JP2008066915A - Radio terminal and radio base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system for reducing or effectively using a waiting time generated during scanning. <P>SOLUTION: A radio base station comprises: a means for transferring duplication of the radio terminal's ID and data packets addressing to the radio terminal to a neighboring base station through a wired interface when a radio terminal under its control, scans the neighboring radio base station; a means for transmitting the data packets to the radio terminal when the ID and the data packets are transferred; and a means for transferring sequence numbers of the data packets which have been transmitted to the neighboring base station through the wired interface. A radio terminal comprises: a scanning means for detecting the neighboring radio base station; and a means for transmitting or receiving the data packets during scanning. The radio terminal also comprises a means for promptly shifting to the scanning of a next channel when there is no other radio base station which uses the same channel. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a handover method for switching a wireless base station in accordance with movement of a wireless terminal in a wireless network such as a wireless LAN (Local Area Network), and more specifically, scanning for detecting neighboring wireless base stations. The present invention relates to a communication method for reducing packet delay time caused by processing.

  IEEE 802.11 is a standard for wireless LANs. In IEEE 802.11, two types of methods, passive scan and active scan, are defined as scan methods for detecting neighboring radio base stations for handover of radio terminals.

  Passive scanning is a method in which a wireless terminal detects surrounding wireless base stations by monitoring beacons periodically transmitted by the surrounding wireless base stations. When neighboring wireless base stations use different channels, the wireless terminal switches to each channel and performs detection in order.

  The active scan is a method in which a wireless terminal broadcasts a probe request packet and receives a response (probe response packet) from a surrounding wireless base station, thereby detecting the surrounding wireless base station. After transmitting the probe request packet, the wireless terminal starts a timer and monitors the channel. There are two types of waiting time for monitoring a channel, which are called the minimum channel waiting time and the maximum channel waiting time, respectively. After transmitting the probe request packet, if the wireless terminal does not receive the probe response packet until the timer reaches the minimum channel waiting time, the wireless terminal switches to the next channel and starts transmitting the probe request packet again. On the other hand, if a probe response packet is received within the minimum channel waiting time, monitoring on that channel is continued until the timer reaches the maximum channel waiting time. When the timer reaches the maximum channel waiting time, the channel is switched to the next channel and transmission of the probe request packet is started again.

  The active scan of the wireless terminal will be described in detail with reference to FIG. It is assumed that the neighboring radio base stations 201 and 202 use the same channel (ch B). The radio terminal 100 starts scanning when the radio wave reception strength with the radio base station to which it belongs deteriorates. When the wireless terminal 100 broadcasts the probe request packet, the surrounding wireless base station 201 and the wireless base station 202 perform carrier sensing on the wireless transmission path and return a probe response packet. FIG. 2 shows an example in which the radio base station 202 successfully returns a probe response packet first. Since the wireless terminal 100 has received the probe response packet within the minimum channel waiting time, the wireless terminal 100 continues monitoring on the channel (ch B). Thereafter, the wireless terminal 100 returns an ACK (Acknowledgement) to the wireless base station 202.

  On the other hand, the radio base station 201 returns a probe response packet after waiting for a random time by the back-off process.

  When the timer of the wireless terminal 100 reaches the maximum channel waiting time, the channel is switched and the same processing as described above is repeated.

  In FIG. 2, DIFS (Distributed Inter Frame Space) and SIFS (Short Inter Frame Space) are gaps between packets. DIFS is defined as 16 μs in IEEE802.11a and 10 μs in IEEE802.11b. On the other hand, SIFS is defined as 34 μs in IEEE802.11a and 50 μs in IEEE802.11b.

  As described above, in the active scan, since the wireless terminal does not need to wait for the beacon of the wireless base station, it can detect the surrounding wireless base station faster than the passive scanning. Since you are not sure if you are using, you need to scan all channels.

On the other hand, in Patent Document 1, a channel used by a neighboring radio base station is obtained by notifying a channel used by a neighboring radio base station from a radio base station to which a radio terminal belongs in advance. A method is disclosed in which a targeted scan can be performed and the time required for the scan is shortened.
JP 2005-86623 A

  However, the method described in Patent Document 1 has a problem that data packets are delayed as shown in FIG. 3 because the channel to be scanned is continuously monitored until the maximum waiting time.

  An object of the present invention is to solve the above-mentioned conventional problems and to provide a system that reduces or effectively uses a waiting time that occurs during scanning.

  In order to solve the above-described conventional problem, the first wireless terminal of the present invention communicates with a plurality of wireless base stations connected to each other by wire or wirelessly while changing a connection-destination wireless base station by a handover process. A wireless terminal in a wireless communication system including a wireless terminal, channel information receiving means for receiving channel information of another wireless base station from a connected wireless base station, and during the scanning operation of the handover process, When receiving probe responses from all the radio base stations that use the channel being scanned included in the used channel information, a data packet transmitting unit that transmits a data packet on the channel is provided.

  A second wireless terminal according to the present invention includes wireless communication including a plurality of wireless base stations connected to each other by wire or wirelessly and a wireless terminal that performs communication while changing a connection-destination wireless base station by a handover process. A wireless terminal in the system, the channel information receiving means for receiving the used channel information of the other wireless base station from the connected wireless base station, and the scanning included in the used channel information during the scanning operation of the handover process And scan control means for terminating the scan of the channel when probe responses are received from all the radio base stations using that channel.

  The first radio base station of the present invention includes a radio terminal including a plurality of radio base stations connected to each other by wire or radio and a radio terminal that performs communication while changing a connection-destination radio base station by handover processing. A wireless base station in a communication system, wherein transfer data receiving means for receiving a data packet addressed to the wireless terminal, and a data packet addressed to the wireless terminal to the wireless terminal during a scanning operation of the handover process by the wireless terminal Transfer data transmission means for transmitting.

  The first radio base station of the present invention may further include sequence number notifying means for transmitting the sequence number of the data packet transmitted to the radio terminal to another radio base station.

  According to the present invention, the radio base station notifies the radio terminal of a list specifying the channels used by the neighboring radio base stations and the number of neighboring radio base stations using the channel. Thus, it is possible to avoid a useless maximum waiting time during scanning.

  Specifically, the useless waiting time can be reduced by ending the scan when it is confirmed that all the radio base stations using the channel being scanned by the radio terminal have responded. In addition, when the wireless terminal confirms that all wireless base stations using the channel being scanned have responded, data transmission can be prevented by transmitting data on the channel being scanned.

  Further, the wireless base station forwards the data packet addressed to the wireless terminal to the surrounding wireless base station to be scanned by the subordinate wireless terminal, so that the surrounding wireless base station can perform the data packet even during scanning. Can be sent.

  Further, even if the wireless base station switches the channel to be scanned by notifying other wireless base stations of the sequence number of the data packet that has been transmitted to the wireless terminal, the packet following the already received packet Can be received from.

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

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of a wireless LAN system including wireless base stations 100 to 300 and wireless terminals in Embodiment 1 of the present invention. Radio base station 100 uses channel A, radio base station 200 uses channel B, and radio base station 300 uses channel C. 4 and 5 are flowcharts showing the operation of the radio base station according to Embodiment 1 of the present invention. FIG. 6 is a flowchart showing the operation of the wireless terminal according to Embodiment 1 of the present invention. FIG. 8 is a block diagram showing an internal configuration of the radio base station according to Embodiment 1 of the present invention. FIG. 9 is a block diagram showing an internal configuration of the radio terminal according to Embodiment 1 of the present invention. FIG. 10 is a diagram illustrating transmission / reception of data packets during scanning by the wireless terminal according to Embodiment 1 of the present invention.

  The operation of the radio base station in the present invention will be described with reference to FIG. 1, FIG. 4, FIG. 5, and FIG.

  When transmitting a data packet from the wireless base station to the wireless terminal, the CPU 17 passes the Ethernet (registered trademark) frame input from the Ethernet (registered trademark) 16 that is an interface with the external network to the baseband processing unit 11. The baseband processing unit 11 includes a media access control (MAC) function such as carrier sense, and a modulation / demodulation function. The data packet modulated by the baseband processing unit 11 is sent out to the wireless transmission path by the high frequency unit 18.

  On the other hand, when the radio base station receives the packet, the CPU 17 passes the data packet demodulated by the baseband processing unit 11 to the Ethernet (registered trademark) 16.

  Next, an operation flow of the radio base station according to Embodiment 1 of the present invention will be described.

  In S101, when the wireless base station 100 is powered on or at any other time, the wireless base station 100 communicates with its surrounding wireless base stations 200 and 300 via its wired channel such as Ethernet (registered trademark). An ID (for example, an identifier such as a MAC address) is notified. As a result, each of the radio base stations 100 to 300 stores in the memory 13 a list in which the channels used by neighboring radio base stations and the number of radio base stations using the channels are specified.

  In step S102, the radio base stations 100 to 300 notify the subordinate radio terminals of the list. The list notified by the radio base station 100 includes one chB radio base station and one chC radio base station. The timing at which the radio base station 100 notifies the list may be any time.

  Next, when the radio base station 100 is notified in S103 that the subordinate radio terminal enters the scan mode, in S104, the radio terminal ID (for example, an identifier such as a MAC address) A copy of the data packet addressed to the wireless terminal is broadcast to the surrounding wireless base stations 200 and 300 via a wire such as Ethernet (registered trademark).

  Next, an operation flow of surrounding radio base stations will be described. Here, as shown in FIG. 1, an example will be described in which a wireless terminal to be scanned first transmits a probe request packet to the wireless base station 200.

  The wireless terminal that received the probe request packet from the wireless terminal in S202 out of the neighboring wireless base stations 200 and 300 that received the wireless terminal ID and the data packet addressed to the wireless terminal in S201 in S201. In step S203, the base station 200 performs carrier sense on the wireless transmission path and returns a probe response packet to the wireless terminal. Thereafter, in S204, the radio base station 200 receives an ACK from the radio terminal.

  Next, in step S205, the radio base station 200 performs carrier sense on the radio transmission path. If the channel change request is received from the radio terminal in step S206, the radio base station 200 ends the scan process for the radio terminal in step S213. To do.

  On the other hand, if a channel switching request from the wireless terminal is not received in S206, the following processing is performed. When the radio base station 200 receives a data packet from the radio terminal in S207, a reception process is started in S208.

  On the other hand, if the data packet from the wireless terminal is not received in S207 and the data packet addressed to the wireless terminal transferred from the wireless base station 100 is held in S209, wireless transmission is performed in S210. Carrier sense the path and transmit a data packet to the wireless terminal. Thereafter, if an ACK is received from the wireless terminal in S211, the sequence number transfer unit 12 of the wireless base station 200 transmits the sequence number of the data packet that has been transmitted to the peripheral wireless via a wire in S212. Notify the base stations 100 and 300. The packet discarding unit 14 of the neighboring radio base stations 100 and 300 that has received the sequence number discards the data packet of the corresponding number.

  In this embodiment, the example in which the data packet is transmitted to the wireless terminal after the ACK returned from the wireless terminal in response to the probe response packet has been described. However, the data packet to be transmitted is multiplexed in the probe response packet. May be.

  Next, the operation of the wireless terminal according to the present invention will be described with reference to FIGS.

  When transmitting a data packet from a wireless terminal, a host CPU ahead of the external interface passes a data frame input from an external interface such as a PC card slot to the baseband processing unit 01. The baseband processing unit 01 includes a media access control (MAC) function such as carrier sense, and a modulation / demodulation function. The packet modulated by the baseband processing unit 01 is sent out to the wireless transmission path by the high frequency unit 05.

  On the other hand, when the wireless terminal receives the packet, the host CPU passes the data frame demodulated by the baseband processing unit 01 to the external interface.

  Next, an operation flow of the wireless terminal according to Embodiment 1 of the present invention will be described.

  In S001, the wireless terminal receives from the wireless base station 100 to which it belongs a list specifying the channels used by neighboring wireless base stations 200 and 300 and the number of wireless base stations using the channel. And stored in the memory 04. If the radio wave reception strength with the radio base station 100 to which it belongs deteriorates in S002, it notifies the radio base station 100 to which it belongs that it enters the scan mode in S003.

  The wireless terminal refers to the list in the memory 04 in S004, and if there is an unscanned channel in S005, switches to the unscanned channel in S007. On the other hand, if there is no unscanned channel, the wireless terminal terminates scanning in S006, switches to the original channel, performs a disconnection process with the wireless base station 100, and nearby wireless base stations 200, 300. Or whether to maintain the connection with the radio base station 100 is determined.

  When the wireless terminal switches to an unscanned channel in S007, it transmits a probe request packet in S008. Furthermore, the timer 03 is started.

  Next, at S009, there is a probe response from the radio base station 200 until the timer 03 reaches a predetermined minimum waiting time, and at S010, the same channel is used according to the list. In order to receive a probe response packet from another wireless base station in S012, until the timer 03 reaches a predetermined maximum waiting time in S011, stand by.

  In the example of FIG. 1, there is no other radio base station that uses the same channel as the radio base station 200. Therefore, in S014, until the timer 03 reaches a predetermined maximum waiting time in S014. The wireless base station 200 transmits or receives data packets.

  As described above, according to the radio base station and the radio terminal of the present invention, it is possible to transmit and receive data packets during scanning as shown in FIG. Furthermore, even if the wireless terminal switches the channel (wireless base station) and continues scanning, it can receive from subsequent packets.

  Note that all the embodiments described above can also be realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include all or part of the structure.

  The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

  Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI, or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

  Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology.

(Embodiment 2)
FIG. 7 is a flowchart showing the operation of the radio terminal according to Embodiment 2 of the present invention. The operation flow of the wireless terminal in the present invention will be described with reference to FIG. Since S301 to S309 are the same as those in the first embodiment, description thereof is omitted.

  There is a probe response from the radio base station 200 until the timer 03 of the radio terminal reaches a predetermined minimum waiting time in S309, and the memory 04 described in the first embodiment in S310. If there is no other radio base station using the same channel, the channel switching notification is transmitted to the radio base station 200, and the process immediately shifts to the next scan.

  On the other hand, if there is another radio base station using the same channel in S310 according to the list, in S012, the timer 03 reaches another predetermined maximum waiting time in S013. To receive a probe response packet from the wireless base station.

  As described above, according to the wireless terminal of the present invention, the time required for scanning can be shortened.

  Note that all the embodiments described above can also be realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include all or part of the structure.

  The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

  Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI, or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

  Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology.

  The communication method and apparatus (wireless terminal and wireless base station) according to the present invention are useful for applications that require delay guarantee such as VoIP.

A diagram showing a wireless network such as a wireless LAN The figure which shows the operation | movement of the active scan of IEEE802.11. The figure which shows the delay of the data packet by the active scan of IEEE802.11. Flow chart showing operation of radio base station in embodiment 1 of the present invention (part 1) Flow chart showing operation of radio base station in embodiment 1 of the present invention (part 2) Flowchart showing the operation of the wireless terminal in Embodiment 1 of the present invention Flowchart showing the operation of the wireless terminal in Embodiment 2 of the present invention The block diagram which shows the internal structure of the wireless base station in this invention The block diagram which shows the internal structure of the radio | wireless terminal in this invention The figure which shows transmission / reception of the data packet during the scanning of the radio | wireless terminal in this invention

Explanation of symbols

100 radio base station (ch A)
200 nearby radio base stations (ch B)
201 Nearby wireless base stations (ch B)
202 Nearby wireless base stations (ch B)
300 nearby radio base stations (ch C)
01 Baseband processing unit (wireless terminal)
02 Scan unit 03 Timer 04 Memory (wireless terminal)
05 High frequency section (wireless terminal)
11 Baseband processor (radio base station)
12 Sequence number transfer unit 13 Memory (radio base station)
14 Packet discard unit 15 Packet buffer 16 External interface (Ethernet (registered trademark))
17 CPU
18 High-frequency section (radio base station)

Claims (9)

A wireless terminal in a wireless communication system comprising a plurality of wireless base stations connected to each other by wire or wireless and a wireless terminal that performs communication while changing a connection-destination wireless base station by handover processing,
Channel information receiving means for receiving channel information of other wireless base stations from the connected wireless base station;
A scan control means for ending the scan of the channel when receiving a probe response from all the radio base stations using the channel being scanned included in the use channel information during the scan operation of the handover process; Wireless terminal equipped with. A wireless terminal in a wireless communication system comprising a plurality of wireless base stations connected to each other by wire or wirelessly and a wireless terminal that performs communication while changing a connection-destination wireless base station by handover processing,
Channel information receiving means for receiving channel information of other wireless base stations from the connected wireless base station;
Data packet transmitting means for transmitting a data packet on the channel when a probe response is received from all the radio base stations using the channel being scanned included in the used channel information during the scanning operation of the handover process And a wireless terminal. A wireless base station in a wireless communication system comprising a plurality of wireless base stations connected to each other by wire or wireless and a wireless terminal that performs communication while changing a connection-destination wireless base station by handover processing,
Transfer data receiving means for receiving a data packet addressed to the wireless terminal;
A wireless base station comprising transfer data transmission means for transmitting a data packet addressed to the wireless terminal to the wireless terminal during the scanning operation of the handover process by the wireless terminal. The radio base station according to claim 3, wherein the transfer data transmission unit transmits a data packet addressed to the radio terminal after receiving an ACK (Acknowledgement) for the probe response packet transmitted to the radio terminal. The radio base station according to claim 3, wherein the transfer data transmitting means multiplexes and transmits a probe response packet with a data packet addressed to the radio terminal. 4. The radio base station according to claim 3, further comprising sequence number notifying means for transmitting a sequence number of a data packet that has been transmitted to the radio terminal to another radio base station. The radio base station according to claim 6, further comprising: a data packet discarding unit that discards a data packet with the sequence number when the radio base station receives the sequence number that has been transmitted from another radio base station. . When the wireless base station starts handover processing from a state in which the wireless base station is connected to and communicates with the own wireless base station, the wireless base station forwards a data packet addressed to the wireless terminal to another wireless base station. The radio base station according to claim 3, further comprising means. The radio base station is
Own station information notifying means for transmitting the own station ID and used channel information to other radio base stations;
Other station information storage means for storing use channel information of other radio base stations received from other radio base stations;
The other station information notifying means for transmitting the channel information of the other radio base station to the radio terminal when the radio terminal is connected to and communicates with the own station. Radio base station.

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