JP3889611B2 - Multiple control device, radio base station, and time slot allocation changing method - Google Patents

Description

【００６４】
次に、制御部８０は、上述の移動局ａの電界強度IaをＲＳＳＩ検出部５４から受け取り、品質指標値テーブル３００の当該タイムスロットを識別するタイムスロット番号により識別される領域から、移動局Ｘの電界強度Ixを読み出し、電界強度比Kaを
Ka ＝ Ia ／ Ix
により算出する。ここで、Ka＞１の場合には、
Ka ＝ Ix ／ Ia
により算出する。
【００６５】
次に、算出した空間相関値Jaと、しきい値テーブル２００に記憶されている空間相関値しきい値J_tとを比較する。また、算出した電界強度比Kaとしきい値テーブル２００に記憶されている電界強度比しきい値K_tとを比較する。
Ja≦Jt かつ Ka≧Ktの場合に、空間多重が可能と判定され、その他の場合に、空間多重が不可能と判定される。
【００６６】
なお、既に複数個（２〜３個）の移動局と空間多重により通信している場合には、制御部８０は、移動局毎に、前記の判定処理を行う。
さらに、制御部８０は、上述の空間相関値Ja時間的変化であるフェージング値Paを
Pa(t_n)=（Ja(t_n)-Ja(t_p)）/(t_n-t_p)
により算出する。
【００６７】
ここで、Ja(t_n)は、現在の時刻t_nにおける応答ベクトルにより算出された空間相関値であり、Ja(t_p)は、時刻ｔ_pにおける前回のフレームの応答ベクトルにより算出された空間相関値である。
なお、上述のタイマ値ｔ１と、t_n及びｔ_pとの関係は、
ｔ１≧(t_n-t_p)
という関係にある。
【００６８】
以上のように、制御部８０は、空間相関値Ja、電界強度比Ka及びフェージング値Paを求め、通信品質予測テーブル４００又は品質予測テーブル５００に格納する。
また、制御部８０は、上述の切替元選択処理により切替元に決定された移動局含むグループの通信品質の予測結果にもとづいて、最終的に強制ＴＣＨ切替を実施するか否かの判定を実施する。
【００６９】
即ち、上述のグループの組み合わせにおいて、１つ組でもしきい値割れが生じている場合、制御部８０は、このグループに属する組み合わせについては、強制ＴＣＨ切替の実施を取りやめる。
（新規接続時の処理）
制御部８０は、次に示すようにして、新規接続時の処理を行う。
【００７０】
即ち、移動局から新規接続の要求がなされた場合、制御部８０は、空スロットの有無を判定し、空スロットが有れば、この空スロットに新規接続を要求した移動局を割り当てる。
一方、空スロットが無ければ、制御部８０は、従来と同様の手順で接続を試みる。即ち、制御部８０は、既に割り当て済みの通話スロットに新規接続を要求した移動局を割り当てるように試みる。
【００７１】
その際、制御部８０は、割り当て済みの移動局及び当該新規接続の移動局に関して、設定レベル以上の通信品質が確保可能かを空間相関値J_X及び電界強度比K_Xにもとづいて判定し、上述の新規接続について実施可否判定を行う。
（通信中の処理）
制御部８０は、次に示すようにして、通信中の処理を行う。
【００７２】
制御部８０は、通信品質が悪いと判定する場合に、移動局に対して、通話スロットを切替るように制御する。
また、ハンドオーバが発生したと判定する場合に、移行先セルの無線チャンネルに切替るように制御する。
２ 無線基地局１００の動作
無線基地局１００の動作について説明する。
（１）空スロット確保処理の動作
空スロット確保処理について、図７に示すフローチャートを用いて説明する。
【００７３】
制御部８０は、通話スロット内ユーザ数が変化する待機し（ステップＳ３０１）、通話スロット内ユーザ数が変化したとき、全通話スロット内に空きスロットがなく、かつ、1多重スロットがあるか否かを判定し（ステップＳ３０２）、これら条件を満足しない場合、処理を終了する。
一方、これら条件を満足する場合、制御部８０は、強制ＴＣＨ切替を試みた回数を示す値Ｍに１を代入し（ステップＳ３０３）、タイマの値を時間ｔ１秒に設定する（ステップＳ３０４）。
【００７４】
そして、制御部８０は、タイマの設定時間分だけ待機し（ステップＳ３０５）、この間、通信品質を予測するために必要な各移動局の応答ベクトル及び電界強度などを収集する。
。 前記タイマの設定時間が過ぎると、制御部８０は、全通話スロットで状態変化があるか否かを判定し（ステップＳ３０６）、全通話スロットで状態変化がある場合、全通話スロット内に空きスロットがなく、かつ、1多重スロットがあるか否かを判定するステップＳ３０２に戻る。
【００７５】
一方、全通話スロットで状態変化がない場合、制御部８０は、Ｍの値が１か否かを判定し（ステップＳ３０７）、Ｍの値が１の場合、上述のステップＳ３０３において、前記変化の原因となった移動局を収容する１多重スロットに最優先順位を付与し、リトライ回数Ｎのデフォルト値を設定し（ステップＳ３０８）、これ以外にも１多重スロットがあるか否かを判定し（ステップＳ３０９）、ある場合には、他の１多重スロットにこの通話スロットに対応づけられている識別番号であるスロット番号の小さい順から大きい順に優先順位を付与し、リトライ回数Ｎのデフォルト値を設定する（ステップＳ３１０）。
【００７６】
以上のステップが実行された後、上述のステップＳ３０７においてＭの値が１でない場合、または、上述のステップＳ３０９において他の１多重スロットが存在しない場合、制御部８０は、最先順位の１多重スロットの移動局を強制ＴＣＨ切替元とし（ステップＳ３１１）、切替先候補の通話スロットに対して強制ＴＣＨ切替を実施した場合の通信品質を予測し（ステップＳ３１２）、最高の通信品質が予想される切替先候補の通話スロット、即ち、トータルポイント数の少ない組み合わせにおける切替元の移動局以外の移動局が割り当てられている通話スロットを切替先の通話スロットとして選択する（ステップＳ３１３）。
【００７７】
そして、制御部８０は、通信品質予測テーブル４００又は５００において、強制ＴＣＨ切替の対象となった組み合わせが属するグループ内の全ての組み合わせについて、空間相関値、電界強度比K_X及びフェージング値P_Xがこれらに対応する各しきい値をクリアするか否かを判定し（ステップＳ３１４）、クリアする場合、ベースバンド部７０から外部の交換機へと向かうＩＳＤＮ回線の通信帯域に空があるか否かを判定し（ステップＳ３１５）、空がない場合、処理を終了する。
【００７８】
このような制御を行うのは、本制御を行っても新規呼が接続できない場合、意味がないためであり、無用な性能劣化の可能性を未然に防ぐことが目的である。一方、空がある場合、制御部８０は、強制ＴＣＨ切替をトライし（ステップＳ３１６）、当該強制ＴＣＨ切替が成功したか否かを判定し（ステップＳ３１７）、成功すれば処理を終了する。
【００７９】
また、当該強制ＴＣＨ切替が失敗した場合、制御部８０は、この切替元となった１多重スロットに対応づけられているリトライ回数を１ディクリメントする（ステップＳ３１８）。
そして、上述のディクリメントが実施された場合、または、ステップＳ３１４における判定においてクリアしなかった場合、制御部８０は、この切替元となった１多重スロットに対応づけられている順位を最低順位に変更し（ステップＳ３１９）、リトライ回数０となった通話スロットの移動局を強制ＴＣＨ切替元の候補から除外し（ステップＳ３２０）、０以外のリトライ回数が対応付けられている通話スロット、即ち、切替元となる候補が存在するか否かを判定し（ステップＳ３２１）、切替元となる候補が存在しない場合、制御部８０は、処理を終了する。
【００８０】
一方、切替元となる候補が存在する場合は、制御部８０は、タイマの値を時間ｔ２秒に設定すると共に、現状のＭの値に１インクリメントした値を新たなＭの値とし（ステップＳ３２２）、タイマの設定時間分だけ待機するステップＳ３０５に戻る。
なお、上述の通信品質予測処理に該当するステップは、Ｓ３０４、Ｓ３０５、Ｓ３１３及びＳ３１４である。
【００８１】
図８は、このような空スロット確保処理が実施された場合における、通話スロットへの移動局に割り当て状況の時系列な変化を示す図である。
空スロットが確保できる場合、制御部８０は、空間多重を行わずに１通話スロットに１移動局のみを割り当てる。
時刻ｔ0において、残り１の空スロットに移動局▲３▼を割り当てたことにより、全通話スロット内に空きスロットがなく、かつ、1多重スロットがある状態となったことを判定し、制御部８０は、空スロット確保処理を開始し、その結果、時刻ｔ１において、スロット３に割り当てられていた移動局▲３▼が、スロット１へと強制ＴＣＨ切替している
そして、ｔ４からｔ６までに示すように、新たに生成された空スロットに新規接続要求を行う移動局を収容することにより、空スロット確保処理が繰り返し実施されることとなる。
【００８２】
やがて、ｔ７に示すように、スロット１及びスロット２にそれぞれ４つの移動局を割り当てた後に、残り１つの空スロットに移動局▲９▼を割り当ててしまうと、もはや空スロットが生成できない状態となる。
この場合、これ以降、従来と同様の接続を試みる。
なお、１通話スロットにおいて最大４つの空間多重までが可能であるが、空間多重されている移動局相互の位置関係により空間多重できる移動局の数は変わるため、ｔ２０に示すように、スロット１において３つの移動局が、スロット２において４つの移動局が、スロット３において１つの移動局がそれぞれ割り当てられている場合であっても、通常の接続が行われる場合が生じる。
【００８３】
以上のように、本第１の実施の形態によれば、無線基地局１００において、空スロットを確保するように恒常的に強制ＴＣＨ切替を実施するため、空スロットが確保される頻度が増加し、この空スロットに新規接続を要求する移動局を割り当てることにより、新規接続が容易となる。
なお、本第1の実施の形態における、空スロット確保処理においては、空間多重数０の空スロットを生成するようにしたが、空間多重数がＭ（Ｍは、１以上、かつ、限界空間多重数（本第1の実施の形態では４）未満のスロット（以下、「低多重スロット」という。）を生成するとしてもよい。
【００８４】
Ｍの値をできるだけ小さくするように試みたうえで、この低多重スロットに新規接続を要求する移動局の割り当て先とすることにより、通信品質上の問題を起こさずスムーズに接続できる頻度が増加する。
また、本第1の実施の形態において、無線基地局１００は、ＰＨＳ移動局と無線接続するとしたが、これに限らず、携帯電話などのように、時分割多重方式及び空間多重方式を併用する無線通信方式であればよい。
【００８５】
また、本第1の実施の形態における、アンテナの数は、４本であったが、この数に限らず何本あってもよい。
その場合、アンテナの本数をＬ本とした場合、最大空間多重数は、Ｌとなる。また、図６において、ケース１及びケース２の場合を例に挙げて説明したが、ケース２のような状態の変化を強制ＴＣＨ切替の実施のトリガとするか否かについては、ユーザ設定により自由に変更できるとしてもよい。
【００８６】
また、本第1の実施の形態においては、空間相関値J_X、電界強度比K_X及びフェージング値P_Xの３つの値にもとづいて、強制ＴＣＨ切替を実施した場合における通信品質の予測を行ったが、これら以外のファクターにもとづいて品質予測を実施してもよい。
その場合、本第1の実施の形態においては、例えば、図５（ｂ）において、組み合わせ５０１における「▲４▼をスロット２へ」は、「▲２▼をスロット３へ」とした場合と同様の品質予測結果が得られるものとして、１つの組み合わせのみを示したが、同じ移動局の組み合わせであっても、切替対象が異なることにより、通信品質の予測値が異なって来る場合においては、切替対象の違いを考慮したよりきめ細かな場合分けを行って、通信品質を予測して行く必要がある。
【００８７】
例えば、空間多重されている各移動局から無線基地局１００への送信タイミングは、各移動局の信号を分離する上では、微妙にずれている方が都合がよい。
そこで、無線基地局１００は、空間多重されている各移動局の送信タイミングが重ならないように、これら移動局に送信タイミングを指示する。
ところが、この指示に対する移動局のレスポンスの速さは、各移動局毎に異なっており、レスポンスの速い移動局を他のスロットに割り当てことは問題ないが、レスポンスの遅い移動局を他のスロットに割り当てるのは問題になると思われる。
【００８８】
このように、例えば、通信品質予測のファクターとして、レスポンスの速さを考慮する場合、上述のように、よりきめ細かな場合分けを行って、通信品質を予測して行く必要がある。
また、本第1の実施の形態では、記載していないが、空スロット確保処理起動中に他の影響でユーザ配置が変わる場合、例えば、既存ユーザが通話を終了した、既存ユーザが性能低下等で強制ＴＣＨ切替を行った又は既存ユーザがハンドオーバで他基地局に移動したなどの現象が生じた場合、制御部８０は、割り込みをかけて本空スロット確保処理を中断するとしてもよい。
【００８９】
その場合、新しい移動局の割り当てが、空スロット確保処理の実施の条件、即ち、全通話スロット内に空きスロットがなく、かつ、１多重スロットあるという条件を満たしている場合、制御部８０は、再度最初から空スロット確保処理を起動する。
一方、上述の条件を満たしていない場合は、制御部８０は、空スロット確保処理は、実施しないこととなる。
【００９０】
また、新規接続を要求する移動局からが再度接続要求がなされた場合、制御部８０は、空スロット確保処理を終了し、端末の要求に従って通常のチャネル切替を実施するとしてもよい。
また、本第1の実施の形態における制御部８０により実施される空スロット確保処理の内容については、あくまで１例に過ぎず、空スロットを確保するように恒常的に強制ＴＣＨ切替を実施する処理であればよい。
【００９１】
図９は、このような異なる事例を挙げた空スロット確保処理のフローチャートであり、重要な部分のみの動作内容を記載している。
図９と図７との相違点について、図７を基準に説明すると、図７におけるステップＳ３０８からステップＳ３１１にかけて、強制ＴＣＨ切替の切替元とする通話スロット及び移動局を決定している部分が異なる。
【００９２】
以下、図９のフローチャートについて説明する。
制御部８０は、通話スロット内ユーザ数が変化する待機し（ステップＳ６０１）、通話スロット内ユーザ数が変化したとき、全通話スロット内に空きスロットがなく、かつ、1多重スロットがあるか否かを判定し（ステップＳ６０２）、これら条件を満足しない場合、処理を終了する。
【００９３】
一方、これら条件を満足する場合、制御部８０は、タイマの設定時間分だけ待機し（ステップＳ６０３）、この間、通信品質を予測するために必要な各移動局の応答ベクトル及び電界強度などを収集する。
前記タイマの設定時間が過ぎると、制御部８０は、全通話スロットで状態変化があるか否かを判定し（ステップＳ６０４）、全通話スロットで状態変化がある場合、全通話スロット内に空きスロットがなく、かつ、1多重スロットがあるか否かを判定するステップＳ６０２に戻る。
【００９４】
一方、全通話スロットで状態変化がない場合、制御部８０は、切替元移動局と切替先移動局との組の通信品質が良いもの、即ち、トータルポイント数の小さいものから順位付けを行って、各組にリトライ回数Nのデフォルト値を設定する（ステップＳ６０５）。
このステップＳ６０５は、図７のステップＳ３０８からステップＳ３１１に相当するステップであり、第１の実施の形態では、最初の強制ＴＣＨの切替元は、通話スロット内のユーザ数を変化させるきっかけとなった移動局であり、他に１多重スロットが存在しても、それら通話スロットの優先順位は、スロット番号順位に付与されていたに過ぎないのに対し、第１の実施の形態では、通信品質予測テーブル４００又は５００のトータルポイント数の小さい順に強制ＴＣＨの切替元を決定するという通信品質に重きを置いた切替元の決定がなされている。
【００９５】
即ち、制御部８０は、上述のトータルポイント数が最小となっている移動局の組み合わせを強制ＴＣＨ切替の対象とする（ステップＳ６０６）。
そして、制御部８０は、強制ＴＣＨ切替の対象となった組み合わせが属するグループ内の全ての組み合わせについて、空間相関値、電界強度比K_X及びフェージング値P_Xがこれらに対応する各しきい値をクリアするか否かを判定し（ステップＳ６０７）、クリアする場合、強制ＴＣＨ切替をトライし（ステップＳ６０８）、当該強制ＴＣＨ切替が成功したか否かを判定し（ステップＳ６０９）、成功すれば処理を終了する。
【００９６】
また、当該強制ＴＣＨ切替が失敗した場合、制御部８０は、切替元選出テーブル６００において、この切替元となった１多重スロットに対応づけられているリトライ回数を１ディクリメントし（ステップＳ６１０）する。
上述のディクリメントが実施された場合、または、ステップＳ６０７における判定においてクリアしなかった場合、制御部８０は、切替元となった１多重スロットに対応づけられている順位を最低順位に変更し（ステップＳ６１１）、リトライ回数０となった通話スロットの移動局を強制ＴＣＨ切替の切替元の候補から除外し（ステップＳ６１２）、０以外のリトライ回数が対応付けられている通話スロット、即ち、切替元となる候補が存在するか否かを判定し（ステップＳ６１３）、切替元となる候補が存在しない場合、制御部８０は、処理を終了する。
【００９７】
一方、切替元となる候補が存在する場合は、制御部８０は、トータルポイント数が最小となっている移動局の組み合わせを強制ＴＣＨ切替の対象とするステップＳ６０６に戻る。
このように、図７のフローチャートに対し、強制ＴＣＨ切替の切替元とする移動局の決定の仕方が異なっていても構わない。
【００９８】
また、図１０は、図７及び図９と異なる空スロット確保処理の1例を示す図である。
制御部８０は、通話スロット内ユーザ数が変化する待機し（ステップＳ７０１）、通話スロット内ユーザ数が変化したとき、全通話スロット内に空きスロットがなく、かつ、1多重スロットがあるか否かを判定し（ステップＳ７０２）、これら条件を満足しない場合、処理を終了する。
【００９９】
一方、これら条件を満足する場合、制御部８０は、タイマの設定時間分だけ待機し（ステップＳ７０３）、この間、通信品質を予測するために必要な各移動局の応答ベクトル及び電界強度などを収集する。
前記タイマの設定時間が過ぎると、制御部８０は、全通話スロットで状態変化があるか否かを判定し（ステップＳ７０４）、全通話スロットで状態変化がある場合、全通話スロット内に空きスロットがなく、かつ、1多重スロットがあるか否かを判定するステップＳ７０２に戻る。
【０１００】
一方、全通話スロットで状態変化がない場合、制御部８０は、切替元移動局と切替先移動局との組の通信品質が良いもの、即ち、トータルポイント数の小さいものから順位付けを行って、各組にリトライ回数Nのデフォルト値を設定する（ステップＳ７０５）。
制御部８０は、上述のトータルポイント数が最小となっている移動局の組み合わせを強制ＴＣＨ切替の対象とする（ステップＳ７０６）。
【０１０１】
そして、制御部８０は、強制ＴＣＨ切替の対象となった組み合わせが属するグループ内の全ての組み合わせについて、空間相関値、電界強度比K_X及びフェージング値P_Xがこれらに対応する各しきい値をクリアするか否かを判定し（ステップＳ７０７）、クリアする場合、強制ＴＣＨ切替をトライし（ステップＳ７０８）、当該強制ＴＣＨ切替が成功したか否かを判定し（ステップＳ７０９）、成功すれば処理を終了する。
【０１０２】
また、当該強制ＴＣＨ切替が失敗した場合、制御部８０は、切替元選出テーブル６００において、この通話スロットに対応づけられているリトライ回数を１ディクリメントする（ステップＳ７１０）。
つまり、図９におけるフローチャートで実施していたような、切替元となった１多重スロットに対応づけられている順位を最低順位に変更する処理は実施しない。
【０１０３】
これにより、強制ＴＣＨ切替が失敗した空間多重条件により、リトライ数が０となるまで、再度、強制ＴＣＨ切替がトライされるとととなる。
上述のディクリメントが実施された場合、または、ステップＳ７０７における判定においてクリアしなかった場合、制御部８０は、リトライ回数０となった通話スロットの移動局を強制ＴＣＨ切替の切替元の候補から除外し（ステップＳ７１１）、０以外のリトライ回数が対応付けられている通話スロット、即ち、切替元となる候補が存在するか否かを判定し（ステップＳ７１２）、切替元となる候補が存在しない場合、処理を終了する。
【０１０４】
一方、切替元となる候補が存在する場合は、制御部８０は、トータルポイント数が最小となっている移動局の組み合わせを強制ＴＣＨ切替の対象とするステップＳ７０６に戻る。
また、第１の実施の形態では、空スロットを確保するように恒常的に強制ＴＣＨ切替を実施しているが、新規接続が要求された時点で、空スロット確保処理を開始して空スロットを確保してもよい。
【０１０５】
その場合、図６のステップＳ３０１における判定の内容が、通話スロット内のユーザ数が変化したことではなく、新規接続の要求がなされたか否かを判定することとなる。
また、図６のフローチャートにおいて、リトライ回数Nの設定値を１多重スロットに対して一律に設定したが、それぞれ異なった回数を個別に設定しても構わない。
【０１０６】
また、第１の実施の形態においては、リトライ回数Nは、切替元となる通話スロットに対応づけているが、切替先となる通話スロットに対応づけてもよい。
（第2の実施の形態）
本発明における第２の実施の形態としての無線基地局１００について説明する。
【０１０７】
第2の実施の形態における、無線基地局は、第1の実施の形態と同様に、ＰＨＳ規格で定められた時分割多重方式により移動局と無線接続し、前記時分割多重に加えて、さらに空間多重を行って移動局と通信する無線基地局であり、図１と同様の機能部を有し、制御部８０により実施される処理の内容が異なる。
ここでは、第1の実施の形態と異なる処理を実施する制御部８０について説明する。
【０１０８】
第１の実施の形態において、制御部８０は、通話スロットへの移動局の割り当て状態が変化したとき、空スロットがなく、かつ、１つの移動局のみが割り当てられている通話スロットがある場合に、空スロット確保処理を実施し、新規接続を要求する移動局を優先的に空スロットに割り当てようとしていたのに対し、第２の実施の形態において、制御部８０は、新規接続を要求している移動局を優先的に１多重以上の通話スロットに割り当てる、つまり、優先的に空間多重を実施する点で異なる。
【０１０９】
より具体的には、制御部８０は、移動局から新規接続が要求された場合、先ず、移動局の割り当てが可能な１多重以上の通話スロットがあるか否かを判定し、このような通話スロットがあれば、移動局の割り当てを試みる。
その際、制御部８０は、第1の実施の形態における通信品質予測処理に相当する処理を以下に示すように実施する。
【０１１０】
即ち、制御部８０は、空間相関値J_X、電界強度比K_X及びフェージング値P_Xにもとづいて、通信品質を予測する。
ここで、フェージング値P_Xは、先に述べたように空間相関値J_Xの単位時間あたりの変化量であるため、通常、異なる通話スロットにおいて得られた空間相関値J_Xにもとづいて算出される。
【０１１１】
しかしながら、新規接続を要求している移動局は、接続要求時において通話スロットを用いて通信していないため、この移動局についてのフェージング値P_Xは、受信用の制御スロットのみを用いて得られる空間相関値J_Xから算出せざるを得ない。
つまり、フェージング値P_Xは、制御スロットの前半に得られる空間相関値J_Xと後半に得られる空間相関値J_Xとから算出される。
【０１１２】
これは、極めて短い時間間隔でサンプリングされたデータであり、通話スロットを用いて通信した場合に比べ、フェージング値P_Xの算出精度が劣っている。
このため、フェージング値P_Xが明らかに大きい場合に限り、この移動局の割り当てを取りやめるように配慮されている。
したがって、フェージングしきい値P_tは、空間相関値しきい値J_t及び電界強度比しきい値K_tに比べ、より緩和された値となっている。
制御部８０は、接続を要求する移動局に関するフェージング値P_Xがフェージングしきい値P_t以下であって、上述の新規接続を要求する移動局の１以上の多重スロットに割り当てを試みるとき、空スロットがある場合、通信品質の予測のために用いる空間相関値しきい値J_t、電界強度比しきい値K_tの値を、空スロットがない場合よりも厳しいハイレベルの値のしきい値を用いて、この新規接続を要求する移動局を１以上の多重スロットに割り当てるか否かを判定する。
【０１１３】
ハイレベルの値のしきい値を用いる理由は、第1の実施の形態に比べ、通信品質予測に用いる評価項目からフェージング値P_Xが除外されるために、通信品質予測精度が低下し、実際に１以上の多重スロットに新規接続を要求する移動局を割り当てたとき、通信品質の不良が生じることを回避するためである。
一方、上述の新規接続を要求する移動局の１以上の多重スロットに割り当てを試みるとき、空スロットがない場合、制御部８０は、通常レベルの値のしきい値を用いて、この新規接続を要求する移動局を１以上の多重スロットに割り当てるか否かを判定する。
【０１１４】
つまり、空スロットがない場合においては、従来どおりの接続を試みる。
図１１は、以上のような処理が実施された場合における、通話スロットへの移動局に割り当て状況の時系列な変化を示す図である。
時刻ｔ0において、移動局▲２▼が新規接続を要求しており、制御部８０は、空間多重数が増大するように、移動局▲２▼をスロット１に空間多重するように試みる。
【０１１５】
その際、この時点において、空スロットが２つ存在し、新規接続を要求する移動局の空間多重がうまく行かなかった場合の割り当て先の余地が残っているため、制御部８０は、スロット１への空間多重の可否判定に用いるしきい値は、通常よりもハイレベルに設定する。
時刻ｔ0においては、このようなしきい値を用いても、空間多重の可否判定がＯＫとなっている。
【０１１６】
時刻ｔ１においては、移動局▲３▼が新規接続を要求しており、制御部８０は、これをスロット１に空間多重するように試みる。
この場合も、この時点において、空スロットが２つ存在するため、制御部８０は、スロット１への空間多重の可否判定に用いるしきい値は、通常よりもハイレベルに設定する。
【０１１７】
しかし、上述の判定において、空間多重不可とされたため、時刻ｔ２において、スロット２に割り当てている。
このような処理を繰り返すことにより、スロット１及びスロット２は次第に埋まって行く。
移動局▲５▼が新規接続を要求しており、制御部８０は、これをスロット１、スロット２の順で空間多重を試みるが成功しない。
【０１１８】
そこで、制御部８０は、空スロットであるスロット３に移動局▲５▼を割り当てている。
以降、空スロットが存在しないので、従来と同様のスロット割り当て手順に従う。
即ち、制御部８０は、通信品質が最も良好となることが予測される通話スロットへと移動局▲５▼を多重する。
【０１１９】
その場合、制御部８０は、空間多重の可否判定に使用するしきい値は、通常レベルの値を設定する。
これは、確実に割り当てがうまく行く空スロットがもはや存在しないため、しきい値をハイレベルに設定した結果、全ての空間多重の可否判定において不可と判定されないようにするためである。
【０１２０】
図１２は、このような通常レベル及びハイレベルのしきい値の１例を示す図である。
しきい値テーブル９００は、空間相関値しきい値J_t、電界強度比しきい値K_t、における通常レベル、ハイレベルのしきい値及び理想値を示し、さらに、フェージングしきい値P_tを示すテーブルであり、このテーブルは、予め情報記憶部に格納されている。
【０１２１】
しきい値（通常レベル）９０１は、通常レベルのしきい値を示し、しきい値（ハイレベル）９０２は、通常レベルのしきい値よりも厳しい値であるハイレベルのしきい値を示し、また、理想値９０３は、理想値を示す。
ここで、空間相関値９０４は、空間相関値しきい値J_tを示し、電界強度比９０５は、電界強度比しきい値K_tを示し、フェージング値９０６は、フェージングしきい値P_tを示している。
【０１２２】
第２の実施の形態における無線基地局１００の動作
図１３は、第２の実施の形態における新規接続を要求する移動局を優先的に空間多重を実施する処理を示すフローチャートである。
制御部８０は、新規接続要求がなされるまで待機し（ステップＳ８０１）、新規接続要求がなされた場合、空スロットがあるか否かを判定（ステップＳ８０２）する。
【０１２３】
空スロットがある場合、制御部８０は、１以上の多重スロットであって、空間多重の余地が残っている通話スロットがあるか否かを判定し（ステップＳ８０３）する。
以上の多重スロットであって、空間多重の余地が残っている通話スロットがある場合、制御部８０は、ハイレベルのしきい値を通信品質の予測に用いるしきい値とし（ステップＳ８０４）、このしきい値をクリアする通信品質が予想されるか否かを判定し（ステップＳ８０５）する。
【０１２４】
このしきい値をクリアした場合、制御部８０は、新規接続の要求を行った移動局を上述の１以上の多重スロットに割り当て（ステップＳ８０６）、処理を終了する。
一方、１以上の多重スロットであって、空間多重の余地が残っている通話スロットがあるか否かを判定するステップＳ８０３において、このような通話スロットが存在しない場合、ハイレベルのしきい値をクリアする通信品質が予想されるか否かを判定するステップＳ８０５において、このようなハイレベルのしきい値をクリアすることができない場合、制御部８０は、新規接続を要求している移動局を空スロットに割り当てる。
【０１２５】
また、上述の新規接続要求がなされた場合において、空スロットがあるか否かを判定するステップＳ８０２において、空スロットがない場合、制御部８０は、通常レベルのしきい値を通信品質の予測に用いるしきい値とし（ステップＳ８０８）、このしきい値をクリアする通信品質が予想されるか否かを判定し（ステップＳ８０９）、クリアする場合には、空スロット以外の通話スロットに新規接続を要求している移動局を割り当てる（ステップＳ８１０）。
【０１２６】
一方、クリアしない場合には、制御部８０は、新規接続を要求している移動局に対し接続を拒否する（ステップＳ８１１）。
以上のように、本第２の実施形態によれば、無線基地局１００において、新規接続の際に積極的に空間多重を実施するため、空スロットが利用されずに残っている機会が増加する。
【０１２７】
また、空間多重の可否判定に際し、空スロットがある場合には、ハイレベルなしきい値を用いて上述の判定を実施するため、より信頼性の高い空間多重を実現でき、仮に、空間多重の不可の判定がなされた場合においても、空スロットが用意されているので、この空スロットに新規接続を要求する移動局を割り当てることによりスムーズな接続がなされる。
【０１２８】
なお、本第２の実施形態では、強制ＴＣＨ切替を実行した結果、新たに空間多重されることとなった通話スロットに割り当てられている移動局の通信品質が不良となった場合について記載していないが、このような場合、第１の実施の形態と同様に、強制ＴＣＨ切替を中止して、他の通話スロットを切替先として空間多重を試みるとしてもよい。
【０１２９】
【発明の効果】
以上の説明から明らかなように、本発明に係る多重制御装置は、時分割多重及び空間多重により複数の移動局と無線通信を行う無線基地局に備えられ、時分割により区分された複数のタイムスロットのいずれかに１以上の移動局を割り当てる空間多重制御装置であって、タイムスロットに割当てている接続中のユーザのうち、他のタイムスロットに割当て先を移行したとしても、移行先のタイムスロットの各接続ユーザの通信特性が良好となることが予測できるものに対し、前記移行を試みることにより、空間多重限界数未満である空間多重数Ｎの低多重タイムスロットが存在する状態を生成するか、または、前記低多重タイムスロットが既に存在する場合に新規ユーザの接続が要求されたとき、前記低多重タイムスロット以外のタイムスロットへの新規ユーザの割り当てを優先的に試みることにより、前記低多重タイムスロットが存在する状態を維持するように、前記空間多重を制御することを特徴とする。
【０１３０】
これにより、新規接続において、前記低多重タイムスロットに対してさらに空間多重することにより、新規接続が容易に実施される。
つまり、前記低多重タイムスロットでは、空間多重数が少ないため、空間多重条件が緩和され、より容易に接続され得る。
また、本発明に係る無線基地局は、時分割により区分された複数のタイムスロットのいずれかに移動局を割り当て、時分割多重及び空間多重により複数の移動局と無線通信を行う無線基地局であって、空間多重限界数未満である空間多重数Ｎの低多重タイムスロットが存在する状態を生成するか、または、当該状態を維持するように、前記割り当ての変更を試みるタイムスロット割り当て変更手段を備えることを特徴とし、本発明に係るタイムスロット割り当て変更方法は、時分割により区分された複数のタイムスロットに移動局を割り当て、複数の移動局と時分割多重及び空間多重により無線通信を行う無線基地局において、前記割り当てを変更するタイムスロット割り当て変更方法であって、移動局の割り当てが１つも行われていない低多重タイムスロットを確保するように前記割り当ての変更を試みるタイムスロット割り当てステップを含むことを特徴とし、また、本発明に係るプログラムは、時分割により区分された複数のタイムスロットに移動局を割り当て、複数の移動局と時分割多重及び空間多重により無線通信を行う無線基地局において、前記割り当てを変更するためのプログラムであって、移動局の割り当てが１つも行われていない低多重タイムスロットを確保するように前記割り当ての変更を試みるタイムスロット割り当てステップをコンピュータに実行させることを特徴とする。
【０１３１】
これにより、前記低多重タイムスロットを新規接続の際の割り当て先として利用することにより、新規接続が容易に実施される。
つまり、上述と同様に前記低多重タイムスロットでは、空間多重数が少ないため、空間多重条件が緩和され、より容易に接続され得る。
また、前記Ｎの数は、０であるとしてもよい。
【０１３２】
これにより、空間多重を実施しなくても接続できるタイムスロットが確保される。
また、前記タイムスロット割り当て変更手段は、前記低多重タイムスロットを生成することにより前記状態を実現するとしてもよい。
これにより、低多重タイムスロットがない状態においても、新たに低多重タイムスロットを生成することにより低多重タイムスロットが確保される。
【０１３３】
また、前記複数のタイムスロットは、１の移動局のみが割り当てられている第１タイムスロットと１以上の移動局が割り当てられている第２タイムスロットとを含み、前記タイムスロット割り当て変更手段は、前記１の移動局の割り当てを第１タイムスロットから第２タイムスロットへと変更することにより、第１タイムスロットを低多重タイムスロットにして前記生成を行うとしてもよい。
【０１３４】
これにより、１つの移動局の前記割り当てを変更するのみで、低多重タイムスロットを生成され、低多重タイムスロットが確保される。
また、前記第２タイムスロットは、複数あり、さらに、前記１の移動局の割り当てを第１タイムスロットから第２タイムスロットへと変更すると想定した場合において、当該変更がなされた後の第２タイムスロットに割り当てられている全ての移動局についての予測通信品質をそれぞれ求める通信品質予測手段と、前記予測通信品質が所定の通信品質を上回る第２タイムスロットのうちの１つを、前記１の移動局の割り当て先に決定する割り当て先決定手段とを備えるとしてもよい。
【０１３５】
これにより、所定の通信品質を確保しつつ、低多重タイムスロットが生成される。
また、前記割り当て先決定手段は、さらに、最も良い予測通信品質が得られる第２タイムスロットを前記割り当て先に決定するとしてもよい。
これにより、第２タイムスロットへの前記１の移動局の割り当て変更した場合における前記通信品質がより高められる。
【０１３６】
また、前記通信品質予測手段は、第２タイムスロットそれぞれに前記予測通信品質の順位付けを行い、前記割り当て先決定手段は、前記最先順位の第２タイムスロットを前記割り当て先に決定するとしてもよい。
これにより、最も良い予測通信品質が得られると思われるタイムスロットが容易に特定される。
【０１３７】
また、さらに、割り当て済み移動局に関する現状における現状通信品質を評価する通信品質評価手段を備え、前記タイムスロット割り当て変更手段は、さらに、前記変更を実行した後、前記割り当て先の第２タイムスロットに割り当てられている移動局において、前記現状通信品質が所定の通信品質を下回る移動局が１つでも存在する場合、前記変更がなされる前の状態に復旧するとしてもよい。
【０１３８】
これにより、現状通信品質の確保を優先しつつ、低多重タイムスロットの確保が実施される。
また、さらに、前記復旧に伴い、当該復旧直前において割り当て先となっていた第２タイムスロットの前記順位を最下位に訂正する訂正手段を備え、前記割り当て先決定手段は、前記訂正がなされたとき、最先順位の第２タイムスロットを前記割り当て先として新たに決定し、前記タイムスロット割り当て変更手段は、さらに、前記新たな割り当て先へと前記変更を実施するとしてもよい。
【０１３９】
これにより、低多重タイムスロットが確保される機会が増加する。
また、前記タイムスロット割り当て変更手段は、所定回数以上前記復旧が繰り返された場合、前記変更を中止するとしてもよい。
これにより、現状通信品質が所定の通信品質以上となる見込みがないスロットに対して無駄な前記変更を繰り返すことが避けられる。
【０１４０】
また、さらに、同一の第２タイムスロットへの前記変更の実施回数が所定回数以上となったとき、当該第２タイムスロットを前記割り当て先の決定の対象から除外する除外手段を備え、前記タイムスロット割り当て変更手段は、前記除外により割り当て先の対象が無くなったとき、前記変更の中止を実施するとしてもよい。
【０１４１】
これにより、全ての第２タイムスロットについて所定回数以上の復旧が繰り返されるときまで前記変更がなされる。
また、第１タイムスロットは、複数存在し、さらに、複数の第１タイムスロットのうち、現時点より最も近い時刻に移動局の割り当て状態に変更が生じたものを、前記１の移動局の割り当て元として選択する割り当て元選択手段を備え、前記タイムスロット割り当て変更手段は、前記選択がなされた割り当て元から前記割り当て先へと前記１の移動局の割り当てを変更するとしてもよい。
【０１４２】
これにより、割り当て状態に変更が生じていない通信品質が良好な移動局について、現状が維持され、割り当て変更の際に懸念される通信品質の一時的な低下が避けられる。
つまり、割り当て変更がなされた移動局については、もともと通信品質の一時的な低下が生じているものと思われ、このような移動局に対し、さらに、割り当て変更を実施して、再度、通信品質が一時的に低下したとしても、これら通信品質の低下の時間間隔は、非常に短いものであり、ユーザにとっては、通信品質の低下が１回しか生じていないように感じられるためメリットがある。
【０１４３】
また、さらに、割り当て済み移動局に関する現状における現状通信品質を評価する通信品質評価手段を備え、前記タイムスロット割り当て変更手段は、さらに、前記変更を実行した後、前記割り当て先の第２タイムスロットに割り当てられている移動局において、前記現状通信品質が所定の通信品質を下回る移動局が１つでも存在する場合、前記変更がなされる前の状態に復旧するとしてもよい。
【０１４４】
これにより、前記現状通信品質が所定の通信品質以上に保たれる。
また、前記複数のタイムスロットそれぞれは、各タイムスロットを特定するための識別子が対応づけられており、さらに、前記各識別子に対応する順位を記憶している記憶手段と、前記復旧に伴い、当該復旧直前において割り当て元となっていた第１タイムスロットに対応付けられている識別子の前記順位を最下位に修正する順位修正手段とを備え、前記割り当て元選択手段は、前記修正がなされたとき、最上位の順位の識別子が対応付けられている第１タイムスロットを前記割り当て元として選択し、前記タイムスロット割り当て変更手段は、さらに、新たに選択された割り当て元から前記割り当て先へと前記変更を実施するとしてもよい。
【０１４５】
これにより、所定の通信品質以上の前記現状通信品質が確保されるまで、前記割り当て変更が繰り返し実施される。
また、前記タイムスロット割り当て変更手段は、所定回数以上前記復旧が繰り返された場合、前記変更を中止するとしてもよい。
これにより、現状通信品質が所定の通信品質以上となる見込みがないスロットに対して無駄な前記変更を繰り返すことが避けられる。
【０１４６】
また、さらに、各第１タイムスロット毎に、各第１タイムスロットを前記割り当て元として前記変更がなされた変更回数をカウントするカウント手段を備え、カウントされた変更回数が所定回数以上である場合、当該カウントの対象となった第１タイムスロットを前記割り当て元の選定の対象から除外する割り当て元除外手段を備え、前記タイムスロット割り当て変更手段は、前記除外により割り当て元の対象が全て無くなったとき、前記変更の中止を実施するとしてもよい。
【０１４７】
これにより、第１タイムスロット毎に前記変更を許容する上限回数の設定が可能となる。
また、前記タイムスロット割り当て変更手段は、前記複数の移動局とは別の移動局から新たな接続の要求が到来したときに、前記変更を試みるとしてもよい。
これにより、前記別の移動局を低多重タイムスロットに割り当てれば、より確実な新規接続が実現される。
【０１４８】
また、前記タイムスロット割り当て変更手段は、低多重タイムスロット以外のスロットを優先的に前記別の移動局の割り当て先にして前記変更を試みるとしてもよい。
既に、低多重タイムスロットがあるとすれば、これにより、この低多重タイムスロットがそのまま残される。
【０１４９】
また、前記低多重タイムスロット以外のスロットは、１以上の移動局が割り当てられている第２タイムスロットであるとしてもよい。
既に、低多重タイムスロットがあるとすれば、これにより、第２タイムスロットを前記別の移動局の割り当て先とすることにより、この低多重タイムスロットの状態を維持しつつ、前記別の移動局が接続される。
【０１５０】
また、前記タイムスロット割り当て変更手段は、前記変更を想定した場合における第２タイムスロットに割り当てられている移動局全てについての予測通信品質が所定の通信品質以上の場合、当該変更を実施し、前記各移動局のいずれかの予測通信品質が所定の通信品質未満で、かつ、低多重タイムスロットが既に存在する場合、前記第２タイムスロットに代えて、当該低多重タイムスロットを新たな前記割り当て先として前記変更を実施し、また、前記各移動局のいずれかの予測通信品質が所定の通信品質未満で、かつ、前記低多重タイムスロットが存在しない場合、当該変更を中止し、前記別の移動局の接続を拒否するとしてもよい。
【０１５１】
これにより、新規接続の実施よりも通信品質の確保を優先し、前記変更が行われる。
また、通信品質予測手段は、通信品質予測手段は、前記低多重タイムスロットが存在しない場合、前記所定の通信品質を示すしきい値の設定を第１のしきい値とし、前記低多重タイムスロットが存在する場合、前記しきい値の設定を第１のしきい値より厳しい第２のしきい値とするとしてもよい。
【０１５２】
これにより、低多重タイムスロットが確保されている間は、第２タイムスロットに割り当てられている移動局の予測通信品質が高められる。
また、さらに、割り当て済み移動局に関する現状における現状通信品質を評価する通信品質評価手段を備え、前記タイムスロット割り当て変更手段は、さらに、前記変更を実行した後、前記割り当て先の第２タイムスロットに割り当てられている移動局において、前記現状通信品質が所定の通信品質を下回る移動局が１つでも存在する場合、前記変更がなされる前の状態に復旧するとしてもよい。
【０１５３】
これにより、所定の通信品質以上の現状通信品質が確保される。
また、前記タイムスロット割り当て変更手段は、前記割り当てがなされている移動局の数に変動が生じたとき、前記変更を試みるとしてもよい。
これにより、新規接続に限らず、割り当てがなされている移動局の数に変動が生じたときを契機として、前記変更が実施されるので、より低多重タイムスロットが確保される頻度が多くなる。
【図面の簡単な説明】
【図１】第１の実施の形態における無線基地局の機能ブロック図である。
【図２】しきい値テーブルの論理的な構成を示す図である。
【図３】品質指標値テーブルの論理的な構成を示す図である。
【図４】（ａ）は、各スロットの移動局の割り当て状況を示す図である。
（ｂ）は、通信品質予測テーブルの論理的な構成を示す図である。
【図５】（ａ）は、各スロットの移動局の割り当て状況を示す図である。
（ｂ）は、通信品質予測テーブルの論理的な構成を示す図である。
【図６】切替元選択処理を説明する図である。
【図７】空スロット確保処理を示す図である。
【図８】空スロット確保処理が実施された場合における、スロットへの移動局に割り当て状況の時系列な変化を示す図である。
【図９】空スロット確保処理を示すフローチャートである。
【図１０】図７及び図９と異なる空スロット確保処理の1例を示す図である。
【図１１】第２の実施の形態における、新規接続を要求する移動局を優先的に空間多重を実施する処理を示す図である。
【図１２】第２の実施の形態における、通常レベル及びハイレベルのしきい値の１例を示す図である。
【図１３】第２の実施の形態における新規接続を要求する移動局を優先的に空間多重を実施する処理を示すフローチャートである。
【図１４】時分割多重方式と空間多重方式との関係を示す図である。
【図１５】従来の無線基地局における新規接続の状況を示す図である。
【符号の説明】
１１、１２、１３、１４ アンテナ部
２１ 無線部
２１、２２、２３、２４ 無線部
５０ 信号処理部
５１ 信号調整部
５３ 応答ベクトル算出部
５４ ＲＳＳＩ検出部
５５ 通信不良検出部
６０ モデム部
７０ ベースバンド部
８０ 制御部
９０ 情報記憶部
１００ 無線基地局
１１１ 送信部
１１２ 受信部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio base station that performs radio communication with a plurality of mobile stations by spatial multiplexing.
[0002]
[Prior art]
In recent years, with an increase in mobile stations such as PHS and mobile phones, social demands for effective use of frequency resources are increasing. One method for meeting this requirement is communication using a spatial multiplexing method in combination with a conventional time division multiplexing method.
FIG. 14 is a diagram illustrating the relationship between the above-described time division multiplexing scheme and the spatial multiplexing scheme.
[0003]
In the time division multiplexing method, one mobile station is assigned to each of a plurality of time slots divided by time division for communication.
The above time slot is divided into a control time slot (hereinafter referred to as “control slot”) and a call time slot (hereinafter referred to as “call slot”). If it sees, three call slots will be prepared with respect to one control slot.
[0004]
Similarly, three call slots are prepared for one control slot as a slot for transmission, and a total of eight slots including the four reception slots constitute one frame.
In the spatial multiplexing method, a radio base station performs multiplexing and communication using a single frequency at the same time between a plurality of mobile stations and radio base stations in different directions, such as by controlling antenna directivity. It is a method.
[0005]
That is, in the spatial multiplexing method, communication is performed by allocating two or more mobile stations to one call slot.
For this reason, the radio waves between the spatially multiplexed mobile stations need to arrive at the radio base station from different directions, and the mobile stations existing in the same directivity pattern formed by the above-described adaptive array antenna can mutually communicate with each other. Radio waves to be transmitted interfere, making communication difficult.
[0006]
FIG. 15 is a diagram illustrating a state of new connection in a conventional radio base station.
Here, it is assumed that a reception slot is taken as an example, and it is assumed that the transmission slot is assigned the same mobile station as the reception slot.
Usually, the radio base station preferentially performs time division multiplexing in which the communication quality is not affected by the positional relationship of the mobile stations so that the communication quality is good.
[0007]
That is, the radio base station first assigns a mobile station requesting a new connection to a call call slot (hereinafter referred to as “empty slot”) to which no mobile station is assigned, and thereafter, for example, FIG. At time t ₀ As shown below, when there are no more empty slots, spatial multiplexing is performed, and two or more mobile stations are assigned to one call slot and communication is attempted.
[0008]
At that time, the radio base station predicts communication quality between each mobile station and the radio base station, and selects a call slot as an allocation destination so as to ensure communication quality equal to or higher than a predetermined threshold value.
More specifically, the radio base station predicts the communication quality as follows. Each radio base station has a predetermined spatial correlation value threshold value J _t And field strength ratio threshold K _t Is remembered.
[0009]
The radio base station is used for notification of this request for a mobile station that has already been assigned based on the state of communication using the call slot for reception, and for a mobile station that has made a new connection request. Based on the state of communication by the control slot for reception, data necessary for the above-described communication quality evaluation is sampled.
Based on the data thus obtained, the radio base station calculates a response vector indicating the direction in which each mobile station exists, and a spatial correlation value J between the two calculated response vectors. _X Calculate
[0010]
Also, the electric field strength of the two mobile stations is measured, and the electric field strength ratio K between the two electric field strengths measured. _X (D wave level ratio) is calculated.
Where electric field strength ratio K _X Is a value greater than 0 and less than or equal to 1, and the calculated electric field strength ratio K _X When is 1 or more, the reciprocal thereof is used.
And the spatial correlation value J of the response vector _X Is the spatial correlation threshold J _t Less than or equal to (Condition 1) and the field strength ratio K between the two field strengths _X Is the field strength ratio threshold K _t When it is larger or equal (condition 2), it is considered that the communication quality between the radio base station and the mobile station is good, so that the radio base station communicates with the mobile station by the spatial multiplexing method.
[0011]
On the other hand, when the condition 1 is not satisfied or when the condition 2 is not satisfied, the communication quality between the radio base station and the mobile station is considered to be poor. Communicate using other call slots or refuse new connections.
[0012]
[Problems to be solved by the invention]
However, as the number of mobile stations to be connected increases, the number of spatial multiplexing increases, so for mobile stations that request a new connection, the number of conditions to be compared increases, and the conditions that can be connected are more satisfied. There is a problem that it becomes difficult and the opportunities for new connections are reduced.
[0013]
Even if the above two conditions are satisfied, for example, the time t in FIG. ₁ As shown in FIG. 6, when the multiplexing is actually performed, the call quality may not be able to secure a predetermined level. In such a case, the assignment to the call slot must be canceled (hereinafter referred to as “switching”). I don't get it.
One reason why such switching occurs is that the accuracy of data sampled from a mobile station that has made a new connection request is low.
[0014]
In other words, as described above, the mobile station that has made a new connection request performs data necessary for communication quality evaluation based on the communication status of the reception control slot. Since the time that can be sampled in the slot is limited to a very short time compared to the call slot for reception, the communication quality evaluation result may be better or worse than actual in an unstable communication state. May not be determined.
[0015]
Furthermore, when the mobile station is moving at high speed, it is desirable to determine the speech slot to be spatially multiplexed after grasping the moving direction, etc., but the data obtained using the control slot for reception is sampled. Since the time is extremely short, there is a problem that time-series data necessary for grasping the moving direction cannot be sufficiently collected.
Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a radio base station that can be easily connected at the time of new connection.
[0016]
It is another object of the present invention to provide a multiplex control apparatus that is provided in the above-described radio base station and that executes processing for achieving the above-described object.
It is another object of the present invention to provide a time slot allocation changing method and program for achieving the above object.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a radio base station according to the present invention allocates a mobile station to any of a plurality of time slots divided by time division, and wirelessly communicates with a plurality of mobile stations by time division multiplexing and spatial multiplexing. A radio base station that performs communication generates a state where there is a low multiplexing time slot having a spatial multiplexing number N that is less than the spatial multiplexing limit number, or changes the assignment so as to maintain the state. A time slot allocation changing means for trying is provided.
[0018]
The multiplex control apparatus according to the present invention is provided in a radio base station that performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing. A spatial multiplexing control apparatus that assigns one or more mobile stations to any one of a plurality of time slots divided by time division, and among assigned users assigned to a time slot, assignees to other time slots Even if it is migrated, by trying the migration for what can be predicted that the communication characteristics of each connected user of the migration destination time slot will be good, Create a state where there are N spatially multiplexed time slots that are less than the spatial multiplexing limit, or When a connection of a new user is requested when the low multiplex time slot already exists, the low multiplex time slot is determined by preferentially trying to assign a new user to a time slot other than the low multiplex time slot. Exist The spatial multiplexing is controlled so as to maintain the state. Further, the time slot allocation changing method according to the present invention is a radio base station that allocates mobile stations to a plurality of time slots divided by time division and performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing. A time slot allocation changing method for changing the allocation, comprising a time slot allocation step for attempting to change the allocation so as to secure a low-multiplex time slot in which no mobile station is allocated. To do.
[0019]
The program according to the present invention assigns a mobile station to a plurality of time slots divided by time division, and changes the assignment in a radio base station that performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing. A time slot allocation step for trying to change the allocation so as to secure a low-multiplex time slot in which no mobile station allocation is performed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
A radio base station 100 as a first embodiment of the present invention will be described.
The radio base station 100 is wirelessly connected to a PHS mobile station (hereinafter referred to as a mobile station) by time division multiplexing (TDMA / TDD, Time Division Multiple Access / Time Division Duplex) defined by the PHS standard. In addition to division multiplexing, spatial multiplexing is further performed to communicate with the mobile station.
(Configuration of radio base station 100)
FIG. 1 is a functional block diagram of a radio base station 100 according to the first embodiment of the present invention.
[0021]
The radio base station 100 includes antenna units 11 to 14, radio units 21 to 24, a signal processing unit 50, a modem unit 60, a baseband unit 70, a control unit 80, and an information storage unit 90.
(1) Baseband unit 70
The baseband unit 70 is connected to the exchange via an ISDN line.
[0022]
The baseband unit 70 receives packet data through the ISDN line, extracts traffic information from the received packet data, performs TDMA modulation processing and spatial multiplexing processing, and extracts the extracted traffic through a plurality of channels. The information is decomposed into a plurality of baseband signals and output to the modem unit 60.
Here, in the TDMA modulation process, four channels are multiplexed in one TDMA / TDD frame according to the PHS standard. One TDMA / TDD frame is composed of four transmission time slots and four reception time slots. One time slot each of a transmission time slot and a reception time slot constitutes one channel by time division multiplexing. Each time slot is 5 ms long. Further, the spatial multiplexing process multiplexes up to four signals for each channel. Therefore, multiplexing is performed by a maximum of 16 channels in one TDMA / TDD frame by TDMA modulation processing and spatial multiplexing processing.
[0023]
One of the four transmission time slots is a control slot for transmission, and the remaining three are call slots for transmission.
One of the four reception time slots is a reception control slot, and the remaining three are reception speech slots.
The baseband unit 70 receives a plurality of baseband signals from the modem unit 60 through a maximum of 16 channels in one TDMA / TDD frame, and generates packet data from the plurality of received baseband signals. Then, the generated packet data is output via the ISDN line.
(2) Modem unit 60
The modem unit 60 receives a baseband signal modulated by π / 4 shift QPSK (Quadrature Phase Shift Keying) from the signal processing unit 50, demodulates the modulated baseband signal, and generates a baseband signal. The baseband signal thus output is output to the baseband unit 70.
[0024]
The modem unit 60 also receives a baseband signal from the baseband unit 70, modulates the received baseband signal with π / 4 shift QPSK, and outputs the modulated baseband signal to the signal processing unit 50.
The modem unit 60 performs the modulation and the demodulation in parallel on a maximum of four TDMA / TDD frames spatially multiplexed on one time division channel.
(3) Information storage unit 90
The information storage unit 90 includes a threshold value table 200, a quality index value table 300, a communication quality prediction table 400, a threshold ideal value table 420, and a switching source selection table 600.
(Threshold table 200)
FIG. 2 is a diagram showing a logical configuration of a threshold value table 200 that is a table storing threshold values used for determining communication quality.
[0025]
The threshold table 200 includes a spatial correlation value threshold J _t , Electric field strength ratio threshold K _t , Fading threshold P _t Consists of.
Spatial correlation threshold J _t Is the spatial correlation value J obtained from the response vector of the communicating mobile station and the response vector of the new mobile station. _X Is the threshold value.
Field strength ratio threshold K _t Is the ratio of the electric field strength of the signal received from the mobile station in communication to the electric field strength of the signal received from the new mobile station, that is, the electric field strength ratio K _X Is the threshold value.
[0026]
Fading threshold P _t Is the spatial correlation value J between the mobile station in communication and the new mobile station. _X Change speed, that is, fading value P _X Is the threshold value.
Fading value P _X Is the spatial correlation value J _X The amount of change per unit time.
Fading value P _X Is larger, the relative movement speed between the mobile stations is estimated to be higher, so there is a high possibility of deviating from the range of the directivity pattern formed by each of the antenna units 11 to 14, and at the same time as these mobile stations. That is, it is not suitable for spatial multiplexing on the same call slot.
(Quality index value table 300)
As shown in FIG. 3 as an example, the quality index value table 300 includes, for each time slot in each TDMA / TDD frame, response vectors 303 and field strengths 304 of mobile stations using four spatially multiplexed channels. It has n areas for storing four sets.
[0027]
Here, n = (number of TDMA / TDD frames) × 4 (number of time slots in the frame).
As shown as an example in FIG. 3, for a time slot with a time slot number 301 of “1”, the response vector of a mobile station using a channel with a spatial multiplexing number 302 of “1” is “R1”, and the electric field strength is , “I1”, the response vector of the mobile station using the channel having the spatial multiplexing number 302 of “2” is “R2”, the electric field strength is “I2”, and the spatial multiplexing number 302 is “3”. And “4” channels are not yet used, so the response vector and field strength are “blank”, respectively.
(Communication quality prediction table 400)
In the present first embodiment, the channel switching in which only one mobile station is allocated and the mobile station allocated to this communication slot is performed regardless of the communication quality of the allocated mobile station. (Hereinafter referred to as “forced TCH switching”). On the other hand, the switching destination of forced TCH switching is the mobile station that is the switching source and all the call slots that are assumed as switching destinations. It is determined based on the prediction result of the communication quality with the mobile station.
[0028]
Here, the above-described mobile station assignment is performed for one reception call slot and transmission call slot constituting one channel, but these two call slots are changed in pairs. Therefore, hereinafter, the description will be made assuming that the call slot indicates both a reception call slot and a transmission call slot.
Here, for convenience, a call slot to which n (n is an integer equal to or greater than 1) mobile stations is referred to as an n-multiplex slot for convenience, and the number of spatial multiplexing in this case (hereinafter referred to as “space”). "Multiple number") is n.
[0029]
As shown in FIG. 4A, consider a case where all three call slots are one multiplex slot.
FIG. 4B is a diagram showing a communication quality prediction table 400 for determining a switching destination in forced TCH switching created by the control unit 80 in such a case.
[0030]
As shown in FIG. 4B as an example, the communication quality prediction table 400 includes a spatial correlation value J calculated based on two response vectors between two mobile stations. _X And this spatial correlation value J _X Fading value P indicating the rate of change of _X And the field strength ratio K between the two mobile stations _X Is shown.
Furthermore, in the communication quality prediction table 400, when there are two or more combinations of the above two mobile stations, the above spatial correlation value J _X , Electric field strength ratio K _X And fading value P _X About each, the point A, the point B, and the point C which show the order | rank of the relative evaluation result in each above-mentioned combination are shown collectively.
[0031]
A combination 401 indicates a set of two mobile stations that are subject to evaluation of communication quality prediction when forced TCH switching is performed.
The spatial correlation value 402 is a spatial correlation value J that is an index indicating the proximity between two mobile stations. _X Is shown.
Point (A) 403 represents each spatial correlation value J described above. _X And this spatial correlation value J _X The order is assigned from near to far from the ideal value.
[0032]
The field strength ratio 404 is a field strength ratio K which is a ratio of field strengths of two mobile stations. _X Is shown.
Point (B) 405 is the above-mentioned electric field strength ratio K _X In addition, the ideal value of this electric field strength ratio (hereinafter referred to as “the ideal value of electric field strength ratio”) K _R The order is from near to far.
[0033]
The fading value 406 is a spatial correlation value J _X Fading value P, which is the amount of change per unit time _X Is shown.
Point (C) 407 represents each fading value P described above. _X This fading value P _X The order is assigned from near to far from the ideal value.
The total point 408 indicates a value obtained by summing the values of point A, point B, and point C for each combination described above.
[0034]
As described above, when the number of spatial multiplexing is 2 or less, the above-described prediction of communication quality may be performed for each combination indicated by the combination 401 in FIG.
However, the frequency with which the spatial multiplexing number actually becomes 2 or less is considered to be low, and as a result of the forced TCH switching as shown in FIG. 5A, the spatial multiplexing number becomes 3 or more. There are many.
[0035]
FIG. 5B shows a communication quality prediction table 500 created by the control unit 80 in place of the communication quality prediction table 400 in such a case.
In the communication quality prediction table 500, each value from the combination 501 to the total point 508 is the same as the combination 401 to the total point 408 in FIG.
[0036]
The multiplex space method 510 is provided for explanation, and is not actually stored as data, and indicates a combination in which a mobile station of one multiplex slot is assigned to one or more multiplex call slots.
Here, a combination of mobile stations assigned to the same call slot can be regarded as belonging to the same group.
[0037]
When a new spatial multiplexing is performed due to the forced TCH switching, there is a risk of affecting the communication quality of all mobile stations belonging to the spatially multiplexed speech slot group. Therefore, it is necessary to predict communication quality in units of groups.
The quality evaluation group 511 indicates a number for identifying such a group.
(Threshold ideal value table 420)
The threshold ideal value table 420 includes a spatial correlation value threshold J _t And the field strength ratio threshold K _t And fading threshold P _t And the spatial correlation value ideal value J corresponding to each of these threshold values _R And the ideal field strength ratio K _R And the fading ideal value P _R Are stored in advance.
[0038]
Spatial correlation value threshold J _t And spatial correlation value J between ideal values _R Spatial correlation value J (including these two values) _X And the field strength ratio threshold K _t And K between the field strength ratio ideal values _R Electric field strength ratio K (including these two values) _X And fading threshold P _t And fading ideal value P _R Fading value P in (including these two values) _X Is determined to have no problem in communication quality.
[0039]
The ideal value 410 is the spatial correlation value ideal value J _R , Field strength ratio ideal value K _R And fading ideal value P _R The set of
The threshold value 411 is a spatial correlation value threshold value J _t , Electric field strength ratio threshold K _t And fading threshold P _t The set of
The switching source selection table 600 is a table for selecting a switching source when there are a plurality of one multiplex slots, that is, when there are a plurality of call slots that can be a switching source in forced TCH switching. A priority order and the number of retries are associated with each call slot.
(4) Signal processor 50
The signal processing unit 50 includes a signal adjustment unit 51, a response vector calculation unit 53, an RSSI detection unit 54, and a communication failure detection unit 55. Specifically, the signal processing unit 50 is realized by a programmable DSP (Digital Signal Processor).
(Signal adjustment unit 51)
The signal adjustment unit 51 receives signals from the radio units 21 to 24, and should be received in the four reception time slots in each TDMA / TDD frame with respect to a portion where the content of the received signal is known in advance. A directivity pattern is formed for each mobile station by adjusting the amplitude and phase of each transmission / reception signal of the radio units 21 to 24 so as to reduce an error with the signal, and thereby received from the radio units 21 to 24. The signals for each mobile station are separated from the spatially multiplexed signals and output to the modem unit 60, and the signals received from the modem unit 60 are spatially multiplexed so as to be transmitted only to the desired mobile station. To ~ 24.
(RSSI detector 54)
For each time slot in each TDMA / TDD frame, the RSSI detection unit 54 detects the electric field strength of the mobile station received by the radio units 21 to 24 in the time slot. The detected electric field strength is output to the control unit 80. For the mobile station with the link channel established, the detected electric field strength is written in an area specified by the time slot and the spatial multiplexing number in the quality index value table 300.
[0040]
The RSSI detection unit 54 performs the above-described detection when a link channel assignment request is received from the mobile station.
(Response vector calculation unit 53)
The response vector calculation unit 53 communicates in the time slot based on the signal received from the radio units 21 to 24 and the signal adjusted by the signal adjustment unit 51 for each time slot in each TDMA / TDD frame. The response vector including the direction information of the mobile station is calculated as follows.
[0041]
Signals X1, X2, X3 and X4 transmitted from the mobile stations a, b, c and d and received by the radio units 21 to 24, respectively, and the mobile station a, mobile station b, mobile For signals Aa, Ab, Ac and Ad that are to be ideally received from station c, mobile station d,
X1 = h1aAa + h1bAb + h1cAc + h1dAd
X2 = h2aAa + h2bAb + h2cAc + h2dAd
X3 = h3aAa + h3bAb + h3cAc + h3dAd
X4 = h4aAa + h4bAb + h4cAc + h4dAd
When expressing
The response vector calculation unit 53 calculates Ra = (h1a, h2a, h3a, h4a).
[0042]
Here, Ra is a response vector of the mobile station a.
Logically, by taking a correlation between the signal X1 received by the radio unit 21 and the signal Aa that should be ideally received from the mobile station a, the signal term of the other station is removed and h1a is obtained. Since it is impossible for the mobile station to know Aa over the entire signal, h1a is asymptotically obtained using the signal Ua of the mobile station a separated by the signal adjustment unit 51 instead of this Aa.
[0043]
h2a, h3a, and h4a are also obtained by correlating the signal received by each radio unit and the signal Ua of the separated mobile station a.
The response vectors Rb, Rc, Rd of the mobile station b, mobile station c, and mobile station d are similarly calculated.
The response vector calculation unit 53 writes the calculated response vector in the area specified by the spatial multiplexing number for identifying the time slot and the spatial multiplexing channel in the quality index value table 300 for the mobile station with the link channel established. .
[0044]
For the mobile station for which no link channel is established, the calculated response vector is output to the control unit 80.
The response vector calculation unit 53 performs the above calculation when there is a link channel allocation request from the mobile station.
(Communication failure detection unit 55)
The communication failure detection unit 55 has a function of monitoring the wireless communication status of all mobile stations in communication and immediately notifying the control unit 80 when a problem occurs in the wireless communication of these mobile stations.
(5) Antenna units 11-14, radio units 21-24
The antenna units 11 to 14 are adaptive array antennas.
[0045]
The antenna units 11 to 14 are connected to the radio units 21 to 24, respectively.
The radio unit 21 includes a transmission unit 111 including a high power amplifier and a reception unit 112 including a low noise amplifier. The transmission unit 111 converts the low frequency signal input from the signal processing unit 50 into a high frequency signal, amplifies the signal to a transmission output level, and outputs the amplified signal to the antenna unit 11. In accordance with an instruction from the control unit 80, the transmission unit 111 adjusts the transmission output by controlling the gain of the high power amplifier. The receiving unit 112 converts the high frequency signal received by the antenna unit 11 into a low frequency signal, amplifies it, and outputs it to the signal processing unit 50.
[0046]
Since the radio units 22, 23, and 24 have the same configuration as the radio unit 21, description thereof is omitted.
(6) Control unit 80
Specifically, the control unit 80 includes a microprocessor, a timer, a ROM (Read Only Memory) in which a computer program (hereinafter referred to as a program) is recorded, a RAM (Random Access Memory) used for work, and the like. The microprocessor achieves its functions by executing a program recorded in the ROM.
[0047]
The control unit 80 controls the overall operation of the radio base station 100.
(Empty slot reservation processing)
The control unit 80 performs the following empty slot securing process so as to constantly secure an empty slot while performing a switching source selection process and a communication quality prediction process, which will be described later.
[0048]
That is, when the allocation state of the mobile station to the call slot changes, the control unit 80 determines whether there is no empty slot and no call slot to which only one mobile station is assigned. If there is a valid call slot, forced TCH switching is performed to reassign this mobile station to another call slot, and an attempt is made to secure an empty slot.
[0049]
This is not the conventional channel switching in which the mobile station is reassigned to another speech slot due to a decrease in communication quality between the mobile station being accommodated and the radio base station 100. Switching is performed regardless of the communication quality between the stations 100.
Further, when trying the forced TCH switching described above, the control unit 80 collects a plurality of data necessary for predicting the communication quality with respect to the allocated mobile stations over a timer value t1 seconds, That is, the spatial correlation value J _X , Electric field strength ratio K _X And fading value P _X Based on the above, it is determined whether or not the communication quality of the set level or higher can be ensured, and further, it is determined whether or not there is a vacancy in the communication band of the ISDN line going from the baseband unit 70 to the external exchange. Whether to implement TCH switching is determined.
[0050]
By the way, generally, as the number of spatial multiplexing increases, the communication quality of mobile stations allocated in the same call slot tends to decrease.
This is because, since radio waves are received at the same frequency and the same call slot, even if it is received by an antenna having directivity such as an adaptive array antenna, it may be affected by radio wave interference in some cases. .
[0051]
That is, the communication quality of the mobile station assigned to one multiplex slot, that is, the mobile station that is the switching source in forced TCH switching is better than the communication quality of the mobile station assigned to 2, 3, and 4 multiplex slots. Therefore, it is considered that the accuracy of the response vector and the electric field strength obtained under such circumstances is also high.
Further, since one multiplex slot is a call slot and data is received until the call is terminated, the fading value P described above is used. _X Sufficient time can be secured to accurately calculate.
[0052]
As a result of this forced TCH switching, the frequency with which empty slots are secured increases.
In addition, when the allocation state of the mobile station to the call slot changes, the control unit 80 performs the following switching source selection process when there are no empty slots and there are two or more multiplex slots. Determine the original call slot.
[0053]
Further, the control unit 80 monitors the traffic on the ISDN line connected to the baseband unit 70.
(Switch source selection process)
FIG. 6 is a diagram illustrating a switching source selection process for determining a call slot as a switching source in the above-described forced TCH switching.
[0054]
The control unit 80 generates a switching source selection table 600 for determining a call slot as a switching source when the forced TCH switching is to be performed, and stores the switching source selection table 600 in the information storage unit 90.
Each time the forced TCH switching described above ends unsuccessfully, the content of the switching source selection table 600 is updated to determine the next calling slot as the switching source, wait for the timer value t2 seconds, and then again Attempt to secure an empty slot.
[0055]
This standby is performed for the purpose of giving an instruction for channel switching from the radio base station 100 to the mobile station within a range not exceeding the limit of response ability on the mobile station side.
As an opportunity to execute the empty slot securing process, one of the mobile stations newly assigned to the empty slot (hereinafter referred to as “Case 1”) and assigned to 2, 3, or 4 multiple slots becomes an empty slot. When the allocation is changed (hereinafter referred to as “Case 2”) and all the call slots are in a spatial multiplexing state of 2 or more, the result of the call being terminated and the connection being released in two of these slots 1 multiplex slot (hereinafter referred to as “Case 3”).
[0056]
FIG. 6 is a diagram showing a switching source selection table 600 for determining a call slot and a mobile station as a switching source.
Here, taking the case 1 and case 2 described above as an example, the update status of this table accompanying the empty slot securing process will be described.
In case 1 and case 2, the control unit 80 is connected to one multiplex slot to which the mobile station whose assignment state to the call slot has finally changed is assigned. Is stored in the switching source selection table 600 in association with 1 which is the highest priority.
[0057]
When the empty slot securing process is executed, the control unit 80 recognizes one multiplexed slot associated with the highest priority as the call slot of the switching source.
The reason for such prioritization is to avoid selecting a mobile station that is already communicating as a switching source mobile station that is predicted to degrade communication quality when forced TCH switching is performed. This is to avoid as much discomfort as possible.
[0058]
By the way, when there is one multiplex slot other than the call slot with the highest priority, the control unit 80 has a small slot number, which is a unique number associated with each call slot. The priority is associated with the larger one.
In addition, the number of retries 3 is associated as a default value for each multiplexed slot that has been associated with the priority order described above and stored in the switching source selection table 600.
[0059]
The above is the process immediately before the empty slot securing process is executed by the control unit 80, and is the process for specifying the call slot and mobile station as the switching source.
In the communication quality prediction table 400, the control unit 80 has the smallest number of total points among the combinations including the mobile station that is the switching source, that is, the combination that is expected to obtain the highest communication quality. And a call slot to which a mobile station that is not a switching source among mobile stations included in the combination is assigned is determined as a switching destination call slot.
[0060]
Based on the determined switching source mobile station and call slot and switching destination call slot, the control unit 80 performs forced TCH switching.
When the forced TCH switching is successful, the control unit 80 ends the switching source selection process.
On the other hand, when the above-mentioned forced TCH switching fails due to poor communication quality or the like, the priority order value of one multiplex slot that is the switching source is changed to the lowest priority order value, and The number of retries associated with one multiplex slot is decremented by 1, and the priority value in the other multiplex slot is incremented.
[0061]
As a result of repeating such processing, when the number of retries associated with one multiplex slot becomes 0, the control unit 80 excludes this one multiplex slot from the candidate of one multiplex slot of the switching source. .
With this exclusion, the control unit 80 reviews the priorities so as to fill in the priority holes of the excluded one multiple slot.
(Communication quality prediction process)
The controller 80 predicts communication quality as follows.
[0062]
The control unit 80 receives, for example, the response vector Ra of the mobile station a that is about to newly perform wireless communication or is already communicating from the response vector calculation unit 53, and identifies the time slot in the quality index value table 300. The response vector Rx of the existing mobile station X is read from the area identified by the slot number, and the spatial correlation value Ja between the mobile station a and the mobile station X is calculated as shown below.
[0063]
[Expression 1]

[0064]
Next, the control unit 80 receives the electric field intensity Ia of the mobile station a described above from the RSSI detection unit 54, and from the region identified by the time slot number identifying the time slot in the quality index value table 300, the mobile station X Read out the field strength Ix of the field strength ratio Ka
Ka = Ia / Ix
Calculated by Here, when Ka> 1,
Ka = Ix / Ia
Calculated by
[0065]
Next, the calculated spatial correlation value Ja and the spatial correlation value threshold value J stored in the threshold value table 200 are displayed. _t And compare. The calculated electric field strength ratio Ka and the electric field strength ratio threshold value K stored in the threshold value table 200 are also shown. _t And compare.
When Ja ≦ Jt and Ka ≧ Kt, it is determined that spatial multiplexing is possible, and in other cases, it is determined that spatial multiplexing is not possible.
[0066]
In addition, when already communicating with a plurality (2 to 3) of mobile stations by spatial multiplexing, the control unit 80 performs the determination process for each mobile station.
Further, the control unit 80 sets the fading value Pa, which is the temporal change of the spatial correlation value Ja described above.
Pa (t _n ) = (Ja (t _n ) -Ja (t _p )) / (T _n -t _p )
Calculated by
[0067]
Where Ja (t _n ) Is the current time t _n Is the spatial correlation value calculated from the response vector at Ja (t _p ) Is the time t _p Is a spatial correlation value calculated from the response vector of the previous frame at.
Note that the above timer value t1 and t _n And t _p The relationship with
t1 ≧ (t _n -t _p )
There is a relationship.
[0068]
As described above, the control unit 80 obtains the spatial correlation value Ja, the electric field strength ratio Ka, and the fading value Pa, and stores them in the communication quality prediction table 400 or the quality prediction table 500.
Further, the control unit 80 determines whether or not to finally perform forced TCH switching based on the prediction result of the communication quality of the group including the mobile station determined as the switching source by the switching source selection process described above. To do.
[0069]
That is, in the above-described group combination, when even one set has a threshold crack, the control unit 80 cancels the forced TCH switching for the combinations belonging to this group.
(Processing at the time of new connection)
The control unit 80 performs processing at the time of new connection as follows.
[0070]
That is, when a request for new connection is made from the mobile station, the control unit 80 determines whether there is an empty slot, and if there is an empty slot, assigns the mobile station that has requested the new connection to this empty slot.
On the other hand, if there is no empty slot, the control unit 80 tries to connect in the same procedure as in the prior art. That is, the control unit 80 attempts to assign the mobile station that has requested new connection to the already assigned call slot.
[0071]
At that time, the control unit 80 determines whether or not communication quality equal to or higher than the set level can be secured for the allocated mobile station and the newly connected mobile station. _X And field strength ratio K _X To determine whether or not to implement the above-described new connection.
(Processing during communication)
The control unit 80 performs processing during communication as follows.
[0072]
When determining that the communication quality is poor, the control unit 80 controls the mobile station to switch the call slot.
Further, when it is determined that a handover has occurred, control is performed to switch to the radio channel of the migration destination cell.
2 Operation of the radio base station 100
An operation of the radio base station 100 will be described.
(1) Empty slot reservation processing operation
The empty slot securing process will be described with reference to the flowchart shown in FIG.
[0073]
The control unit 80 waits for the number of users in the call slot to change (step S301). When the number of users in the call slot changes, there is no empty slot in all the call slots and whether there is one multiplex slot. (Step S302), and if these conditions are not satisfied, the process is terminated.
On the other hand, if these conditions are satisfied, the control unit 80 substitutes 1 for a value M indicating the number of attempts to perform forced TCH switching (step S303), and sets the timer value to time t1 seconds (step S304).
[0074]
Then, the control unit 80 waits for the set time of the timer (step S305), and collects response vectors, electric field strengths and the like of each mobile station necessary for predicting the communication quality during this period.
. When the set time of the timer has passed, the control unit 80 determines whether or not there is a state change in all the call slots (step S306), and if there is a state change in all the call slots, there is an empty slot in all the call slots. And the process returns to step S302 for determining whether or not there is one multiplex slot.
[0075]
On the other hand, when there is no state change in all the call slots, the control unit 80 determines whether or not the value of M is 1 (step S307), and when the value of M is 1, in step S303 described above, the change of the change is made. The highest priority is given to one multiplex slot that accommodates the mobile station that caused the problem, a default value of the number of retries N is set (step S308), and it is determined whether there is another multiplex slot (step S308) Step S309) In some cases, priorities are assigned to the other multiplex slot in ascending order of slot number, which is the identification number associated with this call slot, and the default value of the number of retries N is set. (Step S310).
[0076]
After the above steps are executed, if the value of M is not 1 in the above-described step S307, or if there is no other 1 multiplex slot in the above-described step S309, the control unit 80 performs the multiplex with the highest priority order. The mobile station in the slot is set as the forced TCH switching source (step S311), the communication quality when the forced TCH switching is performed for the call slot of the switching destination candidate is predicted (step S312), and the highest communication quality is expected. A call slot that is a switching destination candidate, that is, a call slot to which a mobile station other than the switching source mobile station in a combination with a small total number of points is assigned is selected as a switching destination call slot (step S313).
[0077]
Then, the control unit 80, for the communication quality prediction table 400 or 500, for all the combinations in the group to which the combination subject to forced TCH switching belongs, the spatial correlation value, the electric field strength ratio K. _X And fading value P _X Determines whether or not to clear each threshold corresponding to these (step S314), and if so, whether or not there is an empty communication band of the ISDN line from the baseband unit 70 to the external exchange. (Step S315), and if there is no space, the process is terminated.
[0078]
The reason why such control is performed is that it is meaningless when a new call cannot be connected even if this control is performed, and the purpose is to prevent the possibility of unnecessary performance degradation. On the other hand, if there is a space, the control unit 80 tries forced TCH switching (step S316), determines whether the forced TCH switching is successful (step S317), and ends the process if successful.
[0079]
If the forced TCH switching fails, the control unit 80 decrements the number of retries associated with one multiplex slot that is the switching source (step S318).
When the decrement described above is performed, or when it is not cleared in the determination in step S314, the control unit 80 sets the rank associated with the one multiplex slot that is the switching source to the lowest rank. Change (step S319), exclude the mobile station of the call slot for which the number of retries is 0 from the candidates for forced TCH switching (step S320), and switch the call slot to which the number of retries other than 0 is associated, that is, switch It is determined whether or not there is a source candidate (step S321). If there is no candidate to be switched, the control unit 80 ends the process.
[0080]
On the other hand, if there is a candidate to be switched, the control unit 80 sets the timer value to time t2 seconds, and sets a value obtained by incrementing the current M value by 1 as a new M value (step S322). ), The process returns to the step S305 in which the timer is set for the set time.
Note that steps corresponding to the above-described communication quality prediction process are S304, S305, S313, and S314.
[0081]
FIG. 8 is a diagram showing a time-series change in the status of assignment to mobile stations to call slots when such an empty slot reservation process is performed.
When an empty slot can be secured, the control unit 80 allocates only one mobile station to one call slot without performing spatial multiplexing.
At time t0, by assigning the mobile station (3) to the remaining one empty slot, it is determined that there are no empty slots in all the call slots and that there is one multiplexed slot, and the control unit 80 Starts empty slot reservation processing, and as a result, mobile station {circle around (3)} assigned to slot 3 is forcibly TCH switched to slot 1 at time t1.
Then, as shown from t4 to t6, the empty slot securing process is repeatedly performed by accommodating the mobile station that makes a new connection request in the newly generated empty slot.
[0082]
Eventually, as shown at t7, after assigning four mobile stations to slot 1 and slot 2, respectively, if mobile station (9) is assigned to the remaining one empty slot, an empty slot can no longer be generated. .
In this case, the same connection as before is attempted thereafter.
Note that although up to four spatial multiplexing is possible in one call slot, the number of mobile stations that can be spatially multiplexed varies depending on the positional relationship between the spatially multiplexed mobile stations. Even when three mobile stations are assigned four mobile stations in slot 2 and one mobile station in slot 3, normal connection may occur.
[0083]
As described above, according to the first embodiment, the radio base station 100 constantly performs forced TCH switching so as to ensure an empty slot, and thus the frequency of securing an empty slot increases. By assigning a mobile station requesting a new connection to this empty slot, a new connection is facilitated.
In the empty slot securing process in the first embodiment, an empty slot having a spatial multiplexing number of 0 is generated, but the spatial multiplexing number is M (M is 1 or more and the limit spatial multiplexing is performed). It is also possible to generate a slot (hereinafter referred to as “low multiplexed slot”) less than the number (4 in the first embodiment).
[0084]
By trying to make the value of M as small as possible and assigning it to a mobile station that requests a new connection in this low multiplexing slot, the frequency of smooth connection without causing problems in communication quality increases. .
In the first embodiment, the radio base station 100 is wirelessly connected to the PHS mobile station. However, the present invention is not limited to this, and the time division multiplexing method and the spatial multiplexing method are used together, such as a mobile phone. Any wireless communication method may be used.
[0085]
In the first embodiment, the number of antennas is four. However, the number is not limited to this number, and any number may be used.
In this case, when the number of antennas is L, the maximum spatial multiplexing number is L. In FIG. 6, the case 1 and the case 2 have been described as examples. However, whether or not the state change as in the case 2 is a trigger for performing forced TCH switching can be freely set by the user setting. It may be possible to change to
[0086]
In the first embodiment, the spatial correlation value J _X , Electric field strength ratio K _X And fading value P _X Based on these three values, communication quality is predicted when forced TCH switching is performed. However, quality prediction may be performed based on other factors.
In that case, in this first embodiment, for example, in FIG. 5B, “4” to slot 2 in combination 501 is the same as “2” to slot 3 ”. Although only one combination is shown as a result of which the quality prediction result is obtained, even if the combination is the same mobile station, switching is performed when the predicted value of communication quality differs due to different switching targets. It is necessary to predict the communication quality by performing more detailed case division considering the difference of objects.
[0087]
For example, it is advantageous that the transmission timing from each spatially multiplexed mobile station to the radio base station 100 is slightly shifted in separating the signals of each mobile station.
Therefore, radio base station 100 instructs these mobile stations on transmission timing so that the transmission timings of the spatially multiplexed mobile stations do not overlap.
However, the response speed of the mobile station in response to this instruction is different for each mobile station, and there is no problem in assigning a mobile station with a fast response to another slot, but a mobile station with a slow response is assigned to another slot. Allocation is likely to be a problem.
[0088]
Thus, for example, when considering the speed of response as a factor for predicting communication quality, it is necessary to predict communication quality by performing more detailed case classification as described above.
In addition, although not described in the first embodiment, when the user arrangement changes due to other influences during the activation of the empty slot reservation process, for example, the existing user has ended the call, the existing user has degraded performance, etc. In the case where a phenomenon such as forced TCH switching or an existing user moving to another base station due to handover occurs, the control unit 80 may interrupt the present empty slot reservation process by interrupting.
[0089]
In that case, when the allocation of the new mobile station satisfies the condition for the implementation of the empty slot securing process, that is, the condition that there is no empty slot in all the call slots and there is one multiplex slot, the control unit 80 The empty slot securing process is started again from the beginning.
On the other hand, when the above conditions are not satisfied, the control unit 80 does not perform the empty slot securing process.
[0090]
Further, when a connection request is made again from a mobile station requesting a new connection, the control unit 80 may end the empty slot securing process and perform normal channel switching according to a request from the terminal.
In addition, the contents of the empty slot securing process performed by the control unit 80 in the first embodiment are merely an example, and the process of constantly performing forced TCH switching so as to secure an empty slot. If it is.
[0091]
FIG. 9 is a flowchart of the empty slot securing process giving such different cases, and describes the operation contents of only the important part.
The difference between FIG. 9 and FIG. 7 will be described with reference to FIG. 7. From step S308 to step S311 in FIG. 7, the part that determines the call slot and mobile station as the switching source of forced TCH switching is different. .
[0092]
Hereinafter, the flowchart of FIG. 9 will be described.
The control unit 80 waits for the number of users in the call slot to change (step S601). When the number of users in the call slot changes, there is no empty slot in all the call slots and whether there is one multiplex slot. (Step S602), and when these conditions are not satisfied, the process is terminated.
[0093]
On the other hand, when these conditions are satisfied, the control unit 80 waits for the set time of the timer (step S603), and collects response vectors and electric field strengths of the respective mobile stations necessary for predicting the communication quality during this period. To do.
When the set time of the timer has passed, the control unit 80 determines whether or not there is a state change in all the call slots (step S604), and if there is a state change in all the call slots, there is an empty slot in all the call slots. The process returns to step S602 where it is determined whether or not there is one multiplex slot.
[0094]
On the other hand, when there is no state change in all the call slots, the control unit 80 ranks the communication source of the pair of the switching source mobile station and the switching destination mobile station with the good communication quality, that is, the one with the smallest total number of points. A default value of the number of retries N is set for each group (step S605).
This step S605 is a step corresponding to step S308 to step S311 of FIG. 7, and in the first embodiment, the first forced TCH switching source triggered the change in the number of users in the call slot. Even if one multiplex slot exists in the mobile station, the priority order of these call slots is only given to the slot number order, whereas in the first embodiment, the communication quality prediction is performed. The switching source is determined with emphasis on the communication quality, in which the switching source of the forced TCH is determined in ascending order of the total number of points in the table 400 or 500.
[0095]
That is, the control unit 80 sets the combination of mobile stations having the minimum total number of points as the target of forced TCH switching (step S606).
Then, the control unit 80 determines the spatial correlation value and the electric field strength ratio K for all combinations in the group to which the combination subjected to forced TCH switching belongs. _X And fading value P _X Determines whether or not to clear each threshold corresponding to these (step S607), if clear, try forced TCH switching (step S608) to determine whether the forced TCH switching is successful If it succeeds, the process is terminated.
[0096]
If the forced TCH switching fails, the control unit 80 decrements the number of retries associated with one multiplex slot that is the switching source in the switching source selection table 600 (step S610). .
When the above decrement is performed, or when it is not cleared in the determination in step S607, the control unit 80 changes the rank associated with the one multiplexed slot that is the switching source to the lowest rank ( Step S611), the mobile station of the call slot that has reached the retry count of 0 is excluded from the candidates for switching source of forced TCH switching (step S612), and the call slot associated with the retry count other than 0, that is, the switching source Is determined (step S613), and when there is no candidate to be switched, the control unit 80 ends the process.
[0097]
On the other hand, if there is a candidate to be switched, the control unit 80 returns to step S606 where the combination of mobile stations having the smallest total number of points is the target of forced TCH switching.
In this way, the method of determining the mobile station that is the switching source of forced TCH switching may be different from the flowchart of FIG.
[0098]
FIG. 10 is a diagram illustrating an example of an empty slot securing process different from those in FIGS. 7 and 9.
The control unit 80 waits for the number of users in the call slot to change (step S701). When the number of users in the call slot changes, there is no empty slot in all the call slots and whether there is one multiplex slot. (Step S702), and when these conditions are not satisfied, the process is terminated.
[0099]
On the other hand, when these conditions are satisfied, the control unit 80 waits for the set time of the timer (step S703), and collects response vectors and electric field strengths of the respective mobile stations necessary for predicting the communication quality during this period. To do.
When the set time of the timer has passed, the control unit 80 determines whether or not there is a state change in all the call slots (step S704), and if there is a state change in all the call slots, there is an empty slot in all the call slots. The process returns to step S702 to determine whether there is one multiplex slot.
[0100]
On the other hand, when there is no state change in all the call slots, the control unit 80 ranks the communication source of the pair of the switching source mobile station and the switching destination mobile station with the good communication quality, that is, the one with the smallest total number of points. A default value of the number of retries N is set for each group (step S705).
The control unit 80 sets the combination of mobile stations having the minimum total number of points as the target of forced TCH switching (step S706).
[0101]
Then, the control unit 80 determines the spatial correlation value and the electric field strength ratio K for all the combinations in the group to which the combination subjected to forced TCH switching belongs. _X And fading value P _X Determines whether or not to clear the respective threshold values corresponding to these (step S707). If clear, the forced TCH switching is tried (step S708), and it is determined whether or not the forced TCH switching is successful. If it succeeds, the process ends.
[0102]
If the forced TCH switching fails, the control unit 80 decrements the number of retries associated with the call slot in the switching source selection table 600 (step S710).
That is, the process of changing the rank associated with one multiplex slot that is the switching source to the lowest rank as performed in the flowchart in FIG. 9 is not performed.
[0103]
Thus, forced TCH switching is tried again until the number of retries becomes 0 due to the spatial multiplexing condition in which forced TCH switching has failed.
When the above-described decrement is performed, or when it is not cleared in the determination in step S707, the control unit 80 excludes the mobile station of the call slot in which the number of retries is 0 from the candidates for switching source of forced TCH switching. (Step S711), it is determined whether or not there is a call slot associated with a retry count other than 0, that is, a candidate to be switched (Step S712), and there is no candidate to be switched The process is terminated.
[0104]
On the other hand, if there is a candidate to be switched, the control unit 80 returns to step S706 where the combination of mobile stations having the smallest total number of points is the target of forced TCH switching.
In the first embodiment, forced TCH switching is constantly performed so as to secure an empty slot. However, when a new connection is requested, an empty slot securing process is started and an empty slot is assigned. It may be secured.
[0105]
In this case, the content of the determination in step S301 in FIG. 6 is not a change in the number of users in the call slot but a determination as to whether or not a new connection request has been made.
In the flowchart of FIG. 6, the setting value of the retry count N is uniformly set for one multiplex slot, but different numbers of times may be individually set.
[0106]
In the first embodiment, the retry count N is associated with the call slot serving as the switching source, but may be associated with the call slot serving as the switching destination.
(Second embodiment)
A radio base station 100 as a second embodiment of the present invention will be described.
[0107]
As in the first embodiment, the radio base station in the second embodiment is wirelessly connected to the mobile station by the time division multiplexing method defined in the PHS standard, and in addition to the time division multiplexing, A radio base station that performs spatial multiplexing and communicates with a mobile station, has the same functional units as those in FIG.
Here, the control unit 80 that performs processing different from that of the first embodiment will be described.
[0108]
In the first embodiment, when the mobile station assignment state to the call slot changes, the control unit 80 has no call slot and a call slot to which only one mobile station is assigned. In the second embodiment, the control unit 80 requests a new connection while the mobile station that requests the empty connection is preferentially assigned to the empty slot by executing the empty slot securing process. A difference is that a given mobile station is preferentially assigned to one or more call slots, that is, spatial multiplexing is preferentially performed.
[0109]
More specifically, when a new connection is requested from the mobile station, the control unit 80 first determines whether or not there is one or more call slots to which the mobile station can be allocated, and such a call is made. If there is a slot, it tries to allocate a mobile station.
At that time, the control unit 80 performs processing corresponding to the communication quality prediction processing in the first embodiment as follows.
[0110]
That is, the control unit 80 determines the spatial correlation value J _X , Electric field strength ratio K _X And fading value P _X Based on this, communication quality is predicted.
Where fading value P _X Is the spatial correlation value J _X Usually, the spatial correlation value J obtained in different call slots is _X Calculated based on
[0111]
However, since the mobile station requesting a new connection is not communicating using the call slot at the time of the connection request, the fading value P for this mobile station _X Is the spatial correlation value J obtained using only the receiving control slot _X It must be calculated from
That is, the fading value P _X Is the spatial correlation value J obtained in the first half of the control slot _X And spatial correlation value J obtained in the second half _X And calculated from
[0112]
This is data sampled at a very short time interval, and compared to the case where communication was performed using a call slot, the fading value P _X The calculation accuracy of is inferior.
For this reason, the fading value P _X Consideration is given to cancel the allocation of this mobile station only if is clearly large.
Therefore, fading threshold P _t Is the spatial correlation threshold J _t And field strength ratio threshold K _t Compared to, the value is more relaxed.
The control unit 80 determines the fading value P related to the mobile station requesting connection. _X Is the fading threshold P _t When there is an empty slot when trying to allocate to one or more multiplex slots of a mobile station requesting a new connection as described above, a spatial correlation threshold J _t , Electric field strength ratio threshold K _t The mobile station that requests this new connection is assigned to one or more multiplex slots using a threshold value of a high level value that is stricter than when there is no empty slot.
[0113]
The reason for using the high-level value threshold is that, compared to the first embodiment, the fading value P _X This is because the communication quality prediction accuracy decreases, and when a mobile station requesting a new connection is actually assigned to one or more multiplex slots, a communication quality failure is avoided.
On the other hand, when an attempt is made to allocate one or more multiplex slots of a mobile station requesting a new connection as described above, if there is no empty slot, the control unit 80 uses the threshold value of the normal level to determine the new connection. It is determined whether the requested mobile station is assigned to one or more multiplex slots.
[0114]
In other words, when there is no empty slot, a conventional connection is attempted.
FIG. 11 is a diagram illustrating a time-series change in the status of assignment to mobile stations to call slots when the above processing is performed.
At time t0, the mobile station (2) requests a new connection, and the control unit 80 attempts to spatially multiplex the mobile station (2) into the slot 1 so that the number of spatial multiplexing increases.
[0115]
At this time, since there are two empty slots and there is room for assignment in the case where the mobile station requesting a new connection is not successfully spatially multiplexed, the control unit 80 moves to slot 1. The threshold used for determining whether or not spatial multiplexing is possible is set to a higher level than usual.
At time t0, even if such a threshold is used, the determination of whether or not spatial multiplexing is possible is OK.
[0116]
At time t1, mobile station {circle around (3)} requests a new connection, and control unit 80 attempts to spatially multiplex this into slot 1.
Also in this case, since there are two empty slots at this time, the control unit 80 sets the threshold used for determining whether or not the spatial multiplexing to the slot 1 is possible to a higher level than usual.
[0117]
However, since it is determined that spatial multiplexing is not possible in the above determination, it is assigned to slot 2 at time t2.
By repeating such a process, the slot 1 and the slot 2 are gradually filled up.
The mobile station {circle over (5)} requests a new connection, and the control unit 80 tries to perform spatial multiplexing in the order of slot 1 and slot 2, but does not succeed.
[0118]
Therefore, the control unit 80 assigns the mobile station (5) to the slot 3, which is an empty slot.
Since there are no empty slots thereafter, the same slot assignment procedure as before is followed.
That is, the control unit 80 multiplexes the mobile station (5) to the call slot where the communication quality is predicted to be the best.
[0119]
In this case, the control unit 80 sets a normal level value as the threshold used for determining whether spatial multiplexing is possible.
This is because, since there is no longer an empty slot that can be allocated successfully, the threshold value is set to a high level, so that it is not determined that all spatial multiplexing is impossible.
[0120]
FIG. 12 is a diagram showing an example of such normal level and high level threshold values.
The threshold table 900 is a spatial correlation value threshold J _t , Electric field strength ratio threshold K _t Show normal level, high level threshold and ideal value at, and fading threshold P _t This table is stored in advance in the information storage unit.
[0121]
A threshold value (normal level) 901 indicates a normal level threshold value, a threshold value (high level) 902 indicates a high level threshold value that is stricter than the normal level threshold value, An ideal value 903 indicates an ideal value.
Here, the spatial correlation value 904 is a spatial correlation value threshold value J _t The field strength ratio 905 is a field strength ratio threshold value K. _t And the fading value 906 indicates the fading threshold P _t Is shown.
[0122]
Operation of radio base station 100 in the second embodiment
FIG. 13 is a flowchart illustrating a process of preferentially performing spatial multiplexing for a mobile station requesting a new connection in the second embodiment.
The control unit 80 waits until a new connection request is made (step S801), and when a new connection request is made, it determines whether there is an empty slot (step S802).
[0123]
When there is an empty slot, the control unit 80 determines whether or not there is a call slot that is one or more multiplex slots and has room for spatial multiplexing (step S803).
When there is a call slot that has the above-described multiplexing slots and still has room for spatial multiplexing, the control unit 80 sets a high-level threshold as a threshold used for prediction of communication quality (step S804). It is determined whether or not communication quality that clears the threshold is expected (step S805).
[0124]
When this threshold value is cleared, the control unit 80 assigns the mobile station that has requested the new connection to the one or more multiplex slots (step S806), and ends the process.
On the other hand, if it is determined in step S803 whether or not there is a call slot that has one or more multiplex slots and still has room for spatial multiplexing, if such a call slot does not exist, a high level threshold is set. In step S805 for determining whether or not the communication quality to be cleared is expected, when such a high-level threshold cannot be cleared, the control unit 80 selects the mobile station requesting a new connection. Assign to an empty slot.
[0125]
Further, when the above-described new connection request is made, in step S802 for determining whether or not there is an empty slot, if there is no empty slot, the control unit 80 uses the normal level threshold to predict communication quality. The threshold value to be used is set (step S808), and it is determined whether or not the communication quality that clears this threshold value is expected (step S809). The requesting mobile station is assigned (step S810).
[0126]
On the other hand, if not cleared, the control unit 80 rejects the connection to the mobile station requesting a new connection (step S811).
As described above, according to the second embodiment, since the radio base station 100 actively performs spatial multiplexing at the time of new connection, the chance of remaining empty slots being increased increases. .
[0127]
In addition, when there is an empty slot when determining whether or not spatial multiplexing is possible, the above determination is performed using a high-level threshold value, so that more reliable spatial multiplexing can be realized. Even when the determination is made, since an empty slot is prepared, a smooth connection is made by assigning a mobile station requesting a new connection to this empty slot.
[0128]
In the second embodiment, as a result of executing forced TCH switching, a case is described in which the communication quality of a mobile station assigned to a call slot that is newly spatially multiplexed becomes poor. However, in such a case, as in the first embodiment, forced TCH switching may be stopped and spatial multiplexing may be attempted using another call slot as a switching destination.
[0129]
【The invention's effect】
As is clear from the above description, the multiplex control apparatus according to the present invention is provided in a radio base station that performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing. A spatial multiplexing control apparatus that assigns one or more mobile stations to any one of a plurality of time slots divided by time division, and among assigned users assigned to a time slot, assignees to other time slots Even if it is migrated, by trying the migration for what can be predicted that the communication characteristics of each connected user of the migration destination time slot will be good, Create a state where there are N spatially multiplexed time slots that are less than the spatial multiplexing limit, or When a connection of a new user is requested when the low multiplex time slot already exists, the low multiplex time slot is determined by preferentially trying to assign a new user to a time slot other than the low multiplex time slot. Exist The spatial multiplexing is controlled so as to maintain the state.
[0130]
Thereby, in the new connection, the new connection is easily performed by further spatially multiplexing the low-multiplex time slot.
That is, since the number of spatial multiplexing is small in the low multiplexing time slot, the spatial multiplexing conditions are relaxed and the connection can be made more easily.
A radio base station according to the present invention is a radio base station that assigns a mobile station to any one of a plurality of time slots divided by time division and performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing. A time slot allocation changing means for generating a state in which there is a low multiplexing time slot having a spatial multiplexing number N that is less than the spatial multiplexing limit number or attempting to change the allocation so as to maintain the state. A time slot assignment changing method according to the present invention is characterized in that a mobile station is assigned to a plurality of time slots divided by time division, and wireless communication is performed with a plurality of mobile stations by time division multiplexing and spatial multiplexing. A time slot allocation changing method for changing the allocation in a base station, wherein no mobile station is allocated. Characterized in that it includes a time slot assignment step that attempts to change the assignment so as to secure heavy time slots, and the program according to the present invention assigns mobile stations to a plurality of time slots divided by time division, In a radio base station that performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing, a program for changing the allocation, which secures a low multiplexing time slot in which no mobile station is allocated In this manner, a time slot allocation step for attempting to change the allocation is executed by a computer.
[0131]
Thereby, a new connection is easily implemented by using the low multiplex time slot as an allocation destination at the time of a new connection.
That is, as described above, in the low multiplex time slot, since the number of spatial multiplexing is small, the spatial multiplexing condition is relaxed and the connection can be made more easily.
The number of N may be 0.
[0132]
This secures a time slot that can be connected without performing spatial multiplexing.
The time slot allocation changing means may realize the state by generating the low multiplexed time slot.
Thereby, even when there is no low multiplex time slot, a low multiplex time slot is secured by newly generating a low multiplex time slot.
[0133]
The plurality of time slots include a first time slot to which only one mobile station is assigned and a second time slot to which one or more mobile stations are assigned, and the time slot assignment changing means includes: The generation may be performed by changing the allocation of the one mobile station from the first time slot to the second time slot so that the first time slot is a low multiplex time slot.
[0134]
As a result, a low multiplex time slot is generated only by changing the assignment of one mobile station, and a low multiplex time slot is secured.
In addition, there are a plurality of the second time slots, and when it is assumed that the allocation of the first mobile station is changed from the first time slot to the second time slot, the second time slot after the change is made. One of the communication quality prediction means for obtaining the predicted communication quality for all mobile stations allocated to the slot and the second time slot in which the predicted communication quality exceeds a predetermined communication quality It may be provided with an assignment destination determination means for determining a station assignment destination.
[0135]
Thereby, a low multiplex time slot is generated while ensuring a predetermined communication quality.
Further, the allocation destination determination means may further determine the second time slot that provides the best predicted communication quality as the allocation destination.
Thereby, the communication quality when the assignment of the first mobile station to the second time slot is changed is further improved.
[0136]
Further, the communication quality prediction means may rank the predicted communication quality for each second time slot, and the allocation destination determination means may determine the second time slot with the highest priority as the allocation destination. Good.
As a result, the time slot that seems to obtain the best predicted communication quality is easily identified.
[0137]
Further, the communication apparatus further comprises communication quality evaluation means for evaluating current communication quality regarding the allocated mobile station, and the time slot assignment changing means further executes the change and then assigns the second time slot to the assignment destination. In the assigned mobile station, when there is even one mobile station whose current communication quality is lower than the predetermined communication quality, the mobile station may be restored to the state before the change is made.
[0138]
As a result, low-multiplex time slots are secured while giving priority to securing current communication quality.
In addition, a correction means for correcting the rank of the second time slot, which was the assignment destination immediately before the restoration, to the lowest level in association with the restoration, the assignment destination determination means, when the correction is made The second time slot with the highest priority may be newly determined as the allocation destination, and the time slot allocation changing unit may further perform the change to the new allocation destination.
[0139]
This increases the chances of securing a low multiplex time slot.
The time slot allocation changing means may stop the change when the recovery is repeated a predetermined number of times.
As a result, it is possible to avoid repeating the useless change for the slot where the current communication quality is not expected to be equal to or higher than the predetermined communication quality.
[0140]
The time slot further includes an excluding means for excluding the second time slot from the determination target of the assignment destination when the number of executions of the change to the same second time slot exceeds a predetermined number. The assignment changing unit may cancel the change when there is no assignment target due to the exclusion.
[0141]
Thereby, the change is made until the restoration is repeated a predetermined number of times or more for all the second time slots.
In addition, there are a plurality of first time slots. Further, among the plurality of first time slots, an assignment source of the one mobile station that has changed in the assignment state of the mobile station at a time closest to the current time The time slot allocation changing unit may change the allocation of the one mobile station from the selected allocation source to the allocation destination.
[0142]
As a result, for mobile stations with good communication quality in which the allocation state has not changed, the current state is maintained, and a temporary decrease in communication quality, which is a concern when changing the allocation, can be avoided.
In other words, for mobile stations that have been reassigned, it is likely that communication quality has temporarily deteriorated. For such mobile stations, the assignment has been further changed, and the communication quality is re-established. Even if the communication quality temporarily decreases, the time interval of the communication quality deterioration is very short, and there is a merit because the user feels that the communication quality is reduced only once.
[0143]
Further, the communication apparatus further comprises communication quality evaluation means for evaluating current communication quality regarding the allocated mobile station, and the time slot assignment changing means further executes the change and then assigns the second time slot to the assignment destination. In the assigned mobile station, when there is even one mobile station whose current communication quality is lower than the predetermined communication quality, the mobile station may be restored to the state before the change is made.
[0144]
As a result, the current communication quality is maintained above a predetermined communication quality.
Each of the plurality of time slots is associated with an identifier for identifying each time slot, and further, storage means for storing a rank corresponding to each identifier, A rank correction unit that corrects the rank of the identifier associated with the first time slot that was the allocation source immediately before the recovery to the lowest level, and the allocation source selection unit, when the correction is made, The first time slot associated with the highest-ranking identifier is selected as the allocation source, and the time slot allocation changing means further changes the change from the newly selected allocation source to the allocation destination. It may be carried out.
[0145]
Thus, the allocation change is repeatedly performed until the current communication quality equal to or higher than a predetermined communication quality is ensured.
The time slot allocation changing means may stop the change when the recovery is repeated a predetermined number of times.
As a result, it is possible to avoid repeating the useless change for the slot where the current communication quality is not expected to be equal to or higher than the predetermined communication quality.
[0146]
In addition, for each first time slot, further comprising a counting means for counting the number of times the change has been made with each first time slot as the assignment source, and when the counted number of changes is a predetermined number or more, An allocation source excluding unit that excludes the first time slot that has been counted from the allocation source selection target, and the time slot allocation changing unit is configured such that when all the allocation source targets are eliminated by the exclusion, The change may be canceled.
[0147]
Thereby, it is possible to set an upper limit number of times for which the change is allowed for each first time slot.
Further, the time slot allocation changing means may try the change when a new connection request arrives from a mobile station different from the plurality of mobile stations.
Thus, a more reliable new connection can be realized by assigning the other mobile station to the low multiplex time slot.
[0148]
Further, the time slot allocation changing means may try the change by preferentially setting a slot other than the low multiplex time slot as an allocation destination of the other mobile station.
If there is already a low multiplex time slot, this leaves the low multiplex time slot intact.
[0149]
The slots other than the low multiplex time slot may be second time slots to which one or more mobile stations are allocated.
If there is already a low multiplex time slot, the second time slot is assigned to the other mobile station, so that the state of the low multiplex time slot is maintained and the other mobile station is maintained. Is connected.
[0150]
The time slot allocation changing means performs the change when the predicted communication quality for all mobile stations allocated to the second time slot when the change is assumed is equal to or higher than a predetermined communication quality, and If the predicted communication quality of any of the mobile stations is less than the predetermined communication quality and a low multiplex time slot already exists, the low multiplex time slot is replaced with the new assignment destination instead of the second time slot. If the predicted communication quality of any of the mobile stations is less than a predetermined communication quality and the low multiple time slot does not exist, the change is stopped and the other mobile The station connection may be refused.
[0151]
Thus, the change is performed with priority given to ensuring communication quality over the implementation of new connection.
Further, the communication quality prediction means uses the threshold setting indicating the predetermined communication quality as a first threshold when the low multiplex time slot does not exist, and sets the low multiplex time slot. May exist, the threshold value may be set to a second threshold value that is stricter than the first threshold value.
[0152]
As a result, while the low multiplex time slot is secured, the predicted communication quality of the mobile station assigned to the second time slot is improved.
Further, the communication apparatus further comprises communication quality evaluation means for evaluating current communication quality regarding the allocated mobile station, and the time slot assignment changing means further executes the change and then assigns the second time slot to the assignment destination. In the assigned mobile station, when there is even one mobile station whose current communication quality is lower than the predetermined communication quality, the mobile station may be restored to the state before the change is made.
[0153]
As a result, the current communication quality equal to or higher than the predetermined communication quality is ensured.
Further, the time slot assignment changing means may try the change when a change occurs in the number of mobile stations to which the assignment is made.
As a result, the change is implemented not only when the connection is new, but also when the number of allocated mobile stations varies, so that the frequency of securing a lower multiplex time slot is increased.
[Brief description of the drawings]
FIG. 1 is a functional block diagram of a radio base station according to a first embodiment.
FIG. 2 is a diagram showing a logical configuration of a threshold table.
FIG. 3 is a diagram showing a logical configuration of a quality index value table.
FIG. 4 (a) is a diagram showing an assignment status of mobile stations in each slot.
(B) is a figure which shows the logical structure of a communication quality prediction table.
FIG. 5 (a) is a diagram showing an assignment status of mobile stations in each slot.
(B) is a figure which shows the logical structure of a communication quality prediction table.
FIG. 6 is a diagram illustrating a switching source selection process.
FIG. 7 is a diagram showing an empty slot securing process.
FIG. 8 is a diagram showing time-series changes in the status of assignment to mobile stations to slots when an empty slot reservation process is performed.
FIG. 9 is a flowchart showing an empty slot securing process.
FIG. 10 is a diagram showing an example of an empty slot securing process different from FIGS. 7 and 9;
FIG. 11 is a diagram illustrating a process of performing spatial multiplexing preferentially for a mobile station requesting a new connection in the second embodiment.
FIG. 12 is a diagram showing an example of normal level and high level threshold values in the second embodiment;
FIG. 13 is a flowchart illustrating a process of preferentially performing spatial multiplexing for a mobile station requesting a new connection in the second embodiment.
FIG. 14 is a diagram illustrating a relationship between a time division multiplexing method and a spatial multiplexing method.
FIG. 15 is a diagram illustrating a state of new connection in a conventional radio base station.
[Explanation of symbols]
11, 12, 13, 14 Antenna part
21 Radio section
21, 22, 23, 24 Radio unit
50 Signal processor
51 Signal adjustment unit
53 Response vector calculation unit
54 RSSI detector
55 Communication failure detection unit
60 Modem part
70 Baseband part
80 Control unit
90 Information storage unit
100 radio base station
111 Transmitter
112 Receiver

Claims (26)

A spatial multiplexing control apparatus that is provided in a radio base station that performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing, and that assigns one or more mobile stations to any of a plurality of time slots divided by time division. And
Among the connected users assigned to the time slot, even if the assignment destination is transferred to another time slot, it can be predicted that the communication characteristics of each connected user of the destination time slot can be improved, Attempting the transition creates a state in which there are N spatially multiplexed time slots that are less than the spatial multiplexing limit, or new users are connected if the low multiplexed time slots already exist Controlling the spatial multiplexing to maintain the presence of the low multiplex time slot by preferentially trying to assign new users to time slots other than the low multiplex time slot when requested. A spatial multiplexing control device. A radio base station that assigns a mobile station to any one of a plurality of time slots divided by time division and performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing,
A time slot allocation changing means for generating a state in which low multiplexing time slots having a spatial multiplexing number N that is less than the spatial multiplexing limit number exist or trying to change the allocation so as to maintain the state; A featured radio base station.   The radio base station according to claim 2, wherein the number of N is 0.   The radio base station according to claim 3, wherein the time slot allocation changing unit realizes the state by generating the low-multiplex time slot. The plurality of time slots include a first time slot to which only one mobile station is assigned and a second time slot to which one or more mobile stations are assigned,
The time slot assignment changing means changes the assignment of the first mobile station from the first time slot to the second time slot, thereby making the first time slot a low multiplexed time slot and performing the generation. The radio base station according to claim 4. There are a plurality of the second time slots,
further,
When it is assumed that the assignment of the one mobile station is changed from the first time slot to the second time slot, the prediction communication for all the mobile stations assigned to the second time slot after the change is made A communication quality prediction means for obtaining each quality,
6. The allocation destination determining means for determining one of second time slots in which the predicted communication quality exceeds a predetermined communication quality as an allocation destination of the one mobile station. Radio base station.   The radio base station according to claim 6, wherein the allocation destination determination unit further determines a second time slot that provides the best predicted communication quality as the allocation destination. The communication quality prediction means ranks the predicted communication quality in each second time slot,
The radio base station according to claim 7, wherein the allocation destination determination unit determines the second time slot having the highest priority as the allocation destination. further,
A communication quality evaluation means for evaluating the current communication quality in the current situation regarding the allocated mobile station is provided.
The time slot assignment changing means further includes, after executing the change, one mobile station whose current communication quality is lower than a predetermined communication quality among the mobile stations assigned to the second time slot of the assignment destination. However, if it exists, the radio base station according to claim 8, wherein the radio base station is restored to the state before the change. further,
Along with the recovery, the correction means for correcting the rank of the second time slot that was assigned immediately before the recovery to the lowest order,
When the correction is made, the allocation destination determination means newly determines the second time slot with the highest priority as the allocation destination,
The radio base station according to claim 9, wherein the time slot allocation changing unit further performs the change to the new allocation destination.   The radio base station according to claim 10, wherein the time slot allocation changing means stops the change when the restoration is repeated a predetermined number of times or more. further,
An exclusion means for excluding the second time slot from the determination target of the assignment destination when the number of times of the change to the same second time slot is equal to or greater than a predetermined number of times,
12. The radio base station according to claim 11, wherein the time slot allocation change unit cancels the change when there is no allocation target due to the exclusion. There are multiple first time slots,
Furthermore, an allocation source selection means for selecting, as the allocation source of the one mobile station, a change in the allocation status of the mobile station at a time closest to the current time among the plurality of first time slots,
7. The radio base station according to claim 6, wherein the time slot allocation changing unit changes the allocation of the one mobile station from the selected allocation source to the allocation destination. further,
A communication quality evaluation means for evaluating the current communication quality in the current situation regarding the allocated mobile station is provided.
The time slot assignment changing means further includes, after executing the change, one mobile station whose current communication quality is lower than a predetermined communication quality among the mobile stations assigned to the second time slot of the assignment destination. However, if it exists, the radio base station according to claim 13, wherein the radio base station is restored to the state before the change. Each of the plurality of time slots is associated with an identifier for specifying each time slot,
further,
Storage means for storing a rank corresponding to each identifier;
Along with the restoration, a rank correction means for correcting the rank of the identifier associated with the first time slot that was the allocation source immediately before the restoration to the lowest order,
The allocation source selection means, when the correction is made, selects the first time slot associated with the highest rank identifier as the allocation source,
The radio base station according to claim 14, wherein the time slot allocation changing unit further performs the change from a newly selected allocation source to the allocation destination.   The radio base station according to claim 15, wherein the time slot allocation changing means stops the change when the restoration is repeated a predetermined number of times or more. further,
For each first time slot, the counter has a counting means for counting the number of times the change has been made with each first time slot as the assignment source,
When the counted number of changes is equal to or greater than a predetermined number of times, an allocation source excluding unit that excludes the first time slot that is the target of the count from the allocation source selection target,
The radio base station according to claim 16, wherein the time slot allocation changing unit cancels the change when all of the allocation source targets disappear due to the exclusion.   4. The radio base station according to claim 3, wherein the time slot allocation changing means tries the change when a new connection request arrives from a mobile station different from the plurality of mobile stations.   19. The radio base station according to claim 18, wherein the time slot assignment changing means tries the change with a slot other than the low multiplexing time slot preferentially assigned to the other mobile station.   The radio base station according to claim 19, wherein the slots other than the low multiplex time slot are second time slots to which one or more mobile stations are allocated.   When the predicted communication quality for all mobile stations assigned to the second time slot when the change is assumed is equal to or higher than a predetermined communication quality, the time slot assignment changing unit performs the change, If the predicted communication quality of any of the stations is lower than the predetermined communication quality and a low multiplex time slot already exists, the low multiplex time slot is used as the new assignment destination instead of the second time slot. If the predicted communication quality of any of the mobile stations is less than a predetermined communication quality and the low multiple time slot does not exist, the change is stopped and the other mobile station The radio base station according to claim 20, wherein the connection is rejected.   The communication quality prediction means sets the threshold value indicating the predetermined communication quality as a first threshold value when the low multiplex time slot does not exist, and sets the threshold when the low multiplex time slot exists. The radio base station according to claim 21, wherein the value is set to a second threshold value that is stricter than the first threshold value. further,
A communication quality evaluation means for evaluating the current communication quality in the current situation regarding the allocated mobile station is provided.
The time slot assignment changing means further includes, after executing the change, one mobile station whose current communication quality is lower than a predetermined communication quality among the mobile stations assigned to the second time slot of the assignment destination. 23. The radio base station according to claim 22, wherein if there is, the radio base station recovers to a state before the change is made.   The radio base station according to claim 3, wherein the time slot allocation changing means tries the change when the number of mobile stations to which the allocation is made varies. A time slot assignment changing method for assigning a mobile station to a plurality of time slots divided by time division and changing the assignment in a radio base station that performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing. ,
A time slot allocation changing method comprising a time slot allocation step for attempting to change the allocation so as to secure a low-multiplex time slot in which no mobile station is allocated. In a radio base station that assigns a mobile station to a plurality of time slots divided by time division and performs radio communication with a plurality of mobile stations by time division multiplexing and spatial multiplexing, a program for changing the assignment,
A program for causing a computer to execute a time slot assignment step that attempts to change the assignment so as to secure a low-multiplex time slot in which no mobile station is assigned.

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