Communication systems are described that use unequally spaced constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. One embodiment is a digital communications system including a transmitter transmitting signals via a communication channel, the transmitter including a coder capable of receiving user bits and outputting encoded bits at a rate, a mapper capable of mapping encoded bits to symbols in a constellation, and a modulator capable of generating a modulated signal for transmission via the communication channel using symbols generated by the mapper, wherein the constellation is unequally spaced and characterizable by assignment of locations and labels of constellation points to maximize parallel decode capacity of the constellation at a given signal-to-noise ratio so that the constellation provides a given capacity at a reduced signal-to-noise ratio compared to a uniform constellation that maximizes the minimum distance between constellation points of the uniform constellation.

Communication systems are described that use unequally spaced constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. One embodiment is a digital communications system including a transmitter transmitting signals via a communication channel, the transmitter including a coder capable of receiving user bits and outputting encoded bits at a rate, a mapper capable of mapping encoded bits to symbols in a constellation, and a modulator capable of generating a modulated signal for transmission via the communication channel using symbols generated by the mapper, wherein the constellation is unequally spaced and characterizable by assignment of locations and labels of constellation points to maximize parallel decode capacity of the constellation at a given signal-to-noise ratio so that the constellation provides a given capacity at a reduced signal-to-noise ratio compared to a uniform constellation that maximizes the minimum distance between constellation points of the uniform constellation.

Communication systems are described that use unequally spaced constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. One embodiment is a digital communications system including a transmitter transmitting signals via a communication channel, the transmitter including a coder capable of receiving user bits and outputting encoded bits at a rate, a mapper capable of mapping encoded bits to symbols in a constellation, and a modulator capable of generating a modulated signal for transmission via the communication channel using symbols generated by the mapper, wherein the constellation is unequally spaced and characterizable by assignment of locations and labels of constellation points to maximize parallel decode capacity of the constellation at a given signal-to-noise ratio so that the constellation provides a given capacity at a reduced signal-to-noise ratio compared to a uniform constellation that maximizes the minimum distance between constellation points of the uniform constellation.

Circuits and methods for reducing the cost and/or power consumption of a user terminal and/or the gateway of a telecommunications system that may include a telecommunications satellite. Embodiments include “chained” feedback-regulated voltage supply circuits. These circuits substantially eliminate the need for separate regulator circuits for each regulated voltage. These circuits are designed to automatically maintain a substantially constant first voltage at a first node for a first load and maintain a substantially constant second voltage at a second node for a second load. Some disclosed configurations of these circuits may be useful to achieve greater current capability at the same voltage without requiring larger switches and higher inductor and capacitor sizes that may be needed in a single (conventional) stage voltage supply circuit.

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 invention relates to a method for adapting a link using a polar-modulation (PQAM) constellation. It applies in particular to the communications in the sub-THz band, in which the oscillator of the receiver has phase fluctuations. In a PQAM-modulation constellation, the modulation symbols are distributed on concentric circles equidistant in the complex plane, each circle including the same number of symbols, the angular distribution of the symbols on a circle being uniform and identical regardless of the circle. The adaptation of the link is carried out by taking into account the thermal noise as well as the phase noise.

A method for Peak to Average Power Ratio (PAPR) reduction at an input of analog to digital converter (ADC) of the receiver, the method includes mapping, by a mapper, an input symbol to an output symbol that maintains a peak power constraint at the input of the ADC; wherein the mapping is responsive to previously transmitted symbols; transmitting the output symbol by the transmitter; receiving, by the receiver, a received symbol that represents the output symbol; and de-mapping the received symbol, by a de-mapper of the receiver, to a de-mapped symbol that represents the input symbol.

A backscatter communication method and apparatus based on pattern-based demodulation is disclosed. The backscatter communication method includes receiving a communication signal, and demodulating the communication signal based on a slope of the communication signal at an edge of each time interval.

A system for retiming a multi-level signal that forms an eye diagram when plotted, such as a PAM4 signal that includes an equalizer configured to create an equalized signal and a first amplifier configured to amplify the equalized signal, responsive to a first amplifier control signal, to create a first amplified signal, and a second amplifier configured to amplify the equalized signal, responsive to a second amplifier control signal, to create a second amplified signal. An eye monitor processes the equalized signal, the first amplified signal, and the second amplified signal to create a first retiming clock phase signal and a second retiming clock phase signal, which control sampling times for flip-flops. One or more delays and one or more emphasis modules are configured to delay and introduce emphasis into an output from the flip-flops, the resulting signals are combined in a summing junction to create the retimed signal.

Communication systems are described that use unequally spaced constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. One embodiment is a digital communications system including a transmitter transmitting signals via a communication channel, the transmitter including a coder capable of receiving user bits and outputting encoded bits at a rate, a mapper capable of mapping encoded bits to symbols in a constellation, and a modulator capable of generating a modulated signal for transmission via the communication channel using symbols generated by the mapper, wherein the constellation is unequally spaced and characterizable by assignment of locations and labels of constellation points to maximize parallel decode capacity of the constellation at a given signal-to-noise ratio so that the constellation provides a given capacity at a reduced signal-to-noise ratio compared to a uniform constellation that maximizes the minimum distance between constellation points of the uniform constellation.