CN1989713B - Discontinuing use of frequency layer aggregation schemes - Google Patents

Abstract

The present invention is directed to discontinuing the use of a frequency layer convergence scheme that facilitates the selection of a cell on a preferred frequency for a joined point-to-multipoint service. In particular, a mobile terminal, which has joined a point-to-multipoint service with a preferred frequency, selects a cell using a frequency layer convergence scheme. The frequency layer convergence scheme facilitates selection of cells on a preferred frequency layer. However, based on the trigger that occurs, the use of the frequency layer convergence scheme is discontinued.

Description

Discontinuing use of frequency layer aggregation schemes

technical field

The present invention relates to cell selection in wireless communication systems, and more particularly to interrupt use of a frequency layer convergence scheme that facilitates cell selection on preferred frequencies of joined point-to-multipoint services.

Background technique

Recently, mobile communication systems have been remarkably developed, but for high-capacity data communication services, the performance of mobile communication systems cannot match that of existing wired communication systems. Therefore, technical development for IMT-2000, which is a communication system allowing large-capacity data communication, is made, and standardization of this technology is actively continued in various companies and organizations.

The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, evolved from the well-known European standard for the Global System for Mobile Communications (GSM). UMTS provides advanced mobile communication services based on GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.

In December 1998, ETSI in Europe, ARIB/TTC in Japan, T1 in the United States, and TTA in Korea formed the Third Generation Partnership Project (3GPP) for generating detailed specifications of the UMTS technology.

Within 3GPP, in order to achieve rapid and efficient technical development of UMTS, five Technical Specification Groups (TSGs) have been established for performing standardization of UMTS by considering the independent characteristics of network elements and their operations.

Each TSG develops, approves, and manages standard specifications in the area concerned. Among these groups, the Radio Access Network (RAN) Group (TSG-RAN) develops the functions, requirements, and interface standards for the UMTS Terrestrial Radio Access Network (UTRAN), the new radio access network, with In support of W-CDMA access technology in UMTS.

Figure 1 illustrates the basic structure of a common UMTS network. As shown in FIG. 1, UMTS is roughly divided into a terminal (or user equipment: UE), a UTRAN 100, and a core network (CN) 200.

UTRAN 100 includes one or more Radio Network Subsystems (RNS) 110,120. Each RNS 110, 120 includes a radio network controller (RNC) 111, and a plurality of base stations or Node Bs 112, 113 managed by the RNC 111. The RNC 111 handles allocation and management of radio resources, and operates as an access point to the core network 200 .

The Node Bs 112, 113 receive information sent by the physical layer of the terminal through the uplink, and send data to the terminal through the downlink. The Node B 112, 113 thus operates as an access point to the UTRAN 100 for the terminal.

The primary function of the UTRAN 100 is to form and maintain Radio Access Bearers (RABs) to allow communication between terminals and the core network 200. The core network 200 applies end-to-end Quality of Service (QoS) requirements to the RAB, and the RAB supports the QoS requirements set by the core network 200 . As the UTRAN 100 forms and maintains RABs, end-to-end QoS requirements are met. RAB service can be further divided into Iu bearer service and radio bearer service. The Iu bearer service supports reliable transmission of user data between the border nodes of the UTRAN 100 and the core network 200.

The core network 200 includes a co-connected Mobile Switching Center (MSC) 210 and a Gateway Mobile Switching Center (GMSC) 220 for supporting Circuit Switched (CS) traffic, and a co-connected Serving GPRS Support Node (SGSN) 230 and Gateway GPRS support Node 240, configured to support packet switching (PS) services.

Services provided to specific terminals are roughly classified into circuit switched (CS) services and packet switched (PS) services. For example, ordinary voice conversation traffic is circuit switched traffic, while web browsing traffic over an Internet connection is classified as packet switched (PS) traffic.

To support circuit switched services, the RNC 111 is connected to the MSC 210 of the core network 200, and the MSC 210 is connected to the GMSC 220 which manages connections with other networks.

To support packet switching services, RNC 111 is connected to SGSN 230 and GGSN 240 of core network 200. SGSN 230 supports packet communication towards RNC 111, while GGSN 240 manages connections to other packet-switched networks, such as the Internet.

Various types of interfaces exist between network components to allow the network components to send and receive information from each other for their mutual communication. The interface between RNC 111 and core network 200 is defined as an Iu interface. In particular, the Iu interface between the RNC 111 and the core network 200 for the packet switching system is defined as "Iu-PS", while the Iu interface between the RNC 111 and the core network 200 for the circuit switching system is defined as "Iu-CS".

FIG. 2 illustrates the structure of a radio interface protocol between a terminal and UTRAN according to 3GPP radio access network standards.

As shown in Figure 2, the radio interface protocol has horizontal layers including the physical layer, data link layer, and network layer, and has a vertical plane including the user plane (U-plane) for sending user data and the user plane (U-plane) for sending control The control plane (C-plane) for information.

The user plane is the area that handles user traffic information, such as voice or Internet Protocol (IP) packets, while the control plane is the area that handles control information, interfaces for the network, maintenance and management calls, and so on.

The protocol layers of FIG. 2 may be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on three lower layers of the Open System Interconnection (OSI) standard model. Each layer is described in detail below.

The first layer (L1), that is, the physical layer, provides information transfer services to the upper layer by using various wireless transmission technologies. The physical layer is connected to an upper layer via a transport channel called a medium access control (MAC) layer. The MAC layer and the physical layer transmit and receive data to and from each other via the transport channel.

The second layer (L2) includes a MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer, and a packet data convergence protocol (PDCP) layer.

The MAC layer provides a MAC parameter allocation service for allocating and reallocating radio resources. The MAC layer is connected to an upper layer called a Radio Link Control (RLC) layer via a logical channel.

Various logical channels are provided according to the kind of information to be transmitted. Generally, when information of a control plane is transmitted, a control channel is used. When transmitting user plane information, traffic channels are used. A logical channel can be a common channel or a dedicated channel, depending on whether the logical channel is shared or not. Logical channels include Dedicated Traffic Channel (DTCH), Dedicated Control Channel (DCCH), Common Traffic Channel (CTCH), Common Control Channel (CCCH), Broadcast Control Channel (BCCH) and Paging Control Channel (PCCH) or shared channel control channel (SHCCH). The BCCH provision includes information utilized by terminals to access a system. UTRAN uses PCCH to access a terminal.

Multimedia Broadcast/Multicast Service (MBMS or "MBMS Service") relates to a method of providing data streams or background services to multiple UEs using downlink-dedicated MBMS radio bearers, utilizing at least one of them. An MBMS service includes one or more sessions, and only when a session is in progress, MBMS data is sent to multiple terminals through the MBMS radio bearer.

As the name suggests, MBMS can be done in broadcast or multicast mode. The broadcast mode is to send multimedia data to all UEs within a broadcast area, eg, within an area where broadcast is available. The multicast mode is to send multimedia data to a specific UE in a multicast area, for example, in an area where a multicast service can be obtained.

For MBMS there are additional traffic and control channels. For example, MCCH (MBMS Point-to-Multipoint Control Channel) is used to send MBMS control information, while MTCH (MBMS Point-to-Multipoint Traffic Channel) is used to send MBMS service data.

The different logical channels available are listed below:

The MAC layer is connected to the physical layer through a transport channel and can be divided into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, and a MAC-hs sublayer according to the type of transport channel to be managed.

The MAC-b sublayer manages BCH (Broadcast Channel), which is a transport channel that handles broadcast of system information. The MAC-d sublayer manages a Dedicated Channel (DCH), which is a dedicated transport channel for a specific terminal. Thus, the MAC-d sublayer of UTRAN is located in a Serving Radio Network Controller (SRNC) that manages a corresponding terminal, and there is also a MAC-d sublayer within each terminal (UE).

The MAC-c/sh sublayer manages common transport channels, such as forward access channel (FACH) or downlink shared channel (DSCH), shared by multiple terminals, or in the uplink radio access channel (RACH) middle. In UTRAN, the MAC-c/sh self-layer is located in the controlling radio network controller (CRNC). Since the MAC-c/sh sublayer manages channels shared by all terminals within a cell area, there exists a single MAC-c/sh sublayer for each cell area. Furthermore, there is one MAC-c/sh sublayer in each terminal (UE). Referring to Fig. 3, a possible mapping between logical channels and transport channels from UE perspective is shown. Referring to Fig. 4, a possible mapping between logical channels and transport channels from the perspective of UTRAN is shown.

The RLC layer supports reliable data transmission and performs segmentation and concatenation functions for multiple RLC Service Data Units (RLC SDUs) delivered from the upper layer. When the RLC layer receives the RLC SDU from the upper layer, the RLC layer adjusts the size of each RLC SDU in an appropriate manner according to the considered processing capacity, and then adds header information to generate a certain data unit. The resulting data unit, called a protocol data unit (PDU), is then delivered to the MAC layer via a logical channel. The RLC layer includes RLC buffers for storing RLC SDUs and/or RLC PDUs.

The BMC layer schedules a cell broadcast message (hereinafter referred to as 'CB message') received from the core network, and broadcasts the CB message to terminals located in a specific cell. The BMC layer of UTRAN generates broadcast/multicast control (BMC) messages by adding information such as message ID (identification), sequence number, and coding scheme to the CB message received from the upper layer, and transmits the BMC message to the RLC layer . The BMC message is transferred from the RLC layer to the MAC layer through a logical channel, namely CTCH (Common Traffic Channel). The CTCH is mapped to a transport channel, FACH, which is mapped to a physical channel, S-CCPCH (Secondary Common Control Physical Channel).

PDCP (Packet Data Convergence Protocol), which is a higher layer of the RLC layer, allows data transmitted through a network protocol such as IPv4 or IPv6 to be efficiently transmitted over a wireless interface having a relatively small bandwidth. For this reason, the PDCP layer reduces unnecessary control information used in a wired network, which is a function called header compression.

The Radio Resource Control (RRC) layer is positioned at the lowest part of the L3 layer. The RRC layer is defined only in the control plane, and handles control of logical channels, transport channels, and physical channels for establishment, reconfiguration, and release or cancellation of radio bearers (RBs). The radio bearer service refers to the service provided by the second layer (L2) for data transmission between the terminal and the UTRAN. Generally, the establishment of a radio bearer involves defining the characteristics of the protocol layer and the processing of channels required for providing specific data services, as well as setting detailed parameters and operation methods for each.

The RLC layer can belong to the user plane or the control plane, depending on the type of layer connected on the upper layer of the RLC layer. That is, if the RLC layer receives data from the RRC layer, the RLC layer belongs to the control plane. Otherwise, the RLC layer belongs to the user plane.

Different possibilities of mapping between radio bearers and transport channels are not always possible. The UE/UTRAN derives possible mappings based on the UE state and the procedures being performed by the UE/UTRAN. The different states and modes are described in detail below.

Different transport channels are mapped to different physical channels. For example, the RACH transport channel is mapped on a given PRACH, the DCH may be mapped on a DPCH, the FACH and PCH may be mapped on an S-CCPCH, the DSCH is mapped on a PDSCH, and so on. The configuration of the physical channel is given by RRC signaling exchange between RNC and UE.

The RRC mode refers to whether there is a logical connection between the terminal's RRC and the UTRAN's RRC. If there is a connection, the terminal is said to be in RRC connected mode. If there is no connection, the terminal is said to be in idle mode. Since an RRC connection exists for a terminal in RRC connected mode, UTRAN can determine the presence of a specific terminal within a cell unit, eg in which cell or group of cells the terminal in RRC connected mode is located and which physical channel the UE is listening to. Therefore, the terminal can be effectively controlled.

In contrast, UTRAN cannot determine the existence of a terminal in idle mode. The presence of idle mode terminals can only be determined via the core network. In particular, the core network can only detect the presence of idle-mode terminals in areas larger than a cell, such as location or routing areas. Therefore, existing idle mode terminals are determined in a large area. In order to receive mobile communication services such as voice or data, an idle mode terminal must move or change to an RRC connected mode. Figure 5 shows the possible transitions between modes and states.

A UE in RRC connected mode can be in different states, such as CELL_FACH state, CELL_PCH state, CELL_DCH state or URA_PCH state. Depending on these states, the UE listens to different channels. For example, a UE in CELL_DCH state will attempt to listen to (in) DCH type transport channels, including DTCH and DCCH transport channels, which may be mapped to a certain DPCH. A UE in CELL_FACH state will listen to several FACH transport channels mapped to certain S-CCPCH physical channels. The UE in the PCH state will monitor the PICH channel and the PCH channel, which are mapped to the determined S-CCPCH physical channel.

In addition, based on the status, the UE also performs different actions. For example, based on different conditions, every time the UE changes from the coverage of one cell to the coverage of another cell, the UE in CELL_FACH will start the CELL update procedure. The UE starts the cell update procedure by sending a cell update message to the Node B to indicate that the UE has changed its location. The UE will then start listening to the FACH. This procedure is additionally used when the UE becomes CELL_PCH state from any other state and the UE does not have a C-RNTI available, such as when the UE originates from CELL_PCH state or CELL_DCH state, or when the UE in CELL_FACH state is out of coverage.

In the CELL_DCH state, the UE is granted dedicated radio resources and can additionally use shared radio resources. This allows UEs to have high data rates and efficient data exchange. However, radio resources are limited. It is the responsibility of UTRAN to allocate radio resources in UEs so that they are used efficiently and ensure that different UEs get the required quality of service.

A UE in the CELL_FACH state does not have dedicated radio resources to which it belongs, but can only communicate with the UTRAN via a shared channel. Therefore, the UE consumes few radio resources. However, the usable data rate is greatly limited. In addition, the UE needs to monitor the shared channel permanently. Therefore, UE battery consumption is increased in case the UE is not transmitting.

A UE in CELL_PCH/URA_PCH state only monitors the paging channel on a dedicated basis and thus minimizes battery consumption. However, if the network wishes to access the UE, it must first indicate this desire on a paging occasion. The network can then access the UE, but only if the UE has answered the page. Moreover, the UE can access the network only after performing the cell update procedure, which introduces additional delay when the UE wants to send data to the UTRAN.

The primary system information is sent on the BCCH logical channel, which is mapped on the P-CCPCH (Primary Common Control Physical Channel). Certain system information blocks may be sent on the FACH channel. When sending system information on FACH, the UE receives either the configuration of FACH on BCCH received on P-CCPCH, or on a dedicated channel. The P-CCPCH is transmitted using the same scrambling code as the P-CPICH (Primary Common Pilot Channel), which is the primary scrambling code of the cell.

Each channel uses a common spreading code in a WCDMA (Wideband Code Division Multiple Access) system. Each code is characterized by its spreading factor (SF), which corresponds to the length of the code. For a given spreading factor, the number of orthogonal codes is equal to the length of the codes. For each spreading factor, a given set of orthogonal codes is numbered from 0 to SF-1 as specified in the UMTS system. Each code can thus be identified by giving its length (ie spreading factor) and code number. The spreading code used by P-CCPCH is always a fixed spreading factor of 256 and number is number 1. According to the system information of the adjacent cell that the UE has read, through the information sent from the network, through the message that the UE has received on the DCCH channel, or by searching the P-CPICH, the UE knows the primary scrambling code, which uses a fixed SF 256 and spreading code number 0 are sent, and it sends a fixed pattern.

System information includes information about neighboring cells, configuration of RACH and FACH transport channels, and configuration of MCCH, which is a channel dedicated to MBMS services. When the UE has selected a cell (in CEL_FACH, CELL_PCH or URA_PCH state), the UE verifies that it has valid system information.

System information is organized in SIB (System Information Block), MIB (Master Information Block) and scheduling blocks. The MIB is sent very frequently and provides timing information for scheduling blocks and the various SIBs. For SIBs linked to a value tag, the MIB also contains information about the last version of a part of the SIB. SIBs that are not linked to a value tag are linked to an expiration timer. If the time at which the SIB was last read is greater than the value of the expiration timer, the SIB linked to the expiration timer becomes invalid and needs to be re-read. SIBs linked to a value tag are valid only if they have the same value tag as broadcast in the MIB. Each block has an area scope of validity, eg cell, PLMN (Public Land Mobile Network) or equivalent PLMN, which indicates in which cell the SIB is valid. A SIB with area scope "cell" is only valid for the cell in which it has been read. A SIB with area scope "PLMN" is valid in the whole PLMN. A SIB with area scope "equivalent PLMN" is valid in the whole PLMN and in equivalent PLMNs.

According to 3GPP standards, a UE in CELL_PCH, URA_PCH or CELL_FACH state, or in idle mode will always try to select/reselect a suitable cell (for non-emergency calls) or an acceptable cell (for emergency calls). In idle mode, when the UE has selected a cell, the UE is usually said to be "camping" on a cell. In RRC connected mode, when the UE is in CELL_PCH, URA_PCH or CELL_FACH state, the UE is simply said to have "selected" a cell.

To facilitate cell reselection, the network sends the system information list of neighboring cells. The list of neighbor cells identifies available cells, which the UE will measure and compare with the cells the UE has currently selected or the cells the UE is camped on. Available cells may be on the same frequency, on other frequencies or other radio access technologies (RATs), such as GSM. A list of cells, and evtl. cells discovered by the UE itself are considered as candidates for cell reselection.

Part of the cell selection/reselection process is based on quality measurements of the different cells that are part of the list of neighbor cells that are candidates for cell reselection. A cell may or may not be part of a Hierarchical Cell Structure (HCS). This is defined in the system information of a given cell. In case of a hierarchical cell structure, each cell has a given priority. Depending on whether a cell is part of a hierarchical cell structure, the cell selection procedure changes.

To decide which candidate cell to reselect, the UE measures the quality of neighboring cells. The UE uses a given formula to establish the rank criteria R of all candidate cells. The formula is based on measurements on the CPICH/P-CCPCH and on information received in the system information of the candidate cell. Standard R corresponds to positive or negative values. The R value can be calculated by the following formula, where R _S is the value for the serving cell and _RN is the R value for the neighboring cell:

The signal value Qoffmbms applies only to those cells (serving or neighboring) that belong to the MBMS preferred frequency (ie where the frequency aggregation scheme is applied). Qmeas gives the quality value of the received signal according to the average CPICH Ec/No or CPICH RSCP for FDD cells, according to the average P-CCPCH RSCP for TDD cells and according to the average received signal level for GSM cells exported. For FDD cells, the measurements used to derive the quality value are indicated in the system information.

The parameters Qhyst, Qoffsets, n, Qoffmbms, TEMP_OFF SET and PENALTY_TIME are signals passed on system information. The timer T is started and stopped for each cell, depending on the radio quality of the cell.

Criterion H is defined if a hierarchical cell structure (HCS) is used. The H criterion is a positive or negative value and is calculated based on information sent in system information and measurements from CPICH/P-CPCCH of candidate cells. In a hierarchical cell structure, cells may have different priorities. Calculate the criterion H according to the following formula

Define TO _n and LN, Q _meas,s and Q _meas,n similarly to the above definition. The goal of this cell structure is to cover users with low mobility as well as users with high mobility in the same area. To optimize capacity, it is best to fit as many cells as possible into a small-sized cell. Thus, this enables the maximum number of users in a given area.

However, for fast moving users, it is better to have a large number of cells to reduce the number of cells changing as the UE moves. In order to distinguish large-scale and small-scale cells, different priorities are assigned to the cells. The UE tends to select the cell with the highest priority. This usually corresponds to a small sized cell, except when the UE is moving fast. The H criterion is used in 3GPP to consider priorities. However, when the UE detects that it is moving fast (ie by detecting that the UE frequently reselects cells), the UE stops using the H criterion and no longer considers the cell's priority. A UE is then said to be in a "high mobility state".

The selection criterion S checks whether the reception quality of the candidate cell is sufficient. For this, the UE measures Q _qualmeas , which represents the E _c /N ₀ of the CPICH of the candidate cell (for FDD cells only). The UE also measures Q _rxlevmeas , which evaluates the RSCP (Received Signal Code Power) of the P-CCPCH for the candidate cell of the TDD cell and the CPICH of the candidate cell for the FDD cell. The UE uses these values in an algorithm, together with the information received in the system information of the candidate cell, to calculate the S value. If the value of S is greater than 0, the cell selection criterion S is implemented. Otherwise, do not execute.

In addition to the above criteria R, H and S, other criteria may determine which cell the UE may select. Information about these criteria is given to UEs as "cell access restrictions", broadcast in system information.

One type of cell access restriction may be "barred cells". Each UE uses a parameter called "Access Class", which gives the category of priority to the UE. The existing access classification is on a scale of 0-15. For each access category in the system information, it can be indicated whether the cell is barred or not. In addition, generally cells can also be barred.

Another type of cell access restriction is when the cell is "reserved for operator". In system information, it may indicate whether the cell is reserved for the operator. Depending on whether the UE classification is operator type, and whether the UE is in an emergency call, the UE can reselect a cell, which is reserved for operator use or not.

Also, access to a cell may be restricted as it is "reserved for future expansion". In system information, it can indicate whether a cell is reserved for future expansion.

Since the PLMN can restrict the access to the cell. Each cell belongs to one or more PLMNs. When the UE is powered on, it selects a PLMN and only changes the selected PLMN through specific signaling. When the UE selects/reselects a cell, it checks whether the selected PLMN corresponds to the PLMN of the cell. The UE may use a list of "equivalent PLMNs", where the "equivalent PLMN" is treated as if it were equal to the selected PLMN. A UE not trying to make an emergency call may select/reselect only cells belonging to the selected PLMN or an equivalent PLMN belonging to the selected PLMN.

Furthermore, an "intra-frequency cell reselection indicator" is also sent in the system information to not allow the UE to reselect another cell on the same frequency when the cell the UE has already selected is barred.

Therefore, the above-mentioned "cell access restriction" attribute limits the number of candidate cells that the UE can consider for cell selection/reselection. Referring to FIG. 6 , the decision process of cell reselection is illustrated.

The main task of the RNC is Radio Resource Management (RRM). In the UMTS standard different RRC states, transport channels and physical channels are available with multiple parameters in order to optimize the use of the available radio resources.

The basic method used for RRM is the RRC state transition between CELL_FACH, CELL_DCH, CELL_PCH and URA_PCH states. Combining these states, the RNC can generally control the number of UEs using a given frequency when different frequencies are available for communication. However, as described above, in the CELL_FACH state, CELL_PCH state and URA_PCH state, based on measurements and different rules, the UE may initiate a change from a cell in a given frequency to a cell in another frequency. Transformation is also based on normal measurement and cell selection/reselection rules or on frequency layer aggregation schemes.

When the UE moves from CELL_DCH state to another state, the UE selects a cell to camp on or connect to. Normally, the UE considers cells on all frequencies unless the RNC indicates a preferred frequency in the Information Element (IE) "Frequency Information". In this case, the UE preferably selects the cell on the preferred frequency if a suitable cell exists on the preferred frequency.

When the UE is in the CELL_FACH state, the RNC can prompt the UE to select a cell on another frequency as the preferred frequency by sending a message including IE "Frequency Information" to the UE. The UE will then select a cell on the preferred frequency.

The 3GPP system can provide Multimedia Broadcast Multicast Service (MBMS). 3GPP TSG SA (business and system aspects) defines various network elements and their functions required to support MBMS services. The cell broadcast service provided by the prior art is limited to a service in which a text type short message is broadcast to a certain area. However, the MBMS service is a more advanced service, in addition to broadcasting multimedia data, it also multicasts multimedia data to terminals (UEs) that have subscribed to the corresponding service.

The MBMS service is a downward-dedicated service, which provides streaming or background services to multiple terminals by using a public or dedicated downward channel. MBMS services are divided into broadcast mode and multicast mode. The MBMS broadcast mode facilitates sending multimedia data to each user located in a broadcast area, while the MBMS multicast service facilitates sending multimedia data to a specific user group located in a multicast area. A broadcast area means an area where a broadcast service is available and a multicast area means an area where a multicast service is available.

FIG. 7 illustrates the process of providing a specific MBMS service by using the multicast mode. Procedures can be divided into two types of actions, transparent and opaque to UTRAN.

The transparent actions are described below. Users who desire to receive MBMS services first need to subscribe in order to be allowed to receive MBMS services, receive information about MBMS services, and join certain MBMS service groups. Service announcements provide a list of services offered to the terminal and other relevant information. Users can then join these services. By joining, the user indicates that the user wants to receive information linked to services to which the user has subscribed and to become part of a group of multicast services. When a user is no longer interested in a given MBMS service, the user leaves the service, that is, the user is no longer a part of the multicast service group. These actions can be carried out using any communication means, ie the actions can be done using SMS (Short Message Service), or through internet access. It is not necessary to use the UMTS system to perform these actions.

For users in a multicast group, in order to receive a service, the following actions opaque to UTRAN are performed. SGSN informs RNC that the session starts. Then the RNC notifies the UEs of the multicast group that a given service has started to start reception of the given service. After the required UE actions and final configuration of the PtM bearer for the given service have been broadcasted, the data transmission starts. When the session is stopped, the SGSN indicates the stopped session to the RNC. The RNC initiates the session stop in turn. The service transmission from the SGSN means providing bearer services to the RNC to transport the data of the MBMS service.

After the notification procedure, other procedures are started between UE and RNC and SGSN to enable data transfer, such as RRC connection establishment, connection establishment towards PS domain, frequency layer convergence and counting.

Can be paralleled with the reception of other services, such as voice or video calls on the CS domain, SMS transmission on the CS or PS domain, data transmission on the PS domain, or reception of any signaling related to UTRAN or PS or CS domain To perform reception of MBMS services.

Contrary to the multicast service, for the broadcast service, as shown in Figure 8, only the announcement of the service has to be done in a transparent manner. No reservations or joins are required. Then, the actions transparent to the RNC are the same as those of the multicast service.

Referring to Fig. 9, a typical session sequence from UTRAN perspective is illustrated. As shown, the SGSN notifies the RNC of the session start (step 1). The RNC then performs a counting procedure which triggers some UEs to establish a connection to the PS domain (step 2). Therefore, establishment of an RRC connection for the UE is initiated. This allows the RNC to estimate the number of UEs in a given cell that are interested in serving. When the UE has established the PS connection, the SGSN starts the Iu link process, and provides the list of multicast services that the UE has joined to the RNC.

For UEs that have established an RRC connection, are interested in a given MBMS service but are not connected to the PS domain, the RNC sends a specific message to the UE, triggering them to establish a PS connection (step 3). When the UE has established a PS connection, the SGSN starts the Iu link process and provides the list of multicast services that the UE has joined to the RNC. For UEs not in CELL_DCH state, the frequency layer convergence scheme allows the RNC to trigger the UEs to change the frequency in which they listen (step 4).

Depending on the Radio Resource Management (RRM) scheme, the RNC establishes a Point-to-Multipoint (PtM) or Point-to-Point (PtP) radio bearer for transferring MBMS services (step 5a or 5b). The RNC transmits data received from the SGSN to UEs that are part of the multicast group. After the data transmission, the SGSN notifies the RNC of the end of the session (step 6). The RNC then releases the PtP or PtM radio bearer for sending MBMS data (step 7a or 7b).

Generally, for a UE in RRC connected state, there are two possibilities. The UE will have an established connection with the PS domain (PMM connection) or the UE will not have an established connection with the PS domain (PMM idle mode). When there is no established connection to the PS domain, the UE will generally have a connection to the CS domain. Otherwise, the UE is not in RRC connected mode.

For MBMS, two additional control channels are introduced. They are MCCH and MICH (MBMS Notification Indicator Channel). As mentioned above, MCCH is mapped on FACH. MICH is new physical channel and is used to inform user to read MCCH channel. The MICH is designed to make the UE perform a DRX (Discontinuous Reception) scheme, which allows to reduce the UE's battery consumption while allowing the UE to still be aware of any traffic that the session is starting. MICH can be used to notify UE of changes in frequency aggregation scheme, configuration changes of Point-to-Multipoint (PtM) bearers, switching between PtM bearers and Point-to-Point (PtP) bearers, etc., all of which require reading MCCH.

The MCCH channel periodically transmits information about effective services, MTCH configuration, frequency aggregation, and so on. Based on different triggers, UE reads MCCH information to receive subscribed services. For example, when a UE is informed of a given service on the MICH, or when the UE is informed via the DCCH channel, the UE may be triggered after cell selection/reselection. The configuration of the MCCH channel is broadcast in system information. MICH configuration (ie, spreading code, scrambling code, spreading factor and other information) is fixed in the standard or given in system information.

The UMTS standard allows the use of different frequency bands for data transmission. The frequency bands in UMTS are usually specified by UARFCN (UTRA Absolute Radio Frequency Channel Number), which defines the used frequency bands. A given PLMN may use different frequencies.

When the network uses different frequencies, UEs in a given area select a frequency based on the quality measured on the frequency. The UE may also select a frequency based on other parameters given in the above system information. In order to balance loads carried by different frequencies, UEs are distributed in different frequencies. If a given MBMS is then sent on a PtM radio bearer to UEs in all frequencies, the transmission must be made in all frequencies.

For increased efficiency, it is advantageous to transmit data on only one frequency and have all UEs interested in a given service reselect a cell in that frequency. Hence, this functionality is called "frequency aggregation". A frequency layer in which the UE will reselect is called a PFL (Preferred Frequency Layer). As shown in Figure 9, a typical MBMS session includes a period of "frequency aggregation" (step 4).

When frequency aggregation processing is used for a given service, information about the preferred frequency for each service is sent in messages on the MCCH or system information. There are different possibilities for reselecting another frequency for the trigger. One possibility is to force the UE to select a cell on a preferred frequency and prohibit all cells on other frequencies from participating in cell reselection/cell selection.

Another possibility is to change the requirements for cell reselection. This can be done by adding an offset to the R criterion, S criterion or H criterion in the formula required to determine whether to perform cell selection. This offset can be added to cells on preferred frequencies or to all cells on non-preferred frequencies. Other possibilities for the UE to reselect the preferred frequency are contemplated.

For a hierarchical cell structure, the UE preferably reselects the cell with the highest priority. If a frequency aggregation scheme is used, it means that the UE must be allowed to select a cell on a preferred frequency regardless of the priority of the preferred frequency. Thus, using a frequency aggregation scheme means that a hierarchical cell structure will no longer be used.

The PRACH channel is an uplink channel shared by different UEs. When a UE wants to send uplink data on the PRACH channel, there is a special mechanism to prevent different UEs from sending at the same time. This mechanism is called "collision avoidance" and is implemented in UMTS based on the slotted Aloha system. The transmission of messages on the PRACH channel is depicted in FIG. 10 .

Before sending on the PRACH channel, the UE sends the preamble to the Node B. The preamble consists of a code (signature) that the UE randomly selects among available labels and sends it on a special physical channel called a RACH subchannel. The UE repeats the transmission several times until a positive or negative acknowledgment indicator is received or a given number of retransmissions is exceeded. The Node B listens to all sub-channels and tries to detect a given flag sent by a UE that wants to access the channel. When the Node B has received the flag, it acknowledges reception on the Special Physical Channel (AICH) by sending a code indicating to the UE whether or not the UE is granted access to the PRACH channel. Thus, simultaneous transmission of several UEs on the PRACH channel is avoided.

When the UE receives a non-acknowledgment message (NACK) or when the UE does not receive any acknowledgment message (ACK) or NACK on the AICH channel, the UE determines whether it is allowed to restart the collision avoidance process. If another collision avoidance process is allowed according to the fixed algorithm, the UE determines the time to wait before the next collision avoidance process starts. When the UE receives the ACK after the collision avoidance process, ie when the UE is granted access to the PRACH, the UE sends the data block group on the PRACH channel.

As mentioned above, the frequency aggregation scheme optimizes the use of radio resources by concentrating all UEs interested in a given service on a given frequency. As a result, some UEs may still select a cell on a preferred frequency because they subscribe to a given MBMS service, although they may not select a cell on a preferred frequency if they are not subscribed to an MBMS service.

A UE that selects a cell on the "preferred frequency" of the MBMS service to receive the MBMS service potentially has poor quality of service. This is because potentially many UEs will select the cell or cells on the preferred frequency in order to receive a given MBMS service on the preferred frequency. Consequently, the load of the cell or cells on that frequency is increased. Furthermore, the radio quality of the cell on the selected preferred frequency may be worse than that of another frequency.

When a UE desires to establish a call or transmit data on the uplink, depending on the state/mode of the UE, according to the current standard, the UE needs to perform different actions, as shown in Table 1.

Table 1

As mentioned above, UEs using the frequency aggregation scheme because of joining the MBMS service will potentially have problems transmitting data on the PRACH channel due to overloaded cells or poor radio quality. Therefore, a special mechanism is needed to overcome these problems.

Furthermore, on transition from CELL_DCH to CELL_FACH, or when the RNC instructs a UE in CELL_FACH state to reselect a cell in a given frequency, the frequency aggregation scheme also conflicts with the information about the preferred frequency sent by the RNC. Thus, the efficiency of the system is potentially reduced since active UEs cannot be maintained on a single frequency.

Contents of the invention

technical problem

The present invention is directed to an outage use frequency layer aggregation scheme which facilitates selection of cells on preferred frequency layers for joining point-to-multipoint services.

The ensuing and partial description will make the foregoing additional features and advantages of the invention more apparent, or allow learning to practice 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.

To achieve these and other advantages and in accordance with the objects of the present invention, as specifically and broadly described herein, the present invention is implemented as a method for selecting a cell by a mobile terminal in a wireless communication system, the method comprising: receiving an Notification of the Multimedia Broadcast Multicast Service MBMS at a preferred frequency, where the preferred frequency is related to the selection of a cell for a mobile terminal using a frequency layer convergence scheme; using a frequency layer convergence scheme for selecting a cell, where the frequency layer convergence scheme facilitates the preference The selection of the cell on the frequency, and upon receipt of a message to initiate the reconfiguration procedure, interrupts the use of the frequency layer convergence scheme.

In one aspect of the invention, the trigger for discontinuing the use of the frequency layer convergence scheme is based on a procedure initiated with the network that fails when the frequency layer convergence scheme is used. Preferably, the process with the network includes establishing a connection with a core network (CN) domain. The CN domain is at least one of a Packet Switched (PS) domain and a Circuit Switched (CS) domain.

In another aspect of the invention, the procedures with the network include a PRACH access procedure, a radio resource control (RRC) procedure for sending information to the network, a medium access control (MAC) procedure for sending data to the network, and At least one of the procedures of selecting a cell on a given frequency according to an order received from the network.

Preferably, the interruption uses the frequency layer convergence scheme until the timer expires. When the frequency layer convergence scheme is interrupted for the first time, when the procedures with the network including the initiation of the PRACH access procedure fail, when the procedures with the network including the initiation of the Media Access Control (MAC) procedure for sending data to the network fail The timer is started upon failure of the procedure, or upon initiation of a procedure with the network including the selection of a cell on a given frequency according to a command received from the network, fails.

The timer's duration value is received from a system information message from the network. Alternatively, the duration value of the timer is a fixed value.

Preferably, the method further comprises selecting a cell on a frequency other than the preferred frequency. Also, the method further includes initiating a procedure with the network and continuing to discontinue use of the frequency layer convergence scheme until the initiated procedure with the network ends. Additionally, the method further includes initiating a procedure with the network, and releasing the connection with the core network (CN) domain when the initiated procedure with the network ends.

In another embodiment of the present invention, a system for selecting a cell by a mobile terminal in a wireless communication system includes: means for receiving a notification of a multimedia broadcast multicast service MBMS with a preferred frequency, wherein the preferred frequency Frequency is associated with selection of a cell for a mobile terminal using a frequency layer convergence scheme; means for using a frequency layer convergence scheme for selecting a cell, wherein the frequency layer convergence scheme facilitates selection of a cell on a preferred frequency; and initiating reconfiguration based on reception Process messages that interrupt devices using frequency layer convergence schemes.

In another aspect of the invention, the trigger for discontinuing the use of the frequency layer convergence scheme is based on a procedure initiated with the network that fails when the frequency layer convergence scheme is used. Preferably, the process with the network includes establishing a connection with a core network (CN) domain. The CN domain is at least one of a Packet Switched (PS) domain and a Circuit Switched (CS) domain.

In another aspect of the present invention, the procedures with the network include a PRACH access procedure, a radio resource control (RRC) procedure for sending information to the network, a medium access control (MAC) procedure for sending data to the network, and at least one of the process of selecting a cell on a given frequency based on an order received from the network.

Preferably, the interruption uses the frequency layer convergence scheme until the timer expires. When the frequency layer convergence scheme is interrupted for the first time, when the procedures with the network including the initiation of the PRACH access procedure fail, when the procedures with the network including the initiation of the Media Access Control (MAC) procedure for sending data to the network fail The timer is started upon failure of the procedure, or upon initiation of a procedure with the network including the selection of a cell on a given frequency according to a command received from the network, fails.

The timer's duration value is received from a system information message from the network. Alternatively, the duration value of the timer is a fixed value.

Preferably, the system further comprises: means for selecting a cell on a frequency other than the preferred frequency. Also, the system further includes means for initiating a procedure with the network, and means for continuing to suspend use of the frequency layer convergence scheme until the initiated procedure with the network ends. Furthermore, the system further comprises means for initiating a procedure with the network, and means for releasing the connection with the core network (CN) domain when the initiated procedure with the network ends.

It is to be understood that both the foregoing general description and the following detailed description of the invention are exemplary and are intended to provide further explanation of the invention as claimed.

Description of drawings

The accompanying drawings, which are included to provide a further explanation of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. Features, elements, and aspects of the invention that are referenced by the same reference numerals in different figures represent the same, equivalent, or similar features, elements, or aspects according to one or more embodiments.

Fig. 1 is a block diagram of a common UMTS network architecture.

FIG. 2 is a block diagram of the structure of the wireless interface protocol between the terminal and the network based on the 3GPP wireless access network standard.

Figure 3 illustrates the mapping in a mobile terminal to logical channels on transport channels.

Figure 4 illustrates the mapping to logical channels on transport channels in the network.

Figure 5 illustrates possible transitions between modes and states in a UMTS network.

Fig. 6 illustrates the decision process of cell selection.

Figure 7 illustrates the process of providing a specific point-to-multipoint service using the multicast mode.

FIG. 8 illustrates a processing procedure for providing a broadcast service.

Figure 9 illustrates the session sequence from the network's point of view.

Fig. 10 is a flowchart of sending messages on the PRACH channel.

FIG. 11 illustrates an interruption of a frequency layer aggregation scheme according to one embodiment of the present invention.

FIG. 12 illustrates a frequency layer convergence scheme using a timer interrupt according to an embodiment of the present invention.

Detailed ways

The present invention relates to a UE that has joined a service in which a "preferred frequency" is defined but does not use a "frequency layer aggregation" scheme in specific cases. For example, when the UE tries to set up a new call, or when the UE fails to access the network on the preferred frequency while using the method that favors the preferred frequency of the joined MBMS service, the frequency layer convergence scheme will not be used.

There are several methods for determining whether the UE should stop applying methods that favor selection of a cell on a given "preferred frequency". Preferably, when the frequency layer aggregation scheme is interrupted for a preferred frequency, any traffic where the preferred frequency is a given frequency should be interrupted.

According to the first embodiment of the present invention, when a determined condition occurs as a result of using the frequency aggregation scheme, the UE stops using the frequency layer aggregation scheme. Preferably, during the PRACH access procedure, when the UE receives the failure of the collision avoidance process in the physical layer in the MAC layer notification, or when the UE receives a NACK on the AICH or does not receive any response from the Node B, or When the MAC procedure for sending data on the preferred frequency fails as a result of the UE using the frequency layer convergence scheme, the UE stops using the scheme.

According to the second embodiment of the present invention, when the UE has to perform a specific procedure, such as when the UE tries to perform an emergency call, the UE stops using the frequency layer convergence scheme. Another specific process is that, for a specific reason, when the NAS (Non-Access Stratum) layer instructs the AS (Access Stratum) of the UE to establish a connection with the CN domain, such as initiating a dialog call, the Initiate a streaming call, initiate an interactive call, initiate a background call, initiate a reservation service call, terminate a dialog call, terminate a streaming call, terminate an interactive call, terminate a background call, emergency call, intra-RAT cell reselection, intra-RAT cell change command , registration, detach, originating high priority signaling, originating low priority signaling, call re-establishment, terminating high priority signaling, terminating low priority signaling, terminating for unknown reasons, or any subset of these reasons .

According to the third embodiment of the present invention, when a UE in CELL_FACH state, CELL_PCH state, URA_PCH state or idle mode is required to select a cell on a given frequency, the UE stops using the frequency layer convergence scheme.

When the UE stops using the frequency layer convergence scheme due to one of the above reasons, a method for restarting the frequency layer convergence scheme also needs to be defined. Preferably, the trigger for restarting the frequency layer convergence solution may be when the process of triggering the stop of the frequency layer convergence solution is successfully completed or unsuccessful. Alternatively, the UE may start the timer T _{freq_conv_int} when the use of the frequency layer convergence scheme is stopped. When the time period of the timer expires, the frequency layer convergence scheme is restarted. Therefore, this limits the outage used by the frequency layer aggregation scheme. Preferably, the timer is broadcast on the system information of the cell.

Referring to FIG. 11 , a method of performing an emergency call by a UE for a frequency layer convergence scheme is illustrated. Initially, a UE in CELL_FACH, CELL_PCH, URA_PCH or idle mode starts to use the frequency layer convergence scheme (step 1). This allows the UE to reselect the preferred frequency. Subsequently, when the NAS indicates that the AS must establish a connection to the CN domain, a UE-specific cause value is given (step 2).

Based on the cause value, the UE may stop using the frequency layer convergence scheme (step 3). Thus, when a UE stops using frequency layer convergence, the UE changes the way it evaluates neighboring cells. When the UE needs to establish a connection to the core network domain when it is in idle mode, CELL_FACH, CELL_PCH, URA_PCH state, it means that the UE must send messages such as cell update, RRC connection request and/or initial direct transfer on the PRACH channel, to the node B (step 4).

When the current cell or cells on the current frequency are loaded, PRACH access may fail on the current frequency (step 5). Finally, since the frequency layer convergence scheme is no longer used, the UE will reselect a cell on another frequency as the preferred frequency (step 6). After cell reselection, access to PRACH will have a higher chance of success because the best cell is selected (step 7).

After the call is completed, the connection to the CN domain is released (step 8). The UE will then restart using the frequency layer convergence scheme, if it is still applied (step 9).

Referring to FIG. 12 , a timer-based UE method for stopping the frequency layer convergence scheme is exemplified. Initially, a UE in CELL_FACH, CELL_PCH, URA_PCH or idle mode starts to use the frequency layer convergence scheme (step 1). This allows the UE to reselect the preferred frequency.

Subsequently, any one of a number of events occurs (step 2). For example, the NAS may indicate to the AS that a connection to the CN domain must be established and give the UE a specific reason value. Otherwise start the RRC procedure requiring transmission in the uplink. Furthermore, data transmission in the upstream can be started. Otherwise the UE is instructed to select a cell on a given preferred frequency.

Thus, the UE stops using the frequency layer convergence scheme. When the UE stops using the frequency layer aggregation scheme, the UE will change the way it evaluates neighboring cells. Furthermore, upon ceasing to use the scheme, the UE starts a timer T _{freq_conv_int} (step 3). The duration of the timer can be a fixed value, or the UE can utilize the value read in the system information.

Then UE sends data to Node B on PRACH (step 4). When the current cell or cells on the current frequency are loaded, the PRACH channel access on the current frequency fails (step 5).

An alternative to starting the timer T _{freq_conv_int} of step 3 is to start it once the first PRACH access procedure has failed (step 6). The PRACH access procedure fails due to receiving a NACK, no response message is received, or when the retry mechanism in the MMAC layer times out such that there are no more retransmissions. The duration of the timer can be a fixed value, or the UE can utilize the value read in the system information.

Finally, since the method of the frequency layer convergence scheme is no longer used, the UE will reselect a cell on another frequency as the preferred frequency (step 7). After cell reselection, access to PRACH will have a higher chance of success because the best cell is selected (step 8).

After the timer T _{freq_conv_int} expires and the call has ended, the connection to the CN domain is released (step 9). The UE will then restart using the frequency layer convergence scheme, if it is still applied (step 10).

Therefore, the present invention ensures that in setting up a new call/emergency call or sending data, UEs that have subscribed to the MBMS service will have the same or similar chances of success as UEs that have not subscribed to the MBMS service.

Although the present invention has been described in the context of mobile communications, the present invention can also be used in any wireless communication system using wireless devices, such as PDAs and laptop computers equipped with wireless communication capabilities. Furthermore, the use of certain terms to describe the present invention should not limit the scope of the present invention to certain types of wireless communication systems. The invention is also applicable to other wireless communication systems using different air interfaces and/or physical layers, eg TDMA, CDMA, FDMA, WCDMA, etc.

The preferred embodiments can be implemented as a method, apparatus or article of manufacture using standard programming and/or engineering techniques to produce software, firmware, hardware, or any combination thereof. As used herein, the term "article of manufacture" refers to a product in hardware logic (such as an integrated circuit chip, a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), etc.) or a computer-readable medium (such as a magnetic storage medium ( such as hard disk drives, floppy disks, magnetic disks, etc.), optical storage (CD-ROM, optical disks, etc.), volatile and nonvolatile memory devices (such as EEPROM, ROM, PROM, RAM, DRAM, SRAM, firmware, programming logic, etc.) to implement code or logic.

Code in the computer readable medium is accessed and executed by a processor. The code implementing the preferred embodiments can be accessed over a transmission medium or from a file server over a network. In this case, the manufactured product in which the code is implemented may include transmission media such as network transmission lines, wireless transmission media, space-propagated signals, radio waves, infrared signals, and the like. Of course, it will be appreciated by those skilled in the art that many modifications may be made to this structure and that the article of manufacture may include any information bearing medium known in the art without departing from the scope of the present invention.

The aforementioned embodiments and advantages are exemplary only and should not be considered as limiting the invention. The teachings of the present invention are readily applicable to other types of devices. The description of the present invention is intended to be illustrative, not to limit the scope of the claims. Many alternatives, modifications and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.

Claims (19)

1. A method for selecting a cell by a mobile terminal in a wireless communication system, the method comprising: receiving a notification of a multimedia broadcast multicast service MBMS having a preferred frequency related to the selection of a cell for a mobile terminal using a frequency layer convergence scheme; using a frequency layer aggregation scheme for cell selection, wherein the frequency layer aggregation scheme facilitates selection of cells on preferred frequencies, and Based on receiving a message to initiate a reconfiguration procedure, the frequency layer convergence scheme is discontinued. 2. The method of claim 1, further comprising discontinuing use of the frequency layer convergence scheme when a procedure with the network initiated while using the frequency layer convergence scheme fails. 3. The method of claim 2, wherein the procedure with the network includes establishing a connection with a core network (CN) domain. 4. The method of claim 3, wherein the CN domain is at least one of a Packet Switched (PS) domain and a Circuit Switched (CS) domain. 5. The method of claim 2, wherein the process with the network comprises at least one of the following: PRACH access procedure, Radio Resource Control (RRC) procedures for sending information to the network, Media Access Control (MAC) procedures for sending data to the network, and The process of selecting a cell on a given frequency based on commands received from the network. 6. The method of claim 5, wherein the interruption uses a frequency layer convergence scheme until expiration of a timer. 7. The method of claim 6, wherein the timer is started when the frequency layer convergence scheme is interrupted for the first time. 8. The method of claim 6, wherein a timer is started when a procedure with the network including initiation of a PRACH access procedure fails. 9. The method of claim 6, wherein the timer is started when a procedure with the network including initiation of a Media Access Control (MAC) procedure for sending data to the network fails. 10. The method of claim 6, wherein the timer is started when an initiated procedure with the network including a procedure for selecting a cell on a given frequency according to a command received from the network fails. 11. The method of claim 6, wherein the duration value of the timer is received in a system information message from the network. 12. The method of claim 6, wherein the duration value of the timer is a fixed value. 13. The method of claim 1, further comprising selecting a cell on a frequency other than the preferred frequency. 14. The method of claim 1, further comprising: initiate the process with the network; and Continue to discontinue use of the frequency layer aggregation scheme until the end of the initiated procedure with the network. 15. The method of claim 1, further comprising: initiate the process with the network; and The connection to the Core Network (CN) domain is released when the initiated procedure with the network ends. 16. The method of claim 1, wherein the use of the frequency layer convergence scheme is interrupted only when the mobile terminal is in CELL_FACH state, CELL_PCH state, URA_PCH state or in idle mode. 17. A method for enabling a mobile terminal to select a cell in a wireless communication system, the method comprising: sending a notification of the Multimedia Broadcast Multicast Service MBMS with a preferred frequency associated with the selection of a cell for a mobile terminal using a frequency layer convergence scheme that facilitates the selection of a cell on a preferred frequency; and A message is sent to initiate a reconfiguration procedure of the mobile terminal to cause interruption of use of the mobile terminal's frequency layer convergence scheme. 18. The method of claim 17, further comprising sending system information to the mobile terminal, the system information including a timer value for a duration of discontinuation of use of the frequency layer convergence scheme. 19. The method of claim 17, wherein the value for the timer is a fixed value.

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