JP4362246B2 - Diversity reception sneak cancel device and relay system - Google Patents

Description

ここで、中継局送信信号Ｔ（ω）と加算部出力信号Ｏ（ω）は（４）式の関係にあり、（４）式を（３）式に代入して（５）式を得る。
【００３８】
【数３】

（５）式の各項を親局送信信号Ｓ（ω）と加算部出力信号Ｏ（ω）について整理して（６）式を得る。
【００３９】
【数４】

（６）を加算部出力信号Ｏ（ω）について解くと（７）式が得られる。
【００４０】
【数５】

系全体の伝達関数をＨ（ω）とすれば、Ｈ（ω）は（８）式で表される。
【００４１】
【数６】

ここで、まずダイバーシティ受信における等価条件として（９）式が成立すると仮定する。
【００４２】
【数７】
D1(ω)・M1(ω)+D2(ω)・M2(ω)＝D(ω) （９）
ここでＤ（ω）は周波数振幅特性が周波数によらず一定で信号の遅延だけが存在する伝達関数である。
【００４３】
さらに、ブランチ＃１およびブランチ＃２における回り込みのキャンセル条件として（１０）式、および（１１）式を仮定する。
【００４４】
【数８】
α・C1(ω)-L1(ω)＝０ (10)
α・C2(ω)-L2(ω)＝０ (11)
（９）式、（１０）式、（１１）式を（８）式に代入すると（１２）式が得られる。
【００４５】
【数９】

すなわち、（９）式に表すダイバーシティ受信における等化条件と（１０）式、（１１）式に示す回り込みキャンセル条件が満足されれば、系の伝達関数は単なる増幅率αと遅延のみで表すことが可能で、無歪み伝送となる。
【００４６】
次に適応フィルタの制御方法について説明する。
【００４７】
図２に示すように、各ブランチの回り込みキャンセルのための減算部３３_−１，３３_−２の出力を観測点とし、ブランチ＃１およびブランチ＃２における観測点をそれぞれ観測点Ｐ１、観測点Ｐ２とする。観測点Ｐ１と観測点Ｐ２における信号のスペクトルをＸ１（ω）、Ｘ２（ω）とするとＸ１（ω）、Ｘ２（ω）は（１３）式、（１４）式で表すことができる。
【００４８】
【数１０】
X1(ω)＝S(ω)・M1(ω)+C1(ω)・T(ω)-O(ω)・L1(ω) (13)
X2(ω)＝S(ω)・M2(ω)+C2(ω)・T(ω)-O(ω)・L2(ω) (14)
（１３）式、（１４）式に（４）式を代入して整理すると（１５）式、（１６）式が得られる。
【００４９】
【数１１】
X1(ω)＝S(ω)・M1(ω)+O(ω)・{α・C1(ω)-L1(ω)} (15)
X2(ω)＝S(ω)・M2(ω)+O(ω)・{α・C2(ω)-L2(ω)} (16)
ここで、ブランチ＃１のキャンセル残差信号のスペクトルをＥ１（ω）、ブランチ＃２のキャンセル残差信号のスペクトルをＥ２（ω）とするとＥ１（ω）、Ｅ２（ω）は（１７）式、（１８）式で表される。
【００５０】
【数１２】
E1(ω)＝α・C1(ω)-L1(ω) (17)
E2(ω)＝α・C2(ω)-L2(ω) (18)
（１７）式、（１８）式を（１５）式（１６）式に代入すると（１９）式、（２０）式が得られる。
【００５１】
【数１３】
X1(ω)＝S(ω)・M1(ω)+O(ω)・E1(ω) (19)
X2(ω)＝S(ω)・M2(ω)+O(ω)・E2(ω) (20)
ここでＯ（ω）はＸ１（ω）、Ｘ２（ω）、Ｄ１（ω）、Ｄ２（ω）を用いて（２１）式で表すことができる。
【００５２】
【数１４】
O(ω)＝X1(ω)・D1(ω)+X2(ω)・D2(ω) (21)
（２１）式を（１９）式、（２０）式に代入し、Ｅ１（ω）、Ｅ２（ω）について解くと（２２）式、（２３）式が得られる。
【００５３】
【数１５】

さらに、（２４）式、（２５）式に示すように観測点Ｐ１における信号のスペクトルＸ１（ω）を親局送信信号Ｓ（ω）で除算した結果をＨ１（ω）、観測点Ｐ２における信号のスペクトルＸ２（ω）を親局送信信号Ｓ（ω）で除算した結果をＨ２（ω）とする。
【００５４】
【数１６】

ここで、Ｈ１（ω）およびＨ２（ω）は、それぞれ観測点Ｐ１および観測点Ｐ２で観測した各ブランチにおける伝搬路の伝達関数に相当しており、観測点Ｐ１および観測点Ｐ２で取得したＯＦＤＭ信号の有効シンボル期間をＦＦＴ（高速フーリエ変換）してＸ１（ω）およびＸ２（ω）を示すキャリアデータを求め、さらに親局波送信信号のスペクトルＳ（ω）のうち既知のキャリアデータで除算することなどで求められる。各ブランチにおける伝搬路の伝達関数の算出法については、本発明者らの発明に係る学会発表論文「地上デジタル放送ＳＦＮにおける放送波中継用回り込みキャンセラの基礎検討」，映像情報メディア学会誌vol.54,No.11,pp.1568-1575（2000）などを参照されたい。
【００５５】
また、（２４）式、（２５）式を（２２）式、（２３）式に代入して整理すると（２６）式、（２７）式が得られる。
【００５６】
【数１７】

ここで、伝達関数Ｄ１（ω）、Ｄ２（ω）は装置自身が設定するため既知であるから、受信アンテナ１１と親局間の伝搬路特性を示す伝達関数Ｍ１（ω），Ｍ２（ω）が求められればブランチ＃１とブランチ＃２の回り込みキャンセル用の適応フィルタ３４_−１，３４_−２の伝達関数Ｌ１（ω），Ｌ２（ω）の補正量であるキャンセル残差信号のスペクトルＥ１（ω），Ｅ２（ω）を算出することが可能であり、Ｅ１（ω）、Ｅ２（ω）を逆フーリエ変換（ＩＦＦＴ）することで、回り込みキャンセル用の適応フィルタ３６_−１，３６_−２のフィルタ係数補正量を求めることができる。
【００５７】
次に、受信アンテナ１１と親局間の伝搬路特性を示す伝達関数Ｍ１（ω），Ｍ２（ω）を算出する手段について説明する。
【００５８】
まず、（１９）式、（２０）式に（２１）式を代入すると（２８）式、（２９）式を得る。
【００５９】
【数１８】
X1(ω)＝S(ω)・M1(ω)+X1(ω)・D1(ω)・E1(ω)+X2(ω)・D2(ω)・E1(ω) (28)
X2(ω)＝S(ω)・M2(ω)+X1(ω)・D1(ω)・E2(ω)+X2(ω)・D2(ω)・E2(ω) (29)
（２８）式、（２９）式をＸ１（ω）、Ｘ２（ω）について整理すると（３０）式、（３１）式が得られる。
【００６０】
【数１９】
X1(ω)・{1-D1(ω)・E1(ω)}-X2(ω)・D2(ω)・E1(ω)=S(ω)・M1(ω) (30)
X2(ω)・{1-D2(ω)・E2(ω)}-X1(ω)・D1(ω)・E2(ω)=S(ω)・M2(ω) (31)
（３０）式、（３１）式は（３２）式に示すようにＸ１（ω）、Ｘ２（ω）についての連立一次方程式となっている。
【００６１】
【数２０】

ここで（３２）式を解くと（３３）式、（３４）式が得られる。
【００６２】
【数２１】

（３３）式、（３４）式を、さらに整理すると（３５）式、（３６）式が得られる。
【００６３】
【数２２】

さらに、（２４）式、（２５）式に（３５）式、（３６）式を代入すると（３７）、（３８）式が得られる。
【００６４】
【数２３】

さらに（３７）式、（３８）式は（３９）式（４０）式のように書き換えられる。
【００６５】
【数２４】

ここでＡ（ω）とＢ（ω）は、それぞれ（４１）式、（４２）式で表される。
【００６６】
【数２５】
A(ω)＝D1(ω)・E1(ω)+D2(ω)・E2(ω) (41)
B(ω)＝M1(ω)・E2(ω)-M2(ω)・E1(ω) (42)
次に、（３９）式、（４０）式をＡ（ω）のべき乗級数に展開すると（４３）式、（４４）式が得られる。
【００６７】
【数２６】

ここで、（４３）式について考察する。中継局の親局受信に使用される受信アンテナ１１は、一般的に高利得であると同時に鋭い指向性を有しているため、親局受信に含まれるレベルの大きい遅延波（マルチパス）の遅延時間は比較的短いのが普通である。言い換えれば、伝達関数Ｍ１（ω）から求めた遅延プロファイル上の応答は遅延時間の短い領域に集まっている。次に、ダイバーシティ合成のための適応フィルタ３４の特性Ｄ１（ω）およびＤ２（ω）は、ダイバーシティ合成のための特性を生成すると同時に、先にも述べたように中継局系で最も狭帯域のＢＰＦの特性も合せて実現するため、伝達関数Ｍ１（ω）およびＭ２（ω）に含まれる遅延波の遅延時間に比べ、比較的大きな遅延時間を有する。また、Ａ（ω）は、Ｄ１（ω）、Ｄ２（ω）の項で成り立っているため、その遅延時間は、Ｄ１（ω）、Ｄ２（ω）と同等もしくはそれ以上となる。
【００６８】
したがって（４３）式の第１項以外は、すべてＤ１（ω）、Ｄ２（ω）以上の遅延時間を有することになり、Ｈ１（ω）の遅延プロファイル上において遅延時間の短い成分のみを取り出すことで、Ｍ１（ω）を分離取得することができる。この処理は周波数軸上ではＬＰＦ（low-pass filter）処理で実現できる。Ｍ２（ω）についても、Ｈ２（ω）に同様の処理を施すことで分離抽出することが可能である。この際、親局波に含まれる遅延波の遅延時間と装置の遅延時間の両方を考慮して、ダイバーシティ合成のための適応フィルタ３４_−１，３４_−２の遅延時間を最適に選ぶことが重要である。
【００６９】
＜周波数特性Ｄ１（ω）、Ｄ２（ω）について＞
ダイバーシティ合成のための適応フィルタ３４_−１の周波数特性Ｄ１（ω）と適応フィルタ３４_−２の周波数特性Ｄ２（ω）は、観測点Ｐ１および観測点Ｐ２で観測した信号の周波数特性から抽出した伝搬路特性Ｍ１（ω）、Ｍ２（ω）を用いて、求めることができる。これは、本発明者らの発明に係る特許出願の明細書（特願２０００−３５３２４５号「ＯＦＤＭデジタル信号中継装置」）や学会発表技術報告「スペースダイバシティを用いた地上デジタル放送の放送波中継の検討」，映像情報メディア学会技術報告Vol.25,No.31,pp.7-12,BCS2001-11（Mar.2001）に記述されているアルゴリズムに基いて決定すればよい。
【００７０】
なお、実際のＤ１（ω）およびＤ２（ω）は、Ｍ１（ω）およびＭ２（ω）を使用し特願２０００−３５３２４５号に記述されているアルゴリズムに基いて算出した特性に狭帯域ＢＰＦの特性を合成することで、親局信号の受信電力よりも回り込みの受信電力が大きい場合でも安定的な回り込みキャンセル動作が可能となる。
【００７１】
＜周波数特性Ｌ１（ω）、Ｌ２（ω）について＞
また、回り込みキャンセル用の適応フィルタ３６_−１の周波数特性Ｌ１（ω）および適応フィルタ３６_−２の周波数特性Ｌ２（ω）は、Ｄ１（ω）とＤ２（ω）とＭ１（ω）とＭ２（ω）を算出した後に、（２６）式と（２７）式を用いて各ブランチにおけるキャンセル残差信号のスペクトルＥ１（ω）およびＥ２（ω）を求め、本発明者らの発明に係る特許出願の明細書（特開２００1−９４５２８号「回り込みキャンセラ」）に記述されているアルゴリズムに基いて決定すればよい。
【００７２】
さらに、観測点Ｐ１または観測点Ｐ２で観測した信号が著しく劣化している場合に、観測信号が著しく劣化しているブランチの出力を停止することで、中継装置としてより安定的に動作させることが可能となる。例えば、観測した信号が著しく劣化していることを判定する方法として、本発明者らの発明に係る特許出願の明細書（特開２００１−１６０７９４号「回り込みキャンセラ」）に記述されているアルゴリズムに基いて回り込みのキャンセル残差による信号の劣化を検知し、一定の閾値を超える場合に、そのブランチのダイバーシティ合成のための適応フィルタ３４および回り込みキャンセル用の適応フィルタ３６の出力を停止し、その後ダイバーシティ合成のための適応フィルタ３４および回り込みキャンセル用の適応フィルタ３６の特性を再度作成することで実現できる。
【００７３】
特開２００１−１６０７９４号のアルゴリズムを簡単に記述すると、このアルゴリズムでは、ループ発振が検出されると、適応フィルタの出力を停止するとともに、中継装置の出力を減力または停止させるように制御する。この制御においては、受信変換部２１を構成するＡＧＣ回路の制御情報および／または送信変換部４１を構成するＡＧＣ回路の制御情報から、それらＡＧＣ回路がその利得を各々に規定された閾値よりも小さくしようと制御していることが判明された場合には、中継装置がループ発振していると判定する。あるいは、入力された回り込み観測信号の周波数振幅特性における振幅の最大値を回り込み観測信号の周波数振幅特性における振幅の最小値で除算した値が第１の閾値を超えたとき中継装置がループ発振していると判定する。さらに、入力された回り込み観測信号の周波数振幅特性における振幅の最大値を回り込み観測信号の周波数振幅特性における振幅の最小値で除算した値が第２の閾値を超えたとき中継装置がループ発振し得る危険性があると判定し、中継装置の出力を減力させて、ループ発振を未然に防止している。
【００７４】
以上、図２はダイバーシティ受信用の受信系統を２式用いたブランチ数２の構成における本発明の動作原理図を示す図であるが、当然ブランチ数Ｌの受信系統を用いた場合においても本発明は有効で、その変形は容易であり、ここでの説明は省略する。
【００７５】
また、ここで説明したダイバーシティのブランチ構成法に関しては、空間ダイバーシティ、偏波ダイバーシティ、角度ダイバーシティなど何れのブランチ構成法においても実現可能である。
【００７６】
【発明の効果】
以上説明したように本発明によれば、ＳＦＮにおいて放送波中継を行う中継局で、複数の受信系統を用いてダイバーシティ受信を行う中継局においても、送信アンテナから各受信系統への電波の回り込みを除去すると共に、各受信系統からの信号をダイバーシティ合成して中継局から再送信することが可能で、さらに、親局信号の受信電力よりも回り込みの受信電力が大きい場合でも安定的な回り込みキャンセル動作を可能とし、ダイバーシティ合成用の適応フィルタの特性と、回り込みキャンセル用の適応フィルタの特性を作成する信号処理も簡便化することが可能な回り込みキャンセル装置及び中継装置を提供することができる。
【図面の簡単な説明】
【図１】 本発明によるダイバーシティ受信用回り込みキャンセル装置及び中継装置の実施形態を示すブロック図である。
【図２】 本発明によるダイバーシティ受信用回り込みキャンセル装置及び中継システムの動作原理をブランチ数２の受信系統を用いた場合を例にブロック図にて示している。
【符号の説明】
１，１１−１，１１−２，・・・，１１−Ｌ ダイバーシティアンテナ ２ 受信装置
３ ダイバーシティ受信用回り込みキャンセル装置
４ 送信装置
５ 送信アンテナ
２１−１，２１−２，・・・，２１−Ｌ 受信変換部
３１−１，３１−２，・・・，３１−Ｌ ダウンコンバータ
３２−１，３２−２，・・・，３２−Ｌ 直交復調部
３３−１，３３−２，・・・，３３−Ｌ 減算部
３４−１，３４−２，・・・，３４−Ｌ ダイバーシティ合成用の適応フィルタ（ＦＩＲフィルタ）
３５ 加算部
３６−１，３６−２，・・・，３６−Ｌ 回り込みキャンセル用の適応フィルタ（ＦＩＲフィルタ）
３７ 直交変調部
３８ アップコンバータ
４１ 送信変換部
４２ 増幅部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a relay system in digital broadcasting and digital transmission based on an OFDM (Orthogonal Frequency Division Multiplexing) system, and in particular, a relay station that performs broadcast wave relay in an SFN (Single Frequency Network). Thus, the present invention relates to a wraparound canceling apparatus and a relay system for performing diversity reception using a reception system having a plurality of branches and removing wraparound of radio waves from a transmission antenna to each reception antenna (hereinafter simply referred to as wraparound).
[0002]
[Summary of Invention]
The present invention relates to the wraparound of radio waves between transmitting and receiving antennas of a relay broadcast station, which is a problem when realizing SFN (Single Frequency Network) by broadcast wave relay in digital broadcasting and digital transmission by OFDM. The present invention relates to a sneak cancel device for canceling out in a circuit and a relay system having a sneak cancel function, and in particular, a relay that receives signals from a master station by a plurality of (the number of branches) receiving systems and combines the received signals with diversity. A wraparound canceling apparatus and a relay system used in a station.
[0003]
[Prior art]
In a conventional relay system that relays OFDM signals, one set of receiving antennas is used for one set of relay systems as a general configuration. As a sneak cancel device having such a configuration, a patent application for a sneak cancel device according to the present invention (Japanese Patent Application Laid-Open No. 11-355160 “wraparound canceller”) and a conference paper “For broadcast wave relay in terrestrial digital direction SFN” "Basic study of wraparound canceller", Journal of the Institute of Image Information and Television Engineers Vol.54, No.11, pp.1568-1575 (2000).
[0004]
In addition, as a relay system for performing diversity reception, patent applications relating to the inventors' invention (Japanese Patent Application Nos. 2000-353245 and 2001-67267 are both “OFDM signal relay devices”) and a conference report “Space Diversity” are disclosed. ”Research on broadcast wave relay of terrestrial digital broadcasting using”, Technical Report Vol.25, No.31, pp.7-12, BCS2001-11 (Mar.2001) of the Institute of Image Information and Television Engineers. Not done.
[0005]
[Problems to be solved by the invention]
Since these conventional sneak cancel devices are algorithms based on the premise that a set of receiving antennas and a set of transmitting antennas are used for a set of relay devices, The algorithm is not adapted to a relay apparatus that performs diversity reception using a reception system having a plurality of branches.
[0006]
In addition, when the diversity receiver and the wraparound cancel device are simply connected in cascade, the wraparound characteristics change by changing the characteristics of each branch for diversity combining, so the diversity combining function and the wraparound cancel function cannot be compatible. It was.
[0007]
An object of the present invention is to provide a wraparound canceling apparatus and a relay system that can perform diversity reception and cancel wraparound at a relay station that relays broadcast waves at the same frequency.
[0008]
[Means for Solving the Problems]
  In order to achieve the above object, according to the present invention, in claim 1, the output from each branch of a receiving system having two or more branches receiving a signal having the same frequency and modulation content is substantially supplied to each subtracted terminal. And a subtraction unit for wraparound cancellation of the same number as the number of branches of the receiving system configured to be input to the subtraction terminal, respectively,
  Each of the outputs of the subtracting unit is input, and an adaptive filter unit for diversity synthesis equal to the number of branches of the receiving system to which filter coefficients for diversity synthesis are given,
  Each output of the adaptive filter unit for diversity combining is input, and an adder for diversity combining whose output is substantially output as a transmission signal of the relay station;
  The output of the adder is input, a filter coefficient for generating a wraparound duplicate signal is given, and the output is for the wraparound cancellation of the same number as the number of branches of the receiving system input to the subtraction terminal of each subtractor The adaptive filter section of
  Diversity reception sneak cancel device characterized by comprisingIn
  The adaptive filter unit for diversity combining provides a filter coefficient that also has a band pass filter characteristic that is the narrowest band in a system through which the OFDM signal of the relay system passes,
  Included in the signal from the master station that is equal to or greater than the delay time from the delay time of the known relay system including the delay by the adaptive filter unit for diversity synthesis and equal to the delay time and less than the delay time by diversity synthesis To detect the separated delayed wave,
  By setting the observation point of the signal to the output position of the subtraction unit, the characteristics of the adaptive filter unit for diversity synthesis and the characteristics of the adaptive filter unit for wraparound cancellation are detected together.It is characterized by that.
[0009]
  In claim 2, in the diversity reception sneak cancel device according to claim 1,
  When it is determined that the signal observed in each branch is significantly deteriorated, the output from the branch to the adder is stopped.It is characterized by the construction.
[0010]
  In claim 3,A relay system comprising the diversity reception sneak cancel device according to claim 1 or 2.It is a feature.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below in detail based on embodiments of the invention with reference to the accompanying drawings. In addition, regarding the display of signals and transfer functions in the following description, it is assumed that uppercase letters represent vectors representing complex numbers, and lowercase letters represent real numbers. Also, ω represents an angular frequency.
[0015]
FIG. 1 is a block diagram showing an embodiment of a relay system according to the present invention. The relay system shown in FIG. 1 includes a diversity antenna 1 having L branches, a receiving device 2, a diversity reception / wraparound canceling device 3, a transmitting device 4, and a transmitting antenna 5.
[0016]
Diversity antenna 1 has a number of branches L (branches # 1, # 2,... #L) receiving antennas 11 (11_-1, 11_-2, ..., 11_-L).
[0017]
The receiving device 2 performs frequency conversion of a signal from the receiving antenna 11 of each branch of the diversity antenna 1 from a receiving frequency to an IF (intermediate frequency) of a specific frequency, and performs bandpass filter processing and gain adjustment to output the receiving converting unit 21 (21_-1, 21_-2, ..., 21_-L).
[0018]
The diversity reception / wraparound canceling apparatus 3 converts a down converter 31 (31) that converts the frequency into a frequency that allows easy signal processing in accordance with the output of the reception antenna 11 of each branch._-1, 31_-2, ..., 31_-L) And an orthogonal demodulator 32 (32) for converting the output signal of the down converter 31 into a complex equivalent baseband signal._-1, 32_-2, ..., 32_-L) And a subtraction unit 33 (33 for canceling the wraparound)_-1, 33_-2, ..., 33_-L), And an FIR filter 34 (34) which is an adaptive filter for performing optimum weighting for each carrier on the signal from the receiving antenna 11 of each branch for diversity combining._-1, 34_-2, ..., 34_-L), An adder 35 for diversity combining the output of the FIR filter 34, and an FIR filter which is an adaptive filter that generates and outputs a duplicate signal of a sneak signal from the filter coefficient into which the output signal of the adder 35 is input and written 36 (36_-1, 36_-2, ..., 36_-L), An orthogonal modulation unit 37 that orthogonally modulates the equivalent baseband signal, and an up-converter 38 that converts the output signal of the orthogonal modulation unit 37 into an IF signal.
[0019]
The transmission device 4 converts the IF signal output from the diversity reception / wraparound cancellation device 3 into a transmission signal having a transmission frequency, amplifies the output signal of the transmission conversion unit 41, and supplies the amplified signal to the transmission antenna 5. An amplification unit 42 is included.
[0020]
The present invention relates to a relay system that performs retransmission at the same frequency. Since the frequency of the reception signal received by the diversity antenna 1 and the frequency of the transmission signal transmitted from the transmission antenna 5 are the same, The local oscillation (local oscillation) used for frequency conversion by the transmission conversion unit 41 is input by distributing the same local oscillation output to each other, or the local oscillation used for each is completely synchronized. Similarly, with respect to the local oscillators used for the down converter 31 and the up converter 38, the same local oscillator outputs are distributed and inputted to each other, or the local oscillators used for each are completely synchronized.
[0021]
In this embodiment, diversity combining and wraparound cancellation are performed in the equivalent baseband. However, in principle, the same can be realized regardless of the frequency such as IF or transmission / reception frequency. .
[0022]
  When this embodiment is performed by digital signal processing, an A / D converter that converts an analog signal into a digital signal is usually inserted between each down-converter 31 and each quadrature demodulator 32, and the digital signal is A D / A converter for converting to an analog signal is inserted between the quadrature modulation 37 and the up-converter 38, but diversity combining and wraparound cancellation are the same in principle regardless of whether the signal is an analog signal or a digital signal. In this embodiment, the A / D converter and the insertion position of the D / A converter are not specified. However, A / D converter in each branchTheWhen used, each A / D converter and D / A converter are operated by the same sampling clock.
[0023]
The principle of the present invention will be described below with reference to the operation principle diagram. FIG. 2 is a block diagram showing the operation principle of the present invention. Here, regarding the display of signals and transfer functions in FIG. 2, it is assumed that uppercase letters represent vectors representing complex numbers, and lowercase letters represent real numbers. Also, ω represents an angular frequency. In FIG. 2, a case where two reception systems of branch # 1 and branch # 2 are used will be described as an example.
[0024]
In FIG. 2, reference numeral 101 denotes a receiving antenna 11 of branch # 1._-1And a transfer function M1 (ω) indicating propagation path characteristics between the master station and the master station, 102 is a receiving antenna 11 of branch # 2._-2Transfer function M2 (ω) indicating the propagation path characteristic between the master station and the master station, 103 is a transfer function C1 (ω) indicating the sneak propagation path characteristic for the branch # 1, and 104 is a transfer function indicating the sneaking propagation path characteristic for the branch # 2. C2 (ω).
[0025]
In FIG. 2, S (ω) is the spectrum of the master station transmission signal, T (ω) is the transmission signal spectrum of the relay station, O1 (ω) is the output signal of branch # 1 at the diversity combining adder input, and O2 (Ω) indicates the output signal of branch # 2 at the diversity combining addition unit input, O (ω) indicates the output signal of the diversity combining addition unit 35, and α indicates the amplification degree of the amplification unit 42.
[0026]
As shown in FIG. 2, the structural feature of the relay system according to the present invention is that a feedback loop for wraparound cancellation is individually arranged for each branch # 1, # 2,. Adaptive filter (FIR filter) 34_-1, 34_-2Are arranged in a common part between the wraparound loop and the feedback loop for cancellation.
[0027]
The advantages of using such a circuit configuration are as follows.
[0028]
<< First advantage >>
Adaptive filter 34 for diversity combining_-1, 34_-2Is not disturbed, that is, the adaptive filter 34 satisfies the wraparound cancellation condition._-1, 34_-2The characteristics of are not related.
[0029]
<< Second advantage >>
The object is to reduce the delay amount of the apparatus. When the reception power of the sneak wave is larger than the reception power of the base station wave, the noise level outside the OFDM signal band rises at the output of the sneak cancel device, and this increased noise causes a loop oscillation and cancels the sneak wave. Will collapse.
[0030]
In order to solve such a problem, that is, in order to realize a stable wraparound cancellation in a negative DU ratio (Desired to Undesired Ratio) state, the present inventor has made a wraparound loop and feedback for cancellation. A proposal was made to arrange a BPF (band-pass filter) having the narrowest pass bandwidth in the relay station system in a common part of the loop (see Japanese Patent Application No. 2000-219277).
[0031]
In the configuration shown in FIG. 2, the adaptive filter 34 for diversity synthesis is used._-1, 34_-2In addition, it is possible to provide a narrow band BPF characteristic, and it is not necessary to newly add a narrow band BPF having a large delay amount, so that an increase in the delay amount of the apparatus can be prevented.
[0032]
《Third advantage》
The number of observation points of the signal serving as a reference for creating the characteristics of the adaptive filter 34 for diversity synthesis and the characteristics of the adaptive filter 36 for wraparound cancellation is the same as the number of branches. For example, when the diversity receiver and the sneak cancel device are simply connected in cascade, the signal before and after the sneak cancel device can be separated even if the multipath delay wave and sneak wave included in the signal from the master station can be separated. Observation points are required, and signal processing is complicated. In the configuration shown in FIG. 2, the number of observation points of the signal can be reduced, and the signal processing for creating the characteristics of the adaptive filter 34 for diversity synthesis and the characteristics of the adaptive filter 36 for wraparound cancellation from the observed signal is simplified. can do.
[0033]
<Operation Principle of the Present Invention>
The operation principle of the present invention will be described below using mathematical expressions.
[0034]
  Diversity synthesis adder35The output signal O1 (ω) of the branch # 1 and the output signal O2 (ω) of the branch # 2 that are the input signals are expressed by the equations (1) and (2).
[0035]
[Expression 1]
O1 (ω) ＝ D1 (ω) ・ {S (ω) ・ M1 (ω) + C1 (ω) ・ T (ω) -O (ω) ・ L1 (ω)} (1)
O2 (ω) ＝ D2 (ω) ・ {S (ω) ・ M2 (ω) + C2 (ω) ・ T (ω) -O (ω) ・ L2 (ω)} (2)
[0036]
The output signal O (ω) of the diversity combining adder is expressed by equation (3) using equations (1) and (2).
[0037]
[Expression 2]

Here, the relay station transmission signal T (ω) and the adder output signal O (ω) are in the relationship of Equation (4), and Equation (5) is obtained by substituting Equation (4) into Equation (3).
[0038]
[Equation 3]

Each term of the equation (5) is arranged for the master station transmission signal S (ω) and the adder output signal O (ω) to obtain the equation (6).
[0039]
[Expression 4]

When (6) is solved for the adder output signal O (ω), equation (7) is obtained.
[0040]
[Equation 5]

Assuming that the transfer function of the entire system is H (ω), H (ω) is expressed by equation (8).
[0041]
[Formula 6]

Here, first, it is assumed that equation (9) is established as an equivalent condition in diversity reception.
[0042]
[Expression 7]
D1 (ω) ・ M1 (ω) + D2 (ω) ・ M2 (ω) ＝ D (ω) (9)
Here, D (ω) is a transfer function in which the frequency amplitude characteristic is constant regardless of the frequency and only a signal delay exists.
[0043]
Furthermore, Equations (10) and (11) are assumed as wraparound cancellation conditions in branch # 1 and branch # 2.
[0044]
[Equation 8]
α ・ C1 (ω) -L1 (ω) = 0 (10)
α ・ C2 (ω) -L2 (ω) = 0 (11)
Substituting Equations (9), (10), and (11) into Equation (8) yields Equation (12).
[0045]
[Equation 9]

That is, if the equalization condition in diversity reception expressed by equation (9) and the wraparound cancellation condition expressed by equations (10) and (11) are satisfied, the transfer function of the system should be expressed only by the amplification factor α and the delay. Can be transmitted without distortion.
[0046]
Next, an adaptive filter control method will be described.
[0047]
As shown in FIG. 2, a subtractor 33 for canceling the wraparound of each branch_-1, 33_-2And the observation points in branch # 1 and branch # 2 are observation point P1 and observation point P2, respectively. If the spectrum of the signal at the observation point P1 and the observation point P2 is X1 (ω) and X2 (ω), X1 (ω) and X2 (ω) can be expressed by equations (13) and (14).
[0048]
[Expression 10]
X1 (ω) ＝ S (ω) ・ M1 (ω) + C1 (ω) ・ T (ω) -O (ω) ・ L1 (ω) (13)
X2 (ω) ＝ S (ω) ・ M2 (ω) + C2 (ω) ・ T (ω) -O (ω) ・ L2 (ω) (14)
By substituting (4) into (13) and (14) and rearranging, (15) and (16) are obtained.
[0049]
## EQU11 ##
X1 (ω) ＝ S (ω) ・ M1 (ω) + O (ω) ・ {α ・ C1 (ω) -L1 (ω)} (15)
X2 (ω) ＝ S (ω) ・ M2 (ω) + O (ω) ・ {α ・ C2 (ω) -L2 (ω)} (16)
Here, assuming that the spectrum of the cancellation residual signal of branch # 1 is E1 (ω) and the spectrum of the cancellation residual signal of branch # 2 is E2 (ω), E1 (ω) and E2 (ω) are expressed by Equation (17). , (18).
[0050]
[Expression 12]
E1 (ω) ＝ α ・ C1 (ω) -L1 (ω) (17)
E2 (ω) ＝ α ・ C2 (ω) -L2 (ω) (18)
When the equations (17) and (18) are substituted into the equations (15) and (16), the equations (19) and (20) are obtained.
[0051]
[Formula 13]
X1 (ω) ＝ S (ω) ・ M1 (ω) + O (ω) ・ E1 (ω) (19)
X2 (ω) ＝ S (ω) ・ M2 (ω) + O (ω) ・ E2 (ω) (20)
Here, O (ω) can be expressed by equation (21) using X1 (ω), X2 (ω), D1 (ω), and D2 (ω).
[0052]
[Expression 14]
O (ω) ＝ X1 (ω) ・ D1 (ω) + X2 (ω) ・ D2 (ω) (21)
Substituting equation (21) into equations (19) and (20) and solving for E1 (ω) and E2 (ω), equations (22) and (23) are obtained.
[0053]
[Expression 15]

Further, as shown in the equations (24) and (25), the result obtained by dividing the spectrum X1 (ω) of the signal at the observation point P1 by the master station transmission signal S (ω) is H1 (ω), and the signal at the observation point P2 H2 (ω) is the result of dividing the spectrum X2 (ω) by the master station transmission signal S (ω).
[0054]
[Expression 16]

Here, H1 (ω) and H2 (ω) correspond to the transfer function of the propagation path in each branch observed at the observation point P1 and the observation point P2, respectively, and OFDM acquired at the observation point P1 and the observation point P2. The effective symbol period of the signal is subjected to FFT (Fast Fourier Transform) to obtain carrier data indicating X1 (ω) and X2 (ω), and further divided by the known carrier data in the spectrum S (ω) of the base station wave transmission signal It is required by doing. As for the calculation method of the transfer function of the propagation path in each branch, a paper published in the academic society related to the inventors' invention “basic examination of wraparound canceller for broadcast wave relay in digital terrestrial broadcasting SFN”, Journal of the Institute of Image Information and Television Engineers vol.54 No. 11, pp. 1568-1575 (2000).
[0055]
Further, when formulas (24) and (25) are substituted into formulas (22) and (23) and rearranged, formulas (26) and (27) are obtained.
[0056]
[Expression 17]

Here, since the transfer functions D1 (ω) and D2 (ω) are known because they are set by the apparatus itself, transfer functions M1 (ω) and M2 (ω) indicating propagation path characteristics between the receiving antenna 11 and the master station are known. Is obtained, the adaptive filter 34 for wraparound cancellation of the branch # 1 and the branch # 2_-1, 34_-2It is possible to calculate spectra E1 (ω) and E2 (ω) of the cancellation residual signal, which are correction amounts of the transfer functions L1 (ω) and L2 (ω) of E1 (ω) and E2 (ω). Is subjected to an inverse Fourier transform (IFFT), so that the adaptive filter 36 for wraparound cancellation_-1, 36_-2The filter coefficient correction amount can be obtained.
[0057]
Next, means for calculating transfer functions M1 (ω) and M2 (ω) indicating propagation path characteristics between the receiving antenna 11 and the master station will be described.
[0058]
First, by substituting equation (21) into equations (19) and (20), equations (28) and (29) are obtained.
[0059]
[Formula 18]
X1 (ω) ＝ S (ω) ・ M1 (ω) + X1 (ω) ・ D1 (ω) ・ E1 (ω) + X2 (ω) ・ D2 (ω) ・ E1 (ω) (28)
X2 (ω) ＝ S (ω) ・ M2 (ω) + X1 (ω) ・ D1 (ω) ・ E2 (ω) + X2 (ω) ・ D2 (ω) ・ E2 (ω) (29)
When formulas (28) and (29) are arranged with respect to X1 (ω) and X2 (ω), formulas (30) and (31) are obtained.
[0060]
[Equation 19]
X1 (ω) ・ {1-D1 (ω) ・ E1 (ω)}-X2 (ω) ・ D2 (ω) ・ E1 (ω) = S (ω) ・ M1 (ω) (30)
X2 (ω) ・ {1-D2 (ω) ・ E2 (ω)}-X1 (ω) ・ D1 (ω) ・ E2 (ω) = S (ω) ・ M2 (ω) (31)
Equations (30) and (31) are simultaneous linear equations for X1 (ω) and X2 (ω) as shown in equation (32).
[0061]
[Expression 20]

If equation (32) is solved here, equations (33) and (34) are obtained.
[0062]
[Expression 21]

When the equations (33) and (34) are further arranged, equations (35) and (36) are obtained.
[0063]
[Expression 22]

Furthermore, when the expressions (35) and (36) are substituted into the expressions (24) and (25), the expressions (37) and (38) are obtained.
[0064]
[Expression 23]

Furthermore, Expressions (37) and (38) can be rewritten as Expressions (39) and (40).
[0065]
[Expression 24]

Here, A (ω) and B (ω) are expressed by equations (41) and (42), respectively.
[0066]
[Expression 25]
A (ω) ＝ D1 (ω) ・ E1 (ω) + D2 (ω) ・ E2 (ω) (41)
B (ω) ＝ M1 (ω) ・ E2 (ω) -M2 (ω) ・ E1 (ω) (42)
Next, when Expressions (39) and (40) are expanded to a power series of A (ω), Expressions (43) and (44) are obtained.
[0067]
[Equation 26]

Here, the equation (43) will be considered. Since the receiving antenna 11 used for the master station reception of the relay station generally has a high directivity and a sharp directivity, a high-level delayed wave (multipath) included in the master station reception is used. The delay time is usually relatively short. In other words, the responses on the delay profile obtained from the transfer function M1 (ω) are gathered in a region with a short delay time. Next, the characteristics D1 (ω) and D2 (ω) of the adaptive filter 34 for diversity combining generate characteristics for diversity combining, and at the same time, the narrowest band in the relay station system as described above. Since the characteristics of the BPF are also realized, the delay time of the delay wave included in the transfer functions M1 (ω) and M2 (ω) is relatively large. Further, since A (ω) is composed of the terms D1 (ω) and D2 (ω), the delay time is equal to or longer than D1 (ω) and D2 (ω).
[0068]
Therefore, except for the first term of the equation (43), all have delay times equal to or greater than D1 (ω) and D2 (ω), and only the component having a short delay time is extracted on the delay profile of H1 (ω). Thus, M1 (ω) can be obtained separately. This processing can be realized by LPF (low-pass filter) processing on the frequency axis. M2 (ω) can also be separated and extracted by applying the same processing to H2 (ω). At this time, considering both the delay time of the delay wave included in the master station wave and the delay time of the apparatus, the adaptive filter 34 for diversity synthesis is used._-1, 34_-2It is important to select the optimal delay time.
[0069]
<Regarding Frequency Characteristics D1 (ω) and D2 (ω)>
Adaptive filter 34 for diversity combining_-1Frequency characteristic D1 (ω) and adaptive filter 34_-2Can be obtained using the propagation path characteristics M1 (ω) and M2 (ω) extracted from the frequency characteristics of the signals observed at the observation point P1 and the observation point P2. This is because the specification of the patent application relating to the inventors' invention (Japanese Patent Application No. 2000-353245 “OFDM digital signal relay device”) and the technical report “Distribution of broadcast waves of terrestrial digital broadcasting using space diversity”. It should be determined based on the algorithm described in “Review”, ITE Technical Report Vol.25, No.31, pp.7-12, BCS2001-11 (Mar.2001).
[0070]
Note that the actual D1 (ω) and D2 (ω) have characteristics calculated based on the algorithm described in Japanese Patent Application No. 2000-353245 using M1 (ω) and M2 (ω). By combining the characteristics, a stable wraparound cancel operation can be performed even when the wraparound received power is larger than the received power of the master station signal.
[0071]
<Regarding the frequency characteristics L1 (ω) and L2 (ω)>
Further, the adaptive filter 36 for wraparound cancellation_-1Frequency characteristic L1 (ω) and adaptive filter 36_-2After calculating D1 (ω), D2 (ω), M1 (ω), and M2 (ω), the frequency characteristic L2 (ω) of the frequency is canceled by canceling each branch using equations (26) and (27). The spectrums E1 (ω) and E2 (ω) of the difference signal are obtained and based on the algorithm described in the specification of the patent application relating to the invention of the present inventors (Japanese Patent Laid-Open No. 2001-94528 “wraparound canceller”). Just decide.
[0072]
Further, when the signal observed at the observation point P1 or the observation point P2 is significantly deteriorated, the output of the branch where the observation signal is significantly deteriorated is stopped, so that the relay device can be operated more stably. It becomes possible. For example, as a method for determining that the observed signal is remarkably deteriorated, an algorithm described in the specification of a patent application related to the inventors' invention (Japanese Patent Laid-Open No. 2001-160794 “wraparound canceller”) is used. Based on this, the signal degradation due to the wraparound cancellation residual is detected, and when a certain threshold value is exceeded, the outputs of the adaptive filter 34 for diversity synthesis and the adaptive filter 36 for wraparound cancellation for that branch are stopped, and then the diversity is stopped. This can be realized by creating again the characteristics of the adaptive filter 34 for synthesis and the adaptive filter 36 for wraparound cancellation.
[0073]
Briefly describing the algorithm disclosed in Japanese Patent Laid-Open No. 2001-160794, in this algorithm, when loop oscillation is detected, the output of the adaptive filter is stopped and the output of the relay device is controlled to be reduced or stopped. In this control, from the control information of the AGC circuit that constitutes the reception conversion unit 21 and / or the control information of the AGC circuit that constitutes the transmission conversion unit 41, these AGC circuits have their gains smaller than the threshold values defined respectively. If it is determined that control is being performed, it is determined that the relay device is oscillating in a loop. Alternatively, when the value obtained by dividing the maximum value of the amplitude in the frequency amplitude characteristic of the input sneak observation signal by the minimum value of the amplitude in the frequency amplitude characteristic of the sneak observation signal exceeds the first threshold, the repeater loops. It is determined that Further, when the value obtained by dividing the maximum value of the amplitude in the frequency amplitude characteristic of the input sneak observation signal by the minimum value of the amplitude in the frequency amplitude characteristic of the sneak observation signal exceeds the second threshold value, the relay apparatus can oscillate in a loop. It is determined that there is a risk, and the output of the relay device is reduced to prevent loop oscillation.
[0074]
As described above, FIG. 2 is a diagram showing an operation principle diagram of the present invention in a configuration with two branches using two reception systems for diversity reception. Of course, the present invention is also applied when a reception system with L branches is used. Is effective and easy to modify, and will not be described here.
[0075]
Further, the diversity branch configuration method described here can be realized by any of the branch configuration methods such as space diversity, polarization diversity, and angle diversity.
[0076]
【The invention's effect】
  As described above, according to the present invention, in a relay station that performs broadcast wave relay in SFN, even in a relay station that performs diversity reception using a plurality of reception systems, the wraparound of radio waves from the transmission antenna to each reception system is performed. In addition to removing, diversity combining of signals from each receiving system and re-transmission from the relay stationIn addition, even if the received power of the wraparound is larger than the received power of the master station signal, stable wraparound cancellation is possible, and the characteristics of the adaptive filter for diversity synthesis and the characteristics of the adaptive filter for wraparound cancellation are created. Simplified signal processingTherefore, it is possible to provide a wraparound cancel device and a relay device that can perform the above.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a diversity reception sneak cancel device and a relay device according to the present invention;
FIG. 2 is a block diagram illustrating an operating principle of a diversity reception sneak cancel device and a relay system according to the present invention, using a reception system with two branches as an example.
[Explanation of symbols]
  1, 11-1, 11-2,..., 11-L Diversity antenna 2 Receiver
  3 DiversityFor receivingRounding cancellation device
  4 Transmitter
  5 Transmitting antenna
  21-1, 21-2, ..., 21-L reception conversion unit
  31-1, 31-2, ..., 31-L Downconverter
  32-1, 32-2, ..., 32-L Quadrature demodulation unit
  33-1, 33-2, ..., 33-L Subtraction unit
  34-1, 34-2, ..., 34-L Adaptive filter for diversity synthesis (FIR filter)
  35 Adder
  36-1, 36-2, ..., 36-L Adaptive filter (FIR filter) for wraparound cancellation
  37 Quadrature modulator
  38 Upconverter
  41 Transmission converter
  42 Amplifier

Claims (3)

An output from each branch of a receiving system having two or more branches that receive a signal having the same frequency and modulation content is substantially input to the subtracted terminal. A number of subtraction units for wraparound cancellation, which are the same as the number of branches of the receiving system configured to be input respectively;
Each of the outputs of the subtracting unit is input, and an adaptive filter unit for diversity synthesis equal to the number of branches of the receiving system to which filter coefficients for diversity synthesis are given,
Each output of the adaptive filter unit for diversity combining is input, and an adder for diversity combining whose output is substantially output as a transmission signal of the relay station;
The output of the adder is input, a filter coefficient for generating a wraparound duplicate signal is given, and the output is for the wraparound cancellation of the same number as the number of branches of the receiving system input to the subtraction terminal of each subtractor The adaptive filter section of
In the diversity reception sneak cancel device characterized by comprising :
The adaptive filter unit for diversity combining provides a filter coefficient that also has a band pass filter characteristic that is the narrowest band in a system through which the OFDM signal of the relay system passes,
Included in the signal from the master station that is equal to or greater than the delay time from the delay time of the known relay system including the delay by the adaptive filter unit for diversity synthesis and equal to the delay time and less than the delay time by diversity synthesis To detect the separated delayed wave,
By setting the observation point of the signal to the output position of the subtraction unit, the characteristics of the adaptive filter unit for diversity synthesis and the characteristics of the adaptive filter unit for wraparound cancellation are detected together. Diversity canceling device for diversity reception characterized by the above. In the diversity reception sneak cancel device according to claim 1,
A diversity reception sneak cancel device configured to stop output from the branch to the adder when it is determined that the signal observed in each branch is significantly deteriorated . A relay system comprising the diversity reception sneak cancel device according to claim 1 .

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