Radio channel estimation
View Patent ↗A device that identifies a current channel estimate based on previously received pilot tones; and iteratively, for each instance of receiving a set of new pilot tones: generates an updated channel estimate by replacing contributions to the current channel estimate that depend from the previously received pilot tones with contributions that depend from the set of new pilot tones; and considers for the next iteration the updated channel estimate as the current channel estimate and the set of new pilot tones as the previously received pilot tones.
1. A method for controlling a radio device to update a channel estimate, the method comprising:
providing a current channel estimate H o (k) based on previously received pilot tones; and
iteratively, for each instance of receiving a set of N p new pilot tones within an n th time sample index, where N and n are integer values:
generating an updated channel estimate H upd (k) by replacing contributions to the current channel estimate H o (k) that depend from the previously received pilot tones with contributions that depend from the set of N p new pilot tones; and
considering for the next iteration the updated channel estimate H upd (k) as the current channel estimate H o (k) and the set of N p new pilot tones as the previously received pilot tones.
2. The method according to claim 1 , wherein a windowing function w(n) is used to define a frequency span in which each of received sets of N p new pilot tones are disposed.
3. The method according to claim 1 , wherein the set of N p new pilot tones within each n th time sample index are uniformly distributed in frequency.
4. The method according to claim 2 , wherein the windowing function is defined for a symbol size N within which each set of the N p new pilot tones are obtained.
5. The method according to claim 2 , wherein the updated channel estimate H upd (k) is obtained by performing on the windowing function a size N Fast Fourier transform
FFT such that
∑
n
=
0
N
-
1
w
(
n
)
ⅇ
j2π
l
-
k
N
n
;
where
l is an index of subcarrier or frequency band of the frequency span within which is received the set of N p new pilot tones of the n th time sample index; and
k is a subcarrier or frequency band for which the updated channel estimate applies.
6. The method according to claim 5 , wherein:
the contributions to the current channel estimate H o (k) that depend from the previously received pilot tones are
∑
l
∈
Ω
p
H
0
(
l
)
1
N
p
∑
n
=
0
N
-
1
w
(
n
)
ⅇ
j2π
l
-
k
N
n
;
and
the contributions that depend from the set of N p new pilot tones are
∑
l
∈
Ω
p
C
(
l
)
1
N
p
∑
n
=
0
N
-
1
w
(
n
)
ⅇ
j2π
l
-
k
N
n
;
where: Ω p is a set of available subcarrier or frequency band indices having a pilot tone; and
C(l) is an estimate of a channel frequency tap at subcarrier or frequency band l.
7. The method according to claim 6 , wherein the updated channel estimate H upd (k) is generated using:
H
upd
(
k
)
=
H
0
(
k
)
+
∑
l
∈
Ω
p
(
C
(
l
)
-
H
0
(
l
)
)
Ψ
(
l
,
k
)
,
where
:
Ψ
(
l
,
k
)
=
1
N
p
∑
n
=
0
N
-
1
w
(
n
)
ⅇ
j2π
l
-
k
N
n
=
0
for
k
≠
m
l
,
and
m
l
=
l
-
N
m
-
1
2
+
1
,
…
,
l
+
N
m
-
1
2
for
each
l
∈
Ω
p
and further where a total of N m subcarriers or frequency bands are updated in each iteration.
8. The method according to claim 1 , wherein the radio device comprises at least a receiver disposed in a user equipment.
9. A user equipment for estimating a channel, the user equipment comprising:
a receiver configured to receive pilot tones; and
processing circuitry configured to
provide a current channel estimate H o (k) based on previously received pilot tones; and
iteratively, for each instance of receiving a set of N p new pilot tones within an n th time sample index, where N and n are integer values:
generate an updated channel estimate H upd (k) by replacing contributions to the current channel estimate H o (k) that depend from the previously received pilot tones with contributions that depend from the set of N p new pilot tones; and
consider for the next iteration the updated channel estimate H upd (k) as the current channel estimate H o (k) and the set of N p new pilot tones as the previously received pilot tones.
10. The user equipment according to claim 9 , wherein a windowing function w(n) is used to define a frequency span in which each of received sets of N p new pilot tones are disposed.
11. The user equipment according to claim 10 , wherein the set of N p new pilot tones within each n th time sample index are uniformly distributed in frequency.
12. The user equipment according to claim 10 , wherein the windowing function is defined for a symbol size N within which each set of the N p new pilot tones are obtained.
13. The user equipment according to claim 10 , wherein the updated channel estimate H upd (k) is obtained by performing on the windowing function a size N Fast Fourier
transform FFT such that
∑
n
=
0
N
-
1
w
(
n
)
ⅇ
j2π
l
-
k
N
n
;
where
l is an index of subcarrier or frequency band of the frequency span within which is received the set of N p new pilot tones of the n th time sample index; and
k is a subcarrier or frequency band for which the updated channel estimate applies.
14. The user equipment according to claim 13 , wherein:
the contributions to the current channel estimate H o (k) that depend from the previously received pilot tones are
∑
l
∈
Ω
p
H
0
(
l
)
1
N
p
∑
n
=
0
N
-
1
w
(
n
)
ⅇ
j2π
l
-
k
N
n
;
and
the contributions that depend from the set of N p new pi ones are
∑
l
∈
Ω
p
C
(
l
)
1
N
p
∑
n
=
0
N
-
1
w
(
n
)
ⅇ
j2π
l
-
k
N
n
;
where: Ω p is a set of available subcarrier or frequency band indices having a pilot tone;
and C(l) is an estimate of a channel frequency tap at subcarrier or frequency band l.
15. The user equipment according to claim 14 , wherein the updated channel estimate H upd (k) is generated using:
H
upd
(
k
)
=
H
0
(
k
)
+
∑
l
∈
Ω
p
(
C
(
l
)
-
H
0
(
l
)
)
Ψ
(
l
,
k
)
,
where
:
Ψ
(
l
,
k
)
=
1
N
p
∑
n
=
0
N
-
1
w
(
n
)
ⅇ
j2π
l
-
k
N
n
=
0
for
k
≠
m
l
,
and
m
l
=
l
-
N
m
-
1
2
+
1
,
…
,
l
+
N
m
-
1
2
for
each
l
∈
Ω
p
and further where a total of N m subcarriers or frequency bands are updated in each iteration.
16. A user equipment comprising:
a receiver configured to receive pilot tones; and
processing circuitry configured to
identify a current channel estimate based on previously received pilot tones; and
iteratively, for each instance of receiving a set of new pilot tones:
generate an updated channel estimate by replacing contributions to the current channel estimate that depend from the previously received pilot tones with contributions that depend from the set of new pilot tones; and
consider for the next iteration the updated channel estimate as the current channel estimate and the set of new pilot tones as the previously received pilot tones.
17. The user equipment of claim 16 , wherein
a windowing function is used to define a frequency span in which each of the received sets of new pilot tones are disposed.
18. The user equipment of claim 16 , wherein
the set of new pilot tones are uniformly distributed in frequency.
19. The user equipment of claim 18 , wherein the windowing function is defined for a symbol size N within which each set of the new pilot tones are obtained.