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

Abstract

A terminal device according to the present invention is connected to a first base station device in a first frequency band, is connected to a base station device different from the first base station device in a second frequency band different from the first frequency band, transmits a prescribed signal in the second frequency band, receives, from the first base station device and on the basis of the reception quality of the prescribed signal at a second base station device that operates in the second frequency band and is not treated as being present at the same position as the first base station device, information that can specify the transmission power for when transmitting a signal to the second base station device, specifies the transmission power on the basis of said information, and implements control so as to transmit a signal to the second base station device in the second frequency band by using said transmission power.

Description

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

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

[0002] From the perspective 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 currently used by radio transmission repeaters used by broadcasting companies and public service radio stations, but this frequency band has now been newly allocated to cellular communications. In such frequency bands, the newly allocated system must operate in a manner that does not interfere with the operations of previous users. For example, in the above-mentioned 2.3 GHz band, interference from cellular communication system signals to previous users' devices (radio transmission repeaters used by broadcasting companies and public service radio stations) must be kept below a predetermined level.

[0003] Here, when a base station device in a cellular communication system transmits a downlink signal, the signal is expected to reach a wide area due to factors such as high transmission power of the signal from the base station device. On the other hand, when a terminal device in the cellular communication system transmits an uplink signal, the signal is expected to reach only a limited area due to relatively low transmission power. Therefore, in order to effectively utilize this frequency band while suppressing interference with radio transmission relay devices used by broadcasting companies and public service radio stations, it is expected that the cellular communication system will transmit only uplink signals. For example, in a cellular communication system, it is expected that a frequency band allocated exclusively for cellular communication will be allocated to uplink and downlink communications, while a frequency band coexisting with other systems will be used auxiliary to strengthen uplink communications.

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

[0005] A terminal device according to one aspect of the present invention comprises 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 transmission means for transmitting a predetermined signal in the second frequency band; a receiving means for receiving information from the first base station device that enables identification of a transmission power when transmitting a signal to the second base station device based on the reception quality of the predetermined signal at a second base station device that operates in the second frequency band and is not treated as being located in the same location as the first base station device; and a control means for identifying the transmission power based on the information and controlling the transmission of a signal to the second base station device in the second frequency band using the transmission power.

[0006] A base station device according to one aspect of the present invention is a base station device operating in a first frequency band, and has an acquisition means for acquiring information on the reception quality when a predetermined signal transmitted from a terminal device in a second frequency band different from the first frequency band is received at a first other base station device that operates in the second frequency band and is not treated as being located in the same location as the base station device, and a transmission means for generating information based on the reception quality that enables the terminal device to identify the transmission power when transmitting a signal to the first other base station device, and transmitting the information to the terminal device in the first frequency band.

[0007] According to the present invention, efficient communication can be achieved in an environment where a specific frequency band is used supplementarily for uplink communication.

[0008] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are designated by the same reference numerals.

[0009] The accompanying drawings are included in and constitute a part of the specification, illustrate embodiments of the present invention, and, together with the description, are used to explain the principles of the present invention. Figure 1 is a diagram showing an example of the configuration of a wireless communication system. Figure 2 is a diagram explaining frequency bands used in each base station device. Figure 3 is a diagram showing an example of a processing procedure at the time of initial connection. Figure 4 is a diagram showing an example of a processing procedure at the time of uplink data transmission. Figure 5 is a diagram showing an example of a processing procedure when changing the destination SUL base station. Figure 6 is a diagram showing an example of the hardware configuration of an apparatus. Figure 7 is a diagram showing an example of the functional configuration of a terminal device. Figure 8 is a diagram showing an example of the functional configuration of a base station device (NUL base station).

[0010] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0011] FIG. 1 shows an example of the configuration of a wireless communication system according to this embodiment. This wireless communication system is a cellular communication system conforming to a standard such as the 5th generation (5G) standard 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, 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 operating in a first frequency band, and provides wireless communication services to a terminal device located within 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 operating in a second frequency band, and provide, for example, cells 131 and 132, respectively. Furthermore, the base station device 101 and the base station device 121 are considered to be located at the same location. That is, although base station device 101 and base station device 121 may actually be located in different locations, they are in a relationship in which the transmission paths between these base station devices and any terminal device are considered to be approximately the same (for example, if they use the same frequency band). Also, base station device 122 is not considered to be located in the same location 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 them and at least the terminal devices are different, such as being located at locations far apart from each other.

[0012] 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 using the first frequency band to transmit uplink signals and receive downlink signals, and, as needed, connects to the base station device 121 or the base station device 122 using the second frequency band to transmit uplink signals. That is, the second frequency band is used supplementarily. Hereinafter, uplink communication using this supplementary frequency band is referred to as SUL (Supplementary UL). Furthermore, a cell provided in the second frequency band for SUL may be called an SUL cell, and a base station device providing the SUL cell may be called an SUL base station. Furthermore, 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. Furthermore, in this embodiment, the second frequency band is assumed to be 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).

[0013] In an environment where an SUL cell is used as described above, the procedure for the terminal device 141 to communicate via the SUL cell needs to be devised. 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 path loss based on the signal transmitted from the SUL base station, and it is not necessarily easy to appropriately set the transmission power of the uplink signal. Furthermore, because the terminal device 141 does not measure the signal transmitted from the 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 such as initial connection and handover.

[0014] In view of these circumstances, this embodiment provides a technology that enables the terminal device 141 to appropriately perform communication in the SUL. Note that, hereinafter, unless otherwise specified, the description will be given assuming that the base station device 101 is the entity responsible for control on the network side. However, 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-described base station device 101 and other base station devices (e.g., base station device 121 and base station device 122) that provide SUL cells having geographical ranges overlapping with the NUL cell provided by the base station device 101 may be implemented as remote radio heads (RRHs) accommodated in a common baseband unit (BBU). In this case, the following control may be performed by the BBU or other devices connected to the BBU. Note that in this case, message transmission and reception via the inter-base station interface between the NUL base station and the SUL base station may not be performed. For example, if both the NUL base station and the SUL base station are accommodated in a common BBU, all information at the NUL base station and the SUL base station is aggregated in that BBU, and therefore there is no need for message exchange 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 the information to that device, and for that device to provide control information generated based on the collected information to the NUL base station, and therefore there is no need for information to be transmitted or received between the base stations.

[0015] 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 area common to the NUL cell provided by the base station device 101. Note that the SUL cells that at least partially overlap with the NUL cell here may be interpreted as SUL cells that may be used in combination with the NUL cell, or may not include SUL cells that are 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 an SUL cell, the terminal device transmits a random access preamble using the radio resources. The base station device 101 collects and compares 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 an SUL with better reception quality. An example of this processing flow is shown in FIG.

[0016] For example, when a NUL base station (e.g., the base station device 101) determines that a terminal device should use the SUL, the NUL base station transmits a message including a connection instruction to the SUL cell to the terminal device (S301). For example, the base station device 101 may determine to have the terminal device 141 use the SUL when the reception quality (e.g., the reference signal received power (RSRP) or the reference signal received quality (RSRQ)) of an uplink reference signal (e.g., the sounding reference signal (SRS)) from the terminal device 141 falls below a predetermined value or exceeds another predetermined value. Note that the 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 the radio resource control (RRC) layer, such as an RRC configuration message. In this message, the resource (frequency and time resource) for transmitting the random access preamble and the configuration information of the sequence to be used for generating the 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 the transmission power to be used when transmitting the random access preamble, as will be described later.

[0017] When the terminal device receives a message including a connection instruction to the SUL base station, it transmits a random access preamble (message 1 of the random access procedure) using resources and sequences in the second frequency band for the SUL cell (S302). These 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. For example, all of the SUL base stations (e.g., 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 (e.g., SINR) upon receiving the random access preamble (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 it has been selected as a connection destination for 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 a connection destination for 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 in the first frequency band (S306). Furthermore, the SUL base station transmits an RRC Connection Setup message to the NUL base station, and the NUL base station provides the message to the terminal device using the first frequency band (S307).Upon receiving the message, the terminal device 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 the connection with the SUL base station, the terminal device can transmit uplink data, for example, by transmitting a scheduling request.

[0018] 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 at the base station device (or 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 in 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.

[0019] In view of these circumstances, the terminal device of this embodiment sets the transmission power of the 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, it 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.

[0020] Here, it is assumed that there is a large discrepancy in the required transmission power value due to the frequency difference between the first frequency band and the second frequency band. For example, if 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 greater than that of the first frequency band. Therefore, for example, when a random access preamble is transmitted at a transmission power determined based on the path loss of the first frequency band, it is assumed that the SUL base station cannot detect the random access preamble. If 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 retransmitting the random access preamble, the terminal device increases its transmission power by a certain amount. In this case, as described above, if there is a large difference in path loss due to the frequency difference between the first frequency band and the second frequency band, it may take a long time for the transmission power of the random access preamble to reach an appropriate power. For this reason, in this embodiment, increase power information specifying the amount of increase in 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 increase power information indicating the amount of increase in transmission power when the random access preamble is retransmitted in the second frequency band, using the RRC Reconfiguration message of S301, SIB1, or the like. The increase in transmission power indicated in the increase power information is determined, for example, based on the difference in the magnitude of free space path loss between the first frequency band and the second frequency band. For example, the difference in the magnitude of free space path loss itself may be specified as the amount of increase in transmission power, or a value obtained by multiplying this difference by a predetermined coefficient (for example, less than 1) may be specified as the amount of increase in transmission power. Note that the increase in transmission power may also be determined without being based on the free space path loss. For example, the increase in transmission power for a frequency difference or a combination of frequency bands used may be experimentally or empirically determined 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.

[0021] The terminal device receives increased power information in S301. Then, for example, if the terminal device does not receive a random access response to a random access preamble transmitted at transmission power determined based on the path loss between the terminal device and the NUL base station in S302, the terminal device determines the power obtained by adding the increase indicated by the increased power information to the initial transmission power as the transmission power for retransmitting the random access preamble. The terminal device then retransmits the random access preamble using the determined transmission power. Note that if the terminal device does not receive a random access response even after the retransmission, it again determines the value obtained by adding the increase 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 if the power obtained by adding the increase 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 terminal device plus the increase amount indicated by the increase power information.

[0022] The terminal device may store the increased power amount that has been increased from the initial transmission of the random access preamble until the time the random access preamble is detected at the SUL base station, and may utilize the increased power amount when transmitting subsequent scheduling requests or data. That is, the terminal device may, for example, identify a path loss based on a downlink signal from the NUL base station, and may add the value of the stored increased power amount to the transmission power identified by a conventional procedure based on the path loss, and use this power as the transmission power of an uplink signal to the SUL base station.

[0023] Even if the terminal device uses such transmission power, there is a possibility that the SUL base station will not be able to accurately receive uplink signals due to the effects of multipath in the second frequency band. In response to this, for example, the terminal device can receive a transmission power control command for the physical uplink control channel (PUCCH) transmitted in the second frequency band, notified via the NUL base station, and control the transmission power based on the command, thereby adjusting the transmission power of the PUCCH to an appropriate value in accordance with the communication environment. Here, since the PUCCH needs to be transmitted periodically, a transmission power control command is transmitted to the terminal device in a timely manner in accordance with the path loss at that time, thereby enabling the path loss to be appropriately adjusted. 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 at a transmission power that deviates from the path loss at the time of transmission. For this reason, in this embodiment, the terminal device stores a cumulative value of changes in the transmission power of the PUCCH from the time the random access preamble is detected at the SUL base station (i.e., from the time the terminal device establishes a connection with the SUL base station) until the PUSCH is transmitted. The terminal device then identifies the cumulative value from the stored information and determines the transmission power of the PUSCH by adding the cumulative value to the transmission power when the random access preamble is detected (at the SUL base station). Here, the transmission power when the random access preamble is detected at 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 at 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 cumulative value to the transmission power of message 3 can be used as the transmission power of the PUSCH. In addition, the cumulative value may simply be added to the transmission power when the random access preamble is detected at the SUL base station, or the cumulative value multiplied by a predetermined coefficient (for example, less than 1) may be added to the transmission power.In addition, the terminal device may hold the transmission power of the PUSH, and in that case, the terminal device may determine the transmission power of the second PUSH, for example, by adding the cumulative value of the change in the transmission power of the PUSH from the time when the first PUSH is transmitted until the time when the second PUSH, which is the next PUSH to be transmitted, is transmitted to the transmission power of the first PUSH.

[0024] Note that 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 using a downlink signal from a 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 changes in the transmission power of the PUCCH. That is, in the first frequency band, the transmission power of the PUSCH is determined based on a 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 a transmission power control command for the PUSCH, if necessary).

[0025] In addition, for example, in response to a scheduling request from a terminal device, 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 to the terminal device. This information may be indicated, for example, in an UL grant allocating resources for a PUSCH. The UL grant is transmitted from the NUL base station to the terminal device using 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 in the second frequency band (S401), the terminal device receives an UL grant in the first frequency band via the NUL base station allocating radio resources for a buffer status report (BSR) (S402). Then, the terminal device transmits a BSR to the SUL base station in the second frequency band, including information on the amount of data to be transmitted stored in the buffer, using the allocated radio resources (S403). Then, the terminal device receives, via the NUL base station, an UL grant specifying radio resources for the PUSCH allocated based on the BSR (S404). The BSR may be transferred, for example, from the SUL base station to the NUL base station. In this case, the NUL base station may determine not to use the second frequency band if radio resources for transmitting the PUSCH can be prepared only in the first frequency band. The NUL base station may also receive, for example, information indicating that no radio resources are available for allocation from the SUL base station. In this case, the NUL base station may determine to have the terminal device transmit the PUSCH only in the first frequency band. Furthermore, the NUL base station may, for example, control the terminal device to transmit the PUSCH using 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 will not 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 will 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 determined transmission power (S406). In this way, the terminal device can appropriately set the transmission power of the uplink signal to be transmitted to the SUL base station.

[0026] The above-described procedure determines 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 in the same location. On the other hand, when the NUL base station and the SUL base station cannot be considered to be located in the same location, such as the relationship between the base station device 101 and the base station device 122, excessive or insufficient transmission power may be set. In other words, the characteristics of the transmission path between the terminal device and the NUL base station may be 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 may not match the path loss between the terminal device and the SUL base station at all.

[0027] In this embodiment, in consideration of such circumstances, the terminal device transmits a predetermined signal (e.g., SRS or PUCCH) in the second frequency band, measures the predetermined signal at an SUL base station, and determines the transmission power of an uplink signal to be transmitted from the terminal device to the SUL base station 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 at the SUL base station from an SUL base station that provides an 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 at an 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 at 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.

[0028] Here, the information notified to the terminal device may include, for example, a first received power of a predetermined signal transmitted from the terminal device at a first SUL base station that is not considered to be co-located with the NUL base station, and a second received power of the predetermined signal transmitted from the terminal device at a second SUL base station that is considered to be co-located with the NUL base station. The received power of the predetermined signal may be a value obtained by subtracting the noise floor value of 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 received power of the predetermined signal. Furthermore, the received strength (including noise power) of the predetermined signal at the SUL base station may be considered to be the received power of the predetermined signal. Furthermore, the information notified to the terminal device may include, instead of the first received power and the second received power, a difference value between these received powers.

[0029] Here, the path loss between the second SUL base station, which is treated as being located in 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 propagation loss in the first frequency band (FSPL1) and the free space propagation 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 received 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. Note 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 in the same position as the NUL base station, as follows: 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, by acquiring the above-mentioned first received power and second received power (or the difference value thereof), the terminal device can estimate the path loss between the first SUL base station, which is not treated as being located in the same position as the NUL base station.Then, based on this path loss, the terminal device can determine the transmission power of the uplink signal to the first SUL base station, as follows: "transmission power = desired received power at the first SUL base station + path loss - antenna gain."

[0030] Furthermore, the information notified to the terminal device may be a value determined solely based on the reception quality (e.g., SNR) of a predetermined signal transmitted by a terminal device at an 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. The NUL base station can then specify the path loss between the SUL base station and the terminal device as follows: "Path loss of SUL base station = Transmission power of terminal device + Antenna gain - Received power of the predetermined signal at the SUL base station." The received power of the predetermined signal at the SUL base station can be specified as the SNR when the predetermined signal is received at the SUL base station minus the noise floor value at the SUL base station. The NUL base station can then 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 determine the transmission power of the uplink signal to the SUL base station, such as "transmission power = desired reception power at the SUL base station + path loss - antenna gain." Note that the NUL base station may notify the terminal device of information on the reception power of a predetermined 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 described above.

[0031] 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 determined 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, the terminal device is notified of the difference between the reception quality of the predetermined signal and the desired reception quality at the SUL base station. As an example, if the SNR of the 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 can increase the power by the notified magnitude. Furthermore, if the reception quality of the predetermined signal at the SUL base station is excessive, the difference between the reception quality of the predetermined signal and the desired reception quality at the SUL base station becomes a negative value, and the terminal device can reduce the transmission power based on that information. Note that in the above example, an example was described in which the difference between the reception quality of the predetermined signal and the desired reception quality at the SUL base station is notified to the terminal device. However, a value obtained by multiplying the difference by a predetermined coefficient (e.g., less than 1) may also be notified to the terminal device.

[0032] The information from the NUL base station to the terminal device can be transmitted using, for example, a MAC CE (medium access control element) of the physical downlink shared channel (PDSCH). That is, a new MAC CE is defined, and information for determining the transmission power for an SUL base station that is not treated as being co-located with the NUL base station can be transmitted by the MAC CE. This is just one example, and the information may be transmitted in a DCI such as the UL grant of S404 described above. When such information is transmitted, the terminal device can be notified of information indicating that the SUL base station to which a signal is to be transmitted is an SUL base station that is not treated as being co-located with the NUL base station. This information can be transmitted to the terminal device together with the information that enables the transmission power to be identified, or, for example, when connecting to the SUL base station.

[0033] In this way, the terminal device can set appropriate transmission power and transmit uplink signals not only to SUL base stations that can be treated as being located in the same position as the NUL base station, but also to SUL base stations that are located in positions significantly different from the NUL base station. The information notified to the terminal device described above may be prepared by the NUL base station or 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.

[0034] It is assumed that once connected to an SUL base station, the terminal device 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 perform a handover of the SUL cell. Note that, here, changing the SUL cell to which the terminal device is connected is referred to as a handover, but it may also be interpreted as a change of secondary cell. Typically, the terminal device measures signals from each base station device and notifies the currently connected base station device of the measurement results, thereby starting processing for handover to a base station device with good reception quality at the terminal device. However, in this embodiment, since the SUL base station does not transmit signals, the terminal device cannot determine which SUL base station will provide good radio quality, and therefore cannot apply a normal handover process.

[0035] For this reason, this embodiment provides a new procedure for performing handover (cell switching) of an SUL base station.

[0036] For example, a terminal device transmits a predetermined signal, and an SUL base station measures the predetermined signal. This predetermined signal may be, for example, an SRS or a PUCCH periodically transmitted to an 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, the SUL base station to which the terminal device is connected measures the reception quality (e.g., SNR) of the predetermined signal. Furthermore, an SUL base station to which the terminal device is not connected measures the reception quality (e.g., interference-to-noise power ratio (INR)) of the interference signal, even though the predetermined signal is an interference signal. Note that radio resources used by the terminal device to transmit the predetermined signal may be uniquely assigned to each terminal device so that it is possible to identify which terminal device transmitted the signal. Furthermore, for example, if the predetermined signal is an SRS, a configuration may be made in which a reference signal of a different sequence is transmitted for each terminal device. Furthermore, the radio resources (and sequences) used by the terminal device when transmitting the predetermined signal are assigned so as to be common to one or more SUL cells overlapping with a NULL 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, when multiple SUL cells overlap with the NUL cell, measurements of predetermined signals transmitted by the terminal device to be performed in parallel in those SUL cells.

[0037] The SNR and INR measured at the SUL base station are provided to, for example, the NUL base station, and the NUL base station determines whether or not to cause the terminal device to 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 results based on the reception quality is provided to the destination base station device, thereby performing processing to change the destination cell. However, in this embodiment, processing to change the destination cell is performed based on the measurement results at each base station device of the signals transmitted by the terminal device.

[0038] 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 at an SUL base station to which the terminal device is not connected exceeds a predetermined value. Furthermore, 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 at a first SUL base station to which the terminal device is not connected becomes greater by a predetermined level or more than the reception quality (SNR) of the predetermined signal transmitted by the terminal device at the second SUL base station to which the terminal device is connected.

[0039] When the NUL base station determines that the terminal device should change the SUL base station to which it is connected, the NUL base station can notify the terminal device of an instruction to change the SUL base station to which it is connected, specifying the new SUL base station, using the first frequency band. 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.

[0040] FIG. 5 shows an example of the process flow for changing the SUL base station to which the terminal device is connected. First, the SUL base stations that provide each of the SUL cells that can be used in combination with the NUL cell to which the terminal device is connected measure a predetermined signal (PUCCH in the example of FIG. 5 ) transmitted by the terminal device (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. For example, received signal power, received interference power, SINR, and the ratio of interference power due to a predetermined signal to other interference and noise power 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 is greater than the SNR by a predetermined level or more. Then, the NUL base station 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 of 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).

[0041] By the above-described processing, in an environment where an SUL base station that does not transmit downlink signals is provided, it becomes possible to continue communication while appropriately changing the SUL base station to which the terminal device should connect.

[0042] FIG. 6 shows an example of the hardware configuration of a terminal device and a base station device according to this embodiment. In one example, the terminal device and the base station device 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 including one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and executes programs stored in the ROM 602 and the storage device 604 to perform overall device processing and each of the above-mentioned processes. 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 the 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, for example, a removable external storage device. The communication circuit 605 is, for example, a circuit for wireless communication of 5G or its successor standards. Although FIG. 6 illustrates one communication circuit 605, the terminal device and base station device may have multiple communication circuits. For example, the terminal device and base station device may have wireless communication circuits for 5G and its successor standard, and a common antenna for these circuits. The terminal device and base station device may have separate antennas suitable for each standard. The base station device may also have a wired communication circuit used when communicating with other base station devices or core network nodes. The terminal device may also have a communication circuit compliant with 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 base station device may have separate communication circuits 605 for each of multiple usable frequency bands, or may have a common communication circuit 605 for at least some of these frequency bands.

[0043] 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 only shows 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 compliant with 5G or subsequent standards generally have. The functional blocks in FIG. 7 are shown only schematically, and the respective functional blocks may be integrated or further subdivided. 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 by a processor within the communication circuit 605 executing predetermined software. Since the details of the processes performed by each functional unit have been described above, the description will not be repeated here, and only the general functions will be outlined.

[0044] The first communication unit 701 connects to and communicates with the NUL base station using a first frequency band. The first communication unit 701 receives downlink signals from the NUL base station and transmits uplink signals to the NUL base station. The second communication unit 702 connects to and communicates with the SUL base station using a second frequency band. Note that control of communication by the second communication unit 702 is performed based on control information received from the NUL base station using the first communication unit 701, and therefore communication by the second communication unit 702 is performed on the premise that a connection with the NUL base station has been established using the first communication unit 701. The second communication unit 702 transmits uplink signals to the SUL base station but does not receive downlink signals. The transmission power setting unit 703 controls the transmission power of uplink signals (e.g., random access preamble, PUCCH, PUSCH, etc.) in the second communication unit 702. The specific processing contents of the transmission power control are as described above, and therefore the description will not be repeated here. Note that the transmission power of the uplink signal in the 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 therefore will not be described here. When the first communication unit 701 receives an instruction to change the SUL base station to which the cell change processing unit 704 is connected from the NUL base station, the cell change processing unit 704 changes the SUL base station to which the cell change processing unit 704 is connected in accordance with the instruction. This processing is also as described above, and therefore the description will not be repeated here.

[0045] 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 only shows functions particularly related to this embodiment, and does not illustrate various other functions that the NUL base station may have. For example, the NUL base station naturally has other functions that terminal devices compliant with 5G and subsequent standards generally have. The functional blocks in FIG. 8 are shown only schematically, and the respective functional blocks may be integrated or further subdivided. 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 by a processor within the communication circuit 605 executing predetermined software. Since the details of the processing performed by each functional unit have been described above, the description will not be repeated here, and only the general functions will be outlined.

[0046] The wireless communication unit 801 wirelessly connects to and communicates with a terminal device using a first frequency band. The wireless communication unit 801 receives uplink signals from the connected terminal device and transmits downlink signals to the terminal device. The inter-base station communication unit 802 transmits and receives information necessary for controlling communication of the terminal device, for example, between one or more SUL base stations that provide SUL cells that overlap 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 communication of the SUL base station of the terminal device from the SUL base station. Furthermore, for example, if the NUL base station determines that settings such as radio resources for transmitting a predetermined signal from the terminal device are common to multiple SUL cells, the inter-base station communication unit 802 may notify the SUL base station of information indicating the settings. Furthermore, the inter-base station communication unit 802 obtains information on the reception quality of signals from the terminal device at the SUL base station 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 the amount of increase in transmission power when retransmitting a random access preamble, information on whether to use the SUL, and changing the connected SUL base station. Details have been described above, so they will not be repeated here. The cell change determination unit 804 determines whether 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 an SUL base station to which the terminal device is not connected. Then, if 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.

[0047] The above-described processing and configuration enable appropriate control of communications by terminal devices in an environment where the second frequency band, which can transmit only uplink signals, is used as a secondary frequency band for uplink communications, thereby contributing to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0048] 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.

[0049] This application claims priority based on Japanese Patent Application No. 2023-150822, filed on September 19, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A terminal device comprising: 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 transmission means for transmitting a predetermined signal in the second frequency band; a receiving means for receiving information from the first base station device that enables identification of a transmission power when transmitting a signal to the second base station device based on a reception quality of the predetermined signal at a second base station device that operates in the second frequency band and is not treated as being in the same location as the first base station device; and a control means for identifying the transmission power based on the information and performing control to transmit a signal to the second base station device in the second frequency band using the identified transmission power.

2. The terminal device of claim 1, wherein the information includes a first reception quality of the specified signal at the second base station device and a second reception quality of the specified signal at a third base station device that operates in the second frequency band and is treated as being located in the same location as the first base station device, and the control means determines a second path loss between the terminal device and the second base station device based on the first reception quality and the second reception quality and a first path loss between the terminal device and the first base station device, and determines the transmission power based on the second path loss.

3. The terminal device described in claim 1, wherein the information includes information indicating a path loss between the terminal device and the second base station device, determined based on the reception quality of the specified signal at the second base station device and a power headroom at the terminal device, and the control means determines the transmission power based on the path loss.

4. The terminal device described in claim 1, wherein the information includes information specifying the amount of power to be increased or decreased in the terminal device, which is determined based on the reception quality of the specified signal in the second base station device and a desired reception quality in the second base station device, and the control means determines the transmission power by increasing or decreasing the power used when transmitting a signal to the second base station device by the amount of power specified by the information.

5. The terminal device according to claim 1, wherein the predetermined signal is a sounding reference signal (SRS) or a physical uplink control channel (PUCCH).

6. A terminal device as described in claim 1, wherein the first frequency band is a frequency band in which both uplink and downlink signals are transmitted, and the second frequency band is a frequency band in which only uplink signals are transmitted.

7. The terminal device of claim 1, wherein the connection means connects to a base station device operating in the second frequency band by a process including transmitting a random access preamble to a plurality of base station devices operating in the second frequency band using common resources, and receiving a random access response from the first base station device in the first frequency band for connecting to a base station device selected based on the wireless quality when the random access preamble is received in each of the plurality of base station devices.

8. The terminal device according to claim 1, wherein the receiving means receives the information via a Medium Access Control (MAC) CE (Control Element) of a Physical Downlink Shared Channel (PDSCH).

9. A base station device operating in a first frequency band, comprising: an acquisition means for acquiring information on reception quality when a predetermined signal transmitted from a terminal device in a second frequency band different from the first frequency band is received at a first other base station device operating in the second frequency band and not treated as being located in the same location as the base station device; and a transmission means for generating information enabling identification of a transmission power when the terminal device transmits a signal to the first other base station device based on the reception quality, and transmitting the information to the terminal device in the first frequency band.

10. The base station device described in claim 9, wherein the acquisition means acquires a first reception quality of the specified signal at the first other base station device, and acquires a second reception quality of the specified signal at a second other base station device that operates in the second frequency band and is treated as being in the same location as the base station device, the transmission means generates the information including the first reception quality and the second reception quality and transmits it to the terminal device, and the transmission power is determined based on a second path loss between the terminal device and the first other base station device that is determined using the first reception quality and the second reception quality and a first path loss between the terminal device and the base station device.

11. A base station device as described in claim 9, further comprising a determination means for determining a path loss between the terminal device and the first other base station device based on the reception quality of the specified signal at the first other base station device and a power headroom at the terminal device, and wherein the transmission means generates the information including the determined path loss and transmits it to the terminal device.

12. A base station device as described in claim 9, further comprising a determination means for determining the amount of power to be increased or decreased in the terminal device based on the reception quality of the specified signal in the first other base station device and a desired quality in the first other base station device, and wherein the transmission means generates the information including a value indicating the amount of power to be increased or decreased in the terminal device and transmits it to the terminal device.

13. The base station apparatus according to claim 9, wherein the first frequency band is a frequency band in which both uplink and downlink signals are transmitted, and the second frequency band is a frequency band in which only uplink signals are transmitted.

14. The base station device according to claim 9, wherein the transmitting means transmits the information to the terminal device via a Medium Access Control (MAC) CE (Control Element) of a Physical Downlink Shared Channel (PDSCH).

15. A control method executed by a terminal device, comprising: 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; transmitting a predetermined signal in the second frequency band; receiving information from the first base station device that enables identification of a transmission power when transmitting a signal to the second base station device based on a reception quality of the predetermined signal at a second base station device that operates in the second frequency band and is not treated as being in the same location as the first base station device; identifying the transmission power based on the information, and performing control to transmit a signal to the second base station device in the second frequency band using the identified transmission power.

16. A control method executed by a base station device operating in a first frequency band, comprising: acquiring information on the reception quality of a predetermined signal transmitted from a terminal device in a second frequency band different from the first frequency band, when the predetermined signal is received at a first other base station device operating in the second frequency band and not treated as being located in the same location as the base station device; generating information that enables the terminal device to identify the transmission power when transmitting a signal to the first other base station device based on the reception quality, and transmitting the information to the terminal device in the first frequency band.

17. A program for causing a computer installed in a terminal device to execute the control method according to claim 15.

18. A program for causing a computer installed in a base station device to execute the control method according to claim 16.

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