Channel information compression device and method, channel information expansion device and method, computer program, receiver, transmitter

The present invention relates to a channel information compression device and method, a channel information expansion device and method, a computer program, a receiver, and a transmitter.

In the next-generation wireless communication system, it is being considered to adopt a MIMO (Multiple Input Multiple Output) system. In a MIMO system, the transmitter performs precoding (Precoding) based on channel information (CSI: Channel State Information) indicating the state of the signal transmission line (communication channel) for the transmitted data, so that precoding is not performed. It is known that the frequency utilization efficiency can be improved as compared with the case (see, for example, Non-Patent Document 1).

In the case of FDD (Frequency Division Duplex), channel information is generally acquired by the receiver, but there are two methods (1) below as methods for precoding transmission data based on the channel information. (2) is known (see, for example, Non-Patent Document 2). (1) The channel response matrix acquired by the receiver is transmitted to the transmitter, and the transmitter performs precoding according to the channel response matrix. (2) A codebook having multiple Precoder indexes is shared between the transmitter and the receiver, and the recorder index according to the channel response matrix acquired by the receiver is used by the transmitter. And the transmitter uses the recorder of the index.

<p><nplcit num="1"><text>M. Vu, A. Paulraj, MIMO Wireless Linear Precoding, IEEE Signal Processing Magazine, Sep. 2007.</text></nplcit><nplcit num="2"><text>3GPP TS 36.211 V.8.7.0, May 2009.</text></nplcit></p>

<p> However, in the conventional method (1) described above, the transmitter can perform precoding using the channel response matrix obtained by the receiver, but the amount of information of the channel response matrix sent from the receiver to the transmitter is Since there are many, the amount of radio resources used for transmitting the information is large. In the conventional method (2), the amount of information sent from the receiver to the transmitter can be reduced, but since the types of recorders that can be represented in the codebook are limited, the channel response matrix obtained by the receiver is accurate. If there is no precoder, the precoding effect will be diminished.</p><p> The present invention has been made in consideration of such circumstances, and provides a channel information compression device and method, a computer program, and a receiver capable of performing information compression while maintaining good accuracy of channel information. Is an issue. Another object of the present invention is to provide a channel information expansion device and method, a computer program, and a transmitter corresponding to the channel information compression device and method, the computer program, and the receiver according to the present invention.</p>

<p> In order to solve the above problems, the channel information compression device according to the present invention includes a time-frequency domain conversion unit that converts channel information representing the state of a communication channel from a time domain to a frequency domain, and the time-frequency domain conversion. An adaptive selection unit that selects a frequency component to be included in the compressed data based on the power from the frequency domain data obtained by the unit, and a compressed data composed of the selected frequency component and the compressed data. It is characterized in that it outputs information that specifies a frequency component that constitutes the above.</p><p> In the channel information compression device according to the present invention, the adaptive selection unit is characterized in that a predetermined number of frequency components are selected in order from the highest power.</p><p> In the channel information compression device according to the present invention, the adaptive selection unit is characterized in that the frequency components are selected in order from the highest power until the total power of the frequency components included in the compressed data reaches a predetermined value.</p><p> In the channel information compression device according to the present invention, the time-frequency domain transforming unit performs discrete cosine transform.</p><p> In the channel information compression device according to the present invention, the time-frequency domain transforming unit performs discrete cosine transform, and the adaptive selection unit has a low frequency until the total power of the frequency components included in the compressed data reaches a predetermined value. The feature is that the frequency components are selected in order from the first.</p><p> The channel information expansion device according to the present invention complements the compressed data of the frequency domain data of the channel information representing the state of the communication channel with the insufficient frequency component based on the information for specifying the frequency component constituting the compressed data. It is characterized by including an information complementing unit for performing the information and a frequency-time domain converting unit for converting the frequency domain data obtained by the complementing from the frequency domain to the time domain.</p><p> In the channel information expansion apparatus according to the present invention, the frequency-time domain transforming unit is characterized in that it performs inverse discrete cosine transform.</p><p> The channel information compression method according to the present invention is a step of converting channel information representing the state of a communication channel from a time domain to a frequency domain, and compression data based on power from the frequency domain data obtained by the conversion. It is characterized by including a step of selecting a frequency component to be included in the data, and a step of outputting compressed data composed of the selected frequency component and information for specifying a frequency component constituting the compressed data.</p><p> The channel information expansion method according to the present invention complements the compressed data of the frequency domain data of the channel information representing the state of the communication channel with the insufficient frequency component based on the information for specifying the frequency component constituting the compressed data. It is characterized by including a step of converting the frequency domain data obtained by the complementation from the frequency domain to the time domain.</p><p> The computer program according to the present invention includes in the compressed data based on the power from the step of converting the channel information representing the state of the communication channel from the time domain to the frequency domain and the frequency domain data obtained by the conversion. A computer program for causing a computer to perform a step of selecting a frequency component and a step of outputting compressed data composed of the selected frequency component and information for specifying a frequency component constituting the compressed data. It is characterized by being. As a result, the above-mentioned channel information compression device can be realized by using a computer.</p><p> The computer program according to the present invention is a step of supplementing the compressed data of the frequency domain data of the channel information representing the state of the communication channel with the insufficient frequency component based on the information for specifying the frequency component constituting the compressed data. It is a computer program for causing a computer to execute the step of converting the frequency domain data obtained by the complementation from the frequency domain to the time domain. As a result, the above-mentioned channel information expansion device can be realized by using a computer.</p><p> The receiver according to the present invention is the receiver of the MIMO system, the time-frequency domain conversion unit for converting the channel information between the transmitter and the self-receiver of the MIMO system from the time domain to the frequency domain, and the time. -From the frequency domain data obtained by the frequency domain converter, an adaptive selection unit that selects the frequency components to be included in the compressed data based on the power, and the compressed data composed of the selected frequency components and the compression. It is characterized by including a transmission unit that transmits information for specifying a frequency component constituting data to the transmitter.</p><p> The transmitter according to the present invention specifies the compressed data of the frequency region data of the channel information between the self-transmitter and the receiver of the MIMO system and the frequency components constituting the compressed data in the transmitter of the MIMO system. A receiver that receives information from the receiver, an information complement that complements the compressed data based on information that identifies the frequency components that make up the compressed data, and an information complement that complements the missing frequency components. A frequency-time region conversion unit that converts the obtained frequency region data from the frequency region to the time region, and a precoding unit that precodes transmission data using the channel information acquired by the frequency-time region conversion unit. It is characterized by having.</p>

<p> According to the present invention, it is possible to obtain an effect that information compression can be performed while maintaining good accuracy of channel information.</p>

<figref num="1">It is a schematic block diagram which shows the structure of the wireless communication system which concerns on one Embodiment of this invention.</figref><figref num="2">It is a block diagram which shows the structure of the channel information compression part 24 shown in FIG.</figref><figref num="3">It is a block diagram which shows the structure of the channel information development part 14 shown in FIG.</figref><figref num="4">This is a specific example for convenience for explaining the channel information compression method and the channel information expansion method according to the embodiment of the present invention.</figref><figref num="5">This is a specific example for convenience for explaining the channel information compression method and the channel information expansion method according to the embodiment of the present invention.</figref>

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a configuration of a wireless communication system according to an embodiment of the present invention. This wireless communication system has a MIMO transmitter 1 and a MIMO receiver 2, and performs MIMO transmission from the MIMO transmitter 1 to the MIMO receiver 2.

In FIG. 1, the MIMO transmitter 1 has a precoding unit 11, a transmitting unit 12, a control information receiving unit 13, and a channel information expanding unit 14. The precoding unit 11 precodes the transmitted data using the channel information (CSI). The transmission unit 12 has a plurality of transmission antennas, and transmits precoded transmission data from the plurality of transmission antennas. The control information receiving unit 13 receives control information from the MIMO receiver 2. This control information includes channel information compressed coded data B and control data C. The channel information expansion unit 14 acquires channel information using the channel information compression coding data B and the control data C. The channel information expansion unit 14 supplies the acquired channel information to the precoding unit 11.

The MIMO receiver 2 includes a receiving unit 21, a channel estimation unit 22, a receiving processing unit 23, a channel information compression unit 24, and a control information transmitting unit 25. The receiving unit 21 has a plurality of receiving antennas, and receives signals transmitted from the plurality of transmitting antennas of the MIMO transmitter 1 by the plurality of receiving antennas. The channel estimation unit 22 estimates channel information (CSI) using the received signal of each receiving antenna. The reception processing unit 23 performs reception processing using channel information and acquires received data.

The channel information compression unit 24 generates the channel information compression coded data B from the channel information estimated by the channel estimation unit 22. The channel information compression unit 24 outputs the channel information compression coded data B and the control data C to the control information transmission unit 25. The control information transmission unit 25 transmits the channel information compressed coded data B and the control data C to the MIMO transmitter 1.

FIG. 2 is a block diagram showing a configuration of the channel information compression unit 24 shown in FIG. FIG. 3 is a block diagram showing the configuration of the channel information expansion unit 14 shown in FIG. First, the channel information compression unit 24 will be described with reference to FIG. In FIG. 2, the channel information compression unit 24 includes a discrete cosine transform (DCT) unit 41, an information compression unit 42, a variable length coding unit 43, and a control unit 44. The information compression unit 42 has an adaptive selection unit 45 and a quantization unit 46.

Channel information (CSI) is input to the DCT unit 41 from the channel estimation unit 22. The DCT unit 41 performs discrete cosine transform of channel information. The discrete cosine transform data obtained by the discrete cosine transform of the channel information is output to the information compression unit 42. The discrete cosine transform data has a DCT coefficient as information on each frequency component.

The information compression unit 42 compresses the information of the frequency component included in the discrete cosine transform data based on the power (reduces the number of bits of the information or deletes the information). The information compression unit 42 outputs the compressed data obtained by information-compressing the discrete cosine transform data (hereinafter, simply referred to as compressed data) to the variable length coding unit 43. The variable-length coding unit 43 encodes the compressed data received from the information compression unit 42 in a variable-length code. The variable-length coding unit 43 outputs the channel information compressed coded data B obtained by the variable-length coding of the compressed data to the control information transmitting unit 25.

In the information compression unit 42, the adaptive selection unit 45 and the quantization unit 46 perform information compression of the discrete cosine transform data. The adaptive selection unit 45 selects a frequency component to be included in the compressed data from the discrete cosine transform data based on the power. The adaptive selection unit 45 outputs the information of the frequency component selected from the discrete cosine transform data to the quantization unit 46. The quantization unit 46 allocates bits to the frequency component information input from the adaptive selection unit 45 according to the instruction from the control unit 44. As a result, compressed data is generated.

The adaptive selection unit 45 outputs the DCT point index information A to the control unit 44. The DCT point index information A is information that identifies the frequency components that make up the compressed data. Specifically, the DCT point index information A is information composed of an identifier of the DCT coefficient (DCT point index), and specifies the DCT coefficient included in the compressed data.

The control unit 44 controls the operations of the quantization unit 46 and the variable length coding unit 43. The control unit 44 outputs the control data C related to the channel information compressed coded data B to the control information transmission unit 25. The control data C includes the DCT point index information A.

Next, the channel information expansion unit 14 will be described with reference to FIG. In FIG. 3, the channel information expansion unit 14 includes a variable length decoding unit 51, an information expansion unit 52, an inverse discrete cosine transform (IDCT) unit 53, and a control unit 54. The information development unit 52 has an inverse quantization unit 55 and an information complementation unit 56. Each part of FIG. 3 corresponds to each part of FIG.

Channel information compressed coded data B is input from the control information receiving unit 13 to the variable length decoding unit 51. The variable length decoding unit 51 performs variable length decoding of the channel information compression coded data B. The variable-length decoding unit 51 outputs the compressed data obtained by the variable-length decoding of the channel information compression coded data B to the information expansion unit 52.

The information expansion unit 52 expands the compressed data received from the variable length decoding unit 51. In the information expansion unit 52, the information expansion of the compressed data is performed by the inverse quantization unit 55 and the information complement unit 56. The information expansion unit 52 outputs the discrete cosine transform data obtained by expanding the compressed data to the IDCT unit 53. The IDCT unit 53 performs inverse discrete cosine transform of the discrete cosine transform data. The IDCT unit 53 outputs the channel information (CSI) obtained by the inverse discrete cosine transform to the precoding unit 11.

The control data C is input to the control unit 54 from the control information receiving unit 13. The control unit 54 controls the operations of the variable length decoding unit 51 and the information expansion unit 52 based on the control data C. The control data C includes the DCT point index information A. The control unit 54 outputs the DCT point index information A included in the control data C to the information complement unit 56.

The inverse quantization unit 55 acquires the frequency component information of the discrete cosine transform data from the compressed data according to the instruction from the control unit 44. The information complementing unit 56 complements the missing frequency component information based on the DCT point index information A with respect to the discrete cosine transform data composed of the frequency component information acquired by the inverse quantization unit 55. As a result, the discrete cosine transform data in which the frequency component is satisfied is generated.

In the present embodiment, DCT is used as the time-frequency domain conversion for converting the channel information from the time domain to the frequency domain, but another time-frequency domain conversion may be used. For example, a discrete Fourier transform (DFT) or a discrete wavelet transform (DWT) may be used as the time-frequency domain transform.

Next, the information compression unit 42 shown in FIG. 2 and the information expansion unit 52 shown in FIG. 3 will be described with reference to examples.

<p> In the first embodiment, when the adaptive selection unit 45 selects the frequency components to be included in the compressed data from the discrete cosine transform data, the adaptive selection unit 45 selects a predetermined number of frequency components in order from the highest power. Hereinafter, the operations of the information compression unit 42 and the information expansion unit 52 according to the first embodiment will be described in detail.</p><p> First, the operation of the information compression unit 42 according to the first embodiment will be described. The adaptive selection unit 45 receives the discrete cosine transform data from the DCT unit 41. The discrete cosine transform data has a DCT coefficient as information on each frequency component. Here, as a specific example for convenience of explanation, it is assumed that the discrete cosine transform data of the DCT result is composed of 15 DCT coefficients having a DCT point index of 0 to 14. The DCT point index "0" corresponds to the DCT coefficient of the direct current (DC) component, and the larger the value of the DCT point index, the higher the DCT coefficient of the high frequency component.</p><p> First, the adaptive selection unit 45 calculates the power value of the frequency component for each DCT point index using the DCT coefficient specified by the DCT point index. Specifically, the DCT coefficient consists of a real part and an imaginary part, and the sum of the square of the real part and the square of the imaginary part of the DCT coefficient is calculated as the power value of the frequency component corresponding to the DCT coefficient. As a result, the adaptive selection unit 45 calculates 15 power values corresponding to each of the DCT point indexes 0 to 14. As specific examples for convenience of explaining the calculation result, FIGS. 4 and 5 are shown.</p><p> Next, the adaptive selection unit 45 compares the 15 power values and selects the DCT point index, which is the maximum power value. Next, the adaptive selection unit 45 compares the remaining 14 power values, excluding the power value of the selected DCT point index, and selects the DCT point index which is the maximum power value. This DCT point index selection operation is repeated for a predetermined number of minutes. Here, as a specific example for convenience of explanation, the predetermined number is 7. As a result, the adaptive selection unit 45 selects the seven DCT point indexes corresponding to the seven power values from the one with the largest power value among the 15 power values. In the examples of FIGS. 4 and 5, the DCT point indexes "0", "4", "2", "3", "9", "1", and "7" are arranged in descending order of power value. Be selected. In the examples of FIGS. 4 and 5, the power values of the DCT point indexes "7" and "12" are equal at "12", but due to the limitation of the number of selections, the smaller (lower frequency component) DCT point. Index "7" is selected.</p><p> Next, the adaptive selection unit 45 selects the DCT point indexes 0, 1, 2, and 3 of the DCT point index selection results from the 15 DCT coefficients constituting the discrete cosine transform data of the DCT results. , "4", "7" and "9", respectively, and output only the seven DCT coefficients corresponding to each to the quantization unit 46. Further, the adaptive selection unit 45 uses the DCT point index "0", "1", "2", "3", "4", "7" and "9" of the DCT point index selection result as the DCT point index information. Output to control unit 44 as A. The control unit 44 includes the DCT point index information A (DCT point index 0, 1, 2, 3, 4, 7, and 9) in the control data C. ..</p><p> The quantization unit 46 allocates bits to the seven DCT coefficients input from the adaptive selection unit 45 according to the instruction from the control unit 44. For example, a predetermined number of bits are uniformly assigned to each of the seven DCT coefficients. Alternatively, from the number of bits that can be assigned, a larger number of bits is assigned to the seven DCT coefficients as the power value increases. The control unit 44 includes this bit allocation information in the control data C. The quantization unit 46 outputs the seven DCT coefficients after bit allocation to the variable length coding unit 43 as compressed data.</p><p> The variable-length coding unit 43 performs variable-length coding of the compressed data received from the quantization unit 46, and outputs the channel information compressed coded data B obtained by the variable-length coding of the compressed data to the control information transmission unit 25. .. The control unit 44 outputs the control data C including the DCT point index information A and the bit allocation information to the control information transmission unit 25. As a result, the control information transmission unit 25 transmits the channel information compressed coded data B and the control data C (DCT point index information A and bit allocation information) to the MIMO transmitter 1.</p><p> Next, the operation of the information development unit 52 according to the first embodiment will be described. For convenience of explanation, the specific example used in the explanation of the information compression unit 42 according to the first embodiment will be used. The channel information compressed coded data B received by the control information receiving unit 13 in the MIMO transmitter 1 is subjected to variable length decoding by the variable length decoding unit 51. The compressed data obtained by the variable length decoding of the channel information compressed coded data B is input to the inverse quantization unit 55 of the information expansion unit 52. Further, the control data C (DCT point index information A and bit allocation information) received by the control information receiving unit 13 is input to the control unit 54. The control unit 54 outputs the DCT point index information A included in the input control data C to the information complement unit 56 and the bit allocation information to the inverse quantization unit 55, respectively.</p><p> The inverse quantization unit 55 acquires the DCT coefficient of the discrete cosine transform data from the compressed data received from the variable length decoding unit 51 based on the bit allocation information received from the control unit 54. Here, seven DCT coefficients are obtained. The inverse quantization unit 55 outputs the acquired seven DCT coefficients to the information complement unit 56.</p><p> Next, when the information complementing unit 56 receives seven DCT coefficients from the inverse quantization unit 55, it complements the insufficient DCT coefficients based on the DCT point index information A received from the control unit 54. Here, the DCT point index information A has DCT point indexes "0", "1", "2", "3", "4", "7" and "9". Therefore, of the 15 DCT coefficients from DCT point index "0" to "14", DCT point index "5", "6", "8", "10", "11", "12", A total of eight DCT coefficients of "13" and "14" are insufficient. As a result, the information complementing unit 56 sets the DCT coefficients of the DCT point indexes "5", "6", "8", "10", "11", "12", "13" and "14" to predetermined values. Complement with "0".</p><p> The information complement unit 56 outputs the discrete cosine transform data having 15 DCT coefficients satisfied by the complement to the IDCT unit 53. The IDCT unit 53 performs inverse discrete cosine transform data and outputs the channel information (CSI) obtained by the inverse discrete cosine transform to the precoding unit 11.</p><p> According to the first embodiment, when selecting the frequency components to be included in the compressed data from the discrete cosine transform data, a predetermined number of frequency components are selected in order from the highest power. As a result, information on high-power frequency components is supplied from the MIMO receiver 2 to the MIMO transmitter 1, so that information compression that maintains high accuracy of channel information can be realized. In particular, when the amount of control information that can be transmitted from the MIMO receiver 2 to the MIMO transmitter 1 is fixed, the first embodiment is effective. Further, since the frequency components to be included in the compressed data are selected in order from the one with the highest power, it is possible to obtain the effect of preventing the frequency components having a relatively high power from being discarded and the accuracy of the channel information from being deteriorated.</p><p> According to the DCT, the information is concentrated on the low frequency component, but the concentration is remarkable as compared with other time-frequency domain transforms (for example, DFT and DWT). Therefore, when the number of frequency components included in the compressed data is constant, it is possible to improve the accuracy of the channel information by using the DCT.</p>

<p> In the second embodiment, when the adaptive selection unit 45 selects the frequency component to be included in the compressed data from the discrete cosine transform data, the power is high until the total power of the frequency components included in the compressed data reaches a predetermined value. Select the frequency components in order from the first. Hereinafter, the operation of the information compression unit 42 according to the second embodiment will be described in detail. Since the operation of the information expansion unit 52 is the same as that of the first embodiment described above, the description thereof will be omitted here.</p><p> First, the operation of the information compression unit 42 according to the second embodiment will be described. As in the case of Example 1 described above, the examples of FIGS. 3 and 4 are used as specific examples for convenience of explanation. The adaptive selection unit 45 receives the discrete cosine transform data from the DCT unit 41. The discrete cosine transform data has a DCT coefficient as information on each frequency component. The discrete cosine transform data of this DCT result is composed of 15 DCT coefficients with DCT point indexes "0" to "14". The DCT point index "0" corresponds to the DCT coefficient of the direct current (DC) component, and the larger the value of the DCT point index, the higher the DCT coefficient of the high frequency component.</p><p> First, the adaptive selection unit 45 calculates the power value of the frequency component for each DCT point index using the DCT coefficient specified by the DCT point index. This power value calculation method is the same as that of the first embodiment described above. As a result, the adaptive selection unit 45 calculates 15 power values corresponding to each of the DCT point indexes 0 to 14 shown in FIGS. 4 and 5.</p><p> Next, the adaptive selection unit 45 compares 15 power values, selects the DCT point index which is the maximum power value, and initializes the maximum power value in the power value addition register in the adaptive selection unit 45. .. Next, the adaptive selection unit 45 compares the remaining 14 power values, excluding the power value of the selected DCT point index, selects the DCT point index which is the maximum power value, and selects the maximum power value. Is added to the holding value of the power value addition register to update and set the power value addition register. The operation of selecting the DCT point index and adding the power value is repeated until the holding value of the power value addition register reaches a predetermined value. That is, each time the power value addition register is set, the holding value of the power value addition register is compared with the predetermined value, and when the holding value of the power value addition register becomes equal to or more than the predetermined value, the DCT point index is selected and the power is selected. End the value addition operation.</p><p> Here, as a specific example for convenience of explanation, the predetermined value is set to 40. As a result, the adaptive selection unit 45 has DCT point indexes "0" (power value = 10) and "4" in order from the largest power value among the 15 power values until the total power value reaches 40. Select a total of 5 (power value = 9), "2" (power value = 8), "3" (power value = 7), and "9" (power value = 7). The predetermined value related to the total power may be a fixed value or may be given as a ratio to the average power.</p><p> Next, the adaptive selection unit 45 selects the DCT point indexes 0, 2, 3, and 4 of the DCT point index selection results from the 15 DCT coefficients constituting the discrete cosine transform data of the DCT results. Only the five DCT coefficients corresponding to "9" and "9" are output to the quantization unit 46. Further, the adaptive selection unit 45 outputs the DCT point indexes 0, 2, 3, 4 and 9 of the DCT point index selection result to the control unit 44 as DCT point index information A. .. The control unit 44 includes the DCT point index information A (DCT point indexes 0, 2, 3, 4, and 9) in the control data C.</p><p> Since the operations of the quantization unit 46, the variable length coding unit 43, and the control unit 44 are the same as those in the above-described first embodiment, the description thereof will be omitted here.</p><p> According to the second embodiment, when selecting the frequency components to be included in the compressed data from the discrete cosine transform data, the power components to be included in the compressed data are included in the compressed data in order from the highest power until the total power of the frequency components reaches a predetermined value. Select the frequency component. As a result, information on high-power frequency components is supplied from the MIMO receiver 2 to the MIMO transmitter 1, so that information compression that maintains high accuracy of channel information can be realized. Further, since the total power of the frequency components included in the compressed data is equal to or more than a predetermined value, the accuracy of the channel information can be kept constant. In particular, when constant accuracy of channel information is required, the second embodiment is effective. Further, since the frequency components to be included in the compressed data are selected in order from the one with the highest power, it is possible to obtain the effect of preventing the frequency components having a relatively high power from being discarded and the accuracy of the channel information from being deteriorated.</p><p> According to the DCT, the information is concentrated on the low frequency component, but the concentration is remarkable as compared with other time-frequency domain transforms (for example, DFT and DWT). Therefore, when the total power of the frequency components included in the compressed data is constant, the number of DCT point indexes transmitted from the MIMO receiver 2 to the MIMO transmitter 1 can be reduced by using the DCT.</p>

<p> Example 3 is an example in which DCT is used as a time-frequency domain conversion for converting channel information from the time domain to the frequency domain. In the third embodiment, when the adaptive selection unit 45 selects a frequency component to be included in the compressed data from the discrete cosine transform data, the frequency is low until the total power of the frequency components included in the compressed data reaches a predetermined value. Select the frequency components in order from the first. This is because in the case of DCT, since the information is concentrated on the low frequency component, the accuracy of the channel information can be kept good even if the information on the high frequency component is reduced or deleted, so the information on the low frequency component is particularly compressed. Include it in the data. Hereinafter, the operations of the information compression unit 42 and the information expansion unit 52 according to the third embodiment will be described in detail. As in the case of Example 1 described above, the examples of FIGS. 3 and 4 are used as specific examples for convenience of explanation.</p><p> First, the operation of the information compression unit 42 according to the third embodiment will be described. The adaptive selection unit 45 receives the discrete cosine transform data from the DCT unit 41. The discrete cosine transform data has a DCT coefficient as information on each frequency component. The discrete cosine transform data of this DCT result is composed of 15 DCT coefficients with DCT point indexes "0" to "14". The DCT point index "0" corresponds to the DCT coefficient of the direct current (DC) component, and the larger the value of the DCT point index, the higher the DCT coefficient of the high frequency component.</p><p> First, the adaptive selection unit 45 selects the smallest DCT point index "0" from the 15 DCT point indexes "0" to "14", and uses the DCT coefficient of the selected DCT point index "0". The power value of the frequency component is calculated, and the power value of the calculation result is initially set in the power value addition register in the adaptive selection unit 45. The power value calculation method is the same as that of the first embodiment described above. Next, the adaptive selection unit 45 selects the smallest DCT point index "1" from the remaining 14 DCT point indexes "1" to "14" except for the selected DCT point index "0". , The power value of the frequency component is calculated using the DCT coefficient of the selected DCT point index "1", and the power value of the calculation result is added to the holding value of the power value addition register to update and set the power value addition register. The operation of selecting the DCT point index and adding the power value is repeated until the holding value of the power value addition register reaches a predetermined value. That is, each time the power value addition register is set, the holding value of the power value addition register is compared with the predetermined value, and when the holding value of the power value addition register becomes equal to or more than the predetermined value, the DCT point index is selected and the power is selected. End the value addition operation.</p><p> Here, as a specific example for convenience of explanation, the predetermined value is set to 40. As a result, the adaptive selection unit 45 has the DCT point index "0" in order from the 15 DCT point indexes "0" to "14" in ascending order of the DCT point index until the total power value reaches 40. (Power value = 10), "1" (Power value = 5), "2" (Power value = 8), "3" (Power value = 7), "4" (Power value = 9), "5" Select a total of 6 (power value = 1). The predetermined value related to the total power may be a fixed value or may be given as a ratio to the average power.</p><p> Next, the adaptive selection unit 45 has 6 DCT point indexes corresponding to the DCT point indexes "0" to "5" of the DCT point index selection result from the 15 DCT coefficients constituting the discrete cosine transform data of the DCT result. Only the DCT coefficient is output to the quantization unit 46. Further, the adaptive selection unit 45 outputs only the maximum DCT point index 5 among the DCT point index selection results to the control unit 44 as DCT point index information A. The control unit 44 includes the DCT point index information A (DCT point index 5) in the control data C.</p><p> Since the operations of the quantization unit 46, the variable length coding unit 43, and the control unit 44 are the same as those in the above-described first embodiment, the description thereof will be omitted here.</p><p> Next, the operation of the information development unit 52 according to the third embodiment will be described. Since the operations of the variable length decoding unit 51, the inverse quantization unit 55, and the control unit 54 are the same as those in the first embodiment, the description thereof will be omitted here.</p><p> When the information complementing unit 56 receives six DCT coefficients from the inverse quantization unit 55, the information complementing unit 56 complements the insufficient DCT coefficients based on the DCT point index information A received from the control unit 54. Here, the DCT point index information A has a DCT point index 5. This DCT point index "5" is the maximum value of the DCT point index of the DCT coefficient received from the inverse quantization unit 55. Therefore, the DCT coefficient after the DCT point index "6" is insufficient. As a result, the information complement unit 56 complements each DCT coefficient of the DCT point indexes 6 to 14 with a predetermined value 0.</p><p> The information complement unit 56 outputs the discrete cosine transform data having 15 DCT coefficients satisfied by the complement to the IDCT unit 53. The IDCT unit 53 performs inverse discrete cosine transform data and outputs the channel information (CSI) obtained by the inverse discrete cosine transform to the precoding unit 11.</p><p> According to the third embodiment, when selecting the frequency components to be included in the compressed data from the discrete cosine transform data, the frequencies are in ascending order until the total power of the frequency components included in the compressed data reaches a predetermined value. Select the frequency component. As a result, information on high-power frequency components is supplied from the MIMO receiver 2 to the MIMO transmitter 1, so that information compression that maintains high accuracy of channel information can be realized. Further, since the total power of the frequency components included in the compressed data is equal to or more than a predetermined value, the accuracy of the channel information can be kept constant. Further, since only one DCT point index is required to be transmitted from the MIMO receiver 2 to the MIMO transmitter 1, the amount of control information transmitted from the MIMO receiver 2 to the MIMO transmitter 1 can be minimized.</p><p> Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like within a range not deviating from the gist of the present invention are also included. For example, the channel information may be a channel response matrix between the plurality of transmitting antennas of MIMO transmitter 1 and the plurality of receiving antennas of MIMO receiver 2. In this case, information compression can be performed while maintaining good accuracy of the channel response matrix. As a result, in the MIMO system, the MIMO transmitter 1 can accurately precode the channel response matrix obtained by the MIMO receiver 2, and the channel response matrix sent from the MIMO receiver 2 to the MIMO transmitter 1 can be accurately precoded. It will be possible to reduce the amount of information. As a result, it is possible to secure the precoding effect and reduce the amount of radio resources used for transmitting the channel response matrix.</p><p> Further, the wireless communication system according to the present invention may use a multi-carrier transmission system or may use a single-carrier transmission system. Examples of the multi-carrier transmission method include an Orthogonal Frequency Division Multiplexing (OFDM) method. Further, the present invention can be applied to a wireless communication system other than a MIMO system, and can compress channel information indicating the state of a communication channel.</p><p> Further, a program for realizing the function of the channel information compression unit 24 shown in FIG. 2 or the function of the channel information expansion unit 14 shown in FIG. 3 was recorded on a computer-readable recording medium and recorded on this recording medium. Load the program into your computer system and get it by row, may be carried out channel information compression processing or channel information expansion processing. The "computer system" referred to here may include hardware such as an OS and peripheral devices. The "computer-readable recording medium" is a writable non-volatile memory such as a flexible disk, a magneto-optical disk, a ROM, or a flash memory, a portable medium such as a DVD (Digital Versatile Disk), or a built-in computer system. A storage device such as a hard disk.</p><p> Furthermore, a "computer-readable recording medium" is a volatile memory inside a computer system that serves as a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line (for example, DRAM (Dynamic)). It also includes those that hold the program for a certain period of time, such as Random Access Memory)). Further, the program may be transmitted from a computer system in which this program is stored in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the "transmission medium" for transmitting a program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. Further, the above program may be for realizing a part of the above-mentioned functions. Further, a so-called difference file (difference program) may be used, which can realize the above-mentioned functions in combination with a program already recorded in the computer system.</p>

1 ... MIMO transmitter, 2 ... MIMO receiver, 11 ... precoding unit, 12 ... transmitter, 13 ... control information receiver, 14 ... channel information expansion unit, 21 ... receiver, 22 ... channel estimate, 23 ... receive processing, 24 ... channel information compression, 25 ... control information transmitter, 41 ... DCT, 42 .. Information compression unit, 43 ... variable length coding unit, 44 ... control unit, 45 ... adaptive selection unit, 46 ... quantization unit, 51 ... variable length decoding unit, 52. .. Information Development Department, 53 ... IDCT Department, 54 ... Control Department, 55 ... Inverse Quantization Department, 56 ... Information Complementary Department