United States Patent
`Mujtaba
`
`19
`
`US006091781A
`Patent Number:
`Date of Patent:
`
`11
`45)
`
`6,091,781
`Jul.18, 2000
`
`54 SINGLESIDEBANDTRANSMISSION OF
`QPSK, QAMAND OTHER SIGNALS
`75 Inventor: Syed Aon Mujtaba, Berkeley Heights,
`N.J.
`
`73 Assignee: Lucent Technologies Inc., Murray Hill,
`N.J.
`
`21 Appl. No.: 08/970,987
`22 Filed:
`Nov. 14, 1997
`(51) Int. Cl. ............................................... H04L27/18
`52 U.S. Cl. ..................
`375/279; 375/270; 375/321
`58 Field of Search ..................................... 375/270, 279,
`375/321, 280, 308, 260,329, 276,340;
`332/103, 108
`
`56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,241,451 12/1980 Maixner et al. ........................ 455/202
`4,358,853 11/1982 Qureshi ............
`... 375/296
`4,803,700 2/1989 Dewey et al. ...
`... 375/321
`5,699.404 12/1997 Satyamurti.......
`340/311.1
`5,729,575 3/1998 Leitch ..........
`... 375/268
`5,892,774 4/1999 Zehavi et al. ............
`... 370/527
`5,909.434 6/1999 Odenwalder et al. ...
`... 370/342
`5,943,361 8/1999 Gilhousen et al. ..................... 375/200
`OTHER PUBLICATIONS
`T.S. Rappaport, “Wireless Communications: Principles and
`Practice,” Prentice-Hall, NJ, pp. 243-247, 1996.
`A.V. Oppenheim and R.W. Schafer, “Discrete-Time Signal
`Processing.” Prentice-Hall, NJ, pp. 676-688, 1989.
`
`J.G. Proakis and M. Salehi, “Communication Systems Engi
`neering.” Prentice-Hall, NJ, pp. 310-317, 1994.
`R.D. Gitlin et al., “Data Communications Principles.” Ple
`num Press, NY, pp. 305-312 and pp. 322–325, 1992.
`
`Primary Examiner Stephen Chin
`ASSistant Examiner Kevin M Burd
`Attorney, Agent, or Firm-Ryan & Mason, L.L.P.
`57
`ABSTRACT
`Methods, apparatus and System for transmitting Signals in
`QPSK, QAM and other similar modulation formats as single
`sideband (SSB) signals. An exemplary SSB-QPSK trans
`mitter receives an in-phase data Signal and a quadrature
`phase data Signal. The in-phase data Signal and a Hilbert
`transform of the quadrature-phase data Signal are modulated
`onto a cosine carrier Signal, the quadrature-phase data Signal
`and a Hilbert transform of the in-phase data Signal are
`modulated onto a Sine carrier Signal, and the modulated Sine
`and cosine carrier Signals are combined to provide a modu
`lated SSB-QPSK signal. The in-phase and quadrature-phase
`data Signals are time-aligned signals which are interpolated
`prior to modulation So as to include Zero values at alternating
`instants of time. Their corresponding Hilbert transforms
`therefore also exhibit alternating Zero values. During
`modulation, the in-phase data Signal can thus be interleaved
`with Hilbert transforms of the quadrature-phase data Signal,
`and the quadrature-phase data Signal can be interleaved with
`Hilbert transforms of the in-phase data Signal, without any
`interference between the Signals. Coherent quadrature detec
`tion may be used to recover both the in-phase and
`quadrature-phase data Signals at a receiver.
`
`19 Claims, 8 Drawing Sheets
`
`
`
`
`
`
`
`
`
`INTERPOLATE
`WITH ZEROS
`
`INTERPOLATE
`WITH ZEROS
`
`
`
`
`
`
`
`
`
`HILBERT
`FILTER
`
`HILBERT
`FILTER
`
`
`
`
`
`Costut)
`BO
`
`78
`
`PULSE
`SHAPING
`FILTER
`
`Zt)
`
`
`
`PULSE
`SHAPING
`FILTER
`
`84
`
`B2
`
`Sintuit)
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 1 of 14
`
`

`

`U.S. Patent
`
`Jul.18, 2000
`
`Sheet 1 of 8
`
`6,091,781
`
`FIG. 1A
`(PRIOR ART)
`12
`
`
`
`Costult)
`
`PULSE SHAPING
`FILTER g(t)
`
`1N
`
`IN-PHASE
`
`QUADRATURE
`PHASE
`
`PULSE SHAPING
`FILTER g(t)
`
`16
`
`
`
`xn)
`
`30
`
`32
`
`FIG. 1B
`(PRIOR ART)
`
`34
`
`Costut)
`
`PULSE SHAPING
`FILTER g(t)
`
`W(t)
`
`
`
`
`
`HILBERT
`FILTER
`
`PULSE SHAPING
`FILTER g(t)
`
`38
`
`AO
`
`42
`
`Sintuit)
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 2 of 14
`
`

`

`U.S. Patent
`
`Jul.18, 2000
`
`Sheet 2 of 8
`
`6,091,781
`
`FIG. 2A
`
`FIG. 2B
`
`10
`
`OB
`
`O6
`
`O4
`
`O2
`
`xn
`
`O5
`
`H(xn) O
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 3 of 14
`
`

`

`U.S. Patent
`US. Patent
`
`Jul.18, 2000
`Jul. 18,2000
`
`Sheet 3 of 8
`Sheet 3 0f8
`
`6,091,781
`6,091,781
`
`
`
`0.5
`
`
`
`x n
`
`O
`
`FIG. 3B
`FIG. 33
`
`ERICSSON V. UNILOC
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`EX. 1035 / Page 4 of 14
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`

`

`U.S. Patent
`US. Patent
`
`Jul.18, 2000
`Jul. 18,2000
`
`Sheet 4 of 8
`Sheet 4 0f8
`
`6,091,781
`6,091,781
`
`FIG. 4A
`FIG.
`4A
`
`1
`llll'lllll
`
`II
`
`II
`
`lll'lllll
`
`lllll'll'l
`
`0.5
`
` 35
`
`35
`
`40
`AO
`
`H(x[n]}
`
`
`
`FIG. 4B
`
`
`
`ERICSSON V. UNILOC
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`EX. 1035 / Page 5 of 14
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`

`

`U.S. Patent
`
`Jul.18, 2000
`
`Sheet 5 of 8
`
`6,091,781
`
`FIG. 5A
`
`DATA AT MODULATOR INPUT
`
`DATA AT MODULATOR OUTPUT
`
`FIG 5B
`
`DATA AT MODULATOR INPUT
`DATA AT MODULATOR OUTPUT
`I-CANEL annang and nating
`O-CHANNEL;
`.
`.
`Hn+1)
`
`FIG. 5C
`
`DATA AT MODULATOR INPUT
`
`DATA AT MODULATOR OUTPUT
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 6 of 14
`
`

`

`U.S. Patent
`
`Jul.18, 2000
`
`Sheet 6 of 8
`
`6,091,781
`
`FIG. E.
`
`
`
`
`
`
`
`
`
`SO N
`
`
`
`
`
`INTERPOLATE
`WITH ZEROS
`
`
`
`INTERPOLATE
`WITH ZEROS
`
`
`
`HILBERT
`FILTER
`
`HILBERT
`FILTER
`
`
`
`
`
`Costult)
`80
`
`78
`
`PULSE
`SHAPING
`FILTER
`
`Z (t)
`
`PULSE
`SHAPING
`FILTER
`
`84
`
`B2
`
`Sintuit)
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 7 of 14
`
`

`

`U.S. Patent
`US. Patent
`
`Jul.18, 2000
`Jul. 18,2000
`
`Sheet 7 of 8
`Sheet 7 0f8
`
`6,091,781
`6,091,781
`
`
`
`Sinlwct)
`
`s
`FIG.7
`
`/
`80\‘
`
`R
`wit)
`e
`
`ERICSSON V. UNILOC
`
`EX. 1035 / Page 8 of 14
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`ERICSSON v. UNILOC
`Ex. 1035 / Page 8 of 14
`
`

`

`U.S. Patent
`US. Patent
`
`Jul. 18,2000
`
`Sheet 8 0f8
`
`6,091,781
`6,091,781
`
`yln]
`
`x[n]
`
`00E 1155150
`
`143 09E
`144145
`L. lfi% a
`EOUALIZER
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`130
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`FIG8
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`ERICSSON V. UNILOC
`
`EX. 1035 / Page 9 of 14
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 9 of 14
`
`

`

`6,091,781
`
`2
`
`1
`SINGLESIDEBAND TRANSMISSION OF
`QPSK, QAMAND OTHER SIGNALS
`
`FIELD OF THE INVENTION
`The present invention relates generally to communication
`Systems and more particularly to communication Systems
`which utilize quaternary-phase-shift-keying (QPSK),
`quaternary-amplitude modulation (QAM) or other similar
`Signal transmission techniques.
`
`1O
`
`(t) = R-X. (x + iy)g (it - are").
`
`(2)
`
`The complex baseband-equivalent representation of the
`transmitted QPSK signal Z(t) may be defined as:
`
`(3)
`Similarly, the complex baseband-equivalent representation
`of the SSB signal w(t) can be written as:
`
`(4)
`where x(t)=H x(t)} and H is the Hilbert transform operator.
`If the conventional QPSK signal as defined in (3) is trans
`formed into an SSB Signal, the resulting Signal is given by:
`(5)
`It can be seen from (5) that a conventional SSB transfor
`mation of a QPSK Signal results in a catastrophic interfer
`ence between the I and Q components that cannot be
`removed at the receiver. As a result, SSB transmission is
`generally not utilized in QPSK communication Systems.
`Similar problems have prevented the use of SSB transmis
`Sion with other types of Similar modulation techniques,
`including quadrature-amplitude modulation (QAM).
`SUMMARY OF THE INVENTION
`The present invention provides techniques which allow
`signals modulated using QPSK, QAM or other similar
`modulation formats to be transmitted as SSB signals. AS a
`result, the invention provides the benefits of SSB transmis
`sion in communication systems utilizing QPSK, QAM and
`other modulation formats. In an illustrative embodiment of
`the invention, an in-phase data Signal Xn and a Hilbert
`transform H, of a quadrature-phase data signal yn are
`modulated onto a cosine carrier Signal, and the quadrature
`phase data signal yn and a Hilbert transform H of the
`in-phase data signal Xn are modulated onto a sine carrier
`Signal. The Xn and yn Signals are time-aligned signals
`which are interpolated prior to modulation So as to include
`Zero values at alternating instants of time. Their correspond
`ing Hilbert transforms H, and H, therefore also exhibit
`alternating Zero values. This arrangement of alternating
`zeros allows xn] to be interleaved with H, and yn) to be
`interleaved with H, without creating any interference
`between Xn and yn in the modulation process. The
`modulated cosine and Sine carrier Signals are then combined
`to generate a modulated SSB-QPSK signal for transmission.
`The SSB-QPSK signal can be demodulated in a receiver
`which uses coherent quadrature detection to recover both the
`Xn and yn data Signals.
`The modulation techniques of the invention provide Sub
`Stantially the same spectral efficiency as conventional SSB
`and QPSK modulation, but can provide advantages over
`both SSB and QPSK in particular applications. For example,
`in the presence of equalization imperfections on Rayleigh
`faded mobile radio channels, the SSB-QPSK modulation of
`the invention can provide better bit error rate (BER) per
`formance than conventional SSB or QPSK modulation.
`
`15
`
`25
`
`35
`
`BACKGROUND OF THE INVENTION
`Modulation techniques based on QPSK are commonly
`used in cellular, personal communication Service (PCS) and
`other types of wireless communication Systems. For
`example, QPSK and offset QPSK (OQPSK) are used in
`digital wireleSS Systems configured in accordance with the
`IS-95 standard as described in TIA/EIA/IS-95, “Mobile
`Station - Base Station Compatibility Standard for Dual
`Mode Wideband Spread Spectrum Cellular System,” June
`1996. Other wireless system standards, including IS-54,
`IS-136 and GSM, also make use of QPSK or a variant
`thereof. FIG. 1A shows a conventional QPSK modulator 10.
`An in-phase (I) Signal Xn is passed through a pulse-shaping
`filter 12, and the output of filter 12 is modulated onto a
`cosine carrier Signal cos(cot) in mixer 14. A quadrature
`phase (Q) Signal yn is passed through a pulse-shaping filter
`16, and the output of filter 16 is modulated onto a sine carrier
`Signal sin(ot) in mixer 18. The I and Q radio frequency
`(RF) signals from mixers 14 and 18 are supplied as inputs to
`a signal combiner 20. The signal combiner 20 combines the
`I and QRF signals to forman output QPSK signal Z(t) which
`may be transmitted over a communication channel to a
`receiver. QPSK modulation thus involves transmitting inde
`pendent signals on the I and Q components of the Signal Z(t).
`Single sideband (SSB) modulation is a modulation tech
`nique that has historically received considerably more atten
`tion for analog rather than digital transmission applications,
`and is described in greater detailin, for example, W. E. Sabin
`40
`and E. O. Schoenike (Eds.) “Single Sideband Systems &
`Circuits,” 2nd Edition, McGraw-Hill, New York, 1995. FIG.
`1B shows a conventional discrete-time SSB modulator 30.
`An in-phase signal xn is passed through a delay element 32
`and a pulse-shaping filter 34, and the output of filter 34 is
`45
`modulated onto cos(cot) in mixer 36. Unlike QPSK
`modulation, which as described above transmits indepen
`dent signals xn and yn in its respective I and Q
`components, SSB modulation transmits Xn in the I com
`ponent and the Hilbert transform of xn in the Q compo
`50
`nent. The Q component in SSB modulator 30 is therefore
`generated by passing Xn through a Hilbert filter 38 and a
`pulse-shaping filter 40, and modulating the output of filter 40
`onto Sin(cot) in mixer 42. A signal combiner 44 combines
`the I and Q RF signals from mixers 36 and 42 to generate an
`SSB signal w(t) for transmission. While SSB modulation
`transmits half the number of bits as QPSK modulation, it
`also utilizes half the bandwidth, Such that SSB and QPSK
`modulation have the same Spectral efficiency.
`A conventional QPSK Signal generally cannot be trans
`mitted as an SSB signal. For example, the QPSK signal Z(t)
`generated by QPSK modulator 10 may be expressed as:
`
`55
`
`60
`
`Given that xn, yne{i+1} for QPSK signaling, the trans
`mitted signal Z(t) can be written as:
`
`65
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1A shows a conventional QPSK modulator.
`FIG. 1B shows a conventional discrete-time SSB modul
`lator.
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 10 of 14
`
`

`

`6,091,781
`
`3
`FIGS. 2A and 2B show an impulse function and its Hilbert
`transform, respectively.
`FIGS. 3A and 3B show an impulse train and its Hilbert
`transform, respectively.
`FIGS. 4A and 4B show a zero-interpolated impulse train
`and its Hilbert transform, respectively.
`FIGS. 5A, 5B and 5C compare modulation formats for
`conventional QPSK, conventional SSB, and SSB-QPSK in
`accordance with an illustrative embodiment of the invention.
`FIG. 6 shows an exemplary SSB-QPSK transmitter in
`accordance with the invention.
`FIG. 7 shows a dual-branch SSB receiver in accordance
`with the invention.
`FIG. 8 shows an SSB-QPSK receiver in accordance with
`the invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`The invention will be illustrated below in conjunction
`with an exemplary communication System utilizing Single
`sideband (SSB) quaternary-phase-shift-keying (QPSK)
`modulation. It should be understood, however, that the
`invention is not limited to use with any particular type of
`communication System or modulation format, but is instead
`more generally applicable to any System in which it is
`desirable to transmit signals modulated using QPSK,
`quaternary-amplitude modulation (QAM) or other similar
`modulation techniques in an SSB format. For example, the
`invention may be used in a variety of wireleSS communica
`tion Systems, including Systems configured in accordance
`with the IS-54, IS-95, IS-136 and GSM standards. Addi
`tional details regarding these and other communication
`systems in which the invention may be utilized can be found
`in, for example, T. S. Rappaport, “WireleSS Communica
`tions: Principles and Practice,” Prentice-Hall, N.J., 1996,
`which is incorporated by reference herein.
`The invention provides techniques which enable signals
`modulated in QPSK, QAM and other similar modulation
`formats to be transmitted as SSB Signals. As a result, the
`invention provides the benefits of SSB transmission in
`communication systems utilizing QPSK, QAM and other
`Similar modulation formats. In order to illustrate the opera
`tion of the invention, the discrete Hilbert transform will first
`be described in greater detail. An ideal Hilbert transformer
`may be considered an all-pass filter that rotates an input
`signal by 90 degrees. The frequency response of the ideal
`Hilbert transformer is therefore given by:
`
`15
`
`25
`
`35
`
`40
`
`45
`
`4
`given application. Certain windowing techniques can also be
`used to further reduce the number of taps. These and other
`details regarding Hilbert transformers are described in, for
`example, A. V. Oppenheim and R. W. Schafer, “Discrete
`Time Signal Processing.” Prentice-Hall, N.J., 1989, which is
`incorporated by reference herein.
`The ideal Hilbert transformer characterized above may be
`made causal by introducing a delay of n=(N-1)/2, assuming
`that N is odd. The resulting impulse response is given by:
`
`2sin (t(n - na)/2)
`7t(n - ind)
`
`it if it
`d
`
`(8)
`
`Due to the JL/2 term appearing in the argument of the Sin
`function in (8), the impulse response hn goes to Zero every
`other time instant, i.e., hn is Zero for n=n, n=n-t2, n=nit4
`and So on. By way of example, FIG. 2A shows an impulse
`function xn and FIG. 2B shows the corresponding impulse
`response hn=H {xn} of the Hilbert transformer for n=9.
`It can be seen from FIG.2B that the impulse response hn
`goes to Zero for values of n=1, 3, 5, 7, 9, 11 and So on.
`If the input to a causal Hilbert transformer is a train of
`impulse functions, such as that shown in FIG. 3A, then the
`alternating Zeros do not appear in the corresponding Hilbert
`transform H{xn}, as shown in FIG. 3B. The train of
`impulse functions in FIG.3A may be expressed as Xö(n-k).
`The corresponding Hilbert transform in FIG. 3B is given by:
`
`X. k
`
`2sin it(n - ind - k)/2)
`7(n - ind - k)
`
`(9)
`
`It can be seen from (9) that, since the index k increments by
`1 during the Summation process, only half of the terms
`contributing to the final sum will be zero. Therefore, for any
`value of n, the Sum would not be Zero, and the alternating
`Zeros illustrated in conjunction with FIG. 2B would there
`fore not appear in the Hilbert transform. This provides an
`illustration of why a QPSK signal cannot be transformed
`into an SSB signal using conventional techniques. More
`particularly, if the signal Xn modulates the cosine carrier
`and its Hilbert transform modulates the Sine carrier, as in the
`conventional SSB modulator 30 of FIG. 1B, modulating the
`QPSK quadrature-phase signal yn on the Sine carrier
`would lead to catastrophic interference with the Hilbert
`transform, as was previously described.
`The invention allows a QPSK signal to be transmitted as
`an SSB signal by recovering the alternating ZeroS in the
`Hilbert transform of in-phase signal Xn, and interleaving
`the quadrature-phase signalyn into Hilbert transform at the
`locations of the alternating Zeros. In other words, in accor
`dance with the invention, the quadrature-phase signal yn
`can be inserted in locations where the Hilbert transform of
`Xn is Zero. For example, if Xn is an impulse train
`containing alternating Zeros as shown in FIG. 4A, Xn can
`be expressed as X6(n-2k), and the corresponding Hilbert
`transform illustrated in FIG. 4B is then given by:
`X. k
`
`2sin it(n - ind -2k)/2)
`7(n - ind - 2k)
`
`(10)
`
`-i 0 < cost
`H(co) = 0 () = 0
`i -it g (0 < 0
`
`50
`
`(6)
`
`The resulting impulse response of the ideal Hilbert trans
`former is then given by:
`
`55
`
`hn =
`
`O
`
`7. st
`
`in th: 0
`
`n = 0
`
`(7)
`
`60
`
`As can be seen from (7), the impulse response of the Hilbert
`transformer is non-causal and infinite in duration. In prac
`tical applications, the Hilbert transformer includes a finite
`number N of filter taps, where N is selected based on the
`degree of SSB Suppression that needs to be achieved in a
`
`65
`
`In the Summation (10), if n-n is even, then the argument of
`the Sin function will remain even over the entire Summation
`process and a Zero Sum would be obtained, as can be seen
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 11 of 14
`
`

`

`25
`
`S
`from FIG. 4B. If the signal x n appears as a delta function
`at nd, i.e., xn]=(n-n), then the value of the Hilbert trans
`form at n=n, would be Zero. Similarly, when Xn=ö(n-n-
`2), the value of the Hilbert transform at n=n-2 would be
`Zero. Thus, wherever xn is non-zero, its Hilbert transform
`at that corresponding instant is Zero and Vice-versa. If yn
`can be generated Such that it is Zero at alternating instants in
`time, then its Hilbert transform would also exhibit alternat
`ing Zeros.
`An illustrative embodiment of the invention thus gener
`ates two signals xn and yn which have a value of Zero at
`alternating instants of time, Such that their Hilbert trans
`forms also exhibit alternating Zeros. If the non-Zero Values
`of Xn and yn are time aligned, then the non-zero values
`of their respective Hilbert transforms are also time aligned.
`As described in conjunction with FIG. 1A, conventional
`QPSK modulation generally transmits xn on the cosine
`carrier and yn on the Sine carrier. A QPSK Signal can be
`transmitted as an SSB signal in accordance with the illus
`trative embodiment of the invention by transmitting the
`Hilbert transform ofxn), designated H., on the Sine carrier,
`and the Hilbert transform ofyn), designated H., on the
`cosine carrier. Thus, if xn] and yn are time aligned, H, will
`interleave with xn without any interference and Similarly
`H will interleave with yn without any interference. These
`and other techniqueS of transmitting a QPSK Signal in an
`SSB format in accordance with the invention will be gen
`erally referred to herein as SSB-QPSK modulation.
`FIGS. 5A, 5B and 5C compare transmission formats for
`conventional QPSK modulation (FIG.5A) and conventional
`SSB modulation (FIG. 5B) with SSB-QPSK modulation in
`accordance with the invention (FIG.5C). It is assumed that
`the transmission bandwidth is the same for each of the three
`transmission formats. In the case of conventional QPSK
`transmission, signal data introduced in the I-channel (i.e.,
`35
`Xn, xn+1), .
`.
`. ) and signal data introduced in the
`Q-channel (i.e., yn, yn+1, ...) are modulated by a QPSK
`modulator onto respective cosine and Sine carriers after
`pulse shaping, as illustrated in FIG. 5A. In the case of
`conventional SSB transmission, Signal data is introduced
`only in the I-channel (i.e., xn, xn+1), . . .), and the SSB
`modulator extracts the Signal data for the Q-channel by
`generating Hilbert transforms (i.e., Han, Hn+1), . . . ) of
`the I-channel data, as illustrated in FIG. 5B.
`In the case of SSB-QPSK modulation, signal data is
`introduced in both the I-channel and the Q-channel as shown
`in FIG. 5C. An SSB-QPSK modulator, to be described in
`greater detail below, interpolates between the introduced
`data with Zeros, and then extracts the Hilbert transforms,
`Such that the introduced data and the corresponding Hilbert
`transforms are arranged as shown for transmission. The
`I-channel in the SSB-QPSK transmission format includes
`the data introduced in the I-channel (i.e., xn, xn+1), . . . )
`interleaved with the Hilbert transforms (i.e., H.,n),
`Hn+1),...) of the data introduced in the Q-channel (i.e.,
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`yn), yn+1), .
`. ). Similarly, the Q-channel in the SSB
`QPSK transmission format includes the data introduced in
`the Q-channel interleaved with the Hilbert transforms (i.e.,
`Hn, Hn+1), . . . ) of the I-channel data.
`FIG. 6 shows an exemplary SSB-QPSK transmitter 60
`which implements the above-described illustrative embodi
`ment of the invention. The transmitter 60 includes interpo
`lation devices 62 and 64 for interpolating with zeros
`between the introduced data of the input signals xn and
`yn, respectively. The interpolated Signal Xn is separated
`into two parts. One part is delayed in a delay element 66, and
`the other part is Hilbert transformed in a Hilbert filter 68.
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`The delayed version of xn from delay element 66 is applied
`to a signal combiner 70, and the Hilbert transform of xn is
`applied to another signal combiner 72. The delay of delay
`element 66 is selected to match the delay introduced by the
`Hilbert filter 68.
`The interpolated Signal yn is similarly processed using
`a Hilbert filter 74 and a delay element 76, with the Hilbert
`transform of yn applied to signal combiner 70, and the
`delayed version ofyn applied to a signal combiner 70. The
`delay in delay element 76 is selected to match the delay
`introduced by the Hilbert filter 74. The signal combiner 70
`thus sums the Hilbert transform of yn with the delayed
`version of xn), and the signal combiner 72 Sums the Hilbert
`transform of xn with the delayed version ofyn, to produce
`I-channel and Q-channel data Signals Similar to those shown
`in FIG. 5C. The summation operations performed by signal
`combiners 70 and 72 in FIG. 6 may thus be viewed as
`time-interleaving operations. The I-channel data Signal is
`then pulse shaped in a filter 78 and the pulse-shaped signal
`is modulated on a cosine carrier Signal cos(cot) in a mixer
`80. Similarly, the Q-channel data Signal is pulse shaped in a
`filter 82 and modulated on a sine carrier signal sin(ot) in a
`mixer 84. The I-channel and Q-channel RF signals from
`mixers 80 and 84 are combined in a signal combiner 86 to
`generate an SSB-QPSK signal Z(t) in accordance with the
`invention.
`The operation of an SSB-QPSK receiver in accordance
`with the invention will be described below in conjunction
`with FIGS. 7 and 8. A conventional single-branch SSB
`receiver implementing a coherent analog demodulation pro
`ceSS mixes a received SSB Signal with a locally-generated
`cosine carrier, and then low pass filters the result to recover
`X(t). Information arriving on the sine term of the SSB signal
`is usually ignored. FIG. 7 shows a dual-branch SSB receiver
`90 in which a received SSB signal w(t) is quadrature
`demodulated in accordance with the invention to recover
`information from both the cosine and Sine terms of the SSB
`Signal. The I-channel information arriving on the cosine
`term of the SSB signal w(t) is coherently demodulated by
`mixing w(t) with cos(cot) in mixer 92, and low pass filtering
`the result in low pass filter (LPF) 94. The output of the LPF
`94 is converted to a digital signal in analog-to-digital (A/D)
`converter 96, and the digital Signal is passed through a
`matched filter (MF) 98 and then applied to an input of a
`signal combiner 100. The Q-channel information arriving on
`the sine term of the SSB signal w(t) is coherently demodu
`lated by mixing w(t) with sin(cot) in mixer 102, and low
`pass filtering the result in LPF 104. The output of the LPF
`104 is converted to a digital signal in AID converter 106, and
`the digital signal is passed through an MF 108. The output
`of the MF 108 is then Hilbert transformed in a Hilbert filter
`(HF) 110.
`From equation (4) above it can be seen that the Q-channel
`information on the sine term of the SSB signal corresponds
`generally to X=H {x}. In order to obtain X from H {x}, the
`receiver 90 makes use of the property of the Hilbert trans
`form that H{H {x}} =-X. Therefore, the output of HF 110,
`which corresponds to H{H{x}} or -X, is inverted by mul
`tiplying it with -1 in multiplier 112, so as to obtain X. The
`output of multiplier 112 is summed with the output of MF 98
`in signal combiner 100, and the result is thresholded in a
`threshold device 114 to recover xn). Since the signals
`applied to signal combiner 100 add coherently while the
`noise adds incoherently, the Signal-to-noise ratio is effec
`tively doubled after the summation in signal combiner 100.
`The receiver 90 thus delivers substantially the same bit error
`rate (BER) performance as a conventional QPSK receiver. In
`
`ERICSSON v. UNILOC
`Ex. 1035 / Page 12 of 14
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`contrast, the BER performance of the above-noted conven
`tional single-branch SSB receiver is approximately 3 dB
`worse than that of either the dual-branch SSB receiver 90 or
`the conventional QPSK receiver.
`FIG. 8 shows an SSB-OPSK receiver 120 in accordance
`with an illustrative embodiment of the invention. The SSB
`OPSK receiver 120 demodulates the above-described SSB
`QPSK Signal using the dual-branch quadrature demodula
`tion techniques illustrated in FIG. 7. An incoming SSB
`QPSK signal is quadrature demodulated, with mixer 122,
`LPF 124, A/D converter 126 and MF 128 used to recover the
`I-channel information on the cosine carrier, and mixer 132,
`LPF 134, A/D converter 136 and MF 138 used to recover the
`Q-channel information on the Sine carrier. The outputs of the
`MFs 128 and 138 are applied to an equalizer 130 which
`removes intersymbol interference (ISI) which may have
`been introduced in the transmission channel. The resulting
`output signals are converted from Serial to parallel form in
`serial-to-parallel (S/P) converters 140 and 150. The cosine
`demodulated I-channel signal at the output of S/P converter
`140 corresponds to a real signal, while the Sine-demodulated
`Q-channel signal at the output of S/P converter 150 corre
`sponds to an imaginary Signal. The real Signal from S/P
`converter 140 is split into an xn] data part and an H, Hilbert
`transform part. Similarly, the imaginary Signal from S/P
`converter 150 is split into ayn data part and an H. Hilbert
`transform part. This composition of the I-channel and
`Q-channel Signals was described above in conjunction with
`FIG. 5C. The H, Hilbert transform part from S/P converter
`140 is processed through Hilbert filter 142 and multiplier
`144 in the manner described in conjunction with FIG. 7, and
`then combined in signal combiner 146 with the yn data part
`from S/P converter 150. The resulting combined signal is
`thresholded in threshold device 148 to yield the output
`signalyn). Similarly, the H. Hilbert transform part from S/P
`converter 150 is processed through Hilbert filter 152 and
`multiplier 154, combined in signal combiner 156 with the
`Xn data part from S/P converter 140, and the resulting
`combined signal is thresholded in threshold device 160 to
`yield the output signal xn.
`The SSB-QPSK modulation techniques of the invention
`provide Substantially the Same spectral efficiency as con
`ventional SSB and QPSK modulation, but can provide
`advantages over both SSB and QPSK in particular applica
`tions. For example, in the presence of equalization imper
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`fections on Rayleigh-faded mobile radio channels, the SSB
`QPSK modulation of the invention can provide better BER
`performance than conventional SSB or QPSK modulation.
`The above-described embodiments of the invention are
`intended to be illustrative only. Numerous alternative
`embodiments within the scope of the following claims will
`be apparent to those skilled in the art.
`What is claimed is:
`1. A method of generating a modulated Single Sideband
`Signal for transmission in a communication System, the
`method comprising the Steps of
`modulating an in-phase data Signal and a Hilbert trans
`form of a quadrature-phase data Signal onto a first
`carrier Signal; and
`modulating the quadrature-phase data Signal and a Hilbert
`transform of the in-phase data Signal onto a Second
`carrier Signal, Such that the modulated first and Second
`carrier Signals when combined provide the modulated
`Single Sideband Signal.
`2. The method of claim 1 wherein the modulated single
`Sideband Signal is a Single Sideband quaternary-phase-shift
`keying (QPSK) signal.
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`3. The method of claim 1 wherein the step of modulating
`an in-phase data Signal and a transform of a quadrature
`phase data Signal onto a first carrier Signal further includes
`modulating an interpolated in-phase data Signal and a Hil
`bert transform of an interpolated quadrature-phase data
`Signal onto a cosine carrier Signal.
`4. The method of claim 1 wherein the step of modulating
`the quadrature-phase data Signal and a transform of the
`in-phase data Signal onto a Second carrier Signal further
`includes modulating an interpolated quadrature-phase data
`Signal and a Hilbert transform of an interpolated in-phase
`data Signal onto a Sine carrier Signal.
`5. The method of claim 1 wherein the in-phase and the
`quadrature-phase data Signals are time-aligned Signals.
`6. The method of claim 1 wherein the step of modulating
`an in-phase data Signal and a transform of a quadrature
`phase data Signal onto a first carrier Signal further includes
`time interleaving portions of the in-phase data Signal with
`Hilbert transforms of portions of the quadrature-phase data
`Signal.
`7. The method of claim 1 wherein the step of modulating
`the quadrature-phase data Signal and a transform of the
`in-phase data Signal onto a Second carrier Signal further
`includes time interleaving portions of the quadrature-phase
`data signal with Hilbert transforms of portions of the
`in-phase data Signal.
`8. The method of claim 1 wherein the in-phase and the
`quadrature-phase signals are interpolated So as to include
`Zero values at alternating instants of time, Such that their
`corresponding Hilbert transforms also exhibit alternating
`Zero values.
`9. An apparatus for of generating a modulated Single
`Sideband Signal for transmission in a communication
`System, the apparatus comprising:
`an in-phase channel operative to modulate an in-phase
`data Signal and a Hilbert transform of a quadrature
`phase data Signal onto a first carrier Signal; and
`a quadrature-phase channel operative to modulate the
`quadrature-phase data Signal and a Hilbert transform of
`the in-phase data Signal onto a Second carrier Signal,
`Such that the modulated first and Second carrier Signals
`when combined provide the modulated Single Sideband
`Signal.
`10. The apparatus of claim 9 wherein the modulated
`Single Sideband Signal is a single Sideband quaternary-phase
`shift-keying (QPSK) signal.
`11. The apparatus of claim 9 wherein the in-phase channel
`is further operative to modulate an interpolated in-phase data
`Signal and a Hilbert transform of an interpolated quadrature
`phase data Signal onto a cosine carrier Signal.
`12. The apparatus of claim 9 wherein the quadrature
`phase channel is further operative to modulate an interpo
`lated quadrature-phase data Signal and a Hilbert transform of
`an interpolated in-phase data Signal onto a Sine carrier
`Signal.
`13. The apparatus of claim 9 wherein the in-phase and the
`quadrature-phase data Signals are time-aligned Signals.
`14. The apparatus of claim 9 wherein the in-phase channel
`is further operative to time-interleave portions of the
`in-phase data Signal with Hilbert transforms of portions of
`the quadrature-phase data Signal.
`15. The