Interference suppression in a CDMA receiver

• US 6,570,909 B1
• Filed: 07/09/1999
• Issued: 05/27/2003
• Est. Priority Date: 07/09/1999
• Status: Expired due to Term

• Current Assignee: HMD Global Oy
• Original Assignee: Nokia Mobile Phones Incorporated (Nokia Corporation)
• Inventors: Tran, Jean-Marie, Kansakoski, Antti
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Kumar, Pankaj
• Application Number:
  US09/350,211
• Time in Patent Office: 1,418 Days
• Field of Search: 375/316, 375/295, 375/224, 375/148, 375/147, 375/144, 375/140, 375/136, 375/130, 375/142, 375/150, 375/143, 375/152, 375/367, 370/335, 370/252, 370/342, 370/441
• US Class Current: 375/148
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception

Abstract

A system and method for canceling interference present in a code-division multiple access (CDMA) channel signal received at a CDMA receiver that is caused by multipath components of a transmitted pilot channel signal or by soft handoff conditions is computationally efficient because it operates at symbol rates. The channel signal from which such multipath interference is canceled can be either a traffic (data) channel or the pilot channel itself. Interference signals are produced in groups corresponding to the fingers of the CDMA rake receiver. The interference signals corresponding to each finger are used to cancel interference in the other fingers.

Claims

1. A method of reducing interference within a received data channel signal in a code-division multiple access (CDMA) receiver including a rake receiver having at least a first finger and a second finger, the method comprising the steps of:

interpolating a value of a pilot channel pseudonoise (pn) sequence between chip period values to produce an interpolated pilot channel on sequence;

producing an interference signal based on a despreading sequence associated with the first finger, and the interpolated pilot channel pn sequence corresponding to the second finger, wherein the step of producing the interference signal comprises the step of correlating the despreading sequence with the interpolated pilot channel pn sequence;

producing a correction signal corresponding to the first finger based on the interference signal and a received pilot signal corresponding to the second finger; and

subtracting the correction signal from the received data channel signal to produce a corrected data channel signal.

2. A method in accordance with claim 1, further comprising the steps of:

producing a second interference signal based on the despreading sequence associated with the first finger of a rake receiver and a second pilot channel pn sequence corresponding to a third finger of the rake receiver; and

producing a second correction signal corresponding to the first finger based on the second interference signal and a received pilot signal corresponding to the third finger,

wherein the step of subtracting comprises the step of subtracting the second correction signal from the received data channel signal to produce the corrected data channel signal.

3. A method in accordance with claim 2 wherein the first finger, the second finger and the third finger are three fingers of n fingers of the rake receiver.

4. A method in accordance with claim 3 further comprising the steps of:

producing n−

1 interference signals corresponding to the first finger, each interference signal of the n−

1 interference signals based on the despreading sequence associated with the first finger, and one of n−

1 pilot channel pn sequences corresponding to the n fingers excluding the first finger; and

producing n−

1 correction signals corresponding to the first finger, each correction signal based on each interference signal of the n−

1 interference signals and a received pilot channel signal corresponding to one of n fingers other than the first finger,

wherein the step of subtracting comprises the step of subtracting the n−

1 correction signals from the received data channel signal to produce the corrected data channel signal.

5. A method in accordance with claim 4 further comprising the steps of:

producing a group of n−

1 interference signals corresponding to each of the n fingers of the rake receiver other than the first finger;

producing a group of n−

1 correction signals corresponding to each of the n fingers of the rake receiver other than the first finger; and

producing a corrected data channel signal for each of the n−

1 fingers other than the first finger by subtracting the group of n−

1 correction signals from a corresponding received data channel signal received by each of the n fingers other than the first finger.

6. A method in accordance with claim 1, further comprising the step of:

digitally filtering the interpolated pilot channel pn sequence, the digital filter having an impulse response in accordance with a function equal to the convolution of an input impulse response of an input filter to the CDMA receiver and an output impulse response of a transmitter filter of a transmitter transmitting the received data channel.

7. A method in accordance with claim 6 wherein the step of producing an interference signal comprises the step of correlating the despreading sequence with the interpolated pilot channel pn sequence after the interpolated pilot channel pn sequence has been filtered in the digital filter.

8. A method in accordance with claim 7 wherein the step of producing the correction signal comprises the step of multiplying the interference signal with the received pilot signal corresponding to the second finger.

9. A method in accordance with claim 1, wherein the stop of producing the correction signal corresponding to the first finger comprises the step of multiplying the interference signal and the received pilot signal.

10. A code-division multiple access (CDMA) receiver having an n-finger rake receiver producing n received traffic channel signals in response to a transmitted traffic channel signal of a CDMA transmitter and a locally generated traffic channel despreading sequence and producing n received pilot channel signals in response to a transmitted pilot channel signal of said transmitter and a locally generated pilot channel pseudonoise (pn) sequence, a method for canceling interference present in a transmitted traffic channel signal at said receiver, the method comprising the steps of:

producing n interpolated pilot channel pn sequences, each interpolated pilot channel pn sequence corresponding to one of said fingers and produced by interpolating values of said locally generated pilot channel pn sequence between chip period values;

producing n groups of n−

1 interference signals, each group of n−

1 interference signals corresponding to one of said fingers, each interference signal of a group corresponding to a finger is produced in response to said locally generated traffic channel despreading sequence corresponding to said finger and one of said n locally generated interpolated pilot channel pn sequences corresponding to another one of said fingers;

producing n groups of n−

1 correction signals, each group of n−

1 correction signals corresponding to one of said fingers, each correction signal of a group corresponding to a finger is produced in response to an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers; and

producing n corrected traffic channel signals, each corrected traffic channel signal corresponding to one of said fingers and produced by subtracting from a received traffic channel signal corresponding to said finger each of said n−

1 correction signals of a group corresponding to said finger.

11. A method in accordance with claim 10 further comprising the step of:

producing n filtered locally generated interpolated pilot channel pn sequences, each filtered locally generated interpolated pilot channel pn sequence corresponding to one of said fingers and produced by providing said locally generated interpolated pilot channel pn sequence to a digital filter having an impulse response approximating a convolution of an output filter of said CDMA transmitter and an input filter of said CDMA receiver;

the step of producing n groups of n−

1 interference signals comprises the step of providing to a cancellation correlator said locally generated traffic channel despreading sequence and one of said n filtered locally generated interpolated pilot channel pn sequences corresponding to another one of said fingers; and

the step of producing n groups of n−

1 correction signals comprises the step of providing to a multiplier an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers.

12. A method in accordance with claim 10, further comprising:

wherein the step of producing n groups of n−

1 interference signals comprises the step of providing to a cancellation correlator said locally generated traffic channel despreading sequence and one of said n interpolated pilot channel pn sequences corresponding to another one of said fingers; and

wherein producing n groups of n−

1 correction signals comprises the step of providing to a multiplier an interference signal corresponding to said another one to said fingers and a received pilot channel signal corresponding to said another one of said fingers.

13. In a code division multiple access (CDMA) receiver having n-finger rake receiver producing n received traffic channel signals in response to a transmitted traffic channel signal of a CDMA transmitter and a locally generated traffic channel despreading sequence and producing n received pilot channel signals in response to a transmitted pilot channel signal of said transmitter and a locally generated pilot channel pseudonoise (pn) sequence, a method for canceling interference present in a transmitted pilot channel signal at said receiver, the method comprising the steps of:

producing n locally generated interpolated pilot channel pn sequences, each locally generated interpolated pilot channel pn sentence corresponding to one of said fingers and produced by interpolating values of said locally generated pilot channel pn sequences between chip period values;

producing n groups of n−

1 interference signals, each group of n−

1 interference signals corresponding to one of said fingers, each interference signal of a group corresponding to a finger is produced in response to said locally generated traffic channel despreading sequence corresponding to said finger and one of said n locally generated interpolated pilot channel pn sequences corresponding to another one of said fingers;

producing n groups of n−

1 correction signals, each group of n−

1 correction signals corresponding to one of said fingers, each correction signal of a group corresponding to a finger is produced in response to an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers; and

producing n corrected pilot channel signals, each corrected pilot channel signal corresponding to a finger and produced by subtracting from a received pilot channel signal corresponding to said finger each of said n−

1 correction signals of a group corresponding to said finger.

14. A method in accordance with claim 13 further comprising the step of:

producing n filtered locally generated interpolated pilot channel pn sequences, each filtered locally generated interpolated pilot channel pn sequence corresponding to one of said fingers and produced by providing said locally generated interpolated pilot channel pn sequence to a digital filter having an impulse response approximating a convolution of an output filter of said CDMA transmitter and an input filter of said CDMA receiver;

wherein the step of producing n groups of n−

1 interference signals comprises the step of providing to a cancellation correlator said locally generated interpolated pilot channel pn sequence and one of said n filtered locally generated interpolated channel pn sequences corresponding to another one of said fingers; and

wherein the step of producing n groups on n−

1 correction signals comprises the step of providing to a multiplier an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers.

15. A method in accordance with claim 13 further comprising the step of:

wherein the step of producing n groups of n−

1 interference signals comprises the step of providing to a cancellation correlator said locally generated pilot channel pn sequence and one of said n filtered interpolated channel pn sequences corresponding to another one of said fingers; and

wherein the step of producing n groups on n−

1 correction signals comprises the step of providing to a multiplier an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers.

16. A noise reduction circuit adapted to be coupled within a code division multiple access (CDMA) receiver including a rake receiver having at least a first finger and a second finger, the CDMA receiver for reducing noise within a received data channel signal transmitted from a transmitter, the noise reduction circuit comprising:

a correlator adapted to correlate an interpolated pilot channel pseudonoise (pn) sequence corresponding to the second finger with despreading sequence corresponding to the second finger with a despreading sequence corresponding to the first finger to produce an interference signal;

a multiplier adapted to multiply the interference signal with a received pilot signal corresponding to the second finger to produce a correction signal; and

a subtractor adapted to subtract the correction signal from the received data channel signal to produce a corrected data channel signal.

17. A noise reduction circuit in accordance with claim 16, wherein the CDMA filter includes an input filter and the transmitter includes an output filter, the noise reduction circuit further comprising:

a digital filter coupled to the correlator, the digital filter having an impulse response in accordance with a function equal to the convolution of an impulse response of the input filter and an impulse response of the output filter.

18. A noise reduction circuit in accordance with claim 17, wherein the digital filter is a digital interpolation filter adapted to interpolate a value or a pilot channel pn sequence between chip period values to produce the interpolated pilot channel pn sequence, the correlator adapted to produce the interference signal by correlating the interpolated pilot channel pn sequence with the despreading sequence.

19. A code division multiple access (CDMA) receiver for reducing interference in a received data channel signal transmitted from a transmitter, the receiver comprising:

a rake receiver comprising a first finger and a second finger, wherein the first finger is adapted to receive the data channel signal;

a noise reduction circuit coupled to the first finger and adapted to produce a correction signal based on a received pilot signal corresponding to the second finger, a pilot channel pseudonoise sequence corresponding to the second finger, and a despreading sequence associated with the first finger;

a subtractor coupled to the first finger and the noise reduction circuit, the subtractor adapted to produce a corrected data channel signal based on the received data signal and the correction signal;

a correlator adapted to correlate the pilot channel pseudonoise (pn) sequence corresponding to the second finger with a despreading sequence corresponding to the first finger to produce an interference signal;

a multiplier adapted to multiply the interference signal with a received pilot signal corresponding to the second finger to produce a correction signal; and

a digital interpolation filter coupled to the correlator, the digital interpolation filter having an impulse response in accordance with a function equal to the convolution of an impulse response of the input filter and an impulse response of an output filter of the transmitter, the digital interpolation filter adapted to interpolate a value of the pilot channel pn sequence between chip period values to produce an interpolated pilot channel pn sequence, the correlator adapted to produce the interference signal by correlating the interpolated pilot channel pn sequence with the despreading sequence.

20. In a code division multiple access (CDMA) receiver having an n-finger rake receiver producing n received traffic channel signals in response to a transmitted traffic channel signal of a CDMA transmitter and a locally generated traffic channel despreading sequence and producing n received pilot channel signals in response to a transmitted pilot channel signal of said transmitter and a locally generated pilot channel pseudonoise (pn) sequence, a system for canceling interference present in a transmitted traffic channel signal at said receiver, the system comprising:

n cancellation circuits, each corresponding to one of said fingers and producing n−

1 interference signals, each interference signal of a group corresponding to a finger produced in response to said locally generated traffic channel despreading sequence corresponding to said finger and one of said n locally generated pilot channel pn sequences corresponding to another one of said fingers;

each cancellation circuit includes an interpolator, said interpolator producing an interpolated pilot channel pn sequence corresponding to one of said fingers and representing interpolated values of said pilot channel pn sequence between chip period values;

each cancellation circuit producing n−

1 correction signals, each correction signal of a group corresponding to a finger produced in response to an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers; and

n correction circuits, each corresponding to a finger and subtracting from a received traffic channel signal corresponding to said finger each of said n−

1 correction signals of a group corresponding to said finger.

21. A system in accordance with claim 20, wherein:

each cancellation circuit includes a digital filter having an impulse response approximating a convolution of an output filter of said CDMA transmitter and an input filter of said CDMA receiver and producing n filtered locally generated pilot channel pn sequences, each filtered locally generated pilot channel pn sequence corresponding to one of said fingers and produced in response to said locally generated pilot channel pn sequence;

each cancellation circuit includes n−

1 cancellation correlators, each producing one of said n−

1 interference signals in response to said locally generated pilot channel pn sequence and one of said n filtered locally generated pilot channel pn sequences corresponding to another one of said fingers; and

each cancellation circuit includes n−

1 multipliers, each producing one of said n−

1 correction signals in response to an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers.

22. A system in accordance with claim 20, wherein:

Each cancellation circuit includes n−

1 cancellation correlators, each producing one of said n−

1 interference signals in response to said locally generated traffic channel despreading sequence arid one of said n filtered locally generated pilot channel pn sequences corresponding to another one of said fingers; and

each cancellation circuit includes n−

1 multipliers, each producing one of said n−

1 correction signals in response to an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers.

23. In a code division multiple access (CDMA) receiver having an n-finger rake receiver producing n received traffic channel signals in response to a transmitted traffic channel signal of a CDMA transmitter and a locally generated traffic channel despreading sequence and producing n received pilot channel signals in response to a transmitted pilot channel signal of said transmitter and a locally generated pilot channel pseudonoise (pn) sequence, a system for canceling interference present in a transmitted pilot channel signal at said receiver, the system comprising:

n cancellation circuits, each corresponding to one of said fingers and producing n−

1 interference signals, each interference signal of a group corresponding to a finger produced in response to said locally generated pilot channel pn sequence corresponding to said finger and one of said n locally generated pilot channel pn sequences corresponding to another one of said fingers;

each cancellation circuit includes an interpolator, said interpolator producing an interpolated pilot channel pn sequence corresponding to one of said fingers and representing interpolated values of said pilot channel pn sequence between chip period values;

each cancellation circuit producing n−

1 correction signals, each correction signal of said grouped corresponding to a finger produced in response to an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers; and

n correction circuits, each corresponding to a finger and subtracting from a received pilot channel signal corresponding to said finger each of said n−

1 correction signals of a group corresponding to said finger.

24. A system in accordance with claim 23, wherein:

each cancellation circuit includes a digital filter having an impulse response approximating a convolution of an output filter of said CDMA transmitter and an input filter of said CDMA receiver and producing n filtered locally generated pilot channel pn sequences, each filtered locally generated pilot channel pn sequence corresponding to one of said fingers and produced in response to said locally generated pilot channel pn sequence;

each cancellation circuit includes n−

1 cancellation correlators, each producing one of said n−

1 interference signals in response to said locally generated traffic channel despreading sequence and one of said n filtered locally generated pilot channel pn sequences corresponding to another one of said fingers; and

each cancellation circuit includes n−

1 multipliers, each producing one of said n−

1 correction signals in response to an interference signal corresponding to said another one of said fingers and a received pilot channel signal corresponding to said another one of said fingers.

25. A system in accordance with claim 23, wherein:

each cancellation circuit includes n−

1 cancellation correlators, each producing one of said n−

1 interference signals in response to said locally generated pilot channel pn sequences and one of said n filtered locally generated pilot channel pn sequences corresponding to another one of said fingers; and

each cancellation circuit includes n−

1 multipliers, each producing one of said n−

1 correction signals in response to an interference signal corresponding to said sootier one of said fingers and a received pilot channel signal corresponding to said another one of said fingers.