JP3613276B2

JP3613276B2 - Spread spectrum communication system and transmission power control method

Info

Publication number: JP3613276B2
Application number: JP2003170187A
Authority: JP
Inventors: 隆矢野; 信数土居
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2003-06-16
Filing date: 2003-06-16
Publication date: 2005-01-26
Anticipated expiration: 2020-01-26
Also published as: JP2004159289A

Description

【０００１】
【発明の属する技術分野】
本発明は、スペクトラム拡散通信システムに関し、更に詳しくは、複数の端末装置が基地局装置と通信を同時に行うセルラ方式のスペクトラム拡散通信システム、およびそれに適用する移動端末装置ならびに送信電力制御方法に関する。
【０００２】
【従来の技術】
例えば、図１０に示すように、交換局１０と接続された複数の基地局１００（１００−ａ、１００−ｂ）を分散配置して複数のセル１（１ａ、１ｂ）を構成し、各セル内で基地局１００と複数の移動端末３００とが通信を行うセルラ方式のスペクトル拡散通信システムにおいて、各基地局１００がセル内の端末に送信する信号の拡散符号として、セル内の各端末毎に固有の直交符号Ｗｉを用いる方式が知られている。
【０００３】
直交符号は、例えば図１１に符号Ｗ０、Ｗ１、Ｗ２、Ｗ３で示す如く、そのうちの任意の２つの符号について直交単位区間にわたって積和演算を行うと、結果が０となる性質をもっている。
【０００４】
従って、基地局がセル内の複数の端末３００−１〜３００−ｎにそれぞれ固有の直交符号Ｗｉ（ｉ＝１〜ｎ）を割当て、１つの端末３００−ｉ宛に送信する信号あるいはデ−タをその端末の固有の直交符号Ｗｉを用いて拡散し、上記端末３００−ｉが自分に割り当てられた固有の直交符号Ｗｉを用いて受信信号を逆拡散するようにしておくと、端末３００−ｉ宛の送信信号と直交するセル内の他の端末宛の送信信号成分は、上記逆拡散処理の過程で完全に除去されてしまい、妨害信号として作用しなくなる。このように各基地局から移動端末への通信に直交符号による拡散を適用した通信方式としては、例えば、米国特許第５１０３４５９号公報に示されている。
【０００５】
然るに、直交符号を用いたセルラ方式のスペクトル拡散通信システムにおいては、各端末には、セル内の基地局から送信された信号の他に、隣接セルを形成する他の基地局からの送信信号も到達する。この場合、他の基地局からの送信信号は、セル内の基地局が送信する信号と直交関係にないため、上述したセル内で固有の直交符号Ｗｉによる逆拡散処理によって除去することができない。すなわち、各端末の受信動作において、他のセルの基地局からの送信信号が妨害要因として作用する。
【０００６】
図１５は、各端末における上述した他の基地局からの送信信号の影響を示した図である。
基地局から送信された信号の受信電力は、基地局からの距離が大きくなるに従って減衰する。従って、基地局１００に近い、セル中心付近に位置した端末３００ａでは、セル内の基地局からの信号の受信電力９１０が大きく、妨害信号として作用するセル外の他の基地局からの信号の受信電力９１１は小さくなるため、高いＳ／Ｎが得られる。これに対して、セル境界に付近に位置した端末３００ｂでは、セル内の基地局からの信号の受信電力９１２が弱く、隣接セルからの妨害信号が上記端末３００ａより大きな電力９１３で受信されるため、結果的にＳ／Ｎが劣化する。
【０００７】
上記理由から、セルラシステムにおいては、各基地局から端末へ送信する信号を、セル中心付近に位置する端末３００ａに対しては小さな送信電力で、また、セル周辺に位置する端末３００ｂに対しては大きな送信電力で出力するように、端末との位置関係によって送信電力を制御することが望まれる。このように端末の位置に応じて送信電力を変えるようにした送信電力制御方法については、例えば、文献Ａ．Ｓａｌｍａｓｉ、Ｋ．Ｓ．Ｇｉｌｈｏｕｓｅｎ、「ＯｎｔｈｅＳｙｓｔｅｍＤｅｓｉｇｎＡｓｐｅｃｔｓｏｆＣｏｄｅＤｉｖｉｓｉｏｎＭｕｌｔｉｐｌｅＡｃｃｅｓｓ（ＣＤＭＡ）ＡｐｐｌｉｅｄｔｏＤｉｇｉｔａｌＣｅｌｌｕｌａｒａｎｄＰｅｒｓｏｎａｌＣｏｍｍｕｎｉｃａｔｉｏｎｓＮｅｔｗｏｒｋ」、ＩＥＥＥＶＴＳ１９９１、ｐｐ．５７−６２に記載されている。
【０００８】
上記文献に記載された制御方式では、各端末装置は、例えば、図１４に示す回路構成によって受信信号のＳ／Ｎを測定して、送信電力の加減を要求する制御信号を基地局に送信し、基地局が、図１２〜図１３に示す回路構成によって、上記電力制御信号に応答した送信信号電力制御動作を行なうようにしている。
【０００９】
基地局の送受信回路部分の構成を示す図１２において、アンテナ１１０で受信された各端末装置からの信号は、サーキュレータ１０９を経て高周波回路１１１に入力され、ベースバンドのスペクトル拡散信号Ｒｘに変換される。上記ベースバンドのスペクトル拡散信号Ｒｘは、セル内に位置している各端末装置に対応付けられた変復調装置１０５−１、１０５−２、……１０５−Ｎに入力され、ここで逆拡散処理と復号処理を施すことによって、各端末毎の送信信号（受信データ）１１２と、端末が上記送信信号に混合して送信してきた電力制御信号ＰＣとが分離される。
【００１０】
各変復調装置１０５−ｉ（ｉ＝１〜Ｎ）から出力された電力制御信号ＰＣは、送信電力制御装置１１６に入力される。送信電力制御装置１１６は、各電力制御信号ＰＣに応じて、各端末装置毎の送信電力指示信号ＰＷを発生する。
【００１１】
上記変復調装置１０５−ｉ（ｉ＝１〜Ｎ）は、各端末装置宛の送信データ１０１に対して、それぞれ符号化処理と、疑似雑音（ＰＮ）発生器１０３で発生した基地局に固有の疑似雑音ＰＮおよび直交符号発生器１０２から発生した直交符号Ｗ１、Ｗ２、Ｗ３、…、ＷＮを用いたスペクトル拡散による変調処理とを施す。スペクトル拡散により変調された信号は、送信電力制御装置１１６から与えられた各端末装置対応の送信電力指示信号ＰＷｉに従った電力で増幅され、送信信号Ｔｘ−ｉ（ｉ＝１〜Ｎ）として出力される。
【００１２】
１０４はパイロット信号の発生装置であり、単純なパターンデータ、例えばオールゼロからなるデータを発生する。このパイロット信号は、疑似雑音発生器１０３から発生される基地局に固有の疑似雑音ＰＮと、直交符号発生器１０２から発生される特定の直交符号Ｗ０とを用いてスペクトル拡散変調された後、パイロット信号として出力される。
【００１３】
各端末宛の送信信号Ｔｘ−ｉ（ｉ＝１〜Ｎ）は、縦続接続された加算器１０７（１０７−０、１０７−１、……）によって順次加算された後、上記パイロット信号と共に高周波回路１０８で伝送周波数帯域の信号に変換され、サーキュレータ１０９、アンテナ１０９を経て空中に送出される。
【００１４】
図１３は、図１２における変復調器１０５−ｉ（ｉ＝１、２、…Ｎ）の構成の１例を示す。
変復調器１０５−ｉに入力された送信データ１０１は、符号化器２０１に入力され、誤り訂正等の符号化処理を受ける。上記符号化された信号は、乗算器２０２によって、直交符号発生器１０２から与えられた直交符号Ｗｉと乗算され、第一次のスペクトル拡散を受け、次に、乗算器２０３によって疑似雑音信号ＰＮと乗算され、第二次のスペクトル拡散を受ける。このようにスペクトル拡散された信号は可変利得増幅器２０４に入力され、送信電力指示信号ＰＷ−ｉで指定された利得で増幅され、送信信号Ｔｘ−ｉとして出力される。
【００１５】
一方、変復調器１０５−ｉに入力された受信信号Ｒｘは、乗算器２０５に入力され、後述する上記信号Ｒｘの送信元となった端末装置でスペクトル拡散のために用いた疑似雑音ＰＮと同じ、疑似雑音発生器２０６で発生した疑似雑音ＰＮを用いて逆拡散処理を受ける。逆拡散された信号は累算器２０７に入力され、一定時間分の信号が累算される。この累算された逆拡散信号は、復号器２０８に入力されて誤り訂正等の復号処理を受け、復号された受信データ１１２と、端末装置が送信してきた電力制御信号ＰＣ−ｉとに分離して出力される。
【００１６】
図１４は、従来の端末装置が備える送受信回路部分の構成を示す。
端末装置において、アンテナ３０１から受信された信号は、サーキュレータ３０２を経て高周波回路３０３に入力され、ベースバンドのスペクトル拡散信号に変換される。
【００１７】
上記ベースバンドのスペクトル拡散信号は、第１の乗算器３０４に入力され、疑似雑音発生器３０５から発生した疑似雑音ＰＮと乗算され、第一次の逆拡散処理を受ける。上記疑似雑音ＰＮは、端末装置を基地局に位置登録した時、上記基地局のＰＮ発生器１０３で発生する固有の疑似雑音ＰＮと同一となるように雑音パターンが設定されている。
【００１８】
上記第一次の逆拡散処理を受けた信号は、第２の乗算器３０７に入力され、直交符号発生器３０６から発生する上記端末に割り当てられた直交符号Ｗｉと乗算され、第二次の逆拡散処理を受ける。上記第二次の逆拡散処理を受けた信号は、累算器３０８に入力され、一定時間分の信号が累算される。累算された信号は、復号器３０９によって復号化され、受信データとなる。
【００１９】
従来技術によれば、各端末装置では、受信信号の振幅に関する確率密度分布において、分散が雑音電力に相当し、平均が信号振幅に相当することを利用して、受信信号のＳ／Ｎを測定している。
【００２０】
このＳ／Ｎ測定のために、従来技術では、累算器３０８の出力を絶対値演算器３２８に入力して得られる絶対値と、上記累算器３０８の出力を自乗演算器３２５に入力して得られる自乗値とを、Ｓ／Ｎ測定器３２９に供給している。上記Ｓ／Ｎ測定器３２９では、自乗値入力の平均値と、絶対値入力の平均の自乗値との差から雑音電力を求め、絶対値入力の平均の自乗値から信号電力を求めることによってＳ／Ｎを測定し、その結果を比較器３３０で、Ｓ／Ｎの基準値とを比較し、基地局に送信電力増減を要求するための電力制御信号ＰＣ−ｉを得ている。
【００２１】
上記電力制御信号ＰＣ−ｉは、混合器３１７で端末からの送信データと混合した後、符号化器３１８で誤り訂正等の符号化処理を施し、この符号化された信号を乗算器３２０に与え、疑似雑音発生器３１９から発生された疑似雑音と乗算することによってスペクトル拡散変調する。スペクトル拡散変調された信号は、高周波回路３２１で伝送周波数帯域の信号に変換された後、サーキュレータ３０２を介してアンテナ３０１に出力され、空中に送出される。
【００２２】
以上の構成により、端末は基地局からの自端末に対する送信信号の受信Ｓ／Ｎを基地局に通知し、基地局は端末の受信Ｓ／Ｎが目標Ｓ／Ｎとなるように送信電力を制御する。
【００２３】
【発明が解決しようとする課題】
上述した従来のスペクトル拡散通信システムでは、各端末装置は、基地局が自分宛に送出した信号のみに基づいてＳ／Ｎを測定している。すなわち、逆拡散して得られる受信信号の振幅の分散を雑音電力とみなし、上記信号の振幅の平均値の自乗を信号電力とみなしてＳ／Ｎを測定している。
【００２４】
然るに、上記従来のＳ／Ｎ測定の原理は、雑音がなければ信号の振幅が一定となることを前提としているが、移動通信システムにおいては、各端末装置の受信信号の振幅が、端末の移動に伴って激しく変動する。従って、各端末で信頼できるＳ／Ｎ測定結果を得るためには、受信信号の略振幅が一定とみなせる程度の比較的短い期間内に測定を完了する必要がある。このため、従来の端末装置では、Ｓ／Ｎ測定回路系３２５〜３２９に極めて高速性能の回路が要求される。もし、回路性能の制約からＳ／Ｎ測定に時間を要する場合は、正しいＳ／Ｎ測定結果が得られないため、端末からの電力制御信号に基づいて、基地局が適切な電力制御を実現できないという問題がある。
【００２５】
この場合、Ｓ／Ｎ測定結果の誤差分を考慮して、基地局が、セル内の各端末に必要以上に大きな電力で信号を送信すると、送信信号は隣接セルに高い電力で侵入し、隣接セル内の端末に強い妨害電波として作用する。一方、基地局が、実際に端末が必要とする電力より小さな電力で送信動作すると、これを受信した端末における通信品質が悪化するという問題がある。
【００２６】
なお、基地局からの送信信号の電力制御方法としては、例えば、各端末装置が、上述した受信信号のＳ／Ｎの代わりに受信データの誤り率を監視し、誤り率が所定の基準に満たない場合に、基地局に送信電力の増加を要求する方式が考えられるが、この方式は、データの誤り率の算出に比較的長時間の監視が必要となるため、電力制御を通信状態の変動に十分に追従できないという問題がある。
【００２７】
本発明の目的は、各端末装置が高いＳ／Ｎで基地局と通信できるスペクトル拡散通信システムおよび電力制御方法を提供することにある。
【００２８】
本発明の他の目的は、各セルにおける同時通信数を増加可能なスペクトル拡散通信システムおよび電力制御方法を提供することにある。
【００２９】
本発明の他の目的は、基地局に送信すべき電力制御のための制御情報を迅速に算出可能な移動端末装置を提供することにある。
【００３０】
【課題を解決するための手段】
上記目的を達成するために、本発明のスペクトル拡散通信システムでは、基地局が、スペクトル拡散のための直交符号系列のうちの少なくとも１つを、パイロット信号や端末に対する送信信号の変調には適用しない、電力制御に専用の符号として割当てることを１つの特徴とする。
【００３１】
また、本発明では、各端末装置（移動端末）が、受信信号を上記基地局でＳ／Ｎ計測専用に割り当てた直交符号により逆拡散した結果得られるノイズ成分の受信電力と、パイロット信号または自端末宛の送信信号のうちの少なくとも一方の受信電力とから、受信信号のＳ／Ｎを求めることを１つの特徴とする。
【００３２】
本発明のスペクトル拡散通信システムでは、各端末装置が、このようにして求めたＳ／Ｎの値に基づいて得られた電力制御情報を基地局に送信し、基地局が、端末装置から受信した上記制御情報に応じて、各端末装置に対する信号の送信電力を制御する。
また、本願発明の他の着眼点は、送信電力制御において、電力制御情報を取得する第１の信号と、制御対象となる第２の信号を異ならせるところにある。
【００３３】
基地局から送出される全ての信号成分は上記制御専用の直交符号と直交しているため、基地局が上記制御専用の直交符号を送信信号の変調に適用しないようにしておき、各端末装置が上記制御専用の直交符号を用いてそれぞれの受信信号を逆拡散処理するようにしておくと、各端末装置では、受信信号からセル内の基地局が送出した各種の信号成分を完全に除去することができる。この場合、他のセルの基地局から送出された信号は、上記逆拡散に用いた特定符号と直交していないため、逆拡散処理で除去されず、雑音成分として残る。従って、上記逆拡散処理によって抽出された雑音成分の自乗平均を求めることによって、雑音電力を迅速、且つ十分な精度で測定することができる。
【００３４】
一方、基地局から送られた信号成分は、各端末に割り当てられた直交符号、またはパイロット信号用に割り当てられた直交符号で受信信号を逆拡散することによって得られるため、その電力値と上記雑音電力とから、Ｓ／Ｎ値を求めることができる。
【００３５】
本発明によれば、各端末が上記Ｓ／Ｎ値に応じた電力制御要求を基地局に通知し、基地局が、各端末からの制御要求に基づいて各端末毎の信号送信電力を制御することによって、各端末装置の通信品質を保証することができる。
【００３６】
なお、上記信号送信電力の制御を、例えば、全ての端末でＳ／Ｎが等しくなるように制御すると、各基地局の送信電力の総和を減少することができるため、結果的に、隣接セルに悪影響を及ぼす雑音電力の値を低下でき、これによって各端末におけるＳ／Ｎを一層改善できるという効果がある。
また、本願発明は、制御情報の基となる信号と制御対象となる信号が同一である「閉ループ制御」ではなく、これらが異なる「開ループ制御」を採用する。閉ループ制御の場合には、制御の遅れまたは誤りにより制御対象信号に変動が生じた場合、その変動が制御情報の誤差となって現れ、さらに制御対象信号が変動するという問題があるが、開ループ制御の考え方を採用する本願発明では、そのような問題がなく安定な制御が可能となる。
【００３７】
【実施例】
図１は、本発明のスペクトル拡散通信システムにおける基地局の構成の１例を示す。図において、従来技術として図１２に示した基地局の構成要素と対応する要素には、同一の符号を付してある。
【００３８】
上記本発明の基地局動作は、前述の従来技術による基地局とほぼ同様であるが、後述するように、直交符号発生器１０２から出力される直交符号のうち、任意の１つ、この実施例ではＷＮが、端末に対する送信データの変調用途から除外され、Ｓ／Ｎ測定専用に割り当てられていると言う点で相違している。
【００３９】
図３は、本発明における端末装置の第１の実施例を示す。図において、回路要素３０１〜３０９は、図１４に示した従来の端末装置の構成要素３０１〜３０９と対応しており、これらの要素からなる受信回路では、従来装置と同様、乗算器３０４で疑似雑音ＰＮによる第１次の逆拡散を受けた受信信号が、乗算器３０７で直交符号Ｗｉによって第２次の逆拡散を受け、端末宛の受信データとして復号される。
【００４０】
この実施例では、上記乗算器３０４で第１次の逆拡散を受けた受信信号を乗算器３１３と３１０に入力する。乗算器３０３に入力された信号は、直交符号発生器３０６から発生される直交符号Ｗ０によって第２次の逆拡散を受ける。上記直交符号Ｗ０は基地局が周期的に出力するパイロット信号の拡散用直交符号と対応しており、上記直交符号Ｗ０により逆拡散した信号を累算器３１４に入力し、一定期間累算することによって、パイロット信号を復調することができる。上記パイロット信号は、自乗器３１５で自乗され、パイロット信号成分の瞬時電力を示す信号となってＳ／Ｎ測定回路３１６の第１端子に入力される。
【００４１】
一方、乗算器３１０に入力された受信信号は、直交符号発生器３０６より発生されたＳ／Ｎ測定専用の直交符号ＷＮによって第２次の逆拡散を受け、逆拡散された信号は、累算器３１１に入力されて一定期間累算される。上記直交符号ＷＮは、基地局で送信信号の変調には用いない特定の直交符号となっているため、この直交符号による逆拡散処理の結果、上記基地局からの送信信号成分を完全に除去し、雑音に相当する成分を抽出できる。従って、乗算器３１１の出力を累算器３１１で一定期間累算し、これを自乗器３１２において自乗演算することによって、雑音成分の瞬時電力を得ることができる。
【００４２】
上記雑音成分の瞬時電力は、Ｓ／Ｎ測定回路３１６の第２端子に入力され、前記パイロット信号成分の瞬時電力との比率を算出することによって、パイロット信号のＳ／Ｎを示す信号が求まる。本実施例では、上記Ｓ／Ｎ信号を比較器３３０において基準Ｓ／Ｎと比較し、基準Ｓ／Ｎとの偏差を示す電力制御信号ＰＣを得ている。この電力制御信号ＰＣは、混合器３１７で送信データと混合した後、符号化器３１８で符号化し、乗算器３２０において疑似雑音発生器３１９から発生した疑似雑音によりスペクトル拡散変調を施した後、高周波回路３２１、サーキュレータ３０２、アンテ３０１を介して基地局に向けて送信される。
【００４３】
図４は、端末装置の第２の実施例を示す。この実施例では、図３における比較器３３０を省略し、Ｓ／Ｎ測定回路から出力されるＳ／Ｎ情報をそのまま電力制御信号ＳＮとして扱い、混合器３１７で送信データと混合した後、符号器３１８、乗算器３２０、高周波回路３２１、サーキュレータ３２１を介して送信するようにしている。
【００４４】
図１に示した基地局１００では、各変復調装置１０５−ｉ（ｉ＝１〜Ｎ−１）が、それと対応する各端末装置からの受信信号を受信データと電力制御信号に分離し、電力制御信号を送信電力制御装置１０６に与えるようになっている。各端末が第１実施例の構造の場合は、電力制御信号ＰＣが分離され、各端末が第２実施例の構造の場合は、電力制御信号ＳＮが分離される。上記送信電力制御装置１０６は、電力制御信号ＰＣまたはＳＮに応じて、各変復調装置１０５−ｉに与えるべき送信電力指示信号ＰＷを発生する。
【００４５】
上記変復調器１０５−ｉの構成を図２に示す。回路要素２０１〜２０７は、図１３に示した従来の変復調装置の回路要素２０１〜２０７と対応している。
【００４６】
端末装置からの受信信号Ｒｘは、乗算器２０５で疑似雑音信号によって逆拡散され、累算器２０７で一定期間累積された後、誤り訂正復号器５０８に入力される。ここで、誤り訂正等の復号処理が行われ、復号された信号から、受信データ１１２と、電力制御信号ＳＮ−ｉまたはＰＣ−ｉが分離される。
【００４７】
端末装置が第１実施例の構成をもつ場合、各変復調装置１０５−ｉにおいて分離した電力制御信号ＰＣ−ｉを、従来と同様の構成をもつ送信電力制御装置１０６に入力し、各端末の受信Ｓ／Ｎが標準Ｓ／Ｎに一致するように、送信電力指示信号ＰＷ−ｉを発生すればよい。
【００４８】
図５は、端末装置が第２実施例の構造を有し、変復調装置１０５が制御信号ＳＮ−ｉ（ｉ＝１〜Ｎ−１）を出力する場合の送信電力制御装置１０６の構成の１例を示す。
【００４９】
電力制御信号ＳＮ−ｉは、各端末と対応するローパスフィルタ４０１−ｉ（ｉ＝１〜Ｎ−１）に入力され、必要以上に高い周波数で変動する高周波成分を除去した後、逆数演算器４０２−ｉ（ｉ＝１〜Ｎ−１）でＳ／Ｎ値の逆数に相当する信号に変換される。上記逆数演算器４０２−ｉの出力は、加算器４０３において加算された後、加算結果が逆数演算器４０４で再度逆数変換される。逆数演算器４０４の出力は、乗算器４０５−（ｉ＝１〜Ｎ−１）に供給され、逆数演算器４０２−ｉ（ｉ＝１〜Ｎ−１）の出力との乗算が行われ、その演算結果が各端末毎の送信電力指示信号ＰＷ−ｉ（ｉ＝１〜Ｎ−１）として出力される。この場合の送信電力指示信号ＰＷ−ｉは、送信電力の重み係数を表しており、端末装置のＳ／Ｎ値が低ければ低い程、送信電力が他の端末より高くなるように信号ＰＷ−ｉの値が決定される。
【００５０】
上記送信電力指示信号ＰＷ−ｉは、それと対応する図２に示す変復調装置１０５−ｉに供給される。変復調装置１０５−ｉにおいて、上記送信電力指示信号ＰＷ−ｉは、送信回路系の増幅器２０４に電力制御入力として入力され、これによって、各端末装置のＳ／Ｎの状態に応じた電力で、送信信号が出力される。
【００５１】
以上の構成において、基地局から送信されるパイロット信号と、基地局から各端末装置に送信される送信信号（データ信号）は、同一の周波数帯域で略同時点で送出されているため、基地局からの距離に応じて各端末装置の受信データ信号に生ずる減衰は、パイロット信号に生ずる減衰と略等しい。また、パイロット信号とデータ信号に生ずる雑音電力は等しい。
【００５２】
従って、上記実施例のように、各端末装置が、パイロット信号の受信電力と、その時点でＳ／Ｎ計測用直交符号を用いて抽出した雑音電力とに基づいてＳ／Ｎを計測し、これを電力制御信号（ＰＣまたはＳＮ）として基地局に送り、基地局が上記電力制御信号に基づいて、各端末対応にＳ／Ｎに反比例した送信電力でデータ信号を送信制御することによって、各端末における受信信号のＳ／Ｎを等しくすることができる。
【００５３】
図１６は、本発明によって各端末のＳ／Ｎが等しくなるように送信電力制御を行った場合の効果を示す図である。本発明によれば、セルの境界付近に位置する端末Ａに対する信号の送信電力に比較して、基地局付近に位置する端末Ｂに対する信号の送信電力が小さくなるように電力制御が行われるため、端末Ａ、Ｂにおける信号の受信電力は、それぞれ９２０、９２２のようになる。
【００５４】
上述した電力制御は、各セルに隣接したセルにおいても同様に行われ、各基地局のトータルの送信電力を減少させる方向に制御が働くため、各セルにおいては、隣接セルからの妨害電波のパワーが減少し、基地局に近い端末に他のセルの基地局から到達する妨害信号の受信電力は９２１のように、また、セル境界の端末に到達する妨害信号の受信電力は９２３のようにそれぞれ低減する。この電力低減の効果は、例えば、正六角形のセルが繰り返して配置された構造を持つスペクトル拡散通信システムにおいては、約７．４ｄＢに相当する。また、妨害信号の電力が低減された分、各セルにおいて同時に通信可能な端末台数（基地局が収容する端末個数）を増加でき、最大で従来の約５．５倍に増加できる。なお、上述した電力制御は、開ループ制御となっているため、安定した制御が行われる。
【００５５】
図６は、本発明による端末装置の第３の実施例を示す。この実施例では、Ｓ／Ｎの測定を、上述したパイロット信号に代えて、各端末宛の送信信号（データ信号）の受信電力と、雑音信号の受信電力とから求めるようにしている。図において、図４と同一の回路要素には同一の符号を付してあり、これらの回路要素は図４と同様の機能をもつ。
【００５６】
本実施例では、直交符号Ｗｉで逆拡散された端末宛の送信信号を累算器３０８で一定期間累算し、その出力を復号器３０９に入力する一方、これを自乗器３２５に入力して受信信号の瞬時電力を得、この受信信号の瞬時電力をＳ／Ｎ測定装置３２６の第２入力とする。上記Ｓ／Ｎ測定装置３２６の第１入力には、直交符号Ｗｎで逆拡散して自乗器３１２から出力される雑音の瞬時電力を与え、これによって受信信号のＳ／Ｎを求める。上記受信信号のＳ／Ｎは、電力制御信号ＳＮ＝ｉとして混合器３１７で送信データ信号と混合された後、符号化回路３１８、乗算器３２０、高周波回路３２１を介して、アンテナ３０１から送出される。
【００５７】
尚、上記受信信号Ｓ／Ｎは、第１実施例と同様に、基準Ｓ／Ｎとの差分をとり、電力制御信号ＰＣとして基地局に送信してもよい。
【００５８】
図７は、基地局の信電力制御装置１０６の他の実施例を示す。この実施例では、各変復調装置１０５ｉ（ｉ＝１〜Ｎ−１）で分離した電力制御信号ＳＮ−ｉ（ｉ＝１〜Ｎ−１）を、ローパスフィルタ６０１−ｉ（ｉ＝１〜Ｎ−１）に入力し、必要以上の高周波変動成分を除去した後、比較器６０３−ｉ（ｉ＝１〜Ｎ−１）で、目標値Ｓ／Ｎ発生回路６０２から出力されるＳ／Ｎ目標値との差を求め、各端末毎に、実際のＳ／Ｎと目標Ｓ／Ｎとの差を積分器６０４−ｉ（ｉ＝１〜Ｎ−１）で積分する。上記各積分器の出力が、各端末に対する送信電力指示信号ＰＷ−ｉ（ｉ＝１〜Ｎ−１）として、図２に示す出力増幅器２０４に与えられる。この送信電力指示信号によって、全ての端末でのＳ／Ｎが等しくなるように送信信号の電力が制御される。本実施例の場合も閉ループ制御となっており、各端末のＳ／Ｎは、伝送系に多少の非線形性が存在していても、目標Ｓ／Ｎに一致するように制御される。
【００５９】
図８は端末装置の第４の実施例を示す。この実施例では、図３で説明した第１の実施例におけるＳ／Ｎ測定装置３１６と、図６で説明した第３実施例におけるＳ／Ｎ測定装置３２６とが併用されている。すなわち、Ｓ／Ｎ測定装置３１６からはパイロット信号のＳ／Ｎ情報が得られ、Ｓ／Ｎ測定装置３２６からは受信信号のＳ／Ｎ情報が得られる。これら２種類のＳ／Ｎ情報は、混合器３２７で送信データと混合され、符号化回路３１８、乗算器３２０、高周波回路３２１、サーキュレータ３０２、アンテナ３０１を介して送出される。
【００６０】
図９は、端末装置が上記第４実施例の構成をもつ場合の基地局における送信電力制御装置１０６の構成を示す。基地局において、各変復調装置１０５−ｉは、端末装置が送ってきた２種類の電力制御信号、すなわち、パイロット信号のＳ／Ｎ（Ｓ／Ｎ−ｉｐ）と、受信信号のＳ／Ｎ（Ｓ／Ｎ−ｉｄ）とを分離して出力する。
【００６１】
このうち、パイロット信号のＳ／ＮであるＳＮ−ｉｐ（ｉ＝１〜Ｎ−１）は、回路要素４０１−ｉ、４０２−ｉ、４０３、４０４、４０５−ｉからなる図５に示した回路と同様の回路構成で、各端末に対する送信電力の第１の重み値を生成する。一方、受信信号のＳ／ＮであるＳＮ−ｉｄ（ｉ＝１〜Ｎ−１）は、回路要素６０１−ｉ、６０２、６０３−ｉ、６０４−ｉからなる図７に示した回路と同様の回路構成で、各端末に対する送信電力の第２の重み値を生成する。上記第２の重み値を、第１の重み値に補正値として作用させることによって、各端末毎の送信電力指示信号ＰＷ−ｉ（ｉ＝１〜Ｎ−１）が得られる。ここで、ローパスフィルタ６０１−ｉの時定数は、ローパスフィルタ４０１−ｉの時定数よりも十分大きな値に設定しておく。
【００６２】
上述した各実施例によれば、端末装置の位置が基地局に近く、基地局からの信号の受信状態が非常によい場合、この端末に対する送信電力が非常に小さくなってしまう可能性がある。この場合は、端末に対する送信電力に下限値を設定しておき、送信電力が所定値以下に下がらないように制御すればよい。
【００６３】
【発明の効果】
本発明によれば、各端末装置においてＳ／Ｎを迅速に測定することができるため、これを電力制御信号として基地局に送信し、基地局が上記電力制御信号に基づいて各端末宛の信号の送信電力を制御することによって、各端末におけるＳ／Ｎが略等しくなるようにすることができる。この結果、各セルにおける基地局からの端末宛の信号の送信電力の総和を必要最小限に抑えることが可能となり、隣接セルにノイズとして作用する妨害電波の電力を低減でき、各セルにおける収容端末個数の増加が可能となる。
【図面の簡単な説明】
【図１】本発明の通信システムにおける基地局装置の構成の１例を示す図。
【図２】上記基地局装置の変復調装置１０５−ｉの詳細を示す図。
【図３】本発明の通信システムに適用する端末装置の第１の実施例を示す構成図。
【図４】本発明の通信システムに適用する端末装置の第２の実施例を示す構成図。
【図５】基地局装置の送信電力制御装置の第１の実施例を示す図。
【図６】本発明の通信システムに適用する端末装置の第３の実施例を示す構成図。
【図７】基地局装置の送信電力制御装置の第２の実施例を示す図。
【図８】本発明の通信システムに適用する端末装置の第４の実施例を示す構成図。
【図９】基地局装置の送信電力制御装置の第３の実施例を示す図。
【図１０】本発明の移動通信システムの全体構成を示す図。
【図１１】スペクトル拡散に用いる直交符号の１例を示す図。
【図１２】従来の技術における基地局装置の構成を示す図。
【図１３】従来の技術における基地局装置の変復調装置の構成の１例を示す図。
【図１４】従来の技術における端末装置の構成の１例を示す図。
【図１５】従来の通信システムにおけるセル内の基地局からの信号成分と他のセルからの妨害成分との関係を説明するための図。
【図１６】本発明の通信システムにおけるセル内の基地局からの信号成分と他のセルからの妨害成分との関係を説明するための図。
【符号の説明】
１０４：パイロット信号発生装置、１０５：変復調装置、
１０６：送信電力制御装置、１０２、３０６：直交符号発生装置、
２０１、３１８：符号化器、２０２：第一次の拡散を行う乗算器、
２０３：第二次の拡散を行う乗算器、２０４：送信電力調整用可変利得増幅器、
２０５：逆拡散を行う乗算器、２０７、３０８、３１１、３１４：累算器、２０８、３０９：復号器、３０４：第一次の逆拡散を行う乗算器、
３０７、３１０、３１３：第二次の逆拡散を行う乗算器、
３２８：絶対値演算器、３１２、３１５、３２５：自乗演算器、
３２０：符号拡散のための乗算器、３１６、３２６、３２９：Ｓ／Ｎ測定装置、３３０：比較器、３１７、３２７：混合器、
４０１、６０１：ローパスフィルタ、４０２、４０４：逆数演算器、
６０３：加算器、６０４：積分器。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spread spectrum communication system, and more particularly to a cellular spread spectrum communication system in which a plurality of terminal apparatuses communicate with a base station apparatus at the same time, a mobile terminal apparatus applied thereto, and a transmission power control method.
[0002]
[Prior art]
For example, as shown in FIG. 10, a plurality of base stations 100 (100-a, 100-b) connected to the switching center 10 are distributed to form a plurality of cells 1 (1a, 1b). In a cellular spread spectrum communication system in which a base station 100 and a plurality of mobile terminals 300 communicate with each other, as a spreading code of a signal transmitted from each base station 100 to a terminal in the cell, for each terminal in the cell A method using a unique orthogonal code Wi is known.
[0003]
For example, as shown by reference characters W0, W1, W2, and W3 in FIG. 11, the orthogonal code has a property that the result becomes 0 when the product-sum operation is performed over the orthogonal unit interval for any two of the codes.
[0004]
Therefore, the base station assigns a unique orthogonal code Wi (i = 1 to n) to each of the plurality of terminals 300-1 to 300-n in the cell, and transmits a signal or data transmitted to one terminal 300-i. Is spread using the unique orthogonal code Wi of the terminal, and the terminal 300-i despreads the received signal using the unique orthogonal code Wi assigned to itself. Transmission signal components addressed to other terminals in the cell orthogonal to the addressed transmission signal are completely removed during the despreading process, and do not act as interference signals. A communication system in which spreading by orthogonal codes is applied to communication from each base station to a mobile terminal is disclosed in, for example, US Pat. No. 5,104,459.
[0005]
However, in a cellular spread spectrum communication system using orthogonal codes, each terminal also receives transmission signals from other base stations forming adjacent cells in addition to signals transmitted from base stations in the cell. To reach. In this case, the transmission signal from another base station is not orthogonal to the signal transmitted by the base station in the cell, and thus cannot be removed by the despreading process using the orthogonal code Wi unique in the cell. That is, in the reception operation of each terminal, a transmission signal from a base station in another cell acts as an interference factor.
[0006]
FIG. 15 is a diagram illustrating the influence of a transmission signal from another base station described above in each terminal.
The received power of the signal transmitted from the base station attenuates as the distance from the base station increases. Therefore, terminal 300a located near the cell center near base station 100 has a large signal reception power 910 from the base station in the cell, and receives signals from other base stations outside the cell that act as interference signals. Since the power 911 is small, a high S / N can be obtained. On the other hand, in the terminal 300b located near the cell boundary, the reception power 912 of the signal from the base station in the cell is weak, and the interference signal from the adjacent cell is received with the power 913 larger than that of the terminal 300a. As a result, S / N deteriorates.
[0007]
For the above reasons, in the cellular system, signals transmitted from each base station to the terminal are transmitted with small transmission power to the terminal 300a located near the cell center, and to the terminal 300b located around the cell. It is desired to control the transmission power according to the positional relationship with the terminal so as to output with a large transmission power. As for the transmission power control method in which the transmission power is changed in accordance with the position of the terminal as described above, for example, see Document A. Salmasi, K.M. S. Gilhouseen, “On the System Designs of Codes of Code Division Multiple Access (CDMA) Applied to Digital Cellular and Personal Communications Network 91Ep. 57-62.
[0008]
In the control method described in the above document, each terminal device measures the S / N of the received signal using, for example, the circuit configuration shown in FIG. 14, and transmits a control signal for requesting transmission power to the base station. The base station performs the transmission signal power control operation in response to the power control signal with the circuit configurations shown in FIGS.
[0009]
In FIG. 12 showing the configuration of the transmission / reception circuit portion of the base station, a signal from each terminal apparatus received by the antenna 110 is input to the high-frequency circuit 111 via the circulator 109 and converted into a baseband spread spectrum signal Rx. . The baseband spread spectrum signal Rx is input to modulation / demodulation devices 105-1, 105-2,... 105-N associated with each terminal device located in the cell. By performing the decoding process, the transmission signal (reception data) 112 for each terminal is separated from the power control signal PC transmitted by the terminal mixed with the transmission signal.
[0010]
The power control signal PC output from each modulation / demodulation device 105-i (i = 1 to N) is input to the transmission power control device 116. The transmission power control device 116 generates a transmission power instruction signal PW for each terminal device according to each power control signal PC.
[0011]
The modem 105-i (i = 1 to N) encodes the transmission data 101 addressed to each terminal device and the pseudo signal unique to the base station generated by the pseudo noise (PN) generator 103. A modulation process by spread spectrum using the orthogonal codes W1, W2, W3,..., WN generated from the noise PN and the orthogonal code generator 102 is performed. The signal modulated by the spread spectrum is amplified by the power according to the transmission power instruction signal PWi corresponding to each terminal device given from the transmission power control device 116, and output as a transmission signal Tx-i (i = 1 to N). Is done.
[0012]
A pilot signal generator 104 generates simple pattern data, for example, data consisting of all zeros. This pilot signal is subjected to spread spectrum modulation using a pseudo noise PN specific to the base station generated from the pseudo noise generator 103 and a specific orthogonal code W0 generated from the orthogonal code generator 102, and then pilot-modulated. Output as a signal.
[0013]
Transmission signals Tx-i (i = 1 to N) addressed to each terminal are sequentially added by cascade-connected adders 107 (107-0, 107-1,...), And then, together with the pilot signal, a high-frequency circuit. The signal is converted into a signal in the transmission frequency band at 108, and sent to the air through the circulator 109 and the antenna 109.
[0014]
FIG. 13 shows an example of the configuration of the modem 105-i (i = 1, 2,... N) in FIG.
The transmission data 101 input to the modem 105-i is input to the encoder 201 and subjected to an encoding process such as error correction. The encoded signal is multiplied by the orthogonal code Wi given from the orthogonal code generator 102 by the multiplier 202 and subjected to the first spread spectrum, and then the pseudo noise signal PN and the multiplier 203 are applied. Multiplied and subjected to second order spread spectrum. The spectrum-spread signal is input to the variable gain amplifier 204, amplified with the gain specified by the transmission power instruction signal PW-i, and output as the transmission signal Tx-i.
[0015]
On the other hand, the received signal Rx input to the modulator / demodulator 105-i is input to the multiplier 205, and is the same as the pseudo noise PN used for spread spectrum in the terminal device that is the transmission source of the signal Rx described later A despreading process is performed using the pseudo noise PN generated by the pseudo noise generator 206. The despread signal is input to an accumulator 207, and a signal for a certain time is accumulated. The accumulated despread signal is input to the decoder 208 and subjected to decoding processing such as error correction, and is separated into the decoded received data 112 and the power control signal PC-i transmitted by the terminal device. Is output.
[0016]
FIG. 14 shows a configuration of a transmission / reception circuit portion included in a conventional terminal device.
In the terminal device, a signal received from the antenna 301 is input to the high frequency circuit 303 via the circulator 302 and converted into a baseband spread spectrum signal.
[0017]
The baseband spread spectrum signal is input to the first multiplier 304, multiplied by the pseudo noise PN generated from the pseudo noise generator 305, and subjected to the first-order despreading process. The pseudo-noise PN has a noise pattern set to be the same as the inherent pseudo-noise PN generated by the PN generator 103 of the base station when the terminal device is registered in the base station.
[0018]
The signal subjected to the first-order despreading process is input to the second multiplier 307, multiplied by the orthogonal code Wi assigned to the terminal generated from the orthogonal code generator 306, and the second-order inverse spread. Receive diffusion treatment. The signal subjected to the second-order despreading process is input to an accumulator 308, where signals for a certain time are accumulated. The accumulated signal is decoded by the decoder 309 to be received data.
[0019]
According to the prior art, each terminal apparatus measures the S / N of the received signal by using the fact that the variance corresponds to the noise power and the average corresponds to the signal amplitude in the probability density distribution regarding the amplitude of the received signal. doing.
[0020]
For this S / N measurement, in the prior art, the absolute value obtained by inputting the output of the accumulator 308 to the absolute value calculator 328 and the output of the accumulator 308 are input to the square calculator 325. The square value obtained in this way is supplied to the S / N measuring device 329. The S / N measuring device 329 obtains noise power from the difference between the mean value of the square value input and the mean square value of the absolute value input, and obtains the signal power from the mean square value of the absolute value input. / N is measured, and the result is compared with the S / N reference value by the comparator 330 to obtain the power control signal PC-i for requesting the base station to increase or decrease the transmission power.
[0021]
The power control signal PC-i is mixed with the transmission data from the terminal by the mixer 317, then subjected to an encoding process such as error correction by the encoder 318, and this encoded signal is given to the multiplier 320. Spread spectrum modulation is performed by multiplying the pseudo noise generated from the pseudo noise generator 319. The signal subjected to spread spectrum modulation is converted into a signal in the transmission frequency band by the high frequency circuit 321, and then output to the antenna 301 via the circulator 302 and transmitted to the air.
[0022]
With the above configuration, the terminal notifies the base station of the reception S / N of the transmission signal from the base station to the terminal, and the base station controls the transmission power so that the reception S / N of the terminal becomes the target S / N. To do.
[0023]
[Problems to be solved by the invention]
In the conventional spread spectrum communication system described above, each terminal apparatus measures the S / N based only on the signal transmitted from the base station to itself. That is, the dispersion of the amplitude of the received signal obtained by despreading is regarded as noise power, and the S / N is measured by regarding the square of the average value of the amplitude of the signal as signal power.
[0024]
However, the principle of the conventional S / N measurement is based on the premise that the signal amplitude is constant if there is no noise. However, in a mobile communication system, the amplitude of the received signal of each terminal device It fluctuates violently with. Therefore, in order to obtain a reliable S / N measurement result at each terminal, it is necessary to complete the measurement within a relatively short period to the extent that the amplitude of the received signal can be regarded as constant. For this reason, in the conventional terminal device, an extremely high-speed performance circuit is required for the S / N measurement circuit systems 325 to 329. If time is required for S / N measurement due to circuit performance constraints, a correct S / N measurement result cannot be obtained, and the base station cannot implement appropriate power control based on the power control signal from the terminal. There is a problem.
[0025]
In this case, considering the error in the S / N measurement result, if the base station transmits a signal with higher power than necessary to each terminal in the cell, the transmission signal enters the adjacent cell with high power and Acts as a strong jamming signal for terminals in the cell. On the other hand, if the base station performs a transmission operation with a power smaller than that actually required by the terminal, there is a problem that the communication quality at the terminal that has received the base station deteriorates.
[0026]
As a method for controlling the power of the transmission signal from the base station, for example, each terminal apparatus monitors the error rate of received data instead of the above-described S / N of the received signal, and the error rate satisfies a predetermined standard. If this is not the case, a method of requesting the base station to increase the transmission power can be considered, but this method requires a relatively long period of time to calculate the data error rate. There is a problem that it is not possible to follow up sufficiently.
[0027]
An object of the present invention is to provide a spread spectrum communication system and a power control method in which each terminal apparatus can communicate with a base station with high S / N.
[0028]
Another object of the present invention is to provide a spread spectrum communication system and a power control method capable of increasing the number of simultaneous communications in each cell.
[0029]
Another object of the present invention is to provide a mobile terminal apparatus capable of quickly calculating control information for power control to be transmitted to a base station.
[0030]
[Means for Solving the Problems]
In order to achieve the above object, in the spread spectrum communication system of the present invention, the base station does not apply at least one of the orthogonal code sequences for spread spectrum to the modulation of the transmission signal for the pilot signal or the terminal. One characteristic is that it is assigned as a dedicated code for power control.
[0031]
In the present invention, each terminal apparatus (mobile terminal) receives the received power of the noise component obtained by despreading the received signal with the orthogonal code assigned exclusively for S / N measurement at the base station, and the pilot signal or the own signal. One feature is to obtain the S / N of the received signal from the received power of at least one of the transmission signals addressed to the terminal.
[0032]
In the spread spectrum communication system of the present invention, each terminal device transmits power control information obtained based on the S / N value thus obtained to the base station, and the base station receives from the terminal device. The transmission power of the signal to each terminal apparatus is controlled according to the control information.
Another point of focus of the present invention is that, in transmission power control, the first signal for acquiring power control information is different from the second signal to be controlled.
[0033]
Since all signal components transmitted from the base station are orthogonal to the orthogonal code dedicated to control, the base station does not apply the orthogonal code dedicated to control to the modulation of the transmission signal, and each terminal device If each received signal is subjected to despreading processing using the orthogonal code dedicated to the control, each terminal device completely removes various signal components transmitted from the base station in the cell from the received signal. Can do. In this case, since the signal transmitted from the base station of another cell is not orthogonal to the specific code used for the despreading, it is not removed by the despreading process and remains as a noise component. Therefore, by obtaining the root mean square of the noise component extracted by the despreading process, the noise power can be measured quickly and with sufficient accuracy.
[0034]
On the other hand, since the signal component sent from the base station is obtained by despreading the received signal with the orthogonal code assigned to each terminal or the orthogonal code assigned for the pilot signal, the power value and the noise The S / N value can be obtained from the electric power.
[0035]
According to the present invention, each terminal notifies the base station of a power control request according to the S / N value, and the base station controls the signal transmission power for each terminal based on the control request from each terminal. As a result, the communication quality of each terminal device can be guaranteed.
[0036]
Note that if the signal transmission power is controlled so that, for example, the S / N is the same for all terminals, the total transmission power of each base station can be reduced. There is an effect that the value of the noise power having an adverse effect can be reduced, and thereby the S / N in each terminal can be further improved.
Further, the present invention employs “open loop control” in which these signals are different from “closed loop control” in which the signal that is the basis of the control information and the signal to be controlled are the same. In the case of closed-loop control, if the control target signal fluctuates due to a control delay or error, the fluctuation appears as an error in the control information, and the control target signal fluctuates. In the present invention employing the concept of control, there is no such problem and stable control is possible.
[0037]
【Example】
FIG. 1 shows an example of the configuration of a base station in a spread spectrum communication system of the present invention. In the figure, elements corresponding to those of the base station shown in FIG.
[0038]
The operation of the base station of the present invention is substantially the same as that of the base station according to the prior art described above, but as will be described later, any one of the orthogonal codes output from the orthogonal code generator 102, this embodiment However, the difference is that the WN is excluded from the use of modulation of transmission data for the terminal and is allocated exclusively for S / N measurement.
[0039]
FIG. 3 shows a first embodiment of the terminal device according to the present invention. In the figure, circuit elements 301 to 309 correspond to the components 301 to 309 of the conventional terminal device shown in FIG. 14, and in the receiving circuit composed of these elements, the multiplier 304 performs pseudo-simulation similarly to the conventional device. The received signal subjected to the first-order despreading due to the noise PN is subjected to the second-order despreading by the orthogonal code Wi in the multiplier 307 and decoded as received data addressed to the terminal.
[0040]
In this embodiment, the received signal subjected to the first-order despreading by the multiplier 304 is input to the multipliers 313 and 310. The signal input to the multiplier 303 is subjected to second-order despreading by the orthogonal code W 0 generated from the orthogonal code generator 306. The orthogonal code W0 corresponds to the spreading orthogonal code of the pilot signal periodically output by the base station, and the signal despread by the orthogonal code W0 is input to the accumulator 314 and accumulated for a certain period. Thus, the pilot signal can be demodulated. The pilot signal is squared by the squarer 315 and input to the first terminal of the S / N measurement circuit 316 as a signal indicating the instantaneous power of the pilot signal component.
[0041]
On the other hand, the received signal input to the multiplier 310 is subjected to second-order despreading by the orthogonal code WN dedicated to S / N measurement generated by the orthogonal code generator 306, and the despread signal is accumulated. It is input to the device 311 and accumulated for a certain period. Since the orthogonal code WN is a specific orthogonal code that is not used for modulation of the transmission signal at the base station, the transmission signal component from the base station is completely removed as a result of the despreading process using the orthogonal code. The component corresponding to noise can be extracted. Therefore, the instantaneous power of the noise component can be obtained by accumulating the output of the multiplier 311 for a certain period of time by the accumulator 311 and calculating the square thereof by the squarer 312.
[0042]
The instantaneous power of the noise component is input to the second terminal of the S / N measurement circuit 316, and a signal indicating the S / N of the pilot signal is obtained by calculating a ratio with the instantaneous power of the pilot signal component. In this embodiment, the S / N signal is compared with the reference S / N in the comparator 330 to obtain a power control signal PC indicating a deviation from the reference S / N. This power control signal PC is mixed with transmission data by a mixer 317, encoded by an encoder 318, subjected to spread spectrum modulation by pseudo noise generated from a pseudo noise generator 319 in a multiplier 320, and then subjected to high frequency. The data is transmitted to the base station via the circuit 321, the circulator 302, and the antenna 301.
[0043]
FIG. 4 shows a second embodiment of the terminal device. In this embodiment, the comparator 330 in FIG. 3 is omitted, the S / N information output from the S / N measurement circuit is handled as it is as the power control signal SN, and after mixing with the transmission data by the mixer 317, the encoder 318, the multiplier 320, the high frequency circuit 321, and the circulator 321 are used for transmission.
[0044]
In the base station 100 shown in FIG. 1, each modulation / demodulation device 105-i (i = 1 to N-1) separates the received signal from each corresponding terminal device into received data and a power control signal, and performs power control. A signal is supplied to the transmission power control apparatus 106. When each terminal has the structure of the first embodiment, the power control signal PC is separated. When each terminal has the structure of the second embodiment, the power control signal SN is separated. The transmission power control device 106 generates a transmission power instruction signal PW to be given to each modulation / demodulation device 105-i according to the power control signal PC or SN.
[0045]
The configuration of the modem 105-i is shown in FIG. The circuit elements 201 to 207 correspond to the circuit elements 201 to 207 of the conventional modem shown in FIG.
[0046]
The received signal Rx from the terminal device is despread by the pseudo noise signal by the multiplier 205, accumulated by the accumulator 207 for a certain period, and then input to the error correction decoder 508. Here, decoding processing such as error correction is performed, and the received data 112 and the power control signal SN-i or PC-i are separated from the decoded signal.
[0047]
When the terminal device has the configuration of the first embodiment, the power control signal PC-i separated in each modulation / demodulation device 105-i is input to the transmission power control device 106 having the same configuration as the conventional one, and received by each terminal. The transmission power instruction signal PW-i may be generated so that the S / N matches the standard S / N.
[0048]
FIG. 5 shows an example of the configuration of the transmission power control apparatus 106 when the terminal apparatus has the structure of the second embodiment and the modem apparatus 105 outputs the control signal SN-i (i = 1 to N−1). Indicates.
[0049]
The power control signal SN-i is input to a low-pass filter 401-i (i = 1 to N−1) corresponding to each terminal, and after removing a high-frequency component that fluctuates at a frequency higher than necessary, an inverse calculator 402 -I (i = 1 to N-1) is converted into a signal corresponding to the reciprocal of the S / N value. The output of the reciprocal calculator 402-i is added by the adder 403, and the addition result is reciprocally converted again by the reciprocal calculator 404. The output of the reciprocal calculator 404 is supplied to a multiplier 405-(i = 1 to N−1), and the output of the reciprocal calculator 402-i (i = 1 to N−1) is multiplied. The calculation result is output as a transmission power instruction signal PW-i (i = 1 to N−1) for each terminal. The transmission power instruction signal PW-i in this case represents a weighting factor of the transmission power, and the signal PW-i is set such that the lower the S / N value of the terminal device, the higher the transmission power than other terminals. The value of is determined.
[0050]
The transmission power instruction signal PW-i is supplied to the modem 105-i shown in FIG. 2 corresponding thereto. In the modem 105-i, the transmission power instruction signal PW-i is input as a power control input to the amplifier 204 of the transmission circuit system, thereby transmitting with the power corresponding to the S / N state of each terminal device. A signal is output.
[0051]
In the above configuration, the pilot signal transmitted from the base station and the transmission signal (data signal) transmitted from the base station to each terminal device are transmitted at substantially the same point in the same frequency band. The attenuation that occurs in the received data signal of each terminal device in accordance with the distance from the terminal is substantially equal to the attenuation that occurs in the pilot signal. Further, the noise power generated in the pilot signal and the data signal is equal.
[0052]
Therefore, as in the above-described embodiment, each terminal apparatus measures the S / N based on the received power of the pilot signal and the noise power extracted using the S / N measurement orthogonal code at that time. Is transmitted to the base station as a power control signal (PC or SN), and the base station performs transmission control of the data signal with transmission power inversely proportional to S / N for each terminal based on the power control signal. The S / N of the received signals at can be made equal.
[0053]
FIG. 16 is a diagram illustrating an effect when transmission power control is performed so that the S / N of each terminal becomes equal according to the present invention. According to the present invention, the power control is performed so that the transmission power of the signal to the terminal B located near the base station is smaller than the transmission power of the signal to the terminal A located near the cell boundary. The received power of the signals at terminals A and B are as shown at 920 and 922, respectively.
[0054]
The power control described above is performed in the same manner in cells adjacent to each cell, and the control works in a direction to reduce the total transmission power of each base station. The received power of the interference signal reaching the terminal near the base station from the base station of another cell is 921, and the received power of the interference signal reaching the terminal at the cell boundary is 923, respectively. To reduce. This power reduction effect corresponds to about 7.4 dB in a spread spectrum communication system having a structure in which regular hexagonal cells are repeatedly arranged, for example. Further, since the power of the interference signal is reduced, the number of terminals that can simultaneously communicate in each cell (the number of terminals accommodated by the base station) can be increased, and can be increased up to about 5.5 times the conventional maximum. In addition, since the electric power control mentioned above is open loop control, stable control is performed.
[0055]
FIG. 6 shows a third embodiment of the terminal device according to the present invention. In this embodiment, the S / N measurement is obtained from the reception power of the transmission signal (data signal) addressed to each terminal and the reception power of the noise signal instead of the above-described pilot signal. In the figure, the same reference numerals are given to the same circuit elements as those in FIG. 4, and these circuit elements have the same functions as those in FIG.
[0056]
In the present embodiment, the transmission signal destined for the terminal despread with the orthogonal code Wi is accumulated for a certain period by the accumulator 308, and the output is input to the decoder 309, while this is input to the squarer 325. The instantaneous power of the received signal is obtained, and the instantaneous power of the received signal is used as the second input of the S / N measuring device 326. The first input of the S / N measuring device 326 is given the instantaneous power of noise despread with the orthogonal code Wn and output from the squarer 312, thereby obtaining the S / N of the received signal. The S / N of the received signal is mixed with the transmission data signal by the mixer 317 as the power control signal SN = i, and then transmitted from the antenna 301 via the encoding circuit 318, the multiplier 320, and the high frequency circuit 321. The
[0057]
The received signal S / N may be differenced from the reference S / N and transmitted to the base station as a power control signal PC, as in the first embodiment.
[0058]
FIG. 7 shows another embodiment of the power control apparatus 106 of the base station. In this embodiment, the power control signal SN-i (i = 1 to N-1) separated by each modem 105i (i = 1 to N-1) is converted into a low-pass filter 601-i (i = 1 to N-). 1), after removing unnecessary high frequency fluctuation components, the S / N target value output from the target value S / N generation circuit 602 is output by the comparator 603-i (i = 1 to N−1). The difference between the actual S / N and the target S / N is integrated for each terminal by the integrator 604-i (i = 1 to N−1). The output of each integrator is given to output amplifier 204 shown in FIG. 2 as transmission power instruction signal PW-i (i = 1 to N−1) for each terminal. With this transmission power instruction signal, the power of the transmission signal is controlled so that the S / N ratios of all terminals are equal. In this embodiment as well, closed-loop control is performed, and the S / N of each terminal is controlled to match the target S / N even if there is some nonlinearity in the transmission system.
[0059]
FIG. 8 shows a fourth embodiment of the terminal device. In this embodiment, the S / N measurement device 316 in the first embodiment described in FIG. 3 and the S / N measurement device 326 in the third embodiment described in FIG. 6 are used in combination. That is, S / N information of the pilot signal is obtained from the S / N measuring device 316, and S / N information of the received signal is obtained from the S / N measuring device 326. These two types of S / N information are mixed with transmission data by a mixer 327 and transmitted via an encoding circuit 318, a multiplier 320, a high frequency circuit 321, a circulator 302, and an antenna 301.
[0060]
FIG. 9 shows the configuration of the transmission power control apparatus 106 in the base station when the terminal apparatus has the configuration of the fourth embodiment. In the base station, each modulation / demodulation device 105-i receives two types of power control signals sent from the terminal device, that is, S / N (S / N-ip) of the pilot signal and S / N (S of the received signal). / N-id) and output.
[0061]
Of these, SN-ip (i = 1 to N−1), which is the S / N of the pilot signal, is the circuit shown in FIG. 5 composed of circuit elements 401-i, 402-i, 403, 404, 405-i The first weight value of the transmission power for each terminal is generated with the same circuit configuration as in FIG. On the other hand, the SN-id (i = 1 to N−1) that is the S / N of the received signal is the same as that of the circuit shown in FIG. A second weight value of transmission power for each terminal is generated with a circuit configuration. By causing the second weight value to act on the first weight value as a correction value, a transmission power instruction signal PW-i (i = 1 to N−1) for each terminal is obtained. Here, the time constant of the low-pass filter 601-i is set to a value sufficiently larger than the time constant of the low-pass filter 401-i.
[0062]
According to each of the above-described embodiments, when the position of the terminal device is close to the base station and the reception state of the signal from the base station is very good, there is a possibility that the transmission power for this terminal becomes very small. In this case, a lower limit value may be set for the transmission power for the terminal, and control may be performed so that the transmission power does not drop below a predetermined value.
[0063]
【The invention's effect】
According to the present invention, since the S / N can be quickly measured in each terminal device, this is transmitted as a power control signal to the base station, and the base station transmits a signal addressed to each terminal based on the power control signal. By controlling the transmission power, the S / N at each terminal can be made substantially equal. As a result, the total transmission power of signals addressed to the terminal from the base station in each cell can be suppressed to the minimum necessary, and the power of interfering radio waves acting as noise on adjacent cells can be reduced. The number can be increased.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a configuration of a base station apparatus in a communication system according to the present invention.
FIG. 2 is a diagram illustrating details of the modem 105-i of the base station device.
FIG. 3 is a block diagram showing a first embodiment of a terminal device applied to the communication system of the present invention.
FIG. 4 is a block diagram showing a second embodiment of a terminal device applied to the communication system of the present invention.
FIG. 5 is a diagram illustrating a first embodiment of a transmission power control apparatus of a base station apparatus.
FIG. 6 is a block diagram showing a third embodiment of a terminal device applied to the communication system of the present invention.
FIG. 7 is a diagram illustrating a second embodiment of the transmission power control apparatus of the base station apparatus.
FIG. 8 is a block diagram showing a fourth embodiment of a terminal device applied to the communication system of the present invention.
FIG. 9 is a diagram illustrating a third embodiment of the transmission power control apparatus of the base station apparatus.
FIG. 10 is a diagram showing an overall configuration of a mobile communication system according to the present invention.
FIG. 11 is a diagram showing an example of orthogonal codes used for spectrum spreading.
FIG. 12 is a diagram showing a configuration of a base station apparatus in a conventional technique.
FIG. 13 is a diagram illustrating an example of a configuration of a modem of a base station device according to a conventional technique.
FIG. 14 is a diagram illustrating an example of a configuration of a terminal device according to a conventional technique.
FIG. 15 is a diagram for explaining the relationship between signal components from a base station in a cell and interference components from other cells in a conventional communication system;
FIG. 16 is a view for explaining the relationship between signal components from base stations in a cell and interference components from other cells in the communication system of the present invention;
[Explanation of symbols]
104: Pilot signal generator, 105: Modulator / demodulator,
106: Transmission power control device, 102, 306: Orthogonal code generation device,
201, 318: Encoder, 202: Multiplier that performs first spreading,
203: Multiplier that performs second spreading, 204: Variable gain amplifier for adjusting transmission power,
205: Multiplier that performs despreading, 207, 308, 311, 314: Accumulator, 208, 309: Decoder, 304: Multiplier that performs first-order despreading,
307, 310, 313: multipliers for performing second order despreading,
328: absolute value calculator, 312, 315, 325: square calculator
320: Multiplier for code spreading, 316, 326, 329: S / N measuring device, 330: Comparator, 317, 327: Mixer,
401, 601: low-pass filter, 402, 404: reciprocal calculator,
603: Adder, 604: Integrator.

Claims

In a base station transmission power control method in a spread spectrum communication system that performs communication by a spread spectrum method between a base station and a plurality of terminal devices,
Transmitting a first signal spread using a specific spreading code from the base station,
Power control information based on the received power of the first signal in the terminal device is received from the terminal device to the base station,
A transmission power control method for setting a transmission power of a second signal that is spread using a spreading code assigned to the terminal apparatus and transmitted from the base station to the terminal apparatus to a transmission power according to the power control information .

In claim 1,
The base station lowers the transmission power of the second signal for a terminal device with high reception power, and increases the transmission power of the second signal for a terminal device with low reception power. A transmission power control method for transmitting the second signal.

In claim 1,
The spreading code and the spreading code are selected from a plurality of different code groups,
The transmission power control method in which the first signal and the second signal are transmitted in the same frequency band at the same time.

The transmission power control method according to claim 1, wherein the first signal is transmitted with a constant transmission power.

In a base station transmission power control method in a spread spectrum communication system that performs communication by a spread spectrum method between a base station and a plurality of terminal devices,
From the base station, a first signal spread using a specific spreading code is transmitted,
Power control information based on the S / N ratio of the first signal in the terminal device is received from the terminal device to the base station,
A transmission power control method for transmitting, from the base station, a second signal spread using a spreading code assigned to the terminal device, with transmission power corresponding to the power control information.

In claim 5,
The base station lowers the transmission power of the second signal for the terminal device with a high S / N and increases the transmission power of the second signal for the terminal device with a low S / N. Transmission power control method.

The transmission power control method according to claim 5, wherein
The spreading code and the spreading code are selected from a plurality of different code groups,
The transmission power control method in which the first signal and the second signal are transmitted in the same frequency band at the same time.

The transmission power control method according to claim 5, wherein
The transmission power control method in which the first signal is transmitted with a constant transmission power.

In a mobile terminal device that performs spread spectrum communication with a base station,
A first high-frequency circuit that converts a transmitted signal in a transmission frequency band into a second-order received spectrum spread signal in a baseband;
A first demodulator that despreads the second received spread spectrum signal using a spread signal PN assigned to a base station and converts it into a first received spread spectrum signal;
A second demodulator that despreads the first received spread spectrum signal using a specific spreading code to extract a first received signal;
A third demodulator for despreading the first received spread spectrum signal using an assigned spreading code to extract a second received signal;
A decoder for decoding the second received signal and converting it into received data;
A power control information generating circuit for generating power control information based on the received power of the first received signal;
A modulator that spreads the power control information using the spreading code PN and converts it into a baseband transmit spectrum spread signal;
A second high frequency circuit for converting the transmission spread spectrum signal into a transmission frequency band signal for transmission;
A mobile terminal device comprising:

The mobile terminal device according to claim 9 , wherein
The mobile terminal apparatus, wherein the spreading code and the spreading code are selected from orthogonal code groups orthogonal to each other.

In a mobile terminal device that performs spread spectrum communication with a base station,
A receiving circuit that receives the first signal spread from the base station and spread using a specific spreading code and the second signal spread using the spread signal assigned to the mobile terminal device; ,
A power control information generating circuit for generating power control information based on the received power of the first signal;
A decoder for converting the second signal into received data;
A transmission circuit for transmitting the power control information to the base station;
A mobile terminal device comprising:

The mobile terminal device according to claim 11 , wherein
The reception circuit despreads the signal transmitted from the base station using the spreading code and extracts the first signal, and the signal transmitted from the base station. A mobile terminal apparatus comprising: a second demodulator that performs despreading using the spreading code and extracts a second signal.

The mobile terminal device according to claim 11 , wherein
The spreading code and the spreading code are selected from a plurality of different code groups,
The first signal and the second signal are transmitted in the same frequency band,
The mobile terminal apparatus, wherein the first signal is transmitted by the base station with a constant transmission power.

In a base station that performs communication using a spread spectrum method with a mobile terminal device,
A first modulator that spreads the first transmission signal using a base station-specific spreading code PN and a specific spreading code to convert the first transmission signal into a first transmission spectrum spread signal;
A second modulator that spreads a second transmission signal using the spreading code PN and a spreading code assigned to the mobile terminal device to convert the second transmission signal into a second transmission spectrum spread signal;
A first high-frequency circuit that superimposes the first transmission spread spectrum signal and the second transmission spread spectrum signal and converts the signal into a transmission frequency band signal for transmission;
A second high frequency circuit for converting the transmitted transmission frequency band signal into a baseband received spread spectrum signal;
A demodulator that despreads the received spread spectrum signal using a spread signal PN assigned to a base station to extract the received signal;
A decoder for converting the received signal into received data and power control information generated based on the received power of the first transmission signal in the mobile terminal device;
The first modulator amplifies the first transmission spread spectrum signal with a predetermined gain, and the second modulator amplifies the second transmission spread spectrum signal with a gain according to the power control information. A base station characterized by that.

The base station according to claim 14 ,
The mobile terminal apparatus, wherein the spreading code and the spreading code are selected from orthogonal code groups orthogonal to each other.

In a base station that performs communication using a spread spectrum method with a mobile terminal device,
A transmission circuit for transmitting a first transmission signal spread using a specific spread signal and a second transmission signal spread using a spread signal assigned to the mobile terminal device;
A receiving circuit for receiving power control information generated based on the received power of the first transmission signal in the mobile terminal device;
The transmission circuit, the base station and transmits over the SL second transmission signal at a transmission power corresponding to the power control information.

The base station according to claim 16 , wherein
The spreading code and the spreading code are selected from a plurality of different code groups,
The transmission circuit transmits the first transmission signal and the second transmission signal in the same frequency band,
The transmission circuit transmits lower transmission power to a mobile terminal device having a large reception power of the first transmission signal and higher transmission to a mobile terminal device having a low reception power of the second transmission signal. The base station transmitting the second transmission signal by power.

In a transmission power control method in a spread spectrum communication system that performs spread spectrum communication between a base station and a plurality of terminal devices,
Receiving a first signal transmitted from the base station and spread using a specific spreading code and a second signal spread using a spread signal assigned to the mobile terminal device;
Generating power control information based on the received power of the first signal;
Converting the second signal into received data;
A transmission power control method characterized by transmitting the power control information to the base station.

The transmission power control method according to claim 18 , wherein
The spreading code and the spreading code are selected from a plurality of different code groups,
The first signal and the second signal are transmitted in the same frequency band,
The transmission power control method, wherein the first signal is transmitted from the base station with a constant transmission power.

In a transmission power control method in a spread spectrum communication system that performs spread spectrum communication between a base station and a plurality of mobile terminal devices,
A first diffused using a specific spreading signals, spread with a spread signal allocated to the mobile terminal device, transmission power sends a second transmission signal of the variable,
Receiving power control information generated based on the received power of the first transmission signal in the mobile terminal device;
A transmission power control method, comprising: controlling transmission power of the second transmission signal in accordance with the power control information.

The transmission power control method according to claim 20 ,
The spreading code and the spreading code are selected from a plurality of different code groups,
The transmission circuit transmits the first transmission signal and the second transmission signal in the same frequency band,
Transmitting the first transmission signal and the second transmission signal in the same frequency band;
The second signal is transmitted with a lower transmission power for the mobile terminal apparatus with a large reception power and with a higher transmission power for the mobile terminal apparatus with a low reception power. Transmission power control method.