JP5146739B2 - Wireless communication apparatus and method, and program - Google Patents

Description

  The present invention relates to a method for determining a transmission rate according to the transmission quality of a wireless transmission path in wireless communication in which a plurality of transmission rates can be selectively used, a wireless communication apparatus and a program for implementing the method.

  In recent years, since it has advantages such as high degree of freedom of installation location of equipment, wireless networks such as wireless LAN (Local Area Network) represented by IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 802.11, It is becoming popular in place of wired networks. In addition, a wide variety of applications that handle large amounts of data, such as images, have frequently accessed the network, and as a result, the required transmission rate in wireless LANs is increasing and throughput is further improved. Is required.

  In order to achieve this purpose, IEEE802.11 makes it possible to use multiple types of transmission rates in the physical layer (PHY layer), and to select the optimal communication rate according to changes in the actual communication environment. (This transmission rate control is called link adaptation). For example, when the actual communication environment changes as shown in FIG. 1 (see the dotted line in the figure), the transmission rate used in the network is changed to match the actual communication environment. (See the solid line in the figure).

  As a result, for example, when the transmission state of the wireless transmission path (hereinafter simply referred to as “transmission path quality”) is good, a high transmission rate is selected to achieve high throughput, while when the transmission path quality is not good, low transmission is performed. A rate (that is, a transmission rate with high error tolerance) is selected, and the reachability of transmission data is improved, and the throughput (transmission information amount) per unit time is improved. Each transmission rate is realized by a combination of a modulation method corresponding to the transmission rate, redundancy (EWC, WiMAX, etc., or the number of antennas in a communication system using MIMO (Multiple Input Multiple Output)), etc. Is.

  Here, the transmission path quality that is a selection criterion when selecting the transmission rate can be estimated by various parameters. For example, the transmission path quality is estimated according to the retransmission condition of the packet, and the transmission rate is determined. Has also been proposed (see Patent Document 1).

  FIG. 2 shows a conventional wireless communication system that determines the transmission rate according to the retransmission status, and FIG. 3 shows a configuration example of the AP 1 included in the system.

  In a conventional wireless LAN system, BSS is controlled by AP1 and one or more STA2-1, 2-2,..., 2-n (hereinafter referred to as STA2 when it is not necessary to distinguish them individually) under the control of AP1. (Base Service Set) is formed, and communication between each STA2 is realized via AP1 (infrastructure mode).

  AP1 (see FIG. 3) constituting this BSS is composed of MAC circuits 11, 18, PHY circuits 12, 17, and RF circuits 13, 16 corresponding to Tx (transmission) and Rx (reception), respectively. In the circuit group on the side, the MAC circuit 11 and the PHY circuit 12 perform processing corresponding to the MAC layer and the PHY layer on the data supplied from the upper layer 19, respectively. As a result, the signal corresponding to the data is up-converted in the RF circuit 13 and output from the antenna 14. On the other hand, on the Rx side, after the signal received by the antenna 15 is down-converted by the RF circuit 16, the PHY circuit 17 and the MAC circuit 18 perform processing corresponding to the PHY layer and the MAC layer to the upper layer 19 Supplied with.

  Data packet retransmission control is executed by the MAC circuit 11 on the Tx side, and the transmission rate used for communication is also determined by the MAC circuit 11 along with this retransmission control. Note that the retransmission control method by the MAC circuit 11 is defined by IEEE802.11. Depending on whether or not the transmission side has received an ACK packet corresponding to a data packet to be transmitted, the retransmission of the data packet is performed. Necessity is determined.

  A specific configuration of the MAC circuit 11 realizing such a function is shown in FIG.

  In the MAC circuit 11, when a packet transmission command is input from the upper layer 19, the packet transmission unit 31 is held in the data buffer 32, and the data packet designated by the command (hereinafter referred to as data packet A). ) Is supplied to the PHY circuit 12.

  At this time, the packet transmission unit 31 supplies the data packet A to the PHY circuit 12 and at the same time controls the sequence number management unit 33 and the sequence number W for the transmission target data packet A held in the data buffer 32. Is granted.

  Further, the packet transmission unit 31 outputs a packet transmission signal indicating that the data packet has been transmitted to the transmission rate determination unit 22 when transmitting the packet.

  The ACK receiving unit 34 has an ACK packet flag indicating that an ACK packet for the transmitted data packet A has been received after the data packet A is transmitted by the packet transmitting unit 31. It is in a state of waiting for the supply from the MAC circuit 18. In this state, when the ACK receiving unit 34 receives the ACK packet flag, it is determined that the data packet A has arrived at the receiving side, and the data packet A to which the sequence number W is assigned is deleted from the data buffer 32.

  On the other hand, when the ACK packet flag is not received, the ACK receiving unit 34 notifies the packet transmitting unit 31 of the fact, and the packet transmitting unit 31 that has received the notification notifies the data buffer 32 in order to retransmit the data packet A. The data packet A held in the PHY circuit 12 is supplied to the PHY circuit 12 again. At this time, the packet transmission unit 31 outputs a packet retransmission signal indicating that the data packet has been retransmitted to the transmission rate determination unit 22.

  On the other hand, in the transmission rate determining unit 22, the packet retransmission count signal output unit 51 executes the following processing.

  (1) When a packet retransmission signal is supplied from the transmission control unit 21 (the packet transmission unit 31), the packet retransmission count signal is supplied to the packet retransmission number holding unit 53.

  (2) When a packet transmission signal is supplied from the transmission control unit 21 (the packet transmission unit 31), the packet transmission count signal is supplied to the packet transmission number holding unit 54.

  In this way, when any count signal is supplied from the packet retransmission count signal output unit 51, the packet retransmission number holding unit 53 transmits the number of data packets (Y) transmitted during the sample period for rate determination. Then, the number of retransmissions (X) of the data packet is counted and supplied to the error rate calculation unit 55.

  As a result, the error rate calculation unit 55 divides the data packet retransmission count (X) by the data packet transmission count (Y) to calculate the error rate.

  The transmission rate determination unit 56 compares the error rate supplied from the error rate calculation unit 55 with the threshold value stored in the threshold value holding unit 57, determines the transmission rate based on the comparison result, and determines a predetermined rate. An information signal is supplied to the PHY circuit 12.

  Specifically, when the error rate exceeds a predetermined threshold value D, the transmission rate determination unit 56 indicates that the currently used transmission rate is more aggressive than the transmission status of the wireless transmission path. It is assumed that an error has occurred, and the transmission rate is determined to be lower than the current rate, and a rate information signal indicating that fact is supplied to the PHY circuit 12.

  If the error rate is lower than the predetermined threshold U, the transmission rate determination unit 56 determines that the transmission rate higher than the currently used transmission rate can be used, makes a determination to increase the transmission rate, and indicates the rate. The information signal is supplied to the PHY circuit 12.

  Further, when the error rate is within the range of the threshold value D and the threshold value U, the transmission rate determination unit 56 determines that the currently used transmission rate is appropriate and indicates that the transmission rate is maintained. Is supplied to the PHY circuit 12. As a result, in the PHY circuit 12, the transmission rate is changed according to the rate information signal supplied from the MAC circuit 11, that is, the modulation method of the data packet supplied from the MAC circuit 11 is changed.

  Note that the transmission rate can be increased or decreased by one step (for example, increased from 12 Mbps to 18 Mbps) or lowered in two steps or more (for example, from 12 Mbps to 24 Mbps). Can be raised).

JP 2004-328652 A

  As described above, in the conventional method, the transmission status of the wireless transmission path, that is, the determination of the difficulty of reaching the data packet is determined based on whether or not the ACK packet is received, that is, whether or not the data packet is retransmitted. The reason why the data packet does not reach the receiving side, that is, the cause of the retransmission of the data packet is that the transmission rate is inappropriate for the transmission quality of the wireless transmission path (the state of the wireless transmission path) If the transmission rate is higher than the rate at which transmission is possible in the case of (1), the data packet collides with a data packet transmitted from another STA 2 and the packet does not reach the receiving side.

  However, in the conventional method, the cause of the retransmission of the data packet is not considered.

  Therefore, even when an appropriate transmission rate is used for the transmission quality of the wireless transmission path, when the data packet is retransmitted due to collision with another data packet, the transmission rate is too aggressive. Thus, a determination is made to lower the transmission rate. That is, in the conventional method, for example, a wireless transmission path that should originally be usable cannot be effectively used.

  The present invention has been made in view of such a situation, and makes it possible to use a transmission rate according to the transmission quality of a wireless transmission path.

According to another aspect of the present invention, there is provided a wireless communication apparatus or program that determines a usage rate of a wireless transmission path in which wireless communication is performed in the wireless communication function in a wireless communication apparatus having a wireless communication function capable of using a plurality of transmission rates. A usage rate calculating means for calculating; and a determining means for determining a transmission rate based on at least the usage rate calculated by the usage rate calculating means , wherein the determining means has the calculated usage rate as a threshold value. A wireless communication device or a program that calculates a data retransmission rate based on the number of data retransmissions performed in a state lower than, and determines the transmission rate based on the calculated retransmission rate.

  According to this configuration, the usage rate of the wireless transmission path is taken into consideration when determining the transmission rate. Normally, when adopting a method that determines the transmission rate only according to various parameters such as the number of retransmissions, the transmission line quality is actually deteriorated, or the transmission line is congested, which causes packet collisions. The STA or AP cannot identify whether a transmission error has occurred. On the other hand, it is assumed that the packet collision rate depends on the usage rate of the wireless transmission path. When the usage rate is high, there is a very high possibility that the cause of the transmission error is packet collision. Therefore, when determining the transmission rate, the transmission rate selection reflecting the actual environment (that is, the transmission path quality) can be realized by considering the usage rate of the wireless transmission path.

Note that the determination unit may exclude the number of retransmissions of data performed in a state where the calculated usage rate exceeds a threshold from the actual number of retransmissions.

  In addition, the communication standard with which the wireless communication apparatus is compliant is arbitrary, and can be applied to various communication schemes that define the rate adaptation function, such as IEEE802.11, WiMAX, LTE, and the like.

  Further, the usage rate calculating means calculates a usage time during which the wireless transmission path for a predetermined measurement time is used, and calculates the usage rate by dividing the calculated usage time by the measurement time. You may do it. The method of calculating the usage time at this time is arbitrary. For example, it is determined using the Duration value in the MAC header constituting the data packet, the LENGTH value and the RATE value in the PHY header, or the signal strength value of the received signal. It is also possible to do so.

  Further, the usage rate calculating means can calculate the usage time using channel information in an information element constituting the received management packet.

According to another aspect of the present invention, there is provided a wireless communication method of a wireless communication apparatus having a wireless communication function capable of using a plurality of transmission rates , wherein the usage rate of a wireless transmission path in which wireless communication is performed by the wireless communication function is set. a utilization calculating step of calculating at least based on the usage rate calculated in the processing of the usage rate calculation step, seen including a determining step of determining a transmission rate, and in the determining step, the use of the calculated In this wireless communication method, a data retransmission rate is calculated based on the number of data retransmissions performed in a state where the rate is below a threshold, and the transmission rate is determined based on the calculated retransmission rate .

In the wireless communication device, the wireless communication method, or the program according to one aspect of the present invention, a usage rate of a wireless transmission path in which wireless communication is performed with a wireless communication function is calculated, and transmission is performed based on at least the calculated usage rate. The rate is determined. In determining the transmission rate, a data retransmission rate is calculated based on the number of data retransmissions performed in a state where the calculated usage rate is below a threshold, and the transmission rate is calculated based on the calculated retransmission rate. It is determined.

  According to the present invention, it is possible to use a transmission rate according to the transmission status of a wireless transmission path.

  FIG. 5 shows a configuration example of a wireless LAN system to which the present invention is applied. In this wireless LAN system, an AP 101 is provided instead of the AP 1 in FIG. The other parts are the same as in FIG.

  That is, this wireless LAN system also conforms to IEEE802.11, AP 101, and a plurality of STA2-1, 2-2, ... 2-n (STA2-3 to 2-n are not shown). Are connected by a wireless network, and a plurality of types of transmission rates are provided in the physical layer. IEEE802.11b has four transmission rates of 1Mbps, 2Mbps, 5.5Mbps, and 11Mbps, and IEEE802.11a / g has eight transmission rates of 6Mbps, 9Mbps, 12Mbps, 18Mbps, 24Mbps, 36Mbps, 48Mbps, and 54Mbps. .

  In IEEE802.11n currently being standardized, it is planned that many higher transmission rates will be prepared.

  In addition to the presence or absence of data packet retransmission by the packet retransmission function at the MAC level defined in IEEE802.11, the AP 101 uses a wireless transmission path usage rate (for example, a packet transmission time rate in a wireless transmission path) (hereinafter referred to as media The transmission rate is determined based on the occupation rate.

  As described above, the reason why the data packet does not reach the receiving side is that the transmission rate inappropriate for the transmission quality of the wireless transmission path is used, and that the data packet is transmitted from another STA2. This is due to the fact that the data packet does not reach the receiving side because it collides with the other data packet. If a collision between data packets occurs even though the transmission quality is ensured, the data packet is retransmitted due to the collision. In this case, although the transmission quality is actually ensured, the transmission rate is unnecessarily lowered, and there is a possibility that transmission rate selection that does not match the actual communication environment is performed. Therefore, in the wireless LAN system according to the present embodiment, the transmission rate caused by the collision of the data packet is detected by detecting the high possibility of the collision with the data packet based on the media occupancy rate. We decided to adopt a method to prevent control as much as possible and to determine the transmission rate according to the actual transmission quality.

  In particular, wireless LAN systems such as those operated by IEEE802.11 have a packet collision prevention mechanism using the CSMA / CA method, so there is a high correlation between media occupancy and packet collision probability. It is expected to be able to accurately detect the possibility of a collision with

  FIG. 6 shows a conceptual diagram of the correlation between the high media occupation rate and the collision probability.

  In CSMA / CA systems such as IEEE802.11, media (ie, wireless transmission path) is acquired by a probabilistic method called random backoff, so STA2 or access that happens to have the same random backoff value. There may be data packet collisions between categories. That is, as shown in the upper part of FIG. 6, if the media occupation ratio is high, a large number of STA2s or access categories exist on the wireless transmission path. Therefore, even if a data packet is thrown, an ACK is caused by a collision. The packet is not returned, and the possibility that the data packet is retransmitted is increased.

  On the other hand, as shown in the lower part of FIG. 6, when the media occupation rate is low, the possibility of collision with other data packets is low, and when the ACK packet does not return, the cause is the transmission rate being used. Is likely inappropriate.

  FIG. 7 is a conceptual diagram of the media occupancy rate using the value of the Duration field (hereinafter referred to as Duration value) of the MAC header of the data packet.

  This Duration value is for a person who has acquired the transmission right defined in IEEE 802.11 to set a transmission prohibited section (hereinafter referred to as NAV) for a third party terminal other than the transmission destination. The occupied time of the wireless transmission path (that is, the time when the transmission right is acquired) is shown. This Duration value is a value obtained by decoding the received data packet up to the MAC header.

  In the example of FIG. 7, the Duration values (p, q, r) of the packets 1, 2, 3 received during a certain measurement time T are acquired, and their added value (that is, the total time) is calculated as the measurement time T The usage time (that is, the occupation time) of the wireless transmission path in FIG. Therefore, the media occupation ratio is obtained by dividing the added value by the measurement time T (formula (1)).

  Media occupation rate = (p + q + r) / T (1)

  The AP 101 notifies the STA2 of the determined transmission rate by transmitting a broadcast signal called a beacon within the network (BSS) (within the dotted frame in FIG. 5).

  FIG. 8 shows a configuration example of the AP 101. In this AP 101, a MAC circuit 111 is provided instead of the MAC circuit 11 of AP1 in FIG. 3, and a duration value extraction unit 112 is further provided. The other parts are the same as those of AP1 in FIG.

  The duration value extraction unit 112 extracts a MAC header from data acquired by the MAC circuit 18 on the Rx side, extracts a duration value from the MAC header, and supplies the extracted duration value to the MAC circuit 111. .

  The MAC circuit 111 calculates a media occupancy based on the duration value supplied from the duration value extraction unit 112 and determines a transmission rate according to the calculated occupancy and the presence / absence of data packet retransmission.

  In this way, a rate information signal indicating the determined transmission rate is supplied from the MAC circuit 111 to the PHY circuit 12, and the PHY circuit 12 determines the transmission rate.

  FIG. 9 shows a functional configuration example of the MAC circuit 111. In FIG. 9, elements similar to those in FIG. 4 described above are denoted by the same reference numerals. Therefore, unless otherwise described, elements having the same reference numerals are configured and executed in the same manner as the elements shown in FIG. Further, the “usage rate calculating unit” in the claims corresponds to, for example, the media occupation rate calculating unit 211 in FIG. 9, and the determining unit corresponds to, for example, the transmission rate determining unit 202 in FIG.

  As shown in FIG. 9, the MAC circuit 111 is provided with a transmission rate determining unit 202 instead of the transmission rate determining unit 22 of the MAC circuit 11 of FIG. It has become.

  Among these elements, the packet collision estimation unit 201 uses the Duration value supplied from the Duration value extraction unit 112 to calculate the occupied time of the wireless transmission path at the measurement time T and divides it by the measurement time T. To calculate the media occupation ratio (Equation 1).

  Further, the packet collision estimation unit 201 detects the high possibility of collision with the data packet based on the calculated media occupancy ratio, and if it is determined that the possibility is high, the packet collision estimation indicating that effect The signal is supplied to the transmission rate determination unit 202.

In order to realize such a function, the packet collision estimation unit 201 includes a media occupation rate calculation unit 211 including a cumulative addition unit 221 and a calculation unit 222, and a threshold comparison unit 212.
The cumulative addition unit 221 cumulatively adds the Duration value supplied from the Duration value extraction unit 112 during the measurement time T, and the value obtained as a result (p + q + r in the example of FIG. 7), that is, the wireless at the measurement time T. The transmission channel occupation time is supplied to the calculation unit 222.

  The calculation unit 222 divides the occupation time supplied from the cumulative addition unit 221 by the measurement time T (that is, calculates equation (1)) to calculate the media occupation rate. The calculated media occupancy rate is supplied to the threshold value comparison unit 212 and is compared with a predetermined threshold value in the threshold value comparison unit 212. As a result of the comparison, if the media occupation ratio is larger than the threshold, the threshold comparison unit 212 determines that there is a high possibility of collision with the data packet, and supplies a packet collision estimation signal to the transmission rate determination unit 202.

  Next, similarly to the transmission rate determination unit 22 in FIG. 4, the transmission rate determination unit 202 calculates an error rate based on the packet transmission signal and the packet retransmission signal from the transmission control unit 21, and the packet collision estimation unit 201. The transmission rate is determined based on the packet collision estimation signal supplied from the network.

  In order to realize such a function, the transmission rate determination unit 202 includes a packet retransmission count signal output unit 231 in addition to the same elements as the elements illustrated in FIG.

  Similar to the packet retransmission count signal output unit 51 in FIG. 4, the packet retransmission count signal output unit 231 sends the packet retransmission count signal to the packet retransmission count holding unit 53 when a packet retransmission signal is supplied from the transmission control unit 21. Supply. Here, as described above, when the cause of packet retransmission is caused by packet collision, if the transmission rate is set based on the retransmission, the transmission rate selection that does not match the actual channel quality may occur. Will be done. Therefore, regarding the retransmission of the packet generated during the period when the packet collision estimation signal is supplied from the transmission rate determining unit 202, it is considered that it is caused by the collision with another data packet, and is a transmission rate determination criterion. There is a need to exclude from the number of retransmissions.

  Therefore, the packet retransmission count signal output unit 231 according to the present embodiment, when a packet collision estimation signal is supplied from the packet collision estimation unit 201 (that is, when the cause of retransmission is estimated to be due to collision), During the supply period, the supply of the packet retransmission count signal to the packet retransmission count holding unit 53 is stopped.

  As a result, the error rate calculation unit 55 excludes the number of retransmissions assumed to be caused by the collision from the number of retransmissions (X) that is a reference for calculating the error rate, and the transmission matches the actual transmission path quality. The rate can be determined by the transmission rate determination unit 56, and therefore, it is possible to prevent the transmission rate from being changed due to the collision.

  Note that the transmission rate can be increased or decreased by one step (for example, increased from 12 Mbps to 18 Mbps) or lowered in two steps or more (for example, from 12 Mbps to 24 Mbps). Can be raised).

  As described above, according to the AP 101 according to the present embodiment, the possibility of collision with a data packet is detected based on the media occupancy rate, and retransmission of the data packet when the possibility is high, Since the error rate is excluded from calculation and the transmission rate is determined based on the error rate, an appropriate transmission rate can be determined according to the actual transmission path quality.

  Therefore, when a transmission rate appropriate for the transmission quality of the wireless transmission path is used, even if a data packet is retransmitted due to a collision with another data packet, the retransmission is considered in calculating the error rate. Therefore, no determination is made to lower the transmission rate. That is, the wireless transmission path that can be originally used can be effectively used.

  Although the case where the AP 101 determines the transmission rate has been described above as an example, the present invention can also be applied to the STA2. In this case as well, since it can be realized by the same configuration as the configuration example of AP1 described above except that the transmission rate is determined on the STA2 side, details are omitted.

  In the above description, as shown in FIG. 7, the measurement period is the period for each measurement time T. However, as shown in FIG. 10, the measurement period is determined while being shifted by a predetermined time S shorter than the measurement time T. You can also. That is, the measurement period can be determined with a window width of time T.

  Further, in the above, when the media occupation rate exceeds the threshold value once, the packet collision estimation signal is output. However, when the media occupation rate exceeds the threshold value a predetermined number of times continuously, the packet collision estimation signal is output. It can also be.

  Further, the threshold value to be compared with the media occupation ratio can be dynamically changed according to the number of STAs 2 registered in the BSS. This is because the probability of data packet collision increases as the number of registered nodes increases.

  Further, when there is a device that uses a 40 MHz bandwidth in an adjacent channel, the threshold value compared with the media occupation rate may be set to a large value, for example, so that the packet collision estimation signal is difficult to be output. Since a device using the 40 MHz bandwidth transmits a beacon in the 40 MHz bandwidth, the presence of a device using the 40 MHz bandwidth can be detected by detecting the beacon.

  In the above, the occupation time of the wireless transmission path of the measurement time T is calculated using the Duration value of the MAC header, but after detecting the data packet, the LENGTH field and the RATE field in the PHY header of the data packet are decoded, The occupation time can also be calculated by obtaining the packet length (bytes) from these values and converting it into time at the transmission rate at that time.

  FIG. 11 shows a configuration example of the AP 101 when the occupation time is calculated from the values of the LENGTH field and the RATE field in the PHY header of the packet and the media occupation rate is calculated. In this AP 101, a packet length calculation unit 113 is provided in place of the duration value extraction unit 112 of the AP 101 in FIG. The other parts are the same as those in FIG. 8, and the description thereof will be omitted as appropriate.

  The packet length calculation unit 113 extracts the PHY header of the data packet decoded by the PHY circuit 17 and extracts the LENGTH field and RATE field values (hereinafter referred to as LENGTH value and RATE value) therefrom.

  The packet length calculation unit 113 calculates the packet length based on the extracted LENGTH value and RATE value, converts it to time at the transmission rate at that time, and supplies the time to the packet collision estimation unit 201 of the MAC circuit 111.

  The time corresponding to the packet length supplied to the packet collision estimation unit 201 is input to the cumulative addition unit 221 of the media occupation rate calculation unit 211, and the cumulative addition unit 221 cumulatively adds the time during the measurement time T. Then, the occupation time is calculated.

  As described above, the calculation unit 222 and the threshold comparison unit 212 supply the packet collision estimation signal to the packet retransmission count signal output unit 231 of the transmission rate determination unit 202 as appropriate.

  It is also possible to calculate the occupancy time at the measurement time T by measuring the time when the signal strength of the received signal becomes a certain level or more and accumulating the time.

  FIG. 12 shows a configuration example of the AP 101 when the occupation time is calculated from the signal intensity to calculate the media occupation rate. This AP 101 is provided with an RSSI extraction unit 114 in place of the duration value extraction unit 112 of the AP 101 in FIG. The other parts are the same as those in FIG. 8, and the description thereof will be omitted as appropriate.

  The RSSI extraction unit 114 extracts an RSSI (Received Signal Strength Indicator) from the received signal input to the RF circuit 16 and supplies it to the MAC circuit 111.

  FIG. 13 shows a configuration example of the MAC circuit 111 in this example. The packet collision estimation unit 201 of the MAC circuit 111 is provided with a cumulative addition unit 251 instead of the cumulative addition unit 221 of FIG.

  The RSSI supplied from the RSSI extraction unit 114 is input to the cumulative addition unit 251. The cumulative addition unit 251 compares the RSSI supplied from the RSSI extraction unit 114 with a predetermined threshold, cumulatively adds the time when the RSSI is larger than the threshold during the measurement time T, and occupies the measurement time T. Time is calculated and supplied to the calculation unit 222.

  As described above, the calculation unit 222 and the threshold comparison unit 212 supply the packet collision estimation signal to the packet retransmission count signal output unit 231 of the transmission rate determination unit 202 as appropriate.

  Further, in addition to the above-described embodiments, it is also possible to use a management packet (Radio Measurement Report) defined in IEEE 802.11k that is currently being formulated. IEEE802.11k is a standard that is being developed for the purpose of reporting PHY / MAC level information as much as possible, and STA (or AP) has the following items to other STAs (or APs), for example: You can request measurement and reporting.

(1) Number of APs in the specified channel or all channels within the range of the station
(2) Beacon signal strength of each AP
(3) The number of frames received within the specified time, all stations that received the frame, the number of frames received, and the average signal strength of each source
(4) Wireless LAN operation level in each channel
(5) Wireless operations other than wireless LAN in each channel that originate from devices such as mobile phones and microwave ovens that may interfere with 802.11 devices
(6) Statistics such as average delay time while waiting for transmission, number of failed transfers, number of FCS errors detected in received frames
(7) Signal length of requesting station measured at requesting station
(8) Location of other stations.
(9) Frame statistics information at PHY level (for example, received power, number of antennas used / number, PHYType, etc.)
(10) BSS establishment information at neighboring APs (for example, TSF counter value, BSSID, Vendor information, etc.)

The above measurement results are described in the management packet and shared between STAs or AP-STAs. Among IE (Information Elements) corresponding to the measurement results,
(a) Channel Load (IE showing CCA busy time rate statistics)
(b) Noise Histogram (received power during NAV, ie IE indicating the probability of STA)
Since each indicates the number of STAs etc. present on the channel and the Busy rate, the media occupation time T can be determined by using these IEs.

Also,
(c) STA Statistics (IE indicating transmission / reception packet counter and retransmission counter)
Is an IE that can be applied to calculate the packet error rate.

  Therefore, appropriate transmission rate selection can be realized by using these IEs included in the management packet.

  Furthermore, the series of processes described above can be executed by hardware or can be executed by software. When a series of processing is executed by software, a program constituting the software executes various functions by installing a computer incorporated in dedicated hardware or various programs. For example, it is installed from a program recording medium in a general-purpose personal computer or the like.

  FIG. 14 is a block diagram illustrating a hardware configuration example of a computer that executes the above-described series of processing by a program.

  In a computer, a CPU (Central Processing Unit) 501, a ROM (Read Only Memory) 502, and a RAM (Random Access Memory) 503 are connected to each other by a bus 504.

  An input / output interface 505 is further connected to the bus 504. The input / output interface 505 includes an input unit 506 made up of a keyboard, mouse, microphone, etc., an output unit 507 made up of a display, a speaker, etc., a storage unit 508 made up of a hard disk or nonvolatile memory, and a communication unit 509 made up of a network interface. A drive 510 for driving a removable medium 511 such as a magnetic disk, an optical disk, a magneto-optical disk, or a semiconductor memory is connected.

  In the computer configured as described above, the CPU 501 loads the program stored in the storage unit 508 to the RAM 503 via the input / output interface 505 and the bus 504 and executes the program, for example. Is performed.

  The program executed by the computer (CPU 501) is, for example, a magnetic disk (including a flexible disk), an optical disk (CD-ROM (Compact Disc-Read Only Memory), DVD (Digital Versatile Disc), etc.), a magneto-optical disk, or a semiconductor. The program is recorded on a removable medium 511 that is a package medium including a memory or the like, or provided via a wired or wireless transmission medium such as a local area network, the Internet, or digital satellite broadcasting.

  The program can be installed in the storage unit 508 via the input / output interface 505 by attaching the removable medium 511 to the drive 510. Further, the program can be received by the communication unit 509 via a wired or wireless transmission medium and installed in the storage unit 508. In addition, the program can be installed in the ROM 502 or the storage unit 508 in advance.

  The program executed by the computer may be a program that is processed in time series in the order described in this specification, or in parallel or at a necessary timing such as when a call is made. It may be a program for processing.

It is a figure explaining transition of a transmission rate. It is a block diagram which shows the structural example of the conventional wireless LAN system. It is a block diagram which shows the structural example of AP1 of FIG. FIG. 4 is a block diagram illustrating a functional configuration example of a MAC circuit 11 in FIG. 3. It is a block diagram which shows the structural example of the wireless LAN system to which this invention is applied. It is a figure explaining the relationship between a media occupation rate and the collision with a data packet. It is a figure explaining a media occupation rate. It is a block diagram which shows the structural example of AP101 of FIG. It is a block diagram which shows the functional structural example of the MAC circuit 111 of FIG. It is another figure explaining a media occupation rate. It is a block diagram which shows the other structural example of AP101 of FIG. It is a block diagram which shows the other structural example of AP101 of FIG. FIG. 13 is a block diagram illustrating a functional configuration example of a MAC circuit 111 in FIG. 12. It is a block diagram which shows the structural example of a computer.

Explanation of symbols

  101 AP, 111 MAC circuit, 112 Duration value extraction unit, 113 packet length calculation unit, 114 RSSI extraction unit, 201 packet collision estimation unit, 202 transmission rate determination unit, 211 media occupation rate calculation unit, 212 threshold comparison unit, 221 accumulation Addition unit, 222 calculation unit, 231 packet retransmission count signal output unit, 251 cumulative addition unit

Claims (8)

In a wireless communication apparatus having a wireless communication function capable of using a plurality of transmission rates,
Usage rate calculating means for calculating a usage rate of a wireless transmission path in which wireless communication is performed by the wireless communication function;
Determining means for determining a transmission rate based on at least the usage rate calculated by the usage rate calculating means ;
The determining means calculates a data retransmission rate based on the number of data retransmissions performed in a state where the calculated usage rate is below a threshold, and determines the transmission rate based on the calculated retransmission rate. wireless communication device. The radio communication apparatus according to claim 1 , wherein the determination unit calculates the retransmission rate by excluding the number of retransmissions of data performed in a state where the calculated usage rate exceeds a threshold from the actual number of retransmissions. . The wireless communication apparatus according to claim 1, wherein the wireless communication function is a function of executing wireless communication compliant with IEEE802.11. The usage rate calculating means calculates a usage time during which the wireless transmission path of a predetermined measurement time is used, and calculates the usage rate by dividing the calculated usage time by the measurement time. The wireless communication device according to 1. The usage rate calculating means calculates the usage time by using a Duration value in a MAC header constituting a data packet, a LENGTH value and a RATE value in a PHY header, or a signal strength value of a received signal. 4. A wireless communication device according to 4 . The wireless communication apparatus according to claim 4, wherein the usage rate calculation unit calculates the usage time by using channel information included in an information element constituting the received management packet. In a wireless communication method of a wireless communication device having a wireless communication function capable of using a plurality of transmission rates,
A usage rate calculating step of calculating a usage rate of a wireless transmission path in which wireless communication is performed by the wireless communication function;
At least, based on the usage rate calculated in the processing of the usage rate calculation step, seen including a determining step of determining a transmission rate,
In the determining step, a data retransmission rate is calculated based on the number of data retransmissions performed in a state where the calculated usage rate is below a threshold, and the transmission rate is determined based on the calculated retransmission rate. wireless communication method for. In a program for causing a computer to function as a wireless communication device having a wireless communication function capable of using a plurality of transmission rates,
Usage rate calculating means for calculating a usage rate of a wireless transmission path in which wireless communication is performed by the wireless communication function;
Determining means for determining a transmission rate based on at least the usage rate calculated by the usage rate calculating means ;
Is a program that causes a computer to function ,
The determining means calculates a data retransmission rate based on the number of data retransmissions performed in a state where the calculated usage rate is below a threshold, and determines the transmission rate based on the calculated retransmission rate. Do
Program .

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