System and method for providing an accurate estimation of received signal interference for use in wireless communications systems

• US 6,661,832 B1
• Filed: 05/11/1999
• Issued: 12/09/2003
• Est. Priority Date: 05/11/1999
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sindhushayana, Nagabhushana T., Esteves, Eduardo A. S.
• Primary Examiner(s): Deppe, Betsy Lee
• Application Number:
  US09/310,053
• Time in Patent Office: 1,673 Days
• Field of Search: 375/144, 375/147, 375/148, 375/224, 375/227, 375/346, 375/347, 370/320, 370/335, 370/342, 370/441, 455/63, 455/65, 455/67.1, 455/67.3, 455/135, 455/226.1, 455/226.2, 455/226.3, 455/296
• US Class Current: 375/144
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 17/336 Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178
• CPC Class Codes: H04L 27/34 Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits

Abstract

A system for providing an accurate interference value signal received over a channel and transmitted by an external transceiver. The system includes a first receiver section for receiving the signal, which has a desired signal component and an interference component. A signal extracting circuit extracts an estimate of the desired signal component from the received signal. A noise estimation circuit provides the accurate interference value based on the estimate of the desired signal component and the received signal. A look-up table transforms the accurate noise and/or interference value to a normalization factor. A carrier signal-to interference ratio circuit employs the normalization factor and the received signal to compute an accurate carrier signal-to-interference ratio estimate. Path-combining circuitry generates optimal path-combining weights based on the received signal and the normalization factor. In the illustrative embodiment, the system further includes a circuit for employing the accurate interference value to compute a carrier signal-to-interference ratio. An optimal path-combining circuit computes optimal path-combining weights for multiple signal paths comprising the signal using the accurate interference value and provides optimally combined signal paths in response thereto. A log-likelihood ratio circuit computes a log-likelihood value based on the carrier signal-to-interference ratio and the optimally combined signal paths. A decoder decodes the received signal using the log-likelihood value. An additional circuit generates a rate and/or power control message and transmits the rate and/or power control message to the external transceiver.

Claims

1. A system for providing an accurate interference energy value for a wireless signal received over a channel, the system comprising:

means for receiving said wireless signal and providing in-phase and quadrature signal samples from said wireless signal in response thereto;

means for extracting a pilot signal from said in-phase and quadrature signal samples and providing an estimate of energy of said wireless signal in response thereto, said estimate lacking an interference component; and

means for calculating said interference energy value based on a measurement of total energy of said wireless signal and said estimate of energy of said wireless signal lacking said interference component.

2. A system for providing an accurate carrier signal-to-interference ratio for facilitating the decoding of a signal received over a channel, the system comprising:

means for receiving a signal over a channel, said received signal comprising one or more chips;

means for providing an estimate of total received energy of each of said one or more chips, said estimate of total received energy having an interference component and a desired signal energy component;

means for extracting from said received signal an estimate of said desired signal energy component;

means for employing said estimate of said desired signal energy component and said estimate of total received energy to provide an estimate of said interference component; and

means for using said estimate of said desired signal energy component and said estimate of said interference component to provide said accurate carrier signal-to-interference ratio.

3. A system for providing optimal inputs to a log-likelihood ratio computer, the system comprising:

a first receiver for receiving a signal over a channel;

an interference calculator for providing a signal representative of interference or noise contained in said received signal and providing a signal-to-interference ratio in response thereto;

an optimal path combiner for employing said signal representative of interference or noise and said received signal to produce an optimal path-combining signal as a first optimal input to said log-likelihood ratio computer; and

an accumulator for accumulating said signal-to-interference ratio to provide an optimal carrier signal-to-interference value as a second optimal input to said log-likelihood ratio computer.

4. A communications system comprising:

a transceiver for transmitting a first signal over a channel at a predetermined rate and power level, said channel introducing noise or interference to said first signal;

means for receiving said first signal and providing in-phase and quadrature samples of said first signal in response thereto, said first signal having a pilot signal component and one or more multipath components;

means for extracting said pilot signal and providing an estimate of total interference energy received via said first signal on a predetermined multipath component based on said pilot signal component and said in-phase and said quadrature samples;

means for generating a power or rate control signal based on said estimate of total interference energy and an estimate of energy associated with said one or more multipath components;

means for transmitting said power or rate control signal to said transceiver;

means for computing optimal path-combining weights for said one or more multipath components based on said estimate of total interference energy and providing optimally combined signal paths in response thereto; and

means for computing a log-likelihood value based on said optimally combined signal paths, said total interference energy, and said estimate of energy associated with said one or more multipath components; and

means for decoding said first signal in response to said log-likelihood value.

5. A path weighting and combining circuit for determining maximal ratio path-combining weights for multiple paths of a received signal that has an interference component, a data component, and a pilot signal component comprising:

a separating circuit for separating said pilot signal component and said data component from said received signal;

a pilot filter for filtering said pilot signal to yield a filtered pilot signal;

an interference estimation circuit for estimating said interference component and providing an interference value in response thereto;

a first multiplier for multiplying said filtered pilot signal by a predetermined constant scaling factor and providing a scaled value in response thereto;

a second multiplier for multiplying said scaled value by a reciprocal of said interference value to yield a weighted signal; and

a conjugation circuit for computing a conjugate of said weighted signal to yield maximal ratio weights in response thereto.

6. A method for providing an accurate noise or interference value for a signal received over a channel and transmitted by an external receiver comprising the steps for:

receiving said signal, said received signal having a desired signal component and an interference or noise component;

extracting an estimate of said desired signal component from said received signal; and

providing said accurate noise or interference value based on said estimate of said desired signal component and said received signal.

7. A system comprising:

a code division multiple access (CDMA) receiver capable of receiving a signal over a wireless channel, the received signal comprising a desired signal component and an interference component;

a carrier signal-to-interference and interference energy estimator connected to the CDMA receiver to generate an interference energy value and a signal-to-interference ratio of the received signal, the carrier signal-to-interference and interference energy estimator comprising a signal extractor to extract an estimate of the desired signal component from the received signal; and

a path combiner connected to the signal extractor to generate summed weighted-path signals in response to the interference energy value and the estimate of the-desired signal component.

8. The system of claim 7, further comprising a log-likelihood ratio generator connected to the path combiner to generate soft decision values based on the summed weighted-path signals.

9. The system of claim 8, wherein the log-likelihood ratio generator is connected to the carrier signal-to-interference and interference energy estimator to generate the soft decision values based on the summed weighted-path signals and the signal-to-interference ratio.

10. The system of claim 8, further comprising a decoder connected to the log-likelihood ratio generator to generate decoded signals based on the soft decision values.

11. The system of claim 10, further comprising a rate and power request generator connected to the carrier signal-to-interference and interference energy estimator to generate a rate control or power fraction request message in response to the signal-to-interference ratio.

12. The system of claim 11, further comprising:

a controller connected to the rate and power request generator; and

an encoder connected to the controller to generate an encoded rate control or power fraction request message.

13. The system of claim 7, wherein the CDMA receiver comprises an intermediate-frequency (IF)-to-baseband converter to generate spread-spectrum in-phase and quadrature signals based on the received signal.

14. The system of claim 13, wherein the signal extractor comprises a pseudo-noise despreader to generate despread in-phase and quadrature signals based on the spread-spectrum in-phase and quadrature signals.

15. The system of claim 14, wherein the signal extractor further comprises a decoverer connected to the pseudo-noise despreader to separate data, signals along a data channel and a pilot signal along a pilot channel from the despread in-phase and quadrature signals.

16. The system of claim 15, wherein the data channel is described by the following equation:

17. The system of claim 15, wherein the carrier signal-to-interference and interference energy estimator further comprises a pilot filter connected to the decoverer to generate a filtered pilot signal.

18. The system of claim 17, wherein the filtered pilot signal is described by the following equation:

19. The system of claim 18, wherein the carrier signal-to-interference and interference estimator further comprises a forward link constant generator capable of generating a forward link constant.

20. The system of claim 19, wherein the forward link constant is described by the following equation:

$c=\frac{1}{M^2}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{I_{\mathrm{or}}}{E_p}$

where c represents the forward link constant, I_or is received energy of desired signal component; and

E_p is pilot chip energy.

21. The system of claim 20, wherein the carrier signal-to-interference and interference energy estimator further comprises a look-up table capable of generating a reciprocal of an interference energy value based on the despread in-phase and quadrature signals, the filtered pilot signal and the forward link constant.

22. The system of claim 21, wherein the path combiner comprises:

a constant generator capable of generating a constant $k=\frac{1}{M}<br><br>\text{\hspace{1em}<br><br>}<br><br>\sqrt{\frac{E_s}{E_p}},$

 

where E_s is modulation symbol energy; and

a multiplier connected to the constant generator and the pilot filter to generate an estimate of a channel coefficient

23. The system of claim 22, wherein the summed path-weighted signals are generated based on the estimate of the channel coefficient, the reciprocal of the interference energy value, and the number of chips per Walsh symbol.

24. A system comprising:

a code division multiple access (CDMA) receiver capable of receiving signals over a wireless channel, the received signals comprising a pilot signal and data signals;

a carrier signal-to-interference and interference energy estimator connected to the CDMA receiver to generate an interference energy value and a signal-to-interference ratio of the received signals, the carrier signal-to-interference and interference energy estimator comprising;

a pilot fingers filter capable of receiving a despread and decovered pilot signal and in response generating a filtered pilot signal;

a pilot energy computer connected to the pilot fingers filter to generate a pilot energy value p²;

a look-up table connected to the pilot energy computer to generate a result equal to 1/(1−

p²); and

a carrier signal-to-interference path accumulator connected to the look-up table to generate an estimate of a total multi-path carrier signal-to-interference ratio; and

a path combiner connected to the carrier signal-to-interference and interference energy estimator to generate summed weighted-path signals comprising in-phase summed weighted-path components and quadrature summed weighted-path;

components.

25. The system of claim 24, further comprising a log-likelihood ratio generator connected to the path combiner to generate soft decision values based on the summed weighted-path signals.

26. The system of claim 25, further comprising a decoder connected to the log-likelihood ratio generator to generate decoded signals based on the soft decision values.

27. The system of claim 25, further comprising a rate and power request generator connected to the carrier signal-to-interference and interference energy estimator to generate a rate control or power fraction request message in response to the signal-to-interference ratio.

28. The system of claim 27, further comprising:

a controller connected to the rate and power request generator; and

an encoder connected to the controller to generate an encoded rate control or power fraction request message.

29. The system of claim 28, wherein the CDMA receiver comprises an intermediate-frequency (IF)-to-baseband converter to generate spread-spectrum in-phase and quadrature signals based on the received signals.

30. The system of claim 24, wherein the path combiner comprises:

a data signal input capable of receiving despread and decovered data signals;

a multiplier connected to the pilot fingers filter and the look-up table to generate a product of the filtered pilot signal and the result of the look-up table;

a demultiplexer coupled to the multiplier and the data signal input to generate in-phase and quadrature components of the data signals over multiple paths; and

a dual maxima generator connected to the demultiplexer to generate the in-phase summed weighted-path components and the quadrature summed weighted-path components.

31. A system comprising:

a code division multiple access (CDMA) receiver capable of receiving signals over a wireless channel and in response generating spread-spectrum in-phase and quadrature signals, the received signals comprising a pilot signal and data signals;

an interference energy estimator connected to the CDMA receiver to generate an interference energy value of the received signals, the interference energy estimator comprising;

a pseudo-noise despreader capable of generating despread in-phase and quadrature signals in response to the spread-spectrum in-phase and quadrature signals;

a decoverer connected to the pseudo-noise despreader to separate the data signals along a data channel and the pilot signal along a pilot channel from the despread in-phase and quadrature signals;

a pilot filter connected to the pilot channel to generate a filtered pilot signal;

a pilot subtractor connected to subtract the pilot signal transmitted along the pilot channel from the filtered pilot signal to generate a signal representative of interference and noise per symbol; and

an interference energy computer connected to the pilot subtractor to generate an interference energy value; and

a path combiner connected to the interference energy estimator to generate summed weighted-path signals based on the interference energy value and the data signals from the data channel.

32. The system of claim 31, further comprising a log-likelihood ratio generator connected to the path combiner to generate soft decision values based on the summed weighted-path signals.

33. The system of claim 32, further comprising a decoder connected to the log-likelihood ratio generator to generate decoded signals based on the soft decision values.

34. The system of claim 31, wherein the CDMA receiver comprises an intermediate-frequency (IF)-to-baseband converter to generate the spread-spectrum in-phase and quadrature signals based on the received signals.

35. The system of claim 31, wherein the interference energy estimator further comprises a look-up table connected to the interference energy computer to generate a reciprocal of the interference energy value.

36. The system of claim 35, wherein the path combiner comprises:

a constant generator capable of generating a constant $k=\frac{1}{M}<br><br>\text{\hspace{1em}<br><br>}<br><br>\sqrt{\frac{E_s}{E_p}},$

where E_s is modulation symbol energy E_p is pilot chip energy, and M is the number of chips per Walsh symbol; and

a multiplier connected to the constant generator and the pilot filter to generate an estimate of a channel coefficient