JP4190962B2

JP4190962B2 - CDMA receiver, and channel estimation apparatus and method thereof

Info

Publication number: JP4190962B2
Application number: JP2003183255A
Authority: JP
Inventors: 研也三浦
Original assignee: NEC Corp; NEC Communication Systems Ltd
Current assignee: NEC Corp; NEC Communication Systems Ltd
Priority date: 2003-06-26
Filing date: 2003-06-26
Publication date: 2008-12-03
Anticipated expiration: 2023-06-26
Also published as: JP2005020445A

Description

【０００１】
【発明の属する技術分野】
本発明は、ＣＤＭＡ通信方式の受信装置と、それに用いられる、受信した拡散符号で拡散された信号を逆拡散して得られた信号に対し、当該信号に挿入されているパイロットシンボルに基づいて当該信号全体の位相の回転を推定し補正するチャネル推定装置及びチャネル推定方法とに関する。
【０００２】
【従来の技術】
ＣＤＭＡ（符号分割多元接続）通信システムでは、送信側は、送信データをチャネル符号化してパイロット信号とともにデータ変調し、拡散符号で拡散後、無線周波数信号に変調して無線送信する。受信側（ＣＤＭＡ受信装置）は、受信した無線周波数信号を拡散符号で拡散された信号に復調し、送信側と同じ拡散符号で逆拡散後、チャネル復号して２値データ判定し、送信データを復元する。
【０００３】
このＣＤＭＡ受信装置において、拡散符号で拡散された受信信号は、複数のマルチパス成分を含んでおり、パス検出回路で主要なパスが検出され（レベルの大きなパスのタイミングの検出）、各主要パスに対応したフィンガー回路でそれぞれ逆拡散された後、レイク合成され、データが復号される。
【０００４】
一方、受信信号は無線区間のフェージングにより、位相回転が発生する。各フィンガー回路では、受信拡散信号を逆拡散して得た信号（シンボル）における位相回転を、当該受信信号に含まれるパイロットシンボル（送信側での送信位相、振幅が既知の信号）に基づいて推定（チャネル推定）するチャネル推定回路を設け、チャネル推定回路からのチャネル推定値に従い、すべてのデータシンボルの位相回転を補正する。送受信信号は複数スロットに分割されたフレームで構成されており、パイロットシンボルは各スロットに複数個挿入されている。
【０００５】
チャネル推定回路は、通常、スロットごとに、該当スロット中の複数のパイロットシンボルを平均して瞬時チャネル推定値を求め、近傍の複数スロット各々のの瞬時チャネル推定値も参照しながら最終的なチャネル推定値を算出している。この複数スロットの瞬時チャネル推定値から最終的なチャネル推定値を算出するための具体的な手段，方法としては、ＷＭＳＡ（マルチスロット重み付き平均化）チャネル推定フィルタを使用する場合もあるが、前回（直前のスロット）の最終的なチャネル推定値に忘却係数を掛けて今回（注目スロット）の瞬時チャネル推定値に加算し今回の最終的なチャネル推定値を求める、より簡易な構成の再帰形フィルタを使用する場合もある。（例えば、特許文献１参照）。
【０００６】
【特許文献１】
特開２００１−７７７４４号公報（第１−２頁、図９）
【０００７】
【発明が解決しようとする課題】
チャネル推定値の算出に、上述の忘却係数を乗じた前回までの推定値を用いる再帰形フィルタを使用する場合、回路構成はＷＭＳＡフィルタを使用する場合よりも簡略化することができる。しかし、忘却係数が固定値だと、フェージング等により同期が不安定な場合に、チャネル推定値は誤差が大きくなり、この結果、同期確立までに時間がかかってしまう。
【０００８】
本発明の目的は、忘却係数による再帰形フィルタを用いてチャネル推定を行う際、フェージングにより受信信号に変動が生じても、検出したパスのレベル状態に応じて忘却係数の値を可変とすることにより、過渡状態でのチャネル推定の誤差を減少させ、同期確立までの時間を改善可能としたＣＤＭＡ受信装置、及びそのチャネル推定装置と方法を提供することにある。
【０００９】
【課題を解決するための手段】
本発明の請求項１に係るチャネル推定装置は、ＣＤＭＡ通信方式の受信装置に用いられ、受信した拡散符号で拡散された信号を逆拡散して得られた信号に対し、当該信号に挿入されているパイロットシンボルに基づいて当該信号全体の位相の回転を推定し補正するチャネル推定装置において、拡散符号で拡散されている受信信号からパスを検出し、そのタイミングを示すパスタイミング情報及びレベルを示すパスレベル情報を出力するパス検出手段と、前記パスタイミング情報に従って前記拡散符号で拡散されている受信信号を逆拡散して得られた信号から所定期間ごとにパイロットシンボルを抽出しその位相回転を判定して瞬時のチャネル推定値を算出し、前回期間における最終的なチャネル推定値に忘却係数を掛けた結果と加算することにより、今回期間における前記拡散して得られた信号全体の位相の回転を補正するための最終的なチャネル推定値として出力し、かつ、前記忘却係数の値を前記パスレベル情報に応じて変化させるチャネル推定手段と、前記チャネル推定手段からのチャネル推定値に基づいて、前記拡散して得られた信号全体の位相の回転を補正する位相補正手段とを備える。
【００１０】
本発明の請求項２に係るチャネル推定装置は、請求項１に係るチャネル推定装置において、前記チャネル推定手段が、受信した前記パイロットシンボルとそのあらかじめ設定された複素共役との乗算を行う乗算手段と、前記乗算手段の出力を複素共役正規化し瞬時のチャネル推定値として出力する複素共役正規化手段と、前記パスレベル情報に基づいてあらかじめ設定された基準忘却係数の値を変更した忘却係数を算出し出力する忘却係数算出手段と、前回の最終的なチャネル推定値に、前記忘却係数算出手段からの忘却係数を掛けた結果を出力する忘却手段と、前記複素共役正規化手段の出力に前記忘却手段からの出力の加算を行い最終的なチャネル推定値として出力する加算手段とを有する。
【００１１】
本発明の請求項３に係るチャネル推定装置は、請求項２に係るチャネル推定装置において、前記忘却係数算出手段が、前記パスレベル情報の示すレベル値が所定の高レベル閾値より高い場合は、前記基準の忘却係数の値そのままを出力忘却係数の値とし、前記レベル値が前記高レベル閾値より低くなるにしたがって前記基準の忘却係数の値を漸次減少した値を出力忘却係数の値とする構成を有する。
【００１２】
本発明の請求項４に係るＣＤＭＡ受信装置は、ＣＤＭＡ通信方式の受信装置において、送信側より送信されたＣＤＭＡ方式の無線信号を受信し拡散符号で拡散されたベースバンドの受信信号として出力する無線受信手段と、前記無線受信手段からの受信信号を該当拡散符号で逆拡散し、ベースバンド信号として出力する復調手段と、前記復調手段からの受信信号を該当符号則で復号し、送信側からの送信データを復元する復号手段とを備え、前記復調手段が、前記無線受信手段からの受信信号と既知のパイロットシンボルとの相関を取り、主要なパスを検出しパスタイミング情報及びパスレベル情報として出力する請求項１記載のパス検出手段と、各々が、割り当てられた前記パス検出手段からのパスタイミングを基に、前記無線受信手段からの受信信号を該当拡散符号で逆拡散しベースバンド信号として出力する逆拡散手段と、前記逆拡散手段の出力受信信号に対しその中のパイロットシンボルの位相を検出することによりフェージングによる受信信号の位相の回転を推定し、対応するパスレベルに応じた忘却係数の値を制御しながら、チャネル推定値として出力する請求項１、２、または３記載のチャネル推定手段と、前記逆拡散手段からの受信信号のすべてのシンボルに対し、前記チャネル推定手段における処理時間分だけ遅らせてから前記チャネル推定手段からのチャネル推定値を掛け、位相の補正を行い出力する請求項１記載の位相補正手段とを有する複数のフィンガー手段と、前記複数のフィンガー手段の出力を加算合成する合成手段とを有している。
【００１３】
本発明の請求項５に係るチャネル推定方法は、ＣＤＭＡ通信方式の受信装置における、受信した拡散符号で拡散された信号を逆拡散して得られた信号に対し、当該信号に挿入されているパイロットシンボルに基づいて当該信号全体の位相の回転を推定し補正するチャネル推定方法において、パス検出手段で、拡散符号で拡散されている受信信号からパスを検出し、そのタイミングを示すパスタイミング情報及びレベルを示すパスレベル情報を求め、チャネル推定手段で、前記パスタイミング情報に従って前記拡散符号で拡散されている受信信号を逆拡散して得られた信号から所定期間ごとにパイロットシンボルを抽出しその位相回転を判定して瞬時のチャネル推定値を算出し、前回期間における最終的なチャネル推定値に忘却係数を掛けた結果と加算することにより、今回期間における前記拡散して得られた信号全体の位相の回転を補正するための最終的なチャネル推定値として算出するとともに、前記忘却係数の値を前記パスレベル情報に応じて変化させ、位相補正手段で、前記最終的なチャネル推定値に基づいて、前記拡散して得られた信号全体の位相の回転を補正する工程を有する。
【００１４】
本発明の請求項６に係るチャネル推定方法は、請求項５に係るチャネル推定方法において、前記チャネル推定手段で、受信した前記パイロットシンボルとそのあらかじめ設定された複素共役との乗算を行い、乗算結果を複素共役正規化して所定期間ごとの瞬時のチャネル推定値を算出し、前記パスレベル情報に基づいてあらかじめ設定された基準忘却係数の値を変更した忘却係数を算出し、今回の前記瞬時のチャネル推定値に、前回の最終的なチャネル推定値に前記算出された忘却係数を掛けた結果を加算し、今回の最終的なチャネル推定値として算出する工程を有する。
【００１５】
本発明の請求項７に係るチャネル推定方法は、請求項６に係るチャネル推定方法において、前記パスレベル情報の示すレベル値が所定の高レベル閾値より高い場合は、前記基準忘却係数の値そのままを算出すべき忘却係数の値とし、前記レベル値が前記高レベル閾値より低くなるにしたがって前記基準忘却係数の値を漸次減少した値を算出すべき忘却係数の値とする工程を有する。
【００１６】
【発明の実施の形態】
まず、本発明の概要を説明する。本発明は、ＣＤＭＡ通信方式の受信装置（ＣＤＭＡ受信装置）における受信信号復調時の忘却係数による再帰形フィルタを用いたチャネル推定において、パスレベルに従い、忘却係数の値を変化させることにより、過渡状態でのチャネル推定の誤差を減少させ、同期確立までに要する時間を短縮することを特徴としている。
【００１７】
ＣＤＭＡ受信装置についてより具体的に説明する。無線受信部は無線周波数信号を受信し、送信側から出力された拡散符号で拡散された信号を出力する。パス検出回路は、無線受信部からの受信信号と既知のパイロット信号（パイロットシンボル：ＰｉｌｏｔＳｙｍｂｏｌ）との相関を取り、パス（そのタイミング及びレベル）を検出し、パスタイミング情報及びパスレベル情報を出力する。主要なパスにそれぞれ割り当てられた各フィンガー部の逆拡散回路は、パス検出回路からの対応するパスタイミング情報を元に受信信号を送信側と同一の拡散符号で逆拡散し出力する。チャネル推定回路は、逆拡散回路からの逆拡散後の受信信号中のパイロット信号の位相からフェージングによる受信信号の位相の回転を推定し、逆拡散回路から出力されたすべての逆拡散後の受信信号の位相を補正する。その際、パス検出回路からのパスレベル情報に基づいて各パイロット信号に対する忘却係数の値を制御し、過渡状態でのチャネル推定の誤差を減少させる。Ｒａｋｅ（レイク）合成回路は、各フィンガー部から出力された信号、すなわち、対応するパスタイミングにより復調され位相回転が補正された受信信号を加算する。復号部は、Ｒａｋｅ合成回路からの信号を復号し送信データを復元する。
【００１８】
次に、本発明の実施の形態について図面を参照して詳細に説明する。
【００１９】
図１は本発明の一実施の形態を示すブロック構成図であり、ＣＤＭＡ受信装置のうち本発明に関係する部分のみを示している。図１において、本例のＣＤＭＡ受信装置は、送信側より送信されたＣＤＭＡ方式の無線信号を受信し拡散符号で拡散されたベースバンドの受信信号（拡散化ベースバンド信号）として出力する無線受信部１と、無線受信部１からの受信信号（拡散化ベースバンド信号）を該当拡散符号で逆拡散し、ベースバンド信号として出力する復調部２と、復調部２からの受信信号（ベースバンド信号）を該当符号則で復号し、送信側からの送信データを復元する復号部６とを備えている。
【００２０】
復調部２は、パス検出回路３と、複数（図示は３つ）のフィンガー部４（４−１〜４−３）と、Ｒａｋｅ（レイク）合成回路５とを有している。
【００２１】
パス検出回路３は、無線受信部１からの受信信号（拡散化ベースバンド信号）と、既知のパイロット信号（シンボル）との相関を取り、主要なパス（そのタイミング及びレベル）を検出し、パスタイミング情報及びパスレベル情報として出力する。
【００２２】
各フィンガー部４（４−１〜４−３）は同一構成でありそれぞれ、パス検出回路３からのパスタイミングを基に、無線受信部１からの受信信号（データシンボル及びパイロットシンボルを含む拡散化ベースバンド信号）を該当拡散符号で逆拡散しベースバンド信号として出力する逆拡散回路４１と、逆拡散回路４１の出力受信信号（逆拡散後のベースバンド信号）に対し、その中のパイロットシンボルの位相を検出することによりフェージングによる受信信号の位相の回転を推定し、チャネル推定値として出力するチャネル推定回路４２と、逆拡散回路４１の出力受信信号をチャネル推定回路４２における処理時間分だけ遅らせる遅延回路４３と、遅延回路４３を通した逆拡散回路４１からの受信信号のすべてのシンボル（データシンボル及びパイロットシンボル）に対しチャネル推定回路４２からのチャネル推定値を掛け、位相の補正を行う乗算器４４とを有している。
【００２３】
Ｒａｋｅ合成回路５は、各フィンガー部４（４−１〜４−３）の出力信号の加算合成を行う。
【００２４】
図２に、チャネル推定回路４２の構成例を示す。
【００２５】
図２においてチャネル推定回路４２は、受信したパイロットシンボルとその複素共役との乗算を行う乗算器４２１と、乗算器４２１の出力（レベル及び位相）を複素共役正規化する複素共役正規化回路４２２と、複素共役正規化回路４２２の出力（瞬時のチャネル推定値）に忘却回路４２６からの出力の加算を行いチャネル推定値（今回の最終的なチャネル推定値）として出力する加算器４２３と、加算器４２３の出力（レベル）を正規化する推定値正規化回路４２４と、基準の忘却係数の値を保持し、パス検出回路３からのパスレベル情報に基づいて基準の忘却係数の値を変更した忘却係数を算出する忘却係数算出回路４２５と、推定値正規化回路４２４を通して加算器４２３から出力された前回のチャネル推定値（前回の最終的なチャネル推定値）を保持し、これに忘却係数算出回路４２５からの忘却係数の値を掛けた結果を加算器４２３へ出力する忘却回路４２６とを有している。
【００２６】
図３に、チャネル信号のフレーム構成を示す。所定周期の１無線フレームは複数のスロット（スロット１〜スロットＮ）に分割される。各スロットはデータ部とパイロット部とに分かれている。パイロットパターンはスロットごとに異なり、フレーム周期となっている。パイロットパターンは数シンボルから構成され、その受信したシンボルは『Ａｅ^Ｊθ』と表される。
【００２７】
なお本発明においては、パス検出回路２と、各フィンガー部４（４−１〜４−３）のチャネル推定回路４２，遅延回路４３，及び乗算器４４とを総称してチャネル推定装置と称する。
【００２８】
次に、図１、２及び３を参照して本実施の形態の動作を説明する。
【００２９】
ＣＤＭＡ無線通信システムの送信側（ＣＤＭＡ送信装置）では、送信データをチャネル符号化してパイロット信号とともにデータ変調し、拡散符号で拡散後、無線周波数信号に変調して無線送信する。
【００３０】
無線受信部１は、この相手先（ＣＤＭＡ送信装置）より送信されたＣＤＭＡ方式の無線周波数信号を受信し拡散符号で拡散されたベースバンドの受信信号（拡散化ベースバンド信号）として、復調部２のパス検出回路３及び各フィンガー部４（４−１〜４−３）へ出力する。
【００３１】
パス検出回路３では、複数のパス（パスタイミング及びパスレベル）を検出し出力し、所定のアルゴリズムに従って各フィンガー部４−１〜４−３へそれぞれ割り当てる（例えば、レベルの上位から選択する）。また、各フィンガー部４−１〜４−３において、逆拡散回路４１にはパスタイミング情報を、チャネル推定回路４２にはパスレベル情報を入力する。
【００３２】
各フィンガー部４−１〜４−３の逆拡散回路４１は、パス検出回路３からのパスタイミングを基に無線受信部１からの受信信号を逆拡散し、各データシンボル及びパイロットシンボルをチャネル推定回路４２及び遅延回路４３へ出力する。
【００３３】
チャネル推定回路４２は、逆拡散回路４１の出力パイロットシンボルに基づいてフェージングによる受信信号の位相の回転を推定し、逆拡散回路４１の全出力シンボルに対し、位相の回転を補正する。
【００３４】
ここで、チャネル推定回路４２の動作の詳細を説明する。
【００３５】
乗算器４２１の一方の入力である受信したパイロットシンボルを『Ａｅ^Ｊθ』とする（Ａ：振幅，θ：位相）。送信側で送信したパイロットシンボルを『１＋ｊ』とすると、乗算器４２１の他方の入力であるその正規化した複素共役は『ｅ^{−Ｊπ／４}』となる。乗算器４２１でこれらを掛け合わせると『Ａｅ^{Ｊ（θ−π／４）}』となり、これがフェージングによる位相の回転を表す。
【００３６】
パイロットシンボルは毎スロット（ｓｌｏｔ）存在し、数ビット存在するので、全てのパイロットシンボルで位相の回転を算出する。複素共役正規化回路４２２で、スロットごとに、それらの位相の回転を平均し、複素共役正規化した値『ｅ^{Ｊ（π／４−θ）}』を出力し、加算器４２３の一方の入力とする。
【００３７】
ここで、加算器４２３から出力された前回のチャネル推定値を『ｅ^Ｊφ』とする。忘却係数算出回路４２５は、パスレベル情報に基づいて忘却係数『λ』を算出する。忘却回路４２６は、この忘却係数『λ』と前回のチャネル推定値『ｅ^Ｊφ』とを掛け合わせた値『λｅ^Ｊφ』を出力し、加算器４２３の他方の入力とする。
【００３８】
加算器４２３は、複素共役正規化回路４２２からの入力『ｅ^{Ｊ（π／４−θ）}』と忘却回路４２４からの入力『λｅ^Ｊφ』とを加算した値『λｅ^Ｊφ＋ｅ^{Ｊ（π／４−θ）}』を、今回のチャネル推定値として出力し、推定値正規化回路４２４によりそのレベルを正規化する。
【００３９】
各フィンガー部４（４−１〜４−３）の乗算器４４で、チャネル推定回路４２から出力されたチャネル推定値を、逆拡散回路３１から出力され遅延回路４３でタイミングを合わされたた全てのシンボルに掛けることにより、受信信号の位相回転が補正される。
【００４０】
各フィンガー部４（４−１〜４−３）の出力は、Ｒａｋｅ合成回路５により加算、合成され、復号部６に入力される。
【００４１】
復号部６は、送信側の符号化則に対応した復号則に従い、送信されたデータを復元する。
【００４２】
次に、チャネル推定回路４２における忘却係数の算出方法の詳細を説明する。
【００４３】
各フィンガー部４のチャネル推定回路４２では、忘却係数λをパス検出回路３からのパスレベルに従って変化させる。同期外れ状態ではチャネル推定値は誤差が大きいので、λを“０”に近づけ、以前の推定値の影響を少なくする。また、同期が安定した場合には微小時間での位相の変化量は微小と考えられるため、予め設定されたλ本来の値（基準値：λ_０）とする。
【００４４】
上記の条件を満たす以下の式を導入しそれに従って忘却係数を制御する。
【００４５】
λ＝λ_０ ×f(X)
ただし、Ｘ：パスレベル、f(X)：Ｘが“０”より大きくなるに従って“０”から“１”の範囲内（０≦f(X)≦１）で漸増する値をとる関数、λ_０：基準忘却係数、である。
【００４６】
図４に、f(X)の一例を示す。パスレベルＸが低レベル閾値Ｘｌ以下の場合は、Ｙ＝f(X)は“０”、Ｘが高レベル閾値Ｘｈ以上の場合は、f(X)は“１”、ＸがＸｌとＸｈとの間の場合は、f(X)はＸの増加に比例して“０”から“１”まで増加する。
【００４７】
なお、低レベル閾値Ｘｌを設けないようにすることもできる。このとき、パスレベルＸが高レベル閾値Ｘｈ以上の場合は、f(X)は“１”とし、Ｘが高レベル閾値より低くなるにしたがってf(X)は“１”より漸次減少した値とする。
【００４８】
【発明の効果】
以上説明したように本発明によれば、以下に記載するような効果を奏する。第１の効果はパスレベルの低い場合、前回のチャネル推定値の重み付け（忘却係数）を小さくすることによりチャネル推定誤差の影響を減少させることができる。第２の効果はチャネル推定値の誤差が減少することにより過渡期における同期確立時間を短縮することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態を示すブロック構成図である。
【図２】図１のチャネル推定回路の構成例を示す図である。
【図３】フレーム及びスロットの構成例を示す図である。
【図４】パスレベルに応じて実際の忘却係数が基準忘却係数より変化する一例を示す図である。
【符号の説明】
１無線受信部
３パス検出回路
４（４−１〜４−３）フィンガー部
５Ｒａｋｅ（レイク）合成回路
６復号部
４１逆拡散回路
４２チャネル推定回路
４３遅延回路
４４，４２１乗算器
４２２複素共役正規化回路
４２３加算器
４２４推定値正規化回路
４２５忘却係数算出回路
４２６忘却回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a receiving apparatus of a CDMA communication system and a signal obtained by despreading a signal spread using a received spreading code based on a pilot symbol inserted in the signal. The present invention relates to a channel estimation apparatus and a channel estimation method for estimating and correcting a phase rotation of an entire signal.
[0002]
[Prior art]
In a CDMA (Code Division Multiple Access) communication system, a transmission side performs channel coding on transmission data, modulates data with a pilot signal, spreads with a spreading code, modulates to a radio frequency signal, and wirelessly transmits. The receiving side (CDMA receiver) demodulates the received radio frequency signal into a signal spread with a spreading code, despreads with the same spreading code as the transmitting side, channel decodes to determine binary data, Restore.
[0003]
In this CDMA receiver, the received signal spread by the spreading code includes a plurality of multipath components, and a main path is detected by a path detection circuit (detection of timing of a path with a large level). Are respectively despread by the finger circuits corresponding to, and then rake-combined to decode the data.
[0004]
On the other hand, the received signal undergoes phase rotation due to fading in the radio section. In each finger circuit, the phase rotation in the signal (symbol) obtained by despreading the received spread signal is estimated based on pilot symbols (signals with known transmission phase and amplitude on the transmission side) included in the received signal. A channel estimation circuit for (channel estimation) is provided, and phase rotation of all data symbols is corrected according to the channel estimation value from the channel estimation circuit. The transmission / reception signal is composed of frames divided into a plurality of slots, and a plurality of pilot symbols are inserted in each slot.
[0005]
The channel estimation circuit usually obtains an instantaneous channel estimation value by averaging a plurality of pilot symbols in the corresponding slot for each slot, and also refers to an instantaneous channel estimation value of each of a plurality of neighboring slots, thereby determining a final channel estimation. The value is calculated. As a specific means and method for calculating a final channel estimation value from the instantaneous channel estimation values of a plurality of slots, a WMSA (multi-slot weighted averaging) channel estimation filter may be used. A recursive filter with a simpler configuration that multiplies the final channel estimate of (previous slot) by the forgetting factor and adds it to the instantaneous channel estimate of this (target slot) to obtain the final channel estimate May be used. (For example, refer to Patent Document 1).
[0006]
[Patent Document 1]
JP 2001-77744 A (page 1-2, FIG. 9)
[0007]
[Problems to be solved by the invention]
When a recursive filter that uses an estimated value up to the previous time multiplied by the above-mentioned forgetting factor is used to calculate the channel estimated value, the circuit configuration can be simplified as compared with the case where a WMSA filter is used. However, if the forgetting factor is a fixed value, when synchronization is unstable due to fading or the like, the channel estimation value has a large error, and as a result, it takes time to establish synchronization.
[0008]
It is an object of the present invention to make the forgetting factor variable according to the level state of the detected path even when fluctuations occur in the received signal due to fading when performing channel estimation using a recursive filter with a forgetting factor. Accordingly, it is an object of the present invention to provide a CDMA receiver that can reduce errors in channel estimation in a transient state and improve the time until synchronization is established, and a channel estimation apparatus and method thereof.
[0009]
[Means for Solving the Problems]
A channel estimation apparatus according to claim 1 of the present invention is used in a receiving apparatus of a CDMA communication system, and is inserted into a signal obtained by despreading a signal spread by a received spreading code. In a channel estimation device that estimates and corrects the rotation of the phase of the entire signal based on the pilot symbols that are present, the path is detected from the received signal spread by the spreading code, and the path timing information indicating the timing and the path indicating the level are detected. Path detection means for outputting level information, and pilot symbols are extracted every predetermined period from a signal obtained by despreading the received signal spread by the spreading code according to the path timing information, and its phase rotation is determined. To calculate the instantaneous channel estimate and add it to the final channel estimate for the previous period multiplied by the forgetting factor Thus, the final channel estimation value for correcting the phase rotation of the entire signal obtained by spreading in the current period is output, and the value of the forgetting factor is changed according to the path level information. Channel estimation means, and phase correction means for correcting the rotation of the phase of the entire signal obtained by spreading based on the channel estimation value from the channel estimation means.
[0010]
The channel estimation apparatus according to claim 2 of the present invention is the channel estimation apparatus according to claim 1, wherein the channel estimation means performs multiplication of the received pilot symbol and its preset complex conjugate. A complex conjugate normalizing means for complex conjugate normalizing the output of the multiplication means and outputting it as an instantaneous channel estimation value, and calculating a forgetting coefficient obtained by changing a value of a reference forgetting coefficient set in advance based on the path level information. Forgetting coefficient calculating means for outputting, forgetting means for outputting a result of multiplying the last final channel estimation value by the forgetting coefficient from the forgetting coefficient calculating means, and the output of the complex conjugate normalizing means to the forgetting means And adding means for adding the outputs from and outputting as final channel estimation values.
[0011]
The channel estimation device according to claim 3 of the present invention is the channel estimation device according to claim 2, wherein the forgetting factor calculation means determines that the level value indicated by the path level information is higher than a predetermined high level threshold. The reference forgetting factor value as it is is used as the output forgetting factor value, and the value obtained by gradually decreasing the reference forgetting factor value as the level value becomes lower than the high level threshold is used as the output forgetting factor value. Have.
[0012]
A CDMA receiving apparatus according to claim 4 of the present invention is a radio receiving apparatus that receives a CDMA radio signal transmitted from the transmitting side and outputs it as a baseband received signal spread by a spreading code in the CDMA communication system receiving apparatus. A receiving unit, a demodulating unit that despreads the received signal from the wireless receiving unit with a corresponding spreading code, and outputs the signal as a baseband signal; a received signal from the demodulating unit is decoded with a corresponding code rule; Decoding means for restoring transmission data, wherein the demodulation means correlates a received signal from the radio reception means with a known pilot symbol, detects a main path, and outputs it as path timing information and path level information The path detection means according to claim 1 and each of said radio reception means based on the path timing from said assigned path detection means. The despreading means for despreading the received signal with the corresponding spreading code and outputting it as a baseband signal, and the phase of the received signal due to fading by detecting the phase of the pilot symbol in the output received signal of the despreading means 4. The channel estimation unit according to claim 1, 2 or 3 which outputs a channel estimation value while controlling the value of the forgetting factor according to the corresponding path level and the reception from the despreading unit The phase correction unit according to claim 1, wherein all symbols of the signal are delayed by a processing time in the channel estimation unit, then multiplied by a channel estimation value from the channel estimation unit, phase corrected, and output. A plurality of finger means; and a synthesis means for adding and synthesizing outputs of the plurality of finger means.
[0013]
The channel estimation method according to claim 5 of the present invention is a pilot inserted in a signal obtained by despreading a signal spread by a received spreading code in a CDMA communication system receiver. In a channel estimation method for estimating and correcting the rotation of the phase of the entire signal based on symbols, path detection means detects a path from a received signal spread with a spreading code, and indicates path timing information and level indicating the timing. Is obtained by despreading the received signal spread by the spreading code in accordance with the path timing information by the channel estimation means, and a pilot symbol is extracted every predetermined period. To calculate the instantaneous channel estimate and multiply the final channel estimate in the previous period by the forgetting factor. Is added as the final channel estimation value for correcting the phase rotation of the entire signal obtained by spreading in the current period, and the value of the forgetting factor is determined according to the path level information. And the phase correction means corrects the phase rotation of the entire signal obtained by the spreading based on the final channel estimation value.
[0014]
The channel estimation method according to claim 6 of the present invention is the channel estimation method according to claim 5, wherein the channel estimation means multiplies the received pilot symbol and its preset complex conjugate, and the multiplication result To calculate the instantaneous channel estimation value for each predetermined period, calculate a forgetting coefficient obtained by changing a preset reference forgetting coefficient value based on the path level information, and calculate the instantaneous channel of this time A step of adding the result obtained by multiplying the estimated final channel estimation value by the calculated forgetting factor to the estimated value, and calculating the final channel estimated value at this time.
[0015]
The channel estimation method according to claim 7 of the present invention is the channel estimation method according to claim 6, wherein when the level value indicated by the path level information is higher than a predetermined high level threshold, the value of the reference forgetting factor is used as it is. And a forgetting coefficient value to be calculated, and a value obtained by gradually decreasing the reference forgetting coefficient value as the level value becomes lower than the high level threshold value.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
First, the outline of the present invention will be described. In the channel estimation using the recursive filter based on the forgetting factor at the time of demodulation of the received signal in the receiving device (CDMA receiving device) of the CDMA communication system, the present invention changes the value of the forgetting factor according to the path level, thereby changing the transient state. It is characterized in that the error in channel estimation at the time is reduced and the time required for establishing synchronization is shortened.
[0017]
The CDMA receiver will be described more specifically. The radio reception unit receives a radio frequency signal and outputs a signal spread by the spreading code output from the transmission side. The path detection circuit correlates a received signal from the radio reception unit with a known pilot signal (pilot symbol), detects a path (its timing and level), and outputs path timing information and path level information. To do. The despreading circuit of each finger assigned to each main path despreads the received signal with the same spreading code as that on the transmission side based on the corresponding path timing information from the path detection circuit, and outputs it. The channel estimation circuit estimates the phase rotation of the received signal due to fading from the phase of the pilot signal in the received signal after despreading from the despreading circuit, and all the despread received signals output from the despreading circuit Correct the phase. At that time, the value of the forgetting coefficient for each pilot signal is controlled based on the path level information from the path detection circuit, and the error of the channel estimation in the transient state is reduced. The rake combining circuit adds the signal output from each finger unit, that is, the received signal demodulated by the corresponding path timing and corrected in phase rotation. The decoding unit decodes the signal from the Rake combining circuit and restores the transmission data.
[0018]
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0019]
FIG. 1 is a block diagram showing an embodiment of the present invention, and shows only a part related to the present invention in a CDMA receiver. In FIG. 1, the CDMA receiving apparatus of this example receives a CDMA radio signal transmitted from the transmitting side and outputs a baseband received signal (spread baseband signal) spread by a spreading code. 1, a demodulator 2 that despreads the received signal (spread baseband signal) from the radio receiver 1 with the corresponding spreading code and outputs it as a baseband signal, and a received signal (baseband signal) from the demodulator 2 And a decoding unit 6 that restores transmission data from the transmission side.
[0020]
The demodulation unit 2 includes a path detection circuit 3, a plurality (three in the drawing) of finger units 4 (4-1 to 4-3), and a Rake synthesis circuit 5.
[0021]
The path detection circuit 3 correlates the received signal (spread baseband signal) from the radio receiver 1 and a known pilot signal (symbol), detects a main path (its timing and level), and Output as timing information and path level information.
[0022]
Each finger unit 4 (4-1 to 4-3) has the same configuration, and based on the path timing from the path detection circuit 3, the received signal from the radio reception unit 1 (spreading including data symbols and pilot symbols) Baseband signal) is despread with the corresponding spreading code and output as a baseband signal, and the output signal of the despreading circuit 41 (baseband signal after despreading) A channel estimation circuit 42 that estimates the phase rotation of the received signal due to fading by detecting the phase and outputs it as a channel estimation value, and a delay that delays the output reception signal of the despreading circuit 41 by the processing time in the channel estimation circuit 42 All symbols (data symbols and data symbols) of the received signal from the circuit 43 and the despread circuit 41 through the delay circuit 43 Multiplied by the channel estimate from the channel estimation circuit 42 to the pilot symbols), and a multiplier 44 for correcting the phase.
[0023]
The Rake combining circuit 5 performs addition combining of the output signals of the finger units 4 (4-1 to 4-3).
[0024]
FIG. 2 shows a configuration example of the channel estimation circuit 42.
[0025]
In FIG. 2, the channel estimation circuit 42 includes a multiplier 421 that performs multiplication of the received pilot symbol and its complex conjugate, and a complex conjugate normalization circuit 422 that performs complex conjugate normalization on the output (level and phase) of the multiplier 421. An adder 423 that adds the output from the forgetting circuit 426 to the output (instantaneous channel estimation value) of the complex conjugate normalization circuit 422 and outputs the result as a channel estimation value (final channel estimation value of this time); An estimated value normalization circuit 424 that normalizes the output (level) of 423, a reference forgetting coefficient value is held, and the forgetting value is changed based on the path level information from the path detection circuit 3 A forgetting coefficient calculation circuit 425 for calculating a coefficient, and a previous channel estimation value output from the adder 423 through the estimation value normalization circuit 424 (the last final channel). It holds the estimated value), and a forgetting circuit 426 to be output to the adder 423 the result of multiplying the value of the forgetting factor from forgetting coefficient calculating circuit 425 thereto.
[0026]
FIG. 3 shows the frame structure of the channel signal. One radio frame having a predetermined period is divided into a plurality of slots (slot 1 to slot N). Each slot is divided into a data part and a pilot part. The pilot pattern differs from slot to slot and has a frame period. The pilot pattern is composed of several symbols, and the received symbol is represented as “Ae ^Jθ ”.
[0027]
In the present invention, the path detection circuit 2, the channel estimation circuit 42, the delay circuit 43, and the multiplier 44 of each finger unit 4 (4-1 to 4-3) are collectively referred to as a channel estimation device.
[0028]
Next, the operation of the present embodiment will be described with reference to FIGS.
[0029]
On the transmission side (CDMA transmission apparatus) of the CDMA wireless communication system, transmission data is channel-encoded and data-modulated with a pilot signal, spread with a spreading code, modulated into a radio frequency signal, and wirelessly transmitted.
[0030]
The radio reception unit 1 receives a CDMA radio frequency signal transmitted from this partner (CDMA transmission device) and demodulates it as a baseband reception signal (spread baseband signal) spread by a spreading code. Are output to the path detection circuit 3 and the finger portions 4 (4-1 to 4-3).
[0031]
The path detection circuit 3 detects and outputs a plurality of paths (path timing and path level), and assigns each of the finger sections 4-1 to 4-3 according to a predetermined algorithm (for example, selects from the higher level). In each finger unit 4-1 to 4-3, path timing information is input to the despreading circuit 41 and path level information is input to the channel estimation circuit 42.
[0032]
The despreading circuit 41 of each finger unit 4-1 to 4-3 despreads the received signal from the radio receiving unit 1 based on the path timing from the path detecting circuit 3, and channel estimates each data symbol and pilot symbol. The data is output to the circuit 42 and the delay circuit 43.
[0033]
The channel estimation circuit 42 estimates the phase rotation of the received signal due to fading based on the output pilot symbol of the despreading circuit 41, and corrects the phase rotation for all output symbols of the despreading circuit 41.
[0034]
Here, details of the operation of the channel estimation circuit 42 will be described.
[0035]
The received pilot symbol which is one input of the multiplier 421 is set to “Ae ^Jθ ” (A: amplitude, θ: phase). When the pilot symbol transmitted on the transmission side is “1 + j”, the normalized complex conjugate that is the other input of the multiplier 421 is “e− ^{Jπ / 4} ”. When these are multiplied by the multiplier 421, “Ae ^{J (θ−π / 4)} ” is obtained, which represents the rotation of the phase due to fading.
[0036]
Since pilot symbols exist every slot and several bits exist, phase rotation is calculated for all pilot symbols. The complex conjugate normalization circuit 422 averages the rotations of the phases for each slot and outputs a complex conjugate normalized value “e ^{J (π / 4−θ)} ”. To do.
[0037]
Here, the previous channel estimation value output from the adder 423 is “e ^Jφ ”. The forgetting factor calculation circuit 425 calculates the forgetting factor “λ” based on the path level information. The forgetting circuit 426 outputs a value “λe ^Jφ ” obtained by multiplying the forgetting factor “λ” by the previous channel estimation value “e ^Jφ ” and ^uses the value as the other input of the adder 423.
[0038]
The adder 423 adds the value “λe ^Jφ + e ^{J (π / 4)} ^obtained by adding the input“ e ^{J (π / 4−θ)} ”from the complex conjugate normalization circuit 422 and the input“ λe ^Jφ ”from the forgetting circuit 424. ^−θ) ”is output as the current channel estimation value, and the estimated value normalization circuit 424 normalizes the level.
[0039]
In the multipliers 44 of the finger units 4 (4-1 to 4-3), the channel estimation values output from the channel estimation circuit 42 are all output from the despreading circuit 31 and timed by the delay circuit 43. By multiplying the symbol, the phase rotation of the received signal is corrected.
[0040]
The outputs of the finger units 4 (4-1 to 4-3) are added and synthesized by the Rake synthesis circuit 5 and input to the decoding unit 6.
[0041]
The decoding unit 6 restores the transmitted data according to a decoding rule corresponding to the encoding rule on the transmission side.
[0042]
Next, details of a method for calculating the forgetting factor in the channel estimation circuit 42 will be described.
[0043]
The channel estimation circuit 42 of each finger unit 4 changes the forgetting factor λ according to the path level from the path detection circuit 3. Since the channel estimation value has a large error in the out-of-synchronization state, λ is brought close to “0” to reduce the influence of the previous estimation value. Further, when the synchronization is stable, the amount of change in phase in a minute time is considered to be minute, so that it is set to a preset λ original value (reference value: λ ₀ ).
[0044]
The following equation that satisfies the above conditions is introduced and the forgetting factor is controlled accordingly.
[0045]
λ = λ ₀ × f (X)
Where X: pass level, f (X): a function that gradually increases in the range from “0” to “1” (0 ≦ f (X) ≦ 1) as X becomes larger than “0”, λ ₀ : Reference forgetting factor.
[0046]
FIG. 4 shows an example of f (X). When the pass level X is less than or equal to the low level threshold value Xl, Y = f (X) is “0”. When X is greater than or equal to the high level threshold value Xh, f (X) is “1”, and X is Xl and Xh. In the case of, f (X) increases from “0” to “1” in proportion to the increase of X.
[0047]
It should be noted that the low level threshold value Xl may not be provided. At this time, when the pass level X is equal to or higher than the high level threshold value Xh, f (X) is set to “1”, and f (X) is gradually decreased from “1” as X becomes lower than the high level threshold value. To do.
[0048]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained. The first effect is that when the path level is low, the influence of the channel estimation error can be reduced by reducing the weight (forgetting factor) of the previous channel estimation value. The second effect is that the synchronization establishment time in the transition period can be shortened by reducing the error of the channel estimation value.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram showing an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration example of a channel estimation circuit in FIG. 1;
FIG. 3 is a diagram illustrating a configuration example of a frame and a slot.
FIG. 4 is a diagram illustrating an example in which an actual forgetting factor changes from a reference forgetting factor according to a pass level.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Radio | wireless receiving part 3 Path | pass detection circuit 4 (4-1 to 4-3) Finger part 5 Rake (rake) composition circuit 6 Decoding part 41 Despreading circuit 42 Channel estimation circuit 43 Delay circuit 44,421 Multiplier 422 Complex conjugate normal Circuit 423 adder 424 estimated value normalization circuit 425 forgetting factor calculation circuit 426 forgetting circuit

Claims

Rotation of the phase of the entire signal based on the pilot symbols inserted in the signal, which is used in a CDMA communication system receiver and obtained by despreading the signal spread with the received spreading code In a channel estimation device for estimating and correcting
Path detection means for detecting a path from a received signal spread by a spreading code and outputting path timing information indicating the timing and path level information indicating the level;
A pilot symbol is extracted every predetermined period from a signal obtained by despreading the received signal spread by the spreading code according to the path timing information, and its phase rotation is determined to calculate an instantaneous channel estimate, As a final channel estimation value for correcting the phase rotation of the entire signal obtained by spreading in the current period by adding the result of multiplying the final channel estimation value in the previous period by the forgetting factor Channel estimation means for outputting and changing the value of the forgetting factor according to the path level information;
A channel estimation device comprising: phase correction means for correcting phase rotation of the entire signal obtained by spreading based on a channel estimation value from the channel estimation means.

The channel estimation means comprises:
Multiplying means for multiplying the received pilot symbol and its preset complex conjugate;
Complex conjugate normalization means for complex conjugate normalizing the output of the multiplication means and outputting it as an instantaneous channel estimate;
Forgetting factor calculating means for calculating and outputting a forgetting factor obtained by changing a value of a preset reference forgetting factor based on the path level information;
Forgetting means for outputting a result of multiplying the last final channel estimation value by the forgetting coefficient from the forgetting coefficient calculating means;
2. The channel estimation apparatus according to claim 1, further comprising addition means for adding the output from the forgetting means to the output of the complex conjugate normalization means and outputting the result as a final channel estimation value.

When the level value indicated by the pass level information is higher than a predetermined high level threshold value, the forgetting factor calculation means uses the value of the reference forgetting factor as it is as the output forgetting factor value, and the level value is the high level threshold value. 3. The channel estimation apparatus according to claim 2, wherein a value obtained by gradually decreasing the value of the reference forgetting factor as a lower value is set as the value of the output forgetting factor.

In a CDMA communication system receiver,
A radio receiving means for receiving a CDMA radio signal transmitted from the transmitting side and outputting it as a baseband received signal spread with a spreading code; and despreading the received signal from the radio receiving means with a corresponding spreading code; Demodulating means for outputting as a baseband signal, and decoding means for decoding the received signal from the demodulating means with a corresponding code rule and restoring transmission data from the transmission side,
The demodulation means comprises:
The path detection unit according to claim 1, wherein a correlation between a received signal from the radio reception unit and a known pilot symbol is obtained, a main path is detected and output as path timing information and path level information;
Each of the despreading means for despreading the received signal from the radio receiving means with a corresponding spreading code and outputting it as a baseband signal based on the assigned path timing from the path detecting means, By detecting the phase of the pilot symbol in the output received signal, the phase rotation of the received signal due to fading is estimated, and output as a channel estimation value while controlling the value of the forgetting factor according to the corresponding path level The channel estimation unit according to claim 1, 2 or 3, and all the symbols of the received signal from the despreading unit are delayed by the processing time in the channel estimation unit and then the channel from the channel estimation unit A plurality of finger means comprising the phase correction means according to claim 1 for multiplying the estimated value, correcting the phase, and outputting the result.
A CDMA receiving apparatus comprising: combining means for adding and combining the outputs of the plurality of finger means.

For a signal obtained by despreading a signal spread with a received spreading code in a CDMA communication system receiver, the phase rotation of the entire signal is estimated based on a pilot symbol inserted in the signal. In the channel estimation method for correcting and correcting,
A path detection means detects a path from a received signal spread by a spreading code, obtains path timing information indicating the timing and path level information indicating a level, and a channel estimation means determines the spreading code according to the path timing information. A pilot symbol is extracted every predetermined period from the signal obtained by despreading the received signal spread in step, and its phase rotation is determined to calculate the instantaneous channel estimate, and the final channel estimation in the previous period By adding the result multiplied by the forgetting factor, it is calculated as a final channel estimation value for correcting the phase rotation of the entire signal obtained by spreading in the current period, and the forgetting factor Change the value according to the path level information,
A channel estimation method, wherein phase correction means corrects the rotation of the phase of the entire signal obtained by spreading based on the final channel estimation value.

The channel estimation means,
Multiplying the received pilot symbol and a preset complex conjugate thereof, and normalizing the multiplication result to calculate an instantaneous channel estimate for each predetermined period;
Calculating a forgetting factor by changing a value of a preset reference forgetting factor based on the path level information;
A result obtained by multiplying the current final channel estimation value by the previous final channel estimation value and the calculated forgetting factor is calculated as the final channel estimation value. Item 6. The channel estimation method according to Item 5.

When the level value indicated by the pass level information is higher than a predetermined high level threshold, the value of the reference forgetting factor is used as the value of the forgetting factor to be calculated, and the level value becomes lower than the high level threshold. 7. The channel estimation method according to claim 6, wherein a value obtained by gradually decreasing the value of the reference forgetting factor is used as the value of the forgetting factor to be calculated.