is simultaneously

using their network

² People are used to high-quality video

² The potential market is huge


Use Cases

• Many applications including … – Delivering multiple HD streams to several receivers– Displaying stored digital contents from media servers to display devices– Browsing contents in distributed devices through big screen TVs

Home PC

STB (Cable TV access)

DTV

Wireless AP(Internet gateway)

Digital cameraCamcorder

PMP

DVD player

Projector

Home theater(AV receiver)

24Digital Media Lab - Sharif University of Technology

Transport Stream

I Frame P Frame B Frame

P Frame PayloadPES Header

SPH TS Header TS Payload ...

Variable length

Fixed lengthSPH TS

HeaderTS

Payload

MAC header

IP header

UDP header PayloadRTP

header


One TS contains audio, video, data

TS Header (4 bytes) has an adaptation field control. This is used among other things to identify the presence of PCR (Program Clock Reference) following the header.


From video frames to 802.11 packets

²Video frames typically span multiple 802.11

packets

²TS header may contain PCR – critical for keeping

audio/video in sync² if lost, quality suffers dramatically

²The effect of 802.11 packet loss is different

depending upon its contents


Video over Wireless Challenges

² Hey, it is wireless

² Interference, path loss

² Limited number of channels in unlicensed bands

² Channel characteristics constantly change (dynamic)

² Medium access non-deterministic (802.11 is originally designed for data)

² STA physically moves in the same BSS

² Inter-stream synchronization

² Between audio rendered at remote speakers and video

² Between one video stream and multiple audio streams


Current 802.11 Mechanisms

² Distributed medium access (EDCA)

² prioritization

² Centralized medium access (HCCA)

² admission control and bandwidth reservation

² Direct Link

² Dynamic channel selection (802.11h)

² RRM/Management (802.11k/v)

² HT (802.11n)

² PHY techniques for improved robustness


802.11k&v Features for Video

² 11k: Frame Request/Report identifies STAs/APs (channel survey).

² 11k: Location (LCI) Request/Report may provide location information

to sort STAs into in-home or external.

² 11k: Noise Histogram and Channel Load

² 11v: Extended Channel Switch permits relocating BSS to selected

channel (selection based on channel survey).

² 11k: Link Measurement and Beacon Request/Report characterize

initial link quality in terms of signal level (RCPI) and SNR (RSNI) for

video stream at setup time.


802.11k features to monitor quality

² 11k: Transmit Stream Measurement Request/Report for direct video stream monitoring using triggered reports (alerts) on transmit stream MSDU retries, discards, failures or long delay.

² 11k: Link Measurement Request/Report to track ongoing video link quality in terms of signal level (RCPI) and SNR (RSNI) for STA to STA streams.

² 11k: Beacon Request/Report to track ongoing video link quality in terms of signal level (RCPI) and SNR (RSNI) for AP to STA streams with conditional reporting (alerts).

² 11v: Presence Request/Report may detect onset of motion of transmitting or receiving STA to indicate changing link conditions.


Limitations in current 802.11 mechanisms

² Limited prioritization

² Lack of inter-layer communication

² Limited set of QoS parameters

² Limited capability to dynamically tweak QoS parameters

² Lack of content-specific methods


Possible areas of work

² MAC-level techniques

² Selective Repetition to mitigate packet loss

² Smart packet drop

² Finer prioritization among streams and within one stream

² Content-specific methods

² QoS policy (establishing, monitoring, adaptation)

² Inter-Layer communication (Vertical interaction)

² PHY-MAC

² MAC-higher layers


Possible solutions: Illustration

MPEG2 Packetized Video Elementary Stream

MPEG2 Packetized Audio Elementary Stream

Other data

MPEG2 Packetized Transport Stream

…

•

• Dynamic QoS• Finer granularity priority levels• Content aware protection, transmission, retransmission, etc.

PHY frame

• Content-aware PHY adaptation• Beamforming / STBC• Coding / Modulation, etc.

MAC frame

… PHY frame

MAC frame


Multiple Priority Levels

² Inter-stream and Intra-Stream priorities

² Real-time video has different QoS requirements compared to stored

media.

² Current standard has provision for video access category and provides

one service to all kinds of video including real-time video, stored media

etc

² Possible scope for improvement

² Use different set of channel access parameters to differentiate premium

content, real-time, stored media content

² For example, more granular control of AIFSN can be used to differentiate

video streams


Content Aware Techniques

² Some video frames are more important than others (I > P > B frames)

² Current MAC/PHY layers don’t differentiate among different frames

² Possible content-specific methods

² MAC Layer

² Frame based retry limits, fragmentation size, QoS parameters

² As a result of PHY/MAC communication:

² Frame based FEC coding, modulation scheme, 802.11n specific features

such as STBC, Beamforming etc.


Summery

² Video is different from data; existing 802.11 mechanisms are not sufficient

² The home networking industry at present is not planning to use 802.11 for

video distribution!

² Instead, cable or powerline are being used

² 802.11 will be the medium of choice only if more is done in a timely

fashion.

The industry is ready for 802.11 based Video Streaming NOW.


VIDEO STREAMING IN MOBILE AD-HOC NETWORKS


Introduction

² Many challenges, and many techniques..

² .. attack different challenges with different techniques

² > 100 papers

² Wireless networks → wireless mesh networks →MANETs → Wireless

Sensor Networks (WSN)

² Download and play → Streaming on demand → Live conversations

² Attack different layers to solve the problem

² A brief overview → work in progress


Figure: Example streaming scenario over a MANET


Traditional Challenges

² Stringent requirements (QoS)

² Bandwidth, limited packet-loss, delay and jitter

² Buffering and re-transmission increase delay

² Download and play vs. Streaming on demand vs. Live conversations

² Network congestion impacts QoS severely

² Streams have steady bit-rates; map to end-to-end network capacity

² Reduce bandwidth with video coding

² Compression, redundancy, reducing resolution


Wireless Channel Challenges

² Wired links: static and reliable (guided and shielded)

² Wireless links: dynamic and unreliable (open medium)

² Shadowing, multi-path fading and hidden node problem

² High chance of packet collisions

² Random packet losses →Not only caused by congestion

² Bandwidth constrained

² High density: Bandwidth !

² Time varying links and capacity regions

² Long-lasting QoS-guarantees are challenging


Multi-hop Induced Challenges

² Increased delay

² Delay increase almost linearly per hop

² Particularly challenging for live streaming

² Increased packet-error rates

² Both intra- and inter-path interference

² Routing (Need to satisfy QoS)

² Routes that give the subjective best video quality

² Requires multi-metric routing

² Hard to obtain a global view


Mobility-Induced Challenges

² Adds dynamicity

² Further complicates getting a global, consistent view of the network

² Partitioning → Delay Tolerant Networking (DTN)

² Re-routing (links break)

² Disruptions in ongoing streams

² Burst of packet loss

² Out-of-order delivery

² Possible oscillating effect


Resource Constrained Devices Challenges

² Heterogeneous devices (PDA’s, Laptops, etc.)

² Computational constraints

² Limits encoding, decoding and transcoding

² Intermediate nodes become bottlenecks

² Battery constraints

² Computation and transmission drain battery

² Empty battery: nodes disappear, causing disruptions and possible partitions

² Memory and storage constraints

² Limits buffering

² For DTN: high requirements on storage space

² Presentational constraints

² Screen resolution


Handling Disconnections Challenges

² High mobility and/or low density² Other causes: obstacles, dying/failing nodes, node/link saturation

² Long lasting: requires delay tolerance

² How to predict partitioning / link disruptions?

²Where to buffer/replicate content?

² Routing through time (not only space) ! Delay tolerant

routing / Space-time routing

² Affect signaling (how to play, pause, start, stop replicas)


Techniques Tree Structure


Video Coding Techniques

² Main goal: Adapt video frames to

optimal bit-rate stream(s)

² Multi-stream Coding

² Combine with multi-path routing

² Layered Coding² Primary path: base layer

² Others: enhancement layers

² Multiple Description Coding (MDC)² All descriptions equally important

² Primary path can break :)

² Handling Transmission Errors

² Traditional channel coding techniques

FEC, Rapture codes


Middleware

² Main goal: Provide interface to application, and allow adaptation of

underlying protocols

² A middleware alone cannot solve challenges

² Few efforts among identified articles

² Could be possible if layers exist as changeable components

² Then, adapt and change layer components dynamically during runtime


Caching and Replication

² Main goal: Provide replicas that are closer in

distance or time (or both)

² Link prediction² Location awareness (e.g., GPS)

² Clustering

² Caching: improve efficiency

² Service Replication: partitioning → delay tolerance,

e.g., NonStop

² Peer-to-Peer Approaches: levitate the best from the

P2P paradigm

² Store-carry-forward: message ferries, exploit

mobility, e.g.,V3 and MOMENTUM


End-to-end Transport Techniques

² Main goal: Signaling and flow-control →avoid congestion

² Rate-control closely related to video coding, since content should not be postponed

² TCP:

² Does not match video transmission (e.g., retransmissions)

² Mistakes packet error as congestion

² Timeout - what happens during partitions?

² UDP: Basically no control!

² How to issue fairness between streams: FairCast

² TRFC (TCP Friendly Rate Control): not intended for MANETs

² Stream Control Transmission Protocol (STCP): does not fully levitate multi-path

routing

² Provide interface to multi-path routing


Routing Techniques

² Main goal: Keep route(s) from source to destination² Cross-layer design, multiple metrics² Single-path routing

² OSLR,AODV: hop-count →no QoS guarantees² QoS Routing ² Hierarchical routing

² Multi-path routing² Multi-path versions of OLSR and AODV² Coding Aware Routing

² Route selection with coding parameters in mind. ² Coding Intrusive Routing

² Coding affected by paths and resources.

² Multi-cast routing² Multiple multi-cast trees

² Energy Aware Routing (WSN)


Lower Level Adaptation

² Main goal: Adapt lower layers

² Increase bandwidth with added multiple-input multiple-output

(MIMO) support , e.g., upcoming 802.11n

² Add QoS support, e.g., 802.11e

² Dynamic re-transmission scheme

² Adapting transmission range (WSN)


Cross-Layer Design

² Main goal: Optimization at all layers

² Examples: Coding aware routing, packet error rate aware coding..

² Most efforts surveyed are in fact of cross-layer design!

² Pro:² Allow optimization based upon conditions (network and application requirements)

² Con:² Design complexity: like code

² Oscillating optimization effect

² Backward compatibility

² Compromise: Do not allow direct interaction, but enable a component for

delegating this

² Holistic approaches


Summary

² Cross-layer approach with upper layers adaptation widely recognized

² Adaptable video coder: rate adaptation with multi-stream coding and

error correction

² Multi-path routing: routes matches video descriptions

² Formulate as an cross-layer optimization problem → Huge solution space

→Considered NP-Hard

² Centralized solution algorithms → distributed algorithm

² Still need adequate signaling → Delay tolerant overlay (cache / proxying)

² More emphasis on resource awareness and mobility


WIRELESS MULTIMEDIA SENSOR NETWORKS (WMSN)


Wireless Sensor Networks

² Wireless Sensor Networks are networks that consists of sensors which

are distributed in an ad hoc manner.

² These sensors work with each other to sense some physical

phenomenon and then the information gathered is processed to get

relevant results.

² Wireless sensor networks consists of protocols and algorithms with

self-organizing capabilities.


Applications of Wireless Sensor networks

The applications can be divided in three categories:

1. Monitoring of objects.

² Structural Monitoring, Eco-physiology, Condition-based Maintenance, Medical

Diagnostics, Urban terrain mapping

2. Monitoring of an area.

² Environmental and Habitat Monitoring, Precision Agriculture, Indoor Climate

Control, Military Surveillance, Treaty Verification, Intelligent Alarms

3. Monitoring of both area and objects.

² Wildlife Habitats, Disaster Management, Emergency Response, Ubiquitous

Computing, Asset Tracking, Health Care, Manufacturing Process Flows

* Classification due to Culler, Estrin, Srivastava


Wireless Multimedia Sensor Networks (WMSN)

² The integration of low-power wireless networking technologies with

inexpensive hardware such as cameras and microphones is now enabling

the development of distributed, networked systems that we refer to as

wireless multimedia sensor networks (WMSNs),

² WMSN: networks of wireless, interconnected smart devices that enable

retrieving video and audio streams, still images, and scalar sensor data.


² Cheap CMOS cameras: Cyclops imaging module is a light-weight imaging

module which can be adapted to MICA2 or MICAz sensor nodes


WMSN Applications

² Boost the existing application of WSNs

² Create new applications²² Home automationHome automation

²² Environment monitoringEnvironment monitoring: Arrays of video sensors already are used

by oceanographers to determine the evolution of sandbars using

image processing techniques.

²² multimedia surveillance sensor networksmultimedia surveillance sensor networks: will be composed by

miniature video cameras and will be able to communicate, to

process and store data relevant to crimes and terrorist attacks


WMSN Applications

²² industrial process controlindustrial process control: will be realized by WMSNs that

will offer time-critical information related to imaging,

temperature, pressure, etc.

²² Advanced health care deliveryAdvanced health care delivery: Telemedicine sensor

networks can be integrated with third and fourth generation

(3G/4G) cellular networks to provide ubiquitous health care

services.

²² traffic avoidance and control systemstraffic avoidance and control systems: will monitor car

traffic and offer routing advices to prevent congestion


What’s so special about WMSNs ?

² [Ian Akyildiz: Dec’06] We have to rethink the computation-

communication paradigm of traditional WSNs

² which focused only on reducing energy consumption

² WMSNs applications have a second goal, as important as the energy

consumption

² delivery of application-level quality of service (QoS)

² mapping of this requirement to network layer metrics, like latency

² This goal has (almost) been ignored in mainstream research efforts on

traditional WSNs



² Resource constraints

² sensor nodes are battery-, memory- and processing-starving

devices

² Variable channel capacity

² multi-hop nature of WMSNs implies that wireless link capacity

depends on the interference level among nodes

² Multimedia in-network processing

² sensor nodes store rich media (image, video), and must retrieve

such media from remote sensor nodes with short latency

Digital Media Lab - Sharif University of Technology64


² High Bandwidth Demand

² Multimedia contents need high BW. So, high data rate and low power,

consumption-transmission techniques must be leveraged

² Multimedia Source Coding Techniques

² Because predictive encoding requires complex encoders, powerful

processing algorithms, and also entails high energy consumption, it may

not be suited for low-cost multimedia sensors

² Cross-layer Coupling of Functionality

² Because of the shared nature of the wireless communication channel, in

multi hop wireless networks, there is a strict interdependence among

functions handled at all layers of the communication stack.


WMSN Architecture


WMSN Layers

² Research challenges at different layers of the protocol stack


Physical Layer

² Among other promising technologies, the UWB technology [5] has the

potential to enable low power consumption, high, data-rate

communication within tens of meters → Time-hopping impulse radio

UWB (TH-IR-UWB)

² Although the UWB transmission technology is advancing rapidly, many

challenges must be solved to enable multi hop networks of UWB devices

² The way to share the medium in UWB


MAC Layer

²MAC layer functions²arbitration of the channel

² providing error control and recovery schemes


MAC Layer-Channel Access Policies

² Based on the nature of channel access, some MAC

protocols are geared to provide high link level throughput,

reduce delays, or guarantee QoS for a given packet type.² Contention-Based Protocols

² Contention-free Single Channel Protocols


Contention-Based Protocols

² Existing schemes are variants of the Carrier Sense

Multiple Access with Collision Avoidance (CSMA/CA)

MAC protocol

² Constraints² Their goal is limiting power consumption, not delay!

² Sleep cycle and Listen cycle synchronization → more delay


Contention-free Single Channel Protocols

² Time-division multiple access (TDMA)

² The frame is organized with a small reservation period (RP)

that is generally contention-based, followed by a

contention-free period that spans the rest of the frame

² Constraints² limited scalability

² complex network-wide scheduling

² Clock drift and synchronization issues


MAC Layer-MIMO

²Multiple input multiple output (MIMO) antenna systems² interference cancellation techniques

² Each sensor may function as a single antenna element, sharing

information and thus simulating the operation of a multiple

antenna array

² Constraints² Complexity


MAC Layer-LINK LAYER ERROR CONTROL

² 2 error control mechanisms

² Automatic Repeat Request (ARQ) ² use bandwidth efficiently at the cost of additional latency involved

with the re-transmission process

² Forward Error Correction (FEC)² Applying different degrees of FEC to different parts of the video

stream, depending on their relative importance (unequal

protection) allows a varying overhead on the transmitted packets


Network Layer

² Several design considerations of traditional WSN routing

are applicable for WMSNs

² network layer functionality of multimedia routing

² Architectural and spatial attributes :because of different types of

sensors with varying capabilities, we need different routing

algorithms

² Real time support: Meeting strict time deadlines


REAL TIME ROUTING PROTOCOLS

Ø SPEED: A Real-Time Routing Protocol for Sensor Networks

Ø MMSPEED: Multipath Multi-SPEED Protocol for QoS guarantee of

reliability and timeliness in wireless sensor networks


Network Layer Routing Protocols


Transport Layer

²WMSN transport layer is more important than WSN one² High data rates

² Sensitivity of multimedia to congestion

² More than one path between source and sink

²Main transport layer function² providing end-to-end congestion control


Transport Layer Protocols

² UDP BASED PROTOCOLS² Usually preferred over TCP

² RTP and RTCP can run over UDP

² TCP AND TCP FRIENDLY SCHEMES FOR WMSNS² Some data such as I-frames are sensitive to loss

² some form of selective reliability, such as that provided by TCP,

must be introduced for these packets in a WMSN.


Transport Layer Protocols


Application Layer

² MULTIMEDIA ENCODING TECHNIQUES AT APPLICATION

LAYER

² The main design objectives of a coder for WMSNs are:

² High compression efficiency

² Low complexity

² Error resiliency

² Existing standards (MPEG or H.263 and H.264) require complex

encoders, powerful processing algorithms, and entail high energy

consumption; whereas, decoders are simpler and loaded with a lower

processing burden


Application Layer

² But, efficient compression can be achieved by leveraging

knowledge of the source statistics at the decoder only →

distributed source coding² the compression of multiple-correlated sensor outputs that do not

communicate with each other

² Joint decoding is performed by a central entity that

receives data independently compressed by different

sensors

² However, practical solutions have not been developed until

recently. Digital Media Lab - Sharif University of Technology82

Application Layer- application specific querying and processing

²application specific querying and processing² Given a source of data (e.g., a video stream), different

applications may require diverse information (e.g., raw

video stream vs. simple scalar or binary information inferred

by processing the video stream)

² it is necessary to develop expressive and efficient querying

languages and distributed filtering and in-network

processing architectures, to enable real-time retrieval of

useful information.


Summery

²WMSNs have different characteristics and requirements

in comparison with WSNs.

² Unique features of WMSNs call for protocol designs that

provide QoS at different layers

²We discussed existing solutions and open research issues

at the physical, link, network, transport, and application

layers of the communication stack.


IPTV OVER WIMAX


What is IPTV

² IPTV is a system where a digital television service is delivered using the IP

protocol over a network infrastructure. It covers both live TV

(broadcasting) as well as stored video (Video on Demand).

² The playback of IPTV requires either a personal computer or a "set-top box"

connected to a TV

² Video content is typically compressed using either a MPEG-2 or a MPEG-4

codec and then sent in an MPEG transport stream delivered via IP Multicast

in case of live TV or via IP Unicast in case of Video on Demand


IPTV Architecture

87

IPTV Architecture[Uilecan07]


4 Major Elements

² Video Head-End

² video is captured and processed before being sent over the IP network

² Service Provider Core/Edge IP Network

² the core network of the service provider and includes hardware from many

vendors to construct this network.

² Access Network

² connects the Service Provider to the Subscriber’s home

² WiMAX is an access network

² Home Network

² distributes the IPTV services throughout the home


IPTV over WiMAX

²Why IPTV over WiMAX?² Maximize the number of subscribers

² In comparison with wired MAN technologies

² Converged wireless broadband access network²more services and better service availability under a common infrastructure

² Supporting the future trends (such as HDTV)² reservation-based bandwidth allocation, cost-effective and infrastructure-free

deployment, and stringent QoS support for the four types of service

² Multicast capability² The multicast technology allows a base station (BS) to send video packets to a

subset number of stations


IPTV over WiMAX

² Why IPTV over WiMAX?

² Mobility

² IPTV is expected to provide ubiquitous access with mobility support.

² advantage of WiMAX is the support for data communications at vehicular

speeds, feature which was impossible until now in regular cable TV systems.

² Overhead

²WiMAX is decapsulating the frames up to the MAC layer, therefore

it can use payload header suppression and compression techniques

in order to reduce the amount of overhead at Physical and MAC

layers.


Constraint/Challenges

² Fading conditions to a subset of all subscriber are diverse. Hence

single-user communication scheme for optimizing data throughput

doesn’t work well

² Lack of standardization

² Instant Channel Change

² There is a delay when the viewer wants to change the channel

² a delay between the time the router stops sending over the old channel and

when it starts sending over the new requested channel


92

Delivering IPTV Services to both Fixed and Mobile Subscribers [Uilecan07]


Layered Video

² Each video stream (or program) is encoded into several sub-streams (i.e.,

layers).

² The first layer is called the base layer, and the others are called the

enhancement layers.

² The more layers a subscriber has received, the better the video quality

² different receivers may receive different numbers of layers according

to their channel quality


² Thus, given this approach of using layered encoded video for video

dissemination, the WiMAX MAC is faced with the following problem

within any scheduling frame:

94

for any time slot within the scheduling frame, which layer of which multicast group should be transmitted at what modulation coding level?


References

1. “Fundamentals of Multimedia”, Chapter 17, Li & Drew cPrentice Hall 2003.

2. Ganesh Venkatesan (Intel), Alex Ashley (NDS), Ed Reuss (Plantronics), Todor

Cooklev (Hitachi),” IEEE 802 Tutorial: Video over 802.11”, March 2007.

3. M. Lindeberg, S. Kristiansen, T. Plagemann and V. Goebel, “Video Streaming

In Mobile Ad-hoc Networks Challenges and Techniques”, Department of

Informatics, University of Oslo, in Workshop: Multimedia in Wireless and

Mobile Networks, 15. June 2009.

4. Uilecan, I.V., C. Zhou, and G.E. Atkin, Framework for Delivering IPTV

Services over WiMAX Wireless Networks. IEEE EIT 2007 Proceedings, 2007: p.

470-475.


References

5. James She, F.H., Pin-Han Ho, and Liang-Liang Xie, IPTV over WiMAX:

Key Success Factors, Challenges, and Solutions. IEEE Communications

Magazine, 2007. 45(8): p. 87-93.

6. IAN F. AKYILDIZ, TOMMASO MELODIA, KAUSHIK R.

CHOWDURY, “WIRELESS MULTIMEDIA SENSOR NETWORKS: A

SURVEY”, IEEE Wireless Communications ,December 2007


97

Any Question

Thank you!Winter 2011


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