KR100392096B1 - A re-transmission method at MAC layer to support hybrid ARQ in W-CDMA system - Google Patents

Abstract

The present invention provides a media in applying a hybrid ARQ mechanism for ensuring efficient data transmission performance in an asynchronous mobile communication system such as a wideband code division multiple access (W-CDMA) system or an asynchronous IMT-2000 system. The present invention relates to a method for improving transmission efficiency by performing fast error recovery through transmission in an access control (MAC) layer. In an operation procedure of a transmitting MAC layer in an asynchronous mobile communication system, a transmission time is transmitted through a physical layer. A first step of storing information on a transport block for each of a plurality of transport channels transmitted in an interval (TTI) unit; And transmitting the transmission block of the corresponding transmission channel received in the transmission time interval unit based on the acknowledgment information for each transmission channel in the transmission time interval unit reported from the receiving side and reported through the physical layer, and the stored information. A second step of retransmission is performed on a channel basis, thereby minimizing the size of the buffer for the soft combine without requiring separate flow control at the physical layer.

Description

A re-transmission method at MAC layer to support hybrid ARQ in W-CDMA system

The present invention relates to a method of transmitting a media access control layer in an asynchronous mobile communication system, and more particularly, to an efficient method in an asynchronous mobile communication system such as a wideband code division multiple access (W-CDMA) system or an asynchronous IMT-2000 system. In applying a hybrid ARQ (HARQ) mechanism for guaranteeing data transmission performance, the transmission efficiency is improved by performing fast error recovery through retransmission in a media access control (MAC) layer. It is about a method for raising.

The HARQ mechanism complements the channel coding method (e.g., convolutional coding or turbo coding, etc.) that can effectively adapt to the distortion of the signal due to interference on the channel, and the ARQ method of confirming transmission by receiving an acknowledgment of the data transmission. By combining them, it is a method to maximize transmission efficiency.

In other words, by applying forward error correction (FEC) coding with a certain level of error correction on the transmitted data, a recovery function for a certain part of the error on the channel is performed. If not, retransmit it to recover. There may be various methods for such HARQ, but generally, HARQ types I, II, and III are mainly used.

In HARQ Type I, the transmitting side transmits the data after transmission after FEC coding with error correction function, and the receiving side performs decoding process, discards any error and transmits the radio link control (hereinafter referred to as RLC) layer. Error recovery can be performed by requesting retransmission through the ARQ mechanism.

In the case of HARQ type II, the transmitting side includes more redundancy information at the time of retransmission than initial transmission, thereby making it possible to respond more strongly to the error. In addition, the receiving side reduces the probability of occurrence of an error by performing a soft combine between data previously received and detected by an error and data received by retransmission.

HARQ type III is basically the same as type II, but the retransmission data has a self-decoder function, that is, to perform error detection on the retransmission data and to perform soft combine only when an error exists.

Currently, in 3GPP, which is currently standardizing the W-CDMA system, HARQ type I has completed the standardization work as an essential item, and HARQ type II / III is pursuing standardization as an optional item.

The main difference between HARQ type I and type II / III is whether or not soft combine is applied. That is, in HARQ Type I, a function of reducing error probability in decoding through soft combine is not included, whereas in Type II / III, a soft combine function is included. Therefore, how efficiently the soft combine can be performed determines the performance of HARQ Type II / III.

Soft combine means that before the corresponding transmission is transmitted based on the sequence number information before decoding it for a data transmission block in which the amount of transmission data is equal to the amount of data according to the channel coding rate by puncturing at the receiving side. It is a method to reduce the error probability by checking whether the block information is stored in the receiving buffer at the receiving side and, if present, combining the information to derive a more accurate data transmission block based on the probability value and decoding it. .

In order to use this method, it is necessary to be able to store the sequence number of the corresponding transport block and the coded symbol level information blocks in the reception buffer of the physical layer related to the transport block in which an error occurs. The symbol level information blocks stored in the reception buffer are used for soft combine when retransmission is performed for a packet data unit (hereinafter referred to as a PDU) that has failed due to a retransmission procedure between the transmitting and receiving RLC layers. If the CRC check on the retransmitted data block after the soft combine determines that there is no error, it is deleted from the buffer of the physical layer. Therefore, this soft combine requires a large amount of memory in the physical layer, which increases in proportion to the retransmission time in the RLC. In addition, in order to perform the soft combine correctly, the FEC coding result value before punching for the data transport block transmitted within the transmission time interval (TTI) should be the same.

However, the layer actually performing retransmission is the RLC layer, and the periodic status report in the RLC can reduce the amount of data transmitted on the channel, but causes a large increase in the amount of buffer for the soft combine at the receiving side. In addition, since RLC retransmission is performed in units of RLCPDUs, it is difficult to maintain the data transmission block transmitted during the TTI performing retransmission when the soft combine for random error data has the same information as when the RLC PDU was initially transmitted. It is very difficult. That is, when the RLC PDU is transmitted, the amount of data transmitted in the same TTI may change in the MAC layer, and different RLC PDUs may be transmitted during the same TTI, making it difficult to apply a soft combine.

In order to solve the conventional soft combine problem, a method of performing TTI retransmission in the physical layer may be used, but in this case, an additional flow control to prevent congestion of data transmission in the MAC layer should be added. . That is, when the TTI unit retransmission is performed in the physical layer, the MAC layer does not know whether to retransmit and thus continuously receives a new data transmission request from the RLC. In this case, the MAC continuously requests data transmission to the physical layer, which means that the physical layer must have a buffer for storing retransmission data and new transmission data at the same time. There was a problem of congestion.

The present invention was created to solve the above-mentioned conventional problems, and an object thereof is to improve the performance of the HARQ type II / III used for improving the data transmission efficiency for an asynchronous mobile communication system. By performing retransmission control in the unit of TTI, unlike the retransmission in the existing physical layer, no separate flow control is required, and the software required for the physical layer at the receiving side due to delay due to the execution of the retransmission mechanism of the existing RLC It is an object of the present invention to provide a method of transmitting a media access control (MAC) layer in an asynchronous mobile communication system, which minimizes the size of a buffer for a combine.

1 is a conceptual diagram for acknowledgment and retransmission of a TTI unit in a transmission / reception side physical layer;

2 is a diagram illustrating a physical layer structure of a transmitting side;

3 is a conceptual flowchart illustrating a data transmission block transmitted in a physical layer and an acknowledgment thereof according to the present invention;

4 is a flowchart illustrating an operation procedure in a transmitting MAC layer according to the present invention;

5 is a flowchart illustrating a redundancy check and processing procedure for an RLC PDU in a transmitting MAC layer according to the present invention.

In order to achieve the above object, a method of transmitting a media access control (MAC) layer in an asynchronous mobile communication system according to the present invention is characterized in that in the operation procedure of a transmitting MAC layer for HARQ in an asynchronous mobile communication system, A first step of storing information on transport blocks for a plurality of transport channels transmitted in units of a transmission time interval (TTI) through a layer; And transmitting the transmission block of the corresponding transmission channel received in the transmission time interval unit based on the acknowledgment information for each transmission channel in the transmission time interval unit reported from the receiving side and reported through the physical layer, and the stored information. And a second step of retransmitting on a channel basis.

In addition, the MAC layer performing the above operating procedure, if the packet data unit received from the upper layer overlaps the data in the transmission window of the MAC layer, characterized in that for discarding the received packet data unit The duplication may be determined based on a comparison of sequence numbers of the RLC.

Hereinafter, a method of transmitting a MAC layer for HARQ in an asynchronous mobile communication system according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In HARQ type II / III, retransmission for transmission error uses the ARQ mechanism in the RLC layer, and soft combines for reducing the error probability of channel coded symbols are performed by the physical layer.

That is, the physical layer on the receiving side identifies the error by decoding the data transport block and checking the CRC of the transport block based on side information. If an error exists, the MAC layer is notified of the error, and the additional information and coded symbol level information of the transport block in which the error occurs are stored in a buffer of the physical layer. After a certain time, the retransmission mechanism in the RLC layer is activated, and the sender retransmits a previously failed transport block. The physical layer on the receiving side decodes the received data and checks whether there is an error in the transport block. In this case, when an error is detected again, when the symbol level information of the transport block previously stored in the buffer and the received symbol level information have the same RLC sequence number as additional information, by combining these pieces of information, more reliable symbol level information is obtained. Create a soft combine to reduce the probability of error by creating an error check.

In order to perform the soft combine, it is necessary to be able to identify which data transmission block the currently received retransmission data transmission block is identical to the previously received data transmission block, which is made possible by passing the sequence number of the RLC PDU. However, even if the coding block in which the transport block is coded by the sequence number of the RLC PDU is identified, if the coding block is concatenated with other data transport blocks at the transmitting side, the transport block without error should be retransmitted. There will be a problem. In order to solve this problem, retransmission is required for transport blocks in a TTI unit.

Currently, as a method for solving the soft combine problem in a W-CDMA system, a method of performing retransmission of a TTI unit in the physical layer is considered. That is, after the transmitting physical layer stores the data of the TTI unit in a coded form and receives an acknowledgment such as ACK or NACK from the receiving physical layer, retransmission of the TTI unit is performed according to the result.

1 is a conceptual diagram for acknowledgment and retransmission in units of TTIs in the physical layer of the transmission and reception side.

In the proposed scheme, the sender and the receiver use a stop-and-wait ARQ having a buffer as much as a round trip delay to guarantee continuous transmission. In this case, although the acknowledgment is made in the physical layer, the transmission speed is increased. However, there is a limitation in that a large amount of information must be stored in the buffer. In addition, since the MAC layer cannot know the data transmission state in the physical layer, a separate flow control mechanism for this should be added between the physical layer and the MAC layer. In addition, since the transport block of the data is coded in units of transport channels, it is more effective to perform retransmissions in units of transport channels rather than overall retransmission in the TTI period.

When transmitting from the transmitting side, CRC addition and concatenation / segmentation are performed on a transport block in units of the same transport channel to transmit data to the physical layer. Thus, only data transport blocks transmitted on the same transport channel affect the soft combine, and transport blocks on other transport channels do not.

2 shows the physical layer structure of the transmitting side.

As shown in the figure, each transport block (TB) at the transmitting side is separated into transport channels (Transport channel 1 and Transport 2) and transmitted to the physical layer (201a, 201b). In the physical layer, after the CRC is calculated and added to the transport block (TB) (CRC Attachment) (202a and 202b) and after concatenation / segmentation (203a and 203b), channel coding is performed. Rate matching 205a and 205b is performed with 204a and 204b. Thereafter, after multiplexing each transport channel (TrCH Multiplexing) (206), interleaving is performed and mapped and transmitted to a physical channel (Physical Channel MApping) (207).

Since the receiving side performs the opposite procedure, separation of the data blocks already coded for each transmission channel is performed before channel decoding. To perform the soft combine, the data block is stored in the form of a symbol before the channel coding step. Therefore, retransmission for supporting soft combine in HARQ may be performed in units of TTI intervals in units of transmission channels.

Based on the above description, the present invention maintains / manages a transmission telegram for each TTI in the MAC layer and performs retransmission according to a response in the physical layer. This will be described in detail with reference to FIGS. 3 and 4. Explain.

3 shows a data transmission block transmitted in the physical layer and an acknowledgment flow thereof according to the present invention.

The sender stores information on the transport block (TB) transmitted in TTI units, that is, a transport channel number such as "TrCH = 1,2 .." and a transport block number such as "TBn = 1,2 .." in the MAC. After decoding the received transport block, the receiving side notifies the transmitting side of the transmission channel in the TTI unit, such as "NACK TrCH = 1, ACK TrCH = 2". Transmission and retransmission on the sending side and acknowledgment on the receiving side are made by the ARQ mechanism having the window size as much as the round trip delay. The physical layer of the transmitting side that receives the ACK / NACK response reports the transmission result to the MAC layer. In this case, the transmission channel information related to the acknowledgment is located at the very beginning of the transmission window. For 1, TBn = 1 and TBn = 2, which are transport blocks in a TTI unit located at the forefront of the transmission window, are moved to the rearmost part to retransmit the corresponding transport blocks. For the transport channel TrCH = 2 receiving the ACK, the transport block of the TTI unit located at the front of the window is removed.

Figure 4 shows the flow of the operation procedure in the transmitting MAC layer according to the present invention.

As shown in the figure, the transmitting side MAC first receives the PDU data from the RLC and includes it in the transmission window in the MAC layer (S401).

Subsequently, after transmitting the transport blocks within the last TTI of the transmission window (S402), a response waits for the next TTI (S403). If the NACK and / or ACK response for each transmission channel transmitted from the receiving physical layer during the response waiting is reported through the transmitting physical layer (S404), this is determined (S404). As a result, if it is NACK, a transmission window as shown in FIG. After moving the transport block of the first part to the last part (S405) and adjusting the parameters of the transmission window (S406), the process is performed again from step S402. If the determination result of step S404 is ACK, the transmission block of the first part of the transmission window is deleted (S407), the parameters of the transmission window are adjusted (S408), and whether or not the data received from the higher layer and the data in the transmission window are duplicated. After performing the check (S409) to perform again from the step S402.

If there is no free space in the transmission window during the step S401, the data PDU is not received from the upper layer RLC. When receiving the data PDU from the RLC layer, which is an upper layer, and including the data PDU in the transmission window, as shown in step S409, the RLC sequence numbers of the additional information necessary for HARQ are compared with each other to check for duplication. If data in the transmission window and newly received RLC PDU data overlap with each other as a result of the comparison in step S409, duplicate transmission is prevented by discarding the data.

FIG. 5 is a flowchart illustrating a redundancy check and processing procedure for the RLC PDU in the MAC layer, that is, a detailed flowchart of the step S409 of FIG. 4.

First, as shown in step S401 of FIG. 4, a data PDU is received from an upper layer RLC layer (S501), and the sequence number of the received data PDU (which can be known from additional information) and the data transmission blocks stored in the transmission window. The sequence numbers are compared (S502).

As a result of the comparison, it is determined whether the sequence numbers are duplicated (S503). If there is a duplicate, the corresponding data PDU is discarded and if there is a duplicate, the process starts again from the step S501 (S504). As shown in FIG. 3, it is added to the end of the transmission window (S505).

In conclusion, the present invention performs retransmission for the transmission data blocks in the MAC layer of the transmitting side, and performs transmission channel acknowledgment per TTI for the physical layer to efficiently support the transmission data blocks. In addition, a duplicate layer checking function has been added in the MAC layer to deal with a case where the MAC layer is duplicated due to the RLC retransmission mechanism.

As described in detail above, a method of transmitting a media access control (MAC) layer in an asynchronous mobile communication system according to the present invention is different from retransmission in a conventional physical layer by performing retransmission control of a TTI unit in the MAC layer. It does not require flow control and minimizes the size of the buffer for the soft combine required for the physical layer on the receiving side due to delay due to the retransmission mechanism of the existing RLC. Accordingly, the present invention can provide flexibility for HARQ type II / III application in asynchronous mobile communication systems such as W-CDMA system and asynchronous IMT-2000 system, and reduce the burden of memory required by hardware. It can be a more realistic alternative, and can secure technological competitiveness in the development and service of asynchronous IMT-2000 system, which is the next generation mobile communication system.

Claims (3)

In the data transmission method in the asynchronous mobile communication system, A first step of storing, in the MAC layer, information on transport blocks for a plurality of transport channels transmitted in units of transmission time intervals (TTIs) through the transmitting physical layer; And A second step of notifying the transmitting side of acknowledgment information for each transmission channel of a transmission time interval unit of the decoding result of the received transmission block at the receiving side; And Based on the acknowledgment information for each transmission channel of the transmission time interval unit and the information of the transport blocks for each transmission channel, the transmission block of the corresponding transmission channel that has been received is retransmitted in the transmission channel unit within the transmission time interval unit. And transmitting the media access control layer in the asynchronous mobile communication system. The method of claim 1, And discarding the received packet data unit when a packet data unit received from a higher layer is overlapped with a data transmission block in a transmission window. The method of claim 2, And determining whether the MAC layer transport block is duplicated based on a comparison of sequence numbers of RLCs.