Clipping of transmission signal

• US 20060154622A1
• Filed: 03/08/2005
• Published: 07/13/2006
• Est. Priority Date: 01/07/2005
• Status: Active Grant

• Current Assignee: RPX Corporation
• Original Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Inventors: Piirainen, Olli
• Granted Patent: US 7,643,801 B2
• Time in Patent Office: Days
• US Class Current: 455/115.100
• CPC Class Codes: H03F 1/0205 in transistor amplifiers
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 2201/3236 A generated signal, e.g. a pulse or an inverted synchronous signal, being added to avoid certain conditions, e.g. clipping
• CPC Class Codes: H04B 1/04 Circuits
• CPC Class Codes: H04B 2001/0416 having gain or transmission power control
• CPC Class Codes: H04L 27/2623 Reduction thereof by clipping

Abstract

A transmitter clips a transmission signal before transmission in order to reduce the strength of at least one peak of the transmission signal exceeding a predetermined threshold. The transmitter includes a clipper having a minimizer, a filter and an adder. The minimizer minimizes of a cost function with respect to an optimization signal, the cost function having weighted terms as a function of the optimization signal. The terms relate to an effective modulation distortion and an effective overshoot exceeding the predetermined threshold. The filter forms a clipping signal by filtering the optimization signal formed as a result of the minimization according to the spectrum emission mask requirements of the radio system. The adder subtracts the clipping signal from the transmission signal.

Claims

1. A method of clipping a transmission signal in a radio system, the method comprising:

clipping a transmission signal in a transmitter before transmission in order to reduce a strength of at least one peak of the transmission signal exceeding a predetermined threshold;

performing a minimization of a cost function with respect to an optimization signal, the cost function having weighted terms as a function of the optimization signal, the weighted terms relating to an effective modulation distortion and an effective overshoot exceeding the predetermined threshold;

forming a clipping signal by filtering the optimization signal formed as a result of the minimization according to spectrum emission mask requirements of a radio system; and

subtracting the clipping signal from the transmission signal.

2. The method of claim 1, the method further comprising performing an iterative algorithm for minimizing the cost function.

3. The method of claim 1, the method further comprising performing an iterative algorithm using a gradient descent for minimizing the cost function.

4. The method of claim 1, the method further comprising forming a term relating to the effective modulation distortion as an effective strength of the optimization signal.

5. The method of claim 1, the method further comprising forming a term relating to the effective modulation distortion as an effective strength of the optimization signal filtered according to the spectrum emission mask requirements of the radio system.

6. The method of claim 1, the method further comprising forming a term relating to the effective modulation distortion as an effective strength of the optimization signal filtered by root raised cosine filtering.

7. The method of claim 1, the method further comprising forming a term relating to the effective modulation distortion as an effective strength of the optimization signal multiplied by a spreading code and filtered by root raised cosine filtering.

8. The method of claim 1, the method further comprising forming a term relating to the effective overshoot exceeding the predetermined threshold by forming a difference of the transmission signal and the clipping signal by subtracting the clipping signal from the transmission signal, and

forming an effective value of the difference of the transmission signal and the clipping signal, if the difference of the transmission signal and the clipping signal is greater than the predetermined threshold.

9. The method of claim 1, the method further comprising processing the transmission signal in a window of a predetermined sequential length, the processing comprising

dividing the transmission signal in the window into at least two subsignals of predetermined sequential lengths;

performing the minimization of a cost function with respect to an optimization subsignal associated to a subsignal for forming a clipping subsignal of a predetermined sublength; and

subtracting the clipping subsignal from at least the subsignal which the optimization subsignal is associated to.

10. The method of claim 9, the method further comprising removing the subsignal from which the clipping subsignal has been subtracted from the window, adding a new subsignal in the window, and performing a clipping procedure to a next subsignal.

11. The method of claim 9, the method further comprising performing a clipping procedure to subsignals in the window one after another successively starting from a first subsignal.

12. The method of claim 1, the method further comprising subtracting the clipping signal from all subsignals on which the optimization subsignal has a non-zero effect.

13. A transmitter in a radio system, the transmitter configured to clip a transmission signal before transmission in order to reduce a strength of at least one peak of the transmission signal exceeding a predetermined threshold, the transmitter including a clipper, said clipper comprising:

a minimizer for minimizing of a cost function with respect to an optimization signal, the cost function having weighted terms as a function of the optimization signal, the weighted terms relating to an effective modulation distortion and an effective overshoot exceeding the predetermined threshold;

a filter for forming a clipping signal by filtering the optimization signal formed as a result of a minimization according to a spectrum emission mask requirements of a radio system; and

an adder for subtracting the clipping signal from the transmission signal.

14. The transmitter of claim 13, wherein the minimizer is configured to perform an iterative algorithm for minimizing the cost function.

15. The transmitter of claim 13, wherein the minimizer is configured to perform an iterative algorithm using a gradient descent for minimizing the cost function.

16. The transmitter of claim 13, wherein the minimizer is configured to form a term relating to the effective modulation distortion as an effective strength of the optimization signal.

17. The transmitter of claim 13, wherein the minimizer is configured to form a term relating to the effective modulation distortion as an effective strength of the optimization signal filtered according to the spectrum emission mask requirements of the radio system.

18. The transmitter of claim 13, wherein the minimizer is configured to form a term relating to the effective modulation distortion as an effective strength of the optimization signal filtered by root raised cosine filtering.

19. The transmitter of claim 13, wherein the minimizer is configured to form a term relating to the effective modulation distortion as an effective strength of the optimization signal multiplied by a spreading code and filtered by root raised cosine filtering.

20. The transmitter of claim 13, wherein the minimizer is configured to form a term relating to the effective overshoot exceeding the predetermined threshold by forming a difference of the transmission signal and the clipping signal by subtracting the clipping signal from the transmission signal, and

the minimizer is configured to form an effective value of the difference of the transmission signal and the clipping signal, if the difference of the transmission signal and the clipping signal is greater than the predetermined threshold.

21. The transmitter of claim 13, wherein the clipper is configured to process the transmission signal in a window of a predetermined length and to divide the transmission signal in the window into at least two subsignals of predetermined lengths;

the minimizer in the clipper is configured to perform the minimization of a cost function with respect to an optimization subsignal associated to a subsignal for forming a clipping subsignal of a predetermined sublength; and

the adder in the clipper is configured to subtract the clipping signal from at least the subsignal associated with the optimization subsignal.

22. The transmitter of claim 21, wherein the clipper is configured to add a new subsignal in the window after a subsignal has been clipped.

23. The transmitter of claim 21, wherein the clipper is configured to perform a clipping procedure to subsignals in the window one after another successively starting from a first subsignal.

24. The transmitter of claim 13, wherein the adder of the clipper is configured to subtract the clipping signal from all subsignals on which the optimization subsignal has a non-zero effect.

25. A base station in a radio system, the base station configured to clip a transmission signal before transmission in order to reduce a strength of at least one peak of the transmission signal exceeding a predetermined threshold, the base station comprising:

a minimizer for minimizing a cost function with respect to an optimization signal, the cost function having weighted terms as a function of the optimization signal, the weighted terms relating to an effective modulation distortion and an effective overshoot exceeding the predetermined threshold;

a filter for forming a clipping signal by filtering the optimization signal formed as a result of a minimization according to a spectrum emission mask requirements of the radio system; and

an adder for subtracting the clipping signal from the transmission signal.

26. A transmitter in a radio system, the transmitter configured to clip a transmission signal before transmission in order to reduce a strength of at least one peak of the transmission signal exceeding a predetermined threshold, the transmitter comprising:

minimizing means for minimizing of a cost function with respect to an optimization signal, the cost function having weighted terms as a function of the optimization signal, the weighted terms relating to an effective modulation distortion and an effective overshoot exceeding a predetermined threshold;

forming means for forming a clipping signal by filtering the optimization signal formed as a result of a minimization according to spectrum emission mask requirements of the radio system; and

subtracting means for subtracting the clipping signal from the transmission signal.

27. A computer program product storing a computer program of instructions for executing a computer process for clipping a transmission signal in a transmitter of a radio system before transmission in order to reduce a strength of at least one peak of the transmission signal exceeding a predetermined threshold, the process comprising:

performing a minimization of a cost function with respect to an optimization signal, the cost function having weighted terms as a function of the optimization signal, weighted the terms relating to an effective modulation distortion and an effective overshoot exceeding the predetermined threshold;

forming a clipping signal by filtering the optimization signal formed as a result of the minimization according to spectrum emission mask requirements of a radio system; and

subtracting the clipping signal from the transmission signal.

28. A computer program embodied on a distribution medium readable by a computer for executing a computer process for clipping a transmission signal in a transmitter of a radio system before transmission in order to reduce a strength of at least one peak of the transmission signal exceeding a predetermined threshold, the process comprising:

performing a minimization of a cost function with respect to an optimization signal, the cost function having weighted terms as a function of the optimization signal, the weighted terms relating to an effective modulation distortion and an effective overshoot exceeding the predetermined threshold;

forming a clipping signal by filtering the optimization signal formed as a result of the minimization according to spectrum emission mask requirements of a radio system; and

subtracting the clipping signal from the transmission signal.

29. The computer program of claim 28, wherein the distribution medium comprises a computer readable medium, a program storage medium, a record medium, a computer readable memory, a computer readable software distribution package, a computer readable signal, a computer readable telecommunications signal, or a computer readable compressed software package.