Abstract: A signal estimator is provided that can track a large frequency offset. A received signal distorted in a transmission path is phase-rotated by the phase rotator (102) and is then estimated by the maximum likelihood sequence estimator (MLSE) (103). The phase detector (105) detects a phase difference between a signal obtained by delaying the phase-rotated signal and information about a minimum path metric in the Viterbi algorithm operation by the MLSE. After the phase difference signal is filtered, the voltage-controlled oscillator (VCO) receives the filtered signal. Then, the phase rotation is controlled with the output of the VCO.

Abstract: In a phase-locked loop circuit with a signal estimator such as MLSE or DDFSE for correctly detecting and correcting a phase deviation, the phase deviation is held within a predetermined value by amplitude limiting a phase deviation signal obtained from a received signal and a replica signal. Thus, the phase deviation signal is free from a large error irrespective of generation of an estimation error in the MLSE or DDFSE.

Abstract: A code-multiplexing communication apparatus includes a splitting unit for splitting incoming serial transmitted data into N (N is integer equal to or greater than 2) number of signal trains; N number of spread unit for performing spreading for each of the N number of signal sequences with use of a spread code; an adding unit adding the N number of signal sequences with the spreading processed by the N number of spread unit, for outputting a code-multiplexed signal; and a modulating unit for modulating the code-multiplexed signal, comprising, filter unit having an inverse characteristic to a frequency characteristic of an autocorrelated distortion caused by the spreading, removing a transmission path distortion.

Abstract: A DC-offset canceller in a receiver of a communication system using a burst signal including a training sequence with a predetermined periodicity at the head thereof is disclosed. In the canceller, a quadrature demodulator 112 converts the received burst signal to a base band signal. An AD converter 113 converts an output signal of the quadrature demodulator to a digital signal. A one-cycle delay element 114 makes a delay of an output signal of the AD converter 113 corresponding to one-cycle of the training sequence. A DC-offset detector 115 detects a DC-offset component in the converted signal by the AD converter 113 on the basis of an output signal of the AD converter 113 and an output signal of the one-cycle delay element 114. A subtractor 116 removes the DC-offset component detected by the DC-offset detector 115 from the output signal of the AD converter 113.

Abstract: A signal estimation loop includes a postcursor estimator which generates all possible postcursor estimation signals in a first past symbol period which is one symbol earlier based on a past estimated signal in a second past symbol period which is at least two symbols earlier. One of the possible postcursor estimation signals is selected based on the estimated signal to output a postcursor estimation signal to a subtracter in the symbol period. The subtracter subtracts the postcursor estimation signal from an input signal to produce a difference signal which is used to generate the estimated signal.

Abstract: A transmitter 100 comprises a signal distributor 101 for outputting a modulation signal and a selection signal, a code generator 102 for generating a spread code, spread devices 103a to 103d for multiplying the spread code by the modulation signal and a selector 104 for selecting the modulation signal based on the selection signal. A receiver 110 comprises a correlator 112 for taking a correlation between the spread code multiplied by the reception signal and the spread code at a timing of the code generator 102, an equalizer 113 for removing a delay from the signal based on the correlation result, a signal location detector 114 for detecting the location of the signal output by the equalizer 113, a demodulator 115 for demodulating the signal output by the equalizer 113 and a coupler 116 for coupling the signal location information detected by the signal location detector 114 with the signal output by the demodulator 115.

Abstract: In order to provide a digital GMSK modulator operating sufficiently stably without aliasing distortion even with a sampling rate of twice of that of input signal, a quasi-GMSK modulator of the invention comprises: integration means (105) for integrating an input signal; filtering means (106, 107) for performing a digital Gaussian filter manipulation of output of the integration means with a low sampling rate of twice or more of a data rate of the output of the integration means; a phase modulator (107, 108 and 111) for obtaining a continuous wave phase-modulated with output of the filtering means; and a limiter (112) for limiting amplitude of the continuous wave within a fixed value.

Abstract: In a code multiplexing communication system, a transmission apparatus includes a code generator, a signal distribution unit, spreading units, a synthesizer, and a modulator, and a reception apparatus includes a correlator, an equalizer, demodulators, and a coupler. The code generator generates n spreading code series which are generated at timings different from the timing of a predetermined spreading code. The signal distribution unit divides a serial input signal having n.times.m bits per symbol timing into n parallel signals each consisting of m bits. The spreading units respectively spectrum-spread the n m-bit output signals by using the n output signals from code generator. The synthesizer synthesizes the output signals from the spreading units. The modulator modulates the output signal from the synthesizer. The correlator calculates the correlation between a baseband signal and the spreading code.

Abstract: A negative-feedback amplifier prevents deterioration of the open-loop gain and the distortion improvement effect despite changes in a sending frequency by demodulating a baseband signal from a carrier and an output signal of an amplifier and a demodulated baseband signal. The negative-feedback amplifier includes a correcting member for correcting a phase error of the demodulated baseband signal caused by a delay in the amplifier for each change of a sending frequency of the carrier.

Abstract: An adaptive equalizer of the present invention equalizes a data symbol sequence containing intersymbol interference and nonlinear distortions extending over several symbols, e.g., a digital signal from the read head of a high density magnetic recording and playback apparatus, thereby producing an equalized output free from such distortions. Presumed value storing means stores a plurality of presumed value signals read out of the combinations of an equalization address signal and a Viterbi transition symbol sequence signal. Error calculating means outputs a plurality of error signals representative of differences between the plurality of presumed value signals and an input data symbol. Viterbi algorithm equalizing means executes equalization according to a Viterbi algorithm and by using the plurality of error signals as branch metrics, thereby producing a presumed symbol associated with the input data symbol, the equalization address signal, and a correction address signal.

Abstract: In a digital data transmission device for transmitting a composite transmission signal comprising a main data signal represented by parallel n bits and a subdata signal, a multilevel encoding unit encodes upper and lower levels of m bits in the main data signal into first and second encoded signals. A first signal converter converts the first and the second encoded signals and an uncoded signal of (n-m) bits in the main data signal to a first converted signal. An inverter inverts the first encoded signal to an inverted signal. A second signal converter converts the inverted signal, the second encoded signal, and the uncoded signal to a second converted signal. A selection unit selects a selected signal from the first and the second converted signals in response to the subdata signal and produces the selected signal as the composite transmission signal.