MXPA97002496A - Modulator and demodulator of mac and blv digi - Google Patents

Abstract

The present invention relates to a synchronous detector for recovering a demodulated digital output data signal from a transmitted digital input data signal regardless of whether the transmitted digital input data stream is modulated according to a vestigial sideband or a scheme quadrature amplitude modulation, the synchronous detector comprising a tuner fixed to a central carrier frequency of a spectrum of modulated data, the tuner comprising real and imaginary arms and a decoder to receive digital data sequences of the real and imaginary arms, the decoder operating selectively according to the duration of a transmitted data symbol

Description

MAC AND B V DIGITAL MODULATOR AND DEMODULATOR This application is a continuation in part of the application of E.U.A. series no. 08 / 223,223, filed April 5, 1994. BACKGROUND OF THE INVENTION Field of the Invention The field of the invention relates to a digital demodulation and decoding method and apparatus for demodulating and decoding a modulated quadrature amplitude and a data signal. digital modulated vestigial sideband that allows the use of substantially the same apparatus to demodulate in any form of modulation. Description of the Related Art Figure 1A is repeated in the present application of E.U.A. applicant's tax code Series no. 08 / 223,223, filed on April 5, 1994, entitled "Synchronous Detector and Methods for Synchronous Detection", incorporated herein by reference, to show a normal amplitude of signals against frequency density spectrum of a modulated information signal via a scheme of vestigial sideband modulation. In particular, Figure 1A shows a modulated vestigial sideband (BLV) information signal modulated around a carrier frequency fc. In particular, the carrier frequency signal is practically absent, the frequency component on the carrier frequency being mainly the information signal. The inclinations on either side of the spectrum of information signal frequency versus amplitude are ideally identical. Referring to Figure 1B, a known modulated quadrature amplitude (MAC) signal has a frequency spectrum that differs from that of Figure 1A in that the MAC carrier frequency signal is symmetrically placed at half of the band between fc shown in Figure 1A and fc + (fb / 2) where fb is the baud rate of the modulated digital data information signal. The MAC modulated information signal is demodulated assuming a central carrier frequency fcs, where "fcs" refers to the frequency value equal to the approximate center of symmetry of the information signal spectrum. In a conventional demodulator for a BLV modulated data signal in which the transmitted carrier is suppressed or partially suppressed, the demodulation apparatus normally includes a synchronous product detector tuned to the carrier frequency fc. In a normal demodulator for the MAC data signal, the demodulator apparatus involves the use of two product detectors, one tuned for fcs, or fc + (fb / 4) and the other for squaring fcs. As television technology has progressed towards the resolution requirements demanded today, allowing the display of a high definition television image, it has become necessary to develop and agree on a modulation scheme for a digital data signal capable of transmission via cable, fiber optic, satellite or aerial at very high frequencies, ultra high, microwave or higher than radio (including light frequencies). The transmitted digital data signal, by itself, includes both a digitized and compressed television information signal and a related stereo audio signal and may also include other data signals. These other data signals may be superimposed on any of the television or stereo audio signals or transmitted separately in a frequency division or time division multiplexer format. The demodulation techniques currently under consideration are subject to considerable controversy and include both BLV and MAC. Some propose a high definition television standard and promote BLV while others promote MAC. For example, 16-MAC is a technique where data points of four characters are separated into two separate sequences of two-character symbols per sequence. The two separate sequences of symbols are fed into the two modulation ports of a quadrature-type modulator. The MAC output signals are double sidebands (as for Figure 1B), and the sidebands do not carry a particular phase relationship, with each other, due to the asymmetry between the two separate sequences of symbols formed during the modulation process. In contrast, 4-BLV is a technique in which the same sequence of four-character tips is separated into two points of two consecutive characters transmitted at double the rate of symbols used in MAC. The width of the band is compared to the width of the band of the modulated MAC signal by eliminating a redundant sideband. The known methods of modulation and demodulation vary between MAC and BLV. So it forms the structure of a modulator circuit or a normal demodulator circuit. In Figure 2 there is shown a BLV demodulation synchronous detector copied substantially from Figure 24 of the application of E.U.A. copendiente of the applicant series no. 08 / 223,223. The BLV demodulator usually varies from one for MAC demodulation in the tuning requirement to different frequencies fc versus fc + (fb / 4) and to maintain control of one or the other tuned frequency output of the voltage controlled oscillator (OCV) of the local vehicle. There is reason to believe that the representatives of "CableLabs", a cable television research and testing facility in the United States, has sought to develop a set of integrated circuits under development, may have resulted in the preparation and filing of patent applications in the United States in accordance with press statements. However, to the knowledge of the applicant, the particular details of the development of "CableLabs" have not been published. Consequently, in view of the controversy surrounding the digital demodulation of BLV and MAC, there remains a need in the art to provide apparatus and a method for digitally demodulating both types of modulation and therefore, decoding a digital information signal thus modulated, Conveniently, said apparatus will avoid any need to re-tune an anticipated carrier frequency, eliminate redundant circuitry and, even, decode any modulated digital data signal without significant loss of content. SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus and method for digitally demodulating both modulated BLV and MAC data. It is a further object of the present invention, that the apparatus to be made, be common, thereby substantially eliminating the redundant circuitry. It is a further object of the present invention to provide a digital decoder to output a demodulated data stream regardless of the way in which the data stream is modulated and transmitted, via BLV or MAC. It is a further object of the present invention to decode both a BLV and a MAC signal substantially without loss of digital data. These and other objects are achieved in accordance with the present invention through recognition that a digital data signal modulated via BLV can be demodulated by assuming a central, symmetric vehicle frequency (fcs). Accordingly, a MAC demodulator circuit tuned to center the frequency can be used to demodulate and pass a modulated decoded digital data signal, either modulation via MAC or BLV to a decoder according to the present invention. In other words, a BLV modulated digital data signal, can be viewed as a deviated, encrypted MAC signal. The received BLV or MAC signal is switched to a decoder, in accordance with the symbol rate, in order to form the decoded and reconstructed serial data stream that was transmitted. The applicant performed a computer simulation, comparing the change of phases of quadrature of deviated key classifying (O-QPSK) and 2-BLV. In accordance with Table I, described herein in greater detail, to do so the applicant used computer circuit simulation software "MATLAB (TM)". Tabia 4B shows a transmitted data sequence and Figures 4D and 4E show the identical sequence received assuming O-QPSK or BLV. According to the simulation results shown, the received data sequences are the same as the data sequences transmitted by any of the demodulation methods. The applicant simulated the output eye patterns of a demodulated 2-BLV signal using a normal BLV demodulator (tuned to fc) and a tuned MAC demodulator for a symmetric center frequency (tuned to fcs) of the signal frequency spectrum of information. The Applicant observed that the eye patterns resulting from the MAC demodulation (O-QPSK) of a BLV modulated digital data signal still presented an "open eye" (Figures 4A-7), even in the presence of a significant transmitted vehicle. (Figures 8A-11). On the other hand, the applicant observed substantial differences in data eye patterns generated during the demodulation of a 2-BLV digital modulated data signal assuming that the tuning frequency of the vehicle is one in the usual fc (via a normal synchronous detector). of BLV) or middle band located symmetrically in fcs = fc + (fb / 4) (via a MAC demodulator). Data eye patterns can be obtained at the output of a digital data scrambler normally by the use of an oscilloscope. In the simulation associated with the development of the present invention, the eye patterns are graphically formed as the computer output of a printer. A random data signal is assumed, which produces the printed output comprising the patterns in which there are open spaces between multiple overlapping sinusoidal signals in fractions of the baud rate or the baud rate of the modulated data signal. The applicant simulated the eye patterns that can be obtained using a MAC demodulator circuit tuned to fc + (/ 4) and a normal BLV demodulator tuned to fc and it was found that the eye patterns of 1-BLV in phase or resulting quadrature, one could distinguish the o £ ro. Therefore, assuming that the BLV modulated data signal is shifted symmetrically around the carrier, then the BLV signal can be seen as an OAM signal in a deviated key (O-QPSK). Consequently, the same signal can be used. electronic circuitry for recovering a digital data signal modulated via any of a MAC or BLV modulation method, assuming a particular decoder algorithm according to the present invention The applicant further simulated the respective constellation patterns spectra resulting from the phase demodulation against quadrature for a 2-BLV digital modulated data signal assuming tuning either in fc or in fc + (fb / 4) A decoding algorithm was then built incorporating means to output a demodulated MAC or BLV data stream including, but not limited to, the switching steps between the phase and quadrature data sequences and, consequently, prod In this case, according to the present invention, a demodulator for demodulating a modulated digital MAC or BLV data signal comprises tuning means for tuning to a central frequency of the frequency spectrum of a modulated information signal and decoding means responsive to the tuning means for decoding the modulated information signal in accordance with the symbol regime of the serial data stream, the serial data stream being a reconstructed serial data stream identical to the transmitted data stream The differences between the respective constellations of the digital modulated MAC or BLV data signal are inherently taken into account. A method for demodulating a digital MAC or BLV modulated data signal comprises the steps of tuning to a central frequency of the frequency spectrum of a modulated information signal and decoding the modulated information signal according to the current symbol regime. digital data. In this way, the hardware tuning and demodulation circuitry can be shared in a demodulator circuit to demodulate either a digital data signal modulated from BLV or MAC while the primary difference in the decoder circuitry to output a demodulated digital data stream, reconstructed by switching between the in-phase and quadrature arms according to the symbol regime of the transmitted data stream. Other advantages of the present invention will be apparent from an understanding of the following detailed description of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A is a graph showing a normal frequency density spectrum of an information signal modulated according to vestigial sideband modulation methods where there is substantially no trace transmitted from the carrier frequency fc Figure 1B, is a graph showing a * spectrum of normal frequency density related to the BLV spectrum of Figure 1A in which the carrier frequency is assumed symmetrically to be located in fc + (fb / 4) or in the middle band of according to a MAC digital modulated data signal that has a baud rate fb, where fcs is the frequency value at the center of symmetry of the information signal spectrum Figure 2A, comprises a block schematic diagram of a modulator for modulating a digital data signal either via BLV or MAC modulation including a MAC / BLV control circuit 12, FIG. 2B, provides more details of the MAC / BLV control circuit 12, to separate an input serial data stream according to its symbol regime in the in-phase components and Quadrature, Figure 2C, is a schematic block diagram of a modulator according to the present invention taken substantially from Figure 33 of my co-pending application which is an alternative mode to that of Figure 2A but which provides inherent cancellation of sound of phases Figure 3A, comprises a schematic block diagram of a demodulator for demodulating a digital modulated data signal of MAC or BLV according to the present invention in In the decoder circuit 50 provides control of clock recovery and carrier recovery control and an output data stream, FIG. 3B, provides particular detail of the decoder 50 for switching between the phase and quadrature arms of the demodulator circuit in accordance with the symbol scheme of the digital input data stream. Figures 4A and 4B, comprise a simulated eye pattern for the demodulated I and Q outputs of a 2-BLV signal assuming demodulation of the center of symmetry fcs since a MAC signal could be normally demodulated, treating the data signal modulated as modulated O-QPSK; Figures 4D and 4E graphically describe the received data sequences on simulated MAC demodulation (O-QPSK) showing that the data sequences received for O-QPSK and BLV are identical to each other and to the transmitted sequences. Figure 5 comprises a simulated constellation for the demodulated digital data signal whose eye patterns for outputs I and Q are shown in Figures 4A and 4B. Figures 6A and 6B, comprise a simulated eye pattern for I and Q outputs of a demodulated 2-BLV signal using a conventional BLV demodulator tuned to a carrier frequency fc shifted to one or the other edge of the frequency spectrum of information as shown in Figure 1A. Figure 7 comprises a simulated 2-BLV constellation for the demodulated digital data signal, whose eye patterns for outputs I and Q are shown in Figures 6A and 6B. Figures 8A-11 comprise simulated eye patterns and constellations for demodulated digital data signals, either assuming a central carrier frequency or a shifted one edge of the spectrum of the information signal frequency as in Figures 4A-8B, but in which a component of significant amplitude in the carrier frequency is transmitted with the 2-BLV signal. Figures 8A and 8B, comprise a simulated eye pattern and constellation for a 2-BLV signal conventionally demodulated with added pilot signal; while Figures 10A and 10B comprise a simulated and constellation eye pattern for a demodulated BLV signal with added pilot signal in accordance with the present invention. DESCRIPTION OF THE PREFERRED MODE AND METHOD According to Figure 1A, a BLV modulated digital data signal has a frequency signal spectrum in which the carrier frequency fc is shifted towards one edge of the frequency spectrum. It is presumed that the information signal, according to the present invention, comprises a digital data signal or data stream having a baud rate fb. The inclination of either side of the frequency spectrum of information signals is substantially identical. It is presumed that the carrier frequency amplitude component is substantially absent. Therefore, only the spectrum of information signals is transmitted, for example, via cable, satellite, fiber optic, aerial or other transmission medium. The baud rate may include a low-speed data signal, audio, stereo audio, high-speed data or high-definition television. The data by themselves may be compressed or not according to well-known techniques. These characteristics of the digital data stream described as one for modulation via BLV, also describe a digital data stream to be modulated by MAC. Referring to FIG. 1B and in accordance with the present invention, a digital data signal modulated by BLV can be considered as a keyed data signal (O-QPSK) of shifted or deviated quadrature MAC phase change having phase and quadrature amplitude components as shown in Figures 4A and 4B where the demodulation is presented at fcs as for Figure 1B. Likewise, a MAC signal can be demodulated from fcs, the center of symmetry of the information signal that has been modulated by MAC. The following Table I provides a computer circuit simulation software file from "MATLAB (TM)" to demonstrate that BLV can be modulated and demodulated from the center frequency fcs, as a MAC signal. It is assumed for the purposes of the simulation, that the BLV symbol regime is twice the O-QPSK symbol regime. In addition, the principles demonstrated by the simulation can be extended to more complicated data modulation schemes such as 4-BLV and so on. TABLE i% File to demonstrate that we can modulate and demodulate a BLV% signal from its center, as a MAC signal. % For this example we will compare O-QPSK and 2BLV. % The BLV symbol rate is double the O-QPSK symbol scheme. graph = 0; % Set is to 1 to plot, 0 to not plot nbits = 512; % No. of characters used in simulation ns_qpsk = nbits / 2; % No. of O-QPSK symbols ns_vsb = nbits; % No. of BLV symbols fs = 8; % Sampling frequency used in simulation Ts = 1; % Symbol time duration for O-QPSK nsf = 8; % Symbol memory number of the "Nyquist" filter. load prbs11a; nbits = min (nbits, length (prbs)); prbs 1 = prbs (1: nbits); nstart = 1 + nsf * fs * Ts; % index where the signal is valid nstop = fs * Ts * nbits; % signal end index t = [0: 1 / fs: nbits * Ts-1 / fs] ':% Vector time associated with simulation% Filter "Nyquist" for arms I and Q of QPSK [b, a] = nyql (nsf * fs * Ts, 1 / (fs * Ts), 50); % BLV filter created by rotating the zeros of the "Nyquist" filter [bt, at] = filt_rot (b, a, 1 / (fs * Ts)); delay_filt = nsf * fs * Ts; % filter delay in no. sample clock% Generate an O-QPSK signal xQPSK = fs * Ts * (zerofill (2 * prbs1 (1: 2: nbits-1) -1, fs * Ts) ... + j * rotatem (zerofill ( 2 * prbs1 (2: 2: nbits) -1-, fs * Ts, fs * Ts / 2)); and QPSK = filter (b, a, xQPSK);% -QPSK filter with "Nyquist" filter% conversion O-QPSK at 2-BLV using a complex exponential.

% Change frequency by 1 / (2 * T). % yVSB = yQPSK. * exp (j * 2 * pi * (1 / (2 * Ts). * t)); xVSB = fs * Ts * (zerofill (2 * prbs1-1.fs * Ts / 2)); yVSB = filter (bt, at, xVSB); % Show the quadrature arm of O-QPSK bl_QPSK = sampbits (imag (yQpSK), [fs, 1 / Ts], 0.0); % Quadrature arm sample O_QPSK bQ_QPSK = sampits (imag (yQPSK), [fs, 1 / Ts], 0.5); % Of a series current using [l, Q, l, Q, l, Q, ....] b_QPSK = [b1_QPSK, bQ_QPSK] :; b_QPSK = b_QPSK (:); % Samples the arm in the BLV phase b_VSB = sampbits (real (yVSB), [fs, 2 / Ts], 0.0); % Convert from opposite signal to 1 and 0 b_QPSK = (b: QPSK > 0.0); b_BLV = (b: VSB > 0.0); figure (1) sub? lot (211) stem (b_QPSK (101: 140 = =; title ('O-QPSK RECEIVED SEQUENCE'); subplot (212) stem (b_VSB (101: 140)); title ('VSB RECEIVED SEQUENCE'); figure (2) stem (prbs1 (101-delay_filt / fs: 140-delay-filt / fs)); title ('TRANSMITTED SEQUENCE'); The additional simulation results are shown in Figures 4A-11. Figures 4A, 4B, and 5-11, are simulations that run according to certain assumed parameters, in particular, all are set at an assumed sampling frequency Fs of 8 Hz and an alpha a = 50%. The center frequency of the deviation MAC signal is 0 Hz using the representation of the complex baseband. In addition, the carrier frequency of the BLV signal is 0 Hz. The duration of the Ts symbol for 2-BLV is half of that for O-QPSK or .5 sec. (where O-QPSK is 1 second) reflecting the deviation of MAC digital current. Figures 4A-7 are simulated results that do not assume carrier pilot. Figures 8A-11 assume a transmitted pilot trace at approximately 0.2 volts (almost 10% of the distance separating the two amplitude levels). Still, if it is desired to transmit more significant carrier levels, a demodulator / decoder, in accordance with the present invention, can be modified in a well-known manner to track and remove the pilot by removing the adverse effect described in the eye pattern. Therefore, with an additional circuit, the transmitted pilot is subtracted from the received waveform.

Referring now to Figure 2A, substantially identical to Figure 7 of my copending application, the similarities between the BLV and MAC modulation of the same digital data stream will now be discussed. However, Figure 2A, an input digital data stream that will be modulated, is fed from the input 8 to the modulator 10 comprising a modulator to modulate the modulation techniques either BLV or MAC. If the digital data signal is to be modulated via MAC, the signal is usually divided into two separate data streams to be fed via dotted line paths from the controller 12 to the filters 16 and 18, and to the real and imaginary arms respectively. A digital data signal to be modulated by BLV is passed via the solid line path to both filters 16 and 18. The oscillator 20 generates a carrier signal at the carrier frequency, either fc (BLV) or fcs (MAC). The carrier signal is provided to both a balanced modulator 22 and an input of, preferably a "Hilbert" filter 26. Since the carrier signal frequency is substantially spectrally pure, the filter 26 is merely a phase change filter of 90. ° on the carrier frequency. The output of the filter 26 is provided to the balanced modulator 24. The output of the actual arm 16 is provided to the balanced modulator 22 to modulate the carrier signal. The output of the balanced modulator 22 is provided to a first adder circuit input 28, is the modulated carrier signal and is provided at the output terminal 14. The modulator shown in Figure 2A can produce simple sideband modulation signals when the imaginary arm 18 is a "Hilbert" filter for providing a 90 ° phase change over the bandwidth of the pass band of the actual arm filter 16. When the summing circuit 28 adds the signals of the balanced modulators 22 and 24, the upper sideband signal is provided in the output terminal 14. When the summer circuit 28 subtracts the signal from the balanced modulator 24 of the balanced modulator signal 22, the modulated carrier provided in the output terminal 14, is the signal of lower lateral band. The modulator 10 may be a MAC modulator when the data input comprises two separate data streams feeding imaginary and real arms 16 and 18. The first data stream is provided to the actual arm filter 16, and the second stream of data is provided to the imaginary arm filter 18. When both real and imaginary arms 16 and 18 are "Nyquist" filters, the carrier signal modulated at the output terminal 14, then it is a modulated quadrature amplitude signal. The modulator 10 can be a BLV modulator when the digital data stream input at the input 8 is passed undivided via the solid line path of the control 12 to the real and imaginary arms 16 and 18. The modulator 10, produces signals modulated vestigial sideband when the weight applied to the real and imaginary arms 16 and 18 are appropriately determined as described more fully in my co-pending application. Referring now to Figure 2B, more particular detail is shown of a MAC / BLV control circuit 12 for a modulator 10 according to the present invention. The current of serial characters is input to a switch to switch between positions A and B according to the duration of the symbol T. Therefore, the switch is in position A when t (time) is at 0, T, 2T, 3T and so on and in B when t is in .5T, 1.5T, 2.5T and so on when A provides a connection to the actual arm filter 16 and B provides a connection to the imaginary arm filter 18. As already stated. described, the modulator operates on the center frequency and filters 16 and 18 are "Nyquist" filters. For example, the switch remains in its position A so that the duration of half the duration of the symbol passes half of a symbol to the real arm. Then, the switch changes to position B and resides in B for half the duration of one symbol to pass the other half of the symbol to the imaginary arm. The switch 12, of course, is appropriately closed and synchronized to do so with the stream of data input characters in series.

The modulator 300 of Figure 2C may be an alternative mode for the modulator 10 shown in Figure 2A. The modulator 300 includes filters of the real and imaginary arms 16 and 18, preferably "Nyquist" filters, and the phase cancellation circuit of the transmitter 310. The sound cancellation circuit of the transmitter 310, includes high-pass filter 312 (or bandpass) and adder 314 to cancel inherent phase sound produced during the modulation process. The output of the adder 314 provides the signal input to the second mixer 318, and the actual arm 16 provides the signal input corresponding to the first mixer 316. The modulator 300 controls the shape of the output spectrum in a modulation circuit of BLV or MAC. Figure 2C can be modified appropriately for O-QPSK by incorporating switch 12 of Figure 2B and operating in fcs. Referring now to Figure 3A, a digital data demodulator / decoder for the MAC or BLV signal to be tuned to the center frequency fcs is shown. The input signal received from an antenna, from a cable, an optical fiber and, as appropriate, already passing through a first demodulation stage at the intermediate frequency, is provided at input 31. The input signal is provided. both mixers 32 and 33 to be mixed with a central carrier frequency in phase or 90 ° out of phase by the "Hilbert" filter 34. The central carrier frequency is provided by oscillator 35 and is adjusted by a control signal output signal. decoding carrier frequency, carrier and clock recovery circuit 50. For example, oscillator 35 may be a voltage controlled oscillator (OCV) and the carrier recovery path may reflect a control voltage generated in a well-known manner to ensure that the fcs output does not creep in from the center of symmetry of the received information signal spectrum. The respective outputs of the mixers 32 and 33 are in turn provided by analog-to-digital data converters 36 and 37 operating in accordance with controlled clock outputs of the clock oscillator 42. The converted digital data streams output respectively of the analog-to-digital converters 36 and 37 operating in accordance with the controlled clock outputs of the clock oscillator 42. Converted digital data streams outputting respectively from analog to digital converters 36 and 37, are provided via digital pass-through or high-pass filters 38 and 39 to the decision circuits (data separators) 40 and 41 that provide binary pulse outputs if a data value, for example, of a received "eye" pattern exceeds an appropriate threshold as distinguished from noise and other possible data values. The digital phase and quadrature data streams are then provided to decode the circuit 50. The main purpose of the decoder circuit 50 is to output a stream of decoded serial characters, the details of which will be further described in relation to the following description of Figure 3B. The decoder circuit 50, in a well-known manner, provides a carrier recovery control signal to adjust the carrier frequency fcs of the carrier oscillator 35 if it is determined from the incoming data stream that the carrier frequency fcs is creeping towards left or to the right of the center of symmetry according to Figure 1B. In addition, in a well-known manner, the decoder circuit 50 provides a clock recovery control signal for controlling the clock oscillator 42 to operate the analog-to-digital converters 36 and 37 in accordance with the data rate. The clock oscillator 42 can be a voltage controlled oscillator (OCV) controlled by a voltage clock frequency control signal generated to ensure that the clock of recovered data, symbol clocks and all other related data clocks is maintained in proper frequency and do not crawl.

Additional details of the decoder circuit are provided in FIG. 3B in which it is shown that decoder circuit 50 operates as a switch between positions A and B. In addition, decoder switch 50 operates to switch between position A and separator output. data 40 and B at the output of the data separator 41 according to the duration of the input data symbol T, just like the analog switch 12 operated as shown in Figure 2B. Switch 50 will be in position A when t is at 0, T, 2T, 3T and so on at position B at t = .5T, 1.5T, 2.5T and so on. The switch 50 remains in one position or the other during 5T to collect half of the symbols in order to reconstruct them in the stream of serial input characters. In accordance with the present invention, filters 38 and 39 are shown as "Nyquist" filters to match the demodulation of a received MAC modulated signal. Also, in contrast to Figure 3A, Figure 3B shows mixers 32 and 33 fed by the cosine and sinus of the carrier frequency, writing to indicate that it is 90 degrees out of phase. While? Ct is used as a symbol, is it intended to be the angular velocity? relate as is well known, with frequency by? = 2 * (p) * f, where t represents the passage of time. Therefore, according to the present invention, a MAC demodulator that incorporates filtering with "Nyquist" and setting to tune the center frequency, demodulates a modulated data signal from the vestigial sideband by switching the separate symbol outputs of the arms together real and imaginary to form a stream of data in series according to the duration of a transmitted symbol. Having described the preferred embodiments of a novel MAC / BLV modulator and, in particular, of a demodulator / decoder to decode either MAC or BLV, it is seen that substantially the same circuitry and frequency (carrier) tuning are used to demodulate any transmitted signal; In addition, no data is lost during the demodulation / decoding process. Modifications and variations to the principles described herein can be made by those skilled in the art to the extent of current teachings for, for example, 4-BLV or 16-MAC data structures or more complicated ones. In addition, the present invention can be used in each of many transmission media including, but not limited to, satellite, cable, fiber optic or aerial transmission media. The described modalities are not intended to be limiting but can be adapted to be used in particular applications depending on economic, reliability and other considerations. What is a preferred embodiment for a particular application can not be preferred in another application. The circuitry described, for example, may take the form of integrated circuits and, in the case of at least the decoder circuit 50, in the form of an integrated circuit of a specific application.

Having thus described the invention with the details and particularity required. Those that are claimed and want to be protected by the Patent Title, is established in the following claims.

Claims (18)

1. CLAIMS 1. A synchronous detector for recovering a digital data signal from the demodulated output of a digital input data signal transmitted regardless of whether the transmitted digital input data stream is modulated according to a vestigial sideband or a modulation scheme of quadrature amplitude, the synchronous detector comprising a tuner fixed to a central carrier frequency of a modulated data spectrum, the tuner comprising real and imaginary arms and a decoder to receive sequences of digital data of the real and imaginary arms, the decoder operating selectively according to the duration of a transmitted data symbol.
2. 2. A synchronous detector according to claim 1, wherein the central carrier frequency of the modulated data spectrum comprises the frequency value of the center of symmetry of the information amplitude transmitted against the frequency spectrum.
3. 3. A synchronous detector according to claim 1, the real and imaginary arms comprising a mixer, an analog-to-digital converter coupled to the mixer and a data separator for outputting digital phase and quadrature data sequences respectively.
4. 4. A synchronous detector according to claim 3, the real and imaginary arms also comprising a filter "Nyquist" coupled to the outputs of the respective analog to digital converters to filter the respective digital signals that will be provided to the respective data separators.
5. 5. A synchronous detector according to claim 1, the decoder comprising particularly a two position switch for switching between an output of the actual arm and an output of the imaginary arm, the switch remaining in each position for a duration 5T equal to half of duration T of the transmitted data symbol.
6. 6. A synchronous detector according to claim 5, the switch to switch to the actual arm position at time t equal to the duration T, the duration of the transmitted data symbol, 2T, 3T and so on and to switch to the imaginary arm position at time t equal to .5T, 1.5T, 2.5T and so on.
7. 7. A modulator for modulating a digital data stream according to any BLV or MAC modulation scheme the modulator comprising a control circuit for alternately switching an input digital data stream to be modulated between a real arm and an imaginary arm and a modulator for modulating the digital data stream so that the carrier frequency is centered approximately symmetrically around the amplitude of data modulated against the frequency spectrum.
8. The modulator according to claim 7, the control circuit comprising a switch for switching between the real and imaginary arms so that the switch is connected to one or the other arm for half the duration of a data symbol transmitted.
9. 9. The modulator according to claim 8, the switch being connected to the real arm at time t equal to T, the duration of a symbol, 2T, 3T and so on and being connected to the imaginary arm at time t equal to .5T, 1.5T, 2.5T and so on.
10. 10. The modulator according to claim 7, the real and imaginary arms each comprising a Nyquist filter and a mixer.
11. 11. The modulator according to claim 7, further comprising a cancellation circuit coupled between the real and imaginary arms.
12. The modulator according to claim 11, the cancellation circuit comprising a stirring cancellation filter, a graduation circuit for adjusting the output of the filter according to a factor k, which may comprise a resistor or an amplifier, and an adder circuit for adding the graduated output of the graduation circuit to the output of an imaginary arm filter.
13. 13. A method for demodulating and decoding a digital data stream modulated according to a vestigial sideband or a quadrature amplitude modulation scheme the method comprising tuning steps in each of a phase and a quadrature arm of a demodulator to a central frequency of the modulated data spectrum and reconstructing the digital data stream according to the symbol regime of the transmitted digital data stream.
14. A method for demodulating and decoding a digital data stream according to claim 13, wherein the step of reconstructing the digital data stream comprises the steps of converting the output of a mixer in each arm to a digital signal and decide if the recovered signal exceeds a predetermined threshold.
15. A method for demodulating and decoding a digital data stream according to claim 13, wherein the step of reconstructing digital data stream comprises the step of switching between the in-phase and quadrature arms according to half of the duration of a transmitted data symbol.
16. 16. A method for demodulating and decoding a digital data stream according to claim 13, further comprising the step of subtracting the transmitted carrier signal from a received signal.
17. 17. A method for modulating a digital data signal according to a vestigial sideband modulation or quadrature amplitude scheme comprising the steps of switching to real and imaginary arms of a modulator according to the duration of a transmitted data symbol and modulating the digital data stream around a carrier frequency symmetrically centered in the modulated digital data signal spectrum.
18. 18. A method for modulating a digital data signal according to claim 15, further comprising the step of canceling phase sound between the real and imaginary arms.