Base station, wireless communication method, and wireless communication system

Abstract

This base station (10) has: a control unit (12) that changes the phase of a signal of at least one layer among signals of a plurality of layers of a reference signal multiplexed using single-user Multiple Input Multiple Output (MIMO); and a transmission unit (11) that multiplexes the signals of the plurality of layers including the signal of the layer in which the phase was changed by the control unit, and that transmits the multiplexed signals to a terminal.

Description

[Technical field]

[0001] The present disclosure relates to a base station, a wireless communication method, a wireless communication system, a terminal, and a program. [Background technology]

[0002] 2. Description of the Related Art In wireless communication systems such as mobile communication, a spatial multiplexing scheme called single-user Multiple Input Multiple Output (MIMO) has been introduced to increase the transmission speed per user (see, for example, Patent Document 1).

[0003] In single-user MIMO, signals equal to the number of spatial multiplexing (number of layers) are transmitted from a base station to one user terminal. The transmitting side adds a demodulation reference signal (DM-RS: De-Modulation Reference Signal), which is a reference signal for demodulation at the receiving side, to the signal of each layer and transmits it.

[0004] The DM-RS is a key signal for separating spatially multiplexed signals, and the receiving side can completely separate the signals of each layer by using the DM-RS. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6469114 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the related technology, for example, communication quality may be degraded. In view of the above-mentioned problems, an object of the present disclosure is to provide a base station, a wireless communication method, a wireless communication system, a terminal, and a program that improve the quality of wireless communication. [Means for solving the problem]

[0007] In a first aspect of the present disclosure, a base station has a control unit that changes the phase of at least one layer signal among multiple layer signals of a reference signal multiplexed in single-user MIMO (Multiple Input Multiple Output), and a transmission unit that multiplexes the multiple layer signals including the layer signal whose phase has been changed by the control unit and transmits the multiple layer signals to a terminal.

[0008] In addition, in a second aspect of the present disclosure, a base station executes a process of changing the phase of a signal of at least one layer among multiple layer signals of a reference signal multiplexed in single-user MIMO (Multiple Input Multiple Output), and a process of multiplexing the signals of the multiple layers including the signal of the layer whose phase has been changed by the phase changing process, and transmitting the multiple layer signals to a terminal.

[0009] In addition, in a third aspect of the present disclosure, there is provided a wireless communication system having a base station and a terminal, wherein the base station has a base station control unit that changes the phase of at least one layer signal among multiple layer signals of a reference signal multiplexed in single-user MIMO (Multiple Input Multiple Output), and a transmission unit that multiplexes the multiple layer signals including the layer signal whose phase has been changed by the base station control unit and transmits the multiple layer signals to the terminal, and the terminal has a receiving unit that receives the multiple layer signals, and a terminal control unit that restores the phase of the layer signal whose phase has been changed by the base station.

[0010] In addition, in a fourth aspect of the present disclosure, a terminal has a receiving unit that receives signals of multiple layers of a reference signal multiplexed in single-user MIMO (Multiple Input Multiple Output), and a control unit that restores the phase of at least one layer signal of the signals of the multiple layers whose phase has been changed by a base station.

[0011] In addition, in a fifth aspect of the present disclosure, a program causes a computer to execute a process of receiving signals of multiple layers of a reference signal multiplexed in single-user MIMO (Multiple Input Multiple Output), and a process of restoring the phase of a signal of at least one layer, among the signals of the multiple layers, the phase of which has been changed by a base station. Effect of the Invention

[0012] According to one aspect, it is possible to improve the quality of wireless communication. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating an example of the configuration of a wireless communication system according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of a configuration of a base station according to an embodiment. [Diagram 3] FIG. 2 is a diagram illustrating an example of a configuration of a terminal according to an embodiment. [Figure 4] FIG. 2 is a sequence diagram showing an example of processing of the wireless communication system according to the embodiment. [Diagram 5] 11 is a flowchart illustrating an example of a phase change process of the base station according to the embodiment. [Figure 6] FIG. 11 is a diagram illustrating an example of a phase change process of a base station according to an embodiment. [Figure 7] 1 is a diagram illustrating an example of a precoding matrix P according to an embodiment. FIG. [Figure 8] FIG. 2 is a diagram illustrating an example of the configuration of a base station and a terminal according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The principles of the present disclosure are described with reference to some exemplary embodiments. It should be understood that these embodiments are set forth for illustrative purposes only, to aid those skilled in the art in understanding and practicing the present disclosure, without implying any limitation on the scope of the present disclosure. The disclosure described herein may be implemented in various ways other than those described below.

[0015] In the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. <System configuration> Fig. 1 is a diagram showing a configuration example of a wireless communication system 1 according to an embodiment. In Fig. 1, the wireless communication system 1 includes a base station 10 and a terminal 20. A range (coverage) in which the terminal 20 can receive radio waves from the base station 10 is also called a cell 30. Note that the number of base stations 10 and terminals 20 is not limited to the example in Fig. 1.

[0017] The base station 10 and the terminal 20 are connected to each other so as to be able to communicate with each other via wireless communication such as a fifth generation mobile communication system (5G), a fourth generation mobile communication system (4G), or a wireless local area network (LAN).

[0018] In addition, the term "base station" (BS) used in this disclosure refers to a device that can provide or host a cell or coverage through which terminals 20 can communicate. Examples of the base station 10 include, but are not limited to, a Node B (NodeB or NB), an Evolved Node B (eNodeB or eNB), a next-generation Node B (gNB), a Remote Radio Unit (RRU), a Radio Head (RH), a Remote Radio Head (RRH), and a low-power node (e.g., a femto node, a pico node), etc.

[0019] The term "terminal" as used in this disclosure refers to any device having wireless or wired communication capabilities. Examples of terminals 20 include, but are not limited to, user equipment (UE), personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs), portable computers, image capture devices such as digital cameras, gaming devices, music storage and playback devices, or Internet appliances that enable wireless or wired Internet access and browsing, etc.

[0020] Communications described in this disclosure may conform to any suitable standard, including, but not limited to, 5G (NR: New Radio), 4G (LTE Advanced, WiMAX2), Long Term Evolution (LTE), Wideband Code Division Multiple Access (W-CDMA), Code Division Multiple Access (CDMA), Global System for Mobile (GSM), etc. Additionally, communications may be performed according to any generation of communications protocols now known or developed in the future.

[0021] In addition to normal data communication, the base station 10 may transmit a downlink Reference Signal (RS) to the terminal 20 in a broadcast, multicast, or unicast manner. Similarly, the terminal 20 may transmit an RS to the base station 10 in an uplink. As used herein, "downlink" refers to a link from the base station 10 to the terminal 20, and "uplink" refers to a link from the terminal 20 to the base station 10. In the following description, an embodiment related to downlink RS transmission will be described.

[0022] For example, the downlink RS is used by the terminal 20 for beam sweeping, channel estimation, demodulation, and other operations for communication. In general, the RS is a signal sequence (also called an "RS sequence") known by both the base station 10 and the terminal 20. For example, the base station 10 generates and transmits an RS sequence based on a certain rule, and the terminal 20 estimates the RS sequence based on the same rule. Examples of the RS include, but are not limited to, a De-Modulation Reference Signal (DM-RS), which is a reference signal for demodulation at the downlink or uplink receiving side, a Channel State Information-Reference Signal (CSI-RS), which is a reference signal transmitted to measure the state of a wireless channel at the receiving side, a Sounding Reference Signal (SRS), a Phase Tracking Reference Signal (PTRS), a fine time and frequency tracking reference signal (TRS), and the like. In the following description, the DM-RS is referred to as the RS.

[0023] <Configuration> Next, the configurations of the base station 10 and the terminal 20 according to the embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a diagram showing an example of the configuration of the base station 10 according to the embodiment. Fig. 3 is a diagram showing an example of the configuration of the terminal 20 according to the embodiment. Note that the configurations shown in Figs. 2 and 3 are merely examples. The names of the components may be any names as long as they can execute the processing of the present disclosure.

[0024] <<Base station 10>> The base station 10 includes a transmitting unit 11 and a control unit 12. The transmitting unit 11 converts digital data into radio waves and transmits the radio waves to the terminal 20 from an antenna in accordance with instructions from the control unit 12. The control unit 12 performs various types of control. For example, the control unit 12 performs various processes for the base station 10 to perform wireless communication with the terminal 20.

[0025] <<Terminal 20>> The terminal 20 has a receiving unit 21 and a control unit 22. The receiving unit 21 receives radio waves transmitted from the base station 10 by an antenna and converts the received radio waves into a digital signal. The control unit 22 performs various controls. For example, the control unit 22 performs various processes for the terminal 20 to perform wireless communication with the base station 10.

[0026] <Processing> Next, an example of processing of the wireless communication system 1 according to the embodiment will be described with reference to Fig. 4. Fig. 4 is a sequence diagram showing an example of processing of the wireless communication system 1 according to the embodiment.

[0027] In step S1, the control unit 12 of the base station 10 determines the DM-RS signal of each of four or more layers (for example, any one of four to eight) of single-user Multiple Input Multiple Output (MIMO).

[0028] Next, the control unit 12 of the base station 10 changes the phase of at least one of the signals of each of the four or more layers (at least some of various signals including DM-RS, etc.) (step S2). Here, the base station 10 may invert the signal of the third layer or the signal of the fourth layer, for example. Here, "inversion" in the present disclosure is not limited to changing the phase by 180 degrees (π), but includes changing the phase substantially by 180 degrees (for example, any of 160 degrees to 200 degrees, etc.).

[0029] Next, the base station 10 multiplexes the signals of each layer including the signal of the layer whose phase has been changed by the process of step S2 (step S3). Here, the control unit 12 of the base station 10 multiplexes the signals of each layer in accordance with, for example, the NR specifications (standards) of Release 15 of the 3GPP (Third Generation Partnership Project).

[0030] For example, when the spatial multiplexing degree is 4 (signals of four layers are multiplexed), base station 10 code division multiplexes the DM-RS signal of the first layer and the DM-RS signal of the second layer in accordance with the specification. Then, base station 10 frequency division multiplexes the DM-RS signal of the third layer and the DM-RS signal of the fourth layer with the DM-RS signal of the first layer and the DM-RS signal of the second layer, respectively, in accordance with the specification. More specifically, base station 10 multiplexes the DM-RS signal x 3 (t) is the DM-RS signal x of the first layer. 1 (t) to subcarrier frequency f s In addition, the base station 10 shifts the DM-RS signal x 4 (t) is the second layer DM-RS signal x 2 (t) to subcarrier frequency f s Shift only.

number

number

[0031] In the following, an example will be described in which the number of layers in single-user MIMO is four, and the signal in the fourth layer is inverted in the process of step S2. In this case, the signal y(t) obtained by combining the signals in each layer is expressed by the following formula (3). Note that the period T is the subcarrier frequency f s (T=1 / f s ).

number

[0032] Equation (3) can be further transformed into the following equation (4).

number

[0033] According to equation (4), the average power E of y(t) is a constant value of 1, as shown in the following equation (5).

number

[0034] In the base station 10, for example, it is assumed that the rated output of an amplifier that outputs a signal to a certain antenna is designed to be the average power of a normal signal (a certain layer signal). Furthermore, it is assumed that the signals of each layer are combined as a signal for the certain antenna by precoding or the like. Even in such a case, the above-mentioned processing of steps S2 and S3 can prevent the power to be output by the amplifier when transmitting a DM-RS signal (symbol) from exceeding the rated output, as shown in formula (5). Therefore, since it is not necessary to reduce the power when transmitting the DM-RS, it is possible to avoid a reduction in coverage due to a reduction in transmission power. Therefore, it is possible to avoid a problem that occurs when the transmission power of the DM-RS fluctuates greatly in a short period of time when transmitting in layers 4 or more in the standardized specifications of NR (5G) in 3GPP, as described below.

[0035] (Problems to be solved by this disclosure) Below, for comparison with the embodiment of the present disclosure, a problem that may occur when the process of step S2 is not performed will be described. In this case, multiplexing is performed as shown in the following equation (6) by the process of step S3. Note that the signal x 1 (t), x 2 (t), x 3 (t), x 4 It is assumed that the multiplexed signal y′(t) and the multiplexed signal y′(t) are each normalized to have an average power of 1.

number

[0036] Equation (6) can be further transformed into the following equation (7).

number

[0037] where x 1 (t)+x 2 Since the average power of (t) is 2, the average power E' of y'(t) is given by the following equation (8).

number

[0038] According to equation (8), the average power E' of y'(t) is the average power E of each layer signal x during one period T in which one symbol of DM-RS is transmitted. 1 (t), x 2 (t), x 3 (t), x 4 It is shown that the power fluctuates between 2 times (3 dB) and 0 times the average power of (t). Note that the period T is 1 / f s (T=1 / f s ).

[0039] In the base station 10, for example, it is assumed that the rated output of an amplifier that outputs a signal to a certain antenna is designed to be the average power of a normal signal (a certain layer signal). Furthermore, it is assumed that the signals of each layer are combined as a signal for the certain antenna by precoding or the like. In such a case, as shown in formula (8), it becomes necessary to output a signal with twice the power of the rated output of the amplifier, and the distortion of the signal output from the amplifier increases, causing deterioration of the transmission spectrum and deterioration of the modulation accuracy. Note that, when the power of the DM-RS signal is reduced to avoid such a situation, it is necessary to keep the power ratio of the DM-RS signal to other signals constant, so that it is necessary to reduce the transmission power of all signals transmitted from the base station 10. This causes a problem that the cell 30 of the base station 10 shrinks.

[0040] Next, the transmitter 11 of the base station 10 transmits the signals of each layer to the terminal 20 by single-user MIMO (step S4). Here, the base station 10 may transmit to the terminal 20 a radio wave in which the signals of each layer (at least a part of various signals including DM-RS, etc.) are combined as a signal for one antenna by precoding or the like. In this case, the base station 10 may transmit, from each of the multiple antennas, the radio wave of the signals of the multiple layers combined by precoding.

[0041] Next, the terminal 20 restores (returns) the phase of the signal of the layer whose phase has been changed by the process of step S2 among the signals of each layer received (step S5). Here, for example, when the signal of the fourth layer has been inverted by the base station 10, the terminal 20 may restore the phase of the signal of the fourth layer by inverting the received signal of the fourth layer again.

[0042] The terminal 20 may obtain information indicating how much the phase of the signal of which layer has been changed by the process of step S2 from the base station 10. In this case, the base station 10 may notify the terminal 20 of the information when the terminal 20 registers its location with the base station 10, for example, when the terminal 20 moves into the cell 30 of the base station 10 or when the power of the terminal 20 is turned on. The base station 10 may also notify the terminal 20 of the information when the terminal 20 requests transmission of data in the downlink. Alternatively, the information may be registered in advance in the base station 10 and the terminal 20.

[0043] Next, the terminal 20 receives data transmitted in each layer from the base station 10 by single-user MIMO based on the DM-RS of each layer (step S6). As a result, the terminal 20 receives various types of data in the downlink.

[0044] <<Phase change processing>> Next, an example of the process of changing the phase of a layer signal in step S2 in FIG. 3 will be described with reference to FIG. 5 to FIG. 7. FIG. 5 is a flowchart showing an example of the phase change process of the base station according to the embodiment. FIG. 6 is a diagram explaining an example of the phase change process of the base station 10 according to the embodiment. FIG. 7 is a diagram explaining an example of the precoding matrix P according to the embodiment. Below, an example will be described in which the number of layers of single user MIMO is four and precoding is performed in two separate steps.

[0045] In step S101, the control unit 12 of the base station 10 multiplies the DM-RS signal of each layer by a precoding matrix P (one example of a "first precoding matrix"). Here, as shown in FIG. 6, the control unit 12 of the base station 10 multiplies the DM-RS signal x 1 (t), x 2 (t), x 3 (t), x 4 (t) is multiplied by a 4-by-4 precoding matrix P.

[0046] The four layer signals x(t), the four calculated signals y(t), and the precoding matrix P are respectively expressed as in the following equation (9).

number

[0047] In the example of FIG. 6, the base station 10 first calculates x'(t)=Px(t) through the process of step S101.

[0048] Next, the control unit 12 of the base station 10 multiplies the DM-RS signal of each layer calculated in step S101 by a precoding matrix Q (an example of a "second precoding matrix") (step S102). Here, the base station 10 calculates y(t)=Qx'(t). In this case, the processes of steps S101 and S102 are expressed as in the following equation (10).

number

[0049] Note that the base station 10 may perform the following process instead of performing precoding twice as in steps S101 and S102. First, the base station 10 calculates QP by matrix-multiplying a precoding matrix P by a precoding matrix Q. Then, the base station 10 may change the phase of at least one layer signal among the signals of the multiple layers by matrix-multiplying x(t), which is a signal of the multiple layers, by QP.

[0050] The base station 10 may be specified by the terminal 20 as a precoding matrix P from among the 4-row, 4-column matrices 701 to 716 shown in Fig. 7. In this case, in the downlink, the terminal 20 may calculate a transfer function of a transmission channel between the base station 10 and the terminal 20 based on the CSI-RS received from the base station 10. Then, the terminal 20 may select an optimal precoding matrix P from among the 4-row, 4-column matrices 701 to 716 shown in Fig. 7 in accordance with the calculated transfer function. Then, the terminal 20 may notify the base station 10 of the selected precoding matrix P.

[0051] Alternatively, the base station 10 may select, as the precoding matrix P, any one of the 4-row, 4-column matrices 701 to 716 shown in Fig. 7. Then, the base station 10 may notify the terminal 20 of the selected precoding matrix P.

[0052] Furthermore, the base station 10 may select one of the patterns of a 4-row, 4-column matrix shown in the following equations (11) and (12) as the precoding matrix Q. Then, the base station 10 may notify the terminal 20 of the selected precoding matrix Q.

[0053] Any of the patterns of 4-row, 4-column matrices shown in the following formulas (11) and (12) can be used for any of the 4-row, 4-column matrices 701 to 716 shown in Fig. 7. In formula (11), the subscripts k, l, m, and n of q are each an integer from 1 to 4. Also, k, l, m, and n are each a different number. Also, +-q indicates that the sign of q may be either positive or negative.

number

number

[0054] In the following, we will show that by using the precoding matrix P shown in FIG. 7 and the precoding matrix Q shown in equations (11) and (12), the average power of each of the four calculated signals y(t) becomes a constant value.

[0055] 7 is used as an example of the precoding matrix P. However, for normalization purposes, values ​​are multiplied by 1 / 2 as shown in the following equation (13).

number

[0056] The following formula (14) is used as an example of the preceding matrix Q. In formula (11), q k , q l , q m , q n The signs of are positive (+), and q k , q l , q m , q n are q 1 , q 2 , q 3 , q 4As described above with respect to equation (11), each row of the precoding matrix Q, q k , q l , q m , q n The signs of can be either positive or negative, and q k , q l , q m , q n are q 1 , q 2 , q 3 , q 4 The above-mentioned items may be different from each other.

number

[0057] In the case of equation (14), QP is calculated as shown in equation (15) below.

number

[0058] Then, by substituting QP of equation (15) into the above-mentioned equation (10), y(t) is calculated as shown in the following equation (16).

number

[0059] Equation (16) can be further transformed into the following equation (17) by substituting equations (1) and (2).

number

[0060] The average power E of each stream of the output signal y(t) is 1, as shown in the following equation (18).

number

[0061] As described above, any of matrices 701 to 716 shown in Fig. 7 may be used as the preceding matrix P, and any of the patterns of matrices shown in equations (11) and (12) may be used as the preceding matrix Q. In any of these cases, the average power E of each stream is 1, as in the examples of equations (13) to (18).

[0062] Modifications of the embodiment of the present disclosure will be described below. Each of the following modifications may be implemented in appropriate combination with the embodiment of the present disclosure.

[0063] <Variation 1> In the above embodiment, an example has been described in which the DM-RS is used as the RS. In the following, an example will be described in which the CSI-RS is further used as the RS.

[0064] In the downlink, the terminal 20 may calculate a transfer function of a transmission path between the base station 10 and the terminal 20 based on the CSI-RS received from the base station 10, and select an optimal precoding matrix P according to the calculated transfer function. Then, the terminal 20 notifies the base station 10 of the selected precoding matrix P.

[0065] Here, a case will be considered in which the DM-RS signal is multiplied by the precoding matrix P and the precoding matrix Q in order to suppress power fluctuations in the DM-RS, and the CSI-RS signal is not multiplied by a precoding matrix. In this case, the transfer function between the base station 10 and the terminal 20 changes due to the DM-RS signal being multiplied by the precoding matrix Q. As a result, the precoding matrix P selected based on the CSI-RS is no longer optimal.

[0066] Therefore, base station 10 multiplies the CSI-RS signal by the same precoding matrix Q as that used for DM-RS. This makes the transfer functions of CSI-RS and DM-RS equivalent in terminal 20. Therefore, terminal 20 can continue to use the precoding matrix P selected based on CSI-RS as the optimal one.

[0067] <Variation 2> FIG. 8 is a diagram showing an example of the configuration of a computer 100 in the case where at least a part of the base station 10 (e.g., the control unit 12) or at least a part of the terminal 20 (e.g., the control unit 22) is realized by a computer and a program. In the example of FIG. 8, the computer 100 includes a processor 101, a memory 102, and a communication interface 103. These parts may be connected by a bus or the like. The memory 102 stores at least a part of a program 104. The communication interface 103 includes an interface required for communication with other network elements. In the case of the base station 10, the communication interface 103 includes, for example, an interface for communication with the terminal 20 via one or more antennas, an interface for communication between base stations, and an interface for communication with various servers on the core net side.

[0068] When the program 104 is executed by the processor 101, the memory 102, etc. in cooperation with each other, the computer 100 performs at least some processing of the embodiment of the present disclosure. The memory 102 may be of any type suitable for a local technology network and may be implemented using any suitable data storage technology, such as, by way of non-limiting example, non-transitory computer-readable storage media, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. Although only one memory 102 is shown in the computer 100, several physically different memory modules may be present in the computer 100. The processor 101 may be of any type suitable for a local technology network and may include one or more of a general-purpose computer, a special-purpose computer, a microprocessor, a digital signal processor (DSP), and a processor based on a multi-core processor architecture, by way of non-limiting example. The computer 100 may have multiple processors, such as application-specific integrated circuit chips that are time-slaved to a clock that synchronizes the main processor.

[0069] The embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic, or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor or other computing device.

[0070] The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as instructions included in program modules, that execute on a target real or virtual processor device to perform the processes or methods of the present disclosure. Program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. The machine-executable instructions of the program modules may be executed in local or distributed devices. In a distributed device, the program modules may be located in both local and remote storage media.

[0071] The program codes for carrying out the methods of the present disclosure may be written in any combination of one or more programming languages. These program codes are provided to a processor or controller of a general purpose computer, a special purpose computer, or other programmable data processing apparatus, and when the program codes are executed by the processor or controller, the functions / operations in the flowcharts and / or implementing block diagrams are performed. The program codes are executed entirely on the machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine, or entirely on a remote machine or server.

[0072] The above program code may be embodied in a machine-readable medium, which may be any tangible medium that may contain or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. The machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read only memory (ROM), an erasable programmable read only memory (EPROM or flash memory), an optical fiber, a portable compact disc read only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0073] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present invention.

[0074] A part or all of the above-described embodiments can be described as, but is not limited to, the following supplementary notes. (Appendix 1) A control unit that changes a phase of at least one layer signal among a plurality of layer signals of a reference signal multiplexed by single-user MIMO (Multiple Input Multiple Output); a transmission unit that multiplexes at least a portion of the signals of the plurality of layers including the signal of the layer whose phase has been changed by the control unit, and transmits the multiplexed signals to a terminal; A base station having (Appendix 2) The base station described in Supplementary Note 1, wherein the control unit inverts the phase of at least one layer signal among the multiple layer signals. (Appendix 3) The base station according to claim 1 or 2, wherein the reference signal includes a De-Modulation Reference Signal (DM-RS) which is a reference signal for demodulation on a terminal side. (Appendix 4) The base station according to claim 3, wherein the reference signal includes a Channel State Information-Reference Signal (CSI-RS), which is a reference signal transmitted to measure the state of a wireless channel at a receiving side. (Appendix 5) The base station according to any one of appendixes 1 to 4, wherein the transmitting unit transmits to a terminal a radio wave in which the signals of the multiple layers, including the signal of the layer whose phase has been changed by the control unit, are combined into a signal intended for one antenna. (Appendix 6) The base station according to any one of Supplementary Notes 1 to 5, wherein the control unit changes a phase of at least one of the signals of the plurality of layers based on a first precoding matrix, a second precoding matrix, and the signals of the plurality of layers. (Appendix 7) The base station described in Supplementary Note 6, wherein the control unit changes a phase of at least one layer signal among the multiple layer signals by matrix-multiplying the first precoding matrix to the multiple layer signals and then matrix-multiplying the second precoding matrix to the multiple layer signals. (Appendix 8) The base station described in Supplementary Note 6, wherein the control unit changes a phase of at least one layer signal among the multiple layer signals by matrix-multiplying the first precoding matrix by the second precoding matrix, and then matrix-multiplying the multiple layer signals. (Appendix 9) 9. The base station according to any one of Supplementary Notes 6 to 8, wherein the first precoding matrix is ​​specified by the terminal based on a downlink Channel State Information-Reference Signal (CSI-RS). (Appendix 10) The base station according to claim 9, wherein the control unit multiplies a downlink Channel State Information-Reference Signal (CSI-RS) by the second precoding matrix. (Appendix 11) The base station A process of changing the phase of at least one layer signal among multiple layer signals of a reference signal multiplexed by single-user MIMO (Multiple Input Multiple Output); a process of multiplexing the signals of the plurality of layers including the signal of the layer whose phase has been changed by the process of changing the phase, and transmitting the multiplexed signals to a terminal; A wireless communication method for performing the above. (Appendix 12) A base station and a terminal are included, The base station, A base station control unit that changes a phase of at least one layer signal among a plurality of layer signals of a reference signal multiplexed by single-user MIMO (Multiple Input Multiple Output); a transmission unit that multiplexes the signals of the plurality of layers including the signal of the layer whose phase has been changed by the base station control unit and transmits the multiplexed signals to the terminal; having The terminal includes: A receiving unit that receives the signals of the plurality of layers; A terminal control unit that restores the phase of a signal of a layer whose phase has been changed by the base station. Wireless communication system. (Appendix 13) The wireless communication system described in Appendix 12, wherein the base station control unit inverts the phase of at least one layer signal among the multiple layer signals. (Appendix 14) A receiver that receives multiple layer signals of reference signals multiplexed by single-user MIMO (Multiple Input Multiple Output); A control unit that restores a phase of at least one layer signal whose phase has been changed by a base station among the signals of the plurality of layers. Terminal. (Appendix 15) The terminal described in Supplementary Note 14, wherein the control unit inverts the phase of at least one layer signal among the signals of the multiple layers, the phase of which has been changed by a base station. (Appendix 16) On the computer, A process of receiving signals of multiple layers of reference signals multiplexed by single-user MIMO (Multiple Input Multiple Output); and a program for executing a process of restoring the phase of at least one layer signal, the phase of which has been changed by a base station, among the signals of the plurality of layers.

[0075] Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0076] This application claims priority to Japanese Patent Application No. 2021-022579, filed on February 16, 2021, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0077] 1. Wireless communication systems 10 base station 11 Transmitter 12 Control section 20 Terminals 21 Receiving section 22 Control section 30 cells

Claims

1. A control means for changing a phase of at least one layer signal among a plurality of layer signals of a reference signal multiplexed by single-user MIMO (Multiple Input Multiple Output); a transmission means for multiplexing at least a part of the signals of the plurality of layers including the signal of the layer whose phase has been changed by the control means and transmitting the multiplexed signals to a terminal; having The reference signal includes a demodulation reference signal (DM-RS: De-Modulation Reference Signal), which is a reference signal for demodulation at the terminal side, and a channel state information reference signal (CSI-RS: Channel State Information-Reference Signal), which is a reference signal transmitted to measure the state of a radio channel at the receiving side. Base station.

2. The base station according to claim 1 , wherein the control means inverts a phase of at least one layer signal among the signals of the plurality of layers.

3. 3. The base station according to claim 1, wherein the transmitting means transmits to the terminal a radio wave in which the signals of the plurality of layers, including the signal of the layer whose phase has been changed by the control means, are combined as a signal intended for one antenna.

4. The base station according to claim 1 , wherein the control means changes a phase of at least one of the signals of the plurality of layers based on a first precoding matrix, a second precoding matrix, and the signals of the plurality of layers.

5. 5. The base station according to claim 4, wherein the control means changes a phase of at least one of the signals of the multiple layers by matrix-multiplying the first precoding matrix to the signals of the multiple layers and then matrix-multiplying the second precoding matrix to the signals of the multiple layers.

6. 5. The base station according to claim 4, wherein the control means changes a phase of at least one of the signals of the plurality of layers by matrix-multiplying the first precoding matrix by the second precoding matrix and then matrix-multiplying the signals of the plurality of layers.

7. The base station A process of changing a phase of at least one layer signal among a plurality of layer signals of a reference signal multiplexed in single-user Multiple Input Multiple Output (MIMO); a process of multiplexing the signals of the plurality of layers including the signal of the layer whose phase has been changed by the process of changing the phase, and transmitting the multiplexed signals to a terminal; Run The reference signal includes a demodulation reference signal (DM-RS: De-Modulation Reference Signal), which is a reference signal for demodulation at the terminal side, and a channel state information reference signal (CSI-RS: Channel State Information-Reference Signal), which is a reference signal transmitted to measure the state of a radio channel at the receiving side. A wireless communication method.

8. A base station and a terminal are included, The base station, A base station control unit that changes a phase of at least one layer signal among a plurality of layer signals of a reference signal multiplexed by single-user MIMO (Multiple Input Multiple Output); a transmitting means for multiplexing the signals of the plurality of layers including the signal of the layer whose phase has been changed by the base station control means and transmitting the multiplexed signals to the terminal; having The reference signal includes a demodulation reference signal (DM-RS: De-Modulation Reference Signal), which is a reference signal for demodulation at the terminal side, and a channel state information reference signal (CSI-RS: Channel State Information-Reference Signal), which is a reference signal transmitted to measure the state of a radio channel at the receiving side; The terminal includes: A receiving means for receiving the signals of the plurality of layers; A terminal control means for restoring the phase of a signal of a layer whose phase has been changed by the base station. Wireless communication system.

Images