Adaptive Kronecker product MIMO precoding for a multi-antenna network entity and a wireless communication device and corresponding methods

Abstract

A network entity comprises a plurality of antenna elements arranged in one or more two dimensional (2D) arrays having one or more columns and rows. The network entity configured to determine at least one set of one or more precoding vectors related to the plurality of antenna elements, wherein each set of precoding vectors is associated with a different Kronecker product tradeoff parameter L≥1; and transmit, at least one set of a plurality of Cell Specific Reference Signals (CRS) to be used to estimate channel state information (CSI) based on the at least one set of precoding vectors and/or at least one Kronecker product tradeoff parameter L.

Claims

1. A network entity, comprising: a plurality of antenna elements arranged in one or more two-dimensional (2D) arrays having one or more columns and rows; at least one processor; and a non-transitory computer-readable storage medium storing at least one program that is executable by the at least one processor, the at least one program comprising instructions to: determine at least one set of one or more precoding vectors related to the plurality of antenna elements, each of the one or more precoding vectors comprising one or more entries, each entry of each precoding vector having a form of w.sup.h×w.sup.v, wherein w.sup.v is a column-specific coefficient and w.sup.h is a row-specific coefficient, wherein each set of one or more precoding vectors is associated with a different Kronecker product tradeoff parameter L≥1, and wherein each value of L indicates that either each column-specific coefficient w.sup.v is repeated on antenna elements forming a sub-array of L columns or each row-specific coefficient w.sup.h is repeated on antenna elements forming a sub-array of L rows; and transmit at least one set of a plurality of Cell-Specific Reference Signals (CRSs) to be used as channel state information (CSI) pilots to estimate CSI based on the at least one set of one or more precoding vectors or at least one Kronecker product tradeoff parameter L, wherein each set of the plurality of CRSs comprises one or more elements, each element of the at least one set of the plurality of CRSs is a vector having a form of p.sup.h×p.sup.v, wherein p.sup.v is a column-specific coefficient and p.sup.h is a row-specific coefficient, and wherein either p.sup.v is repeated on the antenna elements forming the sub-array of L columns or p.sup.h is repeated on the antenna elements forming the sub-array of L rows.

2. The network entity according to claim 1, wherein the at least one program further comprises instructions to: receive a feedback message from a wireless communication device indicating a determined Kronecker product tradeoff parameter L, or a set of precoding vectors or precoding vector indices from a predefined set of precoding vectors corresponding to a value of the determined Kronecker product tradeoff parameter L.

3. The network entity according to claim 2, wherein the at least one program further comprises instructions to: perform a mapping of the received determined Kronecker product tradeoff parameter L to the at least one set of one or more precoding vectors to obtain a mapping result; and determine the set of precoding vectors based on the mapping result.

4. The network entity according to claim 3, wherein the at least one program further comprises instructions to: update the at least one set of the plurality of CRSs to be used as CSI pilots based on the received determined Kronecker product tradeoff parameter L to obtain an updated at least one set of the plurality of CRSs; and transmit the updated at least one set of the plurality of CRSs to one or more wireless communication devices by mapping entries of each element of the at least one set of the plurality of CRSs to corresponding antenna elements of the one or more 2D arrays of the plurality of antenna elements, or by separately sending vertical and horizontal components of the mapping entries of each element of the at least one set of the plurality of CRSs using L-order antenna aggregation, wherein each subarray of L columns or each subarray of L rows is uniquely excited using one determined value of the vertical component p.sup.v or of the horizontal component p.sup.h.

5. The network entity according to claim 1, wherein the at least one program further comprises instructions to: transmit a control message to a wireless communication device, the control message indicating instructions for determining a Kronecker product tradeoff parameter L specified for the wireless communication device.

6. The network entity according to claim 5, wherein the at least one program further comprises instructions to: adjust, for transmission to a wireless communication device, the Kronecker product tradeoff parameter L specified for the wireless communication device based on CSI feedback received from the wireless communication device.

7. The network entity according to claim 1, wherein the at least one program further comprises instructions to: determine, for a first value of a Kronecker tradeoff parameter L or a plurality of precoding vectors corresponding to the first value, the column-specific coefficients w.sup.v or the row-specific coefficients w.sup.h, wherein the determining of the column-specific coefficients w.sup.v is performed independently or semi-independently of the row-specific coefficients w.sup.h, the determining of the row-specific coefficients w.sup.h is performed independently or semi-independently of the column-specific coefficients w.sup.v, and wherein the row-specific coefficients w.sup.h and the column-specific coefficients w.sup.v are determined based on two separate performance criteria.

8. The network entity according to claim 7, wherein the at least one program further comprises instructions to: determine a first Kronecker product tradeoff parameter L based on the two separate performance criteria or a tradeoff between the two separate performance criteria.

9. The network entity according to claim 8, wherein the at least one program further comprises instructions to: update the first Kronecker tradeoff parameter L and transmit a set of CRS required for updating the first Kronecker tradeoff parameter L and for CSI estimation, based on a one-step CRS scheme, wherein the first Kronecker product tradeoff parameter L is updated during each CRS cycle; or update the first Kronecker tradeoff parameter L and transmit the set of CRS required for updating the first Kronecker tradeoff parameter L and for CSI estimation, based on a two-step CRS scheme, wherein the first Kronecker product tradeoff parameter L corresponds to a wireless communication device and is updated only once during a period of CRS cycles comprising at least one cycle.

10. The network entity according to claim 1, wherein the at least one program further comprises instructions to: store, in a Look-Up Table, one or more of the one or more precoding vectors or the at least one Kronecker product tradeoff parameter L.

11. A method, comprising: determining, by a network entity, at least one set of one or more precoding vectors related to a plurality of antenna elements, the network entity comprising the plurality of antenna elements, the plurality of antenna elements being arranged in one or more two-dimensional (2D) arrays, each of the one or more precoding vectors comprising one or more entries, and each entry of each precoding vector having a form of w.sup.h×w.sup.v, wherein w.sup.v is a column-specific coefficient and w.sup.h is a row-specific coefficient, wherein each set of one or more precoding vectors is associated with a different Kronecker product tradeoff parameter L≥1, and wherein each value of L indicates that either each column-specific coefficient w.sup.v is repeated on antenna elements forming a sub-array of L columns or each row-specific coefficient w.sup.h is repeated on antenna elements forming a sub-array of L rows; and transmitting, by the network entity, at least one set of a plurality of Cell-Specific Reference Signals (CRSs) to be used as channel state information (CSI) pilots to estimate CSI based on the at least one set of one or more precoding vectors or at least one Kronecker product tradeoff parameter L, wherein each set of the plurality of CRSs comprises one or more elements, each element of the at least one set of the plurality of CRSs is a vector having a form of p.sup.h×p.sup.v, wherein p.sup.v is a column-specific coefficient and p.sup.h is a row-specific coefficient, and wherein either p.sup.v is repeated on the antenna elements forming the sub-array of L columns or p.sup.h is repeated on the antenna elements forming the sub-array of L rows.

12. A wireless communication device, comprising: at least one processor; and a non-transitory computer-readable storage medium storing at least one program that is executable by the at least one processor, the at least one program comprising instructions to: receive at least one set of a plurality of Cell-Specific Reference Signals (CRSs) from a network entity, wherein the network entity comprises a plurality of antenna elements arranged in one or more two-dimensional (2D) arrays having one or more columns and rows, wherein each set of the at least one set of the plurality of CRSs comprises one or more elements, each element of the at least one set of the plurality of CRSs is a vector having a form of p.sup.h×p.sup.v, wherein p.sup.v is a column-specific coefficient and p.sup.h is a row-specific coefficient, and wherein either p.sup.v is repeated on antenna elements forming a sub-array of L≥1 columns or p.sup.h is repeated on antenna elements forming a sub-array of L rows; estimate Channel State Information (CSI) based on the received at least one set of the plurality of CRSs; and obtain at least one set of one or more precoding vectors related to the plurality of antenna elements, each of the one or more precoding vectors comprising one or more entries, each entry of each precoding vector having a form of w.sup.h×w.sup.v, wherein w.sup.v is a column-specific coefficient and w.sup.h is a row-specific coefficient, wherein each set of one or more precoding vectors is associated with a different Kronecker product tradeoff parameter L, and wherein a value of L indicates that either each column-specific coefficient w.sup.v is repeated on the antenna elements forming the sub-array of L≥1 columns or the row-specific coefficient w.sup.h is repeated on the antenna elements forming the sub-array of L≥1 rows.

13. The wireless communication device according to claim 12, wherein the at least one program further comprises instructions to: determine at least one Kronecker product tradeoff parameter L or a set of one or more precoding vectors or precoding vector indices from a predefined set of precoding vectors corresponding to the determined Kronecker product tradeoff parameter L, based on the estimated CSI.

14. The wireless communication device according to claim 13, wherein the at least one program further comprises instructions to: send a feedback message to the network entity indicating the determined at least one Kronecker product tradeoff parameter L or the set of one or more precoding vectors or the precoding vector indices.

15. The wireless communication device according to claim 14, wherein the at least one program further comprises instructions to: receive an updated set of CRSs from the network entity, based on the determined at least one Kronecker product tradeoff parameter L or the set of one or more precoding vectors or the precoding vector indices.

16. The wireless communication device according to claim 12, wherein the at least one program further comprises instructions to: receive a control message from the network entity, the control message indicating instructions for determining a Kronecker product tradeoff parameter L specified for the wireless communication device.

17. The wireless communication device according to claim 16, wherein the at least one program further comprises instructions to: send an adjusted Kronecker product tradeoff parameter L or CSI feedback required to adjust the determined Kronecker product tradeoff parameter L specified for the wireless communication device to the network entity based on a one-step CRS scheme, wherein the determined Kronecker product tradeoff parameter L is updated and sent during each CRS cycle; or send an adjusted Kronecker product tradeoff parameter L or CSI feedback required to adjust the determined Kronecker product tradeoff parameter L specified for the wireless communication device to the network entity based on a two-step CRS scheme, wherein the determined Kronecker product tradeoff parameter L specified for the wireless communication device is updated and sent only once during a period of CRS cycles comprising at least one cycle.

18. The wireless communication device according to claim 12, wherein the at least one program further comprises instructions to: receive a Look-Up Table (LUT) or an index pointing to a LUT within a plurality of predefined LUTs from the network entity, the LUT or the index indicating the one or more precoding vectors or at least one Kronecker product tradeoff parameter L.

19. A method, comprising: receiving, by a wireless communication device, at least one set of a plurality of Cell-Specific Reference Signals (CRSs) from a network entity, wherein the network entity comprises a plurality of antenna elements arranged in one or more two-dimensional (2D) arrays having one or more columns and rows, wherein each set of the plurality of CRSs comprises one or more elements, each element of the at least one set of the plurality of CRSs is a vector having a form of p.sup.h×p.sup.v, wherein p.sup.v is a column-specific coefficient and p.sup.h is a row-specific coefficient, and wherein either p.sup.v is repeated on antenna elements forming a sub-array of L≥1 columns or p.sup.h is repeated on antenna elements forming a sub-array of L rows; estimating Channel State Information (CSI) based on the received at least one set of the plurality of CRSs; and obtaining at least one set of one or more precoding vectors related to the plurality of antenna elements, each entry of each precoding vector having a form of w.sup.h×w.sup.v, wherein w.sup.v is a column-specific coefficient and w.sup.h is a row-specific coefficient, wherein each set of one or more precoding vectors is associated with a different Kronecker product tradeoff parameter L, and wherein a value of L indicates that either each column-specific coefficient w.sup.v is repeated on the antenna elements forming the sub-array of L≥1 column or the-row specific coefficient w.sup.h is repeated on the antenna elements forming the sub-array of L≥1 rows.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above described aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

(2) FIG. 1 is a schematic view of a network entity comprising a plurality of antenna elements arranged in a 2D array, according to an embodiment of the present invention.

(3) FIG. 2 is a schematic view of a wireless communication device, according to an embodiment of the present invention. The antenna elements of this device can be arranged in a 2D array or in any other geometric setting.

(4) FIGS. 3A and 3B are a schematic view of a MU-MIMO wireless communication system comprising the network entity and the wireless communication device, according to an embodiment of the present invention.

(5) FIG. 4 is an exemplarily schematic view of an adaptive Kronecker product MIMO precoder for a N.sub.h×k 2D antenna array in the case of L=2.

(6) FIG. 5 is an exemplarily schematic view of a CRS pilot mapping using L-order antenna aggregation.

(7) FIG. 6 is a flow diagram of the adaptive Kronecker product codebook MIMO transmission at the network entity.

(8) FIG. 7 is a flow diagram of pilot and data reception of the adaptive Kronecker product codebook MIMO at the wireless communication device.

(9) FIG. 8 is a flow diagram of pilot and data transmission of the adaptive Kronecker product MIMO with CRS antenna aggregation at the network entity during one-step CRS cycle.

(10) FIG. 9 is a flow diagram of pilot and data reception of the adaptive Kronecker product MIMO with CRS antenna aggregation at the wireless communication device during one-step CRS cycle.

(11) FIG. 10 is a flow diagram of adaptive Kronecker product MIMO transmission with CRS antenna aggregation at the network entity during two-step CRS cycle.

(12) FIG. 11 is a flow diagram of pilot and data reception of adaptive Kronecker product MIMO with CRS antenna aggregation at the wireless communication device during two-step CRS cycle.

(13) FIG. 12 is a flowchart of a method for a network entity comprising a plurality of antenna elements arranged in a 2D array, according to an embodiment of the present invention.

(14) FIG. 13 is a flowchart of a method for a wireless communication device, according to an embodiment of the present invention.

(15) FIG. 14 schematically illustrates a conventional 2D antenna array configuration.

(16) FIG. 15 schematically illustrates a conventional MIMO precoder coefficients that satisfy the Kronecker product property.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(17) FIG. 1 is a schematic view of a network entity 100 comprising a plurality of antenna elements 101 arranged in a 2D array, according to an embodiment of the present invention.

(18) The network entity may be for example, a base station, an access point, etc. The 2D array of the network entity 100 of FIG. 1 may have one or more columns and rows.

(19) The network entity 100 configured to determine at least one set of one or more precoding vectors 102, 103 related to the plurality of antenna elements 101, each entry of each precoding vector having a form of w.sup.h×w.sup.v, wherein w.sup.v is a column specific coefficient and w.sup.h is a row specific coefficient; wherein each set of precoding vectors 102, 103 is associated with a different Kronecker product tradeoff parameter L≥1, wherein the value of L indicates that either each column specific coefficient w.sup.v is repeated on antenna elements forming a sub-array of L columns or each row specific coefficient w.sup.h is repeated on antenna elements forming a sub-array of L rows.

(20) The network entity 100 is further configured to transmit, at least one set of a plurality of CRS 104, to be used to estimate CSI based on the at least one set of precoding vectors 102, 103 and/or at least one Kronecker product tradeoff parameter L, wherein each element of the at least one set of CRS 104 is a vector having a form of p.sup.h×p.sup.v, wherein p.sup.v is a column specific coefficient and p.sup.h is a row specific coefficient, and wherein either p.sup.v is repeated on the antenna elements forming the sub-array of L columns or p.sup.h is repeated on the antenna elements forming the sub-array of L rows.

(21) For example, the network entity may transmit (explicitly or implicitly) the Kronecker product tradeoff parameter.

(22) For instance, a user specific adaptive Kronecker product MIMO precoder may be provided with each one of the two terms of the Kronecker product may be computed independently or semi-independently from the other based on a performance or an optimization criterion. Moreover, the adaptation parameter of the Kronecker product may be determined based on a target tradeoff between, e.g., these two performance criteria.

(23) The network entity 100 may comprise a circuitry (not shown in FIG. 1). The circuitry may comprise hardware and software. The hardware may comprise analog or digital circuitry, or both analog and digital circuitry. In some embodiments, the circuitry comprises one or more processors and a non-volatile memory connected to the one or more processors. The non-volatile memory may carry executable program code which, when executed by the one or more processors, causes the device to perform the operations or methods described herein.

(24) Reference is made to FIG. 2 which is a schematic view of a wireless communication device 200, according to an embodiment of the present invention.

(25) The wireless communication device 200 may be, for example, a user terminal, a user equipment (UE), etc.

(26) The wireless communication device 200 configured to receive at least one set of a plurality of CRS 104, from a network entity 100, wherein the network entity 100 comprises a plurality of antenna elements 101 arranged in one or more two dimensional, 2D, arrays having one or more columns and rows, wherein each element of the at least one set of CRS is a vector having a form of p.sup.h×p.sup.v, wherein p.sup.v is a column specific coefficient and p.sup.h is a row specific coefficient, and wherein either p.sup.v is repeated on antenna elements forming a sub-array of L≥1 columns or p.sup.h is repeated on antenna elements forming a sub-array of L rows.

(27) The wireless communication device 200 is further configured to estimate CSI 201 based on the received at least one set of CRS 104.

(28) The wireless communication device 200 is further configured to obtain at least one set of one or more precoding vectors 102, 103 related to the plurality of antenna elements 101, each entry of each precoding vector 102, 103 having a form of w.sup.h×w.sup.v, wherein w.sup.v is a column specific coefficient and w.sup.h is a row specific coefficient, wherein each set of precoding vectors 102, 103 is associated with a different Kronecker product tradeoff parameter L, and wherein the value of L indicates that either each column specific coefficient w.sup.v is repeated on the antenna elements forming the sub-array of L≥1 column or the row specific coefficient w.sup.h is repeated on the antenna elements 101 forming the sub-array of L≥1 rows.

(29) The wireless communication device may comprise a circuitry (not shown in FIG. 2). The circuitry may comprise hardware and software. The hardware may comprise analog or digital circuitry, or both analog and digital circuitry. In some embodiments, the circuitry comprises one or more processors and a non-volatile memory connected to the one or more processors. The non-volatile memory may carry executable program code which, when executed by the one or more processors, causes the device to perform the operations or methods described herein.

(30) Reference is made to FIGS. 3A and 3B which is a schematic view of a MU-MIMO wireless communication system 300 comprising the network entity 100 and the wireless communication device 200, according to an embodiment of the present invention.

(31) In the embodiment of FIGS. 3A and 3B the network entity 100 is based on a BS and the wireless communication device 200 is based on a UE.

(32) The network entity 100 (i.e., the BS) comprises the (optional) module of “family of Kronecker product MIMO codebooks” 301 that stores (for example, in a formula or in look-up table form, etc.) the set of precoding vectors 102, 103 which make a family of MIMO codebooks. Moreover, each codebook may be defined by one value of the Kronecker product tradeoff parameter.

(33) The network entity 100 (i.e., the BS) further comprises the (optional) module of “family of CRS port mapping” 302 which stores (for example, in a formula form or in another mapping representation form) a family of antenna aggregation schemes for the CRS transmission. For instance, each one of these schemes corresponds to a mapping of CRS symbols to antenna elements 101 in which the symbol repeated on a number of array columns that is equal to one of the possible values of the adaptive Kronecker product tradeoff parameter.

(34) The MU-MIMO wireless communication system 300 further comprises the wireless communication device 200 (i.e., the UE). The wireless communication device 200 comprises the module “Kronecker product tradeoff determination” 304. Moreover, the channel estimates (CE) that are obtained at the receiver side (at the wireless communication device 200) based on the CRS pilots 104 are used by the module “Kronecker product tradeoff determination” 304, for example, upon the reception of a “tradeoff parameter search initiation and/or search interval signaling” control message from the network entity 100 (base station/access point). Furthermore, the CRS based CSI estimates are used either to directly determine the best tradeoff parameter value or to prepare a CSI feedback report with multiple CSI values that may help the network entity boo (base station/access point) to determine the best value of this parameter for the wireless communication device 200 (the user terminal).

(35) The output of this module is thus a “Kronecker product tradeoff parameter feedback” 306 that comprises the best value of the tradeoff parameter either in an explicit or in an implicit manner.

(36) The implicit/explicit Kronecker tradeoff parameter feedback 306 received from the wireless communication device 200 (the user terminal) may be used by the “Kronecker product tradeoff parameter tuning” module 303 at the network entity (base station/access point) in order to determine the value of the tradeoff parameter to be used in the subsequent adaptive Kronecker product precoded pilot and data transmissions to the wireless communication device 200 (the user terminal), as it is illustrated by the modules of the block diagram to which the output of this module is connected.

(37) Reference is made to FIG. 4 which is a schematic view of an exemplarily adaptive Kronecker product MIMO precoder 401 for a N.sub.h×N.sub.v 2-dimensional antenna array in case of L=2.

(38) An example of the structure of an adaptive Kronecker product MIMO precoder vector 401 in the case where the tradeoff parameter is set to L=2 is illustrated. Moreover, from the scheme 400 of the FIG. 4, it may be derived, how the entries of this vector 401 are applied to a two-dimensional antenna array (for example, from the plurality of antenna element 101 of the 2D array of the network entity 100).

(39) In addition, in order to give the wireless communication device 100, the possibility to determine both the best value of the Kronecker product tradeoff parameter L and the associated CSI, in some embodiments of the invention a novel mapping of the CRS ports to antenna elements may be provided. The mapping may be based on using a family of antenna aggregation schemes each parameterized with a different value of L. An example of a member of this family corresponding to some CRS antenna aggregation value L>1 is shown in FIG. 5.

(40) Reference is made to FIG. 5 which is an exemplarily schematic view of a CRS pilot mapping 500 for the non-codebook MIMO.

(41) It is worth mentioning that, the conventional antenna aggregation schemes for CRS pilots, correspond to the L=1-member of the proposed family of CRS antenna aggregation schemes. In FIG. 5, on the lefts side, an example of an L-order CRS antenna aggregation scheme to transmit the LN.sub.v vertical components of the CRS pilots is illustrated. Moreover; the indicated reference 501 represents the antenna elements aggregated to transmit the first vertical component of CRS pilots (i.e., the vertical port 1), the indicated reference 502 represents the antenna elements aggregated to transmit the second vertical component of CRS pilots (i.e., the vertical port 2), and the indicated reference 503 represents the antenna elements aggregated to transmit the LN.sub.v-th vertical component of CRS pilots (i.e., the vertical port LN.sub.v). Furthermore, on the right side, an example of an L-order CRS antenna aggregation scheme for transmitting the N.sub.v/L horizontal components of the CRS pilots is also illustrated.

(42) Furthermore, given N.sub.c≥1 possible values of the antenna aggregation parameter {L.sub.1, . . . , L.sub.N.sub.c}, transmitting all of the CRS ports corresponding to these values requires a total of Σ.sub.n=1.sup.N.sup.c(P.sub.v,n+P.sub.h,n) CRS ports, where

(43) $P_{v,n}\le L_n{N}_v\mathrm{and}{P}_{h,n}\le \frac{N_h}{L_n}.$

(44) Note that, the value of Σ.sub.n=1.sup.N.sup.c(P.sub.v,n+P.sub.h,n) may be smaller than the original number of CRS ports in the non-codebook MIMO e.g., N.sub.hN.sub.v. This new pilot mapping may be used with both non-codebook and codebook based Adaptive Kronecker product schemes. Moreover, it is compatible with both of the (conventional) 1-step CRS feedback mode and 2-step CRS feedback mode as it is discussed in the following.

(45) In the following (e.g., FIG. 6 and FIG. 7) codebook based adaptive Kronecker product scheme without CRS antenna aggregation are illustrated.

(46) Reference is made to FIG. 6 which is a flow diagram 600 of the adaptive Kronecker product codebook MIMO transmission at the network entity 100.

(47) In this embodiment, the adaptive Kronecker product MIMO precoders are chosen from a family of N.sub.c codebooks

(48) $C^{\left(L_1\right)},C^{\left(L_2\right)},\mathrm{.Math.},C^{\left(L_{N_c}\right)},$
where N.sub.c is the number of possible values of the Kronecker product tradeoff parameter L. An example method for constructing C.sup.(L) (1≤L≤N.sub.c) is according to Eq. (2).

(49) $\begin{array}{cc}{𝒞}^{\left(L\right)}={\left\{c_{.Math.\frac{N_h}{L}.Math.\left(j-1\right)+i}^{\left(L\right)}={\tilde{c}}_i^h.Math.{\tilde{c}}_j^v\right\}}_{i=1,\mathrm{.Math.},.Math.\frac{N_h}{L}.Math.,j=1,\mathrm{.Math.},{\mathrm{LN}}_v}& \mathrm{Eq}.\left(2\right)\end{array}$

(50) Moreover, the Eq. (3) ad Eq. (4) may be defined as follows:

(51) $\begin{array}{cc}{\tilde{c}}_i^h={\frac{1}{\sqrt{.Math.\frac{N_h}{L}.Math.}}\left[1e^{\mathrm{.Math.}\frac{2\pi \left(i-1\right)L}{.Math.\frac{N_h}{L}.Math.}}\mathrm{.Math.}{e}^{\mathrm{.Math.}\frac{2\pi \left(.Math.\frac{N_h}{L}.Math.-1\right)\left(i-1\right)L}{.Math.\frac{N_h}{L}.Math.}}\right]}^T,i=1,\mathrm{.Math.},.Math.\frac{N_h}{L}.Math.,{\tilde{c}}_{L\left(j-1\right)+i}^v-{\stackrel{\_}{c}}_i^h.Math.{\stackrel{\_}{c}}_j^v,j=1,\mathrm{.Math.},N_v,i=1,\mathrm{.Math.},L,\mathrm{and},{\stackrel{\_}{c}}_i^h={\frac{1}{\sqrt{L}}\left[1e^{\mathrm{.Math.}\frac{2\pi \left(i-1\right)}{L}}\mathrm{.Math.}{e}^{\mathrm{.Math.}\frac{2\pi \left(L-1\right)\left(i-1\right)}{L}}\right]}^T,{\stackrel{\_}{c}}_j^v={\frac{1}{\sqrt{N_v}}\left[1e^{\mathrm{.Math.}\frac{2\pi \left(j-1\right)}{N_v}}\mathrm{.Math.}{e}^{\mathrm{.Math.}\frac{2\pi \left(N_v-1\right)\left(j-1\right)}{N_v}}\right]}^T.& \mathrm{Eq}.\left(3\right)\end{array}$

(52) The setting of the L=1 in the above definition results in the conventional 2D DFT MIMO codebook adopted in the 3GPP standards.

(53) In some embodiments of the invention, the entries of the vectors making up the codebooks are stored in the lookup tables indexed with respect to different possible combinations of the values of N.sub.h, N.sub.v and L. In some other embodiments, these coefficients may be computed, e.g., using the above mathematical formulas (e.g., Eq. (2), Eq. (3) and Eq. (4)) implemented using dedicated code or circuitry at the network entity 100 (transmitting device).

(54) The network entity 100 (base station) uses all the N.sub.c codebooks to precode the CRS pilots on N.sub.c non-overlapping time, frequency, code, power resource subsets (referred to in the flow diagrams as .sub.1, . . . , .sub.N.sub.c). This embodiment is compatible with both one-step and two-step CRS schemes. In the one-step CRS, the value of L is updated during each CRS cycle. In the two-step CRS, the updating is done as follows. With low periodicity, the users may detect the pilot signals on all of these resource subsets in order to update their best value of L (this updating is either done at the receiver side based on this detection or at the transmitter side based on feedback from the receiver with related CSI values resulting from this detection). With a higher periodicity, the users may only detect the pilot signals on the resource subsets corresponding to their optimal value of L and may further feedback only the associated restricted CSI.

(55) The flow diagram of the steps needed to be performed at the network entity 100 (the transmitter side) for pilot and data transmission may be as follows:

(56) At 601, the network entity 100 obtains input data.

(57) The input data may be, for example, one or more of:

(58) N.sub.c non-overlapping subsets .sub.1, . . . , .sub.N.sub.c of radio resource elements with .sub.n being a CRS port subset corresponding to codebook C.sup.(L.sup.n.sup.);

(59) K possibly partially overlapping radio resource subsets .sub.1, . . . , .sub.K to assign to the K receivers for data.

(60) At 602, the network entity 100 determines whether the current slot is a CRS slot or not. Moreover, when it is determines “Yes” the network entity 100 goes to 604, however, when it is determined “No”, the network entity goes to 603.

(61) At 603, the network entity 100 transmits data to the wireless communication device 100 (receiver) k∈{1, . . . , K} precoded with the vectors from the codebook

(62) $C^{\left(L_{n_k}\right)}$
on the resource subset .sub.k, wherein L.sub.n.sub.k is the latest available value of the Kronecker product tradeoff parameter for wireless communication device k.

(63) At 604, the network entity 100 transmits the CRS pilots of the subset .sub.n precoded with the vectors from the codebook C.sup.(L.sup.n.sup.)∀n∈{1, . . . , N.sub.c}.

(64) At 605, the network entity 100 determines if it is required to update the value of L.sub.n.sub.k. Moreover, when it is determines “Yes” the network entity 100 goes to 606, however, when it is determined “No”, the network entity goes to 608.

(65) At 606, the network entity 100 receives a feedback from k corresponding to CSI on all of the subsets .sub.n

(66) At 607, the network entity 100 determines the value of L.sub.n.sub.k based on the obtained CSI feedback. Moreover, the value of the wireless communication device index k will be updated to k+1 and the network entity goes to 605.

(67) At 608, the network entity 100 receives a feedback from k corresponding to CSI on .sub.n.sub.k.

(68) At 609, the network entity 100 signals the value of n.sub.k (or equivalently L.sub.n.sub.k) to the receiver k. Moreover, the value of the k will be updated to k+1 and the network entity goes to 605.

(69) Reference is made to FIG. 7 which is a flow diagram 700 of pilot and data reception of the adaptive Kronecker product codebook MIMO at the wireless communication device 100.

(70) At 701, the wireless communication device 200 determines whether it is need to update the value of L.sub.n.sub.k or not. Moreover, when it is determined “Yes”, the wireless communication device 200 goes to step 702, however, when it is determined “No”, the wireless communication device 200 goes to step 705.

(71) At 702, the wireless communication device 200 detects the CRS pilots on all of the resource subset .sub.n.

(72) At 703, the wireless communication device 200 determines the vectors from the codebook C.sup.(L.sup.n.sup.)∀n∈{1, . . . , N.sub.c} that are the best matches to the channel on .sub.n.

(73) At 704, the wireless communication device 200 sends a feedback message comprising the indexes of all of these vectors (for example, there are at least N.sub.c indexes).

(74) At 705, the wireless communication device 200 determines whether the current slot is a CRS slot or not.

(75) Moreover, when it is determined “Yes”, the wireless communication device 200 goes to step 706, however, when it is determined “No”, the wireless communication device 200 goes to step 707.

(76) At 706, the wireless communication device 200 determines the vectors from the codebook

(77) $C^{\left(L_{n_k}\right)}$
that are the best matches to the channel on .sub.k.

(78) At 707, the wireless communication device 200 receives data and/or the index of .sub.k and the value of L.sub.n.sub.k.

(79) In some embodiments, the codebook and/or the non-codebook adaptive Kronecker product scheme with one-step CRS antenna aggregation may be provided.

(80) For example, in some embodiments, the CRS ports with L-parametrized antenna aggregation corresponding to all of the possible values of the parameter L may be transmitted in every CRS slot. Moreover, the wireless communication device 200 (the receiver) may feedback the estimated CSI corresponding to all of these ports. The flow diagram of the steps needed to be performed at the network entity 100 (transmitter side) is shown in FIG. 8.

(81) Reference is made to FIG. 8 which is a flow diagram 800 of pilot and data transmission of the adaptive Kronecker product MIMO with CRS antenna aggregation at the network entity 100 during one-step CRS cycle.

(82) At 801, the network entity 100 obtains the input data.

(83) The input data may be for example, one or more of:

(84) N.sub.c non-overlapping subsets .sub.1, . . . , .sub.N.sub.c of radio resource elements with .sub.n being a CRS port subset corresponding to one antenna aggregation parameter value L.sub.n;

(85) K possibly partially overlapping radio resource subsets .sub.1, . . . , .sub.K to assign to the K receivers for data.

(86) At 802, the network entity 100 determines whether the current slot is a CRS slot or not. Moreover, when it is determined “Yes”, the network entity 100 goes to step 804, however, when it is determined “No”, the network entity 100 goes to step 803.

(87) At 803, the network entity 100 transmits data to the wireless communication device 200 (the receiver) k∈{1, . . . , K} precoded with the L.sub.n.sub.k-Kronecker product MIMO on the resource subset .sub.k, wherein L.sub.n.sub.k is the latest available value of the Kronecker product tradeoff parameter for communication device k.

(88) At 804, the network entity 100 transmits the CRS pilots of subset .sub.n using the L.sub.n-parametrized antenna aggregation ∀n∈{1, . . . , N.sub.c}.

(89) At 805, the network entity 100 receives feedback from all the receivers corresponding to their CSI on all the subsets .sub.n

(90) At 806, the network entity 100 determines a mapping according to k∈{1, . . . , K}L.sub.n.sub.k ∈{L.sub.1, . . . , L.sub.N.sub.c} that assigns to each wireless communication device k a value L.sub.n.sub.k of the Kronecker product tradeoff parameter.

(91) At 807, the network entity 100 signals the value of n.sub.k (or equivalently L.sub.n.sub.k) to receiver k∀k∈{1, . . . , K}.

(92) Reference is made to FIG. 9 which is a flow diagram 900 of pilot and data reception of the adaptive Kronecker product MIMO with CRS antenna aggregation at the wireless communication device during one-step CRS cycle.

(93) At 901, the wireless communication device 200 determines whether it is needed to update the value of L.sub.n.sub.k or not.

(94) Moreover, when it is determined “Yes”, the wireless communication device 200 goes to step 902, however, when it is determined “No”, the wireless communication device 200 goes to step 905.

(95) At 902, the wireless communication device 200 detects the CRS pilots on all the resource subset .sub.n.

(96) At 903, the wireless communication device 200 estimates the channel vector/matrix on each resource subset .sub.n ∀n∈{1, . . . , N.sub.c}.

(97) At 904, the wireless communication device 200 feedbacks all or a subset of the resulting CSI (for example, at least N.sub.c vectors/matrices, possibly quantized).

(98) At 905, the wireless communication device 200 determines whether the current slot is a CRS slot or not. Moreover, when it is determined “Yes”, the wireless communication device 200 goes to step 906, however, when it is determined “No”, the wireless communication device 200 goes to step 907.

(99) At 906, the wireless communication device 200 estimates the channel vector/matrix on resource subset .sub.n.sub.k.

(100) At 907, the wireless communication device 200 receives data on resources subset .sub.k and/or the index of .sub.k and the value of L.sub.n.sub.k.

(101) In some embodiments, a codebook and/or a non-codebook adaptive Kronecker product scheme may be provided with a two-step CRS antenna aggregation.

(102) For example, the proposed CRS antenna aggregation may be integrated with a two-step CRS transmission that comprises the following. A first (less frequent large-overhead) transmission step: during this step the user terminals report their estimated CSI corresponding to all of the CSR ports (the ports corresponding to all of the possible values of the antenna aggregation parameter L). One of the outcomes of this step is to determine the best antenna aggregation value L for each user terminal (assuming that this value varies more slowly than the wireless channel coefficients). A second (more frequent light-overhead) transmission step: during this step the user terminals feedback their estimated CSI corresponding to only one value of the antenna aggregation parameter L (the value determined after the first step).

(103) Note that, the overhead associated with this pilot scheme may be smaller than the overhead associated with the previous (one-step CRS) embodiment. The flow diagram of the steps needed to be performed at the network entity 100 are shown in FIG. 10.

(104) Reference is made to FIG. 10 which is a flow diagram 1000 of adaptive Kronecker product MIMO transmission with CRS antenna aggregation at the network entity during two-step CRS cycle.

(105) At 1001, the network entity 100 obtains the input data.

(106) For example, the input data may be:

(107) N.sub.c non-overlapping subsets .sub.1, . . . , .sub.N.sub.c of radio resource elements with .sub.n being a CRS port subset corresponding to one antenna aggregation parameter value L.sub.n

(108) K possibly partially overlapping radio resource subsets .sub.1, . . . , .sub.K to assign to the K receivers for data

(109) At 1002, the network entity 100 determines if the current slot a 1.sup.st-step CRS slot? Moreover, when it is determined “Yes”, the network entity 100 goes to step 1003, however, when it is determined “No”, the network entity 100 goes to step 1007.

(110) At 1003, the network entity 100 transmits the N.sub.c CRS subsets .sub.n using the L.sub.n-parametrized antenna aggregation ∀n∈{1, . . . , N.sub.c}.

(111) At 1004, the network entity 100 receives feedback from all the receivers corresponding to their CSI on all the subsets .sub.n.

(112) At 1005, the network entity 100 determine a mapping of k∈{1, . . . , K} to L.sub.n.sub.k∈{L.sub.1, . . . , L.sub.N.sub.c}.

(113) At 1006, the network entity 100 signals the value of n.sub.k (or equivalently L.sub.n.sub.k) to the receiver k ∀k∈{1, . . . , K}.

(114) At 1007, the network entity 100 determines whether the current slot is a 2nd-step CRS slot or not. Moreover, when it is determined “Yes”, the network entity 100 goes to step 1009, however, when it is determined “No”, the network entity 100 goes to step 1008.

(115) At 1008, the network entity 100 transmits data to the receiver k∈{1, . . . , K} precoded with L.sub.n.sub.k-Kronecker product on the resource subset .sub.k.

(116) At 1009, the network entity 100 transmits the N.sub.c CRS subsets .sub.n using the L.sub.n-parametrized antenna aggregation ∀n∈{1, . . . , N.sub.c}.

(117) At 1010, the network entity 100 receives feedback from each receiver k∈{1, . . . , K} corresponding to their CSI on CRS subset .sub.n.sub.k.

(118) Reference is made to FIG. 11 which is a flow diagram 1100 of pilot and data reception of adaptive Kronecker product MIMO with CRS antenna aggregation at the wireless communication device during two-step CRS cycle.

(119) At 1101, the wireless communication device 200 determines whether the current slot contains 1.sup.st-step CRS or not. Moreover, when it is determined “Yes”, the wireless communication device 200 goes to step 1102, however, when it is determined “No”, the wireless communication device 200 goes to step 1106.

(120) At 1102, the wireless communication device 200 detects all the CRS symbols (1.sup.st-step CRS).

(121) At 1103, the wireless communication device 200 computes an estimate of the CSI based on the received pilots.

(122) At 1104, the wireless communication device 200 (optionally) determines the value of L based on the estimated CSI.

(123) At 1105, the wireless communication device 200 feedbacks the estimated CSI (and optionally L).

(124) At 1106, the wireless communication device 200 determines if the current slot contains 2.sup.nd-step CRS? Moreover, when it is determined “Yes”, the wireless communication device 200 goes to step 1108, however, when it is determined “No”, the wireless communication device 200 goes to step 1107.

(125) At 1107, the wireless communication device 200 receives data and/or the index of .sub.k, .sub.k and the value of L.sub.k.

(126) At 1108, the wireless communication device 200 computes an estimate of the CSI on .sub.k based on the received pilots with L.sub.k-parameterized antenna aggregation.

(127) At 1109, the wireless communication device 200 feedbacks the estimated CSI.

(128) Note that, some signaling may be needed to inform the wireless communication device (user terminals) of the particular subset of CRS ports for which the feedback is needed. In FIG. 7 and FIG. 8, the subset signaled to user k is referred to as .sub.k and it corresponds to one value L.sub.k of the antenna aggregation parameter. This signaling may be particularly needed, in embodiments where this value of L.sub.k is determined at the network entity 100 (base station/access point) side.

(129) Reference is made to FIG. 12 which is a flowchart of a method 1200 for a network entity comprising a plurality of antenna elements arranged in a 2D array, according to an embodiment of the present invention. The method 1200 may be carried out by the network entity 100, as it described above.

(130) The method 1200 comprises a step 1201 of determining at least one set of one or more precoding vectors 102, 103 related to the plurality of antenna elements 101, each entry of each precoding vector having a form of w.sup.h×w.sup.v, wherein w.sup.v is a column specific coefficient and w.sup.h is a row specific coefficient; wherein each set of precoding vectors 102, 103 is associated with a different Kronecker product tradeoff parameter L≥1, wherein the value of L indicates that either each column specific coefficient w.sup.v is repeated on antenna elements forming a sub-array of L columns or each row specific coefficient w.sup.h is repeated on antenna elements forming a sub-array of L rows.

(131) The method 1200 further comprises a step 1202 of transmitting, at least one set of a plurality of Cell Specific Reference Signals (CRS) 104, to be used to estimate channel state information, CSI, based on the at least one set of precoding vectors 102, 103 and/or at least one Kronecker product tradeoff parameter L, wherein each element of the at least one set of CRS 104 is a vector having a form of p.sup.h×p.sup.v, wherein p.sup.v is a column specific coefficient and p.sup.h is a row specific coefficient, and wherein either p.sup.v is repeated on the antenna elements forming the sub-array of L columns or p.sup.h is repeated on the antenna elements forming the sub-array of L rows.

(132) FIG. 13 shows a flowchart of a method 1300 for a wireless communication device, according to an embodiment of the present invention. The method 1300 may be carried out by the wireless communication device 200, as it described above.

(133) The method 1300 comprises a step 1301 of receiving at least one set of a plurality of Cell Specific Reference Signals (CRS) 104 from a network entity 100, wherein the network entity 100 comprises a plurality of antenna elements 101 arranged in one or more two dimensional, 2D, arrays having one or more columns and rows, wherein each element of the at least one set of CRS 104 is a vector having a form of p.sup.h×p.sup.v, wherein p.sup.v is a column specific coefficient and p.sup.h is a row specific coefficient, and wherein either p.sup.v is repeated on antenna elements forming a sub-array of L≥1 columns or p.sup.h is repeated on antenna elements forming a sub-array of L rows.

(134) The method 1300 further comprises a step 1302 of estimating Channel State Information (CSI) 201 based on the received at least one set of CRS 104.

(135) The method 1300 further comprises a step 1303 of obtaining at least one set of one or more precoding vectors 102, 103 related to the plurality of antenna elements 101, each entry of each precoding vector 102, 103 having a form of w.sup.h×w.sup.v, wherein w.sup.v is a column specific coefficient and w.sup.h is a row specific coefficient, wherein each set of precoding vectors 102, 103 is associated with a different Kronecker product tradeoff parameter L, and wherein the value of L indicates that either each column specific coefficient w.sup.v is repeated on the antenna elements forming the sub-array of L≥1 column or the row specific coefficient w.sup.h is repeated on the antenna elements forming the sub-array of L≥1 rows.

(136) The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.