Cancellation of pilot and traffic signals

• US 20060034218A1
• Filed: 09/23/2005
• Published: 02/16/2006
• Est. Priority Date: 10/20/1998
• Status: Active Grant

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Ozluturk, Fatih, Sezgin, Nadir
• Granted Patent: US 7,751,465 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception

Abstract

A method for removing selected signals from a received signal prior to decoding begins by receiving communication signals from a transmitter over a CDMA air interface. The received communication signals are input to a traffic signal cancellation system for canceling unwanted traffic signals, thereby producing an output (O). The received communication signals are input to a pilot signal cancellation system for removing a global pilot signal, thereby producing an output (O_add). The output (O_add) of the pilot signal cancellation system is subtracted from the output (O) of the traffic signal cancellation system to provide a cancellation system output.

Claims

1. A method for removing selected signals from a received signal prior to decoding, the method comprising the steps of:

(a) receiving communication signals from a transmitter over a CDMA air interface;

(b) inputting said received communication signals to a traffic signal cancellation system for canceling unwanted traffic signals thereby producing an output (O);

(c) inputting said received communication signals to a pilot signal cancellation system for removing a global pilot signal thereby producing an output (O_add); and

(d) subtracting the output (O_add) of the pilot signal cancellation system from the output (O) of the traffic signal cancellation system to provide a cancellation system output.

2. The method of claim 1 wherein step (b) comprises the steps of:

despreading a desired traffic code from the received signal;

despreading at least one unwanted traffic code from the received signal;

determining the strength of the unwanted traffic code;

determining the unwanted traffic data from the despread unwanted traffic code;

multiplying the strength of the unwanted traffic code and the unwanted traffic data;

cross-correlating a conjugate of the desired traffic code and the unwanted traffic code;

amplifying the result of the cross-correlation of a conjugate of the desired traffic code and the unwanted traffic code according to the result of the multiplication of the strength of the unwanted traffic code and the unwanted traffic data; and

subtracting the result of the amplification from the despread desired traffic code.

3. The method of claim 2 wherein the step of determining the strength of the unwanted traffic code comprises the steps of:

summing a despread unwanted traffic code for a predetermined period of time;

generating a phase output of an unwanted traffic code with a hard decision processor;

filtering the phase output; and

calculating the strength of the unwanted traffic code from the filtering result.

4. The method of claim 1 wherein step (c) comprises the steps of:

despreading a global pilot code from the received signal;

determining the strength of the global pilot code;

cross-correlating the global pilot code and conjugate of a desired traffic code; and

mixing the strength of the global pilot code and the cross-correlation result of the global pilot code and conjugate of the desired traffic code.

5. The method of claim 4 wherein the step of determining the strength of the global pilot code comprises the steps of:

summing the despread global pilot code over a certain period of time;

filtering the summing result; and

calculating the strength of the global pilot code from the result of said filtering.

6. A method for removing a global pilot code from a received signal, the method comprising the steps of:

despreading a global pilot code from a received signal;

determining the strength of the global pilot code;

cross-correlating the global pilot code and a conjugate of a desired traffic code;

despreading the desired traffic code from the received signal; and

subtracting the product of the strength of the global pilot code and the cross-correlation result from the despread desired traffic code.

7. The method of claim 6 wherein the step of determining the strength of the global pilot code comprises the steps of:

summing the despread global pilot code over a predetermined period of time;

filtering the summing result; and

calculating the strength of the global pilot code from the result of said filtering.

8. A method for removing an unwanted traffic signal from a received signal, the method comprising the steps of:

despreading a desired traffic code from the received signal;

despreading at least one unwanted traffic code from the received signal;

determining the strength of the unwanted traffic code;

determining unwanted traffic data from the despread unwanted traffic code;

multiplying the strength of the unwanted traffic code and the unwanted traffic data;

cross-correlating a conjugate of the desired traffic code and the unwanted traffic code;

amplifying the result of the cross-correlation of a conjugate of the desired traffic code and the unwanted traffic code according to the result of the multiplication of the strength of the unwanted traffic code and the unwanted traffic data; and

subtracting the result of the amplification from the despread desired traffic code.

9. The method of claim 8 wherein the step of determining the strength of the unwanted traffic code comprises the steps of:

summing a despread unwanted traffic code for a predetermined period of time;

generating a phase output of an unwanted traffic code with a hard decision processor;

filtering the phase output; and

calculating the strength of the unwanted traffic code from the filtering result.

10. A receiver having a system for canceling a pilot code from a received signal, the receiver comprising:

a global pilot code despreader despreading a global pilot code from a received signal;

means for generating a global pilot code strength from the despread global pilot code;

means for generating a cross-correlation of a conjugate of a desired traffic code and the global pilot code;

a mixer for mixing a global pilot code strength and the output of the cross-correlation of the conjugate of the desired traffic code and the global pilot code;

a desired traffic code despreader for despreading a desired traffic code from the received signal; and

a summer for summing the output of the mixer and the output of the desired traffic code despreader.

11. The receiver according to claim 10 wherein the means for generating a cross-correlation comprises:

a complex conjugate generator for generating a conjugate of the global pilot code;

a desired traffic signal complex conjugate generator;

a mixer for cross-correlating said global pilot signal code and said desired traffic signal complex conjugate code; and

a sum and dump processor for summing over time said cross-correlation product.

12. The receiver according to claim 11 wherein the means for generating a global pilot code strength comprises:

a sum and dump processor coupled to the global pilot code despreader;

a low pass filter coupled to the sum and dump processor; and

a processor for calculating a global pilot code strength.

13. A receiver having a system for removing unwanted traffic signals from a received signal prior to decoding, the receiver comprising:

a desired traffic code despreader for despreading a desired traffic code from a received signal;

at least one unwanted traffic code canceller comprising;

an unwanted traffic code despreader for despreading an unwanted traffic code from the received signal;

means for generating an unwanted traffic code strength from the despread unwanted traffic code and for determining unwanted traffic data;

a multiplier for multiplying the unwanted traffic data and the unwanted traffic code strength;

a cross-correlator for cross-correlation of a conjugate of a desired traffic code and the unwanted traffic code; and

a variable amplifier for amplifying the result of cross-correlation of a conjugate of a desired traffic code and the unwanted traffic code according to the result of the multiplication of the unwanted traffic data and the unwanted traffic code strength; and

a summer for summing the despread desired traffic code and the output of unwanted traffic code canceller.

14. The receiver according to claim 13 wherein the means for generating an unwanted traffic code strength comprises:

a sum and dump processor for generating a summed output of the despread unwanted traffic code for a predetermined period of time;

a hard decision processor for generating a phase output of the despread unwanted traffic code and phase corrected unwanted traffic data;

a low pass filter for processing the output of the hard decision processor; and

a processor for generating a strength of the unwanted traffic code from the output of the filter.

15. A receiver having a means for canceling selected signals from a received signal over a CDMA air interface, the receiver comprising:

an unwanted signal canceller for subtracting an unwanted traffic signal from a received signal; and

a pilot signal canceller for subtracting a pilot signal from a received signal.

16. The receiver of claim 15 wherein the unwanted signal canceller comprises:

a desired traffic code despreader for despreading a desired traffic code from the received signal;

at least one unwanted traffic code canceller comprising;

an unwanted traffic code despreader for despreading an unwanted traffic code from the received signal;

means for generating an unwanted traffic code strength from the despread unwanted traffic code and for determining unwanted traffic data;

a multiplier for multiplying the unwanted traffic data and the unwanted traffic code strength;

a cross-correlator for cross-correlation of a conjugate of a desired traffic code and the unwanted traffic code; and

a variable amplifier for amplifying the result of cross-correlation of a conjugate of a desired traffic code and the unwanted traffic code according to the result of the multiplication of the unwanted traffic data and the unwanted traffic code strength; and

a summer for summing the despread desired traffic code and the output of the unwanted traffic code canceller.

17. The receiver of claim 16 wherein the means for generating an unwanted traffic code strength comprises:

a sum and dump processor for generating a summed output of the despread unwanted traffic code for a predetermined period of time;

a hard decision processor for generating a phase output of the despread unwanted traffic code and phase corrected unwanted traffic data;

a low pass filter for processing the output of the hard decision processor; and

a processor for generating a strength of the unwanted traffic code from the output of the filter.

18. The receiver of claim 15 wherein the pilot signal canceller comprises:

a global pilot code despreader for despreading a global pilot code from the received signal;

means for generating a global pilot code strength from the despread global pilot code;

means for generating a cross-correlation of a conjugate of a desired traffic code and the global pilot code; and

a mixer for mixing a global pilot code strength and the output of the cross-correlation of the conjugate of the desired traffic code and the global pilot code.

19. The receiver of claim 18 wherein the means for generating a cross-correlation comprises:

a complex conjugate generator for generating a conjugate of the global pilot code;

a desired traffic signal complex conjugate generator;

a mixer for cross-correlating said global pilot signal code and said desired traffic signal complex conjugate code; and

a sum and dump processor for summing over time said cross-correlation product.

20. The receiver of claim 18 wherein the means for generating a global pilot code strength comprises:

a sum and dump processor coupled to the global pilot code despreader;

a low pass filter coupled to a sum and dump processor; and

a processor for calculating a global pilot code strength.