ADAPTIVE MULTI-CHANNEL TRANSMITTER LINEARIZATION SYSTEM USING A SHARED FEEDBACK RECEIVER

• US 20120281777A1
• Filed: 05/03/2011
• Published: 11/08/2012
• Est. Priority Date: 05/03/2011
• Status: Active Grant

• Current Assignee: Optis Cellular Technology LLC (Brevet Capital)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Bailey, Kris, Rashev, Peter Zahariev, Ho, Tan
• Granted Patent: US 8,837,620 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H03F 1/3223 using feed-forward H03F1/3211 takes precedence
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0441 with linearisation using feed-forward
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

Pre-distortion techniques, devices and systems for a multi-channel transmitter are described. An adaptation time is provided for each of the transmit chains in the multi-channel transmitter. During each adaptation time an output of a transmit chain is coupled to a shared feedback receiver. The shared feedback receiver generates a feedback signal that is used to vary pre-distortion for that transmit chain. A commutation controller varies at least one of: (a) an amount of the adaptation time for a transmit chain and (b) an order in which each of the transmit chains receives its adaptation time.

Claims

1. A method for adaptively providing pre-distortion in a multi-channel transmitter, wherein each channel is associated with a different transmit chain of elements, said method comprising:

providing an adaptation time for each of said transmit chains, during which adaptation time an output of a respective transmit chain is coupled to a shared feedback receiver which generates a feedback signal that is used to vary pre-distortion for said respective transmit chain; and

varying at least one of;

(a) an amount of said adaptation time for a transmit chain and (b) an order in which each of said transmit chains receives said adaptation time.

2. The method of claim 1, further comprising:

coupling a plurality of said outputs, each of said plurality of outputs associated with a different transmit chain in said multi-channel transmitter, to said shared feedback receiver;

selecting one of said plurality of outputs for processing by said shared feedback receiver during said adaptation period based, at least in part, on a priority queue which is populated in response to input signal level changes; and

providing said feedback signal from said shared feedback receiver to a pre-distortion unit based on said processing of said selected one of said plurality of outputs.

3. The method of claim 2, further comprising:

determining, for one of said transmit chains, said input signal level change associated with its input signal;

adjusting a gain of a gain element in said one of said transmit chains in response to said input signal level change; and

adding an identifier associated with said one of said transmit chains to said priority queue if said input signal level change exceeds a threshold.

4. The method of claim 3, further comprising:

removing said gain when said one of said transmit chains is selected for processing by said shared feedback receiver.

5. The method of claim 4, wherein said step of removing said gain is performed instantaneously.

6. The method of claim 4, wherein said step of removing said gain is performed gradually.

7. The method of claim 6, wherein said step of removing said gain is performed over a plurality of adaptation periods associated with said one of said transmit chains.

8. The method of claim 3, wherein said step of selecting further comprises:

selecting as said one of said plurality of outputs, an output which is associated with a first identifier in said priority queue if said priority queue contains any identifiers; and

otherwise, if said priority queue does not contain any identifiers selecting, as said one of said plurality of outputs, an output associated with a transmit chain based on an arbitration scheme.

9. The method of claim 8, wherein said arbitration scheme is round-robin.

10. The method of claim 1, further comprising:

passing said feedback signal to a spectrum analyzer;

determining, by said spectrum analyzer, a spurious emission level associated with said feedback signal; and

updating at least one parameter which is used in said varying step based on said spurious emission level.

11. The method of claim 10, wherein said at least one parameter is at least one of:

(a) a first adaptation time associated with a transmit chain which is used when an input signal level change associated with said transmit chain does not exceed a threshold, (b) a second adaptation time associated with said transmit chain which is used when said input signal level change associated with said transmit chain exceeds said threshold, (c) an amount of level compensation to be removed by a level limiter during each adaptation time, and (d) said threshold.

12. The method of claim 2, further comprising:

providing a signal associated with a power amplifier model to said pre-distortion unit.

13. The method of claim 1, wherein the step of varying at least one of:

(a) an amount of said adaptation time for a transmit chain and (b) an order in which each of said transmit chains receives said adaptation time is performed based, at least in part, on information received from a baseband modem function.

14. A multi-channel transmitter comprising:

a plurality of different transmit chains, each associated with a different channel;

a shared feedback receiver;

a commutation controller configured to provide an adaptation time for each of said transmit chains, during which adaptation time an output of a respective transmit chain is coupled to said shared feedback receiver which generates a feedback signal that is used to vary pre-distortion for said respective transmit chain,

wherein at least one of;

(a) an amount of said adaptation time for a transmit chain and (b) an order in which each of said transmit chains receives said adaptation time is varied over time.

15. The multi-channel transmitter of claim 14, further comprising:

a plurality of couplers each configured to couple an output associated with a different transmit chain to said shared feedback receiver;

wherein said commutation controller is further configured to select one of said plurality of outputs for processing by said shared feedback receiver during said adaptation period based, at least in part, on a priority queue which is populated in response to input signal level changes; and

wherein said feedback signal is provided from said shared feedback receiver to a pre-distortion unit based on said processing of said selected one of said plurality of outputs.

16. The multi-channel transmitter of claim 15, further comprising:

a level limiter configured to determine, for one of said transmit chains, said input signal level change associated with its input signal, to adjust a gain of a gain element in said one of said transmit chains in response to said input signal level change, and to transmit a corresponding signal to said commutation controller if said input signal level change exceeds a threshold;

wherein said commutation controller adds an identifier associated with said one of said transmit chains to said priority queue in response to receiving said corresponding signal.

17. The multi-channel transmitter of claim 16, wherein said level limiter is further configured to remove said gain when said one of said transmit chains is selected for processing by said shared feedback receiver.

18. The multi-channel transmitter of claim 17, wherein said gain removal is performed instantaneously.

19. The multi-channel transmitter of claim 17, wherein said gain removal is performed gradually.

20. The multi-channel transmitter of claim 19, wherein said gain removal is performed over a plurality of adaptation periods associated with said one of said transmit chains.

21. The multi-channel transmitter of claim 14, wherein said commutation controller is further configured to perform said selecting by selecting as said one of said plurality of outputs, an output which is associated with a first identifier in said priority queue if said priority queue contains any identifiers;

and otherwise, if said priority queue does not contain any identifiers selecting, as said one of said plurality of outputs, an output associated with a transmit chain based on an arbitration scheme.

22. The multi-channel transmitter of claim 21, wherein said arbitration scheme is round-robin.

23. The multi-channel transmitter of claim 14, further comprising:

a spectrum analyzer configured to receive said feedback signal and to determine a spurious emission level associated with said feedback signal,

wherein said commutation controller updates at least one parameter which is used to vary said at least one of;

(a) an amount of said adaptation time for a transmit chain and (b) an order in which each of said transmit chains receives said adaptation time is varied over time.

24. The multi-channel transmitter of claim 23, wherein said at least one parameter is at least one of:

(a) a first adaptation time associated with a transmit chain which is used when an input signal level change associated with said transmit chain does not exceed a threshold, (b) a second adaptation time associated with said transmit chain which is used when said input signal level change associated with said transmit chain exceeds said threshold, (c) an amount of level compensation to be removed by a level limiter during each adaptation time, and (d) said threshold.

25. The multi-channel transmitter of claim 15, further comprising:

a power amplifier model which provides a signal to said pre-distortion unit.

26. The multi-channel transmitter of claim 14, wherein the commutation controller is further configured to receive a signal from a baseband modem function and varies said at least one of:

(a) an amount of said adaptation time for a transmit chain and (b) an order in which each of said transmit chains receives said adaptation time based, at least in part, on information in said signal.