JP4674155B2 - Wireless communication terminal and load distribution method for relay device thereof - Google Patents

Description

  The present invention relates to a wireless communication terminal that performs wireless communication using a wireless local area network (LAN) or the like, and a load distribution method for the relay device.

  In recent years, wireless LANs have become widespread as one of computer communication networks, and are actively used in offices, homes, urban areas (for example, stations, airports, fast food restaurants) and the like. As is well known, in such a wireless LAN, wireless communication is performed between a relay device called an AP (Access Point) and a wireless communication terminal. The wireless LAN is defined in IEEE (Institute of Electrical and Electronics Engineers) 802.11 described in Non-Patent Document 1 below.

  In general, since a wireless communication terminal is movable, it is necessary to switch a connection destination from an AP that is currently connected to an adjacent AP as it moves. For this reason, the wireless communication terminal measures the strength of the received radio wave from the AP, and when the radio wave received from the connected AP becomes weaker due to movement, the wireless communication terminal switches the connection destination to an adjacent AP that can receive a stronger radio wave. Wireless communication can be continued.

  By the way, if a large number of wireless communication terminals happen to gather around one AP and the number of wireless communication terminals connected to this AP increases, this AP becomes overloaded and the wireless transmission / reception speed is reduced. Communication may be impossible. In order to prevent this, a technique called load balancing is known. As a conventionally known load balancing method, there is a technique described in Patent Document 1 below.

  In this technique, the number of terminals connected to the AP is included in the beacon transmitted from the AP, and each terminal is connected to the adjacent AP based on the terminal number information and the radio wave reception intensity from the AP. By determining whether or not to switch to, it is avoided that the load concentrates on one AP. More specifically, the AP includes a terminal monitoring unit that monitors the number of connected terminals, and a terminal number information adding unit that includes the terminal number information acquired by the terminal monitoring unit in the beacon signal. Transmits a beacon signal with terminal number information to each terminal. In addition, the terminal receives terminal number information from each AP, determines whether there is another AP whose number of connected terminals is smaller than a predetermined number than the connected AP, and there is such another AP, and When the reception intensity of radio waves from this AP is greater than or equal to a predetermined value, the connection is switched from the currently connected AP to this other AP.

JP 2002-359864 A "Wireless LAN Medium Control (MAC) and Physical Layer (PHY) Specifications" ANSI / IEEE Std 802.11, 1999 Edition

  However, in the prior art, both the AP and the wireless communication terminal require a unique configuration not defined in IEEE802.11, that is, a unique protocol, and generality and compatibility are lost. However, there is a problem in that it is not possible to cope with the situation where a mixture of the two is mixed, and it is necessary to set a unique protocol for all APs in a certain area, resulting in an increase in equipment cost.

  The present invention has been made paying attention to such conventional problems, and a wireless communication terminal capable of ensuring load versatility while ensuring the versatility of the AP and suppressing an increase in equipment cost, It is another object of the present invention to provide a load balancing method for relay devices.

An invention relating to a wireless communication terminal for solving the above problems
In a wireless communication terminal that communicates with another communication terminal via a relay device that transmits a beacon signal including control data indicating whether there is communication data addressed to the wireless communication terminal for each wireless communication terminal,
A transmission / reception means for transmitting / receiving various signals to / from the relay device;
Analyzing the control data contained in the beacon signal from the relay device received by the transmission / reception means, and obtaining the total number of wireless communication terminals with communication data to be transmitted from the relay device;
Using the total number of wireless communication terminals with communication data to be transmitted from the currently connected relay device and the total number of wireless communication terminals with communication data to be transmitted from the unconnected relay device, obtained by the analyzing means Switching determination means for determining whether to switch the connection target from the currently connected relay device to the non-connected relay device;
Switching control means for switching the connection target to the non-connected relay device when the switch determination means determines that the connection target should be switched from the currently connected relay device to the non-connected relay device. It is characterized by that.

In addition, the load balancing method of the relay device for achieving the above object is as follows:
A relay device that transmits and receives communication data signals to and from one or more wireless communication terminals and transmits a beacon signal including control data indicating whether or not there is communication data addressed to each wireless communication terminal for each wireless communication terminal In the load balancing method of
The wireless communication terminal is
A first beacon signal receiving step for receiving the beacon signal from the currently connected relay device;
Analyzing the control data included in the beacon signal from the currently connected relay device, and determining the total number of wireless communication terminals with communication data to be transmitted from the relay device;
A second beacon signal receiving step for receiving a beacon signal from an unconnected relay device;
Analyzing the control data contained in the beacon signal from the non-connected relay device, a second analysis step of obtaining the total number of wireless communication terminals with communication data to be transmitted from the relay device;
The total number of wireless communication terminals having communication data to be transmitted from the currently connected relay device and the wireless communication terminal having communication data to be transmitted from the non-connected relay device obtained in the first analysis step Switching determination step of determining whether to switch the connection target from the currently connected relay device to the non-connected relay device, using the total number of
When it is determined in the switching determination step that the connection target should be switched from the currently connected relay device to the non-connected relay device, a switching step of switching the connection target to the non-connected relay device is executed. It is characterized by that.

  In the above analysis means or analysis process, the control data is referred to data stored in a virtual bitmap stipulated in IEEE 802.11, and there is communication data to be transmitted from the relay device. Find the total number of terminals.

  Embodiments of a wireless communication system according to the present invention will be described below in detail with reference to the drawings.

  As shown in FIG. 1, the wireless communication system according to the present embodiment includes a plurality of APs 30 and a plurality of computers 3 connected to LANs (A) and (B) via routers 2A and 2B, and an AP 10. Wireless communication terminals 10a, 10b, and 10c that communicate with other terminals are provided. LAN (A) and LAN (B) are connected by an IP (Internet Protocol) network 1. Each of the wireless communication terminals 10a, 10b, and 10c is an information communication terminal having a wireless LAN communication function that operates in compliance with IEEE802.11. For example, a telephone terminal such as a wireless IP telephone, a personal computer, or a PDA (Personal Digital Assistant) A wireless LAN card connected to an information terminal such as a wireless LAN board mounted on the information terminal.

  Each AP 30 has a wireless LAN communication function that operates in conformity with IEEE802.11 and a wired LAN communication function such as Ethernet (registered trademark) that operates in conformity with IEEE802.3, and wireless communication terminals 10a and 10b. , 10c, and wired LAN communication with other devices (such as the computer 3 and the router 2A or 2B) connected to the LAN (A) or (B).

  The routers 2A and 2B are interposed between the LANs (A) and (B) and the IP network 1, and monitor IP packets flowing on the LANs (A) and (B) and IP packets obtained from the IP network 1. , A communication device that routes IP packets based on IP header information (destination IP address information, port number information, etc.) of the IP packets, and the IP packets flowing on the LANs (A) and (B) are transferred to the IP network 1 side. If it is determined that it should be routed, it is transmitted to the IP network 1 side, and the IP packet obtained from the IP network 1 is determined to be routed to the LAN (A), (B) side. In this case, this is sent to the LAN (A), (B) side.

  Each computer 3 has a normal wired LAN board, and is connected to LANs (A) and (B) to transmit and receive IP packets and perform IP communication (LAN communication).

  With the above configuration, the wireless communication terminals 10a, 10b and 10c on the LAN (A) side perform IP communication with other wireless communication terminals on the LAN (A) side and the computer 3 via the AP 30, and the router 2A It is possible to perform IP communication with the wireless communication terminals 10a, 10b, and 10c on the LAN (B) side and the computer 3 via the IP network 1 and the router 2B. Similarly, the wireless communication terminals 10a, 10b, 10c on the LAN (B) side perform IP communication with other wireless communication terminals on the LAN (B) side and the computer 3 via the AP 30, and the router 2B It is possible to perform IP communication with the wireless communication terminals 10a, 10b, and 10c on the LAN (A) side and the computer 3 via the IP network 1 and the router 2A.

  As shown in FIG. 2, each AP 30 includes an antenna 31, an RF (Radio Frequency) unit 32, a baseband unit 33, a MAC (Media Access Controller) layer processing unit 34, a router unit 35, A communication processing unit 40, a program memory 44, and a work memory 45 are provided. The RF unit 32, the baseband unit 33, and the MAC layer processing unit 34 are connected to the communication processing unit 40 via the bus 38.

  The communication processing unit 40 controls the RF unit 32, the baseband unit 33, and the MAC layer processing unit 34 while using the work memory 45 according to the control program and setting data in the program memory 44. The communication processing unit 40 includes a beacon data generation unit 41 that generates beacon data included in a beacon signal, an analysis unit 42 that analyzes a signal input from the antenna 31 or the router unit 35, and an analysis result of the analysis unit 42. And a control unit 43 that controls the RF unit 32, the baseband unit 33, and the MAC layer processing unit 34.

  The router unit 35 refers to an IP header including an IP address of an IP packet received from a network (LAN (A) or (B)), a TCP (Transmission Control Protocol) port number, or a UDP (User Datagram Protocol) port number. Then, the IP packet is routed based on a preset rule.

  The MAC layer processing unit 34 converts the MAC layer of the IP packet between the data link layer of IEEE802.3 that is the Ethernet (registered trademark) standard and the data link layer of IEEE802.11 that is the wireless LAN standard. . The baseband unit 33 modulates an IP packet subjected to MAC processing for IEEE802.11 into a baseband signal, or demodulates the baseband signal and restores the original IP packet. The RF unit 32 uses the baseband signal received from the baseband unit 33 in accordance with IEEE802.11, for example, carrier radio defined by the DS-SS (Direct Sequence Spread Spectrum) method or the FH-SS method (Frequency Hopping Spread Spectrum). The signal is transmitted as a radio signal from the antenna 31 on the frequency. On the contrary, the carrier radio frequency is removed from the radio signal received from the antenna 31 to restore the original baseband signal, which is sent to the baseband unit 33.

  Next, the basic operation of the AP 30 when an IP packet is transmitted from the network (LAN (A) or LAN (B)) via the antenna 31 will be described below.

  The MAC layer processing unit 34 converts the MAC layer of the IP packet received from the network (LAN (A) or LAN (B)) via the router unit 35 from IEEE802.3 for Ethernet (registered trademark) to a wireless LAN. The data is converted into IEEE802.11 and sent to the baseband unit 33. The baseband unit 33 modulates the received IP packet according to IEEE802.11 for wireless LAN, generates a baseband signal, and sends it to the RF unit 32. The RF unit 32 puts the baseband signal from the baseband unit 33 on the carrier radio frequency, and sends out the radio signal from the antenna 31 to the radio terminals 10a, 10b, and 10c.

  Next, a basic operation of the AP 30 when wireless signals are received from the wireless communication terminals 10a, 10b, and 10c will be described.

  When the antenna 31 receives radio signals from the radio communication terminals 10a, 10b, and 10c, the antenna 31 transmits the radio signals to the RF unit 32. The RF unit 32 removes the carrier radio frequency from the radio signal received by the antenna 31 to restore the original baseband signal, and sends it to the baseband unit 33. The baseband unit 33 demodulates the baseband signal, restores it to the original IP packet, and sends it to the MAC layer processing unit 34. The MAC layer processing unit 34 converts the MAC layer of the IP packet from IEEE802.11 for wireless to IEEE802.3 for Ethernet (registered trademark), and sends it to the router unit 34. The router unit 34 transfers the received IP packet to a LAN or the like using the IP address of the received IP packet.

  As shown in FIG. 3, each of the wireless communication terminals 10a, 10b, and 10c includes an antenna 11, an RF unit 12, a baseband unit 13, a MAC layer processing unit 14, an upper layer processing unit 15, and an input unit. An output interface unit 16, an input / output unit 17, a communication processing unit 20, a program memory 24, a work memory 25, a power source 26, and a power supply control unit 27 are provided.

  The RF unit 12, the baseband 13, the MAC layer processing unit 14, the upper layer processing unit 15, and the input / output interface unit 16 are all connected to the communication processing unit 20 via the bus 18. In the present embodiment, the “transmission / reception means” described in the claims includes an antenna 11, an RF unit 12, a baseband unit 13, and a MAC layer processing unit 14.

  The communication processing unit 20 uses the work memory 25 in accordance with the control program and setting data in the program memory 24, while the RF unit 12, the baseband processing unit 13, the MAC layer processing unit 14, and the upper layer processing unit 15. And the input / output interface unit 16. The communication control unit 20 analyzes the content of a signal received by the input / output unit 17 or the antenna 11, and a switching determination unit 22 that determines whether to switch the connection from the currently connected AP to another AP. Then, the RF unit 12, the baseband processing unit 13, the MAC layer processing unit 14, the upper layer processing unit 15, and the power supply control unit 27 are controlled in accordance with the analysis result in the analysis unit 21, the determination result in the switching determination unit 22, and the like. And a control unit 23. The control unit 23 includes a power saving mode control unit 23a that controls a power saving mode, which will be described later, and a switching control unit 23b that performs control for switching the connection from the currently connected AP to another AP.

  The power supply control unit 27 converts the power from the power source 26 into an appropriate voltage and supplies the power to each unit. Further, the power supply control unit 27 turns on / off the power supply to the RF unit 12 in accordance with an instruction from the control unit 23 of the communication processing unit 20. That is, the power supply control unit 27 is an execution part of the power saving mode in which the function is changed between the active state in which the wireless transmission / reception function is operated and the wireless transmission / reception function is stopped and the sleep state is set.

  For example, when the wireless communication terminal is a wireless IP phone, the input / output unit 17 is a voice / data input / output unit, specifically, a speaker, a microphone, an input key, and the like. When the wireless communication terminal is a wireless LAN card, the input / output unit 17 is an input / output unit for data signals, audio signals, and the like from a computer.

  The input / output interface unit 16 performs processing related to an interface for transferring a data signal and a speech encoded signal from the input / output unit 17 to the upper layer processing unit 15 or from the upper layer processing unit 15 to the input / output unit 17. The upper layer processing unit 15 performs IP packet processing related to the network layer / transport layer. Specifically, IP header including IP address, TCP port number, or UDP port number is added / deleted. The MAC layer processing unit 14 performs IP packet processing related to the data link layer. Specifically, in accordance with IEEE802.11, an IP packet storing data and voice bucket data is assembled or disassembled, and MAC address assignment / deletion processing is performed in order to transmit between data link layers. The baseband unit 13 modulates the IP packet to generate a baseband signal, or demodulates the baseband signal to restore the original IP packet.

  The RF unit 12 puts the baseband signal received from the baseband unit 13 on the carrier radio frequency according to IEEE802.11, and transmits it from the antenna 11 as a radio signal. Conversely, the carrier radio frequency is removed from the radio signal received from the antenna 11 to restore the baseband signal, and the baseband signal is sent to the baseband unit 13. The RF unit 12 includes an AGC (Auto Gain Control) unit 12a that detects the radio wave intensity of a signal received by the antenna 11 and controls the intensity of the output radio wave. The radio wave intensity of the signal detected by the AGC unit 12a is sent to the switching determination unit 22 of the communication processing unit 20.

  Next, the basic operation of the radio communication terminals 10a, 10b, and 10c when the data signal or voice encoded signal received or generated by the input / output unit 17 is transmitted as a radio signal from the antenna 11 will be described.

  The input / output interface unit 16 sends the data signal and the voice encoded signal from the input / output unit 17 to the upper layer processing unit 15. The upper layer processing unit 15 performs IP header processing such as IP address assignment / TCP / UDP port number assignment, generates an IP packet, and then sends the IP packet to the MAC layer processing unit 14. The MAC layer processing unit 14 subjects the IP packet from the higher layer processing unit 15 to MAC processing such as MAC address assignment in accordance with IEEE802.11 and sends the IP packet to the baseband unit 13. The baseband unit 13 modulates this IP packet according to IEEE802.11 to generate a baseband signal, and sends it to the RF unit 12. The RF unit 12 puts the baseband signal from the baseband unit 13 on the carrier radio frequency according to IEEE802.11, and transmits it from the antenna 11 to the AP 30 as a radio signal.

  Next, a basic operation of the radio communication terminals 10a, 10b, and 10c when receiving a radio signal transmitted from the AP 30 and outputting a signal to the input / output unit 17 will be described.

  The antenna 11 receives a radio signal from the AP 30 and sends it to the RF unit 12. The RF unit 12 removes the carrier radio frequency from the radio signal, restores the original baseband signal, and sends it to the baseband unit 13. The baseband unit 13 demodulates the baseband signal, restores it to the original IP packet, and sends it to the MAC layer processing unit 14. The MAC layer processing unit 14 deletes the MAC address from this IP packet according to IEEE802.11 and sends it to the upper layer processing unit 15. The upper layer processing unit 15 deletes the TCP / UDP header and the IP header from the IP packet from the MAC layer processing unit 14 based on the setting data, and transmits the obtained data and the audio encoded signal via the input / output interface unit 16. The data is sent to the input / output unit 17.

  Next, the data structure of the beacon signal transmitted from the AP 30 will be described with reference to FIG.

  The AP 30 transmits a beacon signal at a constant cycle to notify each wireless communication terminal whether or not there is data to be transmitted to the wireless communication terminal in the power saving mode. This period is often about 100 ms, for example.

  This beacon signal is defined in IEEE 802.11, a frame control unit 61 in which data of a signal type for indicating that it is a beacon signal is entered, a duration / ID unit 62 in which data of wireless communication time is entered, A DA unit 63 for receiving a destination address, an SA unit 64 for receiving a source address, a BSSID unit 65 for storing an AP 30 address, a sequence control unit 66 for storing a sequence number in a series of sequences, and a notification It has a data main body section 67 for storing data to be received and an FCS section 68 for storing data for transmission error detection.

  The main body data section 67 has a fixed length field 69 for storing management / control data of a predetermined length and a variable length field 70 for storing variable length management / control data.

  The variable length field 70 indicates whether there is an element ID portion 71 in which an element ID is entered, an element length portion 72 in which data of the element length is entered, and data to be notified to the terminal in the power saving mode by broadcast or multicast. Before the beacon including the DTIM (D traffic notification map) is transmitted, the DTIM count unit 72 in which the number of general beacons (beacons including the TIM) is transmitted and the above-mentioned DTIM and the next DTIM are transmitted. A DTIM interval unit 73 for storing the number of general beacons, and a bitmap control unit 75 and a partial virtual bitmap unit 76 described later (the data entering these portions 75 and 76 is the control data described in the claims). Have.

  The element ID portion 71 contains “5” indicating that this element is a TIM (traffic notification map). The bit map control unit 75 and the partial virtual bit map unit 76 contain data indicating the presence / absence of data to be notified from the AP to the terminal in the power saving mode with a unicast address.

  For each terminal ID, “1” is set when there is data, and “0” is set when there is no data. The partial virtual bitmap unit 76 into which this data is stored has a variable length of 1 to 251 bytes. For example, as shown in the figure, “1” is set for the terminal c and the terminal h, that is, the terminal c and the terminal h. When there is transmission data to the other terminal and there is no transmission data in the other terminal, the bit containing significant data in all the virtual bitmap data, that is, from the terminal c of the third bit, for example, a predetermined number of bits, Only the partial virtual bitmap data for 8 bits up to the terminal j is entered. The bitmap control unit 75 stores the start bit (bitmap offset) of the partial virtual bitmap in the entire virtual bitmap and the number of bits (bitmap length) of the partial virtual bitmap.

  Each data included in the above beacon signal is generated by the beacon data generation unit 41 of the AP 30 based on data received from each terminal or data set in advance.

  Next, the operation of the wireless communication terminals 10a, 10b, 10c (hereinafter, the wireless communication terminal code is simply referred to as “10”) for load distribution of the AP 30 will be described with reference to the flowchart shown in FIG.

  When the power of the wireless communication terminal 10 is turned on and enters the power saving mode, the wireless communication terminal 10 notifies the AP 30 that it has entered the power saving mode (S10), and shifts from the active state to the sleep state. Upon receiving this notification, the AP 30 assigns a terminal identification ID called AID to the terminal that issued this notification, and manages this terminal as a terminal in the power saving mode.

  The control unit 23 of the wireless communication terminal 10 refers to the previously set timer and determines whether or not it is just before the scheduled reception time of the beacon signal from the AP 30 (S11). If so, the sleep state is changed to the active state, and the beacon signal from the AP 30 is received. At this time, the radio wave intensity R1 of the beacon signal is detected by the AGC unit 12a of the wireless communication terminal 10 (S12).

  Subsequently, the analysis unit 21 of the wireless communication terminal 10 analyzes the received beacon signal (S13). Here, analysis of a beacon signal will be described with reference to FIG. Temporarily, in the bitmap control unit 75 in the figure, “third bit” is indicated as the start bit, and “8” is indicated as the number of bits of the partial virtual bitmap. It is assumed that the data of “10000100” is stored in the part 76, and the bit corresponding to its own terminal ID is the third bit. In this case, the analysis unit 21 first grasps that there is communication data addressed to the own terminal from the AP 30. Further, it is understood that the number N1 of terminals having data to be transmitted from the AP 30 is two. Note that the data shown in the partial virtual bitmap unit 76 is data only for the wireless communication terminal in the power saving mode and with the data to be transmitted from the AP 30. Therefore, data of a wireless communication terminal that is not in the power saving mode or a wireless communication terminal that is simply connected to the AP 30 is not included.

  Here, what is important is that, in the prior art, the data contained in the partial virtual bitmap unit 76 is used only for determining whether there is communication data addressed to the terminal itself. On the other hand, in the present embodiment, as described above, the number N1 of terminals having data to be transmitted from the AP 30 based on the number of data “1 (data present)” in the partial virtual bitmap unit 76. The number of terminals (not the number of connected terminals as in the prior art) is used as the AP load.

  Next, the switching determination unit 22 determines whether the number of terminals N1 grasped by the analysis unit 21 is greater than a predetermined number TH1, and further determines the radio wave intensity R1 of the beacon signal detected by the AGC unit 12a. If the number N1 of terminals is greater than a predetermined number TH1 or the radio field intensity R1 of the beacon signal is smaller than a predetermined radio field strength TH2, the current connection is determined. It is determined that it is preferable to switch the connection target from the AP 30 to another AP, and the process proceeds to Step 16. If the number N1 of terminals is smaller than the predetermined number TH1 and the radio wave intensity R1 of the beacon signal is larger than the predetermined radio wave intensity TH2, the connection with the currently connected AP 30 should be continued. The data is transmitted / received to / from the AP 30 (S15). When the wireless communication terminal 10 determines that transmission / reception with the AP 30 has ended, the wireless communication terminal 10 transitions to the sleeve state and returns to step 11.

  On the other hand, when the process proceeds to step 16 as a result of the determination in step 14, the switching determination unit 22 uses a function F1 (= N1-αR1 (α: a constant greater than 0)) indicating the degree of necessity of connection target switching. The degree of necessity of switching the connection target for the AP 30 currently connected is obtained. The value of this function increases as the number N1 of connected terminals of the AP 30 increases, and conversely, the value decreases as the radio wave intensity of the signal from the AP 30 increases. Therefore, the connection value increases as the value of this function increases. The need for switching will increase. When the function F1 ′ (= αR1-N1) is adopted instead of the function F1, that is, when the sign of each term of the function F1 is reversed, the smaller the value of the function, the more the connection is made. The necessity of switching the target will increase.

  When the function F1 is obtained, the switching control unit 23b gives an instruction to the RF unit 12 to change the frequency of the carrier wave. And the analysis part 21 judges whether the beacon signal by the carrier changed in the RF part 12 was able to be received, that is, it was judged whether the beacon signal from other adjacent AP was able to be received (S17). . At this time, if a signal is received, the radio wave intensity R2 of the signal received by the AGC 12a is detected (S18). On the other hand, if the beacon signal from another adjacent AP cannot be received even if the frequency of the carrier wave is changed, the process proceeds to step 23.

  When a beacon signal from another adjacent AP can be received, the analysis unit 21 analyzes this beacon signal, and from the data in the partial virtual bitmap unit 76, the terminal of the terminal that has data to be transmitted from this AP. The number N2 is obtained (S19). Then, the switching determination unit 22 uses the function F2 (= N2-αR2 (a constant larger than α: 0)) representing the degree of necessity of switching the connection target to determine the radio field intensity of the beacon signal from this other adjacent AP. Substituting R2 and the number N2 of terminals having data to be transmitted from this AP, the value of the function F2 is obtained (S20). The switching determination unit 22 further determines whether or not F2 <F1 and R2> TH3, that is, the degree of necessity of switching of other adjacent APs is smaller than the degree of necessity of switching of the AP 30 connected so far. In addition, it is determined whether or not the radio wave intensity R2 of the signal from the other AP is larger than a predetermined radio wave intensity TH3 (S21).

  If F2 <F1 or R2> TH3 is not satisfied, the process returns to step 17 to determine whether or not a beacon signal from another adjacent AP has been received. If F2 <F1 and R2> TH3, switching is determined. In order to search for an AP having the minimum value of F2, the unit 22 sets the value of F2 when F2 <F1 as the value of F1, sets this other adjacent AP as a handover candidate, and returns to step 17.

  When there are a plurality of other APs adjacent to the AP 30 that has been connected so far, the processing of the above steps 17 to 22 is repeated, and the AP with the smallest F2 value becomes the final handover candidate. It is determined that all other APs adjacent to the AP 30 have been scanned, and the process proceeds to step 23, where it is determined whether there is another AP adjacent to the handover candidate (S23). If there is no handover candidate, data transmission / reception is performed with the AP 30 connected so far (S15). When there is another AP adjacent to the handover candidate, the switching control unit 23b performs a handover process to another adjacent AP. At this time, the switching control unit 23b creates authentication request data for another adjacent AP, causes the RF unit 12 to transmit the authentication request data on a carrier wave of another adjacent AP, and transmits the other authentication request data. When receiving an authentication approval message from the AP, it creates disconnection request data for the connected AP 30 and causes the RF unit 12 to transmit the disconnection request data on the carrier wave of the connected AP. Then, when receiving the notification that the connection is permitted from the other adjacent AP, the handover process, that is, the switching process of the connection target is finished, and data transmission / reception is performed with the other adjacent AP (S15).

  As described above, in the present embodiment, when the load on the AP 30 increases, the wireless communication terminal 10 performs a handover to another adjacent AP by the autonomous processing of the wireless communication terminal 10, thereby preventing the AP 30 from becoming overloaded. be able to. Moreover, in the present embodiment, the load of the AP 30 is not set to the number of connected terminals of the AP 30, but the number of terminals that have data to be transmitted from the AP 30 is set, so that the wireless communication terminal 10 can detect the beacon signal in conformity with IEEE 802.11. The load of the AP 30 for determining the necessity of switching the connection target can be grasped, and it is not necessary to set a unique protocol for load distribution in the AP 30, and the versatility of the AP 30 can be secured. The increase in equipment cost can be suppressed.

In the present embodiment, F = N−αR is used as a function indicating the degree of necessity of switching the connection target. However, the present invention is not limited to this, and for example, the following (1) to (1) to Other functions may be used as shown in (4).
(1) F = N if the received radio wave intensity R is greater than or equal to the threshold r1, and F = ∞ if it is less than the threshold r1. In this case, if the received radio wave intensity R is equal to or greater than the threshold value r1, the AP is switched based on the determination based only on the number of connected wireless terminals.
(2) F = −R if the number N of wireless terminals with data to be transmitted from the AP is less than the threshold value n, and F = ∞ if the number is greater than or equal to the threshold value n. In this case, if the number N is greater than or equal to the threshold value n, connection to that AP is prohibited and switched to another AP, and if it is less than the threshold value n, the AP is switched to the AP having the highest received radio wave intensity.
(3) Leave F2 = N2−αR2 and F1 = N1−αR1 + βT (where T is the time during which N1 is continuously greater than or equal to the threshold value n, and β is a constant). In this case, when N1 is greater than or equal to the threshold value n, the value of F1 gradually increases as time elapses. Therefore, one of the wireless terminals connected to the AP has the largest received power from the adjacent AP. The wireless terminal is switched to the adjacent AP. Then, the value of N1 decreases, and if it becomes less than the threshold value n, βT also becomes 0, so that further connection switching is prevented. For this reason, excessive handovers in which a plurality of wireless terminals are simultaneously switched and a neighboring AP is newly overloaded are suppressed. When the above function is used, it is necessary to grasp the time during which N1 is continuously greater than or equal to the threshold value n. Therefore, the number N1 obtained in step 13 in FIG. 4 is stored in association with the time at that time. In step 16, when F1 = N1-αR1 + βT is obtained, the time during which N1 is continuously equal to or greater than the threshold value n is obtained based on the data stored in step 14.

  When the sign of each term of the function F2 is reversed and the necessity of switching the connection target increases as the value of this function decreases, the sign of the term of the function F1 is reversed, and the time As the time elapses, the value of F1 is also decreased.

  In order to further suppress unnecessary overhand, (-offset value) may be added to the function F1 as follows.

F1 = N1−αR1 + βT−offset value (4) When N2 of the adjacent AP is equal to or greater than the threshold value n, or when N2 is equal to the threshold value n−1 and N1 is equal to the threshold value n, the connection is switched to the adjacent AP. In order to prevent this, the following may be performed.

  That is, the functions F1 and F2 are determined as follows.

When N2 is less than the threshold value n-1, F2 = N2-αR2
When N2 is equal to the threshold value n-1, F2 = N2-αR2 + βT
(T is the time when N2 is equal to the threshold value n-1)
When N2 is greater than or equal to the threshold value n, F2 = ∞
When N1 is greater than or equal to the threshold value n, F1 = N1−αR1 + βT * (N1−threshold value n + 1)
-Offset value (T is the time when N1 is equal to or greater than the threshold value n)
When N1 is less than the threshold value n, F1 = N1−αR1−offset value Then, connection switching is performed as follows.
a) When N2 is greater than or equal to the threshold value n, the connection is not switched.
b) When N2 is equal to the threshold value n-1 and N1 is larger than the threshold value, the connection may be switched. However, when N1 is equal to the threshold value n, the connection is not switched.

  In the above embodiment, if the number of connected AP terminals N1 and the number of adjacent AP terminals N2 are both equal to or greater than the threshold value n, the connected AP is overloaded, and communication quality decreases. Despite being present, connection switching to another AP is not possible. Therefore, if the connection cannot be switched to another AP, the terminal itself may emit a warning sound or the like to prompt the user to move. Specifically, a warning sound is emitted when N1> TH1 is determined in step 14 in FIG. 4 and no handover candidate is determined in step 23.

  As described above, even when a warning sound is emitted, the overloaded state of the connected AP may continue because the user does not move. In such a case, the wireless terminal may autonomously stop communication. However, since there is no need for a plurality of wireless terminals to stop communication at the same time, two methods will be described here for a case where a wireless terminal with the lowest received power autonomously stops communication.

  The first method is to start the timer a after an overload condition or issue a warning, and when the timer a expires, the wireless terminal whose reception power of the beacon signal is smaller than the threshold value r3 stops its communication and simultaneously Notify the user of the communication stop with a disconnect sound. When there is no wireless terminal having a received power smaller than the threshold r3 and the overload state continues, the timer b is started when the timer a expires, and the received power is compared with the threshold r4 higher than the threshold r3 when the timer b expires. A terminal having a value smaller than the threshold value r4 stops its communication. In this way, a wireless terminal with low received power of a beacon signal may autonomously stop communication.

  In the second method, when the overload state is reached or a warning is issued, the timer a is started, and when the timer a expires, the value of F1 = N1-αR1 + βT−offset value described in (3) above When the value becomes equal to or greater than the threshold value f, the wireless terminal may stop communication.

It is explanatory drawing which shows the structure of the radio | wireless communications system in 1st embodiment which concerns on this invention. It is a functional block diagram of AP in 1st embodiment which concerns on this invention. It is a functional block diagram of the radio | wireless communication terminal in 1st embodiment which concerns on this invention. It is a flowchart which shows operation | movement of the radio | wireless communication terminal in 1st embodiment which concerns on this invention. It is explanatory drawing which shows the data structure in a beacon signal.

Explanation of symbols

10a, 10b, 10c: wireless communication terminal, 11: antenna, 12: RF unit, 13: baseband unit, 14: MAC layer processing unit, 15: upper layer processing unit, 16: input / output interface unit, 17: input / output Unit: 20: communication processing unit, 21: analysis unit, 22: switching determination unit, 23: control unit, 23a: power saving mode control unit, 23b: switching control unit, 26: power supply, 27: power supply control unit, 30: AP (relay device), 31: antenna, 32: RF unit, 33: baseband unit, 34: MAC layer processing unit, 35: router unit, 40: communication processing unit, 41: beacon data generation unit, 42: analysis unit , 43: control unit

Claims (7)

In a wireless communication terminal that communicates with another communication terminal via a relay device that transmits a beacon signal including control data indicating whether there is communication data addressed to the wireless communication terminal for each wireless communication terminal,
A transmission / reception means for transmitting / receiving various signals to / from the relay device;
By analyzing the control data which the contained in the beacon signal from the relay device received by the receiving means and analyzing means for determining the total number of radio communication terminals in the communication data to be transmitted from the relay device,
Using the total number of wireless communication terminals with communication data to be transmitted from the currently connected relay device and the total number of wireless communication terminals with communication data to be transmitted from the unconnected relay device, obtained by the analyzing means Switching determination means for determining whether to switch the connection target from the currently connected relay device to the non-connected relay device;
Switching control means for switching the connection target to the unconnected relay device when the switching determination means determines that the connection target should be switched from the currently connected relay device to the unconnected relay device. ing,
A wireless communication terminal characterized by the above. The wireless communication terminal according to claim 1,
Radio wave intensity detecting means for detecting the radio wave intensity of the signal from the relay device received by the transmitting / receiving means,
The switching determination means further uses the radio field intensity of the signal from the currently connected relay apparatus and the radio field intensity of the signal from the unconnected relay apparatus, detected by the radio field intensity detection means, Determine whether to switch the connection target from the relay device in the middle to the non-connected relay device,
A wireless communication terminal characterized by the above. The wireless communication terminal according to any one of claims 1 and 2,
When the total number of wireless communication terminals that have communication data to be transmitted from the currently connected relay device determined by the analyzing means is greater than a predetermined number, the non-connected relay device by the transmitting / receiving means Control means for receiving the beacon signal of
A wireless communication terminal characterized by the above. The wireless communication terminal according to claim 2,
The total number of wireless communication terminals having communication data to be transmitted from the currently connected relay device determined by the analyzing unit is greater than a predetermined number or detected by the radio wave intensity detecting unit. When the radio field intensity of the signal from the connected relay apparatus is smaller than a predetermined intensity, the transmission / reception means includes a control means for receiving a beacon signal from the non-connected relay apparatus,
A wireless communication terminal characterized by the above. In the radio | wireless communication terminal as described in any one of Claim 1 to 4,
The switching determination unit performs at least the the total number of radio communication terminal as a variable using a function representing the degree of necessity of the connection target switch, whether to switch the connection target determination,
When the function is a function whose necessity for switching the connection target increases as the value obtained by the function increases, the function includes a term whose value increases with time, and the function includes the function In the case of a function whose necessity for switching the connection target increases as the value obtained by the function is smaller, the function includes a term whose value decreases with time.
A wireless communication terminal characterized by the above. In the radio | wireless communication terminal as described in any one of Claim 1 to 5,
The analysis means refers to data stored in a virtual bitmap defined in IEEE802.11 as the control data, and determines the total number of wireless communication terminals with communication data to be transmitted from the relay device.
A wireless communication terminal characterized by the above. A relay device that transmits and receives communication data signals to and from one or more wireless communication terminals and transmits a beacon signal including control data indicating whether or not there is communication data addressed to each wireless communication terminal for each wireless communication terminal In the load balancing method of
The wireless communication terminal is
A first beacon signal receiving step for receiving the beacon signal from the currently connected relay device;
By analyzing the control data which the contained in the beacon signal from the relay device in the currently connected, a first analysis step of obtaining the total number of radio communication terminals in the communication data to be transmitted from the relay device ,
A second beacon signal receiving step for receiving a beacon signal from an unconnected relay device;
By analyzing the control data contained in the beacon signal from the relay device of the non-connection, a second analysis step of obtaining the total number of radio communication terminals in the communication data to be transmitted from the relay device,
The total number of wireless communication terminals having communication data to be transmitted from the currently connected relay device and the wireless communication terminal having communication data to be transmitted from the non-connected relay device obtained in the first analysis step Switching determination step of determining whether to switch the connection target from the currently connected relay device to the non-connected relay device, using the total number of
When it is determined in the switching determination step that the connection target should be switched from the currently connected relay device to the non-connected relay device, a switching step of switching the connection target to the non-connected relay device is executed. ,
A load distribution method for a relay device.

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