WO2013046282A1

WO2013046282A1 - A method and apparatus for reestablishment control in a mobilecommunications system

Info

Publication number: WO2013046282A1
Application number: PCT/JP2011/005539
Authority: WO
Inventors: Hong Tat Toh
Original assignee: Panasonic Corp
Current assignee: Panasonic Corp
Priority date: 2011-09-30
Filing date: 2011-09-30
Publication date: 2013-04-04
Anticipated expiration: 2014-03-30

Abstract

Mobile Terminal in a heterogeneous environment to remove extra operation in the needs to proceed to idle mode and trigger connection establishment procedure is presented. In addition, to avoid unnecessary re-attempt re-establishment is presented. Communication system (300) comprises a first base station (108) for providing a macro cell (102), a second base station (304) for providing a pico cell (302) within the coverage of the macro cell (102), and a mobile terminal (114). The mobile terminal (114) comprises a transceiver configured to connect radio link with the first base station (108) and with the second base station (304) and a reestablishment control unit configured to reestablish radio link via RRC (radio resource control) connection procedure with the first base station (108) after disconnecting radio link with the second base station (304).

Description

A METHOD AND APPARATUS FOR REESTABLISHMENT CONTROL IN A MOBILECOMMUNICATIONS SYSTEM

This invention pertains to mobile communications network. More specifically, it relates to re-attempt re-establishment procedure after the selected cell to perform re-establishment becomes non-suitable. Such re-attempt procedure should enable Mobile Terminal in heterogeneous environment to recover connection faster in a mobile communication system.

In a mobile communication system (e.g. 3GPP Long-term Evolution, LTE Advanced), a Mobile Terminal has the capability to recover connection based on recovery procedures. This recovery capability is known as Re-establishment or NAS (non-access stratum) Recovery. Both Re-establishment and NAS Recovery procedures are used to recover connection upon connection failure.

As illustrate in Figure 1, a mobile communication system (100) in a homogeneous environment is presented. The Mobile Terminal (114) is located near the cell edge of Base Station (108). Due to bad radio reception, the Mobile Terminal (114) encounters radio link failure such that the Mobile Terminal (114) will start cell selection procedure. Upon a suitable cell (e.g. Base Station 110) is selected, the Mobile Terminal (114) will trigger re-establishment procedure. To assure successful re-establishment, the suitable cell that is selected by the Mobile Terminal (114) should be one of the cells under the Base Station in which Mobile Terminal context is stored i.e. prepared cell. Otherwise re-establishment procedure will be failed. Upon prepared cell is selected and perform Re-establishment procedure successfully, the Mobile Terminal (114) can recover connection with Base Station (110). In the event the prepared cell become non-suitable (i.e. cell selection criteria is not met), the Mobile Terminal (114) will encounter re-establishment failure. Thus, the Mobile Terminal (114) will disconnect the connection with Base Station (110) and proceed to idle mode. In this case, the Mobile Terminal (114) will then trigger NAS Recovery procedure. For NAS Recovery procedure, the Mobile Terminal (114) will perform an establishment procedure in order to recover the connection with the Base Station.

As illustrate in Figure 2, upon the Mobile Terminal (114) in connected mode encounter radio link failure as in step 202, the Mobile Terminal (114) will start to search for suitable cell to camp on (204). Upon a suitable cell is detected, the Mobile Terminal (114) will select that cell to camp on (206). For example, as illustrate in Figure 1, Base Station (110) which covers a macro cell (106) is selected by Mobile Terminal (114).

Upon a suitable cell is selected, the Mobile Terminal (114) will send RRC Connection Reestablishment Request (208). However, upon the Mobile Terminal (114) detect the selected cell (i.e. Base Station (110)) becomes non-suitable due to cell selection criteria, similar to that specified in {NPL 3}, is not met (210) before the reception of the response (212), the Mobile Terminal (114) will not reattempt re-establishment procedure and consider re-establishment has failed. This is because in homogeneous environment as illustrated in Figure 1, to select another cell for re-establishment is likely to select non-prepared cell i.e. another Base Station, in which Re-establishment Request will be responded by Re-establishment Reject i.e. another re-establishment is likely to be failed.

In this case after selected cell for re-establishment becomes non-suitable, the Mobile Terminal (114) will consider re-establishment failure, and establishes RRC (radio resource control) connection again i.e. NAS Recovery procedure (218, 220, 222). Compared to re-establishment procedure, NAS recovery involves more signaling load and involves packet loss, while it can recover connection at any cell regardless the cell is prepared or not (i.e. cell under Base Station in which Mobile Terminal Context is stored, or cell NOT under the Base Station).

3GPP TS23.401 SAE 3GPP TS36.331 RRC Protocol 3GPP TS36.304 IDLE Mode 3GPP TS24.301 NAS

This invention introduces a new procedure for Mobile Terminal in heterogeneous environment to support re-attempt re-establishment procedure after the event that the selected cell for re-establishment becomes non-suitable. The Mobile Terminal will perform cell selection procedure to find suitable cell. Upon suitable cell is detected, the Mobile Terminal will check if the synchronization between the Mobile Terminal and the Base Station is maintained; and no failure signaling message is received. Upon the above condition is met, the Mobile Terminal will re-attempt re-establishment procedure.

In addition, the present invention enables Base Station to control whether another cell selection to re-attempt re-establishment is allowed or not after the event that the selected cell for re-establishment becomes non-suitable.

In heterogeneous environment of the mobile communication system (300) as illustrated in Figure 3, where the Base Station (304) which covers (or provides) a small cell (302) exist within the coverage of macro cell (102). A small cell (302) may be, for example, a pico cell. Upon radio link failure occurred, the Mobile Terminal (114) which is connected to the Base Station (108) covering macro cell (102) may select a Base Station (304) covering small cell (302) for re-establishment procedure. In case the Mobile Terminal (114) moves out of small cell (302), and the small cell (302) becomes non-suitable anymore for the Mobile Terminal during re-establishment, according to the prior art, Mobile Terminal (114) will trigger NAS Recovery procedure. However, in the above explained environment, Mobile Terminal (114) is likely to still be in the coverage of the Base Station (108) covering the macro cell (102), in which the UE's context is stored i.e. re-establishment can be successful.

The object of the present invention is to remove extra operation in the needs to proceed to idle mode and trigger connection establishment procedure by Mobile Terminal (114) in a heterogeneous environment. In addition, the object of the present invention is to avoid unnecessary re-attempt re-establishment.

The solution is, in heterogeneous environment, when the selected cell becomes non-suitable during re-establishment, Mobile Terminal re-attempts re-establishment procedure on another selected cell. In addition, Base Station broadcasts a flag to indicate Mobile Terminal to use the above mentioned algorithm.

The extra operation in the needs to proceed to idle mode and trigger connection establishment procedure by Mobile Terminal is removed by the present invention. In addition, unnecessary re-attempt re-establishment can be avoided.

Figure 1 illustrates the system architecture that supports the re-establishment procedure by Mobile Terminal according to the current art procedure. Figure 2 illustrates an operation sequence of the current art procedure in re-establishment procedure by Mobile Terminal in the architecture as shown in Figure 1. Figure 3 illustrates the system architecture that supports the re-attempt re-establishment procedure by Mobile Terminal according to the present invention. Figure 4 illustrates an operation sequence of the present invention in re-attempting re-establishment procedure by Mobile Terminal in the architecture as shown in Figure 1. Figure 5 illustrates an example architecture of a Base Station that implements the present invention. Figure 6 illustrates an example architecture of a Mobile Terminal that implements the present invention. Figure 7 illustrates an operation logic of the Mobile Terminal to re-attempt re-establishment procedure. Figure 8 illustrate an operation logic for the Mobile Terminal to re-attempt re-establishment procedure upon allowable.

(Embodiment 1)
With reference to Figure 4, an operation sequence of the Mobile Terminal (114) to re-attempt re-establishment procedure after the event that the selected cell for re-establishment becomes non-suitable is illustrated. This figure is based on Figure 2 with some modifications. Therefore only the difference is explained here.

As shown in Figure 4, upon the Mobile Terminal (114) encounters radio link failure, the Mobile Terminal (114) will start to search for suitable cell to camp on via cell selection procedure. Upon a suitable cell is detected, the Mobile Terminal (114) will select that cell to camp on (402). For example, as illustrate in Figure 4, Base Station (304) which is covering a pico cell (302) is selected by Mobile Terminal (114).

Upon a suitable cell is selected, the Mobile Terminal (114) will configure the parameters for re-establishment and send to Base Station (304) via RRC Connection Reestablishment Request (404). However, upon the Mobile Terminal (114) detect the selected cell (i.e. Base Station (304)) becomes non-suitable due to cell selection criteria, similar to that specified in {NPL 3}, is not met (406) before the reception of RRC Connection Reestablishment or RRC Connection Reestablishment Reject (408), the Mobile Terminal (114) will continue to perform cell selection procedure to detect suitable cell (410). Upon a suitable cell is detected, the Mobile Terminal (114) will select that cell to camp on (412). For example, as illustrate in Figure 4, Base Station (108) which is covering a macro cell is selected by Mobile Terminal (114). The Mobile Terminal (114) will check for feasibility to re-attempt re-establishment procedure. To ensure the feasibility to support re-attempt re-establishment procedure, the Mobile Terminal (114) and Base Station (108) had to be maintained synchronized. For example, a typical synchronized mechanism may consider the following option:

Option 1: A configured timer
E.g. A configured timer is broadcasted in the macro cell (102) covered by Base Station (108). Such timer will start upon radio link failure detected. This configured timer will only be stopped by Mobile Terminal (114) upon re-attempt re-establishment occurs in the macro cell (108). Upon the configured timer expired, the Mobile Terminal (114) is not allow to perform re-attempt re-establishment in the macro cell (102) covered by Base Station (108) after re-establishment failure.

There can be alternative methods to ensure that the Mobile Terminal (114) and the Base Station (108) maintain synchronization. This does not affect the general principle of the present invention.

By fulfilling the above condition, the Mobile Terminal (114) will configure the parameters for re-establishment and send to Base Station (108) via RRC Connection Re-establishment Request (414). Based on the reception of request message for re-establishment, the Base Station (108) will configure the recovery parameters to Mobile Terminal (114) via RRC Connection Re-establishment (416). With the success configuration of the recovery procedure, the Mobile Terminal (114) will acknowledge to the Base Station (108) via RRC Connection Re-establishment Complete (418).

It is noted that there could be other operations involved in the process. However, for illustration purpose, the above sequence may not necessarily show all the steps.

With reference to Figure 5, an architecture of the Base Station (108) that implements the present invention is shown.

As shown in the figure, the Base Station (108) comprises three major components, namely the Receiver Unit (RU) (502), Reestablish Management Unit (RMU) (506) and Transmitter Unit (TU) (510).

After received uplink signaling message from RU (502) via interface 504, the RMU (506) will decide on the intended cell for recovery configuration to the Mobile Terminal (114). For example, the intended cell to support re-attempt re-establishment should be a prepared cell before the Base Station (108) can start to prepare recovery configuration information. The RMU (506) will pass the recovery configuration information to TU (510) via interface 508. Thus, the Base Station (108) will transmit the recovery configuration information to Mobile Terminal (114) via downlink dedicated signaling, as shown in Figure 4.

With reference to Figure 6, an example architecture of the Mobile Terminal (114) that implements the present invention is presented.

As shown in the diagram, there are four major components in the Mobile Terminal (114), namely the Receiver Unit (RU) (602), Measurement Control Unit (MCU) (606), Reestablishment Control Unit (RCU) (610) and Transmitter Unit (RU) (614).

The RU (602) is in charge of receiving the downlink message. For example, as illustrate in Figure 4, the Mobile Terminal (114) will receive the RRC Connection Re-establishment message from Base Station (108). Upon message is successfully received, RU (602) will pass the received message to RCU (610) via interface 604.

The MCU (606) is in charge of handling the measured and detected cells based on the cell selection criteria, similar to that specified in {3}. When the radio quality of the cell for re-establishment camped on by the Mobile Terminal (114) is below certain signal strength threshold, similar to that specified in {NPL 3}, the MCU (606) will start to monitor the cells as to determine suitable cell. Upon a suitable cell is detected, the MCU (606) will pass this suitable cell to RCU (610) via interface (608).

The RCU (610) is in charge of checking if the synchronization between the Mobile Terminal (114) and the Base Station (108) is maintained before the Mobile Terminal (114) can start to perform re-attempt re-establishment procedure. Upon the above synchronized condition is fulfilled, the RCU (610) will configure the re-establishment request parameters for the re-attempt re-establishment procedure and pass to TU (614) via interface 612. Thus, the Mobile Terminal (114) will send to the Base Station (108) via dedicated signaling, as shown in Figure 4. The protocol used between them is as specified in {NPL 2}.

With reference to Figure 7, an example logic used by the Receiver Unit (RU) (602), Measurement Control Unit (MCU) (606), Reestablishment Control Unit (RCU) (610) and Transmitter Unit (TU) (614) is presented.

As shown in the figure, upon MCU (606) detect radio link failure, as in step 702, the MCU (606) will start to perform cell selection procedure, as in step 704. Upon a cell is detected, the MCU (606) will check if that cell is suitable cell based on cell selection criteria, similar to that specified in {NPL 3}, as in step 706. If the measured result of the detected cell has satisfied the above criteria, the MCU (606) will attempt re-establishment procedure, as in step 708. Otherwise, the MCU (606) will continue to monitor other cell. During re-establishment procedure, the MCU (606) will continue to monitor the radio link of the suitable cell. If the radio link of the suitable cell cannot meet cell selection criteria, similar to that specified in {3}, as in step 710, the MCU (606) will start to perform cell selection procedure as to detect any suitable cell, as in step 712. Upon suitable cell not detected, the MCU (606) will continue to monitor other cell. If a suitable cell is detected and that cell is a potential prepared cell (e.g. Base Station (108) as illustrate in Figure 4), as in step 714, the RCU (610) will check if the synchronization between the Mobile Terminal (114) and the Base Station (108) is maintained or not. Upon synchronization criteria have fulfilled, the RCU (610) will start to configure the re-establishment request parameters for the re-attempt re-establishment procedure, as in step 716. Such parameters information like physical cell identity information, connection radio network temporary identity information, security related information, etc. This information could be obtained from the stored information of the Mobile Terminal (114). Once the relevant information for re-attempt re-establishment procedure is obtained, the RCU (610) will pass this information to TU (614) and send to Base Station (108) via dedicated signaling, as in step 718, as shown in Figure 4. The protocol used between them is as specified in {2}.

There are other methods to trigger re-attempt re-establishment procedure, e.g. potential suitable cell to perform re-attempt re-establishment by network configured, etc. It is noted that the other alternative of trigger the re-attempt re-establishment does not affect the general principle of the present invention.

(Embodiment 2)
In the previous description, the Mobile Terminal (114) would trigger the re-attempt re-establishment when the synchronization between the Mobile Terminal (114) and the Base Station (108) is maintained. However, there will be scenarios whereby the Mobile Terminal (114) is situated near to another Base Station (110), as illustrate in Figure 3, such that the Mobile Terminal (114) will select this Base Station (110) for re-establishment instead of Base Station (304).

In this case, to have macro cell (110) for re-establishment becomes non-suitable, it would imply that the Mobile Terminal (114) may have move away from the coverage of Base Station (108). Thus, the Mobile Terminal (114) may add additional delay for connection recovery if re-attempt re-establishment procedure is triggered. To solve the above issue, with reference to Figure 8, an alternative behavior for Base Station (110, 304 as illustrate in Figure 3) to control if re-attempt re-establishment procedure is allowed or not is presented.

As shown in the figure, an example logic for Mobile Terminal (114) to check and trigger re-attempt re-establishment procedure is presented. This figure is based on Figure 7 with some modifications. Therefore only the difference is explained here.

Upon the triggered of re-establishment procedure in the selected cell, the RCU (610) will read and stored the re-attempt re-establishment control information via broadcast control signaling, as in step 802, e.g. System Information Block message as defined in {NPL 2}. For example, a typical re-attempt re-establishment control information may consider the following option:

Option 1: A broadcasted control flag
E.g. A control flag is broadcasted in the Base Station (110, 112). Such control flag could be set as, e.g. allowed or not allowed, for the Mobile Terminal (114) to carrier out re-attempt re-establishment upon the cell for re-establishment becomes non-suitable.

The MCU (606) will continue to monitor the radio condition of the selected cell for re-establishment. Upon the selected cell fail to meet the cell selection criteria, similar to that specified in {NPL 3}, the RCU (610) will based on the stored re-attempt re-establishment control information to check if the Mobile Terminal (114) is allow to re-attempt re-establishment or not, as in step 804.

If re-attempt re-establishment is allowed, the RCU (610) will proceed to trigger re-attempt re-establishment procedure. If re-attempt re-establishment is not allowed, the RCU (610) will proceed to idle mode, as in step 806 and consider the selected cell for re-establishment has failed.

It is noted that the control to trigger re-attempt re-establishment procedure from Base Station (110, 304 as illustrate in Figure 3) is just one of the possible approaches. There may be alternative approaches, such as broadcasted potential list of recovery cells for Mobile Terminal (114) to perform re-attempt re-establishment procedure after the event that selected cell for re-establishment becomes non-suitable.

With this new behavior, most of the processing sequence and logic described earlier still apply, except for the storing of the control flag information and additional checking procedure of whether re-attempt re-establishment procedure is allowed or not allowed for Mobile Terminal (114).

It is noted that the above variance does not change the general principle of the present invention.

Claims

A mobile terminal for use in a mobile communication system comprising a first base station for providing a macro cell, a second base station for providing a pico cell within the coverage of the macro cell, and a mobile terminal, the mobile terminal comprising:
a transceiver configured to connect radio link with the first base station and with the second base station; and
a reestablishment control unit configured to reestablish radio link via RRC (radio resource control) connection procedure with the first base station after disconnecting radio link with the second base station.
The mobile terminal according to claim 1,
wherein the reestablishment control unit is configured to reestablish radio link via RRC (radio resource control) connection procedure with the first base station, if a flag received from the second base station is indicating that reestablishing radio link via RRC connection procedure is allowed.
The mobile terminal according to claim 1,
wherein the reestablishment control unit is configured to reestablish radio link via RRC (radio resource control) connection procedure with the first base station, if a flag broadcasted from the first base station is indicating that reestablishing radio link via RRC connection procedure is allowed.
The mobile terminal according to claim 1,
wherein the reestablishment control unit is configured to maintain synchronization with the first base station after connecting radio link with the second base station.
A method for reestablishment control in a mobile communication system comprising a first base station for providing a macro cell, a second base station for providing a pico cell within the coverage of the macro cell, and a mobile terminal, the method comprising the following steps performed by the mobile terminal:
connecting radio link with the first base station and with the second base station; and
reestablishing radio link via RRC (radio resource control) connection procedure with the first base station after disconnecting radio link with the second base station.