Interference cancellation system and method and CDMA receiver including an interference cancellation circuit

• US 6,333,947 B1
• Filed: 11/25/1998
• Issued: 12/25/2001
• Est. Priority Date: 11/25/1998
• Status: Expired due to Term

• Current Assignee: Blackberry Limited
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Newson, Paul, van Heeswyk, Frank Martin
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): PHU, PHUONG M
• Application Number:
  US09/199,301
• Time in Patent Office: 1,126 Days
• Field of Search: 375/346, 375/148, 375/347, 375/144, 375/284, 375/285, 375/278, 455/501, 455/570, 455/295, 455/296
• US Class Current: 375/148
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/711 the interference being multi-path interference
• CPC Class Codes: H04L 25/0224 using sounding signals

Abstract

Systems and methods for cancelling interference in received CDMA signals due to known components in the received signals which have been digitized to form a composite digitized baseband signal, for example due to pilot channel components in received CDMA IS-95 3G compliant signals which would otherwise interfere with the detection of unknown data streams. The pilot channel signals are detected, and an estimate of the air interface for each pilot channel signal is made. The pilot channel signals are then passed through a respective model of the air interface, and the resulting output is subtracted from the composite digitized baseband signal, thereby removing interference due to the pilot channel signals.

Claims

1. An interference cancellation circuit for cancelling interference due to known information contained in a component of a digitized baseband composite signal, the circuit comprising:

known information detection and air interface characterization circuitry for detecting said known information stream, demodulating said component and making an air interface characterization which is an estimate of an air interface channel over which the component was transmitted;

digitized baseband component regeneration circuitry for generating an estimated component which is an estimate of said component of the digitized baseband composite signal by modulating said known information stream taking into account said air interface channel characterization;

delay circuitry for delaying the digitized baseband composite signal an amount substantially equal to the time it takes the known information detection and air interface characterization circuitry and component regeneration circuitry to create the estimated component; and

subtraction circuitry for subtracting the estimated component from the delayed digitized baseband composite signal to create a corrected digitized baseband composite signal.

2. A circuit according to claim 1 wherein said air interface characterization comprises an estimated phase shift, an estimated attenuation and an estimated timing for each of several multipaths of said component.

3. The circuit of claim 1 wherein:

said digitized baseband composite signal contains a plurality of mobile station components; and

each said mobile station component includes a respective first component carrying known information and one or more second components carrying unknown information.

4. The circuit of claim 3 wherein for each mobile station component, the respective first component is a pilot channel component.

5. The circuit of claim 1 wherein said known information detection and air interface characterization circuitry comprises:

a searcher for identifying multipaths forming said component containing known information; and

a plurality of tracker fingers each for tracking a respective multipath identified by the searcher and producing a respective multipath estimate consisting of an amplitude, phase and timing of the multipath.

6. The circuit of claim 5 wherein said component regeneration circuitry comprises for each multipath:

a modulator including code spreading and FIR filtering for multiplying the known data by I and Q spreading signals in accordance with said timing estimate;

a phase rotation function for applying a phase shift equal to said estimated phase;

an attenuation function for applying an attenuation equal to said amplitude;

summing circuitry for adding together the output of each multipath reconstructor.

7. An interference cancellation circuit for cancelling interference due to particular components of a composite baseband digitized signal which contains both known and unknown information, the circuit comprising:

known information detection and air interface characterization circuitry for detecting said known information, demodulating each said particular component and making an air interface characterization which is an estimate of an air interface channel over which the particular component was transmitted;

estimation circuitry for making an estimate of the unknown information in each said particular component containing known information;

combining circuitry for combining for each said particular component the known information with the estimated unknown information to make a respective combined information;

digitized baseband component regeneration circuitry for generating an estimated component for each said combined information which is an estimate of the respective particular component of the digitized baseband composite signal by modulating said combined information taking into account said air interface characterization;

delay circuitry for delaying the digitized baseband composite signal an amount substantially equal to the time it takes the known information detection and air interface characterization circuitry and component regeneration circuitry to create the estimated components; and

subtraction circuitry for subtracting the estimated components from the delayed digitized baseband composite signal to create a corrected digitized baseband composite signal.

8. The circuit of claim 7 wherein the composite digitized baseband signal contains signals which are in accordance with the CDMA IS-95 3G standard, and the particular components comprise the pilot channel components of a plurality of users, each pilot channel component carrying known pilot bits and unknown power control bits.

9. The circuit of claim 7 wherein each particular component is a CDMA IS-95 3G pilot channel component, and the remaining components comprise fundamental, supplementary and control components.

10. The circuit of claim 8 wherein said estimation circuitry comprises power control bit detection circuitry for producing an estimate of the received power control bits.

11. The circuit of claim 10 wherein said air interface characterization comprises an estimated phase shift, an estimated attenuation and an estimated timing and wherein said component regeneration circuitry comprises for each multipath:

a multiplexer for combining the estimate of the power control bits with the known pilot channel bits to create the respective combined information;

a modulator including code spreading and FIR filtering for multiplying the combined information by I and Q spreading signals in accordance with said timing estimate;

a phase rotation function for applying a phase shift equal to said estimated phase;

an attenuation function for applying an attenuation equal to said amplitude;

summing circuitry for adding together the output of each multipath reconstructor.

12. A CDMA receiver comprising:

an antenna for receiving an RF composite spread spectrum signal over an air interface;

RF down conversion and A/D conversion circuitry for converting the composite spread spectrum signal into a digitized composite baseband signal;

an interference cancellation circuit for cancelling interference due to pilot channel components of the baseband digitized composite signal which contain both known pilot bits and unknown power control bits, the interference cancellation circuit comprising;

a) pilot channel detection and air interface and characterization circuitry for detecting the pilot channel components present in the composite baseband digitized signal and making a respective channel estimate of an air interface over which each said pilot channel component was received;

b) power control bit detection circuitry for estimating the power control bits in said pilot channel components;

c) combining circuitry for combining for each pilot channel component in a respective combined information the pilot bits with the associated estimated power control bits;

d) pilot channel reconstruction circuitry for creating a regenerated baseband digitized pilot channel component for each said combined information which is an estimate of the pilot channel component as it would have been received taking into account the respective channel estimate;

e) delay circuitry for delaying the digitized baseband composite signal an amount substantially equal to the time it takes to make the estimates of the pilot channel components; and

f) subtraction circuitry for subtracting the estimates of the pilot channel components from the delayed digitized baseband composite signal to produce a corrected composite digitized baseband signal;

a baseband detection unit for each user connected to receive the corrected composite digitized baseband signal and the channel characterization information for that user, for producing one or more received data streams for that user.

13. A receiver according to claim 12 wherein the baseband detection units are also connected to receive the known pilot channel bits, and these are also output as a received data stream for that user.

14. A method of reducing interference due to components carrying known information in a composite digitized baseband signal comprising:

detecting the known information for each said component and producing a respective estimate of an air interface over which each said component was received;

passing the known information for each component through a model of the respective air interface which is based upon the respective estimate of the air interface to produce a respective estimated component;

delaying the composite digitized baseband signal to produce a delayed composite digitized baseband signal an amount of time equal to how long it takes for the steps of detecting and passing;

subtracting the estimated components from the delayed composite digitized baseband signal to produce a corrected composite digitized baseband signal.

15. A method of reducing interference due to particular components of a composite digitized baseband signal, each particular containing a respective known information and a respective unknown information, the method comprising the steps of:

detecting the known information for each particular component and producing a respective estimate of an air interface over which each particular component was received;

making an estimate of each unknown information;

combining the estimate of the unknown information with the respective known information to create a combined information for each said particular component;

passing each combined information through a model of the respective air interface which is based upon the respective estimate of the air interface to produce a respective estimated component;

delaying the composite digitized baseband signal to produce a delayed composite digitized baseband signal an amount of time equal to how long it takes for the steps of detecting, making an estimate, combining and passing; and

subtracting the estimated components from the delayed composite digitized baseband signal to produce a corrected composite digitized baseband signal.