Predistortion for hybrid digital/analog precoders
A 5G base station transmitter at least partially precodes data for beam forming, and generates digital precoded baseband signals. Cross product circuitry coupled to the digital precoder, generates digital cross products of the digital precoded baseband signals. Both the baseband signals and the cross products are put through digital-to-analog converters (DACs), then provided to an analog non-linear precoder. The analog non-linear precoder combines the analog baseband signals, the cross products, with pre-distortion and precoder coefficients to generate a signal that is pre-compensated for power amplifier non-linearity. The pre-compensated signal is amplified by the power amplifier and transmitted via a phased antenna array. The number of extra DACs required for inserting pre-distortion when a hybrid digital/analog precoder is used can be limited to approximately N RF ( N RF - 1 ) 2 , where N RF is the number of outputs of the digital precoder. This is significantly fewer than the number of extra DACs used by other methods.
1. A system comprising:
a predistorter operable to produce a plurality of pre-compensated signals according to a respective plurality of analog baseband signals, a respective plurality of cross-products of the plurality of analog baseband signals, and a plurality of coefficients; and
a plurality of radio frequency (RF) power amplifiers operable to receive the plurality of pre-compensated signals.
2. The system of claim 1 , wherein the predistorter comprises a digital-to-analog converter operable to generate the plurality of analog baseband signals.
3. The system of claim 1 , wherein the predistorter comprises:
a first plurality of complex multipliers associated with the plurality of analog baseband signals; and
a second plurality of complex multipliers associated with the plurality of cross-products of the plurality of analog baseband signals.
4. The system of claim 1 , wherein the plurality of coefficients comprises a precoder coefficient and a digital pre-distortion coefficient.
5. The system of claim 4 , wherein the precoder coefficient is produced in a baseband processor.
6. The system of claim 4 , wherein the plurality of coefficients comprises an adaptive digital pre-distortion coefficient generated according to feedback from the RF power amplifiers.
7. The system of claim 1 , wherein the system is embedded in an integrated circuit.
8. The system of claim 7 , wherein the integrated circuit is a basestation transmitter.
9. The system of claim 1 , wherein the predistorter comprises a digital baseband chip and an analog precoder chip.
10. The system of claim 9 , wherein the plurality of coefficients are generated in the digital baseband chip.
11. A method comprising:
producing, in a predistorter:
a plurality of pre-compensated signals, according to a respective plurality of analog baseband signals,
a respective plurality of cross-products of the plurality of analog baseband signals, and
a plurality of coefficients; and
amplifying the plurality of pre-compensated signals in a respective plurality of radio frequency (RF) power amplifiers.
12. The method of claim 11 , wherein producing the plurality of pre-compensated signals comprises generating the plurality of analog baseband signals from a respective plurality of digital baseband signals.
13. The method of claim 11 , wherein producing the plurality of pre-compensated signals comprises:
producing a cross-product of the plurality of cross-products by multiplying a first one of the plurality of analog baseband signals by a second one of the plurality of analog baseband signals using a complex multiplier; and
scaling the cross-product of the plurality of cross-products by a coefficient of the plurality of coefficients.
14. The method of claim 11 , wherein the plurality of coefficients comprises a precoder coefficient and a digital pre-distortion coefficient.
15. The method of claim 14 , wherein the method comprises producing the precoder coefficient is in a baseband processor.
16. The method of claim 14 , wherein the method comprises generating an adaptive digital pre-distortion coefficient according to feedback from the plurality of RF power amplifiers.
17. The method of claim 11 , wherein the method is performed in an integrated circuit.
18. The method of claim 17 , wherein the integrated circuit is a basestation transmitter.
19. The method of claim 11 , wherein the predistorter comprises a digital baseband chip and an analog precoder chip.
20. The method of claim 19 , wherein the method comprises generating the plurality of coefficients in the digital baseband chip.