# Patent

## Title
Mobile communication method and mobile station

## Abstract

A radio base station PhNB managing a phantom cell is enabled to uniquely identify a mobile station UE in communication in the phantom cell. A mobile communication method according to the present invention includes starting, by the radio base station PhNB#10, a “Non-contention based RA procedure” or a “Contention based RA procedure” with a mobile station UE#1 in communication in a cell #10 under control of the radio base station PhNB#10; and notifying, by the mobile station UE#1, the radio base station PhNB#10 of a C-RNTImacro which is allocated in a cell #1 other than the cell #10.

## Background
TECHNICAL FIELD
The present invention relates to a mobile communication method and a mobile station.
BACKGROUND ART
In LTE (Long Term Evolution), a radio base station eNB is configured to transmit/receive data to and from a mobile station UE performing communications in a cell under the control thereof, with a C-RNTI (Cell-Radio Network Temporary Identifier) allocated to the mobile station UE as illustrated in FIG. 4 (see, Non-patent document 1).
The C-RNTI is allocated on a cell-by-cell basis. In LTE, as illustrated in FIG. 4, a same C-RNTI cannot be allocated to a mobile station UE#1 and a mobile station UE#2 which perform communications in a same cell #A, and a same C-RNTI can be allocated to a mobile station UE#1 (or a mobile station UE#2) and a mobile station UE#3 which perform communications in different cells #A/#B.
Here, the C-RNTI is allocated in “Contention based RA (Random Access) Procedure” or a handover procedure.
In addition, the radio base station eNB is configured to assign resources for transmitting downlink data and uplink data by using the C-RNTI allocated to the mobile station UE.
Meanwhile, in the “Rel-12 workshop” of the 3GPP, many proposals on “Small cell enhancement” have been made as topics of FRA (Future Radio Access).
In such proposals, a concept of “Phantom cell” has been discussed.
As illustrated in FIG. 5, unlike a conventional macro cell, a phantom cell can cover a wider area by linking many “small cells” to form one large cell.
PRIOR ART DOCUMENT
Non-Patent Document


    Non-patent document 1: 3GPP TS36.300


SUMMARY OF THE INVENTION
However, as illustrated in FIG. 6, 65535 C-RNTIs are managed in each cell (a macro cell and a phantom cell), and one C-RNTI has to be allocated to each mobile station UE.
Here, when the coverage area of the phantom cell becomes wider, the number of mobile stations UE performing communications in the phantom cell increases. Accordingly, envisaged is a problem of causing a case in which the phantom cell may run out of C-RNTIs allocatable to the mobile stations UE.
In a conceivable operation for solving the above-described problem, as illustrated in FIG. 7, one C-RNTImacro is allocated to each mobile station UE in a macro cell, while one C-RNTIph is allocated to multiple (a plurality of) mobile stations UE in a phantom cell (in other words, one C-RNTIph is shared between the multiple mobile stations UE).
Meanwhile, according to the specifications of LTE, when a RA procedure is activated under the condition that a connection is already established between a mobile station UE and a radio base station eNB, a notification of a C-RNTI allocated to the mobile station UE with a “UL grant” designated by a “RA response” is sent in “C-RNTI MAC CE” to the radio base station eNB.
In such a case, the following problem occurs. Specifically, in a “Non-contention based RA procedure” or a “Contention based RA procedure,” even if the mobile station UE performing communications in a phantom cell notifies the radio base station PhNB managing the phantom cell of the C-RNTIph allocated in the phantom cell through the “C-RNTI MAC (Media Access Control) CE (Control Element)” as illustrated in FIG. 8, the radio base station PhNB cannot uniquely identify the mobile station UE.
For this reason, the present invention is made with view to the above-described problem, and has an objective to provide a mobile communication method and a mobile station, which enable a radio base station PhNB managing the phantom cell to uniquely identify a mobile station UE performing communications in a phantom cell.
A first feature of the present invention is summarized as a mobile communication method, including: starting, by a radio base station, a random access procedure with a mobile station being in communication in a cell under control of the radio base station; and notifying, by the mobile station, in the random access procedure, the radio base station of a cell identifier which is allocated in a cell other than the cell.
A second feature of the present invention is summarized as a mobile communication method, including: starting, by a radio base station, a random access procedure with a mobile station being in communication in a cell under control of the radio base station; and notifying, by the mobile station, in the random access procedure, the radio base station of a cell identifier which is allocated in a cell designated by the radio base station other than the cell.
A third feature of the present invention is summarized as a mobile station, including: a transmission unit configured to notify a radio base station of a cell identifier in a random access procedure if the random access procedure is started with the radio base station during communication in a cell under control of the radio base station, the cell identifier being an identifier allocated in a cell other than the cell.
A fourth feature of the present invention is summarized as a mobile station, including: a transmission unit configured to notify a radio base station of a cell identifier in a random access procedure if the random access procedure is started with the radio base station during communication in a cell under control of the radio base station, the cell identifier being an identifier allocated in a cell designated by the radio base station other than the cell.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an entire configuration diagram of a mobile communication system according to a first embodiment of the present invention.
FIG. 2 is a functional block diagram of a mobile station according to the first embodiment of the invention.
FIG. 3 is a diagram illustrating an example of a “C-RNTI MAC CE” which is transmitted by the mobile station according to the first embodiment of the invention.
FIG. 4 is a diagram for illustrating a conventional technology.
FIG. 5 is a diagram for illustrating the conventional technology.
FIG. 6 is a diagram for illustrating the conventional technology.
FIG. 7 is a diagram for illustrating the conventional technology.
FIG. 8 is a diagram for illustrating the conventional technology.



DETAILED DESCRIPTION
(Mobile Communication System According to the First Embodiment of the Present Invention)
Described by referring to FIGS. 1 to 3 is a mobile communication system according to a first embodiment of the present invention.
As illustrated in FIG. 1, a mobile communication system according to the present embodiment is an LTE mobile communication system, which includes a radio base station PhNB#10 configured to manage a cell #10, a radio base station eNB#1 configured to manage a cell #1, a radio base station eNB#2 configured to manage a cell #2, and a radio base station eNB#3 configured to manage a cell #3.
Here, the cell #10 is a phantom cell formed by linking multiple small cells and the cells #1 to #3 are macro cells.
As illustrated in FIG. 1, a coverage area of the cell #10 and coverage areas of the cells #1 to #3 are deployed to at least partially overlap each other.
Note that, it is configured in the mobile communication system according to the present embodiment that a same C-RNTIph can be allocated to multiple mobile stations UE in the cell #10.
On the other hand, the mobile communication system according to the present embodiment is configured such that a same C-RNTImacro cannot be allocated to multiple mobile stations UE in the cells #1 to #3.
It is configured in the mobile communication system according to the present embodiment that multiple C-RNTIs (in other words, C-RNTImacro and C-RNTIph) can be allocated to one mobile station UE.
The configurations of the mobile stations UE#1 to UE#3 are basically same with one another, and the description is mainly given below as the configuration of a mobile station UE.
As illustrated in FIG. 2, the mobile station UE according to the present embodiment includes a reception unit 11, a management unit 12, and a transmission unit 13.
The reception unit 11 is configured to receive various kinds of signals from the radio base stations PhNB#10/eNB#1/eNB#2/eNB#3. The transmission unit 13 is configured to transmit various kinds of signals to the radio base stations PhNB#10/eNB#1/eNB#2/eNB#3.
For example, the reception unit 11 is configured to receive a C-RNTImacro allocated to the mobile station UE from the radio base stations eNB#1 to eNB#3.
Also, the reception unit 11 is configured to receive a C-RNTIph allocated to the mobile station UE from the radio base station PhNB#10.
The management unit 12 is configured to manage C-RNTImacro and/or C-RNTIph which is allocated to the mobile station UE in each of the cells #1 to #3/#10.
Here, the transmission unit 13 notifies the radio base station PhNB#10 of a C-RNTImacro or the like which is allocated in a cell other than the cell #10 (for example, the cell #1) in the “RA procedure” when the “Non-contention based RA procedure” or “Contention based RA procedure” is started with the radio base station PhNB#10.
For example, the transmission unit 13 notifies the radio base station PhNB#10 of a C-RNTImacro or the like which is allocated in a cell other than the cell #10 by using a format of the “C-RNTI MAC CE” illustrated in FIG. 3.
In such a case, the transmission unit 13 may also notify the radio base station PhNB#10 of the C-RNTIph allocated in the cell #10.
In the format of “C-RNTI MAC CE” illustrated in FIG. 3, whether or not C-RNTIs are allocated in the cells C0 to C7 can be set in “C0” to “C7” and the C-RNTI allocated in a cell Ci (C0 to C7) can be set in “C-RNTI for Ci (C0 to C7).”
Alternately, whether or not the C-RNTIs allocated in the cells C0 to C7 are reported can be set in “C0” to “C7.”
In addition, the radio base station eNB notifies which of indexes “C0” to “C7” is associated with the cell set for the mobile station UE.
Such notification may be sent in any layer such as RRC layer, PDCP layer, RLC layer, MAC layer, and physical layer.
As illustrated in FIG. 8, in “Non-contention based RA procedure” or “Contention based RA procedure” with the radio base station PhNB#10, the transmission unit 13 notifies the radio base station PhNB#10 of the “C-RNTI MAC CE” on MSG3 (PUSCH corresponding to the “UL grant” designated by the “RA response”).
Here, the “Non-contention based RA procedure” or “Contention based RA procedure” is performed when an uplink synchronization loss occurs or in the handover processing, in other words, when the mobile UE is in the RRC Connected state.
The mobile communication system according to the present embodiment can acquire the C-RNTI allocated to the mobile station UE in other cell in addition to the C-RNTIph allocated to the mobile station UE in the cell #10 based on the “C-RNTI MAC CE” received from the mobile station UE. Thus, even when the same C-RNTIph is allocated to the multiple mobile stations UE in the cell #10, the mobile station UE performing communications in the cell #10 can be uniquely identified.
Also, in a case where the multiple C-RNTIs are allocated to the mobile station UE, when C-RNTIs equal to or more than the C-RNTIs which are needed to identify the mobile station UE by the radio base station eNB, are reported, an overhead becomes large. Thus, it is not desirable in terms of an efficiency of radio resource utilization.
Accordingly, the number of the C-RNTIs to be reported by the mobile station UE may be designated from the radio base station eNB.
The number of the C-RNTIs or for which cell the C-RNTI is to be reported may be notified in any layer such as RRC or PDCP layer, RLC layer, MAC layer, or Physical layer.
Also, the cell to be reported may be designated by an identifier of the cell (PCI: Physical Cell Identifier) or may be designated by Index of cell (for example, Scell Index) which is associated with the PCI.
The features of the present embodiment may also be expressed as follows.
A first feature of the present embodiment is summarized as a mobile communication method, including: starting, by a radio base station PhNB#10, a “Non-contention based RA procedure (non-contention based random access procedure)” or a “Contention based RA procedure (contention based random access procedure),” with a mobile station UE#1 being in communication in a cell #10 under control of the radio base station PhNB#10; and notifying, by the mobile station UE#1, in the “Non-contention based RA procedure” or the “Contention based RA procedure,” the radio base station PhNB#10 of a C-RNTImacro (cell identifier) which is allocated in a cell #1 other than the cell #10.
A second feature of the present embodiment is summarized as a mobile communication method, including: starting, by a radio base station PhNB#10, a RA procedure (random access procedure) with a mobile station UE#1 being in communication in a cell #10 under control of the radio base station PhNB#10; and notifying, by the mobile station UE, in the RA procedure, the radio base station PhNB#10 of a C-RNTI which is allocated in a cell designated by the radio base station PhNB#10 other than the cell #10.
A third feature of the present embodiment is summarized as a mobile station UE, including: a transmission unit 13 configured to notify a radio base station PhNB#10 of a C-RNTImacro in a “Non-contention based RA procedure” or a “Contention based RA procedure” if the “Non-contention based RA procedure” or the “Contention based RA procedure” is started with the radio base station PhNB#10 during communication in a cell #10 under control of the radio base station PhNB#10, the C-RNTImacro being an identifier allocated in a cell #1 other than the cell #10.
In the above-described example, the C-RNTImacro is described as the C-RNTI allocated in the cell #1 other than the cell #10. However, it is not limited to the C-RNTImacro but may be a C-RNTI which is allocated to the mobile station UE in a cell other than the cell #10.
A fourth feature of the present embodiment is summarized as a mobile station UE, including: a transmission unit 13 configured to notify a radio base station PhNB#10 of a C-RNTI in a RA procedure if the RA procedure is started with the radio base station PhNB#10 during communication in a cell #10 under control of the radio base station PhNB#10, the C-RNTI being an identifier allocated in a cell designated by the radio base station PhNB#10 other than the cell #10.
It should be noted that the foregoing operations of the mobile stations UE#1 to UE#3 and the radio base stations eNB#1/eNB#2/eNB#3/PhNB#10 may be implemented by hardware, may be implemented by a software module executed by a processor, or may be implemented in combination of the two.
The software module may be provided in a storage medium in any format, such as a RAM (Random Access Memory), a flash memory, a ROM (Read Only Memory), an EPROM (Erasable Programmable ROM), an EEPROM (Electronically Erasable and Programmable ROM), a register, a hard disk, a removable disk, or a CD-ROM.
The storage medium is connected to a processor so that the processor can read and write information from and to the storage medium. Instead, the storage medium may be integrated in a processor. The storage medium and the processor may be provided inside an ASIC. Such an ASIC may be provided in the mobile stations UE#1 to UE#3 and the radio base stations eNB#1/eNB#2/eNB#3/PhNB#10. Otherwise, the storage medium and the processor may be provided as discrete components inside the mobile stations UE#1 to UE#3 and the radio base stations eNB#1/eNB#2/eNB#3/PhNB#10.
Hereinabove, the present invention has been described in detail by use of the foregoing embodiments. However, it is apparent to those skilled in the art that the present invention should not be limited to the embodiments described in the specification. The present invention can be implemented as an altered or modified embodiment without departing from the spirit and scope of the present invention, which are determined by the description of the scope of claims. Therefore, the description of the specification is intended for illustrative explanation only and does not impose any limited interpretation on the present invention.
Note that the entire content of Japanese Patent Application No. 2012-188692 (filed on Aug. 29, 2012) is incorporated by reference in the present specification.
INDUSTRIAL APPLICABILITY
As described above, the present invention can provide a mobile communication method and a mobile station which enable radio base station PhNB managing a phantom cell to uniquely identify a mobile station performing communications in the phantom cell.
EXPLANATION OF REFERENCE NUMERALS


    eNB#1, eNB#2, eNB#3, PhNB#10 radio base station
    UE mobile station
    11 reception unit
    12 management unit
    13 transmission unit

## Claims

1. A mobile communication method, comprising:
starting, by a radio base station, a random access procedure with a mobile station being in communication in a cell formed by linking several small cells under control of the radio base station; and
notifying, by the mobile station, in the random access procedure, the radio base station of a cell radio network temporary identifier (C-RNTI) which is allocated in a macro cell other than the cell,
wherein a coverage area of the cell partially overlaps a coverage area of the macro cell.

2. A mobile communication method, comprising:
starting, by a radio base station, a random access procedure with a mobile station being in communication in a cell formed by linking several small cells under control of the radio base station; and
notifying, by the mobile station, in the random access procedure, the radio base station of a cell radio network temporary identifier (C-RNTI) which is allocated in a macro cell designated by the radio base station other than the cell,
wherein a coverage area of the cell partially overlaps a coverage area of the macro cell.

3. A mobile station, comprising:
a processor and memory; and
a transmitter that notifies a radio base station of a cell radio network temporary identifier (C-RNTI) stored in the memory in a random access procedure if the random access procedure is started with the radio base station during communication in a cell formed by linking several small cells under control of the radio base station, the C-RNTI being an identifier allocated in a macro cell other than the cell,
wherein a coverage area of the cell partially overlaps a coverage area of the macro cell.

4. A mobile station, comprising:
a processor and memory; and
a transmitter that notifies a radio base station of a cell radio network temporary identifier (C-RNTI) stored in the memory in a random access procedure if the random access procedure is started with the radio base station during communication in a cell formed by linking several small cells under control of the radio base station, the C-RNTI being an identifier allocated in a macro cell designated by the radio base station other than the cell,
wherein a coverage area of the cell partially overlaps a coverage area of the macro cell.