Abstract: In a digital receiver, an equalizing unit includes a power controller adapted to scale received components of a quadrature amplitude modulated signal based on a constellation size of the quadrature amplitude modulated signal. Alternatively, a method of scaling components of a quadrature amplitude modulated signal includes the steps of searching the quadrature amplitude modulated signal to determine a constellation size, and scaling the components of the quadrature amplitude modulated signal based on the constellation size.

Abstract: A desired signal having a wide frequency band and including sequential symbols representing digital values is discriminated from a narrow band interfering signal having a carrier frequency in the wide band by initially applying both signals to a filter so both signals are passed to an output of the filter. In response to the filter output, estimates of the values of received symbols of the desired signal are derived and compared to the filter output to derive an error representing signal. A characteristic of the filter is controlled in response to the error representing signal so the filter is adjusted to reject the interfering signal and pass the desired signal.

Abstract: A waveform equalization coefficient generator for generating equalization coefficients for taps of digital filters for equalizing signal waveforms is disclosed which is smaller in circuit size and consumes less electric power in comparison with conventional waveform equalization coefficient generators. In a data selection means in a complex arithmetic unit, a first data selection unit selects between real part data and imaginary part data of an equalization coefficient, a second data selection unit selects between real part data and imaginary part data of a received signal, and a third data selection unit selects between EI (error data in the I-axis direction) and EQ (error data in the Q-axis direction). A sum-of-products means is provided which has one multiplier and one adder.

Abstract: A polyphase quadrature digital tuner system which converts input signals to baseband inphase and quadrature signal components. The system includes a signal receiver which receives the input signals having a frequency centered around a predetermined carrier frequency. A signal processor continuously samples the input signals and multiplies selected portions of the input signals by a value of 1 or -1 to produce discrete sequences of N input samples, where N is an integer. An inphase signal channel includes a first set of N filters in a first filter stage each having respective filter coefficients, the first set of filters arranged to receive the discrete sequences, and a first signal summer which sums the outputs of the first set of N filters to produce the inphase signal component.

Abstract: Methods and apparatus for detecting and correcting phase and amplitude imbalances existing between I (in-phase) and Q (quadrature phase) signal components of a complex signal, e.g., QAM or OPSK signal, that is being demodulated are described. The phase and amplitude imbalance and correction circuitry of the present invention are implemented as decision directed control loops which can be used in conjunction with an overall decision directed gain control loop. Amplitude imbalance is corrected by adjusting the gain of one of the I and Q signal components. Phase imbalance is corrected by adding a portion of one of the I and Q signal components to the other one of the I and Q signal components. Overall amplitude control is achieved by adjusting the gain of both the I and Q signal components by the same amount.

Abstract: A demodulator using quasi-synchronous detection to demodulate modulated quadrature input signals. The demodulator has a quasi-synchronous detector detecting a modulated quadrature input signal using an output signal of a fixed frequency from a local oscillator, an equalizer equalizing a quadrature channel signal which is a digital signal converted from the detected quadrature signal from the quasi-synchronous detector, and a phase rotator rotating the phase of the equalized quadrature channel signal output from the equalizer. Furthermore, the demodulator has an equalization control unit to generate a tap factor for the equalizer from the quadrature channel signal equalized by the equalizer, using a signal having substantially the same phase as the input-output signals of the equalizer.

Abstract: A system for equalizing an input signal including a datastream modulated on a carrier, with respect to both transmission channel distortions and local receiver distortions, includes a network for frequency downshifting the input signal, a controlled non-recursive filter (20) responsive to the downshifted input signal, and a demodulator (30) for receiving an output signal from the controlled filter. A signal processing network, including a filter network with a transfer function (40, 60, 80, 100) which is the inverse of the transfer function of the controlled filter, responds to an output signal from the demodulator for producing output control signals. The control signals are coupled to a coefficient control input of the non-recursive filter for equalizing the signal with respect to both transmission channel and receiver distortion.

Abstract: A television receiver for processing both analog television signals and digital television signals. Specifically, the television receiver contains a RF/IF front end, an analog-to-digital converter that samples a near baseband signal using a "free running" sample rate, and a combined demodulator that demodulates the digitized analog television signals or the sampled digital television signals. The combined demodulator recovers both pilot and pix carriers as well as provide a passband adaptive equalizer that removes ghosts from analog television signals and intersymbol interference from digital television signals.

Abstract: The invention provides an automatic amplitude equalizer for compensating an amplitude characteristic of an input signal, wherein a control signal for equalizing an inclination amplitude distortion of an input signal is detected making use of a pair of digital demodulated signals to compensate for the amplitude characteristic of the input signal with a high degree of accuracy and which can be constructed with a reduced circuit scale and at a reduce cost.

Abstract: An adaptive channel equalizer for use in OFDM receiver is disclosed.

Abstract: A new filter that may be employed in timing recovery circuits, and automatic gain control circuits, employs a so-called vector tracking filter (VTF). The VTF includes a complex filter with a time constant so long that it might be considered a leaky integrator. In operation, the VTF builds up an average vector (timing (gain) estimate vector) having a direction that is the average of the estimated timing (gain) error, which is stored in the VTF. When the VTF is employed in an automatic gain control arrangement, the vector becomes a scalor and only the amplitude is tracked. When an arbitrary timing (gain) correction is made, to the incoming signal, this causes a rotation of the timing (gain) estimate vector. In order to track this rotation, a comparable rotation is made to the stored timing (gain) estimate vector.

Abstract: A communication device (100) includes an equalizer (126) for correcting imbalance between in-phase and quadrature components of a received signal. The equalizer (126) determines peak amplitude for the in-phase and quadrature components, and the phase imbalance between both components (440). At least one of the in-phase and quadrature components is adjusted based on a function of the phase imbalance, and of the ratio of peak amplitudes of the in-phase and quadrature components (450, 460).

Abstract: A method and apparatus for inter-cross wave compensation. There are provided a frequency conversion unit for performing frequency conversion for one of two received polarized wave signals, an analog/digital converter for converting the one of the polarized wave signals into a digital signal, a digital orthogonal detection unit for obtaining two orthogonal detection signals, and a digital equalizing unit for performing an equalizing process for outputs of the orthogonal detection unit. Further provided are a digital inter-cross wave compensating unit for receiving the other of the two received polarized wave signals as a digital signal and for outputting a signal used for compensating the output of the equalizing unit, and an adding unit for adding the output of the equalizing unit and the output of the digital inter-cross wave compensating unit.

Abstract: A log polar digital filter for processing a digitized log polar signal that is a magnitude signal (r.sub.in) and an angle signal (PHI.sub.in), has a first converter for converting the log polar signal into a converted linear Cartesian signal that includes an in-phase signal (I.sub.in) and a quadrature signal (Q.sub.in). A linear Cartesian digital filter, coupled to the first converter, generates a filtered linear Cartesian signal from the converted linear Cartesian signal. The first converter may adapt a linearization of r.sub.in and compensate for gain errors introduced in an analog circuit that supplies a signal from which the digitized log polar signal is derived. In another feature, a second converter may also be provided for converting the filtered linear Cartesian signal into a filtered log polar signal that includes a filtered magnitude signal (r.sub.filt) and a filtered angle signal (PHI.sub.filt).

Abstract: Improvements to amplitude phased keyed digital communications systems and to the processing of amplitude phase keyed symbols transmitted over radio frequency channels. The present invention provides for an amplitude phased keyed digital communications system including an adaptive baseband equalizer, a digital symbol recovery circuit in accordance with the present invention, and a quadrature demodulator. The adaptive baseband equalizer receives amplitude phased keyed signals and outputs in-phase and quadrature digital amplitude values corresponding to the received amplitude phased keyed signals. The digital symbol recovery circuit comprises a programmable addressable random access memory that stores a plurality of eight bit words comprising decoded symbol sets of the received amplitude phased keyed signals, and outputs the decoded symbol sets in response to addresses corresponding to the in-phase and quadrature output signals.

Abstract: This invention relates to adaptive digital filters for echo cancellation in a bi-directional data transmission channel. Substantial hardware savings for a digital adaptive filter are possible, if hardware structures for performing filter operations are shared. In a digital adaptive filter with resource sharing filter operations are performed sequentially with a limited number of hardware structures. This invention discloses a digital adaptive filter with resource sharing with further hardware savings (FIG. 3). Corresponding to a characteristic decrease of the magnitude of the filter coefficients for echo cancellation, a first and second filter computation means (4.sub.A, 4.sub.B) are connected to a coefficient storage means (3) with a different bit width to receive coefficients (c.sub.0, c.sub.1 . . . c.sub.N/2-2, c.sub.N/2-1 ; c.sub.N/2, c.sub.N/2+1 . . . c.sub.N-2, c.sub.N-1) having different magnitudes and/or a first and second coefficient adapting means (7.sub.A, 7.sub.

Abstract: Carrierless signals of first and second channels pass via filters having quadrature responses and are then added for transmission. A receiver uses adaptive filters which also need quadrature responses to separate the channels effectively. To accommodate misconvergence of the filters giving rise to (a) inverted responses, (b) differential delays, (c) similar or identical responses and/or (d) transposed responses, --and hence incorrect decoding: (a) the transmitter and receiver may employ different coding in each channel, (b) the receiver may calculate the group delay of its filters and correct any error, (c) the receiver may compare the filtered signals and if similar replace one filter response with a quadrature response calculated from the other and/or (d) the receiver may respond to a failure to recognize expected synchronization words by transposing the responses of the filters.

Abstract: An adaptive equalizer is configured to reconstruct electronic signals which are transmitted over signal cables, such as twisted pair cables. The equalizer satisfactorily reconstructs the signals over a broad range of cable lengths. Using the known degradation characteristics for a cable over a desired range of lengths, the adaptive equalizer includes multiple equalization paths, each of which are configured to reconstruct the input voltage signal optimized for a particular cable length. The degraded input signal is split according to a predetermined relationship into an appropriate two of the multiple equalization paths as controlled by a control logic circuit. Though each path is optimized to reconstruct the signal for a particular length of cable, the adaptive control adds a function of the actual cable length for more accurately reconstructing the signal. Each of the two active paths forms a partially reconstructed signal which is summed to form a composite reconstructed output signal.

Abstract: A quadrature sampling system and method (BQS) and a hybrid quadrature sampling and channel equalization system and method (BQS/EQ) which convert input signals to baseband inphase and quadrature signal components. The BQS system includes an inphase signal channel including a first set of K filters, and a signal summer which sums the outputs of the first set of K filters to produce the inphase signal component; a quadrature signal channel including a second set of K filters, and a signal summer which sums the outputs of the second set of K filters to produce the quadrature signal component; and a controlled switch which provides input samples to the inphase and quadrature signal channels so that each filter of both channels receives one input sample of each sequence. The BQS/EQ system includes first and second sets of signal processing filter pairs, each pair including an inphase and a quadrature filter.

Abstract: A blind equalization cost function called the "constrained Hilbert cost function" (CHCF) provides for reliable blind convergence of a two-filter equalizer structure. In particular, the CHCF cost function is designed in such a way that the two filters are constrained to be a Hilbert pair. Advantageously, this technique can be used with any blind equalization algorithms, such as RCA, CMA, and MMA.

Abstract: In a distribution telecommunications system, channel data for performing equalisation on a channel between a central station and an outstation is determined from measurements on pairs of pulses transmitted from the outstation. Each pulse pair comprises a first in-phase pulse and a second quadrature pulse having a predetermined time/phase separation. Coefficients for an active filter provided at the outstation are calculated from the multipath transmissions of the pulses and from the received time/phase separation of those pulses. The filter is then used to pre distort signals transmitted from the outstation.

Abstract: A frequency-domain CAP receiver is provided that reduces the number of operations required to demodulate a CAP signal. The frequency-domain CAP receiver provides computational advantages over an equivalent time-domain version as the filter length required in the receiver increases.

Abstract: A blind equalization technique uses both the "constant modulus algorithm" (CMA) and the "multimodulus algorithm" (MMA) during blind start-up. This approach provides the basis for a "transition algorithm." One example of a transition algorithm is the CMA-MMA transition algorithm in which an adaptive filter simply switches from CMA to MMA. Other examples are variations of the CMA-MMA transition algorithm and are illustrated by the "Constant Rotation CMA-MMA" transition algorithm and the "Dynamic Rotation CMA-MMA" transition algorithm.

Abstract: A blind equalization technique--the multimodulus algorithm (MMA)--adapts coefficients of an equalizer so as to minimize dispersion of the output samples of the equalizer around piecewise linear contours of a signal space. The MMA technique is illustrated in the context of both square and non-square signal point constellations.

Abstract: An interference compensator for compensating interference waves with long delay times generated during digital microwave communications system-based relaying of waves at a single frequency. The compensator receives a demodulated digital signal, passes the signal through shift registers with different delay times, and then, through a forward equalizer, a first backward equalizer, a second backward equalizer and a center equalizer. All equalizers are transversal type equalizers, outputs from which are added as an output. In addition, the compensator is equipped with a delay time control circuit which monitors the tap coefficients of the forward equalizer, the backward equalizers and the center equalizer and controls the delay times of the shift registers so that the tap coefficients become greatest at the center delay circuits of the respective transversal type filters.

Abstract: Analog signals encoded with quadrature amplitude modulation (QAM) pass through a coaxial cable at a particular baud rate. These signals have a carrier frequency individual to the TV station being received. They are mixed with signals from a variable frequency oscillator to produce signals at a particular intermediate frequency (IF). An analog-digital converter (ADC) converts the IF signals to corresponding digital signals which are demodulated to produce two digital signals having a quadrature phase relationship. After being filtered and derotated, the digital signals pass to a symmetrical equalizer including a feed forward equalizer (FFE) and a decision feedback equalizer (DFE) connected to the FFE in a feedback relationship. The DFE may include a slicer providing amplitude approximations of increasing sensitivity at progressive times. Additional slicers in the equalizer combine the FFE and DFE outputs to provide the output data without any of the coaxial cable noise or distortions.

Abstract: An equalizer that mitigates both linear and nonlinear distortions for amplitude phase keyed signals that are processed thereby. Algorithms employed in the equalizer are based on correcting received signals based on symbol transitions between successive symbols. The linear portion of the equalizer is programmable and can use any available algorithm. Programmable linear taps of the equalizer may be programmed in a nonlinear manner by using the lookup tables as amplitude dependent equalizers that are used to process one symbol at a time. In the equalizer, each amplitude level has it's own correction factor by using amplitude dependent coefficients. The equalizer can implement both linear and nonlinear equalization. Equalizer corrections are implemented using predetermined values stored in lookup tables. The equalization corrections are determined in an external computer and are loaded into the lookup tables for each amplitude level of the received signals.

Abstract: A data receiving apparatus comprising: a receiving portion for receiving a desired radio wave signal including a desired baseband signal and an interference radio wave signal including an interference baseband signal, the desired radio wave signal and the interference radio wave signal having substantially the same frequency; first weighting circuit for weighting an output of the receiving circuit with a first coefficient adaptively renewed such that the desired baseband signal is reproduced; a subtracting circuit coupled to the first weighting circuit; a first judging circuit coupled to the first subtracting circuit; a second weighting circuit for weighting the baseband signal with a second coefficient adaptively renewed such that the interference baseband signal is reproduced; a second judging circuit coupled to the second weighting circuit; and a supplying circuit for supplying the reproduced interference baseband signal to the subtracting circuit, the subtracting circuit effecting a subtraction between an

Abstract: A reduced hardware complexity, reduced computational intensity finite impulse response filter architecture for filtering multiple (quadrature) channels of an RF modem comprises a cascaded arrangement of L data register stages through which respective digitally encoded data sample values of a signal to be filtered are sequentially clocked. Each data register stage has a data capacity greater than twice the code width of a respective digitized channel sample, so that each register stage can store both I and Q channel data. A multiplier unit is coupled to the data register and multiplies both I and Q contents of respective ones of the register stages by respective impulse response coefficient values. The resulting I and Q products are summed into I and Q channel convolutional sums.

Abstract: The present invention provides a device and method in multi-access communications system for reliably receiving burst transmissions from users in the presence of narrow band interference. The adaptive interference suppresser incorporates adaptive elements that are updated using a predetermined adaptation algorithm. These adaptive elements are stored in memory at the end of the burst transmission for reuse in receiving a next burst transmission.

Abstract: According to a first aspect, a novel method of performing an eight point quantization is developed. The eight point quantization consists of selecting one eight specific points depending upon the phase of the measured complex error signal. According to a second aspect, a novel method of performing eight-point quantization of an error signal by rotating a measured complex sample point by positive pi/8 and by negative pi/8. Two sign comparisons results in two control signals. These control signals used in conjunction with the signs of the real and imaginary parts of the variable being quantized results in all the information necessary to select one of eight equal and radially symmetric decision regions. According to a third aspect, an efficient hardware circuit implements the complex coefficient update algorithm using the quantization method according to the first aspect on the error signal.

Abstract: An efficient method and apparatus for determining, recording, and analyzing the phase history of a Line-in signal. The Line-in signal is coupled to a conventional demodulator. I and Q components are output by the conventional demodulator and coupled to an IQ quantizer. The IQ quantizer determines a quadrant on an I/Q plot from the amplitude of each component. A histogram is generated which indicates in which quadrant the Line-in signal was for a first sample, and in which quadrant the Line-in signal was for a second sample, the second sample having been taken immediately after the first sample. From this histogram, the number of times the Line-in signal transitions from one quadrant to another over a predetermined period of time is known.

Abstract: An estimator for estimating the amplitude/frequency characteristic of a source signal from which baseband components i and q which are applied to the inputs of said estimator are derived by demodulation using two signals having orthogonal phases. The estimator includes a combiner for generating complex components i+j.multidot.q and q+j.multidot.i from the components i and q and evaluates the relative amplitudes of the complex components in order to produce a coefficient representative of the amplitude/frequency characteristic of the source signal. The invention can be used to implement a frequency equalizer whose estimator operates in the baseband, the estimator possibly driving a transversal filter operating at the intermediate frequency or at the microwave frequency.

Abstract: A modulator that modulates and encodes data using data symbols, interspersed with pilot symbols, for transmission to another modem, and a demodulator that decodes data symbols of a signal received from another modem. In the demodulator, a received signal is sampled at four times the symbol rate. The sampled signal is converted to quadrature signals and low-pass filtered to produce a complex baseband signal. Data symbols in the complex baseband signal are sampled in synchronization with the start of each symbol based on the pilot symbols that are interspersed in the signal. By processing the pilot symbols, full modem synchronization is maintained down to a very low signal-to-noise ratio, through noise bursts, or even when the data symbols representing data are replaced by predefined sequences of data symbols that convey the dots and dashes of Morse code identifying the station transmitting the modulated signal.

Abstract: A transversal type digital roll-off filter receiving a signal n-time sampled from analog signal carrying a pulse train of symbol rate T, includes a transversal type delay line including a plurality of delay elements each having a delay time T/n. Nodes are positioned between adjacent two delay elements. The filter further includes a memory for providing first tap rating ratios to control signals of the nodes and a calculation circuit for monitoring pulse forms of the output signal of the filter, and calculating second ratios to additionally control a central node and every n-th node counted from the central node, where the second ratios are calculated to make the output pulse good in shape. The filter acts as a roll-off filter and as an automatic equalizer. In a method of diagnosing the circuits in the above system, a memory in a transmitter further has second tap rating ratios used to diagnose the system, where the first and second ratios are switchably output to a digital filter in the transmitter.

Abstract: Briefly, in accordance with one embodiment of the invention, an adaptive equalizer comprises: a digital filter including filter tap coefficients; a slicer; and a filter tap coefficient update block. The filter, slicer and coefficient update block are configured so as to perform at least one burst update of the filter tap coefficients. In accordance with another embodiment of the invention, a method of updating the filter tap coefficients of an adaptive equalizer comprises the step of: performing at least one burst update of the filter tap coefficients.

Abstract: A transmitter apparatus for a mobile satellite communication terminal comprises a Nyquist filter having input to it two series of orthogonal data and equalizing them for a waveform, an envelope equalizer equalizing the output of the filter so that the distance of an envelope (locus) on an orthogonal axis is always constant from the origin, a phase modulator receiving the output signals from the envelope equalizer and phase-modulating them, and a power amplifier receiving the output of the phase modulator, and power-amplifying it at a high-frequency band. Thus, it becomes possible to eliminate the effects of AM-PM conversion distortion in the power amplifier.

Abstract: A digital receiver includes a tuner and a demodulator that obtains a modulated signal carried in a received analog signal. A digital-to-analog converter operates at a preselected fixed sampling rate on the modulated signal to produce a first sequence of digitized samples. The first sequence of digitized samples is processed by a digital rotator to frequency-and phase-correct the first sequence of digitized samples. A controllable digital filter processes the first sequence to produce a filter output including a second sequence of digitized samples at a symbol rate. The second sequence is processed to ascertain a symbol rate of the modulated signal. The controllable filter coefficients are automatically varied to accommodate changes in the symbol rate of the modulated signal, so that the sampling rate of the digital-to-analog converter need not change.

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: A digital radio communication system includes a first demodulator, a second demodulator, a non-break switch, and a switching controller. The first demodulator receives a signal from a first antenna and outputs demodulated data and a line quality degradation signal. The second demodulator receives a signal from a second antenna and outputs demodulated data and a line quality degradation signal. The non-break switch receives the demodulated data output from the first and second demodulators and selects and outputs one of the demodulated data. The switching controller receives line quality degradation signals output from the first and second demodulators to output a switching control signal to the non-break switch on the basis of the received line quality degradation signals. The first and second demodulators output the line quality degradation signals before the demodulated data are set in an interrupt state when abrupt frequency selective fading occurs.

Abstract: A transversal type digital roll-off filter receiving a signal n-time sampled from analog signal carrying a pulse train of symbol rate T, includes a transversal type delay line including a plurality of delay elements each having a delay time T/n. Nodes are positioned between adjacent two delay elements. The filter further includes a memory for providing first tap rating ratios to control signals of the nodes and a calculation circuit for monitoring pulse forms of the output signal of the filter, and calculating second ratios to additionally control a central node and every n-th node counted from the central node, where the second ratios are calculated to make the output pulse good in shape. The filter acts as a roll-off filter and as an automatic equalizer. In a method of diagnosing the circuits in the above system, a memory in a transmitter further has second tap rating ratios used to diagnose the system, where the first and second ratios are switchably output to a digital filter in the transmitter.

Abstract: An equalizer employed with a receiver for cancelling an interfering signal due to low cross-polarization isolation. The present equalizer provides a simple and inexpensive cross-polarization interference cancellation system. The equalizer uses an error signal generated in an adaptive baseband equalizer to determine the magnitude of an interfering signal and inputs a cancelling signal to the co-polarized channel until power in the error signal derived from the adaptive baseband equalizer is minimized. In the equalizer, the determination of the magnitude of the interfering signal is performed at baseband (after demodulation but prior to data detection) and the cancellation is performed at RF, prior to dispersive microwave elements. The equalizer enhances the capability for transmitting two unique signals in the same frequency allocation on orthogonal polarizations. The equalizer operates even if the modulations and data rates on the two channels are different.

Abstract: A transversal filter allrate equalizer for use at intermediate frequency. The equalizer includes a signal divider coupled to receive the intermediate frequency input signal and a transversal filter comprising a plurality of analog delay lines and a plurality of multiplying circuits. The plurality of analog delay lines are coupled to the signal divider for producing a time-shifted replica of an intermediate frequency input signal. The plurality of multiplying circuits are respectively coupled to the delay lines for weighting the time-shifted replicas of the input signal by complex numbers, W.sub.i. A signal combiner is coupled to the plurality of multiplying circuits for recombining the time-shifted and weighted replicas of the input signal to produce an equalized output signal. The delay lines operate at an intermediate frequency, and produce a time delay for the modulation and a phase shift for the carrier. The phase shift may be compensated for by adjusting the phases of the tap weights, W.sub.i.

Abstract: A modem (100) includes an equalizer for equalizing a received signal (10) for amplitude jitter distortion. The received signal includes modulated symbols based on a predetermined constellation of points, each point representing a symbol. The modem first extracts a modulated symbol to provide an extracted symbol, R(k), which includes amplitude jitter distortion. The modem then identifies a signal point P.sub.n (k) of the predetermined constellation corresponding to the extracted symbol. Further, the modem determines an error signal (76) based on the amplitude jitter distortion, and then uses the error signal to compensate subsequent extracted symbols for the amplitude jitter distortion.

Abstract: The Self-Adapting Filter is an adaptive interference suppression device t can be used to extract bandspread communication signals from a received signal containing significant structured interference. The filter processes signal quantities consisting of inphase and quadrature (real and imaginary) components of received signal baseband samples. Process weights are calculated directly from the symmetric differences of the signal samples. Calculating the statistics of the samples is not necessary, nor is the calculation and use of signal sample magnitude and phase. By processing components of the received signal baseband samples directly, a simple implementation of an approximate locally optimum processing algorithm is possible enabling simple filter hardware and operation. All processing can be pipelined.

Abstract: A method is presented for efficient VLSI implementation of a narrowband BPSK or QPSK demodulator which minimizes filter processing requirements. The demodulator implements a digital filter which spans a time duration of 8 symbols to realize a square root of raised cosine filter. The disadvantage of a conventional FIR filter, is that it requires a fixed ratio between the input sample rate and the FIR filter output rate. The subject invention employs a unique, flexible digital filter which provides one output per symbol while the input sample rate may vary from a low rate approaching two samples per symbol to over 128 samples per symbol. A key element of this approach is the digital phase locked loop used for symbol tracking which employs a direct digital synthesizer (DDS) as the frequency control element. In addition to providing symbol timing to the accuracy of the sample clock, the DDS also provides a fine measure of symbol timing phase at each sample clock.

Abstract: The present invention provides a downconverter method and apparatus for downconverting a multiphase modulated signal. The downconverter can be implemented in a multi-phase receiver such as a quadrature receiver. An analog-to-digital converter (103) converts an intermediate frequency signal to a digital signal at a sampling rate. A Hilbert transformation filter (104) and a delay element (105) connected in parallel provide respective passband quadrature and in-phase components of the digital signal. A digital translator (107) alters the passband quadrature and in-phase components based on a predetermined pattern to provide a baseband quadrature signal and a baseband in-phase signal. The digital translator (107) can be a pseudorandom sequence demodulator for demodulating a code division multiple access (CDMA) signal. Various types of DC estimation can also be provided in addition to automatic gain control.

Abstract: Adaptive equalizers and processing methods wherein data required to implement an adaptation algorithm is sampled at a rate that is significantly lower than the symbol rate. The adaptation algorithm is processed at this reduced rate, in that updated tap coefficients, sample timing errors and symbol clock error signals are computed at this reduced rate. An advantage of the adaptive equalizer and processing method of the present invention is that the adaptation algorithm may be implemented in equipment that operates at a clock rate that is much less then the symbol rate. In particular, the adaptation algorithm may be computed using software that is resident in inexpensive general purpose digital processor, such as a personal computer, for example.

Abstract: In the following manner, a receiver that receives quadrature modulated signals may determine desired components of the quadrature modulated signals by minimizing effects of transmitted distortion produced by gain, phase, or gain-phase imbalance. A quadrature modulated signal that includes a desired component, a fading component, and a transmitter distortion component is received by the receiver, wherein the transmitter distortion component includes a conjugate component and an imbalance component. The receiver estimates the fading component, the conjugate component, and the imbalance component and determines the desired component based on these estimates and the quadrature modulated signal.