JP4788431B2 - Hard handover method in a mobile communication system having different frequency cells - Google Patents

Hard handover method in a mobile communication system having different frequency cells Download PDF

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JP4788431B2
JP4788431B2 JP2006082992A JP2006082992A JP4788431B2 JP 4788431 B2 JP4788431 B2 JP 4788431B2 JP 2006082992 A JP2006082992 A JP 2006082992A JP 2006082992 A JP2006082992 A JP 2006082992A JP 4788431 B2 JP4788431 B2 JP 4788431B2
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日出海 細部
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本発明は、移動通信システムにおいて異周波セル間をハンドオーバする方法に関する。   The present invention relates to a method for performing handover between different frequency cells in a mobile communication system.

従来、移動通信システムの異周波セル間のハンドオーバでは、現在、移動端末（ＵＥ：User Equipment）のセルの通信品質が、所定値以下でしかも隣接する異周波セルの通信品質が所定値以上であることを無線ネットワーク制御装置（ＲＮＣ：Radio Network Controller）が報告を受けると、制御装置は移動端末にその異周波セルへのハンドオーバ実行を指示する（例えば、非特許文献１参照）。   Conventionally, in handover between different frequency cells of a mobile communication system, the communication quality of a mobile terminal (UE: User Equipment) cell is currently not more than a predetermined value, and the communication quality of an adjacent different frequency cell is not less than a predetermined value. When a radio network controller (RNC) receives a report, the control device instructs the mobile terminal to execute a handover to the different frequency cell (for example, see Non-Patent Document 1).

図１は、従来の異周波セル間のハンドオーバのシーケンスを示す。移動端末から基地局を介して無線ネットワーク制御装置に、一定以上の通信品質を持つ異周波セルを報告する。制御装置は、基地局に、報告された異周波セルの無線リソース確保を要求する。基地局は、制御装置に、無線リソース確保完了を通知する。制御装置は、基地局を介して移動端末に、報告された異周波セルにハンドオーバの実行を通知する。   FIG. 1 shows a conventional handover sequence between different frequency cells. A different frequency cell having a certain communication quality or higher is reported from the mobile terminal to the radio network controller via the base station. The control device requests the base station to secure the radio resource of the reported different frequency cell. The base station notifies the control device of the completion of securing radio resources. The control apparatus notifies the mobile terminal via the base station of the execution of the handover to the reported different frequency cell.

図２は、従来のハンドオーバ実行の流れを示す。ハンドオーバ実行時に移動端末に割り当てられるセルの無線リソースの数は１つのみである。つまり、ハンドオーバ直後に移動端末が通信できるセル数は１つである。   FIG. 2 shows a flow of conventional handover execution. The number of radio resources of the cell allocated to the mobile terminal when executing the handover is only one. That is, the number of cells that the mobile terminal can communicate immediately after handover is one.

現在の周波数のセルの通信品質が悪化していき（Ｓ１１）、その後改善しないまま、異周波セルの通信品質が一定値以上であることを測定すると（Ｓ１２でＹｅｓ）、制御装置は移動端末にハンドオーバを指示し、移動端末は通信品質の良い異周波セルにハンドオーバを実行する（Ｓ１３）。通信品質が一定値以上の異周波セルがない場合は（Ｓ１２でＮｏ）、ハンドオーバせずに通常の呼処理を実行する（Ｓ１４）。   If the communication quality of the cell of the current frequency is deteriorated (S11), and then measured without being improved, the control device determines that the communication quality of the different frequency cell is above a certain value (Yes in S12). Instructing handover, the mobile terminal executes handover to a different frequency cell with good communication quality (S13). When there is no different frequency cell whose communication quality is equal to or higher than a certain value (No in S12), normal call processing is executed without handover (S14).

従来の通信方式では、異周波セル間のハンドオーバでは、ハンドオーバ直後に通信できるセルはひとつのみであるので、通信品質のよい異周波セルが複数存在したとしても、それらのうち最も通信品質の良いセルにのみハンドオーバを実行していた。   In the conventional communication method, in handover between different frequency cells, only one cell can be communicated immediately after handover, so even if there are multiple different frequency cells with good communication quality, the cell with the best communication quality among them. Only handed over.

また、周波数間ハンドオーバ中、ハンドオーバ先基地局は、コンプレストモードにおけるギャップで、ハンドオーバ元基地局がハンドオーバ元周波数にて移動局に送信するデータと同一のデータをハンドオーバ先周波数にて移動局に送信し、移動局は、コンプレストモードにおけるギャップで周波数をハンドオーバ元周波数からハンドオーバ先周波数に切替えて、移動局がハンドオーバ元基地局へ送信するデータと同一のデータをハンドオーバ先基地局に送信する移動通信システムがある（例えば、特許文献１参照）。
“ WCDMA for UMTS : radio access for third generation mobile communications ” Harri Holma, Antti Toskala, 2002 特開２００４−８８５２２号公報 In addition, during the inter-frequency handover, the handover destination base station transmits the same data as the data transmitted from the handover source base station to the mobile station at the handover source frequency to the mobile station at the handover destination frequency in the gap in the compressed mode. Then, the mobile station switches the frequency from the handover source frequency to the handover destination frequency at the gap in the compressed mode, and transmits the same data as the data transmitted from the mobile station to the handover source base station to the handover destination base station. There is a system (see, for example, Patent Document 1).
“WCDMA for UMTS: radio access for third generation mobile communications” Harri Holma, Antti Toskala, 2002 JP 2004-88522 A

しかしながら、通常ハンドオーバ完了までには一定の時間を要する。ハンドオーバ完了までに移動端末の移動または電波状況の変化などにより、そのセルの通信品質が悪化した場合、通信が不安定になってしまう、または通信不可になってしまうという問題が発生する。すなわち、異周波セル間のハンドオーバ直後に、電波状況の変化によって通信が不安定になってしまう場合がある。   However, a certain time is required until the normal handover is completed. If the communication quality of the cell deteriorates due to the movement of the mobile terminal or the change of the radio wave condition before the handover is completed, there arises a problem that the communication becomes unstable or becomes impossible to communicate. That is, immediately after handover between different frequency cells, communication may become unstable due to changes in radio wave conditions.

そこで本発明は、異周波セル間のハンドオーバ直後でも安定した通信を実現できる移動通信システムにおけるハードハンドオーバ方法を提供することを目的とする。   Therefore, an object of the present invention is to provide a hard handover method in a mobile communication system capable of realizing stable communication even immediately after handover between different frequency cells.

上述の課題を解決するため、本発明は、異周波セル間のハンドオーバ実行前に、通信可能な通信品質を持つ異周波セルが複数存在するならば、ハンドオーバ実行前にそれら複数の異周波セルの無線リソースを移動端末に割り当て、ハンドオーバ直後でも複数のセルと通信を可能とすることを特徴とする。   In order to solve the above-described problem, the present invention is designed so that if there are a plurality of different frequency cells having communication quality that can be communicated before performing handover between different frequency cells, the plurality of different frequency cells are A radio resource is allocated to a mobile terminal, and communication with a plurality of cells is possible even immediately after handover.

すなわち、異周波セルにおいて通信可能な通信品質を持つセルが複数存在する場合、通信品質の良いセルから順に複数のセルの無線リソースを割り当てているので、それら通信可能なセルのうち、いくつかのセルの通信品質が悪化したとしても、他のセルの通信品質が良ければハンドオーバ直後でも安定した通信が可能になる。   That is, when there are a plurality of cells having communication quality that can be communicated in different frequency cells, radio resources of a plurality of cells are allocated in order from a cell having good communication quality. Even if the communication quality of a cell deteriorates, stable communication is possible even immediately after handover if the communication quality of other cells is good.

本発明によれば、通信可能な通信品質を持つセルが複数存在するときは、異周波セル間のハンドオーバ後に複数のセルと通信ができるため、通信が不安定になることを予防でき、回線の信頼性向上に寄与することができる。   According to the present invention, when there are a plurality of cells having communicable communication quality, communication with a plurality of cells can be performed after handover between different frequency cells, so that it is possible to prevent instability of communication, It can contribute to the improvement of reliability.

次に、本発明の最良の形態について図面を参照して説明する。   Next, the best mode of the present invention will be described with reference to the drawings.

図３は、本発明のシステム構成を示し、無線ネットワーク側が、無線ネットワーク制御装置（ＲＮＣ＃１００）、基地局（ＮｏｄｅＢ＃１１０，＃１２０）と、基地局配下の各セル（Ｃｅｌｌ＃１１１，＃１２１，＃１２２）から構成されている。セル＃１１１は、基地局＃１１０配下にあり周波数帯＃１を使用し、セル＃１２１，＃１２２は、基地局＃１２０配下にあり周波数帯＃２を使用している。基地局＃１１０と基地局＃１２０は、同一制御装置＃１００配下にある。なお、基地局＃１１０，＃１２０は、異なる制御装置配下にあってもよい。   FIG. 3 shows a system configuration of the present invention. The radio network side includes a radio network controller (RNC # 100), base stations (NodeB # 110, # 120), and cells (Cell # 111, # 120) under the base station. 121, # 122). Cell # 111 is under base station # 110 and uses frequency band # 1, and cells # 121 and # 122 are under base station # 120 and use frequency band # 2. Base station # 110 and base station # 120 are under the same control apparatus # 100. The base stations # 110 and # 120 may be under different control devices.

移動端末１０がセルの通信品質（例えば、受信電力対干渉電力（ＳＩＲ）または信号強度）を測定し、そのセルの通信品質が一定以上または一定以下になると、移動端末１０は、制御装置へ報告する。図５または図６に示すように、移動端末１０は、現在のセル＃１１１の通信品質が閾値１以下になったことを測定すると、制御装置へ通知する。また、移動端末１０は、隣接する異周波のセル＃１２１（あるいはセル＃１２１と＃１２２）の通信品質が閾値２以上となったことを測定すると、制御装置へ通知する。   When the mobile terminal 10 measures the communication quality of a cell (for example, received power versus interference power (SIR) or signal strength), and the communication quality of the cell becomes equal to or higher than a certain level, the mobile terminal 10 reports to the control device. To do. As shown in FIG. 5 or FIG. 6, when the mobile terminal 10 measures that the communication quality of the current cell # 111 is equal to or lower than the threshold value 1, the mobile terminal 10 notifies the control device. Further, when the mobile terminal 10 measures that the communication quality of the adjacent different frequency cell # 121 (or cells # 121 and # 122) is equal to or higher than the threshold value 2, it notifies the control device.

次に、上記システムの動作の流れを図４のフローチャートに示す。今、移動端末１０は、１つのセル＃１１１と通信をしている状況を仮定する。なお、複数のセルと通信していてもかまわない。また、移動端末１０は、セル＃１１１だけでなく隣接する異周波セルの通信品質も測定しているものとする。   Next, the flow of operation of the above system is shown in the flowchart of FIG. Now, it is assumed that the mobile terminal 10 is communicating with one cell # 111. In addition, you may communicate with several cells. In addition, it is assumed that the mobile terminal 10 measures not only the cell # 111 but also the communication quality of adjacent different frequency cells.

図５は、通信可能な異周波セルが複数存在する場合の通信品質を示す。この図５において、現在の周波数のセル＃１１１の通信品質が悪化していき（Ｓ２１）、その後改善しないまま、異周波のセル＃１２１または＃１２２の通信品質が閾値２以上であることを測定すると（Ｓ２２でＹｅｓ）、制御装置＃１００は移動端末１０にハンドオーバを指示する。その際、従来の方法であれば、セル＃１２１または＃１２２のうち通信品質の良い一方のセルにハンドオーバするが、本発明では、図５に示すように、セル＃１２１と＃１２２の通信品質が共に閾値２以上であるなら（Ｓ２３でＹｅｓ）、移動端末１０は、ハンドオーバ可能なセル＃１２１とセル＃１２２があることを制御装置＃１００に通知する。   FIG. 5 shows the communication quality when there are a plurality of different frequency cells that can be communicated. In FIG. 5, the communication quality of the cell # 111 of the current frequency deteriorates (S21), and after that, it is measured that the communication quality of the cell # 121 or # 122 of the different frequency is greater than or equal to the threshold value 2 without improvement. Then (Yes in S22), the control device # 100 instructs the mobile terminal 10 to perform a handover. At that time, in the conventional method, handover is performed to one cell with good communication quality among the cells # 121 or # 122. However, in the present invention, as shown in FIG. Are both greater than or equal to the threshold value 2 (Yes in S23), the mobile terminal 10 notifies the control apparatus # 100 that there is a cell # 121 and a cell # 122 that can be handed over.

ハンドオーバ可能なセルが複数あることが制御装置に通知されると、制御装置＃１００は通知された複数のセルの無線リソースを移動端末１０に割り当てするよう基地局＃１１０に通知する。すると基地局＃１１０は、通知されたセルのChannelization codeや送信電力などの無線リソースを移動端末１０に割り当て（Ｓ２４）、制御装置＃１００へ無線リソース割り当て完了を通知し、その後、移動端末１０はハンドオーバを実行する（Ｓ２５）。   When the control apparatus is notified that there are a plurality of cells that can be handed over, the control apparatus # 100 notifies the base station # 110 to allocate radio resources of the notified plurality of cells to the mobile terminal 10. Then, the base station # 110 allocates radio resources such as the channelization code and transmission power of the notified cell to the mobile terminal 10 (S24), notifies the control apparatus # 100 of completion of radio resource allocation, and then the mobile terminal 10 Handover is executed (S25).

一方、図６に示すように、閾値２を超える異周波セルが１つしか存在しなかった場合は（Ｓ２３でＮｏ）、従来の方法と同様、閾値２を超える異周波セル＃１２１に対してのみハンドオーバ手順が実行される（Ｓ２７）。通信するのに十分でない通信品質のセル＃１２２と通信してしまうと、雑音・干渉の増加を生じ、他の移動端末の通信に悪影響を及ぼすからである。   On the other hand, as shown in FIG. 6, when there is only one different frequency cell exceeding the threshold value 2 (No in S23), for the different frequency cell # 121 exceeding the threshold value 2 as in the conventional method. Only the handover procedure is executed (S27). This is because if communication is performed with the cell # 122 having communication quality that is not sufficient for communication, an increase in noise / interference occurs, which adversely affects the communication of other mobile terminals.

また、通常、移動端末が同時に通信できるセルの数（本明細書ではこれをActive set sizeと呼ぶ）は限られている。もし閾値２を超えるセルの数がActive set sizeを超えてしまっている場合、それらのセルのうち通信品質の良いものからActive set size分の無線リソースを割り当ててからハンドオーバを実行する。   Also, the number of cells that can be simultaneously communicated by a mobile terminal (this is referred to as “Active set size” in this specification) is usually limited. If the number of cells exceeding the threshold 2 exceeds the Active set size, handover is performed after allocating radio resources corresponding to the Active set size from those cells having good communication quality.

本発明の第２の実施例として、その基本的構成は第１の実施例と同様であるが、ハンドオーバを実行するために満たさなければならない閾値と、通信可能なセルとして選択するための閾値に異なる閾値を用いることについて工夫している。   As the second embodiment of the present invention, the basic configuration is the same as that of the first embodiment, but the threshold value that must be satisfied in order to execute the handover and the threshold value for selecting as a communicable cell are set. Devised to use different thresholds.

第１の実施例では、ハンドオーバ後に通信する異周波セルの基準としてセル＃１２１、＃１２２とも１つの閾値２を用いているが、必ずしも１つでなくても良い。ハンドオーバのトリガーとしての閾値と、ハンドオーバ後に通信するセルの基準として用いる閾値を別のものを使用することができる。   In the first embodiment, one threshold value 2 is used for both cells # 121 and # 122 as a reference for different frequency cells to be communicated after handover. Different threshold values can be used as a trigger for handover and a threshold value used as a reference for cells to be communicated after handover.

例えば図７に示すように、セル＃１２１は閾値２、セル＃１２２は閾値３とすることができる。つまり現在のセル＃１１１の通信品質が閾値１以下、かつ最も通信品質の良い異周波セルの通信品質が閾値２以上であることをハンドオーバのトリガーとして使用し、ハンドオーバ後に通信するセルの基準として閾値２より低い閾値３を用いる。図７では、セル＃１２２の通信品質は異周波セル測定開始時に閾値３を超えているので、ハンドオーバ直後に通信するセルとして選択される。   For example, as shown in FIG. 7, the cell # 121 can have a threshold value 2 and the cell # 122 can have a threshold value 3. That is, the fact that the communication quality of the current cell # 111 is equal to or lower than the threshold value 1 and the communication quality of the different frequency cell having the best communication quality is equal to or higher than the threshold value 2 is used as a trigger for handover, A threshold 3 lower than 2 is used. In FIG. 7, since the communication quality of the cell # 122 exceeds the threshold 3 at the start of the different frequency cell measurement, it is selected as a cell to communicate immediately after the handover.

ハンドオーバを行う基準とハンドオーバ後に通信するセルの基準に異なるものを使用する利点として、閾値１ほど通信品質が良くないセルでもハンドオーバ直後に通信するセルとして使用することが可能になるので、Active setとして使用するセルの選択肢を増やすことができることである。   As an advantage of using different criteria for handover and the standard of cells to be communicated after handover, it is possible to use a cell whose communication quality is not as good as threshold 1 as a cell to communicate immediately after handover. It is possible to increase the choices of cells to be used.

以上述べた実施形態では、携帯電話システムに適用した例を示したが、これに限らず、本発明は無線ＬＡＮシステムなどにも適用可能である。   In the embodiment described above, the example applied to the mobile phone system is shown. However, the present invention is not limited to this, and the present invention can also be applied to a wireless LAN system or the like.

従来の異周波セル間のハンドオーバのシーケンス図である。It is the sequence diagram of the hand-over between the conventional different frequency cells. 従来の異周波セル間ハンドオーバの実行を説明するフローチャートである。It is a flowchart explaining execution of the conventional handover between different frequency cells. 本発明のシステム構成図である。It is a system configuration diagram of the present invention. 本発明の動作を説明するフローチャートである。It is a flowchart explaining operation | movement of this invention. 通信可能な異周波セルが複数存在する場合の通信品質の例を示す図である。It is a figure which shows the example of communication quality when multiple different frequency cells which can communicate exist. 通信可能な異周波セルが１つのみ存在する場合の通信品質の例を示す図である。It is a figure which shows the example of communication quality when only one different frequency cell which can communicate exists. 通信可能な異周波セルの通信品質に複数の閾値を設けた例を示す図である。It is a figure which shows the example which provided the some threshold value in the communication quality of the different frequency cell which can communicate.

符号の説明Explanation of symbols

１０ 移動端末
＃１００ 無線ネットワーク制御装置
＃１１０、＃１２０ 基地局
＃１１１、＃１２１、＃１２２ セル 10 Mobile terminal # 100 Radio network controller # 110, # 120 Base station # 111, # 121, # 122 Cell

Claims (6)

異周波セルを有する移動通信システムにおけるハードハンドオーバ方法であって、
移動端末が、異周波セルの通信品質を測定して、無線ネットワークへ送信し、
前記無線ネットワークが、複数の異周波セルの無線リソースを前記移動端末に割り当て、
前記移動端末が、無線リソースの割り当てられたセルへハンドオーバを実行する各ステップを含み、
前記ハンドオーバは、現在通信しているセルの通信品質が第１の閾値以下となり、且つ、隣接する異周波セルの中で最も通信品質の良い異周波セルの通信品質が第２の閾値以上であることを契機として行われ、
前記ハンドオーバ後に通信する異周波セルは前記第２の閾値より低い第３の閾値以上の通信品質の異周波セルから選択されることを特徴とする移動通信システムにおけるハードハンドオーバ方法。 A hard handover method in a mobile communication system having different frequency cells,
The mobile terminal measures the communication quality of the different frequency cell, sends it to the wireless network,
The wireless network allocates radio resources of a plurality of different frequency cells to the mobile terminal,
The mobile terminal, see contains the steps to perform the handover to the allocated cell of the radio resource,
In the handover, the communication quality of the currently communicating cell is equal to or lower than the first threshold, and the communication quality of the different frequency cell having the best communication quality among the adjacent different frequency cells is equal to or higher than the second threshold. It is triggered by that,
A hard handover method in a mobile communication system, wherein a different frequency cell to be communicated after the handover is selected from different frequency cells having a communication quality equal to or higher than a third threshold lower than the second threshold . 前記移動端末は、選択可能なセルのうち、通信品質の良いほうから所定の数のセルを選択することを特徴とする請求項１に記載のハードハンドオーバ方法。 2. The hard handover method according to claim 1, wherein the mobile terminal selects a predetermined number of cells from among the selectable cells having better communication quality. 前記移動端末は複数のセルと通信を行っており、当該複数のセル全ての通信品質が前記第１の閾値以下となり、且つ、隣接する異周波セルの中で最も通信品質の良い異周波セルの通信品質が第２の閾値以上であることを契機として前記ハンドオーバを行うことを特徴とする請求項１又は２に記載のハードハンドオーバ方法。 The mobile terminal is communicating with a plurality of cells, all communication quality the plurality of cells becomes less than the first threshold value, and may most communication quality in the adjacent different frequency cell different frequency cell 3. The hard handover method according to claim 1, wherein the handover is performed when the communication quality is higher than or equal to a second threshold value. 4. 異周波セルを有する移動通信システムにおいて、
移動端末は、異周波セルの通信品質を測定して、無線ネットワークへ送信する手段と、
前記無線ネットワークから無線リソースの割り当てられたセルへハンドオーバを実行する手段とを有し、
前記無線ネットワークは、複数の異周波セルの無線リソースを前記移動端末に割り当てる手段を有し、
前記ハンドオーバは、現在通信しているセルの通信品質が第１の閾値以下となり、且つ、隣接する異周波セルの中で最も通信品質の良い異周波セルの通信品質が第２の閾値以上であることを契機として行われ、
前記ハンドオーバ後に通信する異周波セルは前記第２の閾値より低い第３の閾値以上の通信品質の異周波セルから選択されることを特徴とする移動通信システム。 In a mobile communication system having different frequency cells,
The mobile terminal measures the communication quality of the different frequency cell and transmits to the wireless network;
Means for performing a handover from the radio network to a cell to which radio resources are allocated,
The wireless network may have a means for assigning radio resources of a plurality of different frequency cell to the mobile terminal,
In the handover, the communication quality of the currently communicating cell is equal to or lower than the first threshold, and the communication quality of the different frequency cell having the best communication quality among the adjacent different frequency cells is equal to or higher than the second threshold. It is triggered by that,
The mobile communication system, wherein a different frequency cell to be communicated after the handover is selected from different frequency cells having a communication quality equal to or higher than a third threshold lower than the second threshold . 前記移動端末は、選択可能なセルのうち、通信品質の良いほうから所定の数のセルを選択することを特徴とする請求項４に記載の移動通信システム。 5. The mobile communication system according to claim 4 , wherein the mobile terminal selects a predetermined number of cells from the selectable cells having the better communication quality. 前記移動端末は複数のセルと通信を行っており、当該複数のセル全ての通信品質が前記第１の閾値以下となり、且つ、隣接する異周波セルの中で最も通信品質の良い異周波セルの通信品質が第２の閾値以上であることを契機として前記ハンドオーバを行うことを特徴とする請求項４又は５に記載の移動通信システム。 The mobile terminal is communicating with a plurality of cells, all communication quality the plurality of cells becomes less than the first threshold value, and may most communication quality in the adjacent different frequency cell different frequency cell 6. The mobile communication system according to claim 4, wherein the handover is performed when the communication quality is higher than or equal to a second threshold value. 7.
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