Communications: directive radio wave systems and devices (e.g. – Directive – Utilizing correlation techniques
Reexamination Certificate
1999-12-28
2002-04-23
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Utilizing correlation techniques
C342S372000, C342S373000
Reexamination Certificate
active
06377213
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a wave arrival direction estimating method and an antenna apparatus having a wave arrival direction estimating function, to be applied to a radar, a mobile communication base station, and the like.
This application is based on Japanese Patent Application No. 10-372740, filed Dec. 28, 1998, the entire content of which is incorporated herein by reference.
A technique of estimating a wave arrival direction has been used for various kinds of controls, such as, for example, a tracing of a flying object or a detecting of its arrival direction by radar, a control of directing a beam pattern to a specific mobile station or, on the contrary, not directing a beam pattern to a specific mobile station, from an antenna at a base station of a mobile radio communication system, and a detection of an arrival direction of an interference wave and forming a null of a beam pattern to this direction, and the like.
Among such techniques for estimating a wave arrival direction, there has been known MUSIC (Multiple Signal Classification) method, particularly as a high-resolution estimating technique capable of simultaneously estimating arrival directions of a plurality of waves of the same frequency. Details of this MUSIC are described in R. O. Schmit, “Multiple Emitter Location and Signal Parameter Estimation”, IEEE Trans. Antennas and Propagation, vol. AP-34, no. 3, pp. 276-280, March, 1986 (Document 1).
The MUSIC is an algorithm for estimating wave arrival directions by the following processes. At first, high-frequency signals output from antenna elements constituting an array antenna are input to receivers. Then, a covariance matrix of reception signals from the receiver is obtained, and an eigen value and an eigen vector of this matrix are calculated. By comparing sizes of the eigen value and noise power, the eigen vector is divided into a signal subspace and a noise subspace. Wave arrival directions are estimated by utilizing the orthogonality of the signal subspace and the noise subspace. This method is characterized in that the method is generally called a high-resolution method as the wave arrival direction is estimated by utilizing the null of the beam pattern, and that it is possible to simultaneously estimate directions of arrival waves by the number of “the number of antenna elements minus one”.
However, according to the MUSIC, in order to simultaneously estimate the directions of a plurality of arrival waves, it is necessary to prepare receivers for receiving and demodulating high-frequency signals output from the antenna elements to obtain reception signals by the number of antenna elements. For example, in the case of applying the MUSIC under a propagation environment where the number of arrival waves is unknown, it is necessary to prepare a sufficient number of antenna elements. Accordingly, it is also necessary to provide receivers by the same number as that of the antenna elements. As a result, the size of a wave arrival direction estimating apparatus becomes large, leading to a higher cost of the apparatus.
When the number of the antenna elements increases, the order of the covariance matrix to be used for estimating the wave arrival directions becomes larger. As the covariance matrix is obtained from an average of a large number of reception signals, the volume of data becomes larger and it also takes a long processing time. Further, when the order of the matrix becomes larger at the time of calculating the eigen value of this covariance matrix, the time required for the calculation increases in proportion to the cube of the order. Taking a long time for the calculation becomes a serious problem particularly in the case of estimating the wave arrival direction in on-line processing.
As means for solving the above-described problems of the MUSIC, there have already been proposed the following two techniques.
A first method provides the following processing. As shown in
FIG. 1
, a high-frequency switch
202
sequentially selects high-frequency signals output from antenna elements
201
. Only one high-frequency signal is input to one receiver
203
at one time. A reception signal from the receiver
203
is guided to an arrival direction estimation circuit
204
, and a calculation similar to that of the MUSIC is carried out. Details of this method are described in SEKIZAWA, “Development of Linear Array Antenna for Estimating Arrival Directions of Multiple-waves”, Singaku-Giho, RCS96-128, pp. 7-14, January, 1997 (Document 2).
According to this method, it is possible to provide a small apparatus at low cost, as only one receiver
203
is required. However, as the high-frequency signals output from the antenna elements
201
are sequentially demodulated in time series by the receiver
203
, it is not possible to carry out a precise estimation of the arrival directions when the propagation environment has changed during this processing. Particularly, this problem becomes serious when the number of the antenna elements
201
increases. Further, according to this method, the calculation itself is basically similar to that of the MUSIC, and it is not possible to improve the processing time.
A second method is to use a technique called beam space MUSIC (hereinafter to be referred to as BS-MUSIC). Details of this BS-MUSIC are described in HARRYB. LEE and MICHAELS. WENGROVITZ, “Resolution Threshold of Beamspace MUSIC For Two Closely Spaced Emitters”, IEE Trans. Acoust. Speech and Signal Processing, vol. ASSP-38, no. 9, pp. 1545-1559, September, 1990 (Document 3).
The BS-MUSIC will be explained briefly with reference to FIG.
2
. High-frequency signals output from antenna elements
211
are simultaneously input to a beam synthesis circuit
212
, to form beams of a plurality of antennas. The high-frequency signals for the beams are sequentially received by a receiver
213
, and a wave arrival direction is estimated by an arrival direction estimation circuit
214
based on the reception signals. The difference of algorithms between the MUSIC and the BS-MUSIC is that, according to the BS-MUSIC, a calculation expression includes a weight vector multiplied to a high-frequency signal from each antenna element
211
when an antenna beam has been formed. Basically, the calculation procedure is similar to that of the MUSIC. According to the BS-MUSIC, as shown in
FIG. 2
, only one receiver
213
is necessary in a similar manner to that of the method of the Document 2, and it is possible to provide a small apparatus at low cost.
However, according to the BS-MUSIC, the arrival waves from the directions to which the antenna beams are directed are received by main lobes of the beams, but the arrival waves from the directions to which the antenna beams are not directed are received by side lobes of the beams. This means that the arrival waves received by the side lobes are not substantially received. In other words, while it is possible to estimate the wave arrival directions for the waves to which the beams are directed by the beam synthesis circuit
212
, it is not possible to estimate the wave arrival direction for the waves to which the beams are not directed. However, in the case of applying the BS-MUSIC under the unknown propagation environment, it is necessary to direct antenna beams to all directions in order to estimate the an arrival direction of the wave from all directions. Further, the number of arrival waves that can be separated in the BS-MUSIC is “the number of beams formed by the beam synthesis circuit minus one”, and this number also has a limitation like that of the MUSIC.
Accordingly, in order to carry out a precise estimation of wave arrival direction in the BS-MUSIC under the environment having a potential of existence of a large number of arrival waves, it is necessary to form a large number of antenna beams by using a large number of antenna elements assuming a large number of arrivals of waves. Thus, it is not possible to solve the second problem that it takes a long processing time.
As described above, according to the
Odachi Noriaki
Shoki Hiroki
Blum Theodore M.
Bushiki Kaisha Toshiba
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