United States Patent [19]
`Frenkel
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US005838268A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,838,268
`Nov. 17, 1998
`
`[54] APPARATUS AND METHODS FOR
`MODUIATION AND DEMODUIATION OF
`DATA
`
`[75]
`
`Inventor: Liron Frenkel, Ramat Gan, Israel
`
`[73] Assignee: Orckit Communications Ltd., Tel
`Aviv, Israel
`
`[21] Appl. No.: 818,388
`
`[22]
`
`Filed:
`
`Mar. 14, 1997
`
`[51]
`[52]
`[58]
`
`[56]
`
`Int. CI.6
`.....................................•................ H03M 1/00
`U.S. CI. ................................................................. 341/11
`Field of Search ..................................... 3411111, 112,
`341/114, 113, 115, 116; 332/103; 375/61,
`67
`
`References Cited
`
`u.S. PATENT DOCUMENTS
`
`4,833,706
`5,008,670
`
`5/1989 Hughes-Hartogs ....................... 379/98
`4/1991 Zimmer ................................... 341/113
`
`OlHER PUBLICATIONS
`
`B.R. Saltzberg, "Performance of an Efficient Parallel Data
`Transmission System", IEEE Trans. on Comm. Tech.> vol.
`COM-15, No.6 (Dec. 1967) 805-81l.
`P. Duhamel, "Implementation of 'Split-Radix' FFT Algo(cid:173)
`rithms for Complex, Real, and Real-symmetric Data", IEEE
`Trans. on Acoustics> Speech and Signal Processing> vol.
`ASSP-34, No.2 (Apr. 1986) 285-295.
`I.A.C. Bingham, "Multicarrier Modulation for Data Trans(cid:173)
`mission: An Idea Whose Time Has Come", IEEE Commu(cid:173)
`nication Magazine (May 1990) 5-14.
`
`B. Hirosaki, An Analysis of Automatic Equalizers for
`Orthogonally Multiplexed QAM Systems, IEEE Trans.
`Comm.> vol. COM-28 (Jan. 1980) 73-83.
`P.P. Vaidyanathan, Multirate Systems and Filters Banks
`(Englewood Cliffs: P T R Prentice-Hall, Inc., 1993) pp. 84,
`76,86, 134, 136, 140 and 142.
`A.V. Oppenheim et aI., Discrete-Time Signal Processing
`(Englewood Cliffs: Prentice-Hall, Inc., 1989) pp. 514-520.
`ADSL Standard TIEl.4/95-007R2, pp. 22-49 (no date
`given).
`Primary Examiner-Brian K. Young
`Attorney. Agent> or Firm-Darby & Darby
`
`[57]
`
`ABSTRACT
`
`A signal modulation method comprising receiving at least
`first and second synchronized incoming streams of complex
`symbols, thereby to define a plurality of incoming vectors
`each including at least first and second synchronized com(cid:173)
`plex symbols, mapping each complex symbol into a signal
`component comprising a linear combination of an in-phase
`signal and a quadrature signal, the quadrature signal com(cid:173)
`prising a Hilbert transform of said in-phase signal, wherein
`all of the signal components are substantially mutually
`orthogonal and wherein the frequency spectrums of all
`signal components mapped from a single incoming stream
`are centered around a common frequency location which is
`unique to the single incoming stream and wherein the
`frequency spectrums of signal components mapped from
`different incoming streams having adjacent common fre(cid:173)
`quency locations are partially overlapping and wherein
`signal components mapped from sequential incoming sym(cid:173)
`bols partially overlap in time and combining all of the signal
`components into a representation of an output signal.
`
`30 Claims, 15 Drawing Sheets
`
`INPUT
`BIT
`STREAM
`
`10
`
`---
`COMPLEX
`SYMBOL
`GENERAT-
`ING
`MAPPER
`
`M
`
`NARROW /
`BANDPASS
`OVERLAP-
`PING
`FREQUENCY
`FILTER
`ARRAY
`
`20
`
`f---'>
`
`~O
`. /
`INTERPO
`-LATOR
`
`----+
`
`J
`/ '
`
`40 ~o
`
`~4 OUTPUT
`ANALOG
`SIGNAL
`UP
`ANA(oG
`CONVER- r-+ D/A r-+ FRONT-
`TOR
`END
`
`~
`
`

`
`US. Patent
`
`Nov. 17, 1998
`
`Sheet 1 of 15
`
`5,83 8,268
`
`
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`E53mm&<s_
`
`

`
`US. Patent
`
`Nov. 17, 1998
`
`Sheet 2 of 15
`
`5,838,268
`
`._.Dn__.,.__
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`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 3 of 15
`
`5,838,268
`
`BIT
`LOADING
`TABLE
`I
`
`"-
`
`~O
`
`. /
`
`-l--
`TUPLE TO
`SYMBOL
`MAPPING UNIT
`
`_~O
`
`- -?
`
`{-
`
`160
`
`"'---
`
`COMPLEX
`
`190
`
`TABLE
`
`SCALING J/
`1
`
`~O
`)
`COMPLEX -- A 0 (n
`MULTIPLIER
`
`170
`TUPLE TO _/
`SYMBOL
`MAPPING UNIT
`
`COMPLEX ---
`MULTIPLIER
`
`180
`'/
`A 1 en
`
`180
`
`-'
`
`COMPLEX
`MULTIPLIER
`
`n)
`A N-1(
`
`BIT
`STREAM
`IN
`
`BIT
`STREAM f----7
`TO
`TUPLES
`MULTI-
`PLEXER
`
`TUPLE TO ~o
`-
`~ SYMBOL
`MAPPING UNIT
`
`FIGURE 3
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 4 of 15
`
`5,838,268
`
`AO(n)
`
`Ai (n)
`
`200
`J
`. /
`FIL TER NUMBER 0
`ZERO PAD
`tM ~ go(i) = g(i)
`290
`. /
`FIL TER NUMBER 1
`ZERO PAD
`tM ~ .
`.
`.2Jr.
`g 1 ( 1) = g( l ) • exp( } -
`. 1 . I)
`N
`
`204
`"J
`/"
`
`208
`7
`...-/
`
`~
`
`294
`
`/ '
`
`4
`
`D
`SUM ~
`
`A N_1(n)
`
`29°
`. /
`ZERO PAD
`tM
`
`f-*
`
`FIL TER NUMBER N-1
`
`294
`
`...-/
`
`(i) = g(i). exp(j 2Jr . (N - 1)· i)
`g
`N-I
`N
`
`~
`
`Ao(n)
`
`A 1(n)
`
`210
`.... i)
`
`Co(n)
`
`C 1 (n)
`
`IFFT
`
`FIGURE 4A
`
`MULTIPLY
`AND
`ACCUMULATE
`MACHINE
`Dk(n) =
`
`L:L-l
`i = 0 g( k + iM) .
`
`A N_1(n)
`
`C N_1 (n C(k+iM)modN (n-i)
`where k = 0,1,2, ... , M-1
`
`220
`./
`
`~
`
`Do(n)
`
`D1 (n)
`
`r-tJ°
`
`,.
`
`~
`
`DN_1 (n)
`
`DM_1 (n)
`
`FIGURE 4B
`
`CONCATENATOR
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 5 of 15
`
`5,838,268
`
`~----------------------~260
`
`Define Parameters T, M, L, N j/
`______________________ ~ ____________________ ~270
`Generate "prototype" coefficients g(i), i = 0,1, ... , L*M - 1.
`(Figure 6 or 8)
`
`280
`~---L-e-t-n-=--O-(-n-i-s-t-he~~-s-y-m-b-O-I-n-u-m-b-e-r)----~
`
`!
`
`Input Vector:
`
`290
`
`/
`
`Read vector { A k (n)}
`( k= 0, 1, ... N) into a DSP
`machine
`
`IFFT:
`Use a DSP Machine with an N'th order IFFT
`
`310
`
`method to transform the vector { A k (n) } to the
`
`vector {C k (n)} where k = 0, 1, .... J N-1
`~ ________________ ~ ______________ ~320
`MAC:
`Use a DSP Machine with equation in 220 to
`
`compute the output vector {O k (n) },
`k = 0, 1, ... , M-1 from vector C
`
`Output Vector:
`
`Write vector { 0 k (n) } serially
`(k=O, 1, ... M-1) out of the DSP
`machine
`
`FIGURE 5
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 6 of 15
`
`5,838,268
`
`350
`Define parameters T, ~f,A1and let a=2(llf-T-l)
`360
`t
`\
`Main Frequency Component: Generate a raised cosine function R(f): )
`o :::; f <(I-a)/ 2T
`T
`
`1 -
`TrT(f --)
`2T
`I-sin
`
`a
`
`(l-a)/2T < f < (l+a)/2T
`
`I
`
`r-
`
`R(j)=
`
`T
`2
`
`L..
`
`0
`
`-
`
`I fl > (1 +a)/2T
`
`t
`3~0
`Auxiliary Frequency Component: Generate Am by finding the roots of)
`[I 2(
`1 LV~ 2
`~ 2(
`1 LV~ 2
`A(/) ~R 1 +(T -2) -A (I) + R 1 -(T -2) -A (I)
`]
`=R(r + ~{)R(r -~{)
`t
`P-OFDM signal in frequency: Compute pm from Am and RW
`I 2 2 (
`1 M) 2(
`1 /'..f)
`f -(---) -A
`P(f)= R (f)-A
`f +(---)
`V
`2
`T
`2
`T
`1 LV) (
`1 LV)
`(
`-A f -(-+-) -A f +(-+-)
`2
`T
`T
`2
`t
`P-OFDM Coefficients:
`Sample P(f) in frequency in the interval f = -M 12T to +M 12T,
`and use Discrete Fourier Transform (OFT)
`to compute the coefficients: 9 = DFT( P( f) )
`
`420
`l-/
`
`!
`\.
`390
`
`FIGURE 6
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 7 of 15
`
`5,838,268
`
`5
`
`0
`
`-5
`
`-10
`
`-15
`
`dB -20
`
`-25
`
`-30 f--
`
`-35
`
`-40
`
`-45
`-5
`
`,
`
`{
`
`\
`
`4 0
`
`4~
`
`~o
`
`I
`I
`
`-
`
`-
`
`-4
`
`-3
`
`-2
`
`-1
`
`o
`
`1
`
`2
`
`3
`
`4
`
`5
`
`FIGURE 7
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 8 of 15
`
`5,838,268
`
`i Define Parameters
`
`450
`./
`...--
`T, L, M, N, I, C1, C2, ... C5
`I
`460
`/
`.-
`
`1
`
`Initial Coefficient vector:
`
`Generate a Nyquist signal r(t) with symbol period T.
`r(t) = FT ( R( f) }
`For example,
`where FT is a Fourier Transform.
`
`Let v (0) (i) equal r(t) sampled at rate of (M/I)IT:
`v (0) (i) = r( T * I / M * ( i - L * M / (I *2))) , j= 0, 1,2, ... L * MII-1
`1
`
`4)30
`Define the optimization criteria J(v) for a vector v~
`J(v) =
`C1 * (lSI generated when using v as filter coefficients) +
`C2 * (ICI generated under frequency conversion of v by
`integer multiples of L1f) +
`C3 * (lSI generated by delayed version of v) +
`C4 * (ICI generated by delayed version of v) +
`C5 * (Frequency energy of outband FFT(v) )
`
`41 o
`
`.../'
`
`Use a optimization function (like Matlab 4.2 CONSTR
`comand) with the initial condition vector v (0) (n) and the
`optimization criterion J(v) to find the vector v which
`miminizes J(v).
`494
`~
`../
`Obtain the coefficient vector g by Interpolating vector v by
`the value I
`
`t
`
`FIGURE 8
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 9 of 15
`
`5,838,268
`
`5
`
`0
`
`-5
`
`-10
`
`-15
`
`dB -20
`
`-25
`
`-30
`
`-35
`
`-40
`
`-45
`-5
`
`-4
`
`(
`
`~O
`
`~O
`
`~O
`
`I
`
`-
`
`-
`
`I~~
`-1
`
`\~ ~
`1
`
`~ Il ~
`3
`
`2
`
`o
`
`4
`
`5
`
`FIGURE 9
`
`5~
`
`5 0 ~
`j~ j
`
`-3
`
`-2
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 10 of 15
`
`5,838,268
`
`~
`
`FIL TER NUMBER 0
`go (i) = g(i)
`
`520
`J
`./'
`
`530
`J
`./'
`TAKE ONE OF M
`~M
`
`f-+
`
`GO(n)
`
`E(i)
`
`FIL TER NUMBER 1
`g (i) = g(i) . exp( - j 2Jr ·1 . i)
`N
`1
`
`/
`
`5tO
`
`5;0
`./'
`TAKE ONE OF M
`~M .
`
`4
`
`G 1(n)
`
`5fO
`
`5)30
`
`FIL TER NUMBER N-1
`~ gN_l(i)=g(i)·exp(-j~(N-l)i) ---+
`FIGURE 10A
`
`/
`
`./'
`TAKE ONE OF M
`~M
`
`G N _1 (n
`}
`
`550
`)
`./'
`
`560
`......
`
`FO(n)
`
`GO(n)
`
`MULTIPLY
`AND
`ACCUMULATE
`MACHINE
`
`E(i)
`
`Fk(n) =
`L~j:xo g(k + iN)· E(nM + iN + k)
`
`F 1 (n)
`
`G 1(n)
`
`FFT
`
`where k = 0,1, .... , N -1
`
`FM _1 (n)
`
`G M _1( n)
`
`I M.L-k-1l
`
`and i MAX =
`
`N
`
`FIGURE 108
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 11 of 15
`
`5,838,268
`
`Define Parameters T, M J LJ N
`
`582
`
`Generate "prototype" coefficients g(i), i = 0,1) ... ) L *M - 1 .
`(Figure 6 or 8)
`
`584
`~--------------~--------------~
`
`Let n = -0 (n is the symbol number)
`
`590
`
`Input M samples:
`Read M samples E into memory. Denote these
`samples E(i) where
`i = M * n, M * n + 1, " 'J M * n + M - 1
`
`MAC:
`Use a DSP Machine with equation in 550 to
`
`600
`
`compute the output vector {F k (n) },
`k = OJ 1, "'J N-1 from EO)
`~ ________________ ~ ________________ ~610
`FFT:
`Use a DSP Machine with an Nlth order FFT
`method to transform vector {F k (n) }
`
`to vector {G k (n)}, k= 1, 2J ... , N.
`
`Output Vector:
`
`Write vector { G k (n) }
`(k=O, 1, ... N-1) out of the DSP
`machine
`
`FIGURE 11
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 12 of 15
`
`5,838,268
`
`680
`J
`./"
`EQUALIZER
`COEFFICIENTS
`ESTIMATION
`
`61°
`./'
`
`660
`)
`../
`
`670
`L
`./'
`
`APPLY
`EQUALIZER
`(MULTIP-
`L1ERS)
`
`.
`
`TIMING
`AND
`PHASE
`
`SLICER
`
`. (COMPERA-
`.
`TORS)
`
`GO(n)
`
`G 1 (n)
`
`.
`G N - 1 (n)
`
`FIGURE 12
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 13 of 15
`
`5,838,268
`
`"\ 720
`
`~
`
`"-
`
`BIT
`LOADING V
`TABLE
`I
`_lYO
`
`[
`SYMBOL TO
`TUPLE
`MAPPING UNIT
`
`SYMBOL TO _lYO
`
`/'
`
`TUPLE
`MAPPING UNIT
`
`J,
`
`~O
`
`-
`
`,
`
`BIT
`STREAM
`OUT
`
`...
`
`TUPLES
`TO
`BIT
`STREAM
`
`;yo
`
`... ..
`
`SYMBOL TO
`TUPLE
`MAPPING UNIT
`
`FIGURE 13
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 14 of 15
`
`5,838,268
`
`850
`\.
`---
`
`MAC
`CONTROL-
`LER
`
`730
`SUBSCRIBER
`................................................... ··770·····/············:
`UPSTREAM TRANSMITTER
`./
`-
`7~i--
`P-OFDM
`FEC
`t-----? ENCODER
`MODULATOR ~
`
`DOWNSTREAM RECEIVER
`
`DOWNSTREAM
`
`DIP-
`7~ LEXER
`
`f-.
`
`~
`:
`
`__ ___ o • • • • • • • • • • .... " ' • • • >
`
`750
`
`8rae- DEMODULATOR
`HFC NETWORK )
`
`:
`.. ....................... ' . ....... ...... .. .. ...... , .. .................. ..
`
`,0
`
`. i
`
`"'
`
`8~0
`-
`
`MAC
`CONTROL-
`LER
`
`740
`HEADEND
`... . .. .;/ .... . ....
`..... .. ........... --- ................ ...... . ................
`UPSTREAM RECEIVER 8)0
`820
`'1- FEC
`-----
`P-OFDM
`I+- DECODER i-E-- DEMODOLA TOR ~
`DIP-
`DOWNSTREAM TRANSMITTER 8~ LEXER
`DOWNSTREAM
`MODULATOR
`~
`830
`... , . , , ......................... , ..
`
`~
`
`FJGURE 14
`
`

`
`u.s. Patent
`
`Nov. 17, 1998
`
`Sheet 15 of 15
`
`5,838,268
`
`#k
`I
`
`::-CHA~iNEl"",
`.
`:'
`#k+1
`".
`.
`.
`.
`I
`. )
`'
`
`LCHANNEL\
`v:.·
`
`(1+a)fT
`
`),
`
`CHANNEL X':~· .. · CH·ANNEL· ...
`
`'.
`
`'"
`
`..
`)
`.
`FREQUENCY
`
`,(
`
`.
`
`:
`:
`
`#k+1
`,..
`#k
`,
`I ' I
`(
`
`#
`
`:
`
`~f= 1fT
`FIGURE 158
`PRIOR ART
`
`CHANNEL CHANNEL
`#k.
`.#k+1
`..
`.
`. ,
`~~~
`FREQUENCY
`~~
`~f= 1fT
`FIGURE 15C
`PRIOR ART
`
`'
`
`'", -
`
`-
`
`-
`
`- -"
`
`)
`
`,
`
`-
`
`-
`
`-
`
`-
`
`I
`
`'f
`
`(1+a)fT
`
`.
`.
`: CHANNEL'
`#k+1
`
`(
`
`1fT < ~f < (1+a)fT
`FIGURE 150
`
`)
`
`FREQUENCY
`
`

`
`5,838,268
`
`1
`APPARATUS AND METHODS FOR
`MODULATION AND DEMODULATION OF
`DATA
`
`FIELD OF THE INVENTION
`
`The present invention relates to apparatus and methods
`for modulation and demodulation of data.
`
`BACKGROUND OF THE INVENTION
`
`5
`
`2
`frequencies (as shown in prior art FIG. 15B) and the
`composite spectrum is flat. If a<l, each subband overlaps
`only its immediate neighbors, and orthogonality of the
`sub-bands, with resultant separability in the receiver, is
`achieved by staggering the data, e.g. offsetting by half the
`symbol period Ti2, on alternate in-phase and quadrature sub
`channels.
`(3) DMT-As described in U.S. Pat. No. 4,833,706 and in
`ADSL Standard T1.413/95, the carriers are keyed by the
`10 data, using Quadrature Amplitude Shift Keying (QASK).
`The individual spectra are now sinc functions. As shown in
`prior art FIG. 15C, the individual spectra are not band
`limited, but, as described in the above referenced Bingham
`publication (1990), the signals can still be separated in the
`15 receiver. The frequency division is achieved, not by band(cid:173)
`pass filtering, but by baseband processing. The big advan(cid:173)
`tage of this approach is that both transmitter and receiver can
`be implemented using efficient Fast Fourier Transform
`(FFT) techniques.
`The disclosures of all publications mentioned in the
`specification and of the publications cited therein are hereby
`incorporated by reference.
`
`SUMMARY OF THE INVENTION
`
`Multicarrier modulation schemes and related technologies
`are described in the follmving references:
`L. Doetz, T. E,. Held, and D. L. Martin, "Binary Data
`Transmission Techniques for linear systems", Proc IRE, Vol.
`45, pp. 656-661, May 1957.
`B. R. Saltzberg "Performance of an Efficient Parallel Data
`Transmission System", IEEE Trans. on Comm. Tech .. , Vol.
`COM-IS, no. 6, December 1967
`P. Duhamel, "Implementation of Split-Radix FFT Algo- 20
`rithm for Complex, Real, and Real-Symmetric Data", Vol.
`ASSP-34, pp. 285-295, April 1986
`A. C. Bingham, "Multicarrier Modulation for Data Trans(cid:173)
`mission: An Idea Whose Time Has Come", IEEE Commu(cid:173)
`nication magazine, pp. 5-14, May 1990
`B. Hirosaki, "An analysis of Automatic Equalizers for
`Orthogonally Multiplexed QAM systems", IEEE Trans.
`Commun., vol. COM-28, pp. 73-83, January 1980.
`P. P. Vaidyanathan, M.ultirate Systems and Filter Banks>
`Prentice-Hall, Inc., 1993
`A. V. Oppenheim and R. W. Schafer, Discrete time signal
`processing> Prentice-Hall, 1989.
`The following description of prior multi carrier modula(cid:173)
`tion schemes is summarized from the above-referenced
`publications by Bingham (1990):
`The principle of transmitting data by dividing it into
`several bit streams and using these bit streams to modulate
`several carriers was used 40 years ago in the Collins
`Kineplex system [Doetz 1957]. The basic principle of Mul(cid:173)
`ticarrier Modulation (MCM) is grouping the input data bits
`into blocks of B bits and distributing these bits between the
`several carriers. For an input bit rate of BIT bits per second,
`the block (symbol) rate is lIT. Each time interval T, the B
`bits are used, Bk bits per carrier, to modulate Nc carriers, 45
`which are spaced ""f apart across any usable frequency
`band. The sum over B k , k=l, 2, ... No is equal to B. The
`modulated carriers are summed for transmission, and must
`be separated in the receiver before demodulation.
`Three main methods have been used for this separation
`which are termed herein the FDM (frequency division
`multiplexing), SQAM (staggered quadrature amplitude
`modulation) and DMT (discrete multi -tone) methods respec(cid:173)
`tively. These prior art methods are now described:
`(1) FDM-The earliest MCM modems borrowed from
`conventional FDM technology and used filters to completely
`separate the bands. The transmitted power spectra for jW';t
`two sub-bands of a multi carrier system are shown in prior art
`FIG. 15A. Because of the difficulty of implementing very
`sharp filters, each of the signals must use bandwidth, (l+a)
`iT which is greater than the Nyquist minimum, lIT. The
`efficiency of the band usage is (l/T)J""f=l/(l+a).
`(2) SQAM-{Saltsberg 1967], [Hirosaki 1980]. Theeffi(cid:173)
`ciency of the band was increased to almost 100% by using
`Staggered Quadrature Amplitude Modulation (SQAM). The
`individual transmit spectra of the modulated carriers still use
`an excess bandwidth of a, but they overlap at the -3 dB
`
`25
`
`35
`
`The present invention seeks to provide improved methods
`and apparatus for modulating and demodulating data.
`One object of a preferred embodiment of the present
`invention is to provide a modulation/demodulation scheme
`30 with improved bandwidth efficiency, sharp ingress rejection,
`robustness to time and phase errors and low latency, which
`is therefore suitable for reliable continuous transmission of
`packets in multi-point systems such as HFC (hybrid fiber
`coax).
`According to a preferred embodiment of the present
`invention, a modem is provided which is generally insensi(cid:173)
`tive to timing and phase impairments because it employs
`signals which overlap in frequency and in time but maintain
`orthogonality. Also, unlike SQAM, each signal preferably
`40 includes an in-phase component and a quadrature compo(cid:173)
`nent which is a Hilbert transformation of the in-phase
`component, rather than employing signals which include
`staggered in-phase and quadrature phase components as in
`prior art systems.
`There is thus provided, in accordance with a preferred
`embodiment of the present invention, a signal modulation
`method including receiving at least first and second syn(cid:173)
`chronized incoming streams of complex symbols, thereby to
`define a plurality of incoming vectors each including at least
`50 first and second synchronized complex symbols, mapping
`each complex symbol into a signal component including a
`linear combination of an in-phase signal and a quadrature
`signal, the quadrature signal including a Hilbert transform of
`the in-phase signal, wherein all of the signal components are
`55 substantially mutually orthogonal, and wherein the fre(cid:173)
`quency spectrums of all signal components mapped from a
`single incoming stream are centered around a common
`frequency location which is unique to the single incoming
`stream and wherein the frequency spectrums of signal
`60 components mapped from different incoming streams hav(cid:173)
`ing adjacent common frequency locations are partially
`overlapping, and wherein signal components mapped from
`sequential incoming symbols partially overlap in time, and
`combining all of the signal components into a representation
`65 of an output signal.
`Further in accordance with a preferred embodiment of the
`present invention, each signal component is proportional to
`
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`5,838,268
`
`3
`a temporal translation andlor a frequency translation of each
`other signal component.
`Still further in accordance with a preferred embodiment of
`the present invention, the incoming vectors arrive at a given
`symbol rate and wherein each the signal component includes
`a main frequency component defining a central main fre(cid:173)
`quency value and wherein, for each pair of signal compo(cid:173)
`nents generated from different incoming streams, the dis(cid:173)
`tance between their central main frequency values exceeds
`the symbol rate.
`Additionally in accordance with a preferred embodiment
`of the present invention, each signal component includes a
`main frequency component centered at the common fre(cid:173)
`quency location and auxiliary frequency components
`arranged around the common frequency location.
`Further in accordance with a preferred embodiment: of
`the present invention, the main frequency component of
`each signal component mapped from a particular incoming
`stream overlaps the main frequency component of each
`signal component mapped from an incoming stream having
`an adjacent common frequent location.
`Still further in accordance with a preferred embodiment of
`the present invention, for each pair of signal components
`mapped from incoming streams having adjacent common 25
`frequency locations, the auxiliary frequency components of
`the pair of signal components cancel out interference result(cid:173)
`ing from the partial overlap of their main frequency com(cid:173)
`ponents.
`Additionally in accordance ",rith a preferred embodiment 30
`of the present invention, for each pair of signal components
`mapped from different incoming streams whose main fre(cid:173)
`quency components partially overlap, the auxiliary fre(cid:173)
`quency components of the pair of signal components cancel
`out any interference resulting from the partial overlap of 35
`their main frequency components.
`Further in accordance with a preferred embodiment of the
`present invention, the different incoming streams have non(cid:173)
`adjacent common frequency locations.
`Also provided, in accordance with another preferred 40
`embodiment of the present invention, is a signal demodu(cid:173)
`lation method including receiving an input signal including
`a superposition of mutually orthogonal signal components,
`and generating at least first and second synchronized out(cid:173)
`going streams of complex symbols from the input signal, 45
`thereby to define a plurality of outgoing vectors each includ(cid:173)
`ing at least first and second synchronized outgoing complex
`symbols, wherein each signal component generates a cor(cid:173)
`responding outgoing complex symbol and includes a linear
`combination of an in-phase signal and a quadrature signal, 50
`the quadrature signal including a Hilbert transform of the
`in-phase signal, and wherein the frequency spectrums of all
`signal components generating complex symbols in a single
`outgoing stream are centered around a common frequency
`location which is unique to the single outgoing stream and 55
`wherein the frequency spectrums of signal components
`generating complex symbols in different outgoing streams
`having adjacent common frequency locations are partially
`overlapping, and wherein signal components generating
`sequential outgoing vectors partially overlap in time.
`Further in accordance with a preferred embodiment of the
`present invention, each signal component is mapped from a
`corresponding original complex symboL
`Additionally provided, in accordance with yet another
`preferred embodiment of the present invention, is a signal 65
`modulation system including a complex symbol filter array
`operative to receive at least first and second synchronized
`
`4
`incoming streams of complex symbols, thereby to define a
`plurality of incoming vectors each including at least first and
`second synchronized complex symbols, and to filter each
`complex symbol into a baseband representation of a signal
`5 component including linear combination of an in-phase
`signal and a quadrature signal the quadrature signal includ(cid:173)
`ing a Hilbert transform of the in-phase signal, wherein all of
`the signal components are substantially mutually
`orthogonal, and wherein the frequency spectrums of all
`10 signal components filtered from a single incoming stream
`are centered around a common frequency location which is
`unique to the single incoming stream and wherein the
`frequency spectrums of signal components filtered from
`different incoming streams having adjacent common fre-
`15 quency locations are partially overlapping, and wherein
`signal components filtered from sequential incoming sym(cid:173)
`bols partially overlap in time, and a signal component
`combining unit operative to combine all of the baseband
`representations of the signal components into a representa-
`20 tion of an output signaL
`Further in accordance with a preferred embodiment of the
`present invention, the combining step includes superimpos(cid:173)
`ing all of the baseband representation of the signal
`components, thereby to generate the output signaL
`Still further in accordance with a preferred embodiment of
`the present invention, the combining step includes superim(cid:173)
`posing linear transformation of each of the baseband repre(cid:173)
`sentations of the signal components, thereby to generate the
`output signaL
`Further in accordance with a preferred embodiment of the
`present invention, all signal components mapped from a
`single incoming vector are centered around a common
`temporal location which is unique to the single incoming
`vector.
`Still further in accordance with a preferred embodiment of
`the present invention, all signal components generating a
`single outgoing vector are centered around a common tem(cid:173)
`porallocation which is unique to the single outgoing vector.
`Additionally in accordance with a preferred embodiment
`of the present invention, the representation of an output
`signal includes the output signal itself or samples of the
`output signaL
`Further in accordance with a preferred embodiment of the
`present invention, the system also includes a complex sym(cid:173)
`bol generating mapper operative to receive an input bit
`stream and to generate therefrom at least first and second
`synchronized incoming streams of complex symbols.
`Still further in accordance with a preferred embodiment of
`the present invention, the system also includes a digital
`baseband-to-analog RF conversion unit operative to trans(cid:173)
`late the representation of an output signal into an analog RF
`signaL
`Additionally in accordance with a preferred embodiment
`of the present invention, the digital baseband-to-analog RF
`conversion unit includes an interpolator generating an
`up-sampled output, a digital RF up-converter receiving the
`up-sampled output and generating therefrom a digital rep(cid:173)
`resentation of an RF signal by up-converting the up-sampled
`60 output into RF, a D/A converter operative to convert the
`digital representation of the RF signal into an analog RF
`signal, and an analog front-end operative to receive the
`analog signal from the D/A converter and to filter and to
`amplify the analog signal.
`Further in accordance with a preferred embodiment of the
`present invention, the digital baseband-to-analog RF con(cid:173)
`version unit includes an interpolator generating an
`
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`5,838,268
`
`5
`
`5
`up-sampled output, a digital IF up-converter receiving the
`up-sampled output and generating therefrom a digital rep(cid:173)
`resentation of an IF signal by up-converting the up-sampled
`output into IF, a D/A converter operative to convert the
`digital representation of the IF signal into an analog IF
`signal, and an analog front-end operative to receive the
`analog IF signal from the D/Aconverter, to filter the analog
`IF signal, thereby to generate a filtered signal, to up-convert
`the filtered signal into RF, thereby to generate a filtered RF
`signal, and to amplify the filtered RF signal.
`Also provided, in accordance with another preferred
`embodiment of the present invention, is a signal demodu(cid:173)
`lation system including a narrow bandpass overlapping
`frequency filter array operative to receive an input signal
`transmitted through a communication channel, the input 15
`signal including a channel-distorted superposition of mutu(cid:173)
`ally orthogonal signal components and to generate at least
`first and second synchronized outgoing streams of complex
`values from the input signal, thereby to define a plurality of
`outgoing vectors each including at least first and second 20
`synchronized outgoing complex values, wherein each signal
`component generates a corresponding outgoing complex
`value and includes a linear combination of an in-phase
`signal and a quadrature signal, the quadrature signal includ(cid:173)
`ing a Hilbert transform of the in-phase signal, and wherein 25
`the frequency spectrums of all signal components generating
`complex values in a single outgoing stream are centered
`around a common frequency location which is unique to the
`single outgoing stream and wherein the frequency spectrums
`of signal components generating complex values in different 30
`outgoing streams having adjacent common frequency loca(cid:173)
`tions are partially overlapping, and wherein signal compo(cid:173)
`nents generating sequential outgoing vectors partially over(cid:173)
`lap in time, and a complex symbol detector operative to
`receive from the filter the at least first and second synchro- 35
`nized outgoing streams of complex values and to generate
`therefrom at least first and second streams of complex
`symbols.
`Further in accordance with a preferred embodiment of the
`present invention, the complex symbol detector includes an 40
`equalizer operative to receive the at least first and second
`synchronized outgoing streams of complex values and to
`multiply them by at least first and second complex coeffi(cid:173)
`cients respectively, thereby to generate at least first and
`second streams of equalized complex values respectively, 45
`timing and phase circuitry operative to receive the at least
`first and second equalized complex values and to back-rotate
`them by at least first and second estimated angles respec(cid:173)
`tively which compensate for phase and timing offsets intro(cid:173)
`duced by the communication channel, thereby to generate at 50
`least first and second streams of equalized back-rotated
`values respectively, and a slicer operative to receive the at
`least first and second streams of equalized back-rotated
`values and to map them to first and second streams of
`complex symbols respectively.
`Further in accordance with a preferred embodiment of the
`present invention, the system also includes a demapper
`operative to receive from the complex symbol detector at
`least first and second streams of complex symbols, and to
`demap the first and second streams of complex symbols, 60
`thereby to generate an output bit stream.
`Also provided, in accordance with another preferred
`embodiment of the present invention, is subscriber apparatus
`for a cable modem system, the subscriber apparatus includ(cid:173)
`ing an upstream forward error correction (FEC) encoder 65
`receiving an upstream bit stream and generating an encoded
`bit stream, an upstream modulator receiving the encoded
`
`6
`bitstream from the upstream FEC encoder and generating an
`RF output, a diplexer receiving the RF output and feeding
`the RF output onto a cable and receiving an external
`downstream signal from the cable, a downstream demodu-
`lator receiving the downstream external signal from the
`diplexer and generating a downstream bit stream, and a
`MAC controller operative to generate the upstream bit
`stream and supply the upstream bit stream to the FEC
`encoder and to receive the downstream bit stream, wherein
`10 the upstream modulator includes a signal modulation system
`such as that described above and a complex symbol gener(cid:173)
`ating mapper operative to receive an input bit stream and to
`generate therefrom at least first and second synchronized
`incoming streams of complex symbols.
`Further in accordance with a preferred embodiment of the
`present invention, the system also includes an analog RF to
`digital baseband converter operative to receive an input
`analog RF signal, to convert the input analog RF signal to an
`up-sampled digital representation of a baseband signal cor(cid:173)
`responding to the input analog RF signal, and a decimator
`operative to receive and down-sample the up-sampled digi(cid:173)
`tal representation of the baseband signal and to supply the
`down-sampled digital representation of the baseband signal
`to the narrow bandpass overlapping frequency filter array as
`an input signal.
`Also provided, in accordance with still another preferred
`embodiment of the present invention, is headend apparatus
`for a cable modem system, the headend apparatus including
`an upstream demodulator including a signal demodulation
`system according to claim 24 and also including an analog
`RF to digital baseband converter operative to receive an
`input analog RF signal, to convert the input analog RF signal
`to a digital representation of a baseband signal correspond-
`ing to the input analog RF signal and to supply the digital
`representation of the baseband signal to the narrow bandpass
`overlapping frequency filter array as an input signal, a FEC
`decoder receiving an output from the upstream demodulator,
`a MAC controller receiving an output of the FEC decoder,
`and a downstream modulator receiving an output from the
`MAC controller.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`AND APPENDICES
`The present invention will be understood and appreciated
`from the following detailed description, taken in conjunction
`with the drawings in which:
`FIG. 1 is a simplified block d