JP2009004829A - Base station, server and radio lan system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio LAN system capable of preventing the increase of intervals between packets in roaming operation. <P>SOLUTION: In an upstream packet, a sequence number is added to a mobile station ST packet and the ST packet is transmitted to each of base stations by multicast or broadcast. In each of the base stations AP1, AP2, AP3, the strength of a reception signal of the packet is measured, and a numeric value of the strength of the reception signal is added to the packet and the packet is transmitted to a roaming server SRV. The roaming server SRV in which the cell ID of each of base stations is registered determines whether the packets of the same sequence number have been all received from all registered base stations. If all the packets are received, a packet having the maximum reception signal strength is selected from packets having the same sequence number and having no data error, and only the selected packet is transmitted to a personal computer PC. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a wireless LAN system, and a base station and a server device used for the wireless LAN system.

  The conventional roaming method of the wireless LAN (local area network) system disclosed in Patent Document 1 is as follows. That is, a plurality of base stations (access points) are installed within an assumed movement range of the mobile station (station), and the mobile station receives a beacon signal periodically (for example, every 100 ms) from each base station, The received signal strength (RSSI) of the beacon signal is measured, the received signal strengths are compared with each other for each base station, and the base station having a stronger received signal strength is connected to the line. In such a system, when the mobile station moves and moves away from the currently connected base station, the received signal strength of the beacon signal of the base station decreases accordingly. When the received signal strength of the beacon signal falls below a predetermined threshold, the normal packet communication operation between the mobile station and the base station is temporarily stopped, and the mobile station determines the next connectable base station. Perform the search operation. That is, the mobile station receives a beacon signal transmitted from each base station at each point, and connects the line to the base station having the strongest received signal strength.

Here, the line connection means that a certain mobile station can perform packet communication with a base station having the same cell ID (identifier identifying the base station). A base station can be connected to a plurality of mobile stations, but a mobile station can be connected to only one base station. The mobile station and the base station function as a bridge between the wired line and the wireless line, and relay packets addressed to the MAC address (device-specific address).
JP 2002-26931 A JP 2006-279960 A

  FIG. 11 is a block diagram illustrating a configuration example of the above-described wireless LAN system. In this wireless LAN system 101, a plurality of base stations AP1, AP2, AP3 are connected to a network NETs. The base stations AP1, AP2, AP3 are arranged in a straight line as shown in the figure. A network camera Cn is connected to the mobile station ST, and the mobile station ST moves on a straight line indicated as “movement range”. This straight line is parallel to the direction in which the base stations AP1, AP2, AP3 are arranged. The personal computer PC is connected to the network NETs, and an image taken by the network camera Cn is transmitted to the base stations AP1, AP2 or AP3 by the mobile station ST, and this image can be monitored by the personal computer PC. Note that the base stations AP1, AP2, AP3 are arranged in a straight line, and the mobile station ST moves along a straight line parallel thereto for the convenience of explanation.

  FIG. 12 is a graph for explaining the roaming operation of the wireless LAN system 101. The figure shows the change in RSSI of the beacon signal when the mobile station ST moves on a straight line of the movement range. Initially, the mobile station ST is connected to the base station AP1. Next, when the mobile station ST passes through an intermediate point (roaming boundary) between the base station AP1 and the base station AP2, the RSSI level P1 of the beacon signal from the base station AP1 decreases, and this level P1 becomes a predetermined threshold ( At the time when the roaming threshold (L2) falls below, the mobile station ST once disconnects the line with the base station AP1, and enters an operation for searching for a base station that can be connected next. At this point, since the RSSI level P2 of the beacon signal from the base station AP2 exceeds the level P1, a line is connected between the mobile station ST and the base station AP2.

  13 and 14 are flowcharts for explaining the operation of the mobile station ST of the wireless LAN system 101 in this case. Such processing includes a line connection operation in the first half steps S101 to S107 and a roaming operation (line reconnection operation) in the second half steps S108 to S118.

  First, the line connection operation will be described. When the mobile station ST starts operation, a probe request signal is transmitted to the base stations AP1, AP2, AP3 (step S101). Then, it waits for the response signal from the base station having the same cell ID and the same frequency channel in the communicable area (step S102). If the response signal is not returned even after a lapse of a certain time (N in step S102), the frequency channel is changed (step S103), the process returns to step S101, and the probe request signal is transmitted. If a response signal is returned (Y in step S102), the RSSI of the response signal is recorded (step 104S). Then, it is determined whether or not a probe request signal has been transmitted to all of one or more predetermined frequency channels (step S101) (step S104). If there is an untransmitted frequency channel (step S105). N) The frequency channel is changed (step S102), and the probe request signal is transmitted again (step S101). Such a search operation of the base station is called a scan operation. If a valid base station, that is, a base station that can be connected to a line is not found even if probe request signals are transmitted to all frequency channels, the process returns to step S101 to return to the first frequency channel. Repeat the scan operation from. If there is a base station that can be connected to the line (Y in step S106), the line is connected to the base station (step S107). In this case, when there are a plurality of base stations that can be connected to the line, the line is connected to the base station having the largest RSSI of the response signal.

  Next, the operation proceeds to roaming operation (line reconnection operation). That is, after the line is connected as described above, every time a packet is received (Y in step S108), the packet from the wired line (terminal side) is transmitted to the wireless line (base station side), and the wireless line It operates as a bridge for transmitting the bucket from the (base station side) to the wired line (step S109).

  On the other hand, the RSSI of the beacon signal transmitted by the base station is compared with a preset threshold value (roaming threshold) between bucket transmission and reception when no packet is received (N in step S108) (step S110). When the RSSI value exceeds the roaming threshold (N in Step S111), the process returns to Step S108 and the subsequent steps.

  When the RSSI value is less than or equal to the roaming threshold (Y in Step S111), the same processing as Steps S101 to S107 described above is executed (Steps S112 to S118).

  In the wireless LAN system 101 that performs the roaming operation as described above, after the mobile station ST moves within the moving range, the mobile station ST disconnects the line with the base station AP1 once, and then the mobile station ST and the base station AP2 The mobile station ST cannot perform packet communication with any of the base stations during the time t until the line is connected (the processing period of steps S112 to S118). Therefore, there is a packet interval after the line disconnection with the base station AP1 until the packet communication with the base station AP2 is resumed. In this case, if the packet interval is widened for general packet data, there is no big problem. However, when a moving image from the network camera Cn is monitored on a personal computer PC by streaming, even a slight communication interruption is required. This causes a problem that the image is disturbed.

  In addition, at the roaming boundary, it is generally far from the base station AP1 that has been connected up to now and the base station AP2 that is about to be connected, and the RSSI of the beacon signal is generally far away. The absolute value is a low value and is often close to the communication limit level L1. Furthermore, the RSSI of a beacon signal usually fluctuates due to the general characteristics of wireless communication. For this reason, the number of base station search operations that increase near the roaming boundary increases, and there is a high possibility that the packet interval will further increase.

  Accordingly, an object of the present invention is to prevent a packet interval from occurring during a roaming operation in a wireless LAN system.

  (1) The present invention receives a packet from the mobile station via the first communication interface that performs radio communication with the mobile station, the second communication interface that communicates with the network, and the first communication interface. When the packet is received by the first receiving means and the first receiving means, the measuring means for measuring the received signal strength of the packet, and when the received signal strength is measured by the measuring means, First transmission means for adding information on the received signal strength to the target packet and transmitting the information to a predetermined communication destination via the network by the second communication interface; and from the predetermined communication destination, A second receiving means for receiving a packet via a network and the second communication interface; and a second receiving means for receiving the packet via the second receiving means. When a packet is received is a base station and a, a second transmission means for transmitting to the mobile station via the said packet first communication interface.

  (2) Another aspect of the present invention relates to a third communication interface that communicates with a base station via a network, a fourth communication interface that communicates with a predetermined communication destination, and a plurality of the base stations. A first storage device each storing a first identifier for identifying a packet, a third receiving means for receiving a packet from the base station via the third communication interface, and a third receiving means When the packet is received from the base station, the buffer means for buffering the packet in the second storage device and the packet included in each packet buffered in the second storage device The packet including the same second identifier is received from all of the plurality of base stations by the identifier of 1 and the second identifier for identifying the packet. When it is determined by the packet reception determination means that determines whether or not the packet including the same second identifier has been received from all of the plurality of base stations by the packet reception determination means, The packet specifying means for comparing the received signal strength information of each of the included packets to identify the packet containing the largest received signal strength information, and the packet specified by the packet specifying means to the fourth packet A third transmitting means for transmitting to the predetermined communication destination via a communication interface; a fourth receiving means for receiving a packet from the predetermined communication destination via the third communication interface; When a packet is received from the predetermined communication destination by the receiving means, the third communication interface and the network are connected. And a fourth transmission means for transmitting the packet to the base station.

  (3) In this case, the third storage device that stores the first identifier included in the packet specified by the packet specifying unit, and the packet specifying unit specified by the third transmitting unit An identifier updating unit for updating the first identifier stored in the third storage device with the first identifier included in the packet when transmitting the packet to the predetermined communication destination; When the fourth receiving unit receives a packet from the predetermined communication destination by the fourth receiving unit, the fourth transmitting unit stores the packet in the third storage device. You may make it transmit to the said base station in which the identifier is memorize | stored.

  (4) Another present invention includes a network, a mobile station, the base station described in (1), and the server device described in (2) or (3), wherein the base station is The first communication interface performs radio communication with the mobile station, the second communication interface performs communication with the network, and the server device transmits the base station via the network through the third communication interface. The mobile station communicates with a predetermined communication destination through the fourth communication interface, and the mobile station transmits a packet to be transmitted to the base station to a fifth communication interface that performs radio communication with the base station. An identifier adding unit including a second identifier; and the packet including the second identifier by the identifier adding unit is transmitted to the fifth communication interface. A fifth transmission means for transmitting to the base station via multicast or broadcast via a chaise, and a fifth reception means for receiving a packet from the base station via the fifth communication interface. This is a wireless LAN system.

  According to the present invention, the same packet is transmitted from a mobile station to a plurality of base stations by multicast or broadcast, and the received one of the received base stations having the highest received strength is selected from the same packets received at each base station. Therefore, it is possible to prevent a situation in which it takes time to switch the line at the roaming boundary and there is a packet interval between them.

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

  FIG. 1 is an explanatory diagram showing an overall configuration of a wireless LAN system 1 according to the present embodiment. In this wireless LAN system 1, a plurality of base stations AP1, AP2, AP3 are connected to a network NETs. The base stations AP1, AP2, AP3 are arranged in a straight line as shown in the figure. A network camera Cn is connected to the mobile station ST, and the mobile station ST moves on a straight line indicated as “movement range”. This straight line is parallel to the direction in which the base stations AP1, AP2, AP3 are arranged. The personal computer PC is connected to the network NETs via the roaming server SRV, and an image captured by the network camera Cn is transmitted to the base station AP1, AP2 or AP3 by the mobile station ST, and this image is monitored by the personal computer PC. Can do. Note that the base stations AP1, AP2, AP3 are arranged in a straight line, and the mobile station ST moves along a straight line parallel thereto for the convenience of explanation. Further, the packet format exchanged between the devices conforms to Ethernet (registered trademark) which is a global standard (IEEE802.3).

  Next, the electrical connection of each part will be described.

  FIG. 2 is a block diagram showing electrical connection of the mobile station ST. The mobile station ST performs various calculations and centrally controls each unit, a ROM 12 that stores various programs executed by the CPU 11 and fixed data, and a RAM 13 that is a work area of the CPU 11 via a bus 14. Connected. The bus 14 further includes a wireless communication interface 15 (hereinafter referred to as “I / F”) for performing wireless communication with the base stations AP1, AP2, and AP3, and a communication I / F 16 for performing wired communication with the network camera Cn. Is connected.

  FIG. 3 is a block diagram showing an electrical connection between the base stations AP1, AP2 and AP3. Since the base stations AP1, AP2, AP3 all have the same configuration, here, the base station AP1 will be described as a representative. The base station AP1 performs various calculations and centrally controls each unit, a ROM 22 that stores various programs executed by the CPU 21 and fixed data, and a RAM 23 that is a work area of the CPU 21 via a bus 24. Connected. Furthermore, a wireless communication I / F 25 that performs wireless communication with the mobile station ST and a communication I / F 26 that performs wired communication with the network NETs are connected to the bus 24.

  FIG. 4 is a block diagram showing electrical connection of the roaming server SRV. In the roaming server SRV, a CPU 31 that performs various calculations and centrally controls each unit, a ROM 32 that stores various programs executed by the CPU 31 and fixed data, and a RAM 33 that is a work area of the CPU 31 are connected via a bus 34. Connected. Further, a communication I / F 35 that performs wired communication with the network NETs and a communication I / F 36 that performs wired communication with the personal computer PC are connected to the bus 34.

  Next, the operation of the wireless LAN system 1 will be described.

  FIG. 5 is a flowchart for explaining processing executed by the mobile station ST. As soon as the mobile station ST starts its operation, it starts the bridge operation. That is, each time a packet is received (Y in step S11), the packet transmission direction (up or down) is determined (step S12). If the packet is from a wired line (terminal side) (Y in step S12), a sequence number is attached to this packet as an identifier for identifying the packet (step S13), and the wireless line (base station side) is transmitted by multicast or broadcast. ) (Upstream packet) (step S14). If the packet is from the wireless line (base station side) (N in step S12), the packet is transmitted to the wired line (terminal side) (downstream packet) (step S15).

  FIG. 6 is a flowchart for explaining processing executed by the base stations AP1, AP2, AP3. Since the base stations AP1, AP2, AP3 all perform the same processing, the processing of the base station AP1 will be described as a representative here. As soon as the base station AP1 starts operation, the bridge operation starts. That is, each time a packet is received (step S21), the packet transmission direction (up or down) is determined (step S22). When the packet is from the wired line (roaming server side) (step S22). Y) The packet is transmitted to the wireless line (mobile station side) (downlink packet) (step S23). When the packet is from the wireless line (the mobile station side) (N in step S22), the RSSI of the packet is measured, the RSSI value is attached to the packet (step S24), and the wired line (roaming) (Upstream packet) (step S25).

  FIG. 7 is a flowchart of processing executed by the roaming server SRV. When the roaming server SRV starts operation, the bridge operation starts immediately. That is, each time a packet is received (step S31), the transmission direction of the packet (up or down) is determined (step S32). When the packet is from the base station side (Y in step S32), All packets with the same sequence number are received from the base stations AP1, AP2, AP3. That is, the cell ID of each existing base station is registered (stored in a nonvolatile memory or the like constituting the ROM 32), and all the registered base stations (base stations AP1, AP2, in this example) It can be determined whether or not all packets having the same sequence number have been received from AP3) (step S33). Therefore, packets received from the base stations AP1, AP2 and AP3 are temporarily buffered in the RAM 33 or the like. When all the packets having the same sequence number are received from the respective base stations AP1, AP2, AP3 (Y in step S33), the largest RSSI value among these packets having the same sequence number that have no data error Is selected, and only the packet is transmitted to the personal computer PC side (upstream packet) (step S34), and the cell ID of the base station that has transmitted the packet having the maximum RSSI value is stored in a predetermined area of the RAM 33. (Step S35). The storage of the cell ID of the base station in step S35 in the RAM 33 is updated every time a packet having the RSSI value is selected in step S34.

  On the other hand, when the packet is from the personal computer side (N in step S32), the packet is transmitted to the base station of the cell ID stored in the predetermined area of the RAM 33 (downlink packet) (step S36). .

  FIG. 8 is a communication sequence diagram of the wireless LAN system 1 based on the processes of FIGS. When the bucket Pu from the mobile station ST is received by a plurality of base stations, each base station transmits buckets Pu1, Pu2, Pu3 to the roaming server SRV. The buckets Pu1, Pu2, and Pu3 for the roaming server SRV include the same information as the bucket Pu and the RSSI information when each base station receives the bucket Pu. The roaming server SRV that has received the buckets Pu1, Pu2, Pu3 determines that the data has the same content from the sequence number assigned to the bucket Pu by the mobile station ST, compares the RSSI of each bucket Pu1, Pu2, Pu3, A packet indicating the RSSI (Pu2 in the example of FIG. 8) is sent to the personal computer PC. Although the sequence number here is given to the packet from the mobile station ST as described above, the sequence number defined in the Ethernet (registered trademark) standard may be used. In this example, the roaming server SRV stores that the packet Pu2 from the base station AP2 has been selected, that is, the base station AP2 has the best communication quality with the mobile station ST.

  On the other hand, the roaming server SRV stores the packet Pd from the personal computer PC in the direction of the mobile station ST (stored when the latest upstream packet is received). In the example of FIG. 8, it is transferred to the mobile station ST via the base station AP2).

  FIG. 9 is a graph showing changes in RSSI in each base station when the mobile station ST initially connected to the base station API moves in the direction of the base station AP3 in the wireless LAN system 1. Since the packet transmitted from the mobile station ST is a multi-destination bucket, so-called multicast or broadcast, it can be received by any base station as long as reception power equal to or higher than the communication limit level L1 can be obtained. For example, when the mobile station ST is at an intermediate point (roaming boundary) between the base station API and the base station AP2, a packet from the mobile station ST can be received by either the base station API or AP2. If the distance between the base stations is short, the base station AP3 may be able to receive the data.

  According to the wireless LAN system 1 of the present embodiment, in the uplink packet, the same packet is transmitted from the mobile station ST to the plurality of base stations AP1, AP2, AP3 by multicast or broadcast, and each of these base stations AP1, AP2, AP2 is transmitted. Of the same packets received by AP3, the one with the highest RSSI of the received base station can be selected and sent to the personal computer PC, so it takes time to switch the line at the roaming boundary, and the packet It is possible to prevent a situation where there is an interval.

  In this case, since the packet of the base station having the highest RSSI is used among the packets having no transmission error, not just the packet of the base station having the highest RSSI, an improvement in the reliability of the radio channel can be expected.

  Furthermore, in the downstream packet, the base station having the highest RSSI in the latest upstream packet can be selected and sent to the mobile station ST, so that the base station with the best communication state is selected for communication. It is likely that you can.

  Needless to say, the present invention is not limited to the contents of the embodiments described above. For example, the roaming server SRV described above does not have to be a single device, and may be provided as a function at a predetermined position in the wireless LAN system 1, for example, in a personal computer PC.

  FIG. 10 is a modified example of the wireless LAN system 1 in which the router R is added to the configuration of FIG. 1 so that the roaming server SRV is connected to the upper network NET. If you connect to, you can monitor real-time video through the Internet. Therefore, the wireless LAN system 1 may be configured as shown in FIG.

It is explanatory drawing which shows the whole structure of the wireless LAN system which is one embodiment of this invention. It is a block diagram which shows the electrical connection of a mobile station. It is a block diagram which shows the electrical connection of a base station. It is a block diagram which shows the electrical connection of a roaming server. It is a flowchart explaining the process which a mobile station performs. It is a flowchart explaining the process which a base station performs. It is a flowchart explaining the process which a roaming server performs. It is a communication sequence diagram of a wireless LAN system. It is a graph which shows the change of RSSI in each base station when mobile station ST moves in a wireless LAN system. It is explanatory drawing which shows the whole structure of the modification of a wireless LAN system. It is explanatory drawing explaining the subject of this invention. It is explanatory drawing explaining the subject of this invention. It is explanatory drawing explaining the subject of this invention. It is explanatory drawing explaining the subject of this invention.

Explanation of symbols

1 Wireless LAN system ST Mobile station AP1, AP2, AP3 Base station SRV Roaming server PC Personal computer

Claims (4)

A first communication interface for performing wireless communication with a mobile station;
A second communication interface for communicating with the network;
First receiving means for receiving a packet from the mobile station via the first communication interface;
When the packet is received by the first receiving means, measuring means for measuring the received signal strength of the packet;
When the received signal strength is measured by the measuring means, information on the received signal strength is added to the packet subject to the measurement and transmitted to a predetermined communication destination via the network by the second communication interface. First transmitting means to:
Second receiving means for receiving packets from the predetermined communication destination via the network and the second communication interface;
Second transmission means for transmitting the packet to the mobile station via the first communication interface when the packet is received via the second reception means;
Base station equipped with. A third communication interface for communicating with the base station via the network;
A fourth communication interface for communicating with a predetermined communication destination;
A first storage device respectively storing a first identifier for identifying the base station for a plurality of the base stations;
Third receiving means for receiving packets from the base station via the third communication interface;
Buffer means for buffering the packet in the second storage device when the third receiving means receives the packet from the base station;
The plurality of packets including the same second identifier by the first identifier included in each packet buffered in the second storage device and the second identifier for identifying the packet. A packet reception determination means for determining whether or not received from all of the base stations of
When the packet reception determining means determines that the packet including the same second identifier has been received from all of the plurality of base stations, the received signal strength of each of the packets included in the plurality of packets, respectively Packet specifying means for comparing the information of the above and specifying the packet including the information of the largest received signal strength,
Third transmitting means for transmitting the packet specified by the packet specifying means to the predetermined communication destination via the fourth communication interface;
Fourth receiving means for receiving a packet from the predetermined communication destination via the third communication interface;
A fourth transmission means for transmitting the packet to the base station via the third communication interface and the network when a packet is received from the predetermined communication destination by the fourth reception means;
A server device comprising: A third storage device for storing the first identifier included in the packet specified by the packet specifying means;
When the packet specified by the packet specifying means is transmitted to the predetermined communication destination by the third transmitting means, the first identifier included in the packet is stored in the third storage device. Identifier updating means for updating the first identifier,
Further comprising
When the fourth transmitting means receives a packet from the predetermined communication destination by the fourth receiving means, the first identifier is stored in the third storage device. Send to base station,
The server device according to claim 2. Network,
A mobile station,
A base station according to claim 1;
The server device according to claim 2 or 3,
With
The base station
Performing wireless communication with the mobile station via the first communication interface;
Communicate with the network by the second communication interface;
The server device
Communicate with the base station via the network by the third communication interface;
Communicate with a predetermined communication destination by the fourth communication interface,
The mobile station
A fifth communication interface for performing wireless communication with the base station;
Identifier adding means for including the second identifier in a packet to be transmitted to the base station;
Fifth transmission means for transmitting the packet including the second identifier by the identifier adding means to the base station by multicast or broadcast via the fifth communication interface;
Fifth receiving means for receiving a packet from the base station via the fifth communication interface;
A wireless LAN system.

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