CA2109211A1

CA2109211A1 - Process and arrangement for the differential modulation of signals in a multi-channel transmission system

Info

Publication number: CA2109211A1
Application number: CA002109211A
Authority: CA
Inventors: Andreas Muller
Original assignee: Individual
Current assignee: Daimler Benz AG
Priority date: 1991-05-02
Filing date: 1992-04-14
Publication date: 1992-11-03
Also published as: EP0589895A1; DE4114274A1; AU1643092A; JPH06507053A; WO1992020179A1; FI934830A; FI934830A0; AU652052B2

Abstract

The invention relates to a digital modulation process and an arrangement for a multi-channel transmission system in which the data flow is distributed over a plurality of sub-carriers lying close together in the frequency range. Neighbouring sub-carriers are interlinked in such a way that the data on two adjacent sub-carriers are transmitted in phase difference. If such a frequency-differential modulation is coupled to a prior art differential modulation in which data symbols on a sub-carrier following one another in time are transmitted in phase difference, a markedly better transmission quality is obtained in the signals in the radio channels.

Description

OCT 13 '~3 1~3:40 SPENCEæ,F~NK~CCHNEI~E~W~aH~ P.3.~1?
? ~109211 FILE, ~ McNDED
T-~T TRANSLATION

~0 ~2/20179 PCT/~1~9~/008~1 'e~ ~

D a~D ;~ANGE~ ~OR ~HE D~ u~N~rTA~ ~4I~UI~OM
oY ~ a~EL ~R~D8~I8~ Y8~

'rhe inv~n~ion x~ia~ to a digit;~ odulation me~ho~ and ar! arr~rlgç~e~}t ~or a ~nulti-~h~nnel tran~ is~io~ syste~
Whic~ d~a s~rea~ i~ d~t~cibut~d to a plurality o~
c:arriers ~at l~e~ adjac~nt tu one another in th~3 fr~uer~c:y ~m~in4 o m~ in ratltio~ i~ us~d, among ot:h~;rs, i~ th2 ~O~DM t~:tsda~
ort~sgç~nal ~r~ cy div~ n mult~pl~xin~ ~eth~d e~ployed in dis~i al radioO
~n ~ mul~l-chan~ aodula~ on ~et~ or digi1:a~ da~a ~an~is~ion, the data s~rea~ to be tra~s~nitted i~
di~ribut~d to a nu~er o~ sub-c:arEier~ ~or exampl~, sev~al .

hm~r~d1,, ~hich are 21dj~oe~ ~o one ano~:her in ~h~ f~eg~l3ncy do31~in, with ~h~ ~pe~:tra of t~a~ sub-carr~ ~rs po~3~3ib~ o ~erlappin~ Wit~ thi& ~ann~r of proceeding, ~ data rat~
tr~ itted in ~ach sub-carrier which i lower ~y order~; o~

2 0 mag~aitud~ ~han th~ origlnal d~ rate so that th~ 83~01 OCT 13 'g:~ 10:4; SPENCET;~,FRf~NK&SC~ E'~ SH~, 2109211 P.4~17 ~.,~ ,., ~) 92~20~7~1 PCTJEP92/0084l , ~
duration is corr~pondir~gly lengthened~ ~hi~ h~ ~n `.! advant~ge30u~ eff2~ if e¢hoQs app~ar i~ the trans~ls~ion channel. ~y suitably ~ixing th~ nuT~ber c2 sub-c~arriers, a ..
lt~-~hannc~l modula~ion ~ethod ~an ~lways be de~ d so that t~ bol cluration 1~ long ~ompared tca the m~xim.lm ~cho delay ~ime o ~e expe~ted~
The ~ nf luena~ c~ e~hoe~ can be completely el ila~nated, ~or e~ple, in that the syml~ols are no~ nfi~itted in i~nedia ~ ~ucc~88loll but; I;ha~ ~ prol:ection period is jpravid~d 10 be~ween every ~o suc:c~ sive sy~ol~ which the echo~s of t~e ~ir~'c tr~mi~ted sym~ol die ou~.
m~ en~ine~ring c~f ~ ~aulki-~h~nnel ~o~ulation method ~3~ imol~a~ a aon~iguratlon, for ~xample, ~s a d~gital ~et~c~d, rhaps a~; a pr~gr~ in at l~ast one mic:roproce~sor with . lS: whlch the ~ra~it ~ n~ calc:ulated at ~e trans~i~ting ;:$ n~l in tha c~aplex base ban~ or at an in~rmediate freg~len~
thcd~ known ~ro~ the a~alcg technol~ hi$ tran~DIif ~ :
ig~al ~:z~ 'chen b~ put into thB carrier ~re~ncy po~ition.
.
o~rQs~orld~gly~ na~l is initially receive~ ~y t~e r6ac~iver in an ~ g ~ode, is then converted down to the a~ band or ~o ~n iI~termedia~e ~re~uency and is then : proc~d f~rther in a digital mod~.

~y ,i, ,, !

OCT 13 '93 10:41 ~ENOER,FRflNK&SCHrK IDEP/WF`JSHo P.5/17 . . .
t, 2 ~ O ~ 2 1 `" 110 ~2~2~ PC~ 2~00~
, ,j' The ~ulti-~hannel modulation signal is ~ompo~ed o~ time-~requency ~lot~ The time ~o~ are formed ~y ~e di~crete ~y~bol clo~k, the ixe~uen~y ~lot~ by the sub-aarrier ~ reguency ~pacing. rf m~a~ures ar~ taXen to c:ombat echc~23, s ~or xa~ple, the abov~-mentioned protection p~riod, the $n~1uQncQ o~ the radio ahannel in each time-~e~u~ncy ~o~ is mani~est ~n attenuation and a ph~e ~hift. A~tenuation and ph~ hi~t ar~ gener~lly ~ariable in tima ~nd fr~qu~ncy.
~;. Pre~ bly the known phase ~o~ula~ion is employed as ~he 0 ~odulatlon method::for a ~ub-carrie~ of the multi~ahannel signal. To this er~ he Y~riou5 data ~bols are ~epraduced on different phase sh~pes ~of ~he~ ~ans~it signal~ For . . .
da3l~0dulat~csn, ~h~ chann~ peci~io phase shi~t then acts as ~ an in~er~ere~ce value whl~h ~ust be a~pensat~ by mean~ of ,~ 15 su~able ~easures~ :
: Known methods are the di~erential de~odula~ion ~nd the iff~rential pr~coding. In ~he~e method, tho data are not trarumitt~d in t;:he p~as~ o~ a sym1~ol b~t in the phase ;., ai~re~enc~ o~ tvo ~u~ iYe æy~ol~. In a multi-ch~
'; 20 method, dif~erential de~odul~tion and precoding are pe~fo~med '~ s~p~rately in each ~ub-caxrier.
'`,J ~ ~ .

~1 .

~l -- 3 --~'1 ! i .~
~.i 2 1 ~ ~ 2 ~ ~ 23930 341 . ~ .
~ Differential precoding takes place in the transmitter ; (Figure la) and differential demodulation takes place in the receiver (Figure lb).
The multiplication of complex numbers corresponds to an addition of their phases, the formation of the conjugate complex number corresponds to the inversion of the sign of the phase.
The letter "D" in Figures la and lb identifies a delay by one symbol; the * symbol identifies the conjugate complex component.
Differential demodulation and precoding are based on the assumption that the channel specific phase shift does not change from one symbol to the next. In time variable radio channels, however, this assumption is frequently not met, particularly if multi-channel methods are involved with their .. , relatively long symbol duration. Transmission errors occur here even in the noise-free state.
~:
~ ; The principle that is a duplicate of time differential s~ modulation is frequency differential modulation. The frequency differential modulation is based on the assumptio~ that the channel specific phase shift from-one sub-carrier to the next does not change.~ The time differential modulation and the :
~ frequency differential modulation are described in "Philips .. . .
~esearch ~eports + SuppIements", No. 4, pages 91098 ~1973).
~` It is therefore the object of the invention to provide a modulation method and an arrangement for a multi-channel transmission system with which the transmission quality of the signals of unsteady radio channels is improved.

1:~
~1 2 1 0~211 23930-341 .~i This is accomplished by the characterizing features of patent claims 1 and 2. A further embodiment is de~ined in claim 3.
. ,, ,f~ .

; ,i, _ S

.,.ji .

. . ,~ .

, "
.
., ,;

: ,~

. ~, ~ ` .

;' !
';i .` .
, .'.1 i~
` i ':
~: .
'.` ~

, ~:' ,. .
f ~, .

~.~

~ - 4a -i OCT 1~ ~g3 10:42 SPENCER,FI~PNK~SCHr~IrlER,'Il~SH~ D, ,~17 ` -- 21092~1 1~0 9ZJ20179 PC~EP~OO~1 ~ odi~ents of the invention will now be described with re~erenc~ to 3chematic drawing ~i~ureC.
Figure 2 ~how~ co~pon~nts o~ an ~ml30dimen'c of an .~, arrange~ent at th~ transmitting end ~d an arr~ngement at the

3 5 r-c~iving ~nd, ~ach ha~ing several ~ carrier~i ..., k-l, k, l~tl, . . ~, inluding a mllltip~ ier at both the transmi~t~ng end and the ~eaeivin~ ~nd ~or linkirlg the d~ta af r~specti~e adjacent uib-aarrler~. ~n ~he tran~ ter, fo~ examp~e~ the ~u}tlplied data of #Ub-¢arrier~ k-l and k are ~ed to the ~10 ~ultiplier of sub~ arrier k+l and are multipl~ed with the ,j data or ~ carrier k~ t the rece~ving end, ~his ~ignal o~ ~ub-carr~e~ k~l is ~ultlplied with ~e aon~ug~te complex s~gnal o~ sub-carrier k.: This m~thod is a~lled fxequenay di~erenti~ odulation.
~ ~ Th~ ~hod r-al~;z~d~ with this arrange~ent Ls ~ased on the a~ou~ption ~hat the ~hannel ~peci~ic pba~e s~i~t does not ahAnge ~rom one au~-c~rier to the next. This a~aumption is imilar to th~ in the~known differential ~odul~tion, except ; that freguency inv~riance has taken th~ place o~ ~i~e ~2Q invarianc~. Howe~r r, particularly in multi-chanrt,el mo~ulatiorl m~thods, th~ ~:a~ts,r is fr~ntly mor~ likely ~o sxis~ ir~e the long ~;y~c~l du~tion corre~posld~; ~o fregu~ncy ~pacing ~n the ~ carrier~.

: ~ :
.

~T 13 '~3 10:42 SPEI~CER~F~NK~SCHNEIl:;ER~ lSH~, P.8~17 ,,.~.
.i. .
,.,~
~0 g2/20~.7S ~ EP~/008 i, In a ~u~t~er e~odiment according to Fig~lre 3, an a~range~nt ia 6hown at ~e ~rans~itter and rec:eiver ~n which éimely ;uaae~ e data ~ ; af a ~ a~rier a~; well a~
, dat~ ~ro~ ad~ac~nt ~ub-~arrier~ are linked t~gether. For 5 exa~ple, in sub~ a~er k~1 o~ ~e transmit~er, d~ta tha~ ~re transmit~ed in ~h~ pha~e di~rence o~ two su~c~e~siv~ d~ta ~;~bols are fed to a multiplier together with ~he multiplied da~ of sub-carriers k-l and k. In the receiver, t;his ~ultiplied complex~ signal of sub-carrier k+l i~ ltiplied 3 wîth t~e aon~ugat~ ~o~aplex s~gnal of ~ arrie~ ~. Together ;
h ~e a~n~ug~te o~plex ti~e-delayed ~ignal, ~hi~
i~z ~ultlpl~ed sl~n~l :ls ~h~n fed ~o a fu~hcr ~ul~lplie~. In ~: the ~tran~QLtter, ~he signa~ of the 3ub-~arriers are inltially di~f-ren~ially and :th2n ~requ~nc:y differentially 15 ~ pre~:oded wi~h ~his: doù~le differential modulation and are `'41` ~ ~
th-n de311odula~d ~n;~he~r ceiver, ~irst differentially and h~n f~quenc:y d~er~ntially. The dou~le di~erential :
~odul~tlon ~y al~so be per or~ned at t~e tran~itter a~d ~t ',3~ . ~ t;he rea~r ~ir~t by a frequenc:y differential ~od~lation and 20 ~h~n ~y a dif~eren~lal ~odulati~n., Compar~ld to th~ conventiona~ difr~r~ntial m~dul~t~ n and also comp~red to the fre~uon y diff~tr~n~ial ~o~ulat~on, th~
double di~ferential l~odulation o~er~ the de~isive advantage ~::

CICT 13 '93 10 43 SPENOE2~FRfWK~iSCH~EID~R~ Ho P.9~.7 ~t ,~ , ..
~ ' 2109211 1~0 9~ 0~1,7g ~ EPg:!~OOt~l li that it neithe~ re~uires the as~u:mption o~ ~ ti~e in~r~rianaenor of a ~reque~y ~nvarianae o~ ~e channel ~pecific: ph~e -, ~ift but app~ox~tes ~he ahannel our~e ~h~pe over ti~e and ~re~u~ncy by way o~ a~ plane~ In radio channel~, thi~
5 approxi~ation i~ clearly better than Em approxim~tion by way ;, o~ a pha~- curv~ tha~t i~ cons~ant ov~r tim~ and fr~ ncy, i, respectively.
,~ "

'6 ',' 1, ;iS ~ ' ~' ::
:
: : :

, :
j!

~1 .~ ~

i ::
't, ~;; ' ~ ' ~1 ~ - 7 -!:
~ : .
.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A multi-channel modulation method wherein the data stream is distributed to a plurality of sub-carriers which are adjacent to one another in the frequency domain, characterized in that the data are transmitted in the phase difference of adjacent sub-carriers and in the phase difference of timely successive data symbols in the respective sub-carrier.

2. A receiver and transmitter arrangement for a multi-channel modulation method according to claim 1, characterized in that at the receiving end and at the transmitting end each sub-carrier includes a multiplier which links the data of two timely successive data symbols in the respective sub-carrier and a further multiplier links the data of adjacent sub-carriers.

3. A receiver-and transmitter arrangement for a multi-channel modulation method according to claim 1, characterized in that at the receiving end and at the transmitting end each sub-carrier includes a multiplier which links the data of adjacent sub-carriers and a further multiplier links the data of two timely successive data symbols in the respective sub-carrier.

4. A receiver and transmitter arrangement for a multi-channel modulation method according to claim 2, characterized in that at the receiving end and at the transmitting end each sub-carrier includes a multiplier which links the data of two timely successive data symbols in the respective sub-carrier and said multiplier is followed by a further multiplier which links the data of adjacent sub-carriers.

5. A receiver and transmitter arrangement for a multi-channel modulation method according to claim 2, characterized in that at the receiving end and at the transmitting end each sub-carrier includes a multiplier which links the data of adjacent sub-carriers and said multiplier is followed by a further multiplier which links the data of two timely successive data symbols in the respective sub-carrier.