Delay Estimator and Improved Proportionate Multi-Delay Adaptive Filtering Algorithm

Transcription

1 18 E. VERTELETSKAYA K. SAKHNOV B. ŠIMÁK DELAY ESTIMATOR AND IMPROVED PROPORTIONATE MULTI-DELAY Delay Esimaor and Improved Proporionae Muli-Delay Adapive Filering Algorihm Eaerina VERTELETSKAYA Kirill SAKHNOV Boris ŠIMÁK Dep. o Telecommunicaion Engineering Czech Technical Univ. in Prague Technica Prague 1667 Czech Republic vereea@el.cvu.cz sahnir@el.cvu.cz sima@el.cvu.cz Absrac. This paper perains o speech and acousic signal processing paricularly o he deerminaion o echo pah delay and operaion o echo cancellers. To cancel long echoes he number o eighs in a convenional adapive iler mus be large. The lengh o he adapive iler ill direcly aec boh he degree o accuracy and he convergence speed o he adapaion process. We presen a ne adapive srucure hich is capable o deal ih muliple dispersive echo pahs. An adapive iler according o he presen invenion includes means or soring an impulse response in a memory he impulse response being indicaive o he characerisics o a ransmission line. I also includes a delay esimaor or deecing ranges o samples ihin he impulse response having relaively large disribuion o echo energy. These ranges o samples are being indicaive o echoes on he ransmission line. An adapive iler has a pluraliy o eighed aps each o he eighed aps having an associaed ap eigh value. A ap allocaion/conrol circui esablishes he ap eigh values in response o said deecing means so ha only aps ihin he regions o relaively large disribuions o echo energy are urned on. Thus he convergence speed and he degree o esimaion in he adapaion process can be improved. Keyords Speech enhancemen delay esimaion echo cancellaion. 1. Inroducion Echo cancellers are idely used boh in landline and mobile communicaion o eliminae he echo phenomenon hich grealy aecs he qualiy o speech and audio services. An echo canceller essenially uses a copy o he daa incoming o a lisener o digially esimae he echo ha should reurn on he ougoing line. Having calculaed he esimae he echo canceller subracs he echo esimae rom he ougoing signal such ha he echo cancels ou. Operaion o a prior ar echo canceller ypically involves Fig. 1. Example o an impulse response o an echo pah. an esimaion o he enire echo pah response. The ypical echo pah delay ( d ) is ormed by a pure delay ( r ) and a ail delay ( e ) (see Fig. 1). The pure delay is he acual propagaion ime aen by he signal rom is source o a place here he echo occurs (e.g. hybrid) and bacards. The ail delay on he oher hand is he response o he hybrid circui hich erminaes he ourire line and perorms impedance maching. No all o he echo pah response is relevan o he calculaions o an echo canceller. The pure delay elemen and any porion coming aer he ail delay is no relevan and accordingly need no be involved in he adapaion process o he echo canceller. Since an echo canceller s complexiy is relaed o he number o iler aps i uses he reducion o he number o hese iler aps is imporan or opimizaion o iler operaion. In order o minimize he echo canceller s calculaions an esimae o he echo pah delay needs o be calculaed such ha he acual number o required aps may be deermined. Thereore a mehod deermining he duraion o hese porions o he echo pah response is necessary o opimize an echo canceller. Mehods or deermining pure delay esimaes rom an esimae o he echo pah impulse response are described in [1]-[5]. Reerence [1] perorms a search on he coeiciens o he adapive iler o ind he maximum absolue value corresponding o he pea o he echo pah response. According o ha echnique (illusraed in Fig. ) assuming ha he maximum value a coeicien or iler ap max a value sar is calculaed by subracing a ixed ineger rom max. Assuming ha he hybrid impulse response lass H samples or aps and given he hybrid response sar as

2 RADIOENGINEERING VOL. 1 NO. 1 APRIL Fig.. Graphical vie o echo pah delay esimaion in [1]. Fig. 3. Graphical vie o echo pah delay esimaion in []. sar hen he end o he relevan porion o he impulse response is max + H-1. This provides he boundaries or he segmen e hich is he only porion o he echo pah required or echo cancellaion. Once his is esablished he adapive iler echo canceller operaes on inerval e and ill only use inerval r as pure delay. Hoever a problem ih he echnique described above is is assumpion ha max lies a ixed ineger amoun o samples rom he sar o he hybrid response. When his assumpion is no applicable o a cerain sysem here is an erroneous echo pah calculaion causing he iler o diverge and disrup he communicaion. Thereore i is necessary in implemening his echnique ha here is a calibraion o he ype o line characerisics o each applicaion. Reerence [] describes a o sep mehod ha irs searches or he maximum absolue value ( max_1 ) conained in he irs D coeiciens o he iler. A second sep sars a his posiion and involves a search or he irs ensuing iler coeicien ( max_ ) ih an absolue value hich is K imes greaer han he irs maximum value. The dispersive par o he impulse response is assumed o sar a predeermined number o aps beore his second ap and o las a predeermined number o aps rom his sar posiion. A beginning o he impulse response ( sar ) is calculaed as max_ D. Fig. 3 shos a graphical vie depicing echo pah delay esimaion using he described echnique. The above described mehod assumes ha he irs coeiciens o he impulse response have zero mean. Hoever his assumpion is no alays rue hich may lead o erroneous decisions. For example he esimaed impulse response may conain oscillaions ih raher long periods due o iler coeicien esimaion using elephone band speech signals in he presence o bacground noise rom he near end side. In he mehod described in [3] he echo locaion is deermined by calculaing he echo pah locaion a hich here is a high correlaion beeen he signal ougoing o he echo pah and he reurned echo. The echnique uses normalized cross-correlaion uncion or his purpose. The correlaion is calculaed in a sliding indo having he lengh o he digial adapive iler. The dispersive par is assumed o sar hal he iler lengh beore he posiion o he maximum absolue value o he impulse response esimae. This is no an especially accurae mehod because he ap ih maximum absolue value does no need o be locaed in he cenre o he echo ail. Moreover his mehod breas don i he impulse response consiss o muliple echoes. Reerence [4] describes a mehod ha deermines regions o he impulse response here he energy is concenraed. This is done by summing he absolue values o iler aps ihin a indo ih a predeined lengh and comparing each sum o a ixed hreshold. The indo slides over he impulse response esimae. The posiions exceeding he hreshold are considered o belong o echo conaining regions. The remaining regions are considered o be delays. This mehod gives a raher coarse delay measuremen. Hoever no mehod or choosing a ixed hreshold value is presened. Reerence [5] is similar o reerence [4] in ha i describes a mehod ha deermines here in he iler impulse response he energy is concenraed. According o ha mehod an esimae o he average poer in he aveorm is compued sample by sample and hen a predeermined average poer hreshold is exceeded a sar lag is se. The poer calculaion is coninued unil he ime hen he average poer drops belo a second hreshold indicaing ha he end o he echo signal has been passed. In order o reine he approximae locaion o he echo he mehod uilizes a compuaion reerred o as cenre o echo. This compuaion is done over he enire range o samples beeen he irs and he second lags. I is assumed ha he energy o echo ail is equally disribued abou he esimaed cenre o echo. Then he radius o echo is compued. I is urher uilized o deermine he range abou he cenre o echo hich conains he dispersive par o he echo pah. Hoever an assumpion ha he dispersive region is equally disribued abou he esimaed cenre o echo hich is simply he posiion o he ap ih maximum absolue value is no rue. Thus a mehod and apparaus or accuraely deermining echo pah delay as ell as or accuraely deermining an appropriae number o aps o uilize or a ransversal adapive iler o an echo canceller is required. I is undesirable or an echo canceller o operae a imes hen here is no echo. Running an echo canceller under such circumsances merely creaes compuaional

3 184 E. VERTELETSKAYA K. SAKHNOV B. ŠIMÁK DELAY ESTIMATOR AND IMPROVED PROPORTIONATE MULTI-DELAY noise as a resul o inie ord lengh accuracy in he digial ransversal iler. I is hereore desirable o provide a digial echo canceller srucure hich overcomes hese and oher problems associaed ih convenional echo canceller srucures.. Dealing Wih Addiive and Measuremen Noise The above described procedures assumes ha he echo pah impulse response has been esimaed using signals ha are rich enough (or insance in heir requency conen) o excie all he models o he acual echo pah. In several cases especially i he bacground noise level rom he near end side has been higher han he bacground noise level rom he near end side during a call he impulse response (IR) esimae ill conain errors a requencies ha have been under-represened in he ar end signal. Exisence o his ind o error componens maes he esing procedure less reliable since he variance o his ype o errors is no non. In order o reduce he inluence o his ype o errors on he impulse response esimae he impulse response esimae should preerably irs be processed o remove (suppress) componens ha are normally no presen in elephone band speech signals. Echo cancellers are alays designed o operae or he limied echo pah delay capaciy. This creaes an addiional compuaional noise as a resul o inie ord lengh accuracy. Moreover hen an esimaion process is corruped by random variaions i is said o be aeced by measuremen noise. Since he sandard deviaion is a measure o spread in a daa disribuion hese random variaions can be characerized by he sandard deviaion o he measured signal. Tha is he larger he sandard deviaion he noisier is he measuremen. The procedure o reducing or aenuaing he noise componens o a measured signal is commonly non as ilering. There are many dieren ays o design ilers bu he mos common ones have heir roos in simple averaging. Knon noise reducion echniques can be classiied as ollos: using averaging iler using lo-pass iler by specral subracion (Fourier Wavele hresholding) using convoluion ih smoohing uncions. Consider a hree sage process o smoohing noisy componens. Fig. 4 shos a curve depicing he esimaed impulse response and processed esimae o he echo pah obained by a Muli-Delay bloc Frequency domain (MDF) adapive iler [6]. The depiced esimae o he echo pah impulse response has a lo o noisy componens due o he above discussed reasons. The smoohed version o i as obained in accordance ih he procedure sho in Fig.5. I is a lochar illusraing seps perormed by an algorihm in order o reduce he inluence o measuremen errors. The irs operaion is lo-pass ilering. This is done by ransorming he iler coeiciens using he Fas Fourier Transorm (FFT) ino he requency domain. The requency bins hich lay under he predeined cu-o requency (e.g. F cu = 00 Hz) are removed rom he specrum. Then he inverse FFT (IFFT) is applied o ransorm he iler coeiciens bac ino he ime domain. The second sep uses he exponenially eighed moving average iler. This operaion is perormed in accordance ih he olloing expression 1 1 (1) WIN1 () WIN (3) WIN 1 1 here are he lo-pass ilered coeiciens = 1 L (L is he adapive iler lengh); WIN 1 is a moving indo o values (e.g. 8 samples or 1 ms or 8 Hz sampling rae) ha are used o calculae he average o he daa sequence; α is he iler consan (orgeing acor). 1 Fig. 4. Graphical vie o esimae and processed esimae o he echo pah.

4 RADIOENGINEERING VOL. 1 NO. 1 APRIL Fig. 5. A lo char illusraing a smoohing procedure. Is value dicaes he degree o ilering i.e. ho srong he ilering acion ill be. Since 0 his means ha 0 α < 1. When a large number o poins are being considered α 1 and 1. This means ha he degree o ilering is so big ha he measuremen does no play a par in he calculaion o he average. On he oher exreme i 0 hen hich means ha virually no ilering is being perormed. Aer he previous sep has compleed he averaged iler coeicien should be pos processed in he olloing manner 1 WIN h 1 WIN u u0 WIN1 u u hen hen 0 WIN 1 WIN 1 L 1 here WIN is he second moving indo o values (e.g. 8). The reason or doing his operaion is o aciliae he searching scheme or dispersive regions. The olloing secion describes a proposed mehod or echo canceller hich deermines he dispersive regions rom he processed esimae o he echo pah impulse response. 3. Deermining Dispersive Regions Tha is he overall echo canceller srucure loos lie a convenional echo canceller having a very large apped delay elemen. Bu only cerain groups o aps are acually urned on a any given ime aer he dispersive regions have been deined. The presen algorihm examines he impulse response o he line (hich corresponds o ap eighs or a ransversal iler) and allocaes aps according o here an echo is acually occurring on he line. Consequenly an echo canceller includes a long ransversal iler incorporaed ih he conrol elemen used o esimae he delays and idhs o he dispersive regions. The ransversal adapive iler has lengh large enough so ha he hole echo pah impulse response ( d ) can be esimaed. Delay values are hen esimaed rom he iler coeiciens. When all delays are non he number o iler aps can be grealy reduced. (4) When he connecion sars ( 0 ) he adapive iler is acivaed o esimae he echo pah. Noe some predeermined condiions are employed o decide hen he ranser o iler coeiciens o he conrol neor should occur and hese precondiions are he olloing. Firs he approximae seling ime (1 second + d + 0 ) or he adapive iler is calculaed. Aerards his value is ranserred ino he couner regiser o he conrol neor. This condiion assures he adapive iler ill have enough ime or adapaion bu no guaranee o accuracy. When double-al siuaion is deeced he couner is rozen since he eigh adjusmen process has been prohibied. Aer he seling ime has expired he second condiion is esed. One should sill be aare ha no double-al is presen since near-end speech ill aec he es resul. Thus hen he irs condiion is saisied and here is no near-end speech in he line he shor ime poers o e(n) and y(n) n 1 1 e n R R (5) R e y e n 1 1 y n R (6) y are calculaed and hen heir raio is compared o a small consan value χ. A χ o 0.01 corresponds o a 0 db loss o echo poer. Weighing acor ρ is a consan beeen 0 and 1 or example 17/18. Furhermore he poer may also be esimaed by summing he squares o or example he las 18 samples o e(n) and y(n) bu equaions above require a less complex implemenaion. Alernaively a quaniy called he Echo Reurn Loss Enhancemen (ERLE) represened by he olloing equaion yi inn 1 ERLE( n) 10log10 [ db] n e n i inn 1 may be used or esing he second condiion. When all he condiions are saisied he conrol neor ill copy he iler eighs process hem and perorm he search or he echo delays. The mehod or locaing he dispersive regions o he uncion h() is as ollos: a) ind he maximum (h max ) value o he h() sore is posiion as h max_posiion ; b) calculae he maximum envelope (h max_envelope see Fig. 6) using algorihm shon in Fig. 7; c) search or he 1 s inerval on he le rom he h max_posiion here h max_envelope is consan; d) sore he value o h max_envelope ino variable h max_1_righ ; e) search or he nd inerval on he le rom he h max_posiion here h max_envelope is consan ) sore he value o h max_envelope ino variable h max righ ; g) ind local minimum o he uncion h() ihin he 1 s inerval and sore i as h min_1_righ ; h) ind local minimum o he uncion h() ihin he nd inerval and sore i as h min righ ; i) calculae he 1s condiion (C1) using equaion (7)

5 186 E. VERTELETSKAYA K. SAKHNOV B. ŠIMÁK DELAY ESTIMATOR AND IMPROVED PROPORTIONATE MULTI-DELAY 1 h C1 0 else min_ 1 _ righ h min righ Fig. 6. A graph illusraing a smoohing procedure. 0 j) calculae he nd condiion (C) using equaion (8) h h max_ 1 _ righ max C 1 maxh h max_ 1 _ righ max 0 else righ righ 100% 40% ) calculae he 3 rd condiion (C3) using equaion 1 h C3 0 else max_1 _ righ h max righ 0 (9) (10) l) chec hese hree condiions in accordance ih he coding scheme illusraed in Fig.8; m) deine heher he 1 s region aends o he dispersive par o he echo impulse response (IR); n) copy parameers rom he nd inerval ino he 1 s inerval; o) search or a ne nd inerval on he le rom he 1 s inerval here h max_envelope is consan; p) perorm seps 6-15 again ill he end o he lehand region o he uncion h(); q) repea seps 3-4 again bu or he samples hich lay on he righ side rom he h max. Noe ha hen he end o he dispersive region is ound he seps n) and o) are excluded. Also noe ha in order o simpliy he search operaion only inervals (here h max_envelope has consan values) ih he lengh bigger han e.g. 8 samples may be considered. Aer all he seps have passed he idh o he irs dispersive region ( idh ) can be deermined using he olloing equaion ormulas (11) idh sar end sar h (1) min_1_ righ Fig. 7. An engine or searching max envelope o he posprocessed esimae o echo pah. Fig. 8. A ransiion diagram or esing condiions C1 C C3. sar end h (1) min_1_ righ h. (13) min_1_ le

6 RADIOENGINEERING VOL. 1 NO. 1 APRIL I he case ih muliple dispersive pars is considered he values o he uncion h() hich belong o he deermined dispersive region have o be urned o zero. Aerards he hole searching operaion may be repeaed. Neverheless he ime delay esimae o he enire echo signal should be preerably calculaed in accordance ih he olloing relaionship Delay n T L1 s 0 L1 0 Fig. 9. A simpliied srucure o a ne requency domain iler. n n (14) here T s =1/F s F s is a sampling rae o speech signal (e.g. 8 Hz); is a paricular adapive iler eigh. For he purpose o he subsequen secion deine a binary vecor (BIN) o lengh L. Is elemens are ormed in he olloing manner BIN n 1 i n lays inside he dispersive par o he IR 0 elsehere. (15) Aer he dispersive regions are deermined he conrol circui ses he adapive iler. The acive eigh values are remained urned on. To improve he accuracy o he adapive iler an echo esimae is calculaed only using cerain subiler blocs hich are considered o cover he dispersive par o he echo pah impulse response (IR). 4. Proposed Echo Cancelling Algorihm A simpliied bloc diagram o he proposed adapive iler is shon in Fig. 9. Is srucure consiss o an echo esimaor K shor lengh (N) subiler blocs an oupu muliplexer and a conrol circui. The delay esimaor is a primary hole lengh (L = KN) MDF or any oher requency domain iler [7] incorporaed ih he conrol circui used o esimae he delays and idhs o he reduced dispersive regions. Noe ha he value o L should be large enough so ha he hole echo pah impulse response can be covered. In some commercial echo canceller srucures his value may be up o 4096 samples hich corresponds o he delays up o 51 ms. Echo pah delay can hen be deermined rom he esimaed echo pah impulse response. When all he delay values are non and he binary vecor (BIN) is ormed he number o operaions required or calculaion o he echo signal can be grealy reduced. The oupu muliplexer hich is conrolled by he conrol circui selecs hich coeiciens ihin he adapive iler need o be updaed or no. Noe ha he hole lengh iler sill may uncion as a eigh updaer. Boh ypes o srucures he ull-lengh and he shor one are operaing exclusively. The conrol circui can compare he errors rom hese ilers o deermine hich one is more suiable or ha insan o ime o esimae echo pah. In order o rac he ime variance o he echo pah he conrol circui has o chec or he locaion o he maximum eigh value o he dispersive region o adjus he elemens in he vecor BIN(n) aer a speciied seling ime ( chec ). In his ay each subiler bloc can rac is on dispersive region more eicienly and accuraely. The improvemen in accuracy is a direc resul o he eer eighs needed since he misadjusmen is proporional o he number o eighs [8]. The irs sep o he MDF algorihm is o conver he mos recen overlapped inpu samples o he requency domain as ollos X K m x diagfft 0 m 1 x1 m 1... x m 1 x m x m... x m N N 1 T. (16) The inpu vecors incoming o each o he subiler blocs can be obained via he rame index shiing ihou invoing any compuaion as ollos:

7 188 E. VERTELETSKAYA K. SAKHNOV B. ŠIMÁK DELAY ESTIMATOR AND IMPROVED PROPORTIONATE MULTI-DELAY m X 1 m K 1. X (17) The described approach suggess ha only one FFT is needed per rame ieraion in order o ransorm he inpu vecor ino he requency domain. I implies a signiican compuaion saving. The oupu and he error requencydomain vecors can be expressed and calculaed as K 1 d m las N erms o FFT X m W m (18) 1 E m FFT y m d m (19) N zeros N erms W N zeros N erms m FFT m (0) here W (m) is he h requency coeicien vecor and d(m) is he desired vecor. The IPMDF ime coeicien updae equaions o minimize he Mean Square Error (MSE) are he olloing φ S 1 1 m irs hal o FFT X m S m E m MDF m S m 1 1 X m X m MDF MDF (1) () m 1 m L G mφ m (3) m diagg m g m.. g m G (4) N N 1. N N 1 g 1 N l 1 L j0 1 N l m L m j (5) here = 1 K l = 1 L and μ is he bloc sep-size conrol parameer 0 << λ < 1 is he orgeing acor. Furher e describe ho he binary vecor BIN may be incorporaed ino he IPMDF algorihm. Deine he LxL diagonal selecion marix B(m) B 0... K 1 m diag b m... b m N1 NN and is elemens are deined as ollos (6) 1 BINl 1 l 0... L 1 b l m (7) 0 BINl 0. The ime-domain subiler-selecion rouine is done by muliplying his marix ih he corresponding eighs in every h subiler as shon belo m 1 m L B m G mφ m. (8) Inerchanging beeen he ull-lengh IPMDF and he reduced lengh IPMDF is done every chec milliseconds (e.g. 16 ms). I he perormance o he algorihm decreases he conrol circui originaes a ne search or he acive regions o he echo pah impulse response. 5. Resuls o Experimens To evaluae he perormance o he proposed algorihm e implemened i as ell as convenional adapive ilers in MATLAB environmen. Boh he convenional and he proposed adapive iler srucures are used o cancel simulaed echo signal. The simulaed echo signals are generaed by using he models o he echo pah impulse response speciied in he corresponding ITU-T Recommendaion [9]. For he simulaion he olloing main parameers are used: F s = 8000 Hz L = 104 K = 8 and ERL = -6 db. The perormance o each algorihm is evaluaed by using he normalized Echo Reurn Loss Enhancemen (ERLE) parameer hich is used in real-lie environmen o evaluae he perormance o an echo canceller. ERLE or each algorihm as calculaed according he (7). In each experimen he delay o he echo pah changes aer he predeined period o ime. The example ERLE curves or boh he convenional and he ne srucure are shon in Fig. 10. As i can be seen rom he igure he proposed scheme or he MDF/IPMDF perorms beer over he convenional ully updaed requency domain algorihms. In comparison o convenional algorihms or echo cancelling he compuaional complexiy he convergence speed and he degree o esimaion accuracy in he adapaion process are improved in proposed mehod. I as an objec o his paper o provide an improved echo canceller circui hich reduces compuaional noise hen here is no echo o cancel. I is anoher objec o he presen research o provide an improved echo canceller srucure hich rapidly adaps o inermediae echoes. A mehod o allocaing iler aps in an adapive iler or a ransmission line includes he seps o soring samples o he ransmission line s impulse response in a memory; examining he sored samples o ind ranges o samples o he impulse response having echo energy; and allocaing a variable number o iler aps o he adapive iler only o aps ihin he ranges o samples having echo energy. A delay esimaor deecs ranges o samples ihin he impulse response having echo energy. An adapive iler includes a pluraliy o eighs. A conrol circui acivaes and deacivaes variable numbers o aps in response o he delay esimaor so ha only aps ihin he ranges o samples are acivaed ihin he adapive iler. The oupu muliplexer operaing under he conrol circui selecs he esimaed echo oupus rom a pluraliy o he subiler blocs in order o calculae an echo signal hich is hen subraced rom he incoming signal.

8 RADIOENGINEERING VOL. 1 NO. 1 APRIL Fig. 10. Comparison in erms o misalignmen and ERLE parameers. 6. Conclusion This paper addresses he problem o echo assessmen echo pah s delay esimaion design o robus lo compuaional complexiy and as converging adapive ilers or echo cancellaion. Boh convenional and handsree elephone ses occupy a prominen posiion in communicaions. One o he major problems over a elephone sysem is echo. The adapive ilering algorihms and he deecor o he dispersive regions presened in his paper successully sugges an approved soluion or exising echo problem in he elecommunicaions environmen. During our uure or e inend o upgrade he above described algorihms. The proposed delay esimaor and he conrol circui may be used in conjuncion ih an adjusable delay bloc in order o compensae a la delay presened in he echo pah. Acnoledgemens Thans o he gran SGS No.OHK3-108/10 o he Czech Technical Universiy and he research program MSM o he Minisry o Educaion Youh and Spors o Czech Republic or unding. Reerences [1] MONTAGNA R. NEBBIA L. Mehod o and Device or he Digial Cancellaion o he Echo Generaed in Connecions ih Time-Varying Characerisics. U.S. Paen No [] MALKI K. E. Echo Pah Delay Esimaion. U.S. Paen No [3] VAHATALO A. MAKINEN J. Mehod Deermining he Locaion o Echo in an Echo Canceller. U.S. Paen No [4] YIP P. C-W. ETTER D. M. An adapive muliple echo canceller or sloly ime-varying echo pahs. IEEE Transacions on Communicaions 1990 vol. 38 no. 10 p [5] MARTINEZ A. A. Echo Canceller ih Dynamically Posiioned Adapive Filer Taps. U.S. Paen No [6] SOO J. S. PANG K. K. Mulidelay bloc requency domain adapive iler. IEEE Transacions on Acousics Speech and Signal Processing 1990 vol. 38 no. p [7] KHONG A. W. H. BENESTY J. NAYLOR P. A. An improved proporionae muli-delay bloc adapive iler or pace-siched neor echo cancellaion. In Proceedings o he 13 h European Signal Processing Conerence EUSIPCO '05. Analya (Turey) 005. [8] WAGNER K. M. DOROSLOVACKI M. Proporionae-ype normalized leas mean square algorihms ih gain allocaion moivaed by mean-square-error minimizaion or hie inpu. IEEE Transacions on Signal Processing 011 vol. 59 no. 5 p [9] ITU-T Recommendaion G.168 Digial neor echo cancellers Geneva (Sizerland): ITU 009.