CA1211515A - Combined adaptive equalization and demodulation circuit - Google Patents
Combined adaptive equalization and demodulation circuitInfo
- Publication number
- CA1211515A CA1211515A CA000454069A CA454069A CA1211515A CA 1211515 A CA1211515 A CA 1211515A CA 000454069 A CA000454069 A CA 000454069A CA 454069 A CA454069 A CA 454069A CA 1211515 A CA1211515 A CA 1211515A
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- Prior art keywords
- path
- branches
- phase
- multipliers
- circuit
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/01—Equalisers
Abstract
ABSTRACT:
An adaptive equalizer arrangement for digital transmission system comprises at the output of the trans-mission channel a first in-phase path and in parallel with this first path, a second quadrature path, both paths being of the non-recursive transversal filter type having n branches and (n-1) delay circuits between the inputs of these branches, each of these n branches com-prising, arranged in series, a mixer, a lowpass filter, a multiplier, and having their outputs connected to an adder which is followed by a sampling circuit and there-after by a comparator circuit to decide the symbols (âk;?k) to be transmitted from the outputs of these paths. The arrangement also comprises a third control path which comprises two subtracting circuits to deter-mine the differences (e'k;e"k) between the signals before (Xk;Yk) and after decision (âk;?k) and a control circuit of a voltage-controlled oscillator, 2n phase s ifters and 2n multipliers.
An adaptive equalizer arrangement for digital transmission system comprises at the output of the trans-mission channel a first in-phase path and in parallel with this first path, a second quadrature path, both paths being of the non-recursive transversal filter type having n branches and (n-1) delay circuits between the inputs of these branches, each of these n branches com-prising, arranged in series, a mixer, a lowpass filter, a multiplier, and having their outputs connected to an adder which is followed by a sampling circuit and there-after by a comparator circuit to decide the symbols (âk;?k) to be transmitted from the outputs of these paths. The arrangement also comprises a third control path which comprises two subtracting circuits to deter-mine the differences (e'k;e"k) between the signals before (Xk;Yk) and after decision (âk;?k) and a control circuit of a voltage-controlled oscillator, 2n phase s ifters and 2n multipliers.
Description
PHI ~3-533 1 2~.3.1984 Combined adaptive equalization and demodulation circuit.
The present invention relates to an adaptive equalizer arrangement for digital transmission systems, and more specifically to high-speed systems in which the transmission channel is not known in advance and/or is 5 susceptible to variations with time. It is therefore suit table for use in digital radio links, data transmission over the switched telephone network, digital transmission over cables (special networks of the Traspac type, etc...).
The use of adaptive equalizers in high-speed lo digital transmission systems to compensate for the amplitude and phase distortions ox the channel has been common practice during several years already. After their in-production in systems for data transmission over the switched telephone network -the adaptive equalizers will 15 be used in digital radio links in the near future The equalizers used in practice have generally one of the following structures, (a) a non-recursive transversal filter by a transversal filter having a recursive portion whose input is constituted by the previously decided sum-20 boys. Adapting the equalizer -to the channel and -to its possible variations with time is generally effected with the aid of a method known as the stochastic gradient of the mean-square error. The two equalizer structures men-toned above and their adaption have keen describe din 25~several~articles, inter aria in: I. Mohawk eta "R~éc:epteurs adaptatifs~pour transmission de Dennis à
grange votes Annals des~Télécommunications, Vol. 30, Noah September-October~1975.
The equalizers often operate in the base band 30 and consequently action demodulated signals. On the other Andy tha~systems of a high spectral efficiency employ modulation of two quadrature corollaries. In these systems, to compensate o'er the inter symbol interference in the ; , :
`:
.
.
PMF S3.533 2 29.3.l9~l~
in-phase and quadrature-phase paths and -to compensate for the interference button these two paths, the equalizer must have four branches each of which is constituted by a transversal jilter; the recursive portion, if any, likewise comprises four transversal filters.
Another disadvantage ox base hand equalizers will become apparent in considering the synchronization of` the carrier necessary or the demodulation. Actually the recovery ox the carrier in systems employing modulation lo of -two quadrature carriers utilizes the base band signals and the decisions (see the article by A. Leclert and P. Vanadium, published in IEEE Transactions on Communique-lions, Volt COMMA, No. 1, January l9039 pages 130 to 136).
There are therefore two possibilities: pa) either the sign lo nets at the output of the demodulator and the decision sat this point are -used, in such a case the system is not very robust as it is very sensitive to channel distortions (b) or the two output signals of the equalizer and their decisions are used, in such a case the system is not son-20 sitive to channel distortions. ire, in the latter case, the carrier recovery loop comprises an additional delay which is the propagation time of the signals through the equalizer and which when the equalizer is very long was is the case in data transmission over cables), tends 25 to render the carrier recovery loop instable. The loop Jill then not be capable ox tracking large frequency deviations (as is described in, or example, the article by I Clang and R. Srinivasagopalan, "Carrier recovery or data come monkeyshine systems with adaptive equalization" published 30 in IEEE Transactions on Communications, Vol. COMMA, No. 8, August l9~0, pages 1142 to 1153). The same problem occurs in digital equalizers, even if they do nut comprise many coefficients, as the propagation time cannot be disregarded.
With regard to this delay problem in base band 35 equalizers, intermediate-~requency equalizers, denoted IF equalizers have been introduced (DUD. Ealconer~
"Jointly Adaptive Equalization and Carrier Recovery in Two-Dimensional Digital Communication Systems", BSTJ, I: '"' :
. .
;
3.~3 I
Jo] JO ~Irtrcil lo 9 l~rli';CS I 7-33~l). Lo tile systenls Us c(lllalizatioll, the carrier recovery is very robust buckeyes of` tllo double ac]var~tage that eclualize(l signals are used aloud the Lyle of the Caesar is gut riot of in 5 C0~1~l^0lli~1,", to carrier. rule Il-eqllaLizer of` tile [`alcone-r type) as do also the basi~blnd eqllalizers, utilizes the rneilrl~sclll1-re error criterion Lowry the adaption. Its disadvan-tare is that i-t requires sarnpl iIlg oil the IF-signal at -tile symbol rate wind, four its adaption, tile remod-lllation of lo decisiol-ls oft equalizer. The need Lowry samplirlg old these two I~-signa]s may cause problems for a practical implement t.ltiOil, as the IF-carrier frequency is high. The sampling ox` tile Signal is then very sensitive -to jitter at the sampling instant. In any case, i-t is more difficult -to 15 sample an IF signal than to sample no associated base band Swahili rho invention hurls Err is object to provide an alopecic e~l-ullizer arrangement which acts on a nor~-salnpled Intel e(l-Late-L`re(Luellcy signal but which a-t the same time 20 func-tior1s as a demodulator and whose output is consequently a base band signal.
The invention -therefore relates to an adaptive equalizer arrangement for digital -transmission systems, characterized in that i-t comprises:
I a first in-phase path provided at the out-put of the -transmission chanrlel of the system and whose structure is that of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inp1l-ts of these branches, each of these n branches come 0 prosing, arranged in series:
(a) a mixer;
(b) a Lopez filter;
(c) a multiplier;
the outputs o r these n branches being connected -to aft tackler 35 which is followed by a sampling circuit ial1d thereafter by a comparator circuit for deciding the symbols to be transmitted room the outwit oil -tilts in-pl1ase pith arid of`
the arrangemel1~t;
Pi ` '3.~'3'3 l >9-3-~-9(~4 (") rlrrarged in rl.lral1.el with Ellis rearrest path a second ~!n~drature pettily hicJI assay ills the structure of noll-rccllrsi~-c transversal filter having n branches all no Lola circuits bottle the lo inputs owl` these branches equal owe` these n brarlcl-:les lo wise comprising arranged in series:
(d) a mixer;
(e) a Lopez inter I a multiplier;
the outpllts of these Al branches being connected to an adder weakly is followed by- a sampling circuit and thereafter by a comparator circuit for deciding the symbols by to be transmitted froth the Outpllt or this quadrature peck and of -the arrangelllent~
-the multipliers of the-e furriest no second paths hexing placed in each branch either a-t -the plead be-fore -the co-rrespolld:illg mixers or a-t the output O r the Lopez Litters (3) a third control path comprising:
(g) two subtracting circuits for determining the differences elk and elk between the signals before decision Eli and Ye and after decision ok and by in the comparator circuits;
(h) a voltage controlled oscillator producing 25 a signal of the type Sweeney to y') where ~.~ corresponds to the frequency of -the carrier;
(i) at the output of` this oscillator n first parallel-arranged phase shifters whose outputs apply -to the respective n second inputs of the mixers in the 30 in-phase path a demodulation signal of the type singe t Jo ) where is the phase shift for -the must branch and m varies -from o to (n-1);
(Jo also at -the OiltpUt of -tile vo.Ltage-con--trolled oscillator a r /2 phase shutter :r'ollol~ed by n 35 second parallel-arranged phase shifters whose outputs apply to the n second inputs of the mixers irk the quadrature path a demodullltioll signal of the type cos(C_j -t (k) a control circus t for -tile volt-Pill` Jo 3 5 '9-3.19 co3-ltrol1erl oscil.Lntl):r, tile 'n apse slliL`terc and the no nuLti~-iiers.
roll In~;-entlo~ lo relies ion a variation Lowry-of`, l-o Al six air ilrrll~gelllelll bolt yin tall to third control roll kelp en:
(g) two su~tract:irLg circulates o'er deterrrlining tile di~`ierel~ces eel and e"] bottle the sigrlaLs before and after dec:i.slc)ll yin the comparator circulates;
(h) n volt.lge-contro:lled oscillators whose I outputs Apple- directly to the respective n second inputs of -the mixers in tile infuse path a demo lotion signal o no) where Jo O corresponds to the carrier frequency is -the flus slot Ion the my branch and In varies from O to (n-l), and aptly by means of 15 air/' plus liter a derrlodLll d-ti0n SigIlal Ox` the type coy t ) to -tile respective n second inputs of` the Myers in tulle quack~ature path.
(i) a control circuit o'er -the n voltage-controlled oscillators and the on multipliers.
The above-proposed arrangement has in either Or the two embodiments Ike followirlg advantages: a simple structure with two paths instead of Tory as in the base band equalizer or the intermediate frequency equalizer of the Falconry type, a control of -the carrier recovery loop by 25 equalized sunless, a compensation Or tile major portion of`
two delay ox the equalizer having Ire its consequence for -the carrier recovery loop, the possibility to track larger ireclue:ncy deviations withoutr~aching -the instability threshold no sampling of intermediate frequency and no 30 demodulation of the decisions. Put more concisely, this arrLngernerlt has therefore -the advantage that it is essay sensitive to sampling errors compared with the filter mediate-I`requ~ncy equalizer, gives better perforrllances (less delay in the loop) compared with the basebarld 35 equalizer, and has a mull simpler implementation Thea the intermediate-rrequel-lcy equalizer or the base band eq-n-lli.zer.
Particulars and Advents of` tile i.nve:lltiol-l will now he described in greater detail lay Jay ox` e.~anlple in tile 3 3 (I 3 1 9 I
I () 1 i I i. l l r'; I C l` l ) i () l l lo L t C' S ) I' C ', t, L C . I (- C (I rip I [) L I ] 1 fir drools, in Lucille:
Ida pa sluice a lyrist erl-lr)odilllerlt o-f` the arralLge-Molly lccorcL-i~rl~ -to tile inielltic)ll~ aloud it lo tile control circulate .inclllcled in tli-is en o(.~ilrlenl;
;. .' illustrates tile su~)sti-tu-tiol1 ox` digitally-con~rolle-:LITll.lltipliers ire arLaLog multipliers i71 the embody-Molly keg. pa;
- Fix,-. 3 shows a second embodiment of` the arrange-lo men t according to the invention.
Burr the arrangement according to the invent lion will to described i-t shol1ld be borne in mind -that, when utilizing ampli-tude-modula-tioIl of` two quadrature carriers as the transmission procedure, the signal received 5 has tile shape (-t) = twirl t Bassett (1) here A and By are low-frequerley signals it regarcL
to tulle freqlleney of -the two carriers sin t and essay- t.
These sLgrlals are connected with -the tranjlllitted symbols ED lay relations of the -type:
A = L a h' tot - by h" test By = r by tot a h" to (3) 25 Weller k' and hut are real and imagiIlary parts resee-lively, of the complex impulse response of the transmission channel, and where the terms a and the terms by are symbol trains modulating at the rate 1/T -the two carriers sin t and cost t, respectively (T = symbol period).
In -the embodiment shown in Fig. lathe equalizing arrangement according -to the invention has a non recursive transversal filter structure in which, put more precisely, the output signal I of the -transmission ellanneL eon-Sti-tuting -the input signal Ion the eq-lali~.er arran~,enlent I is applied to an infuse path 1()0 end also to a q~lacLra-lure path 200, which each comprise a non-reeursive trails venal filter having n browns and (n-1) delay erupts 1011 to 10i l and '011 to 20' 1 bet~.reerl -tile inputs oil fill , I 3-l90l to C AL 1C~ Al (1C I I PUKE to to circulates -LO
r, Isle I lo Issue OWE cry if bolt may ILclVt a Lowry TV let ire e~arrlplc I vitality smiting toe -in-(I I I t i O J
isle the transver,~-ll rllt~r or tile in-pllllse pettily I talc i;~pllt swankily of tile (m~1)5t ranch is lam - tar sin TV tar + Jo (troikas I (t-lllr) (4) This vigil lo LO Apple to a mixer 10', itch at a further lo input receives a demo(lulati,~Il sil~,rlal sin Jo to 0 ) supplied by a control path which will be cleicribed hereirclI`ter, end thwarter to a Lopez filter 103 whose output signal is rove Pi = Automat). coy (I + em roommate) 15~ B(t-mT~. sin (; -I Om+,~OmT) (5) In its -turn, this signal lo applied to a multiplier 104 IvhiCIl produces a signal:
nil = rum Put (6) ~ih:icll is conveyed -to ore of` the n inputs of` an adder 105, 20 at -the output of which -the output signal of -the -trays-vernal filter Or the in-phase path 100 is available (as this path comprises n branches, n mixers 102 -to 102 1' n lo~vpass filters 103 to 103 1 end n multipliers 1040 to 104 1 are provided). This output signal of the adder 5 105 and owe` the filter:
m = n-1 K = X (t) (7) ._ m = 0 is then sampled at -the rate 1/T in a sampling circuit 30 106, and the samples -thus formed are compared with thresholds in a comparator circuit 107 -to decide the symbols a transnlitted through the in-phase path 100.
Similarly, in -the transversal filter of the quadrature path 200, -tile signal at eye input of` -the 35 my branch passes -through a mixer "0" and crier demodulation by the signal Casey Ox +~+ 0 ) vouch is also supplied by the said control pall through a Lopez filter 203 and a mllltiplier 20!~ tulle output of -the air-Isle .3.1.9~Ll Cal l t ''0 'I () JIG t (to 'L')- sill I O'er I
13 (t Ill)- coy (i rut Owner) and 5~111( t) _ rl~1 It All adder 205 cnmbi1les the olltputs owl` the n branches by s-upplvin~ a -inlay:
m = n-1 to = Yin ) lo m = 0 heckle is sampled at the same Wright I/T in a circuit 206, the samples supplied by this ci.r(nli-t being compared with thresll(>lds in a circuit 207 -to decide the symbol by -trarlsmitted through the qLLadratllre path 200 (itch Quadram Tory path .'1]50 comprises if branches, -the renla:rlc made in tile l'orel~l;oin~:~ as regards tulle n~LIllber owe` circuits also hellholes Lowry).
The demodulation signal is applied to each of these in-phase and quadrature paths 100 and 200 by a 20 control path, which. comprises a voltage- controlled oscillator 301, on phase shifters 3'10 to 310 1 and 3200 -to 32n I and a control loop for this oscillator -these on please shifters and on multipliers 104 to and 204 to 204 . The n phase shifters 310 to n-1 o n-1 - o 25 31~,l 1 I toll in-phase path 100 are Iced in parallel direct-lye by -the oscillator 301 and -Tyler outputs are connected to the second input of the corresponding mixer 102, while the n phase shifters 320 to 320 -1 of -the quadrature path 200, which are also fed in parallel by the oscillator 301 ought after having passed through a I phase shifter 302, have their outputs connected -to the second input of the corresponding mixers 202 to 202 I these phase shifters are here either capacitive circuits or, which is simpler, delay circuits capable Or being controlled.
The control ox the oscillator 301 is obtained by utilizing as a criterion the search fry the millirrllln mean-sqllare error Jo given 'by:
J = Eel + elk ) ('lo) ..~ "p Pill I 33 9 I') .3. l9($4 where two solely E keynotes the m~t]loma-ticaL c~pectation, the Tories Cal Audi eye be:inlcr give c at (12) eye = Ye - by (13) 5 in ~-]1icl1 t being the sampling i ns-callt, -the no tuitions:
It ( ) t = IT + t ye y ( -t ) r. = It + -to en e I s owl .
10 The grad en-t of J with respect to r i s written:
_ = YE ( e ' k k + e "k a ok (1 If ) o r :
j r YE (e k Pm elk Al (15) where: Pi Pronto t = kit t and em L Em Al -t=kT+to Similarly by wry tying the gradient of J wit to respect to O , i t is found that:
= YE ( e It Ye e It em ) (16) wherein: Yearly = Yet = IT + to Em = Yet = kit + to By using the well-known stochastic gradient algorithm (see the above mentioned article by C. Mecca et at. ), the adaption of -the multipliers 104 to 104 1 and 204 -to 24n 1 -which produce respecter multiplications or 30 attenuations row r1 r2, .. , r 1 in the n branches of the in-phase path 100 and the quadrature path 200, and the adaptation of the phase shifters 310 -to 310 1 and 3200 to 320 1 which likewise produce respect live phase ski Lots 1~ 2 1 in -the n branches of -two paths loo tend 35 200, are realized in accordance with the lo l lowing; -two relations (in itch m always varies loom O to n-1), which gives the expressions of the signals reassured by these multipliers and phase shifters, respectively ( these signals rl51L~
l'~11;` I 10 "3.,.l~;~,4 bill,', i~Cllti(`.~L pharaoh Tao bra1lclles Or Lyle Salk Orderly nuJI1"cr of:` rootless Lowe and 200):
l11 I I ' "111) (17) (Yore I ~rl1 e I I
Lowry no are positive constants representing Ike algoritl111ste1) and which awry sul`ricien-tl~- sr11clll to gurney-tee -the stilt Our tile algOritl1nl.
011 the other Hollywood tile gradient ox Jo Wylie respect to the plus of tune oscillator 301 its written:
¢ (e I Ye e I ) (19) and -this oscillator is consequelltly controlled by the serenely:
'-1; e It Yule - elk Al oriole f`i.:lterrcl-versio]l old this sunnily.
I tile exarrlple of -the arrangement descried will reruns to jig lay the control circuit 350 ox the oscillator 301, the phase shifters 310 -to 3'10 1 and 320 to 320 I and tile multipliers 104 to 104 1 and 20ll to 20~l 1 comprise (see Fig 1b):
(a) -for controlling the oscillator 301 in accord dance with the expression (20), -two multipliers 351 and 352, a subtracter 353 for subtracting the terms e'kYk and 25 eye tolls obtained, and a opus loop filter 35~1 whose Output si.gl1al is calved to -the oscillator 301;
(b) for con-trolling each of the phase shifters in accordance with the expression I likewise two multi-pliers 361 and 362~ a su'b',ractor 363~ a multiplier 36ll 30 which receives the coefficient/-- a-t its second input, and a subtracter 365 l~rhich is associated with a delay circuit 366 producing a time delay T, the output of' this subtracter being applied to -the correspond no phase shifter in the paths 100 and 200 7 (c) for controlling each of the multipliers in accordance with press ion (17), lulls two multipliers 3~1 and 3r~.'s an adder 3~3, a multiplier I Lucia rickshaws the coefficient' a-t its second inputs aloud a subt,r.lctor I ,,, I ~ihicl~ is associated with a Doyle Circulate I p-rod1lcinfr a tithe jelly r, Thea Oil t ply old this suL)tractor lacing appareled to to corresT)ol-ldL7lg mu:L~ip1-Ler in the paths 100 and 200.
It will be Clara that the present invention 5 it rot 'Lit Tao to the embodilnent described above, rerun which virilities gall be proposed without departing iron the SKYE O f` tile inventio:rl.
Ire the adapt tot] of tile phase shifters and the multipliers, it is, for example, sufficient to use the lo signs of c'lj, eke em and Ye and to replace the expressions ('17) and I respectively by the expressions (21) and (22) WlliCIl are much swampier to irnplemerlt:
rum = r -Al sun Snow eel Sony Sill eel) ( 2 1 ) and 15 I = I _f1j (s~c,r~Ym.sgn elk - SglL~,n.Sg:tl eel ) I
(Silas the sufferance ox eel, elk, , ~~' instead old their allele are used, -the use of` either sgnX or sun p gives eclllivalent results and -the same applies ire Sony end 20 So S these terms have I've same signs). Likewise, a simpliI`iecl control of' the oscillator 301 can be obtained by replacing the expression (20) by:
r = sun Ye. sung elk - sun Ok. sun e k (23) This variation is put concretely, obtained on the basis 25 of Fig. lb by arrarlging zero-comparators (not Chilean here) j-us-t 'Burr -the inputs of the two multipliers 351 and 35?, of the on multipliers 361, 362 and of toe on multi-pliers 3~1, 382.
Moreover, -the control circuit 350 as it is desk I cribbed above is of` the analog type, but a digital variationCrLII be proposed, which modifies, in Fig. 1b, the circuit portions situated at the outputs Or multipliers LOWE, I
In this case tile on multipliers lo to Ion I and owe to 20Ll 1 are replaced (see jig. 2) by a Salle number of`
35 series arrangements comprisillg all ampLiri{?r lull aloud a digital con-trolled attenuator l'05 whose parallel inputs are connected to -the outputs (which are equal in nilmber) of an -up/down counter 40~ Lucia is contr~L1e(l by a Nero-L
Ply 'it 3 1" :'~.3.1~
coy nr.ltc)r '10 " this comp~lra1;(>r l)eln{r provi(iecL at the out-Pit ~.~ I IT Taipei s I l(1,'3~
It s1lolll,d also eye noted fat in a second embody-n1eJlt ahoy Foe,. 3, -tulle ply slightly{, rinks ensured 5 by Tao no phase shelters 310 co '~10 1 Ann 3,"0 -to 32() may be 1,r.lllsrerred -to if voltage-corltrolled oscillators 5()10 to 50'1 ,1, icily direct control -the Myers 102 to 10.~ 1 of Tao in-plLase path 100 and, through the I phase shifters I to 5 I also control the mixers 202 to '02 -1 of` tile quadra-tllre pettily 200- the control signals produced by the control circuit 350 remain identical, with -the exception of the control diurnal for the oscillator 301 wllicil does rho t exist any more, as lilts oscillator is no longer presesl-t.
I-L; should also be no-ted that the position owl the multiplier 101~ Sheehan in Fig. pa is not -the only posy s ib.:l.c post lion, it being possible to place these ml,llti-pyres at toe head our n branches of` the filter instead O I Levi g then precede the adders 105 and ~05.
Inlay it should be no-ted -that to explain the opera till principle, -the description has been limited -to aft equalizer in the form of a transversal filter without recursive portion, but it is equally possible to include Such a recursive portion without modification or restriction 25 of the invention. When there is a recursive portion, its input signals may be the previous decisions (in the case of a non-linear equalizer) or delayed versions of the out-put signal of the equalizer (in the case of a linear equalizer
The present invention relates to an adaptive equalizer arrangement for digital transmission systems, and more specifically to high-speed systems in which the transmission channel is not known in advance and/or is 5 susceptible to variations with time. It is therefore suit table for use in digital radio links, data transmission over the switched telephone network, digital transmission over cables (special networks of the Traspac type, etc...).
The use of adaptive equalizers in high-speed lo digital transmission systems to compensate for the amplitude and phase distortions ox the channel has been common practice during several years already. After their in-production in systems for data transmission over the switched telephone network -the adaptive equalizers will 15 be used in digital radio links in the near future The equalizers used in practice have generally one of the following structures, (a) a non-recursive transversal filter by a transversal filter having a recursive portion whose input is constituted by the previously decided sum-20 boys. Adapting the equalizer -to the channel and -to its possible variations with time is generally effected with the aid of a method known as the stochastic gradient of the mean-square error. The two equalizer structures men-toned above and their adaption have keen describe din 25~several~articles, inter aria in: I. Mohawk eta "R~éc:epteurs adaptatifs~pour transmission de Dennis à
grange votes Annals des~Télécommunications, Vol. 30, Noah September-October~1975.
The equalizers often operate in the base band 30 and consequently action demodulated signals. On the other Andy tha~systems of a high spectral efficiency employ modulation of two quadrature corollaries. In these systems, to compensate o'er the inter symbol interference in the ; , :
`:
.
.
PMF S3.533 2 29.3.l9~l~
in-phase and quadrature-phase paths and -to compensate for the interference button these two paths, the equalizer must have four branches each of which is constituted by a transversal jilter; the recursive portion, if any, likewise comprises four transversal filters.
Another disadvantage ox base hand equalizers will become apparent in considering the synchronization of` the carrier necessary or the demodulation. Actually the recovery ox the carrier in systems employing modulation lo of -two quadrature carriers utilizes the base band signals and the decisions (see the article by A. Leclert and P. Vanadium, published in IEEE Transactions on Communique-lions, Volt COMMA, No. 1, January l9039 pages 130 to 136).
There are therefore two possibilities: pa) either the sign lo nets at the output of the demodulator and the decision sat this point are -used, in such a case the system is not very robust as it is very sensitive to channel distortions (b) or the two output signals of the equalizer and their decisions are used, in such a case the system is not son-20 sitive to channel distortions. ire, in the latter case, the carrier recovery loop comprises an additional delay which is the propagation time of the signals through the equalizer and which when the equalizer is very long was is the case in data transmission over cables), tends 25 to render the carrier recovery loop instable. The loop Jill then not be capable ox tracking large frequency deviations (as is described in, or example, the article by I Clang and R. Srinivasagopalan, "Carrier recovery or data come monkeyshine systems with adaptive equalization" published 30 in IEEE Transactions on Communications, Vol. COMMA, No. 8, August l9~0, pages 1142 to 1153). The same problem occurs in digital equalizers, even if they do nut comprise many coefficients, as the propagation time cannot be disregarded.
With regard to this delay problem in base band 35 equalizers, intermediate-~requency equalizers, denoted IF equalizers have been introduced (DUD. Ealconer~
"Jointly Adaptive Equalization and Carrier Recovery in Two-Dimensional Digital Communication Systems", BSTJ, I: '"' :
. .
;
3.~3 I
Jo] JO ~Irtrcil lo 9 l~rli';CS I 7-33~l). Lo tile systenls Us c(lllalizatioll, the carrier recovery is very robust buckeyes of` tllo double ac]var~tage that eclualize(l signals are used aloud the Lyle of the Caesar is gut riot of in 5 C0~1~l^0lli~1,", to carrier. rule Il-eqllaLizer of` tile [`alcone-r type) as do also the basi~blnd eqllalizers, utilizes the rneilrl~sclll1-re error criterion Lowry the adaption. Its disadvan-tare is that i-t requires sarnpl iIlg oil the IF-signal at -tile symbol rate wind, four its adaption, tile remod-lllation of lo decisiol-ls oft equalizer. The need Lowry samplirlg old these two I~-signa]s may cause problems for a practical implement t.ltiOil, as the IF-carrier frequency is high. The sampling ox` tile Signal is then very sensitive -to jitter at the sampling instant. In any case, i-t is more difficult -to 15 sample an IF signal than to sample no associated base band Swahili rho invention hurls Err is object to provide an alopecic e~l-ullizer arrangement which acts on a nor~-salnpled Intel e(l-Late-L`re(Luellcy signal but which a-t the same time 20 func-tior1s as a demodulator and whose output is consequently a base band signal.
The invention -therefore relates to an adaptive equalizer arrangement for digital -transmission systems, characterized in that i-t comprises:
I a first in-phase path provided at the out-put of the -transmission chanrlel of the system and whose structure is that of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inp1l-ts of these branches, each of these n branches come 0 prosing, arranged in series:
(a) a mixer;
(b) a Lopez filter;
(c) a multiplier;
the outputs o r these n branches being connected -to aft tackler 35 which is followed by a sampling circuit ial1d thereafter by a comparator circuit for deciding the symbols to be transmitted room the outwit oil -tilts in-pl1ase pith arid of`
the arrangemel1~t;
Pi ` '3.~'3'3 l >9-3-~-9(~4 (") rlrrarged in rl.lral1.el with Ellis rearrest path a second ~!n~drature pettily hicJI assay ills the structure of noll-rccllrsi~-c transversal filter having n branches all no Lola circuits bottle the lo inputs owl` these branches equal owe` these n brarlcl-:les lo wise comprising arranged in series:
(d) a mixer;
(e) a Lopez inter I a multiplier;
the outpllts of these Al branches being connected to an adder weakly is followed by- a sampling circuit and thereafter by a comparator circuit for deciding the symbols by to be transmitted froth the Outpllt or this quadrature peck and of -the arrangelllent~
-the multipliers of the-e furriest no second paths hexing placed in each branch either a-t -the plead be-fore -the co-rrespolld:illg mixers or a-t the output O r the Lopez Litters (3) a third control path comprising:
(g) two subtracting circuits for determining the differences elk and elk between the signals before decision Eli and Ye and after decision ok and by in the comparator circuits;
(h) a voltage controlled oscillator producing 25 a signal of the type Sweeney to y') where ~.~ corresponds to the frequency of -the carrier;
(i) at the output of` this oscillator n first parallel-arranged phase shifters whose outputs apply -to the respective n second inputs of the mixers in the 30 in-phase path a demodulation signal of the type singe t Jo ) where is the phase shift for -the must branch and m varies -from o to (n-1);
(Jo also at -the OiltpUt of -tile vo.Ltage-con--trolled oscillator a r /2 phase shutter :r'ollol~ed by n 35 second parallel-arranged phase shifters whose outputs apply to the n second inputs of the mixers irk the quadrature path a demodullltioll signal of the type cos(C_j -t (k) a control circus t for -tile volt-Pill` Jo 3 5 '9-3.19 co3-ltrol1erl oscil.Lntl):r, tile 'n apse slliL`terc and the no nuLti~-iiers.
roll In~;-entlo~ lo relies ion a variation Lowry-of`, l-o Al six air ilrrll~gelllelll bolt yin tall to third control roll kelp en:
(g) two su~tract:irLg circulates o'er deterrrlining tile di~`ierel~ces eel and e"] bottle the sigrlaLs before and after dec:i.slc)ll yin the comparator circulates;
(h) n volt.lge-contro:lled oscillators whose I outputs Apple- directly to the respective n second inputs of -the mixers in tile infuse path a demo lotion signal o no) where Jo O corresponds to the carrier frequency is -the flus slot Ion the my branch and In varies from O to (n-l), and aptly by means of 15 air/' plus liter a derrlodLll d-ti0n SigIlal Ox` the type coy t ) to -tile respective n second inputs of` the Myers in tulle quack~ature path.
(i) a control circuit o'er -the n voltage-controlled oscillators and the on multipliers.
The above-proposed arrangement has in either Or the two embodiments Ike followirlg advantages: a simple structure with two paths instead of Tory as in the base band equalizer or the intermediate frequency equalizer of the Falconry type, a control of -the carrier recovery loop by 25 equalized sunless, a compensation Or tile major portion of`
two delay ox the equalizer having Ire its consequence for -the carrier recovery loop, the possibility to track larger ireclue:ncy deviations withoutr~aching -the instability threshold no sampling of intermediate frequency and no 30 demodulation of the decisions. Put more concisely, this arrLngernerlt has therefore -the advantage that it is essay sensitive to sampling errors compared with the filter mediate-I`requ~ncy equalizer, gives better perforrllances (less delay in the loop) compared with the basebarld 35 equalizer, and has a mull simpler implementation Thea the intermediate-rrequel-lcy equalizer or the base band eq-n-lli.zer.
Particulars and Advents of` tile i.nve:lltiol-l will now he described in greater detail lay Jay ox` e.~anlple in tile 3 3 (I 3 1 9 I
I () 1 i I i. l l r'; I C l` l ) i () l l lo L t C' S ) I' C ', t, L C . I (- C (I rip I [) L I ] 1 fir drools, in Lucille:
Ida pa sluice a lyrist erl-lr)odilllerlt o-f` the arralLge-Molly lccorcL-i~rl~ -to tile inielltic)ll~ aloud it lo tile control circulate .inclllcled in tli-is en o(.~ilrlenl;
;. .' illustrates tile su~)sti-tu-tiol1 ox` digitally-con~rolle-:LITll.lltipliers ire arLaLog multipliers i71 the embody-Molly keg. pa;
- Fix,-. 3 shows a second embodiment of` the arrange-lo men t according to the invention.
Burr the arrangement according to the invent lion will to described i-t shol1ld be borne in mind -that, when utilizing ampli-tude-modula-tioIl of` two quadrature carriers as the transmission procedure, the signal received 5 has tile shape (-t) = twirl t Bassett (1) here A and By are low-frequerley signals it regarcL
to tulle freqlleney of -the two carriers sin t and essay- t.
These sLgrlals are connected with -the tranjlllitted symbols ED lay relations of the -type:
A = L a h' tot - by h" test By = r by tot a h" to (3) 25 Weller k' and hut are real and imagiIlary parts resee-lively, of the complex impulse response of the transmission channel, and where the terms a and the terms by are symbol trains modulating at the rate 1/T -the two carriers sin t and cost t, respectively (T = symbol period).
In -the embodiment shown in Fig. lathe equalizing arrangement according -to the invention has a non recursive transversal filter structure in which, put more precisely, the output signal I of the -transmission ellanneL eon-Sti-tuting -the input signal Ion the eq-lali~.er arran~,enlent I is applied to an infuse path 1()0 end also to a q~lacLra-lure path 200, which each comprise a non-reeursive trails venal filter having n browns and (n-1) delay erupts 1011 to 10i l and '011 to 20' 1 bet~.reerl -tile inputs oil fill , I 3-l90l to C AL 1C~ Al (1C I I PUKE to to circulates -LO
r, Isle I lo Issue OWE cry if bolt may ILclVt a Lowry TV let ire e~arrlplc I vitality smiting toe -in-(I I I t i O J
isle the transver,~-ll rllt~r or tile in-pllllse pettily I talc i;~pllt swankily of tile (m~1)5t ranch is lam - tar sin TV tar + Jo (troikas I (t-lllr) (4) This vigil lo LO Apple to a mixer 10', itch at a further lo input receives a demo(lulati,~Il sil~,rlal sin Jo to 0 ) supplied by a control path which will be cleicribed hereirclI`ter, end thwarter to a Lopez filter 103 whose output signal is rove Pi = Automat). coy (I + em roommate) 15~ B(t-mT~. sin (; -I Om+,~OmT) (5) In its -turn, this signal lo applied to a multiplier 104 IvhiCIl produces a signal:
nil = rum Put (6) ~ih:icll is conveyed -to ore of` the n inputs of` an adder 105, 20 at -the output of which -the output signal of -the -trays-vernal filter Or the in-phase path 100 is available (as this path comprises n branches, n mixers 102 -to 102 1' n lo~vpass filters 103 to 103 1 end n multipliers 1040 to 104 1 are provided). This output signal of the adder 5 105 and owe` the filter:
m = n-1 K = X (t) (7) ._ m = 0 is then sampled at -the rate 1/T in a sampling circuit 30 106, and the samples -thus formed are compared with thresholds in a comparator circuit 107 -to decide the symbols a transnlitted through the in-phase path 100.
Similarly, in -the transversal filter of the quadrature path 200, -tile signal at eye input of` -the 35 my branch passes -through a mixer "0" and crier demodulation by the signal Casey Ox +~+ 0 ) vouch is also supplied by the said control pall through a Lopez filter 203 and a mllltiplier 20!~ tulle output of -the air-Isle .3.1.9~Ll Cal l t ''0 'I () JIG t (to 'L')- sill I O'er I
13 (t Ill)- coy (i rut Owner) and 5~111( t) _ rl~1 It All adder 205 cnmbi1les the olltputs owl` the n branches by s-upplvin~ a -inlay:
m = n-1 to = Yin ) lo m = 0 heckle is sampled at the same Wright I/T in a circuit 206, the samples supplied by this ci.r(nli-t being compared with thresll(>lds in a circuit 207 -to decide the symbol by -trarlsmitted through the qLLadratllre path 200 (itch Quadram Tory path .'1]50 comprises if branches, -the renla:rlc made in tile l'orel~l;oin~:~ as regards tulle n~LIllber owe` circuits also hellholes Lowry).
The demodulation signal is applied to each of these in-phase and quadrature paths 100 and 200 by a 20 control path, which. comprises a voltage- controlled oscillator 301, on phase shifters 3'10 to 310 1 and 3200 -to 32n I and a control loop for this oscillator -these on please shifters and on multipliers 104 to and 204 to 204 . The n phase shifters 310 to n-1 o n-1 - o 25 31~,l 1 I toll in-phase path 100 are Iced in parallel direct-lye by -the oscillator 301 and -Tyler outputs are connected to the second input of the corresponding mixer 102, while the n phase shifters 320 to 320 -1 of -the quadrature path 200, which are also fed in parallel by the oscillator 301 ought after having passed through a I phase shifter 302, have their outputs connected -to the second input of the corresponding mixers 202 to 202 I these phase shifters are here either capacitive circuits or, which is simpler, delay circuits capable Or being controlled.
The control ox the oscillator 301 is obtained by utilizing as a criterion the search fry the millirrllln mean-sqllare error Jo given 'by:
J = Eel + elk ) ('lo) ..~ "p Pill I 33 9 I') .3. l9($4 where two solely E keynotes the m~t]loma-ticaL c~pectation, the Tories Cal Audi eye be:inlcr give c at (12) eye = Ye - by (13) 5 in ~-]1icl1 t being the sampling i ns-callt, -the no tuitions:
It ( ) t = IT + t ye y ( -t ) r. = It + -to en e I s owl .
10 The grad en-t of J with respect to r i s written:
_ = YE ( e ' k k + e "k a ok (1 If ) o r :
j r YE (e k Pm elk Al (15) where: Pi Pronto t = kit t and em L Em Al -t=kT+to Similarly by wry tying the gradient of J wit to respect to O , i t is found that:
= YE ( e It Ye e It em ) (16) wherein: Yearly = Yet = IT + to Em = Yet = kit + to By using the well-known stochastic gradient algorithm (see the above mentioned article by C. Mecca et at. ), the adaption of -the multipliers 104 to 104 1 and 204 -to 24n 1 -which produce respecter multiplications or 30 attenuations row r1 r2, .. , r 1 in the n branches of the in-phase path 100 and the quadrature path 200, and the adaptation of the phase shifters 310 -to 310 1 and 3200 to 320 1 which likewise produce respect live phase ski Lots 1~ 2 1 in -the n branches of -two paths loo tend 35 200, are realized in accordance with the lo l lowing; -two relations (in itch m always varies loom O to n-1), which gives the expressions of the signals reassured by these multipliers and phase shifters, respectively ( these signals rl51L~
l'~11;` I 10 "3.,.l~;~,4 bill,', i~Cllti(`.~L pharaoh Tao bra1lclles Or Lyle Salk Orderly nuJI1"cr of:` rootless Lowe and 200):
l11 I I ' "111) (17) (Yore I ~rl1 e I I
Lowry no are positive constants representing Ike algoritl111ste1) and which awry sul`ricien-tl~- sr11clll to gurney-tee -the stilt Our tile algOritl1nl.
011 the other Hollywood tile gradient ox Jo Wylie respect to the plus of tune oscillator 301 its written:
¢ (e I Ye e I ) (19) and -this oscillator is consequelltly controlled by the serenely:
'-1; e It Yule - elk Al oriole f`i.:lterrcl-versio]l old this sunnily.
I tile exarrlple of -the arrangement descried will reruns to jig lay the control circuit 350 ox the oscillator 301, the phase shifters 310 -to 3'10 1 and 320 to 320 I and tile multipliers 104 to 104 1 and 20ll to 20~l 1 comprise (see Fig 1b):
(a) -for controlling the oscillator 301 in accord dance with the expression (20), -two multipliers 351 and 352, a subtracter 353 for subtracting the terms e'kYk and 25 eye tolls obtained, and a opus loop filter 35~1 whose Output si.gl1al is calved to -the oscillator 301;
(b) for con-trolling each of the phase shifters in accordance with the expression I likewise two multi-pliers 361 and 362~ a su'b',ractor 363~ a multiplier 36ll 30 which receives the coefficient/-- a-t its second input, and a subtracter 365 l~rhich is associated with a delay circuit 366 producing a time delay T, the output of' this subtracter being applied to -the correspond no phase shifter in the paths 100 and 200 7 (c) for controlling each of the multipliers in accordance with press ion (17), lulls two multipliers 3~1 and 3r~.'s an adder 3~3, a multiplier I Lucia rickshaws the coefficient' a-t its second inputs aloud a subt,r.lctor I ,,, I ~ihicl~ is associated with a Doyle Circulate I p-rod1lcinfr a tithe jelly r, Thea Oil t ply old this suL)tractor lacing appareled to to corresT)ol-ldL7lg mu:L~ip1-Ler in the paths 100 and 200.
It will be Clara that the present invention 5 it rot 'Lit Tao to the embodilnent described above, rerun which virilities gall be proposed without departing iron the SKYE O f` tile inventio:rl.
Ire the adapt tot] of tile phase shifters and the multipliers, it is, for example, sufficient to use the lo signs of c'lj, eke em and Ye and to replace the expressions ('17) and I respectively by the expressions (21) and (22) WlliCIl are much swampier to irnplemerlt:
rum = r -Al sun Snow eel Sony Sill eel) ( 2 1 ) and 15 I = I _f1j (s~c,r~Ym.sgn elk - SglL~,n.Sg:tl eel ) I
(Silas the sufferance ox eel, elk, , ~~' instead old their allele are used, -the use of` either sgnX or sun p gives eclllivalent results and -the same applies ire Sony end 20 So S these terms have I've same signs). Likewise, a simpliI`iecl control of' the oscillator 301 can be obtained by replacing the expression (20) by:
r = sun Ye. sung elk - sun Ok. sun e k (23) This variation is put concretely, obtained on the basis 25 of Fig. lb by arrarlging zero-comparators (not Chilean here) j-us-t 'Burr -the inputs of the two multipliers 351 and 35?, of the on multipliers 361, 362 and of toe on multi-pliers 3~1, 382.
Moreover, -the control circuit 350 as it is desk I cribbed above is of` the analog type, but a digital variationCrLII be proposed, which modifies, in Fig. 1b, the circuit portions situated at the outputs Or multipliers LOWE, I
In this case tile on multipliers lo to Ion I and owe to 20Ll 1 are replaced (see jig. 2) by a Salle number of`
35 series arrangements comprisillg all ampLiri{?r lull aloud a digital con-trolled attenuator l'05 whose parallel inputs are connected to -the outputs (which are equal in nilmber) of an -up/down counter 40~ Lucia is contr~L1e(l by a Nero-L
Ply 'it 3 1" :'~.3.1~
coy nr.ltc)r '10 " this comp~lra1;(>r l)eln{r provi(iecL at the out-Pit ~.~ I IT Taipei s I l(1,'3~
It s1lolll,d also eye noted fat in a second embody-n1eJlt ahoy Foe,. 3, -tulle ply slightly{, rinks ensured 5 by Tao no phase shelters 310 co '~10 1 Ann 3,"0 -to 32() may be 1,r.lllsrerred -to if voltage-corltrolled oscillators 5()10 to 50'1 ,1, icily direct control -the Myers 102 to 10.~ 1 of Tao in-plLase path 100 and, through the I phase shifters I to 5 I also control the mixers 202 to '02 -1 of` tile quadra-tllre pettily 200- the control signals produced by the control circuit 350 remain identical, with -the exception of the control diurnal for the oscillator 301 wllicil does rho t exist any more, as lilts oscillator is no longer presesl-t.
I-L; should also be no-ted that the position owl the multiplier 101~ Sheehan in Fig. pa is not -the only posy s ib.:l.c post lion, it being possible to place these ml,llti-pyres at toe head our n branches of` the filter instead O I Levi g then precede the adders 105 and ~05.
Inlay it should be no-ted -that to explain the opera till principle, -the description has been limited -to aft equalizer in the form of a transversal filter without recursive portion, but it is equally possible to include Such a recursive portion without modification or restriction 25 of the invention. When there is a recursive portion, its input signals may be the previous decisions (in the case of a non-linear equalizer) or delayed versions of the out-put signal of the equalizer (in the case of a linear equalizer
Claims (5)
PROPERTY OF PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An adaptive equalizer arrangement for digital transmission systems, characterized in that it comprises:
(1) a first in-phase path provided at the output of the transmission channel of the system and whose structure is that of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inputs of these branches, each of these n branches com-prising, arranged in series:
(a) a mixer;
(b) a lowpass filter;
(c) a multiplier;
the outputs of these n branches being connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit for deciding the symbols ?k to be transmitted from the output of this in-phase path and of the arrangement;
(2) arranged in parallel with this first path, a second quadrature path which also has the structure of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inputs of these branches, each of these n branches likewise comprising, arranged in series:
(d) a mixer;
(e) a lowpass filter;
(f) a multiplier;
the outputs of these n branches being connected to an adder which is followed by a sampling circuit and there-after by a comparator circuit for deciding the symbols ?k to be transmitted from the output of this quadrature path and or the arrangement;
the multipliers of these first and second paths being placed in each branch either at the head, before the corresponding mixers, or at the output of the lowpass filters;
(3) a third control path comprising:
(g) two subtracting circuits for determining the differences e'k and e"k between the signals before decision, Xk and Yk, and after decision, ?k and ?k, in the comparator circuits, expressed for the in-phase path and for the quadrature path by the respective expressions:
e'k = Xk - ?k and e"k = Yk - ?k where X(t) and Y(t) are the output signals of the trans-versal filter of the in-phase path and the quadrature path, respectively, and to is the sampling instant;
(h) a voltage-controlled oscillator producing a signal of the type sin (.omega.ot+?) where .omega.o corresponds to the frequency of the carrier, which oscillator is con-trolled by the signal ?k = e'kYk - e"k Xk (i) at the output of this oscillator, n first parallel-ranged phase shifters whose outputs apply to the respective n second inputs of the mixers in the in-phase path a demodulation signal of the type sin(.omega.ot+Y+Om) where Om is the phase shift for the (m+1)st branch and m varies from O to (n-1);
(j) also at the output of the voltage-controlled oscillator, a .pi./2 phase shifter followed by n second parallel-arranged phase shifters whose outputs apply to the n second inputs of the mixers in the quadra-ture path a demodulation signal of the type cos(.omega.ot + ? + Om);
(k) a control circuit for the voltage-controlled oscillator, the 2n phase shifters and the 2n multipliers.
(1) a first in-phase path provided at the output of the transmission channel of the system and whose structure is that of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inputs of these branches, each of these n branches com-prising, arranged in series:
(a) a mixer;
(b) a lowpass filter;
(c) a multiplier;
the outputs of these n branches being connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit for deciding the symbols ?k to be transmitted from the output of this in-phase path and of the arrangement;
(2) arranged in parallel with this first path, a second quadrature path which also has the structure of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inputs of these branches, each of these n branches likewise comprising, arranged in series:
(d) a mixer;
(e) a lowpass filter;
(f) a multiplier;
the outputs of these n branches being connected to an adder which is followed by a sampling circuit and there-after by a comparator circuit for deciding the symbols ?k to be transmitted from the output of this quadrature path and or the arrangement;
the multipliers of these first and second paths being placed in each branch either at the head, before the corresponding mixers, or at the output of the lowpass filters;
(3) a third control path comprising:
(g) two subtracting circuits for determining the differences e'k and e"k between the signals before decision, Xk and Yk, and after decision, ?k and ?k, in the comparator circuits, expressed for the in-phase path and for the quadrature path by the respective expressions:
e'k = Xk - ?k and e"k = Yk - ?k where X(t) and Y(t) are the output signals of the trans-versal filter of the in-phase path and the quadrature path, respectively, and to is the sampling instant;
(h) a voltage-controlled oscillator producing a signal of the type sin (.omega.ot+?) where .omega.o corresponds to the frequency of the carrier, which oscillator is con-trolled by the signal ?k = e'kYk - e"k Xk (i) at the output of this oscillator, n first parallel-ranged phase shifters whose outputs apply to the respective n second inputs of the mixers in the in-phase path a demodulation signal of the type sin(.omega.ot+Y+Om) where Om is the phase shift for the (m+1)st branch and m varies from O to (n-1);
(j) also at the output of the voltage-controlled oscillator, a .pi./2 phase shifter followed by n second parallel-arranged phase shifters whose outputs apply to the n second inputs of the mixers in the quadra-ture path a demodulation signal of the type cos(.omega.ot + ? + Om);
(k) a control circuit for the voltage-controlled oscillator, the 2n phase shifters and the 2n multipliers.
2. An adaptive equalizer arrangement for digital transmission systems, characterized in that it comprises:
(1) a first in-phase path provided at the output of the transmission channel of the system and whose structure is that of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inputs of these branches, each of these n branches com-prising, arranged in series:
(a) a mixer;
(b) a lowpass filter;
(c) a multiplier;
the outputs of these n branches being connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit for deciding, the symbols ?k to be transmitted from the output of this in-phase path and of the arrangement;
(2) arranged in parallel with this first path, a second quadrature path which also has the structure of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inputs of these branches, each of these n branches likewise comprising, arranged in series:
(d) a mixer;
(e) a lowpass filter;
(f) a multiplier;
the outputs of these n branches being connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit to determine the symbols ?k to be transmitted from the output of this quadrature path and of the arrangement;
the multipliers of these first and second paths being placed in each branch either at the head, before the cor-responding multiplying circuits, or at the outputs of the lowpass filters;
(3) a third control path comprising:
(g) two subtracting circuits for deter-mining the differences e'k and e"k between the signals before decision, Xk and Yk, and after decision, âk and ?k, in the comparator circuits, expressed for the in-phase path and for the quadrature path by the respective expres-sions:
e'k = Xk - ?k and e"k = Yk - ?k where X(t) and Y(t) are the output signals of the trans-versal filter of the in-phase path and the quadrature path, respectively, and to is the sampling instant;
(h) n voltage-controlled oscillators whose outputs apply directly to the respective n second inputs of the mixers in the in-phase path a demodulation signal of the type sin (.omega.ot + ? + Om) where .omega.o corresponds to the frequency of the carrier, Om is the phase shift for the (m+1)st branch and n varies from o to (n-1), and apply by-means of a .pi./2 phase shifter a demodulation signal of the type cos(.omega.ot + ? + Om) to the respective n second inputs of the mixers of the quadrature path.
(i) a control circuit for the n voltage-controlled oscillators and the 2n multipliers.
(1) a first in-phase path provided at the output of the transmission channel of the system and whose structure is that of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inputs of these branches, each of these n branches com-prising, arranged in series:
(a) a mixer;
(b) a lowpass filter;
(c) a multiplier;
the outputs of these n branches being connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit for deciding, the symbols ?k to be transmitted from the output of this in-phase path and of the arrangement;
(2) arranged in parallel with this first path, a second quadrature path which also has the structure of a non-recursive transversal filter having n branches and (n-1) delay circuits between the n inputs of these branches, each of these n branches likewise comprising, arranged in series:
(d) a mixer;
(e) a lowpass filter;
(f) a multiplier;
the outputs of these n branches being connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit to determine the symbols ?k to be transmitted from the output of this quadrature path and of the arrangement;
the multipliers of these first and second paths being placed in each branch either at the head, before the cor-responding multiplying circuits, or at the outputs of the lowpass filters;
(3) a third control path comprising:
(g) two subtracting circuits for deter-mining the differences e'k and e"k between the signals before decision, Xk and Yk, and after decision, âk and ?k, in the comparator circuits, expressed for the in-phase path and for the quadrature path by the respective expres-sions:
e'k = Xk - ?k and e"k = Yk - ?k where X(t) and Y(t) are the output signals of the trans-versal filter of the in-phase path and the quadrature path, respectively, and to is the sampling instant;
(h) n voltage-controlled oscillators whose outputs apply directly to the respective n second inputs of the mixers in the in-phase path a demodulation signal of the type sin (.omega.ot + ? + Om) where .omega.o corresponds to the frequency of the carrier, Om is the phase shift for the (m+1)st branch and n varies from o to (n-1), and apply by-means of a .pi./2 phase shifter a demodulation signal of the type cos(.omega.ot + ? + Om) to the respective n second inputs of the mixers of the quadrature path.
(i) a control circuit for the n voltage-controlled oscillators and the 2n multipliers.
3. An arrangement as claimed in Claim 1, charac-terized in that the control circuit comprises:
(a) two multipliers, a subtractor and a loop filter to supply the control signal .epsilon.k for the voltage-controlled oscillator, defined by:
.epsilon.k = e'kYk - e"kXk;
(b) two multipliers, a subtractor, a multi-plier, a subtractor and a delay circuit to supply the control signal O?+1 for the 2n phase shifters in the n branches defined by:
O?+1= O? - .beta.(Y? e'k-X?e"k) where .beta. is a positive constant with .beta.<1;
(c) two multipliers, an adder, a multiplier, a subtractor and a delay circuit to supply the control signal rmk+1 for the 2n multipliers in the n branches de-fined by:
r?+1 = r? - ?(p?e'k+q?e"k), where ? is a positive constant with ? < 1.
(a) two multipliers, a subtractor and a loop filter to supply the control signal .epsilon.k for the voltage-controlled oscillator, defined by:
.epsilon.k = e'kYk - e"kXk;
(b) two multipliers, a subtractor, a multi-plier, a subtractor and a delay circuit to supply the control signal O?+1 for the 2n phase shifters in the n branches defined by:
O?+1= O? - .beta.(Y? e'k-X?e"k) where .beta. is a positive constant with .beta.<1;
(c) two multipliers, an adder, a multiplier, a subtractor and a delay circuit to supply the control signal rmk+1 for the 2n multipliers in the n branches de-fined by:
r?+1 = r? - ?(p?e'k+q?e"k), where ? is a positive constant with ? < 1.
4. An arrangement as claimed in Claim 2, charac-terized in that the control circuit comprises:
(a) two multipliers, a subtractor, a multi-plier, a subtractor and a delay circuit to supply the con-trol signal ?+1 for the n oscillators defined by:
?+1= ?-.beta. (Y? e'k - X? e"k), where .beta. is a positive constant with .beta. < 1;
(b) two multipliers, and adder, a multiplier, a subtractor and a delay circuit to supply the control signal r?+1 for the 2n multipliers of the n branches defined by r?+1 = r? -?(p?e'k+q?e"k), where ? is a positive constant with ? < 1.
(a) two multipliers, a subtractor, a multi-plier, a subtractor and a delay circuit to supply the con-trol signal ?+1 for the n oscillators defined by:
?+1= ?-.beta. (Y? e'k - X? e"k), where .beta. is a positive constant with .beta. < 1;
(b) two multipliers, and adder, a multiplier, a subtractor and a delay circuit to supply the control signal r?+1 for the 2n multipliers of the n branches defined by r?+1 = r? -?(p?e'k+q?e"k), where ? is a positive constant with ? < 1.
5. An arrangement as claimed in one of the Claims 3 and 4, characterized in that the multipliers of the con-trol circuit are preceded by a same number of zero-comparators.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8307910A FR2546008B1 (en) | 1983-05-11 | 1983-05-11 | JOINT ADAPTIVE EQUALIZATION AND DEMODULATION CIRCUIT |
| FR8307910 | 1983-05-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1211515A true CA1211515A (en) | 1986-09-16 |
Family
ID=9288812
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000454069A Expired CA1211515A (en) | 1983-05-11 | 1984-05-10 | Combined adaptive equalization and demodulation circuit |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US4594725A (en) |
| EP (1) | EP0125722B1 (en) |
| JP (1) | JPS59211337A (en) |
| AU (1) | AU563907B2 (en) |
| CA (1) | CA1211515A (en) |
| DE (1) | DE3461977D1 (en) |
| FI (1) | FI76655C (en) |
| FR (1) | FR2546008B1 (en) |
| NO (1) | NO163929C (en) |
Families Citing this family (38)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8406846D0 (en) * | 1984-03-16 | 1984-04-18 | British Telecomm | Digital filters |
| GB2181008B (en) * | 1985-09-25 | 1989-09-20 | Sony Corp | Infinite impulse response filters |
| US4716577A (en) * | 1986-07-07 | 1987-12-29 | Rockwell International Corporation | Autoequalizer |
| FR2627032A1 (en) * | 1988-02-09 | 1989-08-11 | Alcatel Thomson Faisceaux | TRANSVERSE FILTER |
| US4989170A (en) * | 1988-06-09 | 1991-01-29 | National Semiconductor Corporation | Hybrid stochastic gradient for convergence of adaptive filter |
| JPH065822B2 (en) * | 1989-01-19 | 1994-01-19 | 日本電気株式会社 | Parallel processing transversal equalizer |
| SE462942B (en) * | 1989-01-26 | 1990-09-17 | Ericsson Telefon Ab L M | SETTING AND DEVICE FOR FAST SPEED CONTROL OF A COHERENT RADIO RECEIVER |
| SE462943B (en) * | 1989-01-26 | 1990-09-17 | Ericsson Telefon Ab L M | SETTING AND DEVICE FOR FREQUENCY CONTROL OF A COHERENT RADIO RECEIVER |
| FR2644638B1 (en) * | 1989-03-14 | 1991-05-31 | Labo Electronique Physique | |
| US4947408A (en) * | 1989-05-12 | 1990-08-07 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Digital carrier demodulator employing components working beyond normal limits |
| US5067140A (en) * | 1989-08-16 | 1991-11-19 | Titan Linkabit Corporation | Conversion of analog signal into i and q digital signals with enhanced image rejection |
| GB2282030B (en) * | 1993-09-14 | 1997-09-24 | Plessey Semiconductors Ltd | Direct conversion receiver |
| CN1082301C (en) * | 1994-09-10 | 2002-04-03 | 三星电子株式会社 | Digital radio transmission-reception apparatus |
| ES2101639B1 (en) * | 1994-10-21 | 1998-03-01 | Alcatel Standard Electrica | ADAPTIVE EQUALIZER. |
| US7639759B2 (en) * | 2001-04-27 | 2009-12-29 | The Directv Group, Inc. | Carrier to noise ratio estimations from a received signal |
| US7822154B2 (en) * | 2001-04-27 | 2010-10-26 | The Directv Group, Inc. | Signal, interference and noise power measurement |
| US7471735B2 (en) * | 2001-04-27 | 2008-12-30 | The Directv Group, Inc. | Maximizing power and spectral efficiencies for layered and conventional modulations |
| US8005035B2 (en) * | 2001-04-27 | 2011-08-23 | The Directv Group, Inc. | Online output multiplexer filter measurement |
| US7173981B1 (en) | 2001-04-27 | 2007-02-06 | The Directv Group, Inc. | Dual layer signal processing in a layered modulation digital signal system |
| US7245671B1 (en) * | 2001-04-27 | 2007-07-17 | The Directv Group, Inc. | Preprocessing signal layers in a layered modulation digital signal system to use legacy receivers |
| US7423987B2 (en) * | 2001-04-27 | 2008-09-09 | The Directv Group, Inc. | Feeder link configurations to support layered modulation for digital signals |
| US7209524B2 (en) | 2001-04-27 | 2007-04-24 | The Directv Group, Inc. | Layered modulation for digital signals |
| US7483505B2 (en) * | 2001-04-27 | 2009-01-27 | The Directv Group, Inc. | Unblind equalizer architecture for digital communication systems |
| US7502430B2 (en) * | 2001-04-27 | 2009-03-10 | The Directv Group, Inc. | Coherent averaging for measuring traveling wave tube amplifier nonlinearity |
| US7184473B2 (en) * | 2001-04-27 | 2007-02-27 | The Directv Group, Inc. | Equalizers for layered modulated and other signals |
| US7184489B2 (en) * | 2001-04-27 | 2007-02-27 | The Directv Group, Inc. | Optimization technique for layered modulation |
| US7151807B2 (en) * | 2001-04-27 | 2006-12-19 | The Directv Group, Inc. | Fast acquisition of timing and carrier frequency from received signal |
| US7583728B2 (en) * | 2002-10-25 | 2009-09-01 | The Directv Group, Inc. | Equalizers for layered modulated and other signals |
| AU2003280499A1 (en) * | 2002-07-01 | 2004-01-19 | The Directv Group, Inc. | Improving hierarchical 8psk performance |
| ES2604453T3 (en) * | 2002-07-03 | 2017-03-07 | The Directv Group, Inc. | Method and apparatus for layered modulation |
| US7230480B2 (en) * | 2002-10-25 | 2007-06-12 | The Directv Group, Inc. | Estimating the operating point on a non-linear traveling wave tube amplifier |
| US7529312B2 (en) * | 2002-10-25 | 2009-05-05 | The Directv Group, Inc. | Layered modulation for terrestrial ATSC applications |
| CA2503530C (en) | 2002-10-25 | 2009-12-22 | The Directv Group, Inc. | Lower complexity layered modulation signal processor |
| US7474710B2 (en) * | 2002-10-25 | 2009-01-06 | The Directv Group, Inc. | Amplitude and phase matching for layered modulation reception |
| US7463676B2 (en) * | 2002-10-25 | 2008-12-09 | The Directv Group, Inc. | On-line phase noise measurement for layered modulation |
| AU2003282854A1 (en) * | 2002-10-25 | 2004-05-25 | The Directv Group, Inc. | Method and apparatus for tailoring carrier power requirements according to availability in layered modulation systems |
| US7502429B2 (en) * | 2003-10-10 | 2009-03-10 | The Directv Group, Inc. | Equalization for traveling wave tube amplifier nonlinearity measurements |
| US9148162B2 (en) * | 2014-01-15 | 2015-09-29 | Guzik Technical Enterprises | Digital down converter with equalization |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2167441B1 (en) * | 1972-01-10 | 1977-07-15 | Ibm France | |
| FR2216715B1 (en) * | 1973-01-31 | 1976-06-11 | Ibm France | |
| US4475211A (en) * | 1982-09-13 | 1984-10-02 | Communications Satellite Corporation | Digitally controlled transversal equalizer |
-
1983
- 1983-05-11 FR FR8307910A patent/FR2546008B1/en not_active Expired
-
1984
- 1984-05-08 DE DE8484200647T patent/DE3461977D1/en not_active Expired
- 1984-05-08 EP EP84200647A patent/EP0125722B1/en not_active Expired
- 1984-05-08 NO NO841836A patent/NO163929C/en unknown
- 1984-05-08 FI FI841834A patent/FI76655C/en not_active IP Right Cessation
- 1984-05-10 AU AU27878/84A patent/AU563907B2/en not_active Ceased
- 1984-05-10 CA CA000454069A patent/CA1211515A/en not_active Expired
- 1984-05-11 JP JP59094397A patent/JPS59211337A/en active Granted
- 1984-06-28 US US06/608,060 patent/US4594725A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| FR2546008A1 (en) | 1984-11-16 |
| FI76655C (en) | 1988-11-10 |
| JPS59211337A (en) | 1984-11-30 |
| AU2787884A (en) | 1984-11-15 |
| AU563907B2 (en) | 1987-07-23 |
| FI76655B (en) | 1988-07-29 |
| FI841834A (en) | 1984-11-12 |
| NO841836L (en) | 1984-11-12 |
| NO163929C (en) | 1990-08-08 |
| EP0125722A1 (en) | 1984-11-21 |
| EP0125722B1 (en) | 1987-01-07 |
| NO163929B (en) | 1990-04-30 |
| US4594725A (en) | 1986-06-10 |
| DE3461977D1 (en) | 1987-02-12 |
| FI841834A0 (en) | 1984-05-08 |
| JPH0342735B2 (en) | 1991-06-28 |
| FR2546008B1 (en) | 1985-07-12 |
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