JP4774160B2

JP4774160B2 - OFDM receiver

Info

Publication number: JP4774160B2
Application number: JP2001114754A
Authority: JP
Inventors: 鉄也八木; 大介林; 健一郎林
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2000-07-13
Filing date: 2001-04-13
Publication date: 2011-09-14
Anticipated expiration: 2021-04-13
Also published as: JP2002094484A

Description

【０００１】
【発明の属する技術分野】
本発明は、直交周波数分割多重（以下、ＯＦＤＭ（Orthogonal Frequency Division Multiplex））伝送方式の受信装置に関し、特に受信信号に周波数選択性の妨害（同一チャンネル妨害、マルチパス、スプリアスなど）を含む様々な妨害が存在し、その影響により復調性能が悪化する場合の改善技術を含むＯＦＤＭ受信装置に関するものである。
【０００２】
【従来の技術】
近年、デジタル伝送技術の急速な進展により、衛星、ケーブル、地上波などのデジタル放送が本格的な実用化段階に入ろうとしている。特にＯＦＤＭ方式は、欧州における地上波デジタルテレビジョン放送方式として既に実用化が開始され、また日本においても地上波デジタルテレビジョン放送方式及び地上波デジタル音声放送方式として、その採用が決定している。
【０００３】
ＯＦＤＭ伝送方式は、互いに直交する複数のキャリアにデータを割り当てて変調復調を行なうもので、送信側では逆高速フーリエ変換（以下、ＩＦＦＴ（Inverse Fast Fourier Transform））処理を行ない、受信側では高速フーリエ変換（以下、ＦＦＴ（Fast Fourier Transform））処理を行なう。各キャリアは任意の変調方式を用いることが可能であり、ＱＰＳＫ（Quaternary Phase Shift Keying ）やＱＡＭ（Quadrature Amplitude Modulation ）といった同期変調、ＤＱＰＳＫ（Differential Quaternary Phase Shift Keying）などの差動変調が可能である。同期変調方式では、送信信号に対して周期的にパイロット信号を挿入し、受信側でパイロット信号を基に伝送路特性を求めて復調を行なう。差動変調方式では、遅延検波によって復調を行なう。またＯＦＤＭ伝送方式に限らずデジタル伝送方式においては、伝送特性を向上させるため、誤り訂正符号化復号処理を行なう。
【０００４】
しかしながら、伝送路において、マルチパスと呼ばれる反射波の存在による特定キャリアのレベルの落ち込みや、アナログテレビジョン放送による同一チャンネル妨害などが存在すると、復調性能や誤り訂正能力が大きく劣化してしまう場合がある。
【０００５】
このような事態を回避するための従来の技術として、特開平１１−２５２０４０号及び特開平１１−３４６２０５号に示されるものが挙げられる。以下では前者を従来の技術１とし、後者を従来の技術２とし、これらの文献において述べられている技術について、図面を参照して簡単に説明する。
【０００６】
まず、従来の技術１におけるＯＦＤＭ受信装置の構成を図１６に示す。このＯＦＤＭ受信装置では、ＯＦＤＭ伝送信号が受信アンテナ１０１及びＲＦ増幅器１０２を経てチューナ部１０３に入力され、選局が行われる。ここでの選局は、選局情報入力端子１１０に入力される周波数制御信号により、局部発振器１１１の発振周波数を所望のチャンネル周波数に合わせることで行われる。
【０００７】
チューナ部１０３の出力は、アナログ／デジタル（以下、Ａ／Ｄ）変換部１０４でデジタル信号に変換され、直交検波部１０５で直交検波されてベースバンドＯＦＤＭ信号に変換される。このベースバンドＯＦＤＭ信号はＦＦＴ部１０６及び同期再生部１１２に供給される。ＦＦＴ部１０６は入力されたＯＦＤＭ信号を時間領域から周波数領域の信号に変換するものである。尚、Ａ／Ｄ変換クロック及びその他のデジタル回路で使用されるクロック及びタイミング信号は、ベースバンドＯＦＤＭ信号から同期再生部１１２で再生される。
【０００８】
ＦＦＴ部１０６の出力は、ＯＦＤＭ信号のキャリア毎の位相と振幅を示しており、復調部１０７に供給される。復調部１０７は入力されるＯＦＤＭ信号について、その変調方式に対応して同期検波による復調処理を行う。ここで同期検波は、周波数方向に１／３、時間方向に１／４の割合で挿入されているパイロット信号を用いて、各キャリアの伝送路特性を検出し、振幅等化及び位相等化を行うものである。
【０００９】
同期検波では、受信されたＯＦＤＭ信号にはパイロット信号が４シンボル周期で配置されているので、４シンボル周期のパイロット信号により３キャリア間隔の伝送路特性が得られる。そこで、これらを周波数方向に補間することで、全キャリアの伝送路特性を求める。復調された信号は誤り訂正部１０８に入力され、伝送中に生じた誤りが訂正された後、出力端子１０９から出力される。
【００１０】
一方、ＦＦＴ部１０６の出力は妨害検出部１１３にも入力される。妨害検出部１１３は、受信したパイロット信号の状態を判定することで、周波数選択性の妨害の影響を受けているキャリアを判定するものである。その判定結果は復調部１０７や誤り訂正部１０８や同期再生部１１２に出力され、復調性能の改善に供される。
【００１１】
すなわち、復調部１０７では、同期検波時にパイロット信号を用いて各キャリアの伝送路特性を検出し、振幅等化及び位相等化を行っているため、妨害キャリア情報にて妨害の受けている周波数がパイロット信号の周波数と一致している場合には使用せず、妨害の影響を受けていないパイロット信号により補間した信号を用いて、伝送路特性を検出して復調を行う。また、誤り訂正部１０８では、妨害の影響を受けているキャリア情報にて消失訂正などの重み付け処理を行う。一方、同期再生部１１２では、妨害の受けていない信号から誤差の少ない同期再生を行う。
【００１２】
図１７は妨害検出部１１３の具体的な構成を示したＯＦＤＭ受信装置のブロック図である。妨害検出部１１３のパイロット信号抽出部１１３ａには、ＦＦＴ部１０６から高速フーリエ変換された信号が入力される。パイロット信号抽出部１１３ａは入力信号からパイロット信号を抽出するもので、その出力は積分器１１３ｂに出力されると共に、減算部１１３ｃにも供給される。
【００１３】
積分器１１３ｂは、各パイロット信号の振幅を積分することで平均値を求めるもので、この平均値は減算部１１３ｃに供給される。減算部１１３ｃは、各パイロット信号の振幅の平均値と各パイロット信号の振幅との差を検出するもので、その検出出力は各パイロット信号単位の誤差として絶対値演算部１１３ｄに出力される。絶対値演算部１１３ｄでは各パイロット信号の誤差の絶対値が求められる。
【００１４】
絶対値演算部１１３ｄの出力は積分器１１３ｅに供給され、時間方向に各パイロット信号の誤差の積分処理が行われる。この処理結果は各パイロット信号の誤差信号として比較部１１３ｆと平均部１１３ｇに供給される。ここで、各パイロット信号の誤差信号は各パイロット信号のＣ／Ｎ値に対応する。各パイロット信号のＣ／Ｎ値は平均部１１３ｇにより全パイロット信号のＣ／Ｎ値として出力される。一方、比較部１１３ｆは各パイロット信号のＣ／Ｎ値と全パイロット信号のＣ／Ｎ値との比較を行い、比較した結果の差が大きい場合には、周波数選択性の妨害があると判断する。比較部１１３ｆの出力は、前述の妨害キャリア情報として復調部１０７と誤り訂正部１０８と同期再生部１１２とに出力される。
【００１５】
従来の技術２におけるＯＦＤＭ受信装置の構成を図１８に示す。本図において、伝送信号２０１は図示しない受信アンテナで受信されたＯＦＤＭ信号、又はケーブルを通じて伝送されるＯＦＤＭ信号である。伝送信号２０１はチューナ部２０２により選局され、Ａ／Ｄ変換部２０３によりデジタル信号に変換される。続いて、直交検波部２０４で直交検波されてベースバンドＯＦＤＭ信号に変換され、ＦＦＴ部２０５に供給される。ＦＦＴ部２０５は入力された時間領域の信号を周波数領域の信号に変換する。このＦＦＴ出力はＯＦＤＭ信号の各キャリアの位相と振幅を示すもので、復調部２０６に供給される。
【００１６】
復調部２０６では同期検波が行われる。送信側で周波数方向及び時間方向に周期的にパイロット信号が挿入されており、このパイロット信号を抽出して基準値と比較することで各キャリアの伝送路特性を検出し、振幅等化と位相等化とを行う。即ち、パイロット信号は飛び飛びに挿入されているため、時間軸と周波数軸に夫々補間して伝送路特性を求め、この伝送路特性に基づいて等化を行う。
【００１７】
同期検波して等化された信号（復調データ）２０７は、周波数選択性妨害訂正手段を構成する誤り訂正部２０８と妨害検出部２０９とに供給される。妨害検出部２０９はマルチパスやスプリアス、同一チャンネル妨害を検出し、誤り訂正部２０８に対し、該当する位置や妨害の程度を示す妨害検出情報を与える。誤り訂正部２０８は検波後の信号に対して妨害検出部２０９からの妨害検出情報に基づいて重み付けを行い、消失訂正等の誤り訂正を施して出力する。尚、重み付け処理は、妨害検出部２０９の中で行うようにしてもよい。
【００１８】
図１９に妨害検出部２０９の具体的な構成を示す。復調部２０６から入力される復調データは硬判定部２９１にて硬判定され、その硬判定結果が積分器２９２に与えられる。積分器２９２は、各キャリア毎に又はそのうちの一部のキャリア毎に、かつ一定時間毎に積分を行う。積分結果は分散値としてレベル判定部２９３及び重み付け部２９４に出力される。
【００１９】
レベル判定部２９３は、積分器２９２から出力される分散値の大きさから、妨害を受けているキャリアを判別すると共に、どのキャリアに対して重み付けを行うかの重み付けレベルの判定を行う。その判定結果は重み付け部２９４に出力される。重み付け部２９４は、現在の復調データを取り込み、積分器２９２からの各キャリアの分散値と、レベル判定部２９３からのレベル判定結果とから、取り込んだ復調データに対してどの程度の重み付けを行うかの重み付け量を算出する。この重み付け量の情報は誤り訂正部２０８に出力される。誤り訂正部２０８は、入力される復調データに対して、対応する重み付け量に基づいて係数を掛け、誤り訂正処理を行う。
【００２０】
【発明が解決しようとする課題】
以上のように従来のＯＦＤＭ受信装置では、ＦＦＴ出力信号や復調出力信号から周波数選択性の妨害を検出し、その妨害を除去しようとしている。しかしながら、例えば従来の技術１のＯＦＤＭ受信装置の構成においては、図示されていない復調部におけるメモリの他に、積分器１１３ｂ及び積分器１１３ｅにおいて時間方向の積分を行なうためのメモリが更に必要となる。そのメモリ容量は夫々４シンボル分のパイロット信号の本数に相当するものとなる。
【００２１】
また従来の技術２において延べられているＯＦＤＭ受信装置の構成においても、復調部２０６のメモリの他に、積分器２９２において時間方向の積分を行なうためのメモリが必要となる。その容量は、復調部のメモリについては４シンボル分のパイロット信号の本数に相当するものとなる。また積分器２９２のメモリについては、一部のキャリア毎の積分も可能としてはいるものの、この方式における本来の性能を引き出すためには、キャリアの総本数に相当するものとなる。
【００２２】
また従来の技術においては、キャリア変調方式が６４ＱＡＭのような、キャリア夫々に割り当てられた情報信号が、伝送誤りに対する耐性の異なるビットデータを含むような多値変調方式であった場合にも、妨害検出結果に基づいてキャリア単位の重み付け処理を行うため、伝送誤りに対する耐性の大きいビットデータと伝送誤りに対する耐性の小さいビットデータとを同等に扱うこととなる。
【００２３】
本発明は、このような従来の問題点に鑑みてなされたものであって、ＯＦＤＭ伝送信号を受信して復調するに際し、周波数選択性の妨害を受けた場合にもその妨害を検出し、伝送誤りに対する耐性の異なるビットデータを含む多値のキャリア変調方式に対して、効果的に誤り訂正を施して、復調性能や誤り訂正能力などの特性を向上させることを目的とするものである。またこの機能を実現するために、余分なメモリ量を極力必要としないＯＦＤＭ受信装置を実現することを更なる目的とする。
【００２４】
【課題を解決するための手段】
本願の請求項１の発明は、伝送帯域内に互いに直交する周波数で発生される複数のキャリアが夫々に割り当てられた情報信号で変調され、かつ前記情報信号により変調された複数のキャリアに対して既知のパイロット信号が周期的に挿入された直交周波数分割多重（以下、ＯＦＤＭ）伝送信号を受信するＯＦＤＭ受信装置であって、前記ＯＦＤＭ伝送信号を直交検波する直交検波手段と、前記直交検波手段で得られた出力信号を高速フーリエ変換（以下、ＦＦＴ）により時間領域から周波数領域の信号に変換するＦＦＴ手段と、前記ＦＦＴ手段により得られた出力信号からパイロット信号を抽出し、前記パイロット信号及び既知の基準パイロット信号から前記パイロット信号の伝送路特性を推定し、前記パイロット信号の伝送路特性を内部に設けた第１のメモリ手段に蓄積しながら時間軸方向に補間し、更に周波数軸方向に補間して伝送帯域内の全てのキャリアの伝送路特性を推定し、前記キャリアの伝送路特性を用いて前記ＦＦＴ手段により得られた出力信号を等化し、復調信号として出力する復調手段と、前記復調手段により得られたパイロット信号の伝送路特性、及び前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性から、パイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号を基に周波数選択性の妨害を検出し、妨害レベルとして出力する妨害検出手段と、前記復調手段により得られた復調信号を軟判定情報信号に変換し、前記妨害検出手段により得られた妨害レベルを用いて前記軟判定情報信号を補正し、補正された軟判定情報信号に対し誤り訂正復号を行なう誤り訂正手段と、を具備することを特徴とするものである。
【００２５】
本願の請求項２の発明は、伝送帯域内に互いに直交する周波数で発生される複数のキャリアが夫々に割り当てられた所定数のビットデータからなる情報信号により多値変調され、かつ前記情報信号により変調された複数のキャリアに対して既知のパイロット信号が周期的に挿入されたＯＦＤＭ伝送信号を受信するＯＦＤＭ受信装置であって、前記ＯＦＤＭ伝送信号を直交検波する直交検波手段と、前記直交検波手段で得られた出力信号を、ＦＦＴにより時間領域から周波数領域の信号に変換するＦＦＴ手段と、前記ＦＦＴ手段により得られた出力信号からパイロット信号を抽出し、前記パイロット信号及び既知の基準パイロット信号から前記パイロット信号の伝送路特性を推定し、前記パイロット信号の伝送路特性を内部に設けた第１のメモリ手段に蓄積しながら時間軸方向に補間し、更に周波数軸方向に補間して伝送帯域内の全てのキャリアの伝送路特性を推定し、前記キャリアの伝送路特性を用いて前記ＦＦＴ手段により得られた出力信号を等化し、復調信号として出力する復調手段と、前記復調手段により得られたパイロット信号の伝送路特性、及び前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性から、パイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号を基に周波数選択性の妨害を検出し、妨害レベルとして出力する妨害検出手段と、前記復調手段により得られた復調信号を、キャリア変調方式に応じた所定数の軟判定ビットデータからなる軟判定情報信号に変換し、前記軟判定情報信号の夫々の軟判定ビットデータごとに前記妨害検出手段により得られた妨害レベルを補正し、補正された妨害レベルを用いて前記軟判定ビットデータを補正し、補正された軟判定ビットデータに対し誤り訂正復号を行なう誤り訂正手段と、を具備することを特徴とするものである。
【００２６】
本願の請求項３の発明は、伝送帯域内に互いに直交する周波数で発生される複数のキャリアが夫々に割り当てられた所定数のビットデータからなる情報信号により多値変調され、かつ前記情報信号が伝送誤りに対する耐性の異なるビットデータを含み、かつ前記情報信号により変調された複数のキャリアに対して既知のパイロット信号が周期的に挿入されたＯＦＤＭ伝送信号を受信するＯＦＤＭ受信装置であって、前記ＯＦＤＭ伝送信号を直交検波する直交検波手段と、前記直交検波手段で得られた出力信号を、ＦＦＴにより時間領域から周波数領域の信号に変換するＦＦＴ手段と、前記ＦＦＴ手段により得られた出力信号からパイロット信号を抽出し、前記パイロット信号及び既知の基準パイロット信号から前記パイロット信号の伝送路特性を推定し、前記パイロット信号の伝送路特性を内部に設けた第１のメモリ手段に蓄積しながら時間軸方向に補間し、更に周波数軸方向に補間して伝送帯域内の全てのキャリアの伝送路特性を推定し、前記キャリアの伝送路特性を用いて前記ＦＦＴ手段により得られた出力信号を等化し、復調信号として出力する復調手段と、前記復調手段により得られたパイロット信号の伝送路特性、及び前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性からパイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号を基に周波数選択性の妨害を検出し、妨害レベルとして出力する妨害検出手段と、前記復調手段により得られた復調信号をキャリア変調方式に応じた所定数の軟判定ビットデータからなる軟判定情報信号に変換し、前記軟判定情報信号の夫々の軟判定ビットデータごとに、その軟判定ビットデータの伝送誤りに対する耐性が小さい場合には妨害レベルを大きくし、その軟判定ビットデータの伝送誤りに対する耐性が大きい場合には妨害レベルを小さくするように、前記妨害検出手段により得られた妨害レベルを補正し、補正された妨害レベルを用いて前記軟判定ビットデータを補正し、補正された軟判定ビットデータに対し誤り訂正復号を行なう誤り訂正手段と、を具備することを特徴とするものである。
【００２７】
本願の請求項４の発明は、請求項１〜３のいずれか１項のＯＦＤＭ受信装置において、前記妨害検出手段は、前記復調手段により得られたパイロット信号の伝送路特性と、前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性と、からパイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号を内部に設けた第２のメモリ手段を用いて時間軸方向に平均し、平均された誤差信号を前記第２のメモリ手段に蓄積しながら時間軸方向に補間し、平均かつ補間された誤差信号から周波数選択性の妨害を表す妨害レベルを算出し、前記妨害レベルを周波数軸方向に補間して出力することを特徴とするものである。
本願の請求項５の発明は、請求項１〜３のいずれか１項のＯＦＤＭ受信装置において、前記妨害検出手段は、前記復調手段により得られたパイロット信号の伝送路特性と、前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性と、からパイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号を内部に設けた第２のメモリ手段に蓄積しながら時間軸方向に補間し、補間された誤差信号から周波数選択性の妨害を表す妨害レベルを算出し、前記妨害レベルを周波数軸方向に補間して出力することを特徴とするものである。
【００２８】
本願の請求項６の発明は、請求項１〜３のいずれか１項のＯＦＤＭ受信装置において、前記妨害検出手段は、前記復調手段により得られたパイロット信号の伝送路特性と、前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性と、からパイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号から周波数選択性の妨害を表す妨害レベルを算出し、前記妨害レベルを内部に設けた第２のメモリ手段を用いて時間軸方向に平均し、平均された妨害レベルを前記第２のメモリ手段に蓄積しながら時間軸方向に補間し、更に周波数軸方向に補間して出力することを特徴とするものである。
本願の請求項７の発明は、請求項１〜３のいずれか１項のＯＦＤＭ受信装置において、前記妨害検出手段は、前記復調手段により得られたパイロット信号の伝送路特性と、前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性と、からパイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号から周波数選択性の妨害を表す妨害レベルを算出し、前記妨害レベルを内部に設けた第２のメモリ手段に蓄積しながら時間軸方向に補間し、更に周波数軸方向に補間して出力することを特徴とするものである。
【００２９】
本願の請求項８の発明は、請求項１〜３のいずれか１項のＯＦＤＭ受信装置において、前記妨害検出手段は、前記復調手段により得られたパイロット信号の伝送路特性と、前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性と、からパイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号を内部に設けた第２のメモリ手段を用いて時間軸方向に平均し、平均された誤差信号を前記第２のメモリ手段に蓄積しながら時間軸方向に補間し、更に周波数軸方向に補間し、平均かつ補間された誤差信号から周波数選択性の妨害を表す妨害レベルを算出することを特徴とするものである。
【００３０】
本願の請求項９の発明は、請求項１〜３のいずれか１項のＯＦＤＭ受信装置において、前記妨害検出手段は、前記復調手段により得られたパイロット信号の伝送路特性と、前記復調手段内の前記第１のメモリ手段に蓄積された一周期前のパイロット信号の伝送路特性と、からパイロット信号の伝送路特性の時間変動量を表す誤差信号を算出し、前記誤差信号を内部に設けた第２のメモリ手段に蓄積しながら時間軸方向に補間し、更に周波数軸方向に補間し、補間された誤差信号から周波数選択性の妨害を表す妨害レベルを算出することを特徴とするものである。
【００３７】
【発明の実施の形態】
本発明の実施の形態におけるＯＦＤＭ受信装置について、図面を参照して詳細に説明する。
【００３８】
（実施の形態１）
図１は本発明の実施の形態１によるＯＦＤＭ受信装置の全体構成図である。受信アンテナ又はケーブルを通じてＯＦＤＭ伝送信号がＯＦＤＭ受信装置に与えられる。この信号は図示しないチューナ部によって選局され、Ａ／Ｄ変換部によってデジタル信号に変換され、図中の直交検波部１に入力される。
【００３９】
直交検波部１は、入力信号に対し直交検波を行ない、ベースバンドＯＦＤＭ信号に変換する。ＦＦＴ部２は直交検波部１からの信号に対し高速フーリエ変換を行ない、時間領域の信号から周波数領域の信号に変換して出力する。このＦＦＴ出力はＯＦＤＭ伝送信号の各キャリアの位相と振幅とを示すものであり、具体的にはＩ軸方向のレベルとＱ軸方向のレベルとを独立に持つ複素信号の形で取り扱われる。
【００４０】
復調部３は、パイロット発生部３１、第１の複素除算部３２、第１のメモリ部３３、時間軸補間部３４、周波数軸補間部３５、第２の複素除算部３６を含んで構成される。復調部３は入力信号に対し同期検波を行ない、復調された信号を出力する。ここでメモリ部３３は、一周期分のパイロット信号の伝送路特性を蓄積するだけの容量を持つ。図２にパイロット信号配置の具体例を示す。Ｄ１はデータキャリアの位置を示し、Ｐ１はパイロット信号の位置を示す。この例の場合、４シンボルで一周期となっており、必要なメモリ量は全キャリア数の１／３である。
【００４１】
パイロット発生部３１は、入力信号に周期的に挿入されているパイロット信号に対して、同じタイミングで既知のパイロット信号（基準値）を発生する。複素除算部３２は、入力信号に周期的に挿入されているパイロット信号に対し、パイロット発生部３１で発生された既知のパイロット信号（基準値）による複素除算を行ない、パイロット信号の伝送路特性を推定して出力する。図２に示したパイロット信号配置に基づき推定されたパイロット信号の伝送路特性の配置を図３に示す。図３において、Ｃ１はパイロット信号の伝送路特性が得られる位置を示し、Ｃ０の位置では伝送路特性は得られない。
【００４２】
時間軸補間部３４は、複素除算部３２で得られたパイロット信号の伝送路特性をメモリ部３３に順次蓄積すると共に、各周波数軸上でパイロット信号と同じ位置に存在するキャリアに対して、メモリ部３３に蓄積された同じキャリア位置のパイロット信号の伝送路特性を読み出して適用することにより、時間軸方向に伝送路特性を補間（０次補間）して出力する。
【００４３】
なお、時間軸補間部３４は、複素除算部３２で得られたパイロット信号の伝送路特性をメモリ部３３に順次蓄積すると共に、複素除算部３２で得られたパイロット信号の伝送路特性と、メモリ部３３に蓄積されたちょうど一周期前のパイロット信号の伝送路特性とから、各周波数軸上でパイロット信号と同じ位置に存在するキャリアに対して、直線補間（１次補間）して出力する構成としてもよい。これにより、伝送路特性の時間変動に追従した精度の高い補間をすることができ、復調性能の向上を図ることができる。
【００４４】
図３に示したパイロット信号の伝送路特性の配置に基づいた時間軸補間処理の概念図を図４に示す。図４（ａ）の矢印ＴＣは時間軸補間を示す。図４（ｂ）において、Ｃ１はパイロット信号の伝送路特性が得られる位置を示し、Ｃ２は時間軸補間された伝送路特性が得られる位置を示す。Ｃ０の位置では伝送路特性は得られない。
【００４５】
図１の周波数軸補間部３５は、時間軸補間部３４で得られた一定キャリア間隔の伝送路特性をフィルタを通すことで周波数軸方向に補間し、全キャリアの伝送路特性を出力する。図４（ｂ）に示した時間軸補間結果に基づいた周波数軸補間処理の概念図を図５に示す。図５（ａ）の曲線ＦＣは周波数軸補間を示す。図５（ｂ）において、Ｃ１はパイロット信号の伝送路特性が得られる位置を示し、Ｃ２は時間軸補間された伝送路特性が得られる位置を示す。またＣ３は周波数補間された伝送路特性が得られる位置を示す。
【００４６】
図１の複素除算部３６は、復調部３に入力された各キャリア信号に対し、周波数軸補間部３５により得られたキャリアの伝送路特性による複素除算を行ない、除算結果を復調信号として出力する。
【００４７】
妨害検出部４は、誤差算出部４１、第２のメモリ部４２、時間軸補間部４３、妨害算出部４４、周波数軸補間部４５を含んで構成される。妨害検出部４は復調部３において得られたパイロット信号の伝送路特性を用いて、周波数選択性の妨害を検出する。ここでメモリ部４２は一周期分のパイロット信号の誤差信号を蓄積するだけの容量を持つ。
【００４８】
誤差算出部４１は、パイロット信号単位での時間変動を表す誤差信号を算出して出力する。即ち、複素除算部３２で得られたパイロット信号の伝送路特性と、メモリ部３３に蓄積されたちょうど一周期前のパイロット信号の伝送路特性との複素減算を行い、減算結果の複素信号の電力を算出することで、複素信号で表される二つの伝送路特性の信号点間距離の二乗を求め、これを誤差信号として出力する。ここで、復調部３に必須な構成要素であるメモリ部３３を共有して利用することで、図１７の積分器１１３ｂに用いられるような余分なメモリ部を持つことなく誤差信号の算出が行なえる。
【００４９】
なお、誤差算出部４１は、複素除算部３２で得られたパイロット信号の伝送路特性と、メモリ部３３に蓄積されたちょうど一周期前のパイロット信号の伝送路特性との複素減算を行ない、減算結果の複素信号の振幅を算出することで、複素信号で表される二つの伝送路特性の信号点間距離を求め、これを誤差信号として出力する構成としてもよい。
【００５０】
図３に示したパイロット信号の伝送路特性の配置に基づき算出された誤差信号の配置を図６に示す。図６において、Ｅ１は誤差信号が得られる位置を示し、Ｅ０の位置では誤差信号は得られない。
【００５１】
図１の時間軸補間部４３は、誤差算出部４１で得られた誤差信号と、メモリ部４２に蓄積されたちょうど一周期前の誤差信号とから、同じキャリア位置の誤差信号の時間軸方向の平均を算出し、算出結果を新たな誤差信号としてメモリ部４２に順次蓄積すると共に、各周波数軸上でパイロット信号と同じ位置に存在するキャリアに対して、メモリ部４２に蓄積された誤差信号を読み出して適用することにより、時間軸方向に誤差信号を平均かつ補間して出力する。これにより、周波数選択性の妨害を受けているキャリア位置のパイロット信号が、ある時間（シンボル）において基準値のパイロット信号に近くなった場合にも、周波数選択性の妨害の存在を見逃すことなく、妨害の検出精度を向上することができる。
【００５２】
なお、時間軸補間部４３は、誤差算出部４１で得られた誤差信号をメモリ部４２に順次蓄積すると共に、周波数軸上でパイロット信号と同じ位置に存在するキャリアに対して、メモリ部４２に蓄積された同じキャリア位置の誤差信号を読み出して適用することにより、時間軸方向に誤差信号を補間（０次補間）して出力する構成としてもよい。
【００５３】
また、時間軸補間部４３は、誤差算出部４１で得られた誤差信号をメモリ部４２に順次蓄積すると共に、誤差算出部４１で得られた誤差信号と、メモリ部４２に蓄積されたちょうど一周期前の誤差信号とから、周波数軸上でパイロット信号と同じ位置に存在するキャリアに対して、直線補間（１次補間）して出力する構成としてもよい。
【００５４】
図６に示した誤差信号の配置に基づいた時間軸補間処理の概念図を図７に示す。図７（ａ）の矢印ＴＥは平均算出を含めた時間軸補間を示す。図７（ｂ）において、Ｅ１は誤差信号が得られる位置を示し、Ｅ２は時間軸補間された誤差信号が得られる位置を示す。Ｅ０の位置では誤差信号は得られない。
【００５５】
図１の妨害算出部４４は、時間軸補間部４３で得られた誤差信号を周波数軸方向に平均し、時間軸補間部４３で得られた誤差信号を、誤差信号の周波数軸方向の平均により除算し、除算結果を周波数選択性の妨害を表す妨害レベルとして出力する。
【００５６】
なお、妨害算出部４４は、時間軸補間部４３で得られた誤差信号を周波数軸方向に平均し、時間軸補間部４３で得られた誤差信号から、誤差信号の周波数軸方向の平均を減算し、結果を周波数選択性の妨害を表す妨害レベルとして出力する構成としてもよい。
【００５７】
また、妨害算出部４４は、時間軸補間部４３で得られた誤差信号から、所定の定数を減算し、結果を周波数選択性の妨害を表す妨害レベルとして出力する構成としてもよい。
【００５８】
また、妨害算出部４４は、時間軸補間部４３で得られた誤差信号を、所定の定数により除算し、結果を周波数選択性の妨害を表す妨害レベルとして出力する構成としてもよい。
【００５９】
また、妨害算出部４４は、誤差信号を入力とし、周波数選択性の妨害を表す妨害レベルを出力とする所定の入出力テーブルを具備し、時間軸補間部４３で得られた誤差信号を入出力テーブルに与えることにより、妨害レベルを出力する構成としてもよい。
【００６０】
また、妨害算出部４４は、上記の構成以外にも、時間軸補間部４３で得られた誤差信号を基に、いくつかの演算を組み合わせた結果を出力するように構成することも可能である。
【００６１】
上記いずれの構成の場合でも、妨害算出部４４から出力される妨害レベルは、入力された誤差信号の配置と同一の配置で得られる。図７（ｂ）に示した誤差信号の配置に基づき算出された妨害レベルの配置を図８に示す。図８において、Ｉ１は妨害レベルが得られる位置を示し、Ｉ０の位置では妨害レベルは得られない。
【００６２】
図１の周波数軸補間部４５は、妨害算出部４４で得られた一定キャリア間隔の妨害レベルを、隣接するキャリアにも適用することにより周波数軸方向に補間し、全キャリアの妨害レベルとして出力する。
【００６３】
なお、周波数軸補間部４５は、妨害算出部４４で得られた一定キャリア間隔の妨害レベルを、周波数軸方向に直線補間（１次補間）し、全キャリアの妨害レベルとして出力する構成としてもよい。
【００６４】
また、周波数軸補間部４５は、妨害算出部４４で得られた一定キャリア間隔の妨害レベルを、フィルタを通すことで周波数軸方向に補間し、全キャリアの妨害レベルとして出力する構成としてもよい。
【００６５】
図８に示した妨害レベルの配置に基づいた周波数軸補間処理の概念図を図９に示す。図９（ａ）の矢印ＦＩは周波数軸補間を示す。図９（ｂ）において、Ｉ１は妨害レベルが得られる位置を示し、Ｉ２は周波数軸補間された妨害レベルが得られる位置を示す。
【００６６】
なお、上記構成において妨害検出部４は、誤差算出結果を時間軸補間し、妨害算出結果を周波数軸補間しているが、誤差算出結果を時間軸補間し、さらに周波数軸補間した上で妨害レベルを算出する構成としてもよい。また、誤差算出結果から妨害レベルを算出し、妨害算出結果を時間軸補間し、さらに周波数軸補間する構成としてもよい。
【００６７】
次に図１の誤り訂正部５は、軟判定部５１、軟判定補正部５２、誤り訂正復号部５３を含んで構成される。誤り訂正部５は復調部３で得られた復調信号に対し、妨害検出部４で得られた妨害レベルに基づいて補正を施し、誤り訂正復号を行なう。ここで、復調部３で得られた復調信号は、送信装置及び受信装置や伝送路上での様々な妨害により誤りを含んでいる。誤り訂正部５では、復調部３で得られた復調信号を、変調処理において用いた本来の情報信号に対応する軟判定情報信号へと変換し、その軟判定情報信号と、本来の情報信号（受信装置においては既知である情報信号）との距離などを用いて、受信信号の確からしさを表現する。そして誤り訂正部５は、その累積により情報信号の系列を推定する軟判定復号法と呼ばれる方式を用いて誤り訂正復号を行なう。
【００６８】
軟判定復号法の例を図１０に示す。本来の情報信号０と１に対して、その中間及び周辺に段階的に位置する軟判定情報信号が存在する。そして入力された復調信号は、０と１を含む軟判定情報信号のうち、最も近傍に位置する信号に変換される。ここで変換された軟判定情報信号は、本来の情報信号の０か１に近いほど、復号される情報信号の信頼性が高いと言える。また、本来の情報信号０と１の中央、即ち０．５に近いほど、復号される情報信号の信頼性が低いと言える。
【００６９】
図１の軟判定部５１は、復調部３で得られた復調信号を前述の手法により軟判定情報信号へと変換する。軟判定補正部５２は、妨害検出部４で得られた妨害レベルを用いて、軟判定部５１で得られた軟判定情報信号を補正する。具体的には、妨害レベルの大きさに応じて、軟判定情報信号の信頼性をより低くする変換、即ち本来の情報信号の０と１の中央により近い軟判定情報信号への変換を行なう。誤り訂正復号部５３は、軟判定補正部５２で補正された軟判定情報信号に対して誤り訂正復号を行なう。
【００７０】
以上の構成により、ＯＦＤＭ伝送信号を受信して送信データを復調するＯＦＤＭ受信装置において、周波数選択性の妨害を受けた場合にもその妨害を検出し、復調性能や誤り訂正能力などの特性を向上させる効果が得られる。またその効果を得るために、復調部に必須のメモリを共有して誤差検出を行なうなど、余分なメモリ量を必要としない構成にすることができ、総メモリ量の削減が実現される。
【００７１】
（実施の形態２）
次に本発明の実施の形態２におけるＯＦＤＭ受信装置について説明する。図１１は本実施の形態によるＯＦＤＭ受信装置の全体構成図である。ここでは、受信するＯＦＤＭ伝送信号は、夫々のキャリアが所定数のビットデータからなる情報信号によって多値変調されているものとする。尚、実施の形態１におけるＯＦＤＭ受信装置と同一の信号処理を行う構成要素については、図１と同一の符号を付し、それらの説明を省略する。
【００７２】
このＯＦＤＭ受信装置は、直交検波部１、ＦＦＴ部２、復調部３、妨害検出部４Ａ、誤り訂正部５Ａを含んで構成される。妨害検出部４Ａは、ＦＦＴ部２で得られた出力信号から周波数選択性の妨害を検出し、妨害レベルを出力する。復調部３は実施の形態１のものと同一構成である。
【００７３】
なお、妨害検出部４Ａは、図１３に示すように復調部３で得られた復調信号から周波数選択性の妨害を検出し、妨害レベルを出力する構成としてもよい。
【００７４】
誤り訂正部５Ａは、図１２に示すように、軟判定部５１Ａ、軟判定補正部５２Ａ１，５２Ａ２，・・・５２Ａｎ、誤り訂正復号部５３Ａ、レベル補正部５４Ａ１，５４Ａ２，・・・５４Ａｎを含んで構成される。
【００７５】
誤り訂正部５Ａは、復調部３で得られた復調信号を、キャリア変調方式に応じた所定数の軟判定ビットデータからなる軟判定情報信号に変換し、軟判定情報信号の夫々の軟判定ビットデータごとに、妨害検出部４Ａで得られた妨害レベルを補正し、補正された妨害レベルを用いて軟判定ビットデータを補正し、誤り訂正復号を行なう。
【００７６】
軟判定部５１Ａは、復調部３で得られた復調信号を、キャリア変調方式に対応した所定数（ｎとする）の軟判定ビットデータからなる軟判定情報信号へと変換する。
【００７７】
レベル補正部５４Ａ１〜５４Ａｎは、軟判定情報信号の夫々の軟判定ビットデータごとに、妨害検出部４Ａで得られた妨害レベルを補正する。ここで、レベル補正の内容は、夫々の軟判定ビットデータごとに異なるものとしてもよく、また、一部または全部の軟判定ビットデータにおいて共通のものとしてもよい。
【００７８】
軟判定補正部５２Ａ１〜５２Ａｎは、レベル補正部５４Ａ１〜５４Ａｎで夫々補正された妨害レベルを用いて、軟判定部５１Ａで得られた軟判定ビットデータを補正する。具体的には、妨害レベルの大きさに応じて、軟判定ビットデータの信頼性をより低くする変換、即ち本来のビットデータ０と１の中央により近い軟判定ビットデータへの変換を行なう。
【００７９】
誤り訂正復号部５３Ａは、軟判定補正部５２Ａ１〜５２Ａｎで補正された軟判定ビットデータに対して誤り訂正復号を行なう。
【００８０】
なお、ＯＦＤＭ伝送信号の各キャリアが所定数のビットデータからなる情報信号によって多値変調され、かつその情報信号が伝送誤りに対する耐性の異なるビットデータを含んでいるとき、誤り訂正部５Ａは次のような信号処理を行う。即ち、誤り訂正部５Ａは復調部３で得られた復調信号を、キャリア変調方式に応じた所定数の軟判定ビットデータからなる軟判定情報信号に変換し、軟判定情報信号の夫々の軟判定ビットデータごとに、その軟判定ビットデータの伝送誤りに対する耐性が小さい場合には妨害レベルを大きくし、その軟判定ビットデータの伝送誤りに対する耐性が大きい場合には妨害レベルを小さくするように、妨害検出部４Ａで得られた妨害レベルを補正する。そして補正された妨害レベルを用いて軟判定ビットデータを補正し、誤り訂正を行なう構成としてもよい。これにより、周波数選択性の妨害が軟判定情報信号の確からしさに与える影響の度合を、伝送誤りに対する耐性が異なる軟判定ビットデータごとに設定でき、全体の誤り訂正能力を向上することができる。
【００８１】
多値変調方式の例として、６４ＱＡＭのマッピング位相図を図１４に示す。一般に、隣接するマッピング信号点間では全て情報信号が１ビットしか異ならないようにしたものがグレイ符号配置である。Ｉ軸はｂ０，ｂ２，ｂ４に対応したレベルを示し、Ｑ軸はｂ１，ｂ３，ｂ５に対応したレベルを示す。このグレイ符号配置は符号誤り率の観点から優れており、図１４に示す例でもそのようになっている。この場合のキャリア変調に用いる情報信号は６ビットであり、伝送誤りに対する耐性は上位２ビット（ｂ０、ｂ１）が最も大きく、下位２ビット（ｂ４、ｂ５）が最も小さく、中位２ビット（ｂ２、ｂ３）がその中間となっている。
【００８２】
図１５は、キャリア変調方式として６４ＱＡＭを用いた場合の誤り訂正部５Ａの構成図である。この誤り訂正部５Ａは、伝送誤りに対する耐性が三段階に異なる軟判定ビットデータに対して、レベル補正部５４Ａ１〜５４Ａ３を具備することにより、夫々に異なる妨害レベルを適用して誤り訂正を行なう。
【００８３】
図１５の軟判定部５１Ａは、復調部３で得られた復調信号をキャリア変調方式に対応した所定数（６４ＱＡＭの場合は６）の軟判定ビットデータからなる軟判定情報信号へと変換する。レベル補正部５４Ａ１〜５４Ａ３は、伝送誤りに対する耐性の異なる夫々の軟判定ビットデータごとに、妨害検出部４Ａで得られた妨害レベルを補正する。伝送誤りに対する耐性の最も大きい軟判定ビットデータ（ｂ０、ｂ１）に対しては、妨害レベルを小さくする補正を行なう。また、伝送誤りに対する耐性の最も小さい軟判定ビットデータ（ｂ４、ｂ５）に対しては、妨害レベルを大きくする補正を行なう。また、伝送誤りに対する耐性が中間的である軟判定ビットデータ（ｂ２、ｂ３）に対しては、妨害レベルに対する補正を行なわず、入力された妨害レベルをそのまま出力するものとする。
【００８４】
軟判定補正部５２Ａ１〜５２Ａ３は、レベル補正部５４Ａ１〜５４Ａ３で夫々補正された妨害レベルを用いて、軟判定部５１Ａで得られた軟判定ビットデータを補正する。誤り訂正復号部５３Ａは、軟判定補正部５２Ａ１〜５２Ａ３で補正された軟判定ビットデータに対して誤り訂正復号を行なう。
【００８５】
以上の構成により、ＯＦＤＭ伝送信号を受信して復調するＯＦＤＭ受信装置において、周波数選択性の妨害を検出した場合に、伝送誤りに対する耐性の異なる情報信号を含む多値のキャリア変調方式に対して効果的に誤り訂正を施して、復調性能や誤り訂正能力などの特性を向上させる効果が得られる。
【００８６】
なお、本発明の実施の形態１と実施の形態２とは原理的に排他的なものではなく、その両方を組み合わせて実施することも勿論可能である。
【００８７】
さらに、本実施の形態で述べた伝送方式（送受信装置構成）においては、対応するＯＦＤＭ変調装置内での誤り訂正符号化処理には、ある種の畳込み符号化器が用いられ、それに伴って誤り訂正復号処理にはビタビ復号が使用されることが想定される。またその場合、誤り訂正符号化後のビットデータ、又は変調処理後のキャリア信号、又はその両方に対してインターリーブ処理（受信装置側ではデインターリーブ処理）を施すことにより、誤り訂正能力を向上することが可能である。そのようなインターリーブ（デインターリーブ）処理のブロックは、本実施の形態の構成図に記載されていないが、それらのブロックを含む構成とすることも勿論可能である。
【００８８】
【発明の効果】
以上のように本発明によれば、ＯＦＤＭ伝送信号を受信して復調するＯＦＤＭ受信装置において、周波数選択性の妨害を受けた場合にもそれを検出し、伝送誤りに対する耐性の異なる情報信号を含む多値のキャリア変調方式に対して効果的に誤り訂正を施して、復調性能や誤り訂正能力などの特性を向上させる効果が得られる。またその効果を得るために余分なメモリ量を極力必要としない構成を実現できる。
【図面の簡単な説明】
【図１】本発明の実施の形態１におけるＯＦＤＭ受信装置の全体構成を示すブロック図である。
【図２】パイロット信号の配置を示す説明図である。
【図３】パイロット信号の伝送路特性が得られる配置図である。
【図４】パイロット信号の時間軸補間の概念を示す説明図である。
【図５】パイロット信号の周波数軸補間の概念を示す説明図である。
【図６】実施の形態１の誤差算出部から出力される誤差信号の配置図である。
【図７】誤差信号の時間軸補間の概念を示す説明図である。
【図８】実施の形態１の妨害算出部から出力される妨害レベルの配置図である。
【図９】妨害レベルの周波数軸補間の概念を示す説明図である。
【図１０】軟判定復号法の概念を示す説明図である。
【図１１】本発明の実施の形態２（その１）におけるＯＦＤＭ受信装置の全体構成を示すブロック図である。
【図１２】実施の形態２のＯＦＤＭ受信装置に用いられる誤り訂正部の構成図である。
【図１３】本発明の実施の形態２（その２）におけるＯＦＤＭ受信装置の全体構成を示すブロック図である。
【図１４】６４ＱＡＭ変調方式におけるマッピング位相図である。
【図１５】６４ＱＡＭ変調方式を用いた場合の誤り訂正部の構成を示すブロック図である。
【図１６】従来の技術１におけるＯＦＤＭ受信装置の全体構成図である。
【図１７】従来の技術１のＯＦＤＭ受信装置に設けられた妨害検出部の構成図である。
【図１８】従来の技術２におけるＯＦＤＭ受信装置の全体構成図である。
【図１９】従来の技術２のＯＦＤＭ受信装置に設けられた妨害検出部の構成図である。
【符号の説明】
１直交検波部
２ＦＦＴ部
３復調部
４，４Ａ妨害検出部
５，５Ａ誤り訂正部
３１パイロット発生部
３２複素除算部
３３メモリ部
３４時間軸補間部
３５周波数軸補間部
３６複素除算部
４１誤差算出部
４２メモリ部
４３時間軸補間部
４４妨害算出部
４５周波数軸補間部
５１，５１Ａ軟判定部
５２，５２Ａ１〜５２Ａｎ軟判定補正部
５３，５３Ａ誤り訂正復号部
５４Ａ１〜５４Ａｎレベル補正部[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a receiving apparatus of an orthogonal frequency division multiplexing (hereinafter referred to as OFDM) transmission system, and in particular, various types of interference including frequency selective interference (co-channel interference, multipath, spurious, etc.) in a received signal. OFDM reception including improved techniques when interference exists and demodulation performance degrades due to interferenceapparatusIt is about.
[0002]
[Prior art]
In recent years, with the rapid development of digital transmission technology, digital broadcasting such as satellites, cables, and terrestrial waves is about to enter a full-scale practical stage. In particular, the OFDM system has already been put into practical use as a terrestrial digital television broadcasting system in Europe, and in Japan, its adoption has been determined as a terrestrial digital television broadcasting system and a terrestrial digital audio broadcasting system.
[0003]
The OFDM transmission system performs modulation and demodulation by allocating data to a plurality of carriers orthogonal to each other. The transmission side performs inverse fast Fourier transform (hereinafter, IFFT) processing, and the reception side performs fast Fourier transform. Transformation (hereinafter, FFT (Fast Fourier Transform)) processing is performed. Each carrier can use an arbitrary modulation method, and differential modulation such as synchronous modulation such as QPSK (Quaternary Phase Shift Keying) and QAM (Quadrature Amplitude Modulation) and DQPSK (Differential Quaternary Phase Shift Keying) is possible. . In the synchronous modulation method, a pilot signal is periodically inserted into a transmission signal, and a transmission path characteristic is obtained based on the pilot signal on the receiving side and demodulated. In the differential modulation method, demodulation is performed by delay detection. In addition to the OFDM transmission scheme, in the digital transmission scheme, error correction coding / decoding processing is performed in order to improve transmission characteristics.
[0004]
However, if there is a drop in the level of a specific carrier due to the presence of a reflected wave called multipath in the transmission line, or co-channel interference due to analog television broadcasting, the demodulation performance and error correction capability may be greatly degraded. is there.
[0005]
Examples of conventional techniques for avoiding such a situation include those disclosed in JP-A-11-252040 and JP-A-11-346205. In the following, the former is the conventional technique 1 and the latter is the conventional technique 2, and the techniques described in these documents will be briefly described with reference to the drawings.
[0006]
First, FIG. 16 shows a configuration of an OFDM receiving apparatus according to Conventional Technique 1. In this OFDM receiver, an OFDM transmission signal is input to the tuner unit 103 via the receiving antenna 101 and the RF amplifier 102, and tuning is performed. The channel selection here is performed by adjusting the oscillation frequency of the local oscillator 111 to a desired channel frequency by a frequency control signal input to the channel selection information input terminal 110.
[0007]
The output of the tuner unit 103 is converted into a digital signal by an analog / digital (hereinafter, A / D) conversion unit 104, is orthogonally detected by the orthogonal detection unit 105, and is converted into a baseband OFDM signal. This baseband OFDM signal is supplied to the FFT unit 106 and the synchronous reproduction unit 112. The FFT unit 106 converts the input OFDM signal from a time domain signal to a frequency domain signal. Note that the clock and timing signals used in the A / D conversion clock and other digital circuits are reproduced from the baseband OFDM signal by the synchronous reproduction unit 112.
[0008]
The output of the FFT unit 106 indicates the phase and amplitude of each carrier of the OFDM signal and is supplied to the demodulation unit 107. The demodulator 107 performs demodulation processing by synchronous detection on the input OFDM signal corresponding to the modulation method. Here, synchronous detection uses a pilot signal inserted at a rate of 1/3 in the frequency direction and 1/4 in the time direction to detect the channel characteristics of each carrier, and perform amplitude equalization and phase equalization. Is what you do.
[0009]
In synchronous detection, since pilot signals are arranged in a 4-symbol period in the received OFDM signal, transmission path characteristics with a 3-carrier interval can be obtained by the 4-symbol pilot signal. Therefore, the channel characteristics of all carriers are obtained by interpolating these in the frequency direction. The demodulated signal is input to the error correction unit 108, and an error generated during transmission is corrected, and then output from the output terminal 109.
[0010]
On the other hand, the output of the FFT unit 106 is also input to the interference detection unit 113. The interference detection unit 113 determines the carrier that is affected by the interference of frequency selectivity by determining the state of the received pilot signal. The determination result is output to the demodulation unit 107, the error correction unit 108, and the synchronous reproduction unit 112, and is used for improving the demodulation performance.
[0011]
That is, the demodulator 107 detects the channel characteristics of each carrier using pilot signals during synchronous detection, and performs amplitude equalization and phase equalization. When it matches the frequency of the pilot signal, it is not used, and the channel characteristic is detected and demodulated using the signal interpolated by the pilot signal not affected by the interference. Further, the error correction unit 108 performs weighting processing such as erasure correction on the carrier information affected by the interference. On the other hand, the synchronous reproduction unit 112 performs synchronous reproduction with little error from a signal that is not disturbed.
[0012]
FIG. 17 is a block diagram of an OFDM receiver showing a specific configuration of the interference detection unit 113. The signal subjected to the fast Fourier transform from the FFT unit 106 is input to the pilot signal extraction unit 113 a of the interference detection unit 113. The pilot signal extraction unit 113a extracts a pilot signal from the input signal, and its output is output to the integrator 113b and also supplied to the subtraction unit 113c.
[0013]
The integrator 113b obtains an average value by integrating the amplitudes of the pilot signals, and this average value is supplied to the subtraction unit 113c. The subtractor 113c detects a difference between the average value of the amplitude of each pilot signal and the amplitude of each pilot signal, and the detected output is output to the absolute value calculator 113d as an error of each pilot signal. The absolute value calculator 113d calculates the absolute value of the error of each pilot signal.
[0014]
The output of the absolute value calculation unit 113d is supplied to the integrator 113e, and an error integration process of each pilot signal is performed in the time direction. The processing result is supplied to the comparison unit 113f and the averaging unit 113g as an error signal of each pilot signal. Here, the error signal of each pilot signal corresponds to the C / N value of each pilot signal. The C / N value of each pilot signal is output as the C / N value of all pilot signals by the averaging unit 113g. On the other hand, the comparison unit 113f compares the C / N value of each pilot signal with the C / N value of all pilot signals. If the difference between the comparison results is large, it is determined that there is an interference with frequency selectivity. . The output of the comparison unit 113f is output to the demodulation unit 107, the error correction unit 108, and the synchronous reproduction unit 112 as the above-described disturbing carrier information.
[0015]
FIG. 18 shows the configuration of an OFDM receiving apparatus according to Conventional Technique 2. In this figure, a transmission signal 201 is an OFDM signal received by a receiving antenna (not shown) or an OFDM signal transmitted through a cable. The transmission signal 201 is selected by the tuner unit 202 and converted into a digital signal by the A / D conversion unit 203. Subsequently, quadrature detection is performed by the quadrature detection unit 204, converted into a baseband OFDM signal, and supplied to the FFT unit 205. The FFT unit 205 converts the input time domain signal into a frequency domain signal. This FFT output indicates the phase and amplitude of each carrier of the OFDM signal, and is supplied to the demodulator 206.
[0016]
The demodulator 206 performs synchronous detection. Pilot signals are periodically inserted in the frequency direction and time direction on the transmission side, and this pilot signal is extracted and compared with a reference value to detect the channel characteristics of each carrier, and amplitude equalization, phase, etc. And do. That is, since the pilot signal is inserted in a skipped manner, the transmission path characteristics are obtained by interpolation on the time axis and the frequency axis, and equalization is performed based on the transmission path characteristics.
[0017]
A signal (demodulated data) 207 equalized by synchronous detection is supplied to an error correction unit 208 and a disturbance detection unit 209 that constitute frequency selective disturbance correction means. The interference detection unit 209 detects multipath, spurious, and co-channel interference, and provides the error correction unit 208 with interference detection information indicating the corresponding position and the level of interference. The error correction unit 208 weights the detected signal based on the interference detection information from the interference detection unit 209, performs error correction such as erasure correction, and outputs the result. The weighting process may be performed in the interference detection unit 209.
[0018]
FIG. 19 shows a specific configuration of the interference detection unit 209. The demodulated data input from the demodulation unit 206 is hard-decided by the hard decision unit 291, and the hard decision result is given to the integrator 292. The integrator 292 performs integration for each carrier or for some of the carriers, and at regular intervals. The integration result is output to the level determination unit 293 and the weighting unit 294 as a variance value.
[0019]
The level determination unit 293 determines the carrier receiving the interference from the magnitude of the dispersion value output from the integrator 292 and determines the weighting level for which carrier is to be weighted. The determination result is output to the weighting unit 294. The weighting unit 294 captures the current demodulated data, and how much weight is to be applied to the demodulated data captured from the variance value of each carrier from the integrator 292 and the level determination result from the level determination unit 293 The weighting amount is calculated. Information on this weighting amount is output to the error correction unit 208. The error correction unit 208 performs error correction processing by multiplying the input demodulated data by a coefficient based on the corresponding weighting amount.
[0020]
[Problems to be solved by the invention]
As described above, the conventional OFDM receiver detects frequency selective interference from the FFT output signal or the demodulated output signal and attempts to remove the interference. However, for example, in the configuration of the OFDM receiver of the conventional technique 1, in addition to the memory in the demodulator not shown, a memory for performing integration in the time direction in the integrator 113b and the integrator 113e is further required. . The memory capacity corresponds to the number of pilot signals for 4 symbols.
[0021]
Also in the configuration of the OFDM receiver extended in the conventional technique 2, in addition to the memory of the demodulation unit 206, a memory for performing integration in the time direction in the integrator 292 is required. The capacity corresponds to the number of pilot signals for 4 symbols in the memory of the demodulator. Further, the memory of the integrator 292 can be integrated for some carriers, but in order to bring out the original performance in this method, it corresponds to the total number of carriers.
[0022]
Further, in the prior art, even when the information signal assigned to each carrier, such as 64QAM, is a multi-level modulation system including bit data having different tolerances against transmission errors, the interference is also prevented. Since weighting processing in units of carriers is performed based on the detection result, bit data having high resistance to transmission errors and bit data having low resistance to transmission errors are handled equally.
[0023]
The present invention has been made in view of the above-described conventional problems. When receiving and demodulating an OFDM transmission signal, the present invention detects the interference even when it receives a frequency selective interference, and transmits the signal. An object of the present invention is to effectively perform error correction on a multi-level carrier modulation system including bit data having different tolerances against errors to improve characteristics such as demodulation performance and error correction capability. Another object of the present invention is to realize an OFDM receiver that requires as little extra memory as possible in order to realize this function.
[0024]
[Means for Solving the Problems]
In the invention of claim 1 of the present application, a plurality of carriers generated at frequencies orthogonal to each other within a transmission band are modulated with information signals respectively allocated to the plurality of carriers modulated by the information signals. An OFDM receiver for receiving an orthogonal frequency division multiplexing (hereinafter referred to as OFDM) transmission signal into which a known pilot signal is periodically inserted, comprising: orthogonal detection means for orthogonally detecting the OFDM transmission signal; and orthogonal detection means FFT means for converting the obtained output signal from a time domain to a frequency domain signal by fast Fourier transform (hereinafter referred to as FFT), a pilot signal is extracted from the output signal obtained by the FFT means, and the pilot signal and the known The pilot signal transmission path characteristics are estimated from the reference pilot signal of the pilot signal, and the pilot signal transmission path characteristics are Interpolating in the time axis direction while accumulating in the first memory means, and further interpolating in the frequency axis direction to estimate the transmission path characteristics of all carriers in the transmission band, and using the carrier transmission path characteristics, The demodulating means for equalizing the output signal obtained by the FFT means and outputting it as a demodulated signal, the transmission path characteristics of the pilot signal obtained by the demodulating means, and the first memory means in the demodulating means are stored. Then, an error signal representing the amount of time fluctuation of the pilot signal transmission line characteristic is calculated from the pilot signal transmission line characteristic of the previous cycle, and frequency selective interference is detected based on the error signal and output as an interference level. An interference detecting means for converting the demodulated signal obtained by the demodulating means into a soft decision information signal, and using the interference level obtained by the interference detecting means, Correctness and is characterized by comprising error correction means for performing error correction decoding, the relative corrected soft decision information signal.
[0025]
In the invention of claim 2 of the present application, a plurality of carriers generated at frequencies orthogonal to each other within a transmission band are multi-value modulated by an information signal consisting of a predetermined number of bit data allocated to each of the carriers, and the information signal An OFDM receiver for receiving an OFDM transmission signal in which known pilot signals are periodically inserted for a plurality of modulated carriers, wherein the orthogonal detection means performs quadrature detection on the OFDM transmission signal, and the quadrature detection means The FFT means for converting the output signal obtained in step 1 from the time domain to the frequency domain by FFT, and a pilot signal is extracted from the output signal obtained by the FFT means, and the pilot signal and the known reference pilot signal are extracted from the pilot signal. A pilot signal transmission path characteristic is estimated, and a pilot signal transmission path characteristic is provided in the first memory. Interpolating in the time axis direction while accumulating in the means, further interpolating in the frequency axis direction to estimate the transmission path characteristics of all carriers in the transmission band, and using the carrier transmission path characteristics, the FFT means The demodulating means for equalizing the output signal and outputting it as a demodulated signal, the transmission path characteristics of the pilot signal obtained by the demodulating means, and the previous cycle stored in the first memory means in the demodulating means An interference detection means for calculating an error signal indicating a time variation amount of the pilot signal transmission line characteristic from the pilot signal transmission line characteristic, detecting a frequency selective disturbance based on the error signal, and outputting the interference as a disturbance level; The demodulated signal obtained by the demodulating means is converted into a soft decision information signal composed of a predetermined number of soft decision bit data according to a carrier modulation method, and each of the soft decision information signals The interference level obtained by the interference detection means is corrected for each soft decision bit data, the soft decision bit data is corrected using the corrected interference level, and error correction decoding is performed on the corrected soft decision bit data. And error correction means for performing.
[0026]
The invention of claim 3 of the present application is such that a plurality of carriers generated at frequencies orthogonal to each other within a transmission band are subjected to multi-level modulation by an information signal composed of a predetermined number of bit data, and the information signal is An OFDM receiver that receives an OFDM transmission signal that includes bit data with different tolerances against transmission errors and in which known pilot signals are periodically inserted for a plurality of carriers modulated by the information signal, From orthogonal detection means for orthogonal detection of an OFDM transmission signal, FFT means for converting an output signal obtained by the orthogonal detection means from a time domain to a frequency domain signal by FFT, and an output signal obtained by the FFT means A pilot signal is extracted, and a transmission path characteristic of the pilot signal is extracted from the pilot signal and a known reference pilot signal. And interpolating in the time axis direction while accumulating the transmission path characteristics of the pilot signal in the first memory means provided therein, and further interpolating in the frequency axis direction to transmit the transmission paths of all carriers in the transmission band. Estimating the characteristics, equalizing the output signal obtained by the FFT means using the carrier path characteristics of the carrier, and outputting the demodulated signal as a demodulated signal, the transmission path characteristics of the pilot signal obtained by the demodulating means, And calculating an error signal representing a time fluctuation amount of the pilot signal transmission line characteristic from the pilot signal transmission line characteristic of the previous cycle stored in the first memory means in the demodulation unit, and based on the error signal. A disturbance detecting means for detecting a frequency selective disturbance and outputting it as an interference level, and a demodulated signal obtained by the demodulating means for a predetermined number of soft decision bits according to a carrier modulation method Is converted into a soft decision information signal composed of data, and for each soft decision bit data of the soft decision information signal, if the tolerance for transmission errors of the soft decision bit data is small, the interference level is increased and the soft decision bit data is increased. When tolerance against transmission error of decision bit data is large, the disturbance level obtained by the disturbance detection means is corrected so as to reduce the disturbance level, and the soft decision bit data is corrected using the corrected disturbance level. And error correction means for performing error correction decoding on the corrected soft decision bit data.
[0027]
  According to a fourth aspect of the present invention, in the OFDM receiver according to any one of the first to third aspects, the interference detecting means includes a transmission path characteristic of a pilot signal obtained by the demodulating means, An error signal representing the amount of time variation of the pilot signal transmission line characteristic is calculated from the transmission characteristic of the pilot signal of the previous cycle stored in the first memory means, and the error signal is provided inside The second memory means is used for averaging in the time axis direction, and the averaged error signal is interpolated in the time axis direction while accumulating in the second memory means, and frequency selectivity is obtained from the averaged and interpolated error signal. An interference level representing interference is calculated, and the interference level is output after being interpolated in the frequency axis direction.
  According to a fifth aspect of the present invention, in the OFDM receiving apparatus according to any one of the first to third aspects, the disturbance detecting means includes a transmission path characteristic of a pilot signal obtained by the demodulating means, and the demodulating means. An error signal representing the amount of time variation of the pilot signal transmission line characteristic is calculated from the transmission characteristic of the pilot signal of the previous cycle stored in the first memory means, and the error signal is provided inside Interpolating in the time axis direction while accumulating in the second memory means, calculating an interference level representing interference of frequency selectivity from the interpolated error signal, and interpolating the interference level in the frequency axis direction and outputting it. It is a feature.
[0028]
  According to a sixth aspect of the present invention, in the OFDM receiver according to any one of the first to third aspects, the interference detecting means includes a transmission path characteristic of a pilot signal obtained by the demodulating means, An error signal representing a time fluctuation amount of the pilot signal transmission line characteristic is calculated from the transmission line characteristic of the pilot signal of the previous cycle stored in the first memory means, and frequency selectivity of the pilot signal is calculated from the error signal. An interference level representing interference is calculated, the interference level is averaged in the time axis direction using a second memory means provided therein, and the average interference level is accumulated in the second memory means while being time axis It is characterized by interpolating in the direction and further interpolating in the frequency axis direction and outputting.
  The invention according to claim 7 of the present application is the OFDM receiver according to any one of claims 1 to 3, wherein the interference detection means includes transmission path characteristics of a pilot signal obtained by the demodulation means, An error signal representing a time fluctuation amount of the pilot signal transmission line characteristic is calculated from the transmission line characteristic of the pilot signal of the previous cycle stored in the first memory means, and frequency selectivity of the pilot signal is calculated from the error signal. An interference level representing interference is calculated, and the interference level is interpolated in the time axis direction while being accumulated in a second memory means provided therein, and further interpolated in the frequency axis direction and output. is there.
[0029]
  The invention according to claim 8 of the present application is the OFDM receiver according to any one of claims 1 to 3, wherein the interference detection means includes a transmission path characteristic of a pilot signal obtained by the demodulation means, An error signal representing the amount of time variation of the pilot signal transmission line characteristic is calculated from the transmission characteristic of the pilot signal of the previous cycle stored in the first memory means, and the error signal is provided inside Averaged in the time axis direction using the second memory means, interpolated in the time axis direction while accumulating the averaged error signal in the second memory means, further interpolated in the frequency axis direction, averaged and interpolated An interference level representing interference of frequency selectivity is calculated from the error signal.
[0030]
  According to a ninth aspect of the present invention, in the OFDM receiver according to any one of the first to third aspects, the interference detecting means includes a transmission path characteristic of a pilot signal obtained by the demodulating means, An error signal representing the amount of time variation of the pilot signal transmission line characteristic is calculated from the transmission characteristic of the pilot signal of the previous cycle stored in the first memory means, and the error signal is provided inside Interpolating in the time axis direction while accumulating in the second memory means, further interpolating in the frequency axis direction, and calculating an interference level representing interference of frequency selectivity from the interpolated error signal. .
[0037]
DETAILED DESCRIPTION OF THE INVENTION
An OFDM receiver according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0038]
(Embodiment 1)
FIG. 1 is an overall configuration diagram of an OFDM receiving apparatus according to Embodiment 1 of the present invention. An OFDM transmission signal is provided to the OFDM receiver through a receiving antenna or cable. This signal is selected by a tuner unit (not shown), converted to a digital signal by an A / D conversion unit, and input to the quadrature detection unit 1 in the figure.
[0039]
The quadrature detection unit 1 performs quadrature detection on the input signal and converts it to a baseband OFDM signal. The FFT unit 2 performs fast Fourier transform on the signal from the quadrature detection unit 1, converts the signal in the time domain into a signal in the frequency domain, and outputs the signal. This FFT output indicates the phase and amplitude of each carrier of the OFDM transmission signal. Specifically, it is handled in the form of a complex signal having independent levels in the I-axis direction and Q-axis direction.
[0040]
The demodulation unit 3 includes a pilot generation unit 31, a first complex division unit 32, a first memory unit 33, a time axis interpolation unit 34, a frequency axis interpolation unit 35, and a second complex division unit 36. . The demodulator 3 performs synchronous detection on the input signal and outputs a demodulated signal. Here, the memory unit 33 has a capacity for storing the transmission path characteristics of the pilot signal for one period. FIG. 2 shows a specific example of pilot signal arrangement. D1 indicates the position of the data carrier, and P1 indicates the position of the pilot signal. In this example, four symbols form one cycle, and the required memory amount is 1/3 of the total number of carriers.
[0041]
The pilot generating unit 31 generates a known pilot signal (reference value) at the same timing with respect to the pilot signal periodically inserted in the input signal. The complex division unit 32 performs complex division on the pilot signal periodically inserted into the input signal by the known pilot signal (reference value) generated by the pilot generation unit 31 to obtain the transmission path characteristic of the pilot signal. Estimate and output. FIG. 3 shows the arrangement of pilot signal transmission path characteristics estimated based on the pilot signal arrangement shown in FIG. In FIG. 3, C1 indicates a position where the transmission path characteristic of the pilot signal can be obtained, and the transmission path characteristic cannot be obtained at the position of C0.
[0042]
The time axis interpolation unit 34 sequentially accumulates the transmission path characteristics of the pilot signal obtained by the complex division unit 32 in the memory unit 33, and performs memory for the carrier existing at the same position as the pilot signal on each frequency axis. By reading out and applying the transmission path characteristics of the pilot signal at the same carrier position stored in the unit 33, the transmission path characteristics are interpolated (zero-order interpolation) in the time axis direction and output.
[0043]
The time axis interpolation unit 34 sequentially accumulates the pilot signal transmission line characteristics obtained by the complex division unit 32 in the memory unit 33, and also transmits the pilot signal transmission line characteristics obtained by the complex division unit 32 and the memory. Configuration in which linear interpolation (primary interpolation) is performed on the carrier existing at the same position as the pilot signal on each frequency axis based on the transmission path characteristics of the pilot signal just before one cycle accumulated in the unit 33 It is good. This makes it possible to perform highly accurate interpolation following the time variation of the transmission path characteristics, and improve the demodulation performance.
[0044]
FIG. 4 shows a conceptual diagram of the time axis interpolation processing based on the arrangement of the transmission path characteristics of the pilot signal shown in FIG. An arrow TC in FIG. 4A indicates time axis interpolation. In FIG. 4B, C1 indicates a position where the transmission path characteristic of the pilot signal is obtained, and C2 indicates a position where the transmission path characteristic subjected to time axis interpolation is obtained. Transmission path characteristics cannot be obtained at the position of C0.
[0045]
The frequency axis interpolation unit 35 in FIG. 1 interpolates the transmission path characteristics obtained at the constant time interval obtained by the time axis interpolation section 34 in the frequency axis direction through a filter, and outputs the transmission path characteristics of all carriers. FIG. 5 shows a conceptual diagram of frequency axis interpolation processing based on the time axis interpolation result shown in FIG. A curve FC in FIG. 5A shows frequency axis interpolation. In FIG. 5B, C1 indicates a position where the transmission path characteristic of the pilot signal is obtained, and C2 indicates a position where the transmission path characteristic subjected to time axis interpolation is obtained. C3 indicates a position where the frequency-interpolated transmission path characteristic is obtained.
[0046]
The complex division unit 36 in FIG. 1 performs complex division on each carrier signal input to the demodulation unit 3 based on the carrier channel characteristics obtained by the frequency axis interpolation unit 35, and outputs the division result as a demodulated signal. .
[0047]
The interference detection unit 4 includes an error calculation unit 41, a second memory unit 42, a time axis interpolation unit 43, an interference calculation unit 44, and a frequency axis interpolation unit 45. The interference detection unit 4 detects interference of frequency selectivity using the transmission path characteristics of the pilot signal obtained in the demodulation unit 3. Here, the memory unit 42 has a capacity for storing an error signal of the pilot signal for one period.
[0048]
The error calculation unit 41 calculates and outputs an error signal that represents time fluctuation in units of pilot signals. That is, complex subtraction is performed between the transmission path characteristics of the pilot signal obtained by the complex division section 32 and the transmission path characteristics of the pilot signal just one cycle before accumulated in the memory section 33, and the power of the complex signal as a subtraction result is obtained. Is calculated to determine the square of the distance between the signal points of the two transmission path characteristics represented by the complex signal, and this is output as an error signal. Here, by sharing the memory unit 33 that is an essential component of the demodulating unit 3, the error signal can be calculated without having an extra memory unit as used in the integrator 113b of FIG. The
[0049]
The error calculation unit 41 performs a complex subtraction between the transmission path characteristics of the pilot signal obtained by the complex division section 32 and the transmission path characteristics of the pilot signal just before one period accumulated in the memory section 33, and performs subtraction. By calculating the amplitude of the resulting complex signal, a distance between signal points of two transmission path characteristics represented by the complex signal may be obtained and output as an error signal.
[0050]
FIG. 6 shows an arrangement of error signals calculated based on the arrangement of transmission signal characteristics of pilot signals shown in FIG. In FIG. 6, E1 indicates a position where an error signal is obtained, and no error signal is obtained at the position E0.
[0051]
The time axis interpolation unit 43 in FIG. 1 calculates the error signal in the time axis direction of the error signal at the same carrier position from the error signal obtained by the error calculation unit 41 and the error signal stored in the memory unit 42 immediately before one cycle. The average is calculated, and the calculation result is sequentially stored in the memory unit 42 as a new error signal. At the same time, the error signal stored in the memory unit 42 is stored for the carrier existing at the same position as the pilot signal on each frequency axis. By reading and applying, the error signal is averaged and interpolated in the time axis direction and output. As a result, even when the pilot signal at the carrier position receiving the frequency selective interference becomes close to the reference pilot signal at a certain time (symbol), the presence of the frequency selective interference is not overlooked. Interference detection accuracy can be improved.
[0052]
The time axis interpolating unit 43 sequentially accumulates the error signal obtained by the error calculating unit 41 in the memory unit 42 and also stores the error signal in the memory unit 42 for carriers existing at the same position as the pilot signal on the frequency axis. A configuration may be adopted in which the error signal is interpolated (zero-order interpolation) in the time axis direction by reading out and applying the accumulated error signal at the same carrier position.
[0053]
In addition, the time axis interpolation unit 43 sequentially accumulates the error signal obtained by the error calculation unit 41 in the memory unit 42, and the error signal obtained by the error calculation unit 41 and just one accumulated in the memory unit 42. A configuration may be adopted in which linear interpolation (primary interpolation) is performed on the carrier existing at the same position as the pilot signal on the frequency axis from the error signal before the cycle.
[0054]
FIG. 7 shows a conceptual diagram of the time axis interpolation processing based on the error signal arrangement shown in FIG. An arrow TE in FIG. 7A indicates time axis interpolation including average calculation. In FIG. 7B, E1 indicates a position where an error signal is obtained, and E2 indicates a position where an error signal subjected to time axis interpolation is obtained. An error signal cannot be obtained at the position E0.
[0055]
The interference calculation unit 44 in FIG. 1 averages the error signal obtained by the time axis interpolation unit 43 in the frequency axis direction, and the error signal obtained by the time axis interpolation unit 43 is obtained by averaging the error signal in the frequency axis direction. Divide and output the division result as an interference level representing frequency selective interference.
[0056]
The interference calculation unit 44 averages the error signal obtained by the time axis interpolation unit 43 in the frequency axis direction, and subtracts the average of the error signal in the frequency axis direction from the error signal obtained by the time axis interpolation unit 43. Alternatively, the result may be output as an interference level representing frequency selective interference.
[0057]
The interference calculation unit 44 may be configured to subtract a predetermined constant from the error signal obtained by the time axis interpolation unit 43 and output the result as an interference level representing frequency selective interference.
[0058]
Further, the interference calculation unit 44 may be configured to divide the error signal obtained by the time axis interpolation unit 43 by a predetermined constant and output the result as an interference level representing frequency selective interference.
[0059]
Further, the interference calculation unit 44 includes a predetermined input / output table that receives an error signal and outputs an interference level that represents frequency selective interference, and inputs and outputs the error signal obtained by the time axis interpolation unit 43. It is good also as a structure which outputs a disturbance level by giving to a table.
[0060]
In addition to the above configuration, the interference calculation unit 44 can be configured to output a result obtained by combining several calculations based on the error signal obtained by the time axis interpolation unit 43. .
[0061]
In any of the above configurations, the interference level output from the interference calculation unit 44 is obtained in the same arrangement as that of the input error signal. FIG. 8 shows an arrangement of disturbance levels calculated based on the arrangement of error signals shown in FIG. In FIG. 8, I1 indicates a position where the interference level can be obtained, and no interference level is obtained at the position of I0.
[0062]
The frequency axis interpolation unit 45 in FIG. 1 interpolates in the frequency axis direction by applying the interference level at a constant carrier interval obtained by the interference calculation unit 44 to adjacent carriers, and outputs it as the interference level of all carriers. .
[0063]
The frequency axis interpolation unit 45 may be configured to linearly interpolate (primary interpolation) the interference level at a constant carrier interval obtained by the interference calculation unit 44 in the frequency axis direction and output the interference level for all carriers. .
[0064]
Further, the frequency axis interpolation unit 45 may be configured to interpolate the interference level at a constant carrier interval obtained by the interference calculation unit 44 in the frequency axis direction through a filter and output it as the interference level of all carriers.
[0065]
FIG. 9 shows a conceptual diagram of frequency axis interpolation processing based on the arrangement of the interference levels shown in FIG. An arrow FI in FIG. 9A indicates frequency axis interpolation. In FIG. 9B, I1 indicates a position where the interference level can be obtained, and I2 indicates a position where the interference level obtained by frequency axis interpolation can be obtained.
[0066]
In the above configuration, the interference detection unit 4 performs time-axis interpolation on the error calculation result and frequency-axis interpolation on the interference calculation result. However, the interference detection level is obtained by performing time-axis interpolation on the error calculation result and frequency-axis interpolation. It is good also as a structure which calculates. Further, the interference level may be calculated from the error calculation result, the interference calculation result may be subjected to time axis interpolation, and further frequency axis interpolation may be performed.
[0067]
Next, the error correction unit 5 of FIG. 1 includes a soft decision unit 51, a soft decision correction unit 52, and an error correction decoding unit 53. The error correction unit 5 corrects the demodulated signal obtained by the demodulation unit 3 based on the disturbance level obtained by the interference detection unit 4 and performs error correction decoding. Here, the demodulated signal obtained by the demodulator 3 includes errors due to various interferences on the transmission device, the reception device, and the transmission path. The error correction unit 5 converts the demodulated signal obtained by the demodulation unit 3 into a soft decision information signal corresponding to the original information signal used in the modulation process, and the soft decision information signal and the original information signal ( The probability of the received signal is expressed using a distance from an information signal that is known in the receiving apparatus. The error correction unit 5 performs error correction decoding using a method called a soft decision decoding method that estimates a sequence of information signals based on the accumulation.
[0068]
An example of the soft decision decoding method is shown in FIG. With respect to the original information signals 0 and 1, there are soft decision information signals positioned stepwise in the middle and the periphery thereof. The inputted demodulated signal is converted into a signal located closest to the soft decision information signal including 0 and 1. It can be said that the soft decision information signal converted here is more reliable as the decoded information signal is closer to 0 or 1 of the original information signal. Further, it can be said that the reliability of the decoded information signal is lower as it is closer to the center of the original information signals 0 and 1, that is, closer to 0.5.
[0069]
The soft decision unit 51 in FIG. 1 converts the demodulated signal obtained by the demodulation unit 3 into a soft decision information signal by the above-described method. The soft decision correction unit 52 corrects the soft decision information signal obtained by the soft decision unit 51 using the disturbance level obtained by the disturbance detection unit 4. Specifically, conversion that lowers the reliability of the soft decision information signal, that is, conversion to a soft decision information signal closer to the center of 0 and 1 of the original information signal, is performed according to the magnitude of the interference level. The error correction decoding unit 53 performs error correction decoding on the soft decision information signal corrected by the soft decision correction unit 52.
[0070]
With the above configuration, an OFDM receiver that receives an OFDM transmission signal and demodulates transmission data detects the interference even when it receives frequency-selective interference and improves characteristics such as demodulation performance and error correction capability. Effect is obtained. Further, in order to obtain the effect, it is possible to adopt a configuration that does not require an extra memory amount, such as performing error detection by sharing a memory that is essential for the demodulation unit, and a reduction in the total memory amount is realized.
[0071]
(Embodiment 2)
Next, an OFDM receiving apparatus according to Embodiment 2 of the present invention will be described. FIG. 11 is an overall configuration diagram of an OFDM receiver according to this embodiment. Here, it is assumed that the received OFDM transmission signal is multi-level modulated by an information signal in which each carrier is composed of a predetermined number of bit data. Note that components that perform the same signal processing as those of the OFDM receiver in Embodiment 1 are denoted by the same reference numerals as those in FIG. 1, and description thereof is omitted.
[0072]
This OFDM receiver includes a quadrature detection unit 1, an FFT unit 2, a demodulation unit 3, an interference detection unit 4A, and an error correction unit 5A. The interference detector 4A detects frequency selective interference from the output signal obtained by the FFT unit 2 and outputs an interference level. The demodulator 3 has the same configuration as that of the first embodiment.
[0073]
The interference detector 4A may be configured to detect frequency selective interference from the demodulated signal obtained by the demodulator 3 and output the interference level as shown in FIG.
[0074]
As shown in FIG. 12, the error correction unit 5A includes a soft decision unit 51A, soft decision correction units 52A1, 52A2,... 52An, error correction decoding unit 53A, level correction units 54A1, 54A2,. Consists of.
[0075]
The error correction unit 5A converts the demodulated signal obtained by the demodulating unit 3 into a soft decision information signal including a predetermined number of soft decision bit data corresponding to the carrier modulation scheme, and each soft decision bit of the soft decision information signal. For each data, the interference level obtained by the interference detector 4A is corrected, the soft decision bit data is corrected using the corrected interference level, and error correction decoding is performed.
[0076]
Soft decision section 51A converts the demodulated signal obtained by demodulation section 3 into a soft decision information signal composed of a predetermined number (n) of soft decision bit data corresponding to the carrier modulation scheme.
[0077]
The level correction units 54A1 to 54An correct the interference level obtained by the interference detection unit 4A for each soft decision bit data of the soft decision information signal. Here, the content of level correction may be different for each soft decision bit data, or may be common to some or all of the soft decision bit data.
[0078]
The soft decision correction units 52A1 to 52An correct the soft decision bit data obtained by the soft decision unit 51A using the interference levels corrected by the level correction units 54A1 to 54An, respectively. More specifically, conversion that lowers the reliability of the soft decision bit data, that is, conversion to soft decision bit data closer to the center of the original bit data 0 and 1 is performed according to the magnitude of the interference level.
[0079]
The error correction decoding unit 53A performs error correction decoding on the soft decision bit data corrected by the soft decision correction units 52A1 to 52An.
[0080]
When each carrier of the OFDM transmission signal is multi-level modulated by an information signal composed of a predetermined number of bit data, and the information signal includes bit data having different tolerances against transmission errors, the error correction unit 5A Such signal processing is performed. That is, the error correction unit 5A converts the demodulated signal obtained by the demodulating unit 3 into a soft decision information signal composed of a predetermined number of soft decision bit data corresponding to the carrier modulation method, and each soft decision information signal of the soft decision information signal is converted. For each bit data, the interference level is increased when the resistance against the transmission error of the soft decision bit data is small, and the interference level is decreased when the resistance against the transmission error of the soft decision bit data is large. The interference level obtained by the detection unit 4A is corrected. And it is good also as a structure which correct | amends soft decision bit data using the correct | amended interference level, and performs error correction. As a result, the degree of influence of frequency selectivity interference on the accuracy of the soft decision information signal can be set for each soft decision bit data having different tolerances to transmission errors, and the overall error correction capability can be improved.
[0081]
As an example of the multi-level modulation method, a mapping phase diagram of 64QAM is shown in FIG. In general, the Gray code arrangement is such that all information signals differ by only 1 bit between adjacent mapping signal points. The I axis indicates the level corresponding to b0, b2, b4, and the Q axis indicates the level corresponding to b1, b3, b5. This Gray code arrangement is excellent from the viewpoint of code error rate, and is also the case in the example shown in FIG. The information signal used for carrier modulation in this case is 6 bits, and the resistance to transmission errors is the highest in the upper 2 bits (b0, b1), the lowest in the lower 2 bits (b4, b5), and the intermediate 2 bits (b2 , B3) are in the middle.
[0082]
FIG. 15 is a configuration diagram of the error correction unit 5A when 64QAM is used as the carrier modulation method. The error correction unit 5A includes the level correction units 54A1 to 54A3 for soft decision bit data having different resistances to transmission errors in three stages, thereby performing error correction by applying different interference levels.
[0083]
The soft decision unit 51A in FIG. 15 converts the demodulated signal obtained by the demodulation unit 3 into a soft decision information signal composed of a predetermined number (6 in the case of 64QAM) of soft decision bit data corresponding to the carrier modulation scheme. The level correction units 54A1 to 54A3 correct the interference level obtained by the interference detection unit 4A for each soft decision bit data having different tolerances against transmission errors. For soft decision bit data (b0, b1) having the greatest resistance to transmission errors, correction is performed to reduce the interference level. Further, for the soft decision bit data (b4, b5) having the least tolerance against transmission errors, correction for increasing the interference level is performed. Further, for soft decision bit data (b2, b3) having intermediate tolerance against transmission errors, the inputted disturbance level is output as it is without correction for the disturbance level.
[0084]
The soft decision correction units 52A1 to 52A3 correct the soft decision bit data obtained by the soft decision unit 51A using the interference levels corrected by the level correction units 54A1 to 54A3, respectively. The error correction decoding unit 53A performs error correction decoding on the soft decision bit data corrected by the soft decision correction units 52A1 to 52A3.
[0085]
With the above configuration, in an OFDM receiver that receives and demodulates an OFDM transmission signal, it is effective for multi-level carrier modulation schemes including information signals with different tolerances against transmission errors when frequency selective interference is detected. Thus, it is possible to obtain an effect of improving characteristics such as demodulation performance and error correction capability by performing error correction.
[0086]
It should be noted that the first and second embodiments of the present invention are not exclusive in principle, and it is of course possible to implement a combination of both.
[0087]
Furthermore, in the transmission method (transmission / reception device configuration) described in the present embodiment, a certain type of convolutional encoder is used for error correction coding processing in the corresponding OFDM modulation device, and accordingly It is assumed that Viterbi decoding is used for the error correction decoding process. In that case, the error correction capability is improved by performing interleaving processing (deinterleaving processing on the receiving device side) on the bit data after error correction coding and / or the carrier signal after modulation processing. Is possible. Such interleaving (deinterleaving) processing blocks are not described in the configuration diagram of the present embodiment, but it is of course possible to include these blocks.
[0088]
【The invention's effect】
As described above, according to the present invention, in an OFDM receiver that receives and demodulates an OFDM transmission signal, it detects even when it is disturbed by frequency selectivity, and includes information signals with different tolerances against transmission errors. It is possible to effectively perform error correction on the multi-level carrier modulation system and improve characteristics such as demodulation performance and error correction capability. In addition, it is possible to realize a configuration that does not require as much extra memory as possible to obtain the effect.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of an OFDM receiving apparatus according to Embodiment 1 of the present invention.
FIG. 2 is an explanatory diagram showing an arrangement of pilot signals.
FIG. 3 is an arrangement diagram for obtaining transmission path characteristics of a pilot signal.
FIG. 4 is an explanatory diagram showing a concept of time axis interpolation of a pilot signal.
FIG. 5 is an explanatory diagram showing a concept of frequency axis interpolation of a pilot signal.
6 is an arrangement diagram of error signals output from an error calculation unit according to the first embodiment. FIG.
FIG. 7 is an explanatory diagram showing a concept of time axis interpolation of an error signal.
FIG. 8 is a layout diagram of disturbance levels output from the disturbance calculation unit according to the first embodiment.
FIG. 9 is an explanatory diagram showing a concept of interference axis frequency axis interpolation;
FIG. 10 is an explanatory diagram showing a concept of a soft decision decoding method.
FIG. 11 is a block diagram showing an overall configuration of an OFDM receiving apparatus in Embodiment 2 (Part 1) of the present invention.
12 is a configuration diagram of an error correction unit used in the OFDM receiver of Embodiment 2. FIG.
FIG. 13 is a block diagram showing an overall configuration of an OFDM receiver in Embodiment 2 (No. 2) of the present invention.
FIG. 14 is a mapping phase diagram in the 64QAM modulation scheme.
FIG. 15 is a block diagram showing a configuration of an error correction unit when a 64QAM modulation method is used.
FIG. 16 is an overall configuration diagram of an OFDM receiving apparatus according to Conventional Technique 1;
FIG. 17 is a configuration diagram of a disturbance detection unit provided in an OFDM receiver according to the conventional technique 1;
FIG. 18 is an overall configuration diagram of an OFDM receiving apparatus according to Conventional Technique 2.
FIG. 19 is a configuration diagram of a disturbance detection unit provided in an OFDM receiver according to the conventional technique 2.
[Explanation of symbols]
1 Quadrature detection unit
2 FFT section
3 Demodulator
4,4A Interference detection unit
5,5A error correction section
31 Pilot generator
32 Complex division
33 Memory section
34 Time axis interpolation unit
35 Frequency axis interpolation unit
36 Complex division
41 Error calculator
42 Memory section
43 Time axis interpolation unit
44 Interference calculator
45 Frequency axis interpolation unit
51, 51A Soft decision part
52, 52A1-52An Soft decision correction unit
53, 53A Error correction decoder
54A1-54An Level correction unit

Claims

A plurality of carriers generated at frequencies orthogonal to each other in a transmission band are modulated by information signals assigned to the respective carriers, and known pilot signals are periodically inserted into the plurality of carriers modulated by the information signals. An OFDM receiver that receives an orthogonal frequency division multiplexing (hereinafter referred to as OFDM) transmission signal,
Orthogonal detection means for orthogonal detection of the OFDM transmission signal;
FFT means for converting the output signal obtained by the orthogonal detection means from a time domain to a frequency domain signal by fast Fourier transform (hereinafter referred to as FFT);
A pilot signal is extracted from the output signal obtained by the FFT means, a transmission channel characteristic of the pilot signal is estimated from the pilot signal and a known reference pilot signal, and a transmission channel characteristic of the pilot signal is provided therein. 1 is stored in the memory means, and the transmission path characteristics of the pilot signal are interpolated in the time axis direction, and further interpolated in the frequency axis direction to estimate the transmission path characteristics of all carriers in the transmission band, and transmission of the carrier Demodulating means for equalizing the output signal obtained by the FFT means using path characteristics and outputting the demodulated signal;
From the transmission path characteristics of the pilot signal obtained by the demodulation means and the transmission path characteristics of the pilot signal of the previous cycle stored in the first memory means in the demodulation means, the time of the transmission path characteristics of the pilot signal An interference signal detecting means for calculating an error signal representing a variation, detecting a frequency selective interference based on the error signal, and outputting the interference signal as an interference level;
The demodulated signal obtained by the demodulating means is converted into a soft decision information signal, the soft decision information signal is corrected using the disturbance level obtained by the disturbance detecting means, and an error occurs with respect to the corrected soft decision information signal. An OFDM receiving apparatus comprising: error correction means for performing correction decoding.

A plurality of carriers generated at frequencies orthogonal to each other within a transmission band are multi-level modulated by an information signal composed of a predetermined number of bit data allocated to each of the carriers, and a plurality of carriers modulated by the information signal An OFDM receiver for receiving an OFDM transmission signal in which a known pilot signal is periodically inserted,
Orthogonal detection means for orthogonal detection of the OFDM transmission signal;
FFT means for converting an output signal obtained by the quadrature detection means from a time domain to a frequency domain signal by FFT;
A pilot signal is extracted from the output signal obtained by the FFT means, a transmission channel characteristic of the pilot signal is estimated from the pilot signal and a known reference pilot signal, and a transmission channel characteristic of the pilot signal is provided therein. 1 is stored in the memory means, and the transmission path characteristics of the pilot signal are interpolated in the time axis direction, and further interpolated in the frequency axis direction to estimate the transmission path characteristics of all carriers in the transmission band, and transmission of the carrier Demodulating means for equalizing the output signal obtained by the FFT means using path characteristics and outputting the demodulated signal;
From the transmission path characteristics of the pilot signal obtained by the demodulation means and the transmission path characteristics of the pilot signal of the previous cycle stored in the first memory means in the demodulation means, the time of the transmission path characteristics of the pilot signal An interference signal detecting means for calculating an error signal representing a variation, detecting a frequency selective interference based on the error signal, and outputting the interference signal as an interference level;
The demodulated signal obtained by the demodulating means is converted into a soft decision information signal composed of a predetermined number of soft decision bit data according to a carrier modulation method, and the interference is determined for each soft decision bit data of the soft decision information signal. Error correction means for correcting the interference level obtained by the detection means, correcting the soft decision bit data using the corrected interference level, and performing error correction decoding on the corrected soft decision bit data; An OFDM receiver characterized by:

A plurality of carriers generated at frequencies orthogonal to each other within a transmission band are multi-value modulated by an information signal made up of a predetermined number of bit data assigned to each of the carriers, and the information signal has bit data having different tolerances against transmission errors. An OFDM receiver for receiving an OFDM transmission signal in which known pilot signals are periodically inserted for a plurality of carriers modulated by the information signal,
Orthogonal detection means for orthogonal detection of the OFDM transmission signal;
FFT means for converting an output signal obtained by the quadrature detection means from a time domain to a frequency domain signal by FFT;
A pilot signal is extracted from the output signal obtained by the FFT means, a transmission channel characteristic of the pilot signal is estimated from the pilot signal and a known reference pilot signal, and a transmission channel characteristic of the pilot signal is provided therein. 1 is stored in the memory means, and the transmission path characteristics of the pilot signal are interpolated in the time axis direction, and further interpolated in the frequency axis direction to estimate the transmission path characteristics of all carriers in the transmission band, and transmission of the carrier Demodulating means for equalizing the output signal obtained by the FFT means using path characteristics and outputting the demodulated signal;
Time variation of pilot signal transmission line characteristics from pilot signal transmission line characteristics obtained by the demodulating means and pilot signal transmission line characteristics of the previous cycle stored in the first memory means in the demodulating means. An interference signal detecting means for calculating an error signal representing a quantity, detecting a frequency selective interference based on the error signal, and outputting the interference signal as an interference level;
The demodulated signal obtained by the demodulating means is converted into a soft decision information signal made up of a predetermined number of soft decision bit data corresponding to a carrier modulation method, and the soft decision bit data of the soft decision information signal is softened for each soft decision bit data. Obtained by the interference detection means so as to increase the interference level when the tolerance to the transmission error of the decision bit data is small and decrease the interference level when the tolerance to the transmission error of the soft decision bit data is large. Error correction means for correcting an interference level, correcting the soft decision bit data using the corrected interference level, and performing error correction decoding on the corrected soft decision bit data. OFDM receiver.

The interference detection means is
The pilot signal transmission path characteristics obtained by the demodulating means, and the pilot signal transmission path characteristics of the previous cycle stored in the first memory means in the demodulating means, from the pilot signal transmission path characteristics. An error signal representing the amount of time variation is calculated, the error signal is averaged in the time axis direction using the second memory means provided therein, and the averaged error signal is stored in the second memory means, Interpolating the averaged error signal in the time axis direction, calculating an interference level representing interference of frequency selectivity from the averaged and interpolated error signal, and interpolating the interference level in the frequency axis direction for output. The OFDM receiver according to any one of claims 1 to 3, wherein

The interference detection means is
The pilot signal transmission path characteristics obtained by the demodulating means, and the pilot signal transmission path characteristics of the previous cycle stored in the first memory means in the demodulating means, from the pilot signal transmission path characteristics. An error signal representing the amount of time fluctuation is calculated, the error signal is stored in a second memory means provided therein, the error signal is interpolated in the time axis direction, and frequency selectivity interference is generated from the interpolated error signal. 4. The OFDM receiver according to claim 1, wherein an interference level representing the frequency is calculated, and the interference level is output after being interpolated in a frequency axis direction.

The interference detection means is
The pilot signal transmission path characteristics obtained by the demodulating means, and the pilot signal transmission path characteristics of the previous cycle stored in the first memory means in the demodulating means, from the pilot signal transmission path characteristics. An error signal representing the amount of time variation is calculated, an interference level indicating frequency selective interference is calculated from the error signal, and the interference level is averaged in the time axis direction using a second memory means provided therein. The average disturbance level is stored in the second memory means, and the averaged disturbance level is interpolated in the time axis direction and further interpolated in the frequency axis direction and output. 4. The OFDM receiver according to any one of 3 above.

The interference detection means is
The pilot signal transmission path characteristics obtained by the demodulating means, and the pilot signal transmission path characteristics of the previous cycle stored in the first memory means in the demodulating means, from the pilot signal transmission path characteristics. An error signal representing the amount of time variation is calculated, an interference level indicating frequency selective interference is calculated from the error signal, the interference level is stored in a second memory means provided therein, and the interference level is stored in time. 4. The OFDM receiver according to claim 1, wherein the output is interpolated in the axial direction and further interpolated in the frequency axis direction.

The interference detection means is
The pilot signal transmission path characteristics obtained by the demodulating means, and the pilot signal transmission path characteristics of the previous cycle stored in the first memory means in the demodulating means, from the pilot signal transmission path characteristics. An error signal representing the amount of time variation is calculated, the error signal is averaged in the time axis direction using the second memory means provided therein, and the averaged error signal is stored in the second memory means, 2. The interference level representing frequency selective interference is calculated from the averaged and interpolated error signal by interpolating the averaged error signal in the time axis direction and further in the frequency axis direction. The OFDM receiver according to any one of?

The interference detection means is
The pilot signal transmission path characteristics obtained by the demodulating means, and the pilot signal transmission path characteristics of the previous cycle stored in the first memory means in the demodulating means, from the pilot signal transmission path characteristics. An error signal representing the amount of time variation is calculated, the error signal is stored in a second memory means provided therein, the error signal is interpolated in the time axis direction, and further interpolated in the frequency axis direction. 4. The OFDM receiving apparatus according to claim 1, wherein an interference level representing frequency selective interference is calculated from an error signal.