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The entire a!aila&le wireless s%ectrum ranging $rom 7H* to 88 0H* is currentl

di!ided into man small non-o!erla%%ing &ands" which are licensed $or di,erent

communication %ur%oses" such as mo&ile communication" T9 &roadcasting"

satellite communication" maritime communication" etc( This lea!es little room to

allocate new isolated &ands $or new communication sstems and a%%lications(

Howe!er" measurements show that most o$ the allocated s%ectrum is !astl

under-utili*ed at an %articular location and time" es%eciall o!er the T9 &ands(

Cogniti!e radio has emerged as a new technolog that can su&stantiall increase

s%ectrum utili*ation e+cienc & allowing secondar users :unlicensed users; to

share the s%ectrum with %rimar users :licensed users; as long as the inter$erence

caused is maintained &elow a certain %rescri&ed le!el(

An in$ormation-theoretic model has &een %ro%osed to stud the $undamental

limits o$ cog-niti!e radios( 3n this model" one %rimar user is sending in$ormation

to its recei!er" while a secondar user is allowed to communicate with its own

recei!er simultaneousl o!er the same

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Jinhua Jiang

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in!estigates e,ecti!e communication strategies to achie!e the &est

communication rates gi!en limited %ower at each networ# node(

Consider a multi-ho% wireless sensor networ# that is de%loed o!er a &attle$ield to

monitor the mo!ements o$ hea! wea%ons( Two neigh&oring sensors should ha!e

a correlated o&ser!ation o$ the same e!ent( The ma con!e their indi!idual

o&ser!ations inde%endentl to two neigh&oring sensors $or relaing" &ut this

a%%roach is not e+cient in terms o$ %ower consum%tion( 3n $act" m wor# shows

that the correlation &etween o&ser!ation in%uts o,ers a great o%%ortunit to sa!e

transmission %ower i$ the neigh&oring sensors coo%erati!el transmit thecorrelated in$ormation( S%eci$icall" 3 in!estigated the inter$erence channel with

common in$ormation" where correlation &etween the two source in%uts is in the

$orm o$ common in$ormation( 3 %ro%osed a coding scheme that consists o$ three

laers a coo%eration laer regarding the common in$ormation" a colla&oration

laer regarding the crossl o&ser!a&le in$ormation" and a %ri!ate laer( The

resulting achie!a&le rate region leads to strict im%ro!ements o!er the e)isting

results in the 0aussian case" and demonstrates o%timalit in certain s%ecial cases(

>ue to the inherent &roadcasting nature o$ wireless transmissions" $eed&ac# can

&e easil collected at sensor nodes that are ca%a&le o$ recei!ing( 3t has &een

%ro!en that $eed&ac# does increase the ca%acit o$ multi-user channels :in

contrast to the %oint-to-%oint channel case;( Howe!er" the ca%acit regions are

un#nown $or most multi-user channels with $eed&ac#" e)ce%t $or a $ew s%ecial

cases with noiseless $eed&ac#( With the o&5ecti!e to im%ro!e the transmission

rates & e)%loiting $eed&ac# in wireless sensor networ#s" 3 ha!e studied

inter$erence channels with noiseless $eed&ac#" and rela channels with

generali*ed :nois; $eed&ac#( The main idea is to e)tract common in$ormation

$rom the $eed&ac#" which ena&les coo%eration &etween trans-mitting nodes to

achie!e higher transmission rates( The &ene$its o$ $eed&ac# :e!en generali*ed

$eed&ac#; can &e easil seen $rom our results & considering the asm%totics(

Howe!er" the gen-eral o%timalit o$ our results is still un#nown( 3 &elie!e inducingcommon in$ormation to achie!e coo%eration &etween transmitting nodes is not a

general solution to e)%loit $eed&ac#( A general

irections

3 %lan to $urther in!estigate communication networ#s $rom three di,erent

%ers%ecti!es theor" %ractice" and a%%lication( 3 &elie!e %ractice and a%%lication

not onl allow us to !eri$ theories" &ut also can hel% to disco!er limitations o$

e)isting theories and ins%ire de!elo%ment o$ new theories( elow 3 highlight three

to%ics which 3 wish to wor# on in the near $uture(

6 E)%loiting =eed&ac# and Correlation

=irst" 3 would li#e to continue m current research in networ# in$ormation theor"

with a s%eci$ic $ocus on understanding two inherent %ro%erties o$ most wireless

networ#s $eed&ac# and corre-lation( 3 &elie!e that the grand %ro&lem o$ $inding

the ca%acit o$ an ar&itrar wireless networ# cannot &e sol!ed without a thorough

understanding o$ these two %ro%erties( E)isting wor# on these two is relati!el

limited( 3n %articular" almost no ca%acit results ha!e &een re%orted $or multi-user

channels with correlated sources" and !er $ew ca%acit results ha!e &een

esta&lished $or multi-user channels with $eed&ac#( 3 %lan to %er$orm an in-de%th

stud on the structure o$ correlation and $ind out what $orms o$ correlation are

induci&le $rom $eed&ac#" & a%%ling more so%histicated tools $rom statistics( Theresearch out%ut is e)%ected to ha!e a &road range o$ %otential im%lications(

=irstl" it ma hel% to de!elo% new coding schemes to con!e correlated sources

in a networ#" and ma sol!e o%en %ro&lems associated with correlated sources"

such as multi%le access channels with correlated sources" &roadcast channels with

correlated sources" etc( Secondl" it ma answer the 'uestions on how to

e,ecti!el use !arious $orms o$ $eed&ac# nois" 'uanti*ed" or %er$ect" and how to

select the &est $orm o$ $eed&ac# i$ $inite rate o$ $eed-&ac# is allowed( These are

crucial intermediate ste%s towards a com%lete in$ormation-theoretic

understanding o$ communication networ#s(

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Jinhua Jiang 4/4

6 2ractical Code >esigns $or Cogniti!e

Radio Sstems

3 %lan to a%%l the theoretical insights

gained through m %ast wor# to %ractical

design o$ cogniti!e radio sstems( As

discussed earlier" cogniti!e radio is a

%romising candidate $or $uture wireless

technologies" &ut there are still man

im%lementation issues to &e addressed(

@ne #e issue is the code design $or the

cogniti!e radios( 3n order to mitigate the

#nown inter$erence" the cogniti!e userneeds to a%%l a %articular coding

techni'ue called dirt %a%er coding( So

$ar" there e)ists no sim%le

im%lementation o$ dirt %a%er coding to

$ull ca%itali*e the %er$ormance gain o$

this coding techni'ue( @ne o$ the e)isting

im%lementations is using lattice codes"

e)%loiting the $act that lattice codes are

&oth good channel codes and good

source codes( The %er$ormance o$ this

im%lementation is good" &ut thecom%le)it is !er high( 3 %lan to

in!estigate low-com%le)it alternati!es to

lattice codes that %ro!ide a $le)i&le

tradeo, &etween com%le)it and

%er$ormance( Through this research" 3

e)%ect to gain a &etter understanding o$

the com%le)it issue in!ol!ed in cogniti!e

radio sstems( 3 would also li#e to $ind

out how much theoretic %er$ormance can

&e actuall retained with a %ractical code

design o$ moderate com%le)it(

6 Networ# >esign $or Smart 0rid

With &oth theoretical and %ractical

e)%eriences in communication networ#

design" 3 %lan to stud the smart grid"

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which can &e regarded as a great $uture

a%%lication o$ communication networ#s(

The smart grid is an emerging %aradigm

in the %ower industr( 3t aims to re%lace

the current hierarchical" centrall-

controlled" and &roadcasting grid

structure with one that is more

distri&uted" more ro&ust" and more

e+cient( @ne interesting #e ca%a&ilit o$

the smart grid is that it can easil

integrate distri&uted %ower generationwith renewa&le sources such as solar and

wind into the grid( =or e)am%le" a

customer can not onl consume %ower

$rom the grid" &ut also sell &ac# to the

grid the %ower generated with his own

solar %anel( The intelligence and the

distri&uted control mechanisms $or these

e)changes must &e &uilt u%on an

in$rastructure that is e)tremel ro&ust

and ena&les su+cient in$ormation

e)change( To this end" there are man'uestions to &e addressed( =or e)am%le"

do we need to &uild a whole new

communication net-wor# $or the entire

grid Can we im%lement the associated

communication networ# as a sensor

networ# 3$ so" how can we modi$ the

e)isting sensor networ# design such that

it can su%%ort real-time and low-rate

communications with e)tremel high

relia&ilit and securit A%%arentl" all

these issues cannot &e addressed withoutan interdisci%linar e,ort $rom areas li#e

control" communications" and signal

%rocessing( Hence" 3 would li#e to

esta&lish a colla&oration with $uture

colleagues $rom the res%ecti!e areas to

e)%lore these %ro&lems( The research on

smart grid is still in its earl stage" and 3

&elie!e the im%act would &e signi$icant(

3n the long run" 3 would li#e to $urtherde!elo% m e)%ertise and e)tend m

current research in in$ormation theor

and wireless communications( The

o&5ecti!e is to &uild a &etter

understanding on how in$ormation can &e

o%timall communicated o!er a networ#

in terms o$ s%eed" e+cienc" and

relia&ilit( 3 would also li#e to e)%and m

research &eond the sco%e o$

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communication networ#s" & a%%ling m

e)%ertise in in$ormation theor and

wireless communications to new areas

such as smart %ower grid design" &io-

in$ormatics" etc(

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