WO2010038474A1

WO2010038474A1 - Wireless transmission device, mobile station device, and pre-coding method

Info

Publication number: WO2010038474A1
Application number: PCT/JP2009/005092
Authority: WO
Inventors: 貞樹二木; 正悟中尾; 大地今村; 敬岩井
Original assignee: パナソニック株式会社
Priority date: 2008-10-03
Filing date: 2009-10-02
Publication date: 2010-04-08

Abstract

Disclosed is a wireless transmission device that improves the drastic degradation of data throughput in a single carrier frequency division multiple access (SC-FDMA) transmission. A multiplexer (132) multiplies a stream (S₁) and another stream (S₂) by a pre-coding matrix, thereby multiplexing by differentiating an inter-stream power ratio. A code book (131) has candidates for a plurality of pre-coding matrices corresponding to a plurality of power ratios differentiating the inter-stream power ratio and sets the pre-coding matrix from among the candidate matrices. This makes it possible to suppress the degradation of cubic metric (CM) after application of pre-coding, so that it is possible to improve the drastic degradation of data throughput when the pre-coding is applied.

Description

Radio transmission apparatus, mobile station apparatus, and precoding method

The present invention is applied to, for example, a radio transmission apparatus, a mobile station apparatus, and these apparatuses that transmit SC-FDMA (Single-Carrier-Frequency-Division-Multiple-Access) in a radio communication system using MIMO (Multiple-Input-Multiple-Output) communication technology. The present invention relates to a precoding method.

In recent years, MIMO communication technology using array antennas for both transmission and reception has attracted attention as a technology for realizing high-speed transmission by effectively using a limited frequency band. In the MIMO communication technology, in particular, precoding can form directivity by using a beam according to feedback information from a communication partner in a prescribed beam pattern, and can secure the strength of a signal received by the communication partner. . In addition, since precoding can accommodate different mobile station apparatuses in different beams, a multiuser diversity effect can be obtained.

By the way, in the downlink of 3GPP RAN LTE (Long Term Evolution), MIMO communication technology is applied to OFDM (Orthogonal Frequency Division Division Multiplex) transmission to achieve a maximum transmission rate of 300 Mbps, and precoding transmission using rank 2 is also performed. Diversity technology is applied (see Non-Patent Document 1). Here, the rank indicates the number of spatial multiplexing in the case of performing spatial division communication (Space Division Multiplexing: SDM), and rank 2 indicates the case where the number of spatial multiplexing is two.

Also, in the uplink of 3GPP RAN LTE-Advanced, introduction of single-carrier-based SC-FDMA is being studied. In the 3GPP RAN LTE-Advanced uplink, as with the 3GPP RAN LTE downlink, in order to further improve the transmission rate, introduction of MIMO communication technology and precoding transmission diversity technology using rank 2 are introduced. (Hereinafter, the MIMO communication technique and the precoding technique are referred to as “MIMO precoding”).

FIG. 1 shows a codebook used for rank-2 precoding described in Non-Patent Document 1. In the code book shown in FIG. 1, a precoding matrix used at the time of 2-antenna transmission is stored in association with PMI (Precoding Matrix Index) determined by feedback information from a communication partner. In FIG. 1, when a precoding matrix associated with PMI [1] is used, since the data stream is not multiplexed, precoding is not actually applied.

The conventional transmission apparatus multiplexes the precoding matrix corresponding to the optimum PMI based on the rank information and the feedback information from the communication partner in a plurality of data streams from the code book as shown in FIG. Thus, precoding processing is performed.

However, if MIMO precoding for OFDM used in the downlink of 3GPP RAN LTE is applied as it is to SC-FDMA transmission used in the uplink of 3GPP RAN LTE-Advanced, the remaining power of the mobile station device (which can be increased) Depending on the size of the power headroom (hereinafter referred to as “PHR (Power headroom)”), there is a problem that the data throughput is rapidly deteriorated.

Hereinafter, description will be made using FIG. 2 as an example. FIG. 2 is a simulation result showing the relationship between PHR and data throughput when MIMO precoding similar to OFDM is applied to SC-FDMA. In FIG. 2, the horizontal axis indicates PHR, and the vertical axis indicates data throughput. On the horizontal axis, the smaller the PHR, the closer the transmission power is to the maximum transmission power, and there is no sufficient margin for the power that can be amplified. In addition, the larger the PHR, the more the power that can be amplified has a margin and the transmission power has a margin.

In FIG. 2, Th11 indicates a data throughput characteristic when precoding is not applied. Th11 can also be said to be a data throughput when precoding processing is performed using PMI [1] of FIG. 1 as a precoding matrix. Further, Th12 indicates data throughput when precoding is applied using PMI [2] or PMI [3] of FIG. 1 as a precoding matrix.

As can be seen from FIG. 2, when the precoding is not applied, the data throughput is rapidly deteriorated in the region where the PHR is small. On the other hand, when precoding is applied, in a region where PHR is medium, there is a region where the data throughput sharply decreases and the data throughput deteriorates more than the data throughput (Th11) when precoding is not applied. .

As described above, when MIMO precoding similar to OFDM is applied as it is to SC-FDMA, the data throughput is not always better than when precoding is not applied, and depending on the size of PHR, the data throughput is not always good. Data throughput may be degraded compared to when coding is not applied.

An object of the present invention is to provide a radio transmission apparatus, a mobile station apparatus, and a precoding method capable of improving rapid degradation of data throughput in, for example, SC-FDMA transmission.

The wireless transmission apparatus of the present invention includes a multiplexing unit that multiplies the plurality of streams with different power ratios by multiplying the plurality of streams by a precoding matrix, and a plurality of the power ratios. A codebook having a plurality of corresponding candidates for the precoding matrix and setting the precoding matrix from the plurality of candidates.

The mobile station apparatus of the present invention employs a configuration including the above-described radio transmission apparatus.

In the precoding method of the present invention, the plurality of streams are multiplexed with different power ratios between the plurality of streams by multiplying the plurality of streams by a precoding matrix.

According to the present invention, for example, rapid degradation of data throughput can be improved in SC-FDMA transmission.

The figure which shows the code book used for the pre-coding using the rank 2 description of a nonpatent literature 1 The figure which shows the simulation result which shows the relationship between PHR and data throughput Diagram showing simulation results of CM characteristics before and after applying precoding Show simulation results of the CM characteristics when having different power ratio between streams S ₁ and stream S ₂ The block diagram which shows the principal part structure of the transmitter which concerns on Embodiment 1 of this invention. FIG. 10 is a diagram illustrating an example of a precoding matrix in the first embodiment FIG. 3 is a block diagram showing an internal configuration of a multiplexing unit according to the first embodiment. The figure which shows the relationship between PHR at the time of applying the precoding in Embodiment 1, and a data throughput. FIG. 10 is a diagram illustrating an example of a rank 4 precoding matrix according to the first embodiment. The block diagram which shows the principal part structure of the transmitter which concerns on Embodiment 2 of this invention. The figure which shows the relationship between PHR and data throughput after precoding application in Embodiment 2. The figure which shows an example of a of the power ratio setting table which the code book in Embodiment 2 uses The figure which shows the relationship between PHR and data throughput after precoding application in Embodiment 2. The block diagram which shows the principal part structure of the transmitter which concerns on Embodiment 3 of this invention. The figure which shows an example of b1 and b2 The block diagram which shows the principal part structure of the transmitter which concerns on Embodiment 4 of this invention. The figure which shows an example of a of the power ratio setting table which the code book in Embodiment 4 uses

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The inventors of the present invention focused on changes in CM (Cubic-Metric) characteristics before and after applying precoding. CM is an index indicating the power attenuation characteristic like PAR (peak average peak ratio), and the smaller the CM value, the less the amplification characteristic is distorted. SC-FDMA is characterized by a smaller CM value than OFDM.

Fig. 3 shows the simulation results of CM characteristics before and after applying precoding. FIG. 3 shows CMs before and after precoding application when the stream is SC-FDMA (QPSK), SC-FDMA (16QAM), and OFDM, and CM variation amounts before and after precoding application. . FIG. 3 shows simulation results when the OFDM precoding matrix shown in FIG. 1 is used for each modulation scheme.

As shown in FIG. 3, in SC-FDMA, it was confirmed that CM increases greatly when precoding is applied in both QPSK and 16QAM. On the other hand, in OFDM, it was confirmed that the CM hardly changed before and after application of precoding.

As described above, in OFDM, there is almost no variation in CM before and after the application of precoding, whereas in SC-FDMA, CM increases by applying precoding. That is, in OFDM, the power attenuation characteristic does not vary much depending on whether or not precoding is applied, whereas in SC-FDMA, if precoding similar to OFDM is applied as it is, the power attenuation characteristic is greatly degraded. .

In the precoding matrix of FIG. 1, since the sizes of the matrix elements are equal, the two streams S ₁ and S ₂ are combined with the same power ratio. The present inventors paid attention to the power ratio between multiplexed streams and further performed the following simulation.

FIG. 4 shows a simulation result of CM characteristics when the power ratio between the stream S ₁ and the stream S ₂ is different in the case of rank 2.

As can be seen from FIG. 4, when the power ratio between the multiplexed streams is equal (when the power of stream S ₁ : the power of stream S ₂ = 1: 1), it is confirmed that the CM value is the largest. It was done.

In the SC-FDMA, the present inventors paid attention to the fact that the CM differs greatly depending on whether or not precoding is applied, and that the CM changes by changing the power ratio between streams. Focusing on these points, when applying precoding of rank 2 or higher to SC-FDMA, a precoding matrix for changing the power ratio between multiplexed streams is set and applied to the precoding codebook. I did it.

Note that the precoding matrix is a unitary matrix. Also, the precoding matrix is a matrix that takes a value other than 0 or 1 for the power range of another stream when the power of any one of the plurality of streams is fixed to 1.

(Embodiment 1)
FIG. 5 shows a main configuration of the transmission apparatus according to the present embodiment. The transmitting apparatus 100 in FIG. 5 is applied to, for example, an LTE-Advanced mobile station apparatus. 5 is an example in the case of rank 2, that is, the spatial multiplexing number is 2.

Modulation section 110-1 modulates the input data stream to obtain a time domain modulated signal. Modulation section 110-1 outputs a time domain modulation signal to DFT (Discrete Fourier Transform) section 120-1. Similarly, modulation section 110-2 modulates the input data stream, obtains a time domain modulation signal, and outputs the time domain modulation signal to DFT section 120-2.

The DFT units 120-1 and 120-2 perform time-frequency conversion by performing discrete Fourier transform (DFT) on the time domain modulation signal to obtain a frequency domain signal. DFT sections 120-1 and 120-2 output frequency domain signals to precoding section 130.

The precoding unit 130 includes a code book 131 and a multiplexing unit 132.

The code book 131 stores a precoding matrix used in the multiplexing unit 132. A specific example of the precoding matrix will be described later. Codebook 131 receives rank information and PMI as input, and sets a precoding matrix corresponding to rank information and PMI as a precoding matrix used by multiplexing section 132. The code book 131 outputs information on the set precoding matrix to the multiplexing unit 132.

The multiplexing unit 132 multiplies the frequency domain signal by multiplying the precoding matrix set by the codebook 131 to vary the power ratio among the plurality of frequency domain signals. The internal configuration of the multiplexing unit 132 will be described later. Multiplexing section 132 outputs the multiplexed frequency domain signal to IFFT sections 140-1 and 140-2.

IFFT (Inverse Fast Fourier Transform) sections 140-1 and 140-2 map frequency domain signals after precoding to transmission subcarriers, and then perform inverse fast Fourier transform (IFFT) processing to convert them into time domain signals To do. IFFT sections 140-1 and 140-2 output the obtained time domain signals to CP (Cyclic Prefix) adding sections 150-1 and 150-2.

CP adding sections 150-1 and 150-2 copy the data at the end of the block for each block of the transmission data sequence of the time domain signal and insert it at the head of the block, thereby adding CP to the transmission data sequence of the time domain signal. Is added. CP adding sections 150-1 and 150-2 output time domain signals after CP addition to radio transmitting sections 160-1 and 160-2.

Radio transmitting sections 160-1 and 160-2 perform frequency conversion of time domain signals, which are baseband signals output from CP adding sections 150-1 and 150-2, into radio frequency bands.

In this way, in SC-FDMA transmission, directivity is formed by applying MIMO precoding to a plurality of data streams, and signals after the formation of directivity are transmitted from a plurality of antennas.

Hereinafter, the precoding matrix stored in the codebook 131 of the precoding unit 130 will be described.

FIG. 6 shows an example of the precoding matrix stored in the codebook 131. FIG. 6 shows a precoding matrix in the case of rank 2.

In each matrix of FIG. 6, a indicates the power ratio of another stream with respect to the fixed value 1 when the power of any one of a plurality of multiplexed streams is 1 (fixed). And a is a value in the range of 0 <a <1. By setting the value of a to an appropriate value in advance, precoding with different power ratios between multiplexed streams is realized.

At this time, for example, when the stream modulation method is QPSK, the power ratio is set to a value such that the CM becomes small by referring to the simulation result of FIG. Can be reduced. As described above, when the power ratio between the streams to be multiplexed is 1: 1, the CM is the largest. Therefore, by setting the power ratio between the streams to be multiplexed to other than 1: 1, the CM at the time of stream multiplexing is set. Can be reduced.

FIG. 7 shows an internal configuration of multiplexing section 132 that multiplexes streams S ₁ and S ₂ with different power ratios using the above-described precoding matrix.

Amplifier 1321-1, the stream _{S 1} from the DFT section 120-1 a1 (= a) multiplied, and outputs the result to adding section 1322-2. Amplifier 1321-2 is a peripheral stream _{S 2} from the DFT section 120-2 a2 (= a) multiplied, and outputs the result to adding section 1322-1. Thus, the addition section 1322-1, the power ratio between the streams _{S 1} and stream _{S 2} is 1: to be multiplexed in a. Further, the addition section 1322-2, the power ratio between the streams _{S 1} and stream _{S 2} is a: so are multiplexed in one.

The effect of this embodiment will be described with reference to FIG. In the same figure, the data throughput characteristics Th11 and Th12 shown in FIG. 2 are also displayed. Th11 is a data throughput characteristic when a precoding matrix corresponding to PMI [1] in FIG. 1 is applied. Th12 is a data throughput characteristic when a precoding matrix corresponding to PMI [2] and PMI [3] in FIG. 1 is applied. Th101 indicates the data throughput characteristic when precoding is performed using the precoding matrix in the present embodiment.

As can be seen from the comparison between Th101 and Th12, by applying the precoding in the present embodiment, the region where the data throughput characteristic is rapidly deteriorated is extended to the region where the PHR is smaller. This is because the CM value is reduced by setting the power ratio between multiplexed streams to 1: a (0 <a <1). Note that the improvement of the data throughput characteristics and the PHR region until the data throughput characteristics are rapidly deteriorated vary depending on the power ratio between the multiplexed streams.

As described above, in this embodiment, when streams are multiplexed and MIMO transmission is performed, precoding is performed so that the power ratio between the multiplexed streams is different. That is, in the case of rank 2, by setting the power ratio between streams to 1: a (0 <a <1), the amount of CM variation before and after precoding application is reduced. As a result, as shown in FIG. 8, it is possible to improve the degradation of data throughput in a region where the PHR is smaller.

When the difference in data throughput characteristics due to the presence / absence of precoding is small and the difference in CM characteristics due to the presence / absence of precoding is large, a is small (that is, the power difference between streams is large). To do). Also, when the difference in data throughput characteristics depending on whether precoding is applied is large and the difference in CM characteristics depending on whether precoding is applied is small, a is increased (that is, the power difference between the streams is decreased). ) Good.

Also, for example, when precoding into the stream S ₁ and the stream S ₂ using the unitary matrix of PMI [2] in FIG. 6 as the precoding matrix, the multiplexed signals S ′ ₁ and S ′ ₂ after multiplexing are expressed as follows: It is expressed by (1).

As can be seen from the equation (1), the power ratio between the stream S ₁ and the stream S ₂ included in the multiplexed signals S ′ ₁ and S ′ ₂ is 1 + a ² : 1 + a ² = 1: 1, and the multiplexed signal S after multiplexing. _'1, S' power balance between the stream included in ₂ can be kept constant.

Also, by making the precoding matrix a unitary matrix, it is possible to avoid complicated processing in reception processing, particularly channel estimation processing.

As described above, in the present embodiment, the multiplexing unit 132 multiplies the stream S ₁ and the stream S ₂ by the precoding matrix, thereby changing the power ratio between the streams S ₁ and S _2. Multiplex. The codebook 131 has a plurality of precoding matrix candidates corresponding to a plurality of power ratios with different power ratios between streams, and sets a precoding matrix from the plurality of candidates. Thereby, since deterioration of CM after applying precoding can be suppressed, rapid deterioration of data throughput when precoding is applied can be improved.

Also, by making the precoding matrix a unitary matrix, the power balance between the streams can be kept constant, so that it is possible to suppress deterioration in data throughput. Further, by using a unitary matrix, it is possible to avoid complicated processing in reception processing, particularly channel estimation processing.

In the above description, the case where a is set in the range of 0 <a <1 has been described as an example, but the configuration in which a is set in the range of 1 <a, a> −1, −1> a> 0. It is also good. Even in this case, since the power ratio between the multiplexed streams can be other than 1: 1, the same effect as in the case of 0 <a <1 can be obtained.

In the above description, the case where the present invention is applied to rank 2 has been described as an example. However, as with rank 2, the present invention can also be applied to MIMO precoding of rank 3 or higher.

FIG. 9 shows an example of a rank 4 precoding matrix in the present embodiment. FIG. 9 also shows a conventional rank 4 precoding matrix.

In the above description, the case where the multiple access method is SC-FDMA has been described as an example. However, the multiple access method is not limited to SC-FDMA, and other multiple access methods having a lower CM than OFDM. The present invention may be applied to. Even in this case, it is possible to suppress the deterioration of the CM after applying the precoding, and it is possible to improve the rapid deterioration of the data throughput when the precoding is applied as in the case of SC-FDMA.

Further, the precoding matrix may have a configuration in which 1 and a of the precoding matrix in FIG. In short, the precoding matrix is a value other than 0 or 1 when the power of one of the multiple streams is set to 1 (fixed). Any matrix can be used.

That is, as a result of multiplying a plurality of streams by a precoding matrix, multiplexing may be performed with different power ratios between streams. Therefore, as shown in Expression (2), precoding may be applied using a matrix in which 1 and a of the precoding matrix in FIG. 6 are interchanged.

(Embodiment 2)
In this embodiment, when precoding of rank 2 or higher is applied to SC-FDMA, the power ratio between multiplexed streams is changed according to the modulation scheme of each stream. As in the first embodiment, the precoding matrix is a unitary matrix, and when the power of any one of a plurality of streams is 1 (fixed), the power range of the other streams is It is assumed that the matrix takes a value other than 0 or 1. As a result, in addition to the same effects as those of the first embodiment, it becomes possible to more reliably suppress the deterioration of the CM, so that the rapid deterioration of the data throughput can be reliably improved.

FIG. 10 shows a main configuration of the transmission apparatus according to the present embodiment. The transmitting apparatus 200 in FIG. 10 is applied to, for example, an LTE-Advanced mobile station apparatus. In the transmitting apparatus 200 of FIG. 10, the same components as those in FIG. 5 are denoted by the same reference numerals as those in FIG. The transmission apparatus 200 of FIG. 10 includes a precoding unit 210 instead of the precoding unit 130 with respect to the transmission apparatus 100 of FIG. In the present embodiment, it is assumed that the modulation scheme of stream S ₁ is different from the modulation scheme of stream S ₂ .

The precoding unit 210 includes a code book 211 and a multiplexing unit 132.

The code book 211 stores a precoding matrix used in the multiplexing unit 132. A specific example of the precoding matrix will be described later. Codebook 211 receives rank information, PMI, and MCS information of each stream as input, and sets a precoding matrix corresponding to rank information, PMI, and modulation scheme information as a precoding matrix used by multiplexing section 132. . The code book 211 outputs information on the set precoding matrix to the multiplexing unit 132.

Hereinafter, the precoding matrix stored in the codebook 211 of the precoding unit 210 will be described.

As already shown in FIG. 3, even when precoding is applied, the CM varies depending on the modulation scheme of each stream. For example, when precoding is applied to SC-FDMA (QPSK), CM is 2.55, whereas when precoding is applied to SC-FDMA (16QAM), CM is 3.05. It has become. Due to such a difference in CM characteristics, data throughput characteristics change.

FIG. 11 shows the relationship between PHR and data throughput when OFDM precoding is applied. In FIG. 11, Th22 indicates the throughput characteristic when precoding is applied to a stream whose modulation scheme is QPSK. Th23 indicates throughput characteristics when precoding is applied to a stream having a modulation scheme of 16QAM. Th21 indicates a throughput characteristic when precoding is not applied to a stream having a modulation scheme of QPSK.

As can be seen from FIG. 11, the data throughput characteristics vary depending on the modulation method of each stream. For example, when precoding is applied to a stream having a modulation scheme of 16QAM (Th23), the data throughput is higher in a region where the PHR is large compared to QPSK (Th22), and the data throughput is higher in a region where the PHR is medium. Deteriorates rapidly. On the other hand, when precoding is applied to a stream with a modulation scheme of QPSK (Th22), the data throughput is lower in a region where PHR is large compared to 16QAM (Th23), but in a region where PHR is medium, 16QAM (Th23 ) There are areas with higher data throughput. As described above, the CM characteristics change depending on the modulation method, and as a result, the data throughput characteristics fluctuate.

Therefore, in the present embodiment, the codebook 211 has a power ratio setting table, and the precoding matrix used by the multiplexing unit 132 is selected according to the modulation scheme of the multiplexed stream.

FIG. 12 shows an example of the power ratio setting table used by the code book 211. As shown in FIG. 12, when the modulation schemes of the stream S ₁ and the stream S ₂ are both QPSK (case 1), the codebook 211 selects a precoding matrix in which a is 0.4. As a result, when the power of the stream S ₁ is _1, the power of the stream S ₂ is set to 0.4, and the stream S ₁ and the stream S ₂ are multiplexed. Further, when the power of the stream S ₂ is 1, the power of the stream S ₁ is set to 0.4, and the stream S ₁ and the stream S ₂ are multiplexed.

Also, when the modulation scheme of the stream S ₁ is QPSK and the modulation scheme of the stream S ₂ is 16QAM (case 2), the codebook 211 selects a precoding matrix in which a is 0.5. As a result, when the power of the stream S ₁ is _1, the power of the stream S ₂ is set to 0.5, and the stream S ₁ and the stream S ₂ are multiplexed. In addition, when the power of the stream S ₂ is 1, the power of the stream S ₁ is set to 0.5, and the stream S ₁ and the stream S ₂ are multiplexed.

Further, when the modulation schemes of the stream S ₁ and the stream S ₂ are both 16QAM (case 3), the codebook 211 selects a precoding matrix in which a is 0.6. As a result, when the power of the stream S ₁ is _1, the power of the stream S ₂ is 0.6, and the stream S ₁ and the stream S ₂ are multiplexed. Further, when the power of the stream S ₂ is 1, the power of the stream S ₁ is 0.6, and the stream S ₁ and the stream S ₂ are multiplexed.

Note that the code book 211 may have a precoding matrix as shown in FIG. 6, and a may be set according to the modulation scheme of each stream. In short, the multiplexing unit 132 may multiplex a plurality of streams with a power ratio corresponding to the modulation scheme of each stream.

Note that the value of a corresponding to the modulation scheme of each stream is specified in advance in the codebook 211 from the upper layer. In addition, since the modulation scheme information of each stream is necessary information for adaptive modulation, the communication partner does not need to perform new signaling only for setting the power ratio a.

FIG. 13 shows a simulation result showing the relationship between the PHR and the data throughput characteristics when the precoding in the present embodiment is applied. In the figure, the data throughput characteristics Th21, Th22, Th23 when the MIMO precoding for OFDM shown in FIG. 11 is applied are also displayed.

In FIG. 13, Th201 indicates a throughput characteristic when the precoding according to the present embodiment is applied to the streams S ₁ and S ₂ whose modulation scheme is QPSK. Further, Th202 shows throughput characteristics when the stream _{S 1} and the modulation method of the modulation method QPSK has applied a precoding according to the present embodiment in the stream _{S 2} of 16QAM. Further, Th203 indicates a throughput characteristic when the precoding according to the present embodiment is applied to streams S ₁ and S ₂ having a modulation scheme of 16QAM.

As described above, in this embodiment, the streams are multiplexed with different power ratios according to the modulation schemes of the streams. For example, when the modulation schemes of the stream S ₁ and the stream S ₂ are both 16QAM (Th203), by applying the precoding in the present embodiment, the data throughput is slightly deteriorated in the region where the PHR is large compared to the Th23. However, the area of PHR until the data throughput rapidly deteriorates is expanded.

Note that when precoding is applied, if the difference in data throughput due to the difference in modulation scheme is small and the difference in CM characteristics is large, a may be similarly reduced. Further, when precoding is applied, a may be increased similarly when the difference in data throughput characteristics due to the difference in modulation scheme is large and the difference in CM characteristics is small.

As described above, in the present embodiment, the codebook 211 sets precoding matrices from a plurality of candidates according to the modulation schemes of a plurality of streams. As a result, the power ratio between the multiplexed streams differs according to the modulation schemes of a plurality of streams, so that CM deterioration can be suppressed and data throughput deterioration can be improved.

(Embodiment 3)
In the present embodiment, in

Embodiments

1 and 2, each stream is scalar-scaled before precoding is performed.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.

FIG. 14 shows a main configuration of the transmission apparatus according to the present embodiment. The transmitting apparatus 300 in FIG. 14 is applied to, for example, an LTE-Advanced mobile station apparatus. In the transmission apparatus 300 according to the present embodiment in FIG. 14, the same reference numerals as those in FIG. 14 includes an amplifier 310-1 between the DFT unit 120-1 and the precoding unit 130, and the DFT unit 120-2 and the precoding unit 130 are different from the transmission device 100 of FIG. Between the two, an amplifier 310-2 is provided.

The amplifier 310-1 performs scalar multiplication (magnification b1) on the frequency domain signal output from the DFT unit 120-1, and outputs the frequency domain signal after b1 multiplication to the precoding unit 130. Amplifier 310-2 multiplies the frequency domain signal output from DFT section 120-2 by scalar multiplication (magnification b2), and outputs the frequency domain signal after b2 multiplication to precoding section 130. In this way, the amplifiers 310-1 and 310-2 adjust the power ratio of the frequency domain signal input to the precoding unit 130 in advance.

At this time, by setting the value of b1 or b2 in accordance with, for example, the modulation scheme of each stream, the power balance between the streams transmitted from the subsequent antenna can be adjusted. As a result, it is possible to adjust the power balance between the streams while keeping the precoding matrix used in the multiplexing unit 132 of the precoding unit 130 as a unitary matrix. The complexity can be avoided.

FIG. 15 shows an example of the magnifications b1 and b2 of the amplifiers 310-1 and 310-2.

As shown in FIG. 3, the CM value when the stream modulation scheme is 16QAM is larger than that when the stream modulation scheme is QPSK. Therefore, as shown in case 3 of FIG. 15, the modulation scheme is QPSK stream _{S 1,} when a modulation scheme stream _{S 2} is 16QAM, the magnification b2 for stream _{S 2,} compared with the magnification b1 for the stream _{S 1} By reducing the size, the CM of the multiplexed stream can be reduced.

In addition, when performing precoding with the power of any one of the plurality of streams being 1 (fixed), an amplifier that performs scalar multiplication of the stream having the power of 1 is not provided, and the precoding unit 130 You may make it output as it is.

As described above, in the present embodiment, each of a plurality of streams is scalar-multiplied, and precoding is performed on the plurality of scalar-multiplied streams. Thereby, since the power of the stream input to the precoding unit 130 can be adjusted in advance, the power balance between the streams can be adjusted while keeping the precoding matrix in a unitary matrix. In addition, since the power ratio between the multiplexed streams can be made different, it is possible to suppress the deterioration of CM and improve the deterioration of the data throughput, and the processing is complicated in the reception process, particularly the channel estimation process. Can be avoided.

(Embodiment 4)
In this embodiment, when precoding of rank 2 or higher is applied to SC-FDMA, the power ratio between multiplexed streams is changed according to multiple access schemes such as OFDMA and SC-FDMA. As in the first embodiment, the precoding matrix is a unitary matrix, and when the power of any one of a plurality of streams is 1 (fixed), the power range of the other streams is It is assumed that the matrix takes a value other than 0 or 1. As a result, in addition to the same effects as those of the first embodiment, it is possible to more reliably suppress the deterioration of the CM, and thus it is possible to reliably improve the rapid deterioration of the data throughput.

FIG. 16 shows a main configuration of the transmission apparatus according to the present embodiment. The transmission apparatus 400 of FIG. 16 is applied to, for example, an LTE-Advanced mobile station apparatus. Hereinafter, a case will be described as an example where transmission apparatus 400 supports both OFDM and SC-FDMA as multiple access schemes. In addition, in transmitting apparatus 400 according to the present embodiment in FIG. 16, the same components as in FIG. 5 are assigned the same reference numerals as in FIG.

Modulation section 410-1 modulates the input data stream to obtain a time domain modulated signal. Modulation section 410-1 outputs the time domain modulation signal to DFT section 120-1 and selection section 420-1. Similarly, modulation section 410-2 modulates the input data stream, obtains a time domain modulation signal, and outputs the time domain modulation signal to DFT section 120-2 and selection section 420-2.

Selection sections 420-1 and 420-2 receive information on multiple access schemes (hereinafter referred to as “multiple access scheme information”) and are output from DFT sections 120-1 and 120-2 in accordance with the multiple access scheme information. Frequency domain signal or time domain modulation signal output from the modulation units 410-1 and 410-2, and outputs the selected signal to the precoding unit 430.

Specifically, when the multiple access scheme information indicates SC-FDMA, selection sections 420-1 and 420-2 send the frequency domain signals output from DFT sections 120-1 and 120-2 to precoding section 430. Output. On the other hand, when the multiple access scheme information indicates OFDM, selection sections 420-1 and 420-2 output time domain modulation signals output from modulation sections 410-1 and 410-2 to precoding section 430.

The precoding unit 430 includes a code book 431 and a multiplexing unit 132.

The code book 431 stores a precoding matrix used in the multiplexing unit 132. A specific example of the precoding matrix will be described later. The code book 431 receives rank information, PMI, and multiple access scheme information as inputs, and sets a precoding matrix corresponding to the rank information, PMI, and multiple access scheme information as a precoding matrix used by the multiplexing unit 132. The code book 431 outputs information on the set precoding matrix to the multiplexing unit 132.

Hereinafter, the precoding matrix stored in the codebook 431 of the precoding unit 430 will be described.

As already shown in FIG. 3, even when precoding is applied, the CM varies depending on the multiple access method. For example, when precoding is applied to SC-FDMA, CM is 2.55 and 3.05, whereas when precoding is applied to OFDM, CM is 4.00. . Due to such a difference in CM characteristics, data throughput characteristics change.

Therefore, in the present embodiment, the code book 431 has a power ratio setting table and selects the precoding matrix used by the multiplexing unit 132 according to the multiple access scheme.

FIG. 17 shows an example of the power ratio setting table used by the code book 431. As shown in FIG. 17, when the multiple access method is SC-FDMA (case 1), the code book 431 selects a precoding matrix with a being 0.6. As a result, when the power of the stream _{S 1} 1 (fixed), the power of the stream _{S 2} as 0.6, the stream S1 and the stream _{S 2} are multiplexed. Further, when the power of the stream S ₂ is 1 (fixed), the stream S ₁ and the stream S ₂ are multiplexed with the power of the stream S ₁ being 0.6.

When the multiple access method is OFDM (Case 2), the code book 431 selects a precoding matrix in which a is 1.0. That is, when the multiple access method is OFDM, each stream is multiplexed with the same power. Accordingly, precoding as described in Non-Patent Document 1 can be performed.

In this way, when the multiple access scheme is SC-FDMA, multiplexing is performed such that the power ratio between streams is different, and when the multiple access scheme is OFDM, multiplexing is performed so that the power ratio between streams is equal. Will come to be.

The code book 431 may have a precoding matrix as shown in FIG. 6, and a may be set according to the multiple access method. In short, the multiplexing unit 132 may multiplex a plurality of streams at a power ratio corresponding to the multiple access scheme.

At this time, since the information on the multiple access method is necessary information for the modulation, it is not necessary for the communication partner to newly signal only for setting the power ratio a.

As described above, in this embodiment, the code book 431 sets a precoding matrix from candidate matrices according to the multiple access scheme. As a result, even when the transmission apparatus 400 supports a plurality of multiple access schemes, the power ratio between the multiplexed streams can be set to a power ratio that suppresses the degradation of CM according to the multiple access scheme. As a result, degradation of data throughput can be improved.

In the above description, the case where the precoding unit sets a precoding matrix corresponding to PMI based on feedback information from the communication partner has been described, but the reference signal for data demodulation is the same as the data stream. When precoding is performed by multiplying the precoding matrix, the power ratio may be changed by the transmission apparatus.

In the above description, the case where the power ratio between multiplexed streams is set has been described, but the amplitude ratio may be set instead of the power ratio.

In the above embodiment, the case where the present invention is configured by hardware has been described as an example, but the present invention can also be realized by software.

Further, each functional block used in the description of the above embodiment is typically realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

Further, the method of circuit integration is not limited to LSI, and implementation with a dedicated circuit or a general-purpose processor is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

Furthermore, if integrated circuit technology that replaces LSI emerges as a result of advances in semiconductor technology or other derived technology, it is naturally also possible to integrate functional blocks using this technology. Biotechnology can be applied.

The disclosure of the specification, drawings and abstract contained in Japanese Patent Application No. 2008-258547 filed on October 3, 2008 is incorporated herein by reference.

The precoding apparatus and the precoding method according to the present invention are useful as, for example, a radio transmission apparatus, a mobile station apparatus, and a precoding method for transmitting SC-FDMA in a radio communication system using MIMO communication technology.

100, 200, 300, 400 Transmitter 110-1, 110-2, 410-1, 410-2 Modulator 120-1, 120-2

DFT unit

130, 210, 430

Precoding unit

1311, 211, 431 Codebook 132 Multiplexer 140-1, 140-2 IFFT Unit 150-1, 150-2 CP Adder 160-1, 160-2 Radio Transmitter 420-1, 420-2 Selector 1321-1, 1321-2, 310 -1,320-2 Amplifier 1322-1, 1322-2 Adder

Claims

A multiplexing unit that multiplies the plurality of streams with different power ratios by multiplying the plurality of streams by a precoding matrix;
A codebook having a plurality of candidates for the precoding matrix corresponding to a plurality of the power ratios, and setting the precoding matrix from the plurality of candidates;
A wireless transmission device comprising:
The precoding matrix is a unitary matrix;
The wireless transmission device according to claim 1.
The codebook is
Setting the precoding matrix from the candidate matrix based on the number of the plurality of streams and a precoding index;
The wireless transmission device according to claim 1.
The codebook is
Setting the precoding matrix according to a modulation scheme of the plurality of streams;
The wireless transmission device according to claim 1.
The codebook is
Setting the precoding matrix according to a multiple access scheme;
The wireless transmission device according to claim 1.
Amplifying means for multiplying each of the plurality of streams by a scalar and multiplying the plurality of streams multiplied by the scalar by the precoding matrix;
The wireless transmission device according to claim 1.
In accordance with the modulation scheme of the plurality of streams, the scaling factor of the scalar is set.
The wireless transmission device according to claim 6.
A mobile station apparatus comprising the radio transmission apparatus according to claim 1.
By multiplying a plurality of streams by a precoding matrix to multiplex the plurality of streams with different power ratios between the plurality of streams;
Precoding method.