Nec Corporation

Hitosi Matui

Takeshi Yamamoto

Hideho Tomita

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 ( ) and is then estimated by the maximum likelihood sequence estimator (MLSE) ( ). The phase detector ( ) 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.

Signal estimator and program stored memory medium

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.

Phase-locked loop circuits for communication system

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.

Code-multiplexing communication apparatus

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 converts the received burst signal to a base band signal. An AD converter converts an output signal of the quadrature demodulator to a digital signal. A one-cycle delay element makes a delay of an output signal of the AD converter corresponding to one-cycle of the training sequence. A DC-offset detector detects a DC-offset component in the converted signal by the AD converter on the basis of an output signal of the AD converter and an output signal of the one-cycle delay element A subtractor removes the DC-offset component detected by the DC-offset detector from the output signal of the AD converter

DC-offset canceller

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.

Estimator having a feedback loop

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.

Code division multiplexing communication system and method

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.

Quasi-GMSK modulator

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. The equalizer removes a delay distortion caused by a radio transmission path from the output signal from the correlator, and separates the signal into n signals. The demodulators respectively demodulate the n output signals from the equalizer and extract m-bit parallel signals. The coupler synthesizes the m-bit output signals from the demodulators and outputs a serial signal.

Code multiplexing communication system

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.

Negative-feedback amplifier and feedback controlling method thereof

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. Correcting means updates the presumed value signal of the presumed value signal storing means designated by the correction address signal with the input data symbol.

Adaptive equalizer for removing nonlinear distortions from digital

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. A digital data reception device receives as a reception signal the composite transmission signal produced by the digital data transmission device and comprises a processing unit for processing the reception signal to produce a processed signal and a reproducing unit. Supplied with the processed signal, the reproducing unit reproduces the main data signal and the subdata signal as a reproduced main data signal and a reproduced subdata signal.

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Tokyo, Japan

Hitosi Matui