JP2007166120A - Communication apparatus, base station apparatus, and terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication apparatus the throughput of which can be enhanced by suppressing a frame retransmission rate. <P>SOLUTION: The communication apparatus is provided with: a function of transmitting data as frames and retransmitting a frame causing a transmission error on the occurrence of the transmission error; a measurement section (14) for measuring the frame retransmission rate on the basis of frames received per unit time from another communication apparatus during communication; and a transmission rate selection section (15) that selects a data transmission rate higher than a data transmission rate during use among a plurality of predetermined data transmission rates when the frame retransmission rate is a prescribed threshold value or over and a reception level of the signal received from the other communication apparatus is a minimum reception level or over of the data transmission rate higher than the present data transmission rate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a communication apparatus that constitutes a wireless communication system that transmits and receives frame (packet) data, and in particular, when a frame transmission error is detected, a function of retransmitting the frame that has caused the transmission error. It is related with the communication apparatus provided with.

  In recent years, wireless LANs have rapidly become widespread for reasons such as an increase in transmission speed and a reduction in equipment cost in addition to the advantage of not requiring connection cables. In a wireless LAN system, an AP (Access Point) corresponding to a wireless base station and an STA (Station) corresponding to a wireless terminal wirelessly connected thereto exist, and one AP accommodates a plurality of STAs. In wireless communication provided by such a wireless LAN system, the transmission rate is changed by switching the transmission method such as the coding rate and the modulation method in accordance with the change of the radio wave propagation environment, thereby improving the communication quality. . For example, in the IEEE 802.11 wireless LAN system, a fallback method is employed in which the transmission rate to be used is changed according to the signal reception level. In this case, the AP notifies the STA accommodated therein of a usable transmission rate at a constant period, and the AP and the STA determine the transmission rate according to the reception level of the signal.

  In addition to the reception level described above, there are various indicators that indicate the characteristics of the transmission path. As a conventional transmission rate determination method, for example, the reception level and transmission error can be determined under conditions according to the type of information to be transmitted. There is a method for determining an optimal transmission method by measuring transmission path characteristics such as rate and transmission delay time (see Patent Document 1 below).

  In addition, in the IEEE 802.11 wireless LAN system, CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) is adopted as an access control method, and APs and STAs autonomously transmit frames by detecting channel usage. The timing is determined. However, even if CSMA / CA is used, there is a case where frames still collide and frames are lost (frame transmission fails). Therefore, the AP and the STA retransmit the lost frame when a collision occurs. As the number of STAs accommodated by one AP increases, the probability that frames transmitted from the STAs collide with each other as communication traffic increases increases. As a result, the number of retransmissions of frames increases and throughput decreases.

  When the received signal level is low, data transmission is performed at a low transmission rate in order to suppress an increase in the data code error rate. This is because the code error tolerance of transmission data becomes stronger as the lower transmission rate is used.

  In this way, in the conventional wireless LAN system, when the transmission rate is changed according to the transmission path characteristics such as the reception level, transmission error rate, transmission delay time, etc., the reduction in the throughput is suppressed, and when the frame collision occurs Retransmit the frame.

JP 2003-209537 A

  However, when transmitting data of the same size, if a low transmission rate is used, the frame length becomes long, and the probability that a frame collides is higher than when a high transmission rate is used. For this reason, when data is transmitted using a low transmission rate even though the signal reception level is sufficient (high), a number of frame collisions may occur and the throughput may be reduced. was there.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a communication apparatus capable of suppressing the rate of occurrence of frame retransmission and improving the throughput.

  In order to solve the above-described problems and achieve the object, the communication device according to the present invention is a communication having a function of transmitting data by framing data and retransmitting the frame in which the transmission error occurs when a transmission error occurs. A retransmission rate measuring means for measuring a rate occupied by retransmission frames (frame retransmission rate) based on frames received per unit time from other communication devices in communication; and the frame retransmission rate is a predetermined value A plurality of data transmission rates defined in advance when the reception level of the signal received from the other communication device is equal to or higher than a minimum reception level of a data transmission rate higher than the current data transmission rate. A transmission rate selection means for selecting a data transmission rate higher than the data transmission rate in use from among the next communication device In data transmission, characterized by using said selected data transmission rate.

  According to the present invention, it is possible to reduce the number of frame collisions and improve the throughput.

  Embodiments of a communication apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
1 is a configuration example of a first embodiment of a communication system including a base station device (hereinafter referred to as AP: Access Point) and a terminal device (hereinafter referred to as STA: Station) operating as a communication device according to the present invention. FIG. This communication system includes AP 1 and 2 and STAs 5 to 9. AP 1 accommodates STAs 5 and 6 in the wireless area 3, and AP 2 accommodates STAs 7 to 9 in the wireless area 4. AP1 communicates with STAs 5 and 6, and AP2 communicates with STAs 7-9.

  FIG. 2 is a diagram illustrating a configuration example of the AP according to the first embodiment. The AP includes an antenna 11, an A / D conversion unit 12, a reception unit 13, a measurement unit 14, and a transmission rate selection unit 15. A transmission unit 16 and a D / A conversion unit 17. The A / D converter 12 converts a framed analog signal received via the antenna 11 into a digital signal. The reception unit 13 performs decoding processing and demodulation processing on the digital signal converted by the A / D conversion unit, acquires information about the frame and a signal reception level, and notifies the measurement unit 14 of the acquired information. The measurement unit 14 measures the rate of occurrence of frame retransmission per unit time, throughput, and the like based on the information about the notified frame, and the transmission rate selection unit 15 determines the result and the signal reception level notified from the reception unit 13. To notify. The transmission rate selection unit 15 selects a transmission rate based on the information notified from the measurement unit 14. In addition, the transmission unit 16 performs modulation processing and encoding processing on the transmission data. The D / A conversion unit 17 converts the digital signal received from the transmission unit 16 into an analog signal, and the analog signal is transmitted to the STA via the antenna 11.

  FIG. 3 is a diagram showing a fallback threshold defined by IEEE802.11a. The transmission rate selection unit 15 is shown in FIG. 3 when executing a transmission rate selection process described later. Refers to the threshold value. FIG. 4 is a flowchart illustrating an operation example in which the AP according to the first embodiment selects a transmission rate. Hereinafter, the operation in which the AP selects the transmission rate will be described with reference to FIGS. Here, as an example, the operation of AP1 accommodating STAs 5 and 6 will be described.

  The receiving unit 13 of AP1 acquires information on whether or not the received frame is a retransmitted frame (retransmitted frame) and the signal reception level, and notifies the measuring unit 14 (step S11). When the measurement unit 14 determines that the retransmission frame has been received based on the information notified from the reception unit 13, the measurement unit 14 checks whether the retransmission frame is retransmitted from the STA 5 or 6, and indicates the number of times the retransmission frame has been received. The number of retransmissions is counted up (step S12). The number of frame retransmissions is counted individually for each STA. Next, the measurement unit 14 measures the number of frame retransmissions (frame retransmission rate) generated per unit time, and notifies the transmission rate selection unit 15 of the result and the signal reception level notified from the reception unit 13 (Step S14). S13). Note that the frame retransmission rate refers to, for example, the ratio of frames (retransmission frames) retransmitted by the STA among all frames received per unit time from a specific STA.

  The transmission rate selection unit 15 determines whether or not the frame retransmission rate notified from the measurement unit 14 is equal to or greater than a threshold value (step S14). When the frame retransmission rate is equal to or greater than the threshold (step S14, Yes), the transmission rate selection unit 15 refers to the transmission rate vs. the minimum reception level shown in FIG. It is confirmed whether or not the reception level is equal to or higher than the minimum reception level of a transmission rate higher than the currently used transmission rate (whether a transmission rate higher than the current transmission rate can be selected) (step S15). When a transmission rate higher than the currently used transmission rate can be selected (Yes in step S15), the transmission rate selection unit 15 selects and switches a transmission rate higher than the current one from the selectable transmission rates ( Step S16).

  On the other hand, when it is determined in step S14 that the frame retransmission rate is less than the threshold (No in step S14), or in step S15, a transmission rate higher than that currently in use is selected. When it is determined that the transmission rate is not possible (No at Step S15), the transmission rate selection unit 15 selects and switches the transmission rate using a conventionally used method (Step S17). Specifically, when the frame retransmission rate is less than the threshold, the transmission rate selection unit 15 determines that the transmission path state is good and the rate of occurrence of frame collision is low, and the frame retransmission rate is determined based on the signal reception level. The maximum data transmission rate is selected from a plurality of data transmission rates defined in advance so that the threshold value does not exceed the threshold value. If the frame retransmission rate is equal to or higher than the threshold value and a transmission rate higher than that currently in use cannot be selected, it is determined that the transmission path state is inferior, and the transmission rate is lower than that in use. Select.

  As described above, in this embodiment, when the frame retransmission rate per unit time is equal to or higher than the threshold value, the signal reception level is sufficiently high so that a transmission rate higher than the transmission rate in use can be selected. In this case, the base station apparatus switches to a transmission rate higher than the transmission rate in use. As a result, the number of frame collisions can be suppressed and the throughput can be improved.

Embodiment 2. FIG.
Next, the second embodiment will be described. The configuration of the communication system of the present embodiment is the same as that of the communication system of the first embodiment described above. In the present embodiment, an operation will be described in which the AP switches the transmission rate based on the state of throughput per unit time. FIG. 5 is a flowchart illustrating an operation example in which the AP according to the second embodiment selects a transmission rate. Hereinafter, the operation of the AP selecting the transmission rate will be described with reference to FIGS. Here, as an example, the operation of AP1 accommodating STAs 5 and 6 will be described. In FIG. 5, the same processes as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

  After executing step S12, the measurement unit 14 of AP1 measures the throughput per unit time, and notifies the transmission rate selection unit 15 of the result and the signal reception level notified from the reception unit 13 (step S23). The transmission rate selection unit 15 determines whether or not the throughput notified from the measurement unit 14 is equal to or less than a threshold value (step S24). When the throughput is equal to or less than the threshold value (step S14, Yes), the transmission rate selection unit 15 performs the processing after step S15 (steps S15 and 16 or steps S15 and 17) as in the first embodiment. Execute. On the other hand, when the throughput notified from the measurement unit 14 exceeds the threshold value (No at Step S24), the transmission rate selection unit 15 executes Step S17. In step S17, the transmission rate selection unit 15 selects and switches the transmission rate using a conventionally used method based on the frame retransmission rate and the signal reception level. Specifically, when the throughput exceeds the threshold, the transmission rate selection unit 15 determines that the transmission path state is good and the rate of occurrence of frame collision is low, and the throughput is reduced based on the signal reception level. The maximum data transmission rate is selected from a plurality of data transmission rates defined in advance so as not to be below the threshold value. If the throughput is below the threshold and a transmission rate higher than that currently in use cannot be selected, the transmission path condition is judged to be poor and a transmission rate lower than that in use is selected. To do.

  In the present embodiment, the transmission rate selection unit switches the transmission rate based on the throughput per unit time, but in addition to this, the frame per unit time of the first embodiment described above. The operation of selecting the transmission rate based on the retransmission rate may be performed in parallel (the transmission rate is switched even when the frame retransmission rate is equal to or higher than the threshold). Further, it may be determined whether or not to switch the transmission rate based on two conditions of throughput per unit time and frame retransmission rate.

  Thus, in the present embodiment, when the throughput per unit time is equal to or higher than the threshold, and when the signal reception level is high enough to select a transmission rate higher than the transmission rate in use, The base station apparatus switches to a transmission rate higher than the transmission rate in use. As a result, the number of frame collisions can be suppressed and the throughput can be improved.

Embodiment 3 FIG.
Next, Embodiment 3 will be described. The configuration of the communication system of the present embodiment is the same as that of the communication system of the first embodiment described above. In the present embodiment, an operation will be described in which the AP switches the transmission rate when the frame transmission counter reaches the retransmission limit (the number of frame retransmissions reaches a specified number). FIG. 6 is a flowchart illustrating an operation example in which the AP according to the third embodiment selects a transmission rate. Hereinafter, the operation of the AP selecting the transmission rate will be described with reference to FIGS. Here, as an example, the operation of AP1 accommodating STAs 5 and 6 will be described. In FIG. 6, the same processes as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

  When receiving the retransmission frame, the measuring unit 14 of AP1 counts up the number of frame retransmissions indicating the number of retransmission frame receptions in the same manner as in step S12 of the first embodiment described above (step S12). Next, the measurement unit 14 notifies the transmission rate selection unit 15 of the number of frame retransmissions (step S32). The transmission rate selection unit 15 determines whether the number of frame retransmissions notified from the measurement unit 14 has reached the retransmission limit (step S33). When the number of frame retransmission reaches the retransmission limit (step S33, Yes), the transmission rate selection unit 15 performs the processing after step S15 (steps S15 and 16 or steps S15 and 17) as in the first embodiment. ). On the other hand, when the number of frame retransmission notified from the measurement unit 14 has not reached the retransmission limit (No at Step S33), the transmission rate selection unit 15 executes Step S17. In step S17, the transmission rate selection unit 15 selects and switches the transmission rate using a conventionally used method based on the number of frame retransmissions and the signal reception level. Specifically, when the frame retransmission rate calculated based on the number of frame retransmissions is less than the threshold, the transmission rate selection unit 15 determines that the transmission path state is good and the frame collision occurrence rate is low. Based on the signal reception level, the maximum data transmission rate is selected from a plurality of predefined data transmission rates so that the frame retransmission rate does not exceed the threshold value. If the frame retransmission rate is equal to or higher than the threshold value and a transmission rate higher than that currently in use cannot be selected, it is determined that the transmission path state is inferior, and the transmission rate is lower than that in use. Select. Although not shown, when the number of frame retransmission reaches the retransmission limit, the transmission rate selection unit 15 resets the number of frame retransmissions.

  In the present embodiment, the transmission rate selection unit switches the transmission rate based on the number of frame retransmissions. In addition to this, the frame per unit time of the first or second embodiment described above The operation of selecting the transmission rate based on the retransmission rate and / or the operation of selecting the transmission rate based on the throughput per unit time is performed in parallel (the frame retransmission rate is equal to or higher than the threshold and / or the throughput. The transmission rate may be switched when the value becomes equal to or less than the threshold. Also, it may be determined whether to switch the transmission rate based on any two conditions or all three conditions of the three conditions of throughput, frame retransmission rate, and number of frame retransmissions.

  As described above, in the present embodiment, when the number of frame retransmission reaches the retransmission limit, and when the signal reception level is high enough to select a transmission rate higher than the transmission rate in use, the base station apparatus Is switched to a transmission rate higher than the transmission rate in use. As a result, the number of frame collisions can be suppressed and the throughput can be improved.

Embodiment 4 FIG.
Next, the fourth embodiment will be described. The configuration of the communication system of the present embodiment is the same as that of the communication system of the first embodiment described above. In the present embodiment, an operation will be described in which the AP notifies the STA of the selected transmission rate.

  FIG. 7 is a diagram showing a configuration of an IEEE 802.11a radio frame. The radio frame includes a preamble area for storing a preamble signal for establishing synchronization, a SIGNAL area for storing information on a transmission rate and a data length, and a DATA area for storing user data. The DATA area stores a SERVICE area for storing signals used for scramble processing, a PSDU (Presentation-layer Service Data Unit) area for storing user data, and load bits for terminating convolutional coding. And a padding bit region for storing a signal for adjusting the length of the tail region and the DATA region to an integral multiple of OFDM (Orthogonal Frequency Division Multiplexing) symbols. The SERVICE area includes bits reserved for the future, and the reserved bits can be used to store arbitrary information in the same manner as the padding bit area.

  FIG. 8 is a diagram illustrating an example of operations of the AP and the STA according to the fourth embodiment. Hereinafter, an operation in which the AP notifies the STA of the transmission rate will be described with reference to FIGS. Here, as an example, an operation in which AP 1 notifies STA 5 of a transmission rate will be described.

  The STA 5 performs a back-off process after the frame interval of the Distributed Coordination Function Inter Frame Space (DIFS) has elapsed (after the DIFS period has elapsed in FIG. 8). In the back-off process, carrier sense is performed in order to check the status of the random time channel, and when it is confirmed that the channel is free, the STA 5 transmits data to the AP 1. When the data transmitted from the STA 5 is received, the AP 1 transmits an ACK to the STA 5 after a SIFS (Short Inter Frame Space) period, which is a frame transmission interval when transmitting the highest priority frame. Further, when receiving data transmitted from STA 5, AP1 executes any one of the above-described first to third embodiments to determine whether or not to change the transmission rate. If it is determined that the transmission rate is to be changed, the AP 1 broadcasts a transmission rate change notification (frame) to the wireless area 3 after the SIFS period has elapsed since the ACK transmission to the STA 5. Information about the changed transmission rate (the transmission rate selected again by AP1) is stored in the reserved bit area or padding bit area in the SERVICE area of the transmission rate change notification. In addition, all STAs in the wireless area 3 receive the transmission rate change notification, but only the STA 5 that has transmitted data to the AP 1 immediately before changes to the transmission rate stored in the transmission rate change notification. The STA does not change the transmission rate.

  Thus, in the present embodiment, when the base station apparatus reselects the transmission rate (decides to switch to a higher transmission rate than that in use), the terminal that is the target of switching the transmission rate After the end of response processing for data reception of the device (after transmitting ACK), the SIFS period has passed, and the reselected transmission rate is notified by broadcast transmission, and only the terminal device that has transmitted data immediately before Will be changed to the notified transmission rate. Thereby, it is possible to instruct only the terminal device that uses the changed transmission rate to change the transmission rate.

  In addition, the base station apparatus configures and transmits a re-selected transmission rate in an existing reserved area that can configure a frame and set arbitrary data. Thereby, the base station apparatus can easily notify the data transmission rate to the terminal apparatus using the existing frame.

Embodiment 5 FIG.
Next, the fifth embodiment will be described. The configuration of the communication system of the present embodiment is the same as that of the communication system of the first embodiment described above. In the present embodiment, an operation will be described in which the STA switches the transmission rate based on the number of frame retransmissions (frame retransmission rate) generated per unit time.

  FIG. 9 is a diagram illustrating a configuration example of the STA according to the fifth embodiment. The STA includes an antenna 51, an A / D conversion unit 52, a reception unit 53, a measurement unit 54, and a transmission rate selection unit 55. And a transmission unit 56 and a D / A conversion unit 57. The A / D converter 52 converts a framed analog signal received via the antenna 51 into a digital signal. The reception unit 53 performs decoding processing and demodulation processing on the digital signal converted by the A / D conversion unit, acquires information about the frame and a signal reception level, and notifies the measurement unit 54 of the acquired information. The measurement unit 54 measures the frame retransmission rate, the throughput, and the like based on the information about the notified frame, and notifies the transmission rate selection unit 55 of the result and the signal reception level notified from the reception unit 53. The transmission rate selection unit 55 selects a transmission rate based on the information notified from the measurement unit 54. In addition, the transmission unit 56 performs modulation processing and encoding processing on the transmission data. The D / A conversion unit 57 converts the digital signal received from the transmission unit 56 into an analog signal, and the analog signal is transmitted to the AP via the antenna 51.

  FIG. 10 is a flowchart illustrating an operation example in which the STA according to the fifth embodiment selects a transmission rate. Hereinafter, an operation in which the STA selects a transmission rate will be described with reference to FIGS. Here, as an example, the operation of the STA 5 accommodated in the AP 1 will be described.

  The receiving unit 53 of the STA 5 acquires information about whether the received frame is a retransmission frame and the signal reception level, and notifies the measuring unit 54 of the information (step S51). If the measurement unit 54 determines that the retransmission frame has been received based on the information notified from the reception unit 53, the measurement unit 54 counts up the number of frame retransmissions indicating the number of retransmission frame reception (step S52). Next, the measurement unit 54 determines whether the state of the STA 5 has changed as compared with the previous count up of the number of frame retransmissions (whether the state has changed from the moving state to the stopped state, and the moving state from the stopped state). Whether the state has been changed) is determined (step S53). Note that whether or not the state of the STA 5 has changed can be determined by, for example, determining by a change in the signal reception level or by using a movement detection sensor, but the implementation method does not matter. If it is determined that the state has not changed (No in step S53), the measurement unit 54 measures the frame retransmission rate per unit time, and the result and the signal reception level notified from the reception unit 53 are transmitted. The selection unit 55 is notified (step S54). On the other hand, if it is determined that the state has changed (step S53, Yes), the measurement unit 54 determines that the previous measurement result cannot be referred to, and resets (clears) the number of frame retransmissions. To clear the frame retransmission rate (step S58). Thereafter, the transmission rate selection unit 55 selects and switches the transmission rate using a method conventionally used (step S59). Note that the process of selecting and switching the transmission rate by the method conventionally used in step S59 is the same as the process of step S17 (see FIG. 4) of the first embodiment described above.

  The transmission rate selection unit 55 determines whether or not the frame retransmission rate notified from the measurement unit 54 is greater than or equal to a threshold value (step S55). When the frame retransmission rate is equal to or higher than the threshold (step S55, Yes), the transmission rate selection unit 55 refers to the transmission rate vs. the lowest reception level shown in FIG. It is checked whether the reception level is equal to or higher than the minimum reception level of a transmission rate higher than the transmission rate currently in use (whether a transmission rate higher than the current transmission rate can be selected) (step S56). When a transmission rate higher than the currently used transmission rate can be selected (Yes in step S56), the transmission rate selection unit 55 selects and switches a transmission rate higher than the current one from the selectable transmission rates ( Step S57).

  On the other hand, when it is determined in step S55 that the frame retransmission rate is less than the threshold (No in step S55), or in step S56, a transmission rate higher than that currently in use is selected. When it is determined that it is impossible (No at Step S56), the transmission rate selection unit 55 executes Step S59.

  As described above, in the present embodiment, when the frame retransmission rate per unit time is equal to or higher than the threshold value, the signal reception level is sufficiently high so that a transmission rate higher than the transmission rate in use can be selected. If it is higher, the terminal device switches to a transmission rate higher than the transmission rate in use. As a result, the number of frame collisions can be suppressed and the throughput can be improved. In addition, when the terminal apparatus determines that the state has changed (from the moving state to the stopped state, or from the stopped state to the moving state), it resets the frame retransmission rate measurement result. It was. As a result, it is possible to prevent an erroneous transmission rate from being selected based on a low-reliability frame retransmission rate.

Embodiment 6 FIG.
Next, the sixth embodiment will be described. The configuration of the communication system of the present embodiment is the same as that of the communication system of the first embodiment described above. In the present embodiment, an operation will be described in which the STA switches the transmission rate based on the state of throughput per unit time.

  FIG. 11 is a flowchart illustrating an operation example in which the STA according to the sixth embodiment selects a transmission rate. Hereinafter, an operation in which the STA selects a transmission rate will be described with reference to FIGS. Here, as an example, the operation of the STA 5 accommodated in the AP 1 will be described. In FIG. 11, the same processes as those in the above-described fifth embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  After executing step S52, the measurement unit 54 of the STA5 determines whether the state of the STA5 has changed as compared to the previous count up of the number of times of frame retransmission (whether the state has changed from the moving state to the stopped state, and It is determined whether or not a transition is made from the intermediate state to the moving state (step S53). When it is determined that the state has not changed (No in step S53), the measurement unit 54 measures the throughput per unit time, and the result and the signal reception level notified from the reception unit 53 are transmitted to the transmission rate selection unit. 55 is notified (step S64). On the other hand, if it is determined that the state has changed (step S53, Yes), the measurement unit 54 determines that the previous measurement result cannot be referred to, and resets (clears) the number of frame retransmissions. To clear the throughput (step S58). Then, the transmission rate selection unit 55 selects and switches the transmission rate by a conventionally used method (step S59). Note that the process of selecting and switching the transmission rate by the method conventionally used in step S59 is the same as the process of step S17 (see FIG. 5) of the second embodiment described above.

  The transmission rate selection unit 55 determines whether or not the throughput notified in step S64 is equal to or less than a threshold value (step S65). When the throughput is equal to or less than the threshold value (step S65, Yes), the transmission rate selection unit 55 performs the processing after step S56 (steps S56 and 57, or steps S56 and 59) as in the fifth embodiment described above. Execute. On the other hand, when the throughput notified from the measurement unit 54 exceeds the threshold value (No in step S65), the transmission rate selection unit 55 executes step S59.

  In the present embodiment, the transmission rate selection unit switches the transmission rate based on the throughput per unit time. In addition to this, the frame per unit time according to the above-described fifth embodiment. The operation of selecting the transmission rate based on the retransmission rate may be performed in parallel (the transmission rate is switched even when the frame retransmission rate is equal to or higher than the threshold). Further, it may be determined whether or not to switch the transmission rate based on two conditions of throughput per unit time and frame retransmission rate.

  As described above, in the present embodiment, when the throughput per unit time is equal to or higher than the threshold value, and the signal reception level is sufficiently high so that a transmission rate higher than the transmission rate in use can be selected. The terminal device switches to a transmission rate higher than the transmission rate in use. As a result, the number of frame collisions can be suppressed and the throughput can be improved. In addition, when the terminal device determines that the state has changed (from the moving state to the stopping state, or from the stopping state to the moving state), the terminal device is to reset the measurement result of the throughput. . As a result, it is possible to prevent an erroneous transmission rate from being selected based on throughput with low reliability.

Embodiment 7 FIG.
Next, Embodiment 7 will be described. The configuration of the communication system of the present embodiment is the same as that of the communication system of the first embodiment described above. In the present embodiment, an operation will be described in which the STA switches the transmission rate when the frame transmission counter reaches the retransmission limit (the number of frame retransmissions reaches a specified number). FIG. 12 is a flowchart illustrating an operation example in which the STA according to the seventh embodiment selects a transmission rate. Hereinafter, an operation in which the STA selects a transmission rate will be described with reference to FIGS. Here, as an example, the operation of the STA 5 accommodated in the AP 1 will be described. In FIG. 12, the same processes as those in the above-described sixth embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  After executing step S52, the measurement unit 54 of the STA5 determines whether the state of the STA5 has changed as compared to the previous count up of the number of times of frame retransmission (whether the state has changed from the moving state to the stopped state, and It is determined whether or not a transition is made from the intermediate state to the moving state (step S53). When determining that the state has not changed (step S53, No), the measurement unit 54 notifies the transmission rate selection unit 55 of the number of times of frame retransmission (step S72). On the other hand, if it is determined that the state has changed (step S53, Yes), the measurement unit 54 determines that the previous measurement result cannot be referred to, and resets (clears) the number of frame retransmissions ( Step S58). Then, the transmission rate selection unit 55 selects and switches the transmission rate by a conventionally used method (step S59). Note that the process of selecting and switching the transmission rate by the method conventionally used in step S59 is the same as the process of step S17 (see FIG. 6) of the third embodiment described above.

  The transmission rate selection unit 55 determines whether or not the number of frame retransmissions notified from the measurement unit 54 in step S72 has reached the retransmission limit (step S75). When the number of frame retransmissions reaches the retransmission limit (step S75, Yes), the transmission rate selection unit 55 performs the processing after step S56 (steps S56 and 57, or steps S56 and 59), as in the fifth embodiment. ). On the other hand, when the number of frame retransmission notified from the measurement unit 54 has not reached the retransmission limit (No in step S75), the transmission rate selection unit 55 executes step S59. Although not shown, when the number of frame retransmission reaches the retransmission limit, the transmission rate selection unit 55 resets the number of frame retransmissions.

  In the present embodiment, the transmission rate selection unit switches the transmission rate based on the number of frame retransmissions. In addition to this, the frame per unit time of the above-described fifth or sixth embodiment The operation of selecting the transmission rate based on the retransmission rate and / or the operation of selecting the transmission rate based on the throughput per unit time is performed in parallel (the frame retransmission rate is equal to or higher than the threshold and / or the throughput. It is also possible to switch the transmission rate even when the value is below the threshold. Also, it may be determined whether to switch the transmission rate based on any two conditions or all three conditions of the three conditions of throughput, frame retransmission rate, and number of frame retransmissions.

  As described above, in the present embodiment, when the number of frame retransmission reaches the retransmission limit, and when the signal reception level is high enough to select a transmission rate higher than the transmission rate in use, the base station apparatus Is switched to a transmission rate higher than the transmission rate in use. As a result, the number of frame collisions can be suppressed and the throughput can be improved.

  As described above, the communication apparatus according to the present invention is useful for a radio communication system, and in particular, when a transmission error occurs, a base station apparatus and a terminal having a function of retransmitting a frame in which the transmission error has occurred Suitable for equipment.

It is a figure which shows the structural example of the communication system containing the base station apparatus and terminal device which operate | move as a communication apparatus concerning this invention. 3 is a diagram illustrating a configuration example of a base station apparatus according to Embodiment 1. FIG. It is a figure which shows the fallback threshold value prescribed | regulated by IEEE802.11a. 6 is a flowchart illustrating an operation example in which the base station apparatus according to the first embodiment selects a transmission rate. 10 is a flowchart illustrating an operation example in which the base station apparatus according to the second embodiment selects a transmission rate. 10 is a flowchart illustrating an operation example in which a base station apparatus according to Embodiment 3 selects a transmission rate. FIG. 3 is a diagram illustrating a configuration of an IEEE 802.11a radio frame. FIG. 10 is a diagram illustrating an example of operations of a base station device and a terminal device according to a fourth embodiment. FIG. 10 is a diagram illustrating a configuration example of a terminal device according to a fifth embodiment. 10 is a flowchart illustrating an operation example in which a terminal apparatus according to Embodiment 5 selects a transmission rate. 18 is a flowchart illustrating an operation example in which the terminal device according to the sixth embodiment selects a transmission rate. 18 is a flowchart illustrating an operation example in which the terminal device according to the seventh embodiment selects a transmission rate.

Explanation of symbols

1, 2 Base station device 3, 4 Wireless area 5, 6, 7, 8, 9 Terminal device 11, 51 Antenna 12, 52 A / D converter 13, 53 Receiver 14, 54 Measuring unit 15, 55 Transmission rate selection Unit 16, 56 transmission unit 17, 57 D / A conversion unit

Claims (18)

A communication device having a function of retransmitting a frame in which the transmission error occurs when data is framed and transmitted, and a transmission error occurs,
A retransmission rate measuring means for measuring a ratio occupied by retransmission frames (frame retransmission rate) based on frames received per unit time from other communication devices in communication;
Defined in advance when the frame retransmission rate is equal to or higher than a predetermined threshold and the reception level of the signal received from the other communication device is equal to or higher than the minimum reception level of a data transmission rate higher than the current data transmission rate. A transmission rate selection means for selecting a data transmission rate higher than the data transmission rate in use from the plurality of data transmission rates,
With
The communication apparatus using the selected data transmission rate in the next data transmission to be performed with the other communication apparatus. further,
The transmission rate selection means includes
When the frame retransmission rate is less than the threshold value, the maximum number of data transmission rates defined in advance is determined based on the reception level so that the frame retransmission rate does not exceed the threshold value. The communication apparatus according to claim 1, wherein a data transmission rate is selected. further,
The transmission rate selection means includes
When the frame retransmission rate is equal to or higher than a predetermined threshold and the reception level of the signal received from the other communication device is lower than the minimum reception level, use from a plurality of data transmission rates defined in advance The communication apparatus according to claim 1 or 2, wherein a data transmission rate lower than a medium data transmission rate is selected. A communication device having a function of retransmitting a frame in which the transmission error occurs when data is framed and transmitted, and a transmission error occurs,
Throughput measuring means for measuring throughput based on frames received per unit time from other communication devices in communication;
Defined in advance when the throughput is less than a predetermined threshold and the reception level of a signal received from the other communication device is equal to or higher than the minimum reception level of a data transmission rate higher than the current data transmission rate A transmission rate selection means for selecting a data transmission rate higher than the data transmission rate in use from a plurality of data transmission rates;
With
The communication apparatus using the selected data transmission rate in the next data transmission to be performed with the other communication apparatus. further,
The throughput measuring means includes
When the throughput is greater than or equal to the threshold, a maximum data transmission rate is selected from a plurality of data transmission rates that are defined in advance based on the reception level so that the throughput does not become less than the threshold. The communication device according to claim 4, wherein the communication device is selected. further,
The transmission rate selection means includes
When the throughput is less than a predetermined threshold and the reception level of the signal received from the other communication device is less than the minimum reception level, the data transmission rate being used is selected from a plurality of data transmission rates that are defined in advance. 6. The communication apparatus according to claim 4, wherein a data transmission rate lower than the data transmission rate is selected. A communication device having a function of retransmitting a frame in which the transmission error occurs when data is framed and transmitted, and a transmission error occurs,
When a frame received from another communication device in communication is retransmitted, a retransmission counting means for counting up a retransmission counter for counting it,
Specified in advance when the count value reaches a specified count number (retransmission limit) and the reception level of the signal received from the other communication device is equal to or higher than the minimum reception level of a transmission rate higher than the transmission rate in use A transmission rate selection means for selecting a data transmission rate higher than the data transmission rate in use from a plurality of data transmission rates being used;
With
The communication apparatus using the selected data transmission rate in the next data transmission to be performed with the other communication apparatus. further,
The transmission rate selection means includes
When the count value does not reach the retransmission limit and the frame retransmission rate calculated based on the count value is less than a predetermined threshold value, so that the frame retransmission rate does not exceed the threshold value, 8. The communication apparatus according to claim 7, wherein a maximum data transmission rate is selected from a plurality of data transmission rates defined in advance based on the reception level. further,
The transmission rate selection means includes
When the count value reaches the retransmission limit and the reception level of the signal received from the other communication apparatus is less than the minimum reception level, the frame retransmission rate is not less than the threshold value and is defined in advance. 9. The communication apparatus according to claim 8, wherein a data transmission rate lower than a data transmission rate in use is selected from a plurality of data transmission rates. further,
The retransmission rate measuring means includes
The communication apparatus according to claim 1, 2 or 3, wherein the frame retransmission rate is cleared when it is determined that the operation state of the own apparatus has changed. further,
The throughput measuring means includes
The communication apparatus according to claim 4, 5 or 6, wherein the throughput is cleared when it is determined that the operation state of the own apparatus has changed. further,
The retransmission counting means includes
The communication apparatus according to claim 7, 8 or 9, wherein the count number is cleared when it is determined that the operation state of the own apparatus has changed. In a wireless communication system, a base station device that communicates with a terminal device under its own station,
A base station apparatus having the function of the communication apparatus according to any one of claims 1 to 9.   Receiving the data from the terminal device, and after completing the response processing for the data reception, notifying the terminal device of the data transmission rate used in the next data transmission at the first frame transmission timing, The base station apparatus according to claim 13.   The data transmission rate used in the next data transmission is set in an existing area in which arbitrary data can be set in a frame transmitted at the first frame transmission timing. Base station device. In a wireless communication system, a terminal device that communicates with a base station device to which it belongs,
A terminal device having the function of the communication device according to claim 1.   The data transmission is performed using the notified data transmission rate (update transmission rate) thereafter when a frame for notifying the data transmission rate is received from the base station apparatus. The terminal device described.   The terminal apparatus according to claim 17, wherein a data transmission rate set in an existing area in which arbitrary data can be set in the received frame is set as the update transmission rate.

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