JP2009021784A - Wireless communication device - Google Patents

Abstract

To provide a wireless communication apparatus capable of realizing stable communication by increasing an effective communication speed.
A transmitter 16A that transmits a radio signal to a communication partner, a receiver 16B that receives a radio signal from the communication partner, and a radio signal received by the receiver 16B when communication with the communication partner is started. A signal quality measuring unit 14 for measuring quality, a communication speed determining unit 15 for determining an initial communication speed when communicating with a communication partner according to the quality measured by the signal quality measuring unit 14, a transmitting unit 16A and a receiving unit 16B is configured to communicate with the communication partner according to the initial communication speed determined by the communication speed determination unit 15.
[Selection] Figure 2

Description

  The present invention relates to a wireless communication apparatus that transmits and receives data via radio.

  A wireless communication apparatus used in a conventional wireless LAN or the like uses various modulation methods based on OFDM (Orthogonal Frequency Division Multiplexing) and DSSS / CCK (Direct Sequence Spectrum Spread / Complementary Code Keying) in accordance with IEEE 802.11. We are communicating.

  FIG. 7 is a diagram showing the relationship between communication speed and modulation / demodulation in IEEE 802.11a. In wireless communication performed by a wireless communication device compliant with IEEE 802.11, various communication speeds are determined using a coding rate, bit mapping, and the like. In IEEE 802.11a, as shown in FIG. 7, 6 Mbps and 9 Mbps are used. , 12 Mbps, 18 Mbps, 24 Mbps, 36 Mbps, 48 Mbps, and 54 Mbps are defined. Note that in IEEE 802.11b, four types of communication speeds of 1 Mbps, 2 Mbps, 5.5 Mbps, and 11 Mbps are defined.

  In general, modulation and demodulation become more complicated as the communication speed of wireless communication increases. In addition, since wireless communication depends on the S / N ratio of a wireless signal and a spatial propagation model, data transmission over a long distance becomes difficult. On the other hand, wireless communication at a short distance becomes easy to implement at high speed because the SN ratio becomes large.

  In IEEE 802.11, when starting wireless communication, frames are exchanged between the wireless communication device and the access point as shown in FIG. Frames for searching for an access point, ProbeRequest, ProbeResponse, Authentication for authentication, AuthenticationRequest for starting connection with an access point, and AssociationResponse, and AssociationResponse frames are at a relatively low communication rate called a basic rate. Exchanged. For example, in IEEE 802.11a, the communication speed at the start of wireless communication is 6 Mbps to 24 Mbps.

  The reason for exchanging at a low communication speed is that the connection between the wireless communication apparatus and the access point is reliably established. Although communication at a communication speed exceeding the basic rate is not guaranteed at the stage of starting wireless communication, it is desirable that wireless communication be performed at high speed. Depending on the communication environment such as the distance from the wireless communication device to the access point, wireless communication is not necessarily performed at the maximum speed, but a procedure for making wireless communication as fast as possible is disclosed.

  For example, in a conventional wireless communication device, when performing wireless communication, a frame is transmitted to the access point at the maximum speed, and the access point confirms that there is an obstacle between the wireless communication device and the access point. When there is no response, it is known that the communication speed is lowered while trying to retransmit (hereinafter referred to as fallback), and if it still fails, the fallback is repeated while attempting retransmission (for example, patents). Reference 1).

  Here, FIG. 9 shows a diagram representing state transition of the conventional wireless communication apparatus. When the wireless communication device transmits a frame to the access point at the maximum speed in the normal state and transmission fails due to no acknowledgment from the access point, the state of the wireless communication device transitions from the normal state to the retransmission state. . Factors that cause the transmission of the wireless communication device to fail include, for example, that the location of the access point and each wireless communication device is not necessarily placed in a place with good communication conditions, or that an obstacle exists between the wireless communication device and the access point. It exists.

If the retransmission is successful, the state of the wireless communication apparatus transitions from the retransmission state to the normal state. If the retransmission is not successful even after being repeated a specified number of times, the wireless communication apparatus transitions from the retransmission state to the fallback state. If the retransmission succeeds by reducing the communication speed in the fallback state, or if a certain time has passed since the first transmission, the state of the wireless communication device transitions from the fallback state to the normal state, and the wireless communication device The communication speed at the time of sending is restored.
JP 2005-102228 A

  However, in an environment where there is a wireless communication device and an access point in a large office, the conventional wireless communication device first tries to communicate with the access point at the highest speed, and the distance from the wireless communication device to the access point is increased. Even if retransmission is successful when the wireless communication device enters the fallback state, the transmission speed is restored to the maximum speed that is the communication speed before the start of fallback. There was a problem that it took a long time to send. As described above, in the conventional wireless communication apparatus, since it may take a long time to actually transmit the frame, the effective communication speed is low.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a wireless communication device that can realize stable communication by increasing an effective communication speed.

A wireless communication device of the present invention includes a communication unit that transmits and receives a wireless signal to and from a communication partner, a signal quality measurement unit that measures the quality of a wireless signal received by the communication unit when communication with the communication partner is started, A communication speed determining unit that determines an initial communication speed when communicating with a communication partner according to the quality measured by the signal quality measuring unit, wherein the communication unit is an initial value determined by the communication speed determining unit It has the structure which communicates with the said communicating party according to a communication speed.
With this configuration, the initial communication speed when communicating with the communication partner is determined according to the quality of the radio signal when communication with the communication partner is started, and the communication with the communication partner is performed according to the determined initial communication speed. Can be reduced as much as possible, and the effective communication speed can be increased to realize stable communication.

In the wireless communication device of the present invention, the signal quality measurement unit measures the distance from the strength of the wireless signal received by the communication unit to the communication partner as the quality, and the communication speed determination unit It has a configuration for determining an initial communication speed when communicating with a communication partner according to the distance measured by the signal quality measuring unit.
This configuration determines the initial communication speed according to the distance to the communication partner and communicates with the communication partner according to the determined initial communication speed, so that the number of retransmissions can be minimized and the effective communication speed is increased. And stable communication.

In the wireless communication device of the present invention, the signal quality measurement unit measures the modulation accuracy of a radio signal received by the communication unit as the quality, and the communication speed determination unit measures the signal quality measurement unit. The initial communication speed when communicating with the communication partner is determined according to the modulation accuracy.
With this configuration, the initial communication speed is determined according to the modulation accuracy of the radio signal, and communication is performed with the communication partner according to the determined initial communication speed, so that the number of retransmissions can be minimized and the effective communication speed can be increased. And stable communication.

In the wireless communication apparatus of the present invention, the communication unit retransmits the wireless signal when there is no acknowledgment for the wireless signal transmitted to the communication partner after the communication speed determining unit determines the initial communication speed. If retransmission is not successful, the communication speed is changed to a communication speed lower than the initial communication speed, and the communication partner is communicated according to the changed communication speed.
With this configuration, when retransmission is not successful, communication with the communication partner is performed according to a communication speed lower than the initial communication speed, so that the possibility of successful communication with the communication partner during retransmission can be increased.

In the wireless communication device of the present invention, the communication unit changes the communication speed to a lower communication speed than the initial communication speed when the retransmission does not succeed continuously for a predetermined number of times, and performs the communication according to the changed communication speed. It has the structure which communicates with the other party.
With this configuration, when retransmission does not succeed continuously for a predetermined number of times, communication with the communication partner is performed according to a communication speed lower than the initial communication speed, so that the possibility of successful communication with the communication partner during retransmission can be increased. it can.

The wireless communication device of the present invention is higher than the low communication speed and does not exceed the initial communication speed when the communication unit receives an acknowledgment to the wireless signal transmitted to the communication partner according to the low communication speed. The communication speed is changed and communication with the communication partner is performed according to the changed communication speed.
With this configuration, when an acknowledgment is received for a radio signal transmitted to a communication partner according to a communication speed lower than the initial communication speed, the communication speed is increased so as not to exceed the initial communication speed, and communication with the communication partner is performed. The possibility of successful communication with the other party can be increased.

In the wireless communication device of the present invention, when the communication unit receives an acknowledgment for a wireless signal transmitted to the communication partner according to the low communication speed a predetermined number of times, the wireless communication apparatus is higher than the low communication speed and the initial The communication speed is changed so as not to exceed the communication speed, and the communication partner is communicated according to the changed communication speed.
With this configuration, when an acknowledgment for a radio signal transmitted to a communication partner according to a communication speed lower than the initial communication speed is received a predetermined number of times, the communication speed is increased so that the initial communication speed is not exceeded. Since communication is performed, the possibility of successful communication with the communication partner can be further increased.

  As described above, the present invention provides a wireless communication apparatus capable of increasing the effective communication speed and realizing stable communication.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an example of a configuration diagram of a communication system according to an embodiment of the present invention. The communication system shown in FIG. 1 includes a wireless communication device 10 called a station (STA) and an access point (AP) 20 that is a parent device of the wireless communication device 10. Although a plurality of wireless communication devices 10 are illustrated, the wireless communication devices 10 are referred to as a wireless communication device 10-1, a wireless communication device 10-2, and a wireless communication device 10-n in order to distinguish between them.

  The wireless communication apparatus 10 and the access point 20 communicate with each other in accordance with the IEEE 802.11 series standard used in the wireless LAN. Generally, wireless LAN communication methods include an infrastructure mode (infrastructure mode) and an ad hoc mode, and the one shown in FIG. 1 is an infrastructure mode. On the other hand, the ad hoc mode is a mode in which the wireless communication devices 10 communicate with each other without the access point 20 interposed therebetween. In the embodiment of the present invention, an infrastructure mode in which wireless communication is performed while interposing the access point 20 even in communication between the wireless communication devices 10 will be described. However, the present invention is not limited to using the infrastructure mode.

  In IEEE 802.11, when wireless communication is started, frames are exchanged as shown in FIG. The ProbeReq, ProbeRes, Authentication, and Association frames used at the start of wireless communication are exchanged at a relatively low communication speed called a basic rate.

  In the infrastructure mode, the access point 20 transmits a frame called a beacon (hereinafter referred to as a beacon frame) about once every 100 ms. By transmitting a beacon frame, the access point 20 can notify the wireless communication device 10 communicating with the access point 20 or communicating with the access point 20 of information possessed by the access point 20. it can.

  Based on the received beacon frame, the wireless communication device 10 updates information such as timer synchronization with the access point 20 and communication modulation / demodulation. The beacon frame also includes information regarding the communication speed at which communication is possible, and the wireless communication device 10 can determine the communication speed by using the beacon frame.

  FIG. 2 is a block diagram of the wireless communication apparatus according to the embodiment of the present invention. The radio communication apparatus 10 shown in FIG. 2 includes an antenna 11, an RF (Radio Frequency) unit 12, a PHY (physical layer) unit 13, a signal quality measurement unit 14, a communication speed determination unit 15, a transmission unit 16A, and a reception unit 16B. It is constituted by. In addition, each part which comprises the radio | wireless communication apparatus 10 is comprised by an integrated circuit etc.

  The RF unit 12 transmits and receives an electromagnetic wave signal having a specific frequency used for a wireless LAN or the like via the antenna 11. The PHY unit 13 encodes data to be transmitted and decodes a received signal.

  The transmission unit 16A converts data output from a data processing unit (not shown) into a frame conforming to IEEE 802.11, and transmits the converted frame to the destination via the PHY unit 13 and the RF unit 12. ing. The receiving unit 16B receives the frame via the RF unit 12 and the PHY unit 13, and outputs data obtained by removing the header from the frame to the data processing unit. In the embodiment of the present invention, it is assumed that the communication unit of the present invention includes a transmission unit 16A and a reception unit 16B.

  If the receiving unit 16B fails to receive an acknowledgment (ACK frame) for the frame transmitted by the transmitting unit 16A within a predetermined period, the transmitting unit 16A retransmits the same frame as the transmitted frame. . Note that as a retransmission procedure, a method defined in IEEE 802.11 may be adopted. The retransmission procedure defined in IEEE802.11 includes ShortRetry and LongRetry. When the number of retransmissions defined in each of these is exceeded, the retransmission attempt is terminated. The difference between ShortRetry and LongRetry differs depending on the type of frame to be transmitted.

  The signal quality measurement unit 14 measures the quality of the received radio signal when the connection with the access point 20 is started. The communication speed determination unit 15 determines an initial communication speed when communicating with a communication partner according to the quality measured by the signal quality measurement unit 14. When the initial communication speed is determined, the transmission unit 16A and the reception unit 16B communicate with the communication partner according to the determined initial communication speed.

  For example, as a method for measuring the quality of a radio signal, there is a method in which the signal quality measurement unit 14 measures a received signal strength indicator (RSSI) when a beacon frame is received and sets the RSSI as a quality. In consideration of multipath, since RSSI is measured with a value larger than the actual value, the signal quality measurement unit 14 may correct the RSSI to an actual value.

  When the signal quality measurement unit 14 measures RSSI, the communication speed determination unit 15 determines the initial communication speed according to the RSSI according to the correspondence table shown in FIG. FIG. 3 is a correspondence table showing distances to communication partners corresponding to RSSI, and is a correspondence table showing appropriate communication speeds corresponding to distances to communication partners. The correspondence table shown in FIG. 3 shows the relationship that the distance from the access point 20 that is the communication partner is short when the RSSI is large.

  According to the correspondence table shown in FIG. 3, when the RSSI value S when received is S1 <S ≦ S2, the communication speed determination unit 15 determines that the communication partner is at a distance from D6 to D5. Then, it is determined that an appropriate communication speed as the initial communication speed is 9 Mbps. In addition, the distance to the communication partner corresponding to RSSI may be a distance empirically specified from RSSI or a distance calculated from RSSI.

  Further, when obtaining a distance calculated from RSSI, a TPC Report (Transmit Power Control Report) element (hereinafter referred to as TPC information) included in a beacon frame is used. The TPC information represents the signal strength when a communication partner transmits a beacon frame in which this information is set.

  FIG. 4 shows a format of TPC information. In the “Transmit Power” of the TPC information, a dBm value representing the signal strength when the communication partner transmits a beacon frame in which the TPC information is set is set. Note that the TPC information is defined by IEEE 802.11h.

  When the beacon frame is received by the receiving unit 16B, the signal quality measuring unit 14 receives the power obtained from the RSSI that is the signal strength when the beacon frame is received, the transmission power indicated by “Transmit Power” of the TPC information, and From the difference, the distance to the communication partner is estimated using the relational expression shown in [Equation 1]. Note that D represents a distance, n represents a spatial model parameter, and n = 3.3.

    [Formula 1] PassLoss (dB) = 41 + 10 * (Log [D ^ n])

  It is assumed that “Transmit Power” is 11 dBm and the received power is −60 dBm from the RSSI value. If the path loss PassLoss obtained from this result and the relational expression shown in [Equation 1] are used, the distance D becomes about 8 m. Therefore, the signal quality measurement unit 14 determines that the communication partner is at a distance of 8 m, and the communication speed determination unit 15 determines an appropriate communication speed as the initial communication speed according to the correspondence table shown in FIG.

  The signal quality measurement unit 14 does not need to calculate the distance using the relational expression shown in [Equation 1] every time a frame is received, and prepares a correspondence table between path loss and distance, and this correspondence table. The distance may be determined according to

  As a method of measuring the quality of a radio signal, there is a ProbeRes frame as a response after transmitting a ProbeReq frame, and an EVM (Error Vector Magnitude: modulation accuracy) obtained from the ProbeRes is measured to determine the quality of the EVM. There is a way. The EVM is an index value representing the degree of error between an ideal signal of various modulation schemes (BPSK, QPSK, 16QAM, 64QAM, etc.) and an actually received signal. When the signal quality is poor, the EVM becomes a large value.

  For example, IEEE 802.11a stipulates that a condition of EVM ≦ 5.6% is necessary for a communication speed of 54 Mbps. Ideally, an EVM close to 0% is desirable, but the EVM becomes a bad value (large value) as various factors such as degradation of the SN ratio during propagation of a radio signal and multipath overlap. Note that an error rate is obtained for each bit of each demodulated data in the received radio signal, and a total value obtained by adding the error rates of each bit in one frame is EVM.

  When the signal quality measurement unit 14 measures the EVM, the communication speed determination unit 15 determines the communication speed corresponding to the EVM as the initial communication speed according to the correspondence table shown in FIG. FIG. 5 is a correspondence table showing appropriate communication speeds corresponding to the determination values for determining EVM.

  According to the correspondence table shown in FIG. 5, when the EVM when the frame is received is 13%, the communication speed determining unit 15 determines that the frame is between the determination value E3 and the determination value E2, and the initial communication speed. It is determined that the appropriate communication speed is 24 Mbps. In this case, communication can be performed at a communication speed of 24 Mbps with an EVM of up to 15.8% as an allowable value.

  The operation of the wireless communication apparatus 10 configured as described above will be described with reference to the drawings. FIG. 6 is a state transition diagram of the wireless communication device 10.

  When the wireless communication device 10 is activated, the state of the wireless communication device 10 is an initial state, and the sequence procedure shown in FIG. 8 is executed. Thereafter, the signal quality measuring unit 14 measures the quality of the received radio signal such as a beacon frame, and the communication speed determining unit 15 is measured by the signal quality measuring unit 14 according to the correspondence table shown in FIG. 3 or FIG. The initial communication speed when communicating with the communication partner is determined according to the quality. At this time, the state of the wireless communication device 10 changes from the initial state to the optimum communication state (T00). In this state transition, the initial communication speed which is the optimum communication speed is determined, and the wireless communication apparatus 10 maintains a good communication speed with few retransmissions.

  After the state of the wireless communication device 10 transitions to the optimum communication state, the transmission unit 16A normally transmits the frame due to factors such as an obstacle temporarily appearing between the wireless communication device 10 and the access point 20. If not, that is, if the receiving unit 16B has not received an acknowledgment (ACK) in response to the frame within a predetermined period, the state of the wireless communication device 10 transitions from the optimal communication state to the retransmission state (T01).

  In the retransmission state, the transmitter 16A retransmits the frame while maintaining the initial communication speed determined in T00. When the receiving unit 16B has received an acknowledgment (ACK) for a retransmitted frame within a predetermined period, that is, when retransmission is successful, the state of the wireless communication device 10 transitions from the retransmission state to the optimal communication state. (T10). If the retransmission is not successful, the state of the wireless communication device 10 transitions from the retransmission state to the fallback state (T12).

  When the state of the wireless communication device 10 is a retransmission state, when the retransmission is repeated a predetermined number of times and does not succeed, the state of the wireless communication device 10 transitions to the fallback state and the retransmission is being repeated If successful, the state of the wireless communication device 10 may transition to the optimum communication state.

  In the embodiment of the present invention, when the state of the wireless communication device 10 transitions from the initial state to the optimal communication state, the wireless communication device 10 is at the initial communication speed and the optimal communication speed. When the state 10 becomes a retransmission state, it is not necessary to attempt retransmission up to the number of retransmissions specified in IEEE 802.11, and even if retransmissions are repeated less than the number of retransmissions specified, it will not succeed. In some cases, the state of the wireless communication device 10 may transition to the fallback state.

  When the state of the wireless communication device 10 transitions to the fallback state, the transmission unit 16A transmits a frame by reducing the communication speed. For example, the transmission unit 16A reduces the communication speed from 54 Mbps to a communication speed of 48 Mbps or 36 Mbps. . In the fallback state, when the receiving unit 16B can receive an acknowledgment (ACK) for the frame within a predetermined period, that is, when the transmission is successful, the communication speed returns to the initial communication speed, and the state of the wireless communication device 10 is optimal. Transition to the communication state (T20).

  For example, when the state of the wireless communication device 10 is the optimum communication state and the initial communication speed is 48 Mbps, the wireless communication device is subsequently changed when the radio wave environment between the wireless communication device 10 and the access point 20 is temporarily deteriorated. When the state 10 becomes a fallback state and the communication speed drops to 24 Mbps, and the state of the wireless communication apparatus 10 returns to the optimum communication state, the communication speed also returns to 48 Mbps.

  When transitioning from the fallback state to the optimum communication state, the wireless communication device 10 should be able to communicate stably if it communicates with the access point 20 at the initial communication speed. Since the communication speed of the wireless communication device 10 does not return to the maximum communication speed when the transition is made from the fallback state to the optimum communication state as in the prior art, Since the number of failures can be reduced and there is no fallback from the maximum communication speed, the wireless communication device 10 can efficiently perform data transfer.

  Further, when the receiving unit 16B can receive an acknowledgment (ACK) for a transmission frame once after entering the fallback state, the transmitting unit 16A increases the speed from the current communication speed and transmits the frame. Become. However, the upper limit for increasing the speed is up to the initial communication speed.

  Note that when the transition is made from the fallback state to the optimum communication state, the transmission unit 16A may increase the communication speed by one step from the current communication speed. For example, if the state of the wireless communication device 10 is the optimal communication state and the initial communication speed is 48 Mbps, then the radio communication device 10 is in a state where the radio wave environment between the wireless communication device 10 and the access point 20 has deteriorated slightly. Even if the state returns to the optimal communication state via the fallback state and the communication speed returns to 48 Mbps, communication between the wireless communication apparatus 10 and the access point 20 may not be possible. Therefore, the communication speed of the wireless communication device 10 is not returned to 48 Mbps, but is increased to 36 Mbps, which is a communication speed one step higher than 24 Mbps.

  When the state of the wireless communication device 10 transitions from the fallback state to the optimum communication state, the wireless communication device 10 gradually increases to the communication speed that is one step higher. Since the communication speed increases, the optimum communication speed can be updated while adapting to changes in the communication environment actually used.

  In the above description, when the wireless communication device 10 increases the communication speed once lowered to the communication speed of one step, the receiving unit 16B can receive an acknowledgment (ACK) for a retransmitted frame once after entering the fallback state. However, it may be when an acknowledgment (ACK) has been received continuously a plurality of times instead of once. The method in which the wireless communication device 10 increases the communication speed by one step when an acknowledgment (ACK) is received more than once can be accessed with a plurality of predetermined successes without judging only by one success. Used when communication with the point 20 is desired to return to a stable state.

  In the conventional wireless communication apparatus, if the communication speed is lowered in the fallback state and then transmission is successful at the lowered communication speed, communication is performed according to the maximum communication speed defined by the communication standard (for example, 54 Mbps in IEEE802.11a). Communicate with the other party and repeat the transmission again to fall back. In the wireless communication device according to the embodiment of the present invention, the initial communication speed determined when communication with the communication partner is started, the communication speed is lowered in the fallback state as the communication state deteriorates, and then If transmission is successful at the reduced communication speed, communication is performed with the communication partner according to the initial communication speed, so that the number of retransmissions is minimized, and stable communication can be realized by increasing the effective communication speed.

Configuration diagram of a communication system according to an embodiment of the present invention 1 is a block diagram of a wireless communication apparatus according to an embodiment of the present invention. Correspondence table showing distance to communication partner corresponding to RSSI The figure which shows the format of TPC information Correspondence table showing appropriate communication speed corresponding to the determination value for determining EVM State transition diagram of radio communication apparatus according to an embodiment of the present invention The figure which shows the relationship between the communication speed and modulation | alteration demodulation in IEEE802.11a. The figure which shows exchange of a frame between the radio | wireless communication apparatus and access point at the time of starting radio | wireless communication State transition diagram of conventional wireless communication devices

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Wireless communication apparatus 11 Antenna 12 RF part 13 PHY part 14 Signal quality measurement part 15 Communication speed determination part 16A Transmission part 16B Reception part 20 Access point

Claims (7)

A communication unit that transmits and receives radio signals to and from a communication partner;
A signal quality measuring unit for measuring the quality of a radio signal received by the communication unit when communication with the communication partner is started;
A communication speed determining unit that determines an initial communication speed when communicating with a communication partner according to the quality measured by the signal quality measuring unit;
The wireless communication apparatus, wherein the communication unit communicates with the communication partner according to an initial communication speed determined by the communication speed determination unit. The signal quality measurement unit measures the distance from the strength of the radio signal received by the communication unit to the communication partner as the quality,
The wireless communication apparatus according to claim 1, wherein the communication speed determination unit determines an initial communication speed when communicating with a communication partner according to the distance measured by the signal quality measurement unit. The signal quality measurement unit measures the modulation accuracy of the radio signal received by the communication unit as the quality;
The wireless communication apparatus according to claim 1, wherein the communication speed determination unit determines an initial communication speed when communicating with a communication partner according to the modulation accuracy measured by the signal quality measurement unit.   The communication unit retransmits the radio signal when there is no acknowledgment for the radio signal transmitted to the communication partner after the communication speed determination unit determines the initial communication speed, and when the retransmission is not successful, The wireless communication apparatus according to any one of claims 1 to 3, wherein the wireless communication apparatus changes to a communication speed lower than a communication speed and communicates with the communication partner according to the changed communication speed.   The communication unit, when the retransmission does not succeed for a predetermined number of times, changes to a communication speed lower than the initial communication speed, and communicates with the communication partner according to the changed communication speed. Item 5. The wireless communication device according to Item 4.   When the communication unit receives an acknowledgment for the wireless signal transmitted to the communication partner according to the low communication speed, the communication speed is changed to a communication speed higher than the low communication speed and not exceeding the initial communication speed. 6. The wireless communication apparatus according to claim 4, wherein the wireless communication apparatus communicates with the communication partner according to the above.   When the communication unit has received a predetermined number of acknowledgments for a radio signal transmitted to the communication partner according to the low communication speed, the communication unit is changed to a communication speed higher than the low communication speed and not exceeding the initial communication speed. 6. The wireless communication apparatus according to claim 4, wherein communication is performed with the communication partner according to the changed communication speed.

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