Method and apparatus for suppressing co-channel interference in a receiver
View Patent ↗A method of operation of a filter ( 12 ) of a receiver ( 10 ) of a mobile station or a base station of a radio access network and corresponding equipment, the method for use in suppressing co-channel interference and based on separating the in-phase (I) and quadrature phase (Q) components of the received signal and then performing whitening on a symbol-by-symbol basis, i.e. the whitening operation is done within one symbol. The invention provides a filter ( 12 ) including a module ( 12 b ) for performing IQ whitening (either according to the invention or otherwise), and also provides a switch ( 12 a ) that can be used to enable or disable IQ whitening, depending on the character of the received signal, and in particular based on the noise plus interference correlation matrix ({tilde over (R)} ii )
1. A method for use by a receiver of a wireless communication system in receiving over a communication channel a radio transmission of a number of symbols each having an in-phase and a quadrature component, the method including a step ( 11 ) of receiving and sampling the radio transmission so as to provide a succession of samples, and also a step ( 12 ) of filtering the succession of samples, the method characterized in that:
the step ( 12 ) of filtering the succession of samples includes a step ( 12 b ) of whitening the samples on a sample-by-sample basis by evaluating, for each sample in the succession of samples, a noise plus interference correlation matrix ({tilde over (R)} ii ) including information about the correlation of both the in-phase and quadrature phase components of the sample.
2. A method as in claim 1 , wherein the step ( 12 ) of filtering is further characterized by:
a step ( 12 a ) of switching on or off the step ( 12 b ) of whitening the samples, with the switching based on determining whether the communication channel is sensitivity-limited so that noise is present that can be characterized as substantially white.
3. A method as in claim 1 , wherein whether the communication channel is determined to be sensitivity-limited is based on a calculated value of a metric (M tc , M ti ) and a corresponding predetermined threshold (τ tc , τ ti ).
4. A method as in claim 3 , wherein the metric (M tc ) is based on relative values of different components of the noise plus interference correlation matrix ({tilde over (R)} ii ).
5. A method as in claim 3 , wherein the switching is based on comparing the value of a metric (M ti ) defined by
M
ti
=
R
1
ii
R
0
ii
where
R
0
ii
=
E
⌊
i
k
*
i
k
⌋
and
R
1
ii
=
E
⌊
i
k
*
i
k
+
1
⌋
.
6. A method as in claim 3 , wherein the switching is based on examining a second order or a higher order statistic of the noise plus interference signal (i k ) related to the noise plus interference correlation matrix ({tilde over (R)} ii ).
7. A method as in claim 1 , further characterized in that the noise plus interference correlation matrix ({tilde over (R)} ii ) is determined using:
R
~
ii
=
E
[
i
k
i
k
*
]
,
where i k is a noise plus interference signal.
8. A method as in claim 7 , further characterized in that each vector y k representing one symbol is whitened using:
{tilde over (y)} k =Wy k
where W is defined as the inverse of a square root operation on the noise plus interference correlation matrix {tilde over (R)} ii , so that:
W={tilde over (R)} ii −1/2 .
9. A method as in claim 1 , wherein each symbol is indicated by one or more samples, including samples from possibly different antennas.
10. A receiver used as part of or with a wireless communication system, characterized in that it comprises means ( 12 ) for performing the steps ( 12 12 b ) recited in claim 1 .
11. A receiver as in claim 10 , wherein the receiver is part of a mobile station.
12. A receiver as in claim 10 , wherein the receiver is part of a base station of a radio access network of the wireless communication system.
13. A system, comprising a mobile station and a base station used as part of or with a wireless communication system, each including a receiver, characterized in that at least one of the receivers comprises means ( 12 ) for performing the steps ( 12 12 b ) recited in claim 1 .