Terminal device, base station device, control method, and program for auxiliary use of specific frequency band for uplink communication

Abstract

To achieve efficient communication in an environment in which a specific frequency band is used auxiliary for uplink communication.SOLUTION: A control method executed by a terminal device, connects to a first base station device in a first frequency band and connects to a base station device different from the first base station device in a second frequency band different from the first frequency band, receives an instruction from the first base station device in the first frequency band to change a base station device to which the terminal device is connected in the second frequency band from a third base station device to which the terminal device is connected, which operates in the second frequency band, to the second base station device on the basis of a reception quality of an interference signal transmitted from the terminal device at a second base station device to which the terminal device is not connected, which operates in the second frequency band, and changes the base station device to which the second terminal device is connected in the second frequency band on the basis of the instruction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control technique for auxiliary use of a specific frequency band for uplink communication. [Background technology]

[0002] From the viewpoint of efficient use of radio waves, it is effective to further allocate frequency bands allocated for specific uses to other uses. For example, the 2.3 GHz band is used by radio transmission repeaters used by broadcasting companies and public service radio stations, but this frequency band is now newly allocated to cellular communications. In such frequency bands, the newly allocated system must be operated in a manner that does not interfere with the operation of the previous user. For example, in the above-mentioned 2.3 GHz band, interference caused by signals from a cellular communication system to the previous user's equipment (radio transmission repeaters used by broadcasting companies and public service radio stations) must be kept below a specified level.

[0003] Here, when a base station device of a cellular communication system transmits a downlink signal, it is assumed that the signal will reach a wide range due to the large transmission power of the signal from the base station device. On the other hand, when a terminal device of the cellular communication system transmits an uplink signal, it is assumed that the transmission power is relatively small and the signal will reach only a limited range. For this reason, in order to effectively utilize this frequency band while suppressing interference with radio transmission relay devices and public service radio stations used by broadcasting companies, it is assumed that only uplink signals are transmitted in the cellular communication system. For example, in a cellular communication system, it is assumed that a frequency band allocated exclusively for cellular communication is allocated to uplink and downlink communication, while a frequency band coexisting with other systems is used auxiliary to strengthen uplink communication. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a control technique that enables efficient communication in an environment in which a specific frequency band is used auxiliary for uplink communication. [Means for solving the problem]

[0005] A terminal device according to one embodiment of the present invention has a connection means for connecting to a first base station device in a first frequency band and connecting to a base station device different from the first base station device in a second frequency band different from the first frequency band, a receiving means for receiving an instruction in the first frequency band from the first base station device to change a base station device to which the terminal device is connected in the second frequency band from a third base station device to which the terminal device is connected, which operates in the second frequency band, to the second base station device based on a reception quality of an interference signal transmitted from the terminal device at a second base station device to which the terminal device is not connected, which operates in the second frequency band, and a change means for changing the base station device to which the terminal device is connected in the second frequency band based on the instruction.

[0006] A base station device according to one embodiment of the present invention is a base station device operating in a first frequency band, and includes a connection means for connecting to a terminal device in the first frequency band, a determination means for determining to change a base station device to which the terminal device is connected in the second frequency band from a second other base station device to which the terminal device is connected, which operates in the second frequency band different from the first frequency band, to the first other base station device based on a reception quality of an interference signal transmitted from the terminal device in the second frequency band, measured at a first other base station device to which the terminal device is not connected, and a notification means for notifying the terminal device in the first frequency band of an instruction to change the base station device to which the terminal device is connected in the second frequency band from the second other base station device to the first other base station device. Effect of the Invention

[0007] According to the present invention, efficient communication can be achieved in an environment where a specific frequency band is used auxiliary for uplink 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 frequency bands used in each base station device. [Diagram 3] FIG. 11 illustrates an example of a processing procedure at the time of initial connection. [Figure 4] A diagram showing an example of a processing procedure when transmitting uplink data. [Diagram 5] 11 is a diagram showing an example of a processing procedure for changing a connection destination SUL base station. [Figure 6] FIG. 2 illustrates an example of a hardware configuration of the apparatus. [Figure 7] FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal device. [Figure 8] FIG. 2 is a diagram illustrating an example of a functional configuration of a base station device (NUL base station). 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] FIG. 1 shows an example of the configuration of a wireless communication system according to this embodiment. The wireless communication system is a cellular communication system conforming to a standard such as the 5th generation (5G) of the Third Generation Partnership Project (3GPP), and includes, for example, a base station device 101, a base station device 121, a base station device 122, and a terminal device 141. For simplicity of explanation, only a small number of base station devices and terminal devices are shown, but the system may naturally include a larger number of base station devices and terminal devices. The base station device 101 is, for example, a base station device that operates in a first frequency band, and provides wireless communication services to a terminal device staying in a cell 111 using radio resources of the first frequency band. The base station device 121 and the base station device 122 are, for example, base station devices that operate in a second frequency band, and provide, for example, a cell 131 and a cell 132, respectively. In addition, the base station device 101 and the base station device 121 are assumed to be in a relationship in which they are treated as being in the same position. That is, base station device 101 and base station device 121 may actually be located in different positions, but are in a relationship in which the transmission paths between these base station devices and any terminal device are considered to be substantially similar (for example, if the same frequency band is used). Also, base station device 122 is not treated as being in the same position as base station device 101. That is, base station device 101 and base station device 122 are in a relationship in which the transmission paths between at least the terminal devices are different, such as being located far away from each other.

[0011] Here, as shown in FIG. 2, the first frequency band used by the base station device 101 is a frequency band in which both uplink (UL) and downlink (DL) signals are transmitted, and the second frequency band used by the base station device 121 and the base station device 122 is a frequency band in which only uplink signals are transmitted. That is, the base station device 121 and the base station device 122 can be configured to receive signals from terminal devices but not transmit signals to terminal devices. The terminal device 141 mainly connects to the base station device 101 in the first frequency band to transmit uplink signals and receive downlink signals, and connects to the base station device 121 or the base station device 122 in the second frequency band as necessary to transmit uplink signals. That is, the second frequency band is used supplementarily. Hereinafter, uplink communication using this supplementary frequency band is called SUL (Supplementary UL). Also, a cell provided in the second frequency band for SUL may be called a SUL cell, and a base station device providing the SUL cell may be called a SUL base station. Also, uplink communication in a frequency band that also allows downlink communication may be called NUL (Normal UL), a cell provided in the first frequency band for NUL may be called a NUL cell, and a base station device providing the NUL cell may be called a NUL base station. Also, in this embodiment, the second frequency band is a higher frequency band than the first frequency band. Therefore, for example, a signal in the second frequency band has a larger propagation loss than a signal in the first frequency band, and the SUL cells (cells 131 and 132) may be configured to cover a narrower area than the NUL cell (cell 111).

[0012] In an environment in which an SUL cell is used as described above, it is necessary to devise a procedure for the terminal device 141 to communicate via the SUL cell. That is, in the SUL cell, the terminal device 141 transmits an uplink signal, but does not transmit a downlink signal. For this reason, the terminal device 141 cannot estimate a path loss based on a signal transmitted from a SUL base station, and it is not necessarily easy to appropriately set the transmission power of an uplink signal. In addition, since the terminal device 141 does not measure a signal transmitted from a SUL base station, it is not possible to determine which SUL base station the terminal device 141 should be connected to by measurement in the terminal device 141. For this reason, it is expected that conventional processing cannot be directly applied to processing at the time of initial connection or handover.

[0013] In the present embodiment, in consideration of such circumstances, a technique is provided that enables the terminal device 141 to appropriately execute communication in the SUL. In the following description, unless otherwise specified, it is assumed that the control on the network side is performed by the base station device 101, but the control may be performed by another device such as a server on the network, instead of the base station device 101. For example, the above-mentioned base station device 101 and other base station devices (e.g., base station device 121 and base station device 122) that provide a SUL cell having a geographical range overlapping with the NUL cell provided by the base station device 101 may be implemented by a remote radio head (RRH) accommodated in a common baseband unit (BBU), and in this case, the following control may be executed by the BBU or other devices connected to the BBU. In this case, it is not necessary to transmit and receive messages between the NUL base station and the SUL base station via the inter-base station interface. For example, when both the NUL base station and the SUL base station are accommodated in a common BBU, all information in the NUL base station and the SUL base station is consolidated in the BBU, so that there is no need to exchange messages between these base stations. Also, for example, if there is another device that collects information from the SUL base station and performs various controls, it is sufficient for the SUL base station to provide information to that device and for that device to provide control information generated based on the collected information to the NUL base station, so there is no need for information to be sent or received between base stations.

[0014] In this embodiment, for example, radio resources (frequency and time resources) in the second frequency band for transmitting a common random access preamble are prepared for one or more SUL cells (i.e., one or more SUL cells that at least partially overlap with the NUL cell) that provide communication services in a geographical range common to the NUL cell provided by the base station device 101. Note that the SUL cell that at least partially overlaps with the NUL cell here may be read as a SUL cell that may be used in combination with the NUL cell, and may not include a SUL cell that is not used in combination with the NUL cell. Then, when a terminal device (e.g., terminal device 141) connected to the base station device 101 needs to connect to a SUL cell, the terminal device transmits a random access preamble using the radio resources. The base station device 101 may collect and compare the reception quality (e.g., signal-to-noise and interference power ratio (SINR)) of the random access preamble at the base station device 121 and the base station device 122 (SUL base station), and may connect the terminal device to a SUL with better reception quality. An example of the flow of this process is shown in FIG. 3.

[0015] For example, when a NUL base station (e.g., base station device 101) determines that a terminal device should use SUL, the NUL base station transmits a message including a connection instruction to a SUL cell to the terminal device (S301). For example, when the reception quality (e.g., reference signal received power (RSRP) or reference signal received quality (RSRQ)) of an uplink reference signal (e.g., sounding reference signal (SRS)) from the terminal device 141 falls below a predetermined value or exceeds another predetermined value, the base station device 101 may determine to have the terminal device 141 use SUL. Note that a physical uplink control channel (PUCCH) or the like may be the measurement target, and any signal capable of performing measurement may be used as the predetermined signal to be measured. Note that the message including the connection instruction to the SUL base station may be, for example, a message of a radio resource control (RRC) layer such as an RRC Configuration message. Here, in this message, the resource (frequency and time resource) for transmitting a random access preamble and the setting information of a sequence to be used for generating a preamble may be notified. The configuration information may be, for example, a system information block type 1 (SIB1). The configuration information may further include information on transmission power to be used when transmitting the random access preamble, as will be described later.

[0016] When the terminal device receives a message including a connection instruction to the SUL base station, the terminal device transmits a random access preamble (message 1 of the random access procedure) using resources and sequences of the second frequency band for the SUL cell (S302). The resources and sequences are set to be common to SUL cells that can be used in combination with the NUL cell to which the terminal device is connected, and for example, any of a plurality of SUL base stations (for example, base station device 121 and base station device 122) can receive the random access preamble. The SUL base station notifies the NUL base station of the reception quality (for example, SINR) when the random access preamble is received (S303). This notification may include, for example, information to be transmitted to the terminal device in a random access response. The NUL base station determines the SUL base station to which the terminal device should connect based on the notified reception quality. Then, since the SUL base station cannot transmit a random access response, the NUL base station transmits a random access response (message 2 of the random access procedure) to the terminal device in the first frequency band instead of the SUL base station to which the terminal device should connect (S304). At this time, the NUL base station may notify each SUL base station of information indicating whether or not it has been selected as a connection destination of the terminal device. The terminal device then transmits an RRC Connection Request message (message 3 of the random access procedure) using the resources of the specified second frequency band in accordance with the random access response (S305). Upon receiving the message, the SUL base station selected as the connection destination of the terminal device transmits a Contention Resolution (message 4 of the random access procedure) to the NUL base station, and the NUL base station transmits the Contention Resolution to the terminal device using the first frequency band (S306). In addition, an RRC Connection Setup message is transmitted from the SUL base station to the NUL base station, and the NUL base station provides the message to the terminal device using the first frequency band (S307).When the terminal device receives the message, it transmits an RRC Connection Setup Complete message to the SUL base station using the second frequency band. This establishes a connection between the terminal device and the SUL base station. After establishing a connection with the SUL base station, the terminal device can transmit uplink data, for example by transmitting a scheduling request.

[0017] Here, the terminal device generally determines the power obtained by adding the path loss value to the target reception power of the random access preamble in the base station device (the maximum transmission power if this value exceeds the maximum transmission power of the terminal device) as the transmission power when transmitting the random access preamble. This path loss is estimated based on the reception power of the downlink signal transmitted from the base station device. However, since the SUL base station of this embodiment does not transmit a downlink signal, the terminal device cannot estimate the path loss between the SUL base station and the terminal device.

[0018] In view of such circumstances, the terminal device of this embodiment sets the transmission power when transmitting a random access preamble to the NUL base station as the transmission power value of the random access preamble to the SUL base station. That is, since the terminal device can receive a downlink signal from the NUL base station, the terminal device identifies the path loss between the terminal device and the NUL base station based on the signal, and determines the initial transmission power of the random access preamble to be transmitted in S302 based on the path loss.

[0019] Here, it is assumed that there is a large deviation in the required transmission power value due to the frequency difference between the first frequency band and the second frequency band. For example, when the second frequency band is a higher frequency band than the first frequency band, it is assumed that the path loss of the second frequency band is larger than that of the first frequency band. For this reason, it is assumed that, for example, when a random access preamble is transmitted with a transmission power determined based on the path loss of the first frequency band, the SUL base station cannot detect the random access preamble. When the random access preamble is not detected, a random access response is not transmitted, and as a result, the terminal device retransmits the random access preamble. When the terminal device retransmits the random access preamble, it increases its transmission power by a certain amount. At this time, as described above, when there is a large difference in the path loss due to the frequency difference between the first frequency band and the second frequency band, it may take a long time until the transmission power of the random access preamble becomes appropriate. For this reason, in this embodiment, the increase power information specifying the increase amount of the power is transmitted from the network side (i.e., from the NUL base station) to the terminal device. For example, the NUL base station notifies the terminal device of the increase power information indicating the increase amount of the transmission power when the random access preamble is retransmitted in the second frequency band by the RRC Reconfiguration message of S301, SIB1, or the like. The increase amount of the transmission power indicated in the increase power information is determined, for example, based on the difference in the magnitude of the free space path loss between the first frequency band and the second frequency band. For example, the difference in the magnitude of the free space path loss itself may be specified as the increase amount of the transmission power, or a value obtained by multiplying the difference by a predetermined coefficient (for example, less than 1) may be specified as the increase amount of the transmission power. Note that the increase amount of the transmission power may be determined without being based on the free space path loss. For example, the increase amount of the transmission power for the frequency difference or the combination of the frequency bands used may be experimentally or empirically specified and managed as a table. In this case, the increase amount of the transmission power corresponding to the relationship between the first frequency band and the second frequency band may be acquired by referring to the managed table.

[0020] The terminal device receives the increased power information in S301. Then, when the terminal device does not receive a random access response to the random access preamble transmitted at the transmission power specified based on the path loss between the NUL base station in S302, the terminal device determines the power obtained by adding the increase amount indicated by the increased power information to the initial transmission power as the transmission power at the time of retransmission of the random access preamble. Then, the terminal device retransmits the random access preamble using the determined transmission power. Note that, when the terminal device does not receive a random access response even in the retransmission, the terminal device again determines the value obtained by adding the increase amount indicated by the increased power information to the previous transmission power as the next transmission power, and retransmits the random access preamble using the determined power. Note that, when the power obtained by adding the increase amount indicated by the increased power information exceeds its own maximum transmission power, the terminal device may retransmit the random access preamble at the maximum transmission power. In addition, the terminal device may use, as the transmission power when initially transmitting the random access preamble, the transmission power determined based on the path loss between the NUL base station and the NUL base station plus the increase amount indicated by the increase power information.

[0021] The terminal device can store the increased power amount that is increased from the first transmission of the random access preamble to the time when the random access preamble is detected in the SUL base station, and can utilize the increased power amount when transmitting a scheduling request or data thereafter. That is, the terminal device can, for example, identify a path loss based on a downlink signal from the NUL base station, and use the power obtained by adding the value of the stored increased power amount to the transmission power identified by a conventional procedure based on the path loss, as the transmission power of an uplink signal to the SUL base station.

[0022] Even if the terminal device uses such transmission power, there is a possibility that the SUL base station cannot accurately receive the uplink signal due to the influence of multipath in the second frequency band. In response to this, for example, the terminal device receives a transmission power control command notified via the NUL base station for the physical uplink control channel (PUCCH) transmitted in the second frequency band, for example, and controls the transmission power based on the command, thereby making the transmission power of the PUCCH follow the communication environment and set it to an appropriate value. Here, since the PUCCH needs to be transmitted periodically, a transmission power control command is transmitted to the terminal device in a timely manner for the path loss at that time, so that the path loss can be followed appropriately. On the other hand, since the physical uplink shared channel (PUSCH) is transmitted only at the timing when user data is transmitted, it may be transmitted with a transmission power that is different from the path loss at the time of transmission. For this reason, in this embodiment, the terminal device holds an accumulated value of the change in the transmission power of the PUCCH from when the random access preamble is detected in the SUL base station (i.e., when the terminal device establishes a connection with the SUL base station) until the PUSCH is transmitted. Then, the terminal device specifies the accumulated value from the information held, and determines the transmission power of the PUSCH by adding the accumulated value to the transmission power when the random access preamble is detected (in the SUL base station). Here, the transmission power when the random access preamble is detected in the SUL base station is the transmission power when the PUSCH is transmitted immediately after the connection is established, and may be equal to or different from the transmission power of the random access preamble. For example, the transmission power when the random access preamble is detected in the SUL base station is the transmission power of message 3 of the random access procedure. In other words, the power obtained by adding the accumulated value to the transmission power of message 3 can be used as the transmission power of the PUSCH. In addition, a cumulative value may simply be added to the transmission power when the random access preamble is detected in the SUL base station, or a cumulative value multiplied by a predetermined coefficient (e.g., less than 1) may be added to the transmission power.In addition, the terminal device may hold the transmission power of the PUSCH, and in that case, the terminal device may determine the transmission power of the second PUSCH by, for example, adding the cumulative value of the change in the transmission power of the PUCCH from the time when the first PUSCH is transmitted until the time when the second PUSCH, which is the PUSCH to be transmitted next, is transmitted to the transmission power of the first PUSCH.

[0023] The terminal device can execute such a method of determining the transmission power of the PUSCH only in the second frequency band. In the first frequency band, the path loss can be estimated by a downlink signal from the NUL base station, and the transmission power of the PUSCH can be adjusted by tracking the path loss, so there is no need to use the accumulated value of the change in the transmission power of the PUCCH. That is, in the first frequency band, the transmission power of the PUSCH is determined based on the transmission power control command for the PUSCH without using the above-mentioned accumulated value, while in the second frequency band, the transmission power of the PUSCH is determined using the above-mentioned accumulated value (and further using the transmission power control command for the PUSCH as necessary).

[0024] In addition, the NUL base station may transmit information indicating whether to use the first frequency band (NUL) or the second frequency band (SUL) when allocating resources for transmitting user data in response to a scheduling request from the terminal device, to the terminal device. This information may be indicated, for example, in a UL grant that allocates resources for PUSCH. The UL grant is transmitted from the NUL base station to the terminal device by downlink control information (DCI) format 0_0 or 0_1. For example, as shown in FIG. 4, when the terminal device transmits a scheduling request to the connected SUL base station using, for example, a PUCCH of the second frequency band (S401), the terminal device receives an UL grant that allocates radio resources for a buffer status report (BSR) in the first frequency band via the NUL base station (S402). Then, the terminal device transmits a BSR including information on the amount of data to be transmitted stored in the buffer in the allocated radio resources in the second frequency band to the SUL base station (S403). Then, the terminal device receives a UL grant specifying radio resources for PUSCH allocated based on this BSR via the NUL base station (S404). Note that the BSR can be transferred from, for example, the SUL base station to the NUL base station. In this case, for example, when radio resources for transmitting PUSCH can be prepared only in the first frequency band, the NUL base station can decide not to use the second frequency band. Also, for example, the NUL base station may receive information indicating that there are no radio resources to be allocated from the SUL base station, and in this case, can decide to have the terminal device transmit PUSCH only in the first frequency band. Also, for example, the NUL base station may control the terminal device to transmit PUSCH using the radio resources in response to acquiring information indicating the allocation of radio resources from the SUL base station. In this way, the NUL base station can determine whether the PUSCH should be transmitted using the first frequency band or the second frequency band. Then, the NUL base station can include information indicating whether to use the first frequency band (NUL) or the second frequency band (SUL) in the UL grant of S404 and transmit it to the terminal device.When the UL grant indicates that the SUL is not to be used, the terminal device can determine the transmission power of the PUSCH without using the accumulated value (S405). On the other hand, when the UL grant indicates that the SUL is to be used, the terminal device determines the transmission power of the PUSCH using the accumulated value. Then, the terminal device transmits the PUSCH using the transmission power (S406). In this manner, the terminal device can appropriately set the transmission power of the uplink signal to be transmitted to the SUL base station.

[0025] The above-mentioned procedure is a procedure for determining the transmission power in the SUL cell based on the path loss in the NUL cell. This procedure is particularly effective when the NUL base station and the SUL base station can be considered to be located at the same location. On the other hand, when the NUL base station and the SUL base station cannot be considered to be located at the same location, such as the relationship between base station device 101 and base station device 122, excessive or insufficient transmission power may be set. That is, there may be cases where the characteristics of the transmission path between the terminal device and the NUL base station are significantly different from the characteristics of the transmission path between the terminal device and the SUL base station, and the transmission power set in the terminal device based on the path loss of the NUL base station does not match the path loss between the SUL base station at all.

[0026] In this embodiment, in consideration of such circumstances, the terminal device transmits a predetermined signal (for example, SRS or PUCCH) in the second frequency band, measures the predetermined signal in a SUL base station, and determines the transmission power of the uplink signal to be transmitted to the SUL base station in the terminal device based on the reception quality of the measurement result. The NUL base station acquires information indicating the reception quality of the predetermined signal transmitted by the terminal device in the SUL base station from the SUL base station that provides a SUL cell that can be used in combination with the NUL cell provided by the terminal device. Note that only information indicating the reception quality in a SUL base station that is not considered to be located in the same position as the terminal device may be acquired. Then, based on the information indicating the reception quality in the SUL base station, the NUL base station generates information that enables the terminal device to specify the transmission power to be used when transmitting an uplink signal to the SUL base station, and transmits the information to the terminal device in the first frequency band. When the terminal device receives the information, it determines, based on the information, the transmission power to be used when transmitting an uplink signal to the SUL base station, and uses that transmission power to transmit the uplink signal to the SUL base station in the second frequency band.

[0027] Here, the information notified to the terminal device may include, for example, a first reception power of a predetermined signal transmitted from the terminal device at a first SUL base station that is not treated as being located at the same location as the NUL base station, and a second reception power of a predetermined signal transmitted from the terminal device at a second SUL base station that is treated as being located at the same location as the NUL base station. The reception power of the predetermined signal may be a value obtained by subtracting the noise floor value at the SUL base station from the signal-to-noise power ratio (SNR) value of the predetermined signal at the SUL base station. However, this is not limited to this, and the SNR value may be notified instead of the reception power of the predetermined signal. Also, the reception strength (including noise power) of the predetermined signal at the SUL base station may be regarded as the reception power of the predetermined signal. Also, the information notified to the terminal device may include a difference value between the first reception power and the second reception power instead of these reception powers.

[0028] Here, the path loss between the second SUL base station, which is treated as being located at the same position as the NUL base station, and the terminal device can be roughly estimated based on the path loss at the NUL base station. For example, based on the path loss at the NUL base station (PLN) and the difference (FSPL2-FSPL1) between the free space path loss in the first frequency band (FSPL1) and the free space path loss in the second frequency band (FSPL2), the path loss (PLS2) between the second SUL base station and the terminal device can be estimated as PLS2=PLN+(FSPL2-FSPL1). Here, the path loss (PLS2) between the terminal device and the second SUL base station, the transmission power PT of a predetermined signal at the terminal device, the reception power PR2 at the second SUL base station, and the antenna gain G at the second SUL base station have a relationship such as PT+G-PLS2=PR2. Similarly, the path loss (PLS1) between the terminal device and the first SUL base station, PT, the received power PR1 at the first SUL base station, and the antenna gain G at the first SUL base station have a relationship such as PT+G-PLS1=PR1. It is assumed that the first SUL base station and the second SUL base station have the same antenna gain. In this case, the difference PR1-PR2 between the first received power (PR1) and the second received power (PR2) notified to the terminal device as described above is PLS2-PLS1. Therefore, the terminal device can calculate the path loss (PLS1) between the first SUL base station, which is not treated as being located at the same position as the NUL base station, as PLS1=PLS2-(PLS2-PLS1)=PLN+(FSPL2-FSPL1)-(PR1-PR2). The difference in free space propagation loss between the first frequency band and the second frequency band is a constant value regardless of distance, and the result calculated in advance can be stored in the terminal device. Therefore, the terminal device can estimate the path loss between the first SUL base station, which is not treated as being located at the same position as the NUL base station, by acquiring the above-mentioned first reception power and second reception power (or the difference between them).Then, based on this path loss, the terminal device can determine the transmission power of the uplink signal to the first SUL base station, such as "transmission power = desired received power at the first SUL base station + path loss - antenna gain."

[0029] Also, the information notified to the terminal device may be a value determined based only on the reception quality (e.g., SNR) of a predetermined signal transmitted by the terminal device in a SUL base station that is not treated as being located in the same position as the NUL base station. For example, the NUL base station can specify the transmission power when the terminal device transmits a predetermined signal by acquiring information on the power headroom of the PUSCH in the terminal device in advance. Then, the NUL base station can specify the path loss between the SUL base station and the terminal device, such as "path loss of SUL base station = transmission power of terminal device + antenna gain - reception power of a predetermined signal in SUL base station". Note that the reception power of a predetermined signal in the SUL base station can be specified as a value obtained by subtracting the noise floor value in the SUL base station from the SNR when the predetermined signal is received in the SUL base station. Then, the NUL base station can notify the terminal device of the specified path loss between the SUL base station and the terminal device. When the terminal device receives this path loss value, it can specify the transmission power of an uplink signal to the SUL base station, such as "transmission power = desired reception power in SUL base station + path loss - antenna gain". In addition, the NUL base station may notify the terminal device of information regarding the received power of a specified signal at the SUL base station, and the terminal device may determine the path loss between the SUL base station and the terminal device by the calculation as described above.

[0030] Furthermore, the information notified to the terminal device may include information specifying the magnitude of power to be increased or decreased in the terminal device, which is specified based on the reception quality of a predetermined signal at the SUL base station and the desired reception quality at the SUL base station. For example, a difference value between the reception quality of a predetermined signal and the desired reception quality at the SUL base station is notified to the terminal device. As an example, when the SNR of a predetermined signal at the SUL base station is 5 dB and the desired SNR is 8 dB, information indicating that the transmission power should be increased by 3 dB is notified to the terminal device. The terminal device may increase the power by the notified magnitude. Furthermore, when the reception quality of a predetermined signal at the SUL base station is excessive, the difference value between the reception quality of the predetermined signal and the desired reception quality at the SUL base station becomes a negative value, so that the terminal device can reduce the transmission power based on the information. In the above example, an example has been described in which the difference value between the reception quality of a predetermined signal and the desired reception quality at the SUL base station is notified to the terminal device, but a value obtained by multiplying the difference value by a predetermined coefficient (for example, less than 1) may be notified to the terminal device.

[0031] The notification of information from the NUL base station to the terminal device can be performed, for example, by using a MAC CE (medium access control element) of a physical downlink shared channel (PDSCH). That is, a new MAC CE is defined, and information for determining the transmission power for a SUL base station that is not treated as being located at the same location as the NUL base station can be notified by the MAC CE. This is just one example, and the information may be notified in DCI such as the UL grant of S404 described above. When such information is notified, information indicating that the SUL base station to which the signal is to be transmitted is a SUL base station that is not treated as being located at the same location as the NUL base station can be notified to the terminal device. This information can be notified to the terminal device together with the above-mentioned information that enables identification of the transmission power, or, for example, when connecting to the SUL base station.

[0032] In this manner, the terminal device can set appropriate transmission power and transmit uplink signals not only to a SUL base station that can be treated as being in the same position as the NUL base station, but also to a SUL base station that is located in a position significantly different from the NUL base station. The information notified to the terminal device described above may be prepared in the NUL base station, or may be prepared by a node other than the NUL base station. For example, the information may be prepared by a network node that can communicate with the NUL base station and the SUL base station. The information may also be prepared in a BBU that accommodates the NUL base station and the SUL base station. In either case, however, the NUL base station provides the information to the terminal device using the first frequency band.

[0033] It is assumed that the terminal device, once connected to the SUL base station, moves while performing uplink communication in the second frequency band and deviates from the range of the SUL cell provided by the SUL base station. In this case, in order to continue communication in the second frequency band, it is necessary to execute handover of the SUL cell. Note that here, a change of the SUL cell to which the terminal device is connected is called a handover, but it may be read as a change of the secondary cell. Usually, the terminal device measures signals from each base station device and notifies the connected base station device of the measurement result, thereby starting a process for handover to a base station device with good reception quality in the terminal device. However, in this embodiment, since the SUL base station does not transmit a signal, the terminal device cannot determine which SUL base station has good radio quality with the SUL base station, and cannot apply a normal handover process.

[0034] For this reason, in this embodiment, a new procedure for performing handover (cell switching) of the SUL base station is provided.

[0035] For example, a terminal device transmits a predetermined signal, and a SUL base station measures the predetermined signal. The predetermined signal may be, for example, an SRS or a PUCCH periodically transmitted to a SUL base station to which the terminal device is connected. The SUL base station then measures the radio quality of the predetermined signal. For example, a SUL base station to which the terminal device is connected measures the reception quality (for example, SNR) of the predetermined signal. In addition, a SUL base station to which the terminal device is not connected measures the reception quality (for example, interference-to-noise power ratio (INR)) of the interference signal, even though the predetermined signal is an interference signal. Note that radio resources for the terminal device to transmit the predetermined signal may be uniquely assigned to each terminal device so as to be able to identify which terminal device transmitted the signal. Also, for example, when the predetermined signal is an SRS, a configuration may be made such that a reference signal of a different sequence is transmitted for each terminal device. Also, the radio resources (and sequences) used when the terminal device transmits the predetermined signal are assigned so as to be common to one or more SUL cells overlapping with a NUL cell. The allocation of radio resources (and sequences) is notified from the NUL base station to the terminal device using the first frequency band. This allows the SUL cells to measure the predetermined signal transmitted by the terminal device in parallel when multiple SUL cells overlap with the NUL cell.

[0036] The SNR and INR measured in the SUL base station are provided to, for example, the NUL base station, and the NUL base station determines whether or not to have the terminal device switch the destination cell based on the acquired SNR and INR. That is, conventionally, the terminal device measures the reception quality of signals from each base station device, and a report of the measurement result is provided to the destination base station device based on the reception quality, thereby performing a process of changing the destination cell, but in this embodiment, the process of changing the destination cell is performed based on the measurement result at each base station device of the signal transmitted by the terminal device.

[0037] The NUL base station may determine to change the base station device to which the terminal device is connected in the second frequency band from the second SUL base station to the first SUL base station, for example, based on the fact that the reception quality (INR) of a predetermined signal (interference signal) transmitted by the terminal device in a SUL base station to which the terminal device is not connected exceeds a predetermined value. The NUL base station may also determine to change the base station device to which the terminal device is connected in the second frequency band from the second SUL base station to the first SUL base station, for example, based on the fact that the reception quality (INR) of a predetermined signal (interference signal) transmitted by the terminal device in a first SUL base station to which the terminal device is not connected becomes greater than the reception quality (SNR) of the predetermined signal transmitted by the terminal device in the second SUL base station to which the terminal device is connected by a predetermined level or more.

[0038] When the NUL base station determines that the terminal device should change the SUL base station to which it is connected, it may use the first frequency band to notify the terminal device of an instruction to change the SUL base station to which it is connected, specifying the new SUL base station. Upon receiving the instruction, the terminal device changes the connection destination of the second frequency band to the specified SUL base station based on the instruction.

[0039] FIG. 5 shows an example of the flow of a process for changing a destination SUL base station. First, in the SUL base station that provides each of the SUL cells that can be used in combination with the NUL cell to which the terminal device is connected, a predetermined signal (PUCCH in the example of FIG. 5) transmitted by the terminal device is measured (S501). Here, the SUL base station to which the terminal device is connected measures the SNR based on the predetermined signal, and the SUL base station to which the terminal device is not connected measures the INR based on the predetermined signal. Then, the SUL base station notifies the NUL base station of the measured SNR or INR (S502, S503). Note that the SNR and INR are examples of reception quality, and for example, the received signal power, the received interference power, the SINR, the ratio of interference power by a predetermined signal to other interference and noise power, etc. may be measured and reported to the NUL base station. Based on the report, the NUL base station may decide to change the SUL base station to which the terminal device is connected, for example, when the INR exceeds a predetermined value or when the INR becomes greater than the SNR by a predetermined level or more. The NUL base station then transmits to the terminal device, for example, an instruction to release the connection with the currently connected SUL base station (S504) and an instruction to connect to the new destination SUL base station (S506). The instructions S504 and S506 may be transmitted by two separate messages as shown in Fig. 5, or may be transmitted at the same time by one message. Based on receiving the instructions, the terminal device executes processing to release the connection with the currently connected SUL base station (S505), and executes processing to connect to the new destination SUL base station (S507).

[0040] By the above-described processing, in an environment where SUL base stations that do not transmit downlink signals are provided, it becomes possible to continue communications while appropriately changing the SUL base station to which the terminal device should connect.

[0041] FIG. 6 shows an example of the hardware configuration of the terminal device and base station device according to the present embodiment. In one example, the terminal device and base station device are configured to include a processor 601, a ROM 602, a RAM 603, a storage device 604, and a communication circuit 605. The processor 601 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 device and each of the above-mentioned processes by reading and executing a program stored in the ROM 602 or the storage device 604. The ROM 602 is a read-only memory that stores information such as programs and various parameters related to the processing executed by the terminal device and base station device. The RAM 603 functions as a workspace when the processor 601 executes a program, and is a random access memory that stores temporary information. The storage device 604 is configured, for example, by a removable external storage device. The communication circuit 605 is configured, for example, by a circuit for wireless communication of 5G or its successor standard. Although one communication circuit 605 is illustrated in FIG. 6, the terminal device and the base station device may have multiple communication circuits. For example, the terminal device and the base station device may have wireless communication circuits for 5G and its successor standard, and a common antenna for those circuits. The terminal device and the base station device may have separate antennas suitable for each standard. The base station device may further have a wired communication circuit used when communicating with other base station devices or nodes of the core network. The terminal device may further have a communication circuit conforming to a wireless communication standard other than the cellular communication standard, such as a wireless local area network (LAN) or Bluetooth (registered trademark). The terminal device and the base station device may have separate communication circuits 605 for each of a plurality of available frequency bands, or may have a common communication circuit 605 for at least a part of those frequency bands.

[0042] FIG. 7 shows an example of the functional configuration of a terminal device according to this embodiment. The terminal device includes, for example, a first communication unit 701, a second communication unit 702, a transmission power setting unit 703, and a cell change processing unit 704 as its functions. Note that FIG. 7 shows only functions particularly related to this embodiment, and various other functions that the terminal device may have are omitted from the illustration. For example, the terminal device naturally has other functions that terminal devices conforming to 5G and subsequent standards generally have. In addition, the functional blocks in FIG. 7 are shown in a schematic manner, and each functional block may be integrated and realized, or may be further subdivided. In addition, each function in FIG. 7 may be realized, for example, by the processor 601 executing a program stored in the ROM 602 or the storage device 604, or may be realized, for example, by a processor present inside the communication circuit 605 executing a predetermined software. Note that the details of the processing performed by each functional unit are as described above, and the description will not be repeated here, and only the rough functions will be outlined.

[0043] First communication unit 701 uses a first frequency band to connect to a NUL base station and communicates. First communication unit 701 receives a downlink signal from the NUL base station and transmits an uplink signal to the NUL base station. Second communication unit 702 uses a second frequency band to connect to a SUL base station and communicates. Note that control of communication by second communication unit 702 is performed based on control information received from the NUL base station using first communication unit 701, and therefore communication by second communication unit 702 is performed on the premise that a connection with the NUL base station is established using first communication unit 701. Second communication unit 702 transmits an uplink signal to a SUL base station, but does not receive a downlink signal. Transmission power setting unit 703 controls the transmission power of uplink signals (e.g., random access preamble, PUCCH, PUSCH, etc.) in second communication unit 702. Specific processing contents of transmission power control are as described above, and therefore will not be described repeatedly here. The transmission power of the uplink signal in first communication unit 701 is also set based on an instruction from the NUL base station, but this processing is similar to conventional transmission power control and will not be described here. When first communication unit 701 receives an instruction from the NUL base station to change the destination SUL base station, cell change processing unit 704 changes the destination SUL base station in accordance with the instruction. This processing is also as described above and will not be described here repeatedly.

[0044] FIG. 8 shows an example of the functional configuration of a base station device (NUL base station) according to this embodiment. The NUL base station includes, for example, a wireless communication unit 801, an inter-base station communication unit 802, a control information notification unit 803, and a cell change determination unit 804 as its functions. Note that FIG. 8 shows only functions particularly related to this embodiment, and various other functions that the NUL base station may have are omitted from the illustration. For example, the NUL base station naturally has other functions that terminal devices conforming to 5G and subsequent standards generally have. Also, the functional blocks in FIG. 8 are shown in a schematic manner, and each functional block may be integrated and realized, or may be further subdivided. Also, each function in FIG. 8 may be realized, for example, by the processor 601 executing a program stored in the ROM 602 or the storage device 604, or may be realized, for example, by a processor present inside the communication circuit 605 executing predetermined software. Note that the details of the processing performed by each functional unit are as described above, and the description will not be repeated here, and only the rough functions will be outlined.

[0045] The wireless communication unit 801 wirelessly connects to and communicates with the terminal device using a first frequency band. The wireless communication unit 801 receives an uplink signal from the connected terminal device and transmits a downlink signal to the terminal device. The inter-base station communication unit 802 transmits and receives information required for controlling the communication of the terminal device between, for example, one or more SUL base stations that provide a SUL cell that overlaps with a NUL cell provided by the wireless communication unit 801. For example, the inter-base station communication unit 802 may receive downlink control information that needs to be transmitted for the communication of the SUL base station of the terminal device from the SUL base station from the SUL base station. Also, for example, when the NUL base station determines that the settings of the wireless resources, etc., for the terminal device to transmit a predetermined signal are common to a plurality of SUL cells, the inter-base station communication unit 802 may notify the SUL base station of information indicating the settings. Also, information on the reception quality of the signal from the terminal device at the SUL base station is obtained from the SUL base station. Other information to be exchanged between the NUL base station and the SUL base station is transmitted and received via the inter-base station communication unit 802. The control information notification unit 803 notifies the terminal device of control information for communication with the SUL base station. The control information can be various information such as an increase in transmission power when retransmitting a random access preamble, information on whether or not to use the SUL, and a change in the connected SUL base station. The details have been described above and will not be repeated here. The cell change determination unit 804 determines whether or not the terminal device should change the connected SUL base station based on at least the reception quality of a signal (interference signal) transmitted from the terminal device at a SUL base station to which the terminal device is not connected. Then, when the cell change determination unit 804 determines that the connected SUL base station should be changed, it transmits an instruction to change the connected SUL base station to the terminal device via the control information notification unit 803.

[0046] The above-mentioned processing and configuration make it possible to appropriately control the communication of terminal devices in an environment where the second frequency band, which can transmit only uplink signals, is used as a supplementary component in uplink communication. This makes it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0047] 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 connection means for connecting to a first base station device in a first frequency band and connecting to a base station device different from the first base station device in a second frequency band different from the first frequency band; a receiving means for receiving, in the first frequency band, an instruction from the first base station device to change a destination base station device in the second frequency band from a third base station device, which operates in the second frequency band and is connected to the terminal device, to the second base station device based on a reception quality of an interference signal transmitted from the terminal device at a second base station device, which operates in the second frequency band and is not connected to the terminal device; a change means for changing a destination of the second frequency band to the second base station device based on the instruction; A terminal device comprising:

2. 2. The terminal device according to claim 1, wherein the reception quality of the interference signal is acquired by the second base station device measuring a signal transmitted by the terminal device to the third base station device.

3. The terminal device according to claim 2, characterized in that a change to the second base station device as a connected base station device in the second frequency band is decided based on the reception quality of the interference signal becoming greater than a predetermined level or more in the third base station device than the reception quality of the signal transmitted by the terminal device to the third base station device.

4. The terminal device according to claim 1, characterized in that, based on the reception quality of the interference signal exceeding a predetermined value, it is decided to change the connected base station device in the second frequency band to the second base station device.

5. 5. The terminal device according to claim 1, wherein the first frequency band is a frequency band in which both an uplink signal and a downlink signal are transmitted, and the second frequency band is a frequency band in which only an uplink signal is transmitted.

6. A base station device operating in a first frequency band, A connection means for connecting to a terminal device in the first frequency band; a determination means for determining to change a base station device to which the terminal device is connected in the second frequency band from a second other base station device to which the terminal device is connected, the second other base station device operating in the second frequency band different from the first frequency band, based on a reception quality of an interference signal transmitted from the terminal device in the second frequency band, the reception quality being measured in a first other base station device to which the terminal device is not connected; a notification means for notifying the terminal device, in the first frequency band, of an instruction to change a connection destination base station device in the second frequency band from the second other base station device to the first other base station device; A base station device comprising:

7. The base station device according to claim 6, characterized in that the reception quality of the interference signal is acquired by the first other base station device measuring a signal transmitted by the terminal device to the second other base station device.

8. The base station device according to claim 7, characterized in that the determination means determines to change the destination base station device in the second frequency band from the second other base station device to the first other base station device based on the fact that the reception quality of the interference signal at the second other base station device becomes greater than a predetermined level or more than the reception quality of the signal transmitted by the terminal device to the second other base station device.

9. The base station device according to claim 6, further comprising: means for notifying, to the terminal device, a unique allocation of radio resources in the second frequency band to be used for transmitting a signal used to measure the reception quality of the interference signal, using the first frequency band.

10. The base station device according to claim 6, characterized in that the determination means determines to change the connected base station device in the second frequency band from the second other base station device to the first other base station device based on the reception quality of the interference signal exceeding a predetermined value.

11. 11. The base station device according to claim 6, wherein the first frequency band is a frequency band in which both uplink signals and downlink signals are transmitted, and the second frequency band is a frequency band in which only uplink signals are transmitted.

12. A control method executed by a terminal device, comprising: connecting to a first base station device in a first frequency band and connecting to a base station device different from the first base station device in a second frequency band different from the first frequency band; receiving, in the first frequency band, an instruction from the first base station device to change a destination base station device in the second frequency band from a third base station device, which operates in the second frequency band and is connected to the terminal device, to the second base station device based on a reception quality of an interference signal transmitted from the terminal device at a second base station device, which operates in the second frequency band and is not connected to the terminal device; changing a connection destination of the second frequency band to the second base station device based on the instruction; A control method comprising:

13. A control method executed by a base station device operating in a first frequency band, comprising: Connecting to a terminal device in the first frequency band; determining, based on a reception quality of an interference signal transmitted from the terminal device in the second frequency band, which is measured at a first other base station device that operates in a second frequency band different from the first frequency band and to which the terminal device is not connected, to change a base station device to which the terminal device is connected in the second frequency band from a second other base station device that operates in the second frequency band and to which the terminal device is connected, to the first other base station device; notifying the terminal device, in the first frequency band, of an instruction to change a connection destination base station device in the second frequency band from the second other base station device to the first other base station device; A control method comprising:

14. A program for causing a computer installed in a terminal device to execute the control method according to claim 12.

15. A program for causing a computer installed in a base station device to execute the control method according to claim 13.

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