Adaptive Voice Smoothing with Optimal Playback Delay Based on the ITU-T E-Model

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1 Adapve Voce Smoohng wh Opmal Playback Delay Baed on he ITU-T E-Model Shyh-Fang Huang, Ec Hao-Kuang Wu 2, and Pao-Ch Chang 3 Depamen of Eleconc Engneeng, Naonal Cenal Unvey, Tawan, hf@vaplab.ee.ncu.edu.w 2 Depamen of Compue Scence & Infomaon Engneeng, Naonal Cenal Unvey, Tawan, hao@ce.ncu.edu.w 3 Depamen of Communcaon Engneeng, Naonal Cenal Unvey, Tawan, pcchang@ce.ncu.edu.w Abac. Peceved voce qualy manly affeced by IP newok mpamen uch a delay, je and packe lo. Adapve moohng buffe a he ecevng end can compenae fo he effec of je baed on a adeoff beween delay and lo o achve a be voce qualy. Th wok fomulae an onlne lo model whch ncopoae buffe ze and apple he ITU-T E-model appoach o opmze he delay-lo poblem. Dnc fom he ohe opmal moohe, he popoed opmal moohe uable fo mo of codec cae he lowe complexy. Snce he adapve moohng cheme noduce vaable playback delay, he buffe e-ynchonzaon beween he capue and he playback become eenal. Th wok alo peen a buffe e-ynchonzaon algohm baed on lence kppng o peven unaccepable nceae n he buffe peloadng delay and even buffe oveflow. Smulaon expemen valdae ha he popoed adapve moohe achve gnfcan mpovemen n he voce qualy. Inoducon The apd poge of he developmen of IP-bae newok ha enabled numeou applcaon ha delve no only adonal daa bu alo mulmeda nfomaon n eal me. The nex geneaon newok, lke an ALL-IP newok, a fuue end o negae all heeogeneou wed and wele newok and povde eamle woldwde mobly. In an All-IP newok, one evoluon of he new geneaon Inene applcaon wll ealze VoIP evce ha people can alk feely aound hough he moble-phone, he dekop and VoIP elephone a any me and place. Unfounaely, he IP-baed newok do no guaanee he avalable bandwdh and aue he conan delay je (.e., he delay vaance) fo eal me applcaon. In ohe wod, ndvdual anmon delay fo a gven flow of packe n a newok may be connung o change caued by vayng affc load and dffeng oung pah due o congeon, o ha he packe newok delay fo a connuou ee of neval (.e.

2 alkpu) a he eceve may no be he ame (.e. conan) a he ende. In addon, a packe delay may noduce by he gnal hand-ou o he dffeence of bandwdh anpoaon n wele/fxed newok. Fo delay enve applcaon, a domnang poon of packe loe mgh be lkely due o delay conan. A lae packe ha ave afe a delay hehold deemned by playback me eaed a a lo packe. A gh delay hehold no only degade he qualy of playback bu alo educe he effecve bandwdh becaue a lage facon of delveed packe ae dopped. In fac, delay and lo ae nomally no ndependen of each ohe. In ode o educe he lo mpac, a numbe of applcaon ulze an adapve moohng echnque n whch buffe ae adoped o educe he qualy damage caued by lo packe. Howeve, a lage buffe wll noduce exceve end-o-end delay and deeoae he mulmeda qualy n neacve ealme applcaon. Theefoe, a adeoff equed beween nceaed packe lo and buffe delay o acheve afacoy eul fo playou buffe algohm. In he pa, he wok on he degadaon of he voce qualy conde he effec of packe lo, bu no ha of packe delay. Whn leaue on pedcng delay, he ue of Paeo dbuon n [] of compung he dbuon paamee and ebuldng he new dbuon o pedc he nex packe delay, and he ue of neual newok model o lean affc behavo [2]. The ue of Paeo dbuon o a neual newok model eque elavely hgh complexy o a long leanng peod. Theefoe, we conde he moohe [3]-[9] whch employ acal newok paamee elaed wh he voce chaacec,.e. lo, delay and alk-pu ha have gnfcan nfluence o he voce qualy. They deec delay pke n affc and quckly calculae he equed buffe ze o keep he qualy a good a poble. The E-model a compuaonal model, andadzed by ITU-T n G.07, G.09 and G.3 whch ue he vaou anmon paamee o pedc he ubjecve qualy of packezed voce. Unfounaely, he E-model complex o analyze n he opmzaon poce. An alenave udy o apply a mplfed E-model, f popoed by R. Cole and J. Roenbluh [0], baed upon obeved anpo meauemen n he VoIP gaeway and he anpo pah. Auho ndcaed he mplfed E-model mehod eque moe paen cae fo ace o enhance he valdaon. Azo and Lobna [], and L. Sun and E. Ifeacho [2] popoed o ulze a mplfed E-model ha conde he lo and delay ogehe o e a dje me, whch he opmal playou delay deved by a dynamc pogammng-baed oluon. Howeve, he uably and he accuacy of a mplfed E-model wll be lmed by nonypcal affc paen. Fo pecepual-baed buffe opmzaon cheme fo VoIP, voce qualy evaluaed a a key mec nce epeen ue peceved QoS. Howeve, eque an effcen and accuae objecve way o opmze peceved voce qualy. To conde he well-defned delay and lo mpamen of he E-model, we employ a complee E- model fo he qualy opmzaon o oban opmal peceved voce qualy. In a packe wchng newok, whou a eynchonzaon cheme, a playback clock wh a mno fequency eo wll evenually caue a buffe oveflow o an undeflow a he ecevng end. The oveflow packe ae uually dcaded due o he fne buffe ze and he eal-me equemen. Th dconnuy caued by dcaded packe mgh ceae an unpleaan effec o he playback qualy becaue he

3 lo packe could be he mpoan pa of he gnal. Th effec moe eou fo audo gnal han vdeo gnal becaue human ea ae moe enve o he connuy of ound han human eye. The conbuon of h pape ae hee-fold: () A new mehod opmzng voce qualy fo VoIP ealy appled o codec whch wee well-defned n he ITU-T E- model. () Dffeen fom he ohe opmal moohe, ou opmal moohe ha he lowe complexy wh O ( n). () A feable cheme noduced o olve he buffe e-ynchonzaon poblem. 2 Relaed Wok The Spke Deecon (SD) algohm ha been uded by many eeache [3]-[9]. A delay pke defned a a udden and gnfcan nceae of newok delay n a ho peod ofen le han one ound-p. Th algohm adju he moohng ze,.e. playback delay, a he begnnng of each alk-pu. The eul of h algohm ae heefoe compaed o he eul obaned heen. The SD Algohm n [3] emae he playou me p of he f packe n a alk-pu fom he mean newok delay d and he vaance v fo packe a p = + d + γ v () whee epeen he me a whch packe geneaed a he endng ho and γ a conan faco ued o e he playou me o be fa enough beyond he delay emae uch ha only a mall facon of he avng packe could be lo due o lae aval. The value of γ = 4 ued n mulaon [3]. The emae ae ecompued each me a packe ave, bu only appled when a new alk-pu naed. The mean newok delay d and vaance v ae calculaed baed on a lnea ecuve fle chaacezed by he faco α and β. If n > d If n d - - d = d v = v d = d v = v + ( )n + ( )d + ( )n + ( )d n n (SPIKE_MODE) whee n he oal delay noduced by he newok [3] and ypcal value of α and β ae and 0.75 [], epecvely. The decon o elec α and β baed on he cuen delay condon. The condon n > d epeen newok congeon (SPIKE_MODE) and he wegh β ued o emphaze he cuen newok delay. On he ohe hand, n d epeen newok affc able, and α ued o emphaze he long-em aveage. (2)

4 In emang he delay and vaance, he SD Algohm ulze only wo value, α and β, whch ae mple bu may no be adequae, paculaly when he affc unable. Fo example, an unde-emaed poblem when a newok become pked, bu he delay n ju below he d, he SD Algohm wll evaluae he newok o be able and wll no ene he SIPKE_MODE. 3 Adapve Smoohe wh Opmal Delay-Lo Tade off The popoed opmal moohe deved ung he E-model o ade off he delay and lo. Th mehod nvolve, f, buldng he affc delay model and he lo model. Second, he delay and lo mpamen of he E-model ae calculaed accodng o he delay and he lo model. Thd, he E-model ank R maxmzed and hu he delay and lo opmzed oluon obaned. 3. E-model Decpon In he E-model, a ang faco R epeen voce qualy and conde elevan anmon paamee fo he condeed connecon. I defned n [3] a: R = Ro I Id Ie _eff + A (3) Ro denoe he bac gnal-o-noe ao, whch deved fom he um of dffeen noe ouce whch conan ccu noe and oom noe, end and eceve loudne ang. I denoe he um of all mpamen aocaed wh he voce gnal, whch deved fom he ncoec loudne level, non-opmum deone and quanzng doon. Id epeen he mpamen due o delay of voce gnal, ha he um of Talke Echo delay (Ide), Lene Echo delay (Idle) and end-o-end delay (Idd). Ie _ eff denoe he equpmen mpamen, dependng on he low b ae codec (Ie, Bpl) and packe lo (Ppl) level. Fnally, he advanage faco A no elaon o all ohe anmon paamee. The ue of faco A n a pecfc applcaon lef o he degne decon. 3.2 The Delay and Lo Model n E-model Fo peceved buffe degn, ccal o undeand he delay dbuon modelng a decly elaed o buffe lo. The chaacec of packe anmon delay ove Inene can be epeened by acal model whch follow Exponenal dbuon fo Inene packe (fo an UDP affc) ha been hown o conen wh an Exponenal dbuon [4]. In ode o deve an onlne lo model, he packe endo-end delay aumed a an exponenal dbuon wh paamee µ a he

5 ecevng end fo low complexy and eay mplemenaon. The CDF of he delay dbuon F ( ) can alo be epeened by [5] F( ) and he PDF of he delay dbuon f ( ) f ( ) = df( ) d u = e (4) µ = µ e whee µ defned a he nvee of he aveage mean delay. In a eal-me applcaon, a packe lo ha olely caued by exa delay can be deved fom he delay model f ( ). The value of b epeen he moohng me fo a moohe. When a packe delay exceed b, a packe lo wll occu. The lo funcon l(b ) can be deved a (5) λ µ b µ b ( ) f ( ) d = ( e ) = e + e = e l b = b b () 3.3 Opmzaon on E-model The delay and lo faco ove anmon have geae mpac o he voce qualy han he envonmen o equpmen. To mplfy he opmzaon complexy, and nvegae on delay and lo mpamen, we make hee aumpon n a communcaon connecon a he followng: (). The ccu noe, oom noe and emnae gnal wll no change. ( Ro and I ae fxed). (). An echo delay n he Sende/Receve wll no change. (Ide and Idle ae fxed). (). A codec wll no change (Ie fxed). In [3], R ewen a Eq. (7) whee Idd appoxmaed by ( Ro I Ide Idle + A) Idd Ie _ eff R = (7) ( + X ) Idd = , 3 X ln 00 X =, ln ( 2) (8) and when T > 00 m and Idd =0 when T 00, a a

6 Ie _ eff = Ie + 95 ( Ie) Ppl Ppl + Bpl (9) Faco Ie and Bpl ae defned n [] and T a one-way abolue delay fo echofee connecon. Due o he hee aumpon above, he opmzaon poce can be concenaed on he paamee of Idd and Ie_eff. Eq. (7) deved o yeld Eq. (0) R = Con an X ( X ) ( Ie) Ppl Ppl + Bpl, (0) The dffeenal equaon when > 00 m dr d agned o zeo o maxmze R o yeld he be qualy. Accodng o Eq. (), he lo pobably Ppl = e µ b, o we can ge R µ 5 ' X X ' µ e Bpl 25 ( ) + X X X + X µ µ Bpl + e + 2 Bpl e ' = = () log, X = 00, X log 2 ' = log 2 cuen The oluon fo ae dffcul o ge decly fom Eq. () nce conan he complex polynomal and exponenal funcon, Theefoe, we wll y o olve he be moohng me wh a numecal appoach. We noce he followng hee condon. (). In Eq. (8), when he moohng me 00 m, Idd zeo (no delay mpamen). I mple a moohe hould e he mnmum moohng delay o 00 m o peven he mo packe lo. (). The maxmum end-o-end delay of 250m accepable fo mo ue applcaon o peven eou voce qualy deucon. (). Fo a common low b ae codec, lke G.723. and G.729, he fame ae 30 m and 0 m, epecvely, o he gcd(0,30) 0 m. Baed on he above condon, we can udy he ffeen cae, = 0 m, 2 = 20 m,, 5 = 250 m, o calculae he coepondence, µ, µ 2,, µ 5, by he numecal analy n Eq. () and an eo le han Table how he moohng me coepondng o µ. We can obeve ha a µ nceae, he moohe wll enlage he moohng me o mooh he lae packe. Accodng o Table, he popoed moohe wll calculae he cuen µ ( µ ) a he begnnng of each alk-pu and each fo a mnmum n whch afe µ n µ cuen. The opmal moohng me wll be 00 + n 0 m o keep he opmal voce qualy.

7 Table. The elaon of moohng me and aval ae moohng me µ (/ec) moohng me µ (/ec) = 0 m µ = = 90 m µ =.95 9 µ µ 8.52 µ 2 9. µ µ µ = 20 m µ 2 = = 200 m = 3 = 30 m µ 3 =.49 = 20 m = 4 = 40 m µ 4 = = 220 m = 5 = 50 m µ 5 = = 230 m = = 0 m µ = = 240 m = 7 = 70 m µ = = 250 m = 7 µ = 80 m = 4 Buffe Re-ynchonzaon A neceay condon ha a moohe can wok coecly he ynchonzaon beween he capue and he playback. Th econ popoe a buffe e-ynchonzaon machne (BRM) o help ynchonzaon and he clock df analy of eynchonzaon o valdae he effecvene. 4. Buffe Re-ynchonzaon Machne Th wok popoe a ynchonzaon cheme ha egmen audo gnal by deecng lence. The mmach beween he capue and he playback clock olved by kppng lence a he ecevng end. The duaon of he len peod may be hoened neglgbly degadng he qualy of playback. An acve packe conan vocecompeed daa, wheea a len packe doe no. Skppng ome len packe wll no gnfcanly degade he qualy of he voce, bu can effcenly peven he buffe fom oveflowng. Noably, k (could be adjued) connuou len packe could be ulzed o epaae dffeen alkpu. Fgue depc he buffe e-ynchonzaon algohm. In-ae, Smooh-ae, Play-ae and Skp-ae ae ued o epeen he voce confeence nalng, he buffe moohng, he buffe playng ou, and he len packe kppng, epecvely, and A and S epeen an acve packe and a len packe, epecvely. In he In-ae he buffe wa fo he f avng packe o nalze a voce confeence. If In-ae eceve an S, ay n In-ae; ohewe when an A eceved, he Smooh-ae acvaed o mooh he packe. In he Smooh-ae, he moohng me b compued by applyng he opmal adapve moohe algohm dynamcally. When he buffe moohng me ove b, he Play-ae acvaed; ohewe ay n Smooh-ae fo moohng. In he Play-Sae he packe feched fom he buffe and played ou. In fechng poce, when encoune hee conecuve S packe, mplyng ha he alk-pu can be ended, he buffe e-

8 ynchonzaon pocedue hen wche o he Skp-ae. In he Skp-ae, f A feched fom buffe, mean he new alk-pu ha begun, and hen kp emaned len packe n he buffe, and wche o he Smooh-ae o mooh he nex alkpu. Ohewe, f S feched fom buffe, mple cuen alk-pu no ended and wll be decoded o play ou a he ame ae. Wh he above fou-ae machne, he moohe can mooh he packe a he begnnng of he alkpu o avod buffe undeflow n he Smooh-ae and kp he len packe a he end of he alkpu o peven he oveflow n he Skp-ae. S Buffe<b In A Smooh Buffe>=b A A o Numbe of S <= k Play Numbe of S > k Skp S Fg.. Buffe Re-ynchonzaon Machne 4.2 Effecvene of Re-ynchonzaon To demonae he effecvene of e-ynchonzaon machne fo buffe oveflow, we analyze he clock nconence conan a he followng. C and C epeen he ende clock (fame/ec) and he eceve clock, epecvely, and M a and M denoe he mean acve packe and mean len packe n a alkpu, epecvely. The buffe oveflow caued by he clock nconence (dffeence) wll occu when C lage han C condon. C C, he dffeence value by ubacng he eceve clock fom he ende clock, epeen he pove clock df beween he C C M + M fame _me epeen ende and he eceve. Theefoe, ( ) (( ) ) he mean exa buffe ze caued by he pove clock df fo a mean alkpu me. In ode o dnguh he conecuve alkpu, a leae k len packe ae ulzed. Theefoe, he moohe ha M k len packe o be kpped and eynchonze wh he followng alkpu. When he e-ynchonzaon machne afe ( C C ) ( ( M + M ) fame _ me) ( M k) a a (2), he buffe oveflow caued by he pove clock df wll no occu.

9 5 Smulaon 5. Smulaon Confguaon A e of mulaon expemen ae pefomed o evaluae he effecvene of he popoed adapve moohng cheme. The OPNET mulaon ool ae adoped o ace he voce affc anpoed beween wo dffeen LAN fo a VoIP envonmen. Nney peonal compue wh G.729 affc ae deployed n each LAN. The duaon and fequency of he connecon me of he peonal compue follow Exponenal dbuon. Ten fve-mnue mulaon wee un o pobe he backbone newok delay paen, whch wee ued o ace he adapve moohe and compae he effec of he ognal wh he adaped voce qualy lae. *90 Roue T Roue *90 Fg. 2. The mulaon envonmen of VoIP delay (m) 400 Vaance Packe Numbe Talk Spu (a) The delay of affc Fg. 3. VoIP affc paen (b) The vaance of affc Fg. 2 how he ypcal newok opology n whch a T (.544 Mbp) backbone connec wo LAN, and 00 Mbp lne ae conneced whn each LAN. The popagaon delay of all lnk aumed o be a conan value and wll be gnoed (he devave value wll be zeo) n he opmzaon poce. The buffe ze of he bolenecked oue aumed o be nfne nce he pefomance compaon of adapve moohe wll be affeced by ovedue packe lo (ove he deadlne) and no affeced by he packe lo n oue buffe. The newok end-o-end delay of a G.729 packe wh daa fame ze (0 bye) and RTP/UDP/IP heade (40 bye) meaued fo en fve-mnue mulaon by employng he OPNET mulaon newok. Fgue 3(a) and 4(b) l one of he end-o-end affc delay paen and he coepondng delay vaance fo VoIP affc obeved a a gven eceve.

10 5.2 Voce Qualy n moohe The e equence ampled a 8 khz, econd long, and nclude Englh and Mandan enence poken by male and female. Fg. 4 how he E-model coe R of he voce qualy. I how ha he opmal mehod ha he gnfcan mpovemen n he voce qualy ove SD moohe, becaue ou popoed opmal moohe uly opmze wh he delay and lo mpamen n a anmon plannng of he E- model Rank of E-model (coe) Smoohe SD Opmal Numbe of Talkpu Fg. 4. The qualy coe of moohe 5.3 Re-ynchonzaon Effecvene fo he Pove Clock Df A lenng evaluaon expemen wa pefomed o analyze he equed pope numbe of len packe o egmen he conecuve alk-pu well. I wa found n ou expemen ha a lea hee len packe (e.q. 0 m pe packe n G.729) ae equed o epaae alkpu. We analyze he G.729 voce ouce ued n ou expemen and fnd he pecenage of he mean acve and mean len egmen lengh n a alkpu ae 0.5 and 0.49 epecvely, and he maxmum alkpu lengh 257 packe. p =3 adoped o egmen he conecuve alkpu. Fom he Eq. (2), we can calculae he effecve clock df beween he ende and he eceve C C hould be le han o equal o ( ) ( 257) = (fame/ec). Nomally, he clock df wll no be ove 47.8 (fame/ec) when a ende of G.729 anm 00 (fame/ec) o he newok. Conequenly, he moohe can avod he buffe oveflow well n ou cae. Concluon Th acle popoe an adapve moohng algohm ha ulze he complee E- model o opmze he moohng ze o oban he be voce qualy. The buffe eynchonzaon algohm alo popoed o peven buffe oveflow by kppng

11 ome len packe of he al of alk-pu. I can effcenly olve he mmach beween he capue and he playback clock. Numecal eul have hown ha ou popoed mehod can ge gnfcan mpovemen n he voce qualy whch balance he age delay and lo. Refeence []. Bazauka V., Seflng R.: Robu and effcen emaon of he al ndex of a onepaamee paeo dbuon. Noh Amecan Acuaal Jounal avalable a hp:// (2000) [2]. Ten P. L., Yuang M. C.: Inellgen voce moohe fo lence-uppeed voce ove nene. IEEE JSAC, Vol. 7, No.. (999) 29-4 [3]. Ramjee R., Kue J., Towley D., Schulznne H.: Adapve playou mechanm fo packezed audo applcaon n wde-aea newok. Poc. IEEE INFOCOM. (994) 80-8 [4]. Jeke D. R., Maag W., Samad B.: Adapve play-ou algohm fo voce packe. Poc. IEEE Conf. on Commun., Vol. 3. (200) [5]. Pno J., Chenen K. J.: An algohm fo playou of packe voce baed on adapve adjumen of alkpu lence peod. Poc. IEEE Conf. on Local Compue Newok. (999) []. Lang Y. J., Fabe N., God B.,: Adapve playou chedulng ung me-cale modfcaon n packe voce communcaon. Poc. IEEE Conf. on Acouc, Speech, and Sgnal Poceng, Vol. 3. (200) [7]. Kanal A., Kaandka A.: Adapve delay emaon fo low je audo ove Inene. IEEE GLOBECOM, Vol. 4. (200) [8]. Anandakuma A. K., McCee A., Pakoy E.: An adapve voce playou mehod fo VOP applcaon. IEEE GLOBECOM, Vol. 3. (200) [9]. DeLeon P., Seenan C. J.: An Adapve pedco fo meda playou buffeng. Poc. IEEE Conf. on Acouc, Speech, and Sgnal Poceng, Vol.. (999) [0]. Cole R., Roenbluh J.: Voce ove IP pefomance monong, Jounal on Compue Commun. Revew, Vol. 3. (200) []. Azo L., Lobna M.: Speech playou buffeng baed on a mplfed veon of he ITU- T E-model. IEEE Sgnal Poceng Lee, Vol., I 3. (2004) [2]. Sun L., Ifeacho E.: New model fo peceved voce qualy pedcon and he applcaon n playou buffe opmzaon fo VoIP newok. Poc. ICC. (2004) [3]. ITU-T Recommendaon G.07,: The E-model, a Compuaonal Model fo ue n Tanmon Plannng. (2003) [4]. Bolo J. C.: Chaacezng end-o-end packe delay and lo n he nene. Jounal of Hgh-Speed Newok, Vol. 2. (993) [5]. Fujmoo K., Aa S., Muaa M.: Sacal Analy of Packe Delay n he Inene and Applcaon o Playou Conol fo Seamng Applcaon. IEICE Tan. Commun., Vol. E84-B, No.. (200) []. ITU-T SG2 D.0: Emae of Ie and Bpl fo a ange of Codec. (2003)