A nonlinear compensator is provided to include a decomposition circuit and a plurality of filter elements. The decomposition circuit has a nonlinear frequency response characteristic and the decomposition circuit is configured to receive an input signal and decompose the input signal into decomposed signals corresponding to positive and negative frequency signal components of the input signal. Each of the plurality of filter elements is configured to receive at least portions of the decomposed signals and apply filter element characteristics to the decomposed signals with the filter element characteristics that are matched to the nonlinear frequency response of the decomposition circuit.

Systems and methods of transmitting direct detection optical signal are provided. A direct detection optical transmitter according to illustrative embodiments includes a Mach Zehnder Modulator (MZM) configured to modulate laser light based on an electrical drive signal to generate a modulated optical signal and a complementary-modulated optical signal. The optical transmitter includes an optical finite impulse response (FIR) filter configured to receive the complementary-modulated optical signal and generate a filtered optical signal. The optical transmitter includes a polarization rotator configured to receive the filtered optical signal and output a rotated optical signal. The optical transmitter includes an optical combiner configured to combine the modulated optical signal and the rotated optical signal. The optical transmitter includes an output port configured to output the combined optical signal.

A signal processing method, a signal filtering apparatus, and a signal processing apparatus are provided. An input signal may be input into a filter having a passband, a superfluous signal of the passband may be output from the filter, and a target signal may be obtained by subtracting the superfluous signal from the input signal.

A signal processing method, a signal filtering apparatus, and a signal processing apparatus are provided. An input signal may be input into a filter having a passband, a superfluous signal of the passband may be output from the filter, and a target signal may be obtained by subtracting the superfluous signal from the input signal.

A communication device comprises a receiver including at least two receive antennas and configured to receive at least one reference signal of a plurality of reference signals, each reference signal being transmitted from at least one base station at a predefined reference signal transmission time; a controller configured to switch between at least two receive configurations of the at least two antennas during a reception period of the at least one reference signal; and a signal quality determiner configured to determine a parameter indicative of a first signal quality of the received reference signal for each receive configuration.

A signal processing method, a signal filtering apparatus, and a signal processing apparatus are provided. An input signal may be input into a filter having a passband, a superfluous signal of the passband may be output from the filter, and a target signal may be obtained by subtracting the superfluous signal from the input signal.

A jones matrix is obtained using coefficients of an equalizer; a parameter of the jones matrix is obtained; a coefficient of an X axis polarization state or a Y axis polarization state in the coefficients is adjusted using the parameter of the jones matrix when the coefficients have singularity characteristics, or energy corresponding to each coefficient of X or Y axis polarization state under each order of a filter in the equalizer is determined using two coefficients of an X or Y axis polarization state in the equalizer coefficients; and a central position of a coefficient tap of X or Y axis polarization state of the equalizer is adjusted using the energy corresponding to each coefficient of X or Y axis polarization state under each order of the filter when the coefficient tap of the X axis or Y axis polarization state of the equalizer deviates from the central position.

A fading assessment unit 34 assesses the degree of fading of a received radio wave. An SNR calculation unit 33 calculates an SNR value of a signal based on the radio wave. A communication mode determination unit 35 determines the communication mode of communication from a transmission side of the radio wave on the basis of the result of the assessment by the fading assessment unit 34 and the SNR value calculated by the SNR calculation unit 33.

A signal processing method, a signal filtering apparatus, and a signal processing apparatus are provided. An input signal may be input into a filter having a passband, a superfluous signal of the passband may be output from the filter, and a target signal may be obtained by subtracting the superfluous signal from the input signal.

A method and apparatus may include receiving a transmission. The method can also include determining a sparsifying dictionary that sparsely approximates a data vector of the transmission. The determining the sparsifying dictionary includes performing a fast Fourier transform and/or an inverse fast Fourier transform. The method also includes configuring a filter based on the determined sparsifying dictionary.