Systems and methods for signal predistortion

Abstract

A single or multistage signal predistorter includes an input coupled to receive an information signal comprising input samples and an output coupled to the high power amplifier, the signal predistorter configured to receive an input sample, generate a distortion sample based on an estimate of nonlinearity of the high power amplifier at an operating saturation level, modify the input sample with a correction term to generate a predistortion signal, wherein the correction term is proportional to the distortion sample, and further wherein the predistortion signal comprises the information signal modified to account for nonlinearities in the high power amplifier.

Description

TECHNICAL FIELD[0001]The disclosed technology relates generally to communication systems, and more particularly, some embodiments relate to systems and methods for performing signal predistortion.DESCRIPTION OF THE RELATED ART[0002]A goal of communication system designers is to increase power efficiency in digital communication systems. One conventional technique for increasing efficiency is to operate High Power Amplifiers (HPAs) close to saturation. Examples of these systems are narrowband systems such as those used on the return link in satellite communications systems, or wideband systems such as those employing code-division multiple access (CDMA), orthogonal frequency-division multiple access (FDMA), or multicarrier systems. However, a downside to increasing power efficiency in this way is spectral regrowth caused by operating the HPA close to saturation. Spectral regrowth is energy from the modulated signal that spreads into adjacent channels due to the amplifier's inherent n...

AI Technical Summary

Benefits of technology

[0004]Embodiments of the systems and methods disclosed herein provide an innovative form of signal predistortion to suppress, in some cases significantly, the spectral regrowth as well as in-band distortion simultaneously. This may be done in some embodiments while keeping the HPA operating efficiently near saturation. As a result of the suppression of spectral regrowth, the technology disclosed herein can also allow closer spacing of adjacent carriers in the frequency domain, which can result in higher levels of spectral efficiency.

[0005]The system can be configured to employ successive predistortion and can be further configured to operate at the signal level, or at multiple samples per symbol. Embodiments of the disclosed technology can further include an adjustable memory span that can be selected to account for memory effects associated with the HPA. In some embodiments, it can be memoryless, which is adequate for memoryless HPAs or for conditions in which the symbol rate is much smaller than the bandwidth of the HPA. Other embodiments can be configured to deliberately introduce memory to further suppress mean-square error (MSE) and provide a tuning feature to balance levels of suppressing spectral regrowth versus in-band distortion, measured in terms of ACI and MSE in decibels (dBs). In some embodiments, significant gains can be achieved as compared with systems that do not use the disclosed predistortion techniques. Additionally, embodiments can be implemented allowing tuning the system to trade-off levels of spectral growth suppression and in-band distortion.

[0006]Because configurations can be implemented to reduce spectral regrowth and in band distortion, excellent system performance can be achieved while maintaining high efficiency in both power and bandwidth resources. In various embodiments, the signal predistortion is provided at the transmitter, prior to the HPA, to mitigate the unwanted nonlinear effects caused by operating the HPA at or near saturation.

Problems solved by technology

However, a downside to increasing power efficiency in this way is spectral regrowth caused by operating the HPA close to saturation.

This spectral regrowth can cause adjacent channel interference (ACI), and potentially violates out-of-band emission requirements set by regulatory commissions.

Furthermore, this can also cause in-band distortion, manifested as clustering in a scatter plot at the receiver and quantified by mean-square error (MSE) relative to nominal constellation.

Both effects can severely degrade performance if left unmitigated.

Another conventional solution is to sample at the symbol rate and modify transmitted symbols, however this generally can only correct for in-band distortion and cannot compensate for spectral regrowth.

Other conventional predistortion methods require special transmit and receive filters which is not desirable in practical systems.

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