bc hội thảo năm 1999 về mã hóa ngồn kênh

7/31/2019 BC hi tho nm 1999 v m ha ngn knh

1/26

WORKSHOP REPORT

Bo co hi thoThe views expressed here are those of the participants of this workshop and do not

necessarily reflect the views of any organization public or privateQuan im th hin y l nhng ngi tham gia hi tho ny v khng nht thitphn nh quan im ca bt k t chc cng cng hay t nhn.Executive Summary

Tm ttAs described in the recent report of the Presidents Information TechnologyAdvisory Committee (PITAC), improvements in information technology are

transforming the way we work, learn,communicate, access information, practice

health care, buy and sell goods, conduct research, understand our environment,

build things, and run government agencies. Behind many of these developments

and the developments needed for future information technologies are past andfuture advances in communicationsNh c m t trong bo co gn y ca Ch tch ban t vn cng ngh thng tin(PITAC), s pht trintrong cng ngh thng tin angthay i cchchng ti lm vic, hc tp,giao tip,truy cp thng tin, thc hnhchm sc sc khe, mua v bn hng ho, tin hnhnghin cu, hiu rmi trngca chng ta,xy dng mi th,v vn hnh cc c quanchnh ph.ng saurt nhiunhng pht trinv nhng pht trincnthit cho cng nghthng tin trong tng lai l nhngtinb trong qu khv tng laica truyn thng

For the past 50 years, the field of communications has developed under the

assumption that the two basic components of the communications problem can be

performed independently with no performance degradations relative to jointdesign. Briefly, this idea, known as the separation principle, states that sourcecoding or efficient information representationand channel coding orprotection of information from corruption by noisecan and should be performedindependently. By dividing a single difficult problem into two simpler problems,

the separation principle has led to 50 years of enormous advances in

communications theory and technology. Examples of technologies made possible

by communications advances include CD ROMs, fast modems, wireless

communication systems, and the InternetTrong vng 50 nm qua, lnh vc truyn thng pht trin theo ginh rnghai thnhphn c bn ca vn truyn thng c thc thc hin c lp khng c sgim sthiu sut so vi thit k chung.Tm li, tng ny, c gi l "nguyn tc tch," nir hn rng "m ha ngun" - i din thng tin hiu qu v "knh m ha" - bo v thng tint sai lch bi nhiu - c thv nn c thc hin c lp.Bng cch chia mt vnkh khn vo hai vn n gin hn, nguyn tc tch dn n 50 nm tin b to lntrong L thuyt thong tin v truyn thng.V d v cc cng ngh c thc thc hinbinhng tin b thng tin lin lc bao gm CD ROM,fast modems, h thng wiles v internet


2/26

Ironically, many of the modern information technology systems made possible by

advances achieved through the use of the separation principle actually violate the

conditions upon which the optimality of that principle relies. For such systems,

performance improvements may be achieved by moving from separate design and

operation of source and channel codes to joint source-channel code design andoperationTr tru thay,rt nhiucc h thngcng ngh thng tinhin ic th c thc hinbinhng tin bt c thng quavic s dng ccnguyn tctch bitthc s vi phm cciu kinti uca nguyn tc.i vih thng nh vy,ci thin hiu sutc th tcbng cch di chuynt thit kring bit vhot ng ca ngun v m ha knh tithit k"joint source-channel code " v vn hnhThe following report describes discussions and findings of the NSF-Sponsored

Workshop on Joint Source-Channel Coding. The workshop was held in San Diego,

California on October 12 and 13, 1999. Twenty-two experts, coming from a variety

of different disciplines and points of view, participated in the workshop. The goals

of the workshop were to: provide a contextual basis for understanding the array ofapplications in which source-channel coding can play a central role;assess the

potential impact of source-channel coding technology in those applications;

identify and characterize the major open research problems associated with the

design, development, and deployment of source-channel coding technology; and

develop a conceptual framework for future cross-cutting research activities in this

inherently interdisciplinary area.Cc bo co sau y m tcc cuc tho lunv kt qu caHi thoc titr trncc knh m ngunphnNSF.Hi thoc t chcti San Diego, California vo ngy12 thng 10 v 13 nm 1999.Hai mi hai chuyn gia, nt

nhiulnh vc khc nhauv quan im,tham gia hi tho.Cc mc tiuca hi tho:cung cpmtcs theo ngcnh cho s hiu bitcc mng ca ccngdng, trongngun knh m ha c thng mtvai tr trung tm, nh gitc ng tim tngca cngngh m ha ngunknhtrong cc ng dng, xc nhv m t c immlnnghincucc vn lin quannthit k,pht trin,v trin khaicng ngh mha ngun knh v pht trin mtkhung khi nimcho cc hot ng nghin cu xuynsut trong tng lai trong lnh vc nyvn lin ngnh.The committees results include a careful description of system properties that leadto the violation of the separation principle. These properties include existence of

critical resource constraints (such as power constraints for hand-held wireless

devices), networks (such as the Internet) in which users must share channel

resources, applications (such as multimedia communications) characterized bysource or channel heterogeneity, and systems (such as mobile communications

devices) with unknown or time-varying source and channel properties. The

committees assessment is that these properties pervade an enormous array ofinformation systems, including many key network technologies. Wireless

communications systems and the Internet are two prime examples considered in

this report. Given the pervasive nature of these properties, the committee


3/26

recommends focused research in this area in order to: (1) advance the theory

needed for characterizing the per-formance and fundamental limitations of joint

source-channel coding systems, (2) develop methods for designing joint source-

channel coding systems, and (3) apply the theory and design techniques to address

practical problems. The committee also puts forward recommendations for

encouraging productive research interaction between industry and academia in this

area of enormous interest and importance to both.Cc kt qucay ban bao gmmt m tcnthnca cc thuc tnh h thngdn nvicvi phmnguyn tctch.Cc tnh cht ny bao gms tn ti cahn ch ngun lcquantrng(chnghnnh hn chnng lng chothitbcm taykhng dy), mng(chnghnnh Internet) m ngi dngphi chia s cc ngun ti nguyn knh, cc ngdng(chng hnnhtruyn thnga phng tin)cc trng bingun hoc khngng nhtknh,v h thng(chnghnnh cc thit b lin lcdi ng)vi m ngunkhng rhocbin thin theo thi gianv cc c tnhknh.y bannh gi l cc thuc tnh ny trnngpmt mngrtlnca cc h thng thng tin, bao gm cc cng ngh mng quantrng.H thng thng tin lin lc khng dy v Internet l hai v d in hnhc xem xt trong

bo co ny.Do tnh chtph bincacc thuc tnh ny,y ban nghnghin cu tptrung trong lnh vc ny: (1) ci tin nhng l thuyt cn thit m t hiu nng v cbnca doanhngunhthng knh m ha ,(2)pht trin cc phng phpthit kni ngun v m ha knh, v (3) p dng cc lthuytv k thutthitk gii quytvn thc t.y ban cnga rakhuynnghkhuyn khchs tng tc nghin cusnxutgia cng nghipv hc thuttrong lnh vcny,quan tm rt lnv tm quan trngcho c hai.II Introduction and Motivation

Advances in information technology are transforming the way we live our lives.

The impact is pervasive, affecting everything from communications to health care,

commerce, and education. Since much of information technology is, at its core,

communications technology, developments in communications represent keyenabling advances for the information technology revolution currently underway

Nhng tin b trong cng nghthng tin ang thay i cch chng ta sng .Tc ng lan ta,nh hng n tt c mi th t vic trao i thng tin chm sc sc khe, thng mi v giodc.K t khi cng ngh thng tin pht trin, ti ct li ca n, cng ngh truyn thng, phttrin ca truyn thng i din cho nhng tin b quan trng thun li cho cuc cch mng cngngh thng tin hin ang tin hnh

The field of communications describes the theory, methodologies, and

technologies for transmitting and storing information. The information consideredincludes sources such as text, speech, images, audio, video, and scientific data.

Traditionally, the notion of a communications system divides into two separate

functions or subsystems. The first, called a source code or compressionalgorithm, aims to provide an efficient representation of the information; efficientdata representations speed information transmission and minimize information

storage-space requirements. The second, called a channel code or error control


4/26

code, works towards correcting or concealing errors arising from flaws in thestorage or transmission system; channel codes protect information from corruption

due to effects like electronic noise in a circuit, damage to a storage device (such as

a scratch on a compact disk), loss of information packets in a network, and failure

of a communications link

Cc lnh vc truyn thng m t l thuyt, phng php, v cng ngh truyn ti v lu trthng tin. Cc thng tin c coi l bao gm cc ngun nh li ni, vn bn, hnh nh, mthanh, video, v d liu khoa hc. Theo truyn thng, khi nim v mt h thng truynthng chia thnh hai chc nng ring bit hoc h thng con. Vic u tin, c gi lmt "mngun" hay "thut ton nn," nhm mc ch cung cp mt i din hiu qu ca thng tin, dliu hiu qui din tc truyn ti thng tin v gim thiu yu cu khng gian lu tr thngtin. Th hai, c gi l mt "knh m" hoc "M kim sot li," cng trnh hng ti sacha hoc che giu li pht sinh t cc l hng trong h thng lu tr hoc truyn ti, ms knh bo v thng tin t nhiu do hiu ng nhn in t trong mt mch, thit hicho mt thit blu tr(chng hn nh mt vt try xc trn mt a nh gn ) ,

mt mt ca cc gi thng tintrong mt mng , v li ca mt lin kt truyn thng

The separation principle, which divides a single communications system into

separate source coding and channel coding subsystems that are then designed and

run independently, is both extremely powerful and extremely limiting to the

advancement of communications technology. The power of the separation

approach is that it divides a single complex problem into two simpler problems.

This divide and conquer strategy has led to a wide variety of advances in both the

theory and the practical design of source coding and channel coding systems.

Theoretical advances include greater understanding of optimal source coding and

channel coding methodologies andtheir performance. Practical advances include good, fast algorithms for source

coding and channel coding. For example, modern compression systems typically

halve the file size or transmission time needed for text and reduce by a factor of 40

or more those required for good image reproduction. Similarly, advances in

channel coding have led to channel coding methods achieving reliable information

communications and storage; in fact, the performance of these techniques is

nearing the theoretical limits for simple common channels (e.g., single-user

Gaussian noise on linear channels). These advances have enabled a wide array of

information technologies, including CD

ROMs, fast modems, wireless communications, the Internet, and digital librariesCc nguyn tc tch, phn chia mt h thngtruyn thng thng duy nht vo cc mhangun ring bit v cc knh m ha h thng con ny sau cthit k vchy clp,c haicc k mnh mv cc khnchs tin b cacng ngh truyn thng.Scmnh caphng php tch l n phn chia mt vn phc tp thnh hai vn n ginhn.Phn chia v chin lcchinh phc cc ny dn nmt lot cctin btrong lthuytv thit kthc t ca m ha ngun v cc knh m ha h thng.L thuyt nngcao bao gms hiu bit su sc hnca cc m ha ngunti uv phng php m ha


5/26

knh v hiu sut ca chng.Tin bthc hnhtt, cc thut ton nhanh chng cho mha ngun v m ha knh. V d, h thng nn hin ithnggim mt nakch thctptin hocthi gian truyncn thit chovn bnv gimbi mt nhn tca 40 hoc nhiuhnnhng ngicn thit ti tohnh nh tt.Tngtnhvy, nhng tin b trong mha knh dn nphng php m ha knhtc cc truyn thng thng tin ng tincy v lu tr,trn thc t,vic thc hincc k thut ny l gngii hn l thuyt cho cc

knh n ginph bin(v d,ngi s dng duy nht Gaussian trn ccknh tuyn tnh). Nhng tin b ny cho php mt mngrngcacng ngh thng tin, baogm c CD ROM, fast modem, truyn thng khng dy, Internet, v cc th vinkthuts

A communication system in which the source code and channel code are designed

or operated in a dependent fashion is called a joint source-channel code. Unlikeseparation-based techniques, joint source-channel code design techniques rely on

the joint or cooperative optimization of communication system components.

Further, the joint source-channel coding approach allows for strategies where the

choice of source coding parameters varies over time or across users in a manner

that in some way depends on the channel or network characteristics. Likewise,joint source-channel coding techniques allow for systems in which the choice of

channel code, modulation, or network parameters varies with the source

characteristics. In short, joint source-channel coding applies to any system in

which the conditions of the separation theorem are violated and thus dependence of

the source and channel code arises.

Mt h thng thng tin lin lc, trong cc m ngun v m knh c thitkhochotngtrong mt cch phthucc gi lmt "doanh ngun knh m".Khngging nhtch da trn k thut, doanh m ngun knh k thut thit kda trn vic ti uhadoanh, hp tc xca cc thnh phnh thng thng tin lin lc.Hnna, cc knh tipcn m ngun chung cho php cc chin lcni ms la chn mha cc thng sngun thay itheo thi gianhoc quangi s dng trongmt cch m mtcch no ph thuc vo cc knh hoc cc c tnhmng.Tng t nh vy, cc kthutm hangun knh chung cho php cc h thng m trong s la chn ca mknh, iu ch,hoc cc thng smng khc nhau vi c imngun.Trong ngnhn,doanh ngun knh m ha p dng i vibt k h thngtrong cc iu kinca nhl tch vi phmv do ph thuc vongun v m knh pht sinh.

Given the above observations about the conditions under which the assumptions forseparationfail, we next list four examples of conditions under which we expectsignificant gains from jointsource-channel coding. First, gains are expected for systems

with critical resource constraints. Examples of potential resource constraints includerate or bandwidth for data transmission, complexityfor low-cost systems, power forhand-held devices, and delay for real-time systems. Joint source-channel coding yieldsperformance improvements in such scenarios by allowing for optimal allocation of asingle users resources between the source code, channel code, and modulationscheme of his system. The goal here is to choose the allocation that yields the bestend-to-end system performance. For example, in a system in which power is a criticallylimited resource, the power required to compress a signal should be no larger than the


6/26

power savings achieved by reducing the source description length. Likewise in real-time systems, where delay limitations represent a critical constraint, the delayintroduced by the source code must be justified by a greater reduction in the timerequired to transmit the data using the more efficient data representation. Byencouraging careful tradeoffs between the resources consumed by the source code and

those consumed by the channel code and modulation schemes, critical resourceconstraints create fertile environments for the application of joint source-channel codingtechniques.

Vinhng quan st trn vcc iu kintheo cc gi nh cho ly thn khng, chng titiptheo danh sch bnv d v cciu kintheo chng ti hy vngli nhunngkt jointsource knh m ha. Th nht,li nhund kincho cc h thng c hn ch ngunlc quan trng.V d v cchn ch ngun lctimnngbao gmhoctc bng thng truyn d liuphc tp choh thngchi ph thp,nng lng cho cc thitbcm tay,v schm tr cho cc hthngthi gian thc. Lin ngun knh m ha ci tin hiusutsnlngtrong cc tnh hungnhvybng cch cho phpphn b ti ucc ngun tinguyn camtngi dng duy nhtgia ccm ngun, m knh, v iu ch

s h thngca mnh.Mc tiuyl chnphn bsn lnghthng end-to-endhiusuttt nht.V d, trongmt h thngtrong quyn lc l mt ngun tinguynquan hnch,sc mnhcnthit nntn hiukhng ln hncc khon titkimint cbng cch gim di m tngun.Tng t nh vy trong h thngthigian thc", trong hn chs chm tri din cho mthnch quan trng, s chm trgiithiu cam ngunphic iu chnh bimc gim nhiu hn trong thi gian cn thittruyn tid liubng cch sdngbiu din d liuhiu qu hn. Bykhuyn khchs cn bnggiacc ngun ti nguyntiu th bi cc m ngunv nhngngitiu th bi cc m knh v n iu chcn thn,hn ch ngunlc quan trngto ra mi trngmu m chovic p dng cc k thut mha ngun knh chung.

A second example of a scenario where the potential performance benefitsof joint sourcechannel coding are high is multiuser systems with sharedchannels. Wired data networks, where packets of information travel througha sequence of shared links on their way from their point of origin to theirpoint of destination, are one example of this type of shared-resourceenvironment. Wireless communications systems, where users attempting tosend information through the system compete for the limited systembandwidth, are a second example. In systems in which users share acommon channel, the signals transmitted by different users can interferewith each other. Thus one users source contributes to the noise inanother users channel. The competition for network resources and thedependence of the channel on the sources feeding information into thechannel make shared-channel environments prime candidates forapplication of joint sourcechannel coding solutions. In particular, while jointdesign of source and channel codes across users in a shared-channelenvironment is typically not possible, some form of cooperation can limit


7/26

interference between users and thereby lead to better overall systemperformance. System protocols establish a framework in which these typesof cooperation take place. For example, in packet based networks, systemprotocols describe methods for breaking a single users information intopackets and routing those information packets, along with the packets fromother users, through the network. In some sense, the protocol becomes thechannel through which the data description passes. Here joint source-channel coding techniques lend insight into how to achieve better systemperformance. In particular, we can engineer the source to match thechannel by modifying source rates to send more information when networkcongestion is low and less when network congestion is high. Likewise, wecan engineer the channel or the network protocols to match the sourcestatistics. For example, in packet networks we can use the bits in theheaders of data packets to instruct the routers on which packets have low

priority and can be dropped if necessary to avoid overflow. This approach,which is analogous to existing methods for using bits in the data packetbody to describe to the source and channel decoder how to decode aparticular transmitted message, allows for control of the channel based onthe importance of the information in the source. These joint source-channelcoding approaches for engineering sources that yield better channels andchannels that behave in ways better suited to the source are a naturalmatch for shared-channel environments

Mt v d th hai ca mt kch bn m nhng li ch v hiu sut m ha sourcechannel phn

cao l h thng a ngi dng vi cc knh chia s. C dy mng d liu, ni m cc gi dliu thng tin du lch thng qua mt chui cc lin kt chia strn con ng ca mnh t quanim ca h vquan im ca hn, l mt trong nhng v d ca loi hnh ny chia s tinguyn mi trng. H thng truyn thng khng dy, ni ngi dng c gng gi thng tinthng qua h thng cnh tranh cho cc bng thng h thng gii hn, l mt v d thhai. Trong cc h thng trong ngi s dng chia s mt knh chung, cc tn hiu ctruyn bi ngi dng khc nhau c th can thip vi nhau. Nh vy, "ngun" ca mt ngis dng gp phn vo ting n ca ngi s dng khc cnh tranh "knh." i vi ti nguynmng v s ph thuc ca knh trn ngun nui dng thng tin vo cc knh lm cho mitrng chia s knh chnh ng c vin cho cc ng dng gii php m ha sourcechanneldoanh.c bit, trong khi thit k chung ca ngun v m knh trn ngi s dng trong mtmi trng chia sknh thng khng c th, mt s hnh thc hp tc c th hn ch s can

thip gia ngi s dng v do dn n hiu sut h thng tng th tt hn. H thng giaothc thit lp mt khun khtrong cc loi hp tc din ra. V d, trong gi tin da trnmng, cc giao thc h thng m tcc phng php ph v thng tin ca mt ngi dngduy nht thnh cc gi v nh tuyn cc gi thng tin, cng vi cc gi tin t nhng ngidng khc, thng qua mng. Trong mt ngha no , giao thc trthnh "knh" thng qua m t d liu i qua.Di y doanh ngun knh k thut m ha cho vay ci nhn su scvo lm thno t c hiu sut h thng tt hn.c bit, chng ta c th ks mngun ph hp vi cc knh bng cch thay i t l ngun gi thng tin khi tc nghn


8/26

mng l thp v t khi tc nghn mng l cao. Tng tnh vy, chng ta c th ks knhhay giao thc mng - ph hp vi s liu thng k ngun.V d, trong cc mng gi, chngti c th s dng cc bit trong cc tiu ca gi d liu hng dn cc bnh tuyn mtrn cc gi tin c mc u tin thp v c thc gim nu cn thit trnh trn. Cchtip cn ny, l tng tnh phng php hin c s dng cc bit trong c th gi dliu m t ngun v b gii m knh lm thno gii m mt thng ip truyn c th,

cho php kim sot cc knh da trn tm quan trng ca thng tin trong ngun. Nhngphng php tip cn ngun knh chung m ha cho cc ngun k thut nng sut tt hn ccknh v cc knh hot ng trong nhng cch tt hn ph hp vi ngun l mt trn u tnhin cho mi trng chia s knh

A third basic scenario in which significant gains are expected from the application

of joint source-channel coding methodologies is in multiuser systems with

heterogeneous sources, channels, topologies, or users. Source heterogeneity arises

from the fact that different data types traversing a single communications system

have different sensitivities to loss, corruption, and delay. Channel heterogeneity

arises from the fact that different channels within a single network may havedifferent noise characteristics, available rates, and, in packet networks, delay and

jitter. User heterogeneity refers to the differences between the needs and quality-

of-service requirements of different users, the different computational capabilities

of their systems, and the different bandwidth access available to them.

Heterogeneity of topology refers to the fact that the same network can be

simultaneously used as a point-to-point communication system (with or without

feedback), a broadcast system, a multiple access system, and so on. A variety of

joint source-channel coding techniques may be employed in networks exhibiting

these types of heterogeneity. For systems with heterogeneous sources, unequal

error protection can be used to protect more error- or channels or users, layered ormultire solution source coding allows transmission at multiple rates (for multiple

channels) or makes information simultaneously accessible with different

reproduction qualities to multiple users with varying needs and system capabilities;

the result is a democratization of information access, where information can bemade available to all users despite the potentially very different bandwidths and

computational capabilities of their access devices. Finally, network topology can

affect the choice of source and channel codes. For example, separation is known to

fail for some network topologies even when the sources and channel are known

and the system delay and complexity are unconstrained. Further, feedback in anetwork system topology can affect source and channel coding choices. For

example, using feedback to request repeated transmission of missing or corrupted

data packets can obviate traditional channel coding; prioritization of packets by

relative importance of the included source content can then lead to prioritized

repeat requests for scenarios where delay constraints are tight. The matching of

source coding parameters to heterogeneous channels and networks and channel


9/26

coding parameters, modulation techniques, and network protocols to source

characteristics in these heterogeneous environments are inherently joint source-

channel coding approaches

Mt kch bn c bn th ba, trong mc tng ng k t vic p dng cc phng php m

ha ngun knh chung trong cc h thng a ngi dng vi ngun khng ng nht, ccknh, cu trc lin kt, hoc ngi s dng.Ngun khng ng nht pht sinh t thc t l cckiu d liu khc nhau vt qua mt h thng thng tin lin lc duy nht c nhy cm khcnhau tht thot, tham nhng, s chm tr v.Knh khng ng nht pht sinh t thc t lcc knh khc nhau trong mt mng duy nht c th c c im ting n khc nhau, t l csn, v, trong cc mng gi tin chm tr v jitter.Ngi s dng khng ng nht cp ns khc bit gia nhu cu v yu cu cht lng dch v ca ngi s dng khc nhau, khnng tnh ton khc nhau ca h thng ca h, v bng thng truy cp khc nhau c sn choh.Tnh khng ng nht ca cu trc lin kt cp n thc t l cng mt mng c thc ng thi s dng nh mt h thng thng tin lin lc im -im (c hoc khng c phnhi), mt h thng pht sng, mt h thng truy cp nhiu, v do . Mt lot cc k thut mha phn ngun knh c th c s dng trong mng li trin lm cc loi khng ng

nht.i vi h thng vi cc ngun khng ng nht, bt bnh ng bo v li c th c sdng bo v li hoc nhiuknh hoc ngi s dng, lp hoc multiresolution ngun mha cho php truyn nhiu mc thu (i vi nhiu knh khc nhau) hoc lm cho thng tinng thi tip cn vi cht lng sinh sn khc nhau cho nhiu ngi dng vi nhu cu v khnng h thng khc nhau, kt qu l mt "dn ch" ca truy cp thng tin, ni thng tin c thc thc hin cho tt c ngi dng mc d bng thng c kh nng rt khc nhau v khnng tnh ton ca cc thit b truy cp ca h. Cui cng, mng topo c th nh hng n sla chn m ngun v knh.V d, tch c bit n tht bi cho mt s mng cu trc linkt ngay c khi cc ngun v knh c bit n v s chm tr v phc tp h thng khngb gii hn.Hn na, thng tin phn hi trong mt cu trc lin kt h thng mng c th nhhng n ngun v knh m ha s la chn.V d, s dng thng tin phn hi yu cutruyn lp i lp li ca d liu b mt hoc b hng cc gi tin c th phong nga m ha knh

truyn thng, u tin cc gi tin vo tm quan trng tng i ca ni dung ngun bao gmsau c th dn n yu cu lp li u tin cho cc kch bn hn ch s chm tr chtch.Ph hp vi m ha cc thng s ngun knh khng ng nht v mng li v knh mha cc thng s, k thut iu ch, v cc giao thc mng vi c im ngun trong cc mitrng khng ng nht l phng php tip cn ngun vn doanh knh m ha

The fourth and final category of problems in which joint source-channel coding is

expected to achieve significant gains is applications characterized by unknown or

time-varying sources, channels, or networks. The issues arising here are the same

as those considered for systems with heterogeneous sources, channels, networks, or

users, and the techniques that arise to combat these problems are likewise similar.

The difference here is that the potential variation occurs across time for a single

source, channel, or network rather than varying across space or system use. The

goal for time-varying systems is to achieve graceful performance fluctuations as

the system evolves and changes with time

Cc th loi tht v cui cng ca cc vn trong m ha ngun doanh knh d kinst c mc tng ng k l cc ng dng c trng bi cc ngun khng rhoc bin


10/26

thin theo thi gian, cc knh, hoc mng.Cc vn pht sinh y gingnhnhng ngi xem xt h thng vi ngun khng ng nht, cc knh, mng, hoc ngis dng, v cc k thut pht sinh chng li nhng vn ny l tng tnh vytngt.S khc bit y l s bin i tim nng xy ra qua thi gian cho mt knh duynht, ngun, hoc mng ch khng phi l khc nhau qua khng gian hay hthng sdng.Mc tiu cho cc h thng thay i theo thi gian l t c hiu sut bin

ngduyn dng nh h thng pht trin v thay i theo thi gian

Examples of existing technologies and applications in which the above-described

characteristics appear are bountiful. For example, second generation (G2) voice-

oriented digital cellular phones combine critical resource constraints, a shared-

channel environment, and extreme channel variations over time and space. Critical

resource constraints include power constraints for handheld devices and delay

constraints for real-time voice communications. The very noisy shared

channel environment arises in part from extreme competition for bandwidth, a

problem that increases as cellular systems increase in popularity and use. Further,

wireless channels experience extreme variations over time and user location due tochanges in such characteristics as distance from base stations, interference from

other users, shadowing effects, and fading characteristics. The combined effect of

all of these characteristics makes digital cellular telephony a prime candidate

for the application of joint source-channel coding techniques.

Cc th loi tht v cui cng ca cc vn trong m ha ngun doanh knh d kinst c mc tng ng k l cc ng dng c trng bi cc ngun khng rhoc binthin theo thi gian, cc knh, hoc mng.Cc vn pht sinh y gingnhnhng ngi xem xt h thng vi ngun khng ng nht, cc knh, mng, hoc ngi

s dng, v cc k thut pht sinh chng li nhng vn ny l tng tnh vytngt.S khc bit y l s bin i tim nng xy ra qua thi gian cho mt knh duynht, ngun, hoc mng ch khng phi l khc nhau qua khng gian hay hthng sdng.Mc tiu cho cc h thng thay i theo thi gian l t c hiu sut binngduyn dng nh h thng pht trin vthay i theo thi gian

Another existing system exhibiting many of the above characteristics is the

Internet. Due to its shared-channel environment and heterogeneous components,

the Internet is characterized by extreme channel variations over space and time.

Variations over space describe the variations between the channels observed by

different sender-receiver pairs in the network. These variations can be extreme,with bandwidths ranging from 10s of kbps (kilobits per second) to 10s of Mbps

(megabits per second), packet loss probabilities varying from fractions of a percent

to 25% or more, and delay and jitter varying from milliseconds to seconds. In

addition to these variations over space, are variations over time. A single linksbandwidth, packet loss probability, delay, and


11/26

jitter can vary enormously over time as competing processes begin and end. In

distance learning, for example, downloading a web page during a real-time video

transmission can cause severe performance degradations. User mobility adds

further heterogeneity to the system, bringing with it all of the time and space

variations described above for cellular telephony systems. Finally, network

topology further complicates the issue since the Internet is simultaneously used for

pointto-point, broadcast, multiple access, and feedback communications

applications

Mth thng hin ctrng byrt nhiucc c im trn l Internet.Do mi trng chiascc knh ca nv cc thnh phnkhng ng nht, Internet c c trng bis thayi knh ccv khng gian v thi gian.Bin th trong khng gian m tcc bin thgia ccknh quan st bingi gi,nhncc cp khc nhau trong mng.S bin i nyc thckhc nghit,vibng thng khc nhau, t 10 kbps (kilobits mi giy)n10 Mbps(megabits mi giy),xc sutmt gi tin khc nhau t vi phncamtphn trmn25% hoc nhiu hn,v s chm tr v jitter khc nhau tphn nghn giyn giy.Ngoira cc bin th trn khng gian, s thay i theo thi gian.Mt lin ktduynhtcabngthng, xc sutmt gi tin,chm tr, v jitter c thrt khc nhautheo thi gian khi cc qutrnh cnh tranhbt u vkt thc.Trong o to t xa, v d, ti vmt trang web trongmttruyn video thi gian thcc th gy ra s gim sthiu sut nghim trng.Ngi sdngdi ngb sung thmtnh khng ng nhthn navo h thng, mang theo tt ccc thi gian v s bin ikhng gian m t trncho cc h thnginthoi di ng.Cuicng, cu trc lin ktmng liphc tp thmvn k t khi Internetngthis dngcho pointto im,pht sng,a truy cp, v cc ngdngthng tin phn hithng tin lin lc

Other examples of current systems and applications characterized by the above

properties of critical resource constraints, shared channels, system heterogeneities,and time variance are numerous. The tight delay constraints of video telephony,

video conferencing, and video-on-demand applications create a resource-

constrained environment. In video broadcast applications, differences between the

systems and links of different users create a system characterized by user

heterogeneity. The desire for ubiquitous access, fast browsing, and easy

downloading in a large data bases such as a digital library creates another

heterogeneous user and channel environment. By failing

to meet the separation theorems conditions for optimality, each of these

applications becomes a candidate for the application of joint source-channel codingtechniques

Cc v d khcca cc h thnghin hnh v cc ng dngc trng bicc tnh chthnch ngun lc quan trng trn, cc knh chia s, heterogeneities h thng, v ngthigian rt nhiu.Hn chschmtrchtchca in thoi video, hi ngh truyn hnh, vccng dng video theo yu cuto ramt mi trng ti nguyn hn ch.Trong cc ngdngchng trnh truyn hnh, s khc bitgiacc h thng vlin kt ca ccngi dng


12/26

khc nhau to ra mththngctrngbitnh khng ng nht cangisdng.Mongmun truy cp mi ni,duyt web nhanh v ti vd dngtrong mtcsd liu lnchnghn nhmt th vinkthutsto ra mtngisdngkhng ng nht v mitrng knh. Bng khng p ng cc iu kincanh l tch cho ti u,cc ng dngny tr thnh mtng c vin chovic p dngk thut m ha knh ngun doanh

With advances in information technology, the properties that cause the separation

theorem to fail are becoming more common. For example, G2.5 and G3 digital

cellular systems will add simultaneous data transmission to their voice services,

allow variable data rates (with up to 2 Mbps for stationary conditions and up to 144

kbps for high mobility), run the Internet protocol on top of the data link, and offer

multimedia (image, video, and audio) services on top of the Internet protocol. As a

result, these future systems will be characterized by even greater source, channel,

and user heterogeneity and more time variance than G2 systems. Similarly, next

generation Internet will add even greater channel and source heterogeneities to analready diverse environment. New Internet channel heterogeneities will arise from

both the increase, by several orders of magnitude, of allowed transmission capacity

for high-end users and the increase in use by low-data-rate mobile users. Increased

use of multimedia applications over the Internet will likewise lead to greater source

heterogeneities. Other future applications in which joint source-channel coding

may play a significant role include last mile technologies, distributed sensor arrays,

network transport of digital video and images, packet-switched video conferencing,

multimedia delivery on digital subscriber loops, and digital audio delivery systemsVi nhng tin b trong cng ngh thng tin, cc ti sn gy ra cc nh l tchbit khng tr nn ph bin hn.V d, G2.5 v G3 h thng k thut s ding s thm ng thi truyn d liu vi cc dch v ting ni ca h, cho php tc d liubin (ln ti 2Mbps i vi iu kin vn phng phm v ln n 144 kbps cho di ng cao),chy giao thc Internet trnlin kt d liu, v cung cp a phng tin (hnh nh, video, v mthanh) dch v trn u trang ca giao thc Internet.Kt qu l, cc h thngny trongtng lai sc c trng bi ngun thm ch cn ln hn, knh, v tnh khngng nht ca ngi s dng v phng sai nhiu thi gian hnhn so vi cc hthng G2.Tng tnh vy, Internet th h k tip s thm knh ln

hn v heterogeneities ngun n mt mi trng c a dng.Heterogeneities knh Internet mi s pht sinh t c hai tng, mt sn thng cacng , dung lng truyn dn cho php ngi dng cao cp v tng sdng bingi s dng in thoi di ng tc d liu thp. Tng cng s dng cc ngdngaphng tin trn Internet tng tnh vy s dn n heterogeneities ngun lnhn.Cc ng dng khc trong tng lai, trong doanh ngun-knh m ha c thng mtvai tr quan trng bao gm cng ngh dm cui cng, mng cm bin phnphi, mng li giao thng vn ti ca video k thut s v hnh nh, hi ngh truyn


13/26

hnh chuyn mch gi, giao hng thu bao k thut sa phng tin trncc vng lp, v cc h thng phn phi m thanh k thut s

There are many other examples of the successful use of very simple joint source-

channel coding techniques in existing systems. For example, error concealment is

used in video telephony and conferencing to hide the effects of uncorrectedchannel errors. Video-on-demand systems use prioritized automatic repeat requests

so that higher priority data such as audio may be reliably received at the expense of

losing lower priority data such as video when high loss conditions are experienced.

Finally, video broadcast applications very commonly use layered coding in order

to simultaneously provide lower quality data reproductions to users with lower

available datarates and higher quality data reproductions to users with higher

available data-rates using a single embedded data description

C rt nhiu v dkhc cavic s dng thnh cng k thutrt n gin lin ngun knhm

ha trong h thng hin c.V d,che giulic s dng trongin thoi videov hi nghtruynnnhng nh hng cali knh cha c sa cha.Video theoyucuh thngs dngcc yu culp lit ngu tin cc d liuu tin cao hnnh mthanh c thc mt cch ng tin cynhn cti cc chi phcavicmt d liuu tinthp hnnh video,khi iu kinmt mt cao c kinh nghim.Cui cng,cc ng dngvideo pht sng rtthng cs dngnhiu lp m ha ng thicungcpd liuchtlngthp hnbn saocho ngi dngvi datarates c snthp hnvcht lng caohnd liubn saocho ngi dngd liuc sncao hnt ls dngd liu mtmt nhng

The properties given above as examples of appropriate scenarios for the use of

joint source channel coding and the joint source-channel coding techniques brieflydescribed there barely scratch the surface of the problem and its solution. A more

detailed description of a single system gives a better picture of the system

characteristics of which joint source-channel coding may eventually take

advantage

Cc ti sna ra trn l v d v cckch bn thch hp cho vic s dng mha knhlin ngun v cc knh k thut chung ngun m ha m t ngn gn c hu nhkhngxc b mtca vn vgii phpca n.Mt m tchi tit hn vmth thng duynht cho mthnh nh tt hncc c tnhhthng trong cc knh mha ngundoanhcui cng c thtn dng li th

Example: The InternetAs described earlier, the Internet is an example of a network in which there are

tremendous channel variations over time and space. Not noted earlier, however, is

the fact that the channel variation is also correlated in time and space. The

correlation in time arises from channel memory. Much of the packet loss

experienced in packet-based channels arises from buffer overflow. Since

buffers,once full, take time to drain, packet losses in a network often occur in


14/26

bursts. The correlation in space arises from the shared-channel environment. For

example, two neighboring paths through a network may share one or more nodes

or links. Overflow in a shared node generally results in lost packets for both

channels. Correlations may also exist for two paths not sharing any nodes since

both may be affected by high transmission rates on a third path that crosses both of

them

V d: InternetNh c m ttrc , Internet l mt v d ca mt mng, trong c nhng binthknh to ln v thi gian v khng gian. Khng ghi nhn trc , tuy nhin, l mt thctrng s bin i knh l c lin quan trong thi gian v khng gian. Cc mi tng quantrongthi gian pht sinh t b nh knh. Phn ln s mt mt gi tin c kinh nghimtrongcc knh da trn gi tin xut pht t li trn bm. K t khi bm, mt ln y,mt thi gian ro nc, tn tht gi tin trong mt mng thng xy ra trong v

n. Ccmi tng quan trong khng gian pht sinh tmi trng chia s knh. V d, hai conng ln cn thng qua mt mng li c th chia s mt hoc nhiu hn cc nt hoc linkt. Trn trong mt nt c chia s ni chung kt qu trong cc gi d liu b mt cho chai knh. Tng quancng c th tn ti hai con ng khng chia s bt k nt v c haiu c th bnh hng bi tc truyn cao trn mt con ng th ba i qua chaingitrong s h

These characteristics create many challenges and opportunities for joint source-

channel coding in networked environments. Even in the simplest case, with only a

single sender and a single receiver, the channel between the sender and receiver is

not known a priori, is in fact time varying, and the memory of the channel isusually large compared to the delay constraint for the application. If there is a

single sender broadcasting (actually, multicasting) to multiple receivers, then

the sender must deal with coding for a heterogeneous mixture of unknown but

correlated channels. This is the problem of joint source-channel coding for the

broadcast channel. One way to deal with this problem is with feedback from the

receivers to the sender. Each receiver can report, for example, its average

transmission rate, loss rate, delay, and jitter. Such receiver reports are highly

correlated because the network paths between adjacent receivers have many links

in common. Although it is known that feedback from a single receiver to a single

sender does not increase the capacity of a memoryless channel, the broadcastfeedback problem involves multiple receivers and a channel with memory. In this

environment, there is good reason to take advantage of feedback, which in a highly

connected network is readily available (although over unreliable channels).

Feedback from the multiple receivers to the single sender can be considered a

problem in joint source-channel coding for the so-called multiple access channel. It

is known that source coding for correlated sources plus channel coding for the


15/26

multiple access channel is inferior, in general, to joint source-channel coding. In

other words, in multiuser communication networks, it is known that the separation

theorem does not hold, even when the sources and channels are known and the

delay is unconstrained

Nhng c im ny to ra nhiu thch thc v c hi cho doanh ngun knh m hatrong mi trng mng. Ngay c trong trng hp n gin, vi chngi gi v nginhn mt, knh gia ngi gi v ngi nhn khng bit mt u tin, trong thi gianthct khc nhau, v b nh ca knh thng l ln so vi hn ch s chm tr cho ngdng. Nu c mt ngi gi pht sng duy nht (trn thc t, multicasting) nhiu nginhn, sau ngi gi phi i ph vi m ha cho mt hn hp khng ng nht ca ccknhkhng r nhngtng quan.y l vn ca doanh ngun knh m ha cho ccknhpht sng. Mt cch i ph vi vn ny l thng tin phn hi tngi nhn chongi gi. Mi ngi nhn c th bo co, v d, tc truyn ti trung bnh, t l mt, chmtr v jitter. Bo co nhn nh vy l lin quan cht ch bi v mng li ngligia thu lin k c nhiu lin kt chung. Mc d n c bit n thng tin phn hi tmtmy thu duy nht mt ngi gi nkhng lm tngnng lc ca mt knhmemoryless, vn qung b thng tin phn hi lin quan n nhiu ngi nhn v l mtknh vi b nh. Trong mi trng ny, l l do tt tn dng li th thng tin phnhi, trong mt mng li kt ni c sn (mc d trn cc knh khng ng tin cy). Thng tinphn hi t nhiu ngi nhn cho ngi gi c thc coi l mt vn trong ccknh mha ngun doanh cho cc knh truy cp nhiu ci gi l.c bit, ngun m ha cho ccngun tng quan cng vi knh m ha cho cc knh truy cp nhiu l km,nichung, cc knh m ha ngun chung. Ni cch khc, mng li truyn thng a ngidng, n c bit rng cc nh l tch bit khng t chc, ngay c khi cc ngunv ccknh c bit n v s tr hon l khng b gii hn

The transport of multimedia data across networks like the Internet poses even more

problems. Existing reliable transport protocols (TCP/IP) are matched to dataapplications requiring guaranteedrobust performance. To guarantee robust

performance, TCP/IP requests retransmission of all lost or corrupted packets,

thereby achieving the desired protection from noise at the expense of an imposed

delay. Unfortunately, the resulting delay makes these protocols a poor choice for

real-time data traffic, which is characterized by high delay sensitivity and variable

tolerances to noise. In the networking field, two approaches to this problem have

emerged: integrated services and differentiated services. The integrated services

approach stresses guaranteed qualities of service for different service classes, while

the differentiated services approach stresses different, though not guaranteed,

qualities of service for different service classes. Guaranteed quality ofservice is more difficult to implement and consumes more network resources, but

provides stable channels for traditional separation-based source coding algorithms

such as MPEG video. On the other hand, differentiated services, in conjunction

with joint source-channel coding, could prove to be significantly more resource-

efficient than integrated services. As an example, a simple differentiated


16/26

services protocol that calls for lower priority packets to be dropped during

congestion before higher priority packets would obviate the need for explicit

channel coding and unequal error protection. This could result in a lower

transmission rate, higher quality, lower delay, and lower network resource usage

compared to a separation-based solution. In general, information placed in

packet headers (such as priority tags, protocol parameters, or even programmatic

scripts destined for active routers) can be used by joint source-channel coders to

change the way different packets are handled by the network, potentially as a

function of buffer delay, packet loss, changing transmission bandwidth, and so

forth, either measured by the routers directly, or received as feedback from

downstream routers. The Internet provides a rich variety of research problems in

joint source-channel coding. The solutions to these problems would likely have a

major impact on networks of the future

Vic vn chuyn cc d liu a phng tin qua mng nh Internet t ra vn thm chnhiu hn na.Hin ti cc giao thc giao thng vn ti ng tin cy (TCP / IP) l ph hp vicc ng dng d liu i hi hiu sut guaranteedrobust. m bo hiu sut mnh m, TCP/ IP truyn li yu cu ca tt c cc gi d liu b mt hoc b hng, do t c bo vmong mun t ting n ti cc chi ph ca mt s chm tr p dng.Tht khng may, s chmtr kt qu lm cho cc giao thc ny mt s la chn cho ngi nghothi gian thc d liulu lng truy cp, c c trng bi s chm tr nhy cm cao v dung sai bin vi tingn.Trong lnh vc mng, hai cch tip cn vn ny ni ln: cc dch v tch hp v dchv khc nhau.Cc dch v tch hp phng php tip cn nhn mnh cc phm cht ca dchv bo lnh cho cc lp hc dch v khc nhau, trong khi cch tip cn cc dch v khc nhaunhn mnh khc nhau, mc d khng m bo, cht lngca dch v cho cc lp hc dch vkhc nhau.m bo cht lngdch v l kh khn hn thc hin v tiu th ti nguyn

mng nhiu hn, nhng cung cp cc knh n nh cho truyn thng da trn thut ton mngun tch m ha, chng hn nh video MPEG. Mt khc, dch v khc nhau, kt hp vi ccknh m ha ngun chung, c th chng minh c nhiu hn ng k ti nguyn hiu quhn so vi cc dch v tch hp.V d, mt s khc bit n gindch v giao thc m cccuc gi cho gi u tin thp hn b rt trong khi tc nghn trc gi u tin cao hn s phongnga s cn thit m ha knh r rng v bo v li khng ng u.iu ny c th dnn mt tc truyn ti thp hn, cht lng cao hn, s chm tr thp hn, v s dng tinguyn mng thp hn so vi mt gii php da trn tch.Ni chung, thng tin c t trongtiu gi tin (chng hn nh th u tin, giao thc thng s, hoc cc kch bn thm ch cchng trnh dnh cho cc b nh tuyn hot ng) c th c s dng bi cc lp trnh vindoanh ngun knh thay i cch cc gi d liu khc nhau c x l bi h thng mng,c kh nng nh mt chc nng ca b m gi tin, chm trmt mt, thay i bng thng

truyn ti, v vv, hoc o bng cc b nh tuyn trc tip, hoc nhn thng tin phn hi t ccb nh tuyn h lu.Internet cung cp mt phong ph a dng ca cc vn nghin cutrong cc knh m ha ngun doanh.Cc gii php cho nhng vn ny c th s c mt tcng ln n mng li ca tng lai

III Research Goals and Challenges


17/26

Three pressing research goals for joint source and channel coding are (1) develop

appropriate theory for characterizing the performance and fundamental limitations

of joint source-channel coding systems, (2) determine methods for designing joint

source-channel coding systems, and (3) apply the theory and design techniques to

address practical problems. A variety of more specific research objectives

addressing these problems is listed below. These objectives represent many of

the significant research goals in joint source-channel coding. The order in which

these items are listed reflects no prioritization over the described projects. Much of

this research is expected to be multidisciplinary in nature, combining expertise

from such areas as signal communications and information theory, networking and

queuing theory, as well as input from areas including economics and psychology

Ba mc tiu nghin cunhncho ngun doanh v m ha knh l (1) pht trin l thuytphhp vic imhiu sut v cc hn chc bn ca cc h thng mha ngunknh doanh, (2) xc nh phng phpthit k cc h thng mha ngun knh doanh, v (3)p dng ccl thuytv k thutthitk gii quytvn thc t.Mt lot ccmc tiunghin cuc th hngiiquytnhng vn nyclit kdi y.Nhng mc tiui din chonhiunghin cumc tiu quan trngtrong cc knh m ha ngun chung. Trnh t, trong cc mt hng nyc litk phn nh khng c u tinivicc d nc m t.Phnlnca nghin cu nydkin sc tnh a ngnhtrong t nhin,kt hp chuyn mntcc lnh vcnhtruyn thng tn hiu vl thuyt thng tin, mngv l thuytxp hng, cngnh l uvo t cc khu vc bao gmc kinh tv tm l hc

Performance and Fundamental LimitsMany of the major challenges in developing appropriate theory for joint source-

channel coding are related to understanding the tradeoffs between the quality,delay, complexity, channel usage, and power inherent in code design. Quality

refers to the end-to-end distortion between the original data and its reproduction.

Delay refers to the difference between the times at which data enters the encoder

and exits the decoder. Complexity refers to the requirements of the encoding and

decoding algorithms, including such things as number of arithmetic operations per

data sample and memory use, which may be heavily influenced by implementation

considerations. (Complexity is also a primary factor in determining how much

power a particular joint source-channel coding implementation consumes.)

Channel usage refers to issues such as the number of channel uses per sample,

channel bandwidth, and channel signal-to-noise ratio (which includes both channel

noise and transmit power); both implementation and transmit power use become

important factors in energy-limited applications (e.g., battery-powered devices). It

is also important to limit transmit power when one users transmitted power cansignificantly impact the performance of others. While development of a

comprehensive theoretical framework for joint source-channel coding is a suitable


18/26

long-term goal, it is evident from prior work that completely characterizing the

relevant tradeoffs between quality, delay, complexity, channel usage, and power is

extremely difficult, and that achieving progress in this area is very challenging

Hiu sut v cc gii hn c bnNhiu ngi trong s nhng thch thc ln trong l thuyt thch hp pht trin cho knhmha ngun doanh lin quan n s hiu bit cn bng gia cht lng, chm tr, phc tp, sdng knh,v sc mnh vn c trong thit k m. Cht lng cp n s bin dng end-to-endgia cc d liu gc v sinh sn ca n. S chm tr lin quan n s khc bit gia cc ln m dliu nhp vo cc b m ha v ra khi cc b gii m. Phc tp lin quann cc yu cu ca cc thutton m ha v gii m, bao gm c nhng thnh slng php tnh s hc trn d liu mu v sdng b nh, m c th bnh hng nng n bi nhng cn nhc thc hin. ( phc tp cng lmt yu t chnh trong vic xc nh mt ngun doanh c th thc hin m ha knh tiu th bao nhiunng lng.) S dng knh cp n cc vn nh slng cc knh s dng cho mi mu,bngthng knh v knh t l tn hiu-to-noise (trong bao gm c hai knh ting n v truyn ti innng), c hai thc hin v truyn ti in nng s dng trthnh yu t quan trng trong vic ngdng nng lng hn ch (v d, cc thit b chy bng pin). N cng rt quan trng hn ch truyn ti

in nng khi cng sut pht ca mt ngi s dng c thtc ng ng k hiu sut ca ngikhc. Trong khi pht trin mt khun kh lthuyt ton din m ha ngun knh lin l mt mctiu di hn ph hp, n l iu hin nhin t cng vic trc khi hon ton c trng cho s cnbng gia cht lngc lin quan, chm tr, phc tp, s dng knh, v sc mnh v cng kh khn,v nhng tin bt c trong lnh vc ny l rt kh khn

Potential projects in this area include:

The development of a theoretical framework for joint source-channel coding,

suitable for both point-to-point communications and network communications, that

includes the relevant tradeoffs between quality, delay, complexity, channel usage,

and power. Such a framework is needed for both lossless and lossy datarequirements and for situations where synchronization is an issue.

The development of performance measures appropriate for joint source-channel

code designand evaluation, possibly including such things as performance bounds

or different quality metrics for lossless and lossy coding applications

D n tim nngtrong lnh vc ny bao gm:S pht trin ca mt khung l thuyt cho cc knh m ha ngun doanh, thch hp choc hai im-im truyn thng v truyn thng mng, bao gm s cn bng c linquangia cht lng, chm tr, phc tp, s dng knh in,. Mt khun khnh vy l cnthit cho c hai lossless v lossy yu cu d liu, v cho tnh hung m ng b ha l mt vn

.S pht trin cc bin php thc hin thch hp cho doanh knh nhgi m ngundesignand, c th bao gm c nhng th chng hn nh gii hn hiusut hoc s liucht lng khc nhau cho lossless v cc ng dng m ha lossy.

ModelsModern communication systems are complex. Analytical research is typically

based on the study of relatively simple models (abstracted from physical or


19/26

idealized systems). There is great need for the development of tractable source and

channel models for use in joint source-channel coding research. The models

developed should be rich enough to capture the features and constraints of the

problems at hand yet simple enough to provide the insight necessary for algorithm

development. Such models could be developed progressively from consideration of

simple point-to-point communication systems to more complex multiuser networks

and should be driven by corresponding developments in theory

H thng truyn thng hin i rt phc tp. Nghin cu phn tch thng c datrnnghin cu cc m hnh tngi n gin (tm tt t h thng vt l hay l tngha).C l rt cn thit cho s pht trin ca ngun d lam v cc m hnh knh sdngtrong nghin cu chung m ha ngun knh.Cc m hnh pht trin nn c phongph, nm bt cc tnh nng v hn ch trong nhng vn bn tay n gin, cung cp ci nhn su sc cn thit cho s pht trin thut ton. Cc m hnh nh vy cthc pht trin dn dn t xem xt cc h thng thng tin lin lc im-im n gin vicc mng a ngi dng phc tp hn v cn c thc y bi s pht trin tngngtrong

l thuyt

Models needed include:

Models for speech, video, images, audio, and text that can be used to devise better

source codes;

Models for the output of source encoders for use in the design of channel codes

(e.g., for unequal error protection);

Models for wireless channels that capture the effects of mobility and multiple

access;

Models for Internet traffic that can be used when devising end-to-end protocols

M hnh cn thit bao gm:M hnh bi pht biu, video, hnh nh, m thanh, vn bn c thc s dnga racc m ngun tt hn;M hnh cho u ra ca b m ha m ngun s dng trong vic thit k m s knh (vd, bo v li bt bnh ng);M hnh cho cc knh khng dy nm bt c tc ng ca di ng v truy cp nhiu;M hnh cho lu lng truy cp Internet c thc s dng khi t ra cc giao thcend-to-end

Design

Systematic design methodologies are required to broaden the applicability of jointsource-channel coding techniques. Potential projects include the development of

design methodologies that addressing the following problems:Thit kPhng phpthit kh thngcn thit mrngkh nng p dngca knhngundoanhk thut m ha.D n tim nngbao gms pht trin caphng php thit kgii quytcc vn sau y:


20/26

Channel-optimized source coding, including error concealment and recovery

methods;

Source-optimized channel coding, including unequal error protection methods;

Synchronization;

Feedback in source-channel coding;

Coding for time-varying sources or channels;

Multiple description coding;

Robustness to model variations;

Flexibility to different data types.

Knh ti u ha m ngun, bao gm che giu li v phng php phc hi;Ngun-ti u ha knh m ha, bao gm cc phng php bo v li khng ng u;ng b;Thng tin phn hi trong knh m ha ngun;

M ha cho cc ngun hoc cc knh thay i theo thi gian;Nhiu m t m ha;Mnh m bin i m hnh;Tnh linh hot cc d liu khc nhau.

ApplicationsJoint source-channel coding theory and design techniques should be applied to

address practical problems, including the design of joint source-channel codes for

multiuser or network systems. One challenge to the accomplishment of this goal is

the fact that network protocols attempt to isolate link and applications layersa

separation-style approach. In contrast, joint source-channel coding inherentlyinvolves interaction between the link and applications layers. A challenge of

joint source-channel coding is to find ways for the application layer to crack

through the network stack all the way to the link layer. Another challenge is to use

joint source-channel coding research to inform protocol design.

Specific projects include

Phnngun knh m ha l thuytv k thutthitk nn c p dng gii quytvn thc t, bao gmcvic thit k cc knh m ngun chung cho cc h thnga ngidng hocmng.Mt thch thc hon thnh mc tiu nyl mt thc trng cc giaothcmngc gng c lp cc lplin kt vngdng - mt cch tip cn theo phong

cch tch bit.Ngc li, m ha knh chung ngunvnlin quan ns tng tcgiacc lin ktv cc ng dnglp.Mt thch thcca knh m ha ngun doanh l tmcch cho lp ng dng crackthng qua mng li cc ngn xptt c cccch cclplin kt.Mt thch thc khcl s dng chung ngun knh nghin cu m ha thng bocho thit kgiao thc.D n c th bao gmEvaluation of the effects of network protocols, including the need for networks to

handle a variety of data sources;


21/26

Evaluation of the effects of packetization and routing;

Re-examination of the typical network separation of channel coding into the

physical layer

and source coding into the application layer;

Application-specific needs for asymmetry in encoding and decoding complexity;

Power allocation in shared-resource environments

IV Roles of Academia and Industry

Little is currently understood theoretically about joint source-channel coding, and

advances will require contributions from both industry and academia. It is

therefore of interest to determine how best to encourage productive interaction

between industry and academia in the context of joint source-channel coding.

Several characteristics distinguish this topic, and may have bearing on interactions

between industry and academia. Foremost, the problem area is of great immediate

interest to both academicians and members of industry. In addition, joint source-

channel coding requires systems-level design and optimization, which industry is

perhaps more inclined towards than academia. Further, it is an area in which

applications are expected to strongly motivate and inform the theory, and vice-

versa. Finally, it is an area where fast-paced development outstrips theoretical

understanding

t hiuv mt l thuytv cc knh m ha ngun doanh, v tin bs yu cung gp t c

hai ngnh cng nghipv cc hc vin.Do , quan tm xc nhcch tt nht khuynkhch s tng tcsn xutgia cng nghipv cc hc vintrong bi cnh ccknh mha ngun doanh. Mt s c imphn bitch ny, v c thmang vtng tc giacc ngnh cng nghipv cc hc vin.Trc tin,cc vn khu vclrt lnngay lp tcquan tm nc haivin s hn lm v cc thnh vin ca ngnh cng nghip. Ngoira,ngun doanh-knh m ha i hih thngthit k v ti u ha,ngnh cng nghip c lnhiu hnnghing v phahn so vicc hc vin.Hn na,n l mt khu vcng dngdkin sthc ymnh m v thng bo l thuyt,v ngc li.Cui cng, n lmtkhuvcninhp pht trin nhanh chng vt xashiubitl thuyt

The emphasis and role of research in this area is likely to be different for industry

and academia. The pace of development in the wireless and Internet industries, as

well as the competitive climate in these areas, has largely necessitated theallocation of research resources on the part of industry to shorter-term goals.

However, there are important, fundamental, longer-term research topics that need

to be pursued if the technology is to advance to its potential. As academics take up

more of the fundamental research agenda, it is important that they work closely

with industry for a number of reasons. First, close ties between industry and

academia allow for fundamental research based on practical insights into where the


22/26

most important research problems lie. Second, these ties allow for design choices

informed by an understanding of their theoretical implications

Nhn mnh vai tr ca nghin cu trong lnh vc ny l c khnng th khc nhau cho ngnhcng nghip v cc hc vin. Tc pht trin cc ngnh cng

nghip khng dy vInternet, cng nh kh hu cnh tranh trong cc lnh vc ny, phn ln ihi phi phn bcc ngun lc nghin cu trn mt phn ca ngnh cngnghip mc tiu ngn hn. Tuy nhin, c quan trng, c bn, di hn ti nghin cu cnphi c theo ui cng ngh ny l thc y tim nng ca n. Nh cc hcgi ca chng trnh ngh snghin cu c bn, iu quan trng rng h lm vic cht ch vicc ngnh cng nghipcho mt s l do.u tin, mi quan h cht ch gia cng nghip vcc hc vin chophp nghin cu c bn da trn nhng hiu bit thc t vo cc vn nghin cu quan trng nht nm. Th hai, cc mi quan h ny cho php la chn thitk thng bo mt s hiu bit v ngha l thuyt ca h

Areas of interaction

The time from algorithm development to implementation is rapidly decreasing due

to advances in processor speeds and memory as well as feature size reduction in

VLSI. It is therefore becoming possible to devise sophisticated algorithms for end-

to-end optimization, whether at the level of a single wireless link, or of an end-to-

end Internet protocol. As discussed earlier, the development of good source and

channel models is critical to such end-to-end optimizations. Given the wealth of

real-world experience available in industry and the traditional academic strengths

in abstract reasoning, model development is a prime area for industry-academic

collaboration. Another broad area for industry-academic cooperation is in the

formulation of design criteria. Since the objective of joint source-channel coding is

to perform end-to-end optimization, an understandingof the constraints facing the engineers who will ultimately build the system is

important even in the earliest phases of algorithm development. For example, the

need for low power consumption in small hand-held devices implies certain

limitations on the complexity of transmitter and receiver algorithms in such

devices. On the other hand, advances in VLSI may temper such

limitations in the long term. Such rapid changes in technology make close

interaction between academia and industry a must in formulating meaningful

problems. Another example pointed out at the workshop was that, from an overall

systems perspective, it is often preferable to provide a flexible framework that

allows for system-wide optimization, rather than over-optimizing for a specific

source or channel model. Multimedia transmission over heterogeneous networks is

an example of a broad class of applications that could benefit from such a flexible

framework. Industry-academic interactions allows such tradeoffs between

flexibility and optimality to be made in an informed fashion. Finally, while the

development of fundamental theory and algorithms is, of necessity, based on


23/26

somewhat idealized models, simulation and testing in a realistic environment is an

area in which industry has substantially more resources than are typically available

in university laboratories. Such performance evaluation is therefore a major area of

potential collaboration between industry and academia, especially because it is the

first step to potential technology transfer. An example of this is the implementation

and evaluation of joint source-channel codes in a wireless mobile environment,

which would not be possible to recreate at a large scale in a university environment

Cc khu vc ca s tng tcThi gian t pht trin thut ton thc hin nhanh chng gim do nhng tin b trong tc x l v b nh cng nh tnh nng gim kch thc trong VLSI. Do , c th a ra nhngthut ton phc tp ti u ha end-to-end, cho d cp ca mt lin kt khng dy duynht, hoc ca mt giao thc Internet end-to-end. Nh tho lun trc , s pht trin cam ngun v cc m hnh knh l rt quan trng ti u ha nh end-to-end. Vi s giu cca kinh nghim thc t trong ngnh cng nghip v cc im mnh truyn thng hc tp llun tru tng, m hnh pht trin l mt khu vc chnh cho ngnh cng nghip -hc hp

tc. Mt khu vc rng ln cho ngnh cng nghip-hc hp tc trong vic xy dng cc tiuchun thit k.K t khi mc tiu ca knh m ha ngun doanh l thc hin end-to-end tiu ha, hiu bit v cc kh khn phi i mt vi cc k s ngi cui cng s xy dng hthng quan trng l ngay c trong nhng giai on u tin ca pht trin thut ton. V d, nhucu tiu th in nng thp trong cc thit b cm tay nh ng nhng hn ch nht nh vos phc tp ca thut ton truyn v nhn trong cc thit b nh vy. Mt khc,tin b trongVLSI c th bnh tnh hn ch nh vy trong di hn.Nhng thay i nhanh chng trong cngngh tng tc cht ch gia hc vin v ngnh cng nghip phi xy dng cc vn c ngha.Mt v d khc ch ra ti hi tho rng, t mt quan im v h thng tng th, nthng thch hp hn cung cp mt khun kh linh hot cho php ti u ha h thngrng, ch khng phi l ti u ha cho mt ngun c th hoc m hnh knh. a phng tintruyn ti trn cc mng khng ng nht l mt v d ca mt lp rng cc ng dng c th

hng li t mt khun kh linh hot nh vy.Cng nghip-hc tp tng tc cho php cnbng gia tnh linh hot v ti u c thc hin trong mt thi trang thng bo. Cui cng,trong khi s pht trin ca l thuyt c bn v cc thut ton l cn thit, da trn cc m hnhphn no l tng ha, m phng v th nghim trong mt mi trng thc t l mt khu vctrong cng nghip c ngun ti nguyn ng k hn so vi thng c sn trong phng thnghimtrng i hc.nh gi hiu sut nh vy l do mt khu vc chnh ca s hp tctim nng gia ngnh cng nghip v cc hc vin, c bit l bi v n l bc u tin chuyn giao cng ngh tim nng.Mt v d ca vic ny l vic thc hin v nh gi ca ccknh m ngun chung trong mt mi trng in thoi di ng khng dy, trong s khngth ti to quy m ln trong mi trng i hc Modes of Interaction

There are many fruitful ways in which academia and industry can interact. Perhapsthe most obvious is through joint research projects. These can take the form of true

collaborations between engineers from both organizations, but more often consist

of academia performing research and reporting results to industry. This approach is

often a result of the need for industry to remain silent about research approaches

that they believe will be important to short term competitiveness. Indeed, even the


24/26

knowledge of which problems need attention in the short term can represent a

competitive advantage

C rt nhiu cchhiu qu trong hc vin vngnh cng nghipc th tng tc.C l rrng nht l thng qua cc d nnghin cu chung.y c thmang hnh thccahp

tc thc s giacc k s tcc t chc,nhngthng xuyn hnbao gm cc hcvinthchinnghin cu v bo co ktqucho ngnh cng nghip.Cch tip cn nythngl kt qu cas cn thit chongnh cng nghipgi im lng vphng php nghincu m htin rng s l quan trngnkh nng cnh tranhngn hn.Tht vy,ngay cnhngkin thctrong vncn c quan tmtrong ngn hnc thi din cho mtlith cnh tranhPerhaps the most serious impediment to joint research projects between academia

and industry is the intellectual property (IP) issue. The usual opening stance of

both organizations is sole ownership of all IP, with no rights for the other party

without additional licensing fees. Much attention has been focused on large efforts

involving centers, with relatively less attention for smaller (e.g., single

investigator) projects. Some progress has been made on both fronts, and IPagreements have been reached in many cases. Nevertheless, much work remains to

resolve this thorny issue.C l tr ngi ln nht i vi cc d n nghin cu chung gia cc hc vin v ngnh cngnghip l s hu tr tu (IP) vn . Lp trng m thng thng ca c hai t chcny l duynht quyn s hu ca tt c cc IP, khng c quyn cho bn kia m khng cnl ph cp giyphp b sung. Nhiu s ch tp trung vo nhng n lc ln lin quann trung tm, vis quan tm tng i t hn cho nhhn (v d, iu tra vin duy nht)cc d n. Mt s tinbc thc hin trn c hai mt trn, v cc tha thun IP t c trong nhiu trnghp. Tuy nhin, vn cn nhiu vic gii quyt vn gai gc.

Other modes of interaction between academia and industry exist and can be quitefruitful. Many of these involve exchange or visits of personnel. Internships for

students or faculty in industry can provide perspective, direction, and research

ideas to be followed upon return to academia. Likewise, visits by industrial

researchers to academic labs can benefit the university lab as well

as the industrial visitor. While relatively uncommon in U.S. industry, Japanese and

Korean engineers often visit university research labs. While similar to internships

(although usually more focused and shorter term), faculty consulting can provide

similar benefits to both academia and industry. On the other side of the equation,

industrial practitioners frequently teach courses at universities, and can co-adviserfor theses and dissertations. One final and highly successful mode of

academic/university interaction is through entrepreneurship and start-up companies

Phng thc khc ca stng tc gia hc vin v ngnh cng nghip tn ti v c thc kh hiu qu. Nhiu ngi trong s ny lin quan n trao i v thm ving canhnvin.Thc tp cho sinh vin hoc ging vin trong ngnh cng nghip c th cungcp quanim, nh hng v nghin cu tng sau khi tr li hc vin. Tng tnh vy, chuyn


25/26

thm ca cc nh nghin cu cng nghip phng th nghim hc tp c thmang li li chcho phng th nghim trng i hc cng l ngi truy cp cngnghip. Trong khi tngi ph bin trong ngnh cng nghip M,cc ks Nht Bn v HnQuc thng xuyn gh thm cc phng th nghim trng i hc nghin cu. Trongkhi tng tnh thc tp (mc d thut ngthng tp trung hn v ngn hn), ging vin tvn c th cung cp cc li ch tng t cho c hai hc vin v ngnh cng nghip. pha bn

kia ca phng trnh, cc hc vin cng nghipthng xuyn ging dy cc kha hc ti cctrng i hc, v c th c vn cho cclun n v lun vn. Mt ch cui cng v rt thnhcng ca hc /trng i hctng tc l thng qua tinh thn kinh doanh v bt u cc cngty

There are a variety of ways in which the NSF fosters cooperation between

academia and industry. Perhaps the most direct is via matching funds that leverage

industrial contributions. Currently, most of the matching is done via large NSF

supported centers (such as the ERC and UICRC). We encourage funding for

smaller scale programs (e.g., individual PI) such as the GOALI and CAREER

programs. Programs that sponsor industrial implementation of research (e.g.,SBIR) help spur innovation and move ideas from academia to industry and should

be encouraged as wellC rt nhiu cch khc nhau trong NSF thc y hp tc gia hc vin v ngnh cngnghip. C l trc tip nht l thng qua ph hp vi qu tn dng cc khon ng gpcngnghip. Hin nay, hu ht ph hp vi thc hin thng qua ln NSF h tr cc trungtm (nh ERC v UICRC). Chng ti khuyn khch ti tr cho chng trnh quy m nhhn(v d, c nhn PI) nh GOALI v S NGHIPchng trnh.Cc chng trnh ti tr thc hin cng nghip ca nghin cu(v d, SBIR)gip thc y cc tng i mi v di chuyn t gii hc vin cho ngnh cngnghip v cn c khuyn khch nh

On a more intellectual side, the NSF in cooperation with joint industrial andacademic panels can identify areas of mutual interest to both communities and

promote them via calls for proposals. Finally, to ameliorate the intellectual

property impediments mentioned earlier, the NSF can help

establish general guidelines for IPR agreements. This could be done either by

publicizing existing standards or conventions, or by convening industrial and

academic representatives to devise a general framework, or even model

agreements, for the sharing of intellectual property rights

Trn mt kha cnh tr tu, NSF hp tc vi cc tm doanh cng nghip v hc thut c thxc

nh cc lnh vc hai bn cng quan tm cho c cng ng v thc y h thng qua cc cucgi cho cc xut. Cui cng, ci thin cc tr ngi s hu tr tu cp trc, NSF c th gipthit lp cc hng dn chung cho cc tha thun quyn s hu tr tu.iu ny c thcthc hin bng cch cng b cc tiu chun hin c hoc quy c, hoc bng cchtriutp cc i din cng nghip v hc thut a ra mt khun kh chung,hoc thmch l tha thun m hnh cho vic chia s quyn s hu tr tu

V Concluding Remarks


26/26

This report describes the findings of the 1999 NSF SponsoredWorkshop on Joint

Source-Channel Coding Research. The report and its recommendations address

three main goals. First, the report provides a view of the conditions and scenarios

in which joint source-channel coding can potentially achieve performance

improvements over independent source and channel code designs. These

conditions include resource-constraints, multiuser interactions, heterogeneity, and

time-variation or uncertainty. Second the report describes key research goals and

challenges in the field of joint source-channel coding. This summary includes

specific suggestions for research leading to advancement of theory, design, and

application of joint source-channel codes. Third, the report comments on the roles

of academia and industry in meeting the research challenges discussed. In

particular, the report suggests specific research problems for which collaboration

could be particularly beneficial and suggests methods for encouraging productive

interactions between companies and universities in tackling this problem of great

interest to bothBo co ny m tnhng pht hinca NSF SponsoredWorkshop nm 1999v nghincu chung M Ngun-Channel. Bo co v kin nghcaa ch ba mc tiu chnh.utin, bo co cung cpmt ci nhntrong cc iu kin v tnh hungtrong cc knhmha ngun doanh c kh nng c thtcnhngci tin hiu sut trn m ngunc lpv thitk m knh. Nhngiu kin ny bao gm cc ti nguyn hn ch,tng tca ngidng, tnh khng ng nht, vthi gianbin ihoc khng chc chn.Bo co th hai mtmc tiu nghin cuquantrngv thch thctrong lnh vc mha ca doanh ngun knh. Bn tm tt nybaogm cc gi c th chonghin cu hngutin b cal thuyt, thit k, v p dng cc knh m ngun chung. Th ba, cc kinbo co vvai tr ca cchc vin vngnh cng nghiptrong vic p ng nghincunhng thch thctho lun.c bit,bo cocho thy cc vn nghin cuc

th cho s hp tcc thcc bit c liv xut cc phngphp khuyn khch tng tc sn xutgia cng ty vtrng i hctrong vic giiquytvn nyquan tm rt lncho c hai

bc hội thảo năm 1999 về mã hóa ngồn kênh

Documents