JP2006311253A - Handover method of wireless data communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable handover of a mobile terminal (MSS) in wireless data communication of a P-MP system with which a radio base station (BS) and the mobile terminal (MSS) communicate via a relay station (RS). <P>SOLUTION: (1) An MSS2 receives a neighboring BS advertisement message from an RS1-1 which is under connecting. (2) The MSS2 scans the neighboring BS, RS and obtains information of the neighboring BS, RS. (3) As a result of the scan, the MSS2 determines handover to an RS1-2 and transmits a handover (HO) request message which includes an identifer of the RS1-2 to a BS1 via the RS1-1. (4) The BS1 judges whether it is support enable at a handover point for request band and QoS of the MSS2 and transmits a handover confirm message if handover is possible. (5) The MSS2 transmits a handover indication message in which starting time of handover etc. is included to the BS1 via the RS1-1. (6) The MSS2 performs high-speed ranging processing with the RS1-2 of the handover point. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wireless data communication handover method, and more particularly, to a handover method suitable for P-MP wireless data communication via a relay station.

  Non-Patent Document 1 defines a standard for high-speed wireless data communication (IEEE802.16). The IEEE802.16 physical layer supports single carrier, OFDM (Orthogonal Frequency Division Multiplexing) and OFDMA (Orthogonal Frequency Division Multiple Access) as modulation schemes. Hereinafter, a wireless data communication method compliant with IEEE802.16 will be described by taking as an example a case where OFDM is used as a modulation method.

  IEEE 802.16 defines P-MP (point-to-multipoint) as one of the communication modes. In this P-MP, BS (radio base station) transmits and receives all SS (subscriber terminals). Scheduling opportunities enables efficient communication and guaranteed quality of service (QoS).

  FIG. 7 is a diagram showing an example of an OFDM frame configuration in the P-MP scheme, and is included in the broadcast message field in the first DL (downlink) burst following the preamble and FCH (Frame Control Header). Scheduling information is stored in the MAP message.

  In this scheduling information, downlink slot information and uplink slot information to be assigned to each SS are stored, and the SS receives these pieces of information to determine when the data for itself arrives and You can know when to send data. Hereinafter, the MAP message included in the broadcast message field in the first DL burst following the FCH is simply expressed as a MAP message.

  Each BS is given a 48-bit unique identifier called Base Station ID (BSID), and the SS identifies each BS by BSID. The upper 24 bits of the BSID identify the business operator, and each BS is identified by the lower 24 bits within the same business operator.

  FIG. 8 is a diagram showing a frame structure of a MAC (Media Access Control) header defined by IEEE 802.16. A connection ID for uniquely identifying a connection is given to each connection. A space for this connection ID is prepared in the MAC header of IEEE802.16, and BS and SS identify a packet by this connection ID.

  The SS performs a process called ranging in order to adjust the transmission / reception timing and transmission power with the BS when joining the network and periodically after joining. When joining the network, ranging is performed during the initial ranging period assigned by the BS. The initial ranging period is contention-based, and the SS transmits an RNG-REQ (ranging request) message to the BS during this period. If the BS that received the RNG-REQ needs to adjust the SS, information such as the transmission output, frequency, and transmission timing is sent to the RNG-RSP with a ranging continuation notification (Ranging Status = continue in the RNG-RSP). Register to the (ranging response) message and respond to the SS.

  The SS that has received the ranging continuation notification RNG-RSP adjusts the transmission output, frequency, and transmission timing, and then transmits the RNG-REQ to the BS again in the initial ranging period allocated from the BS to the SS. When the transmission output of the SS satisfies a preset value, the BS returns an RNG-RSP with a ranging success notification (Ranging Status = success in the RNG-RSP) to the SS.

  Such ranging ends when an RNG-RSP accompanied by a ranging success notification is received by the SS. The ranging performed after the SS participates in the network is performed in the same initial ranging period as in the network participation or the initial ranging period allocated for the SS.

  The BS transmits data to the SS using a burst profile described in “Downlink Operational Burst Profile” of RNG-RSP. SS transmits data to BS using burst profile described in UIUC of UL-MAP. The burst profile described in UIUC of this UL-MAP is specified by BS. Here, the burst profile is a parameter set such as a modulation scheme or FEC code type.

  On the other hand, while Non-Patent Document 1 described above is intended for a stationary SS, Non-Patent Document 2 uses some of the same physical layer and MAC layer as Non-Patent Document 1 while using several new By adding a simple message, the standard for high-speed wireless data communication for mobile SS (MSS) is defined, which is called IEEE802.16e (hereinafter referred to as 802.16e).

  In IEEE802.16e, the current BS (serving BS) broadcasts information (frequency, etc.) of neighboring BSs (neighboring BSs) as neighboring BS advertisement messages, and MSS can easily scan these neighboring BSs. As a result of scanning, it is possible to hand over to the optimal BS. Here, the serving BS can acquire information on the neighboring BS by transmitting a scan report including the BSID and CINR (Carrier-to-Interference-Noise Ratio) of the neighboring BS to the serving BS. .

  Hereinafter, in the network topology shown in FIG. 9, the procedure when the MSS 2 communicating with the BS 3 hands over to the BS 4 according to the IEEE 802.16e standard will be described along the sequence flow of FIG.

Procedure 1: MSS2 receives neighboring BS information from BS3 which is a serving BS.
Procedure 2: MSS2 starts scanning neighboring BS.
Procedure 3: MSS3 that has decided to execute handover transmits a handover (HO) request message to BS3. This message includes the handover destination BSID (here, BS4 BSID).
Procedure 4: BS3 that has received the handover request message transmits a handover pre-notification message to BS4. This message includes the identifier of the MSS2 requesting handover, the parameters of the connection held by the MSS2, the bandwidth and QoS parameters required for the MSS2.
Procedure 5: BS4 that has received the handover advance notification message returns it to BS3 with a prior notification response message. This message includes information such as whether QoS necessary for MSS2 can be supported.
Procedure 6: BS3 that has received the advance notification response message transmits a handover confirmation message for handover to BS4, and transmits a handover response message to MSS2. The handover response message includes the BS4 BSID, the number of CIDs held in the MSS2, and the new CID in the BS4 corresponding to the CID in the BS3.
Procedure 7: The MSS2 that has received the handover response message transmits a handover indication message to the BS3 to start the handover. This message includes a handover start time and the like.
Procedure 8: MSS2 completes the handover by executing a high-speed ranging process with BS4.
IEEE Standard for Local and metropolitan area networks-Part 16: Air Interface for Fixed Broadband Wireless Access Systems, IEEE 802.16 -2004, Oct, 2004. Draft IEEE Standard for Local and metropolitan area networks-Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems, IEEE P802.16e / D5a, Dec. 02, 2004.

  In wireless data communication, there is a dead zone where the MSS cannot communicate with the BS even though the MSS is in the service area due to the influence of radio wave attenuation caused by shielding by obstacles located between the transmitting and receiving antennas. In order to perform high-speed wireless data communication, it is necessary to use a high frequency. However, since the wavelength is short and the straightness of radio waves increases, it is expected that the dead zone will increase. As a method for eliminating such a dead zone, a method is considered in which a relay station (Relay Station) is installed between the BS and the MSS, and the BS and the MSS communicate via the RS. However, when an RS is added to a P-MP wireless data communication system, the MSS cannot be handed over from the currently communicating RS or BS to another RS or BS.

  The object of the present invention is to solve the above-mentioned problems of the prior art, in P-MP wireless data communication in which a wireless base station (BS) and a mobile terminal (MSS) communicate via a relay station (RS). It is to enable handover of a terminal (MSS).

In order to achieve the above object, the present invention provides a handover method in P-MP wireless data communication in which a plurality of mobile terminals are connected directly to one wireless base station or indirectly through a relay station. The method includes the following procedure.
(1) A procedure in which a radio base station recognizes a neighboring relay station, a procedure in which the radio base station assigns a unique identifier (BSID) to each recognized relay station, and a relay station in communication with a mobile terminal A procedure for providing information including at least an identifier of each station to the mobile terminal regarding a radio base station or relay station adjacent to the mobile station, and a procedure for the mobile terminal searching for a handover destination based on the provided information; The mobile terminal determines a handover destination based on the search result, the mobile terminal transmits a handover request including a handover destination identifier to the radio base station, and the radio base station A procedure of transmitting a handover confirmation message including the identifier of the mobile terminal to the determined handover destination; and the radio base station identifies the handover destination to the mobile terminal. A procedure for transmitting a handover confirmation message including an identifier, a procedure for the mobile terminal to transmit a handover indication message to the radio base station via the relay station, and the mobile terminal and the handover destination And a procedure for executing the process.
(2) The radio base station that has received the handover request from the mobile terminal further determines whether the handover destination is another radio base station or its subordinate, and the handover destination is another radio base station or its radio And a procedure for transmitting a handover pre-notification message including information on the mobile terminal that has transmitted the handover request to the other radio base station, and a handover pre-notification response message returned in response to the handover pre-notification message And a procedure for determining whether or not the requested handover is possible based on the handover advance notification response message, and when the handover is determined to be possible, A handover confirmation message including a terminal identifier is transmitted to the handover destination. That.
(3) The radio base station assigns an identifier unique to the number of hops from the own station to each relay station.
(4) The mobile terminal recognizes the number of hops from the radio base station to each station based on the identifier of each station, and preferentially determines a station with a small number of hops as a handover destination.

According to the present invention, the following effects are achieved.
(1) In P-MP wireless data communication, reliable handover is possible even in an environment where a wireless base station and a mobile terminal communicate indirectly via a relay station.
(2) Handover is possible even if the handover destination is another radio base station different from the currently connected radio base station or a relay station under the radio base station. Also, if the handover destination is a relay station under the currently connected radio base station, compared to the case where the handover destination is a relay station under another radio base station different from the currently connected radio base station, The amount of control messages can be reduced.
(3) Since the identifier assigned to each relay station by the radio base station is a value unique to the number of hops from the radio base station, the mobile terminal uses the positional relationship between the radio base station and each relay station as the identifier of each relay station. Can be recognized based on.
(4) When the mobile terminal determines the handover destination, the number of hops between the radio base station and the relay station can be recognized based on the identifier of each relay station. This makes it possible to easily select the optimum relay station.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating an example of a P-MP network configuration to which a handover method according to the present invention is applied. Within a radio wave reach of a radio base station (BS1), two relay stations (RS1- 1, RS1-2) is located, and the relay station (RS2-1) is located within the radio wave reach of the radio base station (BS2).

  FIG. 2 is a diagram showing the configuration of the BSID assigned to the BS and each RS in the present embodiment, and the upper 24 bits of the BSID expressed by all 48 bits is an operator ID, and this operator ID is excluded. Of the remaining 24 bits, the upper 21 bits represent a domain, and BSs or RSs having the same upper 21 bits are defined as “within the same BS domain”. The lower 3 bits of the BSID assigned to the BS are all “0”, and the lower 3 bits of the BSID assigned to each RS are other than that. Allocation of BSID to each RS is done automatically by BS.

  The remaining 24 bits excluding the BSID operator ID [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0] (for example, BS1 in FIG. 1) [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] The address value is incremented by “1” for the RS first connected to the own station (for example, RS1-1 in FIG. 1). 0 0 1 0 0 1] is assigned, and this address is stored as an assigned address in a table or the like. Next, when the RS (for example, RS1-2 in FIG. 1) is connected, the table is referred to, and the value of the latest assigned address is further incremented by “1” [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0] is assigned to the RS.

  When the mobile terminal (MSS) hands over the connection destination from the current BS or RS to another BS or RS, the BS or RS in the same BS domain as the current connection destination BS is the BSID. A handover request message including the lower 3 bits of is used as an identifier. MSS performs handover to the same BS domain by comparing the upper 21 bits of the remaining 24 bits excluding the operator ID between the BS and RS of the current connection destination BS or RS and the BSID of the handover destination BS or RS. It is determined whether or not.

  Next, in the network topology shown in FIG. 1, the procedure when the MSS 2 communicating with RS 1-1 hands over to RS 1-2 will be described along the sequence flow of FIG.

Procedure 1: MSS2 receives a neighbor BS advertisement message from the connected RS1-1.
Procedure 2: MSS2 scans neighboring BSs and neighboring RSs. Here, the RS 1-1 receives information on the neighboring BSs and neighboring RSs by receiving a scan report including the neighboring BSs and the BSIDs and CINRs of neighboring RSs from the MSS2.
Procedure 3: When MSS2 determines the handover to RS1-2 as a result of the scan, MSS2 transmits a handover (HO) request message including the lower 3 bits of the BSID of RS1-2 as an identifier to BS1 via RS1-1.
Procedure 4: When BS1 receives the handover request message, BS1 determines whether the requested bandwidth and QoS of MSS2 can be supported by the handover destination BS (that is, its own) or RS, and if handover is possible, MSS sends the MSS to the handover destination RS. A handover confirmation message including an identifier is transmitted. When the handover destination is the BS itself, the handover confirmation message need not be transmitted. Also, the BS transmits a handover response message to MSS2. This message includes the lower 3 bits of the BSID of the handover destination (RS1-2).
Procedure 5: Upon receiving the handover response message, the MSS 2 transmits a handover indication message including the start time of the handover to the BS 1 via the RS 1-1.
Procedure 6: MSS2 executes high-speed ranging processing with the handover destination RS1-2, and the handover is completed.

  Next, in the network topology shown in FIG. 1, the procedure when MSS1 communicating with RS1-1 hands over to RS2-1 under the control of BS2 with a different BS domain from BS1 is shown in the sequence flow of FIG. It explains along. MSS1 determines that handover is in a different BS domain when the upper 21 bits of the remaining 24 bits excluding the operator ID of the RS1-1 BSID being connected and the RS2-1 BSID of the handover destination are not the same. To do.

Procedure 1: MSS1 receives a neighbor BS advertisement message from RS1-1.
Procedure 2: MSS1 scans adjacent BSs and RSs.
Procedure 3: When MSS1 determines handover to RS2-1 as a result of the scan, MSS1 transmits a handover request message to BS1 via RS1-1.
Procedure 4: BS1 that has received the handover request message transmits a handover pre-notification message to BS2 using a backbone network in which the BSs are connected by wire. This message includes the identifier of MSS1 requesting handover, the parameters of the connection held by MSS1, the bandwidth and QoS parameters required for MSS1, and the like.
Procedure 5: BS2 that has received the handover advance notification message returns to BS1 with a prior notification response message. This message includes information on whether or not QoS necessary for the MSS can be supported.
Procedure 6: A handover confirmation message including the identifier of MSS1 is transmitted from BS1 to RS2-1. BS1 transmits a handover response message to MSS1 via RS1-1.
Procedure 7: MSS1 sends a handover indication message to BS1.
Procedure 8: MSS1 completes the handover by executing a high-speed ranging process with the handover destination RS2-1.

  5 and 6 are diagrams schematically showing a BSID allocation method for each RS when data communication between the BS and the MSS is performed via a plurality of RSs. Of the 48-bit BSID, the remaining 18 bits, excluding the operator ID, are used for identifying the BS domain, and the lower 6 bits are used for identifying the RS. The lower 6 bits of the BSID assigned to the BS are all “0”.

  The BSID assigned to the RS located in the first hop from the BS is all “0” in the lower 3 bits of the lower 6 bits, and only the upper 3 bits are unique values according to the connection order to the BS. It becomes. In the BSID assigned to the RS located at the second hop from the BS, the upper 3 bits of the lower 6 bits are the same as the upper 3 bits of the lower 6 bits of the BSID of the RS of the first hop in the BS direction. Allocation of BSID to these RSs is also performed automatically by BS.

  For example, when considering a BS in which the remaining 24 bits excluding the BSID operator ID are [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0] (for example, BS1 in FIG. 5). ), BSID [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0] is assigned to the RS first connected to BS1 (for example, RS1-1 in FIG. 5). BSID [0 0 0 00 0 0 0 0 0 0 0 assigned to the next connected RS (for example, RS1-2 in FIG. 5) is obtained by incrementing the upper 3 bits of the lower 6 bits by “1”. 0 0 0 0 1 0 1 0 0 0 0] is automatically assigned.

  Also, in the RS connected to the RS (for example, RS1-1-1 connected to RS1-1 in FIG. 5), the upper 3 bits of the lower 6 bits are the same as the connected RS (RS1-1). BSID [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 1] in which the lower 3 bits are incremented by “1” is assigned. Similarly, BSID [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 1] is assigned to RS1-2-1 connected to RS1-2 in FIG.

  In this way, in this embodiment, the hierarchical connection state between the BS and each RS is expressed hierarchically as a part of the BSID, so the positional relationship between the BS and each RS can be determined by referring to the BSID of each RS. It becomes easy to recognize. Therefore, when selecting the connection destination immediately after starting MSS or when selecting the handover destination, even if the reception power of each candidate is within the preset allowable range and it is difficult to judge superiority or inferiority By referring to the candidate BSID, the RS closer to the BS or the BS itself can be preferentially selected as the connection destination.

  In the above-described embodiment, among the 48-bit BSIDs, the remaining 24 bits, excluding the operator ID, are used for the upper 18 bits for BS domain identification, and the lower 6 bits are used for relay station (RS) identification. Although described above, the present invention is not limited to this, and the number of bits allocated to the identification of the BS domain and the relay station may be appropriately changed according to the scale of the network, the number of accommodated terminals, and the like.

  The present invention has been described above with reference to preferred embodiments. However, the present invention is not necessarily limited to the above-described embodiments, and various changes can be made without departing from the concept of the present invention.

1 is a diagram illustrating a configuration of a P-MP network to which a handover system according to the present invention is applied. FIG. It is the figure which expressed typically the structure of BSID assigned to BS and each RS. 5 is a sequence flow showing an example of a handover procedure according to the present invention. It is the sequence flow which showed another example of the handover procedure which concerns on this invention. It is the figure which showed typically the allocation method of BSID to each RS in case the data communication between BS and MSS is performed via several RS. It is the figure which showed typically the allocation method of BSID to each RS in case the data communication between BS and MSS is performed via several RS. [Fig. 3] Fig. 3 is a diagram illustrating an example of an OFDM frame configuration in the P-MP scheme. FIG. 3 is a diagram illustrating a frame structure of a MAC header defined by IEEE 802.16. It is the figure which showed an example of the network topology to which IEEE802.16e is applied. It is the sequence flow which showed the handover procedure by IEEE802.16e.

Explanation of symbols

BS ... Radio base station
RS ... Relay station
SS: Subscriber terminal
MSS ... mobile terminal

Claims (4)

In a handover method in P-MP wireless data communication in which a plurality of mobile terminals are connected directly to one wireless base station or indirectly via a relay station,
A procedure for the wireless base station to recognize neighboring relay stations;
A procedure in which a radio base station assigns a unique identifier (BSID) to each recognized relay station;
A procedure in which a relay station communicating with a mobile terminal provides the mobile terminal with information including at least an identifier of each station regarding a radio base station or relay station adjacent to the mobile station;
A procedure for the mobile terminal to search for a handover destination based on the provided information;
A procedure in which the mobile terminal determines a handover destination based on the search result;
A procedure in which the mobile terminal transmits a handover request including an identifier of a handover destination to the radio base station;
A procedure in which the radio base station transmits a handover confirmation message including an identifier of the mobile terminal to the determined handover destination;
A procedure in which the radio base station transmits a handover confirmation message including a handover destination identifier to the mobile terminal;
The mobile terminal transmits a handover indication message to the radio base station via the relay station;
A handover method for wireless data communication, comprising: a procedure in which the mobile terminal and a handover destination execute the ranging process. The radio base station that has received the handover request from the mobile terminal further includes:
A procedure for determining whether the handover destination is another radio base station or its subordinate,
When the handover destination is another radio base station or its subordinate, a procedure for transmitting a handover pre-notification message including information on the mobile terminal that has transmitted the handover request to the other radio base station;
Receiving a handover advance notification response message returned in response to the handover advance notification message;
Determining whether the requested handover is possible based on the handover pre-notification response message,
The handover method of wireless data communication according to claim 1, wherein if it is determined that the handover is possible, a handover confirmation message including an identifier of the mobile terminal is transmitted to a handover destination.   3. The wireless data communication handover method according to claim 1, wherein the wireless base station assigns a unique identifier to the number of hops from the own station to each relay station.   The radio terminal according to claim 3, wherein the mobile terminal recognizes the number of hops from the radio base station to each station based on an identifier of each station, and preferentially determines a station with a small number of hops as a handover destination. Data communication handover method.

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