KR20140071637A - Method and apparatus for performing hybrid automatic retransmit request (harq) in voice over long term evolution (lte) system - Google Patents

Abstract

A method of receiving data in a wireless communication system is provided. The terminal receives the downlink data from the base station through the first subframe. The UE determines whether a reception error has occurred in the downlink data. When a reception error occurs in the downlink data, the terminal receives retransmission data of the downlink data. The retransmission data is received via the second sub-frame. The second sub-frame is transmitted after a predetermined time from the first sub-frame.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and an apparatus for performing HARQ in a voice over LTE system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to wireless communication, and more particularly, to a method and apparatus for performing Hybrid Automatic Retransmission Request (HARQ) in a voice over LTE (Long Term Evolution) system.

3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is an enhanced version of UMTS (Universal Mobile Telecommunication System) and is introduced in 3GPP release 8. 3GPP LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink and Single Carrier-Frequency Division Multiple Access (SC-FDMA) in the uplink. 3GPP LTE uses Multiple Input Multiple Output (MIMO) that supports up to four antennas. Recently, 3GPP LTE-A (LTE-advanced), an evolution of 3GPP LTE, is being discussed.

In order to increase the competitiveness of user equipment (UE), it is necessary to reduce power consumption. The voice data is transmitted every specific period. In the voice over LTE environment, Semi-Persistent Scheduling (SPS) and Connected DRX (Discontinuous Reception) are used.

A method for saving the power consumption of the terminal is needed.

The present invention provides a method and apparatus for performing hybrid automatic retransmit request (HARQ) in a voice over LTE (Long Term Evolution) system.

The present invention provides a method and apparatus for performing HARQ that does not transmit HARQ NACK through a Physical Uplink Control Channel (PUCCH) when an error occurs in downlink (DL) transmission.

According to an embodiment of the present invention, a method of receiving data by a terminal in a wireless communication system is provided. The method includes receiving downlink data from a base station through a first subframe, checking whether a reception error has occurred with the downlink data, and transmitting the downlink data And receiving retransmission data of the mobile station. The retransmission data is received via a second sub-frame, and the second sub-frame is transmitted after a predetermined time from the first sub-frame.

According to another embodiment of the present invention, a terminal in a wireless communication system is provided. The terminal includes a radio frequency (RF) unit for transmitting and receiving a radio signal, and a processor connected to the RF unit and implementing a radio interface protocol. Wherein the processor is configured to receive downlink data from a base station through a first subframe, to check whether a reception error has occurred with the downlink data, and to retransmit the downlink data when a reception error occurs with the downlink data And receives data. The retransmission data is received via a second sub-frame, and the second sub-frame is transmitted after a predetermined time from the first sub-frame.

The power consumption of the user equipment (UE) can be saved.

A power saving area can be further secured.

The performance of the terminal is improved.

1 shows a wireless communication system to which the present invention is applied.
2 is a block diagram illustrating a radio protocol architecture for a user plane.
3 is a block diagram illustrating a wireless protocol structure for a control plane.
Figure 4 shows the DRX cycle.
5 shows an active period of 3GPP LTE.
FIG. 6 shows an example of the transition of the DRX cycle.
7 shows operations of the UE and the base station when an error is found in the DL transmission.
8 is a schematic diagram illustrating a subframe configuration in a case where a mobile station transmits an HARQ ACK to a base station.
FIG. 9 is a schematic diagram illustrating a subframe configuration when a mobile station transmits HARQ NACK to a base station.
FIG. 10 specifically shows subframe 0 (sf 0) to subframe 4 (sf 4) when the UE transmits HARQ NACK to the base station.
FIG. 11 shows operations of a terminal and a base station according to an embodiment of the present invention when an error is found in the DL transmission.
12 is a schematic diagram showing a subframe structure according to an embodiment of the present invention when an error is found in the DL transmission.
FIG. 13 shows subframe 0 (sf 0) to subframe 4 (sf 4) in the case of FIG. 12 in more detail.
FIG. 14 shows a method of receiving data in a terminal in a wireless communication system according to an embodiment of the present invention.
15 is a block diagram illustrating a terminal in which an embodiment of the present invention is implemented.

1 shows a wireless communication system to which the present invention is applied. This may be referred to as Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) or Long Term Evolution (LTE) / LTE-A system.

The E-UTRAN includes a base station (BS) 20 that provides a control plane and a user plane to a user equipment (UE) 10. The terminal 10 may be fixed or mobile and may be referred to by other terms such as a Mobile Station (MS), a User Terminal (UT), a Subscriber Station (SS), a Mobile Terminal (MT) . The base station 20 is a fixed station that communicates with the terminal 10 and may be called by other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point (AP) have.

The base stations 20 may be interconnected via an X2 interface. The base station 20 is connected to an S-GW (Serving Gateway) through an MME (Mobility Management Entity) and an S1-U through an EPC (Evolved Packet Core) 30, more specifically, an S1-MME through an S1 interface.

The EPC 30 is composed of an MME, an S-GW, and a P-GW (Packet Data Network-Gateway). The MME has information on the access information of the terminal and the capability of the terminal, and this information is mainly used for managing the mobility of the terminal. The S-GW is a gateway having an E-UTRAN as an end point, and the P-GW is a gateway having a PDN as an end point.

The layers of the radio interface protocol between the UE and the network are divided into L1 (first layer), L1 (second layer), and the like, based on the lower three layers of the Open System Interconnection (OSI) L2, and L3 (third layer). Among them, the physical layer belonging to the first layer provides an information transfer service using a physical channel, An RRC (Radio Resource Control) layer located at Layer 3 controls the radio resources between the UE and the network. To this end, the RRC layer exchanges RRC messages between the UE and the BS.

2 is a block diagram illustrating a radio protocol architecture for a user plane. 3 is a block diagram illustrating a wireless protocol structure for a control plane. The user plane is a protocol stack for transmitting user data, and the control plane is a protocol stack for transmitting control signals.

2 and 3, a physical layer (PHY layer) provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to a MAC (Medium Access Control) layer, which is an upper layer, through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. The transport channel is classified according to how the data is transmitted through the air interface.

Data moves between physical layers between different physical layers, i. E. Between the transmitter and the physical layer of the receiver. The physical channel is modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and uses time and frequency as radio resources.

The function of the MAC layer includes a mapping between a logical channel and a transport channel and a multiplexing / demultiplexing into a transport block provided as a physical channel on a transport channel of a MAC SDU (Service Data Unit) belonging to a logical channel. The MAC layer provides a service to a Radio Link Control (RLC) layer through a logical channel.

The function of the RLC layer includes concatenation, segmentation and reassembly of the RLC SDUs. In order to guarantee various QoSs required by a radio bearer (RB), the RLC layer includes a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode ; AM). ≪ / RTI > AM RLC provides error correction through ARQ (Automatic Repeat Request).

The functions of the Packet Data Convergence Protocol (PDCP) layer in the user plane include transmission of user data, header compression and ciphering. The function of the PDCP layer in the user plane includes transmission of control plane data and encryption / integrity protection.

The RRC layer is defined only in the control plane. The RRC layer is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of radio bearers. RB denotes a logical path provided by a first layer (PHY layer) and a second layer (MAC layer, RLC layer, PDCP layer) for data transmission between a UE and a network.

The fact that the RB is set means that the characteristics of the radio protocol layer and the channel are specified to provide a specific service and each specific parameter and operation method is set. RB can be divided into SRB (Signaling RB) and DRB (Data RB). The SRB is used as a path for transmitting the RRC message in the control plane, and the DRB is used as a path for transmitting the user data in the user plane.

When there is an RRC connection between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in an RRC_CONNECTED state, and if not, it is in an RRC_IDLE state.

Data is transmitted from the network to the terminal over the downlink transport channel. The downlink transmission channel for transmitting data from the network to the terminal includes a BCH (Broadcast Channel) for transmitting system information and a downlink SCH (Shared Channel) for transmitting user traffic or control messages. In case of a traffic or control message of a downlink multicast or broadcast service, it may be transmitted through a downlink SCH, or may be transmitted via a separate downlink MCH (Multicast Channel). Meanwhile, the data is transmitted from the terminal to the network through the uplink transmission channel. The uplink transmission channel for transmitting data from the UE to the network includes a random access channel (RACH) for transmitting an initial control message and an uplink SCH (Shared Channel) for transmitting user traffic and control messages.

A logical channel mapped to a transport channel is a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), a multicast traffic Channel).

A physical channel is composed of a plurality of sub-carriers in a frequency domain and a plurality of symbols in a time domain. One sub-frame includes a plurality of symbols in the time domain and a plurality of sub-carriers in the frequency domain. One subframe is composed of a plurality of resource blocks, and one resource block is composed of a plurality of symbols and a plurality of subcarriers. A resource block is a unit of resource allocation, and includes a plurality of OFDM symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of a particular symbol (e.g., the first symbol) of a corresponding subframe for a physical downlink control channel (PDCCH), i.e., an L1 / L2 control channel. A transmission time interval (TTI), which is a unit time at which a subframe is transmitted, may be 1 ms corresponding to one subframe.

As disclosed in 3GPP TS 36.211 V10.5.0, in 3GPP LTE, a physical channel includes a Physical Downlink Shared Channel (PDSCH), a Physical Uplink Shared Channel (PUSCH) and a Physical Downlink Control Channel (PDCCH) Control Format Indicator Channel), PHICH (Physical Hybrid-ARQ Indicator Channel), and PUCCH (Physical Uplink Control Channel).

The PCFICH transmitted in the first OFDM symbol of the subframe carries a control format indicator (CFI) regarding the number of OFDM symbols (i.e., the size of the control region) used for transmission of the control channels in the subframe. The UE first receives the CFI on the PCFICH, and then monitors the PDCCH.

The PDCCH is a downlink control channel and is also referred to as a scheduling channel in that it carries scheduling information. The control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes a resource allocation (also referred to as a DL grant) of the PDSCH, a resource allocation (also referred to as an UL grant) of the PUSCH, a set of transmission power control commands for individual UEs in any UE group And / or Voice over Internet Protocol (VoIP).

In 3GPP LTE, blind decoding is used to detect PDCCH. The blind decoding demodulates a desired identifier in a CRC (Cyclic Redundancy Check) of a received PDCCH (referred to as a candidate PDCCH), checks a CRC error, and confirms whether the corresponding PDCCH is its own control channel .

The base station determines the PDCCH format according to the DCI to be transmitted to the UE, attaches the CRC to the DCI, and masks the CRC with a unique identifier (referred to as RNTI (Radio Network Temporary Identifier)) according to the owner or use of the PDCCH .

We now describe DRX (Discontinuous Reception) in 3GPP LTE.

DRX is a technique for reducing the battery consumption of the UE by allowing the UE to monitor the downlink channel discontinuously.

Figure 4 shows the DRX cycle.

The DRX cycle represents a periodic repetition of the On-Duration after the inactivity period. The DRX cycle includes the On-period and the Off-period. The On interval is a period during which the UE monitors the PDCCH within the DRX cycle.

If DRX is set, the UE monitors the PDCCH only in the On-interval and may not monitor the PDCCH in the Off-interval.

The OnDuration Timer is used to define the On-interval. That is, the On-interval can be defined as an interval during which the OnDuration Timer is operating. The OnDuration Timer may indicate the number of consecutive PDCCH-subframes at the beginning of the DRX cycle. The PDCCH-subframe indicates a subframe in which the PDCCH is monitored.

In addition to the DRX cycle, a period in which the PDCCH is monitored can be further defined. The period in which the PDCCH is monitored is collectively referred to as an active time.

The drx-Inactivity Timer disables DRX. When the drx-Inactivity Timer is in operation, the UE continuously monitors the PDCCH regardless of the DRX cycle. The drx-Inactivity Timer starts when the initial UL Grant or DL Grant is received on the PDCCH. The drx-Inactivity Timer may indicate the number of consecutive PDCCH-subframes after successfully decoding the PDCCH indicating initial UL or DL user data transmission for the UE.

The HARQ RTT Timer defines the minimum interval in which the UE expects to retransmit DL HARQ. The HARQ RTT Timer may indicate the minimum amount of subframe before the terminal expects DL HARQ retransmission.

The drx-Retransmission Timer defines the interval during which the UE monitors the PDCCH while expecting DL retransmission. The drx-Retransmission Timer may indicate the maximum number of consecutive PDDCH-subframes while the UE expects DL retransmission. After the initial DL transmission, the terminal drives the HARQ RTT Timer. If the UE finds an error in the initial DL transmission, it transmits a NACK to the Node B and drives the DRX-Retransmission Timer after expiration of the HARQ RTT Timer. The terminal monitors the PDCCH for DL retransmission from the base station while the drx-Retransmission Timer is in operation.

The active time period may include an On-period for periodically monitoring the PDCCH and a period for monitoring the PDCCH due to the occurrence of an event.

When the DRX cycle is set, the activation interval is

- the interval during which the OnDuration Timer, the drx-Inactivity Timer, the drx-Retransmission Timer or the mac-Contention Resolution timer is driven;

- the interval during which a Scheduling Request is sent or pending via the PUCCH;

An interval in which uplink grant for pending HARQ retransmission can occur and data exists in the corresponding HARQ buffer; or

- The PDCCH indicating a new transmission addressed to the C-RNTI of the UE includes a period during which the PDCCH is not received after successful reception of a random access response for the preamble selected by the UE.

5 shows an active period of 3GPP LTE.

If DRX is set, the terminal shall, for each subframe:

If the HARQ RTT Timer expires in the corresponding subframe and the data of the HARQ process is not successfully decoded,

- It can drive drx-Retransmission Timer for the corresponding HARQ process.

- DRX Command If you receive a MAC CE (control element)

- Stop the OnDuration Timer and drx-Inactivity Timer.

- If the drx-Inactivity Timer is discarded or the DRX Command MAC CE is received in the corresponding subframe,

- If Short DRX Cycle is set:

- drx-ShortCycle Run or restart timer and use Short DRX cycle.

- Otherwise:

- Use Long DRX cycle.

- If the drx-ShortCycle timer is discarded in the corresponding subframe:

- Use Long DRX cycle.

- Short DRX Cycle is used and [(SFN * 10) + number of subframes] modulo (shortDRX-Cycle) = (drxStartOffset) modulo (shortDRX-Cycle);

- If a long DRX cycle is used and [(SFN * 10) + number of subframes] modulo (longDRX-Cycle) = drxStartOffset:

- Start the OnDuration Timer.

During the active period, a subframe for the PDCCH-subframe is not required for uplink transmission for half-duplex FDD terminal operation, and the subframe is part of the set measurement gap If not:

- Monitor the PDCCH.

If the PDCCH indicates a DL transmission or a DL assignment is set in the corresponding subframe:

- It drives the HARQ RTT Timer for the corresponding HARQ process.

- Stop the drx-Retransmission Timer for the corresponding HARQ process.

- if the PDCCH indicates a new transmission (DL or UL):

- Drive or restart the drx-Inactivity Timer.

There are two types of DRX cycle: Long DRX cycle and Short DRX cycle. The long DRX cycle of the long cycle can minimize the battery consumption of the UE, and the short DRX cycle of the short cycle can minimize the data transmission delay.

FIG. 6 shows an example of the transition of the DRX cycle.

When an initial transmission is received from the base station, a drx-Inactivity Timer (also referred to as a first timer or an inactivity timer) is started (S610). The terminal continually monitors the PDCCH while the drx-Inactivity Timer is in operation.

If the DRX-Inactivity Timer expires or the DRX command is received from the base station, the UE transitions to the Short DRX Cycle (S620). Then, a drx-shortCycle timer (also referred to as a second timer or a DRX cycle timer) is started. If the Short DRX Cycle is not set in advance, the UE transitions to the Long DRX cycle.

The DRX command may be transmitted as a MAC CE and may be referred to as a DRX indicator indicating a transition to DRX. The DRX Command MAC CE is identified through the LCID (Logical Channel ID) field of the MAC PDU subheader.

The terminal operates in the Short DRX cycle while the drx-shortCycle timer is in operation. When the drx-shortCycle timer expires, the UE transitions to the Long DRX cycle

If the Short DRX Cycle is set in advance, the UE transitions to a short DRX cycle. If the short DRX cycle is not set in advance, it can be transited to the long DRX cycle.

The value of the HARQ RTT Timer is fixed to 8 ms (or 8 subframes), and other timer values such as OnDuration Timer, drx-Inactivity Timer, drx-Retransmission Timer, or mac- . The base station can set the long DRX cycle and the short DRX cycle through the RRC message.

In the above process, the DRX Command MAC CE is a MAC CE used when the BS instructs the UE to transition to the DRX state. As shown in the above process, if the UE receives the DRX Command MAC CE from the base station, it transitions to the Short DRX state if the Short DRX Cycle is set, or to the Long DRX state.

The long DRX cycle and the short DRX cycle are only examples, and an additional DRX cycle can be set.

Meanwhile, as described above, in general, when a base station receives an HARQ NACK signal from a terminal, it performs HARQ retransmission. 7 shows operations of the UE and the base station when an error is found in the DL transmission.

Referring to FIG. 7, the eNB transmits downlink data to the UE (S710). For convenience of explanation, a subframe in which downlink data is transmitted is defined as N. Step S710 is referred to as first downlink data transmission in contrast to the downlink data retransmission (S740) to the terminal UE by the base station eNB, which will be described later.

The UE confirms a reception error of the first downlink data (S720). For example, the UE can confirm a CRC failure for the first downlink data. Here, CRC failure may mean failure of demasking for CRC. As another example of the reception error, a part of the received data may be missing or defective.

If it is determined that the first downlink data is normally received, the UE transmits an HARQ ACK to the eNB. On the other hand, if downlink data is not normally received, e.g., a CRC failure occurs, the UE transmits an HARQ NACK to the eNB (S730). The HARQ ACK and the HARQ NACK are transmitted after the fourth subframe from the subframe in which the downlink data is received, i.e., on the ( N + 4) th subframe.

When the HARQ NACK is received from the UE, the eNB performs retransmission for the first downlink data (S740). In contrast to the downlink initial transmission (S710) to the terminal UE by the above-described base station (eNB), step S740 is referred to as second downlink data transmission. That is, the second downlink data is retransmission data for the first downlink data.

Table 1 below shows the configuration of Semi-Persistent Scheduling (SPS) and DRX in a voice over LTE environment. Other specifications in a voice over LTE environment may refer to 3GPP TS 36.213 (PHY spec), 36.321 (MAC spec) and 36.331 (RRC spec), which were launched in March 2012.

As described above, when the downlink data is normally received, the UE transmits an HARQ ACK to the Node B. 8 is a schematic diagram illustrating a subframe configuration in a case where a mobile station transmits an HARQ ACK to a base station.

According to Table 1, since the Short DRX Cycle is 20ms and the TTI, which is a unit time in which a subframe is transmitted in general, is set to 1ms, one Short DRX Cycle includes 20 subframes as shown in FIG. At this time, the first subframe and the second subframe, that is, the subframe 0 (sf 0) and the subframe 1 (sf 1) correspond to the active period.

The UE monitors the PDCCH in subframe 0 (sf 0). Since the DL / UL grant is performed through the PDCCH, the UE can decode the PDSCH based on the scheduling information included in the PDCCH. The UE determines whether an error has occurred in the received downlink data, and determines whether to transmit an ACK or a NACK to the base station based on whether an error has occurred. In the case of FIG. 8, since the reception error for the downlink data has not occurred, the UE transmits an HARQ ACK through the PUCCH in subframe 4 (sf 4). Then, the terminal operates in a power saving area for a total of 15 ms from the subframe 5 (sf 5) to the subframe 19 (sf 19) in order to reduce power consumption.

FIG. 9 is a schematic diagram illustrating a subframe configuration when a mobile station transmits HARQ NACK to a base station.

As in the case of Fig. 8, subframe 0 (sf 0) and subframe 1 (sf 1) correspond to the activation period. Also, the subframe 8 (sf 8), during which the drx-Retransmission Timer operates, corresponds to the active period. The UE monitors the PDCCH in subframe 0 (sf 0). Also, it is determined whether an error has occurred in the received downlink data, and whether to transmit an ACK or a NACK to the base station based on whether an error has occurred or not is determined. In the case of FIG. 9, since a reception error has occurred with respect to the downlink data, the UE transmits HARQ NACK through the PUCCH in subframe 4 (sf 4). Meanwhile, a power saving area in the case where the UE transmits HARQ NACK to the base station includes a subframe 5 (sf 5) to a subframe 7 (sf 7), a subframe 9 (sf 9) to a subframe 19 sf 19) for a total of 13 ms.

FIG. 10 specifically shows subframe 0 (sf 0) to subframe 4 (sf 4) when the UE transmits HARQ NACK to the base station.

Referring to FIG. 10, the OnDuration Timer operates in subframe 0 (sf 0). That is, the subframe 0 (sf 0) is the On period. The UE monitors the PDCCH in subframe 0 (sf 0). In the subframe 1 (sf 1), the drx-Inactivity Timer operates.

Upon acquiring the PDCCH, i.e. DL grant, in the subframe 0 (sf 0), the UE performs decoding of the PDSCH data. In general, decoding of the PDSCH data proceeds over subframe 0 (sf 0) to subframe 2 (sf 2). When an error occurs in DL transmission, for example, when a CRC failure occurs, the UE generates an HARQ NACK in subframe 2 (sf 2) and encodes the PUCCH. After the PUCCH is encoded, the UE transmits a HARQ NACK through the PUCCH from the subframe 4 (sf 4) to the base station.

As described above, when an error occurs in the DL transmission, for example, when a CRC failure occurs, the UE transmits an HARQ NACK to the Node B, and when the Node B (eNB) receives the HARQ NACK, . However, the NACK transmission of the UE causes the power saving period to be reduced, which may degrade the performance of the UE.

Accordingly, the present invention provides a HARQ performance method that does not transmit HARQ NACK even if an error occurs in a DL transmission when an SPS is activated in a connected DRX state.

FIG. 11 shows operations of a terminal and a base station according to an embodiment of the present invention when an error is found in the DL transmission.

Referring to FIG. 11, the eNB transmits downlink data to the UE (S1110). For convenience of explanation, a subframe in which downlink data is transmitted is defined as N. (Step S1110) is referred to as first downlink data transmission in contrast to the downlink data retransmission (S1140) to the terminal UE by the base station (eNB), which will be described later.

The UE confirms a reception error of the first downlink data (S1120). For example, the UE can confirm a CRC failure for the first downlink data.

If it is determined that the first downlink data is normally received, the UE transmits an HARQ ACK to the eNB. The HARQ ACK is transmitted after the fourth subframe from the subframe in which the downlink data is received, i.e., on the ( N + 4) th subframe. On the other hand, if the downlink data is not normally received, for example, if a CRC failure occurs, the UE does not take any action for retransmission of downlink data (S1130). That is, the UE does not transmit the HARQ NACK to the eNB.

If the HARQ ACK is not received from the UE, the eNB performs retransmission for the first downlink data (S1140). In contrast to the downlink initial transmission (S1110) to the terminal UE by the base station (eNB), the step S1140 is referred to as a second downlink data transmission. That is, the second downlink data is retransmission data for the first downlink data. As described above, since the UL ACK / NACK timing for the DL data is the ( N + 4) th subframe, if the HARQ ACK is not received in the ( N + 4) th subframe, It determines that the first downlink data is not received, and performs the second downlink data transmission. The second downlink data transmission may be performed at a predetermined time between the UE and the BS. For example, the second downlink data transmission may be performed in the N + 4 + Kth subframe. That is, the UL ACK / NACK timing for the DL data may be performed in the Kth subframe. At this time, K may be set to 4. If K is set to 4, the second downlink data transmission is performed in the ( N + 8) th subframe. Hereinafter, for convenience of explanation, it is assumed that K is set to 4.

12 is a schematic diagram showing a subframe structure according to an embodiment of the present invention when an error is found in the DL transmission.

As in the case of FIGS. 8 and 9, the subframe 0 (sf 0) and the subframe 1 (sf 1) correspond to the active period. Also, the subframe 8 (sf 8), during which the drx-Retransmission Timer operates, corresponds to the active period. The UE receives the PDCCH through subframe 0 and determines whether to transmit an ACK to the base station based on whether an error has occurred in the DL transmission. In the case of FIG. 12, since an error has occurred in the DL transmission, the UE does not transmit the HARQ ACK using the PUCCH in subframe 4 (sf 4). Therefore, according to an embodiment of the present invention, a power saving area is divided into subframes 3 (sf 3) to 7 (sf 7), subframes 9 (sf 9) to sf 19 ). That is, since the power saving period can be set to start from the subframe 3 (sf 3), a power saving period corresponding to two subframes can be additionally secured. In this case, a total power saving interval of 15 ms is secured.

Meanwhile, according to Table 1, the HARQ RTT Timer can be set to 8 ms and the drx-Retransmission Timer can be set to 1 ms. As described above, the HARQ RTT Timer defines a period during which the UE monitors the PDCCH while expecting DL retransmission, and the drx-Retransmission Timer defines a period during which the UE monitors continuous PDCCH while expecting DL retransmission . If the HARQ RTT Timer is discarded in the corresponding subframe and the data of the HARQ process is not successfully decoded, the UE can drive the DRX-Retransmission Timer for the HARQ process. Therefore, if an error is found in the initial DL transmission as in the case of FIG. 12, the UE drives the DRX-Retransmission Timer after expiration of the HARQ RTT Timer. The terminal monitors the PDCCH for DL retransmission from the base station while the drx-Retransmission Timer is in operation. For example, when the drx-Retransmission Timer is driven in subframe 8 (sf 8), the UE can monitor the PDCCH for DL retransmission from the base station in subframe 8 (sf 8).

FIG. 13 shows subframe 0 (sf 0) to subframe 4 (sf 4) in the case of FIG. 12 in more detail.

Referring to FIG. 13, the OnDuration Timer operates in subframe 0 (sf 0). That is, the subframe 0 (sf 0) is the On period. The UE monitors the PDCCH in subframe 0 (sf 0). In the subframe 1 (sf 1), the drx-Inactivity Timer operates. Upon acquiring the PDCCH, i.e. DL grant, in the subframe 0 (sf 0), the UE performs decoding of the PDSCH data. The decoding of the PDSCH data may proceed from subframe 0 (sf 0) to subframe 2 (sf 2). When an error occurs in the DL transmission, for example, when a CRC failure occurs, the UE does not perform any procedure for HARQ ACK or HARQ NACK under subframe 3 (sf 3). Therefore, the power saving period can be started from the subframe 3 (sf 3).

FIG. 14 shows a method of receiving data in a terminal in a wireless communication system according to an embodiment of the present invention.

The terminal receives the downlink data from the base station through the first subframe (S1410). The first subframe may mean subframe 0 (sf 0) in the embodiment of Figs. 11-13. The UE can monitor the PDCCH including the information on the resource allocation of the downlink data in the first subframe. As described above, the PDCCH monitor can be performed based on the OnDuration Timer.

The MS determines whether a reception error has occurred in the received downlink data (S1420). If a reception error occurs, the terminal can wait without taking any action to retransmit the downlink data. That is, it is possible to operate as a power saving period up to the subframe in which the retransmission data is received. A subframe in which the retransmission data is received may be indicated by an HARQ RTT Timer. For example, when the retransmission data is transmitted 8 ms after the downlink data, the HARQ RTT Timer is set to 8 ms. On the other hand, the downlink data reception error can be confirmed based on whether CRC failure has occurred or not.

If a reception error occurs, the terminal receives the retransmission data transmitted after a predetermined time (S1430). The predetermined time may be a predetermined value or a value negotiated between the terminal and the base station in the initial access procedure. For example, it may be determined that the retransmission data is transmitted through a subframe located after 8 subframes from a subframe in which the predetermined time is 8 ms, i.e., the downlink data is transmitted. The terminal can drive the drx-Retransmission Timer for this purpose. The drx-Retransmission Timer indicates an interval for monitoring a PDCCH including information on resource allocation of retransmission data.

Meanwhile, the downlink data to which the present invention is applied is preferably based on a voice over LTE (Long Term Evolution) system. This is because the characteristic of voice data is transmitted every predetermined period and is insensitive to loss, so that transmission and reception of voice data are periodically performed by the SPS.

15 is a block diagram illustrating a terminal in which an embodiment of the present invention is implemented.

The terminal 50 includes a processor 51, a memory 52, and a radio frequency unit 53. The memory 52 is connected to the processor 51 and stores various information for driving the processor 51. [ The RF unit 53 is connected to the processor 51 to transmit and / or receive a radio signal.

The processor 51 implements the proposed functions, procedures and / or methods. For example, in the embodiment of Figs. 11-13, the operation of the terminal may be implemented by the processor 51. Fig.

The processor may comprise an application-specific integrated circuit (ASIC), other chipset, logic circuitry and / or a data processing device. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The RF unit may include a baseband circuit for processing the radio signal. When the embodiment is implemented in software, the above-described techniques may be implemented with modules (processes, functions, and so on) that perform the functions described above. The module is stored in memory and can be executed by the processor. The memory may be internal or external to the processor and may be coupled to the processor by any of a variety of well known means.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders or simultaneously . In addition, those skilled in the art will recognize that the steps depicted in the flowchart illustrations are not exclusive, that other steps may be included, or that one or more steps in the flowchart may be deleted without affecting the scope of the present invention. .

Claims (12)

A method for receiving data by a terminal in a wireless communication system,
Receiving downlink data from a base station through a first subframe;
Confirming whether a reception error has occurred in the downlink data; And
Receiving retransmission data of the downlink data when a reception error occurs in the downlink data,
Wherein the retransmission data is received via a second sub-frame and the second sub-frame is transmitted after a predetermined time from the first sub-frame. The method according to claim 1,
Wherein the downlink data is based on a voice over LTE (Long Term Evolution) system. The method according to claim 1,
Wherein whether a reception error occurs in the downlink data is determined based on whether a cyclic redundancy check (CRC) failure of the downlink data occurs. The method according to claim 1,
Wherein the retransmission data is received after a point in time indicated by an HARQ RTT Timer. 5. The method of claim 4,
And the HI ACU ality timer is set to 8 ms. The method according to claim 1,
The step of receiving the downlink data comprises:
Driving an OnDuration Timer indicating an interval for monitoring a Physical Uplink Control Channel (PDCCH) including information on resource allocation of the downlink data; And
And monitoring the PDCCH based on the on-duration timer. The method according to claim 1,
The step of receiving the retransmission data
Driving a DRX-Retransmission Timer (DRX-Retransmission Timer) indicating a period for monitoring a Physical Uplink Control Channel (PDCCH) including information on resource allocation of the retransmission data; And
And monitoring the PDCCH based on the dial X-retransmission timer. A terminal in a wireless communication system,
A radio frequency (RF) unit for transmitting and receiving a radio signal; And
And a processor coupled to the RF unit to implement a wireless interface protocol, the processor comprising:
Receives downlink data from a base station through a first subframe,
Whether or not a reception error has occurred in the downlink data,
Wherein the retransmission data is received through a second subframe, and the second subframe is retransmitted from the first subframe to a predetermined subframe when a reception error for the downlink data occurs. Lt; RTI ID = 0.0 > time. ≪ / RTI > 9. The method of claim 8,
Wherein the downlink data is based on a voice over LTE (Long Term Evolution) system. 9. The method of claim 8,
Wherein whether a reception error occurs in the downlink data is determined based on whether a cyclic redundancy check (CRC) failure of the downlink data occurs. 9. The method of claim 8,
Wherein the retransmission data is received after a point of time indicated by the HARQ RTT Timer. 12. The method of claim 11,
And the HI ACU ality timer is set to 8 ms.

Images