JP2008086003A - Mimo antenna apparatus and wireless communication apparatus having it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform both interference wave suppression and MIMO demodulation in a MIMO antenna apparatus. <P>SOLUTION: A MIMO antenna apparatus comprises a plurality of antenna elements 1a, 1b, and 1c for receiving wireless signals; a demodulation circuit 3 which performs the MIMO-demodulation of each received signal to generate a demodulated signal and also decides the signal quality of the demodulated signal; a signal level detection circuit 4 for detecting a signal level of each received signal; and a controller 5. The controller 5, when a signal quality of the demodulated signal is lower than a threshold T1, (1) when signal levels of all the received signal are not lower than a threshold T2, the number of data streams of a MIMO communication system used by a transmission side wireless station apparatus and the demodulation circuit 3 is decreased, and (2) when a signal level of at least one received signal is lower than the threshold T2, a modulation-demodulation method of a MIMO communication system used by the transmission side wireless station apparatus and the demodulation circuit 3 is changed to a modulation-demodulation method using a lower transmission rate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an antenna device for a wireless communication device controlled to maintain good communication quality while increasing communication capacity and realizing high-speed communication in mobile communication using a mobile phone or the like, and in particular, a MIMO antenna. The present invention relates to a device and a wireless communication device including the device.

  As an antenna device that employs MIMO (Multi-Input Multi-Output) technology that simultaneously transmits and receives radio signals of a plurality of channels using a plurality of antenna elements, there is a MIMO antenna device disclosed in Patent Document 1, for example.

  In the mobile communication system provided with the MIMO antenna apparatus of Patent Document 1, the transmission side encodes a transmission signal by a communication path encoder to generate M signals on the transmission side, and M of these M signals are generated. To generate M complex modulation signals (modulation symbols), and then a complex matrix operation unit generates a complex matrix composed of these M complex modulation signals and M × L complex coefficients. To generate L complex signals, and the generated L complex signals are transmitted by L transmission antenna elements. At this time, the beam forming is achieved for the radio signals respectively transmitted from the L transmitting antenna elements by executing the matrix operation so that the complex matrix calculating unit gives different complex weights to the M modulated signals. Is done. As a result, the mobile communication system of Patent Document 1 aims to obtain a transmission diversity effect in addition to beamforming for interference wave suppression. Further, the present invention provides a data transmission method in which the modulation method and the transmission speed are appropriately controlled even when the environment of the propagation channel is dynamically changed due to the diversity effect. Furthermore, the mobile communication system of Patent Document 1 includes N × M complex coefficients by a MIMO demodulator for N received signals received using N receiving antenna elements on the receiving side. Multiplying the complex matrix to generate M complex signals (received symbols), M demodulating each of the M complex signals by M demodulators to generate M demodulated signals, and then channel decoding The communication unit decodes the M demodulated signals by the transmitter and outputs the decoded data as received data. At this time, by applying a MMSE (Minimum Mean Square Error) algorithm to reduce interference in the MIMO demodulator on the receiving side, it becomes possible to minimize the influence of noise and interference. .

  As described above, in the mobile communication system of Patent Document 1, on the transmission side, M modulation signals are multiplied by a complex matrix composed of M × L elements to generate L complex signals. A MIMO antenna apparatus capable of high-speed data communication by transmission path multiplexing by transmitting from L transmission antenna elements, and capable of extending the interference limit by reducing interference at the MIMO demodulator on the receiving side Can be provided.

  Furthermore, as a conventional MIMO antenna apparatus provided with a transversal filter, there is a MIMO antenna apparatus disclosed in Patent Document 2, for example.

  A MIMO-OFDM receiver provided with the MIMO antenna apparatus of Patent Document 2 removes interference waves by transversal filters provided for a plurality of receiving antenna elements, and then performs MIMO demodulation. This enables MIMO reception even in an environment with interference waves. Therefore, according to Patent Document 2, in a multipath environment where co-channel interference exists, interference can be suppressed, timing reproduction and degradation of channel estimation accuracy can be compensated, and high-speed signal transmission can always be realized. A MIMO-OFDM receiver can be provided. As described above, the MIMO-OFDM receiver disclosed in Patent Document 2 can perform MIMO reception even in an environment with interference waves by performing MIMO demodulation after removing the interference waves using a transversal filter provided for each reception antenna element. Thus, a MIMO-OFDM receiver equipped with a MIMO antenna device that enables high-speed wireless transmission is provided.

Japanese Patent Application Laid-Open No. 2004-266586. Japanese Patent Laying-Open No. 2005-065197.

  The conventional MIMO antenna device described in Patent Document 1 has the following problems. In this conventional example, for the purpose of speeding up data transmission as much as possible, by providing M modulators and L transmission antenna elements on the transmission side, transmission diversity effect in addition to beamforming for interference wave suppression Is disclosed. However, since the MIMO antenna apparatus of Patent Document 1 has a large number of transmitting antenna elements, it is extremely difficult to mount a plurality of antenna element groups on a small device having a wavelength of one wavelength or less, such as a cellular phone. It was difficult. In addition, even when the MIMO antenna apparatus disclosed in Patent Document 1 is used for a mobile phone base station, there are problems in that the cost increases due to an increase in the number of antenna elements and the control becomes complicated.

  On the other hand, the conventional MIMO antenna device using a plurality of transversal filters described in Patent Document 2 has the following problems. In this conventional example, since a transversal filter is provided for each receiving antenna element, it is possible to suppress the interference wave, but there is a drawback that the receiving circuit scale becomes large. That is, it is impossible to configure the MIMO antenna device of the conventional example in a small shape or to be used for a portable wireless device that is driven by a battery.

  The object of the present invention is to solve the above problems and achieve high quality by combining interference wave suppression and MIMO demodulation processing when a desired reception quality cannot be obtained even with a small-sized MIMO antenna apparatus. It is another object of the present invention to provide a MIMO antenna apparatus capable of performing high-speed communication and a wireless communication apparatus for a mobile unit including the same.

According to the MIMO antenna apparatus according to an aspect of the present invention,
In a MIMO antenna apparatus for receiving a plurality of radio signals transmitted after being modulated by a MIMO (Multi-Input Multi-Output) communication system having a predetermined number of data streams and a modulation / demodulation method by a transmitting-side radio station apparatus,
A plurality of antenna elements respectively receiving the plurality of radio signals;
Detecting means for detecting the received signal level of each of the plurality of radio signals;
MIMO demodulating means for demodulating the plurality of radio signals to generate a first demodulated signal and determining signal quality of the first demodulated signal;
A wireless transmission means for wirelessly transmitting a control signal for controlling a MIMO communication scheme used by the transmission-side radio station apparatus to the transmission-side radio station apparatus;
The radio transmission means so as to change at least one of the number of data streams and the modulation / demodulation method of the MIMO communication system used by the transmission side radio station apparatus and the MIMO demodulation means based on the received signal level and the signal quality And control means for controlling the transmission side radio station apparatus by transmitting the control signal to the MIMO demodulation means,
In the case where the signal quality of the first demodulated signal is less than a predetermined first threshold,
(1) A data stream of a MIMO communication scheme used by the transmitting radio station apparatus and the MIMO demodulating means when the received signal level relating to all of the plurality of radio signals is equal to or higher than a predetermined second threshold value. Reduce the number,
(2) Modulation / demodulation of a MIMO communication method used by the transmitting-side radio station apparatus and the MIMO demodulating means when a received signal level related to at least one of the plurality of radio signals is less than the second threshold value. The method is changed to a modulation / demodulation method having a transmission rate lower than the current transmission rate.

  In the MIMO antenna apparatus, when the signal quality of the first demodulated signal is equal to or higher than the first threshold value, the control means sets the received signal level related to all of the plurality of radio signals to the second level. The modulation / demodulation method of the MIMO communication method used by the transmitting-side radio station apparatus and the MIMO demodulation means is changed to a modulation / demodulation method having a transmission rate higher than the current transmission rate. Features.

  In the MIMO antenna apparatus, the control means performs demodulation by the MIMO demodulation means when the number of data streams of the MIMO communication scheme used by the transmitting radio station apparatus and the MIMO demodulation means is reduced to a predetermined number. When the number of times exceeds a predetermined maximum number of times of demodulation, the number of data streams of the MIMO communication scheme used by the transmitting side radio station apparatus and the MIMO demodulating means is increased.

The MIMO antenna device is
When the number of data streams is one, adaptive demodulation means for generating a second demodulated signal by weighting and demodulating the plurality of radio signals so that the main beam is directed in the direction of the desired wave signal;
Switch means for switching to input the plurality of radio signals to the MIMO demodulation means or the adaptive demodulation means,
The control means further controls the switch means to switch the switch means to input the plurality of radio signals to the MIMO demodulating means, and the signal quality of the first demodulated signal is the first threshold value. If it is less than the value,
(1) The number of data streams of the MIMO communication scheme used by the transmitting-side radio station apparatus and the MIMO demodulating means when the received signal level related to all of the plurality of radio signals is equal to or higher than the second threshold value. Control the switch means to switch the switch means to input the plurality of radio signals to the adaptive demodulation means,
(2) Modulation / demodulation of a MIMO communication method used by the transmitting-side radio station apparatus and the MIMO demodulating means when a received signal level related to at least one of the plurality of radio signals is less than the second threshold value. The method is changed to a modulation / demodulation method having a transmission rate lower than the current transmission rate.

  In the MIMO antenna apparatus, the adaptive demodulation means weights the plurality of radio signals so as to direct the main beam in the direction of the desired wave signal by executing a repetitive iterative process. .

  Further, in the MIMO antenna apparatus, the control means controls the switch means so as to switch the switch means to input the plurality of radio signals to the MIMO demodulation means, and the signal quality of the first demodulated signal. Is equal to or higher than the first threshold, and when the received signal level related to all of the plurality of radio signals is equal to or higher than the second threshold, the transmitting-side radio station apparatus and the MIMO demodulating means The modulation / demodulation method of the MIMO communication system used by the method is changed to a modulation / demodulation method having a transmission rate higher than the current transmission rate.

  Still further, in the MIMO antenna apparatus, when the control means controls the switch means to switch the switch means to input the plurality of radio signals to the adaptive demodulation means, the demodulation by the adaptive demodulation means. When the number of times exceeds a predetermined maximum number of demodulations, the switch unit is switched to control the switch unit to input the plurality of radio signals to the MIMO demodulator unit, and the transmitting side radio station apparatus and the MIMO demodulator The number of data streams of the MIMO communication scheme used by the means is increased.

  In the MIMO antenna apparatus, the radio transmission unit transmits the control signal to the transmitting-side radio station apparatus using at least one of the plurality of antenna elements.

  In addition, according to the present invention, there is provided a wireless communication apparatus including the MIMO antenna apparatus.

  According to the present invention, by providing the above configuration, the number of data streams in the MIMO communication scheme can be reduced based on the signal quality of the demodulated signal and the signal level of the received signal, and / or the MIMO communication scheme. By changing the modulation / demodulation method, the number of MIMO communication system data streams and the modulation / demodulation method are adaptively controlled when a desired reception quality cannot be obtained even with a small-sized MIMO antenna apparatus. Furthermore, it is possible to provide a MIMO antenna apparatus capable of performing high-quality and high-speed communication by achieving both interference wave suppression and MIMO demodulation processing, and a mobile radio communication apparatus including the MIMO antenna apparatus. .

  The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows. In MIMO wireless communication that performs adaptive modulation, when the demodulated signal quality falls below a threshold value, the reception signal level of each antenna element constituting the MIMO antenna apparatus is acquired, and these reception signal levels are set to a predetermined reception level. When the power is higher than the power, the transmission side radio station apparatus is notified, and one of a plurality of M transmission data streams is reduced. When the number of data streams is reduced to one, the amplitude and phase of a plurality of received signals may be controlled using an adaptive demodulator, thereby directing the beam in the direction of the desired wave signal and in the direction of the interference wave signal. You can turn the null. On the other hand, if it is less than the threshold value, the transmitting side radio station apparatus is notified to transmit using a modulation / demodulation method having a lower transmission rate. As a result, high-quality and high-speed communication can be realized by combining high-speed wireless transmission of MIMO communication and interference wave suppression technology of an adaptive array antenna.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference numerals throughout the drawings to describe the embodiment of the present invention, and repeated description thereof is omitted.

First embodiment.
FIG. 1 is a block diagram showing a configuration of a MIMO antenna apparatus according to the first embodiment of the present invention. Hereinafter, the MIMO antenna apparatus of the present embodiment will be described with reference to FIG. In FIG. 1, three receiving antenna elements 1a, 1b, and 1c respectively receive and receive three different radio signals transmitted from a transmitting-side radio station apparatus (not shown) using a predetermined MIMO communication system. The antenna elements 1 a, 1 b, and 1 c input received radio signals to the analog / digital (A / D) conversion circuit 2. The A / D conversion circuit 2 includes three A / D converters corresponding to each input radio signal, and A / D conversion processing is separately performed on each radio signal by these A / D converters. The processed signals (hereinafter referred to as received signals) are output to the MIMO demodulation circuit 3 and the signal level detection circuit 4, respectively. The MIMO demodulator circuit 3 performs a MIMO demodulation process on the three received signals and outputs one demodulated signal, and determines the bit error rate (BER) of the demodulated signal as a reference representing the signal quality of the demodulated signal. The information of the determination result is output to the controller 5. As the signal quality, a packet error rate may be used instead of the bit error rate (BER), or a throughput (for example, represented by a rate of received data) may be used. The signal level detection circuit 4 detects the signal levels of the three reception signals, and outputs detection result information to the controller 5. The signal level is detected, for example, in the form of carrier power to noise power ratio (CNR) or desired signal power to interference signal power and noise power ratio (SINR). Also, the MIMO demodulation circuit 3 sends the number of times of demodulating the received signal data (hereinafter referred to as the number of demodulations) to the controller 5 in units of, for example, a predetermined amount of data (number of bits or number of packets). Based on the BER and signal level information, the controller 5 executes a MIMO adaptive control process to be described later with reference to FIGS. 7 and 8, whereby the transmitting-side radio station apparatus and the MIMO demodulation circuit 3 use it. Change the communication method.

  In this embodiment, the communication method used in the transmitting-side radio station apparatus and the MIMO demodulation circuit 3 is determined by the number of communication data streams and the communication modulation / demodulation method. Specifically, the MIMO antenna apparatus and the transmitting-side radio station apparatus can selectively execute any one of the MIMO communication using one to three data streams. When the number of data streams is one, this is also referred to as SISO (Single-Input Single-Output) communication. Also, the MIMO antenna apparatus and the transmitting-side radio station apparatus can selectively perform MIMO communication (or SISO communication) using any one of a plurality of modulation / demodulation methods having different transmission rates. Are listed in order of increasing, it is possible to selectively use any one of BPSK, QPSK, 16QAM, and 64QAM. Note that the modulation / demodulation method to be used is not limited to the methods listed above, and can be changed according to the embodiment. When changing the communication method used by the transmitting-side radio station apparatus and the MIMO demodulator circuit 3 (that is, when changing at least one of the number of data streams and the modulation / demodulation method), the controller 5 connects to the radio transmitter circuit 6 and the radio transmitter circuit 6 The transmission antenna element 7 is used to transmit a control signal for requesting the transmission side radio station apparatus to change the modulation process of the communication method (that is, MIMO communication or SISO communication) in the transmission side radio station apparatus, At the same time, the demodulation processing of the communication method (that is, MIMO communication or SISO communication) used in the MIMO demodulation circuit 3 is changed.

  The MIMO antenna apparatus according to the present embodiment includes a high-frequency filter that separates a signal having a predetermined frequency from each radio signal received by the receiving antenna elements 1a, 1b, and 1c, and amplifies the signal before the A / D conversion circuit 2. It is preferable to provide a high-frequency amplifier for performing as necessary. Further, the MIMO antenna apparatus of the present embodiment includes a high-frequency circuit such as a mixer for converting the frequency of each received signal output from the A / D conversion circuit 2, an intermediate frequency circuit, and a preceding stage of the MIMO demodulation circuit 3. It is preferable to provide a signal processing circuit or the like as necessary. The components listed above are omitted in the present specification and drawings for the sake of simplicity.

  Here, as an example, a case where the number of receiving antenna elements is three will be described as an example, but a configuration with two or four or more receiving antenna elements is also possible. Further, the case where the number of transmitting antenna elements is one will be described as an example, but a configuration in which a plurality of transmitting antenna elements are provided is also possible.

  According to the MIMO antenna apparatus of the present embodiment described above, with the above configuration, the controller 5 determines the number of data streams of the MIMO communication scheme based on the signal quality of the demodulated signal and the signal level of the received signal. Even if a small-sized MIMO antenna apparatus does not achieve the desired reception quality by performing reduction and / or changing the modulation / demodulation method of the MIMO communication system, the data stream of the MIMO communication system A MIMO antenna apparatus capable of high-quality and high-speed communication can be provided by adaptively controlling the number and the modulation / demodulation method.

  FIG. 2 is a block diagram showing a configuration of a MIMO antenna apparatus according to a modification of the present embodiment. In the MIMO antenna apparatus of this modification, the transmission antenna element 7 of FIG. 1 is integrated with one of the reception antenna elements 1a, 1b, 1c for MIMO reception (in the case of FIG. 2, the antenna element 1c). It is characterized by having the structure made. In FIG. 2, the antenna element 1c includes an antenna duplexer (duplexer) 21 at the lower end thereof, and a radio signal received by the antenna element 1c is input to the A / D conversion circuit 2 via the antenna duplexer 21, The radio signal output from the radio transmission circuit 6 excites the antenna element 1 c via the antenna duplexer 21. The antenna duplexer 21 is used to separate the reception signal and the transmission signal when the frequencies of the reception signal and the transmission signal are different. The receiving antenna element with which the transmitting antenna element 7 is integrated may be either the receiving antenna element 1a or 1b. With the above configuration, the MIMO antenna apparatus of the modification of FIG. 2 can reduce the number of antenna elements in the apparatus, and can efficiently realize the MIMO antenna apparatus in a small mobile radio communication terminal.

  In the modification of FIG. 2, the configuration in which only one receiving antenna element is used as the transmitting antenna element has been described as an example. However, the present invention is not limited to this, and a plurality of receiving antenna elements 1a, 1b, 1c A configuration in which two or more are used as transmitting antenna elements is also possible. Thereby, even at the time of transmission, an improvement in antenna gain due to the effect of beam forming by the array can be expected. Furthermore, when two or more of the plurality of receiving antenna elements 1a, 1b, and 1c are used as transmitting antenna elements, it is possible to execute transmission diversity and MIMO transmission represented by switching diversity by switching control. . This makes it possible to transmit a more stable and faster wireless signal. In the modification of FIG. 2, the configuration using the antenna duplexer 21 for separating the reception signal and the transmission signal has been described as an example. However, the configuration is not limited to this, and a configuration using a switch or a circulator is also possible. is there. The switch is optimal when the signal transmission time and the signal reception time are different, and the circulator can be used even when there is no frequency difference and time difference between the transmission signal and the reception signal.

  Next, an example in which the MIMO antenna apparatus according to the present embodiment is mounted as a portable wireless communication apparatus will be described with reference to FIGS. FIG. 3 is a perspective view illustrating a configuration of a portable wireless communication device including the MIMO antenna device according to the first implementation example of the present embodiment.

  The portable wireless communication apparatus of FIG. 3 includes an upper casing 31 and a lower casing 32 that are substantially rectangular parallelepiped shapes, and are configured as a foldable mobile phone connected by a hinge portion 33. The upper casing 31 includes a speaker 35 and a display 36, and the lower casing 32 includes a keyboard 37 and a microphone 38. Inside the upper housing 31, a strip conductor 1aa is provided so as to be close to the left end thereof and parallel to the longitudinal direction of the portable wireless communication device, and the strip conductor 1aa is a hinge constituting a part of the hinge portion 33. The strip conductor 1aa and the hinge conductor 1ab are both electrically connected to the partial conductor 1ab and operate as the receiving antenna element 1a. Similarly, a strip conductor 1ba is provided in the upper housing 31 so as to be close to the right end thereof and parallel to the longitudinal direction of the portable wireless communication device. The strip part conductor 1ba and the hinge part conductor 1bb are electrically connected to the constituent hinge part conductor 1bb, and both operate as the receiving antenna element 1b. In the lower housing 32, a receiving antenna element 1c made of a strip-shaped conductor bent into a U-shape is provided. In the mounting example shown in FIG. 3, a part of the reception antenna element 1 c is provided so as to penetrate the boom portion 34 protruding from the lower end of the lower housing 32, but instead of the reception antenna element 1 c. The entirety may be provided inside the lower housing 32. Further, a transmitting antenna element 7 made of a rod-shaped conductor is provided so as to protrude from the lower housing 32. The portable wireless communication apparatus includes a wireless communication circuit 39 including the A / D conversion circuit 2, the MIMO demodulation circuit 3, the signal level detection circuit 4, the controller 5, and the wireless transmission circuit 6 of FIG. The / D conversion circuit 2 is connected to the reception antenna elements 1a, 1b, and 1c, and the wireless transmission circuit 6 of the wireless communication circuit 39 is connected to the transmission antenna element 7.

  FIG. 4 is a perspective view illustrating a configuration of a portable wireless communication device including the MIMO antenna device according to the second implementation example of the present embodiment. In this implementation example, the rod-shaped transmitting antenna element 7 of FIG. 3 is removed, and instead, the wireless communication circuit 39 further includes an antenna duplexer 21, and any one of the receiving antenna elements 1a, 1b, and 1c. (For example, the receiving antenna element 1a) is shared with the transmitting antenna element. According to the portable radio communication device of the implementation example of FIG. 4, by removing the antenna element protruding outside the device, a portable radio communication device more compact than the case of the implementation example of FIG. 3 can be provided.

  Furthermore, FIG. 5 is a perspective view showing a configuration of a portable wireless communication apparatus including a MIMO antenna apparatus according to a third implementation example of the present embodiment. In this configuration, the portable wireless communication device includes two receiving antenna elements 1 a and 1 b provided in the upper casing 31 and one transmitting antenna element 7 provided in the lower casing 32. As an option, the antenna duplexer 21 may be provided in the wireless communication circuit 39, and either of the reception antenna elements 1a and 1b may be shared as another transmission antenna element, and transmission diversity may be performed by two transmission antenna elements.

  FIG. 6 is a perspective view showing a configuration of a portable wireless communication apparatus including a MIMO antenna apparatus according to a fourth implementation example of the present embodiment. In this configuration, the portable wireless communication apparatus includes two antenna elements 1a and 1b in the upper casing 31, and one of them is shared as a transmission antenna element. According to this configuration, the internal structure can be greatly simplified as compared with the portable wireless communication device according to another implementation example.

  Hereinafter, the operation principle of the MIMO antenna apparatus of this embodiment will be described. It should be noted that in this specification, mathematical formulas input in an image and mathematical formulas input in a text are mixedly used, and in order to identify each mathematical formula, a series of serial numbers (1) described at the end of each mathematical formula. , (2),... Are referred to as “expression (1), expression (2),.

  The MIMO communication system increases the transmission capacity by spatially multiplexing a plurality of signal sequences transmitted simultaneously in the same frequency band by using a plurality of antenna elements in each of a transmitter and a receiver, and performs MIMO demodulation. This is a technique for increasing the total transmission rate for a plurality of later signal sequences. Here, as an example, description will be made based on the eigenmode transmission method. When the number of antenna elements of the transmitter and the receiver is n, the received signal y can be expressed by the following equation.

[Equation 1]
y = Hx + w (1)

Here, y representing a received signal is a vector of size n, and each element thereof represents a signal received by each antenna element of the receiver. H is a matrix of size n × n and is called a channel matrix, and each element H _ij is a propagation coefficient between the j-th antenna element of the transmitter and the i-th antenna element of the receiver, that is, Represents the amount of phase rotation and the amount of amplitude attenuation of signals transmitted and received between these antenna elements. Also, x representing the transmitted signal, the size is a vector of n, and each element x _i is a signal transmitted from each antenna element of the transmitter, represent signals that are orthogonal to each other. w is a vector of size n, each element of which represents the thermal noise received at each antenna element of the receiver.

  In order to obtain the channel matrix H at the receiver, the receiver stores a predetermined pilot signal x in advance, the transmitter transmits this known pilot signal x to the receiver, and the receiver Based on the stored pilot signal x and received signal y (ie, transmitted pilot signal x), a channel matrix H is calculated from Equation (1).

  Here, when the singular value decomposition (SVD) for the channel matrix H is performed, the following equation is obtained.

In Equation (2), U, Σ, and V are each a matrix of size n × n, and Σ is the i-th row and i-th column element σ _i (0 ≦ i ≦ q) and other elements Is a matrix of zero. U _i and v _i are i-th column vectors of matrices U and V, respectively, and are orthogonal to other column vectors. q is the rank of the channel matrix H. In the following description, it is assumed that q = n. The superscript H represents a complex conjugate transpose. Here, the matrix U and V, the size satisfies the following equation with respect to the unit matrix I _n of n × n.

[Equation 2]
_{^{U H U = I n (3}} )
[Equation 3]
V ^H V = I _n (4)

  Further, when eigenvalue decomposition (EVD) is performed, the following equation is obtained.

In equation (5), λ _i is the eigenvalue of the product HH ^H of the channel matrix, and λ _i = σ _i ² .

The vector u _i ^H, the matrix is orthogonal to the other row vectors, which are elements of U ^H, are used to weight the signals transmitted from the respective antenna elements of the transmitter (amplitude and phase), the vector u _i Are orthogonal to other column vectors that are elements of the matrix U, and are used to weight signals received at each antenna element of the receiver. By using weights in this way, orthogonal directivity can be obtained.

Here, from Expression (1), the received signal power is Hx (Hx) ^H = HH ^H xx ^H. The matrix xx ^H represents the transmission signal power. However, since the elements of the vector x are signals orthogonal to each other, the matrix xx ^H is a diagonal matrix diag [x ₁ x ₁ ^* , x ₂ x ₂ ^* ,..., X _n x _n ^* ]. On the other hand, the matrix HH ^H is a diagonal matrix diag [λ ₁ , λ ₂ ,..., Λ _q ]. That is, a plurality of propagation paths can be separated by using orthogonal weights in the antenna elements of the transmitter and the receiver, and the received signal power at this time is λ _i x _i x _i ^* . When the signals x _i are all equal, the received signal power in each propagation path is a ratio of the eigenvalues λ _i .

  Here, the derivation of the received signal power will be specifically described by taking as an example a MIMO communication system in which the number of antenna elements of the transmitter is two and the number of antenna elements of the receiver is two. In this case, the channel matrix H and the transmission signal vector x transmitted from the antenna element of the transmitter are expressed by the following equations.

  Here, if w is a noise vector (amplitude ratio with respect to the transmission signal vector x) received by the antenna element of the receiver, the reception signal vector y can be obtained by the following equation.

Next, a covariance matrix R _yy of the received signal vector is obtained by the following equation.

In the above equation, the vector y ^H is expressed by the following equation.

Usually, in a MIMO communication system, different signals transmitted from different antenna elements of a transmitter are uncorrelated with each other. Here, the fact that the transmission signal is uncorrelated will be described. It is assumed that the transmission signal sequence is a one-dimensional signal sequence composed of elements “−1” and “1”. For example, an example in which the transmission signal vectors x ₁ and x ₂ each have four elements is shown below.

[Equation 4]
x ₁ = (1, -1,1,1) (11)
[Equation 5]
x ₂ = (1,1, -1,1) (12)

If the correlation is defined as the sum of products of each element of the signal sequence divided by the number of sequences, the correlation value R ₁₂ of the transmission signal vectors x ₁ and x ₂ is expressed by the following equation.

[Equation 6]
R ₁₂ = (1 · 1 + (− 1) · 1 + 1 · (−1) + 1 · 1) / 4 = 0 (13)

That is, it is uncorrelated if the correlation value R ₁₂ is 0. Conversely, the correlation value is 1 when x ₁ = x ₂ . Further, the noise vector is uncorrelated with the transmission signal vector, and the noise vectors received by different antenna elements are also uncorrelated with each other.

As described above, the expected value of the covariance matrix R _yy of Equation (9) can be calculated as the following equation using the received signal power.

  Here, the following equation was used based on the assumption about the transmission signal vector.

According to the operation principle of the MIMO antenna apparatus described above, the transmission capacity C _MIMO of the MIMO communication system is given by the following equation.

Here, SNR is the total transmission signal power to noise ratio, that is, SNR / n = x _i x _i ^* . The unit of the transmission capacity C _MIMO is [bit / second / Hz]. On the other hand, in the case of normal one-to-one communication (SISO) using one antenna element in the transmitter and one antenna element in the receiver, the transmission capacity C _SISO is obtained by the following equation.

In Expression (17), h is a propagation coefficient, and the unit of the transmission capacity C _SISO is [bit / second / Hz].

For example, in order to simplify the comparison between Expression (16) and Expression (17), hh ^* = λ _i = λ and SNR · λ / n >> 1. At this time, the transmission capacity C _MIMO in Expression (16) is calculated as follows.

On the other hand, the transmission capacity C _SISO of the equation (17) is calculated as the following equation.

For example, when n = 4 and SNR · λ = 1024, MIMO transmission capacity C _MIMO = 4 · (10−2) = 32 [bits / second / Hz] and SISO transmission capacity C _SISO = 10 [bits] / Sec / Hz], and it can be seen that the MIMO transmission capacity is higher than the SISO transmission capacity.

  As described above, the MIMO antenna apparatus spatially multiplexes signals by allocating orthogonal directivities to a plurality of signal sequences to increase the transmission capacity, and thereby the sum of a plurality of signal sequences after MIMO demodulation. The transmission speed can be increased.

According to equation (16), it is understood that the MIMO transmission capacity increases as the eigenvalue λ _i calculated from the channel matrix H increases. Since the eigenvalue λ _i is obtained from each element of the channel matrix H, the above means that the larger the elements of the channel matrix H, the faster the transmission is possible. Further, as described in Equation (1), the received signal includes a thermal noise vector w. Since an actual receiver cannot remove the thermal noise component, this becomes an error factor in calculating the eigenvalue λ _i from the channel matrix H. Accordingly, obtaining as much received signal power as possible leads to an increase in transmission speed in the MIMO antenna apparatus.

  On the other hand, when there is an interference wave, Expression (1) is as follows.

[Equation 7]
_{y = Hx + H i + w} (20)

Here, H _i is a vector of size n, and each element represents an interference wave signal received by each antenna element of the receiver. Here, the interference wave signal is a signal of the same channel interference wave of the same frequency that has arrived from the adjacent base station apparatus or a desired wave signal, but has arrived via a different long path, resulting in a time delay. A delayed wave signal is shown. The delayed wave signal deteriorates the quality of screen display as a ghost of television broadcasting, for example, in analog wireless communication such as television broadcasting or radio broadcasting. On the other hand, in digital wireless communication, thermal noise, an interference wave signal of the same channel, and a delayed wave signal all directly affect the bit error of the desired wave signal, thereby degrading the signal quality of the desired wave.

In Expression (20), when each element of the vectors H _i and w is sufficiently smaller than each element of the vector Hx, high-speed communication is possible because SINR is large, but each element of the vectors H _i and w When the signal reaches a level that cannot be ignored, the error rate performance of the demodulated signal rapidly deteriorates. For example, in the case of QPSK modulation, SINR is required to be approximately 13 dB in order to satisfy an error rate of 10 ⁻⁶ .

Here, from the equation (20), the factors that degrade the demodulated signal quality can be classified into elements of the interference wave signal vector _Hi and elements of the thermal noise vector w. Thermal noise is determined by the bandwidth of the modulation signal and the noise performance of the receiver, so there is little variation due to the surrounding environment. That is, the SINR decreases mainly when the received signal level decreases. On the other hand, even when the received signal level is large, the SINR is small if the signal level of the interference wave signal is also large. That is, when the signal quality of the demodulated signal is deteriorated, it is important to determine whether it is caused by a decrease in the received signal level or an interference wave signal. Here, the signal quality represents a bit error rate (BER), a packet error rate, or a throughput. Based on the above operation principle, a method for controlling the MIMO antenna apparatus of the present embodiment will be described below.

FIG. 7 is a flowchart showing a MIMO adaptive control process executed by the controller 5. In the initial state, the MIMO antenna apparatus and the transmitting-side radio station apparatus execute MIMO communication using three data streams and a predetermined modulation / demodulation method, and the MIMO antenna apparatus receives the three receiving antenna elements 1a, 1b, and 1c. All of the radio signals are received. In step S1 of FIG. 7, the controller 5 causes the MIMO demodulation circuit 3 to perform demodulation processing based on each received signal acquired by the A / D conversion circuit 2, and determines the BER as the signal quality of the demodulated signal. Information of the determination result is acquired from the MIMO demodulation circuit 3. Next, in step S2, the controller 5 determines whether or not the BER of the demodulated signal is equal to or greater than a predetermined threshold value T1, and if it is less than the threshold value T1, the controller 5 proceeds to step S3 and exceeds the threshold value T1. If there is, the process proceeds to step S7. Here, the threshold value T1 of the BER is set to, for example, 10 ⁻⁶ when the MIMO demodulator circuit 3 acquires an instantaneous BER (that is, a BER measured in a very short time interval), When the MIMO demodulator circuit 3 acquires the BER time-averaged over a predetermined time in consideration of the Rayleigh fading multiwave environment, it is set to 10 ⁻² , for example. Next, in step S3, the controller 5 causes the signal level detection circuit 4 to detect the signal level of each reception signal based on each reception signal acquired by the A / D conversion circuit 2, and detects the information of the detection result as signal level detection. Obtained from circuit 4. In step S4, the controller 5 determines whether or not there is a received signal having a signal level less than a predetermined threshold value T2. If the signal levels of all the received signals are equal to or higher than the threshold value T2, step S4 is performed. The process proceeds to S5, and if not, the process proceeds to Step S6.

Here, the threshold T2 of the signal level of the received signal is determined by (a) a modulation / demodulation method (that is, BPSK, QPSK, 16QAM, or 64QAM) used by the MIMO antenna apparatus and the transmitting-side radio station apparatus, and (b ) Depending on whether the signal quality of the demodulated signal and the signal level of each received signal are acquired as instantaneous values or time averaged values. Here, with reference to FIG. 9 and FIG. 10, the determination of the threshold value T2 of the signal level of the received signal will be described. In the graphs of FIGS. 9 and 10, CNR is used as an example of the signal level of the received signal. FIG. 9 is a graph showing instantaneous CNR and BER. In this case, the CNR threshold value is set to a value corresponding to BER = 10 ⁻⁶ set as the instantaneous BER threshold value for each modulation / demodulation method, that is, CNR = 11 dB in the case of BPSK. In the case of QPSK, CNR = 14 dB is set, in the case of 16 QAM, CNR = 21 dB is set, and in the case of 64 QAM, CNR = 27 dB is set. FIG. 10 is a graph showing time-averaged CNR and BER. In this case, the CNR threshold value is set to a value corresponding to BER = 10 ⁻² set as the time-averaged BER threshold value for each modulation / demodulation method, that is, CNR = 14 dB in the case of BPSK. In the case of QPSK, CNR = 17 dB is set, in the case of 16 QAM, CNR = 23 dB is set, and in the case of 64 QAM, CNR = 28 dB is set. The signal level threshold value T2 is not limited to the value exemplified above, and can be set to a value corresponding to a signal level (for example, power) that is error-free in each modulation / demodulation method used.

  In step S5, the controller 5 reduces the number of data streams of the MIMO communication between the transmitting side radio station apparatus and the MIMO demodulation circuit 3. For example, when the transmitting-side radio station apparatus and the MIMO antenna apparatus are performing MIMO communication using three data streams, MIMO communication using two data streams or SISO communication using one data stream is performed. Change the communication method to execute. When the number of data streams becomes 1 by reducing the number of data streams in step S5 (when step S10 is YES), the controller 5 proceeds to the SISO communication process of step S11. If NO, the process proceeds to step S12.

  FIG. 8 is a subroutine showing step S11 of the SISO communication process of FIG. In step S14 of FIG. 8, the controller 5 continues the demodulation process (that is, the demodulation process of SISO communication) to the MIMO demodulation circuit 3 so as to demodulate only the received signal received by the receiving antenna element having the maximum signal level. Let Next, in step S15, the controller 5 determines whether the number of demodulation processes by the MIMO demodulation circuit 3 has exceeded a predetermined maximum number of demodulations. The maximum number of demodulations in step S15 is determined as a period for monitoring the radio wave condition. Alternatively, in step S15, instead of comparing the number of demodulation processes with the maximum number of demodulations, it may be determined whether or not the demodulation process by the MIMO demodulation circuit 3 has timed out continuously for a predetermined time. Until it is determined in step S15 that the number of demodulation processes exceeds the maximum number of demodulations, the process returns to step S14 and the demodulation process is continued. If the maximum number of demodulations is exceeded, the controller 5 in step S16, The number of data streams of the station apparatus and the MIMO demodulation circuit 3 is increased, and the communication system is changed from SISO to MIMO. In step S16, the controller 5 initializes the number of data streams to be preferably the maximum value (ie, 3). After increasing the number of data streams, the controller 5 returns to step S1.

  As a modification, in step S10, it is determined whether or not the number of data streams is reduced to a predetermined number other than 1 (for example, 2). If YES, the SISO communication process in step S11 is not performed. Only step S16 of FIG. 8 may be executed. According to this, the range in which the number of data streams is changed is limited, and the number of data streams can be changed while always performing MIMO communication without performing SISO communication.

  In step S6, the controller 5 changes the modulation / demodulation method of the transmission side radio station apparatus and the MIMO demodulation circuit 3 to a modulation / demodulation method with a transmission rate lower than the current transmission rate. For example, when the transmitting-side radio station apparatus and the MIMO antenna apparatus are performing MIMO communication using 64QAM, the transmission side radio station apparatus and the MIMO antenna apparatus are changed to MIMO communication using any modulation / demodulation method of 16QAM, QPSK, or BPSK. After changing the modulation / demodulation method, the controller 5 proceeds to step S12.

  When the BER of the demodulated signal is greater than or equal to the threshold value T1 in step S2, the process proceeds to step S7 as described above. In step S7, similarly to step S3, the controller 5 causes the signal level detection circuit 4 to detect the signal level of each reception signal based on each reception signal acquired by the A / D conversion circuit 2, and determines the detection result. Information is acquired from the signal level detection circuit 4. In step S4, the controller 5 determines whether or not there is a received signal having a signal level lower than the threshold value T2 as in the case of step S4, and the signal levels of all the received signals are equal to or higher than the threshold value T2. If there is, the process proceeds to step S9, and if not, the process proceeds to step S12. In step S9, the controller 5 changes the modulation / demodulation method of the transmission-side radio station apparatus and the MIMO demodulation circuit 3 to a modulation / demodulation method with a transmission rate faster than the current transmission rate. For example, when the transmitting-side radio station apparatus and the MIMO antenna apparatus are performing MIMO communication using BPSK, the transmission side radio station apparatus and the MIMO antenna apparatus are changed to MIMO communication using any one of the modulation / demodulation methods of QPSK, 16QAM, and 64QAM. After changing the modulation / demodulation method, the controller 5 proceeds to step S12. The controller 5 causes the MIMO demodulation circuit 3 to continue the demodulation process in step S12, and then, in step S13, the number of demodulation processes by the MIMO demodulation circuit 3 is equal to a predetermined maximum demodulation number (for example, the same number as the maximum demodulation number in step S15). If the maximum number of demodulations has been exceeded, the process returns to step S1. If not, the process returns to step S12 and the MIMO demodulation circuit 3 continues the demodulation process. As a modified example, when the BER of the demodulated signal is equal to or greater than the threshold value in step S2, the controller 5 returns to step S1 and continues the demodulation process to the MIMO demodulator circuit 3 without executing steps S7 to S9. You may let them.

  As described above, according to the MIMO antenna apparatus of the present embodiment, the number of data streams in the MIMO communication scheme is reduced based on the signal quality of the demodulated signal and the signal level of the received signal, and / or the MIMO. By changing the modulation / demodulation method of the communication system, even if the MIMO antenna apparatus has a small shape, if the desired reception quality cannot be obtained, the number of data streams and the modulation / demodulation method of the MIMO communication system are adaptively controlled. By doing so, it is possible to provide a MIMO antenna apparatus capable of high-quality and high-speed communication, and a wireless communication apparatus for a mobile body including the same.

Second embodiment.
FIG. 11 is a block diagram showing a configuration of a MIMO antenna apparatus according to the second embodiment of the present invention. In addition to the configuration of the MIMO antenna apparatus shown in FIG. 1, the MIMO antenna apparatus of the present embodiment connects the adaptive demodulation circuit 12 and the A / D conversion circuit 2 to either the MIMO demodulation circuit 3 or the adaptive demodulation circuit 12. And a switch circuit 11. When receiving an interference wave signal, the MIMO antenna apparatus of the present embodiment switches the switch circuit 11 so as to execute a demodulation process using a repetitive calculation by the adaptive demodulation circuit 12 under a predetermined condition. It is characterized by that.

  The switch circuit 11 includes three switches corresponding to the three reception signals output from the A / D conversion circuit 2, and these switches send the three reception signals to the MIMO demodulation circuit 3 under the control of the controller 5. Each is input or input to the adaptive demodulation circuit 12. The three received signals input to the adaptive demodulation circuit 12 are adjusted in amplitude by the amplitude adjusters 13a, 13b, and 13c, respectively, and then adjusted in phase by the phase shifters 14a, 14b, and 14c, respectively. Here, the amplitude adjustment amounts by the amplitude adjusters 13a, 13b, and 13c and the phase adjustment amounts by the phase shifters 14a, 14b, and 14c are obtained by obtaining three received signals and performing weight calculation (details will be described later) based on these signals. Controlled by the amplitude phase controller 17. The received signals after the amplitude and phase adjustment are synthesized by the synthesizer 15, and then the demodulator 16 performs a demodulation process on the synthesized received signal and outputs a demodulated signal. As the signal quality, a packet error rate or a throughput may be used instead of the bit error rate (BER). Each of the MIMO demodulator circuit 3 and the adaptive demodulator circuit 12 gives the controller 5 the number of times (demodulation number) of demodulating received signal data, for example, in units of a predetermined amount of data (number of bits or number of packets). send. The controller 5 executes a MIMO adaptive control process to be described later with reference to FIGS. 13 and 14 based on the information on the BER, the signal level, and the number of demodulations, whereby the transmission side radio station apparatus and the MIMO demodulation circuit 3 Change the communication method used.

  FIG. 12 is a block diagram showing a configuration of a MIMO antenna apparatus according to a modification of the present embodiment. As in the modification of the first embodiment shown in FIG. 2, the MIMO antenna apparatus of this modification uses the transmission antenna element 7 in FIG. 11 as the reception antenna elements 1a, 1b, 1c for MIMO reception. 1 (in the case of FIG. 12, the antenna element 1 c) is integrated. With the above configuration, the MIMO antenna apparatus according to the modification of FIG. 12 can reduce the number of antenna elements in the apparatus.

  In the MIMO demodulation, generally, a known signal (reference signal) is stored in advance in the reception-side radio station apparatus, and the same signal as this known signal is transmitted from the transmission-side radio station apparatus to the reception-side radio station apparatus. The apparatus detects the amplitude and phase of the received signal by calculating the correlation between the previously stored known signal and the received known signal. Here, the method for calculating the correlation is performed by multiplying the complex conjugate of the known signal stored in advance by the receiving-side radio station apparatus and the received known signal. Further, when the known signal includes a plurality of bits, it is possible to calculate the correlation for each bit and use the sum or average value as the correlation value. Also, in different signal sequences (streams), the same signal as the known signal is transmitted from the transmitting side radio station apparatus at different times, and propagation demodulation is performed for each stream in the receiving side radio station apparatus, thereby enabling MIMO demodulation. However, if the interference wave signal is strong, the correlation cannot be calculated in the first place. This is because the correlation with the known signal is lowered by adding the interference wave signal to the received signal.

  As described above, when an interference wave signal is received, it is assumed that normal MIMO demodulation is not possible. Therefore, an adaptive array antenna interference suppression technique for controlling the received signal to approach the known signal is required. Adaptive array antennas operate to maximize SINR as a result of improving signal quality. In particular, when the interference wave signal is not a known signal, adaptive control by repetitive calculation is preferable. The MIMO antenna apparatus according to the present embodiment includes the adaptive demodulation circuit 12 so that the above-described suitable processing can be executed.

  FIGS. 13 and 14 are flowcharts showing the MIMO adaptive control process executed by the controller 5 of FIG. In step S <b> 21 of FIG. 13, the controller 5 initializes the switch circuit 11 to be connected to the MIMO demodulation circuit 3. In step S22, the controller 5 causes the MIMO demodulation circuit 3 to perform demodulation processing based on each received signal acquired by the A / D conversion circuit 2, and determines the BER as the signal quality of the demodulated signal. Result information is obtained from the MIMO demodulator circuit 3. Next, in step S23, the controller 5 determines whether or not the BER of the demodulated signal of the MIMO demodulator circuit 3 is equal to or greater than a predetermined threshold value T1, and if it is less than the threshold value T1, the process proceeds to step S24. If it is equal to or greater than the threshold value T1, the process proceeds to step S29. Here, the threshold value T1 of BER is set in the same manner as in step S2 of FIG. Next, in step S24, the controller 5 causes the signal level detection circuit 4 to detect the signal level of each reception signal based on each reception signal acquired by the A / D conversion circuit 2, and detects the detection result information as a signal level detection. Obtained from circuit 4. In step S25, the controller 5 determines whether or not there is a reception signal having a signal level less than a predetermined threshold T2, and when the signal level of at least one reception signal is less than the threshold T2. The process proceeds to step S26, and if not, the process proceeds to step S32 in FIG. Here, the threshold T2 of the signal level is set in the same manner as in step S4 in FIG. In step S26, as in step S6 of FIG. 7, the controller 5 changes the modulation / demodulation method of the transmission-side radio station apparatus and the MIMO demodulation circuit 3 to a modulation / demodulation method with a transmission rate lower than the current transmission rate. In step S27, the demodulation process is continued by the MIMO demodulation circuit 3, and then in step S28, the controller 5 causes the number of demodulation processes by the MIMO demodulation circuit 3 to exceed a predetermined maximum number of demodulations, as in step S13 of FIG. If the maximum number of demodulations has been exceeded, the process returns to step S22. If not, the process returns to step S27 to allow the MIMO demodulation circuit 3 to continue the demodulation process.

  When the BER of the demodulated signal is not less than the threshold value T1 in step S23, the process proceeds to step S29 as described above. Steps S29 to S31 are the same as steps S7 to S9 in FIG. 7, and in step S29, the controller 5 applies each signal level detection circuit 4 to each signal level detection circuit 4 based on each reception signal acquired by the A / D conversion circuit 2. The signal level of the received signal is detected, and information on the detection result is acquired from the signal level detection circuit 4. In step S30, the controller 5 determines whether or not there is a received signal having a signal level lower than the threshold value T2 as in step S25, and the signal levels of all the received signals are equal to or higher than the threshold value T2. If there is, the process proceeds to step S31. If not, the process proceeds to step S27. In step S31, the controller 5 changes the modulation / demodulation method of the transmission side radio station apparatus and the MIMO demodulation circuit 3 to a modulation / demodulation method with a transmission rate faster than the current transmission rate, as in step S9 of FIG. After changing the modulation / demodulation method, the controller 5 proceeds to step S27.

  If the signal levels of all received signals are greater than or equal to the threshold value T2 in step S25, the process proceeds to step S32 in FIG. 14 as described above. In step S32, the controller 5 reduces the number of MIMO communication data streams between the transmitting-side radio station apparatus and the MIMO demodulation circuit 3 to one, and changes the communication method so that SISO communication is executed. The controller 5 connects the switch 11 to the adaptive demodulation circuit 12 in step S33, and causes the adaptive demodulation circuit 12 to perform demodulation processing based on each received signal acquired by the A / D conversion circuit 2 in step S34. The adaptive demodulator circuit 12 receives each reception signal so that the main beam of the MIMO antenna apparatus is directed in the direction of the desired wave signal, or the null is directed in the direction of the desired wave signal and in the direction of the interference wave signal. The signal is weighted and demodulated. The weighting (that is, the weight calculation) by the adaptive demodulation circuit 12 will be described later in detail. Next, in step S35, the controller 5 determines whether the demodulation processing by the adaptive demodulation circuit 12 exceeds a predetermined maximum number of demodulations (for example, the same number as the maximum number of demodulations in step S28), and exceeds the maximum number of demodulations. If so, the process proceeds to step S36 in order to examine again the status of the desired wave signal and the interference wave signal when using MIMO communication, and if not, the process returns to step S34 to continue the demodulation process to the adaptive demodulation circuit 12. Let In step S36, the controller 5 changes the communication method used in the transmission side radio station apparatus to MIMO, and returns to step S21 in FIG. Here, the change of the communication method in step S36 includes increasing the number of data streams of the communication method used in the transmitting-side radio station apparatus so as to be preferably the maximum value (that is, three).

  As described above, according to the MIMO antenna apparatus of the present embodiment, MIMO that can perform processing for interference wave suppression including using adaptive demodulation according to the status of the desired wave signal and the interference wave signal. An antenna device can be realized. In particular, when the desired wave signal is strong (that is, when step S23 is YES), the signal level detection circuit 4 detects the signal level of the received signal in step S29, and the threshold value for switching the demodulation method to adaptive demodulation. If the received signal level is higher than (that is, the threshold value T2 of step S25) (that is, if step S30 is YES), in step S31, the modulation / demodulation method of the radio signal to be transmitted is fast. The transmission side radio station apparatus is notified to change to the modulation / demodulation method (for example, increase the number of modulation / demodulation methods). As a result, high-speed and high-quality communication can be realized. In addition, by setting the maximum number of times of demodulation in steps S28 and S35, it is possible to determine a period for re-monitoring the radio wave condition, and it is possible to optimally cope with changes in the propagation environment of the desired wave signal and the interference wave signal. Can be realized.

  Hereinafter, the demodulation processing by the adaptive demodulation circuit 12 in step S34 will be described. In this embodiment, the amplitude / phase controller 17 performs adaptive demodulation processing by iterative calculation using only the reception signals of the three reception antenna elements 1a, 1b, and 1c. This processing depends on the number of reception antenna elements. Obviously, it can be changed.

  Signals received by the receiving antenna elements 1 a, 1 b, and 1 c are converted into digital signals by the A / D conversion circuit 2 and input to the amplitude / phase controller 17 via the switch circuit 11. The digital signal can be regarded as a vector having three elements in this embodiment. The amplitude / phase controller 17 adjusts the amplitude so that the signal quality (for example, BER) obtained as a result of demodulating the synthesized output signal obtained by synthesizing each received signal after amplitude and phase control by the synthesizer 15 with the demodulator 16 is the best. Amplitude adjustment amounts by the adjusters 13a, 13b, and 13c and phase adjustment amounts by the phase shifters 14a, 14b, and 14c are determined. A method for calculating the amplitude adjustment amounts by the amplitude adjusters 13a, 13b, and 13c and the phase adjustment amounts (hereinafter referred to as weights) by the phase shifters 14a, 14b, and 14c will be described below.

  The weight Wi for each of the receiving antenna elements 1a, 1b, and 1c is defined by the following equation.

[Equation 8]
Wi = Ai · exp (j · φi) (21)

  In formula (21), j is an imaginary unit. The parameter i takes values 1, 2, and 3, and corresponds to signals received by the receiving antenna elements 1a, 1b, and 1c, respectively. Ai represents the amplitude adjustment amount, and φi represents the phase adjustment amount. In the following description, for simplification, a method for calculating the weight w (t) for one received signal s (t) received by any one of the receiving antenna elements 1a, 1b, 1c will be described. To do.

  There are several methods for obtaining the weight. Here, an example using the Least Means Descent (LMS) method is shown. In this method, the receiving-side radio station apparatus that performs adaptive demodulation processing holds a known signal sequence (or reference signal) r (t) in advance, and the desired wave signal includes this known reference signal r (t). The transmitted radio station apparatus transmits and controls the amplitude adjustment amount and the phase adjustment amount of the received desired wave signal so as to be close to the reference signal held by the received desired wave signal. In the present embodiment, it is assumed that the reference signal is held in the amplitude phase controller 17 as an example. Specifically, the amplitude phase controller 17 multiplies the digital signal s (t) received and input to the adaptive demodulation circuit 12 by a weight w (t) having amplitude and phase components. The regulators 13a, 13b, and 13c and the phase shifters 14a, 14b, and 14c are controlled. A residual e (t) between the signal obtained by multiplying the weight w (t) by the digital signal s (t) and the reference signal r (t) is obtained. At this time, the residual e (t) is obtained by the following equation.

[Equation 9]
e (t) = r (t) −w (t) × s (t) (22)

  Here, the residual e (t) takes a positive or negative value. Therefore, the minimum value of the squared value of the residual e (t) obtained by the equation (22) is obtained incrementally (that is, repeated calculation is executed). Accordingly, the weight w (t, m + 1) obtained by the (m + 1) th iteration calculation is obtained by the following equation using the mth weight w (t, m).

[Equation 10]
w (t, m + 1) = w (t, m) + u × s (t) × e (t, m) (23)

  Here, u is called a step size. If the step size u is large, there is an advantage that the number of iterations for the weight to converge to the minimum value is reduced. However, if the step size u is too large, it vibrates near the minimum value. There is a disadvantage that it ends up. Therefore, it is necessary to be careful in selecting the step size u depending on the system. On the contrary, by decreasing the step size u, the weight stably converges to the minimum value, but the number of repeated calculations increases. As the number of repeated calculations increases, it takes time to obtain the weight. If the weight calculation time is slower than the change time of the surrounding environment (for example, several milliseconds), the signal quality using this weight cannot be improved. Therefore, when determining the step size u, it is necessary to select a fast and stable convergence condition as much as possible. Further, the residual e (t, m) in the equation (23) is defined by the following equation.

[Equation 11]
e (t, m) = r (t) −w (t, m) × s (t) (24)

  Equation (23) is updated incrementally using the value of Equation (24). Note that the maximum number of iterations for obtaining the weight is set so that the weight calculation time does not become slower than the switching time of the wireless system.

  Here, the weight calculation method based on the steepest descent method has been described as an example, but the present invention is not limited to this. For example, it is also possible to use an RLS (Recursive Least-Squares) method or an SMI (Sample Matrix Inversion) method that can make a determination earlier. Although the calculation time is shortened by this method, the calculation in the amplitude phase controller 17 becomes complicated.

  Further, when the signal system modulation method is constant envelope modulation having a constant envelope such as digital phase modulation, CMA (Constant Modulus Algorithm) can also be used.

  As described above, according to the embodiment of the present invention, in the MIMO antenna apparatus capable of performing adaptive demodulation processing, the MIMO antenna apparatus is configured when the signal quality of the demodulated signal is equal to or lower than the threshold value T1. A MIMO antenna apparatus that obtains a reception signal level in each antenna element and enables optimal MIMO communication according to a wireless environment in which a desired wave signal and an interference wave signal exist based on the obtained reception signal level. Can be realized.

  According to the present invention, based on the signal quality of the demodulated signal and the signal level of the received signal, the number of data streams in the MIMO communication scheme is reduced and / or the modulation / demodulation method in the MIMO communication scheme is changed. Therefore, even a small-sized MIMO antenna apparatus can perform high-quality and high-speed communication by combining interference wave suppression and MIMO demodulation processing when desired reception quality cannot be obtained. An antenna device and a wireless communication device for a mobile body including the antenna device can be provided.

  As a further modification according to the second embodiment, when one interference wave signal exists when performing MIMO communication using three data streams, wireless communication is performed using MIMO communication using two data streams. Can be configured, and MIMO demodulation can be performed by repeatedly performing adaptive control for each data stream.

  As described above, according to the configuration of the present embodiment, even if the MIMO antenna apparatus has a small shape, the number of MIMO communication system data streams and the modulation / demodulation method are applied when a desired reception quality cannot be obtained. A MIMO antenna apparatus capable of performing high-speed and high-speed communication by controlling both the interference control and the interference wave suppression and the MIMO demodulation processing, and a mobile communication apparatus having the MIMO antenna apparatus Can be provided.

It is a block diagram which shows the structure of the MIMO antenna apparatus which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the MIMO antenna device which concerns on the modification of the 1st Embodiment of this invention. It is a perspective view which shows the structure of the portable radio | wireless communication apparatus provided with the MIMO antenna apparatus based on the 1st implementation example of the 1st Embodiment of this invention. It is a perspective view which shows the structure of the portable radio | wireless communication apparatus provided with the MIMO antenna apparatus based on the 2nd implementation example of the 1st Embodiment of this invention. It is a perspective view which shows the structure of the portable radio | wireless communication apparatus provided with the MIMO antenna apparatus based on the 3rd implementation example of the 1st Embodiment of this invention. It is a perspective view which shows the structure of the portable radio | wireless communication apparatus provided with the MIMO antenna apparatus based on the 4th implementation example of the 1st Embodiment of this invention. It is a flowchart which shows the MIMO adaptive control process performed by the controller 5 of FIG. It is a subroutine which shows step S11 of the SISO communication process of FIG. It is a graph which shows instantaneous CNR and BER for demonstrating determination of the threshold value in the MIMO adaptive control process of FIG. FIG. 8 is a graph showing time-averaged CNR and BER for explaining threshold determination in the MIMO adaptive control process of FIG. 7. FIG. It is a block diagram which shows the structure of the MIMO antenna device which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the MIMO antenna device which concerns on the modification of the 2nd Embodiment of this invention. It is a flowchart which shows the 1st part of the MIMO adaptive control process performed by the controller 5 of FIG. It is a flowchart which shows the 2nd part of the MIMO adaptive control process performed by the controller 5 of FIG.

Explanation of symbols

1a, 1b, 1c ... receiving antenna element,
1aa, 1ba ... strip conductors,
1ab, 1bb ... hinge part conductor,
2 ... A / D conversion circuit,
3 ... MIMO demodulation circuit,
4 ... signal level detection circuit,
5 ... Controller,
6 ... wireless transmission circuit,
7: Transmitting antenna element,
11 ... Switch circuit,
12 ... Adaptive demodulation circuit,
13a, 13b, 13c ... amplitude adjusters,
14a, 14b, 14c ... phase shifter,
15 ... Synthesizer,
16 ... demodulator,
17 ... Amplitude phase controller,
21 ... Antenna duplexer,
31 ... upper housing,
32 ... lower housing,
33 ... Hinge part,
34 ... Boom part,
35 ... Speaker,
36 ... display,
37 ... Keyboard,
38 ... Microphone,
39: Wireless communication circuit.

Claims (9)

In a MIMO antenna apparatus for receiving a plurality of radio signals transmitted after being modulated by a MIMO (Multi-Input Multi-Output) communication system having a predetermined number of data streams and a modulation / demodulation method by a transmitting-side radio station apparatus,
A plurality of antenna elements respectively receiving the plurality of radio signals;
Detecting means for detecting the received signal level of each of the plurality of radio signals;
MIMO demodulating means for demodulating the plurality of radio signals to generate a first demodulated signal and determining signal quality of the first demodulated signal;
A wireless transmission means for wirelessly transmitting a control signal for controlling a MIMO communication scheme used by the transmission-side radio station apparatus to the transmission-side radio station apparatus;
The radio transmission means so as to change at least one of the number of data streams and the modulation / demodulation method of the MIMO communication system used by the transmission side radio station apparatus and the MIMO demodulation means based on the received signal level and the signal quality And control means for controlling the transmission side radio station apparatus by transmitting the control signal to the MIMO demodulation means,
In the case where the signal quality of the first demodulated signal is less than a predetermined first threshold,
(1) A data stream of a MIMO communication scheme used by the transmitting radio station apparatus and the MIMO demodulating means when the received signal level relating to all of the plurality of radio signals is equal to or higher than a predetermined second threshold value. Reduce the number,
(2) Modulation / demodulation of a MIMO communication method used by the transmitting-side radio station apparatus and the MIMO demodulating means when a received signal level related to at least one of the plurality of radio signals is less than the second threshold value. A MIMO antenna apparatus, wherein the method is changed to a modulation / demodulation method having a transmission rate lower than a current transmission rate.   When the signal quality of the first demodulated signal is equal to or higher than the first threshold value, the control means has a received signal level related to all of the plurality of radio signals equal to or higher than the second threshold value. 2. The modulation / demodulation method of the MIMO communication system used by the transmitting-side radio station apparatus and the MIMO demodulation means is changed to a modulation / demodulation method having a transmission rate higher than the current transmission rate. The MIMO antenna apparatus described.   In the case where the number of data streams of the MIMO communication scheme used by the transmission side radio station apparatus and the MIMO demodulation unit is reduced to a predetermined number, the control unit sets the predetermined number of demodulations by the number of demodulations by the MIMO demodulation unit. 3. The MIMO antenna apparatus according to claim 1, wherein when the number exceeds, the number of data streams of the MIMO communication scheme used by the transmitting-side radio station apparatus and the MIMO demodulating means is increased. The MIMO antenna device is
When the number of data streams is one, adaptive demodulation means for generating a second demodulated signal by weighting and demodulating the plurality of radio signals so that the main beam is directed in the direction of the desired wave signal;
Switch means for switching to input the plurality of radio signals to the MIMO demodulation means or the adaptive demodulation means,
The control means further controls the switch means to switch the switch means to input the plurality of radio signals to the MIMO demodulating means, and the signal quality of the first demodulated signal is the first threshold value. If it is less than the value,
(1) The number of data streams of the MIMO communication scheme used by the transmitting-side radio station apparatus and the MIMO demodulating means when the received signal level related to all of the plurality of radio signals is equal to or higher than the second threshold value. Control the switch means to switch the switch means to input the plurality of radio signals to the adaptive demodulation means,
(2) Modulation / demodulation of a MIMO communication method used by the transmitting-side radio station apparatus and the MIMO demodulating means when a received signal level related to at least one of the plurality of radio signals is less than the second threshold value. The MIMO antenna apparatus according to claim 1, wherein the method is changed to a modulation / demodulation method having a transmission rate lower than a current transmission rate.   5. The MIMO antenna apparatus according to claim 4, wherein the adaptive demodulation means weights the plurality of radio signals so as to direct a main beam in a direction of a desired wave signal by executing a repetitive iterative process. .   The control means controls the switch means to switch the switch means to input the plurality of radio signals to the MIMO demodulating means, and the signal quality of the first demodulated signal is the first threshold value. In the above case, when the received signal level related to all of the plurality of radio signals is equal to or higher than the second threshold value, the MIMO communication scheme used by the transmitting radio station apparatus and the MIMO demodulating means 6. The MIMO antenna apparatus according to claim 4, wherein the modulation / demodulation method is changed to a modulation / demodulation method having a transmission rate higher than a current transmission rate.   When the control means controls the switch means to switch the switch means to input the plurality of radio signals to the adaptive demodulation means, the number of times of demodulation by the adaptive demodulation means exceeds a predetermined maximum number of demodulations. And switching the switch means to control the switch means so as to input the plurality of radio signals to the MIMO demodulator means, and the MIMO communication system used by the transmitting radio station apparatus and the MIMO demodulator means. The MIMO antenna apparatus according to any one of claims 4 to 6, wherein the number of data streams is increased.   The radio transmission means transmits the control signal to the transmission-side radio station apparatus using at least one of the plurality of antenna elements. MIMO antenna device.   A wireless communication apparatus comprising the MIMO antenna apparatus according to any one of claims 1 to 8.

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