COMMUNICATION SYSTEM AND METHOD, BASE STATION, AND USER TERMINAL

Abstract

Provided a method in a mobile communication system comprising a base station adapted to create a precoding matrix for applying to data to be transmitted to a user terminal by using a channel estimate determined from a Reference Signal (RS) transmitted from the user terminal to the base station, the user terminal being adapted to transmit to the base station a Channel State Information (CSI) report, wherein the method comprises: the base station creating a relationship between the received CSI report and Interference pluses Noise covariance matrix that reflects amount of interference and noise observed at the user terminal's antennas, the base station determining the Interference pluses Noise covariance matrix based on the created relationship, and the base station using the determined Interference pluses Noise covariance matrix to estimate SINR for each data layer conditioned on the precoding matrix.

Claims

1. A method in a mobile communication system comprising a base station communicating via a radio link with at least a user terminal adapted to transmit to the base station a Channel State Information (CSI) report representing a channel state for communication from the base station to the user terminal, the base station being adapted to create a precoding matrix for applying to data to be transmitted to the user terminal (Base station-created precoding matrix) by using a channel estimate determined from a Reference Signal (RS) transmitted from the user terminal to the base station, the method comprising: the base station creating a relationship between the received CSI report and an Interference pluses Noise covariance matrix that reflects an amount of interference and noise observed at a plurality of antennas of the user terminal; the base station determining the Interference pluses Noise covariance matrix based on the created relationship; and the base station using the determined Interference pluses Noise covariance matrix to estimate a first Signal to Interference pluses Noise Ratio (SINR) for each data layer conditioned on the Base station-created precoding matrix.

2. The method according to claim 1, further comprising: in creating the relationship between the received CSI report and the Interference pluses Noise covariance matrix, the base station expressing first information included in the received CSI report in terms of second information included in the received CSI report and the Interference pluses Noise covariance matrix, wherein the first information is an SINR for each data layer conditioned on a precoding matrix created by the user terminal, and the second information is the precoding matrix created by the user terminal.

3. The method according to claim 1, further comprising: the base station first specifying to the user terminal which elements in the Interference pluses Noise covariance matrix are of interest; and the user terminal creating the CSI report by taking in account the elements specified by the base station.

4. A base station comprising: a reception unit to receive from a user terminal a Channel State Information (CSI) report representing a channel state for communication from the base station to the user terminal; and a precoding matrix creation unit to create a precoding matrix for applying to data to be transmitted to the user terminal (Base station-created precoding matrix), by using a channel estimate determined by the base station from a Reference Signal (RS) transmitted from the user terminal to the base station; a relationship creation unit to create a relationship between the received CSI report and an Interference pluses Noise covariance matrix that reflects an amount of interference and noise observed at a plurality of antennas of the user terminal; a determination unit to determine the Interference pluses Noise covariance matrix based on the created relationship; and a channel quality estimation unit to use the determined Interference pluses Noise covariance matrix to estimate a Signal to Interference pluses Noise Ratio (SINR) for each data layer conditioned on the Base station-created precoding matrix.

5. The base station according to claim 4, wherein the received CSI report includes: first information indicating an SINR for each data layer conditioned on a precoding matrix created by the user terminal; and second information indicating the precoding matrix created by the user terminal, wherein the relationship creation unit expresses the first information in terms of the second information and the Interference pluses Noise covariance matrix, as the relationship between the received CSI report and the Interference pluses Noise covariance matrix.

6. The base station according to claim 4, further comprising: a report request unit to first specify to the user terminal which elements in the Interference pluses Noise covariance matrix are of interest, when requesting the user terminal to create the CSI report.

7. A user terminal comprising: a plurality of antennas; a report creation unit to create a Channel State Information (CSI) report representing a channel state for communication from a base station to the user terminal by taking into account a specification from the base station related to an Interference pluses Noise covariance matrix that reflects an amount of interference and noise observed at the plurality of antennas; and a transmitter to transmit the created CSI report to the base station.

8. A base station comprising: a receiver configured to receive a first signal that includes first information indicating a first precoding matrix and second information indicating a first signal to interference pluses noise Ratio (SINR) that is estimated conditioned on the first precoding matrix; a determiner configured to determine a modulation and coding scheme (MCS) for a second precoding matrix based on the first precoding matrix and the first SINR; a coding and modulating unit configured to code and modulate a second signal based on the determined MCS; a precoder configured to precode the coded and modulated second signal by using the second precoding matrix; and a transmitter configured to transmit the precoded second signal.

9. The base station according to claim 8, wherein the determiner calculates a second SINR based on the first precoding matrix and the first SINR and determines the MCS for the second precoding matrix based on the calculated second SINR.

10. The base station according to claim 9, wherein the second information indicates the first SINR for each data layer, and the determiner calculates the second SINR for each data layer.

11. The base station according to claim 8, wherein the second precoding matrix is independent of the first precoding matrix.

12. A user terminal comprising: a transmitter configured to transmit a first signal that includes first information indicating a first precoding matrix and second information indicating a signal to interference pluses noise ratio (SINR) that is estimated conditioned on the first precoding matrix; and a receiver configured to receive a second signal, the second signal being coded and modulated by using a modulation and coding scheme (MCS) for a second precoding matrix, the MCS being determined based on the first precoding matrix and the SINR, the second signal being precoded with the second precoding matrix.

13. The user terminal according to claim 12, wherein the second information indicates the SINR for each data layer.

14. The user terminal according to claim 12, wherein the second precoding matrix is independent of the first precoding matrix.

15. A communication system comprising: a user terminal; and a base station, wherein the user terminal includes: a plurality of antennas; a generator to generate a report including information on a first precoding matrix created by the user terminal and information on a first signal to interference pluses noise Ratio (SINR) estimated by the user terminal conditioned on the first precoding matrix; a transmitter to transmit the report via the antennas to the base station, a receiver to receive via the antennas a signal transmitted from the base station, the signal being coded and modulated and further precoded by the base station, and wherein the base station includes: a plurality of antennas; a receiver to receive via the antennas the report from the user terminal; a determiner to determine a value of an interference pluses noise covariance matrix, based on the first SINR and the first precoding matrix included in the report; a precoding matrix generator to generate a second precoding matrix; an estimator to estimate a second SINR based on the determined value of the Interference pluses Noise covariance matrix, the second SINR being conditioned on the second precoding matrix; a selector to select a modulation and coding scheme (MCS) based on the estimated second SINR; a precoder to precode, using the second precoding matrix, a signal that is modulated and coded based on the selected MCS; and a transmitter to transmit the precoded signal via the antennas to the user terminal.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0073] FIG. 1 is a diagram illustrating a base station estimating downlink channel matrix by exploiting uplink-downlink channel reciprocity property in a related art.

[0074] FIG. 2 is a diagram illustrating a base station creating a precoding matrix for each user terminal for MU-MIMO operation in a related art.

[0075] FIG. 3 illustrates in a table format mapping between MCS and SINR in a related art.

[0076] FIG. 4 is a sequence diagram illustrating operations of user terminals creating a channel quality report in a related art.

[0077] FIG. 5 is a diagram illustrating an example of a mobile communication system in common for all exemplary embodiments of the present invention.

[0078] FIG. 6 is a diagram illustrating an example of a base station used in common for all exemplary embodiments of the present invention.

[0079] FIG. 7 is a diagram illustrating a user terminal used in common for all exemplary embodiments of the present invention.

[0080] FIG. 8

[0081] FIG. 7 is a diagram illustrating an example of operations of the overall system according to the first exemplary embodiment.

[0082] FIG. 9 is a flow chart illustrating an example of operations of a base station according to a first exemplary embodiment.

[0083] FIG. 10 is a diagram illustrating operations of the overall system according to a second exemplary embodiment.

[0084] FIG. 11 is a flow chart illustrating operations of a base station according to the second exemplary embodiment.

[0085] FIG. 12

[0086] FIG. 11 is a flow chart illustrating operations of a user terminal according to the second exemplary embodiment.

DESCRIPTION OF EMBODIMENTS

[0087] The following describes exemplary embodiments of the present invention with reference to the drawings. For illustrating modes of the present invention, the embodiments are constructed by assuming the application in the TDD LTE system.

[0088] First, a mobile communication system and devices, which are used in common for describing the present invention, will be described with reference to FIGS. 5 to 7.

[0089] FIG. 5 illustrates an example of a mobile communication system according to the exemplary embodiments. Referring to FIG. 5, the system comprises a base station (10) with multiple antennas (101), and a user terminal (20) with multiple antennas (201). The user terminal (20) is located in a base station radio coverage (30) and can communicate with the base station (10) in both uplink and downlink directions. Specifically, the user terminal (20) can transmit Uplink reference signal (Uplink RS, which is equivalent to Sounding Reference Signal (SRS) in LTE system) from M antennas 21R and CSI report to the base station (10) via uplink channel. The base station (10) can transmit Downlink RS (equivalent to CSI-RS in LTE system) and control signal and data to the user terminal (20) via downlink channel.

[0090] Note that in FIG. 5, the system is provided with a single user terminal only for the sake of simplifying explanation. In fact, the present invention can obviously be applied to a system with multiple user terminals.

[0091] FIG. 6 illustrates an example of an arrangement of the base station (10). Referring to FIG. 6, a plurality of base station antennas (101) are used for both receiving uplink signals and transmitting downlink signals from and to the user terminal (20), respectively.

[0092] Uplink/Downlink Multiplexer (102) multiplexes reception of Uplink signals and transmission of Downlink signals, in time.

[0093] Uplink RS/CSI report Demultiplexer (103) demultiplexes the reception of Uplink signals into, reception of Uplink RS and reception of CSI report. Demultiplexed Uplink RS and CSI report are supplied to Channel reciprocity-based downlink channel matrix Estimator (104) and CSI report and Interference pluses Noise covariance matrix relationship Creator (111), respectively.

[0094] Downlink RS/CSI report request/Data Multiplexer (108) multiplexes Downlink RS, CSI report request, and transmit data into Downlink signals.

[0095] Channel reciprocity-based downlink channel matrix Estimator (104), upon reception of the Uplink RS from the Uplink RS/CSI report Demultiplexer (103), estimates a downlink channel matrix from the base station (10) to each user terminal (20), by exploiting uplink-downlink channel reciprocity property. The estimation process of the downlink channel matrix is similar to that in the related art described with reference to FIG. 1.

[0096] Base-station-created precoding matrix Generator (105) obtains the estimated downlink channel matrix from the Channel reciprocity-based downlink channel matrix Estimator (104) and creates a Base-station-created precoding matrix for each user terminal 20. The creation process of the Base-station-created precoding matrix is similar to that in the related art described with reference to FIG. 2.

[0097] The Base-station-created precoding matrix is then applied to modulated data to be transmitted to the user terminal. The modulated data is obtained by coding (by a coder not shown) and modulating (by a modulator not shown) each layer of multiple-layer data stored in Data Buffer (107) with MCS selected by MCS Selector (106).

[0098] The modulated data having the precoding matrix applied thereto is mapped to Base station antennas (101) and transmitted through Downlink RS/CSI report request/Data Multiplexer (108) to the user terminal (20).

[0099] Downlink RS/CSI report request/Data Multiplexer (108) is also in charge of multiplexing transmissions of Downlink RS generated from Downlink RS Generator (109) and CSI report request generated from CSI report request Generator (110) besides transmission of modulated data having the precoding matrix applied thereto.

[0100] The Downlink RS is necessary for the user terminal (20) in estimating downlink channel matrix for later creating CSI report. The CSI report request is necessary for the user terminal (20) in creating the CSI report according to an instruction from the base station (10).

[0101] When the CSI report and Interference pluses Noise covariance matrix relationship Creator (111) receives the CSI report supplied from the Uplink RS/CSI report Demultiplexer (103), a process to provide MCS Selector (106) with necessary information for selecting appropriate MCS for each data layer of the user terminal (20) is started.

[0102] More specifically, the CSI report and Interference pluses Noise covariance matrix relationship Creator (111) takes into account the CSI report request corresponding to the received CSI report, and creates a relationship between the received CSI report and a still-unknown Interference pluses Noise covariance matrix. The Interference pluses Noise covariance matrix R.sub.I+N reflects an amount of interference and noise observed at the user terminal's antennas.

[0103] Then, Interference pluses Noise covariance matrix Determiner (112) uses the created relationship to determine a value of Interference pluses Noise covariance matrix.

[0104] After that, SINR conditioned on Base-station-created precoding matrix Estimator (113) uses the determined value of the Interference pluses Noise covariance matrix from the Interference pluses Noise covariance matrix Determiner (112) and the Base-station-created precoding matrix created by the Base-station-created precoding matrix Generator (105) to estimate SINR for each data layer observed at the user terminal (20).

[0105] Finally, MCS Selector (106) receives the estimated SINR for each data layer conditioned on the Base-station-created precoding matrix from the SINR conditioned on Base-station-created precoding matrix Estimator (113), and uses the estimated SINR to select the highest MCS for each data layer that satisfies a predefined data transmission error rate. The selection can be done, for example, by using the SINR-MCS mapping table similar to the table of the related art described with reference to FIG. 3.

[0106] FIG. 7 illustrates an example of an arrangement of the user terminal (20). Referring to FIG. 7, a plurality of user terminal antennas (201) are used for both receiving downlink signals and transmitting uplink signals from and to the base station (10), respectively.

[0107] Uplink/Downlink Multiplexer (202) multiplexes reception of Downlink signals and transmission of Uplink signals in time.

[0108] Downlink RS/CSI report request/Data Demultiplexer (203) demultiplexes the received Downlink signals to Downlink RS, CSI report request, and Data.

[0109] Uplink RS/CSI report Multiplexer (207) multiplexes Uplink RS generated by Uplink RS generator (208), and CSI report by Uplink RS/CSI report Multiplexer (207) to Uplink signals.

[0110] Data reception Processor (204), upon reception of the modulated data having the Base-station-created precoding matrix applied thereto and transmitted from the base station (10), performs data reception processes that include demodulation and decoding.

[0111] Downlink RS-based downlink channel matrix Estimator (205), upon reception of the Downlink RS transmitted from the base station (10), estimates downlink channel matrix from the base station (10) to the user terminal (20), itself.

[0112] CSI report Generator (206) obtains the estimated downlink channel matrix and the CSI report request transmitted by the base station (10).

[0113] Then, CSI report Generator (206) creates CSI report according to an instruction in the received CSI report request. The process for creating CSI report is similar to that in the related art described with reference to FIG. 4.

[0114] Specifically, the CSI report created by the CSI report Generator (206) contains information on a User-created precoding matrix, and information on SINR for each data layer conditioned on the User-created precoding matrix.

[0115] The created CSI report is then transmitted to the base station (10) through Uplink RS/CSI report Multiplexer (207).

[0116] Uplink RS Generator (208) generates Uplink RS to be transmitted to the base station (10) through Uplink RS/CSI report Multiplexer (207). The Uplink RS is necessary for the base station (10) in estimating downlink channel matrix by exploiting uplink-downlink channel reciprocity property for later creating Base-station-created precoding matrix.

[0117] In the following, based on the system and devices described with reference to FIGS. 5 to 7, details specific to two exemplary embodiments of the present invention will be described in respective order. Moreover, for clarity of explanation, it is assumed hereinafter that the base station (10) has 4 antennas and the user terminal (20) has 2 antennas, though not limited thereto. In the base station (10), each codeword is mapped to 2 layers (2-layer data).

First Exemplary Embodiment

[0118] A summary and then details of a first exemplary embodiment will be described below. In summary, a method provided by the first exemplary embodiment comprises the following steps.

[0119] The base station (10) receives CSI report from a user terminal (20).

[0120] The base station (10) then creates a relationship between the received CSI report and a still-unknown Interference pluses Noise covariance matrix that reflects an amount of interference and noise observed at the user terminal's antennas.

[0121] The base station (10) then determines a value of the Interference pluses Noise covariance matrix based on the created relationship with an assumption that the Interference pluses Noise covariance matrix is a diagonal matrix. Such assumption is valid in most mobile communication system that has the user terminal's antenna spacing larger than half-wavelength of an operational frequency.

[0122] After that, the base station (10) uses the determined Interference pluses Noise covariance matrix to estimate the SINR for each data layer conditioned on the Base-station-created precoding matrix.

[0123] Finally, the base station (10) selects MCS for each data layer based on the estimated SINR.

[0124] The following describes details of the first exemplary embodiment with reference to FIGS. 8 and 9.

<System Operations>

[0125] FIG. 8 illustrates operations for the overall system comprising both the base station (10) and the user terminal (20).

[0126] Referring to FIG. 8, at a beginning, the user terminal (20) transmits Uplink RS to the base station (10) (operation S1101).

[0127] The base station (10) uses the Uplink RS to estimate a 2×4 downlink channel matrix (H) by exploiting uplink-downlink channel reciprocity (operation S1102). Note that operation S1101 and S1102 are similar to those in the related art described with reference to FIG. 1.

[0128] Next, the base station (10) creates a 4×2 Base-station-created precoding matrix (F.sub.Base-created) (operation S1103). The base station (10) can use a method to create the Base-station-created precoding matrix, similar to that in the related art described with reference to in FIG. 2.

[0129] In order to obtain the CSI report from the user terminal (20), the base station (10) first transmits Downlink RS to the user terminal (20) (operation S1104).

[0130] The user terminal (20) then estimates downlink channel matrix by using the Downlink RS (operation S1105).

[0131] Then, the base station (10) transmits CSI report request to the user terminal (20) (operation S1106).

[0132] Finally, the user terminal (20) creates CSI report (operation S1107) and transmits the CSI report to the base station (10) (operation S1108). The process of requesting and reporting the CSI report from operation S1104 to S1108 can use the processes in the related art described with reference to FIG. 4.

[0133] Therefore, the base station (10) receives the CSI report that comprises two information items, namely:

(i) 4×2 User-created precoding matrix; and
(ii) SINR for each data layer conditioned on the User-created precoding matrix.

[0134] For the sake of simplicity, the 4×2 User-created precoding matrix is hereinafter denoted by F.sub.User-created and the SINR for each data layer conditioned on the User-created precoding matrix by γ.sub.User-created(m), where m denotes a data layer index and mε{1,2}.

[0135] On reception of the CSI report from the user terminal (20), the base station (10) creates a relationship between the received CSI report and the still-unknown 2×2 Interference pluses Noise covariance matrix (R.sub.I+N) that reflects an amount of interference and noise observed at the user terminal's antennas (operation S1109).

[0136] Then, the base station (10) determines a value of the Interference pluses Noise covariance matrix (R.sub.I+N) based on the created relationship (operation S1110).

[0137] After that, the base station (10) uses the determined Interference pluses Noise covariance matrix (R.sub.I+N) to estimate a new SINR per each data layer that is conditioned on the Base-station-created precoding matrix (F.sub.Base-created) (operation S1111).

[0138] More specific details of operation S1109 to S1111 will be explained in later section that describes the base station operation.

[0139] Moreover, for the sake of simplicity, the new SINR per each data layer that is conditioned on the Base-station-created precoding matrix (F.sub.Base-created) is hereinafter denoted by γ.sub.Base-created(m), where m denotes a data layer index and mε{1,2}.

[0140] After the base station (10) has obtained the estimate of SINR per each data layer conditioned on the Base-station-created precoding matrix (γ.sub.Base-created(m)), the base station (10) can select an appropriate MCS for each data layer (operation S1112). The selection of MCS can be based on the MCS-SINR mapping table similar to the one used in the related art described with reference to FIG. 3.

<Base Station Operations>

[0141] FIG. 9 is a flow chart illustrating operations of the base station (10). For the sake of simplicity of the explanation, it is assumed that the base station (10) has already created the Base-station-created precoding matrix, and has already requested for the CSI report. Therefore, referring to FIG. 9, in the first operation S1201, the base station (10) is regularly checking whether the CSI report has been received.

[0142] Upon reception of the CSI report, the base station (10) creates the relationship between the received CSI report and a still-unknown 2×2 Interference pluses Noise covariance matrix (R.sub.I+N) (operation S1202).

[0143] The base station (10) creates the relationship between the received CSI report and the Interference pluses Noise covariance matrix (R.sub.I+N) by expressing the received SINR for each data layer conditioned on the User-created precoding matrix (γ.sub.User-created(m)) in terms of the received User-created precoding matrix (F.sub.User-created) and Interference pluses Noise covariance matrix (R.sub.I+N). Such relationship can be expressed mathematically as shown below.

[00001]$\begin{array}{cc}{\gamma }_{\mathrm{User}-\mathrm{created}}\left(m\right)=\frac{{P_S\left[\left(G_U^H.Math.{\mathrm{HF}}_{\mathrm{User}-\mathrm{created}}\right).Math.{\left(G_U^H.Math.{\mathrm{HF}}_{\mathrm{User}-\mathrm{created}}\right)}^H\right]}_{\left(m,m\right)}}{{\left[G_U^H.Math.R_{I+N}.Math.G_U\right]}_{\left(m,m\right)}},\mathrm{for}.Math..Math.m\in \left\{1,2\right\}& \left(\mathrm{Eq}..Math.1\right)\end{array}$

where P.sub.S is Average transmit power per data layer, which is already known by the base station (10) as a relative power with respect to Downlink RS transmit power.

[0144] G.sub.U is a 2×2 receiving matrix at the user terminal based on the User-created precoding matrix, which can be assumed by the base station in the absence of such information from the user terminal. For example when it is assumed that ZF (zero-forcing) receiver is used, G.sub.U is given as follows:

G.sub.U=[)HF.sub.User-created).sub.H(HF.sub.User-created)].sup.−1(HF.sub.User-created).sup.H  (Eq. 2)

[0145] In Eq. 1, [X].sub.(a,b) indicates (a, b) element of matrix X.

[0146] Note: Assuming that a received vector y(k) observed at the user terminal k is modeled as y(k)=HFs(k)+v(k), where H is a channel matrix from a base station to the user terminal k, F is a precoding matrix, s(k) is a symbol vector, and v(k) is a noise vector (interference pluses noise vector), the Eq. 1 is based on the following well known formula:

[00002]$\mathrm{SINR}=\frac{{.Math.G^H.Math.\mathrm{HF}.Math.}^2}{G^H.Math.R_{I+N}.Math.G},$

where G is a receiving matrix, R.sub.I+N is an Interference pluses Noise covariance matrix: R.sub.I+N=E{v(k)v(k)).sup.H}, and a symbol power E{s.sup.2(k)} is normalize to E{s.sup.2(k)}=1, where E{.} indicates expectation.

[0147] After the relationship between the received CSI report and the 2×2 Interference pluses Noise covariance matrix (R.sub.I+N) is created, the base station (10) determines the value of Interference pluses Noise covariance matrix (R.sub.I+N) (operation S1203).

[0148] Specifically, the received values of SINR for each data layer conditioned on the User-created precoding matrix (γ.sub.User-created(m)) and the received value of User-created precoding matrix (F.sub.User-created) are substituted in (Eq. 1) to form a system of 2 equations having the same unknown 2×2 Interference pluses Noise covariance matrix (R.sub.I+N).

[0149] Then, the base station (10) assumes that the Interference pluses Noise covariance matrix is a diagonal matrix

R.sub.I+N=diag{R.sub.1,R.sub.2},  (Eq. 3)

[0150] and then solves the system of equations for their diagonal element values. Such assumption is valid in most mobile communication system that has the user terminal's antenna spacing larger than half-wavelength of the operational frequency.

[0151] The values of R.sub.1 and R.sub.2 under the assumption that the user terminal using the ZF receiver are shown below.

[00003]$\begin{array}{cc}{R}_1=P_S\left[\frac{{.Math.G_{U,22}.Math.}^2}{{.Math.G_{U,21}.Math.}^2}.Math.\frac{1}{{\gamma }_{\mathrm{User}-\mathrm{created}}\left(1\right)}-\frac{1}{{\gamma }_{\mathrm{User}-\mathrm{created}}\left(2\right)}\right]/\hspace{1em}\left[\frac{{.Math.G_{U,11}.Math.}^2.Math.{.Math.G_{U,22}.Math.}^2}{{.Math.G_{U,21}.Math.}^2}-{.Math.G_{U,12}.Math.}^2\right]& \left(\mathrm{Eq}..Math.4.Math.a\right)\\ R_2=P_S\left[\frac{1}{{\gamma }_{\mathrm{User}-\mathrm{created}}\left(2\right)}-\frac{{.Math.G_{U,12}.Math.}^2}{{.Math.G_{U,11}.Math.}^2}.Math.\frac{1}{{\gamma }_{\mathrm{User}-\mathrm{created}}\left(1\right)}\right]/\hspace{1em}\left[{.Math.G_{U,22}.Math.}^2-\frac{{.Math.G_{U,12}.Math.}^2.Math.{.Math.G_{U,21}.Math.}^2}{{.Math.G_{U,11}.Math.}^2}\right]& \left(\mathrm{Eq}..Math.4.Math.b\right)\end{array}$

[0152] where G.sub.U,ab indicates (a, b) element of matrix G.sub.U.

[0153] Note: The outline of the derivation of R.sub.1 and R.sub.2 is as follows. Assuming that G.sub.U is the ZF receiver, a matrix: (G.sub.U.sup.HHF.sub.User-created) in the numerator in the (Eq. 1) is a 2×2 identity matrix I, and the matrix enclosed in the parentheses in the numerator in the (Eq. 1) becomes P.sub.SI. The diagonal elements ((1,1) and (2,2) elements) of a matrix: G.sub.U.sup.HR.sub.I+NG.sub.U in the denominator in the (Eq. 1) are respectively given as: G.sub.11R.sub.1G.sub.11+G.sub.21R.sub.2G.sub.21, and G.sub.12R.sub.1G.sub.12+G.sub.22R.sub.2G.sub.22. Thus, (Eq. 1) is rewritten to the following simultaneous linear equations with two unknowns (R.sub.1, R.sub.2):

[00004]$G_{11}^2.Math.R_1+G_{21}^2.Math.R_2=\frac{P_s}{{\gamma }_{\mathrm{User}-\mathrm{created}}\left(1\right)}$$G_{12}^2.Math.R_1+G_{22}^2.Math.R_2=\frac{P_s}{{\gamma }_{\mathrm{User}-\mathrm{created}}\left(2\right)}$

[0154] Solving the above equations, R.sub.1 and R.sub.2 are given as the (Eq. 4a) and (Eq. 4b), respectively.

[0155] Once the value of Interference pluses Noise matrix (R.sub.I+N) is determined, the base station (10) uses that value to estimate the new SINR for each data layer that is conditioned on the Base-station-created precoding matrix (operation S1204).

[0156] The estimation is performed by modifying (Eq. 1) to take into account the Base-station-created precoding matrix (F.sub.Base-created) instead of the User-created precoding matrix (F.sub.User-created), and substituting in the value of the determined Interference pluses Noise covariance matrix. The mathematical expression of the new SINR for each data layer conditioned on the Base-station-created precoding matrix can be given below.

[00005]$\begin{array}{cc}{\gamma }_{\mathrm{Base}-\mathrm{created}}\left(m\right)=\frac{{P_S\left[\left(G_B^H.Math.{\mathrm{HF}}_{\mathrm{Base}-\mathrm{created}}\right).Math.{\left(G_B^H.Math.{\mathrm{HF}}_{\mathrm{Base}-\mathrm{created}}\right)}^H\right]}_{\left(m,m\right)}}{{\left[G_B^H.Math.R_{I+N}.Math.G_B\right]}_{\left(m,m\right)}},\mathrm{for}.Math..Math.m\in \left\{1,2\right\}& \left(\mathrm{Eq}..Math.5\right)\end{array}$

[0157] where G.sub.B is a 2×2 receiving matrix at the user terminal based on the Base-station-created precoding matrix, which can be assumed by the base station in the absence of such information from the user terminal. For example when it is assumed that ZF receiver is used, G.sub.B is given below:

G.sub.B=[(HF.sub.Base-created).sup.H(HF.sub.Bsse-created)].sup.−1(HF.sub.Base-created).sup.H,  (Eq. 6)

[0158] Finally, the base station (10) uses the estimated SINR conditioned on the Base-station-created precoding matrix (γ.sub.Base-created(m)) to select MCS (operation S1205).

[0159] The selection of MCS can be based on the MCS-SINR mapping table similar to the one used in the related art described with reference to FIG. 3.

<User Terminal Operations>

[0160] Operations of the user terminal (20) in the first exemplary embodiment are similar to the operations in the related art described with reference to FIG. 4. Therefore, their drawings and detailed explanations are omitted.

Advantageous Effects

[0161] According to the above described first exemplary embodiment, the information of SINR for each data layer conditioned on the Base-station-created precoding matrix can be made available at the base station in most of mobile communication system that has the user terminal's antenna spacing larger than half-wavelength of the operational frequency. Therefore, the base station can further use that information to select appropriate MCS for the Base-station-created precoding matrix and to maximize both user terminal's throughput and network capacity.

Second Exemplary Embodiment

[0162] The second exemplary embodiment makes modification to the first exemplary embodiment by adding 2 major operations.

[0163] The first operation includes the base station creating and transmitting to the user terminal composite CSI reports request that specifies different version of Interference pluses Noise covariance matrix for each composite CSI report. The different version of Interference pluses Noise covariance matrix indicates different elements in the Interference pluses Noise covariance matrix that are of interest to the base station.

[0164] The second operation includes the user terminal receiving the composite CSI reports request, creating and transmitting composite CSI reports to the base station according to the composite CSI reports request. The user terminal creates each of composite CSI reports by using different version of Interference pluses Noise covariance matrix specified by the base station.

[0165] With the first and second operations, the base station in the second exemplary embodiment exemplary embodiment can determine values of multiple versions of Interference pluses Noise covariance matrix, and combine them into one representative Interference pluses Noise covariance matrix.

[0166] The representative Interference pluses Noise covariance matrix would then be a general matrix rather than a diagonal matrix as in the first exemplary embodiment. The representative Interference pluses Noise covariance matrix is therefore valid for any mobile communication system and not limited to the one that has the user terminal's antenna spacing larger than half-wavelength of the operational frequency. Using this representative matrix, the base station can estimate the SINR conditioned on the Base-station-created precoding matrix and later select appropriate MCS.

[0167] The following describes details of the second exemplary embodiment with reference to FIGS. 10 to 12.

<System Operations>

[0168] FIG. 10 is a sequence chart illustrating operations for the overall system according to the second exemplary embodiment which comprises both the base station (10) and the user terminal (20) as illustrated in FIG. 1.

[0169] Referring to FIG. 10, at a beginning, the base station creates the 4×2 Base-station-created precoding matrix (F.sub.Base-created) and the user terminal estimates the 2×4 downlink channel matrix (H) by using the Downlink RS, similar to operations S1101 to S1105 (FIG. 8) according to the first exemplary embodiment.

[0170] The base station (10) then generates composite CSI reports request, wherein the request specifies different version of 2×2 Interference pluses Noise covariance matrix for each composite CSI report (operation S2101).

[0171] The different version of Interference pluses Noise covariance matrix indicates different elements in the Interference pluses Noise covariance matrix that are of interest to the base station. The base station (10) then transmits the composite CSI reports request to the user terminal (20) (operation S2102). More specific details of operation S2101 will be explained in later section that describes the base station operation.

[0172] Once the user terminal (20) receives the composite CSI reports request, the user terminal (20) creates composite CSI reports according to the request (operation S2103). The user terminal (20) creates each of composite CSI reports by using different version of Interference pluses Noise covariance matrix specified by the base station (10). The results are a User-created precoding matrix and corresponding SINR for each of composite CSI reports.

[0173] Then, the user terminal (20) transmits the composite CSI reports to the base station (10) (operation S2104). More specific details of operation S2103 will be explained later in section that describes the user terminal operation.

[0174] The base station (10), after receiving the composite CSI reports, creates relationships between the received composite CSI reports and the corresponding versions of Interference pluses Noise covariance matrix (operation S2105).

[0175] Then, the base station (10) determines the values of multiple versions of Interference pluses Noise covariance matrix based on the created relationships (operation S2106).

[0176] The base station (10), using the determined multiple versions of Interference pluses Noise covariance matrix, creates the representative Interference pluses Noise covariance matrix (operation S2107).

[0177] After that, the base station (10) estimates the SINR for each data layer conditioned on the Base-station-created precoding matrix by using the created representative Interference pluses Noise covariance matrix (operation S2108).

[0178] Finally, the base station (10) selects MCS based on the estimated SINR (operation S2109). More specific details of operation S2105 to S2109 will be explained later in section that describes the base station operation.

<Base Station Operations>

[0179] FIG. 11 is a flow chart illustrating operations of the base station (10). Here, it is assumed that the base station (10) has already created the Base-station-created precoding matrix (F.sub.Base-created). Therefore, in the first operation S2201 in FIG. 11, the base station (10) generates composite CSI reports request, wherein the request specifies different version of 2×2 Interference pluses Noise covariance matrix for each composite CSI report. The different version of Interference pluses Noise covariance matrix indicates different elements in the Interference pluses Noise covariance matrix that are of interest to the base station (10).

[0180] For clarity of explanation, the following describes an example of the base station (10) creating the request for two composite CSI reports.

[0181] The request specifies two Interference pluses Noise covariance matrices denoted by R.sub.I+N.sup.(1) and R.sub.I+N.sup.(2) for use in the creation of the first and second composite CSI reports, respectively. R.sub.I+N.sup.(1) and R.sub.I+N.sup.(2) are defined as shown below.

[00006]$\begin{array}{cc}{R}_{I+N}^{\left(1\right)}=\left[\begin{array}{cc}{R}_{11}& 0\\ 0& R_{22}\end{array}\right]& \left(\mathrm{Eq}..Math.7.Math.a\right)\\ R_{I+N}^{\left(2\right)}=\left[\begin{array}{cc}0& R_{12}\\ R_{21}& 0\end{array}\right]& \left(\mathrm{Eq}..Math.7.Math.b\right)\end{array}$

[0182] Next, the base station (10) transmits the request for 2 composite CSI reports to the user terminal (20) (operation S2202).

[0183] After that, the base station (10) regularly checks whether the 2 composite CSI reports have been received (operation S2203).

[0184] Here, it is assumed that the 2 composite CSI reports from the user terminal comprise 2 sets of 4×2 User-created precoding matrix and SINR for each data layer conditioned on the User-created precoding matrix. Specifically, the first set of User-created precoding matrix and corresponding SINR are denoted as F.sub.User-created.sup.(1) and γ.sub.User-created(m), respectively, where m indicates a data layer index and mγ{1,2}.

[0185] On the other hand, the second set of User-created precoding matrix and corresponding SINR are denoted by F.sub.User-created.sup.(2) and, respectively.

[0186] More specific details of how F.sub.User-created.sup.(1), F.sub.User-created.sup.(2), γ.sub.User-created(m).sup.(1) and γ.sub.User-created(m).sup.(2) are created will be explained later in section that describes the user terminal operation. However, it is noted here that F.sub.User-created.sup.(1) and γ.sub.User-created(m).sup.(1) are created based on R.sub.I+N.sup.(1) and F.sub.User-created.sup.(2) and γ.sub.User-created(m).sup.(2) are created based on R.sub.I+N.sup.(2).

[0187] After the base station (10) receives the 2 composite CSI reports from the user terminal (20), the base station (10) initializes composite CSI report processing order index i=1 (operation S2204).

[0188] Then, the base station (10) creates a relationship between the first composite CSI report and the first Interference pluses Noise covariance matrix R.sub.I+N.sup.(1) (operation S2205). This is done by modifying (Eq. 1) to take into account F.sub.User-created.sup.(1), γ.sub.User-created(m).sup.(1), and R.sub.I+N.sup.(1). The resulting mathematical expression is shown below.

[00007]$\begin{array}{cc}{\gamma }_{\mathrm{User}-\mathrm{created}}^{\left(1\right)}\left(m\right)=\frac{{P_S\left[\left(G_U^{\left(1\right).Math.H}.Math.{\mathrm{HF}}_{\mathrm{User}-\mathrm{created}}^{\left(1\right)}\right).Math.{\left(G_U^{\left(1\right).Math.H}.Math.{\mathrm{HF}}_{\mathrm{User}-\mathrm{created}}^{\left(1\right)}\right)}^H\right]}_{\left(m,m\right)}}{{\left[G_U^{\left(1\right).Math.H}.Math.R_{I+N}^{\left(1\right)}.Math.G_U^{\left(1\right)}\right]}_{\left(m,m\right)}},\mathrm{for}.Math..Math.m\in \left\{1,2\right\}& \left(\mathrm{Eq}..Math.8\right)\end{array}$

[0189] where G.sub.U.sup.(1) is a 2×2 receiving matrix at the user terminal based on the User-created precoding matrix F.sub.User-created.sup.(1), which can be assumed by the base station in the absence of such information from the user terminal. When it is assumed that ZF receiver is used, G.sub.U.sup.(1) is given as follows:

G.sub.U.sup.(1)=[(HF.sub.User-created).sup.H(HF.sub.User-created)].sup.−1(HF.sub.User-created).sup.H  (Eq. 9)

[0190] Then, based on (Eq. 8), the base station (10) determines the values of the first Interference pluses Noise covariance matrix R.sub.I+N.sup.(1)(operation S2206). Since a method for the determination is well known to those skilled in the arts, their details are omitted for conciseness.

[0191] Next, the base station (10) checks whether all of 2 composite CSI reports have been processed (operation S2207).

[0192] If there is remaining composite CSI report left to be processed, the processing order index i is incremented by one (operation S2208) and operation S2205 and S2206 are repeated. In this case, this implies the operations are repeated on the second composite CSI report, which would create a relationship between F.sub.User-created.sup.(2), γ.sub.User-created(m).sup.(2), and R.sub.I+N.sup.(2), and eventually determine the value of R.sub.I+N.sup.(2). Since the creation of such relationship and the determination of R.sub.I+N.sup.(2) are similar to the operations on the first composite CSI report described previously, their details are omitted for conciseness.

[0193] Once all of 2 composite CSI reports have been processed, the base station (10) creates the representative Interference pluses Noise covariance matrix from the first and second matrices R.sub.I+N.sup.(1) and R.sub.I+N.sup.(2), respectively (operation S2209).

[0194] The representative Interference pluses Noise covariance matrix are denoted as R.sub.1+N. The R.sub.1+N can be created by the following equation.

R.sub.I+N=R.sub.I+N.sup.(1)+R.sub.I+N.sup.(2)  (Eq. 10)

[0195] It is noted here that the representative Interference pluses Noise covariance matrix R.sub.I+N is a general matrix rather than a diagonal matrix as in the first exemplary embodiment. This implies that R.sub.I+N can accurately reflect interference and noise observed at the user terminal's antennas in any mobile communication system, not limited to the one that has the user terminal's antenna spacing larger than half-wavelength of the operational frequency.

[0196] After the representative Interference pluses Noise covariance matrix R.sub.I+N is created, the base station (10) uses it to estimate the SINR conditioned on the Base-station-created precoding matrix (F.sub.Base-created) (operation S2210).

[0197] The estimation is performed by modifying (Eq. 5) to take into account the representative Interference pluses Noise covariance matrix R.sub.I+N. The mathematical expression for the SINR for each data layer denoted by γ.sub.Base-created(m) is shown below.

[00008]$\begin{array}{cc}{\gamma }_{\mathrm{Base}-\mathrm{created}}\left(m\right)=\frac{{P_S\left[\left(G_B^H.Math.{\mathrm{HF}}_{\mathrm{Base}-\mathrm{created}}\right).Math.{\left(G_B^H.Math.{\mathrm{HF}}_{\mathrm{Base}-\mathrm{created}}\right)}^H\right]}_{\left(m,m\right)}}{{\left[G_B^H.Math.{\stackrel{\_}{R}}_{I+N}.Math.G_B\right]}_{\left(m,m\right)}},\mathrm{for}.Math..Math.m\in \left\{1,2\right\}& \left(\mathrm{Eq}..Math.11\right)\end{array}$

[0198] Finally, the base station (10) uses the estimated SINR conditioned on the Base-station-created precoding matrix (γ.sub.Base-created(m)) to select MCS (operation S2211). The selection of MCS can be based on the MCS-SINR mapping table similar to the one used in the related art described in FIG. 3.

<User Terminal Operations>

[0199] FIG. 12 is a flow chart illustrating operations of the user terminal (20). Here, it is assumed that the user terminal (20) has already estimated the downlink channel matrix (H) by using the Downlink RS. Therefore, in the first operation S2301, the user terminal (20) regularly checks whether the request for 2 composite CSI reports have been received.

[0200] Upon reception of the request for 2 composite CSI reports from the base station (10), the user terminal (20) initializes the composite CSI report processing order index i=1 (operation S2302).

[0201] Then, the user terminal (20) creates the first composite CSI report based on the specified first Interference pluses Noise covariance matrix R.sub.I+N.sup.(1)(operation S2303).

[0202] Specifically, the user terminal (20) first substitutes non-zero elements of R.sub.I+N.sup.(2) with values of Interference pluses Noise covariance matrix that the user terminal estimates by itself (User-estimated Interference pluses Noise covariance matrix).

[0203] The details of deriving the User-estimated Interference pluses Noise covariance matrix are omitted here, since it is well known that the User-estimated Interference pluses Noise covariance matrix can easily be derived at the user terminal (20) by using the downlink channel matrix (H) and the Downlink RS.

[0204] Next, the user terminal (20) creates the 4×2 User-created precoding matrix F.sub.User-created.sup.(1) that maximizes the received SINR calculated by using the first Interference pluses Noise covariance matrix R.sub.I+N.sup.(1).

[0205] The mathematical expression of F.sub.User-created.sup.(1) in terms of R.sub.I+N.sup.(1) is given as below.

[00009]$\begin{array}{cc}{F}_{\mathrm{User}-\mathrm{created}}^{\left(1\right)}=\arg .Math..Math.\underset{\tilde{F}\in C^{4\times 2}}{\max }.Math.\left\{\underset{m=1}{\overset{2}{.Math.}}.Math.{\log }_2\left(1+\frac{{P_S\left[\left({\tilde{G}}^H.Math..Math.H.Math.\tilde{F}\right).Math.{\left({\tilde{G}}^H.Math..Math.H.Math.\tilde{F}\right)}^H\right]}_{\left(m,m\right)}}{{\left[{\tilde{G}}^H.Math.R_{I+N}^{\left(1\right)}.Math.\tilde{G}\right]}_{\left(m,m\right)}}\right)\right\}& \left(\mathrm{Eq}..Math.12\right)\end{array}$

[0206] where C.sup.4×2 is a space of 4×2 matrix with complex number elements,

[0207] {tilde over (G)} is a 2×2 receiving matrix at the user terminal based on the User-created precoding matrix {tilde over (F)}. For example when the ZF receiver is used, {tilde over (G)} is given as below.

[00010]$\begin{array}{cc}\tilde{G}={\left[{\left(H.Math.\tilde{F}\right)}^H.Math.\left(H.Math.\tilde{F}\right)\right]}^{-1}.Math.{\left(H.Math.\tilde{F}\right)}^H,& \left(\mathrm{Eq}..Math.13\right)\end{array}$

[0208] It is noted here that solution of (Eq. 12) in LTE system typically uses a predefined set of 4×2 matrices denoted as codebook, instead of C.sup.4×2. This reduces the solution to finding the matrix in the codebook that maximizes the expression in (Eq. 12) and using that matrix as F.sub.User-created.sup.(1).

[0209] Next, the SINR for each data layer conditioned on the created User-created precoding matrix F.sub.User-created.sup.(1) is determined by using again the first Interference pluses Noise covariance matrix R.sub.I+N.sup.(1). This is equivalent to the following mathematical expression.

[00011]$\begin{array}{cc}{\gamma }_{\mathrm{User}-\mathrm{created}}^{\left(1\right)}\left(m\right)=\frac{{P_S\left[\left({\stackrel{\_}{G}}_U^{\left(1\right).Math.H}.Math.{\mathrm{HF}}_{\mathrm{User}-\mathrm{created}}^{\left(1\right)}\right).Math.{\left({\stackrel{\_}{G}}_U^{\left(1\right).Math.H}.Math.{\mathrm{HF}}_{\mathrm{User}-\mathrm{created}}^{\left(1\right)}\right)}^H\right]}_{\left(m,m\right)}}{{\left[{\stackrel{\_}{G}}_U^{\left(1\right).Math.H}.Math.R_{I+N}^{\left(1\right)}.Math.{\stackrel{\_}{G}}_U^{\left(1\right)}\right]}_{\left(m,m\right)}},\mathrm{for}.Math..Math.m\in \left\{1,2\right\}& \left(\mathrm{Eq}..Math.14\right)\end{array}$

[0210] where G.sub.U.sup.(1) is a 2×2 receiving matrix at the user terminal based on the User-created precoding matrix F.sub.User-created.sup.(1). For example, when the ZF receiver is used, G.sub.U.sup.(1) is given as below.

G.sub.U.sup.(1)=[(HF.sub.User-Created.sup.(1)).sup.H(HF.sub.User-Created.sup.(1))].sup.−1(HF.sub.User-Created.sup.(1)).sup.H,  (Eq. 15)

[0211] After the first composite CSI report is created, the user terminal (20) checks whether all of 2 composite CSI reports have been created (operation S2304).

[0212] If there is remaining composite CSI report left to be processed, the processing order index i is incremented by one (operation S2305) and operation S2303 is repeated.

[0213] In this case, this implies the operation is repeated on the second composite CSI report, which would create the User-created precoding matrix F.sub.User-created.sup.(2) and the corresponding SINK γ.sub.User-created.sup.(2)(m) by using the second Interference pluses Noise covariance matrix R.sub.I+N.sup.(2). Since such operation is similar to the operation on the first composite CSI report, its detail is omitted for brevity.

[0214] Once all 2 composite CSI reports are created, the user terminal (20) transmits them to the base station (10) (operation S2306).

Advantageous Effects

[0215] According to the above described second exemplary embodiment, the information of SINR for each data layer conditioned on the Base-station-created precoding matrix can be made available at the base station in any mobile communication system, not limiting to the one that has the user terminal's antenna spacing larger than half-wavelength of the operational frequency. Therefore, the second exemplary embodiment is superior to the first exemplary embodiment in that it is applicable to wider range of mobile communication system conditions.

<Generalization and Variation of Embodiments>

[0216] Although the previous description on the second exemplary embodiment used specific examples of the base station and the user terminal having 4 and 2 antennas, respectively, the embodiment can be applied to any antenna configurations.

[0217] To generalize, under the condition that the number of antennas at the base station is always greater than the user terminal, the number of data layer and the dimension of the Interference pluses Noise covariance matrix solely depend on the number of antennas at the user terminal. That is to say, if the user terminal has M antennas, then, there will be M data layers and the Interference pluses Noise covariance matrix will have a dimension of M×M.

[0218] In this case, the base station can create the composite CSI reports request by specifying M different versions of Interference pluses Noise covariance matrix. Each version specifies different M non-zero elements and conforms to be an Hermitian matrix. The M non-zero elements condition ensures that the number of elements to be determined is the same as the number of SINR per data layer received from the user terminal according to one composite CSI report.

[0219] The Hermitian matrix condition ensures that the property of covariance matrix always holds and the resulting SINR per each data layer determined by the user terminal is always real and positive.

[0220] Variations of the exemplary embodiments are as follows, but not limited thereto.

[0221] One variation is the method to request and transmit the composite CSI reports. Instead of the base station using a single request as in the above described embodiments, it can use multiple requests transmitted over multiple time slots, wherein each request asks for different composite CSI report.

[0222] Similarly, instead of the user terminal transmitting the composite CSI reports in one shot, it can transmit each of the reports over multiple time slots.

[0223] Finally, as a general note for both the first and second exemplary embodiments, although the application in the TDD LTE system is assumed, the embodiments are not limited to only such application.

[0224] For example, in the FDD (Frequency Division Duplex) LTE system that uses a pair of carrier frequencies close together for uplink and downlink communication, the uplink-downlink channel reciprocity property still holds, and thus the present invention can also be applied.

[0225] It is noted that In PTL1-PTL3 in the citation list, there is not disclosed any arrangement in which a base station creates a relationship between a CSI report received from a user equipment and Interference pluses Noise covariance matrix that reflects amount of interference and noise observed at the user terminal's antennas; and the base station determines the Interference pluses Noise covariance matrix based on the created relationship; and the base station, using the determined Interference pluses Noise covariance matrix, estimates SINR for each data layer conditioned on the Base station-created precoding matrix.

[0226] Each disclosure of the above listed Patent Literatures and Non-Patent Literatures is incorporated by reference into the present document. Modifications and adjustments of embodiments and examples are possible within bounds of the entire disclosure (including the scope and range of each of the claims) of the present invention, and also based on fundamental technological concepts thereof. Furthermore, a wide variety of combinations and selections of various disclosed elements is possible within the scope of the claims of the present invention. That is, the present invention clearly includes every type of transformation and modification that a person skilled in the art can realize according to technological concepts and the entire disclosure including the scope of the claims.

REFERENCE SIGNS LIST

[0227] 10, 10R base station [0228] 11R antennas [0229] 12-1 User terminal 1's Base-station-created precoding matrix [0230] 12-2 User terminal 2's Base-station-created precoding matrix [0231] 20, 20R user terminal [0232] 21R antennas [0233] 22-1, 22-2 Receiving matrix [0234] Base station radio coverage [0235] 101 Base station antennas [0236] 102 Uplink/Downlink Multiplexer [0237] 103 Uplink RS/CSI report Demultiplexer [0238] 104 Channel reciprocity-based downlink channel matrix Estimator [0239] 105 Base-station-created precoding matrix Generator [0240] 106 MCS Selector [0241] 107 Data Buffer [0242] 108 Downlink RS/CSI report request/Data Multiplexer [0243] 109 Downlink RS Generator [0244] 110 CSI report request Generator [0245] 111 CSI report and Interference pluses Noise covariance matrix relationship Creator [0246] 112 Interference pluses Noise covariance matrix Determiner [0247] 113 SINR conditioned on Base-station-created precoding matrix Estimator [0248] 201 User terminal's antennas [0249] 202 Uplink/Downlink Multiplexer [0250] 203 Downlink RS/CSI report request/Data Demultiplexer [0251] 204 Data reception Processor [0252] 205 Downlink RS-based downlink channel matrix Estimator [0253] 206 CSI report Generator [0254] 207 Uplink RS/CSI report Multiplexer [0255] 208 Uplink RS Generator