JP4198570B2 - Adaptive antenna transmission apparatus and adaptive antenna transmission method - Google Patents

Description

  The present invention is used in a wireless communication system using an adaptive antenna. In particular, the present invention relates to propagation environment estimation of an adaptive antenna and directivity control for fading compensation.

  An adaptive antenna is an antenna that performs directivity control so as to multiplex incoming waves having a high correlation with a desired signal and suppress incoming waves with a low correlation. The directivity control method in the conventional adaptive antenna transmission apparatus is shown below.

  FIG. 6 shows a directivity control method in a conventional adaptive antenna transmission apparatus that does not estimate the propagation environment of downlink communication (see, for example, Non-Patent Document 1). The conventional adaptive antenna apparatus includes a plurality of antenna elements 4011 to 401N, weighting means 4021 to 402N for imposing complex weights connected to the antenna elements, weight control apparatus 402 for controlling the weight of each weighting means 4021 to 402N, From the reference signal generating device 404 and the combining and branching device 405 for synthesizing the complex weighted signals connected to the antenna elements 4011 to 401N at the time of reception and for branching the input signal to the weighting means 4021 to 402N at the time of transmission. Composed.

で与えられる。ただし、

である。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、アンテナの相関行列Ｒ_xxおよ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。 Generally, when signals received by a plurality of antenna elements 4011 to 401N of an adaptive antenna apparatus are x1 to xN, weight values set in the weighting means 4021 to 402N are w1 to wN, and a desired signal component is represented as d. The value of the weight that forms the directivity so that the square of the error from the desired signal is minimized is

Given in. However,

It is. When the propagation environment during uplink communication and the propagation environment during downlink communication can be regarded as exactly the same, the antenna correlation matrix R _xx and the steering vector r _xd for the desired user do not change, so the value of the weight during uplink communication Is directly applied to downlink communication, directivity that minimizes the square error of the communication path can be formed. Therefore, when the propagation environments of uplink communication and downlink communication are almost equal, it may be configured by an array antenna configured by a plurality of antenna elements.

  However, in an FDD system having different frequencies for uplink communication and downlink communication, or an environment with large environmental fluctuations, the correlation matrix Rxx defined between the antennas defined in (Equation 4) cannot be estimated, and the directivity in the adaptive antenna transmission apparatus There is a problem that the control method does not work.

  A method has been proposed in which a propagation environment is estimated at a receiving station in downlink communication, and a propagation environment estimation result is fed back to a transmitting station to form downlink directivity (for example, see Non-Patent Document 2). The operation is shown below.

  In downlink communication, a signal is transmitted by periodically inserting a probing signal between information signals. The probing signal is used to estimate a transfer function between each antenna of the transmitting station and the receiving station. In a section in which a probing signal is transmitted, a different probing signal sequence is transmitted from each antenna. Here, the probing signal transmitted from each antenna is assumed to be a signal sequence known to all receiving stations. At the receiving station, the received signal is correlated with each probing signal transmitted from each antenna, and a complex correlation value is obtained for each probing signal of each antenna. This complex correlation value is fed back to the transmitting station in uplink communication and reflected in the formation of the directivity of the adaptive antenna. In this method, the propagation environment between each antenna of the transmitting station and the receiving station can be estimated by obtaining a correlation value with the probing signal of each antenna at the receiving station.

  When this method is used, since different signals are transmitted from the respective antennas, beam forming cannot be performed. Therefore, there is a problem of causing interference to neighboring cells that use the same channel. Further, when the number of antenna elements increases, the signal sequence length of the probing signal becomes longer, which causes a problem that the throughput decreases.

  There has been proposed a method of estimating the arrival direction of an incoming wave during uplink communication, estimating a transfer function from the estimation result, and forming directivity (for example, see Non-Patent Document 3). Even in FDD systems having different frequencies for up-and-down communication, the arrival direction of incoming waves does not change in up-and-down communication, and directivity is formed only from arrival direction information.

However, this method is based on the premise that the propagation environment is accurately estimated using a high-precision resolution algorithm such as the ESPRIT algorithm. However, in a real environment, there are a large number of multipath waves, and it is difficult to accurately estimate the direction of arrival. Since this method is directivity control based only on direction-of-arrival information, there is a problem that transmission quality significantly deteriorates when an error occurs in direction-of-arrival estimation.
RAMonzingoandT.W.Miller, Introduction to Adaptive Arrays, John Wiley & Sons, Inc. 1980 DerlekGerlacha, ArlogyaswamiPaulraj, "Base Station Antenna Arrays with Mobile toBaseFeedback," Conference Record of The Twenty-Seventh AsilomarConferenceon, 1993 B. Lindmark, M. Ahlberg, M. Nilsson, and C. Beckman, "Performance analysis of applying up-link estimates in down-link beamforming using a dualpolarized array," Vehicular Technology Conference Proceedings, 2000. VTC2000-Spring Tokyo. 2000 IEEE 51st, Page (s ): 690-694vol.2,2000 VahidTarokh, et.al "Space-TimeCodes for High Data Rate Wireless Communication: Performance Criterion and Code Construction", IEEE Trans. Information Theory, Vol. 44, No. 2, MARCH, 1998.

  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, if a signal is transmitted from each antenna in order to estimate the transfer function, there is a problem that transmission quality deteriorates because directivity cannot be formed when the transfer function is estimated. In addition, in the conventional transfer function estimation method, in order to estimate the transfer function between the transmitting station antenna and the receiving station, it is necessary to transmit a predetermined signal sequence. It was. In addition, in the method of estimating the arrival direction from the received signal in the uplink communication and estimating the downlink transfer function, there is a problem that the transmission quality is significantly deteriorated when the arrival direction estimation error occurs.

  The present invention has been carried out against such a background. By forming a plurality of beams from one sample data, the influence of propagation environment estimation error can be reduced without reducing the throughput. It is an object of the present invention to provide an adaptive antenna transmission apparatus and an adaptive antenna transmission method that can be used.

  According to a first aspect of the present invention, an encoder that generates a K number of output signals using a transmission signal to a terminal station as an input signal, and an output signal of the encoder as an input signal, the same number as the number of antenna elements. The K directivity forming devices that output M signals, the directivity control device that controls the directivity of the directivity forming devices, and the m th signal of the K directivity forming devices are combined. This is an adaptive antenna transmission apparatus comprising M combining means and M antenna elements that radiate output signals of the combining means.

の変換を行う信号系列変換手段を備え、前記指向性制御装置は、前記ｒ₁〜ｒ_Mおよびｒ′₁〜ｒ′_Mに基づき指向性制御を行う手段を備えたところにある。 Here, a feature of the present invention is that the M antenna elements are configured by equally spaced linear array antennas, and M receptions transmitted from the terminal station received by the M antenna elements. Using the signal as an input signal, for these M received signals

And a signal stream conversion means for converting, the directional control device, Ru near where comprising means for performing directivity control on the basis of the r ₁ ~r _M and r _'1 ~r' _M.

That is, the received signal of the T symbol _{(r 1 ', r 2'} , ..., r M ') T is _{(r 1, r 2, ...} , r M) to change a phase of each incoming wave with respect to T In this case, it becomes a received signal. Therefore, two received signal vectors when the phase of the incoming wave changes can be obtained from the received signal of one sample.

  Thereby, a plurality of beams can be formed from these data. As the beam forming method, for example, the direction of arrival estimation is performed from the received signal using the direction of arrival estimation algorithm, a beam having a peak in the direction of the estimation result is formed, and the direction of arrival estimation algorithm from the output signal of the signal sequence conversion means There is a method of estimating the direction of arrival using, and forming a beam having a peak in the direction of the estimation result.

  By configuring in this way, a plurality of beams can be formed from data of one sample, and a diversity effect can be obtained. Since this method does not require feedback, the throughput characteristics do not deteriorate. In addition, since transmission diversity can be performed between a plurality of different directivity patterns, stable transmission quality can be obtained even in a multi-wave environment where arrival direction estimation is not successful. A plurality of beams for performing transmission diversity can be formed.

の演算によって求められた相関行列Ｒの固有ベクトルのうち固有値の大きい方からＫ個の固有ベクトルを選択し、この固有ベクトルを前記重み付け手段に重み付け値として与える手段を備えることができる。 The directivity forming apparatus includes branching means for branching an input signal into M pieces, and M weighting means for weighting each of the M signals branched by the branching means, and the directivity control apparatus comprises: ,

Select the K eigenvectors from the largest eigenvalues of the eigenvectors of the correlation matrix R obtained in the calculation, Ru can be provided with a means for providing the eigenvectors as a weighting value to the weighting means.

A means for determining a threshold value of the eigenvalue in advance and determining the number K of output signals of the encoder and the number K of the directivity forming devices according to the number of eigenvalues exceeding the threshold; the weighting values in the device, Ru can be provided with means for the eigenvector corresponding to each eigenvalue exceeds the threshold value.

  Thus, if only eigenvectors for eigenvalues exceeding the threshold value are used, a diversity effect can be obtained without radiating radio waves in unnecessary directions.

Further, the M antenna elements, instead of the equal interval linear array antenna is constituted by the sub-array antenna composed of a plurality of antennas, the antenna arrangement of each sub-array antenna Ru can also be the same.

  According to a second aspect of the present invention, an encoder for generating K output signals using a transmission signal to a terminal station as an input signal, and an output signal of the encoder as an input signal, the same number as the number of antenna elements. The K directivity forming devices that output M signals, the directivity control device that controls the directivity of the directivity forming devices, and the m th signal of the K directivity forming devices are combined. This is an adaptive antenna transmission method applied to an adaptive antenna transmission apparatus provided with M combining means and M antenna elements that radiate output signals of the combining means.

の変換を行い、前記指向性制御装置により、前記ｒ₁〜ｒ_Mおよびｒ′₁〜ｒ′_Mに基づき指向性制御を行うところにある。 Here, a feature of the present invention is that the M antenna elements are configured by an equally spaced linear array antenna, and M received signals transmitted from the terminal station received by the M antenna elements. For the M received signals

It performs the conversion, by the directivity control unit, Ru near the place of performing directivity control on the basis of the r ₁ ~r _M and r _'1 ~r' _M.

の演算によって求められた相関行列Ｒの固有ベクトルのうち固有値の大きい方からＫ個の固有ベクトルを選択し、この固有ベクトルを前記重み付けの際の重み付け値として与えることができる。 The directivity forming device branches the input signal into M signals, weights each of the branched M signals, and the directivity control device

Select the K eigenvectors from the largest eigenvalues of the eigenvectors of the correlation matrix R obtained in the operation it might give the eigenvector as a weighted value when the weighting.

A threshold value of the eigenvalue is set in advance, and the number K of output signals of the encoder and the number K of the directivity forming devices are determined based on the number of eigenvalues exceeding the threshold, and the weighting value in the directivity forming device and Ru can be eigenvectors corresponding to each eigenvalue exceeds the threshold value.

Wherein the M antenna elements in place at regular intervals linearly array antenna constituted by the sub-array antenna composed of a plurality of antennas, the antenna arrangement of each sub-array antenna Ru can also be the same.

  According to the present invention, by forming a plurality of beams from data of one sample, it is possible to reduce the influence of propagation environment estimation error without reducing the throughput.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a first embodiment of the present invention, and shows a form in which directivity control is performed using an input signal sequence and a complex conjugate value of an input signal. In this figure, reference numeral 101 is an encoder, reference numerals 1021 to 102K are directivity forming apparatuses, reference numeral 103 is a directivity control apparatus, reference numerals 1041 to 104M are combiners, reference numerals 1051 to 105M are antenna elements, and reference numeral 106 is a signal sequence conversion. Means.

  A transmission signal to the terminal station is first input to the encoder 101 for each T symbol. The encoder generates a T × B symbol signal for a T symbol input signal. Here, B is the number of beams. As a signal generation method, for example, STC can be used (for example, see Non-Patent Document 4). The encoded signal is transmitted from each beam by assigning a transmission signal to each beam by a serial-parallel converter. Here, each beam is formed by the directivity forming devices 1021 to 102K. The directivity determination method formed by the directivity forming apparatus will be described below.

The directivity control apparatus 103 performs control using received signals r _{1 to} r _M received by the antenna elements 1051 to 105M and r ₁ ′ to r _M ′ obtained by converting the received signals at 106 as follows. Is called.

Here, when an L-wave arrival wave arrives at an equally spaced linear array antenna, the received signal rm at the antenna _m is expressed by the following equation.

Here, A _l represents the amplitude of the incoming wave 1, φ _l represents the phase of the incoming wave 1, and θ _l represents the arrival direction of the incoming wave 1. At this time, the complex conjugate value of the received signal can be expressed as follows.

（式６）と（式７）とを比較すると、到来方向に関する成分は等しく、到来位相の成分が変化していることが分かる。したがって（ｒ₁′，ｒ₂′，…，ｒ_M′）Tは（ｒ₁，ｒ₂，…，ｒ_M）Tに対して各到来波の位相がある変化をした場合の受信信号となる。したがって１サンプルの受信信号から、到来波の位相が変化した場合の２つの受信信号ベクトルを得ることができる。 Here, m ′ is m ′ = M + 1−m, and φ ₁ ^′ is the following equation.

Comparing (Equation 6) and (Equation 7), it can be seen that the components related to the arrival direction are equal and the component of the arrival phase changes. Therefore, (r ₁ ′, r ₂ ′,..., R _M ′) T is a received signal when the phase of each incoming wave changes with respect to (r ₁ , r ₂ ,..., R _M ) T. . Thus from one sample of the received signal, it is possible to obtain two reception signal vector when the phase of the incoming wave is changed.

  Therefore, a plurality of beams can be formed from these data. As a beam forming method, for example, an arrival direction estimation is performed from a received signal using an arrival direction estimation algorithm, a beam 1 having a peak in the direction of the estimation result is formed, and an arrival direction is estimated from an output signal of the signal sequence conversion means 106. There is a method in which the direction of arrival is estimated using the above algorithm and a beam 2 having a peak in the direction of the estimation result is formed.

  By configuring in this way, a plurality of beams can be formed from data of one sample, and a diversity effect can be obtained. Since this method does not require feedback, the throughput characteristics do not deteriorate. In addition, since transmission diversity can be performed between a plurality of different directivity patterns, stable transmission quality can be obtained even in a multi-wave environment where arrival direction estimation is not successful.

FIG. 2 is a diagram showing a directivity forming apparatus 103K in the second embodiment of the present invention. In this embodiment, directivity formation is realized by complex weighting for signals to each antenna, and each weight value is formed by an eigenvector beam obtained from the received signal sequence converted by the received signal sequence and the signal sequence converting means. In the figure, reference numeral 20k1 is a branching means for branching the input signal into M, and reference numerals 202K1 to 202KM are complex weighting means. The directivity control device 103 performs the following calculation on the input signal to obtain a correlation matrix between the antennas.

Then select the K eigenvectors from the larger eigenvalues of the eigenvectors of the correlation matrix R, the eigenvectors Ru can form multiple beams be used as the value of the weights of the weighting means.

Furthermore, if a threshold value is provided for each eigenvalue, K is determined by the number of values equal to or greater than a certain threshold value, and only eigenvectors corresponding to eigenvalues greater than the threshold value are used, radio waves are emitted in unnecessary directions. let Ru it is possible to obtain a diversity effect without. The means for determining K is not shown in the figure, but is provided in the directivity control device 103, and the directivity forming devices 1021 to 102K are connected to any directivity forming device according to the value of K. The operation may be instructed to be paused, or a means for determining K may be separately provided outside the figure, and the directivity forming apparatuses 1021 to 102K may have any directivity depending on the value of K. The forming apparatus may be instructed to pause its operation.

Further, in the configuration shown in FIG. 1, the equally-spaced linear array antenna (an example of four elements) shown in FIG. 3 is used. However, as shown in FIG. 4, this is composed of a plurality of antennas and the antenna arrangement is the same. in a Ru can be replaced by a sub-array antennas (example in which the sub-array antenna with 3 elements).

  FIG. 5 shows the effect of the present invention. Evaluation was performed with the following parameters. The number of antenna elements in the base station is 8, the number of beams in the proposed method is 2 beams, the incoming wave is 100 waves, the central direction of the arrival direction is 0 degree, and the propagation environment is flat fading. The angle spread at the base station is assumed to have a Laplacian distribution, and the spread angle is a parameter.

  The transfer function between each antenna and the base station antenna in the uplink can be estimated without error, the angle spread is the same in the uplink and downlink, and the arrival direction and arrival phase of the elementary waves are set independently. As a method of the present invention, here, two of the eigenvectors of the correlation matrix of (Equation 9) having the larger eigenvalue are selected to form directivity. The number of trials was 10,000.

  In the conventional method, the direction of arrival is estimated from the phase inclination of the signal received by each antenna, and equal gain combining directivity is formed in the estimated direction. The evaluation was performed with the characteristics of the reception level 1% value (vertical axis in FIG. 3) with respect to the angular spread (horizontal axis in FIG. 3). In the conventional method, as the angular spread increases, the power of the path other than the beam direction increases, so that the reception level characteristic deteriorates. In contrast, according to the present invention, the diversity effect increases as the angular spread increases, and the reception level characteristic is improved. In particular, an improvement effect of 10 dB is obtained in an environment with an angular spread of 10 degrees.

  As described above, in the present invention, a plurality of beams can be formed from which one can obtain a diversity effect even from one sample data. Therefore, it is possible to reduce the influence of the propagation environment estimation error without lowering the throughput and to obtain good transmission quality.

  According to the present invention, by forming a plurality of beams from data of one sample, it is possible to reduce the influence of propagation environment estimation error without reducing the throughput, thereby reducing the deterioration of communication quality. Therefore, it is possible to improve the service quality for the terminal station user and contribute to the expansion of opportunities for user solicitation.

The block diagram of the adaptive antenna transmitter of 1st embodiment of this invention. The block diagram of the directivity formation apparatus of 2nd embodiment of this invention. The block diagram of an equally-spaced linear array antenna. The block diagram of a subarray antenna. The figure for demonstrating the effect of this invention. The figure for demonstrating the directivity control method in the conventional adaptive antenna transmitter.

Explanation of symbols

101 Encoders 1021 to 102K Directivity forming device 103 Directivity control devices 1041 to 104M Synthesizers 1051 to 105M Antenna element 106 Signal sequence conversion means 20k1 Branch means 202k1 to 202kM Complex weighting means 301 Propagation environment estimation error detection means 4011 to 401N Antenna elements 4021 to 402N Weighting device 402 Weight control device 404 Reference signal generating device 405 Combining and branching device

Claims (6)

An encoder that takes a transmission signal to the terminal station as an input signal and generates K output signals;
K directivity forming devices that use the output signal of this encoder as an input signal and output M signals as many as the number of antenna elements;
A directivity control device for controlling the directivity of the directivity forming device;
M combining means for combining the m-th signals of the K directivity forming devices;
In an adaptive antenna transmission apparatus comprising M antenna elements that radiate output signals of the combining means,
The M antenna elements are configured by equally spaced linear array antennas,
M received signals transmitted from the terminal station received by the M antenna elements are used as input signals, and the M received signals are

Comprising a signal series conversion means for converting
The directivity control apparatus comprises means for performing directivity control on the basis of the r ₁ ~r _M and r _'1 ~r' _M,
The directivity forming device is:
Branching means for branching the input signal into M pieces;
M weighting means for weighting each of the M signals branched by the branching means;
With
The directivity control device includes:

An adaptive antenna transmitting apparatus comprising: means for selecting K eigenvectors having the largest eigenvalue among eigenvectors of the correlation matrix R obtained by the calculation of and providing the eigenvector as a weighting value to the weighting means . Means for presetting a threshold value of the eigenvalue, and determining the number K of signals output from the encoder and the number K of directivity forming devices according to the number of eigenvalues exceeding the threshold value;
The adaptive antenna transmission apparatus according to claim 1, further comprising: means for setting a weighting value in the directivity forming apparatus to an eigenvector corresponding to each eigenvalue exceeding the threshold value.   3. The adaptive antenna transmission according to claim 1, wherein the M antenna elements are configured by subarray antennas configured by a plurality of antennas instead of the equally spaced linear array antennas, and the antenna arrangement of each of the subarray antennas is the same. apparatus. An encoder that takes a transmission signal to the terminal station as an input signal and generates K output signals;
K directivity forming devices that use the output signal of this encoder as an input signal and output M signals as many as the number of antenna elements;
A directivity control device for controlling the directivity of the directivity forming device;
M combining means for combining the m-th signals of the K directivity forming devices;
In an adaptive antenna transmission method applied to an adaptive antenna transmission apparatus comprising M antenna elements that radiate output signals of the combining means,
The M antenna elements are constituted by equally spaced linear array antennas,
M received signals transmitted from the terminal station received by the M antenna elements are used as input signals, and the M received signals are

Conversion
By the directivity control unit, it has rows directivity control based on the r ₁ ~r _M and r _'1 ~r' _M,
The directivity forming device branches the input signal into M signals, weights each of the branched M signals,
By the directivity control device,

An adaptive antenna transmission method characterized in that K eigenvectors are selected from the eigenvectors of the correlation matrix R obtained by the above calculation from the eigenvectors having the larger eigenvalues, and these eigenvectors are given as weighting values in the weighting . Predetermining a threshold value of the eigenvalue, and determining the number K of signals output from the encoder and the number K of directivity forming devices according to the number of eigenvalues exceeding the threshold value,
The adaptive antenna transmission method according to claim 4, wherein the weighting value in the directivity forming device is an eigenvector corresponding to each eigenvalue exceeding the threshold.   6. The adaptive antenna transmission according to claim 4 or 5, wherein the M antenna elements are configured by subarray antennas including a plurality of antennas instead of the equally spaced linear array antennas, and the antenna arrangement of each of the subarray antennas is the same. Method.

Images