Method and device for efficient precoder search
The disclosure relates to a method performed in a wireless device for establishing a feedback metric. The wireless device is configured with a grouping of available precoding matrix indicators, PMIs, of a codebook, the grouping comprising two or more groups each of which comprises an exclusive subset of the available precoding matrix indicators, PMIs. The method comprises: identifying for one or more rank indicator, RI, hypotheses a respective parent PMI providing the highest link quality metric, LQM; establishing for one or more of the identified parent PMIs, a respective set of child PMIs; determining a link quality metric, LQM for each child PMIs of the established one or more sets of child PMIs; and establishing the feedback metric to be the child PMI having the highest link quality metric, LQM. The disclosure also relates to a wireless device, method in a network node, network node, computer programs and computer program products.
1. A method performed in a wireless device for establishing a feedback metric, wherein the wireless device is configured with a grouping of available precoding matrix indicators (PMIs) of a codebook having a symmetrical structure, the grouping comprising two or more groups each of which comprises an exclusive subset of the available precoding matrix indicators (PMIs) the method comprising:
identifying for each of one or more rank indicator (RI) hypotheses, a respective parent PMI of the two or more groups providing a highest link quality metric (LQM);
establishing for one or more of the identified parent PMIs of the two or more groups, a respective set of child PMIs wherein a child PMI generating vector is obtainable by a linear transformation of a parent PMI generating vector defined from the codebook, where the linear transformation is a diagonal matrix comprising the appropriate phase shifters;
determining a link quality metric (LQM) for each child PMIs of the established one or more sets of child PMIs; and
establishing the feedback metric to be the child PMI having the highest link quality metric (LQM).
2. The method as claimed in claim 1 , wherein the establishing comprises establishing a respective set of child PMIs for the identified parent PMI of each group of the grouping.
3. The method as claimed in claim 2 , wherein the determining comprises determining a respective link quality metric (LQM) for all child PMIs of the respective sets of child PMIs of each identified parent PMI.
4. The method as claimed in claim 1 , wherein the determining comprises determining a respective link quality metric (LQM) for each child PMIs only for the parent PMI, among the identified respective parent PMIs, having the highest link quality metric (LQM).
5. The method as claimed in claim 1 , wherein the establishing the feedback metric further comprises establishing a rank indicator (RI) to be the rank indicator (RI) hypothesis corresponding to the group to which the parent PMI belongs which has the child PMI having the highest link quality metric (LQM).
6. The method as claimed in claim 1 , wherein the identifying for each group a respective parent PMI providing the highest link quality metric (LQM) comprises:
determining for each parent PMI of each of the one or more groups a respective post-processing signal to interference plus noise ratio (SINR) or a respective signal to interference plus noise ratio (SINR);
determining for each parent PMI a respective link quality metric (LQM) based on the respective determined post-processing signal to interference plus noise ratios (SINRs) or the respective signal to interference plus noise ratios (SINRs); and
identifying the parent PMI of each group having the highest link quality metric (LQM).
7. The method as claimed in claim 1 , wherein the identifying for each group a respective parent PMI providing the highest link quality metric (LQM) comprises receiving from a network node a configuration indicating in a bitmap pattern the respective parent PMI.
8. The method as claimed in claim 1 , wherein the wireless device is adapted to receive up to four precoded multiple-input, multiple output (MIMO) streams and wherein the diagonal matrix comprising the appropriate phase shifters comprises:
u
c
=
[
1
0
0
0
0
exp
(
j
κθ
)
0
0
0
0
exp
(
j
2
κθ
)
0
0
0
0
exp
(
j
3
κθ
)
]
u
p
,
κ
=
c
-
p
,
c
≠
p
,
{
c
,
p
}
∈
{
0
,
1
,
…
15
}
,
θ
=
[
-
π
,
π
]
,
wherein u c comprises a set of child PMIs and u p comprises a parent PMI.
9. A wireless device for establishing a feedback metric, wherein the wireless device is configured with a grouping of available precoding matrix indicators (PMIs) of a codebook having a symmetrical structure, the grouping comprising two or more groups each of which comprises an exclusive subset of the available precoding matrix indicators (PMIs) the wireless device comprising:
a processor; and
an antenna device,
wherein the wireless device is configured to:
identify for each of one or more rank indicator (RI) hypothesis a respective parent PMI of the two or more groups providing a highest link quality metric (LQM);
establish for one or more of the identified parent PMIs of the two or more groups, a respective set of child PMIs, wherein a child PMI generating vector is obtainable by a linear transformation of a parent PMI generating vector defined from the codebook, where the linear transformation is a diagonal matrix comprising the appropriate phase shifters;
determine a link quality metric (LQM) for each child PMIs of the established one or more sets of child PMIs; and
establish the feedback metric to be the child PMI having the highest link quality metric (LQM).
10. The wireless device as claimed in claim 9 , configured to establish a respective set of child PMIs by establishing a respective set of child PMIs for the identified parent PMI of each group of the grouping.
11. The wireless device as claimed in claim 10 , configured to determine by determining a respective link quality metric (LQM) for all child PMIs of the respective sets of child PMIs of each identified parent PMI.
12. The wireless device as claimed in claim 9 , configured to determine by determining a respective link quality metric (LQM) for each child PMIs only for the parent PMI, among the identified respective parent PMIs, having the highest link quality metric (LQM).
13. The wireless device as claimed in claim 9 , configured to further establish a rank indicator (RI) to be the rank indicator (RI) hypothesis corresponding to the group to which the parent PMI belongs which has the child PMI having the highest link quality metric (LQM).
14. The wireless device as claimed in claim 9 , configured to identify for each group a respective parent PMI providing the highest link quality metric (LQM) by:
determining for each parent PMI of each of the one or more groups a respective post-processing signal to interference plus noise ratio (SINR) or a respective signal to interference plus noise ratio (SINR);
determining for each parent PMI a respective link quality metric (LQM) based on the respective determined post-processing signal to interference plus noise ratios (SINRs) or the respective signal to interference plus noise ratios (SINRs); and
identifying the parent PMI of each group having the highest link quality metric (LQM).
15. The wireless device as claimed in claim 9 , configured to identify for each group a respective parent PMI providing the highest link quality metric (LQM) by receiving from a network node a configuration indicating in a bitmap pattern the respective parent PMI.
16. The wireless device as claimed in claim 9 , wherein the wireless device is adapted to receive up to four precoded multiple-input, multiple output (MIMO) streams and wherein the diagonal matrix comprising the appropriate phase shifters comprises:
u
c
=
[
1
0
0
0
0
exp
(
j
κθ
)
0
0
0
0
exp
(
j
2
κθ
)
0
0
0
0
exp
(
j
3
κθ
)
]
u
p
,
κ
=
c
-
p
,
c
≠
p
,
{
c
,
p
}
∈
{
0
,
1
,
…
15
}
,
θ
=
[
-
π
,
π
]
,
wherein u c comprises a set of child PMIs and u p comprises a parent PMI.
17. A nontransitory computer readable medium comprising a computer program for a wireless device for establishing a feedback metric, the computer program comprising computer program code, which, when executed in a processor of the wireless device causes the wireless device to perform a method, wherein the wireless device is configured with a grouping of available precoding matrix indicators (PMIs) of a codebook having a symmetrical structure, the grouping comprising two or more groups each of which comprises an exclusive subset of the available precoding matrix indicators (PMIs) and wherein the method comprises:
identifying for each of one or more rank indicator (RI) hypotheses, a respective parent PMI of the two or more groups providing a highest link quality metric (LQM);
establishing for one or more of the identified parent PMIs of the two or more groups, a respective set of child PMIs wherein a child PMI generating vector is obtainable by a linear transformation of a parent PMI generating vector defined from the codebook, where the linear transformation is a diagonal matrix comprising the appropriate phase shifters;
determining a link quality metric (LQM) for each child PMIs of the established one or more sets of child PMIs; and
establishing the feedback metric to be the child PMI having the highest link quality metric (LQM).