Provided are methods and systems for receiving and processing optical signals. A dual single side band (SSB) modulation scheme is utilized to take advantage of a given wavelengths' bandwidth. Modulation schemes are employed that modulate each SSB with their In-phase (I) and Quadrature (Q) components. The methods and systems discussed utilize an adaptive equalizer and an LMS algorithm to remove imaging components of the left and right SSBs provided by the modulators. The adaptive equalizer and the LMS algorithm also compensate for linear and nonlinear distortions. Various algorithms can be employed, including but not limited to, algorithms for updating crosstalk coefficients in the equalizer, where the cross talk coefficients are induced from the imaging from the modulation of the dual SSB signal, and for updating coefficients relating to linear and nonlinear distortion.

An error correction circuit includes a first error correction circuit, a second error correction circuit and a controller. The first error correction circuit performs an error correction in a first correction scheme. The second error correction circuit performs an error correction in a second correction scheme. A correction performance of the second correction scheme is lower than a correction performance of the first correction scheme. The controller makes the first error correction circuit perform error correction of a received signal when a capacity of the received signal is smaller than or equal to a processing capacity of the first error correction circuit, and makes the first error correction circuit and the second error correction circuit perform error correction of the received signal when the capacity of the received signal is larger than the processing capacity of the first error correction circuit.

A communications system receives a plurality of input data streams and applies a different orthogonal function to each of the plurality of input data streams. The system processes each of the plurality of input data streams to spatially locate a first group of the plurality of input data streams onto a first carrier signal and to spatially locate a second group of the plurality of input data streams onto a second carrier signal. The system temporally locates the first carrier signal and the second carrier signal onto a third carrier signal and transmits the third carrier signal over a communications link.

A method for modulating data for transmission within a communication system. The method includes establishing a time-frequency shifting matrix of dimension N×N, wherein N is greater than one. The method further includes combining the time-frequency shifting matrix with a data frame to provide an intermediate data frame. A transformed data matrix is provided by permuting elements of the intermediate data frame. A modulated signal is generated in accordance with elements of the transformed data matrix.

A system and method involve receiving, at a processor, a phase modulated signal such as an optical or electromagnetic signal, using one or more samples of an in-phase component I(t) and a quadrature component Q(t) of the received phase modulated signal to generate, at the processor, a processed signal using the equation [A−B×I(t)]×Q(t), where A and B are numerical parameters, and inputting the processed signal into a receiver operatively connected to the processor. The processed signal may be filtered prior to being input into the receiver. Parameters A and B may be selected to vary complexity and performance of the receiver while controlling distortion for different modulation indices.

The present disclosure relates to a 5G or pre-5G communication system to be provided for supporting a higher data transmission rate beyond 4G communication systems such as LTE. A method for modulation in a transmitter for transmitting a signal in a wireless communication system according to an embodiment of the present invention comprises: a step for determining a modulation scheme; a step for, if the determined modulation scheme corresponds to a specific modulation scheme, converting encoded information bits to quadrature amplitude modulation (QAM) symbols in accordance with a predetermined QAM modulation order, selecting a sequence corresponding to an element of an integer vector in a predetermined sequence set, repeating the converted QAM symbols for a predetermined sequence length, and outputting signals by multiplying the repeated QAM symbols and the selected sequence; and a step for transmitting the outputted signals to a receiver.

We disclose an optical add-drop multiplexer that can apply different routing operations to different subcarriers of a data frame. In an example embodiment, the digital signal processor (DSP) of the optical add-drop multiplexer carries out subcarrier-specific add, drop, and pass-through operations in the electrical frequency domain, which enables the DSP to only partially unwrap the pass-through subcarriers, thereby at least partially avoiding some of the more processing-power-hungry DSP operations and reducing the sub-wavelength routing latency accordingly. Also disclosed is an example data-frame structure that can be used to provide subcarrier-specific routing instructions to the optical add-drop multiplexer.

A method and an apparatus relating to an OFDM data communications system where the sub-carriers are modulated using differential quadrature phase-shift keying (DQPSK). The multi-carrier transmitted signal is directly generated by means of summation of pre-computed sample points. As part of the multi-carrier signal generation, a signal for the guard interval is established. In an acoustic application of this approach, direct radiation of the sub-carrier approach is facilitated. Symbol synchronization in the receiver is based on signal correlation with the missed sub-carrier. Separation of the sub-carriers in the receiver by means of correlation of the received signal and reference signals that are derived from a table of pre-computed values. Optimal non-coherent processing of the sub-carriers without any phase tracking procedures is achieved.

Orthogonal Time Frequency Space (OTFS) is a novel modulation scheme with significant benefits for 5G systems. The fundamental theory behind OTFS is presented in this paper as well as its benefits. We start with a mathematical description of the doubly fading delay-Doppler channel and develop a modulation that is tailored to this channel. We model the time varying delay-Doppler channel in the time-frequency domain and derive a new domain (the OTFS domain) where we show that the channel is transformed to a time invariant one and all symbols see the same SNR. We explore aspects of the modulation like delay and Doppler resolution, and address design and implementation issues like multiplexing multiple users and evaluating complexity. Finally we present some performance results where we demonstrate the superiority of OTFS.

There is provided a multi-flow optical transceiver that includes (a) a plurality of wavelength-tunable light sources, (b) a plurality of optical modulation units which modulates light with an input signal, (c) an optical multiplexing/demultiplexing switch which couples light from at least one of the wavelength-tunable light sources to at least one of the optical modulation units with any power, (d) an optical coupling unit which couples a plurality of lights, modulated by a plurality of the optical modulation units, to at least one waveguide, (e) at least one multiple carrier generating unit which generates multiple carries, arranged at equal frequency intervals, from light of the wavelength-tunable light source, and (f) a wavelength separation unit which branches the multiple carriers from the multiple carrier generating unit for each wavelength.