Digital pre-distortion for frequency range 2 systems

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 . The method of claim 1 , wherein the loop-back signals are combined using power and phase information of each of the antenna paths.

3 . The method of claim 1 , wherein the LUT comprises an amplitude-amplitude (AMAM) and amplitude-phase (AMPM) LUT.

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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . The UE of claim 13 , wherein the LUT comprises an amplitude-amplitude (AMAM) and amplitude-phase (AMPM) LUT.

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 . 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 . 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 . 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 . 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 . 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.