JP6418334B2 - Communication system and method, base station, and user terminal - Google Patents

Description

  The present invention relates to a mobile communication system and method, a base station, and a user terminal.

  In recent years, the explosive increase in mobile data communication traffic due to the widespread use of smartphones and other smart devices has accelerated the use of various technologies for mobile network operators or the study of their use. ing. One of the main realization technologies is MIMO (Multi-Inputs and Multi-Outputs) technology.

  Specifically, the MIMO technology has already been standardized in the LTE: Long-Term Evolution and LTE-Advanced standards of the 3GPP: Third Generation Partnership Project. The MIMO technology includes two sub-categories: Single-User MIMO (SU-MIMO) and Multi-User MIMO (MU-MIMO). SU-MIMO technology enables simultaneous transmission of multilayer data and sharing of frequency resources between a base station and a single user terminal. On the other hand, in addition to providing the same advantages as SU-MIMO, MU-MIMO technology can enable simultaneous data transmission and sharing of frequency resources between a base station and multiple user terminals. Therefore, to maximize network capacity, mobile operators around the world are considering the use of MU-MIMO technology.

  MU-MIMO is most effective when the channel from the base station to all the user terminals under its control can be accurately known. This is the channel reciprocity between the downlink direction channel and the reverse direction (uplink direction) channel, especially for the downlink (base station to user terminal) that occupies most of the mobile data communication traffic. It can be easily implemented in a Time-Division Duplexing (TDD) system including a base station configured to utilize the characteristics.

  FIG. 1 shows a typical example of a related art system in which channel reciprocity between one base station and one user terminal is utilized by the base station.

  Referring to FIG. 1, the user terminal 20R receives an uplink reference signal (uplink RS (Reference Signal), which corresponds to a sounding reference signal (SRS) in the LTE system) from M antennas 21R. Transmit (operation S11).

  The base station 10R receives the uplink RS transmitted from each of the antenna (s) 21R of the user terminal 20R (operation S12).

Then, the base station 10R is to estimate the channel from all user terminals of the antenna 21R to all the base station antenna 11R, obtains the uplink channel matrix _{H U} (operation S13). H _U is an N _T × M impulse response matrix. N _T is the number of antennas 11R of the base station 10R, and M is the number of antennas 21R of the user terminal 20R.

Finally, the base station 10R, call channel reciprocity property (the invoke), a downlink channel matrix _{H D} using uplink channel matrix _{H U,} determined as H D ^{= H} _{H U.} Here, H _D is the impulse response matrix of M × N _T, the superscript H denotes the complex conjugate transpose or Hermitian transpose (operation S14).

  When base station 10R obtains all downlink channel matrices (plurality) for all user terminals, base station 10R precodes each user terminal (hereinafter also referred to as “base station created precoding matrix”). Can be created. The data of the user terminal for which the precoding matrix is set can be prevented from interfering with the data of other user terminals. There are several ways to create a precoding matrix.

FIG. 2 is a diagram for explaining an example of a block-diagonalization (BD) precoding method described in Non-Patent Document 1. FIG. 2 shows that base station 10R creates two base stations for user terminals 1 and 2 when downlink channel matrices H ₁ and H ₂ are known for user terminals 1 and 2 respectively. The example of creating precoding matrices F ₁ and F ₂ (12-1 and 12-2) is illustrated.

In order to ensure that the data of one user terminal does not interfere with the data of the other user terminal, the base station 10R uses the base station created precoding matrix (F ₁ , F ₂ ) for the _one user terminal. (F ₁ , F ₂ ) corresponds to a null space matrix (V ₂ ⁽ⁿ⁾ , V ₁ ⁽ⁿ⁾ ) of the channel of the other user terminal. That is,
F ₁ = V ₂ ⁽ⁿ⁾ and F ₂ = V ₁ ⁽ⁿ⁾
It is.
Where V _i ⁽ⁿ⁾ (i = 1, 2) each form a null space orthogonal basis of H _i (channel matrix from base station to i-th user terminal). To do.

More specifically, let _NT be the number of antennas 11R of the base station 10R. The number of antennas (21R-i) (i = 1, 2) of the i-th user terminal (20R-i) is N _ri (= M). However, Nr = N _r1 + N _r2 (= 2M). H _i is the downlink channel matrix (N _ri × N _T impulse response matrix with rank L _i ). H _i by using the SVD (singular value decomposition), is decomposed as follows.
H _i = U _i D _i [V _i ^(S) V _i ⁽ⁿ⁾ ] ^H
here,
U _i (i = 1, 2) is a unitary matrix of (N _r −N _ri ) × (N _r −N _ri ),
D _i (i = 1, 2) has a positive singular value of L _i (rank of H _i ) and zero in the diagonal component and zero in the non-diagonal component (N _r −N _ri ) × _NT matrix,
^{_{V i (S) (i =}} 1,2) is a matrix of _{N T} × _{L i} with _{N T} orthogonal vectors corresponding to the positive singular values of _{L i} as column vectors,
^{_{V i (n) (i =}} 1,2) is a matrix of _{N T} × with orthogonal vectors of _{N T} which corresponds to the singular values of zero as a column vector _(N T -L _i).

In the base station 10R, each modulated codeword (a codeword from an encoder (not shown) is modulated by a modulator (not shown)) is mapped to one or a plurality of layers. The number of layers is less than or equal to the number of transmit antenna ports. Each layer is mapped to one or more transmit antenna ports associated with a physical transmit antenna by a precoding matrix. In the base station 10R, each of the _{N T} antennas respectively connected to adders 13-1 to _{13-N T} of, for the user terminal 1 and 2, adding the mapped layer (associated mapped layers).

  When one user terminal (20R-1 / 20R-2) receives a signal transmitted from the base station 10R, this one user terminal will cause interference from the other user terminal (20R-2 / 20R-1). I do not receive it.

  Therefore, the user terminal extracts only the multi-layer data for the user terminal itself, for example, by using Zero-Forcing (ZF) or Minimum Mean Squared Error (MMSE) criterion. In addition, the reception matrix G can be adjusted.

Note: The following is an overview of the zero forcing (ZF) receiver. The received signal (vector) r observed at the user terminal is
r = Hx + v
Assuming that x is a transmission vector, H is a channel matrix from the base station to the user terminal, and v is a noise vector (additive white gausian noise (AWGN)), If the channel state information (CSI) is complete, the ZF estimation of the transmission vector is
y ~ = G (Hx + v) = x + Gv
Can be expressed as Here, G = [H ^H H] ⁻¹ H ^H is the ZF receiver, and the superscript −1 represents the inverse of the matrix. H ⁺ = [H ^H H] ⁻¹ H ^H is a pseudo inverse matrix (the left inverse of H, ie, H ⁺ H = I, where I is a unit matrix).

  Interference between user terminals (Inter-User Interference (IUI)) can be handled by the base station-generated precoding matrix, but the base station maximizes the throughput of each user terminal and hence the network capacity. Therefore, it is still necessary to select an appropriate modulation and coding scheme (MCS) for each data layer.

  The selection of MCS by the base station is performed as follows, for example.

  The base station first obtains the received channel quality observed by each user terminal conditioned on the base station created precoding matrix. The received channel quality reflects the power of the desired signal relative to the power of interference and noise appearing at the user terminal. Interference in this case may be due to incomplete nulling of inter-user interference by the base station serving the user terminal, or of signals from neighboring base stations serving different user terminals. Involves unwanted signals generated by transmission.

  Next, the maximum MCS that satisfies a predetermined data transmission error rate is determined using the reception channel quality. The most commonly used receive channel quality metric is the signal to interference noise ratio (SINR) defined as the desired signal power divided by the sum of the interference and noise power. plus Noise Ratio).

  FIG. 3 shows an example of an MCS-SINR mapping table showing an example of how to map SINR to MCS. FIG. 3 is taken from Section 7.2.3 Channel Quality Indicator (CQI) definition of Non-Patent Document 2.

Referring to FIG. 3, QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), and 64QAM are given to “modulation”.
“Code rate” is k / n, which is useful information of each k bits while the encoder generates n bits of data (of which nk is redundant).
"Spectral efficiency (usage) (C) (bit / s / Hz)" is the net bit rate (bit / s) divided by the communication channel bandwidth (Herz) (excluding error correction codes) Useful information rate) or maximum throughput.
With respect to “SINR”, from the well-known Shannon's channel capacity equation, the spectral efficiency (C) is given by C = log ₂ (1 + SINR). Therefore, SINR (dB) is given by log ₁₀ (2 ^C −1).

  Therefore, in conclusion, the base station selects the appropriate MCS for each data layer and determines the SINR observed by the user terminal conditioned on the base station created precoding matrix in order to maximize the channel (network) capacity. Need to get.

  In a mobile communication system such as LTE, there are several mechanisms for a user terminal to report the received SINR observed by the user terminal to the base station. Non-Patent Document 2 Section 7.2 UE procedure for reporting Channel State Information (CSI) describes in detail such a mechanism. ing.

  FIG. 4 is a simplified sequence chart illustrating the CSI reporting operation disclosed in Non-Patent Document 2. Here, the system according to this example includes only one base station and two user terminals for simplicity.

  Both user terminals 1 and 2 (20R-1, 20R-2) first transmit a downlink reference signal (downlink RS, which is a channel in the LTE system) transmitted from each of the antennas of the base station to each user terminal. A status information reference signal (corresponding to a CSI-RS) is received (operation S21).

Next, user terminals 1 and 2 (20R-1, 20R-2) respectively transmit downlink channel matrices H ₁ and H ₂ from the base station antenna to user terminals 1 and 2 based on the received downlink RS. Estimate (operations S22-1 and S22-2).

  The base station 10R transmits a channel quality information report request to each of the user terminals 1 and 2 (20R-1 and 20R-2) (operations S23-1 and S23-2).

After that, the user terminals 1 and 2 (20R-1 and 20R-2) use the estimated channel to _{precode the} matrices F _{user1-created} and F _{user2-created} (hereinafter referred to as user) in order to maximize the received SINR. Created precoding matrix) (operations S24-1, S24-2).

Next, user terminals 1 and 2 (20R-1 and 20R-2) estimate the received SINR of each data layer conditioned on the user-created precoding matrices F _{user1-created} and F _{user2-created} , respectively (operation S25-1, S25-2).

Finally, the user terminal 1 (20R-1) reports both the user-created precoding matrix F _{user1-created} and the received SINR conditioned on F _{user1-created} to the base station 10R (operation S26-1), The user terminal 2 (20R-2) reports both the user _-created precoding matrix F _{user2-created} and the received SINR conditioned on the user _-created precoding matrix F _{user2-created} to the base station 10R (operation S26-2). ).

  More specifically, in LTE, a user terminal selects one precoding matrix from a predetermined set of precoding matrices (candidate: called codebook) known to both the user terminal and the base station. Thus, the process of creating a user-created precoding matrix is performed. The user terminal reports the user-created precoding matrix and the corresponding SINR to the base station using a precoding matrix index (PMI) index and a channel quality indicator (CQI) index, respectively. . The higher the CQI (0 to 15) reported from the user terminal to the base station, the further efficiencies are achieved by the base station using a higher modulation scheme (QPSK to 64QAM) and a faster code rate.

Patent Document 1 describes a method in eNodeB in a MIMO system. This method receives a signal (s) from (one) user equipment in a space division multiplex group, estimates uplink channel characteristics according to the received signals, and determines between uplink channel characteristics and downlink channel characteristics. Determining a downlink precoding matrix using zero forcing; and, based on the determined downlink precoding matrix, a downlink signal to the user equipment in the space division multiplex group Sending. The user equipment determines whether the measured downlink vector channel process satisfies a predetermined condition. If the condition is met, the user equipment transmits information corresponding to the estimated downlink vector channel process to the eNodeB to perform channel reciprocity calibration.
Patent Document 2 discloses extraction means for a base station to extract a matrix component for a stream closest to a channel matrix indicating a channel state in a channel transmission path in a precoding matrix corresponding to PMI received from a mobile station device. Describes a MIMO system having generating means for generating precoding weights based on the matrix components extracted by the extracting means. The user apparatus measures the amount of channel change using the received signal from the receiving antenna. Based on the measured channel change amount, the user apparatus depends on the phase and amplitude control amount (precoding weight (precoding matrix)) that maximizes the reception SINR of transmission data from each of the transmission antennas of the base station eNodeB. The PMI is selected, and the selected PMI is fed back as channel information to the base station eNodeB via the uplink. In response to the PMI fed back from the user apparatus UE, the base station eNodeB transmits data to which precoding is applied to the user apparatus.

Special table 2012-531132 gazette JP 2011-151540 A

Q. H. Spencer, A. L. Swindlehurst, and M. Haardt, "Zero-forcing methods for downlink spatial multiplexing in multiuser MIMO channels," IEEE Transactions on Signal Processing, vol. 52, no. 2, Feb. 2004 3GPP TS 36.213 V11.7.0, "Technical specification: Physical layer procedures (Release 11)," 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA), Jun. 2014

  The analysis of related technology is shown below.

  The mechanism of the related art mobile communication system such as Non-Patent Document 2 fails to provide sufficient information to the base station to select an appropriate MCS for the base station generated precoding matrix. Yes. This is because, in the related art, the received SINR reported by the user terminal is conditioned on the user generated precoding matrix instead of the base station generated precoding matrix. These two types of precoding matrices can be very different from each other in MU-MIMO operation.

  Specifically, the base station created precoding matrix takes into account the channels to all user terminals to prevent data from one user terminal from interfering with all other user terminals. The user-created precoding matrix only considers the channel to one user terminal itself. Therefore, it is impossible in MU-MIMO to create a precoding matrix for effectively avoiding interference between user equipments (UEs) only from a user-created precoding matrix.

  The present invention has been achieved in view of the above problems, and one of its purposes is to enable a base station to estimate a received SINR observed by a user terminal conditioned on a base station created precoding matrix. A method and system is provided.

According to one aspect of the present invention, there is provided a method in a mobile communication system including a base station that communicates with at least one user terminal via a radio link, wherein the base station transmits from the user terminal to the base station. Creating a precoding matrix (base station creation precoding matrix) to be applied to data transmitted to the user terminal using channel estimation determined from the uplink reference signal (uplink RS) performed And
The base station notifies the user terminal of a base station creation precoding matrix, and the user terminal estimates a signal-to-interference and noise ratio (SINR) for each data layer conditioned on the notified precoding matrix, and estimates A method is provided for reporting the received SINR to a base station.

According to another aspect of the present invention, a user terminal for a mobile communication system comprising:
A transmitter for transmitting an uplink reference signal (uplink RS) to the base station;
A receiving unit that receives a precoding matrix generated by the base station and notified by the base station, using a channel estimation determined from an uplink RS, to be applied to data transmitted to the user terminal by the base station; ,
A user terminal including a channel quality report creation unit that estimates a signal-to-interference noise ratio (SINR) for each data layer conditioned on the precoding matrix notified by the base station and reports the estimated SINR to the base station. Provided.

According to yet another aspect of the present invention, the channel estimation determined from the uplink reference signal (uplink RS) transmitted from the user terminal to the base station is used to apply to the data transmitted to the user terminal. A generator for generating a precoding matrix of
A channel quality report requesting unit that notifies the user terminal of a precoding matrix and requests the user terminal to report a signal-to-interference noise ratio (SINR) conditioned on the precoding matrix notified to the user terminal by the base station. And a base station is provided.

  According to a further aspect of the present invention, there is provided a communication system including a user terminal and a base station respectively presented in each of the above aspects. According to still another aspect of the present invention, there is provided a computer-readable fixed storage medium that stores a program for causing a base station to execute the processes shown in the above viewpoints. Furthermore, a non-transitory computer-readable storage medium that stores a program for causing a user terminal to execute the processes described in the above aspects is also provided.

  ADVANTAGE OF THE INVENTION According to this invention, the information of the reception SINR observed by the user terminal conditioned by the base station preparation precoding matrix can be made available in the base station. Thus, the base station further uses this information to select an appropriate MCS for the base station created precoding matrix and to maximize both user terminal throughput and network capacity. Can do.

FIG. 10 is a diagram illustrating that a base station estimates a downlink channel matrix by using uplink-downlink channel reciprocity characteristics in the related art. FIG. 6 is a diagram illustrating that a base station creates (one) precoding matrix for each user terminal for MU-MIMO operation in the related art. It is a figure which illustrates the format mapping between MCS and SINR in related technology with a table. It is a sequence diagram explaining operation which a user terminal produces a channel quality report in related technology. It is a figure explaining an example of the mobile communication system of one exemplary embodiment of the present invention. It is a figure explaining an example of the base station of exemplary embodiment of this invention. It is a figure explaining an example of the user terminal according to exemplary embodiment of the present invention. FIG. 6 illustrates an example of overall system operation according to an exemplary embodiment of the present invention. 5 is a flowchart illustrating an example of base station operation according to an exemplary embodiment of the present invention. 6 is a flowchart illustrating an example of operation of a user terminal according to an exemplary embodiment of the present invention.

  Exemplary embodiments of the present invention are described below with reference to the drawings. For the purpose of describing aspects of the invention, these exemplary embodiments are configured for application in a TDD LTE system.

  First, the mobile communication system and apparatus are commonly used to describe the present invention, and will be described with reference to FIGS.

  FIG. 5 illustrates an example of a mobile communication system according to an exemplary embodiment. Referring to FIG. 5, the system includes a base station (10) having a plurality of antennas (101) and a user terminal (20) having a plurality of antennas (201). The user terminal (20) is located in the 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 an uplink RS (corresponding to SRS in the LTE system) and an SINR report to the base station (10) via the uplink channel. The base station (10) can transmit a downlink RS (corresponding to CSI-RS in the LTE system), a control signal, and data to the user terminal (20) via the downlink channel.

  It should be noted that in FIG. 5, the system has only one user terminal, but this is merely for ease of explanation. In fact, the present invention is obviously applicable to a system having a plurality of user terminals.

  FIG. 6 illustrates an example of the configuration of the base station (10). Referring to FIG. 6, multiple base station antennas (101) are used for both receiving uplink signals from user terminals (20) and transmitting downlink signals to user terminals (20).

  The uplink / downlink multiplexer (multiplexer) (102) multiplexes the reception of uplink signals and the transmission of downlink signals in time.

  The uplink RS / SINR report demultiplexer (demultiplexer) (103) separates uplink signal reception into uplink RS reception and SINR report reception. For the separated uplink RS and SINR reports, the former is supplied to the channel reciprocity-based downlink channel matrix estimator (104) and the latter to the MCS selector (106).

  Downlink RS / SINR report request / data multiplexer (108) multiplexes downlink signal transmission, downlink RS transmission, SINR report request transmission, and data transmission into downlink signals (Downlink Signals). .

  The downlink channel matrix estimator (104) based on channel reciprocity, upon receiving the uplink RS from the uplink RS / SINR report demultiplexer (103), utilizes the uplink and downlink channel reciprocity characteristics to A downlink channel matrix from the station (10) to each user terminal (20) is estimated. The downlink channel matrix estimation process is similar to that of the related art described with reference to FIG.

  A base station generation precoding matrix generator (105) receives the estimated downlink channel matrix from the downlink channel matrix estimator (104) based on channel reciprocity, and generates base station generation precoding for each user terminal. Create a matrix. The base station creation precoding matrix creation process is the same as that in the related art described with reference to FIG.

  The base station generated precoding matrix is then applied to the modulated data to be transmitted to the user terminal. The modulated data is encoded (by an encoder (not shown)) and is stored in the data buffer (107) by the MCS selected by the MCS selector (106) in each layer of the multilayer data (by the modulator (not shown)). ) Obtained by modulation.

  The modulated data to which the precoding matrix is applied is mapped to the base station antenna (101) and transmitted to the user terminal (20) via the downlink RS / SINR report request / data multiplexer (108).

  The downlink RS / SINR report request / data multiplexer (108) generates the downlink RS and SINR report request generated from the downlink RS generator (109) in addition to the transmission of the modulation data to which the precoding matrix is applied. It also has a function of multiplexing transmission of the SINR report request generated from the device (110).

  The downlink RS is necessary when the user terminal (20) estimates the downlink channel matrix to later create a SINR report. The SINR report request includes a notification of a base station creation precoding matrix and a request content instructing the user terminal to use the notified precoding matrix to create the SINR report.

  In order to supply the MCS selector (106) with information necessary to select an appropriate MCS for each data layer of the user terminal (20), the uplink RS / SINR report demultiplexer (103) A SINR report conditioned on the coding matrix is received from the user terminal and the information is transferred to the MCS selector (106). Therefore, the MCS selector (106) can use the information to select the highest MCS for each data layer that satisfies a predetermined data transmission error rate. This selection can be performed using a SINR-MCS mapping table similar to the related art table described with reference to FIG.

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

  The uplink / downlink multiplexer (202) temporally multiplexes the reception of downlink signals and the transmission of uplink signals.

  The downlink RS / SINR report request / data demultiplexer (203) separates reception of the downlink signal into reception of the downlink RS, reception of the SINR report request, and reception of data.

  The uplink RS / SINR report multiplexer (207) multiplexes uplink RS transmissions and SINR report transmissions into uplink signals.

  When the data reception processor (204) receives the modulation data transmitted from the base station (10) after applying the base station creation precoding matrix in the base station (10), the data reception processor (204) executes a data reception process including demodulation and decoding To do.

  When the downlink channel matrix estimator (205) based on the downlink RS receives the downlink RS transmitted from the base station (10), the downlink channel from the base station (10) to the user terminal (20) itself Estimate the matrix.

  The SINR report generator (206) obtains the estimated downlink channel matrix and the SINR report request transmitted by the base station (10). Next, the SINR report generator (206) creates a SINR report conditioned on the notified base station creation precoding matrix as directed by the base station (10). Then, the created SINR report is transmitted to the base station (10) via the uplink RS / SINR report multiplexer (207).

  The uplink RS generator (208) generates an uplink RS to be transmitted to the base station (10) via the uplink RS / SINR report multiplexer (207). The uplink RS is required when the base station (10) estimates the downlink channel matrix by using the uplink and downlink channel reciprocity characteristics later to create the base station created precoding matrix.

  In the following, the detailed operation of the exemplary embodiment of the present invention will be described based on the system and apparatus described with reference to FIGS. Furthermore, for ease of understanding the description, in the following, it is assumed that the base station (10) has four antennas and the user terminal (20) has two antennas, but this is not limitative. Not.

<System operation>
FIG. 8 illustrates the operation of the entire system including both the base station (10) and the user terminal (20).

  Referring to FIG. 8, first, the user terminal (20) transmits an uplink RS to the base station (10) (operation S1101).

  The base station (10) estimates the 2 × 4 downlink channel matrix (H) using the uplink RS and the uplink / downlink channel reciprocity (operation S1102). Note that operations S1101 and S1102 are the same as those in the related technology described with reference to FIG.

Next, the base station (10) creates a 4 × 2 base station creation precoding matrix (F _Base-created ) (operation S1103). The base station (10) can use the related art method described for FIG. 2 to create the precoding matrix.

  Next, the base station (10) transmits the downlink RS to the user terminal (20) (operation S1104). Next, the user terminal (20) estimates a 2 × 4 downlink channel matrix (H) using the downlink RS (operation S1105). Note that the estimation of the channel matrix by the downlink RS is the same as that in the related technique described with reference to FIG.

Next, the base station (10) transmits a notification of the base station creation precoding matrix (F _Base-created ) and a SINR report request to the user terminal (20) (operation S1106).

Upon receiving these notifications and requests, the user terminal (20) uses the estimated downlink channel matrix (H) and the notified base station created precoding matrix (F _Base-created ) for each data layer. The received SINR is estimated (operation S1107). More specific details of the operation S1107 will be described in the user terminal operation described later.

After creating the SINR report conditioned on the base station creation precoding matrix (F _Base-created ), the user terminal (20) transmits the SINR report to the base station (operation S1108).

  Finally, the base station (10) selects an MCS using the received SINR report (operation S1109). The selection of the MCS can be based on an MCS-SINR mapping table similar to that used in the related art described with reference to FIG.

<Operation of base station>
FIG. 9 illustrates the operation of the base station (10). For simplicity of explanation, it is assumed that the base station (10) has already created a base station created precoding matrix. Accordingly, referring to FIG. 9, in the first operation S1201, the base station (10) transmits a notification of the base station creation precoding matrix and a request for SINR report to the user terminal.

  Next, the base station (10) constantly checks whether or not the SINR report conditioned on the base station creation precoding matrix is received (operation S1202).

  When receiving the SINR report, the base station finally selects an MCS using the information (operation S1203).

  In the case of the LTE system, the notification of the base station creation precoding matrix and the request for SINR report can be transmitted using radio resource control (RRC) signaling. Specifically, an existing message such as an RRC connection reconfiguration message is a base station creation precoding matrix when the base station (10) desires a precoding matrix notification and a SINR report request. Can be used to convey an information element (IE) that describes to the user terminal (20).

<User terminal operation>
FIG. 10 illustrates the operation of the user terminal (20). For simplicity of explanation, it is assumed that the user terminal (20) has already estimated the downlink channel matrix (H) using the downlink RS. Therefore, referring to FIG. 10, in the first operation S1301, the user terminal (20) constantly checks whether a notification and a request from the base station are received.

である。 Upon receiving the notification of the base station creation precoding matrix (F _Base-created ) and the SINR report request, the user terminal (20) receives the estimated downlink channel matrix (H) and the notified base station creation precoding matrix. Using (F _Base-created ), the reception SINR is estimated for each data layer (operation S1302). Specifically, the user terminal (20) estimates the SINR for each data layer represented by γ (m) by using the following mathematical formula. Where m is the data layer index,

It is.

（式１）

(Formula 1)

Here, P _S is the average transmit power per data layer, those known to the user terminal (20) as a relative power for the downlink RS transmit power.

G is a 2 × 2 reception matrix in the user terminal based on the base station created precoding matrix (F _Base-created ). For example, if a ZF receiver is used, G is given as:

（式２）

(Formula 2)

は行列Ｘの（ａ，ｂ）成分を示す。 here,

Indicates the (a, b) component of the matrix X.

R _{I + N} is an interference noise covariance matrix that reflects the amount of interference and noise observed at the user terminal antenna, and is well known as being derived using the downlink channel matrix (H) and the downlink RS. is there.

ここで、Ｇは受信行列、Ｒ_Ｉ＋Ｎは干渉雑音共分散行列：Ｒ_Ｉ＋Ｎ＝
Ｅ｛ｖ（ｋ）ｖ（ｋ）^Ｈ｝であり、シンボルパワー（symbol power）Ｅ｛ｓ^２（ｋ）｝はＥ｛ｓ^２（ｋ）｝＝１に正規化されている。 Supplement: The received vector y (k) observed at the user terminal k is y (k) = HFs (k) + v (k),
Here, H is a channel matrix from the base station to user terminal k, F is a precoding matrix, s (k) is a symbol vector, and v (k) is a noise vector (interference noise vector). 1 is based on the following well-known formula:

Here, G is a reception matrix, R _{I + N} is an interference noise covariance matrix: R _{I + N} =
E {v (k) v (k) ^H }, and symbol power E {s ² (k)} is normalized to E {s ² (k)} = 1.

  After creating the SINR (γ (m)) for each data layer conditioned in the base station creation precoding matrix, the user terminal (20) finally transmits these SINRs to the base station (10) (operation S1303). ).

  For LTE systems, SINR reports can be sent to the base station (10) using a physical layer procedure for reporting channel state information (CSI). Specifically, the user terminal first quantizes the SINR for each data layer into a channel quality indicator (CQI) index format. Next, the user terminal transmits these CQI indexes together with a physical uplink control channel (Physical Uplink Control Channel: PUCCH) or a physical uplink shared channel (PUSCH).

<Advantageous effect>
According to the exemplary embodiment described above, the received SINR information observed by the user terminal conditioned on the base station created precoding matrix can be made available at the base station. Therefore, this information can be used to select an appropriate MCS for the base station generated precoding matrix and to maximize both user terminal throughput and network capacity.

<Generalization and variations>
Although all the descriptions of the exemplary embodiments of the present invention have been made assuming application in a TDD LTE system, the presented embodiments are not limited to only such applications. For example, in an FDD (Frequency Division Duplex) LTE system that uses a pair of carrier frequencies that are close to each other for uplink and downlink communications, the uplink and downlink channel reciprocity characteristics are still maintained. Therefore, the present invention is also applicable.

  Although the variation of embodiment is as follows, it is not limited to them.

  One variation is a method of notifying a user terminal of a base station created precoding matrix and requesting an SINR report. Instead of the base station sending both notifications and requests in a single message, the base station may separate these notifications and requests into different messages for transmission in different time slots. it can. This is beneficial if the frequencies required to transmit the precoding matrix notification and the SINR report request are different.

  For example, when the created base station creation precoding matrix changes at a rate slower than the reception SINR for each data layer, the notification message can be transmitted with a longer period than the request message. In this case, when receiving only the request message, the user terminal can use the latest notified base station creation precoding matrix to estimate the SINR.

  In the LTE system, when the base station created precoding matrix notification and the SINR report request are transmitted separately, the RRC signal and the uplink downlink control indicator (DCI) format carry the notification and the request, respectively. Can be used for

  In Patent Document 1 and Patent Document 2 listed above, the base station communicates with at least one user terminal via a radio link, and the base station transmits an uplink reference signal (uplink RS) transmitted from the user terminal to the base station. Adapted to create a precoding matrix (base station creation precoding matrix) for application to data transmitted to the user terminal using the channel estimation determined from The base station creation precoding matrix is notified; and the configuration in which the user terminal estimates and reports the signal-to-interference noise ratio (SINR) for each data layer conditioned on the notified precoding matrix is not described.

  The disclosures of the patent documents and non-patent documents listed above are incorporated herein by reference. Modifications and adjustments of the embodiments and examples are within the scope of the entire disclosure of the present invention (including the frame or scope of each claim), and based on the basic technical idea of the present invention. Is possible. Furthermore, various combinations and selections of the disclosed elements are possible within the scope of the claims of the present invention. That is, the present invention clearly includes all types of variations and modifications that can be realized by those skilled in the art according to the entire disclosure including the technical idea and scope of the claims.

10, 10R base station 11R antenna 12-1 base station creation precoding matrix 12-2 for user terminal 1 base station creation precoding matrix 20 for user terminal 2, 20R user terminal 21R antenna 22-1, 22-2 reception matrix 30 Base Station Radio Coverage 101 Base Station Antenna 102 Uplink / Downlink Multiplexer 103 Uplink RS / SINR Report Demultiplexer 104 Downlink Channel Matrix Estimator Based on Channel Reciprocity 105 Base Station Created Precoding Matrix Generator 106 MCS Selector 107 Data Buffer 108 Downlink RS / SINR Report Request / Data Multiplexer 109 Downlink RS Generator 110 SINR Report Request Generator 201 User Terminal Antenna 202 Uplink / Downlink Multiplexor 203 downlink RS / SINR report request / data demultiplexer 204 data receiving processor 205 downlink channel matrix estimator 206 based on downlink RS SINR report generator 207 uplink RS / CSI report multiplexer 208 uplink RS generator

Claims (10)

A method in a mobile communication system comprising a base station communicating with at least one user terminal via a radio link, comprising:
The base station uses a channel estimation determined from an uplink reference signal (uplink RS) transmitted from the user terminal to the base station, and applies a base station creation pre-application applied to data transmitted to the user terminal. Configured to create a coding matrix,
The base station notifies the user terminal of the base station creation precoding matrix,
The user terminal is estimated and the base station creates a precoding matrix notified using the channel matrix to the user terminal from the base station, the signal to interference noise ratio of each data layer a (SINR) by the base station And reporting the estimated SINR to a base station. Upon estimating the SINR, the user terminal may first the channel matrix from the base station using said transmit downlink reference signals to the user terminal (downlink RS), to the user terminal from the base station Estimate
The user terminal uses the channel matrix H estimated, notified the base station creates a precoding matrix F _{Base-created,} the reception matrix G based on the base station creates a precoding matrix in the user terminal, the data SINR per layer :

(Where, m is the data layer index, P _S is the average transmit power per data layer, R I _{+ N} is the interference noise covariance matrix, shoulder H matrix is Hermitian operator representing a transpose conjugate, (m, m) is a matrix The m-th row and m-th column component) is estimated. The base station generated precoding matrix is generated by a block diagonalization precoding method, and is configured to prevent data from one user terminal from interfering with data of another user terminal. The method according to 1 or 2 . A user terminal for a mobile communication system,
A transmitter for transmitting an uplink reference signal (uplink RS) to the base station ;
An estimation unit that estimates a channel matrix from the base station to the user terminal using a downlink reference signal (downlink RS) transmitted from the base station to the user terminal;
The created by the base station using the estimated channel matrix from the uplink RS, reception for receiving the applied Ru base station creates a precoding matrix in the data sent to the user terminal by the base station from the base station And
The signal-to-interference and noise ratio (SINR) for each data layer is estimated using the base station creation precoding matrix notified by the base station and the channel matrix from the base station to the user terminal, and the estimated A channel quality report generator for reporting SINR to the base station;
Including a user terminal. The channel quality report creation unit
Estimating a channel matrix from the base station to the user terminal using a downlink reference signal (downlink RS) transmitted from the base station to the user terminal;
Using the channel matrix H estimated, the a base station creates a precoding matrix F _Base-created notified by the base station, a reception matrix G based on the base station creates a precoding matrix in the user terminal, data layer For each SINR :

(Where, m is the data layer index, P _S is the average transmit power per data layer, R I _{+ N} is the interference noise covariance matrix, shoulder H matrix is Hermitian operator representing a transpose conjugate, (m, m) is a matrix The mth row, mth column component) of the user terminal according to claim 4 . An estimation unit that estimates a channel matrix from the base station to the user terminal based on an uplink reference signal (uplink RS) transmitted from the user terminal to the base station ;
And using said channel matrix generator for generating a base station creates a precoding matrix to be applied to the data to be transmitted to the user terminal,
The base station creation precoding matrix is notified to the user terminal, the base station creation precoding matrix notified to the user terminal by the base station, and the base station estimated by the user terminal to the user terminal A channel quality report requesting unit that requests the user terminal to report a signal-to-interference noise ratio (SINR) estimated by the user terminal using a channel matrix ;
Including base stations. The generation unit generates the base station creation precoding matrix configured to prevent data from one user terminal from interfering with other user terminals by a block diagonalization precoding method. Item 7. The base station according to Item 6 . A communication system including a user terminal and a base station,
The base station
A generator for generating a base station creation precoding matrix for application to a signal transmitted to the user terminal;
The base station creation precoding matrix is notified to the user terminal, the base station creation precoding matrix notified to the user terminal by the base station, and the base station estimated by the user terminal to the user terminal A channel quality report requesting unit that requests the user terminal to report a signal-to-interference noise ratio (SINR) estimated by the user terminal using a channel matrix ;
A receiver for receiving the SINR estimated and reported by the user terminal;
A selector for selecting a modulation and coding scheme (MCS) based on the received SINR;
Applying a precoding matrix generated by the base station to a signal encoded and modulated based on the selected MCS;
A transmitter for transmitting the precoded signal to the user terminal;
Including
The user terminal is
A receiving unit for receiving the base station creation precoding matrix notified by the base station ;
Using the base station creation precoding matrix notified by the base station and the channel matrix from the base station to the user terminal estimated by the user terminal, the signal-to-interference noise ratio ( SINR ) of each data layer is calculated. A channel quality report generator for estimating and reporting the estimated SINR to the base station;
The receiving unit receives a signal to which the base station-created precoding matrix is applied from the base station . The base station is transmitted from the user terminal, estimation for estimating a channel matrix from the base station using the received uplink reference signal (UL RS) by a plurality of antennas of said base station to said user terminal Part
The generation unit generates the base station creation precoding matrix using the channel matrix estimated by the estimation unit ,
The user terminal estimates a channel matrix from the base station to the user terminal using downlink reference signals (downlink RSs) transmitted from the base station and received by a plurality of antennas of the user terminal. With an estimator ,
The channel quality report creation unit estimates the SINR for each data layer by using the channel matrix estimated by the estimation unit and the base station creation precoding matrix notified by the base station, and calculates the estimated SINR. The communication system according to claim 8 , which reports to the base station . In the base station, the generating unit is configured to generate the base station-generated precoding matrix configured to prevent data from one user terminal from interfering with other user terminals by a block diagonalization precoding method. The communication system according to claim 8 or 9, wherein the communication system is created .

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