Method and apparatus providing unbiased signal-to-noise ratio estimation and its application to discontinuous transmission detection
View Patent ↗Disclosed are a method and an apparatus to estimate a signal-to-noise ratio (SNR) of a signal. The method includes sampling the signal, correlating and channel estimating the sampled signal, symbol combining the correlated and channel estimated signal, such as by using a maximal-ratio combining technique, estimating pilot channel and noise power to obtain a combined pilot power and noise variance estimate and inputting the symbol combined signal and the pilot power and noise variance estimate to an Eb/Nt (SNR) estimator. The method further includes, in the Eb/Nt estimator, subtracting a noise term, multiplied by a constant, from the combined signal power and computing a ratio of the unbiased signal power to the noise power to obtain an unbiased (Eb/Nt) estimate. Having obtained obtain the unbiased (Eb/Nt) estimate, the method may integrate the unbiased (Eb/Nt) estimate for a frame duration and compare the integrated unbiased (Eb/Nt) value to a predetermined threshold value to make a decision as to whether the frame was a transmitted frame or an untransmitted (DTX) frame.
1. A method to estimate a signal-to-noise ratio (SNR) of a signal, compnsing:
sampling the signal;
correlating and filtering the sampled signal;
symbol combining the correlated and filtered signal;
estimating pilot channel and noise power to obtain a combined pilot power and noise variance estimate;
inputting the symbol combined signal and the pilot power and noise variance estimate to an (Eb/Nt) estimator and subtracting a noise term, multiplied by a constant, from the combined signal power; and
computing a ratio of the unbiased signal power to the noise power to obtain an unbiased (Eb/Nt) estimate, to determine a status of a received signal for making at least one discontinuos transmission (DTX) decision within a communication terminal as to whether a frame was a transmitted frame or an unstransmitted frame.
2. A method as in claim 1 , further comprising:
integrating the unbiased (Eb/Nt) estimate for a frame duration; and
comparing the integrated unbiased (Eb/Nt) value to a predetermined threshold value to make a DTX decision as to whether the frame was a transmitted frame or an untransmitted frame.
3. A method as in claim 2 , where the method is executed by a CDMA mobile station, and further comprising considering the DTX decision during mobile station power control processing.
4. A method as in claim 1 , where symbol combining comprises multiplying a complex traffic signal by the complex conjugate of the pilot signal, and demultiplexing to obtain a scalar stream of traffic signals.
5. A method as in claim 1 , where computing the ratio of the unbiased signal power to the noise power to obtain an unbiased (Eb/Nt) estimate is performed in accordance with:
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p
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2
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p
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p
2
σ
2
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
6. A method as in claim 1 , where correlating uses a correlator comprises of L fingers, and where computing the ratio of the unbiased signal power to the noise power to obtain an unbiased (Eb/Nt) estimate is performed in accordance with:
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where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
7. A method as in claim 1 , where correlating uses a correlator comprises of L fingers, and where computing the ratio of the unbiased signal power to the noise power to obtain an unbiased (Eb/Nt) estimate is performed in accordance with:
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L
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p
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,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
8. A method as in claim 1 , where symbol combining uses a maximal-ratio combining technique.
9. Apparatus to estimate a signal-to-noise ratio (SNR) of a signal, comprising:
an analog to digital converter for sampling the signal;
a correlator and channel filter for correlating and filtering the sampled signal;
a symbol combiner for combining the correlated and filtered signal;
an estimator for estimating pilot channel and noise power to obtain a combined pilot power and noise variance estimate; and
an (Eb/Nt) estimator having inputs for inputting the symbol combined signal and the pilot power and noise variance estimate, said (Eb/Nt) estimator comprising a subtractor for subtracting a noise term, multiplied by a constant, from the combined signal power, and means for computing a ratio of the unbiased signal power to the noise power to obtain an unbiased (Eb/Nt) estimate for use in determining at least a status of a received signal for making at least one discontinuos transmission (DTX) decision within a communication terminal as to whether a frame was a transmitted frame or an untrasmitted frame.
10. An apparatus as in claim 9 , further comprising:
an integrator for integrating the unbiased (Eb/Nt) estimate for a frame duration; and
a comparator for comparing the integrated unbiased (Eb/Nt) value to a predetermined threshold value to make a DTX decision as to whether the frame was a transmitted frame or an untransmitted frame.
11. An apparatus as in claim 10 , where said apparatus forms a part of a CDMA mobile station, and further comprising a controller that considers the DTX decision when performing mobile station power control processing.
12. An apparatus as in claim 9 , where said symbol combiner a multiplier for multiplying a complex traffic signal by the complex conjugate of the pilot signal, and a demultiplexer that outputs a scalar stream of traffic signals.
13. An apparatus as in claim 9 , where said (Eb/Nt) estimator computes the ratio of the unbiased signal power to the noise power to obtain the unbiased (Eb/Nt) estimate in accordance with:
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b
N
t
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unbias
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2
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t
2
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p
)
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p
2
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2
)
p
2
σ
2
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
14. An apparatus as in claim 9 , where said correlator comprises L fingers, and where said (Eb/Nt) estimator computes the ratio of the unbiased signal power to the noise power to obtain the unbiased (Eb/Nt) estimate in accordance with:
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b
N
t
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unbias
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p
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2
σ
i
2
)
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i
=
1
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p
i
2
σ
i
2
)
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
15. An apparatus as in claim 9 , where said correlator comprises L fingers, and where said (Eb/Nt) estimator computes the ratio of the unbiased signal power to the noise power to obtain the unbiased (Eb/Nt) estimate in accordance with:
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b
N
t
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unbias
=
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=
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L
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p
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2
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p
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p
i
2
σ
i
2
)
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∑
i
=
1
L
p
i
2
σ
i
2
)
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
16. An apparatus as in claim 9 , where said symbol combiner uses a maximal-ratio combining technique.
17. A CDMA mobile station operable with a base station capable of transmitting a signal on a frame-by-frame basis in accordance with a discontinuous transmission (DTX) technique, comprising:
a receiver for receiving the transmitted signal;
an analog to digital converter for sampling the received signal;
a correlator and channel filter for correlating and filtering the sampled signal;
a symbol combiner for combining the correlated and filtered signal;
an estimator for estimating pilot channel and noise power to obtain a combined pilot power and noise variance estimate;
an (Eb/Nt) estimator having inputs for inputting the symbol combined signal and the pilot power and noise variance estimate, said (Eb/Nt) estimator comprising a subtractor for subtracting a noise term, multiplied by a constant, from the combined signal power, and means for computing a ratio of an unbiased signal power to the noise power to obtain an unbiased (Eb/Nt) estimate;
an integrator for integrating the unbiased (Eb/Nt) estimate for a frame duration; and
a comparator for comparing the integrated unbiased (Eb/Nt) value to a predetermined threshold value to make a DTX decision as to whether the frame was a transmitted frame or an untransmitted frame.
18. A mobile station as in claim 17 , further comprising a controller that considers the DTX decision when performing mobile station power control processing.
19. A mobile station as in claim 17 , where said (Eb/Nt) estimator computes the ratio of the unbiased signal power to the noise power to obtain the unbiased (Eb/Nt) estimate in accordance with:
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b
N
t
)
unbias
=
(
p
t
)
2
-
(
N
t
2
N
p
)
(
p
2
σ
2
)
p
2
σ
2
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
20. A mobile station as in claim 17 , where said correlator comprises L fingers, and where said (Eb/Nt) estimator computes the ratio of the unbiased signal power to the noise power to obtain the unbiased (Eb/Nt) estimate in accordance with:
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t
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unbias
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=
1
L
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p
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i
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p
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1
L
p
i
2
σ
i
2
)
(
∑
i
=
1
L
p
i
2
σ
i
2
)
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
21. A mobile station as in claim 17 , where said correlator comprises L fingers, and where said (Eb/Nt) estimator computes the ratio of the unbiased signal power to the noise power to obtain the unbiased (Eb/Nt) estimate in accordance with:
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b
N
t
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unbias
=
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i
=
1
L
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p
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i
2
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p
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p
i
2
σ
i
2
)
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∑
i
=
1
L
p
i
2
σ
i
2
)
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
22. A mobile station as in claim 17 , where said symbol combiner uses a maximal-ratio combining technique.
23. A mobile station as in claim 17 , where the receiver receives one of a Forward Dedicated Control Channel (F-DCCH), a Forward Supplemental Channel 1 (F-SCH1), and a Forward Supplemental Channel 2 (F-SCH2).
24. A mobile station operable with a base station capable of transmitting a signal on a frame-by-frame basis in accordance with a discontinuos transmission (DTX) technique, comprising:
a receiver operable during a frame time;
coupled to said receiver, an unbiased (Eb/Nt) estimator; and
a controller, coupled to said unbiased (Eb/Nt) estimator, for determining a DTX status of a frame based on an output of said unbiased (Eb/Nt) estimator; wherein the unbiased estimator is determined in accordance with:
(
E
b
N
t
)
unbias
=
(
p
t
)
2
-
(
N
t
2
N
p
)
(
p
2
σ
2
)
p
2
σ
2
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.
25. A CDMA mobile station operable with a base station capable of transmitting a signal on a frame-by-frame basis in accordance with a discontinuos transmission (DTX) technique, comprising:
a receiver operable during a frame time;
coupled to said receiver, an unbiased (Eb/Nt) estimator; and
a power controller, coupled to said unbiased (Eb/Nt) estimator, for making a power control decision in accordance with at least a DTX status of a frame, the DTX status being determined based on a comparison of an output of said unbiased (Eb/Nt) estimator to a threshold value; wherein the unbiased estimator is determined in accordance with:
(
E
b
N
t
)
unbias
=
(
p
t
)
2
-
(
N
t
2
N
p
)
(
p
2
σ
2
)
p
2
σ
2
,
where (pt) 2 is the energy of a complex traffic signal, p 2 is the energy of a pilot symbol, N t and N p are traffic symbol correlation length and pilot symbol correlation length, respectively, and σ 2 is the noise variance.