JP2005136884A - Radio communication apparatus and frame redirection method in radio communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accelerate the speed of a wireless LAN using a radio communication apparatus with a comparatively low throughput. <P>SOLUTION: When a MAC header of a received frame is detected, the creation of a reply frame corresponding to the received frame is started (steps S4-S5). An FCS added in the end of the received frame is utilized to check normality of the received frame (step S8). When the received frame is normal, the reply frame previously created in step S5 is redirected to a source of the received frame (step S10). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wireless communication apparatus and a wireless frame return method used in a wireless communication system.

  In recent years, with the spread of personal computers and their speeding up, speeding up of LANs for connecting computers has been promoted. On the other hand, an environment in which the arrangement of each computer can be flexibly changed and an environment in which a LAN cable does not need to be laid are desired, and wireless LANs are becoming widespread. Against this background, the IEEE 802.11 committee has been established, and “IEEE 802.11” as a wireless LAN standard has been standardized.

  In a wireless LAN, a radio frame transmitted from a certain node is usually transmitted to a plurality of nodes provided in the system. Here, the transmission destination address and the transmission source address are given to the radio frame. Then, the node corresponding to the transmission destination address captures the data stored in the received radio frame and returns a reply frame to the transmission source of the radio frame. In this case, the reply frame is an ACK frame, and is returned to notify the transmission source that the radio frame has been normally received. As described above, in a wireless LAN, data transmission is normally performed while confirming the normality of wireless frame transmission.

In order to increase the speed of data transmission in the wireless LAN as described above, it is necessary to shorten the time from when the wireless frame is received to when the reply frame is transmitted at the wireless frame transmission destination node. For this reason, this time is prescribed in IEEE 802.11. For example, the time from when a radio frame is received to when an ACK frame is transmitted is defined as an SISF (Short Inter Frame Space) time, which is “16 μs” in IEEE802.11a and “10 μs” in IEEE802.11b. (For example, see Non-Patent Document 1).
"802.11 High Speed Wireless LAN Textbook Hideaki Matsue, Masahiro Morikura IDG Japan ISBN4-87280-490-2" 47-84

  However, in the conventional technique, when each node receives a radio frame, first, the normality of the frame is confirmed using an FCS (Frame Check Sequence) field added at the end thereof. Subsequently, when the received frame is normal, it is confirmed whether the frame is addressed to the own node by detecting the transmission destination address. If the received frame is addressed to the own node, a reply frame to be returned to the transmission source of the frame is created and transmitted.

  As described above, conventionally, after confirming the normality of the FCS, the address is confirmed and a reply frame is created. For this reason, when the processing capability of the wireless communication apparatus is not sufficient, it is difficult to execute those processes within a predetermined time defined by IEEE 802.11. At this time, if the transmission of the reply frame is delayed, the transmission source of the wireless frame determines that the transmission of the wireless frame has failed, and the wireless frame is retransmitted depending on the protocol.

This problem can be solved if the processing capability of the wireless communication device is high. However, if the processing capability is increased, it will not be possible to answer the request for cost reduction of the wireless communication device.
An object of the present invention is to realize a high-speed wireless LAN even when a wireless communication apparatus having a relatively low processing capability is used.

  When the wireless communication device of the present invention confirms that the received frame is normal by the creating means for creating a reply frame corresponding to the received frame, the confirming means for confirming the normality of the received frame, and the confirming means Transmission means for transmitting the reply frame to the transmission source of the received frame. Then, the creation means starts creating the reply frame before the confirmation means confirms the normality of the received frame.

  According to the present invention, it is possible to start creating a reply frame before receiving the frame to the end. Therefore, even when the reply frame must be transmitted within a predetermined time from the end of the received frame, and even when the processing capability of the wireless communication device is relatively low, the reply is surely made within the predetermined time. Frames can be created and transmitted.

  The creating unit may start creating the reply frame immediately after detecting the header area storing the transmission source address of the received frame. When a return frame is returned to the transmission source of the received frame, the transmission source address stored in the header area of the received frame may be set as the transmission frame destination address. That is, after detecting the header area, it is possible to start creating a reply frame without waiting for the end of reception of the subsequent data string.

  The confirmation means may confirm the normality of the frame by using a code given at the end of the received frame. Alternatively, the transmission means may discard the reply frame without transmitting it when the confirmation means does not confirm that the received frame is normal.

  According to another aspect of the present invention, there is provided a wireless communication apparatus comprising: a creating unit that creates a second frame corresponding to a received first frame; a confirmation unit that confirms the normality of the first frame; Transmitting means for transmitting the second frame to the transmission source of the first frame when it is confirmed that the first frame is normal; Then, the creation means starts creating the second frame before the confirmation means confirms the normality of the first frame. According to the present invention, in the sequence in which the second frame is transmitted due to the reception of the first frame, the creation of the second frame can be started before the first frame is received to the end. Therefore, even when the processing capability of the wireless communication apparatus is relatively low, the second frame can be transmitted within a short period from the end of reception of the first frame.

  According to the present invention, since the creation of a reply frame can be started before the frame is received to the end, even when the processing capability of the wireless communication device is relatively low, within a predetermined time from the end of the received frame A reply frame can be reliably created and transmitted.

Embodiments of the present invention will be described below with reference to the drawings. Here, it is assumed that the wireless communication system to which the present invention is applied is a wireless LAN specified in IEEE 802.11.
FIG. 1 is a diagram illustrating a basic sequence when a radio frame is transmitted in the radio communication system according to the embodiment. Here, it is assumed that there are four wireless communication nodes A to D, and the wireless communication node A transmits a data frame. Each wireless communication node is a wireless communication device having a function of transmitting and receiving signals via a wireless network. The wireless communication system of the embodiment may be infrastructure mode communication provided with an access point (master unit) or ad hoc communication without an access point.

  When the wireless communication node A transmits data to the wireless communication node B, the wireless communication node A transmits a data frame 1 in which the address of the wireless communication node B is set as a transmission destination address to the wireless network. At this time, the data frame 1 is received by the wireless communication nodes B, C, and D. Then, each of the wireless communication nodes B, C, and D detects the transmission destination address set in the received frame, and confirms whether the received frame is a frame addressed to the own node. In this case, the wireless communication node B recognizes that the received frame is a frame addressed to its own node. Then, the wireless communication node B returns a reply frame corresponding to the received frame (data frame 1) to the wireless communication node A that is the transmission source of the data frame 1. In this case, this reply frame is an ACK (Acknowledgment) frame for notifying that the data frame 1 has been normally received.

  When data is transmitted from the wireless communication node A to the wireless communication node C, the data frame 2 in which the address of the wireless communication node C is set as the transmission destination address is transmitted to the wireless network. In this case, the wireless communication node C recognizes that the received frame is a frame addressed to its own node. Then, the wireless communication node C returns a reply frame corresponding to the received frame (data frame 2) to the wireless communication node A that is the transmission source of the data frame 2.

  In the example illustrated in FIG. 1, when the wireless communication node A receives a corresponding ACK frame within a predetermined time after transmitting a data frame, the wireless communication node A regards that the data transmission is successful and proceeds to the next process. . On the other hand, when the corresponding ACK frame cannot be received within a predetermined time, it is considered that the data transmission has failed, and for example, the previously transmitted data is retransmitted. That is, if the return of the ACK frame is delayed, data retransmission is executed and the throughput of the entire wireless network may be reduced.

  FIG. 2A shows a data frame format. The data frame is composed of “preamble”, “PLCP header”, “MAC header (header area storing the transmission source address of the received frame)”, “data payload”, and “FCS”. The “preamble” is located at the beginning of the frame and is used to establish synchronization. The “PLCP header” specifies a transmission rate, a modulation method, and the like. The “MAC header” includes “frame control”, “duration”, “addresses 1 to 3”, and “sequence control”. In “frame control”, control information such as information for identifying a frame type (data frame, management frame, control frame, etc.) is set. “Duration” designates a scheduled period for using the wireless line. “Address 1”, “Address 2”, and “Address 3” designate the transmission destination address, the transmission source address, and the identifier of the basic service set (BSS) of the data frame, respectively. “Sequence control” designates a sequence number for controlling the transmission order.

The “data payload” is the main body of the data frame and stores data to be transmitted. “FCS (Frame Check Sequence)” is a code for detecting an error in the MAC header and data payload in a device that receives the data frame.
FIG. 2B is a diagram showing a format of an ACK frame as a reply frame. The ACK frame is composed of “preamble”, “PLCP header”, “MAC header”, and “FCS”. These areas are basically the same as the data frame, but “address 2” and “address 3” are not set in the ACK frame. The “frame type” set in the frame control area of the MAC header of the ACK frame displays a control frame.

FIG. 3 is a diagram illustrating a configuration of the wireless communication terminal 1 according to the embodiment. However, only the functions directly related to the operation of the present invention are illustrated here.
The input / output unit 11 terminates the wireless line, writes the wireless frame received via the wireless network to the reception memory 12, and sends the transmission frame stored in the transmission memory 13 to the wireless network in accordance with an instruction from the CPU 17. . The reception memory 12 is a dual port RAM, for example, and stores a frame received via the input / output unit 11. The transmission memory 13 is a dual port RAM, for example, and temporarily stores frames created by the CPU 17.

  The communication protocol processing unit 14 processes a frame according to a communication protocol in the wireless communication network to which the wireless communication device 1 belongs. When a predetermined trigger (for example, detection of a MAC header, completion of frame reception, etc.) is detected, the interrupt controller 15 is notified accordingly. The interrupt controller 15 generates an interrupt for the CPU 17 in accordance with the notification from the communication protocol processing unit 14.

  The ROM 16 stores various programs describing the operation of the wireless communication device 1. As programs directly related to the present invention, a transmission frame creation program, an FCS check program, and a transmission instruction program are stored. The CPU 17 controls the operation of the wireless communication device 1 by executing a program stored in the ROM 16. Further, the CPU 17 executes a program corresponding to the interrupt generated by the interrupt controller 15.

  These programs do not need to be stored in the ROM 16, and may be stored in a RAM area (not shown). Further, these programs do not need to be fixedly stored in the wireless communication terminal, and may be downloaded from outside to a RAM area (not shown) and executed.

FIG. 4 is a flowchart showing the operation of the wireless communication device 1. Here, processing related to an operation in which the wireless communication apparatus 1 creates and returns a reply frame corresponding to the received frame will be described.
Step S1 is a state waiting for reception of a radio frame. Then, when reception of a radio frame is started (step S2), a transition is made to a state of waiting for completion of detection of the MAC header of the frame (step S3). The start of reception of the radio frame may be detected, for example, when the power of the received wave exceeds a predetermined value, or the “preamble” added to the head of the radio frame. You may make it detect with extraction as an opportunity.

  The received frames are written to the reception memory 12 in order from the beginning. That is, the “preamble”, “PLCP header”, “MAC header”, “data payload”, and “FCS” of the received frame are sequentially written in the reception memory 12. At this time, the communication protocol processing unit 14 detects the MAC header from the bit string constituting the received frame. Then, when the reception of the MAC header is completed, the communication protocol processing unit 14 notifies the interrupt controller 15 to that effect, and the interrupt controller 15 generates an interrupt corresponding to the notification. Thereby, the CPU 17 recognizes that the MAC header has been received (step S4).

  When recognizing that the MAC header has been received, the CPU 17 creates a reply frame corresponding to the received frame in step S5. Here, it is assumed that the reply frame is the ACK frame shown in FIG. In this case, “address 1 (destination address)” set in the MAC header of the received frame is set as “source address” of the return frame, and “address 2” set in the MAC header of the received frame “(Transmission source address)” is set as the “transmission destination address” of the reply frame. As a result, this reply frame is returned to the transmission source of the received frame. When recognizing that the MAC header has been received, the CPU 17 creates a reply frame as described above and shifts to a state of waiting for the end of frame reception (step S6).

  When the communication protocol processing unit 14 detects the end of reception of the frame, it notifies the interrupt controller 15 to that effect. Then, the interrupt controller 15 generates an interrupt corresponding to the notification. Thereby, the CPU 17 recognizes that the reception of the frame has been completed (step S7).

  When the CPU 17 recognizes that the reception of the frame has been completed, in step S8, the CPU 17 checks the normality of the frame using the FCS assigned to the end of the frame. Further, in step S9, it is determined whether or not the received frame is a frame addressed to the own node by examining “address 1 (destination address)” of the received frame. If the normality of the received frame is confirmed by the FCS check and the received frame is a frame addressed to the own node, the reply frame created in step S5 is transmitted in step S10. As a result, this reply frame is returned to the transmission source of the received frame. On the other hand, if the normality of the received frame cannot be confirmed by the FCS check, or if the received frame is not a frame addressed to the own node, the reply frame created in step S5 is discarded without being transmitted.

  Note that the execution order of steps S8 and S9 may be reversed, and the process of step S9 may be executed before the reception of the frame ends. In the above-described embodiment, the creation of a reply frame is started when it is recognized that the MAC header has been received. However, the present invention is not limited to this, and is received by the FCS check in step S8. Widely applied to the method of starting the creation of a reply frame before confirming the normality of the frame.

  Further, the process of step S9 may be executed between step S4 and step S5. In this case, if the received frame is a frame addressed to the own node, the process proceeds to step S5. On the other hand, if the received frame is not a frame addressed to the own node, the process skips step S5 and proceeds to step S6 or returns to step S1.

  As described above, when the wireless communication device 1 detects the MAC header of the received frame, the wireless communication device 1 starts creating a corresponding reply frame without waiting for the completion of reception of the frame. For this reason, at the time when reception of the radio frame is completed, part or all of the processing for creating a reply frame has already been completed. Therefore, even when the prescribed value of the period from when the reception of the radio frame is completed until the reply frame is transmitted is short and the processing capacity of the CPU 17 is relatively low, the creation of the reply frame is not delayed. .

In this embodiment, the creation means, the confirmation means, and the transmission means described in the claims are realized by the CPU 17 executing a transmission frame creation program, an FCS check program, and a transmission instruction program, respectively (steps). S5, S8, S10).
FIG. 5 is a diagram for explaining reply frame creation / return timing. Here, it is assumed that reception of a radio frame is started at time T0 and reception of the frame is ended at time T2. In addition, it is assumed that time t from the end of a certain frame to the start of transmission of a reply frame corresponding to the frame (that is, a period from time T2 to time T3) is determined in advance.

  In the prior art, the creation of a reply frame is started after the normality of the received frame is confirmed by the FCS check. That is, it is necessary to execute both the FCS check process and the process of creating a reply frame within “time t”. For this reason, when the processing capability of the wireless communication apparatus is not sufficient, there is a possibility that transmission of the reply frame may be delayed.

  On the other hand, when detecting the MAC header of the received frame at time T1, the wireless communication device 1 according to the embodiment starts creating a reply frame prior to the FCS check. That is, the wireless communication apparatus 1 may create a reply frame between time T1 and time T3. Therefore, even when “time t” is short and the processing capability of the wireless communication device 1 is relatively low, the creation of the reply frame is not delayed. Here, “time t” corresponds to, for example, the IEEE 802.11 SIFS time. The SIFS time is 16 μs in IEEE 802.11a and 10 μs in IEEE 802.11b.

  In the example shown in FIG. 5, the creation of a reply frame is started when the MAC header is detected at time T1, but the present invention is not limited to this, and reception is performed by FCS check at time T2. Widely applied to the method of starting the creation of a reply frame before confirming the normality of the frame. Further, the creation of the reply frame may be started before time T1.

  Furthermore, in the above-described embodiment, the case where the ACK frame corresponding to the received frame is returned has been described. However, the present invention is not limited to this, and the frame (first frame) corresponding to the received frame (first frame) is described. 2 frames) and can be applied. For example, the present invention can be applied to a process in which a wireless communication apparatus that has received an RTS (Request to Send) frame transmits a CTS (Clear to Send) frame. In addition, when one data is divided into a plurality of data frames and transmitted, in a communication mode that requires an ACK frame for each data frame, the next data frame is transmitted when the ACK frame is received. The present invention can also be applied to processing.

  Further, in the above-described embodiment, the description has been made by taking up IEEE 802.11, but the present invention is not limited to this.

It is a figure which shows the basic sequence at the time of transmitting a frame in the radio | wireless communications system of embodiment. (A) is a data frame format, and (b) is a diagram showing an ACK frame format. It is a figure which shows the structure of the radio | wireless communication terminal of embodiment. It is a flowchart which shows operation | movement of a radio | wireless communication apparatus. It is a figure explaining the creation / return timing of a reply frame.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wireless communication apparatus 11 Input / output part 12 Reception memory 13 Transmission memory 14 Communication protocol processing part 15 Interrupt controller 16 ROM
17 CPU

Claims (6)

Creating means for creating a reply frame corresponding to the received frame;
Confirmation means for confirming the normality of the received frame;
Transmitting means for transmitting the reply frame to the transmission source of the received frame when the confirmation means confirms that the received frame is normal;
Have
The wireless communication apparatus, wherein the creation means starts creating the reply frame before the confirmation means confirms the normality of the received frame. The wireless communication device according to claim 1,
The radio communication apparatus, wherein the creating means starts creating the reply frame immediately after detecting a header area storing a transmission source address of a received frame. The wireless communication device according to claim 1,
The wireless communication apparatus, wherein the confirmation means confirms the normality of the frame by using a code given at the end of the received frame. The wireless communication device according to claim 1,
The wireless communication apparatus, wherein the transmission means discards the reply frame without transmitting it when the confirmation means does not confirm that the received frame is normal. Creating means for creating a second frame corresponding to the received first frame;
Confirmation means for confirming the normality of the first frame;
Transmitting means for transmitting the second frame to the transmission source of the first frame when the confirmation means confirms that the first frame is normal;
Have
The radio communication apparatus, wherein the creation means starts creating the second frame before the confirmation means confirms the normality of the first frame. A frame return method executed in a wireless communication node provided in a wireless communication network,
Creating a reply frame corresponding to the received frame;
Checking the normality of the received frame;
A step of transmitting the reply frame when it is confirmed that the received frame is normal;
Have
A frame reply method, wherein the creation of the reply frame is started before the normality of the received frame is confirmed.

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