Methods and Apparatuses for Reducing Feedback Overhead

Abstract

The embodiments herein relate to method performed by a radio network node, a network node, a method performed by a UE and a UE for reducing feedback overhead. The method performed by the UE comprises at least: decomposing each entry corresponding to a (i, j)-th combining coefficient of a precoder matrix into at least two coefficients; quantizing, separately, each of said at least two coefficients with a least one bit, and reporting information related to at least one phase value or at least one amplitude value or at least one phase value and an amplitude value of said quantized coefficient.

Claims

1. A method performed by a User Equipment (UE) for reducing feedback overhead related to Channel State Information (CSI) in a communications network employing Multi Input Multi Output (MIMO) operation, the method comprising: decomposing each entry corresponding to a (i,j)-th combining coefficient of a precoder matrix W.sub.2.sup.(r) into at least two coefficients, wherein r denotes a r-th transmission layer; said (i,j)-th combining coefficient is associated with a i-th beam and a j-th delay, and wherein each combining coefficient is associated with an amplitude and a phase-information; wherein the decomposed (i,j)-th combining-coefficient of said matrix W.sub.2.sup.(r) is given by:
[W.sub.2.sup.(r)].sub.i,j=a.sub.ib.sub.i,j, where b.sub.i,j is a complex-valued normalized combining coefficient associated with the i-th beam and j-th delay, and a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam; quantizing, separately, each of said at least two coefficients with at least one bit; and reporting information related to at least one phase value or at least one amplitude value or at least one phase value and an amplitude value of said quantized coefficient.

2. The method according to claim 1, wherein the precoder matrix W.sub.2.sup.(r) belongs to a precoder matrix F.sup.(r) being a product of a wideband first-stage precoder matrix F.sub.1.sup.(r) containing 2L spatial beams identical for all subbands, said matrix W.sub.2.sup.(r), and a matrix K.sub.F.sup.(r) composed of a number of basis vectors used to perform a compression in a frequency domain.

3. The method according to claim 1, wherein the precoder matrix W.sub.2.sup.(r) contains complex combining coefficients associated with 2L spatial beams, or only a subset of the 2L spatial beams, and/or basis vectors, or only a subset of the basis vectors.

4. The method according to claim 1, further comprising reporting only the phase values, only the amplitude values, or the amplitude and phase values of K strongest coefficients of matrix W.sub.2.sup.(r), where the value of the parameter K is configurable by a radio network node or gNB.

5. The method according to claim 1, further comprising applying different quantization levels for the phase values of the coefficients b.sub.i,j.

6. The method according to claim 2, further comprising reporting indices of Discrete Fourier Transform/Discrete Cosine Transform (DFT/DCT) vectors associated with the matrix K.sub.F.sup.(r).

7. The method according to claim 6, further comprising selecting the DFT/DCT vectors from a set of predefined DFT/DCT basis vectors, where each DFT/DCT basis vector is associated with an index.

8. The method according to claim 7, further comprising reporting a bitmap, where each bit in the bitmap is associated with an index “d” from the set of Discrete Fourier Transform/Discrete Cosine Transform (DFT/DCT) basis vectors associated with the matrix K.sub.F.sup.(r).

9. A User Equipment (UE) for reducing feedback overhead related to Channel State Information (CSI) in a communications network employing Multi Input Multi Output (MIMO) operation, the UE comprising a processor and a memory containing instructions executable by said processor whereby the UE is operative to: decompose each entry corresponding to a (i,j)-th combining coefficient of a precoder matrix W.sub.2.sup.(r) into at least two coefficients, wherein r denotes a r-th transmission layer; said (i,j)-th combining coefficient is associated with a i-th beam and a j-th delay, and wherein each combining coefficient is associated with an amplitude and a phase-information; wherein the decomposed (i,j)-th combining-coefficient of said matrix W.sub.2.sup.(r) is given by:
[W.sub.2.sup.(r)].sub.i,j=a.sub.ib.sub.i,j, where b.sub.i,j is a complex-valued normalized combining coefficient associated with the i-th beam and j-th delay, and a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam; quantize, separately, each of said at least two coefficients with at least one bit; and report information related to at least one phase value or at least one amplitude value or at least one phase value and an amplitude value of said quantized coefficient. 25

10. A method performed by a radio network node or gNB for reducing feedback overhead related to Channel State Information (CSI) in a communications network employing Multi Input Multi Output (MIMO) operation, the method comprising: receiving, from a User Equipment (UE), a report including information related to at least one phase value or at least one amplitude value or at least one phase value and an amplitude value of each quantized coefficient which is quantized with at least one bit by the UE; wherein each entry corresponding to a (i,j)-th combining coefficient of a precoder matrix W.sub.2.sup.(r) is decomposed by the UE into at least two coefficients, wherein r denotes a r-th transmission layer; said (i,j)-th combining coefficient is associated with a i-th beam and a j-th delay, and wherein each combining coefficient is associated with an amplitude and a phase-information; wherein the decomposed (i,j)-th combining-coefficient of said matrix W.sub.2.sup.(r) is given by:
[W.sub.2.sup.(r)].sub.i,j=a.sub.ib.sub.i,j, where b.sub.i,j is a complex-valued normalized combining-coefficient associated with the i-th beam and j-th delay, and a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam.

11. The method according to claim 10, further comprising configuring the UE to feedback the amplitude and/or phase values of K strongest coefficients of matrix W.sub.2.sup.(r), wherein the value of K is configurable by the radio network node or the gNB.

12. The method according to claim 10, further comprising configuring the UE to report only the amplitude and/or phase information for a subset of the coefficients in W.sub.2.sup.(r)

13. The method according to claim 10, further comprising configuring the UE to quantize the real-valued coefficients a.sub.i (and/or d.sub.j) equally with N.sub.a (and/or N.sub.d) bits, wherein a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam.

14. The method according to claim 10, further comprising configuring the UE to report only the phase values, only the amplitude values, or the amplitude and phase values of the quantized non-zero coefficients b.sub.i,j.

15. The method according to claim 10, further comprising configuring the UE to report a bitmap, where each bit in the bitmap is associated with an index “d” from a set of DFT/DCT basis vectors.

16. A radio network node or a gNB for reducing feedback overhead related to Channel State Information (CSI) in a communications network employing Multi Input Multi Output (MIMO) operation, the gNB comprising a processor and a memory containing instructions executable by said processor whereby the gNB is operative to: receive, from a User Equipment (UE), a report including information related to at least one phase value or at least one amplitude value or at least one phase value and an amplitude value of each quantized coefficient which is quantized with at least one bit by the UE; wherein each entry corresponding to a (i,j)-th combining coefficient of a precoder matrix W.sub.2.sup.(r) is decomposed by the UE into at least two coefficients, wherein r denotes a r-th transmission layer; said (i,j)-th combining coefficient is associated with a i-th beam and a j-th delay, and wherein each combining coefficient is associated with an amplitude and a phase-information; wherein the decomposed (i,j)-th combining-coefficient of said matrix W.sub.2.sup.(r) is given by:
[W.sub.2.sup.(r)].sub.i,j=a.sub.ib.sub.i,j, where b.sub.i,j is a complex-valued normalized combining-coefficient associated with the i-th beam and j-th delay, and a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam.

17. The method according to claim 1, further comprising reporting a bitmap wherein each bit in the bitmap is associated with said coefficient b.sub.i,j and when a bit is set to one, the phase and amplitude values associated with the coefficient b.sub.i,j are reported.

18. The method according to claim 17, wherein the bitmap comprises K or less than K ‘1’s.

19. The method according to claim 1, further comprising reporting the amplitude and phase information with respect to the non-zero coefficients of the quantized matrix W.sub.2.sup.(r).

20. The method according to claim 1, further comprising reporting information related to only the phase values, only the amplitude values, or only the amplitude and the phase values of the quantized non-zero coefficients b.sub.i,j.

21. The method according to claim 10, further comprising receiving from the UE a bitmap wherein each bit in the bitmap is associated with said coefficient b.sub.i,j and when a bit is set to one, the phase and amplitude values associated with the coefficient b.sub.i,j are reported.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Examples of embodiments and advantages of the embodiments herein are described in more detail with reference to attached drawings in which:

[0041] FIG. 1 depicts an example network scenario wherein embodiments herein may be employed.

[0042] FIG. 2 illustrates amplitude distribution of the combining coefficients in matrix W.sub.2.sup.(r)

[0043] FIG. 3 Amplitude distribution of coefficients b.sub.i,j for scheme 3 according to an embodiment herein.

[0044] FIG. 4 illustrates a flowchart of a method performed by a UE according to some exemplary embodiments herein.

[0045] FIG. 5 is a block diagram depicting a UE according to exemplary embodiments herein.

[0046] FIG. 6 is a block diagram depicting a radio network node according to exemplary embodiments herein.

DETAILED DESCRIPTION

[0047] In the following is presented a detailed description of the exemplary embodiments in conjunction with the drawings, in several scenarios, to enable easier understanding of the solution(s) described herein.

[0048] As previously described, in 3GPP new radio system, two types of codebook, namely Type-1 and Type-2 codebook, have been standardized for the CSI feedback in the support of advanced MIMO operation.

[0049] The present embodiments address the problem of how to efficiently quantize and report the transformed combining coefficients in order to reduce CSI feedback overhead in a communications network employing beamforming.

A. Quantization and Reporting of Complex Combining Coefficients of Matrix W.sub.2.sup.(r):

[0050] W.sub.2.sup.(r) which was previously presented in equation (3) and repeated below is the overall precoder which may be written as

F.sup.(r)=F.sub.1.sup.(r)W.sub.2.sup.(r)K.sub.F.sup.(r).sup.T,  (3)

[0051] Each complex coefficient in W.sub.2.sup.(r) in (3) is associated with a specific delay (in the transformed domain) as each DFT/DCT basis vector models a linear phase increase over the subbands. W.sub.2.sup.(r) contains complex-combining coefficients. The values of N.sub.1 and N.sub.2 are design parameters and may be included in a configuration of an antenna array at a gNB, which antenna array may for example be dual-polarized, although the embodiments herein are not restricted to dual-polarized antenna arrays.

[0052] An approach for quantizing the amplitude and phase values of the coefficients in W.sub.2.sup.(r), according to an exemplary embodiment, is to quantize directly each amplitude and phase value with N.sub.1 and N.sub.2 bits, respectively.

[0053] For example, assuming that matrix W.sub.2.sup.(r) contains UD coefficients, then UD(N.sub.1+N.sub.2) bits are required for reporting the amplitude and phase information of W.sub.2.sup.(r) to the gNB. However, as mentioned previously, each of the U beams are typically associated with only a set of delays and not all D delays. Therefore, the matrix W.sub.2.sup.(r) may be considered as a sparse matrix where a large number of the coefficients are close to zero.

[0054] In the following description, the matrix W.sub.2.sup.(r)∈.sup.U×D in equation (3) may contain the complex combining coefficients associated with all (2L) spatial beams (i.e., U=2L), or only a subset of spatial beams (e.g., U<2L), and/or all (V) delays/basis vectors (i.e., D=V), or only a subset of delays/basis vectors (e.g., D<V).

1. Selection and Reporting of Non-Zero Coefficients by Using a Bitmap

[0055] In order to save feedback overhead for reporting a quantized version of W.sub.2.sup.(r), an approach according to an exemplary embodiment is to feedback only the amplitude and phase-information of the non-zero coefficients of matrix W.sub.2.sup.(r) and to indicate by a bitmap the indices of the reported coefficients. For example, the first bit in the bitmap may be associated with the first coefficient, the second bit with the first coefficient of matrix W.sub.2.sup.(r) and so on. When a bit in the bitmap is set to ‘1’ the corresponding coefficient (amplitude and/or phase) may be reported and otherwise not. In this way, the overhead for reporting the combining coefficients may be largely reduced; however, the number of feedback bits is not fixed and may vary for each reporting instance. (see below how he number of feedback bits may be fixed).

2. Selection and Reporting of K Strongest Coefficients

[0056] In order to fix the number of feedback bits for reporting the combining coefficients, the receiver may be configured to feedback the amplitude and/or phase values of the K strongest coefficients of matrix W.sub.2.sup.(r), where the value of the parameter K is configurable by the gNB. The K strongest coefficients may be represented by the K entries having the highest amplitude (or power) over the elements in W.sub.2.sup.(r). When a bit in the bitmap is set to ‘1’, the UE may be configured to report the phase and/or amplitude values of the associated coefficient b.sub.i,j to the gNB. The bitmap may hence contain no more than K ‘1’s.

[0057] In order to increase the flexibility of selecting the coefficients and to improve the system performance, the receiver (e.g. a UE or another gNB) may be configured to select K.sub.u strongest coefficients per row/beam out of matrix W.sub.2.sup.(r), where the parameters K.sub.u may be configurable by the gNB (transmitter). Note that the values of K.sub.u may be identical for a set of rows/beams of matrix W.sub.2.sup.(r). In such a case, a single parameter R may be used to configure multipole parameters K.sub.d.

[0058] Similarly, the receiver may be configured to select K.sub.d strongest coefficients per column/delay out of matrix W.sub.2.sup.(r), where the parameters K.sub.d may be configurable by the gNB. Note that the values of K.sub.d may also be identical for a set of columns/delays of matrix W.sub.2.sup.(r). In such a case, a single parameter O is used to configure multiple parameters K.sub.d.

3. Selection of Submatrices of F.sub.2.sup.(r) for Reporting

[0059] According to an exemplary embodiment, to reduce the overhead for reporting the coefficients in W.sub.2.sup.(r), the receiver may be configured to report only the amplitude and/or phase information for a subset of the coefficients in W.sub.2.sup.(r). The subset of coefficients in W.sub.2.sup.(r) may contain the combining coefficients associated with the “strongest” beams and/or “strongest” delays. In such a case, the rows and/or columns of W.sub.2.sup.(r) may be assumed to be ordered in such a way that the combining-coefficients satisfy:

[00001]$\underset{\forall j}{.Math.}.Math.{\left[W_2^{\left(r\right)}\right]}_{1,j}.Math.\ge \underset{\forall j}{.Math.}.Math.{\left[W_2^{\left(r\right)}\right]}_{2,j}.Math.\ge \mathrm{.Math.}\ge \underset{\forall j}{.Math.}.Math.{\left[W_2^{\left(r\right)}\right]}_{U,j}.Math.$$\mathrm{and}\text{/}\mathrm{or}$${\Sigma }_{\forall i}.Math.{\left[W_2^{\left(r\right)}\right]}_{i,1}.Math.\ge {\Sigma }_{\forall i}.Math.{\left[W_2^{\left(r\right)}\right]}_{i,2}.Math.\ge \mathrm{.Math.}\ge {\Sigma }_{\forall i}.Math.{\left[W_2^{\left(r\right)}\right]}_{i,D}.Math..$

[0060] In an example, the receiver may be configured to report the amplitude and/or phase information of the coefficients associated with the U′ “strongest” beams. The receiver may then report the amplitude and/or phase information of the coefficients: {[W.sub.2.sup.(r)].sub.i,j: i=1, . . . , U′, ∀.sub.j}.

[0061] In another example, the receiver may be configured to report the amplitude and/or phase information of the coefficients associated with the D “strongest” delays. The receiver may report the amplitude and/or phase information of the coefficients: {[W.sub.2.sup.(r)].sub.i,j: j=1, . . . , D′, ∀i}.

[0062] In another example, the receiver may be configured to report the amplitude and/or phase information of the coefficients associated with the U′ “strongest” beams and D “strongest” delays. The receiver may report the amplitude and/or phase information of the coefficients: {[W.sub.2.sup.(r)].sub.i,j: i=1, . . . , U′, j=1, . . . , D′}.

[0063] In order to further significantly reduce the feedback overhead for reporting a quantized version of W.sub.2.sup.(r), three decomposition and quantization schemes for W.sub.2.sup.(r) are described according to some embodiments herein:

1. Scheme 1

[0064] The first scheme decomposes the (i,j)-th combining-coefficient of matrix W.sub.2 associated with the i-th beam and j-th delay into two coefficients, a.sub.i and b.sub.i,j,

[W.sub.2.sup.(r)].sub.i,j=a.sub.ib.sub.i,j,

where b.sub.i,j is the complex-valued normalized combining-coefficient associated with the i-th beam and j-th delay, and a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam. Note that the calculation of the values a.sub.i is implementation specific.

2. Scheme 2

[0065] The second scheme decomposes the (i,j)-th combining-coefficient of matrix W.sub.2.sup.(r) associated with the i-th beam and j-th delay into two coefficients, d.sub.j and b.sub.i,j,

[W.sub.2.sup.(r)].sub.i,j=d.sub.jb.sub.i,j,

where b.sub.i,j is the complex-valued normalized combining-coefficient associated with the i-th beam and j-th delay, and d.sub.j is a real-valued coefficient representing a common amplitude for the combining coefficients for all beams associated with the j-th delay. Note that the calculation of the values d.sub.j is implementation specific.

3. Scheme 3

[0066] The third scheme decomposes the (i,j)-th combining-coefficient of matrix W.sub.2.sup.(r) (associated with the i-th beam and j-th delay into three coefficients, a.sub.j and b.sub.i,j,

[W.sub.2.sup.(r)].sub.i,j=a.sub.id.sub.jb.sub.i,j,

where b.sub.i,j is the complex-valued normalized combining-coefficient associated with the i-th beam and j-th delay, d.sub.j is a real-valued coefficient representing a common amplitude for the combining coefficients for all beams associated with the j-th delay, and a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam. Note that the calculation of the values a.sub.i and d.sub.j are implementation specific.

[0067] The receiver may be configured to represent the combining coefficients or only a set of the combining coefficients in W.sub.2.sup.(r) by scheme 1, scheme 2, or scheme 3. Note that the proposed schemes can also be combined for representing the combining coefficients. For example, the receive may be configured to represent a first set of combining coefficient of W.sub.2.sup.(r) by scheme 1 or scheme 2, and a second set of the combining coefficients of W.sub.2.sup.(r) by scheme 3.

4. Quantization of Coefficients a.sub.i, b.sub.i,j and d.sub.j

[0068] After the decomposition of each entry of W.sub.2.sup.(r) into the coefficients a.sub.i and b.sub.i,j, or d.sub.j and b.sub.i,j, or a.sub.i, d.sub.j and b.sub.i,j, the coefficients are quantized separately in according with an embodiment. The main advantage of the above decomposition schemes is that the amplitude values of b.sub.i,j may be quantized with a significantly lower number of bits than the amplitude values of the combining-coefficients in W.sub.2.sup.(r). Therefore, the feedback overhead for reporting the amplitude values of the entries in W.sub.2.sup.(r) advantage be significantly reduced when applying one of the proposed decomposition schemes.

[0069] For example, the receiver may be configured to quantize the real-valued coefficients a.sub.i (and/or d.sub.j) equally with N.sub.a (and/or N.sub.d) bits. Each complex-valued coefficient b.sub.i,j may be quantized with N.sub.b,1 and N.sub.b,2 bits for the amplitude and phase, respectively, where N.sub.b,1 may be lower than N.sub.b,2.

Feedback Overhead Saving for Scheme 1:

[0070] For scheme 1, assuming there are UD combining coefficients contained in matrix W.sub.2.sup.(r)∈.sup.U×D, a total of UN.sub.a+UD(N.sub.b,1 N.sub.b,2) bits are required for reporting the amplitude and phase information of the coefficients a.sub.i and b.sub.i,j. In contrast, when directly quantizing the entries of matrix W.sub.2.sup.(r) with N.sub.a bits per amplitude and N.sub.a bits per phase, 2UDN.sub.a bits are required for reporting the coefficients of W.sub.2.sup.(r). Assuming that the phase values of b.sub.i,j are quantized equally with N.sub.b,2=N.sub.a bits, the amount of feedback that may be saved by scheme 1 may be given by U(D(N.sub.a−N.sub.b,1)−N.sub.a) bits. For typical values for the number of beams (U), delays (D) and quantization bits (N.sub.a) of U=8, D=4, N.sub.a=4, and N.sub.b,1=2, a total of 32 bits may be saved for the amplitude and phase reporting compared to the direct quantization of the entries in W.sub.2.sup.(r).

Feedback Overhead Saving for Scheme 2:

[0071] For scheme 2, assuming again there are UD combining coefficients contained in matrix W.sub.2.sup.(r)∈.sup.U×D, a total of DN.sub.d+UD(N.sub.b,1+N.sub.b,2) bits are required for reporting the amplitude and phase information of the coefficients d.sub.j and b.sub.i,j. Assuming that the phase values of b.sub.i,j are quantized equally with N.sub.b,2=N.sub.d bits, the amount of feedback that may be saved by scheme 2 is given by D(U(N.sub.d−N.sub.b,1)−N.sub.d) bits. For typical values for the number of beams (U), delays (D) and quantization bits (N.sub.d) of U=8, D=4, N.sub.d=4, and N.sub.b,1=2, a total of 48 bits may be saved for the amplitude and phase reporting compared to the direct quantization of the entries in W.sub.2.sup.(r).

Feedback Overhead Saving for Scheme 3:

[0072] For scheme 3, assuming again there are UD combining coefficients contained in matrix W.sub.2.sup.(r)∈.sup.U×D, a total of UN.sub.a+DN.sub.d+UD(N.sub.b,1+N.sub.b,2) bits are required for reporting the amplitude and phase information of the coefficients a.sub.i, d.sub.j and b.sub.i,j. Assuming that the real-valued coefficients a.sub.i and d.sub.j are equally quantized with N.sub.a=N.sub.d bits and the phase values of b.sub.i,j are quantized with N.sub.b,2=N.sub.a bits, the amount of feedback that may be saved by scheme 3 is given by UD(N.sub.a−N.sub.b,1)−(U+D)N.sub.a bits. For typical values for the number of beams (U), delays (D) and quantization bits (N.sub.a) of U=8, D=4, N.sub.a=4, and N.sub.b,1=1, a total of 48 bits may be saved for the amplitude and phase information reporting compared to the direct quantization of the entries in W.sub.2.sup.(r).

5. Selection and Reporting of Non-Zero Coefficients b.sub.i,j by Using a Bitmap

[0073] To reduce the overhead for reporting the coefficients in W.sub.2.sup.(r), the UE may be configured to report only the phase values, only the amplitude values, or the amplitude and phase values of the quantized non-zero coefficients b.sub.i,j. To indicate the indices of the quantized non-zero coefficients b.sub.i,j, the receiver may be configured to report in addition to the amplitude and/or phase information a bitmap, where each bit in the bitmap is associated with a coefficient b.sub.i,j. For example, the first bit may be associated with coefficient b.sub.i,j, the second bit with coefficient b.sub.1,2, etc. When a bit in the bitmap is set to one, the UE may report the phase and/or amplitude values of the associated coefficient b.sub.i,j to the gNB. The bitmap may hence contain P “1”'s, where P corresponds to the number of non-zero coefficients b.sub.i,j.

6. Selection and Reporting of K Strongest Coefficients b.sub.i,j

[0074] To reduce the overhead for reporting the coefficients in W.sub.2.sup.(r) and to fix the number of feedback bits for CSI reporting, the UE may be configured to report only the phase values, only the amplitude values, or the amplitude and phase values of the K strongest coefficients of matrix W.sub.2.sup.(r), where the value of the parameter K is configurable by the gNB.

[0075] The K strongest coefficients may be represented by the K entries having the highest amplitude (or power) over the elements in W.sub.2.sup.(r). To indicate the indices of the K strongest elements, the receiver may be configured to report in addition to the K amplitude and/or phase information a bitmap, where each bit in the bitmap is associated with a coefficient b.sub.i,j. For example, the first bit may be associated with coefficient b.sub.1,1, the second bit with coefficient b.sub.1,2, etc. When a bit in the bitmap is set to one, the UE may report the phase and/or amplitude values of the associated coefficient b.sub.i,j to the gNB. The bitmap may hence contain K “1”'s. In the case the number of non-zero amplitude values of the quantized matrix W.sub.2.sup.(r) is less than K, the UE may report only the amplitude and/or phase information with respect to the non-zero coefficients of the quantized matrix W.sub.2.sup.(r). The bitmap may then contain less than K “1”'s.

[0076] The amount of feedback required for reporting the amplitude and phase information is given (for scheme 3) by UN.sub.a+DN.sub.a+K(N.sub.b,1+N.sub.b,2) bits for the amplitude and phase information of W.sub.2.sup.(r) and UD bits for the bitmap. Hence, a total of (UD−K)(N.sub.b,1+N.sub.b,2)−UD bits may be saved compared to the case of reporting the amplitude and phase information of all coefficients in W.sub.2.sup.(r) to the gNB.

[0077] In order to increase the flexibility of selecting the coefficients and to improve the system performance, the receiver may be configured to select K.sub.u strongest coefficients per row/beam out of matrix W.sub.2.sup.(r), where the parameters K.sub.u may be configurable by the gNB. Note that the values of K.sub.u may be identical for a set of rows/beams of matrix W.sub.2.sup.(r). In such a case, a single parameter R may be used to configure multipole parameters K.sub.d.

[0078] Similarly, the receiver may be configured to select K.sub.d strongest coefficients per column/delay out of matrix W.sub.2.sup.(r), where the parameters K.sub.d may be configurable by the gNB. Note that the values of K.sub.d can also be identical for a set of columns/delays of matrix W.sub.2.sup.(r). In such a case, a single parameter O is used to configure multiple parameters K.sub.d.

7. Reporting of Phase-Only Information of Matrix B without Bitmap Indication and 1-Bit Amplitude Quantization

[0079] FIG. 2 and FIG. 3 show the amplitude distribution of the combining coefficients in matrix W.sub.2.sup.(r) and the amplitude distribution of coefficients b.sub.i,j when applying the proposed third decomposition scheme according to previously described embodiment.

[0080] As shown, when applying the proposed third decomposition scheme, the coefficients b.sub.i,j may be efficiently represented by only two quantization levels in contrast to combining coefficients in matrix W.sub.2.sup.(r). The amplitude information of the coefficients b.sub.i,j can therefore be quantized using only one bit for the amplitude values. The receiver may therefore to be configured with N.sub.b,1=1 and each amplitude value may be represented by two quantization levels “a” and “b”, where for example “a” and/or “b” are given by “a=0” and “b=1”. The bits in the bitmap then directly correspond to the two quantization levels of the amplitude values of the coefficients b.sub.i,j and an additional report of the amplitude values of b.sub.i,j is not required. As N.sub.b,1=1, the amount of feedback for reporting the phase values is drastically reduced as well, since a reporting of the phase values associated with zero amplitude coefficients is not required. The same quantization levels may also be used for scheme 1 and scheme 2 for quantizing coefficients b.sub.i,j.

[0081] Note that the above also holds for scheme 1 and scheme 2, i.e. the receiver may be configured with N.sub.b,1=1 each amplitude value may be represented by two quantization levels “a” and “b”, where for example “a” and/or “b” are given by “a=0” and “b=1”.

8. Different Quantization Levels for the Phase Values of b.sub.i,j

[0082] To further reduce the overhead for reporting the phase information of the coefficients b.sub.i,j, the receiver may be configured to apply different quantization levels for the phase values of the coefficients b.sub.i,j. For example, the receiver may configured to use N.sub.b,2′ bits for the phase values associated with the non-zero coefficients and the U′ strongest beams and N.sub.b,2″ bits for the phase values associated with the non-zero coefficients and the remaining beams, where N.sub.b,2′>N.sub.b,2″.

B. Reporting of the Indices Associated with the Selected DFT/DCT Vectors:

[0083] In addition to the reporting of quantized coefficients of matrix W.sub.2.sup.(r), the following describes an approach for efficiently reporting the indices of the DFT/DCT vectors associated with the complex combining coefficients of matrix K.sub.F.sup.(r) according with an exemplary embodiment herein. The DFT/DCT vectors are selected from a set of predefined DFT/DCT basis vectors, where each DFT/DCT basis vector is associated with an index. For example, when there are S DFT/DCT basis vectors, the first DFT/DCT basis vector is associated with a first index (“1”), the second DFT/DCT basis vector is associated with a second index (“1”), and the last DFT/DCT basis vector is associated with the index (“S”). When reporting D selected DFT/DCT basis vectors, D┌log.sub.2(S)┐ feedback bits are required.

[0084] Instead of directly reporting the indices of the DFT/DCT basis vectors, the receiver may be configured to report a bitmap, where each bit in the bitmap is associated with an index “d” from the set of basis vectors.

[0085] For example, the first bit may be associated with index 1, the second bit with index 2, etc. A “1” in a bitmap at position “d” indicates then the selection of the DFT/DCT vector associated with the index “d”.

[0086] As an example, when the number of subbands S=13 and D=6, the amount of feedback required to report the indices of the selected DFT/DCT vectors is given by D┌log.sub.2(S)┐=24, where in contrast only S=13 bits are required when using a bitmap.

[0087] According to an embodiment, when the reported bitmap is comprised of a “1” at position “1”, then the amplitude and phase values of the leading beam must be considered as follows:

[0088] A “1” at position 1 of the bitmap indicates that the amplitude and phase of the combining coefficient of the leading beam associated with index “1” are given by 1 and 0, respectively, and are not reported. The amplitude and phase values of the remaining combining coefficients of the leading beam associated with other indices are given by 0 and 0, respectively, and are not reported. The amplitude and phase associated with the leading beam are known at the gNB.

[0089] As initially described, the proposed solutions are suitable for the 3GPP Rel-15 framework. Below is presented modifications (1)-(7) that are herein suggested by the inventors to the Rel. 15 framework according to some embodiments herein [0090] (1) The number of leading beams (B) for which the amplitude values of b.sub.i,j shall be reported to the gNB is given by B=2L or 2L−1 for the proposed CSI reporting using DFT/DCT transformation instead of B=4, 4, and 6 for L=2, 3, and 4 as in current Rel. 15, where L is the number of spatial beams configured. [0091] (2) All quantized amplitude and phase values of b.sub.i,j associated with the first leading beam are not reported to the gNB. [0092] (3) When N.sub.a=3, the amplitude set for quantizing a.sub.i is given

{1, √{square root over (0.5)}, √{square root over (0.25)}, √{square root over (0.125)}, √{square root over (0.0625)}, √{square root over (0.0313)}, √{square root over (0.0156)}, 0} [0093] (4) When N.sub.d=3, the amplitude set for quantizing d.sub.j is given uniform

{1, √{square root over (0.5)}, √{square root over (0.25)}, √{square root over (0.125)}, √{square root over (0.0625)}, √{square root over (0.0313)}, √{square root over (0.0156)}, 0} [0094] (5) When N.sub.d=2, the amplitude set for quantizing d.sub.j is given

{1, √{square root over (0.5)}, √{square root over (0.25)}, 0} [0095] (6) The amplitude set for quantization of b.sub.i,j is given {0, 1}. [0096] (7) The phase set for quantizing b.sub.i,j is given by a 8 PSK, or 16 PSK constellation.

[0097] It should be mentioned that differently to equation (3) above, one may introduce in the following a new transformation/decomposition of the U×S matrix F.sub.2.sup.(r) that may be combined with the above mentioned three decomposition/quantization schemes. Compared to equation (3), the following transformation/decomposition reduces further the overhead of reporting the combining coefficients when combined with the above-mentioned three decomposition/quantization schemes. The frequency domain combining coefficient matrix F.sub.2.sup.(r) is decomposed into three matrices,

F.sub.2.sup.(r)=A.sup.(r)F.sub.2.sup.(r)B.sup.(r),

where [0098] A.sup.(r) is a real-valued U×U diagonal matrix containing U “wideband” amplitude coefficients of the respective rows/beams of matrix F.sub.2.sup.(r), [0099] F.sub.2.sup.(r) is a complex-valued U×S matrix containing US “subband” combining coefficients of the U beams and S subbands, and [0100] B.sup.(r) is a real-valued S×S diagonal matrix containing S values on its diagonal.

[0101] The matrix A.sup.(r) contains the values of the “average” amplitudes of the rows/beams of the combining coefficients of matrix F.sub.2.sup.(r). The matrix B.sup.(r) is a normalization matrix that forces the S combining coefficients in the row of matrix F.sub.2.sup.(r) which are associated with the leading beam to be “1”. Note that the leading beam is associated with the highest “wideband” amplitude coefficient of matrix A.sup.(r). By considering now a transformation on the subband coefficient matrix F.sub.2.sup.(r), the frequency domain combining coefficients F.sub.2.sup.(r) may be written as.

F.sub.2.sup.(r)=A.sup.(r)W.sub.2.sup.(r)C.sup.(r)K.sub.F.sup.(r).sup.TB.sup.(r),

=W.sub.2.sup.(r)K.sub.F.sup.(r).sup.TB.sup.(r)

where W.sub.2.sup.(r)=A.sup.(r)W.sub.2.sup.(r)C.sup.(r) with W.sub.2.sup.(r)∈.sup.2L×V containing 2L×V complex-combining coefficients associated with the V basis vectors in matrix K.sub.F.sup.(r)∈.sup.V×S (see equation (3)) and C.sup.(r) is a V×V diagonal matrix containing the “common” amplitude values of the V basis vectors.

[0102] The quantization and reporting of W.sub.2.sup.(r) is as previously described

[0103] For Reporting of B.sup.(r) the receiver (or e.g. the UE) may be configured to report or not to report the S coefficients of the diagonal matrix B.sup.(r) using N.sub.B bits per coefficients. When the receiver is configured not to report the S coefficients, the transmitter (e.g. the gNB) assumes that the matrix B.sup.(r) is given by an identity matrix when reconstructing the precoder matrix. Note that the coefficients in matrix B.sup.(r) may be represented by only two quantization levels “a” and “b”, where for example “a” and/or “b” are given by “a=√{square root over (0.5)}” and “b=1”.

[0104] It should be mentioned that all parameters and denoted values may take any suitable values and some or all are design parameters which when used achieve the technical effects and advantages of the embodiments described in this disclosure.

[0105] Referring to FIG. 4, there is illustrated a flowchart of a method performed by a UE 500 for reducing feedback overhead related to CSI in a communications network employing MIMO operation, the method comprises: [0106] (401) decomposing each entry corresponding to a (i, j)-th combining coefficient of a precoder matrix, W.sub.2.sup.(r), into at least two coefficients, wherein r denotes a r-th transmission layer; said (i, j)-th combining coefficient is associated with a i-th beam and a j-th delay, and wherein each combining coefficient is associated with an amplitude and a phase-information; [0107] (402) quantizing, separately, each of said at least two coefficients with a least one bit, and [0108] (403) reporting information related to at least one phase value or at least one amplitude value or at least one phase value and an amplitude value of said quantized coefficient.

[0109] The method performed by the UE, according to some embodiments herein is presented in the subject-matter of each of the claims listed below.

[0110] In order to perform the previously described process or method steps related to the UE, embodiments herein include a UE for reducing feedback overhead in a communications network. As shown in FIG. 5, the UE 500 comprises a processor 510 or processing circuit or a processing module or a processor or means 510; a receiver circuit or receiver module 540; a transmitter circuit or transmitter module 550; a memory module 520 a transceiver circuit or transceiver module 530 which may include the transmitter circuit 550 and the receiver circuit 540. The UE 500 further comprises an antenna system 560 which includes antenna circuitry for transmitting and receiving signals to/from at least a radio network node or gNB. The antenna system may employ beamforming as previously described.

[0111] The UE 500 may operate in any radio access technology including 2G, 3G, 4G or LTE, LTE-A, 5G, WLAN, and WiMax etc. that support beamforming technology.

[0112] The processing module/circuit 510 includes a processor, microprocessor, an application specific integrated circuit (ASIC), field programmable gate array (FPGA), or the like, and may be referred to as the “processor 510.” The processor 510 controls the operation of the network node 500 and its components. Memory (circuit or module) 520 includes a random access memory (RAM), a read only memory (ROM), and/or another type of memory to store data and instructions that may be used by processor 510. In general, it will be understood that the UE 500 in one or more embodiments includes fixed or programmed circuitry that is configured to carry out the operations in any of the embodiments disclosed herein.

[0113] In at least one such example, the UE 500 includes a microprocessor, microcontroller, DSP, ASIC, FPGA, or other processing circuitry that is configured to execute computer program instructions from a computer program stored in a non-transitory computer-readable medium that is in, or is accessible to the processing circuitry. Here, “non-transitory” does not necessarily mean permanent or unchanging storage, and may include storage in working or volatile memory, but the term does connote storage of at least some persistence. The execution of the program instructions specially adapts or configures the processing circuitry to carry out the operations disclosed herein including any one of the claims listed below. Further, it will be appreciated that the UE 500 may comprise additional components not shown in FIG. 5.

[0114] As previously presented, the UE 500 is operative to: decompose each entry corresponding to a (i, j)-th combining coefficient of a precoder matrix W.sub.2.sup.(r), into at least two coefficients, wherein r denotes a r-th transmission layer; said (i, j)-th combining coefficient is associated with a i-th beam and a j-th delay, and wherein each combining coefficient is associated with an amplitude and a phase-information; quantize, separately, each of said at least two coefficients with a least one bit, and reporting information related to at least one phase value or at least one amplitude value or at least one phase value and an amplitude value of said quantized coefficient.

[0115] The UE is configured to decompose using a first scheme, the (i,j)-th combining-coefficient of said matrix W.sub.2.sup.(r) associated with the i-th beam and j-th delay into two coefficients, a.sub.i and b.sub.i,j,

[W.sub.2.sup.(r)].sub.i,j=a.sub.ib.sub.i,j,

where b.sub.i,j is complex-valued normalized combining-coefficient associated with the i-th beam and j-th delay, and a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam.

[0116] The UE 500 is configured to decompose using a second scheme, the (i,j)-th combining-coefficient of matrix W.sub.2.sup.(r) associated with the i-th beam and j-th delay into two coefficients, d.sub.j and b.sub.i,j,

[W.sub.2.sup.(r)].sub.i,j=d.sub.jb.sub.i,j,

where b.sub.i,j is the complex-valued normalized combining-coefficient associated with the i-th beam and j-th delay, and d.sub.j is a real-valued coefficient representing a common amplitude for the combining coefficients for all beams associated with the j-th delay.

[0117] The UE 500 is configured to decompose, using a third scheme the (i,j)-th combining-coefficient of matrix W.sub.2.sup.(r) associated with the i-th beam and j-th delay into three coefficients, a.sub.j, d.sub.j and b.sub.i,j,

[W.sub.2.sup.(r)].sub.i,j=a.sub.id.sub.jb.sub.i,j,

where b.sub.i,j is the complex-valued normalized combining-coefficient associated with the i-th beam and j-th delay, d.sub.j is a real-valued coefficient representing a common amplitude for the combining coefficients for all beams associated with the j-th delay, and a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam.

[0118] The UE 500 is configured to represent the combining coefficients or only a set of the combining coefficients in W.sub.2.sup.(r) by the first scheme, the second scheme, or the third scheme.

[0119] Additional details relating to the functionality or actions performed by the UE have already been disclosed (see method steps performed by the UE).

[0120] There is also provided a computer program comprising instructions which when executed on at least one processor 510 of the UE, cause the processor 510 to carry out the method according to any one of the claims listed below.

[0121] There is also provided a method performed by a radio base station or a radio network node or a gNB 700 according to some exemplary embodiments:

[0122] The method for reducing feedback overhead related to CSI in the communications network employing MIMO operation comprises:

[0123] (601) receiving, from a UE 500 a report including information related to at least one phase value or at least one amplitude value or at least one phase value and an amplitude value each quantized coefficient which is quantized with a least one bit by a UE 500; wherein each entry corresponding to a (i, j)-th combining coefficient of a precoder matrix W.sub.2.sup.(r), is decomposed by the UE 500 into at least two coefficients, wherein r denotes a r-th transmission layer; said (i, j)-th combining coefficient is associated with a i-th beam and a j-th delay, and wherein each combining coefficient is associated with an amplitude and a phase-information;

[0124] The method comprises configuring the UE to feedback the amplitude and/or phase values of K strongest coefficients of matrix W.sub.2.sup.(r), wherein the value of K is configurable by radio network node (700) or the gNB.

[0125] The method comprises configuring the UE comprises configuring the UE to select K.sub.u strongest coefficients per row/beam out of matrix W.sub.2.sup.(r), where the parameters K.sub.u is configurable by the radio base station or gNB.

[0126] The method comprises configuring the UE to select K.sub.d strongest coefficients per column/delay out of matrix W.sub.2.sup.(r), where the parameters K.sub.d is configurable by the radio base station (700) or gNB.

[0127] The method comprises configuring the UE to report only the amplitude and/or phase information for a subset of the coefficients in W.sub.2.sup.(r).

[0128] The method comprises configuring the UE to represent the combining coefficients or only a set of the combining coefficients in W.sub.2.sup.(r) by the first scheme or the second scheme or the third scheme.

[0129] The method comprises configuring the UE to quantize the real-valued coefficients a.sub.i (and/or d.sub.j) equally with N.sub.a (and/or N.sub.d) bits, wherein a.sub.i is a real-valued coefficient representing a common amplitude for the combining coefficients for all delays associated with the i-th beam.

[0130] The method comprises configuring the UE comprises configuring the UE to report only the phase values, only the amplitude values, or the amplitude and phase values of the quantized non-zero coefficients b.sub.i,j.

[0131] The method comprises configuring the UE configuring the UE to report a bitmap, where each bit in the bitmap is associated with an index “d” from a set of DFT/DCT basis vectors.

[0132] Additional functions performed by the radio network node 700 has already been disclosed and need no repetition.

[0133] In order to perform the previously described process or method steps related to the radio network node, some embodiments herein include a radio network node 700 for reducing feedback overhead in a communications network.

[0134] As shown in FIG. 7, the radio network node 700 comprises a processor 710 or processing circuit or a processing module or a processor or means 710; a receiver circuit or receiver module 740; a transmitter circuit or transmitter module 770; a memory module 720 a transceiver circuit or transceiver module 730 which may include the transmitter circuit 770 and the receiver circuit 740. The radio network node 700 further comprises an antenna system 760 which includes antenna circuitry for transmitting and receiving signals to/from at least network nodes and other UEs etc. The antenna system employs beamforming as previously described.

[0135] The radio network node 700 may operate in any radio access technology including 2G, 3G, 4G or LTE, LTE-A, 5G, WLAN, and WiMax etc. that support beamforming technology.

[0136] The processing module/circuit 710 includes a processor, microprocessor, an application specific integrated circuit (ASIC), field programmable gate array (FPGA), or the like, and may be referred to as the “processor 710.” The processor 710 controls the operation of the UE 700 and its components. Memory (circuit or module) 720 includes a random access memory (RAM), a read only memory (ROM), and/or another type of memory to store data and instructions that may be used by processor 710. In general, it will be understood that the radio network node 700 in one or more embodiments includes fixed or programmed circuitry that is configured to carry out the operations in any of the embodiments disclosed herein.

[0137] In at least one such example, the radio network node 700 includes a microprocessor, microcontroller, DSP, ASIC, FPGA, or other processing circuitry that is configured to execute computer program instructions from a computer program stored in a non-transitory computer-readable medium that is in, or is accessible to the processing circuitry. Here, “non-transitory” does not necessarily mean permanent or unchanging storage, and may include storage in working or volatile memory, but the term does connote storage of at least some persistence. The execution of the program instructions specially adapts or configures the processing circuitry to carry out any the operations disclosed herein. Further, it will be appreciated that the radio network node 700 may comprise additional components not shown in FIG. 7. For reducing feedback overhead related to Channel State Information, CSI, in a communications network employing Multi Input Multi Output, MIMO operation, the gNB is operative to perform any one of the claims listed below.

[0138] Additional functions performed by the radio network node 700 have already been disclosed and need not be repeated again.

[0139] There is also provided a computer program comprising instructions which when executed on at least one processor 710 of the radio network node 700, cause the at least said one processor 710 to carry out the method according to any of the claims listed below.

[0140] A carrier containing the computer program is also provided, wherein the carrier is one of a computer readable storage medium; an electronic signal, optical signal or a radio signal.

[0141] As evident from the detailed description presented above, several advantages are achieved by the disclosed embodiments.

[0142] Throughout this disclosure, the word “comprise” or “comprising” has been used in a non-limiting sense, i.e. meaning “consist at least of”. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. The embodiments herein may be applied in any wireless systems including GSM, 3G or WCDMA, LTE or 4G, LTE-A (or LTE-Advanced), 5G, WiMAX, WiFi, satellite communications, TV broadcasting etc. that may employ beamforming technology.

REFERENCES

[0143] [1] Samsung, “Revised WID: Enhancements on MIMO for NR”, RP-182067, 3GPP RAN #81, Gold Coast, Australia, Sep. 10-13, 2018. [0144] [2] Fraunhofer I I S, Fraunhofer H H I, “Enhancements on Type II CSI reporting scheme,” R1-1806124, Busan, South Korea, May 21-25, 2018. [0145] [3] Fraunhofer I I S, Fraunhofer H H I, “Enhancements on Type-II CSI reporting,” R1-1811088, Chengdu, China, Oct. 8-12, 2018. [0146] [4] Fraunhofer I I S, Fraunhofer H H I, “Space-delay versus sub-band precoding for mmWave channels,” R1-1800597, Vancouver, Canada, Jan. 22-26, 2018. [0147] [5] Ericsson, “On CSI enhancements for MU-MIMO support,” R1-1811193, Chengdu, China, Oct. 8-12, 2018. [0148] [6] Huawei, HiSilicon, “Discussion on CSI enhancement for MU-MIMO,” R1-1810103, Chengdu, China, Oct. 8-12, 2018. [0149] [7] Fraunhofer I I S, Fraunhofer H H I, “Enhancements on Type II CSI reporting scheme,” R1-1813130, Spokane, USA, Nov. 12-16, 2018. [0150] [8] 3GPP TS 38.214 V15.3.0, “3GPP; TSG RAN; NR; Physical layer procedures for data (Release 15)”, September 2018. [0151] [9] Nokia, Nokia Shanghai Bell, “CSI feedback overhead reduction for MU-MIMO enhancements,” R1-1813488, Nov. 12-16, 2018.