l|||||llllllllIllIlllllllll||||l|||||llllllllllllllllllllllllllllllllllllll
`
`USOO5168509A
`[I1] Patent Number:
`[45] Date of Patent:
`
`5,168,509
`Dec. 1, 1992
`
`Radio System With 64 QAM Modulation”, T. Noguchi,
`et al., 1983.
`Proceedings of International Conference on Communi
`cations, pp. 1482-1486 (46.7), “6GHZ 14OMBPS Digi
`tal Radio Repeater With 256QAM Modulation", Y.
`Yoshida, et al., 1986.
`Lin, et al., Error Control Coding Fundamentals and Ap
`plications Prentice-Hall, Inc., N.J., 1983, pp. 34-39,
`85293,.141-151, and 170-177.
`Primary Examiner-—Curtis Kuntz
`Assistant Examiner-T. Ghebretinsae
`Attorney, Agent, or Firm—Foley & Lardner
`[57]
`ABSTRACT
`In a multi-level QAM communication system, Reed
`Solomon encoders and Reed-Solomon decoders are
`employed foi error correction purposes. The phase
`ambiguity of the received signal is eliminated with dif
`ferential coding. The multi-level QAM communication
`system utilizing n bits (“n" being an integer) QAM
`signal having 2" signal points, comprises: a quadrature
`differential encoder/decoder unit for differentially en
`coding/decoding n pieces of input digital signal series
`to produce 11 pieces of differentially coded signal series;
`an error correction unit including a Reed-Solomon
`encoder and a Reed~Solomon decoder, provided inside
`the quadrature differential encoder/decoder unit along
`a signal processing path of the input digital signal series,
`for error-correcting the n pieces of differentially-coded
`signal series by utilizing at least one of the digital signal
`series with employment of a Reed-Solomon code; and,
`a QAM modulator/demodulator unit for QAM
`modulating/demodulating n pieces of error-corrected
`signal series so as to produce 2" QAM signals.
`
`16 Claims, 14 Drawing Sheets
`
`1 00
`
`{15
`
`[17-1
`18-1
`(16-1
`QUADRATURE
`[p
`DIFFERENTIAL
`DECODER
`17 18-2
`z
`-2 B
`0
`w
`gltlizFApgéaNrTqgf
`-- 5
`a,
`__
`DECODER
`gm
`2% 17-3 ouADRAruRE
`1253 §
`w 3
`_ DlFFERENTlAL
`II
`E B
`JtLUD R
`18*; E
`o
`R _l 9 5
`UADRATU E
`DIFFERENTIAL
`18 _5 E
`DECODER
`\
`—o> o
`I74
`l8 -6
`4
`18 -7
`l8 -s
`/
`
`United ‘States Patent [19]
`Nakamura et a1.
`
`[54] QUADRATURE AMPLITUDE
`MODULATION COMMUNICATION
`SYSTEM WITH TRANSPARENT ERROR
`CORRECTION
`[75] Inventors: Makoto Nakamura, Kanagawa;
`Tomoko Kodama, Yokohama, both of
`Japan
`Kabushiki Kaisha Toshiba, Kawasaki,
`Japan
`.
`[21] Appl. No.: 507,303
`[22] Filed:
`Apr. 10, 1990
`[30]
`Foreign Application Priority Data
`Apr. 12. 1989 [JP]
`Japan .................................. .. 1-90623
`Apr. 28. 1989 [JP]
`Japan ................................ .. 1-111622
`
`[73] Assignee:
`
`[51] Int. Cl.5 ................................. .. H04L 05/12
`
`[52] US. Cl. . . . . . . . . . . . . . . . . . .
`
`. . . . .. 375/39; 371/375
`
`[58] Field of Search ..................... .. 375/39, 27, 42, 27,
`375/39, 42; 371/371, 37.5, 43
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`4,553,237 11/1985 Nakamura ........................... .. 375/39
`
`FOREIGN PATENT DOCUMENTS
`
`0111349 9/1981 Japan ................................ .. 371/375
`0219252 9/1988 Japan .... ..
`375/39
`
`OTHER PUBLICATIONS
`IEEE Transactions on Communication Technology,
`vol. COM-19, No. 5, pp. 8212-8835, “A High-Speed
`Sequential Decoder: Prototype Design and Test", G.
`D. Forney, et al.. Oct. 1971.
`Proceedings of International Conference on Communi
`cations, pp. 1472-1477 (F24). “oGl-lz 135MBPS Digital
`
`[12-1
`QUADRATURE
`DIFFERENTIAL
`
`r13.1
`
`(14
`
`m
`5
`E
`m
`E
`5
`n-
`E
`
`z
`QUADRATURE
`DIFFERENTIAL 12-; g
`g“
`"’ 3
`5 o
`a g
`I: w
`13-:
`’
`
`8%??343725
`ENCODER
`_|
`
`88§€§€~R1EE
`ENcooER
`
`114 \I2
`'‘
`
`-
`
`z
`— g
`o
`a‘ IF
`w a
`Q 8
`3:’ E
`.
`
`a:
`8
`5
`‘t
`D
`8
`__._.
`8
`g CHANNEL
`2 0 l9 - 5 2
`z
`g o
`g g
`E
`F 0 ~
`5
`._ 2,, _
`o u,
`3 g
`'T" LLI O
`_ 3:’ E
`
`\l 6 ~2
`
`1
`
`Petitioner Samsung - SAM1021
`
`

`
`US. Patent
`
`Dec. 1, 1992
`
`Sheet 1 of 14
`
`5,168,509
`
`PRIOR ART
`FIG.1
`(GRAY MAPPING)
`Q
`[1001
`
`[191
`
`[go]
`
`(01)
`[1?]
`[1°11
`
`(0.0)
`
`[1°11
`[1011
`
`[1%]
`
`[1°01
`
`[0"11
`[g1]
`
`[60]
`
`[091
`(11)
`[0?]
`[Q3]
`(10)
`[60]
`
`l
`
`(m1)
`mp2]
`
`PRIOR ART
`FIG.2
`(QUADRANT SYMMETRY MAPPING)
`Q
`[100]
`
`[0011
`
`[go]
`(01)
`
`[091
`(11)
`[0?]
`[1001
`(10)
`
`l
`
`(um
`[12.02]
`
`[1"01
`[9:11
`
`[1?]
`[1011
`
`[1°11
`[1;]
`
`(00>
`
`O
`
`[00]
`
`O
`
`[1o]
`
`O
`
`[01]
`
`[6o]
`
`2
`
`

`
`U.S. Patent
`
`Dec. 1, 1992
`
`Sheet 2 of 14
`
`5,168,509
`
`S'lVN|WH3.L .LndJ.flO
`
`Wmmmaooma
`._<:zmmmE_o
`
`mE_.:<ma<:o
`
`Eooomo
`
`J:_.t
`
`mm:»<mo<:o
`
`._<:zmmm&_o
`
`Eooomo
`
`7mEooomo
`._<:zmmm_u_u__oE—mm_.fi<mo<:c
`o._<:.zmmmu:_o
`m_m2.<mo<:o
`NOWOTOS-G338I-—— -II
`
`H0.|.V"|flGOlN3Cl
`WVO
`
`._mzz<:o
`
`8
`
`uonnnaow
`
`WVO
`
`.
`
`HBOOONB
`NOWOTOS-0338
`
`HEGOONEI
`NOINOTOS-G338
`
`rnmmnoozmE
`mE:...<ma<:oE._<:zmEm&_oLmE3<mo<:oI
`mm3<mo<:o
`._<Fzmmm&_omu
`
`mmnoozm
`
`._<:.zumm&_o
`
`1_<FzmEm_“_n__o-mm::Eo<:o-mmaoozm
`
`munoozm
`
`.S'lVNl|/\lE:I3l mam
`
`3
`
`
`
`
`
`
`
`

`
`U.S. Patent
`
`Dec. 1, 1992
`
`Sheet 3 of 14
`
`5,168,509
`
`75Tm._<z_s=mFmm
`
`.mmE.<E<:o.11E:
`
`
`Eaoomoqm._<:.zmmm&_oB.m§»<...__o<:o1
`
`Eooomom~.m_._<:.zmE&a._...
`EnoomaMu._<:.zmmmu_n__o
`mE:»<mo<:omw-11
`
`._l2:m.12:u-2:W—1....E.Md_mmooomo‘..<FzmEm&_o
`mE:»<mo<:oIas
`
`1....Mm.
`
`.5..._._.:O
`
`aw
`
`R
`
`..%_ldSd5_.—mEv...1.w.0E.w.M1%mmmo3m.11aN_.O-l.—VHI:3LIMom.mo080onG.1.1..0EH11mmF..1J.2..W...11
`_-m_-8$_-mm72_-_Pmmomm._<z_s=..m:
`.av.1.mmww.E.v.1.MMn.oMMMWummaoozmo1waWaow._<_Emmm&amEm1EVmHmm3<E<:o_.WW11WWWo00mmooozmmN.1EvuvE.wMmE._<:2mEn_u__om1m1mm:.r<mo<:o
`U...ad47H1a.70EMmw.M.5V&4.11.
`..mD...m,m0..EEooozmEMM%wm._<:.zmE&_aN.Z1mm:._.<mo<:o./7up7:
`Hdv.mzz<zow.uatm.5»<ma<:o
`.II._4I.
`1<_1m1__mm%
`
`1.:
`
`to:
`
`5.12.
`
`«.8
`
`~.2w.mm~.Nm~.m_N.om
`
`4
`
`
`
`
`

`
`U.S. Patént
`
`Dec. 1, 1992
`
`Sheet 4 of 14
`
`5,168,509
`
`m A525:
`
`8 m
`
`5.355; 0 5m
`hm m>ZOU
`
`5
`
`

`
`U.S. Patent
`
`C8D
`
`
`
` x9mmooomozos_o._om.n_HE
`
`ed:
`
`J,Nm
`2nfiuflw
`
`
`zo_»<u3mounmwmmmw..,_mn~~mJ225zoflmmmwmomma
`
`
`
`.._<=2OZ>.._On_
`
`.m5W...
`
`41
`
`5,168,509
`
`h8EEm>zooS._m..:<m<n_\
`
`._m.:<m<._
`
`:m+
`
`h
`
`
`
`E._._oEzoozo_5E.mo.\zo:omcmou
`
`
`
`::oc_o><._wn
`
`m_s_omoz>m
`
`moizmzmo
`
`ms_omoz>m
`
`6
`
`
`

`
`US. Patent
`
`Dec. 1, 1992
`
`Sheet 6 of 14
`
`5,168,509
`
`
`
`\ .9" "_\“E c
`
`‘BX
`
`emu
`
`‘mu
`
`
`
`=3 t M...“ ‘w mm o u_\uTO1|$1||1.
`
`1 {mg Wu 1 an “5.0 Av
`
`a8 zam?mw . max *
`
`
`
`.8 :QMHG 0cm lax
`
`z 6? “55A
`
`8%
`/ BX (cm
`
`1.1%
`
`7
`
`

`
`U.S. Patent
`
`Dec. 1, 1992
`
`Sheet 7 of 14
`
`5,168,509
`
`S'|VNlWH3.L mamo
`
`‘P
`""
`
`®1
`
`HEGOOSCI OBS
`
`(ABJEWWAS LNVHOVDU)
`HOJ.V'lflC|0W3C| WVDJQSZ
`
`89.35
`
`
`
`0mm:»<mo<:c._.m—
`
`3::.
`
`._<:zm_E&_n
`
`mmnoomo
`
`ozm
`
`8
`
`(AELLBWWAS LNVHOVDD)
`H0.LV'1fiO0W WVD-992
`
`m
`
`HSCIOONE CH8
`
`5:
`
`ugmmmooozm
`mmooozm
`m=.._:»<mn_<:o
`._<Pzmmm”_u__a
`
`mmnouzm
`
`S'|VNlWH3.L .LfldNl
`
`8
`
`an
`
`\
`
`ad:
`
`mmmm
`
`an
`
`mm
`
`
`
`
`

`
`U.S. Patent
`
`Dec. 1, 1992
`
`Sheet 8 of 14
`
`5,168,509
`
`STVNIWHBJ. mama
`
`‘P
`18-2
`218
`
`«p
`'7
`‘P
`'1"
`Q ooowm
`F‘
`'1
`"— T
`
`18-4
`
` E2’
`DECODERFlDECODER
`
`3:
`"20:
`E223
`9:t‘d°
`:>'-:8
`CD0
`
`56
`
`5
`LO
`
`$
`LO
`
`Haclooacl
`cue
`LOm
`
`uaoooaa
`H.L’v
`
`83003.30
`is
`I
`
`(AULBWWAS mvuovno)
`8OJ.V'1nGOWElC! WVD-QSZ
`
`cHAI~_I_r~_:gzL20
`
`51m
`
`FlG.9
`
`$
`
`51A54
`
`(AELLBWWAS mvuovno)
`uo.Lv'IncIow wvo-992
`
`(D
`07.
`V 0?.
`Lu
`DJ
`D
`0
`0
`O
`92’
`"E3
`flu; mu
`
`3 I 3 I 8 I
`“W
`
`H300 N3
`
`QUADRATUREDIFFERENTIALENCODER
`
`'7
`‘P
`‘P
`T
`‘P
`N
`11-a
`IOv---I--1'''''''‘'''
`.—
`r-'
`1-
`F"
`F‘
`""
`
`STVNIWHSJ. .LndN|
`
`
`
`9
`
`

`
`U.S. Patent
`
`Dec. 1, 1992
`
`Sheet 9 of 14
`
`STVNIINHEJ. .Lfld.LnO
`
`§l
`
`o
`1'—
`I
`(D
`u.
`
`|\
`
`(D
`
`5
`
`uaoooaa
`
`B300 30
`
`8
`i
`gs
`g‘
`0
`
`' (aaoa AVH9)
`uorrlnaow wvo-992
`
`1STENCODER
`
`ENCODER
`
`HSCIOONE
`GUS
`
`HBCIOONEI
`Hi?
`
`HEIGOONB "IVl.LN3H3:J:lIG
`38 FLLVBGVHO
`
`STVNIWHSL .Lf'|dNl
`
`
`
`10
`
`

`
`US. Patent
`
`Dec. 1, 1992
`
`Sheet 10 of 14
`
`5,168,509
`
`wmabéago
`
`mum
`
`m m Y O __H_... i 80 SM 1! O 1
`
`
`
`
`WERUEWW 5&5
`
`w]. E5085 w
`
`~ 2 ._<_Ewmmn_u=o .iimwmmnwnm v:
`“.2 6 @1 8L Wm N NE m1 omL ".2
`8.7 l é K mm K W W” K mm K E m u xx Him w In i ii
`“NI mmazmngc _ / 72 Kt Ni 21 2 942.2: \
`
`m .98 GH 3.7 I! \l” \/ l .78 3H.
`\U 0 O 11 BM Mm l m M Ill
`é N mm 5% w P N L... a
`VW HTWW i WM WW - f
`
`mm;
`
`/
`
`11
`
`

`
`U.S. Patent
`
`Dec. 1, 1992
`
`Sheet 11 of 14
`
`5,168,509
`
`
`
`5.a__.fimmm_m
`
`Eooomo
`
`._<:.zmmm&_o+3Ema
`
`
`
`
`
`
`
`mmnoozu7—._<=zmmm_&_o
`
`uonnnaowaa WVO-#9
`
`m..._E<:a<:o.._mzz$._.mm£:<mn<_..o
`
`
`
`3:z%.mm_.m_m
`
`
`
`m._<z_sEE9<z_s_$»
`
`
`FlIInIanFl2.2«.273«.8mm8<.mwT8ia..~_:
`
`.mE:»<mo<:o mm:.e<:n<:o
`
`
`
`N_..®_..._
`
`.£2“-2
`
`12
`
`HO.I.V'|flClOW WVO-#9
`
`
`

`
`U.S. Patent
`
`Dec. 1, 1992
`
`Sheet 12 of 14
`
`5,168,509
`
`F|G.13
`
`S"|VNlWH3J.
`
`AMB|GU|TY-
`
`ELIMINATED DATA
`
`PHASE-
`
`gr‘:
`E5
`<§%§
`25$:
`oUm<
`
`13
`
`

`
`US. Patent
`
`Dec. 1, 1992
`
`Sheet 13 of 14
`
`5,168,509
`
`PRIOR ART
`F|G.14
`(NATURAL BINARY MAPPING)
`
`O.
`(1.1)
`o
`
`(0.1)
`O
`
`(0.1)
`O
`
`(1.1)
`O
`
`(0.0)
`O
`
`(1 ,0)
`O
`
`(0.0)
`‘O
`
`(1.0)
`O
`
`(161,)
`(P51)
`[0.0]
`(0,0)
`(1 .0)
`O
`O
`
`(161)
`(031)
`[1 ,0]
`(0.0)
`(1 ,0)
`O
`O
`
`|
`
`(11.01)
`
`[|2,Q2]
`
`14
`
`

`
`US. Patent
`
`Dec. 1, 1992
`
`Sheet 14 of 14
`
`5,168,509
`
`PRIoR ART
`FIGJSA NATURAL BINARY MAPPING
`
`HASE
`EFERENCE
`RROR
`
`RECEIVED DATA
`II If" III/2
`Q1 (12-- Qn/z
`x1 x2-— xrI/z
`Y1 y2—- yn/z
`0
`n/Z Y1 Y2"" VII/2
`Y1 352-"- III/2
`11’
`5E1 Y2"- in/z V1 V2" VII/2
`31r/2 VI 72""- 7n/2 x1 x2-- xn/z
`
`PRIOR ART
`FIG.15B
`
`PHASE
`REFERENCE
`ERR 0R
`
`GRAY MAPPING
`
`RECEIVED DATA
`
`yI ya"- Yn/2
`x1 x2-- XII/2
`0
`TI/Z Y1 Y2"- Yn/Z Y1 X2-- XII/2
`1r
`Y1 x2--- Xn/2 yI y2-—- Yn/Z
`31t/2 V1 V2“ Yn/2 X1 X2‘" XII/2
`
`PRIoR ART
`F|G.15C QUADRANT SYMMETRY MAPPING
`
`RECEIVED DATA
`PHASE
`REFERENCE
`II If" ln/z
`Q1 Q2‘" Qn/z
`ERROR
`x1 x2—-- Xn/2 y1 y2-- VII/2
`0
`1r/2 yI x2-- XII/2
`YI y2—- Yn/Z
`11'
`5Z1 xz--- XII/2
`V1 y2—- yn/2
`37t/2 71 X2'''' XII/2
`X1 y2"_ VII/2
`
`15
`
`

`
`1
`
`5,168,509
`
`2
`ambiguity in the reproduced carrier waves can be re
`solved. In general, since a 1 bit error is expanded to a
`continuous 2-bit error, the differential encoding/decod- .
`ing method has the advantage that a circuit arrange
`ment thereof is simple, although the bit error rate in the
`received signal series is increased as compared with that
`of the ?rst-mentioned solution method for judging the
`absolute phase. Moreover, to suppress an increase of a
`bit error rate caused by a differential coding method,
`there is another method in which signal point mapping
`of a QAM signal is quadrant symmetry mapping. In
`accordance with the last-mentioned method, since the
`judgement concerning the upper 2 bits of the input
`digital signals which is determined by the orthogonal
`axes (i.e., I-axis and Q-axis) on the phase plane is ad
`versely in?uenced by the phase ambiguity, the differen
`tial coding operation is required. However, the judge
`ment concerning other bits thereof which is determined
`by the respective amplitude levels of the I-axis and
`Q-axis, is not adversely in?uenced by the phase ambigu
`ity, so that no differential coding operation is required.
`Although the QAM modulation method has the ad
`vantage of higher frequency utilization, there is a draw
`back in that when the number of the bits transmitted
`with l symbol, namely the value of f‘n”, is increased, the
`bit error rate is deteriorated even when the transmission
`power per 1 bit is selected to be equal. Under such a
`circumstance, it is required to improve the bit error rate
`in the multi-level QAM communication system by em
`ploying an error correcting method. On the other hand,
`a QAM modulation system is originally employed so as
`to increase the frequency utilization ef?ciency, and
`accordingly, there is a severe restriction in the available
`frequency band in systems which employ the QAM
`modulation method, such as a digital microwave radio
`communication system. As a consequence, it is expected
`to utilize a higher coding rate having a less redundant
`bit to be added to the input digital signal in the error
`correcting method.
`Furthermore, various limitations are provided in ap
`plying the‘ error correcting method to the QAM com
`munication system with employment of the above
`described differential coding system. First, when the
`error correcting encoder and decoder are provided
`outside the differential encoding/decoding processors,
`since the 1 bit error occurring on the signal transmission
`channel is expanded to the 2-bit error due to the differ
`ential decoding process, the loads required for the error
`correcting encoder and decoder become large. In other
`words, error correction codes having greater correc
`tion capability are required so as to achieve the same
`reliability as that of the other case where the error cor
`recting encoder and decoder are provided inside the
`differential encoding/decoding processors. As a result,
`since the redundant bit number to be added to the input
`digital signal is increased, there are problems in that the
`resultant utilization ef?ciency of frequency is lowered
`and the circuit arrangement of the error correcting
`decoder becomes extensive.
`It should be understood that the expression “outside”
`and “inside” described above are de?ned as follows.
`That is, for instance, the error correcting encoder and
`decoder are positioned outside the differential en
`coding/decoding circuits in a circuit arrangement pro
`vided along the ?ow path of an input digital signal (i.e.,
`along a signal processing sequence).
`
`QUADRATURE AMPLITUDE MODULATION
`COMMUNICATION SYSTEM WITH
`TRANSPARENT ERROR CORRECTION
`
`10
`
`25
`
`35
`
`40
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention generally relates to a multi
`level QAM (quadrature amplitude modulation) system
`for transferring a digital signal by utilizing multi-level
`quadrature amplitude modulation. More speci?cally,
`the present invention is directed to a QAM communica
`tion system capable of increasing signal transmission
`reliability by employing a transparent error correcting
`method.
`2. Description of the Related Art
`In a multi-level quadrature amplitude modulation
`(QAM) communication system in which multi-bit data
`such as 4 bit data and 8 bit data are transferred with
`reference to one signal point on a phase plane coordi
`nate including 2" (“n" being the data bit number) signal
`points and original data are reproduced based upon the
`relationship between the amplitude and phase, utiliza
`tion ef?ciency for a frequency becomes high so that this
`QAM communication system has been widely utilized
`in digital microwave communications and digital mo
`bile communications.
`As previously stated, the signal transmission of the
`multi-level QAM communication system is carried out
`by employing the QAM signals produced by synthesiz
`ing two orthogonal I-channel and Q-channel signals
`corresponding to each m-level amplitude-modulated
`signal. Each of these multi-level QAM signals owns m2
`(=2") pieces of signal points. For instance, if "m” is
`selected to be 16 (n=8), this multi-level QAM signal is
`equal to 256 pieces of QAM signals having 256 signal
`points.
`In a QAM type receiving system employing synchro
`nous demodulation, a carrier wave is ?rst_reproduced
`from this multi~level QAM signal, and then demodu
`lated by utilizing 2 orthogonal-reproduced carrier
`waves having different phases with each other at 90°
`(degrees), and thereafter “n" pieces of digital signal
`series are obtained in total by way of the multi-level
`identi?cation. In general, there is a drawback in this
`QAM receiving system in that the phases of the repro
`duced carrier waves derived from the carrier wave
`reproducing circuit have a so-called "phase ambiguity",
`i.e., the phase becomes any of 0°, 90°, 180°, and 270°.
`Generally speaking. since a transmission signal series
`cannot be correctly reproduced if phase ambiguity ex
`ists, it is required to employ same means for eliminating
`the adverse in?uences caused by this phase ambiguity.
`To this end, there are some solutions to resolve such a
`phase ambiguity. That is, for instance, a known signal
`55
`series is periodically transmitted, whereas the phases of
`the reproduced carrier waves are discriminated based
`upon the relationship between this known signal series
`and the signal which has been demodulated and judged
`by the reproduced carrier waves having the phase ambi
`guity at the signal reception side. Otherwise, a transmis
`sion information signal is differential-encoded so as to
`be transmitted, which does not directly correspond to
`the transmission phase, but corresponds to a relative
`phase difference of a continuous transmitting symbol.
`At a signal reception end, when this differential
`encoded signal is differential-encoded after being de
`modulated by the reproduced carrier waves, the phase
`
`65
`
`45
`
`50
`
`60
`
`16
`
`

`
`10
`
`35
`
`5,168,509
`3
`4
`generally differential-encoded/decoded by employing
`Conversely, in the case in which the error correcting
`encoder and decoder are provided inside the differential
`the quadrant differential encoder/decoder.
`encoding/decoding circuits along the signal processing
`On the other hand, there exist a natural binary map- ,
`path, the adverse influence caused by the phase ambigu
`ping method, a Gray code mapping method and a quad
`ity in the reproduced carrier waves is not yet resolved
`rant symmetry mapping method as a signal point map
`ping method for mapping 2" pieces of signal points from
`at the input unit of the error correcting encoder. As a
`the n bits of the digital signals.
`result, in such a case, it is required to employ such an
`As typical examples, FIG. 1 represents signal point
`error correcting code, namely a transparent error cor
`recting code, even if the input signal is adversely in?u
`mapping for a l6-QAM communication system employ
`ing the Gray mapping method, whereas FIG. 2 repre
`enced by the phase ambiguity in the reproduced carrier
`sents another signal point mapping for a l6-QAM com
`waves, e.g., there is bit inversion of the input signal, the
`munication system employing quadrant symmetry map
`error correction can be correctly performed with re
`ping. Further, FIG. 14 indicates signal point mapping
`spect to the bit-inverted input signals.
`employing natural binary mapping. As is apparent from
`As an error correcting code, there are a binary error
`FIG. 1, the respective signal points are symmetrically
`correcting code and a nonbinary error correcting code.
`positioned with respect to the respective I and Q coor
`When a transparent binary error correcting encoder is
`dinate axes in Gray coded mapping. To the contrary,
`employed inside differential encoding/decoding cir
`the signal points positioned in the respective quadrants
`cuits, the transparency can be established by employing
`are arranged in quadrant symmetry mapping in such a
`error correcting encoders/decoders in “n" pieces of a
`manner that these signal points are rotated with respect
`signal series. However, this system has a drawback in
`to those of the adjoining quadrants.
`that when the multiple number of the QAM system is
`In these mapping methods shown in FIGS. 1. 2 and
`increased, the total number of the required error cor
`14, the in?uences caused by the phase shifts of 11/2, 17'.
`recting encoders/decoders is also increased. In addi
`and 31r/2, which are given to the received signal series,
`tion, there is a drawback in the binary error correcting
`are expressed in FIGS. 15A to 15C:
`code such that it is very difficult to produce a code
`In general, it is known that the transmission capacity
`whose coding rate is extremely high. When the decod
`and frequency utilization efficiency in such a multi-level
`ing delay time of the error correcting code is, for in
`QAM communication system can be increased by in
`stance, 63 symbols, even the resultant coding rate of the
`creasing the signal points. However, the more the bit
`binary BCH (Bose-Chaudhuri-Hocquenghem) .codes
`numbers are increased, the more the bit error rate is
`(63, 57) is 90.5%, by which a single error can be cor
`increased due to imperfections in the systems. It is de
`rected, and thus the frequency band is expanded by
`sired that the error correction encoding/ decoding oper
`approximately 10%. On the other hand, when the non
`ations be performed by slightly lowering the frequency
`binary error correcting code is employed, many diffi
`utilization efficiency so as to improve the QAM com
`culties may occur in realizing the above-described
`munication quality.
`transparent conditions. Although it has been proposed
`Thus, as previously stated, in the case that the error
`that the signal point mapping of the QAM signal is the
`correction encoder and decoder are provided outside
`natural binary mapping and the Lee error correcting
`the differential encoding/decoding circuits along the
`code is employed, since only such a case that errors
`signal processing path, since the continuous bit errors
`occur in the signal points near the transmission signal
`are produced by the differential encoding operation, the
`points can be corrected based upon the Lee error cor
`error correcting capability of the error correction code
`recting code, the error correcting effect cannot be ex
`must be emphasized or an interleaver must be em
`pected in a communication channel or path which are
`ployed.
`subjected to a fading phenomenon. In addition, the
`However, when the error correcting capability of the
`coding rate of the Lee error correcting code is not
`error correction code is increased, the frequency utiliza
`always as good as other nonbinary codes.
`tion efficiency is deteriorated. When the interleaver is
`As previously described, in the conventional QAM
`newly employed, not only the circuit scale of the entire
`communication system employing the binary error cor
`system becomes large, but also the decoding delay time
`recting code, there are problems since the coding rate
`is increased. As a consequence, it is generally accepted
`cannot be high so that the efficiency in the frequency
`to arrange such an error correction encoder/decoder
`utilization is lowered and also the total number of the
`inside the differential encoder/decoder.
`required error correcting encoders/decoders to per
`It should be noted that when the error correcting
`form the differential encoding operation is necessarily
`encoder/decoder are arranged inside the differential
`increased. Furthermore, in accordance with the con
`encoder/decoder, error correction must be correctly
`ventional QAM communication system employing the
`performed even when the signal series are varied as
`Lee error correcting code, there are drawbacks in that
`represented in FIG. 14 due to the ambiguity of the
`error correction can be executed limited only to the
`capture phase in the reproduced carrier wave, and si
`signal points having a small distance on signal point
`multaneously, the phase ambiguity must be preserved
`mapping.
`even when the error correction encoding/decoding
`The above-described problems of the conventional
`operations are carried out. It should be also noted that
`multi-level QAM communication system will now be
`the error correction code which can satisfy such a con
`described in detail.
`dition is called as a transparent code with respect to
`That is. while the original data is reproduced from
`phase rotation in an input signal.
`the received signal in the conventional multi-level
`Conventional circuit arrangements for the transpar
`QAM communication system, since the capture phase
`ent codes with respect to the phase rotations in the input
`of the reproduced carrier wave has phase ambiguity
`signals, have been proposed in Japanese KOKAI (Dis
`such as O, 1r/2, n' or 317/2 radians, the two digital signal
`closure) patent application No. 63-219252, and "6GHZ
`series to determine the quadrant of the phase plane are
`I4OMBPS DIGITAL RADIO REPEATER WITH
`
`50
`
`55
`
`65
`
`17
`
`

`
`5,168,509
`
`6
`BRIEF DESCRIPTION OF THE DRAWINGS
`For a better understanding of the present invention, _
`reference is made to the following detailed descriptions
`in conjunction with the drawings, in which:
`FIGS. 1 and 2 schematically illustrate known signal
`point mappings;
`FIG. _3 is a schematic block diagram of a QAM (quad
`rature amplitude modulation) communication system
`100 employing a ?rst basic idea, according to a ?rst
`preferred embodiment of the present invention;
`FIG. 4 is a schematic block diagram of another QAM
`communication system 200 employing the ?rst basic
`idea, according to a second preferred embodiment of
`the present invention;
`FIG. 5 is a schematic block diagram of an internal
`circuit of the Reed-Solomon encoder l3 employed in
`the second QAM system 200;
`FIG. 6 is a schematic block diagram of an internal
`circuit of the Reed~Solomon decoder 16 employed in
`the second QAM system 200;
`FIG. 7 is a schematic block diagram of an internal
`circuit of the syndrome generator 50 employed in the
`second QAM system 200;
`FIG. 8 is a schematic block diagram of a 256-QAM
`communication system 300 employing a second basic
`idea, according to a third preferred embodiment of the
`present invention;
`FIG. 9 is a schematic block diagram of another 256
`QAM communication system 400 employing the second
`basic idea, according to a fourth preferred embodiment
`of the present invention;
`FIG. 10 is a schematic block diagram of a still further
`256-QAM communication system 500 arranged by uti
`lizing the second basic idea, according to a ?fth pre
`ferred embodiment of the present invention;
`FIG. 11 is a schematic block diagram of a 64-QAM
`communication system 600 constructed by using the
`third basic idea, according to a sixth preferred embodi
`ment of the present invention;
`FIG. 12 is a schematic block diagram of another
`64-QAM communication system 700 employing the ?rst
`basic idea, according to a seventh preferred embodi
`ment of the present invention;
`FIG. 13 is a schematic block diagram of another
`256-QAM communication system 800 employing a
`unique word adder/detector and no quadracture differ
`ential encoder/decoder, according to an eighth pre
`ferred embodiment of the present invention;
`FIG. 14 schematically illustrates natural binary map
`ping; and,
`FIGS. 15A to 15C are tables for explaining phase
`reference error effects occurring in the three typical
`mapping methods.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`Basic Ideas
`Before describing various preferred embodiments,
`two basic ideas of the present invention will now be
`summarized.
`A multi-level QAM (quadrature amplitude modula~
`tion) communication system according to the ?rst basic
`idea of the present invention, is featured by employing
`error correcting means for performing both encoding
`and decoding operations of the Reed-Solomon code
`under the condition that 'all or a portion of “n" pieces of
`
`5
`256QAM MODULATION" by Y. Yoshida et al., Pro
`ceedings of International Conference on Communica
`tions 1986, No. 46-7, pages 1482 to 1486.
`In the multi-level QAM communication system as
`disclosed in the above-described Japanese KOKAI pa
`tent application No. 63-219252, there are various draw
`backs. That is, since the error correction encoding/de
`coding operations are independently performed with
`respect to each of "n" pieces of a digital signal series
`which constitute the in-phase channel and also the
`channel orthogonal to the in-phase channel, “n" pieces
`of encoders and decoders are required. As a result, the
`scale of the entire apparatus becomes large.
`On the other hand, in the multi-level QAM communi’
`cation system as described in the above publication, i.e.,
`ICC ’86, No. 46-7, there is employed such an en
`coding/decoding method with employment of the Lee
`error correction code, for the respective signal series
`combinations between n/2 series combinations to con
`stitute the in-phase channel and n/2 series combinations
`to constitute the orthogonal channel. However, this
`conventional communication system is limited to such a
`natural binary mapping method for mapping the n bits
`data to the signal points. Furthermore, there are many
`other limitations for the constituting methods of the
`error correction codes.
`
`30
`
`SUMMARY OF THE INVENTION
`The present invention has been made in an attempt to
`solve the conventional problems, and therefore has a
`primary object to provide a QAM (quadrature ampli
`tude modulation) communication system capable of
`realizing a higher coding rate and higher reliability.
`Moreover, the present invention has a secondary
`object to provide a multi-level QAM communication
`system in which both the error control code and map
`ping methods are freely selected, a total quantity of
`encoders/decoders is smaller than a bit number of input
`digital data, and a transparent error correction coding
`for a phase rotation can be realized.
`In addition, a third object of the present invention is
`to provide a multi-level QAM communication system in
`which clock frequencies of the error correction en
`coder/decoder can be lowered with respect to a modu~
`lation frequency of a quadrature amplitude modulator.
`A quadrature amplitude modulation system, accord- .
`ing to the present invention, comprises:
`50
`differential encoder/decoder means (12;17) for differ
`entially encoding/decoding n pieces of input digital
`signal series to resolve phase ambiguity contained in the
`differentially encoded input signal series;
`error correction means including a Reed-Solomon
`encoder (13;83) and a Reed-Solomon decoder (16;87),
`provided inside said differential encoder/decoder
`means (12;17) along a signal processing path of said
`input
`digital
`signal
`series,
`for
`error-control
`encoding/decoding said n pieces of differentially-coded
`signal series by utilizing at least one of said digital signal
`series to correct errors with employment of Reed-Solo
`mon codes; and,
`means
`QAM
`modulator/demodulator
`(14;15;34;36;80;82) for QAM-modulating/demodulating
`n pieces of error-control-coded signal series so as to
`produce 2" QAM signals.
`
`65
`
`18
`
`

`
`10
`
`25
`
`5,168,509
`7
`an input signal series for determining signal point map
`ping is used as a symbol. Also, in case the differential
`coding operation is performed by employing natural
`code mapping, such an error correcting means is em
`ployed to independently perform both encoding and
`decoding operations for the Reed-Solomon code with
`respect to two “1" and “Q" channels orthogonal to each
`other. Although there are many generator polynomials
`for constructing the Reed-Solomon code, such a Reed
`Solomon code so that codeword polynomials are not
`divisible by x-l (namely, the generator polynomial is
`not divisible by “it-l”) is utilized so as to establish
`transparency.
`In the above-described ?rst QAM communication
`system, when (u,k) linear block codes are employed, a
`frequency band width expanding rate for in?uencing
`the QAM communication system is determined by the
`coding rate of the block codes. To correct a t-symbol,
`all of the linear block codes must satisfy a limit formula
`of t§(u-k)/2. In other words, a redundant symbol num
`ber (u-k) cannot be reduced by twice the correction
`capability. A Reed-Solomon code can satisfy this limit
`formula. so that the frequency expanding rate can be
`suppressed to a minimum value in such a QAM commu
`nication system employing a Reed-Solomon code.
`Due to the phase ambiguity of the reproduced carrier
`waves, the respective “1" and “Q" channels cause signal
`changes different from each other. However, this ad
`verse influence can be eliminated by independently
`performing both the encoding and decoding operations
`of the Reed-Solomon code with respect to two “I’” and
`‘*Q“ channels orthogonal to each other.
`Furthermore, even when the signals are inverted in
`the QAM communication circuit due to the phase ambi
`guity of the reproduced carrier waves, the transparency
`can be established by utilizing such a Reed-Solomon
`code in which a generator polynomial is not divisible by
`x—- 1. That is, in case signal point mapping corresponds
`to natural code mapping, a necessary/satisfactory con
`dition such that a Reed-Solomon code is equal to a
`transparent code, is as follows: Any codeword polyno
`mial of the code is not divisible by x- 1. Another multi
`level QAM communication system according to a sec
`ond basic idea, has the following features:
`In a multi-level QAM communication system in
`which a bit number of transmitted/received data is
`equal to “n‘” and there are provided 2" pieces of signal
`points, an error correction coding operation is sepa
`rately carried out with respect to each of signal series
`used for determining a quadrant of a phase plane, and
`also with respect to to other signal series among “n"
`pieces of signal series for determining a signal.
`As represented in FIG. 15C, in a multi-level differen
`tial QAM communication system in which signal point
`mapping is determined based upon quadrant symmetry
`mapping, a bit inversion and a signal series substitution
`may occur with re