Method and apparatus for determining signal-to-interference ratio with reduced bias effect
View Patent ↗A method and apparatus for estimating a signal-to-interference ratio (SIR) of baseband signals which are received and processed by a data demodulator to provide demodulated signals to a SIR estimator. The SIR estimator receives the demodulated symbols from the data demodulator and estimates the average signal power of the demodulated symbols as a function of a median based average power value m d and a mean based average power value m e of the demodulated symbols for each quadrant of a quadrature phase shift keying (QPSK) constellation. The function is used to determine a minimum value m between m d and m e . The SIR estimator estimates the average effective interference power of the demodulated symbols and calculates the SIR by dividing the estimated average signal power of the demodulated symbols by the estimated average effective interference power of the demodulated symbols. The SIR estimator reduces bias effects on SIR estimation.
1. A method of estimating a signal-to-interference ratio (SIR) of baseband signals which are received and processed by a data demodulator to provide demodulated symbols to a SIR estimator, the method comprising:
(a) the SIR estimator receiving the demodulated symbols from the data demodulator;
(b) the SIR estimator estimating the average signal power of the demodulated symbols as a function of a median based average power value m d and a mean based average power value m e of the demodulated symbols for each quadrant of a quadrature phase shift keying (QPSK) constellation;
(c) the SIR estimator estimating the average effective interference power of the demodulated symbols; and
(d) the SIR estimator calculating the SIR by dividing the estimated average signal power of the demodulated symbols by the estimated average effective interference power of the demodulated symbols.
2. The method of claim 1 wherein the function of the median based average power value and the mean based average power value is to provide a minimum value function for determining a minimum value m between the median based average power value m d and the mean based average power value m e .
3. The method of claim 2 wherein the average signal power of the demodulated symbols is equal to the magnitude squared of the minimum of the absolute value of the median based average power value m d and the absolute value of the mean based average power value m e averaged over all of the quadrants of the QPSK constellation.
4. The method of claim 1 wherein the demodulator is configured as a multi-user detection (MUD) receiver or a single-user detection (STUD) receiver.
5. The method of claim 1 wherein the demodulated symbols are included in a burst of a dedicated physical channel (DPCH).
6. The method of claim 1 wherein the demodulated symbols are QPSK data symbols.
7. The method of claim 1 wherein the demodulated symbols are binary phase shift keying (BPSK) data symbols.
8. The method of claim 1 wherein step (b) further includes performing the following calculation to determine an average signal power estimate E{ } of the demodulated symbols where:
E
{
S
k
d
2
}
=
min
(
[
1
4
·
∑
i
=
1
4
median
(
y
k
(
Q
i
)
)
]
,
[
1
4
·
∑
i
=
1
4
mean
(
y
k
(
Q
i
)
)
]
)
2
wherein S k d is the k-th demodulated desired QPSK signal, y k is the k-th demodulated symbol, Q i denotes the quadrants i of the QPSK constellation, median (y k (Q i )) and mean(y k (Q i )) denote the median and mean values, respectively, of the symbols in the i-th quadrant Q i , and min([median value], [mean value]) represents a minimum value function for determining a minimum value between the median and mean values.
9. The method of claim 8 wherein step (c) further includes performing the following calculation to determine the average effective interference power E{ } of the demodulated symbols:
E
{
n
k
e
2
}
=
1
4
{
∑
i
=
1
4
1
N
Q
i
∑
k
=
1
N
Q
i
y
k
(
Q
i
)
-
q
i
·
E
{
s
k
d
2
}
2
}
,
wherein n k e denotes the total effective interference, N Q represents the number of the demodulator output symbols belonging to the i th quadrant region after making blind based symbol decisions respectively, y k (Q i ) is the k-th output symbol, which is in the i th quadrant. √{square root over (E{|S k d | 2 })} represents the average signal amplitude estimate and q i , for i=1, 2, 3 and 4, respectively, represents the i-th QPSK constellation signal point denoted as follows:
q
1
=
1
+
j
2
,
q
2
=
-
1
+
j
2
,
q
3
=
-
1
-
j
2
,
q
4
=
1
-
j
2
,
where j is an imaginary number.
10. The method of claim 9 wherein step (d) further includes performing the following calculation to determine the SIR of the demodulated symbols:
SIR
=
min
(
[
1
4
·
∑
i
=
1
4
median
(
y
k
(
Q
i
)
)
]
,
[
1
4
·
∑
i
=
1
4
mean
(
y
k
(
Q
i
)
)
]
)
2
-
C
1
4
·
{
∑
i
=
1
4
1
N
Q
i
·
∑
k
=
1
N
Q
i
y
k
(
Q
i
)
-
q
i
·
E
{
s
k
d
2
}
2
}
,
where C is a correction term determined by performing the following calculation:
C
=
[
1
4
·
∑
i
=
1
4
median
(
y
k
(
Q
i
)
)
]
-
[
1
4
·
∑
i
=
1
4
mean
(
y
k
(
Q
i
)
)
]
2
.
11. The method of claim 9 wherein step (d) further includes performing the following calculation to determine a correction term C: C=|m d −m e | 2 where
m
d
=
1
4
·
∑
i
=
1
4
median
(
y
k
(
Q
i
)
)
and
m
e
=
1
4
·
∑
i
=
1
4
mean
(
y
k
(
Q
i
)
)
.
12. A method of estimating a signal-to-interference ratio (SIR) of a sequence of data symbols, the method comprising:
(a) receiving the sequence of data symbols;
(b) estimating the average signal power of the sequence of symbols as a function of a median based average power value m d and a mean based average power value m e of the symbols;
(c) estimating the average effective interference power of the sequence of symbols; and
(d) calculating the SIR by dividing the estimated average signal power of the sequence of symbols by the estimated average effective interference power of the sequence of symbols.
13. The method of claim 12 wherein the function of the median based average power value and the mean based average power value is to provide a minimum value function for determining a minimum value m between the median based average power value m d and the mean based average power value m e .
14. The method of claim 13 wherein the average signal power of the sequence of symbols is equal to the magnitude squared of the minimum of the absolute value of the median based average power value m d and the absolute value of the mean based average power value m e averaged over all of the quadrants of a quadrature phase shift keying (QPSK) constellation.
15. The method of claim 14 wherein step (d) further includes performing the following calculation to determine a correction term C: C=|m d −m e | 2 , where
m
d
=
1
4
·
∑
i
=
1
4
median
(
y
k
(
Q
i
)
)
and
m
e
=
1
4
·
∑
i
=
1
4
mean
(
y
k
(
Q
i
)
)
,
y k is the k-th symbol in the sequence of symbols, Q i denotes the quadrants i of the QPSK constellation, and median(y k (Q i )) and mean(y k (Q i )) denote the median and mean values, respectively, of the symbols in the i-th quadrant Q i .