Method and apparatus providing inter-transmission point phase relationship feedback for joint transmission CoMP
Systems and techniques for joint transmission cooperative multi-point. A set of n CSI reference signal resources are to be measured by a user device. The n CSI reference signal resources include at least one CSI reference signal resource spanning over at least two transmission points. Channel state information feedback corresponding to each CSI reference signal resource is configured. Upon receiving CSI from the user device, at least one precoder is selected for coherent joint cooperative multipoint transmission based on inter-transmission point phase relationship information. A co-phasing factor is derived from transmitted precoders over a cross-cell CSI reference signal resource, the derivation including transmission of reference signals using first and second precoding vectors on two ports, computation of a third vector using feedback based on the precoded reference signals, and computation of the co-phasing factor based on the first, second, and third vectors.
1. An apparatus comprising:
at least one processor;
memory storing a program of instructions;
wherein the memory storing the program of instructions is configured to, with the at least one processor, cause the apparatus to at least:
computing a co-phasing coefficient value for maximizing signal to noise ratio of a composite channel for transmission to a user device, the composite channel comprising first and second transmission points, wherein computing the co-phasing value comprises:
receiving first, second, and third precoding matrix indicators, wherein the third precoding matrix indicator is computed based on transmission of the first and second precoding matrix indicators over a joint channel state information reference signal resource from first and second transmission points; and
calculating the co-phasing coefficient value based on the first, second, and third precoding matrix indicators;
wherein the first and second precoding matrix indicators are computed based on feedback by a user device based, respectively, on transmissions of first and second channel state information reference resources from first and second transmission points, respectively, and
wherein the third precoding matrix indicator is based on simultaneous transmission of a rotation precoding vector by the first and second transmission points; and
based on the computing, performing a coherent joint cooperative multipoint transmission.
2. The apparatus of claim 1 , wherein:
the first precoding matrix indicator is computed by the user device based on a transmission of the first channel state information reference signal resource by the first transmission point, wherein the user device measures and returns the first precoding matrix indicator along with a first channel quality indicator and first reference index; and
the second precoding matrix indicator is computed by the user device based on a transmission of the second channel state information reference signal resource by the second transmission point, wherein the user device measures and returns the second precoding matrix indicator along with a second channel quality indicator and second reference index.
3. The apparatus of claim 2 , wherein:
the third precoding matrix indicator is computed based on simultaneous respective transmissions by the first and second transmission points over one port of a third channel state information reference signal resource.
4. The apparatus of claim 3 , wherein the third channel state information reference signal resource comprises a two-port reference signal with one port from the first transmission point and one port from the second transmission point.
5. The apparatus of claim 1 , wherein the rotation precoding vector is:
R
1
=
R
2
H
=
[
1.0000
0.3334
-
0.4714
ⅈ
0.3334
-
0.4714
ⅈ
0.3332
+
0.9429
ⅈ
]
.
6. A method comprising:
computing a co-phasing coefficient value for maximizing signal to noise ratio of a composite channel for transmission to a user device, the composite channel comprising first and second transmission points, wherein computing the co-phasing value comprises:
receiving first, second, and third precoding matrix indicators, wherein the third precoding matrix indicator is computed based on transmission of the first and second precoding matrix indicators over a joint channel state information reference signal resource from first and second transmission points; and
calculating the co-phasing coefficient value based on the first, second, and third precoding matrix indicators;
wherein the first and second precoding matrix indicators are computed based on feedback by a user device based, respectively, on transmissions of first and second channel state information reference resources from first and second transmission points, respectively, and
wherein the third precoding matrix indicator is based on simultaneous transmission of a rotation precoding vector by the first and second transmission points; and
based on the computing, performing a coherent joint cooperative multipoint transmission.
7. The method of claim 6 , wherein:
the first precoding matrix indicator is computed by the user device based on a transmission of the first channel state information reference signal resource by the first transmission point, wherein the user device measures and returns the first precoding matrix indicator along with a first channel quality indicator and first reference index; and
the second precoding matrix indicator is computed by the user device based on a transmission of the second channel state information reference signal resource by the second transmission point, wherein the user device measures and returns the second precoding matrix indicator along with a second channel quality indicator and second reference index.
8. The method of claim 7 , wherein:
the third precoding matrix indicator is computed based on simultaneous respective transmissions by the first and second transmission points over one port of a third channel state information reference signal resource.
9. The method of claim 8 , wherein the third channel state information reference signal resource comprises a two-port reference signal with one port from the first transmission point and one port from the second transmission point.
10. The method of claim 6 , wherein the rotation precoding vector is:
R
1
=
R
2
H
=
[
1.0000
0.3334
-
0.4714
ⅈ
0.3334
-
0.4714
ⅈ
0.3332
+
0.9429
ⅈ
]
.
11. A computer program product embodied on a non-transitory readable medium storing a computer program of instructions, execution of which by a processor configures an apparatus to control or carry out at least:
computing a co-phasing coefficient value for maximizing signal to noise ratio of a composite channel for transmission for transmission to a user device, the composite channel comprising first and second transmission points, wherein computing the co-phasing value comprises:
receiving first, second, and third precoding matrix indicators, wherein the third precoding matrix indicator is computed based on transmission of the first and second precoding matrix indicators over a joint channel state information reference signal resource from first and second transmission points; and
calculating the co-phasing coefficient value based on the first, second, and third precoding matrix indicators;
wherein the first and second precoding matrix indicators are computed based on feedback by a user device based, respectively, on transmissions of first and second channel state information reference resources from first and second transmission points, respectively, and
wherein the third precoding matrix indicator is based on simultaneous transmission of a rotation precoding vector by the first and second transmission points; and
based on the computing, performing a coherent joint cooperative multipoint transmission.
12. The computer program product of claim 11 , wherein:
the first precoding matrix indicator is computed by the user device based on a transmission of the first channel state information reference signal resource by the first transmission point, wherein the user device measures and returns the first precoding matrix indicator along with a first channel quality indicator and first reference index; and
the second precoding matrix indicator is computed by the user device based on a transmission of the second channel state information reference signal resource by the second transmission point, wherein the user device measures and returns the second precoding matrix indicator along with a second channel quality indicator and second reference index.
13. The computer program product of claim 12 , wherein:
the third precoding matrix indicator is computed based on simultaneous respective transmissions by the first and second transmission points over one port of a third channel state information reference signal resource.
14. The computer program product of claim 13 , wherein the third channel state information reference signal resource comprises a two-port reference signal with one port from the first transmission point and one port from the second transmission point.
15. The computer program product of claim 11 , wherein the rotation precoding vector is:
R
1
=
R
2
H
=
[
1.0000
0.3334
-
0.4714
ⅈ
0.3334
-
0.4714
ⅈ
0.3332
+
0.9429
ⅈ
]
.
16. A method comprising:
configuring a two-port channel state information reference signal resource across two cells of a wireless cellular network,
wherein the two ports are first and second ports, and
wherein first and second precoding vectors, respectively, are used for transmission on the first and second ports of the resource, and wherein a third precoding matrix indicator is based on simultaneous transmission of a rotation precoding vector by the first and second transmission points: and deriving a co-phasing factor for cooperative multipoint transmission based on the transmitted precoding vectors: and
based on the configuring and deriving, performing a coherent joint cooperative multipoint transmission.
17. The method of claim 16 , where at least one of the precoding vectors is chosen for alternate physical resource blocks from columns of a 2×2 rotation matrix.