[DESCRIPTION]

[invention Title]

METHOD FOR TRANSMITTING AND RECEIVING PAGING MESSAGE IN WIRELESS COMMUNICATION SYSTEM [Technical Field]

The present invention relates to a wireless terminal and a wireless communication system that provides wireless communication, and more particularly, to a method in which a system with two or more frequency bands provides User

Equipments (UEs) with multimedia and broadcast services with a quality higher than a specific level while efficiently notifying the UEs of the presence of unicast service data when the system provides multimedia and broadcast services over one of the frequency bands.

[Background Art]

FIG. 1 illustrates a network structure of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), which is a mobile communication system to which the related art and the present invention are applied. The E-UTRAN has been evolved from the conventional UTRAN and its basic standardization process is currently underway in 3GPP. The E-UTRAN system is also referred to as a Long Term Evolution (LTE) system.

The E-UTRAN includes base stations which will each be referred to as an eNode B or an eNB for short. The eNBs are connected through X2 interfaces. Each eNB is connected to User Equipments (UEs) and is connected to an Evolved Packet

Core (EPC) through an Sl interface.

Radio interface protocol layers between UEs and the network can be divided into a Ll layer (first layer), a L2 layer (second layer), and a L3 layer (third layer) based on the lower three layers of the Open System Interconnection (OSI) reference model widely known in communication systems. A physical layer included in the first layer provides an information transfer service using a physical channel. A Radio Resource Control (RRC) layer located at the third layer controls radio resources between UEs and the network. To accomplish this, the RRC layer exchanges RRC messages between UEs and the network. FIG. 2 illustrates a radio interface protocol structure between a UE and a

UTRAN based on the 3GPP radio access network standard. The radio interface protocol of FIG. 2 is divided horizontally into a physical layer, a data link layer, and a network layer and is divided vertically into a user plane for data/information transmission and a control plane for signaling. The protocol layers of FIG. 2 can be divided into a Ll layer (first layer), a L2 layer (second layer), and a L3 layer (third layer) based on the lower three layers of the Open System Interconnection (OSI) reference model widely known in communication systems.

A physical layer, which is the first layer, provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to a Medium Access Control (MAC) layer above the physical layer through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. Data transfer between different physical layers, specifically between the respective physical layers of transmitting and receiving ends, is performed through the physical channel. The physical channel is modulated according to the

Orthogonal Frequency Division Multiplexing (OFDM) method, using time and frequencies as radio resources.

The MAC layer, which is the second layer, provides a service to a Radio Link

Control (RLC) layer above the MAC layer through a logical channel. The RLC layer of the second layer supports reliable data transfer. Functions of the RLC layer may be embodied in a function block in the MAC. In this case, the RLC layer may not be provided. A PDCP layer of the second layer performs a header compression function to reduce the size of each IP packet header containing relatively large, unnecessary control information in order to efficiently transmit IP packets such as IPv4 or IPv6 packets in a radio interval with a small bandwidth.

A Radio Resource Control (RRC) layer located at the top of the third layer is defined only in the control plane and is responsible for control of logical, transport, and physical channels in association with configuration, re-configuration, and release of radio bearers (RBs). The RB is a service that the second layer provides for data communication between the UE and the UTRAN. The UE is in a connected mode if there is an RRC connection between the RRC layer of the radio network and the RRC layer of the UE. Otherwise, the UE is in an RRC idle mode.

A Non-Access Stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management. One cell included in the eNB is set to provide a bandwidth such as 1.25, 2.5, 5,

10, or 20MHz to provide a downlink or uplink transmission service to UEs. Here, different cells may be set to provide different bandwidths.

Downlink channels used to transmit data from the network to the UE include a Broadcast Channel (BCH) used to transmit system information, a Paging Channel

(PCH) used to transmit paging messages, and a downlink Shared Channel (SCH) used to transmit user traffic or control messages. Control messages or traffic of a downlink multicast or broadcast service may be transmitted through a downlink SCH and may also be transmitted through different downlink multicast channels (MCHs). Uplink channels used to transmit data from the UE to the network include a Random Access Channel (RACH) used to transmit initial control messages and an uplink SCH used to transmit user traffic or control messages.

Examples of a logical channel, which is located above the transport channel and is mapped to the transport channel, include a Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a Multicast Control Channel (MCCH), and a Multicast Traffic Channel (MTCH).

FIG. 3 illustrates conventional control channel transmission. The physical channel includes a number of subframes on the time domain and a number of subcarriers on the frequency domain. One subframe includes a plurality of resource blocks, each of which includes a plurality of symbols and a plurality of subcarriers. In each subframe, specific subcarriers of specific symbols (for example, the first symbol) of the subframe can be used for a Physical Downlink Control Channel (PDCCH), i.e., an L1/L2 control channel. One subframe corresponds to 0.5ms and a Transmission

Time Interval (TTI), which is a unit data transmission time, is lms corresponding to two subframes.

Reference will now be made to a Multimedia Broadcast/Multicast Service (MBMS). The MBMS provides a streaming or background service to a plurality of UEs using a downlink only MBMS bearer service.

The MBMS is divided into a broadcast mode and a multicast mode. The

MBMS broadcast mode is a service of transmitting multimedia data to all users in a broadcast area where a broadcast service is available. The MBMS multicast mode is a service of transmitting multimedia data to a specific user group in a multicast area where a multicast service is available. Conventional paging channel transmission will now be described with reference to FIG. 4. When receiving a paging message, the UE can perform Discontinuous Reception (DRX) in order to reduce power consumption. To accomplish this, the network constructs a number of paging occasions in each period of time, which is referred to as a paging DRX cycle, and a specific UE receives a specific paging occasion to obtain a paging message. The UE receives no paging channel at any time other than the specific paging occasion. One paging occasion corresponds to one TTI.

The following is a description of an MBMS dual layer service. The network may have one or more frequency bands in one area. However, if the respective ranges of the cells of two frequency bands are identical, it is inefficient to transmit the same MBMS service over each of the frequencies. To solve this, if a plurality of frequency bands are available, the eNB allocates a specific one of the frequency bands exclusively to the MBMS to provide an MBMS service over the specific frequency band and to provide other services of each UE (for example, a unicast service) over the other frequencies. That is, when a number of frequency bands are available, in order to increase the efficiency of the provision of the MBMS service, the eNB sets one of the frequency bands as an MBMS dedicated layer (or frequency band) so that only the MBMS service is allowed to be provided over the MBMS dedicated layer. In other words, the eNB does not provide a unicast service for a specific UE only over the MBMS dedicated

layer to efficiently provide the MBMS service. Accordingly, channels not associated with the MBMS (for example, channels such as an RACH and a UL-SCH) are not used in the MBMS dedicated layer. Any paging message is also not transmitted over the MBMS dedicated layer. If a number of frequency bands are available in one area and the MBMS service is provided over only one of the frequency bands, it is necessary for UEs in the area to switch to the frequency band in order to receive the MBMS service. However, each UE may desire to receive the unicast service at the same time. When receiving a unicast paging message, the UE must be able to immediately receive the paging message.

Regardless of whether or not a MBMS service is provided over a frequency band set to provide MBMS services, each UE can receive a paging message transmitted over another frequency band at any time if the UE is capable of receiving more than one frequency band at the same time. However, while receiving the MBMS service, a single-receiver UE cannot normally receive a paging message transmitted over another frequency band if the UE is capable of receiving only one frequency band.

[Disclosure]

[Technical Problem] An object of the present invention devised to solve the problem lies on providing a paging message transmission method in which a Base Station, which has a plurality of frequency bands and provides a specific service over a dedicated frequency

band, can provide a UE with a service with a quality desired by a user of the UE while efficiently transmitting a paging message to the UE.

Another object of the present invention devised to solve the problem lies on providing a paging message receiving method in which a UE, which receives a specific service over a dedicated frequency band included in the plurality of frequency bands, can receive a service with a quality desired by a user of the UE while efficiently receiving a paging message.

[Technical Solution]

The first object of the present invention can be achieved by providing a method to transmit a paging message to a User Equipment (UE) in a wireless communication system, the UE receiving a service of a dedicated frequency band, the method including a Base Station transmitting a paging message including identifier and location information of a UE to be paged to the UE, and receiving a paging response message from the UE in response to the paging message. Preferably, the location information includes information of one of a plurality of tracking areas included in a cell of the dedicated frequency band.

Preferably, in the process of transmitting the paging message to the UE, the Base Station transmits the paging message to the UE in a different paging interval according to the location information of the UE. The first object of the present invention can also be achieved by providing a method to transmit a paging message to a User Equipment (UE) in a wireless communication system, the UE receiving a service of a dedicated frequency band, the

method including a Base Station transmitting data of the service of the dedicated frequency band to a UE having information of a paging gap, and suspending transmitting the data during an interval of the paging gap and transmitting a paging message to the UE. Preferably, the information of the paging gap is transmitted to the UE through one of an MCCH or an MSCH.

The second object of the present invention can be achieved by providing a method of a User Equipment (UE) to receive a paging message in a wireless communication system, the UE receiving a service of a dedicated frequency band, the method including the UE receiving a paging message including identifier and location information of the UE from a Base Station, and transmitting a paging response message to the Base Station if the location information included in the paging message is identical to registered location information.

Preferably, the method further includes checking system information of the dedicated frequency band and registering location information of the UE if a location area included in the cell does not include the registered location information.

The second object of the present invention can also be achieved by providing a method of a User Equipment (UE) to receive a paging message in a wireless communication system, the UE receiving a service of a dedicated frequency band, the method including the UE switching from a dedicated frequency band for the service to a non-dedicated frequency band according to a predetermined period, and checking whether or not a paging message has been received from a Base Station over the non- dedicated frequency band.

Preferably, in the process in which the UE switches from the dedicated

frequency band to the non-dedicated frequency band, the UE transmits information of the predetermined period to the Base Station.

Preferably, the predetermined period is information transmitted from the Base Station to the UE. Preferably, the UE switches from the dedicated frequency band to the non- dedicated frequency band without receiving a BCH.

The second object of the present invention can also be achieved by providing a method of a User Equipment (UE) to receive a paging message in a wireless communication system, the UE receiving a service of a dedicated frequency band, the method including the UE switching from a dedicated frequency band for the service to a non-dedicated frequency band during an interval of a paging gap, and checking whether or not a paging message has been received from a Base Station over the non-dedicated frequency band.

Preferably, the paging gap is defined for each MBMS service or each MBMS dedicated layer.

[Advantageous Effects]

According to the invention, a UE can receive a paging message while receiving a specific service over a frequency band dedicated to the specific service without reducing the quality of the service and a Base Station can determine appropriate timing of paging without reducing the quality of the service provided to a UE for appropriate paging.

[Description of Drawings] In the drawings:

FIG. 1 illustrates a schematic structure of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN); FIG. 2 illustrates a conventional radio protocol structure;

FIG. 3 illustrates conventional control channel transmission; FIG. 4 illustrates conventional paging channel transmission; FIG. 5 illustrates an example cell size of an MBMS dedicated layer (or frequency band) and an example cell size of a general frequency band; FIG. 6 is a signal flow diagram of a method to transmit and receive a paging message according to an embodiment of the invention;

FIG. 7 is a signal flow diagram of a method to transmit and receive a paging message according to another embodiment of the invention;

FIG. 8 is a signal flow diagram of a method to transmit and receive a paging message according to another embodiment of the invention; and FIG. 9 illustrates an example operation of a UE of FIG. 8.

[Mode for Invention]

Reference will now be made in detail to the preferred embodiments of the present invention. The embodiments of the invention can be modified into various other forms and the scope of the invention is not limited to the embodiments described below.

In the following description, it is assumed for ease of explanation that a specific

service, which each UE receives from a Base Station using a dedicated frequency band, is an MBMS service. The invention can be applied not only to a wireless communication system that provides the MBMS service but also to any wireless communication system that provides services to UEs over a dedicated frequency band. One embodiment of the invention suggests that a Base Station transmits a paging message to a UE over a specific MBMS dedicated frequency band (or layer) through which only MBMS services are provided. However, in this process, the size of a cell in the MBMS dedicated layer is much greater than the size of a cell in a frequency band other than the MBMS dedicated layer. For example, as shown in FIG. 5, an MBMS dedicated layer cell may be greater than the total of a number of cells (Mixed Cell A, Mixed Cell B, and Mixed Cell C) in a general frequency band. In FIG. 5, a UEl is still in the MBMS dedicated layer cell although it has moved from a position A in the mixed cell B to a position B in the mixed cell C. In this case, transmitting a paging message over the MBMS dedicated layer causes problems. For example, let us assume that a UE having a serial No. 3333 is located in each of the mixed cell A and the mixed cell C. In this case, when a UE with the serial No. 3333 is paged over the MBMS dedicated layer, both the UEs in the cells A and C will respond to the paging. This makes the paging message indefinite.

Accordingly, when the Base Station transmits paging messages over the MBMS dedicated layer, the Base Station also needs to notify each UE of information of the tracking area (TA) where a UE to be paged by each paging message is located. This is because the ID of each UE is allocated on a TA basis.

FIG. 6 is a signal flow diagram of a method to transmit and receive a paging message according to an embodiment of the invention.

First, when a Base Station 120 also transmits a paging message, the Base

Station 120 transmits information as to where a UE 110 to be paged is located together with an identifier of the UE 110 to be paged (610). That is, in this process, when transmitting a paging message, the UE also transmits location information (for example, TA information) of a UE to be paged.

Here, the Base Station 120 can set a different paging interval according to the location information. That is, the Base Station 120 can transmit a paging message using a different paging interval according to information of the locations of each UE. For example, the Base Station 120 can use subframe 0 when transmitting a paging message to a UE 110 corresponding to TAl and can use subframe 1 when transmitting a paging message to a UE 110 corresponding to TA2. In this case, through system information, the Base Station 120 notifies UEs corresponding to different location information of a time interval in which the paging message is transmitted. When receiving information regarding the time interval from the Base Station 120, each UE 110 determines the time when the paging message is transmitted to a range in which the UE 110 is included and determines whether or not the UE 110 has received any paging message in the interval.

In the above process, the Base Station 120 transmits information as to which location information area (i.e., which TAs) the cell of the MBMS dedicated layer includes, through system information of the MBMS dedicated layer, in order to allow the UE 110 to perform a location information registration process at an appropriate time. The UE 110 checks which location area the MBMS dedicated layer cell includes through the system information and performs a new location information registration process if the location information the UE 110 has registered through another frequency

band is absent.

If the UE 110, which has stayed in the MBMS dedicated layer, moves to enter a new MBMS dedicated layer cell, the UE 110 determines which location area the new

MBMS dedicated layer cell includes by checking system information of the new MBMS dedicated layer cell and performs a location information registration process if the location area is different from that previously registered by the UE 110.

When receiving a paging message, the UE 110 checks whether or not the paging message includes location information. If the paging message includes location information, the UE 110 checks whether or not location information registered by the UE 110 is identical to the location information included in the paging message

(620).

The UE 110 performs a process of responding to the network if the two location information are identical and does not respond if the two location information are different (630). Here, the process of responding to the network may include a process of transmitting a paging response message from the UE 110 to the Base Station 120.

FIG. 7 is a signal flow diagram of a method to transmit and receive a paging message according to another embodiment of the invention.

With reference to FIG. 7, we will describe how a single-receiver UE periodically switches between an MBMS dedicated layer and an MBMS non-dedicated layer.

The UE 110, which has been receiving an MBMS service over the MBMS dedicated layer, switches to the MBMS non-dedicated layer in each paging message check interval set in the MBMS non-dedicated layer (710) and periodically checks whether or not the UE 110 has received any paging message.

In this process 710, serious delay may occur if the UE 110 reads a BCH each time it returns to the MBMS non-dedicated layer. Thus, it is preferable that the UE 110 not read the BCH when periodically returning from the MBMS dedicated layer to the MBMS non-dedicated layer. In another embodiment of the invention, the UE 110, which has been receiving the MBMS service over the MBMS dedicated layer, does not read the BCH when it temporarily switches to the MBMS non-dedicated layer in order to check the paging message.

The UE 110 must be certain that no change has been made to a PCH setting previously known to the UE 110 when the UE 110 has been set such that it does not read the BCH when switching to the MBMS non-dedicated layer. Accordingly, if any change is made to system information or channel setting information of the MBMS non- dedicated layer cell, the MBMS dedicated layer cell notifies UEs of the change. If a UE 110 is notified of the change of the channel setting information of the MBMS non- dedicated layer cell, then the UE 110 switches to the MBMS non-dedicated layer to receive new system information. If the UE 110 moves to the cell of the MBMS non- dedicated layer in order to check paging information after the UE 110 has stayed in the MBMS dedicated layer, then the UE 110 checks a sync channel (SCH) to compare its code with the code of an SCH of a most recent cell from which the UE 110 has previously received information. If the two SCH codes are identical, the UE 110 omits the BCH reception and immediately reads a PCH or determines that it has moved to the same cell as the previous cell. The UE 110 receives system information if the two SCH codes are different.

Allowing the UE 110 to periodically switch between the MBMS dedicated layer and the MBMS non-dedicated layer makes it difficult to guarantee the MBMS service

quality since the UE 110 cannot receive the MBMS service, causing losses in the MBMS service, while it is in the MBMS non-dedicated layer. In this case, we can consider a method in which the UE 110 notifies the Base Station 120 that the UE 110 is receiving an MBMS service over the MBMS dedicated layer. That is, before switching from the MBMS non-dedicated layer to the MBMS dedicated layer in order to receive the MBMS service, the UE 110 may notify the Base Station 120 that the UE 110 will switch to the MBMS dedicated layer in order to receive the MBMS service.

Together with the Base Station 120, the UE 110 can also perform resetting of paging message reception. Specifically, the UE 110 can notify the Base Station 120 of information regarding the time or intervals at which the UE 110 will again switch to the MBMS non-dedicated layer to check the paging message. Alternatively, the Base Station 120 can notify the UE 110 of the time or intervals at which the Base Station 120 transmits the paging message. That is, the UE 110 can notify the Base Station 120 of when the UE 110 receives the paging message or the Base Station 120 can notify the UE 110 of when the Base Station transmits the paging message. Based on values set in this manner, the UE 110 can periodically check the paging message in the MBMS non- dedicated layer.

If the UE 110 receives the paging message from the Base Station 120 (720), then the UE 110 performs a process of responding to the network, for example transmitting a paging response message to the Base Station 120 (730).

Regardless of whether or not the UE 110 has received the paging message, the UE 110 switches to the dedicated frequency band upon start of a specific period of time to switch to the dedicated frequency band (740).

If the UE 110 switches to the dedicated frequency band, the UE 110 receives a

specific service (for example, the MBMS service) of the dedicated frequency band from the Base Station 120 (750).

FIG. 8 is a signal flow diagram of a method to transmit and receive a paging message according to another embodiment of the invention. To accomplish the objects of the invention, this embodiment suggests a method to synchronize MBMS service data transmission over an MBMS dedicated layer with paging message transmission over an MBMS non-dedicated layer.

In the invention, the term "paging gap" refers to a time interval during which the Base Station 120 transmits no data to the UE 110 to allow the UE 110 to receive a paging message. Specifically, the paging gap is a time during which the Base Station

120 does not transmit MBMS service data over the MBMS dedicated layer so that the

UE 110 receives the paging message over the MBMS non-dedicated layer.

During the paging gap, the UE 110 switches from the MBMS dedicated layer to the MBMS non-dedicated layer to check whether or not it has received any paging message (811). Here, the Base Station 120 stops MBMS service data transmission during the paging gap (812).

When receiving a paging message, the UE 110 sends a response to the paging message to the network (830).

Since the position of the paging check interval during which each UE receives the paging message is different, the time during which the paging message is transmitted to the UE 110 over the MBMS non-dedicated layer must match the paging gap in the MBMS dedicated layer. Accordingly, if the Base Station 120 receives a paging message from a Core Network (CN) in an interval other than the paging check interval originally specified for the UE 110, the Base Station 120 stores the paging

message and then transmits it in the paging gap interval.

If the UE 110 has not received the paging message or after the UE 110 transmits a paging response message to the Base Station 120, the UE 110 switches to the MBMS dedicated layer (840) and receives the MBMS service (850). However, in FIG. 8, the paging gap is applied only to a single-receiver UE which has switched to the MBMS dedicated layer in order to receive the MBMS service. For example, the paging gap is unnecessary when the UE 110 is receiving no MBMS service or when the UE 110 is a dual-receiver UE or the like. Accordingly, the network must be aware of whether or not the UE 110 is receiving an MBMS service through the MBMS dedicated layer. Thus, when transmitting a paging message to the Base Station 120, the core network transmits list information of MBMS services joined by the UE 110, together with the paging message. When the Base Station 120 transmits the paging message to the UE 110, the Base Station 120 determines, based on the list information, whether it is to transmit the paging message in the originally set paging check interval or to transmit it in the paging gap interval.

On the other hand, when the UE 110 switches to the MBMS dedicated layer in order to receive a specific MBMS service, the UE 110 can notify the Base Station 120 of information of the service which it switches to the MBMS dedicated layer in order to receive. The Base Station 120 can determine when to send the paging message to the UE 110 according to the notified information of the service to be provided to the UE 110.

Preferably, if the UE 110 decides to no longer receive the MBMS service and returns to the MBMS non-dedicated layer after switching to the MBMS dedicated layer in order to receive a specific MBMS service provided over the MBMS dedicated layer,

the UE 110 notifies the Base Station 120 of the decision. That is, the UE 110 notifies the Base Station 120 of whether or not to use the paging gap. Thus, the UE can check whether or not a paging message has been received during the interval of the paging gap if the UE is set such that the paging gap is necessary for the UE and during an originally set paging check interval if it is set such that the paging gap is unnecessary for the UE.

In addition, when the UE 110 has moved from one cell to a new cell, the UE

110 can notify the previous cell that it is no longer necessary to especially consider paging timing of the UE 110 since the UE 110 has moved to another cell or the UE 110 can notify the new cell that it is necessary to consider the special paging timing of the UE 110.

In FIG. 8, the paging gap may be determined for each MBMS service and may also be determined for each MBMS dedicated layer cell. When the paging gap is determined for each MBMS dedicated layer cell, all MBMS services have the paging gap in the same time interval. FIG. 9 illustrates an example of the operation of the UE 110 of FIG. 8.

As shown in FIG. 9, first and second MBMS services (MBMS 1 and MBMS 2) are provided over an MBMS dedicated layer, and a paging gap of the MBMS service 1 occurs between 400ms and 500ms and a paging gap of the MBMS service 2 occurs between 750ms and 850ms. Information of the paging gaps is transmitted through an MBMS Control Channel (MCCH) or an MBMS Scheduling Channel (MSCH).

If the UE 110 is receiving the MBMS service 1 in the example of FIG. 9, the UE 110 switches to an MBMS non-dedicated layer in the gap between 400ms and 500ms to check whether or not the UE 110 has received any paging message. The Base Station 120 transmits the paging message to the UE 110 during the interval if it is

notified that the UE 110 has joined the MBMS service 1.

However, it will be difficult for the UE 110 to determine when it is to switch to the MBMS non-dedicated layer if the UE 110 has joined both the MBMS service 1 and the MBMS service 2. Accordingly, all MBMS services may have the paging gap in the same time interval.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[Industrial Applicability]

The present invention relates to a method in which a wireless communication system with two or more frequency bands can provide User Equipments (UEs) with multimedia and broadcast services with a quality higher than a specific level while efficiently notifying the UEs of the presence of unicast service data when the system provides multimedia and broadcast services over one or more of the frequency bands. The invention is applied to devices such as a UE and a Base Station included in the wireless communication system and an algorithm using the method.