JP5411785B2 - Wireless communication apparatus and wireless communication method - Google Patents

Description

  The present invention relates to a radio communication technique, and more particularly to a radio communication technique for performing a handover based on a rate fallback scheme.

  In a wireless digital communication system, a station (wireless station) employs an access algorithm to obtain access rights to a transmission medium (for example, a radio frequency range). For example, systems that comply with the IEEE 802.11 Wireless LAN standard generally use CSMA / CA (Carrier Sense Multiple Access with Collision Aidance) algorithms. The CSMA / CA algorithm initially waits for the medium, and when the signal level falls below a certain threshold, it waits for a further random time before starting to transmit a frame. Specifically, the 802.11 standard provides a mechanism for reducing the probability of collision by using a random backoff counter and using a priority window for transmission of a specific packet. However, even if the CSMA / CA algorithm is used, the collision cannot be completely suppressed. For example, when the values of the random back-off counter match at two or more stations, transmissions are started at the same time, and a collision occurs. Even if no collision occurs, the frame may not be transmitted or acknowledged correctly.

  The 802.11 standard includes an acknowledgment mechanism that confirms that a frame has been successfully received. When the receiving station receives the frame without error, it sends an acknowledgment (ACK) frame to the transmitting station. This ACK mechanism protects the system from packet loss (eg, due to collisions). When a collision occurs, one or two stations will not receive an ACK frame for each transmitted frame. In some cases other than the collision, an ACK frame for the transmitted frame may not be received. For example, (i) inherent detection failure (relation between false alarm probability and detection probability), (ii) signal quality is low (excessive time spreading), (iii) signal power is weak (distance is too long) ), (Iv) Interference at the receiving station.

  The 802.11 implementation necessarily includes a number of mechanisms that can be used to overcome the problem of not being able to successfully transmit a frame. If the sending station does not receive the ACK frame, the sending station can retransmit the original frame up to N times. The sending station increases the random access time with each retransmission. The transmitting station can retransmit on any of these retries using any modulation scheme deemed appropriate. For example, the sending station can continuously retransmit the original frame at a lower rate (and therefore with a more stable modulation) according to a rate fallback algorithm. This retransmission is performed until the maximum number of retries (N) is reached or an ACK frame is received. The data transport layer of the destination station may conclude that the frame has been lost, for example because there is a missing sequence number that the transport layer assigns to each packet. Frame loss can adversely affect overall system performance. For example, the TCP / IP transport layer usually reduces its transmission rate when multiple packet losses are detected, but this temporarily reduces the total throughput of the system.

In the technique described in Patent Document 1 below, the following technique is proposed as a rate fallback method and apparatus in a wireless communication system.
(1) When an affirmative response (hereinafter referred to as ACK) from the AP for the transmission frame is not received, the wireless LAN terminal shifts to a retransmission state.
(2) The wireless LAN terminal that has entered the retransmission state first tries frame retransmission at the same rate.
(3) When the number of retransmissions at the same rate exceeds a specified value, the retry number expiration avoidance algorithm enters a fallback state and gradually decreases the transmission rate.

  This can reduce the transmission rate when retransmitting the current frame in order to increase the probability that the current frame is successfully transmitted and acknowledged.

JP 2005-102228 A

Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (1999); IEEE Std 802.11a; High-speed Physical Layer in the 5 GHz band; 1999; IEEE Std 802.11b; Higher-Speed Physical Layer Extension in the 2.4 GHz Band; 1999; or IEEE Std 802.11g / D1.1; Further Higher-Speed Physical Layer Extension in the 2.4 GHz Band; Draft version 200;

  10 to 12 are diagrams showing problems of the conventional technique described in Patent Document 1. FIG. FIG. 10 is a diagram illustrating an example of a scene that is a problem of the conventional technique described in Patent Document 1. In FIG. Here, a description will be given of a system including terminal A, AP1 (currently connected AP) 61, AP2 (connection candidate AP) 71. The horizontal axis is the time axis (from t101 to t123). First, as a setting condition of the terminal A and the AP (1) 61, the terminal A recognizes the connection candidate AP (2) 71 that can be handed over by the peripheral search. The wireless LAN support rates of AP (1) 61 are 11 Mbps and 5.5 Mbps. The prescribed number of retransmissions for determining the rate fallback of the terminal A1 is 3 (uniform).

  As a problem in this case, the wireless LAN terminal apparatus is handed over to the AP (2) 71 soon. Therefore, it is not necessary to ensure the communication accuracy with the AP 1 at the same level as usual during this period (the handover to the AP 2 should be performed as soon as possible without wasting the bandwidth of the AP 1).

Nevertheless, there is a problem that the following processing cannot be realized.
(1) Change of the specified number of retransmissions for determining fallback ⇒ If the number of retransmissions can be reduced, AP1 bandwidth consumption can be suppressed and the handover time can be shortened.
(2) Fallback rate range change (lower limit rate) ⇒ If low-rate communication can be suppressed, AP1 bandwidth consumption can be suppressed and handover time can be shortened.

  FIG. 12 is a diagram illustrating an example of a conventional fallback rate table. Here, it is assumed that the support rate of the connected AP is 802.11a / b / g full.

  FIG. 11 is a flowchart showing the flow of processing in the prior art. The description will be given with reference to FIG. First, processing is started in step S101 (START), and in step S102, it is determined whether or not terminal A is in a wireless LAN area (whether or not an AP is connected). Since communication is possible only in a wireless LAN area (AP connection), determination is necessary. If it is out of radio range (NO), the fallback operation is stopped (step S112: END).

  If it is within the wireless LAN area (AP connection) (YES), the process proceeds to step S103, and a data transmission request from an upper layer is generated. In step S104, wireless LAN frame transmission processing is performed. In step S105, it is determined whether or not an ACK from the AP has been received. If received (YES), the process returns to step S102, and if not received (not completed), (NO) a fallback operation is started. That is, the process proceeds to step S106, and a fallback pattern No that matches the initial rate = the current wireless transmission rate is searched from the rate table of FIG.

  Next, in step S107, wireless LAN frame retransmission processing is performed. Next, in step S108, it is determined whether or not ACK is received from the AP. If NO, the process proceeds to step S109, and it is determined whether or not the current retransmission number counter = retransmission Max (3 in FIG. 10). Times).

  If YES, the process returns to step S102. If NO in step S109, the process proceeds to step S111, the retransmission counter is incremented by 1, and the rate corresponding to the number of retransmissions is changed from 11 Mbps here to 5.5 Mbps in the rate table so that the wireless LAN transmission unit ( And return to step S107. In the case of YES, the process proceeds to step S110, the wireless LAN frame retransmission is completed, the retransmission counter is reset, the frame is discarded, and the process returns to step S102.

  When the example of the fallback rate table of the prior art of FIG. 12 is used, the number of retransmissions and the transmission rate are set as follows regardless of the communication state (good / bad) with the currently connected AP (example) .

1) The initial wireless LAN transmission rate is 24Mbps⇒Fallback pattern No.4
<Retransmission 1st> 24Mbps
<Second retransmission> 11Mbps
<Retransmission 3rd time> 5.5Mbps
<Retransmission 4th time> 2Mbps
<5th retransmission> 1Mbps
<6th retransmission> 1Mbps

2) The initial wireless LAN transmission rate is 1Mbps⇒Fallback pattern No.12
<Retransmission 1st time> 1Mbps
<Second retransmission> 1Mbps
<Retransmission 3rd time> 1Mbps
<Retransmission 4th time> 1Mbps
<5th retransmission> 1Mbps
<6th retransmission> 1Mbps

In this manner, in an environment where a handover (hereinafter referred to as “HO”) candidate APs with poor wireless communication conditions of the currently connected AP and better wireless communication conditions than the currently connected AP exist in the vicinity. When applying the technique described in Patent Document 1, the following problems arise.
(1) When frame retransmission and rate fallback similar to normal (when there is no HO candidate AP in the vicinity) are performed, there is a problem that the bandwidth of the currently connected AP is wasted.
(2) There is a problem that redundant time occurs in the handover process because frame retransmission and rate fallback are performed in the same manner as usual (when there is no HO candidate AP in the vicinity).

  The object of the present invention is to solve the problems (1) and (2).

The present invention is characterized in that the following measures are taken in addition to rate fallback control only when a HO candidate AP exists in the vicinity of a mobile terminal (own device) (when detected by the mobile terminal). .
1) Reduce the number of retransmissions for each rate from the normal time.
2) The rate is not lowered to the lower limit of the support rate with which the currently connected AP can communicate.

  However, when there is no HO candidate AP in the vicinity (when it is not detected by the mobile terminal), the normal operation is performed.

  According to an aspect of the present invention, a wireless communication apparatus having a control unit that controls frame transmission and having a rate fallback mechanism is different from a first access point to which the wireless communication apparatus is connected. Communication with the second access point by comparing the wireless LAN scan control unit for detecting the second access point with the communication state with the first access point and the communication state with the second access point And a communication control unit that performs control to reduce the number of retransmissions for each transmission rate with respect to the first access point when the state is good as compared with a case where the second access point is not detected. A communication device is provided.

  When the wireless LAN scan control unit detects the second access point, the wireless LAN scan control unit preferably includes a communication control unit that performs control so as not to lower the rate to a lower limit of a support rate at which communication is possible with the currently connected access point.

  When the wireless LAN scan control unit does not detect the second access point, it is preferable to perform a normal rate fallback mechanism operation.

  According to another aspect of the present invention, in a wireless communication method having a rate fallback mechanism, a step of detecting a second access point that is different from the first access point being connected to, The communication state with the access point and the communication state with the second access point are compared, and when the communication state with the second access point is good, retransmission at each transmission rate for the first access point There is provided a wireless communication method, comprising: a communication control step for performing control to reduce the number of times compared to a case where the second access point is not detected.

According to the present invention, in the process up to the start of HO, the redundant frame transmission to the currently connected AP is suppressed, thereby enabling the following.
(1) The bandwidth load of the currently connected AP can be reduced.
(2) The handover time can be shortened.

It is a figure which shows the example of an external appearance structure of the mobile telephone shown as an example of the radio | wireless communication apparatus (mobile station) by one embodiment of this invention. It is a figure which shows the example of 1 structure of the mobile telephone system containing the mobile telephone 1 shown in FIG. It is a figure which shows the usage example of the wireless LAN terminal by this Embodiment. It is a figure which shows the example by this Embodiment which gave the countermeasure with respect to a prior art, and is a figure corresponding to FIG. It is a figure which shows the mode of communication when the HO preparation state is considered. It is a flowchart figure which shows the flow of the process by this Embodiment (process of the terminal A), and is a figure corresponding to FIG. FIG. 13 is a flowchart showing the flow of processing according to the present embodiment (processing of terminal A), corresponding to FIG. 11, and following FIG. 6A. FIG. 7 is a diagram illustrating an example of a fallback rate table according to the present embodiment, and FIG. 7 is a table at the same time as FIG. FIG. 8 is a diagram illustrating an example of a fallback rate table in the HO preparation state. It is a figure which shows the mode of communication when the conventional HO preparation state is not considered. It is a figure which shows an example of the scene used as the problem of the prior art described in patent document 1. FIG. It is a flowchart figure which shows the flow of a process of a prior art. It is a figure which shows the example of a fallback rate table of a prior art.

(Definition)
In this specification, the following terms are defined as follows.
1) Access point (AP): A device that communicates with a wireless communication terminal as a WLAN base station and realizes connection to the Internet via a communication network. The range that can be covered by one AP is limited, and the radio wave condition is also deteriorated by obstacles such as walls. When a terminal is used in a wide range, it is possible to connect to an AP having good radio wave conditions by installing a plurality of APs and performing handover between them.
2) Communication network: A network for realizing mutual communication between connected terminals and further for communication via the Internet communication network.
3) CPU (Central Processing Unit): a control unit that operates a program stored in a program storage area and performs various controls.
4) Wireless LAN scan control unit: Acquires and aggregates information such as BSSID / SSID / RSSI of peripheral APs, and uses it to determine a handover destination.
5) Wireless LAN connection control unit: Controls connection to AP and handover control for wireless LAN transmission unit and wireless LAN reception.
6) Wireless LAN data communication control unit: Based on a request from the application layer, the transmission data for the AP is transferred to the wireless LAN transmission unit, and necessary data extracted from the wireless LAN frame received from the AP is transmitted from the wireless LAN reception unit. Receive and forward to application layer.
7) Wireless LAN data retransmission control unit: When the ACK for the wireless LAN data transmitted to the AP cannot be received, the same data retransmission control is performed.
8) Wireless LAN rate fallback control unit: Determines the rate of wireless LAN transmission data based on the retransmission status in the wireless LAN data retransmission control unit.
9) Key part: Accepts input from a user who intends to operate.

10) Audio input / output means: composed of a microphone and a receiver. Audio is input and output during a call (wireless LAN Voice Over Internet Protocol or a mobile phone network).
11) Storage section: Storage area for data and programs.
12) WLAN setting area: An area for storing various settings related to the wireless LAN (SSID information, authentication information, handover threshold, etc.). Based on the information in this area, connection and handover control are performed.
13) Program storage area: Stores programs to be run on the CPU.
14) Wireless LAN transmission unit: Performs radio frame construction, radio modulation, and rate control necessary for AP connection, handover, and data communication in accordance with designation from the CPU side. For rate control, the initial rate is determined for each of the three types of frames (management frame, control frame, and data frame) defined by the 802.11 standard. In general, since the management frame needs to be transmitted reliably, a lower rate of the corresponding rates is applied to the initial rate.
15) Wireless LAN receiving unit: Performs demodulation and wireless frame analysis on the wireless signal received from the AP, and handles necessary data to the CPU.
16) Wireless LAN RSSI measurement unit: Measures the reception level of a wireless signal from an AP.
17) Wireless LAN transmission error measurement unit: Calculates a transmission error rate based on the number of wireless LAN frame transmission errors obtained from the wireless LAN transmission unit.
18) Wireless LAN reception error measurement unit: Calculates a transmission error rate based on the number of wireless LAN frame reception errors obtained from the wireless LAN reception unit.
19) Antenna switch: Isolates a radio signal received from an AP via an antenna and a radio transmission signal transmitted to the AP.

  AP is Access Point and SSID is Service Set Identifier. This is an identifier of the wireless LAN network set in the AP. Specify a string of up to 32 characters.

  The BSSID is a 48-bit numeric value that identifies the Basic Service Set Identifier AP. Each AP's MAC address uniquely identifies each AP.

  RSSI is Received Signal Strength Identifier and is the received signal strength of WLAN.

  FER is Frame Error Rate, which is a WLAN frame error rate.

HO is Hand Over and switches connection from one AP to another.
VoIP is a Voice Over Internet Protocol, and transmits and receives voice data using a TCP / IP network such as the Internet or an intranet.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an external configuration example of a mobile phone shown as an example of a wireless communication apparatus (mobile station) according to the present embodiment. A foldable mobile phone 1 shown in FIG. 1 includes a housing 2, a hinge portion 4 configured to be foldable while connecting upper and lower housings, an LCD display portion 3 provided on the upper housing, and a voice. A receiver 5 for receiving, a microphone 11 for inputting voice, a key unit 7 for performing various input operations, and an antenna (internal antenna in this figure) 15 are provided.

  FIG. 2 is a diagram showing a configuration example of a mobile phone system including the mobile phone 1 shown in FIG. As a whole, the mobile phone 1 includes a first access point 61 that is currently connected, a communication network NT, and an access point 71 that is a HO candidate. The mobile phone 1 includes a display unit 3, voice input / output units 5 and 11, a key unit 7, a CPU (control unit) 17, a storage unit (memory) 33, and an antenna 15. Further, a wireless LAN transmission unit 41, a wireless LAN reception unit 45, a wireless LAN transmission error measurement unit 47, a wireless LAN reception error measurement unit 51, and a wireless LAN RSSI measurement unit 53 that connect the CPU 17 and the antenna switch are provided. The CPU 17 includes a wireless LAN scan control unit 21, a wireless LAN connection control unit 23, a wireless LAN data communication control unit 25, a wireless LAN rate fallback control unit 27, and a wireless LAN data retransmission control unit 31. The storage unit 33 includes a program storage area 35 and a WLAN setting area 37.

  Table 1 shows an example of a WLAN setting area. In the wireless setting, a connection destination SSID, an authentication method, and a HO threshold are set as follows.

  The HO threshold becomes an index that triggers the start of a handover operation to another connection candidate AP with good communication conditions below this value. In the above example, the RSSI value of the currently connected AP is adopted as the target value to be referred to as a comparison with the HO threshold.

An index other than RSSI, for example, a radio frame transmission error rate and a reception error rate may be used as the HO threshold.
For example, if the setting is 10%, a scan is performed when the total of the transmission error rate and the reception error rate exceeds 10%, and a handover is attempted.

  The transmission error rate is a rate at which ACK is not received from the AP with respect to the wireless LAN transmission frame to the AP, and the reception error rate is a rate at which an error is detected in the wireless LAN frame received from the AP.

  FIG. 3 is a diagram illustrating a usage example of the wireless LAN terminal according to the present embodiment. For example, two APs (AP (1) 61, AP (2) 71) are installed in the VoIP communication network in the office. .

  Terminal (A) 1 and terminal (B) 1 b are in a wireless LAN VoIP call via AP (1) 61. In this state, the terminal A (1) moves to (L1) to be in the position of the terminal (A) 1a, and the received RSSI is in the state of AP (2) 71> AP (1) 61. Here, both the terminal (A) 1a and the terminal (B) 1b set the RSSI value (HO threshold value) of the currently connected AP that becomes the HO operation trigger to −60 dBm.

  7 and 8 are diagrams illustrating an example of a fallback rate table according to the present embodiment. FIG. 7 is the same normal table as FIG. FIG. 8 is a diagram illustrating an example of a fallback rate table in the HO preparation state. The HO preparation state table is configured to suppress rate fallback of less than 11 Mbps. If it is such a structure, it will not be limited to the value of FIG.

  FIG. 4 is a diagram illustrating an example according to the present embodiment in which countermeasures for the prior art are taken, and corresponds to FIG. 10. Similar to FIG. 10, a description will be given of a system including terminal A, AP1 (currently connected AP) 61, AP2 (connection candidate AP) 71. The horizontal axis is the time axis (from t1 to t10). First, as a setting condition of the terminal A and the AP (1) 61, the terminal A recognizes the connection candidate AP (2) 71 that can be handed over by the peripheral search.

The operation will be described in time series in FIG. First, frame transmission (11M) is performed from the terminal A toward the base station AP1 at time t1. Next, at time t2, the communication station ACK is returned from the base station AP1 to the terminal A. Next, assume that AP2> AP1 at time t3 due to a change in the communication environment due to movement or the like. If ACK is not received even if frame transmission is performed at time t4, for example, frame retransmission processing is performed only once at time t6, and if ACK (t7) is not received yet, frame retransmission processing is stopped, and handover is performed at time t8. Execute the process. Thereafter, frame communication is performed from terminal A to AP2 at time t9 (t9), and communication resumes when ACK arrives at t10. Here, the difference from FIG. 10 is that the number of retransmissions of frame communication when ACK does not arrive (change in communication status is estimated) is reduced. That is, in the example according to the present embodiment, the following devices are made.
(1) Reducing the number of retransmissions for each rate from the normal time. In this example, since AP2 exists in the vicinity, the normal number of retransmissions of 3 is reduced to 1.
(2) The rate is not lowered to the lower limit of the communicable rate of the currently connected AP. In this example, since AP2 exists in the vicinity, the lower limit rate of the rate fallback is set to 11 Mbps (not lowered to 5.5 Mbps).

  As described above, in the wireless communication apparatus, if there is a second access point that is a candidate for handover with better wireless communication conditions than the first access point that is currently connected in the vicinity, the number of retransmissions for each rate can be reduced from the normal time. Control to reduce.

  Furthermore, if there is a second access point that is a candidate for handover with better wireless communication conditions than the currently connected first access point in the vicinity, the rate is reduced to the lower limit of the support rate at which communication is possible with the currently connected access point. Do not lower.

  6A and 6B are flowcharts showing the flow of processing according to the present embodiment (processing of terminal A), which corresponds to FIG. First, when the process is started (step S1: START), it is determined whether or not the wireless LAN is within the range (AP is connected?). If NO, the process proceeds to step S19 and the process ends (END). On the other hand, if YES, the AP is connected, the process proceeds to step S3, a data transmission request is generated, wireless LAN frame transmission processing is performed in step S4, and whether or not ACK is received from the AP in step S5. Determine. If “YES” in this determination, the process returns to step S2, and a further data transmission request is generated from the terminal A. If “NO” in the step S5, the process proceeds to a step S6 to determine whether or not the state of the currently connected AP1 is equal to or less than a HO (handover) threshold value. Here, two types of tables of “normal time” and “in HO ready state” in FIGS. 7 and 8 are used properly. Note that “in the HO preparation state” refers to a state in which the communication state of the currently connected AP is lower than the HO threshold described in the display 1 and there are connection candidate APs in the vicinity. On the other hand, the normal time indicates a state other than the HO preparation state.

  If NO in step S6, the process proceeds to step S8, and a fallback pattern No that matches the initial rate = the current wireless transmission rate is searched from the normal rate table (FIG. 7). If YES in step S6, the process advances to step S7 to determine whether there is a connection candidate AP. In the case of NO, that is, when there is no connection HO candidate even if the communication state is bad, rate fallback is performed in the same manner as the conventional processing of FIG. That is, first, the process proceeds to step S9 to perform wireless LAN frame retransmission processing. Next, in step S10, it is determined whether or not ACK can be received from the AP. If YES, the process returns to step S2. If NO, the process proceeds to step S11, and it is determined whether or not the current retransmission number counter = retransmission Max. If NO, the process proceeds to step S12, the retransmission counter is incremented by 1, a rate corresponding to the number of retransmissions is set in the wireless LAN transmission unit in the rate table, and the process returns to step S9. If YES in step S11, the process proceeds to step S13, and the wireless LAN frame retransmission is terminated. The retransmission counter is reset and the frame is discarded. Then, the process returns from step S13 to step S2.

  If YES in step S7, the process proceeds to step S14, and a fallback pattern No that matches the initial rate = the current wireless transmission rate is searched from the HO ready state rate table (FIG. 8). Next, the process proceeds to step S15, and a radio frame retransmission process is performed. Next, in step S16, it is determined whether or not there is an ACK received from the AP. If ACK is received from the AP (YES), the process returns to step S2. If no ACK is received from the AP (NO), the process proceeds to step S17, and it is determined whether the next retransmission is permitted with the current fallback pattern.

  The wireless LAN rate fallback control unit 27 can determine whether or not the next retransmission is permitted in the current fallback pattern.

  Whether the next retransmission is permitted is determined based on whether or not the retransmission Max number (no retransmission to 4 times) corresponding to any one of the fallback patterns No shown in FIG. 8 acquired in S14 of FIG. 6B has been reached. It is.

  If NO, the process proceeds to step S13. If YES, the process proceeds to step S18, the retransmission counter is incremented by 1, and a rate corresponding to the number of retransmissions is set in the wireless LAN transmission unit in the rate table. Return to.

  The following are examples of fallback patterns during normal times and in the HO preparation state.

  Normally, when the initial wireless LAN transmission rate is 24 Mbps, the fallback pattern is No. 4 from FIG. 7, and the first retransmission is 24 Mbps, the second retransmission is 11 Mbps, the third retransmission is 5.5 Mbps, and the fourth retransmission is 2 Mbps. The fifth retransmission is 1 Mbps, and the sixth retransmission is 1 Mbps. For example, if the initial wireless LAN transmission rate is 1 Mbps, the fallback pattern is No. 12 from FIG. 7, the first retransmission is 1 Mbps, the second retransmission is 1 Mbps, the third retransmission is 1 Mbps, the fourth retransmission is 1 Mbps, The fifth retransmission is 1 Mbps, and the sixth retransmission is 1 Mbps.

  On the other hand, in the HO preparation state, if the initial wireless LAN transmission rate is 24 Mbps, the fallback pattern is No. 4 from FIG. 8, the first retransmission is 24 Mbps, the second retransmission is 11 Mbps, and the initial wireless LAN transmission rate is If it is 1 Mbps, it is fallback pattern No12 from FIG. 8, and retransmission is not performed.

  As described above, in the process according to the present embodiment, the fallback pattern is made different depending on whether the state is the HO preparation state or the normal state, and in the case of the HO preparation state, the retransmission is suppressed quickly. Handover can be performed.

  That is, if there is a second access point that is a candidate for handover with better wireless communication conditions than the currently connected first access point in the vicinity, the rate is reduced to the lower limit of the support rate that can be communicated with the currently connected access point. Control without lowering. When there is no handover candidate access point in the vicinity, normal operation is performed.

  9 and 5 are diagrams illustrating the effects of the communication technique according to the present embodiment. FIG. 9 is a diagram illustrating a state of communication when a conventional HO preparation state is not considered. Terminal A, AP1, and AP2 exist. First, when frame communication is performed at terminal A and communication is performed at 11M to AP1, an ACK indicating communication OK is returned from AP1. Here, when a change in communication conditions due to movement (AP2> AP1) occurs, frame communication is performed, and then ACK does not arrive, so even if frame retransmission is performed at the first, second, third, and 11M, ACK Has not arrived. Therefore, in the conventional technique, fallback (fallback upon expiration of the specified number of retransmissions (three times), change from 11 Mbps to 5.5 Mbps), frame transmission to AP1, and retransmission (from the first to the third) are performed. However, if ACK does not arrive, handover to AP2 is performed, and frame transmission and ACK reception are repeated.

  On the other hand, in the communication technique according to the present embodiment shown in FIG. 5, when a change in communication conditions due to movement (AP2> AP1) occurs, for example, only one frame transmission (11M) and one frame retransmission (11M) are performed. Since the handover process is performed, the bandwidth load in the network band of AP1 can be reduced in the period from the frame retransmission (second time) in FIG. 9 to the frame retransmission (third time) after the fallback process. .

  Further, it is possible to shorten the handover time to the AP 2 between the handover of FIG. 5 and the handover of FIG. 9, and there is an effect that a quick handover process can be performed.

  In the above-described embodiment, the configuration and the like illustrated in the accompanying drawings are not limited to these, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  In addition, a program for realizing the functions described in the present embodiment is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed to execute processing of each unit. May be performed. The “computer system” here includes an OS and hardware such as peripheral devices.

  Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.

  The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the above-described functions, or may be a program that can realize the above-described functions in combination with a program already recorded in a computer system.

  The present invention is applicable to mobile communication devices.

DESCRIPTION OF SYMBOLS 1 ... Folding type mobile phone, 2 ... Housing, 3 ... Display part, 4 ... Hinge part, 5 ... Receiver, 7 ... Key part, 11 ... Microphone, 15 ... Antenna, 21 ... Wireless LAN scan control part, 23 ... Wireless LAN connection control unit, 25 ... Wireless LAN data communication control unit, 27 ... Wireless LAN rate fallback control unit, 31 ... Wireless LAN data retransmission control unit, 33 ... Storage unit, 35 ... Program storage area, 37 ... WLAN setting area, NT ... communication network, 71 ... access point of candidate HO, 17 ... CPU, 41 ... wireless LAN transmission unit, 45 ... wireless LAN reception unit, 47 ... wireless LAN transmission error measurement unit, 51 ... wireless LAN reception error measurement unit, 53: Wireless LAN RSSI measurement unit, 61: First access point currently connected.

Claims (3)

In a wireless communication apparatus having a control unit for controlling frame transmission and having a rate fallback mechanism,
A wireless LAN scan control unit for detecting a second access point different from the first access point to which the wireless communication device is connected;
When the communication state with the first access point is compared with the communication state with the second access point, and the communication state with the second access point is good, the transmission rate for the first access point the retry count for each, have a, a communication control unit that performs control to reduce than if the second access point is not detected,
When the wireless LAN scan control unit detects the second access point,
The frame transmission rate, even down in the current first communication possible support rate range in the connected access point, characterized by having a communication control unit for performing control not lowered until the lower limit of support rate Wireless communication device. The wireless communication apparatus according to claim 1 , wherein when the wireless LAN scan control unit does not detect the second access point, a normal rate fallback mechanism operation is performed. In a wireless communication method with a rate fallback mechanism,
Detecting a second access point different from the connected first access point;
When the communication state with the first access point is compared with the communication state with the second access point, and the communication state with the second access point is good, the transmission rate for the first access point the retry count for each, have a, and a communication control step for controlling to reduce than if the second access point is not detected,
When the second access point is detected, control is performed so that the frame transmission rate is not lowered to the lowest support rate even if the frame transmission rate is lowered within the range of the support rate communicable with the currently connected first access point. wireless communication method and performing.

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