TECHNICAL FIELD

The present invention relates to a radio communication system in which a radio station communicates with a radio terminal by using a plurality of cells.

BACKGROUND ART

In order to improve the deterioration of communication quality due to drastic increases in mobile traffic in recent years and achieve faster communication, the standardization of Carrier Aggregation (CA) functions that enable a radio terminal (User Equipment (UE)) to communicate with a radio base station (eNode B (eNB)) by using a plurality of cells has been undertaken in the 3GPP Long Term Evolution (LTE). Note that the cells that a UE (User Equipment) can use in CA are limited to a plurality of cells of one eNB (i.e., a plurality of cells served by one eNB).

The cells that are used by a UE in CA are categorized into a Primary Cell (PCell) that has already been used as a serving cell when the CA is started and a Secondary Cell(s) (SCell(s)) that is used in addition to the PCell or in dependence thereon. Each SCell can be used by a UE as the need arises, and the use of them can be stopped. Note that starting the use of an SCell is called “activating” or “activation”. Similarly, stopping the use of an SCell is called “deactivating” or “deactivation”. Non-Access Stratum (NAS) mobility information, security information (security input) and the like are transmitted and received through a PCell during radio connection (re)-establishment (RRC connection Establishment/Re-establishment) (see Non-patent Literature 1). A downlink (DL) Carrier and an uplink (UL) Carrier corresponding to a PCell are called “DL Primary Component Carrier (PCC)” and “UL PCC”, respectively. Similarly, a DL Carrier and a UL Carrier corresponding to a SCell are called “DL Secondary Component Carrier (SCC)” and “UL SCC”, respectively.

An operation that is performed to change a radio resource configuration (i.e., RRC information) in an SCell when downlink data (DL data) is transmitted/received in CA is explained with reference toFIG. 11(Non-patent Literature 2). Here, it is assumed that a UE uses a first cell (Cell1) and a second cell (Cell2) served by an eNB as a PCell and an SCell, respectively. In a step S1, the eNB transmits, to the UE, configuration information for the SCell (i.e., the Cell2) (RRC Connection Reconfiguration (SCell configuration)). In a step S2, the UE performs configuration of radio parameters and the like for the SCell (i.e., the Cell2) (SCell configuration). In a step S3, the UE reports the completion of the configuration of the SCell to the eNB (RRC Connection Reconfiguration Complete).

In a step S4, the eNB transmits to the UE an instruction about the start of the use (called “Activation”) of the SCell (Activation control element (activation of SCell)). In a step S5, the UE starts to use the SCell (SCell activation). In steps S6and S7, the eNB transmits DL data to the UE by using the PCell or the SCell, or both of them.

In a step S8, the eNB determines that it needs to change the radio resource configuration of the SCell (i.e., the Cell2) and hence transmits to the UE the configuration information related to the SCell that should be changed (RRC Connection Reconfiguration (SCell modification)). In a step S9, the UE updates the configuration of the SCell (SCell modification). In a step S10, the UE reports, to the eNB, the completion of the configuration change of the SCell (RRC Connection Reconfiguration Complete). Note that the eNB does not transmit DL data to the UE in the SCell (i.e., the Cell2) until the eNB receives the report of configuration change completion from the UE.

In steps S11and S12, the eNB transmits DL data to the UE by using the PCell or the SCell, or both of them.

A radio resource configuration of the SCell in the CA can be appropriately changed through the procedure shown inFIG. 11. Note that data transmission/reception is suspended while the eNB and the UE is configuring or updating radio parameters and the like by the RRC Connection Reconfiguration. For example, the eNB suspends DL data transmission to the UE and the UE suspends the DL data reception from the eNB.

CITATION LIST

Non Patent Literature

Non-patent Literature 1: 3GPP TS 36.300 V11.3.0, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 11)”, Section 7.5, September 2012Non-patent Literature 2: 3GPP TS 36.331 V11.2.0, “Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification (Release 11)”, Section 5.3.5.3, December 2012Non-patent Literature 3: 3GPP RWS-120046, Samsung Electronics, “Technologies for Rel-12 and Onwards”, 3GPP TSG RAN Workshop on Rel-12 and Onwards, Ljubljana, Slovenia, 11-12 Jun. 2012Non-patent Literature 4: 3GPP RWS-120010, NTT DOCOMO, “Requirements, Candidate Solutions & Technology Roadmap for LTE Rel-12 Onward”, 3GPP TSG RAN Workshop on Rel-12 and Onwards, Ljubljana, Slovenia, 11-12 Jun. 2012

SUMMARY OF INVENTION

Technical Problem

Further, inter-base station carrier aggregation (inter-eNB CA) in which cells of different radio base stations (eNBs) are simultaneously used has been proposed (Non-patent Literatures 3 and 4). For example, a cell of a macro base station (Macro eNB (MeNB)) and a cell of a low-power base station (Low Power Node (LPN)) are simultaneously used as a PCell and an SCell, respectively. In inter-base station (or inter-eNB) carrier aggregation, bearers are independently configured in the PCell and the SCell and communication is performed between an UE and the MeNB and between the UE and the LPN.

In the inter-eNB CA, it is also conceivable that the MeNB controls the configuration of radio parameters and the like of both the PCell and the SCell. However, for example, when the MeNB attempts to change radio parameters or the like of the SCell in a manner similar to that for ordinary CA (i.e., intra-eNB CA) when DL data is being transmitted in the SCell, the UE suspends the reception of the DL data in the SCell while the UE is changing radio parameters of the SCell under the instruction from the MeNB. Meanwhile, it is conceivable that the LPN that serves the SCell does not recognize that the UE is changing the radio parameter and thus continues to transmit the DL data. Accordingly, the transmission of the DL data that is performed when the UE is changing the radio parameter fails, thus possibly causing packet losses at the worst.

One of the objects of the present invention is to provide a radio communication system, a radio station, a radio terminal, a communication control method, and a program which are contribute to prevention or reduction of data transmission/reception failures which would otherwise occur while configuration of radio parameters or the like is being changed by a radio terminal in carrier aggregation of a plurality of cells served by different radio stations.

Solution to Problem

In a first aspect, a radio communication system includes a first radio station that serves a first cell, a second radio station that serves a second cell, and a radio terminal capable of performing carrier aggregation using the first and second cells. The first radio station is configured to perform, with the radio terminal, radio resource control for the first and second cells in order to perform the carrier aggregation. The first radio station is also configured to transmit, to the second radio station, update information regarding an update to a configuration related to the radio resource control for the second cell.

In a second aspect, a first radio station that serves a first cell includes a communication control unit. The communication control unit supports carrier aggregation using the first cell and a second cell served by a second radio station. The communication control unit performs, with a radio terminal, radio resource control for the first and second cells in order to perform the carrier aggregation. Further, the communication control unit transmits, to the second radio station, update information regarding an update to a configuration related to the radio resource control for the second cell.

In a third aspect, a second radio station that serves a second cell includes a communication control unit. The communication control unit supports carrier aggregation using a first cell served by a first radio station and the second cell. The communication control unit receives, from the first radio station, update information regarding an update to a configuration related to a radio resource control for the second cell. The radio resource control is performed between the first radio station and a radio terminal.

In a fourth aspect, a radio terminal includes a communication control unit that supports carrier aggregation using a first cell served by a first radio station and using a second cell served by a second radio station. The communication control unit performs, with the first radio station, radio resource control for the first and second cells in order to perform the carrier aggregation. Further, the communication control unit receives, from the first radio station, configuration information related to the radio resource control for the second cell.

In a fifth aspect, a communication control method in a first radio station that serves a first cell includes:

(a) performing, with a radio terminal, radio resource control for the first cell and a second cell served by a second radio station, in order to perform a carrier aggregation using the first and second cells; and

(b) transmitting, to the second radio station, update information regarding an update to a configuration related to the radio resource control for the second cell.

In a sixth aspect, a communication control method in a second radio station that serves a second cell includes receiving, from a first radio station, update information regarding an update to a configuration related to radio resource control for the second cell. The radio resource control is performed between the first radio station and a radio terminal for carrier aggregation using a first cell served by the first radio station and the second cell.

In a seventh aspect, a communication control method in a radio terminal includes performing, with a first radio station, radio resource control for a first cell served by the first radio station and a second cell served by a second radio station, in order to perform carrier aggregation using the first and second cells. Further, the performing includes receiving, from the first radio station, configuration information related to the radio resource control for the second cell.

In an eighth aspect, a program includes instructions for causing a computer to perform a communication control method according to the above-described fifth aspect.

In a ninth aspect, a program includes instructions for causing a computer to perform a communication control method according to the above-described sixth aspect.

In a tenth aspect, a program includes instructions for causing a computer to perform a communication control method according to the above-described seventh aspect.

Advantageous Effects of Invention

According to the above-described aspects, it is possible to provide a radio communication system, a radio station, a radio terminal, a communication control method, and a program which are contribute to prevention or reduction of data transmission/reception failures which would otherwise occur while the configuration of radio parameters or the like is being changed by a radio terminal in carrier aggregation of a plurality of cells served by different radio stations.

