JP3912511B2 - Positioning satellite signal receiver and positioning satellite signal receiving method - Google Patents

Description

この（式Ｑ１）の処理は、変数ｔの値が「１」だけ前の値Ｓ［ｋ］_ｏｌｄに、現在の変数ｔの値についての次の項
ｄ［ｔ×Ｎ＋ｋ］×ｅｘｐ（２πｊ・ｒ・ｔ／Ｍ）
を加算する演算である。
【０２８１】
データｄ（ｎ）は、Ａ／Ｄ変換器１８からの１ビットのＩＦデジタルデータをサンプリングしたデータであるので、ｄ［ｔ×Ｎ＋ｋ］は＋１または−１となる。そのため、（式Ｑ１）の演算は、一つの足し算または引き算になる。
【０２８２】
また、ｅｘｐ（２πｊ・ｒ・ｔ／Ｍ）においては、変数はｔのみであり、ｔは、０からＭ−１の値しかとらないので、この項ｅｘｐ（２πｊ・ｒ・ｔ／Ｍ）の値を、Ｍ点のテーブルとして記憶しておき、そのテーブルを用いることにより、この項ｅｘｐ（２πｊ・ｒ・ｔ／Ｍ）をｔの変更の度に毎回計算しなくてもよくなり、計算を早くすることができる。
【０２８３】
ステップＳ１５４の（式Ｑ１）の計算が終了したら、変数ｔを「１」だけインクリメントする（ステップＳ１５５）。そして、変数ｔがＭより小さいか否か判別し（ステップＳ１５６）、変数ｔがＭより小さいときには、ステップＳ１５４に戻って、前記（式Ｑ１）の計算を繰り返す。変数ｔがＭ以上のときには、次の（式Ｑ２）を計算する（ステップＳ１５７）。
【０２８４】
Ｓ［ｋ］＝Ｓ［ｋ］_ｏｌｄ×ｅｘｐ（２πｊ・ｒ・ｋ／Ｌ）・・・（式Ｑ２）
この（式Ｑ２）の処理は、変数ｋの値が「１」だけ前の値Ｓ［ｋ］_ｏｌｄに、現在の変数ｋの値についての次の項
ｅｘｐ（２πｊ・ｒ・ｋ／Ｌ）
を乗算する演算である。
【０２８５】
ステップＳ１５７の（式Ｑ２）の計算が終了したら、求めたＳ［ｋ］の値を前処理部１３０が備えるメモリに書き込む（ステップＳ１５８）。次に、変数ｋを「１」だけインクリメントする（ステップＳ１５９）。そして、変数ｋがＮより小さいか否か判別し（ステップＳ１６０）、変数ｋがＮより小さいときには、ステップＳ１５２に戻って、以上の計算処理を繰り返す。変数ｋがＮ以上のときには、前処理を終了して、高速フーリエ変換処理を開始する。
【０２８６】
以上の前処理により、ＦＦＴの対象となるのは、拡散符号のＭ周期分の全データ数のＬ点から、拡散符号の１周期分のＮ点に減るので、ＦＦＴ演算を高速にすることができる。
【０２８７】
〔デジタルマッチドフィルタによる同期捕捉の第５の例〕
この同期捕捉の第５の例は、第４の例と同様に、ＤＳＰ２３において、ＦＦＴ処理部１０１でＦＦＴ処理を行う前に、データサンプル数を低減する前処理を行って、処理の高速化を図るものである。
【０２８８】
この第５の例の場合におけるＤＳＰ２３の構成例は、前述した第４の例の場合の図２３に示したものと同じである。ただし、第５の例では、前処理部１３０で行う前処理の内容が第４の例とは異なる。
【０２８９】
この第５の例も、ＲＡＭ２２に取り込まれたＭ周期分のデータは、同じ拡散符号の１周期分のデータが、Ｍ回繰り返されるものに等しく、同期捕捉の第２の例において説明したように、周波数成分としては、拡散符号の１周期分のデータが備えるものしか存在しないことから、前処理部１３０においては、前記拡散符号のＭ周期分のデータ量から、拡散符号の１周期分のデータ量に減らす処理を行う。
【０２９０】
図３９は、この第５の例の前処理を説明するための図である。図３９の例においては、サンプリング回路２１でのサンプリング周波数は、４．０９６ＭＨｚであり、また、Ｍ＝１６、つまり、１６ミリ秒単位でＲＡＭ２２にデータを取り込んで、ＦＦＴ処理をする場合である。
【０２９１】
図３９に示すように、この例において、ＲＡＭ２２に記憶するＩＦデータは、拡散符号の１周期分の１６個のデータ群ｄ１（ｎ）、ｄ２（ｎ）、ｄ３（ｎ）、・・・、ｄ１６（ｎ）からなる。そして、この例の場合、データ群ｄ１（ｎ）、ｄ２（ｎ）、ｄ３（ｎ）、・・・、ｄ１６（ｎ）のそれぞれは、４０９６点のポイントからなり、１６ミリ秒分のデータ全体では、６５５３６点のポイントからなる。
【０２９２】
そして、１６個のデータ群ｄ１（ｎ）、ｄ２（ｎ）、ｄ３（ｎ）、・・・、ｄ１６（ｎ）のそれぞれの先頭から、同じポイント位置の値は、ＧＰＳ衛星信号の場合には、拡散符号の同じ成分を有しているはずである。しかも、前述したように、各ポイントのデータは、１ビットである。
【０２９３】
以上のことを考慮して、この第５の例の場合には、前処理部１３０に備えるメモリ１３０ＭＥＭとして、１ワードが１６ビットで、４０９６ワード分の容量を有するメモリを用いる。
【０２９４】
そして、１６個の拡散符号１周期分のデータ群ｄ１（ｎ）、ｄ２（ｎ）、ｄ３（ｎ）、・・・、ｄ１６（ｎ）のそれぞれの先頭から、同じポイント位置のデータは、１ワードを構成するように、メモリ１３０ＭＥＭの同じワードアドレスに書き込むようにする。この結果、１６ミリ秒分のデータは、メモリ１３０ＭＥＭに、４０９６ワードのデータとして取り込まれる。
【０２９５】
ＦＦＴ演算処理は、この１６ビット１ワードのデータについて実行するようにする。ＤＳＰ２３が、１６ビット単位の処理が可能であるものであった場合には、ＦＦＴの際のメモリアクセス回数は、４０９６回となり、前処理を行わない場合の６５５３６回に比較して、１６分の１にすることができ、ＦＦＴ処理を高速化することができる。
【０２９６】
上述のことを、一般化すると、拡散符号の１周期分のデータ数がＮであるデータのＭ周期分を処理単位としてＦＦＴ処理する場合において、前処理部１３０では、同じ拡散符号の成分となる位置のデータを、メモリ１３０ＭＥＭの同じワードアドレスに書き込むようにする。
【０２９７】
すなわち、ＮＭ個のデータを［０］から順に番号をつけたとき、０，Ｎ，２Ｎ，・・・，（Ｍ−１）Ｎ番目のデータは、メモリＭＥＭのワードアドレス「０」に書き込み、１，１＋Ｎ，１＋２Ｎ，・・・，１＋（Ｍ−１）Ｎ番目のデータは、メモリＭＥＭのワードアドレス「１」に書き込み、・・・・、（Ｎ−１），（Ｎ−１）＋Ｎ，（Ｎ−１）＋２Ｎ，・・・，（Ｎ−１）＋（Ｍ−１）Ｎ番目のデータは、メモリＭＥＭのワードアドレス「Ｎ−１」に書き込むようにするものである。
【０２９８】
ＦＦＴ演算処理は、このＭビット１ワードのデータについて実行するようにする。ＤＳＰ２３が、ｗビット単位の処理が可能であるものであった場合には、ＦＦＴの際のメモリアクセス回数は、Ｎ×Ｍ／ｗ回となり、前処理を行わない場合のＮＭ回に比較して、ｗ分の１にすることができ、ＦＦＴ処理を高速化することができる。
【０２９９】
以上説明した第１〜第５の例の同期捕捉方法は、従来の手法であるスライディング相関器が原理的に時間を要するのに対し、ＦＦＴを用いたデジタルマッチドフィルタによる処理を高速なＤＳＰで行うようにしたことにより、処理時間の大幅な短縮が期待できる。特に、第２の例〜第５の例の場合には、拡散符号のＭ周期単位でＦＦＴ処理をするようにしたことにより、同期捕捉を高感度で行うことができる。
【０３００】
さらに、第３の例〜第５の例の場合には、拡散符号のＭ周期単位でＦＦＴ処理を、より高速に行うようにすることができる。
【０３０１】
したがって、同期捕捉の第２の例を用いるＧＰＳ受信機の実施形態の場合と同様にして、同期捕捉の第３の例〜第５の例を高感度モードのときに用いるようにし、高速モードのときには、通常のように、相関点を検出する単位データ長は、拡散符号の１周期長とするようにすることができる。
【０３０２】
また、高感度モードのみでなく、高速モードにおいても、この同期捕捉の第３の例〜第５の例を用いるようにしてもよい。
【０３０３】
さらに、高感度モードのみでなく、高速モードにおいても、この同期捕捉の第３の例〜第５の例を用いる場合において、相関点を検出する単位データ長を決める前記Ｍの値を、高感度モードでは、高速モードの場合よりも大きくするように構成してもよい。
【０３０４】
なお、以上の同期捕捉の例に用いたデジタルマッチドフィルタによる相関計算の方法は、ＧＰＳ衛星からの信号に限らず、拡散符号でデータをスペクトラム拡散した信号により搬送波が変調されている受信信号の拡散符号およびキャリアの同期捕捉を行う場合に適用可能である。ただし、第２の例、第３の例、第４の例および第５の例は、ＧＰＳ衛星信号のように、拡散符号の１周期の複数倍の周期がデータビットとなっていて、拡散符号の複数周期分の信号は、同じ信号となっている必要がある。
【０３０５】
以上のような同期捕捉方法によって、同期捕捉部２０で４個以上のＧＰＳ衛星からの信号の同期捕捉ができれば、ＧＰＳ受信機としては、それらの拡散符号の位相とＩＦキャリア周波数とからＧＰＳ受信機の位置と速度を計算することが可能である。つまり、同期保持部３０を設けなくても測位演算を行うことは可能である。
【０３０６】
しかし、ＧＰＳ受信機として十分な高精度の測位および速度計算を行うためには、高精度で拡散符号の位相とＩＦキャリア周波数を検出する必要があり、そのためには、サンプリング回路２１におけるサンプリング周波数を高くする、ＲＡＭ２２に取り込むＩＦデータの時間長を長くするといったことが必要になる。
【０３０７】
さらに、同期捕捉部２０にデジタルマッチドフィルタを用いた構成とした場合には、デジタルマッチドフィルタ自身は、同期保持機能を有しないことをも考慮しなければならない。
【０３０８】
また、ＧＰＳ受信機の外部から航法メッセージを取得しないとすると、同期捕捉部２０は、４個以上のＧＰＳ衛星の航法メッセージを２０ｍｓ毎に復調する必要があり、ＤＳＰ２３は常に同期の検出と航法メッセージの復調をかなり高速に行う必要がある。
【０３０９】
以上のように、同期捕捉部２０のみにより、ＧＰＳ受信機の位置計算および速度計算を十分な精度で行おうとすると、ハードウェアのサイズ増によるコストアップと消費電力増となり、ＧＰＳ受信機を実際に製造する際の大きな問題となってしまう。
【０３１０】
そこで、この実施形態では、粗い精度での同期捕捉を専用の同期捕捉部２０で行い、複数のＧＰＳ衛星信号の同期保持および航法メッセージの復調は同期保持部３０で行うものとしている。そして、同期捕捉部２０は、検出したＧＰＳ衛星番号と、その拡散符号の位相と、ＩＦキャリア周波数と、相関検出信号からなる信号強度の情報を、制御演算部４０を通じて同期保持部３０にデータとして渡し、後述するように、同期保持部３０は、そのデータを初期値として動作を開始するようにする。
【０３１１】
［同期保持部３０の構成］
複数のＧＰＳ衛星信号の同期保持を並列して行うために、同期保持部３０は、１つずつのＧＰＳ衛星信号を１チャンネルとして、複数チャンネル分を備える構成とされる。
【０３１２】
図４０は、この実施形態における同期保持部３０の構成例を示す。この同期保持部３０は、ｎチャンネル分のチャンネル同期保持部３０ＣＨ１、３０ＣＨ２、・・・、３０ＣＨｎと、コントロールレジスタ３３とからなる。チャンネル同期保持部３０ＣＨ１、３０ＣＨ２、・・・、３０ＣＨｎのそれぞれは、コスタスループ３１とＤＬＬ（Ｄｅｌａｙ Ｌｏｃｋｅｄ Ｌｏｏｐ）３２とを備える。
【０３１３】
コントロールレジスタ３３は、制御演算部４０のＣＰＵ４１に接続され、後述するように、コスタスループ３１やＤＬＬ３２のループフィルタのパラメータや、フィルタ特性を定めるためのデータを受け取り、ＣＰＵ４１により指示されるチャンネルの、ＣＰＵ４１により指示される部位に、そのデータを設定するようにする。また、コントロールレジスタ３３は、コスタスループ３１やＤＬＬ３２のループフィルタからの相関値情報や周波数情報を受け取り、ＣＰＵ４１からのアクセスに応じてそれらの情報をＣＰＵ４１に渡すようにする。
【０３１４】
〔コスタスループ３１と、ＤＬＬ３２の構成〕
図４１はコスタスループ３１の構成例を示すブロック図であり、また、図４２は、ＤＬＬ３２の構成例を示すブロック図である。
【０３１５】
コスタスループ３１は、ＩＦキャリア周波数の同期保持、送信データである航法メッセージの抽出を行う部分であり、ＤＬＬ３２は、ＧＰＳ衛星信号の拡散符号の位相同期保持を行う部分である。そして、コスタスループ３１とＤＬＬ３２とが協働し、ＧＰＳ衛星信号についてスペクトラム逆拡散を行って、スペクトラム拡散前の信号を得るとともに、このスペクトラム拡散前の信号を復調して航法メッセージを得て、制御演算部４０のＣＰＵ４１に供給する。以下、コスタスループ３１とＤＬＬ３２との動作について具体的に説明する。
【０３１６】
〔コスタスループ３１について〕
周波数変換部１０からのＩＦデータは、乗算器２０１に供給される。この乗算器２０１には、図４２に示すＤＬＬ３２の拡散符号発生器３２０からの拡散符号が供給される。
【０３１７】
ＤＬＬ３２の拡散符号発生部３２０からは、一致（プロンプト）拡散符号Ｐ、進み（アーリ）拡散符号Ｅ、遅れ（レート）拡散符号Ｌの、３つの位相の拡散符号が発生する。ＤＬＬ３２では、後述するように、進み拡散符号Ｅおよび遅れ拡散符号Ｌと、ＩＦデータとの相関を計算し、それぞれの相関値が等しくなるように、拡散符号発生器３２０からの拡散符号の発生位相を制御し、これにより、一致拡散符号Ｐの位相が、ＧＰＳ衛星信号の拡散符号の位相と一致するようにする。
【０３１８】
コスタスループ３１の逆拡散用の乗算器２０１には、拡散符号発生器３２０からの一致拡散符号Ｐが供給されて、逆拡散される。この乗算器２０１からの逆拡散されたＩＦデータは、乗算器２０２および２０３に供給される。
【０３１９】
コスタスループ３１は、図４１に示すように、乗算器２０２および２０３と、ローパスフィルタ２０４，２０５と、位相検出器２０６と、ループフィルタ２０７と、ＮＣＯ（Ｎｕｍｅｒｉｃａｌ Ｃｏｎｔｒｏｌｌｅｄ Ｏｓｃｉｌｌａｔｏｒ；数値制御型発振器）２０８と、相関検出器２０９と、２値化回路２１０と、ロック判定部２１１と、スイッチ回路２１２とからなっている。
【０３２０】
ローパスフィルタ２０４，２０５のカットオフ周波数情報と、ループフィルタ２０７のフィルタ特性を定めるパラメータと、ＮＣＯ２０８の発振中心周波数を定めるための周波数情報とは、後述するように、同期捕捉部２０での同期捕捉結果に基づいて、ＣＰＵ４１からコントロールレジスタ３３を通じて設定される。
【０３２１】
スイッチ回路２１２は、コスタスループ３１のループを開閉制御するためのもので、ＣＰＵ４１からの切り換え制御信号によりオンオフされる。なお、同期保持動作がスタートする前の初期的な状態では、スイッチ回路２１２はオフとされ、ループ開の状態とされ、後述するように、同期保持動作がスタートして、コスタスループの相関検出器２０９の相関出力が有意なレベルとなったときに、このスイッチ回路２１２がオンとされて、ループ閉とされるようにされる。
【０３２２】
乗算器２０１において逆拡散された信号は、乗算器２０２、２０３に供給される。これら乗算器２０２，２０３には、制御演算部４０のＣＰＵ４１からの周波数情報により、ほぼＩＦキャリア周波数にされたＮＣＯ２０８からの、直交位相のＩ（Ｓｉｎｅ）信号と、Ｑ（Ｃｏｓｉｎｅ）信号とが供給される。
【０３２３】
これら乗算器２０２および２０３の乗算結果は、ローパスフィルタ２０４および２０５を通じて位相検出器２０６に供給される。ローパスフィルタ２０４および２０５は、制御演算部４０のＣＰＵ４１からのカットオフ周波数情報の供給を受け、これに供給された信号の帯域外ノイズを除去するものである。
【０３２４】
位相検出器２０６は、ローパスフィルタ２０４および２０５からの信号に基づいて、ＩＦキャリアとＮＣＯ２０８からの周波数信号との位相誤差を検出し、この位相誤差をループフィルタ２０７を介してＮＣＯ２０８に供給する。これによりＮＣＯ２０８が制御されて、ＮＣＯ２０８からの出力周波数信号の位相が、ＩＦキャリア成分に同期するようにされる。
【０３２５】
なお、ループフィルタ２０７は、制御演算部４０のＣＰＵ４１から供給されるパラメータに応じて、位相検出器２０６からの位相誤差情報を積分して、ＮＣＯ２０８を制御するＮＣＯ制御信号を形成するものである。ＮＣＯ２０８は、ループフィルタ２０７からのＮＣＯ制御信号によって、前述したように、ＮＣＯ２０８からの出力周波数信号の位相が、ＩＦキャリア成分に同期するようにされる。
【０３２６】
また、コスタスループ３１のローパスフィルタ２０４および２０５の出力は、相関検出器２０９に供給される。相関検出器２０９は、これに供給されるローパスフィルタ２０４および２０５の出力信号をそれぞれ自乗して加算して出力する。この相関検出器２０９の出力は、ＩＦデータと拡散符号発生器３２０からの一致拡散符号Ｐとの相関値ＣＶ（Ｐ）示すものである。この相関値ＣＶ（Ｐ）は、コントロールレジスタ３３を通じて制御演算部４０のＣＰＵ４１に渡される。
【０３２７】
そして、ローパスフィルタ２０４の出力信号は２値化回路２１０に供給されており、この２値化回路２１０より航法メッセージデータが出力される。
【０３２８】
また、相関検出器２０９からの相関値ＣＶ（Ｐ）出力は、ロック判定部２１１に供給される。ロック判定部２１１は、相関値ＣＶ（Ｐ）出力と、予め定められているスレッショールド値とを比較し、相関値ＣＶ（Ｐ）出力がスレッショールド値よりも大きいときには、同期保持がロック状態であることを示し、相関値ＣＶ（Ｐ）出力がスレッショールド値よりも小さいときには、同期保持がアンロック状態であることを示すロック判定出力を出力する。
【０３２９】
この実施形態では、このロック判定出力は制御演算部４０のＣＰＵ４１に送られ、ＣＰＵ４１は、このロック判定出力から、同期保持部３０のロック状態、アンロック状態を認識するようにする。
【０３３０】
〔ＤＬＬ３２について〕
図４２に示すように、ＤＬＬ３２においては、周波数変換部１０からのＩＦデータは、乗算器３０１および３１１に供給される。そして、乗算器３０１には、拡散符号発生器３２０からの進み拡散符号Ｅが供給され、また、乗算器３１１には、拡散符号発生器３２０からの遅れ拡散符号Ｌが供給される。
【０３３１】
乗算器３０１は、ＩＦデータと進み拡散符号Ｅとを乗算することにより、スペクトラム逆拡散を行い、この逆拡散がなされた信号を乗算器３０２、３０３に供給する。そして、乗算器３０２には、前述のコスタスループ３１のＮＣＯ２０８からのＩ信号が供給され、乗算器３０３には、ＮＣＯ２０８からのＱ信号が供給される。
【０３３２】
乗算器３０２は、逆拡散されたＩＦデータとＮＣＯ２０８からのＩ信号とを乗算し、その結果をローパスフィルタ３０４を通じて相関検出器３０６に供給する。同様に、乗算器３０３は、逆拡散されたＩＦデータとＮＣＯ２０８からのＱ信号とを乗算し、その結果をローパスフィルタ３０５を通じて相関検出器３０６に供給する。
【０３３３】
なお、ローパスフィルタ３０４、３０５は、コスタスループ３１のローパスフィルタ２０４，２０５と同様に、制御演算部４０のＣＰＵ４１からのカットオフ周波数情報の供給を受け、これに供給された信号の帯域外ノイズを除去するものである。
【０３３４】
相関検出器３０６は、これに供給されるローパスフィルタ３０４，３０５からの出力信号をそれぞれ自乗して加算して出力する。この相関検出器３０６からの出力は、ＩＦデータと、拡散符号発生器３２０からの進み拡散符号Ｅとの相関値ＣＶ（Ｅ）示すものである。この相関値ＣＶ（Ｅ）は、位相検出器３２１に供給されるとともに、コントロールレジスタ３３に格納され、制御演算部４０のＣＰＵ４１が用いることができるようにされる。
【０３３５】
同様に、乗算器３１１は、ＩＦデータと遅れ拡散符号Ｌとを乗算することにより、スペクトラム逆拡散を行い、この逆拡散がなされた信号を乗算器３１２、３１３に供給する。乗算器３１２には、前述したように、ＮＣＯ２０８からのＩ信号が供給され、乗算器３１３には、ＮＣＯ２０８からのＱ信号が供給される。
【０３３６】
乗算器３１２は、逆拡散されたＩＦデータとＮＣＯ２０８からのＩ信号とを乗算し、その結果をローパスフィルタ３１４を通じて相関検出器３１６に供給する。同様に、乗算器３１３は、逆拡散されたＩＦデータとＮＣＯ２０８からのＱ信号とを乗算し、その結果をローパスフィルタ３１５を通じて相関検出器３１６に供給する。ローパスフィルタ３１４、３１５は、前述のローパスフィルタ３０４、３０５と同様に、制御演算部４０のＣＰＵ４１からのカットオフ周波数情報の供給を受け、これに供給された信号の帯域外ノイズを除去するものである。
【０３３７】
相関検出器３１６は、これに供給されるローパスフィルタ３１４，３１５からの出力信号をそれぞれ自乗して加算し、その演算結果を出力する。この相関検出器３１６からの出力は、ＩＦデータと、拡散符号発生器３２０からの遅れ拡散符号Ｌとの相関値ＣＶ（Ｌ）を示すものである。この相関値ＣＶ（Ｌ）は、位相検出器３２１に供給されるとともに、コントロールレジスタ３３に格納され、制御演算部４０のＣＰＵ４１が用いることができるようにされる。
【０３３８】
位相検出器３２１は、相関検出器３０６からの相関値ＣＶ（Ｅ）と、相関検出器３１６からの相関値ＣＶ（Ｌ）との差分として、一致拡散符号とＧＰＳ衛星信号の拡散符号との位相差を検出し、その位相差に応じた信号をループフィルタ３２２を介してＮＣＯ３２３の数値制御信号として供給する。
【０３３９】
拡散符号発生器３２０には、このＮＣＯ（Ｎｕｍｅｒｉｃａｌ Ｃｏｎｔｒｏｌｌｅｄ Ｏｓｃｉｌｌａｔｏｒ；数値制御型発振器）３２３の出力信号が供給されており、このＮＣＯ３２３の出力周波数が制御されることにより、拡散符号発生器３２０からの拡散符号の発生位相が制御される。
【０３４０】
なお、ＮＣＯ３２３は、後述するように、同期捕捉部２０の同期捕捉結果に応じた制御演算部４０のＣＰＵ４１からの初期発振周波数を制御する周波数情報の供給を受ける。
【０３４１】
以上のＤＬＬ３２におけるループ制御により、ＮＣＯ３２３が制御されて、拡散符号発生器３２０は、相関値ＣＶ（Ｅ）と相関値ＣＶ（Ｌ）とが同じレベルとなるように、拡散符号Ｐ、Ｅ，Ｌの発生位相を制御する。これにより、拡散符号発生器３２０から発生する一致拡散符号Ｐが、ＩＦデータをスペクトラム拡散している拡散符号と位相同期するようにされ、この結果、一致拡散符号ＰによりＩＦデータが正確に逆スペクトラム拡散され、コスタスループ３１において、２値化回路２１０から航法メッセージデータが復調されて出力される。
【０３４２】
そして、その航法メッセージデータの復調出力は、図示しないデータ復調回路に供給されて制御演算部４０で使用可能なデータに復調された後、制御演算部４０に供給される。制御演算部４０では、航法メッセージデータは、測位計算に用いられ、また、適宜、軌道情報（アルマナック情報やエフェメリス情報）が抽出されて、軌道情報用メモリ４６に格納される。
【０３４３】
なお、ＤＬＬ３２のループフィルタ３２２は、前述したコスタスループ３１のループフィルタ２０７と同様に、制御演算部４０のＣＰＵ４１から供給されるパラメータに基づいて、位相検出器３２１からの位相誤差情報を積分して、ＮＣＯ３２３を制御するＮＣＯ制御信号を形成するものである。
【０３４４】
ＤＬＬ３２においても、ループフィルタ３２２と、ＮＣＯ３２０との間に、ループの開閉制御用のスイッチ回路３２４が設けられ、ＣＰＵ４１からの切り換え制御信号によりオンオフされる。
【０３４５】
なお、同期保持動作がスタートする前の初期的な状態では、スイッチ回路３２４はオフとされ、ループ開の状態とされ、後述するように、同期保持動作がスタートして、コスタスループの相関検出器２０９の相関出力が有意なレベルとなったときに、このスイッチ回路３２４がオンとされて、ループ閉とされるようにされる。
【０３４６】
［同期捕捉から同期保持への移行について］
この実施形態では、前述したように、同期捕捉部２０は、検出したＧＰＳ衛星番号と、その拡散符号の位相と、ＩＦキャリア周波数と、信号強度の情報とを、データとして制御演算部４０のＣＰＵ４１に渡す。なお、信号強度の情報は、同期保持処理への移行のための情報としては、必須のものではない。
【０３４７】
取得したデータに基づいて制御演算部４０のＣＰＵ４１は、同期保持部３０に供給するデータを生成し、それを同期保持部３０に渡す。同期保持部３０はそのデータを初期値として同期保持動作を開始するようにする。
【０３４８】
制御演算部４０のＣＰＵ４１から同期保持部３０に渡されるデータは、ＤＬＬ３２の拡散符号発生器３２０からの拡散符号の発生位相を制御するＮＣＯ３２３の初期発振周波数（発振中心周波数）を決定するための数値情報と、コスタスループ３１のＮＣＯ２０８の初期発振周波数（発振中心周波数）を決定するための数値情報と、ループフィルタ２０７および３２２のフィルタ特性を決定するためのパラメータと、ローパスフィルタ２０４，２０５，３０４，３０５，３１４，３１５のカットオフ周波数を決定して、その周波数帯域の広狭を決定するための係数情報である。
【０３４９】
このとき、ＣＰＵ４１から同期保持部３０に供給される情報は、同期保持部３０で、拡散符号の同期保持およびＩＦキャリアの同期保持を開始するＧＰＳ衛星番号、位相や周波数、また、フィルタ特性を定めるための初期値データであるが、ＣＰＵ４１は、同期捕捉部２０で同期捕捉した結果として検出された拡散符号の位相およびＩＦキャリア周波数の近傍から同期保持を開始するように、前記初期値データを生成する。
【０３５０】
したがって、同期保持部３０では、同期捕捉部２０で検出された拡散符号の位相近傍および検出されたＩＦキャリア周波数の近傍から同期保持動作を開始して、迅速に同期保持のロック状態にすることができるようになる。
【０３５１】
ところで、ＧＰＳ受信機が位置および速度を計算するためには、同期捕捉開始から４個以上のＧＰＳ衛星に対して同期を確立し、保持しなければならない。同期捕捉部２０と同期保持部３０および両者を制御するＣＰＵ４１とによって、４個以上のＧＰＳ衛星からの信号の同期を保持するまでの過程の一例を次に説明する。
【０３５２】
〔同期捕捉・同期保持過程の一例〕
この例では、同期捕捉部２０は、ＧＰＳ衛星信号の一つを同期捕捉すると、すぐに、ＣＰＵ４１に、同期保持動作開始のための割り込み指示と、同期捕捉結果としてのＧＰＳ衛星番号、その拡散符号の位相、ＩＦキャリア周波数、相関検出レベルを表わす信号強度を転送し、転送が終わると別のＧＰＳ衛星についての同期捕捉に移る。
【０３５３】
ＣＰＵ４１は、同期捕捉部２０からの割り込み指示を受け取る毎に、同期保持部３０に対して独立のチャンネルの割り当てを行うと共に、初期値の設定を行って、同期保持動作を開始させるようにする。
【０３５４】
図４３は、この同期捕捉・同期保持過程の一例における同期捕捉部２０での同期捕捉処理の流れを説明するためのフローチャートである。
【０３５５】
まず、同期捕捉のための初期設定を行う（ステップＳ１７１）。この初期設定においては、同期捕捉のためにサーチするＧＰＳ衛星およびそのサーチの順番を、ＧＰＳ受信機が軌道情報用メモリ４６に記憶している有効な軌道情報に基づいて設定する。また、その軌道情報から、ドップラーシフトを考慮したキャリア周波数を計算して、サーチするＩＦキャリア周波数の中心と範囲を設定するようにする。
【０３５６】
また、電源投入前の過去の動作で得た大体の発振器誤差が、ＧＰＳ受信機で判明しているのであれば、ＧＰＳ受信機位置を電源投入時に記憶されている位置、すなわち、前回電源を切る直前の位置と仮定して、軌道情報から計算したドップラーシフトに合わせて、サーチするＩＦキャリア周波数の中心と範囲を決めるようにすると、さらに同期保持に至るまでに要する時間を短縮できる。
【０３５７】
初期設定が終了したら、サーチの順番に従って、同期捕捉する一つのＧＰＳ衛星を設定する（ステップＳ１７２）。これにより、同期捕捉対象の衛星番号が決まり、また、相関を検出しようとする拡散符号が決まる。
【０３５８】
次に、同期捕捉部２０では、ＲＡＭ２２に、サンプリング回路２１でサンプリングしたＩＦデータの取り込みを開始し、この開始タイミングで、タイマをスタートさせる（ステップＳ１７３）。ここで、このタイマとしては、制御演算部４０のタイマ４５を用いるようにする。このタイマ４５は、後述のように、同期保持処理スタートタイミングを設定する際にも用いられる。
【０３５９】
次に、ＤＳＰ２３において、前述したデジタルマッチドフィルタを用いた同期捕捉の例のいずれかを用いて、ステップＳ１７２で設定したＧＰＳ衛星信号の拡散符号について相関検出処理を行う（ステップＳ１７４）。
【０３６０】
そして、ＧＰＳ衛星信号の拡散符号について相関が検出されたか否か、つまり、ＧＰＳ衛星信号の同期捕捉ができたか否か判別し（ステップＳ１７５）、相関が検出できたときには、ＣＰＵ４１に対して割り込み指示を発生させると共に、同期捕捉の検出結果として、ＧＰＳ衛星番号、拡散符号の位相、ＩＦキャリア周波数、信号強度の情報をＣＰＵ４１に渡す（ステップＳ１７６）。
【０３６１】
そして、サーチすべきＧＰＳ衛星のすべてについての同期捕捉サーチが終了したか否か判別し（ステップＳ１７７）、未だサーチすべきＧＰＳ衛星が残っているときには、ステップＳ１７２に戻り、同期捕捉する次のＧＰＳ衛星を設定して、以上の同期捕捉処理を繰り返す。また、ステップＳ１７７で、サーチすべきすべてのＧＰＳ衛星についての同期捕捉が終了したと判別したときには、同期捕捉動作を終了して、同期捕捉部２０を待機状態（スタンバイ状態）にする。
【０３６２】
また、ステップＳ１７５で相関が検出できないと判別したときには、その状態が予め定めた所定時間以上経過したか否か判別し（ステップＳ１７８）、所定時間経過していなければ、ステップＳ１７５に戻って、相関検出を継続する。
【０３６３】
ステップＳ１７８で、所定時間経過したと判別したときには、ステップＳ１７７に進み、サーチすべきＧＰＳ衛星のすべてについての同期捕捉サーチが終了したか否か判別し、未だサーチすべきＧＰＳ衛星が残っているときには、ステップＳ１７２に戻り、同期捕捉する次のＧＰＳ衛星を設定し、以上の同期捕捉処理を繰り返す。
【０３６４】
また、ステップＳ１７７で、サーチすべきすべてのＧＰＳ衛星についての同期捕捉が終了したと判別したときには、同期捕捉動作を終了して、同期捕捉部２０を待機状態（スタンバイ状態）にする。
【０３６５】
この実施形態では、ＣＰＵ４１は、同期捕捉部２０への電源供給のオンオフ制御、または、この同期捕捉部２０に対する逓倍／分周回路３からの動作クロックの供給のオンオフ制御を行うことができるように構成されており、上記の同期捕捉部２０のスタンバイ状態では、ＣＰＵ４１により、同期捕捉部２０への電源の供給はオフ、または、動作クロックの供給が停止されて、不要な消費電力が抑えられている。
【０３６６】
同期捕捉部２０を、上述のように、デジタルマッチドフィルタで構成すると、ＤＳＰ２３でのＦＦＴ計算を速くするためには高いクロックで動作させることが望ましく、したがって、動作時の消費電力が大きくなるが、同期捕捉部２０において、初期設定したすべてのＧＰＳ衛星からの信号の同期捕捉検出が終わり、同期保持部３０で４個以上の同期保持ができていれば、同期捕捉部２０の役割は終了する。
【０３６７】
この実施形態では、上述のように、ＣＰＵ４１は、同期捕捉部２０の役割終了後は、スタンバイ状態にしているので、同期捕捉部２０における不要な消費電力が抑えられている。
【０３６８】
なお、上記の例では、初期設定したすべてのＧＰＳ衛星についての同期捕捉が完了した後、ＣＰＵ４１は、同期捕捉部２０をスタンバイ状態に移行させるようにしたが、同期保持部３０で同期保持できたＧＰＳ衛星が４個以上になったことを確認してから、ＣＰＵ４１が同期捕捉部２０をスタンバイ状態に移行させるようにしてもよい。
【０３６９】
なお、ＣＰＵ４１は、一旦、スタンバイ状態になった同期捕捉部２０を、再同期捕捉が必要な状態になったときに、動作状態に復帰させるようにすることができることは勿論である。
【０３７０】
次に、同期捕捉部２０からの割り込み指示を受けたＣＰＵ４１による同期保持部３０の制御処理について、図４４および図４５のフローチャートを参照しながら説明する。
【０３７１】
図４４は、ＣＰＵ４１が、同期捕捉部２０から、割り込み指示および同期捕捉結果としての拡散符号の位相、ＩＦキャリア周波数、ＧＰＳ衛星番号、信号強度の情報を受け取ったときに、同期保持部３０においてチャンネル割り当てし、同期保持スタートをさせるための処理である。また、図４５は、ＣＰＵ４１が、同期保持スタートさせた同期保持部３０の各１チャンネルにおいての同期保持処理制御のためのフローチャートである。まず、図４４の同期保持スタート処理について説明する。
【０３７２】
まず、ＧＰＳ受信機への電源投入時などにおいて、ＣＰＵ４１は、同期保持部３０のＮＣＯ、ローパスフィルタ、ループフィルタなどへ定数の初期設定を行っておく（ステップＳ１８１）。なお、このとき、コスタスループ３１およびＤＬＬ３２は、いずれも初期状態はループ開とされる。
【０３７３】
次に、ＣＰＵ４１は、同期捕捉部２０からの割り込み指示を監視し（ステップＳ１８２）、割り込み指示を検出したときには、同期捕捉部２０から、ＧＰＳ衛星番号、拡散符号の位相、ＩＦキャリア周波数、信号強度の情報を受け取ると共に、同期保持部３０に対して、受け取ったＧＰＳ衛星番号に対して独立のチャンネルを割り当てるようにする設定する（ステップＳ１８３）。
【０３７４】
そして、ＣＰＵ４１は、同期捕捉部２０から受け取った拡散符号の位相から、同期保持スタートタイミングを計算するとともに、同期保持部３０の、割り当てられたチャンネル内の各部に供給する初期値を、同期捕捉部２０から受け取ったＩＦキャリア周波数に基づいて生成する（ステップＳ１８４）。
【０３７５】
そして、ＣＰＵ４１は、生成した初期値を、コントロールレジスタ３３を通じて同期保持部３０の、ステップＳ１８３で割り当てられたチャンネル内の各部に送ると共に、同期保持部３０の、ステップＳ１８３で割り当てられたチャンネル内の拡散符号発生器３２０からの一致拡散符号Ｐの発生位相を、前記同期保持スタートタイミングとするように制御して、同期保持動作をスタートさせる（ステップＳ１８５）。なお、このとき、コスタスループ３１およびＤＬＬ３２のループは開のままとする。
【０３７６】
以上のようにして、同期捕捉されたＧＰＳ衛星信号について、同期保持のためのチャンネルが割り当てられ、同期保持スタートを行ったら、ステップＳ１８２に戻り、次の割り込みを待つ。
【０３７７】
次に、以上のようにしてスタートしたチャンネル毎の同期保持処理を、図４５のフローチャートについて説明する。
【０３７８】
ＣＰＵ４１は、まず、同期保持部３０からの相関値ＣＶ（Ｐ）が有意なレベルになったか否か判別し（ステップＳ１９１）、相関値ＣＶ（Ｐ）が有意なレベルになったら、コスタスループ３１およびＤＬＬ３２のループを閉じて、同期保持動作を行う（ステップＳ１９２）。
【０３７９】
次に、ＣＰＵ４１は、同期保持部３０のコスタスループ３１のロック判定部２１１からのロック判定出力を監視し（ステップＳ１９３）、同期保持部３０のロックを確認したときには、同期保持しているＧＰＳ衛星の数を１だけインクリメントし（ステップＳ１９４）、同期保持状態を継続する（ステップＳ１９５）。
【０３８０】
そして、ＣＰＵ４１は、この同期保持動作中において、コスタスループ３１のロック判定部２１１からのロック判定出力を監視し（ステップＳ１９６）、同期保持のロックを確認したときには、ステップＳ１９５に戻って、同期保持状態を継続する。そして、ステップＳ１９６で同期保持のロックが外れたと判別したときには、同期保持しているＧＰＳ衛星の数を１だけデクリメントし（ステップＳ１９７）、同期保持が外れたときの処理を行うようにする。この同期保持が外れたときの処理については、後述する。
【０３８１】
ＣＰＵ４１は、同期保持部３０で４個以上のＧＰＳ衛星信号の同期保持ができたと判別したときには、ＧＰＳ受信機の位置の計算および速度の計算を行うようにする。
【０３８２】
ステップＳ１９１において、相関値ＣＶ（Ｐ）が有意なレベルにならないと判別したときには、その状態が予め定めた所定時間以上経過しかたどうか判別し（ステップＳ１９９）、所定時間以上経過したと判別したときには、図４４のステップＳ１８３で割り当てた同期保持部３０のチャンネルを空きチャンネルに戻し、当該チャンネルの同期保持を停止する（ステップＳ２００）。
【０３８３】
また、ステップＳ１９３において、ロック判定出力によりロック状態が検出できなかったときには、その状態が予め定めた所定時間以上経過しかたどうか判別し（ステップＳ２０１）、所定時間以上経過したと判別したときには、ステップＳ１８３で割り当てた同期保持部３０のチャンネルを空きチャンネルに戻し、当該チャンネルの同期保持を停止する（ステップＳ２００）。
【０３８４】
ステップＳ１９９、ステップＳ２０１およびステップＳ２００の部分は、次のような理由により設けられたものである。すなわち、同期捕捉部２０が検出した相関が有意なレベルであっても、ノイズで偶々発生した偽の同期である場合もあり得る。突発的に生じたような持続性のない偽の同期に対しては、同期保持部３０で同期が確立することはない。そこで、同期保持部３０で一定のサーチ時間内に同期が確立できない場合には、同期保持動作を停止して、割り当てられたチャンネルを、空きチャンネルの状態に戻し、次の割り込みを待つようにしたものである。
【０３８５】
ところで、前述の図４４のステップＳ１８４では、ＣＰＵ４１は、同期捕捉部２０で検出した拡散符号の位相に、同期保持部３０の拡散符号発生器３２０からの拡散符号の位相を合わせるように、同期保持部３０の同期保持スタートタイミングを計算する必要があるが、その計算の際には、同期捕捉部２０で、一つのＧＰＳ衛星信号についての同期捕捉が完了するまでに所定時間が経過しており、ドップラーシフトと、ＧＰＳ受信機の基準発振器２の誤差の影響を受けることを考慮する必要がある。
【０３８６】
後者の問題は、ＩＦキャリア周波数が、周波数変換部１０からのＩＦデータのメモリに取り込むためのサンプリングクロックを生成している大元の基準発振器２の誤差を含むことによる。
【０３８７】
なお、この実施形態では、同期捕捉部２０と同期保持部３０とが同じ基準発振器２を発信源とするクロックで動作しているので、同期捕捉部２０と同期保持部３０とでは、全く同じ周波数誤差を持つことになる。したがって、ＩＦキャリアの同期に関しては、同期保持部３０が同期捕捉部２０で検出したＩＦキャリア周波数を初期値として動作を開始することに関しては、全く問題ない。
【０３８８】
以上のようにして、同期捕捉部２０は、ＣＰＵ４１が軌道情報から決めたＧＰＳ衛星を検出していく順番に従って有意な相関をサーチする。そして、同期捕捉部４１が確実な信号強度で最初の衛星を検出できたら、ＣＰＵ４１は、第１の例と同様に、同期保持部３０の１つのチャンネルを割当て、検出された衛星番号と拡散符号の位相、ＩＦキャリア周波数を設定して、同期保持動作を開始する。
【０３８９】
［その他の実施形態］
以上の実施形態の説明では、同期捕捉部２０からの検出結果は、ＣＰＵ４１を介して同期保持部３０に渡すようにしたが、前述したように、同期捕捉部２０から、同期保持部３０に直接的に渡すように構成することができるものである。
【０３９０】
また、上述の例では、同期捕捉部２０には、デジタルマッチドフィルタを用いた例としたが、この発明では、粗い精度の同期捕捉を同期捕捉部が行い、その結果を同期保持部に渡して、同期確立までを高速化することが目的であるので、同期捕捉部２０は、デジタルマッチドフィルタを用いた例に限られるものではない。
【０３９１】
また、デジタルマッチドフィルタには、上述の例のようなＦＦＴを用いた例のみではなく、前述したように、トランスバーサルフィルタを用いた構成とすることができるものである。
【０３９２】
なお、室内では高感度モード、戸外では高速モードとする場合において、ＧＰＳ受信機に室内か戸外かを検出する手段を設けて、その検出結果に応じて、測位モードを自動的に設定するようにすることもできる。室内か戸外かの検出手段としては、例えば、ＧＰＳ受信機の筐体に対して、回転軸を中心にして、常に、電波の放射方向が鉛直方向を向くように送信アンテナを取り付けると共に、その放射電波の反射波の受信手段とを取り付け、室内であれば、受信手段により放射電波の反射波が得られるが、戸外であれば、反射波が殆ど得られないことなどを利用することができる。
【０３９３】
なお、以上は，ＧＰＳ衛星信号の場合であるが、この出願は、ＧＰＳ衛星信号に限らず、例えば欧州の各国が中心となって構築が進められているＧＡＬＩＬＥＯなど、拡散符号を用いたものであれば、適用可能である。
【０３９４】
【発明の効果】
以上説明したように、この発明によれば、同期捕捉が高速に行える高速モードと、同期捕捉が高感度で行える高感度モードとを備え、使用環境に応じて切り換えが可能とされるので、測位用衛星信号についての同期捕捉が、使用環境条件に合わせて、迅速、かつ、正確に行えるようになる。
【０３９５】
そして、受信機の動作環境を、ユーザから提供してもらうようにすることにより、受信機は適切な測位モードに切り換わることができるので、結果的に測位するまでの時間を速くすることができるようになる。
【０３９６】
また、この発明によれば、受信機が測位状況をユーザに告知するようにしたことにより、測位までのユーザのいらいら感を緩和することができる。
【０３９７】
また、この発明によれば、同期捕捉と同期保持とを機能分離し、同期捕捉を高速化できるようにしたことで、従来のＧＰＳ受信機よりＧＰＳ信号との同期までに要する時間が短くなり、ＧＰＳ受信機は、電源オン後に速やかに位置、速度を表示できるようになったので、高速モードと高感度モードとの２つのモードを有効に切り換え利用することができる。すなわち、高速モードおよび高感度モードのいずれであっても、測位までの時間が比較的短くなり、使用者にいらいら感を与えることを緩和することができる。
【図面の簡単な説明】
【図１】この発明による測位用衛星信号の受信機の実施形態の構成例を示すブロック図である。
【図２】実施形態の受信機の外観の一例を示す図である。
【図３】図１の実施形態の受信機の一部である同期捕捉部の構成例を示すブロック図である。
【図４】図３の例の同期捕捉部の一部を構成するＤＳＰの内部構成例を示すブロック図である。
【図５】デジタルマッチドフィルタを用いた拡散符号の相関結果の例を示す図である。
【図６】受信信号のキャリアと拡散符号との同期を取る方法の一般的な例を説明するための図である。
【図７】この発明の実施の形態において、同期捕捉方法の第１の例を説明するための図である。
【図８】同期捕捉方法の第１の例の動作を考慮した要部の構成を示す図である。
【図９】同期捕捉方法の第１の例の動作を説明するためのフローチャートの一部を示す図である。
【図１０】同期捕捉方法の第１の例の動作を説明するためのフローチャートの一部を示す図である。
【図１１】同期捕捉方法の第１の例の動作を説明するためのフローチャートの一部を示す図である。
【図１２】同期捕捉方法の第１の例の動作を考慮した要部の構成を示す図である。
【図１３】この発明の実施形態における測位モードの設定動作を説明するためのフローチャートの一部を示す図である。
【図１４】この発明の実施形態における測位モードの設定動作を説明するためのフローチャートの一部を示す図である。
【図１５】この発明の実施形態における測位モードの設定動作の説明に供する図である。
【図１６】この発明の実施形態における測位モードの設定動作の説明に供する図である。
【図１７】この発明の実施形態における測位モードの設定動作の説明に供する図である。
【図１８】この発明の実施形態における測位モードの設定動作を説明するためのフローチャートの一部を示す図である。
【図１９】図１８の実施形態における測位モードの設定動作の説明に供する図である。
【図２０】この発明の実施形態の測位モードの選択操作処理を説明するためのフローチャートである。
【図２１】図２０の測位モードの選択操作処理動作の説明に供する図である。
【図２２】図２０の測位モードの選択操作処理動作の説明に供する図である。
【図２３】この発明による受信機の他の実施形態の外観例を示す図である。
【図２４】他の実施形態における測位モードの選択操作処理を説明するためのフローチャートである。
【図２５】同期捕捉方法の第２の例を説明するための図である。
【図２６】同期捕捉方法の第２の例を説明するための図である。
【図２７】同期捕捉方法の第２の例の動作を考慮した要部の構成を示す図である。
【図２８】同期捕捉方法の第３の例を説明するための図である。
【図２９】同期捕捉方法の第３の例を説明するための図である。
【図３０】同期捕捉方法の第３の例を説明するための図である。
【図３１】同期捕捉方法の第３の例を説明するための図である。
【図３２】同期捕捉方法の第３の例を説明するための図である。
【図３３】同期捕捉方法の第３の例を説明するための図である。
【図３４】同期捕捉方法の第３の例の動作を説明するためのフローチャートの一部を示す図である。
【図３５】同期捕捉方法の第３の例の動作を説明するためのフローチャートの一部を示す図である。
【図３６】同期捕捉方法の第３の例の動作を説明するためのフローチャートの一部を示す図である。
【図３７】同期捕捉方法の第４の例を説明するためのブロック図である。
【図３８】同期捕捉方法の第４の例の要部の動作を説明するためのフローチャートを示す図である。
【図３９】同期捕捉方法の第５の例の要部の動作を説明するための図である。
【図４０】図１の一部である同期保持部の構成例を示すブロック図である。
【図４１】図４０の同期保持部の一部を構成するコスタスループの構成例を示すブロック図である。
【図４２】図４０の同期保持部の一部を構成するＤＬＬの構成例を示すブロック図である。
【図４３】同期捕捉処理の一例の流れを説明するためのフローチャートである。
【図４４】同期保持スタート処理の流れを説明するためのフローチャートである。
【図４５】チャンネル毎同期保持処理の流れを説明するためのフローチャートである。
【図４６】ＧＰＳ衛星からの信号の構成を示す図である。
【図４７】従来のキャリアおよび拡散符号の同期処理を説明するための図である。
【図４８】この発明の実施の形態の説明に用いる図である。
【符号の説明】
１０…周波数変換部、２０…同期捕捉部、２１…サンプリング回路、２２…ＲＡＭ、２３…ＤＳＰ、２４…ＤＳＰ用メモリ、３０…同期捕捉部、３１…コスタスループ、３２…ＤＬＬ、３３…コントロールレジスタ、４０…制御部、４１…ＣＰＵ、４４…時計回路、４５…タイマ、４６…軌道情報用メモリ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a receiver for positioning satellite signals such as a GPS (Global Positioning System) receiver, and more particularly to synchronization of spread codes and carrier waves for received signals from artificial satellites (hereinafter simply referred to as satellites). Regarding capture.
[0002]
[Prior art]
In a GPS system that measures the position of a moving object using an artificial satellite, a GSP receiver receives signals from four or more GPS satellites, calculates the position of the receiver from the received signals, and informs the user. Is the basic function.
[0003]
The GPS receiver demodulates a received signal from a GPS satellite (hereinafter, this signal is referred to as a GPS satellite signal) to acquire GPS satellite orbit data, and from the GPS satellite orbit and time information and the GPS satellite signal delay time. The three-dimensional position of the receiver is derived by simultaneous equations. The reason why the signals from the four GPS satellites are necessary for the positioning calculation is that there is an error between the time in the GPS receiver and the time of the satellite, and the influence of the error is removed.
[0004]
In the case of a consumer-use GPS receiver, a spread spectrum radio wave called an L1 band, C / A (Clear and Acquisition) code from a GPS satellite (Navstar) is received and a positioning calculation is performed.
[0005]
The C / A code is a PN (Pseudorandom Noise) code having a transmission signal speed (chip rate) of 1.023 MHz and a code length of 1023, for example, a Gold code, and a signal obtained by spreading 50 bps data. This is a signal obtained by modulating a BPSK (Binary Phase Shift Keying) carrier wave having a frequency of 1575.42 MHz (hereinafter referred to as a carrier). In this case, since the code length is 1023, as shown in FIG. 46A, the C / A code has 1023 chips as one period (and therefore one period = 1 millisecond). It is to repeat.
[0006]
The PN sequence code (spreading code) of this C / A code is different for each GPS satellite, but which GPS satellite uses which PN sequence code can be detected in advance by the GPS receiver. Has been. In addition, the GPS receiver can know from which GPS satellite the signal from which GPS satellite can be received by the navigation message described later. Therefore, in the GPS receiver, for example, in the case of three-dimensional positioning, radio waves from four or more GPS satellites that can be acquired at that point and at that point are received, the spectrum is despread, and the positioning calculation is performed. Try to find the position.
[0007]
Then, as shown in FIG. 46B, one bit of the satellite signal data (navigation message data) is transmitted for 20 periods of the PN sequence code, that is, in units of 20 milliseconds. That is, the data transmission rate is 50 bps. The 1023 chips for one period of the PN sequence code are inverted when the bit is “1” and when it is “0”.
[0008]
As shown in FIG. 46C, in GPS, one word is formed with 30 bits (600 milliseconds). Then, as shown in FIG. 46D, 10 words form one subframe (6 seconds). As shown in FIG. 46E, a preamble that always has a prescribed bit pattern is inserted into the first word of one subframe even when the data is updated, and data is transmitted after this preamble. It will be.
[0009]
Furthermore, one frame (30 seconds) is formed by 5 subframes. The navigation message is transmitted in data units of one frame. The first three subframes of this one-frame data are orbit information unique to the satellite called ephemeris information. The ephemeris information is repeatedly sent in units of one main frame (30 seconds), and includes parameters for obtaining the orbit of the satellite that transmits the information, and the transmission time of the signal from the satellite.
[0010]
In other words, the second word of the three subframes of the ephemeris information includes time data called “Week Number” and “TOW (Time Of Week)”. The Week Number is information that counts up every week, starting from January 6, 1980 (Sunday) as the 0th week. Further, TOW is information on the time to count up every 6 seconds (counting up at a subframe period) with 0 am on Sunday as 0.
[0011]
All of the GPS satellites have an atomic clock and use common time information, and the transmission time of the signal from the GPS satellite is synchronized with the atomic clock. The absolute time is obtained by receiving the above two time data. The value of 6 seconds or less is synchronized with the time of the satellite with the accuracy of the reference oscillator provided in the GPS receiver in the process of synchronously locking to the satellite radio wave.
[0012]
Further, the PN sequence code of each GPS satellite is generated in synchronization with the atomic clock. Further, from this ephemeris information, the position of the satellite and the speed of the satellite used for the positioning calculation in the GPS receiver are obtained.
[0013]
The ephemeris information is a highly accurate calendar that is updated relatively frequently by control from the control station on the ground. In the GPS receiver, by holding this ephemeris information in a memory, the ephemeris information can be used for positioning calculation. However, due to its accuracy, the usable lifetime is normally about 2 hours, and the GPS receiver monitors the elapse of time from the time when the ephemeris information is stored in the memory. The ephemeris information in the memory is updated and rewritten.
[0014]
In order to acquire new ephemeris information from the GPS receiver and update the contents of the memory to the acquired ephemeris information, at least 18 seconds (for 3 subframes) are required. When it is removed, 30 seconds are required continuously.
[0015]
The navigation message of the remaining two subframes of the data of one frame is information commonly transmitted from all the satellites called almanac information. This almanac information is required for 25 frames in order to acquire all information, and includes approximate position information of each GPS satellite, information indicating which GPS satellite can be used, and the like.
[0016]
This almanac information is also updated every few days under the control of the control station on the ground. This almanac information can also be stored and used in the GPS receiver's memory, but its lifetime is set to several months. Normally, every few months, the almanac information in the memory is GPS Updated with new information obtained from the satellite. If this almanac information is stored in the memory of the GPS receiver, it is possible to calculate which channel should be assigned to which channel after the power is turned on.
[0017]
In order to receive the GPS satellite signal by the GPS receiver and obtain the above-mentioned data, the same PN sequence code as the C / A code used in the GPS satellite to be received prepared in the GPS receiver. (Hereinafter, the PN sequence code is referred to as a PN code), the GPS satellite signal is captured by phase synchronization of the C / A code for the GPS satellite signal, and spectrum despreading is performed. When phase synchronization with the C / A code is taken and despreading is performed, bits are detected, and a navigation message including time information and the like can be acquired from a GPS satellite signal.
[0018]
The acquisition of the GPS satellite signal is performed by the phase synchronization search of the C / A code. In this phase synchronization search, the correlation between the PN code of the GPS receiver and the PN code of the received signal from the GPS satellite is detected, For example, when the correlation value of the correlation detection result is larger than a predetermined value, it is determined that the two are synchronized. When it is determined that the synchronization is not achieved, the phase of the PN code of the GPS receiver is controlled using some synchronization method so as to synchronize with the PN code of the received signal.
[0019]
By the way, as described above, a GPS satellite signal is a signal obtained by BPSK modulation of a carrier using a signal obtained by spreading data with a spreading code. Therefore, in order for a GPS receiver to receive the GPS satellite signal, However, it is necessary to synchronize the carrier and data, but the synchronization of the spreading code and the carrier cannot be performed independently.
[0020]
In the GPS receiver, the received signal is usually converted to an intermediate frequency within several MHz, and the above-mentioned synchronization detection processing is performed on the intermediate frequency signal. The carrier mainly includes a frequency error due to Doppler shift according to the moving speed of the GPS satellite, and a frequency error of the local oscillation signal generated from the local oscillator inside the GPS receiver when the received signal is converted into an intermediate frequency signal. Is included.
[0021]
Therefore, the carrier frequency in the intermediate frequency signal is unknown due to these frequency error factors, and the frequency search is required. In addition, since the synchronization point (synchronization phase) within one cycle of the spread code depends on the positional relationship between the GPS receiver and the GPS satellite, it is also unknown, so that some kind of synchronization method is necessary as described above. Become.
[0022]
In the conventional GPS receiver, the synchronization detection for the carrier and the spread code is performed by the sliding correlation accompanied by the frequency search, and at the same time, the synchronization acquisition and the synchronization holding operation are performed by the DLL (Delay Locked Loop) and the Costas loop. ing. This will be described below.
[0023]
As a clock for driving the PN code generator of the GPS receiver, a clock obtained by dividing a reference frequency oscillator prepared in the GPS receiver is generally used. As this reference frequency oscillator, a high-precision crystal oscillator is used, and a local oscillation signal used to convert a received signal from a GPS satellite into an intermediate frequency signal is generated from the output of the reference frequency oscillator.
[0024]
FIG. 47 is a diagram for explaining the frequency search described above. That is, when the frequency of the clock signal driving the PN code generator of the GPS receiver is a certain frequency f1, the phase synchronization search for the PN code, that is, the phase of the PN code is sequentially shifted by one chip, By detecting the correlation between the GPS reception signal and the PN code at each chip phase and detecting the peak value of the correlation, the phase (spread code phase) that can synchronize the PN code is detected.
[0025]
When the frequency of the clock signal is f1, if there is no phase that is synchronized in all phase searches for 1023 chips, the carrier frequency is not synchronized. For example, the frequency division ratio for the reference frequency oscillator is changed. The frequency of the drive clock signal is changed to the frequency f2, and the phase search for 1023 chips is performed in the same manner. This is repeated by changing the frequency of the drive clock signal stepwise as shown in FIG. The above operation is a frequency search.
[0026]
When the frequency of the drive clock signal that can be synchronized is detected by this frequency search, the final PN code synchronization is acquired at the clock frequency. The carrier frequency can be detected from the clock frequency at this time. Thereby, even if there is a deviation in the oscillation frequency of the crystal frequency oscillator, the satellite signal can be captured.
[0027]
[Problems to be solved by the invention]
By the way, in the conventional GPS receiver, there has been no idea of switching the synchronization acquisition mode in consideration of the use environment.
[0028]
For this reason, for example, a conventional GPS receiver using a digital matched filter can quickly capture and synchronize in an environment where the radio wave from the satellite is strong, but it also receives noise radio waves and so-called multipaths. Therefore, it may be difficult to obtain an accurate position.
[0029]
In addition, in a place where radio waves from satellites such as indoors are weak, the sensitivity of a conventional GPS receiver using a digital matched filter is low, so it takes time to capture the synchronization, which gives an annoyance to the user. there were.
[0030]
In view of the above points, the present invention provides a positioning satellite receiver and a positioning satellite signal receiving method that can be expected to be able to perform synchronization acquisition of GPS satellite signals quickly and accurately in accordance with environmental conditions. The purpose is to provide.
[0031]
[Means for Solving the Problems]
In order to solve the above problem, a positioning satellite signal receiver according to the invention of claim 1
While substantially changing the phase of the spreading code on the receiving side, detecting the correlation between the spreading code of the received signal from the satellite and the spreading code on the receiving side and performing synchronization acquisition of the spreading code of the received signal, A high-speed mode in which the substantial phase change width of the spreading code on the receiving side is large, and a high-sensitivity mode in which the substantial phase change width is small, and
A mode switching operation means for accepting a switching selection operation between the high speed mode and the high sensitivity mode;
Synchronization acquisition means for executing the acquisition with the mode switched by the mode switching operation means as the current mode;
With
The synchronization acquisition means includes Using fast Fourier transform processing A digital matched filter is used, and at least in the high sensitivity mode, the received signal data from the positioning satellite for M periods (M is a power of 2 or more) of the spreading code is used as a unit.
It is characterized by that.
[0032]
According to the positioning satellite signal receiver having the above-described configuration, the positioning satellite signal receiver includes a high-speed mode in which synchronization acquisition can be performed at high speed and a high-sensitivity mode in which synchronization acquisition can be performed with high sensitivity. Since the switching is enabled, the synchronous acquisition of the positioning satellite signal can be performed quickly and accurately in accordance with the use environment conditions.
[0033]
According to a second aspect of the present invention, a positioning satellite signal receiver comprises:
While detecting the correlation between the spreading code of the received signal from the positioning satellite and the spreading code of the receiving side while substantially changing the phase of the spreading code on the receiving side, A high-speed mode in which the substantial phase change width of the spreading code on the receiving side is large, and a high-sensitivity mode in which the substantial phase change width is small,
Either one of the high-speed mode or the high-sensitivity mode as a current mode, and synchronization acquisition means for performing the synchronization acquisition;
Discriminating means for discriminating whether the synchronization acquisition is difficult in the current mode;
In the determination means, when it is determined that the synchronization acquisition is difficult in the current mode, the mode change means for changing the current mode to the other one of the high speed mode and the high sensitivity mode;
With
The synchronization acquisition means includes Using fast Fourier transform processing A digital matched filter is used, and at least in the high sensitivity mode, the received signal data from the positioning satellite for M periods (M is a power of 2 or more) of the spreading code is used as a unit.
It is characterized by that.
[0034]
According to the second aspect of the present invention, a high-speed mode in which synchronization acquisition can be performed at high speed and a high-sensitivity mode in which synchronization acquisition can be performed with high sensitivity are provided, and mode switching is automatically performed according to the use environment. Acquisition of satellite signals can be performed quickly and accurately in accordance with the use environment conditions.
[0043]
DETAILED DESCRIPTION OF THE INVENTION
In the conventional method of performing synchronization acquisition on the carrier and spreading code simultaneously with the above-described sliding correlation with frequency search, DLL (Delay Locked Loop) and Costas loop, the synchronization holding operation is performed in the conventional method. As described above, the sliding correlation method accompanied by the problem is not suitable for high-speed synchronization in principle, and there is a problem that it takes time to synchronize spreading codes and carriers. If it takes time to synchronize the spread code and the carrier in this way, the response of the GPS receiver is slowed, resulting in inconvenience in use.
[0044]
Conventionally, in an actual GPS receiver, in order to improve this problem, it is necessary to search for synchronization points in parallel by increasing the number of channels. Is complicated, and the cost is high, and since the synchronization point is searched in parallel with multiple channels, the power consumption is large. The problem of power consumption is a big problem in the case of a portable GPS receiver.
[0045]
Further, in the case of the above-described conventional method, the synchronization acquisition and the synchronization maintenance of the spread code and the carrier are integrally performed by the sliding correlation accompanied by the frequency search, the DLL (Delay Locked Loop), and the Costas loop. Therefore, for example, when the signal from the GPS satellite is interrupted, it is necessary to perform synchronization acquisition and synchronization maintenance again, and the time until resynchronization acquisition and resynchronization maintenance becomes longer. is there.
[0046]
Further, in the conventional case described above, the synchronization acquisition and the synchronization maintenance of the spread code and the carrier are integrally performed by a sliding correlation accompanied by a frequency search, a DLL (Delay Locked Loop), and a Costas loop. Therefore, if you try to increase the sensitivity of the GPS receiver, the processing time for acquisition and maintenance of synchronization will be considerably longer in principle, so it is not easy to increase the sensitivity of the GPS receiver. There was also.
[0047]
The embodiment described below improves the above problems. Hereinafter, embodiments of a positioning satellite signal receiver according to the present invention will be described with reference to the drawings, taking a GPS receiver as an example.
[0048]
[Overall Configuration of GPS Receiver of Embodiment]
FIG. 1 is a block diagram illustrating a configuration example of a GPS receiver according to this embodiment, and FIG. 2 is a diagram illustrating an appearance of the GPS receiver according to this embodiment. As shown in FIG. 1, the GPS receiver of this embodiment includes a frequency conversion unit 10, a synchronization acquisition unit 20, a synchronization holding unit 30, a control calculation unit 40, a GPS antenna 1, and a crystal oscillator with temperature compensation. The circuit includes a reference oscillation circuit 2, a timing signal generation circuit 3, a crystal oscillation circuit 4, a display 5, an operation button group 6, a jog dial 7, and a map memory 8.
[0049]
The control operation unit 40 has a CPU (Central Processing Unit) 41, a program ROM (Read Only Memory) 42, a work area RAM (Random Access Memory) 43, and real time (RTC (Real Time Clock)). The clock circuit 44, the timer 45, the orbit information memory 46, the display interface 47, the operation button interface 48, the jog dial decoder 49, and the map memory 8 are connected to each other.
[0050]
The display interface 47 is connected to a display 5 made of, for example, an LCD (Liquid Crystal Display). As will be described later, a map for displaying the current location is displayed on the screen of the display 5 under the control of the CPU 41, and an operation menu is displayed.
[0051]
The operation button group 6 is connected to the operation button interface 48. In this example, the operation button group 6 includes a map enlargement button 61, a map reduction button 62, and a cursor button 63 for moving the cursor position back and forth and left and right, as shown in FIG.
[0052]
A jog dial 7 is connected to the jog decoder 49. The jog dial 7 is an operation unit having a plurality of roles such as a role as an up / down key and a role as a determination key. In the case of this example, the jog dial 7 is constituted by a circular dial knob that can rotate as shown in the external view of the GPS receiver in FIG.
[0053]
The jog dial 7 serves as an up / down key by the rotation of the dial knob. Further, the jog dial 7 has a function as a non-locking push button when pressed in the radial direction. The function of this push button serves as a decision key.
[0054]
The operation input of the jog dial 7 is detected by the jog dial decoder 49, and information indicating whether the operation input is rotation of the dial knob or depression of the dial knob is sent from the jog dial decoder 49 to the CPU 41.
[0055]
The CPU 41 receives the operation button input information and the operation input information of the jog dial 7 from the jog dial decoder 49 in the program written in the ROM 44, analyzes them, and performs processing corresponding thereto. Further, the CPU 41 stores necessary information in the RAM 43 and the trajectory information memory 46, and sends information for displaying a predetermined display image on the display screen of the display 5 through the display interface 47. Like that.
[0056]
In addition, the CPU 41 supplies a control signal such as a mode switching signal to the synchronization acquisition unit 20 and receives information as described later from the synchronization acquisition unit 20 to control the synchronization holding unit 30 or a GPS satellite. And processing to notify the user of the status of radio waves from. Further, the CPU 41 executes a positioning calculation process based on radio waves from four or more satellites held in synchronization. That is, the CPU 41 of the control calculation unit 40 controls the entire GPS receiver and performs positioning calculation.
[0057]
The timer 45 is used for generation of various timing signals necessary for the operation of each unit and for time reference. The orbit information memory 46 is a non-volatile memory in which orbit information composed of almanac information and ephemeris information extracted from GPS satellite signals is stored. The ephemeris information is updated with respect to the orbit information memory 46, for example, every two hours, and the almanac information is updated, for example, every few days or months.
[0058]
In this example, the map memory 8 is composed of a semiconductor memory storing map data, but a detachable card type memory can also be used.
[0059]
In the GPS receiver of FIG. 1, the reference clock signal from the reference oscillation circuit 2 is supplied to the multiplication / division circuit 3 and, as will be described later, to the local oscillation circuit 15 for frequency conversion of the frequency conversion unit 10. Supplied. The multiplier / divider circuit 3 multiplies and divides the reference clock signal to generate a clock signal to be supplied to the synchronization acquisition unit 20, the synchronization holding unit 30, the control operation unit 40, and the like. The multiplication / division circuit 3 is controlled by the CPU 41 of the control calculation unit 40 for the multiplication ratio and the division ratio.
[0060]
The clock signal from the crystal oscillation circuit 4 is for the clock circuit 44 of the control arithmetic unit 40. A clock signal other than the clock circuit 44 of the control arithmetic unit 40 is used as a clock signal from the multiplier / divider circuit 3.
[0061]
[Configuration of Frequency Conversion Unit 10]
As described above, the GPS satellite signal is a signal transmitted from each GPS satellite, and transmission data of 50 bps is determined for each GPS satellite with a transmission signal speed of 1.023 MHz and a code length of 1023. A carrier (carrier wave) having a frequency of 1575.42 MHz is BPSK-modulated with a signal (C / A code) spectrum-spread by a PN code (spreading code) of the specified pattern.
[0062]
A GPS satellite signal of 1575.42 MHz received by the antenna 1 is supplied to the frequency converter 10. In the frequency converter 10, the GPS satellite signal received by the antenna 1 is amplified by the low noise amplifier circuit 11, and then supplied to the bandpass filter 12 to remove unnecessary band components. The signal from the band pass filter 12 is supplied to the intermediate frequency conversion circuit 14 through the high frequency amplifier circuit 13.
[0063]
The output of the reference oscillation circuit 2 is supplied to a local oscillation circuit 15 of a PLL (Phase Locked Loop) synthesizer system, and the local oscillation whose frequency ratio is fixed to the output frequency of the reference oscillator 2 from the local oscillation circuit 15 Output is obtained. Then, this local oscillation output is supplied to the intermediate frequency conversion circuit 14, and the GPS satellite signal is low-frequency converted into an intermediate frequency signal of an intermediate frequency that is easy to process, for example, 1.023 MHz.
[0064]
The intermediate frequency signal from the intermediate frequency conversion circuit 14 is amplified by the amplification circuit 16, band-limited by the low-pass filter 17, and then a 1-bit digital signal (hereinafter referred to as IF data) by the A / D converter 18. ). This IF data is supplied to the synchronization capturing unit 20 and the synchronization holding unit 30.
[0065]
That is, in this embodiment, the IF data is not supplied to a conventional synchronization acquisition / synchronization holding integrated circuit such as a sliding correlation and Costas loop + DLL, but a functionally separated synchronization acquisition unit 20; It is supplied to the synchronization holding unit 30.
[0066]
In this embodiment, the synchronization acquisition unit 20 performs synchronization acquisition for a GPS satellite signal, that is, phase detection of a spread code of the GPS satellite signal and detection of a frequency of an intermediate frequency signal (hereinafter referred to as IF carrier frequency). The synchronization holding unit 30 holds the spread code of the GPS satellite signal captured by the synchronization capturing unit 20 and the IF carrier in synchronization.
[0067]
[Configuration of Synchronization Capturing Unit 20 and Synchronization Holding Unit 30]
In this embodiment, as will be described later, the synchronization acquisition unit 20 captures a predetermined amount of IF data from the frequency conversion unit 10 into a memory, and for the IF data captured in the memory, a spread code of a GPS satellite signal, The correlation calculation with the spreading code corresponding to the spreading code of each GPS satellite possessed by the GPS receiver is performed, and phase synchronization acquisition of the spreading code and IF carrier frequency detection are performed.
[0068]
As for the phase synchronization acquisition of a spread code, there is a method using a matched filter as a method for performing synchronization acquisition of a spread spectrum signal at high speed without using the above-described sliding correlation technique.
[0069]
The matched filter can be digitally realized by a transversal filter. In recent years, spreading code synchronization has been achieved by a digital matched filter using fast Fourier transform (hereinafter referred to as FFT (Fast Fourier Transform)) processing due to improvements in hardware capabilities typified by DSP (Digital Signal Processor). Has been realized at high speed. However, the digital matched filter itself does not have a function of maintaining the synchronization of the spread code.
[0070]
The latter method using the FFT processing is based on a correlation calculation speed-up method that has been known for a long time, and will be described later when there is a correlation between the spread code on the receiver side and the spread code of the received signal. A correlation peak as shown in FIG. 5 is detected, and the peak position is the leading phase of the spread code. Therefore, by detecting this correlation peak, the synchronization of the spread code can be captured, that is, the phase of the spread code in the received signal can be detected.
[0071]
The carrier (intermediate frequency) of the received signal can be detected together with the phase of the spread code by an operation in the FFT frequency domain by a method using FFT. The phase of the spread code is converted into a pseudorange, and if four or more satellites are detected, the position of the GPS receiver can be calculated. Further, when the carrier frequency is detected, the Doppler shift amount is known, and thereby the speed of the GPS receiver can be calculated.
[0072]
As described above, in this embodiment, correlation calculation is performed on a spread code by a digital matched filter using fast Fourier transform (hereinafter referred to as FFT (Fast Fourier Transform)) processing, and synchronization acquisition processing is performed based on the correlation calculation. To do at high speed.
[0073]
The GPS satellite signal received by the antenna 1 includes signals from a plurality of GPS satellites. The synchronization acquisition unit 20 prepares spread code information for all GPS satellites. By using the information of the spread codes being used, the correlation between the spread codes of a plurality of GPS satellite signals that can be used by the GPS receiver at that time is calculated, and the synchronization acquisition of the plurality of GPS satellite signals is performed. It is possible to
[0074]
The synchronization acquisition unit 20 detects which GPS satellite has acquired the synchronization by detecting which GPS satellite has been used to acquire the synchronization code. For example, a GPS satellite number is used as the identifier of the GPS satellite that has been acquired by synchronization.
[0075]
The synchronization acquisition unit 20 then synchronizes and acquires the satellite number information of the GPS satellite, the information of the phase of the spread code detected by the synchronization acquisition, the information of the IF carrier frequency, and, if necessary, the degree of correlation. The signal strength information consisting of the correlation detection signal indicating the above is passed to the synchronization holding unit 30.
[0076]
The method of passing the satellite number, spreading code phase, IF carrier frequency, and signal strength information detected by the synchronization acquisition unit 20 to the synchronization holding unit 30 is determined after determining the data format, interrupt method, etc. There are a method of passing directly from the capturing unit 20 to the synchronization holding unit 30 and a method of passing through the control calculation unit 40.
[0077]
In the former case, information to be passed to the synchronization holding unit 30 is generated by the DSP 23 of the synchronization capturing unit 20. Or the control part comprised by DSP is provided in the synchronous holding | maintenance part 30, for example, It is set as the structure which produces | generates required information in the synchronous holding | maintenance part 30 based on the information from the synchronous acquisition part 20 with the control part.
[0078]
In the latter case, the CPU 41 of the control calculation unit 40 can control and pass information through the CPU 41, and the CPU 41 can control the synchronization capturing unit 20 and the synchronization holding unit 30. It becomes easier to set various synchronization procedures according to the phase correction of the code and the situation of the synchronization acquisition unit 20 and the synchronization holding unit 30.
[0079]
Therefore, in the embodiment described below, as a method of passing the satellite number, the phase of the spreading code, the IF carrier frequency, and the signal strength information from the synchronization acquisition unit 20 to the synchronization holding unit 30, the control calculation unit 40 is used. Is adopted.
[0080]
[Configuration of Synchronization Acquisition Unit 20]
FIG. 3 shows an example of the configuration of the synchronization acquisition unit 20. In this example, a sampling circuit 21, a RAM (Random Access Memory) 22 for data buffer, a DSP (Digital Signal Processor) 23, and a program are shown. A memory unit 24 for the DSP 23 including a ROM (Read Only Memory) and a RAM for a work area is provided. The DSP 22 and the DSP memory unit 24 are connected to the CPU 41 of the control calculation unit 40.
[0081]
In the sampling circuit 21, 1.023 MHz IF data from the frequency conversion unit 10 is sampled at a predetermined frequency more than twice, and each sampling value is written in the RAM 22. The RAM 22 has a capacity for storing IF data for a predetermined time length. In the DSP 23, the synchronization acquisition process is performed in units of IF data having a time length corresponding to the capacity of the RAM 22.
[0082]
In other words, in this example, the DSP 23 performs high-speed acquisition of the spread code with a digital matched filter using fast Fourier transform (hereinafter referred to as FFT (Fast Fourier Transform)) processing on the IF data taken into the RAM 22. Then, as a result of the synchronization acquisition, the DSP 23 detects the GPS satellite number acquired in synchronization, the phase of the spread code of the GPS satellite signal acquired in synchronization and the IF carrier frequency thereof.
[0083]
The sampling frequency in the sampling circuit 21 determines the detection accuracy of the phase of the spread code. This sampling frequency needs to be at least twice the maximum frequency included in the IF signal from the sampling theorem, and is preferably an integer multiple of the IF carrier frequency.
[0084]
Further, the detection accuracy of the IF carrier frequency is determined by the time length of the processing unit in the DSP 23 determined by the capacity of the RAM 22. The time length of the processing unit in the DSP 23 is desirably an integral multiple of one period of the spread code, and in particular, a power of 2 as described later.
[0085]
Here, if the sampling frequency in the sampling circuit 21 is α times the chip rate of the spreading code and the time length of the IF data fetched into the RAM 22 is β times (β milliseconds) of one cycle of the spreading code, the DSP 23 performs FFT. By operating in the frequency domain, the phase of the spread code can be detected with an accuracy of 1 / α chip, and the IF carrier frequency can be detected with an accuracy of 1 / β kHz (± 1/2 β kHz).
[0086]
In this embodiment, the DSP 23 can select a high-speed mode or a high-sensitivity mode as a synchronization acquisition search mode (hereinafter referred to as a positioning mode). As described later, the high-speed mode is intended to perform coarse acquisition search and to detect the phase of the spread code and IF carrier frequency at high speed, and is effective when the radio wave from the satellite is strong. It is.
[0087]
The high-sensitivity mode, as described later, is intended to perform precise acquisition search and ensure detection of the spread code phase and IF carrier frequency. It is effective when.
[0088]
In this example, the switching between the two modes can be selected between automatic (auto mode) and manual (manual mode). Then, the CPU 41 of the control calculation unit 40 performs synchronization acquisition so as to perform a synchronization acquisition search operation in any one of the positioning modes automatically set for switching or the positioning mode set by a manual switching operation by the user. The DSP 23 of the unit 20 is controlled.
[0089]
In the auto mode, in this example, the initial mode is always the high-speed mode, and when the satellite radio wave reception (synchronization acquisition) is not possible in the high-speed mode, the automatic mode is automatically switched to the high-sensitivity mode. Then, when the received electric field intensity of the radio wave from the GPS satellite is increased in the high sensitivity mode and the state is restored to the state where the synchronization acquisition in the high speed mode is possible again, the high speed mode is restored.
[0090]
Of course, it is possible to designate either the high sensitivity mode or the high speed mode as the initial mode of the auto mode according to user settings.
[0091]
Next, some examples of synchronization acquisition by a digital matched filter using FFT in the DSP 23 will be described in detail.
[0092]
[First example of synchronization acquisition by digital matched filter]
In this example, the sampling frequency in the sampling circuit 21 is 4.096 MHz, which is almost four times the chip rate of the spread code. The RAM 22 stores data of 4096 sample points, which is one cycle (1 millisecond) of the spread code. The DSP 23 obtains the synchronization by calculating the correlation between the spread code of the GPS satellite signal and the spread code of the GPS receiver by the correlation calculation using FFT with respect to the data of 1 millisecond unit captured in the RAM 22. . Since one period of the spreading code is 1023 chips, the phase of the spreading code can be detected with an accuracy of 1/4 chip. The IF carrier frequency detection accuracy is 1 kHz because FFT processing is performed in units of 1 millisecond.
[0093]
In this example, as shown in FIG. 3, the DSP 23 reads IF data in 1-millisecond units written in the RAM 22, performs FFT processing in the FFT processing unit 101, and writes the FFT result in the memory 102. The FFT results written in the memory 102 are sequentially read out according to the read control of the read address control unit 109 and supplied to the multiplication unit 103. The read address control unit 109 does not only read the FFT results from the memory 102 sequentially.
[0094]
In this example, the output of the correlation point detection unit 108 is supplied to the read address control unit 109, and when the correlation point detection unit 108 fails to obtain a correlation peak, the read address of the FFT result from the memory 102 is set. Control to shift the initial value is also performed.
[0095]
On the other hand, the spreading code generation unit 104 generates a spreading code that is considered to be the same series as the spreading code used for the received signal from the GPS satellite. In practice, the spread code generator 104 sequentially switches and outputs spread codes of a plurality of GPS satellites prepared in advance.
[0096]
The spread code for one period (1023 chips) from the spread code generation unit 104 is supplied to the FFT processing unit 105 and subjected to FFT processing, and the processing result is supplied to the memory 106. From the memory 106, the FFT results are read in order from the lowest frequency according to the read control of the read address control unit 110 and supplied to the multiplier 103. In this example, the read address control unit 110 always performs only the process of reading the FFT results from the memory 106 in order from the lowest frequency.
[0097]
Multiplier 103 multiplies the FFT result of the received signal from memory 102 and the FFT result of the spread code from memory 106, and calculates the degree of correlation between the received signal and the spread code in the frequency domain. Here, the multiplication in the multiplication unit 105 is an operation of multiplying one of the complex conjugate of the discrete Fourier transform result of the received signal and the discrete Fourier transform result of the spread code by the other. The multiplication result is supplied to the inverse FFT processing unit 107, and the frequency domain signal is returned to the time domain signal.
[0098]
The inverse FFT result obtained from the inverse FFT processing unit 107 is a correlation detection signal in the time domain between the received signal and the spread code. The correlation detection signal is supplied to the correlation point detection unit 108.
[0099]
This correlation detection signal indicates the correlation value in each chip phase for one cycle of the spread code, and the spread code in the received signal having a predetermined strength or more and the spread code from the spread code generation unit 104 In the phase in which 1 and 2 are synchronized (phase in units of one period of the spreading code), as shown in FIG. 5, the correlation value at one phase of the 1023 chips is a predetermined threshold value. A correlation waveform showing a peak value exceeding the value is obtained. The chip phase at which this peak value is the phase of the correlation point, and is the leading phase of one cycle of the spread code of the GPS satellite signal with respect to the spread code on the GPS receiver side.
[0100]
On the other hand, when the received signal is less than or equal to a predetermined strength, a correlation waveform with a peak value as shown in FIG. 5 is obtained even if the spreading code in the received signal and the spreading code from the spreading code generator 104 are synchronized. In any chip phase, a peak exceeding a predetermined threshold value does not stand.
[0101]
For example, the correlation point detection unit 108 determines whether the received signal and the spread code are synchronized depending on whether a peak value exceeding a predetermined value is present in the correlation detection signal supplied to the correlation point detection unit 108. Detect if.
[0102]
When the correlation point detection unit 108 detects that synchronization is established, the phase of the peak value is detected as a correlation point, that is, the phase of the spread code of the GPS satellite signal. Then, the DSP 23 recognizes the GPS satellite number depending on which GPS satellite the spreading code from the spreading code generation unit 104 at that time is for.
[0103]
Although the correlation detection signal shown in FIG. 5 is in the time domain, the correlation peak is detected only when the carrier component in the intermediate frequency reception signal is correctly removed by the processing described later.
[0104]
Then, the frequency of the removed carrier component becomes the IF carrier frequency including the Doppler shift corresponding to the correlation point where the peak value exceeding the predetermined value stands. Therefore, the IF carrier frequency including this Doppler shift is detected by the DSP 23 as a result of the correlation point detection.
[0105]
When synchronization acquisition for one GPS satellite is completed as described above, in this example, the spreading code generated from the spreading code generator 104 is changed to one corresponding to the spreading code of another GPS satellite signal, Repeat the above process. Even when synchronization cannot be achieved, the DSP 23 changes the spreading code generated from the spreading code generator 104 to one corresponding to the spreading code of another GPS satellite signal, and repeats the above processing.
[0106]
Then, in the DSP 23, when the synchronization acquisition processing for all GPS satellites to be searched is completed, or the spread codes for four or more GPS satellites are synchronized by the information from the CPU 41 of the control calculation unit 40, for example. Then, the synchronization acquisition process is completed.
[0107]
The DSP 23 supplies the control calculation unit 40 with information including the GPS satellite number acquired as a result of the synchronization acquisition, the phase of the spread code of the GPS satellite signal acquired in synchronization and the IF carrier frequency thereof. Further, in this example, the DSP 23 also supplies the control arithmetic unit 40 with the peak value of the correlation point for each GPS satellite signal acquired in synchronization.
[0108]
In the above description, processing of the carrier of the received signal is not considered, but actually, the received signal r (n) includes a carrier as shown in Expression (3) in FIG. In this equation (3), A represents amplitude, d (n) represents data, fo represents carrier angular frequency in the intermediate frequency signal, and n (n) represents noise.
[0109]
Assuming that the sampling frequency in the sampling unit 21 is fs and the number of samplings for one period of the spreading code is N (and therefore 0 ≦ n <N), the discrete frequency k after discrete Fourier transform (0 ≦ k <N) The relationship with the actual frequency f is
For 0 ≦ k ≦ N / 2, f = k · fs / N,
For N / 2 <k <N, f = (k−N) · fs / N (f <0)
It is. Note that due to the nature of the discrete Fourier transform, R (k) and C (k) exhibit circularity when k <0 and k ≧ N.
[0110]
In order to obtain the data d (n) from the received signal r (n), the spread code c (n) and the carrier cos2πnf ₀ It is necessary to remove the carrier component in synchronization with. That is, in the equation (2) shown in FIG. 48 described later, when a carrier component is included only in R (k), a correlation waveform having a peak as shown in FIG. 5 cannot be obtained.
[0111]
In this embodiment, the spread code c (n) and the carrier cos 2πnf are obtained by a simple configuration that only performs processing in the frequency domain by FFT. ₀ And the carrier component can be removed.
[0112]
In other words, in this embodiment, the FFT result of the spread code from the spread code generation unit 104 obtained from the FFT processing unit 105 is obtained as usual by the read address control unit 110 under the control of the arithmetic control unit 40. The frequency components are always read from the memory 106 in order from the lowest frequency component and supplied to the multiplier 103.
[0113]
On the other hand, for the FFT result of the received signal from the GPS satellite obtained from the FFT processing unit 101, the read start address for the FFT result from the memory 102 is shifted from the address position of the lowest frequency component by an amount corresponding to the carrier frequency. Under the control of the arithmetic control unit 40, the read address control unit 109 controls the address so that the address becomes the same.
[0114]
In other words, even if all the frequency components of the memory 102 are read out starting from the frequency component of a certain address phase, if the correlation peak is not obtained, the read address control unit 109 shifts the read start address from the memory 102. The FFT result is sequentially read again from the shift-controlled address.
[0115]
At this time, in this embodiment, the read address control unit 109 receives the mode switching control from the control calculation unit 40 and increases the shift amount per read start address when the positioning mode is the high speed mode. The coarse search is performed, and when the positioning mode is the high sensitivity mode, the shift amount per read start address is minimized (shifted to the address position of the adjacent frequency component) and the fine search is performed. To.
[0116]
That is, from the memory 102, the read start address is shift-controlled according to the control from the read address control unit 109, and the FFT result of the received signal is read sequentially multiple times. The shift control amount at this time is finely changed in the high sensitivity mode, and coarsely changed in the high speed mode.
[0117]
That is, in the high sensitivity mode, when the FFT result from the certain read start address is not read from the memory 102, the read address control unit 109 sets the read start address for the memory 102 when the correlation peak is not obtained. The FFT result is read out by shifting to the address of one higher frequency or one lower frequency adjacent to the previous one. Then, such fine shift control of the read start address is repeated until a correlation peak is obtained.
[0118]
On the other hand, in the high-speed mode, when a correlation peak is not obtained in reading the FFT result from a certain read start address from the memory 102, the read address control unit 109 reads the read start address for the memory 102. Are shifted to address positions separated by n (n is an integer equal to or greater than 2), and shift control is performed so as to start reading the FFT result from the memory 102 from high frequency or low frequency components separated by n. Then, such coarse shift control of the read start address is repeated until a correlation peak is obtained.
[0119]
If the spread code from the spread code generation unit 104 and the spread code included in the received signal are of the same series, the memory 102 at any read start address is controlled by the shift control of the read start address. The correlation peak is obtained for the FFT result from the FFT and the FFT result from the memory 106.
[0120]
By the way, the carrier frequency of the received signal detected based on the accurate estimation of the Doppler shift amount for the GPS satellite from which the received signal was obtained and the accurate calibration of the oscillation frequency and time information inside the GPS receiver. If the information is generated inside the GPS receiver or acquired from the outside, the read address control unit 109 shifts the read start address of the memory 102 by the carrier frequency, thereby detecting the correlation point. In the unit 108, a correlation peak is immediately obtained.
[0121]
However, when the carrier frequency is unknown, as described above, the search start address from the memory 102 is sequentially shifted by the shift amount corresponding to the positioning mode, and a search is performed to obtain a correlation peak. Search for the read start address.
[0122]
Thus, by reading out the FFT result of the received signal r (n) from the memory 102 by shifting by the carrier frequency of the received signal, it is equivalent to the FFT result of the received signal from which the carrier component has been removed, as will be described later. If an FFT result can be obtained and the result of multiplication of the FFT result from which the carrier component is removed and the FFT result for one cycle of the spread code is despread, a peak is reliably generated at the correlation point as shown in FIG. Correlation detection output is obtained.
[0123]
As will be described later, instead of controlling the read address of the FFT result from the memory 102, the FFT result read address of the spread code from the memory 106 is controlled to receive the FFT result of the spread code. It is also possible to remove the carrier component in the same manner as described above by adding the signal r (n) for the carrier and multiplying by the multiplier 103.
[0124]
Hereinafter, the removal of the carrier component by the synchronization of the carrier of the received signal and the spread code by the control of the read address from the memory 102 or the memory 106 will be described in more detail together with the operation of the digital matched filter processing in the DSP 23. To do.
[0125]
In this embodiment, the DSP 23 performs digital matched filter processing. The principle of this digital matched filter processing is the convolution of the time domain as shown in the equation (1) in FIG. This is based on the theorem that Fourier transform is multiplication in the frequency domain.
[0126]
In this equation (1), r (n) represents the received signal in the time domain, and R (k) represents its discrete Fourier transform. Further, c (n) represents a spreading code from the spreading code generator, and C (k) represents its discrete Fourier transform. n is a discrete time and k is a discrete frequency. F [] represents the Fourier transform.
[0127]
When the correlation function of the two signals r (n) and c (n) is defined again as f (n), the discrete Fourier transform F (k) of f (n) has a relationship as shown in Expression (2) in FIG. become. Therefore, if r (n) is a signal from the frequency converter 10 and c (n) is a spreading code from the spreading code generator 104, the correlation function f (n) of r (n) and c (n). Can be calculated by the following procedure according to the above equation (2), regardless of the normal definition equation.
[0128]
Calculate the discrete Fourier transform R (k) of the received signal r (n).
[0129]
Calculate the complex conjugate of the discrete Fourier transform C (k) of the spreading code c (n).
[0130]
-F (k) of Formula (2) is calculated from the complex conjugate of R (k) and C (k).
[0131]
Calculate the correlation function f (n) by inverse discrete Fourier transform of F (k).
[0132]
As described above, if the spread code included in the received signal r (n) matches the spread code c (n) from the spread code generator 104, the correlation function f (n calculated by the above procedure is used. ) Is a time waveform that causes a peak at a correlation point as shown in FIG. As described above, in this embodiment, the FFT and inverse FFT speed-up algorithms are applied to the discrete Fourier transform and the inverse Fourier transform, so that the calculation is performed much faster than the correlation is calculated based on the definition. Can do.
[0133]
Next, synchronization between the carrier included in the received signal r (n) and the spreading code will be described.
[0134]
As described above, the received signal r (n) includes a carrier as shown in Expression (3) in FIG. In order to obtain the data d (n) from the received signal r (n), the spread code c (n) and the carrier cos 2πnf ₀ Must be removed in synchronization with That is, in the above-described equation (2) in FIG. 48, when only a carrier is included in R (k), a correlation waveform as shown in FIG. 5 cannot be obtained.
[0135]
As described above, if the Doppler shift amount is accurately estimated and the oscillation frequency and time information inside the GPS receiver are accurate, the carrier frequency f of the received signal r (n) is obtained. ₀ Becomes known. In this case, as shown in FIG. 6, a multiplier 121 is provided in the previous stage of the FFT processing unit 101, and in this multiplier 121, the received signal r (n) and the frequency f from the signal generator 122 are provided. ₀ The carrier component can be removed from the received signal r (n) before performing the FFT by performing frequency conversion by multiplying with the carrier.
[0136]
In this case, the FFT result of the received signal r (n) from which the carrier component has been removed is obtained from the memory 102, and this FFT result and the FFT result of the spread code c (n) are multiplied by the multiplier 103. Since multiplication is performed, a time waveform that causes a peak at the correlation point as shown in FIG. 5 is reliably obtained as the output of the inverse FFT processing unit 107.
[0137]
As described in parentheses in FIG. 6, instead of removing the carrier component from the received signal r (n), a multiplier 121 is provided in the preceding stage of the FFT processing unit 105 for the spread code c (n). In the multiplier 121, the spread code c (n) and the frequency f from the signal generator 122 ₀ The same applies to the case where a carrier component is added to the spread code by multiplying the carrier code by frequency conversion.
[0138]
That is, in this case, the carrier component included in the FFT result of the received signal read from the memory 102 is synchronized with the added carrier component included in the FFT result of the spread code read from the memory 106. From the inverse FFT processing unit 107, a correlation detection output that produces a peak at a correlation point as shown in FIG. 5 is obtained.
[0139]
However, in the case of the method of multiplying the signal in the time domain by the signal of the carrier frequency as shown in FIG. 6, a multiplication unit for removing the carrier component is particularly necessary, the configuration becomes complicated, and the multiplication operation is performed. There is a disadvantage that the processing speed is reduced by this amount. Further, when the carrier frequency is unknown, a means for performing a frequency search is further required with the signal generator 22 as a variable frequency oscillator configuration.
[0140]
On the other hand, the frequency multiplication as described above can be expressed as an equation (4) in FIG. In this equation (4), F [] is the discrete Fourier transform, φ ₀ Is the phase difference from the carrier, k ₀ Is f ₀ K corresponding to, f ₀ = K ₀ Fs / N. From this equation (4), the FFT of the signal obtained by frequency-converting the received signal r (n) as shown in FIG. 6 is expressed as R (k), which is the FFT of r (n), for the carrier frequency k. ₀ Only shifted form.
[0141]
From the above, the configuration of FIG. 6 can be replaced with the configuration of FIG. That is, instead of multiplying the received signal r (n) or the spread code c (n) by the carrier frequency, the read address when reading the FFT result of the received signal or the FFT result of the spread code from the memory 102 or the memory 106 is The shift is made by the carrier frequency.
[0142]
In this case, in FIG. 7, when the received signal r (n) is shifted, down conversion is performed. ₀ > 0, and if the spreading code c (n) is shifted, up-conversion ₀ <0.
[0143]
As described above, if the FFT property shown in the equation (4) is used, the signal generator 122 of FIG. 6 is not necessary, and the read address phase from the memory of the FFT result is shifted as shown in FIG. It is only necessary to do this, which simplifies the configuration and speeds up the processing.
[0144]
It should be noted that the phase difference φ in the above equation (4) ₀ Is unknown and is ignored in FIG. 7. For example, the correlation function f ′ (n) () obtained as the result of the inverse FFT of F ′ (k) calculated by equation (5) in FIG. 0 ≦ n <N) is a complex number, and its real part is f _R '(N), imaginary part is f _I If '(n)', then the correlation peak amplitude | f '(n) | is obtained as shown in equation (6) in FIG. 48, and the phase φ is as shown in equation (7) in FIG. Exp (jφ on the right side of Equation (4) ₀ ) Multiplication may be omitted. Note that the phase φ is changed to two values different from each other by π corresponding to the sign of the data d (n) in the equation (3). ₀ It becomes the value with added.
[0145]
FIG. 8 shows an example of a configuration diagram in which the operation of the synchronization acquisition process in the DSP 23 is reflected in the block diagram of FIG. 4 when the carrier frequency of the GPS satellite signal is known. The output of each block in FIG. 8 shows the signal outputs r (n) and c (n) and the calculation results R (k), C (k), and f ′ (n) as described above. FIG. 8 shows a state in which the address shift amount of the read start address in the memory 102 is just equivalent to the carrier frequency.
[0146]
Next, when the carrier frequency is unknown, the read address control unit 109 shift-controls the read start address based on the correlation detection output from the correlation point detection unit 108 as shown in FIG. That is, the read address control unit 109 analyzes the correlation result of the correlation point detection unit 108 and performs shift control of the read start address of the memory 102 (or the memory 106) until a correlation peak is obtained.
[0147]
In this case, the read address control unit 109 recognizes whether the positioning mode at that time is the high-speed mode or the high-sensitivity mode based on the positioning mode information from the control calculation unit 40, and shifts according to the positioning mode of the recognition result. The shift control of the read start address of the memory 102 (or the memory 106) is performed by the amount.
[0148]
In this case, the initial value of the read start address of the FFT result of the memory 102 (or the memory 106) is a predicted address determined from past data. In other words, the read address control unit 109 sets the read start address from the memory 102 of the FFT result of the received signal r (n) as the initial value of the read start address using the predicted address determined from the past data as the initial value of the read start address. At the center, change control is performed based on the correlation detection output of the correlation point detection unit 108 with a shift amount corresponding to the positioning mode so that the correlation point detection unit 108 can obtain a peak as shown in FIG.
[0149]
When the correlation point detection unit 108 obtains a peak as shown in FIG. 5, the read address control unit 109 stops the shift control of the read start address at the shift amount at that time. The phase of the spread code and the carrier frequency are obtained from the address shift position at the time of the stop.
[0150]
The flow of processing in the synchronization acquisition unit 20 in the first example of synchronization acquisition will be described with reference to the flowcharts of FIGS. Note that the flowcharts of FIGS. 9 to 11 mainly correspond to software processing in the DSP 23.
[0151]
First, the IF data from the frequency conversion unit 10 is sampled by the sampling circuit 21 and taken into the RAM 22 as a signal r (n) (step S1). Next, the signal r (n) is subjected to FFT processing by the FFT processing unit 101, and the FFT result R (k) is written in the memory 102 (step S2). Next, the FFT result C (k) of the spread code corresponding to the GPS satellite that received the signal is set in the memory 106 (step S3).
[0152]
Next, the initial value k of the shift amount of the read start address from the memory 102 of the FFT result R (k) of the received signal r (n). ₀ 'Is determined from past data (step S4). And the determined initial value k ₀ 'Is set as the shift amount k of the read start address of the FFT result from the memory 102, and the shift control change count v is set to the initial value v = 0 (step S5).
[0153]
Next, the FFT result R (k) of the received signal r (n) is read from the memory 102 with the read start address shifted by k ′ (step S6). Then, the read FFT result R (k−k ′) is multiplied by the complex conjugate of the FFT result C (k) of the spread code to obtain a correlation function F ′ (k) (step S7).
[0154]
Next, inverse FFT of the correlation function F ′ (k) is performed to obtain a time domain function f ′ (n) (step S8). For this function f ′ (n), a peak value f ′ (np) is obtained (step S9), and it is determined whether or not the peak value f ′ (np) is greater than a preset threshold value fth. (Step S11 in FIG. 10).
[0155]
In step S11, when it is determined that the peak value f ′ (np) is larger than the preset threshold value fth, the discrete time (spread code phase) np for taking the peak value f ′ (np) is set. It is detected as a correlation point (step S12).
[0156]
Then, it is determined whether or not the detected correlation point np is the fourth one (step S13). When it is determined that the correlation point np is the fourth, the receiver position calculation process is started, and the synchronization holding unit 30 holds the synchronization. Processing is performed (step S14). Thereafter, the process proceeds to step S15. The process in step S14 may be performed for the fourth and subsequent items.
[0157]
Note that the error of the Doppler shift amount for the GPS satellite being received and the oscillation frequency of the GPS receiver can be estimated from the shift amount k ′ of the read start address when the correlation point np detected in step S12 is obtained. it can. That is, the carrier frequency of the received signal can be detected.
[0158]
If it is determined in step S13 that the detected correlation point np is other than the fourth one, it is determined whether or not the above-described spread code synchronization search process has been completed for all satellites to be searched (step S15). When it is determined that the spread code synchronization search process for all the satellites to be searched is finished, the search operation is finished (step S16).
[0159]
If it is determined in step S15 that there is a satellite for which the spread code synchronization search has not ended, the satellite for which the spread code synchronization search is performed next is selected and spread to the spread code c (n) used by the selected satellite. The sign is changed (step S17). And it returns to step S3 and performs the process after step S3 mentioned above.
[0160]
If the peak value f ′ (np) is smaller than the preset threshold value fth as a result of the determination in step S11 and the correlation point cannot be detected, it is determined what the current mode is (see FIG. 11 step S21). When it is determined that the current mode is the high sensitivity mode, the shift control change count v is set to a preset maximum value v. _max It is determined whether it is smaller than (step S22). This maximum value v _max Corresponds to 1 kHz when converted to frequency.
[0161]
Then, the number of shift control changes v is a preset maximum value v. _max When it is determined that the shift control change number is smaller than 1, the shift control change count v is incremented by 1 (v = v + 1), and a new shift amount k ′ is
k ′ = k ′ + (− 1) ^v × v
(Step S23), and then the process returns to step S6 in FIG. Then, the processes after step S6 described above are repeated.
[0162]
When it is determined in step S21 that the current mode is the high speed mode, in the high speed mode, the shift of the read start address from the memory 102 is performed by n times the shift amount in the high sensitivity mode (n is an integer of 2 or more). Therefore, n times the number of shift control changes v is a preset maximum value v _max It is determined whether it is smaller than (step S24).
[0163]
Then, n times the shift control change count v is set to the preset maximum value v. _max When it is determined that the shift control change number is smaller than 1, the shift control change count v is incremented by 1 (v = v + 1), and a new shift amount k ′ is
k ′ = k ′ + (− 1) ^v × n × v
(Step S25), and then the process returns to step S6 in FIG. Then, the processes after step S6 described above are repeated.
[0164]
In step S22, the shift control change count v is set to the preset maximum value v. _max In step S24, n times the shift control change count v is set to the preset maximum value v. _max If it is determined that the number of times is greater than the predetermined number of times, it is determined whether or not the number of times determined to be larger is equal to or greater than a predetermined number of times predetermined for the current data in the RAM 22 (step S26). If not, the process returns to step S1, new data is taken into the RAM 22, and the above processing is repeated.
[0165]
If it is determined in step S26 that the number of times is equal to or greater than the predetermined number, it is determined whether or not the above-described spread code synchronization search process has been completed for all satellites to be searched (step S27). When it is determined that the spread code synchronization search process has been completed, the synchronization acquisition unit 20 notifies the control calculation unit 40 that the synchronization acquisition has not been performed (step S28), and the search operation ends (step S29).
[0166]
If it is determined in step S27 that there is a satellite to be searched for which the spread code synchronization search has not been completed, the satellite for which the spread code synchronization search is performed next is selected, and the spread code c (n) used by the selected satellite is selected. ) Is changed (step S30). And it returns to step S3 and performs the process after step S3 mentioned above.
[0167]
FIG. 12 shows a configuration diagram in which the processing operation of the first example of synchronization acquisition as described above is reflected in the block diagram of the internal configuration of the DSP 23 in FIG. The output of each block in FIG. 12 shows the signal output and the calculation result as described above.
[0168]
As described above, according to the first example of the acquisition process in the DSP 23, when the digital matched filter is configured using the FFT in the GPS receiver, the FFT result of the received signal is obtained as shown in FIG. A correlation point np indicating a peak greater than or equal to a predetermined value can be obtained by shifting the read start address from the memory by the carrier frequency and multiplying by the spread code. If the correlation point np is known for four GPS satellites, that is, four types of spreading codes c (n), the GPS receiver position can be calculated.
[0169]
That is, according to the first example, when performing digital matched filter processing using FFT, in order to synchronize the carrier of the received signal and the spread code, the multiplication of the received signal without performing multiplication in the time domain. When multiplying the FFT result and the FFT result of the spreading code in the frequency domain, the carrier of the received signal is shifted by a simple method of shifting one of the FFT result of the received signal and the FFT result of the spreading code. Components can be removed.
[0170]
8 and 12, the read address of the memory 102 is shifted for the FFT result R (k) of the received signal, but the read address of the memory 106 for the FFT result C (k) of the spread code is shifted. May be shifted in the opposite direction to the case of the FFT result R (k) of the received signal (in the form of up-conversion by a multiplier).
[0171]
In the description of the first example described above, the spread code generator 104 and the FFT processing unit 105 are provided separately, but the spread codes corresponding to the respective GPS satellites are subjected to FFT in advance. Is stored in the memory, the FFT calculation of the spread code c (n) when receiving the satellite signal can be omitted.
[0172]
[Setting process of positioning mode]
Next, positioning mode setting processing in the GPS receiver of this example will be described with reference to FIG. 13 and the flowchart of FIG. Each step in the flowcharts of FIG. 13 and FIG. 14 mainly shows the processing operation of the CPU 41 of the control calculation unit 40.
[0173]
First, it waits for the power to be turned on (step S41). When the power is turned on, the last positioning mode of the previous time is detected (step S42). Next, it is determined whether the detected positioning mode is the auto mode or the manual mode (step S43).
[0174]
If it is determined that the manual mode is selected, it is determined whether the mode is the high speed mode or the high sensitivity mode (step S44). When it is determined in step S44 that the mode is the high speed mode, the high speed mode is notified to the synchronization acquisition unit 20, and the positioning mode of the synchronization acquisition unit 20 is set to the high speed mode (step S45).
[0175]
Next, it is determined whether or not a notification indicating that the satellite radio wave cannot be received and the satellite radio wave cannot be received is received from the synchronization acquisition unit 20 (step S46). As shown in FIG. 15, for example, “The radio wave could not be received in the high-speed mode” is displayed on the screen of the display 5 of the GPS receiver, and the current mode is the high-speed mode and the current mode is the satellite radio wave. The user is notified that the data cannot be received (step S47).
[0176]
At this time, in the case of an auto mode, which will be described later, an inquiry about switching to the high sensitivity mode is made. However, in the manual mode, since the purpose is to prompt the user to switch, the notification as described above is performed. Of course, in the notification display of FIG. 15, a notification for prompting the user to change the positioning mode or to prompt the user to move to a place where the radio wave is stronger may be performed.
[0177]
The user can change the positioning mode to the high sensitivity mode or move to a place with strong radio waves by looking at the notification display in FIG. In addition, since the current status of the GPS receiver can be known by this notification display, it is possible to prevent the user from getting frustrated without displaying the positioning result.
[0178]
In step S46, when a notification indicating that satellite radio waves cannot be received is not received, and after step S47, it is determined whether or not there has been an instruction to change the positioning mode by the user using, for example, the jog dial 7 (step S48). When it is determined that there is no change instruction, it is determined whether or not the power is turned off (step S55). When the power is turned off, the positioning mode at that time is set as the last mode and a nonvolatile memory (not shown) (Omitted) (step S56), and this processing routine is terminated. If the power is not turned off, the process returns to step S45.
[0179]
If it is determined in step S48 that there has been an instruction to change the positioning mode, positioning mode selection change processing is executed (step S49), the positioning mode determined as the change result is recognized (step S50), and then step Return to S43.
[0180]
If it is determined in step S44 that the mode is the high sensitivity mode, the synchronization capturing unit 20 is notified of the high sensitivity mode, and the positioning mode of the synchronization capturing unit 20 is set to the high sensitivity mode (step S51).
[0181]
Next, it is determined whether or not a satellite radio wave has been received from the synchronization acquisition unit 20 but a notification that the positioning position may not be accurate has been received (step S52), and when it is determined that the notification has been received. As shown in FIG. 16, on the screen of the GPS receiver display 5, for example, “High sensitivity mode, but the radio wave may be weak and the position may not be accurate” is displayed, and the current mode is high sensitivity. The user is notified that the current mode is the mode and that the accurate positioning position cannot be detected in the current mode (step S53). Also in this case, in the notification display of FIG. 16, a notification for urging movement to a place where the radio wave is stronger may be performed together.
[0182]
By this notification display, the user can know the current status of the GPS receiver, and can accurately use the positioning result.
[0183]
In step S52, when a notification that the positioning position may not be accurate is not received, and next to step S53, it is determined whether or not there is an instruction to change the positioning mode by the user using the jog dial 7, for example. (Step S54) When it is determined that there is no change instruction, it is determined whether or not the power is turned off (Step S57). When the power is turned off, the positioning mode at that time is set as the last mode and the non-volatile memory. (Not shown) is stored (step S58), and this processing routine is terminated. If the power is not turned off, the process returns to step S51.
[0184]
If it is determined in step S54 that there has been a positioning mode change instruction, positioning mode selection change processing is executed (step S49), the positioning mode determined as the change result is recognized (step S50), and then step Return to S43.
[0185]
If it is determined in step S43 that the positioning mode is the auto mode, in this example, the initial mode of the auto mode is the high speed mode, so the positioning mode of the synchronization acquisition unit 20 is set to the high speed mode ( Step S61 in FIG. 14).
[0186]
Next, it is determined whether or not a notification indicating that the satellite radio wave cannot be received and the satellite radio wave cannot be received is received from the synchronization acquisition unit 20 (step S62). As shown in FIG. 17, the display 5 of the GPS receiver displays, for example, “The radio wave could not be received in the high speed mode. The reception starts in the high sensitivity mode.”, And the current mode is set to the auto mode. Since the satellite radio wave cannot be received in the high speed mode and in the current mode, the user is notified that the mode is changed to the high sensitivity mode (step S63). Then, the positioning mode of the synchronization acquisition unit 20 is changed to the high sensitivity mode (step S64).
[0187]
Thereafter, it is determined whether or not the received electric field strength has increased due to the movement of the position of the GPS receiver (step S65), and when it has increased, the positioning mode of the synchronization acquisition unit 20 is returned to the high sensitivity mode (step S66). Then, the process returns to step S62.
[0188]
If it is determined in step S65 that the received electric field strength is not increased, it is determined whether or not the user has instructed to change the positioning mode (step S67). If it is determined that there has been no change instruction, the process returns to step S65. If it is determined in step S67 that a positioning mode change instruction has been issued, positioning mode selection change processing is executed (step S69), the positioning mode determined as the change result is recognized (step S70), and then step Return to S43.
[0189]
If no notification indicating that satellite radio waves cannot be received is not received in step S62, it is determined whether or not the user has instructed to change the positioning mode (step S68). If it is determined that there has been no change instruction, the process returns to step S62. . If it is determined in step S68 that there is an instruction to change the positioning mode, positioning mode selection change processing is executed (step S69), the positioning mode determined as the change result is recognized (step S70), and then step Return to S43.
[0190]
The operation process for the auto mode of FIG. 14 can also be as shown in FIG. That is, in the example of FIG. 18, steps S71 and S72 are provided instead of step S63 in the flowchart of FIG.
[0191]
In the example of FIG. 18, when it is determined in step S62 that a notification indicating that satellite radio waves cannot be received has been received, as shown in FIG. Could n’t receive the radio signal. Is it okay to start receiving in the higher sensitivity mode? ”And that the current mode is the auto mode high-speed mode and that the current mode cannot receive satellite radio waves, A notification is made to inquire the user whether the mode can be changed to the high sensitivity mode (step S71). At this time, as shown in FIG. 19, for example, [YES] and [NO] are displayed together on the screen of the display 5 as a display for accepting the user's response input to the inquiry.
[0192]
Then, the user's response is discriminated (step S72), and when [YES] is selected and the change to the high sensitivity mode is approved, the positioning mode of the synchronization acquisition unit 20 is changed to the high sensitivity mode (step S64). ).
[0193]
If [NO] is selected by the user and the change to the high sensitivity mode is rejected, the process proceeds to step S68 to determine whether or not the user has instructed to change the positioning mode. When it is determined, the process returns to step S62. Others are the same as in the example of FIG.
[0194]
According to the example of FIG. 18, the positioning mode reflecting the user's will can be switched even in the auto mode, which is convenient.
[0195]
[Positioning mode selection operation processing]
Next, the positioning mode selection changing process in steps S49 and S69 in the above example will be described with reference to the flowchart of FIG. Each step of the flowchart of FIG. 20 mainly shows the processing operation of the CPU 41 of the control calculation unit 40.
[0196]
First, the user rotates the jog dial 7 to select menu display, and determines whether or not the positioning mode is selected from the menu (step S80). When the positioning mode is selected, the CPU 41 of the control calculation unit 40 As shown in FIG. 21, the menu and options for the auto mode and the manual mode are displayed on the screen of the display 5 (step S81).
[0197]
In this state, the jog dial 7 or the cursor button 63 is used to determine whether or not an option selection of either the auto mode or the manual mode has been performed (step S82), and when it is determined that the mode option is not selected. Then, it is determined whether or not the cancel is selected by the jog dial 7 (step S83). When it is determined that the cancel is selected, this processing routine is ended. When it is determined that the cancellation has not been selected, the process returns to step S82.
[0198]
If it is determined in step S82 that the mode option has been selected, it is determined which is selected (step S84). When it is determined that the selected mode is the auto mode, the CPU 41 of the control calculation unit 40 determines the positioning mode of the synchronization acquisition unit 20 as the auto mode (step S85).
[0199]
As described above, in this example, in the auto mode, the initial mode is the high-speed mode, so that the synchronization capturing unit 20 is notified. After step S85, the process returns to step S80. Receiving this notification, the DSP 23 of the synchronization acquisition unit 20 is set to the high-speed mode, and performs a synchronization acquisition operation with coarse read address shift of the memory 102.
[0200]
When it is determined in step S84 that the manual mode has been selected, as shown in FIG. 22, choices between the high speed mode and the high sensitivity mode are displayed on the screen of the display 5 of the GPS receiver (step S86).
[0201]
In this state, the jog dial 7 or the cursor button 63 is used to determine whether an operation of selecting a mode option of the high speed mode or the high sensitivity mode has been performed (step S87), and when it is determined that the mode option is not selected. Then, it is determined whether or not cancellation is selected by the jog dial 7 (step S88), and when it is determined that cancellation is selected, the process returns to step S80. If it is determined in step S88 that the cancellation has not been selected, the process returns to step S87.
[0202]
When it is determined in step S87 that the mode option has been selected, it is determined which is selected (step S89). When it is determined that the selected mode is the high sensitivity mode, the CPU 41 of the control calculation unit 40 determines the positioning mode of the synchronization acquisition unit 20 as the high sensitivity mode, and notifies the synchronization acquisition unit 20 to that effect. (Step S90). When it is determined that the selected high-speed mode is selected, the CPU 41 of the control calculation unit 40 determines the positioning mode of the synchronization acquisition unit 20 as the high-speed mode, and notifies the synchronization acquisition unit 20 accordingly ( Step S91).
[0203]
The synchronization acquisition unit 20 that has received the notification performs the synchronization acquisition operation by finely shifting the read start address of the memory 102 in the high sensitivity mode as described above, and starts the read of the memory 102 in the high speed mode. Synchronous acquisition operation is performed with a rough shift of the address. After step S90 and step S91, the process returns to step S80.
[0204]
As described above, according to the first example of the synchronization acquisition, even if the carrier frequency of the received signal from the GPS satellite is unknown, the processing in the frequency domain by FFT is actively used to The carrier component can be removed by detecting the synchronization between the carrier and the spreading code. Therefore, the detection of the correlation point between the GPS reception signal and the spread code by the digital matched filter using FFT can be realized with a high speed and simple configuration. The IF carrier frequency can be detected from the shift amount of the read start address of the memory 102.
[0205]
And according to the above-mentioned example, a GPS receiver is equipped with two modes, a high-speed mode and a high-sensitivity mode, so that positioning can always be performed quickly and accurately according to the reception location and reception environment. It becomes possible to.
[0206]
According to the above example, the high-speed mode and the high-sensitivity mode can be switched and selected by the user's manual operation, and the current mode and the reception status of the satellite wave are notified to the user. Based on the notification, the user can select an appropriate positioning mode.
[0207]
In the GPS receiver of the above-described example, when the satellite radio wave is weak and it is difficult to receive in the high speed mode, the positioning mode can be automatically changed to the high sensitivity mode, which is convenient. Further, since the user is notified at that time, the user can accurately grasp the current reception status of the GPS receiver.
[0208]
In addition, when the user obtains approval when switching the positioning mode from the high-speed mode to the high-sensitivity mode, it is possible to realize an auto mode of the positioning mode giving priority to the convenience for each user.
[0209]
In addition, you may make it always display what the present positioning mode is on the screen of the display 5 of a GPS receiver.
[0210]
In the above example, the FFT calculation of the spread code c (n) at the time of receiving the satellite signal is omitted by storing in the memory the spread code corresponding to each satellite that has been FFTed beforehand. can do. That is, the spread code generator 104 and the FFT processor 105 in FIG. 4 can be omitted.
[0211]
[Other examples of positioning mode selection processing]
FIG. 23 shows the appearance of the GPS receiver in this example. In this example, the jog dial 7 described above can be used to select and set the positioning mode, and operation buttons 64, 65, 65, 65, 65, 65, 66, and when any one of these operation buttons 64, 65, 66 is pressed, the GPS receiver performs synchronization acquisition in a positioning mode determined in advance corresponding to each operation button. It is.
[0212]
That is, in this example, the operation button 64 is an “indoor” button, and when the operation button 64 is pressed, the GPS receiver is set to perform synchronization acquisition in the high sensitivity mode. The operation button 65 is an “outdoor” button. When the operation button 65 is pressed, the GPS receiver is set to perform synchronization acquisition in the high-speed mode.
[0213]
Further, the operation button 66 is a “valley between buildings” button, and when this operation button 66 is pressed, the GPS receiver is set to perform synchronization acquisition in the high-speed mode. Since there are many multipaths in the valleys of the building, the synchronization acquisition unit 20 is controlled so as to select a more accurate radio wave.
[0214]
That is, the synchronization capturing unit 20 is in a state where a plurality of radio waves are captured simultaneously in an environment where the received electric field strength is strong and there are many multipaths. In this case, the radio wave reflected on the building or the like is delayed compared to the direct wave from the satellite. Therefore, in the GPS receiver, when the building valley button 66 is operated, among the plurality of radio waves captured at the same time, not the strength of the correlation, but the one that reaches the GPS receiver earliest (the most phasewise) (With a small delay) is captured as a direct wave from the satellite.
[0215]
FIG. 24 is a flowchart for explaining the positioning mode selection processing of the GPS receiver in this example. Each step in this flowchart is mainly executed by the CPU 41 of the control calculation unit 40.
[0216]
First, similarly to step S80 of FIG. 20, the user rotates the jog dial 7, selects menu display, determines whether or not the positioning mode is selected from the menu (step S101), and the positioning mode is selected. Then, the processing after step S81 in FIG. 20 is performed, and the process returns to step S101.
[0217]
In this example, when it is determined in step S101 that the positioning mode is not selected from the menu, it is determined whether or not the “indoor” button 64 is pressed (step S102), and it is determined that the button is pressed. Sometimes, the CPU 41 of the control calculation unit 40 determines the positioning mode of the synchronization acquisition unit 20 as the high sensitivity mode, and notifies the synchronization acquisition unit 20 accordingly (step S103). Then, the process returns to step S101.
[0218]
If it is determined in step S102 that the “indoor” button 64 has not been pressed, it is determined whether or not the “outdoor” button 65 has been pressed (step S104). If it is determined that the button has been pressed, the CPU 41 of the control calculation unit 40 Then, the positioning mode of the synchronization acquisition unit 20 is determined as the high-speed mode, and that is notified to the synchronization acquisition unit 20 (step S105). Then, the process returns to step S101.
[0219]
If it is determined in step S104 that the “outdoor” button 65 has not been pressed, it is determined whether or not the “building valley” button 66 has been pressed (step S106). If it is determined that the button has been pressed, the control calculation unit 40 The CPU 41 determines the positioning mode of the synchronization acquisition unit 20 as the high-speed mode, and notifies the synchronization acquisition unit 20 of that fact and an instruction to perform the synchronization acquisition process considering the multipath described above (step S107). . Then, the process returns to step S101.
[0220]
According to this example, the user operates the operation button indicating the environment in which the GPS receiver is currently used without knowing which environment the high sensitivity mode and the high speed mode are adapted to. The effect is that the GPS receiver can be set to an appropriate positioning mode.
[0221]
Also in this example, the screen of the display 5 displays the indoor mode, the outdoor mode, the valley mode of the building, or the corresponding high sensitivity mode or high speed mode, respectively, and the user indicates what the current mode is. You may make it alert | report.
[0222]
[Second example of synchronization acquisition by digital matched filter]
As described above, when the correlation point between the received signal and the spread code is detected by the digital matched filter, the unit data length for detecting the correlation point is usually set to one cycle length of the spread code.
[0223]
However, in the received signal from the GPS satellite, as described above, one bit of the data is for 20 cycles of the spread code, and the code of the same pattern is used for the 20 cycles. In the second example of the synchronization acquisition, the unit data length for detecting the correlation point between the received signal and the spread code by the digital matched filter is set to a plurality of cycle lengths of the spread code by making use of this characteristic. The sampling frequency in the sampling circuit 21 may be the same as in the above example.
[0224]
According to the second example of this synchronization acquisition, the IF carrier frequency detection accuracy is improved and the reception sensitivity is improved by performing FFT calculation processing on the received signal in units of a plurality of cycles of the spread code. Compared with the method of accumulating time domain signals, it is easier to perform synchronization acquisition of spreading codes and search for IF carrier frequencies. Hereinafter, the second example of the synchronization acquisition will be further described.
[0225]
In the time domain, there is a prior example in which a correlation point is detected for data of one cycle length obtained by performing cumulative addition over M cycles (M is an integer of 2 or more) of spreading codes (for example, US Pat. No. 4,998,111). Or "An Introduction to Snap Track ^TM Server-Aided GPS Technology, ION GPS-98 Proceedings ").
[0226]
That is, as shown in FIG. 25, in the method of the preceding example, the multiplication result of the spread code and the received signal r (n) is cumulatively added over M periods. The method of the preceding example uses the periodicity of the received signal from the GPS satellite and the statistical property of noise to increase the C / N, and the carrier of the received signal and the spreading code can be synchronized in advance. In this state, the C / N is improved M times, and therefore the reception sensitivity (correlation point detection sensitivity) is improved M times. And it improves to M times the detection accuracy of the carrier frequency.
[0227]
However, if the carrier of the received signal and the spreading code are not synchronized, M carriers having different phases are added and synthesized. In the result of cumulative addition, the essential GPS signal is canceled and the correlation peak is It cannot be detected.
[0228]
For this reason, when the carrier frequency of the received signal is unknown, it is necessary to search for the carrier frequency, and it is necessary to perform an inefficient operation such as performing cumulative addition for each frequency to be searched.
[0229]
On the other hand, in the first example of the above-described synchronization acquisition, the carrier of the received signal and the spreading code are determined by a simple method of shifting the read address from the memory of the FFT result in the frequency domain as described above. Therefore, the effect of cumulative addition can be maximized.
[0230]
In the second example of the synchronization acquisition, similarly to the first example described above, the carrier frequency of the received signal from the GPS satellite is unknown, and the carrier frequency is searched. In this case, the received signal r For (n), FFT is performed every M cycles of the spread code. Then, the carrier frequency of the received signal is searched for every M cycles of the spread code by controlling the shift amount of the read address from the memory of the FFT result of the received signal.
[0231]
The data d (n) in the equation (3) of FIG. 48 described above can be ignored since it becomes a fixed value of 1 or -1 during the M period of the spread code if M ≦ 20. Then, equation (3) becomes
r (n) = A · c (n) cos2πnf ₀ + N (n)
When this is a discrete Fourier transform with M period length, the number of data is M × N (N is the number of data for one period of the spread code), so the relationship between k after the discrete Fourier transform and the actual frequency f is sampling For frequency fs
For 0 ≦ k ≦ MN / 2, f = kfs / MN
And
For MN / 2 <k <MN, f = (k−MN) fs / MN (where f <0)
Thus, the resolution becomes M times.
[0232]
However, the spread code c (n) is a periodic signal, and if the time of one period length is T (T = 1 millisecond in the GPS C / A code), the frequency component has an accuracy of f = 1 / T or less. There is no. Therefore, every M frequency components of the spread code c (n) in the FFT result R (k) (where 0 ≦ k <MN) after the discrete Fourier transform of the received signal r (n), that is, MN Concentrating on N points in the data, and the amplitude is cumulatively added for M periods, and therefore becomes M times the same frequency component in one period length. For simplicity of explanation, FIG. 26 shows a spectrum example when M = 4.
[0233]
In the example of FIG. 26, the signal spectrum is every M = 4, and there is no signal component between them. Except for N points, the frequency component of the spread code c (n) is zero. On the other hand, noise n (n) is an aperiodic signal in many cases, so that energy is distributed to all MN frequency components. Therefore, in the sum of N frequency components of the spread code c (n) in the FFT result R (k) of the received signal r (n), C / N is improved M times as in the cumulative addition in the time domain. Will do.
[0234]
In the received signal r (n), the carrier component cos2πnf shown in Expression (3) ₀ If there is not, the frequency component of the spread code c (n) in the FFT result R (k) is concentrated in k = i × M (where 0 ≦ i <N). In the third example, the readout address of the FFT result R (k) from the memory is set to k = (i × M) −k per one cycle of the spread code. ₀ K for carrier frequency ₀ Only to cyclically shift.
[0235]
The configuration of the DSP 23 of the second example described above is the same as that shown in FIG. 4, but the capacity of the RAM 22 is set to M cycles of the spread code, for example, 16 cycles (16 milliseconds). Then, the capture processing operation is performed in units of data corresponding to M cycles of the spreading code. FIG. 27 shows a configuration diagram in which the above-described capture processing operation is reflected in the internal configuration of the DSP 23.
[0236]
That is, the FFT processing unit 101 obtains an FFT result R (K) having the FFT operation processing unit as the M period of the spread code and writes it in the memory 104. In FIG. 27, 0 ≦ k <N and 0 ≦ K <MN.
[0237]
Then, the read address is shift-controlled from this memory 102 and the FFT result is read out and supplied to the multiplier 103, and multiplied by the complex conjugate of the FFT result C (k) of the spread code c (n) from the memory 106. Is done.
[0238]
In the case of the third example, the correlation function F (k) obtained from the multiplication unit 103 is as shown in the equation (8) in FIG. In Equation (8), k is k in the complex conjugate of the FFT result C (k) of the spreading code, and k ₀ For f ₀ = K ₀ Fs / MN.
[0239]
At this time, in FIG. 27, the correlation function f ′ (n) obtained from the inverse FFT processing unit 107 has M peaks in the range of 0 ≦ n <MN because R (K) includes an M-cycle spreading code. Will appear. However, since one correlation point may be detected for one cycle of the spreading code, the calculation in the inverse FFT processing unit 107 is 0 ≦, as in the case of the first and second embodiments described above. Only the range of n <N is required, and calculation in N ≦ n <MN is not necessary.
[0240]
As described above, according to the second example, by increasing the FFT of the received signal r (n) to M times one cycle of the spread code, the detection sensitivity of the correlation point, and thus the reception sensitivity is improved. be able to. In this case, the larger M is, the higher the reception sensitivity is. Therefore, it is possible to control the reception sensitivity by controlling the value of M.
[0241]
From the above, in the embodiment of the GPS receiver using the second example of the synchronization acquisition, the second example of the synchronization acquisition is used in the high sensitivity mode, and in the high speed mode, Thus, the unit data length for detecting the correlation point is set to one cycle length of the spread code.
[0242]
Note that the second example of the synchronization acquisition may be used not only in the high sensitivity mode but also in the high speed mode.
[0243]
Further, in the case of using the second example of the synchronization acquisition not only in the high sensitivity mode but also in the high speed mode, the value of M that determines the unit data length for detecting the correlation point is set to the high speed mode in the high sensitivity mode. You may comprise so that it may become larger than the case of.
[0244]
Even in the case of the second example of the synchronization acquisition, the spread code c at the time of receiving the satellite signal is stored in the memory by storing in advance the spread codes corresponding to the respective satellites. The FFT calculation of (n) can be omitted.
[0245]
[Third example of synchronization acquisition by digital matched filter]
In the second example of the above-described synchronization acquisition, the received signal r (n) including M periods (M> 1) of the spread code is subjected to FFT processing, thereby enabling search for an unknown carrier frequency and reception. Although the sensitivity can be improved, the number of data samples is changed from N to M times M in the case of one spread code period, so that the FFT calculation time becomes long and the memory 102 Capacity increases. A third example of synchronization acquisition improves on this problem.
[0246]
As shown in FIG. 26, since there are only M frequency components in the FFT result R (K) when the M period (M> 1) of the spread code is used as the FFT processing unit, M of those frequency components exist. Components between every other frequency component are not necessary.
[0247]
Here, the FFT result R (K) (where 0 ≦ K <NM) is changed to R (i × M), R (i × M + 1), R (i × M + 2),..., R (i × M + M -1) Divide into M groups (0 ≦ i <N). For simplicity of explanation, FIGS. 28 to 31 show examples of split spectrums of each set when M = 4 sets. Although the carrier frequency is unknown, one of the M sets has the energy of the GPS signal to be detected for correlation. In the example of FIGS. 28 to 31, the frequency component of the received signal r (n) is included in the set of R (i × M) in FIG. 28, and the other three split spectrums have only noise. ing.
[0248]
In an actual signal, the carrier frequency k ₀ Is exactly k ′ = k ₀ For example, k ₀ Is k ₀ 'And k ₀ Between '+1', that is, k ₀ '≦ K <k ₀ If it is '+1, k' = k ₀ 'And k' = k ₀ Correlation is detected both with '+1, k ₀ The closer to, the greater the correlation.
[0249]
When the FFT result R (K) is divided into M sets as described above, if M is a power of 2, each set can be calculated independently from the nature of the FFT calculation procedure.
[0250]
FIG. 32 is a signal flow diagram of FFT calculation of eight pieces of data g (0) to g (7). If the FFT result G (K) in FIG. 32 is divided into every fourth data, (G (0), G (4)), (G (1), G (5)), (G (2)) , G (6)), (G (3), G (7)). If attention is paid to (G (0), G (4)), it is understood that only the calculation shown in FIG. 33 is sufficient. The structure of this calculation is the same in the other groups (G (1), G (5)), (G (2), G (6)), (G (3), G (7)). It will be.
[0251]
When these four sets of data are examined one by one, first, (G (0), G (4)) is calculated, and when the examination is completed, the memory storing (G (0), G (4)) is stored. Open and go to the next group. (G (1), G (5)), (G (2), G (6)), (G (3), G (7)) By performing the above, the memory can have a memory capacity that is ¼ that of obtaining FFT for G (0) to G (7) collectively. The number of multiplications is the same when the calculation is divided into M and when the FFT calculation is performed collectively.
[0252]
The same as the above example, by making M a power of 2, R (i × M), R (i × M + 1), R (i × M + 2),..., R (i × M + M− The capacity of the memory that can be applied to 1) and stores the FFT result is 1 / M of MN, that is, N. In addition, when detecting correlation in the order of R (i × M), R (i × M + 1), R (i × M + 2),. If points can be detected, there is no need to examine the remaining pairs, so it can be expected that the processing time will be shorter than when the received signals for each M cycles of the spread code are detected by FFT processing.
[0253]
The flow of processing in the synchronization acquisition unit 20 in the third example of synchronization acquisition described above will be described with reference to the flowcharts of FIGS. In the examples of FIGS. 34 and 35, in order to minimize the number of FFTs, the carrier frequency search is performed for all the target satellites for each FFT set. Note that the flowcharts of FIGS. 34 and 35 mainly correspond to software processing in the DSP 23.
[0254]
First, a variable u (0 ≦ u <M) for the number of divided groups of R (K) (where 0 ≦ K <NM and K = i × M + u) is initialized (step S111), and then the frequency The IF data from the conversion unit 10 is sampled by the sampling circuit 21, and the sampling data is converted into M cycles of the spread code, for example, 16 cycles (16 milliseconds), and the signal r (n) (where 0 ≦ n ≦ MN ) To the RAM 22 (step S112). Next, the signal r (n) is FFTed by the FFT processing unit 101, and the FFT result R (K) is written in the memory 102 (step S113). Next, the FFT result C (k) of the spread code corresponding to the GPS satellite that received the signal is set in the memory 106 (step S114).
[0255]
Next, the initial value k of the shift amount of the read address from the memory 102 of the FFT result R (K) of the received signal r (n). ₀ 'Is determined from, for example, past data (step S115). And the determined initial value k ₀ 'Is set as the shift amount k of the read address of the FFT result from the memory 102, and the shift control change count v is set to the initial value v = 0 (step S116).
[0256]
Next, the FFT result R (K) of the received signal r (n) is read from the memory 102 with its read address shifted by k ′ (step S117). Then, the readout FFT result R (K−k ′) is multiplied by the complex conjugate of the FFT result C (k) of the spread code to obtain a correlation function F ′ (k) (step S118).
[0257]
Next, inverse FFT of the correlation function F ′ (k) is performed to obtain a time domain function f ′ (n) (step S119). Then, a peak value f ′ (np) is obtained for this function f ′ (n) (step S120), and it is determined whether or not the peak value f ′ (np) is larger than a preset threshold value fth. (Step S121 in FIG. 35).
[0258]
In step S121, when it is determined that the peak value f ′ (np) is larger than the preset threshold value fth, the discrete time (spread code phase) np for taking the peak value f ′ (np) is set. It is detected as a correlation point (step S122).
[0259]
Then, it is determined whether or not the detected correlation point np is the fourth one (step S123). When it is determined that the detected correlation point np is the fourth, the CPU 41 starts the receiver position calculation process, and the synchronization holding unit 30. The synchronization holding process is performed (step S124). Thereafter, the process proceeds to step S125. The process in step S124 may be performed for the fourth and subsequent items.
[0260]
It should be noted that the Doppler shift amount for the GPS satellite being received and the GPS receiver from the variable u regarding the number of divided sets of the shift amount k ′ and R (k) when the correlation point np detected in step S122 is obtained. The error of the oscillation frequency can be estimated.
[0261]
If it is determined in step S123 that the detected correlation point np is other than the fourth one, it is determined whether or not the above-described spread code synchronization search process has been completed for all satellites to be searched (step S125). When it is determined that the spread code synchronization search process for all satellites has been completed, it is determined whether or not the variable u is smaller than the maximum value M (step S127). If it is smaller, the variable u is incremented (step S128), and thereafter Then, the process returns to step S113, and the processes after step S113 are repeated.
[0262]
If it is determined in step S127 that the variable u is equal to or greater than the maximum value M, the search operation is terminated (step S129).
[0263]
If it is determined in step S125 that there is a satellite for which the spread code synchronization search has not ended, the satellite for which the spread code synchronization search is performed next is selected, and the spread code c (n) used by the selected satellite is spread. The sign is changed (step S126). And it returns to step S114 and performs the process after step S114 mentioned above.
[0264]
As a result of the determination in step S121, when the peak value f ′ (np) is smaller than the preset threshold value fth and a correlation point cannot be detected, it is determined what the current mode is (see FIG. 11 step S21). When it is determined that the current mode is the high sensitivity mode, the shift control change count v is set to a preset maximum value v. _max Or less (step S131 in FIG. 36). This maximum value v _max Corresponds to 1 kHz when converted to frequency.
[0265]
The shift control change count v is a preset maximum value v. _max It is determined whether it is smaller than (step S132). This maximum value v _max Corresponds to 1 kHz when converted to frequency.
[0266]
The shift control change count v is a preset maximum value v. _max When it is determined that the shift control change number is smaller than 1, the shift control change count v is incremented by 1 (v = v + 1), and a new shift amount k ′ is
k ′ = k ′ + (− 1) ^v × v
(Step S133), the process returns to Step S117. Then, the processes after step S117 described above are repeated.
[0267]
In step S132, the shift control change count v is set to a preset maximum value m. _max If it is determined that the number of times is greater than the predetermined number of times, it is determined whether or not the number of times determined to be larger is equal to or greater than a predetermined number of times predetermined for the current data in the RAM 22 (step S136). If not, the process returns to step S112, new data is taken into the RAM 22, and the above processing is repeated.
[0268]
If it is determined in step S136 that the number of times is equal to or greater than the predetermined number, it is determined whether or not the above-described spread code synchronization search process has been completed for all satellites to be searched (step S137). When it is determined that the spread code synchronization search process has been completed, it is determined whether or not the variable u is smaller than the maximum value M (step S138). If it is smaller, the variable u is incremented (step S139), and then the process returns to step S113. Then, the processing after step S113 is repeated.
[0269]
If it is determined in step S138 that the variable u is equal to the maximum value M or greater than the maximum value M, the control calculation unit 40 is notified that synchronization acquisition has failed (step S140), and then the search operation is performed. The process ends (step S141).
[0270]
If it is determined in step S137 that there is a satellite for which the spread code synchronization search has not ended, the satellite for which the spread code synchronization search is performed next is selected, and the spread code c (n) used by the selected satellite is spread. The sign is changed (step S142). And it returns to step S114 and performs the process after step S114 mentioned above.
[0271]
In addition, when the carrier frequency is known, it corresponds to R (i × M), R (i × M + 1), R (i × M + 2),..., R (i × M + M−1). If only the signal is calculated, the method of FFT of the received signal in units of time including multiple periods of the spread code can be similarly applied.
[0272]
[Fourth example of acquisition of synchronization by digital matched filter]
In the case of the second and third examples of the synchronization acquisition described above, M cycles of the spread code are taken into the RAM 22, and the DSP 23 reads the data for the M cycles and performs the FFT processing as described above. The synchronization acquisition process is performed. For this reason, there is a possibility that the processing data amount in the DSP 23 is large, the calculation amount is large, and the processing speed is slow.
[0273]
As described in the second example, the fourth example of this acquisition of synchronization captures IF data for M cycles of a spread code, for example, 16 cycles (16 milliseconds), into the RAM 22, and data for the M cycles. The unit performs synchronization acquisition processing with FFT operation. Before performing FFT processing in the FFT processing unit 101, preprocessing for reducing the number of data samples is performed to increase the processing speed. It is. Note that the sampling frequency in the sampling circuit 21 is, for example, 4.096 MHz.
[0274]
FIG. 37 shows a configuration example of the DSP 23 in the fourth example. In the fourth example, a pre-processing unit 130 is provided before the FFT processing unit 101. Other configurations are the same as those in the above example.
[0275]
The preprocessing unit 130 includes a RAM, and the memory capacity is one cycle of the spread code. That is, in this fourth example, the data for M cycles taken into the RAM 22 is equivalent to the data for one cycle of the same spreading code being repeated M times, and will be described in the second example of synchronization acquisition. As described above, since there is only a frequency component having data for one cycle of the spreading code, the preprocessing unit 130 determines one cycle of the spreading code from the data amount of M cycles of the spreading code. To reduce the amount of data in minutes.
[0276]
In this fourth example, as a preprocessing, a subset of discrete Fourier transform of data d (n) for M periods (0 ≦ n <L, L is the total number of data for M periods of the spread code) ( An algorithm for calculating S [0], S [1]... S [N-1] (where N is the number of sampling data for one period of the spread code) is performed. Here, the subset S [k] (k is a discrete frequency after the discrete Fourier transform and 0 ≦ k <N) can be defined as follows.
[0277]
S [k] = D [k × M + r]
Where D is the discrete Fourier transform of the data d,
M = L / N,
r is a constant according to the Doppler frequency, 0 ≦ r <M.
[0278]
FIG. 38 is a flowchart for executing an algorithm performed by the preprocessing unit 130.
[0279]
First, the variable k is initialized (k = 0) (step S151), and then S [k] = 0 is set to initialize the subset S [k] (step S152). Then, a repetitive variable t (0 ≦ t <M) is initialized (t = 0) (step S153). Next, the following (formula Q1) is calculated (step S154).
[0280]

This processing of (Formula Q1) is performed by the value S [k] where the value of the variable t is “1” before. _old To the next term for the value of the current variable t
d [t × N + k] × exp (2πj · r · t / M)
Is an operation to add.
[0281]
Since data d (n) is data obtained by sampling 1-bit IF digital data from the A / D converter 18, d [t × N + k] is +1 or −1. Therefore, the calculation of (Formula Q1) is one addition or subtraction.
[0282]
Further, in exp (2πj · r · t / M), the variable is only t, and t takes only a value from 0 to M−1, so that the term exp (2πj · r · t / M) By storing the value as a table of M points and using this table, this term exp (2πj · r · t / M) does not have to be calculated every time t is changed. Can be fast.
[0283]
When the calculation of (formula Q1) in step S154 is completed, the variable t is incremented by “1” (step S155). Then, it is determined whether or not the variable t is smaller than M (step S156). When the variable t is smaller than M, the process returns to step S154, and the calculation of (formula Q1) is repeated. When the variable t is greater than or equal to M, the following (formula Q2) is calculated (step S157).
[0284]
S [k] = S [k] _old Xexp (2πj · r · k / L) (formula Q2)
This processing of (Formula Q2) is performed by the value S [k] in which the value of the variable k is "1" before _old To the next term for the current value of the variable k
exp (2πj · r · k / L)
Is an operation of multiplying by.
[0285]
When the calculation of (Formula Q2) in Step S157 is completed, the obtained value of S [k] is written in the memory included in the preprocessing unit 130 (Step S158). Next, the variable k is incremented by “1” (step S159). Then, it is determined whether or not the variable k is smaller than N (step S160). When the variable k is smaller than N, the process returns to step S152 and the above calculation process is repeated. When the variable k is greater than or equal to N, the preprocessing is terminated and the fast Fourier transform process is started.
[0286]
With the above preprocessing, the FFT target is reduced from the L point of the total number of data for the M cycles of the spreading code to the N point for one cycle of the spreading code, so that the FFT operation can be speeded up. it can.
[0287]
[Fifth example of synchronization acquisition by digital matched filter]
As in the fourth example, the fifth example of the synchronization acquisition performs a preprocessing for reducing the number of data samples in the DSP 23 before the FFT processing unit 101 performs the FFT process, thereby increasing the processing speed. It is intended.
[0288]
The configuration example of the DSP 23 in the case of the fifth example is the same as that shown in FIG. 23 in the case of the fourth example. However, in the fifth example, the contents of the preprocessing performed by the preprocessing unit 130 are different from those in the fourth example.
[0289]
In this fifth example as well, the data for M cycles taken into the RAM 22 is equivalent to the data for one cycle of the same spreading code being repeated M times, as described in the second example of synchronization acquisition. Since there is only a frequency component having data for one cycle of the spreading code, the pre-processing unit 130 determines the data for one cycle of the spreading code from the data amount of M cycles of the spreading code. Reduce the amount.
[0290]
FIG. 39 is a diagram for explaining the preprocessing of the fifth example. In the example of FIG. 39, the sampling frequency in the sampling circuit 21 is 4.096 MHz, and M = 16, that is, a case where data is taken into the RAM 22 in units of 16 milliseconds and FFT processing is performed.
[0291]
As shown in FIG. 39, in this example, the IF data stored in the RAM 22 is 16 data groups d1 (n), d2 (n), d3 (n),. d16 (n). In this example, each of the data groups d1 (n), d2 (n), d3 (n),..., D16 (n) consists of 4096 points, and the entire data for 16 milliseconds. Then, it consists of 65536 points.
[0292]
From the head of each of the 16 data groups d1 (n), d2 (n), d3 (n),..., D16 (n), the value of the same point position is , Should have the same component of the spreading code. Moreover, as described above, the data of each point is 1 bit.
[0293]
Considering the above, in the case of the fifth example, as the memory 130MEM included in the preprocessing unit 130, a memory having 16 bits per word and a capacity of 4096 words is used.
[0294]
The data at the same point position from the head of each of the 16 data groups d1 (n), d2 (n), d3 (n),. Write to the same word address of the memory 130MEM to form a word. As a result, the data for 16 milliseconds is taken into the memory 130MEM as 4096 word data.
[0295]
The FFT operation process is executed for the 16-bit 1-word data. If the DSP 23 is capable of 16-bit processing, the number of memory accesses during FFT is 4096, which is 16 minutes compared to 65536 when no preprocessing is performed. 1 and the FFT processing can be speeded up.
[0296]
To generalize the above, in the case where FFT processing is performed with M cycles of data whose number of data for one cycle of the spread code is N as processing units, the preprocessing unit 130 uses the same spread code component. The position data is written to the same word address in the memory 130MEM.
[0297]
That is, when NM pieces of data are numbered sequentially from [0], 0, N, 2N,..., (M−1) Nth data is written to the word address “0” of the memory MEM. 1,1 + N, 1 + 2N,..., 1+ (M−1) Nth data is written to the word address “1” of the memory MEM,..., (N−1), (N−1) + N , (N−1) + 2N,..., (N−1) + (M−1) The Nth data is written to the word address “N−1” of the memory MEM.
[0298]
The FFT operation process is executed for this M-bit 1-word data. If the DSP 23 is capable of processing in units of w bits, the number of memory accesses during FFT is N × M / w times, compared to NM times when no preprocessing is performed. , And the FFT processing can be speeded up.
[0299]
The synchronization acquisition methods of the first to fifth examples described above are time-consuming in principle by the sliding correlator that is a conventional method, but the processing by the digital matched filter using FFT is performed by a high-speed DSP. By doing so, a significant reduction in processing time can be expected. In particular, in the case of the second to fifth examples, synchronization acquisition can be performed with high sensitivity by performing the FFT process in units of M cycles of the spread code.
[0300]
Furthermore, in the case of the third example to the fifth example, the FFT process can be performed at higher speed in units of M cycles of the spread code.
[0301]
Accordingly, the third to fifth examples of synchronization acquisition are used in the high sensitivity mode in the same manner as in the embodiment of the GPS receiver using the second example of synchronization acquisition. Sometimes, as usual, the unit data length for detecting the correlation point can be one cycle length of the spread code.
[0302]
Further, the third to fifth examples of the synchronization acquisition may be used not only in the high sensitivity mode but also in the high speed mode.
[0303]
Further, in the case of using the third to fifth examples of the synchronization acquisition not only in the high sensitivity mode but also in the high speed mode, the value of M for determining the unit data length for detecting the correlation point is set to the high sensitivity. The mode may be configured to be larger than that in the high-speed mode.
[0304]
Note that the correlation calculation method using the digital matched filter used in the above example of synchronization acquisition is not limited to the signal from the GPS satellite, but the spread of the received signal in which the carrier wave is modulated by the signal obtained by spectrum-spreading the data with a spreading code. The present invention can be applied to the case where code and carrier synchronization acquisition is performed. However, in the second example, the third example, the fourth example, and the fifth example, a period that is a multiple of one period of the spreading code is a data bit, as in a GPS satellite signal, and the spreading code The signals for a plurality of periods must be the same signal.
[0305]
If the synchronization acquisition unit 20 can acquire signals from four or more GPS satellites by the synchronization acquisition method as described above, the GPS receiver can determine the GPS receiver from the phase of these spreading codes and the IF carrier frequency. It is possible to calculate the position and velocity. That is, the positioning calculation can be performed without providing the synchronization holding unit 30.
[0306]
However, in order to perform positioning and velocity calculation with sufficient accuracy as a GPS receiver, it is necessary to detect the phase of the spread code and the IF carrier frequency with high accuracy. It is necessary to increase the time length of IF data fetched into the RAM 22.
[0307]
Furthermore, when the digital acquisition filter 20 is configured to use a digital matched filter, it must be considered that the digital matched filter itself does not have a synchronization holding function.
[0308]
If the navigation message is not acquired from the outside of the GPS receiver, the synchronization acquisition unit 20 needs to demodulate the navigation messages of four or more GPS satellites every 20 ms, and the DSP 23 always detects synchronization and the navigation message. Need to be demodulated at a fairly high speed.
[0309]
As described above, if the GPS receiver position calculation and speed calculation are performed with sufficient accuracy only by the synchronization acquisition unit 20, the cost increases due to the increase in the size of the hardware and the power consumption increases. It becomes a big problem at the time of manufacture.
[0310]
Therefore, in this embodiment, the synchronization acquisition with coarse accuracy is performed by the dedicated synchronization acquisition unit 20, and the synchronization holding unit 30 performs synchronization holding of a plurality of GPS satellite signals and demodulation of the navigation message. Then, the synchronization acquisition unit 20 transmits the detected GPS satellite number, the phase of the spread code, the IF carrier frequency, and the signal strength information including the correlation detection signal as data to the synchronization holding unit 30 through the control calculation unit 40. As will be described later, the synchronization holding unit 30 starts the operation using the data as an initial value.
[0311]
[Configuration of Synchronization Holding Unit 30]
In order to perform synchronization holding of a plurality of GPS satellite signals in parallel, the synchronization holding unit 30 includes a plurality of channels with each GPS satellite signal as one channel.
[0312]
FIG. 40 shows a configuration example of the synchronization holding unit 30 in this embodiment. The synchronization holding unit 30 includes channel synchronization holding units 30CH1, 30CH2,..., 30CHn for n channels and a control register 33. Each of the channel synchronization holding units 30CH1, 30CH2,..., 30CHn includes a Costas loop 31 and a DLL (Delay Locked Loop) 32.
[0313]
The control register 33 is connected to the CPU 41 of the control calculation unit 40 and receives parameters for determining the loop filter parameters of the Costas loop 31 and DLL 32 and filter characteristics, as will be described later. The data is set in the part designated by the CPU 41. The control register 33 receives correlation value information and frequency information from the Costas loop 31 and the loop filter of the DLL 32, and passes the information to the CPU 41 in response to access from the CPU 41.
[0314]
[Configuration of Costas Loop 31 and DLL 32]
FIG. 41 is a block diagram illustrating a configuration example of the Costas loop 31, and FIG. 42 is a block diagram illustrating a configuration example of the DLL 32.
[0315]
The Costas loop 31 is a part that holds IF carrier frequency synchronization and extracts a navigation message that is transmission data, and the DLL 32 is a part that holds phase synchronization of a spread code of a GPS satellite signal. The Costas loop 31 and the DLL 32 cooperate to perform spectrum despreading on the GPS satellite signal to obtain a pre-spread signal, and to demodulate the pre-spread signal to obtain a navigation message for control. It supplies to CPU41 of the calculating part 40. FIG. Hereinafter, the operation of the Costas loop 31 and the DLL 32 will be specifically described.
[0316]
[About Costas Loop 31]
The IF data from the frequency conversion unit 10 is supplied to the multiplier 201. The multiplier 201 is supplied with the spreading code from the spreading code generator 320 of the DLL 32 shown in FIG.
[0317]
The spread code generator 320 of the DLL 32 generates three phase spread codes: a coincidence (prompt) spread code P, a lead (early) spread code E, and a delay (rate) spread code L. In the DLL 32, as will be described later, the correlation between the forward spreading code E and the delayed spreading code L and the IF data is calculated, and the generation phase of the spreading code from the spreading code generator 320 is set so that the respective correlation values are equal. , So that the phase of the coincidence spreading code P matches the phase of the spreading code of the GPS satellite signal.
[0318]
The despreading multiplier 201 of the Costas loop 31 is supplied with the coincidence spreading code P from the spreading code generator 320 and is despread. The despread IF data from the multiplier 201 is supplied to multipliers 202 and 203.
[0319]
As shown in FIG. 41, the Costas loop 31 includes multipliers 202 and 203, low-pass filters 204 and 205, a phase detector 206, a loop filter 207, an NCO (Numerically Controlled Oscillator) 208, and , A correlation detector 209, a binarization circuit 210, a lock determination unit 211, and a switch circuit 212.
[0320]
The cutoff frequency information of the low-pass filters 204 and 205, the parameters that determine the filter characteristics of the loop filter 207, and the frequency information that determines the oscillation center frequency of the NCO 208 are synchronized with the synchronization acquisition unit 20, as will be described later. Based on the result, it is set from the CPU 41 through the control register 33.
[0321]
The switch circuit 212 is for opening and closing the loop of the Costas loop 31 and is turned on / off by a switching control signal from the CPU 41. In an initial state before the synchronization holding operation is started, the switch circuit 212 is turned off and the loop is opened. As described later, the synchronization holding operation is started and a Costas loop correlation detector is detected. When the correlation output 209 reaches a significant level, the switch circuit 212 is turned on to close the loop.
[0322]
The signal despread in the multiplier 201 is supplied to the multipliers 202 and 203. These multipliers 202 and 203 are supplied with the quadrature phase I (Sine) signal and the Q (Cosine) signal from the NCO 208 that are substantially set to the IF carrier frequency based on the frequency information from the CPU 41 of the control calculation unit 40. Is done.
[0323]
The multiplication results of the multipliers 202 and 203 are supplied to the phase detector 206 through the low-pass filters 204 and 205. The low-pass filters 204 and 205 receive cutoff frequency information from the CPU 41 of the control calculation unit 40 and remove out-of-band noise from signals supplied thereto.
[0324]
The phase detector 206 detects a phase error between the IF carrier and the frequency signal from the NCO 208 based on the signals from the low-pass filters 204 and 205, and supplies this phase error to the NCO 208 via the loop filter 207. As a result, the NCO 208 is controlled so that the phase of the output frequency signal from the NCO 208 is synchronized with the IF carrier component.
[0325]
Note that the loop filter 207 integrates the phase error information from the phase detector 206 in accordance with parameters supplied from the CPU 41 of the control calculation unit 40 to form an NCO control signal for controlling the NCO 208. As described above, the NCO 208 is configured such that the phase of the output frequency signal from the NCO 208 is synchronized with the IF carrier component by the NCO control signal from the loop filter 207.
[0326]
The outputs of the low-pass filters 204 and 205 of the Costas loop 31 are supplied to the correlation detector 209. The correlation detector 209 squares the output signals of the low-pass filters 204 and 205 supplied thereto, adds them, and outputs the result. The output of the correlation detector 209 indicates the correlation value CV (P) between the IF data and the coincidence spread code P from the spread code generator 320. The correlation value CV (P) is passed to the CPU 41 of the control calculation unit 40 through the control register 33.
[0327]
The output signal of the low-pass filter 204 is supplied to the binarization circuit 210, and navigation message data is output from the binarization circuit 210.
[0328]
Further, the correlation value CV (P) output from the correlation detector 209 is supplied to the lock determination unit 211. The lock determination unit 211 compares the correlation value CV (P) output with a predetermined threshold value. When the correlation value CV (P) output is larger than the threshold value, the synchronization hold is locked. When the correlation value CV (P) output is smaller than the threshold value, a lock determination output indicating that the synchronization holding is in the unlocked state is output.
[0329]
In this embodiment, this lock determination output is sent to the CPU 41 of the control calculation unit 40, and the CPU 41 recognizes the lock state and the unlock state of the synchronization holding unit 30 from this lock determination output.
[0330]
[About DLL32]
As shown in FIG. 42, in the DLL 32, the IF data from the frequency conversion unit 10 is supplied to multipliers 301 and 311. The multiplier 301 is supplied with the forward spreading code E from the spreading code generator 320, and the multiplier 311 is supplied with the delayed spreading code L from the spreading code generator 320.
[0331]
The multiplier 301 performs spectrum despreading by multiplying IF data and the advance spread code E, and supplies the despread signals to the multipliers 302 and 303. The multiplier 302 is supplied with the I signal from the NCO 208 of the aforementioned Costas loop 31, and the multiplier 303 is supplied with the Q signal from the NCO 208.
[0332]
The multiplier 302 multiplies the despread IF data by the I signal from the NCO 208 and supplies the result to the correlation detector 306 through the low-pass filter 304. Similarly, the multiplier 303 multiplies the despread IF data and the Q signal from the NCO 208 and supplies the result to the correlation detector 306 through the low-pass filter 305.
[0333]
Note that the low-pass filters 304 and 305 receive the cutoff frequency information from the CPU 41 of the control calculation unit 40 as in the case of the low-pass filters 204 and 205 of the Costas loop 31, and reduce the out-of-band noise of the signal supplied thereto. To be removed.
[0334]
The correlation detector 306 squares and adds the output signals from the low-pass filters 304 and 305 supplied thereto and outputs the result. The output from the correlation detector 306 indicates the correlation value CV (E) between the IF data and the forward spread code E from the spread code generator 320. The correlation value CV (E) is supplied to the phase detector 321 and stored in the control register 33 so that the CPU 41 of the control calculation unit 40 can use it.
[0335]
Similarly, the multiplier 311 performs spectrum despreading by multiplying the IF data and the delay spread code L, and supplies the despread signals to the multipliers 312 and 313. As described above, the multiplier 312 is supplied with the I signal from the NCO 208, and the multiplier 313 is supplied with the Q signal from the NCO 208.
[0336]
The multiplier 312 multiplies the despread IF data by the I signal from the NCO 208 and supplies the result to the correlation detector 316 through the low-pass filter 314. Similarly, the multiplier 313 multiplies the despread IF data by the Q signal from the NCO 208 and supplies the result to the correlation detector 316 through the low-pass filter 315. The low-pass filters 314 and 315 receive cut-off frequency information from the CPU 41 of the control calculation unit 40 and remove out-of-band noise from signals supplied thereto, as with the low-pass filters 304 and 305 described above. is there.
[0337]
The correlation detector 316 squares and adds the output signals from the low-pass filters 314 and 315 supplied thereto, and outputs the calculation result. The output from the correlation detector 316 indicates the correlation value CV (L) between the IF data and the delayed spread code L from the spread code generator 320. The correlation value CV (L) is supplied to the phase detector 321 and stored in the control register 33 so that the CPU 41 of the control calculation unit 40 can use it.
[0338]
The phase detector 321 calculates the difference between the coincidence spread code and the spread code of the GPS satellite signal as a difference between the correlation value CV (E) from the correlation detector 306 and the correlation value CV (L) from the correlation detector 316. A phase difference is detected, and a signal corresponding to the phase difference is supplied as a numerical control signal of the NCO 323 via the loop filter 322.
[0339]
An output signal of the NCO (Numerically Controlled Oscillator) 323 is supplied to the spread code generator 320, and the spread frequency from the spread code generator 320 is controlled by controlling the output frequency of the NCO 323. The generation phase of the code is controlled.
[0340]
As will be described later, the NCO 323 is supplied with frequency information for controlling the initial oscillation frequency from the CPU 41 of the control calculation unit 40 according to the synchronization acquisition result of the synchronization acquisition unit 20.
[0341]
The NCO 323 is controlled by the loop control in the DLL 32 described above, and the spread code generator 320 allows the spread code P, E, L so that the correlation value CV (E) and the correlation value CV (L) have the same level. Controls the generation phase. As a result, the coincidence spread code P generated from the spread code generator 320 is phase-synchronized with the spread code in which IF data is spread spectrum. As a result, the coincidence spread code P causes the IF data to be accurately reverse spectrum. The navigation message data is demodulated and output from the binarization circuit 210 in the Costas loop 31.
[0342]
The demodulated output of the navigation message data is supplied to a data demodulation circuit (not shown), demodulated into data usable by the control calculation unit 40, and then supplied to the control calculation unit 40. In the control calculation unit 40, the navigation message data is used for positioning calculation, and orbit information (almanac information and ephemeris information) is extracted as appropriate and stored in the orbit information memory 46.
[0343]
The loop filter 322 of the DLL 32 integrates the phase error information from the phase detector 321 based on the parameters supplied from the CPU 41 of the control calculation unit 40, similarly to the loop filter 207 of the Costas loop 31 described above. The NCO control signal for controlling the NCO 323 is formed.
[0344]
Also in the DLL 32, a switch circuit 324 for loop opening / closing control is provided between the loop filter 322 and the NCO 320, and is turned on / off by a switching control signal from the CPU 41.
[0345]
In an initial state before the synchronization holding operation is started, the switch circuit 324 is turned off and the loop is opened. As described later, the synchronization holding operation is started and the correlation detector of the Costas loop is started. When the correlation output 209 reaches a significant level, the switch circuit 324 is turned on to close the loop.
[0346]
[Transition from synchronization acquisition to synchronization maintenance]
In this embodiment, as described above, the synchronization acquisition unit 20 uses the detected GPS satellite number, the phase of the spread code, the IF carrier frequency, and the signal strength information as data as the CPU 41 of the control calculation unit 40. To pass. The signal strength information is not essential as information for shifting to the synchronization holding process.
[0347]
Based on the acquired data, the CPU 41 of the control calculation unit 40 generates data to be supplied to the synchronization holding unit 30 and passes it to the synchronization holding unit 30. The synchronization holding unit 30 starts the synchronization holding operation using the data as an initial value.
[0348]
The data passed from the CPU 41 of the control arithmetic unit 40 to the synchronization holding unit 30 is a numerical value for determining the initial oscillation frequency (oscillation center frequency) of the NCO 323 that controls the generation phase of the spread code from the spread code generator 320 of the DLL 32. Information, numerical information for determining the initial oscillation frequency (oscillation center frequency) of the NCO 208 of the Costas loop 31, parameters for determining the filter characteristics of the loop filters 207 and 322, low-pass filters 204, 205, 304, This is coefficient information for determining the cutoff frequencies of 305, 314, and 315 and determining the width of the frequency band.
[0349]
At this time, the information supplied from the CPU 41 to the synchronization holding unit 30 determines the GPS satellite number, phase and frequency at which the synchronization holding unit 30 starts the synchronization holding of the spread code and the synchronization holding of the IF carrier, and the filter characteristics. The CPU 41 generates the initial value data so as to start synchronization holding from the vicinity of the phase of the spread code and the IF carrier frequency detected as a result of synchronization acquisition by the synchronization acquisition unit 20. To do.
[0350]
Therefore, the synchronization holding unit 30 can start the synchronization holding operation from the vicinity of the phase of the spread code detected by the synchronization acquisition unit 20 and the vicinity of the detected IF carrier frequency to quickly set the synchronization holding locked state. become able to.
[0351]
By the way, in order for the GPS receiver to calculate the position and velocity, it is necessary to establish and maintain synchronization for four or more GPS satellites from the start of synchronization acquisition. Next, an example of a process until the synchronization acquisition unit 20 and the synchronization holding unit 30 and the CPU 41 that controls both of them hold the synchronization of signals from four or more GPS satellites will be described.
[0352]
[Example of synchronization acquisition / synchronization holding process]
In this example, when the synchronization acquisition unit 20 acquires one of the GPS satellite signals in synchronization, the CPU 41 immediately sends an interrupt instruction for starting the synchronization holding operation, the GPS satellite number as the synchronization acquisition result, and its spreading code. The signal strength representing the phase, IF carrier frequency, and correlation detection level is transferred, and when the transfer is completed, the synchronization acquisition for another GPS satellite is started.
[0353]
Each time the CPU 41 receives an interrupt instruction from the synchronization acquisition unit 20, the CPU 41 assigns an independent channel to the synchronization holding unit 30, sets an initial value, and starts a synchronization holding operation.
[0354]
FIG. 43 is a flowchart for explaining the flow of the synchronization acquisition process in the synchronization acquisition unit 20 in an example of the synchronization acquisition / synchronization holding process.
[0355]
First, initial setting for acquisition of synchronization is performed (step S171). In this initial setting, a GPS satellite to be searched for acquisition of synchronization and the search order are set based on valid orbit information stored in the orbit information memory 46 by the GPS receiver. Also, the carrier frequency considering the Doppler shift is calculated from the trajectory information, and the center and range of the IF carrier frequency to be searched are set.
[0356]
Also, if the GPS receiver has known the approximate oscillator error obtained in the past operation before turning on the power, the GPS receiver position is stored at the time of turning on the power, that is, the power is turned off last time. If the center and range of the IF carrier frequency to be searched are determined in accordance with the Doppler shift calculated from the trajectory information on the assumption that the position is the immediately preceding position, the time required until synchronization can be further reduced.
[0357]
When the initial setting is completed, one GPS satellite to be synchronously acquired is set according to the search order (step S172). As a result, the satellite number to be synchronized is determined, and the spread code for which the correlation is to be detected is determined.
[0358]
Next, the synchronization acquisition unit 20 starts fetching IF data sampled by the sampling circuit 21 into the RAM 22, and starts a timer at this start timing (step S173). Here, the timer 45 of the control calculation unit 40 is used as this timer. The timer 45 is also used when setting the synchronization holding process start timing, as will be described later.
[0359]
Next, in the DSP 23, correlation detection processing is performed on the spread code of the GPS satellite signal set in step S172, using any of the above-described examples of synchronization acquisition using the digital matched filter (step S174).
[0360]
Then, it is determined whether or not a correlation has been detected with respect to the spread code of the GPS satellite signal, that is, whether or not the GPS satellite signal has been acquired synchronously (step S175). And the information of the GPS satellite number, the phase of the spread code, the IF carrier frequency, and the signal strength are passed to the CPU 41 as a detection result of the synchronization acquisition (step S176).
[0361]
Then, it is determined whether or not the synchronization acquisition search for all of the GPS satellites to be searched has been completed (step S177), and if there are still GPS satellites to be searched, the process returns to step S172 and the next GPS to be synchronized and acquired. Set the satellite and repeat the above acquisition process. If it is determined in step S177 that the synchronization acquisition has been completed for all GPS satellites to be searched, the synchronization acquisition operation is terminated and the synchronization acquisition unit 20 is set to a standby state (standby state).
[0362]
When it is determined in step S175 that the correlation cannot be detected, it is determined whether or not the state has exceeded a predetermined time (step S178). If the predetermined time has not elapsed, the process returns to step S175 to return to the correlation. Continue detection.
[0363]
When it is determined in step S178 that the predetermined time has elapsed, the process proceeds to step S177, where it is determined whether or not the synchronization acquisition search for all the GPS satellites to be searched has been completed, and when there are still GPS satellites to be searched. Returning to step S172, the next GPS satellite to be synchronized is set, and the above-described synchronization capturing process is repeated.
[0364]
If it is determined in step S177 that the synchronization acquisition has been completed for all GPS satellites to be searched, the synchronization acquisition operation is terminated and the synchronization acquisition unit 20 is set to a standby state (standby state).
[0365]
In this embodiment, the CPU 41 can perform on / off control of power supply to the synchronization capturing unit 20 or on / off control of operation clock supply from the multiplication / frequency dividing circuit 3 to the synchronization capturing unit 20. In the standby state of the synchronization acquisition unit 20 described above, the CPU 41 turns off the power supply to the synchronization acquisition unit 20 or stops the operation clock supply, thereby suppressing unnecessary power consumption. Yes.
[0366]
When the synchronization acquisition unit 20 is configured with a digital matched filter as described above, it is desirable to operate with a high clock in order to speed up the FFT calculation in the DSP 23, and thus power consumption during operation increases. When the synchronization acquisition unit 20 finishes detecting synchronization acquisition of signals from all the initially set GPS satellites and the synchronization holding unit 30 holds four or more synchronizations, the role of the synchronization acquisition unit 20 ends.
[0367]
In this embodiment, as described above, the CPU 41 is in a standby state after the end of the role of the synchronization capturing unit 20, so that unnecessary power consumption in the synchronization capturing unit 20 is suppressed.
[0368]
In the above example, the CPU 41 shifts the synchronization acquisition unit 20 to the standby state after completing the synchronization acquisition for all the initially set GPS satellites. However, the synchronization holding unit 30 can hold the synchronization. After confirming that the number of GPS satellites is four or more, the CPU 41 may cause the synchronization acquisition unit 20 to shift to a standby state.
[0369]
Of course, the CPU 41 can return the synchronization acquisition unit 20 once in the standby state to the operation state when the synchronization acquisition unit 20 needs to be re-synchronized.
[0370]
Next, the control processing of the synchronization holding unit 30 performed by the CPU 41 that has received an interrupt instruction from the synchronization capturing unit 20 will be described with reference to the flowcharts of FIGS. 44 and 45.
[0371]
44, when the CPU 41 receives from the synchronization acquisition unit 20 information on the phase of the spread code, IF carrier frequency, GPS satellite number, and signal strength as an interrupt instruction and synchronization acquisition result, This is a process for allocating and starting synchronization holding. FIG. 45 is a flowchart for controlling synchronization holding processing in each channel of the synchronization holding unit 30 that has been started to hold synchronization by the CPU 41. First, the synchronization holding start process of FIG. 44 will be described.
[0372]
First, when the GPS receiver is turned on, the CPU 41 performs initial setting of constants to the NCO, low-pass filter, loop filter, etc. of the synchronization holding unit 30 (step S181). At this time, the Costas loop 31 and the DLL 32 are both initially in the loop open state.
[0373]
Next, the CPU 41 monitors the interrupt instruction from the synchronization acquisition unit 20 (step S182), and when detecting the interrupt instruction, the CPU 41 receives the GPS satellite number, the phase of the spread code, the IF carrier frequency, and the signal strength from the synchronization acquisition unit 20. Is set so that an independent channel is assigned to the received GPS satellite number (step S183).
[0374]
Then, the CPU 41 calculates the synchronization holding start timing from the phase of the spread code received from the synchronization acquisition unit 20, and also supplies the initial value supplied to each part in the allocated channel of the synchronization holding unit 30 to the synchronization acquisition unit 20. Is generated based on the IF carrier frequency received from (step S184).
[0375]
Then, the CPU 41 sends the generated initial value to each part in the channel assigned in step S183 of the synchronization holding unit 30 through the control register 33, and also in the channel assigned in step S183 in the synchronization holding unit 30. The generation phase of the coincidence spread code P from the spread code generator 320 is controlled to be the synchronization hold start timing, and the synchronization hold operation is started (step S185). At this time, the Costas loop 31 and DLL 32 remain open.
[0376]
As described above, a channel for holding synchronization is assigned to the GPS satellite signal acquired in synchronization, and when synchronization holding is started, the process returns to step S182 to wait for the next interrupt.
[0377]
Next, the synchronization holding process for each channel started as described above will be described with reference to the flowchart of FIG.
[0378]
First, the CPU 41 determines whether or not the correlation value CV (P) from the synchronization holding unit 30 has become a significant level (step S191), and when the correlation value CV (P) has become a significant level, the Costas loop 31. Then, the loop of the DLL 32 is closed and the synchronization holding operation is performed (step S192).
[0379]
Next, the CPU 41 monitors the lock determination output from the lock determination unit 211 of the Costas loop 31 of the synchronization holding unit 30 (step S193). Is incremented by 1 (step S194), and the synchronization holding state is continued (step S195).
[0380]
Then, during this synchronization holding operation, the CPU 41 monitors the lock determination output from the lock determination unit 211 of the Costas loop 31 (step S196), and when the synchronization holding lock is confirmed, returns to step S195 to hold the synchronization holding. Continue state. When it is determined in step S196 that the synchronization holding lock is released, the number of GPS satellites held in synchronization is decremented by 1 (step S197), and the processing when the synchronization holding is released is performed. Processing when the synchronization hold is lost will be described later.
[0381]
When the CPU 41 determines that the synchronization holding unit 30 has held the synchronization of four or more GPS satellite signals, the CPU 41 calculates the position of the GPS receiver and the velocity.
[0382]
When it is determined in step S191 that the correlation value CV (P) does not reach a significant level, it is determined whether or not the state has exceeded a predetermined time (step S199). When it is determined that the predetermined time has elapsed, The channel of the synchronization holding unit 30 assigned in step S183 in FIG. 44 is returned to the empty channel, and the synchronization holding of the channel is stopped (step S200).
[0383]
In step S193, when the lock state cannot be detected by the lock determination output, it is determined whether or not the predetermined time has passed for a predetermined time (step S201), and when it is determined that the predetermined time has passed, step S183 is determined. The channel of the synchronization holding unit 30 assigned in step 1 is returned to the empty channel, and the synchronization holding of the channel is stopped (step S200).
[0384]
Steps S199, S201, and S200 are provided for the following reason. That is, even if the correlation detected by the synchronization capturing unit 20 is at a significant level, there may be a false synchronization that occurs accidentally due to noise. The synchronization holding unit 30 does not establish synchronization for a false synchronization that does not persist, such as occurs unexpectedly. Therefore, if synchronization cannot be established within a certain search time by the synchronization holding unit 30, the synchronization holding operation is stopped, the assigned channel is returned to the free channel state, and the next interrupt is waited for. Is.
[0385]
By the way, in step S184 of FIG. 44 described above, the CPU 41 holds the synchronization so that the phase of the spreading code from the spreading code generator 320 of the synchronization holding unit 30 matches the phase of the spreading code detected by the synchronization acquisition unit 20. It is necessary to calculate the synchronization hold start timing of the unit 30, but at the time of the calculation, a predetermined time has elapsed until the synchronization acquisition of one GPS satellite signal is completed in the synchronization acquisition unit 20, and the Doppler It is necessary to consider that it is affected by the shift and the error of the reference oscillator 2 of the GPS receiver.
[0386]
The latter problem is due to the fact that the IF carrier frequency includes an error of the original reference oscillator 2 that generates a sampling clock to be taken into the memory of the IF data from the frequency converter 10.
[0387]
In this embodiment, since the synchronization acquisition unit 20 and the synchronization holding unit 30 operate with a clock having the same reference oscillator 2 as a transmission source, the synchronization acquisition unit 20 and the synchronization holding unit 30 have exactly the same frequency. It will have an error. Therefore, regarding the synchronization of the IF carrier, there is no problem with respect to starting the operation using the IF carrier frequency detected by the synchronization acquisition unit 20 by the synchronization holding unit 30 as an initial value.
[0388]
As described above, the synchronization acquisition unit 20 searches for a significant correlation according to the order in which the CPU 41 detects the GPS satellites determined from the orbit information. When the synchronization acquisition unit 41 can detect the first satellite with a reliable signal strength, the CPU 41 assigns one channel of the synchronization holding unit 30 and detects the detected satellite number and spreading code, as in the first example. The phase and IF carrier frequency are set, and the synchronization holding operation is started.
[0389]
[Other Embodiments]
In the above description of the embodiment, the detection result from the synchronization acquisition unit 20 is passed to the synchronization holding unit 30 via the CPU 41. However, as described above, the detection result directly from the synchronization acquisition unit 20 to the synchronization holding unit 30 is provided. Can be configured to be handed over.
[0390]
In the above example, a digital matched filter is used as the synchronization acquisition unit 20. However, in the present invention, the synchronization acquisition unit performs coarse accuracy synchronization acquisition, and passes the result to the synchronization holding unit. Since the purpose is to speed up the establishment of synchronization, the synchronization acquisition unit 20 is not limited to an example using a digital matched filter.
[0390]
Further, the digital matched filter is not limited to the example using the FFT as in the above example, but can be configured to use the transversal filter as described above.
[0392]
When the high sensitivity mode is set indoors and the high speed mode is set outdoors, the GPS receiver is provided with means for detecting whether it is indoors or outdoors, and the positioning mode is automatically set according to the detection result. You can also As a means for detecting indoors or outdoors, for example, a transmission antenna is attached to the housing of a GPS receiver so that the radiation direction of the radio wave is always in the vertical direction around the rotation axis. It is possible to use that the reflected wave of the radiated radio wave can be obtained by the receiving means if it is indoors, while the reflected wave of the radio wave is received indoors, but the reflected wave is hardly obtained if it is outdoors.
[0393]
The above is the case of the GPS satellite signal, but this application is not limited to the GPS satellite signal, but uses a spreading code such as GALILEO, which is being developed mainly in European countries. If applicable, it is applicable.
[0394]
【The invention's effect】
As described above, according to the present invention, the high-speed mode in which synchronization acquisition can be performed at high speed and the high-sensitivity mode in which synchronization acquisition can be performed with high sensitivity can be performed according to the use environment. Acquisition of satellite signals can be performed quickly and accurately in accordance with the use environment conditions.
[0395]
Then, by having the operating environment of the receiver provided by the user, the receiver can be switched to an appropriate positioning mode, resulting in a faster time until positioning. It becomes like this.
[0396]
Further, according to the present invention, since the receiver notifies the user of the positioning situation, the user's irritation to the positioning can be alleviated.
[0397]
In addition, according to the present invention, the function of the synchronization acquisition and the synchronization holding is separated, and the synchronization acquisition can be speeded up, so that the time required for the synchronization with the GPS signal from the conventional GPS receiver is shortened, Since the GPS receiver can display the position and speed promptly after the power is turned on, the GPS receiver can be switched between the high speed mode and the high sensitivity mode effectively. That is, in any of the high-speed mode and the high-sensitivity mode, the time until positioning is relatively short, and it is possible to mitigate giving an irritating feeling to the user.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of an embodiment of a positioning satellite signal receiver according to the present invention;
FIG. 2 is a diagram illustrating an example of an appearance of a receiver according to the embodiment.
FIG. 3 is a block diagram illustrating a configuration example of a synchronization acquisition unit that is a part of the receiver of the embodiment of FIG. 1;
4 is a block diagram showing an example of the internal configuration of a DSP that constitutes a part of the synchronization acquisition unit in the example of FIG. 3;
FIG. 5 is a diagram illustrating an example of a correlation result of spreading codes using a digital matched filter.
FIG. 6 is a diagram for explaining a general example of a method for synchronizing a received signal carrier and a spread code;
FIG. 7 is a diagram for explaining a first example of a synchronization acquisition method in the embodiment of the present invention;
FIG. 8 is a diagram illustrating a configuration of a main part considering an operation of a first example of a synchronization acquisition method.
FIG. 9 is a diagram showing a part of a flowchart for explaining the operation of the first example of the synchronization acquisition method;
FIG. 10 is a diagram showing a part of a flowchart for explaining the operation of the first example of the synchronization acquisition method;
FIG. 11 is a diagram showing a part of a flowchart for explaining the operation of the first example of the synchronization acquisition method;
FIG. 12 is a diagram illustrating a configuration of a main part in consideration of the operation of the first example of the synchronization acquisition method.
FIG. 13 is a view showing a part of a flowchart for explaining a positioning mode setting operation in the embodiment of the present invention;
FIG. 14 is a view showing a part of a flowchart for explaining a positioning mode setting operation in the embodiment of the present invention;
FIG. 15 is a diagram for explaining positioning mode setting operation according to the embodiment of the present invention;
FIG. 16 is a diagram for explaining positioning mode setting operation in the embodiment of the present invention;
FIG. 17 is a diagram for explaining positioning mode setting operation in the embodiment of the present invention;
FIG. 18 is a view showing a part of a flowchart for explaining the positioning mode setting operation in the embodiment of the present invention;
FIG. 19 is a diagram for explaining positioning mode setting operation in the embodiment of FIG. 18;
FIG. 20 is a flowchart for explaining positioning mode selection operation processing according to the embodiment of the present invention;
FIG. 21 is a diagram for explaining the positioning mode selection operation processing operation of FIG. 20;
22 is a diagram for explaining the positioning mode selection operation processing operation of FIG. 20;
FIG. 23 is a diagram showing an example of the external appearance of another embodiment of a receiver according to the present invention.
FIG. 24 is a flowchart for explaining positioning mode selection operation processing in another embodiment;
FIG. 25 is a diagram for explaining a second example of the synchronization acquisition method;
FIG. 26 is a diagram for explaining a second example of the synchronization acquisition method;
FIG. 27 is a diagram illustrating a configuration of a main part in consideration of the operation of the second example of the synchronization acquisition method.
FIG. 28 is a diagram for explaining a third example of the synchronization acquisition method;
FIG. 29 is a diagram for explaining a third example of the synchronization acquisition method;
FIG. 30 is a diagram for explaining a third example of the synchronization acquisition method;
FIG. 31 is a diagram for explaining a third example of the synchronization acquisition method;
FIG. 32 is a diagram for explaining a third example of the synchronization acquisition method;
FIG. 33 is a diagram for explaining a third example of the synchronization acquisition method;
FIG. 34 is a diagram showing a part of a flowchart for explaining the operation of the third example of the synchronization acquisition method;
FIG. 35 is a diagram showing a part of a flowchart for explaining the operation of the third example of the synchronization acquisition method;
FIG. 36 is a diagram showing a part of a flowchart for explaining the operation of the third example of the synchronization acquisition method;
FIG. 37 is a block diagram for explaining a fourth example of the synchronization acquisition method;
FIG. 38 is a flowchart for explaining the operation of the main part of the fourth example of the synchronization acquisition method;
FIG. 39 is a diagram for explaining the operation of the main part of the fifth example of the synchronization acquisition method;
40 is a block diagram illustrating a configuration example of a synchronization holding unit that is a part of FIG. 1. FIG.
41 is a block diagram illustrating a configuration example of a Costas loop that constitutes a part of the synchronization holding unit of FIG. 40. FIG.
42 is a block diagram illustrating a configuration example of a DLL that constitutes a part of the synchronization holding unit of FIG. 40. FIG.
FIG. 43 is a flowchart for explaining an exemplary flow of a synchronization acquisition process;
FIG. 44 is a flowchart for explaining a flow of a synchronization holding start process.
FIG. 45 is a flowchart for explaining the flow of synchronization holding processing for each channel;
FIG. 46 is a diagram showing a configuration of a signal from a GPS satellite.
FIG. 47 is a diagram for explaining conventional carrier and spreading code synchronization processing;
FIG. 48 is a diagram used for describing an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Frequency conversion part, 20 ... Synchronization acquisition part, 21 ... Sampling circuit, 22 ... RAM, 23 ... DSP, 24 ... Memory for DSP, 30 ... Synchronization acquisition part, 31 ... Costas loop, 32 ... DLL, 33 ... Control register , 40 ... control unit, 41 ... CPU, 44 ... clock circuit, 45 ... timer, 46 ... memory for trajectory information

Claims (12)

While substantially changing the phase of the spreading code on the receiving side, detecting the correlation between the spreading code of the received signal from the satellite and the spreading code on the receiving side and performing synchronization acquisition of the spreading code of the received signal, A high-speed mode in which the substantial phase change width of the spreading code on the receiving side is large, and a high-sensitivity mode in which the substantial phase change width is small, and
A mode switching operation means for accepting a switching selection operation between the high speed mode and the high sensitivity mode;
Synchronization acquisition means for executing the acquisition with the mode switched by the mode switching operation means as the current mode;
With
The synchronization acquisition means uses a digital matched filter using a fast Fourier transform process , and at least in the high sensitivity mode, for the positioning for M periods (M is a power of 2 of 2 or more) of the spread code. A satellite signal receiver for positioning, characterized in that the signal is received in units of data received from the satellite. While detecting the correlation between the spreading code of the received signal from the positioning satellite and the spreading code of the receiving side while substantially changing the phase of the spreading code on the receiving side, A high-speed mode in which the substantial phase change width of the spreading code on the receiving side is large, and a high-sensitivity mode in which the substantial phase change width is small,
Either one of the high-speed mode or the high-sensitivity mode as a current mode, and synchronization acquisition means for performing the synchronization acquisition;
Discriminating means for discriminating whether the synchronization acquisition is difficult in the current mode;
In the determination means, when it is determined that the synchronization acquisition is difficult in the current mode, the mode change means for changing the current mode to the other one of the high speed mode and the high sensitivity mode;
With
The synchronization acquisition means uses a digital matched filter using a fast Fourier transform process , and at least in the high sensitivity mode, for the positioning for M periods (M is a power of 2 of 2 or more) of the spread code. A satellite signal receiver for positioning, characterized in that the signal is received in units of data received from the satellite. The positioning satellite signal receiver according to claim 2,
One of the high speed mode and the high sensitivity mode can be selected and set as an initial mode of the current mode. A positioning satellite signal receiver, characterized in that: In the positioning satellite signal receiver according to any one of claims 1 to 3,
The synchronization acquisition means preprocesses the received signal data from the positioning satellite for M periods (M is a power of 2 greater than or equal to 2) of the spreading code at least in the high sensitivity mode, and performs the spreading. A satellite signal receiver for positioning, characterized in that the number of data corresponding to one cycle of a code is calculated, and the data corresponding to one cycle of the spreading code as a result of the preprocessing is subjected to correlation calculation using the digital matched filter. . Te receiver smell of positioning satellite signals of claim 4,
Pre Symbol pretreatment, the data of the received signal from the spreading code for M cycles of said positioning satellite (d [0] ··· d [ MN-1] (N is the one period of the spread code The number of received signal data from the positioning satellite))) is calculated by executing an algorithm for calculating a subset (S [0]... S [N-1]) of the Fourier transform. Satellite signal receiver.
However,
S [k] = D [k × M + r]
D is the Fourier transform of the data d,
k = 0, 1,..., N−1
r is a constant depending on the Doppler frequency, 0 ≦ r <M The positioning satellite signal receiver according to claim 5 ,
In the preprocessing, when the total number of received signal data from the positioning satellites for M cycles of the spreading code is MN, every M data is collectively stored in a memory as one word. By doing so, the memory stores the received signal data from the positioning satellite for M cycles of the spreading code as M words.
A satellite signal receiver for positioning, wherein fast Fourier transform is performed on data in units of words written in the memory. While detecting the correlation between the spreading code of the received signal from the positioning satellite and the spreading code of the receiving side while substantially changing the phase of the spreading code on the receiving side, A high-speed mode in which the substantial phase change width of the spreading code on the receiving side is large, and a high-sensitivity mode in which the substantial phase change width is small,
Receiving a switching selection operation between the high speed mode and the high sensitivity mode through a mode switching operation means;
A synchronization acquisition step of executing the synchronization acquisition with the mode switched by the mode switching operation means as the current mode;
With
In the synchronization acquisition step, a digital matched filter using a fast Fourier transform process is used , and at least in the high sensitivity mode, the positioning code for M periods (M is a power of 2 of 2 or more) of the spread code. A satellite signal reception method for positioning, characterized in that data is received in units of satellite reception signals. While detecting the correlation between the spreading code of the received signal from the positioning satellite and the spreading code of the receiving side while substantially changing the phase of the spreading code on the receiving side, A high-speed mode in which the substantial phase change width of the spreading code on the receiving side is large, and a high-sensitivity mode in which the substantial phase change width is small,
Either one of the high-speed mode or the high-sensitivity mode as a current mode, and a synchronization acquisition step for performing the synchronization acquisition;
A determination step of determining whether the synchronization acquisition is difficult in the current mode;
In the determining step, when it is determined that the synchronization acquisition is difficult in the current mode, the mode changing step of changing the current mode to the other one of the high speed mode and the high sensitivity mode;
With
In the synchronization acquisition step, a digital matched filter using a fast Fourier transform process is used , and at least in the high sensitivity mode, the positioning code for M periods (M is a power of 2 of 2 or more) of the spread code. A satellite signal reception method for positioning, characterized in that data is received in units of satellite reception signals. The positioning satellite signal receiving method according to claim 8 ,
Either of the high speed mode or the high sensitivity mode can be selected and set as an initial mode of the current mode. A positioning satellite signal receiving method, wherein: In the receiving method of positioning satellite signals according to one of claims 7 to claim 9,
In the synchronization acquisition step, at least in the high-sensitivity mode, the spread signal data is preprocessed for M periods (M is a power of 2 greater than or equal to 2) of the spreading code, and the spreading is performed. A positioning satellite signal receiving method, wherein the number of data corresponding to one period of a code is calculated, and the data corresponding to one period of the spread code as a result of the preprocessing is subjected to correlation calculation using the digital matched filter. . Te receiving method smell of the positioning satellite signals of claim 10,
Pre Symbol pretreatment, the data of the received signal from the spreading code for M cycles of said positioning satellite (d [0] ··· d [ MN-1] (N is the one period of the spread code The number of received signal data from the positioning satellite))) is calculated by executing an algorithm for calculating a subset (S [0]... S [N-1]) of the Fourier transform. Satellite signal reception method.
However,
S [k] = D [k × M + r]
D is the Fourier transform of the data d,
k = 0, 1,..., N−1
r is a constant depending on the Doppler frequency, 0 ≦ r <M The positioning satellite signal receiving method according to claim 11 ,
In the preprocessing, when the total number of received signal data from the positioning satellites for M cycles of the spreading code is MN, every M data is collectively stored in a memory as one word. By doing so, the memory stores the received signal data from the positioning satellite for M cycles of the spreading code as M words.
A method of receiving a positioning satellite signal, wherein fast Fourier transform is performed on data in units of words written in the memory.

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