Less Complex Channel Estimation Technique for MIMO OFDM system

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1 Iteratoal Research Joural of Eeer ad Techoloy IRJET) e-iss: Volume: 3 Issue: 4 Ar-216 wwwrjetet -ISS: Less Comlex Chael Estmato Techque for MIMO OFDM system 1 Sadeekumar S Gamt, 2 Prof Sarma K ada, 3 Prof Dharmedra Chauha 1 MTech Studet, Electrocs ad Commucato, Chadubha S Patel Isttute of Techoloy, Gujarat, Ida 2 Asso, Professor, Electrocs ad Commucato, Chadubha SPatel Isttute of Techoloy, Gujarat,Ida 3 Ass, Professor, Electrocs ad Commucato, Chadubha SPatel Isttute of Techoloy, Gujarat, Ida *** Abstract - Chael estmato of multle ut multle outut orthooal frequecy dvso multlex system for coheret system s very much crucal I ths aer we had troduced a ew chael estmato techque based o artfcal tellece It s desed ad ts erformace of the techque s comared to the tradtoal techque lke least square or LS), least mea square or LMS), mmum mea square or MMSE) alorthms ad artfcal tellece by us comuter smulatos Key Words: MIMO-OFDM, chael estmato, moble commucato system, artfcal tellece, LS, MMSE 1ITRODUCTIO The multle-ut multle-outut MIMO) orthooal frequecy dvso multlex OFDM) s oe of the most roms techques the curret era It s wdely used wreless commucatos Estmato of Chael has bee successfully used to mrove the erformace of OFDM systems For stace, df-feretal detecto would result a 3-dB loss sal-to-ose rato SR) comared wth coheret detecto, where chael arameters are requred Most dversty schemes are desed wth the assumto that the chael formato s avalable For examle, chael estmato s crucal for the recever comb or decod of sace-tme code Therefore, chael estmato s essetal MIMO-OFDM system des Varous OFDM chael estmato schemes have bee roosed the lterature, mostly for sle atea system [14], [15] I ths aer, we cosder chael estmato for trasmt dversty us sace tme cod for OFDM systems Assum that the chael s quas-statoary ad the sychrozato s erfect, we are terested chael estmators based o a sle block of OFDM data The receved sal s a suerosto of dfferet sa trasmtted from dfferet trasmt ateas smultaeously Wth the assumto of tol-erable leakae, Fourer trasform model based alorthms were studed [1], [2], [16], ad [17] Later, a reduced comlexty detecto scheme was studed by exlot the correlato of the adjacet subchael resoses [3] A olyomal model based aroach was develoed [12] These tycal schemes [2], [9], [1] assume a maxmum delay rofle ad do ot adat to sarse chael codtos or hher delay rofles Cosequetly, the estmato accuracy wll be deraded uder these codtos ote that the chael mue resose s characterzed by the delays of the aths, therefore, estmat tme of arrva TOAs) s oe way to mrove chael est- mato A multdmesoal maxmumlkelhood ML) search s oe soluto but a rohbtvely comlex task A umber of alteratves have bee roosed to reduce the comlexty The alterat rojecto AP) method [5] s terest due to ts ood erformace A chael estmato scheme va ear-ml TOA estmato, wth ts root AP, was reseted [11] wth ood erformaces owever, the AP alorthm stll suffers from hh comutatoal costs, esecally whe the umber of aths s ukow 2 OFDM Parameters Table 1 ts the ma arameters of the draft OFDM stadard A key arameter whch larely affected the choce of the other arameters s the uard terval of 8 s Ths uard terval rovdes robustess to root-mea-squared delay sreads u to several hudreds of aosecods, deed o the cod rate ad modulato used I ractce, ths meas that the modulato s robust eouh to be used ay door evromet, clud lare factory bulds It ca ao be used outdoor evromets, althouh drectoal ateas may be eeded ths case to reduce the delay sread to a accetable amout ad to crease the rae 216, IRJET Imact Factor value: 445 ISO 91:28 Certfed Joural Pae 229

2 Iteratoal Research Joural of Eeer ad Techoloy IRJET) e-iss: Volume: 3 Issue: 4 Ar-216 wwwrjetet -ISS: Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mbt/s Modulato Cod rate umber of subcarrers 52 umber of lots 4 OFDM symbol durato 4 µs Guard terval Subcarrer sac BPSK, QPSK, 16-QAM, 64-QAM 1/2, 2/3, ¾ 8 s 3125 kz -3 db Badwdth 1656 Mz Chael sac 2 Mz Table 1: Ma Parameters of the OFDM stadard I order to lmt the relatve amout of ower ad tme set o the uard tme to 1 db, the symbol durato was chose to be 4 s Ths ao determed the subcarrer sac to be 3125 kz, whch s the verse of the symbol durato mus the uard tme By us 48 data subcarrers, ucoded data rates of 12 to 72 Mbs ca be acheved by us varable modulato tyes from BPSK to 64-QAM I order to correct for subcarrers dee fades, forward or correcto across the subcarrers s used wth varable cod rates, v coded data rates from 6 u to 54 Mbs Covolutoal cod s used wth the dustry stadard rate 1/2, costrat leth 7 code wth eerator olyoma 133,171) her cod rates of 2/3 ad 3/4 are obtaed by uctur the rate 1/2 code 3 System Descrto I The block daram of a OFDM system The bary formato data are roued ad maed to multamltude-mult-hase sa I ths aer, we cosder the 16-QAM modulato After lot serto, the modulated data Xk) are set to a IDFT ad are trasformed ad multlexed to x as II x IFFT{ X k)} 1 k III X k) e j 2k/ For =, 1, 2, -1 IV where s the umber of subcarrers The uard terval s serted to revet ossble ter-symbol terferece OFDM systems, ad the resultat samles x are V x x x, 1, 1,1, 1 VI where s the umber of samles the uard terval The trasmtted sal s the set to a frequecy selectve multath fad chael The receved sal ca be rereseted by VII y x h w VIII IX Where h s the chael mue resose CIR) ad w s the Addtve Whte Gaussa ose AWG) ad s the crcular covoluto The chael mue resose h ca be exressed as [17] h r 1 X h e j2f D T ) XI Where r the total umber of roaato aths, h s the comlex mue resose of the th ath, f D s the th ath s Doler frequecy shft whch causes Iter chael Iterferece ICI) of the receved sa, τ s the delay sread dex, ad s the th ath delay tme ormalzed by the saml tme After remov the uard terval from y, the receved samles y are set to a Fast Fourer Trasform FFT) block to demultlex the mult-carrer sa XII 1 k) FFT{ y } 1 y e j2k/ XIII If we assume that the uard terval s loer tha the leth of chae1 mue resose- there s o ter-symbol terferece betwee OFDM symbo- the demultlexed samles k) ca be rereseted by XIV k) X k) k) W k), k,1, 1 s f DT ) j2f DT 2 j k f DT XV Where k) h e e ad Wk) s XVI the Fourer trasform of the AWG wk) XVII After that, the receved lot sa fk) are extracted from f k), the chael trasfer fucto fk) ca be obtaed from the formato carred by fk) Wth the kowlede of the chael resoses fk), the trasmtted data samles fxk) ca be recovered by smly dvd the receved sal by the chael resose: XVIII y k) xˆ k) ˆ k) 216, IRJET Imact Factor value: 445 ISO 91:28 Certfed Joural Pae 2291

3 Iteratoal Research Joural of Eeer ad Techoloy IRJET) e-iss: Volume: 3 Issue: 4 Ar-216 wwwrjetet -ISS: XIX where ^ k) s a estmate of k) After sal dema, the source bary formato data are recostructed at the recever outut XX The OFDM trasmsso scheme makes t easy to ass lots both tme ad frequecy doma two major tyes of lot arraemet The frst kd of lot arraemet show t s deoted as block-tye lot arraemet The lot sal s assed to a artcular OFDM block, whch s set erodcally tme doma Ths tye of lot arraemet s esecally sutable for slowfad rado chae The estmato of chael resose s usually obtaed by ether LS or MMSE estmates of tra lots [5] XXI The secod kd of lot arraemet, s deoted as comb-tye lot arraemet The lot sa are uformly dstrbuted wth each OFDM block Assum that the ayloads of lot sa of the two arraemets are the same, the comb-tye lot assmet has a hher retrasmsso rate Thus, the comb-tye lot arraemet system s rovdes better resstace to fast-fad chae Sce oly some sub-carrers cota the lot sal, the chael resose of olot subcarrers wll be estmated by terolat ehbor lot sub-chae Thus, the combtye lot arraemet s sestve to frequecy selectvty whe comar to the block-tye lot arraemet system That s, the lot sac f), must be much smaller tha the coherece badwdth of the chael f)c [3] 4 Chael Estmato For comb-tye lot sub-carrer arraemet, the lot sa Xm) ;m = ; 1; ; - 1, are uformly serted to Xk) That s, the total sub-carrers are dvded to rous, each wth L = / adjacet sub-carrers I each rou, the frst sub-carrer s used to trasmt lot sal The OFDM sal modulated o the kth sub-carrer ca be exressed as X k) X ml l) Let X f ormato data, [ ) [ ) L 1) 1) l l 1,2,, L 1 1)] 1) L 1))] be the chael resose of lot carrers, ad [ ) 1) 1)] be a vector of receved lot sa The receved lot sal vector ca be exressed as X W T X ) X 1) X 1) where W s the vector of Gaussa ose lot subcarrers A LS Estmato I covetoal comb-tye lot based chael estmato methods, the estmato of lot sa, s based o the LS method s ve by ˆ, [ X, 1 ), 1), ) 1) X ) X 1) X 1)] 1) 1) The LS estmate of s suscetble to AWG ad Iter- Carrer Iterferece ICI) Because the chael resoses of data subcarrers are obtaed by terolat the chael characterstcs of lot subcarrers, the erformace of OFDM systems whch are based o comb-tye lot arraemet s hhly deedet o the rorousess of estmate of lot sa Thus, a estmate better tha the LS estmate s requred The MMSE estmate has bee show to be better tha the LS estmate for chael estmato OFDM systems based o block-tye lot arraemet The Mea Square Error MSE) estmato, ve [17], shows that MMSE estmate has about 1-15 db a SR over the LS estmate for the same MSE values The major drawback of the MMSE estmate s ts hh comlexty, whch rows exoetally wth the observato samles B MMSE Estmato The MMSE estmator emloys the secod order statstcs of the chael codtos order to mmzes Mea Square Error MSE) Let R hh, R, ad R be the autocovarace matrx of h,, ad, resectvely ad R h be the cross covarace matrx betwee h ad Ao σ 2 w deotes the AWG varace E{ w 2 } Assume the chael vector h, ad the AWG w are ucorrelated, t ca be derved that [18] R E{ } E{ Fh) Fh) } Where FR hh F Where 216, IRJET Imact Factor value: 445 ISO 91:28 Certfed Joural Pae 2292

Iteratoal Research Joural of Eeer ad Techoloy IRJET) e-iss: 2395-56 Volume: 3 Issue: 4 Ar-216 wwwrjetet -ISS: 2395-72 Ad 1) k j 2, k 1 e 1) 1) 1) s called as the twdle factor matrx Assum R hh thus R

4 Iteratoal Research Joural of Eeer ad Techoloy IRJET) e-iss: Volume: 3 Issue: 4 Ar-216 wwwrjetet -ISS: Ad 1) k j 2, k 1 e 1) 1) 1) s called as the twdle factor matrx Assum R hh thus R ) ad σ w2 are kow at the recever advace, the MMSE estmator of the h s ve hˆ R R MMSE At last t ca be estmated that mmss=dshfd MMSE emloys the secod order statstcs of the chael for estmato Sometmes the chael statstcs are ot avalable, so t s dffcult to estmate the chael ths stuato owever, OFDM systems the sal ca be avalable at the recever by meas of lot carrers Our Proosed Alorthm: 1 The Alorthm s as follows: 1) Italze the observato wehts w = 1=; = 1;, 2,, 2) For m = 1 to M a) Ft a classfer Tm)x) to the tra data us wehts w b) Comute c) Comute d) Set w w c T h x )) / lo w ex e) Re-ormalze w m) m) I C w lo K 1) T x ))) 3) Outut C x) ar max M k m1 I T IV SIMULATIO RESULTS x) k) The OFDM system chael estmato was smulated wth LS, MMSE, BLUE ad AdaBoost methods I all smulatos we have used QAM16 as the modulato scheme for the dvdual carrers Other arameters of the smulato are ve the TableI Fure3 shows comarso of Bt Error Rate BER) for LS, MMSE, BLUE ad AdaBoost Fure3 shows that the AdaBoost alorthm mroves the erformace secally low SR values owever, at hh SR both MMSE ad AdaBoost show a smlar erformace Furtheremore, AdaBoost ves better erformace whe comared to LS ad BLUE evertheless, BLUE ad LS are erform same or we ca tell BLUE ves very maral mrovemet to LSThe reaso for ths erformace crease s because of the covarace matrx used the BLUE As our ose s ASWG ad t has varace of 1 so the BLUE s erformace s all most that of LS alorthm V COCLUSIO The comutatoal comlexty of the MMSE creases exoetally as the umber of carrer creases, whereas the comutatoal comlexty s ot exoetal the case of Our alorthm ece, Our roosed alorthm ca be emloyed whe a hh umber of carrers s requred Furthermore, as t s a classfcato alorthm so the recever sde we wll requre a searate demaer or decoder) to et the desred data bts AdaBoost ot oly creases the erformace of the OFDM systems t ao 216, IRJET Imact Factor value: 445 ISO 91:28 Certfed Joural Pae 2293

5 Iteratoal Research Joural of Eeer ad Techoloy IRJET) e-iss: Volume: 3 Issue: 4 Ar-216 wwwrjetet -ISS: reders the QAM ma obsolete ad thereby reduc the comlexty of recever dess REFERECES [1] G Easo, B oble, ad I Seddo, O certa tera of Lschtz-akel tye volv roducts of Bessel fuctos, Phl Tras Roy Soc Lodo, vol A247, , Arl 1955 refereces) [2] J Clerk Maxwell, A Treatse o Electrcty ad Maetsm, 3rd ed, vol 2 Oxford: Claredo, 1892, [3] IS Jacobs ad CP Bea, Fe artcles, th flms ad exchae asotroy, Maetsm, vol III, GT Rado ad Suhl, Eds ew ork: Academc, 1963, [4] K Esa, Ttle of aer f kow, uubhed [5] R cole, Ttle of aer wth oly frst word catalzed, J ame Stad Abbrev, ress [6] orozu, M rao, K Oka, ad Taawa, Electro sectroscoy studes o maeto-otcal meda ad lastc substrate terface, IEEE Trasl J Ma Jaa, vol 2, , Auust 1987 [Dests 9th Aual Cof Maetcs Jaa, 31, 1982] [7] M ou, The Techcal Wrter s adbook Mll Valley, CA: Uversty Scece, , IRJET Imact Factor value: 445 ISO 91:28 Certfed Joural Pae 2294

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