METHOD AND APPARATUS FOR COMPLEMENTARY CUMULATIVE DISTRIBUTION DRIVEN LEVEL CONVERGENCE FOR SPECTRUM SENSING

• US 20090135969A1
• Filed: 11/28/2007
• Published: 05/28/2009
• Est. Priority Date: 11/28/2007
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Psysby, Daniel G., Corke, Robert J.
• Granted Patent: US 8,306,162 B2
• Time in Patent Office: Days
• US Class Current: 375/345
• CPC Class Codes: H03M 1/185 the determination of the range being based on more than one digital output value, e.g. on a running average, a power estimation or the rate of change

Abstract

A method for use in a digital communications receiver for controlling an input signal level (200) into an analog-to-digital converter (ADC) initially receives a sample sequence (201) where a threshold crossing rate is measured as a percentage samples of an input signal that exceed the threshold (203). The error between the measured threshold crossing rate and a desired reference threshold crossing rate is calculated (205) and an error signal is then utilized in a feedback loop to control the receiver gain such that the error is reduced (207).

Claims

1. A method for use in a communications receiver for controlling an input signal level into an analog-to-digital converter (ADC) comprising the steps of:

measuring a threshold crossing rate as a percentage samples of an input signal that exceed the threshold;

computing an error between the measured threshold crossing rate and a desired reference threshold crossing rate; and

utilizing an error signal in a feedback loop to control the receiver gain such that the error is reduced.

2. A method for use in a communications receiver as in claim 1, wherein the percentage of samples are a predetermined number of the last samples received.

3. A method for use in a communications receiver as in claim 1, further comprising the step of:

determining the threshold crossing rate based a clipping rate of the input signal.

4. A method for use in a communications receiver as in claim 1, further comprising the step of:

allowing the input signal to operate over an amplitude distribution for achieving a predetermined level of clipping.

5. A digital communications receiver comprising:

at least one controllable amplifier stage; and

at least one analog-to-digital converter (ADC) for receiving a signal from the at least one controllable amplifier stage; and

at least one gain controller and

wherein the at least one gain controller operates using the steps of;

receiving at least one input sample x(n);

calculating a complementary cumulative distribution function (CCDF) for sample x(n) based upon the function

6. A digital communications receiver as in claim 5, wherein the difference is an error value e(n) which equals CCDF(n)−

target CCDF.

7. A digital communications receiver as in claim 5, wherein the at least one controllable amplifier stage further operates using the step of:

8. A digital communications receiver as in claim 5, wherein the control value is represented by the equation:

v(n)=fnc1[e(n), e(n−

1), . . . e(n−

N))] if the error power is greater than an error threshold value and fnc1 is a one from the group of scaling function, a linear combination function;

a non-linear function or combinations thereof.

9. A digital communications receiver as in claim 7, wherein the control value is represented by the equation:

v(n)=fnc2[e(n), e(n−

1), . . . e(n−

N))] if the error power is lesser than an error threshold value and fnc2 is a one from the group of scaling function, a linear combination function, a non-linear function or combinations thereof.

10. A method for use in a digital communications receiver for controlling an input signal level of an amplifier before supplying the signal to an analog-to-digital converter (ADC), the method comprising the steps of:

receiving a radio frequency (RF) input signal;

measuring a threshold crossing rate as a percentage of a predetermined number of signal samples that exceed a predetermined threshold;

computing an error between the measured threshold crossing rate and a desired reference value for providing an error signal; and

using the error signal in a feed back loop to calculate a gain control value for the amplifier to reduce error in the ADC.

11. A method for use in a digital communications receiver for controlling an input signal level as in claim 10, wherein the threshold crossing rate is measured based upon the complementary cumulative distribution function (CCDF) such that CCDF(n)=P[x(n)≧

γ

] where x(n) is sample sequence and γ

is the clipping level of the ADC.

12. A method for use in a digital communications receiver for controlling an input signal level as in claim 10, wherein the error signal e(n)=CCDF(n)−

a target CCDF value.

13. A method for use in a digital communications receiver for controlling an input signal level as in claim 10, wherein the gain control value v(n)=fnc[c(n), e(n−

1) . . . e(n−

N) where fnc is an error multiplier based on error power.