Wide bandwidth digital pre-distortion (DPD) in a remote unit(s) for a wireless communications system (WCS)

1. A wireless communications system (WCS), comprising:

a plurality of remote units, wherein at least one remote unit among the plurality of remote units comprises:

a first transceiver circuit configured to:

receive a first downlink digital communications signal corresponding to a first signal bandwidth; and

convert the first downlink digital communications signal into a first downlink radio frequency (RF) communications signal corresponding to a first processing bandwidth that is at least three times the first signal bandwidth;

a second transceiver circuit configured to:

receive a second downlink digital communications signal corresponding to a second signal bandwidth; and

convert the second downlink digital communications signal into a second downlink RF communications signal corresponding to a second processing bandwidth that is at least three times the second signal bandwidth; and

a combining circuit coupled to the first transceiver circuit and the second transceiver circuit, the combining circuit configured to output at least one downlink RF communications signal comprising the first downlink RF communications signal and the second downlink RF communications signal and corresponding to a carrier bandwidth, wherein the carrier bandwidth is greater than or equal to a sum of the first signal bandwidth and the second signal bandwidth and narrower than a sum of the first processing bandwidth and the second processing bandwidth.

2. The WCS of claim 1 , further comprising a central unit configured to communicate a plurality of downlink communications signals and a plurality of uplink communications signals with the plurality of remote units via a plurality of communications mediums, wherein the central unit is configured to:

generate the first downlink digital communications signal and the second downlink digital communications signal among the plurality of downlink communications signals; and

provide the first downlink digital communications signal and the second downlink digital communications signal to the first transceiver circuit and the second transceiver circuit in the at least one remote unit, respectively.

3. The WCS of claim 2 , wherein:

the plurality of communications mediums comprises a plurality of optical fiber-based communications mediums, respectively;

the central unit comprises:

a plurality of electrical-to-optical (E/O) converters configured to convert the plurality of downlink communications signals into a plurality of downlink optical communications signals; and

a plurality of optical-to-electrical (O/E) converters configured to convert a plurality of uplink optical communications signals into the plurality of uplink communications signals; and

the plurality of remote units comprises:

a plurality of remote unit O/E converters configured to convert the plurality of downlink optical communications signals into the plurality of downlink communications signals; and

a plurality of remote unit E/O converters configured to convert the plurality of uplink communications signals into the plurality of uplink optical communications signals.

4. The WCS of claim 1 , wherein:

the first transceiver circuit comprises:

a first digital-to-analog converter (DAC) configured to convert the first downlink digital communications signal corresponding to the first signal bandwidth into the first downlink RF communications signal corresponding to the first processing bandwidth;

a first downlink filter configured to pass the first downlink RF communications signal inside the first processing bandwidth and block the first downlink RF communications signal outside the first processing bandwidth; and

a first power amplifier having the first processing bandwidth and configured to amplify the first downlink RF communications signal; and

the second transceiver circuit comprises:

a second DAC configured to convert the second downlink digital communications signal corresponding to the second signal bandwidth into the second downlink RF communications signal corresponding to the second processing bandwidth;

a second downlink filter configured to pass the second downlink RF communications signal inside the second processing bandwidth and block the second downlink RF communications signal outside the second processing bandwidth; and

a second power amplifier having the second processing bandwidth and configured to amplify the second downlink RF communications signal.

5. The WCS of claim 4 , wherein:

the first transceiver circuit further comprises a first digital routing circuit configured to receive the first downlink digital communications signal via a first digital interface; and

the second transceiver circuit further comprises a second digital routing circuit configured to receive the second downlink digital communications signal via a second digital interface.

6. The WCS of claim 5 , wherein each of the first digital interface and the second digital interface is configured to operate as a common public radio interface (CPRI).

7. The WCS of claim 4 , wherein:

the first transceiver circuit further comprises:

a first digital pre-distortion (DPD) circuit configured to digitally pre-distort the first downlink digital communications signal based on a first digital feedback signal corresponding to the first processing bandwidth;

a first coupler coupled to the first power amplifier and configured to generate a sample of the first downlink RF communications signal corresponding to the first processing bandwidth; and

a first feedback path coupled between the first coupler and the first DPD circuit, the first feedback path configured to convert the sample of the first downlink RF communications signal to the first digital feedback signal; and

the second transceiver circuit further comprises:

a second DPD circuit configured to digitally pre-distort the second downlink digital communications signal based on a second digital feedback signal corresponding to the second processing bandwidth;

a second coupler coupled to the second power amplifier and configured to generate a sample of the second downlink RF communications signal corresponding to the second processing bandwidth; and

a second feedback path coupled between the second coupler and the second DPD circuit, the second feedback path configured to convert the sample of the second downlink RF communications signal to the second digital feedback signal.

8. The WCS of claim 4 , wherein:

the first transceiver circuit further comprises a first isolation circuit, the first isolation circuit comprising at least two first isolators coupled in series between the first power amplifier and the combining circuit; and

the second transceiver circuit further comprises a second isolation circuit, the second isolation circuit comprising at least two second isolators coupled in series between the second power amplifier and the combining circuit.

9. The WCS of claim 1 , wherein the combining circuit comprises a coupler coupled to the first transceiver circuit and the second transceiver circuit, the coupler configured to combine the first downlink RF communications signal and the second downlink RF communications signal to generate the at least one downlink RF communications signal.

10. The WCS of claim 9 , wherein the coupler is a three decibel (3 dB) hybrid coupler.

11. The WCS of claim 9 , wherein the coupler is a two-way combiner.

12. The WCS of claim 9 , wherein the combining circuit further comprises a signal filter coupled to the coupler and configured to pass the at least one downlink RF communications signal inside the carrier bandwidth and block the at least one downlink RF communications signal outside the carrier bandwidth.

13. The WCS of claim 9 , wherein the combining circuit comprises:

a first signal filter coupled between the first transceiver circuit and the coupler, the first signal filter configured to pass the first downlink RF communications signal inside the carrier bandwidth and block the first downlink RF communications signal outside the carrier bandwidth; and

a second signal filter coupled between the second transceiver circuit and the coupler, the second signal filter configured to pass the second downlink RF communications signal inside the carrier bandwidth and block the second downlink RF communications signal outside the carrier bandwidth.

14. The WCS of claim 1 , wherein one of the first transceiver circuit and the second transceiver circuit further comprises an uplink path configured to receive an uplink RF communications signal and convert the uplink RF communications signal into an uplink digital communications signal.

15. The WCS of claim 1 , further comprising:

an existing transceiver circuit configured to comprise the first transceiver circuit; and

an add-on transceiver circuit configured to comprise the second transceiver circuit.

16. The WCS of claim 15 , wherein the second transceiver circuit further comprises an uplink path configured to receive an uplink RF communications signal and convert the uplink RF communications signal into an uplink digital communications signal.

17. A method for supporting wide bandwidth digital pre-distortion (DPD) in a remote unit for a wireless communications system (WCS), comprising:

in a first transceiver circuit:

receiving a first downlink digital communications signal corresponding to a first signal bandwidth; and

converting the first downlink digital communications signal into a first downlink radio frequency (RF) communications signal corresponding to a first processing bandwidth that is at least three times the first signal bandwidth;

in a second transceiver circuit:

receiving a second downlink digital communications signal corresponding to a second signal bandwidth; and

converting the second downlink digital communications signal into a second downlink RF communications signal corresponding to a second processing bandwidth that is at least three times the second signal bandwidth; and

outputting, via a combining circuit, at least one downlink RF communications signal comprising the first downlink RF communications signal and the second downlink RF communications signal and corresponding to a carrier bandwidth, wherein the carrier bandwidth is greater than or equal to a sum of the first signal bandwidth and the second signal bandwidth and narrower than a sum of the first processing bandwidth and the second processing bandwidth.

18. The method of claim 17 , further comprising providing the first downlink digital communications signal and the second downlink digital communications signal from a central unit to the first transceiver circuit and the second transceiver circuit, respectively.

19. The method of claim 17 , further comprising:

in the first transceiver circuit:

converting the first downlink digital communications signal corresponding to the first signal bandwidth into the first downlink RF communications signal corresponding to the first processing bandwidth;

passing the first downlink RF communications signal inside the first processing bandwidth and blocking the first downlink RF communications signal outside the first processing bandwidth; and

amplifying the first downlink RF communications signal; and

in the second transceiver circuit:

converting the second downlink digital communications signal corresponding to the second signal bandwidth into the second downlink RF communications signal corresponding to the second processing bandwidth;

passing the second downlink RF communications signal inside the second processing bandwidth and blocking the second downlink RF communications signal outside the second processing bandwidth; and

amplifying the second downlink RF communications signal.

20. The method of claim 19 , further comprising:

receiving the first downlink digital communications signal via a first digital interface that is a common public radio interface (CPRI); and

receiving the second downlink digital communications signal via a second digital interface that is the CPRI.

21. The method of claim 19 , further comprising:

in the first transceiver circuit:

digitally pre-distorting the first downlink digital communications signal based on a first digital feedback signal corresponding to the first processing bandwidth;

generating a sample of the first downlink RF communications signal corresponding to the first processing bandwidth; and

converting the sample of the first downlink RF communications signal to the first digital feedback signal; and

in the second transceiver circuit:

pre-distorting the second downlink digital communications signal based on a second digital feedback signal corresponding to the second processing bandwidth;

generating a sample of the second downlink RF communications signal corresponding to the second processing bandwidth; and

converting the sample of the second downlink RF communications signal to the second digital feedback signal.

22. The method of claim 17 , further comprising combining the first downlink RF communications signal and the second downlink RF communications signal to generate the at least one downlink RF communications signal.

23. The method of claim 22 , further comprising passing the at least one downlink RF communications signal inside the carrier bandwidth and blocking the at least one downlink RF communications signal outside the carrier bandwidth.

24. The method of claim 22 , further comprising:

passing the first downlink RF communications signal inside the carrier bandwidth and blocking the first downlink RF communications signal outside the carrier bandwidth; and

passing the second downlink RF communications signal inside the carrier bandwidth and blocking the second downlink RF communications signal outside the carrier bandwidth.

25. The method of claim 17 , further comprising, in one of the first transceiver circuit and the second transceiver circuit, receiving an uplink RF communications signal and converting the uplink RF communications signal into an uplink digital communications signal.

26. The method of claim 17 , further comprising:

providing the first transceiver circuit in an existing transceiver circuit; and

providing the second transceiver circuit in an add-on transceiver circuit.

27. The method of claim 26 , further comprising receiving an uplink RF communications signal and converting the uplink RF communications signal into an uplink digital communications signal in the second transceiver circuit.