Cancellation of pilot and traffic signals

• US 20030035404A1
• Filed: 10/08/2002
• Published: 02/20/2003
• 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 M., Sezgin, Nadir
• Granted Patent: US 6,603,743 B2
• Time in Patent Office: Days
• US Class Current: 370/342
• 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 global pilot and unwanted traffic signal canceler for a spread spectrum communication system receiver that reduces their contributive noise effects. The present invention effectively cancels the global pilot and unwanted, active traffic signals prior to decoding a desired traffic signal at the receiver. The system and method decreases the bit error rate (BER) yielding an increased signal-to-noise ratio.

Claims

1. A cancellation system for removing selected signals from a traffic signal prior to decoding in a receiver that receives communication signals from a transmitter over a CDMA air interface, the system comprising:

a system input for receiving the communication signals;

said system input inputted as input to a traffic signal cancellation system having an output equal to the desired traffic signal minus the unwanted traffic signals;

said signal input also inputted as input to a pilot signal cancellation system, the system processing the input to remove a global pilot signal and having an output equal to the desired traffic signal minus the global pilot signal; and

whereby the output of the pilot signal cancellation system is subtracted from the output of the traffic signal cancellation system to provide the cancellation system output.

2. The cancellation system according to claim 1 wherein the traffic cancellation system comprises a desired traffic signal despreader coupled to a sum and dump processor to produce an output and an unwanted traffic signal canceler, the canceler comprising:

an unwanted traffic signal despreader having a signal input coupled to said system input and a summed output;

the unwanted traffic signal despreader comprising an unwanted traffic signal code generator and a mixer for mixing an output of the generator with the input to produce a unwanted traffic signal canceler output;

said unwanted traffic signal despreader summed output coupled to a hard decision processor having a phase output and a data output;

said hard decision processor phase output coupled to a low pass filter, said low pass filter having an output;

said low pass filter output coupled to an input of a processor that filters the product of the unwanted traffic signal to desired traffic signal cross-correlation outputting the unwanted traffic signal strength;

said processor output multiplied with said hard decision data output with a first multiplier having an output delivered to an adjustable amplifier;

an unwanted traffic code generator output coupled to an input of a complex conjugate processor having an output;

said complex conjugate output mixed with a complex conjugate of the desired traffic signal code by a first mixer having an output;

said first mixer output coupled to an input of a first sum and dump processor having an output;

said first sum and dump processor coupled to an input of an amplifier having an adjustable gain controlled by said multiplier output; and

said output of said amplifier is coupled to an adder which subtracts the output of each variable amplifier from the output of the desired traffic signal despreader to get the output of the traffic signal cancellation system.

3. The cancellation system according to claim 1 wherein the pilot signal cancellation system comprises:

a global pilot despreader coupled to said input having a summed output;

a desired traffic signal and global pilot cross-correlation means having an output;

said global pilot despreader output coupled to a pilot strength determining means, said determining means having an output;

said pilot strength determining means output multiplied with said cross-correlation means output; and

said multiplied product is said output.

4. The cancellation system according to claim 3 wherein said cross-correlation means comprises:

a global pilot spreading code complex conjugate code generator;

a desired traffic signal complex conjugate code generator;

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

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

5. The cancellation system according to claim 4 wherein said means to derive said global pilot signal strength further comprises:

a low-pass filter having an output; and

a processor coupled to said low-pass filter deriving and outputting the global pilot signal strength.

6. A global pilot signal cancellation system for use in a receiver that receives communication signals from a transmitter over a CDMA air interface that removes the global pilot signal from a desired traffic signal prior to decoding, the system comprising:

an input for receiving the communication signals and a system output;

said input coupled to a global pilot despreader and a desired traffic signal despreader each having a summed output;

a desired traffic signal and global pilot cross-correlation means;

said global pilot despreader output coupled to a pilot strength determining means, said determining means having an output;

said pilot strength determining means output multiplied with said cross-correlation means output; and

said multiplied product subtracted from a summed output of said desired traffic signal despreader output outputting the desired traffic signal free from the global pilot signal.

7. The global pilot signal cancellation system according to claim 6 wherein said means to derive said global pilot signal strength further comprises:

a low-pass filter having an output; and

a processor coupled to said low-pass filter deriving and outputting the global pilot signal strength.

8. A traffic signal cancellation system for use in a receiver that receives communication signals from transmitter over a CDMA air interface that removes at least one unwanted traffic signal from a desired traffic signal prior to decoding, the system comprising:

an input for receiving the communication signals and a system output;

said input coupled to a desired traffic signal despreader having a first summed output;

an at least one unwanted traffic signal canceler comprising;

an unwanted traffic signal despreader having an input coupled to said first summed output and a second summed output;

the unwanted traffic signal despreader comprising an unwanted traffic signal code generator and a mixer for mixing an output of the generator with the input to produce a unwanted traffic signal despreader output;

said unwanted traffic signal despreader summed output coupled to a hard decision processor having a phase output and a data output;

said hard decision processor phase output coupled to a low pass filter, said low pass filter having an output;

said low pass filter output coupled to an input of a processor that filters the product of the unwanted traffic signal to desired traffic signal cross-correlation outputting the unwanted traffic signal strength;

said processor output multiplied with said hard decision data output with a multiplier having an output delivered to an adjustable amplifier;

an unwanted traffic code generator output coupled to an input of a complex conjugate processor having an output;

said complex conjugate output mixed with a complex conjugate of the desired traffic signal code by a mixer having an output;

said mixer output coupled to an input of a second sum and dump processor having an output;

said second sum and dump processor coupled to an input of an amplifier having an adjustable gain controlled by said multiplier output; and

said output of said amplifier is coupled to an adder which subtracts the output of each variable amplifier from the output of the desired traffic signal despreader to get the output of the traffic cancellation system.