Control method, terminal device, and base station device for flexibly using rach procedure configuration in cellular communication system

Abstract

This base station device, conforming to the cellular communication standard of the 3rd Generation Partnership Project (3GPP), notifies a terminal device of a plurality of pieces of configuration information that make it possible to respectively specify periods in which the base station device can receive a random access preamble for a random access procedure from the terminal device.

Description

Base station apparatus, terminal apparatus, and control method for flexibly applying RACH procedure settings in a cellular communication system

[0001] The present invention relates to a configuration technique for a random access procedure in a cellular communication system.

[0002] The cellular communication standard of the Third Generation Partnership Project (3GPP (registered trademark)) specifies a random access procedure (RACH procedure) for a terminal device to establish a connection with a base station device and establish uplink timing synchronization. The RACH procedure is executed in various situations, such as when transitioning from a disconnected state to a connected state, during handover, and during recovery from a beam failure (Beam Failure Recovery). The base station device transmits information, via SIB1 or an RRC Reconfiguration message, that enables the terminal device to identify a PRACH Occasion for transmitting a random access preamble (RAP) in the RACH procedure (see Non-Patent Document 1). SIB1 stands for System Information Block Type 1, and RRC stands for Radio Resource Control.

[0003] 3GPP TS38.211 V. 18.5.0, January 2025

[0004] To save network power, the application of a technology called Cell Discontinuous Reception (DRX), which sets a period during which a base station device does not receive signals, is being considered. When Cell DRX is used, if a PRACH Occasion is included in the period during which the base station device does not receive signals, even if a terminal device transmits a RAP, the RAP is not received by the base station device. Therefore, it is assumed that the base station device notifies the terminal device of configuration information related to the RACH procedure in consideration of Cell DRX. However, if such notification is required at the start and end of the Cell DRX period, signaling overhead may increase. This also applies to cases other than Cell DRX, such as when a base station device is required to temporarily set more PRACH Occasions due to an extension of network functionality.

[0005] The present invention provides a technique that enables flexible application of settings related to RACH procedures in a cellular communication system.

[0006] A base station device according to one aspect of the present invention is a base station device that complies with the cellular communication standard of the Third Generation Partnership Project (3GPP), and has a notification means for notifying a terminal device of multiple setting information that enables the base station device to identify periods during which it can receive a random access preamble for a random access procedure from the terminal device.

[0007] A terminal device according to one aspect of the present invention is a terminal device that complies with the cellular communication standard of the Third Generation Partnership Project (3GPP), and has: a receiving means for receiving from a base station device a plurality of setting information that enables each of the setting information to identify a period during which the base station device can receive a random access preamble for a random access procedure; a determining means for determining a frequency and time resource for transmitting the random access preamble to the base station device from the plurality of setting information; and an executing means for transmitting the random access preamble at the frequency and time resource to execute the random access procedure.

[0008] According to the present invention, it is possible to flexibly apply settings related to the RACH procedure in a cellular communication system.

[0009] 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.

[0010] The accompanying drawings are incorporated into and constitute a part of the specification, illustrate embodiments of the present invention, and are used, together with the description, to explain the principles of the present invention. FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. FIG. 2 is a diagram illustrating the relationship between Cell DRX control and PRACH Occasion. FIG. 3 is a diagram illustrating an example of a period during which a base station device can receive a random access preamble, which is set taking into account Cell DRX control. FIG. 4A is a diagram illustrating an example of configuration information. FIG. 4B is a diagram illustrating an example of configuration information. FIG. 5 is a diagram illustrating an example of a period during which a base station device can receive a random access preamble, which is set taking into account Cell DRX control. FIG. 6 is a diagram illustrating an example of the relationship between a PRACH configuration index and a corresponding parameter set. FIG. 7 is a diagram illustrating an example of the hardware configuration of a base station device and a terminal device. FIG. 8 is a diagram illustrating an example of the functional configuration of a base station device. FIG. 9 is a diagram illustrating an example of the functional configuration of a terminal device. FIG. 10 is a diagram illustrating an example of the flow of processing executed in a wireless communication system.

[0011] 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.

[0012] 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 the cellular communication standard of the Third Generation Partnership Project (3GPP (registered trademark)) and includes a base station device 101, a base station device 102, and a terminal device 111. Note that the terminal device 111 is located in a cell formed by the base station device 101, but may be in a connected state (e.g., an RRC Connected state) or a non-connected state (e.g., an RRC Inactive state or an RRC Idle state) with the base station device 101. Note that RRC stands for Radio Resource Control. The base station device 102 forms a cell adjacent to the cell formed by the base station device 101. Note that, for simplicity of explanation, only one base station device and one terminal device are shown in FIG. 1, but naturally, multiple such devices may exist.

[0013] The terminal device 111 initiates a random access (RA) procedure in various situations, such as establishing a connection with the base station device 101, recovery when uplink timing synchronization is lost, and recovery (Beam Failure Recovery (BFR)) when a failure occurs in a connection with a beam formed by the base station device 101. The RA procedure is initiated by the terminal device 111 transmitting a random access preamble (RAP) to the base station device 101. In response to receiving the RAP, the base station device 101 transmits a random access response (RAR). Upon receiving the RAR, the terminal device 111 transmits an RRC message requesting connection establishment using the timing advance value and resources specified in the RAR. The base station device 101 confirms, using the RRC message, that the terminal device 111 is the terminal device to be connected, and then establishes the connection and transmits an RRC message for connection setup to the terminal device 111. This allows the terminal device 111 to establish uplink timing synchronization and establish a connection with the base station device 101. Here, the frequency and time resources allowed for transmitting a RAP are determined in advance by the base station device 101, and configuration information that enables the terminal device 111 to identify these resources is transmitted from the base station device 101. The base station device 101 broadcasts or individually transmits this configuration information, for example, by using System Information Block Type 1 (SIB1) or an RRC Reconfiguration message. By acquiring this configuration information from the base station device 101 in advance, the terminal device 111 can transmit a RAP on the resources identified by the configuration information when an RA procedure should be performed. Note that these resources are called Physical Random Access Channel (PRACH) Occasions. PRACH Occasions are prepared periodically (at equal time intervals), and the terminal device 111 transmits a RAP in a PRACH Occasion after deciding to perform an RA procedure.

[0014] In this embodiment, in order to save power in the network, the base station device 101 operates by using a Cell DRX (Discontinuous Reception) function to provide a period during which wireless signals are not received at predetermined time intervals. Hereinafter, this period may be referred to as a Non-Active period, and a period during which the base station device 101 can receive wireless signals may be referred to as an Active period. The Cell DRX Active period or Non-Active period is notified from the base station device 101 to the terminal device 111. For example, the base station device 101 may notify the terminal device 111 of the cycle at which the Active period or Non-Active period arrives, the length of the Active period, and a time offset value (from a predetermined timing such as a subframe boundary) until the Active period begins. The Cell DRX setting can be individually notified from the base station device 101 to the terminal device 111 using, for example, an RRC Reconfiguration message. This setting may also be transmitted simultaneously to multiple terminal devices. The base station device 101 does not receive uplink signals such as a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH), a RACH, or a scheduling request (SR) during a non-active period. Therefore, when Cell DRX is used, as shown in FIG. 2 , even if a RAP is transmitted in a PRACH occasion set during a non-active period, the base station device 101 cannot receive the RAP. For this reason, it is assumed that the base station device 101 notifies the base station device 101 of a configuration change using SIB1 or an RRC Reconfiguration message, for example, whenever a period during which no radio signals are received arrives, so that RAPs are not transmitted during that period. However, in this case, signaling overhead increases significantly, and the communication efficiency of the entire system may decrease. Furthermore, in an environment in which the base station device 101 performs power saving control, if resources that allow RAPs to be received appropriately are not configured, power saving performance may become insufficient.

[0015] For this reason, the present embodiment provides a technology that enables at least one of appropriately setting a period during which the base station device 101 can receive a RAP and enabling the terminal device 111 to recognize resources for transmitting the RAP, while preventing a significant increase in signaling overhead in an environment where power saving control is performed. An example of a method for the terminal device 111 to efficiently identify resources for transmitting the RAP will be described below. Note that, although several aspects will be described below, these may be used in any combination. Also, an example will be described below in which Cell DRX is used to not set PRACH Occasions or to reduce the number of PRACH Occasions in a specific period, but this is not limiting. For example, depending on the functionality provided by the network, it may be necessary to increase the number of PRACH Occasions in a specific period. In such a case, the following method may also be applied.

[0016] In this method, the terminal device 111 identifies a period during which a RAP is received at the base station device 101 by performing a logical product of the Cell DRX Active period and the PRACH Occasion period. In this case, the period during which a RAP is received at the base station device 101 is, for example, as shown in FIG. 3 . The terminal device 111 receives information capable of identifying the Cell DRX Active period and information capable of identifying a conventional PRACH Occasion from the base station device 101. The terminal device 111 then identifies PRACH Occasions using a conventional method, and identifies PRACH Occasions that exist within the Cell DRX Active period as resources from which a RAP can be transmitted. The terminal device 111 initiates an RA procedure, for example, when uplink timing synchronization is lost or when a BFR occurs. At that time, the terminal device 111 specifies a period in which the RAP can be transmitted as described above, and transmits the RAP to the base station device 101 within that period. The base station device 101 measures an uplink signal from the terminal device 111, and when determining that uplink timing synchronization has been lost, can instruct the terminal device 111 to perform an RA procedure by a Physical Downlink Control Channel (PDCCH) order of DCI format1_0. Furthermore, when the terminal device 111 measures a downlink signal from the base station device 101, detects a beam failure, and determines to perform BFR, it may start the RA procedure in accordance with a preset setting for the RA procedure.

[0017] Note that the base station device 101 may specify a period in which RAP can be received by performing a logical product between the Cell DRX Active period and the PRACH Occasion period, and notify the terminal device 111 of information indicating that period. The base station device 101 may notify the terminal device 111 of information indicating this period by including it in at least one of RACH-configcommon, RACH-configdedicated, and RACH-configgeneric in an RRC Reconfiguration message. Furthermore, information indicating this period for BFR may be notified by being included in RACH-ConfigBFR. Note that information that enables identification of a PRACH Occasion can be notified, for example, as configuration information that associates a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) with a PRACH Occasion. This configuration information is notified, for example, by parameters ssb-perRACH-OccasionAndCB-PreamblesPerSSB, a frequency domain parameter msg1-FrequencyStart, and a time domain parameter PRACH configuration index. The configuration information can have, for example, a configuration as shown in FIG. 4A. In FIG. 4A, prach-ConfigurationIndex corresponds to the PRACH configuration index and represents parameters related to the PRACH Occasion in the time domain. The meaning of this value will be described later. msg1-FDM indicates the number of PRACH Occasions multiplexed in the frequency domain. A value of 1, 2, 4, or 8 is set, with the value "1" indicating no multiplexing, and the values ​​"2," "4," and "8" indicating 2, 4, and 8 multiplexing in the frequency domain, respectively. msg1-FrequencyStart is a parameter related to the PRACH Occasion in the frequency domain, and indicates from which resource block within the uplink Bandwidth Part (BWP) the PRACH Occasion starts."zeroCorrelationZoneConfig" is a parameter that specifies the amount of cyclic shift of the Zaddoff-chu sequence stored in the RAP. "preambleReceivedTargetPower" indicates the power intensity required for receiving the RAP on the network (base station device) side. "preambleTransMax" indicates the maximum number of times the RAP is transmitted. "powerRampingStep" indicates the step size for increasing the transmission power when transmitting the next RAP if no RAR is received after transmitting the RAP. "ra-ResponseWindow" indicates the reception window of the RAR.

[0018] In one example, the base station device 101 may enable these parameters only during the active period of Cell DRX and disable (do not use) them during the non-active period. The base station device 101 identifies information about the period for receiving RAPs by performing a logical AND between the active period of Cell DRX and the PRACH Occasion used when Cell DRX is not activated, which is identified based on these parameters. The base station device 101 may then notify the terminal device 111 of information about the identified period. Alternatively, the base station device 101 may generate configuration information such that the PRACH Occasion is set only during the active period when Cell DRX is activated, without taking into account the PRACH Occasion when Cell DRX is not activated, and notify the terminal device 111 of the configuration information. Here, the configuration information notified to the terminal device 111 may have the format of a PRACH configuration index. That is, a PRACH configuration index corresponding to parameters that identify a PRACH Occasion taking Cell DRX into consideration is notified to the terminal device 111. This PRACH configuration index may be the PRACH configuration index specified in 3GPP (registered trademark) standard TS38.211, or may be a newly defined PRACH configuration index.

[0019] Note that if the base station device 101 maintains a non-active period for a long period of time, it is expected that the timing at which the terminal device 111 starts the RA procedure will be significantly delayed. For this reason, when the base station device 101 sets a non-active period longer than a predetermined length, the base station device 101 may hand over a connected terminal device to another base station device (for example, the base station device 102). Furthermore, the base station device 101 may change configuration information such as a threshold for cell selection so that a non-connected terminal device moves to a cell provided by another base station device (performs cell reselection).

[0020] Note that the above example has been described focusing on the configuration information for the RA procedure for the base station device 101 that provides the cell to which the terminal device 111 is connected or located, but configuration information for the RA procedure for a neighboring cell can also be notified to the terminal device 111. That is, when performing an RA procedure with another base station device (e.g., the base station device 102) that provides a neighboring cell by handover (HO), conditional handover (CHO), or Layer 1 / Layer 2 Triggered Mobility (LTM), information that enables identification of a period during which the other base station device can receive a RAP can be notified to the terminal device 111. In one example, when the base station device 102 identifies the period during which it can receive the RAP as described above and receives a HANDOVER REQUEST from the base station device 101, it can include the information in a HANDOVER REQUEST ACKNOWLEDGE and transmit it to the base station device 101. Furthermore, the base station device 102 can notify the base station device 101 of information that enables identification of a conventional PRACH Occasion (while Cell DRX is not activated) and information that enables identification of an Active period or a Non-Active period in Cell DRX. Then, the base station device 101 notifies the terminal device 111 of the information received from the base station device 102. Based on the information, the terminal device 111 identifies a period in which the base station device 102 can receive a RAP, and can perform HO / CHO / LTM by transmitting a RAP to the base station device 102 within that period, thereby connecting to a cell provided by the base station device 102. Note that the base station device 101 may identify a period in which the base station device 102 can receive a RAP from information that enables identification of a conventional PRACH Occasion and information that enables identification of an Active period or a Non-Active period in Cell DRX, received from the base station device 102, and notify information indicating that period to the terminal device 111. In other words, the period in which the base station device 102 can receive a RAP may be identified by the base station device 102 or the terminal device 111, or may be identified by the base station device 101.Furthermore, the base station device 101 may transmit, in a HANDOVER REQUEST, information requesting the base station device 102 to provide information enabling the base station device 102 to identify a period during which the base station device 102 can receive a RAP. Here, the base station device 101 may request information indicating the period as information enabling the base station device 102 to identify a period during which the base station device 102 can receive a RAP, or may request information enabling the base station device 102 to identify a conventional PRACH Occasion and information enabling the base station device 102 to identify an Active period or a Non-Active period of Cell DRX.

[0021] Note that when CHO or LTM is used, it can be assumed that the time difference between the timing at which the terminal device 111 receives information for an RA procedure in a neighboring cell from the base station device 101 and the timing at which the terminal device 111 changes its connection destination to the base station device 102 will be relatively large. For this reason, a situation may arise in which the base station device 102 has not activated Cell DRX at the timing at which the terminal device 111 receives information for the RA procedure, but the base station device 102 has activated Cell DRX at the timing at which the terminal device 111 attempts to change its connection destination. In this case, if the base station device 102 is in a Non-Active period at the timing at which the terminal device 111 transmits a RAP to switch its connection destination to the base station device 102, the base station device 102 will not be able to receive the RAP. As a result, the terminal device 111 may not be able to connect to the base station device 102. For this reason, when the base station device 102 activates Cell DRX, that information may be notified to the terminal device 111. For example, the base station device 101 before the change of connection destination may notify the terminal device 111 of the activation of Cell DRX in the base station device 102 that is a candidate for the connection destination. As described above, the base station device 102 transmits to the base station device 101, in a HANDOVER REQUEST ACKNOWLEDGE, information specifying an Active period or a Non-Active period when Cell DRX is activated, and information on a period during which RAPs can be received. Then, when the base station device 102 subsequently activates Cell DRX, it may transmit information indicating the activation of Cell DRX to the base station device 101 that transmitted the HANDOVER REQUEST ACKNOWLEDGE. Note that, if an expiration date is set for the information included in the HANDOVER REQUEST ACKNOWLEDGE, and if a handover based on that information has not been executed and there is a HANDOVER REQUEST ACKNOWLEDGE whose expiration date has not yet passed, the base station device 102 may transmit that information to the destination base station device.The terminal device 111 stores in advance information about the period during which the base station device 102 can receive a RAP when Cell DRX is activated. Then, while the base station device 102 does not activate Cell DRX, the terminal device 111 can identify a RAP Occasion using a conventional method, and when the base station device 102 activates Cell DRX, the terminal device 111 can identify the period during which the base station device 102 can receive a RAP using the above-described method. Furthermore, information indicating that the base station device 102 has activated Cell DRX may be notified to the terminal device 111, along with information indicating that the base station device 102 has activated Cell DRX. Note that the base station device 102 may notify the terminal device 111 that it has activated Cell DRX via an RRC Reconfiguration message, a Medium Access Control-Control Element (MAC CE), or Downlink Control Information (DCI).

[0022] Note that while in a disconnected state, the terminal device 111 can receive the above-mentioned information via a System Information Block (SIB). That is, the base station device 101 and the base station device 102 can broadcast information for specifying a period during which the RAP can be received, using an SIB (e.g., SIB1). For example, the base station device 101 and the base station device 102 can broadcast information that specifies a PRACH Occasion (when Cell DRX is not activated) and information that specifies an Active period or a Non-Active period when Cell DRX is activated, in an SIB. The terminal device 111 can receive the SIB and, by receiving this information, specify a period during which the base station device 101 and the base station device 102 can receive the RAP. The terminal device 111 can then establish a connection with the base station device 101 or 102 by transmitting a RAP during the specified period. The terminal device 111 may acquire this information in an RRC Release message when transitioning from a connected state to an unconnected state. That is, when releasing the connection with the terminal device, the base station device 101 or 102 may transmit an RRC Release message including information that enables identification of a period during which a RAP can be received. Furthermore, when the terminal device 111 receives such information during the connected state, the base station device 101 may maintain the information without deleting it even after transitioning to the unconnected state, and transmit a RAP based on the information when the next RACH procedure is performed. In this case, if the terminal device 111 should maintain and use the information regarding the RACH procedure acquired during the connected state during the unconnected state, the base station device 101 may notify the terminal device 111 of information instructing such operation (for example, in an RRC Release message). In one example, this information may be an identifier that indicates the use of the same parameters as those obtained during the connected state.On the other hand, when the terminal device 111 is to perform the RACH procedure using second setting information different from the first setting information notified during the connected state, the base station device 101 can notify the terminal device 111 of the second setting information in an RRC Release message. Also, the base station device 101 may broadcast the second setting information in SIB1.

[0023] As described above, the period in which the base station device 101 can receive a RAP is identified by the logical product of the period of a PRACH Occasion when Cell DRX is not activated and the Active period in Cell DRX, and thus the terminal device 111 can identify the period in which the base station device 101 cannot receive a RAP while sufficiently ensuring the power saving performance of Cell DRX. This makes it possible to prevent the terminal device 111 from transmitting a RAP unnecessarily (during the period in which the base station device 101 cannot receive a RAP) while sufficiently saving power in the network, and enables efficient communication related to the RACH procedure.

[0024] In the above example, a period in which the base station device 101 can receive a RAP is not set during a non-active period of Cell DRX. However, this is not limiting. For example, a period in which the base station device 101 can receive a RAP may be set even during a non-active period. In this case, as shown in FIG. 5 , the period in which the base station device 101 can receive a RAP may be set less frequently than a period of a PRACH Occasion when Cell DRX is not activated. For example, this setting may be performed by lengthening the arrival cycle of the period in which the base station device 101 can receive a RAP during a non-active period of Cell DRX, or by reducing the number of subframes in which the period is set. According to this, the base station device 101 sets the period in which RAPs can be received in the Non-Active period of Cell DRX at a low frequency, thereby achieving a certain level of power saving performance while preventing the occurrence of a situation in which the terminal device 111 is unable to transmit RAPs for a long period of time.

[0025] The base station device 101 notifies the terminal device 111 of information that enables identification of a PRACH Occasion to be used during an Active period of Cell DRX and information that enables identification of a PRACH Occasion to be used during a Non-Active period of Cell DRX (a period during which the base station device 101 can receive a RAP). Here, this processing will be explained using FIG. 6 as an example. FIG. 6 is a diagram excerpting a portion of a table that specifies a PRACH configuration index and parameters for calculating a PRACH Occasion, as specified in TS38.211 of 3GPP (registered trademark). For example, it is assumed that a first PRACH configuration index = 103 is specified in the information that enables identification of a PRACH Occasion to be used during an Active period. In this case, PRACH Occasions exist in subframes 2 and 7, and six PRACH Occasions are configured in the time domain within one time slot (when the subcarrier spacing is 30 kHz, 12 PRACH Occasions are configured in the time domain within one subframe). In contrast, for example, assume that a second PRACH configuration index of 160 is specified in the information that enables identification of a PRACH Occasion to be used during a Non-Active period. In this case, a PRACH Occasion exists in subframe 1, and two PRACH Occasions are configured in the time domain within one time slot (when the subcarrier spacing is 30 kHz, four PRACH Occasions are configured in the time domain within one subframe). The terminal device 111 receives this configuration information. 4A, the setting information provided to the terminal device 111 may be information that specifies other setting items for settings with different PRACH configuration indexes. Items common to multiple pieces of setting information may be notified only once, and only information unique to each piece of setting information may be notified in association with the identifier of the setting information.In one example, in the configuration shown in Fig. 4A, the first piece of configuration information may include all information, and the second and subsequent pieces of configuration information may store only the value of the PRACH configuration index. Furthermore, information common to multiple pieces of configuration information may not be included in the first piece of configuration information, but may be specified as a separate information item. Furthermore, in some or all of the multiple pieces of configuration information, only part of the information in the PRACH configuration index may be used as information on the periodicity of PRACH Occasions, as shown in Fig. 4B, for example.

[0026] During the Cell DRX Active period, the terminal device 111 calculates a PRACH Occasion using the setting of PRACH configuration index = 103. Then, as the base station device 101 transitions to a Non-Active period, the terminal device 111 voluntarily changes the setting to be used to the setting of PRACH configuration index = 160 and calculates a PRACH Occasion. As a result, as the base station device 101 transitions from the Cell DRX Active period to the Non-Active period, the arrival cycle of the period in which the base station device 101 can receive RAPs becomes longer, and fewer PRACH Occasions are set. Furthermore, the base station device 101 may not need to notify the terminal device 111 in advance of multiple pieces of configuration information (for example, a PRACH configuration index). For example, the base station device 101 may notify the terminal device 111 of the configuration information to be used in the next period (the active period in the case of a transition to an active period, or the non-active period in the case of a transition to a non-active period) when a transition between an active period and a non-active period of Cell DRX is triggered. Furthermore, in the above example, an example has been described in which a PRACH configuration index is notified as an example of configuration information, but, for example, at least any of the periodicity of a PRACH Occasion, the subframe number in which a PRACH Occasion is set, the starting symbol position of a PRACH Occasion within a subframe, the number of PRACH slots within a subframe, the number of PRACH Occasions in the time domain within a PRACH slot, and the duration of a PRACH may be notified to the terminal device 111 as configuration information. That is, by changing only some of the parameters corresponding to the PRACH configuration index in FIG. 6 , the period during which the base station device 101 can receive RAPs during a non-active period may be set to be shorter than during an active period. Alternatively, both the value of the PRACH configuration index and the value indicating the parameter to be changed may be notified.In this case, the terminal device 111 can replace the parameter indicated as a parameter to be changed from the parameter group indicated by the PRACH configuration index with the notified value.

[0027] The base station device 101 may notify the terminal device 111 of multiple pieces of configuration information, and then notify the terminal device 111 of an instruction indicating which of the multiple pieces of configuration information to use. For example, the base station device 101 may notify the terminal device 111 of multiple PRACH configuration indexes by an RRC message or an SIB. The base station device 101 may then notify the terminal device 111 of information indicating which of the multiple PRACH configuration indexes is to be applied, for example, by a DCI (PDCCH). This reduces the frequency of transmission and reception of RRC messages with large amounts of data, and enables efficient configuration switching by switching the configuration using a DCI (PDCCH) with a relatively small amount of data. The DCI may specify a value of the PRACH configuration index to be used (for example, "103"). Alternatively, a corresponding identification number may be assigned to each of multiple PRACH configuration indexes notified in an RRC message or an SIB, and the PRACH configuration index to be used may be specified in DCI by the identification number. For example, the base station device 101 may assign an identification number "0" to PRACH configuration index=103 and an identification number "1" to PRACH configuration index=160 in the RRC message and the SIB. Then, in DCI, the identification number "0" or "1" may indicate which of PRACH configuration index=103 or PRACH configuration index=160 should be used. According to this, when the number of PRACH configuration indices that can be set at one time by an RRC message or an SIB is n, it becomes possible to specify the configuration to be used in DCI by ceil(log n) bits. Note that ceil(x) is a ceiling function that returns the smallest integer equal to or greater than x.

[0028] In one example, since a PRACH Occasion can be configured in multiple subframes, it is possible to use a PRACH Occasion in only some of the multiple subframes and not use a PRACH Occasion in some of the remaining subframes. For example, assuming a table such as that shown in FIG. 6 , two configurations, PRACH configuration index = 102 and PRACH configuration index = 103, are notified from the base station device 101 to the terminal device 111 via an RRC message or an SIB. Here, for example, it is assumed that the base station device 101 determines to configure a PRACH Occasion in subframes 2 and 7 during the Active period of Cell DRX, and not to configure a PRACH Occasion in subframe 2 during the Non-Active period. In this case, the base station device 101 can notify the terminal device 111 by DCI that PRACH configuration index = 103 should be used in the active period. Then, the base station device 101 can notify the terminal device 111 by DCI that PRACH configuration index = 102 should be used in the non-active period. As a result, the PRACH Occasion of subframe 2 will not be used in the non-active period.

[0029] In the above example, the process of specifying the active and non-active periods of Cell DRX and the PRACH Occasion settings to be used in each period and switching the settings to be used in each period has been described. However, instead of the information on the active and non-active periods of Cell DRX, the terminal device may acquire information indicating the activation period for enabling a PRACH Occasion and the deactivation period for deactivating it, and specify the PRACH Occasion setting to be used. In this case, the base station device may provide the terminal device with information for specifying the activation period and deactivation period of a RACH Occasion (e.g., information on the start frame and end frame of the activation period or deactivation period, and information on the cycle of activation or deactivation), similar to the information on the active and non-active periods of Cell DRX. For example, after receiving DCI including an instruction to enable a PRACH occasion, the terminal device may determine a PRACH transmission resource and transmit a RAP to the base station device within a set activation period. The terminal device may start a timer indicating the activation period based on the instruction to enable the PRACH occasion and disable the PRACH occasion after the timer expires. If the terminal device transmits a RAP within the validity period but is unable to successfully transmit the RAP by the expiration of the validity period (timer), the terminal device may attempt to transmit the RAP again in the next PRACH occasion. The next PRACH occasion may be a PRACH occasion defined by a conventional method or may be a PRACH occasion identified as in the present embodiment.

[0030] Furthermore, the PRACH MASK Index may be used to specify whether to enable or disable a portion of a PRACH Occasion. Different PRACH MASK Indexes may be specified for different PRACH configuration Indexes. Regarding the value of the PRACH MASK Index previously set via an RRC message or SIB, a change of the PRACH MASK Index may be indicated using a MAC CE or DCI.

[0031] In another example, the base station device 101 may notify the terminal device 111 by DCI that some of the parameters corresponding to one PRACH configuration index notified to the terminal device 111 by way of an RRC message or an SIB should be changed. For example, the base station device 101 may notify the terminal device 111 by way of an RRC message or an SIB of only PRACH configuration index=103, and may notify the terminal device 111 by way of DCI of an instruction indicating that a PRACH Occasion should not be set in subframe 2 during the Non-Active period of Cell DRX. That is, only one PRACH configuration index may be notified by way of an RRC message or an SIB, and an instruction to change only some of the parameters corresponding to that index may be transmitted by way of DCI. Note that, in the above example, an example has been described in which a PRACH Occasion is not configured in subframe 2, but the present invention is not limited to this. For example, at least one of the periodicity of the PRACH Occasion, the starting symbol position of the PRACH Occasion in a subframe, the number of PRACH slots in a subframe, the number of PRACH Occasions in the time domain in a PRACH slot, and the PRACH duration may be notified to the terminal device 111 by DCI as a change target. Furthermore, on or off of these parameters may be notified, or alternative values ​​to be used in place of values ​​corresponding to the PRACH configuration index may be notified as the values ​​of these parameters. For example, when PRACH configuration index = 103, 0, 2, 4, 6, 8, 10, 14, 16, 18, 20, 22, and 24 are identified as the start symbol positions of PRACH Occasions within a subframe, but the terminal device 111 can be notified that PRACH Occasions are set only at 0, 2, and 4 among these symbol positions, and that PRACH Occasions are not set at other symbol positions.Furthermore, a new PRACH configuration index value may be assigned to such a setting (where only 0, 2, and 4 are used as the starting symbol positions of the PRACH Occasion within a subframe, and other parameters are the same as those for PRACH configuration index=103). This assignment may be performed independently by the base station device 101. That is, the base station device 101 or the base station device 102 (or the network operator) may independently define a PRACH configuration index value associated with a specific parameter. Then, the base station device 101 or the base station device 102 (or the network operator) may notify the terminal device 111 of the independently defined PRACH configuration index value and information on the associated parameters. In this case, there are two types of PRACH configuration indexes: a PRACH configuration index defined in the 3GPP (registered trademark) cellular communication standard, and a PRACH configuration index uniquely defined by the base station device 101, a network operator, etc. The terminal device 111 can notify the base station device 101 of information on whether or not the use of the uniquely defined PRACH configuration index is supported, using capability information (UE capability). Only when the base station device 101 receives capability information indicating that the terminal device 111 supports a uniquely defined PRACH configuration index from the terminal device 111, the base station device 101 can notify the terminal device 111 of information about the uniquely defined PRACH configuration index and notify the terminal device 111 of the PRACH Occasion setting using the index.Note that information on the uniquely defined PRACH configuration index can be notified from the base station device 101 to the terminal device 111, for example, by using an RRC message, together with corresponding parameters (PRACH Occasion periodicity, subframe number in which the PRACH Occasion is set, start symbol position of the PRACH Occasion within the subframe, number of PRACH slots within the subframe, number of PRACH Occasions in the time domain within the PRACH slot, and PRACH duration). Note that, for example, when a network operator defines a unique PRACH configuration index, the information may be notified to the terminal device 111 only once when the terminal device 111 is powered on. Also, for example, the information may be notified to the terminal device 111 when location registration (Tracking Area Update, etc.) is performed.

[0032] Furthermore, in the above example, the process of assigning a PRACH configuration index has been described as being performed independently by the base station device 101 or the network operator, but this is not limiting. For example, in addition to the conventional PRACH configuration index assignment currently defined in the 3GPP (registered trademark) cellular communication standard, a new, different PRACH configuration index assignment may be commonly defined (for example, in the standard). This allows the newly defined PRACH configuration index to be commonly used by base station devices of multiple operators.

[0033] Note that only one of the multiple settings may be enabled, or multiple settings may be enabled in parallel. When multiple settings are enabled and the PRACH Occasions identified by the multiple settings overlap, the terminal device 111 may determine not to use the overlapping PRACH Occasions. In one example, when the above-mentioned PRACH configuration index=102 and PRACH configuration index=103 are enabled in parallel, the terminal device 111 may determine not to use the PRACH Occasion of subframe 7. In one example, when PRACH configuration index=102 is set for another terminal device that complies with a legacy standard and cannot be set to multiple PRACH configuration indexes, this other terminal device can transmit a RAP only in the PRACH Occasion of subframe 7. Then, the terminal device 111 can transmit a RAP only in the PRACH Occasion of subframe 2. This makes it possible to separate the PRACH Occasions used by the terminal device 111 and the PRACH Occasions used by terminal devices that comply with the legacy standard. Furthermore, the terminal device 111 may determine that only the PRACH Occasion identified by a setting selected according to a predetermined rule, such as a setting with a smaller identifier number, is valid. In one example, when PRACH configuration index=102 and PRACH configuration index=103 are enabled in parallel, the above-described predetermined rule can be specified such that the configuration of PRACH configuration index=102 is used in subframe 7, and the configuration of PRACH configuration index=103 is used in subframe 2.Furthermore, when the PRACH configuration index=103 and the PRACH configuration index=161 in FIG. 6 are enabled in parallel, the above-described predetermined rule may be specified so that the configuration of the PRACH configuration index=161 is used in subframe 7 and the configuration of the PRACH configuration index=103 is used in subframe 2. In one example, if a time-domain PRACH Occasion identified by a first PRACH configuration index and a time-domain PRACH Occasion identified by a second PRACH configuration index overlap and the frequency-domain PRACH Occasion identified by msg1-FrequencyStart are the same, it may be determined not to use the time-domain PRACH Occasion identified by the second PRACH configuration index.

[0034] In the above example, a case has been described in which PRACH Occasions that the terminal device 111 can use or cannot use are specified by subframe numbers, but this is not limiting. For example, PRACH Occasions that can be used (enabled) or cannot be used (disabled) may be specified by numbers (RO numbers) assigned to each PRACH Occasion. In one example, a group of RO numbers to be enabled or disabled may be identified and notified to the terminal device 111 so that multiple PRACH Occasions corresponding to the same time interval (for example, frequency multiplexed) are simultaneously enabled or disabled. In this case, it should be noted that rules for assigning RO numbers are predetermined, and the base station device 101 and the terminal device 111 need to have a common understanding of RO numbers.

[0035] As described above, a PRACH Occasion can be identified by configuration information that associates (maps) an SSB with a PRACH Occasion. Then, mapping of multiple patterns with PRACH Occasions can be dynamically specified via an SIB. That is, the time and frequency locations of multiple PRACH Occasions can be specified by an SIB, and some (e.g., one) of the patterns specified by the SIB can be specified and enabled by a DCI. Furthermore, the time and frequency locations of some PRACH Occasions can be specified, and the remaining PRACH Occasions can be multiplexed and arranged in at least one of the time direction and the frequency direction based on the specified time and frequency locations. In this case, the number of multiplexed PRACH Occasions in the time direction and / or the frequency direction can be specified.

[0036] For example, when multiplexing in the time direction is performed, multiple RACH-ConfigCommons may be specified in the SIB. That is, by specifying multiple RACH-configcommons, multiple time direction parameters may be specified by parameters related to the PRACH in each RACH-configcommon (each parameter in the PRACH configuration index). The parameters here may include, for example, the periodicity of the PRACH Occasion, the subframe number in which the PRACH Occasion is set, the start symbol position of the PRACH Occasion in the subframe, the number of PRACH slots in the subframe, the number of PRACH Occasions in the time domain in the PRACH slot, and the duration of the PRACH. Furthermore, when multiplexing in the frequency direction is performed, multiple msg1-FrequencyStart parameters may be set. These pieces of setting information are notified from the base station device 101 to the terminal device 111 via, for example, an SIB.

[0037] Then, for one or more of the plurality of RACH-configcommons, the contents of one or more of its parameters can be changed. For example, the parameter n fThe terminal device 111 may be notified by DCI that "x" in mod x = y will be changed from 1 to 2. Furthermore, for example, the terminal device 111 may be notified by DCI that the subframe number in which the PRACH Occasion is set will be changed from [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] to [0, 1, 2, 3]. Furthermore, the terminal device 111 may be notified by PDCCH using DCI that the frequency position specified by msg1-FDM or msg1-FrequencyStart will be changed from one frequency position to another frequency position. The terminal device 111 identifies the PRACH Occasion based on the information specified by the DCI. Note that new parameters may be defined. Furthermore, new values ​​may be defined for existing parameters, such as defining a new value such as 32 or 64 for the above-mentioned value "x" that determines the periodicity. The newly defined parameters and values ​​can be notified from the base station device 101 to the terminal device 111 in an RRC message or SIB to notify the information.

[0038] Furthermore, multiple combinations of a parameter PRACH configuration index for specifying the time position of a resource and a parameter msg1-FrequencyStart for specifying the frequency position of the resource can be notified in advance from the base station device 101 to the terminal device 111 by an RRC message. Then, the PRACH Occasion to be actually used can be indicated by DCI or MAC CE. Furthermore, this parameter combination may include msg1-FDM, which indicates the number of resources multiplexed in the frequency direction.

[0039] A PRACH occasion and an association period with an SSB (association period, association pattern period) may be newly defined. When this information is changed, a notification may be transmitted to the terminal device 111 via DCI. That is, when the PRACH configuration period that was conventionally set using a PRACH configuration index is changed, the association period and association pattern period are changed accordingly. In response to this, a new association period and association pattern period may be defined depending on the SSB period and whether or not an SSB with a specific index is transmitted. The newly defined association period and association pattern period can then be notified to the terminal device 111 .

[0040] For example, the PRACH configuration period for six SSBs is set to 10 milliseconds (ms). While 60 ms is sufficient to configure a PRACH Occasion corresponding to six SSBs, conventional regulations require the association pattern to be 80 ms. In contrast, for example, when the PRACH configuration period for six SSBs is 10 ms, a new setting of an association pattern of 60 ms can be defined and notified to the terminal device 111. Furthermore, a setting in which the association pattern is 60 ms when the PRACH configuration period for six SSBs is 10 ms, and a setting in which the association pattern is 120 ms when the PRACH configuration period for six SSBs is 20 ms may be newly defined and notified to the terminal device 111. When two settings are notified to the terminal device 111, which of them to use can be specified by, for example, DCI.

[0041] Note that, when the base station device 101 performs beamforming when transmitting an SSB or during an RA procedure, the terminal device 111 determines a PRACH occasion to use according to the selected SSB. In order to perform such processing, the terminal device 111 needs to store correspondence information indicating which of multiple SSBs corresponding to multiple beams formed by the base station device 101 multiple PRACH occasions specified by a PRACH configuration index, frequency, and time position correspond to which. This correspondence information can be fixedly determined and stored in advance in the memory of the terminal device 111. Furthermore, the base station device 101 may provide the correspondence information to the terminal device 111 by an RRC message such as an SIB or RRC Reconfiguration, or a PDCCH such as DCI.

[0042] The base station apparatus 101 can notify the terminal apparatus 111 in advance of multiple combinations of PRACH Occasion and SSB settings using an RRC message, and can separately instruct the terminal apparatus 111 by DCI or MAC CE which setting to actually use from the multiple combinations. The SSB setting includes information indicating the SSB periodicity specified by ssb-periodicityServingCell and the SSB transmission pattern specified by ssb-PositionsInBurst.

[0043] Furthermore, when the base station device 101 and the terminal device 111 support beamforming, in order for the terminal device 111 to identify a beam to be used for each PRACH occasion, information on the relationship between the SSB and the PRACH occasion (SSB / PRACH relationship information) is notified from the base station device 101 to the terminal device 111. When the PRACH occasion is changed, the base station device 101 updates the SSB / PRACH relationship information in accordance with the change, and notifies the terminal device 111 of the updated SSB / PRACH relationship information. For example, assume that RO numbers "0" and "1" correspond to SSB#0, RO numbers "2" and "3" correspond to SSB#1, and RO numbers "4" and "5" correspond to SSB#2, and that the base station device 101 is operating in a state in which PRACH Occasions with RO numbers "0" to "5" are available. Then, for network power saving, the base station device 101 transitions from that state to a state in which only PRACH Occasions with RO numbers "0" to "2" are used. If the SSB / PRACH relationship information is maintained without being updated at this time, no PRACH Occasion corresponding to SSB#2 will exist. Therefore, if the terminal device 111 selects SSB#2, it will be unable to identify a PRACH Occasion on which to transmit a RAP, and will be unable to execute the RA procedure. Therefore, the base station device 101 can update the SSB / PRACH relationship information so that, for example, RO number "0" corresponds to SSB#0, RO number "1" corresponds to SSB#1, and RO number "2" corresponds to SSB#2.

[0044] The base station apparatus 101 may notify the terminal apparatus 111 in advance of multiple patterns of combinations of PRACH occasions and corresponding SSB / PRACH related information using an RRC message, and may instruct the terminal apparatus 111 by DCI or MAC CE which combination to actually use. According to this method, it is possible to simultaneously change the PRACH occasion and the SSB / PRACH related information using DCI or MAC CE, which have small signaling overhead.

[0045] It should be noted that, during communication in the RRC connected state, the terminal device 111 associates the CSI-RS, not the SSB, with the PRACH Occasion. In this case, instead of the above-described SSB / PRACH relationship information, CSI-RS / PRACH relationship information is prepared, thereby enabling the same processing as described above to be performed.

[0046] Conventionally, PRACH occasions are associated with SSBs using ssb-perRACH-OccasionAndCB-PreamblesPerSSB, with values ​​set as {1 / 8, 1 / 4, 1 / 2, 1, 2, ...}, where 1 / 8 means that one SSB is associated with eight PRACH occasions, 1 / 4 means that one SSB is associated with four PRACH occasions, 1 means that one SSB is associated with one PRACH occasion, and so on.

[0047] The base station device 101 may use SSB or CSI-RS as a reference signal for sensing an object or a terminal device. For example, the base station device 101 may estimate the position of an object or a terminal device based on the strength (RSRP) or direction of a reflected wave from the object or the terminal device. The base station device 111 may determine that there are no terminals or that there are few terminal devices in a direction in which a reflected wave is not detected, and may disable PRACH Occasions in that direction or lengthen the period so that fewer resources are used for PRACH Occasions. The base station device 101 may notify the terminal device of the result of this determination. When the base station device 101 uses CSI-RS as a reference signal for sensing, it may notify the terminal device of an RA-occasion list that specifies the relationship between a CSI-RS resource ID and a PRACH Occasion. Note that the RA-occasion list is just an example, and the relationship between the CSI-RS or SSB and the PRACH Occasion may be notified to the terminal device by other methods. The method of specifying the PRACH Occasion to be enabled or disabled by the RO number assigned to each PRACH Occasion has been described above. However, instead of the RO number, the specification may be performed using the SSB index or CSI-RS index associated with the RO number. The terminal device can identify the PRACH Occasion that can or cannot be used from the SSB index or CSI-RS index based on the relationship information such as the RA-occasion list received from the base station device 101. The base station device 101 may notify the terminal device of the PRACH Occasion to be enabled or disabled using the SSB index or the CSI-RS resource ID. Furthermore, when the base station device disables a PRACH Occasion, the base station device may accordingly update the association between the SSB and the PRACH Occasion.For example, when the PRACH Occasion associated with SSB #2 is disabled, if the amount of PRACH transmitted in SSB #2 is small, the base station device 101 may instruct the terminal devices under SSB #2 to use the PRACH Occasion of SSB #3.

[0048] When the terminal device 111 is notified of the deactivation of a PRACH Occasion (non-availability / deactivation or release), it stores the received settings and does not transmit a RAP on the deactivated PRACH Occasion in accordance with the settings. Note that when the terminal device 111 receives a notification of the activation of a PRACH Occasion (availability / activation or setup), it can transmit a RAP based on the settings. Furthermore, when the terminal device 111 receives a notification of a change in a PRACH Occasion, it stores the received settings and transmits a RAP on the designated PRACH Occasion in accordance with the settings. Furthermore, the terminal device 111 may receive information indicating the relationship between a CSI-RS and an SSB (for example, a Quasi Co-Location (QCL) relationship) without receiving an RA-occasion list. Then, when the terminal device 111 receives information such as invalidation or a setting change of a PRACH Occasion that specifies a CSI-RS, the terminal device 111 may perform processing based on the received information regarding a PRACH Occasion associated with an SSB that has a QCL relationship with the specified CSI-RS. That is, the terminal device 111 may treat a PRACH Occasion associated with an SSB that has a QCL relationship with the specified CSI-RS as invalid, or may transmit a RAP on that PRACH Occasion. The base station device 101 can notify the terminal device of the PRACH Occasion activation / deactivation status (availability / (de)activation / setup / release) or a setting change related to the PRACH Occasion by using an SIB (e.g., SIB1), a cell-based DCI, a message such as a short message, etc. The PRACH MASK Index can be applied to both of the two types of PRACH Occasions specified by the above-mentioned two types of PRACH configuration Index.

[0049] The base station device 101 may periodically perform the above-described sensing. When the base station device 101 receives a reflected wave corresponding to a sensing signal in a specific direction in which PRACH Occasions have been disabled or the amount thereof has been reduced, the base station device 101 may estimate that a terminal device is present in the direction of the beam, and may enable or increase the amount of PRACH Occasions directed in that direction. The base station device 101 may notify the terminal device of the changed configuration information using a message such as an SIB (e.g., SIB1), a cell-based DCI, or a short message.

[0050] A PRACH Occasion is associated with an SSB using ssb-perRACH-occasion and CB-Preamble per SSB. Therefore, the base station device 101 may disable a PRACH Occasion in a direction in which no SSB is being transmitted.

[0051] Furthermore, in the above example, an example has been described in which the base station device 101 performs sensing to configure a PRACH Occasion, but this is not limiting. For example, when a terminal device is in a connected state, the base station device 101 does not need to measure reflected waves from the terminal device. The base station device 101 may identify unnecessary (allowed to be disabled) PRACH Occasions, for example, based on measurement results reported from the terminal device. The base station device 101 transmits measurement configurations for the beam (SSB or CSI-RS) of the serving cell to the terminal device. The terminal device measures a reference signal based on beam information configured using conventional procedures and reports the measurement results to the base station device 101. The base station device 101 may aggregate measurement results reported from multiple terminal devices and determine that no terminal device exists in the direction of a beam not included in the reported results, or that there are few terminal devices present in that direction. The base station device 101 may then decide to change or deactivate (deactivate / release) parameters related to the periodicity of PRACH Occasions associated with that beam direction. The base station device 101 then notifies the terminal device of the content of that decision. The base station device 101 may, for example, transmit information specifying an RA-occasion list associated with a CSI-RS resource ID to the terminal device. Furthermore, if an RA-occasion list is not indicated, the base station device 101 notifies the terminal device of information indicating the relationship between CSI-RS and SSB (for example, the QCL relationship). When notifying the terminal device of a PRACH Occasion to be enabled or disabled, the base station device 101 may use an SSB index or a CSI-RS index associated with the RO number instead of the RO number, as in the above example. The base station device may notify the terminal device of the enablement or disablement of the PRACH Occasion by the SSB index or the CSI-RS resource ID.

[0052] For example, the base station device 101 may lengthen the SSB period (e.g., change it from 20 ms to 160 ms) for power saving control, or may shorten the SSB period (e.g., change it from 160 ms to 20 ms) by stopping power saving control. In this case, the base station device 101 may also change the associated PRACH Occasion at the same time. When changing parameters related to the RA procedure after changing the SSB period, the base station device 101 may broadcast an update message in SIB1. Furthermore, the base station device 101 may notify the terminal device 111 in advance of parameters related to the RA procedure related to each of multiple SSB patterns, and, when changing the SSB period, may notify the terminal device 111 of information specifying one of the multiple configured patterns that corresponds to the changed SSB period, for example, using DCI or MAC CE. According to this method, the base station apparatus 101 notifies the terminal apparatus 111 of the setting change using DCI or MAC CE, which has a relatively small amount of data, without retransmitting SIB1, which includes many parameters, and therefore, signaling overhead can be reduced.

[0053] It should be noted that different Cell DRX parameters may be used in two mutually adjacent cells. For example, when the congestion level differs for each cell, different Cell DRX parameters may be configured for each cell according to the cell capacity required for each cell and notified to the terminal device. The terminal device may receive, for example, information about the serving cell and information about the neighboring cell from the base station device of the serving cell. In one example, the base station device of the serving cell may include configuration information about the Cell DRX of the neighboring cell in information about a candidate neighboring cell to which the destination cell is switched by LTM, and notify the terminal device of the information. This information may also be notified to the terminal device by SIB, DCI, MAC CE, or the like. Naturally, the same Cell DRX parameters may be used in the serving cell and the neighboring cell. In this case, by not including information specifying individual parameters related to the Cell DRX of the neighboring cell in the information about the neighboring cell, the terminal device may be implicitly notified that the Cell DRX parameters of the neighboring cell are the same as those of the serving cell. In one example, if the configuration information for a first neighboring cell includes Cell DRX parameters and the configuration information for a second neighboring cell does not include Cell DRX parameters, it may be indicated that Cell DRX parameters different from those of the serving cell are used in the first neighboring cell and that Cell DRX parameters identical to those of the serving cell are used in the second neighboring cell. Also, information explicitly indicating that the Cell DRX parameters of the neighboring cell are the same as (or different from) those of the serving cell may be included in the configuration information for the neighboring cells and transmitted to the terminal device.

[0054] In a neighboring cell, the period during which the base station device of the neighboring cell can receive a RAP transmitted by a terminal device may be a PRACH Occasion that is located within a Cell DRX Active period, among PRACH Occasions when Cell DRX is not activated. In this case, the terminal device may identify the frequency and time resource for transmitting the RAP by calculating the logical product of the Cell DRX Active period of the neighboring cell and the PRACH Occasion when Cell DRX is not activated. Note that the base station device may perform a logical product calculation and notify the terminal device of information about the period during which the base station device of the neighboring cell can receive the RAP. Furthermore, the base station device of the neighboring cell may set a period during the Cell DRX Non-Active period during which it receives a relatively small number of RAPs, and information about the period in this case may be notified as described above. The terminal device can operate to transmit a RAP during a period when a base station device of a neighboring cell can receive the RAP, for example, for HO or reconnection to a neighboring cell, or for establishing uplink synchronization before cell switching in LTM (early UL synchronization with an LTM candidate cell).

[0055] As described above, SSBs and PRACH Occasions may be associated with each other. This association may be determined in advance by a predetermined rule, but the rule may be dynamically changed. In this case, information indicating the relationship between the SSBs and PRACH Occasions may be notified to a terminal device by broadcast information such as an SIB or dedicated signaling such as a PDCCH. For example, an instruction indicating that a terminal device under the control of a beam of SSB #1 should use a PRACH Occasion associated with SSB #0 is transmitted from a base station device to the terminal device. This instruction may be transmitted from the base station device to the terminal device by an RRC message, an SIB, a DCI, or the like. Furthermore, for example, the rule may be dynamically changed depending on the traffic situation of the cell, and the identified PRACH Occasion may be enabled / disabled. For example, a setting may be made so that a terminal device under the beam of SSB #1 uses a PRACH Occasion associated with SSB #0, but the setting may be disabled (deactivation / release) or enabled (activation / setup) depending on the traffic situation. Note that, although the base station device cannot accurately count the number of idle terminals under the cell or SSB, it can estimate the number of terminal devices present in the area in a disconnected state using parameters such as UE Context Release Request, Number of UE Context Release, and Number of UE related to the SSB beam Index. Then, when the number of terminal devices connected or expected to be connected to the beam corresponding to each SSB or CSI-RS is zero (or is equal to or less than a predetermined threshold), the base station device can stop using the PRACH Occasion associated with that SSB or CSI-RS. That is, the base station device can disable the PRACH Occasion associated with that SSB or CSI-RS.

[0056] In this way, when Cell DRX is used in a network, it is possible to flexibly configure PRACH Occasions. Note that the state in which Cell DRX is used is one example, and for example, a configuration may be performed to increase the number of PRACH Occasions in a specific period. In other words, the above-described processing can be applied in any situation in which flexible configuration of PRACH Occasions is performed.

[0057] FIG. 7 shows an example of the hardware configuration of a base station device (base station device 101 and base station device 102) and a terminal device (terminal device 111) according to this embodiment. In one example, the base station device and the terminal device include a processor 701, a ROM 702, a RAM 703, a storage device 704, and a communication circuit 705. The processor 701 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 performs the overall processing of the device and each of the above-mentioned processes by reading and executing programs stored in the ROM 702 or the storage device 704. The ROM 702 is a read-only memory that stores information such as programs and various parameters related to the processing performed by the base station device and the terminal device. The RAM 703 functions as a workspace when the processor 701 executes a program and is also a random access memory that stores temporary information. The storage device 704 is, for example, a removable external storage device. The communication circuit 705 is configured, for example, by a circuit for wireless communication of 5G or a successor standard. While FIG. 7 illustrates one communication circuit 705, the base station device and the terminal device may have multiple communication circuits. For example, the base station device and the terminal device may have wireless communication circuits for 5G and a successor standard, respectively, and a common antenna for these circuits. The base station device and the terminal device may also 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 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 base station device and the terminal device may have separate communication circuits 705 for each of multiple available frequency bands, or may have a common communication circuit 705 for at least some of these frequency bands.

[0058] FIG. 8 shows an example of the functional configuration of a base station device. The base station device includes, for example, a setting notification unit 801, a usage setting instruction unit 802, and a communication control unit 803. Note that FIG. 8 only shows functions particularly related to this embodiment, and various other functions that the base station device may have are omitted from the illustration. For example, the base station device naturally has other functions that base station 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 701 executing a program stored in the ROM 702 or the storage device 704, or by a processor within the communication circuit 705 executing predetermined software. The details of the processing performed by each functional unit will not be described here, and only their general functions will be outlined.

[0059] The setting notification unit 801 notifies the terminal device of setting information regarding a period during which the base station device or another base station device providing a neighboring cell can receive a random access preamble (RAP). The setting notification unit 801 can identify the period by, for example, calculating the logical product of the period of a PRACH Occasion when Cell DRX is not activated and the active period of Cell DRX, and notify the terminal device of the period. The setting notification unit 801 can also notify the terminal device of information on a PRACH Occasion when Cell DRX is not activated and information on the active period of Cell DRX. The setting notification unit 801 may also notify the terminal device of the setting information in various formats as described above. The setting notification unit 801 may also notify the terminal device of, for example, two or more pieces of the setting information. For example, the setting notification unit 801 can notify the terminal device of setting information for the active period and non-active period of Cell DRX, and for each of the active period and non-active period of other predetermined communication control. The setting notification unit 801 can also receive setting information for other base station devices that provide neighboring cells from other base station devices, and provide the setting information to the terminal device. The setting notification unit 801 can notify the terminal device of the setting information using, for example, an RRC message, an SIB, or the like.

[0060] When two or more pieces of configuration information are notified to the terminal device, the usage setting instruction unit 802 transmits, to the terminal device, information instructing which of the pieces of configuration information to use. The usage setting instruction unit 802 transmits the instruction information to the terminal device using, for example, DCI or MAC CE. Note that it may be predetermined that the terminal device will use the two or more pieces of notified configuration information according to a predetermined rule, in which case the usage setting instruction unit 802 may be omitted. For example, the usage setting instruction unit 802 may be omitted when a rule is used that, when overlapping PRACH Occasions are specified in two pieces of configuration information, the PRACH Occasions are not used, or when a rule is used that all of the PRACH Occasions specified in any of the two or more pieces of configuration information are used.

[0061] The communication control unit 803 performs a process of detecting a RAP from the terminal device during a period in which the base station device can receive a RAP, which has been notified to the terminal device by the setting notification unit 801 (and in some cases the usage setting instruction unit 802), and when a RAP is detected, performs a connection process with the terminal device. Note that the setting notification unit 801 may set a resource in which a RAP can be received for each beam, and the communication control unit 803 may identify a beam selected by the terminal device based on the resource in which the RAP was detected, and perform control to establish a connection with the terminal device using that beam.

[0062] FIG. 9 shows an example of the functional configuration of a terminal device. The terminal device includes, for example, a setting acquisition unit 901, an instruction receiving unit 902, and a communication unit 903. Note that FIG. 9 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. 9 are shown only schematically, and the respective functional blocks may be integrated or further subdivided. Each function in FIG. 9 may be realized, for example, by the processor 701 executing a program stored in the ROM 702 or the storage device 704, or by a processor within the communication circuit 705 executing predetermined software. Details of the processes performed by each functional unit will not be described here, and only their general functions will be outlined.

[0063] The setting acquisition unit 901 acquires, from a base station device, setting information that enables identification of a period during which the base station device or another base station device providing a neighboring cell can receive a RAP. When the setting acquisition unit 901 receives multiple pieces of setting information, the instruction receiving unit 902 receives an instruction as to which of the pieces of setting information to use. Note that, when multiple pieces of setting information are received, rules for how to identify a period during which the base station device or another base station device can receive a RAP are predefined, and if no instruction as to which setting information to use is received, the instruction receiving unit 902 may be omitted. The communication unit 903 transmits a RAP in a frequency and time resource in which the base station device (or another base station device) identified based on the setting information acquired by the setting acquisition unit 901 (and, as necessary, instructed to use by the instruction receiving unit 902) can receive the RAP, thereby establishing a connection with the base station device (or another base station device).

[0064] An example of the flow of processing executed in a wireless communication system is shown in Fig. 10. Note that the example of Fig. 10 shows an example of a rough flow of processing executed, and the details and variations described above will not be repeated here.

[0065] In this process, the base station device transmits, to the terminal device, information that enables the base station device (or another base station device) to identify frequencies and time resources at which the RAP can be received, as configuration information related to the RA procedure (S1001). The base station device may notify the terminal device of multiple pieces of configuration information that enable the base station device (or another base station device) to identify frequencies and time resources at which the RAP can be received. The base station device transmits this configuration information to the terminal device via an RRC message (e.g., an RRC Reconfiguration message) or an SIB. Furthermore, if the base station device has transmitted multiple pieces of configuration information to the terminal device, the base station device may optionally transmit instruction information that instructs the terminal device which of the pieces of configuration information to use (S1002). The base station device may notify this instruction information via DCI or MAC CE. Note that, if rules for how to use multiple pieces of configuration information are defined in advance, S1002 may be omitted. In one example, the rules for how to use the multiple pieces of configuration information may be notified in S1001. Based on the configuration information received in S1001 (and, if necessary, based on the instruction received in S1002), the terminal device identifies the frequency and time resource at which the base station device (or another base station device) can receive the RAP (S1003). The terminal device may, for example, identify the frequency and time resource for each of multiple beams formed by the base station device. The terminal device then initiates the RA procedure by transmitting a RAP at the identified frequency and time resource, thereby establishing a connection with the base station device (S1004). To establish a connection with another base station device, the terminal device may identify the frequency and time resource at which the other base station device can receive the RAP, and transmit the RAP at the identified resource to establish a connection with the other base station device. The terminal device may also select a destination beam from among the beams formed by the base station device (or another base station device) according to a predetermined rule, such as a beam with a radio quality equal to or higher than a predetermined level, and transmit the RAP at the frequency and time resource identified in S1003 for that beam.The base station device can identify the beam to be used for establishing a connection and communicating with the terminal device depending on which frequency and time resource the RAP is detected in.

[0066] In this embodiment, a base station device notifies a terminal device of multiple pieces of configuration information, each of which can identify a frequency and time resource (PRACH Occasion) on which the base station device can receive the RAP. Then, for example, by using a DCI or MAC CE with a small amount of data, which of the multiple pieces of configuration information should be used thereafter, the base station device can flexibly change the configuration of the resource on which the base station device can receive the RAP while preventing a significant increase in signaling overhead. Furthermore, by causing the terminal device to use the multiple pieces of configuration information in accordance with a predetermined rule, the base station device can receive the RAP during a period when the RAP cannot be configured as a conventional PRACH Occasion. Furthermore, by using the predetermined rule, the base station device can flexibly configure the resource on which the base station device can receive the RAP while further reducing signaling overhead. In one example, when a base station device operates in an Active period and a Non-Active period of a predetermined communication control (e.g., Cell DRX), the base station device is notified of the switching between the Active period and the Non-Active period, and the terminal device changes the rule to be applied in response to the switching, thereby enabling the base station device to flexibly switch the configuration of resources in which the base station device can receive RAPs. Also, when the Active period and the Non-Active period of the predetermined communication control are alternately switched at a predetermined cycle, by notifying the terminal device in advance of the switching information, signaling at the time of the switching can be omitted, thereby making it possible to suppress signaling overhead.

[0067] As described above, in this embodiment, it is possible to flexibly apply settings related to the RACH procedure in a cellular communication system, thereby contributing to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0068] 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.

[0069] This application claims priority to U.S. Provisional Patent Application No. 63 / 572,636, filed April 1, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A base station device that complies with the cellular communication standard of the Third Generation Partnership Project (3GPP), and has a notification means for notifying a terminal device of multiple pieces of setting information that enable the base station device to identify periods during which the base station device can receive a random access preamble for a random access procedure from the terminal device.

2. A terminal device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: a receiving means for receiving from a base station device a plurality of pieces of setting information that enable each of the pieces of setting information to specify a period during which the base station device can receive a random access preamble for a random access procedure; a determining means for determining a frequency and time resource for transmitting the random access preamble to the base station device from the plurality of pieces of setting information; and an executing means for transmitting the random access preamble at the frequency and time resource to execute the random access procedure.

3. The terminal device according to claim 2, wherein the receiving means further receives instruction information from the base station device after receiving the plurality of pieces of setting information from the terminal device, the instruction information indicating which of the plurality of pieces of setting information should be used.

4. The terminal device according to claim 3, wherein the receiving means receives the plurality of pieces of configuration information by a Radio Resource Control (RRC) message or a System Information Block (SIB), and receives the instruction information by a Medium Access Control-Control Element (MAC CE) or Downlink Control Information (DCI).

5. The terminal device according to claim 2, wherein each of the plurality of pieces of configuration information includes a Physical Random Access Channel (PRACH) configuration index associated with a plurality of parameters.

6. The terminal device according to claim 5, further comprising: an acquisition means for acquiring, from the base station device, information defining a second PRACH configuration index different from a predefined first PRACH configuration index and a plurality of corresponding parameters.

7. The terminal device according to claim 6, wherein the acquisition means acquires information defining the second PRACH configuration index and the corresponding plurality of parameters in response to transmitting, to the base station device, information indicating that the terminal device has the capability to use a newly defined PRACH configuration index associated with a plurality of parameters.

8. A terminal device according to any one of claims 2 to 7, wherein the plurality of pieces of setting information include setting information when Cell Discontinuous Reception (DRX) is not activated in the base station device, and setting information when Cell DRX is activated in the base station device.

9. The terminal device according to any one of claims 2 to 7, wherein one of the plurality of pieces of setting information includes information on a period during which Cell Discontinuous Reception (DRX) is activated in the base station device, and information specifying a Physical Random Access Channel (PRACH) Occasion when Cell Discontinuous Reception (DRX) is not activated in the base station device.

10. A terminal device according to any one of claims 2 to 9, wherein each of the plurality of setting information further includes information indicating a frequency position at which the base station device can receive the random access preamble from the terminal device.

11. A terminal device described in any one of claims 2 to 10, further comprising a detection means for detecting beam failure in a beam used in communication with the base station device, and the execution means executes the random access procedure in response to the detection of the beam failure.

12. A control method executed by a base station device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising notifying a terminal device of multiple pieces of setting information that enable the base station device to specify periods during which a random access preamble for a random access procedure can be received from the terminal device.

13. A control method executed by a terminal device compliant with the 3rd Generation Partnership Project (3GPP) cellular communication standard, comprising: receiving, from a base station device, a plurality of pieces of configuration information each capable of specifying a period during which the base station device can receive a random access preamble for a random access procedure; determining, from the plurality of pieces of configuration information, a frequency and time resource for transmitting the random access preamble to the base station device; and transmitting the random access preamble on the frequency and time resource to execute the random access procedure.

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