JP2009171317A - Radio communication device, its control method and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a calibration process in a radio communication device, thereby utilizing a radio communication system efficiently. <P>SOLUTION: In this radio communication device, a plurality of antennas are used on the transmitting side and on the receiving side, respectively, and a signal is multiplexed between the transmitting side and the receiving side to form a plurality of space streams for carrying out radio communications. Whenever a spectrum is received (S507), a distortion of the received spectrum is detected and a frequency of detecting the distortion is counted (S509). When the frequency exceeds a threshold value, a calibration process for forming the plurality of space streams is executed (S511). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wireless communication device, a control method thereof, and a computer program.

  There is a wireless transmission line as a data transfer transmission line, and there is a wireless LAN standard IEEE 802.11 as a general wireless transmission line. In wireless communication such as this wireless LAN, there is an increasing demand for data transfer that requires large capacity and real-time performance, such as audio data and video data that is streamed.

  A method (IEEE802.11e) that gives priority to such demand according to the type of data to be transmitted and preferentially transmits higher priority data is a means for realizing QoS technology. As being considered and proposed.

  In addition, a broadband wireless transmission scheme that adopts a MIMO (Multi-Input Multi-Output) transmission scheme as a means for realizing large-capacity transmission is being studied. The MIMO transmission system is planned to be adopted in IEEE802.11n which is currently formulating a standard in the wireless LAN standard IEEE802.11. This MIMO transmission system is equipped with a plurality of antenna elements on the transmission side and the reception side, and by forming a plurality of logical spatial streams by space division multiplexing, the transmission capacity is expanded without increasing the frequency band to be used. Technology.

  FIG. 3 is a diagram for explaining the outline of the MIMO transmission scheme that is scheduled to be adopted in IEEE802.11n. Shown here is a representation of a MIMO channel transmission path.

Reference numeral 301 denotes a transmission path in wireless communication including an array antenna having M antennas on the transmitting side and N antennas on the receiving side. This shows a channel response matrix in which the transmission path facing each antenna is represented by a matrix of a ₁₁ ... A _NM .

302 is a diagram in which the channel response matrix of the transmission line 301 is expressed by an equivalent circuit by performing singular value decomposition (SVD). This equivalent circuit is expressed by the eigenvector E _t ^H of the transmitting antenna, the eigenvector E _r of the receiving antenna, and eigenpaths √λ ₁ , √λ ₂ ,..., √λ _M0 .

By performing singular value decomposition (SVD) on the channel response matrix of the transmission path 301, it is possible to form a maximum of M ₀ (the smaller value of N and M) independent transmission paths. This virtual path is called an eigenpath (√λ ₁ , √λ ₂ ,..., √λ _M0 ). This expresses the ability to transmit independent M ₀ transmission streams without interference. Further, the amplitude gain of the eigenpath is √λ _i , and the size of the transmission capacity varies depending on the size of the eigenpath.

Actually, in order to perform wireless transmission using the above-described MIMO transmission scheme, it is necessary to set eigenvectors E _t ^H and _Er in advance on the transmission side and the reception side. As a method of setting the eigenvectors E _t ^H and _Er , there is a calibration process performed between the transmitting side and the receiving side facing each other. In the calibration process, a test signal is transmitted from the transmission side, and calculation is performed based on information obtained by receiving the signal on the reception side to determine the eigenvector _Er . In addition, the transmission side determines the eigenvector E _t ^H by feeding back the information to the transmission side.

As a technique related to the above-described calibration processing, there is a wireless communication system described in JP-A-2005-142715 (Patent Document 1). This is because the transmission side receives the reference signal transmitted from the reception side, acquires channel information, and determines the eigenvector E _t ^H from this channel information. Then, the transmission side calculates a weight for each signal to be multiplexed, and transmits the training signal given the weight to the reception side. The receiving side that has received the training signal determines the eigenvector _Er based on the training signal. Furthermore, a technique for executing the calibration process using a RTS (Request to Send) / CTS (Clear to Send) method is described as a part related to the IEEE 802.11 standard.

  Similarly, there exists a radio | wireless communications system as described in Unexamined-Japanese-Patent No. 2006-33658 (patent document 2). This also describes a technique for executing a calibration process similar to the above using the RTS / CTS method.

JP 2005-142715 A JP 2006-33658 A

  Specifically, Patent Documents 1 and 2 described above describe a method for compressing the amount of information fed back from the receiver side to the transmission side in order to realize the MIMO transmission method, and a method for simplifying the feedback setup procedure. Disclose. Also disclosed is a method for performing a calibration process without being affected by interference waves and interference waves from peripheral stations by using broadcast.

  However, these Patent Documents 1 and 2 propose the procedure and method of the calibration process itself. Therefore, when a wireless communication system composed of a plurality of wireless terminals is assumed, it is not described at what timing calibration processing is executed according to changes in usage pattern, radio wave environment, or usage status.

  For example, according to the techniques described in Patent Documents 1 and 2, the calibration process is executed even when it is not necessary to form a wireless transmission path using the MIMO transmission method for a wireless communication system including a plurality of wireless terminals. Will do. Therefore, it is difficult to realize an efficient usage form of the entire wireless communication system.

  Accordingly, an object of the present invention is to improve the calibration process in a wireless communication apparatus, and thereby to enable efficient use of the wireless communication system.

  According to one aspect of the present invention, wireless communication is performed by using a plurality of antennas on each of a transmission side and a reception side, and multiplexing a signal between the transmission side and the reception side to form a plurality of spatial streams. A wireless communication apparatus in a communication system, wherein detection means for detecting distortion of a received spectrum and execution of calibration processing for forming the plurality of spatial streams based on a detection result of the distortion by the detection means There is provided a wireless communication apparatus characterized by comprising control means for controlling.

  ADVANTAGE OF THE INVENTION According to this invention, the calibration process in a radio | wireless communication apparatus is improved, Thereby, utilization of an efficient radio | wireless communications system is attained.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, It shows only the specific example advantageous for implementation of this invention. In addition, not all combinations of features described in the following embodiments are indispensable as means for solving the problems of the present invention.

<Embodiment 1>
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In particular, in wireless communication, wireless communication using various related standards including the IEEE 802.11 standard and IEEE 802.11n that is an extension of this standard is assumed. Note that the present invention is applicable not only within the scope of the mechanism proposed as the IEEE802.11 standard and IEEE802.11n as an extension of this standard, but also to a communication system compliant with another communication protocol.

  FIG. 1 is a configuration diagram illustrating an example of a wireless communication system according to the present embodiment.

  This wireless communication system accommodates a plurality of wireless communication devices. The wireless communication device includes an STA as a wireless terminal and an AP as a base station. In order to explain the effects of the present invention in an easy-to-understand manner, a specific system configuration will be described as a specific example, and the following description will be given. Therefore, the present invention can be applied to other system configurations including STAs and APs.

  Reference numeral 10 denotes an STA 1 having a video data transmission function, which is a digital video camera capable of transmitting a video stream using a wireless LAN communication function, for example. Reference numeral 20 denotes an STA 2 having a video data receiving function, which is a television capable of receiving a video stream using a wireless LAN communication function, for example. Reference numeral 30 denotes an AP that accommodates STAs such as 10 and 20, and is an access point in a wireless LAN, for example. Then, when STA1 and STA2 establish a logical connection relationship with the AP, a network (BSS) composed of the AP and the STA1 and STA2 under the AP is formed.

  Here, considering the video data transmission method in the case of performing the operation of transmitting the video acquired by the digital video camera to the television and displaying the video on the television, there are roughly two methods. . One is a video data transmission method via an access point, and the other is a video data transmission method for direct transmission between a digital video camera and a television.

  According to the IEEE 802.11 standard, a video data transmission method via an access point is formed by forming a communication path from the STA1 to the AP and a communication path from the AP to the STA2, and transferring the video data from the STA1 to the STA2. There is a way to transmit via.

  On the other hand, two methods can be considered as methods for directly transmitting video data. One of them is that a direct communication path is formed between STA1 and STA2 using DLS (Direct Link Setup), which is an IEEE 802.11e standard, and video data is transferred from STA1 to STA2 by a transmission method that guarantees QoS. This is a direct transmission method.

  The other is that when the STA1 has the function of an access point, the function is switched from the STA to the AP, and a new network that connects the STA2 to the subordinates is newly constructed. Is directly transmitted from STA1 to STA2.

  Next, an outline of the configuration of a wireless communication unit for performing wireless transmission by the MIMO transmission method will be described. In the MIMO transmission scheme, a plurality of antenna elements are provided on the transmission side and the reception side, and signals are multiplexed between the transmission side and the reception side by space division multiplexing to form a plurality of logical spatial streams. As a result, the transmission capacity is expanded without increasing the frequency band to be used. FIG. 2 is a block diagram illustrating a configuration of a wireless communication unit included in an STA and an AP that are wireless communication apparatuses accommodated in the wireless communication system illustrated in FIG.

A control unit 201 controls the entire wireless communication unit. In executing the calibration processing, the control unit 201 also performs processing such as generation of a calibration signal and calculation of eigenvectors E _t ^H and E _r for setting a plurality of eigen paths. In addition, the control unit 201 includes a unit that receives a reception quality degradation notification from a reception quality degradation detection unit 218 described later as one of the units that receive a trigger for executing calibration. The control unit 201 further includes means for transmitting each threshold value for detecting distortion of the reception spectrum to the reception quality deterioration detection unit 218.

  A reception MAC processing unit 202 is a part that performs processing on the reception side of a MAC (Medium Access Control) layer indicated by the wireless LAN standard IEEE802.11. The MAC frame received from the receiving PHY processing unit 204, which will be described later, is analyzed.

  A transmission MAC processing unit 203 is a part that performs processing on the transmission side of the MAC layer indicated by the wireless LAN standard IEEE802.11. The data to be transmitted is subjected to MAC processing to form a MAC frame, which is transmitted to a transmission PHY processing unit described later.

  Reference numeral 204 denotes a reception PHY processing unit, which is a part that performs processing on the reception side of the PHY layer shown in the wireless LAN standard IEEE802.11. Processing such as AD conversion / demodulation / decoding is performed on an OFDM signal received by an antenna 217 described later.

  Reference numeral 205 denotes a decoding unit. Based on the data demodulated by the demodulator 206 described later, the divided data is decoded.

  A demodulation unit 206 demodulates each subcarrier of the received OFDM signal.

A reception weighting processing unit 207 performs channel estimation and channel equalization on each subcarrier Fourier-transformed by an FFT processing unit 208 (to be described later), and further performs processing for correcting steady phase rotation. Detection and correction of stationary phase rotation is performed using a pilot subcarrier signal among subcarriers. Further, the received signal strength of each subcarrier calculated by the reception weighting processing unit and the detected steady phase rotation are also passed to a reception quality deterioration detection unit 218 described later. Further, reception weighting processing is performed for each subcarrier. The weighting process is a process for changing time information and size (amplitude). This is also a process based on the eigenvectors E _t ^H and E _r calculated by executing a calibration process or the like.

  An FFT processing unit 208 performs a process of collectively demodulating multicarriers of OFDM signals transmitted from a receiving unit 209 described later.

  A receiving unit 209 performs gain adjustment, AD conversion, carrier frequency synchronization, symbol timing synchronization, and the like on analog data received from an antenna 217 described later.

  A transmission PHY processing unit 210 is a part that performs processing on the transmission side of the PHY layer indicated by the wireless LAN standard IEEE802.11. The MAC frame formed by the transmission MAC processing unit 203 is subjected to processing such as encoding / modulation / DA conversion.

  Reference numeral 211 denotes an encoding unit that encodes a MAC frame using a convolutional code when OFDM is used in a wireless LAN.

  A modulation unit 212 performs interleaving processing on the encoded transmission bits, and divides the data into subcarriers for modulation.

A transmission weighting processing unit 213 performs weighting processing on each of the plurality of streams. This weighting process is a process of changing time information and size (amplitude). This is also a process based on the eigenvectors E _t ^H and E _r calculated by executing a calibration process or the like.

  An IFFT processing unit 214 performs an inverse Fourier transform on the modulated signal divided into subcarriers.

  A transmission unit 215 applies guard interval addition / symbol shaping / DA conversion to each subcarrier subjected to inverse Fourier transform, and transmits the subcarrier to a selector 216 described later.

  Reference numeral 216 denotes a selector, which determines whether to use an antenna 217, which will be described later, for transmission / reception according to the state of the communication device, and switches the connection with the antenna 217 based on the determination.

  An antenna 217 receives radio waves from other communication devices and transmits radio waves to other communication devices. In this embodiment, a plurality of antennas 217 and 217 are shared between the transmission side and the reception side, and the transmission side / reception side is switched by the selector 216 as described above.

In order to execute wireless communication by the MIMO transmission method in the wireless communication system as shown in FIG. 1, it is necessary to perform calibration processing for calculating eigenvectors E _t ^H and _Er . The calibration process is a process necessary for forming a plurality of spatial streams using a plurality of antennas. In the calibration process, for example, the eigenvector _Er is determined by performing calculation based on information obtained by transmitting a test signal from the transmitting side and receiving the signal on the receiving side. In addition, the transmission side determines the eigenvector E _t ^H by feeding back the information to the transmission side. The operation of this calibration process will be described below assuming a plurality of cases.

  A reception quality degradation detection unit 218 extracts the signal strength of each subcarrier and the steady phase rotation amount using pilot subcarriers as reception quality from the reception weighting processing unit 207. In addition, the control unit 201 sends a condition that the OFDM reception spectrum is distorted in advance as each threshold value described later. The reception quality degradation detection unit 218 detects reception quality degradation by comparing the reception quality received from the reception weighting processing unit 207 with the condition regarded as reception quality degradation received from the control unit 201.

  The above is the basic configuration of the wireless communication unit provided in the communication device accommodated in the wireless communication system in the present embodiment. Note that the configuration given as an example is an arrangement of functional blocks in each process for explanation. Therefore, for example, function blocks that can be shared by the reception PHY processing unit 204 and the transmission PHY processing unit 210 may have a shared configuration.

  Next, reception quality deterioration detection processing executed by the reception quality deterioration detection unit 218 will be described. Two indicators of reception intensity and phase rotation in the spectrum of the received OFDM signal are used as indicators for detection of reception quality deterioration. First, the case where reception intensity is used will be described. FIG. 4A shows an example of the reception spectrum of the OFDM signal. Since fading occurs in a multipath environment or the like, distortion may occur in the effective frequency band as shown in FIG. 4A. The occurrence of this distortion is referred to as reception quality deterioration detection. Here, the intensity of the spectrum is compared with a predetermined threshold, and when the threshold is exceeded, it is determined that the spectrum is distorted (distortion is detected). Based on the detection result, the control unit 201 controls execution of calibration processing for forming a plurality of spatial streams. There are various methods for providing the threshold. Hereinafter, three methods will be described as an example.

  In the first distortion detection method, as shown in FIG. 4B, when the reception intensity exceeds a predetermined threshold value indicating an upper limit or falls below a threshold value indicating a lower limit, the spectrum is distorted. It is the method of judging.

  As shown in FIG. 4C, the second distortion detection method calculates the difference between the maximum reception intensity and the minimum reception intensity, compares the difference with a predetermined threshold value, and the obtained difference exceeds the threshold value. In addition, it is a method for determining that the spectrum is distorted.

  The third distortion detection method is a method that considers the average value of the received intensity. First, a threshold value is set in advance as shown in FIG. 4D for each average value of received intensity. And when the OFDM signal is received, the average value of the reception strength of the subcarrier is calculated, the signal strength width according to the average value is set, and when the reception strength that does not fall within the signal strength width is observed, This is a method for determining that the spectrum is distorted. In this method, since the threshold is set based on the average value of the reception intensity, effective distortion detection can be realized when the average reception intensity varies due to movement of the wireless device.

  In using the above first to third distortion detection methods, all subcarriers and frequency regions constituting the spectrum of the OFDM signal may be targeted, or specific subcarriers and frequency regions may be extracted. good. For example, it is possible to extract only pilot subcarriers and use them for distortion detection.

  In OFDM modulation of a wireless LAN, since subcarriers are not arranged at the center frequency, it is generally known that reception intensity is detected near the center frequency. Therefore, when using a method of continuously detecting the reception intensity in the frequency domain, it is effective to remove the reception intensity near the center frequency as a measurement target.

  Next, a method using phase rotation will be described.

  When using an OFDM modulation scheme in a wireless LAN, the demodulator may be provided with a function of correcting a steady phase rotation that is regularly rotated in a certain direction for each subcarrier after Fourier transform and channel equalization. It is common. In order to correct this steady phase rotation, a method using a pilot subcarrier is known. The demodulator compares the known pilot subcarriers with the received pilot subcarriers, detects the average phase rotation of the pilot subcarriers, and uses it to correct other subcarriers. Here, a method of using phase rotation is a method in which a threshold value is given to the amount of phase rotation in advance and the threshold value is detected as distortion when the average phase rotation of the reception spectrum exceeds.

  Note that only one of the first to third distortion detection methods using the reception intensity may be applied, or only a method using phase rotation may be applied, or a combination of the two may be used. Also good.

  Further, in the above-described distortion detection method, it is preferable to switch the observed subcarrier and frequency domain according to the communication mode. In the example of FIGS. 4A to 4D, an effective frequency band of 20 MHz is assumed. However, it is preferable that a communication mode using a wider effective frequency band can be supported. For example, in the IEEE802.11n standard for wireless LAN, two types of communication modes are used: a first communication mode using a frequency bandwidth of 20 MHz, or a second communication mode using a frequency bandwidth of 40 MHz. Is scheduled. Therefore, the present invention that changes the subcarrier and frequency domain to be observed for distortion detection according to the communication mode used in the wireless communication system is suitable for a communication system such as IEEE 802.11n.

  In the present embodiment, for example, the frequency at which strain is detected by the method described above is measured, and the fact that the frequency exceeds a certain threshold value is used as a calibration trigger. Moreover, it is also preferable to switch each threshold value demonstrated above according to communication mode. Thereby, a more effective calibration trigger condition can be set. For example, when the 40 MHz communication mode is used in the IEEE802.11n standard, the error occurrence frequency increases compared to the case where the 20 MHz communication mode is used. In view of this, when using the 40 MHz communication mode, the threshold value may be changed so that the allowable range of distortion is narrower than when using the 20 MHz communication mode.

  Furthermore, in IEEE802.11n, STBC (Space Time Block Code) technology capable of obtaining a transmission diversity effect and LDPC (Low Density Parity Check Code) having excellent error correction capability can be used as an option. . Therefore, when STBC or LDPC is used, the demodulation accuracy is expected to be improved. Therefore, the threshold value used for distortion detection may be changed from the case where these are not used.

  It goes without saying that the present invention can be applied to any method other than the method using the received intensity and the method using phase rotation shown in FIGS. 4B, 4C, and 4D as long as it can detect the distortion of the received spectrum. Furthermore, IEEE 802.11n is scheduled to be able to perform wireless communication using a plurality of spatial streams. By observing the distortion of all reception spectra among the plurality of spatial streams, a flexible trigger condition for executing calibration can be set. That is, a wide range of trigger conditions can be set, such as when a distortion occurs in the reception spectrum of one spatial stream, or when a distortion occurs in the reception spectrum of all the spatial streams.

  FIG. 5 is a flowchart showing a processing procedure from reception of a spectrum to execution of calibration processing when STA1 (or STA2) performs data transfer in the wireless area of the AP.

  The general flow will be described. First, a threshold value for spectrum distortion detection is set in the reception quality deterioration detection unit 218 (S504, S506). Next, the STA1 or AP receives the OFDM signal (S507). Detection of distortion in the reception spectrum and calculation of distortion frequency are performed (S509). If the strain occurrence frequency exceeds the threshold value, calibration processing is executed (S511). The above is the overall flow. This will be described in detail below.

S501 (Terminal symbol)
This terminal symbol indicates the start of this flowchart. This state is a state before STA1 and AP finish logical connection (association) and before data transfer is started.

S502 (condition judgment symbol)
This condition determination symbol indicates that the process branches on the condition that the logical connection between the STA1 and the AP is disconnected. If the logical connection between the STA1 and the AP is disconnected, the process proceeds to the terminal symbol (S513), and if not, the process proceeds to the condition determination symbol (S503).

S503 (condition judgment symbol)
This condition determination symbol indicates that the reception quality deterioration detection unit 218 branches based on whether or not a threshold value for determining that distortion has occurred in the reception spectrum has already been set. If the threshold has already been set, the process proceeds to the condition determination symbol S505. If the threshold has not yet been set, the process proceeds to the processing symbol S504.

S504 (processing symbol)
This processing symbol indicates processing for setting a threshold value for determining that the reception spectrum is distorted in the reception quality deterioration detection unit 218. The threshold setting method may be realized in any form. For example, there is a method in which each threshold value is set in the reception quality deterioration detection unit 218 through the control unit 201 when the user continues to input setting information and there is an input from the user. If no setting information is input from the user, a threshold value as an initial value may be held in the reception quality degradation detection unit 218 and applied.

S505 (condition judgment symbol)
This condition determination symbol indicates that a branch is made based on whether there is a change request for each threshold set in the reception quality deterioration detection unit 218. The request for changing the threshold value is made by the user to the control unit 201, for example. In addition, when the frequency region used for data transfer is changed to 20 MHz / 40 MHz, for example, the control unit 201 of the wireless unit may automatically issue a change request. If there is a change request, the process branches to the processing symbol S506, and if there is no request, the process branches to the condition determination symbol S507.

S506 (processing symbol)
This processing symbol indicates processing for resetting each threshold set in the reception quality deterioration detection unit 218. The resetting procedure or the like may be dynamically switched according to the change request type issued in the condition determination symbol S505. For example, for a change request based on input from the user, the user may wait for input. In addition, when the control unit 201 automatically issues, one of a plurality of threshold values stored in advance may be used by the control unit 201 or the reception quality deterioration detection unit 218.

S507 (condition judgment symbol)
This processing symbol indicates that the communication device branches on the condition that it receives an OFDM signal addressed to itself from the antenna 217. If an OFDM signal addressed to itself is received, the process branches to the condition determination symbol S508. If not received, the process branches to the condition determination symbol S507.

S508 (condition judgment symbol)
This processing symbol indicates that the process branches based on whether or not the frequency width has changed between the received OFDM signal and the previously received OFDM signal. In IEEE802.11n, as described above, two types of communication modes are planned to be used: when using a 20 MHz wide frequency and when using a 40 MHz wide frequency. If there is a change in the frequency width, the process branches to the processing symbol S512. If there is no change, the process branches to the condition determination symbol S509.

S509 (condition judgment symbol)
This condition determination symbol indicates that a branch is made based on whether or not the distortion occurrence frequency of the received OFDM signal exceeds a preset threshold value. As for the frequency of occurrence of distortion, every time the reception quality deterioration detection unit 218 receives an OFDM signal, it observes whether the signal is distorted and updates the frequency of occurrence of distortion. If the distortion occurrence frequency exceeds the threshold set in S504 or S508, the process branches to the processing symbol S510. If not, the process branches to the condition determination symbol S502.

S510 (processing symbol)
This processing symbol indicates processing in which the reception quality deterioration detection unit 218 notifies the control unit 201 that the frequency of occurrence of distortion of the OFDM signal has exceeded a preset threshold value.

S511 (processing symbol)
This processing symbol indicates processing for executing calibration for executing wireless communication by the MIMO transmission method. This calibration process is executed from a wireless device (STA1 or AP) that has determined that the communication partner is compatible with the MIMO transmission method. At this time, the procedure used is performed by transmission / reception of a MAC frame defined by IEEE802.11n. However, when performing transmission weighting processing at the time of transmission of the counterpart device, a calibration execution request packet for causing the counterpart device to perform calibration is transmitted. The above processing is performed when the transmission MAC processing unit 203 and the transmission PHY processing unit 210 receive a command from the control unit 201. The control unit 201 calculates eigenvectors E _t ^H and E _r from the calibration processing result. Based on the result, processing for setting a predetermined value to the transmission weighting processing unit 213 of the transmission PHY processing unit 210 and the reception weighting processing unit 207 of the reception PHY processing unit 204 is performed. When this processing is completed, it is possible to start wireless transmission using a MIMO transmission scheme that uses a plurality of stable spatial streams.

S512 (processing symbol)
This processing symbol indicates processing for resetting the history of distortion occurrence frequency stored in the reception quality deterioration detection unit 218.

S513 (terminal symbol)
This terminal symbol indicates the end of this flowchart. This state indicates a state in which the logical connection between the STA1 and the AP is disconnected.

  According to the above embodiment, for example, in a wireless communication system using a wireless communication method (SVD-MIMO transmission method), a spatial stream is appropriately formed according to a change in the reception spectrum of an OFDM signal and a desired transmission capacity is obtained. It is possible to form a wireless transmission path.

  In more detail, even if a change in the indoor radio wave environment (for example, opening / closing of a door) occurs after the calibration process is performed once, and distortion occurs when receiving the spectrum of the OFDM signal, calibration is performed at an appropriate timing. Can be executed. Therefore, it is possible to maintain a spatial stream optimal for the wireless communication system.

  In addition, even when reception spectrum distortion occurs due to a change in radio wave environment due to movement of a wireless terminal in the wireless communication system, it is possible to execute calibration processing at an appropriate timing. Therefore, it is possible to maintain a spatial stream optimal for the wireless communication system.

  In addition, a recording medium in which a program code of software for realizing the functions of the above-described embodiments is recorded is supplied to the system or apparatus, and the computer (CPU or MPU) of the system or apparatus stores the program code stored in the recording medium. Read and execute. It goes without saying that the object of the present invention can also be achieved by this.

  In this case, the program code itself read from the computer-readable recording medium realizes the functions of the above-described embodiments, and the recording medium storing the program code constitutes the present invention.

  As a recording medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  In addition, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also the following cases are included. That is, based on the instruction of the program code, an OS (operating system) running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. .

  Further, the program code read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. After that, based on the instruction of the program code, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing, and the function of the above-described embodiment is realized by the processing. Needless to say.

The block diagram of the radio | wireless communications system in embodiment. The block diagram of the radio | wireless communication part with which STA and AP accommodated in the radio | wireless communications system in embodiment are equipped. FIG. 3 is a conventional MIMO transmission path expression diagram. The figure which shows an example of an OFDM reception spectrum. The figure explaining the 1st distortion | strain detection method in embodiment. The figure explaining the 2nd distortion | strain detection method in embodiment. The figure explaining the 3rd distortion | strain detection method in embodiment. 5 is a flowchart illustrating a processing procedure related to execution of calibration processing in the embodiment.

Explanation of symbols

10 STA1
20 STA2
30 AP

Claims (15)

A wireless communication apparatus in a wireless communication system that uses a plurality of antennas on each of a transmission side and a reception side and multiplexes signals between the transmission side and the reception side to form a plurality of spatial streams to perform wireless communication. ,
Detection means for detecting distortion of the received spectrum;
Control means for controlling execution of a calibration process for forming the plurality of spatial streams based on the detection result of the distortion by the detection means;
A wireless communication apparatus comprising: The modulation method in the wireless communication system uses OFDM,
The wireless communication system according to claim 1, wherein the detection means detects using at least one of reception intensity and phase rotation amount of a subcarrier constituting an OFDM signal.   The radio communication apparatus according to claim 2, wherein the subcarrier includes a pilot subcarrier.   The radio communication apparatus according to claim 2 or 3, wherein the detection unit determines that the spectrum is distorted when a reception intensity of the subcarrier exceeds a predetermined threshold value.   The detection means determines that the spectrum is distorted when the reception intensity of the subcarrier exceeds a predetermined threshold value indicating a predetermined upper limit or falls below a threshold value indicating a lower limit. The wireless communication apparatus according to claim 2, wherein the wireless communication apparatus is a wireless communication apparatus.   The detection means calculates a difference between the maximum reception intensity and the minimum reception intensity of the subcarrier, and determines that the spectrum is distorted when the difference exceeds a predetermined threshold. The wireless communication apparatus according to claim 2, wherein the wireless communication apparatus is a wireless communication apparatus.   The detection means calculates an average value of the reception strength of the subcarrier, sets a signal strength width according to the average value, and when the reception strength of the subcarrier that does not fall within the signal strength width is observed The wireless communication apparatus according to claim 2, wherein the spectrum is determined to be distorted.   The detection means calculates an average phase rotation of the subcarrier, and determines that the spectrum is distorted when the average phase rotation exceeds a predetermined threshold. The wireless communication device according to 2 or 3.   9. The control unit according to claim 1, wherein the control unit measures the frequency at which strain is detected by the detection unit, and executes the calibration process when the frequency exceeds a predetermined threshold. The wireless communication device according to any one of the above.   The wireless communication apparatus according to claim 2, wherein the detection unit switches a subcarrier to be observed according to a communication mode of the wireless communication system.   The wireless communication apparatus according to claim 4, wherein the detection unit changes the threshold according to a communication mode of the wireless communication system.   The communication mode includes a first communication mode using a first frequency bandwidth and a second communication mode using a second frequency bandwidth wider than the first frequency bandwidth. The wireless communication apparatus according to claim 10 or 11. The detection means detects distortions of all spectra received in all spatial streams,
The wireless communication apparatus according to claim 1, wherein the control unit executes the calibration process when the detection unit detects distortion of at least one spectrum. Method for controlling radio communication apparatus in radio communication system for performing radio communication by using a plurality of antennas on each of transmission side and reception side and multiplexing signals between transmission side and reception side to form a plurality of spatial streams Because
A detection process for detecting the distortion of the received spectrum;
A control step for controlling execution of a calibration process for forming the plurality of spatial streams based on the detection result of the strain in the detection step;
A method for controlling a wireless communication apparatus, comprising:   The computer program for making a computer perform the control method of the radio | wireless communication apparatus of Claim 14.

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