Communications method and apparatus include encoding information into a high-peakedness designed pulse train, converting the designed pulse train into a low-peakedness signal suitable for modulating a narrowband carrier to generate a physical communication signal with desired spectral and temporal properties, and generating and transmitting the physical communication signal. The communications method and apparatus also include receiving and demodulating the physical communication signal, and further converting the demodulated signal into a high-peakedness received pulse train corresponding to the designed pulse train, so that the encoded information may be extracted from the received pulse train.

Embodiments of a noise-shaping crest factor reduction method for a carrier signal (and a device that performs the method) include (a) clipping the carrier signal by selecting at least one carrier signal peak that has a magnitude exceeding a predetermined crest factor reduction threshold, (b) subtracting the resulting clipped signal from the carrier signal, (c) confining, by a noise shaping filter, the resulting clipping noise signal in a frequency band corresponding to that of the carrier signal, and (d) subtracting the resulting spectrally shaped clipping noise signal from a delayed version of the carrier signal. The confining process includes selecting first sub-areas of the noise shaping filter response at one or more guard bands, selecting at least one second sub-area of the noise shaping filter response elsewhere in the frequency band, and setting the first sub-areas to a first predetermined magnitude higher than the magnitude of the second sub-area.

Embodiments include methods and devices for processing a digital composite signal generated at a first sampling rate. The signal includes at least first and second carrier-bands arranged to define a first inner gap between the carrier-bands. The first inner gap includes at least a first gap between the highest frequency of the first carrier-band and the lowest frequency of the second carrier-band. The digital composite signal has a predetermined instantaneous bandwidth that is lower than a sampling bandwidth. An outer gap located outside the instantaneous bandwidth and within the sampling bandwidth is determined. The first inner gap is reduced to define a second inner gap, where a width of the second inner gap is related to a width of the outer gap. The resulting folded digital composite signal is decimated to a second sampling rate lower than the first sampling rate thereby creating a decimated folded digital composite signal.

A receiver circuit comprising: an input terminal configured to receive an input-signal; a feedforward-ADC configured to provide a feedforward-digital-signal based on the input-signal; a feedforward-DAC configured to provide a feedforward-analogue-signal based on the feedforward-digital-signal; a feedforward-subtractor configured to provide an error-signal based on the difference between the feedforward-analogue-signal and the input-signal; an error-LNA configured to provide an amplified-error-signal based on the error-signal; an error-ADC configured to provide a digital-amplified-error-signal based on the amplified-error-signal; a mixer configured to down-convert a signal in a signal path between the input terminal and the error-ADC; and an error-cancellation-block configured to provide an error-cancelled-signal based on a difference between the digital-amplified-error-signal and the feedforward-digital-signal.

A receiver circuit comprising: an input terminal configured to receive an input-signal; a feedforward-ADC configured to provide a feedforward-digital-signal based on the input-signal; a feedforward-DAC configured to provide a feedforward-analogue-signal based on the feedforward-digital-signal; a feedforward-subtractor configured to provide an error-signal based on the difference between the feedforward-analogue-signal and the input-signal; an error-LNA configured to provide an amplified-error-signal based on the error-signal; an error-ADC configured to provide a digital-amplified-error-signal based on the amplified-error-signal; a mixer configured to down-convert a signal in a signal path between the input terminal and the error-ADC; and an error-cancellation-block configured to provide an error-cancelled-signal based on a difference between the digital-amplified-error-signal and the feedforward-digital-signal.

A radio device includes an amplifier; a storage that stores therein distortion compensation coefficients each of which compensates distortion that is generated in the amplifier; an updater that reads, from the storage in a first time section, the distortion compensation coefficients associated with a portion of an input signal input during the first time section and stores the read distortion compensation coefficients in a memory, and that updates, in a second time section, the distortion compensation coefficients stored in the memory and writes the updated distortion compensation coefficients in the storage; and a controller that controls the updater such that, when the same input signal is repeatedly input, the distortion compensation coefficients associated with a portion that is different from the portion of the input signal input the last time are stored in the memory in the first time section.

An OFDM system uses a normal mode which has a symbol length T, a guard time TG and a set of N sub-carriers, which are orthogonal over the time T, and one or more fallback modes which have symbol lengths KT and guard times KTG where K is an integer greater than unity. The same set of N sub-carriers is used for the fallback modes as for the normal mode. Since the same set of sub-carriers is used, the overall bandwidth is substantially constant, so alias filtering does not need to be adaptive. The Fourier transform operations are the same as for the normal mode. Thus fallback modes are provided with little hardware cost. In the fallback modes the increased guard time provides better delay spread tolerance and the increased symbol length provides improved signal to noise performance, and thus increased range, at the cost of reduced data rate.

An OFDM system uses a normal mode which has a symbol length T, a guard time TG and a set of N sub-carriers, which are orthogonal over the time T, and one or more fallback modes which have symbol lengths KT and guard times KTG where K is an integer greater than unity. The same set of N sub-carriers is used for the fallback modes as for the normal mode. Since the same set of sub-carriers is used, the overall bandwidth is substantially constant, so alias filtering does not need to be adaptive. The Fourier transform operations are the same as for the normal mode. Thus fallback modes are provided with little hardware cost. In the fallback modes the increased guard time provides better delay spread tolerance and the increased symbol length provides improved signal to noise performance, and thus increased range, at the cost of reduced data rate.

Apparatus and methods for disrupting or preventing periodicity in DTC circuits are provided. In an example, a communication circuit can include a digital-to-time converter (DTC) and a processing path coupled to the DTC. The DTC can be configured to receive reference information, modulation information and first dither information, and to provide a modulated signal using the reference information, the modulation information and the first dither information. The processing path can be configured to receive second dither information and to cancel the first dither information using the second dither information, wherein the DTC is configured to disrupt processing periodicity of the communication circuit using the first dither information.

Apparatus and methods for disrupting or preventing periodicity in DTC circuits are provided. In an example, a communication circuit can include a digital-to-time converter (DTC) and a processing path coupled to the DTC. The DTC can be configured to receive reference information, modulation information and first dither information, and to provide a modulated signal using the reference information, the modulation information and the first dither information. The processing path can be configured to receive second dither information and to cancel the first dither information using the second dither information, wherein the DTC is configured to disrupt processing periodicity of the communication circuit using the first dither information.