WO2014038295A1

WO2014038295A1 - Base station, wireless communication system and method

Info

Publication number: WO2014038295A1
Application number: PCT/JP2013/069534
Authority: WO
Inventors: 徹内野; 耕平清嶋
Original assignee: 株式会社エヌ・ティ・ティ・ドコモ
Priority date: 2012-09-06
Filing date: 2013-07-18
Publication date: 2014-03-13
Also published as: JP2014053726A; JP6038556B2

Abstract

An aspect of the present invention relates to a base station, which comprises: a signal transmitting/receiving unit that communicates wireless signals with a user apparatus; a cell managing unit that manages a primary cell and one or more secondary cells to be allocated to the user apparatus so as to communicate the wireless signals; and a validity determining unit that determines whether feedback information received from the user apparatus is valid. When the cell managing unit determines that a secondary cell having been set in the user apparatus has been activated in response to an event that the cell managing unit instructs the user apparatus to cause the secondary cell to transition to the active state, the cell managing unit monitors feedback information from the secondary cell. If feedback information having been regarded, by the validity determining unit, as valid is not received within a predetermined time interval, the cell managing unit determines that the secondary cell is in the inactive state.

Description

Base station, radio communication system and method

The present invention relates to wireless communication technology, and more particularly, to wireless communication using carrier aggregation.

Currently, 3GPP (3rd Generation Partnership Project) is standardizing LTE-A (Long Term Evolution-Advanced) as the next generation communication standard of LTE (Long Term Evolution). In the LTE-A system, a carrier aggregation (CA) technology is introduced in order to achieve a throughput that exceeds the LTE system while ensuring backward compatibility with the LTE system. In carrier aggregation technology, an LTE carrier (also referred to as a component carrier) having a maximum bandwidth of 20 MHz supported by the LTE system is used as a basic component, and by using these multiple component carriers at the same time, wider bandwidth communication is possible. It is intended to be realized.

In carrier aggregation, for example, the arrangement of component carriers as shown in FIG. 1 is assumed. In Case 1, two adjacent 20 MHz bands can be used as a 40 MHz band by carrier aggregation. Case 1 is effectively used in a case where a continuous band larger than 20 MHz can be secured, and can achieve a throughput higher than that of the LTE system while ensuring backward compatibility with the LTE system. In case 2, two 10 MHz bands separated from each other can be used as a 20 MHz band by carrier aggregation. Case 2 is effectively used when the frequency band allocation to the operator is fragmented, and can achieve a throughput higher than that of the LTE system while ensuring backward compatibility with the LTE system. .

In carrier aggregation, a user equipment (User Equipment: UE) can communicate with a base station (evolved NodeB: eNB) using a plurality of component carriers simultaneously. In carrier aggregation, a highly reliable primary cell (Primary Cell: Pcell) that ensures connectivity with user equipment and a secondary cell (Secondary Cell: Scell) that is additionally set in the user equipment connected to the primary cell And are set. For example, in the specific example shown in FIG. 1, one of the two component carriers may be set as a primary cell and the other may be set as a secondary cell.

The primary cell is a cell similar to the LTE system, and is a cell for ensuring connectivity between the user apparatus and the network. That is, in the primary cell, a user equipment, PDCCH (Physical Downlink Control Channel) and receives the PDSCH (Physical Downlink Shared Channel), PUCCH (Physical Uplink Control Channel), PUSCH (Physical Uplink Shared Channel) and PRACH (Physical Random Access (Channel) can be transmitted. Moreover, when changing a primary cell, the user apparatus needs to perform a handover.

On the other hand, the secondary cell is a cell that is added to the primary cell and set in the user apparatus. The addition and deletion of the secondary cell are executed by RRC (Radio Resource Control) configuration. In the secondary cell, the user apparatus does not transmit PUCCH and PRACH. In addition, immediately after the secondary cell is set in the user apparatus, it is in an inactive state, and communication or scheduling is possible only when it is activated in the MAC (Medium Access Control) layer. For this reason, in order to make the set secondary cell in a communicable state, that is, in a schedulable state, it is necessary to change the secondary cell to the active state.

In the currently studied LTE-A system, in order to transition the secondary cell to an active state and an inactive state, as shown in FIG. 2, the base station transmits a MAC CE (Control Element) to the user equipment in the MAC layer. By transmitting, the user equipment is instructed to activate / deactivate the set secondary cell. When receiving the explicit state transition instruction, the user apparatus transitions the secondary cell to the instructed state.

Further, when receiving the MAC CE for activating the secondary cell from the base station, the user apparatus activates the secondary cell and activates the Scell Deactivation Timer. On the other hand, the base station also activates the Scell Deactivation Timer at the timing when the MAC CE is transmitted or when a delivery confirmation (ACK) for the MAC CE is received from the user apparatus. That is, the base station and the user apparatus hold their own Scell Deactivation Timer and manage the state of the activated secondary cell. After the Scell Deactivation Timer is activated, when the base station schedules a new radio resource to the user apparatus in the secondary cell, the base station and the user apparatus restart their Scell Deactivation Timer. After that, when the Scell Deactivation Timer expires or receives an explicit state transition instruction for deactivating the secondary cell from the base station, the user apparatus transitions the secondary cell to the inactive state. The base station also deactivates the secondary cell when the Scell Deactivation Timer managed for the secondary cell expires or receives a notification from the user device that the secondary cell is deactivated. The radio resource scheduling to the user apparatus in the secondary cell is stopped. In this way, it is possible to match the active state / inactive state of the secondary cell between the base station and the user apparatus.

For further details, refer to, for example, 3GPP TS 36.300 V 10.7.0 (2012-03).

However, as shown in FIG. 3, the MAC CE transmitted from the base station in order to activate the set secondary cell is not properly received by the user apparatus, and the base station may not be able to receive this due to noise or interference. If it is erroneously determined that an ACK has been received from the user equipment for the transmitted MAC CE (NACK / DTX → ACK error), the user equipment keeps the secondary cell in an inactive state, while the base station has the secondary cell active It will be mistaken for transition to the state. That is, a mismatch between the active state / inactive state of the secondary cell occurs between the base station and the user apparatus. In this case, as shown in FIG. 3, since the base station misidentifies that the secondary cell is in an active state, the radio resource of the secondary cell is scheduled to the user apparatus, and the radio resource is wasted. Will be.

Such a state mismatch of the secondary cell between the base station and the user apparatus is resolved by expiration of the Scell Deactivation Timer. However, the state mismatch continues until the expiration of the Scell Deactivation Timer, and radio resources of the secondary cell continue to be wasted. This is undesirable from a resource saving perspective.

In addition, it is specified that the mobile station feeds back CSI (Channel State Information) to the activated secondary cell. CSI is normally fed back to the base station by PUCCH (Physical Uplink Control Channel) in the primary cell. However, if PUSCH (Physical Uplink Channel) is assigned at the transmission timing of CSI, the PUSCH is assigned to the PUSCH. It is also stipulated that CSI be piggybacked. When a secondary cell state mismatch occurs between the base station and the mobile station, the base station performs a decoding process assuming that CSI is piggybacked during PUSCH reception, while the mobile station performs piggybacking. Therefore, PUSCH decoding processing based on appropriate rate matching cannot be performed and decoding cannot be performed into a normal signal, and thus stable communication cannot be provided.

In view of the above problems, an object of the present invention is to provide a technique for quickly resolving a state mismatch of secondary cells between a base station and a user apparatus.

In order to solve the above problems, an aspect of the present invention includes a signal transmission / reception unit that communicates a radio signal with a user apparatus, a primary cell that is allocated to the user apparatus to communicate the radio signal, and one or more secondary cells. A base station having a cell management unit to manage and a validity determination unit that determines whether feedback information received from the user apparatus is valid, wherein the cell management unit is a secondary cell set in the user apparatus If the secondary cell is determined to be activated in response to instructing the user apparatus to transition to an active state, the feedback information from the secondary cell is monitored and determined to be valid by the validity determination unit. If the received feedback information is not received within a predetermined period, the secondary cell A base station that is determined to be a blanking state.

According to the present invention, it becomes possible to quickly resolve the state mismatch of the secondary cell between the base station and the user apparatus.

FIG. 1 is a diagram schematically illustrating carrier aggregation. FIG. 2 is a diagram schematically illustrating an operation example of the Scell Deactivation Timer. FIG. 3 is a diagram schematically showing a state mismatch of the Scell Deactivation Timer. FIG. 4 is a diagram schematically illustrating a process of eliminating Scell state mismatch according to an embodiment of the present invention. FIG. 5 is a diagram schematically illustrating a wireless communication system according to an embodiment of the present invention. FIG. 6 is a block diagram illustrating a configuration of a base station according to an embodiment of the present invention. FIG. 7 is a flowchart showing a process for eliminating a state mismatch according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In the embodiments disclosed below, a wireless communication system capable of using carrier aggregation will be described. In carrier aggregation, a base station (evolved NodeB: eNB) is added as needed after a primary cell for maintaining communication connection with a user equipment (User Equipment: UE) and a connection to the primary cell by the user equipment. Secondary cell. When the base station instructs the user apparatus to transition the secondary cell assigned to the user apparatus to the active state and receives an acknowledgment (ACK) from the user apparatus, the base station recognizes that the secondary cell has transitioned to the active state. . However, if the instruction is not received by the user apparatus for some reason, and if the base station determines that an ACK has been received from the user apparatus due to noise or interference (NACK / DTX → ACK error), the base station and the user apparatus Between the active states of the secondary cell.

In an embodiment to be described later, in order to resolve this discrepancy, the base station monitors the feedback information transmitted from the active secondary cell periodically or according to an instruction from the base station within a predetermined period. If it is not possible to receive valid feedback information, it is determined that the secondary cell has not transitioned to the active state and is in an inactive state.

That is, as shown in FIG. 4, the base station first transmits a MAC CE for transitioning the secondary cell allocated to the user apparatus to the active state. At this time, it is assumed that the user apparatus cannot receive the MAC CE for some reason such as deterioration of the communication state, and the secondary cell is not shifted to the active state. Further, it is assumed that the base station determines that the user apparatus has received ACK from the user apparatus due to the influence of noise or interference, even though the user apparatus has not transmitted ACK to the MAC CE (NACK / DTX → ACK error). In this case, the base station will mistakenly recognize that the secondary cell has transitioned to the active state, and a mismatch in the active state of the secondary cell will occur between the base station and the user apparatus.

In order to quickly resolve this discrepancy, the base station monitors feedback information such as CQI (Channel Quality Indicator) and SRS (Sounding Reference Symbol) that should be periodically reported from the active secondary cell in a predetermined period. If the feedback information is not received within the period, or if the feedback information is not valid even if received, the secondary cell has not transitioned to the active state and is in an inactive state Change the perception. As a result, in the secondary cell that the base station misidentifies as being in the active state, it is possible to quickly eliminate the situation of scheduling radio resources to the user apparatus, and it is possible to avoid waste of radio resources.

First, a radio communication system according to an embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram schematically illustrating a wireless communication system according to an embodiment of the present invention.

As shown in FIG. 5, the wireless communication system 10 is a wireless communication system that realizes wireless communication using carrier aggregation, such as an LTE-A (Long Term Evolution Advanced) system. The radio communication system 10 includes a base station (eNB) 100 and one or more user apparatuses (UE) 200. Typically, the user apparatus 200 may be any appropriate user apparatus having a wireless communication function such as a mobile phone or a smartphone as illustrated.

The base station 100 wirelessly connects to the user apparatus 200, thereby transmitting downlink (DL) data received from a communication-connected upper station or server (not shown) to the user apparatus 200 and from the user apparatus 200. The received uplink (UL) data is transmitted to an upper station (not shown). In a typical hardware configuration, the base station 100 has a CPU (Central Processing Unit) such as a processor, a memory device such as a RAM (Random Access Memory), an auxiliary storage device such as a hard disk device, and a communication for communicating radio signals. It comprises an interface device for exchanging various data and / or instructions with a device, a host station, an external server, an operator, and the like. Each function of the base station 100 to be described later loads data and programs stored in the auxiliary storage device to the memory device via the communication device and / or the interface device, and the CPU processes the data according to the loaded program. It is realized by.

Next, a configuration of a base station according to an embodiment of the present invention will be described with reference to FIG. FIG. 6 is a block diagram illustrating a configuration of a base station according to an embodiment of the present invention.

As illustrated in FIG. 6, the base station 100 includes a DL signal transmission unit 110, a UL signal reception unit 120, a cell management unit 130, and a feedback information validity determination unit 140.

The DL signal transmission unit 110 transmits a radio signal including a data signal and / or a control signal to the user apparatus 200 via the primary cell and / or the secondary cell. For example, the DL signal transmission unit 110 converts data provided from the server in response to a request from the user apparatus 200 into a radio signal and transmits the radio signal to the requesting user apparatus 200. Also, the DL signal transmission unit 110 converts control information such as scheduling information and various signaling necessary for wireless communication with the user apparatus 200 into a radio signal, and transmits the radio signal to the user apparatus 200.

The UL signal receiving unit 120 receives a radio signal including a data signal and / or a control signal from the user apparatus 200 via the primary cell and / or the secondary cell. For example, when the user apparatus 200 transmits a data signal using radio resources of the assigned primary cell and / or secondary cell, the UL signal reception unit 120 transfers the received data signal to a transmission destination server. In addition, when the user apparatus 200 transmits a control signal using radio resources of the assigned primary cell and / or secondary cell, the UL signal reception unit 120 uses the received control signal for subsequent communication, and / Or forward to higher station.

The cell management unit 130 manages a primary cell and one or more secondary cells that the base station 100 can provide. A primary cell (Primary Cell: Pcell) is a highly reliable cell that ensures connectivity with the user apparatus 200, and the user apparatus 200 needs to execute a handover when changing the primary cell. The secondary cell (Secondary Cell: Scell) is a cell that is added to the primary cell and set in the user apparatus 200. The addition and deletion of the secondary cell is performed by RRC configuration.

The secondary cell is in an inactive state immediately after being set in the user apparatus 200 by the RRC configuration. For this reason, in order to make the set secondary cell in a communicable state, that is, in a schedulable state, it is necessary to change the secondary cell to the active state. For example, in the LTE-A system, in order to transition the secondary cell to the active state and the inactive state, the base station 100 transmits the MAC CE to the user apparatus 200 in the MAC layer, thereby changing the user apparatus 200 to the active state / Transition to inactive state.

Further, when receiving the MAC CE for activating the secondary cell from the base station 100, the user apparatus 200 activates the secondary cell and deactivates the secondary cell when the timer expires. Start the Scell Deactivation Timer, which is a timer. On the other hand, when the base station 100 also receives a delivery confirmation (ACK) for the MAC CE from the user apparatus 200 or transmits a MAC CE to the user apparatus 200, the base station 100 determines that the secondary cell is activated and performs Scell Deactivation. Start Timer. That is, the base station 100 and the user apparatus 200 hold their own Scell Deactivation Timer and manage the state of the activated secondary cell. After the Scell Deactivation Timer is activated, when the cell management unit 130 schedules a new radio resource in the user cell to the user apparatus, the cell management unit 130 and the user apparatus 200 reset their Scell Deactivation Timer and restart. Thereafter, when the Scell Deactivation Timer expires or when an explicit state transition instruction for deactivating the secondary cell is transmitted from the base station 100 to the user apparatus 200, the user apparatus 200 selects the secondary cell. The base station 100 also transitions to the inactive state, and the secondary cell is also deactivated by receiving an ACK for the expiration of the Scell Deactivation Timer managed for the secondary cell or the state transition instruction. Recognize and stop scheduling to the user apparatus 200 in the secondary cell.

When the cell management unit 130 receives an ACK for the MAC CE for activating the secondary cell transmitted to the user apparatus 200 from the user apparatus 200 (or transmits the MAC CE), the cell management unit 130 is periodically reported from the user apparatus 200. The feedback information for the secondary cell is monitored. This is because feedback information such as CQI and SRS is periodically reported from the user apparatus 200 for the active secondary cell, or feedback is reported according to an instruction from the base station. When the cell management unit 130 cannot receive feedback information from the user apparatus 200 within a predetermined period after receiving the ACK from the user apparatus 200 (or transmitting the MAC CE), the secondary cell is in an active state. It is determined that it is in an inactive state.

Furthermore, when the cell management unit 130 receives feedback information from the secondary cell within the predetermined period, the cell management unit 130 transmits the received feedback information to the feedback information validity determination unit 140, and the feedback information is not noise or interference. To determine whether the feedback information is valid. When the feedback information validity determination unit 140 determines that the feedback information is valid, the cell management unit 130 determines that the secondary cell is in an active state, and the secondary information is transmitted between the base station 100 and the user apparatus 200. It is determined that the cell states match. On the other hand, when the feedback information validity determination unit 140 determines that the feedback information is not valid, the cell management unit 130 continues to monitor further feedback information until a predetermined period elapses. In this way, the cell management unit 130 monitors the feedback information from the secondary cell in a predetermined period, and the feedback information determined to be valid by the feedback information validity determination unit 140 cannot be received within the predetermined period. If it is determined that the secondary cell is in an inactive state.

When determining that the secondary cell is in an inactive state, the cell management unit 130 stops the Scell Deactivation Timer, instructs the secondary cell to activate again, and / or inactivates the secondary cell. It may be possible to instruct the conversion.

The predetermined period may be set according to the frequency of reporting feedback information when the secondary cell is in an active state, for example. As an example, the predetermined period may be set to a period corresponding to a predetermined reporting opportunity of feedback information. Note that the shorter the period is set, the earlier the state mismatch between the base station 100 and the user apparatus 200 can be resolved. On the other hand, when the period is set to be short, even if the secondary cell appropriately transitions to the active state in response to the state transition instruction from the base station 100, that is, the base station 100 and the user apparatus 200 Even if the status recognition of the secondary cell is consistent with the cell management unit 130, the cell management unit 130 appropriately transitions to the active state due to the temporary reception failure of the feedback information due to the deterioration of the communication state within the period. There is a possibility that the secondary cell is mistaken as an inactive state and a state mismatch occurs. On the other hand, when the period is set to be long, the possibility of such misidentification can be reduced, but the state mismatch between the base station 100 and the user apparatus 200 due to the NACK / DTX → ACK error in the base station 100 can be quickly performed. It cannot be resolved. Therefore, in consideration of the balance between the former case in which the secondary cell that has appropriately transitioned to the active state is misidentified as an inactive state and the latter case in which misperception due to NACK / DTX → ACK error is prolonged, It is preferable to set the period. For example, in order to avoid the former case, when the cell management unit 130 determines that the secondary cell is in an inactive state, the cell management unit 130 transmits a MAC CE for deactivating the secondary cell to the user apparatus 200, and You may make it aim at the state agreement of the said secondary cell between the station 100 and the user apparatus 200. FIG. Alternatively, if the cell management unit 130 determines that the secondary cell is in an inactive state, the cell management unit 130 may retransmit the MAC CE for activating the secondary cell to the user apparatus 200 and try to activate the secondary cell again. Good.

The feedback information validity determination unit 140 determines whether the feedback information received from the user device 200 is valid. This validity determination is not based on the quality of the content of the feedback information itself, but based on whether the feedback information is transmitted for feedback from the user apparatus 200, not noise or interference. It is. Specifically, when the feedback information is the channel state information (CQI or the like) of the secondary cell, the feedback information validity determination unit 140 does not determine the validity of the feedback information based on the quality of the channel state information, The validity of the feedback information is determined based on the received power state of the channel state information in the UL signal receiving unit 120 and the received power state such as SIR (Signal to Interference Ratio). That is, when the index (reception power level, SIR value, etc.) indicating the reception power state of the feedback information is higher than a predetermined threshold, the feedback information validity determination unit 140 determines that the feedback information is valid, and does not In this case, it may be determined that the feedback information is not valid. For this reason, even if the value of the channel state information received from the user apparatus 200 is outside the range of values indicating a good channel state, the received power level of the received feedback information is a received power level that can be reliably determined as not noise. As long as the feedback information validity determination unit 140 determines that the feedback information is valid. After executing the validity determination of the feedback information received from the cell management unit 130, the feedback information validity determination unit 140 notifies the cell management unit 130 of the determination result of the validity of the feedback information.

Next, with reference to FIG. 7, a process for eliminating the state mismatch of the secondary cells according to an embodiment of the present invention will be described. FIG. 7 is a flowchart showing a process for eliminating a state mismatch according to an embodiment of the present invention.

As shown in FIG. 7, in step S <b> 101, the cell management unit 130 instructs to activate the secondary cell set in the user apparatus 200. For example, the cell management unit 130 instructs the DL signal transmission unit 110 to transmit a MAC CE for activating the secondary cell to the user apparatus 200, and receives an ACK to the MAC CE (or the MAC It is determined that the secondary cell has been activated.

In step S102, the cell management unit 130 determines whether feedback information has been received from the user apparatus 200 within the predetermined period in the secondary cell. When the feedback information is received within the predetermined period (S102: YES), the flow proceeds to step S103, and the cell management unit 130 determines whether the received feedback information is valid or the feedback information validity determination unit 140. Let me determine. On the other hand, when the feedback information is not received within the predetermined period (S102: NO), the flow moves to step S105, and the cell management unit 130 does not transition the active state to the secondary cell. Judged to be active. In this case, the cell management unit 130 may stop the Scell Deactivation Timer, instruct the secondary cell to activate again, and / or instruct the secondary cell to deactivate. Good.

In step S103, the feedback information validity determination unit 140 determines whether the feedback information received from the cell management unit 130 is valid. Specifically, the feedback information validity determination unit 140 determines the validity of the feedback information based on the reception power of the feedback information in the UL signal reception unit 120 and the received power state such as SIR. If the feedback information is valid (S103: YES), the flow moves to step S104, and the cell management unit 130 determines that the secondary cell is in an active state. On the other hand, when the feedback information is not valid (S103: NO), the flow returns to step S102, and the cell management unit 130 determines the feedback information received from the secondary cell until the valid feedback information is received. Monitor during the period.

As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the specific embodiment mentioned above, In the range of the summary of this invention described in the claim, various deformation | transformation・ Change is possible.

This international application claims priority based on Japanese Patent Application No. 2012-196184 filed on September 6, 2012, and the entire contents of 2012-196184 are incorporated herein by reference.

10 radio communication system 100 base station 110 DL signal transmission unit 120 UL signal reception unit 130 cell management unit 140 feedback information validity determination unit 200 user apparatus

Claims

A signal transmission / reception unit for communicating a radio signal with the user apparatus;
A cell management unit for managing a primary cell and one or more secondary cells allocated to the user apparatus for communicating the radio signal;
An effectiveness determination unit that determines whether feedback information received from the user device is valid;
A base station having
When the cell management unit determines that the secondary cell is activated in response to instructing the user apparatus to transition the secondary cell set in the user apparatus to an active state, feedback from the secondary cell A base station that monitors information and determines that the secondary cell is in an inactive state when feedback information determined to be valid by the validity determination unit is not received within a predetermined period.
The base station according to claim 1, wherein the validity determination unit determines whether the feedback information is valid based on a reception power state of the feedback information received by the signal transmission / reception unit.
The cell management unit has received a delivery confirmation from the user apparatus in response to instructing the user apparatus to transition a secondary cell set in the user apparatus to an active state, or has performed the instruction The base station according to claim 1, wherein it is determined that the secondary cell has been activated.
The base station according to claim 1, wherein the cell management unit stops a deactivation timer managed for the secondary cell when it is determined that the secondary cell is in an inactive state.
The base station according to claim 1, wherein the cell management unit re-instructs the secondary cell to activate when determining that the secondary cell is in an inactive state.
The base station according to claim 1, wherein the cell management unit instructs the secondary cell to be deactivated when it is determined that the secondary cell is in an inactive state.
The base station communicates with the user equipment using carrier aggregation;
The primary cell is a cell for maintaining a communication connection with the user equipment,
The base station according to claim 1, wherein the secondary cell is a cell assigned in addition to the primary cell.
A user device;
A base station in communication connection with the user equipment;
A wireless communication system comprising:
The base station
A signal transmission / reception unit for communicating a radio signal with the user device;
A cell management unit for managing a primary cell and one or more secondary cells allocated to the user apparatus for communicating the radio signal;
An effectiveness determination unit that determines whether feedback information received from the user device is valid;
A base station having
When the cell management unit determines that the secondary cell is activated in response to instructing the user apparatus to transition the secondary cell set in the user apparatus to an active state, feedback from the secondary cell A wireless communication system that monitors information and determines that the secondary cell is in an inactive state when feedback information determined to be valid by the validity determination unit is not received within a predetermined period.
A method in a base station for communication connection with a user apparatus via a primary cell and one or more secondary cells,
Instructing the user device to transition a secondary cell set in the user device to an active state;
Monitoring feedback information from the secondary cell determined to have been activated in response to the instruction;
Determining that the secondary cell is in an inactive state if feedback information determined to be valid is not received within a predetermined period of time;
Having a method.