JP2004173145A - Communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a selection method of wireless circuit taking in account the traffic of the wireless circuit in a network communication using a plurality of wireless circuits, and to achieve a communication method that improves the reduction of transmission efficiency which occurs when there is a difference of traffic between the wireless circuits. <P>SOLUTION: Wireless stations 205, 206 located in places, where they can detect the electric waves of a plurality of wireless circuits, use the information of a predicted 'packet error rate' of each wireless circuit and 'band occupancy' informed from each control station, and calculate a transmission succeeding rate when using each wireless circuit. Then, the wireless stations select and use a wireless circuit having the highest transmission success rate. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、無線のネットワークシステムにおいて、無線回線の動的選択によりパケット通信を効率的に行うための通信方法に関する。
【０００２】
【従来の技術】
従来は主にパーソナルコンピュータ（以降、ＰＣと略する）同士でのデータ交換、またはホストコンピュータとＰＣ間でのデータ交換のために、ネットワークにより相互間を接続した。
【０００３】
従来の技術の無線ネットワークでの無線回線の動的選択について図１をもとに説明する。図１は２つの制御局で構成される無線ネットワーク構成図である。図１により、制御局１０１は無線回線００１を管理し、無線回線００１を時分割的に共有している無線局２０１〜２０６間の通信を制御しているが、制御局１０２は無線回線００２を管理し、無線回線２０２を時分割的に共有している無線局２０７、２０８間の通信を制御している。ここで、両制御局の電波が到達する範囲内に存在する無線局２０５と無線局２０６に注目する。無線局２０５や無線局２０６は両制御局からの電波を検知できるのでどちらの制御局に接続するかを選択することが出来る。すなわち、無線回線００１か無線回線００２かどちら使用するかを決めることが出来る。このとき、無線回線の選択基準として平均受信電力を用いる場合、無線局２０５や無線局２０６から制御局１０１までの距離が無線局２０５や無線局２０６から制御局１０２までの距離より短く、ほとんどの場合電波３０１の平均受信電力のほうが電波３０２より強いので、無線局２０５と無線局２０６は無線回線００１を選択し、制御局１０１に接続している。無線回線の選択基準は平均受信電力以外にＳＮＲ （Ｓｉｇｎａｌ ｔｏ ｎｏｉｓｅ ｒａｔｉｏ）やＣＮＲ（Ｃａｒｒｉｅｒ ｔｏ ｎｏｉｓｅ ｒａｔｉｏ）などもよく用いられる。
【０００４】
【非特許文献１】
Ｃ．アピチャイチャルームウォン、他２名、「場所選択送信電力制御による適応ゾーン選択方式を用いた適応変調無線パケット通信システム」、社団法人電子情報通信学会、平成１３年４月１日発行、電子情報通信学会論文誌Ｂ Ｖｏｌ．Ｊ８４−Ｂ Ｎｏ．４ ｐｐ．６９７−７０６
【０００５】
【発明が解決しようとする課題】
従来方法（例えば、非特許文献１参照。）では、複数の制御局からの電波が到達する場所に位置する無線局２０５、２０６のような無線局は検知できる複数の無線回線の電波の受信電力などのような受信特性のみを考慮して無線回線を選択するので、各無線回線のトラヒック状態を考慮できず、トラヒック量が多い無線回線００１のような無線回線を選択してしまう。その結果、無線局２０５、２０６のような無線局は電波の受信特性が比較的良好な無線回線００１を利用するにもかかわらず、無線回線００１が占有されていない時間帯（帯域）が少ないので、帯域を確保できる確率が低いのである。そこで、もし無線局２０５、２０６はトラヒック量が少ない無線回線００２を選択して制御局１０２にアクセスすれば電波の特性が比較的若干悪くても、無線回線００２が占有されていない時間帯が多いので、帯域を確保できる確率が高いのである。総合的に考えると、無線局２０５、２０６のような無線局はトラヒック量の比較的少ない無線回線００２を利用するほうが無線回線００１を利用するよりシステム全体の伝送効率および無線回線利用効率が高くなる。従って、電波の特性のみを無線回線の選択基準とした従来方法は無線回線の「トラヒック量」を考慮しておらず、電波の特性のみ考慮するため、もっとも伝送品質が高い無線回線を選択できるが、無線局がトラヒック量が非常に高い無線回線を選択する場合、どれほど良い伝送品質を保証できても確保可能な帯域が足りなければその無線回線を利用する意味がなく、システム全体の伝送効率を低下させることも考えられる。すなわち、従来方法は各無線回線においてトラヒック量の格差がある時のために伝送効率および無線回線利用効率を高める十分な工夫がなされていなかった。
【０００６】
それゆえに、本発明の目的は、電波の特性に加え、トラヒック量を考慮した無線回線の選択方式を提供し、それによって、無線ネットワークにおける伝送効率および無線回線利用率を改善することである。
【０００７】
【課題を解決するための手段】
この課題を解決するために、発明は、以下に述べるような手段を有しており、それによって以下のような効果を奏する。
【０００８】
第１の発明は、複数の無線局が１つ無線回線を時分割的に使用して通信を行うための方法であって、前記複数の無線局のいずれかが、前記複数の無線局間の通信を制御する制御局となる場合であって、異なる無線回線を制御している前記制御局が近隣して存在する場合、前記制御局は、自分自身が制御している無線回線のトラヒック量を監視し、「トラヒック情報」を各無線局に報知し、前記無線局は、自分自身が検知できるすべての無線回線の伝搬路特性を測定し、これらの「伝搬路特性」と、検知可能な各制御局から報知された前記トラヒック情報とを考慮して、無線回線を選択することを特徴とする。
【０００９】
第２の発明は、第１の発明において、無線局は各無線回線の伝搬路特性の測定結果に基づいて各無線回線の「パケット誤り率」を算出することを特徴とする。
【００１０】
第３の発明は、第１の発明において、制御局は自分自身が制御している無線回線のトラヒック量を観測し、「帯域占有率」を計算し、無線局らに報知することを特徴とする。
【００１１】
第４の発明は、第１の発明において、無線局は送信時の最適な無線回線を判断する基準として「送信成功確率」を用い、「送信成功確率＝（１−帯域占有率）＊（１−パケット誤り率）」という式を利用し、各無線回線の送信成功確率を計算して、送信成功確率が一番高い無線回線を選択することを特徴とする。
【００１２】
第５の発明は、第１の発明において、制御局は自分自身が制御している無線回線のトラヒック量を観測し、無線回線のトラヒック量の変動に応じて、トラヒック情報を更新し、更新されたトラヒック情報を無線局らに報知することを特徴とする。
【００１３】
第６の発明は、第１の発明において、無線局は自分自身が検知できる各無線回線の伝搬路特性を周期的に測定し、各無線回線の伝搬路特性の変化に応じて、前記パケット誤り率の情報を更新することを特徴とする。
【００１４】
【発明の実施の形態】
以下、本発明の実施の形態について詳細に説明する。説明の都合上、本発明を徹底的に理解いただくために特定の数、時間、構造およびその他のパラメータを提示する。以下の段階で本発明を実地する方法の例を挙げる。
【００１５】
図２は、本発明の実施形態に係る無線ネットワークシステムの構成を示す図である。図２において、無線ネットワークシステムは、８つの無線局（２０１〜２０８）と２つの制御局（１０１、１０２）で構成される。制御局１０１、１０２はそれぞれ異なる無線回線を管理し、自分自身の電波が到達する範囲内に存在する無線局間の通信を制御する機能を持っている。
【００１６】
次に動作を説明する。制御局１０１、１０２はそれぞれ自分の無線回線の使用状況を常に観測し、決まった一定時間内でどれくらいの割合で無線局が無線回線を利用しているかを計算し、計算した結果を周期的に無線局ら２０１〜２０８に報知する。以下では、この報知情報を「帯域占有率」と呼ぶことにする。
【００１７】
図３に、基地局におけるこのような動作の手順を示す。
【００１８】
１．調べの終了時点ｔｚを更新する。ｔｚ＝前回のｔｚ＋帯域占有率を更新する周期Ｔｘ（３１０）。
【００１９】
２．無線回線の使用状況を調べる時間の幅Ｔｓを決定する（３１１）。
【００２０】
３．無線回線の合計使用時間Ｔａｌｌと無線局のカウンターｉをゼロにする（３１２）。
【００２１】
４．管理しているすべての無線局の無線回線の使用状況を調べ終わるまで、以下のステップを繰り返す（管理しているすべての無線局の数をＮとする）。
【００２２】
ａ．無線局のカウンターｉが（Ｎ−１）より大きければステップ（３１７）に移行する（３１３）。
【００２３】
ｂ．過去に観測し記録しておいたデータに基づいて、（ｔｚ−Ｔｓ）時点からｔｚまで無線局ｉが無線回線を使用する時間Ｔｉを計算する（３１４）。
【００２４】
ｃ．無線回線の合計使用時間ＴａｌｌにＴｉを加算する（３１５）。
【００２５】
ｄ．次の無線局の使用状況を調べるためｉに１を加算し、続いてステップ（３１３）に戻る（３１６）。
【００２６】
５．「帯域占有率」＝Ｔａｌｌ／Ｔｓを計算する（３１７）。
【００２７】
６．計算した「帯域占有率」を下り回線を用いて無線局らに報知する（３１８）。
【００２８】
７．上記の動作を周期的に行うため、ｔｚの時点から帯域占有率を更新する周期Ｔｘの時間が経過するとステップ（３１０）に戻る（３１９）。
【００２９】
無線局２０１〜２０８はそれぞれ各無線回線の電波を周期的に検知し、電波の受信特性ＣＮＲ（Ｃａｒｒｉｅｒ ｔｏ Ｎｏｉｓｅ Ｒａｔｉｏ）を測定して、送信時の電波のＣＮＲを予測する。次に、無線局は予測したＣＮＲを用いて、パケット誤り率（ＰＥＲ：Ｐａｃｋｅｔ Ｅｒｒｏｒ Ｒａｔｅ）対ＣＮＲ特性を参照し、パケット誤り率を判定する。パケット誤り率（ＰＥＲ：ＰａｃｋｅｔＥｒｒｏｒ Ｒａｔｅ）対ＣＮＲ特性は実験や計算機シミュレーションなどにより予め求められる必要があると思われるが、パケット誤り率とＣＮＲの関係を表す近似式などを用いてパケット誤り率を算出してもよい。なお、電波の受信特性はＣＮＲの代わりに受信電力やＳＮＲなどを用いてもよい。無線局２０５、２０６以外の無線局は１つのみの制御局からの電波しか検知できないため、無線回線の選択を行わないとする。一方、無線局２０５、２０６は予測した各無線回線の「パケット誤り率」と、各制御局から報知された「帯域占有率」との情報を用いて、各無線回線を利用する時の送信成功確率を次式で求める。送信成功確率＝（１−帯域占有率）＊（１−パケット誤り率）。無線局２０５、２０６は各無線回線における送信成功率を上記の式で計算し、送信成功率が一番高い無線回線を選択し、その無線回線を制御している制御局にアクセスする。
【００３０】
たとえば、図２では無線回線００１、００２の帯域占有率＝０．５、０．３、無線局２０５から見た無線回線００１、００２におけるパケット誤り率＝０．１、０．３である場合、無線回線００１における送信成功確率＝（１−０．５）＊（１−０．１）＝０．５＊０．９＝０．４５ 無線回線００２における送信成功確率＝（１−０．３）＊（１−０．３）＝０．７＊０．７＝０．４９となり、無線局２０５から見て無線回線００２における送信成功確率が無線回線００１における送信成功確率より高いため、無線局２０５は無線回線００２を利用してパケット通信を行う。無線回線無線局２０５、２０６は上記の「帯域占有率」および「パケット誤り率」が周期的に更新するため、各無線回線のトラヒック状態および電波の特性の変化に応じて周期的に「送信成功率」が一番高い無線回線を正確に選択できる。その結果、各無線回線にトラヒック量が均等に分布されてない時においてもシステム全体の伝送効率や無線回線の利用効率を高めることが出来る。
【００３１】
図４に無線局における上記のような動作の手順を示す。
【００３２】
１．無線回線の選択を開始する（４０１）。例、無線局の電源を入れた時や無線局の設置場所が変更された時など無線回線の選択が必要になる。また、周期的に無線回線の選択を行うことも考えられる。
【００３３】
２．検知できる無線回線の電波の数Ｍを求める（４０２）。Ｍが２以上の場合のみステップ（４０３）に移行する。
【００３４】
３．無線回線のカウンターｊをゼロにする（４０３）。
【００３５】
４．検知できるすべての無線回線におけるパケット誤り率を求め終わるまで、以下のステップを繰り返す。
【００３６】
ａ．無線回線のカウンターｊが（Ｍ−１）より大きければステップ（４１０）に移行する（４０４）。
【００３７】
ｂ．無線回線ｊの電波の受信特性を測定する（４０５）。例、ＣＮＲなど。
【００３８】
ｃ．ステップ（４０５）と同時に無線回線ｊで報知されている帯域占有率を読み取り、記憶しておく（４０６）。これによって、無線回線ｊの帯域占有率ＢＷＯｊが求められる。
【００３９】
ｄ．測定されたＣＮＲを用いて、予め用意されたパケット誤り率対平均ＣＮＲの特性からパケット誤り率を求める（４０７）。これによって、無線回線ｊのパケット誤り率ＰＥＲｊが求められる。
【００４０】
ｅ．ステップ（４０６）で記憶されておいた「帯域占有率」と、ステップ（４０７）で求められた「パケット誤り率」とを用いて、無線回線ｊの送信成功確率を求める（４０８）。無線回線ｊの送信成功確率ＰＲＯＢｊ＝（１−ＢＷＯｊ）＊（１−ＰＥＲｊ）。
【００４１】
ｆ．次の無線回線の送信成功確率を求めるためｊに１を加算し、続いてステップ（４０４）に戻る（４０９）。
【００４２】
５．送信成功確率が一番低い無線回線ｋを求める（４１０）。ここで、ｊ＝０〜（Ｍ−１）とし、ｋ＝定数とするとＰＲＯＢｋ≦ＰＲＯＢｊ。
【００４３】
６．無線局は無線回線ｋを管理している制御局に接続する（４１１）。
【００４４】
【発明の効果】
第１の発明では、複数の無線回線の電波を検知できる無線局は各無線回線の「伝搬路特性」だけではなく、各制御局から送られてくる「トラヒック情報」も考慮し無線回線を選択するため、各無線回線においてトラヒック量の格差がある時には、トラヒック量が比較的少なく帯域を確保できる確率が高い無線回線を選択する確率が高くなる。電波の特性のみを考慮した従来方法と比べて比較的伝送品質が悪い無線回線を利用する確率が高くなるが、選択する無線回線のトラヒック量が多く中々帯域を確保できないことを効率よく避けることが出来るため、総合的に考えるとシステム全体の伝送効率および無線回線利用効率を高めることが出来る。
【００４５】
第２の発明では、伝搬路特性の測定結果に基づいて各無線回線の「パケット誤り率」を算出するため、無線局は各無線回線の伝搬路特性を簡易に把握することができ、各無線回線の伝搬路特性を反映させた無線回線の選択を行うことができる。
【００４６】
第３の発明では、制御局は自分自身が制御している無線回線のトラヒック状態を定量的に表す「帯域占有率」を無線局らに報知するため、無線局は各無線回線のトラヒック量を簡易に把握することができ、各無線回線のトラヒック量を反映させた無線回線の選択を行うことができる。
【００４７】
第４の発明では、無線局は「送信成功確率＝（１−帯域占有率）＊（１−パケット誤り率）」のような一次方程式を用いるため、送信成功確率が一番高い無線回線を判断するため計算量を必要最小限に抑えることができる。
【００４８】
第５の発明では、無線局は無線回線のトラヒック量の変動に応じたトラヒック情報を常に把握できるので、最適な無線回線選択の精度を高めることができ、伝送効率および無線回線利用効率を常に高く保つことができる安定的な無線パケット通信システムを実現できる。
【００４９】
第６の発明では、無線局は無線回線の伝搬路特性の変化に応じたパケット誤り率の情報を常に把握できるので、最適な無線回線選択の精度を高めることができ、伝送効率および無線回線利用効率を常に高く保つことができる安定的な無線パケット通信システムを実現できる。
【図面の簡単な説明】
【図１】従来の無線回線選択例を示す図
【図２】本発明の実施形態に係る無線ネットワークシステムのイメージを示す図
【図３】制御局における動作の手順を示すフローチャート
【図４】無線局における動作の手順を示すフローチャート
【符号の説明】
００１ 無線回線
００２ 無線回線
１０１ 制御局
１０２ 制御局
２０１ 無線局
２０２ 無線局
２０３ 無線局
２０４ 無線局
２０５ 無線局
２０６ 無線局
２０７ 無線局
２０８ 無線局
３０１ 電波
３０２ 電波[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a communication method for efficiently performing packet communication by dynamically selecting a wireless channel in a wireless network system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a personal computer (hereinafter, abbreviated as a PC) has been connected to each other by a network mainly for data exchange between the computers or data exchange between a host computer and a PC.
[0003]
The dynamic selection of a wireless channel in a wireless network according to the related art will be described with reference to FIG. FIG. 1 is a configuration diagram of a wireless network composed of two control stations. According to FIG. 1, the control station 101 manages the wireless channel 001 and controls communication between the wireless stations 201 to 206 sharing the wireless channel 001 in a time-division manner. It manages and controls communication between the wireless stations 207 and 208 that share the wireless line 202 in a time-division manner. Here, attention is paid to the wireless station 205 and the wireless station 206 existing within the range where the radio waves of both control stations reach. Since the radio stations 205 and 206 can detect radio waves from both control stations, it is possible to select which control station to connect to. That is, it is possible to determine whether to use the wireless line 001 or the wireless line 002. At this time, when the average received power is used as the selection criterion of the wireless channel, the distance from the wireless station 205 or the wireless station 206 to the control station 101 is shorter than the distance from the wireless station 205 or the wireless station 206 to the control station 102, and almost all In this case, since the average received power of the radio wave 301 is stronger than the radio wave 302, the radio stations 205 and 206 select the radio line 001 and connect to the control station 101. As a criterion for selecting a wireless channel, SNR (Signal to noise ratio), CNR (Carrier to noise ratio), and the like are often used in addition to the average received power.
[0004]
[Non-patent document 1]
C. Apichai Chaloom Wong, and 2 others, "Adaptive Modulation Wireless Packet Communication System Using Adaptive Zone Selection Method by Location Selection Transmission Power Control", The Institute of Electronics, Information and Communication Engineers, issued April 1, 2001, Electronic Information and Communication Transactions of the Society B Vol. J84-B No. 4 pp. 697-706
[0005]
[Problems to be solved by the invention]
In the conventional method (for example, see Non-Patent Document 1), radio stations such as the radio stations 205 and 206 located at locations where radio waves from a plurality of control stations reach can detect the reception power of the radio waves of a plurality of radio lines. Since the radio channel is selected only by taking into account the reception characteristics as described above, the traffic state of each radio channel cannot be considered, and a radio channel such as the radio channel 001 having a large traffic volume is selected. As a result, the wireless stations such as the wireless stations 205 and 206 use the wireless line 001 having relatively good radio wave reception characteristics, but have a small time zone (band) in which the wireless line 001 is not occupied. Therefore, the probability that the band can be secured is low. Therefore, if the radio stations 205 and 206 select the radio channel 002 with a small traffic amount and access the control station 102, the radio channel 002 is often not occupied even if the radio wave characteristics are relatively poor. Therefore, there is a high probability that the band can be secured. Comprehensively, a wireless station such as the wireless stations 205 and 206 uses the wireless line 002 having a relatively small traffic amount to increase the transmission efficiency and the wireless line use efficiency of the entire system as compared with the wireless line 001. . Therefore, the conventional method using only the characteristics of the radio wave as a criterion for selecting the radio line does not consider the "traffic volume" of the radio line, but considers only the characteristics of the radio wave, so that the radio line with the highest transmission quality can be selected. However, if a wireless station selects a wireless line with a very high traffic volume, no matter how good the transmission quality can be guaranteed, there is no point in using the wireless line if there is not enough available bandwidth, and the transmission efficiency of the entire system will be reduced. It is conceivable to lower it. In other words, the conventional method has not been sufficiently devised to increase the transmission efficiency and the wireless line utilization efficiency when there is a difference in the amount of traffic in each wireless line.
[0006]
SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method of selecting a radio channel in consideration of the amount of traffic in addition to the characteristics of radio waves, thereby improving transmission efficiency and radio channel utilization in a radio network.
[0007]
[Means for Solving the Problems]
In order to solve this problem, the present invention has the following means, and has the following effects.
[0008]
A first invention is a method in which a plurality of wireless stations perform communication using one wireless line in a time-division manner, wherein any one of the plurality of wireless stations performs communication between the plurality of wireless stations. In the case where the control station controls communication, and the control station controlling a different radio channel is present in the vicinity, the control station determines the traffic volume of the radio channel controlled by itself. Monitoring, and broadcasts "traffic information" to each wireless station.The wireless station measures the propagation path characteristics of all the radio lines that can be detected by itself, and these "propagation path characteristics" and each of the detectable A radio channel is selected in consideration of the traffic information notified from the control station.
[0009]
A second invention is characterized in that, in the first invention, the wireless station calculates a “packet error rate” of each wireless channel based on the measurement result of the propagation path characteristics of each wireless channel.
[0010]
The third invention is characterized in that, in the first invention, the control station observes a traffic volume of a radio line controlled by itself, calculates a “bandwidth occupancy”, and notifies the radio stations and the like. I do.
[0011]
In a fourth aspect based on the first aspect, the wireless station uses “transmission success probability” as a criterion for determining an optimal wireless channel at the time of transmission, and “transmission success probability = (1−band occupancy ratio) * (1 -Packet error rate), the transmission success probability of each wireless channel is calculated, and the wireless channel having the highest transmission success probability is selected.
[0012]
In a fifth aspect based on the first aspect, the control station observes the traffic volume of the radio channel controlled by itself, updates the traffic information in accordance with the fluctuation of the traffic volume of the radio channel, and updates the traffic information. The traffic information is reported to wireless stations and the like.
[0013]
In a sixth aspect based on the first aspect, the wireless station periodically measures channel characteristics of each wireless channel that can be detected by the wireless station, and determines the packet error according to a change in the channel characteristics of each wireless channel. It is characterized in that rate information is updated.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. For purposes of explanation, specific numbers, times, structures and other parameters are set forth in order to provide a thorough understanding of the present invention. The following steps provide examples of how to implement the invention.
[0015]
FIG. 2 is a diagram showing a configuration of the wireless network system according to the embodiment of the present invention. In FIG. 2, the wireless network system includes eight wireless stations (201 to 208) and two control stations (101, 102). Each of the control stations 101 and 102 has a function of managing a different wireless line and controlling communication between wireless stations existing within a range where radio waves of the control stations 101 and 102 can reach.
[0016]
Next, the operation will be described. Each of the control stations 101 and 102 always observes the usage status of its own wireless line, calculates how much the wireless station uses the wireless line within a fixed time, and periodically calculates the calculation result. The wireless stations 201 to 208 are notified. Hereinafter, this broadcast information is referred to as “bandwidth occupancy”.
[0017]
FIG. 3 shows a procedure of such an operation in the base station.
[0018]
1. Update the check end time tz. tz = previous tz + bandwidth occupancy update period Tx (310).
[0019]
2. The time width Ts for checking the usage status of the wireless line is determined (311).
[0020]
3. The total use time Tall of the radio line and the counter i of the radio station are set to zero (312).
[0021]
4. The following steps are repeated until the use status of the wireless lines of all the managed wireless stations is checked (N is the number of all managed wireless stations).
[0022]
a. If the counter i of the wireless station is larger than (N-1), the process proceeds to step (317) (313).
[0023]
b. Based on the data observed and recorded in the past, a time Ti during which the wireless station i uses the wireless line from the time (tz-Ts) to tz is calculated (314).
[0024]
c. Ti is added to the total use time Tall of the wireless line (315).
[0025]
d. In order to check the use status of the next wireless station, 1 is added to i, and then the process returns to step (313) (316).
[0026]
5. “Band occupancy” = Tall / Ts is calculated (317).
[0027]
6. The calculated "bandwidth occupancy" is reported to the wireless stations using the downlink (318).
[0028]
7. In order to perform the above operation periodically, the process returns to the step (310) when the time of the cycle Tx for updating the bandwidth occupancy has elapsed from the time tz (319).
[0029]
Each of the wireless stations 201 to 208 periodically detects a radio wave of each radio line, measures a radio reception characteristic CNR (Carrier to Noise Ratio), and predicts a CNR of the radio wave at the time of transmission. Next, using the predicted CNR, the radio station refers to a packet error rate (PER) versus CNR characteristic and determines the packet error rate. It is considered that the packet error rate (PER) versus CNR characteristic needs to be obtained in advance by experiments, computer simulations, and the like, but the packet error rate is calculated using an approximate expression that expresses the relationship between the packet error rate and the CNR. May be. Note that the reception characteristics of radio waves may use reception power, SNR, etc. instead of CNR. Since radio stations other than the radio stations 205 and 206 can detect only radio waves from only one control station, it is assumed that no radio line is selected. On the other hand, the wireless stations 205 and 206 use the predicted “packet error rate” of each wireless channel and the “bandwidth occupancy” notified from each control station to transmit successfully when using each wireless channel. The probability is calculated by the following equation. Transmission success probability = (1−band occupancy rate) * (1−packet error rate). The wireless stations 205 and 206 calculate the transmission success rate in each wireless line by the above formula, select the wireless line having the highest transmission success rate, and access the control station controlling the wireless line.
[0030]
For example, in FIG. 2, when the bandwidth occupancy of the wireless channels 001 and 002 is 0.5 and 0.3, and the packet error rate of the wireless channels 001 and 002 viewed from the wireless station 205 is 0.1 and 0.3, Transmission success probability in wireless line 001 = (1-0.5) * (1-0.1) = 0.5 * 0.9 = 0.45 Transmission success probability in wireless line 002 = (1-0.3) * (1-0.3) = 0.7 * 0.7 = 0.49, and the transmission success probability on the wireless link 002 is higher than the transmission success probability on the wireless link 001 as viewed from the wireless station 205. Performs packet communication using the wireless line 002. Since the above-mentioned “bandwidth occupancy rate” and “packet error rate” are periodically updated, the wireless line wireless stations 205 and 206 periodically transmit “successful transmission” according to changes in the traffic state of each wireless line and the characteristics of radio waves. You can accurately select the wireless line with the highest rate. As a result, the transmission efficiency of the entire system and the utilization efficiency of the wireless channel can be improved even when the traffic volume is not evenly distributed in each wireless channel.
[0031]
FIG. 4 shows a procedure of the above operation in the radio station.
[0032]
1. The selection of a wireless line is started (401). For example, when the power of the radio station is turned on or when the installation location of the radio station is changed, it is necessary to select a radio line. It is also conceivable to select a wireless line periodically.
[0033]
2. The number M of radio waves that can be detected is obtained (402). The process proceeds to step (403) only when M is 2 or more.
[0034]
3. The counter j of the wireless line is set to zero (403).
[0035]
4. The following steps are repeated until the packet error rates of all detectable wireless channels have been obtained.
[0036]
a. If the radio line counter j is larger than (M-1), the process proceeds to step (410) (404).
[0037]
b. The reception characteristic of the radio wave of the wireless line j is measured (405). For example, CNR.
[0038]
c. At the same time as the step (405), the bandwidth occupancy broadcast on the radio line j is read and stored (406). Thus, the bandwidth occupancy BWOj of the wireless line j is obtained.
[0039]
d. Using the measured CNR, the packet error rate is determined from the previously prepared characteristics of the packet error rate versus the average CNR (407). Thereby, the packet error rate PERj of the wireless channel j is obtained.
[0040]
e. Using the “bandwidth occupancy” stored in step (406) and the “packet error rate” obtained in step (407), the transmission success probability of the wireless channel j is obtained (408). The transmission success probability PROBj of the wireless channel j = (1-BWOj) * (1-PERj).
[0041]
f. In order to obtain the transmission success probability of the next wireless channel, 1 is added to j, and the process returns to step (404) (409).
[0042]
5. The wireless link k with the lowest transmission success probability is determined (410). Here, if j = 0 to (M−1) and k = constant, PROBk ≦ PROBj.
[0043]
6. The wireless station connects to the control station managing the wireless channel k (411).
[0044]
【The invention's effect】
In the first invention, a radio station capable of detecting radio waves of a plurality of radio lines is selected in consideration of not only "propagation path characteristics" of each radio line but also "traffic information" sent from each control station. Therefore, when there is a difference in the amount of traffic in each wireless line, the probability of selecting a wireless line having a relatively small amount of traffic and a high probability of securing a band increases. Compared to the conventional method that considers only the characteristics of radio waves, the probability of using a wireless line with relatively poor transmission quality increases, but it is possible to efficiently avoid the fact that the amount of traffic on the selected wireless line is too large to secure a medium bandwidth. Therefore, the transmission efficiency and the wireless channel utilization efficiency of the entire system can be improved when considered comprehensively.
[0045]
In the second invention, since the “packet error rate” of each wireless channel is calculated based on the measurement result of the channel characteristics, the wireless station can easily grasp the channel characteristics of each wireless channel, and It is possible to select a wireless channel reflecting the channel characteristics of the channel.
[0046]
In the third invention, since the control station notifies the wireless stations of the "bandwidth occupancy" that quantitatively indicates the traffic state of the wireless line controlled by itself, the wireless station determines the traffic volume of each wireless line. It is possible to easily grasp and select a wireless line reflecting the traffic volume of each wireless line.
[0047]
In the fourth invention, since the wireless station uses a linear equation such as “transmission success probability = (1−band occupancy ratio) × (1−packet error rate)”, the wireless station determines the wireless line with the highest transmission success probability. Therefore, the amount of calculation can be minimized.
[0048]
According to the fifth aspect, since the wireless station can always grasp the traffic information according to the fluctuation of the traffic amount of the wireless line, the accuracy of the optimal wireless line selection can be improved, and the transmission efficiency and the wireless line use efficiency can always be increased. A stable wireless packet communication system that can be maintained can be realized.
[0049]
According to the sixth aspect, the radio station can always grasp the information of the packet error rate according to the change of the propagation path characteristic of the radio channel, so that the accuracy of the optimal radio channel selection can be improved, and the transmission efficiency and the radio channel utilization can be improved. A stable wireless packet communication system that can always maintain high efficiency can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of conventional wireless channel selection. FIG. 2 is a diagram showing an image of a wireless network system according to an embodiment of the present invention. FIG. 3 is a flowchart showing an operation procedure in a control station. Flow chart showing the procedure of operation in the station [Explanation of reference numerals]
001 Radio line 002 Radio line 101 Control station 102 Control station 201 Radio station 202 Radio station 203 Radio station 204 Radio station 205 Radio station 206 Radio station 207 Radio station 208 Radio station 301 Radio 302 Radio

Claims (6)

複数の無線局が１つの無線回線を時分割的に使用して通信を行うための方法であって、前記複数の無線局のいずれかが、前記複数の無線局間の通信を制御する制御局となる場合であって
異なる無線回線を制御している前記制御局が近隣して存在する場合に、
前記制御局は、
自分自身が制御している無線回線のトラヒック量を観測して、「トラヒック情報」を各無線局に報知し、
前記各無線局は、
自分自身が検知できるすべての無線回線の伝搬路特性を測定しこれらの伝搬路特性と、検知可能な各制御局から報知された前記トラヒック情報とを考慮して、無線回線を選択することを特徴とする通信方法。A method in which a plurality of wireless stations perform communication using one wireless line in a time-division manner, wherein one of the plurality of wireless stations controls a communication between the plurality of wireless stations. And when the control station controlling a different radio line is present in the vicinity,
The control station comprises:
Observes the traffic volume of the radio line controlled by itself, notifies "traffic information" to each radio station,
Each said radio station,
The wireless channel is selected by measuring the channel characteristics of all wireless lines that can be detected by itself and considering these channel characteristics and the traffic information notified from each detectable control station. Communication method. 前記無線局は各無線回線の伝搬路特性の測定結果に基づいて各無線回線の「パケット誤り率」を算出する請求項１に記載の通信方法。The communication method according to claim 1, wherein the wireless station calculates a "packet error rate" of each wireless channel based on a measurement result of a propagation path characteristic of each wireless channel. 前記制御局は自分自身が制御している無線回線の「帯域占有率」を計算し、無線局らに報知する請求項１に記載の通信方法。The communication method according to claim 1, wherein the control station calculates a "bandwidth occupancy rate" of a wireless channel controlled by the control station and notifies the wireless station of the calculated bandwidth occupancy rate. 前記無線局は送信時の無線回線を判断する基準として「送信成功確率」を用い、「送信成功確率＝（１−帯域占有率）＊（１−パケット誤り率）」という式を利用し、各無線回線の送信成功確率を計算して、送信成功確率が一番高い無線回線を選択する請求項１に記載の通信方法。The wireless station uses “transmission success probability” as a criterion for determining a wireless channel at the time of transmission, and uses the expression “transmission success probability = (1−bandwidth occupancy) × (1−packet error rate)”. The communication method according to claim 1, wherein the transmission success probability of the wireless line is calculated, and the wireless line having the highest transmission success probability is selected. 前記制御局は自分自身が制御している無線回線のトラヒック量を観測し、無線回線のトラヒック量の変動に応じて、前記トラヒック情報を更新し、更新されたトラヒック情報を前記無線局らに報知する請求項１に記載の通信方法。The control station observes the traffic volume of the radio channel controlled by itself, updates the traffic information according to the fluctuation of the traffic volume of the radio channel, and notifies the radio stations of the updated traffic information. The communication method according to claim 1, wherein 前記無線局は自分自身が検知できるすべての無線回線の伝搬路特性を周期的に測定し、各無線回線の伝搬路特性の変化に応じて、前記パケット誤り率の情報を更新する請求項１に記載の通信方法。2. The radio station according to claim 1, wherein the radio station periodically measures channel characteristics of all radio channels that can be detected by itself, and updates the information on the packet error rate in accordance with a change in channel characteristics of each radio channel. The communication method described.

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