JP2004242151A - Adaptive antenna device and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adaptive antenna device which can control a directivity highly precisely in an outgoing communication even when propagation environments are different between an incoming communication and the outgoing communication and can improve a throughput in a digital radio transmission, and to provide its control method. <P>SOLUTION: This adaptive antenna device has: first directivity forming devices 1011 to 101N; first compositing units 1021 to 102N for compositing the n-th output signals of the respective first directivity forming devices; second directivity forming devices 1031 to 103N for using signals of the first compositing units as an input signal and outputting M-piecec signals equal to the number of antenna elements; second compositing units 1041 to 104N for compositing the m-th output signals of the respective directivity forming devices; and M-pieces antenna elements. The first directivity forming devices consist of: first branching devices 1061 to 106N for branching the input signal into N-pieces signals; and first weighting devices 10711 to 107NN for weighting output signals of the first directivity forming devices. The weighting value of the n-th first weighting device of respective first directivity controllers is controlled by a terminal station n. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

で与えられる。ただし、
【数４】

【数５】

【数６】

である。
【０００５】
上り通信時の伝搬環境と下り通信時の伝搬環境がまったく同一とみなせる場合には、アンテナ間の相関行列Ｒ_ＸＸ 及び希望ユーザに対するステアリングベクトルｒ_Ｘｄに変化が生じないため、上り通信時の重みの値を下り通信にもそのまま適用すれば、通信路の２乗誤差を最小とする指向性を形成することができる。したがって、上り通信と下り通信の伝搬環境がほぼ等しい場合には、単に複数のアンテナ素子で構成するアレーアンテナで構成すればよい。
【０００６】
ところが上り通信と下り通信での周波数が異なるＦＤＤシステムや、環境変動の大きい環境では、（式４）で定義したアンテナ間の相関行列Ｒ_ＸＸを推定することができず、適応アンテナ装置が動作しないという問題がある。
【０００７】
下り通信において受信局で伝搬環境を推定し、伝搬環境の推定結果を送信局にフィードバックし、送信局における適応アンテナ装置で下り回線用の指向性形成を行う方法が提案されている（例えば、非特許文献２参照）。以下にその動作を示す。
下り通信では情報信号の間にプロービング信号を周期的に挿入して信号を伝送する。プロービング信号は送信局の各アンテナ素子と受信局との間の伝達関数の推定に用いる。
【０００８】
プロービング信号を伝送する区間では、各アンテナ素子から異なったプロービング信号系列を送信する。ここで、各アンテナ素子から送信するプロービング信号は、全受信局が既知の信号系列とする。受信局では受信信号に対して、送信局の各アンテナ素子から送信される各プロービング信号との相関演算を行い、各アンテナ素子からのプロービング信号ごとに複素相関値を求める。
【０００９】
この複素相関値を上り通信において送信局にフィードバックし、適応アンテナの指向性形成に反映させる。この方法では、各アンテナのプロービング信号との相関値を受信局において求めることによって、送信局の各アンテナ素子と受信局の間の伝搬環境を推定することができる。
この方法を利用する場合には各アンテナ素子から異なった信号が送信されるため、ビーム形成を行うことができない。
したがって、同一チャネルを利用する周辺セルに対して干渉を与えてしまうという問題がある。また、アンテナ素子数が増大すると、プロービング信号の信号系列長が長くなるため、スループットが低下するという問題が生じる。
【００１０】
【非特許文献１】
Ｒ．Ａ．Ｍｏｎｚｉｎｇｏ ａｎｄ Ｔ．Ｗ．Ｍｉｌｌｅｒ，Ｉｎｔｒｏｄｕｃｔｉｏｎ ｔｏ Ａｄａｐｔｉｖｅ Ａｒｒａｙｓ， Ｊｏｈｎ Ｗｉｌｅｙ ＆ Ｓｏｎｓ，Ｉｎｃ．１９８０
【非特許文献２】
Ｄｅｒｌｅｋ Ｇｅｒｌａｃｈａ， Ａｒｌｏｇｙａｓｗａｍｉ Ｐａｕｌｒａｊ，“Ｂａｓｅ Ｓｔａｔｉｏｎ Ａｎｔｅｎｎａ Ａｒｒａｙｓ ｗｉｔｈ Ｍｏｂｉｌｅ ｔｏ Ｂａｓｅ Ｆｅｅｄｂａｃｋ，”Ｃｏｎｆｅｒｅｎｃｅ Ｒｅｃｏｒｄ ｏｆ Ｔｈｅ Ｔｗｅｎｔｙ−Ｓｅｖｅｎｔｈ Ａｓｉｌｏｍａｒ Ｃｏｎｆｅｒｅｎｃｅ ｏｎ，１９９３
【００１１】
【発明が解決しようとする課題】
ディジタル無線伝送での下り通信における指向性制御では、送信局アンテナと受信局との間の伝達関数を推定する必要がある。ところが、伝達関数を推定するために、送信局で各アンテナ素子から信号を送信すると、伝達関数推定時に指向性形成ができないため、他システムや同一周波数チャネルを利用する他セルに多大な干渉を与えてしまうという問題があった。
【００１２】
また、従来の伝達関数推定方法では送信局アンテナと受信局との間の伝達関数を推定するためには、予め定められた信号系列を送信する必要があるため、スループットが低下するという問題があった。
本発明はこのような事情に鑑みてなされたものであり、ディジタル無線伝送において、上り通信と下り通信の伝搬環境が異なる場合でも下り通信における高精度の指向性制御を行うことができ、かつスループットの向上を図った適応アンテナ装置及びその制御方法を提供することを目的とする。
【００１３】
【課題を解決するための手段】
上記目的を達成するために、請求項１に記載の発明は、Ｎ（Ｎは２以上の自然数）個の端末局に対して、指向性を形成する基地局に設けられた適応アンテナ装置であって、
各端末局への送信信号をそれぞれ、入力信号とし、Ｎ個の出力信号を生成する第一の指向性形成装置と、
前記各第一の指向性形成装置のｎ（但し、１≦ｎ≦Ｎ；ｎは自然数）番目の出力信号を合成する第一の合成器と、
該第一の合成器の信号を入力信号とし、アンテナ素子数と同数のＭ（Ｍ≧Ｎ；Ｍは自然数）個の信号を出力する第二の指向性形成装置と、
前記各第二の指向性形成装置のｍ（１≦ｍ≦Ｍ；ｍは自然数）番目の出力信号を合成する第二の合成器と、
Ｍ個のアンテナ素子とを有し、
前記第一の指向性形成装置は、入力信号をＮ個の信号に分岐する第一の分岐装置と、該第一の分岐装置の出力信号に重み付けを行う第一の重み付け装置とからなり、
前記各第一の指向性制御装置のｎ番目の第一の重み付け装置の重みの値は端末局ｎによって制御されることを特徴とする。
【００１４】
また、請求項２に記載の発明は、請求項１に記載のアンテナ装置において、前記第二の指向性形成装置は入力信号をＭ個の信号に分岐する第二の分岐装置と、
前記第二の分岐装置の出力信号に重み付けを行うＭ個の第二の重み付け装置とからなり、
前記第一の重み付け装置の重みの値Ｗ_{１，ｋ，ｊ}及び第二の重み付け装置の重みの値Ｗ_{２，ｊ，ｊ ’}を、
【数７】

【数８】

（ただし、ここで値ｗ_{２，ｊ，ｊ ’}はｊ番目の第二の指向性形成装置のｊ’番目の第二の重み付け装置の重みの値、値ｗ’_{１，ｋ，ｊ}は端末局ｊが式（９）により決定した重みの値であり、（ｔ_ｎ）は今回の演算タイミング時における値であることを、また（ｔ_ｎ−１）は前回の演算タイミング時における値であることを、それぞれ示している。）
となるように決定することを特徴とする。
【００１５】
また、請求項３に記載の発明は、複数の端末局に対して、指向性を形成する基地局に設けられた適応アンテナ装置の制御方法であって、
各端末局への送信信号に対して複数の指向性パターンを形成し、該複数の指向性パターンの合成を端末局側からのフィードバック情報に基づいて制御することを特徴とする。
【００１６】
【発明の実施の形態】
以下、図面を参照して本発明の実施形態について説明する。
本発明の第１実施形態に係る適応アンテナ装置の構成を図１に示す。本実施形態は、送信信号に対して複数の指向性パタンを形成し、複数の指向性パタンの合成を端末局によって制御することにより、高精度の指向性形成を少ないフィードバック情報から行うことを可能としている。
【００１７】
図１において符号１０１１〜１０１Ｎは第一の指向性形成装置、符号１０２１〜１０２Ｎは第一の合成器、符号１０３１〜１０３Ｎは第二の指向性形成装置、符号１０４１〜１０４Ｍは第二の合成器、符号１０５１〜１０５Ｍはアンテナ素子、符号１０６１〜１０６Ｎは第一の分岐装置、符号１０７１１〜１０７ＮＮは第一の重み付け装置である。
【００１８】
基地局はまず上り通信時に伝搬環境の推定を行う。伝搬環境推定としては、たとえば、上り、下り回線においても到来波の到来方向は変化しないとみなし、上り通信時の信号から各到来波の到来方向推定を行う方法などが用いられる。到来方向推定のアルゴリズムにはＭＵＳＩＣ法やＥＳＰＲＩＴ法などの高分解能の到来方向推定アルゴリズムを用いることもできる。
【００１９】
次に、上り通信時に推定した伝搬環境をもとに、第二の指向性形成装置で形成する指向性を決定する。指向性の決定方法としては、たとえば上り通信時に推定した到来方向に対して主ビームを向ける方法や、二乗誤差最小（ＭＭＳＥ）アルゴリズムを用いて、希望している信号に対してメインビームを向け、他の信号に対してヌルを形成する方法などを用いることができる。
【００２０】
このように決定した第二の指向性形成装置の指向性パタンを用いて、下り通信を開始する。下り通信時には各端末局では各第二の指向性形成装置で形成される指向性パタンと端末局アンテナの間の伝達関数を推定する。伝達関数の推定は、例えば、各指向性パタンから異なったタイミングでプローブ信号を送信することによって実施することができる。また同一タイミングで、異なった拡散符号を用いて各指向性パタンからプローブ信号を送信する方法を用いることもできる。
【００２１】
さらに推定した伝達関数から例えば以下の式に基づいて、第一の重み付け装置の重みの値を決定する。
【数９】

ここで、ｗ_{１，ｋ，ｎ} はｋ番目の端末局に対する第一の指向性形成装置のｎ番目の第一の重み付け装置の重みの値，Ｈ_ｋ，ｎはｋ番目の第二の指向性形成装置と端末局ｎの間の伝達関数である。
【００２２】
上式のように制御することによって、
【数１０】

となり、ｋ番目の端末局への信号が端末局ｎに干渉を与えることがなくなる。したがって、端末局ｎでは推定した伝達関数ｈ_ｋ，ｎ の値が大きく、干渉を受けている信号に対して、上式の計算を行い、第一の重み付け装置における重み付け値をフィードバックすればよい。端末局数をＮとした場合、全ての干渉が問題となった場合でも、フィードバックする重み付け値の数はＮ−１個となる。
【００２３】
これに対して、従来の全伝達関数をフィードバックさせる方法ではＭ個の伝達関数をフィードバックする必要がある。
一般にアンテナ素子数Ｍの方が端末局数Ｎよりも大きいため、本発明によってフィードバックする情報量を削減することができる。また本発明では端末局数に対してアンテナ素子数が大きくなればなるほど、大きなフィードバック量の削減効果が期待できる。
【００２４】
図３に、本発明に係る適応アンテナ装置と、従来の適応アンテナ装置（Ｄｅｒｌｅｋ Ｇｅｒｌａｃｈａ，Ａｒｌｏｇｙａｓｗａｍｉ Ｐａｕｌｒａｊ，“Ｂａｓｅ Ｓｔａｔｉｏｎ Ａｎｔｅｎｎａ Ａｒｒａｙｓ ｗｉｔｈ Ｍｏｂｉｌｅ ｔｏ Ｂａｓｅ Ｆｅｅｄｂａｃｋ，”Ｃｏｎｆｅｒｅｎｃｅ Ｒｅｃｏｒｄ ｏｒ Ｔｈｅ Ｔｗｅｎｔｙ−Ｓｅｖｅｎｔｈ Ａｓｉｌｏｍａｒ Ｃｏｎｆｅｒｅｎｃｅ ｏｎ，１９９３）の性能の比較を示す。なお、端末局数は２、基地局のアンテナ素子数は８素子とした。
【００２５】
また、変調方式はＱＰＳＫ、各端末局での到来波は１００波とし、各端末局の位置は、基地局を基準として端末局１を−２０度方向、端末局２を１０度方向とした。基地局での角度広がりは５度、端末局での角度広がりは３６０度とした。上り通信時には到来方向推定を行うものとし、到来方向推定では角度広がりの中心方向を誤差無く推定できるものとした。
最大ドップラー周波数ｆｄｍａｘΔＴは０．３とした。ここで△Ｔは端末局で推定した伝搬環境を指向性形成に反映させるまでに要する時間である。図に示すように，本発明によってフィードバック情報量を１／２０に抑えることが可能となっていることが判る。
【００２６】
本発明の第２実施形態に係る適応アンテナ装置の要部の構成を図２に示す。本実施形態では、端末局からのフィードバック情報を第二の指向性形成装置の指向性制御に反映させ、伝搬環境の変動への追従性を高めることを可能にしている。
本実施形態に係る適応アンテナ装置の基本構成は図１に示した第１実施形態に係る適応アンテナ装置と同じであるが、第１実施の形態と異なるのは、第二の重み付け装置の重みの値についても端末局からのフィードバック情報に基づいて制御するようにしている点である。
【００２７】
この図において符号２０１１〜２０１Ｎは第二の分岐装置、符号２０２１１〜２０２ＮＭは第二の重み付け装置である。
端末局ｋへの送信信号は端末局ｎでは以下のように受信される。
【数１１】

ここでｗ_{２，ｊ，ｊ ’}はｊ番目の第二の指向性形成装置のｊ’番目の第二の重み付け装置の重みの値、ｈ_{ｊ ’ ，ｎ} は基地局のアンテナ素子ｊ’と端末局ｎの間の伝達関数である。
【００２８】
上り通信と下り通信の伝搬環境が大きく異なるような環境では第二の指向性形成装置で形成する指向性も、下り通信の伝搬環境にあわせて更新していく必要がある。このような場合には、第一の重み付け装置の値、第二の重み付け装置の値を以下のように設定する。
【数１２】

【数１３】

【００２９】
ただし、ここで値ｗ_{２，ｊ，ｊ ’}はｊ番目の第二の指向性形成装置のｊ’番目の第二の重み付け装置の重みの値、値ｗ’_{１，ｋ，ｊ}は端末局ｊが式（９）により決定した重みの値であり、（ｔ_ｎ）は今回の演算タイミング時における値であることを、また（ｔ_ｎ−１）は前回の演算タイミング時における値であることを、それぞれ示している。
このように構成することで、下り通信の伝搬環境が変動する環境においても本発明の適応アンテナの動作が可能となる。
【００３０】
【発明の効果】
以上に説明したように本発明によれば、各端末局への送信信号に対して複数の指向性パターンを形成し、該複数の指向性パターンの合成を端末局側からのフィードバック情報に基づいて制御するようにしたので、上り通信と下り通信の伝搬環境が異なる場合でも下り通信における高精度の指向性制御を行うことができ、かつスループットの向上が図れる。
【図面の簡単な説明】
【図１】本発明の第１実施形態に係る適応アンテナ装置の構成を示すブロック図。
【図２】本発明の第２実施形態に係る適応アンテナ装置の要部の構成を示すブロック図。
【図３】本発明に係る適応アンテナ装置と従来のアンテナ装置との性能を比較して示した図。
【図４】従来の適応アンテナ装置の構成を示すブロック図。
【符号の説明】
１０１１〜１０１Ｎ…第一の指向性形成装置
１０２１〜１０２Ｎ…第一の合成器
１０３１〜１０３Ｎ…第二の指向性形成装置
１０４１〜１０４Ｍ…第二の合成器
１０５１〜１０５Ｍ…アンテナ素子
１０６１〜１０６Ｎ…第一の分岐装置
１０７１１〜１０７ＮＮ…第一の重み付け装置
２０１１〜２０１Ｎ…第二の分岐装置
２０２１１〜２０２ＮＭ…第二の重み付け装置
４０１１〜４０１Ｎ…アンテナ素子
４０２１〜４０２…Ｎ重み付け装置
４０３…重み制御装置
４０４…基準信号発生装置
４０５…合成及び分岐装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an adaptive antenna device suitable for use in a base station of a wireless communication system and a control method thereof.
[0002]
[Prior art]
The adaptive antenna device is an antenna device that combines an incoming wave with a high correlation with a desired signal and performs directivity control so as to suppress an incoming wave with a low correlation.
Hereinafter, a conventional beam control method of the adaptive antenna apparatus in the downlink will be described.
FIG. 4 shows a configuration of a conventional adaptive antenna apparatus that does not estimate the propagation environment of downlink communication (for example, see Non-Patent Document 1).
[0003]
In FIG. 4, the conventional adaptive antenna apparatus includes a plurality of antenna elements 4011 to 401N, weighting means 4021 to 402N for imposing a complex weight connected to each antenna element, and a weight for controlling the weight of each weighting means 4021 to 402N. The control device 403, the reference signal generating device 404, and a signal for combining complex weighted signals connected to the antenna elements 4011 to 401N at the time of reception, and a signal for branching an input signal to weighting means 4021 to 402N at the time of transmission. And a branching device 405.
[0004]
In general, signals received by a plurality of antenna elements 4011 to 401N of an adaptive antenna device are x1 to xN, weight values set in weighting means 4021 to 402N are w1 to wN, and a desired signal component is represented by d. The value of the weight forming the directivity so that the square of the error from the desired signal is minimized is
[Equation 3]

Given by However,
(Equation 4)

(Equation 5)

(Equation 6)

It is.
[0005]
If the propagation environment at the time of uplink communication and the propagation environment at the time of downlink communication can be considered to be exactly the same, there is no change in the correlation matrix _RXX between antennas and the steering vector _rXd for the desired user. If the value is applied to downlink communication as it is, directivity that minimizes the square error of the communication path can be formed. Therefore, when the propagation environments of the uplink communication and the downlink communication are almost equal, it is sufficient to simply configure the array antenna with a plurality of antenna elements.
[0006]
However, in an FDD system having different frequencies in uplink communication and downlink communication, or in an environment with large environmental fluctuations, the correlation matrix _RXX between antennas defined in (Equation 4) cannot be estimated, and the adaptive antenna apparatus does not operate. There is a problem.
[0007]
In downlink communication, a method has been proposed in which a propagation environment is estimated at a receiving station, the estimation result of the propagation environment is fed back to a transmitting station, and directivity for a downlink is formed by an adaptive antenna device at the transmitting station (for example, a non-propagating method). Patent Document 2). The operation will be described below.
In downlink communication, a probing signal is periodically inserted between information signals to transmit a signal. The probing signal is used to estimate a transfer function between each antenna element of the transmitting station and the receiving station.
[0008]
In a section where a probing signal is transmitted, a different probing signal sequence is transmitted from each antenna element. Here, the probing signal transmitted from each antenna element is a signal sequence known to all receiving stations. The receiving station performs a correlation operation on the received signal with each probing signal transmitted from each antenna element of the transmitting station, and obtains a complex correlation value for each probing signal from each antenna element.
[0009]
This complex correlation value is fed back to the transmitting station in uplink communication, and is reflected in forming the directivity of the adaptive antenna. In this method, the propagation environment between each antenna element of the transmitting station and the receiving station can be estimated by obtaining the correlation value of each antenna with the probing signal at the receiving station.
When this method is used, different signals are transmitted from each antenna element, so that beam forming cannot be performed.
Therefore, there is a problem that interference is caused to neighboring cells using the same channel. In addition, when the number of antenna elements increases, the signal sequence length of the probing signal increases, which causes a problem that the throughput decreases.
[0010]
[Non-patent document 1]
R. A. Monzingo and T.M. W. Miller, Introduction to Adaptive Arrays, John Wiley & Sons, Inc. 1980
[Non-patent document 2]
Derek Gerlach, Argyaswami Paulraj, "Base Station Antenna Arrays with Mobile to Base Feedback," Conference Record of the Third Century.
[0011]
[Problems to be solved by the invention]
In directivity control in downlink communication in digital wireless transmission, it is necessary to estimate a transfer function between a transmitting station antenna and a receiving station. However, when a signal is transmitted from each antenna element at the transmitting station to estimate the transfer function, directivity cannot be formed at the time of transfer function estimation, so that a great deal of interference occurs in other systems or other cells using the same frequency channel. There was a problem that would.
[0012]
Further, in the conventional transfer function estimating method, it is necessary to transmit a predetermined signal sequence in order to estimate the transfer function between the transmitting station antenna and the receiving station. Was.
The present invention has been made in view of such circumstances, and in digital wireless transmission, it is possible to perform high-precision directivity control in downlink communication even when the propagation environment of uplink communication and downlink communication is different, and achieve high throughput. It is an object of the present invention to provide an adaptive antenna device and a control method therefor, which improve the performance.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is an adaptive antenna apparatus provided in a base station that forms directivity for N (N is a natural number of 2 or more) terminal stations. hand,
A first directivity forming apparatus that takes a transmission signal to each terminal station as an input signal and generates N output signals,
A first combiner that combines an nth (where 1 ≦ n ≦ N; n is a natural number) output signal of each of the first directivity forming devices;
A second directivity forming device that receives the signal of the first combiner as an input signal and outputs M (M ≧ N; M is a natural number) signals of the same number as the number of antenna elements;
A second combiner that combines an m-th (1 ≦ m ≦ M; m is a natural number) output signal of each of the second directivity forming devices;
M antenna elements,
The first directivity forming device includes a first branching device that branches an input signal into N signals, and a first weighting device that weights an output signal of the first branching device.
The weight value of the n-th first weighting device of each first directivity control device is controlled by a terminal station n.
[0014]
The invention according to claim 2 is the antenna device according to claim 1, wherein the second directivity forming device is configured to branch an input signal into M signals,
M output from the second branching device weights the second weighting device, comprising:
The weight value W _{1, k, j} of the first weighting device and the weight value W _{2, j, j ′} of the second weighting device are
(Equation 7)

(Equation 8)

(Where the value w _{2, j, j ′} is the value of the weight of the j′-th second weighting device of the j-th second directivity forming device, and the values w ′ _{1, k, j} are the terminal stations j is the value of the weight determined by equation (9), (t _n ) is the value at the current calculation timing, and (t _n-1 ) is the value at the previous calculation timing Are shown respectively.)
Is determined so that
[0015]
According to a third aspect of the present invention, there is provided a method of controlling an adaptive antenna device provided in a base station forming directivity for a plurality of terminal stations,
A plurality of directivity patterns are formed for a transmission signal to each terminal station, and the synthesis of the plurality of directivity patterns is controlled based on feedback information from the terminal station side.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of the adaptive antenna device according to the first embodiment of the present invention. In the present embodiment, by forming a plurality of directional patterns on a transmission signal and controlling the synthesis of the plurality of directional patterns by a terminal station, it is possible to perform highly accurate directivity formation from a small amount of feedback information. And
[0017]
1, reference numerals 1011 to 101N denote a first directivity forming device, reference numerals 1021 to 102N denote a first combiner, reference numerals 1031 to 103N denote a second directivity forming device, and reference numerals 1041 to 104M denote a second combiner. Reference numerals 1051 to 105M indicate antenna elements, reference numerals 1061 to 106N indicate first branching devices, and reference numerals 10711 to 107NN indicate first weighting devices.
[0018]
The base station first estimates a propagation environment during uplink communication. As the propagation environment estimation, for example, a method of estimating the arrival direction of each arriving wave from a signal at the time of uplink communication, assuming that the arrival direction of the arriving wave does not change in the uplink and the downlink, is used. A high-resolution direction-of-arrival estimation algorithm such as the MUSIC method or the ESPRIT method may be used as the direction-of-arrival estimation algorithm.
[0019]
Next, the directivity formed by the second directivity forming device is determined based on the propagation environment estimated during uplink communication. The directivity may be determined by, for example, directing the main beam to the direction of arrival estimated at the time of uplink communication, or directing the main beam to a desired signal using a minimum square error (MMSE) algorithm. A method of forming a null with respect to another signal can be used.
[0020]
The downlink communication is started using the directivity pattern of the second directivity forming device determined in this way. At the time of downlink communication, each terminal station estimates a transfer function between the directivity pattern formed by each second directivity forming device and the terminal station antenna. The transfer function can be estimated, for example, by transmitting a probe signal from each directional pattern at a different timing. A method of transmitting a probe signal from each directional pattern at the same timing using different spreading codes can also be used.
[0021]
Further, the value of the weight of the first weighting device is determined from the estimated transfer function based on, for example, the following equation.
(Equation 9)

Here, w _{1, k, n} is the value of the weight of the n-th first weighting device of the first directivity forming device for the k-th terminal station, and H _{k, n} is the k-th second directivity. The transfer function between the forming device and the terminal station n.
[0022]
By controlling as in the above equation,
(Equation 10)

The signal to the k-th terminal station does not interfere with the terminal station n. Therefore, in the terminal station n, the value of the estimated transfer function h _{k, n} is large, and the above equation is calculated for the signal receiving the interference, and the weighting value in the first weighting device may be fed back. Assuming that the number of terminal stations is N, the number of weighting values to be fed back is N-1 even if all interferences become a problem.
[0023]
On the other hand, in the conventional method of feeding back all transfer functions, it is necessary to feed back M transfer functions.
In general, since the number M of antenna elements is larger than the number N of terminal stations, the present invention can reduce the amount of information to be fed back. Further, in the present invention, the larger the number of antenna elements with respect to the number of terminal stations, the greater the effect of reducing the amount of feedback can be expected.
[0024]
FIG. 3 shows an adaptive antenna device according to the present invention and a conventional adaptive antenna device (Derek Gerlach, Arrogyswami Paulraj, "Base Station Antenna Arrays with Mobile to Energy terrestrial access fee feedback." 2 shows a comparison of the performances of the two. The number of terminal stations was 2, and the number of antenna elements of the base station was 8.
[0025]
The modulation method is QPSK, the incoming wave at each terminal station is 100 waves, and the position of each terminal station is -20 degrees in terminal station 1 and 10 degrees in terminal station 2 with respect to the base station. The angle spread at the base station was 5 degrees, and the angle spread at the terminal station was 360 degrees. It is assumed that the arrival direction is estimated at the time of uplink communication, and the center direction of the angular spread can be estimated without error in the arrival direction estimation.
The maximum Doppler frequency fdmaxΔT was set to 0.3. Here, ΔT is the time required until the propagation environment estimated by the terminal station is reflected on the formation of directivity. As shown in the figure, it can be seen that the present invention makes it possible to reduce the amount of feedback information to 1/20.
[0026]
FIG. 2 shows a configuration of a main part of an adaptive antenna device according to a second embodiment of the present invention. In the present embodiment, the feedback information from the terminal station is reflected on the directivity control of the second directivity forming device, and it is possible to enhance the follow-up to the fluctuation of the propagation environment.
The basic configuration of the adaptive antenna apparatus according to the present embodiment is the same as that of the adaptive antenna apparatus according to the first embodiment shown in FIG. 1, but differs from the first embodiment in that the weight of the second weighting apparatus is different. The point is that the value is also controlled based on the feedback information from the terminal station.
[0027]
In this figure, reference numerals 2011 to 201N indicate second branching devices, and reference numerals 20211 to 202NM indicate second weighting devices.
The transmission signal to the terminal station k is received by the terminal station n as follows.
[Equation 11]

Here, w _{2, j, j ′} is the weight value of the j′-th second weighting device of the j-th second directivity forming device, and h _{j ′ , n} are the antenna element j ′ of the base station and the terminal. Transfer function between stations n.
[0028]
In an environment in which the propagation environments of uplink communication and downlink communication are significantly different, it is necessary to update the directivity formed by the second directivity forming device in accordance with the propagation environment of downlink communication. In such a case, the value of the first weighting device and the value of the second weighting device are set as follows.
(Equation 12)

(Equation 13)

[0029]
Here, the value w _{2, j, j ′} is the value of the weight of the j′-th second weighting device of the j-th second directivity forming device, and the value w ′ _{1, k, j} is the terminal station j. Is the value of the weight determined by equation (9), (t _n ) is the value at the current calculation timing, and (t _n-1 ) is the value at the previous calculation timing. , Respectively.
With this configuration, the adaptive antenna of the present invention can operate even in an environment where the propagation environment of downlink communication fluctuates.
[0030]
【The invention's effect】
As described above, according to the present invention, a plurality of directivity patterns are formed for a transmission signal to each terminal station, and the synthesis of the plurality of directivity patterns is performed based on feedback information from the terminal station side. Since the control is performed, even when the propagation environments of the uplink communication and the downlink communication are different, highly accurate directivity control in the downlink communication can be performed, and the throughput can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an adaptive antenna device according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a main part of an adaptive antenna device according to a second embodiment of the present invention.
FIG. 3 is a diagram showing a comparison between the performance of an adaptive antenna device according to the present invention and the performance of a conventional antenna device.
FIG. 4 is a block diagram showing a configuration of a conventional adaptive antenna device.
[Explanation of symbols]
1011 to 101N first directivity forming devices 1021 to 102N first combiners 1031 to 103N second directivity forming devices 1041 to 104M second combiners 1051 to 105M antenna elements 1061 to 106N First branching devices 10711 to 107NN first weighting devices 2011 to 201N second branching devices 20211 to 202NM second weighting devices 4011 to 401N antenna elements 4021 to 402 N weighting devices 403 weight control devices 404: Reference signal generator 405: Combining and branching device

Claims (3)

An adaptive antenna device provided in a base station forming directivity for N (N is a natural number of 2 or more) terminal stations,
A first directivity forming device that takes a transmission signal to each terminal station as an input signal and generates N output signals,
A first combiner for combining an n-th (where 1 ≦ n ≦ N; n is a natural number) output signal of each of the first directivity forming devices;
A second directivity forming device that receives the signal of the first combiner as an input signal and outputs M (M ≧ N; M is a natural number) signals of the same number as the number of antenna elements;
A second synthesizer that synthesizes an m-th (1 ≦ m ≦ M; m is a natural number) output signal of each of the second directivity forming devices;
And M antenna elements,
The first directivity forming device includes a first branching device that branches an input signal into N signals, and a first weighting device that weights an output signal of the first branching device.
The adaptive antenna device, wherein a value of a weight of an n-th first weighting device of each of the first directivity control devices is controlled by a terminal station n. A second branching device that branches the input signal into M signals,
M output from the second branching device weights the second weighting device, comprising:
The weight value w1 _{, k, j} of the first weighting device and the weight value w2 _{, j, j ′} of the second weighting device are

(Where the value w _{2, j, j ′} is the value of the weight of the j′-th second weighting device of the j-th second directivity forming device, and the values w ′ _{1, k, j} are the terminal stations j is the value of the weight determined by equation (9), (t _n ) is the value at the current calculation timing, and (t _n-1 ) is the value at the previous calculation timing Are shown respectively.)
The adaptive antenna device according to claim 1, wherein the adaptive antenna device is determined such that For a plurality of terminal stations, a control method of the adaptive antenna device provided in the base station forming the directivity,
Control of an adaptive antenna apparatus, wherein a plurality of directivity patterns are formed for a transmission signal to each terminal station, and the synthesis of the plurality of directivity patterns is controlled based on feedback information from the terminal station side. Method.

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