JP2005236555A - Radio terminal, radio base station, and network system using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a handover free of a momentary break and to realize communication free of quality deterioration by efficiently transferring packets which are buffered during transfer. <P>SOLUTION: A radio terminal has a wireless interface which can be connected to a radio base station. Provided is a movement notification means of transmitting a movement notice packet to a radio base station which is connected before a handover through a radio base station which is connected before the handover when the handover is carried out. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radio terminal, a radio base station, and a network system using them for realizing uninterrupted handover in a mobile communication network using a plurality of wireless LAN base stations (access points).

  Conventionally, layer 2 transfer for transferring a packet by a layer 2 address (MAC address) is used as a route selection method of a wireless communication network. In layer 2 forwarding, packets are forwarded by the destination MAC address of the packet, so that handover can be performed without disconnection of higher layer connections such as IP (internet protocol) and the like even at the time of handover. (See Non-Patent Documents 1 and 2).

  FIG. 8 illustrates and describes a configuration example of a layer 2 transport network using a plurality of wireless LAN base stations. A GW (gateway) is a computer for connecting to another network such as the Internet. The SV (server) is a computer for storing information and sending the information to terminals in the network. BS0, BS1, BS2, BS3, BS4 and BS5 are wireless base stations (access points) connected to each other by wire or wirelessly. The base station has a layer 2 switch function, and transfers packets on the network according to the address table on the base station. MT0 and MT1 are wireless terminals. The layer 2 transport network has a tree structure with the GW at the top, and there is no loop in the path, so that packets do not fall into an infinite loop on the path. The wireless terminals MT0 and MT1 measure the received signal strength from the connected base station, and when the received power strength falls below a certain threshold, disconnect the line, search for another base station, and reconnect. Performing a handover.

FIG. 9 illustrates a conceptual diagram of a packet flow at the time of handover of a wireless LAN terminal in a layer 2 transport network. In FIG. 9, SV is a server, BS0, BS1, BS2, BS3, and BS4 are radio base stations (access points) each having a layer 2 switch function, and MT is a terminal. FIG. 9 shows a state in which a packet is transferred from the server SV to the terminal MT. More specifically, FIG. 9A shows a state before the terminal moves, and FIG. 9B shows a state immediately after the terminal moves. (See Non-Patent Document 2). After moving, the terminal MT broadcasts a movement notification packet to all base stations / terminals in the network via the base station BS1. As a result, the address table on the base station through which the movement notification packet has passed is updated, and packets transmitted from the server SV thereafter are transferred based on the new route information (see Non-Patent Document 1).
Manabu Kanazawa, Satoshi Suzuki, Takashi Kameda, Shinji Ueda, Hiroyuki Nakase, Kazuo Tsubouchi, "Layer 2 Transport Suitable for Wireless Networks", Internet Conference 2001 (IC2001) Proceedings, pp.67-75, 2001 Takashi Kameda, Gakushi Kanazawa, Daisuke Komaba, Keigo Kana, Hiroyuki Nakase, Kazuo Tsubouchi, "Layer 2 Transport Network for Mobile Communications", IEICE Technical Report, IA2003-4, pp.19-24, May 2003

  However, when the sliding window protocol used in TCP (transmission control protocol) is used, in a steady communication state, as shown in FIG. A large number of packets flow from the server SV to the network at a time according to the size. If there is a difference in the transmission speed between the line between the server SV and the radio base station BS0 and the line between the radio base station BS0 and the radio terminal MT, and the transmission speed of the line between the radio base station BS0 and the radio terminal MT is small, the radio Packets accumulate in the base station BS0. Then, when handover occurs before the packets accumulated in this way are transmitted to the terminal MT and the line between the base station BS0 and the terminal MT is disconnected, the accumulated packets as shown in FIG. Does not reach the base station BS0.

  Further, when the base station BS4 is congested on the network path, for example, packets are accumulated in the radio base station BS0 even when the packet arrival at the base station BS0 is delayed from the handover time, and FIG. Thus, the accumulated packet does not reach the terminal MT and remains accumulated in the base station BS0. In the state where packets are accumulated in the base station BS0 as shown in FIG. 9B, the ACK (response) packet to be transmitted when the terminal MT receives the accumulated packets is not transmitted to the server SV. Even if the address table of each base station is rewritten to the correct path information state by the notification packet, the unreachable packet is not retransmitted from the server SV until the TCP retransfer timeout time elapses. From the above, when the terminal moves, the throughput significantly deteriorates.

  Similarly, in UDP (user datagram protocol), the unreachable packet is not retransmitted because the line is switched before the packet arrives at the terminal, resulting in a packet loss. As described above, the throughput deteriorates when the terminal moves.

  Further, when the moving speed of the terminal MT is relatively high, the received power value fluctuates greatly, and a handover occurs at an incorrect timing by only one received power measurement. Through this useless handover, the throughput is lowered.

  The present invention has been made paying attention to the above circumstances, and its first object is to realize means for efficiently transferring packets accumulated in the base station, and to solve the problem of deterioration in throughput even during handover. Is to give. The second object is to provide means for controlling the handover in accordance with the moving state of the terminal, thereby reducing the wasteful handover and solving the problem of the degradation of the throughput.

  In order to achieve the above object, in the first aspect of the present invention, when performing a handover in a radio terminal having a radio interface connectable to a radio base station, via a radio base station connected after the handover, There is provided a wireless terminal comprising a movement notification means for transmitting a movement notification packet to a wireless base station connected before handover.

  In the second aspect of the present invention, in a radio terminal having a radio interface connectable to a radio base station, an apparatus for measuring the received power intensity of a transmission signal from a connection base station of the radio terminal, and the received power There is provided a wireless terminal comprising a value storage device and a function of performing a threshold determination using a plurality of received power values stored by the storage device and determining a handover.

  Further, in the third aspect of the present invention, in a wireless terminal having a wireless interface connectable to a wireless base station, a storage device for past handover history of the wireless terminal, and a received power threshold value that determines execution of handover from the handover history There is provided a wireless terminal comprising a handover threshold determination means for determining

  Moreover, in the 4th aspect of this invention, the radio | wireless terminal with the characteristic which has the said 1st and 2nd function simultaneously is provided.

  And in the 5th aspect of this invention, the radio | wireless terminal with the characteristic which has the said 1st and 3rd function simultaneously is provided.

  Furthermore, according to a sixth aspect of the present invention, there is provided a wireless terminal having a feature having the first to third functions at the same time.

  In the seventh aspect of the present invention, a total of two or more interfaces including at least one of one or more wireless interfaces and one or more wired interfaces, and a terminal capable of communicating via each interface and the interface In a wireless base station having a layer 2 switch function capable of performing path control based on a MAC address using the layer 2 address table storing the relationship with the MAC address of the base station and the address table, a movement notification packet is transmitted. A function to change the address table based on the received information, and if the movement notification packet received thereafter is addressed to the base station, the packet addressed to the terminal is updated according to the address table updated by the movement notification packet. Transfer function and received movement notification packet In the case of non-addressed base station, a radio base station, characterized in that it comprises a and a function of transferring a movement notification packet received according to the updated address table is provided.

  Furthermore, in the eighth aspect of the present invention, a wireless base station including a wireless base station having the function of the seventh aspect, a gateway for connecting to another network, and a server for transmitting information to the terminal are wired. Or a wirelessly connected terminal arranged in a tree structure, including a wireless terminal having the characteristics of any one of claims 1, 4, 5 and 6, and a base station connected by a wireless line, and the terminal is connected to another terminal in the network. A network system that enables communication with computers in other networks via a terminal, a server, or a gateway is provided.

  According to the present invention, it is possible to efficiently transfer a buffered packet at the time of transfer, so that it is possible to realize an uninterrupted handover, and a wireless terminal, a wireless base station, and a wireless terminal that realize communication without quality degradation. The used network system can be provided.

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

  FIG. 1 shows and describes the configuration of a wireless terminal according to the first embodiment of the present invention.

  As shown in FIG. 1, the wireless terminal includes a transceiver unit 1, a signal processing unit / input unit / display unit 2, and a movement notification packet generator 3. The movement notification packet generator 3 includes a handover completion detection unit 3a, a movement notification packet generation unit 3b, and a movement history storage unit 3c.

  That is, the wireless terminal is a wireless terminal having a transceiver unit 1 as a wireless interface connectable to a wireless base station (not shown), and performs handover by way of the wireless base station connected after the handover when performing handover. It is characterized by comprising a movement notification packet generator 3 that transmits a movement notification packet to a previously connected radio base station.

  Hereinafter, the operation of the movement notification packet generator 3 will be described in detail with reference to the flowchart of FIG. When the movement notification packet generator 3 of the wireless terminal detects that the handover is completed from the signal from the transmitter / receiver unit 1 (step S1), the movement notification packet generation unit 3b uses the wireless base station connected before the movement. A movement notification packet destined for the station MAC address is generated and sent to the transceiver unit 1 (step S2).

  The wireless terminal is a wireless terminal having a wireless interface connectable to the wireless base station, a device for measuring the received power intensity of a transmission signal from the connected base station of the wireless terminal, a storage device for the received power value, A configuration may be provided in which a threshold is determined using a plurality of received power values stored in the storage device and a handover is determined. Alternatively, in a wireless terminal having a wireless interface connectable to a wireless base station, a storage device for past handover history of the wireless terminal, and a handover threshold determining means for determining a received power threshold for determining handover execution from the handover history It is good also as composition to do.

  Next, FIG. 3 shows and describes the configuration of a radio base station according to the second embodiment of the present invention.

  As shown in FIG. 3, the radio base station includes a transceiver unit 5, a signal processing unit / input unit / display unit 6, and a movement notification packet control device 4. The movement notification packet control device 4 includes a movement notification packet processing unit 4a and an address table 4b.

  In this radio base station, the function of receiving the movement notification packet and changing the address table based on the information is updated, and the movement notification packet received thereafter is updated by the movement notification packet when it is addressed to the base station. It has a function of transferring a packet addressed to the terminal according to the address table and a function of transferring the received movement notification packet according to the updated address table when the received movement notification packet is not addressed to the base station.

  Hereinafter, the operation of the movement notification packet control device 4 will be described in detail with reference to the flowchart of FIG. When it is detected that the transceiver unit 5 has received the movement notification packet (step S11), the movement notification packet processing unit 4a updates the address table 4b in accordance with the source MAC address (step S12). Next, when the destination MAC address is addressed to the own base station (step S13), the accumulated packets are transferred to the terminal based on the route information in the updated address table (step S15). If the destination MAC address is other than the destination base station, the received movement notification packet is transferred to the interface to which the destination MAC address is connected according to the address table 4a (step S14).

  Next, FIGS. 5A to 5D are conceptual diagrams of a network system according to the third embodiment of the present invention, and the operation thereof will be described.

  In FIGS. 5A to 5D, SV is a server. MT0 is a wireless terminal having the characteristics of the first embodiment described above. BS0, BS1 and BS2 are radio base stations (access points) each having the layer 2 switch function and the characteristics of the second embodiment described above. The base station BS0 is a radio base station connected before the movement of the terminal MT0, and the base station BS1 is a radio base station connected after the movement. 5A to 5D show a state in which a packet is transferred from the server SV to the terminal MT0. Hereinafter, the operation will be described in detail.

  In FIG. 5A, first, it is assumed that the radio terminal MT0 is connected to the radio base station BS0 via a radio channel and is in a steady state. At this time, a large number of packets are transmitted from the server SV to the mobile station based on the TCP window size notified from the wireless terminal MT0. In FIG. 5B, when the radio terminal MT0 is moving away from the radio base station BS0 and the reception power falls below the reception power threshold, the radio terminal MT0 stops the connection with the radio base station BS0 and increases the reception power. Search for the base station you have. When the wireless terminal MT0 disconnects from the wireless base station BS0, a large amount of packets sent to the wireless terminal MT0 remain in the wireless base station BS0.

  In FIG. 5C, after the wireless terminal MT0 is connected to the wireless base station BS1 which is a new connection destination, the movement notification packet is transferred to the wireless base station BS0 connected before the movement. In the meantime, since it is transferred in the order of BS 1 → BS 2 → BS 0, the address table on the radio base stations BS 1, BS 2, BS 0 is rewritten, and the new route information of the radio terminal MT 0 is recognized by each base station. In FIG. 5 (d), using this movement notification packet as a trigger, the packet buffered in the radio base station BS0 is transferred to the radio terminal MT0 via the radio base station BS1 in accordance with the route information of the updated address table. Packets from the server SV also reach the radio terminal MT0 via the radio base station BS1 according to the updated route information in the address table.

  Next, FIG. 6 shows and describes the configuration of a wireless terminal according to the fourth embodiment of the present invention.

  As shown in FIG. 6, the wireless terminal includes a transceiver unit 1, a signal processing unit / input unit / display unit 2, and a handover control unit 7. The handover control device 7 includes a received power measuring unit 7a, a handover control unit 7b, a movement history storage unit 7c, and a received power history storage unit 7d.

  In such a configuration, the wireless terminal measures the received signal strength by the received power measuring unit 7a based on the transmitted received signal. The handover control unit 7b determines the handover timing based on the current received signal strength, the past received power information from the received power history storage unit 7d, and the movement frequency information from the movement history storage unit 7c.

  Hereinafter, the operation of the handover control device 7 will be described with reference to the flowchart of FIG.

  Under the initial state (step S21), the received power measuring unit 7a measures the received power Pin at the current time and stores it in the received power history storage unit 7d (step S22).

  The handover control unit 7b first derives a received power value variable Pin 'that has undergone a certain calculation from the received power history (step S23). For example, Pin ′ is calculated as shown in Equation (1) using the received power Pin (n) n unit times before the current time and the forgetting factor α (0 <α <= 1).

Pin '= Pin (0) + Σ _n α ⁿ {Pin (n) −Pin (0)} (1)
Next, the handover control unit 7b obtains the number of movements F per unit time based on the information in the movement history storage unit 7c (step S24). The power threshold value Pth for handover is determined by the following formula (2) or formula, depending on the number of movements F, the reference threshold value Pdef, the fluctuation threshold width Pf, the coefficient β (β> = 1), and the coefficient γ (0 <= γ <= 1). Calculated as one of (3).

Pth = Pdef + β ^F Pf (2)
Pth = Pdef + γF x Pf (3)
The above Pin 'and Pdef values are
Pin '<Pth (4)
If the above relationship is satisfied (step S26), a handover instruction is sent to the transceiver unit 1 and the handover is executed (step S27). If the above relationship is not satisfied, the process returns to step S22 and the above operation is repeated.

  By adding such a function to a radio terminal and a radio base station, inter-cell handover without data loss becomes possible.

  As described above, according to the embodiment of the present invention, it is possible to realize an uninterrupted handover by efficiently transferring a buffered packet at the time of transfer, and communication without quality degradation. It is possible to provide an uninterrupted handover wireless terminal, a wireless base station, and a network system using them.

  That is, according to the embodiment of the present invention, as shown in FIG. 5, packets accumulated in the base station BS0 to which the terminal was connected before moving are transferred to the terminal MT via the connected base station BS1 after moving. A radio base station having a function of performing packet transfer between base stations to be transferred can be provided.

  Further, in order to achieve the purpose of controlling the handover in accordance with the moving state of the terminal and thereby providing a means for solving the problem of throughput degradation by reducing unnecessary handover, the received power history, the handover An uninterrupted handover wireless terminal having a handover determination function using a frequency history is provided.

  In addition, according to the above-described embodiment of the present invention, it is possible to realize a wireless LAN terminal controlling handover timing in accordance with the movement state of the terminal, thereby reducing unnecessary handover and improving throughput. Is possible.

  In view of the purpose of realizing efficient transfer of packets accumulated in the base station and providing a means for solving the problem of throughput degradation even during handover, efficient transfer of packets accumulated in the base station is performed. As a result, it is possible to perform handover without interruption without degradation of throughput even during handover.

  The embodiment of the present invention has been described above, but the present invention is not limited to this, and it is needless to say that various improvements and modifications can be made without departing from the spirit of the present invention. For example, a technical idea as a network control method using a wireless terminal, a wireless base station, and a network system using the wireless terminal having the above-described features is also included.

The block diagram of the radio | wireless terminal which concerns on the 1st Embodiment of this invention. 6 is a flowchart for explaining in detail the operation of the movement notification packet generator 3; The block diagram of the wireless base station which concerns on the 2nd Embodiment of this invention. 7 is a flowchart for explaining in detail the operation of the movement notification packet control device 4; The conceptual diagram of the network system which concerns on the 3rd Embodiment of this invention. The block diagram of the radio | wireless terminal which concerns on the 4th Embodiment of this invention. 7 is a flowchart for explaining the operation of the handover control device 7 in detail. The figure which shows the structural example of the layer 2 transport network which concerns on the prior art using several wireless LAN base station. The conceptual diagram of the flow of the packet at the time of the hand-over of a wireless LAN terminal in the layer 2 transport network which concerns on a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Transmitter-receiver part, 2 ... Signal processing part, input part, display part, 3 ... Movement notification packet generator, 4 ... Movement notification packet generator, 5 ... Handover control apparatus.

Claims (8)

In a wireless terminal having a wireless interface connectable to a wireless base station,
A wireless terminal comprising a movement notification means for transmitting a movement notification packet to a wireless base station connected before a handover via a wireless base station connected after the handover when performing a handover. In a wireless terminal having a wireless interface connectable to a wireless base station,
An apparatus for measuring the received power intensity of a transmission signal from a connection base station of the wireless terminal;
A storage device for the received power value;
A wireless terminal comprising a function of performing threshold determination using a plurality of received power values stored in the storage device and determining a handover. In a wireless terminal having a wireless interface connectable to a wireless base station,
A storage device for past handover history of the wireless terminal;
A wireless terminal comprising handover threshold determination means for determining a received power threshold for determining execution of a handover from a handover history.   A wireless terminal having a feature having the functions of claim 1 and 2 simultaneously.   A wireless terminal having the characteristics of the functions of claims 1 and 3 simultaneously.   A wireless terminal having the characteristics of the functions of claims 1, 2 and 3 simultaneously. A total of two or more interfaces by at least one of one or more wireless interfaces and one or more wired interfaces;
A layer 2 address table storing the relationship between each interface and the MAC address of a terminal or base station that can communicate via the interface;
In the radio base station having a layer 2 switch function capable of performing path control by MAC address using the address table,
The function of receiving the movement notification packet and changing the address table based on the information, and if the movement notification packet received thereafter is addressed to the base station, the terminal according to the address table updated by the movement notification packet And a function of transferring a packet sent to the mobile station and a function of transferring the received packet of the mobile notification according to the updated address table when the received mobile report packet is not addressed to the base station. base station. A radio base station including a radio base station having the function of claim 7;
A gateway to connect to other networks,
The server that sends the information to the terminal
Wired or wirelessly connected and arranged in a tree structure, a terminal including a wireless terminal having the characteristics of any one of claims 1, 4, 5 and 6 is connected to a base station by a wireless line, and the terminal is connected to the network. A network system that enables communication with another network computer via another terminal, server, or gateway.

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