JP4930137B2 - Wireless communication apparatus, wireless communication method and program - Google Patents

Description

  The present invention relates to a wireless communication device, a wireless communication method, and a program, and in particular, a wireless communication device having a wireless LAN communication function for changing a communication rate and transmitting a frame to another wireless communication device, and wireless communication The present invention relates to a method and a program.

  Japanese Unexamined Patent Application Publication No. 2005-102228 discloses an improvement plan for rate fallback (hereinafter also simply referred to as “fallback”) at the time of retransmission in a wireless LAN system compliant with the IEEE802.11 series. In the same publication, as shown in FIG. 7, when an acknowledgment (ACK frame) for a transmission frame cannot be received, the probability that a retransmission frame is normally transmitted and an acknowledgment (ACK frame) can be received, and In order to prevent the influence from affecting the subsequent frames, it has been proposed to temporarily lower the communication rate only for the frames.

JP 2005-102228 A

  However, in the above-described prior art, as a result of the fallback, as shown in FIG. 8, the frame size is variable and the communication medium is occupied by a very large frame, so that the throughput of the entire wireless LAN system is increased. (See “Data / Management Frame after Falling Back Communication Rate” in FIG. 8).

  In particular, when there is a difference in transmission power between wireless communication devices, a frame has arrived from the wireless communication device on the transmission side, but an acknowledgment (ACK frame) cannot be received from the wireless communication device on the reception side. It is possible that the communication rate falls more than necessary and falls into a state.

  The present invention has been made in view of the above-described circumstances, and the object of the present invention is to reduce the overall throughput generated when an acknowledgment (ACK frame) cannot be received on the frame transmission side of the wireless LAN system. It is to suppress the decline.

  According to the first aspect of the present invention, a wireless communication apparatus having a wireless LAN communication function for changing a communication rate and transmitting / receiving a frame to / from another wireless communication apparatus, when operating as a transmission side, When an ACK frame for the received data or management frame is not received, the same frame is retransmitted at the same rate until the predetermined number of rate change retransmissions, and when operating as a receiving side, it is received from another wireless communication terminal There is provided a wireless communication apparatus characterized by lowering the transmission rate of an ACK frame before the number of retransmission frame receptions reaches the predetermined rate change retransmission number.

  According to a second aspect of the present invention, there is provided a wireless communication method between wireless communication devices having a wireless LAN communication function of changing a communication rate and transmitting a frame to another wireless communication device, When the transmitting-side radio communication apparatus fails to receive the ACK frame for the transmitted data or management frame, it retransmits the same frame at the same rate until the predetermined number of rate change retransmissions, and the receiving-side radio communication apparatus However, there is provided a wireless communication method characterized in that an ACK frame is transmitted at a reduced transmission rate before the number of times of receiving the retransmitted frame reaches the predetermined rate change retransmission number.

  According to a third aspect of the present invention, there is provided a program for changing a communication rate and causing another wireless communication apparatus to execute a wireless communication apparatus having a wireless LAN communication function for transmitting a frame. When the ACK frame for the transmitted data or the management frame is not received, the process of resending the same frame at the same rate until the predetermined rate change retransmission count is operated as the receiving side. A program for causing the wireless communication apparatus to execute a process of reducing the communication rate and transmitting an ACK frame before the number of retransmission frames received from another wireless communication terminal reaches the predetermined rate change retransmission number. Is provided.

  According to the present invention, it is possible to suppress a decrease in overall throughput that occurs when an acknowledgment (ACK frame) cannot be received on the frame transmission side of a wireless LAN system, in other words, to communicate with more wireless communication devices. It becomes possible to give an opportunity. The reason is that even if the ACK frame cannot be received on the transmitting side, the same frame is transmitted a predetermined number of times without changing the communication rate. This is because the communication rate of the ACK frame having a small influence on the size is lowered before the number of times is reached.

[First Embodiment]
Next, the best mode for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a wireless LAN terminal (wireless communication apparatus) according to an embodiment of the present invention. Referring to FIG. 1, a wireless LAN terminal 100 including a control unit 101, a MAC (Medium Access Control) unit 102, a PHY (RF) unit 103, a storage unit 104, a clock unit 105, and a power supply unit 106. It is shown.

  The control unit 101 executes software such as an operating system (OS), an application program, and a TCP / IP communication program, and transmits / receives application data to / from other wireless LAN terminals via the MAC unit 102 and the PHY (RF) unit 103. Do.

  The MAC unit 102 performs frame transmission / reception with other stations by controlling the PHY (RF) unit 103 according to the MAC protocol defined in the IEEE 802.11 standard.

  The PHY (RF) unit 103 transmits / receives a frame to / from another wireless device, that is, another wireless LAN terminal through the communication medium with the communication rate and modulation method instructed from the MAC unit 102.

  The storage unit 104, the clock unit 105, and the power supply unit 106 are well known to those skilled in the art and are not directly related to the present invention, and thus the description thereof is omitted.

  Next, the flow of the frame transmission / reception operation between the wireless LAN terminals 100 will be described with reference to the sequence chart of FIG. Hereinafter, the wireless LAN terminal 100 on the transmission side that transmits the frame first is the wireless LAN terminal 100a, and the wireless LAN terminal 100 that transmits an acknowledgment (ACK frame) to the frame from the wireless LAN terminal 100a is the wireless LAN terminal 100b. Will be described.

  Referring to FIG. 2, first, when the wireless LAN terminal 100a transmits a data frame or a management frame (data / management frame) (step S1), the wireless LAN terminal 100b receives the data / management frame normally. (Step S2), an ACK frame that is an affirmative response is transmitted (Step S3).

  Here, it is assumed that the wireless LAN terminal 100a cannot receive the ACK frame. In this case, the wireless LAN terminal 100a retransmits the same frame as the previous one after setting the retransmission bit of the frame control field shown in FIG. 3 (steps S4 and S5).

  The receiving-side wireless LAN terminal 100b determines whether or not the received frame is a retransmission frame based on the state of this retransmission bit (step S6). When the retransmission bit is set, the wireless LAN terminal 100b on the receiving side further refers to the sequence number in the sequence control field in FIG. 3 and the MAC address (addresses 1 and 2), and the received frame was previously received. It is confirmed that it is the same as the frame (step S7).

  Here, when it can be confirmed that the same frame has been retransmitted (both YES in steps S6 and S7), the wireless LAN terminal 100b performs fallback to gradually reduce the transmission communication rate, and performs wireless communication. An ACK frame is transmitted to the LAN terminal 100a (steps S8 and S9).

  Since the communication range is generally widened by the fallback, there is a possibility that the wireless LAN terminal 100a that could not receive the previous ACK frame having a high communication rate can normally receive the ACK frame after the fallback. Get higher.

  In the example of FIG. 2, it has been described that the wireless LAN terminal 100a can receive the ACK frame in the first fallback. However, when the ACK frame after the fallback cannot be received, the wireless LAN terminal 100a is determined in advance. The data / management frame is retransmitted at the same rate until the specified rate change retransmission count is reached. In this case, the wireless LAN terminal 100b repeats the same operation in response to reception of the retransmission frame, performs further fallback, and transmits an ACK frame. Thereby, the possibility that the ACK frame can be normally received on the wireless LAN terminal 100a side gradually increases.

  FIG. 4 shows the present invention under the conditions that the initial communication rate is 11 Mbps, the communication rate after fallback is 1 Mbps, the data frame size is 1500 bytes (12000 bits), and the frame size is 14 bytes (112 bits). It is the figure showing the transmission time of each frame at the time of applying and performing a fallback only by the receiving side.

  Referring to FIG. 4, even if the wireless LAN terminal 100a on the transmission side cannot receive the ACK frame for the original data frame or management frame, the data frame or management is maintained while maintaining the same communication rate of 11 Mbps. The frame is resent. On the other hand, the reception-side wireless LAN terminal 100b performs fallback by receiving the retransmission frame and lowers the transmission rate of the ACK frame from 11 Mbps to 1 Mbps, and transmits the ACK frame. The effect is clear when compared with FIG. 8 showing the frame transmission time by the conventional fallback control under the same conditions.

  As described above, since the configuration is such that only the receiving side wireless LAN terminal falls back and transmits the ACK frame, the data / management frame having a size larger than the ACK frame is transmitted to the transmitting side wireless LAN terminal. The effect that the occupation time of the communication medium can be shortened compared to the fallback can be obtained.

  Although omitted in the above description, when communication is performed between a plurality of wireless LAN terminals, since the communication medium is shared, the occupation time of the communication medium by the specific wireless LAN terminal can be shortened. It also means that more wireless LAN terminals are given communication opportunities.

  In addition, since the communication rate of the wireless LAN terminal on the transmission side is maintained, an effect of preventing a decrease in throughput is obtained as compared with the conventional method.

[Second Embodiment]
Next, a second embodiment in which changes are made to the first embodiment will be described. As long as the conditions have not changed when the fallback is applied to the ACK frame, it is highly likely that the wireless LAN terminal 100a cannot receive the frame transmitted from the wireless LAN terminal 100b at the communication rate before the fallback. .

  Therefore, the present embodiment is characterized in that the wireless LAN terminal 100b that has performed the fallback of the ACK frame applies the communication rate after the fallback to the subsequent data / management frame.

  FIG. 5 is a diagram showing the transmission time of each frame when the wireless LAN terminal 100b that has received the retransmission frame performs fallback and transmits an ACK frame and a data / management frame to be transmitted subsequently. Note that the communication rate and frame size are the same as in the example of FIG. In the example of FIG. 5, by receiving the retransmission frame, the receiving wireless LAN terminal 100b performs fallback and lowers the transmission rate of the ACK frame from 11 Mbps to 1 Mbps, and applies 1 Mbps after this fallback, Subsequent data frames or management frames are transmitted.

  As a result, the possibility that the wireless LAN terminal 100a can normally receive the data / management frame transmitted by the wireless LAN terminal 100b that was the initial receiving side is improved.

[Third Embodiment]
Next, a description will be given of a third embodiment in which changes are made to the first and second embodiments. The cause of having to perform the fallback includes a very short temporary change in the communication environment. In such a case, there is a high possibility that the next ACK frame can be normally received.

  Therefore, in the present embodiment, the number of consecutive receptions of retransmitted frames (RCn) is set to a predetermined threshold (RTn) so as to prevent unconditional fallback in an environment in which changes in the communication environment frequently occur. A change has been made to perform a fallback if the number is exceeded. However, it is assumed that the threshold (RTn) is set to a value smaller than the number of rate change retransmissions at which the transmission side repeats retransmission of the same frame at the same rate.

  FIG. 6 is a sequence chart showing the flow of frame transmission / reception between wireless LAN terminals according to the present embodiment. Steps S21 to S27, steps S32 and S33 in FIG. 6 are the same as steps S1 to S7, S9 and S10 in FIG. 2 showing the sequence of the first embodiment, and thus are omitted.

  The difference from the first embodiment is that even if it can be confirmed that the same frame has been retransmitted (YES in both steps S26 and S27), the storage unit does not immediately perform fallback. A point that increments the retransmission frame reception counter RCn held in 104 (step S28), and a point that the retransmission frame reception counter RCn is cleared when it cannot be confirmed that the same frame has been retransmitted continuously ( Step S31).

  Therefore, if the wireless LAN terminal 100b on the receiving side determines that the number of times of continuous reception of retransmitted frames (RCn) has exceeded a predetermined threshold value RTn (YES in step S29), the wireless LAN terminal 100b performs fallback and An ACK frame is transmitted to 100a (steps S30 and S32).

  According to the present embodiment that operates as described above, retransmission of the ACK frame at the current high rate is attempted several times, and the communication performance is continuously improved when the distance between the wireless LAN terminals is increased. Falldown can only be performed if it falls.

  In each of the embodiments described above, the number of times that the transmission side repeats retransmission of the same frame at the same rate when the ACK frame cannot be received (rate change retransmission number) is described as being predetermined. A configuration may be adopted in which the number of retransmissions (rate change retransmissions) is designated each time. In this case, for example, the transmission side wireless LAN terminal 100a notifies the wireless LAN terminal 100b of the number of rate change retransmissions in advance. Even in this case, the wireless LAN terminal 100b sets a threshold value RTn smaller than the number of rate change retransmissions so as to lower the transmission rate of the ACK frame at least before reaching the designated rate change number of retransmissions. It is possible to prevent the fallback first.

  The preferred embodiments of the present invention have been described above. However, those skilled in the art will recognize that the radio communication apparatus on the receiving side that has received the retransmission frame first reduces the communication rate of the ACK frame without departing from the gist of the present invention. Various possible modifications and substitutions can be made.

  For example, the present invention is equipped with a wireless LAN function such as a mobile phone having a wireless LAN function compliant with the IEEE802.11 series standard, a personal handyphone system (PHS), a personal data assistant (PDA). The present invention can be applied to all wireless communication devices.

It is a block diagram showing the structure of the wireless LAN terminal which concerns on one Embodiment of this invention. 6 is a sequence chart showing a flow of frame transmission / reception between wireless LAN terminals according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of an IEEE 802.11 frame structure and a frame control field thereof. It is a figure for demonstrating the shortening effect of the frame transmission time by this invention. It is a figure for demonstrating the effect | action and effect of the 2nd Embodiment of this invention. It is a sequence chart showing the flow of the frame transmission / reception between the wireless LAN terminals which concern on the 3rd Embodiment of this invention. It is the sequence chart showing the flow of the frame transmission / reception between the conventional wireless LAN terminals. It is the figure showing the frame transmission time by the conventional fallback control on the same conditions as FIG.

Explanation of symbols

100, 100a, 100b Wireless LAN terminal 101 Control unit 102 MAC (Medium Access Control) unit 103 PHY (RF) unit 104 Storage unit 105 Clock unit 106 Power supply unit

Claims (12)

A wireless communication device having a wireless LAN communication function for changing a communication rate and transmitting / receiving a frame to / from another wireless communication device,
When operating as a transmitting side, when the ACK frame for the transmitted data or management frame is not received, the same frame is retransmitted at the same rate until the predetermined number of rate change retransmissions,
When operating as a receiving side, lowering the transmission rate of the ACK frame before the number of retransmission frames received from other wireless communication terminals reaches the predetermined rate change retransmission number,
A wireless communication device. When operating as a transmitting side, notifying the wireless communication device on the receiving side of the predetermined rate change retransmission count;
The wireless communication apparatus according to claim 1. Transmitting the ACK frame while maintaining the current communication rate until the number of receptions of the same retransmission frame exceeds the number of reception side rate change retransmissions smaller than the predetermined rate change retransmission number;
The wireless communication device according to claim 1, wherein the wireless communication device is a wireless communication device. If there is a frame to be transmitted continuously to the wireless communication terminal that has transmitted the ACK frame, transmitting using the communication rate at the time of transmitting the ACK frame,
The wireless communication apparatus according to any one of claims 1 to 3. A wireless communication method between wireless communication devices having a wireless LAN communication function of changing a communication rate and transmitting a frame to another wireless communication device,
When the transmitting side wireless communication device fails to receive the ACK frame for the transmitted data or management frame, it retransmits the same frame at the same rate until the predetermined number of rate change retransmissions,
A wireless communication device on the receiving side transmits an ACK frame at a lower transmission rate before the number of times of reception of the retransmitted frame reaches the predetermined number of rate change retransmissions;
A wireless communication method characterized by the above. Further, the transmitting-side wireless communication apparatus notifies the receiving-side wireless communication apparatus of the predetermined rate change retransmission count,
The wireless communication method according to claim 5. The reception-side wireless communication apparatus maintains the current communication rate and transmits an ACK frame until the number of receptions of the same retransmission frame exceeds the number of reception-side rate change retransmissions smaller than the predetermined rate change retransmission number thing,
The wireless communication method according to claim 5 or 6. When the reception-side wireless communication device transmits a frame following the ACK frame to the transmission-side wireless communication device, the frame is transmitted at a communication rate when the ACK frame is transmitted;
The wireless communication method according to any one of claims 5 to 7. A program for changing a communication rate and causing another wireless communication device to execute a wireless communication device having a wireless LAN communication function for transmitting a frame,
When operating as a transmission side, when an ACK frame for the transmitted data or management frame cannot be received, a process of retransmitting the same frame at the same rate until a predetermined rate change retransmission count,
When operating as a receiving side, a process of lowering the communication rate and transmitting an ACK frame before the number of retransmission frames received from another wireless communication terminal reaches the predetermined rate change retransmission number,
A program to be executed by each of the wireless communication devices.   10. The program according to claim 9, wherein, when operating as a transmission side, the program further causes the radio communication device to execute processing for notifying the radio communication device on the reception side of the predetermined number of rate change retransmissions. Transmitting the ACK frame while maintaining the current communication rate until the number of receptions of the same retransmission frame exceeds the number of reception side rate change retransmissions smaller than the predetermined rate change retransmission number;
The program according to claim 9 or 10, wherein: If there is a frame to be transmitted continuously to the wireless communication terminal that has transmitted the ACK frame, transmitting using the communication rate at the time of transmitting the ACK frame,
The program according to any one of claims 9 to 11.

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