JP2004336659A - Ofdm signal demodulating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the input amplitude up to the saturation when A/D convering. <P>SOLUTION: An OFDM signal demodulating device is provided with a saturation sampling point detection circuit 201 which specifies a saturation sampling point, a saturation sampling point information holding circuit 202 which holds the position information and a value of the saturation sampling point detected by the saturation sampling point detection circuit 201, and a sub-carrier discrete Fourier conversion circuit 203 which performs a discrete Fourier conversion to a single of a plurality of specific sub-carriers. Furthermore, the OFDM signal demodulating device is provided with a signal complement device having an amplitude correction value calculation circuit 204 which calculates an amplitude correction value, based on the calculation result of a sub-carrier whose known value is modulated by the sub-carrier discrete Fourier conversion circuit 203, and the place information of the saturation sampling point of the saturation sampling point information holding circuit 202; and a complement data calculation circuit 205 which calculates complement data, based on the amplitude correction value of the amplitude correction value calculation circuit 204, and the place information of the saturation sampling point of the saturation sampling point information holding circuit 202. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００１５】
【数２】

【００１６】
ＯＦＤＭ信号変調器では、一般的に数２に示すようにＸ０からＸｎ（ｎ＝Ｎ−１）の信号を逆フーリエ変換してｘ０からｘｎまでが送信される。ＯＦＤＭ復調器では数１に示すように、受信した信号ｘ０からｘｎをフーリエ変換してＹ０からＹｎを得る。Ｘ３、Ｘ５が既知の値（仮にそれぞれＡ，Ｂとする）として送信され、ｘ２、ｘ３が復調時の飽和により実際の値がｘ２＋ｘ’２、ｘ３＋ｘ’３であるとすれば、数１の行列式より数３及び数４の２つの式を得る。
【００１７】
【数３】

【００１８】
【数４】

【００１９】
次に、数５から数８までの連立方程式を解くことによりｘ’２、ｘ’３を導くことができる。導かれたｘ’２、ｘ’３をｘ２、ｘ３から減ずることにより飽和した値を補完することができる。
【００２０】
【数５】

【００２１】
【数６】

【００２２】
【数７】

【００２３】
【数８】

【００２４】
上記の方法を利用することにより、既知のＸｎがｍ点ある場合に、数１よりｍ個の方程式を得て、連立方程式を解くことによりｍ個までの飽和点を補完することができる。上記飽和サンプリングポイントは、デジタル直交検波器出力におけるＩ成分またはＱ成分の振幅絶対値が一定の閾値以上となるポイントまたは電力値が一定の閾値以上になるポイントを検索することにより検出することができる。
【００２５】
以下、数値を用いて説明を行う。ここでは、サブキャリア数が１６（Ｎ＝１６）であり、既知の値のサブキャリアが４個（ｍ＝４）であるＯＦＤＭ信号変復調器を用い、ＯＦＤＭ信号復調器のＡ／Ｄ変換器は４ビットの分解能であるものとする。またＸ０、Ｘ６、Ｘ７、Ｘ８が既知の値（０）である。ＯＦＤＭ信号変調器により図５に示す１６ＱＡＭ変調でマッピングされた信号を図６に示し、変調器の出力信号を図７に示す。
【００２６】
ＯＦＤＭ信号復調器において、Ａ／Ｄ変換前に信号が図８（ａ）に示すように飽和が生じないように振幅調整を行った後に直交検波した結果を図９のＩ（ａ）、Ｑ（ａ）に示し、復調した結果を図１０（ａ）に示す。図１０（ａ）より、Ｘ１２の復調結果がマッピングの境界にあり、復調に誤りを生じることがわかる。
【００２７】
さらにＡ／Ｄ変換前に信号が図８（ｂ）のように飽和するよう振幅調整を行った後に直交検波した結果を、図９のＩ（ｂ）、Ｑ（ｂ）に示し、復調した結果を図１０（ｂ）に示す。図１０（ｂ）の結果は図１０（ａ）の場合より多くのポイントで復調に誤りが生じていることがわかる。このようにＡ／Ｄ変換器への入力が飽和していない場合、量子化誤差の影響で復調誤りが発生し、飽和している場合は、飽和することによる影響で復調誤りが発生する。そこで、図１のように飽和している信号に対して、デジタル処理の補完器を導入することにより復調誤りの改善を行う。
【００２８】
ここでは、電力値（Ｉ成分とＱ成分の二乗和）が４９以上のポイントを飽和サンプリングポイントとすると、ｘ０とｘ８の２点が飽和サンプリングポイントとなる。Ｘ６、Ｘ７が既知の値（０）であることを用いて、２点の飽和サンプリングポイントの補完を行うものとして、まず図９のＩ（ｂ）、Ｑ（ｂ）に示すｘ０〜ｘ１５の値から離散フーリエ変換を行いＹ６、Ｙ７を計算する。
Ｙ６＝−４．５３６−ｊ３．０２１
Ｙ７＝−５．０４４−ｊ３．４０８
【００２９】
次に連立方程式をたて、解を求める。
Ｙ６＝Ｗ（０×６）ｘ’０＋Ｗ（８×６）ｘ’８
Ｙ７＝Ｗ（０×７）ｘ’０＋Ｗ（８×７）ｘ’８
ｘ’０＝ｘ’０ｒ＋ｊｘ’０ｉ、Ｘ’８＝ｘ’８ｒ＋ｊｘ’８ｉとして上の式を展開すると
１×ｘ’０ｒ＋０×ｘ’０ｉ＋１×ｘ’８ｒ＋０×ｘ’８ｉ＝−４．５３６
０×ｘ’０ｒ＋１×ｘ’０ｉ＋０×ｘ’８ｒ＋１×ｘ’８ｉ＝−３．０２１
１×ｘ’０ｒ＋０×ｘ’０ｉ−１×ｘ’８ｒ＋０×ｘ’８ｉ＝−５．０４４
０×ｘ’０ｒ＋１×ｘ’０ｉ＋０×ｘ’８ｒ−１×ｘ’８ｉ＝−３．４０８
となる。ガウスの消去法を用いて解を導出すると
ｘ’０＝ｘ’０ｒ＋ｊ×ｘ’０ｉ＝−４．７９０−ｊ３．２１５
ｘ’８＝ｘ’８ｒ＋ｊ×ｘ’８ｉ＝ ０．２５４＋ｊ０．１９４
となる。
【００３０】
図９のＩ（ｂ）、Ｑ（ｂ）に示したｘ０、ｘ８からｘ’０、ｘ’８をそれぞれ減じてフーリエ変換を行った結果を図１１に示す。図１１に示すとおり、マッピング誤差が小さくなり、誤りを改善することができる。
【００３１】
以下、本発明の実施の形態による信号補完器について説明を行う。ここでは、サブキャリアが６４ポイント（Ｎ＝６４）で２７番、２８番のサブキャリアに既知のデータとして０が代入されたＯＦＤＭ信号を用いる。（Ｘ２７＝Ｘ２８＝０）
【００３２】
まず、本発明の第１の実施の形態によるＯＦＤＭ信号復調装置について図面を参照しつつ説明を行う。図２は、本実施の形態による信号補完器の構成例を示すブロック図である。図２に示すように、本実施の形態による信号補完器は、飽和サンプリングポイント検出回路２０１と、飽和サンプリングポイント情報保持回路２０２と、サブキャリア離散フーリエ変換回路２０３と、振幅補正値算出回路２０４と、補完データ算出回路２０５と、バッファ２０６と、波形補正回路２０７とを備えている。
【００３３】
飽和サンプリングポイント検出回路２０１は、飽和サンプリングポイントを特定し、飽和サンプリングポイント情報保持回路２０２は、飽和サンプリングポイント検出回路２０１で検出された飽和サンプリングポイントの場所情報と値とを保持する。サブキャリア離散フーリエ変換回路２０３は、１つあるいは複数の特定のサブキャリアに対する離散フーリエ変換を行う。振幅補正値算出回路２０４はサブキャリア離散フーリエ変換回路の演算結果と飽和サンプリングポイント情報検出回路の飽和サンプリングポイントの場所情報と値を基に、多元１次連立方程式の近似解を求める。補完データ算出回路２０５は振幅補正値算出回路２０４の振幅補正値と飽和サンプリングポイント情報保持回路２０２の飽和サンプリングポイントの場所情報と値とを基に補完データを算出する。バッファ２０６は補完前の信号を演算の間保持するためのバッファであり、波形補正回路２０７は飽和サンプリングポイント情報検出回路の飽和サンプリングポイントの場所情報を基にバッファ２０６内の飽和サンプリングポイントを補完データ算出回路２０５の補完データに修正して出力を行う。
【００３４】
まず補完前の信号が飽和サンプリングポイント検出回路２０１に入力する。飽和サンプリングポイント検出回路２０１は図１２に示すようにＩ^２＋Ｑ^２を演算する電力算出回路１６０１と、Ａ≧Ｂならば飽和と判断し、Ａ＜Ｂならば非飽和と判断する飽和判断回路１６０２と、飽和判断に用いられるＡ／Ｄ変換後に表現できる電力最大値を出力する回路１６０３とを有する。飽和サンプリングポイント検出回路２０１では、図１２に示すように、補完前の信号の電力値が、Ａ／Ｄ変換後で表現できる理論的な電力最大値であれば飽和しているものとして６４ポイントすべてを比較し、飽和しているか否かの情報と補完前の信号値を飽和サンプリングポイント情報検出回路２０２へ出力する。ここで、飽和点は前記のような最大値ではなく、ある定数Ｐより大きければ飽和しているものとしたり、補完前の信号の絶対振幅値がある定数Ｔより大きければ飽和しているものとしたりすることも可能である。
【００３５】
飽和サンプリングポイント情報保持回路２０２は図１３に示すように、飽和ポイントであればカウンタ値（場所情報）とＩ，Ｑの値をメモリへ保持させる飽和ポイント場所情報算出回路１７０１と、飽和ポイント場所情報算出回路出力を保持するメモリ１７０２と、Ｉ，Ｑ信号が入力される毎に１加算を行うカウンタ１７０３とを有している。飽和サンプリングポイント情報保持回路２０２では図１３に示すように、飽和サンプリングポイント検出回路２０１の飽和情報から飽和サンプリングポイントの場所情報と値とを検出し保持する。また、補完前の信号は同時にサブキャリア離散フーリエ変換回路２０３及びバッファ２０６に入力される。ここでは入力信号の３番と８番が飽和していたものとする。サブキャリア離散フーリエ変換回路２０３は、図１４に示す複素乗算器１８０１、１８０４と、加算器１８０２、１８０５と、後述する連立方程式演算に用いるＷの値を保持するメモリ１８０３とを有している。
【００３６】
サブキャリア離散フーリエ変換回路２０３では、図１４に示すようにサブキャリア２７番、２８番に対して補完前の信号を離散フーリエ変換する。変換された値をそれぞれＦ２７、Ｆ２８とする。振幅補正値算出回路２０４は、図１５に示すように、Ｗの値を保持するメモリ１９０１と、飽和サンプリングポイント場所情報とサブキャリア離散フーリエ変換結果とメモリ出力とを基に複素四則演算を行い、ｘ８を算出する複素四則演算器（ｘ８計算）１９０２と、複素四則演算器（ｘ８計算）の出力を基にｘ３を算出する複素四則演算器（ｘ３計算）１９０３とを有している。
【００３７】
振幅補正値算出回路２０４では、図１９に示すように、飽和サンプリングポイント情報保持回路２０２の飽和サンプリングポイントの場所情報とサブキャリア離散フーリエ変換回路２０３の離散フーリエ変換結果と、Ｘ２７＝Ｘ２８＝０の前提条件より連立方程式を以下のように置く。
Ｗ（３×２７）×ｘ３＋ｗ（８×２７）×ｘ８＝ｆ２７ （１）
Ｗ（３×２８）×ｘ３＋ｗ（８×２８）×ｘ８＝ｆ２８ （２）
【００３８】
上記の連立方程式の解をガウスの消去法を用いて求める。式（２）にＷ（３×２７）÷Ｗ（３×２８）を乗算し、
｛Ｗ（３×２８）×ｘ３＋Ｗ（８×２８）｝×Ｗ（３×２７）÷Ｗ（３×２７）÷Ｗ（３×２８）
より式（１）を減算すると、
０＋｛Ｗ（８×２８）×Ｗ（３×２７）÷Ｗ（３×２８）−Ｗ（８×２７）｝×ｘ８＝Ｆ２８×Ｗ（３×２７）÷Ｗ（３×２８）−Ｆ２７となり、
ｘ８＝Ｆ２８×Ｗ（３×２７）÷Ｗ（３×２８）−Ｆ２７÷｛Ｗ（８×２８）×Ｗ（３×２７）÷Ｗ（３×２８）−Ｗ（８×２７）｝
を求めることができ、求められたｘ８を（１）式に代入することによってｘ３を求めることができる。
【００３９】
補完データ算出回路２０５は、図１６に示すように飽和サンプリングポイントの信号値から振幅補正値を減算する手段２００１を備える。補完データ算出回路２０５は、飽和サンプリングポイント情報保持回路２０２の飽和サンプリングポイントの場所情報と信号値を用いて、飽和サンプリングポイントの信号値から振幅補正値算出回路２０４の解を減算し、補完データとして出力する。波形補正回路２０７は、図１７に示すようにセレクタ２１０１により構成され、バッファ２０６の信号を順次出力して、その際に飽和サンプリングポイント情報保持回路２０２の飽和サンプリングポイントの場所情報から、飽和点の信号を補完データ算出回路２０５の出力に切り替えることによって補完を行う。
【００４０】
飽和している点に対して補完を行わずに離散フーリエ変換を行った場合には全キャリアの信号に歪みが発生し復号に失敗する可能性があるのに対して、補完を行うことにより歪みを低減することができ、正確な復号を行うことが可能となる。
【００４１】
次に、本発明の第２の実施の形態によるＯＦＤＭ信号復調装置について図面を参照して説明を行う。図３は本実施の形態によるＯＦＤＭ信号復調装置に用いられる信号補完器の構成例を示すブロック図である。図３に示す信号補完器は、飽和サンプリングポイント検出回路３０１と、飽和サンプリングポイント情報保持回路３０２と、サブキャリア離散フーリエ変換回路３０３と、振幅補正値算出回路３０４と、補完データ算出回路３０５と、バッファ３０６と、波形補正回路３０７と、サンプリングポイント数計数回路３０８と、を備えている。飽和サンプリングポイント検出回路３０１は飽和サンプリングポイントを特定し、飽和サンプリングポイント数計数回路３０８は前記飽和サンプリングポイント検出回路３０１で検出された飽和サンプリングポイント数をカウントする。飽和サンプリングポイント情報保持回路３０２は、飽和サンプリングポイント検出回路３０１で検出された飽和サンプリングポイントの場所情報と値を保持する。サブキャリア離散フーリエ変換回路３０３は１つあるいは複数の特定のサブキャリアに対する離散フーリエ変換を行う。振幅補正値算出回路３０４はサブキャリア離散フーリエ変換回路の演算結果と飽和サンプリングポイント情報保持回路３０２の飽和サンプリングポイントの場所情報の値を基に、多元１次連立方程式の近似解を求める。補完データ算出回路３０５は振幅補正値算出回路の振幅補正値と飽和サンプリングポイント情報保持回路３０２の飽和サンプリングポイントの場所情報と値を基に補完データを算出する。バッファ３０６は補完前の信号を演算の間保持するためのバッファであり、波形補正回路３０７は飽和サンプリングポイント情報保持回路３０２の飽和サンプリングポイントの場所情報を基にバッファ３０６内の飽和サンプリングポイントを補完データ算出回路３０５の補完データに修正して出力を行う。
【００４２】
ここで振幅補正値算出回路３０４と補完データ算出回路３０５と、波形補正回路３０７は、飽和サンプリングポイント数計数回路３０８のカウント出力がｍ個以下であれば各演算を行い、ｍ個を超える場合は演算を行わずに補正を行わない。
【００４３】
まず、補完前の信号は飽和サンプリングポイント検出回路３０１に入力される。飽和サンプリングポイント検出回路３０１では補完前の信号の電力値が、Ａ／Ｄ変換後で表現できる理論的な最大値であれば飽和しているものとして６４ポイントすべてを比較し、飽和しているか否かの情報と補完前の信号値とを、飽和サンプリングポイント数計数回路３０８と飽和サンプリングポイント情報保持回路３０２へ出力する。
【００４４】
飽和サンプリングポイント数計数回路３０８は図１８に示すようにカウンタ２２０１を有しており、飽和サンプリングポイントの数をカウントし、保持する。飽和サンプリングポイント情報保持回路３０２では、飽和サンプリングポイント検出回路３０１の飽和情報から飽和サンプリングポイントの場所情報と値とを検出して保持する。また、補完前の信号は、同時にサブキャリア離散フーリエ変換回路３０３及びバッファ３０６に入力される。ここでは、入力信号の３番と８番と９番が飽和していたものとする。サブキャリア離散フーリエ変換回路３０３は、サブキャリア２７番、２８番に対して補完前の信号を離散フーリエ変換する。変換された値をそれぞれＦ２７、Ｆ２８とする。振幅補正値算出回路３０４は飽和サンプリングポイント数計数回路３０８からの出力がｍ個（ここでは２個）を超える３であるため、演算を行わない。
【００４５】
補完データ算出回路３０５は、飽和サンプリングポイント数計数回路３０８からの出力が３であるため、演算を行わない。波形補正回路３０７は図１９に示すようにセレクタ２３０１を有しており、飽和サンプリングポイント数がｍ個を超える場合には出力をバッファ出力に固定し、ｍ個以下である場合は、飽和サンプリングポイント場所情報に従って出力をバッファ出力と補完データとに切り替える。波形補正回路３０７では、飽和サンプリングポイント数計数回路３０８からの出力が３であるため、バッファ３０６の信号を順次出力する。飽和している点がｍ個を超える場合には、補完データの値が正しい値ではなくなるため、各演算回路を停止させることにより余分な電力の消費を抑えることが可能である。
次に本発明の第３の実施の形態によるＯＦＤＭ信号復調装置について説明する。
【００４６】
図４は、本実施の形態による信号補完器の構成例を示すブロック図である。図４に示す信号補完器は、飽和サンプリングポイント検出回路４０１と、飽和サンプリングポイント情報保持回路４０２と、サブキャリア離散フーリエ変換回路４０３と、振幅補正値算出回路４０４と、補完データ算出回路４０５と、バッファ４０６と、波形補正回路４０７と比較器４０８と、を備えている。飽和サンプリングポイント検出回路４０１は飽和サンプリングポイントを特定し、飽和サンプリングポイント情報保持回路４０２は飽和サンプリングポイント検出回路４０１で検出された飽和サンプリングポイントの場所情報と値を保持する。サブキャリア離散フーリエ変換回路４０３は、１又は複数の特定のサブキャリアに対する離散フーリエ変換を行う。振幅補正値算出回路４０４はサブキャリア離散フーリエ変換回路の演算結果と飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの場所情報の値とに基づいて、多元１次連立方程式の近似解を求める。補完データ算出回路４０５は、振幅補正値算出回路４０４の振幅補正値と飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの場所情報との値を基に補完データを算出する。
【００４７】
バッファ４０６は、演算の間補完前の信号を保持するためのバッファであり、比較器４０８は、飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの信号値の絶対値と補完データ算出回路４０５からの補完データの絶対値とを比較する。補完データの絶対値が飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの値の絶対値以上である場合は、補完データとして補完データ算出回路４０５からの補完データを出力し、補完データの絶対値が飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの値の絶対値より小さい場合は、飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの信号値を出力する。波形補正回路４０７は飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの場所情報を基にバッファ４０６内の飽和サンプリングポイントを比較器４０８の補完データに修正して出力を行う。
【００４８】
まず、補完前の信号は飽和サンプリングポイント検出回路４０１に入力される。飽和サンプリングポイント検出回路４０１では補完前の信号の電力値が、Ａ／Ｄ変換後で表現できる理論的な最大値であれば飽和しているものとして６４ポイントすべてを比較し、飽和しているか否かの情報と補完前の信号値を飽和サンプリングポイント情報保持回路４０２へ出力する。飽和サンプリングポイント情報保持回路４０２では飽和サンプリングポイント検出回路４０１の飽和情報から飽和サンプリングポイントの場所情報と値を検出し、保持する。また補完前の信号は同時にサブキャリア離散フーリエ変換回路４０３及びバッファ４０６に入力される。
【００４９】
ここでは入力信号の３番と８番が飽和していたものとする。サブキャリア離散フーリエ変換回路４０３は、サブキャリア２７番、２８番に対して補完前の信号を離散フーリエ変換する。変換された値をそれぞれＦ２７、Ｆ２８とする。振幅補正値算出回路４０４では前記実施の形態１記載の振幅補正値算出回路４０４と同様にｘ３、ｘ８が求められる。
【００５０】
補完データ算出回路４０５は、飽和サンプリングポイント情報検出回路４０２の飽和サンプリングポイントの場所情報と信号値を用いて、飽和サンプリングポイントの信号値から振幅補正値算出回路４０４の解を減算し、補完データとして出力する。比較器４０８は図２０に示すようにセレクタ２４０１を有しており、飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの信号値の絶対値と補完データ算出回路４０５からの補完データの絶対値とを比較し、補完データの絶対値が飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの値の絶対値以上である場合は、補完データとして補完データ算出回路４０５からの補完データを出力し、補完データの絶対値が飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの値の絶対値より小さい場合は、飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの信号値を出力する。波形補正回路４０７はバッファ４０６の信号を順次出力して、その際に飽和サンプリングポイント情報保持回路４０２の飽和サンプリングポイントの場所情報から、飽和点の信号を補完データ算出回路４０５出力に切り替えることによって補完を行う。補完を行う信号のノイズ、振幅補正値算出を行う際の演算誤差等による飽和しているサンプリングポイントの誤った値での補正を防止することが可能となる。
【００５１】
以上に説明したように、本実施の形態によるＯＦＤＭ復調装置によれば、フーリエ変換を行う前に飽和したデータを補完することが可能となるため、Ａ／Ｄ変換時の入力振幅を飽和が発生するまで大きくとることができる。また、高分解能で高精度なＡ／Ｄ変換器を用いる必要がないという利点がある。
以上、本実施の形態に沿って説明したが、本発明はこれらの例に限定されるものではなく、種々の変形が可能であるのは言うまでもない。
【００５２】
【発明の効果】
以上述べたとおり、本発明のＯＦＤＭ信号復調装置によれば、フーリエ変換を行う前に飽和したデータを補完することが可能となるため、Ａ／Ｄ変換時の入力振幅を飽和が発生するまで大きくとることができる。また、高分解能で高精度なＡ／Ｄ変換器を用いる必要がないという利点がある。
【図面の簡単な説明】
【図１】本発明の実施の形態によるＯＦＤＭ信号復調装置の基本構成例を示すブロック図である。
【図２】本実施の形態による補完回路の第１構成例を示すブロック図である。
【図３】本実施の形態による補完回路の第２構成例を示すブロック図である。
【図４】本実施の形態による補完回路の第３構成例を示すブロック図である。
【図５】１６ＱＡＭでマッピングされた離散フーリエ変換前の信号例を示す図である。
【図６】図５の信号のマッピング図である。
【図７】図５の信号の送信波形を示す図である。
【図８】図７の波形をＡ／Ｄ変換した信号であり、（ａ）は、飽和させずにＡ／Ｄ変換を行った信号、（ｂ）は、飽和させてＡ／Ｄ変換を行った信号例を示す図である。
【図９】図８の信号に対する直交検波後の各々の信号を示す図である。
【図１０】図９の信号に対する各々の離散フーリエ変換後の信号を示す図である。
【図１１】本実施の形態による信号補完器を用いた場合の図９のＩ（ｂ）、Ｑ（ｂ）に示したｘ０、ｘ８からｘ’０、ｘ’８をそれぞれ減じてフーリエ変換を行った結果を示す図である。
【図１２】本実施の形態による飽和サンプリングポイント検出回路の構成例を示す図である。
【図１３】本実施の形態による飽和サンプリングポイント情報保持回路の構成例を示す図である。
【図１４】本実施の形態によるサブキャリア離散フーリエ変換回路の構成例を示す図である。
【図１５】本実施の形態による振幅補正値算出回路の構成例を示す図である。
【図１６】本実施の形態による補完データ算出回路の構成例を示す図である。
【図１７】本実施の形態による波形補正回路の第１構成例を示す図である。
【図１８】本実施の形態による飽和サンプリングポイント数計数回路の構成例を示す図である。
【図１９】本実施の形態による波形補正回路の第２構成例を示す図である。
【図２０】本実施の形態による比較器の構成例を示す図である。
【図２１】一般的なＯＦＤＭ信号復調装置の構成例を示す図である。
【符号の説明】
１０１ 周波数変換器、１０２ 振幅増幅器、１０３ Ａ／Ｄ変換器、１０４
デジタル直交検波器、１０５ 離散フーリエ変換器、１０６ 符号判定器、１０７ 信号補完器、２０１ 飽和サンプリングポイント検出回路、２０２ 飽和サンプリングポイント情報保持回路、２０３ サブキャリア離散フーリエ変換回路２０４ 振幅補正値算出回路、２０５ 補完データ算出回路、２０６ バッファ、２０７ 波形補正回路、３０１ 飽和サンプリングポイント検出回路、３０２飽和サンプリングポイント情報保持回路、３０３ サブキャリア離散フーリエ変換回路、３０４ 振幅補正値算出回路、３０５ 補完データ算出回路、３０６バッファ、３０７ 波形補正回路、３０８ 飽和サンプリングポイント数計数回路、４０１ 飽和サンプリングポイント検出回路、４０２ 飽和サンプリングポイント情報保持回路、４０３ サブキャリア離散フーリエ変換回路、４０４ 振幅補正値算出回路、４０５ 補完データ算出回路、４０６ バッファ、４０７波形補正回路、４０８ 比較器、１６０１ 電力算出回路、１６０２ 飽和判断回路、１６０３ Ａ／Ｄ変換後に表現できる電力最大値、１７０１ 飽和ポイント情報算出回路、１７０２ メモリ、１７０３ カウンタ、１８０１ 複素乗算器、１８０２ 加算器、１８０３ メモリ（Ｗ）、１８０４ 複素乗算器、１８０５ 加算器、１９０１ メモリ（Ｗ）、１９０２ 複素四則演算器（ｘ８計算）、１９０３ 複素四則演算器（ｘ３計算）、２００１ 飽和サンプリングポイントの信号値−振幅補正値、２１０１ セレクタ、２２０１ カウンタ、２３０１ セレクタ、２４０１ セレクタ、２５０１ 周波数変換器、２５０２ 振幅増幅器、２５０３ Ａ／Ｄ変換器、２５０４ デジタル直交検波器、２５０５離散フーリエ変換器、２５０６ 符号判定器。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an OFDM signal demodulation device and an OFDM signal modulation device in a communication system for performing digital wireless communication using an OFDM (Orthogonal Frequency Division Multiplexing) signal, and more particularly to an OFDM signal receiving device. The present invention relates to a technique related to a discrete Fourier transform (hereinafter, referred to as DFT).
[0002]
[Prior art]
In recent years, in terrestrial digital television broadcasting and next-generation high-speed wireless LANs, the OFDM scheme has attracted attention as a large-capacity data transmission scheme. The OFDM system is a type of a multi-carrier transmission system for transmitting an information signal using a plurality of carriers, and is characterized in that the subcarriers have a frequency relationship that is orthogonal to each other.
[0003]
In the OFDM signal, serially / parallel-converted encoded data is allocated to a plurality of subcarriers having a frequency relationship orthogonal to each other in a modulator, and each of the digital data is subjected to inverse discrete Fourier transform (frequency domain is converted to time domain) by digital modulation. After that, the data is generated by performing parallel-to-serial conversion, and the demodulation device reproduces the original coded data by performing a process reverse to that of the modulation device side.
[0004]
Here, when generating an OFDM signal, some subcarriers may not be used. This includes a carrier corresponding to a DC component. These are defined as unused subcarriers, and the power is set to 0. This is realized by inserting null data into a portion corresponding to an unused subcarrier of a signal to be subjected to inverse discrete Fourier transform in the OFDM signal modulation device.
[0005]
Another property of the OFDM signal is that the crest factor (the ratio between the peak value and the average value) is large. For this reason, in the OFDM signal demodulator, amplitude adjustment is performed before A / D conversion so that the signal is not saturated. For example, there is disclosed a technique of forming a peak value prediction signal on the reception side, subtracting the peak value prediction signal from the transmission signal, and performing power control on the transmission side that performs peak suppression on the transmission signal (eg, Patent Document 1).
[0006]
As another example, an example of a conventional OFDM signal demodulation device will be described with reference to FIG. As shown in FIG. 21, the OFDM signal demodulation device includes a frequency converter 2501 that converts the frequency of a received signal into a predetermined band, an amplitude amplifier 2502 that adjusts the amplitude of an output signal of the frequency converter 2501, and an amplitude amplifier 2502. An A / D converter 2503 for A / D converting the output signal, a digital quadrature detector 2504 for separating the output signal of the A / D converter 2503 into a real component and an imaginary component, and an output signal of the digital quadrature detector 2504 The apparatus includes a discrete Fourier transformer 2505 that performs a discrete Fourier transform, and a sign determiner 2506 that demodulates an output signal of the discrete Fourier transformer 2505.
[0007]
First, a received signal is input to a frequency converter 2501 that performs frequency conversion to a predetermined band. Next, the amplitude of the frequency-converted signal is adjusted by an amplitude amplifier 2502 so that saturation does not occur at the time of A / D conversion in the subsequent stage. The signal whose amplitude has been adjusted is A / D converted by an A / D converter 2503 and input to a digital quadrature detector 2504. The digital quadrature detector performs digital quadrature detection, and the result is input to the discrete Fourier transformer 2505. The output signal of the discrete Fourier transformer 2505 is input to a code decision unit 2506 that performs demodulation, and demodulation is performed. As described above, conventionally, amplitude adjustment is performed in the demodulator so that the signal is not saturated before A / D conversion, and Fourier transform is performed after performing quadrature detection and guard section removal.
[0008]
[Patent Document 1]
JP 2003-008455 A
[0009]
[Problems to be solved by the invention]
However, an OFDM signal having a very large difference in signal amplitude such that the ratio between the maximum value of the amplitude of the input signal and the average of the absolute values may reach 50: 1 is used. When the amplitude is adjusted as a reference to avoid saturation of the A / D converter, the average value of the absolute value of the input signal amplitude becomes smaller than the dynamic range of the A / D converter, and equivalently, the input signal A problem occurs in that the resolution of the A / D converter is reduced and the influence of a quantization error on an input signal is increased.
The present invention aims to improve the effects of the above-mentioned saturation.
[0010]
[Means for Solving the Problems]
According to an aspect of the present invention, N (N is a natural number of N ≧ 1) subcarriers are provided, and m (m is a natural number of N ≧ m ≧ 1) subcarriers are known values. An OFDM signal demodulator that processes and demodulates a modulated Orthogonal Frequency Division Multiplexing (hereinafter, referred to as “OFDM”) signal in the order of A / D conversion, digital orthogonal detection, and discrete Fourier transform. Accordingly, there is provided an OFDM signal demodulator characterized by comprising a signal complementer for complementing a saturated A / D conversion output prior to a discrete Fourier transform by inputting a large amplitude signal.
[0011]
According to the OFDM signal demodulation device, since the signal complementer for complementing the saturated A / D conversion output prior to the discrete Fourier transform is provided, demodulation is performed by performing the discrete Fourier transform on the saturated A / D conversion output. Errors can be reduced.
[0012]
The signal complementer performs a discrete Fourier transform on an output of the digital quadrature detector to reproduce a signal waveform for each subcarrier, and the digital quadrature detector selected for the discrete Fourier transform. At the sampling point of the output of the above, when the amplitude absolute value of the I component which is the 0-degree component or the Q component which is the 90-degree component becomes a certain value or more, or the power value which is the sum of squares of the IQ component at the sampling point A saturated sampling point detecting means for judging the sampling point as a saturated sampling point when the value exceeds a certain value, and a saturated sampling point for holding saturated sampling point information including a signal value of the saturated sampling point and a sampling timing. Information holding means;
An amplitude correction value calculating unit that calculates an amplitude correction value at the saturation sampling point based on the saturation sampling point information and a calculation result of the discrete Fourier transform unit on the subcarrier modulated with the known value; Complementary data calculation means for calculating the amplitude value of a saturated sampling point based on point information and the amplitude correction value, and means for correcting the output of a digital quadrature detector based on the saturation sampling point information and the complementary data
It is preferable to provide
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The OFDM signal demodulation device according to the present invention reduces the problems caused by amplitude adjustment for avoiding saturation by accepting the saturation of the A / D converter due to the input signal, and digitally processes the signal of the saturated portion by digital processing. It is characterized in that the effect of saturation is reduced by complementing. The signal complementing means in the OFDM signal demodulator is as follows. The Fourier transform and the inverse Fourier transform are generally represented by the solution of the following determinant.
[0014]
(Equation 1)

[0015]
(Equation 2)

[0016]
In the OFDM signal modulator, signals from X0 to Xn (n = N-1) are generally subjected to inverse Fourier transform as shown in Expression 2, and x0 to xn are transmitted. In the OFDM demodulator, as shown in Expression 1, the received signals x0 to xn are Fourier-transformed to obtain Y0 to Yn. Assuming that X3 and X5 are transmitted as known values (assumed to be A and B, respectively) and x2 and x3 are actual values x2 + x'2 and x3 + x'3 due to saturation at the time of demodulation, a matrix of Formula 1 Equations 2 and 3 are obtained from the equations.
[0017]
[Equation 3]

[0018]
(Equation 4)

[0019]
Next, x'2 and x'3 can be derived by solving the simultaneous equations of Equations 5 to 8. By subtracting the derived x'2, x'3 from x2, x3, saturated values can be complemented.
[0020]
(Equation 5)

[0021]
(Equation 6)

[0022]
(Equation 7)

[0023]
(Equation 8)

[0024]
By using the above method, if there are m known Xn points, m equations can be obtained from Equation 1 and the simultaneous equations can be solved to complement up to m saturation points. The saturation sampling point can be detected by searching for a point where the amplitude absolute value of the I component or the Q component in the digital quadrature detector output is equal to or greater than a certain threshold or a point where the power value is equal to or greater than a certain threshold. .
[0025]
Hereinafter, description will be made using numerical values. Here, an OFDM signal modulator / demodulator in which the number of subcarriers is 16 (N = 16) and the number of subcarriers of a known value is 4 (m = 4) is used, and the A / D converter of the OFDM signal demodulator is It is assumed that the resolution is 4 bits. X0, X6, X7, and X8 are known values (0). FIG. 6 shows a signal mapped by the OFDM signal modulator by the 16QAM modulation shown in FIG. 5, and FIG. 7 shows an output signal of the modulator.
[0026]
In the OFDM signal demodulator, the result of quadrature detection after performing amplitude adjustment before the A / D conversion so that the signal does not cause saturation as shown in FIG. 8A is shown by I (a), Q ( FIG. 10A shows the result of demodulation, and FIG. 10A shows the result. From FIG. 10A, it can be seen that the demodulation result of X12 is at the boundary of the mapping and an error occurs in the demodulation.
[0027]
Further, the result of quadrature detection after performing amplitude adjustment so that the signal is saturated as shown in FIG. 8B before A / D conversion is shown in I (b) and Q (b) of FIG. Is shown in FIG. The result of FIG. 10B shows that errors occur in demodulation at more points than in the case of FIG. As described above, when the input to the A / D converter is not saturated, a demodulation error occurs due to a quantization error, and when the input is saturated, a demodulation error occurs due to the saturation. Therefore, for a signal that is saturated as shown in FIG. 1, a demodulation error is improved by introducing a complementer for digital processing.
[0028]
Here, assuming that a point where the power value (sum of squares of the I component and the Q component) is 49 or more is a saturation sampling point, two points x0 and x8 are saturation sampling points. Assuming that two saturated sampling points are complemented by using that X6 and X7 are known values (0), values of x0 to x15 shown in I (b) and Q (b) of FIG. And perform discrete Fourier transform to calculate Y6 and Y7.
Y6 = −4.536−j3.021
Y7 = -5.044-j3.408
[0029]
Next, a simultaneous equation is established to find a solution.
Y6 = W (0 × 6) x′0 + W (8 × 6) x′8
Y7 = W (0 × 7) x′0 + W (8 × 7) x′8
When the above expression is expanded as x′0 = x′0r + jx′0i, X′8 = x′8r + jx′8i,
1 × x′0r + 0 × x′0i + 1 × x′8r + 0 × x′8i = −4.536
0 × x′0r + 1 × x′0i + 0 × x′8r + 1 × x′8i = −3.021
1 × x′0r + 0 × x′0i−1 × x′8r + 0 × x′8i = −5.044
0 × x′0r + 1 × x′0i + 0 × x′8r−1 × x′8i = −3.408
It becomes. Deriving the solution using Gaussian elimination
x′0 = x′0r + j × x′0i = −4.790−j3.215
x′8 = x′8r + j × x′8i = 0.254 + j0.194
It becomes.
[0030]
FIG. 11 shows a result obtained by subtracting x′0 and x′8 from x0 and x8 shown in I (b) and Q (b) in FIG. 9 and performing Fourier transform. As shown in FIG. 11, the mapping error is reduced, and the error can be improved.
[0031]
Hereinafter, a signal complementer according to an embodiment of the present invention will be described. Here, an OFDM signal in which 0 is substituted as known data in the 27th and 28th subcarriers with 64 subcarriers (N = 64) is used. (X27 = X28 = 0)
[0032]
First, an OFDM signal demodulation device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram illustrating a configuration example of the signal complementer according to the present embodiment. As shown in FIG. 2, the signal complementer according to the present embodiment includes a saturation sampling point detection circuit 201, a saturation sampling point information holding circuit 202, a subcarrier discrete Fourier transform circuit 203, and an amplitude correction value calculation circuit 204. , A complementary data calculation circuit 205, a buffer 206, and a waveform correction circuit 207.
[0033]
The saturation sampling point detection circuit 201 specifies the saturation sampling point, and the saturation sampling point information holding circuit 202 holds the location information and the value of the saturation sampling point detected by the saturation sampling point detection circuit 201. The subcarrier discrete Fourier transform circuit 203 performs a discrete Fourier transform on one or a plurality of specific subcarriers. The amplitude correction value calculation circuit 204 obtains an approximate solution of a multiple linear simultaneous equation based on the operation result of the subcarrier discrete Fourier transform circuit and the location information and value of the saturation sampling point of the saturation sampling point information detection circuit. The complementary data calculation circuit 205 calculates complementary data based on the amplitude correction value of the amplitude correction value calculation circuit 204 and the location information and value of the saturation sampling point of the saturation sampling point information holding circuit 202. The buffer 206 is a buffer for holding the signal before complementation during the calculation, and the waveform correction circuit 207 complements the saturated sampling point in the buffer 206 based on the location information of the saturation sampling point of the saturation sampling point information detection circuit. The output is corrected to the complementary data of the calculation circuit 205.
[0034]
First, a signal before complementation is input to the saturation sampling point detection circuit 201. As shown in FIG. 12, the saturation sampling point detection circuit 201 ² + Q ² , A saturation determination circuit 1602 that determines saturation if A ≧ B, and determines non-saturation if A <B, and a maximum power that can be expressed after A / D conversion used for saturation determination. And a circuit 1603 that outputs In the saturation sampling point detection circuit 201, as shown in FIG. 12, if the power value of the signal before complementation is a theoretical maximum power value that can be expressed after A / D conversion, it is determined that all the 64 points are saturated. And outputs the information on whether or not the signal is saturated and the signal value before complementation to the saturated sampling point information detecting circuit 202. Here, it is assumed that the saturation point is not the maximum value as described above, but is saturated if it is larger than a certain constant P, or is saturated if the absolute amplitude value of the signal before complementation is larger than a certain constant T. It is also possible.
[0035]
As shown in FIG. 13, a saturation sampling point information holding circuit 202 stores a counter value (location information) and values of I and Q in a memory if the saturation point, and a saturation point location information. It has a memory 1702 for holding the output of the calculation circuit and a counter 1703 for adding 1 each time the I and Q signals are input. As shown in FIG. 13, the saturation sampling point information holding circuit 202 detects and holds the location information and the value of the saturation sampling point from the saturation information of the saturation sampling point detection circuit 201. The signal before complementation is input to the subcarrier discrete Fourier transform circuit 203 and the buffer 206 at the same time. Here, it is assumed that the third and eighth input signals are saturated. The subcarrier discrete Fourier transform circuit 203 includes complex multipliers 1801 and 1804, adders 1802 and 1805 shown in FIG. 14, and a memory 1803 for holding a value of W used for simultaneous equation calculation described later.
[0036]
In the subcarrier discrete Fourier transform circuit 203, as shown in FIG. 14, the signal before complementation on the subcarriers 27 and 28 is subjected to discrete Fourier transform. The converted values are F27 and F28, respectively. As shown in FIG. 15, the amplitude correction value calculation circuit 204 performs a complex four arithmetic operation based on the memory 1901 holding the value of W, the saturation sampling point location information, the subcarrier discrete Fourier transform result, and the memory output, It has a complex four arithmetic operation unit (x8 calculation) 1902 for calculating x8, and a complex four arithmetic operation unit (x3 calculation) 1903 for calculating x3 based on the output of the complex four arithmetic operation unit (x8 calculation).
[0037]
In the amplitude correction value calculation circuit 204, as shown in FIG. 19, the location information of the saturation sampling point of the saturation sampling point information holding circuit 202, the result of the discrete Fourier transform of the subcarrier discrete Fourier transform circuit 203, and X27 = X28 = 0 Based on the preconditions, the simultaneous equations are set as follows.
W (3 × 27) × x3 + w (8 × 27) × x8 = f27 (1)
W (3 × 28) × x3 + w (8 × 28) × x8 = f28 (2)
[0038]
The solution of the above simultaneous equations is obtained using Gaussian elimination. Equation (2) is multiplied by W (3 × 27) ÷ W (3 × 28),
｛W (3 × 28) × x3 + W (8 × 28)｝ × W (3 × 27) ÷ W (3 × 27) ÷ W (3 × 28)
Subtracting equation (1),
0+ ｛W (8 × 28) × W (3 × 27) ÷ W (3 × 28) -W (8 × 27)｝ × x8 = F28 × W (3 × 27) ÷ W (3 × 28) -F27 Becomes
x8 = F28 × W (3 × 27) ÷ W (3 × 28) -F27 ÷ ｛W (8 × 28) × W (3 × 27) ÷ W (3 × 28) -W (8 × 27)}
Can be obtained, and x3 can be obtained by substituting the obtained x8 into the equation (1).
[0039]
The complementary data calculation circuit 205 includes means 2001 for subtracting the amplitude correction value from the signal value at the saturation sampling point as shown in FIG. The supplementary data calculation circuit 205 subtracts the solution of the amplitude correction value calculation circuit 204 from the signal value of the saturation sampling point using the location information and the signal value of the saturation sampling point of the saturation sampling point information holding circuit 202, and generates the complement data. Output. The waveform correction circuit 207 is composed of a selector 2101 as shown in FIG. 17 and sequentially outputs the signals of the buffer 206. At this time, the information of the location of the saturation sampling point of the saturation sampling point information holding circuit 202 is used to determine the saturation point. The complement is performed by switching the signal to the output of the complement data calculation circuit 205.
[0040]
If the discrete Fourier transform is performed without performing interpolation on a saturated point, distortion may occur in the signals of all carriers and decoding may fail. Can be reduced, and accurate decoding can be performed.
[0041]
Next, an OFDM signal demodulator according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing a configuration example of a signal complementer used in the OFDM signal demodulator according to the present embodiment. The signal complementer shown in FIG. 3 includes a saturation sampling point detection circuit 301, a saturation sampling point information holding circuit 302, a subcarrier discrete Fourier transform circuit 303, an amplitude correction value calculation circuit 304, a complement data calculation circuit 305, A buffer 306, a waveform correction circuit 307, and a sampling point number counting circuit 308 are provided. The saturation sampling point detection circuit 301 specifies a saturation sampling point, and the saturation sampling point number counting circuit 308 counts the number of saturation sampling points detected by the saturation sampling point detection circuit 301. The saturation sampling point information holding circuit 302 holds the location information and the value of the saturation sampling point detected by the saturation sampling point detection circuit 301. The subcarrier discrete Fourier transform circuit 303 performs a discrete Fourier transform on one or more specific subcarriers. The amplitude correction value calculation circuit 304 obtains an approximate solution of a multiple linear simultaneous equation based on the operation result of the subcarrier discrete Fourier transform circuit and the value of the location information of the saturation sampling point of the saturation sampling point information holding circuit 302. The complementary data calculation circuit 305 calculates complementary data based on the amplitude correction value of the amplitude correction value calculation circuit and the location information and value of the saturation sampling point of the saturation sampling point information holding circuit 302. The buffer 306 is a buffer for holding the signal before complement during the calculation, and the waveform correction circuit 307 complements the saturated sampling point in the buffer 306 based on the location information of the saturated sampling point of the saturated sampling point information holding circuit 302. The output is corrected to the complementary data of the data calculation circuit 305.
[0042]
Here, the amplitude correction value calculation circuit 304, the supplementary data calculation circuit 305, and the waveform correction circuit 307 perform each operation if the count output of the saturation sampling point number counting circuit 308 is m or less, and if the count output exceeds m, No correction is performed without performing calculations.
[0043]
First, the signal before complementation is input to the saturation sampling point detection circuit 301. If the power value of the signal before complementation is the theoretical maximum value that can be expressed after A / D conversion, the saturation sampling point detection circuit 301 compares all 64 points as being saturated, and determines whether the signal is saturated. The information and the signal value before complementation are output to the saturated sampling point number counting circuit 308 and the saturated sampling point information holding circuit 302.
[0044]
The saturation sampling point number counting circuit 308 has a counter 2201 as shown in FIG. 18, and counts and holds the number of saturation sampling points. The saturation sampling point information holding circuit 302 detects and holds the location information and the value of the saturation sampling point from the saturation information of the saturation sampling point detection circuit 301. The signal before complementation is input to the subcarrier discrete Fourier transform circuit 303 and the buffer 306 at the same time. Here, it is assumed that the third, eighth, and ninth input signals are saturated. The subcarrier discrete Fourier transform circuit 303 performs a discrete Fourier transform on a signal before complementation on subcarriers 27 and 28. The converted values are F27 and F28, respectively. The amplitude correction value calculation circuit 304 does not perform the operation because the output from the saturation sampling point number counting circuit 308 is 3 exceeding m (here, 2).
[0045]
The complementary data calculation circuit 305 does not perform the calculation because the output from the saturation sampling point number counting circuit 308 is 3. As shown in FIG. 19, the waveform correction circuit 307 has a selector 2301. When the number of saturation sampling points exceeds m, the output is fixed to the buffer output. The output is switched between buffer output and complementary data according to the location information. In the waveform correction circuit 307, since the output from the saturated sampling point number counting circuit 308 is 3, the signals of the buffer 306 are sequentially output. If the number of saturation points exceeds m, the value of the complementary data is not correct, and thus, it is possible to suppress unnecessary power consumption by stopping each arithmetic circuit.
Next, an OFDM signal demodulator according to a third embodiment of the present invention will be described.
[0046]
FIG. 4 is a block diagram illustrating a configuration example of the signal complementer according to the present embodiment. The signal complementer shown in FIG. 4 includes a saturation sampling point detection circuit 401, a saturation sampling point information holding circuit 402, a subcarrier discrete Fourier transform circuit 403, an amplitude correction value calculation circuit 404, a complement data calculation circuit 405, A buffer 406, a waveform correction circuit 407, and a comparator 408 are provided. The saturation sampling point detection circuit 401 specifies a saturation sampling point, and the saturation sampling point information holding circuit 402 holds the location information and the value of the saturation sampling point detected by the saturation sampling point detection circuit 401. The subcarrier discrete Fourier transform circuit 403 performs a discrete Fourier transform on one or more specific subcarriers. The amplitude correction value calculation circuit 404 obtains an approximate solution of a multiple linear simultaneous equation based on the operation result of the subcarrier discrete Fourier transform circuit and the value of the location information of the saturated sampling point of the saturated sampling point information holding circuit 402. The complementary data calculation circuit 405 calculates complementary data based on the value of the amplitude correction value of the amplitude correction value calculation circuit 404 and the value of the location of the saturation sampling point of the saturation sampling point information holding circuit 402.
[0047]
The buffer 406 is a buffer for holding a signal before complementation during the operation, and the comparator 408 is a buffer for holding the absolute value of the signal value of the saturation sampling point of the saturation sampling point information holding circuit 402 and the signal from the complementing data calculation circuit 405. Compare the absolute value of the complement data. If the absolute value of the complementary data is equal to or greater than the absolute value of the value of the saturation sampling point of the saturation sampling point information holding circuit 402, the complementary data from the complementary data calculation circuit 405 is output as the complementary data, and the absolute value of the complementary data becomes If the absolute value of the value of the saturation sampling point of the saturation sampling point information holding circuit 402 is smaller than the absolute value, the signal value of the saturation sampling point of the saturation sampling point information holding circuit 402 is output. The waveform correction circuit 407 corrects the saturation sampling point in the buffer 406 to complementary data of the comparator 408 based on the location information of the saturation sampling point in the saturation sampling point information holding circuit 402 and outputs the corrected data.
[0048]
First, the signal before complementation is input to the saturation sampling point detection circuit 401. If the power value of the signal before complementation is the theoretical maximum value that can be expressed after A / D conversion, the saturation sampling point detection circuit 401 compares all 64 points as being saturated and determines whether or not the signal is saturated. This information and the signal value before complementation are output to the saturation sampling point information holding circuit 402. The saturation sampling point information holding circuit 402 detects the location information and the value of the saturation sampling point from the saturation information of the saturation sampling point detection circuit 401 and holds it. The signal before complementation is input to the subcarrier discrete Fourier transform circuit 403 and the buffer 406 at the same time.
[0049]
Here, it is assumed that the third and eighth input signals are saturated. The subcarrier discrete Fourier transform circuit 403 performs a discrete Fourier transform on a signal before complementation on subcarriers 27 and 28. The converted values are F27 and F28, respectively. In the amplitude correction value calculation circuit 404, x3 and x8 are obtained similarly to the amplitude correction value calculation circuit 404 described in the first embodiment.
[0050]
The supplementary data calculation circuit 405 subtracts the solution of the amplitude correction value calculation circuit 404 from the signal value of the saturation sampling point using the location information and the signal value of the saturation sampling point of the saturation sampling point information detection circuit 402, and generates the complementary data. Output. The comparator 408 has a selector 2401 as shown in FIG. 20, and calculates the absolute value of the signal value of the saturation sampling point of the saturation sampling point information holding circuit 402 and the absolute value of the complementary data from the complementary data calculation circuit 405. If the absolute value of the complementary data is greater than or equal to the absolute value of the saturation sampling point value of the saturation sampling point information holding circuit 402, the complementary data from the complementary data calculation circuit 405 is output as the complementary data, and When the absolute value is smaller than the absolute value of the value of the saturation sampling point of the saturation sampling point information holding circuit 402, the signal value of the saturation sampling point of the saturation sampling point information holding circuit 402 is output. The waveform correction circuit 407 sequentially outputs the signal of the buffer 406, and at that time, switches the signal of the saturation point from the location information of the saturation sampling point of the saturation sampling point information holding circuit 402 to the output of the complementary data calculation circuit 405 to complement. I do. It is possible to prevent correction of a sampling point that is saturated due to a noise of a signal to be complemented, a calculation error when calculating an amplitude correction value, or the like, with an erroneous value.
[0051]
As described above, according to the OFDM demodulator according to the present embodiment, it is possible to complement data that has been saturated before performing Fourier transform, and therefore, the input amplitude during A / D conversion may be saturated. You can take it large until you do. Further, there is an advantage that it is not necessary to use a high-resolution and high-precision A / D converter.
Although the embodiments have been described above, the present invention is not limited to these examples, and it goes without saying that various modifications are possible.
[0052]
【The invention's effect】
As described above, according to the OFDM signal demodulation device of the present invention, it is possible to complement data that has been saturated before performing Fourier transform, so that the input amplitude at the time of A / D conversion is increased until saturation occurs. Can be taken. Further, there is an advantage that it is not necessary to use a high-resolution and high-precision A / D converter.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a basic configuration example of an OFDM signal demodulation device according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a first configuration example of a complementary circuit according to the present embodiment;
FIG. 3 is a block diagram showing a second configuration example of the complementary circuit according to the embodiment;
FIG. 4 is a block diagram showing a third configuration example of the complementary circuit according to the present embodiment;
FIG. 5 is a diagram illustrating an example of a signal before discrete Fourier transform mapped by 16QAM.
FIG. 6 is a mapping diagram of the signal of FIG. 5;
FIG. 7 is a diagram showing a transmission waveform of the signal of FIG. 5;
8A and 8B are signals obtained by A / D conversion of the waveform in FIG. 7; FIG. 8A shows a signal obtained by performing A / D conversion without saturation; FIG. 8B shows a signal obtained by performing A / D conversion after saturation; FIG. 3 is a diagram illustrating an example of a signal.
9 is a diagram illustrating each signal after quadrature detection of the signal in FIG. 8;
FIG. 10 is a diagram showing signals after discrete Fourier transform on the signals of FIG. 9;
11 is a diagram illustrating a Fourier transform performed by subtracting x′0 and x′8 from x0 and x8 shown in I (b) and Q (b) of FIG. 9 when the signal complementer according to the present embodiment is used; It is a figure showing the result of having performed.
FIG. 12 is a diagram illustrating a configuration example of a saturation sampling point detection circuit according to the present embodiment;
FIG. 13 is a diagram illustrating a configuration example of a saturation sampling point information holding circuit according to the present embodiment;
FIG. 14 is a diagram illustrating a configuration example of a subcarrier discrete Fourier transform circuit according to the present embodiment.
FIG. 15 is a diagram illustrating a configuration example of an amplitude correction value calculation circuit according to the present embodiment;
FIG. 16 is a diagram illustrating a configuration example of a complementary data calculation circuit according to the present embodiment;
FIG. 17 is a diagram illustrating a first configuration example of the waveform correction circuit according to the present embodiment;
FIG. 18 is a diagram showing a configuration example of a saturation sampling point number counting circuit according to the present embodiment.
FIG. 19 is a diagram showing a second configuration example of the waveform correction circuit according to the present embodiment.
FIG. 20 is a diagram showing a configuration example of a comparator according to the present embodiment.
FIG. 21 is a diagram illustrating a configuration example of a general OFDM signal demodulation device.
[Explanation of symbols]
101 frequency converter, 102 amplitude amplifier, 103 A / D converter, 104
Digital quadrature detector, 105 discrete Fourier transformer, 106 code determiner, 107 signal complementer, 201 saturated sampling point detection circuit, 202 saturated sampling point information holding circuit, 203 subcarrier discrete Fourier transform circuit 204 amplitude correction value calculation circuit, 205 complementary data calculation circuit, 206 buffer, 207 waveform correction circuit, 301 saturation sampling point detection circuit, 302 saturation sampling point information holding circuit, 303 subcarrier discrete Fourier transform circuit, 304 amplitude correction value calculation circuit, 305 complementary data calculation circuit, 306 buffer, 307 waveform correction circuit, 308 saturated sampling point number counting circuit, 401 saturated sampling point detection circuit, 402 saturated sampling point information holding circuit, 403 subcarrier discrete file Lie transform circuit, 404 Amplitude correction value calculation circuit, 405 complementary data calculation circuit, 406 buffer, 407 waveform correction circuit, 408 comparator, 1601 power calculation circuit, 1602 saturation judgment circuit, 1603 Maximum power that can be expressed after A / D conversion , 1701 saturation point information calculation circuit, 1702 memory, 1703 counter, 1801 complex multiplier, 1802 adder, 1803 memory (W), 1804 complex multiplier, 1805 adder, 1901 memory (W), 1902 complex arithmetic unit ( x8 calculation), 1903 complex arithmetic operation unit (x3 calculation), 2001 Saturation sampling point signal value-amplitude correction value, 2101 selector, 2201 counter, 2301 selector, 2401 selector, 2501 frequency converter, 2502 amplitude amplifier, 2503 A / D conversion , 2504 digital quadrature detector, 2505 a discrete Fourier transformer, 2506 code determiner.

Claims (12)

Orthogonal frequency division multiplexing (Orthogonal) in which N (N is a natural number of N ≧ 1) subcarriers are provided, and m (m is a natural number of N ≧ m ≧ 1) are modulated with a known value. Frequency Division Multiplexing: hereinafter, referred to as “OFDM”.) An OFDM signal demodulator that processes and demodulates a signal in the order of A / D conversion, digital quadrature detection, and discrete Fourier transform.
An OFDM signal demodulator comprising a signal complementer for complementing an A / D conversion output saturated prior to a discrete Fourier transform. The OFDM signal demodulation device according to claim 1, wherein the complement is performed between digital quadrature detection and discrete Fourier transform. The signal complementer comprises:
A saturation sampling point detection circuit for specifying a saturation sampling point;
A saturation sampling point information holding circuit that holds the location information and the value of the saturation sampling point detected by the saturation sampling point detection circuit,
A subcarrier discrete Fourier transform circuit that performs a discrete Fourier transform on one or more specific subcarriers,
An amplitude correction value calculation circuit that calculates an amplitude correction value based on a calculation result of the subcarrier discrete Fourier transform circuit of a subcarrier having a known value modulated and location information of a saturation sampling point of the saturation sampling point information holding circuit. When,
2. The circuit according to claim 1, further comprising a complementary data calculation circuit that calculates complementary data based on the amplitude correction value of the amplitude correction value calculation circuit and the location information of the saturation sampling point of the saturation sampling point information holding circuit. An OFDM signal demodulator according to any of the preceding claims. Further, a buffer for holding the signal before interpolation during the operation,
4. A waveform correction circuit for correcting a saturation sampling point in the buffer to complementary data of the complementary data calculation circuit based on location information of the saturation sampling point of the saturation sampling point information holding circuit and outputting the corrected data. An OFDM signal demodulator according to any of the preceding claims. The signal complementer comprises:
A discrete Fourier transform unit that performs a discrete Fourier transform on the output of the digital quadrature detector and reproduces a signal waveform for each subcarrier,
At the sampling point of the output of the digital quadrature detector selected for the discrete Fourier transform, when the amplitude absolute value of the I component which is a 0-degree component or the Q component which is a 90-degree component becomes larger than a certain value; or A saturation sampling point detecting means for determining that the sampling point is a saturation sampling point when the power value, which is the sum of squares of the IQ components at the sampling point, becomes a certain value or more;
Saturation sampling point information holding means for holding saturation sampling point information including the signal value of the saturation sampling point and sampling timing,
An amplitude correction value calculating unit that calculates an amplitude correction value at the saturation sampling point based on the saturation sampling point information and an operation result of the discrete Fourier transform unit on the subcarrier modulated with the known value;
Based on the saturation sampling point information and the amplitude correction value, a complementary data calculation unit that calculates the amplitude value of the saturation sampling point,
2. The OFDM signal demodulator according to claim 1, further comprising: means for correcting an output of a digital quadrature detector based on the saturation sampling point information and the complementary data. The signal complementer comprises:
Further, there is provided a saturated sampling point number counting means for counting the number s (s is a natural number of N ≧ s ≧ 1) of saturated sampling points in the discrete Fourier transform window,
If the number n of the saturated sampling points is m ≧ s, data complement is performed on the saturated sampling points of the corresponding discrete Fourier transform window. If m <s, the data of the corresponding discrete Fourier transform window is The OFDM signal demodulation device according to claim 5, wherein control is performed such that data complementation is not performed on the saturated sampling point. The signal complementer comprises:
The absolute value j of the signal output from the saturated sample point information detecting means and the absolute value k of the complementary data are compared. If j ≦ k, it is determined that the data is saturated, and the data is complemented at the saturated point. 6. The OFDM signal demodulation device according to claim 5, wherein when j> k, it is determined that the signal is non-saturated, and control is performed so as not to perform data complement at the saturation point. An OFDM signal having N (N is a natural number of N ≧ 1) subcarriers, of which m (m is a natural number of N ≧ m ≧ 1) modulated with a known value, is represented by A / It is suitable for use in an OFDM signal demodulator that processes and demodulates in the order of D conversion, digital quadrature detection, and discrete Fourier transform.
A discrete Fourier transform unit that performs a discrete Fourier transform on the output of the digital quadrature detector and reproduces a signal waveform for each subcarrier,
At the sampling point of the output of the digital quadrature detector selected for the discrete Fourier transform, when the amplitude absolute value of the I component which is a 0-degree component or the Q component which is a 90-degree component becomes larger than a certain value; or A saturation sampling point detecting means for determining that the sampling point is a saturation sampling point when the power value, which is the sum of squares of the IQ components at the sampling point, becomes a certain value or more;
Saturation sampling point information holding means for holding saturation sampling point information including the signal value of the saturation sampling point and sampling timing,
An amplitude correction value calculating unit that calculates an amplitude correction value at the saturation sampling point based on the saturation sampling point information and an operation result of the discrete Fourier transform unit on the subcarrier modulated with the known value;
Based on the saturation sampling point information and the amplitude correction value, a complementary data calculation unit that calculates the amplitude value of the saturation sampling point,
Means for correcting the output of the digital quadrature detector based on the saturation sampling point information and the complementary data. An OFDM signal having N (N is a natural number of N ≧ 1) subcarriers, of which m (m is a natural number of N ≧ m ≧ 1) modulated with a known value, is represented by A / An OFDM signal demodulation method for processing and demodulating in the order of D conversion, digital quadrature detection, and discrete Fourier transform,
An OFDM signal demodulation method, comprising a signal complementing step of complementing a saturated A / D conversion output prior to a discrete Fourier transform. The signal complementing step includes:
Performing a discrete Fourier transform on the output of the digital quadrature detector, and a discrete Fourier transform step of reproducing a signal waveform for each subcarrier;
At the sampling point of the output of the digital quadrature detector selected for the discrete Fourier transform, when the amplitude absolute value of the I component which is a 0-degree component or the Q component which is a 90-degree component becomes larger than a certain value; or A saturation sampling point detecting step of determining that the sampling point is a saturation sampling point when the power value which is the sum of squares of the IQ components at the sampling point is equal to or greater than a certain value;
Based on the saturation sampling point information including the signal value of the saturation sampling point and the sampling timing, and the calculation result by the discrete Fourier transform means for the subcarrier modulated with the known value, the amplitude correction value at the saturation sampling point Calculating an amplitude correction value to be calculated;
Based on the saturation sampling point information and the amplitude correction value, a complementary data calculation step of calculating the amplitude value of the saturation sampling point,
The OFDM signal demodulation method according to claim 9, further comprising: a correction step of correcting an output of a digital quadrature detector based on the saturation sampling point information and the complementary data. An OFDM signal having N (N is a natural number of N ≧ 1) subcarriers, of which m (m is a natural number of N ≧ m ≧ 1) modulated with a known value, is represented by A / A program for causing a computer to execute an OFDM signal demodulation process of processing and demodulating in the order of D conversion, digital quadrature detection, and discrete Fourier transform,
An OFDM signal demodulation processing program including a signal complementing procedure for complementing a saturated A / D conversion output prior to a discrete Fourier transform. The signal complementing procedure includes:
Performing a discrete Fourier transform on the output of the digital quadrature detector, and a discrete Fourier transform procedure for reproducing a signal waveform for each subcarrier;
At the sampling point of the output of the digital quadrature detector selected for the discrete Fourier transform, when the amplitude absolute value of the I component which is a 0-degree component or the Q component which is a 90-degree component becomes larger than a certain value; or When a power value that is the sum of squares of the IQ component at the sampling point is equal to or greater than a certain value, a saturated sampling point detection procedure for determining the sampling point as a saturated sampling point;
Based on the saturation sampling point information including the signal value of the saturation sampling point and the sampling timing, and the calculation result by the discrete Fourier transform means for the subcarrier modulated with the known value, the amplitude correction value at the saturation sampling point An amplitude correction value calculation procedure to be calculated;
Based on the saturation sampling point information and the amplitude correction value, a complementary data calculation procedure for calculating the amplitude value of the saturation sampling point,
12. The program according to claim 11, further comprising: a correction procedure for correcting an output of a digital quadrature detector based on the saturation sampling point information and the complementary data.

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