JP3582489B2

JP3582489B2 - Mobile communication system and channel switching method

Info

Publication number: JP3582489B2
Application number: JP2001000289A
Authority: JP
Inventors: 功鈴木
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2000-09-05
Filing date: 2001-01-05
Publication date: 2004-10-27
Anticipated expiration: 2021-01-05
Also published as: JP2002159038A

Description

【０００１】
【発明の属する技術分野】
本発明は移動通信システム及びチャネル切替方法に係り、特に無線パケット通信機能を有する携帯電話機と相手端末との間で通信する移動通信システム及び使用チャネルを切り替えるチャネル切替方法に関する。
【０００２】
【従来の技術】
従来の移動通信システムでは、中継局としての複数の基地局がそれぞれ固有の通信エリアを有し、携帯電話機等の移動体端末が、在圏する通信エリアの中心に位置する基地局との間で無線通信を行う。基地局は上位の統括局を介して公衆網等に接続されるので、基地局を介して移動体端末と公衆網の相手端末との通話を可能にしている。この移動通信システムにおける基地局は、移動体端末との間で割り当てたチャネルのタイムスロットを使用して無線通信を行う。
【０００３】
また、通話品質を向上させるため、移動体端末が通信中以外の一又は二以上の基地局から制御チャネルで送信されている電波の電界強度を測定し、その測定電界強度のうち最も電界強度の強い電波を送信している基地局へ通話チャネルを切り替える（いわゆるハンドオーバする）ことも従来より知られている。更に、従来の移動通信システムでは、パケット通信を行う移動体端末が、受信電界強度が劣化したり、受信データの誤り率が所定のしきい値より悪くなった場合にも、通話チャネルの切り替えを行う。
【０００４】
【発明が解決しようとする課題】
しかるに、パケット通信機能を有する移動体端末と通信する従来の移動通信システムでは、受信電界強度の劣化や受信データの誤り率、周辺チャネルの電界強度だけを判断基準としてパケット通信を行うチャネルの切替を行っているため、現在パケット通信しているチャネルの受信電界強度が高く、受信データの誤り率も良好な場合であっても、同一のパケット通信可能なチャネルを使用している移動体端末が多数存在していると、通信負荷が多くなり、通信速度が低下してしまう。
【０００５】
そのような状況においても、携帯電話機は何もできない状態で、低下した通信速度でパケット通信を継続するしかなく、通信負荷を分散できない状況になっていて、無線資源を有効利用できていない。また、従来は、伝送する情報量を確保するために、パケット通信を行えるチャネル数を複数通知することができない。
【０００６】
本発明は以上の点に鑑みなされたもので、通信中の移動体端末側から通信量の低い通話チャネルへ切り替え得る移動通信システム及びチャネル切替方法を提供することを目的とする。
【０００７】
また、本発明の他の目的は、パケット通信を行えるチャネル数を複数通知し得る移動通信システム及びチャネル切替方法を提供することにある。
【０００８】
更に、本発明の他の目的は、移動体端末自身で自動的に通信負荷の軽いチャネルを選択し得る移動通信システム及びチャネル切替方法を提供することにある。
【０００９】
【課題を解決するための手段】
上記の目的を達成するため、本発明の移動通信システムは、複数の基地局が自身の通信エリア内に在圏する移動体端末との間で無線電波でパケット通信する移動通信システムにおいて、複数の基地局は、自身の通信エリア内の第１の通信量を計算する計算手段と、第１の通信量とパケット通信可能なチャネルの情報を周辺の基地局へ定期的に送出する送出手段と、他の基地局から受信した第１の通信量とパケット通信可能なチャネルの情報を、自局の通信エリアに在圏する移動体端末に報知する報知手段とをそれぞれ有し、移動体端末は、パケット通信中の基地局から送信された第１の通信量とパケット通信可能なチャネルの情報を受信する受信手段と、受信したチャネルの情報に基づいて、その情報で指定されたパケット通信中の基地局以外の基地局で使用している周波数の受信電界強度を測定する電界強度測定手段と、パケット通信中の基地局の第２の通信量を計算する通信量計算手段と、受信電界強度の測定結果と所定のしきい値とを比較し、かつ、第２の通信量と受信手段で受信した第１の通信量とを比較する比較手段と、比較手段により受信電界強度の測定結果が所定のしきい値よりも大で、かつ、第２の通信量の方が第１の通信量よりも所定値以上大であるとの比較結果が得られたときは、受信手段により受信したパケット通信可能なチャネルに切り替える切替手段とを有し、移動体端末は通信負荷が軽い方の基地局との間で通信する構成としたものである。
【００１０】
この発明では、移動体端末が基地局との間でパケット通信中に、他の基地局で使用している周波数の受信電界強度の測定結果が所定のしきい値よりも大で、かつ、パケット通信中の第２の通信量の方が他の基地局の第１の通信量よりも所定値以上大であるとの比較結果が得られたときは、受信したパケット通信可能なチャネル情報に基づいて、上記の他の基地局のチャネルに切り替えるようにしたため、負荷が少ない方の基地局との間でパケット通信ができる。
【００１１】
ここで、上記の報知手段は、アイドルユニットを用いて第１の通信量とパケット通信可能なチャネルの情報を、パケット通信中の移動体端末に報知することが、パケット通信の負荷軽減にとって望ましい。
【００１２】
また、基地局の計算手段は、１スーパーフレーム中の通信使用スロット数の積算値をスーパーフレーム単位で計算し、前回の積算値と今回の積算値に重み付けを行って移動平均を算出し、この移動平均を最新の積算値とすると共に第１の通信量として求めることを特徴とする。
【００１３】
また、本発明の移動通信システムは、上記の目的を達成するため、複数の基地局が自身の通信エリア内に在圏する移動体端末との間で無線電波でパケット通信する移動通信システムにおいて、複数の基地局は、自身の通信エリア内のパケット通信量を計算する計算手段と、パケット通信量とパケット通信可能なチャネルの情報を周辺の基地局へ定期的に送出する送出手段と、他の基地局から受信したパケット通信量とパケット通信可能なチャネルの情報を、自局の通信エリアに在圏する移動体端末に報知する報知手段とをそれぞれ有する構成とし、また、移動体端末は、パケット通信中の基地局から送信されたパケット通信量とパケット通信可能なチャネルの情報を受信する受信手段と、受信したチャネルの情報に基づいて、その情報で指定されたパケット通信中の基地局以外の基地局で使用している周波数の受信電界強度を測定する電界強度測定手段と、パケット通信中の現在のチャネルのすべてのパケットの第１の通信量と、パケット通信中の現在のチャネルの自局宛のパケットの第２の通信量をそれぞれ計算する通信量計算手段と、第１の通信量から第２の通信量に所定値を乗算した値を差し引いた値をしきい値として算出するしきい値計算手段と、受信電界強度の測定結果と所定の判定値とを比較し、かつ、受信手段で受信したパケット通信量としきい値計算手段で計算されたしきい値とを比較する比較手段と、比較手段により受信電界強度の測定結果が判定値よりも大で、かつ、パケット通信量の方がしきい値よりも小であるとの比較結果が得られたときは、受信手段により受信したパケット通信可能なチャネルに切り替える切替手段とを有する構成としたものである。
【００１４】
この発明では、移動体端末が基地局との間でパケット通信中に、他の基地局で使用している周波数の受信電界強度の測定結果が所定のしきい値よりも大で、かつ、パケット通信中の現在のチャネルの第１のパケット通信量から自局宛のパケットの第２の通信量に所定の値を乗算した値を差し引いて得られたしきい値よりも、受信した周辺基地局でのパケット通信量の方が小であるときには、受信したパケット通信可能なチャネル情報に基づいて、上記の他の基地局のチャネルに切り替えるようにしたため、負荷が少ない方の基地局との間でパケット通信ができる。
【００１５】
また、本発明は、パケット通信可能なチャネルの情報が、群分け数と指定群からなるチャネル切替指定群と周波数コードを少なくとも含んでおり、移動体端末は、移動体端末１つ１つに固有な番号の移動局識別子を、受信したチャネル切替指定群中の群分け数で除算した余りが、受信したチャネル切替指定群中の指定群と一致したときにのみ、比較手段による比較動作を行うことを特徴とする。
【００１６】
更に、上記の目的を達成するため、本発明方法は、基地局の通信エリア内に在圏する移動体端末が、該基地局との間で無線電波でパケット通信しているチャネルを切り替える移動通信システムのチャネル切替方法において、基地局は、自身の通信エリア内の第１の通信量を計算し、その第１の通信量とパケット通信可能なチャネルの情報を周辺の基地局へ定期的に送出すると共に、周辺の基地局からの第１の通信量とパケット通信可能なチャネルの情報をパケット通信中の移動体端末に送信し、移動体端末は、パケット通信中の基地局の第２の通信量を計算する第１のステップと、パケット通信中の基地局から送信された第１の通信量とパケット通信可能なチャネルの情報を受信する第２のステップと、受信したチャネルの情報に基づいて、その情報で指定されたパケット通信中の基地局以外の基地局で使用している周波数の受信電界強度を測定する第３のステップと、受信電界強度の測定結果と所定のしきい値とを比較し、かつ、第２の通信量と第２のステップで受信した第１の通信量とを比較する第４のステップと、受信電界強度の測定結果が所定のしきい値よりも大で、かつ、第２の通信量の方が第１の通信量よりも所定値以上大であるとの比較結果が得られたときは、受信したパケット通信可能なチャネルに切り替える第５のステップとを含むことを特徴とする。
【００１７】
この発明も、受信したパケット通信可能なチャネル情報に基づいて、上記の他の基地局のチャネルに切り替えるようにしたため、負荷が少ない方の基地局との間でパケット通信ができる。
【００１８】
また、更に、本発明方法は上記の目的を達成するため、基地局は、自身の通信エリア内のパケット通信量を計算し、そのパケット通信量とパケット通信可能なチャネルの情報を周辺の基地局へ定期的に送出すると共に、周辺の基地局からのパケット通信量とパケット通信可能なチャネルの情報をパケット通信中の移動体端末に送信し、移動体端末は、パケット通信中の現在のチャネルのすべてのパケットの第１の通信量と、パケット通信中の現在のチャネルの自局宛のパケットの第２の通信量をそれぞれ計算する第１のステップと、第１の通信量から第２の通信量に所定値を乗算した値を差し引いた値をしきい値として算出する第２のステップと、パケット通信中の基地局から送信されたパケット通信量とパケット通信可能なチャネルの情報を受信する第３のステップと、受信したチャネルの情報に基づいて、その情報で指定されたパケット通信中の基地局以外の基地局で使用している周波数の受信電界強度を測定する第４のステップと、受信電界強度の測定結果と所定の判定値とを比較し、かつ、第３のステップで受信したパケット通信量と第２のステップで算出したしきい値とを比較する第５のステップと、受信電界強度の測定結果が判定値よりも大で、かつ、パケット通信量の方がしきい値よりも小であるとの比較結果が得られたときは、受信したパケット通信可能なチャネルに切り替える第６のステップとを含むことを特徴とする。
【００１９】
この発明では、移動体端末自身で計算した現在のチャネルの全体のパケット通信量と自局宛のパケット通信量とから計算したしきい値と、受信した周辺基地局でのチャネルのパケット通信量とを比較し、その比較結果に基づいて、チャネル切替を行うか否か選択することにより、常に負荷が少ない方の基地局との間でパケット通信ができる。
【００２０】
【発明の実施の形態】
次に、本発明の実施の形態について図面と共に説明する。図１は本発明になる移動通信システムの一実施の形態のシステム構成図を示す。同図において、移動体端末の一例としての、無線パケット通信機能を有した携帯電話機（ＭＳ）１及び２が、基地局（ＢＳ）３の通信エリアＡ１内に在圏している。また、携帯電話機２は基地局（ＢＳ）４の通信エリアＡ２内にも在圏している。従って、携帯電話機１は基地局３との間でのみパケット通信可能であり、携帯電話機２は基地局３及び４のどちらともパケット通信可能な位置にある。ここでは、携帯電話機１及び２は基地局３との間で無線パケット通信しているものとする。
【００２１】
パケット処理装置５は、基地局３及び４から受信した携帯電話機１、２からのパケットデータを、携帯電話機１、２がチャネル切替した時などに発生する信号の重複及び欠落を補修し、補修後のパケットデータをゲートウェイ装置６に送出する。ゲートウェイ装置６は、入力されたパケットデータに対しプロトコル変換及びアドレス変換等を行った後、インターネット７へ送出する。
【００２２】
一方、インターネット７より携帯電話機へデータ送出要求があった時は、ゲートウェイ装置６が、該当する携帯電話機が通信可能なパケット処理装置を検索し、プロトコル変換処理後にパケットデータとして、検索したパケット処理装置（図１の５とする）へ伝送する。また、該当携帯電話機の情報も伝送する。
【００２３】
パケット処理装置５は、ゲートウェイ装置６から伝送された該当の携帯電話機が在圏している基地局を探し出し、該当する基地局へパケットデータを伝送する。基地局は無線通信を用いて該当の携帯電話機へパケットデータを送信する。また、基地局３、４間で個々のパケット通信可能なチャネル情報と、パケット通信可能なチャネルの通信量を相互に通知し合う機能を有する。
【００２４】
次に、本実施の形態の動作について、図１乃至図６を参照して説明する。本実施の形態では、時分割多元接続（ＴＤＭＡ：ＴｉｍｅＤｉｖｉｓｉｏｎＭｕｌｔｉｐｌｅｘＡｃｃｅｓｓ）方式のディジタル携帯電話機を使用したパケット通信方式での動作を説明する。いま、基地局３の通信エリアＡ１内に在圏している携帯電話機１及び２が、基地局３とパケット通信状態にあるものとする。ただし、携帯電話機２は基地局４の通信エリアＡ２内にも在圏しており、基地局４ともパケット通信可能な位置にある。
【００２５】
基地局３は携帯電話機１及び２との間で、無線電波を用いて図２に示すタイミングで信号をＴＤＭＡ方式で伝送している。すなわち、図２において、無線通信の伝送タイミングには、最小単位である６．６７ｍｓｅｃのスロットが３つで１つのサブフレーム（２０ｍｓｅｃ）を構成し、また、３６個のサブフレームで１つのスーパーフレーム（７２０ｍｓｅｃ）を構成している。
【００２６】
また、基地局３は携帯電話機１及び２に対して、送出したいパケットデータを同一のスロット番号のタイミングに分割して伝送する。図２では、基地局３は携帯電話機１（ＭＳ１）に対して伝送するパケットデータを６個のスロット単位に分割して、スロット番号＃０を使用して送出している。また、携帯電話機２（ＭＳ２）に対して伝送するパケットデータは２つあり、一つは４個のスロット単位に分割され、もう一つは２個のスロット単位に分割され、いずれもスロット番号＃２を使用して伝送される。
【００２７】
なお、携帯電話機１及び２に伝送するパケットデータが無い場合は、基地局３は図２に「ＩＤＬＥ」で示す、アイドルユニットと呼ばれる基地局情報（主にレイヤ１レベルの無線通信パラメータ）を携帯電話機１及び２に伝送する。
【００２８】
更に、基地局３は携帯電話機１及び２に対して、何スロット分のデータを伝送したいのかを各スロットの先頭の８ビットを用いて通知している。この８ビットの情報をＷ情報ビットと呼ぶ。Ｗ情報ビットの使用方法について図３を用いて説明する。Ｗ情報ビットは、図３（Ａ）にフォーマットを示すように、先頭の１ビットをＦ１と呼び、次の１ビットをＦ２と呼ぶ。Ｆ１は該当のスロットが先頭のユニットがどうかを示し、値が「０」のときは非先頭ユニット、「１」のときは先頭ユニットであることを示す。また、Ｆ２は該当のスロットが最終のユニットかどうかを示し、値が「０」のときは非最終ユニット、「１」のときは最終ユニットであることを示す。
【００２９】
Ｗ情報ビットの残りの６ビットはＷ０と呼び、Ｆ２が最終ユニットを示している場合は有効バイト数を示し、Ｆ２が最終ユニットでないことを示している場合は、残りのユニット数（Ｗｒ）を示す。Ｗｒについては、図２に示すように、先頭からカウントダウンされて使用される。Ｗｒが「０」のとき、すなわち、Ｗ情報ビットのすべてが「０」のスロットがアイドルユニットである。
【００３０】
以上をまとめると、Ｆ１＝１、Ｆ２＝０のとき図３（Ｂ）に示す先頭ユニットであり、Ｆ１＝Ｆ２＝０のとき図３（Ｃ）に示すように、先頭ユニットでも最終ユニットでもない継続ユニットであり、Ｆ１＝０、Ｆ２＝１のとき図３（Ｄ）に示す最終ユニットであり、Ｗｒが有効バイト数Ｌを示し、更に、Ｆ１＝Ｆ２＝Ｗｒ＝０のときは図３（Ｅ）に示すアイドルユニットである。
【００３１】
本実施の形態は、アイドルユニットの未使用個所に、他のパケット通信可能なチャネルの情報を設定するようにしたものである。このアイドルユニットについて図４と共に更に詳細に説明する。
【００３２】
図４において、アイドルユニットの１１オクテットまでは従来と同じであり、１２オクテットからを本実施の形態で新たに設定した。以下、追加した各オクテットについて説明するに、１２オクテット目の８ビットには「チャネル切替指定群」が設定される。このチャネル切替指定群は、該当アイドルユニットを受信しているすべての携帯電話機が一斉に通知するチャネルに切り替わらないように制御するために使用する。このチャネル切替指定群の上位４ビットを使用して、携帯電話機を何群に分割するかを指定し、残りの下位４ビットで群分けした群を指定する。
【００３３】
次の１３オクテット目と１４オクテット目の計１６ビットには、他のパケット通信可能なチャネルの周波数コードを通知するために使用する。１３オクテット目の上位４ビットには周波数帯識別子を通知するために使用し、１３オクテット目の下位４ビットと１４オクテット目の計１２ビットを周波数コードを通知するために使用する。１５オクテット目は、パケット通信可能なカラーコード、１６オクテット目は、パケット通信可能なチャネルのスクランブルコードを通知するために使用する。最後の１７オクテット目は通信量通知で、他のパケット通信可能なチャネルの現在の通信状態（パケット通信量）を通知するために使用する。
【００３４】
次に、本発明による通信状態を示す通信量を計算するアルゴリズムの一実施の形態について、図５のフローチャートと共に説明する。本アルゴリズムは基地局側で使用するが、携帯電話機によってはそのまま使用する。まず、通信量平均値Ｍａｖｇ及び変数Ｉｎｉｔをそれぞれ０に初期化し（ステップ１０１）、続いて１スーパーフレームでの通信量積算値Ｍｓｕｍ及びスロットカウント数ｎをそれぞれ０に初期化する（ステップ１０２）。
【００３５】
続いて、スロット割り込みを検出すると（ステップ１０３）、スロットカウント数ｎが「１０７」より大であるかどうかチェックし（ステップ１０４）、「１０７」以下であるときには、１スーパーフレーム以内のスロットであるので、Ｗ情報ビットがすべて「０」かどうかチェックする（ステップ１０５）。
【００３６】
Ｗ情報ビットのいずれかが「０」であれば、アイドルユニット以外のユニットであると判断して通信量積算値Ｍｓｕｍを「１」だけインクリメントした後（ステップ１０６）、スロットカウント数ｎを「１」だけインクリメントする（ステップ１０７）。Ｗ情報ビットがすべて「０」であれば、アイドルユニットであると判断して、通信量積算値Ｍｓｕｍのインクリメントは行わず、スロットカウント数ｎだけを「１」だけインクリメントする（ステップ１０７）。ステップ１０７の処理後は再びステップ１０３に戻り、スロット割り込みを検出する。
【００３７】
一方、ステップ１０４でスロットカウント数ｎが「１０７」より大、すなわち、ｎ＝１０８と判定されたときは、１スーパーフレーム分のスロットの通信量積算が終ったと判断して、変数Ｉｎｉｔが「０」かどうか判定する（ステップ１０８）。変数Ｉｎｉｔはステップ１０１で最初に「０」に初期化されているので、最初の１スーパーフレームのときにはＩｎｉｔが「０」であり、このときには通信量平均値Ｍａｖｇに１スーパーフレームでの通信量積算値Ｍｓｕｍをそのまま代入し、かつ、変数Ｉｎｉｔを「１」に設定する（ステップ１０９）。これにより、２番目以降のスーパーフレームでは、Ｉｎｉｔの値は「１」である。
【００３８】
他方、ステップ１０８で変数Ｉｎｉｔが「１」であると判定されたとき、すなわち、２番目以降のスーパーフレームであると判定された時には、
Ｍａｖｇ＝（Ｍａｖｇ＋Ｍｓｕｍ×２）／３
なる演算式により、通信量平均値Ｍａｖｇを算出する（ステップ１１０）。この演算式は、前回の通信量平均値Ｍａｖｇと今回の１スーパーフレームでの通信量積算値Ｍｓｕｍを２倍した値とを加算し、その加算値を１／３倍に平均化した値を今回の通信量平均値Ｍａｖｇとしたものである。
【００３９】
ステップ１０９又は１１０の処理が終ると、再びステップ１０２に戻り、通信量積算値Ｍｓｕｍ及びスロットカウント数ｎを「０」に初期化し、再び上記と同様にして次の１スーパーフレームの通信量平均値Ｍａｖｇを算出する。すなわち、２番目以降のスーパーフレームについては、スーパーフレーム単位で前回の通信量平均値Ｍａｖｇと今回の１スーパーフレームでの通信量積算値Ｍｓｕｍに重み付けを行って移動平均を計算し、最新の通信量平均値Ｍａｖｇとする（ステップ１０３〜１０８、１１０）。
【００４０】
図１の基地局３及び４は上記のアルゴリズムに従って、各々独立に自局での通信量平均値Ｍａｖｇを計算しており、算出したその通信量平均値Ｍａｖｇとパケット通信可能なチャネルの情報を周辺の基地局（基地局３の場合は基地局４、基地局４の場合は基地局３）に対してパケット処理装置５を通して定期的に送出し合っており、基地局３（４）は他の基地局４（３）から受信した上記の通信量平均値Ｍａｖｇとパケット通信可能なチャネルの情報を、図４に示したアイドルユニットの追加情報を用いて、自局の通信エリアに在圏する携帯電話機に報知する。携帯電話機は上記の通信量平均値Ｍａｖｇとパケット通信可能なチャネルの情報を受信すると、必要に応じてチャネル切替を行う。
【００４１】
次に、携帯電話機の上記のチャネル切替動作について、図６のフローチャートを参照して説明する。まず、携帯電話機がパケット通信中にアイドルユニットを受信したかどうか監視しており（ステップ２０１）、アイドルユニットを受信すると、受信したそのアイドルユニットの１２オクテット目の「チャネル切替指定群」の群分け数を用いて自群を計算する。その具体的な計算方法は、携帯電話機に書き込まれた携帯電話機１つ１つに固有な番号である移動局識別子を、受信したアイドルユニット内の群分け数で除算し、余りを求める。求めた余りと「チャネル切替指定群」の指定群と一致するかチェックする（ステップ２０２）。これは、通信負荷が軽いチャネルへ一斉に携帯電話機がチャネル切替をしないようにするためである。
【００４２】
一致した場合には、アイドルユニットで指定された周波数コードの周辺基地局のチャネルの受信電界強度を従来と同様の方法で測定する（ステップ２０３）。続いて、携帯電話機は、測定した受信電界強度を受信したアイドルユニット内で通知されるＦＥＣ制御判定パラメータのＲＳＳＩ判定値と比較する（ステップ２０４）。ＦＥＣ制御判定パラメータのＲＳＳＩ判定値は、無線パケット通信を行う上で誤り訂正機能無しでも問題なくパケット通信が可能な受信電界強度のしきい値を示している。
【００４３】
従って、ＦＥＣ制御判定パラメータのＲＳＳＩ判定値よりも測定電界強度の方が高ければ、チャネル切替後も問題なくパケット通信を継続できることが保証されていると判断して、携帯電話機は自身が図５と同様のアルゴリズムで算出した、現在パケット通信中の基地局のチャネルのパケット通信量よりも、パケット通信中の基地局からアイドルユニット内の通信量通知で報知された周辺基地局の通信量平均値Ｍａｖｇに所定の値αを加算した値の方が小さいかどうか比較する（ステップ２０５）。上記の所定の値αは、後述するチャネル切替によりチャネル切替先の基地局の負荷が、チャネル切替元の基地局の負荷よりも大きくならないようにするための調整量である。
【００４４】
携帯電話機は自身のパケット通信量よりも、周辺基地局の通信量平均値Ｍａｖｇに所定の値αを加算した値の方が小さいとの比較結果が得られたときは、携帯電話機はアイドルユニットで通知されたパケット通信可能な周辺基地局のチャネルへチャネル切替動作を行う（ステップ２０６）。このチャネル切替動作自体は従来より知られているので詳細には説明しないが、チャネル切替要求を制御チャネルで通信中の基地局へ通知すると、パケット処理装置を介して切替先の基地局とのチャネル切替が行われる。
【００４５】
なお、ステップ２０２で移動局識別子を、受信したアイドルユニット内の群分け数で除算したときの余りと「チャネル切替指定群」の指定群とが一致しないとの比較結果が得られた場合、あるいはステップ２０４で測定電界強度がＦＥＣ制御判定パラメータのＲＳＳＩ判定値以下であると判定された場合、あるいはステップ２０５で携帯電話機のパケット通信量が周辺基地局の通信量平均値Ｍａｖｇ以下であると判定された場合は、上記のチャネル切替手順は実行せず、ステップ２０１に戻りアイドルユニットの受信を監視する。
【００４６】
このように、本実施の形態によれば、例えば図１の携帯電話機１及び２が基地局３との間でパケット通信中には、基地局４が算出した自身の通信エリアＡ２内での通信量平均値Ｍａｖｇとパケット通信可能なチャネルの情報が基地局３に対してパケット処理装置５を通して定期的に送出されており、基地局３は基地局４から受信した上記の通信量平均値Ｍａｖｇとパケット通信可能なチャネルの情報を、図４に示したアイドルユニットの追加情報を用いて、自局の通信エリアＡ１に在圏する携帯電話機１及び２に報知する。
【００４７】
ここで、携帯電話機２は、自身が計算した基地局３との間の現在通信中のパケット通信量よりも、アイドルユニット内の通信量通知で報知された基地局４の通信量平均値Ｍｓｕｍの方が小さいとの比較結果を得たときは、アイドルユニットで通知されたパケット通信可能な基地局４のチャネルへ携帯電話機主導でチャネル切替動作を行う（ただし、前述したように、移動局識別子を、受信したアイドルユニット内の群分け数で除算したときの余りと「チャネル切替指定群」の指定群とが一致し、かつ、測定電界強度がＦＥＣ制御判定パラメータのＲＳＳＩ判定値より大であるものとする。）。
【００４８】
これにより、チャネル切替後は、基地局３との通信よりも高速度で通信が可能になる。また、アイドルユニットを用いて複数のパケット通信可能なチャネルを報知できるので、基地局のパケット通信の負荷をより一層軽減できる。
【００４９】
次に、本発明の他の実施の形態について説明する。上記の実施の形態では、通信状態を示す通信量は、図５のフローチャートのアルゴリズムに従って、基地局側が計算するように説明したが、この実施の形態では、図７のフローチャートのアルゴリズムに従って、移動電話機側で自分宛（自局宛）の通信量を計算する点に特徴がある。
【００５０】
図７のフローチャートと共に移動電話機による通信量計算アルゴリズムについて説明するに、まず、自局宛の通信量平均値ＯＭａｖｇ及び変数Ｉｎｉｔをそれぞれ０に初期化し（ステップ３０１）、続いて自局宛の１スーパーフレーム（７２０ｍｓｅｃ）での通信量積算値ＯＭｓｕｍ及びスロットカウント数ｎをそれぞれ０に初期化する（ステップ３０２）。
【００５１】
続いて、スロット割り込みを検出すると（ステップ３０３）、スロットカウント数ｎが「１０７」より大であるかどうかチェックし（ステップ３０４）、「１０７」以下であるときには、１スーパーフレーム以内のスロットであるので、Ｗ情報ビットがすべて「０」かどうかチェックする（ステップ３０５）。
【００５２】
Ｗ情報ビットのいずれかが「０」であれば、アイドルユニット以外のユニットであると判断して、そのユニットに自局宛のデータが存在するかどうか判定し（ステップ３０６）、存在する場合は、自局宛通信量積算値ＯＭｓｕｍを「１」だけインクリメントした後（ステップ３０７）、スロットカウント数ｎを「１」だけインクリメントする（ステップ３０８）。
【００５３】
Ｗ情報ビットがすべて「０」であれば、アイドルユニットであると判断して、自局宛通信量積算値ＯＭｓｕｍのインクリメントは行わず、スロットカウント数ｎだけを「１」だけインクリメントする（ステップ３０５、３０８）。また、アイドルユニット以外のユニットでも、そのユニットに自局宛のデータが存在しない場合にも、同様に、自局宛通信量積算値ＯＭｓｕｍのインクリメントは行わず、スロットカウント数ｎだけを「１」だけインクリメントする（ステップ３０６、３０８）。ステップ３０８の処理後は再びステップ３０３に戻り、スロット割り込みを検出する。
【００５４】
一方、ステップ３０４でスロットカウント数ｎが「１０７」より大、すなわち、ｎ＝１０８と判定されたときは、１スーパーフレーム分のスロットの通信量積算が終ったと判断して、変数Ｉｎｉｔが「０」かどうか判定する（ステップ３０９）。変数Ｉｎｉｔはステップ３０１で最初に「０」に初期化されているので、最初の１スーパーフレームのときにはＩｎｉｔが「０」であり、このときには自局宛通信量平均値ＯＭａｖｇに１スーパーフレームでの自局宛通信量積算値ＯＭｓｕｍをそのまま代入し、かつ、変数Ｉｎｉｔを「１」に設定する（ステップ３１０）。これにより、２番目以降のスーパーフレームでは、Ｉｎｉｔの値は「１」である。
【００５５】
他方、ステップ３０９で変数Ｉｎｉｔが「１」であると判定されたとき、すなわち、２番目以降のスーパーフレームであると判定された時には、
ＯＭａｖｇ＝（ＯＭａｖｇ＋ＯＭｓｕｍ×２）／３
なる演算式により、自局宛通信量平均値ＯＭａｖｇを算出する（ステップ３１１）。この演算式は、前回の自局宛通信量平均値ＯＭａｖｇと今回の１スーパーフレームでの自局宛通信量積算値ＯＭｓｕｍを２倍した値とを加算し、その加算値を１／３倍に平均化した値を今回の自局宛通信量平均値ＯＭａｖｇとしたものである。
【００５６】
ステップ３１０又は３１１の処理が終ると、再びステップ３０２に戻り、自局宛通信量積算値ＯＭｓｕｍ及びスロットカウント数ｎを「０」に初期化し、再び上記と同様にして次の１スーパーフレームの自局宛通信量平均値ＯＭａｖｇを算出する。すなわち、２番目以降のスーパーフレームについては、スーパーフレーム単位で前回の自局宛通信量平均値ＯＭａｖｇと今回の自局宛の１スーパーフレームでの通信量積算値ＯＭｓｕｍに重み付けを行って移動平均を計算し、最新の自局宛通信量平均値ＯＭａｖｇとする（ステップ３０３〜３０９、３１１）。
【００５７】
次に、携帯電話機のチャネル切替動作の他の実施の形態について、図８のフローチャートを参照して説明する。まず、携帯電話機がパケット通信中にアイドルユニットを受信したかどうか監視しており（ステップ４０１）、アイドルユニットを受信すると、受信したそのアイドルユニットの１２オクテット目の「チャネル切替指定群」の群分け数を用いて自群を計算する。その具体的な計算方法は、図６のステップ２０２で説明した方法と同じであり、携帯電話機に書き込まれた携帯電話機１つ１つに固有な番号である移動局識別子を、受信したアイドルユニット内の群分け数で除算し、余りを求める。求めた余りと「チャネル切替指定群」の指定群と一致するかチェックする（ステップ４０２）。
【００５８】
一致した場合には、アイドルユニットで指定された周波数コードの周辺基地局のチャネルの受信電界強度を従来と同様の方法で測定する（ステップ４０３）。続いて、携帯電話機は、測定した受信電界強度を受信したアイドルユニット内で通知されるＦＥＣ制御判定パラメータのＲＳＳＩ判定値と比較する（ステップ４０４）。ＦＥＣ制御判定パラメータのＲＳＳＩ判定値よりも測定電界強度の方が高ければ、チャネル切替後も問題なくパケット通信を継続できることが保証されていると判断して、携帯電話機は次式を満足するかどうか判定する（ステップ４０５）。
【００５９】
通信量通知＜Ｍａｖｇ−ＯＭａｖｇ×２
ここで、上式中、Ｍａｖｇは携帯電話機が現在パケット通信を行っているチャネルにおいて、携帯電話機内部で図５と同様のアルゴリズムで算出して得たパケット通信量（平均値）であり、自局宛のパケットだけでなく他局宛のパケットも含めた、自局が現在パケット通信しているチャネルでの全体のパケット通信量である。また、ＯＭａｖｇは、現在パケット通信を行っているチャネルにおいて、図７と共に説明したアルゴリズムで算出した自局宛だけのパケットの通信量平均値である。
【００６０】
また、上式中の「通信量報知」は、現在通信中の基地局の周辺基地局で図５のフローチャートに従って算出され、パケット通信可能なチャネルの情報と共に周辺基地局から定期的に送出され、現在通信中の基地局を通して携帯電話機により受信された、アイドルユニットの１７オクテット目の「通信量通知」が示すパケット通信量（図５、図６のＭａｖｇに相当）である。
【００６１】
従って、上記の式は、携帯電話機内部で計算したパケット通信量Ｍａｖｇから自局宛通信量平均値ＯＭａｖｇを２倍した値を差し引いた値をしきい値とし、そのしきい値が、基地局から受信したアイドルユニットの通信量通知（パケット通信量）よりも大きいかどうかの不等式を示しており、この不等式を満足する場合は、アイドルユニットで通知された周辺基地局のチャネルのパケット通信量の方が少ないので、現在パケット通信中のチャネルからアイドルユニット内の通信量通知で報知された周辺基地局のチャネルに切り替えるチャネル切替手順を実行する（ステップ４０６）。
【００６２】
なお、上式において、自局宛通信量平均値ＯＭａｖｇを２倍した値を差し引く理由は、上記のチャネル切替により、携帯電話機がそれまでパケット通信していたチャネルの方が通信量が少なくなり、上記のチャネル切替を繰り返す、ということがないようにするためである。
【００６３】
上記のチャネル切替動作自体は従来より知られているので詳細には説明しないが、チャネル切替要求を制御チャネルで通信中の基地局へ通知すると、パケット処理装置を介して切替先の基地局とのチャネル切替が行われる。
【００６４】
なお、ステップ４０２で移動局識別子を、受信したアイドルユニット内の群分け数で除算したときの余りと「チャネル切替指定群」の指定群とが一致しないとの比較結果が得られた場合は指定群と一致しないので、また、ステップ４０４で測定電界強度がＦＥＣ制御判定パラメータのＲＳＳＩ判定値以下であると判定された場合は、チャネル切替後のパケット通信を継続できることが保証されていないので、また、ステップ４０５で前述した不等式を満足しないと判定された場合は、チャネル切替後のチャネルのパケット通信量がチャネル切替前のチャネルでの自局宛のパケット通信量よりも確実に少なくなるとはいえないので、上記のチャネル切替手順は実行せず、ステップ４０１に戻りアイドルユニットの受信を監視する。
【００６５】
このように、本実施の形態によれば、移動通信機側で現在通信中のチャネルのパケット通信量及び自局宛のパケット通信量平均値を計算し、それらの計算結果とアイドルユニットで報知された周辺基地局のパケット通信量（通信量通知）に基づいて、チャネル切替手順を実行するか否か決定しているので、チャネル切替実行後には、通信負荷の軽い基地局との間で通信速度の低下をもたらすことなくパケット通信を確実に継続することができる。
【００６６】
なお、本発明は以上の実施の形態に限定されるものではなく、例えば、図５に示す通信量を示すバロメータとしてアイドルユニットの数に変更してもよく、また、通信量計算アルゴリズムにおけるステップ１１０、３１１の演算式以外の他の重み付けも可能である。
【００６７】
また、以上の実施の形態では、基地局間での通信量の情報交換で説明したが、本来は１つの基地局内でも複数のパケット通信可能チャネルを運用することが可能なため、１つの基地局で複数のパケット通信可能チャネルとした場合でも、同一の方法が適用できる。また、ステップ２０４と２０５の順序、ステップ４０４と４０５の順序は逆であってもよい。更に、携帯電話機以外のバケット通信機能を持つ携帯型情報端末など他の移動体端末にも適用可能である。
【００６８】
【発明の効果】
以上説明したように、本発明によれば、受信したパケット通信可能なチャネル情報に基づいて、通信負荷の軽い他の基地局のチャネルに移動体端末主導で切り替えることにより、負荷が少ない方の基地局との間でパケット通信ができるようにしたため、パケット通信可能なチャネルを受信電界強度や受信データの品質だけでなく、その時々の通信状態に応じて通信負荷の軽い基地局との間に切り替え、移動体端末主導で通信速度の低下をもたらすことなくパケット通信を継続することができ、無線資源の有効利用ができる。
【００６９】
また、本発明によれば、アイドルユニットの未使用部分を用いて複数のパケット通信可能なチャネルを移動体端末へ通知するようにしたため、パケット通信を行えるチャネルを通知する数を伝送する情報量を従来よりも削減することができ、パケット通信の負荷をより一層軽減することができる。
【００７０】
また、更に、本発明によれば、移動体端末自身で計算した現在のチャネルの全体のパケット通信量と自局宛のパケット通信量とから計算したしきい値と、受信した周辺基地局でのチャネルのパケット通信量とを比較し、その比較結果に基づいて、チャネル切替を行うか否か選択することにより、常に負荷が少ない方の基地局との間でパケット通信ができると共に、上記のしきい値の設定により、通信負荷が軽いチャネルへ一斉に移動体端末でチャネル切替しないように制御することができる。また、移動体端末の自局宛のパケット通信量を勘案して上記のチャネル切替ためのしきい値を計算しているので、チャネル切替後にはチャネル切替前よりも確実に通信負荷の軽いチャネルへ切替できる。
【図面の簡単な説明】
【図１】本発明の一実施の形態のシステム構成図である。
【図２】図１の基地局から携帯電話機への信号送信タイミングを示す図である。
【図３】Ｗ情報ビットの使用方法説明図である。
【図４】本発明で用いるアイドルユニットの一例の説明図である。
【図５】本発明における通信量計算アルゴリズムの一実施の形態を示すフローチャートである。
【図６】本発明における携帯電話機の一実施の形態の動作説明用フローチャートである。
【図７】本発明における通信量計算アルゴリズムの他の実施の形態を示すフローチャートである。
【図８】本発明における携帯電話機の他の実施の形態の動作説明用フローチャートである。
【符号の説明】
１、２携帯電話機（ＭＳ）
３、４基地局（ＢＳ）
５パケット処理装置
６ゲートウェイ装置
７インターネット
Ａ１、Ａ２通信エリア[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mobile communication system and a channel switching method, and more particularly to a mobile communication system for communicating between a mobile phone having a wireless packet communication function and a partner terminal and a channel switching method for switching a channel to be used.
[0002]
[Prior art]
In a conventional mobile communication system, a plurality of base stations serving as relay stations each have a unique communication area, and a mobile terminal such as a mobile phone communicates with a base station located at the center of a communication area where the mobile station is located. Perform wireless communication. Since the base station is connected to a public network or the like via a higher-level control station, it is possible to make a call between the mobile terminal and the other terminal of the public network via the base station. A base station in this mobile communication system performs wireless communication using a time slot of a channel allocated to a mobile terminal.
[0003]
Further, in order to improve the communication quality, the mobile terminal measures the electric field strength of the radio wave transmitted from one or more base stations other than the base station which is not communicating with the control channel, and among the measured electric field strengths, Switching a communication channel to a base station transmitting a strong radio wave (so-called handover) has been conventionally known. Further, in the conventional mobile communication system, the mobile terminal performing packet communication switches the communication channel even when the received electric field strength is deteriorated or the error rate of the received data becomes worse than a predetermined threshold. Do.
[0004]
[Problems to be solved by the invention]
However, in a conventional mobile communication system that communicates with a mobile terminal having a packet communication function, switching of a channel for performing packet communication is performed based only on the deterioration of the received electric field strength, the error rate of received data, and the electric field strength of peripheral channels. Therefore, even if the receiving field strength of the channel currently performing packet communication is high and the error rate of the received data is good, many mobile terminals use the same channel capable of performing packet communication. If it exists, the communication load increases, and the communication speed decreases.
[0005]
Even in such a situation, the mobile phone cannot do anything, but only has to continue packet communication at a reduced communication speed, and the communication load cannot be distributed, and wireless resources cannot be used effectively. Conventionally, in order to secure the amount of information to be transmitted, it is not possible to notify a plurality of channels that can perform packet communication.
[0006]
The present invention has been made in view of the above points, and an object of the present invention is to provide a mobile communication system and a channel switching method capable of switching from a communicating mobile terminal to a communication channel with a low traffic.
[0007]
It is another object of the present invention to provide a mobile communication system and a channel switching method capable of notifying a plurality of channels capable of performing packet communication.
[0008]
It is a further object of the present invention to provide a mobile communication system and a channel switching method in which a mobile terminal itself can automatically select a channel with a light communication load.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a mobile communication system according to the present invention provides a mobile communication system in which a plurality of base stations perform packet communication by radio waves with mobile terminals located within their own communication area. A base station for calculating a first traffic in the communication area of the base station; a transmitting means for periodically transmitting information on the first traffic and a channel capable of packet communication to a peripheral base station; Notifying means for notifying the mobile terminal located in the communication area of the own station of the information of the first communication amount and the channel capable of packet communication received from the other base station, respectively, Receiving means for receiving information on a first communication amount and a channel capable of packet communication transmitted from a base station in packet communication, and a base station in packet communication specified by the information based on the received channel information Station Electric field intensity measuring means for measuring the received electric field intensity of the frequency used in the base station, communication amount calculating means for calculating the second communication amount of the base station during packet communication, and the measurement result of the received electric field intensity Comparing means for comparing the second communication amount with the first communication amount received by the receiving means; and comparing the measurement result of the received electric field strength by the comparing means with a predetermined threshold value. If a comparison result that the value is larger than the value and the second communication amount is larger than the first communication amount by a predetermined value or more is obtained, the packet communication enabled channel received by the receiving unit is obtained. Switching means for switching to And the mobile terminal communicates with the base station whose communication load is lighter. It is configured.
[0010]
According to the present invention, during the packet communication between the mobile terminal and the base station, the measurement result of the reception electric field strength of the frequency used by another base station is larger than a predetermined threshold value, and When a comparison result is obtained that the second communication volume during communication is larger than the first communication volume of the other base station by a predetermined value or more, based on the received packet-communicable channel information. Since the channel is switched to the channel of the other base station, packet communication can be performed with the base station having a smaller load.
[0011]
Here, it is desirable for the above-mentioned notifying means to notify the mobile terminal during packet communication of the first communication amount and the information of the channel capable of performing packet communication using the idle unit, in order to reduce the load of packet communication.
[0012]
The calculating means of the base station calculates an integrated value of the number of communication slots used in one superframe in superframe units, weights the previous integrated value and the current integrated value to calculate a moving average, It is characterized in that the moving average is obtained as the latest integrated value and also as the first communication amount.
[0013]
Further, the mobile communication system of the present invention, in order to achieve the above object, in a mobile communication system in which a plurality of base stations perform packet communication with mobile terminals located within their own communication area by radio waves, A plurality of base stations, calculating means for calculating the amount of packet communication within their own communication area, sending means for periodically sending information on the amount of packet communication and a channel capable of packet communication to peripheral base stations; Notifying means for notifying the mobile terminal located in the communication area of its own station of the information on the packet communication volume and the channel capable of packet communication received from the base station, respectively, and the mobile terminal Receiving means for receiving information on the amount of packet communication transmitted from the base station in communication and information on the channels that can perform packet communication, and specifying the information based on the information on the received channel. Electric field intensity measuring means for measuring a received electric field intensity of a frequency used by a base station other than the base station performing packet communication, a first communication amount of all packets of a current channel during packet communication, A communication amount calculating means for calculating a second communication amount of a packet addressed to the own station of a current channel during packet communication; and subtracting a value obtained by multiplying a second communication amount by a predetermined value from the first communication amount. Threshold value calculating means for calculating the value as a threshold value, comparing the measurement result of the received electric field strength with a predetermined judgment value, and calculating the packet communication amount received by the receiving means and the threshold value calculating means. A comparison means for comparing the threshold value with the threshold value, and a comparison result obtained that the measurement result of the received electric field strength is larger than the determination value and the packet communication traffic is smaller than the threshold value. When it is received, Ri is obtained by a configuration having a switching means for switching the received packet communication-possible channels.
[0014]
According to the present invention, during the packet communication between the mobile terminal and the base station, the measurement result of the reception electric field strength of the frequency used by another base station is larger than a predetermined threshold value, and The received peripheral base station is smaller than a threshold value obtained by subtracting a value obtained by multiplying a second communication amount of a packet addressed to the own station by a predetermined value from a first packet communication amount of a current channel under communication. When the amount of packet communication in is smaller, the channel is switched to the channel of the other base station based on the received channel information capable of performing packet communication. Packet communication is possible.
[0015]
Further, in the present invention, the information of the channel capable of performing packet communication includes at least a channel switching designation group including a grouping number and a designation group and a frequency code, and the mobile terminal is unique to each mobile terminal. Only when the remainder obtained by dividing the mobile station identifier having the proper number by the grouping number in the received channel switching designated group matches the designated group in the received channel switching designated group, the comparing operation by the comparing means is performed. It is characterized by.
[0016]
Furthermore, in order to achieve the above object, the method of the present invention is directed to a mobile communication system in which a mobile terminal located in a communication area of a base station switches a channel for performing packet communication with the base station by radio waves. In the system channel switching method, a base station calculates a first traffic in its own communication area, and periodically sends the first traffic and information on a channel capable of packet communication to a neighboring base station. And transmitting the first communication amount from the peripheral base station and information of the channel capable of performing packet communication to the mobile terminal performing packet communication, and the mobile terminal performs the second communication of the base station performing packet communication. A first step of calculating the amount, a second step of receiving the information of the first communication amount and the channel capable of performing the packet communication transmitted from the base station performing the packet communication, and based on the information of the received channel. , The third step of measuring the received electric field strength of the frequency used by the base station other than the base station performing the packet communication specified by the information of the received packet, and comparing the measured result of the received electric field strength with a predetermined threshold value And a fourth step of comparing the second communication amount with the first communication amount received in the second step, and the measurement result of the received electric field strength is larger than a predetermined threshold value, and And a fifth step of switching to a channel capable of receiving a packet when a comparison result that the second traffic is larger than the first traffic by a predetermined value or more is obtained. It is characterized by.
[0017]
According to the present invention, the channel is switched to the channel of the other base station based on the received channel information capable of packet communication, so that packet communication can be performed with the base station having the smaller load.
[0018]
Furthermore, in order to achieve the above object, the method of the present invention calculates the amount of packet communication within its own communication area, and stores the information on the amount of packet communication and the channel capable of performing packet communication with the neighboring base stations. To the mobile terminal that is performing packet communication, and transmits information on the amount of packet communication from neighboring base stations and information on the channels that can perform packet communication to the mobile terminal that is currently performing packet communication. A first step of calculating a first communication amount of all packets, a second communication amount of a packet addressed to the own station of the current channel during the packet communication, and a second communication from the first communication amount A second step of calculating, as a threshold, a value obtained by subtracting a value obtained by multiplying the amount by a predetermined value, and information on a packet communication amount and a channel capable of packet communication transmitted from the base station during packet communication A third step of receiving, and a fourth step of measuring, based on the received channel information, the received field strength of a frequency used by a base station other than the base station in packet communication specified by the information. And a fifth step of comparing the measurement result of the received electric field strength with a predetermined judgment value, and comparing the packet traffic received in the third step with the threshold value calculated in the second step. When the comparison result that the measurement result of the received electric field strength is larger than the determination value and the packet communication amount is smaller than the threshold value is obtained, the channel for the received packet communication is set. And a sixth step of switching.
[0019]
In the present invention, the threshold calculated from the total packet traffic of the current channel calculated by the mobile terminal itself and the packet traffic addressed to the own station, the received packet traffic of the channel at the peripheral base station received, and Are compared, and whether or not to perform channel switching is selected based on the comparison result, so that packet communication can always be performed with the base station having a smaller load.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a system configuration diagram of an embodiment of a mobile communication system according to the present invention. In the figure, mobile phones (MS) 1 and 2 having a wireless packet communication function as an example of a mobile terminal are located in a communication area A1 of a base station (BS) 3. The mobile phone 2 is also located in the communication area A2 of the base station (BS) 4. Therefore, the mobile phone 1 can perform packet communication only with the base station 3, and the mobile phone 2 is at a position where packet communication can be performed with any of the base stations 3 and 4. Here, it is assumed that the mobile phones 1 and 2 are performing wireless packet communication with the base station 3.
[0021]
The packet processing device 5 repairs the packet data from the mobile phones 1 and 2 received from the base stations 3 and 4 to repair duplication and omission of signals generated when the mobile phones 1 and 2 switch channels, etc. Is transmitted to the gateway device 6. The gateway device 6 performs protocol conversion, address conversion, and the like on the input packet data, and then sends the packet data to the Internet 7.
[0022]
On the other hand, when there is a data transmission request from the Internet 7 to the mobile phone, the gateway device 6 searches for a packet processing device with which the corresponding mobile phone can communicate, and after the protocol conversion processing, finds the packet processing device as packet data. (5 in FIG. 1). Also, the information of the corresponding mobile phone is transmitted.
[0023]
The packet processing device 5 searches for a base station in which the mobile phone transmitted from the gateway device 6 is located, and transmits the packet data to the relevant base station. The base station transmits packet data to the corresponding mobile phone using wireless communication. In addition, the base station 3 and 4 have a function of mutually notifying channel information that allows packet communication and communication traffic of a channel that can perform packet communication.
[0024]
Next, the operation of the present embodiment will be described with reference to FIGS. In the present embodiment, an operation in a packet communication system using a digital mobile phone of a time division multiple access (TDMA: Time Division Multiplex Access) system will be described. Now, it is assumed that the mobile phones 1 and 2 located in the communication area A1 of the base station 3 are in a packet communication state with the base station 3. However, the mobile phone 2 is also located within the communication area A2 of the base station 4, and is in a position where packet communication with the base station 4 is possible.
[0025]
The base station 3 transmits signals between the mobile phones 1 and 2 at a timing shown in FIG. That is, in FIG. 2, in the transmission timing of the wireless communication, one subframe (20 msec) is composed of three slots of 6.67 msec, which is the minimum unit, and one superframe is composed of 36 subframes. (720 msec).
[0026]
The base station 3 transmits packet data to be transmitted to the mobile phones 1 and 2 at the same slot number timing. In FIG. 2, the base station 3 divides the packet data to be transmitted to the mobile phone 1 (MS1) into six slot units, and transmits the packet data using the slot number # 0. Also, there are two pieces of packet data to be transmitted to the mobile phone 2 (MS2), one is divided into four slot units, and the other is divided into two slot units. 2 is transmitted.
[0027]
If there is no packet data to be transmitted to the mobile phones 1 and 2, the base station 3 transmits base station information (mainly layer 1 level wireless communication parameters) called an idle unit, which is indicated by "IDLE" in FIG. Transmit to telephones 1 and 2.
[0028]
Further, the base station 3 notifies the mobile phones 1 and 2 of the number of data slots to be transmitted using the first 8 bits of each slot. This 8-bit information is called a W information bit. A method of using the W information bit will be described with reference to FIG. As shown in the format of FIG. 3A, the first bit of the W information bit is called F1, and the next bit is called F2. F1 indicates whether the slot is the head unit. When the value is “0”, it indicates a non-head unit, and when the value is “1”, it indicates a head unit. F2 indicates whether the corresponding slot is the last unit. When the value is “0”, it indicates a non-final unit, and when the value is “1”, it indicates a last unit.
[0029]
The remaining 6 bits of the W information bit are called W0, indicating the number of valid bytes when F2 indicates the last unit, and indicating the number of remaining units (Wr) when F2 indicates that it is not the last unit. Show. As shown in FIG. 2, Wr is used after being counted down from the head. When Wr is "0", that is, the slot in which all the W information bits are "0" is an idle unit.
[0030]
In summary, when F1 = 1 and F2 = 0, the head unit is as shown in FIG. 3B, and when F1 = F2 = 0, as shown in FIG. 3C, the head unit is neither the head unit nor the last unit. When F1 = 0 and F2 = 1, this is the last unit shown in FIG. 3D, Wr indicates the number of valid bytes L, and when F1 = F2 = Wr = 0, FIG. This is the idle unit shown in E).
[0031]
In the present embodiment, information of another channel capable of packet communication is set in an unused portion of an idle unit. This idle unit will be described in more detail with reference to FIG.
[0032]
In FIG. 4, up to 11 octets of the idle unit is the same as the conventional one, and 12 octets are newly set in the present embodiment. In the following, each added octet will be described. A “channel switching designation group” is set in 8 bits of the 12th octet. The channel switching designation group is used to control not to switch to the channel to which all the mobile phones receiving the idle unit are notified at the same time. Using the upper 4 bits of the channel switching designation group, the number of groups into which the mobile phone is to be divided is designated, and the group divided by the remaining lower 4 bits is designated.
[0033]
A total of 16 bits at the next 13th octet and 14th octet are used to notify the frequency code of another channel capable of packet communication. The upper 4 bits of the 13th octet are used to report the frequency band identifier, and the lower 4 bits of the 13th octet and the total of 12 bits of the 14th octet are used to report the frequency code. The fifteenth octet is used for notifying a color code capable of performing packet communication, and the sixteenth octet is used for notifying a scramble code of a channel capable of performing packet communication. The last 17 octet is a communication amount notification, which is used to notify the current communication state (packet communication amount) of another channel capable of packet communication.
[0034]
Next, an embodiment of an algorithm for calculating a communication amount indicating a communication state according to the present invention will be described with reference to a flowchart of FIG. Although this algorithm is used on the base station side, it is used as it is for some mobile phones. First, the communication average value Mavg and the variable Init are initialized to 0 (step 101), and subsequently, the communication integrated value Msum and the slot count n in one superframe are initialized to 0 (step 102).
[0035]
Subsequently, when a slot interrupt is detected (step 103), it is checked whether or not the slot count number n is greater than “107” (step 104). If the slot count number n is less than “107”, the slot is within one superframe. Therefore, it is checked whether all W information bits are "0" (step 105).
[0036]
If any of the W information bits is "0", it is determined that the unit is a unit other than the idle unit, and the communication amount integrated value Msum is incremented by "1" (step 106). "(Step 107). If all the W information bits are "0", it is determined that the unit is an idle unit, and the communication count integrated value Msum is not incremented, and only the slot count n is incremented by "1" (step 107). After the process of step 107, the process returns to step 103 again to detect a slot interrupt.
[0037]
On the other hand, when it is determined in step 104 that the slot count number n is greater than “107”, that is, n = 108, it is determined that the accumulation of the traffic volume of one superframe slot has been completed, and the variable Init is set to “0”. Is determined (step 108). Since the variable Init is initially initialized to “0” in step 101, Init is “0” at the time of the first one superframe, and at this time, the traffic volume average value Mavg is integrated with the traffic volume in one superframe. The value Msum is substituted as it is, and the variable Init is set to “1” (step 109). Thus, in the second and subsequent superframes, the value of Init is “1”.
[0038]
On the other hand, when it is determined in step 108 that the variable Init is “1”, that is, when it is determined that the superframe is the second or subsequent superframe,
Mavg = (Mavg + Msum × 2) / 3
An average traffic value Mavg is calculated by the following equation (step 110). This arithmetic expression is obtained by adding the previous traffic average value Mavg and a value obtained by doubling the current traffic integrated value Msum in one superframe, and averaging the sum to 1/3 times the current value. Is the communication traffic average value Mavg.
[0039]
When the processing of step 109 or 110 is completed, the processing returns to step 102 again, the communication amount integrated value Msum and the slot count number n are initialized to “0”, and the communication amount average value of the next one superframe is again performed in the same manner as described above. Calculate Mavg. That is, for the second and subsequent superframes, a moving average is calculated by weighting the previous traffic average value Mavg and the current traffic integrated value Msum in one superframe in superframe units, and calculating the latest traffic volume. The average value is set to Mavg (steps 103 to 108, 110).
[0040]
Each of the base stations 3 and 4 in FIG. 1 independently calculates the average communication amount Mavg of the own station according to the above algorithm, and transmits the calculated average communication amount Mavg and information on the channel capable of packet communication to the surroundings. (The base station 4 in the case of the base station 3 and the base station 3 in the case of the base station 4) through the packet processing device 5 at regular intervals, and the base station 3 (4) Using the above average traffic value Mavg received from the station 4 (3) and the information of the channel capable of packet communication, the mobile phone located in the communication area of the own station using the additional information of the idle unit shown in FIG. To inform. When the mobile phone receives the above-mentioned average communication value Mavg and the information of the channel in which the packet communication is possible, the mobile phone switches the channel as necessary.
[0041]
Next, the above-described channel switching operation of the mobile phone will be described with reference to the flowchart of FIG. First, it is monitored whether or not the mobile phone has received an idle unit during packet communication (step 201). When the idle unit is received, a grouping of the "channel switching designation group" of the received octet in the 12th octet is performed. Calculate your group using numbers. The specific calculation method is to divide the mobile station identifier, which is a number unique to each mobile phone written in the mobile phone, by the number of groups in the received idle unit to obtain a remainder. It is checked whether the obtained remainder matches the designated group of the “channel switching designated group” (step 202). This is to prevent the mobile phone from switching channels simultaneously to a channel with a light communication load.
[0042]
If they match, the received electric field strength of the channel of the peripheral base station of the frequency code specified by the idle unit is measured by the same method as the conventional one (step 203). Subsequently, the mobile phone compares the measured received electric field strength with the RSSI determination value of the FEC control determination parameter notified in the idle unit that has received the signal (step 204). The RSSI determination value of the FEC control determination parameter indicates a threshold value of the received electric field strength at which packet communication can be performed without any problem without performing an error correction function in performing wireless packet communication.
[0043]
Therefore, if the measured electric field strength is higher than the RSSI determination value of the FEC control determination parameter, it is determined that packet communication can be continued without any problem even after the channel switching, and the mobile phone determines itself as shown in FIG. The average traffic value Mavg of the neighboring base stations notified by the communication amount notification in the idle unit from the base station performing the packet communication rather than the packet communication amount of the channel of the base station currently performing the packet communication calculated by the same algorithm. Then, it is determined whether or not a value obtained by adding a predetermined value α to is smaller (step 205). The above-mentioned predetermined value α is an adjustment amount for preventing the load of the base station of the channel switching destination from becoming larger than the load of the base station of the channel switching source due to the channel switching described later.
[0044]
When the mobile phone obtains a comparison result that the value obtained by adding the predetermined value α to the average traffic value Mavg of the peripheral base station is smaller than its own packet communication traffic, the mobile phone is an idle unit. A channel switching operation is performed to the channel of the peripheral base station which can communicate the notified packet (step 206). This channel switching operation itself is conventionally known, and will not be described in detail. However, when a channel switching request is notified to a base station that is communicating on a control channel, a channel with a switching destination base station is transmitted via a packet processing device. Switching is performed.
[0045]
Note that if a comparison result is obtained in step 202 that the remainder obtained by dividing the mobile station identifier by the number of groupings in the received idle unit does not match the specified group of “channel switching specified group”, or When it is determined in step 204 that the measured electric field strength is equal to or smaller than the RSSI determination value of the FEC control determination parameter, or in step 205, it is determined that the packet communication amount of the mobile phone is equal to or smaller than the average communication amount Mavg of the peripheral base station. In this case, the above channel switching procedure is not executed, and the process returns to step 201 to monitor the reception of the idle unit.
[0046]
As described above, according to the present embodiment, for example, while the mobile phones 1 and 2 in FIG. 1 perform packet communication with the base station 3, the communication within the communication area A2 calculated by the base station 4 is performed. The information on the average value Mavg and the channel that can perform packet communication is periodically transmitted to the base station 3 through the packet processing device 5. The base station 3 receives the information on the average communication value Mavg received from the base station 4. The information of the channel capable of packet communication is reported to the mobile phones 1 and 2 located in the communication area A1 of the own station using the additional information of the idle unit shown in FIG.
[0047]
Here, the mobile phone 2 calculates the average of the communication amount average Msum of the base station 4 notified by the communication amount notification in the idle unit, rather than the packet communication amount currently being communicated with the base station 3 calculated by itself. If the comparison result indicates that the mobile station identifier is smaller than that of the mobile station, the mobile phone initiates the channel switching operation to the channel of the packet-capable base station 4 notified by the idle unit. The remainder when divided by the number of groupings in the received idle unit matches the designated group of “channel switching designated group”, and the measured electric field strength is larger than the RSSI decision value of the FEC control decision parameter .).
[0048]
Thereby, after the channel switching, communication at a higher speed than communication with the base station 3 becomes possible. Also, since a plurality of channels capable of packet communication can be broadcast using the idle unit, the load of packet communication on the base station can be further reduced.
[0049]
Next, another embodiment of the present invention will be described. In the above embodiment, the description has been made such that the communication amount indicating the communication state is calculated by the base station according to the algorithm of the flowchart of FIG. 5, but in this embodiment, the mobile telephone is calculated according to the algorithm of the flowchart of FIG. It is characterized in that the side calculates the communication traffic addressed to itself (addressed to its own station).
[0050]
A description will be given of the communication volume calculation algorithm by the mobile phone together with the flowchart of FIG. 7. First, the communication volume average value OMavg and the variable Init destined for the own station are each initialized to 0 (step 301). The communication amount integrated value OMsum and the slot count number n in the frame (720 msec) are initialized to 0 (step 302).
[0051]
Subsequently, when a slot interrupt is detected (step 303), it is checked whether the slot count number n is greater than “107” (step 304). If the slot count number n is less than “107”, the slot is within one superframe. Therefore, it is checked whether all the W information bits are "0" (step 305).
[0052]
If any of the W information bits is "0", it is determined that the unit is a unit other than the idle unit, and it is determined whether or not the unit has data addressed to its own station (step 306). Then, after incrementing the communication amount integrated value OMsum to the own station by "1" (step 307), the slot count number n is incremented by "1" (step 308).
[0053]
If all the W information bits are "0", it is determined that the unit is an idle unit, and the own station-addressed communication amount integrated value OMsum is not incremented, and only the slot count n is incremented by "1" (step 305). , 308). Also, in the case of a unit other than the idle unit, even when there is no data addressed to the own station in that unit, similarly, the increment of the communication amount integrated value OMsum addressed to the own station is not performed, and only the slot count n is set to “1”. Is incremented by one (steps 306 and 308). After the process of step 308, the process returns to step 303 again to detect a slot interrupt.
[0054]
On the other hand, when it is determined in step 304 that the slot count number n is larger than “107”, that is, n = 108, it is determined that the accumulation of the traffic volume of one superframe slot has been completed, and the variable Init is set to “0”. Is determined (step 309). Since the variable Init is initially initialized to "0" in step 301, Init is "0" at the time of the first one superframe, and at this time, the local station average communication amount OMavg is set to one superframe. The communication amount integrated value OMsum for the own station is substituted as it is, and the variable Init is set to “1” (step 310). Thus, in the second and subsequent superframes, the value of Init is “1”.
[0055]
On the other hand, when it is determined in step 309 that the variable Init is “1”, that is, when it is determined that the superframe is the second or subsequent superframe,
OMavg = (OMavg + OMsum × 2) / 3
The following formula is used to calculate the local station average communication amount OMavg (step 311). This equation is obtained by adding the previous average value OMavg of the communication amount addressed to the own station and the value obtained by doubling the integrated value OMsum of the communication amount addressed to the own station in one superframe this time, and reducing the added value to 1/3. The averaged value is used as the current average communication amount OMavg addressed to the own station.
[0056]
When the processing of step 310 or 311 is completed, the processing returns to step 302 again, the communication amount integrated value OMsum addressed to the own station and the slot count number n are initialized to “0”, and the same operation as that of the next superframe is performed again in the same manner as described above. The station-directed communication average value OMavg is calculated. That is, for the second and subsequent superframes, the moving average is weighted by superimposing a weight on the previous traffic average value OMvg addressed to the own station and the current accumulated traffic value OMsum in one superframe addressed to the own station. The calculated value is set as the latest communication amount average value OMavg addressed to the own station (steps 303 to 309 and 311).
[0057]
Next, another embodiment of the channel switching operation of the mobile phone will be described with reference to the flowchart of FIG. First, it is monitored whether or not the mobile phone has received an idle unit during packet communication (step 401). When the idle unit is received, a grouping of the "channel switching designation group" of the received octet of the 12th octet is performed. Calculate your group using numbers. The specific calculation method is the same as the method described in step 202 of FIG. 6, and the mobile station identifier written to the mobile phone, which is a number unique to each mobile phone, is stored in the received idle unit. Divide by the number of groupings to find the remainder. It is checked whether the obtained remainder matches the designated group of “channel switching designated group” (step 402).
[0058]
If they match, the received electric field strength of the channel of the peripheral base station of the frequency code specified by the idle unit is measured by a method similar to the conventional method (step 403). Subsequently, the mobile phone compares the measured received electric field strength with the RSSI determination value of the FEC control determination parameter notified in the idle unit that has received the signal (step 404). If the measured electric field strength is higher than the RSSI determination value of the FEC control determination parameter, it is determined that packet communication can be continued without any problem even after channel switching, and whether the mobile phone satisfies the following equation. A determination is made (step 405).
[0059]
Communication amount notification <Mavg-OMavg × 2
Here, in the above equation, Mavg is the packet communication amount (average value) calculated by the same algorithm as in FIG. 5 inside the mobile phone in the channel where the mobile phone is currently performing packet communication. This is the total packet traffic on the channel on which the local station is currently performing packet communication, including not only packets addressed to other stations but also packets addressed to other stations. Further, OMavg is an average value of the communication amount of the packet addressed to the own station calculated by the algorithm described with reference to FIG. 7 in the channel currently performing the packet communication.
[0060]
In addition, the “communication amount notification” in the above equation is calculated according to the flowchart of FIG. 5 in the peripheral base station of the base station that is currently communicating, and is periodically transmitted from the peripheral base station along with information of a channel that can perform packet communication. This is the packet traffic (corresponding to Mavg in FIGS. 5 and 6) received by the mobile phone through the currently communicating base station and indicated by the “communication traffic notification” on the 17th octet of the idle unit.
[0061]
Therefore, the above equation sets the threshold value to be a value obtained by subtracting a value obtained by doubling the average value OMavg of the communication traffic addressed to the own station from the packet communication traffic Mavg calculated inside the mobile phone. An inequality indicating whether or not the received traffic is larger than the received traffic notification (packet traffic) of the idle unit. If this inequality is satisfied, the packet traffic of the channel of the peripheral base station reported by the idle unit is shown. Therefore, a channel switching procedure for switching from the channel currently performing packet communication to the channel of the neighboring base station notified by the communication amount notification in the idle unit is executed (step 406).
[0062]
In the above formula, the reason why the value obtained by doubling the average value OMavg of the communication amount to the own station is subtracted is that the channel switching causes the communication amount of the channel on which the mobile phone has been performing packet communication to be smaller, This is to prevent the above-described channel switching from being repeated.
[0063]
The above-described channel switching operation itself is conventionally known, and therefore will not be described in detail.However, when a channel switching request is notified to a base station that is communicating on a control channel, communication with a switching destination base station is performed via a packet processing device. Channel switching is performed.
[0064]
If it is determined in step 402 that the remainder obtained by dividing the mobile station identifier by the number of groupings in the received idle unit does not match the specified group of the “channel switching specified group”, the mobile station identifier is specified. If the measured electric field strength is determined to be equal to or less than the RSSI determination value of the FEC control determination parameter in step 404 because it does not match the group, it is not guaranteed that packet communication after channel switching can be continued. If it is determined in step 405 that the above inequality expression is not satisfied, it cannot be said that the packet traffic of the channel after the channel switching is certainly smaller than the packet traffic of the channel before the channel switching to the own station. Therefore, the above channel switching procedure is not executed, and the process returns to step 401 to monitor the reception of the idle unit.
[0065]
As described above, according to the present embodiment, the mobile communication device calculates the packet communication amount of the currently communicating channel and the average value of the packet communication amount addressed to its own station, and reports the calculation result and the idle unit. Since it is determined whether or not to execute the channel switching procedure based on the packet communication amount (communication amount notification) of the neighboring base station, the communication speed with the base station with a light communication load after executing the channel switching is determined. Packet communication can be surely continued without causing a decrease in the packet communication.
[0066]
The present invention is not limited to the above embodiment. For example, the barometer indicating the traffic shown in FIG. 5 may be changed to the number of idle units. Weighting other than the arithmetic expression 311 is also possible.
[0067]
Further, in the above embodiment, the information exchange of the communication amount between base stations has been described. However, since a plurality of packet communicable channels can be operated even within one base station, one base station can be operated. , The same method can be applied even when a plurality of packet communication channels are used. Also, the order of steps 204 and 205 and the order of steps 404 and 405 may be reversed. Further, the present invention can be applied to other mobile terminals such as a portable information terminal having a bucket communication function other than the mobile phone.
[0068]
【The invention's effect】
As described above, according to the present invention, based on the received packet-communicable channel information, the mobile terminal takes the initiative to switch to another base station channel with a lighter communication load, so that the base station with the smaller load can be used. Packet communication with stations has been made possible, so that the channels that can perform packet communication can be switched between the base station and the base station with a light communication load according to the current communication conditions as well as the reception field strength and received data quality. In addition, packet communication can be continued without lowering the communication speed led by the mobile terminal, and wireless resources can be effectively used.
[0069]
Further, according to the present invention, since a plurality of channels capable of performing packet communication are notified to the mobile terminal using the unused portion of the idle unit, the information amount for transmitting the number of notification of the channels capable of performing packet communication is reduced. Thus, the load can be reduced as compared with the conventional case, and the load of packet communication can be further reduced.
[0070]
Further, according to the present invention, a threshold calculated from the total packet traffic of the current channel calculated by the mobile terminal itself and the packet traffic addressed to the own station, By comparing the amount of packet communication with the channel and selecting whether or not to perform channel switching based on the comparison result, packet communication can always be performed with the base station having a smaller load, and the above-described operation can be performed. By setting the threshold value, it is possible to control so that the mobile terminal does not simultaneously switch channels to a channel with a light communication load. In addition, since the above-mentioned threshold for channel switching is calculated in consideration of the amount of packet communication addressed to the mobile station of the mobile terminal, a channel having a lighter communication load after the channel switching than the channel switching before the channel switching is reliably performed. Can be switched.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram according to an embodiment of the present invention.
FIG. 2 is a diagram showing a signal transmission timing from the base station to the mobile phone in FIG. 1;
FIG. 3 is an explanatory diagram of how to use W information bits.
FIG. 4 is an explanatory diagram of an example of an idle unit used in the present invention.
FIG. 5 is a flowchart showing an embodiment of a traffic calculation algorithm according to the present invention.
FIG. 6 is a flowchart illustrating an operation of the embodiment of the mobile phone according to the present invention.
FIG. 7 is a flowchart showing another embodiment of the traffic calculation algorithm according to the present invention.
FIG. 8 is a flowchart for explaining the operation of another embodiment of the mobile phone according to the present invention.
[Explanation of symbols]
1, 2 mobile phone (MS)
3, 4 base station (BS)
5 Packet processing device
6 gateway device
7 Internet
A1, A2 communication area

Claims

In a mobile communication system in which a plurality of base stations perform packet communication by radio waves with mobile terminals located within their own communication area,
Calculating means for calculating a first traffic in the communication area of the plurality of base stations;
Sending means for periodically sending the information of the first communication amount and the channel capable of performing packet communication to a peripheral base station;
Notifying means for notifying the mobile terminal located in the communication area of the own station of the information on the first communication amount and the channel capable of packet communication received from another base station, The terminal is
Receiving means for receiving information on the first communication amount and a channel capable of packet communication transmitted from the base station during packet communication;
Based on the received information on the channel, an electric field intensity measuring unit that measures a received electric field intensity of a frequency used by a base station other than the base station performing the packet communication specified by the information,
Communication amount calculation means for calculating a second communication amount of the base station during packet communication;
Comparing means for comparing the measurement result of the reception electric field strength with a predetermined threshold value, and comparing the second communication amount with the first communication amount received by the receiving unit;
A comparison is made that the result of the measurement of the received electric field strength by the comparing means is larger than a predetermined threshold value and that the second traffic is larger than the first traffic by a predetermined value or more. when the result is obtained, that have a switching means for switching to the packet communication-possible channels received by the receiving unit, the mobile terminal is communicating with the base station towards the communication load is light Characteristic mobile communication system.

2. The mobile communication system according to claim 1, wherein the notifying unit notifies the mobile terminal that is performing packet communication of the first communication amount and information of a channel capable of performing packet communication using an idle unit. .

The calculating means of the base station calculates an integrated value of the number of communication slots used in one superframe in superframe units, weights the previous integrated value and the current integrated value to calculate a moving average, and calculates the moving average. 2. The mobile communication system according to claim 1, wherein an average is obtained as the latest integrated value and the first communication amount is obtained.

In a mobile communication system in which a plurality of base stations perform packet communication by radio waves with mobile terminals located within their own communication area,
Calculating means for calculating the packet traffic in its own communication area,
Sending means for periodically sending the information of the packet communication amount and the channel capable of packet communication to a peripheral base station;
Notifying means for notifying the mobile terminal located in the communication area of its own station with information on the packet communication amount and the channel capable of packet communication received from another base station, and the mobile terminal ,
Receiving means for receiving information on the packet communication volume and the channel capable of packet communication transmitted from the base station during packet communication,
Based on the received information on the channel, an electric field intensity measuring unit that measures a received electric field intensity of a frequency used by a base station other than the base station performing the packet communication specified by the information,
Communication amount calculation means for calculating a first communication amount of all packets of the current channel during the packet communication and a second communication amount of packets addressed to the own station of the current channel during the packet communication;
Threshold calculation means for calculating, as a threshold, a value obtained by subtracting a value obtained by multiplying the second traffic by a predetermined value from the first traffic;
Comparing means for comparing the measurement result of the received electric field strength with a predetermined judgment value, and comparing the packet traffic received by the receiving means with the threshold value calculated by the threshold value calculating means; When,
When the result of measurement of the received electric field strength is larger than the determination value by the comparing means, and the comparison result that the packet traffic is smaller than the threshold is obtained, mobile communication system have a switching means for switching to the packet communication-possible channels received by the receiving means, said mobile terminal, characterized in that the communication with the base station towards the communication load is light.

The mobile communication system according to claim 4, wherein the notifying unit notifies the mobile terminal that is performing packet communication of the packet communication amount and information of a channel that can perform packet communication using an idle unit.

The communication amount calculation means of the base station calculates an integrated value of the number of communication slots used in one superframe in superframe units, calculates a moving average by weighting the previous integrated value and the current integrated value, This moving average is determined as the first communication amount, and the integrated value of the number of communication use slots addressed to the own station in one superframe is calculated in superframe units, and the integrated value in the previous superframe addressed to the own station is calculated. 5. The mobile communication system according to claim 4, wherein the moving average is calculated by weighting the integrated value in one superframe addressed to the own station and this time, and the moving average is calculated as the second communication amount. .

The information of the channel capable of performing packet communication includes at least a channel switching designation group including a grouping number and a designation group and a frequency code, and the mobile terminal has a number unique to each of the mobile terminals. Only when the remainder obtained by dividing the mobile station identifier by the number of groupings in the received channel switching designated group matches the designated group in the received channel switching designated group, the comparing operation by the comparing means is performed. The mobile communication system according to claim 1, wherein:

In a channel switching method of a mobile communication system, a mobile terminal located in a communication area of a base station switches a channel that performs packet communication with the base station by radio waves.
The base station calculates a first traffic in its own communication area, periodically transmits the first traffic and information of a channel capable of packet communication to a nearby base station, The first communication amount from the base station and information of a channel capable of packet communication are transmitted to the mobile terminal performing packet communication, and the mobile terminal includes:
A first step of calculating a second communication amount of the base station during packet communication, and receiving information of the first communication amount and a channel capable of packet communication transmitted from the base station during packet communication A second step, and a third step of measuring, based on the received information on the channel, a received electric field strength of a frequency used by a base station other than the base station performing the packet communication specified by the information. A fourth step of comparing the measurement result of the reception electric field strength with a predetermined threshold value, and comparing the second communication amount with the first communication amount received in the second step; And a comparison result that the measurement result of the reception electric field strength is larger than a predetermined threshold value and the second traffic is larger than the first traffic by a predetermined value or more. When it is obtained, the received packet And a fifth step of switching the possible channels, the mobile terminal channel switching method characterized by switching the channel of the base station towards the communication load is light.

The said base station broadcasts the said 1st traffic from the said neighboring base station and the information of the channel which can perform packet communication to the said mobile terminal which is performing packet communication using an idle unit, The characterized by the above-mentioned. Item 9. The channel switching method according to Item 8.

In a channel switching method of a mobile communication system, a mobile terminal located in a communication area of a base station switches a channel that performs packet communication with the base station by radio waves.
The base station calculates the amount of packet communication in its own communication area, periodically transmits the information on the amount of packet communication and the channel capable of performing packet communication to peripheral base stations, and transmits the information from the peripheral base station. The packet communication amount and information of a channel capable of packet communication are transmitted to the mobile terminal during packet communication, and the mobile terminal includes:
A first step of calculating a first communication amount of all packets of the current channel during packet communication and a second communication amount of packets of the current channel during packet communication addressed to the own station; A second step of calculating, as a threshold, a value obtained by subtracting a value obtained by multiplying the second communication amount by a predetermined value from the first communication amount, and the packet communication transmitted from the base station during packet communication A third step of receiving information on the amount and the channel capable of packet communication, and a frequency used by a base station other than the base station in packet communication specified by the information based on the received information on the channel. A fourth step of measuring the received electric field intensity of the packet, comparing the measurement result of the received electric field intensity with a predetermined determination value, and comparing the packet communication amount received in the third step with the second A fifth step of comparing with the threshold value calculated in the step, and the measurement result of the received electric field strength is larger than the determination value, and the packet communication amount is smaller than the threshold value. when the comparison result is obtained with it are seen including a sixth step of switching in the received packet communication-possible channels, the mobile terminal is to switch to the channel of the base station towards the communication load is light A channel switching method characterized by the following.

The said base station alert | reports the said packet communication volume from the said base station and the information of the channel which can perform packet communication to the said mobile terminal during packet communication using an idle unit, The characterized by the above-mentioned. The described channel switching method.