KR100360778B1 - Apparatus and method for MAC frame construction for OFDM based on wireless LAN - Google Patents

Abstract

The present invention provides a medium access control (MAC: Medium) for efficiently handling information transmission between a mobile station and a base station in a wireless LAN system transmitting an IP packet or an ATM cell using an orthogonal frequency division multiplexing (OFDM) modulation scheme. Access Control (media access control) frame composition device and method to provide.

According to the present invention, in a method of configuring a medium access control (MAC) frame of a wireless LAN system for transmitting an IP packet or an ATM cell by orthogonal frequency division multiplexing (OFDM) modulation scheme, The MAC frame of the WLAN system, characterized in that the uplink transmission section is formed at the beginning of the uplink transmission section to enable fast contention signal processing, thereby freeing time to process the result of the upstream contention section in hardware implementation. A configuration method is provided.

Description

Apparatus and method for MAC frame construction for OFDM based on wireless LAN}

The present invention relates to an apparatus and method for configuring a medium access control (MAC) frame, and more particularly, to a wireless LAN for transmitting an IP packet or an ATM cell in an orthogonal frequency division multiplexing (OFDM) modulation scheme. An apparatus and method for constructing a MAC frame for efficiently processing information transfer between a mobile station and a base station in a local area network (LAN) system.

Conventional Local Area Network (LAN) technology mainly uses data spreading between a base station and a mobile terminal in a spread spectrum method, and a carrier access multiple access (CSMA / CA) based on a distributed control method in which a medium access control method is also standardized. Since it is based on a Contention Avoidance technique, there is a problem in that it is unsuitable for recent high-speed multimedia service transmission. In order to overcome this problem, Orthogonal Frequency Division Multiplex (OFDM) scheme has recently been standardized in the physical layer, and research and standardization of a time division multiple access scheme of a central control scheme in the MAC layer is in progress.

The present invention has been made to solve the above problems of the prior art, MAC frame configuration for efficiently handling the information transfer between the mobile station and the base station in a wireless LAN system for transmitting IP packets or ATM cells in an OFDM modulation scheme It is an object of the present invention to provide an apparatus and method.

1 is a configuration diagram of a wireless LAN system applied to the present invention,

2 is a configuration diagram of a TDMA / TDD frame according to an embodiment of the present invention,

3 is a diagram illustrating a PDU configuration according to an embodiment of the present invention;

4 is a configuration diagram of a frame header shown in FIG. 2,

5 is a configuration diagram of a base station and a terminal according to an embodiment of the present invention;

FIG. 6 is a diagram illustrating the configuration of the MAC frame processor shown in FIG. 5.

According to the present invention for achieving the above object, Medium Access Control (MAC) of a WLAN system for transmitting an IP packet or an ATM cell in an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme. In the frame configuration method, the uplink transmission section is formed at the beginning of the uplink transmission section so that fast contention processing can be performed, so as to secure a spare time for processing the result of the uplink contention section in the hardware implementation. Provided is a method of configuring a MAC frame of a wireless LAN system.

In addition, a downlink transmission region including a frame header, a downlink control signal transmission region and a downlink data signal transmission region; In a medium access control (MAC) frame of a wireless LAN system, which includes an uplink transmission zone, an uplink control signal transmission zone, and an uplink data signal transmission zone, fast contention signal processing is possible. The uplink contention transmission area is located at the beginning of the uplink contention area so as to secure a free time for processing the result of the uplink contention time in a hardware implementation. A readable recording medium is provided.

In addition, in a MAC (Medium Access Control) frame processing apparatus of a wireless LAN system that transmits an IP packet or an ATM cell in an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme, fast contention signal processing is performed. The uplink contention period is formed at the beginning of the uplink period so that the MAC frame includes a means for securing a spare time for processing the result of the uplink contention in hardware. A MAC frame processing apparatus of a LAN system is provided.

In the following, with reference to the accompanying drawings, a preferred embodiment according to the present invention will be described in detail.

1 is a configuration diagram of a wireless LAN system to which the present invention is applied.

The base station 120, which is connected to the Ethernet or the external network 110 by wire, has a wireless transmitter and receiver, and the service area 160 is schematically represented by a solid line. A total of N mobile terminals 130 to 150, which also have a wireless transmission / reception function, communicate with the base station 120 through a wireless channel 170. In this case, since the N mobile terminals 130 to 150 and the base station 120 share one radio channel 70, time slots are different for each mobile terminal using a time division multiple access scheme. To prevent collisions of information on the wireless channel. In addition, the downlink transmission period for transmitting data from the base station 120 to each mobile terminal and the uplink transmission period for transmitting data from the mobile terminal to the base station 120 also use separate time domains. This is generally called TDMA / TDD (Time Division Multiple Access / Time Division Duplex).

In the WLAN system of FIG. 1, a TDMA / TDD frame should be configured for information transmission between a base station and each mobile station. In the standardized OFDM scheme, one OFDM symbol consists of 64 subcarriers. Data can be transmitted on 48 subcarriers, and each subcarrier is Binary Phase Shift Keying (BPSK) / Quadrature Phase Shift Keying (QPSK) / Quadrature Amplitude Modulation (QAM). Spherical Amplitude Modulation) A modulated signal can be loaded so that the number of bits transmitted per OFDM symbol is changed, thereby enabling high-speed data transmission with variable speed.

This is shown in [Table 1]. In the following, '/ h' means hexadecimal.

[Table 1] Number of bits per OFDM symbol according to modulation method

Code Modulation method Coding rate Baud rate Number of data bits per symbol 8 / h to F / h - - - Spare 1 / h 64 QAM 3/4 54 Mbps 216 (27) 2 / h 16 QAM 9/16 27 Mbps 108 (13.5) 3 / h 16QAM 3/4 36 Mbps 144 (18) 4 / h QPSK 1/2 12 Mbps 48 (6) 5 / h QPSK 3/4 18 Mbps 72 (9) 6 / h BPSK 1/2 6 Mbps 24 (3) 7 / h BPSK 3/4 9 Mbps 36 (4.5)

In [Table 1], a coding rate means a coding rate of a convolutional error correction code used to overcome a poor radio wave propagation environment.

In Table 1, the minimum common multiple of the number of data bits per symbol is 54 bytes. That is, when the data length is 54 bytes, no matter what modulation scheme is used, it is an integer multiple of the OFDM symbol. If the length of the data does not become an integer multiple of the OFDM symbol, the physical layer requires a process of inserting zero bits to match the number of bits per symbol.

That is, separate control data for operation or control of the entire system must be transmitted between the base station 120 and the terminals 130 to 150 in addition to user data. These control data do not need the various modulation schemes shown in [Table 1] and are relatively important, so they use the strongest BPSK and code rate 1/2 for the poor radio propagation environment. In this case, the minimum unit must be an integer multiple of 3 bytes. MAC frames are constructed based on these values.

2 is a configuration diagram of a TDMA / TDD frame applied to the present invention.

One frame has a fixed value of a certain length and is divided into a downlink transmission section for transmitting data from the base station to the mobile terminal and an uplink transmission section for transmitting data from the mobile terminal to the base station. The downlink transmission section is divided into a frame header, a control signal transmission section, and a data transmission section. The uplink transmission section is divided into a control signal transmission section, a data transmission section, and a contention channel transmission section. The length of the entire frame is fixed.

All parts except the uplink interval are allocated by the base station in a reserved manner, so that there is no contention of data between terminals during this time. The upcoming transmission interval is used only when each terminal is first powered on or requests to allocate radio resources. Since this portion is not a reservation method, each terminal can competitively access a time slot of this portion. have. Therefore, there is a possibility that a collision of data occurs. When a collision occurs, it is common to apply a separate conflict resolution algorithm to resolve the conflict.

The configuration of FIG. 2 has been accommodated in the present invention in a schematic manner that has recently been studied. In general, the uplink transmission interval is inserted at the last position of the uplink transmission interval, but in one embodiment according to the present invention, it is positioned at the beginning of the uplink transmission interval to process the result of the upcoming competition interval in actual hardware implementation. The spare time was secured. By doing this, it is possible to notify each terminal of the result of the uplink contention transmission interval in the next frame.

The length of data allocated to each transmission interval shown in FIG. 2 is always allocated such that the total length of the data is an integer multiple of the OFDM symbol length, unlike the conventional spread spectrum scheme. That is, the frame header, the control signal, and the contention transmission interval signal transmitted in OFDM-BPSK are all allocated by an integer multiple of 3 bytes, and the data transmission interval using various types of modulation schemes shown in [Table 1] is 54 bytes. Assign as integer multiple. In this way, transmission is possible without inserting unnecessary bits in order to match the number of data bits in the OFDM symbol in the physical layer.

3 is a configuration diagram of a protocol data unit (PDU) according to an embodiment of the present invention, which will be described in detail as follows.

The PDU is used for transmitting user data, and the C-PDU is used for transmitting control signals in the MAC layer. The type of user data may be in the form of an IP packet or an ATM cell.

In FIG. 3, the type area indicates the type and type of the corresponding data, the sequence number area indicates the sequence number for the IP packet, and Frag. When a long IP packet is divided into 48 bytes and transmitted, the area is used to identify each fragment. In addition, the user data area is an area to which an IP packet (or ATM cell) is mapped, and the CRC area is attached with a cyclic redundancy check code for the corresponding PDU.

An example of the type region of the PDU is shown in [Table 2].

Table 2 Example of PDU Type Areas

Type code meaning 00 / h Spare 8x / h Indicates that split pieces remain 9x / h Indicate whether to resend Ax / h Display additional radio resource requests 01 / h IP packet / ATM Cell data 02 / h Indicates that it is control data 03 / h to 7F / h Spare

As can be seen from above, the type region of the PDU is used to distinguish what kind of actual data of the PDU is, and to request additional channels without repetitive transmission of the corresponding PDU and the contention channel in the UE.

In FIG. 3, the type area of the contents of the C-PDU indicates the type and type of the corresponding control data, and the control data area is allocated control and operation management information for processing the media access control function, and the CRC area is the corresponding C. A circular redundancy check code for the PDU is attached.

An example of the type region of the C-PDU is shown in [Table 3].

[Table 3] Example of the Type Area of C-PDU

Type code function meaning 00 / h reserved Spare 01 / h association Request Notify the base station when the terminal powers on for the first time 02 / h association Response Base station responds to association request 03 / h association Confirm Confirmation response to association response 04 / h disassociation Request association release request 05 / h to 7F / h reserved Spare 80 / h Resource Request Radio resource allocation request from terminal 81 / h Alive request The base station periodically checks whether the connection with the terminal is valid 82 / h Alive response UE's response to the Alive request 83 / h ACK Acknowledgement Signal 84 / h to FF / h reserved reserved

4 is a configuration diagram of a frame header according to an embodiment of the present invention, which will be described in detail as follows.

The total length of the frame header consists of 9 + 6 * n bytes to be an integer multiple of the OFDM symbol. N is the sum of the number of mobile terminals allocated to the current frame.

The frame header includes a network address, a base station address, a power control bit, a channel status indication bit indicating a channel state, an uplink contention number bit specifying a number of contention slots, a terminal information area providing allocation information for each terminal, and contention. It consists of a race slot result bit that notifies the reception of a slot and a spare and cyclic redundancy check code.

An embodiment of the frame header is shown in [Table 4].

Table 4 Example of Frame Header

Contents meaning Network address Specify at initialization Base station address Specify at initialization Power control Specify the transmit power strength and the desired receive strength with 4 bits each, and encode the strength in 16 steps with 4 bits each: 0 / h: x dB1 / h: x + y dB .... F / h: x + 15y dB Channel status Current radio resource allocation status 0 / h: not busy 1 / h: busy Other: Reserved Upcoming Competition Slots Indicates whether the upstream contention slot in the previous frame is received normally Terminal information Detailed information of each assigned terminal Upcoming Competition Results Indicates whether the upstream contention slot in the previous frame is received normally Spare Spare CRC Cyclic redundancy check code

Each terminal information area is composed of a terminal address, a connection identifier, a type, a modulation scheme applied, a start position of a slot allocated within a frame, the number of slots allocated to the corresponding terminal, and a reserved bit, and has a total size of 6 bytes.

An embodiment of the terminal information area is shown in [Table 5].

[Table 5] Embodiment of the terminal information area

Contents meaning Terminal address Terminal identification number assigned by base station at initialization Connection identifier When providing connectivity services, a number to distinguish each service Kinds TABLE 6 Modulation method Code value of [Table 1] Starting position Displays the start position of the PDU allocated to the UE in 13 MAC bits in all MAC frames. Number of slots allocated Specify the total number of PDUs assigned to the terminal, up to 64 Spare Spare

As shown in [Table 5], the category area can be sufficiently used as part of the control data transmission as shown in [Table 6], and information such as additional radio resource request or retransmission request during data transmission from the terminal to the base station. Can be delivered to the base station without a separate C-PDU.

An example of the type area in the terminal information area is shown in [Table 6].

[Table 6] Embodiments of the Type Area in the Terminal Information Area

Type code function meaning 0x Upward PDU Display Upward PDU 01 / h Display Empty PDU 02 / h Indicates that it was resent 03 / h Display additional radio resource requests 04 / h ACK indication for previous PDU 05 / h to 7F / h Spare 8x Downward PDU Mark Downward PDU 81 / h Display Empty PDU 82 / h Indicates that it was resent 83 / h - 84 / h ACK indication for previous PDU 85 / h to FF / h Spare

If the frame is formed of the entire frame structure shown in FIG. 2, the data structure shown in FIGS. 3 and 4, and the frame header structure, each time slot is allocated to an integer multiple of the OFDM symbol required for the physical layer, so that the physical layer is allocated. During signal modulation and demodulation, the unnecessary process can be reduced by counting the number of data input from the MAC layer and mapping directly without zero-padding for adjusting the data length by an integer multiple of the OFDM symbol. On the other hand, each terminal first receives the frame header from the base station, and then analyzes each slot information to determine whether there is information assigned to the corresponding frame, and by analyzing the contents, to the self without conflict in the frame Data can be transmitted to the base station through the assigned slot.

5 is a configuration diagram of a base station and a terminal according to an embodiment of the present invention, wherein the base station and the terminal are composed of a physical layer processor 510, a MAC processor 520, and a host 530.

The host 530 is a user's notebook computer and the like. That is, in the case of a terminal, the host 530 is responsible for processing an application layer and a TCP / IP layer function and transmitting and receiving an IP packet in a Windows OS environment. The MAC processor 520 receives an IP packet or an ATM cell from the host 530, configures a MAC frame, and sends the MAC frame to the physical layer processor 500. The physical layer processor 500 is required at the physical layer. After inserting a preamble and a header, and transmits the data wirelessly through the antenna. Meanwhile, the data received from the antenna is removed from the preamble and the header in the physical layer to extract the original MAC frame. The extracted MAC frame data is decrypted by the MAC processor 520 and converted into an IP packet, and then transmitted to the host 530 again.

6 is a block diagram of the MAC frame processor illustrated in FIG. 5, wherein the MAC frame processor includes a shared data store 605, a packet divider 610, a PDU generator 615, a TDMA / TDD frame transmitter 620, First buffer 625, transmission timing generator 630, C-PDU generator 635, C-PDU receiver 640, channel allocation processor 645, second buffer 650, TDMA / TDD frame The receiver 655 includes a receiver 655, a PDU receiver 660, a packet assembler 665, and a reception timing generator 670.

First, the IP packet transmission process is as follows.

As shown in FIG. 6, an IP packet is exchanged with a host using the shared data storage 605. In other words, the host writes an IP packet to be transmitted to the shared data store 605. SRAM and the like are generally used as the shared data storage 605. The channel allocation processor 645 periodically checks whether a host writes a new packet to the shared data store 605. If it is determined that a new packet has been received, the following procedure is performed.

The first stored IP packet is divided in 48 byte units in the packet divider 610. This time the FDU of the PDU. The value of the area is determined. The divided data forms the PDU shown in FIG. 4 in the PDU generator 615 and stores the PDU. The channel allocation processor 645 is responsible for controlling the output order of each stored PDU, and informs the TDMA / TDD frame transmitter 620 of the PDU list to be transmitted through the current frame. The TDMA / TDD frame transmitter 620 receives a PDU list from the channel allocation processor 645 to generate a frame header, and reads a corresponding PDU from the PDU generator / storage 615 to form a MAC frame. . The formed MAC frame is written to the first buffer 625 for delivery to the physical layer. The first buffer 625 is used because the operation clock speeds of the physical layer processor and the MAC processor are different, and have a first in first out (FIFO) structure. After the MAC frame data is written to the first buffer 625, the MAC layer is transmitted over the air by requesting transmission to the physical layer processor. Meanwhile, the channel allocation processor 645 instructs the C-PDU generator 635 to generate and transmit a C-PDU when necessary to transmit control and operation management data. The generated C-PDU is sent to the TDMA / TDD frame transmitter 620 to form a MAC frame with other data. The transmission timing generator 630 is responsible for generating a transmission timing signal of the MAC processor.

The IP packet reception process is as follows.

As shown in FIG. 6, the physical layer processor wirelessly receives data and writes the data to the second buffer 650. The second buffer 650 is a first in first out (FIFO) buffer. When the data is full in the second buffer 650, the TDMA / TDD frame receiver 655 reads it to identify whether it is a C-PDU or a PDU, and if it is a C-PDU, the C-PDU receiver 640. Send to). According to the result processed by the C-PDU receiver 640, the contents related to channel allocation are transferred to the channel allocation processor 645 so that the channel allocation processor 645 updates the channel allocation. Typically, the information content from the C-PDU receiver 640 to the channel allocation processor 645 is retransmission request information, channel request information of the terminal, and the result of contention channel processing.

The received PDU is inputted to the PDU receiver 660 and converted into an IP packet. The type of each PDU is identified and the information of the corresponding UE is passed to the channel allocation processor 645. Since the IP packet passed through the PDU receiver 660 is obtained by dividing the original IP packet into 48-byte units, the packet assembler 665 divides each divided packet into the original IP packet to convert the original IP packet into the original IP packet. Assemble with The assembled original IP packet is stored in the shared data store 605. Upon completion of storage in the shared data store 605, the MAC processor informs the host that an IP packet has been received as an interrupt. The host receiving the interrupt completes the reception by reading the IP packet in the shared data store 605. The reception timing generator 670 is responsible for generating a reception timing signal of the MAC processor.

On the other hand, the configuration and operation of the terminal side is similar to the operation in the base station described above, but there are some differences.

First, the reception process is as follows.

The MAC frame data received from the physical layer processor extracts frame header information from the TDMA / TDD receiver 665 to determine whether there is information allocated to itself. If there is information allocated, only the corresponding PDU is processed as in the base station. If no channel is assigned, no reception is performed.

The transmission process is as follows.

First, if the PDU is allocated to itself by extracting the frame header information in the reception process, the following procedure is performed. The process up to the PDU generator 615 in the transmission process is the same as in the base station. Since the terminal does not generate a TDMA / TDD frame, the TDMA / TDD frame transmitter 620 bypasses and writes a PDU to the first buffer 625. The subsequent procedure is the same as in the base station. If no channel is allocated, no transmission is made.

The present invention as described above is recorded on a computer-readable recording medium, and can be processed by a computer.

As described in detail above, the present invention provides an apparatus and method for constructing a MAC frame, which can be utilized for early construction of a 25Mbps high-speed WLAN system using an OFDM modulation scheme.

The technical spirit of the present invention has been described above with reference to the accompanying drawings, but this is by way of example only and not by way of limitation to the present invention. In addition, it is obvious that any person skilled in the art may make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (7)

In the method of configuring a medium access control (MAC) frame of a wireless LAN system transmitting an IP packet or an ATM cell by Orthogonal Frequency Division Multiplexing (OFDM) modulation method, Dividing a time division multiple access / time division duplex (TDMA / TDD) frame into a downlink transmission interval and an uplink transmission interval; And When each terminal requests power on or radio resource allocation, the uplink transmission section is located at the first portion of the uplink transmission section, and the rest of the uplink transmission section is allocated in a reserved manner. And configuring the TDMA / TDD frame, And a length of data allocated to each transmission interval is allocated to be an integer multiple of an OFDM symbol length. The method of claim 1, The frame header, the control signal and the competitive transmission interval signal constituting the MAC frame are formed by an integer multiple of 3 bytes, and the data transmission interval is formed by an integer multiple of 54 bytes. How to configure MAC frame. A downlink transmission region including a frame header, a downlink control signal transmission region, and a downlink data signal transmission region; In a medium access control (MAC) frame of a wireless LAN system including an uplink transmission area including an uplink contention transmission area, an uplink control signal transmission area, and an uplink data signal transmission area, When each terminal requests power on or radio resource allocation, the uplink transmission section is located at the first portion of the uplink transmission section, and the rest of the uplink transmission section is allocated in a reserved manner. And constituting the TDMA / TDD frame, and assigning a length of data allocated to each of the transmission intervals to be an integer multiple of the length of an OFDM symbol. . The method of claim 3, wherein The PDU (Protocol Data Unit) included in the MAC frame and used to transmit user data, A type area for inputting, modifying, retrieving, and deleting the type and type of the corresponding data; A sequence number area for inputting, modifying, inquiring, and deleting sequence numbers for IP packets; A fragment that can be entered, modified, inquired, and deleted to identify each fragment as it is sent, when long IP packets are sent in 48-byte segments. An area; A user data area that can be entered, modified, inquired and deleted to map an IP packet or ATM cell; A computer-readable recording medium having recorded thereon a PDU, comprising a CRC area for inputting, modifying, inquiring, and deleting a cyclic redundancy check code for the PDU. The method of claim 3, wherein The C-PDU included in the MAC frame and used to transmit user data, A kind area for inputting, modifying, inquiring, and deleting the type and form of the control data; A control data area for inputting, modifying, inquiring, and deleting control and operation management information for processing a MAC function; A computer-readable recording medium having recorded a C-PDU, comprising a CRC area for inputting, modifying, inquiring, and deleting a cyclic redundancy check code for the C-PDU. The method of claim 3, wherein The frame header, A network address area for entering, modifying, inquiring, and deleting a network address; A base station address area for entering, modifying, querying, and deleting base station addresses; A power control bit area for inputting, modifying, inquiring, and deleting the power control bits; A channel status display area for inputting, modifying, viewing, and deleting channel status; An upcoming contention slot number area for inputting, modifying, retrieving, and deleting the number of contention slots; A terminal information area capable of inputting, modifying, inquiring, and deleting allocation information for each terminal; A contention slot result area for inputting, modifying, retrieving, and deleting contention slots; A computer-readable recording medium having a frame header recorded thereon including a CRC area for inputting, modifying, inquiring and deleting a cyclic redundancy check code. In the MAC (Medium Access Control) frame processing apparatus of a wireless LAN system for transmitting an IP packet or an ATM cell by Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme, Means for dividing a time division multiple access / time division duplex (TDMA / TDD) frame into a downlink transmission interval and an uplink transmission interval; And When each terminal requests power on or radio resource allocation, the uplink transmission section is located at the first portion of the uplink transmission section, and the rest of the uplink transmission section is allocated in a reserved manner. Means for constructing the TDMA / TDD frame, MAC frame processing apparatus of a wireless LAN system, characterized in that the length of the data allocated to each transmission interval is allocated to be an integer multiple of the OFDM symbol length.