CN1848832A - Radio communication apparatus and radio communication method - Google Patents

Abstract

Radio communication apparatus includes unit dividing transmit data into first-and-second streams, unit subjecting first-and-second streams to serial-to-parallel conversion to obtain data signals, unit modulating data signals into OFDM-modulation signals corresponding to first and second streams using subcarriers, unit acquiring channel responses between communication and receiving apparatuses, unit computing singular values lambda<SUB>1</SUB><SUP>(k) </SUP>and lambda<SUB>2</SUB><SUP>(k) </SUP>of channel matrix corresponding to k<SUP>th </SUP>subcarrier in subcarriers, based on channel responses, unit assigning weights corresponding to singular values lambda<SUB>1</SUB><SUP>(k) </SUP>and lambda<SUB>2</SUB><SUP>(k) </SUP>to first-and-second streams where correspondence of weights to streams is different by subcarrier, unit multiplying, by each of assigned weights, OFDM-modulation signals corresponding to each of first and second streams, and acquire first-and-second signals corresponding to first-and-second streams, unit adding first-and-second signals to acquire added signals, unit subjecting added signals to inverse-Fourier transform, and unit transmitting, to receiving apparatus, signals output from subjecting unit.

Description

Radio communication apparatus and radio communication method

Technical Field

The present invention relates to a radio communication apparatus and method, and more particularly, to a radio communication apparatus and method of an OFDM-based spatial multiplexing transmission scheme.

Background

A method for distributing a transmission signal to a plurality of RF (radio frequency) units and simultaneously transmitting signals of the same frequency through a plurality of antennas has been proposed as a technique for improving a radio communication rate (see, for example, U.S. patent nos.6058105 and 6144711). In this method, signals of the same frequency are transmitted using different digital beams, and a receiving terminal receives multiplexed signals transmitted through different routes and separates them to decode.

As a result, the transmission rate can be increased according to the number of multiplexed signals without widening the frequency bandwidth used for communication. Thus, the method may improve spectral efficiency and thereby improve throughput.

On the other hand, in a multipath channel in which a plurality of signals having different propagation delay times between transmitting and receiving terminals are transmitted, waveform distortion caused by ISI (inter-symbol interference) may be a significant factor that degrades communication quality. A system using Orthogonal Frequency Division Multiplexing (OFDM) is referred to as a system capable of compensating for waveform distortion caused by ISI when it receives signals having different propagation delay times.

In the OFDM transmission scheme, subcarriers have different channel responses. Accordingly, if the method proposed in U.S. patent nos.6058105 and 6144711 is used as an OFDM transmission scheme, different digital beams are used for different subcarriers. In this case, in the related art, digital beams that cause all subcarriers to provide high reception power are allocated only to specific signals, which inevitably increases the characteristic difference between spatially multiplexed signals. Therefore, a signal having a high multi-level modulation number or a high coding rate has to be distributed as a spatial multiplexing signal, and accordingly, a high-precision RF unit capable of transmitting and receiving such a signal is required.

As described above, in the conventional radio communication apparatus, there is a large difference in received power between multiplexed signals. This means that the channel response of a signal with high received power cannot be fully exploited unless a modulation scheme or coding rate of high transmission rate is used for the signal. Accordingly, it is necessary to use an accurate apparatus capable of transmitting and receiving a signal of a high transmission rate. There is a need to reduce the cost of radio communication devices and to reduce the substrate area of integrated circuits incorporated in the devices.

Disclosure of Invention

According to an aspect of the present invention, there is provided a radio communication apparatus for transmitting data to a receiving apparatus, comprising: a dividing unit configured to divide transmission data into a first stream and a second stream; a serial-to-parallel conversion unit configured to subject the first stream and the second stream to serial-to-parallel conversion to obtain a plurality of data signals; a modulation unit configured to modulate the data signal into a plurality of OFDM modulated signals corresponding to the first stream and the second stream using a plurality of subcarriers; an acquisition unit configured to acquire a plurality of channel responses between the radio communication apparatus and the reception apparatus; a calculation unit configured to calculate a singular value λ of a channel matrix corresponding to a k-th (k is a natural number) subcarrier included in the subcarriers, based on the acquired channel response₁ ^(k)And λ₂ ^(k)(ii) a A weight assignment unit configured to assign a weight corresponding to the singular value λ₁ ^(k)And λ₂ ^(k)A plurality of weights are assigned to the first stream and the second stream, wherein the correspondence of each weight to each stream differs according to subcarriers; a multiplication unit configured to multiply each assigned weight by an OFDM modulated signal corresponding to each of the first and second streams and obtain first and second signals corresponding to the first and second streams; an adding unit configured to add the first signal and the second signal and obtain an added signal; an inverse fourier transform unit configured to subject the added signal to an inverse fourier transform; and a transmission unit configured to transmit the signal output from the inverse fourier transform unit to a receiving apparatus.

According to another aspect of the present invention, there is provided a radio communication apparatus for transmitting data to a receiving apparatus, comprising: a dividing unit configured to divide transmission data into at least three streams; a serial-to-parallel conversion unit configured to subject the stream to serial-to-parallel conversion to obtain a plurality of data signals; a modulation unit configured to modulate the data signal into a plurality of streams corresponding to the at least three streams using a plurality of subcarriersAn OFDM modulation signal; an acquisition unit configured to acquire a plurality of channel responses between the radio communication apparatus and the reception apparatus; a calculation unit configured to calculate a singular (singular) value λ of a channel matrix corresponding to a k-th (k is a natural number) subcarrier included in the subcarriers, based on the obtained channel response₁ ^(k)，λ₂ ^(k)，...，λ_m ^(k)(m is a natural number of not less than 3); a weight assignment unit configured to assign a weight corresponding to the singular value λ₁ ^(k)，λ₂ ^(k)，...，λ_m ^(k)Is assigned to the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)≥...≥λ_m ^(k)(ii) a A multiplication unit configured to multiply each assigned weight by an OFDM modulated signal corresponding to each stream and obtain m signals; an adding unit configured to add the m signals and obtain an added signal; an inverse fourier transform unit configured to subject the added signals to inverse fourier transform; and a transmission unit configured to transmit the signal output from the inverse fourier transform unit to a receiving apparatus.

According to another aspect of the present invention, there is provided a radio communication apparatus for transmitting data to a receiving apparatus, comprising: a dividing unit configured to divide transmission data into at least three streams; a serial-to-parallel conversion unit configured to subject the stream to serial-to-parallel conversion to obtain a plurality of data signals; a modulation unit configured to modulate the data signal into a plurality of OFDM modulated signals corresponding to the at least three streams using a plurality of subcarriers; an acquisition unit configured to acquire a plurality of channel responses between the radio communication apparatus and the reception apparatus; a calculation unit configured to calculate a singular value λ of a channel matrix corresponding to a k-th (k is a natural number) subcarrier included in the subcarriers, from the acquired channel response₁ ^(k)And λ₂ ^(k)(ii) a A weight assignment unit configured to assign a weight corresponding to the singular valueλ₁ ^(k)And λ₂ ^(k)To the OFDM modulated signals corresponding to two of the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)(ii) a A multiplication unit configured to multiply each assigned weight by an OFDM modulated signal corresponding to each stream, and obtain a first signal and a second signal; an adding unit configured to add the first signal and the second signal and obtain an added signal; an inverse fourier transform unit configured to subject the added signals to inverse fourier transform; and a transmission unit configured to transmit the signal output from the inverse fourier transform unit to a receiving apparatus.

According to still another aspect of the present invention, there is provided a radio communication method for use in a radio communication apparatus for transmitting data to a receiving apparatus, including: dividing transmission data into a first stream and a second stream; subjecting the first stream and the second stream to serial-to-parallel conversion to obtain a plurality of data signals; modulating the data signal into a plurality of OFDM modulated signals corresponding to the first stream and the second stream using a plurality of subcarriers; acquiring a plurality of channel responses between a radio communication apparatus and a receiving apparatus; from the obtained channel response, a singular value λ of a channel matrix corresponding to a k-th (k is a natural number) subcarrier included in the subcarriers is calculated₁ ^(k)And λ₂ ^(k)(ii) a Corresponding to singular value λ₁ ^(k)And λ₂ ^(k)A plurality of weights are assigned to the first stream and the second stream, wherein the correspondence of each weight to each stream differs according to subcarriers; multiplying each assigned weight by an OFDM modulated signal corresponding to each of the first and second streams and obtaining a first signal and a second signal; adding the first signal and the second signal and obtaining an added signal; subjecting the added signals to an inverse fourier transform; and transmitting the signal output from the inverse fourier transform unit to the receiving device.

Drawings

Fig. 1 is a block diagram illustrating a radio communication apparatus according to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating an example of a machine for obtaining the encoded signal appearing in FIG. 1;

FIG. 3 is a block diagram illustrating another example of a machine for obtaining the encoded signal appearing in FIG. 1;

fig. 4 is a diagram for explaining calculation by the weight rectangular drop multiplier;

FIG. 5 is a block diagram illustrating a machine incorporated in a receiving terminal for performing channel response estimation;

fig. 6 is a block diagram illustrating another machine incorporated in a receiving terminal for performing channel response estimation;

fig. 7 is a diagram illustrating an example of allocation of weight vectors in the first embodiment;

fig. 8 is a diagram illustrating an example of allocation of weight vectors in the second embodiment;

fig. 9 is a diagram illustrating another allocation example of weight vectors in the second embodiment;

fig. 10 is a diagram illustrating an example of allocation of weight vectors in the third embodiment;

fig. 11 is a block diagram illustrating a radio communication apparatus according to a fifth embodiment of the present invention;

fig. 12 is a diagram illustrating an example of power characteristics of a power amplifier included in each RF unit appearing in fig. 11;

fig. 13 is a diagram illustrating an example of allocation of weight vectors in the sixth embodiment;

fig. 14 is a diagram illustrating another allocation example of weight vectors in the sixth embodiment;

fig. 15 is a diagram illustrating an example of allocation of weight vectors in the seventh embodiment;

fig. 16 is a diagram illustrating another allocation example of weight vectors in the seventh embodiment;

fig. 17 is a diagram illustrating still another allocation example of weight vectors in the seventh embodiment;

fig. 18 is a diagram illustrating still another allocation example of weight vectors in the seventh embodiment;

fig. 19 is a diagram illustrating an example of allocation of weight vectors in the eighth embodiment;

fig. 20 is a diagram illustrating another allocation example of weight vectors in the eighth embodiment; and

fig. 21 is a diagram illustrating an example of allocation of transmission power and an example of allocation of weight vectors in the tenth embodiment.

Detailed Description

A radio communication apparatus according to an embodiment of the present invention is specifically described with reference to the drawings.

The radio communication apparatus and method can improve the transmission rate of the spatial multiplexing signal as a whole without using any precise means.

(first embodiment)

A radio communication apparatus according to a first embodiment is first explained with reference to fig. 1. Fig. 1 is a block diagram illustrating an example in which the number of coded signals to be multiplexed is 2 and the number of RF units is 4.

As shown in the figure, the radio communication apparatus of the first embodiment includes serial-to- parallel converters 101 and 102, modulators 103 and 104, weight matrix multiplier 105, inverse fourier transformers 106 to 109, parallel-to-serial converters 110 to 113, GI insertion units 114 to 117, RF units 118 to 121, transmission antennas 122 to 125, weight matrix generation unit 126, and weight control unit 127. Further, in the example of fig. 1, the number of coded signals to be multiplexed is 2, and the two coded signals 1 and 2 are OFDM-modulated, then subjected to weighting processing by the weight matrix multiplier 105, and allocated to a plurality of RF units.

Serial-to- parallel converters 101 and 102 allocate input coded signals 1 and 2 to subcarriers. Serial-to- parallel converters 101 and 102 convert the input coded signal into parallel signals as many as the number of data subcarriers used for OFDM modulation. For example, if the number of OFDM data subcarriers is 100, the number of outputs of each serial-to-parallel converter is 100.

Note that the encoded signals 1 and 2 may employ any encoding scheme, such as Reed-Solomon (Reed-Solomon) encoding, convolutional encoding, turbo encoding, or Low Density Parity Check (LDPC) encoding. Further, the encoding scheme of this embodiment is not limited thereto. This is sufficient if the receiving terminal can decode the signal according to the coding scheme. An example of an encoding machine for acquiring the encoded signals 1 and 2 is described subsequently with reference to fig. 2 and 3.

The modulators 103 and 104 OFDM-modulate output signals (i.e., parallel signals) of the serial- parallel converters 101 and 102. That is, the modulators 103 and 104 modulate the coded signals 1 and 2 in units of subcarriers. The modulation scheme used for modulators 103 and 104 may be Phase Shift Keying (PSK), such as BPSK or QPSK, or Quadrature Amplitude Modulation (QAM), such as 16QAM, 32QAM, 64QAM, or 256 QAM. Also, the modulation scheme in this embodiment is not limited to the two modulation schemes described above, but may be any other modulation scheme. This is sufficient if the receiving terminal as the destination of the radio communication apparatus of the embodiment can decode the modulation scheme.

The weight matrix generation unit 126 generates weights according to a channel response between the transmitting terminal and the receiving terminal. The weight control unit 127 assigns the weights generated by the weight matrix generation unit 126 to the weight matrix multiplier 105.

The weight matrix multiplier 105 receives modulated signals obtained by performing modulation in units of subcarriers, and multiplies them by respective weights assigned by the weight control unit 127, thereby accumulating (multiplexing) the signals. In the example of fig. 1, the weight matrix multiplier 105 distributes the code signals corresponding to the four RF units 118 to 121. The weight matrix multiplier 105 multiplies a weight corresponding to the number of RF units by a signal obtained by performing modulation in units of subcarriers. The multiplication operation of the weight matrix multiplier 105 is explained later with reference to fig. 4.

The inverse fourier transformers 106 to 109 inverse fourier transform the output signals of the weight matrix multiplier 105. At this time, the inverse fourier transform may be an Inverse Fast Fourier Transform (IFFT) or an Inverse Discrete Fourier Transform (IDFT).

The parallel-to-serial converters 110 to 113 perform parallel-to-serial conversion on the output signals of the inverse fourier transformers 106 to 109. That is, the parallel-to-serial converters 110 to 113 each convert the received parallel signal into a timing signal.

The GI insertion units 114 to 117 add guard time Slots (GIs) to the timing signals. The guard slot is a scheme generally used in the OFDM transmission scheme and does not affect the characteristics in the embodiment of the present invention. Therefore, a detailed description of the guard slot is not given.

The RF units 118 to 121 convert the reception signals into analog signals using their respective digital-to-analog (D/a) converters (not shown), then convert the analog signals into RF signals using their respective frequency converters (not shown), and output them to the transmission antennas 122 to 125 via Power Amplifiers (PAs) (not shown). Since the RF units 118 to 121 are general-purpose units and have no particular function, they are not specifically described. The transmit antennas 122 to 125 may be of any type. This is sufficient if they can transmit signals with the required frequency.

As described above, the radio communication apparatus of this embodiment transmits a modulated signal using different weights in units of subcarriers. As a result, each modulated signal is transmitted using a different directional digital beam. Therefore, the radio communication apparatus can significantly change the transmission characteristics according to the weight for transmission. The radio communication apparatus in the present embodiment can perform transmission using the optimal weight if the optimal weight is determined according to the channel response between the transmitting and receiving terminals. The estimation of the channel response is explained later with reference to fig. 5 and 6.

Referring now to fig. 2 and 3, it is illustrated how the encoded signals 1 and 2 are generated.

The encoded signals 1 and 2 input to the serial- parallel converters 101 and 102 are acquired by the signal distributor 201 (or 302), the encoding units 202 and 203 (or 301), and the interleavers 204 and 205 (or 303, 304) shown in fig. 2 (or 3).

The coding scheme used in the coding unit is, for example, reed-solomon coding, convolutional coding, turbo coding or LDPC coding. The encoded signals 1 and 2 are obtained by encoding a single data stream into a code. As shown in fig. 2, the data stream may be divided into two by a signal distributor 201 and then encoded by two encoding units 202 and 203. Alternatively, as shown in fig. 3, the data stream may be first encoded by the encoding unit 301 and then divided into two by the signal splitter 302. This is sufficient if two encoded signals are generated. Further, to prevent burst errors, interleavers 204 and 205 permute (permate) the encoded signals so that the signal order is changed in an order known to the receiving terminal. Note that the interleavers 204 and 205 may permute the signals with the same rule or different rules. This is sufficient if the receiving terminal is aware of the rule.

Referring to fig. 4, a description is given of signals output from the weight matrix multiplier 105 of fig. 1. Fig. 4 shows the case where only the kth (k is a natural number) subcarrier, which is used for weight calculation by the weight matrix multiplier 105, is correlated.

It is assumed here that the modulation signal of the k-th subcarrier output from the modulator 103 is s₁ ^(k)And the modulation signal of the k-th subcarrier output from the modulator 104 is s₂ ^(k). Since the modulated signals are processed by the four RF units 118 to 121 and transmitted through the four transmission antennas 122 to 125, each modulated signal is provided with four weights as shown in fig. 4The multiplication is repeated. As a result, the signal x output from the weight matrix multiplier 105 to the inverse fourier transformer n (n is 1, 2, 3, 4) is output_n ^(k)Is given by:

x_n ^(k)＝w_1.n ^(k)·s₁ ^(k)+w_2.n ^(k)·s₂ ^(k) …(1)

accordingly, a transmission signal vector corresponding to the kth subcarrier and having the output signals of the inverse fourier transformers 106 to 109 as elements is given by:

$x^{\left(k\right)}={\left[\begin{array}{cccc}{x_1}^{\left(k\right)},& {x_2}^{\left(k\right)},& {x_3}^{\left(k\right)},& {x_4}^{\left(k\right)}\end{array}\right]}^T$

<math> <mrow> <msup> <mrow> <mo>=</mo> <msub> <mi>w</mi> <mn>1</mn> </msub> </mrow> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>&CenterDot;</mo> <msup> <msub> <mi>s</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>+</mo> <msup> <msub> <mi>w</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>&CenterDot;</mo> <msup> <msub> <mi>s</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> </mrow> </math>

$=\left[\begin{array}{cc}{w_1}^{\left(k\right)},& {w_2}^{\left(k\right)}\end{array}\right]\left[\begin{array}{c}{s_1}^{\left(k\right)}\\ {s_2}^{\left(k\right)}\end{array}\right]$

<math> <mrow> <msup> <mrow> <mo>=</mo> <mi>w</mi> </mrow> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msup> <msub> <mi>s</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> </mtd> </mtr> <mtr> <mtd> <msup> <msub> <mi>s</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> </mtd> </mtr> </mtable> </mfenced> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

in the above equation, w^(k)Is a weight matrix, w₁ ^(k)And w₂ ^(k)Is a weight vector and is given by:

w₁ ^(k)＝[w_1，1 ^(k)，w_1，2 ^(k)，w_1，3 ^(k)，w_1，4 ^(k)]^T …(3-1)

w₂ ^(k)＝[w_2，1 ^(k)，w_2，2 ^(k)，w_2，3 ^(k)，w_2，4 ^(k)]^T …(3-2)

where T denotes transpose. Weight matrix multiplier 105 outputs x_n ^(k)To an inverse fourier transformer n. Referring to fig. 5 and 6, the method for determining the weights is explained immediately after the method for acquiring the channel response is explained.

Referring now to fig. 5, an example of a channel response estimation unit incorporated in a receiving terminal for transmitting a channel response to a radio communication apparatus in the present embodiment is explained.

A method for transmitting a channel response estimated by a receiving terminal to a radio communication apparatus is exemplarily illustrated as one of methods for transmitting a channel response to a radio communication apparatus. Generally, in radio communication, a known signal for channel response estimation is transmitted together with a data signal, and thus a receiving terminal can estimate a channel response using the known signal.

As shown in fig. 5, the receiving terminal for transmitting the channel response to the radio communication apparatus of the present embodiment includes: reception antennas 501 and 502, RF units 503 and 504, GI removal units 505 and 506, serial- parallel converters 507 and 508, FFT units 509 and 510, and channel response estimation unit 511.

The RF units 503 and 504 convert signals received via the receiving antennas 501 and 502, respectively, into digital signals. Each of the RF units 503 and 504 is a general RF unit including a low noise amplifier, a frequency converter, a filter, and an analog-to-digital (a/D) converter, and thus is not specifically illustrated.

GI removing units 505 and 506 remove guard slots from the digital signals as output signals of the RF units 503 and 504, respectively.

The serial-to- parallel converters 507 and 508 convert the digital signal from which the guard slots are removed or the timing signal into a parallel signal.

The FFT units 509 and 510 convert the parallel signals into frequency domain signals. The FFT unit can be replaced by DET. This is sufficient if they can convert the time domain signal into a frequency domain signal.

The channel response estimation unit 511 estimates a channel response from the output signals of the FFT units 509 and 510. This will be explained in detail.

It is assumed here that the kth subcarrier signal received by the receiving antenna m and the RF unit m of the receiving terminal and converted into a frequency domain signal by the corresponding FFT unit is y_m ^(k). In this case, a reception vector y including signals received as elements by the RF units 503 and 504^(k)Given by:

y^(k)＝[y₁ ^(k)，y₂ ^(k)]^T

＝H^(k)x^(k)+n^(k) …(4)

wherein n is^(k)Is a noise vector representing the noise corresponding to the k-th subcarrier of the RF unit incorporated in the receiving terminal. Further, in equation (4), the number of RF units incorporated in the receiving terminal is set to 2. However, the number of RF units is not limited to 2. This is sufficient if the receiving terminal can receive the multiplexed signal transmitted from the radio communication apparatus.

H in equation (4)^(k)Is a channel matrix corresponding to the kth subcarrier and using responses between transmitting and receiving terminals as elements. The dimension of the channel matrix is (the number of RF units incorporated in the receiving terminal) × (the number of RF units incorporated in the radio communication apparatus). In the examples in fig. 1 and 5, as represented in equations (2) and (4), the number of RF units (118 to 121) incorporated in the radio communication apparatus is 4, and the number of RF units (503 and 504) incorporated in the receiving terminal is 2. Thus, the channel matrix is a (2 × 4) matrix.

In general, in radio communications, if the channel response matrix H^(k)Is unknown, the received signal cannot be decoded. The radio communication apparatus thus transmits a signal known to the receiving terminal as a transmission signal x included in equation (4) for channel response estimation^(k). The channel response estimation unit 511 may derive the signal y from the obtained signal y^(k)And x^(k)Estimating a channel response matrix H^(k)。

Referring to fig. 6, there is illustrated a channel response estimator for estimating an impulse response and performing fourier transform on the impulse response, which is different from that in fig. 5, and incorporated in a receiving terminal for transmitting the channel response to the radio communication apparatus of the embodiment.

The receiving terminal shown in fig. 6 includes receiving antennas 501 and 502, RF units 503 and 504, impulse response estimation units 601 and 602, and FFT units 507 and 508. In fig. 6, elements similar to those in fig. 5 are denoted by corresponding reference numerals and thus are not described.

Impulse response estimation units 601 and 602 receive digital signals as output signals of the RF units 503 and 504, and estimate impulse responses from the digital signals. FFT units 509 and 510 perform fourier transform on the impulse response to acquire a channel response. Even though in the case of fig. 6, the FFT unit is used to perform fourier transform, any scheme different from the FFT unit may be adopted. This is sufficient if the time domain signal can be converted into a frequency domain signal.

In the configuration of fig. 6, as in the case of fig. 5, estimation of the impulse response is performed using a known signal transmitted from the radio communication apparatus. In addition, for example, the impulse response estimation units 601 and 602 adopt a least-squares method or a minimum mean-square error (MMSE) method as a scheme for estimating an impulse response from a known signal. Since these methods are not indispensable in the examples of the present invention, they are not described in detail. Also, the estimation scheme is not limited to the least squares method or the least squares method, and any scheme that can perform impulse response estimation may be employed.

As described with reference to fig. 5 and 6, the channel response is transmitted to the radio communication apparatus by transmitting the channel response obtained by the receiving terminal to the radio communication apparatus. In general, in radio communication other than broadcasting, the radio communication apparatus and the receiving terminal in the embodiment can access each other. That is, one of the terminals transmits a signal to the other at one time and receives a signal from the other at another time. Accordingly, the receiving terminal can transmit the estimated channel response to the radio communication apparatus. Thus, the receiving terminal feeds the estimated channel response back to the radio communication device, whereby the radio communication device can acquire the channel response.

Further, as described above, in general, a radio communication apparatus and a receiving terminal access each other, and therefore the former sometimes receives a signal transmitted from the latter. In this case, the response of the channel from the receiving terminal to the radio communication apparatus can be estimated by the method described with reference to fig. 5 and 6, using the known signal for channel response estimation related to the known signal. The response of the channel from the receiving terminal to the radio communication device is substantially the same as the response of the channel from the radio communication device to the receiving terminal if the same frequency is used for communication. Thus, the channel response for a transmission may be estimated from the channel response estimated during reception.

As described above, in the radio communication apparatus, several methods for acquiring the channel response are possible. The radio communication apparatus of the present embodiment may adopt any one of the methods.

A method for determining the weights using the weight matrix multiplier 105 and based on the channel responses obtained as described above will now be described. The weight matrix generation unit 126 determines weights.

The weight vector w corresponding to the radio communication apparatus in fig. 1 is known₁ ^(k)And w₂ ^(k)Can be used for dredgingOptimized by performing Singular Value Decomposition (SVD) on the channel matrix. Using SVD, channel matrix H^(k)May be represented by the following formula (5):

$H^{\left(k\right)}=U^{\left(k\right)}{D}^{\left(k\right)}{V}^{{\left(k\right)}^H}$

<math> <mrow> <mo>=</mo> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msup> <msub> <mi>u</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>,</mo> </mtd> <mtd> <msup> <msub> <mi>u</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> </mtd> </mtr> </mtable> </mfenced> <mi>diag</mi> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msub> <mi>&lambda;</mi> <mn>1</mn> </msub> <mo>,</mo> </mtd> <mtd> <msub> <mi>&lambda;</mi> <mn>2</mn> </msub> </mtd> </mtr> </mtable> </mfenced> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msup> <msub> <mi>v</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> </mtd> </mtr> <mtr> <mtd> <msup> <msub> <mi>v</mi> <mn>2</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> </mtd> </mtr> </mtable> </mfenced> </mrow> </math>

<math> <mrow> <mo>=</mo> <msub> <mi>&lambda;</mi> <mn>1</mn> </msub> <msup> <msub> <mi>u</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <msup> <msub> <mi>v</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> <mo>+</mo> <msub> <mi>&lambda;</mi> <mn>2</mn> </msub> <msup> <msub> <mi>u</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <msup> <msub> <mi>v</mi> <mn>2</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>5</mn> <mo>)</mo> </mrow> </mrow> </math>

where H represents the complex conjugate transpose,is a diagonal matrix, u₁ ^(k)And u₂ ^(k)Is a vector having the same number of elements as the number of RF units of the receiving terminal, and v₁ ^(k)And v₂ ^(k)Is a vector having the same number of elements as the number of RF units of the radio communication apparatus. These vectors are orthogonal vectors satisfying the following equations (6-1) and (6-2):

<math> <mrow> <msup> <msub> <mi>v</mi> <mi>i</mi> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> <msup> <msub> <mi>v</mi> <mi>j</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>=</mo> <msub> <mi>&delta;</mi> <mi>ij</mi> </msub> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msup> <msub> <mi>u</mi> <mi>i</mi> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> <msup> <msub> <mi>u</mi> <mi>j</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>=</mo> <msub> <mi>&delta;</mi> <mi>ij</mi> </msub> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein delta_ijIs the increase in Kronecker (Kronecker) represented by the following equation (7):

<math> <mrow> <msub> <mi>&delta;</mi> <mi>ij</mi> </msub> <mo>=</mo> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <mn>1</mn> </mtd> <mtd> <mrow> <mo>(</mo> <mi>i</mi> <mo>=</mo> <mi>j</mi> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> </mtd> <mtd> <mrow> <mo>(</mo> <mi>i</mi> <mo>&NotEqual;</mo> <mi>j</mi> <mo>)</mo> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>7</mn> <mo>)</mo> </mrow> </mrow> </math>

radio communication device usage v₁ ^(k)And v₂ ^(k)As weight vectors and transmit them for signaling. If v is₁ ^(k)(w₁ ^(k)＝v₁ ^(k)) Used as transmission signal s₁ ^(k)And v is₂ ^(k)(w₂ ^(k)＝v₂ ^(k)) Used as transmission signal s₂ ^(k)Then, the received signal represented by equation (4) can be represented by the following equation (8):

y^(k)＝λ₁ ^(k)u₁ ^(k)s₁ ^(k)+λ₂ ^(k)u₂ ^(k)s₂ ^(k)+n^(k) …(8)

due to u₁ ^(k)And u₂ ^(k)Are orthogonal (refer to equation (6)), so s₁ ^(k)And s₂ ^(k)Can be prepared by mixing u₁ ^(k)HAnd u₂ ^(k)HMultiplied by the received signal y^(k)Extracted as expressed by equations (9-1) and (9-2) below:

<math> <mrow> <msup> <msub> <mi>s</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>&ap;</mo> <msup> <msub> <mi>u</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> <mo>&CenterDot;</mo> <msup> <mi>y</mi> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>/</mo> <msup> <msub> <mi>&lambda;</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>9</mn> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msup> <msub> <mi>s</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>&ap;</mo> <msup> <msub> <mi>u</mi> <mn>2</mn> </msub> <mrow> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </mrow> </msup> <mo>&CenterDot;</mo> <msup> <mi>y</mi> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>/</mo> <msup> <msub> <mi>&lambda;</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>9</mn> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

in addition to the above-described methods, a Zero Forcing (ZF) method for multiplying a generalized inverse matrix of a channel response matrix, an MMSE method for multiplying a weight matrix for minimizing an average value of squared errors, or a method for performing maximum likelihood detection using a replica signal are exemplified as a method for extracting a transmission signal from a reception signal. In this embodiment, the receiving method is not limited to a specific one, but any scheme different from the above-described method may be adopted.

Signal s extracted from the received signal at the receiving terminal₁ ^(k)And s₂ ^(k)The SN ratio of (A) can be represented by the following formulae (10-1) and (10-2):

(λ₁ ^(k))²|s₁ ^(k)|²/‖n^(k)‖² …(10-1)

(λ₂ ^(k))²|s₂ ^(k)|²/‖n^(k)‖² …(10-2)

in which n is enclosed^(k)The absolute value of the label represents the squared norm of the vector. Since the average power is fixed between the modulated signals to be multiplexed, it is apparent that the SN ratio of each spatial multiplexing signal of the k-th subcarrier is determined by the singular value λ of the channel matrix corresponding to the k-th subcarrier₁ ^(k)And λ₂ ^(k)And (4) determining. Further, since the subcarriers have different channel matrices in an environment where a plurality of multiplexed electric waves having different delays are transmitted, the SN ratios differ between the subcarriers.

If only weight vectors with higher singular values are assigned to a particular signal in each subcarrier, i.e. if λ₁ ^(k)≥λ₂ ^(k)And signal s₁ ^(k)Weight w of₁ ^(k)Is set to v₁ ^(k)Then, in each subcarrier, the SN ratio of each signal modulated by the modulator 103 in fig. 1 is larger than the SN ratio of each signal modulated by the modulator 104 in fig. 1. The signal modulated by modulator 103 is thus qualitatively different from the signal modulated by modulator 104Of the signal of (1).

In order to perform efficient communication in the above-described environment, it is necessary to transmit the encoded signals 1 and 2 (shown in fig. 1) by setting the transmission rate of the signal 1 higher than that of the signal 2. In order to increase the transmission rate, it is necessary to increase the coding rate or the number of multi-level modulations of the modulator. However, since the transmission signal must be generated accurately, if the transmission rate increases, the transmission signal will be significantly affected by non-idealities of the analog circuit, such as non-linear distortion of the power amplifier. As a result, sufficient performance may not be obtained even if the channel response is high.

According to the above, in the first embodiment of the present invention, the weight control unit 127 performs control for assigning weights so that signal streams may have the same characteristics on the reception side.

Referring to fig. 7, the weight assignment control performed by the radio communication apparatus of the first embodiment is explained. In the case of fig. 7, the number of subcarriers is 8. Considering the signal modulated by the modulator 103, corresponding to the respective higher singular values λ₁ ^(k)Vector v of₁ ⁽¹⁾，v₁ ⁽²⁾，v₁ ⁽³⁾And v₁ ⁽⁴⁾Is allocated to subcarrier f₁，f₂，f₃And f₄Corresponding to the respective lower singular value λ₂ ^(k)Vector v of₂ ⁽⁵⁾，v₂ ⁽⁶⁾，v₂ ⁽⁷⁾And v₂ ⁽⁸⁾Is allocated to subcarrier f₅，f₆，f₇And f₈。

Conversely, consider a signal modulated by modulator 104, corresponding to respective lower singular values λ₂ ^(k)Vector v of₂ ⁽¹⁾，v₂ ⁽²⁾，v₂ ⁽³⁾And v₂ ⁽⁴⁾Is allocated to subcarrier f₁，f₂，f₃And f₄Corresponding to respective higher singular values λ₁ ^(k)Vector v of₁ ⁽⁵⁾，v₁ ⁽⁶⁾，v₁ ⁽⁷⁾And v₁ ⁽⁸⁾Is allocated to subcarrier f₅，f₆，f₇And f₈. As a result, at subcarrier f₁，f₂，f₃And f₄In the above, a signal modulated by the modulator 103, i.e., a coded signal 1, is received at an SN ratio higher than that of a coded signal 2; and in subcarrier f₅，f₆，f₇And f₈Coded signal 2 is received with a high SN ratio. Thus, in general, the code signals 1 and 2 are transmitted with substantially the same SN ratio.

The above-described weight assignment with respect to subcarriers will be compared with the case where subcarriers are not considered, the singular vector corresponding to a higher singular value is assigned as a weight vector to only a specific signal, and the singular vector corresponding to a lower singular value is assigned as a weight vector to another signal. In the latter case, it is assumed that the channel response of the signal with the higher singular value is better than that of the other signal. Also, assuming that 256QAM is selected as a modulation scheme suitable for a better channel response and is used to transmit a signal having a higher singular value, 16QAM is selected for transmitting a signal having a lower singular value.

In the former case, i.e., in the radio communication apparatus of the first embodiment, since all signals have substantially the same reception power, they can be transmitted by 64 QAM. In contrast, in the former case, the transmitting and receiving terminals must employ an RF unit that can transmit and receive 256QAM signals. Generally, the greater the number of multilevel modulations, the more accuracy the RF unit needs. Further, because the signals differ significantly in received power, the load on the RF unit is not small. On the other hand, in the radio communication apparatus of the first embodiment, the signal can have a relatively constant received power, and thus the RF unit can be prevented from being overloaded without reducing the overall throughput.

As described above, in the first embodiment, the spatial multiplexing signalThe characteristic difference between the numbers is reduced to suppress the load on the transmitting and/or receiving terminal. Therefore, no precise device is required. Even a standard device can sufficiently utilize the channel response by increasing the transmission rate of the spatial multiplexing signal as a whole, rather than increasing the transmission rate of a specific signal. Further, the required substrate area is reduced because no precision devices are required. Also, in order to improve the accuracy of channel response estimation at the receiving terminal, the channel response of a certain subcarrier can be estimated from the weighted sum of the estimated channel responses of subcarriers in the vicinity of the certain subcarrier, using the correlation of channel responses between the channel responses of adjacent subcarriers. If the weight vector is allocated as shown in fig. 7, the subcarrier f₁To f₄And f₅To f₈The correlation of the channel responses in (1) increases, that is to say the weighted sum of the channel responses of the adjacent subcarriers can be exploited. Although the number of carriers is set to eight in this embodiment, the present invention is not limited to this.

(second embodiment)

The radio communication apparatus according to the second embodiment is similar in configuration to the radio communication apparatus of the first embodiment shown in fig. 1, and is also similar to the first embodiment in that different beams corresponding to subcarriers are used to multiplex signals for transmission. The second embodiment is different from the first embodiment in the manner of allocation, that is, the manner of allocating singular vectors corresponding to higher and lower singular values to a spatial-multiplexed signal in units of subcarriers.

The channel response is different between subcarriers, and subcarrier f₁To f₄Is not always equal to the subcarrier f₅To f₈The average power of (c). In subcarriers with high average power, a modulated signal assigned singular vectors corresponding to higher singular values may have higher performance.

A second embodiment relates to a modulation signal for overcoming the above-mentioned situationWeight assignment method of heterogeneity of characteristic difference between numbers. Fig. 8 shows an example of assigning weight vectors to subcarriers in the second embodiment. In this example, weights are assigned to the modulated signal such that singular vectors corresponding to high singular values are assigned to every other subcarrier. In particular, considering the signal modulated by the modulator 103, the vectors v corresponding to the respective higher singular values₁ ⁽¹⁾，v₁ ⁽³⁾，v₁ ⁽⁵⁾，v₁ ⁽⁷⁾Are respectively allocated to subcarriers f₁，f₃，f₅And f₇And vectors v corresponding to the respective lower singular values₂ ⁽²⁾，v₂ ⁽⁴⁾，v₂ ⁽⁶⁾，v₂ ⁽⁸⁾Are respectively allocated to subcarriers f₂，f₄，f₆And f₈。

Even if the subcarriers have different channel responses, the channel responses are not completely independent of each other. Generally, closer to the subcarriers, higher correlation is possessed. Therefore, if singular vectors corresponding to higher and lower singular values are alternately allocated as weights to modulation signals of adjacent subcarriers as in the second embodiment, the difference in channel power between the modulation signals can be further reduced than in the first embodiment.

As described above, in the second embodiment, it is proposed to assign singular vectors corresponding to higher and lower singular values to modulation signals of adjacent subcarriers. However, the correlation of channel responses between some subcarriers close to each other and between adjacent subcarriers is considered to be high. Therefore, as shown in fig. 9, the allocation of the singular vector can be switched in units of two or more subcarriers. As with the first embodiment, this allows the channel responses of certain subcarriers to be subject to a weighted sum calculation that is used when the receiving terminal estimates the channel response of a given subcarrier. As a result, the same advantages as those obtained in the first embodiment can also be obtained.

As described above, the second embodiment can reduce the characteristic difference between the spatially multiplexed signals, thereby reducing the load in the RF unit.

(third embodiment)

The radio communication apparatus according to the third embodiment is similar in configuration to the radio communication apparatus of fig. 1, and is similar to the first and second embodiments in that different beams corresponding to subcarriers are used to multiplex signals for transmission. The third embodiment is different from the first and second embodiments in that, when singular vectors corresponding to higher singular values are allocated to a spatial-multiplexed signal in units of subcarriers, the allocation manner is changed according to the subcarriers allocated before the components of the continuous coded signal are permuted by the interleaver.

According to the third embodiment, if convolutional coding is adopted as a coding scheme in a radio communication apparatus, it is necessary to use an interleaver because convolutional coding does not exhibit a high error correction capability for consecutive errors. Therefore, adjacent subcarriers are not allocated to a continuous signal, but separate subcarriers are allocated to a continuous signal.

On the other hand, in the case where the weight providing high received power and the weight providing low received power are allocated in units of subcarriers as in the foregoing embodiment, if the weight control unit 127 performs weight allocation without considering the use of an interleaver, it is possible to continuously allocate the weight causing low received power to the output of the encoding unit. This may cancel out the effect of the interleaver, thereby reducing the error correction capability.

If the entire width of several subcarriers, which are the unit of allocating the components of the continuously encoded signal, is made equal to the width of several subcarriers, which are the unit of changing the weight allocation manner, the high power component and the low power component of the signal acquired after encoding may appear alternately.

The above method will be explained in more detail by using an interleaver according to IEEE 802.11a as an example. In IEEE 802.11a, convolutional coding is adopted as a coding sideA method for preparing a medical liquid. The components of the signal obtained after encoding are permuted by an interleaver, then allocated to subcarriers, and modulated in units of subcarriers. As a result, the components of the encoded signal are allocated to every third subcarrier in accordance with the order change rule of the interleaver of IEEE 802.11 a. That is, the component is divided into subcarriers f₁，f₄，f₇，...。

As shown in fig. 10, when the above-described interleaver is used, the weight control unit 127 of this embodiment assigns weights providing high reception power to the subcarriers f output from the modulator 103 and assigned to the subcarriers₁，f₂And f₃And assigns a weight providing low received power to the subcarrier f output from the modulator 103 and assigned to the subcarrier f₄，f₅And f₆The modulated signal of (2). As a result, the modulated signal alternately exhibits high reception power and low reception power, which prevents a reduction in error correction performance. The same can be said for the modulated signal output from the modulator 104. Thus, the modulated signals output from the modulators 103 and 104 generally exhibit substantially the same received power. Further, these modulated signals alternately exhibit high reception power and low reception power, which prevents degradation of the error correction performance.

As described above, in the third embodiment, the load on the transmitting or receiving terminal is reduced by reducing the characteristic difference between the spatial multiplexing signals. Therefore, no precise device is required. Even standard devices can fully utilize the channel response by increasing the transmission rate of the spatially multiplexed signal as a whole, rather than increasing the transmission rate of a particular signal. Further, the required substrate area is reduced because no precision devices are required. Also, since the output of the encoder does not continuously exhibit low power but alternately exhibits high power and low power, excellent error correction performance can be achieved. Although in the third embodiment, the number of subcarriers is set to 12 as shown in fig. 10, it is not limited to 12.

(fourth embodiment)

The radio communication apparatus according to the fourth embodiment is similar in configuration to the radio communication apparatus of the first embodiment shown in fig. 1, and is similar to the first to third embodiments in that different beams corresponding to subcarriers are used to multiplex signals for transmission. The fourth embodiment is different from the first to third embodiments in that only in the case where the average value of the singular values of each channel matrix exceeds a preset threshold value, weights for providing high reception power are assigned to modulation signals output from different modulators and corresponding to subcarriers.

If the weight for providing high received power is assigned only to the modulated signals of all subcarriers output from a specific modulator, the received power of the modulated signal of the specific modulator becomes significant as described in the first embodiment. When the absolute value of the channel response is low, a multi-level modulation scheme of a high order cannot be employed even if power concentrates on the modulated signal output from a specific modulator. In this case, however, the above problem does not occur because the absolute value of the channel response is low. Therefore, even if the weight assignment control as described in the first to third embodiments is performed, no significant advantage can be obtained.

Therefore, in the fourth embodiment, only when the maximum singular value is not less than the preset threshold, the weight control unit 127 detects the maximum singular value of the channel matrix obtained by the weight matrix generation unit, and performs weight control using the scheme explained in the first, second, or third embodiment.

As described in the first embodiment, the singular values of the channel matrix are proportional to the corresponding received powers. In other words, each received power may be estimated from the corresponding singular value, and a modulation scheme suitable for the estimated received power may be selected. Thus, the modulation scheme may be determined by singular values. That is, when the singular value exceeds a certain threshold, it may be determined that it is necessary to use a multilevel modulation scheme of a high order that is difficult to implement. Thus, complicated weight assignment control is performed only when necessary, thereby omitting a process for meta.

As described above, in the fourth embodiment, only in the case where the reception power of the transmission signal is high and a modulation scheme of a high order is required, the characteristic difference between the spatial multiplexing signals is reduced, whereby the load on the transmission or reception terminal can be reduced. Therefore, no precise device is required. Even a standard device can sufficiently utilize the channel response by increasing the transmission rate of the spatial multiplexing signal as a whole, instead of increasing the transmission rate of a specific signal. Further, since an accurate device is not required, the required substrate area can be reduced. Also, when the reception power is low and it is not necessary to apply a modulation scheme of a high order, weight control is not performed to omit an unnecessary process and thereby reduce power consumption.

(fifth embodiment)

Fig. 11 shows a configuration example of a radio communication apparatus according to the fifth embodiment. The radio communication apparatus according to the fourth embodiment is similar to the configuration of the first embodiment shown in fig. 1, and is also similar to the first to fourth embodiments in that different beams corresponding to subcarriers are used to multiplex signals for transmission. The fifth embodiment is similar to the fourth embodiment in that weights for providing high received power are assigned to modulation signals output from different modulators and corresponding to subcarriers only in the case where the average value of singular values of each channel matrix exceeds a preset threshold. The fifth embodiment is different from the fourth embodiment in that the threshold value is changed according to the characteristic of each RF unit.

As shown in fig. 11, in the fifth embodiment, the RF unit performance observation unit 1101 observes the characteristics of the RF units 118 to 121, and changes the threshold value used when the weight control unit 127 assigns the weight that supplies high received power to the modulation signals output from the different modulators and corresponding to the subcarriers, according to the characteristics obtained by the observation. Control performed when the characteristics of the power amplifier included in each of the RF units 118 to 121 are changed will be described below.

Fig. 12 shows an example of power characteristics of a power amplifier. In fig. 12, the horizontal axis indicates input power, and the vertical axis indicates output power. In the power amplifier, as shown by a dotted line in fig. 12, it is desirable that the output power is proportional to the input power. However, as shown by a solid line in fig. 12, generally when the input power reaches a predetermined level, the output power is saturated, and an output power level above a certain level cannot be obtained. When the output power possesses such a non-linear characteristic, the communication quality is degraded. Generally, the greater the number of multilevel modulations of a signal, the greater the effect of nonlinear distortion on the signal and the more significant the degradation in signal quality.

To avoid such non-linear distortion, the average input power is typically set so as to operate the power amplifier in a region of high linearity characteristics so as to input a signal at a power level lower than the level causing distortion. The difference between the average input power and the power causing the distortion is called the back-off power. Generally, the larger the back-off power, the smaller the nonlinear distortion, and the larger the back-off power, the lower the power efficiency. Thus, it is undesirable to increase the back-off power beyond the required power.

Note that the above input/output characteristics will vary depending on the temperature of the device. Depending on the temperature, the input-output characteristics may be changed as shown by the dotted and dashed lines in fig. 12, whereby the output power may be increased. If this occurs, the actual transmission power may exceed the preset transmission power in the radio communication system. To avoid this, a correction process is generally performed in which the power output level from each RF unit 118 to 121 is measured, and the average input power is reduced if the output power is high, and the average input power is increased to increase the output power if the output power is low. If the output power is high as shown in fig. 12, the average input power is reduced.

As a result, the back-off power increases, and thus the range in which the power amplifier exhibits linear characteristics becomes large. In this case, even with the high-order multilevel modulation, the influence of the linear distortion on the power amplifier is reduced. Therefore, as in the first to third embodiments, it is not necessary to assign weights for providing high received power to the modulated signals output from the different modulators and corresponding to the subcarriers. That is, the threshold used in the fourth embodiment may be increased to expand the range in which the weight for providing high received power is assigned only to the modulation signal output from a specific modulator.

As described above, in the fifth embodiment, the threshold used in the fourth embodiment varies depending on the characteristics of each of the RF units 118 to 121. Specifically, the RF unit performance observation unit 1101 measures the power levels of the signals output from the RF units 118 to 121, and inputs a signal for controlling the average power of the power amplifiers to be input to the RF units 118 to 121 to the weight control unit 127. Further, the weight control unit 127 increases the threshold value used in the fourth embodiment if the average input power is low, and decreases the threshold value if the average input power is high.

As described above in detail, in the fifth embodiment, whether a modulation scheme of a high order is applicable is determined according to the characteristics of each RF unit, and the modulation scheme of the high order is applied only when the modulation scheme of the high order is applicable, thereby preventing degradation of communication quality, simplifying the process of the weight control unit, and reducing power consumption. In contrast, if a modulation scheme of a high order is not suitable for a transmission signal even if the reception power of the transmission signal is high, the difference in characteristics between the spatial multiplexing signals is reduced. Thus, the reduction of the communication rate is minimized by increasing the transmission rate of the spatial multiplexing signal as a whole, rather than increasing the transmission rate of only a specific signal.

(sixth embodiment)

The radio communication apparatus according to the sixth embodiment is similar to the configuration of the radio communication apparatus shown in fig. 1, and is also similar to the first to fifth embodiments in that the weight vector is determined by the channel response, and signals are multiplexed with different beams between subcarriers for transmission. The former case is also the same as the latter case in that singular vectors corresponding to higher and lower singular values are allocated to modulated signals of different subcarriers. The sixth embodiment is different from the first to fifth embodiments in that the number of signals to be multiplexed, i.e., the number of data streams for transmitting information streams (see fig. 2), is divided into three or more, which is different from the first to fifth embodiments.

The number of encoded signals in fig. 1 increases as the number of signals to be multiplexed increases. Although fig. 1 shows only two code signals 1 and 2, code signals corresponding to the number of spatial multiplexing signals are input. In this case, if the encoded signals are generated by a plurality of encoding units shown in fig. 2, the number of outputs of the signal distributor in fig. 2 increases according to the number of spatial multiplexing signals, and the number of encoding units connected to the distributor also increases. In contrast, in the case where a plurality of coded signals are generated by a single coding unit as shown in fig. 3, the number of outputs of the signal distributor shown in fig. 3 increases according to the number of spatial multiplexing signals.

Further, in fig. 1, the number of serial-to-parallel converters for receiving the encoded signals also increases according to the increase in the number of spatial multiplexing signals, and the number of modulators connected to the respective serial-to-parallel converters increases accordingly. In the weight matrix multiplier 105, the modulated signals corresponding to the subcarriers are each multiplied by the same number of weights as the inverse fourier converters 106 to 109, and all the spatial multiplex signals are accumulated (multiplexed) and output. The number of cells connected after the weight matrix multiplier 105 is unchanged.

In this case, it is necessary for the radio communication apparatus and the receiving terminal to incorporate RF units larger in number than the spatial multiplexing signals. Assuming that the number of RF units included in the radio communication apparatus is N, the number of RF units included in the receiving terminal is M, and the number of spatially multiplexed signals is L, a channel response matrix h (k) of the k-th subcarrier is given by:

$H^{\left(k\right)}=U^{\left(k\right)}{D}^{\left(k\right)}{V}^{{\left(k\right)}^H}$

<math> <mrow> <mo>=</mo> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msup> <msub> <mi>u</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>,</mo> </mtd> <mtd> <msup> <msub> <mi>u</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>,</mo> </mtd> <mtd> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>,</mo> </mtd> <mtd> <msup> <msub> <mi>u</mi> <mi>R</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> </mtd> </mtr> </mtable> </mfenced> <mi>diag</mi> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msub> <mi>&lambda;</mi> <mn>1</mn> </msub> <mo>,</mo> </mtd> <mtd> <msub> <mi>&lambda;</mi> <mn>2</mn> </msub> <mo>,</mo> </mtd> <mtd> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>,</mo> </mtd> <mtd> <msub> <mi>&lambda;</mi> <mi>R</mi> </msub> </mtd> </mtr> </mtable> </mfenced> <msup> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msup> <msub> <mi>v</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>,</mo> </mtd> <mtd> <msup> <msub> <mi>v</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>,</mo> </mtd> <mtd> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>,</mo> </mtd> <mtd> <msup> <msub> <mi>v</mi> <mi>R</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> </mtd> </mtr> </mtable> </mfenced> <mi>H</mi> </msup> </mrow> </math>

<math> <mrow> <mo>=</mo> <msub> <mi>&lambda;</mi> <mn>1</mn> </msub> <msup> <msub> <mi>u</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <msup> <msub> <mi>v</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> <mo>+</mo> <msub> <mi>&lambda;</mi> <mn>2</mn> </msub> <msup> <msub> <mi>u</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <msup> <msub> <mi>v</mi> <mn>2</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> <mo>+</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <msub> <mi>&lambda;</mi> <mi>R</mi> </msub> <msup> <msub> <mi>u</mi> <mi>R</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <msup> <msub> <mi>v</mi> <mi>R</mi> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </msup> </msup> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>11</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein,

R＝min(M，N) …(12-1)

L≤R …(12-2)

if the number of spatial multiplexing signals is less than R, L singular vectors corresponding to the L highest singular values are used as weight vectors.

Further, when the number of spatial multiplexing signals is 3 or more, as in the first and second embodiments, singular vectors corresponding to higher and lower singular values are assigned to modulation signals as weight vectors.

Referring to fig. 13, the allocation of singular vectors when the number of spatial multiplexing signals is 3 is explained. In the example in fig. 13, the number of subcarriers is 8. Further, considering a modulated signal obtained by modulation by the modulator 103, a singular vector corresponding to the highest singular value is allocated to the subcarrier f₁，f₂And f₃The singular vector corresponding to the second highest singular value is allocated to the subcarrier f₄，f₅And f₆And the singular vector corresponding to the lowest singular value is allocated to the subcarrier f₇And f₈. Likewise, considering the modulated signals obtained by the modulation of the modulators 2 and 3, weight vectors are assigned as shown in fig. 13.

Thus, also when the number of spatially multiplexed signals is 3, as in the first embodiment, the difference in characteristics between the signals can be reduced. Further, the same advantages as the second embodiment can be obtained by assigning the weight vectors as shown in fig. 14.

Although the above relates to the case where the number of spatial multiplexing signals is 3, the case where the number of spatial multiplexing signals is 4 can be said to be the same. Further, although the number of subcarriers is set to 8 in the fifth embodiment, it is not limited to 8 similarly to the first to fifth embodiments.

As described above, even when the number of spatially multiplexed signals is 3 or more, the characteristic difference between the signals can be reduced, thereby reducing the load of the RF unit. At this time, if the signal bandwidth is divided into groups corresponding to the number of spatially multiplexed signals and control is performed in units of groups, the correlation of channel responses between adjacent subcarriers increases, which makes it possible for the receiving terminal to perform an averaging process with respect to frequency when estimating the channel responses. As a result, the estimation accuracy with respect to the channel matrix is improved. Further, if weights for providing high reception power are allocated to modulation signals output from different modulators in units of several subcarriers, the modulation signals are made more uniform in reception characteristics. Further, if the entire width of several subcarriers, which are a unit for switching the weight from one to another, is made equal to the entire width of several subcarriers, which are a unit for allocating the encoded signal components by the interleaver, the encoded signal may alternately exhibit high and low received power levels. That is, the encoded signal is prevented from continuously exhibiting low reception power, and as a result, degradation in decoding performance can be avoided. If the weight assignment control is performed only when the singular value of each channel matrix exceeds the preset threshold, unnecessary control can be avoided, which reduces power consumption. In addition, if the threshold value varies according to the performance of each RF unit, control suitable for each RF unit can be achieved.

(seventh embodiment)

The radio communication apparatus according to the seventh embodiment is similar in configuration to the sixth embodiment, and also similar to the sixth embodiment, the weight vector is determined by the channel response, and three or more signals are multiplexed with different beams between subcarriers for transmission. The seventh embodiment is different from the sixth embodiment in the way of weight vector assignment.

Referring to fig. 15, the weight vector allocation method used in the seventh embodiment will be described using a case where the number of spatial multiplexing signals is 3.

In the example of fig. 15, it is assumed that the singular value λ of the channel response corresponding to the k-th subcarrier of the 3 spatially multiplexed signals₁ ^(k)、λ₂ ^(k)And λ₃ ^(k)The following relationship is satisfied:

λ₁ ^(k)≥λ₃ ^(k)≥λ₂ ^(k) …(13)

as shown in fig. 15, when the singular value λ_i ^(k)(i-1, 2, 3) satisfies the relationship given by expression (13), corresponds to the maximum singular value λ₁ ^(k)And the singular vector of (a) and the singular value of λ corresponding to the minimum value₂ ^(k)Are assigned to different subcarriers of each signal modulated by modulators 1 and 3. It is desirable that this allocation enables the signal modulated by modulator 2 to have substantially the same power as the signal modulated by modulator 1 or 3, with the singular vectors corresponding to the second highest singular values being allocated to all the subcarriers of modulator 2.

Therefore, signals modulated by different modulators can be controlled to have substantially the same received power only by uniformly allocating singular vectors corresponding to specific singular values to signals modulated by some of the modulators, rather than uniformly allocating singular vectors corresponding to all singular values to all signals modulated by all modulators.

Further, as shown in fig. 16, the same advantage obtained by the second embodiment can be obtained by assigning weights to the modulators such that the singular vectors corresponding to the largest singular values are assigned to every other subcarrier.

Further, in the case of fig. 15 and 16, the second highest singular value λ is corresponded to₃ ^(k)Is assigned to all subcarriers of the signal modulated by modulator 2, while the assignment of the weights is switched between the signals modulated by modulators 1 and 3. However, the same advantages can be obtained even from the case shown in fig. 17 or 18, where the maximum and minimum singular values λ are corresponded to₁ ^(k)And λ₂ ^(k)Are assigned to the subcarriers of each signal modulated by modulators 1 and 2.

Further, the seventh embodiment can provide the same advantages as the third embodiment if the entire width of several subcarriers, which are a unit for switching the weight corresponding to the maximum singular value from one to another, is made the same as the width of several subcarriers, which are a unit for allocating the components of the signal output from each coding unit.

In addition, when the singular vectors corresponding to the maximum singular values are allocated to the modulation signals output from the different modulators in units of subcarriers only in the case where the corresponding singular values exceed the preset threshold, the operation of controlling the weights may be stopped when the weight allocation is not necessary. As a result, power consumption can be reduced as in the fourth embodiment. Also, if the threshold value varies according to the state of each RF unit, control may be performed according to the state of each RF unit, thereby providing the same advantages as the fifth embodiment.

As described above, in the seventh embodiment, the difference in the reception characteristics between the spatially multiplexed signals can be minimized, thereby reducing the load on the RF unit. In addition, since the difference in the reception characteristics between the modulation signals of all the modulators can be reduced without performing weight distribution on all the modulation signals output from all the modulators, the control can be simplified. At this time, if the signal bandwidth is divided into groups corresponding to the number of spatially multiplexed signals and control is performed in units of groups, the correlation of channel responses between adjacent subcarriers increases, which enables the receiving terminal to perform an averaging process with respect to frequency when estimating the channel responses. As a result, the estimation accuracy with respect to the channel matrix is improved. Further, if weights for providing high reception power are assigned to modulation signals output from different modulators in units of several subcarriers, the modulation signals have more uniform reception characteristics. Further, if the entire width of several subcarriers, which are a unit for switching the weight from one to another, is made equal to the entire width of several subcarriers, which are a unit for allocating the components of the encoded signal by the interleaver, the encoded signal components may alternately exhibit high and low received power levels. That is, the encoded signal is prevented from continuously exhibiting low reception power, and therefore, degradation of decoding performance can be avoided. If the weight assignment control is performed only when the average value of the singular values of each channel matrix exceeds a preset threshold, unnecessary control can be avoided, which reduces power consumption. In addition, if the threshold value varies according to the performance of each RF unit, control suitable for each RF unit can be achieved.

(eighth embodiment)

The radio communication apparatus according to the eighth embodiment is similar in configuration to the seventh embodiment, and also similar to the seventh embodiment, the weight vector is determined according to the channel response, and three or more signals are multiplexed with different beams between subcarriers for transmission. The eighth embodiment is also similar to the seventh embodiment in that complex weight assignment is performed only for a part of the spatially multiplexed signal. The eighth embodiment is different from the seventh embodiment in that weight vectors are assigned not to make all spatial multiplexing signals uniform in channel response but to reduce differences in characteristics between only a few signals in the spatial multiplexing signals.

Fig. 19 shows an example of allocation of weight vectors in the eighth embodiment, using a case where the number of spatial multiplexing signals is 3 as an example.

In the sixth embodiment, the assignment of weight vectors to subcarriers is controlled so that singular vectors corresponding to the largest singular values are assigned to signals modulated by all modulators. In the seventh embodiment, singular vectors corresponding to the highest and lowest (third highest) singular values are allocated to different subcarriers in a single modulator, thereby enabling the received powers of all spatial multiplexing signals to be uniform.

However, when the correlation of the channel response between the antennas is high, the difference between the highest and lowest singular values is large. Therefore, if singular vectors corresponding to the highest and lowest singular values are allocated to different subcarrier numbers of a signal modulated by a single modulator as in the sixth or seventh embodiment, the difference in received power between subcarriers is not small. This results in a degradation of performance when a common modulation scheme must be allocated to all subcarriers. In particular, if the coding rate is high, the degradation becomes significant.

According to the above, when the singular value λ of the channel response corresponding to the k-th subcarrier of the three spatial multiplexing signals₁ ^(k)，λ₂ ^(k)And λ₃ ^(k)The weight assignment as shown in fig. 19 is performed when the following relationship is satisfied:

λ₁ ^(k)≥λ₂ ^(k)≥λ₃ ^(k) …(14)

as a result, the signals modulated by the modulators 1 and 2 have substantially the same reception characteristics as in the first embodiment. Further, since in the eighth embodiment, only singular vectors corresponding to the highest and second highest singular values are allocated to the signals modulated by the modulators 1 and 2, the power difference between subcarriers of the signals modulated by the modulators 1 and 2 is small, which is different from the sixth and seventh embodiments. Further, since only the singular vectors corresponding to the third highest (i.e., lowest) singular values are allocated to all subcarriers of the signal modulated by the modulator 3, the power difference between subcarriers is similar to that in the conventional scheme, i.e., no degradation occurs as compared with the conventional scheme.

As described above, in the eighth embodiment, the difference in characteristics between the spatially multiplexed signals can be reduced, thereby reducing the load in the RF unit. Also, when the channel of the antenna has high correlation or the coding rate is high, the power difference between subcarriers of the signal is reduced, and thus degradation of characteristics can be avoided.

Further, as shown in fig. 20, if two weights are alternately assigned to adjacent subcarriers of each signal modulated by the modulators 1 and 2, the same advantages as those obtained by the second embodiment can also be obtained.

Further, the seventh embodiment can provide the same advantages as the third embodiment if the entire width of several subcarriers, which are the unit of switching the weight assigned to the maximum singular value from one to another, is made equal to the width of several subcarriers, which are the unit of assigning the signal component output from each coding unit.

In addition, when the singular vectors corresponding to the maximum singular values are allocated to the modulation signals output from the different modulators in units of subcarriers only in the case where the corresponding singular values exceed the preset threshold, the operation of controlling the weights may be stopped when the weight allocation is not necessary. As a result, power consumption can be reduced as in the fourth embodiment. Also, if the threshold value varies according to the state of each RF unit, control may be performed according to the state of each RF unit, thereby providing the same advantages as the fifth embodiment.

(ninth embodiment)

The radio communication apparatus according to the ninth embodiment is similar in configuration to the radio communication apparatuses of the sixth to eighth embodiments, and also similar to the radio communication apparatuses of the sixth to eighth embodiments, in that weight vectors are determined according to channel responses, and three or more signals are multiplexed with different beams between subcarriers for transmission. The ninth embodiment differs from the seventh embodiment in that it is selected whether weight assignment should be performed so that all the spatially multiplexed signals have substantially the same characteristics or whether weight assignment should be performed so as to reduce the difference in characteristics between only some of the spatially multiplexed signals, in accordance with the singular value of each channel response.

As explained in the eighth embodiment, when the difference between the highest singular value and the third highest singular value is large, the decoding performance may be degraded. However, if the channel matrix is substantially an orthogonal matrix, the difference between the highest singular value and the third highest singular value is not large, and the problem does not occur. In this case, the weight assignment employed in the sixth or seventh embodiment provides a more superior characteristic than that obtained in the eighth embodiment, because in the former, power is less likely to be concentrated on a specific signal.

Therefore, in the ninth embodiment, the ratio of the third highest singular value to the highest singular value is calculated. Further, if the calculated ratio is not less than the preset threshold, the weights corresponding to the highest singular value and the third highest singular value are prevented from being assigned to the modulation signal output from the specific modulator, similarly to the eighth embodiment. In contrast, if the calculated ratio is smaller than the preset threshold, weights corresponding to the highest singular value and the third highest singular value are assigned to the modulated signal, similarly to the sixth or seventh embodiment.

In the above control processing, when the difference between the highest singular value and the third highest singular value is large, the weight corresponding to the second highest singular value higher than the third highest singular value is assigned to the modulation signals output from the modulators 1 and 2. Therefore, the difference in received power between subcarriers of the modulated signal output from the modulator 1 or 2 is smaller than that in the sixth or seventh embodiment, thereby preventing degradation in decoding performance. In contrast, when the difference between the highest singular value and the third highest singular value is small, weights corresponding to the highest singular value and the third highest singular value are assigned to the modulation signals output from the modulators 1 and 2. As a result, the received power difference between the modulated signals output from the modulators is smaller than in the eighth embodiment.

As described above, in the ninth embodiment, the difference in characteristics between the spatially multiplexed signals can be reduced, thereby reducing the load on each RF unit. Further, since the manner of controlling the weights is changed according to the difference between the highest singular value and the third highest singular value, the power difference between subcarriers can be reduced, thereby preventing degradation of decoding performance.

As shown in fig. 20, if two weights are alternately assigned to subcarriers corresponding to the modulated signals output from each modulator, the same advantage as the second embodiment can be obtained.

In addition, if the entire width of several subcarriers, which are units for switching the weight from one to another, is made equal to the entire width of several subcarriers, which are units for allocating components of the encoded signal by the interleaver, the same advantage as the third embodiment can be obtained.

Further, if singular vectors corresponding to the highest singular values are allocated to modulation signals output from different modulators only in the case where the average value of the singular values of each channel matrix exceeds a preset threshold, unnecessary weight allocation control can be avoided, which reduces power consumption as in the fourth embodiment. In addition, as in the fifth embodiment, if the threshold value varies depending on the state of each RF unit, control suitable for each RF unit can be realized.

(tenth embodiment)

The tenth embodiment is similar in the configuration of the apparatus to the first to fifth embodiments, and is similar in that singular vectors corresponding to higher singular values are allocated to modulated signals output from different modulators in units of several subcarriers so that the spatial-multiplexed signals have substantially the same characteristics. The tenth embodiment is different from the first to ninth embodiments in that transmission signals are transmitted at different transmission power levels.

As shown in expression (10), even if transmission signals are transmitted at the same transmission power, the reception power levels of the signals at the receiving terminals are different. It is known that a higher channel capacity can be obtained in the case where a larger transmission power is given to a signal having a higher channel response than in the case where equal power is given to (imaginary) all signals. When the total transmission power is constant, the optimum transmission power level assigned to each transmission signal is theoretically detected by the formula given below:

<math> <mrow> <msub> <mi>&gamma;</mi> <mi>i</mi> </msub> <mo>=</mo> <mi>&mu;</mi> <mo>-</mo> <mfrac> <msub> <mi>N</mi> <mn>0</mn> </msub> <mrow> <msub> <mi>E</mi> <mi>s</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>&lambda;</mi> <mi>i</mi> </msub> </mrow> </mfrac> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>15</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein gamma is_iIs assigned to be assigned to correspond to the ith high singular value λ_iWeight of the singular vector of (a) and the transmission power of the transmitted signal, N₀Is the noise/power density of the receiving terminal, E_sIs the average power of the modulated signal. Further, μ is a constant, which is set to make the total transmission power constant. From equation (15), it can be understood that the higher the singular value, the higher the transmission power.

Referring to fig. 21, a case where different transmission power levels are allocated to transmission signals will be explained. As shown in fig. 21, in the tenth embodiment, singular vectors corresponding to different singular values are allocated to signals of different subcarriers as in the first to ninth embodiments. In the related art, the difference in characteristics between the spatial multiplexing signals is increased by transmission power control, whereas in the sixth embodiment, the channel capacity is increased by transmission power control, and the difference in characteristics between the spatial multiplexing signals can be reduced. Even though the example of fig. 21 only relates to the way of weight vector allocation shown in fig. 13, similar transmission signal power control can be applied to the cases of fig. 7 to 10 and fig. 13 to 20.

As described above, in the tenth embodiment, transmission power control is performed so as to maximize the channel capacity, and thus the difference in characteristics between the spatial multiplexing signals can be minimized without reducing the channel capacity.

(eleventh embodiment)

A radio communication apparatus according to a seventh embodiment is similar in configuration to the first embodiment shown in fig. 1, and is also similar to the first to tenth embodiments in that signals are multiplexed for transmission using different beams corresponding to subcarriers. The eleventh embodiment is different from the first to tenth embodiments in the way of determining the weight vector from the channel response.

In the first to tenth embodiments, singular value decomposition is performed on the channel response, and singular vectors or scalar products of singular vectors (tenth embodiment) are used as weight vectors. However, the weight vector used in the embodiment of the present invention is not limited thereto. For example, the channel matrix H^(k)The transposed complex conjugate vector of the row vector of (a) may be used as the weight vector.

It is assumed here that the channel matrix is given by:

$H^{\left(k\right)}=\left[\begin{array}{cccc}{h_{11}}^{\left(k\right)}& {h_{12}}^{\left(k\right)}& {h_{13}}^{\left(k\right)}& {h_{14}}^{\left(k\right)}\\ {h_{21}}^{\left(k\right)}& {h_{22}}^{\left(k\right)}& {h_{23}}^{\left(k\right)}& {h_{24}}^{\left(k\right)}\end{array}\right]$

<math> <mrow> <mo>=</mo> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>T</mi> </msup> </msup> </mtd> </mtr> <mtr> <mtd> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>T</mi> </msup> </msup> </mtd> </mtr> </mtable> </mfenced> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>16</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein h is₁ ^(k)And h₂ ^(k)The following relationship is satisfied:

h₁ ^(k)＝[h₁₁ ^(k) h₁₂ ^(k) h₁₃ ^(k) h₁₄ ^(k)]^T …(17-1)

h₂ ^(k)＝[h₂₁ ^(k) h₂₂ ^(k) h₂₃ ^(k) h₂₄ ^(k)]^T …(17-2)

in the above equation, the number of RF units incorporated in the radio communication apparatus is set to 4, and the number of RF units incorporated in the receiving terminal is set to 2. However, in the embodiment, the numbers are not limited to them, and may be set to an arbitrary value.

In this case, a weight vector given by:

<math> <mrow> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> </msup> <mo>/</mo> <mo>|</mo> <mo>|</mo> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>|</mo> <mo>|</mo> <mi>and</mi> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> </msup> <mo>/</mo> <mo>|</mo> <mo>|</mo> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>|</mo> <mo>|</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>18</mn> <mo>)</mo> </mrow> </mrow> </math>

if these weight vectors are used, the in-phase synchronized signal can be transmitted to the receiving terminal. The received power obtained by the receiving terminal when using the weight vector may be estimated from the vector norm.

If the following equation (19) is satisfied, higher reception power can be obtained by the reception terminal in the case of the following equation (20) than in the case of the following equation (21):

‖h₁ ^(k)‖＞‖h₂ ^(k)‖ …(19)

<math> <mrow> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> </msup> <mo>/</mo> <mo>|</mo> <mo>|</mo> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>|</mo> <mo>|</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>20</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> </msup> <mo>/</mo> <mo>|</mo> <mo>|</mo> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>|</mo> <mo>|</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>21</mn> <mo>)</mo> </mrow> </mrow> </math>

therefore, when the weight vector is allocated to the kth subcarrier so that the signal s is modulated₁ ^(k)Can be received with high reception power, the following equations (22-1) and (22-2) are satisfied:

<math> <mrow> <msup> <msub> <mi>w</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>=</mo> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> </msup> <mo>/</mo> <mo>|</mo> <mo>|</mo> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>|</mo> <mo>|</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>22</mn> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msup> <msub> <mi>w</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>=</mo> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> </msup> <mo>/</mo> <mo>|</mo> <mo>|</mo> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>|</mo> <mo>|</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>22</mn> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

on the other hand, the current rightThe weight vector is allocated to the k subcarrier to modulate the signal s₂ ^(k)The following equations (23-1) and (23-2) are satisfied when it can be received with high reception power:

<math> <mrow> <msup> <msub> <mi>w</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>=</mo> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> </msup> <mo>/</mo> <mo>|</mo> <mo>|</mo> <msup> <msub> <mi>h</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>|</mo> <mo>|</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>23</mn> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msup> <msub> <mi>w</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>=</mo> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> </msup> <mo>/</mo> <mo>|</mo> <mo>|</mo> <msup> <msub> <mi>h</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>|</mo> <mo>|</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mn>23</mn> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

although the signals corresponding to the weight vectors have the same transmission power level in equations (22-1), (22-2), (23-1) and (23-2), they may have different transmission power levels as in the tenth embodiment.

As described above, the eleventh embodiment can provide the same advantages as the first to tenth embodiments even if SVD is not performed.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims (20)

1. A radio communications apparatus for transmitting data to a receiving apparatus, comprising:

a dividing unit configured to divide transmission data into a first stream and a second stream;

a serial-to-parallel conversion unit configured to subject the first stream and the second stream to serial-to-parallel conversion to obtain a plurality of data signals;

a modulation unit configured to modulate the data signal into a plurality of OFDM modulated signals corresponding to the first stream and the second stream using a plurality of subcarriers;

an acquisition unit configured to acquire a plurality of channel responses between the radio communication apparatus and the reception apparatus;

a calculation unit configured to calculate a singular value λ of a channel matrix corresponding to a kth (k is a natural number) subcarrier included in the subcarriers, based on the acquired channel response₁ ^(k)And λ₂ ^(k)；

A weight assignment unit configured to assign a weight corresponding to the singular value λ₁ ^(k)And λ₂ ^(k)A plurality of weights are assigned to the first stream and the second stream, wherein the correspondence of each weight to each stream differs according to subcarriers;

a multiplication unit configured to multiply each assigned weight by an OFDM modulated signal corresponding to each of the first and second streams and obtain first and second signals corresponding to the first and second streams;

an adding unit configured to add the first signal and the second signal and obtain an added signal;

an inverse fourier transform unit configured to subject the added signals to inverse fourier transform; and

a transmission unit configured to transmit the signal output from the inverse fourier transform unit to a receiving apparatus.

2. The apparatus of claim 1, wherein the transmit data is divided into a first stream and a second stream before being encoded by one of reed-solomon encoding, convolutional encoding, and Low Density Parity Check (LDPC) encoding.

3. The apparatus of claim 1, wherein the weight assigning unit alternately assigns the corresponding singular values λ₁ ^(k)And λ₂ ^(k)Is assigned to the subcarriers.

4. The apparatus of claim 1, wherein the weight assigning unit alternately assigns the corresponding singular values λ₁ ^(k)And λ₂ ^(k)The weights of (a) are assigned to subcarrier groups, each of the groups including two or more subcarriers.

5. The apparatus as claimed in claim 1, wherein if the radio communication apparatus gives different levels of transmission power to the subcarriers, the weight assignment unit is to correspond to the singular value λ according to the different levels of transmission power₁ ^(k)And λ₂ ^(k)Is assigned to the stream.

6. The apparatus of claim 1, wherein the weight assigning unit successively assigns a plurality of the corresponding singular values λ to some of the subcarriers₁ ^(k)Is assigned to the spatial multiplexing signal and the number of the subcarriers is equal to the width of the close signal assigned before it is permuted by the interleaver.

7. The apparatus of claim 1, wherein λ is a singular value if₁ ^(k)Is greater than the threshold value, the weight assignment unit will correspond to the singular value λ₁ ^(k)And λ₂ ^(k)Is assigned to the first stream and the second stream, wherein the correspondence of each weight to each stream differs according to subcarriers.

8. The apparatus of claim 7, wherein the transmission unit comprises:

a plurality of RF units including respective power amplifiers;

a measurement unit configured to measure power of a plurality of signals output from the RF unit; and

a controller unit configured to determine a first average power of a signal input to each power amplifier based on the measured power,

wherein each of the RF units sets the second average power of the signal input to each of the power amplifiers to the decided first average power,

the weight assignment unit changes the threshold value according to the set average power.

9. A radio communications apparatus for transmitting data to a receiving apparatus, comprising:

a dividing unit configured to divide transmission data into at least three streams;

a serial-to-parallel conversion unit configured to subject the stream to serial-to-parallel conversion to obtain a plurality of data signals;

a modulation unit configured to modulate the data signal into a plurality of OFDM modulated signals corresponding to the at least three streams using a plurality of subcarriers;

an acquisition unit configured to acquire a plurality of channel responses between the radio communication apparatus and the reception apparatus;

a calculation unit configured to calculate a singular value λ of a channel matrix corresponding to a kth (k is a natural number) subcarrier included in the subcarriers, based on the acquired channel response₁ ^(k)，λ₂ ^(k)，...，λ_m ^(k)(m is a natural number of not less than 3);

a weight assignment unit configured to assign a weight corresponding to the singular value λ₁ ^(k)，λ₂ ^(k)，...，λ_m ^(k)Is assigned to the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)≥...≥λ_m ^(k)；

A multiplication unit configured to multiply each assigned weight by an OFDM modulated signal corresponding to each stream and obtain m signals;

an adding unit configured to add the m signals and obtain an added signal;

an inverse fourier transform unit configured to subject the added signals to inverse fourier transform; and

a transmission unit configured to transmit the signal output from the inverse fourier transform unit to a receiving apparatus.

10. The apparatus of claim 9, wherein:

a calculation unit calculates a singular value lambda of a channel matrix corresponding to the k-th subcarrier from the acquired channel response₁ ^(k)，λ₂ ^(k)And λ₃ ^(k)(ii) a And

the weight distribution unit will correspond to the singular value lambda₁ ^(k)And λ₂ ^(k)Is assigned to the subcarriers of the OFDM modulated signal corresponding to the signals of two of said streams, assuming λ₁ ^(k)≥λ₃ ^(k)≥λ₂ ^(k)。

11. The apparatus of claim 9, wherein the calculation unit calculates a singular value λ of a channel matrix corresponding to a k-th subcarrier from the acquired channel response₁ ^(k)，λ₂ ^(k)And λ₃ ^(k)(ii) a And

the weight distribution unit will correspond to the singular value lambda₁ ^(k)And λ₂ ^(k)To the OFDM modulated signals corresponding to two of the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)≥λ₃ ^(k)And λ₁ ^(k)Average value of (A) and λ₃ ^(k)Is not less than a preset threshold,

the weight distribution unit will correspond to the singular value lambda₁ ^(k)、λ₂ ^(k)And λ₃ ^(k)Is assigned to the OFDM modulated signal corresponding to the stream, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)≥λ₃ ^(k)And λ₁ ^(k)Average value of (A) and λ₃ ^(k)Is less than a preset threshold.

12. The apparatus of claim 9, wherein the calculation unit calculates a singular value λ of a channel matrix corresponding to a k-th subcarrier from the obtained channel response₁ ^(k)，λ₂ ^(k)And λ₃ ^(k)(ii) a And

the weight distribution unit will correspond to the singular value lambda₁ ^(k)And λ₂ ^(k)To the OFDM modulated signals corresponding to two of the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)≥λ₃ ^(k)And λ₁ ^(k)Average value of (A) and λ₃ ^(k)Is not less than a preset threshold,

the weight distribution unit will correspond to the singular value lambda₁ ^(k)And λ₃ ^(k)To the OFDM modulated signals corresponding to two of the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)≥λ₃ ^(k)And λ₁ ^(k)Average value of (A) and λ₃ ^(k)Is less than a preset threshold.

13. The apparatus as claimed in claim 9, wherein the weight assigning unit alternately assigns the weight corresponding to the singular value λ₁ ^(k)，λ₂ ^(k)，...，λ_m ^(k)The weight of (c).

14. The apparatus of claim 9, wherein the weight assigning unit alternately assigns the corresponding singular values λ₁ ^(k)，λ₂ ^(k)，...，λ_m ^(k)The weights of (a) are assigned to subcarrier groups, each of the groups including two or more subcarriers.

15. A radio communications apparatus for transmitting data to a receiving apparatus, comprising:

a dividing unit configured to divide transmission data into at least three streams;

a serial-to-parallel conversion unit configured to subject the stream to serial-to-parallel conversion to obtain a plurality of data signals;

a modulation unit configured to modulate a data signal into a plurality of OFDM modulated signals corresponding to the at least three streams using a plurality of subcarriers;

an acquisition unit configured to acquire a plurality of channel responses between the radio communication apparatus and the reception apparatus;

a calculation unit configured to calculate a singular value λ of a channel matrix corresponding to a k-th (k is a natural number) subcarrier included in the subcarriers, from the acquired channel response₁ ^(k)And λ₂ ^(k)；

A weight assignment unit configured to assign a weight corresponding to the singular value λ₁ ^(k)And λ₂ ^(k)To the OFDM modulated signals corresponding to two of the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)；

A multiplication unit configured to multiply each assigned weight by an OFDM modulated signal corresponding to each stream and obtain a first signal and a second signal;

an adding unit configured to add the first signal and the second signal and obtain an added signal;

an inverse fourier transform unit configured to subject the added signals to inverse fourier transform; and

a transmission unit configured to transmit the signal output from the inverse fourier transform unit to a receiving apparatus.

16. The apparatus of claim 15, wherein the weight assigning unit alternately assigns the weights corresponding to the singular values λ₁ ^(k)And λ₂ ^(k)The weight of (c).

17. The apparatus of claim 15, wherein the weight assigning unit alternately assigns the corresponding singular values λ₁ ^(k)And λ₂ ^(k)The weights of (a) are assigned to subcarrier groups, each of the groups including two or more subcarriers.

18. A radio communication method used in a radio communication apparatus for transmitting data to a receiving apparatus, comprising:

dividing transmission data into a first stream and a second stream;

subjecting the first stream and the second stream to serial-to-parallel conversion to obtain a plurality of data signals;

modulating a data signal into a plurality of OFDM modulated signals corresponding to the first and second streams using a plurality of subcarriers;

acquiring a plurality of channel responses between a radio communication apparatus and a receiving apparatus;

calculating a singular value λ of a channel matrix corresponding to a kth (k is a natural number) subcarrier included in the subcarriers, based on the obtained channel response₁ ^(k)And λ₂ ^(k)；

Will correspond to the singular value λ₁ ^(k)And λ₂ ^(k)A plurality of weights are assigned to the first stream and the second stream, wherein the correspondence of each weight to each stream differs according to subcarriers;

multiplying each assigned weight by an OFDM modulated signal corresponding to each of the first and second streams and obtaining a first signal and a second signal;

adding the first signal and the second signal and obtaining an added signal;

subjecting the added signals to an inverse fourier transform; and

the signal output from the inverse fourier transform unit is transmitted to a receiving apparatus.

19. A radio communication method for use in a radio communication apparatus for transmitting data information to a receiving apparatus, comprising:

dividing transmission data into at least three streams;

subjecting the stream to serial-to-parallel conversion to obtain a plurality of data signals;

modulating a data signal into a plurality of OFDM modulated signals corresponding to the at least three streams using a plurality of subcarriers;

acquiring a plurality of channel responses between a radio communication apparatus and a receiving apparatus;

calculating a singular value λ of a channel matrix corresponding to a kth (k is a natural number) subcarrier included in the subcarriers, based on the acquired channel response₁ ^(k)，λ₂ ^(k)，...，λ_m ^(k)(m is a natural number of not less than 3);

will correspond to the singular value λ₁ ^(k)，λ₂ ^(k)，...，λ_m ^(k)Is assigned to the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)≥...λ_m ^(k)；

Multiplying each assigned weight by the OFDM modulated signal corresponding to each stream, and obtaining m signals;

adding the m signals to obtain an added signal;

subjecting the added signals to an inverse fourier transform; and

the signal obtained by the inverse fourier transform is transmitted to the receiving apparatus.

20. A radio communication method used in a radio communication apparatus for transmitting data to a receiving apparatus, comprising:

dividing transmission data into at least three streams;

subjecting the stream to serial-to-parallel conversion to obtain a plurality of data signals;

modulating a data signal into a plurality of OFDM modulated signals corresponding to the at least three streams using a plurality of subcarriers;

acquiring a plurality of channel responses between a radio communication apparatus and a receiving apparatus;

calculating a singular value λ of a channel matrix corresponding to a kth (k is a natural number) subcarrier included in the subcarriers, based on the acquired channel response₁ ^(k)And λ₂ ^(k)；

Will correspond to the singular value λ₁ ^(k)And λ₂ ^(k)To the OFDM modulated signals corresponding to two of the streams, wherein the correspondence of each weight to each stream differs according to subcarriers, assuming λ₁ ^(k)≥λ₂ ^(k)；

Multiplying each assigned weight by an OFDM modulated signal corresponding to each stream, and obtaining a first signal and a second signal;

adding the first signal and the second signal to obtain an added signal;

subjecting the added signals to an inverse fourier transform; and

the signal obtained by the inverse fourier transform is transmitted to the receiving apparatus.

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