KR20200112668A - Method of retransmission for downlink transmission in wireless communicaiton system and apparatus for the same - Google Patents

Abstract

Disclosed are a retransmission method for downlink transmission in a wireless communication system and an apparatus therefor. According to an embodiment of the present invention, a retransmission method for downlink transmission comprises the steps of: receiving a plurality of feedback signals corresponding to a transmission error from a plurality of terminals corresponding to point-to-multipoint transmission; generating retransmission data corresponding to the plurality of feedback signals; and transmitting the retransmission data to the plurality of terminals.

Description

Retransmission method for downlink transmission in a wireless communication system, and apparatus therefor {METHOD OF RETRANSMISSION FOR DOWNLINK TRANSMISSION IN WIRELESS COMMUNICAITON SYSTEM AND APPARATUS FOR THE SAME}

The present invention relates to a hybrid automatic repeat request (HARQ) technology, and in particular, to a retransmission technology applicable to a multicast/broadcast (point-to-multipoint) downlink service.

The wireless communication system uses hybrid automatic repeat request (HARQ) technology as one of technologies for improving the reliability of data transmission. This technology continues to be used in 5G NR (New Radio) following 3G and 4G LTE (Long Term Evolution). In the HARQ scheme, after data is transmitted through a downlink (DL) or an uplink (UL), if data decoding fails, additional retransmission is performed to increase the probability of successful data decoding at the receiving end. In 3G, 4G LTE, and 5G NR, HARQ is supported for DL/UL point-to-point unicast data transmission.

In a wireless communication system, data to be transmitted through a physical channel from the physical layer comes down from a higher layer (MAC layer) in the form of a transport block (TB), and this TB is a smaller unit, a code block. ; After splitting into CB), each of them undergo channel encoding. CBs encoded through channel encoding are concatenated again and transmitted through a physical channel.

In 3G, 4G LTE, and 5G NR, reception success/failure is basically determined in units of TB to determine whether to retransmit, and in case of downlink data transmission, if decoding is successfully performed, an ACK signal is sent, otherwise, a NACK signal is sent. Feedback. In this case, the receiving end may determine whether or not the decoding succeeds in units of CB by performing channel decoding after receiving the data. After channel decoding, when an error is detected in at least one CB or an error is detected in the TB among CBs constituting the TB, retransmission is performed in units of TB by feeding back a NACK signal.

Since the transmitting end does not know the CB in which the decoding failed and an error occurred among the transmitted one or more CBs, additional bits that can increase the decoding success probability for each CB for all the CBs constituting the TB are transmitted. In this case, it can be seen that resources for transmitting additional bits for a CB that succeed in decoding without additional bits are wasted.

In 5G NR, for resource-efficient retransmission in case of unicast transmission, a method of feeding back decoding success/failure in units of code block groups (CBG) smaller than TB and larger than CB is included in the standard. , This is called a CBG-based HARQ scheme. Using the CBG HARQ scheme, it is possible to efficiently utilize physical layer resources by reducing the amount of additional bit transmission associated with CBs successfully decoded. However, there is a disadvantage in that control information transmitted through the feedback channel increases, and resource waste still occurs because CGs in which errors occur in the CBG cannot be accurately known.

Separately, in the case of simultaneous transmission of the same data to a plurality of terminals, the same data is transmitted to multiple terminals simultaneously using the same resource rather than a unicast transmission in which separate resources are allocated to each terminal to transmit data. Cast/broadcast (point-to-multipoint) transmission is efficient. This multicast/broadcast transmission method is called MBMS (Multimedia Broadcast Multicast Services) of 3G and eMBMS (evolved MBMS)/Further evolved MBMS (FeMBMS) technology of 4G LTE, and MBMS is largely MBSFN (Multicast Broadcast Single Frequency Network) method. And SC-PTM (Single Cell Point To Multipoint).

Until 4G LTE, this MBMS technology operated in a downlink-only manner without the help of an uplink (UL), and for this reason, the HARQ technique based on ACK/NACK feedback through the uplink was not used.

An object of the present invention is a multicast/broadcast (point-to-multipoint) transmission environment in which the same data is simultaneously transmitted to a plurality of terminals using the same resource, or in a unicast transmission environment, a hybrid automatic retransmission request ( HARQ) service is provided.

In addition, an object of the present invention is to generate optimal retransmission data by comprehensively considering the transmission environment of multiple terminals in a multicast/broadcast (point-to-multipoint) transmission environment, and provide the generated retransmission data to multiple terminals. Is to do.

In addition, an object of the present invention is to transmit/receive a control signal for generating optimal retransmission data in a multicast/broadcast (point-to-multipoint) transmission environment by comprehensively considering the transmission environment of multiple terminals. .

The retransmission method for downlink transmission according to the present invention for achieving the above object includes a plurality of feedbacks corresponding to transmission errors from a plurality of terminals corresponding to point-to-multipoint transmission. Receiving signals; Generating retransmission data corresponding to the plurality of feedback signals; And transmitting the retransmission data to the plurality of terminals.

In this case, the step of generating the retransmission data may generate the retransmission data which increases the decoding probability of a plurality of code blocks included in the transmission block irrespective of the code block in which the transmission error occurs. In this case, the plurality of code blocks may be all code blocks included in the transport block.

In this case, the step of generating the retransmission data includes generating additional code blocks by using physical layer code block level coding (CB-Level FEC) in which each of the plurality of code blocks is an information symbol. step; And generating the retransmission data using bits capable of reconstructing the additional code blocks.

In this case, each of the additional code blocks may correspond to each of the parity symbols generated by the physical layer code block level coding.

In this case, each of the additional code blocks may have the same length as the length of the longest code block among the plurality of code blocks.

In this case, the retransmission data may be used to recover a code block corresponding to the transmission error by using code block level decoding performed including decoding results of previously transmitted code blocks.

In this case, the code block level decoding is performed on a binary erasure channel (BEH) in which code blocks and additional code blocks corresponding to the transmission failure are lost. It can be decryption.

In this case, the code block corresponding to the transmission error may be recovered using code blocks that have been successfully decoded.

In this case, the plurality of feedback signals may include the number of code blocks corresponding to the transmission error.

In this case, the retransmission method for downlink transmission may further include transmitting a control signal corresponding to the retransmission data to the plurality of terminals. In this case, the control signal may include information corresponding to the number of the additional code blocks.

In this case, a plurality of terminals may calculate the number of the additional code blocks using MCS information and resource information corresponding to the retransmission data.

In this case, generating the retransmission data may include determining a retransmission group using the plurality of feedback signals; And generating the retransmission data by using additional bits for each of the code blocks included in the retransmission group. In this case, the retransmission group may be a transport block or a code block group.

In addition, the base station of the wireless communication system according to an embodiment of the present invention, at least one processor; An RF unit controlled by the processor and transmitting/receiving radio signals; And a memory connected to the processor and storing at least one instruction executed by the processor. In this case, the at least one command receives a plurality of feedback signals corresponding to a transmission error from a plurality of terminals corresponding to point-to-multipoint transmission, and the plurality of feedback signals Generates retransmission data corresponding to the retransmission data, and transmits the retransmission data to the plurality of terminals.

In this case, the retransmission data may be data that increases the decoding probability of a plurality of code blocks included in the transmission block irrespective of the code block in which the transmission error occurs.

At this time, the retransmission data may be generated using bits capable of reconstructing additional code blocks. In this case, the additional code blocks may be generated using physical layer code block level coding (CB-Level FEC) in which each of the plurality of code blocks is an information symbol.

In this case, each of the additional code blocks may correspond to each of the parity symbols generated by the physical layer code block level coding.

In this case, each of the additional code blocks may have the same length as the length of the longest code block among the plurality of code blocks.

In addition, the terminal of the wireless communication system according to an embodiment of the present invention, at least one processor; An RF unit controlled by the processor and transmitting/receiving radio signals; And a memory connected to the processor and storing at least one instruction executed by the processor. In this case, the at least one command transmits a feedback signal corresponding to a transmission error of the first transmitted data, receives retransmission data corresponding to the feedback signal, and uses the retransmission data to correspond to the transmission error. The code block is restored, and the retransmission data is data that increases the decoding probability of a plurality of code blocks included in the transmission block irrespective of the code block in which the transmission error occurs.

At this time, the retransmission data may be generated using bits capable of reconstructing additional code blocks. In this case, the additional code blocks may be generated using physical layer code block level coding (CB-Level FEC) in which each of the plurality of code blocks is an information symbol.

In this case, each of the additional code blocks may correspond to each of the parity symbols generated by the physical layer code block level coding.

According to the present invention, resource-efficient hybrid automatic retransmission request (HARQ) service is possible in a point-to-multipoint transmission environment or a unicast transmission environment in which the same data is simultaneously transmitted to a plurality of terminals using the same resource.

In addition, the present invention may generate optimal retransmission data (retransmission packet) by comprehensively considering a transmission environment of a plurality of terminals in a point-to-multipoint transmission environment, and provide the generated retransmission data to a plurality of terminals.

In addition, the present invention may generate optimal retransmission data by comprehensively considering the transmission environment of a plurality of terminals in a point-to-multipoint transmission environment.

1 is a block diagram showing a transport block processing process according to an embodiment of the present invention.
2 is a block diagram showing a retransmission process according to an embodiment of the present invention.
3 is a diagram showing an example in which the number or location of code blocks in which a decoding error occurs in a plurality of terminals receiving the same transport block is different from each other.
4 is a diagram illustrating an example in which retransmission is performed based on a code block group according to an embodiment of the present invention.
5 is a block diagram showing a retransmission process based on block level coding of a physical layer code according to an embodiment of the present invention.
6 is a diagram illustrating an example of block-level coding of a physical layer code as a parity check matrix.
7 is a flowchart illustrating an example of a case in which a terminal calculates the number of additional code blocks from an MCS.
8 is a flowchart illustrating an example in which two retransmission schemes are selectively used.
9 is a flowchart illustrating an example of a retransmission method for downlink transmission according to an embodiment of the present invention.
10 is a flowchart illustrating an example of a method of receiving a retransmission signal according to an embodiment of the present invention.
11 is a block diagram showing a wireless communication system in which an embodiment of the present invention is implemented.

The present invention will be described in detail with reference to the accompanying drawings as follows. Here, repeated descriptions, well-known functions that may unnecessarily obscure the subject matter of the present invention, and detailed descriptions of configurations are omitted. Embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer explanation.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In particular, the present invention is a case in which at least one terminal feeds back a NACK signal during point-to-multipoint transmission including point-to-point transmission, hybrid It includes a method of generating retransmission data (retransmission packet) to be transmitted through a Hybrid Automatic Repeat Request (HARQ) process, a method of transmitting/receiving a control signal related thereto, and operations of a base station and a terminal associated therewith.

1 is a block diagram showing a transport block processing process according to an embodiment of the present invention.

Referring to FIG. 1, it can be seen that a physical layer transport block commonly based on 3G, 4G LTE, and 5G NR standards is divided into code blocks.

That is, the TB CRC addition unit 110 adds CRC (cyclical redundancy check) bits to a transport block (TB) provided from an upper layer, and the CB division and CRC addition unit 120 transmits the CRC bits added. The block is divided into code blocks having a length shorter than that of the transport block, and CRC bits are added to each of the divided code blocks. In this case, the CRC bits added to the transport block and the CRC bits added to the code block may be used at the receiving end to detect errors in the transport block or code block.

Physical layer channel coding is performed in units of code blocks. In this case, the lengths of the divided code blocks may be different.

That is, channel coding is performed in units of code blocks by the channel coding unit 130. Each of the code blocks may be independently channel-coded at the physical layer. In this case, the used channel coding may be a turbo code for 3G and 4G LTE, and a low-density parity-check code (LDPC) for 5G NR. Encoded code blocks (encoded CBs) generated through channel coding have a longer length than code blocks.

The buffer 140 stores channel-coded code blocks.

After channel coding, only as many bits as the number of bits used for initial transmission calculated from physical layer resources used for transmission and MCS (Modulation and Coding Scheme) among the bits included in the coded code block are selected, and this process is rated. This is called rate matching. That is, bits necessary for transmission are selected by the rate matching unit 150. The rate matching unit 150 may conceptually store codeword bits generated through channel encoding in a circular buffer, and perform a process of fetching as many bits as necessary for transmission, and this process is CBRM ( It is also referred to as circular buffer rate matching).

The code block combiner 160 concatenates selected bits through rate matching for each code block, and the combined bits are transmitted through a physical channel through a modulation process.

At the receiving end, a channel decoding process is performed for each code block, and tabular decoding or LDPC decoding may be performed.

When an error is found in one or more code blocks through the code block CRC at the receiving end or an error is found in the transport block through the transport block CRC, a decoding error may be declared and a NACK signal is fed back to request retransmission.

When the transmitting end receives the NACK feedback signal, it is possible to increase the probability that the code block is successfully decoded at the receiving end by configuring and transmitting additional bits from codeword bits generated through channel encoding and stored in the buffer.

In retransmission, similar to the initial transmission, additional bits to be transmitted are configured from the bits stored in the buffer for each code block, and these additional bits are also concatenated and transmitted. In this way, it may be expressed as a redundancy version (RV), which determines positions of bits to be retrieved from among codeword bits stored in a buffer during initial transmission or retransmission. 3G, 4G LTE, and 5G NR are all RVs, and four positions are allowed, and the RV value at the time of initial transmission and retransmission may be different, and the RV value is a part of downlink control information (DCI) from the base station to the terminal. Can be delivered to.

2 is a block diagram showing a retransmission process according to an embodiment of the present invention.

Referring to FIG. 2, when a retransmission request for an initial transmission occurs, it can be seen that blocks 210 and 220 for processing the retransmission request are included.

2, a TB CRC adding unit 110, a CB division and CRC adding unit 120, a channel coding unit 130, a buffer 140, a rate matching unit 150, and a code block combining unit 160 Has already been described with reference to FIG. 1.

Similar to the initial transmission, the retransmission bit selection unit 210 selects additional bits to be retransmitted from the bits stored in the buffer for each code block.

The retransmission bit combiner 220 concatenates the selected additional bits, and the combined bits are retransmitted through a physical channel through a modulation process.

In particular, in 5G NR, the retransmission operation as shown in FIG. 2 may be performed in units of all code blocks (CBs) belonging to the transport block (TB) (transport block units), and is smaller than the transport block (TB). It may be performed in units of a code block group (CBG) that is a unit greater than or equal to (CB). CBG unit retransmission is a code block group (CBG) unit consisting of one or more code blocks, when the terminal feeds back whether the decoding was successful in the form of ACK / NACK, the base station based on this, all codes constituting the CBG including the decoding error Only the extra bits for the blocks (CBs) can be retransmitted. In this case, in order to support retransmission in units of CBG, a CBG transmission information (CBGTI) field and a CBG flushing out information (CBGFI) field may be included in the DCI.

In particular, since the MBMS technology of 5G NR may include uplink (UL) signal transmission for MBMS, design of a resource-efficient HARQ scheme for point-to-multipoint transmission using 5G NR is very important.

That is, in point-to-multipoint transmission such as multicast/broadcast, much more various situations may occur than unicast, and HARQ service needs to be provided in consideration of such various situations. For example, in multicast/broadcast transmission, the physical channel between the base station and the terminal may vary according to the physical location of the terminal in the cell, and similarly, the magnitude or type of interference experienced by the terminal may vary. Therefore, in such an environment, a code block in which a decoding error occurs may be different for each terminal. The technical idea of the present invention is that when a plurality of terminals receiving a multicast/broadcast transmission signal detect decoding errors for different code blocks, the base station can generate an optimal retransmission signal.

3 is a diagram showing an example in which the number or location of code blocks in which a decoding error occurs in a plurality of terminals receiving the same transport block is different from each other.

Referring to FIG. 3, a transport block including 8 code blocks (CB 0, CB1, CB2, CB3, CB4, CB5, CB6, CB7) through broadcasting transmission from a base station through first transmission is You can see that it is being sent. That is, in the example shown in FIG. 3, the same transport block is simultaneously transmitted to a plurality of terminals through the same resource, and the number or location of code blocks (CBs) in which a decoding error occurs may be different for each terminal. In FIG. 3, a code block in which a decoding error occurs is indicated by an X.

Depending on the embodiment, retransmission may be performed in units of a code block group (CBG) during point-to-multipoint transmission. At this time, the terminal receiving the point-to-multipoint transmission explicitly indicates the code block group (CBG) including the code block (CB) that failed to decode based on the code block group (CBG) when a decoding error occurs. Can be delivered to the base station. In this case, a signal fed back by the terminal for HARQ may include bits identifying a code block group (CBG) in which a decoding error has occurred. For example, a signal fed back by the terminal for HARQ may be composed of a number of bits corresponding to the number of code block groups, and a code block group composed of only code blocks that succeeded in decoding is indicated as 0, and a code block that fails to decode The included code block group may be represented by 1.

When the base station receives the ACK/NACK feedback signal in units of code block groups from multiple terminals that have received the point-to-multipoint signal, the base station transmits a packet to be retransmitted in a point-to-multipoint method or a point-to-point method. Configurable.

When the point-to-multipoint method is used, all CBGs in which a decoding error occurs in one or more terminals are included in the retransmission target packet, and the base station transmits the retransmission packet as additional parity bits for CBs included in the corresponding CBGs. It can be configured and retransmitted in a point-to-multipoint method.

4 is a diagram illustrating an example in which retransmission is performed based on a code block group according to an embodiment of the present invention.

4, a NACK signal for a code block group (CBG 3) is fed back from a terminal (UE A), and a NACK signal for a code block group (CBG 1) is fed back from a terminal (UE B, UE C). I can see that it is.

In the example shown in FIG. 4, the base station may configure and transmit retransmission bits for code blocks included in the code block group CBG 1 and the code block group CBG 3 upon retransmission.

In this case, code block groups included in the retransmission packet may be explicitly notified to the UE by using the CBGTI field included in the DCI for configuring the physical resource through which the retransmission packet is transmitted to the UE. After receiving the retransmission packet in a point-to-multipoint manner, the UE may decode the code block that fails to decode once again by additionally using only a portion including the code block that the UE fails to decode.

Depending on the embodiment, during point-to-multipoint retransmission, additional bits for increasing the decoding probability of a plurality of code blocks may be transmitted instead of transmitting additional bits for increasing a decoding success probability for each code block. . In this case, the plurality of code blocks may be all code blocks in the transport block, but may be some preset code blocks in the transport block.

That is, according to such an embodiment, even if the code block CB in which an error occurs in the transport block TB is not accurately known, it is useful for decoding the corresponding code block, and a code block in which an error occurs in a plurality of terminals. When the positions of are different, decoding errors of different code blocks can be recovered by using the same additional bit.

To this end, after parity symbols generated through encoding having one code block as one information symbol are generated as additional code blocks, Binary bits can be transmitted. In this case, coding is performed by considering a code block composed of a plurality of binary bits as one symbol. Encoding using binary bits constituting a code block as information bits, such as channel coding such as turbo coding or LDPC coding described with reference to FIG. 1, is performed by considering each of the code blocks as one information symbol. The latter is called physical layer code block level coding (CB-level FEC or CBL-FEC) to distinguish coding. In particular, the physical layer code block level coding is different from the packet-based coding performed in an upper layer such as an application layer in that it is performed by considering each of the code blocks of the physical layer as one information symbol.

At this time, the physical layer code block level coding may take the form of a systematic code, and for this purpose, bits capable of restoring the code blocks generated from the transport block are transmitted in the first transmission, and retransmitted. If necessary, bits capable of restoring additional code blocks generated through physical layer code block level coding may be transmitted.

In this case, the physical layer code block level coding (CBL-FEC) may be applied to a code block before or after the CRC bits are attached.

The additional code blocks generated by the physical layer code block level coding are also coded through turbo coding or LDPC coding for each code block, like the existing code blocks, and then transmitted through a physical channel.

5 is a block diagram showing a retransmission process based on block level coding of a physical layer code according to an embodiment of the present invention.

Referring to FIG. 5, it can be seen that a block 510 for block-level encoding of a physical layer code and blocks 530, 540, 550, and 560 for retransmission are included.

5, a TB CRC addition unit 110, a CB division and CRC addition unit 120, a channel coding unit 130, a buffer 140, a rate matching unit 150, and a code block combining unit 160 Has already been described with reference to FIG. 1.

The physical layer code block level encoding unit 510 performs physical layer code block level encoding performed by considering each of the code blocks as one information symbol. As a result of performing physical layer code block level encoding, parity symbols are generated, and the generated parity symbols correspond to additional code blocks.

Since the physical layer code block level encoding is systematic encoding, bits corresponding to the code blocks among the physical layer code block level encoding results may be provided to the channel coding unit 130 at the time of initial transmission. Bits corresponding to additional code blocks among the results of the physical layer code block level encoding may be provided to the channel coding unit 530.

The channel coding unit 530 differs only in that the target of channel coding is bits corresponding to the additional code block, and the same operation as the channel coding unit 130 is performed. However, the channel coding unit 530 may perform channel coding in the same manner as the channel coding unit 130 or may perform channel coding in a different manner.

The buffer 540 stores bits corresponding to the channel-coded additional code blocks.

The rate matching unit 550 selects bits necessary for transmission. In this case, an MCS (MCS ₂ ) different from the MCS (MCS ₁ ) applied to the rate matching unit 150 may be applied to the rate matching unit 550.

The retransmission bit combiner 560 concatenates the selected additional bits, and the combined bits are retransmitted through a physical channel through a modulation process.

Hereinafter, the physical layer code block level coding will be described in more detail.

6 is a diagram illustrating an example of block-level coding of a physical layer code as a parity check matrix.

Referring to FIG. 6, a result of the physical layer code block level coding using ₆ code blocks (s ₁ , s ₂ , s ₃ , s ₄ , s ₅ , s ₆ ), 4 additional code blocks (p ₁ , It can be seen that p ₂ , p ₃ , p ₄ ) are generated.

In the example illustrated in FIG. 6, each of information symbols corresponds to each of code blocks CB generated from a transport block TB. In addition, each of the parity symbols corresponds to each of the additional code blocks generated by the physical layer code block level coding.

The parity check matrix illustrated in FIG. 6 represents a relationship between information symbols and parity symbols. After generating parity symbols by the physical layer code block level coding, the relationship between the code blocks and the additional code blocks is determined from the relationship between the information symbols and the parity symbols.

In FIG. 6, s _i denotes an i-th code block, and p _j denotes a j-th additional code block. Since the code block and the additional code block are each long binary vector, mod2 addition of symbols in FIG. 6 may actually correspond to component-wise mod2 addition between binary vectors.

At this time, if the lengths of the code blocks generated from the transport block are different, mod2 addition is performed after matching the length by padding a short code block with zeros based on the longest code block. I can.

As a result, each of the additional code blocks may have the same length as the longest code block among the code blocks.

In FIG. 6, the physical layer code block level coding defined by the parity check matrix is exemplified, but the physical layer code block level coding is a binary linear code including LDPC code, non-binary RS code, Raptor code, and non-binary Raptor-Q code. A variety of encodings can be used.

After receiving the retransmission packet, the receiver (terminal) first performs turbo decoding or LDPC decoding to decode the additional code blocks, and then performs code block level decoding (CBL-FEC decoding) including the decoding result of the first transmitted code blocks. ) Can be performed.

Code block level decoding may be decoding a code block level code in which code blocks and additional code blocks are information symbols and parity symbols, respectively, in a binary erasure channel (BEC). In this case, code blocks in which an error occurs during channel decoding, such as turbo decoding or LDPC decoding, and additional code blocks are processed as loss, and code block level decoding may be performed.

In the case of point-to-multipoint transmission, code blocks processed as loss and additional code blocks may be different for each terminal.

If there is a code block in which a decoding error has occurred after the initial transmission, when information symbols corresponding to the code block are recovered through code block level decoding on a binary loss channel (BEC), the code block in which the error has occurred is decoded. It can be recovered by using the code blocks that succeeded. For example, a code block in which an error has occurred may be generated through component-wise mod2 addition of one or more code blocks successfully decoded.

As a result, even if the code blocks in which the error occurs are different for each terminal, an additional code block can be commonly applied to the code blocks in error through code block level decoding.

As described above, additional code blocks generated through physical layer code block level coding may be encoded using a modulation and coding scheme (MCS) different from code blocks generated from a transport block (TB).

The number of additional code blocks generated through physical layer code block level encoding and the MCS (MCS ₂ ) applied to the additional code block are the number of first transmitted code blocks, the number of terminals simultaneously received through point-to-multipoint And the amount of allocated radio resources. At this time, the MCS (MCS ₂ ) applied to the additional code block is set to be more robust (lower MCS index, lower spectral efficiency) than the MCS (MCS ₁ ) applied to the code block, so that the decoding success probability of the additional code block is reduced. You can increase it.

Hereinafter, a UL feedback signal and a DL control signal for retransmission based on physical layer code block level coding will be described.

In order for the UE to identify the number of additional code blocks included in the retransmission packet, the following two methods can be used.

Method 1) The base station explicitly transmits the modulation order used in the retransmission packet and the number of additional code blocks to the terminal through DCI.

Method 2) When the base station transmits MCS information to the terminal, the terminal checks the modulation order from the MCS, derives a virtual TBS (Transport Block Size) of the retransmission packet from the MCS, and calculates the number of additional CBs using this. .

In retransmission based on physical layer code block level coding, it is not necessary to transmit the redundancy version (RV) field required in the existing retransmission method. In the case of using method 1), MCS indexes reserved in the MCS index table of 3GPP TS 38.214 can be used to inform the terminal of the used modulation order. In addition, in order to limit the number of bits for expressing the number of additional code blocks, the number of possible additional code blocks may be limited to several. For example, the number of bits for expressing the number of additional code blocks may be set equal to the number of bits used in the RV field.

In the case of using method 2), an MCS index that is not reserved in the MCS index table of 3GPP TS 38.214 as an MCS index included as part of the DCI must be used, and the UE determines the virtual TBS from the allocated resources and the number of layers and the MCS index. The number of additional code blocks included during retransmission can be derived by dividing the derived virtual TBS by the length of the code block derived at the first transmission.

In this case, if x is not an integer by dividing the derived virtual TBS by the length of the first transmitted code block, the base station and the terminal are to derive the number of additional code blocks in the form of floor(x) or ceiling(x). Can be promised in advance. In this case, floor(x) is the largest integer not greater than x, and ceiling(x) is the smallest integer not less than x.

7 is a flowchart illustrating an example of a case in which a terminal calculates the number of additional code blocks from an MCS.

Referring to FIG. 7, upon retransmission, the base station transmits an MCS to the terminal through DCI (S710).

The terminal receiving the MCS derives a virtual TBS from the number of allocated resources and layers, such as the number of resource blocks (RBs), and the MCS index (S720).

The UE derived the virtual TBS divides the derived TBS by the length of the CB derived at the time of initial transmission (S730).

As described above, when a value obtained by dividing the derived TBS by the length of a CB derived at the time of initial transmission is an integer, it may be used as the number of additional CBs as it is.

If a value obtained by dividing the derived TBS by the length of the CB derived at the time of initial transmission is not an integer, the following step (S740) may be performed.

The terminal calculates the number of additional code blocks by using the value (x) obtained by dividing the TBS by the length of the CB derived at the first transmission (S740).

In this case, in step S740, the number of additional code blocks may be calculated using floor(x) or ceiling(x).

When the physical layer code block level coding is used, in addition to the method of sending a NACK signal in units of a transport block (TB) or in units of a code block group (CBG) when a decoding error occurs at the receiving end, the number of code blocks with a decoding error You can give feedback. In this case, the base station may configure a retransmission packet by selecting a suitable number of additional code blocks after receiving all the number of code blocks in which a decoding error has occurred from a plurality of terminals. In this case, the number of additional code blocks included in the retransmission packet may be obtained based on a terminal having the largest number of code blocks in which a decoding error occurs among a plurality of terminals.

Hereinafter, an embodiment in which transmission block (TB) based retransmission, code block group (CBG) based retransmission, and physical layer code block level coding based retransmission methods are selectively used during point-to-multipoint transmission will be described. In this case, point-to-point retransmission and point-to-multipoint retransmission may be selectively used for retransmission.

The physical layer code block level coding-based retransmission method can be used with other retransmission methods, and one of the various retransmission methods is the area broadcasted during point-to-multipoint transmission, the number of terminals simultaneously received, and feedback. It may be selected based on the number/ratio of NACK signals. In addition, in the case of supporting HARQ based on a code block group (CBG), a retransmission method may be selected based on a matching degree of NACK per CBG fed back for each terminal. For example, when the CBG in which an error occurs between terminals is the same, a CBG-based retransmission method is used, and when the CBG in which an error occurs between terminals is inconsistent, a physical layer code block level encoding-based retransmission may be used. In this case, the selection of such a retransmission scheme may be signaled to the terminal through an RRC message, an MCA control element (CE) message, or a DCI.

When NACK is continuously fed back even after one retransmission, additional code blocks are continuously generated and transmitted through physical layer code block level encoding, thereby lowering the effective code rate of the physical layer code block level encoding. Alternatively, the effective code rate of the turbo code/LDPC code of the corresponding code blocks may be lowered by additionally transmitting the code blocks that have already been transmitted and the parity for the additional code blocks.

For example, for retransmission, one of 1) TB or CGB-based retransmission for transmitting additional bits for the first transmitted code blocks, and 2) physical layer code block level coding-based retransmission for generating and transmitting additional code blocks. HARQ service may be provided in a manner.

8 is a flowchart illustrating an example in which two retransmission schemes are selectively used.

Referring to FIG. 8, after initial transmission is performed (S810), it is determined whether a decoding error has occurred (S820).

As a result of the determination in step S820, if a decoding error has not occurred, the procedure ends.

As a result of the determination in step S820, if a decoding error has occurred, it is determined whether retransmission based on physical layer code block level encoding (CBL-FEC) has been set (S830).

As a result of the determination in step S830, if retransmission based on physical layer code block level encoding (CBL-FEC) is set, retransmission based on physical layer code block level encoding is performed (S850).

As a result of the determination in step S830, if retransmission based on physical layer code block level encoding (CBL-FEC) is not set, retransmission based on a transport block (TB) or a code block group (CBG) is performed (S840).

Depending on the embodiment, the base station notifies the terminal in advance of the number or time point at which retransmission based on physical layer code block level encoding can be performed among possible retransmissions, and retransmission based on physical layer code block level encoding only when the corresponding condition is satisfied. Can be done. In addition, the base station selects one of point-to-multipoint retransmission and point-to-point retransmission upon retransmission based on the number of terminals sending NACK feedback and the number of CBG NACKs or the number of CBs in which a decoding error occurs. Can be used. For example, when the number of terminals fed back a NACK signal is less than a certain number, a point-to-point retransmission method may be used, and in other cases, point-to-multipoint retransmission may be used.

Furthermore, the retransmission method according to an embodiment of the present invention is an enhanced layer or a base layer when transmitting a superposition based on a MUST (Multi-User Superposition Transmission) in point-to-multipoint transmission. ), it is applicable even when retransmission is performed.

9 is a flowchart illustrating an example of a retransmission method for downlink transmission according to an embodiment of the present invention.

Referring to FIG. 9, in the retransmission method for downlink transmission according to an embodiment of the present invention, first transmission data including one or more code blocks is transmitted (S910).

In this case, a detailed process of generating a code block from a transport block and generating first transmission data using the code block has been described in detail with reference to FIGS. 1, 2 and 5.

In addition, the retransmission method for downlink transmission according to an embodiment of the present invention includes a plurality of feedback signals corresponding to transmission errors from a plurality of terminals corresponding to point-to-multipoint transmission. Receive them (S920).

In this case, the plurality of feedback signals may include the number of code blocks corresponding to the transmission error.

Further, in the retransmission method for downlink transmission according to an embodiment of the present invention, retransmission data corresponding to the plurality of feedback signals is generated (S930).

In this case, step S930 may generate the retransmission data that increases the decoding probability of a plurality of code blocks included in the transmission block irrespective of the code block in which the transmission error occurs. In this case, the plurality of code blocks may be all code blocks included in the transport block. In this case, the plurality of code blocks may be some of the code blocks included in the transport block.

In this case, step S930 is added using a physical layer code block level encoding (CB-Level FEC) in which each of the plurality of code blocks is each of the plurality of code blocks as one information symbol. The method may include generating code blocks and generating the retransmission data using bits capable of reconstructing the additional code blocks.

In this case, each of the additional code blocks may correspond to each of the parity symbols generated by the physical layer code block level coding.

In this case, each of the additional code blocks may have the same length as the length of the longest code block among the plurality of code blocks.

In this case, the retransmission data may be used to recover a code block corresponding to the transmission error by using code block level decoding performed including decoding results of previously transmitted code blocks.

In this case, the code block level decoding may be decoding on a binary erasure channel (BEC) in which a code block corresponding to the transmission error and an additional code block are processed as disappearance.

In this case, the code block corresponding to the transmission error can be recovered using code blocks that have been successfully decoded.

According to an embodiment, step (S930) includes determining a retransmission group using the plurality of feedback signals and generating the retransmission data using additional bits for each of the code blocks included in the retransmission group. Can include. For example, the retransmission group may be a transport block including all code blocks in which a decoding error has occurred in a plurality of terminals. For example, the retransmission group may be a code block group including all code blocks issued by a decoding error from a plurality of terminals.

In addition, the retransmission method for downlink transmission according to an embodiment of the present invention transmits the retransmission data to the plurality of terminals (S940).

According to an embodiment, the retransmission method illustrated in FIG. 9 may further include transmitting a control signal corresponding to the retransmission data to the plurality of terminals. In this case, the control signal may include information corresponding to the number of the additional code blocks.

According to an embodiment, the plurality of terminals may calculate the number of the additional code blocks using MCS information corresponding to the retransmission data and resource information such as the number of resource blocks (RBs) or the number of layers.

10 is a flowchart illustrating an example of a method of receiving a retransmission signal according to an embodiment of the present invention.

Referring to FIG. 10, in the method for receiving a retransmission signal according to an embodiment of the present invention, a feedback signal corresponding to a transmission error of the first transmitted data is transmitted (S1010).

In addition, the method for receiving a retransmission signal according to an embodiment of the present invention receives retransmission data corresponding to the feedback signal (S1020).

In this case, the retransmission data may be data that increases the decoding probability of a plurality of code blocks included in the transmission block irrespective of the code block in which the transmission error occurs.

At this time, the retransmission data may be generated using bits capable of reconstructing additional code blocks. In this case, the additional code blocks may be generated using physical layer code block level coding (CB-Level FEC) in which each of the plurality of code blocks is used as one information symbol.

In this case, each of the additional code blocks may correspond to each of the parity symbols generated by the physical layer code block level coding.

In this case, each of the additional code blocks may have the same length as the length of the longest code block among the plurality of code blocks.

In addition, the method for receiving a retransmission signal according to an embodiment of the present invention restores a code block corresponding to the transmission error by using the retransmission data (S1030).

In this case, in step S1030, a code block corresponding to the transmission error may be restored using code block level decoding performed including decoding results of the previously transmitted code blocks.

In this case, the code block level decoding may be decoding on a binary erasure channel (BEC) in which a code block corresponding to the transmission error and an additional code block are processed as loss.

11 is a block diagram showing a wireless communication system in which an embodiment of the present invention is implemented.

Referring to FIG. 11, the terminal 1100 includes a memory 1105, a processor 1110, and an RF unit 1115. The memory 1105 is connected to the processor 1110 and stores various information for driving the processor 1110. The memory 1105 may store at least one or more instructions executed by the processor 1110. The RF unit 1115 is controlled by the processor 1110 and transmits and/or receives a radio signal. For example, the RF unit 1115 may receive an RRC message, configuration and/or control information such as DCI, and a downlink signal such as PDSCH from the base station 1150. In addition, the RF unit 1115 may transmit an uplink signal such as PUSCH and HARQ ACK/NACK to the base station 1150 or may transmit and receive PSSCH with another terminal (not shown).

The processor 1110 implements the functions, processes and/or methods of the terminal proposed in this specification. Specifically, the processor 1110 performs the operation of the terminal described with reference to FIG. 10. For example, the processor 1110 may restore a code block in which an error occurs by using a retransmission signal based on physical layer code block level encoding according to an embodiment of the present invention. In this case, the retransmission data included in the retransmission signal may be data that increases the decoding probability of a plurality of code blocks included in the transmission block irrespective of the code block in which a transmission error occurs. At this time, the retransmission data is generated using bits capable of restoring additional code blocks, and the additional code blocks are physical layer code block level encoding in which each of the plurality of code blocks is an information symbol. It can be created using (CB-Level FEC). In this case, each of the additional code blocks may correspond to each of the parity symbols generated by the physical layer code block level coding.

In all embodiments of the present specification, the operation of the terminal 1100 may be implemented by the processor 1110.

The memory 1105 may store control information, setting information, and the like according to the present specification, and provide the control information, setting information, and the like to the processor 1110 according to a request of the processor 1110.

The base station 1150 includes a processor 1155, a memory 1160, and an RF unit 1165. The memory 1160 is connected to the processor 1155 and stores various information for driving the processor 1155. The memory 1160 may store at least one or more instructions executed by the processor 1155. The RF unit 1165 is controlled by the processor 1155 and transmits and/or receives a radio signal. The processor 1155 implements the function, process and/or method of the base station proposed in this specification. In the above-described embodiment, the operation of the base station may be implemented by the processor 1155. The processor 1155 may generate retransmission data using the physical layer code block level encoding disclosed in the present specification and transmit the retransmission data to a plurality of terminals.

In this case, the retransmission data may be data that increases the decoding probability of a plurality of (all) code blocks included in the transmission block irrespective of the code block in which the transmission error occurs.

In this case, the retransmission data may be generated using bits capable of restoring additional code blocks, and the additional code blocks are at the level of a physical layer code block in which each of the plurality of code blocks is an information symbol. It can be generated using encoding (CB-Level FEC).

In this case, each of the additional code blocks may correspond to each of the parity symbols generated by the physical layer code block level coding.

In this case, each of the additional code blocks may have the same length as the length of the longest code block among the plurality of code blocks.

The processor may include an Application-Specific Integrated Circuit (ASIC), another chipset, a logic circuit, and/or a data processing device. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium, and/or other storage device. The RF unit may include a baseband circuit for processing a radio signal. When the embodiment of the present invention is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) performing the above-described function. The module may be stored in a memory and executed by a processor. The memory may be inside or outside the processor, and may be connected to the processor by various well-known means.

The retransmission scheme based on physical layer code block level coding described through an embodiment of the present invention can be applied not only to a point-to-multipoint transmission environment but also to a point-to-multipoint transmission environment such as unicast, and uplink feedback is possible. It can also be applied to no blind HARQ retransmission.

As described above, the retransmission method and apparatus for downlink transmission of a wireless communication system according to the present invention are not limited to the configuration and method of the embodiments described above, but the embodiments are various All or part of each of the embodiments may be selectively combined and configured to be modified.

1100: terminal
1150: base station
1110, 1155: processor
1105. 1160: memory
1115, 1165: RF unit

Claims (20)

Receiving a plurality of feedback signals corresponding to a transmission error from a plurality of terminals corresponding to point-to-multipoint transmission;
Generating retransmission data corresponding to the plurality of feedback signals; And
Transmitting the retransmission data to the plurality of terminals
Including, retransmission method for downlink transmission. The method according to claim 1,
The step of generating the retransmission data
A retransmission method for downlink transmission, wherein the retransmission data is generated to increase a decoding probability of a plurality of code blocks included in a transmission block regardless of the code block in which the transmission error occurs. The method according to claim 2,
The step of generating the retransmission data
Generating additional code blocks by using physical layer code block level coding (CB-Level FEC) in which each of the plurality of code blocks is an information symbol; And
Generating the retransmission data using bits capable of reconstructing the additional code blocks
Including, retransmission method for downlink transmission. The method of claim 3,
Each of the additional code blocks
Retransmission method for downlink transmission corresponding to each of the parity symbols generated by the physical layer code block level encoding. The method of claim 4,
Each of the additional code blocks
Retransmission method for downlink transmission, having the same length as the length of the longest code block among the plurality of code blocks. The method of claim 5,
The retransmission data is
A retransmission method for downlink transmission, which is used to recover a code block corresponding to the transmission error by using code block level decoding performed including decoding results of previously transmitted code blocks. The method of claim 6,
The code block level decoding is
Retransmission method for downlink transmission, which is decoding on a binary erasure channel (BEC) in which a code block corresponding to the transmission error and an additional code block are processed as disappearance. The method of claim 7,
The code block corresponding to the transmission error is
Retransmission method for downlink transmission, which is recovered using code blocks successfully decoded. The method of claim 8,
The plurality of feedback signals are
Retransmission method for downlink transmission, including the number of code blocks corresponding to the transmission error. The method of claim 8,
Further comprising the step of transmitting a control signal corresponding to the retransmission data to the plurality of terminals,
The control signal comprises information corresponding to the number of the additional code blocks, a retransmission method for downlink transmission. The method of claim 8,
The plurality of terminals
Retransmission method for downlink transmission, calculating the number of the additional code blocks using MCS information and resource information corresponding to the retransmission data. The method according to claim 1,
The step of generating the retransmission data
Determining a retransmission group using the plurality of feedback signals; And
Generating the retransmission data using additional bits for each of the code blocks included in the retransmission group
Including, retransmission method for downlink transmission. In the base station of a wireless communication system,
At least one processor;
An RF unit controlled by the processor and transmitting/receiving radio signals; And
A memory connected to the processor and storing at least one or more instructions executed by the processor,
The at least one command is
Receiving a plurality of feedback signals corresponding to a transmission error from a plurality of terminals corresponding to point-to-multipoint transmission,
Generating retransmission data corresponding to the plurality of feedback signals,
The base station for transmitting the retransmission data to the plurality of terminals. The method of claim 13,
The retransmission data is
The base station, which is data for increasing a decoding probability of a plurality of code blocks included in a transmission block irrespective of the code block in which the transmission error occurs. The method of claim 14,
The retransmission data is
Generated using bits that can restore additional code blocks,
The additional code blocks are
The base station, which is generated by using physical layer code block level coding (CB-Level FEC) in which each of the plurality of code blocks is an information symbol. The method of claim 15,
Each of the additional code blocks
The base station corresponding to each of the parity symbols generated by the physical layer code block level coding. The method of claim 16,
Each of the additional code blocks
The base station having a length equal to the length of the longest code block among the plurality of code blocks. In the terminal of the wireless communication system,
At least one processor;
An RF unit controlled by the processor and transmitting/receiving radio signals; And
A memory connected to the processor and storing at least one or more instructions executed by the processor,
The at least one command is
Transmits a feedback signal corresponding to the transmission error of the first transmitted data,
Receiving retransmission data corresponding to the feedback signal,
Restoring a code block corresponding to the transmission error using the retransmission data,
The retransmission data is data that increases a decoding probability of a plurality of code blocks included in a transmission block irrespective of the code block in which the transmission error occurs. The method of claim 18,
The retransmission data is
Generated using bits that can restore additional code blocks,
The additional code blocks are
The terminal is generated using physical layer code block level coding (CB-Level FEC) in which each of the plurality of code blocks is an information symbol. The method of claim 19,
Each of the additional code blocks
The terminal corresponding to each of the parity symbols generated by the physical layer code block level coding.

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