An optical receiver apparatus includes a photo detector that detects amplitude modified optical signals transmitted through an optical transmission channel and mapped to constellation points and converts the optical signal into electrical signals, a sampling circuit that samples the electrical signals and generates digital signals, and a signal processing circuit that has a two-step equalization algorithm converging actual constellation points into desired constellation points. The two-step equalization algorithm includes a first equalization algorithm that uses multiple modulus in performing an error signal calculation, and a second equalization algorithm that includes a filtering procedure that compares actual constellation points with desired constellation points and an adjustment procedure that iteratively adjusts parameters of the filtering procedure in accordance with the comparison result.

A method and system for simultaneous mitigation of optical impairment from both equalizer-phase noise interaction (EPNI) and fiber nonlinear effects (FNE) is disclosed. In one embodiment, the method is directed to simultaneous mitigation of optical impairment from both equalizer-phase noise interaction (EPNI) and fiber nonlinear effects (FNE) using a fast-adaptive multi-tap digital filter.

In one embodiment, an apparatus includes: a first radio receiver to receive and downconvert a first radio frequency (RF) signal to a first digital signal; a second radio receiver to receive and downconvert a second RF signal to a second digital signal; a correlation circuit to receive the first and second digital signals and determine a correlation between the first and second digital signals; a weight calculation circuit to determine a first weight value and a second weight value based at least in part on the correlation; and a combiner circuit to combine the first and second digital signals according to the first and second weight values.

Systems and methods for classifying a modulation scheme of a wireless signal are described. In some embodiments, a system receives a wireless signal modulated based on a modulation scheme having a constant modulus. The system can generate a resampled signal from the wireless signal based on features extracted from the wireless signal and perform blind equalization on the resampled signal based on a constant modulus criterion to generate an equalized signal. Then, the system can cause a modulation classifier to classify the received wireless signal to a modulation scheme from a plurality of predetermined modulation schemes based on the equalized signal. By preconditioning the wireless signal to reduce feature variability imparted by a propagation channel onto the wireless signal, the system can increase the classification accuracy of the modulation classifier.

A method for equalizing a wireless communication channel includes transmitting a data signal over a primary channel. During transmission of the data signal, a corresponding data signal is sent over a secondary channel. The information received from the secondary channel is compared to the information received from the primary channel and differences between the information received from each of the channels are observed. These differences are used as inputs to an equalizer algorithm that may be used to reduce distortion of the data signal sent over the primary channel.

A method and apparatus for equalization in a communication system. The method includes receiving an input of a block of symbols, filtering the input in the frequency domain, calculating an error factor in the time domain based on the filtered input, updating tap weights of the equalizer in the frequency domain using circular correlation based on the error factor and the conjugate of the input in the frequency domain, and outputting the filtered input.

A receiving device includes: a resampler to convert a sampling rate of a reception signal, and output a first signal that is a signal having been subjected to sampling rate conversion; an equalizer to perform an adaptive equalization process using the first signal as an input, and output a second signal that is a signal having been subjected to the adaptive equalization process and having a sampling rate that is an integer fraction of an input signal; a correlation calculator to calculate a correlation function between the first signal and the second signal; and a rate controller to control a rate conversion ratio for sampling rate conversion in the resampler on a basis of the correlation function.

A blind channel equalizer device for a radiofrequency receiver suitable for modulating the constant envelope signal of the transmission includes: an adjustable linear digital filter, defined at a point in time by the coefficients) thereof, able to filter an input signal in order to produce an output signal; an estimator able to estimate a power of the input signal; an adapter able to adapt the filter by calculating the coefficients of the filter at a point in time by subtracting, from the filter coefficients at a preceding point in time, the gradient of a cost function assigned with a correction coefficient. The cost function includes a first distance criterion between the square of the output signal and the power, wherein the correction coefficient is a product including a constant convergence coefficient and a scaling coefficient inversely proportional to the square of the power. Also disclosed is a related Radiofrequency receiver.

This invention is designed for use in transmission of data between downhole module in a wellbore and a controlling module at the surface. The invention provides an apparatus for receiving data signals from a telemetry module comprising first and second adaptive equalisers, and in which in a first modulation mode the coefficients of the first adaptive equaliser are updated until an error signal falls below a predetermined threshold and in a second modulation mode the coefficients of the first adaptive equaliser are locked and coefficients of the second adaptive equaliser are updated to continually minimise an error signal in which the number of bits encoded by the symbols of the first signal in an initial modulation mode is fewer than the number of bits encoded by the symbols of the second signal in a subsequent modulation mode.

A system can be configured to control an equalizer circuit to equalize a data signal without requiring prior knowledge of the data signal's data rate. In an example, the system includes an equalizer circuit configured to equalize a data signal based on an equalizer control signal to produce an equalized signal, and a pattern detector configured to detect a specified data pattern in the equalized signal at each of multiple sampling rates. A control circuit can be configured to generate a preferred equalization control signal based on a sampling rate, selected from the multiple sampling rates, at which the pattern detector detects the specified data pattern in the equalized signal.