JP4139257B2

JP4139257B2 - Wireless packet communication method and wireless packet communication device

Info

Publication number: JP4139257B2
Application number: JP2003097965A
Authority: JP
Inventors: 健悟永田; 信也大槻; 智明熊谷; 聡相河
Original assignee: Nippon Telegraph and Telephone Corp
Current assignee: Nippon Telegraph and Telephone Corp
Priority date: 2003-04-01
Filing date: 2003-04-01
Publication date: 2008-08-27
Anticipated expiration: 2023-04-01
Also published as: JP2004304707A

Description

【０００１】
【発明の属する技術分野】
本発明は、利用可能な複数の伝送速度の中から一の伝送速度を選定してＯＦＤＭ（Orthogonal Frequency Division Multiplexing：直交周波数分割多重) 信号を伝送する無線パケット通信方法および無線パケット通信装置に関する。
【０００２】
【従来の技術】
無線パケット通信は、無線ＬＡＮをはじめとする様々なシステムで採用されている通信形態である。無線ＬＡＮの規格については、IEEE802.11委員会で標準化が進められているが、その中に変調方式としてＯＦＤＭを採用しているIEEE802.11ａ規格やIEEE802.11ｇ規格がある。このIEEE802.11ａ規格などの物理層では、複数の伝送速度が規定されているので、送信するパケットごとに利用可能な伝送速度の中から一の伝送速度を選定するための伝送速度選定機能が必要となる。
【０００３】
図５は、伝送速度選定機能を含む従来の無線パケット通信装置の構成例を示す（非特許文献１）。図において、送信回路１１は入力された送信データフレームに対して、伝送速度選定回路１７が選定した伝送速度に応じた適切な変調処理および送信処理を行い、送信アンテナ１２を介して無線パケット信号として送信する。同時に送信回路１１は、送信完了を示す送信完了信号を伝送成否判定回路１５へ出力する。伝送成否判定回路１５は、この送信完了信号を受けると経過時間Ｔの計数を開始する。
【０００４】
一方、通信相手の無線パケット装置は、無線パケット信号を正常に受信するとその旨を示す無線制御信号（到達確認信号）を送信する。受信回路１４は、受信アンテナ１３を介してこの到達確認信号を受信すると伝送成否判定回路１５へ通知する。伝送成否判定回路１５は、経過時間Ｔが所定時間Ｔ0 を経過する前に、対応する到達確認信号が入力されたことをもって送信データフレームの伝送が成功したと判断し、伝送成否回数算出回路１６へ通知する。なお、経過時間Ｔが所定時間Ｔ0 を超過しても到達確認信号が入力されずにタイムアウトすると、対応する送信データフレームの伝送が失敗したと判断する。
【０００５】
伝送成否回数算出回路１６は、直近の連続伝送成功回数Ｓおよび連続伝送失敗回数Ｆを記憶しており、その値は伝送成否判定回路１５から入力される伝送成否の判定結果によって更新される。例えば、伝送失敗後に３回連続して伝送が成功すると、Ｓ：３、Ｆ：０となり、その後に伝送が失敗すると、Ｓ：０、Ｆ：１となる。伝送速度選定回路１７は、内部に伝送速度増加用閾値Ｕ、伝送速度減少用閾値Ｄおよび伝送速度定着用閾値Ｃの３つのパラメータを保持し、以下の規則に従って次回の送信に用いる伝送速度を選定する。
【０００６】
伝送速度選定回路１７は、連続伝送成功回数Ｓをカウントして伝送速度増加用閾値Ｕに達すると（Ｓ≧Ｕ）、現在使用中の伝送速度よりも一段階高い伝送速度が利用可能であれば、その伝送速度を次回の送信時に使用する伝送速度として選定し、連続伝送成功回数Ｓを０にクリアする。その後、伝送成功が伝送速度定着用閾値Ｃの回数だけ連続する前に（Ｓ≧Ｃとなる前に）伝送が失敗すると、ただちに元の伝送速度に戻す。一方、伝送成功が伝送速度定着用閾値Ｃの回数だけ連続すると（Ｓ≧Ｃ）、その伝送速度が定着したとみなし、その後に伝送が失敗した場合には連続伝送失敗回数Ｆのカウントに入る。
【０００７】
連続伝送失敗回数Ｆをカウントして伝送速度減少用閾値Ｄに達すると（Ｆ≧Ｄ）、現在使用中の伝送速度よりも一段階低い伝送速度が利用可能であれば、その伝送速度を次回の送信時に使用する伝送速度として選定し、連続伝送失敗回数Ｆを０にクリアする。それ以外の場合（Ｓ＜ＵかつＦ＜Ｄ）は、現在使用中の伝送速度と同一の伝送速度を維持する。
【０００８】
ここで、Ｕ＝８、Ｄ＝３、Ｃ＝２の場合における伝送速度の増減パターンの一例を図６に示す。縦軸は伝送速度、横軸は伝送成否の経過を○と×で示す。このように、過去の送信成否情報を用いて伝搬路の状況を推定することにより、次回の送信において適切と考えられる伝送速度を選定することができる。
【０００９】
【非特許文献１】
井上他、「IEEE802.11無線ＬＡＮにおけるレートアダプテーション機能」、2002年電子情報通信学会ソサイエティ大会、B-5-192
【００１０】
【発明が解決しようとする課題】
IEEE802.11ａ規格では、ＱＰＳＫや16ＱＡＭ等の変調方式と符号化率の組み合わせで伝送速度を規定している。一般に、同一の伝搬環境下であっても、変調方式や符号化率等が異なると、同一のパケット誤り率を得るために必要なＣＮＲは異なる。そのため、一段階高い伝送速度を選定するための判断材料として、使用中の伝送速度における連続伝送成功回数Ｓを用いている従来の方法では、その条件（上記の例ではＳ≧Ｕ）を満たしたとしても、必ずしも一段階高い伝送速度にしたときに伝送が成功するとは限らない。
【００１１】
例えば、端末がある伝送速度では安定的に通信できるが、さらにその上の伝送速度で通信を行うには通信品質が不十分であるようなＣＮＲで通信している場合に、Ｓ≧Ｕになって一段階高い伝送速度に移行すると、その伝送速度での伝送が失敗することになる。ここで、Ｓ≧Ｃとなる前に（例えば伝送速度アップ後すぐに）伝送が失敗すると、ただちに元の伝送速度に戻るようにしているが、その伝送速度になると伝送成功が連続することになり、再度Ｓ≧Ｕになって一段階高い伝送速度に移行する。このように伝送成功と伝送失敗を繰り返すことにより、スループットが劣化する問題があった。
【００１２】
なお、伝送速度定着用閾値Ｃを用いなければ、上記の伝搬路の状況で一旦伝送速度をアップすると、伝送速度減少用閾値Ｄに達するまで伝送失敗が繰り返されることになり、さらにスループットが劣化する。伝送速度定着用閾値Ｃを用いた制御は、これを改善するものとして提案されている。
【００１３】
本発明は、一段階高い伝送速度へ移行すると伝送が失敗するような伝搬路の状況でも、連続伝送成功回数Ｓが伝送速度増加用閾値Ｕに達しただけで一段階高い伝送速度へ移行していた従来の問題点を考慮し、伝搬路の状況に応じて一段階高い伝送速度への移行を抑制することができる無線パケット通信方法および無線パケット通信装置を提供することを目的とする。
【００１４】
【課題を解決するための手段】
請求項１に記載の発明は、複数の伝送速度の中から一の伝送速度を選定してＯＦＤＭ信号を伝送する際に、所定回数連続して伝送成功した場合に現在使用中の伝送速度より一段階高い伝送速度に移行する無線パケット通信方法において、所定回数連続して伝送成功したときに、伝搬路のＣＮＲ値と、１ＯＦＤＭシンボルに含まれる全サブキャリアまたは一部のサブキャリアの信号振幅値または信号電力値の分散値を検出し、そのＣＮＲ値に対する分散値が前記一段階高い伝送速度で伝送成功が見込める値であるか否かによって推定し、伝送成功と推定されるときに一段階高い伝送速度へ移行し、伝送失敗と推定されるときには一段階高い伝送速度へ移行しないように制御する。この処理手順の一例を図１に示す。
【００１５】
また、一段階高い伝送速度における伝送成否は、伝送速度ごとに伝送成否の履歴を蓄積し、伝送速度ごとに所定の伝送回数に対する伝送失敗回数の割合（パケット誤り率）、または所定期間における連続伝送成功回数の平均値、または所定期間中に所定回数以上連続して伝送成功した確率（連続伝送成功確率）のいずれかを用いて推定してもよい（請求項２）。
【００１８】
請求項３に記載の発明は、複数の伝送速度の中から一の伝送速度を選定してＯＦＤＭ信号を伝送する際に、所定回数連続して伝送成功した場合に現在使用中の伝送速度より一段階高い伝送速度に移行する無線パケット通信装置において、受信電力値または受信電力と相関が高い係数に基づいて伝搬路のＣＮＲ値を検出し、さらにＯＦＤＭ信号のサブキャリアごとの信号振幅値または信号電力値に基づいて１ＯＦＤＭシンボルに含まれる全サブキャリアまたは一部のサブキャリアの信号振幅値または信号電力値の分散値を検出する伝搬路情報生成回路と、所定回数連続して伝送成功し、分散値が一段階高い伝送速度およびＣＮＲ値に対して伝送成功が見込める値であり、かつその伝送速度が利用可能であれば、一段階高い伝送速度を次回の送信時に使用する伝送速度として選定する伝送速度選定回路とを備える。
【００１９】
請求項４に記載の発明は、複数の伝送速度の中から一の伝送速度を選定してＯＦＤＭ信号を伝送する際に、所定回数連続して伝送成功した場合に現在使用中の伝送速度より一段階高い伝送速度に移行する無線パケット通信装置において、伝送速度ごとに伝送成否の履歴を蓄積し、伝送速度ごとに所定の伝送回数に対する伝送失敗回数の割合（パケット誤り率）、または所定期間における連続伝送成功回数の平均値、または所定期間中に所定回数以上連続して伝送成功した確率（連続伝送成功確率）のいずれかの伝搬路情報を算出する伝搬路情報生成回路と、所定回数連続して伝送成功し、一段階高い伝送速度における伝搬路情報が伝送成功を見込める値であり、かつその伝送速度が利用可能であれば、一段階高い伝送速度を次回の送信時に使用する伝送速度として選定する伝送速度選定回路とを備える。
【００２０】
【発明の実施の形態】
（第１の実施形態）
図２は、本発明の無線パケット通信装置の第１の実施形態を示す。図において、送信回路１１、送信アンテナ１２、受信アンテナ１３、受信回路１４、伝送成否判定回路１５、伝送成否回数算出回路１６の構成により、送信データフレームの伝送成否に応じて、連続伝送成功回数Ｓおよび連続伝送失敗回数Ｆを更新する機能については、従来装置と同様である。
【００２１】
本実施形態の特徴は、受信回路１４が出力する受信電力値と装置固有の雑音指数に基づいて伝搬路のＣＮＲ値を検出するＣＮＲ値検出回路２１と、ＣＮＲ値検出回路２１から出力される伝搬路のＣＮＲ値と、伝送成否回数算出回路１６から出力される連続伝送成功回数Ｓおよび連続伝送失敗回数Ｆを判断材料として、送信回路１１に対して次回の送信時に使用する伝送速度を選定する伝送速度選定回路２２を備えるところにある。伝送速度選定回路２２は、伝送速度増加用閾値Ｕ、伝送速度減少用閾値Ｄ、伝送速度定着用閾値Ｃ、さらに伝送速度ごとのＣＮＲ閾値の４つのパラメータを保持し、以下の規則に従って次回の送信に用いる伝送速度を選定する。
【００２２】
伝送速度選定回路２２は、連続伝送成功回数Ｓをカウントして伝送速度増加用閾値Ｕに達すると（Ｓ≧Ｕ）、ＣＮＲ値検出回路２１で得たＣＮＲ値と現在使用中の伝送速度よりも一段階高い伝送速度におけるＣＮＲ閾値とを比較し、ＣＮＲ値がＣＮＲ閾値よりも大きくかつその伝送速度が利用可能であれば、現在使用中の伝送速度よりも一段階高い伝送速度を次回の送信時に使用する伝送速度として選定し、連続伝送成功回数Ｓを０にクリアする。また、Ｓ≧Ｕになっても、ＣＮＲ値が一段階高い伝送速度におけるＣＮＲ閾値よりも小さければ、伝送速度をアップすることにより伝送失敗になる確率が高いと判断し、現在使用中の伝送速度を維持する。
【００２３】
また、伝送速度をアップ後において連続伝送成功回数Ｓと伝送速度定着用閾値Ｃとの関係における伝送速度の選定、連続伝送失敗回数Ｆと伝送速度減少用閾値Ｄとの関係における伝送速度の選定については従来の伝送速度選定回路１７と同様である。なお、本実施形態では、伝送成功確率が高い場合に一段階高い伝送速度に移行するので、伝送速度定着用閾値Ｃは必ずしも用いなくてもよい。
【００２４】
このように、本実施形態の構成では、受信電力値から得た伝搬路のＣＮＲ値を用いて伝送速度を変更した後の伝送成功確率を推定することにより、従来のように伝送速度のアップ、伝送失敗、伝送速度のダウンを繰り返すような事態を回避することができる。
【００２５】
なお、本実施形態のＣＮＲ値検出回路２１では、受信信号（例えば到達確認信号）の受信電力値から伝搬路のＣＮＲ値を検出する構成であるが、ＡＧＣ（自動利得制御）係数等の受信電力と相関の高い係数からＣＮＲ値を算出するようにしてもよい。また、受信信号に受信処理のためのプリアンブル信号を付加する場合には、このプリアンブル信号の受信電力値を用いてもよい。また、到達確認信号に先方の受信回路で検出した伝搬路のＣＮＲ値をデータとして付加し、そのＣＮＲ値を用いてもよい。また、各伝送速度におけるＣＮＲ閾値は、理論計算やシミュレーションあるいは実験等によって所定の伝送成功確率が得られる値があらかじめ設定されるものとする。
【００２６】
（第２の実施形態）
図３は、本発明の無線パケット通信装置の第２の実施形態を示す。図において、送信回路１１、送信アンテナ１２、受信アンテナ１３、受信回路１４、伝送成否判定回路１５、伝送成否回数算出回路１６の構成により、送信データフレームの伝送成否に応じて、連続伝送成功回数Ｓおよび連続伝送失敗回数Ｆを更新する機能については、従来装置と同様である。
【００２７】
本実施形態の特徴は、受信回路１４が出力するＯＦＤＭ信号のサブキャリアごとの信号電力値に基づいて１ＯＦＤＭシンボルに含まれる全サブキャリアの信号電力値の分散値を検出する分散値検出回路２３と、分散値検出回路２３から出力される分散値と、伝送成否回数算出回路１６から出力される連続伝送成功回数Ｓおよび連続伝送失敗回数Ｆを判断材料として、送信回路１１に対して次回の送信時に使用する伝送速度を選定する伝送速度選定回路２４を備えるところにある。伝送速度選定回路２４は、伝送速度増加用閾値Ｕ、伝送速度減少用閾値Ｄ、伝送速度定着用閾値Ｃ、さらに伝送速度ごとの分散閾値の４つのパラメータを保持し、以下の規則に従って次回の送信に用いる伝送速度を選定する。
【００２８】
伝送速度選定回路２４は、連続伝送成功回数Ｓをカウントして伝送速度増加用閾値Ｕに達すると（Ｓ≧Ｕ）、分散値検出回路２３で得た分散値と現在使用中の伝送速度よりも一段階高い伝送速度における分散閾値とを比較し、分散値が分散閾値よりも小さくかつその伝送速度が利用可能であれば、現在使用中の伝送速度よりも一段階高い伝送速度を次回の送信時に使用する伝送速度として選定し、連続伝送成功回数Ｓを０にクリアする。また、Ｓ≧Ｕになっても、分散値が一段階高い伝送速度における分散閾値よりも大きければ、伝送速度をアップすることにより伝送失敗になる確率が高いと判断し、現在使用中の伝送速度を維持する。
【００２９】
また、伝送速度をアップ後において連続伝送成功回数Ｓと伝送速度定着用閾値Ｃとの関係における伝送速度の選定、連続伝送失敗回数Ｆと伝送速度減少用閾値Ｄとの関係における伝送速度の選定については従来の伝送速度選定回路１７と同様である。なお、本実施形態では、伝送成功確率が高い場合に一段階高い伝送速度に移行するので、伝送速度定着用閾値Ｃは必ずしも用いなくてもよい。
【００３０】
このように、本実施形態の構成では、サブキャリアごとの信号電力値から得た分散値を用いて伝送速度を変更した後の伝送成功確率を推定することにより、従来のように伝送速度のアップ、伝送失敗、伝送速度のダウンを繰り返すような事態を回避することができる。
【００３１】
なお、本実施形態の分散値検出回路２３では、ＯＦＤＭ信号の１ＯＦＤＭシンボルに含まれる全サブキャリアの信号電力値の平均値を求め、その平均値を用いて全サブキャリアの信号電力値の分散値を算出する構成であるが、１ＯＦＤＭシンボルに含まれる一部のサブキャリアの分散値を検出するようにしてもよい。また、１ＯＦＤＭシンボルに含まれる全サブキャリアまたは一部のサブキャリアの信号振幅値に基づいて、信号振幅値の分散値を検出するようにしてもよい。また、サブキャリアごとの信号電力値または信号振幅値は、受信回路１４で行う同期捕捉用の伝搬路推定値から算出することも可能である。また、各伝送速度における分散閾値は、理論計算やシミュレーションあるいは実験等によって所定の伝送成功確率が得られる値があらかじめ設定されるものとする。
【００３２】
（第３の実施形態）
伝搬路の状況を推定するに当たり、第１の実施形態ではＣＮＲ値を用い、第２の実施形態では分散値を用いたが、伝搬路のＣＮＲ値が異なれば第２の実施形態における分散閾値も異なる。すなわち、ＣＮＲ値が低いときは分散値をより低くしなければ所定の伝送成功率は得られず、ＣＮＲ値が高ければ分散値が多少大きくても所定の伝送成功率が得られる。第３の実施形態では、伝送速度およびＣＮＲ値に応じて最適な分散閾値を設定するようにしたものである。
【００３３】
図４は、本発明の無線パケット通信装置の第３の実施形態を示す。図において、送信回路１１、送信アンテナ１２、受信アンテナ１３、受信回路１４、伝送成否判定回路１５、伝送成否回数算出回路１６の構成により、送信データフレームの伝送成否に応じて、連続伝送成功回数Ｓおよび連続伝送失敗回数Ｆを更新する機能については、従来装置と同様である。
【００３４】
本実施形態の特徴は、受信回路１４が出力する受信電力値（受信電力と相関の高い係数）から伝搬路のＣＮＲ値を検出し、さらにサブキャリアごとの信号電力値（信号振幅値）に基づいて１ＯＦＤＭシンボルに含まれる全サブキャリア（一部のサブキャリア）の信号電力値（信号振幅値）の分散値を検出する伝搬路情報生成回路２５と、伝搬路情報生成回路２５から出力されるＣＮＲ値および分散値と、伝送成否回数算出回路１６から出力される連続伝送成功回数Ｓおよび連続伝送失敗回数Ｆを判断材料として、送信回路１１に対して次回の送信時に使用する伝送速度を選定する伝送速度選定回路２６を備えるところにある。伝送速度選定回路２６は、伝送速度増加用閾値Ｕ、伝送速度減少用閾値Ｄ、伝送速度定着用閾値Ｃ、さらに伝送速度ごとに各ＣＮＲ値における分散閾値の４つのパラメータを保持し、以下の規則に従って次回の送信に用いる伝送速度を選定する。
【００３５】
伝送速度選定回路２６は、連続伝送成功回数Ｓをカウントして伝送速度増加用閾値Ｕに達すると（Ｓ≧Ｕ）、伝搬路情報生成回路２５で得られる分散値と現在使用中の伝送速度よりも一段階高い伝送速度とＣＮＲ値における分散閾値とを比較し、分散値が分散閾値よりも小さくかつその伝送速度が利用可能であれば、現在使用中の伝送速度よりも一段階高い伝送速度を次回の送信時に使用する伝送速度として選定し、連続伝送成功回数Ｓを０にクリアする。また、Ｓ≧Ｕになっても、分散値が一段階高い伝送速度とＣＮＲ値における分散閾値よりも大きければ、伝送速度をアップすることにより伝送失敗になる確率が高いと判断し、現在使用中の伝送速度を維持する。
【００３６】
また、伝送速度をアップ後において連続伝送成功回数Ｓと伝送速度定着用閾値Ｃとの関係における伝送速度の選定、連続伝送失敗回数Ｆと伝送速度減少用閾値Ｄとの関係における伝送速度の選定については従来の伝送速度選定回路１７と同様である。なお、本実施形態では、伝送成功確率が高い場合に一段階高い伝送速度に移行するので、伝送速度定着用閾値Ｃは必ずしも用いなくてもよい。
【００３７】
このように、本実施形態の構成では、受信電力値から得た伝搬路のＣＮＲ値と、サブキャリアごとの信号電力値（信号振幅値）から得た分散値を用い、ＣＮＲ値における分散閾値との比較によって伝送速度を変更した後の伝送成功確率を推定することにより、従来のように伝送速度のアップ、伝送失敗、伝送速度のダウンを繰り返すような事態を回避することができる。
【００３８】
なお、本実施形態の伝搬路情報生成回路２５では、第１の実施形態のＣＮＲ値検出回路２１および第２の実施形態の分散値検出回路２３と同様の上記方法により各ＣＮＲ値および分散値を検出することができる。また、各伝送速度とＣＮＲ値における分散閾値は、理論計算やシミュレーションあるいは実験等によって所定の伝送成功確率が得られる値があらかじめ設定されるものとする。
【００３９】
（第４の実施形態）
以上示した実施形態では、ＣＮＲ値または分散値を検出し、閾値との比較によって一段階高い伝送速度における伝送成否を推定していたが、伝送速度ごとに伝送成否の履歴を蓄積し、その情報を用いて一段階高い伝送速度における伝送成否を推定してもよい。その方法としては、例えば、伝送速度ごとの伝送成否の履歴から所定の伝送回数に対する伝送失敗回数の割合（パケット誤り率）を算出し、一段階高い伝送速度における伝送成否を推定する。あるいは、伝送速度ごとに所定期間における連続伝送成功回数の平均値を算出し、一段階高い伝送速度における伝送成否を推定する。あるいは、伝送速度ごとに所定期間中に所定回数以上連続して伝送成功した確率（連続伝送成功確率）を算出し、一段階高い伝送速度における伝送成否を推定する。なお、それらの算出期間として、全通信期間あるいは直近の所定の伝送回数（伝送期間）を対象としたり、直近の期間における算出値が大きく反映されるように重み付け処理をしてもよい。
【００４０】
【発明の効果】
以上説明したように、本発明の無線パケット通信方法および無線パケット通信装置は、伝搬路のＣＮＲ値、サブキャリアごとの信号電力値（信号振幅値）から得た分散値、あるいはＣＮＲ値と分散値、あるいは伝送速度ごとに伝送成否の履歴に基づいて、現在使用中の伝送速度に対して１段階高い伝送速度における伝送成否を推定し、伝送成功が見込める場合に１段階高い伝送速度に移行することにより、伝搬路の状況に適した伝送速度を選定することができる。その結果、単純に伝送速度を高くして伝送失敗になる確率を低減でき、スループットを向上させることができる。
【図面の簡単な説明】
【図１】本発明の無線パケット通信方法の処理手順を示すフローチャート。
【図２】本発明の無線パケット通信装置の第１の実施形態を示す図。
【図３】本発明の無線パケット通信装置の第２の実施形態を示す図。
【図４】本発明の無線パケット通信装置の第３の実施形態を示す図。
【図５】伝送速度選定機能を含む従来の無線パケット通信装置の構成例を示す図。
【図６】従来の無線パケット通信装置における伝送速度の増減パターンの一例を示す図。
【符号の説明】
１１送信回路
１２送信アンテナ
１３受信アンテナ
１４受信回路
１５伝送成否判定回路
１６伝送成否回数算出回路
１７，２２，２４，２６伝送速度選定回路
２１ＣＮＲ値検出回路
２３分散値検出回路
２５伝搬路情報生成回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio packet communication method and a radio packet communication apparatus that transmit an OFDM (Orthogonal Frequency Division Multiplexing) signal by selecting one transmission rate from a plurality of available transmission rates.
[0002]
[Prior art]
The wireless packet communication is a communication form adopted in various systems including a wireless LAN. The standardization of the wireless LAN is being promoted by the IEEE802.11 committee. Among them, there are the IEEE802.11a standard and the IEEE802.11g standard that employ OFDM as a modulation method. In the physical layer such as the IEEE802.11a standard, a plurality of transmission rates are defined, so a transmission rate selection function is required to select one transmission rate from the available transmission rates for each packet to be transmitted. It becomes.
[0003]
FIG. 5 shows a configuration example of a conventional wireless packet communication device including a transmission rate selection function (Non-Patent Document 1). In the figure, the transmission circuit 11 performs appropriate modulation processing and transmission processing according to the transmission rate selected by the transmission rate selection circuit 17 on the input transmission data frame, and as a radio packet signal via the transmission antenna 12. Send. At the same time, the transmission circuit 11 outputs a transmission completion signal indicating transmission completion to the transmission success / failure determination circuit 15. The transmission success / failure determination circuit 15 starts counting the elapsed time T when receiving this transmission completion signal.
[0004]
On the other hand, when the wireless packet device of the communication partner normally receives the wireless packet signal, it transmits a wireless control signal (reach confirmation signal) indicating that fact. The reception circuit 14 notifies the transmission success / failure determination circuit 15 when the arrival confirmation signal is received via the reception antenna 13. The transmission success / failure determination circuit 15 determines that the transmission of the transmission data frame is successful when the corresponding arrival confirmation signal is input before the elapsed time T elapses the predetermined time T0, and the transmission success / failure count calculation circuit 16 Notice. When the elapsed time T exceeds the predetermined time T0 and time-out occurs without receiving the arrival confirmation signal, it is determined that transmission of the corresponding transmission data frame has failed.
[0005]
The transmission success / failure number calculation circuit 16 stores the latest continuous transmission success number S and the continuous transmission failure number F, and the values are updated by the transmission success / failure determination result input from the transmission success / failure determination circuit 15. For example, when transmission succeeds three times after transmission failure, S: 3 and F: 0 are obtained, and when transmission fails thereafter, S: 0 and F: 1 are obtained. The transmission speed selection circuit 17 stores therein three parameters of a transmission speed increase threshold U, a transmission speed decrease threshold D, and a transmission speed fixing threshold C, and selects a transmission speed to be used for the next transmission according to the following rules. To do.
[0006]
When the transmission speed selection circuit 17 counts the number of successful continuous transmissions S and reaches the transmission speed increase threshold U (S ≧ U), if a transmission speed that is one step higher than the transmission speed currently in use is available. The transmission speed is selected as the transmission speed to be used at the next transmission, and the continuous transmission success count S is cleared to zero. Thereafter, if transmission fails before the transmission success continues for the number of times of the threshold C for fixing the transmission speed (before S ≧ C), the original transmission speed is immediately restored. On the other hand, if the transmission success continues for the number of times of the threshold C for fixing the transmission speed (S ≧ C), it is considered that the transmission speed has been fixed.
[0007]
When the transmission speed reduction threshold value D is reached after counting the number of consecutive transmission failures F (F ≧ D), if a transmission speed that is one step lower than the currently used transmission speed is available, the transmission speed is set to the next time. Select the transmission speed to be used during transmission, and clear the continuous transmission failure frequency F to zero. In other cases (S <U and F <D), the same transmission rate as the currently used transmission rate is maintained.
[0008]
Here, FIG. 6 shows an example of an increase / decrease pattern of the transmission rate when U = 8, D = 3, and C = 2. The vertical axis indicates the transmission speed, and the horizontal axis indicates the success or failure of the transmission with ◯ and X. Thus, by estimating the state of the propagation path using the past transmission success / failure information, it is possible to select a transmission rate that is considered appropriate in the next transmission.
[0009]
[Non-Patent Document 1]
Inoue et al., “Rate Adaptation Function for IEEE802.11 Wireless LAN”, 2002 IEICE Society Conference, B-5-192
[0010]
[Problems to be solved by the invention]
In the IEEE802.11a standard, a transmission rate is defined by a combination of a modulation scheme such as QPSK or 16QAM and a coding rate. In general, even under the same propagation environment, the CNR required to obtain the same packet error rate differs depending on the modulation scheme, coding rate, and the like. Therefore, in the conventional method using the number of successful continuous transmissions S at the transmission rate in use as a judgment material for selecting a higher transmission rate by one step, the condition (S ≧ U in the above example) is satisfied. However, transmission does not always succeed when the transmission speed is increased by one step.
[0011]
For example, if the terminal can communicate stably at a certain transmission rate, but further communicates with a CNR that has insufficient communication quality to communicate at a higher transmission rate, S ≧ U. If the transmission rate is shifted to a higher level, transmission at that transmission rate will fail. Here, if transmission fails before S ≧ C (for example, immediately after the transmission speed is increased), the transmission speed is immediately returned to the original transmission speed. However, when the transmission speed is reached, transmission success continues. Again, S ≧ U and the transmission speed is shifted to one step higher. As described above, there is a problem that throughput is deteriorated by repeating transmission success and transmission failure.
[0012]
If the transmission speed fixing threshold C is not used, once the transmission speed is increased in the above-described propagation path condition, transmission failure is repeated until the transmission speed reduction threshold D is reached, and the throughput further deteriorates. . Control using the threshold C for fixing the transmission speed has been proposed as an improvement.
[0013]
The present invention shifts to a higher transmission rate just by reaching the transmission rate increase threshold U even in the situation of a propagation path in which transmission fails when the transmission rate is increased by one step. In view of the above-described conventional problems, an object of the present invention is to provide a wireless packet communication method and a wireless packet communication apparatus that can suppress a shift to a higher transmission rate depending on the state of the propagation path.
[0014]
[Means for Solving the Problems]
According to the first aspect of the present invention, when one transmission rate is selected from a plurality of transmission rates and an OFDM signal is transmitted, the transmission rate is one higher than the currently used transmission rate when transmission is successful a predetermined number of times. In the wireless packet communication method for shifting to a higher transmission rate, when transmission succeeds a predetermined number of times, the CNR value of the propagation path and the signal amplitude value of all subcarriers or a part of subcarriers included in one OFDM symbol or A dispersion value of the signal power value is detected, and the dispersion value with respect to the CNR value is estimated based on whether or not the transmission success can be expected at the above-mentioned one-step higher transmission speed. Control is made so as not to shift to a higher transmission rate when it is estimated that transmission has failed. An example of this processing procedure is shown in FIG.
[0015]
In addition, transmission success / failure at a higher transmission rate is stored as a transmission success / failure history for each transmission rate, and the ratio of the number of transmission failures (packet error rate) to a predetermined number of transmissions for each transmission rate, or continuous transmission for a predetermined period. mean value of the number of successes, or may be estimated using any of the probability that transmitted successfully continuously for a predetermined number of times or more (continuous transmission success probability) for a predetermined period (claim 2).
[0018]
According to the third aspect of the present invention, when one transmission rate is selected from a plurality of transmission rates and an OFDM signal is transmitted, the transmission rate is one higher than the currently used transmission rate when transmission is successful a predetermined number of times. In a wireless packet communication apparatus that shifts to a higher transmission rate, a CNR value of a propagation path is detected based on a received power value or a coefficient highly correlated with the received power, and further, a signal amplitude value or signal power for each subcarrier of an OFDM signal A propagation path information generation circuit for detecting a dispersion value of signal amplitude values or signal power values of all subcarriers or a part of subcarriers included in one OFDM symbol based on the value, and a transmission value succeeding a predetermined number of times, Is a value that can be transmitted successfully for a higher transmission rate and CNR value, and if that transmission rate is available, the next higher transmission rate is And a transmission rate selection circuit for selecting a transmission rate to be used for.
[0019]
In the invention according to claim 4 , when an OFDM signal is transmitted by selecting one transmission speed from among a plurality of transmission speeds, the transmission speed that is currently used is one when the transmission succeeds a predetermined number of times. In a wireless packet communication device that shifts to a higher transmission rate, a history of transmission success / failure is accumulated for each transmission rate, and the ratio of the number of transmission failures (packet error rate) to a predetermined number of transmissions for each transmission rate, or continuous for a predetermined period A propagation path information generation circuit that calculates propagation path information of either the average value of the number of successful transmissions or the probability of successful transmission more than a predetermined number of times during a predetermined period (continuous transmission success probability); If transmission is successful and the propagation path information at a higher transmission rate is a value that can be expected to be successful, and that transmission rate is available, the higher transmission rate is used for the next transmission. And a transmission rate selection circuit for selecting a transmission rate to be.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 2 shows a first embodiment of the wireless packet communication apparatus of the present invention. In the figure, due to the configuration of the transmission circuit 11, the transmission antenna 12, the reception antenna 13, the reception circuit 14, the transmission success / failure determination circuit 15, and the transmission success / failure number calculation circuit 16, the number of successful continuous transmissions S depends on the transmission success / failure of the transmission data frame. The function of updating the continuous transmission failure frequency F is the same as that of the conventional apparatus.
[0021]
The present embodiment is characterized in that a CNR value detection circuit 21 that detects a CNR value of a propagation path based on a reception power value output from the reception circuit 14 and a noise figure specific to the device, and a propagation output from the CNR value detection circuit 21 Transmission for selecting the transmission rate to be used for the next transmission to the transmission circuit 11 using the CNR value of the path, the number S of continuous transmission successes and the number of continuous transmission failures F output from the transmission success / failure calculation circuit 16 as judgment materials A speed selection circuit 22 is provided. The transmission speed selection circuit 22 holds four parameters of a transmission speed increase threshold U, a transmission speed decrease threshold D, a transmission speed fixing threshold C, and a CNR threshold for each transmission speed, and the next transmission according to the following rules. Select the transmission speed to be used for.
[0022]
When the transmission speed selection circuit 22 counts the number of successful continuous transmissions S and reaches the threshold U for transmission speed increase (S ≧ U), the transmission speed selection circuit 22 determines the CNR value obtained by the CNR value detection circuit 21 and the transmission speed currently in use. If the CNR value is larger than the CNR threshold value and the transmission rate is available, the transmission rate that is one step higher than the currently used transmission rate is set for the next transmission. The transmission speed to be used is selected, and the number of successful continuous transmissions S is cleared to zero. Even if S ≧ U, if the CNR value is smaller than the CNR threshold value at a transmission rate that is one step higher, it is determined that there is a high probability of transmission failure by increasing the transmission rate. To maintain.
[0023]
In addition, after increasing the transmission rate, selection of the transmission rate in the relationship between the number of successful continuous transmissions S and the threshold C for fixing the transmission rate, and selection of the transmission rate in the relationship between the number of consecutive transmission failures F and the threshold D for decreasing the transmission rate. Is the same as the conventional transmission speed selection circuit 17. In the present embodiment, when the transmission success probability is high, the transmission speed is shifted to one step higher. Therefore, the transmission speed fixing threshold C is not necessarily used.
[0024]
Thus, in the configuration of this embodiment, by estimating the transmission success probability after changing the transmission rate using the CNR value of the propagation path obtained from the received power value, the transmission rate is increased as in the past. It is possible to avoid a situation in which transmission failure and transmission speed decrease are repeated.
[0025]
The CNR value detection circuit 21 of the present embodiment is configured to detect the CNR value of the propagation path from the received power value of the received signal (for example, arrival confirmation signal), but the received power such as an AGC (automatic gain control) coefficient is used. The CNR value may be calculated from a coefficient having a high correlation. In addition, when a preamble signal for reception processing is added to the received signal, the received power value of this preamble signal may be used. Alternatively, the CNR value of the propagation path detected by the other receiving circuit may be added as data to the arrival confirmation signal, and the CNR value may be used. In addition, the CNR threshold value at each transmission rate is set in advance to a value that can obtain a predetermined transmission success probability by theoretical calculation, simulation, experiment, or the like.
[0026]
(Second Embodiment)
FIG. 3 shows a second embodiment of the wireless packet communication apparatus of the present invention. In the figure, due to the configuration of the transmission circuit 11, the transmission antenna 12, the reception antenna 13, the reception circuit 14, the transmission success / failure determination circuit 15, and the transmission success / failure number calculation circuit 16, the number of successful continuous transmissions S depends on the transmission success / failure of the transmission data frame. The function of updating the continuous transmission failure frequency F is the same as that of the conventional apparatus.
[0027]
A feature of the present embodiment is that a dispersion value detection circuit 23 that detects dispersion values of signal power values of all subcarriers included in one OFDM symbol based on the signal power value of each subcarrier of the OFDM signal output from the reception circuit 14; Then, the dispersion value output from the dispersion value detection circuit 23 and the continuous transmission success count S and the continuous transmission failure count F output from the transmission success / failure calculation circuit 16 are used as judgment materials for the next transmission to the transmission circuit 11. A transmission speed selection circuit 24 for selecting a transmission speed to be used is provided. The transmission speed selection circuit 24 holds four parameters of a transmission speed increase threshold U, a transmission speed decrease threshold D, a transmission speed fixing threshold C, and a dispersion threshold for each transmission speed, and the next transmission according to the following rules. Select the transmission speed to be used for.
[0028]
When the transmission speed selection circuit 24 counts the number of successful continuous transmissions S and reaches the threshold U for transmission speed increase (S ≧ U), the transmission speed selection circuit 24 determines the dispersion value obtained by the dispersion value detection circuit 23 and the transmission speed currently in use. Compare with the dispersion threshold at one step higher transmission rate, and if the dispersion value is smaller than the dispersion threshold and the transmission rate is available, the transmission rate one step higher than the transmission rate currently in use is The transmission speed to be used is selected, and the number of successful continuous transmissions S is cleared to zero. Even if S ≧ U, if the dispersion value is larger than the dispersion threshold at a transmission rate that is one step higher, it is determined that there is a high probability of transmission failure by increasing the transmission rate, and the currently used transmission rate To maintain.
[0029]
In addition, after increasing the transmission rate, selection of the transmission rate in the relationship between the number of successful continuous transmissions S and the threshold C for fixing the transmission rate, and selection of the transmission rate in the relationship between the number of consecutive transmission failures F and the threshold D for decreasing the transmission rate. Is the same as the conventional transmission speed selection circuit 17. In the present embodiment, when the transmission success probability is high, the transmission speed is shifted to one step higher. Therefore, the transmission speed fixing threshold C is not necessarily used.
[0030]
As described above, in the configuration of this embodiment, the transmission rate is increased as in the conventional case by estimating the transmission success probability after changing the transmission rate using the dispersion value obtained from the signal power value for each subcarrier. It is possible to avoid such a situation that the transmission failure and the transmission speed are repeatedly reduced.
[0031]
In the variance value detection circuit 23 of this embodiment, the average value of the signal power values of all subcarriers included in one OFDM symbol of the OFDM signal is obtained, and the variance value of the signal power values of all subcarriers is obtained using the average value. However, dispersion values of some subcarriers included in one OFDM symbol may be detected. Further, the variance value of the signal amplitude value may be detected based on the signal amplitude values of all subcarriers or a part of the subcarriers included in one OFDM symbol. Further, the signal power value or the signal amplitude value for each subcarrier can be calculated from a channel estimation value for synchronization acquisition performed by the receiving circuit 14. Further, the dispersion threshold at each transmission rate is set in advance to a value at which a predetermined transmission success probability can be obtained by theoretical calculation, simulation, experiment, or the like.
[0032]
(Third embodiment)
In estimating the state of the propagation path, the CNR value is used in the first embodiment, and the dispersion value is used in the second embodiment. However, if the CNR value of the propagation path is different, the dispersion threshold in the second embodiment is also set. Different. That is, when the CNR value is low, a predetermined transmission success rate cannot be obtained unless the dispersion value is lowered. When the CNR value is high, a predetermined transmission success rate can be obtained even if the dispersion value is somewhat large. In the third embodiment, an optimum dispersion threshold is set according to the transmission rate and the CNR value.
[0033]
FIG. 4 shows a third embodiment of the wireless packet communication apparatus of the present invention. In the figure, due to the configuration of the transmission circuit 11, the transmission antenna 12, the reception antenna 13, the reception circuit 14, the transmission success / failure determination circuit 15, and the transmission success / failure number calculation circuit 16, the number of successful continuous transmissions S depends on the transmission success / failure of the transmission data frame. The function of updating the continuous transmission failure frequency F is the same as that of the conventional apparatus.
[0034]
The feature of this embodiment is that the CNR value of the propagation path is detected from the received power value (coefficient having a high correlation with the received power) output from the receiving circuit 14, and further based on the signal power value (signal amplitude value) for each subcarrier. A propagation path information generation circuit 25 for detecting a dispersion value of signal power values (signal amplitude values) of all subcarriers (partial subcarriers) included in one OFDM symbol, and a CNR output from the propagation path information generation circuit 25 Transmission for selecting a transmission rate to be used for the next transmission to the transmission circuit 11 using the value and dispersion value, and the number of continuous transmission successes S and the number of continuous transmission failures F output from the transmission success / failure calculation circuit 16 as judgment materials A speed selection circuit 26 is provided. The transmission speed selection circuit 26 holds four parameters of a transmission speed increase threshold U, a transmission speed decrease threshold D, a transmission speed fixing threshold C, and a dispersion threshold for each CNR value for each transmission speed. To select the transmission rate to be used for the next transmission.
[0035]
When the transmission speed selection circuit 26 counts the number of successful continuous transmissions S and reaches the transmission speed increase threshold U (S ≧ U), the transmission value selection circuit 26 calculates the dispersion value obtained by the propagation path information generation circuit 25 and the transmission speed currently in use. If the dispersion value is smaller than the dispersion threshold and the transmission rate is available, a transmission rate that is one step higher than the transmission rate currently in use is compared. It is selected as the transmission rate to be used at the next transmission, and the number of successful continuous transmissions S is cleared to zero. Even if S ≧ U, if the dispersion value is higher by one step and the dispersion threshold value in the CNR value, it is determined that the probability of transmission failure is high by increasing the transmission speed, and is currently in use. Maintaining the transmission speed.
[0036]
In addition, after increasing the transmission rate, selection of the transmission rate in the relationship between the number of successful continuous transmissions S and the threshold C for fixing the transmission rate, and selection of the transmission rate in the relationship between the number of consecutive transmission failures F and the threshold D for decreasing the transmission rate. Is the same as the conventional transmission speed selection circuit 17. In the present embodiment, when the transmission success probability is high, the transmission speed is shifted to one step higher. Therefore, the transmission speed fixing threshold C is not necessarily used.
[0037]
As described above, in the configuration of the present embodiment, using the CNR value of the propagation path obtained from the received power value and the variance value obtained from the signal power value (signal amplitude value) for each subcarrier, By estimating the transmission success probability after changing the transmission rate by comparing the above, it is possible to avoid the situation where the transmission rate is increased, the transmission is failed, and the transmission rate is decreased as in the conventional case.
[0038]
In the propagation path information generation circuit 25 of this embodiment, each CNR value and dispersion value is obtained by the same method as the CNR value detection circuit 21 of the first embodiment and the dispersion value detection circuit 23 of the second embodiment. Can be detected. Further, it is assumed that a dispersion threshold value for each transmission rate and CNR value is set in advance to a value that provides a predetermined transmission success probability by theoretical calculation, simulation, experiment, or the like.
[0039]
(Fourth embodiment)
In the embodiment described above, the CNR value or the dispersion value is detected, and the transmission success / failure at the transmission rate higher by one level is estimated by comparison with the threshold value. May be used to estimate transmission success or failure at a higher transmission rate. As the method, for example, the ratio of the number of transmission failures to the predetermined number of transmissions (packet error rate) is calculated from the history of transmission success / failure for each transmission rate, and the transmission success / failure at one step higher transmission rate is estimated. Alternatively, the average value of the number of successful continuous transmissions for a predetermined period is calculated for each transmission rate, and the success or failure of transmission at one step higher transmission rate is estimated. Alternatively, the probability of successful transmission for a predetermined number of times or more (successful continuous transmission probability) is calculated for each transmission rate for a predetermined period, and the success or failure of transmission at one step higher transmission rate is estimated. Note that the calculation period may be the entire communication period or the most recent predetermined number of transmissions (transmission period), or may be weighted so that the calculated value in the most recent period is largely reflected.
[0040]
【The invention's effect】
As described above, the wireless packet communication method and the wireless packet communication device of the present invention can perform the CNR value of the propagation path, the variance value obtained from the signal power value (signal amplitude value) for each subcarrier, or the CNR value and the variance value. Alternatively, based on the transmission success / failure history for each transmission rate, estimate the transmission success / failure at a transmission rate that is one step higher than the currently used transmission rate, and shift to a higher transmission rate when transmission success is expected. Thus, it is possible to select a transmission rate suitable for the situation of the propagation path. As a result, it is possible to simply increase the transmission speed and reduce the probability of transmission failure, thereby improving the throughput.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a processing procedure of a wireless packet communication method of the present invention.
FIG. 2 is a diagram showing a first embodiment of a wireless packet communication device of the present invention.
FIG. 3 is a diagram showing a second embodiment of the wireless packet communication device of the present invention.
FIG. 4 is a diagram showing a third embodiment of the wireless packet communication device of the present invention.
FIG. 5 is a diagram showing a configuration example of a conventional wireless packet communication device including a transmission rate selection function.
FIG. 6 is a diagram showing an example of a transmission rate increase / decrease pattern in a conventional wireless packet communication device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Transmission circuit 12 Transmission antenna 13 Reception antenna 14 Reception circuit 15 Transmission success / failure determination circuit 16 Transmission success / failure number calculation circuit 17, 22, 24, 26 Transmission rate selection circuit 21 CNR value detection circuit 23 Dispersion value detection circuit 25 Propagation path information generation circuit

Claims

When selecting one transmission rate from multiple transmission rates and transmitting an OFDM signal, a wireless packet that shifts to a transmission rate that is one step higher than the transmission rate currently in use when transmission succeeds a predetermined number of times. In the communication method,
When transmission success consecutively a predetermined number of times, the CNR value of the propagation path to detect the variance of the signal amplitude or signal power values of all the sub-carrier or some sub-carriers included in 1OFDM symbol, the CNR value The dispersion value for is estimated by whether or not the transmission success can be expected at the one-step higher transmission speed ,
The wireless packet communication method, wherein when the transmission is estimated to be successful, the transition is made to the one-step higher transmission rate, and when it is estimated that the transmission is unsuccessful, the transition is not made to the one-step higher transmission rate.

When selecting one transmission rate from multiple transmission rates and transmitting an OFDM signal, a wireless packet that shifts to a transmission rate that is one step higher than the transmission rate currently in use when transmission succeeds a predetermined number of times. In the communication method,
When transmission succeeds for a predetermined number of times, a history of transmission success / failure is accumulated for each transmission speed, and the ratio of the number of transmission failures to the predetermined number of transmissions (packet error rate) for each transmission speed, or continuous transmission success for a predetermined period Calculate the propagation path information of either the average value of the number of times or the probability that the transmission has succeeded more than the predetermined number of times during the predetermined period (successful transmission success probability), and the propagation path information at the one-step higher transmission speed is successfully transmitted. Estimated based on whether or not the value can be expected ,
The wireless packet communication method, wherein when the transmission is estimated to be successful, the transition is made to the one-step higher transmission rate, and when it is estimated that the transmission is unsuccessful, the transition is not made to the one-step higher transmission rate.

When selecting one transmission rate from multiple transmission rates and transmitting an OFDM signal, a wireless packet that shifts to a transmission rate that is one step higher than the transmission rate currently in use when transmission succeeds a predetermined number of times. In the communication device,
A CNR value of a propagation path is detected based on the received power value or a coefficient highly correlated with the received power, and all subcarriers included in one OFDM symbol based on the signal amplitude value or signal power value for each subcarrier of the OFDM signal. Or a propagation path information generation circuit for detecting a dispersion value of signal amplitude values or signal power values of some subcarriers;
If the transmission succeeds a predetermined number of times, and the dispersion value is a value at which the transmission success can be expected with respect to the one-step higher transmission rate and the CNR value, and the transmission rate is available, the one-step higher transmission. A wireless packet communication apparatus comprising: a transmission speed selection circuit that selects a speed as a transmission speed to be used at the next transmission.

When selecting one transmission rate from multiple transmission rates and transmitting an OFDM signal, a wireless packet that shifts to a transmission rate that is one step higher than the transmission rate currently in use when transmission succeeds a predetermined number of times. In the communication device,
The transmission success / failure history is accumulated for each transmission speed, and the ratio of the number of transmission failures (packet error rate) to the predetermined number of transmissions for each transmission speed (the packet error rate), the average value of the number of successful continuous transmissions in a predetermined period, or predetermined during a predetermined period A propagation path information generation circuit for calculating any propagation path information of the probability of successful transmission over the number of times (continuous transmission success probability);
If the transmission succeeds a predetermined number of times, and the propagation path information at the one-step higher transmission rate is a value that can be transmitted successfully, and the transmission rate is available, the one-step higher transmission rate is set at the next transmission. A wireless packet communication apparatus comprising: a transmission rate selection circuit that selects a transmission rate to be used.