Method for clipping a wideband radio signal and corresponding transmitter

• US 20020042253A1
• Filed: 10/05/2001
• Published: 04/11/2002
• Est. Priority Date: 10/06/2000
• Status: Active Grant

• Current Assignee: Alcatel SA (Nokia Corporation)
• Original Assignee: Alcatel SA (Nokia Corporation)
• Inventors: Dartois, Luc
• Granted Patent: US 7,466,966 B2
• Time in Patent Office: Days
• US Class Current: 455/127.1
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 2200/102 A non-specified detector of a signal envelope being used in an amplifying circuit
• 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

Abstract

The invention relates notably to a method for clipping a wideband signal in order to eliminate signal overshots having an amplitude above a predefined threshold before submitting the wideband signal to a power amplifier.

According to the invention, the method comprises the steps of:

i. subtracting from the wideband signal filtered pulses in phase the said wideband signal, each filtered pulse corresponding to an overshot, the amplitude of each filtered pulse being dependent on the amplitude of the corresponding overshot and on the predefined threshold.

ii. repeating at least two successive iterations of step i on said wideband signal.

Claims

1. / Method for clipping a wideband signal in order to eliminate signal overshots having an amplitude above a predefined threshold before submitting said wideband signal to a power amplifier, said method comprising the steps of:

i subtracting from said wideband signal filtered pulses in phase with said wideband signal, each of said filtered pulses corresponding to one of said overshots, the amplitude of each of said filtered pulses being dependent on the amplitude of said corresponding overshot and on said predefined threshold;

ii repeating at least two successive iterations of step i on said wideband signal.

2. / Method according to claim 1, further comprising the steps of:

selecting a predefined number of signal overshots in a time window having a predefined duration;

generating a digital pulse train in phase with said signal, the amplitude of each pulse being equal to the difference between said overshot amplitude and said predefined amplitude threshold if said signal amplitude is higher than said predefined threshold;

filtering said pulse train by a low pass filter; and

subtracting said filtered pulse train from said wideband signal.

3. / Method according to claim 2, further comprising a step of oversampling said wideband signal at a predefined oversampling rate, said pulse train being generated at said oversampling rate.

4. / Method according to claim 1, further comprising a step of hard clipping after said iterations of step i.

5. / Method according to claim 1, wherein said wideband signal is a CDMA signal.

6. / Method according to claim 1, wherein said wideband signal is a multi-carrier signal constituted by a superposition of several CDMA signals on adjacent carriers.

7. / Transmitter for transmitting a wideband signal on a radio interface, said transmitter comprising a signal synthesis module, a clipping module to eliminate signal overshots above a predefined threshold, and a power amplifier, said clipping module comprising:

a pulses generator for generating filtered pulses in phase with said wideband signal, each of said filtered pulses corresponding to one of said overshot, the amplitude of each of said filtered pulses being dependent on the amplitude of said corresponding overshot;

a subtractor for subtracting said filtered pulses from said wideband signal; and

a loop for repeating at least twice the processing of said wideband signal by said clipping module.

8. / Transmitter according to claim 7, characterized in that said clipping module is implemented on a DSP or a FPGA.

9. / Transmitter according to claim 7, characterized in that it is used in a base station of a CDMA radio communication network.