Base station device, terminal device, communication method, and program in a communication system that forms a beam in downlink and communicates

Abstract

To appropriately select and use a transmission method using a plurality of antennas according to a situation.SOLUTION: A base station device including a plurality of antennas transmits a predetermined signal for estimation of a transmission path by a terminal device from each of the plurality of antennas, over an entire available frequency band, receives, from the terminal device, information about a precoding matrix which the base station device should use for each of a plurality of frequency domains, forms a beam based on a frequency resource that should be used for signal transmission to the terminal device and notified information, and transmits a signal to the terminal device. Each of the plurality of frequency domains is a part of the available frequency band.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a communication system that uses a plurality of antennas to form beams for communication in downlink. [Background technology]

[0002] In the technical field of wireless communication, a technique is known that effectively utilizes spatial resources by using multiple antennas in order to improve throughput and expand communication capacity. This technique includes, for example, multiple input multiple output (MIMO) and antenna diversity. In a cellular communication system, a terminal device may observe a channel state information reference signal (CSI-RS) transmitted from a base station device and estimate a state of a downlink transmission path based on the CSI-RS. Then, the terminal device identifies one of a plurality of precoding matrix indicator (PMI) values ​​corresponding to a plurality of antenna weight patterns prepared in advance based on the estimation result, and notifies the base station device of the identified PMI value. The base station device may form a beam using an antenna weight corresponding to the notified PMI, and communicate with the terminal device. In a technique using PMI, a beam can be set with little feedback by having the terminal device perform a transmission path estimation, select a roughly suitable beam based on the transmission path estimation value, and feed back only the selection result. Summary of the Invention [Problem to be solved by the invention]

[0003] CSI-RS is transmitted only in a specific frequency region that is a part of the available frequency band. Therefore, the state of the transmission path measured by the terminal device is also related to that specific frequency region and may not be suitable for other frequency regions of the available frequency band. In such a case, the beam corresponding to the PMI notified by the terminal device may not be suitable for the frequency resource when a signal is transmitted from the base station device to the terminal device.

[0004] The present invention provides a technique that enables forming an appropriate beam for frequency resources used for communication. [Means for solving the problem]

[0006] In addition, the terminal device according to one aspect of the present invention receives signals from each of a plurality of antennas of the base station device over the entire available frequency band. and others, For estimating a transmission path by the terminal device 1. Predetermined signal receiving information indicating whether a first predetermined signal is to be transmitted, and when information indicating that the first predetermined signal is to be transmitted is received, A receiving means for receiving the When information indicating that the first predetermined signal is transmitted from the base station device is received, The above 1. Estimates the state of the transmission path for each of a number of frequency domains based on a given signal and when information indicating that the first predetermined signal is transmitted from the base station device is not received, estimating a transmission path based on a second predetermined signal transmitted in a narrower frequency range than the first predetermined signal. An estimation means and a method for estimating a transmission path based on the estimated state of the transmission path. Before A determination means for determining a precoding matrix to be used by the base station device; The above Precoding matrix is determined by a result of estimating a transmission path based on the first predetermined signal or is determined by a result of estimating a transmission path based on the second predetermined signal, and the precoding matrix is ​​indicated. information and and a transmitting means for transmitting the plurality of frequency ranges to the base station device, each of the plurality of frequency ranges being a part of the available frequency band. Effect of the Invention

[0007] According to the present invention, it is possible to form an appropriate beam for the frequency resources used for communication. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Diagram 2] FIG. 2 is a diagram illustrating an example of the hardware configuration of a base station device and a terminal device. [Diagram 3] FIG. 2 is a diagram illustrating an example of a functional configuration of a base station device. [Figure 4] FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal device. [Diagram 5] FIG. 11 is a diagram illustrating an example of a flow of processing performed by a base station device. [Figure 6] FIG. 11 is a diagram illustrating an example of a flow of processing executed by a terminal device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. In addition, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] (System Configuration) An example of the configuration of a wireless communication system according to this embodiment is shown in Fig. 1. The wireless communication system is, for example, a long-term evolution (LTE) or fifth-generation (5G) cellular communication system, and includes a base station device 101 having multiple antennas and a terminal device 102 having one or more antennas.

[0011] In this wireless communication system, the base station device can form a beam based on an estimated value of the state of the transmission path between the base station device and the terminal device, and transmit a wireless signal (wireless frame) to the terminal device. Note that, throughout the present embodiment and the appended claims, the state of the transmission path between the base station device and the terminal device refers to the state of the transmission path between each of the multiple antennas of the base station device and each of one or more antennas of the terminal device. For example, when the base station device has N antennas and the terminal device has M antennas, the states of N×M transmission paths are estimated. For example, the base station device multiplies the wireless frame to be transmitted by the antenna weight for each of the multiple antennas calculated based on the estimated value of the state of the transmission path, and transmits the multiplied signal in parallel from the multiple antennas.

[0012] In addition, for example, when the terminal device has multiple antennas, the base station device can transmit multiple data streams to the terminal device in parallel. That is, it is possible to use MIMO (Multiple-Input Multiple-Output) technology in which the base station device and the terminal device use multiple antennas to transmit and receive multiple streams between each other. In this method, multiple data streams can be spatially multiplexed and transmitted in the same frequency band and time. In this case, for example, an antenna weight matrix (precoding matrix) of the number of transmitting antennas x the number of receiving antennas is multiplied by a vector indicating each data stream to generate a vector of the data stream to be transmitted by each transmitting antenna. Then, each of the multiple antennas of the base station device (transmitting side) transmits a corresponding element of the vector. According to this, in one example, it is possible to extract the multiple transmitted streams with high quality from the signal received by each antenna of the terminal device (receiving side).

[0013] As a method for a base station device to form a beam and transmit a signal, a method is known in which a plurality of candidates of precoding matrices that the base station device can use are prepared in advance, and a terminal device determines which of the candidates the base station device should use. In this method, the terminal device estimates the state of a transmission path based on a CSI-RS (Channel State Information Reference Signal) received from the base station device, and selects a beam suitable for the estimated state of the transmission path from among the precoding matrices prepared in advance. Then, the terminal device notifies the base station device of information identifying the selected beam as a PMI (Precoding Matrix Indicator). The base station device identifies a precoding matrix to be used based on the PMI, forms a beam using the identified precoding matrix, and transmits a signal.

[0014] However, as described above, the CSI-RS is transmitted only in a part of the frequency range of the available frequency band. Therefore, the terminal device can appropriately estimate the transmission path in the part of the frequency range and select the PMI. On the other hand, the state of the transmission path may be different for other frequency ranges. Therefore, for example, the beam specified by the PMI may not be appropriate in the frequency resource that the base station device has determined to be used when transmitting a signal such as user data to the terminal device. In this embodiment, in consideration of such circumstances, the base station device transmits a predetermined signal such as an SRS (Sounding Reference Signal) over the entire available frequency band. Note that the SRS is an example, and other signals capable of transmission path estimation may also be used. Here, since the power density during signal transmission per certain frequency range is constant, the base station device can transmit the predetermined signal with sufficient power over the entire available frequency band. Therefore, even if the terminal device is located sufficiently far from the base station device, the predetermined signal can be received with sufficient power.

[0015] The terminal device receives the predetermined signal at each of one or more antennas, and estimates the state of the transmission path for each of the multiple frequency regions based on the predetermined signal. The multiple frequency regions are each a part of a frequency band available in the wireless communication system. The multiple frequency regions may be configured so that they do not overlap with each other, for example, by dividing the available frequency band, or two or more frequency regions may be configured to include frequency ranges that overlap with each other in part. However, the multiple frequency regions are set so that any one of the multiple frequency regions does not include or is not included in another frequency region. Furthermore, each frequency region may be set so that the entire available frequency band is covered by the multiple frequency regions, or each frequency region may be set so that some (for example, a small range) frequency regions are not included in the multiple frequency regions. Based on the estimated state of the transmission path for each of the multiple frequency regions, the terminal device selects a precoding matrix to be used by the base station device from among candidates of precoding matrices available to the base station device. Then, the terminal device notifies the base station device of the PMI corresponding to the selected precoding matrix for each of the multiple frequency regions. In addition, when this notification is made, for example, a message directly describing the PMI value in each frequency region may be transmitted, or a message including a reference PMI value and a difference value of PMI in each frequency region may be transmitted. In one example, the reference PMI value is a PMI value suitable for the entire available frequency band, and the difference value of PMI in each frequency region may be information indicating whether the PMI value is the same or different. The reference PMI value may be a PMI value in any frequency region. According to this, the base station device can, for example, identify a frequency region in which a PMI common to the reference PMI can be used, and perform resource allocation so as to transmit a signal to the terminal device in that frequency region.

[0016] In addition, the base station device may transmit information indicating that a predetermined signal such as SRS is to be transmitted (indicating whether or not the predetermined signal is to be transmitted) to enable the terminal device to estimate the transmission path. In one example, the base station device may individually transmit setting information indicating that the predetermined signal is to be transmitted to the terminal device by an RRC (radio resource control) message. At this time, the radio resource (frequency and time resources such as transmission timing in each frequency band) for transmitting the predetermined signal may be notified. In addition, the base station device may notify the presence or absence of transmission of the predetermined signal and the radio resource at the time of transmission by a signal other than the RRC message. In addition, the base station device may broadcast the presence or absence of transmission of a predetermined signal such as SRS by, for example, system information (SI). When a predetermined signal such as SRS is not transmitted, the terminal device may select a precoding matrix (PMI) used by the base station device based on the CSI-RS. In addition, the CSI-RS is an example, and in this case, the terminal device may estimate the transmission path and select a precoding matrix based on another signal having a narrower frequency range than the predetermined signal transmitted by the base station device.

[0017] As described above, according to the present embodiment, the base station device can transmit a predetermined signal such as SRS that enables the terminal device to estimate a transmission path, thereby enabling the terminal device to select a beam to be used by the base station device in each frequency region. This allows the base station device to form a beam suitable for the frequency resource to be used in downlink communication.

[0018] (Device configuration) Next, an example of the hardware configuration of the base station device and the terminal device as described above will be described with reference to FIG. 2. In one example, the base station device and the terminal device are configured to include a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. The processor 201 is a computer configured to include one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and executes the overall processing of the base station device and the terminal device and each of the above-mentioned processes by reading and executing a program stored in the ROM 202 or the storage device 204. The ROM 202 is a read-only memory that stores information such as programs and various parameters related to the processing executed by the base station device and the terminal device. The RAM 203 functions as a workspace when the processor 201 executes a program, and is a random access memory that stores temporary information. The storage device 204 is configured, for example, by a removable external storage device. The communication circuit 205 is configured, for example, by a circuit for wireless communication of LTE or 5G. 2 illustrates one communication circuit 205, the base station device and the terminal device may have multiple communication circuits, such as wireless communication circuits for LTE and 5G and wired communication circuits for wired communication. The base station device and the terminal device may have separate communication circuits 205 for each of multiple available frequency bands, or may have a common communication circuit 205 for at least some of the frequency bands.

[0019] FIG. 3 shows an example of the functional configuration of the base station device according to this embodiment. The base station device has, for example, a communication unit 301, a transmission path estimation signal transmission unit 302, a beam setting unit 303, and an information notification unit 304 as an example of the functional configuration. FIG. 3 shows only a part of the functions of the base station device that is related to the description of this embodiment, and the base station device naturally has a function as a base station device of a general cellular communication system. The base station device may have a function other than the function shown in FIG. 3 and the general-purpose function as a base station device. The functional blocks in FIG. 3 are shown in a schematic manner, and each functional block may be realized by being integrated, or may be further subdivided. Each function in FIG. 3 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or may be realized, for example, by a processor present inside the communication circuit 205 executing predetermined software.

[0020] The communication unit 301 performs wireless communication with the terminal device. The communication unit 301 forms beams using a plurality of antennas and transmits signals. The transmission path estimation signal transmission unit 302 executes processing for transmitting a predetermined signal (e.g., SRS) for the terminal device to estimate a transmission path via the communication unit 301. Here, the predetermined signal is transmitted over the entire usable frequency band, unlike, for example, a Channel State Information-Reference Signal (CSI-RS) that is transmitted only in a partial frequency range. The terminal device receives the predetermined signal and performs transmission path estimation based on the received predetermined signal. Then, the terminal device specifies a precoding matrix suitable for use by the base station device for each of a plurality of frequency regions from among a plurality of precoding matrix candidates based on the estimated value of the transmission path. Note that each of the plurality of frequency regions is a part of the frequency band that can be used in the wireless communication system. The specified precoding matrix is ​​notified to the base station device by a signal including information on the result of the specification.

[0021] The beam setting unit 303 acquires information on the precoding matrix for each of a plurality of frequency regions from the terminal device via the communication unit 301. Then, the beam setting unit 303 sets an antenna weight to be used by the communication unit 301 using a precoding matrix for a frequency region corresponding to a frequency resource used when the communication unit 301 transmits a signal to the terminal device. This allows the communication unit 301 to transmit a signal to the terminal device using a beam suitable for the frequency resource to be allocated. The information notifying unit 304 notifies the terminal device of various information via the communication unit 301. For example, when the transmission path estimation signal transmitting unit 302 transmits a predetermined signal such as an SRS, the information notifying unit 304 may notify the terminal device via the communication unit 301 of information indicating that the predetermined signal is to be transmitted. Note that the information indicating that the predetermined signal is to be transmitted may be expressed as 1-bit information. In one example, a reserved bit in an existing signal such as system information or a message of a higher layer may be set to 1 to indicate that the predetermined signal is to be transmitted. In addition, a bit indicating whether or not to transmit a specific signal may be added to an existing message, or a new message may be separately defined.

[0022] FIG. 4 shows an example of the functional configuration of the terminal device according to this embodiment. The terminal device has, for example, a communication unit 401, a transmission path estimation unit 402, a beam determination unit 403, and an information receiving unit 404 as an example of the functional configuration. FIG. 4 shows only a part of the functions of the terminal device that are related to the description of this embodiment, and the terminal device naturally has functions as a terminal device of a general cellular communication system. The terminal device may have functions other than the functions shown in FIG. 4 and the general-purpose functions as a terminal device. The functional blocks in FIG. 4 are shown in a schematic manner, and each functional block may be realized by being integrated, or may be further subdivided. Each function in FIG. 4 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or may be realized, for example, by a processor present inside the communication circuit 205 executing predetermined software.

[0023] The communication unit 401 performs wireless communication with the base station device. In addition, when the terminal device has multiple antennas, the communication unit 401 can form beams using the multiple antennas to transmit and receive signals to and from the base station device. The transmission path estimation unit 402 receives a predetermined signal, such as an SRS, transmitted from the base station device over the entire frequency band, and estimates the state of the transmission path between each of one or more antennas of the base station device and each of the multiple antennas of the terminal device. The transmission path estimation unit 402 obtains an estimate of the state of the transmission path for each of the multiple frequency regions, for example. In addition, each of the multiple frequency regions is a part of the frequency band available in the wireless communication system.

[0024] The beam determination unit 403 determines a precoding matrix to be used by the base station device for each of the multiple frequency regions by selecting it from among precoding matrix candidates prepared in advance. Then, the beam determination unit 403 notifies the base station device of information on the selected precoding matrix for each of the multiple frequency regions. For example, the PMI for each of the multiple frequency regions may be notified to the base station device. Also, for example, a PMI suitable for the entire available frequency band may be set as a reference PMI, and a difference value between the PMI value and each of the multiple frequency regions may be notified to the base station device. At this time, the base station device may be notified of the reference PMI value and a bitmap indicating whether the PMI value for each of the multiple frequency regions is equal to the reference PMI value. Also, the PMI value with the highest occurrence frequency among the PMIs for each of the multiple frequency regions may be used as the reference PMI value.

[0025] The information receiving unit 404 receives information indicating whether or not a predetermined signal such as SRS is transmitted by the base station device. When the information receiving unit 404 receives information indicating that the predetermined signal is transmitted, the transmission channel estimating unit 402 performs transmission channel estimation based on the predetermined signal. Then, as described above, the beam determining unit 403 determines a precoding matrix for each of the multiple frequency domains and notifies the base station device of the result. On the other hand, when the information receiving unit 404 receives information indicating that the predetermined signal is not transmitted, the transmission channel estimating unit 402 may perform transmission channel estimation based on, for example, CSI-RS. Then, the beam determining unit 403 selects a precoding matrix based on the transmission channel estimation value and notifies the base station device of the corresponding PMI. Note that the information notified to the base station device may include, for example, information indicating whether to notify PMI related to multiple frequency domains determined based on a predetermined signal or to notify one PMI determined based on CSI-RS.

[0026] (Processing flow) Next, an example of the flow of the process executed by the base station device and the terminal device will be described with reference to Figures 5 and 6. Figure 5 shows an example of the flow of the process executed by the base station device, and Figure 6 shows an example of the flow of the process executed by the terminal device. This process is started, for example, by the processor 201 of the base station device or the terminal device starting a program stored in the ROM 202.

[0027] First, the base station device notifies the terminal device of information indicating that a predetermined signal for transmission path estimation such as SRS will be transmitted (S501), and the terminal device receives the notification (S601). The notification may be notified to the terminal device individually, or may be notified to a plurality of terminal devices simultaneously by broadcast or multicast. In one example, the notification notifies the frequency and time resources from which the predetermined signal for transmission path estimation is transmitted. The predetermined signal is transmitted over the entire available frequency band, but may be transmitted at different timings for each frequency domain, or may be transmitted simultaneously in all frequency bands. Here, when the predetermined signal is transmitted simultaneously in all frequency bands, only the transmission timing may be notified. When the predetermined signal is transmitted at different timings for each frequency domain, the transmission timing may be indicated individually for each of the frequency domains divided into a plurality of domains. For example, a reference transmission timing for a reference frequency domain may be indicated, and for other frequency domains, the transmission timing may be indicated by a difference (offset value) from the reference transmission timing. This notification does not necessarily have to be transmitted and received.

[0028] Then, the base station device transmits a predetermined signal for transmission channel estimation (S502), and the terminal device receives the signal for transmission channel estimation and performs transmission channel estimation for each of a plurality of frequency regions based on the signal (S602). Here, each of the plurality of frequency regions is a part of a frequency band available in the wireless communication system. Note that the base station device may indicate that a predetermined signal is to be transmitted by indicating that the predetermined signal includes a predetermined signal within the predetermined signal, and in this case, the notification of S501 and the transmission of the predetermined signal of S502 may be performed simultaneously (in the same subframe). Also, in a case where the base station device is always supposed to transmit a predetermined signal, the transmission and reception of the notifications of S501 and S601 may be omitted.

[0029] The terminal device selects and determines a precoding matrix for each of the multiple frequency regions from among precoding matrix candidates prepared in advance based on the transmission channel estimation value for the multiple frequency regions (S603). Then, the terminal device notifies the base station device of information on the determined precoding matrix (S604). Note that the terminal device may transmit, for example, information indicating the PMI for each frequency region to the base station device. At this time, as described above, the reference PMI and the difference value between the PMI in each frequency region and the reference PMI may be transmitted, or the value of the PMI in each frequency region itself may be transmitted without using the reference PMI. Also, only information on whether the PMI in each frequency region is equal to the reference PMI may be notified.

[0030] The base station device receives information about the precoding matrix from the terminal device (S503). Then, the base station device determines a frequency resource to be used in signal transmission to the terminal device (S504), identifies a PMI for a frequency domain corresponding to the frequency resource, forms a beam with a precoding matrix corresponding to the PMI, and transmits a signal to the terminal device (S505). Note that the base station device may select a frequency resource that can use the same antenna weight, for example. That is, a frequency domain with a common PMI may be identified, and a frequency resource to be used may be determined within the range of the frequency domain.

[0031] In this way, the base station device transmits a predetermined signal for the terminal device to estimate a transmission path, such as SRS, over the entire available frequency band. This allows the terminal device to perform transmission path estimation over the entire available frequency band, and to select an appropriate precoding matrix for each frequency region corresponding to a part of a wide range of frequency bands. This allows the base station device to form a beam suitable for the frequency resource used for signal transmission to the terminal device, and to transmit signals to the terminal device with high efficiency.

[0032] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. A terminal device, a receiving means for receiving information indicating whether a first predetermined signal for estimating a transmission path by the terminal device is to be transmitted from each of a plurality of antennas of the base station device over an entire usable frequency band, and receiving the first predetermined signal when information indicating that the first predetermined signal is to be transmitted is received; an estimation means for estimating a state of a transmission path for each of a plurality of frequency domains based on the first predetermined signal when information indicating that the first predetermined signal is transmitted from the base station device is received, and for estimating a transmission path based on a second predetermined signal transmitted in a frequency range narrower than that of the first predetermined signal when information indicating that the first predetermined signal is transmitted from the base station device is not received; A determination means for determining a precoding matrix to be used by the base station apparatus based on the estimated state of the transmission path; a transmitting means for transmitting, to the base station device, information indicating whether the determined precoding matrix has been determined based on a result of estimating a transmission channel based on the first predetermined signal or a result of estimating a transmission channel based on the second predetermined signal, and information indicating the precoding matrix; having Each of the plurality of frequency ranges is a portion of the available frequency band. A terminal device comprising:

2. 2. The terminal device according to claim 1, wherein the transmitting means transmits, to the base station device, a PMI (Precoding Matrix Indicator) in each of the plurality of frequency domains as information indicating the precoding matrix determined by a result of estimating a transmission path based on the first predetermined signal.

3. 3. The terminal device according to claim 1, wherein the first predetermined signal is a Sounding Reference Signal (SRS).

4. 4. The terminal device according to claim 1, wherein the plurality of frequency domains are set such that two or more of the plurality of frequency domains include frequency ranges that overlap with each other in a portion of the frequency domains.

5. A communication method performed by a terminal device, comprising: receiving information indicating whether a first predetermined signal for estimating a transmission path by the terminal device is to be transmitted from each of a plurality of antennas of the base station device over an entire usable frequency band, and receiving the first predetermined signal when information indicating that the first predetermined signal is to be transmitted is received; when information indicating that the first predetermined signal is transmitted from the base station device is received, estimating a state of a transmission path for each of a plurality of frequency domains based on the first predetermined signal, and when information indicating that the first predetermined signal is transmitted from the base station device is not received, estimating a transmission path based on a second predetermined signal transmitted in a frequency range narrower than that of the first predetermined signal; determining a precoding matrix to be used by the base station apparatus based on the estimated state of the transmission path; transmitting, to the base station device, information indicating whether the determined precoding matrix has been determined based on a result of estimating a transmission channel based on the first predetermined signal or a result of estimating a transmission channel based on the second predetermined signal, and information indicating the precoding matrix; Including, Each of the plurality of frequency ranges is a portion of the available frequency band. A communication method comprising:

6. A program for causing a computer to function as each of the means included in the terminal device according to any one of claims 1 to 4.

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