WO1985004541A1 - Systeme de communication a bande laterale simple - Google Patents

Systeme de communication a bande laterale simple Download PDF

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Publication number
WO1985004541A1
WO1985004541A1 PCT/US1985/000302 US8500302W WO8504541A1 WO 1985004541 A1 WO1985004541 A1 WO 1985004541A1 US 8500302 W US8500302 W US 8500302W WO 8504541 A1 WO8504541 A1 WO 8504541A1
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WO
WIPO (PCT)
Prior art keywords
elements
data signal
signal
sideband
carriers
Prior art date
Application number
PCT/US1985/000302
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English (en)
Inventor
Peter Dimitrios Karabinis
Original Assignee
American Telephone & Telegraph Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by American Telephone & Telegraph Company filed Critical American Telephone & Telegraph Company
Publication of WO1985004541A1 publication Critical patent/WO1985004541A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/02—Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation

Definitions

  • the present invention relates to a digital communications system which transmits a single-sideband signal comprising modulated quadrature-related carriers.
  • Digital communication systems utilize a myriad of modulation formats.
  • elements of a data signal modulate quadrature-related carrier signals.
  • This type of modulation has a variety of names, such as phase shift keying (PSK), quadrature amplitude modulation (QAM), and asynchronous phase shift keying (APSK).
  • PSK phase shift keying
  • QAM quadrature amplitude modulation
  • APSK asynchronous phase shift keying
  • the information conveyed by the data signal is, of course, virtually limitless and can include voice, video, facsimile and the like.
  • the transmission channel carrying the modulated carriers is also not limited and, at present, may include air, wire or lightguide.
  • a problem in practically all communications systems is that the transmission channel is band-limited. That is, there is a finite frequency interval which can be used to convey information. This limitation arises because of system and/or device requirements. While the severity of this problem does vary from system to system, it still can be said that the ability to convey still more information in a given frequency interval would be highly desirable.
  • One technique to increase the information- carrying capacity of a digital system transmitting modulated quadrature-related carriers is to increase the number of permissible modulation states.
  • An example of this technique is exemplified by the design and deployment of 64 QAM systems in lieu of 16 QAM systems in applications requiring greater capacity.
  • the problem with this technique is that the change in the number of modulation states requires at least the design and development of new modulators and demodulators. This effort is often expensive and the resulting equipment, at times, can not be retrofitted into operational systems without great expense.
  • Another technique to increase system capacity has been to utilize single-sideband signals instead of double- sideband signals. This technique is rather simple to implement and has been- routinely used in formats which modulate a single carrier signal. Unfortunately, this technique has not been used for systems utilizing quadrature-related carriers because there was no known way of intelligently decoding the received signal after single- sidebanding. Summary of the invention
  • the present invention is intended for use in digital communications systems wherein elements of a data signal modulate quadrature-related carrier signals. To reduce the required bandwidth, the resulting modulated quadrature-related carriers are transformed into a single- sideband signal. After propagation through the transmission channel, the received single-sideband signal is demodulated into received signal elements. Each of these elements includes an element of the data signal along with a spurious signal introduced by the single-sideband transformation. To recover the data signal elements, each received signal element is altered to form at least one estimate of the corresponding data signal element. Each estimate formed is then compared against a set of permissible data signal element values and the estimate is outputted if a preselected criterion is met.
  • a feature of the present invention is that it can be implemented within existing digital communications systems to provide a substantial increase in information- carrying capacity within some preselected bandwidth.
  • a further feature of the present invention is that it can be used with conventional demodulation and equalization techniques.
  • FIG. 1 is a block schematic diagram of a communications system which incorporates the present invention
  • FIG. 2 is a plot of the signal space diagram of the signal levels transmitted by the communications system of FIG. 1;
  • FIG. 3 is a detailed schematic diagram of decoders 118 or 119 shown in the communications system of FIG. 1.
  • FIG. 1 shows an exemplary QAM communications system which incorporates the present invention.
  • a digital data signal on lead 120 is coupled to QAM modulator 101.
  • serial-to-parallel converter 121 spreads successive data signals on lead 120 over four paths 131,132,133, and 134.
  • Digital-to-analog (D/A) converter 122 quantizes the signals appearing on leads 131 and 132 into a number of signal voltages which appear on lead 135.
  • D/A converter 132 quantizes the signals on leads 133 and 134 into a number of signal voltages which are coupled to lead 136.
  • Multipliers 127 and 128 receive the signal voltages on leads 135 and 136 after they are respectively smoothed by Nyquist filters 124 and 125. " Multiplier 127 modulates the amplitude of a carrier signal generated by oscillator 126 with the signals on lead 135 after filtering. In similar fashion, multiplier 128 modulates the amplitude of a second carrier signal with the signals on lead 136 after smoothing by Nyquist filter 125. The second carrier signal supplied to multiplier 128 is generated by shifting the carrier signal generated by oscillator 126 by minus tt / 2 radians via phase shifter 129.
  • the pair of carrier signals supplied to multipliers 127 and 128 are in spatial quadrature to one another and the products provided by multipliers 128 and 129 are each double-sideband signals.
  • Summer 130 then adds the products provided by multipliers 128 and 129 and outputs this sum, also a double-sideband signal onto lead 102.
  • these components modulate quadrature-related carriers with elements of a data signal, wherein one element of the data signal comprises the signals appearing on leads 131,132 or 135 or 137 while the other data signal element comprises the signals appearing on leads 133,134 or 136 or 138.
  • one element of the data signal comprises the signals appearing on leads 131,132 or 135 or 137 while the other data signal element comprises the signals appearing on leads 133,134 or 136 or 138.
  • D/A converters 122 and 123 we can graphically depict all of the possible combinations of transmitted carrier signal amplitudes which represent the data signal on a cartesian coordinate plot. Such a plot is commonly referred to as a signal space diagram.
  • FIG. 2 shows the signal space diagram for the illustrative transmitter of FIG. 1.
  • the data signal element appearing on lead 137 is designated as the "I” or in-phase element of the data signal while the data signal element appearing on lead 138 is referred to as the "Q" or quadrature element.
  • the permissible values of the "I” and “Q” elements are I and +3 volts and all possible combinations of these permissible values form 16 signal states, designated as 201 , in FIG. 2.
  • the output of summer 130 is coupled to a transmission channel which propagates the information to system receiver 11.
  • a filter 103 is added to the transmitter to convert the double-sideband signal at the output of summer 130 into a single-sideband signal thereby reducing the bandwidth required for signal transmission.
  • This bandwidth reduction also permits the transmission of a second single-sideband QAM signal in the recovered frequency interval.
  • the resulting capacity of two 16 QAM single-sideband signals is equivalent to that of a 256 QAM double-sideband signal.
  • the double-sideband to single-sideband signal conversion corrupts the operation of conventional QAM receiver circuitry and additional functional capability is required in the receiver to intelligently recover the data signal elements.
  • the present invention is also applicable to radio systems wherein additional circuitry is often disposed between summer 130 and the transmission channel to shift the frequency of the transmitted carriers to a higher frequency band.
  • the present invention is not limited to QAM systems and, indeed, may be utilized in any system which transmits a signal comprising modulated quadrature-related carriers which are modulated in phase or amplitude or some combination of phase and amplitude.
  • equation (2) can be rewritten as:
  • Equation (5) where i(t) and q(t) are the Hilbert transforms of i(t) and q(t), respectively.
  • equation (5) A comparison of equation (5) with equation (1) reveals that the effect of eliminating one of the sidebands of the QAM signal of equation (1) contaminates i(t) with the Hilbert transform of g(t) and contaminates q(t) with the Hilbert transform of i(t) . Consequently, the receiver of FIG. 1 must be provided with the capability of eliminating q(t) and i(t) to respectively recover the i(t) and q(t) components.
  • transmission channel 105 is dispersive and introduces distortion comprising intersymbol interference (ISI), cross-rail interference (X-rail ISI) and Gaussian noise (n(t)).
  • ISI intersymbol interference
  • X-rail ISI cross-rail interference
  • n(t) Gaussian noise
  • s(t) ss _ is coupled through a conventional QAM demodulator 107, two received data elements i'(t) and q'(t) are formed on leads 110 and 111.
  • the generation of i'(t) and q'(t) is accomplished by extracting the quadrature-related carriers from the received signal using well-known carrier recovery techniques.
  • the ISI and X-rail ISI in equations (6) and (7) can be eliminated by coupling i'(t) and q'(t) through conventional transversal equalizers 112 and 113 which are configured to operate on i'(t) and q'(t) as if
  • n_i-t,.(kT) and ny.-t.-tkT represent the Gaussian noise in the received signal components after equalization.
  • Sampler 114 is controlled by a timing signal on lead 108 which is supplied by conventional timing recovery circuitry (not shown) in the receiver.
  • the Hilbert transform of i(t) at the k sampling time is a function of q(t) at the (k-1) and (k+1) sampling times wherein the (k-1 ) and (k+1 ) sampling times are respectively one sampling time immediately preceding and one sampling time immediately succeeding the k sampling time.
  • the Hilbert transform of q(t) at the kth sampling time is a function of i(t) at the (k-1) and (k+1) sampling times wherein the (k-1) and (k+1) sampling times are respectively one sampling time immediately preceding and one sampling time immediately succeeding the k sampling time.
  • Each summer forms one of these estimates by subtracting a different one of the seven possible values of q(t) from i E (kT) .
  • Each of leads 321-327 supplies a different value of *(t) from a source of reference voltages (not shown).
  • Selection circuit 318 comprising multiple threshold detectors, compares each estimate against the permissible values of i(t), namely, + 1 and +_ 3 volts, and selects the estimate of i(kT) which is closest to any of the permissible values. This selected estimate is outputted on lead 150.
  • Decoder 119 performs an identical operation on each sample q E (kT), with the estimate of q(kT) closest to one of the permissible values of q(t) being outputted on lead 151 in FIG. 1.
  • leads 150 and 151 couples the selected estimates of i(t) and q(t) to timing recovery and other receiver circuitry for further signal processing not connected with the present invention.
  • ambiguities i.e., there are two or more estimates formed which are equally close to different permissible data element values.
  • This problem can be avoided by using one set of values for i(t) and a different set of values for q(t). For example, for the illustrative 16 QAM signal constellation shown in FIG. 2, values of i(t) equal to +_ 1 and +_ 3 volts and the values of q(t) equal to + 1.5 and + 4.5 volts provide signal states 201 ' which circumvent the aforesaid ambiguity problem.
  • decoders 118 and 119 comprise circuitry which simultaneously provides seven possible estimates of i(t) and q(t) using parallel signal processing
  • the decoders could comprise only one adder which sequentially forms seven estimates of i(t) or q(t).
  • selection circuit 318 compares each estimate against the permissible values of a data element and any estimate which falls within a predetermined interval surrounding each permissible value would be outputted. Upon selecting an estimate, selector circuit 318 would inhibit the outputting of any other estimate until the next sample is received from sampler 114.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

Procédé de réduction de la largeur de bande à utiliser dans des systèmes numériques où des éléments de signal de donnée modulent des porteurs apparentés à la quadrature. Cette modulation, appelée modulation d'amplitude de quadrature (QAM) ou manipulation de déphasage (TSQ), produit un signal de bande latérale double qui est transmis dans une multitude de systèmes de communication. Conformément avec la présente invention, le signal de bande latérale double décrit ci-dessus est filtré (103) pour former un signal de bande latérale simple avant la transmission. Alors que cette utilisation d'un signal de bande latérale simple, en lieu et place d'un signal de bande latérale double, double effectivement la capacité du système en permettant l'utilisation de deux systèmes de communication dans la largeur de bande occupée auparavant par un système, le procédé de filtrage (103) contamine les éléments du signal de données. Afin de récupérer les éléments du signal de données au récepteur, des éléments du signal reçu sont formés par extraction des signaux porteurs (107). Ensuite, ces éléments du signal reçu sont modifiés par des quantités présélectionnées pour former des évaluations de chaque élément du signal de données (301, 302 ... 307). La comparaison des évaluations formées (318) par rapport à l'ensemble des valeurs permises pour chaque élément du signal de données détermine ensuite quelle évaluation est correcte.
PCT/US1985/000302 1984-03-28 1985-02-21 Systeme de communication a bande laterale simple WO1985004541A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US59411784A 1984-03-28 1984-03-28
US594,117 1984-03-28

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0617531A1 (fr) * 1993-03-25 1994-09-28 Matsushita Electric Industrial Co., Ltd. Système de transmission multirésolution
WO1997001894A1 (fr) * 1995-06-28 1997-01-16 Deutsche Telekom Ag Procede et circuit de modulation pour transmettre des signaux de donnees
US6256357B1 (en) 1992-03-26 2001-07-03 Matsushita Electric Industrial Co., Ltd. Communication system
US6549716B1 (en) 1992-03-26 2003-04-15 Matsushita Electric Industrial Co., Ltd. Communication system
USRE38483E1 (en) 1992-03-26 2004-03-30 Matsushita Electric Industrial Co., Ltd. Communication system
US6724976B2 (en) 1992-03-26 2004-04-20 Matsushita Electric Industrial Co., Ltd. Communication system
US6728467B2 (en) 1992-03-26 2004-04-27 Matsushita Electric Industrial Co., Ltd. Communication system
USRE42643E1 (en) 1991-03-27 2011-08-23 Panasonic Corporation Communication system
USRE43093E1 (en) 1992-03-26 2012-01-10 Panasonic Corporation Communication system

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3443229A (en) * 1966-04-13 1969-05-06 Bell Telephone Labor Inc Quadrature-carrier vestigial-sideband data transmission
US3522537A (en) * 1966-07-25 1970-08-04 Western Union Telegraph Co Vestigial sideband transmission system having two channels in quadrature
US3605017A (en) * 1969-06-06 1971-09-14 Eg & G Inc Single sideband data transmission system
US3849730A (en) * 1973-06-20 1974-11-19 Bell Telephone Labor Inc Carrier recovery in vestigial sideband data receivers
US4439863A (en) * 1980-11-28 1984-03-27 Rockwell International Corporation Partial response system with simplified detection
US4461011A (en) * 1979-04-30 1984-07-17 Gte Network Systems Incorporated Method and apparatus for converting binary information into a high density single-sideband signal
US4470145A (en) * 1982-07-26 1984-09-04 Hughes Aircraft Company Single sideband quadricorrelator

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3443229A (en) * 1966-04-13 1969-05-06 Bell Telephone Labor Inc Quadrature-carrier vestigial-sideband data transmission
US3522537A (en) * 1966-07-25 1970-08-04 Western Union Telegraph Co Vestigial sideband transmission system having two channels in quadrature
US3605017A (en) * 1969-06-06 1971-09-14 Eg & G Inc Single sideband data transmission system
US3849730A (en) * 1973-06-20 1974-11-19 Bell Telephone Labor Inc Carrier recovery in vestigial sideband data receivers
US4461011A (en) * 1979-04-30 1984-07-17 Gte Network Systems Incorporated Method and apparatus for converting binary information into a high density single-sideband signal
US4439863A (en) * 1980-11-28 1984-03-27 Rockwell International Corporation Partial response system with simplified detection
US4470145A (en) * 1982-07-26 1984-09-04 Hughes Aircraft Company Single sideband quadricorrelator

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE42643E1 (en) 1991-03-27 2011-08-23 Panasonic Corporation Communication system
US6256357B1 (en) 1992-03-26 2001-07-03 Matsushita Electric Industrial Co., Ltd. Communication system
US6549716B1 (en) 1992-03-26 2003-04-15 Matsushita Electric Industrial Co., Ltd. Communication system
USRE38483E1 (en) 1992-03-26 2004-03-30 Matsushita Electric Industrial Co., Ltd. Communication system
US6724976B2 (en) 1992-03-26 2004-04-20 Matsushita Electric Industrial Co., Ltd. Communication system
US6728467B2 (en) 1992-03-26 2004-04-27 Matsushita Electric Industrial Co., Ltd. Communication system
USRE38513E1 (en) 1992-03-26 2004-05-11 Matsushita Electric Industrial Co., Ltd. Communication system
USRE41146E1 (en) 1992-03-26 2010-02-23 Panasonic Corporation Communication system
USRE43093E1 (en) 1992-03-26 2012-01-10 Panasonic Corporation Communication system
EP0617531A1 (fr) * 1993-03-25 1994-09-28 Matsushita Electric Industrial Co., Ltd. Système de transmission multirésolution
WO1997001894A1 (fr) * 1995-06-28 1997-01-16 Deutsche Telekom Ag Procede et circuit de modulation pour transmettre des signaux de donnees

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