Method for receiving a multicast signal in a wireless communication system and device for this purpose

Abstract

Method for receiving a multicast signal by means of a user device, UE, in a wireless communication system, the method comprising: Receiving information from a network about a shared resource to send a data negative acknowledgment (NACK) signal and a control NACK signal; Monitoring a network control signal to terminate a multicast signal; Receiving the multicast signal from the network by decoding the multicast signal based on the control signal, on the basis that the control signal has been successfully received; and Sending the data NACK signal (S707) to the network based on the fact that decoding the multicast signal has failed, where the control NACK signal is sent to the network on the basis that the reception of the control signal has failed (S703), where the shared resource is used to transmit at least one of the data NACK or the control NACK.

Description

Technical area

[0001] The present invention relates to a wireless communication system and, more particularly, to a method for receiving a multicast signal in a wireless communication system and an apparatus therefor. background

[0002] The 3GPP LTE (“3rd Generation Partnership Project Long Term Evolution”, hereinafter abbreviated: LTE) communication system is schematically described as an example of a wireless communication system to which the present invention is applicable.

[0003] Fig. Figure 1 is a schematic diagram of an E-UMTS network structure as an example of a wireless communications system. E-UMTS ("Evolved Universal Mobile Telecommunications System") is a system that evolved from a conventional UMTS ("Universal Mobile Telecommunications System"). Currently, basic standardization work for E-UMTS is underway by 3GPP. E-UMTS is commonly referred to as the LTE system. Individual contents of the technical specifications for UMTS and E-UMTS refer to Release 7 and Release 8 of the "3rd Generation Partnership Project; Technical Specification Group Radio Access Network," respectively.

[0004] With reference to Fig. 1, E-UMTS includes a user equipment (UE), an eNode B (eNB), and an access gateway (AG) connected to an external network such that it is located at the end of a network (E-UTRAN). The eNode B can be configured to simultaneously transmit multiple data streams for a broadcast service, a multicast service, and / or a unicast service.

[0005] An eNode B includes at least one cell. The cell provides a downlink transmission service or an uplink transmission service to a plurality of user devices by being set to one of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz bandwidths. Different cells can be configured to provide corresponding bandwidths, respectively. An eNode B controls data transmissions / receptions to / from a plurality of user devices. For downlink (hereinafter abbreviated: DL) data, the eNode B informs a corresponding user device of a time / frequency region on which data is transmitted, encoding, data size, HARQ (Hybrid Automatic Repeat and Request)-related information, and the like by transmitting DL termination information.Furthermore, for uplink (hereinafter abbreviated: UL) data, the eNode B informs a corresponding device of the time / frequency region usable by the corresponding user device, encoding, data size, HARQ-related information, and the like by sending UL termination information to the corresponding user device. Interfaces for user traffic transmission or control traffic transmission can be used between eNode Bs. A core network (CN) consists of an AG (access gateway) and a network node for user registration of a user device and the like. The AG manages mobility of the user device through a unit of TA (tracking area) consisting of a plurality of cells.

[0006] Wireless communication technologies up to LTE have been developed based on WCDMA. However, the demands and expectations of users and service providers are constantly increasing. Furthermore, as various types of radio access technologies are constantly being developed, new technological advancements must demonstrate future competitiveness. Reducing costs per bit, increasing service availability, flexible frequency band utilization, simple structure / open interfaces, and reasonable power consumption of user equipment, among other things, are necessary for future competitiveness.

[0007] US 2008 / 0 168 321 A1 describes a method and apparatus for transmitting a reverse ACK / NACK for a forward control channel in a mobile communication system supporting HARQ. Control information for decoding a packet is received from a base station via the forward control channel. The packet from the base station is received via a forward data channel in a HARQ scheme. An ACK / NACK for the control information is transmitted to the base station via a first reverse ACK channel when an mth subpacket corresponding to each retransmission of the packet is received from the base station. Here, m is a predetermined integer greater than or equal to two. RevelationTechnical Problem

[0008] Based on the foregoing discussion, it is an object of the present invention to provide a method for receiving a multicast signal in a wireless communication system and an apparatus therefor. Technical solution

[0009] The invention is defined in the independent claims. Features of some embodiments are defined in the subclaims.

[0010] Preferably, the method further comprises the step of receiving information about a common resource for transmitting the data NACK signal and the control NACK signal from the network, wherein the data NACK signal and the control NACK signal can be transmitted to the network by the common resource.

[0011] Preferably, the control NACK signal and the data NACK signal may be sent to the network after retransmission of the multicast signal has been performed a preset number of times.

[0012] Further preferably, a transmission power of the control NACK signal may be configured to be higher than that of the data NACK signal. In this case, the transmission powers of the control NACK signal and the data NACK signal may be increased according to a retransmission count of the multicast signal.

[0013] A user equipment (UE) in a wireless communication system according to one aspect of the present invention comprises a wireless communication module; and a processor connected to the wireless communication module, and attempting to receive from a network a control signal for terminating a multicast signal, receiving the multicast signal from the network and performing decoding based on the control signal, and sending a data negative acknowledgment (-NACK-) signal to the network when decoding of the multicast signal fails, wherein the processor sends a control NACK signal to the network when reception of the control signal has failed.

[0014] Preferably, the processor may receive information about a common resource for transmitting the data NACK signal and the control NACK signal from the network and may transmit the data NACK signal and the control NACK signal to the network through the common resource.

[0015] Preferably, the processor may transmit the control NACK signal and the data NACK signal to the network after retransmitting the multicast signal a preset number of times.

[0016] Further preferably, the processor may configure a transmission power of the control NACK signal to be higher than that of the data NACK signal. In this case, the processor may increase the transmission powers of the control NACK signal and the data NACK signal according to a retransmission count of the multicast signal.

[0017] Additionally, the control signal may contain information indicating an absence of a multicast channel being transmitted by the network. Beneficial effects

[0018] According to the embodiment of the present invention, when an error occurs in packets sent through a multicast channel in a wireless communication system, efficiency recovery of the error can be performed, whereby reliability can be enhanced.

[0019] It will be understood by those skilled in the art that the effects attainable by the present invention are not limited to what has been particularly described above, and other advantages of the present disclosure will become more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings. Short description of the drawings Fig. 1 is a diagram schematically illustrating a network structure of an E-UMTS as an exemplary radio communication system. Fig. Figure 2 is a diagram illustrating structures of a control plane and a user plane of a radio interface protocol between a UE and an E-UTRAN based on the 3GPP Radio Access Network specification. Fig. Figure 3 is a diagram illustrating physical channels used in a 3GPP system and a common signal transmission method using them. Fig. Figure 4 is a diagram illustrating the structure of a radio frame used in an LTE system. Fig. Figure 5 is a diagram illustrating the structure of a DL radio frame used in an LTE system. Fig. Figure 6 is a diagram illustrating the structure of a UL subframe in an LTE system. Fig. 7 is a diagram illustrating a flowchart of a method for receiving a multicast channel according to the embodiment of the present invention. Fig. 8 is a block diagram of a communication device according to an embodiment of the present invention. Best mode for carrying out the invention

[0020] The configuration, operation, and other features of the present invention will become clear from the embodiments of the present invention described with reference to the accompanying drawings. The following embodiments are examples of an application of the technical features of the present invention to a 3rd Generation Partnership Project (3GPP) system.

[0021] Although the embodiments of the present invention are described based on an LTE system and an LTE-Advanced (LTE-A) system, the LTE system and the LTE-A system are purely exemplary, and the embodiments of the present invention can be applied to any communication system as defined above. In the present disclosure, a base station (eNB) may be used as a term with a broad meaning, including a remote radio head (RRH), an eNB, a transmission point (TP), a reception point (RP), a relay, etc.

[0022] Fig. Figure 2 is a diagram illustrating the control plane and user plane structures of a radio interface protocol between a UE and an E-UTRAN based on 3GPP Radio Access Network specifications. The control plane refers to a path used to transmit control messages used by the UE and the network to manage a call. The user plane refers to a path on which data generated in an application layer, such as voice data or internet packet data, is transmitted.

[0023] A first-layer physical layer provides an information transmission service to an upper layer using a physical channel. The physical layer is connected to a media access control (MAC) layer of an upper layer via a transmission channel. Data is transmitted between the MAC layer and the physical layer via the transmission channel. Data is also transmitted between a physical layer of a transmitter and a physical layer of a receiver via a physical channel. The physical channel uses time and frequency as radio resources. Specifically, the physical channel is modulated using an orthogonal frequency-division multiple access (OFDMA) scheme in DL and a single-carrier frequency-division multiple access (SC-FDMA) scheme in UL.

[0024] The second-layer MAC layer provides a service to an upper-layer radio link control (RLC) layer over a logical channel. The second-layer RLC layer supports reliable data transmission. The RLC layer's function may be implemented using a functional block within the MAC layer. A second-layer Packet Data Convergence Protocol (PDCP) layer performs a header compression function to reduce unnecessary control information for efficient transmission of an Internet Protocol (IP) packet, such as an IPv4 or IPv6 packet, over a radio interface that has a relatively narrow bandwidth.

[0025] A radio resource control (RRC) layer, located at the lowest level of a third layer, is defined only in the control plane. The RRC layer controls logical channels, transmission channels, and physical channels in relation to the configuration, reconfiguration, and release of radio bearers. A radio bearer refers to a service provided by the second layer to transmit data between the UE and the network. For this purpose, the RRC layer of the UE and the RRC layer of the network exchange RRC messages. The UE is in RRC connected mode when an RRC connection has been established between the RRC layer of the radio network and the RRC layer of the UE. Otherwise, the UE is in RRC idle mode. A non-access stratum (NAS) layer, located at an upper level of the RRC layer, performs functions such as session management and mobility management.

[0026] A cell constructing an eNB is configured with one of the bandwidths of 1.25, 2.5, 5, 10, 15, and 20 MHz and provides DL or UL transmission services to a plurality of UEs. Different cells can be configured to provide different bandwidths.

[0027] DL transmission channels for data transmission from the network to the UE include a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting paging messages, and a DL shared channel (SCH) for transmitting user traffic or control messages. Traffic or control messages of a DL multicast or broadcast service can be transmitted through the DL SCH or through an additional DL multicast channel (MCH). UL transmission channels for data transmission from the UE to the network include a random access channel (RACH) for transmitting initial control messages and a UL SCH for transmitting user traffic or control messages.Logical channels, which are placed at an upper level of the transmission channels and mapped to the transmission channels, 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).

[0028] Fig. Figure 3 is a diagram illustrating physical channels used in a 3GPP system and a common signal transmission method using them.

[0029] When power is turned on or the UE enters a new cell, the UE performs an initial cell search procedure, such as acquiring synchronization with an eNB (S301). For this purpose, the UE may establish synchronization with the eNB by receiving a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH) from the eNB and obtain information such as a cell identity (ID). Thereafter, the UE may acquire broadcast information within the cell by receiving a physical broadcast channel from the eNB. In the initial cell search procedure, the UE may monitor a DL channel status by receiving a downlink reference signal (DL RS).

[0030] Upon completion of the initial cell search procedure, the UE may obtain more accurate system information by receiving a physical downlink control channel (PDCCH) and by receiving a physical downlink shared channel (PDSCH) based on information carried on the PDCCH (S302).

[0031] When the UE initially accesses the eNB or when radio resources for signal transmission to the eNB are not available, the UE may perform a random access procedure with the eNB (S303 to S306). For this purpose, the UE may transmit a specific sequence through a physical random access channel (PRACH) as a preamble (S303 and S305) and receive a response message to the preamble through the PDCCH and the PDSCH associated with the PDCCH (S304 and S306). In the case of a contention-based random access procedure, the UE may additionally perform a contention resolution procedure.

[0032] After performing the above procedures, the UE may receive a PDCCH / PDSCH (S307) and transmit a physical uplink shared channel (PUSCH) / physical uplink control channel (PUCCH) (S308) as a general UL / DL signaling procedure. Specifically, the UE receives downlink control information (DCI) through the PDCCH. The DCI contains control information, such as resource allocation information, for the UE and has different formats according to its intended use.

[0033] Control information that the UE sends to the eNB on UL or receives from the eNB on DL includes a DL / UL acknowledgement / negative acknowledgement (ACK / NACK) signal, a channel quality indicator (CQI), a precoding matrix index (PMI), a rank indicator (RI), and the like. In the 3GPP LTE system, the UE can send control information such as CQI / PMI / RI through a PUSCH and / or a PUCCH.

[0034] Fig. Figure 4 is a diagram illustrating the structure of a radio frame used in an LTE system.

[0035] With reference to Fig. 4, the radio frame has a length of 10 ms (327,200 × Ts) and contains 10 equally sized subframes. Each subframe has a length of 1 ms and contains two slots. Each slot has a length of 0.5 ms (15,360 Ts). In this case, Ts denotes a sampling time, which is given by Ts = 1 / (15 kHz × 2,048) = 3.2552 × 10 -8(approximately 33 ms). Each slot contains a plurality of OFDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. In the LTE system, one RB contains 12 subcarriers × 7 (or 6) OFDM symbols. A transmission time interval (TTI), which is a unit time for data transmission, may be determined in units of one or more subframes. The structure of the radio frame described above is purely exemplary, and various modifications may be made to the number of subframes included in a radio frame, the number of slots included in a subframe, or the number of OFDM symbols included in a slot.

[0036] Fig. 5 is a diagram illustrating control channels included in a control region of a subframe in a DL radio frame.

[0037] With reference to Fig. 5, a subframe contains 14 OFDM symbols. The first to third of the 14 OFDM symbols can be used as a control region, and the remaining 11 to 13 OFDM symbols can be used as a data region, according to the subframe configuration. Fig. 5, R0 to R3 represent reference signals (RS) or pilot signals for antennas 0 to 3, respectively. The RS are fixed to a predetermined pattern within the subframe regardless of the control region and the data region. Control channels are allocated to resources in the control region that are not used for RS. Traffic channels are allocated to resources in the data region that are not used for RS. The control channels allocated to the control region include a physical control format indicator channel (PCFICH), a physical hybrid ARQ indicator channel (PHICA), a physical downlink control channel (PDCCH), etc.

[0038] The PCFICH, the physical control format indicator channel, informs a UE about the number of OFDM symbols used in each subframe for the PDCCH. The PCFICH is placed in the first OFDM symbol and configured with priority over the PHICH and the PDCCH. The PCFICH is formed from four resource element groups (REGs), each of which is distributed across the control region based on a cell ID. A REG contains four resource elements (REs). An RE indicates a minimum physical resource defined by an OFDM symbol as a subcarrier. The PCFICH value indicates values ​​from 1 to 3 or values ​​from 2 to 4 depending on the bandwidth and is modulated using quadrature phase-shift keying (QPSK).

[0039] The PHICH, the physical hybrid ARQ indicator channel, is used to carry a HARQ ACK / NACK signal for UL transmission. This means that the PHICH indicates a channel through which DL ACK / NACK information for UL HARQ is sent. The PHICH contains a REG and is cell-specifically scrambled. The ACK / NACK signal is indicated by 1 bit and is modulated using binary phase-shift keying (BPSK). The modulated ACK / NACK signal is spread with a spreading factor (SF) of 2 or 4. A plurality of PHICHs mapped to the same resource form a PHICH group. The number of PHICHs multiplexed into the PHICH groups is determined depending on the number of spreading codes. The PHICH (group) is repeated three times to achieve diversity gain in the frequency domain and / or the time domain.

[0040] The PDCCH is assigned to the first n OFDM symbols of a subframe. In this case, n is an integer equal to or greater than 1, pointed to by the PCFICH. The PDCCH is composed of one or more control channel elements (CCEs). The PDCCH informs each UE or UE group of information related to the resource allocation of transmission channels, i.e., a paging channel (PCH) and a downlink shared channel (DL-SCH), UL termination grant, HARQ information, etc. The PCH and the DL-SCH are transmitted through a PDSCH. Therefore, the eNB and the UE transmit and receive data through the PDSCH, except for special control information or service data.

[0041] Information indicating to which UE or UEs PDSCH data is to be transmitted, and information indicating how UEs should receive and decode the PDSCH data are transmitted on the PDCCH. For example, assuming that a cyclic redundancy check (CRC) of a particular PDCCH is masked by a radio network temporary identity (RNTI), A', and information about data transmitted using a radio resource 'B' (e.g., frequency placement) as well as using a DCI format 'C', i.e., transport format information (e.g., a transport block size, a modulation scheme, coding information, etc.), is transmitted in a particular subframe, a UE located in a cell monitors the PDCCH, i.e., it blindly decodes the PDCCH, using RNTI information thereon in a search space.If one or more UEs with RNTI 'A' are present, the UEs receive the PDCCH and a PDSCH indicated by 'B' and 'C' based on the received PDCCH information.

[0042] Fig. Figure 6 is a diagram illustrating the structure of a UL subframe in an LTE system.

[0043] With reference to Fig. 6, an uplink subframe is divided into a region to which a PUCCH is assigned to transmit control information and a region to which a PUSCH is assigned to transmit user data. The PUSCH is assigned to the center of the subframe, whereas the PUCCH is assigned to both ends of a data region in the frequency domain. The control information transmitted on the PUCCH includes an ACK / NACK, a Channel Quality Indicator (CQI) representing a downlink channel status, an RI for multiple-input, multiple-output (MIMO), a Scheduling Request (SR) indicating a request for allocation of UL resources, etc. A PUCCH of a UE uses one RB that occupies different frequencies in each slot of a subframe. That is, two RBs assigned to the PUCCH frequency hop across the slot boundary. In particular, in Fig. 6 PUCCHs for m=0, m=1, m=2 and m=3 assigned to a subframe.

[0044] In the present invention, a reliability enhancing method in HARQ operation for recovering from a packet error when the packet error occurs in a multicast operation for receiving a signal transmitted from a transmitter in a plurality of receivers.

[0045] In particular, the present invention can be applied to communication technology for a next-generation communication system that requires high reliability and low latency, such as a vehicle control signal to be transmitted to an autonomous vehicle. For example, the conventional communication system aims to achieve a block error rate (BLER) of 10-2, which is usually considered, whereas the next-generation communication system aims to achieve a BLER << 10-2, for example, a BLER of 10-5, which may require very high reliability. Since this service also requires very low latency, successful transmission and reception should be completed within a very short, restrictive time.

[0046] Although the following description is based on a downlink where a transmitter is an eNB and a sender is a UE, the description is applicable to an uplink where the UE is a transmitter and the eNB is a receiver, or device-to-device (D2D) communication for directly transmitting data from one UE to another UE.

[0047] First, the sender sends multicast data, and the receiver that received the multicast data reports HARQ-ACK to the sender. This is helpful for improving reliability. The reason for this is that even if one receiver fails to decode the data, the sender can retransmit the corresponding data. However, since multiple receivers attempt to receive the same data, the decoding results will not be the same, and the problem of HARQ acknowledgement being sent from the corresponding receiver should be properly addressed. Although an independent resource can be used for a single receiver, this causes excessive resource consumption. On the other hand, if receivers attempting to receive the same data share a single HARQ acknowledgement resource, it is beneficial in that resource consumption can be reduced.

[0048] Furthermore, since the decoding results of each receiver are different from each other, normal transmission cannot be performed if each decoding result is sent to a resource shared by the respective receivers. As a method to solve this, the receiver that failed to decode sends a NACK signal, while the receiver that successfully decode can be made to not send any signal. In this case, the sender can identify whether at least one receiver failed to decode or whether all receivers successfully decode.

[0049] However, this operation has a disadvantage in that it cannot detect a failure to decode a termination message used to terminate multicast data. If a particular receiver fails to decode the termination message, the receiver determines that no corresponding data has been transmitted and will not send a HARQ acknowledgement signal. If the other receivers have successfully received the data, no HARQ acknowledgement signal will be sent. Therefore, since the sender determines that all receivers have successfully received the data and does not attempt to retransmit, the receiver that failed to decode the termination message will again be unable to receive the corresponding data.

[0050] To solve this problem, the present invention proposes a method for notifying a sender whether decoding of a termination message for terminating multicast data has been successfully performed.

[0051] First, the sender and receivers configure a set of time and / or frequency resources to which a termination message can be sent to terminate a specific service. Additionally, the termination message for terminating a specific service can be determined in advance using several transmission parameters. Examples of transmission parameters include CRC mask, scrambling sequence generation parameters, and DM-RS sequence generation parameters. A receiver attempting to receive a specific service attempts to receive a termination message by using a corresponding parameter in a corresponding resource set.

[0052] If the receiver fails to receive a multicast termination message within a specific time and / or frequency resource, the receiver generates a signal indicating this reception failure and notifies the sender of the generated signal. Hereinafter, this signal is referred to as a control NACK, while a signal transmitted during a multicast data reception failure is referred to as a data NACK. It is assumed that a termination message corresponding to a data NACK has been received in order to transmit the data NACK.

[0053] A resource for control NACK can be separated from a resource for data NACK. If control NACK has not been received but data NACK has been received, the sender can identify that all receivers have received a termination message normally and therefore information related to the received data has been stored in a soft buffer of all receivers, even if an error has occurred. Therefore, although retransmission is performed using less time / frequency / power, all receivers can complete decoding normally by combining the information stored therein. On the other hand, if control NACK is received—since this means that a particular receiver does not store any information—the particular receiver can be made to use a sufficient resource such that the desired decoding behavior can be achieved by retransmission alone.

[0054] Alternatively, the dedicated receiver can be configured to have the control NACK and the data NACK use the same resource, i.e., a shared resource. In this case, the resource of the data NACK cannot be designated using a scheduling message, and use of a specific resource can be scheduled in advance between the sender and the receiver through a separate channel or higher-layer signaling. The receiver transmits the control NACK and the data NACK using the corresponding resource without identifying them from each other. This method has the advantage of reducing HARQ-ACK resource consumption.

[0055] If there is no multicast data to be transmitted by a resource set that has been designated in advance, the sender cannot send a termination message. In this case, since all receivers will send the control NACK, a signal of too high power will be sent to the corresponding resource, which may affect other communications in the form of interference. To avoid interference, the sender can be operated to send a specific termination message from a corresponding resource set, but the corresponding termination message does not terminate any multicast data. In another sense, the sender can be operated to indicate that no multicast data is being transmitted. In particular, the corresponding termination message is characterized by the size of the frequency and / or time resource being terminated becoming zero.

[0056] If very high reliability is required, at least a certain number of repeated transmissions or retransmissions can be performed. In this case, the transmitter performs a certain number of repeated transmissions or retransmissions regardless of the receiver's acknowledgement. At this time, the receiver can reduce unnecessary interference by not allowing transmissions to be performed before a certain number of retransmissions, even if a control NACK or data NACK occurs.

[0057] Additionally, when the receiver sends HARQ acknowledgement, the receiver can configure a control NACK transmission power different from the data NACK transmission power. For example, since sufficient retransmission is required when a termination message is not received, the receiver can configure a higher control NACK power so that a control NACK error can be reduced and retransmission can begin as soon as possible. Alternatively, as described above, if the sender does not send the termination message because there is no multicast data to transmit, a higher data NACK power can be configured to reduce interference.

[0058] The power for transmitting HARQ feedback from multicast can be controlled according to the retransmission count of the corresponding data. When there is no retransmission or a small number of retransmissions, since a relatively large number of receivers are likely to fail to receive, the HARQ feedback transmission power of a single receiver can be reduced, thereby reducing interference. Even in this case, a final signal generated by summing signals from multiple receivers can be reliably received by the transmitter.

[0059] However, with respect to transmissions that occur after a large number of retransmissions have been performed, since only a small number of receivers fail to receive, it may be preferable to transmit HARQ feedback with high power. For example, a HARQ feedback transmission power can be configured by an incremental function for the retransmission counts of corresponding data transmissions. For this purpose, previously generated retransmission counts can be included in the termination message.

[0060] Fig. 7 is a diagram illustrating a flowchart of a method for receiving a multicast channel according to the embodiment of the present invention.

[0061] With reference to Fig. 7, in step 701, a UE attempts to receive a control signal for terminating a multicast signal from a network. If reception of the control signal fails, the UE transmits a control NACK signal, i.e., Control NACK, to the network, as shown in step 703. In this case, the control signal may contain information indicating an absence of a multicast channel transmitted by the network. All UEs may therefore be prevented from transmitting the Control NACK signal. Particularly when very high reliability is to be provided, it is preferable that the Control NACK signal be transmitted after retransmission of the multicast signal has been performed a preset number of times.

[0062] If the control signal is successfully received, the UE performs decoding based on the control signal by receiving the multicast signal from the network in step 705. If decoding the multicast signal failed, the UE transmits a data NACK signal, i.e., data NACK, to the network in step 707. Specifically, the data NACK signal and the control NACK signal may be fed back using the same resource. Furthermore, if very high reliability is to be provided, it is preferable that the data NACK signal be transmitted after retransmitting the multicast signal in the same manner as the control NACK signal a preset number of times.

[0063] Additionally, it may be preferable that the control NACK signal be configured with a higher power than the data NACK signal so that retransmission can begin as soon as possible. Furthermore, when retransmission is not occurring or there is a small number of retransmissions, since a relatively large number of receivers are likely to fail to receive, it is preferable that the transmission powers of the control NACK signal and the data NACK signal be increased according to the retransmission number of the multicast signal.

[0064] Fig. 8 is a block diagram of a communication device according to an embodiment of the present invention.

[0065] With reference to Fig. 8, a communication device 800 includes a processor 810, a memory 820, a radio frequency (RF) module 830, a display module 840, and a user interface module 850.

[0066] The communication device 800 is shown for descriptive purposes, and some modules thereof may be omitted. In addition, the communication device 800 may include other necessary modules. In addition, some modules of the communication device 800 may be subdivided. The processor 810 is configured to perform an operation of the embodiment of the present invention described with reference to the drawings. For a detailed description of the operation of the processor 810, reference may be made to the description in connection with Fig. 1 to 7.

[0067] The memory 820 is connected to the processor 810 to store an operating system, an application, program code, data, and the like. The RF module 830 is connected to the processor 810 to perform a function of converting a baseband signal into a radio signal or converting a radio signal into a baseband signal. The RF module 830 performs analog conversion, amplification, filtering, and frequency upconversion, or the reverse. The display module 840 is connected to the processor 810 to display a variety of information. A known device, such as a liquid crystal display (LCD), a light-emitting diode (LED), or an organic light-emitting diode (OLED), can be used as the display module 840, although not limited thereto.The user interface module 850 is connected to the processor 810 and may be configured by a combination of well-known user interfaces, such as a keypad and a touch screen.

[0068] The above-described embodiments are proposed by combining constituent components and features of the present invention according to a predetermined format. The individual constituent components or features should be understood as optional factors unless additionally noted. If necessary, the individual constituent components or features may not be combined with other components or features. Furthermore, some constituent components and / or features may be combined to implement the embodiments of the present invention. The order of processes to be disclosed in the embodiments of the present invention may be changed. Some components or features of any embodiment may also be included in other embodiments or replaced with those of the other embodiments, if necessary.Furthermore, it is to be understood that some claims that refer to specific claims may be combined with other claims that refer to claims other than the specific claims to form the embodiment, or to add new claims by amendment after the application has been filed.

[0069] The aforementioned embodiments of the present invention are disclosed based on a data communication relationship between a base station and a user equipment. Certain processes to be directed by the base station in the present invention may also be directed by an upper node of the base station, if necessary. In other words, it will be understood by those skilled in the art that several processes for enabling the base station to communicate with the user equipment in a network composed of multiple network nodes including the base station may be directed by the base station or network nodes other than the base station. The term "base station" may be replaced by the terms base station, Node-B, eNode-B (eNB), or access point, if necessary.

[0070] The embodiments of the present invention may be implemented by a variety of means, for example, hardware, firmware, software, or a combination thereof. In the case where the present invention is implemented by hardware, the present invention may be implemented by application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), a processor, a controller, a microcontroller, a microprocessor, etc.

[0071] When processes or functions of the present invention are implemented by firmware or software, the present invention may be implemented in a variety of formats, such as modules, procedures, functions, etc. The software code may be stored in a memory unit for execution by a processor. The memory unit may be located inside or outside the processor so that it can communicate with the aforementioned processor via a variety of well-known parts.

[0072] It will be understood by those skilled in the art that numerous modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Therefore, 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

[0073] Although the method for receiving a multicast signal in a wireless communication system and the apparatus therefor have been described based on the 3GPP LTE system, the method and apparatus are applicable to various wireless communication systems in addition to the 3GPP LTE system.

Claims

[1] A method for receiving a multicast signal by a user equipment, UE, in a wireless communication system, the method comprising: Receiving, from a network, information about a shared resource to send a data negative acknowledgment, NACK, signal and a control NACK signal; Monitoring a network control signal for terminating a multicast signal; Receiving the multicast signal from the network by performing decoding of the multicast signal based on the control signal, on the basis that the control signal has been successfully received; and Sending the data NACK signal (S707) to the network on the basis that decoding of the multicast signal has failed, wherein the control NACK signal is sent to the network on the basis that the reception of the control signal has failed (S703), wherein the shared resource is used to transmit at least one of the data NACK or the control NACK. [2] The method of claim 1, wherein the control signal includes information indicating an absence of a multicast channel transmitted by the network. [3] The method of claim 1, wherein the control NACK signal and the data NACK signal are sent to the network after retransmission of the multicast signal has been performed a preset number of times. [4] The method of claim 1, wherein a transmission power of the control NACK signal is configured to be higher than that of the data NACK signal. [5] The method according to claim 1, wherein transmission powers of the control NACK signal and the data NACK signal are increased according to retransmission numbers of the multicast signal. [6] User equipment, UE, (800) adapted to operate in a wireless communication system, the UE comprising: a wireless communication module (830); and a processor (810) configured to control the wireless communication module, the process being configured to: Receiving, from a network, information about a shared resource to send a data negative acknowledgment, NACK, signal and a control NACK signal; Monitoring a network control signal for terminating a multicast signal; Receiving the multicast signal from the network by performing decoding of the multicast signal based on the control signal, on the basis that the control signal has been successfully received; and Sending the data NACK signal (S707) to the network on the basis that decoding of the multicast signal has failed, wherein the control NACK signal is sent to the network on the basis that the reception of the control signal has failed (S703), wherein the shared resource is used to transmit at least one of the data NACK or the control NACK. [7] The UE of claim 6, wherein the control signal contains information indicating an absence of a multicast channel transmitted by the network. [8] The UE of claim 6, wherein the processor sends the control NACK signal and the data NACK signal to the network after retransmitting the multicast signal a preset number of times. [9] The UE of claim 6, wherein the processor configures a transmission power of the control NACK signal to be higher than that of the data NACK signal. [10] The UE of claim 6, wherein the processor increases transmission powers of the control NACK signal and the data NACK signal according to retransmission numbers of the multicast signal. [11] A processor device configured to control a user equipment, UE, to receive a multicast signal in a wireless communication system, the processor device comprising: at least one processor (810); and at least one computer memory (820) operatively connected to the at least one processor and storing instructions that, when executed by the at least one processor (810), perform operations comprising: Receiving, from a network, information about a shared resource to send a data negative acknowledgment, NACK, signal and a control NACK signal; Monitoring a network control signal for terminating a multicast signal; Receiving the multicast signal from the network by performing decoding of the multicast signal based on the control signal, on the basis that the control signal has been successfully received; and Sending the data NACK signal (S707) to the network on the basis that decoding of the multicast signal has failed, wherein the control NACK signal is sent to the network based on the reception of the control signal having failed (S703), wherein the shared resource is used to transmit at least one of the data NACK or the control NACK.

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