A frequency and/or time transfer apparatus, including a modulator system is disclosed. The modulator system includes a port for providing a first modulated signal to a remote location via a communication path and for receiving a second modulated signal from the remote location via the communication path. The modulator system is configured in operation to utilise a first modulation signal to produce the first modulated signal, the first modulated signal comprising the first modulation signal imprinted onto a first carrier signal, and to provide a reverse modulation for the second modulated signal. The first modulation signal is periodic. There exists a reversing modulation signal which reverses and is reversed by the first modulation signal.

A system and method are disclosed to characterize and correct for the effects of IQ skew and insertion loss in a coherent optical transmitter. The coherent optical transmitter receives a digital data signal including in-phase (I) and quadrature (Q) components and generates corresponding first and second dither signals. The first dither signal may be combined with the I component and the second dither signal may be combined with the Q component to generate I and Q combined signals, which may be converted into I and Q analog waveforms. An optical signal may be generated corresponding to the I and Q analog waveforms for transmission over an optical fiber. The IQ skew and/or insertion loss for the coherent optical transmitter may then be calculated based on the optical signal using the disclosed dither tone processing techniques in order to correct IQ skew and/or insertion loss impairment.

A wireless access system includes: a centralized control station; and an access point. The access point performs a pulse width modulation process on an analog uplink signal, thereby to generate an analog modulation signal; and converts the analog modulation signal to an optical uplink signal. The centralized control station converts the optical uplink signal to an electrical uplink signal; performs, on the electrical uplink signal, a filtering process for extracting an analog extraction signal including a signal component corresponding to the analog uplink signal; and converts the analog extraction signal to a digital uplink signal representing a signal level of the analog extraction signal by two or more bits.

The present invention discloses a digital signal processor, including: a signal generation unit, configured to generate a first digital signal and a second digital signal; a first modulation unit, configured to modulate the first digital signal to obtain a third digital signal; a second modulation unit, configured to modulate the second digital signal to obtain a fourth digital signal; a first phase shifting unit, configured to perform phase shifting on the third digital signal, to output the third digital signal and a fifth digital signal; a second phase shifting unit, configured to perform phase shifting on the fourth digital signal, to output the fourth digital signal and a sixth digital signal; an adder, configured to calculate a sum of the third digital signal and the fourth digital signal, to obtain a seventh digital signal; and a subtractor, configured to subtract the sixth digital signal from the fifth digital signal.

A transceiver architecture for wireless base stations wherein a broadband radio frequency signal is carried between at least one tower-mounted unit and a ground-based unit via optical fibers, or other non-distortive media, in either digital or analog format. Each tower-mounted unit (for both reception and transmission) has an antenna, analog amplifier and an electro-optical converter. The ground unit has ultrafast data converters and digital frequency translators, as well as signal linearizers, to compensate for nonlinear distortion in the amplifiers and optical links in both directions. In one embodiment of the invention, at least one of the digital data converters, frequency translators, and linearizers includes superconducting elements mounted on a cryocooler.

It is provided a signal processing system, comprising at least a first, a second and a third digital-to-analog converter (DAC); a processing unit configured for splitting a sampled signal into a first and a second signal corresponding to different frequency portions of the sampled signal, transmitting the first signal to the first DAC, splitting the second signal into a first and a second subsignal and transmitting the first subsignal to the second DAC and the second subsignal to the third DAC, the first subsignal corresponding to the real part of the second signal and the second subsignal corresponding to the imaginary part of the second signal; an IQ mixer configured for mixing an analog output signal of the second DAC and an analog output signal of the third DAC and a combiner for combining an analog output signal of the first DAC and an output signal of the IQ mixer.

A semiconductor device of an embodiment includes first and second couplers, an encoding circuit, and a demodulating circuit. The encoding circuit executes differential Manchester encoding on digital data based on a clock inputted thereto via the first coupler and outputs an encoded data. The demodulating circuit includes a first sampling circuit which samples the encoded data inputted via the second coupler based on a sampling frequency set to be two times higher than that of the encoded data and which outputs first sample data, a second sampling circuit which samples the encoded data at a timing earlier than that in the first sampling circuit and which outputs second sample data, a determination circuit which determines whether or not the first and the second sample data match each other, and a selection circuit which selects first phase data or second phase data from the first sample data.

Present invention provides an optical communication system that controls reception sensitivity of an optical receiver. The communication system (100) according to the present invention comprising: an optical transmitter (1) to which an transmission signal is input, and which modulates the transmission signal to an optical signal and transmits the optical signal; and an optical receiver (2) that receives the optical signal and demodulates the optical signal to an transmission signal. And the optical receiver (2) includes a photoelectric conversion means (10) for converting the optical signal into an analog electric signal, a conversion and demodulation means (25) for converting the analog electric signal into a digital signal and demodulating the signal to the transmission signal, and an amplitude control means (102) for controlling amplitude of the analog electric signal, and the amplitude control means (102) controls the amplitude of the analog electric signal in accordance with wavelength dispersion of the optical signal.

An encoder for generating an optical data code from a symbol performs a symbol mapping and an encoding, wherein the symbol mapping performs providing a first constellation format having first and second amplitude rings with circular grids corresponding to phase angles, providing a second constellation format having the first and second amplitude rings with the circular grids corresponding to the phase angles, applying a first part of the symbol to one of the first and second constellation formats to represent the first part of the symbol by one of the first and second amplitude rings with one of the circular grids, and applying a second part of the symbol to another one of the first and second constellation formats to represent the second part of the symbol by one of the first and second amplitude rings with one of the circular grids. The first and the second constellation can be mapped to subcarrier modulation in three different ways.

Embodiments of the present invention provide data transmission and receiving methods based on an orthogonal frequency division multiplexing technology, and an apparatus. According to the present invention, grouping and differential encoding are performed on multiple subcarriers, and further, carrier location adjustment is performed, so as to effectively improve non-linear tolerance of a multi-subcarrier system.