Title of Invention	A METHOD OF CONTROLLING A USER EQUIPMENT CAPABLE OF RECEIVING A POINT-TO-MULTIPOINT SERVICE IN A WIRELESS COMMUNICATION SYSTEM
Abstract	A method of controlling a user equipment (UE) capable of receiving a point- to-multipoint service in a wireless communication system is disclosed. The method performed by the UE and comprises the steps of receiving a point-to- multipoint service and performing a cell reselection based on control information received from a base station in response to completion of the receiving of the point-to- multipoint service wherein the cell reselection is performed among multiple frequencies by using the control information, wherein the point-to-multipoint service is received based on a frequency indicated by the control information and wherein the cell reselection is performed among the multiple frequencies without measuring all candidate frequencies, wherein the control information includes frequency layer convergence (FLC) information, wherein the FLC information indicates at least one preferred frequency, wherein the FLC information includes an offset to be applied to the at least one preferred frequency, and wherein the offset is added to a quality measurement value of a cell positioned at the at least one preferred frequency so that the added value is used when comparing the cell with another cell during the cell reselection.

Title of Invention

A METHOD OF CONTROLLING A USER EQUIPMENT CAPABLE OF RECEIVING A POINT-TO-MULTIPOINT SERVICE IN A WIRELESS COMMUNICATION SYSTEM

Abstract

A method of controlling a user equipment (UE) capable of receiving a point- to-multipoint service in a wireless communication system is disclosed. The method performed by the UE and comprises the steps of receiving a point-to- multipoint service and performing a cell reselection based on control information received from a base station in response to completion of the receiving of the point-to- multipoint service wherein the cell reselection is performed among multiple frequencies by using the control information, wherein the point-to-multipoint service is received based on a frequency indicated by the control information and wherein the cell reselection is performed among the multiple frequencies without measuring all candidate frequencies, wherein the control information includes frequency layer convergence (FLC) information, wherein the FLC information indicates at least one preferred frequency, wherein the FLC information includes an offset to be applied to the at least one preferred frequency, and wherein the offset is added to a quality measurement value of a cell positioned at the at least one preferred frequency so that the added value is used when comparing the cell with another cell during the cell reselection.

Full Text	Technical Field [1] The present invention relates generally to point-to-multipoint service in a wireless communication system and, more particularly, to terminal distribution control for point-to-multipoint service. Background Art [2] The "UMTS (universal mobile telecommunications system) is a third generation mobile communications system evolved from the European GSM (Global System for Mobile Communications) system and aims to provide improved mobile com- munication services based on a GSM core network and a wideband code division . multiple access (W-CDMA) technology. [3] Figure 1 is a block diagram illustrating a structure of a UMTS network. [4] Referring to Figure 1, the UMTS system generally consists of a terminal (e.g., user equipment (UE)), a UTRAN (UTMS radio access network) and a GN (core network). The UTRAN includes one or more RNSs (radio network sub-systems). Each RNS includes a single RNC (radio network controller) and one or more base stations (e.g., node-Bs) managed by the RNC. Each Node B managed by the RNC receives in- formation sent from a physical layer of a terminal on the uplink, and transmits data to the terminal on the downlink. Thus, the node-B serves as an access point to the UTRAN for the terminal. The RNC allocates and manages radio resources, and serves as an access point to the CN for the UTRAN. [5] Figure 2 is a diagram illustrating a connection structure between a UTRAN and a terminal in a UMTS network. As such, Figure 2 shows an exemplary architecture of radio interface protocols between a terminal and a UTRAN based on a 3GPP radio access network specification. [6] Referring to Figure 2, the radio protocol is horizontally arranged to include a physical layer, a data link layer and a network layer. The radio protocol is vertically divided into a user plane for transmitting data information and a control plane for transferring control signals. Furthermore, the protocol layers shown in Figure 2 may be divided into a first layer L1, a second layer L2 and a third layer L3, based upon the • three lower layers of an open system interconnection (OSI) specification model that is well-known in the art of communications systems. [7] The first layer L1 (e.g., the physical layer) uses physical channels to provide in- formation transfer service to its upper layers. The physical layer is connected via a transport channel to a medium access control (MAC) layer located at an upper layer thereof. Data between the medium access control layer and the physical layer is transferred via this transport channel. Furthermore, the data between different physical layers, i.e. between physical layers of transmitting side and receiving side, is transferred via the physical layer. [8] The MAC layer of the second layer L2 provides services to an upper radio link control (RLC) layer via a logical channel. The RLC layer of the L2 supports reliable data transmissions and performs segmentation and concatenation of RLC SDUs (service data units). [9] The RRC (Radio Resource Control) layer positioned in the lowest portion of the third layer (L3) is defined in the control plane and controls the transport channels and the physical channels for establishment, reconfiguration, and release of radio bearers (RBs). The RB indicates a service by the L2 for a data transfer between the terminal and the UTRAN. In general, establishing the RB denotes processes of stipulating the characteristics of a protocol layer and a channel, which are required for providing a specific service, and setting corresponding parameters and operation methods. [ 10] When the RRC layer of a specific terminal and the RRC layer of the UTRAN are connected to each other to exchange RRC messages, the corresponding terminal is in a RRC connected state. On the contrary, when not connected to each other, the cor- responding terminal is in an idle state. The terminal in the RRC connected state is further divided into URA_PCH state and CELL_PCH state, CELLJFACH state and CELLJDCH state. Terrninals in the idle state or the URA_PCH state and CELLJPCH state use a discontinuous reception (DRX) method to reduce power consumption, thereby discontinuously receiving a physical channel (i.e., SCCPCH (secondary common control physical channel)) to which a physical channel (i.e., PICH (paging indicator channel)) and a transport channel (i.e., PCH (paging channel)) are mapped. The terminal is in a sleeping mode during the remaining time periods excluding those times when receiving the PICH or the SCCPCH. The terminal performing the DRX method wakes up once per DRX cycle length to receive a PI (paging indicator) of the PICH channel. [11] The terminal in the RRC connected state may further have a signaling connection with the CN. In this case, the signaling connection indicates a path for exchanging control messages between the terminal and the CN. The RRC connected state denotes a connection between the terminal the UTRAN, while the signaling connection denotes a connection between the terminal and the CN. The terminal uses the signaling connection to inform the CN of its position and/or to request services. The terminal should be in the RRC connected state to have a signaling connection. [12] A MBMS (multimedia broadcast / multicast service) is described below. [13] The MBMS refers to a service for providing streaming or background services to a plurality of terminals using a downlink dedicated MBMS bearer service. In the UTRAN, the MBMS bearer uses a point-to-multipoisit radio bearer (RB) and a point- to-point RB. At this time, the point-to-multipoint RB uses a common channel (e.g., using the SCCPCH as a physical layer) so that a plurality of terminals subscribed to a corresponding service may receive the service. [14] The MBMS is divided into a broadcast mode and a multicast mode. The MBMS broadcast mode is a service for transmitting multimedia data to all users within a broadcast area. Conversely, the MBMS multicast mode is a service for transmitting the multimedia data only to a specific user group within a multicast area. The broadcast area refers to a region in which it is possible to transmit the broadcast service, and the multicast area refers to a region in which it is possible to transmit the multicast service. [15] Figure 3 is a diagram illustrating an example of the UMTS network providing a point-to-multipoint service to the terminal. [16] Referring to Figure 3, a UE1 performs a subscribing process in order to receive an MBMS service. The UE1 also receives a service announcement provided by the network regarding the MBMS service. Subscribing refers to the establishment of a re- lationship between a service provider and a user. A service announcement refers to providing the terminal an index and other information related to the services to be provided. For example, a terminal that desires to receive the MBMS service of a multicast mode should join a multicast group. The multicast group refers to a group of terminals receiving a specific multicast service. Joining refers to a user merging with other users in a multicast group to receive a particular multicast service. The terminal may inform the UMTS network that it desires to receive specific multicast data through MBMS multicast joining. On the contrary, leaving is a procedure in which a terminal that joined a specific multicast group releases its joining to the multicast group. Each terminal performs such subscribing, joining and leaving processes. The terminal may perform the subscribing, joining, and leaving processes any time of before, during, or after data transmission. [17] During performance of a specific MBMS service, one or more sessions may se- quentially be generated with respect to the MBMS service. If data to be transmitted for the specific MBMS service is generated in a MBMS service source, the CN notifies a session start to the RNC. However, if there is no data to be transmitted for the specific MBMS service in the MBMS service source, the CN notifies a session end to the RNC. The data transmission with respect to the specific MBMS service may be carried out between the session start and the session end. At this time, the data transmitted through the data transmission process is transmitted only to terminals that have joined the multicast group. [18] In the session start process, the UTRAN receives the session start notification from the CN and transfers a MBMS notification to the tenninals. The MBMS notification refers to the UTRAN informing a terminal that the data transmission of the specific MBMS service in a cell is imminent. The MBMS notification may be transmitted multiple times before the transmission of the data pertaining to the service. When carrying out the MBMS notification process, the UTRAN may also count the number of terminals receiving the specific MBMS service within a cell. The counting may be used for determining whether a point-to-multipomt KB or a point-to-point RB is set as the RB for transmitting the specific MBMS service data, or whether no RB is set. [19] The UTRAN internally establishes a threshold value to select an appropriate MBMS RB. After the UTRAN counts the number of terminals, if the counted number of terminals receiving the corresponding MBMS service within the corresponding cell is smaller than the threshold value, the UTRAN establishes a point-to-point RB. However, a point-to-multipoint RB is established if the counted number of terminals is greater than the threshold value. After determining the MBMS RB, the UTRAN informs the terminals of the establishment information of the corresponding RB. [20] When the point-to-point RB is established for the specific service, the terminals that desire to receive the service must be in the RRC connected mode state. However, when the point-to-multipoint RB is established for the specific service, the terminals that desire to receive the service do not have to be in the RRC connected mode state. That is, terminals in an idle state may also receive the MBMS service data by using the point-to-multipoint RB. However, if no terminals are counted, the UTRAN does not establish any RB and does not transmit the MBMS service data. As such, the UTRAN establishing an RB when there is no user who wants to receive the service may cause undesirable consumption of radio resources. The UTRAN initiates a transmission for MBMS service data received from the CN during a session using the determined RB. [21] During the counting process, the UTRAN does not have any information pertaining to terminals in an RRC idle mode. Accordingly, when the terminals in the RRC idle mode are requested by the UTRAN for counting (with respect to MBMS services subscribed by the terminals), the terminals in the RRC idle mode implement an RRC connection with the UTRAN. As a result, the terminals notify the UTRAN that the terminals in the RRC idle mode want to receive the specific MBMS service. [22] However, when the terminals have a signaling connection with the SGSN (serving general packet radio service support node), the SGSN informs the UTRAN of in- formation related to the MBMS of the terminals. The information includes a list of MBMS services subscribed to by the terminals. Therefore, the UTRAN may recognize whether the terminals have subscribed to a specific MBMS service. Accordingly, the terminals do not respond to the request for the counting from the UTRAN. Terminals which do not have the signaling connection with the SGSN but are in the RRC connected state may inform the UTRAN of the list of MBMS services subscribed to by the terminals. Hence, the UTRAN may recognize the number of terminals desiring to receive the specific MBMS service without receiving any response from the terminals in the RRC connected state. [23] The UTRAN may perform the counting process during a session of the MBMS service or in the initial step of the MBMS service. Tliis is because, during the MBMS session, the terminal may move into another cell, turn off its power, or discontinue use of the MBMS service. Therefore, the number of terminals desiring to receive the MBMS service in a cell may change. Thus, the UTRAN may perform the counting process to establish the RB more efficiently even while the MBMS session is ongoing. [24] A FLC (Frequency Layer Convergence) is described below. [25] In the UMTS system, a base station may actually use one or more frequency bandwidths. That is, because all users may not receive services with appropriate qualities using only one frequency bandwidth in an area where many users are congregated (e.g., in a hot-spot), service providers consider the service demand in a region where the base station is positioned in order to provide services by using more than one frequency bandwidth. [26] When one base station uses several frequencies, for example several adjacent frequencies, the propagation characteristics of radio waves in each frequency have many similarities. If one MBMS service is provided using a power level corresponding to approximately ten percent of the entire power available for a specific frequency in a specific cell, when the base station provides the same MBMS service at other frequencies, significant radio resources may be consumed. [27] Therefore, when a base station uses several frequencies, the base station selects one frequency among the available frequencies to provide the MBMS service. The terminals then move to the selected frequency. The preceding operations are referred to as FLC (Frequency Layer Convergence). The specific: frequency selected by the base station to provide the MBMS service is referred to as a preferred frequency. [28] In FLC, when notifying terminals of a MBMS start, the base station informs the terminals of the preferred frequency on which the MBMS service is provided to induce the terminals to move to the specific frequency. To this end, the base station informs the terminals positioned at frequencies other than the preferred frequency that the MBMS service is provided only at the preferred frequency. Then, the terminals carry out a cell reselection procedure. When a condition for changing a cell is satisfied, the terminals reselect a cell to move to the preferred frequency. [29] The cell reselection by the terminals is described below. [30] The cell reselection process is a process for positioning a terminal in a cell that provides services of at least a minimum quality. In this process, the terminal compares ■ the quality of a serving cell against the quality of a neighboring cell. If the quality of the neighboring cell is superior to that of the serving cell, the terminal reestablishes the neighboring cell as its serving cell. [31] Cell quality may be influenced by radio wave environment, which may change in an irregular manner. As a result, a terminal located at a boundary of more than two cells frequently performs cell reselection in an alternating fashion (e.g., selecting different cells in turn). Whenever cell reselection is performed, the terminal must re- register its location with a new cell or temporarily stop data transmissions. Ac- cordingly, cell reselection should not be performed more frequently than necessary, to prevent waste of resources. Accordingly, when the quality of the serving cell is higher than a specific reference value, the terminal does not perform cell reselection. The specific reference value is set at a value by which services may be provided at a sat- isfactory level to the terminal. That is, even if the serving cell does not provide better quality than neighboring cells, if the quality of the serving cell is higher than the specific reference, then the terminal does not perform cell reselection. [32] When a base station uses several frequencies, each frequency may be for a particular cell, and the cell reselection is used in Cell_PCH, Cell_FACH, URA_PCH and idle mode in which the UTRAN does not assign a cell where the terminal should be positioned. [33] FLC is described in relationship with cell reselection, below. When a frequency in a cell in which a terminal is positioned is not a preferred frequency, the terminal receives information regarding the preferred frequency from a base station at an initial step of the MBMS service. However, as described above, if the quality of the cell in which the terminal is positioned exceeds a specific reference value, the terminal does not perform the cell reselection process. Because the MBMS service subscribed by the terminal is provided only at the preferred frequency, if the terminal does not move to the preferred frequency, the terminal may not receive the service to which it subscribed. Therefore, in order for the terminal to receive the service to which it has subscribed, when a specific MBMS service is provided only at a preferred frequency and the terminal does not position itself at the preferred frequency, the terminal performs the cell reselection process even if the quality of the serving cell where the terminal is positioned is higher than the specific reference value. [34] In the cell reselection process, the base station informs the terminal of an offset value to facilitate the selection of the preferred frequency by the terminal. The offset value is added to a quality measurement value of a cell positioned at the preferred frequency or is excluded from a quality measurement value of a cell not positioned at the preferred frequency. A specific frequency or a specific cell is determined to have a quality better than that of other cells based on this offset value. Accordingly, the base station may increase the probability that the terrninal moves to the preferred frequency or the specific cell. [35] As mentioned above, the PLC is a method for j^atiomiig apluraUty of teirohiails at a specific frequency bandwidth in a certain area. That is, using this ELC method, the base station may reduce consumption of radio resources to provide the MBMS service to the terminals. [363 However, the PLC deliberately changes a distribution of terminals in order to position many teimijials at a preferred frequency. As a result, many terminals are positioned at the preferred frequency, but a relatively small number of terminals are positioned at other frequencies. Therefore, a load is converged only upon a specific cell, causing an imbalance between the frequencies and cells. In addition, as compared to a uniform distribution of terminals over several cells, when BLC is implemented, the terminals may receive services of lesser quality, resulting in an inefficient allocation of radio resources. [37] As described above, at the initial step of the MBMS service, the terminal performs the cell reseleetion process to move into the cell of tbs preferred frequency on the basis of information transmitted from the base station even if the quality of the serving cell in which the terminal is positioned exceeds a certain reference value. However, after completing the MBMS service, when the quality of the cell is which the terminal is positioned exceeds the specific reference value, the terminal does not move into a new cell but remains positioned at the preferred frequency. That is, the state of the MBMS service start, i.e. that terminals positioned at other fluencies are converged upori the preferred frequency, continues until after the MBMS service is completed. A problem may occur, however, in which the number of terminals to which a cell may provide services with the appropriate quality is exceeded. This problem may continue even after the MBMS service has ended. [38] In general, if the terminal is positioned in a cell with the best quality, much data may be exchanged with the base station even with relatively low power. However, depending on the current FLC method of the MBMS service, although, the terminal may receive a service with far better quality from another frequency or cell after the MBMS service is completed, the terminal does not change the frequency. Instead, the terminal remains continuously positioned at the same frequency as long as the quality of the currently selected cell is higher than a certain reference value. This distribution of terminals after the MBMS service is completed may waste power in terminals. WO 2004/073322 discloses general knowledge of cell-reselection scheme. In particular, it discloses preforming reseleetion communication and receiving response related to the reseleetion. It fails to disclose a solution to any of the technical problems that arise when cell-reselection is performed after MBMS or point-to-multipoint service is completed. US 7940724 discloses general knowledge of cell-reselection scheme. In particular, it discloses preforming reseleetion communication and receiving cell-reselection assistance information. It fails to disclose a solution to any of the technical problems that arise when cell-reselection is performed after MBMS or point-to-multipoint service is completed. Disclosure of Inventioii Technical Problem [39] Accordingly, the present invention is directed to terminal distribution control for point-to-multipoint service that substantially obviates one or more problem's due to limitations and disadvantages of the related art. [40] An object of the present invention is to provide uniform distribution of terminals that were converged upon a specific preferred frequency due to FLC (Frequency Layer Convergence), over several frequencies upon point-to-multipoint service completion. [41] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be. realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. Technical Solution [42] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, in one embodiment, a method for controlling a user equipment (UE) capable of receiving a point- to-multipoint service in a wireless communication system comprises receiving a point- to-multipoint service and performing a cell reselection in response to completion of the receiving of the point-to-multipoint service. The cell reselection is performed among multiple frequencies. [43] The cell reselection may be performed in response to signaling from the network. . The cell reselection may be performed regardless of whether cell reselection criteria are satisfied. The cell reselection criteria may comprise at least one of a cell reselection reference value between frequencies and a cell reselection reference value within a frequency. [44] The cell reselection criteria may be embodied in frequency layer dispersion (ELD) information. Alternatively, the cell reselection criteria may be embodied in frequency layer convergence (FLC) information. [45] The point-to-multipoint service may be a multimedia service. The point- to-multipoint service may be received from a UTMS terrestrial radio network (UTRAN)- The cell reselection may be performed among available frequencies. [46] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Brief Description of the Accompanying Drawings [47] The accompanying drawings, which are included, to provide a further un- derstanding of the invention and are incorporated in and constitute a part of this ap- plication,, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. • [48] Figure 1 is a block diagram illustrating a structure of a UMTS network. [49] Figure 2 is a diagram illustrating a connection structure between a UTRAN and a terminal in a UMTS network. [50] Figure 3 is a diagram illustrating an example of the UMTS network providing a point-to-multipoint service to the terminal. [51] Figure 4 is a diagram illustrating terminal distribution control for a point- to-multipoint service, according to an embodiment of the present invention. Mode for Invention [52] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. [53] The present invention may be embodied in a mobile communications system such as the UMTS (Universal Mobile Telecommunications System) developed by the 3GPP. However, the present invention may also be applied to communications systems operated using other specifications. Furthermore, the point-to-multipoint service ■ referred to herein may be a multimedia broadcast/multicast service (MBMS) or other type of service. Additionally, the terminal referred to herein, may be a user equipment (UE) or other type of terminal. [54] Using the present invention, a UTRAN may utilize and share resources more ef- ficiently. Furthermore, a terminal may receive services in a cell more efficiently and with better quality. In one embodiment, a terminal moving into a preferred frequency by FLC (Frequency Layer Convergence) performs cell reselection and moves to a frequency with a relatively better quality, after a corresponding MBMS service is completed. That is, when the MBMS service is completed, the terminal is notified of the completion of the MBMS service by the base station and performs a cell re- selection process. In.the cell reselection process, the terminal searches available frequencies as candidate frequencies. The completion of an MBMS service is also known as the end of ah MBMS session. [55] Furthermore, when the MBMS service is completed, the base station may uniformly distribute many terminals converged upon a preferred frequency over several frequencies. The base station may recognize the load generated in each cell at each frequency. Therefore, the base station may regulate FLC information to congregate multiple terminals on a specific frequency bandwidth. The specific ■ - frequency bandwidth that the multiple terminals are converged upon by the base station is the preferred frequency. Alternatively, the base station may instruct the multiple terminals to be distributed over several frequency bandwidths. [56] The FLC information may include details regarding the frequencies that each MBMS is being transmitted. The FLC information may also include details regarding measuring parameters, measurement compensated values, or offsets to be applied to cells when the terminal performs cell reselection. Furthermore, the FLC information may include a basis for determining a cell change, or instructions regarding whether the cell reselection should be performed with respect to various frequencies. [57] When the base station provides the MBMS service, if the number of terminals converged on the preferred frequency is not high enough to cause problems in providing other services, or if the terminals have already been converged to maximum capacity on another frequency and additional terminals may not be converged on the another frequency, the base station does not instruct the terminals to perform cell re- selection, even if the MBMS service is completed. However, when the base station is required to distribute terminals converged on the preferred frequency over several frequencies, the base station may instruct the terminal to perform cell reselection, even though the quality of a preferred frequency in a cell at which the terminal is currently positioned is greater than a cell reselection reference value. [58] Figure 4 is a diagram illustrating terminal distribution control for a point- to-multipoint service, according to an embodiment of the present invention. [59] Referring to Figure 4, the base station transmits ELC information and the terminals move to the preferred frequency based on the FLC information. The terminals then receive the MBMS service. When the MBMS service is completed, the terminals may perform cell reselection by measuring the qualities of available frequencies and selecting a frequency in a cell having the best quality. The selected frequency may be in the current serving cell or another cell. If the terminal selects a frequency in another cell, the another cell is designated as the serving cell. The selection of a new serving cell may occur regardless of whether the quality of the new serving cell is higher than the cell reselection reference value. The cell reselection reference value may preferably be a cell reselection reference value between frequencies (Sintersearch) or a cell re- selection reference value within a frequency (Sintrasearch). [60] After the MBMS session ends, the terminal may perform cell reselection regardless of the cell reselection reference value until the terminal measures qualities of several frequencies in order to select a frequency to be positioned. The terminal then moves to the selected frequency. Furthermore, cell reselection may be performed when the quality value of the serving cell is less than a specific reference value. [61] During reception of the MBMS service by the terminal, when PLC information (e.g., information regarding a preferred frequency) is changed, when FLC information is not being transmitted from the base station, or when the base station notifies the terminal that the FLC is not being used, the terminal may perform cell reselection regardless of the cell reselection reference value with respect to available frequencies. Available frequencies are frequencies adjacent to the serving cell where the terminal is positioned. [62] Furthermore, in another embodiment, a plurality of frequencies may be established as the preferred frequency. In such case, service quality may be maintained despite convergence. To this end, the base station may assign a plurality of frequencies as the preferred frequency and inform the terminal through a MCCH (MBMS Control Channel). Upon receiving the notification from the base station that more than one frequency is assigned as the preferred frequency, the terminal adds an offset value, which may be provided by the base station, to the preferred frequency to perform cell reselection. [63] In cell reselection, if a plurality of preferred frequencies are related to a specific MBMS service transmitted from the base station, the terminal may select an arbitrary frequency and then select a cell that has the arbitrary frequency bandwidth as its serving cell. Furthermore, if a plurality of preferred frequencies related to the specific MBMS service are transmitted from the base station, the terminal may measure the _ quality of the cell of the preferred frequency bandwidth to select a frequency bandwidth with an optimal quality and set the cell of the corresponding frequency bandwidth as its serving cell. [64] Furthermore, in cell reselection, when the number of preferred frequencies related to the specific MBMS service received from the base station is changed, the terminal measures each frequency bandwidth to select an arbitrary bandwidth and then moves to the corresponding frequency bandwidth. Additionally, during cell reselection, when the number of preferred frequencies related to the specific MBMS service received from the base station is changed, the terminal measures each frequency bandwidth to select a frequency bandwidth which provides the best quality and then moves into the cor- responding frequency bandwidth. Also, in the cell reselection process, when the FLC information transmitted from the base station to the terminal does not include the in- formation related to the preferred frequency, the terminal performs the cell reselection process by searching available frequencies as candidate frequencies. [65] However, once the MBMS service is completed, when the cell reselection process is required to search several frequencies as candidate frequencies, measurement of the qualities with respect to available frequencies by the terminal in order to determine a cell to be positioned may require a significant time period. This time period for measurement may result in an increase in service disconnection time for the terminal. Therefore, after the MBMS service is completed, when the terminal performs cell re- selection by searching various frequencies as candidate frequencies, the terminal may not measure all frequencies. Rather, the terrninal may select an arbitrary frequency among the available frequencies, and move to the cell of the arbitrary frequency. [66] In one embodiment, a method for controlling a user equipment (UE) capable of receiving a point-to-multipoint service in a wireless communication system comprises receiving a point-to-multipoint service and performing a cell reselection in response to completion of the receiving of the point-to-multipoinl: service. The cell reselection is performed among multiple frequencies. [67] The cell reselection may be performed in response to signaling from the network. The cell reselection may be performed regardless of whether cell reselection criteria are satisfied. The cell reselection criteria may comprise at least one of a cell reselection reference value between frequencies and a cell reselection reference value within a frequency. [68] The cell reselection criteria may be embodied in frequency layer dispersion (FLD) information. Alternatively, the cell reselection criteria may be embodied in frequency layer convergence (PLC) information. [69] The point-to-multipoint service may be a multimedia service. The point- to-multipoint service may be received from a UTMS terrestrial radio network (UTRAN). The cell reselection may be performed among available frequencies. [70] The present invention may provide for, after an MBMS service is completed, the terminal may perform cell reselection. Accordingly, the terminal may move into a cell in which a service is provided with an optimal quality. Therefore, load may be minimized from being converged upon a specific cell. [71] It will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modi- fications and variations of this invention provided they come within the scope of the appended claims and their equivalents. WE CLAIM: 1. A method for controlling a user equipment (UE) configured to receive a point- to-multipoint service in a wireless communication system, the method performed by the UE and comprising: receiving the point-to-multipoint service; completing the reception of the point-to-multipoint service by releasing a point-to-multipoint radio bearer; and performing a cell reselection based on control information received from a base station after the completion of the reception of the point-to-multipoint service; wherein the control information includes a first parameter associated with measurement between frequencies and a second parameter associated with measurement within a frequency, wherein performing the cell reselection comprises: selecting a frequency randomly from among a plurality of frequencies using the control information; and selecting a suitable cell within the selected frequency, wherein the point-to-multipoint service is received based on a frequency indicated by the control information, wherein the cell reselection is performed when the UE decides to no longer receive the point-to-multipoint service, and wherein the cell reselection is performed among the multiple frequencies without measuring all candidate frequencies, wherein the control information further includes frequency layer convergence (FLC) information, wherein the FLC information indicates at least one preferred frequency, wherein the FLC information includes an offset to be applied to the at least one preferred frequency, and wherein the offset is added to a quality measurement value of a cell positioned at the preferred frequency for comparing the cell with another cell during the cell reselection. 2. The method as claimed in claim 1, wherein the cell reselection is performed if a variable related to previous frequency information for the point-to- multipoint service is not empty. Abstract A Method of Controlling a User Equipment Capable of Receiving a Point-to-Multipoint Service in a Wireless Communication System A method of controlling a user equipment (UE) capable of receiving a point- to-multipoint service in a wireless communication system is disclosed. The method performed by the UE and comprises the steps of receiving a point-to- multipoint service and performing a cell reselection based on control information received from a base station in response to completion of the receiving of the point-to- multipoint service wherein the cell reselection is performed among multiple frequencies by using the control information, wherein the point-to-multipoint service is received based on a frequency indicated by the control information and wherein the cell reselection is performed among the multiple frequencies without measuring all candidate frequencies, wherein the control information includes frequency layer convergence (FLC) information, wherein the FLC information indicates at least one preferred frequency, wherein the FLC information includes an offset to be applied to the at least one preferred frequency, and wherein the offset is added to a quality measurement value of a cell positioned at the at least one preferred frequency so that the added value is used when comparing the cell with another cell during the cell reselection.

Full Text

Technical Field
[1] The present invention relates generally to point-to-multipoint service in a wireless
communication system and, more particularly, to terminal distribution control for
point-to-multipoint service.
Background Art
[2] The "UMTS (universal mobile telecommunications system) is a third generation
mobile communications system evolved from the European GSM (Global System for
Mobile Communications) system and aims to provide improved mobile com-
munication services based on a GSM core network and a wideband code division .
multiple access (W-CDMA) technology.
[3] Figure 1 is a block diagram illustrating a structure of a UMTS network.
[4] Referring to Figure 1, the UMTS system generally consists of a terminal (e.g., user
equipment (UE)), a UTRAN (UTMS radio access network) and a GN (core network).
The UTRAN includes one or more RNSs (radio network sub-systems). Each RNS
includes a single RNC (radio network controller) and one or more base stations (e.g.,
node-Bs) managed by the RNC. Each Node B managed by the RNC receives in-
formation sent from a physical layer of a terminal on the uplink, and transmits data to
the terminal on the downlink. Thus, the node-B serves as an access point to the
UTRAN for the terminal. The RNC allocates and manages radio resources, and serves
as an access point to the CN for the UTRAN.
[5] Figure 2 is a diagram illustrating a connection structure between a UTRAN and a
terminal in a UMTS network. As such, Figure 2 shows an exemplary architecture of
radio interface protocols between a terminal and a UTRAN based on a 3GPP radio
access network specification.
[6] Referring to Figure 2, the radio protocol is horizontally arranged to include a
physical layer, a data link layer and a network layer. The radio protocol is vertically
divided into a user plane for transmitting data information and a control plane for
transferring control signals. Furthermore, the protocol layers shown in Figure 2 may be
divided into a first layer L1, a second layer L2 and a third layer L3, based upon the •
three lower layers of an open system interconnection (OSI) specification model that is
well-known in the art of communications systems.
[7] The first layer L1 (e.g., the physical layer) uses physical channels to provide in-

formation transfer service to its upper layers. The physical layer is connected via a
transport channel to a medium access control (MAC) layer located at an upper layer
thereof. Data between the medium access control layer and the physical layer is
transferred via this transport channel. Furthermore, the data between different physical
layers, i.e. between physical layers of transmitting side and receiving side, is
transferred via the physical layer.
[8] The MAC layer of the second layer L2 provides services to an upper radio link
control (RLC) layer via a logical channel. The RLC layer of the L2 supports reliable
data transmissions and performs segmentation and concatenation of RLC SDUs
(service data units).
[9] The RRC (Radio Resource Control) layer positioned in the lowest portion of the
third layer (L3) is defined in the control plane and controls the transport channels and
the physical channels for establishment, reconfiguration, and release of radio bearers
(RBs). The RB indicates a service by the L2 for a data transfer between the terminal
and the UTRAN. In general, establishing the RB denotes processes of stipulating the
characteristics of a protocol layer and a channel, which are required for providing a
specific service, and setting corresponding parameters and operation methods.
[ 10] When the RRC layer of a specific terminal and the RRC layer of the UTRAN are
connected to each other to exchange RRC messages, the corresponding terminal is in a
RRC connected state. On the contrary, when not connected to each other, the cor-
responding terminal is in an idle state. The terminal in the RRC connected state is
further divided into URA_PCH state and CELL_PCH state, CELLJFACH state and
CELLJDCH state. Terrninals in the idle state or the URA_PCH state and CELLJPCH
state use a discontinuous reception (DRX) method to reduce power consumption,
thereby discontinuously receiving a physical channel (i.e., SCCPCH (secondary
common control physical channel)) to which a physical channel (i.e., PICH (paging
indicator channel)) and a transport channel (i.e., PCH (paging channel)) are mapped.
The terminal is in a sleeping mode during the remaining time periods excluding those
times when receiving the PICH or the SCCPCH. The terminal performing the DRX
method wakes up once per DRX cycle length to receive a PI (paging indicator) of the
PICH channel.
[11] The terminal in the RRC connected state may further have a signaling connection
with the CN. In this case, the signaling connection indicates a path for exchanging
control messages between the terminal and the CN. The RRC connected state denotes a
connection between the terminal the UTRAN, while the signaling connection denotes a
connection between the terminal and the CN. The terminal uses the signaling
connection to inform the CN of its position and/or to request services. The terminal
should be in the RRC connected state to have a signaling connection.

[12] A MBMS (multimedia broadcast / multicast service) is described below.
[13] The MBMS refers to a service for providing streaming or background services to a
plurality of terminals using a downlink dedicated MBMS bearer service. In the
UTRAN, the MBMS bearer uses a point-to-multipoisit radio bearer (RB) and a point-
to-point RB. At this time, the point-to-multipoint RB uses a common channel (e.g.,
using the SCCPCH as a physical layer) so that a plurality of terminals subscribed to a
corresponding service may receive the service.
[14] The MBMS is divided into a broadcast mode and a multicast mode. The MBMS
broadcast mode is a service for transmitting multimedia data to all users within a
broadcast area. Conversely, the MBMS multicast mode is a service for transmitting the
multimedia data only to a specific user group within a multicast area. The broadcast
area refers to a region in which it is possible to transmit the broadcast service, and the
multicast area refers to a region in which it is possible to transmit the multicast service.
[15] Figure 3 is a diagram illustrating an example of the UMTS network providing a
point-to-multipoint service to the terminal.
[16] Referring to Figure 3, a UE1 performs a subscribing process in order to receive an
MBMS service. The UE1 also receives a service announcement provided by the
network regarding the MBMS service. Subscribing refers to the establishment of a re-
lationship between a service provider and a user. A service announcement refers to
providing the terminal an index and other information related to the services to be
provided. For example, a terminal that desires to receive the MBMS service of a
multicast mode should join a multicast group. The multicast group refers to a group of
terminals receiving a specific multicast service. Joining refers to a user merging with
other users in a multicast group to receive a particular multicast service. The terminal
may inform the UMTS network that it desires to receive specific multicast data
through MBMS multicast joining. On the contrary, leaving is a procedure in which a
terminal that joined a specific multicast group releases its joining to the multicast
group. Each terminal performs such subscribing, joining and leaving processes. The
terminal may perform the subscribing, joining, and leaving processes any time of
before, during, or after data transmission.
[17] During performance of a specific MBMS service, one or more sessions may se-
quentially be generated with respect to the MBMS service. If data to be transmitted for
the specific MBMS service is generated in a MBMS service source, the CN notifies a
session start to the RNC. However, if there is no data to be transmitted for the specific
MBMS service in the MBMS service source, the CN notifies a session end to the RNC.
The data transmission with respect to the specific MBMS service may be carried out
between the session start and the session end. At this time, the data transmitted through
the data transmission process is transmitted only to terminals that have joined the

multicast group.
[18] In the session start process, the UTRAN receives the session start notification from
the CN and transfers a MBMS notification to the tenninals. The MBMS notification
refers to the UTRAN informing a terminal that the data transmission of the specific
MBMS service in a cell is imminent. The MBMS notification may be transmitted
multiple times before the transmission of the data pertaining to the service. When
carrying out the MBMS notification process, the UTRAN may also count the number
of terminals receiving the specific MBMS service within a cell. The counting may be
used for determining whether a point-to-multipomt KB or a point-to-point RB is set as
the RB for transmitting the specific MBMS service data, or whether no RB is set.
[19] The UTRAN internally establishes a threshold value to select an appropriate
MBMS RB. After the UTRAN counts the number of terminals, if the counted number
of terminals receiving the corresponding MBMS service within the corresponding cell
is smaller than the threshold value, the UTRAN establishes a point-to-point RB.
However, a point-to-multipoint RB is established if the counted number of terminals is
greater than the threshold value. After determining the MBMS RB, the UTRAN
informs the terminals of the establishment information of the corresponding RB.
[20] When the point-to-point RB is established for the specific service, the terminals
that desire to receive the service must be in the RRC connected mode state. However,
when the point-to-multipoint RB is established for the specific service, the terminals
that desire to receive the service do not have to be in the RRC connected mode state.
That is, terminals in an idle state may also receive the MBMS service data by using the
point-to-multipoint RB. However, if no terminals are counted, the UTRAN does not
establish any RB and does not transmit the MBMS service data. As such, the UTRAN
establishing an RB when there is no user who wants to receive the service may cause
undesirable consumption of radio resources. The UTRAN initiates a transmission for
MBMS service data received from the CN during a session using the determined RB.
[21] During the counting process, the UTRAN does not have any information pertaining
to terminals in an RRC idle mode. Accordingly, when the terminals in the RRC idle
mode are requested by the UTRAN for counting (with respect to MBMS services
subscribed by the terminals), the terminals in the RRC idle mode implement an RRC
connection with the UTRAN. As a result, the terminals notify the UTRAN that the
terminals in the RRC idle mode want to receive the specific MBMS service.
[22] However, when the terminals have a signaling connection with the SGSN (serving
general packet radio service support node), the SGSN informs the UTRAN of in-
formation related to the MBMS of the terminals. The information includes a list of
MBMS services subscribed to by the terminals. Therefore, the UTRAN may recognize
whether the terminals have subscribed to a specific MBMS service. Accordingly, the

terminals do not respond to the request for the counting from the UTRAN. Terminals
which do not have the signaling connection with the SGSN but are in the RRC
connected state may inform the UTRAN of the list of MBMS services subscribed to by
the terminals. Hence, the UTRAN may recognize the number of terminals desiring to
receive the specific MBMS service without receiving any response from the terminals
in the RRC connected state.
[23] The UTRAN may perform the counting process during a session of the MBMS
service or in the initial step of the MBMS service. Tliis is because, during the MBMS
session, the terminal may move into another cell, turn off its power, or discontinue use
of the MBMS service. Therefore, the number of terminals desiring to receive the
MBMS service in a cell may change. Thus, the UTRAN may perform the counting
process to establish the RB more efficiently even while the MBMS session is ongoing.
[24] A FLC (Frequency Layer Convergence) is described below.
[25] In the UMTS system, a base station may actually use one or more frequency
bandwidths. That is, because all users may not receive services with appropriate
qualities using only one frequency bandwidth in an area where many users are
congregated (e.g., in a hot-spot), service providers consider the service demand in a
region where the base station is positioned in order to provide services by using more
than one frequency bandwidth.
[26] When one base station uses several frequencies, for example several adjacent
frequencies, the propagation characteristics of radio waves in each frequency have
many similarities. If one MBMS service is provided using a power level corresponding
to approximately ten percent of the entire power available for a specific frequency in a
specific cell, when the base station provides the same MBMS service at other
frequencies, significant radio resources may be consumed.
[27] Therefore, when a base station uses several frequencies, the base station selects one
frequency among the available frequencies to provide the MBMS service. The
terminals then move to the selected frequency. The preceding operations are referred to
as FLC (Frequency Layer Convergence). The specific: frequency selected by the base
station to provide the MBMS service is referred to as a preferred frequency.
[28] In FLC, when notifying terminals of a MBMS start, the base station informs the
terminals of the preferred frequency on which the MBMS service is provided to induce
the terminals to move to the specific frequency. To this end, the base station informs
the terminals positioned at frequencies other than the preferred frequency that the
MBMS service is provided only at the preferred frequency. Then, the terminals carry
out a cell reselection procedure. When a condition for changing a cell is satisfied, the
terminals reselect a cell to move to the preferred frequency.
[29] The cell reselection by the terminals is described below.

[30] The cell reselection process is a process for positioning a terminal in a cell that
provides services of at least a minimum quality. In this process, the terminal compares
■ the quality of a serving cell against the quality of a neighboring cell. If the quality of
the neighboring cell is superior to that of the serving cell, the terminal reestablishes the
neighboring cell as its serving cell.
[31] Cell quality may be influenced by radio wave environment, which may change in
an irregular manner. As a result, a terminal located at a boundary of more than two
cells frequently performs cell reselection in an alternating fashion (e.g., selecting
different cells in turn). Whenever cell reselection is performed, the terminal must re-
register its location with a new cell or temporarily stop data transmissions. Ac-
cordingly, cell reselection should not be performed more frequently than necessary, to
prevent waste of resources. Accordingly, when the quality of the serving cell is higher
than a specific reference value, the terminal does not perform cell reselection. The
specific reference value is set at a value by which services may be provided at a sat-
isfactory level to the terminal. That is, even if the serving cell does not provide better
quality than neighboring cells, if the quality of the serving cell is higher than the
specific reference, then the terminal does not perform cell reselection.
[32] When a base station uses several frequencies, each frequency may be for a
particular cell, and the cell reselection is used in Cell_PCH, Cell_FACH, URA_PCH
and idle mode in which the UTRAN does not assign a cell where the terminal should
be positioned.
[33] FLC is described in relationship with cell reselection, below. When a frequency in
a cell in which a terminal is positioned is not a preferred frequency, the terminal
receives information regarding the preferred frequency from a base station at an initial
step of the MBMS service. However, as described above, if the quality of the cell in
which the terminal is positioned exceeds a specific reference value, the terminal does
not perform the cell reselection process. Because the MBMS service subscribed by the
terminal is provided only at the preferred frequency, if the terminal does not move to
the preferred frequency, the terminal may not receive the service to which it
subscribed. Therefore, in order for the terminal to receive the service to which it has
subscribed, when a specific MBMS service is provided only at a preferred frequency
and the terminal does not position itself at the preferred frequency, the terminal
performs the cell reselection process even if the quality of the serving cell where the
terminal is positioned is higher than the specific reference value.
[34] In the cell reselection process, the base station informs the terminal of an offset
value to facilitate the selection of the preferred frequency by the terminal. The offset
value is added to a quality measurement value of a cell positioned at the preferred
frequency or is excluded from a quality measurement value of a cell not positioned at

the preferred frequency. A specific frequency or a specific cell is determined to have a
quality better than that of other cells based on this offset value. Accordingly, the base
station may increase the probability that the terrninal moves to the preferred frequency
or the specific cell.
[35] As mentioned above, the PLC is a method for j^atiomiig apluraUty of teirohiails at
a specific frequency bandwidth in a certain area. That is, using this ELC method, the
base station may reduce consumption of radio resources to provide the MBMS service
to the terminals.
[363 However, the PLC deliberately changes a distribution of terminals in order to
position many teimijials at a preferred frequency. As a result, many terminals are
positioned at the preferred frequency, but a relatively small number of terminals are
positioned at other frequencies. Therefore, a load is converged only upon a specific
cell, causing an imbalance between the frequencies and cells. In addition, as compared
to a uniform distribution of terminals over several cells, when BLC is implemented, the
terminals may receive services of lesser quality, resulting in an inefficient allocation of
radio resources.
[37] As described above, at the initial step of the MBMS service, the terminal performs
the cell reseleetion process to move into the cell of tbs preferred frequency on the basis
of information transmitted from the base station even if the quality of the serving cell
in which the terminal is positioned exceeds a certain reference value. However, after
completing the MBMS service, when the quality of the cell is which the terminal is
positioned exceeds the specific reference value, the terminal does not move into a new
cell but remains positioned at the preferred frequency. That is, the state of the MBMS
service start, i.e. that terminals positioned at other fluencies are converged upori the
preferred frequency, continues until after the MBMS service is completed. A problem
may occur, however, in which the number of terminals to which a cell may provide
services with the appropriate quality is exceeded. This problem may continue even
after the MBMS service has ended.
[38] In general, if the terminal is positioned in a cell with the best quality, much data
may be exchanged with the base station even with relatively low power. However,
depending on the current FLC method of the MBMS service, although, the terminal
may receive a service with far better quality from another frequency or cell after the
MBMS service is completed, the terminal does not change the frequency. Instead, the
terminal remains continuously positioned at the same frequency as long as the quality
of the currently selected cell is higher than a certain reference value. This distribution
of terminals after the MBMS service is completed may waste power in terminals.
WO 2004/073322 discloses general knowledge of cell-reselection scheme. In particular, it
discloses preforming reseleetion communication and receiving response related to the reseleetion.
It fails to disclose a solution to any of the technical problems that arise when cell-reselection is
performed after MBMS or point-to-multipoint service is completed.
US 7940724 discloses general knowledge of cell-reselection scheme. In particular, it discloses
preforming reseleetion communication and receiving cell-reselection assistance information. It
fails to disclose a solution to any of the technical problems that arise when cell-reselection is
performed after MBMS or point-to-multipoint service is completed.
Disclosure of Inventioii

Technical Problem
[39] Accordingly, the present invention is directed to terminal distribution control for
point-to-multipoint service that substantially obviates one or more problem's due to
limitations and disadvantages of the related art.
[40] An object of the present invention is to provide uniform distribution of terminals
that were converged upon a specific preferred frequency due to FLC (Frequency Layer
Convergence), over several frequencies upon point-to-multipoint service completion.
[41] Additional advantages, objects, and features of the invention will be set forth in
part in the description which follows and in part will become apparent to those having
ordinary skill in the art upon examination of the following or may be learned from
practice of the invention. The objectives and other advantages of the invention may be.
realized and attained by the structure particularly pointed out in the written description
and claims hereof as well as the appended drawings.
Technical Solution
[42] To achieve these objects and other advantages and in accordance with the purpose
of the invention, as embodied and broadly described herein, in one embodiment, a
method for controlling a user equipment (UE) capable of receiving a point-
to-multipoint service in a wireless communication system comprises receiving a point-
to-multipoint service and performing a cell reselection in response to completion of the
receiving of the point-to-multipoint service. The cell reselection is performed among
multiple frequencies.
[43] The cell reselection may be performed in response to signaling from the network. .
The cell reselection may be performed regardless of whether cell reselection criteria
are satisfied. The cell reselection criteria may comprise at least one of a cell reselection
reference value between frequencies and a cell reselection reference value within a
frequency.
[44] The cell reselection criteria may be embodied in frequency layer dispersion (ELD)
information. Alternatively, the cell reselection criteria may be embodied in frequency
layer convergence (FLC) information.
[45] The point-to-multipoint service may be a multimedia service. The point-
to-multipoint service may be received from a UTMS terrestrial radio network
(UTRAN)- The cell reselection may be performed among available frequencies.
[46] The foregoing and other objects, features, aspects and advantages of the present
invention will become more apparent from the following detailed description of the
present invention when taken in conjunction with the accompanying drawings. It is to
be understood that both the foregoing general description and the following detailed
description of the present invention are exemplary and explanatory and are intended to

provide further explanation of the invention as claimed.
Brief Description of the Accompanying Drawings
[47] The accompanying drawings, which are included, to provide a further un-
derstanding of the invention and are incorporated in and constitute a part of this ap-
plication,, illustrate embodiments of the invention and together with the description
serve to explain the principles of the invention. •
[48] Figure 1 is a block diagram illustrating a structure of a UMTS network.
[49] Figure 2 is a diagram illustrating a connection structure between a UTRAN and a
terminal in a UMTS network.
[50] Figure 3 is a diagram illustrating an example of the UMTS network providing a
point-to-multipoint service to the terminal.
[51] Figure 4 is a diagram illustrating terminal distribution control for a point-
to-multipoint service, according to an embodiment of the present invention.
Mode for Invention
[52] Reference will now be made in detail to the preferred embodiments of the present
invention, examples of which are illustrated in the accompanying drawings. Wherever
possible, the same reference numbers will be used throughout the drawings to refer to
the same or like parts.
[53] The present invention may be embodied in a mobile communications system such
as the UMTS (Universal Mobile Telecommunications System) developed by the
3GPP. However, the present invention may also be applied to communications systems
operated using other specifications. Furthermore, the point-to-multipoint service
■ referred to herein may be a multimedia broadcast/multicast service (MBMS) or other
type of service. Additionally, the terminal referred to herein, may be a user equipment
(UE) or other type of terminal.
[54] Using the present invention, a UTRAN may utilize and share resources more ef-
ficiently. Furthermore, a terminal may receive services in a cell more efficiently and
with better quality. In one embodiment, a terminal moving into a preferred frequency
by FLC (Frequency Layer Convergence) performs cell reselection and moves to a
frequency with a relatively better quality, after a corresponding MBMS service is
completed. That is, when the MBMS service is completed, the terminal is notified of
the completion of the MBMS service by the base station and performs a cell re-
selection process. In.the cell reselection process, the terminal searches available
frequencies as candidate frequencies. The completion of an MBMS service is also
known as the end of ah MBMS session.
[55] Furthermore, when the MBMS service is completed, the base station may
uniformly distribute many terminals converged upon a preferred frequency over

several frequencies. The base station may recognize the load generated in each cell at
each frequency. Therefore, the base station may regulate FLC information to
congregate multiple terminals on a specific frequency bandwidth. The specific ■ -
frequency bandwidth that the multiple terminals are converged upon by the base
station is the preferred frequency. Alternatively, the base station may instruct the
multiple terminals to be distributed over several frequency bandwidths.
[56] The FLC information may include details regarding the frequencies that each
MBMS is being transmitted. The FLC information may also include details regarding
measuring parameters, measurement compensated values, or offsets to be applied to
cells when the terminal performs cell reselection. Furthermore, the FLC information
may include a basis for determining a cell change, or instructions regarding whether
the cell reselection should be performed with respect to various frequencies.
[57] When the base station provides the MBMS service, if the number of terminals
converged on the preferred frequency is not high enough to cause problems in
providing other services, or if the terminals have already been converged to maximum
capacity on another frequency and additional terminals may not be converged on the
another frequency, the base station does not instruct the terminals to perform cell re-
selection, even if the MBMS service is completed. However, when the base station is
required to distribute terminals converged on the preferred frequency over several
frequencies, the base station may instruct the terminal to perform cell reselection, even
though the quality of a preferred frequency in a cell at which the terminal is currently
positioned is greater than a cell reselection reference value.
[58] Figure 4 is a diagram illustrating terminal distribution control for a point-
to-multipoint service, according to an embodiment of the present invention.
[59] Referring to Figure 4, the base station transmits ELC information and the terminals
move to the preferred frequency based on the FLC information. The terminals then
receive the MBMS service. When the MBMS service is completed, the terminals may
perform cell reselection by measuring the qualities of available frequencies and
selecting a frequency in a cell having the best quality. The selected frequency may be
in the current serving cell or another cell. If the terminal selects a frequency in another
cell, the another cell is designated as the serving cell. The selection of a new serving
cell may occur regardless of whether the quality of the new serving cell is higher than
the cell reselection reference value. The cell reselection reference value may preferably
be a cell reselection reference value between frequencies (Sintersearch) or a cell re-
selection reference value within a frequency (Sintrasearch).
[60] After the MBMS session ends, the terminal may perform cell reselection regardless
of the cell reselection reference value until the terminal measures qualities of several
frequencies in order to select a frequency to be positioned. The terminal then moves to

the selected frequency. Furthermore, cell reselection may be performed when the
quality value of the serving cell is less than a specific reference value.
[61] During reception of the MBMS service by the terminal, when PLC information
(e.g., information regarding a preferred frequency) is changed, when FLC information
is not being transmitted from the base station, or when the base station notifies the
terminal that the FLC is not being used, the terminal may perform cell reselection
regardless of the cell reselection reference value with respect to available frequencies.
Available frequencies are frequencies adjacent to the serving cell where the terminal is
positioned.
[62] Furthermore, in another embodiment, a plurality of frequencies may be established
as the preferred frequency. In such case, service quality may be maintained despite
convergence. To this end, the base station may assign a plurality of frequencies as the
preferred frequency and inform the terminal through a MCCH (MBMS Control
Channel). Upon receiving the notification from the base station that more than one
frequency is assigned as the preferred frequency, the terminal adds an offset value,
which may be provided by the base station, to the preferred frequency to perform cell
reselection.
[63] In cell reselection, if a plurality of preferred frequencies are related to a specific
MBMS service transmitted from the base station, the terminal may select an arbitrary
frequency and then select a cell that has the arbitrary frequency bandwidth as its
serving cell. Furthermore, if a plurality of preferred frequencies related to the specific
MBMS service are transmitted from the base station, the terminal may measure the _
quality of the cell of the preferred frequency bandwidth to select a frequency
bandwidth with an optimal quality and set the cell of the corresponding frequency
bandwidth as its serving cell.
[64] Furthermore, in cell reselection, when the number of preferred frequencies related
to the specific MBMS service received from the base station is changed, the terminal
measures each frequency bandwidth to select an arbitrary bandwidth and then moves to
the corresponding frequency bandwidth. Additionally, during cell reselection, when the
number of preferred frequencies related to the specific MBMS service received from
the base station is changed, the terminal measures each frequency bandwidth to select a
frequency bandwidth which provides the best quality and then moves into the cor-
responding frequency bandwidth. Also, in the cell reselection process, when the FLC
information transmitted from the base station to the terminal does not include the in-
formation related to the preferred frequency, the terminal performs the cell reselection
process by searching available frequencies as candidate frequencies.
[65] However, once the MBMS service is completed, when the cell reselection process
is required to search several frequencies as candidate frequencies, measurement of the

qualities with respect to available frequencies by the terminal in order to determine a
cell to be positioned may require a significant time period. This time period for
measurement may result in an increase in service disconnection time for the terminal.
Therefore, after the MBMS service is completed, when the terminal performs cell re-
selection by searching various frequencies as candidate frequencies, the terminal may
not measure all frequencies. Rather, the terrninal may select an arbitrary frequency
among the available frequencies, and move to the cell of the arbitrary frequency.
[66] In one embodiment, a method for controlling a user equipment (UE) capable of
receiving a point-to-multipoint service in a wireless communication system comprises
receiving a point-to-multipoint service and performing a cell reselection in response to
completion of the receiving of the point-to-multipoinl: service. The cell reselection is
performed among multiple frequencies.
[67] The cell reselection may be performed in response to signaling from the network.
The cell reselection may be performed regardless of whether cell reselection criteria
are satisfied. The cell reselection criteria may comprise at least one of a cell reselection
reference value between frequencies and a cell reselection reference value within a
frequency.
[68] The cell reselection criteria may be embodied in frequency layer dispersion (FLD)
information. Alternatively, the cell reselection criteria may be embodied in frequency
layer convergence (PLC) information.
[69] The point-to-multipoint service may be a multimedia service. The point-
to-multipoint service may be received from a UTMS terrestrial radio network
(UTRAN). The cell reselection may be performed among available frequencies.
[70] The present invention may provide for, after an MBMS service is completed, the
terminal may perform cell reselection. Accordingly, the terminal may move into a cell
in which a service is provided with an optimal quality. Therefore, load may be
minimized from being converged upon a specific cell.
[71] It will be apparent to those skilled in the art that various modifications and
variations may be made in the present invention without departing from the spirit or
scope of the inventions. Thus, it is intended that the present invention covers the modi-
fications and variations of this invention provided they come within the scope of the
appended claims and their equivalents.

WE CLAIM:
1. A method for controlling a user equipment (UE) configured to receive a
point- to-multipoint service in a wireless communication system, the method
performed by the UE and comprising:
receiving the point-to-multipoint service;
completing the reception of the point-to-multipoint service by releasing a
point-to-multipoint radio bearer; and
performing a cell reselection based on control information received from a
base station after the completion of the reception of the point-to-multipoint
service;
wherein the control information includes a first parameter associated with
measurement between frequencies and a second parameter associated with
measurement within a frequency,
wherein performing the cell reselection comprises:
selecting a frequency randomly from among a plurality of frequencies
using the control information; and
selecting a suitable cell within the selected frequency,
wherein the point-to-multipoint service is received based on a frequency
indicated by the control information,
wherein the cell reselection is performed when the UE decides to no longer
receive the point-to-multipoint service, and
wherein the cell reselection is performed among the multiple frequencies
without measuring all candidate frequencies,
wherein the control information further includes frequency layer
convergence (FLC) information,
wherein the FLC information indicates at least one preferred frequency,
wherein the FLC information includes an offset to be applied to the at least
one preferred frequency, and

wherein the offset is added to a quality measurement value of a cell
positioned at the preferred frequency for comparing the cell with another cell
during the cell reselection.
2. The method as claimed in claim 1, wherein the cell reselection is
performed if a variable related to previous frequency information for the point-to-
multipoint service is not empty.

Abstract

A Method of Controlling a User Equipment Capable of
Receiving a Point-to-Multipoint Service in a
Wireless Communication System
A method of controlling a user equipment (UE) capable of receiving a
point- to-multipoint service in a wireless communication system is disclosed. The
method performed by the UE and comprises the steps of receiving a point-to-
multipoint service and performing a cell reselection based on control information
received from a base station in response to completion of the receiving of the point-to-
multipoint service wherein the cell reselection is performed among multiple
frequencies by using the control information, wherein the point-to-multipoint service
is received based on a frequency indicated by the control information and wherein the
cell reselection is performed among the multiple frequencies without measuring all
candidate frequencies, wherein the control information includes frequency layer
convergence (FLC) information, wherein the FLC information indicates at least one
preferred frequency, wherein the FLC information includes an offset to be applied to
the at least one preferred frequency, and wherein the offset is added to a quality
measurement value of a cell positioned at the at least one preferred frequency so that
the added value is used when comparing the cell with another cell during the cell
reselection.

A METHOD OF CONTROLLING A USER EQUIPMENT CAPABLE OF RECEIVING A POINT-TO-MULTIPOINT SERVICE IN A WIRELESS COMMUNICATION SYSTEM

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