CANCELLATION OF PILOT AND TRAFFIC SIGNALS

• US 20100260238A1
• Filed: 06/25/2010
• Published: 10/14/2010
• Est. Priority Date: 10/20/1998
• Status: Active Grant

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Sezgin, Nadir, Ozluturk, Fatih M.
• Granted Patent: US 8,369,385 B2
• Time in Patent Office: Days
• 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 a selected signal from a received signal, the method comprising:

receiving code division multiple access (CDMA) signals including a first signal and a second signal, the first signal being spread with a first spreading code and the second signal being spread with a second spreading code;

despreading the received CDMA signals with a complex conjugate of the first spreading code to generate a first de-spread signal;

despreading the received CDMA signals with a complex conjugate of the second spreading code to generate a second de-spread signal;

generating a symbol value based on the second de-spread signal;

generating a second signal strength based on the second de-spread signal;

calculating a correlation of the second spreading code and a complex conjugate of the first spreading code;

generating a cancellation signal component based on the correlation, the second signal strength, and the symbol value; and

subtracting the cancellation signal component from the first de-spread signal.

2. The method of claim 1 wherein the second signal strength is generated by:

generating a phase error between the symbol value and the second de-spread signal in a constellation;

derotating the second de-spread signal by the phase error;

low-pass-filtering the derotated second de-spread signal; and

dividing a low-pass-filtered value by a product of the second spreading code and the complex conjugate of the second spreading code.

3. The method of claim 1 further comprising:

despreading the received CDMA signals with a complex conjugate of a pilot spreading code to generate a third de-spread signal;

generating a pilot signal strength based on the third de-spread signal;

calculating a second correlation of the pilot spreading code and a complex conjugate of the first spreading code;

generating a second cancellation signal component based on the second correlation and the pilot signal strength; and

subtracting the second cancellation signal component from the first de-spread signal.

4. The method of claim 3 wherein the pilot signal strength is generated by:

low-pass-filtering the third de-spread signal; and

dividing the low-pass-filtered third de-spread signal with a product of the pilot spreading code and a complex conjugate of the first spreading code.

5. A method for removing the pilot signal from a received signal, the method comprising:

receiving code division multiple access (CDMA) signals including a first signal and a pilot signal, the first signal being spread with a first spreading code and the pilot signal being spread with a pilot spreading code;

despreading the received CDMA signals with a complex conjugate of the first spreading code to generate a first de-spread signal;

despreading the received CDMA signals with a complex conjugate of the pilot spreading code to generate a second de-spread signal;

generating a pilot signal strength based on the second de-spread signal;

calculating a correlation of the pilot spreading code and a complex conjugate of the first spreading code;

generating a pilot cancellation signal component based on the correlation and the pilot signal strength; and

subtracting the pilot cancellation signal component from the first de-spread signal.

6. The method of claim 5 wherein the pilot signal strength is generated by:

low-pass-filtering the second de-spread signal; and

dividing the low-pass-filtered second de-spread signal with a product of the pilot spreading code and a complex conjugate of the first spreading code.

7. An apparatus configured to remove a selected signal from a received signal, the apparatus comprising:

a receiver for receiving code division multiple access (CDMA) signals including a first signal and a second signal, the first signal being spread with a first spreading code and the second signal being spread with a second spreading code;

a first despreader for despreading the received CDMA signals with a complex conjugate of the first spreading code to generate a first de-spread signal;

a second despreader for despreading the received CDMA signals with a complex conjugate of the second spreading code to generate a second de-spread signal;

a hard decision processor for generating a symbol value based on the second de-spread signal;

a signal strength generation device for generating a second signal strength based on the second de-spread signal;

a correlator for calculating a correlation of the second spreading code and a complex conjugate of the first spreading code;

a cancellation signal generation device for generating a cancellation signal component based on the correlation, the second signal strength, and the symbol value; and

a subtractor for subtracting the cancellation signal component from the first de-spread signal.

8. The apparatus of claim 7 wherein the signal strength generation device comprises:

a hard decision processor for generating a phase error between the symbol value and the second de-spread signal in a constellation, and derotating the second de-spread signal by the phase error;

a low-pass filter for low-pass-filtering the derotated second de-spread signal; and

a divider for dividing an output from the low-pass-filter by a product of the second spreading code and the complex conjugate of the second spreading code.

9. The apparatus of claim 7 further comprising:

a third despreader for despreading the received CDMA signals with a complex conjugate of a pilot spreading code to generate a third de-spread signal;

a pilot signal strength generator for generating a pilot signal strength based on the third de-spread signal;

a second correlator for calculating a second correlation of the pilot spreading code and a complex conjugate of the first spreading code; and

a second cancellation signal generator for generating a second cancellation signal component based on the second correlation and the pilot signal strength, wherein the subtractor subtracts the second cancellation signal component from the first de-spread signal.

10. The apparatus of claim 9 wherein the pilot signal strength generator comprises:

a low-pass filter for low-pass-filtering the third de-spread signal; and

a divider for dividing an output from the low-pass-filter with a product of the pilot spreading code and a complex conjugate of the first spreading code.

11. An apparatus for removing the pilot signal from a received signal, the method comprising:

a receiver for receiving code division multiple access (CDMA) signals including a first signal and a pilot signal, the first signal being spread with a first spreading code and the pilot signal being spread with a pilot spreading code;

a first despreader for despreading the received CDMA signals with a complex conjugate of the first spreading code to generate a first de-spread signal;

a second despreader for despreading the received CDMA signals with a complex conjugate of the pilot spreading code to generate a second de-spread signal;

a pilot signal strength generator for generating a pilot signal strength based on the second de-spread signal;

a correlator for calculating a correlation of the pilot spreading code and a complex conjugate of the first spreading code;

a cancellation signal generator for generating a pilot cancellation signal component based on the correlation and the pilot signal strength; and

a subtractor for subtracting the pilot cancellation signal component from the first de-spread signal.

12. The apparatus of claim 11 wherein the pilot signal strength generator comprises:

a low-pass filter for low-pass-filtering the second de-spread signal; and

a divider for dividing an output from the low-pass-filter with a product of the pilot spreading code and a complex conjugate of the first spreading code.