Adaptive multi-users interference reduction and cancellation in a CDMA network
First Claim
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1. A method for reducing interference adaptively in a CDMA receiver, comprising the steps of:
- demodulating a baseband signal to determine target symbols, wherein the target symbols are transmitted at a relatively low symbol rate and low signal power;
demodulating the baseband signal to determine interfering symbols, wherein the interfering symbols are transmitted at a relatively high symbol rate and a high signal power;
modulating the interfering symbols to generate a cancellation signal; and
subtracting the cancellation signal from the base band signal to reduce interference in the target symbols.
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Abstract
A method reduces interference adaptively in a CDMA receiver. A baseband signal is demodulated to determine target symbols. The baseband signal is also demodulated to estimate interfering symbols. The interfering symbols are modulated to generate a cancellation signal, and the cancellation signal is subtracted from the base band signal to reduce interference in the target symbols.
13 Citations
17 Claims
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1. A method for reducing interference adaptively in a CDMA receiver, comprising the steps of:
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demodulating a baseband signal to determine target symbols, wherein the target symbols are transmitted at a relatively low symbol rate and low signal power;
demodulating the baseband signal to determine interfering symbols, wherein the interfering symbols are transmitted at a relatively high symbol rate and a high signal power;
modulating the interfering symbols to generate a cancellation signal; and
subtracting the cancellation signal from the base band signal to reduce interference in the target symbols. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
measuring a signal-to-noise ratio (SNR) of the target symbols; and
subtracting the cancellation signal when the signal to noise ratio is greater than a predetermined threshold.
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5. The method of claim 1 wherein the target symbols are modulated with a first Walsh code selected from a set of first Walsh codes and the interfering symbols are modulated with a second Walsh code selected from a set of second Walsh codes, and further comprising:
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correlating all members of the second set of Walsh codes; and
selecting a particular second Walsh code with a maximum likelihood correlation to demodulate the baseband signal to estimate the interfering symbols.
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6. The method of claim 5 wherein a length of the first Walsh codes is substantially shorter than a length of the second Walsh codes.
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7. The method of claim 1 further comprising:
matching a power level of the cancellation signal with a power level of the baseband signal.
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8. The method of claim 1 further comprising:
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de-spreading the baseband signal; and
delaying the de-spreaded baseband signal before determining the target symbols.
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9. The method of claim 8 wherein the delay is equal to a length of time required to produce the cancellation signal.
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10. An apparatus for reducing interference adaptively in a CDMA receiver, comprising:
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a first demodulator to determine target symbols from a baseband signal, wherein the target symbols are transmitted at a relatively low symbol rate and low signal power;
a second demodulating to determine interfering symbols from the baseband signal, wherein the interfering symbols are transmitted at a relatively high symbol rate and a high signal power;
a modulator to generate a cancellation signal from the interfering signal; and
an adder to subtract the cancellation signal from the base band signal to reduce interference in the target symbols. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
means for measuring a signal-to-noise ratio (SNR) of the target symbols, and wherein the adder subtracts the cancellation signal when the signal to noise ratio is greater than a predetermined threshold.
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14. The apparatus of claim 10 wherein the target symbols are modulated with a first Walsh code selected from a set of first Walsh codes and the interfering symbols are modulated with a second Walsh code selected from a set of second Walsh codes, and further comprising:
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means for correlating all members of the second set of Walsh codes; and
means for selecting a particular second Walsh code with a maximum likelihood correlation to demodulate the baseband signal to estimate the interfering symbols.
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15. The apparatus of claim 10 further comprising:
a gain controller to match a power level of the cancellation signal with a power level of the baseband signal.
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16. The apparatus of claim 10 further comprising:
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a de-spreader de-spreading the baseband signal;
a delay controller delaying the de-spreaded baseband signal before determining the target symbols.
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17. The method of claim 16 wherein the delay is equal to a length of time required to produce the cancellation signal.
Specification