Method and apparatus employed in a user equipment for interference signal code power and noise variance estimation
View Patent ↗Method and apparatus employed by a UE for interference signal code power noise variance estimation employing a reduced number of samples utilizing the equation σ ^ n 2 = T · ∑ i = 1 N sample h n ( i ) 2 , where T = G · γ ( r ) N sample , where N sample =L chest −N pl ·K max , where γ ( r ) = [ 1 + ( 1 r - 1 ) · ln ( 1 - r ) ] - 1 and where r = N sample L chest . As an alternative, a recursive technique may be employed wherein the noise variance is estimated from the ignored coefficients of the estimated channel output and upgraded recursively as per the following: σ ^ n 2 = 1 KW ∑ j = 1 K ∑ i = 1 W h i ( j ) - h ^ i ( j ) 2 , where ĥ i (j) are the channel estimates after the post processing and the noise variance estimates {circumflex over (σ)} n−1 2 , and the initial values of ĥ i (j) are all zeros.
1. A method for estimating noise variance, the method comprising:
performing channel estimation on a midamble portion of a received burst to obtain a plurality of channel coefficients where active midambles are not known; and
estimating noise variance based on equation
σ
^
n
2
=
T
·
∑
i
=
l
N
sample
h
n
(
i
)
2
,
where
T
=
G
·
γ
(
r
)
N
sample
,
r
=
N
sample
L
chest
,
N sample =L chest −N pl ·K max , h n(i) , (i=1,2,. . .,L chest ), represents channel coefficients, L chest is an output length of the channel estimation, N pl is a maximum number of paths per channel, K max is a maximum number of midamble shifts, n(i) is an index of i-th smallest estimated channel coefficient, G is a burst-dependent constant,
γ
(
r
)
=
⌊
1
+
(
1
r
-
1
)
·
ln
(
1
-
r
)
⌋
-
1
,
and i is an index.
2. The method of claim 1 wherein, when the received burst is burst type 1 , G is set to 400.
3. The method of claim 1 wherein, when the received burst is burst type 2 , G is set to 169.
4. The method of claim 1 wherein, when the received burst is burst type 3 , G is set to 400.
5. The method of claim 1 comprising obtaining the scaling constant T from a look-up table, wherein T increases with an increasing value of midamble shifts.
6. The method of claim 5 wherein the scaling constant is selected in accordance with permissible midamble shifts which are 4 , 8 and 16 , when the received burst is burst type 1 .
7. The method of claim 5 wherein the scaling constant is selected in accordance with permissible midamble shifts which are 3 and 6 , when the received burst is burst type 2 .
8. A user equipment (UE) for estimating noise variance, the UE comprising:
a channel estimator for performing a channel estimation on a midamble portion of a received burst to obtain a plurality of channel coefficients where active midambles are not known; and
a noise variance estimator for estimating noise variance based on equation
σ
^
n
2
=
T
·
∑
i
=
l
N
sample
h
n
(
i
)
2
,
where
T
=
G
·
γ
(
r
)
N
sample
,
r
=
N
sample
L
chest
,
N sample =L chest −N pl ·K max , where h n(i) , (i=1,2,. . ., L chest ), represents channel coefficients, L chest is an output length of the channel estimator, N pl is a maximum number of paths per channel, K max is a maximum number of midamble shifts, n(i) is an index of i-th smallest coefficient in the channel estimation, G is a burst constant,
γ
(
r
)
=
⌊
1
+
(
1
r
-
1
)
·
ln
(
1
-
r
)
⌋
-
1
,
and i is an index.
9. The UE of claim 8 wherein, when the received burst is burst type 1 , G is set to 400.
10. The UE of claim 8 wherein, when the received burst is burst type 2 , G is set to 169.
11. The UE of claim 8 wherein, when the received burst is burst type 3 , G is set to 400.
12. The UE of claim 8 wherein the scaling constant T is obtained from a look-up table, wherein T increases with an increasing value of midamble shifts.
13. The UE of claim 12 further comprising a scaling constant selector for selecting the scaling constant in accordance with permissible midamble shifts which are 4, 8 and 16, when the received burst is burst type 1 .
14. The UE of claim 12 further comprising a scaling constant selector for selecting the scaling constant in accordance with permissible midamble shifts which are 3 and 6, when the received burst is a burst type 2 .
15. The UE of claim 8 wherein the noise variance estimator utilizes the number of active midamble shifts for revising the noise variance estimation.
16. A method for estimating noise variance, the method comprising:
(a) performing a channel estimation on a midamble portion of a received burst, where active midambles are not known, to obtain a plurality of channel impulse responses; and
(b) recursively estimating noise variance based on equation;
σ
^
n
2
=
1
KW
∑
j
=
1
K
∑
i
=
1
W
h
i
(
j
)
-
h
^
i
(
j
)
2
,
where ĥ i (j) are channel estimates after post processing with the noise variance estimates {circumflex over (σ)} n−1 2 , and initial values of ĥ i (j) are all zeros.
17. The method of claim 16 wherein six (6) recursions are performed during step (b).
18. The method of claim 17 wherein the noise variance is estimated from ignored co-efficients of the estimated channel impulse responses.
19. A user equipment (UE) for estimating noise variance, the UE comprising:
a channel estimator for performing a channel estimation on a midamble portion of a received burst, where active midambles are not known, to obtain a plurality of channel impulse responses; and
a noise variance estimator for recursively estimating noise variance based on the equation:
σ
^
n
2
=
1
KW
∑
j
=
1
K
∑
i
=
1
W
h
i
(
j
)
-
h
^
i
(
j
)
2
,
where ĥ i (j) are channel estimates after post processing with the noise variance {circumflex over (σ)} n−1 2 , and initial values of ĥ i (j) are all zeros, the noise variance being estimated from ignored coefficients of the estimated channel output and upgraded recursively.
20. A UE according to claim 19 wherein the noise variance estimator performs six (6) recursions.