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US-12620944-B2 - Digital pre-distortion for frequency range 2 systems

US12620944B2US 12620944 B2US12620944 B2US 12620944B2US-12620944-B2

Abstract

Methods and devices are provided in which a processor of a user equipment (UE) combines loop-back signals from a plurality of antenna paths of the UE to generate a combined signal. The loop-back signals are based on a signal transmitted over the antenna paths. The processor determines power amplifier (PA) polynomials based on a comparison of the combined signal to the signal transmitted over the antenna paths. The processor generates a single look-up table (LUT) for the PA polynomials. The processor applies the single LUT to a transmitted signal of the UE to compensate for PA non-linearity.

Inventors

  • Yanru TANG
  • Hou-Shin Chen
  • Sahana SADAGOPAN
  • Bhupinder SACHDEV
  • Pranav Dayal

Assignees

  • SAMSUNG ELECTRONICS CO., LTD.

Dates

Publication Date
20260505
Application Date
20230615

Claims (20)

  1. 1 . A method comprising: combining, by a processor of a user equipment (UE), loop-back signals from a plurality of antenna paths of the UE to generate a combined signal, wherein the loop-back signals are based on a signal transmitted over the antenna paths; determining, by the processor, power amplifier (PA) polynomials based on a comparison of the combined signal to the signal transmitted over the antenna paths; generating, by the processor, a single look-up table (LUT) for the PA polynomials; and applying, by the processor, the single LUT to a transmitted signal of the UE to compensate for PA non-linearity.
  2. 2 . The method of claim 1 , wherein the loop-back signals are combined using power and phase information of each of the antenna paths.
  3. 3 . The method of claim 1 , wherein the LUT comprises an amplitude-amplitude (AMAM) and amplitude-phase (AMPM) LUT.
  4. 4 . The method of claim 3 , wherein: the loop-back signals are captured at a first power and a second power that is lower than the first power; determining the PA polynomials comprises estimating a first PA polynomial from data received at the first power, and a second PA polynomial from data received at the second power; and the single LUT is based on the first PA polynomial and the second PA polynomial.
  5. 5 . The method of claim 4 , wherein the first PA polynomial is used in a high power region and the second PA polynomial is used in a low power region.
  6. 6 . The method of claim 5 , wherein a switching point between the high power region and the low power region minimizes AMAM difference between the first PA polynomial and the second PA polynomial.
  7. 7 . The method of claim 5 , wherein the switching point between the high power region and the low power region is set as a constant.
  8. 8 . The method of claim 4 , wherein the first PA polynomial is used to calculate AMAM, the second PA polynomial is used to calculate AMPM if AM is below an AM threshold, and the first PA polynomial is used to calculate AMPM if the AM is greater than or equal to the AM threshold.
  9. 9 . The method of claim 8 , wherein the AM threshold is set based on a normalized correlation of estimated PA response from the first and second PA polynomials in a small region.
  10. 10 . The method of claim 3 , wherein generating the single LUT comprises maintaining a constant AMPM in a small AM region in case of a single power data capture.
  11. 11 . The method of claim 1 , further comprising: controlling digital gain before applying the single LUT to compensate for gain difference introduced by the single LUT.
  12. 12 . The method of claim 11 , further comprising: applying close loop power control (CLPC) to adjust digital gain and variable gain amplifier (VGA) gain after applying the LUT to compensate for gain loss due to temperature rise.
  13. 13 . A user equipment (UE) comprising: a processor; and a non-transitory computer readable storage medium storing instructions that, when executed, cause the processor to: combine loop-back signals from a plurality of antenna paths of the UE to generate a combined signal, wherein the loop-back signals are based on a signal transmitted over the antenna paths; determining power amplifier (PA) polynomials based on a comparison of the combined signal to the signal transmitted over the antenna paths; generate a single look-up table (LUT) for the PA polynomials; and apply the single LUT to a transmitted signal of the UE to compensate for PA non-linearity.
  14. 14 . The UE of claim 13 , wherein the LUT comprises an amplitude-amplitude (AMAM) and amplitude-phase (AMPM) LUT.
  15. 15 . The UE of claim 14 , wherein: the loop-back signals are captured at a first power and a second power that is lower than the first power; in determining the PA polynomials, the processor is further configured to estimate a first PA polynomial from data received at the first power, and a second PA polynomial from data received at the second power; and the single LUT is based on the first PA polynomial and the second PA polynomial.
  16. 16 . The UE of claim 15 , wherein: the first PA polynomial is used in a high power region and the second PA polynomial is used in a low power region; and a switching point between the high power region and the low power region: minimizes AMAM difference between the first PA polynomial and the second PA polynomial; or is set as a constant.
  17. 17 . The UE of claim 15 , wherein the first PA polynomial is used to calculate AMAM, the second PA polynomial is used to calculate AMPM if AM is below an AM threshold, and the first PA polynomial is used to calculate AMPM if the AM is greater than or equal to the AM threshold.
  18. 18 . The UE of claim 14 , wherein generating the single LUT comprises maintaining a constant AMPM in a small AM region in case of a single power data capture.
  19. 19 . The method of claim 1 , further comprising: controlling digital gain before applying the single LUT to compensate for gain difference introduced by the single LUT.
  20. 20 . A user equipment (UE) comprising: a plurality of antennas, each having a respective antenna path for transmission of a signal and reception of a respective loop-back signal; at least one power amplifier (PA); and a processor configured to: combine the loop-back signals from the antenna paths to generate a combined signal; determine PA polynomials based on a comparison of the combined signal to the signal transmitted over the antenna paths; generate a single look-up table (LUT) for the PA polynomials; and apply the single LUT to a transmitted signal to compensate for non-linearity of the at least one PA.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims the priority benefit under 35 U.S.C. § 119(c) of U.S. Provisional Application No. 63/446,127, filed on Feb. 16, 2023, the disclosure of which is incorporated by reference in its entirety as if fully set forth herein. TECHNICAL FIELD The disclosure generally relates to signal quality improvement using digital pre-distortion (DPD). More particularly, the subject matter disclosed herein relates to improvements to DPD for frequency range 2 (FR2) systems. SUMMARY Power amplifiers (PAs) of a wireless communication system are inherently nonlinear, which causes in-band distortion, resulting in degradation of system error vector magnitude (EVM) performance. To solve this problem, DPD is used to compensate for PA non-linearity in order to improve signal quality. A look-up-table (LUT) approach may be adopted, in which amplitude-to-amplitude (AMAM) and amplitude-to-phase (AMPM) LUTs are constructed and applied to digital baseband signals to pre-compensate for PA non-linearity and improve system EVM performance. One issue with the above approach is that, in FR2, each transmitter is equipped with multiple antennas. A DPD block should be designed considering PA characteristics of all of the antennas. To overcome these issues, systems and methods are described herein for applying DPD to an FR2 system having multiple transmit (Tx) antennas, and generating an LUT by considering PA characteristics of all of the antennas. The above approaches improve on previous methods because power DPD training improves performance for all power levels, and only requires a single LUT to reduce storage requirements and facilitate software implementation. Specifically, a single AMAM and AMPM LUT may be used to improve EVM performance for all power levels for FR2 systems. In an embodiment, a method is provided in which a processor of a user equipment (UE) combines loop-back signals from a plurality of antenna paths of the UE to generate a combined signal. The loop-back signals are based on a signal transmitted over the antenna paths. The processor determines PA polynomials based on a comparison of the combined signal to the signal transmitted over the antenna paths. The processor generates a single LUT for the PA polynomials. The processor applies the single LUT to a transmitted signal of the UE to compensate for PA non-linearity. In an embodiment, a UE is provided that includes a processor and a non-transitory computer readable storage medium storing instructions. When executed, the instructions cause the processor to combine loop-back signals from a plurality of antenna paths of the UE to generate a combined signal. The loop-back signals are based on a signal transmitted over the antenna paths. The instructions also cause the processor to determine PA polynomials based on a comparison of the combined signal to the signal transmitted over the antenna paths, and generate a single LUT for the PA polynomials. The instructions further causes the processor to apply the single LUT to a transmitted signal of the UE to compensate for PA non-linearity. In an embodiment, a UE is provided that includes a plurality of antennas, each having a respective antenna path for transmission of a signal and reception of a respective loop-back signal. The UE also includes at least one PA and a processor. The processor is configured to combine loop-back signals from a plurality of antenna paths to generate a combined signal, and determine PA polynomials based on a comparison of the combined signal to the signal transmitted over the antenna paths. The processor is also configured to generate a single LUT for the PA polynomials, and apply the single LUT to a transmitted signal of the UE to compensate for non-linearity of the at least one PA. BRIEF DESCRIPTION OF THE DRAWING In the following section, the aspects of the subject matter disclosed herein will be described with reference to exemplary embodiments illustrated in the figures, in which: FIG. 1 is a diagram illustrating a communication system, according to an embodiment; FIG. 2 is a diagram illustrating a signal path of a UE, according to an embodiment; FIG. 3 is a diagram illustrating a linear system from DPD input to PA output, according to an embodiment; FIG. 4 is a flowchart illustrating a DPD training method, according to an embodiment; and FIG. 5 is a block diagram of an electronic device in a network environment, according to an embodiment. DETAILED DESCRIPTION In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. It will be understood, however, by those skilled in the art that the disclosed aspects may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail to not obscure the subject matter disclosed herein. Reference throughout this specification to “one emb