Communication device, communication method, and program for communicating using multiple beam forming techniques

Abstract

To appropriately select and use transmitting techniques with a plurality of antennas in accordance with situations.SOLUTION: A communication device estimates a state of a transmission path between the communication device and a partner device by using a wireless signal transmitted from the partner device, acquires information on a beam which is to be used when the communication device transmits a signal to the partner device, which is decided by the partner device on the basis of a wireless signal transmitted by the communication device, forms a first beam in transmission of a signal to the partner device on the basis of the estimated state of the transmission path or forms a second beam in transmission of a signal to the partner device on the basis of the acquired information and then communicates with the partner device. The communication device during communication with the partner device using the first beam performs control of switching the beam to be used from the first beam to the second beam on the basis of a first wireless quality of a first wireless signal transmitted with the first beam and a second wireless quality of a second wireless signal transmitted with a predetermined beam related to the second beam.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a control technique for a communication device that forms beams using a plurality of antennas. [Background technology]

[0002] In the technical field of wireless communication, there are known techniques for effectively utilizing spatial resources by using multiple antennas in order to improve throughput and expand communication capacity, including, for example, multiple-input multiple-output (MIMO) and antenna diversity.

[0003] In a cellular communication system, a base station device can estimate the state of a transmission path based on an uplink signal (e.g., a Sounding Reference Signal (SRS) or a Demodulation Reference Signal (DMRS)) transmitted from a terminal device. The base station device can then adjust antenna weights based on the estimated value to form a beam that is narrow and has a sufficiently high gain in the direction of direction to communicate with the terminal device. As described above, this method allows the base station device to form a beam that has a sufficiently high gain in the direction of direction and is suitable for the terminal device, and therefore allows data to be transmitted to the terminal device with high throughput. This method can also be used in a Frequency Division Duplex (FDD) system, but is particularly useful in a Time Division Duplex (TDD) system.

[0004] Also, in a cellular communication system, a terminal device may observe a CSI-RS (Channel State Information Reference Signal) transmitted from a base station device and estimate the state of a downlink transmission path based on the CSI-RS. Then, the terminal device may specify one of a plurality of PMI (Precoding Matrix Indicator) values ​​corresponding to a plurality of antenna weight patterns prepared in advance based on the estimation result, and notify the base station device of the specified 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 technology using PMI, a beam can be set with little feedback by having the terminal device perform 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]

[0005] In the method in which the base station device directly estimates the transmission path and forms a beam, a unique beam is formed according to the position of the terminal device, and thus high throughput can be obtained. On the other hand, in this method, the beam width is narrowed in order to increase the gain of the beam toward the direction of the terminal device. Therefore, when the terminal device moves, a mismatch occurs between the direction of the beam and the position of the terminal device, and the throughput may also decrease. In contrast, in the method in which the terminal device feeds back the value of the PMI, a beam roughly directed toward the direction of the terminal device is used, and therefore the maximum throughput is relatively low, but the degree of degradation of the throughput due to the movement of the terminal device is not large.

[0006] The present invention provides a technique for appropriately selecting and using a transmission method using multiple antennas depending on the situation. [Means for solving the problem]

[0007] A communication device according to one aspect of the present invention includes an estimation means for estimating a state of a transmission path between the communication device and the other device using a wireless signal transmitted from the other device, an acquisition means for acquiring information regarding a beam determined by the other device based on the wireless signal transmitted by the communication device, the beam being determined when the communication device transmits a signal to the other device, and a signal processing means for forming a first beam when transmitting a signal to the other device based on the estimated state of the transmission path, or forming a second beam when transmitting a signal to the other device based on the acquired information. The second beam has a wider beam width than the first beam. and a control means for controlling the communication means to switch the beam to be used from the first beam to the second beam based on a first wireless quality in the other device for a first wireless signal transmitted in the first beam and a second wireless quality in the other device for a second wireless signal transmitted in a predetermined beam for determining the second beam while communicating with the other device using the first beam. Effect of the Invention

[0008] According to the present invention, it is possible to appropriately select and use a transmission technique using a plurality of antennas depending on the situation. [Brief description of the drawings]

[0009] [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 a hardware configuration of a base station device. [Diagram 3] FIG. 2 is a diagram illustrating an example of a functional configuration of a base station device. [Figure 4] FIG. 11 is a diagram illustrating an example of a flow of processing executed by a base station device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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.

[0011] (System Configuration) 1 shows an example of the configuration of a wireless communication system according to this embodiment. 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. Note that this is just one example, and the following discussion can be applied to any wireless communication system in which a communication device having multiple antennas forms beams using the multiple antennas and wirelessly communicates with a partner device having one or more antennas.

[0012] 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 radio signal (radio frame) to the base station 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 indicates the state of the transmission path between each of a plurality of 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 calculates a weight to be multiplied on the radio frame to be transmitted at each of the plurality of antennas based on the estimated value of the state of the transmission path, and transmits the radio frame to be transmitted multiplied by the weight from the plurality of antennas in parallel. Note that, for example, when the terminal device has a plurality of antennas, the base station device can transmit a plurality of data streams in parallel to the terminal device. That is, it is possible to use MIMO (Multiple-Input Multiple-Output) technology in which the base station device and the terminal device both use a plurality of antennas to transmit and receive a plurality of streams. 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 described above, the base station device can estimate the state of the transmission path based on a radio signal such as an SRS (Sounding Reference Signal) transmitted from the terminal device, and calculate a precoding matrix based on the transmission path estimation value. In addition, a plurality of candidates for precoding matrices that the base station device can use may be prepared in advance, and the terminal device may determine which of the candidates the base station device should use. In this case, the terminal device notifies the base station device of information specifying the determined beam as a PMI (Precoding Matrix Indicator), and the base station device can determine the precoding matrix to be used based on the PMI.

[0014] The first beam formed by the base station device by estimating the state of the transmission path is the beam most suitable for the state of the transmission path at the time when the terminal device transmits a radio signal. However, this first beam has a narrow beam width and is vulnerable to changes in the state of the transmission path when the terminal device moves, and when such changes occur, the throughput may deteriorate rapidly. On the other hand, the second beam obtained by the terminal device determining a precoding matrix to be used from among the precoding matrix candidates is the most suitable among the candidates at the time of the determination, but in most cases, its performance is insufficient compared to the first beam. That is, in the method using PMI, only a limited number of precoding matrix candidates are prepared to reduce the amount of feedback, so the second beam is roughly suitable for the state of the transmission path in the terminal device, but is not optimal. For this reason, the second beam is generally inferior to the first beam in terms of quality such as throughput. On the other hand, since the second beam is set to roughly suit the state of the transmission path, even if the state of the transmission path at the terminal device changes, sufficient gain tends to be obtained as long as the change is not significant.

[0015] In this embodiment, a technology is provided for appropriately switching and using beams based on the characteristics of such beams. Note that, in the following, a base station device capable of switching between a first beam and a second beam to communicate with a terminal device is described, but this is only an example, and for example, a terminal device may execute a similar process, or a similar process may be executed in another wireless communication system.

[0016] In this embodiment, while forming a first beam and communicating with a terminal device, the base station device transmits a first radio signal such as a demodulation reference signal (DMRS) or a channel state information reference signal (CSI-RS) using the first beam. The base station device may also transmit a second radio signal such as a CSI-RS using a predetermined beam (having a relatively wide beam width) so that the terminal device can determine the PMI. The terminal device then receives the first radio signal transmitted using the first beam and measures a first radio quality related to the first radio signal. The terminal device also receives a second radio signal transmitted using the predetermined beam and measures a second radio quality related to the second radio signal. These radio qualities may be, for example, a signal-to-interference and noise ratio (SINR), but may also be, for example, a signal-to-noise ratio (SNR) or a received signal strength. The base station device then determines whether to switch the beam to be used from the first beam based on the SRS to the second beam based on the PMI based on the first radio quality and the second radio quality. If the base station device determines to switch, it uses the second beam instead of the first beam, and if it determines not to switch, it continues to use the first beam to transmit data to the terminal device.

[0017] In one example, the base station device may determine to switch the beam to be used from the first beam to the second beam based on the difference between the first wireless quality and the second wireless quality becoming equal to or lower than a predetermined level. For example, the base station device may determine to switch the beam to be used from the first beam to the second beam based on the first wireless quality becoming lower than the second wireless quality. Note that the first beam generally has a narrow beam width, and it is assumed that the gain obtained in signal transmission to the terminal device will deteriorate sharply when the state of the transmission path changes due to the terminal device moving or the like. For this reason, when the level difference between the first wireless quality and the second wireless quality approaches to such an extent that a sign of deterioration of the first wireless quality is observed, control may be executed to switch the beam to be used to the second beam. That is, the beam to be used may be switched from the first beam to the second beam when the first wireless quality is higher than the second wireless quality. Furthermore, the beam used may be switched from the first beam to the second beam after a value obtained by subtracting the second wireless quality level from the first wireless quality level falls below a negative predetermined value.

[0018] The terminal device may transmit a report on the first radio quality and a report on the second radio quality to the base station device. The base station device may determine whether to switch to the second beam as described above based on the reported values. The terminal device may also report information generated based on the first radio quality and the second radio quality to the base station device. For example, information indicating a difference between the first radio quality and the second radio quality may be generated and notified to the base station device. In one example, the difference may be indicated in 16 steps and reported as 4-bit information. Note that the number of steps and the number of bits are only examples, and 8 steps may be indicated by 3 bits, or 64 steps may be indicated by 6 bits. In one example, the steps may be in 1 dB increments, but may have any increment width, such as 2 dB increments, 0.5 dB increments, or a non-uniform increment width determined in advance.

[0019] In addition, the base station device may receive an SRS from the terminal device during communication using the second beam, calculate the wireless quality assuming that the first beam is formed based on the SRS, and compare the wireless quality with the wireless quality measured by the terminal device in communication using the second beam to determine whether to switch the beam to be used to the first beam. For example, the base station device may estimate the state of the transmission path, such as the path loss, based on the SRS, and estimate the first reception power of the signal in the terminal device based on the gain obtained when the first beam is formed and the transmission power available to the base station device. Then, the base station device may receive a report of the second reception power of the signal transmitted using the second beam from the terminal device, and determine to use the first beam when the first reception power exceeds the second reception power by exceeding a predetermined level. Note that the reception power is an example of wireless quality, and other indicators may be used. In addition, the base station device may determine to use the first beam when the first reception power exceeds the second reception power by exceeding a predetermined level for a predetermined period of time. In this manner, switching from the second beam to the first beam may be performed in a similar manner to that described above.

[0020] According to the above-mentioned process, it is possible to appropriately switch between the first beam based on the SRS and the second beam based on the PMI based on the state of the transmission line in the terminal device. For example, when it is assumed that the gain obtained by the first beam decreases according to a change in the state of the transmission line due to the movement of the terminal device, etc., and sufficient throughput cannot be obtained, it is possible to use the second beam with relatively high stability. This increases the stability of communication, while using the first beam with a higher gain when the state of the transmission line is stable because the terminal device is stationary, etc., thereby improving the throughput of the entire system.

[0021] (Device configuration) Next, an example of the hardware configuration of the base station device as described above will be described with reference to FIG. 2. In one example, the base station device includes a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. The processor 201 is a computer including 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 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. 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, for example, a removable external storage device. The communication circuit 205 is, for example, a circuit for wireless communication of LTE or 5G. 2 illustrates one communication circuit 205, the base station device may have multiple communication circuits, such as wireless communication circuits for LTE and 5G and a wired communication circuit for wired communication. The base station 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.

[0022] 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 channel estimation unit 302, a candidate matrix holding unit 303, an information acquisition unit 304, and a beam forming control unit 305 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. In addition, 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. In addition, 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.

[0023] The communication unit 301 forms a beam based on the state of the transmission path between the terminal device and the communication unit 301, and performs wireless communication with the terminal device. The communication unit 301 is configured to form and transmit a high-gain beam in a predetermined direction, for example, by multiplying a modulated signal to be transmitted to the terminal device by a predetermined weight for each transmitting antenna and transmitting the signal in parallel. The communication unit 301 can transmit multiple signal streams in parallel by multiplying each of the multiple signal streams by a separate antenna weight and transmitting the signal in a separate direction. In this case, a waveform in which the components of the multiple signal streams are added together is sent out from each antenna.

[0024] The transmission channel estimation unit 302 performs transmission channel estimation based on an uplink radio signal received from the terminal device. The transmission channel estimation unit 302 performs transmission channel estimation based on, for example, an SRS received from the terminal device, and stores the result as an estimated value of a downlink transmission channel. Note that the SRS is an example of an uplink radio signal, and transmission channel estimation may be performed using other radio signals. The candidate matrix storage unit 303 stores a plurality of candidates of a pre-determined precoding matrix. Note that an indicator is attached to each of the plurality of candidates, and a precoding matrix to be used is specified by the PMI from the terminal device.

[0025] The communication unit 301 generates a precoding matrix based on the state of the transmission path estimated by the transmission path estimation unit 302, forms a first beam using the matrix, and can communicate with the terminal device. Also, the communication unit 301 selects a precoding matrix specified by a PMI from the terminal device from among the precoding matrix candidates stored in the candidate matrix storage unit 303, forms a second beam using the matrix, and can communicate with the terminal device.

[0026] The information acquisition unit 304 acquires information for determining whether to use the first beam or the second beam. For example, during communication using the first beam, the information acquisition unit 304 acquires information capable of identifying a first wireless quality in the terminal device for a first wireless signal transmitted in the first beam from the terminal device via the communication unit 301. Also, the information acquisition unit 304 acquires a second wireless quality in the terminal device for a second wireless signal transmitted in a predetermined beam related to the second beam (for example, used for determining the second beam). The first wireless quality and the second wireless quality may be, for example, a signal-to-interference-and-noise ratio (SINR). Also, the first wireless signal may be, for example, a DMRS transmitted immediately before user data addressed to the terminal device. Also, the first wireless signal may be, for example, a CSI-RS specific to the terminal device, transmitted using the first beam. Also, another signal may be used as the first wireless signal. The second radio signal may be, for example, a cell-specific (common to terminal devices in the cell) CSI-RS. Note that the CSI-RS is, for example, a predetermined beam for selecting the second beam, mapped to resources based on the number of ports of the CSI-RS, and transmitted at a predetermined period. Note that the predetermined beam is a beam with a wider beam width than a terminal device-specific beam formed based on the SRS or the like, and may be an omnidirectional beam.

[0027] In one example, the information acquisition unit 304 may acquire one piece of information generated based on the first wireless quality and the second wireless quality. This piece of information may be, for example, a difference value between the first wireless quality and the second wireless quality. A value obtained by subtracting the second wireless quality from the first wireless quality may be notified from the terminal device to the base station device as 4-bit information in 16 steps, for example, less than 0 dB, 0 dB or more and less than 1 dB, 1 dB or more and less than 2 dB, . . ., 13 dB or more and less than 14 dB, and 14 dB or more. Note that this is only an example, and the difference value may be expressed in a step width of, for example, 2 dB increments. Also, 32 steps of information may be notified using 5 bits, or only 8 steps of information may be notified using 3 bits. Also, only the difference value may be notified, or either the first wireless quality or the second wireless quality may be notified together with the difference value. For example, the terminal device may notify the base station device of the first wireless quality and the difference value. The base station device may configure the terminal device with respect to the information to be notified. For example, the terminal device may be notified of configuration information indicating whether to notify only the difference value, to notify the first wireless quality or the second wireless quality and the difference value, or to notify the first wireless quality and the second wireless quality, by an RRC message when establishing a connection.

[0028] The information acquisition unit 304 may receive a signal transmitted from a terminal device, and calculate an estimated value of the wireless quality corresponding to the first wireless quality or the second wireless quality based on the signal. For example, the information acquisition unit 304 measures the amplitude fluctuation and the phase rotation amount when the signal transmitted from each antenna of the terminal device arrives at each antenna of the base station device. Then, the information acquisition unit 304 multiplies the signal to be transmitted from each antenna in accordance with the antenna weight corresponding to the first beam and the predetermined beam by the amplitude fluctuation and the phase rotation amount measured at each antenna based on the signal transmitted from one antenna of the terminal device. Then, by adding up all the results of the multiplication, it is possible to estimate how the signal is received at one antenna of the terminal device. In this way, the information acquisition unit 304 can estimate the first wireless quality or the second wireless quality within its own device without receiving a report from the terminal device.

[0029] The beam forming control unit 305 determines whether to use the first beam or the second beam based on the first wireless quality and the second wireless quality acquired by the information acquisition unit 304, or the difference between them. Then, the beam forming control unit 305 controls the communication unit 301 to form a beam based on the determination. For example, the beam forming control unit 305 performs control to use the first beam at the time of initial connection. Then, the beam forming control unit 305 switches the beam used for communication from the first beam to the second beam based on, for example, the difference between the levels of the first wireless quality and the second wireless quality becoming equal to or less than a predetermined level. As an example, the beam forming control unit 305 may switch the beam used for communication from the first beam to the second beam based on the level of the first wireless quality becoming lower than the level of the second wireless quality.

[0030] (Processing flow) Next, an example of the flow of processing executed by the base station device according to this embodiment will be described with reference to Fig. 4. This processing can be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204. Note that the criteria for switching the beam used by the base station device are as described above, so only an example of the flow of processing executed by the base station device will be outlined here, and the details will not be repeated.

[0031] First, the base station device establishes a connection with the terminal device and starts communication with a first beam (S401). For example, the base station device causes the terminal device with which the connection has been established to transmit an SRS, forms a first beam based on the result of measuring the SRS, and transmits user data to the terminal device. Then, the base station device transmits a first radio signal such as a DMRS or a CSI-RS using the first beam immediately before transmitting the user data (S402), and causes the terminal device to measure a first radio quality related to the first radio signal. Even during communication using the first beam, the base station device transmits a second radio signal by periodically transmitting a CSI-RS using a predetermined beam related to a second beam based on the PMI (S403). Note that the base station device periodically transmits a CSI-RS with a predetermined beam even when not connected to the terminal device. Also, as described above, the base station device transmits a DMRS before transmitting user data to the terminal device. As such, the order of S401 to S403 is merely an example, and these steps may be executed in a different order.

[0032] After that, the base station device receives a report on the first wireless quality of the first wireless signal and the second wireless quality of the second wireless signal from the terminal device (S404). This report may be, for example, a report including information indicating the first wireless quality and the second wireless quality, or a report including information indicating a level difference between the first wireless quality and the second wireless quality (and information indicating the first wireless quality or the second wireless quality as necessary). Note that, in a case where the base station device can estimate the first wireless quality and the second wireless quality using an uplink signal transmitted from the terminal device, the processes of S402 to S403 may be replaced with measuring the uplink wireless signal and calculating the wireless quality.

[0033] After that, the base station device determines whether to switch the beam to be used from the first beam to the second beam based on the relationship between the first wireless quality and the second wireless quality (S405). If the base station device determines not to switch from the first beam to the second beam (NO in S405), the process returns to S401 and continues to monitor whether the first wireless quality has deteriorated to a degree approaching the second wireless quality. On the other hand, if the base station device determines to switch from the first beam to the second beam (YES in S405), the base station device switches the beam to be used to the second beam and transmits a signal (user data) to the terminal device (S406). The base station device periodically transmits CSI-RS, and the terminal device that observes it estimates the state of the downlink transmission path and notifies the base station device of the PMI identified based on the estimation result. The base station device communicates with the second beam using the precoding matrix specified by the PMI received from the terminal device.

[0034] The base station device may then switch back to the first beam when it is determined that the state of the transmission path of the terminal device is stable after switching to the second beam. When switching back to the first beam, the base station device may execute the process of FIG. 4 again.

[0035] By the above-mentioned processing, the base station device can appropriately switch between the first beam using a precoding matrix generated from an estimate of the state of the transmission path based on the radio signal from the terminal device and the second beam using a precoding matrix according to the result selected by the terminal device from among multiple candidates, depending on the situation of the terminal device. This enables stable and high-quality communication suited to the situation by using the second beam when the state of the transmission path changes significantly, such as when the terminal device is moving, and by using the first beam when the state of the transmission path changes little.

[0036] 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. 1. A communication device, comprising: an estimation means for estimating a state of a transmission path between the communication device and the counterpart device using a wireless signal transmitted from the counterpart device; an acquisition means for acquiring information regarding a beam identification when the communication device transmits a signal to the counterpart device, the information being determined by the counterpart device based on a wireless signal transmitted by the communication device; a communication means for forming a first beam when transmitting a signal to the other device based on the estimated state of the transmission path, or forming a second beam when transmitting a signal to the other device based on the acquired information, the second beam having a beam width wider than that of the first beam, and communicating with the other device; a control means for controlling the communication means to switch a beam to be used from the first beam to the second beam based on a first wireless quality in the counterpart device for a first wireless signal transmitted in the first beam and a second wireless quality in the counterpart device for a second wireless signal transmitted in a predetermined beam related to the second beam while communicating with the counterpart device using the first beam; A communication device comprising:

2. The communication device according to claim 1, characterized in that the control means controls to switch from the first beam to the second beam based on the difference between the first wireless quality and the second wireless quality being below a predetermined level.

3. The communication device according to claim 1 or 2, characterized in that the control means controls to switch from the first beam to the second beam based on the first wireless quality falling below the second wireless quality.

4. A communication device as described in any one of claims 1 to 3, characterized in that the control means determines whether to switch the beam to be used from the first beam to the second beam based on a report on the first wireless quality and a report on the second wireless quality received from the other device by the communication means.

5. A communication device as described in any one of claims 1 to 3, characterized in that the control means determines whether to switch the beam to be used from the first beam to the second beam based on a report generated based on the first wireless quality and the second wireless quality obtained from the counterpart device and received from the counterpart device by the communication means.

6. The communication device according to claim 1 , wherein the first radio signal includes a demodulation reference signal or a channel state information reference signal.

7. The communication device according to claim 1 , wherein the second radio signal includes a channel state information reference signal.

8. 8. The communication device according to claim 1, wherein the communication device is a base station device in a cellular communication system, and the counterpart device is a terminal device in the cellular communication system.

9. 9. The communication device according to claim 8, wherein the estimation means estimates a state of a transmission path between the communication device and the counterpart device based on a sounding reference signal (SRS) transmitted from the terminal device.

10. The communication device according to claim 8 or 9, characterized in that the acquisition means acquires a PMI (Precoding Matrix Indicator) as information regarding the identification of a beam when the communication device transmits a signal to the other device.

11. A control method performed by a communication device, comprising: The communication device is configured to communicate with the other device by forming a first beam when transmitting a signal to the other device based on a state of a transmission path between the communication device and the other device estimated using a wireless signal transmitted from the other device, or by forming a second beam when transmitting a signal to the other device based on information regarding a beam specification when the communication device transmits a signal to the other device, the second beam having a beam width wider than that of the first beam, the second beam being determined by the other device based on the wireless signal transmitted by the communication device, The control method is characterized in that it includes, while communicating with the other device using the first beam, controlling to switch the beam to be used from the first beam to the second beam based on a first wireless quality in the other device for a first wireless signal transmitted in the first beam and a second wireless quality in the other device for a second wireless signal transmitted in a predetermined beam related to the second beam.

12. A program for causing a computer to function as each of the means included in the communication device according to any one of claims 1 to 10.

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