Method, information processing device, user equipment, and program

Abstract

The present invention improves received-signal power by combining received signals cooperatively transmitted from a plurality of transmission / reception points. In the present invention, a computer executes: acquiring, for each of the plurality of transmission / reception points that cooperatively transmit signals to a first device, an error included in a phase rotation amount of received signals in the first device; and selecting, on the basis of the error for each of the plurality of transmission / reception points, a first transmission / reception point, from among the plurality of transmission / reception points, that is a transmission source of a signal serving as a reference when obtaining a phase offset, which is a phase difference between the received signals in the first device.

Description

Method, Information Processing Apparatus, User Equipment, and Program

[0001] The present disclosure relates to wireless communication.

[0002] In wireless communication such as 5th Generation Mobile Communication System (5G), distributed MIMO (Multi-Input Multi-Output) is proposed, in which one or more distributed stations near a mobile station are selected from a plurality of distributed stations distributed within the communication area of one base station for communication. According to distributed MIMO, by appropriately combining radio waves transmitted simultaneously from a plurality of distributed stations, the received signal power at the mobile station can be improved and the throughput can be increased. Also, in distributed MIMO, since the base stations are distributed, the dead spots of radio waves can be reduced and the influence of obstacles can be reduced.

[0003] In coordinated transmission between a plurality of distributed base stations (mTRP, hereinafter referred to as distributed stations) such as distributed MIMO, a technique called Coherent Joint Transmission (CJT) is used to improve the received signal power when signals from each distributed station are combined by receiving the transmission signals from each distributed station in the same phase at a UE (User Equipment). For example, in coordinated transmission by N distributed stations, assuming that the transmission power of each distributed station is equal, theoretically, by CJT, the received signal power at the UE is N squared times the received signal power of a signal from one distributed station. By improving the received signal power by CJT, an improvement in throughput and a reduction in latency can be achieved.

[0004] When there is an offset in the phase of the carrier wave between a plurality of distributed stations performing coordinated transmission, a loss of received signal power occurs when the received signals at the UE are combined. The loss of received signal power is the difference between the theoretical value of the received signal power obtained by CJT and the actually obtained received signal. To correct the phase offset of the carrier wave of each distributed station, the UE measures the phase offset value for each distributed station and reports it to each distributed station.

[0005] The phase offset reported by the UE is determined as the difference between the phase rotation amount measured from the received signal from a reference distributed station and the phase rotation amount measured from the received signals from other distributed stations (for example, Non-Patent Document 1).

[0006] 3GPP TSG RAN WG1 #118 RAN1 Chair's Notes (2024-08-19)

[0007] One aspect of this disclosure is to provide a method, information processing device, user equipment, and program capable of improving the power of a received signal by combining received signals transmitted in coordination from multiple transmission and reception points.

[0008] One aspect of the present disclosure is a method in which a computer performs the following: for each of a plurality of transmitting and receiving points that transmit signals in coordination to a first device, it obtains an error included in the phase rotation amount obtained from the received signal in the first device; and, based on the error for each of the plurality of transmitting and receiving points, it selects from the plurality of transmitting and receiving points a first transmitting and receiving point which is the source of a signal that serves as a reference when determining the phase offset, which is the phase difference between received signals in the first device.

[0009] Another aspect of the present disclosure is an information processing apparatus comprising a control unit that performs the following: acquiring an error included in the phase rotation amount obtained from the received signal in the first device for each of a plurality of transmitting and receiving points that transmit signals in coordination with the first device; and selecting a first transmitting and receiving point from the plurality of transmitting and receiving points, which is the source of a signal that serves as a reference when determining the phase offset, which is the phase difference between received signals in the first device, based on the error for each of the plurality of transmitting and receiving points.

[0010] Another aspect of this disclosure is a program for causing a computer to perform the following actions: acquire an error included in the phase rotation amount obtained from the received signal in the first device for each of a plurality of transmitting and receiving points that transmit signals in coordination with the first device; and, based on the error for each of the plurality of transmitting and receiving points, select a first transmitting and receiving point from the plurality of transmitting and receiving points which is the source of a signal that serves as a reference when determining the phase offset, which is the phase difference between received signals in the first device.

[0011] Another aspect of the present disclosure is a method for a user device (UE) to perform the following: receive a plurality of signals transmitted in coordination from a plurality of transmission and reception points; and determine a phase offset, which is the phase difference between the received signals from a first transmission and reception point, which is the source of a reference signal, and at least one other transmission and reception point among the plurality of transmission and reception points, selected from the plurality of transmission and reception points based on the error contained in the phase rotation amount obtained from the received signals for each of the plurality of transmission and reception points.

[0012] Another aspect of the present disclosure is a user device comprising a control unit that performs the following: receiving a plurality of signals transmitted in coordination from a plurality of transmitting and receiving points; and determining a phase offset, which is the phase difference between the received signals from a first transmitting and receiving point, which is the source of a reference signal, and at least one transmitting and receiving point other than the first transmitting and receiving point, selected from the plurality of transmitting and receiving points based on the error contained in the amount of phase rotation obtained from the received signals for each of the plurality of transmitting and receiving points.

[0013] Another aspect of the present disclosure is a program for causing a computer to perform the following: receive a plurality of signals transmitted in coordination from a plurality of transmission and reception points; and determine a phase offset, which is the phase difference between the received signals from a first transmission and reception point, which is the source of a reference signal, and at least one other transmission and reception point among the plurality of transmission and reception points, selected from the plurality of transmission and reception points based on the error contained in the phase rotation amount obtained from the received signals for each of the plurality of transmission and reception points.

[0014] According to one aspect of this disclosure, a method, information processing device, user equipment, and program can be provided that can improve the power of a received signal by combining received signals transmitted in coordination from multiple transmission and reception points.

[0015] Figure 1 shows an example of the system configuration of a communication system. Figure 2 shows an example of the hardware configuration of a control device. Figure 3 shows an example of the functional configuration of a control device. Figure 4 shows an example of the hardware configuration of a UE. Figure 5 shows an example of the functional configuration of a UE. Figure 6 shows an example of the allocation of radio resources for measuring radio wave propagation characteristics to candidate stations in the first embodiment. Figure 7 is an example of the flowchart for the selection process of distributed stations and reference stations that perform coordinated transmission to a UE by the control device according to the first embodiment. Figure 8 shows an example of the sequence of processing related to the reporting of phase offset in a communication system. Figure 9 shows an example of the allocation of radio resources for measuring radio wave propagation characteristics to candidate stations according to a modified example of the first embodiment. Figure 10 is an example of the flowchart for the selection process of distributed stations and reference stations that perform coordinated transmission to a UE by the control device according to the second embodiment. Figure 11 shows an example of the sequence of processing related to the reporting of phase offset in a communication system.

[0016] In one aspect of this disclosure, the phase offset is obtained more accurately by selecting a transmission / reception point with a small error in measuring the phase rotation amount from among a plurality of transmission / reception points performing coordinated transmission as a reference transmission / reception point. More specifically, one aspect of this disclosure is a method in which a computer performs the following: for each of a plurality of transmission / reception points that transmit signals in coordination to a first device, it obtains an error included in the phase rotation amount of the received signal in the first device; and based on the said error for each of the plurality of transmission / reception points, it selects a first transmission / reception point from the plurality of transmission / reception points that is the source of the signal that serves as the reference when determining the phase offset, which is the phase difference between received signals in the first device.

[0017] The computer that performs this method is, for example, a computer that operates as a control device for controlling a base station, a base station and relay station that perform coordinated transmission, or a computer that operates as the first device. The first device is, for example, a terminal station and a relay station that receive signals transmitted by coordinated transmission. The terminal station is, for example, a user device such as a smartphone, tablet terminal, and in-vehicle device. The terminal station is also called a mobile station. However, it is not limited to this, and the terminal station may be a stationary user device that does not move. The transmitting and receiving point emits a beam. The transmitting and receiving point includes, for example, a base station and a relay station.

[0018] In one aspect of this disclosure, in the first device, a first transmitting / receiving point, which is the source of a reference signal used when determining the phase offset of signals transmitted in coordination from multiple transmitting / receiving points, is selected based on the error included in the phase rotation amount. For example, the transmitting / receiving point with the smallest error included in the phase rotation amount may be selected as the first transmitting / receiving point. This improves the accuracy of the phase offset obtained by the first device. By correcting the phase of the carrier wave of the signals transmitted from each transmitting / receiving point based on the phase offset, the probability that signals from each transmitting / receiving point arrive at the first device in phase increases, and the received signal power during received signal synthesis by CJT is improved.

[0019] In one aspect of the present disclosure, the computer may obtain the variation in error contained in the phase rotation amount obtained from the received signal from each of the plurality of transmitting and receiving points based on statistics of K phase rotation amounts obtained from a first signal transmitted and received K times between the transmitting and receiving point and the first device, where K is a positive integer. More specifically, the computer may obtain the deviation of K phase rotation amounts as the variation in error contained in the phase rotation amount for each of the plurality of transmitting and receiving points. In this case, the computer may select a first transmitting and receiving point from the plurality of transmitting and receiving points based on the deviation for each of the plurality of transmitting and receiving points. The deviation of the phase rotation amount may be obtained from the average value of the K phase rotation amounts and the K phase rotation amounts, or from the linear approximation of the K phase rotation amounts at each acquisition point and the K phase rotation amounts.

[0020] The error in the phase rotation amount obtained from a received signal from a single transmitting / receiving point is, for example, a phase rotation amount caused by interference, and is an uncorrelated value for each measurement. Therefore, it is difficult to directly obtain the error in the phase rotation amount from the received signal through measurement. According to one aspect of this disclosure, the error in the phase rotation amount, which is difficult to measure directly, can be obtained as a statistic of K phase rotation amounts obtained from a first signal transmitted and received K times between the transmitting / receiving point and the first device.

[0021] The first signal may be a signal transmitted from the transmitting / receiving point towards the first device. In this case, the K phase rotation amounts for each of the plurality of transmitting / receiving points may be obtained by the first device measuring the first signal transmitted K times from each of the plurality of transmitting / receiving points. The first signal may be a CSI-RS (Channel State Information - Reference Signal). In this case, the first transmitting / receiving point that serves as the reference for determining the phase offset is selected based on the K phase rotation amounts measured by the first device, so that the first transmitting / receiving point can be selected with greater accuracy and with less variation in the error of the phase rotation amount.

[0022] Alternatively, the first signal may be a signal transmitted from the first device in the direction of the transmitting / receiving point. In this case, the K phase rotation amounts may be obtained by the transmitting / receiving point measuring the first signal transmitted K times. The first signal may be an SRS (Sounding Reference Signal). In this case, for example, the K phase rotation amounts for each transmitting / receiving point can be obtained without having the first device report the K phase rotation amounts for each transmitting / receiving point using wireless resources, thus reducing the use of wireless resources.

[0023] In one aspect of this disclosure, the first signals transmitted K times may be arranged within the same slot. This allows the measurement of the phase rotation amount of the first signals transmitted K times to be completed within the same slot, thereby reducing the time required to acquire the K phase rotation amounts.

[0024] Alternatively, the first signal, which is transmitted K times, may be arranged across multiple slots. This means that the number of transmissions K of the first signal is no longer limited to the number of symbols in a slot, allowing for an increase in the number of phase rotation amounts to be statistically analyzed, and enabling more accurate statistics on phase rotation amounts.

[0025] Another aspect of this disclosure can also be identified as an information processing device that performs the processing of the above method. The information processing device includes a control unit that performs the following: for each of a plurality of transmitting and receiving points that transmit signals in coordination to a first device, an error included in the phase rotation amount obtained from the received signal at the first device; and, based on the error for each of the plurality of transmitting and receiving points, a first transmitting and receiving point that is the source of the signal that serves as the reference signal when determining the phase offset, which is the phase difference between received signals at the first device. The control unit is, for example, a processor such as a CPU (Central Processing Unit).

[0026] Another aspect of this disclosure is a method for a user device (UE) to perform the following actions: receive a plurality of signals transmitted in coordination from a plurality of transmission / reception points; and determine a phase offset, which is the phase difference between the received signals from a first transmission / reception point that is the source of a reference signal, and at least one other transmission / reception point among the plurality of transmission / reception points, selected from the plurality of transmission / reception points based on the error contained in the phase rotation amount obtained from the received signals for each of the plurality of transmission / reception points. The UE is, for example, a smartphone, a tablet terminal, and an in-vehicle device. However, it is not limited to these, and the UE may also be a stationary PC (Personal Computer) and a fixedly installed IoT device.

[0027] In one aspect of this disclosure, the UE may receive information relating to a plurality of transmission and reception points and information relating to a first transmission and reception point from a second device. The second device is, for example, a control device that controls the plurality of transmission and reception points, or a base station which is one of the plurality of transmission and reception points.

[0028] In one aspect of this disclosure, the variation in error included in the phase rotation amount obtained from the received signal from each of the plurality of transmitting and receiving points may be obtained based on statistics of K phase rotation amounts obtained from a first signal transmitted and received K times between the transmitting and receiving point and the first device, where K is a positive integer. The variation in error included in the phase rotation amount may be obtained, for example, as the deviation of the K phase rotation amounts. In this case, the first transmitting and receiving point may be selected from the plurality of transmitting and receiving points based on the deviation for each of the plurality of transmitting and receiving points.

[0029] The UE may further perform the following actions: receive a first signal transmitted K times from each of multiple transmission / reception points; obtain K measured values ​​of phase rotation from the first signal received K times for each of the multiple transmission / reception points; and transmit the K measured values ​​of phase rotation for each of the multiple transmission / reception points to a second device. In this case, the second device may select the first transmission / reception point based on the K measured values ​​of phase rotation for each of the multiple transmission / reception points. The first signal may be CSI-RS. Since the first transmission / reception point that serves as the reference for determining the phase offset is selected based on the K measured values ​​of phase rotation measured by the UE, it is possible to select a first transmission / reception point with a more accurate and smaller error in phase rotation.

[0030] The UE may further transmit the first signal K times. In this case, the second device may obtain K phase rotation measurements obtained from the first signal received K times for each of the plurality of transmitting and receiving points, and select the first transmitting and receiving point based on the K phase rotation measurements for each of the plurality of transmitting and receiving points. The first signal may be an SRS. In one aspect of the present disclosure, for example, the UE does not report the K phase rotation measurements for each transmitting and receiving point to the second device using radio resources, thereby reducing the use of radio resources in selecting the first transmitting and receiving point that serves as the basis for determining the phase offset.

[0031] Another aspect of the present disclosure can also be identified as a user device that performs the processing of the above method. The user device includes a control unit that performs: receiving a plurality of signals transmitted in coordination from a plurality of transmission and reception points; and determining a phase offset, which is the phase difference between the received signals from a first transmission and reception point that is the source of a reference signal, and at least one other transmission and reception point among the plurality of transmission and reception points, selected from the plurality of transmission and reception points based on an error in the amount of phase rotation obtained from the received signals for each of the plurality of transmission and reception points.

[0032] Another embodiment of the method can also be defined as a program for causing a computer to execute, and a computer-readable, non-temporary storage medium on which the program is recorded.

[0033] Embodiments of this disclosure will be described below with reference to the drawings. The configurations of the following embodiments are illustrative, and this disclosure is not limited to the configurations of these embodiments.

[0034] <First Embodiment> Figure 1 shows an example of the system configuration of the communication system 100. The communication system 100 is a distributed MIMO system including user equipment (UE) 2, a control device 1, and a plurality of distributed base stations. The communication system 100 is a wireless communication system of, for example, 5G, LTE (Long Term Evolution), and mobile communication methods of 5G or later. The control device 1 is a device on the core network to which the distributed base stations are connected. However, it can also be considered that the control device 1 is the core network itself, or a system included in the core network. The core network includes, for example, an optical fiber network. The control device 1 controls the distributed base stations and the UE 2.

[0035] The distributed base stations, together with other distributed base stations within the same communication area, provide a wireless access network to UE 2 located within that communication area. The three distributed base stations (RU#1 to #3) shown in Figure 1 are assumed to be located within the same communication area. Each distributed base station is connected to the control unit 1.

[0036] A distributed base station is equipped with an antenna capable of forming multiple beam patterns. The antenna used in a distributed base station is, for example, an adaptive array antenna. An adaptive array antenna is an array antenna in which multiple antenna elements are arranged. The adaptive array antenna can electrically change its beam pattern by adaptively controlling the weighting of each antenna element according to the radio wave propagation environment. A beam pattern can also be described as the directivity of the beam formed by the adaptive array antenna. The beam pattern of a distributed base station is controlled by a control device 1. Note that a distributed base station may have one antenna or multiple antennas.

[0037] UE 2 is a terminal station such as a smartphone, tablet, wearable device, or in-vehicle data communication device. However, it is not limited to these, and UE 2 may be a stationary terminal device such as an IoT device. Alternatively, a relay station that relays wireless communication between a distributed base station and a terminal station can be used as a mobile station instead of UE 2. Relay stations include small base stations, mobile base stations, in-vehicle devices, and smartphones. In the following embodiments, it is assumed that UE 2 has one antenna. However, it is not limited to these, and UE 2 may have multiple antennas.

[0038] In the example shown in Figure 1, distributed base station RU#1 contains transmission and reception points m_(0), m_(1), and m_(2), distributed base station RU#2 contains transmission and reception points m_(3) and m_(4), and distributed base station RU#3 contains transmission and reception points m_(5) and m_(6). Distributed base station RU#1 transmits three beams: b0, b1, and b2. Distributed base station RU#1 is also represented as the transmission and reception points m_(0), m_(1), and m_(2) of beams b0, b1, and b2. The string after the underscore or the string in parentheses is shown as a subscript in the figure. Distributed base station RU#2 transmits two beams: b3 and b4. Distributed base station RU#3 transmits two beams: b5 and b6. UE 2 uses the beam with the best communication quality from among beams b0-b6 to perform communication. UE 2 is an example of the "first device." Hereafter, distributed base stations will simply be referred to as "distributed stations."

[0039] Each distributed station (or transmitting / receiving point) and UE 2 are synchronized. The control device 1 allocates radio resources to the signals transmitted from each transmitting / receiving point so that the signals transmitted from each transmitting / receiving point arrive at UE 2 simultaneously. UE 2 receives notification from the control device 1 of the allocation of radio resources for the signals transmitted from each distributed station and receives the signals transmitted from the transmitting / receiving points of each distributed station according to the configuration of those radio resources. The objective of CJT is for the signals transmitted from the transmitting / receiving points of each distributed station with each beam pattern to arrive at UE 2 in phase. To achieve this, it is required that the signal transmitted from each transmitting / receiving point is on a carrier wave with the phase offset from the received signal from a reference transmitting / receiving point corrected. The reference transmitting / receiving point is selected by the control device 1 from among a plurality of transmitting / receiving points that perform coordinated transmission to UE 2. Hereinafter, when referred to as "phase offset," it refers to the phase offset of the signal in question from the received signal from the reference transmitting / receiving point. Hereinafter, the signal from the reference transmitting / receiving point will be referred to as the reference signal.

[0040] The phase offset of a signal from a single transmission / reception point is measured by UE 2 using a measurement signal from that transmission / reception point and reported to the control device 1. In the first embodiment, UE 2 divides the channel bandwidth into a plurality of subbands and obtains a phase offset value for each subband. For each subband, UE 2 measures the amount of phase rotation between the target signal and the reference signal, and obtains the phase offset value of the target signal by subtracting the amount of phase rotation of the reference signal from the amount of phase rotation of the target signal. For example, the measurement signal for the phase offset can be a CSI-RS (Channel State Information - Reference Signal), a signal for measuring the phase offset, or a data signal.

[0041] In the following first embodiment, for the sake of simplicity, it will be assumed that one distributed station is equipped with one transmitting / receiving point. However, one distributed station may be equipped with multiple transmitting / receiving points, in which case, "distributed station" should be replaced with "transmitting / receiving point" in the following description. Furthermore, the reference distributed station will be referred to as the reference station below.

[0042] Here, the phase rotation amount of the received signal measured in UE 2 includes errors due to noise, interference, and deviations in the oscillator, etc. For example, the phase rotation amount measured at distributed station #n at timing k is expressed as φ_(n,k) + Δ_(n,k). φ_(n,k) is the phase rotation amount that is originally obtained by measurement. Δ_(n,k) is the error during measurement.

[0043] For example, if there are distributed stations #1 to #3, the amount of phase rotation measured at distributed stations #1 to #3 at timing k will be {φ_(1,k) + Δ_(1,k), φ_(2,k) + Δ_(2,k), φ_(3,k) + Δ_(3,k)}. For example, let's assume that the error Δ_(1,k) = Δ_(2,k) = 0, and Δ_(1,k) = Δ_(2,k) << Δ_(3,k), and that distributed station #3 is selected as the reference station. In this case, the phase offset of distributed station #1 is Φ_(1,k) = φ_(1,k) - φ_(3,k) - Δ_(3,k), and the phase offset of distributed station #2 is Φ_(2,k) = φ_(2,k) - φ_(3,k) - Δ_(3,k). An error Δ_(3,k) is added to the phase offset of both distributed station #1 and distributed station #2. On the other hand, if distributed station #1 or distributed station #2 is selected as the base station, the error Δ_(3,k) is added only to distributed station #3. In other words, if a distributed station with a large error in the amount of phase rotation is selected as the base station, the error from the desired phase offset value may also be large. If the error in the phase offset value is large, even if the phase of the carrier wave from each distributed station is corrected based on that phase offset value, there is a high possibility that the phases of the received signals from each distributed station that reach UE 2 will not be synchronized, and the loss due to the synthesis of received signals by CJT may increase. Therefore, one of the criteria for selecting a base station is that the error in the amount of phase rotation is small.

[0044] However, the errors during the measurement of the phase rotation amount are uncorrelated between measurements. Therefore, the error of the phase rotation amount is likely to differ between the time when the reference station is selected and the time when the UE 2 receives the data signal targeted by the CJT. In addition, it is difficult to obtain only the error component from the measured value of the phase rotation amount of the received signal at a certain time. Therefore, in the first embodiment, it is assumed that the phase rotation amount φ_(n,k) that is intended to be obtained by the original measurement at each distributed station has a substantially constant or substantially linear correlation between measurements, and based on the statistics of the plurality of phase rotation amounts obtained by multiple measurements, a distributed station with a small variation in the error of the phase rotation amount between measurements is selected as the reference station. More specifically, in the first embodiment, in the UE 2, among the plurality of distributed stations, a distributed station with a small deviation of the plurality of phase rotation amounts obtained by the measurements in the reception of the plurality of signals is selected as the reference station. Thereby, the received signal power by the synthesis of the received signals of the CJT in the UE 2 can be improved.

[0045] FIG. 2 is a diagram illustrating the hardware configuration of the control device 1. The control device 1 includes a CPU 101, a main storage device 102, an external storage device 103, and a communication device 104. The CPU 101 is also called a processor. The CPU 101 is not limited to a single processor and may have a multi-processor configuration. In addition to the CPU 101, a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP), etc. may be provided. Further, the CPU 101 may cooperate with a hardware circuit such as a Field Programmable Gate Array (FPGA).

[0046] The CPU 101 executes a computer program deployed executable in the main memory device 102 and provides the processing of the control device 1. The main memory device 102 stores the computer program executed by the CPU 101, the data processed by the CPU 101, etc. The main memory device 102 is a Dynamic Random Access Memory (DRAM), a Static Random Access Memory (SRAM), a Read Only Memory (ROM), etc. Further, the external storage device 103 is used, for example, as a storage area that supplements the main memory device 102, and stores the computer program executed by the CPU 101, the data processed by the CPU 101, etc. The external storage device 103 is a hard disk drive, a Solid State Drive (SSD), etc. Further, a drive device for a removable storage medium may be connected to the control device 1. The removable storage medium is, for example, a Blu-ray Disc, a Digital Versatile Disc (DVD), a Compact Disc (CD), a flash memory card, etc. The CPU 101 is an example of the "control unit" of the "information processing device".

[0047] The communication device 104 communicates with an external network such as a distributed base station and the Internet via, for example, an optical fiber. The communication device 104 of the control device 1 may be one device or a combination of multiple devices. The control device 1 is an example of a "computer" and an "information processing device". Note that the hardware configuration of the control device 1 is not limited to that shown in FIG. 2.

[0048] FIG. 3 is a diagram showing an example of the functional configuration of the control device 1. The control device 1 includes a control unit 11 as a functional configuration. The functions of the control unit 11 are achieved by the CPU 101 executing a predetermined program.

[0049] The control unit 11 controls the CJT. More specifically, the control unit 11 selects a distributed station and a reference station that perform cooperative transmission to the UE 2, allocates radio resources for phase offset measurement, allocates radio resources for reporting of the UE 2, and performs phase offset compensation, etc.

[0050] The control unit 11 selects a plurality of candidate distributed stations to perform coordinated transmission to UE 2. Hereinafter, the candidate distributed stations to perform coordinated transmission to UE 2 will be referred to as candidate stations. Candidate stations selected are, for example, distributed stations located within a predetermined range from the location of UE 2, and / or distributed stations whose received signal strength is above a predetermined threshold. The received signal strength is RSSI (Received Signal Strength Indicator) or RSRP (Reference Signal Received Power). However, the method of selecting candidate stations is not limited to a specific method.

[0051] The control unit 11 acquires multiple phase rotation values ​​for each of the multiple candidate stations in UE 2, and based on statistical errors during measurement, selects multiple distributed stations to perform coordinated transmission to UE 2 and a reference station among the multiple distributed stations. First, in order to acquire multiple phase rotation values ​​for each candidate station in UE 2, the control unit 11 causes each candidate station to transmit CSI-RS in a burst manner over a short period of time. More specifically, for each candidate station, the control unit 11 allocates radio resources for measuring radio wave propagation characteristics by arranging K CSI-RS in the same slot in the downlink. K indicates the number of CSI-RS transmissions. K is a positive integer. The resource blocks in which the CSI-RS are arranged may be the same or different for each candidate station.

[0052] The control unit 11 notifies UE 2 of the allocation of radio resources for measuring radio wave propagation characteristics for each candidate station and instructs UE 2 to perform the measurement. The allocation of radio resources for measuring radio wave propagation characteristics for each candidate station is also notified to each candidate station. Furthermore, the control unit 11 allocates radio resources for reporting the measurement results of radio wave propagation characteristics to UE 2 for the uplink and notifies UE 2 of this allocation. The allocation of radio resources is also called scheduling and is notified via the control channel using DCI (Downlink Control Information).

[0053] In the first embodiment, when each candidate station receives notification of the allocation of radio resources for measuring radio wave propagation characteristics, it transmits CSI-RS in bursts K times within the same slot. UE 2 receives the K CSI-RS transmitted from each candidate station within the same slot and measures the radio wave propagation characteristics, including the phase rotation amount, for each received CSI-RS for each candidate station. UE 2 reports the measurement results of the radio wave propagation characteristics for K times, including the measured value of the phase rotation amount, for each candidate station to the control device 1. The measurement results of the radio wave propagation characteristics are expressed as a complex number in the following equation 1. H_(n,k) represents the radio wave propagation characteristics of the received CSI-RS from candidate station #n in the kth measurement. a_(n,k) represents the amplitude of the received CSI-RS from candidate station #n in the kth measurement. φ_(n,k) represents the phase rotation amount of the received CSI-RS from candidate station #n in the kth measurement. The variable k represents the measurement number and can take values ​​from 0 to K-1. The variable n represents the candidate station number.

[0054] When the control unit 11 receives the measurement results of the radio wave propagation characteristics for K times for each candidate station, it calculates the average value φ_(n) of the phase rotation amount φ_(n, k) for each candidate station using the following equation 2. In equation 2, an upper bar is attached to φ to indicate that it is an average value. Furthermore, using the average value φ_(n), the control unit 11 calculates the standard deviation σ_(n) of the phase rotation amount φ_(n, k) for each candidate station using the following equation 3.

[0055] The control unit 11 considers the standard deviation σ_(n) as the degree of variation in the error of the phase rotation amount of the signal from candidate station #n at the time of measurement in UE 2, and selects the candidate station with the smallest standard deviation σ_(n) as the reference station. A small standard deviation σ_(n) indicates that there is little variation in the error of the phase rotation amount. The control unit 11 also selects a predetermined number of top candidate stations with small standard deviations σ_(n) as distributed stations that will perform coordinated transmission to UE 2. Hereinafter, when simply referred to as "distributed stations," it refers to distributed stations that perform coordinated transmission to UE 2, excluding the reference station.

[0056] Furthermore, the index indicating the degree of variation in the error of the phase rotation amount of the signal from candidate station #n during measurement in UE 2 is not limited to the standard deviation. For example, the deviation σ´_(n) obtained according to the following equation 4 using the linear approximation φ^_(n,k) of the phase rotation amount φ_(n,k) may be used. "^" is a symbol indicating that it is an approximation or estimate. The smaller the deviation σ´_(n), the less variation there is in the error of the phase rotation amount. The method for obtaining the linear approximation φ^_(n,k) of the phase rotation amount φ_(n,k) may be any well-known method and is not limited to a specific method. For example, the linear approximation φ^_(n,k) of the phase rotation amount φ_(n,k) may be obtained by executing a predetermined program or a predetermined function.

[0057] When the control unit 11 selects the distributed stations and the reference station to perform coordinated transmission to UE 2, it allocates radio resources for phase offset measurement on the downlink and radio resources for UE 2 reporting on the uplink for phase offset compensation. The control unit 11 notifies UE 2 of the information regarding the distributed stations and the reference station, and the allocation of radio resources for phase offset measurement on the downlink and radio resources for UE 2 reporting on the uplink.

[0058] Upon receiving the phase offset measurement results for each distributed station from UE 2, the control unit 11 performs phase offset compensation for each distributed station based on the phase offset measurement results. In phase offset compensation, the control unit 11 calculates the phase correction value for each subband relative to the carrier wave for each distributed station and notifies the phase correction value for each subband. Alternatively, the control unit 11 may calculate the phase correction value for each subband relative to the carrier wave for each distributed station, perform phase correction of the carrier wave based on the phase correction value for each subband, and notify information about the carrier wave after phase correction. The phase correction value for each subband may be obtained, for example, as a value obtained by inverting the sign of the phase offset in that subband. However, this is not limited to this, and the method of determining the phase correction value is not limited to a specific method. As a result, the distributed stations will transmit signals using a carrier wave whose phase has been shifted and corrected by the notified phase correction value in each subband of the carrier wave frequency. Note that the functional configuration of the control device 1 shown in Figure 3 is an example, and the functional configuration of the control device 1 is not limited to the example shown in Figure 3.

[0059] Figure 4 shows an example of the hardware configuration of UE 2. UE 2 includes a CPU 201, main memory 202, external storage 203, wireless communication device 204, and antenna 205. The CPU 201, main memory 202, and external storage 203 are the same as those of CPU 101, main memory 102, and external storage 103.

[0060] The wireless communication device 204 is connected to the antenna 205 and, through the antenna 205, connects to a wireless access network, for example, by a 5G or later mobile wireless communication system, and receives wireless signals from distributed base stations. The wireless communication device 204 is also connected to the control device 2 on the control plane. Note that the hardware configuration of the UE 2 is not limited to that shown in Figure 4. Depending on the type, the UE 2 may further include a touch panel display, microphone, speaker, and operation buttons in addition to the components shown in Figure 4.

[0061] Figure 5 shows an example of the functional configuration of UE 2. UE 2 comprises a control unit 21 and a measurement unit 22. The functions of the control unit 21 and the measurement unit 22 are achieved by the CPU 201 executing a predetermined program.

[0062] The control unit 21 controls the measurement and reporting of radio wave propagation characteristics in UE 2. Radio wave propagation characteristics include phase rotation and phase offset. The control unit 21 receives from the control device 1 information regarding the distributed stations to be measured, the allocation of radio resources for measuring radio wave propagation characteristics, and the allocation of radio resources for reporting. Information regarding the distributed stations to be measured includes, for example, information regarding each of several candidate stations, and information regarding the reference station and at least one distributed station that perform coordinated transmission to UE 2.

[0063] The control unit 21 outputs information regarding the distributed stations to be measured, and the allocation of radio resources for measuring radio wave propagation characteristics, to the measurement unit 22. The control unit 21 receives from the measurement unit 22 the measurement results of the CSI-RS radio wave propagation characteristics received from the distributed stations to be measured. The control unit 21 uses the reporting radio resources notified by the control device 1 to report the measurement results of the radio wave propagation characteristics for the distributed stations to be measured to the control device 1. In the report to the control device 1, information such as RSRP (Reference Signal Received Power) obtained from the CSI-RS measurement may also be transmitted in addition to the phase rotation amount and phase offset, or if the type of information to be reported, such as the phase rotation amount or phase offset, is specified, only the specified type of information may be transmitted.

[0064] The measurement unit 22 receives from the control unit 21 information regarding the distributed stations to be measured and the allocation of radio resources for measuring radio wave propagation characteristics, which are notified by the control device 1. The distributed stations to be measured transmit CSI-RS at predetermined intervals in synchronization according to the allocation of radio resources for measuring radio wave propagation characteristics. The measurement unit 22 receives the CSI-RS transmitted from the distributed stations to be measured according to the allocation of radio resources for measuring radio wave propagation characteristics. Each time the measurement unit 22 receives CSI-RS, it estimates the radio wave propagation characteristics of the received CSI-RS from the distributed stations to be measured and obtains, for example, the radio wave propagation characteristics shown in Equation 1 above as one of the measurement results, and outputs the measurement result to the control unit 21. From the radio wave propagation characteristics of Equation 1 above, the amplitude and phase rotation amount at the k-th measurement are obtained.

[0065] The measurement unit 22 converts the radio wave propagation characteristics of the received CSI-RS from the distributed station to be measured from the time domain to the frequency domain, for example, using a discrete Fourier transform (FFT), and obtains the phase rotation amount for each of a predetermined number of subbands. The phase offset value is also obtained by the measurement unit 22 for each distributed station as the difference between the phase rotation amount of the received signal and the phase rotation amount of the received signal from the reference station in each subband. The phase offset value for each distributed station is output to the control unit 21 as one of the measurement results of the radio wave propagation characteristics. In the first embodiment, when "measuring the phase rotation amount" and "measuring the phase offset," the measurement unit 22 may also measure other information that can be measured from the received CSI-RS in addition to the phase rotation amount and phase offset value. The measurement results are output to the control unit 21 and may be transmitted to the control device 1 together with the phase rotation amount and phase offset value. The functional configuration of UE 2 is not limited to the example shown in Figure 5.

[0066] Figure 6 shows an example of the allocation of radio resources for measuring radio wave propagation characteristics to candidate stations in the first embodiment. In Figure 6, the radio resources in the same slot are shown for candidate stations #1 to #3. In the example shown in Figure 6, it is assumed that the number of CSI-RS transmissions transmitted in bursts for measuring radio wave propagation characteristics is K = 3. Therefore, in the radio resources in the same slot for each of candidate stations #1 to #3, the CSI-RS is arranged in three symbols. Also, the CSI-RS is arranged in the same resource block among candidate stations #1 to #3. However, the CSI-RS may be arranged in different resource blocks among the candidate stations.

[0067] Figure 7 is an example of a flowchart for the selection process of distributed stations and reference stations that perform coordinated transmission to the UE 2 of the control device 1 according to the first embodiment. The process shown in Figure 7 may be executed, for example, each time a radio frame starts. However, it is not limited to this, and the process shown in Figure 7 may also be executed, for example, when a predetermined time has elapsed, such as the time equivalent to a predetermined number of radio frames, since the completion of the previous execution, or when it is determined that a re-selection of distributed stations should be made based on the measurement results of radio wave propagation characteristics reported by the UE 2. The main entity executing the process shown in Figure 7 is the CPU 101 of the control device 1, but for convenience, the functional components will be described as the main components. The same applies to the flowcharts from Figure 7 onward.

[0068] In OP101, the control unit 11 selects candidate stations to perform coordinated transmission to UE 2. In OP102, the control unit 11 allocates radio resources for measuring radio wave propagation characteristics for each candidate station in the downlink. In the allocation of radio resources in OP102, K CSI-RS units are placed in the same slot. In OP103, the control unit 11 allocates radio resources for reporting radio wave propagation characteristics for UE 2 in the uplink.

[0069] In OP104, the control unit 11 notifies UE 2 of information regarding each candidate station, the allocation of radio resources for measuring radio wave propagation characteristics for each candidate station, and the allocation of radio resources for reporting about UE 2. The control unit 11 also notifies each candidate station of the allocation of radio resources for measuring radio wave propagation characteristics for each candidate station and the allocation of radio resources for reporting about UE 2.

[0070] In OP105, the control unit 11 determines whether or not it has received a report of the measurement results of the radio wave propagation characteristics from UE 2. If a report of the measurement results of the radio wave propagation characteristics is received from UE 2 (OP105: YES), the process proceeds to OP106. Until a report of the measurement results of the radio wave propagation characteristics is received from UE 2 (OP105: NO), the control unit 11 remains in standby mode. If a predetermined time elapses without a report of the measurement results of the radio wave propagation characteristics being received from UE 2, an error occurs, and the process shown in Figure 7 may be terminated.

[0071] In OP106, the control unit 11 determines whether it has received K reports of the measurement results of radio wave propagation characteristics from UE 2. If the number of reports of the measurement results of radio wave propagation characteristics from UE 2 has reached K (OP106: YES), the process proceeds to OP107. If the number of reports of the measurement results of radio wave propagation characteristics from UE 2 has not reached K (OP106: NO), the process proceeds to OP105.

[0072] In OP 107, the control unit 11 obtains a reference value for the measured phase rotation amount included in the measurement results of the radio wave propagation characteristics from UE 2 for each candidate station. The reference value is, for example, an average value or a linear approximation. Whether to use an average value or a linear approximation as the reference value may be specified by the administrator of the communication system 100. In OP 108, the control unit 11 obtains the deviation of the measured phase rotation amount for each candidate station using the reference value obtained in OP 107.

[0073] In OP 109, the control unit 11 selects a predetermined number of candidate stations with small deviations obtained in OP 108 from among the candidate stations as distributed stations to perform coordinated transmission to UE 2. Alternatively, the control unit 11 may select candidate stations whose deviations obtained in OP 108 are below a predetermined threshold from among the candidate stations as distributed stations to perform coordinated transmission to UE 2. In OP 110, the control unit 11 selects the candidate station with the smallest deviation obtained in OP 108 as the reference station. After that, the process shown in Figure 7 is completed.

[0074] Note that the selection process for distributed stations and reference stations shown in Figure 7 is just one example and is not limited to the process shown in Figure 7. For example, the allocation of radio resources for radio wave propagation measurement in OP 102 and the allocation of radio resources for reporting to UE 2 in OP 103 may be performed at the same time. In the example shown in Figure 7, UE 2 reports the measurement results of the radio wave propagation characteristics of each candidate station each time it receives CSI-RS (OP 105, OP 106), but instead, UE 2 may report the measurement results of the radio wave propagation characteristics of each candidate station for K times all at once.

[0075] Figure 8 shows an example of a processing sequence related to the reporting of phase offset in the communication system 100. In Figure 8, the control device 1 and UE 2 of the communication system 100 are shown separately.

[0076] In S11, the control device 1 selects several candidate stations to perform coordinated transmission to UE 2 (Figure 7, OP101). In S12, the control device 1 allocates radio resources for measuring radio wave propagation characteristics to each candidate station (Figure 7, OP102) and allocates radio resources for reporting to UE 2 (Figure 7, OP103). In S13, the control device 1 notifies UE 2 of information regarding each candidate station, the allocation of radio resources for measuring radio wave propagation characteristics, and the allocation of radio resources for reporting to UE 2 (Figure 7, OP104). Each candidate station is also notified of the allocation of radio resources for measuring radio wave propagation characteristics and the allocation of radio resources for reporting to UE 2.

[0077] In S21, CSI-RS is transmitted from each candidate station according to the allocation of radio resources for measuring radio wave propagation characteristics. In S22, UE 2 measures the radio wave propagation characteristics for each CSI-RS transmitted from each candidate station. In S23, UE 2 transmits the measurement results of the radio wave propagation characteristics for each candidate station according to the allocation of radio resources for reporting, and the control device 1 receives them (Figure 7, OP105: YES). The process from S21 to S23 is repeated K times. After the process from S21 to S23 has been repeated K times, the process in S31 is performed.

[0078] In S31, the control device 1 acquires the deviation of the measured phase rotation amount for each candidate station (Figure 7, 107-OP108), and selects the top predetermined number of candidate stations with the smallest deviations as distributed stations to perform coordinated transmission to UE 2 (Figure 7, OP109). In S32, the control device 1 selects the candidate station with the smallest deviation as the reference station (Figure 7, OP110).

[0079] In S41, the control device 1 allocates radio resources for measuring the phase offset and allocates radio resources for reporting to UE 2. In S42, the control device 1 notifies UE 2 of information regarding the base station and distributed stations, the allocation of radio resources for measuring the phase offset, and the allocation of radio resources for reporting by UE 2. The base station and distributed stations are also notified of the allocation of radio resources for measuring the phase offset and the allocation of radio resources for reporting by UE 2.

[0080] In S43, UE 2 receives CSI-RS transmitted from the base station and each distributed station and obtains the phase offset for each distributed station. In S44, UE 2 reports the phase offset for each distributed station according to the allocation of radio resources for reporting. In S45, the control device 1 performs phase offset compensation for each distributed station based on the phase offset. This corrects the phase of the carrier wave transmitted from each distributed station, bringing the phases of the signals arriving simultaneously at UE 2 from the base station and each distributed station closer to the same phase, and improving the received signal power by combining the received signals of the CJT.

[0081] In the first embodiment, the control device 1 considers the deviation of the measured phase rotation amount for K cycles in UE 2 as the degree of variation in the error of the phase rotation amount of the received signal at the time of measurement in UE 2, and selects the candidate station with the smallest deviation as the reference station. This reduces the variation in the error of the phase rotation amount of the reference signal at the time of phase offset measurement, and the phase offset for each distributed station is acquired with high accuracy. As the phase offset is acquired with high accuracy, the phase correction of the carrier wave transmitted from each distributed station is performed with high accuracy, the phases of the signals that arrive simultaneously at UE 2 from the reference station and each distributed station become closer to being in phase, and the received signal power by combining the received signals of the CJT is improved.

[0082] If UE 2 has multiple antennas, the control device 1 may select a reference antenna and then select a reference station based on a report from UE 2 of the measurement results of the radio wave propagation characteristics for CSI-RS received at the reference antenna. The reference antenna may be determined by the control device 1 and notified to UE 2. Alternatively, UE 2 may select the reference antenna. For example, the antenna with the highest average SNR value for each distributed station may be selected as the reference antenna.

[0083] <Modification of the First Embodiment> In the first embodiment, the K CSI-RS transmitted in bursts from each candidate station are arranged within the same slot. Instead, in this modification, the K CSI-RS transmitted in bursts from each candidate station are arranged across multiple slots. This allows each candidate station to transmit more CSI-RS in bursts than the number of symbols contained in one slot, thereby increasing the number of samples of the phase rotation measurement for each candidate station. For example, in 5G, the number of symbols contained in one slot is 14.

[0084] Figure 9 shows an example of the allocation of radio resources for measuring radio wave propagation characteristics according to a modification of the first embodiment. In Figure 9, the radio resources of three consecutive slots are shown for candidate stations #1 to #3. Three CSI-RS units are also arranged in each of the three consecutive slots.

[0085] Let T_(slot) be the number of slots where the burst-transmitted CSI-RS signals are placed. Let K_(slot) be the number of CSI-RS signals placed in each slot. In this case, the number of burst-transmitted CSI-RS signals K = T_(slot) * K_(slot). Therefore, in the example shown in Figure 9, T_(slot) = 3 and K_(slot) = 3, so K = 3 * 3 = 9 CSI-RS signals are transmitted in bursts from each candidate station, and 9 phase rotation measurement values ​​are obtained for each transmitting station.

[0086] In this modified example, for candidate station #n, the average value φ_(n) (with an upper bar attached to φ in the equation) of the ks-th phase rotation amount φ_(n, ts, ks) in slot ts is given by equation 5 below, and the standard deviation σ_(n) is given by equation 6 below. ts is a variable indicating the slot number. ts takes values ​​from 0 to T_(slot)-1. ks is a variable indicating the number of the CSI-RS placed in one slot. ks takes values ​​from 0 to K_(slot)-1.

[0087] When a linear approximation φ^(n, ts, ks) is used as the reference value, the deviation σ'(n) can be calculated using the following equation 7.

[0088] In the example shown in Figure 9, the CSI-RS is located in the same resource block in each of the slots #1 to #3 between candidate stations #1 to #3. However, this is not limited to this, and the CSI-RS may be located in different resource blocks between the same slots between candidate stations.

[0089] According to this modified version, the number of samples of phase rotation measurement values ​​used to determine the statistics (deviation) of phase rotation can be greater than the number of symbols contained in one slot. This allows for more accurate statistics on phase rotation for each candidate station, and enables the selection of a reference station that can further reduce the loss of received signal power during received signal synthesis by CJT.

[0090] As another modification of the first embodiment, instead of UE 2 reporting the measurement results of the radio wave propagation characteristics of K received CSI-RS signals from each candidate station to the control device 1 (for example, S23 in Figure 8), UE 2 may report the measured values ​​of the phase rotation amount of K received CSI-RS signals for each candidate station. Alternatively, instead of UE 2 reporting the measurement results of the radio wave propagation characteristics of the received CSI-RS signals for each candidate station to the control device 1 each time a CSI-RS signal is received from each candidate station, UE 2 may report the measurement results of the radio wave propagation characteristics of K received CSI-RS signals from each candidate station to the control device 1 all at once.

[0091] <Second Embodiment> In the first embodiment, CSI-RS is transmitted in bursts K times from each candidate station, and the measurement results of the radio wave propagation characteristics for each candidate station are obtained by UE 2, and the base station and distributed stations are selected based on these results. In the second embodiment, each candidate station measures the radio wave propagation characteristics of a reference signal transmitted in bursts on the uplink from UE 2, and the measurement results of the radio wave propagation characteristics by each candidate station are used as estimated results of the measurement results of the radio wave propagation characteristics of the received signal measured by UE 2 for each candidate station, and the base station and distributed stations are selected. In the second embodiment, the same explanation as in the first embodiment is omitted. In the second embodiment, the system configuration, the hardware configuration and functional configuration of the control device 1 and UE 2 are the same as in the first embodiment. The uplink reference signal used in the second embodiment is, for example, SRS (Sounding Reference Signal).

[0092] In the second embodiment, the control unit 11 of the control device 1 allocates radio resources for measuring radio wave propagation characteristics to UE 2 in the uplink. In the second embodiment, K SRSs are arranged in the same slot. The control unit 11 notifies UE 2 and each candidate station of the allocation of radio resources for measuring radio wave propagation characteristics.

[0093] The control unit 11 receives measurement results of the radio wave propagation characteristics of the SRS transmitted K times in bursts from UE 2 from each candidate station. The measurement results of the radio wave propagation characteristics of the received SRS at candidate station #n are expressed in the same way as the measurement results of the radio wave propagation characteristics of the received CSI-RS from candidate station #n by UE 2, which are expressed by Equation 1 in the first embodiment. Therefore, in the second embodiment, the control unit 11 uses the measurement results of the radio wave propagation characteristics of the received SRS at candidate station #n as the estimated result of the measurement results of the radio wave propagation characteristics of the received CSI-RS from candidate station #n by UE 2 to select the distributed station and the reference station. In the second embodiment, for each candidate station, the control unit 11 uses the K phase rotation amounts included in the measurement results of the radio wave propagation characteristics of the received SRS to determine the deviation of the phase rotation amount in the same way as in the first embodiment, and selects the reference station and the distributed station based on the said deviation.

[0094] In the second embodiment, when the control unit 21 of UE 2 receives notification from the control device 1 of the allocation of radio resources for measuring radio wave propagation characteristics in the uplink, it transmits SRS K times in accordance with the allocation of the radio resources.

[0095] Figure 10 is an example of a flowchart of the selection process for distributed stations and reference stations that perform coordinated transmission to UE 2 by the control device 1 according to the second embodiment. The process shown in Figure 10 is performed, similar to the first embodiment, for example, at the start of each radio frame and when it is determined that a re-selection of distributed stations is necessary based on the measurement results of radio wave propagation characteristics reported by UE 2.

[0096] In OP201, the control unit 11 selects candidate stations to perform coordinated transmission to UE 2. In OP202, the control unit 11 allocates radio resources for measuring radio wave propagation characteristics for UE 2 on the uplink. In the allocation of radio resources in OP202, K SRSs are placed within the same slot.

[0097] In OP203, the control unit 11 notifies UE 2 of information regarding each candidate station and the allocation of radio resources for measuring the radio wave propagation characteristics of UE 2. The control unit 11 also notifies each candidate station of the allocation of radio resources for measuring the radio wave propagation characteristics of UE 2.

[0098] In OP204, the control unit 11 determines whether or not it has received reports of the measurement results of radio wave propagation characteristics for K times from all candidate stations. If reports of the measurement results of radio wave propagation characteristics for K times have been received from all candidate stations (OP204: YES), the process proceeds to OP205. Until reports of the measurement results of radio wave propagation characteristics for K times have been received from all candidate stations (OP204: NO), the control unit 11 remains in standby mode. If a predetermined time has elapsed without reports of the measurement results of radio wave propagation characteristics for K times being received from all candidate stations, the process proceeds to OP205, and the processing from OP205 onward may be carried out using the received reports of the measurement results of radio wave propagation characteristics for each candidate station.

[0099] In OP205, the control unit 11 obtains a reference value for the measured phase rotation amount included in the measurement results of the radio wave propagation characteristics from each candidate station. The reference value is, for example, an average value or a linear approximation. In OP206, the control unit 11 obtains the deviation of the measured phase rotation amount for each candidate station using the reference value obtained in OP205.

[0100] In OP207, the control unit 11 selects a predetermined number of candidate stations with the smallest deviations obtained in OP206 from among the candidate stations as distributed stations to perform coordinated transmission to UE2. In OP208, the control unit 11 selects the candidate station with the smallest deviation obtained in OP206 as the reference station. After that, the process shown in Figure 10 is completed. Note that the selection process for distributed stations and reference stations shown in Figure 10 is an example and is not limited to the process shown in Figure 10.

[0101] Figure 11 shows an example of a processing sequence related to the reporting of phase offset in the communication system 100. In Figure 11, the control device 1, UE 2, and one candidate station representing multiple candidate stations are extracted and shown from the communication system 100.

[0102] In S51, the control device 1 selects several candidate stations to perform coordinated transmission to UE 2 (Figure 10, OP201). In S52, the control device 1 allocates radio resources for measuring radio wave propagation characteristics to UE 2 on the uplink (Figure 10, OP202). In S53, the control device 1 notifies UE 2 of information regarding each candidate station and the allocation of radio resources for measuring radio wave propagation characteristics (Figure 10, OP203). Each candidate station is also notified of the allocation of radio resources for measuring radio wave propagation characteristics.

[0103] In S61, UE 2 transmits SRS according to the allocation of radio resources for measuring radio wave propagation characteristics. In S62, each candidate station measures the radio wave propagation characteristics for each SRS transmitted from UE 2. In S63, each candidate station transmits the measurement result of the radio wave propagation characteristics of the received SRS, and the control device 1 receives it. The process from S61 to S63 is repeated K times. After the process from S61 to S63 is repeated K times and the control device 1 has received the measurement results of the radio wave propagation characteristics of K received SRS from all candidate stations, the process in S71 is performed.

[0104] The processing from S71 onwards is the same as the processing from S31 onwards in Figure 9. The control device 1 acquires the deviation of the measured phase rotation amount for each candidate station, selects the distributed station and the reference station based on the deviation (S71, S72), allocates radio resources for measuring the phase offset and allocates radio resources for reporting to UE 2 (S73), and notifies UE 2 and each candidate station (S74). When UE 2 receives the CSI-RS, it acquires the phase offset for each distributed station (S75) and reports it to the control unit 21 (S76). The control device 1 performs phase offset compensation for each distributed station based on the phase offset (S77).

[0105] In the second embodiment, UE 2 transmits SRS in bursts on the uplink, and distributed stations and reference stations are selected using the measurement results of the radio wave propagation characteristics at each candidate station for the SRS. In the second embodiment, since the measurement results of the radio wave propagation characteristics for each candidate station are not reported from UE 2 during the selection process of distributed stations and reference stations, the use of radio resources for such reporting can be reduced.

[0106] In the second embodiment, as with the modification of the first embodiment, the SRS transmitted K times in bursts from UE 2 may be arranged across multiple slots. If UE 2 has multiple antennas, the control device 1 may select a reference antenna and select a reference station based on the report from UE 2 of the measurement results of the radio wave propagation characteristics from each candidate station for the SRS transmitted from the reference antenna. The reference antenna may be determined by the control device 1 and notified to UE 2. Alternatively, UE 2 may select the reference antenna. For example, the antenna with the highest average SNR value for each distributed station may be selected as the reference antenna.

[0107] <Other Embodiments> The embodiments described above are merely examples, and this disclosure may be modified as appropriate without departing from its essence.

[0108] In the first and second embodiments, the candidate station with the smallest phase rotation deviation is selected as the reference station; however, the selection criteria for the reference station are not limited to this. For example, the reference station may be randomly selected from among candidate stations whose phase rotation deviation is below a predetermined threshold.

[0109] In the first and second embodiments, the phase rotation deviation obtained from the measurement results of radio wave propagation characteristics for each candidate station, acquired within the same radio frame in which the reference station selection is performed, was used. Alternatively, in addition to the phase rotation deviation obtained from the measurement results of radio wave propagation characteristics for each candidate station, acquired within the same radio frame in which the reference station selection is performed, the phase rotation deviation obtained from the measurement results of radio wave propagation characteristics for each candidate station acquired in a predetermined number of preceding radio frames may be used. For example, the average value of the phase rotation deviations between these radio frames may be calculated for each candidate station, and the candidate station with the smallest average value may be selected as the reference station.

[0110] In the first and second embodiments, a reference station is selected based on the phase rotation deviation of each candidate station. However, the reference station may also be selected by considering factors other than the phase rotation deviation, such as the positional relationship with the reference station, the received signal strength (L1-RSRP), and / or the interference amount (L1-SINR). For example, a candidate station whose positional relationship with UE 2 satisfies a predetermined condition may be selected as the reference station from among candidate stations whose phase rotation deviation is below a predetermined threshold. For example, a reference station may be selected from among candidate stations whose phase rotation deviation is below a predetermined threshold and whose L1-RSRP is above a predetermined threshold or whose L1-SINR is below a predetermined threshold.

[0111] In the first and second embodiments, the control device 1 selects the reference station, but is not limited to this, and the UE 2 may also select the reference station. In the first embodiment, when the UE 2 selects the reference station, the UE 2 may not report the measurement results of the radio wave propagation characteristics of the CSI-RS transmitted in bursts K times for each candidate station to the control device 1, but instead determine the deviation of the phase rotation amount for each candidate station from the measurement results, select the reference station and distributed stations based on the deviations, and notify the control device 1 of the distributed stations and the reference station. In the second embodiment, when the UE 2 selects the reference station, the UE 2 may transmit the SRS in bursts K times, obtain the measurement results of the radio wave propagation characteristics of the received SRS at each candidate station from the control device 1 or each candidate station, determine the deviation of the phase rotation amount for each candidate station based on the measurement results, select the reference station and distributed stations based on the deviations, and notify the control device 1 of the distributed stations and the reference station.

[0112] The processing of the control device 1 in the first and second embodiments may be performed by any of the base stations among the distributed stations, or by any of the relay stations if the signal to UE 2 is relayed by one or more relay stations. Furthermore, if the signal to UE 2 is relayed by one or more relay stations, the relay station may perform the same processing on the transmitting and receiving point as UE 2 in the first and second embodiments.

[0113] In the first and second embodiments, the process for selecting a reference station among a plurality of distributed stations that perform coordinated transmission to UE 2 was described. If UE 2 is equipped with a plurality of antennas, the reference station selection process of the first or second embodiment may be applied to the selection of a reference antenna in UE 2. For example, after a reference station is selected by the method described in the first or second embodiment, UE 2 may be instructed to transmit K SRS signals in bursts from each antenna, and for each antenna, the deviation in the amount of phase rotation may be determined based on the measurement results of the radio wave propagation characteristics for the received SRS at the reference station, and the antenna with the smallest deviation may be selected as the reference antenna. For example, after a reference station is selected by the method described in the first or second embodiment, the reference station may be instructed to transmit K CSI-RS signals in bursts to UE 2, and for each antenna, the deviation may be determined based on the measurement results of the radio wave propagation characteristics for the received CSI-RS at UE 2, and the antenna with the smallest deviation may be selected as the reference antenna. The selection of the reference antenna may be performed by either the control device 1 or the UE 2.

[0114] In the first and second embodiments, the communication system 100 was described on the premise that it is a distributed MIMO system. However, it is not limited to this, and the reference station selection process described in the first and second embodiments is applicable to systems in which coordinated transmission is performed, such as MIMO systems.

[0115] Furthermore, the processes and means described in this disclosure can be freely combined and implemented, provided that no technical inconsistencies arise.

[0116] Furthermore, a process described as being performed by a single device may be divided and executed by multiple devices. Conversely, a process described as being performed by different devices may be executed by a single device. In a computer system, the hardware configuration (server configuration) by which each function is implemented can be flexibly changed.

[0117] The present disclosure can also be realized by supplying a computer program implementing the functions described in the embodiments above to a computer, and having one or more processors in the computer read and execute the program. Such a computer program may be provided to the computer by a non-temporary computer-readable storage medium that can be connected to the computer's system bus, or it may be provided to the computer via a network. The non-temporary computer-readable storage medium includes any type of disk, such as magnetic disks (floppy disks, hard disk drives (HDDs), etc.), optical disks (CD-ROMs, DVDs, Blu-ray discs, etc.), read-only memory (ROM), random access memory (RAM), EPROM, EEPROM, magnetic cards, flash memory, or optical cards, and any type of medium suitable for storing electronic instructions.

[0118] 1...Control unit 2...UE 11...Control unit 21...Control unit 22...Measurement unit 100...Communication system 101...CPU 102...Main memory 103...External memory 104...Communication device

Claims

1. A method for a computer to perform the following: acquire an error included in the phase rotation amount obtained from the received signal in the first device for each of a plurality of transmitting and receiving points that transmit signals in coordination to the first device; and, based on the error for each of the plurality of transmitting and receiving points, select a first transmitting and receiving point from the plurality of transmitting and receiving points which is the source of the signal that serves as the reference signal when determining the phase offset, which is the phase difference between received signals in the first device.

2. The method according to claim 1, wherein the computer obtains the variation in the error included in the phase rotation amount obtained from the received signal from each of the plurality of transmitting and receiving points based on statistics of K phase rotation amounts obtained from a first signal transmitted and received K times (K: positive integer) between the transmitting and receiving point and the first device.

3. The method according to claim 2, wherein the computer obtains the deviations of the K phase rotation amounts as the variation of the error included in the phase rotation amount for each of the plurality of transmitting and receiving points, and selects the first transmitting and receiving point from the plurality of transmitting and receiving points based on the deviations for each of the plurality of transmitting and receiving points.

4. The method according to claim 3, wherein the computer obtains the average value of the K phase rotation amounts for each of the plurality of transmitting and receiving points, and obtains the deviation from the average value and the K phase rotation amounts.

5. The method according to claim 3, wherein the computer obtains linear approximations of K phase rotation amounts corresponding to each of the K phase rotation amounts for each of the plurality of transmitting and receiving points, and obtains the deviation from the linear approximations of the K phase rotation amounts and the K phase rotation amounts.

6. The method according to claim 2, wherein the first signal is a signal transmitted from the transmitting / receiving point toward the first device, and the K phase rotation amounts for each of the plurality of transmitting / receiving points are obtained by the first device measuring the first signal transmitted K times from each of the plurality of transmitting / receiving points.

7. The method according to claim 6, wherein the first signal is a CSI-RS (Channel State Information - Reference Signal).

8. The method according to claim 2, wherein the first signal is a signal transmitted from the first device in the direction of the transmitting and receiving point, and the K phase rotation amounts for each of the plurality of transmitting and receiving points are obtained by each of the plurality of transmitting and receiving points measuring the first signal transmitted K times.

9. The method according to claim 8, wherein the first signal is an SRS (Sounding Reference Signal).

10. The method according to claim 2, wherein the first signal transmitted K times is arranged in the same slot.

11. The method according to claim 2, wherein the first signal transmitted K times is arranged across a plurality of slots.

12. An information processing device comprising: a control unit that performs the following: for each of a plurality of transmitting and receiving points that transmit signals in coordination with a first device, an error included in the phase rotation amount obtained from the received signal in the first device; and, based on the error for each of the plurality of transmitting and receiving points, a first transmitting and receiving point that is the source of the signal used as a reference when determining the phase offset, which is the phase difference between received signals in the first device, from the plurality of transmitting and receiving points.

13. A program for a computer to perform the following: acquire an error included in the phase rotation amount obtained from the received signal at the first device for each of a plurality of transmitting and receiving points that transmit signals in coordination with the first device; and, based on the error for each of the plurality of transmitting and receiving points, select a first transmitting and receiving point from the plurality of transmitting and receiving points that is the source of the signal that serves as the reference signal when determining the phase offset, which is the phase difference between received signals at the first device.

14. A method for a user device (UE) to perform the following: receive a plurality of signals transmitted in coordination from a plurality of transmission / reception points; and determine a phase offset, which is the phase difference between the received signals from a first transmission / reception point, which is the source of a reference signal, selected from the plurality of transmission / reception points based on the error contained in the phase rotation amount obtained from the received signals for each of the plurality of transmission / reception points; and at least one other transmission / reception point among the plurality of transmission / reception points.

15. The method according to claim 14, further comprising the UE receiving information relating to the plurality of transmitting and receiving points and information relating to the first transmitting and receiving point from a second device.

16. The method according to claim 15, wherein the variation in the error included in the phase rotation amount obtained from the received signal from each of the plurality of transmitting and receiving points is obtained based on statistics of K phase rotation amounts obtained from a first signal transmitted and received K times (K: positive integer) between the transmitting and receiving point and the UE.

17. The method according to claim 16, wherein the variation in the error included in the phase rotation amount for each of the plurality of transmitting and receiving points is obtained as the deviation of the K phase rotation amounts, and the first transmitting and receiving point is selected from the plurality of transmitting and receiving points based on the deviation for each of the plurality of transmitting and receiving points.

18. The method according to claim 16, wherein the UE further includes receiving the first signal transmitted K times (K: a positive integer) from each of the plurality of transmitting and receiving points, obtaining K measured values ​​of phase rotation amounts from the first signal received K times for each of the plurality of transmitting and receiving points, and transmitting the K measured values ​​of phase rotation amounts for each of the plurality of transmitting and receiving points to the second device, the second device selecting the first transmitting and receiving point based on the K measured values ​​of phase rotation amounts for each of the plurality of transmitting and receiving points.

19. The method according to claim 16, wherein the first signal is a CSI-RS (Channel State Information - Reference Signal).

20. The method according to claim 16, further comprising the UE transmitting the first signal K times (K: a positive integer), wherein the second device obtains K measured values ​​of phase rotation amounts obtained from the first signal received K times for each of the plurality of transmitting and receiving points, and selects the first transmitting and receiving point based on the K measured values ​​of phase rotation amounts for each of the plurality of transmitting and receiving points.

21. The method according to claim 20, wherein the first signal is an SRS (Sounding Reference Signal).

22. The method according to claim 16, wherein the first signal transmitted K times is arranged in the same slot.

23. The method according to claim 16, wherein the first signal transmitted K times is arranged across a plurality of slots.

24. A user device comprising a control unit that performs the following: receiving a plurality of signals transmitted in coordination from a plurality of transmitting and receiving points; and determining a phase offset, which is the phase difference between the received signals from a first transmitting and receiving point, which is the source of a reference signal, and at least one transmitting and receiving point other than the first transmitting and receiving point, selected from the plurality of transmitting and receiving points based on the error contained in the amount of phase rotation obtained from the received signals for each of the plurality of transmitting and receiving points.

25. A program for a computer to perform the following: receive multiple signals transmitted in coordination from multiple transmission / reception points; and determine a phase offset, which is the phase difference between the received signals from a first transmission / reception point, which is the source of a reference signal, and at least one other transmission / reception point among the multiple transmission / reception points, selected from the multiple transmission / reception points based on the error contained in the phase rotation amount obtained from the received signals for each of the multiple transmission / reception points.

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