KR20050100882A - Method and apparatus for receiving control message using sequence numbers in multimedia broadcast/multicast service - Google Patents

Abstract

The present invention relates to a method for efficiently receiving a control message for MCCH service in a mobile communication system. If the user terminal receives a plurality of data units including one control message and does not successfully receive all of the data units necessary to assemble the control message, then the user terminal selectively receives only data units that have not been successfully received in the next transmission period. A control message is constructed by combining with data units that have been received and successfully received in the previous period. The present invention increases the probability of receiving a control message in a wireless channel environment having a high error rate and optimizes the operation of the terminal.

Description

METHOD AND APPARATUS FOR RECEIVING CONTROL MESSAGE USING SEQUENCE NUMBERS IN MULTIMEDIA BROADCAST / MULTICAST SERVICE}

The present invention relates to a Multicast Multimedia Broadcast Service (hereinafter referred to as an MBMS service), and more particularly, to a method and apparatus for receiving control information for an MBMS service.

Due to the development of communication technology, the services provided by the mobile communication system using the wideband code division multiple access (CDMA) scheme are not only conventional voice services but also large capacity such as packet data and circuit data. It is evolving into packet service communication for transmitting data and multimedia broadcasting / communication for transmitting multimedia service. Accordingly, in order to support the multimedia broadcasting / communication, an MBMS service that provides a service from one or more multimedia data sources to a plurality of user equipments (hereinafter referred to as UEs) has been discussed.

The MBMS service refers to a service for transmitting the same multimedia data to multiple receivers through a wireless network. In this case, by allowing multiple receivers to share one radio channel, it is possible to save radio transmission resources. The MBMS service supports multimedia transmission forms such as real-time video, audio, still images, and text. The MBMS service is a service that can simultaneously provide audio data and video data according to the multimedia transmission format, and requires a large amount of transmission resources. In the case of the MBMS service, since the same data must be transmitted to a plurality of cells in which users are located, one-to-one (Point to Point: PtP) or one-to-many (Point to Multiple :) according to the number of users located in each cell Called PtM).

In order to receive MBMS service, UEs must first acquire control information on a transport channel carrying an MBMS service data stream, that is, an MBMS transport channel (hereinafter referred to as MTCH). The control information may include code information on a physical channel to which the transport channel is mapped, a service identifier for the MBMS service, information indicating that the MBMS service is started, information on types of services available at a corresponding time in a specific cell, and the like. Include. The control information is transmitted through an MBMS control channel (hereinafter referred to as MCCH), which is a separate common channel distinguished from the transport channel.

The MCCH is configured for each cell and all user terminals located in the cell should be able to access the MCCH. Therefore, the MCCH must have sufficient power level to be transmitted until cell change. However, since this may result in excessive consumption of forward transmission resources, instead of reducing the MCCH transmission output, the same message containing one MBMS control information (hereinafter referred to as MBMS control message) within one modification period (Modification Period) By retransmitting a number of times per repetition, a scheme for increasing the likelihood that a terminal located in a cell change successfully receives an MBMS control message has been introduced.

If the size of the MBMS control message is small, there is no problem in performing retransmission, but if the size of the MBMS control message is large, the transmission efficiency is disadvantageous. In such a case, it is more preferable that the MBMS control message is divided into smaller appropriately sized segments and transmitted. That is, when retransmission of the MBMS control message is required, all segments segmented from the MBMS control message are retransmitted.

In order to completely receive the MBMS control message, the user must receive all of the divided segments without error. Since the MBMS control message contains control information necessary for reception of the MTCH, the UE needs to acquire the MBMS control message as soon as possible in order to use the MBMS service. As an example, since information such as a probability value used by UEs to receive a specific MBMS service to attempt RRC connection establishment is updated with a relatively short period, it should be obtained as soon as possible. However, if some segments of the MBMS control message are not received, the UE discards all the remaining segments and waits to receive the segments of the next MBMS control message which is retransmitted. This delays the delivery of the MBMS control message, resulting in a delay in the reception of the MBMS service.

Accordingly, an object of the present invention, which was devised to solve the problems of the prior art operating as described above, is to provide a method and apparatus for efficiently receiving an MBMS control message in an MBMS system.

In order to achieve the above object, an embodiment of the present invention provides a terminal that receives a segment in a communication system in which a control message for a multimedia broadcasting / multicast (MBMS) service is divided into a plurality of segments and transmitted. In the method for obtaining the control message,

Receiving segments including a control message in one transmission period within one change period,

Storing at least one error free segment of the received segments;

Determining whether all segments necessary for assembling the control message exist by referring to the stored segments;

If all the segments do not exist, attempting to receive the remaining segments needed to assemble the control message in subsequent transmission periods within the modification period;

And if the reception of the remaining segment succeeds in subsequent transmission periods within the change period, combining the previously received segments with the remaining segments to form a control message.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the preferred embodiment of the present invention. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

The present invention described below is for quickly and efficiently receiving an MBMS control message including MBMS control information in a mobile communication system providing an MBMS service.

First, the MBMS service applied to the present invention will be described.

1 shows a simplified configuration diagram of a mobile communication system for an MBMS service. Here, an example of applying a MBMS service to a 3GPP (3rd Generation Project Partnership) system, which is a standard of third generation asynchronous mobile communication, is illustrated.

Referring to FIG. 1, UEs 161, 162, 163, 171, and 172 refer to terminal devices or subscribers capable of receiving MBMS services, and are referred to as cell 1 160 and cell 2 170. Is controlled by a base station apparatus, Node B, which wirelessly transmits MBMS related data to subscribers. A Radio Network Controller (RNC) 140 controls the plurality of cells 160 and 170, selectively transmits multimedia data to a specific cell, and is configured to provide MBMS service. Control the wireless channel. The connection between the RNC 140 and the UEs 161-172 is called a Radio Resource Control (RRC) interface.

The RNC 140 is connected to a Packet Switched or Packet Service (PS) network such as the Internet by a Serving GPRS Support Node (hereinafter referred to as 'SGSN') 130. Communication between the RNC 140 and the PS network is made by packet switched signaling (PS signaling). In particular, the connection between the RNC 140 and the SGSN 130 is called an Iu-PS interface.

SGSN 130 controls the MBMS-related services of each subscriber. Representative examples of the role played by the SGSN 130 include managing a service related data of each subscriber and selectively transmitting multimedia data to a specific RNC 140.

The Transit NW 120 provides a communication path between the Broadcast Multicast Service Center (BM-SC) 110 and the SGSN 130 and to an external network through a Gateway GPRS Support Node (GGSN). Can be connected. The BM-SC 110 is responsible for scheduling MBMS data as a source of MBMS data.

Meanwhile, the RNC 140 is connected to a circuit switched (CS) network by a mobile switching center (hereinafter referred to as 'MSC') 150. The CS network refers to a voice-based legacy communication network that is connection-based. Communication between the RNC 140 and the MSC 150 is performed by circuit switched signaling (CS signaling). In particular, the connection between the RNC 140 and the MSC 150 is called an Iu-CS interface. MBMS data streams are delivered to UEs 161, 162, 163, 171 and 172 via the transport network 120, SGSN 130, RNC 140, Node B and cells 160, 170.

Although not shown in FIG. 1, there may be a plurality of SGSNs for one MBMS service and a plurality of RNCs for each SGSN. Each SGSN is an RNC 140, and each RNC performs selective data transmission to each of a plurality of cells, and for this purpose, a list of nodes to which a data stream should be delivered (that is, SGSN is a list of RNCs and an RNC List) and the like, and selectively transmit MBMS data only to the stored nodes later.

2 illustrates a hierarchical structure of a Uu interface for communication of data and signaling messages between a terminal and an RNC. Herein, the control plane is used to exchange control signals between the UE and the RNC, and the user plane is used to transmit actual data.

Referring to FIG. 2, the control plane 100 includes a radio resource control (RRC) layer 102, a radio link control (RLC) layer 210, a media access control (MAC) layer 112, and physical: The PHY layer (hereinafter referred to as PHY) layer 114 exists, and the user plane 102 includes a packet data control protocol (PDCP) layer 206, a broadcast / multicast control (BMC) layer 108, an RLC layer 110, and a MAC. There is a layer 112, a physical layer 114. In a typical case, the physical layer 114 of the layers is located in each cell, that is, Node Bs, and is located in the RNC from the MAC layer 112 to the RRC layer 104.

The physical layer 114 is a layer that provides an information transmission service using a radio transfer technology, and corresponds to a first layer of an Open Systems Interconnection (OSI) model. The physical layer 114 and the MAC layer 112 are connected by transport channels, which are defined by the manner in which specific data is processed in the physical layer.

The MAC layer 112 and the RLC layer 110 are connected through a logical channel. The MAC layer 112 transmits the data delivered by the RLC layer 110 through the logical channel to the physical layer through an appropriate transport channel, and the data transmitted by the physical layer 114 through the transport channel through an appropriate logical channel. It serves to deliver to the RLC layer 110. In addition, by inserting additional information into the data received through the logical channel or the transport channel or by analyzing the inserted additional information to take appropriate action, and controls the random access operation.

The RLC layer 110 is responsible for establishing and releasing logical channels. The RLC layer 110 may operate in one of three operation modes, that is, an acknowledgment mode (AM), an unacknowledged mode (UM), and a transparent mode (TM), and provide different functions for each operation mode. In particular, the RLC layer 110 divides / concatenates a service data unit (hereinafter referred to as SDU) from an upper layer into an appropriate size or a protocol data unit (hereinafter referred to as RLC PDU) from an lower layer. It is responsible for assembling them, and for error correction through ARQ (Automatic Repeat reQuest).

The PDCP layer 106 is located above the RLC layer 110 in the user plane 102. The PDCP layer 106 compresses and restores headers of data transmitted in the form of IP packets, and provides an RNC service to a specific terminal with mobility. It is responsible for the lossless transfer of data, etc. under the situation that is changed. The PDCP layer 106 is responsible for lossless SRNS relocation support and header compression in the case of normal services, but in the case of MBMS services, lossless SRNS (Serving RNS) redirection is due to broadcast / multicasting characteristics. There is no need to support allocation. Here, SRNS reassignment refers to a process of resetting the other RNC to the SRNC by a UE moved to a cell controlled by another RNC other than the SRNC. The BMC layer 108 is located above the RLC layer 110 and supports a broadcast service for transmitting the same data to a plurality of unspecified terminals in a specific cell.

The RRC layer 104 is responsible for allocating and releasing radio resources between the UTRAN and the terminal. The RRC layer 104 manages radio resources allocated to terminals in an RRC connected mode, manages mobility of the terminals, and delivers core network signals to the terminals to be transmitted to the terminals. Etc.

Since the MBMS control message is control information, it is generated by the RRC layer 204 of the control plane 200. If the corresponding entity of the RLC layer 210 is to operate as UM (these RLC entities are called UM RLC entities), the control message is split / concatenated and assembled by the RLC layer 210. On the other hand, when the corresponding entity of the RLC layer 210 becomes a TM (these RLC entities are called TM RLC entities), the division / concatenation and assembly of control messages are performed by the RRC layer 204.

3 is a diagram illustrating transmission of an MBMS control message in an MBMS system.

Referring to FIG. 3, a repetition period 304 indicates a transmission period of an MBMS control message, and a modification period 302 indicates an update period of an MBMS control message. Most MBMS control messages are sent periodically except for event-occurring messages caused by MBMS events. The MBMS control message is sent every transmission period 304 and repeatedly sent within one change period 302. Therefore, the update of the MBMS control message is possible only when the change cycle 302 is changed. Typically, the change period 302 is set to a relatively long period of 5 seconds or more.

4 illustrates operations of an RNC and a UE for transmitting an MBMS control message through an MCCH. Herein, when the RLC entity operates as a TM, the RNC and the UE show an operation in each RRC layer.

Referring to FIG. 4, the RRC entity responsible for the RRC layer of the RNC splits the MBMS control message according to the size of the MBMS control message to be transmitted or, if necessary, according to the MCCH transport block size of the TM RLC entity. Here, a case in which one MBMS control message is divided into four segments RRC # 1, RRC # 2, RRC # 3, and RRC # 4 is illustrated. Each segment includes information such as message type, segment count, segment index, and the like, and is transmitted to the TM RLC entity of the lower layer. The information indicates which MBMS control message each segment belongs to.

If all of the segments RRC # 1, RRC # 2, RRC # 3, and RRC # 4 of the control message transmitted in the first transmission period in one change period have not been successfully received, the RRC layer of the UE Recombination cannot be performed and thus the original MBMS control message cannot be constructed.

If the third segment RRC # 3 among the control messages is not successfully received in the first transmission period 420, the UE that fails to reconstruct the remaining segments and thus does not configure the original MBMS control message may receive the second transmission period 430. Receives all segments needed to assemble a control message again. Since the reception processes of each transmission period are performed completely independently, even if the third segment RRC # 3 is successfully received in the second transmission period 430, the first segment RRC # 4 is not successfully received. As in the transmission period 420, the terminal does not perform recombination. Then, the UE attempts to receive all the segments again in the next transmission period 440. When the UE successfully receives all the segments, the terminal may perform recombination and generate the MBMS control message.

This is a problem caused by determining whether the UE successfully receives the MBMS control message unit and discards all successfully received or successfully decoded segments when it fails to properly receive a single control message or fails to decode. Therefore, if the UE does not properly receive any segmented message belonging to one MBMS control message, the terminal may receive all segments in one transmission cycle until all the segments are required to assemble one control message until the MBMS control message is constructed. The receiving operation is repeatedly performed.

As such, when an error occurs in the transmission of the MBMS control message, the terminal re-receives all segments included in the MBMS control message, resulting in an overhead of the terminal operation. In addition, the larger the size of the control message, the larger the number of segments, and thus, the lower the probability of successfully receiving all segments, the terminal is inefficient in receiving and decoding the same segments several times in order to construct one MBMS control message. Action shall be taken. If the MBMS control message is changed every transmission period, this operation is necessary, but as shown in FIG. 3, the RRC operation of the UE is inefficient because the MBMS control message does not change within one change period.

In the preferred embodiment of the present invention, to compensate for unnecessary operations that may occur in the RRC layer when transmitting an MBMS control message using TM RLC, whether an error occurs in transmission of the MBMS control message is determined whether it is received in segments of the MBMS control message. Then, we propose a method of receiving only segments that have not been successfully received in the next transmission period and combining them with other segments already received in the previous period.

5 illustrates the operation of the RRC layer for receiving MBMS control messages using TM RLC in accordance with a preferred embodiment of the present invention. Here, only the operation of the RRC layer of the terminal on the receiving side is shown.

Referring to FIG. 5, in the first transmission period 510, the UE successfully receives only the remaining segments except the third segment RRC # 3. However, due to the reception failure of the third segment RRC # 3, the UE cannot generate the MBMS control message. In this case, the terminal receives the successfully received segments RRC # 1, # 2, # using information such as message type, segment count, and segment index included in each of the segments RRC # 1, # 2, and # 4. Store 4 in the buffer.

Instead of receiving all segments in the second transmission period 520, the terminal receives only the third segment RRC # 3, which failed to receive in the first transmission period 510. That is, the terminal receives data only at timing for the third segment RRC # 3. If the third segment RRC # 3 is successfully received in the second transmission period 520, the UE combines the third segment RRC # 3 with other segments RRC # 1, # 2, # 4 stored in the buffer Configure MBMS control messages.

If the second transmission period 520 fails to receive the third segment RRC # 3, the second transmission period 520 continues to try to receive the third segment RRC # 3 in the next transmission period within the same change period.

In order for the UE to combine the segments of the previous transmission period and the segments of the current transmission period, the MBMS control message of the previous transmission period and the MBMS control message of the current transmission period must be identical. If it is not the same, that is, the updated control message is different, the terminal will generate an error for receiving incorrect information.

As described above with reference to FIG. 4, messages periodically transmitted within one change cycle have the same contents. That is, one control message is repeatedly transmitted within one change period. However, if the change cycle is changed, the control message can be updated. Therefore, the RNC should inform the terminal that the same MBMS control message in the change period is transmitted to the terminal or that the updated MBMS control message in the change period is transmitted. When the terminal generates an MBMS control message by combining segments of the updated MBMS control message due to a wrong change cycle and segments of the MBMS control message before the update before the change period, the information partially no longer useful before the update And partly because the updated information is mixed to obtain incorrect information. If the RNC transmits an incorrect MBMS control message between change periods, the UE shall not combine segments belonging to each other.

To this end, the RNC inserts and transmits a 1-bit modified identifier along with information such as message type, segment count, and segment index in each segment. When the UE successfully receives the segments in different transmission periods, the UEs generate the MBMS control message by combining only the segments having the same value by comparing the change identifiers of the segments with each other. If segments with different change identifiers are received, this means that the MBMS control message has been updated. Therefore, the segments previously stored in the buffer are discarded, the segments of the current transmission period are stored instead, and the segments of the next period are waited.

In another embodiment, the UE determines whether the change cycle is changed by using scheduling information of the RRC layer from the RNC. If the change cycle is changed, discard the segments stored in the buffer and wait for new segments.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

In the present invention operating as described in detail above, the effects obtained by the representative ones of the disclosed inventions will be briefly described as follows.

The present invention increases the probability of successful transmission of an MBMS control message by selecting and receiving only segments that fail to receive without having to receive all segments again in the next transmission period whenever the UE fails to receive some segments of the MBMS control message. There is an effect that can minimize unnecessary motion.

1 is a simplified block diagram of a mobile communication system for an MBMS service to which the present invention is applied;

2 is a diagram illustrating a hierarchical structure of a Uu interface for communication of data and signaling messages between a terminal and an RNC to which the present invention is applied.

3 illustrates the transmission of an MBMS control message.

4 is a diagram illustrating operations of an RNC and a terminal for transmitting an MBMS control message through an MCCH;

5 illustrates the operation of an RRC layer for receiving MBMS control messages using TM RLC in accordance with a preferred embodiment of the present invention.

Claims (6)

In the communication system for dividing and transmitting a control message for a multimedia broadcasting / multicast (MBMS) service into a plurality of segments, a method for acquiring the control message by the terminal receiving the segments, Receiving segments including a control message in one transmission period within one change period, Storing at least one error free segment of the received segments; Determining whether all segments necessary for assembling the control message exist by referring to the stored segments; If all the segments do not exist, attempting to receive the remaining segments needed to assemble the control message in subsequent transmission periods within the modification period; And if the reception of the remaining segment succeeds in subsequent transmission periods within the change period, combining the previously received segments with the remaining segment to form a control message. The method of claim 1, wherein the segments are: The message type, segment count and segment index. The method of claim 2, wherein the determining is performed. And determining by referring to a message type, a segment count, and a segment index of the stored segments. 3. The method of claim 2, wherein the segments further comprise a change identifier. The method of claim 4, wherein the attempting process comprises: Receive one segment in the reception period of the remaining segment in the next transmission period, and determine whether the change identifier of the received segment is the same as the change identifier of the previously received segments, and if the same, the reception of the previously received segment The method according to claim 1, characterized in that determined to succeed. The method of claim 1, wherein the attempting process comprises: It is determined whether or not the change cycle is changed in the next transmission period according to the scheduling information received from the system. If it does not change, it attempts to receive the remaining segments in the next transmission cycle, and discards the previously received segments if the change cycle is changed. Said method, characterized in that.