CA1194953A - Echo phase compensating device and application thereof to echo cancellation devices - Google Patents
Echo phase compensating device and application thereof to echo cancellation devicesInfo
- Publication number
- CA1194953A CA1194953A CA000406048A CA406048A CA1194953A CA 1194953 A CA1194953 A CA 1194953A CA 000406048 A CA000406048 A CA 000406048A CA 406048 A CA406048 A CA 406048A CA 1194953 A CA1194953 A CA 1194953A
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- Canada
- Prior art keywords
- phase
- echo
- magnitude
- dwn
- output
- Prior art date
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B3/00—Line transmission systems
- H04B3/02—Details
- H04B3/20—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
- H04B3/23—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers
- H04B3/232—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers using phase shift, phase roll or frequency offset correction
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
- Bidirectional Digital Transmission (AREA)
- Communication Control (AREA)
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention relates to the simul-taneous two-way data transmission on 2-wire circuit, and more particularly to the technique of echo cancel-lation. The rapid fluctuations wn are actualized with a first phase actualization loop, and the slow fluctua-tions un with a second phase actualization loop, from the increase dwn = .alpha.Im (en.sigma.n*); un and wn are added for obtaining the natural phase .sigma.n of the echo. The invention applies to the cancellation of echos bearing phase and frequency drift.
The present invention relates to the simul-taneous two-way data transmission on 2-wire circuit, and more particularly to the technique of echo cancel-lation. The rapid fluctuations wn are actualized with a first phase actualization loop, and the slow fluctua-tions un with a second phase actualization loop, from the increase dwn = .alpha.Im (en.sigma.n*); un and wn are added for obtaining the natural phase .sigma.n of the echo. The invention applies to the cancellation of echos bearing phase and frequency drift.
Description
i3 ~ he pres~nt invention relateYI to the 3imulta-neou~ two-~ay data transmi~io~ on 2-wi.re circult 9 and more particularly to the t0chnique of echo cancellation.
It i~ kno~n that a t~chnique allowing sl~ulta-neoun two-~ay data tran~misslon on two-wire line~ for ~xample by means of modems (modulator-d.emodulators) i~
that of "echo cancellation". ~h~n the ~lodems o~ each of th~
two end~ emit in the ame frequency ban,d, to recei~e th~
u~eful ~ignal, the echo~ mu~t be cancelled. To thi~ end, echo cancelling device~ furni~h an e~timation of the echo~
and ~ubtract lt fro~ the signal received.
These echo~ are u~ually compo~d of a local echo due to the mismatching of the differential circuit ensurine 4 wire - 2 wire passRge on ~hich di~tant echo~ due to reflectlons of the signal transmitted by rea~o~ of i~pedan-ce mismatchings, are superpo~ed. TheBe l~tter echo~ thu~
bear, at recep*ion, frequency drift, i.e, th2 carrier fre-quency of the dl~tant ~cho i~ no longer the ~ame a~ that from the ~ignal emitted.
Thuc, uhen the ~ignal emitted i~ ~odulated by a carrier frequency fc, the echo arri~en, ~odulated by the same carrier ~requency ~c subjected to ,R phase ~hirt ~n ~h~re ~n Y 2 ~ ~ fnT ~ ~0, L\f being the ~r~quency drift of the echo, T the ~ampling periodO To cancel ~uch an ~cho, it must be reconstituted by modulatin~ it by the same carrier frequency fc, with9 at instant nT, a phase ~n which i8 an estimation of the ~Dha~e ~ of thi~
echo. At each saMpling instant nT~ the e~timated echo ~,i' 9~3 signal must, at reception, then be c;ubtracted from the signal received.
In an echo cancelling device known in the prior art, at emission, the signal is in the form of a series An of complex data which are modulated by means of a modulator by the carrier frequency fc. A
differential circuit ensures coupling of the line with the emission and reception o~ the modem. rrhe signal hn received at instant nT is composed of the useful signal coming from the distant end and from an echo signal gn which is written:
= ~ A k~ke ~(2~ fc ~n) with ~n = 2~ ~ fnT + ~o~l]
and where rk is the sampled impulse response returned into baseband of the echo signal.
At reception before demodulation, by means of a demodulator, there is subtracte!d from each sample hn received a sample ~n of correction ~o furnish a sample en due to a subtraction circuit, en and ~n being complex. It will be noted that the signal hn is a complex signal phase shifted by ~2 by means of a separator circuit inserted at reception between the differential circuit and the subtraction circuit.
This sample en is then applied to the input of a demodulator. The known echo cancellation devices, enabling the phase ~n of the echo to be compensated, are formed by a first system for reactualization of the
It i~ kno~n that a t~chnique allowing sl~ulta-neoun two-~ay data tran~misslon on two-wire line~ for ~xample by means of modems (modulator-d.emodulators) i~
that of "echo cancellation". ~h~n the ~lodems o~ each of th~
two end~ emit in the ame frequency ban,d, to recei~e th~
u~eful ~ignal, the echo~ mu~t be cancelled. To thi~ end, echo cancelling device~ furni~h an e~timation of the echo~
and ~ubtract lt fro~ the signal received.
These echo~ are u~ually compo~d of a local echo due to the mismatching of the differential circuit ensurine 4 wire - 2 wire passRge on ~hich di~tant echo~ due to reflectlons of the signal transmitted by rea~o~ of i~pedan-ce mismatchings, are superpo~ed. TheBe l~tter echo~ thu~
bear, at recep*ion, frequency drift, i.e, th2 carrier fre-quency of the dl~tant ~cho i~ no longer the ~ame a~ that from the ~ignal emitted.
Thuc, uhen the ~ignal emitted i~ ~odulated by a carrier frequency fc, the echo arri~en, ~odulated by the same carrier ~requency ~c subjected to ,R phase ~hirt ~n ~h~re ~n Y 2 ~ ~ fnT ~ ~0, L\f being the ~r~quency drift of the echo, T the ~ampling periodO To cancel ~uch an ~cho, it must be reconstituted by modulatin~ it by the same carrier frequency fc, with9 at instant nT, a phase ~n which i8 an estimation of the ~Dha~e ~ of thi~
echo. At each saMpling instant nT~ the e~timated echo ~,i' 9~3 signal must, at reception, then be c;ubtracted from the signal received.
In an echo cancelling device known in the prior art, at emission, the signal is in the form of a series An of complex data which are modulated by means of a modulator by the carrier frequency fc. A
differential circuit ensures coupling of the line with the emission and reception o~ the modem. rrhe signal hn received at instant nT is composed of the useful signal coming from the distant end and from an echo signal gn which is written:
= ~ A k~ke ~(2~ fc ~n) with ~n = 2~ ~ fnT + ~o~l]
and where rk is the sampled impulse response returned into baseband of the echo signal.
At reception before demodulation, by means of a demodulator, there is subtracte!d from each sample hn received a sample ~n of correction ~o furnish a sample en due to a subtraction circuit, en and ~n being complex. It will be noted that the signal hn is a complex signal phase shifted by ~2 by means of a separator circuit inserted at reception between the differential circuit and the subtraction circuit.
This sample en is then applied to the input of a demodulator. The known echo cancellation devices, enabling the phase ~n of the echo to be compensated, are formed by a first system for reactualization of the
- 2 --~g495~
coefficients Ck, for example in accordance with the algorithm of the gradient:
-~ (2~ fen T + n) Cnk+l = Ck + ~ enAn_k [2]
where the coefficients Ck are eomplex, where 7 is a real positive eonstant, and by a second system for reactua-lization of the phase ~n of the echo, the phase ~n also being reactualized in accordance with the algorithm of the gradient ~ n+l ~n + (en n ) [3]
where ~n is the reconstituted echo and ~n~ its conju-gated complex and d iS a real positive constant.
At the output of the cancellation device, the reconstituted eeho is written:
,, n k Ck A ke ~(2~1fcn T + n) [5~
Sueh an eeho eaneellation deviee has been deseribed, for example, in an artiele whieh appeared in IEEE TRANS. COM. 25, No. 7, July 77, pages 654 to 666.
Sueh phase reaetualization systems are aeeep table for eompensating a slow phase variation or a very slight frequeney drift. However, when the phase varia-tion eomprises a eonsiderable frequeney drift, sueh systems are highly insuffieient. In partieular, when the useful signal-to-eeho ratio, the eeho bearing drift, is weak, the phase eompensation is no longer acceptable.
~ 9~s~3 In fact, it wo~ld necessitate adopting, in phase reactualization algorithm [3], too - 3a -4~
great a coefficient a, which would deteriorate per~ormance~
in the ab~ence of frequency drlft.
The inventors of th~ present in~ention, M~r~.
COLIN de YERDIERE, LANGLOIS and ~r~. ~LCCHI; the latter working ~lth th~ CNRS~ Laboratoire deJ Slgnau~ ~t Systèm~
(L.2 .S. ), have sought to overcome the~ drawback~ of the pha~e reactualization de~ices to cancel echo in order to allo~ a co~siderable frequ~ncy drift o~` the echo to be corrected.
The in~ention ~entially con~i~t~ in di~po~ing a firYt phane Yariation ~tem for tha 810w pha~e fluctua-ti~n un and a second phase ~ariation ~y~te~ for the rapid pha~ fluctuatio~ w~, the total pha~e varlation ~n bei~g : obtalned at tha output of an addition circuitp said addition circuit receiving th0 Bignals Un and wn from ~aid flr~t and Qecond ~y~tem~.
According to ~ first feature, at each sampling : in~tant nT, from a mag~itud~ d~, the magnitude dwn repr~-~enting tha lma~inary part of th~ product Or con~ugated complex echo correction 6nff by the data oi~nal en obtained at tha output of the echo cancellation d~Yice, after elimi-nation of said echo, ~aid product being multipli0d by a coeff1ci~nt of proportionality, th~ p~ha~e co~pensation sy~tem according to the in~ention oompr:ise~ mean~ for addlng, at each ~ampling in~tant, the 810~ pha~e variation un with the rapid ~ha~e variation wn, ~aid addition mean~
~urni~hing at the output the naturel pha~ ~n of th~ 0cho, ~aid ~lo~ variatioll un being obtained from ~aid incr~a~e dw by fir~t mean~, ~aid rapid variation bein~ obtained from 3aid increa~e dwn by second ~ean~.
Moreover, ~aid fir~t mean~ furni~hin~ un at th~
output co~pri~e mean~ for adding the f.luctuation~ un lY
of the preceding sampllng in~tant, w1t]h the magnitud0 T.Fn, T being equal to the 8~mpllng pe:riod, ~aid ~agnitud0 Fn belng obtalned by ~ean~ for a~dition of the ~agnitude Fn 1~ of the preceding ~ampling in~tant, ~ith a ma~itud~
dFn, ~aid 0agnitude dFn bei~ obta~ned by maan~ for addit1on of ~aid increa~e dwn, weighted by a con~tant ~ , with th~
magnitud~ d~n_l of the pr0ceding ~a~pl:Ln~ in~tant, ~aid ~agnitude d~n 1 al~o belng w~ightsd by anoth~r ~o~stant (l-S), ~ and S bei~g real pssit1Ye conl~tant3.
According to a preferred e~bodiment of ~he inven-tio~, the con~tant i~ equal to 1.
Accord~ng to a ~urther feature of the in~æntion, said ~eco~d mean~ furni~hi~ the rapid fluctuation~ wn comprise ~an~ for adding aaid increa~e dWn ~lth th~ ma-gnitudc wn 1 of *he preceding samplins in3tant.
The in~ention enable~ echo~ b~aring a considerable fr~uency drift to be ea~ily corrected"
The in~ention will be more roadily under~tood o~
reading the followlng de~cription wlth referenc~ to th~
accompanyi~g drawing~, in wh~ch :
Fig. 1 iB a general repre~en1;atlon of a ~nown echo cancellation device.
Fig. 2 ~how~ a known ~yRtem o~ reactualization D~ the phase of an scho canccllation de~Yice.
Fig. 3 shows a decomposition according to the invention of the echo phase fluctuations.
Fig. 4 shows the phase correction loops accor-ding to the invention.
Fig. 5 is a preferred embodiment of the inven-tion of Fig. 4.
Fig. 1 illustrates an echo cancelling device known in the prior art. At emission, the signal is in the form of a series An of complex data which are modulated by means of a modulator 1 by the carrier frecIuency fc~ A differential circuit 2 ensures cou-pling of the line with the emission and reception of the modem. The si~nal hn received at instant nT is composed of the useful signal coming from the distant end and from an echo signal gn which is defined in accordance with the aforesaid rela-t:Lon [1~ .
At reception before demodulation, by means of the demodulator 4, there is subtracl,ed from each sample hn received a sample ~n of correction to furnish a sample en due to the subtraction circuit 6, en and ~n being complex. It will be noted that the signal hn is a complex signal phase shifted by ~2 by means of a sepa-rator circuit 7 inserted at reception between the diffe-rential circuit,2 and the subtraction circuit 6.
This sample en is then applied to the input of the demodulator 4. The known echo cancellation devices 5, enabling the phase ~n of the echo to be .~
i3 compensated, are formed by a first system 51 for reac-tualization of the coefficients Ck~ for example in accordance with the aforesaid algorithm [2] and by a second system 52 for reactualizat:lon of the phase 0n of the echo, the phase ~n being reactualized in accor-dance with the aforesaid algorithm [3] .
At the output of the cancellation device 5, the reconstituted echo ~n is defined in accordance with the aforesaid relation [5]
Fig. 2 shows the known systems of reactua-lization of the phase ~n of an echo cancellation device, which comprises a circuit 21 for mu]tiplication of the estimated conjugated complex value -n~ reconstituted for the preceding sample by the value en furnished by the subtraction circuit 6 of Fig. 1. The circuit 22 receiving the result of multiplication of the circuit 21 furnishes at the output the pure imaginary part of this magnitude which is then multiplied by ~ by means of the multiplication circuit 23. ~ is an appropriately selected constant extracted from a memory 24.
The magnitude furnished at the output of the circuit 23 is added with the value ~' furnished at n-l the output of a circuit 25 delaying by a sampling pe-riod T. The result obtained at the output of the addi-tion circuit 25 is ~n' value of the phase shift of the echo for each sampling instant nT according to a known estimation of first order. This est:imation is written by the relation ~n n-l n - 6a -i~,.!
The invention consists in decomposing the phase ~n into two components un and wn, one, un, coxresponding to a slow drift phenomenon capable of decreasing or - 6b -~¢~953 increa~ing, the other, w , corr~ponding to a rapld pheno-~enon, and 1n extracting from the rapidi pheno~enon at each ~amplin~ in~tant 9 the re~idue~ of ~low phenomenDn~ The pha~e ~n~ at instant nT, i~ then ~riSt~n a~ the ~um of th0 compon~nt~ un and wn.
Referring to ~ig. 3, the compcnent u repre~e~t~
a m0an value o~ tha phase ~hil~t u repr0s~nt~ ~mall ampli~
tude variation~ about this mean drift value~
T~o different ~y~t~mA of reactualization o~ each of the~e t~ component~ are di3po~ed accordlng t~ the ln-~ention.
The component ~ 1~ reacSualized acc~rding to the in~entl~n by mean~ of a phase loop Df the first ord~r whil3t the co~ponent un i~ reactualized acc~rdin~ to the invention by mean~ of ~ phas~e loop of a higher ordierO
One ftr~tly form~ the increa~e dwn ~rom the conjugated comple~ r~constituted echo and ~rom ~n~ th~
compl~ v~lue of the u~eful signRl afte~r ~ubtractio~ of the echo. To thl~ end, a multlplication circuit 31 reoei~
~ing en and ~n~ furnishe~ a magnitude alc the ~nput of a circult 32 whlch allo~ only the imaginary part at the out-put to pasc. Thi~ magnitude i~ mulSipll~d by a by ~ean~ of a multiplication circuit 33 furnishing at the output dw 9 the increaae of thc rapid componentO The! con~teLnt ~ 1B
extracted from a memory 34.
dw iB wrltten :
dw~ _ ~ ~ (en ~-n ) L6 J
5~
According to the invention, there are ~xtracted from thi1 ~agnitude dwn the reBidu~ of 910w phenomenon u . To this end, dw i~ applied to the :Lnput o~ a flr0t rcactualization aystem aff~ctin~ s~era:l proces~ing~ of the ~lgnal dwn written mathematically :
n = (1 -~ ) dF~ 1 ~ ~ B d~
F ~ d~
n n-l u z u ~ T F
n n-l n ~here ~ a~d ~ ~re appropriately chosen con~tant~ and T i~
equal to the ~ampling period, Referring to Flg. 4, thi~ fir~t ~e~ctualizat$on ~y3tem i~ compo~ed of a first circuit 3~3 for ~ultiplication of the ter~ d~ by a ~uitably choae~ csn~tant ~ extracted fro~ a ~amory 39. Thi~ magnltude ~S dwn i~ applied~ at th~
outp~lt of the clrc~it 38g to the input of an add~tion cir-cu~t 40, Thia addition circuit 40 furni~lhe~ at the output a magnitude d~ . The other lnput of thi~; addition circuit ~0 receive~ the magnltude dFn 1 of prec~,ding ~a~pllng instant (n-l)T, contain~d in a register 41 delaying the 8a~pling tl~e T9 ~ald magnit~de d~n 1 bei~g we~ghted by an appropriately cho~en coefficient (l-b). A m~ltipllc~ti~n circult 42 effect~ this weighting of dF 1~ the con~tant 1 -~ b0-lng e~tracted ~rom a me~ory 43.
The term dF la then applied to the input of a c~rcuit Is4 for addition of ano~her loop effecting a fllte-ring, ~ritten aa follow~ :
5~3 F = ~ ~ dF
n n-1 n The output of the circuit 44 furni~he3 in f~ct F whilst the other input of circuit 44 r~c3i~ th~ term F 1 contained i~ th~ ~hlft regiat~r 45 d~l~yi~ by 3ampling ti~e T.
The ter~ F~ Dbtained at th2 output ~r the circuit 44 i~ ~pplied to th~ input of a MultlplicQti~l~ circult 46 ~hich multiplie~ it by the ~agnitude T ~qu~l ~o th~ 3~m plin~ pericd o~tract~d from a memorr 47~ Th~ output of th~
~ultiplication circuit 46 i8 co~nected to the input of an additi~n cir~ult 48 whlch furnishes ~t the output th~ ~low phase fluctuations u~O The ~ther lnput ~D~ the ~ddition circult 48 r~caiYe~ the term un 1 ~tored in a shift regi~-ter 49 delaying by a uampling time T. ~li~ new loop thu~
affect~ a~othsr flltering~ written A~ ~13110W~:
u = u ~ 5` F`
n n-l n The co~ponent un furnl~had by the ~ddit~on clrcui* 48 i3 applied to the lnput of an ~ddition cirouit 37 ~here it iu added to the other component ~n corre~pon-dl~g to the rapid fluctu~tion~. Yha addi.tion circuit 37thu~ furnishe~ at the output the pha~a ~ e3timat~d for ~a~ple n.
The compnnent wn, pra~ent on th~ ~ther input of the addition circuit 37 i~ alao obtained~ from the ~ncrea~
dwn, but by ~ean~ of a ~imple filtering. Thl~ magnitude dw i~ applled to the input ~f an addition circult 35 which effecta the sum of thi~ magnitude dwn with tha value ~n 1 furnished at the preceding ~amplin~ in~tant
coefficients Ck, for example in accordance with the algorithm of the gradient:
-~ (2~ fen T + n) Cnk+l = Ck + ~ enAn_k [2]
where the coefficients Ck are eomplex, where 7 is a real positive eonstant, and by a second system for reactua-lization of the phase ~n of the echo, the phase ~n also being reactualized in accordance with the algorithm of the gradient ~ n+l ~n + (en n ) [3]
where ~n is the reconstituted echo and ~n~ its conju-gated complex and d iS a real positive constant.
At the output of the cancellation device, the reconstituted eeho is written:
,, n k Ck A ke ~(2~1fcn T + n) [5~
Sueh an eeho eaneellation deviee has been deseribed, for example, in an artiele whieh appeared in IEEE TRANS. COM. 25, No. 7, July 77, pages 654 to 666.
Sueh phase reaetualization systems are aeeep table for eompensating a slow phase variation or a very slight frequeney drift. However, when the phase varia-tion eomprises a eonsiderable frequeney drift, sueh systems are highly insuffieient. In partieular, when the useful signal-to-eeho ratio, the eeho bearing drift, is weak, the phase eompensation is no longer acceptable.
~ 9~s~3 In fact, it wo~ld necessitate adopting, in phase reactualization algorithm [3], too - 3a -4~
great a coefficient a, which would deteriorate per~ormance~
in the ab~ence of frequency drlft.
The inventors of th~ present in~ention, M~r~.
COLIN de YERDIERE, LANGLOIS and ~r~. ~LCCHI; the latter working ~lth th~ CNRS~ Laboratoire deJ Slgnau~ ~t Systèm~
(L.2 .S. ), have sought to overcome the~ drawback~ of the pha~e reactualization de~ices to cancel echo in order to allo~ a co~siderable frequ~ncy drift o~` the echo to be corrected.
The in~ention ~entially con~i~t~ in di~po~ing a firYt phane Yariation ~tem for tha 810w pha~e fluctua-ti~n un and a second phase ~ariation ~y~te~ for the rapid pha~ fluctuatio~ w~, the total pha~e varlation ~n bei~g : obtalned at tha output of an addition circuitp said addition circuit receiving th0 Bignals Un and wn from ~aid flr~t and Qecond ~y~tem~.
According to ~ first feature, at each sampling : in~tant nT, from a mag~itud~ d~, the magnitude dwn repr~-~enting tha lma~inary part of th~ product Or con~ugated complex echo correction 6nff by the data oi~nal en obtained at tha output of the echo cancellation d~Yice, after elimi-nation of said echo, ~aid product being multipli0d by a coeff1ci~nt of proportionality, th~ p~ha~e co~pensation sy~tem according to the in~ention oompr:ise~ mean~ for addlng, at each ~ampling in~tant, the 810~ pha~e variation un with the rapid ~ha~e variation wn, ~aid addition mean~
~urni~hing at the output the naturel pha~ ~n of th~ 0cho, ~aid ~lo~ variatioll un being obtained from ~aid incr~a~e dw by fir~t mean~, ~aid rapid variation bein~ obtained from 3aid increa~e dwn by second ~ean~.
Moreover, ~aid fir~t mean~ furni~hin~ un at th~
output co~pri~e mean~ for adding the f.luctuation~ un lY
of the preceding sampllng in~tant, w1t]h the magnitud0 T.Fn, T being equal to the 8~mpllng pe:riod, ~aid ~agnitud0 Fn belng obtalned by ~ean~ for a~dition of the ~agnitude Fn 1~ of the preceding ~ampling in~tant, ~ith a ma~itud~
dFn, ~aid 0agnitude dFn bei~ obta~ned by maan~ for addit1on of ~aid increa~e dwn, weighted by a con~tant ~ , with th~
magnitud~ d~n_l of the pr0ceding ~a~pl:Ln~ in~tant, ~aid ~agnitude d~n 1 al~o belng w~ightsd by anoth~r ~o~stant (l-S), ~ and S bei~g real pssit1Ye conl~tant3.
According to a preferred e~bodiment of ~he inven-tio~, the con~tant i~ equal to 1.
Accord~ng to a ~urther feature of the in~æntion, said ~eco~d mean~ furni~hi~ the rapid fluctuation~ wn comprise ~an~ for adding aaid increa~e dWn ~lth th~ ma-gnitudc wn 1 of *he preceding samplins in3tant.
The in~ention enable~ echo~ b~aring a considerable fr~uency drift to be ea~ily corrected"
The in~ention will be more roadily under~tood o~
reading the followlng de~cription wlth referenc~ to th~
accompanyi~g drawing~, in wh~ch :
Fig. 1 iB a general repre~en1;atlon of a ~nown echo cancellation device.
Fig. 2 ~how~ a known ~yRtem o~ reactualization D~ the phase of an scho canccllation de~Yice.
Fig. 3 shows a decomposition according to the invention of the echo phase fluctuations.
Fig. 4 shows the phase correction loops accor-ding to the invention.
Fig. 5 is a preferred embodiment of the inven-tion of Fig. 4.
Fig. 1 illustrates an echo cancelling device known in the prior art. At emission, the signal is in the form of a series An of complex data which are modulated by means of a modulator 1 by the carrier frecIuency fc~ A differential circuit 2 ensures cou-pling of the line with the emission and reception of the modem. The si~nal hn received at instant nT is composed of the useful signal coming from the distant end and from an echo signal gn which is defined in accordance with the aforesaid rela-t:Lon [1~ .
At reception before demodulation, by means of the demodulator 4, there is subtracl,ed from each sample hn received a sample ~n of correction to furnish a sample en due to the subtraction circuit 6, en and ~n being complex. It will be noted that the signal hn is a complex signal phase shifted by ~2 by means of a sepa-rator circuit 7 inserted at reception between the diffe-rential circuit,2 and the subtraction circuit 6.
This sample en is then applied to the input of the demodulator 4. The known echo cancellation devices 5, enabling the phase ~n of the echo to be .~
i3 compensated, are formed by a first system 51 for reac-tualization of the coefficients Ck~ for example in accordance with the aforesaid algorithm [2] and by a second system 52 for reactualizat:lon of the phase 0n of the echo, the phase ~n being reactualized in accor-dance with the aforesaid algorithm [3] .
At the output of the cancellation device 5, the reconstituted echo ~n is defined in accordance with the aforesaid relation [5]
Fig. 2 shows the known systems of reactua-lization of the phase ~n of an echo cancellation device, which comprises a circuit 21 for mu]tiplication of the estimated conjugated complex value -n~ reconstituted for the preceding sample by the value en furnished by the subtraction circuit 6 of Fig. 1. The circuit 22 receiving the result of multiplication of the circuit 21 furnishes at the output the pure imaginary part of this magnitude which is then multiplied by ~ by means of the multiplication circuit 23. ~ is an appropriately selected constant extracted from a memory 24.
The magnitude furnished at the output of the circuit 23 is added with the value ~' furnished at n-l the output of a circuit 25 delaying by a sampling pe-riod T. The result obtained at the output of the addi-tion circuit 25 is ~n' value of the phase shift of the echo for each sampling instant nT according to a known estimation of first order. This est:imation is written by the relation ~n n-l n - 6a -i~,.!
The invention consists in decomposing the phase ~n into two components un and wn, one, un, coxresponding to a slow drift phenomenon capable of decreasing or - 6b -~¢~953 increa~ing, the other, w , corr~ponding to a rapld pheno-~enon, and 1n extracting from the rapidi pheno~enon at each ~amplin~ in~tant 9 the re~idue~ of ~low phenomenDn~ The pha~e ~n~ at instant nT, i~ then ~riSt~n a~ the ~um of th0 compon~nt~ un and wn.
Referring to ~ig. 3, the compcnent u repre~e~t~
a m0an value o~ tha phase ~hil~t u repr0s~nt~ ~mall ampli~
tude variation~ about this mean drift value~
T~o different ~y~t~mA of reactualization o~ each of the~e t~ component~ are di3po~ed accordlng t~ the ln-~ention.
The component ~ 1~ reacSualized acc~rding to the in~entl~n by mean~ of a phase loop Df the first ord~r whil3t the co~ponent un i~ reactualized acc~rdin~ to the invention by mean~ of ~ phas~e loop of a higher ordierO
One ftr~tly form~ the increa~e dwn ~rom the conjugated comple~ r~constituted echo and ~rom ~n~ th~
compl~ v~lue of the u~eful signRl afte~r ~ubtractio~ of the echo. To thl~ end, a multlplication circuit 31 reoei~
~ing en and ~n~ furnishe~ a magnitude alc the ~nput of a circult 32 whlch allo~ only the imaginary part at the out-put to pasc. Thi~ magnitude i~ mulSipll~d by a by ~ean~ of a multiplication circuit 33 furnishing at the output dw 9 the increaae of thc rapid componentO The! con~teLnt ~ 1B
extracted from a memory 34.
dw iB wrltten :
dw~ _ ~ ~ (en ~-n ) L6 J
5~
According to the invention, there are ~xtracted from thi1 ~agnitude dwn the reBidu~ of 910w phenomenon u . To this end, dw i~ applied to the :Lnput o~ a flr0t rcactualization aystem aff~ctin~ s~era:l proces~ing~ of the ~lgnal dwn written mathematically :
n = (1 -~ ) dF~ 1 ~ ~ B d~
F ~ d~
n n-l u z u ~ T F
n n-l n ~here ~ a~d ~ ~re appropriately chosen con~tant~ and T i~
equal to the ~ampling period, Referring to Flg. 4, thi~ fir~t ~e~ctualizat$on ~y3tem i~ compo~ed of a first circuit 3~3 for ~ultiplication of the ter~ d~ by a ~uitably choae~ csn~tant ~ extracted fro~ a ~amory 39. Thi~ magnltude ~S dwn i~ applied~ at th~
outp~lt of the clrc~it 38g to the input of an add~tion cir-cu~t 40, Thia addition circuit 40 furni~lhe~ at the output a magnitude d~ . The other lnput of thi~; addition circuit ~0 receive~ the magnltude dFn 1 of prec~,ding ~a~pllng instant (n-l)T, contain~d in a register 41 delaying the 8a~pling tl~e T9 ~ald magnit~de d~n 1 bei~g we~ghted by an appropriately cho~en coefficient (l-b). A m~ltipllc~ti~n circult 42 effect~ this weighting of dF 1~ the con~tant 1 -~ b0-lng e~tracted ~rom a me~ory 43.
The term dF la then applied to the input of a c~rcuit Is4 for addition of ano~her loop effecting a fllte-ring, ~ritten aa follow~ :
5~3 F = ~ ~ dF
n n-1 n The output of the circuit 44 furni~he3 in f~ct F whilst the other input of circuit 44 r~c3i~ th~ term F 1 contained i~ th~ ~hlft regiat~r 45 d~l~yi~ by 3ampling ti~e T.
The ter~ F~ Dbtained at th2 output ~r the circuit 44 i~ ~pplied to th~ input of a MultlplicQti~l~ circult 46 ~hich multiplie~ it by the ~agnitude T ~qu~l ~o th~ 3~m plin~ pericd o~tract~d from a memorr 47~ Th~ output of th~
~ultiplication circuit 46 i8 co~nected to the input of an additi~n cir~ult 48 whlch furnishes ~t the output th~ ~low phase fluctuations u~O The ~ther lnput ~D~ the ~ddition circult 48 r~caiYe~ the term un 1 ~tored in a shift regi~-ter 49 delaying by a uampling time T. ~li~ new loop thu~
affect~ a~othsr flltering~ written A~ ~13110W~:
u = u ~ 5` F`
n n-l n The co~ponent un furnl~had by the ~ddit~on clrcui* 48 i3 applied to the lnput of an ~ddition cirouit 37 ~here it iu added to the other component ~n corre~pon-dl~g to the rapid fluctu~tion~. Yha addi.tion circuit 37thu~ furnishe~ at the output the pha~a ~ e3timat~d for ~a~ple n.
The compnnent wn, pra~ent on th~ ~ther input of the addition circuit 37 i~ alao obtained~ from the ~ncrea~
dwn, but by ~ean~ of a ~imple filtering. Thl~ magnitude dw i~ applled to the input ~f an addition circult 35 which effecta the sum of thi~ magnitude dwn with tha value ~n 1 furnished at the preceding ~amplin~ in~tant
3'~ 3 and conserved by means of the ~hift regi~ter 36 delaying by timR T.
The ra~id phenomenon ~ i~ thu~ reactualized in accordance with the algorithm of gradlent :
~n = Wn-1 ~ d~n X~o~lng that d~
Thu9 9 the ~lo~ phenomenon i~ reactualiz~d according to the invention by m~an~ of a pha~e corr~cti~n loop of the third order whil~t t~e rapid phenomo~on i~
r~act~allzed by ~ean~ of a pha~e correction loop of the firYt order.
Th~ choic~ Or ~h~ con tant~ S r~ult~ fro~
a compromise bet~een the rapidity ~f ~cqulring th~ ~tima-tio~ of the fr~q~ency drift and the acclspted de~radatio~
in the ab~ence of frequency drift o~ the echo~ ~owe~er, i~ usually ohoaen to be greater tha~ 1~.
Fig. 5 3ho~e a preferred embodi~e~t of the in~ention for which ~= 1. In thi3 way 7 the 810w pha~e variation loop i~ ~implified ~n~ the al~Sorithm3 are written aa follows :
2 0 ~ a u~ +
w a w ~ dw n n-l n dWn = a ~ ( ~ n en) ,> L
u ~ u + T.F
n n-l n n-l + T d n "
~here u ~epresent~ the pha3e correction, which i5 the s~me as elimin~ting the filtering of the term dF O Referrin~
_ 1 ~
to Fig. ~, the addition circuit 44 receive~ at it~ input directly the term ~ dwn which lt adds with Fn 1~ furnii~h~d by th~ delay T circult 45 to furni~h at the output the ter~ ~n at the input of the multiplicatlon circuit 460 In thi~ way, only the loop formed by th~ delay oircuit 41 and the m~ltipllcation circuit 42 iB eli~inated. ~he alow pha~e variation reactuallYiation ~yste~ pa~s~ fro~ the third to the ~econd order.
Simulation~ of tha embodiment of ~lg. 5 hav~
made it po~ibl~ to obtain very ~ati~ifactory pha3e reac-tualizRtion re3ult~, to cancel echo. In the pr~ferred ~y~tem Or ~ig. 5 9 the value~ of ~ and ~, in permanent regime, vary f~om 10 3 to 10 for and 10 to 10 3 for ~.
It i~ ~imply nece~ary that t:he coefficient be le8~ than ~ to ha~e an integration and ~ufficient precl~ion on the e3ti~ation of the frequency drift of the echo. On the contrary, if ~ i~ too ~mall, the ti~e neces-~ary for obtaining a good estimiation ~f the frequellcy drlft ~ill be too great. For ~ery lo~ value~ Or ~9 the e~tlmation of the dri~t not b~ing obtai:n~d a~ r~pidly9 the quality of ~imultaneous two-way tra:ni~iislon 16 degradsd.
The pre~ent ~y~t~ of r~sactua.lization of the phas~ ~ accordin~ to thc invcntion la Is~entially conc~r ned wlth an increa~e dwn form~gd from thls data ~ignal en after cancellation of the echo in the comple~ do~ain.
However, the pha~e reactualization ~y~ t~3m according to the invention is also applicable on reconstitutlng only the ~eal part of en.
The lncrea~e d~n i~ then ~ritt~n :
dw~= ~ sn ~ ( ~n and Fig~. 4, 5 and eq~ations [7~ rem~ll unchang~d.
The pre~nt system for reactu~li2ation of pha~e ~ n according to thc ln~ention i3 appli.ed bDth to a ~i~nal A in ba~ band a~ shown in ~i~. 1 and to a ~lgnal A
in pa~ band in which case modulation occurs, in th~
canc0llation device, a little different;ly. In f~ct9 lt i~
known that, when the cancellation deYic:e 5 operate~ i~ base band a~ ~ho~n in ~ig. l, thc coefficiemt~Cn are formed by a reactu~lization y~te~ 51 d~rectly fro~ the cu~plex data ~ignal A . Modulation by a carrier ~ign.al fc pha~e ~hifted by a pha~e ~n furnished by the pha~e reactuallz~tion By3te~ according to the in~ention therefor~ occur~ at the output of the ~y~tem for raactual1zatlon of the coefficientsO
~ oweYer, t~a phase comp2n~ation ~y~tem accordin~
*o tha inventlon would ~l~o be applied to an echo canc~l-lation dc~ice functioning in pa~ band, The ~y~te~ ~orreactu~ ation of the coef~icient Cn t:hen r~c~ive~ thc d~ta ~ignal A~ already modulated by the carrler fr~q~ency fc and the phase shift of ~ furni~hed lby the pha~e co~pen~ation sy~tem according to the in~vention 10 effected vnly at the output of the ~y~tem ~or reactu~lizRtion of the ~oefficientR.
The ra~id phenomenon ~ i~ thu~ reactualized in accordance with the algorithm of gradlent :
~n = Wn-1 ~ d~n X~o~lng that d~
Thu9 9 the ~lo~ phenomenon i~ reactualiz~d according to the invention by m~an~ of a pha~e corr~cti~n loop of the third order whil~t t~e rapid phenomo~on i~
r~act~allzed by ~ean~ of a pha~e correction loop of the firYt order.
Th~ choic~ Or ~h~ con tant~ S r~ult~ fro~
a compromise bet~een the rapidity ~f ~cqulring th~ ~tima-tio~ of the fr~q~ency drift and the acclspted de~radatio~
in the ab~ence of frequency drift o~ the echo~ ~owe~er, i~ usually ohoaen to be greater tha~ 1~.
Fig. 5 3ho~e a preferred embodi~e~t of the in~ention for which ~= 1. In thi3 way 7 the 810w pha~e variation loop i~ ~implified ~n~ the al~Sorithm3 are written aa follows :
2 0 ~ a u~ +
w a w ~ dw n n-l n dWn = a ~ ( ~ n en) ,> L
u ~ u + T.F
n n-l n n-l + T d n "
~here u ~epresent~ the pha3e correction, which i5 the s~me as elimin~ting the filtering of the term dF O Referrin~
_ 1 ~
to Fig. ~, the addition circuit 44 receive~ at it~ input directly the term ~ dwn which lt adds with Fn 1~ furnii~h~d by th~ delay T circult 45 to furni~h at the output the ter~ ~n at the input of the multiplicatlon circuit 460 In thi~ way, only the loop formed by th~ delay oircuit 41 and the m~ltipllcation circuit 42 iB eli~inated. ~he alow pha~e variation reactuallYiation ~yste~ pa~s~ fro~ the third to the ~econd order.
Simulation~ of tha embodiment of ~lg. 5 hav~
made it po~ibl~ to obtain very ~ati~ifactory pha3e reac-tualizRtion re3ult~, to cancel echo. In the pr~ferred ~y~tem Or ~ig. 5 9 the value~ of ~ and ~, in permanent regime, vary f~om 10 3 to 10 for and 10 to 10 3 for ~.
It i~ ~imply nece~ary that t:he coefficient be le8~ than ~ to ha~e an integration and ~ufficient precl~ion on the e3ti~ation of the frequency drift of the echo. On the contrary, if ~ i~ too ~mall, the ti~e neces-~ary for obtaining a good estimiation ~f the frequellcy drlft ~ill be too great. For ~ery lo~ value~ Or ~9 the e~tlmation of the dri~t not b~ing obtai:n~d a~ r~pidly9 the quality of ~imultaneous two-way tra:ni~iislon 16 degradsd.
The pre~ent ~y~t~ of r~sactua.lization of the phas~ ~ accordin~ to thc invcntion la Is~entially conc~r ned wlth an increa~e dwn form~gd from thls data ~ignal en after cancellation of the echo in the comple~ do~ain.
However, the pha~e reactualization ~y~ t~3m according to the invention is also applicable on reconstitutlng only the ~eal part of en.
The lncrea~e d~n i~ then ~ritt~n :
dw~= ~ sn ~ ( ~n and Fig~. 4, 5 and eq~ations [7~ rem~ll unchang~d.
The pre~nt system for reactu~li2ation of pha~e ~ n according to thc ln~ention i3 appli.ed bDth to a ~i~nal A in ba~ band a~ shown in ~i~. 1 and to a ~lgnal A
in pa~ band in which case modulation occurs, in th~
canc0llation device, a little different;ly. In f~ct9 lt i~
known that, when the cancellation deYic:e 5 operate~ i~ base band a~ ~ho~n in ~ig. l, thc coefficiemt~Cn are formed by a reactu~lization y~te~ 51 d~rectly fro~ the cu~plex data ~ignal A . Modulation by a carrier ~ign.al fc pha~e ~hifted by a pha~e ~n furnished by the pha~e reactuallz~tion By3te~ according to the in~ention therefor~ occur~ at the output of the ~y~tem for raactual1zatlon of the coefficientsO
~ oweYer, t~a phase comp2n~ation ~y~tem accordin~
*o tha inventlon would ~l~o be applied to an echo canc~l-lation dc~ice functioning in pa~ band, The ~y~te~ ~orreactu~ ation of the coef~icient Cn t:hen r~c~ive~ thc d~ta ~ignal A~ already modulated by the carrler fr~q~ency fc and the phase shift of ~ furni~hed lby the pha~e co~pen~ation sy~tem according to the in~vention 10 effected vnly at the output of the ~y~tem ~or reactu~lizRtion of the ~oefficientR.
Claims (8)
1. Device for compensating echo phase for data transmission employing an echo cancellation device consisting in actualizing the natural phase .theta.n of the echo, at each sampling instant nT, from a magnitude dwn, said magnitude dwn representing the imaginary part of the product of the conjugated complex echo correction .sigma.n?
by the data signal en obtained at the output of the echo cancellation device, after elimination of said echo, said product being multiplied by a coefficient .alpha. of proportio-nality, wherein said system comprises means for adding, at each sampling instant, the slow phase variation un with the rapid phase phase variation wn, said addition means furnishing at the output the naturel phase .theta.n of the echo, said slow variation un being obtained from the increase dwn by first means, said rapid variation being obtained from the increase dwn by second means.
by the data signal en obtained at the output of the echo cancellation device, after elimination of said echo, said product being multiplied by a coefficient .alpha. of proportio-nality, wherein said system comprises means for adding, at each sampling instant, the slow phase variation un with the rapid phase phase variation wn, said addition means furnishing at the output the naturel phase .theta.n of the echo, said slow variation un being obtained from the increase dwn by first means, said rapid variation being obtained from the increase dwn by second means.
2. The phase compensation device of Claim 1, wherein said first means furnishing un at the output comprise means for adding the fluctuations un-1 of the preceding sampling instant with the magnitude T.Fn, T
being equal to the sampling period, said magnitude Fn being obtained by means for adding the magnitude Fn-1 of the precedinc sampling instant with a magnitude dFn, said magnitude dFn being obtained by means for adding said increase dwn, weighted by a positive constant , with the magnitude dFn-1 of the preceding sampling instant, said magnitude dFn-1 also being weighted by another real positive constant (1 - .delta.).
being equal to the sampling period, said magnitude Fn being obtained by means for adding the magnitude Fn-1 of the precedinc sampling instant with a magnitude dFn, said magnitude dFn being obtained by means for adding said increase dwn, weighted by a positive constant , with the magnitude dFn-1 of the preceding sampling instant, said magnitude dFn-1 also being weighted by another real positive constant (1 - .delta.).
3. The phase compensation device of Claim 2, wherein .delta. is equal to 1.
4. The phase compensation device of Claim 1, wherein said second means furnishing the rapid fluc-tuations wn comprise means for adding said increase dwn with the magnitude wn-1 of the preceding sampling instant.
5. The phase compensation device of Claims 1, 2 or 3, wherein the data signal en obtained at the output of the echo cancellation device is complex.
6. The phase compensation device of Claims 1, 2 or 3, wherein the data signal en obtained at the output of the echo cancellation device is real.
7. An echo cancellation device comprising a phase compensation device as defined in Claims 1, 2 or 3, wherein it operates in base band insofar as the coefficients are modulated by a carrier frequency fc phase shifted by said phase .theta.n.
8. An echo cancellation device comprising a phase compensation device as defined in Claims 1, 2 or 3, wherein it operates in pass band insofar as the coefficients are formed from the incoming signal already modulated by the carrier frequency fc and said phase shift .theta.n is applied only at the output of the coefficient reactualization system.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR81.13498 | 1981-07-09 | ||
| FR8113498A FR2509552A1 (en) | 1981-07-09 | 1981-07-09 | ECHO PHASE COMPENSATION DEVICE AND ITS APPLICATION TO ECHO CANCELLATIONS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1194953A true CA1194953A (en) | 1985-10-08 |
Family
ID=9260379
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000406048A Expired CA1194953A (en) | 1981-07-09 | 1982-06-25 | Echo phase compensating device and application thereof to echo cancellation devices |
Country Status (11)
| Country | Link |
|---|---|
| EP (1) | EP0070236B1 (en) |
| JP (1) | JPS5817735A (en) |
| CA (1) | CA1194953A (en) |
| DE (1) | DE3262044D1 (en) |
| DK (1) | DK307782A (en) |
| ES (1) | ES513728A0 (en) |
| FI (1) | FI73553C (en) |
| FR (1) | FR2509552A1 (en) |
| HU (1) | HU186079B (en) |
| NO (1) | NO157679C (en) |
| SU (1) | SU1414332A3 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3327467A1 (en) * | 1983-07-29 | 1985-02-14 | Siemens AG, 1000 Berlin und 8000 München | METHOD AND CIRCUIT ARRANGEMENT FOR COMPENSATING ECHO SIGNALS |
| NZ214905A (en) * | 1985-01-29 | 1988-09-29 | British Telecomm | Noise cancellation by adaptive filter compensates for timing variations |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4072830A (en) * | 1976-10-04 | 1978-02-07 | Bell Telephone Laboratories, Incorporated | Variable phase shifter for adaptive echo cancellers |
-
1981
- 1981-07-09 FR FR8113498A patent/FR2509552A1/en active Granted
-
1982
- 1982-06-25 CA CA000406048A patent/CA1194953A/en not_active Expired
- 1982-07-05 ES ES513728A patent/ES513728A0/en active Granted
- 1982-07-06 SU SU823463653A patent/SU1414332A3/en active
- 1982-07-07 EP EP82401285A patent/EP0070236B1/en not_active Expired
- 1982-07-07 DE DE8282401285T patent/DE3262044D1/en not_active Expired
- 1982-07-08 HU HU822228A patent/HU186079B/en unknown
- 1982-07-08 DK DK307782A patent/DK307782A/en not_active Application Discontinuation
- 1982-07-08 FI FI822436A patent/FI73553C/en not_active IP Right Cessation
- 1982-07-08 JP JP57117860A patent/JPS5817735A/en active Granted
- 1982-07-08 NO NO822375A patent/NO157679C/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5817735A (en) | 1983-02-02 |
| SU1414332A3 (en) | 1988-07-30 |
| FI822436L (en) | 1983-01-10 |
| ES8305172A1 (en) | 1983-03-16 |
| DK307782A (en) | 1983-01-10 |
| NO157679C (en) | 1988-04-27 |
| FI822436A0 (en) | 1982-07-08 |
| JPS644699B2 (en) | 1989-01-26 |
| ES513728A0 (en) | 1983-03-16 |
| HU186079B (en) | 1985-05-28 |
| FI73553B (en) | 1987-06-30 |
| EP0070236B1 (en) | 1985-01-23 |
| FR2509552A1 (en) | 1983-01-14 |
| DE3262044D1 (en) | 1985-03-07 |
| NO822375L (en) | 1983-01-10 |
| FI73553C (en) | 1987-10-09 |
| EP0070236A1 (en) | 1983-01-19 |
| NO157679B (en) | 1988-01-18 |
| FR2509552B1 (en) | 1983-12-02 |
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