Patent Application
20160007243
Priority to Korean patent application number 2014-0082439 filed on Jul. 2, 2014, the entire disclosure of which is incorporated by reference herein, is claimed.
1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for mobility management in small cell environment.
2. Discussion of the Related Art
A cellular mobile communication system is a system in which respective different frequencies are allocated to neighboring cells with the mobile communication service regions being divided into several cell units, and the arrangement of the cells is made in order to reuse the frequency spatially by using the same frequency band for the two cells between which there is no occurrence of any interferences due to being faraway from each other, or a separate interference control method may be used while the same frequency is allocated to the neighboring cells.
A user equipment (UE) that connects through the wireless access network provided by such a cellular mobile communication system may perform communication by residing in or connecting to unprescribed cell, and perform cell change. In case that cell change is made in an environment that a communication is performed by connecting to a cell, a handover may be performed in order to solve the problem of call severance. The handover is referred to as a function that a stable state of telephone conversation is maintained by an automatic tuning being made on a new traffic channel of the adjacent communication service region when a UE gets out of the present communication service region (hereinafter, source cell) and moves to the adjacent communication service region (hereinafter, target cell) as the UE moves.
There are mainly three methods for preparing for heavy increase of traffics in this mobile communication system. The first method is to increase the spectral efficiency of frequency, the second method is to further increase using frequency bands, and the third method is to increase the density of small cells.
In case of selecting the third method in which small cells are dense, due to the nature of the small cells that the coverage is relatively small in small cell environment, the radio link failure (RLF) or the cell change according to the movement of a UE may frequently occur compared with the existing mobile communication system. In this case, the mobile management of the UE should be performed, however, the mobile management method considered in the current mobile communication system (particularly long term evolution (LTE) or LTE-Advanced (LTE-A), hereinafter, LTE may include LTE-A) has a problem that is not optimized in the capacity-based small cell deployment environment, since it is based on the macro cell coverage based cell arrangement. For example, there exists the recovery procedure for the RLF as one of the mobile management methods in the current mobile system, but as it is optimized in the macro cell, a problem may arise that the RLE recovery performance is deteriorated if it is applied to the small cell as it is. Consequently, the mobile management method that is optimized in small cell environment is required.
It is a principal object of the present invention is to provide a method and apparatus for mobility management in small cell environment.
It is another object of the present invention is to increase the recovery performance for the radio link failure (RLF) in small cell environment.
It is further object of the present invention is to provide the UE context information management method for the small cell environment.
It is still further object of the present invention is to provide a method and apparatus for the UE mobility management based on the multiple preparation method (MPM).
It is further object of the present invention is to provide a method and apparatus for the UE mobility management based on the context fetch method (CFM).
According to an aspect of the present invention, a wireless communication system that supports mobility management in a small cell environment is provided. The wireless communication system includes a user equipment configured to measure a signal strength of multiple small cells around and transmit the measurement result through a serving cell, and multiple small base stations configured to store user equipment context information in determined preparation cells among the multiple small cells based on the measurement result, in case that the user equipment context information for cell A among the preparation cells is changed, wherein the multiple small base stations update the changed user equipment context information.
Also, the small cells of which signal strength exceed a threshold value Tprep for preparation based on the measurement result of the user equipment may be determined to be the preparation cells.
Also, the user equipment context information for the preparation cells may include physical IDs of each of the cells and C-RNTI of the user equipment for the corresponding cell.
Also, in case that signal strength of cell B among the multiple small cells exceeds the threshold value Tprep for the preparation, the serving base station may transmit multiple preparation request message that includes the user equipment context information for the preparation cells to small base station B that operates cell B, the small base station B may transmit multiple preparation request ACK message that includes the user equipment context information for corresponding cell B to the serving base station, and the serving base station may transmit preparation information transfer message that indicates to add the user equipment context information for cell B to the remainder base stations except the serving base station.
Also, in case that signal strength of cell C among the preparation cells is the same or smaller than the threshold value Tcancel for release of the preparation, the serving base station may transmit multiple preparation deletion message that indicates un-preparation of cell C to small base station C and remainder base stations except the serving base station among the multiple base stations.
Also, a change of the user equipment context information for the cell A may be generated as the user equipment succeeds the radio link failure recovery to corresponding cell A. In this case, the change of the user equipment context information for cell A may be that C-RNTI of the user equipment for cell A is changed.
Also, the serving base station may transmit a multiple preparation request message that instructs to update the changed user equipment context information for cell A to remainder base stations except the serving base station among the multiple base stations, and the remainder base stations may update the changed user equipment context information based on the multiple preparation request message.
According to an aspect of the present invention, a small base station A that supports mobility management in a small cell environment is provided. The small base station A includes a receiving unit configured to receive a first measurement report including a first measurement result for cell B from a user equipment through cell A, a storage unit configured to store user equipment context information for cell A, a control unit configured to perform a preparation decision for cell B in case that signal strength of cell B exceeds a threshold value Tprep for preparation based on the first measurement result for cell B, and generates a first multiple preparation request message including the user equipment context information for cell A, and a transmitting unit configured to transmit the first multiple preparation request message generated to a small base station B that operates cell B, wherein the receiving unit receives a first multiple preparation request ACK message including the user equipment context information for cell B from small base station B, and wherein the control unit controls such that the user equipment context information for the cell B as well as the user equipment context information for cell A is to be stored in the storage unit.
According to yet another aspect of the present invention, a method of mobility management in small cell environment is provided. The method includes receiving a first measurement report including a first measurement result for cell B from a user equipment through cell A, storing user equipment context information for cell A, performing a preparation decision for cell B in case that signal strength of cell B exceeds a threshold value Tprep for preparation based on the first measurement result for cell B, generating a first multiple preparation request message including the user equipment context information for cell A, transmitting the first multiple preparation request message generated to a small base station B that operates cell B, receiving a first multiple preparation request ACK message including the user equipment context information for cell B from small base station B, and controlling such that the user equipment context information for the cell B as well as the user equipment context information for cell A is to be stored in the storage unit.
Hereinafter, the preferred embodiment of the present invention now will be described in detail by reference to the accompanying exemplary drawings in this specification. In attaching reference numerals to elements in each drawing, it should be understood that the same reference numeral is used for the same element even if the element is shown in different drawings. In addition, in case that the detailed description for the related known elements and functions is determined to obscure the inventive concept in this specification, the redundant description for the same element will be omitted.
In addition, the present specification describes wireless communication network as an object, the tasks performed in the wireless communication network may be performed during the process of controlling the network in the system (for example, a base station) that controls the corresponding wireless communication network and transmitting data, or performed by the user equipment that is coupled to the corresponding wireless network.
Referring to
A user equipment (UE) 12 may be fixed or have mobility, and may be called other terms such as a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, a handheld device, and the like.
Hereinafter, downlink refers to transmission link from the eNB 11 to the UE 12 and uplink refers to transmission link from the UE 12 to the eNB 11. In downlink, a transmitter may be a part of the eNB 11 and a receiver may be a part of the UE 12. In uplink, a transmitter may be a part of the UE 12 and a receiver may be a part of the eNB 11. There is no limitation in the multi access method which is applied to the wireless communication system. Various multi access methods may be used such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA, OFDM-CDMA. As the uplink transmission and the downlink transmission, a Time Division Duplex (TDD) scheme transmitted using different times and a Frequency Division Duplex (FDD) scheme transmitted using different frequencies.
The layers of the radio interface protocol between the UE 12 and the eNB 11 may be divided into the first layer (L1), the second layer (L2) and the third layer (L3) based on the lower three layers of the Open System Interconnection (OSI) model which is well known in communication systems. Among the layers, the physical layer which is included in the first layer provides the information transfer service using physical channel, and the Radio Resource Control (RRC) layer which is located on the third layer exchanges RRC messages and controls the radio resources between the UE and the network. The RRC layer is in relation to the configuration, re-configuration and release of Radio Bearer (RB), and in charge of controlling logical channels, transmission channels and physical channels. The RB means the logical path which is provided by the first layer (PHY layer) and the second layer (Medium Access Control (MAC) layer, Radio Link Control (RLC) layer and Packet Data Convergence Protocol (PDCP) layer) for data transmission between the UE and network. The RB is divided by Signaling RB (SRB) and Data RB (DRB) again. The SRB is used for the path to transmit RRC messages and Non-Access Stratum (NAS) messages on control plane, and the DRB is used for the path to transmit user data on user plane.
There exist a few physical channels used in the physical layer. As a downlink physical channel, the physical downlink control channel (PDCCH) may notify the resource allocation of Paging Channel (PCH) and Downlink Shared Channel (DL-SCH) and Hybrid Automatic Repeat Request (HARQ) information in relation to the DL-SCH. The PDCCH may carry the uplink grant that notifies the resource allocation of the uplink transmission. The UE may perform monitoring the PDCCH based on cell-radio network temporary identifier (C-RNTI) which is an intrinsic identifier of the UE. The DL-SCH is mapped to a Physical Downlink Shared Channel (PDSCH). A physical control format indicator channel (PCFICH) notifies the number of OFDM symbol which is used for the PDCCHs to the UE, and is transmitted in every frame. A Physical Hybrid ARQ Indicator Channel (PHICH) is a downlink channel, carries Hybrid Automatic Repeat Request (HARQ) Acknowledgement (ACK)/Non-acknowledgement (NACK) signals which are the responses to the uplink transmission. The HARQ ACK/NACK signals may be called the HARQ-ACK signal.
As an uplink physical channel, the physical uplink control channel (PUCCH) carries the uplink control information such as the HARQ-ACK which is the response to the downlink transmission and channel status information (CSI) that represents downlink channel state, such as a Channel Quality Indicator (CQI), a precoding matrix index (PMI), a precoding type indicator (PTI), rank indicator (RI), and so an. A Physical Uplink Shared Channel (PUSCH) carries an Uplink Shared Channel (UL-SCH). A Physical Random Access Channel (PRACH) carries a random access preamble.
The UE that accesses the network may perform communication with an unprescribed cell according to channel environment and mobility state, or may perform cell change. In case of the cell change, handover (HO) may be performed to solve the problem of call severance that occurs when moving to neighboring cell.
Referring to
eNB A determines whether handover is performed based on the measurement report and transmits handover request (HO request) to eNB B (step, S210), and receives request Ack (HO request Ack) message from eNB B. In this case, the UE may be positioned at position A which is adjacent to the boundary of cell A.
The handover request message may include, for example, handover preparation information (HandoverPreparationInformation). The handover preparation information may include the C-RNTI for the UE at cell A and the physical cell ID of cell A. In addition, the handover request Ack message may include the information for handover command. The information for handover command may include the C-RNTI for the UE at cell B and the physical cell ID of cell B. The handover request message and the handover request Ack message may be transmitted through X2 interface. The X2 interface may be called X2 Application Protocol (X2AP). In this case, eNB A and eNB B may include both of the C-RNTI for the UE at cell A and C-RNTI for the UE at cell B as the UE context information.
eNB A transmits the handover command for eNB B to a UE through the RRC connection reconfiguration message (step, S230). The UE configures a radio link with eNB B based on the handover command, and transmits the RRC connection reconfiguration complete message to eNB B (step, S240). Later, eNB B transmits UE context release message to eNB A (step, S250). In this case, the UE may be positioned as position B passing through the region where cell A and cell B are overlapped. The UE context release message may be transmitted through X2 interface.
After eNB A receives the UE context release message, eNB A drives UE context storing timer Tstore
In the current standard in relation to the handover procedure, the important information which is exchanged between two eNBs includes the physical cell ID of each cell of each eNB and the C-RNTI for the UE. In addition, these two parameters are the important parameters that are available to find which is the UE context information relevant to the UE that tries RLF recovery among the pieces of UE context information kept by the cell in which the RLF recover is tried, even in case of the Radio Link Failure (RLF). For example, the channel quality becomes deteriorated during the handover procedure and the RLF may occur during preparing the handover, or in case of not receiving the handover command within a predetermined time due to the bad link state, the signal from the source eNB is becoming weak and the RLF may occur.
Table 1 below represents the possibility of the RLF recovery to each cell according to position in case that the RLF occurs during the handover procedure.
Referring to Table 1, in case that a UE tries the RLF recovery at position A, the RLF recovery to cell A is possible, but the RLF recovery to cell B or cell C is impossible. This is because only eNB A keeps the UE context information for the corresponding UE at the corresponding timing. In case that the UE tries the RLF recovery and the like, the cell in which the UE context information for the corresponding UE exists may be defined as the prepared cell. That is, in this case, cell A is the prepared cell and the remainder cells are the unprepared cells.
In addition, in case that a UE tries the RLF recovery between position A and position B, the RLF recover to cell A or cell B is possible, but the RLF recover to cell C is impossible. This is because both of eNB A and eNB B keep the UE context information for the corresponding UE at the corresponding timing. In this case, both cell A and cell B are the prepared cells and cell C is the unprepared cell.
In addition, in case that a UE tries the RLF recovery at position B, the RLF recover to cell B is possible, but the RLF recover to cell A or cell C is impossible. This is because only eNB B keeps the UE context information for the corresponding UE since eNB A releases the UE context information for the corresponding UE at the corresponding timing. In this case, cell B is the prepared cell and the remainder cells are the unprepared cells.
In case that the RLF occurs and the UE tries the RLF recovery when complying with the current long term evolution (LTE, including LTE-A) standard, as aforementioned, normally it is available for the RLF recovery to a specific cell, exceptionally, in the section (position A and position B) where the UE context information for the corresponding UE is maintained in two eNBs, one cell of the maximum two cells (cell A and cell B) is selected and the RLF recovery may be performed. That is, the RLF recovery in the current LTE standard is available for the maximum two cells and only for a short time will be, therefore, it contains high possibility that the RLF recovery is made to the unprepared cells. Such a try of the RLF recovery that is made to the unprepared cells failed and may cause a service interruption for the UE. In the meantime, in the current standard, in order to avoid the RLF recovery to the unprepared cells, a reactive resource management (for example, mobility robustness optimization (MRO)) is adopted. The active resource management may accompany the mobility parameter adjustment based on statistical information gathering related to the RLF. However, the resource management method for avoiding the RLF recovery try to the unprepared cell in the current mobile communication system, is optimized in homogeneous macro cells.
Meanwhile, in order to solve the problem of heavy increase in traffics, currently the way is considered to increase the density of small cells. If following the way of increasing the density of small cells, tries for the RLF recovery increase in number and may happen randomly. In case that the RLF recovery method based on the resource management method optimized in the existing homogeneous macro cells is applied to the heterogeneous network (HetNet) environment where are there exist multiple dense small cells as it is, the performance of the RLF recovery may be deteriorated. As the UE context information is maintained for the current one cell or the maximum for the two cells for a short moment, there is high possibility that the UE tries to the RLF recovery to the cell that are not prepared in the heterogeneous network environment in which there are multiple dense small cells. Accordingly, there is a need of introducing the multiple preparation method (MPM) in which the UE context information is maintained in the multiple cells according to a predetermined condition in order to increase the performance of a UE's RLF recovery and mobility robustness in the heterogeneous network environment. However, in case of introducing the MPM based on the UE context information maintaining method based on the current C-RNTI, as shown in
Referring to
The UE performs the RLF recovery procedure through the RRC connection reestablishment request message (step, S310). Herein, as cell A, cell B, and cell C are the prepared cells, the UE may perform any one of cell A, cell B, and cell C. Assuming below that a UE performs the RLF recovery to cell C, the RLF recovery procedure may be performed as below.
The UE performs the contention-based random access procedure. That is, the UE randomly selects one of the contention-based random access preambles, transmits the selected preamble to small eNB C through the random access channel (RACH), and small eNB C transmits the random access response (RAR) message to the UE. In this case, a temporary radio network temporary ID (T-RNTI) that represents a temporary UE ID may be included in the random access response message. For example, the T-RNTI may be determined in the MAC layer. Assuming below that the value of T-RNTI is set to 1600. After that, the UE transmits the RRC connection reestablishment request message to small eNB C. The RRC connection reestablishment request message may include the UE identification information, and the identification information may include the C-RNTI information of the corresponding UE. Small eNB C recognizes the UE by comparing the identification information included in the RRC connection reestablishment request message and the UE context information previously saved. Small eNB C updates the C-RNTI of the corresponding UE in the serving cell C. For example, the UE may update to 1600 from 20100, the existing C-RNTI value.
After that, small eNB C transmits the RRC connection reestablishment message to the UE, the UE performs the parameter change related to the RRC in the UE layer based on the parameter related to the RRC that is included in the RRC connection reestablishment message, and transmits the RRC connection reestablishment complete message to small eNB C.
Meanwhile, since the UE context information of small eNB C only is updated, in this case, the UE may not perform the RLF recovery any more based on the UE context information that is retained in small eNB A and small eNB B. That is, even though the RLF may occur again after the RLF recovery procedure is performed, the RLF recovery to cell A and cell B is impossible, the UE may perform the RLF recovery procedure to only cell C that succeeded in the first RLF recovery.
Accordingly, in case of using the UE context information maintaining method based on the existing C-RNTI even in case of retaining the UE context information in multiple cells, the RLF recovery to another cell is impossible even though the RLF may occur once the RLF recovery procedure is performed.
Therefore, the present invention suggests a method for raising the RLF recovery possibility of small cell in the heterogeneous network environment including multiple dense small cells.
Method 1: The UE Mobility Management Method Based on the Multiple Preparation Method (MPM)
Referring to
(b) shows that the preparation for the corresponding cells is done when UEs come in the region where cells are overlapped according to the mobility path of the UE. For example, if the UE moves to P2, the preparations for cell A, cell B, and cell C may be performed, and if the UE moves to P5, cell A may release the UE context information.
In case of being based on the MPM as shown in
Particularly, referring to
Referring to
In the situation that a UE is wirelessly linked to cell A as the current serving cell, event A occurs and the UE context information at cell A may be changed (step, S500). For example, event A may include the addition/deletion of the bearer at cell A. In this case, the UE context information of cell B and cell C should be changed. Accordingly, eNB A transmits the preparation update message to eNB B and eNB C (steps, S505 and S510). eNB B and eNB C transmit the preparation update Ack message to eNB A, respectively (steps, S515 and S520). The preparation update message and the preparation update Ack message may be transmitted through the X2 interface.
Meanwhile, later, the RLF occurs to the UE, and the UE may perform the RLF recovery to cell A (event B, step, S525). In case that the RLF recovery is successful, the C-RNCT at cell A for the corresponding UE may be changed as described above. In this case, since the RLF recovery to cell B or cell C becomes impossible, eNB A transmits the preparation update message to eNB B and eNB C (steps, S530 and S535). Based on this, eNB B and eNB C may update the C-RNTI information for cell A at cell B and cell C, and may set up such that the RLF recovery to cell B or cell C is possible. For example, when the UE performs the RLF recovery to cell A, in case the C-RNTI value of the UE for cell A is changed from 100 to 16771, in order to also update the changed C-RNTI value for cell A to cell B and cell C, eNB A may transmit the preparation update message to eNB B and eNB C. Later, each of eNB B and eNB C transmit the preparation update Ack message to eNB A (steps, S540 and S545).
The particular operation of the MPM according to Method 1 of the present invention may be performed as follows.
Referring to
Referring to
In case that a UE moves to P1 and the signal strength of cell B exceeds Tprep (the event A4-1), cell B as well as cell A are prepared cells.
In case that a UE moves to P2 and the signal strength of cell B becomes greater than that of cell A (event A3-1), the UE performs handover from cell A to cell B. That is, the serving cell is changed to cell B. In this case, the prepared cells are still both of cell A and cell B.
In case that a UE moves to P3 and the signal strength of cell C exceeds Tprep (the event A4-1), cell C as well as cell A and cell B are prepared cells. In this case, the serving cell is still cell B.
In case that a UE moves to P4 and the signal strength of cell C becomes greater than that of cell B (event A3-1), the UE performs handover from cell B to cell C. That is, the serving cell is changed to cell C. In this case, the prepared cells are still cell A, cell B and cell C.
In case that a UE moves to P5 and the signal strength of cell A is smaller than or the same as Tcancel (the event A4-2), cell A cancels (or releases) the preparation, and only cell B and cell C are the prepared cells. In this case, the serving cell is cell C.
In case that a UE moves to P6, since the signal strength of cell B is less than Tcancel (the event A4-2), cell B cancels (or releases) the preparation, and only cell C is the prepared cell.
Referring to
Small eNB A performs a preparation decision (step, S805), and transmits a multiple preparation request message to small eNB B (step, S810). The multiple preparation request message may be transmitted through the X2 interface (or X2AP).
The multiple preparation request message may include, for example, the parameter represented in Table 2 below.
Table 2 include the list of information which is reserved (or stored), and c-RNTI 100 and phyCellId 501 in the search ID filed of item [0] represent to reserve (or store) the information that C-RNTI value of cell A whose physical cell ID is 501.
Small eNB B generates the UE context information in cell B, and transmits multiple preparation request ACK message to small eNB A (step, S815). The multiple preparation request ACK message may be transmitted through the X2 interface.
The multiple preparation request ACK message may include the parameter, for example, shown as in Table 3 as follows.
Table 3 includes the result of the request and the list of the information that is reserved (or saved), the phyCellId502, the c-RNTI 65280 of the search ID filed of item [0] shows that the information is going to be reserved or saved that the value of C-RNTI of cell B whose physical cell ID is 502 is 65280.
In such an environment, both cell A and cell B save the UE context information for the corresponding UE. The UE context information may include the both C-RNTI in cell A (e.g. value 100) and C-RNTI in cell B (e.g. value 65280). When each cell is handed over to another cell, the RRC message (including the parameter related to RRC) made by another cell that is going to be transmitted to the UE is exchanged.
After that, in case that the UE moves to position P2, the handover procedure is performed to cell B according to the event A3-1 for cell B (step, S820). This is the case that the signal strength SS of cell B measured by the UE is bigger than that of cell A. More particularly, small eNB A transmits the RRC connection reconfiguration message including the command of handover to cell B to the UE. The UE transmits a random access preamble to small eNB B through RACH. The random access preamble may be one preamble that is randomly selected among the contention-based random access preambles. Small eNB B transmits the random access response (RAR) message to the UE. The UE, hereafter, transmits the RRC connection reconfiguration complete message to small eNB B. In this case, the serving cell for the corresponding UE is to be cell B.
Referring to
Small eNB B performs preparation decision (step, S905), and transmits multiple preparation request message to small eNB C (step, S910). The multiple preparation request message may be transmitted through the interface X2 (or X2AP).
The multiple preparation request message may include the parameter as shown in the following Table 4.
Table 4 includes the list of the information that is reserved (or saved), the phyCellId502, the c-RNTI 65280 of the search ID filed of item [0] shows that the information is going to be reserved (or saved) that the value of C-RNTI of cell B whose physical cell ID is 502 is 65280. Additionally, the phyCellId501, the c-RNTI 100 of the search ID filed of item [1] shows that the information is going to be reserved (or saved) that the value of C-RNTI of cell A whose physical cell ID is 501 is 100.
Small eNB C generates the UE context information in cell C and transmits the multiple preparation request ACK message to small eNB B (step, S915). The multiple preparation request ACK message may be transmitted through the interface X2.
The multiple request ACK message may include the parameter, for example, as shown in the following Table 5.
Table 5 includes the result of the request and the list of the information that is reserved (or saved), the phyCellId503, the c-RNTI 20100 of the search ID filed of item [0] shows that the information is going to be reserved or saved that the value of C-RNTI of cell C whose physical cell ID is 503 is 20100.
Small eNB B performs the transmission of the preparation information to small eNB A (step, S920). The preparation information may be transmitted through the interface X2 and includes C-RNTI in cell C.
The preparation information to be transmitted, for example, may include the parameter as shown in Table 6 as below.
Table 6 includes the list of the information that is reserved (or saved), the phyCellId503, the c-RNTI 20100 of the search ID filed of item [0] shows that the information is going to be reserved (or saved) that the value of C-RNTI of cell C whose physical cell ID is 503 is 20100.
In such an environment, all of cell A, cell B, and cell C save the UE context information for the corresponding UE. The UE context information may include all the C-RNTI in cell A (e.g. value 100), C-RNTI in cell B (e.g. value 65280), and C-RNTI in cell C (e.g. value 20100). Each cell has the RRC message for the handover to the other two cells.
After that, in case that the UE moves to position P4, the handover procedure is performed to cell C according to the event A3-1 for cell C (step, S92). This is the case that the signal strength SS of cell C measured by the UE is bigger than that of cell B. More particularly, small eNB B transmits the RRC connection reconfiguration message including the command of handover to cell C to the UE. The UE transmits a random access preamble to small eNB C through RACH. The random access preamble may be one preamble that is randomly selected among the contention-based random access preambles. Small eNB C transmits the random access response (RAR) message to the UE. The UE, hereafter, transmits the RRC connection reconfiguration complete message to small eNB C. In this case, the serving cell for the corresponding UE is to be cell C.
Referring to
Small eNB C performs the un-preparation decision (step, S1005), and transmits the first multiple preparation delete message to small eNB A and small eNB B (step, S1010, S1015). The first multiple preparation delete message includes the message that commands cell A to be unprepared. The first multiple preparation delete message may be transmitted through the interface X2 (or X2AP).
The first multiple preparation delete message may include the parameter as shown in the following Table 7, for example.
Table 7 includes the list of the information that is deleted (or unprepared), the phyCellId501, the c-RNTI 100 of the search ID filed of item [0] shows that the information is going to be deleted (or unprepared) that the value of C-RNTI of cell A whose physical cell ID is 501 is 100.
In such an environment, cell A deletes the UE context information for the corresponding UE, and both cell B and cell C save the UE context information of which C-RNTI in cell A for the corresponding UE is deleted. Accordingly, the UE context information may include the both C-RNTI in cell B (e.g. value 65280) and C-RNTI in cell C (e.g. value 20100). In this case, when being handed over to another cell, cell B and cell C exchange the RRC message (including the parameter related to RRC) made by another cell that is going to be transmitted to the UE.
Hereinafter, in case that the UE moves to position P6, the event A4-2 for cell B happens according to the measurement result of the UE (step, S1020). This is the case that the signal strength SS of cell B is smaller than or equal to Tcancel.
Small eNB C performs the un-preparation decision (step, S1025) and transmits the second multiple preparation delete message to small eNB B (step, S1030). The second multiple preparation delete message includes the information that commands cell B to be unprepared. The second multiple preparation delete message may be transmitted through the interface X2 (or X2AP).
The second multiple preparation delete message, for example, may include the parameter as shown in the following Table 8.
Table 8 includes the list of the information that is deleted (or unprepared), the phyCellId502, the c-RNTI 65280 of the search ID filed of item [0] shows that the information is going to be deleted (or unprepared) that the value of C-RNTI of cell B whose physical cell ID is 502 is 65280.
In such an environment, cell B deletes the UE context information for the corresponding UE, and cell C save the UE context information of which C-RNTI in cell B for the corresponding UE is deleted. Accordingly, the UE context information may include the C-RNTI in cell C (e.g. value 20100). That is, in the UE context information of cell C is left the information of cell C itself but not left the RRC parameter for the handover to another cell.
Referring to
Small eNB A performs the preparation decision (step, S1105) and transmits the multiple preparation request message to small eNB B (step, S1110). The multiple preparation request message may be transmitted through the interface X2 (or X2AP).
The multiple preparation request message may include the C-RNTI of cell A for the corresponding UE, and include the parameter as shown in the following Table 9, for example.
Small eNB B generates the UE context information in cell B and transmits the multiple preparation request ACK message to small eNB A (step, S1115). The multiple preparation request ACK message may be transmitted through the interface X2.
The multiple preparation request ACK message may include the C-RNTI of cell B for the corresponding UE and include the parameter as shown in the following Table 10, for example.
In such circumstances like this, cell A and cell B both save the UE context information for the corresponding UE. The UE context information may include both the C-RNTI in cell A (for example, value 100) and the C-RNTI in cell B (for example, value 65280). When being handed over to another cell, each cell exchanges the RRC message (including the parameter related to the RRC) made by another cell that is going to be transmitted to the UE.
Referring to
Small eNB A performs the preparation decision (step, S1205), and transmits the multiple preparation request message to small eNB C (step, S1210). The multiple preparation request message may be transmitted through the interface X2 (or X2AP).
The multiple preparation request message may include the C-RNTI of cell A and the C-RNTI of cell B for the corresponding UE, and include the parameter as shown in the following Table 11, for example.
Small eNB C generates the UE context information in cell C and transmits the multiple preparation request ACK message to small eNB A (step, S1215). The multiple preparation request ACK message may be transmitted through the interface X2.
The multiple preparation request ACK message may include the C-RNTI of cell C for the corresponding UE and include the parameter as shown in the following Table 12, for example.
Small eNB A performs the transmission of the preparation information to small eNB B (step, S1220). Herein, the preparation information may be transmitted through interface X2, and include the C-RNTI in cell C for the corresponding UE.
The preparation information to be transmitted, for example, may include the parameter as shown in the following Table 13.
In such circumstances like this, cell A, cell B, and cell C save the UE context information for the corresponding UE. The UE context information may include all of the C-RNTIs in cell A (for example, value 100), the C-RNTI in cell B (for example, value 65280) and the C-RNTI in cell C (for example, value 20100). Each cell may have the RRC message (RRC parameter) for the handover to the other two cells.
Referring to
Referring to
Small eNB A transmits the multiple preparation request message to small eNB B and small eNB C (step, S1405, S1410). The multiple preparation request message, for example, may include the parameter shown as in the following Table 14.
Each of small eNB B and small eNB C transmits the multiple preparation request ACK message to small eNB A (step, S1415, S1420). The multiple preparation request ACK message that is transmitted from small eNB B and small eNB C may include the parameter as shown in each of the following Table 15 and Table 16, for example.
Small eNB A performs the transmission of the preparation information to small eNB B and small eNB C (step, S1425, 1430). The preparation information that is transmitted to eNB B and small eNB C may include the parameter as shown in each of the following Table 17 and Table 18, for example.
In this case, each of cell A, cell B and cell C may keep the UE context information which is changed (or updated). In addition, in this case, each cell may have the RRC message (the RRC parameter) for handover into the other two cells. Through the procedure described above, all of cell A, cell B and cell C may be prepared, and in this case, a UE is able to perform the RLF recovery to any cell of the three cells, also, is able to perform prompt handover (HO) to any cell. Herein, it is the same as described above that the multiple preparation request message, the multiple preparation request ACK message and the preparation information may be transmitted through the X2 interface (or X2AP).
Referring to
Referring to
Small eNB A transmits the multiple preparation request message to small eNB B and small eNB C (steps, S1605 and S1610). The multiple preparation request message may include, for example, the parameters represented in following Table 19.
Table 19 includes the list of the information being reserved (or stored), c-RNTI 300 and phyCellId 501 of the change ID field in section[0] represent that parameters c-RNTI 100 and phyCellId 501 are to be changed to c-RNTI 300 and phyCellId 501.
Through the multiple preparation request message, cell B and cell C may have the changed RRC message (the RRC parameter) for handover to cell A.
Each of Small eNB B and small eNB C transmits the multiple preparation request ACK message to small eNB A (steps, S1615 and S1620). The multiple preparation request ACK message which is transmitted from each of small eNB B and small eNB C may include, for example, the parameters represented in following Table 20 and Table 21.
In this case, each of cell A, cell B and cell C may keep the UE context information which is changed (or updated). In addition, in this case, each cell may have the RRC message (the RRC parameter) for handover into the other two cells. Through the procedure described above, all of cell A, cell B and cell C may be prepared, and in this case, a UE is able to perform the RLF recovery to any cell of the three cells, also, is able to perform prompt handover (HO) to any cell. Herein, it is the same as described above that the multiple preparation request message, the multiple preparation request ACK message and the preparation information may be transmitted through the X2 interface (or X2AP).
Method 2: The UE Mobility Management Method Based on the Context Fetch Method (CFM)
Referring to
Although the possibility of RLF recovery to small cell is increased by introducing the CFM, it is required to design the protocol standard for Xn-C which is Xn interface on the Control Plane for connecting the master eNB and the small eNBs. In addition, S1-U (GTP (GPRS Tunneling Protocol)-U) on the User Plane may be used or Xn-U which is Xn interface on a new User Plane may be introduced. Hereinafter, the Xn interface may include Xn-C and Xn-U.
Referring to
Hereinafter, the UE mobility management methods according to the CFM of the present invention are suggested.
Referring to
The dotted lines in
Also, the alternate long and short dash lines show boundaries for the addition and deletion of each cell. For example, in case a UE enters into the alternate long and short dash line, it may be considered that the measurement result of the corresponding cell satisfies a predetermined threshold value Taddcell for the adding cell (the event A4-1). In case that a UE moves out of the alternate long and short dash line, it may be considered that the measurement result of the corresponding cell satisfies a predetermined threshold value Tdelcell for the releasing cell (the event A4-2).
The small cell boundary may be determined based on the threshold value Tborder.
Referring to
In case that a UE moves to P0 and the signal strength of cell A exceeds Tprep (the event A4-1), cell A as well as cell B become the prepared cells.
In case that a UE moves to Pa and the signal strength of cell A exceeds Tborder (the event A4-1), it is interpreted that the UE enters within the boundary of cell A.
In case that a UE moves to Pb and the signal strength of cell A exceeds Taddcell (the event A4-1), the addition of cell A (cell A is usable) is determined.
In case that a UE moves to P1 and the signal strength of cell A exceeds Tprep (the event A4-1), cell X, cell A and cell B are the prepared cells.
In case that a UE moves to Pc and the signal strength of cell A is smaller or the same as Tdellcell (the event A4-2), the deletion of cell A (cell A is not usable) is determined.
In case that a UE moves to P3 and the signal strength of cell A exceeds Tprep (the event A4-1), cell X, cell A, cell B and cell C are the prepared cells.
In case that a UE moves to P5 and the signal strength of cell A is smaller or the same as Tcancel (the event A4-2), cell A cancels (or releases) the preparation, and only cell X, cell B and cell C are the prepared cells.
In case that a UE moves to Pd and the signal strength of cell A exceeds Taddcell (the event A4-1), the addition of cell C (cell C is usable) is determined.
In case that a UE moves to P6 and the signal strength of cell A is smaller or the same as Tcancel (the event A4-2), cell B cancels (or releases) the preparation, and only cell X and cell C are the prepared cells.
First of all, referring to
Macro eNB X performs the preparation decision to cell A (step, S2105), and transmits the multiple preparation request message to small eNB A (step, S2110).
Small eNB A transmits the multiple preparation request ACK message to macro eNB X (step, S2115), and performs the preparation for cell A (step, S2120). The multiple preparation request message and the multiple preparation request ACK message may be transmitted through the Xn interface (or Xn Application Protocol (XnAP)).
The detour two-way path is set up for the Xn-U between macro eNB X and small eNB A (that is, Xn traffic path) (step, S2125).
Later, in case that the UE moves to position Pb, according to the measurement result of the UE, the event A4-1 for the case that the signal strength (SS) of cell A is greater than Taddcell occurs (step, S2130).
Macro eNB X performs the small cell addition decision (step, S2135), and transmits the Dual Cell RRC Connection Reconfiguration message for cell A to the UE (step, S2140).
The UE transmits the Dual Cell RRC Connection Reconfiguration Complete message to macro eNB X (step, S2145). In this case, the UE may transmit the Dual Cell RRC Connection Reconfiguration Complete message to small eNB A as well as to macro eNB X (not shown).
The UE transmits the random access preamble for the random access procedure to small eNB A through the RACH (step, S2150). Small eNB B transmits the random access response (RAR) message to the UE (step, S2155). Later, the UE transmits the RRC connection reconfiguration complete message to small eNB A (step, S2160). Small eNB A transmits the multiple preparation request ACK message to macro eNB X (step, S2165). The multiple preparation request ACK message may be transmitted through the Xn interface (or Xn Application Protocol (XnAP)). In this case, the UE may set up the uplink traffic detour ON (step, S2170), and macro eNB X may set up the downlink traffic detour ON (step, S2175). For example, in this case, the downlink packet may be transmitted to the UE through cell A, and the uplink packet may be transmitted macro eNB X through cell A.
Small eNB A performs the cell A addition procedure for the corresponding UE (step, S2180).
Through the procedures described above, macro eNB X may transmit or receive the whole or a part of the uplink/downlink packet for the UE through cell X, and small eNB A may transmit or receive the whole or a part of the uplink/downlink packet for the UE through cell A.
Later, referring to
Macro eNB X performs the preparation decision for cell B (step, S2205), and transmits the multiple preparation request message to small eNB B (step, S2210).
Small eNB B transmits the multiple preparation request ACK message to macro eNB X (step, S2215), and performs the preparation for cell B (step, S2220). The multiple preparation request message and the multiple preparation request ACK message may be transmitted through the Xn interface (or XnAP).
Macro eNB X and small eNB B set up the detour two-way path for the Xn-U (step, S2225).
Macro eNB X transmits the multiple preparation update request message to small eNB A in order to update the UE context information for cell C in cell A (step, S2230), and small eNB A transmits the multiple preparation update request ACK message to macro eNB X (step, S2235). The multiple preparation update request message and the multiple preparation update request ACK message may be transmitted through the Xn interface (or XnAP).
Later, in case that the UE moves to position Pc, according to the measurement result of the UE, the event A4-2 for the case that the signal strength of cell A is as the same or smaller than Tdelcell occurs (step, S2240).
Macro eNB X performs the small cell non-usage decision for cell A (step, S2245). The small cell non-usage decision may be called the small cell deletion decision.
Macro eNB X transmits the Dual Cell RRC Connection Release message for cell A to the UE (step, S2250). Through this, macro eNB X may notify that the resource of cell A is not usable to the UE.
The UE transmits the Dual Cell RRC Connection Release Complete message to macro eNB X (step, S2255). The Dual Cell RRC Connection Release message and the Dual Cell RRC Connection Release Complete message may be transmitted through the Xn interface (or XnAP).
Macro eNB X transmits the UE Non-Usage Request message to small eNB A (step, S2260). Through this, macro eNB X may notify that it does not provide service to the UE to small eNB A through cell A.
Small eNB A sets up the cell A non-usage for the corresponding UE (step, S2265), and transmits the UE Non-Usage Request ACK message to macro eNB X (step, S2270). The UE Non-Usage Request message and the UE Non-Usage Request ACK message may be transmitted through the Xn interface (or XnAP).
Later, referring to
Macro eNB X performs the preparation decision for cell C (step, S2305), and transmits the multiple preparation request message to small eNB C (step, S2310).
Small eNB C transmits the multiple preparation request ACK message to macro eNB X (step, S2315), and performs the preparation for cell C (step, S2320). The multiple preparation request message and the multiple preparation request ACK message may be transmitted through the Xn interface (or XnAP).
Macro eNB X and small eNB C set up the detour two-way path for the Xn-U (step, S2325).
In order to update the UE context information for cell C to cell A and cell B, macro eNB X transmits the multiple preparation update request to small eNB A and small eNB B (steps, S2330 and S2340), and small eNB A and small eNB B transmit the Multiple Preparation Update ACK Request to macro eNB X (steps, S2335 and S2345). The multiple preparation update request and the multiple preparation update request may be transmitted through the Xn interface (or XnAP).
Later, in case that the UE moves to position P5, according to the measurement result of the UE, the event A4-2 for the case that the signal strength of cell A is as the same or smaller than Tcancel occurs (step, S2350).
Macro eNB X performs the un-preparation decision for cell A (step, S2355), and transmits the UE context release message to small eNB A (step, S2360).
Small eNB A performs the small cell un-preparation for cell A based on the UE context release message (step, S2365), and transmits the UE context release ACK message to macro eNB X (step, S2370). The UE context release message and the UE context release ACK message may be transmitted through the Xn interface (or XnAP).
Macro eNB X and small eNB A release the detour two-way path for the Xn-U (step, S2375).
Macro eNB X transmits the multiple preparation update request message to small eNB B and small eNB C in order to update the related information according to the preparation release of cell A to cell B and cell C (steps, S2380 and S2390), and small eNB B and small eNB C transmit the multiple preparation update request ACK message to macro eNB X (steps, S2385 and S2395).
Later, referring to
Macro eNB X performs the small cell non-usage decision for cell B (step, S2405).
Macro eNB X transmits the Dual Cell RRC Connection Release message for cell B to the UE (step, S2410). Through this, macro eNB X may notify that the resource of cell B is not usable to the UE.
The UE transmits the Dual Cell RRC Connection Release Complete message to macro eNB X (step, S2415). The Dual Cell RRC Connection Release message and the Dual Cell RRC Connection Release Complete message may be transmitted through the Xn interface (or XnAP).
Macro eNB X transmits the UE Non-Usage Request message to small eNB B (step, S2420). Through this, macro eNB X may notify that it does not provide service to the UE to small eNB A through cell B.
Small eNB B sets up the cell B non-usage for the corresponding UE (step, S2425), and transmits the UE Non-Usage Request ACK message to macro eNB X (step, S2430).
The UE Non-Usage Request message and the UE Non-Usage Request ACK message may be transmitted through the Xn interface (or XnAP).
Later, in case that the UE moves to position P6, according to the measurement result of the UE, the event A4-2 for the case that the signal strength of cell B is as the same or smaller than Tcancel occurs (step, S2435).
Macro eNB X performs the un-preparation decision for cell A (step, S2440), and transmits the UE context release message to small eNB B (step, S2445).
Small eNB B performs the small cell un-preparation for cell B based on the UE context release message (step, S2450), and transmits the UE context release ACK message to macro eNB X (step, S2455). The UE context release message and the UE context release ACK message may be transmitted through the Xn interface (or XnAP).
Macro eNB X and small eNB B release the detour two-way path for the Xn-U (step, S2460).
Macro eNB X transmits the multiple preparation update request message to small eNB C in order to update the related information according to the preparation release of cell B (step, S2465), and small eNB C transmits the multiple preparation update request ACK message to macro eNB X (step, S2470). The multiple preparation update request message and the multiple preparation update request ACK message may be transmitted through the Xn interface (or XnAP).
Referring to
Referring to
In case that a UE moves to P0 and the signal strength of cell A exceeds Tprep (the event A4-1), cell A as well as cell B become the prepared cells.
In case that a UE moves to Pa and the signal strength of cell A exceeds Tborder (the event A4-1), the addition of cell A (cell A is usable) is determined.
In case that a UE moves to P1 and the signal strength of cell B exceeds Tprep (the event A4-1), cell X, cell A and cell B are the prepared cells.
In case that a UE moves to P2 and the signal strength of cell B is greater than the signal strength of cell A (the event A3-1), the small cell handover from cell A to cell B for the UE is performed.
In case that a UE moves to P3 and the signal strength of cell C exceeds Tprep (the event A4-1), cell X, cell A, cell B and cell C are the prepared cells.
In case that a UE moves to P4 and the signal strength of cell C is greater than the signal strength of cell B (the event A3-1), the small cell handover from cell B to cell C for the UE is performed.
In case that a UE moves to P5 and the signal strength of cell A is smaller or the same as Tcancel (the event A4-2), cell A cancels (or releases) the preparation, and only cell X, cell B and cell C are the prepared cells.
In case that a UE moves to P6 and the signal strength of cell B is smaller or the same as Tcancel (the event A4-2), cell B cancels (or releases) the preparation, and only cell X and cell C are the prepared cells.
First of all, referring to
Macro eNB X performs the preparation decision to cell A (step, S2705), and transmits the multiple preparation request message to small eNB A (step, S2710).
Small eNB A transmits the multiple preparation request ACK message to macro eNB X (step, S2715), and performs the preparation for cell A (step, S2720). The multiple preparation request message and the multiple preparation request ACK message may be transmitted through the Xn interface (or XnAP).
The detour two-way path is set up for the Xn-U between macro eNB X and small eNB A (that is, Xn traffic path) (step, S2725).
Later, in case that the UE moves to position Pa, according to the measurement result of the UE, the event A4-1 for the case that the signal strength of cell A is greater than Tborder occurs (step, S2730).
Macro eNB X performs the small cell addition decision for cell A (step, S2735), and transmits the Dual Cell RRC Connection Reconfiguration message for cell A to the UE (step, S2740).
The UE transmits the Dual Cell RRC Connection Reconfiguration Complete message to macro eNB X (step, S2745). In this case, the UE may transmit the Dual Cell RRC Connection Reconfiguration Complete message to small eNB A as well as to macro eNB X (not shown).
The UE transmits random access preamble for the random access procedure to small eNB A through the RACH (step, S2750). Small eNB A transmits the random access response (RAR) message to the UE (step, S2755). Later, the UE transmits the RRC connection reconfiguration complete message to small eNB A (step, S2760). Small eNB A transmits the multiple preparation request ACK message to macro eNB X (step, S2765). The multiple preparation request ACK message may be transmitted through the Xn interface (or XnAP). In this case, the UE may set up the uplink traffic detour ON (step, S2770), and macro eNB X may set up the downlink traffic detour ON (step, S2775). For example, in this case, the downlink packet may be transmitted to the UE through cell A, and the uplink packet may be transmitted macro eNB X through cell A.
Small eNB A performs the cell A addition procedure for the corresponding UE (step, S2780).
Through the procedures described above, macro eNB X may transmit or receive the whole or a part of the uplink/downlink packet for the UE through cell X, and small eNB A may transmit or receive the whole or a part of the uplink/downlink packet for the UE through cell A.
Later, referring to
Macro eNB X performs the preparation decision for cell B (step, S2805), and transmits the multiple preparation request message to small eNB B (step, S2810).
Small eNB B transmits the multiple preparation request ACK message to macro eNB X (step, S2815), and performs the preparation for cell B (step, S2820). The multiple preparation request message and the multiple preparation request ACK message may be transmitted through the Xn interface (or XnAP).
Macro eNB X and small eNB B set up the detour two-way path for the Xn-U (step, S2825).
Macro eNB X transmits the multiple preparation update request message to small eNB A in order to update the UE context information for cell C in cell A (step, S2830), and small eNB A transmits the multiple preparation update request ACK message to macro eNB X (step, S2835). The multiple preparation update request message and the multiple preparation update request ACK message may be transmitted through the Xn interface (or XnAP).
Later, in case that the UE moves to position P2, according to the measurement result of the UE, the event A4-1 for the case that the signal strength of cell B is greater than the signal strength of cell A occurs (step, S2840).
Macro eNB X performs the Small Cell HO Decision from cell A to cell B (step, S2845). Macro eNB X sets up the DL traffic detour to cell A as OFF (step, S2850). That is, it stops the DL traffic (or packet) transmission through cell A for the corresponding UE.
Macro eNB X transmits the Dual Cell RRC Connection Reconfiguration message toward cell B to the UE (step, S2855). The UE transmits the Dual Cell RRC Connection Reconfiguration Complete message to macro eNB X (step, S2860).
The UE transmits the Dual Cell RRC Small Cell Detach message for cell A to small eNB A (step, S2865). In this case, the UE deletes the information for small cell A yet. Small eNB A transmits the Small Cell Status Indication message that represents the detachment of cell A to macro eNB X (step, S2870).
The UE sets up the UL traffic detour for cell A as OFF (step, S2875), and small eNB A performs the cell A detach for the corresponding UE (step, S2880).
Later, the UE transmits the random access preamble for the random access procedure toward cell B to small eNB B through the RACH (step, S2885). Small eNB B transmits the random access response (RAR) message to the UE (step, S2886). Later, the UE transmits the RRC connection reconfiguration complete message to small eNB B (step, S2887). Small eNB B transmits the Small Cell Status Indication message that represents the attachment of cell B to macro eNB X (step, S2888). In this case, the UE may set up the uplink traffic detour ON (step, S2889), and macro eNB X may set up the downlink traffic detour ON (step, S2890). Small eNB B performs the cell B attach procedure for the corresponding UE (step, S2895). That is, in this case, the UE may transmit the UL traffic through cell B, and macro eNB X may transmit the DL traffic toward cell B.
Later, referring to
Macro eNB X performs the preparation decision for cell C (step, S2905), and transmits the multiple preparation request message to small eNB C (step, S2910).
Small eNB C transmits the multiple preparation request ACK message to macro eNB X (step, S2915), and performs the preparation for cell C (step, S2920). The multiple preparation request message and the multiple preparation request ACK message may be transmitted through the Xn interface (or XnAP).
Macro eNB X and small eNB C set up the detour two-way path for the Xn-U (step, S2925).
Macro eNB X transmits the multiple preparation update request message to small eNB A and small eNB B in order to update the UE context information for cell C in cell A and cell B (steps, S2930 and S2940), and small eNB A and small eNB B transmit the multiple preparation update request ACK message to macro eNB X (steps, S2935 and S2945). The multiple preparation update request message and the multiple preparation update request ACK message may be transmitted through the Xn interface (or XnAP).
Later, referring to
Macro eNB X performs the Small Cell HO Decision from cell B to cell C (step, S2845). Macro eNB X configures the DL traffic detour to cell B as OFF (step, S3010). That is, it stops the DL traffic (or packet) transmission through cell B for the corresponding UE.
Macro eNB X transmits the Dual Cell RRC Connection Reconfiguration message toward cell C to the UE (step, S3015). The UE transmits the Dual Cell RRC Connection Reconfiguration Complete message to macro eNB X (step, S3020).
The UE transmits the Dual Cell RRC Small Cell Detach message for cell B to small eNB B (step, S3025). In this case, the UE deletes the information for small cell B yet. Small eNB B transmits the Small Cell Status Indication message that represents the detachment of cell B to macro eNB X (step, S3030).
The UE sets up the UL traffic detour for cell B as OFF (step, S3035), and small eNB B performs the cell B detach for the corresponding UE (step, S3040).
Later, the UE transmits the random access preamble for the random access procedure toward cell B to small eNB B through the RACH (step, S3045). Small eNB C transmits the random access response (RAR) message to the UE (step, S3050). Later, the UE transmits the RRC connection reconfiguration complete message to small eNB C (step, S3055). Small eNB C transmits the Small Cell Status Indication message that represents the attachment of cell C to macro eNB X (step, S3060). In this case, the UE may set up the uplink traffic detour ON (step, S3065), and macro eNB X may set up the downlink traffic detour ON (step, S3070). Small eNB B performs the cell C attach procedure for the corresponding UE (step, S3075). In this case, the UE may transmit the UL traffic through cell C, and macro eNB X may transmit the DL traffic toward cell C.
Later, in case that the UE moves to position P5, according to the measurement result of the UE, the event A4-2 for the case that the signal strength of cell A is as the same or smaller than Tcancel occurs (step, S3100).
Macro eNB X performs the un-preparation decision for cell A (step, S3105), and transmits the Dual Cell RRC Connection Release message for cell A to the UE (step, S3110). The UE transmits the Dual Cell RRC Connection Release Complete message to macro eNB X (step, S3115).
Macro eNB X transmits the UE context release message for cell A to small eNB A (step, 3120). Small eNB A performs the small cell un-preparation for cell A based on the UE context release message (step, S3125), and transmits the UE context release ACK message to macro eNB X (step, S3130). The UE context release message and the UE context release ACK message may be transmitted through the Xn interface (or XnAP).
Macro eNB X and small eNB A release the detour two-way path for the Xn-U (step, S3135).
Macro eNB X transmits the multiple preparation update request message to small eNB B and small eNB C in order to update the related information according to the preparation release of cell A to cell B and cell C (steps, S3140 and S3150), and small eNB B and small eNB C transmit the multiple preparation update request ACK message to macro eNB X (steps, S3145 and S3155).
Later, referring to
Macro eNB X performs the un-preparation decision for cell B (step, S3205), and transmits the Dual Cell RRC Connection Release message for cell B to the UE (step, S3210). The UE transmits the Dual Cell RRC Connection Release Complete message to macro eNB X (step, S3215).
Macro eNB X transmits the UE context release message for cell B to small eNB A (step, 3220). Small eNB B performs the small cell un-preparation for cell B based on the UE context release message (step, S3225), and transmits the UE context release ACK message to macro eNB X (step, S3230). The UE context release message and the UE context release ACK message may be transmitted through the Xn interface (or XnAP).
Macro eNB X and small eNB B release the detour two-way path for the Xn-U (step, S3235).
Macro eNB X transmits the multiple preparation update request message to small eNB B and small eNB C in order to update the related information according to the preparation release of cell B to cell C (step, S3240), and small eNB C transmits the multiple preparation update request ACK message to macro eNB X (step, S3245). The multiple preparation update request message and the multiple preparation update request ACK message may be transmitted through the Xn interface (or XnAP).
Referring to
The receiving unit 3305 receives the measurement report from a UE. The measurement report may be received from the UE through cell A operated by the eNB 3300. The cell A may be the serving cell for the UE. The eNB 3300 may be called eNB A. However, herein the expression of the eNB A is not to limit the eNB 3300 according to the present invention, but to distinguish the other eNBs (for example, eNB B and eNB C) which will be described below. The measurement report may include the measurement result for cell A. Also, the measurement report may include the measurement result of cell B and cell C, the neighboring cells. Herein, cell A, cell B and cell C may be small cells. The measurement result includes the strength of signals.
The decision unit 3311 performs the preparation decision for the neighboring cells based on the measurement report (or the measurement result). Herein, the preparation decision represents the decision that stores (or keeps) the UE context information for the corresponding UE for a specific cell among the neighboring cells, and the cell in which the UE context information for the corresponding UE exists may be called the prepared cell or the preparation cell. In this case, the preparation cells according to the MPM may store (or keep) the UE context information for all of the preparation cells for the corresponding UE.
For example, if the signal strength of a specific cell among the neighboring cells exceeds the threshold value Tprep, the decision unit 3311 may perform the preparation decision for the specific cell. Herein, the specific cell may be cell B and/or cell C described above.
Meanwhile, the measurement result for the neighboring cells which are included in the measurement result which is transmitted by a UE may be changed according to the move of the UE or the propagate environment. For example, if the UE is positioned on P1 of
In addition, the preparation unit 3311 may also perform the un-preparation decision. For example, if the signal strength of a cell among the preparation cells is the same or smaller than a threshold value Tcancel for preparation release, the preparation unit 3311 may perform the un-preparation decision for the corresponding cell.
Also, if the UE context information for cell A is changed, the decision unit 3311 may decide the update of the changed UE context information for cell A for remainder preparation cells as well as cell A according to the MPM. For example, according to the success of the RLF recovery to cell A by the UE, the C-RNTI value of the UE for cell A may be changed. In this case, the decision unit 3311 determines that the UE context information for cell A is changed, and may decide the update of the changed UE context information for the remainder cell except cell A among the preparation cells.
The message processing unit 3312 generates the message for processing the related operation based on the decision of the decision unit 3311, and interprets and processes the message received by the receiving unit 3305.
As an example, in case that the decision unit 3311 performs the preparation decision for a specific cell (for example, cell C), the message processing unit 3312 may generate the (first) multiple preparation request message that indicates the multiple preparation of the specific cell. In this case, the multiple preparation request message may include the UE context information for the other preparation cells. In addition, in this case, for the remainder preparation cells (for example, cell B) except the serving cell (cell A) and the specific cell, the message processing unit 3312 may generate the preparation information transfer message that includes the UE context information for the specific cell in order to add the UE context information for the specific cell. In this case, the transmitting unit 3320 may transmit the multiple preparation request message to the eNB (for example, eNB C) that operates the specific cell (for example, cell C). Also, the transmitting unit 3320 may transmit the preparation information transfer message to the eNBs (for example, eNB B) that operates the remainder preparation cells (for example, cell B).
As another example, in case that the decision unit 3311 performs the un-preparation decision for the specific cell (for example, cell B) among the preparation cells, the message processing unit 3312 generates the multiple preparation deletion message that indicates the un-preparation for the specific cell. In this case, the transmitting unit 3320 transmits the preparation deletion message to the eNBs (for example, eNB B and eNB C) that operate the specific cell in which the un-preparation is decided or the remainder preparation cells (for example, cell C).
As still another example, in case that the decision unit 3311 decides the update for the changed UE context information due to the change of the UE context information for a specific cell (for example, cell A) among the preparation cells, the message processing unit 3312 may generate the (second) multiple preparation request message that indicates the update of the changed UE context information for the specific cell. In this case, the transmitting unit 3320 transmits the multiple preparation request message to the eNBs (for example, eNB B and eNB C) that operate the remainder preparation cells (for example, cell B and cell C) except the specific cell.
The receiving unit 3305 receives the (first) multiple preparation request ACK message that corresponds to the multiple preparation request message and the (second) multiple preparation request ACK message that corresponds to the multiple preparation request message that indicates the update of the changed UE context information for the specific cell.
The storage unit 3315 may store (or keep) the UE context information for the preparation cells according to the MPM and update it.
Referring to
The master eNB receiving unit 3405 receives the measurement report from the UE. The measurement report may be received from the UE through cell X which is operated by the master eNB 3400. The cell X may be the serving cell for the UE. The master eNB 3400 may be called master eNB X. The measurement report may include the measurement result of cell A, cell B and cell C which are the neighboring small cells. The measurement result includes the signal strength.
The master eNB control unit 3410 performs the preparation decision for the neighboring cells based on the measurement report (or the measurement result). Herein, the preparation decision represents the decision of storing (or keeping) the UE context information for the corresponding UE for a specific cell among the neighboring cells, and the cell in which the UE context information for the corresponding UE exists may be called the prepared cell or the preparation cell. In this case, the master eNB storage unit 3415 may stores (or keeps) the UE context information for all preparation cells for the corresponding UE according to the CFM. For example, in case that the signal strength of a specific cell among the neighboring cells exceeds the threshold value Tprep for preparation, the master eNB control unit 3410 may perform the preparation decision for the specific cell. Herein, the specific cell may be cell B and/or cell C described above. Meanwhile, according to the move of the UE or the propagation environment, the measurement result for the neighboring cells which are included in the measurement report which is transmitted from the UE may be changed. For example, in case that the UE is located at P1 of
In case that the master eNB control unit 3410 performs the preparation decision for a specific cell (for example, cell A and/or cell B), the master eNB control unit 3410 may generate the multiple preparation request message for indicating the multiple preparation of the specific cell. In this case, the multiple preparation request message may include the UE context information for the other preparation cells. Also, in this case, the master eNB control unit 3410, in order to add the UE context information for the specific cell with respect to the remainder preparation cells (for example, in case that cell A is the preparation cell and the specific cell is cell B) except the specific cell, may generate the multiple preparation update request message that includes the UE context information for the specific cell. In this case, the master eNB transmitting unit 3420 may transmit the multiple preparation request message to the eNB (for example, eNB B) that operates the specific cell (for example, cell B). Also, the master eNB transmitting unit 3420 may transmit the multiple preparation update request message to the eNB (for example, eNB A) that operates the remainder preparation cell (for example, cell A).
In addition, the master eNB control unit 3410 may also perform the un-preparation decision. For example, in case that the signal strength of a cell among the preparation cells is the same or smaller than Tcancel for preparation release, the master eNB control unit 3410 may perform the un-preparation decision for the corresponding cell.
In case that the master eNB control unit 3410 performs the un-preparation decision for a specific cell (for example, cell A) among the preparation cells, the master eNB control unit 3410 generates the UE context release message that indicates the preparation release for the specific cell. Also, the master eNB control unit 3410 may generate the multiple preparation update request message that instructs the deletion of the UE context information for the specific cell with respect to the remainder cells (for example, cell B) except the specific cell. In this case, the master eNB transmitting unit 3420 may transmit the UE context release message to the eNB (for example, eNB A) that operates the specific cell in which the un-preparation is decided. Also, the master eNB transmitting unit 3420 may transmit the multiple preparation update request message to the eNB (for example, eNB B) that operates the remainder preparation cell (for example, cell B).
In addition, the master eNB receiving unit 3405 receives the multiple preparation update request ACK message that corresponds to multiple preparation update request message instructing the multiple preparation of the specific cell, and receives the UE context release ACK message that corresponds to the UE context release message, may receive the (first) multiple preparation update request ACK message that corresponds to the multiple preparation update request message instructing the multiple preparation for the specific cell, and may receive the (second) multiple preparation update request ACK message that corresponds to the multiple preparation update request message instructing the deletion of the UE context information for the specific cell.
The eNB A 3430 includes an eNB A receiving unit 3435, an eNB A control unit 3440, an eNB A storage unit 3445 and an eNB A transmitting unit 3450. The eNB A control unit 3440 performs the process and control to perform the operation according to Method 2 of the present invention described above.
The eNB A receiving unit 3435 receives the multiple request message that indicates the multiple preparation of cell A from the master eNB 3400. Also, the eNB A receiving unit 3435 receives the multiple preparation update request message from the master eNB 3400. In addition, the master eNB A receiving unit 3435 receives the UE context release message from the master eNB 3400.
The eNB A control unit 3440 interprets and processes the message received by the eNB A receiving unit 3435. The eNB A control unit 3440 performs the cell preparation procedure based on the multiple preparation request message, and stores (or keeps) the UE context information for the preparation cells in the eNB A storage unit 3445. Also, the eNB A control unit 3440 may detect the addition of the other preparation cells based on the multiple preparation request message that indicates the multiple preparation of the specific cell, and further store the UE context information for the preparation cell which is added to the eNB A storage unit 3445. In addition, the eNB A control unit 3440 may perform the cell preparation deletion procedure based on the UE context release message, and delete the UE context information for the preparation cells from the eNB A storage unit 3445.
The eNB A transmitting unit 3450 may transmit the multiple preparation request ACK message, the (first) multiple preparation update request ACK message and the UE context release ACK message.
The eNB B 3460 includes an eNB B receiving unit 3465, an eNB B control unit 3470, an eNB B storage unit 3475 and an eNB B transmitting unit 3480. The eNB B control unit 3470 performs the process and control to perform the operation according to Method 2 of the present invention described above.
The eNB B receiving unit 3465 receives the multiple request message that indicates the multiple preparation of cell B from the master eNB 3400. Also, the eNB B receiving unit 3465 receives the (second) multiple preparation update request message that instructs the deletion of the UE context information for the specific cell from the master eNB 3400.
The eNB B control unit 3470 interprets and processes the message received by the eNB B receiving unit 3465. The eNB B control unit 3470 performs the cell preparation procedure based on the multiple preparation request message, and stores (or keeps) the UE context information for the preparation cells in the eNB AB storage unit 3475. Also, the eNB B control unit 3470 may detect the preparation release of the other preparation cells based on the multiple preparation update request message that indicates the deletion of the UE context information for the specific cell, and delete (or update) the UE context information for the preparation released cell from the eNB B storage unit 3475.
The eNB A transmitting unit 3450 may transmit the multiple preparation request ACK message and the (second) multiple preparation update request ACK message.
According to the present invention, in the new mobile communication system environment, the wireless resource management can be effectively performed.
So far, the present invention has been described by reference to the drawings and the embodiments as an example, and it should be understood by those skilled in the art, however, that the present invention can be modified or changed in various ways without departing from the technical principles and scope. Accordingly, the embodiments disclosed in the present invention are not intended to limit the scope of the inventive concept of the present invention, but to describe, and the scope of the inventive concept of the present invention is not limited to the embodiment. The scope of the present invention should be interpreted by the claims below, and it should be interpreted that all inventive concepts within the equivalent scope are included in the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2014-0082439 | Jul 2014 | KR | national |
