Inter-carrier interference reduction for multi-carrier signals
In mobile wireless communication systems the channel between the transmitter and receiver varies during a transmission. This is often referred to as fading, of which different kinds exist—each resulting in different impairments with specific properties. A low complexity scheme is described to reduce the noise created by inter-carrier interference or ICI. The method makes use of the guard interval and assumes slow variation of the channel. It is not restricted to wireless communication and can be used in any environment with varying channels.
1. A method of estimating an inter-carrier interference (ICI) for a multi-carrier signal received from a channel, in which signal symbols are separated by a guard interval including a cyclic extension of a symbol, the method comprising:
estimating the inter-carrier interference by a controller using a function:
A
~
(
n
)
=
rx
(
n
)
-
rx
(
n
-
N
)
N
for n=[N−G, N−1],
where:
rx(n) is the received signal at time n,
rx(n-N) is the received signal at time n-N,
N is the symbol length (not including the cyciic extention),
G is the cyciic extention length;
the estimating of the inter-carrier interference being in a time-domain before time-domain-to-frequency processing of the received multi-carrier signal.
2. The method according to claim 1 , wherein the estimated inter-carrier-interference is given by
ICI
estimated
(
n
)
=
(
n
-
N
-
1
2
)
·
A
~
(
n
)
for n=[N−G, N−1],
where: ICI estimated (n) is the estimated inter-carrier interference.
3. A method according to claim 1 , further comprising estimating the channel impulse response length.
4. A method of reducing an inter-carrier interference (ICI) for a received multicarrier signal in which symbols are separated by a guard interval including a cyclic extension of a symbol the method comprising:
estimating, by a processing apparatus in a receiver, the inter-carrier interference using a function:
A
~
(
n
)
=
rx
(
n
)
-
rx
(
n
-
N
)
N
for n=[N−G, N−1],
where:
rx(n) is the received signal at time n,
rx(n-N) is the received signal at time n-N,
N is the symbol length (not including the cyciic extention),
G is the cyciic extention length;
the estimating of the inter-carrier interference being in a time-domain before time-domain-to-frequency processing of the received multicarrier signal: and using the estimation of ICI to reduce the ICI in the received multicarrier signal.
5. A method according to claim 4 further comprising using a windowing function which determines an amount of the estimated ICI that is used to compensate the received multicarrier signal.
6. A method according to claim 5 wherein the windowing function at least one of (1) equals an average power of A (n=N) divided by the average power of A(n) and (2) is calculated using the function:
WIN
(
n
)
=
E
{
A
~
(
N
-
1
)
2
}
E
{
A
~
(
n
)
2
}
for n=[N−G, N−1], where:
E
{
A
~
(
N
-
1
)
2
}
=
E
{
rx
(
N
-
1
)
-
rx
(
-
1
)
N
2
}
E
{
A
~
(
n
)
2
}
≅
E
{
rx
(
n
)
-
rx
(
n
-
N
)
N
2
}
.
7. A method according to claim 5 wherein reducing the ICI in the received multicarrier signal is calculated using the function:
rx
ICI
reduced
(
n
)
≅
rx
(
n
)
-
(
n
-
N
-
1
2
)
·
A
~
(
n
)
or
rx
ICI
reduced
(
n
)
=
rx
(
n
)
-
(
n
-
N
-
1
2
)
·
WIN
(
n
)
·
A
~
(
n
)
for n=[N−G, N−1],
where WIN(n) is a windowing function which determines an amount of the estimated ICI that is used to compensate the received signal.
8. A method according to claim 6 wherein reducing the ICI in the received multicarrier signal is calculated using the function:
rx
ICI
reduced
(
n
)
≅
rx
(
n
)
-
(
n
-
N
-
1
2
)
·
A
~
(
n
)
or
rx
ICI
reduced
(
n
)
=
rx
(
n
)
-
(
n
-
N
-
1
2
)
·
WIN
(
n
)
·
A
~
(
n
)
for n=[N−G, N−1],
where WIN(n) is the windowing function which determines an amount of the estimated ICI that is used to compensate the received signal.
9. A method according to claim 1 wherein the multi-carrier signal is at least a one of an orthogonal frequency division multiplexed (OFDM) signal and a discrete multi-tone (DMT) signal.
10. A system for estimating an inter-carrier interference (ICI) for a received multi-carrier signal in which symbols are separated by a guard interval including a cyclic extension of a symbol, the system comprising:
a receiver, the receiver comprising a controller configured to estimate the inter-carrier interference using a function:
A
~
(
n
)
=
rx
(
n
)
-
rx
(
n
-
N
)
N
for n=[N−G, N−1],
where:
rx(n) is the received signal at time n,
rx(n-N) is the received signal at time n-N,
N is the symbol length (not including the cyciic extention),
G is the cyciic extention length;
the receiver being adapted to estimate the inter-carrier interference in a time-domain before time-domain-to-frequency processing of the received multi-carrier signal.
11. The system of claim 10 , wherein the receiver uses the following function to estimate the inter-carrier-interference:
ICI
estimated
(
n
)
=
(
n
-
N
-
1
2
)
·
A
~
(
n
)
for n=[N−G, N−1],
where: ICI estimated (n) is the estimated inter-carrier interference.
12. The system of claim 10 , wherein the receiver is further adapted to reduce the ICI according to
rx
ICI
reduced
(
n
)
≅
rx
(
n
)
-
(
n
-
N
-
1
2
)
·
A
~
(
n
)
or
rx
ICI
reduced
(
n
)
=
rx
(
n
)
-
(
n
-
N
-
1
2
)
·
WIN
(
n
)
·
A
~
(
n
)
for n=[N−G, N−1],
where WIN(n) is a windowing function which determines an amount of the estimated ICI that is used to compensate the received multi-carrier signal.