JP4377543B2 - Interference signal canceller - Google Patents

Description

【００２９】
ここで、信号ｒ１は或る時刻にシフトレジスタに入力される信号であり、いずれの記憶素子Ｓ1〜Ｓn-1も通過せずに乗算器Ｊ1へ出力される信号である。また、信号ｒ２〜ｒｎはそれぞれ当該時刻に各記憶素子Ｓ1〜Ｓn-1から出力される信号であり、それぞれ各乗算器Ｊ2〜Ｊnへ出力される信号である。
【００３０】
各乗算器Ｊ1〜Ｊnにはそれぞれ上記した各信号ｒ１〜ｒｎが入力されるとともに、後述するフィルタタップ係数演算制御部２４からの各タップ係数制御信号ｈ１〜ｈｎが入力され、各乗算器Ｊ1〜Ｊnでは入力した２つの信号を乗算して（すなわち、各信号ｒ１〜ｒｎを各タップ係数制御信号ｈ１〜ｈｎで重み付けして）当該乗算結果を加算器Ｋ1〜Ｋn-1へ出力する。
ここで、フィルタタップ係数演算制御部２４から出力されるフィルタタップ係数系列ｈ（ｔ）は式２で示される。なお、ｈ（ｔ）はベクトルである。
【００３１】
【数２】

【００３２】
また、各乗算器Ｊ1〜Ｊnから出力される乗算結果は加算器Ｋ1〜Ｋn-1により総和され、当該総和結果が適応フィルタ２２から出力される。ここで、後述するように本例のフィルタタップ係数系列ｈ（ｔ）は、当該総和結果が受信信号中に含まれる干渉信号成分と同じ信号となるように、フィルタタップ係数演算制御部２４により逐次更新される。
具体的に、適応フィルタ２２から出力される信号（すなわち、上記した総和結果）ＦＭ（ｔ）は式３で示される。ここで、式３中のΣは和を表している。
【００３３】
【数３】

【００３４】
なお、本明細書で用いる記号“＊”は、当該記号の前後に配置される記号同士の乗算を示し、特に、ベクトル同士の乗算は、２つのベクトルの内積値を算出する演算を表している。
【００３５】
上記のようにして適応フィルタ２２では、フィルタタップ係数演算制御部２４からのタップ係数制御信号に応じて、入力した遅延信号ｒ（ｔ−τ）から上記した干渉信号成分を抽出し、干渉波抽出信号ＦＭ（ｔ）として減算器２３へ出力する。
【００３６】
減算器２３は遅延していない入力信号ｒ（ｔ）と適応フィルタ２２からの出力信号ＦＭ（ｔ）とを入力し、当該入力信号ｒ（ｔ）から当該出力信号ＦＭ（ｔ）を減算して当該減算結果ｅ（ｔ）を出力する機能を有している。
ここで、上記した減算結果ｅ（ｔ）は本例の干渉信号除去装置から出力される信号であり、式４で示される。
【００３７】
【数４】

【００３８】
本例では、後述するフィルタタップ係数演算制御部２４からのタップ係数制御信号が逐次更新されることで、上記した干渉波抽出信号ＦＭ（ｔ）が受信信号中の干渉信号と同じ信号となるため、上記した減算結果ｅ（ｔ）は受信信号から当該干渉信号を除去した信号、すなわちＣＤＭＡ方式による拡散信号（理想的には、当該拡散信号のみ）となる。
【００３９】
フィルタタップ係数演算制御部２４には遅延素子２１から出力される信号ｒ（ｔ−τ）と減算器２３から出力される信号ｅ（ｔ）とが入力され、フィルタタップ係数演算制御部２４はこれらの信号を用いて、適応フィルタ２２から出力される信号ＦＭ（ｔ）が干渉信号成分と同じ信号になるようなタップ係数制御信号を演算し、演算したタップ係数制御信号を適応フィルタ２２へ出力する機能を有している。
【００４０】
本例のフィルタタップ係数演算制御部２４では例えばＬＭＳ（Least Mean Square）やＲＬＳ（Recursive Least Square）等のアルゴリズムを用いて上記したタップ係数制御信号を演算することができ、本例では一例として、ＬＭＳアルゴリズムを用いた場合を説明し、また、ＲＬＳアルゴリズムを用いた場合についても後述する。
まず、ＬＭＳの一般式を説明する。
ＬＭＳの更新式は一般に式５で示される。
【００４１】
【数５】

【００４２】
ここで、ｈ（ｔ）は時刻ｔにおけるフィルタタップ係数系列であり、μは収束の時間や精度に関係する係数であるステップサイズパラメータであり、ｅ（ｔ）は時刻ｔにおけるエラー信号であり、ｕ（ｔ）は時刻ｔにおける入力信号系列である。
また、上記したエラー信号ｅ（ｔ）は一般には式６で示される。
【００４３】
【数６】

【００４４】
ここで、ｄ（ｔ）は通常ユニークワードやトレーニング信号と呼ばれるものであり、送信側と受信側とで予め定められた既知の信号が用いられる。上記式５や式６を用いた演算アルゴリズムでは、フィルタタップ係数系列を逐次更新することで、エラー信号ｅ（ｔ）を０に収束させることができる。
【００４５】
次に、上記のＬＭＳアルゴリズムを本例に当てはめた場合を説明する。
上記した式５を本例の場合に当てはめると、ｈ（ｔ）はフィルタタップ係数演算制御部２４から適応フィルタ２２へ出力されるフィルタタップ係数系列であり、ｕ（ｔ）は遅延素子２１からフィルタタップ係数演算制御部２４へ出力される信号系列（上記式１に示したもの）である。
また、本例では、上記したエラー信号ｅ（ｔ）として減算器２３から出力される信号（上記式４に示したもの）を用いており、これが本例の干渉除去回路における特徴点となっており、通常のＬＭＳアルゴリズムとは異なる処理となっている。
【００４６】
まず、仮に、遅延素子２１が備えられていない場合を考えると、上記した演算アルゴリズムはエラー信号ｅ（ｔ）を０に近づけるため、減算器２３から出力される信号ｅ（ｔ）は０に収束し、受信信号中の干渉信号ばかりでなくＣＤＭＡ方式による拡散信号までをも除去するフィルタタップ係数系列ｈ（ｔ）が生成されてしまう。
【００４７】
一方、本例では上記した遅延素子２１が備えられているため、遅延素子２１からフィルタタップ係数演算制御部２４に入力される信号ｒ（ｔ−τ）と減算器２３を介してフィルタタップ係数演算制御部２４に入力される信号ｅ（ｔ）との間には遅延時間τの時間差がある。
【００４８】
ここで、例えばＣＤＭＡ方式による拡散信号ｒ（ｔ）と当該信号に比べて１チップ時間以上遅延した拡散信号ｒ（ｔ−τ）とは無相関の信号となるため、上記した演算アルゴリズムではエラー信号ｅ（ｔ）を０に収束させようとする場合に、ｕ（ｔ）の拡散信号成分はｒ（ｔ）と無相関になっていることから誤差ｅ（ｔ）となって残る。つまり、上記式４において、入力信号系列ｕ（ｔ）を加え続けると拡散信号成分の影響は理論的に０となるため、当該拡散信号成分が除去されずに誤差ｅ（ｔ）となって残ることになる。一方、チップデータに比べて時間的に緩やかに変動する干渉信号成分は例えば数チップ時間程度の遅延があっても相関を有するため、当該干渉信号成分のみを受信信号から除去することができるフィルタタップ係数系列ｈ（ｔ）が生成される。
【００４９】
すなわち、本例に適用した上記の演算アルゴリズムでは、ｕ（ｔ）とｅ（ｔ）とで相関のある成分（すなわち、干渉信号成分）を適応フィルタ２２からの出力信号中に残す一方、相関のない成分（すなわち、拡散信号成分）については適応フィルタ２２からの出力信号中に残さないようなフィルタタップ係数系列ｈ（ｔ）を生成することができる。
このような演算アルゴリズムにより、本例の適応フィルタ２２では受信信号中の干渉信号成分のみを抽出して減算器２３へ出力することができ、減算器２３では受信信号から干渉信号成分のみを除去した信号（すなわち、ＣＤＭＡ方式による拡散信号）を出力することができる。
【００５０】
以上のように、上記図６に示した干渉信号除去装置では、拡散信号の特性を利用することで、ＣＤＭＡ方式により拡散変調された広帯域の拡散信号と狭帯域の干渉信号とを含む受信信号から当該干渉信号を適応的に除去することができ、これにより、受信品質の劣化を防ぎ、受信品質を向上させることができる。
【００５１】
なお、上記図６では、減算器２３から出力される信号を遅延させない構成を示したが、例えば図８に示すように減算器３３に入力される受信信号を遅延素子３１により遅延させる一方、適応フィルタ３２やフィルタタップ係数演算制御部３４に入力される受信信号を遅延させないような構成によっても上記と同様な効果を得ることができる。ここで、図８に示した構成は、遅延素子３１が減算器３３側に備えられているといった点を除いては、上記図６に示した構成とほぼ同様である。
【００５２】
また、上記したＬＭＳアルゴリズム以外のアルゴリズムを用いて上記と同様な干渉除去の効果を得ることもでき、一例として、上記図６に示した構成においてＲＬＳアルゴリズムを用いた場合の更新式の具体例を示しておく。なお、以下では、説明の便宜上から、上記したｕ（ｔ）やｈ（ｔ）やｅ（ｔ）やｄ（ｔ）やｒ（ｔ）に相当するものについては同じ符号を用いて示す。
【００５３】
例えば、上記式１で示したｕ（ｔ）と同様な成分から成るｎ行１列のベクトルを入力系列ｕ（ｔ）とし、上記式２で示したｈ（ｔ）と同様にｎ個のフィルタタップ係数から成るｎ行１列のベクトルをフィルタタップ係数系列ｈ（ｔ）とする。
また、上記式６に示したエラー信号ｅ（ｔ）に相当するものとして、ＲＬＳにおけるエラー信号ｅ（ｔ）は式７で示される。なお、ｕ^T（ｔ）はｕ（ｔ）を転置したものを示す。
【００５４】
【数７】

【００５５】
ここで、本例では、ｄ（ｔ）としては例えば減算器２３に入力される受信信号ｒ（ｔ）が用いられ、また、上記式７中のｕ^T（ｔ）＊ｈ（ｔ）が適応フィルタ２２から出力される干渉波抽出信号に相当する。すなわち、上記したＬＭＳアルゴリズムを用いた場合と同様に、上記式７に示したエラー信号ｅ（ｔ）としては減算器２３から出力される信号が用いられ、これが本例の特徴点となっている。なお、上記したＬＭＳアルゴリズムを用いた場合と同様に、遅延素子２１が備えられていない場合にはエラー信号ｅ（ｔ）は０に収束する。
【００５６】
また、例えばｎ行ｎ列の行列である係数誤差相関行列Ｐ（ｔ）及びｎ行１列のベクトルであるゲインベクトルｋ（ｔ）を用いて、ＲＬＳの更新式は式８〜式１０で示される。
【００５７】
【数８】

【００５８】
【数９】

【００５９】
【数１０】

【００６０】
また、上記したフィルタタップ係数系列ｈ（ｔ）の初期値ｈ（０）としては例えば式１１に示すようにゼロベクトルが用いられ、上記した係数誤差相関行列Ｐ（ｔ）の初期値Ｐ（０）としては例えば式１２に示すように行数と列数とが一致する対角要素が全て正の実数ｃであってそれ以外の要素が０である行列が用いられる。なお、ｈ^T（０）はｈ（０）を転置したものを示す。また、式１２中のＩは行数と列数とが一致する対角要素が全て１であってそれ以外の要素が０であるｎ行ｎ列の行列を示す。
【００６１】
【数１１】

【００６２】
【数１２】

【００６３】
以上に示したＲＬＳの更新式に従ってフィルタタップ係数演算制御部２４がフィルタタップ係数系列ｈ（ｔ）を順次更新することで、例えば上記したＬＭＳアルゴリズムを用いた場合と同様に、適応フィルタ２２から出力される信号を次第に実際の干渉信号成分に近づけることができ、これにより、ＣＤＭＡ方式により拡散変調された広帯域の拡散信号と狭帯域の干渉信号とを含む受信信号から当該干渉信号を除去することができる。
【００６４】
次に、図９には、ＣＤＭＡ信号（希望信号）とＦＭ信号（干渉信号）とを含む受信信号のＩ成分及びＱ成分を入力して、当該Ｉ成分ｒＩ（ｔ）及び当該Ｑ成分ｒＱ（ｔ）から当該ＦＭ信号を除去する干渉信号除去装置の一例を示してある。この干渉信号除去装置では、ＣＤＭＡ方式により拡散変調された拡散信号と干渉信号とを含む受信信号のＩ成分及びＱ成分から当該干渉信号を除去するに際して、時間差手段４１ａ、４１ｂがＩ成分を分配して得られる２つの信号間及びＱ成分を分配して得られる２つの信号間に拡散符号の１チップ分以上の時間差を与え、抽出手段４２ａ、４２ｂ、４３ａ、４３ｂが時間差を与えた一方のＩ成分及びＱ成分から成る受信信号と他方のＩ成分及びＱ成分から成る受信信号との間で相関のある信号成分を干渉信号成分として当該干渉信号成分のＩ成分及びＱ成分を抽出し、除去手段４４ａ、４４ｂ、４５ａ、４５ｂが抽出した干渉信号成分のＩ成分を受信信号のＩ成分から除去するとともに抽出した干渉信号成分のＱ成分を受信信号のＱ成分から除去する。
【００６５】
具体的には、同図に示した干渉信号除去装置には、受信信号から直交検波されたＩ相の信号（Ｉ成分）を遅延させる遅延素子４１ａと、受信信号から直交検波されたＱ相の信号（Ｑ成分）を遅延させる遅延素子４１ｂと、後述するフィルタタップ係数演算制御部４６からのタップ係数制御信号に従って遅延したＩ成分やＱ成分から干渉信号成分を抽出する４つの適応フィルタ４２ａ、４２ｂ、４３ａ、４３ｂと、干渉信号成分のＩ成分を加算する加算器４４ａと、干渉信号成分のＱ成分を加算する加算器４４ｂと、受信信号のＩ成分から干渉信号成分のＩ成分を除去する減算器４５ａと、受信信号のＱ成分から干渉信号成分のＱ成分を除去する減算器４５ｂと、減算器４５ａ、４５ｂからの出力信号と遅延した受信信号のＩ成分及びＱ成分とに基づくタップ係数制御信号を適応フィルタ４２ａ、４２ｂ、４３ａ、４３ｂへ出力するフィルタタップ係数演算制御部４６とが備えられている。
【００６６】
同図に示した回路の構成例及び動作例を説明する。
この回路には受信機により受信信号から直交検波されたＩ成分ｒＩ（ｔ）及びＱ成分ｒＱ（ｔ）が入力され、この入力信号ｒＩ（ｔ）、ｒＱ（ｔ）には、例えばＣＤＭＡ方式により拡散変調された広帯域の拡散信号と狭帯域を用いた通信方式による干渉信号（例えばＦＭ変調信号）が含まれている。ここで、上記図６を用いて説明した場合と同様に、ｔは時刻を示しており、本例では１サンプル時間を最小単位とする整数の離散値であるとする。
【００６７】
上記したＩ成分ｒＩ（ｔ）は、まず２つの信号に分配されて、一方の信号が遅延素子４１ａに入力される一方、他方の信号が減算器４５ａに入力される。同様に、上記したＱ成分ｒＱ（ｔ）は、まず２つの信号に分配されて、一方の信号が遅延素子４１ｂに入力される一方、他方の信号が減算器４５ｂに入力される。
【００６８】
各遅延素子４１ａ、４１ｂは、例えば上記図６に示した遅延素子２１と同様に、入力した信号を拡散符号の１チップ分の時間幅以上遅延させて出力する機能を有している。なお、２つの遅延素子４１ａ、４１ｂでは同じ遅延時間を与えている。また、上記図６を用いて説明した場合と同様に、具体的には、遅延素子４１ａから出力されるＩ成分の信号はｒＩ（ｔ−τ）と表され、遅延素子４１ｂから出力されるＱ成分の信号はｒＱ（ｔ−τ）と表される。ここで、τは遅延素子４１ａ、４１ｂにより与えられる遅延時間である。
【００６９】
遅延素子４１ａから出力される信号ｒＩ（ｔ−τ）は２つの適応フィルタ４２ａ、４３ａ及びフィルタタップ係数演算制御部４６に入力され、遅延素子４１ｂから出力される信号ｒＱ（ｔ−τ）は２つの適応フィルタ４２ｂ、４３ｂ及びフィルタタップ係数演算制御部４６に入力される。
【００７０】
各適応フィルタ４２ａ、４２ｂ、４３ａ、４３ｂの構成は、例えば上記図７に示したものと同様である。ここで、本例で４つの適応フィルタ４２ａ、４２ｂ、４３ａ、４３ｂを備えているのはＩ相及びＱ相の複素演算を行うためであり、具体的には、受信信号のＩ成分及びＱ成分のそれぞれの中に干渉信号成分のＩ成分とＱ成分との両方が含まれるためである。また、本例では、Ｉ相とＱ相との２種類のフィルタタップ係数系列ｈＩ（ｔ）、ｈＱ（ｔ）が用いられる。なお、ｈＩ（ｔ）及びｈＱ（ｔ）はベクトルである。
【００７１】
具体的に、本例では、適応フィルタ４２ａが入力した受信信号のＩ成分ｒＩ（ｔ−τ）から干渉信号成分のＩ成分を抽出し、適応フィルタ４３ａが入力した受信信号のＩ成分ｒＩ（ｔ−τ）から干渉信号成分のＱ成分を抽出し、適応フィルタ４２ｂが入力した受信信号のＱ成分ｒＱ（ｔ−τ）から干渉信号成分のＱ成分を抽出し、適応フィルタ４３ｂが入力した受信信号のＱ成分ｒＱ（ｔ−τ）から干渉信号成分のＩ成分を抽出することができるようなフィルタタップ係数系列ｈＩ（ｔ）、ｈＱ（ｔ）が後述するフィルタタップ係数演算制御部４６により生成される。
【００７２】
加算器４４ａは２つの適応フィルタ４２ａ、４３ｂから出力される信号を加算して減算器４５ａへ出力する機能を有しており、減算器４５ａへ出力される当該加算結果は受信信号のＩ成分中の干渉信号成分（すなわち、干渉信号成分のＩ成分）ＦＭＩ（ｔ）となる。なお、本例では、加算器４４ａが一方の適応フィルタ４３ｂから出力される信号の正負を反転させて上記した加算を行うこととしたが、このような正負の反転が例えば上記した適応フィルタ４３ｂや後述するフィルタタップ係数演算制御部４６により行われる場合には、加算器４２ａでは上記のような正負の反転は行われなくてよい。
【００７３】
加算器４４ｂは２つの適応フィルタ４２ｂ、４３ａから出力される信号を加算して減算器４５ｂへ出力する機能を有しており、減算器４５ｂへ出力される当該加算結果は受信信号のＱ成分中の干渉信号成分（すなわち、干渉信号成分のＱ成分）ＦＭＱ（ｔ）となる。
【００７４】
ここで、上記した加算器４４ａから出力される干渉信号成分のＩ成分ＦＭＩ（ｔ）は式１３で示され、上記した加算器４４ｂから出力される干渉信号成分のＱ成分ＦＭＱ（ｔ）は式１４で示される。なお、式１３及び式１４中のｕＩ（ｔ）及びｕＱ（ｔ）はベクトルであり、これらｕＩ（ｔ）及びｕＱ（ｔ）は例えば上記図６を用いた説明中において式１で示したｕ（ｔ）のＩ成分及びＱ成分に相当している。
【００７５】
【数１３】

【００７６】
【数１４】

【００７７】
減算器４５ａは遅延していないＩ成分の入力信号ｒＩ（ｔ）と加算器４５ａからの出力信号ＦＭＩ（ｔ）とを入力し、当該入力信号ｒＩ（ｔ）から当該出力信号ＦＭＩ（ｔ）を減算して当該減算結果ｅＩ（ｔ）を出力する機能を有している。
同様に、減算器４５ｂは遅延していないＱ成分の入力信号ｒＱ（ｔ）と加算器４４ｂからの出力信号ＦＭＱ（ｔ）とを入力し、当該入力信号ｒＱ（ｔ）から当該出力信号ＦＭＱ（ｔ）を減算して当該減算結果ｅＱ（ｔ）を出力する機能を有している。
ここで、上記した減算結果ｅＩ（ｔ）、ｅＱ（ｔ）は本例の干渉信号除去装置から出力される信号である。
【００７８】
本例では、後述するフィルタタップ係数演算制御部４６からのタップ係数制御信号が逐次更新されることで、上記したＩ成分及びＱ成分の干渉波抽出信号ＦＭＩ（ｔ）、ＦＭＱ（ｔ）がそれぞれ受信信号のＩ成分及びＱ成分中の干渉信号と同じ信号となるため、上記した減算結果ｅＩ（ｔ）、ｅＱ（ｔ）はそれぞれ受信信号のＩ成分及びＱ成分から当該干渉信号を除去した信号、すなわちＣＤＭＡ方式による拡散信号（理想的には、当該拡散信号のみ）となる。
【００７９】
フィルタタップ係数演算制御部４６には２つの遅延素子４１ａ、４１ｂから出力される信号ｒＩ（ｔ−τ）、ｒＱ（ｔ−τ）と２つの減算器４５ａ、４５ｂから出力される信号ｅＩ（ｔ）、ｅＱ（ｔ）とが入力され、フィルタタップ係数演算制御部４６はこれらの信号を用いて、各適応フィルタ４２ａ、４２ｂ、４３ａ、４３ｂから出力される信号が上記したような干渉信号成分となるようなタップ係数制御信号を演算してそれぞれの適応フィルタ４２ａ、４２ｂ、４３ａ、４３ｂへ出力する機能を有している。なお、本例では、例えば２つの適応フィルタ４２ａ、４２ｂへ同じタップ係数制御信号が出力される一方、残りの２つの適応フィルタ４３ａ、４３ｂへ同じタップ係数制御信号が出力されることで、上記式１３や上記式１４で示した干渉信号成分ＦＭＩ（ｔ）、ＦＭＱ（ｔ）が生成されるように設定してある。
【００８０】
本例のフィルタタップ係数演算制御部４６では、例えば上記図６を用いた説明において示したＬＭＳの複素演算用のアルゴリズムを用いてタップ係数制御信号を演算している。なお、このアルゴリズムにおけるＬＭＳの更新式は式１５及び式１６で示される。
【００８１】
【数１５】

【００８２】
【数１６】

【００８３】
ここで、ｈＩ（ｔ）やｈＱ（ｔ）は時刻ｔにおけるフィルタタップ係数系列であり、μは収束の時間や精度に関係する係数であるステップサイズパラメータであり、ｕＩ（ｔ）やｕＱ（ｔ）は上記のようにそれぞれ適応フィルタ４２ａ、４３ａのシフトレジスタ内や適応フィルタ４２ｂ、４３ｂのシフトレジスタ内における入力信号系列である。また、上記図６を用いて説明した場合と同様に、ｅＩ（ｔ）やｅＱ（ｔ）としては、それぞれ減算器４５ａや減算器４５ｂから出力される信号を用いている。なお、ｕＩ（ｔ）及びｕＱ（ｔ）は上記したようにベクトルである。
【００８４】
本例では、上記図６を用いて説明した場合と同様に、上記のような演算アルゴリズムによりフィルタタップ係数系列ｈＩ（ｔ）、ｈＱ（ｔ）を順次更新していくことで、拡散信号成分についてはその無相関性により除去されず、且つ、比較的相関性のある干渉信号成分を除去することができるフィルタタップ係数系列ｈＩ（ｔ）、ｈＱ（ｔ）を生成することができる。
また、本例では、フィルタタップ係数系列ｈＩ（ｔ）、ｈＱ（ｔ）を演算するに際してＩ成分及びＱ成分の両方を考慮しているため、干渉除去の精度を更に向上させることができる。
【００８５】
以上のように、上記図９に示した干渉信号除去装置では、拡散信号の特性を利用することで、ＣＤＭＡ方式により拡散変調された拡散信号と干渉信号とを含む受信信号のＩ成分及びＱ成分から当該干渉信号を除去することができ、これにより、受信品質の劣化を防ぎ、受信品質を向上させることができる。
【００８６】
なお、上記図９では、上記図６を用いて説明した場合と同様に、減算器４５ａ、４５ｂから出力される信号を遅延させない構成を示したが、例えば図１０に示すように減算器５５ａ、５５ｂに入力される受信信号を遅延素子５１ａ、５１ｂにより遅延させる一方、適応フィルタ５２ａ、５２ｂ、５３ａ、５３ｂやフィルタタップ係数演算制御部５６に入力される受信信号を遅延させないような構成によっても上記と同様な効果を得ることができる。ここで、図１０に示した構成は、遅延素子５１ａ、５１ｂが減算器５５ａ、５５ｂ側に備えられているといった点を除いては、上記図９に示した構成とほぼ同様であり、以上に示した構成部分と共に加算器５４ａ、５４ｂも備えられている。
【００８７】
また、例えば上記図６を用いて説明した場合と同様に、上記した複素演算用のＬＭＳアルゴリズム以外のアルゴリズムを用いて上記と同様な干渉除去の効果を得ることもでき、一例として、上記図９に示した構成において複素演算用のＲＬＳアルゴリズムを用いた場合について示しておく。なお、以下では、説明の便宜上から、上記したｕＩ（ｔ）及びｕＱ（ｔ）やｈＩ（ｔ）及びｈＱ（ｔ）やｅＩ（ｔ）及びｅＱ（ｔ）やｒＩ（ｔ）及びｒＱ（ｔ）に相当するものについては同じ符号を用いて示す。
【００８８】
複素演算用のＲＬＳアルゴリズムでは、例えば上記式７〜上記式１０で示したｕ（ｔ）やｈ（ｔ）やｅ（ｔ）やｋ（ｔ）やＰ（ｔ）等の全てのパラメータが複素数の要素から構成される。ここで、γ及びωを実数として、虚数部を表す記号としてｊを用いると、任意の複素数要素は（γ＋ｊω）と表される。
そして、複素演算用のＲＬＳアルゴリズムでは、例えば上記した各パラメータの実数部と虚数部とを分離してそれぞれＩ成分のパラメータ及びＱ成分のパラメータとして用いることで、上記図６を用いた説明において示したような逐次更新処理を複素演算において実現する。
【００８９】
なお、具体的に本例の場合には、例えばｕ（ｔ）の実数部をｕＩ（ｔ）とするとともに虚数部をｕＱ（ｔ）とし、ｈ（ｔ）の実数部をｈＩ（ｔ）とするとともに虚数部をｈＱ（ｔ）とし、ｅ（ｔ）の実数部をｅＩ（ｔ）とするとともに虚数部をｅＱ（ｔ）とする等して、受信信号のＩ成分ｒＩ（ｔ）及びＱ成分ｒＱ（ｔ）から干渉信号成分を除去する処理が行われる。
【００９０】
以上に示したように、例えば複素演算用のＲＬＳアルゴリズムを用いた場合においても、上記した複素演算用のＬＭＳアルゴリズムを用いた場合と同様に、ＣＤＭＡ方式により拡散変調された拡散信号と干渉信号とを含む受信信号のＩ成分及びＱ成分から当該干渉信号を除去することができる。
【００９１】
【発明が解決しようとする課題】
ここで、上記従来例で示したような干渉信号除去装置により干渉除去を行った場合の様子を具体的に示す。
図１１には、干渉信号が除去される前における受信信号のスペクトルの一例を示してあり、この受信信号としてはＣＤＭＡ信号に２波のＦＭ信号が干渉したものを示してある。なお、同図中や後述する図１２中や後述する図１３中のグラフの横軸は周波数（ＭＨｚ）を示しており、縦軸は信号のスペクトル強度を示している。
【００９２】
また、図１２には、上記図１１に示した受信信号を例えば上記図６に示したような干渉信号除去装置に入力して、当該干渉信号除去装置により当該受信信号に含まれる干渉信号（ここでは、２波のＦＭ信号）を除去した直後（干渉信号除去処理の操作の開始直後）における（当該干渉信号除去装置からの）出力信号のスペクトルの一例を示してある。図１２に示されるように、干渉信号除去処理の開始直後において干渉信号除去装置から出力される信号では、ＣＤＭＡ信号成分が減衰させられることなく、ＦＭ信号成分のみが減衰させられている。
【００９３】
しかしながら、上記従来例で示したような干渉信号除去装置では、干渉信号除去処理を開始した後にそのまま当該処理を続けていくと、次第に受信信号中のＣＤＭＡ信号成分までも減衰させてしまい、このような減衰が時間の経過と共に進行していってしまうといった不具合があった。
【００９４】
具体的に、図１３には、上記図１２に示した状態から干渉信号除去処理をしばらくの時間継続した場合における（干渉信号除去装置からの）出力信号のスペクトルの一例を示してある。図１３に示されるように、干渉信号除去処理を開始してからしばらくの時間が経過すると、前記出力信号中に残されるべきＣＤＭＡ信号成分が大きく減衰させられてしまうことが生じる。
このように、従来の干渉信号除去装置では、狭帯域干渉信号を適応的に除去する能力を有してはいるものの、希望波であるＣＤＭＡ信号も時間の経過と共に徐々に除去していってしまうといった不具合があった。
【００９５】
ここで、このような不具合が生じる理由としては、干渉信号の周波数の近傍に位置するＣＤＭＡ信号の周波数成分は当該干渉信号と相関があるためであり、つまり、上記したＬＭＳ等の演算アルゴリズムによって、干渉信号の周波数の近くに位置するＣＤＭＡ信号の周波数成分も、当該干渉信号との間で相関のある信号成分として抽出されてしまうためである。従って、ＣＤＭＡ信号の帯域に関して、干渉信号周辺の帯域のＣＤＭＡ信号も当該干渉信号と共に除去されてしまい、この結果として、干渉除去後の受信信号のビット誤り率が劣化してしまうという問題が起こっていた。
【００９６】
また、図１４には、上記従来例で示したような干渉信号除去装置を用いて干渉除去を行った場合における干渉信号除去の特性の一例を示してある。なお、同図では、干渉信号除去特性として受信信号のビット誤り率（ＢＥＲ：Bit Error Ratio）が変化する様子を示してあり、干渉信号除去装置により干渉除去を行わない場合（キャンセルなしの場合）における特性例を（ａ）で示す一方、干渉信号除去装置により干渉除去を行った場合（キャンセル有りの場合）における特性例を（ｂ）で示してある。
【００９７】
また、同図では、広帯域の希望信号としてＣＤＭＡ信号を用いる一方、狭帯域の干渉信号としてＦＳＫ（Frequency Shift Keying）信号を用いた場合を示してあり、干渉信号が１波である場合の例を示してある。また、同図中のグラフの横軸は干渉信号当たりのＤ／Ｕ（（希望の入力信号の電力）／（狭帯域干渉信号の電力））［ｄＢ］を示しており、縦軸は受信機におけるビット誤り率を示している。
【００９８】
同図に示されるように、Ｄ／Ｕが比較的小さい場合（つまり、狭帯域干渉信号の電力が広帯域希望信号の電力と比べて十分に大きい場合）には、干渉信号除去装置により干渉除去を行うことで、ビット誤り率の特性を向上させることができる。一方、Ｄ／Ｕが比較的大きい場合（つまり、狭帯域干渉信号の電力が広帯域希望信号の電力と比べて同程度である場合、或いは、広帯域希望信号の電力と比べて小さい場合）には、干渉信号除去装置により干渉除去を行うことによって、却ってビット誤り率の特性を劣化させてしまうことが生じる。
【００９９】
ここで、このような劣化が生じる理由としては、上記と同様な理由が考えられ、すなわち、受信信号から狭帯域干渉信号の周波数成分を抽出して、当該抽出結果を受信信号から除去する処理において、干渉信号除去装置が干渉信号と同時に広帯域希望信号の周波数成分までも抽出して除去してしまうためであると考えられる。
【０１００】
また、図１５（ａ）及び同図（ｂ）には、上記従来例で示したような干渉信号除去装置を用いて、広帯域信号と狭帯域干渉信号とを含む受信信号から当該干渉信号を除去する場合の様子の一例を示してある。
具体的に、同図（ａ）には、広帯域信号の電力と比べて或る狭帯域干渉信号の電力が十分に大きい場合（例えば図中の▲１▼や▲３▼の干渉信号）の例を示してあり、この場合には、上述のように、干渉除去を行うことで受信品質を改善することができる。
【０１０１】
なお、同図（ａ）には、広帯域信号に干渉する３つの信号▲１▼、▲２▼、▲３▼を示してあり、また、干渉除去前の受信信号の様子を左側のグラフに示す一方、干渉除去後の受信信号の様子を右側のグラフに示してある。また、これらのグラフの横軸は周波数を示しており、縦軸はスペクトル強度を示している。
【０１０２】
一方、同図（ｂ）には、広帯域信号の電力と比べて各狭帯域干渉信号の電力が（ほぼ）等しい場合（或いは、小さい場合についても同様）の例を示してあり、この場合には、上述のように、狭帯域干渉信号と共に広帯域信号の周波数成分までもが抽出されて除去されてしまうことから、干渉信号除去装置から出力される信号が（当該干渉信号除去装置の）後段の回路で復調処理される際において、受信品質の劣化が無視できないくらいに大きくなってしまう。
【０１０３】
このため、同図（ｂ）に示したような場合には、例えば干渉信号除去装置により干渉除去を行わない方が、ＣＤＭＡ信号の特質でもある干渉信号の抑圧効果によって、受信品質がよくなるとも言える。
なお、同図（ｂ）には、広帯域信号に干渉する３つの信号▲４▼、▲５▼、▲６▼を示してあり、また、干渉除去前の受信信号の様子を左側のグラフに示す一方、干渉除去後の受信信号の様子を右側のグラフに示してある。また、これらのグラフの横軸は周波数を示しており、縦軸はスペクトル強度を示している。
【０１０４】
また、例えば上記図６に示したような干渉信号除去装置では、上記式５に示したような適応アルゴリズムを用いてフィルタタップ係数系列ｈ（ｔ）を更新することから、上記式５に示した次回のフィルタタップ係数系列ｈ（ｔ＋１）の演算の度毎に常に前回までの演算結果（ｈ（ｔ））が蓄積される。このため、このような干渉信号除去装置では、例えば帯域制限フィルタによる符号間干渉の影響等により、広帯域信号の信号成分までも抽出されて当該広帯域信号の一部も除去されてしまう可能性があり、このような場合においても、上述したのと同様に、受信機での復調処理において受信品質の劣化が無視できないくらいに大きくなってしまうことが生じ得る。
【０１０５】
以上のように、上記従来例で示したような干渉信号除去装置では、例えば上記図１４に示されるような干渉信号除去特性を示し、つまり、広帯域信号の電力と比べて狭帯域信号の電力が小さくなる場合には干渉除去を行わない場合より受信品質の特性が劣化してしまうことがあるといった不具合があった。
【０１０６】
具体的に、現状考えられている通信方式では、例えばＣＤＭＡ方式とＴＤＭＡ方式とを共用するような状況やＣＤＭＡ方式とＦＤＭＡ方式とを共用するような状況などにおいて、上記従来例で示したような干渉信号除去装置を組み込んだ受信機を用いた場合に、受信信号に干渉信号が存在しないようなときには、却って受信品質が低下してしまうことが生じ、また、例えば干渉信号の除去を行わない場合と比べて、基地局装置により収容可能な移動局装置の数（ユーザ数）が減少してしまうことや通話エリアが小さくなってしまうことが生じるといった問題が予想される。
【０１０７】
本発明は、このような従来の課題を解決するために為されたもので、広帯域の希望信号と狭帯域の干渉信号とを含んだ入力信号から当該干渉信号を除去するに際して、希望信号までも除去してしまうことを抑制する干渉信号除去装置を提供することを目的とする。
【０１０８】
【課題を解決するための手段】
上記目的を達成するため、本発明に係る干渉信号除去装置では、次のようにして、広帯域の希望信号と狭帯域の干渉信号とを含んだ入力信号から当該干渉信号を除去する。
すなわち、入力信号に基づいて当該入力信号に含まれる干渉信号をその抽出量を抑制（つまり、例えば従来例で示した場合と比べて小さく）して抽出し、抽出した干渉信号を当該入力信号から除去する。
【０１０９】
従って、入力信号に基づいて当該入力信号から抽出される干渉信号の抽出量が抑制されるため、広帯域の希望信号と狭帯域の干渉信号とを含んだ入力信号から希望信号（例えば干渉信号の周波数帯域内にある希望信号成分や、干渉信号の周波数帯域に隣接する帯域にある希望信号成分）までも除去してしまうことを抑制することができる。
【０１１０】
一例として、広帯域の希望信号としてＣＤＭＡ信号が用いられた場合には、受信機により受信した信号（ＣＤＭＡ信号と狭帯域干渉信号とを含んだ信号）から干渉信号を除去するに際して、当該干渉除去の能力を制御することにより、ＣＤＭＡ信号成分までも除去してしまうことを抑制することができ、これにより、例えば従来と比べて、干渉除去後における受信信号のビット誤り率の特性を向上させることができる。
【０１１１】
つまり、本来、ＣＤＭＡ方式のようなスペクトル拡散方式による（拡散された）信号は拡散利得による耐干渉能力が高いため、狭帯域干渉信号を必要以上に除去しなくとも、拡散された希望波（ＣＤＭＡ信号等）の信号電力と同程度のレベルまで狭帯域干渉信号の電力を減衰させることができればよい。このため、ＣＤＭＡ信号等の成分が除去されない程度まで干渉除去能力を抑圧することにより、例えば干渉信号成分が受信信号中に多少残留しても、ＣＤＭＡ信号等の成分の除去が抑制されることから、総じて、干渉除去後のビット誤り率を改善することができる。
【０１１２】
なお、例えば受信系の伝送路で複数の狭帯域干渉信号が広帯域希望信号に重畳されて受信機により受信されるような場合には、受信信号を複数の帯域に分割して、これら各帯域がそれぞれ１つ（或いは複数）の干渉信号を含むようにし、当該各帯域毎にその帯域に含まれる干渉信号に適した干渉除去を行うことにより、それぞれの干渉信号に応じた干渉除去を行うことを実現することができる。
【０１１３】
ここで、広帯域の希望信号としては、種々な信号が用いられてもよく、例えばＣＤＭＡ方式により拡散された信号等を用いることができる。
また、狭帯域の干渉信号としては、種々な信号が用いられてもよく、例えばＦＭ信号やＦＳＫ信号等を用いることができる。
【０１１４】
また、入力信号に基づいて干渉信号の抽出量を抑制する仕方としては、種々な仕方が用いられてもよく、例えば、入力信号に含まれる希望信号や干渉信号の状況に応じて、干渉信号の抽出量を抑制するか否かを制御したり、抑制する場合にはその抑制の程度を制御したりするのが好ましい。
【０１１５】
また、本発明に係る干渉信号除去装置では、一実施態様として、次のような構成により、広帯域の希望信号と狭帯域の干渉信号とを含んだ入力信号から当該干渉信号を除去する。
すなわち、抽出手段が入力信号から干渉信号を抽出し、除去手段が抽出される干渉信号を入力信号から除去し、抽出制御手段が除去手段の除去結果に基づいて抽出手段による干渉信号の抽出を制御し、抽出量抑制手段が入力信号に基づいて抽出手段による干渉信号の抽出量を抑制する。
【０１１６】
ここで、除去手段の除去結果に基づいて抽出手段による干渉信号の抽出を制御する仕方としては、例えば、除去手段により干渉除去が行われた後の入力信号に含まれる干渉信号の成分が最小（理想的には、ゼロ）となるように制御する仕方が用いられる。そして、本発明では、抽出量抑制手段が、このような制御の仕方に対して、干渉信号の抽出量を抑制する。
【０１１７】
なお、例えば上記図６に示したような干渉信号除去装置を例とすると、適応フィルタから本発明に言う抽出手段が構成され、減算器から本発明に言う除去手段が構成され、フィルタタップ係数演算制御部から本発明に言う抽出制御手段が構成される。そして、本発明では、更に、干渉信号の抽出量を抑制する抽出量抑制手段を設ける。
【０１１８】
また、本発明に係る干渉信号除去装置では、好ましい態様として、抽出量抑制手段は、入力信号に含まれる希望信号と干渉信号との電力差に基づいて抽出手段による干渉信号の抽出量を抑制する。つまり、例えば、ＣＤＭＡ信号と狭帯域干渉信号とを含む信号を受信する場合には、ＣＤＭＡ信号の受信電力と狭帯域干渉信号の受信電力との差に応じて干渉信号の抽出量を抑制する。
なお、入力信号に含まれる希望信号の電力レベルや干渉信号の電力レベルは、例えば当該入力信号のスペクトル分析を行うこと等により検出することが可能である。
【０１１９】
ここで、広帯域信号（希望信号）と狭帯域干渉信号との電力差に基づいて干渉信号の抽出量を抑制する仕方の具体的な一例を以下の（１）〜（４）に示す。
（１）広帯域信号の電力が狭帯域干渉信号の電力よりも５ｄＢ分以上大きい場合には、干渉除去が行われないように、干渉信号の抽出量を（ゼロに）抑制する。
（２）広帯域信号の電力と狭帯域干渉信号の電力との差が±５ｄＢ以内である場合には、干渉信号の帯域内にある広帯域信号がそれほど除去されないことを実現すべく、弱い干渉除去が行われるように、干渉信号の抽出量を比較的大きく抑制する。
【０１２０】
（３）広帯域信号の電力よりも狭帯域干渉信号の電力の方が５ｄＢ〜３５ｄＢ分大きい場合には、これらの信号の電力に応じて、上記（２）の場合よりも干渉除去能力を強めて、干渉信号の抽出量を抑制する。
（４）広帯域信号の電力よりも狭帯域干渉信号の電力の方が３５ｄＢ分以上大きい場合（例えば干渉信号除去能力の限界値近傍であるような場合）には、干渉除去能力の制御が行われずに最大限の干渉除去が行われるように、干渉信号の抽出量を抑制しない。
【０１２１】
このように、例えば入力信号に含まれる干渉信号に応じて、所定の大きさ以上の電力の干渉信号に関して（のみ）その抽出量を抑制しないようにし、また、それぞれの干渉信号に応じて抽出量を抑制した干渉信号除去処理を行うようにすることにより、干渉信号の除去が行われない方が入力信号の特性がよいような場合には当該干渉信号の除去が行われないようにすることや、干渉信号の抽出量を或る程度抑制した方が干渉除去後における入力信号の特性がよいような場合には当該干渉信号の抽出量を適度に抑制すること等が実現される。このため、例えば従来において干渉信号を除去する際に本来的に（受信）処理を行いたい希望信号までも含まれて除去されてしまうことで生じていた入力信号の（受信）品質の劣化を防止することができ、これにより、干渉除去後における入力信号のビット誤り率の特性を向上させることができる。
【０１２２】
また、本発明に係る干渉信号除去装置では、他の態様として、抽出量抑制手段は、入力信号に含まれる希望信号の電力に基づいて抽出手段による干渉信号の抽出量を抑制する。つまり、例えば、ＣＤＭＡ信号と狭帯域干渉信号とを含む信号を受信する場合には、ＣＤＭＡ信号の受信電力に応じて干渉信号の抽出量を抑制する。
【０１２３】
ここで、図２（ａ）及び同図（ｂ）には、上記したような本発明に係る干渉信号除去装置を用いて、広帯域信号と狭帯域干渉信号とを含む受信信号から当該干渉信号を除去する場合の様子の一例を示してある。
【０１２４】
具体的に、同図（ａ）には、広帯域信号の電力と比べて或る狭帯域干渉信号の電力が十分に大きい場合の例を示してあり、この場合には、それぞれの干渉信号毎に適した干渉除去を行うようにし、つまり、広帯域信号と同程度の受信レベルの狭帯域干渉信号（例えば図中の▲２▼の干渉信号）については干渉除去処理を行わずにその干渉信号成分を残し、受信レベルの強い狭帯域干渉信号（例えば図中の▲１▼の干渉信号）についてはその抽出量を抑制せずに干渉除去を行い、比較的受信レベルの弱い狭帯域干渉信号（例えば図中の▲３▼の干渉信号）についてはその抽出量を抑制した干渉除去を行うことにより、干渉除去処理後の広帯域信号の品質を例えば従来と比べて改善することができる。
【０１２５】
なお、同図（ａ）には、広帯域信号に干渉する３つの信号▲１▼、▲２▼、▲３▼を示してあり、また、干渉除去前の受信信号の様子を左側のグラフに示す一方、干渉除去後の受信信号の様子を右側のグラフに示してある。また、これらのグラフの横軸は周波数を示しており、縦軸はスペクトル強度を示している。
【０１２６】
一方、同図（ｂ）には、広帯域信号の電力と比べて各狭帯域干渉信号の電力が（ほぼ）等しい場合（或いは、小さい場合についても同様）の例を示してあり、この場合には、広帯域信号と非常に近い受信レベルの狭帯域干渉信号（例えば図中の▲５▼及び▲６▼の干渉信号）については干渉除去処理を行わずにその干渉信号成分を残し、比較的受信レベルの弱い狭帯域干渉信号（例えば図中の▲４▼の干渉信号）についてはその抽出量を抑制した干渉除去を行うことにより、干渉除去処理後の広帯域信号の品質を例えば従来（入力された受信信号に対して、全ての狭帯域干渉信号を除去した場合）と比べて改善することができる。
【０１２７】
なお、同図（ｂ）には、広帯域信号に干渉する３つの信号▲４▼、▲５▼、▲６▼を示してあり、また、干渉除去前の受信信号の様子を左側のグラフに示す一方、干渉除去後の受信信号の様子を右側のグラフに示してある。また、これらのグラフの横軸は周波数を示しており、縦軸はスペクトル強度を示している。
また、上記図２（ａ）及び同図（ｂ）中で、干渉除去後における広帯域信号の周波数スペクトルの落ち込みは、当該干渉除去に際して広帯域信号成分が除去された部分を表している。
【０１２８】
このように、本発明に係る干渉信号除去装置では、入力信号に含まれる希望信号や干渉信号に応じた干渉除去を行うことにより、例えば狭帯域干渉信号の電力が広帯域希望信号の電力よりも小さいような場合において入力信号の特性を改善することができ、また、例えば入力信号に複数の狭帯域干渉信号が含まれるような場合においても各干渉信号毎に柔軟に干渉除去を行うことが可能である。
【０１２９】
【発明の実施の形態】
本発明の一実施例に係る干渉信号除去装置を図面を参照して説明する。
なお、本実施例では、干渉信号除去装置は例えば無線通信を行う受信機に設けられており、当該受信機により受信される信号（広帯域の希望信号と狭帯域の干渉信号とを含んだ信号）に含まれる干渉信号を除去する。
図１には、本発明に係る干渉信号除去装置の一例を示してあり、この装置には、干渉信号抽出部１と、合成器２と、干渉信号推定部３と、抽出量抑制部４とが備えられている。なお、ｔは時刻を示す。
【０１３０】
干渉信号推定部３は、例えば広帯域の希望信号と複数の狭帯域の干渉信号とが合成された受信信号ｒ（ｔ）及び干渉除去後の受信信号ｅ（ｔ）を入力して、当該干渉除去後の受信信号ｅ（ｔ）に含まれる干渉信号を推定し、当該推定結果を干渉信号抽出部１に通知する。
干渉信号抽出部１は、受信信号ｒ（ｔ）を入力して、干渉信号推定部３から通知される推定結果に基づいて当該受信信号ｒ（ｔ）から干渉信号（とみなされるもの）Ｖ（ｔ）を抽出し、当該干渉信号Ｖ（ｔ）を合成器２へ出力する。
【０１３１】
合成器２は、受信信号ｒ（ｔ）と干渉信号抽出部１からの干渉信号Ｖ（ｔ）とを逆位相で（つまり、干渉信号Ｖ（ｔ）が受信信号ｒ（ｔ）から除去されるように）合成して、干渉信号Ｖ（ｔ）が除去された後の受信信号ｅ（ｔ）を出力する。なお、合成器２から出力される干渉除去後の受信信号ｅ（ｔ）の一部は上記した干渉信号推定部３に入力されて、干渉信号の推定に用いられる。
【０１３２】
抽出量抑制部４は、受信信号ｒ（ｔ）を入力し、当該受信信号ｒ（ｔ）に含まれる希望信号の電力や干渉信号の電力に基づいて、例えば当該干渉信号の電力が比較的小さいような場合には、干渉信号抽出部１で抽出される干渉信号Ｖ（ｔ）の量が抑制されるように（つまり、前記推定結果に基づく干渉信号の抽出量より小さくなるように）、干渉信号推定部３を制御する。
【０１３３】
以上のように、本例の干渉信号除去装置では、入力信号に基づいて干渉信号除去処理における干渉信号の抽出量を抑制することが行われ、これにより、例えば広帯域希望信号の電力と比べて狭帯域干渉信号の電力が同程度である場合や或いは小さいような場合に、広帯域信号までもが除去されてしまうことを抑制することができる。このため、本例の干渉信号除去装置では、例えば従来と比べて、干渉除去後の入力信号（広帯域信号）の受信品質を改善することができ、これにより、干渉除去後における入力信号（広帯域信号）のビット誤り率の特性を向上させることができる。
【０１３４】
一例として、広帯域希望信号としてＣＤＭＡ信号が用いられ、狭帯域干渉信号としてＦＭ信号等が用いられた場合には、本例のような干渉信号除去装置を受信機に設けることにより、受信機では、例えば干渉信号の残留をＣＤＭＡ信号と同程度のレベルまで許容することにより、受信帯域全体として、干渉除去後の受信信号のビット誤り率の特性を向上させることができる。
【０１３５】
ここで、本例では、干渉信号抽出部１から本発明に言う抽出手段が構成され、合成器２から本発明に言う除去手段が構成され、干渉信号推定部３から本発明に言う抽出制御手段が構成され、抽出量抑制部４から本発明に言う抽出量抑制手段が構成されている。
【０１３６】
ここで、本発明に係る干渉信号除去装置の構成としては、必ずしも以上に示したものに限られず、種々な構成が用いられてもよい。具体的には、例えば上記図６や上記図８や上記図９や上記図１０に示したような構成の装置に、本発明に係る干渉信号除去装置を適用することも可能である。
【０１３７】
また、本発明に係る干渉信号除去装置の適用分野としては、必ずしも以上に示したものに限られず、本発明は、種々な分野に適用することが可能なものである。具体的には、例えばＣＤＭＡ方式を採用した受信機に限られず、本発明は、例えば種々な通信方式を採用する基地局装置や移動局装置や中継局装置等の受信機に適用することも可能なものである。
【０１３８】
また、本発明に係る干渉信号除去装置により行われる各種の処理としては、例えばプロセッサ（例えばＣＰＵやＭＰＵやＤＳＰ等）やメモリ等を備えたハードウエア資源においてプロセッサがＲＯＭに格納された制御プログラムを実行することにより制御される構成が用いられてもよく、また、例えば当該処理を実行するための各機能手段が独立したハードウエア回路として構成されてもよい。
また、本発明は上記の制御プログラムを格納したフロッピーディスクやＣＤ−ＲＯＭ等のコンピュータにより読み取り可能な記録媒体として把握することもでき、当該制御プログラムを記録媒体からコンピュータに入力してプロセッサに実行させることにより、本発明に係る処理を遂行させることができる。
【０１３９】
【発明の効果】
以上説明したように、本発明に係る干渉信号除去装置によると、広帯域の希望信号と狭帯域の干渉信号とを含んだ入力信号から当該干渉信号を除去するに際して、入力信号に基づいて当該入力信号に含まれる干渉信号をその抽出量を抑制して抽出し、抽出した干渉信号を当該入力信号から除去するようにしたため、入力信号から希望信号までも除去してしまうことを抑制することができ、これにより、干渉除去後における入力信号（希望信号）の品質を例えば従来と比べて向上させることができる。
【図面の簡単な説明】
【図１】 本発明に係る干渉信号除去装置の一例を示す図である。
【図２】 本発明に係る干渉信号除去装置を用いて広帯域信号と狭帯域干渉信号とを含む受信信号から当該干渉信号を除去する場合の様子の一例を示す図である。
【図３】 従来例に係る干渉信号除去装置の一例を示す図である。
【図４】 拡散符号系列の一例を説明するための図である。
【図５】 ＣＤＭＡ方式による広帯域の拡散信号と狭帯域の干渉信号とを含む受信信号のスペクトルの一例を示す図である。
【図６】 干渉信号除去装置の一例を示す図である。
【図７】 適応フィルタの構成例を示す図である。
【図８】 干渉信号除去装置の一例を示す図である。
【図９】 干渉信号除去装置の一例を示す図である。
【図１０】 干渉信号除去装置の一例を示す図である。
【図１１】 ＣＤＭＡ信号に２波のＦＭ信号が干渉した受信信号のスペクトルの一例を示す図である。
【図１２】 干渉信号除去処理の開始直後において干渉信号除去装置から出力される信号のスペクトルの一例を示す図である。
【図１３】 干渉信号除去処理を開始してからしばらくの時間が経過した場合において干渉信号除去装置から出力される信号のスペクトルの一例を示す図である。
【図１４】 干渉信号除去装置による干渉信号除去特性の一例を示す図である。
【図１５】 干渉信号除去装置を用いて広帯域信号と狭帯域干渉信号とを含む受信信号から当該干渉信号を除去する場合の様子の一例を示す図である。
【符号の説明】
１・・干渉信号抽出部、 ２・・合成器、 ３・・干渉信号推定部、
４・・抽出量抑制部、[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an interference signal removal apparatus that removes an interference signal from an input signal including a wideband desired signal and a narrowband interference signal, and more particularly to interference signal removal that suppresses removal of a desired signal. Relates to the device.
[0002]
[Prior art]
For example, a received signal received by a receiver may include a signal (interference signal) that interferes with the desired signal, as well as a signal desired to be received (desired signal).
First, a wideband desired signal and a narrowband interference signal will be described using an IEEE 802.11 wireless LAN as an example.
[0003]
Note that the terms “broadband” and “narrowband” are used in a relative sense, and specifically, a signal having a sufficiently wide occupied bandwidth compared to the occupied bandwidth of a narrowband interference signal. This is referred to as a broadband signal. For example, a signal having an occupied bandwidth that is 10 times or more the occupied bandwidth of a narrowband interference signal is referred to as a broadband signal. As an example, in the wireless LAN described here, the occupied bandwidth of a wideband signal is, for example, 26 MHz (frequency per wave), and the occupied bandwidth of a narrowband signal is, for example, 2 MHz (frequency per wave).
[0004]
In the wireless LAN of IEEE802.11, when broadly divided, a direct spreading (DSSS) method and a frequency hopping (FHSS: Frequency Hopping Spread Spectrum) method are used. A signal based on the DSSS scheme can be regarded as a wideband signal, while a signal based on the FHSS scheme can be regarded as a narrowband signal. And in both systems, wireless communication is performed using the same frequency band, and since mutual interference is allowed systematically, interference occurs between the signals of both systems.
[0005]
Here, the DSSS method is a communication method in which a narrowband signal is communicated (transmitted) as a wideband signal by frequency spreading, and the signal is returned to the original narrowband signal in the demodulation process on the receiving side. For this reason, in the DSSS scheme, the interference signal can be suppressed by spreading the narrowband interference signal included in the received signal into the wideband signal in the demodulation process. A ratio before and after such diffusion is called a diffusion rate. For example, when the diffusion rate is 128, a gain of about 21 dB (more precisely, 10 LOG128) is obtained.
[0006]
On the other hand, the FHSS system is a system for communicating a narrowband signal using a wideband by changing its transmission frequency at specific time intervals. For this reason, in the FHSS method, the occupied bandwidth when a specific time is fixed is narrowed to, for example, 2 MHz, and the power per band of the DSSS method is relatively low, so the FHSS method is adopted. The influence of interference can be suppressed by the reception filter of the receiver.
[0007]
In the FHSS system, for example, even when another communication device performs signal communication using the FHSS system with a different hopping pattern, the probability of using the same frequency at the same time is low. Interference at is almost no problem. Furthermore, since the FHSS system can perform frequency hopping using a wider band than the DSSS system, even when strong interference occurs from the DSSS system, signal reception is performed in a frequency band that is not subject to interference. It is possible.
[0008]
However, in the above-described DSSS system, the spreading factor may be lowered in order to increase the signal transmission rate. As a specific example, when the spreading factor is lowered to 11, the gain is lowered to about 10 dB (more precisely, 10 LOG11), and when the spreading factor is lower than that, the gain is further lowered, and the interference signal is reduced. The suppression effect may not be obtained.
In addition, for example, a standard such as Bluetooth (short range mobile service) using the FHSS system has begun to be widely used as a wireless interface between portable devices, so that the probability that a signal by the DSSS system is subject to interference is increasing.
[0009]
As another example, interference in an adjacent frequency band may occur between a communication signal of W-CDMA (Wideband-Code Division Multiple Access) method and a communication signal of PHS (Personal Handyphone System) method, Interference may occur between a 2.4 GHz band wireless LAN (IEEE 802.11) wideband signal and a Bluetooth narrowband signal, or a CDMA communication signal and a TDMA (Time Division Multiple Access) or FDMA (Frequency Division Multiple Access) communication signals may cause interference due to sharing of frequency bands, unexpected interference with external waves, and the like.
[0010]
Conventionally, as a technique for removing the interference as described above, an interference signal removal method using an adaptive algorithm, an interference signal removal method using a notch filter, and the like have been studied. As an example, “Application of Complex Multirate Filter Bank to DS-CDMA / TDMA Signal Batch Receiver Sharing Frequency Band” (The Institute of Electronics, Information and Communication Engineers Journal B-II Vol. J80-BII No12 December 1997) ” Describes a technique for removing a narrowband signal that interferes with a wideband signal by a notch filter using a multirate filter bank. However, this technique has a problem in that, when removing a narrowband signal, a component of a wideband signal that is a desired wave is also removed by a filter, so that a bit error rate after interference wave removal is deteriorated.
[0011]
Next, an example of an interference signal removing apparatus according to a conventional example is shown. The interference signal removal apparatus is provided in a receiver that performs wireless communication, for example, and removes an interference signal included in a signal received by the receiver.
FIG. 3 shows an example of an interference signal removal apparatus, which includes an interference signal extraction unit 11, a combiner 12, and an interference signal estimation unit 13. Here, t indicates time.
[0012]
The interference signal estimation unit 13 receives a received signal r (t) obtained by combining a desired signal in a wide band and a plurality of narrowband interference signals and a received signal e (t) after interference removal, and performs general adaptation. An interference signal included in the received signal r (t) is estimated using an algorithm, and an interference signal estimation coefficient h (t + 1) based on the estimation result is output to the interference signal extraction unit 11.
The interference signal extraction unit 11 receives the reception signal r (t), and based on the interference signal estimation coefficient h (t + 1) input from the interference signal estimation unit 13, the interference signal extraction unit 11 receives the interference signal (and What is considered) V (t) is extracted, and the interference signal V (t) is output to the combiner 12.
[0013]
The synthesizer 12 has the reception signal r (t) and the interference signal V (t) from the interference signal extraction unit 11 in opposite phases (that is, the interference signal V (t) is removed from the reception signal r (t). The received signal e (t) after the interference signal V (t) is removed. Part of the received signal e (t) after interference output output from the synthesizer 12 is input to the interference signal estimation unit 13 and used for estimation of the interference signal.
[0014]
Next, an example of an interference signal removal apparatus in the CDMA system or the CDMA system is shown.
For example, in a mobile communication system using the DS-CDMA system, multiplex communication between a plurality of mobile station apparatuses and a base station apparatus is realized by assigning different spreading codes to each mobile station apparatus. Specifically, each mobile station device transmits a signal to be transmitted after being spread-modulated with a spreading code assigned to itself, while the base station device receives the signal using the spreading code assigned to each mobile station device. The signal from the desired mobile station apparatus is demodulated by despreading the signal. Similarly, the mobile station apparatus demodulates the signal addressed to itself by despreading the received signal from the base station apparatus using the spreading code assigned to itself.
[0015]
FIG. 4 shows an example of a spread code sequence composed of, for example, a PN (pseudo noise signal) sequence.
As shown in the figure, one unit (one symbol) of spreading code is composed of a plurality of chip data (for example, a sequence of “1” values and “−1” values). A plurality of different spreading codes can be generated by making the patterns different. Here, the spreading code has a characteristic that, for example, if a certain spreading code is shifted by one chip time or more, there is no correlation with the spreading code.
[0016]
In addition, the same figure shows the time width of one chip data (chip section Tc) and the time width of a spread code for one symbol (bit section T). Here, the time width of the spreading code for one symbol is the transmission data (for example, “1” value) transmitted from the transmitter (for example, mobile station apparatus or base station apparatus) to the receiver (for example, base station apparatus or mobile station apparatus). And “0” value). That is, the change speed of the chip data constituting the spreading code is very high compared to the switching speed (symbol switching speed) of transmission data spread-modulated by the spreading code.
[0017]
As described above, in such wireless communication, other than the intention (that is, other than the CDMA system), a narrowband signal or the like is present in the wideband frequency band that is permitted to use the frequency and used for communication. In some cases, interference may occur when mixed. If such an interference signal is larger than the level of interference caused by noise or the like assumed at the time of system design, for example, bit errors increase and reception quality at the receiver may be significantly degraded.
[0018]
In addition, as described above, for the purpose of effective use of frequency bands, for example, a communication method using a relatively wide frequency band such as a CDMA method and a communication using a narrow band such as an FM (frequency modulation) method. It is also conceivable to realize multiplex communication with a method that performs this. Specifically, for example, it is possible in principle to multiplex signals in the analog communication system such as the FM system in the frequency band of spread signals by the CDMA system to achieve effective use of the frequency band. However, if the CDMA receiver cannot remove the FM signal or the like from the received signal, the signal and the spread signal interfere with each other, increasing bit errors and degrading the reception quality.
[0019]
FIG. 5 shows an example of a spectrum of a received signal including a spread signal (CDMA signal) by the CDMA method and a signal (FM interference wave) by the FM method, the horizontal axis indicates the frequency, and the vertical axis indicates the frequency. The spectrum intensity is shown.
[0020]
Hereinafter, an example of an interference signal removing device (interference removing circuit) described in Japanese Patent Application No. 11-197296 will be described with reference to FIGS. The interference signal removal apparatus described in this document is provided in, for example, a base station apparatus, a mobile station apparatus, a relay station apparatus, etc. that adopts the CDMA system, and a wideband spread signal and a narrowband that are spread-modulated by the CDMA system The interference signal is removed from the received signal including the interference signal and the I component and Q component of the received signal, and in particular, the interference signal is removed using the characteristics of the spread signal.
[0021]
FIG. 6 shows an example of an interference signal removal apparatus that receives a reception signal including a CDMA signal (desired signal) and an FM signal (interference signal) and removes the FM signal from the input signal r (t). It is. In this interference signal removing apparatus, when removing the interference signal from the received signal including the spread signal spread and modulated by the CDMA method and the interference signal, the time difference means 21 distributes the received signal between the two signals obtained. A time difference of one chip or more of the spread code is given, and the extraction means 22 and 24 extract a signal component correlated between the two signals given the time difference as an interference signal component, and the interference signal component extracted by the removal means 23 is extracted. Remove from received signal.
[0022]
Specifically, the interference cancellation apparatus shown in the figure includes a delay element 21 that delays a received signal, and an interference signal component from the received signal that is delayed according to a tap coefficient control signal from a filter tap coefficient calculation control unit 24 described later. , A subtractor 23 that removes the interference signal component from the received signal, and a filter that outputs to the adaptive filter 22 a tap coefficient control signal based on the output signal from the subtractor 23 and the delayed received signal. A tap coefficient calculation control unit 24 is provided.
[0023]
A configuration example and an operation example of the circuit shown in FIG.
The circuit receives a signal r (t) received by a receiver, and the input signal r (t) includes, for example, a spread signal that is spread-modulated by a CDMA method and an interference signal (a communication method using a narrow band). For example, an FM modulated signal) is included. Here, t indicates time, and in this example, it is assumed to be an integer discrete value having one sample time as a minimum unit.
[0024]
The input signal r (t) described above is first divided into two signals, and one signal is input to the delay element 21 while the other signal is input to the subtractor 23.
The delay element 21 has a function of delaying an input signal by a time width corresponding to one chip of a spread code and outputting the delayed signal. This time difference is set in advance to a value that can eliminate the correlation component of the spread signal between the two signals and leave the correlation component of the interference signal to be removed, for example. .
[0025]
Specifically, a signal output from the delay element 21 is represented as r (t−τ), where τ is a delay time given by the delay element 21.
The signal r (t−τ) output from the delay element 21 is input to the adaptive filter 22 and the filter tap coefficient calculation control unit 24.
[0026]
Here, FIG. 7 shows a configuration example of the adaptive filter 22.
The adaptive filter 22 shown in the figure includes, for example, a shift register composed of (n-1) storage elements S1 to Sn-1 arranged in series, n multipliers J1 to Jn, n-1) adders K1 to Kn-1 are provided. Note that n is the number of filter taps.
[0027]
A signal r (t−τ) output from the delay element 21 is input to the shift register, and this signal is stored in a plurality of storage elements S1 to Sn−1 in time series. The signals stored in the storage elements S1 to Sn-1 are sequentially shifted to the subsequent storage elements.
Specifically, for example, a sequence u (t) in the shift register of the signal r (t−τ) input to the shift register is expressed by Equation 1. Here, u (t) is a vector.
In this specification, when a symbol used to represent a signal or the like does not indicate that it is a vector or a matrix, the symbol is assumed to be a scalar.
[0028]
[Expression 1]

[0029]
Here, the signal r1 is a signal input to the shift register at a certain time, and is a signal output to the multiplier J1 without passing through any of the storage elements S1 to Sn-1. Signals r2 to rn are signals output from the storage elements S1 to Sn-1 at the time, respectively, and are signals output to the multipliers J2 to Jn, respectively.
[0030]
The multipliers J1 to Jn receive the above-described signals r1 to rn, and receive tap coefficient control signals h1 to hn from a filter tap coefficient calculation control unit 24, which will be described later. In Jn, the input two signals are multiplied (that is, the signals r1 to rn are weighted by the tap coefficient control signals h1 to hn), and the multiplication results are output to the adders K1 to Kn-1.
Here, the filter tap coefficient series h (t) output from the filter tap coefficient calculation control unit 24 is expressed by Expression 2. Note that h (t) is a vector.
[0031]
[Expression 2]

[0032]
The multiplication results output from the multipliers J1 to Jn are summed by the adders K1 to Kn-1, and the summation results are output from the adaptive filter 22. Here, as will be described later, the filter tap coefficient sequence h (t) of this example is sequentially generated by the filter tap coefficient calculation control unit 24 so that the sum result is the same signal as the interference signal component included in the received signal. Updated.
Specifically, a signal output from the adaptive filter 22 (that is, the above-described total result) FM (t) is expressed by Equation 3. Here, Σ in Equation 3 represents the sum.
[0033]
[Equation 3]

[0034]
The symbol “*” used in this specification indicates multiplication between symbols arranged before and after the symbol, and in particular, multiplication between vectors represents an operation for calculating an inner product value of two vectors. .
[0035]
As described above, the adaptive filter 22 extracts the interference signal component from the input delay signal r (t−τ) in accordance with the tap coefficient control signal from the filter tap coefficient calculation control unit 24, and extracts the interference wave. The signal FM (t) is output to the subtracter 23.
[0036]
The subtractor 23 receives the input signal r (t) that has not been delayed and the output signal FM (t) from the adaptive filter 22, and subtracts the output signal FM (t) from the input signal r (t). It has a function of outputting the subtraction result e (t).
Here, the above-described subtraction result e (t) is a signal output from the interference signal removal apparatus of this example, and is expressed by Expression 4.
[0037]
[Expression 4]

[0038]
In this example, since the tap coefficient control signal from the filter tap coefficient calculation control unit 24 described later is sequentially updated, the above-described interference wave extraction signal FM (t) becomes the same signal as the interference signal in the received signal. The subtraction result e (t) is a signal obtained by removing the interference signal from the received signal, that is, a spread signal by CDMA (ideally, only the spread signal).
[0039]
The filter tap coefficient calculation control unit 24 receives the signal r (t−τ) output from the delay element 21 and the signal e (t) output from the subtractor 23. Is used to calculate a tap coefficient control signal such that the signal FM (t) output from the adaptive filter 22 is the same signal as the interference signal component, and outputs the calculated tap coefficient control signal to the adaptive filter 22. It has a function.
[0040]
The filter tap coefficient calculation control unit 24 of this example can calculate the tap coefficient control signal described above using an algorithm such as LMS (Least Mean Square) and RLS (Recursive Least Square), for example. In this example, A case where the LMS algorithm is used will be described, and a case where the RLS algorithm is used will also be described later.
First, the general formula of LMS will be described.
The update formula of LMS is generally shown by Formula 5.
[0041]
[Equation 5]

[0042]
Here, h (t) is a filter tap coefficient series at time t, μ is a step size parameter that is a coefficient related to convergence time and accuracy, e (t) is an error signal at time t, u (t) is an input signal sequence at time t.
Further, the error signal e (t) described above is generally expressed by Equation 6.
[0043]
[Formula 6]

[0044]
Here, d (t) is usually called a unique word or a training signal, and a known signal predetermined on the transmission side and the reception side is used. In the arithmetic algorithm using the above formulas 5 and 6, the error signal e (t) can be converged to 0 by sequentially updating the filter tap coefficient series.
[0045]
Next, a case where the above LMS algorithm is applied to this example will be described.
When Equation 5 is applied to this example, h (t) is a filter tap coefficient series output from the filter tap coefficient calculation control unit 24 to the adaptive filter 22, and u (t) is a filter from the delay element 21. It is a signal sequence (shown in the above equation 1) output to the tap coefficient calculation control unit 24.
Further, in this example, the signal (shown in the above equation 4) output from the subtractor 23 is used as the error signal e (t) described above, and this is a feature point in the interference removal circuit of this example. Therefore, the processing is different from the normal LMS algorithm.
[0046]
First, if the case where the delay element 21 is not provided is considered, the calculation algorithm described above brings the error signal e (t) close to 0, so the signal e (t) output from the subtractor 23 converges to 0. Then, a filter tap coefficient series h (t) that removes not only the interference signal in the received signal but also the spread signal by the CDMA method is generated.
[0047]
On the other hand, since the delay element 21 described above is provided in this example, the filter tap coefficient calculation is performed via the signal r (t−τ) input from the delay element 21 to the filter tap coefficient calculation control unit 24 and the subtractor 23. There is a time difference of the delay time τ from the signal e (t) input to the control unit 24.
[0048]
Here, for example, the spread signal r (t) by the CDMA system and the spread signal r (t−τ) delayed by one chip time or more compared to the signal become an uncorrelated signal. When e (t) is to be converged to 0, the spread signal component of u (t) remains uncorrelated with r (t) and remains as error e (t). In other words, in the above equation 4, if the input signal sequence u (t) is continuously added, the influence of the spread signal component becomes theoretically 0, so that the spread signal component is not removed and remains as an error e (t). It will be. On the other hand, an interference signal component that fluctuates gradually in time compared to chip data has a correlation even if there is a delay of, for example, several chip hours, so that only the interference signal component can be removed from the received signal. A coefficient series h (t) is generated.
[0049]
That is, in the above calculation algorithm applied to this example, a component (that is, an interference signal component) having a correlation between u (t) and e (t) is left in the output signal from the adaptive filter 22, while the correlation A filter tap coefficient series h (t) that does not remain in the output signal from the adaptive filter 22 can be generated for components that are not present (that is, spread signal components).
By such an arithmetic algorithm, the adaptive filter 22 of this example can extract only the interference signal component in the received signal and output it to the subtracter 23. The subtractor 23 removes only the interference signal component from the received signal. A signal (that is, a spread signal by the CDMA system) can be output.
[0050]
As described above, the interference signal removal apparatus shown in FIG. 6 uses the characteristics of the spread signal to detect the received signal including the wideband spread signal and the narrowband interference signal that are spread-modulated by the CDMA method. It is possible to adaptively remove the interference signal, thereby preventing deterioration of reception quality and improving reception quality.
[0051]
6 shows a configuration in which the signal output from the subtractor 23 is not delayed, the received signal input to the subtractor 33 is delayed by the delay element 31 as shown in FIG. The same effect as described above can be obtained by a configuration that does not delay the received signal input to the filter 32 and the filter tap coefficient calculation control unit 34. Here, the configuration shown in FIG. 8 is substantially the same as the configuration shown in FIG. 6 except that the delay element 31 is provided on the subtractor 33 side.
[0052]
In addition, it is possible to obtain the same interference removal effect as described above by using an algorithm other than the above-described LMS algorithm. As an example, a specific example of the update formula when the RLS algorithm is used in the configuration shown in FIG. I will show you. In the following, for convenience of explanation, components corresponding to the above u (t), h (t), e (t), d (t), and r (t) are denoted by the same reference numerals.
[0053]
For example, an n-row 1-column vector composed of the same components as u (t) shown in the above equation 1 is used as the input sequence u (t), and n filters are provided in the same manner as h (t) shown in the above equation 2. A vector of n rows and 1 column composed of tap coefficients is defined as a filter tap coefficient series h (t).
Further, the error signal e (t) in the RLS is expressed by Equation 7 as equivalent to the error signal e (t) shown in Equation 6 above. U ^T (T) shows the transposed u (t).
[0054]
[Expression 7]

[0055]
Here, in this example, as d (t), for example, the received signal r (t) input to the subtracter 23 is used, and u in the above equation 7 ^T (T) * h (t) corresponds to the interference wave extraction signal output from the adaptive filter 22. That is, as in the case of using the above-described LMS algorithm, the signal output from the subtractor 23 is used as the error signal e (t) shown in the above equation 7, which is a feature of this example. . As in the case of using the LMS algorithm described above, the error signal e (t) converges to 0 when the delay element 21 is not provided.
[0056]
Also, for example, using the coefficient error correlation matrix P (t), which is an n-by-n matrix, and the gain vector k (t), which is an n-by-1 vector, RLS update equations are expressed by Equations 8 to 10. It is.
[0057]
[Equation 8]

[0058]
[Equation 9]

[0059]
[Expression 10]

[0060]
Further, as the initial value h (0) of the filter tap coefficient series h (t) described above, for example, a zero vector is used as shown in Expression 11, and the initial value P (0) of the coefficient error correlation matrix P (t) described above is used. For example, as shown in Expression 12, a matrix in which all diagonal elements having the same number of rows and columns are positive real numbers c and the other elements are 0 is used. H ^T (0) indicates the transposed h (0). Further, I in Expression 12 represents an n-by-n matrix in which all diagonal elements having the same number of rows and columns are 1 and the other elements are 0.
[0061]
[Expression 11]

[0062]
[Expression 12]

[0063]
The filter tap coefficient calculation control unit 24 sequentially updates the filter tap coefficient series h (t) in accordance with the RLS update formula shown above, so that the output from the adaptive filter 22 is performed, for example, as in the case of using the LMS algorithm described above. Can be gradually brought closer to the actual interference signal component, thereby removing the interference signal from the received signal including the wideband spread signal and the narrowband interference signal spread-modulated by the CDMA method. it can.
[0064]
Next, in FIG. 9, the I component and the Q component of the received signal including the CDMA signal (desired signal) and the FM signal (interference signal) are input, and the I component rI (t) and the Q component rQ ( An example of an interference signal removing apparatus for removing the FM signal from t) is shown. In this interference signal removal apparatus, when removing the interference signal from the I component and Q component of the received signal including the spread signal spread and modulated by the CDMA method and the interference signal, the time difference means 41a and 41b distribute the I component. The time difference of one chip or more of the spread code is given between the two signals obtained by dividing the Q component and the two signals obtained by distributing the Q component, and the extraction means 42a, 42b, 43a, 43b provide one time difference. Extracting and removing the I and Q components of the interference signal component using the signal component having a correlation between the received signal consisting of the component and the Q component and the received signal consisting of the other I component and the Q component as an interference signal component 44a, 44b, 45a, 45b removes the I component of the interference signal component extracted from the I component of the received signal and determines whether the extracted Q component of the interference signal component is the Q component of the received signal. To remove.
[0065]
Specifically, the interference signal removal apparatus shown in the figure includes a delay element 41a that delays an I-phase signal (I component) quadrature-detected from the received signal, and a Q-phase signal quadrature-detected from the received signal. A delay element 41b that delays a signal (Q component), and four adaptive filters 42a and 42b that extract interference signal components from I and Q components delayed according to a tap coefficient control signal from a filter tap coefficient calculation control unit 46 described later. 43a, 43b, an adder 44a for adding the I component of the interference signal component, an adder 44b for adding the Q component of the interference signal component, and a subtraction for removing the I component of the interference signal component from the I component of the received signal 45a, a subtractor 45b for removing the Q component of the interference signal component from the Q component of the received signal, an output signal from the subtractors 45a and 45b, and an I component and a Q component of the delayed received signal, Tap coefficient control signal to the adaptive filter 42a based, 42b, 43a, and the filter tap coefficient calculation control unit 46 to be output to 43b are provided.
[0066]
A configuration example and an operation example of the circuit shown in FIG.
This circuit receives an I component rI (t) and a Q component rQ (t) quadrature-detected from the received signal by the receiver, and the input signals rI (t) and rQ (t) are input, for example, by the CDMA method. A wideband spread signal subjected to spread modulation and an interference signal (for example, an FM modulation signal) by a communication method using a narrow band are included. Here, as in the case described with reference to FIG. 6 above, t indicates time, and in this example, it is assumed to be an integer discrete value having one sample time as the minimum unit.
[0067]
The above-described I component rI (t) is first divided into two signals, and one signal is input to the delay element 41a, while the other signal is input to the subtractor 45a. Similarly, the above-described Q component rQ (t) is first divided into two signals, and one signal is input to the delay element 41b, while the other signal is input to the subtractor 45b.
[0068]
Each delay element 41a, 41b has a function of delaying an input signal by a time width corresponding to one chip of a spread code and outputting the same as the delay element 21 shown in FIG. The two delay elements 41a and 41b give the same delay time. Similarly to the case described with reference to FIG. 6, specifically, the I component signal output from the delay element 41a is expressed as rI (t−τ), and the Q signal output from the delay element 41b. The component signal is represented as rQ (t−τ). Here, τ is a delay time given by the delay elements 41a and 41b.
[0069]
The signal rI (t−τ) output from the delay element 41a is input to the two adaptive filters 42a and 43a and the filter tap coefficient calculation control unit 46, and the signal rQ (t−τ) output from the delay element 41b is 2 The two adaptive filters 42 b and 43 b and the filter tap coefficient calculation control unit 46 are input.
[0070]
The configuration of each adaptive filter 42a, 42b, 43a, 43b is the same as that shown in FIG. 7, for example. Here, the reason why the four adaptive filters 42a, 42b, 43a, 43b are provided in this example is to perform I-phase and Q-phase complex operations, specifically, the I component and Q component of the received signal. This is because both the I component and the Q component of the interference signal component are included in each of. In this example, two types of filter tap coefficient series hI (t) and hQ (t) of I phase and Q phase are used. Note that hI (t) and hQ (t) are vectors.
[0071]
Specifically, in this example, the I component of the interference signal component is extracted from the I component rI (t−τ) of the received signal input by the adaptive filter 42a, and the I component rI (t of the received signal input by the adaptive filter 43a. -Τ) extracts the Q component of the interference signal component, extracts the Q component of the interference signal component from the Q component rQ (t-τ) of the received signal input by the adaptive filter 42b, and receives the received signal input by the adaptive filter 43b. Filter tap coefficient series hI (t) and hQ (t) that can extract the I component of the interference signal component from the Q component rQ (t−τ) of the filter component are generated by the filter tap coefficient calculation control unit 46 described later. The
[0072]
The adder 44a has a function of adding the signals output from the two adaptive filters 42a and 43b and outputting the result to the subtracter 45a. The addition result output to the subtractor 45a is the I component of the received signal. Interference signal component (that is, the I component of the interference signal component) FMI (t). In this example, the adder 44a inverts the sign of the signal output from the one adaptive filter 43b and performs the above-described addition. However, such inversion of the positive / negative is performed by, for example, the above-described adaptive filter 43b or When performed by a filter tap coefficient calculation control unit 46 described later, the adder 42a does not need to perform the above-described positive / negative inversion.
[0073]
The adder 44b has a function of adding the signals output from the two adaptive filters 42b and 43a and outputting the result to the subtracter 45b. The addition result output to the subtractor 45b is included in the Q component of the received signal. Interference signal component (ie, Q component of the interference signal component) FMQ (t).
[0074]
Here, the I component FMI (t) of the interference signal component output from the adder 44a is expressed by the equation 13, and the Q component FMQ (t) of the interference signal component output from the adder 44b is expressed by the equation. 14. Note that uI (t) and uQ (t) in Equation 13 and Equation 14 are vectors, and these uI (t) and uQ (t) are represented by Equation 1 in the description using FIG. 6, for example. This corresponds to the I component and Q component of (t).
[0075]
[Formula 13]

[0076]
[Expression 14]

[0077]
The subtracter 45a inputs the input signal rI (t) of the I component which is not delayed and the output signal FMI (t) from the adder 45a, and the output signal FMI (t) from the input signal rI (t). It has a function of subtracting and outputting the subtraction result eI (t).
Similarly, the subtracter 45b receives the undelayed Q component input signal rQ (t) and the output signal FMQ (t) from the adder 44b, and outputs the output signal FMQ ( It has a function of subtracting t) and outputting the subtraction result eQ (t).
Here, the subtraction results eI (t) and eQ (t) described above are signals output from the interference signal removing apparatus of this example.
[0078]
In this example, the tap coefficient control signal from the filter tap coefficient calculation control unit 46, which will be described later, is sequentially updated, so that the I-component and Q-component interference wave extraction signals FMI (t) and FMQ (t) are respectively obtained. Since the signal is the same as the interference signal in the I component and Q component of the received signal, the subtraction results eI (t) and eQ (t) are signals obtained by removing the interference signal from the I component and Q component of the received signal, respectively. That is, the spread signal is CDMA (ideally, only the spread signal).
[0079]
The filter tap coefficient calculation control unit 46 includes signals rI (t−τ) and rQ (t−τ) output from the two delay elements 41a and 41b and signals eI (t) output from the two subtractors 45a and 45b. ) And eQ (t) are input, and the filter tap coefficient calculation control unit 46 uses these signals to convert the signals output from the adaptive filters 42a, 42b, 43a, 43b into interference signal components as described above. The tap coefficient control signal is calculated and output to each of the adaptive filters 42a, 42b, 43a, 43b. In this example, for example, the same tap coefficient control signal is output to the two adaptive filters 42a and 42b, while the same tap coefficient control signal is output to the remaining two adaptive filters 43a and 43b. 13 and the interference signal components FMI (t) and FMQ (t) expressed by the above equation 14 are set.
[0080]
The filter tap coefficient calculation control unit 46 of this example calculates the tap coefficient control signal using, for example, the LMS complex calculation algorithm shown in the description with reference to FIG. The LMS update formula in this algorithm is shown by formula 15 and formula 16.
[0081]
[Expression 15]

[0082]
[Expression 16]

[0083]
Here, hI (t) and hQ (t) are filter tap coefficient series at time t, μ is a step size parameter that is a coefficient related to convergence time and accuracy, and uI (t) and uQ (t ) Are input signal sequences in the shift registers of the adaptive filters 42a and 43a and in the shift registers of the adaptive filters 42b and 43b, respectively. Similarly to the case described with reference to FIG. 6, signals output from the subtracter 45a and the subtracter 45b are used as eI (t) and eQ (t), respectively. Note that uI (t) and uQ (t) are vectors as described above.
[0084]
In this example, similarly to the case described with reference to FIG. 6, the filter tap coefficient series hI (t) and hQ (t) are sequentially updated by the arithmetic algorithm as described above. Can be generated by the filter tap coefficient series hI (t) and hQ (t) that are not removed by the uncorrelation and can remove the relatively correlated interference signal components.
In this example, since both the I component and the Q component are taken into account when calculating the filter tap coefficient series hI (t) and hQ (t), the accuracy of interference removal can be further improved.
[0085]
As described above, in the interference signal removal apparatus shown in FIG. 9, the I component and Q component of the received signal including the spread signal and the interference signal spread-modulated by the CDMA method by using the characteristics of the spread signal. The interference signal can be removed from the signal, thereby preventing the reception quality from deteriorating and improving the reception quality.
[0086]
9 shows a configuration in which the signals output from the subtracters 45a and 45b are not delayed, as in the case described with reference to FIG. 6, but for example, as shown in FIG. The delay signal 51a, 51b delays the received signal input to 55b, while the configuration does not delay the received signal input to the adaptive filters 52a, 52b, 53a, 53b and the filter tap coefficient calculation control unit 56. The same effect can be obtained. Here, the configuration shown in FIG. 10 is substantially the same as the configuration shown in FIG. 9 except that the delay elements 51a and 51b are provided on the subtracters 55a and 55b side. An adder 54a, 54b is also provided with the components shown.
[0087]
Further, for example, similarly to the case described with reference to FIG. 6, it is possible to obtain the same interference removal effect as described above by using an algorithm other than the above-described complex operation LMS algorithm. The case where the RLS algorithm for complex operation is used in the configuration shown in FIG. In the following, for convenience of explanation, uI (t), uQ (t), hI (t), hQ (t), eI (t), eQ (t), rI (t), and rQ (t) are described above. ) Are indicated using the same reference numerals.
[0088]
In the RLS algorithm for complex operation, for example, all parameters such as u (t), h (t), e (t), k (t), and P (t) shown in the above formulas 7 to 10 are complex numbers. It is composed of elements. Here, when γ and ω are real numbers and j is used as a symbol representing the imaginary part, an arbitrary complex number element is represented as (γ + jω).
In the RLS algorithm for complex operation, for example, the real part and the imaginary part of each parameter described above are separated and used as an I component parameter and a Q component parameter, respectively, and shown in the description using FIG. Such a sequential update process is realized in a complex operation.
[0089]
Specifically, in this example, for example, the real part of u (t) is uI (t), the imaginary part is uQ (t), and the real part of h (t) is hI (t). The imaginary part is set to hQ (t), the real part of e (t) is set to eI (t) and the imaginary part is set to eQ (t). Processing for removing the interference signal component from the component rQ (t) is performed.
[0090]
As described above, even when the RLS algorithm for complex operation is used, for example, as in the case of using the LMS algorithm for complex operation described above, the spread signal and the interference signal spread and modulated by the CDMA method are used. The interference signal can be removed from the I component and Q component of the received signal including.
[0091]
[Problems to be solved by the invention]
Here, a state in the case where interference removal is performed by the interference signal removal apparatus as shown in the conventional example will be specifically shown.
FIG. 11 shows an example of the spectrum of the received signal before the interference signal is removed. As the received signal, a signal in which two FM signals interfere with the CDMA signal is shown. The horizontal axis of the graph in FIG. 12 or later-described FIG. 12 or later-described FIG. 13 indicates the frequency (MHz), and the vertical axis indicates the spectral intensity of the signal.
[0092]
Also, FIG. 12 shows that the received signal shown in FIG. 11 is input to an interference signal removing apparatus such as that shown in FIG. 6 and the interference signal contained in the received signal (here FIG. 4 shows an example of the spectrum of the output signal (from the interference signal removal apparatus) immediately after removing the two-wave FM signal (immediately after the start of the interference signal removal processing operation). As shown in FIG. 12, in the signal output from the interference signal removal apparatus immediately after the start of the interference signal removal process, only the FM signal component is attenuated without attenuation of the CDMA signal component.
[0093]
However, in the interference signal removal apparatus as shown in the above conventional example, if the process is continued as it is after the interference signal removal process is started, the CDMA signal component in the received signal is gradually attenuated. There has been a problem that a slow decay has progressed over time.
[0094]
Specifically, FIG. 13 shows an example of the spectrum of the output signal (from the interference signal removal device) when the interference signal removal processing is continued for a while from the state shown in FIG. As shown in FIG. 13, when a certain time has elapsed since the start of the interference signal removal process, the CDMA signal component to be left in the output signal may be greatly attenuated.
As described above, the conventional interference signal removing apparatus has the ability to adaptively remove the narrowband interference signal, but gradually removes the CDMA signal as the desired wave as time passes. There was a malfunction.
[0095]
Here, the reason why such a problem occurs is that the frequency component of the CDMA signal located in the vicinity of the frequency of the interference signal has a correlation with the interference signal, that is, by the above-described arithmetic algorithm such as LMS, This is because the frequency component of the CDMA signal located near the frequency of the interference signal is also extracted as a signal component having a correlation with the interference signal. Therefore, with respect to the band of the CDMA signal, the CDMA signal in the band around the interference signal is also removed together with the interference signal. As a result, the bit error rate of the received signal after the interference removal is deteriorated. It was.
[0096]
FIG. 14 shows an example of interference signal removal characteristics when interference removal is performed using the interference signal removal apparatus as shown in the conventional example. In the figure, a state in which the bit error ratio (BER) of the received signal changes as interference signal cancellation characteristics is shown, and when interference cancellation is not performed by the interference signal cancellation device (when cancellation is not performed). On the other hand, the characteristic example in (a) is shown in (a), and the characteristic example in the case where interference removal is performed by the interference signal removal apparatus (in the case of cancellation) is shown in (b).
[0097]
In the figure, a CDMA signal is used as a wideband desired signal, while an FSK (Frequency Shift Keying) signal is used as a narrowband interference signal, and an example in which the interference signal is one wave is shown. It is shown. In addition, the horizontal axis of the graph in the figure represents D / U ((desired input signal power) / (narrowband interference signal power)) [dB] per interference signal, and the vertical axis represents the receiver. The bit error rate at.
[0098]
As shown in the figure, when the D / U is relatively small (that is, when the power of the narrowband interference signal is sufficiently larger than the power of the wideband desired signal), the interference signal removal device performs interference cancellation. By doing so, the characteristics of the bit error rate can be improved. On the other hand, when the D / U is relatively large (that is, when the power of the narrowband interference signal is approximately the same as the power of the wideband desired signal, or when the power of the wideband desired signal is small), If the interference signal is removed by the interference signal removal device, the bit error rate characteristics may be deteriorated.
[0099]
Here, a reason similar to the above can be considered as the reason why such deterioration occurs, that is, in the process of extracting the frequency component of the narrowband interference signal from the received signal and removing the extraction result from the received signal. This is probably because the interference signal removal device extracts and removes the frequency component of the desired broadband signal simultaneously with the interference signal.
[0100]
15A and 15B, the interference signal is removed from the received signal including the wideband signal and the narrowband interference signal by using the interference signal removal apparatus as shown in the conventional example. An example of how to do this is shown.
Specifically, FIG. 5A shows an example in which the power of a certain narrowband interference signal is sufficiently larger than the power of a wideband signal (for example, interference signals (1) and (3) in the figure). In this case, the reception quality can be improved by performing interference cancellation as described above.
[0101]
FIG. 4A shows three signals (1), (2), and (3) that interfere with a wideband signal, and the left side graph shows the state of the received signal before interference removal. On the other hand, the state of the received signal after interference removal is shown in the graph on the right side. Moreover, the horizontal axis of these graphs indicates the frequency, and the vertical axis indicates the spectrum intensity.
[0102]
On the other hand, FIG. 4B shows an example in which the power of each narrowband interference signal is (almost) equal (or the same when it is small) compared to the power of the wideband signal. As described above, since the frequency component of the wideband signal is extracted and removed together with the narrowband interference signal, the signal output from the interference signal removal device is a circuit in the subsequent stage (of the interference signal removal device). When the demodulation process is performed by the receiver, the degradation of the reception quality becomes so large that it cannot be ignored.
[0103]
For this reason, in the case as shown in FIG. 5B, it can be said that, for example, when the interference signal is not removed by the interference signal removal device, the reception quality is improved due to the interference signal suppression effect which is also a characteristic of the CDMA signal. .
FIG. 4B shows three signals (4), (5), and (6) that interfere with the broadband signal, and the state of the received signal before the interference removal is shown in the left graph. On the other hand, the state of the received signal after interference removal is shown in the graph on the right side. Moreover, the horizontal axis of these graphs indicates the frequency, and the vertical axis indicates the spectrum intensity.
[0104]
Further, for example, in the interference signal removal apparatus as shown in FIG. 6, the filter tap coefficient series h (t) is updated using the adaptive algorithm as shown in the above expression 5, so that the above expression 5 is obtained. Every time the next filter tap coefficient series h (t + 1) is calculated, the previous calculation result (h (t)) is always accumulated. For this reason, in such an interference signal removal device, there is a possibility that even a signal component of the wideband signal is extracted and a part of the wideband signal is removed due to the influence of intersymbol interference by a band limiting filter, for example. Even in such a case, as described above, it is possible that the degradation of the reception quality becomes so large that it cannot be ignored in the demodulation process at the receiver.
[0105]
As described above, the interference signal canceling apparatus as shown in the conventional example shows the interference signal canceling characteristic as shown in FIG. 14, for example, that is, the power of the narrowband signal is higher than the power of the wideband signal. When it is smaller, there is a problem that the reception quality characteristic may be deteriorated compared to the case where interference cancellation is not performed.
[0106]
Specifically, in the currently considered communication scheme, for example, in the situation where the CDMA scheme and the TDMA scheme are shared, or in the situation where the CDMA scheme and the FDMA scheme are shared, as shown in the conventional example above When a receiver incorporating an interference signal removal device is used, if there is no interference signal in the reception signal, the reception quality may be deteriorated. For example, the interference signal is not removed. In comparison with the above, problems such as a decrease in the number of mobile station apparatuses (number of users) that can be accommodated by the base station apparatus and a decrease in the call area are expected.
[0107]
The present invention has been made to solve such a conventional problem, and when removing an interference signal from an input signal including a wideband desired signal and a narrowband interference signal, the desired signal is also included. An object of the present invention is to provide an interference signal removing device that suppresses the removal.
[0108]
[Means for Solving the Problems]
In order to achieve the above object, the interference signal removal apparatus according to the present invention removes the interference signal from the input signal including the wideband desired signal and the narrowband interference signal as follows.
That is, based on the input signal, the interference signal included in the input signal is extracted with a reduced extraction amount (that is, smaller than that shown in the conventional example, for example), and the extracted interference signal is extracted from the input signal. Remove.
[0109]
Accordingly, since the extraction amount of the interference signal extracted from the input signal based on the input signal is suppressed, the desired signal (for example, the frequency of the interference signal) is obtained from the input signal including the wideband desired signal and the narrowband interference signal. It is possible to suppress the removal of the desired signal component in the band and the desired signal component in the band adjacent to the frequency band of the interference signal.
[0110]
As an example, when a CDMA signal is used as a wideband desired signal, when the interference signal is removed from a signal (a signal including a CDMA signal and a narrowband interference signal) received by the receiver, the interference removal By controlling the capability, it is possible to suppress the removal of even the CDMA signal component, thereby improving the bit error rate characteristics of the received signal after interference removal, for example, compared to the conventional case. it can.
[0111]
In other words, since a signal by a spread spectrum method (spread) such as the CDMA method has a high anti-interference ability due to the spread gain, a spread desired wave (CDMA) can be obtained without removing the narrowband interference signal more than necessary. It is sufficient that the power of the narrowband interference signal can be attenuated to the same level as the signal power of the signal. For this reason, by suppressing the interference removal capability to such an extent that components such as CDMA signals are not removed, for example, even if some interference signal components remain in the received signal, removal of components such as CDMA signals is suppressed. Overall, the bit error rate after interference cancellation can be improved.
[0112]
For example, when a plurality of narrowband interference signals are superimposed on a wideband desired signal and received by a receiver on a transmission path of a receiving system, the received signal is divided into a plurality of bands, By including one (or a plurality) of interference signals for each band and performing interference removal suitable for the interference signals included in each band, interference removal corresponding to each interference signal can be performed. Can be realized.
[0113]
Here, various signals may be used as the wideband desired signal. For example, a signal spread by the CDMA method may be used.
Various signals may be used as narrowband interference signals. For example, FM signals, FSK signals, and the like can be used.
[0114]
Various methods may be used as a method of suppressing the amount of interference signal extraction based on the input signal. For example, depending on the desired signal included in the input signal and the state of the interference signal, the interference signal It is preferable to control whether or not to suppress the extraction amount, and to control the degree of suppression in the case of suppression.
[0115]
Moreover, in the interference signal removal apparatus according to the present invention, as one embodiment, the interference signal is removed from an input signal including a wideband desired signal and a narrowband interference signal by the following configuration.
That is, the extraction means extracts the interference signal from the input signal, the removal means removes the extracted interference signal from the input signal, and the extraction control means controls the extraction of the interference signal by the extraction means based on the removal result of the removal means The extraction amount suppression unit suppresses the extraction amount of the interference signal by the extraction unit based on the input signal.
[0116]
Here, as a method of controlling the extraction of the interference signal by the extraction unit based on the removal result of the removal unit, for example, the component of the interference signal included in the input signal after the interference removal is performed by the removal unit is minimum ( Ideally, a method of controlling to be zero) is used. And in this invention, an extraction amount suppression means suppresses the extraction amount of an interference signal with respect to such a control method.
[0117]
For example, taking the interference signal removal apparatus as shown in FIG. 6 as an example, the extraction means according to the present invention is configured from the adaptive filter, the removal means according to the present invention is configured from the subtractor, and the filter tap coefficient calculation is performed. An extraction control means according to the present invention is configured from the control unit. And in this invention, the extraction amount suppression means which suppresses the extraction amount of an interference signal is further provided.
[0118]
In the interference signal removal apparatus according to the present invention, as a preferred aspect, the extraction amount suppression unit suppresses the extraction amount of the interference signal by the extraction unit based on a power difference between the desired signal and the interference signal included in the input signal. . That is, for example, when receiving a signal including a CDMA signal and a narrowband interference signal, the extraction amount of the interference signal is suppressed according to the difference between the reception power of the CDMA signal and the reception power of the narrowband interference signal.
Note that the power level of the desired signal and the power level of the interference signal included in the input signal can be detected, for example, by performing spectrum analysis of the input signal.
[0119]
Here, specific examples of how to suppress the extraction amount of the interference signal based on the power difference between the wideband signal (desired signal) and the narrowband interference signal are shown in the following (1) to (4).
(1) When the power of the wideband signal is larger by 5 dB or more than the power of the narrowband interference signal, the extraction amount of the interference signal is suppressed (to zero) so that interference cancellation is not performed.
(2) When the difference between the power of the wideband signal and the power of the narrowband interference signal is within ± 5 dB, weak interference removal is performed in order to realize that the wideband signal within the band of the interference signal is not so much removed. As is done, the amount of interference signal extraction is relatively large.
[0120]
(3) When the power of the narrowband interference signal is larger by 5 dB to 35 dB than the power of the wideband signal, the interference removal capability is strengthened according to the power of these signals than in the case of (2) above. The amount of interference signal extraction is suppressed.
(4) When the power of the narrowband interference signal is greater than the power of the wideband signal by 35 dB or more (for example, in the vicinity of the limit value of the interference signal removal capability), the interference removal capability is not controlled. Therefore, the extraction amount of the interference signal is not suppressed so that the maximum interference removal is performed.
[0121]
In this way, for example, according to the interference signal included in the input signal, the extraction amount is not suppressed (only) with respect to the interference signal having power of a predetermined magnitude or more, and the extraction amount is determined according to each interference signal. By performing the interference signal removal process that suppresses the interference signal, the interference signal is prevented from being removed when the characteristics of the input signal are better when the interference signal is not removed. When the interference signal extraction amount is suppressed to some extent and the characteristics of the input signal after interference removal are good, it is possible to appropriately suppress the interference signal extraction amount. For this reason, for example, when the interference signal is removed in the past, it is possible to prevent the deterioration of the (reception) quality of the input signal that is caused by the removal of the desired signal that is originally intended to be received (reception). Thereby, the bit error rate characteristic of the input signal after interference cancellation can be improved.
[0122]
Moreover, in the interference signal removal apparatus according to the present invention, as another aspect, the extraction amount suppression unit suppresses the extraction amount of the interference signal by the extraction unit based on the power of the desired signal included in the input signal. That is, for example, when receiving a signal including a CDMA signal and a narrowband interference signal, the extraction amount of the interference signal is suppressed according to the reception power of the CDMA signal.
[0123]
Here, in FIG. 2A and FIG. 2B, the interference signal is received from the received signal including the wideband signal and the narrowband interference signal by using the interference signal removing apparatus according to the present invention as described above. An example of how it is removed is shown.
[0124]
Specifically, FIG. 4A shows an example in which the power of a certain narrowband interference signal is sufficiently larger than the power of a wideband signal. In this case, for each interference signal, Appropriate interference cancellation is performed, that is, a narrowband interference signal having a reception level comparable to that of a wideband signal (for example, the interference signal (2) in the figure) is not subjected to interference cancellation processing, and the interference signal component is removed. For the narrowband interference signal having a strong reception level (for example, the interference signal (1) in the figure), the interference is removed without suppressing the extraction amount, and the narrowband interference signal having a relatively weak reception level (for example, the figure). For the interference signal (3) in the middle, the quality of the broadband signal after the interference removal processing can be improved, for example, by performing interference removal while suppressing the amount of extraction.
[0125]
FIG. 4A shows three signals (1), (2), and (3) that interfere with a wideband signal, and the left side graph shows the state of the received signal before interference removal. On the other hand, the state of the received signal after interference removal is shown in the graph on the right side. Moreover, the horizontal axis of these graphs indicates the frequency, and the vertical axis indicates the spectrum intensity.
[0126]
On the other hand, FIG. 4B shows an example in which the power of each narrowband interference signal is (almost) equal (or the same when it is small) compared to the power of the wideband signal. For narrowband interference signals (for example, interference signals (5) and (6) in the figure) having a reception level very close to that of the wideband signal, the interference signal component is left without performing interference removal processing, and the reception level is relatively high. For narrow-band interference signals with weakness (for example, interference signal (4) in the figure), by performing interference removal while suppressing the amount of extraction, the quality of the wideband signal after interference removal processing is improved, for example, to the conventional (input reception) This can be improved compared to a case where all narrowband interference signals are removed from the signal.
[0127]
FIG. 4B shows three signals (4), (5), and (6) that interfere with the broadband signal, and the state of the received signal before the interference removal is shown in the left graph. On the other hand, the state of the received signal after interference removal is shown in the graph on the right side. Moreover, the horizontal axis of these graphs indicates the frequency, and the vertical axis indicates the spectrum intensity.
Further, in FIG. 2A and FIG. 2B, the drop in the frequency spectrum of the wideband signal after the interference removal represents a portion from which the wideband signal component has been removed during the interference removal.
[0128]
Thus, in the interference signal removal apparatus according to the present invention, the interference signal corresponding to the desired signal or the interference signal included in the input signal is removed, for example, so that the power of the narrowband interference signal is smaller than the power of the wideband desired signal, for example. In such a case, it is possible to improve the characteristics of the input signal, and for example, even when the input signal includes a plurality of narrowband interference signals, it is possible to perform interference removal flexibly for each interference signal. is there.
[0129]
DETAILED DESCRIPTION OF THE INVENTION
An interference signal removing apparatus according to an embodiment of the present invention will be described with reference to the drawings.
In this embodiment, the interference signal removal apparatus is provided in a receiver that performs wireless communication, for example, and a signal received by the receiver (a signal including a desired signal in a wide band and an interference signal in a narrow band). The interference signal contained in is removed.
FIG. 1 shows an example of an interference signal removal apparatus according to the present invention. This apparatus includes an interference signal extraction unit 1, a combiner 2, an interference signal estimation unit 3, an extraction amount suppression unit 4, and the like. Is provided. Note that t indicates time.
[0130]
The interference signal estimation unit 3 receives, for example, a reception signal r (t) obtained by combining a desired signal in a wide band and a plurality of narrow-band interference signals and a reception signal e (t) after interference removal, and the interference cancellation The interference signal included in the subsequent received signal e (t) is estimated, and the estimation result is notified to the interference signal extraction unit 1.
The interference signal extraction unit 1 receives the reception signal r (t), and based on the estimation result notified from the interference signal estimation unit 3, the interference signal extraction unit 1 interprets the reception signal r (t) as an interference signal V ( t) is extracted, and the interference signal V (t) is output to the combiner 2.
[0131]
The synthesizer 2 has the reception signal r (t) and the interference signal V (t) from the interference signal extraction unit 1 in opposite phases (that is, the interference signal V (t) is removed from the reception signal r (t). The received signal e (t) after the interference signal V (t) is removed. Part of the received signal e (t) after interference output output from the combiner 2 is input to the above-described interference signal estimation unit 3 and used for estimation of the interference signal.
[0132]
The extraction amount suppression unit 4 receives the received signal r (t), and based on the power of the desired signal and the power of the interference signal included in the received signal r (t), for example, the power of the interference signal is relatively small. In such a case, interference is performed so that the amount of the interference signal V (t) extracted by the interference signal extraction unit 1 is suppressed (that is, smaller than the amount of interference signal extracted based on the estimation result). The signal estimation unit 3 is controlled.
[0133]
As described above, in the interference signal removal apparatus of the present example, the amount of interference signal extraction in the interference signal removal processing is suppressed based on the input signal, so that, for example, it is narrower than the power of the wideband desired signal. When the power of the band interference signal is about the same or small, it is possible to suppress the removal of even the wideband signal. For this reason, in the interference signal removal apparatus of this example, it is possible to improve the reception quality of the input signal (broadband signal) after the interference removal, for example, compared to the conventional case. ) Bit error rate characteristics can be improved.
[0134]
As an example, when a CDMA signal is used as a wideband desired signal and an FM signal or the like is used as a narrowband interference signal, an interference signal removal apparatus such as this example is provided in the receiver. For example, by allowing the residual interference signal to the same level as the CDMA signal, it is possible to improve the bit error rate characteristics of the reception signal after interference cancellation as a whole reception band.
[0135]
Here, in this example, the interference signal extraction unit 1 constitutes the extraction means according to the present invention, the combiner 2 constitutes the removal means according to the present invention, and the interference signal estimation unit 3 refers to the extraction control means according to the present invention. The extraction amount suppression means according to the present invention is configured from the extraction amount suppression unit 4.
[0136]
Here, the configuration of the interference signal removal apparatus according to the present invention is not necessarily limited to the configuration described above, and various configurations may be used. Specifically, for example, the interference signal removing apparatus according to the present invention can be applied to apparatuses having the configurations shown in FIG. 6, FIG. 8, FIG. 9, and FIG.
[0137]
Further, the field of application of the interference signal removal apparatus according to the present invention is not necessarily limited to the above-described fields, and the present invention can be applied to various fields. Specifically, the present invention is not limited to a receiver adopting, for example, a CDMA method, and the present invention can also be applied to a receiver such as a base station device, a mobile station device, a relay station device, or the like that adopts various communication methods. It is a thing.
[0138]
In addition, various processes performed by the interference signal removal apparatus according to the present invention include, for example, a control program stored in a ROM in a hardware resource including a processor (for example, a CPU, MPU, DSP, etc.), a memory, and the like. A configuration controlled by execution may be used, and for example, each functional unit for executing the processing may be configured as an independent hardware circuit.
Further, the present invention can be grasped as a computer-readable recording medium such as a floppy disk or a CD-ROM storing the above control program, and the control program is input from the recording medium to the computer and executed by the processor. Thus, the processing according to the present invention can be performed.
[0139]
【The invention's effect】
As described above, according to the interference signal removal device of the present invention, when removing the interference signal from the input signal including the wideband desired signal and the narrowband interference signal, the input signal is based on the input signal. The interference signal included in the signal is extracted while suppressing the extraction amount, and the extracted interference signal is removed from the input signal, so that it is possible to suppress removal of the desired signal from the input signal, Thereby, the quality of the input signal (desired signal) after interference removal can be improved as compared with, for example, the conventional case.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of an interference signal removing apparatus according to the present invention.
FIG. 2 is a diagram illustrating an example of a state in which an interference signal is removed from a received signal including a wideband signal and a narrowband interference signal by using the interference signal removal apparatus according to the present invention.
FIG. 3 is a diagram illustrating an example of an interference signal removing apparatus according to a conventional example.
FIG. 4 is a diagram for explaining an example of a spreading code sequence.
FIG. 5 is a diagram illustrating an example of a spectrum of a received signal including a wideband spread signal and a narrowband interference signal by a CDMA system.
FIG. 6 is a diagram illustrating an example of an interference signal removal apparatus.
FIG. 7 is a diagram illustrating a configuration example of an adaptive filter.
FIG. 8 is a diagram illustrating an example of an interference signal removing device.
FIG. 9 is a diagram illustrating an example of an interference signal removing apparatus.
FIG. 10 is a diagram illustrating an example of an interference signal removing device.
FIG. 11 is a diagram illustrating an example of a spectrum of a reception signal in which two FM signals interfere with a CDMA signal.
FIG. 12 is a diagram illustrating an example of a spectrum of a signal output from the interference signal removal apparatus immediately after the start of the interference signal removal process.
FIG. 13 is a diagram illustrating an example of a spectrum of a signal output from the interference signal removal device when a certain amount of time has elapsed since the start of the interference signal removal processing.
FIG. 14 is a diagram illustrating an example of interference signal removal characteristics by the interference signal removal device.
FIG. 15 is a diagram illustrating an example of a state in which an interference signal is removed from a reception signal including a wideband signal and a narrowband interference signal using the interference signal removal apparatus.
[Explanation of symbols]
1 .... Interference signal extraction unit, 2 .... Synthesizer, 3 .... Interference signal estimation unit,
4. Extraction amount control part,

Claims (1)

In an interference signal removing apparatus for removing an interference signal from a signal including a desired signal in a wide band and an interference signal in a narrow band,
An interference signal estimation unit, an interference signal extraction unit, a combiner, and an extraction amount suppression unit,
The interference signal estimation unit inputs a signal including the desired signal in the wide band and the interference signal in the narrow band and a part of the signal after the interference signal output from the combiner is removed, Estimating the interference signal included in the signal after the signal is removed, and notifying the interference signal extraction unit of the estimation result,
The interference signal extraction unit inputs a signal including the wideband desired signal and a narrowband interference signal, and extracts an interference signal from the signal based on an estimation result notified from the interference signal estimation unit. , Outputting the interference signal to the combiner,
The synthesizer synthesizes the signal including the desired signal in the wide band and the interference signal in the narrow band and the interference signal from the interference signal extraction unit in opposite phases, and outputs the signal after the interference signal is removed. Output,
The extraction amount suppression unit receives a signal including the wideband desired signal and a narrowband interference signal, and based on a power difference between the desired signal and the interference signal included in the signal, the interference signal extraction unit Having a function of controlling the interference signal estimation unit so that the amount of the interference signal extracted in (1) is suppressed,
An interference signal removing apparatus characterized by the above.

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