JP2010035002A - Radio apparatus, radio communication method and communication program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately hand over a terminal with degraded communication quality. <P>SOLUTION: The radio equipment is installed inside a covering area of a base station to monitor communication, between the base station and terminals and includes: a reception means for receiving frames transmitted from the terminals and the base station; an information storage means for storing the received frame information; a statistical information acquisition means for acquiring statistical information indicating the status of radio link between the terminals and the base station, on the basis of the information stored in the information storage means; a reception power measurement means for measuring the reception power from the terminals; and a message transmission means for transmitting to the terminals a first connection cancel message of the radio link that has the address of the base station as a sender's address, when the reception power is larger than power threshold and when the statistical information does not satisfy the specified communication quality standard. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless device, a wireless communication method, and a communication program in a wireless local area network (LAN) system, for example, a handover technique.

  In recent years, wireless LAN systems that realize high-speed data transmission wirelessly have become widespread. As one form of the wireless LAN system, it is composed of a plurality of base stations (access points) and a plurality of terminals (stations), and each terminal communicates wirelessly with one base station and communicates with the network via the base station. There is a form to connect. If the terminal is out of the area covered by the base station with which it is communicating, or if it is within the area but the received power from the base station is weak and sufficient communication quality cannot be obtained, the base station will transfer to another base station. It is possible to continue high-quality communication by performing a handover.

  In the wireless LAN standardized by IEEE802.11, the handover algorithm is not clarified, so the handover algorithm depends on the manufacturer of the wireless LAN product. Among the wireless LAN products that are already widely used, there are terminals that continue to connect to the original base station even though the communication quality is poor and the communication quality can be improved by handing over to another base station. Such a terminal not only deteriorates the communication quality of the terminal itself but also uses extra radio resources. Furthermore, there is a demerit that power consumption increases due to retransmission.

  As a method for solving this problem, it is conceivable to improve the hand-over algorithm of the terminal, but it is difficult to collect terminals that have already spread widely and replace them with new terminals. Therefore, a technique has been proposed in which the base station is devised and the terminal is urged to perform handover by control from the base station.

  For example, Patent Document 1 discloses a technique aimed at distributing the load on a base station. The base station controller instructs the base station that has become overloaded to lower the transmission power to the base station, and causes the terminal to induce handover to another base station.

However, in Patent Document 1, since the load distribution of the base station is an object, the threshold parameters for reducing the power are only the load of the base station and the QoS class. When the communication load of a terminal is degraded although the load on the base station is small, it is not possible to induce a handover to another base station that is more appropriate for the terminal. Furthermore, depending on the handover algorithm of the terminal, even if the transmission power is reduced, the handover is not always performed to another base station, and the communication quality may be simply deteriorated. After all, Patent Document 1 cannot solve the above problem.
JP 2008-42451 A

  The present invention provides a wireless device, a wireless communication method, and a communication program that can appropriately hand over a terminal whose communication quality has deteriorated.

A wireless device as one embodiment of the present invention includes:
A wireless device that is disposed within a coverage area of a base station and monitors communication between the base station and a terminal,
Receiving means for receiving a frame transmitted from the terminal and a frame transmitted from the base station;
Information storage means for storing information of frames respectively received from the terminal and the base station;
Statistical information acquisition means for acquiring statistical information representing a state of a radio link between the terminal and the base station based on information in the information storage means;
Received power measuring means for measuring received power from the terminal;
First determination means for determining whether or not the received power is greater than a power threshold;
Second determination means for determining whether or not the statistical information satisfies a predetermined communication quality standard;
When the received power is greater than the power threshold and the statistical information does not satisfy the predetermined communication quality criterion, a first connection release message of the radio link having the address of the base station as a source address is transmitted. Message sending means for sending to the terminal;
It is provided with.

A wireless communication method as one aspect of the present invention includes:
A wireless communication method that is arranged in a cover area of a base station and monitors communication between the base station and a terminal,
A receiving step of receiving a frame transmitted from the terminal and a frame transmitted from the base station;
An information storage step of storing information on frames received from the terminal and the base station in an information storage unit;
A statistical information acquisition step for acquiring statistical information indicating a state of a radio link between the terminal and the base station, based on information in the information storage means;
A received power measuring step of measuring received power from the terminal;
A first determination step of determining whether or not the received power is greater than a power threshold;
A second determination step of determining whether or not the statistical information satisfies a predetermined communication quality standard;
When the received power is greater than the power threshold and the statistical information does not satisfy the predetermined communication quality criterion, a first connection release message of the radio link having the address of the base station as a source address is transmitted. A message sending step to send to the terminal;
It is provided with.

A communication program as one aspect of the present invention is:
A communication program arranged in a cover area of a base station and executed in a computer that monitors communication between the base station and a terminal,
A receiving step of receiving a frame transmitted from the terminal and a frame transmitted from the base station;
An information storage step of storing information on frames received from the terminal and the base station in an information storage unit;
A statistical information acquisition step for acquiring statistical information indicating a state of a radio link between the terminal and the base station, based on information in the information storage means;
A received power measuring step of measuring received power from the terminal;
A first determination step of determining whether or not the received power is greater than a power threshold;
A second determination step of determining whether or not the statistical information satisfies a predetermined communication quality standard;
When the received power is greater than the power threshold and the statistical information does not satisfy the predetermined communication quality criterion, a first connection release message of the radio link having the address of the base station as a source address is transmitted. A message sending step to send to the terminal;
It is provided with.

  According to the present invention, it is possible to appropriately hand over a terminal whose communication quality has deteriorated.

Abbreviations used in this specification or drawings and their meanings are shown below.

ACK: Acknowledge, Acknowledgment
RSSI: Received Signal Strength Indicator
SIFS: Short Inter Frame Space, shortest frame transmission interval (sifth)
SW: Switch
MAC: Media Access Control
RTS: Request To Send
CTS: Clear To Send

  Hereinafter, the present embodiment will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a configuration of a communication system according to the first embodiment of the present invention.

  This communication system includes a plurality of base stations AP 1 and AP 2, a terminal STA, and a wireless device (wireless communication device) 101.

  The plurality of base stations AP1 and AP2 and the terminal STA all comply with at least one of the wireless LAN standards IEEE802.11a, b, and g.

  The wireless device 101 can receive and transmit a frame conforming to at least one of the wireless LAN standards IEEE802.11a, b, and g.

  The plurality of base stations AP1, AP2 and the wireless device 101 each have a cover area, and can communicate with a wireless LAN device existing in the cover area. Radio apparatus 101 is arranged in the coverage areas of base stations AP1 and AP2 and in the vicinity of the edge of the coverage area of base station AP1.

  The terminal STA is a mobile terminal such as a notebook PC, and can perform wireless communication with the base stations AP1 and AP2 in accordance with the wireless LAN standard.

  In FIG. 1, since the terminal STA is within the coverage area of the base station AP1, it can communicate with the base station AP1. When the terminal STA moves to the right in FIG. 1, the terminal STA moves out of the coverage area of the base station AP1 and cannot communicate with the base station AP1. Instead, since the mobile station enters the coverage area of the base station AP2, the terminal STA can continue communication by communicating with the base station AP2 if it can be handed over from the base station AP1 to the base station AP2.

  FIG. 2 is a block diagram showing a configuration of radio apparatus 101 according to the first embodiment of the present invention.

  The wireless device 101 includes an antenna unit 11, a SW unit 12, a wireless LAN demodulation unit (reception unit, reception power measurement unit) 13, an information acquisition unit 14, an information storage unit 15, and a control unit (statistical information acquisition unit). , First determination means, second determination means) 16 and wireless LAN modulation section (message transmission means) 17.

  The antenna unit 11 receives the wireless LAN signal and outputs it to the SW unit 12. Also, the wireless LAN signal input from the SW unit 12 is output.

  The wireless LAN demodulation unit 13 demodulates the wireless LAN signal input from the SW unit 12 and outputs the demodulated data to the information acquisition unit 14 together with the reception time of the wireless LAN signal. Further, the wireless LAN demodulation unit 13 acquires the received power of the wireless LAN signal and outputs it to the information acquisition unit 14. As the received power, an RSSI output value built in the wireless device 101 is used. RSSI is included in the wireless LAN demodulation unit 13. The reception time is the time managed by the wireless device 101 (the time of the system timer built in the wireless device 101).

  The information acquisition unit 14 acquires a part of header information (a transmission source address, a transmission destination address, a MAC frame subtype, a retry flag, etc.) from the demodulated data input from the wireless LAN demodulation unit 13, and the acquired header information Then, the received power (RSSI output value) and the reception time from the wireless LAN demodulation unit 13 are stored in the information storage unit 15 (see FIGS. 4 and 6 described later). The information storage unit 15 stores information within a certain time from the current time, and deletes other information.

  Based on the data in the information storage unit 15, the control unit 16 calculates statistical information (such as an ACK response rate or the number of duplicate frames from the terminal to the base station or vice versa) regarding the radio link between the base station and the terminal. When the calculated statistical information does not satisfy the predetermined communication quality standard and the received power (RSSI output value) is larger than the power threshold, the control unit 16 uses the transmission source address as the base station address. The connection release message (wireless LAN control information) is generated and output to the wireless LAN modulation unit 17.

  The wireless LAN modulation unit 17 generates and modulates a wireless LAN signal based on the wireless LAN control information input from the control unit 16 and outputs the wireless LAN signal to the SW unit 12.

  Here, the information acquisition unit 14 in FIG. 2 will be described in more detail.

  As described above, the information acquisition unit 14 acquires part of the header information, reception time, and reception power (RSSI output value).

  The header information includes, for example, a transmission source MAC address, a transmission destination MAC address, a MAC frame subtype, and a retry flag indicating whether it is retransmission.

  The MAC frame subtype includes data, ACK, RTS, CTS, Association Request, Association Response, Beacon, etc., and can be recognized by reading the frame control field of the MAC header. The source MAC address and the destination MAC address are described in the MAC header, and can be recognized by reading the MAC header. The retry flag can also be recognized by reading the frame control field of the MAC header.

  Depending on the MAC frame subtype, the MAC header may include the destination MAC address but not the source MAC address. For example, the source MAC address is not included in ACK or CTS. This is because the source MAC address can be identified on the receiving side without clearly indicating the source MAC address. For example, if data is transmitted from the base station AP-1 to the terminal STA-1, when the terminal STA-1 successfully demodulates the data frame, the SIFS (Short Inter Frame Space ) Is to be transmitted to the base station AP-1. That is, even if the MAC header does not include information that the source MAC address is the terminal STA-1, it can be recognized that the source MAC address is the terminal STA-1. Therefore, in this case, the wireless LAN demodulation unit 13 adds the transmission source MAC address and outputs it to the information acquisition unit 14 even if the transmission source MAC address is not included in the MAC header.

  In addition, there is a frame whose transmission destination MAC address is not limited, such as a broadcast frame transmitted by the base station, but the information acquisition unit 14 discards the frame without acquiring information about the frame.

  FIG. 7 shows a communication flow between the radio apparatus 101, the terminal STA, and the base stations AP1 and AP2.

  Initially, the terminal STA and the base station AP1 are in data communication (S11). The base stations AP1 and AP2 are in the coverage area of the wireless device 101.

  The wireless device 101 monitors a frame transmitted from the terminal STA to the base station AP1 when the terminal STA is within the coverage area of the wireless device 101 and measures the received power of the frame (acquires an RSSI output value). In addition, the frame transmitted from the base station AP1 to the terminal STA is monitored (S12, S13).

  Then, the wireless device 101 stores the average RSSI of frames transmitted from the terminal STA to the base station AP1 and the ACK response rate (statistical information) of the terminal STA for the data frame transmitted from the base station AP1 to the terminal STA. Calculate based on the data. When the average RSSI is equal to or less than a threshold value (power threshold value), or when the ACK response rate is equal to or greater than the threshold value (ACK threshold value), the wireless device 101 transmits nothing to the terminal STA. As statistical information, other indicators, for example, the ACK response rate of the base station AP1 to the data frame transmitted from the terminal STA to the base station AP1, the number of duplicate frames of the data frame transmitted from the terminal STA to the base station AP1, the terminal from the base station AP1 The number of overlapping frames of data frames transmitted to the STA may be calculated.

  When the terminal STA eventually moves (S14) and the communication quality between the terminal STA and the base station AP1 deteriorates (S15), the average RSSI is greater than the power threshold and the ACK response rate is lower than the ACK threshold. (S16, S17, S18).

  Therefore, the wireless device 101 uses the transmission source address as the base station AP1, and transmits a frame including a connection release message to the terminal STA (S19). Also, a frame including a connection release message is transmitted to the base station AP1 with the source address as the terminal STA (S20).

  The terminal STA that has received the connection release message newly searches for a base station (S21). Although there is a low possibility that a broadcast signal from the remote base station AP1 can be received (S23), it is highly possible that a broadcast signal from the nearby base station AP2 can be received instead (S22).

  The terminal STA that has received the broadcast signal from the base station AP2 transmits a connection request message to the base station AP2 (S24), the base station AP2 returns a connection response message (S25), and between the terminal STA and the base station AP2 Thus, communication can be started, and handover can be performed (S26). Further, since the base station AP1 has received the connection release message, the base station AP1 deletes the presence of the terminal STA from the table (data in the information storage unit) managed by the base station AP1.

  By operating the wireless device 101 as described above, it is possible to appropriately perform handover for the terminal STA moving between the base stations AP1 and AP2.

  Hereinafter, a communication flow between the radio apparatus 101, the terminal STA, and the base stations AP1 and AP2 will be described using a specific example.

  The wireless device 101 monitors the transmission frame of the terminal STA and the transmission frame of the base station AP1, which is the communication partner, when the terminal STA moves and enters the coverage area of the wireless device 101, and stores information in the information storage unit 15 ( Stores header information, reception time, received power (RSSI output value)). Then, the wireless apparatus 101 calculates, for example, the average RSSI of the transmission frame of the terminal STA, the ACK response rate of the terminal STA as statistical information, and the ACK response rate of the base station AP1.

  FIG. 3 shows a state in which a base station AP1 with a MAC address of 10000001 and a terminal STA1 with a MAC address of 10000002 are communicating with good communication quality. When the communication quality between the terminal STA1 and the base station AP1 is good, the terminal STA1 has a high probability of returning ACK for the transmission data frame from the base station AP1, and the base station AP1 receives ACK for the transmission data frame of the terminal STA1. The probability of returning is high. Information stored in the information storage unit in the wireless device at this time is, for example, as shown in FIG. The number of ACK frames transmitted by the terminal STA1 with respect to 10 frames of data transmitted by the base station AP1 is nine. Therefore, the ACK response rate of terminal STA1 is 90%. Since the number of data frames transmitted from terminal STA1 to base station AP1 is 0, the ACK response rate of base station AP1 cannot be calculated. Therefore, when the parameter required for calculating the ACK response rate, the average RSSI, or the like is 0 or extremely small, it is set to a value that represents the best communication quality. For example, 100% for the ACK response rate, 0 for the number of duplicate frame transmissions, and a predetermined maximum value for the average RSSI.

  On the other hand, when the terminal STA moves, is located at the edge of the coverage area of the base station AP1, and is located within the coverage area of the wireless device 101, the terminal STA1 acknowledges the transmission data frame from the base station AP1. The base station AP1 has a low probability of returning ACK for the transmission data frame of the terminal STA1. FIG. 5 shows a state in which the base station AP1 and the terminal STA1 are communicating with each other with poor communication quality. Information stored in the information storage unit 15 in the wireless device 101 at this time is, for example, as shown in FIG. The number of ACK frames transmitted by the terminal STA1 with respect to 10 frames of data transmitted by the base station AP1 is five. Therefore, the ACK response rate of terminal STA1 is 50%. Since the number of data frames transmitted from terminal STA1 to base station AP1 is 0, the ACK response rate of base station AP1 cannot be calculated. As described above, in this case, the ACK response rate of the base station AP1 is 100%.

  If the handover algorithm of the terminal STA1 is appropriate, the connection with the base station AP1 is canceled, the connection with the base station AP2 is switched, and the communication should be continued. However, if the handover algorithm of the terminal STA1 is not appropriate, the terminal STA1 and the base station AP1 continue to communicate with each other with the communication quality deteriorated, so that desired communication cannot be performed. Furthermore, since data is continuously retransmitted many times, it affects other wireless LAN systems, and wireless resources cannot be used effectively. Furthermore, there is a demerit that power consumption increases due to retransmission.

  In such a case, the wireless device 101 sets the transmission source address of the frame to 10000001, which is the same as that of the base station AP1, generates and modulates a frame including a connection release message, and transmits it to the terminal STA1 (FIG. 7). (See S19). At this time, the condition for transmitting the frame including the connection release message is that the average RSSI (average received power) of the frame of the terminal STA1 is larger than the power threshold and the ACK of the terminal STA1 or the base station AP This is when the response rate is lower than the ACK threshold. For example, assuming that the power threshold is −40 dBm and the ACK threshold is 60%, in the case of FIG. 4 (the average RSSI of the terminal STA1 is −50 dBm, the ACK response rate of the terminal STA1 is 90%, and the ACK of the base station AP1 Although the frame containing the connection release message is not transmitted when the response rate is 100%, in the case of FIG. 6 (average RSSI is -30 dBm, terminal STA1 has an ACK response rate of 50%, and base station AP1 has an ACK response rate of 100%) Since both conditions are satisfied, a frame including a connection release message is transmitted to the terminal STA1.

  In the specific example described above, the ACK response rate is calculated as statistical information, but an example in the case of calculating the number of overlapping frames is shown below. First, the number of overlapping frames will be briefly described. When a frame transmitted from the transmitting terminal is normally received by the partner terminal, but the ACK from the partner terminal is not normally received by the transmitting terminal, the same frame will be transmitted again from the transmitting terminal. The number of times the duplicate frame is transmitted corresponds to the number of duplicate frames. A retry flag is used to calculate the number of duplicate frames. When the retry flag of a frame transmitted from the transmitting terminal first indicates retransmission (here, “1”) after ACK is returned from the partner terminal, the frame is Consider duplicate frames.

  In the example shown in FIG. 4, the frame transmitted at the time of 4.000 msec includes a retry flag of “1”, but this is because the frame transmitted at the previous time of 3.000 msec did not reach the partner terminal. Therefore, the frame transmitted at time 4.000 msec does not correspond to a duplicate frame. Therefore, the number of overlapping frames transmitted from the base station AP1 to the terminal STA1 is zero. Since the number of data frames transmitted from terminal STA1 to base station AP1 is 0, the number of overlapping frames transmitted from terminal STA1 to base station AP1 cannot be calculated. As described above, in this case, the number of overlapping frames transmitted from the terminal STA1 to the base station AP1 is zero.

  On the other hand, in the example shown in FIG. 6, the number of frames transmitted from the base station AP1 with the retry flag “1” immediately after the terminal STA1 returns ACK is two. Therefore, the number of overlapping frames transmitted from the base station AP1 to the terminal STA1 is two. Since the number of data frames transmitted from terminal STA1 to base station AP1 is 0, the number of overlapping frames transmitted from terminal STA1 to base station AP1 cannot be calculated. As described above, in this case, the number of overlapping frames transmitted from the terminal STA1 to the base station AP1 is zero.

  When the threshold of the number of duplicate frames (number threshold) is 1.5 and the average RSSI (average received power) power threshold is -40 dBm, both conditions are satisfied in the case of FIG. A frame including the message is transmitted to terminal STA1. Only when the number of duplicate frames is larger than the number threshold and the ACK response rate is smaller than the ACK threshold, a frame including the connection release message may be transmitted to the terminal STA1.

(Second embodiment)
In this embodiment, only a predetermined specific terminal is handed over by the operation of the wireless device, and other terminals (for example, a terminal to which an appropriate handover algorithm is applied) are assumed by the operation of the wireless device. It is characterized by not allowing a handover. Hereinafter, this embodiment will be described in detail.

  FIG. 8 is a block diagram showing a configuration of a radio apparatus according to the second embodiment of the present invention. The difference from FIG. 2 is that a MAC address storage unit (address storage means) 22 and a MAC address reference unit 21 are added. Since the others are the same as those in FIG. 2, the same reference numerals are given to the elements having the same names, and redundant explanations are omitted.

  The MAC address storage unit 22 stores a plurality of predetermined specific MAC addresses. Specifically, the MAC address of the base station and the MAC address of the target terminal to be handed over by the operation of the wireless device are stored in advance. The MAC address storage unit 22 outputs the stored MAC address to the MAC address reference unit 21.

  The MAC address reference unit 21 receives information (header information, reception time, reception power (RSSI output value)) from the information acquisition unit 14, and receives the MAC address output from the MAC address storage unit 22. The MAC address reference unit 21 compares the source MAC address included in the information input from the information acquisition unit 14 with the MAC address output from the MAC address storage unit 22. If at least one of the MAC addresses stored in the MAC address storage unit 22 is the same as the source MAC address, then the destination MAC address is compared with the MAC address output from the MAC address storage unit 22 To do. If at least one of the MAC addresses stored in the MAC address storage unit 22 is the same as the destination MAC address, the information from the information acquisition unit 14 is output to the information storage unit 15. If they are not the same, nothing is output to the information storage unit 15.

  With the above configuration, it is possible to hand over only a predetermined specific terminal communicating with a predetermined base station by the operation of the radio apparatus. With respect to a terminal to which an appropriate handover algorithm is applied, it is not necessary to acquire and store information in particular unless it is registered in the MAC address storage unit 22. In addition, for terminals to which an appropriate handover algorithm has not been applied (terminals that continue to connect to the original base station despite the poor communication quality and improved communication quality when handed over to another base station), the MAC address Is registered in the MAC address storage unit 22, not only can the terminal be handed over to improve the communication quality of the terminal, but also radio resources can be used effectively. Further, since the retransmission probability is reduced, there is a merit that power consumption is reduced.

  In the above example, the base station and terminal MAC addresses to be handed over by the operation of the wireless device are stored in the MAC address storage unit 22, and both the transmission source address and the transmission destination address of the frame are stored in the MAC address storage unit 22. Information is stored only when it is stored, but the MAC address storage unit 22 stores only the MAC address of the terminal that is the target of handover by the wireless device, and the source address and destination address Information may be stored when any one of these is stored in the MAC address storage unit 22.

(Third embodiment)
FIG. 9 is a block diagram showing a radio apparatus according to the third embodiment of the present invention. The difference from FIG. 8 is that a threshold value storage unit 23 is added. Since the others are the same as those in FIG. 8, the same reference numerals are given to the elements having the same names, and redundant description is omitted.

  The threshold storage unit 23 stores a statistical information threshold (for example, an ACK threshold) in association with a predetermined MAC address, and outputs the statistical information threshold to the control unit 16.

  For example, the threshold value storage unit 23 sets the ACK threshold value 40 in the initial state for the MAC address 10000001 of the base station AP1, the MAC address 10000002 of the terminal STA1, and the MAC address 10000003 of the base station AP2 as the statistical information threshold values. Suppose you remember%. Threshold values other than the ACK threshold value are stored by the control unit 16 and are constant regardless of the MAC address. Here, the power threshold is set to -40 dBm.

  In the state shown in FIG. 5, if the information in the information storage unit 15 is as shown in FIG. 6, the average received power of the frame transmitted by the terminal STA1 is −30 dBm, which is larger than the power threshold value −40 dBm. However, the ACK response rate is 50%, which is equal to or higher than the initial ACK threshold value of 40%. Therefore, in this state, the wireless device 101 does not transmit a connection release message.

  Furthermore, it is assumed that the terminal STA1 moves as shown in FIG. 10 and the information in the information storage unit 15 becomes as shown in FIG. 11, for example. The average received power of the frame transmitted by the terminal STA1 is −35 dBm, which is larger than the power threshold value −40 dBm. The ACK response rate is 20%, which is smaller than the initial ACK threshold value of 40%. Therefore, in this case, the wireless device 101 transmits a connection release message.

  Even if the communication quality as shown in FIG. 10 is very poor, since the terminal STA1 does not spontaneously hand over to the base station AP2, the handover algorithm implemented in the terminal STA1 is not appropriate, and the terminal will actively It seems that STA1 should be handed over. Therefore, in order to change the ACK threshold value of terminal STA1, control unit 16 outputs a control message to threshold value storage unit 23 so as to increase the ACK threshold value corresponding to the MAC address of terminal STA1. The threshold value storage unit 23 updates the MAC address threshold value input from the control unit 16 from 40% to 60% of the initial value. In this way, in the future, it becomes possible to promptly perform handover in the situation shown in FIG. Here, the updated threshold value is predetermined as one of 60%, and the threshold value is stored so as to raise the threshold value of the ACK response rate corresponding to the same MAC address twice or more from the control unit 16. Even if a control message is input to the unit 23, the threshold value storage unit 23 does not further increase the threshold value. However, a plurality of changed threshold values may be prepared, and the threshold value may be increased step by step each time a control message is input.

  By configuring as described above, even if the communication quality is very poor, it is possible to actively promote handover to a terminal that does not perform handover. On the other hand, to a terminal that performs handover before the communication quality becomes very poor On the other hand, it is not necessary to send a connection release message.

(Fourth embodiment)
FIG. 12 is a block diagram showing a configuration of a radio apparatus according to the fourth embodiment of the present invention.

  The difference from FIG. 8 is that an adaptive modulation rate correspondence storage unit 24 is added. Since the others are the same as those in FIG. 8, the same reference numerals are given to the elements having the same names, and redundant description is omitted.

  The adaptive modulation rate correspondence storage unit 24 stores different ACK threshold values for each transmission rate (determined by a combination of a modulation scheme and a coding rate) received by the wireless device.

  For example, the ACK threshold is decreased as the transmission rate is higher, and the ACK threshold is increased as the transmission rate is lower.

  That is, when the transmission rate is high, there is a high possibility that the communication quality will be recovered by reducing the transmission rate a little by adaptive modulation even if the communication quality is poor. In such a case, it is better not to perform handover. Therefore, if the ACK threshold value is reduced, a connection release message is not transmitted from the wireless device before the transmission rate is changed by adaptive modulation. However, there is a case where the adaptive modulation algorithm of the base station or the terminal is inadequate and the transmission rate is not changed by adaptive modulation even though the communication quality is poor. In such a case, when the value falls below the ACK threshold, a connection release message is transmitted to prompt the terminal for handover.

  On the other hand, when the transmission rate is low, there is a high possibility that communication can be performed at a higher modulation rate by performing handover even if the ACK response rate is high to some extent. Therefore, if the ACK threshold value is increased, the possibility of transmitting a connection release message can be increased, and the frequency utilization efficiency of the entire system can be increased by handing over the terminal.

(Fifth embodiment)
FIG. 13 is a diagram showing a configuration of a communication system according to the fifth embodiment of the present invention. The communication system includes a base station AP1, a base station AP2 based on an embodiment of the present invention, and a terminal STA. Conforms to at least one of the g standards. Each of the plurality of base stations AP1 and AP2 has a cover area and can communicate with a wireless LAN device existing in the cover area.

  The terminal STA is a mobile terminal such as a notebook PC, and can perform wireless communication with the base stations AP1 and AP2 in accordance with the wireless LAN standard. In FIG. 13, since the terminal STA is within the coverage area of the base station AP1, it can communicate with the base station AP1. When the terminal STA moves in the right direction in FIG. 13, the terminal STA moves out of the coverage area of the base station AP1 and cannot communicate with the base station AP1. Instead, since it enters the coverage area of the base station AP2, if the handover from the base station AP1 to the base station AP2 can be performed, communication can be continued by communicating with the base station AP2.

  The base station AP2 according to the present invention can be configured as shown in the block diagram of FIG. Since it is as having mentioned above about FIG. 12, description is abbreviate | omitted.

  FIG. 14 shows an operation flow of the communication system of FIG.

  Initially, the terminal STA and the base station AP1 are in data communication (S31).

  The base station AP2 monitors the frame transmitted from the terminal STA to the base station AP1, measures the received power of the frame, and monitors the frame transmitted from the base station AP1 to the terminal STA (S32, S33).

  Then, the base station AP2 calculates the average RSSI of frames transmitted from the terminal STA to the base station AP1, and the ACK return rate (statistical information) of the terminal STA for the data frame transmitted from the base station AP1 to the terminal STA. Here, if RSSI is lower than the power threshold or the ACK response rate is higher than the ACK threshold, base station AP2 does not transmit anything to terminal STA.

  When the terminal STA eventually moves (S34) and the communication quality between the terminal STA and the base station AP1 deteriorates (S35), the average RSSI is larger than the power threshold and the ACK response rate is smaller than the ACK threshold ( S36, S37, S38).

  Therefore, the base station AP2 sets the transmission source address as the base station AP1, and transmits a frame including the connection release message to the terminal STA (S39). Also, a frame including a connection release message is transmitted to the base station AP1 with the source address as the terminal STA (S40).

  The terminal STA that has received the connection release message newly searches for a base station (S41). Although it is unlikely that a broadcast signal from the base station AP1 that is far away can be received (S43), it is highly likely that a broadcast signal from the nearby base station AP2 can be received (S42).

  The terminal STA that has received the broadcast signal from the base station AP2 transmits a connection request message to the base station AP2 (S44), the base station AP2 returns a connection response message (S45), and between the terminal STA and the base station AP2 Communication can be started (S46), and handover can be performed. Since the base station AP1 receives the connection release message, the base station AP1 deletes the presence of the terminal STA from the table (data in the information storage unit 15) managed by the base station AP1.

  As described above, since the base station AP2 operates, the terminal STA moving between the base stations AP1 and AP2 can be handed over. That is, the base station AP2 can hand over a terminal communicating with the base station AP1 in a state of poor communication quality to the own station.

(Sixth embodiment)
FIG. 15 is a diagram showing a block diagram of a base station according to the sixth embodiment of the present invention. This base station can be used as, for example, the base station AP2 in the communication system shown in FIG. The block diagram of this base station is basically the same as that in FIG. 12 except that an RSSI-adaptive modulation rate correspondence storage unit 25 is added instead of the adaptive modulation rate correspondence storage unit 24. Since others are the same as those in FIG. 12, elements having the same names are denoted by the same reference numerals, and redundant description is omitted.

  The RSSI-adaptive modulation rate correspondence storage unit 25 can demodulate a frame with a certain probability or higher when a base station demodulates a signal at a certain transmission rate (specified by a combination of a modulation multi-level number and a coding rate). Is stored as a power threshold value for each transmission rate.

  For example, the power threshold is set higher as the transmission rate is higher, and the power threshold is set lower as the transmission rate is lower. If the terminal needs a high transmission rate due to a request from an upper layer such as an application, it is necessary to communicate at a high transmission rate even after handover. One condition for performing handover is that the received power is more than the received power at the transmission rate at the handover destination base station. Thus, by setting in advance the power threshold value corresponding to the transmission rate, it becomes possible to continue communication with the handover destination base station (AP2 in this case) without lowering the transmission rate.

(Seventh embodiment)
FIG. 16 shows another operation flow of the communication system of FIG. The same steps as those in FIG. 14 are denoted by the same reference numerals, and redundant description is omitted.

  Similarly to FIG. 14, when terminal STA moves and the communication quality between terminal STA and base station AP1 deteriorates, the average RSSI is larger than the power threshold and the ACK response rate is smaller than the ACK threshold (S38). ).

  Therefore, the base station AP2 increases the transmission power of the notification signal (beacon frame or notification frame) (S47). The base station AP2 transmits a notification frame when the first notification means for transmitting the notification frame with a predetermined power and the statistical information (ACK response rate, etc.) do not satisfy a predetermined communication quality standard (ACK threshold, etc.). First instruction means for instructing transmission with a power larger than a predetermined power is included.

  The terminal STA having deteriorated communication quality newly searches for a base station, but transmits a connection request message to the base station AP2 because the transmission power of the notification signal of the base station AP2 is large (S44). The base station AP2 that has received the connection request message from the terminal STA transmits a connection response message (S45).

  As described above, the terminal STA can be handed over to the base station AP2 by increasing the power of the broadcast signal.

(Eighth embodiment)
FIG. 17 shows another operation flow of the communication system of FIG. The same steps as those in FIG. 14 are denoted by the same reference numerals, and redundant description is omitted.

  Similarly to FIG. 16, when the terminal STA moves and the communication quality between the terminal STA and the base station AP1 deteriorates, the average RSSI is larger than the power threshold and the ACK response rate is smaller than the ACK threshold (S38). ).

  Therefore, the base station AP2 shortens the transmission interval of the notification signal (S48) and transmits the notification signal at a short transmission interval (S42a to S42d). The base station AP2 transmits a notification frame when the second notification means for transmitting the notification frame at a predetermined cycle and the statistical information (ACK response rate, etc.) do not satisfy a predetermined communication quality standard (ACK threshold, etc.). Second instruction means for instructing transmission at a cycle shorter than the predetermined cycle.

  The terminal STA whose communication quality has deteriorated searches for a new base station, but since the transmission interval of the broadcast signal of the base station AP2 is short, the presence of the base station AP2 can be immediately confirmed and connected to the base station AP2. A request message is transmitted (S44). The base station AP2 that has received the connection request message from the terminal STA transmits a connection response message (S45).

  If the transmission interval before shortening the transmission interval of the notification signal is T, the transmission interval after shortening the transmission interval is T / n (n is an integer of 2 or more), and the base station AP2 transmits Even when there is another terminal that intermittently receives the broadcast signal, there is no adverse effect on the other terminal.

  As described above, the terminal STA can be handed over to the base station AP2 by shortening the transmission interval of the broadcast signal.

(Ninth embodiment)
FIG. 18 is a diagram showing a configuration of a communication system according to the ninth embodiment of the present invention. The difference from FIG. 13 is that the base station AP1 and the base station AP2 are connected via the switching hub. The base station AP2 can perform wired communication with the base station AP1 via the switching hub 102.

  FIG. 19 is a diagram showing an operation flow of the communication system of FIG. The same steps as those in FIG. 14 are denoted by the same reference numerals, and redundant description is omitted.

  Similarly to FIG. 14, when terminal STA moves and the communication quality between terminal STA and base station AP1 deteriorates, the average RSSI is larger than the power threshold and the ACK response rate is smaller than the ACK threshold (S38). ). Therefore, the base station AP2 issues an instruction to the base station AP1 via the switching hub 102 to transmit a connection release message to the terminal STA (S51).

  Receiving the instruction, the base station AP1 transmits a connection release message to the terminal STA (S52). The terminal STA that has received the connection release message searches for a new base station (S41) and can connect to the base station AP2.

  As described above, by instructing the base station AP2 to transmit a connection release message to the base station AP1 via the switching hub 102, the terminal STA can be handed over to the base station AP2. In this embodiment, an instruction is issued by wire, but an instruction may be issued wirelessly.

  In addition, the radio | wireless apparatus and base station demonstrated by each embodiment are realizable also by using a general purpose computer apparatus as basic hardware, for example. That is, the SW unit, the wireless LAN demodulation unit, the information acquisition unit, the control unit, the wireless LAN modulation unit, and the MAC address reference unit can be realized by causing a processor mounted on the computer device to execute a program. At this time, the wireless device and the base station may be realized by installing the above-described program in a computer device in advance, or may be stored in a storage medium such as a CD-ROM or the above-described program via a network. You may implement | achieve by distributing and installing this program in a computer apparatus suitably. The information storage unit, threshold storage unit, adaptive modulation rate compatible storage unit, RSSI-adaptive modulation rate compatible storage unit, and MAC address storage unit are built-in or externally attached to the above computer device, hard disk or CD -R, CD-RW, DVD-RAM, DVD-R and other storage media can be used as appropriate.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The figure which shows the structure of the communication system which concerns on 1st embodiment of this invention. The block diagram which shows the structure of the radio | wireless apparatus which concerns on 1st embodiment of this invention. The figure which shows a mode that the base station and the terminal are communicating in the state with favorable communication quality. The figure which shows an example of the information in the information storage part in the state of FIG. The figure which shows a mode when the base station and the terminal are communicating in the state with bad communication quality. The figure which shows an example of the information in the information storage part in the state of FIG. The figure which shows the communication flow between a radio | wireless apparatus, a terminal, and two base stations. The block diagram which shows the structure of the radio | wireless apparatus which concerns on 2nd embodiment of this invention. The figure which shows the block diagram of the radio | wireless apparatus which concerns on 3rd embodiment of this invention. The figure which shows a mode when a base station and a terminal are communicating in the state whose communication quality is still worse than FIG. The figure which shows an example of the information in the information storage part in the state of FIG. The block diagram which shows the structure of the radio | wireless apparatus which concerns on 4th embodiment of this invention. The figure which shows the structure of the communication system which concerns on 5th embodiment of this invention. The figure which shows the operation | movement flow of the communication system of FIG. The figure which shows the block diagram of the base station which concerns on the 6th Embodiment of this invention. The figure which shows the other operation | movement flow of the communication system of FIG. The figure which shows the other operation | movement flow of the communication system of FIG. The figure which shows the structure of the communication system which concerns on the 9th embodiment of this invention. The figure which shows the operation | movement flow of the communication system of FIG.

Explanation of symbols

101: Wireless device 11: Antenna unit 12: SW unit 13: Wireless LAN demodulation unit (reception means, reception power measurement means)
14: Information acquisition unit 15: Information storage unit 16: Control unit (statistical information acquisition unit, first determination unit, second determination unit)
17: Wireless LAN modulation section (message transmission means, notification means)
21: MAC address reference unit 22: MAC address storage unit (address storage means)
23: Threshold storage unit 24: Adaptive modulation rate correspondence storage unit 25: RSSI-adaptive modulation rate correspondence storage unit
STA: Terminal (station)
AP1, AP2: Base station (access point)

Claims (14)

A wireless device that is disposed within a coverage area of a base station and monitors communication between the base station and a terminal,
Receiving means for receiving a frame transmitted from the terminal and a frame transmitted from the base station;
Information storage means for storing information of frames respectively received from the terminal and the base station;
Statistical information acquisition means for acquiring statistical information representing a state of a radio link between the terminal and the base station based on information in the information storage means;
Received power measuring means for measuring received power from the terminal;
First determination means for determining whether or not the received power is greater than a power threshold;
Second determination means for determining whether or not the statistical information satisfies a predetermined communication quality standard;
When the received power is greater than the power threshold and the statistical information does not satisfy the predetermined communication quality criterion, a first connection release message of the radio link having the address of the base station as a source address is transmitted. Message sending means for sending to the terminal;
A wireless device comprising: The radio apparatus according to claim 1, wherein the message transmission unit further transmits a second connection release message of the radio link with a source address as the address of the terminal to the base station. The statistical information acquisition means includes, as the statistical information, an ACK response rate from the terminal to the base station, an ACK response rate from the base station to the terminal, the number of duplicate frames transmitted from the terminal to the base station, The radio apparatus according to claim 1, wherein at least one of the number of times of transmission of duplicate frames from the base station to the terminal is acquired. The information storage means, as the frame information,
The source address,
Destination address,
At least the former of the retry flag indicating whether the frame type and retransmission, or
The wireless device according to any one of claims 1 to 3, wherein the wireless device is stored. An address storage means for storing the address of the terminal;
The radio apparatus according to claim 4, wherein the statistical information acquisition unit stores the information only for a terminal having an address stored in the address storage unit. The second determination unit changes a communication quality standard to be applied to the terminal to a higher quality standard when the first connection release message is transmitted to the terminal.
The wireless device according to claim 1, wherein the wireless device is a wireless device. The second determination means uses, as the predetermined communication quality standard, a lower quality standard as the transmission rate of the transmission signal of the terminal is higher, and a higher quality standard as the transmission rate of the transmission signal of the terminal is lower. The radio apparatus according to claim 1, wherein the radio apparatus is characterized. The radio apparatus according to any one of claims 1 to 7, wherein the radio apparatus is a second base station arranged so that a cover area overlaps with the base station. The first determination means uses, as the power threshold, a higher value as the transmission rate of the transmission signal of the terminal is higher, and a lower value as the transmission rate of the transmission signal of the terminal is lower. The wireless device according to claim 8. First notification means for transmitting a notification frame with a predetermined power;
First instruction means for instructing the first notification means to transmit the notification frame at a power higher than the predetermined power when the statistical information does not satisfy the predetermined communication quality standard;
The wireless device according to claim 8, further comprising: Second notification means for transmitting a notification frame at a predetermined period;
Second instruction means for instructing the second notification means to transmit the notification frame at a cycle shorter than a predetermined cycle when the statistical information does not satisfy the predetermined communication quality standard;
The wireless device according to claim 8, further comprising: When the statistical information does not satisfy the predetermined communication quality standard, the message transmission means transmits a first connection release message to the terminal instead of transmitting a first link to the terminal. The radio apparatus according to any one of claims 8 to 11, wherein an instruction message instructing transmission of a release message to the terminal is transmitted to the base station. A wireless communication method that is arranged in a cover area of a base station and monitors communication between the base station and a terminal,
A receiving step of receiving a frame transmitted from the terminal and a frame transmitted from the base station;
An information storage step of storing information on frames received from the terminal and the base station in an information storage unit;
A statistical information acquisition step for acquiring statistical information indicating a state of a radio link between the terminal and the base station, based on information in the information storage means;
A received power measuring step of measuring received power from the terminal;
A first determination step of determining whether or not the received power is greater than a power threshold;
A second determination step of determining whether or not the statistical information satisfies a predetermined communication quality standard;
When the received power is greater than the power threshold and the statistical information does not satisfy the predetermined communication quality criterion, a first connection release message of the radio link having the address of the base station as a source address is transmitted. A message sending step to send to the terminal;
A wireless communication method comprising: A communication program arranged in a cover area of a base station and executed in a computer that monitors communication between the base station and a terminal,
A receiving step of receiving a frame transmitted from the terminal and a frame transmitted from the base station;
An information storage step of storing information on frames received from the terminal and the base station in an information storage unit;
A statistical information acquisition step for acquiring statistical information indicating a state of a radio link between the terminal and the base station, based on information in the information storage means;
A received power measuring step of measuring received power from the terminal;
A first determination step of determining whether or not the received power is greater than a power threshold;
A second determination step of determining whether or not the statistical information satisfies a predetermined communication quality standard;
When the received power is greater than the power threshold and the statistical information does not satisfy the predetermined communication quality criterion, a first connection release message of the radio link having the address of the base station as a source address is transmitted. A message sending step to send to the terminal;
A communication program with

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