A method and apparatus for processing a signal to generate equalizer codes, which are used to control equalization of the signal, that comprises processing the signal to identify the eyes of the signal, and for each eye, calculating an eye height and calculating a noise value. For each eye, squaring the eye height to generate an eye height product and dividing the eye height product by the noise value to generate a Q.sup.2 value. Using the calculated Q.sup.2 values optimizing, through adaptation, the equalizer codes. Calculating the noise values may include calculating an ISI value for each band of the signal and then calculating the eye height for each eye as the difference between the adjacent upper average value and the adjacent lower average value. Then, for each eye, calculating a noise value by summing the ISI value for the band above the eye and the band below the eye.

The embodiments described herein provide systems and methods for digital correction in low intermediate frequency (IF) receivers. Specifically, the embodiments described herein use digital correction techniques that can correct for signal distortions in low IF receivers caused by I-Q imbalance, including both I-Q magnitude imbalance and I-Q phase imbalance. In general, the embodiments described herein are implemented to at least partially cancel an image of a blocking signal in the complex digital signal. Such a cancellation can be implemented to at least partially cancel an image of blocking signal where that image occurs at or near the intermediate frequency. In one embodiment, a corrector is implemented in a low RF receiver and is configured to receive a complex digital signal that includes an image of a blocking signal. Such a low RF receiver can further include a trainer configured to train the corrector to generate the cancellation signal.

The embodiments described herein provide systems and methods for digital correction in low intermediate frequency (IF) receivers. Specifically, the embodiments described herein use digital correction techniques that can correct for signal distortions in low IF receivers caused by I-Q imbalance, including both I-Q magnitude imbalance and I-Q phase imbalance. In general, the embodiments described herein are implemented to at least partially cancel an image of a blocking signal in the complex digital signal. Such a cancellation can be implemented to at least partially cancel an image of blocking signal where that image occurs at or near the intermediate frequency. In one embodiment, a corrector is implemented in a low RF receiver and is configured to receive a complex digital signal that includes an image of a blocking signal. Such a low RF receiver can further include a corrector controller to selectively enable the corrector.

An estimating apparatus for bias drift of a transmitting end modulator, a compensating apparatus, a receiver and a method are disclosed. Estimation and compensation of the bias drift are performed directly at the receiving end according to phase recovered received signals, with no need of providing an extra bias control circuit at the transmitting end. Estimating and compensating for the bias drift includes recovering received signals by removing a frequency difference and a phase difference between a transmitting end laser and a receiving end laser producing phase recovered received signals, estimating the bias drift of the transmitting end modulator according to the phase recovered received signals and compensating the bias drift of the transmitting end modulator in a receiver.

Embodiments of this disclosure provide a phase noise compensation apparatus and method and a receiver, in which modified signals are determined according to estimated values of an imperfection parameter of a transmitter and training sequence signals in transmission signals, and phase noises of the received signals are determined according to the modified signals, hence, an effect of the imperfection parameter of the transmitter on the phase noise is taken into account, and the phase noise may be accurately estimated, thereby performing compensation on the phase noise, and ensuring a transmission efficiency and performance of the system.

Devices and methods for estimation of quadrature signal imbalance are provided. A quadrature signal is coupled to a computing system. The computing system determines several points on a symmetry function of corrected quadrature signals, and identifies a symmetry point that may satisfy a threshold level. An imbalance corresponding to the identified symmetry point may be used as an imbalance estimate. The imbalance estimate can be used for imbalance correction. Multiple imbalance estimates can be combined to reduce random errors caused by noise. Triangulation can be used to identify a value of symmetry that satisfies a threshold level. Triangulation allows the determination of the location of a symmetry trough by calculating as few as four symmetry points, thereby permitting embodiments to track rapidly changing imbalance. The disclosed embodiments may be employed in optical velocimetry systems, detection and ranging systems such as radar, sonar, and lidar, ultrasonics, and communications systems.

Embodiments of this disclosure provide a phase noise compensation apparatus and method and a receiver, in which modified signals are determined according to estimated values of an imperfection parameter of a transmitter and training sequence signals in transmission signals, and phase noises of the received signals are determined according to the modified signals, hence, an effect of the imperfection parameter of the transmitter on the phase noise is taken into account, and the phase noise may be accurately estimated, thereby performing compensation on the phase noise, and ensuring a transmission efficiency and performance of the system.

The proposed solution relates to a method and an apparatus in a communication system. The solution includes receiving as an input a frame including of a set of data symbols and reference symbols, each data symbol forming a rectangular symbol constellation of samples, derotating the first symbol of the set on the basis of the reference symbols, and setting phase rotating angle of the first symbol as zero. The solution further includes for each following successive symbol in the set of symbols: performing equalization; reducing the number of samples in the constellation by selecting samples in two or more corners of the constellation by utilizing two or more threshold values; estimating the phase rotating angle of the symbol from the reduced number of samples and derotating the symbol on the basis of the determined phase rotating angle.

A system and method for estimating clock drift in underwater instruments is provided. The method can include transmitting a signal from a source to a plurality of underwater receivers or a single receiver. Upon recovery of the underwater receivers, an initial sampling frequency value can be used to generate received data waveforms from data stored on each underwater device. The generated received waveforms can be used to generate a channel estimate for each receiver, and the channel estimates can be used to provide an estimate of the source motion during the transmission. The estimated source motion can then be used to estimate the clock drift.

A system and method for estimating clock drift in underwater instruments is provided. The method can include transmitting a signal from a source to a plurality of underwater receivers or a single receiver. Upon recovery of the underwater receivers, an initial sampling frequency value can be used to generate received data waveforms from data stored on each underwater device. The generated received waveforms can be used to generate a channel estimate for each receiver, and the channel estimates can be used to provide an estimate of the source motion during the transmission. The estimated source motion can then be used to estimate the clock drift.