JP3798766B2 - Optical wireless communication system and optical receiver used in this optical wireless communication system - Google Patents

Description

【００２４】
式（１）の左辺のベクトルは、Ｓ１、Ｓ２、〜、Ｓｍを要素として配列したベクトルであり、これをＳで示す。右辺のベクトルは、Ｉ１、Ｉ２、〜、Ｉｎ要素として配列したベクトルであり、これをＩで示す。
【００２５】
また、信号処理部２２に入力されるｍ個の受光信号Ｓ１、Ｓ２、〜、Ｓｍと、信号処理部２２から出力されるｎ個の受信信号Ｏ１、Ｏ２、〜、Ｏｎとの関係は、φ11〜φnmを要素とする行列Φを用いて次式（２）のように示すことができる。
【数２】

【００２６】
式（２）の左辺のベクトルは、Ｏ１、Ｏ２、〜、Ｏｎを要素として配列したベクトルであり、これをＯで示す。
【００２７】
従って、受信信号Ｏ１、Ｏ２、〜、Ｏｎと送信信号Ｉ１、Ｉ２、〜、Ｉｎとの関係は、次式（３）で示される。
【数３】

【００２８】
すなわち、Ｏ＝Φ＊Ｈ＊Ｉと書くことができる。式（３）の右辺Φ＊Ｈは、ｎ行ｎ列の正方行列となり、行列Φを適切に決めることにより対角化することが可能である。すなわち、送信部１２から受信部２１に伝達される伝達係数行列Φと、信号処理部２２における伝達係数行列Ｈとの行列積Φ＊Ｈを、行列Φの各要素φ11〜φnmを適切に決めることにより対角化することができる。
【００２９】
以下に、Φを求める手順の例につき説明する。行列Φの要素φ11〜φnmの値はそれぞれ制御することができる。そこで、まず、信号処理部２２の伝達行列Ｈの要素を、次式（４）に示すように、要素φi,j＝1（i＝j）で、φi,j＝0（i≠j）となるように設定する。また、送信側の送信信号Ｉi（i＝1…n）を、一つを残してすべてゼロになるように設定する。
【００３０】
【数４】

【００３１】
式（４）においては、送信信号Ｉ１以外が全てゼロである場合を示す。式（４）から、ｈi,1＝Ｏi／Ｉ１（i＝1…n）を求めることができる。次に、送信信号Ｉ２以外をゼロとすることにより、ｈi,2＝Ｏi／Ｉ２（i＝1…n）を求めることができる。これを繰り返すことにより、最終的にｈi,j＝Ｏi／Ｉj（i＝1…n，j＝1…n）を求めることができる。
【００３２】
次に、ｈi,j（i＝n+1…m，j＝1…n）を求めるには、φi,j＝1{（i＝1，j＝n+1），（i＝2，j＝n+2）…（i＝m-n，j＝m）}、かつ、φi,j＝0｛その他｝とし、送信信号Ｉを、一つを残してすべてゼロになるように設定すればよい。その結果、ｈn+i,j＝Ｏi／Ｉj（i＝1…m-n，j＝1…n）を得ることができる。
【００３３】
以上より、信号処理部２２の伝達行列Ｈを特定の値とし、さらに、送信信号Ｉを一つを除きゼロに設定することにより、送信装置１０から光受信部へ伝達される伝達係数行列Φの各要素を算出することができる。
【００３４】
次に、行列Φと行列Ｈとの行列積は正方行列である。従って逆行列が存在し、これを（Φ・Ｈ）^-1・（Φ・Ｈ）＝Ｅと書くことができる。なお行列Ｅは単位行列である。従って、（Φ・Ｈ）^-1・Φを新しくΨと書くことにより、Ψ・Ｈ＝Ｅとすることができる。すなわち、Ｏ＝Ψ・Ｈ・Ｉ＝Ｅ・Ｉであり、送信装置１０から受信装置２０に伝達される伝達係数行列Φに依存せず、各送信信号Ｉ１〜Ｉｎを完全に独立した状態で伝送することが可能となる。
行列Ψを求めるには、Φを仮に設定し、Φ・Ｈの逆行列を求める。求めた逆行列とΦとの行列積を取ることで、（Φ・Ｈ）^-1・Φを求めることができる。
【００３５】
図３は、図２の構成をより詳細に示すブロック図である。図３に示されるように、送信部１２（図１）はそれぞれ送信信号Ｉ１〜Ｉ４が入力される光源２０１、２０３、２０５、２０７と、各光源ごとに設けられるレンズ２０２、２０４、２０６、２０８とを備える。各光源とレンズとの組を、投光器と称する。各レンズは各光源から出力される光信号を集束させる。
【００３６】
受信部２１は、空間を介して到来する複数系統の光信号を集光するレンズ２０９と、集積化された６個のフォトダイオード２１０、２１１、２１２、２１３、２１４、２１５とを備える。各フォトダイオードから出力される受光信号Ｓ１〜Ｓ６は信号処理部２２に入力され、４系統の受信信号Ｏ１〜Ｏ４が出力される。
【００３７】
図３において、光源２０１、２０３、２０５、２０７から出力される光信号はレンズ２０２，２０４，２０６，２０８によりその出力光ビーム広がり角を小さくされ、レンズ２０９に到達する。レンズ２０９は受信した光ビームをフォトダイオード上に集光させる。各フォトダイオード２１０、２１１、２１２，２１３、２１４、２１５の受光信号Ｓ１〜Ｓ６は、信号処理部２２に入力される。
【００３８】
図３に示すように、４個の光源から出力された光ビームは、それぞれフォトダイオード２１１、２１２、２１３、２１４により電気信号に変換される。フォトダイオード２１０、２１５上には、殆ど光信号が集光しないものとする。
【００３９】
フォトダイオード２１０、２１５に光信号が入力されない場合には、伝達係数行列Ｈを次式（５）のように記すことができる。
【数５】

【００４０】
式（５）は、それぞれ４つの投光器からの光信号が、独立にフォトダイオードに入力されたという仮定に基づく。
【００４１】
次に、信号処理部２２の伝達係数行列Ｈは、式（６）に示すようにΦを設定することにより行列Φとの行列積が単位行列になることが容易に分かる。
【数６】

【００４２】
行列Ｈと行列Φとの行列積を式（７）に示す。
【数７】

【００４３】
式（７）に示されるように、Ｏi＝Ｉi（i＝1,2,3,4）となり、信号処理部２２の処理により、送信信号Ｉ１〜Ｉ４を受信装置２０側においてそれぞれ独立して再現できることが分かる。
【００４４】
図４は、図３の受信装置２０が一方の方向（図中上方向）に傾いた状態を示す図である。図４に示すように、レンズ２０９を含む受信装置２０全体が上向きに傾いた場合を考える。この場合、レンズ２０９により絞り込まれた光ビームは、フォトダイオード２１０、２１１、２１２、２１３で受光され、フォトダイオード２１４、２１５には光が入射されない。この場合、伝達係数行列Ｈは次式（８）のように表すことができる。
【００４５】
【数８】

【００４６】
すなわち、この場合も、それぞれ４つの投光器からの光信号が独立にフォトダイオードに入力されたことになる。ただし、フォトダイオードに入射する光ビームが図３に比べて一つずつずれたことが示される。
【００４７】
次に、信号処理部２２の伝達係数行列Ｈは、式（９）に示すようにΦを設定することにより行列Φとの行列積を単位行列とすることができる。
【数９】

【００４８】
行列Ｈと行列Φの行列積を次式（１０）に示す。
【数１０】

【００４９】
式（１０）に示されるように、Ｏi＝Ｉi（i＝1,2,3,4）となり、信号処理部２２の処理により、送信信号Ｉ１〜Ｉ４を受信装置２０側においてそれぞれ独立して再現できることが分かる。また受信装置２０が上向きに傾いていても、信号処理部２２の出力Ｏi（i＝1,2,3,4）には、受信装置２０が傾いていない場合（図３）と同じ信号が出力されることが分かる。
【００５０】
図５は、図３の受信装置が他方の方向（図中下方向）に傾いた状態を示す図である。図５に示すように、レンズ２０９を含む受信装置２０全体が下向きに傾いた場合を考える。この場合、レンズ２０９により絞り込まれた光ビームは、フォトダイオード２１２、２１３、２１４、２１５で受光され、フォトダイオード２１０、２１１には光が入射されない。この場合、伝達係数行列Ｈは次式（１１）のように表すことができる。
【００５１】
【数１１】

【００５２】
すなわち、この場合も、それぞれ４つの投光器からの光信号が独立にフォトダイオードに入されたことになる。ただし、フォトダイオードに入射する光ビームが、図４から逆方向に一つずれたことを示している。
【００５３】
次に、信号処理部２２の伝達係数行列Ｈは、式（１２）に示すようにΦを設定することにより行列Φとの行列積を単位行列とすることができる。
【数１２】

【００５４】
行列Ｈと行列Φとの行列積を式（１３）に示す。
【数１３】

【００５５】
式（１３）に示されるように、Ｏi＝Ｉi（i＝1,2,3,4）となり、信号処理部２２の処理により、送信信号Ｉ１〜Ｉ４を受信装置２０側においてそれぞれ独立して再現できることが分かる。また受信装置２０が下向きに傾いていても、信号処理部２２の出力Ｏi（i＝1,2,3,4）には、受信装置２０が傾いていない場合（図３）と同じ信号が出力されることが分かる。
【００５６】
図３〜図５においては、送信装置１０から送出される光信号が受信装置２０のフォトダイオードにおいて独立して受信される場合が示される。このほか各フォトダイオードには、送信装置１０の複数の投光器出力が混在して入力される場合もある。このような場合でも信号処理部２２は、送信装置１０入力信号を独立して再現することができる。
【００５７】
図６は、信号処理部２２の一構成例を示す図である。図６において、受光信号Ｓ１〜Ｓ６はそれぞれ４系統に分岐され、いずれも乗算器３０１により行列Φの要素φij（i＝1…4，j＝1…6）と個別に乗算されたのち、系統ごとに加算器３０２により互いに加算される。このような構成により行列演算が実施される。
【００５８】
このように本実施形態では、送信信号Ｉ１〜Ｉｎを要素として配列したベクトルＩと、受光信号Ｓ１〜Ｓｍを要素として配列したベクトルＳとを、信号処理部２２における伝達係数行列Ｈを用いてＳ＝Ｈ＊Ｉなる式により互いに関係づける。また、受信信号Ｏ１〜Ｏｎを要素として配列したベクトルＯとベクトルＳとを、送信部１２から受信部２１に伝達される伝達係数行列Φを用いてＯ＝Φ＊Ｓなる式により互いに関係づける。そして、Ｏ＝Φ＊Ｈ＊Ｉなる式においてΦ＊Ｈを対角化することにより、空間を介して伝送される光信号の空間的な重なりをキャンセルし、各光信号から受信信号Ｏ１〜Ｏｎを独立して再生するようにしている。
【００５９】
このようにしたので、受信装置２０側において伝送信号を完全に再生することができ、しかも、伝送信号を分配した光信号のビットレートをもとの伝送信号よりも遅くすることができる。従って、伝送すべき伝送情報のビットレートが比較的高速であっても、送信ビームの広がり角度を大きくすることができるとともに、受信装置２０の方向精度を緩和することが可能となる。すなわち、高速信号を複数の光源を用いて並列に伝送することにより光ビーム１本あたりの伝送データ速度を低速とし、所定の受信ＳＮ比を得る受光電力を下げることができ、これにより送信装置１０からの出力ビーム広がりを大きくすることができる。従って、光送信出力電力の制限のもとで情報伝送の高速化を図り得る光無線通信システムおよびこの光無線通信システムで用いられる光受信装置を提供することができる。
【００６０】
（第２の実施形態）
図７は、本発明に関わる光無線通信システムの第２の実施の形態における要部構成を示すブロック図である。図７においては、信号処理部２２が送信装置１０側に設置される。図７において、ｎ系統の送信信号Ｉ１〜Ｉｎは信号処理部２２に入力され、ｍ系統の送信信号Ｓ１〜Ｓｍが生成される。各送信信号Ｓ１〜Ｓｍは、それぞれ光源４０２，４０４，４０６により光信号に変換される。各光源４０２，４０４，４０６から送出される光信号は、自由空間に放射されたのちｎ個の受光器４０３、４０５、４０７に到達し、受光信号Ｏ１、Ｏ２、〜、Ｏｎに変換される。
【００６１】
図７において、送信信号Ｓ１、Ｓ２、〜、Ｓｍと、受光信号Ｏ１、Ｏ２、〜、Ｏｎとの関係は次式（１４）のように示すことができる。
【数１４】

【００６２】
また、信号処理部２２に関わるｎ個の送信信号Ｉ１、Ｉ２、〜、Ｉｎと、ｍ個の送信信号Ｓ１、Ｓ２、〜、Ｓｍとの関係とから、受信装置２０における出力信号Ｏ１、Ｏ２、〜、Ｏｎと送信装置１０における入力信号Ｉ１、Ｉ２、〜、Ｉｎとの関係は、次式（１５）で示される。
【数１５】

【００６３】
すなわち、第１の実施形態と同様に、行列式によりＯ＝Ｈ＊Φ＊Ｉと書くことができる。式（１５）の右辺Ｈ＊Φは、ｎ行ｎ列の正方行列となり、行列Φを適切に決めることにより、Ｈ＊Φを対角化することが可能である。
【００６４】
以下に、本実施形態においてΦを求める手順の例につき説明する。行列Φの要素φ11〜φnmの値はそれぞれ制御することができる。そこで、まず、信号処理部２２の伝達行列Ｈの要素を、次式（１６）に示すように、要素φi,j＝1（i＝j）で、φi,j＝0（i≠j）となるように設定する。また、送信側の送信信号Ｉi（i＝1…n）を、一つを残してすべてゼロになるように設定する。
【００６５】
【数１６】

【００６６】
式（１６）においては、送信信号Ｉ１以外が全てゼロである場合を示す。式（１６）より、ｈi,1＝Ｏi／Ｉ１（i＝1…n）を求めることができる。次に、送信信号Ｉ２以外をゼロとすることにより、ｈi,2＝Ｏi／Ｉ２（i＝1…n）を求めることができる。これを繰り返すことにより、最終的にｈi,j＝Ｏi／Ｉj（i＝1…n，j＝1…n）を求めることができる。
【００６７】
次に、ｈi,j（i＝1…n，j＝n+1…m）を求めるには、φi,j＝1{（i＝n+1，j＝1），（i＝n+2，j＝2）…（i＝m，j＝m-n）}、かつ、φi,j＝0｛その他｝とし、送信信号Ｉを、一つを残してすべてゼロになるように設定すればよい。その結果、ｈi,n+j＝Ｏi／Ｉj（i＝1…n，j＝1…m-n）を得ることができる。
【００６８】
以上より、信号処理部２２の伝達行列Ｈを特定の値とし、さらに、送信信号Ｉを一つを除きゼロに設定することにより、送信装置１０から光受信部へ伝達される伝達係数行列Φの各要素を算出することができる。
【００６９】
次に、行列Φと行列Ｈとの行列積は正方行列である。従って逆行列が存在し、これを（Ｈ・Φ）・（Ｈ・Φ）^-1＝Ｅと書くことができる。よってΦ・（Ｈ・Φ）^-1＝ξと置くと、Ｈ・ξ＝Ｅとすることができる。すなわち、Ｏ＝Ｈ・ξ・Ｉ＝Ｅ・Ｉであり、送信装置１０から受信装置２０に伝達される伝達係数行列Φに依存せず、各送信信号Ｉ１〜Ｉｎを完全に独立した状態で伝送することが可能となる。
【００７０】
行列ξを求めるには、Φを仮に設定し、Ｈ・Φの逆行列を求める。求めた逆行列とΦとの行列積を取ることで、ξ＝Φ・（Ｈ・Φ）^-1から求めれば良い。
【００７１】
図８は、図７の構成をより詳細に示すブロック図である。図８に示されるように、送信信号Ｉ１、Ｉ２は信号処理部２２により処理され、送信信号Ｓ１、Ｓ２、Ｓ３、Ｓ４が生成出力される。各送信信号Ｓ１、Ｓ２、Ｓ３、Ｓ４は、光源５０２、５０４、５０６、５０８とレンズ５０３、５０５、５０７、５０９とをそれぞれ組み合わせた投光器により光信号に変換され、送信装置１０から出力される。
【００７２】
送信装置１０から出力された光ビームはレンズ５１０により集光され、フォトダイオード５１１、５１２により受光信号Ｏ１、Ｏ２に変換される。受信装置２０における受信信号Ｏ１、Ｏ２と、送信装置１０における送信信号Ｉ１、Ｉ２との関係を式（１７）に示す。
【数１７】

【００７３】
第１の実施形態と同様に、Ｈは送信装置１０から受信装置２０への伝達係数行列、Φは信号処理部２２の伝達係数行列である。式（１７）に示すようにΦを設定することにより、Ｏ１＝Ｉ１、Ｏ２＝Ｉ２が得られる。
【００７４】
図９は、図８の受信装置２０が一方の方向（図中上方向）に傾いた状態を示す図である。図９に示すように、レンズ５１０を含む受信装置２０全体が上向きに傾いた場合を考える。この場合、図８の状態から行列Ｈが変化する。しかしながらこの場合においても、式（１８）に示すように行列Φを変化させることにより、Ｏ１＝Ｉ１、Ｏ２＝Ｉ２なる結果を得られる。
【数１８】

【００７５】
図１０は、図８の受信装置２０が他方の方向（図中下方向）に傾いた状態を示す図である。この場合においても、行列Ｈは図８の状態から変化する。しかしながらこの場合においても、式（１９）に示すように行列Φを変化させることにより、Ｏ１＝Ｉ１、Ｏ２＝Ｉ２なる結果を得られる。
【数１９】

【００７６】
式（１７）、式（１８）、式（１９）に示すように、受信装置２０が送信装置１０からの光ビームの光軸に対して傾いていても、信号処理部２２の伝達係数行列Φを変化させることにより、受信装置２０おいて同一の受信信号を得ることができる。
【００７７】
図１１は、本実施形態に関わる信号処理部２２の構成例を示す図である。この構成においては、各送信信号Ｉ１，Ｉ２ごとに４系統のスイッチ６０１を設ける。そして、受信装置２０の傾きに応じて各スイッチ６０１を切り替えることにより、各送信信号Ｉ１，Ｉ２ごとに適用すべき伝達係数行列Φの要素φij（i＝1…4，j＝1…2）を変化させるようにしている。各送信信号Ｉ１，Ｉ２は各要素ごとに乗算されたのち加算器６０２において加算され、送信信号Ｓ１〜Ｓ４が得られる。なおスイッチ６０１をどのような切替状態に設定するかは、送信装置１０と受信装置２０との間でのデータリンク処理部３０（図１）を介した情報の授受により決定される。このような構成においても、第１の実施形態と同様の効果を得ることができる。
【００７８】
（第３の実施の形態）
図１２は、本発明に関わる光無線通信システムの第３の実施の形態における要部構成を示すブロック図である。図１２においては、信号処理部が送信装置１０側と受信装置２０側とに設置される。図１２において、ｎ系統の送信信号Ｉ１〜Ｉｎは信号処理部７０１に入力され、ｐ系統の送信信号Ｓ１〜Ｓｐが生成される。ここではｐをｎ以上の自然数とする。送信信号Ｓ１〜Ｓｐは光源７０２，７０４，７０６により光信号に変換される。各光源７０２，７０４，７０６から送出される光信号は、自由空間に放射されたのちｍ個の受光器７０３、７０５、７０７に到達し、受光信号Ｔ１、Ｔ２、〜、Ｔｍに変換される。ここでは、ｍをｎ以上の自然数とする。受光信号Ｔ１、Ｔ２、〜、Ｔｍは第２の信号処理部７０８に入力され、ｎ個の受信信号Ｏ１、Ｏ２、〜、Ｏｎが生成出力される。
【００７９】
図１２において、送信信号Ｓ１〜Ｓｐと受光信号Ｔ１〜Ｔｍとの関係は、式（２０）のように示すことができる。
【数２０】

【００８０】
また、信号処理部７０１に入力されるｎ個の送信信号Ｉ１、Ｉ２、〜、Ｉｎと、ｐ個の出力信号とＳ１、Ｓ２、〜、Ｓｐとの関係、および、信号処理部７０８に入力される受光信号Ｔ１、Ｔ２、〜、Ｔｍとｎ個の受信信号Ｏ１、Ｏ２、〜、Ｏｎとの関係とから、受信信号Ｏ１、Ｏ２、〜、Ｏｎと、送信信号Ｉ１、Ｉ２、〜、Ｉｎとの関係は次式（２１）で示される。
【数２１】

【００８１】
すなわち、行列式によりＯ＝α＊Ｈ＊β＊Ｉと書くことができる。行列αはα11〜αnmを要素とする行列であり、行列βはβ11〜βpnを要素とする行列である。式（２１）の右辺α＊Ｈ＊βはｎ行ｎ列の正方行列となり、行列αとβを適切に決めることにより、α＊Ｈ＊βを対角化することが可能である。ここで、行列αは第２の信号処理部７０８の伝達係数行列であり、行列βは第１の信号処理部７０１の伝達係数行列である。
【００８２】
行列βの要素が、βi,j＝1（i＝j）｛i＝1…p，j＝1…n，p>＝n｝の場合と、βi,j＝0｛i,jはその他｝の場合と、βi,j＝1（i＝j+p-n）｛i＝p-n+1…p，j＝1…n，p>＝n｝の場合と、βi,j＝0｛i,jはその他｝の場合とに分け、対角成分のみが１でありそれ以外の要素が０であるとすると、第１の実施の形態と同様に考えることができる。
【００８３】
第２の実施例にも記したように、送信側に配置される信号処理部は、その伝達係数行列の要素が対角成分のみ１となる場合のみを考えればよい。すなわち、送信側の第１の信号処理部７０１に入力される入力信号同士を合成すると、光信号が電力加算される。電力加算された光信号は、受信側で分離することは困難である。これは、光信号に生じる干渉を考慮しないことによる。逆に言えば、複数の光源で干渉を起こすことは避けるようにする必要がある。具体的には、複数の光源の波長をそれぞれ分離したり、ＬＥＤなどのコヒーレンシーの低い光源を使う必要がある。以下に、その具体例につき説明する。
【００８４】
図１３は、図１２の構成をより詳細に示すブロック図である。図１３に示されるように、送信信号Ｉ１、Ｉ２は信号処理部８０１により処理され、送信信号Ｓ１、Ｓ２、Ｓ３、Ｓ４が生成出力される。各送信信号Ｓ１、Ｓ２、Ｓ３、Ｓ４は、光源８０２、８０４、８０６、８０８とレンズ８０３、８０５、８０７、８０９とをそれぞれ組み合わせた投光器により光信号に変換され、送信装置１０から出力される。
【００８５】
送信装置１０から出力された光ビームはレンズ８１０により集光され、フォトダイオード８１１、８１２、８１３、８１４により受光信号Ｔ１、Ｔ２、Ｔ３、Ｔ４に変換されて出力される。受光信号Ｔ１〜Ｔ４は信号処理部８１５により処理されて受信信号Ｏ１、Ｏ２が生成出力される。受信装置２０の受信信号Ｏ１、Ｏ２と、送信装置１０の送信信号Ｉ１、Ｉ２との関係を式（２２）に示す。
【数２２】

【００８６】
式（２２）において、行列Ｈは送信装置１０から受信装置２０への伝達係数行列、行列αは第２の信号処理部８１５の伝達係数行列、βは第１の信号処理部８０１の伝達係数行列である。式（２２）に示すように、αとβとを適切に設定することにより、Ｏ１＝Ｉ１、Ｏ２＝Ｉ２が得られる。
【００８７】
図１４は、図１３の受信装置２０が一方の方向（図中上方向）に傾いた状態を示す図である。この場合、図１３の状態から行列Ｈが変化する。しかしながらこの場合においても、式（２３）に示すように行列αを変化させることにより、Ｏ１＝Ｉ１、Ｏ２＝Ｉ２なる結果を得られる。
【００８８】
【数２３】

【００８９】
一方、式（２４）に示すように、行列αは変化させずに行列βを変化させることにより、Ｏ１＝Ｉ１、Ｏ２＝Ｉ２なる関係を得ることも可能である。
【００９０】
【数２４】

【００９１】
図１５は、図１３の受信装置２０が他方の方向（図中下方向）に傾いた状態を示す図である。この場合においても、式（２３）または式（２４）に示すように行列αまたは行列βを変化させることにより、Ｏ１＝Ｉ１、Ｏ２＝Ｉ２なる結果を得ることができる。
【００９２】
以上のように本実施形態においても、式（２２）、式（２３）、式（２４）に示されるように各信号処理部の伝達係数行列を変化させることにより、受信装置２０において同一の受信結果を得ることができる。従って本実施形態においても第１および第２の実施形態と同様の効果を得ることができる。
【００９３】
なお本発明は、上記第１〜第３の実施形態そのままに限定されるものではない。例えば上記各実施形態においては、光源とレンズとを組み合わせたものを投光器とした。すなわち光源ごとに個別にレンズ用意したが、これに代えて、複数の光源からの光ビームを一つのレンズにより集束させるようにしても良い。また、受信装置２０において一つのレンズと複数の受光器の構成を示したが、複数のレンズと複数の受光器により受信装置２０を構成することも可能である。さらに信号処理部の例として乗算器と加算器とを備える構成を記したが、これに代えて、例えばディジタル処理を用いるなどの種々の変形例が考えられる。
【００９４】
また本発明は、実施段階ではその要旨を逸脱しない範囲で構成要素を変形して具体化できる。また、上記実施形態に開示されている複数の構成要素の適宜な組み合わせにより、種々の発明を形成できる。例えば、実施形態に示される全構成要素から幾つかの構成要素を削除してもよい。さらに、異なる実施形態にわたる構成要素を適宜組み合わせてもよい。
【００９５】
【発明の効果】
以上詳しく述べたように本発明によれば、光送信出力電力の制限のもとで情報伝送の高速化を図り得る光無線通信システムおよびこの光無線通信システムで用いられる光受信装置を提供することができる。
【図面の簡単な説明】
【図１】 本発明に関わる光無線通信システムの第１の実施の形態を示すブロック図。
【図２】 図１の送信装置１０および受信装置２０の要部構成を示すブロック図。
【図３】 図２の構成をより詳細に示すブロック図。
【図４】 図３の受信装置が一方の方向（図中上方向）に傾いた状態を示す図。
【図５】 図３の受信装置が他方の方向（図中下方向）に傾いた状態を示す図。
【図６】 信号処理部２２の一構成例を示す図。
【図７】 本発明に関わる光無線通信システムの第２の実施の形態における要部構成を示すブロック図。
【図８】 図７の構成をより詳細に示すブロック図。
【図９】 図８の受信装置２０が一方の方向（図中上方向）に傾いた状態を示す図。
【図１０】 図８の受信装置２０が他方の方向（図中下方向）に傾いた状態を示す図。
【図１１】 信号処理部２２の他の構成例を示す図。
【図１２】 本発明に関わる光無線通信システムの第３の実施の形態における要部構成を示すブロック図。
【図１３】 図１２の構成をより詳細に示すブロック図。
【図１４】 図１３の受信装置２０が一方の方向（図中上方向）に傾いた状態を示す図。
【図１５】 図１３の受信装置２０が他方の方向（図中下方向）に傾いた状態を示す図。
【符号の説明】
１０…送信装置、１１…分配処理部、１２…送信部、１３…送信制御部、２０…受信装置、２１…受信部、２２…信号処理部、２３…再生処理部、２４…受信制御部、２４ａ…演算処理部、３０…データリンク処理部、１００…送信装置、１０１，１０３…光源、１０２，１０４…受光器、２０１，２０３…光源、２０２，２０４，２０９…レンズ、２１０〜２１５…フォトダイオード、３０１…乗算器、３０２…加算器、４０２，４０４…光源、４０３，４０５…受光器、５０２，５０４…光源、５０３，５０５，５１０…レンズ、５１１，５１２…フォトダイオード、６０１…スイッチ、６０２…加算器、７０１…第１の信号処理部、７０２，７０４…光源、７０３，７０５…受光器、７０８…第２の信号処理部、８０１…第１の信号処理部、８０２，８０４…光源、８０３，８０５，８１０…レンズ、８１１，８１２…フォトダイオード、８１５…第２の信号処理部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical wireless communication system that transmits information through a free space using a light beam, and an optical receiver used in the optical wireless communication system. In particular, the present invention relates to an optical wireless communication system and an optical receiver that apply space division multiplexing technology.
[0002]
[Prior art]
An optical wireless communication system (or optical wireless) that transmits and receives an optical signal through free space does not require a station opening license. For this reason, the modulation band can be freely set, and it is considered to be an effective means for transmitting a large amount of data at high speed by radio. In addition, optical wireless is line-of-sight communication, and it is difficult to eavesdrop on radio waves, so that secure communication is possible.
[0003]
Well-known indoor optical wireless systems include remote control devices such as home audio / video equipment control and television receiver channel selection. Since the data transmission rate required for this type of device is relatively low at 1 Mbit / s or less, a sufficient SN ratio can be obtained on the receiving side even if the spread angle of the light beam transmitted from the transmission device is widened. It is possible to keep.
[0004]
In recent optical wireless communication systems, there is a need to increase the capacity of data transmission. For example, in a wall-mounted television in which a tuner unit and a display unit are separate, an application in which video data is transmitted from the tuner unit to the display unit requires a transmission capacity of about 100 Mbit / s.
[0005]
The transmission capacity mainly depends on an SN ratio (Signal to Noise Ratio) that can be secured on the receiving side. In order to ensure the S / N ratio, it is only necessary to increase the received optical power, and the simplest method is to increase the optical transmission output power. However, the optical transmission output power is strictly limited to ensure the safety of the user, and the upper limit is strictly set in the safety standards distributed by IEC, JIS, and the like. Therefore, in the existing large-capacity optical wireless communication system, the transmission light beam divergence angle is reduced to increase the optical power density on the receiving side, thereby obtaining a high SN ratio and increasing the transmission speed.
[0006]
However, if the light beam divergence angle is reduced, it is required to precisely match the optical axis between the transmitter and the receiver. Further, since the light receiving element for high-speed transmission needs to reduce its parasitic capacitance, the diameter of the light receiving part cannot be increased. For these reasons, in order to realize high-speed and large-capacity communication while suppressing the optical transmission output power, the direction of the light beam output from the transmitter and the direction of the light receiving part of the optical receiver are finely adjusted and adjusted. It is required to keep the later state.
[0007]
This requirement is difficult to achieve, especially in home applications. For example, vibrations caused by the user's walking easily cause transmission failure. Although such a situation can be dealt with by incorporating an automatic adjustment mechanism of the optical axis in the system, there is a concern that the configuration becomes very complicated, leading to an increase in cost. Furthermore, the requirement for severe accuracy in optical axis alignment means that the installation positions of the transmitter and the optical receiver are limited. This is also not preferable for household use.
[0008]
A technique related to this type of system is disclosed in Patent Document 1 below. This document describes a multi-polarization sensitive detection configuration that improves cross-channel interference and improves transmission reliability by applying weighting processing to multiple signals in a spatial division multiplexing transmission system using polarization multiplexing. ing.
[0009]
[Patent Document 1]
JP-A-6-75138 (paragraph numbers [0007] to [0011], FIG. 2)
[0010]
[Problems to be solved by the invention]
As described above, in the existing optical wireless communication system, due to the difficulty in adjusting the optical axis between the transmitter and the optical receiver under the limitation of the optical transmission output power, and the limitation of the cost, There is a problem that it is difficult to realize high-speed and large-capacity communication.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical wireless communication system capable of speeding up information transmission under the restriction of optical transmission output power and an optical receiver used in the optical wireless communication system. It is to provide.
[0011]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention converts transmission information into transmission signals of n (n is a natural number of 2 or more) systems.In time divisionDistributing means for distributing (for example, distribution processing unit 11), transmitting means for electrically / optically converting each of the n systems of transmission signals and transmitting n systems of optical signals to space (for example, transmitting section 12), and the systems of n systems The optical signal is converted from light to electricity to m (m isnLight receiving means (for example, receiving unit 21) that generates light receiving signals of the above-described natural number) system, signal processing means (for example, signal processing unit 22) that generates n systems of received signals from the m systems of light receiving signals,The n-system signals distributed by the distribution means are electrically / optically converted by the transmitting means and transmitted as optical signals, then received by the light-receiving means, optically / electrically converted, and output as m-system received light signals. Φ * H, where H is the transfer coefficient matrix up to and H is the transfer coefficient matrix of the signal processing means for generating n received signals from the m received light signals output from the light receiving means. Arithmetic means (for example, arithmetic processing unit 24a) for calculating each element of the transfer coefficient matrix Φ so that is a diagonal matrix, and the signal processing means is the transfer coefficient matrix calculated by the arithmetic means A matrix operation using each element of Φ is performed on the m systems of received light signals to generate the n systems of received signals.
[0012]
  By taking such measures, for example, transmission information having a transmission rate of 100 Mbit / s is converted into 10 (= n) transmission signals each having a transmission rate of 10 Mbit / s.In time divisionDistributed,Electrical / optical conversionIt is sent to space as an optical signal. The optical signals of these 10 systems arrive at each of the light receiving elements of the light receiving means including, for example, 12 (= m) light receiving elements, and a signal in a state where the optical signals of each system are mixed is photoelectrically converted in each light receiving element. Is done. That is, 12 light reception signals are generated, and 10 reception signals are generated from these light reception signals by the signal processing means.
[0013]
At that time, a matrix H that associates a vector I in which ten transmission signals are arranged as elements and a vector S in which twelve light reception signals are arranged as elements by an expression S = H * I, and ten received signals. Is defined as a matrix Φ that associates the vector O and the vector S, which are arranged as elements, with an expression O = Φ * S, the vector O is represented by an expression O = Φ * H * I. Since the vector I is already known, it should be possible to generate the vector O, that is, ten systems of received signals by diagonalizing Φ * H, and this processing is performed by the calculation means. The matrix Φ is a transmission coefficient matrix transmitted from the transmission means to the light receiving means, and the matrix H is a transmission coefficient matrix in the signal processing means.
[0014]
By diagonalizing Φ * H, the spatial overlap of the 10 optical signals transmitted through the space is canceled. Therefore, space division multiplex transmission is realized. At that time, the bit rate of each optical signal is 1 / n of transmission information to be transmitted. As n is increased, the bit rate of each optical signal can be freely reduced. As a result, it is possible to improve the signal-to-noise ratio related to signal transmission while relaxing various requirements relating to optical axis alignment and the like. Therefore, it is possible to increase the speed of information transmission under the restriction of optical transmission output power.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing a first embodiment of an optical wireless communication system according to the present invention. This system includes a transmission device 10, a reception device 20 that receives an optical signal transmitted from the transmission device via a space, and a data link that mediates exchange of various control information between the transmission device 10 and the reception device 20. And a processing unit 30.
[0016]
In FIG. 1, transmission information introduced into the transmission device 10 is distributed to a plurality of systems of transmission signals by a distribution processing unit 11. The bit rate of each distributed transmission signal is lower than that of transmission information. Each transmission signal is photoelectrically converted by the transmission unit and transmitted to the space as an optical signal having the same wavelength.
[0017]
Each optical signal arrives at the receiving unit 21 of the receiving device and is optical / electrically converted to generate a light receiving signal. The received light signal is introduced into the signal processing unit 22, and a plurality of received signals are generated. This received signal is input to the reproduction processing unit 23 to reproduce the transmission information.
[0018]
In the transmission device 10, various controls for the distribution processing unit 11 and the transmission unit 12 are performed by the transmission control unit 13. In the receiving device 20, various controls are performed on the receiving unit 21, the signal processing unit 22, and the reproduction processing unit 23 by the reception control unit 24. The transmission control unit 13 and the reception control unit 24 exchange information with each other via the data link processing unit 30.
[0019]
By the way, the reception control unit 24 includes an arithmetic processing unit 24a. The arithmetic processing unit 24 a calculates a coefficient for separating the reception signal from the light reception signal from the reception unit 21. That is, the arithmetic processing unit 24a has a matrix Φ for diagonalizing the matrix product Φ * H of the transmission coefficient matrix Φ transmitted from the transmission unit 12 to the reception unit 21 and the transmission coefficient matrix H in the signal processing unit 22. Calculate each element.
[0020]
FIG. 2 is a block diagram illustrating the main configuration of the transmission device 10 and the reception device 20 of FIG. The n (n is a natural number) transmission signals I1 to In generated by the distribution processing unit 11 in FIG. 1 are converted into optical signals by the light sources 101, 103, and 105, respectively. As the light source, an LED (light emitting diode) or an LD (semiconductor laser) can be used, and a logical binary electric signal is converted into an optical signal by turning on and off the applied current. Since the LD has a laser oscillation threshold value, an appropriate bias current is supplied in advance. Optical signals transmitted from the light sources 101, 103, and 105 are radiated to free space. A radiation angle may be reduced using a lens.
[0021]
Each optical signal is converted into electrical signals S1, S2,..., Sm by light receivers 102, 104, 106. In the present embodiment, the number of light receivers is m, which is a natural number greater than n. The light receivers 102, 104, and 106 may be any one that can convert an optical signal into an electric signal, such as a photodiode, an avalanche photodiode, or a photoconductor.
[0022]
The received light signals S1, S2,..., Sm respectively output from the m light receivers are input to the signal processing unit 22. The signal processing unit 22 outputs n-system received signals O1, O2,...
[0023]
2, the relationship between transmission signals I1, I2,..., In input to n light sources and light reception signals S1, S2,..., Sm output from m light receivers is expressed as h11 to hmn. It can be expressed as the following equation (1) using a matrix H as an element.
[Expression 1]

[0024]
The vector on the left side of Equation (1) is a vector in which S1, S2,..., Sm are arranged as elements. The vector on the right side is a vector arranged as I1, I2,..., In elements, and this is indicated by I.
[0025]
The relationship between the m received light signals S1, S2,..., Sm input to the signal processing unit 22 and the n received signals O1, O2,. It can be expressed as the following equation (2) using a matrix Φ having elements of ˜φnm.
[Expression 2]

[0026]
The vector on the left side of Equation (2) is a vector in which O1, O2,.
[0027]
Therefore, the relationship between the reception signals O1, O2,... On and the transmission signals I1, I2,.
[Equation 3]

[0028]
That is, O = Φ * H * I can be written. The right side Φ * H of Equation (3) is a square matrix of n rows and n columns, and can be diagonalized by appropriately determining the matrix Φ. That is, the matrix product Φ * H of the transmission coefficient matrix Φ transmitted from the transmission unit 12 to the reception unit 21 and the transmission coefficient matrix H in the signal processing unit 22 is appropriately determined for each element φ11 to φnm of the matrix Φ. Can be diagonalized.
[0029]
Hereinafter, an example of a procedure for obtaining Φ will be described. The values of the elements φ11 to φnm of the matrix Φ can be controlled. Therefore, first, the elements of the transfer matrix H of the signal processing unit 22 are represented by the following expression (4): element φi, j = 1 (i = j) and φi, j = 0 (i ≠ j) Set as follows. Further, the transmission signal Ii (i = 1... N) on the transmission side is set to be all zero except for one.
[0030]
[Expression 4]

[0031]
Equation (4) shows a case where all signals other than the transmission signal I1 are zero. From equation (4), hi, 1 = Oi / I1 (i = 1... N) can be obtained. Next, hi, 2 = Oi / I2 (i = 1... N) can be obtained by setting the values other than the transmission signal I2 to zero. By repeating this, finally, hi, j = Oi / Ij (i = 1... N, j = 1... N) can be obtained.
[0032]
Next, to obtain hi, j (i = n + 1 ... m, j = 1 ... n), φi, j = 1 {(i = 1, j = n + 1), (i = 2, j = N + 2)... (I = mn, j = m)} and φi, j = 0 {other}, and the transmission signal I may be set to be all zero except for one. As a result, hn + i, j = Oi / Ij (i = 1... M-n, j = 1... N) can be obtained.
[0033]
From the above, by setting the transfer matrix H of the signal processing unit 22 to a specific value and setting the transmission signal I to zero except for one, the transfer coefficient matrix Φ transmitted from the transmission device 10 to the optical reception unit Each element can be calculated.
[0034]
Next, the matrix product of the matrix Φ and the matrix H is a square matrix. Therefore, there is an inverse matrix, which is (Φ · H)^-1• (Φ · H) = E can be written. The matrix E is a unit matrix. Therefore, (Φ · H)^-1• By writing Φ as Ψ, Ψ · H = E can be obtained. That is, O = Ψ · H · I = E · I, and the transmission signals I1 to In are transmitted in a completely independent state without depending on the transfer coefficient matrix Φ transmitted from the transmission device 10 to the reception device 20. It becomes possible to do.
In order to obtain the matrix Ψ, Φ is temporarily set and an inverse matrix of Φ · H is obtained. By taking the matrix product of the obtained inverse matrix and Φ, (Φ · H)^-1・ Φ can be obtained.
[0035]
FIG. 3 is a block diagram showing the configuration of FIG. 2 in more detail. As shown in FIG. 3, the transmission unit 12 (FIG. 1) has light sources 201, 203, 205, and 207 to which transmission signals I1 to I4 are input, and lenses 202, 204, 206, and 208 provided for each light source. With. A set of each light source and lens is referred to as a projector. Each lens focuses an optical signal output from each light source.
[0036]
The receiving unit 21 includes a lens 209 that collects a plurality of systems of optical signals that arrive via a space, and six integrated photodiodes 210, 211, 212, 213, 214, and 215. The received light signals S1 to S6 output from each photodiode are input to the signal processing unit 22, and four received signals O1 to O4 are output.
[0037]
In FIG. 3, the optical signals output from the light sources 201, 203, 205, and 207 have their output light beam divergence angles reduced by the lenses 202, 204, 206, and 208 and reach the lens 209. The lens 209 collects the received light beam on the photodiode. The received light signals S <b> 1 to S <b> 6 of the photodiodes 210, 211, 212, 213, 214, and 215 are input to the signal processing unit 22.
[0038]
As shown in FIG. 3, the light beams output from the four light sources are converted into electric signals by the photodiodes 211, 212, 213, and 214, respectively. It is assumed that almost no optical signal is collected on the photodiodes 210 and 215.
[0039]
When no optical signal is input to the photodiodes 210 and 215, the transfer coefficient matrix H can be expressed as the following equation (5).
[Equation 5]

[0040]
Equation (5) is based on the assumption that the optical signals from each of the four projectors are independently input to the photodiode.
[0041]
Next, it can be easily understood that the transfer coefficient matrix H of the signal processing unit 22 has a unit product of a matrix product with the matrix Φ by setting Φ as shown in Expression (6).
[Formula 6]

[0042]
The matrix product of the matrix H and the matrix Φ is shown in Equation (7).
[Expression 7]

[0043]
As shown in Expression (7), Oi = Ii (i = 1, 2, 3, 4), and the transmission signals I1 to I4 are independently reproduced on the receiving device 20 side by the processing of the signal processing unit 22. I understand that I can do it.
[0044]
FIG. 4 is a diagram illustrating a state in which the receiving device 20 in FIG. 3 is tilted in one direction (upward in the drawing). As shown in FIG. 4, consider a case where the entire receiving device 20 including the lens 209 is inclined upward. In this case, the light beam focused by the lens 209 is received by the photodiodes 210, 211, 212, and 213, and no light is incident on the photodiodes 214 and 215. In this case, the transfer coefficient matrix H can be expressed as the following equation (8).
[0045]
[Equation 8]

[0046]
That is, also in this case, the optical signals from the four projectors are independently input to the photodiodes. However, it is shown that the light beam incident on the photodiode is shifted one by one as compared with FIG.
[0047]
Next, the transfer coefficient matrix H of the signal processing unit 22 can set a matrix product with the matrix Φ as a unit matrix by setting Φ as shown in the equation (9).
[Equation 9]

[0048]
The matrix product of the matrix H and the matrix Φ is shown in the following equation (10).
[Expression 10]

[0049]
As shown in Expression (10), Oi = Ii (i = 1, 2, 3, 4), and the transmission signals I1 to I4 are independently reproduced on the receiving apparatus 20 side by the processing of the signal processing unit 22. I understand that I can do it. Even if the receiving device 20 is tilted upward, the output Oi (i = 1, 2, 3, 4) of the signal processing unit 22 outputs the same signal as when the receiving device 20 is not tilted (FIG. 3). You can see that
[0050]
FIG. 5 is a diagram illustrating a state in which the receiving apparatus in FIG. 3 is tilted in the other direction (downward in the figure). As shown in FIG. 5, consider a case where the entire receiving device 20 including the lens 209 is inclined downward. In this case, the light beam narrowed down by the lens 209 is received by the photodiodes 212, 213, 214, and 215, and no light is incident on the photodiodes 210 and 211. In this case, the transfer coefficient matrix H can be expressed as in the following equation (11).
[0051]
## EQU11 ##

[0052]
That is, also in this case, the optical signals from the four projectors are independently input to the photodiodes. However, the light beam incident on the photodiode is shifted by one in the reverse direction from FIG.
[0053]
Next, the transfer coefficient matrix H of the signal processing unit 22 can set a matrix product with the matrix Φ as a unit matrix by setting Φ as shown in the equation (12).
[Expression 12]

[0054]
A matrix product of the matrix H and the matrix Φ is shown in Expression (13).
[Formula 13]

[0055]
As shown in Expression (13), Oi = Ii (i = 1, 2, 3, 4), and the transmission signals I1 to I4 are independently reproduced on the receiving apparatus 20 side by the processing of the signal processing unit 22. I understand that I can do it. Even if the receiving device 20 is inclined downward, the output Oi (i = 1, 2, 3, 4) of the signal processing unit 22 outputs the same signal as when the receiving device 20 is not inclined (FIG. 3). You can see that
[0056]
3 to 5 show a case where the optical signal transmitted from the transmission device 10 is received independently by the photodiode of the reception device 20. In addition, a plurality of projector outputs of the transmission device 10 may be input to each photodiode in a mixed manner. Even in such a case, the signal processing unit 22 can reproduce the input signal of the transmission device 10 independently.
[0057]
FIG. 6 is a diagram illustrating a configuration example of the signal processing unit 22. In FIG. 6, the received light signals S1 to S6 are branched into four systems, each of which is multiplied by an element φij (i = 1... 4 and j = 1... 6) of the matrix .PHI. And adder 302 adds each other. With such a configuration, matrix operation is performed.
[0058]
As described above, in the present embodiment, the vector I in which the transmission signals I1 to In are arranged as elements and the vector S in which the light reception signals S1 to Sm are arranged as elements are converted into S using the transfer coefficient matrix H in the signal processing unit 22. = H * I are related to each other. Further, the vector O and the vector S arranged with the received signals O1 to On as elements are related to each other by the equation O = Φ * S using the transfer coefficient matrix Φ transmitted from the transmitting unit 12 to the receiving unit 21. Then, by diagonalizing Φ * H in the equation O = Φ * H * I, the spatial overlap of the optical signals transmitted through the space is canceled, and the received signals O1 to On from each optical signal. To play independently.
[0059]
Since it did in this way, the transmission signal can be completely reproduced | regenerated in the receiver 20 side, and also the bit rate of the optical signal which distributed the transmission signal can be made slower than the original transmission signal. Therefore, even if the bit rate of transmission information to be transmitted is relatively high, the spread angle of the transmission beam can be increased and the direction accuracy of the receiving device 20 can be reduced. That is, by transmitting a high-speed signal in parallel using a plurality of light sources, the transmission data rate per light beam can be reduced, and the received light power for obtaining a predetermined reception S / N ratio can be reduced. The output beam spread from can be increased. Therefore, it is possible to provide an optical wireless communication system capable of speeding up information transmission under the restriction of optical transmission output power and an optical receiver used in this optical wireless communication system.
[0060]
(Second Embodiment)
FIG. 7 is a block diagram showing the main configuration of the optical wireless communication system according to the second embodiment of the present invention. In FIG. 7, the signal processing unit 22 is installed on the transmission device 10 side. In FIG. 7, n-system transmission signals I1 to In are input to the signal processing unit 22, and m-system transmission signals S1 to Sm are generated. The transmission signals S1 to Sm are converted into optical signals by the light sources 402, 404, and 406, respectively. The optical signals transmitted from the respective light sources 402, 404, and 406 reach the n light receivers 403, 405, and 407 after being radiated into free space, and are converted into the received light signals O1, O2,.
[0061]
In FIG. 7, the relationship between the transmission signals S1, S2,..., Sm and the light reception signals O1, O2,.
[Expression 14]

[0062]
Further, from the relationship between the n transmission signals I1, I2, ..., In related to the signal processing unit 22 and the m transmission signals S1, S2, ..., Sm, the output signals O1, O2, The relationship between On and On and the input signals I1, I2,..., In in the transmission apparatus 10 is expressed by the following equation (15).
[Expression 15]

[0063]
That is, as in the first embodiment, O = H * Φ * I can be written by a determinant. The right side H * Φ of Expression (15) is a square matrix of n rows and n columns, and H * Φ can be diagonalized by appropriately determining the matrix Φ.
[0064]
Hereinafter, an example of a procedure for obtaining Φ in the present embodiment will be described. The values of the elements φ11 to φnm of the matrix Φ can be controlled. Therefore, first, the elements of the transfer matrix H of the signal processing unit 22 are represented by the following expression (16): element φi, j = 1 (i = j) and φi, j = 0 (i ≠ j). Set as follows. Further, the transmission signal Ii (i = 1... N) on the transmission side is set to be all zero except for one.
[0065]
[Expression 16]

[0066]
Equation (16) shows a case where all signals other than the transmission signal I1 are zero. From equation (16), hi, 1 = Oi / I1 (i = 1... N) can be obtained. Next, hi, 2 = Oi / I2 (i = 1... N) can be obtained by setting the values other than the transmission signal I2 to zero. By repeating this, finally, hi, j = Oi / Ij (i = 1... N, j = 1... N) can be obtained.
[0067]
Next, to obtain hi, j (i = 1... N, j = n + 1... M), φi, j = 1 {(i = n + 1, j = 1), (i = n + 2 , J = 2)... (I = m, j = mn)} and φi, j = 0 {other}, and the transmission signal I may be set to be all zero except for one. As a result, hi, n + j = Oi / Ij (i = 1... N, j = 1... Mn) can be obtained.
[0068]
From the above, by setting the transfer matrix H of the signal processing unit 22 to a specific value and setting the transmission signal I to zero except for one, the transfer coefficient matrix Φ transmitted from the transmission device 10 to the optical reception unit Each element can be calculated.
[0069]
Next, the matrix product of the matrix Φ and the matrix H is a square matrix. Therefore, there is an inverse matrix, and this is expressed as (H · Φ) · (H · Φ)^-1= E can be written. Therefore Φ ・ (H ・ Φ)^-1By setting = ξ, H · ξ = E can be obtained. That is, O = H · ξ · I = E · I, and the transmission signals I1 to In are transmitted in a completely independent state without depending on the transmission coefficient matrix Φ transmitted from the transmission device 10 to the reception device 20. It becomes possible to do.
[0070]
In order to obtain the matrix ξ, Φ is temporarily set and an inverse matrix of H · Φ is obtained. By taking the matrix product of the obtained inverse matrix and Φ, ξ = Φ · (H · Φ)^-1You can ask for it.
[0071]
FIG. 8 is a block diagram showing the configuration of FIG. 7 in more detail. As shown in FIG. 8, the transmission signals I1 and I2 are processed by the signal processing unit 22, and the transmission signals S1, S2, S3, and S4 are generated and output. Each of the transmission signals S1, S2, S3, and S4 is converted into an optical signal by a projector that combines the light sources 502, 504, 506, and 508 and the lenses 503, 505, 507, and 509, and is output from the transmission apparatus 10.
[0072]
The light beam output from the transmission device 10 is collected by the lens 510 and converted into light reception signals O1 and O2 by the photodiodes 511 and 512. The relationship between the reception signals O1 and O2 in the reception device 20 and the transmission signals I1 and I2 in the transmission device 10 is shown in Expression (17).
[Expression 17]

[0073]
As in the first embodiment, H is a transfer coefficient matrix from the transmission device 10 to the reception device 20, and Φ is a transfer coefficient matrix of the signal processing unit 22. By setting Φ as shown in Expression (17), O1 = I1 and O2 = I2 are obtained.
[0074]
FIG. 9 is a diagram illustrating a state in which the receiving device 20 in FIG. 8 is tilted in one direction (upward in the figure). As shown in FIG. 9, a case is considered where the entire receiving device 20 including the lens 510 is inclined upward. In this case, the matrix H changes from the state of FIG. However, even in this case, the result of O1 = I1 and O2 = I2 can be obtained by changing the matrix Φ as shown in the equation (18).
[Formula 18]

[0075]
FIG. 10 is a diagram illustrating a state in which the receiving device 20 in FIG. 8 is tilted in the other direction (downward in the drawing). Also in this case, the matrix H changes from the state of FIG. However, even in this case, the result of O1 = I1 and O2 = I2 can be obtained by changing the matrix Φ as shown in the equation (19).
[Equation 19]

[0076]
As shown in Expression (17), Expression (18), and Expression (19), even if the reception apparatus 20 is inclined with respect to the optical axis of the light beam from the transmission apparatus 10, the transfer coefficient matrix Φ of the signal processing unit 22 is used. By changing the signal, the receiving device 20 can obtain the same received signal.
[0077]
FIG. 11 is a diagram illustrating a configuration example of the signal processing unit 22 according to the present embodiment. In this configuration, four systems of switches 601 are provided for each transmission signal I1, I2. Then, by switching each switch 601 in accordance with the inclination of the receiving device 20, the element φij (i = 1... 4, j = 1... 2) of the transfer coefficient matrix Φ to be applied to each transmission signal I1, I2. I try to change it. The transmission signals I1 and I2 are multiplied for each element and then added in the adder 602 to obtain transmission signals S1 to S4. Note that the switching state of the switch 601 is determined by the exchange of information between the transmission device 10 and the reception device 20 via the data link processing unit 30 (FIG. 1). Even in such a configuration, the same effect as in the first embodiment can be obtained.
[0078]
(Third embodiment)
FIG. 12 is a block diagram showing the main configuration of the third embodiment of the optical wireless communication system according to the present invention. In FIG. 12, signal processing units are installed on the transmitting device 10 side and the receiving device 20 side. In FIG. 12, n-system transmission signals I1 to In are input to a signal processing unit 701, and p-system transmission signals S1 to Sp are generated. Here, p is a natural number greater than or equal to n. The transmission signals S1 to Sp are converted into optical signals by the light sources 702, 704, and 706. The optical signals transmitted from the light sources 702, 704, and 706 reach the m light receivers 703, 705, and 707 after being radiated into free space, and are converted into the received light signals T1, T2,. Here, m is a natural number greater than or equal to n. The received light signals T1, T2,..., Tm are input to the second signal processing unit 708, and n received signals O1, O2,.
[0079]
In FIG. 12, the relationship between the transmission signals S1 to Sp and the light reception signals T1 to Tm can be expressed as shown in Expression (20).
[Expression 20]

[0080]
Also, the n transmission signals I1, I2,..., In that are input to the signal processing unit 701, the relationship between the p output signals and S1, S2,..., Sp, and the signal processing unit 708. From the relationship between the received light signals T1, T2,..., Tm and the n received signals O1, O2,..., On, the received signals O1, O2,. Is represented by the following equation (21).
[Expression 21]

[0081]
That is, O = α * H * β * I can be written by a determinant. The matrix α is a matrix having elements α11 to αnm, and the matrix β is a matrix having elements β11 to βpn. The right side α * H * β of equation (21) is a square matrix of n rows and n columns, and α * H * β can be diagonalized by appropriately determining the matrices α and β. Here, the matrix α is a transfer coefficient matrix of the second signal processing unit 708, and the matrix β is a transfer coefficient matrix of the first signal processing unit 701.
[0082]
The elements of the matrix β are βi, j = 1 (i = j) {i = 1... P, j = 1... N, p> = n}, and βi, j = 0 {i, j is other} .Beta.i, j = 1 (i = j + pn) {i = p-n + 1 ... p, j = 1 ... n, p> = n} and .beta.i, j = 0 {i, If j is the other}, and only the diagonal component is 1 and the other elements are 0, it can be considered as in the first embodiment.
[0083]
As described in the second embodiment, the signal processing unit arranged on the transmission side only needs to consider the case where the element of the transfer coefficient matrix is 1 only in the diagonal component. That is, when the input signals input to the first signal processing unit 701 on the transmission side are combined, the optical signal is power-added. It is difficult to separate the optical signal with the added power on the receiving side. This is because the interference generated in the optical signal is not taken into consideration. In other words, it is necessary to avoid interference with a plurality of light sources. Specifically, it is necessary to separate the wavelengths of a plurality of light sources or to use light sources with low coherency such as LEDs. Specific examples thereof will be described below.
[0084]
FIG. 13 is a block diagram showing the configuration of FIG. 12 in more detail. As shown in FIG. 13, the transmission signals I1 and I2 are processed by a signal processing unit 801, and transmission signals S1, S2, S3, and S4 are generated and output. Each of the transmission signals S1, S2, S3, and S4 is converted into an optical signal by a projector that is a combination of the light sources 802, 804, 806, and 808 and the lenses 803, 805, 807, and 809, and is output from the transmission apparatus 10.
[0085]
The light beam output from the transmitter 10 is collected by the lens 810, converted into light reception signals T1, T2, T3, and T4 by the photodiodes 811, 812, 813, and 814, and output. The received light signals T1 to T4 are processed by a signal processing unit 815 to generate and output received signals O1 and O2. The relationship between the reception signals O1 and O2 of the reception device 20 and the transmission signals I1 and I2 of the transmission device 10 is shown in Expression (22).
[Expression 22]

[0086]
In Expression (22), a matrix H is a transfer coefficient matrix from the transmission apparatus 10 to the reception apparatus 20, a matrix α is a transfer coefficient matrix of the second signal processing unit 815, and β is a transfer coefficient matrix of the first signal processing unit 801. It is. As shown in Expression (22), O1 = I1 and O2 = I2 can be obtained by appropriately setting α and β.
[0087]
FIG. 14 is a diagram illustrating a state in which the receiving device 20 in FIG. 13 is tilted in one direction (upward in the figure). In this case, the matrix H changes from the state of FIG. However, even in this case, the result of O1 = I1 and O2 = I2 can be obtained by changing the matrix α as shown in the equation (23).
[0088]
[Expression 23]

[0089]
On the other hand, as shown in Expression (24), it is possible to obtain a relationship of O1 = I1 and O2 = I2 by changing the matrix β without changing the matrix α.
[0090]
[Expression 24]

[0091]
FIG. 15 is a diagram illustrating a state in which the receiving device 20 in FIG. 13 is tilted in the other direction (downward in the drawing). Even in this case, the results of O1 = I1 and O2 = I2 can be obtained by changing the matrix α or the matrix β as shown in the equation (23) or the equation (24).
[0092]
As described above, also in the present embodiment, the reception device 20 receives the same reception by changing the transfer coefficient matrix of each signal processing unit as shown in Expression (22), Expression (23), and Expression (24). The result can be obtained. Therefore, also in this embodiment, the same effect as the first and second embodiments can be obtained.
[0093]
The present invention is not limited to the above first to third embodiments. For example, in each of the above embodiments, a projector is a combination of a light source and a lens. That is, a lens is prepared for each light source, but instead, a light beam from a plurality of light sources may be converged by a single lens. In addition, although the configuration of one lens and a plurality of light receivers is shown in the reception device 20, the reception device 20 can be configured by a plurality of lenses and a plurality of light receivers. Furthermore, although a configuration including a multiplier and an adder has been described as an example of the signal processing unit, various modifications such as using digital processing can be considered instead.
[0094]
Further, the present invention can be embodied by modifying the constituent elements without departing from the spirit of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.
[0095]
【The invention's effect】
As described above in detail, according to the present invention, there is provided an optical wireless communication system capable of speeding up information transmission under the restriction of optical transmission output power and an optical receiver used in the optical wireless communication system. Can do.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of an optical wireless communication system according to the present invention.
2 is a block diagram showing a main configuration of a transmission device 10 and a reception device 20 in FIG.
FIG. 3 is a block diagram showing the configuration of FIG. 2 in more detail.
4 is a diagram showing a state in which the receiving apparatus of FIG. 3 is tilted in one direction (upward in the figure).
5 is a diagram showing a state in which the receiving apparatus of FIG. 3 is tilted in the other direction (downward in the figure).
FIG. 6 is a diagram showing a configuration example of a signal processing unit 22;
FIG. 7 is a block diagram showing a main configuration of a second embodiment of an optical wireless communication system according to the present invention.
FIG. 8 is a block diagram showing the configuration of FIG. 7 in more detail.
9 is a diagram showing a state in which the receiving device 20 of FIG. 8 is tilted in one direction (upward in the figure).
10 is a diagram illustrating a state in which the receiving device 20 in FIG. 8 is tilted in the other direction (downward in the drawing).
11 is a diagram showing another configuration example of the signal processing unit 22. FIG.
FIG. 12 is a block diagram showing the main configuration of a third embodiment of an optical wireless communication system according to the present invention.
13 is a block diagram showing the configuration of FIG. 12 in more detail.
14 is a diagram showing a state in which the receiving device 20 of FIG. 13 is tilted in one direction (upward in the figure).
15 is a diagram showing a state in which the receiving device 20 of FIG. 13 is tilted in the other direction (downward in the figure).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Transmission apparatus, 11 ... Distribution processing part, 12 ... Transmission part, 13 ... Transmission control part, 20 ... Reception apparatus, 21 ... Reception part, 22 ... Signal processing part, 23 ... Reproduction processing part, 24 ... Reception control part, 24a ... arithmetic processing unit, 30 ... data link processing unit, 100 ... transmission device, 101, 103 ... light source, 102, 104 ... light receiver, 201, 203 ... light source, 202, 204, 209 ... lens, 210-215 ... photo Diode, 301 ... Multiplier, 302 ... Adder, 402, 404 ... Light source, 403, 405 ... Light receiver, 502, 504 ... Light source, 503, 505, 510 ... Lens, 511, 512 ... Photo diode, 601 ... Switch, 602: Adder, 701: First signal processing unit, 702, 704 ... Light source, 703, 705 ... Light receiver, 708 ... Second signal processing unit, 801 ... First signal processing Department, 802, 804 ... light source, 803,805,810 ... lens, 811 ... photodiode, 815: second signal processing unit

Claims (6)

Distribution means for distributing transmission information to transmission signals of n (n is a natural number of 2 or more) system in a time- sharing manner;
Transmitting means for electrically / optically converting each of the n-system transmission signals and transmitting the n-system optical signals to space;
A light receiving means for optically / electrically converting the n optical signals to generate a light receiving signal of m (m is a natural number equal to or greater than n );
Signal processing means for generating n systems of received signals from the m systems of received light signals;
The n-system signals distributed by the distribution means are electrically / optically converted by the transmitting means and transmitted as optical signals, then received by the light-receiving means, optically / electrically converted, and output as m-system received light signals. Φ * H, where H is the transfer coefficient matrix up to and H is the transfer coefficient matrix of the signal processing means for generating n received signals from the m received light signals output from the light receiving means. Computing means for calculating each element of the transfer coefficient matrix Φ so that is a diagonal matrix,
The signal processing means performs matrix calculation on each element of the transfer coefficient matrix Φ calculated by the calculation means on the m light reception signals to generate the n reception signals. Wireless communication system. The transmission means includes
N light sources for electrical / optical conversion of the n transmission signals,
The optical wireless communication system according to claim 1, further comprising a lens that collimates optical signals output from the n light sources. The light receiving means is
A lens for condensing the n-system optical signals coming through the space;
2. The optical wireless communication system according to claim 1, further comprising m light receiving elements that respectively optically / electrically convert the n optical signals collected by the lens. An optical wireless communication system for performing space division multiplexing and transmitting an optical signal between a transmission device and a reception device,
The transmitter is
Distribution means for distributing transmission information to transmission signals of n (n is a natural number of 2 or more) system in a time- sharing manner;
Transmission means for electrically / optically converting each of the n-system transmission signals and transmitting the n-system optical signals to space,
The receiving device is:
A light receiving means for optically / electrically converting the n optical signals coming through the space to generate m (m is a natural number greater than or equal to n ) optical signals;
Signal processing means for generating n systems of received signals from the m systems of received light signals;
The n-system signals distributed by the distribution means are electrically / optically converted by the transmitting means and transmitted as optical signals, then received by the light-receiving means, optically / electrically converted, and output as m-system received light signals. Φ * H, where H is the transfer coefficient matrix up to and H is the transfer coefficient matrix of the signal processing means for generating n received signals from the m received light signals output from the light receiving means. And calculating means for calculating each element of the transfer coefficient matrix Φ so that becomes a diagonal matrix,
The signal processing means performs matrix calculation on each element of the transfer coefficient matrix Φ calculated by the calculation means on the m light reception signals to generate the n reception signals. Wireless communication system. An optical wireless communication system for performing space division multiplexing and transmitting an optical signal between a transmission device and a reception device,
The transmitter is
Distribution means for distributing transmission information to n (n is a natural number of 2 or more) distribution signals in a time- sharing manner;
Signal processing means for generating m (m is a natural number greater than or equal to n ) transmission signals from the n distribution signals;
A transmission means for electrically / optically converting the m system transmission signals and transmitting the m system optical signals to space,
The receiving device is:
A light receiving means for optically / electrically converting the m systems of light signals coming through the space to generate n systems of light reception signals;
The n-system signals distributed by the distribution means are electrically / optically converted by the transmitting means and transmitted as optical signals, then received by the light-receiving means, optically / electrically converted, and output as m-system received light signals. Φ * H, where H is the transfer coefficient matrix up to and H is the transfer coefficient matrix of the signal processing means for generating n received signals from the m received light signals output from the light receiving means. And calculating means for calculating each element of the transfer coefficient matrix Φ so that becomes a diagonal matrix,
The signal processing means performs matrix operation on each element of the transfer coefficient matrix Φ calculated by the operation means on the n distribution signals to generate the m transmission signals. Wireless communication system. Distributing means for distributing optical information to n (n is a natural number of 2 or more) transmission signals in a time division manner used in an optical wireless communication system for transmitting optical signals by space division multiplexing, and the n transmission signals An optical receiver that receives the n optical signals output from an optical transmitter provided with a transmission unit that electrically / optically converts and transmits n optical signals to space,
A light receiving means for optically / electrically converting the n optical signals to generate a light receiving signal of m (m is a natural number equal to or greater than n );
Signal processing means for generating n systems of received signals from the m systems of received light signals;
The n-system signals distributed by the distribution means are electrically / optically converted by the transmitting means and transmitted as optical signals, then received by the light-receiving means, optically / electrically converted, and output as m-system received light signals. Φ * H, where H is the transfer coefficient matrix up to and H is the transfer coefficient matrix of the signal processing means for generating n received signals from the m received light signals output from the light receiving means. Computing means for calculating each element of the transfer coefficient matrix Φ so that is a diagonal matrix,
The signal processing means performs matrix calculation on each element of the transfer coefficient matrix Φ calculated by the calculation means on the m light reception signals to generate the n reception signals. Receiver device.

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