US-12627538-B2 - Methods of nonlinearity estimation, reporting, and compensation

Abstract

In one aspect, a method performed by a transmitter in a first device for signaling a nonlinearity profile of distortion of transmissions in a communications network is provided. The method includes generating an amplitude tracking reference signal (ATRS), wherein the ATRS comprises information indicating a nonlinearity profile of distortions of transmissions by the transmitter, and transmitting the generated ATRS towards a second device. In another aspect, a method performed by a receiver in a second device for identifying a nonlinearity profile of distortion of transmissions in a communications network by a transmitter in a first device is provided. The method includes receiving an ATRS from the first device, wherein the ATRS comprises information indicating a nonlinearity profile of distortions of transmissions by the transmitter and identifying the nonlinearity profile of distortion of transmissions by the transmitter based on the ATRS.

Inventors

• Ali Behravan
• Hamed FARHADI

Assignees

• TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Dates

Publication Date

20260512

Application Date

20211111

Claims (20)

1. 1 . A method performed by a transmitter in a first device for signaling a nonlinearity profile of distortion of transmissions in a communications network, the method comprising: generating an amplitude tracking reference signal (ATRS), wherein the ATRS comprises information indicating a nonlinearity profile of distortions of transmissions by the transmitter; and transmitting the generated ATRS towards a second device.
2. 2 . The method of claim 1 , further comprising: receiving a first message from the second device, wherein the first message comprises information relating to an identified nonlinearity profile of distortions of transmissions by the transmitter based on the information in the ATRS.
3. 3 . The method of claim 2 , further comprising: configuring the transmitter based on the information relating to the identified nonlinearity profile.
4. 4 . The method of claim 3 , wherein the configuring comprises one or more of: performing digital pre-distortion at the transmitter to reduce a distortion, adapting a Modulation Coding Scheme (MCS) index, controlling transmit power of the transmitter, adapting a number of transmit information layers in a multi-antenna system, adapting a crest factor reduction (CFR) that reduces peak to average power ratio of a signal, adapting a radio resource mapping, or configuring a carrier aggregation.
5. 5 . The method of claim 1 , further comprising: transmitting a second message towards the second device, the second message comprising information indicating a capability of the first device to transmit the ATRS.
6. 6 . The method of claim 5 , further comprising: receiving a third message in response to the second message, the third message comprising a configuration of a transmission of the ATRS.
7. 7 . The method of claim 1 , further comprising: receiving a fourth message from the second device, the fourth message comprising a request for an ATRS from the transmitter.
8. 8 . The method of claim 1 , further comprising: receiving a fifth message from the second device, the fifth message comprising information indicating a capability of the second device to identify the nonlinearity profile of distortions of transmissions by the transmitter based on an ATRS.
9. 9 . The method of claim 1 , wherein the information indicating the nonlinearity profile of distortions of transmission by the transmitter comprises a preconfigured sequence of symbols over a preconfigured period having a varying range of amplitudes.
10. 10 . The method of claim 1 , further comprising: mapping the generated ATRS to one or more radio resource blocks across a time-frequency domain based on a rate of change of nonlinearity of distortions in the time-frequency domain.
11. 11 . A method performed by a receiver in a second device for identifying a nonlinearity profile of distortion of transmissions in a communications network by a transmitter in a first device, the method comprising: receiving an amplitude tracking reference signal (ATRS) from the first device, wherein the ATRS comprises information indicating a nonlinearity profile of distortions of transmissions by the transmitter; and identifying the nonlinearity profile of distortion of transmissions by the transmitter based on the ATRS.
12. 12 . The method of claim 11 , further comprising: configuring the receiver based on the identified nonlinearity profile of distortions of transmission by the transmitter.
13. 13 . The method of claim 11 , further comprising: generating a first message, wherein the first message comprises information relating to the identified nonlinearity profile of distortions of transmission by the transmitter; and transmitting the first message towards the first device.
14. 14 . The method of claim 11 , further comprising: receiving a second message from the first device, the second message comprising information indicating a capability of the first device to transmit the ATRS.
15. 15 . The method of claim 14 , further comprising: generating a third message in response to the second message, the third message comprising a configuration of a transmission of the ATRS; and transmitting the third message towards the first device.
16. 16 . The method of claim 11 , further comprising: generating a fourth message, the fourth message comprising a request for an ATRS; and transmitting the fourth message towards the first device.
17. 17 . The method of claim 11 , further comprising: generating a fifth message, the fifth message comprising information indicating a capability of the second device to identify the nonlinearity profile of distortions of transmissions by the transmitter based on an ATRS; and transmitting the fifth message towards the first device.
18. 18 . The method of claim 11 , wherein the information indicating the nonlinearity profile of distortions of transmissions by the transmitter comprises a preconfigured sequence of symbols over a preconfigured period having a varying range of amplitudes.
19. 19 . A first device comprising a transmitter adapted to: generate an amplitude tracking reference signal (ATRS), wherein the ATRS comprises information indicating a nonlinearity profile of distortions of transmissions by the transmitter; and transmit the generated ATRS towards a second device.
20. 20 . A second device comprising a receiver adapted to: receive an amplitude tracking reference signal (ATRS) from a first device in a communications network, wherein the ATRS comprises information indicating a nonlinearity profile of distortions of transmissions by a transmitter of the first device; and identify the nonlinearity profile of distortion of transmissions by the transmitter based on the ATRS.

Description

CROSS REFERENCE TO RELATED APPLICATION(S) This application is a 35 U.S.C. § 371 National Stage of International Patent Application No. PCT/EP2021/081382, filed Nov. 11, 2021, the disclosure of which is incorporated herein by reference in its entirety. TECHNICAL FIELD Disclosed are embodiments related to nonlinearity estimation, reporting, and compensation in communications networks. Introduction Impact of Nonlinearity on Communication Systems In orthogonal frequency division multiplexing (OFDM), parallel data symbols modulate several closely spaced subcarriers in order to cope with the frequency selectivity of the channel in high data rate transmission. The narrowband sub-channels experience almost flat fading in a highly time dispersive multipath channel. OFDM as well as another variation, Discrete Fourier Transform Spread OFDM (DFTS-OFDM), are used in 3GPP Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (E-UTRA) and 5G NR as main modulation schemes in downlink and uplink. A major problem in OFDM systems is high peak-to-average power ratio (PAPR) due to aggregation of many independent modulation symbols. High PAPR causes either non-efficient use of the high-power amplifiers or high nonlinearity distortion in the system. FIG. 2 illustrates a representation of 16 Quadrature Amplitude Modulation (QAM)-OFDM in the in-phase/quadrature (I/Q) plane at a receiver when a soft-limiter nonlinearity is used at the transmitter. FIG. 2 shows an (I/Q) representation of a received modulation constellation when OFDM modulated symbols go through a soft-limiter nonlinearity, with input-output characteristic: y={x❘"\[LeftBracketingBar]"x❘"\[RightBracketingBar]"≤thx❘"\[LeftBracketingBar]"x❘"\[RightBracketingBar]"·th❘"\[LeftBracketingBar]"x❘"\[RightBracketingBar]">th Note that the cloud around each constellation point is due to only the nonlinear distortion, and there is no channel noise. FIG. 3 illustrates instantaneous power per mean power of OFDM symbols before and after a soft limiter. FIG. 3 shows a cumulative distribution function (CDF) of the instantaneous power of the OFDM signal relative to its mean power, before and after a soft-limiter. As illustrated in FIGS. 2-3, the nonlinearity causes a distortion on the received symbols that appears as a noise-like cloud, and the instantaneous power of the signal (i.e. the amplitude) of the transmit signal is clipped. FIG. 4 illustrates distortion distributions due to power amplifier nonlinearities in the spatial and frequency domain in a Multiple-Input Multiple-Output (MIMO)-OFDM system with two transmit antenna. FIG. 4 shows the transmitted signal power and the corresponding distortion power due to power amplifier nonlinearities in OFDM signal in multi-antenna systems. As shown in FIG. 4, in multi-antenna systems, the distortion is not limited to the directions and the subcarriers in which the signals are transmitted, but there are also distortions in certain new directions and subcarriers. FIG. 5 illustrates a link performance of a two-antenna system in the presence of different levels of distortions due to power amplifier nonlinearities. The throughput in the presence of different level of distortions measured by error vector magnitude (EVM) is shown. In a power amplifier, the nonlinear conversion from input amplitude to output amplitude (amplitude modulation to amplitude modulation, or AM/AM) is likely a smooth curve. Note that in addition to amplitude distortion, most power amplifiers have a phase distortion as a function of the input amplitude variation, which is called amplitude modulation to phase modulation conversion (AM/PM). A phase conversion causes a rotation in the signal constellation in FIG. 2. PA Nonlinearity Compensation To reduce the distortion due to nonlinearity, a predistorter can be implemented before the nonlinearity at the transmitter or a nonlinear equalizer is used at the receiver to compensate for the nonlinearity effects. In both of these solutions, an estimate of the nonlinearity profile is needed to design the predistorter or the equalizer. FIG. 6 is a schematic diagram of a transmitter and a receiver with digital pre-distortion at the transmitter side. In this system, the transmitter 602 includes a predistorter 603, which is a functional block located prior to the power amplifier (PA) 611. The predistorter 603 can be implemented in the digital baseband domain and generates a complementary nonlinearity to that of the PA 611 so that the overall system has linear or approximately linear characteristics. The predistorted baseband signal 601 is then converted to the analog domain using a digital to analog converter (DAC) 605, and is up-converted to the Radio Frequency (RF) domain using an I/Q modulator 607 and next fed to the PA 611 and antenna 613. To be able to synthesize the predistorter 603, a portion of the signal from the PA 611 is extracted, e.g. using a signal splitter or a coupler, and is down-converted to t