Patent Application
20110149913
This application claims the benefit of Korean Patent Application No. 10-2009-0125988, filed on Dec. 17, 2009, Korean Patent Application No. 10-2009-0126044, filed on Dec. 17, 2009, Korean Patent Application No. 10-2010-0057440, filed on Jun. 17, 2010, and Korean Patent Application No. 10-2010-0057441, filed on Jun. 17, 2010, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method and a serving base station for determining a handover type, and a method for a handover between base stations in a wireless mobile communication system using a carrier aggregation that may provide a criterion for determining a handover within a base station or a handover between base stations, based on a carrier aggregation.
2. Description of the Related Art
A mobility management method used in an existing cellular mobile communication system may perform an access mobility management through a handover, based on a determination of an algorithm managing network resources based on existing cell concepts. However, the existing mobility management method does not consider a carrier aggregation (CA) environment and thus, there is a desire for a new approach to a method of mobility management. Accordingly, there is a need to provide a mobility management method suitable for a CA environment, for example, non-matching of a coverage, non-matching of an uplink/downlink frequency, and the like.
An aspect of the present invention provides a mobility management method of a user equipment in a cellular mobile communication environment using a carrier aggregation (CA), to establish a concept of a handover between base stations and a handover within a base station, and to provide a criterion required to perform the handover.
Another aspect of the present invention also provides a method applicable to an inter-evolved nodeB (eNodeB) handover among mobility management methods of a user equipment in a cellular mobile communication environment using a CA.
According to an aspect of the present invention, there is provided a method of determining a handover type of a serving base station being currently connected by a user equipment in a wireless mobile communication system using a CA, the method including: collecting measurement information required to determine an optimal frequency band set to be used for the handover; performing data processing of the collected measurement information to determine a temporary frequency band set for a downlink handover or an uplink handover; and determining the optimal frequency band set for the downlink handover or the uplink handover, depending on whether the determined temporary frequency band set supported by the serving base station and whether the determined temporary frequency band set supported by a neighboring base station of the serving base station.
The collecting may include collecting, by the serving base station, information measured by the user equipment using a Radio Resource Control (RRC) interface, information measured within the serving base station, received using a Control Service Access Point (CSAP) interface, and resource information of the neighboring base station using an X2 interface.
The performing of the data processing may include performing radio condition related processing, traffic load processing, and interference related processing based on the collected measurement information.
When the determined temporary frequency band set corresponds to the optimal frequency band set for the downlink handover and supported by the neighboring base station, the determining of the optimal frequency band set may include selecting, from the neighboring base station or the serving base station, the optimal frequency band set for the uplink handover.
The method may further include determining a type of the downlink handover based on a number of frequency bands with respect to a downlink being currently used by the user equipment and a number of frequency bands included in an optimal frequency band set with respect to the downlink when the optimal frequency band set for the uplink handover is selected from the neighboring base station.
The method may further include determining a type of the uplink handover based on a number of frequency bands with respect to an uplink being currently used by the user equipment and a number of frequency bands included in an optimal frequency band set with respect to the uplink.
When the determined temporary frequency band set corresponds to the optimal frequency band set for the uplink handover and supported by the neighboring base station, the determining of the optimal frequency band set may include selecting, from the neighboring base station or the serving base station, the optimal frequency band set for the downlink handover.
The method may further include determining a type of the downlink handover based on a number of frequency bands with respect to a downlink being currently used by the user equipment and a number of frequency bands included in an optimal frequency band set with respect to the downlink when the optimal frequency band set for the downlink handover is selected from the neighboring base station.
The method may further include determining a type of the uplink handover based on a number of frequency bands with respect to an uplink being currently used by the user equipment and a number of frequency bands included in an optimal frequency band set with respect to the uplink.
According to another aspect of the present invention, there is provided a serving base station for determining a type of a handover type of a user equipment in a wireless mobile communication system using a CA, the serving base station including: a collecting unit to collect measurement information required to determine an optimal frequency band set to be used for the handover; a data processor to perform data processing of the collected measurement information, and to thereby determine a temporary frequency band set for a downlink handover or an uplink handover; and a determining unit to determine the optimal frequency band set for the downlink handover or the uplink handover, depending on whether the determined temporary frequency band set supported by the serving base station and whether the determined temporary frequency band set supported by a neighboring base station of the serving base station.
The collecting unit may collect information measured by the user equipment using a Radio Resource Control (RRC) interface, information measured within the serving base station, received using a Control Service Access Point (CSAP) interface, and resource information of the neighboring base station using an X2 interface.
The data processor may perform radio condition related processing, traffic load processing, and interference related processing based on the collected measurement information.
When the determined temporary frequency band set corresponds to the optimal frequency band set for the downlink handover and supported by the neighboring base station, the determining unit may select, from the neighboring base station or the serving base station, the optimal frequency band set for the uplink handover.
When the determined temporary frequency band set corresponds to the optimal frequency band set for the uplink handover and supported by the neighboring base station, the determining unit may select, from the neighboring base station or the serving base station, the optimal frequency band set for the downlink handover.
According to still another aspect of the present invention, there is provided a method for a handover between base stations in a wireless mobile communication system using a CA, the method including: receiving and storing measurement information associated with neighboring base stations positioned around a serving base station; analyzing the measurement information to determine, as a candidate group, resources of neighboring base stations having a downlink quality greater than a reference value; reserving a resource of a neighboring base station having a greatest downlink quality in the candidate group as a resource to be used for a handover of a user equipment; performing the handover of the user equipment to the neighboring base station having the greatest downlink quality through the reserved resource; and cancelling the reserved resource when the downlink quality of the reserved resource becomes to be less than the reference value.
According to yet another aspect of the present invention, there is provided a method for an inter-eNodeB handover in a wireless mobile communication system using a CA, the method including: storing and processing measurement information received using an RRC interface and a CSAP interface; performing inter-eNodeB information exchange and resource preparation using an X2 interface; and determining a target eNodeB based on the measurement information and a resource preparation state of a neighboring eNodeB to perform a handover. When determining the target eNodeB in a candidate group of a final stage, history information regarding inter-eNodeB handover may be used for a handover decision.
The received measurement information may include downlink measurement information for each CC with respect to current serving eNodeB and neighboring base stations, and may additionally include information in an aspect of policy and uplink measurement information measured in source eNodeB.
The history information may store information regarding a serving base station of a user equipment while the user equipment is moving between eNodeBs in a state where the user equipment is wirelessly connected to a network. The information may include a CA ID associated with each component carrier (CC) associated with a frequency bandwidth. The CA ID is defined herein as an ID that can include information for separating the frequency bandwidth and globally uniquely identify a (DL) CC of corresponding eNodeB. However, it is only an example and thus, the CA ID may be modified in any type and thereby be used.
Specifically, the CA ID includes information regarding which base station includes which frequency bandwidth (which CC) and thereby may globally uniquely identify a CC of a corresponding base station. The history information may include a previous serving base station CA ID that is information of a previous serving base station while the user equipment is moving to another base station (eNodeB), a cell type, a duration time, downlink signal-to-noise (SNR) quality information of a current serving base station and the previous serving base station at a point in time of movement, and the like.
The history information may be recorded by the current serving base station. In the case of handover through X2AP, previous record may be handed over. Also, the history information may be transferred by using the user equipment as a medium, through a handover message of an RRC protocol and a handover complete message.
When the history information is transferred through the X2AP, the history information may be transferred through a message design for a new signal of X2AP of the user equipment or using existing handover related message.
The method may further include: analyzing, for each CC based on the stored history information, a frequency of the user equipment from current CA to another CA when the inter-eNodeB handover of the user equipment is determined; and performing the handover to a CA having a greatest frequency of the user equipment.
The method may further include determining the handover as an unnecessary handover and maintaining a CC set being currently used by the user equipment, when a duration time of the user equipment in the CA having the greatest frequency is less than a predetermined reference value, or when the handover having a relatively short duration time is frequently performed while a radio quality approaching a predetermined reference value.
According to a further another aspect of the present invention, there is provided a method for an inter-eNodeB handover in a wireless mobile communication system using a CA, the method including: determining, by a source base station to determine a CC set to be assigned to a user equipment when a handover preparation process for requesting handover between base stations is not performed; preparing a call preparation process through a handover request between the source base station and neighboring base stations and an acceptance of the handover request; and performing a handover by assigning, to the user equipment, one of CC sets received from the neighboring base stations when the determined CC set is different from the received CC sets.
The performing may include: performing again the call preparation process when a signal quality of the determined CC set is less than a signal quality of the received CC set; and performing the handover by assigning, to the user equipment, a CC set having a greatest signal quality among the CC sets received from the neighboring base stations.
Among the CC sets received from the neighboring base stations, all the CC sets having a signal quality greater than a minimum signal quality of each CC of the source base station may be assigned to the user equipment.
According to embodiments of the present invention, when performing a mobility management of a user equipment in a carrier aggregation (CA) environment, for example, when performing inter-evolved NodeB (eNodeB) handover (HO), it is possible to decrease an unnecessary handover and make a robust handover.
Also, according to embodiments of the present invention, by providing a criterion required for determining a type of a handover based on a CA environment, it is possible to increase a system capacity, and to effectively perform a handover within a base station or a handover between base stations.
These and/or other aspects, features, and advantages of the invention will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. Exemplary embodiments are described below to explain the present invention by referring to the figures.
When it is determined detailed description related to a related known function or configuration they may make the purpose of the present invention unnecessarily ambiguous in describing the present invention, the detailed description will be omitted here. Also, terms used herein are defined to appropriately describe the exemplary embodiments of the present invention and thus may be changed depending on a user, the intent of an operator, or a custom. Accordingly, the terms must be defined based on the following overall description of this specification.
Hereinafter, the network system will be described based on a next generation mobile communication system including, as technology applicable to all the cellular mobile communication systems, a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) structure and an International Mobile Telecommunication (IMT)-Advanced structure.
In the network system of
An access gateway (aGW) 40 may include a Mobility Management Entity (MME) and an SAE gateway (S-GW). The aGW 40 denotes a mobile communication system management entity. The aGW 40 corresponds to a node similar to a serving General Packet Radio Service (GPRS) support node (SGSN) and a gateway GPRS support node (GGSN) in WCDMA. A user equipment (UE) 10 may be a communicable mobile station, for example, a mobile phone, a laptop, a notebook, and the like.
From viewpoint of eNodeB, a radio interface between the eNodeB (1) 20 and the UE 10, an X2 interface between the eNodeB (1) 20 and the eNodeB (2) 30, and an S1 interface between the eNodeB (2) 30 and the aGW 40 exist. From viewpoint of a control plane of a Radio Network Layer (RNL), the radio interface may be referred to as a Radio Resource Control (RRC) interface, the S1 interface may be referred to as an S1 Application Part (S1AP) interface, and the X2 interface may be referred to as an X2AP interface. The above interface may be defined as a protocol. Procedures for each function may be defined. Messages to be used, information associated with each of the messages, and the like may be defined in a corresponding procedure.
Generally, 3GPP series may perform mobility management of a Network Controlled Mobile Assisted (NCMA) type. Specifically, in the case of the 3GPP series, a network (eNodeB in
Referring to
Accordingly, each of the D-RRMs 50 and 60 may control a resource of the UE through signaling using an RRC protocol between each of the eNodeB 1 and the eNodeB 2 and the UE, or may receive a report about a measurement with respect to circumstances (DL Meas, L2 Meas) in the UE. Here, DL Meas indicates a downlink measurement and L2 Meas indicates an L2 measurement.
The D-RRM 50 may interface with an MME through signaling using an S1AP protocol, and may interface with neighboring eNodeB through signaling using an X2AP protocol. Also, the D-RRM 50 may receive a report about resource control and measurement (N.UL Meas, N.L2 Meas) within eNodeB through CSAPL1 and CSAPL2 within the eNodeB. Here, N.UL Meas indicates a network uplink measurement and N.L2 Meas indicates a network L2 measurement.
Accordingly, the D-RRM 50 may perform integral and systematical mobility management based on information obtained using the aforementioned various interfaces.
The aforementioned function of the D-RRM 50 performing the integral and systematical mobility management is herein referred to as Connection Mobility Control (CMC), which will be described later. In addition to the CMC, The D-RRM 50 may include a Traffic and Load Control (TLC) function and an Interference Coordination Control (ICC) function. The mobility management in the CMC based on the TLC and the ICC will be further described.
Referring to
The RRC protocol and CSAP may be used for mobility management. The S1AP that is an interface protocol between the eNodeB and the MME may be used to perform a portion of a mobility management function (e.g., a change of a data path and a signal between eNodeB and aGW according to change of eNodeB). The X2AP may be used to perform a portion of the mobility management function (e.g., handover preparation and exchanging of handover information between base stations).
Specifically, the RRC corresponds to an interface protocol between the UE and the eNodeB, and the X2AP corresponds to an interface protocol between the eNodeB and another eNodeB. The CSAP corresponds to a Control Service Access Point between L1 (PHY) and L2 (Media Access Control (MAC), RLC, Packet Data Convergence Protocol (PDCP), and GPRS Tunneling Protocol (GTP)) of the eNodeB of the CSAP. The S1AP corresponds to an interface protocol between the eNodeB and the MME.
From viewpoint of a control standard protocol and a local interface, the RRC, the X2AP, the SLAP, and the CSAP correspond to a control plane. Measurement monitoring and control may be for quick and robust handover in an aspect of general mobility management. The D-RRM may perform handover prediction, handover decision, handover coordination, and handover optimization using the aforementioned interfaces.
Referring to
A diagram 421 shows the frequency bandwidth separated into FA1, FA2, and FA3. As shown in a diagram 422, when inter-cell interference exists, it is possible to prevent the interference by performing cell planning of using a frequency reuse factor as “3”.
A diagram 431 shows a case where a cell is sectored using a directional antennal to increase a total data throughput of the cell in a single base station. Here, each of FA1, FA2, and FA3 is sectored into three sectors by employing the directional antennal with respect to the single base station. A diagram 432 shows an embodiment of planning the cell of the diagram 431.
A diagram 441 illustrates an example of cell planning using only FA1 when interference does not exist due to the characteristic of the radio transmission scheme. In this case, a frequency reuse factor of FA1 is “1” as shown in a diagram 442.
A diagram 451 illustrates an example of a mobile communication provider assigned with frequencies of FA2 and FA3 even though inter-cell interference does not exist, and a diagram 452 illustrates an example of cell planning in the case of the diagram 451. In a case where each cell employs the same radio scheme, when a wirelessly connected UE moves from an FA1 cell to another FA1 cell, this movement may be defined as intra-frequency handover. When the UE moves from one cell to a different cell such as movement from a FA1 cell to a FA2 cell, this movement may be defined as inter-frequency handover. In
As described above, a frequency reuse factor may be set to “1” when inter-cell interference does not exist. When the inter-cell interference exists due to a radio transmission scheme, cell planning may be performed so that the frequency reuse factor may be at least “1” by dividing the frequency bandwidth assigned to the mobile communication provider, or a separate interference alignment scheme may be employed while setting the frequency reuse factor to “1”. Even though the radio access scheme does not cause the inter-cell interference, it is possible to divide the assigned frequency bandwidth and thereby use the divided frequency bandwidth.
Among major terms used in a carrier aggregation (CA) environment, a component carrier (CC) corresponds to an available frequency band and herein indicates an available frequency band used for a CA. The term “CA” indicates a set of CCs simultaneously operable when transmitting and receiving data between a base station and a UE, or a concept of a possible simultaneous operation of the CCs.
For example, from viewpoint of a base station, CC1, CC2, and CC3 may be used for a downlink, and CC4, CC5, and CC6 may be used for an uplink. Based on CA capability of UE connected to the above base station, the UE may substantially use CC1 and CC2 for the downlink, and use CC4 and CC6 for the uplink. With the above assumption, a CC set being used by the UE (UCcc) may be defined as DL {CC1, CC2} and UL {CC4, CC6}.
When a single available frequency carrier is CC in
The term “CC set” used herein may indicate a set of frequency bands available in the same base station for CA. The CA may indicate a set of CCs simultaneously operable in the single base station or a possible simultaneous operation of the CCs in the same base station. Each of an UL CC set and a DL CC set may be defined.
CC1, CC2, and CC3 may be consecutively assigned as shown in a diagram 510, or may be inconsecutively assigned as shown in a diagram 520 to thereby have different frequency bandwidths, for example, FB1, FB2, and FB3. Also, all of CC1, CC2, and CC3 may be assigned to a single provider, or a portion thereof may be assigned to different providers.
When a radio access scheme where interference does not exist or an interference alignment scheme exists, CC1, CC2, and CC3 of a diagram 521 may have the same cell coverage as shown in a diagram 522. CC planning may be performed for each of base stations 51, 52, and 53 so that CC1, CC2, and CC3 may be simultaneously operated in a single base station, for example, the base station 51. This may indicate that the single base station, for example, the base station 51 may transfer data using all of CC1, CC2, and CC3 based on a performance of a terminal, that is, a UE.
As shown in a diagram 531, it is possible to increase a total data throughput of the same base station by sectoring CC1, CC2, and CC3. Cell planning of a diagram 532 may be performed.
Referring to
A diagram 611 illustrates an example of CC planning where a coverage of CC1 is smaller than a coverage of CC2 and CC3 in all the base stations 61, 62, and 63. A diagram 612 illustrates an example of CC planning where all of CC1, CC2, and CC3 have the same coverage in a base station 64, a coverage of CC1 is smaller than a coverage of CC2 and CC3 in a base station 65, and CC1 is absent in a base station 66.
In an existing cell concept, a UL frequency bandwidth and a DL frequency bandwidth may constitute a single pair, and a cell is described based on a DL coverage in
However, in the CA environment, when a CA technology is applied to a single base station 71, a number of frequency bands for DL may be different from a number of frequency bands for UL. As shown in
Diagrams 811 and 812 show a handover between CC sets (CC1 and CC2) operated in the same base station (eNodeB 1), which is referred to as Intra-eNodeB Batch HO.
Referring to the diagram 811, since a UE uses CC2 while using CC1, first Intra-eNodeB Batch HO occurs. Since the UE uses CC1 while using CC2, second Intra-eNodeB Batch HO occurs.
Referring to the diagram 812, a first type corresponds to Intra-eNodeB CC Breakup HO that the UE simultaneously uses two CC sets (CC1 and CC2) while using only a single CC (CC1). A second type corresponds to Intra-eNodeB CC Union HO that the UE uses only a single CC (CC1) while simultaneously using two CC sets (CC1 and CC2).
Diagrams 821 and 822 show a handover between base stations based on a CC circumstance. Referring to the diagram 821, a first type corresponds to Inter-eNodeB Intra-CC Batch HO that the UE moves to CC1 of another base station (eNodeB 2) while using single CC1 in a previous base station (eNodeB 1). A second type corresponds to Inter-eNodeB Inter-CC Batch HO that the UE moves to CC2 of another base station (eNodeB1) while using CC1 in a single base station (eNodeB 2).
Referring to the diagram 822, a first type corresponds to Inter-eNodeB CC Breakup HO that the UE uses CC1 and CC2 for handover to another base station (eNodeB 2) while using CC1 in a previous base station (eNodeB1). A second type corresponds to Inter-eNodeB CC Union HO that the UE uses only single CC1 of another base station (eNodeB 1) while using CC1 and CC2 in a single base station (eNodeB 2).
A diagram 831 shows CC More Split Breakup HO where the UE uses additional CC while using at least one CC, CC Less Split Breakup HO where a number of CCs decreases, and CC Maintain Split Breakup HO where a number of CCs is maintained in a handover. A call of the diagram 831 is referred to as a split phenomenon. The split phenomenon may occur in Intra-eNodeB or in Inter-eNodeB.
Generally, in handover, UL and DL may constitute a pair. UL handover may also be performed based on DL. The handover of
[Handover Process]
Hereinafter, a handover process will be described by separating the handover process into three operations.
A first operation corresponds to a measurement monitoring and information collecting operation. A D-RRM of a framework as shown in
A second operation corresponds to a handover preparation and decision operation. CMC may prepare currently available CC sets based on processed data, and may determine whether handover is to be substantially performed.
A third operation corresponds to a handover execution operation. A UE may be handed over at an appropriate point in time and thereby be moved to another eNodeB, i.e., a different cell to establish a new connection.
Selectively, in the second operation, CMC may accept a request of TLC or ICC and thereby perform the handover. According to an embodiment of the present invention, a handover type may be determined by considering a CA environment introduced to perform the aforementioned three operations.
The D-RRM may prepare candidate CC sets to determine a handover type of
Specifically, in the information collecting operation, the UE may measure information associated with a radio link quality (L1 DL Meas) for each CC being currently used, a state of UL traffic buffer (L2 Meas) for each CC being currently used, and the like. The UE may report to a current serving base station (eNodeB) about the measurement result using an RRC protocol.
As shown in
Referring to
In
Measurement values measured by L1 and L2 of the base station may be expressed by the following Table 2:
Measurement values measured in L1 and L2 of the UE may be expressed by the following Table 3:
In Table 3, each of a UL buffer amount and a DL interference level may be classified into good, average, and poor, and thereby be operated. Consequently, for the mobility management in the CA environment, the D-RRM may perform management and update of semi-static information as shown in Table 1, and may obtain information measured through CSAP in the base station of the D-RRM as shown in Table 2, and information measured by the UE as shown in Table 3 through RRC. Specifically, the D-RRM may perform the mobility management in the CA environment, based on the above information as shown in Table 1, Table 2, and Table 3.
In general, a handover in the CA environment may occur in the following three cases:
Specifically, in a first case where SNR quality of currently connected CCs is deteriorated, in a second case where interference is relieved in a system aspect, and in a third case where a load distribution of a system level is required based on a traffic situation, the handover may occur.
According to an embodiment of the present invention, an example where the first case is handled by CMC of the D-RRM, the second case is handled by ICC, and the third case is handled by TLC will be described.
Initially, the second case where the interference is relieved in the system aspect will be further described.
When an ICC function is included in the D-RRM, ICC may perform interference control by means of UL/DL Physical Resource Block (PRB) use policy and proactive approach for each CC according to the interference coordination policy described above with Table 1. The interference control may be referred to as interference indication. The proactive approach indicates preventively controlling of interference according to a pre-defined interference standard.
ICC may perform the interference control using reaction approach based on a measurement result of an interference level (ULCCIL, DLCCIL) for each CC used by a corresponding UE, which is described above with reference to Table 2 and Table 3. Information received by CMC from ICC according to the interference control of ICC is defined herein as interference indication. The reaction approach indicates that interference is later controlled based on an interference occurrence result.
In a proactive aspect, the interference indication may indicate refraining or recommending use of a particular PRB resource in CC used by the corresponding UE since the interference is controlled, or may indicate forbidding use of corresponding CC or using of the corresponding CC.
In a reactive aspect, the interference indication may indicate requesting of a reaction based on an interference level occurring in CC used by the corresponding UE. For example, the interference level “good” corresponds to a case where a relatively large amount of interference exists in PRB being used in corresponding CC used by the UE. Accordingly, as a reaction, it is possible to move to another PRB in the same CC, or to move from current CC to another CC.
Specifically, the embodiment is based on the CA environment and thus, an operation of moving from current PRB to another PRB in the same CC may be performed by means of a MAC scheduler. Accordingly, the aforementioned interference indication of ICC may be interpreted as a meaning of controlling the corresponding UE to not use corresponding CC due to an interference issue. CMC of the D-RRM recognizing the above interference indication may not use the corresponding CC.
Hereinafter, the third case where the load distribution of the system level is required based on the traffic situation will be further described.
When a TLC function is included in the D-RRM, TLC may perform overload indication control by considering or referring to the aforementioned information with reference to Table 1, Table 2, and Table 3. For example, in the aforementioned information, the maximum capacity of DL and UL for each CC (DLMC (Parm 1-1), ULMC (Parm 1-2)) and quality ((Parm 1-4), (Parm 1-5)) may be considered. Also, the available capacity of UL and DL (DLCCAC (Parm 2-1), ULCCAC (Parm 2-2)), the traffic buffer amount of UL and DL (DLCCBA (Parm 2-3), ULCCBA (Parm 3-1)) may be referred to.
The overload indication control indicates that TLC informs, based on the aforementioned information, CMC to constrain random UE using random CC. When the determined overload indication is received from TLC, and when the corresponding UE is using the corresponding CC, CMC may perform a most appropriate type of handover without using the corresponding CC.
[Handover Type Decision of
Hereinafter, a method of determining, by the D-RRM of the current base station of
One of the greatest changes in the handover in the CA environment may include that Intra-eNodeB HO may occur, and that UL handover and DL handover of Intra-eNodeB HO may separately occur in independent time. Intra-eNodeB HO corresponds to a handover where CC is changed in the same base station.
In the case of Inter-eNodeB HO, UL handover and DL handover may need to be simultaneously performed. Inter-eNodeB HO may consider only DLENODEBCCSNR quality (Parm 3-2 of Table 3) which is similar to an existing handover, and may also consider ULCCQ quality (Parm 2-4 of Table 2) and DLENODEBCCSNR. Specifically, when a Best CC set (BCcc) is determined in one link (e.g., DL), and when the determined BCcc set indicates Inter-eNodeB HO, BCcc of another link (e.g., UL) may also be determined from CCs of a target base station. In a state where both UL BCcc and DL BCcc with respect to the target base station are secured, Inter-eNodeB HO needs to be performed. This is because BCcc corresponds to a CC set of the target eNodeB. BCcc indicates a CC set determined to be most appropriate for a UE, which is being currently serviced in a serving base station.
When comparing UL (UCcc) and DL (UCcc) in a current serving base station with UL (BCcc) and DL (BCcc) determined by the serving base station, a DL based handover type of
When comparing UL (UCcc) and DL (UCcc) in the current serving base station with UL (BCcc) and DL (BCcc) determined by the serving base station, a comparison result may be Inter-eNodeB HO. In this case, UL only HO, DL only HO, or UL/DL simultaneous HO may occur, which may be a union type or a split type.
Also, when comparing UL (UCcc) and DL (UCcc) in the current serving base station with UL (BCcc) and DL (BCcc) determined by the serving base station, a comparison result may be Inter-eNodeB HO. In this case, UL/DL simultaneous HO may be performed. Also, Inter-eNodeB CC Breakup HO of the diagram 822 may occur in DL, and Inter-eNodeB Intra-CC Batch HO of the diagram 821 may occur in UL, which may be a union type or a split type.
Similarly, in the case of Inter-eNodeB HO, UL and DL simultaneously HO may need to be performed with respect to the target eNodeB. However, their types may be the same as each other or be different from each other. A procedure of determining the above type will be described with reference to
When handover execution is performed after handover decision, a serving base station may transmit, to a UE, an RRCConnectionReconfiguration (for HO) message. The serving base station may integrally provide information associated with PHY/MAC/RLC/PDCP required to use the determined UL and/or DL BCcc and connection relationship between mutual entities.
When the transmitted RRCConnectionReconfiguration message includes an Intra-eNodeB HO command, the serving base station may continuously maintain a status of the serving base station, and the UE may transmit, to the serving base station, an RRCConnectionReconfigurationComplete message that is a response message to the RRCConnectionReconfiguration message.
Also, when the transmitted RRCConnectionReconfiguration message includes an Inter-eNodeB HO command, the serving base station may lose the status of the serving base station and become a neighboring base station. The UE may transmit, to the corresponding neighboring base station, an RRCConnectionReconfigurationComplete message that is a response message to the RRCConnectionReconfiguration message.
Referring again to
Also, when BCcc to be determined on the UL or DL side is determined in CC within a source base station, and when the determined BCcc is different from UCcc, Intra-eNodeB HO may occur. However, when only a UL case is different, UL only Intra-eNodeB HO may occur. When only a DL case is different, DL only Intra-eNodeB HO may occur.
When the determined UL or DL BCcc is CC of a neighboring base station, a handshake message exchange with the neighboring base station may be required. Parm 4-2-3 determined through the above exchange may be determined as finally cooperated BCcc. The handshake message exchange may correspond to a process of transmitting, by the serving base station, a handover request message (4-1) of Table 4 to the neighboring base station, and transmitting, by the neighboring base station as a response, a handover request acknowledgment (ACK) message (4-2) of Table 4 to the serving eNodeB. A process of determining, by the neighboring base station, Parm 4-2-3 will be omitted.
Hereinafter, cases of a handover type based on a variety of situations will be described.
serving base station UCcc
UE1 UL UCcc=eNodeB1 {CC6}
UE1 DL UCcc=eNodeB1 {CC1, CC2, CC3}
Case 1
UE1 UL UCcc=eNodeB 1 {CC6}
UE1 DL UCcc=eNodeB1 {CC1, CC2, CC3}
Case 2
UE1 UL BCcc=eNodeB1 {CC6}
UE1 DL BCcc=eNodeB1 {CC2, CC3}
Case 3
UE1 UL BCcc=eNodeB1 {CC5}
UE1 DL BCcc=eNodeB1 {CC1, CC2, CC3}
Case 4
UE1 UL BCcc=eNodeB2 {CC5}
UE1 DL BCcc=eNodeB1 {CC2,CC3}
Case 4-1
UE1 UL BCcc=eNodeB2 {CC5}
UE1 DL BCcc=eNodeB2 {CC1,CC3}
[UCcc AND Case 1. BCcc]
HO does not occur.
[UCcc AND Case 2. BCcc]
Only [DL HO Execution] occurs, and a handover type corresponds to Intra-eNodeB CC Less Split Breakup HO.
[UCcc AND Case 3. BCcc]
Only [UL HO Execution] occurs, and a handover type corresponds to Intra-eNodeB CC Batch HO.
[UCcc AND Case 4. BCcc]
In Case 4, it can be recognized that inter-eNodeB exists in UL BCcc.
Transmits the handover request message (4-1) of Table 4 to eNodeB 2 (Parm 4-1-4 corresponds to only DL case. Here, CC of DLENODEBCCSNR of eNodeB 2 over (Parm 1-6) DLCCTH of Table 1 may be input in a descending order). If (Parm 4-2-2) of the handover request ACK message (4-2) of Table 4 in response to the above message is a success, (Parm 4-2-3) is updated with BCcc.
When BCcc received as a response corresponds to Case 4-1, [DL HO Execution] and [UL HO Execution] may need to be processed into a single message and thereby simultaneously be processed. The former (DL) corresponds to Inter-eNodeB CC Less Split Breakup HO, and the latter (UL) corresponds to Inter-eNodeB Inter-CC Batch HO.
[Data Processing]
Data processing used for HO decision corresponds to a process of receiving handover related information through RRC, X2AP, and CSAP in the framework of
[Data Processing-Radio Condition Related Processing as a CMC Function]
In
A group of CC sets being currently used may be generally managed based on two types. One type is defined as CC set (UCcc) of a serving base station being currently used by UE, and may be managed with respect to UL and DL. Another type is defined as BCcc. With respect to each of the serving base station and neighboring base station, radio condition may be measured in UL and DL. A CC set (Measured CC (MCcc) based on the measured radio condition may be prepared. Here, CC having a best condition to be used in the MCcc is defined as BCcc.
[UCcc]
UE1−DL UCcc=eNodeB1 {CC1, CC2}
UE1−UL UCcc=eNodeB1 {CC6}
Indicates that UE1 is using CC6 of eNodeB1 for UL, and is using CC1 and CC2 for DL.
[MCcc]
UE1−DL MCcc=eNodeB1 {CC1,CC2,CC3}
UE1−DL MCcc=eNodeB2 {CC1,CC2,CC3}
UE1−UL MCcc=eNodeB1 {CC4,CC5,CC6}
A D-RRM of a serving base station (eNodeB 1) may control a measurement target for each CC. For example, through measurement control, the serving base station (eNodeB 1) may instruct UE1 to measure DLENODEBCCSNR (Parm 3-2) with respect to DL CC1, CC2, and CC3 of the serving base station (eNodeB 1), and with respect to DL CC1, CC2, and CC3 of a neighboring base station (eNodeB 2).
Also, the serving base station (eNodeB 1) may instruct L1 of the serving base station (eNodeB 1) to measure ULCCQ (Parm 2-4) with respect to UL CC4, CC5, and CC6 of the serving base station (eNodeB 1) being currently used by UE1.
For each CC, a DLENODEBCCSNR measurement value with respect to DL and UL CCQ measurement value with respect to UL may be obtained from MCcc determined through the measurement control.
[BCcc]
In the case of DL, if DLENODEBCCSNR with respect to each CC member of UCcc is greater than ‘DLCCTH (Parm 1-6)+DLCCTHMargin’, DL UCcc=DL BCcc.
In the case of UL, if ULCCQ with respect to each CC member of UCcc is greater than ‘ULCCTH (Parm 1-6)+ULCCTHMargin’, UL UCcc=UL BCcc.
Here, a margin (DLCCTHMargin, ULCCTHMargin) value in a system operation may be applicable to DLCCTH and ULCCTH.
In the case of DL, if DLENODEBCCSNR with respect to each CC member of UCcc becomes to be less than ‘DLCCTH (Parm 1-6)+DLCCTHMargin’, DL BCcc may be calculated as follows:
A. Algorithm DL BCcc Determining Process:
In a.1.4, a handshake process with a neighboring base station using 4-1 and 4-2 that are X2AP messages may be sequentially performed, or may be performed in parallel with a neighboring base station satisfying a condition of a.1.1, or may be performed in a case where a DLENODEBCCSNR value exceeds a predetermined reference value. When using X2AP, DL BCcc may need to be transferred through (Parm 4-2-3).
In the case of UL, if ULCCQ with respect to each CC member of UCcc becomes to be less than ‘ULCCTH (Parm 1-6)+ULCCTHMargin’, UL BCcc may be calculated as follows:
B. Algorithm UL BCcc Determining Process:
[Data Processing—Traffic Load Related Processing as a TLC Function]
TLC of D-RRM present in a single base station may forbid or recommend using of CCs of the base station of the TLC. TLC of the D-RRM may transmit and receive a handshake message or an instruction to and from TLC of a neighboring base station through an X2AP interface, and thereby forbid or recommend using of CC in a traffic load balancing level. It is defined herein as Traffic Load Indication (TLI), which indicates constraining using of CC with respect to a particular UE within the base station of the TLC of the D-RRM. According to the above definition, corresponding CC may need to be excluded from a.1.1 and a.1.3.1 of A algorithm and b.1.1, and b.1.3.1 of B algorithm.
[Data Processing—Interference Coordination Related Processing as an ICC Function]
ICC of D-RRM present in a single base station may forbid or recommend using of CCs of the base station of the ICC.
ICC of D-RRM may transmit and receive a handshake message or an instruction to and from ICC of D-RRM of a neighboring base station through an X2AP interface, and thereby may forbid or recommend its D-RRM CMC from or for using of CC in an interference coordination level.
It is defined herein as Interference Coordination Indication (ICI), which indicates constraining using of CC with respect to a particular UE within the base station of the ICC of the D-RRM. According to the above definition, corresponding CC may need to be excluded from a.1.1 and a.1.3.1 of A algorithm and b.1.1, and b.1.3.1 of B algorithm.
Hereinafter, a process of determining a handover type will be described with reference to
In operation 905, a serving base station may collect measurement information through RRC, CSAP, and X2AP.
In operation 910, CMC of D-RRM of the serving base station may perform the aforementioned data processing. As described above, the data processing may include radio condition processing, traffic/load processing, and interference processing.
When BCcc of DL is changed as a result of the data processing in operation 915, the serving base station may determine whether the changed BCcc is included in a CC set of the serving base station in operation 920. Specifically, in operation 920, the serving base station may determine whether HO occurring due to use of the changed BCcc corresponds to inter-eNodeB HO. The inter-eNodeB HO corresponds to HO occurring between base stations.
When the changed BCcc is included in the CC set of the serving base station, that is, when the HO does not correspond to the inter-eNodeB HO, the serving base station may perform a process C of
When the changed BCcc corresponds to a target base station (e.g., eNodeB 2) as a determination result of operation 920, that is, when the HO corresponds to the inter-eNodeB HO, the serving base station may perform DL/UL CC indication processing in operation 925. The DL/UL CC indication processing indicates that whether to perform inter-eNodeB HO from DL viewpoint is considered together with UL.
If DL/UL CC indication is false in operation 930, the serving base station may exclude CC of the target base station (eNodeB 2) from DL BCcc, and may determine BCcc in intra-eNodeB corresponding to a subsequent priority, that is, in CC of the serving base station (eNodeB 1) in operation 935.
Conversely, if DL/UL CC indication is s true in operation 930, the serving base station may determine UL BCcc among CCs of the target base station (eNodeB 2) in operation 940. Here, a handover type may be determined by means of comparison with respect to a number of members of UCcc, a number of members of BCcc, and CC. Accordingly, a UL handover type and a DL handover type may be the same or different.
When BCcc of UL is changed as a result of the data processing in operation 945, the serving base station may determine whether the changed BCcc is included in the CC set of the serving base station in operation 950. Specifically, in operation 950, the serving base station may determine whether HO occurring due to use of the changed BCcc corresponds to inter-eNodeB HO.
When the changed BCcc is included in the CC set of the serving base station, that is, when the HO does not correspond to the inter-eNodeB HO, the serving eNodeB may perform a process D of
When the changed BCcc corresponds to the target base station (e.g., eNodeB 2) as a determination result of operation 950, that is, when the HO corresponds to the inter-eNodeB HO, the serving base station may perform UL/DL CC indication processing in operation 955. The UL/DL CC indication processing indicates that whether to perform inter-eNodeB handover in a UL aspect is considered together with DL.
If UL/DL CC indication is false in operation 960, the serving base station may exclude CC of the target base station (eNodeB 2) from UL BCcc, and may determine BCcc in intra-eNodeB corresponding to a subsequent priority, that is, CC of the serving base station (eNodeB 1) in operation 965.
Conversely, if UL/DL CC indication is true in operation 960, the serving base station may determine DL BCcc among CCs of the target base station (eNodeB 2) in operation 970. Here, a handover type may be determined by means of comparison with respect to a number of members of UCcc, a number of members of BCcc, and CC. Accordingly, a UL handover type and a DL handover type may be the same or different.
As described above with reference to
When UL BCcc is changed and the changed UL BCcc indicates inter-eNodeB HO, UL/DL HO Execution may need to be performed at the same point in time by changing DL BCcc to CC of the target base station (eNodeB 2). Here, in the case of inter-eNodeB HO, DL HO and UL HO may be simultaneously performed, however, the DL HO type and the UL HO type may be different.
In operation 1005, a serving base station may verify a number of members of DL UCcc being used by a UE. When the number of members of DL UCcc=1, the serving base station may verify whether a number of members of changed DL BCcc=1 in operation 1010.
In operation 1015, the serving base station may determine whether DL UCcc is the same as DL BCcc. Specifically, the serving base station may determine whether a frequency band being currently used in a downlink is matched with a candidate frequency band to be used for handover. When the frequency band is matched with the candidate frequency band, the serving base station may determine a handover type as inter-eNodeB intra-CC Batch HO in operation 1020, which is described above with reference to the diagram 821 of
Conversely, when DL UCcc is different from DL BCcc in operation 1015, the serving base station may determine the handover type as inter-eNodeB inter-CC Batch HO in operation 1025, which is described above with reference to the diagram 821 of
When the number of members of DL BCcc≠1 in operation 1010, the serving base station may determine the handover type as inter-eNodeB CC Breakup HO in operation 1030, which is described above with reference to the diagram 822 of
When the number of members of DL UCcc≠1 in operation 1005, the serving base station may verify whether the number of members of DL BCcc=1 in operation 1035.
When the number of members of DL BCcc=1, the serving base station may determine the handover type as inter-eNodeB CC Union HO in operation 1040, which is described above with reference to the diagram 822 of
When the number of members of DL BCcc≠1 in operation 1035, the serving base station may compare the number of members of DL UCcc with the number of members of DL BCcc in operation 1045.
When the number of members of DL BCcc is greater than the number of members of DL UCcc in operation 1045, the serving base station may determine the handover type as inter-eNodeB CC more split Breakup HO in operation 1050, which is described above with reference to the diagram 831 of
When the number of members of DL UCcc is the same as the number of members of DL BCcc in operation 1055, the serving base station may determine the handover type as inter-eNodeB CC maintain split Breakup HO in operation 1060, which is described above with reference to the diagram 831 of
When the number of members of DL UCcc is not the same as the number of members of DL BCcc in operation 1055, that is, when the number of members of DL UCcc is greater than the number of members of DL BCcc in operation 1055, the serving base station may determine the handover type as inter-eNodeB CC less split Breakup HO in operation 1065, which is described above with reference to the diagram 831 of
Operations 1105 through 1165 of
In operation 1205, a serving base station may verify a number of members of DL UCcc being used by a UE. When the number of members=1, the serving base station may verify whether a number of members of DL BCcc, changed in operation 915 of FIG. 9,=1 in operation 1210.
When the number of members of DL BCcc=1, the serving base station may determine a handover type as intra-eNodeB CC Batch HO in operation 1215, which is described above with reference to the diagram 811 of
When the number of members of DL BCcc≠1 in operation 1210, the serving base station may determine the handover type as intra-eNodeB CC Breakup HO in operation 1220, which is described above with reference to the diagram 812 of
When the number of members of DL UCcc≠1 in operation 1205, the serving base station may verify whether the number of members of DL BCcc=1 in operation 1225.
When the number of members of DL BCcc=1, the serving base station may determine the handover type as intra-eNodeB CC Union HO in operation 1230, which is described above with reference to the diagram 812 of
When the number of members of DL BCcc≠1 in operation 1225, the serving base station may compare the number of members of DL UCcc with the number of DL BCcc in operation 1235.
When the number of members of DL BCcc is greater than the number of members of DL UCcc in operation 1235, the serving base station may determine the handover type as inter-eNodeB CC more split Breakup HO in operation 1240, which is described above with reference to the diagram 831 of
When the number of members of DL UCcc is the same as the number of members of DL BCcc in operation 1245, the serving base station may determine the handover type as inter-eNodeB CC maintain split Breakup HO in operation 1250, which is described above with reference to the diagram 831 of
When the number of members of DL UCcc is not the same as the number of members of DL BCcc in operation 1245, that is, when the number of members of DL UCcc is greater than the number of members of DL BCcc, the serving base station may determine the handover type as inter-eNodeB CC less split Breakup HO in operation 1255, which is described above with reference to the diagram 831 of
Operations 1305 through 1355 of
[UL/DL CC Indication Processing or DL/UL CC Indication Processing of
Hereinafter, DL/UL CC indication processing performed in operation 925 of
When DL BCcc is determined as inter-eNodeB, the serving base station may perform DL/UL CC indication processing. When UL BCcc is determined as inter-eNodeB, the serving base station may perform UL/DL CC indication processing. CC indication processing corresponds to a process of determining whether inter-eNodeB determined in a predetermined link (e.g., DL) is valid in another eNodeB.
For example, in a state where DL BCcc indicating inter-eNodeB is determined according to the aforementioned A. algorithm, DL/UL CC indication processing may be performed. The above process may correspond to a process of considering whether to change UL in a state where even DL UCcc being currently used by a serving base station may transmit data. When BCcc is determined as inter-eNodeB in a UL aspect, DL/UL CC indication may be determined as true whereby a subsequent procedure may be proceeded for inter-eNodeB HO. However, when BCcc is determined as intra-eNodeB in a UL aspect, true or false may be determined by collectively analyzing BCcc of inter-eNodeB meaning and BCcc of intra-eNodeB meaning, obtained from A. algorithm. If true, the subsequent procedure may be performed for inter-eNodeB HO. If false, a process of finding BCcc in intra-eNodeB in a state where DL BCcc that is a result of A. algorithm is excluded.
Similarly, in a state where UL BCcc indicating inter-eNodeB is determined according to the aforementioned B. algorithm, UL/DL CC indication processing may be performed. The above process may correspond to a process of considering whether to change DL in a state where even UL UCcc being currently used by the serving base station may transmit data. When BCcc is determined as inter-eNodeB in a DL aspect, UL/DL CC indication may be determined as true whereby a subsequent procedure may be proceeded for inter-eNodeB HO. However, when BCcc is determined as intra-eNodeB in a DL aspect, true or false may be determined by collectively analyzing BCcc of inter-eNodeB meaning and BCcc of intra-eNodeB meaning, obtained from B. algorithm. If true, the subsequent procedure may be performed for inter-eNodeB HO. If false, a process of finding BCcc in intra-eNodeB in a state where UL BCcc that is a result of B. algorithm is excluded.
If the indication is true, the serving base station may follow a negotiation result using 4-1 and 4-2 of Table 4. Conversely, if the indication is false, the serving base station may recalculate satisfying BCcc in intra-eNodeB in a state where the determined inter-eNodeB BCcc is excluded.
In operation 1405, a serving base station may collect measurement information required to determine an optimal frequency band set to be used for the handover.
In operation 1410, the serving base station may perform data processing of the collected measurement information. Operation 1410 is similar to operation 910 of
In operation 1415, the serving base station may determine a temporary frequency band set for DL HO or a temporary frequency band set for UL HO. The temporary frequency band set for DL HO may be, for example, DL BCcc described above with reference to
In operation 1420, the serving base station may determine an optimal frequency band set for UL HO or DL HO, depending on whether the determined temporary frequency band set supported by the serving base station, and whether the determined temporary frequency band set supported by a neighboring base station of the serving base station. Specifically, the serving base station may determine the optimal frequency band set depending on whether the determined temporary frequency band set corresponds to HO within a base station, or HO between base stations. Operation 1420 is similar to operations 920 through 940 of
When the determined temporary frequency band set is the optimal frequency band set for DL HO, and supported by the neighboring base station, the optimal frequency band set for UL HO may be selected from the neighboring base station or the serving base station in operation 1420, which is similar to operation 935 or 940 of
Also, when the determined temporary frequency band set is the optimal frequency band set for UL HO, and supported by the neighboring base station, the optimal frequency band set for DL HO may be selected from the neighboring base station or the serving base station in operation 1420, which is similar to operation 965 or 970 of
In operation 1425, the serving base station may determine a HO type based on a number of frequency bands within a frequency band set (e.g., DL UCC or UL UCcc) being used by the UE and a number of frequency bands within the optimal frequency band set (e.g., DL BCcc or UL BCcc).
Referring to
The collecting unit 1510 may collect measurement information required to determine an optimal frequency band set to be used for the handover.
The data processor 1520 may perform data processing of the collected measurement information, and thereby determine a temporary frequency band set (DL BCcc, UL BCcc) for DL HO or UL HO.
The determining unit 1530 may determine the optimal frequency band set for DL HO or UL HO, depending on whether the determined temporary frequency band set supported by the serving base station 1500 and whether the determined temporary frequency band set supported by a neighboring base station of the serving base station.
In
Events cited in the present invention may include A4-1, A4-2, and A3-1. A4-1 indicates an event where DLENBCCSNR of a neighboring base station becomes to be greater than a reference value TH1, and A4-2 indicates an event where DLENBCCSNR of the neighboring base station becomes to be less than the reference value TH1. A3-1 indicates an event where DLENBCCSNR of the neighboring base station becomes to be greater than DLENBCCSNR of the current serving base station.
In the present invention, TH1 of A4-1 is referred to as TPREP, and TH1 of A4-2 is referred to as TRMT. TPREP and TRMT may be set to be the same as each other or to be different from each other. When DLENBCCSNR of the neighboring base station becomes to be greater than TPREP, that is, when the event of A4-1 occurs, the serving base station may prepare a resource through information exchange with the neighboring base station. Also, when DLENBCCSNR of the neighboring base station becomes to be less than TRMT, the serving base station may release the prepared resource through information exchange with a corresponding base station.
Referring to
The UE may be positioned in ICR, CER-I, or CER-II based on an A4-1, A4-2 event satisfaction condition with respect to neighboring DLENBCCSNR values. Specifically, that the UE is positioned in ICR may indicate that all of DLENBCCSNR values with respect to all CCs of neighboring base stations are less than TPREP.
That the UE is positioned in CER-I may indicate that all of DLENBCCSNR values with respect to all CCs of neighboring base stations are greater than TPREP, and also exist in only a single neighboring base station. Also, that the UE is positioned in CER-II may indicate that all CCs of neighboring base stations are greater than TPREP, and also exist in at least two neighboring base stations.
In the case of the automatic resource reservation and cancellation in the CA environment proposed according to an embodiment of the present invention, resource reservation and cancellation may be performed with respect to neighboring base stations along the region of
When the UE is positioned in a position 1820, and when event A3-1 where DLENBCCSNR with respect to random CCs of eNodeB 2 becomes to be greater than a DLENBCCSNR value of CC being used by the UE in eNodeB 1 occurs, eNodeB 1 may perform HO decision and execution in operation 1930. Accordingly, the serving base station is changed from eNodeB 1 to eNodeB 2. eNodeB 1 becomes a neighboring base station of eNodeB 2.
When the UE is positioned in a position 1830, and when event A4-2 where DLENBCCSNR value with respect to CCs of eNodeB 2 becomes to be less than TRMT occurs, eNodeB 2 that is a current serving base station may instruct eNodeB 1, which is a corresponding neighboring base station, to perform resource release in operation 1980.
The automatic resource reservation and cancellation may be performed based on DLENBCCSNR measured by the UE. With respect to CC of neighboring base stations
having triggered A4-1, a serving base station and a neighboring base station enable advanced resource preparation in operation 1915 by transmitting and receiving handover request in operation 1910 and handover request ACK in operation 1920 using an X2AP protocol message.
With respect to CC of neighboring base stations having triggered A4-2, the serving base station and the neighboring base station enable resource release of operation 1980 using an X2AP protocol message, i.e., UE context release of operation 1975.
The UE may provide measured DLENBCCSNR values to the serving base station using an RRC protocol message that is a measurement report. The serving base station enables CMC of D-RRM to directly determine an event based on DLENBCCSNR collected in the D-RRM. The UE may directly determine the event through measurement control, and provide the determined event to the serving base station using the RRC protocol message that is a measurement report (see operations 1905, 1925, and 1970).
In operation 1905, the UE may report event A4-1 in a form of a measurement report message. The event A4-1 corresponds to an event according to DLENBCCSNR measured in neighboring base stations (eNodeB 2, eNodeB 3). The event A4-1 indicates that a result of measuring, by the UE, an SNR quality (DLENBCCSNR of Table 3) with respect to a reference signal of each CC of the neighboring base station (eNodeB2, eNodeB 3) increases to be above a threshold value TPREP determined in a network.
The above measurement report message may be reported to the current serving base station (eNodeB 1) through an RRC interface. A handover request and a handover request ACK may be transmitted in an X2AP form whereby advanced resource preparation (operation 1915) with respect to corresponding neighboring base stations having triggered A4-1 is enabled.
In operation 1910, the current serving base station (eNodeB 1) may transmit the handover request to neighboring base stations (eNodeB 2, enodeB3) having triggered A4-1, using X2AP. Referring to
Information that needs to be included in operations 1910 and 1920 or in operations 1935 and 1945 in the CA environment are shown in Table 5. Additionally, Table 5 shows an embodiment of information to be substantially included with the following assumption.
The assumption for Table 5 follows as:
1. As shown in
2. In eNodeB 1, UE1 is using CC1, CC2, and CC3 for DL, and is using CC6 for UL. After the UE1 is handed over to eNodeB 2, the UE1 uses CC3 for DL and uses CC5 for UL.
3. HO is executed according to UE1 mobility path of
4. Like the base station 62 of
5. Like the base station 64 of
When UE is connected to a network, the UE may have a serving base station, and have a 1-tier neighboring base station based on the serving base station. Specifically, D-RRM of a base station may be in a “serving (source) [CMC]” state or a “neighboring (target) [CMC]” state. Due to the handover, the “serving (source) [CMC]” state may be switched to the “neighboring (target) [CMC]” state. Conversely, the “neighboring (target) [CMC]” state may be switched to the “serving (source) [CMC]” state. The above relationships are shown of
Advanced Resource Preparation of Operation 1915 in Automatic Resource Reservation of
The advanced resource preparation corresponds to a process of transmitting in advance a handover request to CC of a neighboring base station having triggered event A4-1 to thereby prepare a handover. In this CA environment, the neighboring base station receiving the handover request may prepare a handover with respect to a corresponding UE using a CC set of the neighboring base station, which is different from an existing handover. CMC of D-RRM of the neighboring base station may exclusively charge the handover to one of CCs of the neighboring base station, or may distribute the handover to a plurality of CCs. The neighboring base station may report to the serving base station about how the CCs are distributed, using handover request ACK.
A flow 201 of
In operation 2011, the neighboring base station (eNodeB 2) may receive a handover request for advanced HO preparation. The received handover request may include information corresponding to 4-1 message of Table 5.
In operation 2012, the neighboring base station (eNodeB 2) may perform CC decision and resource reservation based on the received information and neighboring base station circumstance.
In operation 2013, the neighboring base station (eNodeB 2) may include, in handover request ACK, information corresponding to 4-2 message of Table 5 and thereby transfer handover request ACT to a serving base station (eNodeB 1). Here, a process of determining information to be transmitted to the serving base station may follow the following algorithm.
Prompt resource preparation of operation 1940 in the handover decision and execution process of
[Algorithm A] Advanced HO Preparation—a processing process in eNodeB 2 when eNodeB 2 receives a handover request message (4-1 of Table 5) from eNodeB 1:
1. Obtains information of eNodeB 2:
2. Processes information of 4-1 message of Table 5:
3. Performs processing so as to determine Parm 4-2-3, 4-2-4, and 4-2-5 in 4-2 message of Table 5.
4. Generates 4-2 Message of Table 5 Based on Result Obtained from 3.
A flow 212 of
A “serving (source) [CMC]” state 2100 indicates a state of eNodeB 1 in the scenario of
In operation 2111, a serving base station (eNodeB 1) may collect measurement data using RRC and CSAP.
When event A4-1 occurs based on the collected data, the serving base station (eNodeB 1) may transmit a handover request to a neighboring base station having triggered A4-1. Here, the handover request is to request advanced resource preparation.
In operation 2121, the neighboring base station may transmit handover request ACK to the serving base station (eNodeB 1), and may perform advanced resource preparation.
In operation 2122, the neighboring base station may store or update information contained in the handover request. For example, the information may include HO CC candidate group information and Parm 4-2-1 through 5 of Table 5.
<Resource Release of Operation 1980 in Automatic Resource Cancellation of FIG. 19>
(Position 1830 of UE1 of
According to the scenario of
Accordingly, in operation 1970, UE may transfer, to the serving base station (eNodeB 2), event A4-2 with respect to eNodeB 1 and a measurement value to determine event A4-2 through a measurement report that is an RRC protocol message. Specifically, the measurement report may be transferred to CMC of D-RRM of the serving base station (eNodeB 2).
In operation 1975, the serving base station (eNodeB 2) may transmit, to the neighboring base station (eNodeB 1) having triggered A4-2, UE context release that is an X2AP protocol message.
In operation 1980, the neighboring base station (eNodeB 1) may perform resource release. Internal information of UE context release that is the X2AP protocol message may include (Parm 4-3-1) and/or (Parm 4-3-2) information of Table 5.
Referring to the scenario of
The flow 202 of
In operation 2021, the neighboring base station (eNodeB 1) may receive the UE context release message in the “neighboring (target) [CMC]” of CMC.
In operation 2022, the neighboring base station (eNodeB 1) may release a resource with respect to corresponding UE.
The flow 212 of
In the flow 212, a “serving (source) [CMC]” state indicates a state where UE1 of
In operation 2111, the serving base station (eNodeB 2) may collect measurement data using RRC and CSAP.
In operation 2123, the serving base station (eNodeB 2) may perform advanced HO preparation, or may determine UE context release based on the collected measurement data.
In operation 2124, when event A4-2 occurs by determining the UE context release, the serving base station (eNodeB 2) may transmit UE context release (resource release) to the neighboring base station having triggered A4-2
<HO Decision and Execution Process of FIG. 19>
(UE1 of
Hereinafter, an example where eNodeB 1 uses CC1, CC2, and CC3 as DLCC in a state where UE1 of
In operation 1930 of
In general, in operation 1920, the serving base station (eNodeB 1) may receive the X2AP message with respect to a base station having triggered A3-1, and store information of (Parm 4-2-1 to 5) of Table 5.
When a handover to the neighboring base station (eNodeB 2) is determined in operation 1920, the serving base station (eNodeB 1) may transfer, to the UE, an RRC ConnectionReconfiguration message for the handover in operation 1950.
However, even though the handover to the neighboring base station (eNodeB 2) is determined in operation 1930, information of (Parm 4-2-1 to 5) associated with the neighboring base station (eNodeB 2) may not be stored in the serving base station (eNodeB 1). In this case, in operation 1935, the serving base station (eNodeB 1) may transfer the handover request to the neighboring base station (eNodeB 2).
In operation 1940, the neighboring base station (eNodeB 2) may perform prompt resource preparation so as to obtain information. Operation 1940 is the same as the aforementioned operation 1915 of
Specifically, when information of (Parm 4-2-1 to 5) associated with the neighboring base station (eNodeB 2) exists after the HO decision, the serving base station (eNodeB 1) may immediately transmit, to the UE, RRC ConnectionReconfiguration for HO in operation 1950. Conversely, when information of (Parm 4-2-1 to 5) does not exist, the serving base station (eNodeB 1) and the neighboring base station (eNodeB 2) may perform a process indicated by a dotted line in
If the handover request received from the neighboring base station (eNodeB 2) is success in operation 1945, the serving base station (eNodeB 1) may transmit, to the UE, RRC ConnectionReconfiguration for HO in operation 1950.
In operation 1955, the UE may be reconfigured based on information contained in RRC ConnectionReconfiguration, and may transmit, to a target base station (eNodeB 2), an RRC message such as RRC ConnectionReconfiguration Complete.
In operations 1960 and 1965, the target base station (eNodeB 2) may transmit and receive, to and from aGW or MME, a procedure (Path Switch Request, Path Switch Request ACK) for a data path change defined in an S1AP protocol message. Through this, a handover is over.
Hereinafter, the HO decision and execution process of
The flow 211 of
When UE1 is positioned in the position 1820 of
A first operation is an operation of determining a handover based on a radio quality (e.g., in the case of UL, ULCCQ of Table 2, and in the case of DL, DLENBCCSNR of Table 3).
A second operation is an operation of analyzing and determining whether the determined handover is unnecessary based on the HO decision made in the first operation. The second operation corresponds to a selection.
When Inter-eNodeB HO is determined through the aforementioned two operations, the serving base station (eNodeB 1) may transmit, to UE, RRC ConnectionReconfiguration for HO in operation 2115, and may be shifted to a “neighboring (target) base station” state.
However, when it is not Inter-eNodeB HO, the serving base station (eNodeB1) may maintain the “serving (source) base station” state. Here, when information of (Parm 4-2-1 to 5) associated with a target base station to which the handover is determined in the first operation does not exist, the source base station (eNodeB 1) may transmit a message of operation 2118 (operation 1935 of
In the HO decision shown in the flow 211 of
A flow 203 of
A “neighboring (target) [CMC]” state indicates that UE1 is positioned in the position 1820, and a state of the neighboring base station (eNodeB 2) of
In operation 2031, a neighboring base station (eNodeB 2) may receive, from UE, RRC Connection Reconfiguration Complete for HO.
In operation 2032, the neighboring base station (eNodeB 2) may transmit, to MME, Path Switch Request (corresponding to operation 1965 of
When Path Switch Request ACK is received from MME in operation 2033, the neighboring base station (eNodeB 2) may be switched to a serving base station, which becomes a “serving (source) [CMC]” state.
<Flow 211
Hereinafter, the flow 211 of
In operation 2111, UE may measure an SNR quality (DLENBCCSNR of Table 3) with respect to a reference signal for CC operated by neighboring base stations, and may generate event A3-1 from a measurement result.
Event A3-1 indicates a case where one of results of measuring DLENBCCSNR with respect to CCs of neighboring base stations becomes to be greater than DLENBCCSNR measurement value of each CC corresponding to UCcc of a current source base station (e.g., CC information used by UE1, i.e., (Parm 4-1-5) when a serving base station of UE1 is eNodeB 1). UCcc indicates a CC set used by current UE, and BCcc indicates a best CC set most appropriate for current UE.
In operation 1925 of
Referring again to the flow 211 of
BCcc may be determined based on information of the message of operations 1915 and 1940 of
<Flow 211 of
When BCcc determined in operation 2112 indicates inter-eNodeB HO, it depends on DLENBCCSNR measurement value and thus, unnecessary handover such as ping pong may not be reduced. Accordingly, operation 2113 corresponding to the second phase may be additionally performed.
In operation 2113, the serving base station (eNodeB 1) may determine whether inter-eNodeB HO using the determined BCcc is unnecessary, based on accumulated history information.
According to an embodiment of the present invention, when a handover between base stations is performed in a state where UE1 is connected to a network, CMC of D-RRM of each base station may accumulate history information. CMC of D-RRM may verify a mobility pattern of UE1 based on the accumulated history information, and may secondarily verify whether handover to a target base station along the verified mobility pattern is appropriate.
When a normal handover is performed along a mobility path of UE of
Referring to Table 6, the stored history information may include CA ID, a cell type, a duration time of UE in eNodeB, and a signal quality measured for HO decision (i.e., DLENBCCSNR information of source CA-ID and DLENBCCSNR information of target base station CA-ID).
CA ID indicates an ID that may separate base stations and a frequency bandwidth used by each base station, and may configure the separated frequency bandwidth using a global unique value. When CA ID has DL frequency bandwidth (FB1, FB3) as shown in
Meanings contained in above CA ID may be separately expressed, and the separated meanings may be separately included in the history information. For example, CA ID may be separated into eNodeB ID, FB ID, cell ID, and the like, and thereby be recorded in the history information. Table 6 shows an example of history information with respect to each CA ID.
Specifically, when a normal handover is performed along the mobility path of UE in
In Table 6, the cell type is classified into large, medium, and small. The cell type may be further classified. Also, the duration time of UE in CA may be indicated as an integer greater than or equal to, for example, “0”. When the duration time exceeds a predetermined maximum value, the duration time may be set as a maximum value and thereby be recorded.
Every time handover occurs, history information of Table 6 may be moved from the previous serving base station before the handover to the serving base station after the handover. Accordingly, the current serving base station may have the history information as shown in Table 6.
When the current serving base station (eNodeB 1) determines inter-eNodeB HO in operation 2112 of
When inter-eNodeB HO from UCcc to BCcc is determined, the serving base station (eNodeB 1) may analyze a frequency, continuity, temporal property, and the like of a pattern from the stored history information, based on the determined matters, and may determine whether inter-eNodeB HO using the above pattern is appropriate.
The pattern corresponds to information determined in the aforementioned first phase, i.e., UCcc→BCcc. The frequency denotes a number of times that the pattern occurs in a corresponding history. The continuity denotes a state that the pattern is continuously repeated (e.g., eNodeB1 (DL−CC1, CC3)→eNodeB 2 (DL−CC3)→eNodeB1 (DL−CC1, CC3)→eNodeB 2 (DL−CC3)). The temporal property is to determine whether the pattern has occurred within a few minutes based on a current point in time. The temporal property may be classified into old information, intermediate information, and just previous information.
With respect to applying of the frequency, the continuity, and the temporal property for determining whether the HO using the pattern is appropriate, a priority and a combination scheme may be adjusted depending on a system operation circumstance. Selectively, a recorded DLENBCCSNR set may also be additionally used. For example, an algorithm may be designed so that a difference between currently measured DLENBCCSNR values and DLENBCCSNR measurement value of history information may be calculated and the DLENBCCSNR set may be excluded or be further considered depending on a calculation result.
<Flow 211 of
An embodiment of the present invention using A3-1, A3-1′, and Rn when the BCcc determined in the flow 211 of
As shown in
For example, A3-1 corresponds to an event that may manage mobility of UE, and may also quickly proceed or delay handover based on hysteresis or time-to-trigger when the hysteresis or the time-to-trigger exists. Specifically, A3-1 indicates that operation 2112 is performed using a measurement value to which hysteresis or time-to-trigger is applied. A3-1′ indicates that hysteresis=0 and time-to-trigger=0 and thus, operation 2112 is performed using a measurement value.
Rn is described as follows:
CHO(SS) sorts, in a descending order for each CC, a quality measured with respect to DLENBCCSNR of neighboring base stations.
CHO(RE) sorts, in a descending order for each CC, a difference between a quality measured with respect to DLENBCCSNR of neighboring base stations and a previously measured quality.
PHO sorts, in a descending order of DLENBCCSNR for each CC, neighboring base stations having CC of DLENBCCSNR greater than communicable reference value (Thc).
RHO indicates that information (4-2 information of Table 5) with respect to 1920 and 1940 is received through operations 1915 and 1940 of
Events occurring when orders of CHO(SS), CHO(RE), and PHO are changed are defined as R1, R2, and R3, respectively.
Hereinafter, a method for inter-eNodeB HO in a wireless mobile communication system using CA based on the aforementioned information will be briefly described.
When a serving base station connected by UE may determine BCcc based on only a measurement value of DLENBCCSNR, and when the determined BCcc indicates inter-eNodeB and BCcc∉RHO, the serving base station may perform prompt resource preparation through operations 1935 through 1945 of
When (Parm 4-2-2) of a message transmitted from a corresponding neighboring base station is a success, the serving base station may update BCcc with (Parm 4-2-3). According to an embodiment of the present invention, when BCcc∉RHO even though advanced resource preparation is performed, TLC may compulsorily release a resource reserved for handover resource preparation so as to manage load.
Hereinafter, a case where the preparation process of
When the serving base station connected by the UE determines BCcc based on only the measurement value of DLENBCCSNR, and when the determined BCcc indicates inter-eNodeB, and (Parm 4-2-3) to a corresponding target base station is prepared, a handover may be immediately performed, or prompt resource preparation may be performed again through operations 1935 through 1945. Here, when the prepared (Parm 4-2-3) is not used, DLENBCCSNR signal quality with respect to stored CC determined by (Parm 4-2-3) may be relatively low.
Referring to
In operation 110, when the determined BCcc corresponds to inter-eNodeB, event Rn may occur in the serving (source) base station.
When Rn=R2 in operation 120, the serving (source) base station may perform hysteresis information update as shown in Table 7 with respect to DLENBCCSNR of a corresponding base station in operation 130.
In operation 140, the serving (source) base station may reconsider and update BCcc by applying the updated hysteresis information.
When BCcc to be used by the UE is found in the updated BCcc in operation 150, the serving (source) base station may determine whether the found BCcc is changed compared to previous BCcc in operation 160.
When not changed, the serving (source) base station may go to operation 100 to wait for an event.
Conversely, when changed, the serving (source) base station may determine whether the changed BCcc is included in RHO in operation 170.
When BCcc is not included in RHO, the serving (source) base station may perform prompt resource preparation (operations 1935 through 1945 of
When a prompt preparation of operation 180 fails, the serving (source) base station 100 may enter a no BCcc found state in operation 190.
Conversely, when the changed BCcc is included in RHO in operation 170, the serving (source) base station may enter the BCcc found state of operation 100 to wait for the subsequent operation.
When event A3-1 occurs by applying new history information and time-to-trigger in operation 210, the serving (source) base station may update BCcc in operation 220.
When the updated BCcc is determined to be changed in operation 230, and when the changed BCcc is not included in RHO in operation 240, the serving (source) base station may perform prompt resource preparation (operations 1935 through 1945 of
When the prompt resource preparation succeeds, the serving (source) base station may transmit 1950 of
Conversely, when the updated BCcc is determined to be not changed in operation 230, the serving (source) base station may enter the BCcc found state of operation 100 to wait for the subsequent operation.
Also, when the changed BCcc is included in RHO in operation 240, the prompt resource preparation (operations 1935 through 1945 of
When event A3-1′ to which the new hysteresis and time-to-trigger is not applied occurs in operation 310 of
When the updated BCcc is determined to be changed in operation 330, and when the changed BCcc=PHO1 of the same serving (source) base station in operation 340, the serving (source) base station may determine whether to perform preparation (operations 1935 through 1945 of
Also, when the changed BCcc≠PHo1 of the same serving (source) base station in operation 340, the serving (source) base station may update hysteresis information in operation 350. Specifically, BCcc may affect update by applying the changed hysteresis.
Also, when the changed BCcc≠PHO1 of the same serving (source) base station in operation 340, the serving (source) base station may perform operation 240.
When BCcc is not determined by the serving (source) base station and thereby, the serving (source) base station is in no BCcc found state in operation 400, the serving (source) base station may trigger event Rn in operation 415.
When Rn=R2 in operation 420, the serving (source) base station may update hysteresis information as shown in Table 7 in operation 430.
In operation 440, the serving (source) base station may update BCcc by applying the updated hysteresis information.
When BCcc to be used by UE is found in the updated BCcc in operation 450, the serving (source) base station may determine whether BCcc is included in RHO in operation 460.
When BCcc is included in RHO in operation 460, the serving (source) base station may update the found BCcc in operation 470 and may enter a BCcc found state in operation 480.
Conversely, when BCcc is not included in RHO in operation 460, and when prompt resource preparation (operations 1935 through 1945 of
When A3-1 occurs in operation 510, the serving (source) base station may update hysteresis information as shown in Table 7 in operation 520 and then go to operation 400.
<Hysteresis Information Update Described in FIGS. 23 Through 25>
Hysteresis information update of
Initially, a magnitude of a change amount is predefined as LARGE, MEDIUM, and SMALL based on a change amount (CHO(RE)) level of DLENBCCSNR for each CC and for each current base station. Also, a difference between a minimum value and a maximum value of applicable hysteresis is also predefined as LARGE, MEDIUM, and SMALL. This is to induce handover to be performed with respect to CC having increasing CHO(RE) rather to select CC having a greatest DLENBCCSNR, and to delay a handover with respect to CC having decreasing CHO(RE). Classification of the above value may need tuning according to a system.
For example, CHO(RE) Large is defined as at least 20, MEDIUM is defined as 19 to 10, and SMALL is defined as less than 9. Hysteresis LARGE is defined as at least 10, MEDIUM is defined as 9 to 5, and SMALL is defined as less than 4. Also, “delta hysteresis” is defined as 2.
It is assumed that a radio quality (i.e., DLENBCCSNR) with respect to CC1 of a neighboring base station is previously 10 and currently 10, a radio quality with respect to CC2 is previously 5 and currently 18, a radio quality with respect to CC3 is previously 3 and currently 50, and hysteresis being applied to CC1, CC2, and CC3 are 11, 3, and 8.
Here, CHO(RE)CC1 is 5, CHO(RE)CC2 is 13, and CHO(RE)CC3 and 47. When they are classified according to the above classes, CHO(RE)CC1 is SMALL, CHO(RE)CC2 is MEDIUM, and CHO(RE)CC3 is LARGE.
With respect to CC1, CHO(RE) is SMALL and current hysteresis is 11 corresponding to LARGE and thus, current hysteresis may increase by the delta hysteresis. Accordingly, new hysteresis becomes 13 according to Table 7.
With respect to CC2, CHO(RE) is MEDIUM and current hysteresis is 3 corresponding to SMALL and thus, current hysteresis may be maintained by the delta hysteresis. Accordingly, new hysteresis may be 3 that is the previous hysteresis according to Table 7.
With respect to CC3, CHO(RE) is LARGE and current hysteresis is 8 corresponding to MEDIUM and thus, current hysteresis may decrease by the delta hysteresis. Accordingly, new hysteresis becomes 6 according to Table 7.
The above-described exemplary embodiments of the present invention may be recorded in computer-readable media including program instructions to implement various operations embodied by a computer. The media may also include, alone or in combination with the program instructions, data files, data structures, and the like. Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM disks and DVDs; magneto-optical media such as floptical disks; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, and the like. Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter. The described hardware devices may be configured to act as one or more software modules in order to perform the operations of the above-described exemplary embodiments of the present invention, or vice versa.
Although a few exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described exemplary embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2009-0125988 | Dec 2009 | KR | national |
| 10-2009-0126044 | Dec 2009 | KR | national |
| 10-2010-0057440 | Jun 2010 | KR | national |
| 10-2010-0057441 | Jun 2010 | KR | national |
