KR20100100655A - Method and apparatus for multicast transmission in wireless network - Google Patents

Abstract

PURPOSE: A method for transmitting multicast and an apparatus thereof for controlling error in case the length of data packets is different from each other in wireless network are provided to reduce the retransmission frequency of the data packet. CONSTITUTION: A transmission data processing unit(210) performs the processing for transmitting a plurality of data packets to a receiving station. A transmission buffer(230) especially stores a plurality of data packets from the transmission data processor flow. A coding unit(240) receives message packet loss information about a plurality of data packets from the receiving station. The coding unit codes a plurality of data packets stored in a transmission buffer to one data packet.

Description

METHOD AND APPARATUS FOR MULTICAST TRANSMISSION IN WIRELESS NETWORK}

The present invention relates to a method and apparatus for multicast transmission in a wireless network.

Wireless Local Area Networks (WLANs) are widely used in homes and businesses. Wireless LAN technology, represented by IEEE 802.11, allows existing wired network connections to be accessed wirelessly using radio waves.

On the other hand, when wirelessly connected using radio waves, it is easy to be exposed to interference such as multi-path, collision, noise, and the like, so that reliable data transmission is difficult. In particular, wireless LANs are more difficult to reliably transmit data in multicast transmissions in which data is simultaneously transmitted to a plurality of receivers due to the characteristics of a medium access control (MAC) layer.

For reliable multicast transmission in wireless LAN environment, forward error correction (FEC) scheme is considered. The FEC technique is a method in which a transmitter carries an additional bit in each packet and transmits an error, and when an error occurs, the receiver recovers the error using the additional bit. According to the FEC technique, when communicating in a wireless environment having a high probability of error or when transmitting a large packet, a waste of bandwidth is large. In addition, when a collision occurs between frames transmitted from a plurality of transmitters, there is a problem that the receiver cannot recover an error.

In addition, for reliable multicasting in a wireless LAN environment, a packet retransmission scheme using acknowledgment / negative-acknowledgement (ACK / NACK) is considered. According to the packet retransmission scheme, each receiving station reports the reception status of the data packet to the transmitting station, and the transmitting station retransmits the lost data packet to recover from the error. However, the packet retransmission scheme has a problem in that the probability of packet retransmission increases linearly with the number of receiving stations. For example, in a unicast transmission in which one transmitting station transmits a packet to one receiving station, if the packet error probability is 0.001, when the transmitting station transmits 1000 packets, one packet is retransmitted. However, in a multicast transmission in which one transmitting station transmits a packet to 100 receiving stations, if the packet error probability is 0.001, the transmitting station retransmits one packet every 10 packets. As described above, when the number of retransmissions of packets increases in proportion to the number of receiving stations in the multicast transmission presupposing a plurality of receiving stations, there is a problem that the performance of the system is degraded.

An object of the present invention is to provide a reliable multicasting method and apparatus in a wireless network. In particular, the present invention provides a method and apparatus for reducing the number of retransmissions of data packets for error control when a transmitting station performs multicast transmission to a plurality of receiving stations.

A multicast transmission method of a transmitting station in a wireless network according to an aspect of the present invention includes transmitting a plurality of data packets to a plurality of receiving stations, wherein the loss of the data packets from at least one receiving station of the plurality of receiving stations is achieved. Receiving information about the data packet, coding the plurality of data packets into one data packet based on the information about the loss of the data packet, and sending an error control frame including the coded data packet to the plurality of receiving stations. Transmitting.

In a wireless network according to an aspect of the present invention, a method of controlling an error in a multicast transmission of a transmitting station includes: receiving a data block including a plurality of data packets from a transmitting station, Checking whether there is a lost data packet, if there is a lost data packet, transmitting packet loss information to the transmitting station, receiving an error control frame comprising a data packet coded based on the packet loss information And recovering the lost data packet using the error control frame and the plurality of data packets.

A transmitting station according to an aspect of the present invention receives a plurality of data packets from an upper layer and performs a process for transmitting the plurality of data packets to a receiving station, and the plurality of data from the transmitting data processing section. A transmission buffer for storing packets per flow and a coding unit for coding the plurality of data packets stored in the transmission buffer into one data packet when the packet loss information of the plurality of data packets is received from the receiving station. .

A receiving station according to an aspect of the present invention receives a data block including a plurality of data packets from a transmitting station and checks whether there is a lost data packet in the data block, the received data processor If there is a data packet, when receiving an error control frame including a packet loss information generation unit for generating and transmitting packet loss information to the transmitting station and a data packet coded based on the packet loss information from the transmitting station, And a decoding unit for recovering the lost data packet using an error control frame and the plurality of data packets.

It is possible to multicast transmission of a plurality of data packets to a plurality of receiving stations, and to reduce the number of data packet retransmissions of the transmitting station when an error occurs in the data packet. Further, the transmitting station can easily control the error even when the lengths of the plurality of data packets are different. Therefore, it is possible to provide a wide application field to a higher layer.

1 is a diagram illustrating a wireless network system according to an embodiment of the present invention.
2 is a diagram illustrating an internal structure of a MAC layer of a transmitting station in a wireless network system according to an embodiment of the present invention.
3 is a diagram illustrating an internal structure of a MAC layer of a receiving station in a wireless network system according to an embodiment of the present invention.
4 is a diagram illustrating a multicast transmission and error control method of a transmitting station in a wireless network system according to an embodiment of the present invention.
5 is a diagram illustrating a method of transmitting a plurality of data packets by a transmitting station according to an embodiment of the present invention, and FIG. 6 is a diagram of a method of recovering a lost data packet using a coded data packet. Drawing.
7 is a diagram illustrating a method of transmitting a plurality of data packets by a transmitting station according to another embodiment of the present invention, and FIG. 8 is a diagram of a method of recovering lost data packets by using a coded data packet by a receiving station. Drawing.
9 and 10 are examples of an error control frame according to an embodiment of the present invention, respectively.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise.

In this specification, a receiving station is a mobile station (MS), a terminal (terminal), a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), a user device. A user equipment (UE), an access terminal (AT), and the like may also be referred to, and include all or some functions of a mobile station, a terminal, a mobile terminal, a subscriber station, a portable subscriber station, a user device, an access terminal, and the like. You may.

In the present specification, the transmitting station includes a base station (BS), an access point (AP), a radio access station (RAS), a node B (Node B), an advanced node B (evolved NodeB, eNodeB). , May also refer to a base transceiver station (BTS), a mobile multihop relay (MMR) -BS, and the like, and all or the like, such as a base station, an access point, a wireless access station, a node B, an eNodeB, a transceiver base station, an MMR-BS, or the like. It may also include some functionality.

In the present specification, multicast transmission is a method in which one transmitting station simultaneously transmits data to a plurality of receiving stations. Multicast transmission may be used interchangeably with terms such as broadcast transmission, point to multipoint transmission, and the like.

1 is a diagram illustrating a wireless network system according to an embodiment of the present invention.

Referring to FIG. 1, a wireless network system includes a transmitting station 10 and a plurality of receiving stations 20-1, 20-2, and 20-3. The transmitting station 10 multicasts data to a plurality of receiving stations 20-1, 20-2, and 20-3. The wireless network system may be, for example, a wireless LAN system.

2 is a diagram illustrating an internal structure of a MAC layer of a transmitting station in a wireless network system according to an embodiment of the present invention, and FIG. 3 is a diagram of an inside of a MAC layer of a receiving station in a wireless network system according to an embodiment of the present invention. 4 is a diagram illustrating a multicast transmission and error control method of a transmitting station in a wireless network system according to an embodiment of the present invention.

2 and 3, the transmitting station 200 includes a transmission data processing unit 210, a transmission data header processing unit 220, a transmission buffer 230, a coding unit 240, an error control header processing unit 250, The packet loss information processor 260 is included. The receiving station 300 may include the reception data processing unit 310, the reception data header processing unit 320, the reception buffer 330, the decoding unit 340, the error control header processing unit 350, and the packet loss information generation unit 360. Include.

The transmission data processing unit 210 of the transmitting station 200 receives data (for example, a MAC service data unit (SDU)) from an upper layer. The transmission data processing unit 210 processes data from an upper layer and generates a data packet (for example, a MAC protocol data unit (PDU)) to be transmitted to a lower layer or a receiving station. (Sequence Number Assignment), Integrity Protection, Fragmentation, Encryption and Integrity. The transmission data header processing unit 220 adds a header and cyclic redundancy check (CRC) data to a data packet received from the transmission data processing unit 210 and transmits the data packet to a plurality of receiving stations. Meanwhile, the transmitting station 200 stores a copy of the data packet processed by the transmission data processing unit 210 in the transmission buffer 230 for each flow for error control. The data packet stored in the transmission buffer 230 may be used for generating an error control frame.

The receiving station 300 receives a plurality of data packets from the transmitting station 200. The receiving data header processing unit 320 of the receiving station 300 removes the header from the received data packet, checks the CRC, and detects an error. The received data processor 310 processes the data packet to generate data (for example, MAC SDU) to be transmitted to a higher layer, for example, removes a copy of the data packet, reorders the data packet, Decryption and Integrity checks, fragment rearrangements, integrity protection, and replay detection are delivered to higher layers. Meanwhile, the receiving station 300 may store a copy of the data packet processed by the receiving data processor 310 in the receiving buffer 330 for each flow for error control.

Hereinafter, when an error occurs in the data packet received by the receiving station 300 from the transmitting station 200, a method for controlling the error will be described with reference to FIGS.

The transmitting station 200 stores the data packets processed by the transmission data processing unit 210 in the transmission buffer 230 for each flow (S300), and receives the plurality of data packets processed by the transmission data processing unit 210. (S310). For convenience of description, although the transmitting station 200 is shown as transmitting a data packet to one receiving station 300, the transmitting station 200 multicasts the data packet to a plurality of receiving stations (300) can do.

The receiving data header processing unit 320 of the receiving station 300 checks whether an error has occurred in the data packet received from the transmitting station 200 (S320), and the receiving data processing unit 310 transfers the data packet to a higher layer. A process for delivering is performed (S330). The reception buffer 330 stores a copy of the received data packet for each flow (S340). The reception buffer 330 may further store common header information of the data packet.

If an error is detected in the received data packet, the packet loss information generation unit 360 of the receiving station 300 generates the packet loss information and transmits the packet loss information to the transmitting station 200 (S350). Packet loss information may be transmitted via, for example, an ACK / NACK message. The ACK / NACK message may be transmitted using a general ACK / NACK transmission technique or a block ACK technique. In the block ACK scheme, when the transmitting station 200 transmits a data block including a plurality of data packets to the receiving station 300, the receiving station 300 informs of which data packet among the data blocks was successfully received. In this case, the packet information received in a predetermined interval is stored in one packet at a time and sent.

On the other hand, when the transmitting station 200 multicasts to the plurality of receiving stations 300, each receiving station 300 performs steps S320 to S350. However, when the receiving station 300 transmits the packet loss information by using the block ACK scheme in step S350, when the receiving station 300 hears that the neighboring receiving station transmits the block ACK to avoid collisions, it receives the packet loss information. It may not transmit a block ACK.

The packet loss information processing unit 260 of the transmitting station 200 receives the packet loss information from the receiving station 300, and calculates a coding condition using the packet loss information (S360). A coding condition is a combination condition of packets that makes it possible to recover its lost packets at all receiving stations when the transmitting station codes a plurality of data packets and multicasts them to the plurality of receiving stations. do. That is, the coding condition is to create a combination of sequential data packets so that none of two or more lossy receiving stations within a plurality of coded data packets are combined, but the largest number of data packets are combined so that a single retransmitted coding packet is possible. This is to ensure the integrity of a large number of data packets.

The coding unit 240 of the transmitting station 200 generates an error control frame using the data packet stored in the transmission buffer 230 (S370). In this case, the coding unit 240 codes a plurality of data packets stored in the transmission buffer into one data packet to generate an error control frame. Coding a plurality of data packets into one data packet may be referred to as network coding. Here, the network coding may be performed by performing an exclusive OR on a plurality of data packets. A detailed method of generating an error control frame using network coding will be described later.

The error control header processing unit 250 of the transmitting station 200 performs processing for the header and CRC of the error control frame (S380), and transmits the error control frame to the receiving station 300 (S390).

When the receiving station 300 receives the error control frame from the transmitting station 200, the error control header processing unit 350 of the receiving station 300 checks whether an error of the error control frame occurs through the CRC check (S400). . The transmitting station 200 may add an identifier indicating that the frame is an error control frame to the error control frame, and the receiving station 300 may recognize that the frame is an error control frame using the identifier.

The decoding unit 340 of the receiving station 300 decodes the error control frame using the error control frame received from the transmitting station 200 and the data packet stored in the receiving buffer 330 to recover the lost data packet ( S410). Thereafter, the reception data header processing unit 320 of the reception station 300 attaches a header to the recovered data packet using common header information of the data packet stored in the reception buffer 330, and transmits the header to the reception data processing unit 320. . The reception data processor 310 stores the data packet and the recovered data packet stored in the reception buffer 330 according to the sequential number, and transfers the data packet to the upper layer in data block units.

5 is a diagram illustrating a method of transmitting a plurality of data packets by a transmitting station according to an embodiment of the present invention, and FIG. 6 is a diagram of a method of recovering a lost data packet using a coded data packet. Drawing. It is assumed that the transmitting station transmits data packet 1, data packet 2 and data packet 3 to the plurality of receiving stations, and receives packet loss information from at least one receiving station.

Referring to FIG. 5, in order for a transmitting station to code data packet 1, data packet 2, and data packet 3, a specific bit array (End of Sequence, EoS) is inserted at the end of the payload of each data packet. do. A specific bit array is an area used to find a payload (ie, an actual data portion) in a process of decoding and decoding a plurality of data packets having different payload lengths.

The transmitting station compares the lengths of the data packet 1, the data packet 2 and the data packet 3 into which the specific bit array is inserted, and finds the length of the longest data packet. It is assumed here that the length of data packet 1 is the longest.

The transmitting station adds padding bits to the last points of data packet 2 and data packet 3 such that the length of data packet 2 and data packet 3 is equal to the length of data packet 1.

The transmitting station codes Data Packet 1, Data Packet 2 and Data Packet 3 which are equal in length. XOR operations can be used for coding.

Referring to Fig. 6, the receiving station can recover the lost data packet using the coded data packet received from the transmitting station. Here, it is assumed that at the initial transmission of the transmitting station, data packet 1 and data packet 3 are normally received, and data packet 2 is lost. The receiving station recovers the data packet 2 using the coded data packet received from the transmitting station, the data packet 1 and the data packet 3 received from the transmitting station and stored in the receiving buffer. For example, the receiving station may recover data packet 2 by XORing the coded data packet, data packet 1 and data packet 3.

The receiving station finds the last point of a specific bit array, i.e., the interval of a specific bit array, from the last point of recovered data packet 2, and the payout of the actual data packet 2 from the beginning of the recovered data packet 2 to the beginning of the specific bit array. Determined to be a load.

7 is a diagram illustrating a method of transmitting a plurality of data packets by a transmitting station according to another embodiment of the present invention, and FIG. 8 is a diagram of a method of recovering lost data packets by using a coded data packet by a receiving station. Drawing.

Referring to Fig. 7, in order for the transmitting station to code data packet 1, data packet 2 and data packet 3, the transmitting station obtains the length of each data packet and stores it in the length information field. Next, the transmitting station compares the lengths of data packet 1, data packet 2 and data packet 3, and selects the longest data packet. It is assumed here that the length of data packet 1 is the longest.

The transmitting station adds padding bits to the last points of data packet 2 and data packet 3 such that the length of data packet 2 and data packet 3 is equal to the length of data packet 1.

The transmitting station codes Data Packet 1, Data Packet 2 and Data Packet 3 which are equal in length. XOR operations can be used for coding.

Referring to FIG. 8, a receiving station may recover data packet 2 by receiving a coded data packet from a transmitting station and performing an XOR operation on the coded data packet, the normally received data packet 1, and the data packet 3.

The coding unit finds the length of the data packet 2 from the length definition field of the recovered data packet 2, and determines the payload of the actual data packet 2 from the start point of the data packet 2 to the defined length.

9 and 10 are examples of an error control frame according to an embodiment of the present invention, respectively.

Referring to FIG. 9, an error control frame includes a frame body, and the frame body includes a coded data packet illustrated in FIG. 5. Referring to FIG. 10, an error control frame includes a frame body, and the frame body includes a coded data packet illustrated in FIG. 6.

Such an error control frame may have a newly defined frame structure or a previously defined frame structure. For example, a structure of a block ACK request frame may be used as an error control frame. A block ACK request frame is a frame used by a transmitting station to request a block ACK to a receiving station to know which data packet was successfully received after transmitting a data block containing a plurality of data packets to the receiving station.

As shown in FIG. 9 and FIG. 10, the block ACK request frame used for the error control frame includes a frame control field, a duration / ID field, a destination address (DA) field, and a departure point in addition to the frame body. It may further include a Source Address (SA) field, a Block ACK Request (BAR) control field, and a Frame Check Sum (FCS) field. The frame control field includes information on the type of a frame, and the interval / ID field includes a network allocation vector. The DA field contains a destination, i.e. a recipient station address, and the SA field contains a source, i. The BAR field includes block ACK request control information and includes a TID (Traffic ID) field including priority information for guaranteeing quality of service (QoS). The FCS is a field for checking an error of a block ACK request frame.

Meanwhile, the error control frame may include identification information indicating that the frame is an error control frame or indicating that a network coded data packet is transmitted. For example, in order to transmit a data packet coded using a structure of a block ACK request frame, an identifier indicating that the frame is an error control frame may be inserted into a BAR control field of the block ACK request frame. That is, the 12-bit except for the TID field among the BAR control fields may be used to inform that the corresponding frame is an error control frame.

If the frame is an error control frame, the coded data packet may be inserted between the BAR control field and the FCS field. That is, in the general block ACK request frame, there is a block ACK start sequence control field between the BAR control field and the FCS field. In order to use the block ACK request frame as an error control frame, a start sequence (Strat Sequence) field, an end sequence field, and a data packet body field may be inserted at the position of the block ACK start sequence control field. Here, the data packet body field includes a coded data packet. The coded data packet may be generated by the method illustrated in FIGS. 5 and 7. The start sequence field contains the sequence of the first data packet that started coding, and the last sequence field contains the sequence of the last coded data packet.

As described above, by using an error control frame in which a plurality of data packets are coded, it is possible to reduce the frequency of retransmission of the data packet for an error that occurs when the transmitting station performs multicast transmission to the plurality of receiving stations. In addition, by supporting a variable length error control frame, it is possible to facilitate the implementation of the application layer and provide a wide range of applications.

The embodiments of the present invention described above are not only implemented through the apparatus and the method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiments of the present invention or a recording medium on which the program is recorded.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (20)

In a multicast transmission method of a transmitting station in a wireless network,
Sending a plurality of data packets to a plurality of receiving stations;
Receiving information about the loss of the data packet from at least one receiving station of the plurality of receiving stations;
Coding the plurality of data packets into one data packet based on the information about the loss of the data packet; And
Transmitting an error control frame containing the coded data packet to the plurality of receiving stations. The method of claim 1,
The coding step,
Inserting a bit array at a last point of each of the plurality of data packets;
Inserting padding bits into the remaining data packets such that the length of the remaining data packets excluding the longest data packet among the inserted data packets is equal to the length of the longest data packet; And
Coding the plurality of data packets into the one data packet. The method of claim 1,
The coding step,
Storing information on the length of each of the plurality of data packets in a length information field of each data packet;
Inserting padding bits into the remaining data packets such that the length of the remaining data packets except for the longest one among the plurality of data packets is equal to the length of the longest data packet; And
Coding the plurality of data packets into the one data packet. The method of claim 1,
The coding step,
XOR-operating the plurality of data packets and coding the data packets into one data packet. The method of claim 1,
The transmitting step,
Generating an error control frame including the coded data packet; And
Transmitting the error control frame to the plurality of receiving stations. The method of claim 5,
The error control frame is transmitted using a structure of a block ACK request (BAR) frame. A method for a receiving station to control an error during multicast transmission of a transmitting station in a wireless network, the method comprising:
Receiving a data block comprising a plurality of data packets from a transmitting station;
Checking whether there are lost data packets in the plurality of data packets;
If there is a lost data packet, sending packet loss information to the transmitting station;
Receiving an error control frame including a coded data packet based on the packet loss information; And
Recovering the lost data packet using the error control frame and the plurality of data packets. The method of claim 7, wherein
The recovering step,
Recovering the lost data packet by performing an XOR operation on the data packet not lost and the error control frame among the plurality of data packets. The method of claim 7, wherein
The recovering step,
Finding a predetermined bit array interval from the last point of the recovered data packet; And
And checking from the start point of the recovered data packet to the start point of the bit array as the payload of the recovered data packet. The method of claim 7, wherein
The recovering step,
Confirming the length of the recovered data packet from the length information field of the recovered data packet; And
Identifying an area corresponding to the length at a start point of the recovered data packet as a payload of the recovered data packet. The method of claim 7, wherein
The error control frame includes a data packet obtained by XORing the plurality of data packets. A transmission data processing unit which receives a plurality of data packets from an upper layer and performs processing for transmitting the plurality of data packets to a receiving station;
A transmission buffer for storing the plurality of data packets for each flow from the transmission data processing unit; And
And a coding unit for coding the plurality of data packets stored in the transmission buffer into one data packet when receiving packet loss information for the plurality of data packets from the receiving station. The method of claim 12,
The coding unit inserts a bit array at a last point of each of the plurality of data packets, and the length of the remaining data packets except the longest data packet among the data packets into which the bit array is inserted is equal to the length of the longest data packet. And a padding bit is inserted into the remaining data packet, and the XOR operation of the plurality of data packets is coded into the one data packet. The method of claim 12,
The coding unit stores information about the length of each of the plurality of data packets in a length information field of each data packet, and the length of the remaining data packets except for the longest data packet among the plurality of data packets is the length of the longest data packet. And a padding bit is inserted into the remaining data packet to be equal to a length, and the XOR operation of the plurality of data packets is coded into the one data packet. The method of claim 12,
And a transmitting unit for transmitting the one data packet coded by the coding unit using a structure of a block ACK request frame. A reception data processing unit which receives a data block including a plurality of data packets from a transmitting station and checks whether there are any lost data packets in the data block;
A packet loss information generation unit for generating packet loss information and transmitting the packet loss information to the transmitting station when the data packet is lost in the data block; And
And a decoding unit for recovering the lost data packet by using the error control frame and the plurality of data packets when receiving an error control frame including a data packet coded based on the packet loss information from the transmitting station. Recipient. The method of claim 16,
And the decoding unit recovers the lost data packet by performing an XOR operation on the data packet not lost and the error control frame among the plurality of data packets. The method of claim 16,
The decoding unit searches for a section of a predetermined bit array from the last point of the recovered data packet, and receives a receiving station that checks the start point of the recovered data packet from the start point of the recovered data packet as the payload of the recovered data packet. . The method of claim 16,
The decoding unit checks the length of the recovered data packet from the length information field of the recovered data packet, and checks the region corresponding to the length at the start point of the recovered data packet as the payload of the recovered data packet. Recipient. The method of claim 16,
And if the neighboring receiving station detects transmitting the packet loss information for the data block, the packet loss information generation unit does not transmit the packet loss information to the transmitting station.

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