Cancellation of pilot and traffic signals

• US 7,751,465 B2
• Filed: 09/23/2005
• Issued: 07/06/2010
• Est. Priority Date: 10/20/1998
• Status: Expired due to Fees

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Ozluturk, Fatih, Sezgin, Nadir
• Primary Examiner(s): Bates; Kevin
• Assistant Examiner(s): Nguyen; Van Kim T
• Application Number:
  US11/234,768
• Publication Number:
  US 20060034218A1
• Time in Patent Office: 1,747 Days
• Field of Search: 370/286, 370/320, 370/342, 375/144, 375/147, 375/148, 375/346, 375/348
• US Class Current: 375/148
• 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 an unwanted traffic signal and a global pilot signal from a received signal prior to decoding, the method comprising:

receiving code division multiple access (CDMA) communication signals from a transmitter over an air interface, the communication signals including a desired traffic signal, an unwanted traffic signal, and a global pilot signal, the unwanted traffic signal being spread with an unwanted traffic code and the global pilot signal being spread with a pilot signal code;

inputting the received communication signals to a traffic signal canceller configured to cancel a cross-correlation of an unwanted traffic signal and the desired traffic signal, thereby producing a traffic signal canceller output (O);

inputting the received communication signals to a pilot signal canceller configured to produce a pilot signal canceller output for removing a cross-correlation of the global pilot signal and the desired traffic signal; and

subtracting the pilot signal canceller output from the traffic signal canceller output.

2. The method of claim 1 wherein inputting the received communication signals to a traffic signal canceller comprises:

despreading a desired traffic code from the received communication signals;

despreading at least one unwanted traffic code from the received communication signals;

determining a 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.

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

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 inputting the received communication signals to a pilot signal canceller comprises:

despreading a global pilot code from the received communication signals;

determining a 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 the conjugate of the desired traffic code to generate the pilot signal canceller output.

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

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 the filtering.

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

despreading a global pilot code from a received signal;

determining a 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 determining the strength of the global pilot code comprises:

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 the filtering.

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

despreading a desired traffic code from the received signal;

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

determining a 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 determining the strength of the unwanted traffic code comprises:

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 configured to cancel a pilot code from a received signal, the receiver comprising:

a global pilot code despreader configured to despread a global pilot code from a received signal;

a first generator configured to generate a global pilot code strength from the despread global pilot code;

a second generator configured to generate a cross-correlation of a conjugate of a desired traffic code and the global pilot code;

a mixer configured to mix the 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 configured to despread the desired traffic code from the received signal; and

a subtractor configured to subtract the output of the mixer from the output of the desired traffic code despreader.

11. The receiver according to claim 10 wherein the second generator comprises:

a complex conjugate generator configured to generate a conjugate of the global pilot code;

a desired traffic signal complex conjugate generator;

a mixer configured to cross-correlate the global pilot signal code and the desired traffic signal complex conjugate code; and

a sum and dump processor configured to sum the cross-correlation product over time.

12. The receiver according to claim 11 wherein the first generator 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 configured to calculate the global pilot code strength.

13. A receiver configured to remove an unwanted traffic signal from a received signal prior to decoding, the receiver comprising:

a desired traffic code despreader configured to despread a desired traffic code from a received signal;

at least one unwanted traffic code canceller comprising;

an unwanted traffic code despreader configured to despread an unwanted traffic code from the received signal;

a generator configured to generate an unwanted traffic code strength from the despread unwanted traffic code and to determine unwanted traffic data;

a multiplier configured to multiply unwanted traffic data and the unwanted traffic code strength;

a cross-correlator configured to cross-correlate a conjugate of a desired traffic code and the unwanted traffic code; and

a variable amplifier configured to amplify the result of a 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 subtractor configured to subtract an output of the unwanted traffic code canceller from the despread desired traffic code.

14. The receiver according to claim 13 wherein the generator comprises:

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

a hard decision processor configured to generate a phase output of the despread unwanted traffic code and phase corrected unwanted traffic data;

a low pass filter configured to process the output of the hard decision processor; and

a processor configured to generate the strength of the unwanted traffic code from the output of the filter.

15. A receiver configured to remove an unwanted traffic signal and a global pilot signal from a received code division multiple access (CDMA) signal, the receiver comprising:

a receiving unit configured to receive a CDMA signal from a transmitter over an air interface, the received signal including a desired traffic signal, an unwanted traffic signal, and a global pilot signal, the unwanted traffic signal being spread with an unwanted traffic code and the global pilot signal being spread with a pilot signal code;

an unwanted signal canceller configured to remove a cross-correlation of the unwanted traffic signal and the desired traffic signal and to produce an unwanted signal canceller output;

a pilot signal canceller configured to produce a pilot signal canceller output for removing a cross-correlation of the global pilot signal and the desired traffic signal; and

an adder configured to subtract the pilot signal canceller output from the unwanted traffic canceller output.

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

a desired traffic code despreader configured to despread a desired traffic code from the received signal;

at least one unwanted traffic code canceller comprising;

an unwanted traffic code despreader configured to despread an unwanted traffic code from the received signal;

a generator configured to generate an unwanted traffic code strength from the despread unwanted traffic code and to determine unwanted traffic data;

a multiplier configured to multiply unwanted traffic data and the unwanted traffic code strength;

a cross-correlator configured to cross-correlate a conjugate of a desired traffic code and the unwanted traffic code; and

a variable amplifier configured to amplify the result of a 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 subtractor configured to subtract an output of the unwanted traffic code canceller from the despread desired traffic code.

17. The receiver according to claim 16 wherein the generator comprises:

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

a hard decision processor configured to generate a phase output of the despread unwanted traffic code and phase corrected unwanted traffic data;

a low pass filter configured to process the output of the hard decision processor; and

a processor configured to generate the strength of the unwanted traffic code from the output of the filter.

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

a global pilot code despreader configured to despread a global pilot code from the received signal;

a first generator configured to generate a global pilot code strength from the despread global pilot code;

a second generator configured to generate a cross-correlation of a conjugate of a desired traffic code and the global pilot code; and

a mixer configured to mix the 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 according to claim 18 wherein the second generator comprises:

a complex conjugate generator configured to generate a conjugate of the global pilot code;

a desired traffic signal complex conjugate generator;

a mixer configured to cross-correlate the global pilot signal code and the desired traffic signal complex conjugate code; and

a sum and dump processor configured to sum the cross-correlation product over time.

20. The receiver according to claim 18 wherein the first generator 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 configured to calculate the global pilot code strength.