WO1991020140A1 - Procede de synchronisation de la modulation d'amplitude en quadrature de phase - Google Patents

Procede de synchronisation de la modulation d'amplitude en quadrature de phase Download PDF

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Publication number
WO1991020140A1
WO1991020140A1 PCT/US1991/003784 US9103784W WO9120140A1 WO 1991020140 A1 WO1991020140 A1 WO 1991020140A1 US 9103784 W US9103784 W US 9103784W WO 9120140 A1 WO9120140 A1 WO 9120140A1
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WO
WIPO (PCT)
Prior art keywords
qam
signal
information
subchannels
synchronizing
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Application number
PCT/US1991/003784
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English (en)
Inventor
Steven C. Jasper
James A. Butler
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Motorola, Inc.
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Publication date
Application filed by Motorola, Inc. filed Critical Motorola, Inc.
Publication of WO1991020140A1 publication Critical patent/WO1991020140A1/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
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/38—Demodulator circuits; Receiver circuits
    • H04L27/3818—Demodulator circuits; Receiver circuits using coherent demodulation, i.e. using one or more nominally phase synchronous carriers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J7/00—Automatic frequency control; Automatic scanning over a band of frequencies
    • H03J7/02—Automatic frequency control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/261—Details of reference signals
    • H04L27/2613—Structure of the reference signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2673—Details of algorithms characterised by synchronisation parameters
    • H04L27/2675—Pilot or known symbols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H04L27/2637—Modulators with direct modulation of individual subcarriers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver

Definitions

  • This invention relates to communications methods.
  • this invention relates to so called quadrature amplitude modulation, or QAM, which is a modulation technique used to convey information, including digital information, using less bandwidth than other types of modulation such as FM or AM.
  • QAM quadrature amplitude modulation
  • QAM is well known in communications art and combines characteristics of both phase modulation and amplitude modulation to reduce the bandwidth required to carry a certain amount of information in an information-bearing signal.
  • information is conveyed using changes in both the amplitude of a carrier wave and the relative phase angle of the carrier signal with respect to a reference angle.
  • QAM modulation to convey digital data, 2, 3, 4, or more, bits of digital information can be conveyed per QAM signal element.
  • Multi-carrier QAM is a technique in which an information- bearing signal, such as serial digitized voice, digital data from a computer or other machine for example, is divided up into multiple, separate, frequency division multiplexed QAM signals.
  • Each QAM signal occupies a discrete frequency band (with each of the bands being substantially frequency adjacent to the others) and carries a portion of the information in the information-bearing signal.
  • a QAM signal conveys information using both the amplitude of a carrier wave and the phase angle.
  • the magnitude and phase angles of a carrier are represented as vectors (which have a magnitude and phase angle with respect to some reference axis) that point to various points or loci on a Cartesian plane, each locus on the plane identifies a particular binary value.
  • Each vector can be represented as a carrier having a particular amplitude level with a carrier signal at some distinct phase angle.
  • a vector having a unit length of one at a forty five degree angle with respect to the x-axis might "point" to a point identified as representing a binary value or pattern of 0010.
  • a vector with a unit length of one-half and at forth five degrees might point to a point identified as representing a binary value of 0110.
  • a vector with length equal to one, at zero degrees might represent 0000, and so on.
  • the relative magnitude and phase angle of a carrier signal correspond to the relative magnitude and phase of a vector that points to a particular point in a plane, which represents binary values assigned to the point.
  • a transmitted signal that represents a vector that points to a particular point on a plane, which point is established to represent some binary value, is detected, demodulated and decoded by the receiver to yield the binary value represented by the vector.
  • Vectors of varying magnitude and phase angles can represent multiple binary values.
  • the number of discernible amplitudes and phase angles will increase the number of bits of information representable by each QAM signal element. Increasing the number of possible amplitude levels and decreasing phase angle differences will increase the transmitter power required.
  • Sending streams of vectors represented as bursts of amplitude and phase-modulated RF carrier, is a way of sending streams of digital information.
  • Multilevel QAM is well known art. See for example "All About Modems" copyright 1981 by Universal Data Systems, Inc. or other digital communications texts.)
  • a receiver To coherently detect information from QAM elements in a QAM signal, a receiver must be able to accurately differentiate between amplitude variations in the carrier wave as well as phase angle changes. In many environments, phase jitter or phase shift may accompany fading and multi-path signal propagation. A receiver must be able to reliably detect phase angle changes and carrier amplitude despite fading and multi-path propagation. When multi-carrier QAM is used, each QAM signal may experience its own fading requiring that each QAM signal have its own synchronizing sequence.
  • a synchronizing sequence of QAM signal elements that permit a receiver to synchronize to, or lock up with, the QAM transmitter may assist the receiver in locating the relative timing of an information stream.
  • Arbitrary synchronizing sequences for a QAM receiver may provide no real benefit however, if the synchronizing sequence requires relatively complex computational activities to be carried on by the receiver.
  • a QAM communications system that simplifies the complexity of a QAM receiver would be an improvement over the prior art.
  • a synchronizing sequence that is adapted for use with multichannel
  • QAM would be an improvement over the prior art.
  • a QAM receiver that must detect the synchronizing sequences might be simplified if the synchronizing sequences are chosen to reduce computational complexity required to identify signalling sequences in multiple QAM channels.
  • Other benefits from a preferred synchronizing sequence are also realized as well, including simplified automatic frequency control for the receiver IF stages and improved synchronization timing.
  • the method includes providing a signal vector synchronizing sequence that is a stream of QAM signal elements, to a QAM information signal, and in particular to substantially each QAM channel of a multi-carrier QAM system.
  • the synchronizing sequences are selected to minimize computation time required by a QAM receiver.
  • QAM subchannels centered about a center frequency When a base-band QAM signal is up-shifted in frequency, the QAM subchannels comprising a multi-carrier QAM system can be shifted by slightly different amounts whereby the channels can be frequency centered about some frequency.) are paired.
  • One QAM subchannel of a pair of subchannels, the first subchannel, has a center frequency, fi, offset from the center frequency fo of the multi-carrier signal by some amount - ⁇ fl.
  • the other QAM subchannel of a pair of subchannels, the second subchannel has its own center frequency, f2, offset from the center frequency fo of the multi- carrier signal fo by an amount equal to + ⁇ fl.
  • the synchronizing sequence is comprised of complex vectors and their complex conjugates.
  • the QAM signal vector synchronizing sequence in the first subchannel and the signal vector synchronizing sequence in the second subchannel are complex conjugates of each other.
  • QAM subchannels have signal vector synchronizing symbols in substantially each pair of subchannels that are complex conjugates.
  • the vector synchronizing sequences are chosen so that when they are added, or summed, prior to transmission, the addition of the paired signal vector synchronizing sequences produces a resultant signal that has only a real component, i.e. a signal with no imaginary component, on the real axis. Detection of the synchronizing sequence can be simplified by designing a receiver filter that looks only for the waveform produced by vector pairs having no angular component.
  • the synchronizing sequence added to each channel that is comprised of pairs of complex numbers and complex conjugates a QAM receiver must look for only a particular wave form to detect the timing of a QAM information stream.
  • Figure 1 shows a block diagram of a four-subchannel QAM transmitter.
  • Figure 2 shows a diagram of the transmit spectrum from the transmitter of figure 1.
  • Figure 3 shows a representation of synchronizing sequences and information present in each of the subchannels shown in figure 1.
  • Figure 4 shows a block diagram of a QAM receiver that might be capable of demodulating the information present in the information shown in figure 3 and figure 2.
  • Figure 5 shows a block diagram of a fractional part of the receiver shown in figure 4.
  • Figures 6A and 6B show embodiments of a sync matched filter.
  • Figure 7 shows a signal constellation for a 16 level QAM communications system.
  • Figure 8 shows a representative phasor diagram of vectors produced by the synchronizing sequence shown in figure 3.
  • Figures 9 shows a transmit spectrum for a three-subchannel
  • Figure 10 shows a transmit spectrum for a six-subchannel QAM signal.
  • Figure 11 shows a method of generating an AFC control signal.
  • Figure 12 shows an alternative method of generating an AFC control signal.
  • Figure 1 shows a simplified block diagram of a four subchannel
  • the QAM transmitter (10) formats information from a serial data source (12) into four subchannels, wherein each subchannel carries a fractional amount of the information in the original serial bit stream (12).
  • the serial bit stream (12) may originate from virtually any particular source.
  • the serial bit stream might be digitized voice information, data from a computer or the like, or any other similar source of such information.
  • serial data of the serial bit stream (12) is reformatted by a serial to parallel converter (14), which divides the serial bit stream into four different data streams.
  • the serial to parallel symbol converter (14) formats 16 bits of serial data from the serial data source (12) into four, four bit data words.
  • the data words from the serial to paralled converter (14) form a stream of discrete samples of information from the serial bit stream (12).
  • four-bit data words are converted into complex QAM symbols, in this case, 16QAM symbols, which correspond to the sixteen points in the constellation shown in figure 7.
  • Figure 7 shows a constellation map of a 16 level QAM signal. Each point on this constellation map is assigned a binary bit pattern corresponding to every possible binary bit pattern representable by four bits.
  • a bit pattern produced by the serial to parallel converter (14) of all zeros might be represented by a vector with 6 magnitude Ml, at 45 degrees. This vector might be transmitted as a carrier wave of a certain amplitude Ml and with a certain phase-shift of ⁇ l, identifiable by a receiver as a 45 degree phase shift from some other reference value. Synchronization symbols are inserted in a sync insertion block
  • the actual synchronization symbols might be generated by a microcomputer, a suitable digital signal processor or other suitable device.
  • the data from the serial to parallel converter (14) is a stream of samples, the synchronization symbols are also discrete samples of information.
  • the output of the synchronization symbol insertion block (16) is coupled to a pulse shaping filter (18) which band limits the frequency spectrum of the composite signals from the synchronization symbol insertion block (16).
  • the synchronization symbol insertion block (16) might also add an optional pilot signal to the signal output from the serial to parallel converter (14) forming thereby a signal which is a composite of the information signal, pilot and sync symbols.
  • the output of the pulse shaping filter (18) is coupled to a modulator (20) which multiplies the output of the pulse shaping filter (18) by a sine wave quantity equal to e(J2 ⁇ fit) w here i runs from 1 to 4.
  • the output of the first modulator stage (20) is a complex zero IF signal which is summed together in a summer (22) with the signals from other pulse shaping filters and modulators (18b through d and 20b through d, respectively,) as shown.
  • the complex zero IF output from the summer (22) is frequency shifted by an IF up-converter, or modulator (24) to some carrier frequency, fo, amplified by an RF amplifier (26) for subsequent broadcasting on antenna (28).
  • Each of the QAM subchannels broadcast from the antenna occupies its own frequency spectrum as a result of the modulation process used in the transmitter (10).
  • Figure 2 shows a representation of the transmit energy spectrum output from the transmitter (10) shown in figure 1.
  • the frequency spectrum output from the transmitter (10) is as shown in figure 2 with four subchannels (32, 34, 36 and 38) centered about a center frequency fo.
  • each subchannel (32, 34, 36 and 38) has its own center frequency fi+f ⁇ , f2+f ⁇ » f3+f ⁇ > and f4+fo respectively (42, 44, 46 and 48 respectively).
  • Figure 3 shows a representative diagram of the information that might be present on each of the subchannels 1 through 4 shown in figure 2.
  • subchannel 1 (52) is shown with a series of synchronizing sequences designated Sn, S12, through S ⁇ n .
  • Subchannel 2 (54) has its own series of synchronizing symbols S21, S22» through S2n- Similarly, subchannels
  • the synchronizing sequences are added as a header to the information in a frame, or time slot, used to transmit the QAM.
  • Alternate embodiments of the invention would include interleaving the synchronizing sequences in the data, placing the synchronizing sequences in the middle of the data stream or at the end of a data stream.
  • Figure 3 also shows that each QAM subchannel has a synchronizing sequence.
  • Alternate embodiments of the invention would include appending such synchronizing sequences to less than all of the
  • QAM subchannels For example, only channels one and four, or, only channels two and three, shown in figure 3, might have sync sequences added to them.
  • Figure 4 shows a simplified block diagram of a simplified block diagram of a QAM receiver.
  • a frequency preselector (62) detects the RF energy in the transmit spectrum shown in figure 2 and presents this information to an IF stage (64) as shown the output of which is a zero IF signal, comprised of streams of complex quantities known or referred to as an in-phase and quadrature components of a zero-IF signal.
  • This zero IF down converter (64) might include an automatic frequency control input that permits it to track shifts in frequency of the signal received by the receiver.
  • a sync detection circuit (66) monitors these zero
  • the sync detection circuit (66) includes circuitry to precisely identify, from the synchronizing sequences added to the information in the QAM subchannels, when information in the QAM subchannels should be sampled for detection.
  • the zero-IF signal from the zero-IF converter 64 is coupled to four subchannel receivers that each include subchannel mixers (65a through 65d) and reciever pulse-shaping filters (67a through 67d).
  • the subchannel mixers multiply the zero-IF signal by a signal, e ⁇ 3-----i- , where fi is the subchannel center frequency for the respective subchannels, one through four; t is time.
  • the output of a subchannel mixer is a signal centered about zero hertz, which is filtered by a pulse shaping filter, (67a through 67d) to remove noise and any undesired subchannel signals.
  • the output of the pulse shaping filters is sampled at a rate determined by the sync detection circuit (66).
  • the sampled outputs of the pulse shaping filters are input to symbol detector blocks, (69a through 69d) that estimate the information symbols originally transmitted.
  • AFC block (68) Automatic frequency control is provided by an AFC block (68).
  • the AFC block (68) receives the sampled output of the pulse shaping filters during the times when sync symbols are present, as determined by the sync detection block (66). Stated alternatively, the AFC block only utilizes sync symbol samples, xij, (where i is the subchannel number and j is the sync symbol number) from the pulse shaping filters when sync symbols are present.
  • the sync symbol smples, xij correspond to the originally transmitted sync symbol vectors, Sij.
  • the output of the AFC block is coupled to the zero-IF converter (64), or to possibly other frequency shifting stages between the preselector (62) and the symbol detectors (69a through 69d) to track received signal frequency shifts.
  • Figure 5 shows a simplified block diagram of a sync matched filter and other circuitry associated with the sync detector (66) of figure 4.
  • a complex zero IF from the IF (64) of the receiver (60) is input to a synchronization matched filter (660) which is a filter whose impulse response closely approximates complex conjugate of the time reversed transmitted composite waveform.
  • a synchronization matched filter (660) which is a filter whose impulse response closely approximates complex conjugate of the time reversed transmitted composite waveform.
  • the synchronization matched filter (660) tests only for the waveform from the transmitter due to the sequences of synchronization symbols Sij where i is the subchannel number and j is the synchronizing symbol time index, or number, sent. This filter (660) does not test for information in the QAM frame.)
  • the output of the synchronization matched filter (660) is coupled to a magnitude squaring block (670) which computes the square of the amplitude of the synchronization matched filter (660) output and allows the determination of the power level of the signal detected by the synchronization matched filter (660).
  • the output of the magnitude squaring block (660) is compared against a threshold in a comparator (680) to determine whether or not the synchronization matched filter (660) has found a synchronization pattern from the transmitter (10). (As shown in figure 5A, the threshold can be chosen to discriminate against noise.)
  • the output of the magnitude squaring block is also coupled to a peak timing detector circuit (690).
  • the peak timing detector circuit (690) finds the time of the occurrence of the peak output value from the magnitude squaring block.
  • the time of occurrence of the peak output value from the magnitude squaring block provides timing information of the QAM symbol times to enable accurate symbol sampling by the receiver (60).
  • the output 692 of the sync detection block (66) controls when symbols are to be acquired.
  • the receiver elements shown in figure 4, excluding the preselector (62) and zero IF (64) are performed by a digital signal processor, such as a Motorola DSP 56000.
  • the first synchronizing vector Sn is arbitrarily chosen at a 45 degree angle with a particular magnitude of Ml. Its complex conjugate is used as the synchronizing symbol for subchannel 4 and is shown as S41.
  • the synchronizing symbols for subchannels 2 and 3 are also shown with the synchronizing vector for subchannel 2 represented by S 21 and synchronizing vector for subchannel 3 shown as S3 1 . Similar diagrams could be shown for other symbols occuring at a particular time, comprising synchronization sequences, i.e. S12, S22. S32, S42, etc.
  • the complex zero IF denoted as the real portion (A) and the imaginary portion (B) is coupled to a complex filter comprised of elements 662, 664, 666, and 668. Each element has a real scalar input and real scalar output.
  • S(t) represents the waveform of the composite of the synchronization symbol elements sent by the transmitter.
  • FIG. 6b A simplification of the receiver shown in figure 6a, and one which is made possible by the use of complex synchronization vectors and their complex conjugates in paired, or matched, QAM subchannels, in accordance with the method of the invention, is shown in figure 6b.
  • the complex zero IF signal is coupled to a filter comprised that is matched to the waveform produced by synchronization vectors that are complex conjugates of each other and which when modulated and added together prior to transmission produce a constant phase waveform.
  • the filter shown in figure 6b is considerably simpler than that shown in figure 6a.
  • FIG. 9 shows 3 subchannels with first and second subchannels evenly displaced about a center frequency fo- The third subchannel must of course be centered about fo for the sync matched filter of figure 6b to detect synchronization.
  • An odd number of subchannels requires that the synchronizing sequences inserted into subchannels 1 and 2, be complex conjugates of each other. Since the resultant of these two synchronizing sequences when added together yields a real value, the synchronizing sequence added to subchannel 3 must be real valued.
  • 1 (which would also require of course the accompanying circuitry and the receiver) might include a transmitter with several subchannels such as that shown in figure 10. Six subchannels might be centered around fo with the subchannels grouped as 2 and 3, 1 and 4, and 5 and 6. The addition of complex vectors and conjugates of these complex vectors would still produce a resultant synchronizing vector that would reside on the real axis.
  • any multi-carrier QAM system described herein not all of the paired subchannels need to have the complex vector/complex conjugate vector synchronizing sequences added to them.
  • at least one pair of the paired subchannels must have the synchronizing sequence described herein added to it to permit simplified synchronization detection. (The requirement that the subchannels be centered about a center frequency still holds.)
  • Using synchronizing sequences with a multi-carrier QAM system permits an improved automatic frequency control signal to be derived from the synchronizing sequences. Since the transmitter and receiver each attempt to demodulate signals at some frequency fo, the fo frequency of the transmitter and receiver may be slightly offset with respect to each other, an AFC control signal by which the receiver (or possible the transmitter) operating frequency can be adjusted improves the QAM system performance. (The AFC control signal generated by the receiver might possible be returned to the transmitter where it could possibly be used to shift the transmitters fo to align with the receivers fo.)
  • the successive synchronizing sequences used to calculate the AFC signal must be temporally adjacent, i.e., they must be adjacent, in time, to the other symbols used in the calculation.
  • the receiver For each of said N QAM subchannels, there is an expected phase angle difference between synchronizing symbols.
  • the receiver will normally know this expected phase angle difference in advance.
  • the method of generating an AFC control signal generation requires that for each of said N QAM subchannels, the expected phase angle difference between successive synchronizing vectors, Sij, should be subtracted from the actual phase angle difference between temporally adjacent synchronizing vector samples, xij, forming thereby a series of numbers representing phase angle errors. (If the fo frequencies of the transmitter and receiver were identical, the actual phase angle differences would be equal to the expected phase angle differences.
  • the series of numbers obtained from this previous step is operated upon to form a weighted average phase angle.
  • each of the differences forming this series was multiplied by a scalar value proportional to the product of the amplitudes of the temporally adjacent sync symbols xij.
  • the resultant is divided by by a factor equal to 2 ⁇ T, producing a frequency error signal, where T is the time between successive synchronizing vectors in the subchannel, and where phase angles are in radians.
  • T is the time between successive synchronizing vectors in the subchannel, and where phase angles are in radians.
  • This estimated frequency offset may be further filtered to produce an
  • each synchronizing symbol vector xij is multiplied by a quantity equal to the complex conjugate of the previous synchronizing vector xi j-1.
  • Each of these vector products is rotated by the negative of the expected phase angle difference between the corresponding sync symbols, Sij and Sij-i, forming another vector.
  • a sum of all these vectors, for all sync symbols and for all subchannels is formed.
  • the phase of this resultant vector (y) is the weighted average phase angle.

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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

Dans un système de communication à modulation d'amplitude en quadrature de phase (10, 60), une nouvelle séquence de vecteurs de synchronisation (S11, S12,...S1n; S21, S22,...S2n; S31, S32,...S3n; S41, S42,...S4n) ajoutée aux voies de transfert des informations (32, 34, 36, 38) simplifie l'acquisition par un récepteur (60) de la synchronisation et du rythme. Ces vecteurs de synchronisation (S11, S12,...S1n; S21, S22,...S2n; S31, S32,...S3n; S41, S42,...S4n) produisent des signaux permettant une génération améliorée des signaux de commande de CAF.
PCT/US1991/003784 1990-06-12 1991-05-30 Procede de synchronisation de la modulation d'amplitude en quadrature de phase WO1991020140A1 (fr)

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Cited By (3)

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EP0549445A1 (fr) * 1991-12-26 1993-06-30 Thomson-Csf Procédé de transmission de signaux de référence dans un système de transmission de données sur plusieur porteuses
GB2271693A (en) * 1992-10-13 1994-04-20 Motorola Israel Ltd Communications system having pilot signals transmitted over frequency divided channels
EP0735730A2 (fr) * 1995-03-28 1996-10-02 Matsushita Electric Industrial Co., Ltd. Dispositif de commande automatique de fréquence

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Cited By (5)

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Publication number Priority date Publication date Assignee Title
EP0549445A1 (fr) * 1991-12-26 1993-06-30 Thomson-Csf Procédé de transmission de signaux de référence dans un système de transmission de données sur plusieur porteuses
FR2685839A1 (fr) * 1991-12-26 1993-07-02 Thomson Csf Procede de modulation et de demodulation coherent pour la transmission de donnees haut debit en hf.
US5572548A (en) * 1991-12-26 1996-11-05 Thomson-Csf Method of coherent modulation and demodulation for high frequency data transmission at high bit rate
GB2271693A (en) * 1992-10-13 1994-04-20 Motorola Israel Ltd Communications system having pilot signals transmitted over frequency divided channels
EP0735730A2 (fr) * 1995-03-28 1996-10-02 Matsushita Electric Industrial Co., Ltd. Dispositif de commande automatique de fréquence

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