A dither amplitude circuit has a current circuit for receiving DC voltage signals and generating a direct current on a basis thereof, and generating a dither signal, and a dither current on the basis thereof, applying the dither current to the direct current in order to obtain a drive current, artificially modulating the amplitude of the dither signal or a directly modulated drive current with an amplitude modulation deviation on a periodic basis such that a quantization threshold is reliably exceeded. The dither amplitude circuit also has a return current detection circuit that generates numerous quantized digital values in a time period on a basis of the drive current flowing through a load, such that the dither amplitude can be determined from the numerous digital values.

A method and an apparatus for satellite laser broadband demodulation are provided. The method includes: setting a residual carrier to a carrier acquisition range of a receiver, pulling the residual carrier to an MHz level by adjusting a frequency of a local oscillator laser, and obtaining a precise carrier frequency according to an accurate frequency acquisition, such that the residual carrier enters a fast acquisition band of a carrier tracking phase-locked loop. After carrier acquisition is achieved, carrier tracking and data recovery processing are performed. According to the present disclosure, signal equalization of an ultra-high bandwidth/ultra-high bit rate can be implemented, and carrier acquisition, tracking, and demodulation are quickly achieved for a modulation signal in a high dynamic range.

A transmitter includes: a modulation circuit that modulates a data sequence using QAM by mapping the data sequence to only four symbols each of which differs in phase by 90 degrees from an adjacent one of the four symbols and at least two of which have different amplitudes; and a transmission circuit that wirelessly transmits the data sequence mapped to the four symbols through the modulation by the modulation circuit, by assigning the data sequence mapped to the four symbols through the modulation by the modulation circuit to different subcarriers for Orthogonal Frequency Division Multiplexing (OFDM).

A transmitter includes: a modulation circuit that modulates a data sequence using QAM by mapping the data sequence to only four symbols each of which differs in phase by 90 degrees from an adjacent one of the four symbols and at least two of which have different amplitudes; and a transmission circuit that wirelessly transmits the data sequence mapped to the four symbols through the modulation by the modulation circuit, by assigning the data sequence mapped to the four symbols through the modulation by the modulation circuit to different subcarriers for Orthogonal Frequency Division Multiplexing (OFDM).

The present disclosure provides a method for symbol compensation. The method comprises, for a symbol consisting of a first portion and a second portion: estimating a length of the first portion; calculating an average power of the first portion and an average power of the second portion based on the length of the first portion; determining a relative scaling factor by which the average power of the first portion is scaled relative to that of the second portion; and compensating for the first portion based on the relative scaling factor.

Communication systems are described that use geometrically shaped constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. In several embodiments, the geometrically shaped is optimized based upon a capacity measure such as parallel decoding capacity or joint capacity. In many embodiments, a capacity optimized geometrically shaped constellation can be used to replace a conventional constellation as part of a firmware upgrade to transmitters and receivers within a communication system. In a number of embodiments, the geometrically shaped constellation is optimized for an Additive White Gaussian Noise channel or a fading channel.

A transmitter includes: a modulation circuit that modulates a data sequence using QAM by mapping the data sequence to only four symbols each of which differs in phase by 90 degrees from an adjacent one of the four symbols and at least two of which have different amplitudes; and a transmission circuit that wirelessly transmits the data sequence mapped to the four symbols through the modulation by the modulation circuit, by assigning the data sequence mapped to the four symbols through the modulation by the modulation circuit to different subcarriers for Orthogonal Frequency Division Multiplexing (OFDM).

Certain aspects of the present disclosure relate to methods and apparatus for wireless communication, and more particularly, to methods and apparatus for controlling spurious emissions on devices that support millimeter wave communications. An example method includes providing a local oscillator (LO) signal generated by an LO chain to at least one of a baseband portion or a radio frequency (RF) portion coupled to the baseband portion, detecting interference in the LO signal, and controlling a gain component of the LO chain to adjust an amplitude of the LO signal, based on the detected interference.

A carrier-phase recovery method includes: (i) applying a first carrier-phase recovery algorithm to complex-valued symbols of a signal received by a product detector, yielding coarse phase-estimates, the signal being modulated per an M-QAM scheme; (ii) modelling the coarse phase-estimates as a weighted sum of M probability-density functions of an M-component mixture model; (iii) optimizing the M probability-density functions with an expectation-maximization algorithm to yield M optimized probability-density functions; (iv) mapping, based on the M optimized probability-density functions, the coarse phase-estimates to one of M symbols corresponding to the QAM scheme, each coarse phase-estimate mapped to a same symbol belonging to a same one of M clusters; (v) applying a second carrier-phase recovery algorithm to each of the M clusters to generate refined phase-estimates each corresponding to a respective coarse phase-estimate; and (vi) mapping, based on the M optimized probability-density functions, each refined phase-estimate to one of the M symbols.

A receiver receives binary information from a transmission using a binary amplitude shift keying where information symbols are represented by a signal including a first power state and a second power state. A duration of a bit includes a first part where the second power state is applied irrespective of which binary value is represented, and a second part where a binary value is represented by any of the first power and a third power state or a combination pattern of the first power state and the third power state. A sampling circuit is arranged to retrieve samples of the received signal during the second part and discard samples during the first part. A duration of the retrieving of samples is selected to be a time corresponding to the duration of the second part plus a time based on an expected synchronization error.