Abstract: A device and a method correct deviation when transferring an information-carrying signal between a transmitter and a receiver. The transmitter can transmit with a plurality of frequencies generated by a voltage-controlled oscillator used for phase demodulation. The receiver demodulates the modulated information-carrying signal. A detector measures the deviation of the modulated information-carrying signal via the information-carrying signal demodulated in the receiver. The frequencies of the demodulated information-carrying signal can be adjusted so that the correct deviation is obtained, and a correct phase demodulation can be carried out.

Abstract: Briefly, in accordance with one embodiment of the invention, an oscillator frequency offset error estimator at the receiving end of a wireline communications system comprises: a phase comparator adapted to compare two successive signal samples, each signal sample being derived from a baseband signal transmitted via the wireline communications system. The phase comparator is further adapted to have at least one of the two signal samples provided along a signal path through a phase shifter and a time delay.

Abstract: A communication device which is capable of automatically discriminating whether a received signal is a carrier-wave-modulated signal or a single-pulse-modulated signal and obtaining a corresponding demodulated signal, thereby reducing a burden to a user in using the device. The device comprises a demodulating circuit for demodulating a carrier-wave-modulated signal, a demodulating circuit for demodulating single-pulse-modulated signal, a switch circuit for selecting either of two demodulating circuits and a carrier detecting circuit for detecting the presence or absence of a carrier-frequency component of the carrier-wave-modulated signal, characterized that the switch circuit selects an output of the demodulating circuit for the carrier-wave-modulated signal when the carrier of the carrier-wave-modulated signal is detected by the carrier detecting circuit.

Abstract: A system and method for synchronizing a Costas Loop for demodulating a received spread-spectrum signal using a squaring device, a filter, a phase detector, a phase unwrapping subsystem, an oscillator, a derotator and a decision device. Phase-shift-keying modulation is removed from a received spread-spectrum signal through squaring. An in-phase component and a quadrature-phase component of the received spread-spectrum signal are filtered to generate an arbitrary phase angle, .theta.(t). A value of .theta. proportional to .theta.(t) is then estimated. The estimated .theta. value is processed to obtain an estimate for the .phi. value, and a cosine and a sine of the estimated .phi. value are generated by the oscillator. The derotator derotates the in-phase-component and the quadrature-phase component of the received spread-spectrum signal with the cosine and the sine of the estimated .theta. value to generate a demodulated signal. The decision device evaluates the demodulated signal and outputs data.

Abstract: The method makes it possible digitally to evaluate the phase of any carrier that has been subjected to rPSK modulation subsequent to clock recovery, sampling, and digitizing the in-phase and quadrature components of the samples, by processing that is performed in polar coordinates and that comprises reducing the range over which the phase of each sample is defined to a range of +.pi./r to -.pi./r and then seeking the center of gravity over 2.sup.N successive samples (N being an integer) by performing successive averaging calculations, each time on two values, in application of an N-stage tree structure. Each average of two values is associated with an index indicative of the degree of reliability of the average, and those averages which are associated with a small reliability index are ignored while calculating subsequent averages in the tree structure.

Abstract: A method of estimating signal quality in a radio demodulator receiving an input stream of symbols includes the steps of sampling a phase-only portion of each of the symbols in the input stream, determining a phase error for each of the samples of the phase-only portions, and calculating a signal quality estimate from a plurality of the sample phase errors. The signal quality estimate may be an average magnitude of a predetermined number of sample phase errors. The input stream may be symbols in the preamble, or symbols in the data signal that follows.

Abstract: Delayed symbols (204), including a current symbol (205), are compared by a comparator (206) with at least one predetermined pattern when the current symbol is equivalent to one of a set of predetermined values. Alternatively, a sign of the current symbol is compared with signs of a previous and a subsequent symbol when the current symbol is equivalent to one of the set of predetermined values. When the current symbol is equivalent to one of the set of predetermined values and when either the delayed symbols are equivalent to one of the at least one predetermined pattern or the sign of the current symbol matches the signs of the previous and subsequent symbols, a symbol corrector (208) applies a predetermined function to the current symbol to produce a received symbol (210).

Abstract: When a signal modulated by a multi-subcarrier modulation scheme is to be demodulated, an amplitude detection unit sequentially detects the amplitudes of a subcarrier-synthesized signal to accurately set a symbol discrimination timing for the modulated signal within a short period of time. A reference amplitude storage unit stores a reference amplitude at a portion corresponding to a predetermined reference symbol portion included in the received signal. A correlation calculation unit sequentially calculates correlation values between amplitudes sequentially detected by the amplitude detection unit and the reference amplitude. A discrimination timing determination unit determines a symbol discrimination timing on the basis of time representing a maximum value of the correlation values sequentially calculated by the correlation calculation unit. When the signal modulated by the multi-subcarrier modulation scheme is to be demodulated, a phase detection unit detects a phase .theta.

Abstract: A method in which correctable I/Q imbalance errors in a complex receiver can be detected and compensated for digitally without the use of special calibration signals. Differential D.C. offset errors are compensated by averaging the incoming I.sub.d and Q.sub.d digital signals and subtracting from them an expected value of differential D.C. offset, for example, computed from the long term average of the I and Q signals to create I' and Q' signals. Differential gain imbalance errors are corrected by calculating a root means square average of the I' and Q' digital signals and applies to them compensation coefficients K.sub.x and K.sub.y determined from either the RMS average or from a Stochastic Gradient Algorithm. The DSP compensates for the quadrature phase errors by calculating a compensation matrix which is independent of the frequency of the carrier and applies the compensation matrix to the I' and Q' digital signals.

Abstract: Apparatus for correcting quadrature error in a quadrature modulator and/or in a demodulator for a signal having a plurality of phase states, or of amplitude and phase states. The correction apparatus comprises a processor (51) which, when the apparatus is used to correct quadrature error in a demodulator, transforms the levels P and Q of the digital signals output by the demodulation stage into corrected levels P' and Q' that satisfy any one of the following eight relationships: ##STR1## These corrected levels are then applied to decision element (72), optionally after their maximum levels have equalized. The apparatus combines correction accuracy with cheapness, and it enables any quadrature error to be corrected.

Abstract: A method for detecting a locked condition of a demodulator of at least one signal that may have discrete levels defining a constellation of nominal points in a plane. The method includes the steps of defining reference areas about the nominal points, a reference area being separated from another by a band or an angular sector crossing the origin of the constellation plane, and indicating a locked condition if the ratio of points occurring in the reference areas is above the probability for points to occur in the reference areas when the demodulator is wrongly adjusted.

Abstract: A method and apparatus for improved mobile radio telecommunications employs the transmission of a pilot reference signal within the coherence band of the modulated carrier wave. The receiver in this system uses instantaneous phase estimation techniques of the pilot and carrier received waveforms to provide immunity from phase distortion introduced by the channel.

Abstract: A common transceiver circuit for use as either a modulator or demodulator and that is implemented through a shared resource approach. This approach is particularly, though not exclusively, suited for with quadrature amplitude modulated (QAM) or vestigial sideband (VSB) signals. Specifically, a QAM transceiver circuit (400), through strategically located multiplexing stages, physically re-uses both a complex Nyquist filter (310, 320) and an equalizer (140) for demodulation and modulation. Additionally, tap coefficients of the complex Nyquist filter are set such that a center frequency of an otherwise baseband Nyquist filter is translated upward to a symbol rate in order to eliminate a separate complex mixer (250, 260). Similarly, a VSB transceiver circuit (700), also through strategically located multiplexing stages, physically re-uses a complex vestigial Nyquist filter (610), a complex mixer (620) and an equalizer (785) during demodulation and modulation.

Abstract: A locally coherent Quadrature Phase Shift Keying (QPSK) detector that uses a normalized fourth power weighting technique to generate an ambiguous local phase reference of a current symbol. A phase adjusted previous symbol reference is used to resolve the ambiguity using differentially coded data and yield current soft symbol information.

Abstract: Systems and methods according to the present invention provide a combination of demodulation and decoding, termed decodulation herein. By using knowledge of known symbols, decoding known symbols first, and then using the information obtained by decoding known symbols to decode unknown symbols, improved performance can be achieved. This technique can also be used to alleviate the conventional 3dB loss suffered systems using differentially coding and modulation as compared to coherent detection systems.

Abstract: The present invention relates to a quasi-synchronous detection and demodulation circuit with a contingent demodulation carrier phase removing function and to a frequency discriminator used in the above circuit and for detecting with a good accuracy the difference between the carrier frequency of a modulated wave and a reference carrier frequency for demodulation. In order to detect a normal frame pattern by a frame pattern detecting means, the quasi-synchronous detection and demodulation circuit compensates an output carrier phase issued from a carrier generating means to add to a phase rotation means and removes a contingent demodulated carrier phase. The frequency discriminator limits a frequency deviation to less than an upper value according to the accuracy of a reference carrier signal.

Abstract: The present invention concerns a signal processor module (SPU,AVF) which is adapted to check if a received vector (RV) representing a received signal in a QAM signal vector plane is located in the intersection zone of a first and second zone (ABCDEF,ab) of this signal vector plane. The intersection zone is well chosen so that the phase angle difference (Da) between the received vector (RV) and an expected vector (EV) which represents a signal which should have been received instead of the received signal and which is located in the intersection zone, is limited.

Abstract: A clock recovery circuit capable of outputting decision point data without causing any slip of a recovered clock in the case of operation in a continuous mode in a demodulator in which received signals are sampled by a fixed frequency clock to obtain the recovered clock and symbol data are demodulated by using this recovered clock. A shift register stores digital received signals obtained by an A/D conversion of quasi-coherent detection received signals, and a clock phase estimator calculates an estimated phase difference between an output value of a phase generator operated by the fixed frequency clock and a symbol clock of the received signals and outputs timing information and phase information of a decision point for discriminating the data of the received signals. An interpolator inputs the output signal of the clock phase estimator, takes in the digital received signals from the shift register and calculates decision point data by interpolation to output the same.

Abstract: A cellular subscriber modem for receiving CCITT-type quadrature amplitude modulated (QAM) signals. The cellular modem includes a novel symbol detector that converts received symbol information to polar notation. The detector's constellation thresholds include a circular threshold having a radius greater than the magnitude of the innermost symbols, but less than the magnitude of the outermost symbols, and radially spaced thresholds, which further discriminate between the outermost symbols. As a result, special cellular-compatible modem equipment need not be connected between the public-access switched telephone network and the computer equipment at the other end, which means that a CCITT-compatible cellular subscriber modem can then be treated as any other type of CCITT-modem. The detector may be implemented in the software of a standard modem processor, or as several analog comparator circuits.

Abstract: A method is described for detecting erasures in a stream of sets of digital signal values received at a receiver side after transmission from a transmission side. Subsets of these sets are modulated on distinct carrier signals, each transmitted and received thus modulated carrier signal corresponding to one of a number of predetermined subset related points and to a receipt point on a carrier dependent modulation representing map respectively. The method includes the steps of:selecting for each receipt point the nearest of the predetermined subset related points;calculating a distance between the receipt point and the nearest subset related point and multiplying this distance with a map dependent weight factor;summing the thus obtained weighted distances for all subsets of a set; andmarking the latter set as an erasure when the thus obtained result exceeds a predetermined threshold.

Abstract: An apparatus for demodulating a phase modulation wave reduces an error rate of a demodulating circuit to perform a delay detection of an n-phase shift keying modulation wave without raising a clock frequency. When converting the received n-phase shift keying modulation wave into a rectangular wave, a waveform converting circuit for converting the n-phase shift keying modulation wave into a rectangular wave of a duty ratio which is larger or smaller than 50% is used. The rectangular wave is clocked through parallel registers of different lengths, outputs of the registers being operated on by exclusive-OR gates with the rectangular wave. Outputs of the gates are applied to respective one of a pair of counters, operated by a common clock signal, during periods of equality of outputs signals of the gates to provide a function of discriminating reproduction. A parallel/series converting circuit arranges upper bits and lower bits for reconstruction of each symbol of an original data message.

Abstract: A clock recovery circuit capable of outputting decision point data without causing any slip of a recovered clock in the case of operation in a continuous mode in a demodulator in which received signals are sampled by a fixed frequency clock to obtain the recovered clock and symbol data are demodulated by using this recovered clock. A shift register stores digital received signals obtained by an A/D conversion of quasi-coherent detection received signals, and a clock phase estimator calculates an estimated phase difference between an output value of a phase generator operated by the fixed frequency clock and a symbol clock of the received signals and outputs timing information and phase information of a decision point for discriminating the data of the received signals. An interpolator inputs the output signal of the clock phase estimator, takes in the digital received signals from the shift register and calculates decision point data by interpolation to output the same.

Abstract: Frame synchronization for data transmitted using quadrature amplitude modulation is achieved by providing that one symbol per frame is chosen from a larger signal point constellation than the remaining symbols. Thus, bits are assembled into groups of unequal size to control the mapping between the data and the signal points. Where constellations having a number of points not equal to a power of two, these may be coded in groups; or the data may be converted into a mixed-base number the bases of which correspond to the number of points in the respective constellations.

Abstract: A television receiver includes a synchronous demodulator including a bi-phase stable PLL for controlling sampling of the received signal to produce data. A phase inverter reverses the phase of the data in response to a control signal. Data segment sync characters are recovered with a sync correlation filter that also yields a sign bit indicating polarity. If the sign bit is wrong for a predetermined number of data segment sync characters, a control signal is produced to operate the phase inverter.

Abstract: A received signal sample sequence is inversely modulated by a symbol sequence forming the trellis state at the immediately preceding time, by which a reference signal is generated. This reference signal and the inner product of the received signal sample at the current time and a candidate symbol phase are used as a branch metric to make a sequence estimation by the Viterbi algorithm.

Abstract: A demodulation apparatus of digital detection processing type of the invention offers versatility as consumer equipment in mobile communications, ATV, satellite broadcasting, CATV, and the like. A modulated wave output is obtained by multiplying an input digitally modulated wave signal by a local oscillating signal from a local oscillator. The obtained modulated wave output has a center frequency which is substantially equal to the symbol frequency. The modulated wave output is A/D converted at a rate which is four times as high as the symbol frequency, so as to be output as interleaved I and Q digital data. The I and Q data is split, and the split I and Q data are multiplied by coefficients of "+1" and "-1", respectively. The multiplied two output signals are selectively output. Thus, the data multiplied by the coefficients of "+1" and "-1" are alternately output for the I and Q signals, so as to perform the digital detection.

Abstract: A digital demodulator and method for demodulating digital data representing a phase shift keyed (PSK) signal are provided. The demodulator comprises a phase detector, automatic frequency controller, automatic timing recovery controller, data decoder, and unique word detector. According to the method of the present invention, a PSK signal is received and digitized to substantially remove the signal's amplitude characteristics. The phase detector receives an input of the digital data and based upon transitions in the data from a high state to low state and from a low state to a high state, provides phase estimates. The phase estimates are converted by the data decoder into binary data representing the symbols transmitted to form the PSK signal. A number of overlapping windows of digital data are used to determine phase estimates.

Abstract: Efficiency of a digital link, e.g., a microwave link, is improved by coding numeric signals for transmission so as to transmit selected sequences, in terms of peak power of a filtered signal, for transmission through the link. The most favorable numeric sequences may be encoded by baseband numeric coding.

Abstract: To prevent a coefficient vector for a modulated wave candidate of repeated identical codes from diverging, an error calculating part (36) calculates the difference between a vector X(i) with elements of input signals x(i) at N successive times and a vector Y.sub.m (i) of N replica signals y.sub.m (i) received from a transversal filter (34) to obtain an error vector E.sub.m (i), the square of the norm of which is supplied to a maximum likelihood sequence estimating portion (31), when signal estimation is carried out. In addition, a code sequence candidate {a.sub.m } is produced and a corresponding modulated wave candidate s.sub.m is generated. The filter (34) calculates the inner product of the modulated wave candidate s.sub.m and the coefficient vector W.sub.m (i-1) corresponding to each state to produce y.sub.m (i). W.sub.m (i-1) of each state is updated to W.sub.m (i) using an inner product vector of a generalized inverse matrix produced from s.sub.

Abstract: A multiple-modulation communication system includes a transmitter that modulates and transmits communication signals modulated by a first modulation technique and communication signals modulated by a second modulation technique. The first modulation technique and the second modulation technique are different. The communication system also includes a receiver capable of receiving the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique and demodulating the communication signals.

Abstract: The invention relates to a method for demodulating a digitally modulated signal and to a demodulator. According to the method, a signal (S) to be received is mixed essentially to quadrature related I and Q baseband signals. For improving the interference tolerance of the demodulator, for instance, differences (.alpha.) between directional angles (.beta., .gamma.) of sequential shifts of a signal point on I/Q plane are measured from the baseband signals and said difference is utilized for decision-making concerning a received symbol.

Abstract: A digital demodulator and method for demodulating digital data representing a phase shift keyed (PSK) signal are provided. The demodulator comprises a phase detector, automatic frequency controller, automatic timing recovery controller, data decoder, and unique word detector. According to the method of the present invention, a PSK signal is received and digitized to substantially remove the signal's amplitude characteristics. The phase detector receives an input of the digital data and based upon transitions in the data from a high state to low state and from a low state to a high state, provides phase estimates. The phase estimates are converted by the data decoder into binary data representing the symbols transmitted to form the PSK signal. A number of overlapping windows of digital data are used to determine phase estimates.

Abstract: The present invention relates to a quasi-synchronous detection and demodulation circuit with a contingent demodulation carrier phase removing function and to a frequency discriminator used in the above circuit and for detecting with a good accuracy the difference between the carrier frequency of a modulated wave and a reference carrier frequency for demodulation. In order to detect a normal frame pattern by a frame pattern detecting means, the quasi-synchronous detection and demodulation circuit compensates an output carrier phase issued from a carrier generating means to add to a phase rotation means and removes a contingent demodulated carrier phase. The frequency discriminator limits a frequency deviation to less than an upper value according to the accuracy of a reference carrier signal.

Abstract: An in-phase component and a quadrature component of a digitized input DQPSK modulated signal are provided from interpolation filters, respectively. An instantaneous amplitude and an instantaneous phase of the input signal for each symbol clock are detected from the in-phase and quadrature components and are fed to adders. At the same time, that one of symbols "0, 0," "0, 1," "1, 0" and "1, 1" which corresponds to the instantaneous phase is detected by a symbol detector. An ideal reference signal generating part generates an ideal amplitude component and an ideal phase component corresponding to the detected symbol and provides them to a parameter calculating part. In an I-Q origin offset detecting part, an I-Q origin offset is calculated on the basis of the relationship between a triangle formed by the current detected vector corresponding to an ideal symbol and a vector detected one symbol clock before and a triangle formed by the said two vectors.

Abstract: A frequency offset compensation method has the steps of raising the detected signal to the M-th power to remove a modulation factor from the received signal, and accumulating the M-th power signals for N (N is an integer) symbols to derive a phase component of the accumulated M-th power signals. Then, the derived phase component is divided into M so as to obtain an estimation value with respect to phase shift due to frequency offset which represents frequency deviation from a true carrier frequency contained in the received signal, and the received signal is multiplied by the obtained estimation value in a form of conjugate complex number to remove the phase shift due to the frequency offset from the received signal.

Abstract: A circuit and method for demodulating a .pi./4-DQPSK (differentially quadrature phase shift keying) modulated signal. A receiving .pi./4-DQPSK modulated signal is shifted to a base band and simultaneously separated to an I channel and Q channel. The separated I channel and Q channel signals are converted into digital data. The digitally converted data is stored in a memory and decoded to binary data by phase comparison or Viterbi algorithm.

Abstract: A method for demodulating pulse messages, which have been converted into modulated signals, preferably for wireless digitized speech transmission, which is distinguished by minimal technical outlay and which can be carried out using circuits which can be designed in integrated circuit technology. The signal which is to be demodulated is subjected to quadrature modulation. Of the two quadrature components which have been thereby obtained one is subjected to a differentiation or an integration and the signal obtained in this manner and the signal of the other quadrature component are supplied, after analog-to-digital conversion, to in each case one comparator (9, 10). The digital output signals of the two comparators (9, 10) are assembled by means of a coincidence gate (11) to form the pulse message.

Abstract: A method is disclosed of demodulating a signal (20) modulated by differential quadrature phase shift keying so that two bits of information are coded into each symbol period. The method comprises using a high frequency clock to determine the time taken (t.sub.1, t.sub.2, t.sub.3, t.sub.4), for the modulated signal to execute a predetermined number of cycles, such as 21, in the symbol period (T) and comparing the time thereby determined with the time (t.sub.o) of execution of the predetermined number of cycles for an unmodulated signal.

Abstract: In a digital wireless communication system operating between a first unit and a second unit, the first unit transmits a digitally encoded RF signal at a first frequency in a plurality of a non-contiguous time slots to the second unit. The second unit receives the digitally encoded RF signals. The received RF digitally encoded signal is converted to an intermediate frequency (IF). An A to D converter samples the received IF digitally encoded signals and generates a plurality of discrete binary symbols during one of the plurality of non-contiguous time slots. A phase error signal is generated for each one of the plurality of discrete binary symbols. A frequency error signal is generated for the subsequent symbol in accordance with .DELTA.f(n+1)=.DELTA.f(n)+g.sub.1 (.crclbar.(n)-.crclbar.(n)). The conversion of the RF signal to intermediate frequency is controlled in response to the frequency error signal.

Abstract: An object of the present invention is to provide a soft decision circuit by which the reception accuracy can be improved. Each of first and second receivers of the soft decision circuit includes a phase amount detector for detecting a phase amount of a receive signal, an I table and a Q table for converting the phase amount into orthogonal I/Q signals, an A/D converter for converting a receive level signal of the receive signal into a digital value, a log linear table for converting an output of the A/D converter into a squared value of a true value, and first and second multipliers for multiplying outputs of the I table and the Q table with the output of the log linear table to weight the outputs of the I table and the Q table.

Abstract: A data receiving apparatus includes: a receiving portion for receiving a QPSK (PSK, GMSK) signal using a local oscillation signal; a forward (FWD) equalizing portion for effecting a FWD equalization to the PSK signal using FWD tap coefficients, including a FWD main tap coefficient, successively renewed; a backward equalizing portion for effecting a backward equalization to the PSK signal using backward tap coefficients, including a backward main tap coefficient, successively renewed; and a prediction portion for predicting a phase difference between a carrier frequency of the PSK signal and the local oscillation frequency according to the FWD and backward main tap coefficients. In this apparatus, the FWD and backward equalizing portions effect FWD and backward equalizing training processings using the sync word in the PSK signal in the FWD and backward directions to determine the FWD and backward tap coefficients before FWD and backward equalizations respectively.

Abstract: An automatic frequency control apparatus used in an MPSK communication system detects a frequency offset between a carrier and a local oscillation signal for adjustment of a local oscillation frequency. A phase difference detector generates a first phase difference detection signal having, as a phase value, a difference between the phases of various samples of the sampled signal. A phase altering unit generates a second phase difference detection signal having a phase value different from that of the first phase difference detection signal. A frequency offset signal generator estimates transmission phase information by using the phase value of the second phase difference detection signal and reference phase signals used for MPSK modulation, thereby generating a frequency offset signal which is determined by the transmission phase signal and the second phase difference detection signal.

Abstract: At the transmitter side of a signal transmission system, carrier waves are modulated according to an input signal for producing relevant signal points in a signal space diagram. The input signal is divided into two, first and second, data streams. The signal points are divided into signal point groups to which data of the first data stream are assigned. Also, data of the second data stream are assigned to the signal points of each signal point group. A difference in the transmission error rate between the first and second data streams is developed by shifting the signal points to other positions in the space diagram. At the receiver side of a signal transmission, the first and/or second data streams can be reconstructed from a received signal. In TV broadcast service, a TV signal is divided by a transmitter into two, low and high, frequency band components which are designated as a first and a second data stream respectively.

Abstract: A selectable demodulator (32) operates in the phase domain to implement a coherent demodulation path (40) and a differentially coherent demodulation path (42). The coherent path (40) includes a differential encoder circuit (46) to produce coherently demodulated differential data. Magnitude converters (62, 62') convert phase errors in each path into magnitude values. A comparison circuit (66) compares magnitude values from the two paths (40, 42) and selects the path encountering the least phase error. A selection circuit (60) provides data codes demodulated in accordance with the selection.

Abstract: In a communications system, an apparatus and method for detecting a valid signal from noise. An adaptive threshold is used to qualify a received signal. The adaptive threshold is set according to the number of false detects occurring within a given time interval. The number of false detects is initially determined by a quick qualification process. This initial number is subsequently adjusted by a more accurate qualification process. The transmitted signal is modulated with a particular pattern. Upon receiving the signal, it is demodulated to retrieve that pattern. The demodulated pattern is correlated against multiple reference patterns and combined to provide a measure of peak correlation that is independent of pattern phase. Furthermore, a tone detector is used to distinguish valid signals from interfering tones. Two different types of detection methods are performed in parallel. One is based on the energy of the received signal, whereas the other is based on the correlation of the received signal.

Abstract: Information often modulates an underlying carrier signal, thereby producing a modulated information signal 70. This same carrier signal is required, with a few modifications, to demodulate the modulated information signal. This required signal is called the demodulator reference signal. It must be complex, that is, it must contain separate in-phase and quadrature outputs. A degraded version 10 of this signal is often available with the correct frequency, but with the wrong phase and amplitude, and with a direct current (dc) offset. The present invention 68 produces a digital demodulator reference signal 38, 46 from the degraded signal 10. It eliminates dc offset with a dc blocker 18, adjusts amplitude with a scaler 14, adjusts phase with a first Hilbert transformer 20, multipliers 26 and 28 and summer 34, and produces in-phase and quadrature outputs with a second Hilbert transformer 36 cascaded with the first.

Abstract: A demodulator (20) demodulates a received signal having phase information into a demodulated signal by differential detection. The demodulator comprises a delay section (22-1 to 22-3) which is supplied with an input signal based on a received signal. The delay section delays the input signal to produce first through third delayed signals which have first through third delayed times different from one another. A differential detecting section (23-1, 23-2) carries out differential detection in accordance with the input signal and the first through the third delayed signals to produce first and second output signals. A first correcting section (24) corrects the first delayed signal on the basis of the first output signal to produce a first corrected signal. A second correcting section (25) corrects the second delayed signal on the basis of the second output signal to produce a second corrected signal.

Abstract: A modulation circuit for a digital signal recorder includes first and second high-pass filters for removing the direct current component in the output of the coded I and Q channels and for converting a 4-levels signal into a 7-levels signal. Additionally, a carrier signal generator for generating a carrier signal, a modulator for performing quadrature amplitude and phase modulations on the outputs of first and second high-pass filters using the carrier signal, a pilot signal generator for generating a pilot signal and combining the pilot signal with the output of modulator and for outputting the result for transmission or recording are also provided.

Abstract: A digitized quasi-phase synchronous phase detecting signal of the PSK signal is used to generate digitized quasi-synchronous phase detecting signal phase-corrected by phase correcting data and a first phase display data indicating the phase of the carrier of the PSK signal is generated from the phase-corrected digitized quasi-synchronous phase detecting signal. Alternatively, the digitized quasi-synchronous phase detecting signal of the PSK signal is used to generate second phase display data indicating the phase of the carrier of the PSK signal and third phase-corrected phase display data is generated from the second phase display data. The first or third phase display data is used to generate fourth phase display data indicating the phase assigned to the code of the PSK signal and a decoded digitized code is generated from the fourth phase display data.

Abstract: In quadrature amplitude modulation, circular concentric decision regions capitalize on the observation that when the sample matrix is rotating, it is possible to identify samples more accurately by the radius of their orbit rather than their phase at any given time. The first embodiment provides that a scalar 1.sub.i is calculated for each constellation point so that the constellation point corresponding to the minimum 1.sub.i value is the symbol which the decision device decides was transmitted. The nearest constellation point having the minimum magnitude difference represents the decision. In the second embodiment, two complementary weighting factors are used to provide a weighted average of the two decision criteria in order to make the correct decision. .alpha. is the weight for representing standard rectangular decision regions, while (1-.alpha.) is the weight for representing the circular decision regions. The range for .alpha. is 0<.alpha..ltoreq.1. The variable .alpha.