JP2016072680A - Radio communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adaptively determine an optimal combination of a modulation system and transmission power to be allocated to each of eigen modes under a condition that a transmission rate is fixed, in a MIMO eigen mode transmission system.SOLUTION: For each of combination patterns with the equal transmission rate among combination patterns of modulation systems, power distribution calculation means 12 calculates an expression of a MER margin Δμafter power distribution represented by a parameter of only a power distribution ratio pand calculates the power distribution ratio pin such a manner that the MER margins Δμof the eigen modes become equal. For each of the combination patterns of the modulation systems, MER margin calculation means 13 calculates the MER margin Δμby substituting the calculated power distribution ratio pinto the expression of the MER margin Δμ. Modulation system/power determination means 14 determines the combination pattern of the modulation system and the power distribution ratio phaving the greatest MER margin value among the calculated MER margins Δμ.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a MIMO (Multiple Input and Multiple Output) eigenmode transmission system, and in particular, adaptively determines an optimal combination of the number of modulation bits allocated to each eigenmode and a transmission power distribution. The present invention relates to a wireless communication device.

  Conventionally, as a means for dramatically increasing the transmission capacity without changing the frequency bandwidth, a MIMO technique that uses a plurality of antennas in each of the transmitting station and the receiving station has attracted attention. The MIMO technology is characterized in that the transmission capacity is increased by spatially multiplexing a plurality of substreams and transmitting them in parallel within the same channel.

  In a MIMO system for unidirectional communication, a transmission side cannot obtain transmission path information (hereinafter referred to as channel information), and thus a spatially multiplexed signal must be separated by a detector on the reception side. In this system, one substream is generally allocated for each transmission antenna, and it is theoretically assumed that the power allocated to each substream is always equal without changing the distribution ratio in a variable transmission path. It is considered optimal.

  On the other hand, in a bidirectional MIMO system, instead of simply allocating a substream for each transmission antenna, a plurality of antennas are used as a transmission array for each substream to form an appropriate beam according to the condition of the transmission path. To send. This makes it possible to achieve more efficient transmission characteristics that cannot be achieved with a unidirectional MIMO system.

  The optimal transmit / receive beam is obtained by singular value decomposition (SVD) of a channel matrix obtained by digitizing channel information, using the right singular matrix as a transmission weight for forming a transmit beam, and using the left singular matrix as a receive beam. It is formed by using it as a receiving weight for.

ＵはＭ×Ｋ次の左特異行列、Σはチャネル行列Ｈの特異値を要素とするＫ×Ｋ次の対角行列、ＶはＮ×Ｋ次の右特異行列である。Ｋはチャネル行列Ｈのランクである。Ｍ，Ｎ，Ｋは正の整数である。 When the number of transmitting antennas is N, the number of receiving antennas is M, and the M × N-th order channel matrix is H, the channel matrix H is decomposed into singular values as follows.

U is an M × K-order left singular matrix, Σ is a K × K-order diagonal matrix whose elements are singular values of the channel matrix H, and V is an N × K-order right singular matrix. K is the rank of the channel matrix H. M, N, and K are positive integers.

The transmission weight F is a right singular matrix V as follows.

The Nth-order transmission signal vector x is expressed by the following equation with the Kth-order information signal vector as s.

Here, if the complex Gaussian noise vector is n, the received signal vector y is expressed by the following equation.

Also, the reception weight G is a complex conjugate transpose of the left singular matrix U when the singular value decomposition of the channel matrix H is performed as follows.

は次式で表される。

Signal vector detected at the receiver

Is expressed by the following equation.

  In this way, the channel matrix H is subjected to singular value decomposition, the right singular matrix V is used as the transmission weight F, and the complex conjugate transpose of the left singular matrix U is used as the reception weight G, thereby virtually orthogonal K pieces. Can be separated into channels. Each orthogonal channel is called an eigenmode, and a MIMO transmission scheme using this technique is called an eigenmode transmission scheme.

  The transmission weight F represented by the equation (2) is treated as having the same power distribution to each eigenmode. However, by adaptively changing the transmission power distribution as well as the number of modulation bits (modulation scheme) assigned to each eigenmode symbol according to the propagation environment, the transmission capacity is increased and the bit error rate (BER) is increased. ) It is possible to improve the characteristics.

When the transmission power distribution is taken into consideration, the equation (2) is expressed by the following equation using the transmission power distribution matrix W ^1/2 .

Here, W is a diagonal matrix whose elements are the power distribution ratios p ₁ ,..., P _K to each eigenmode as follows, and the transmission power distribution matrix W ^1/2 is a diagonal matrix. It is the square root of W.

は、前記式（６）に代わりに、次式で表される。

At this time, the signal vector detected on the receiving side

Is represented by the following equation instead of the equation (6).

  By the way, in order to maximize the transmission capacity or minimize the bit error rate, the following methods have been proposed as adaptively controlling the number of modulation bits and transmission power allocated to each eigenmode. Yes. For example, the method disclosed in Patent Document 1 is an adaptive control method based on the water injection theorem, and an eigenvalue is obtained by solving simultaneous equations based on the channel matrix H and the like. Used as a weight. According to this method, the best assignment can be obtained from the viewpoint of information theory. The technique disclosed in Patent Document 2 or Non-Patent Document 1 is a control method that does not use the water injection theorem, and searches for combinations of modulation methods and transmission power distribution for minimizing the approximation formula of the bit error rate. To do.

JP 2001-237751 A JP 2005-252834 A

K. Miyashita, et al., “High data-rate transmission with eigenbeam-space division multiplexing (E-SDM) in a MIMO channel,” IEEE VTC Fall, Sept. 2002, pp. 1302-1306.

  However, in the conventional MIMO eigenmode transmission system, the above-described method of Patent Document 1 has a problem in terms of transmission characteristics and hardware implementation when the number of modulation bits to be allocated is only a discrete combination as in the actual system. There was a problem that it was not sufficient in terms of ease.

  Further, in the methods of Patent Document 2 and Non-Patent Document 1 described above, it is necessary to search for all combinations of modulation schemes and transmission power distributions in the process of minimizing the approximation formula of the bit error rate. In order to determine whether or not it is optimization, it is necessary to calculate the total throughput and the like. For this reason, this method has a problem that the calculation amount is large and the processing load is high.

  Accordingly, the present invention has been made to solve the above-described problems, and its object is to provide each eigenmode for minimizing the bit error rate under the condition that the transmission rate is constant in the MIMO eigenmode transmission system. It is an object of the present invention to provide a radio communication apparatus and method capable of easily obtaining a combination of modulation bit numbers to be allocated to and allocation of transmission power with a small amount of calculation.

  In order to achieve the above object, the wireless communication apparatus according to the present invention distributes the information bit sequence to be transmitted to each eigenmode, modulates the information bits of each eigenmode with a predetermined modulation scheme, and allocates a predetermined power distribution. In the radio communication apparatus of the MIMO eigenmode transmission system that distributes the transmission power of the information bits and transmits the information bit in the MIMO transmission scheme, the modulation scheme to be allocated to each eigenmode and the modulation scheme / power allocation determination that determines the power allocation A modulation unit that modulates the information bits in which the information bit sequence is allocated to each eigenmode by the modulation scheme of each eigenmode determined by the modulation scheme / power distribution determination unit, and the modulation unit The transmission power of the information bits of each eigenmode modulated by the eigenmode before each eigenmode determined by the modulation scheme / power distribution determination unit. A power distribution unit that distributes by power distribution, wherein the modulation scheme / power distribution determination unit is a combination pattern of modulation schemes of each eigenmode, and a predetermined bit for each combination pattern having the same transmission rate A MER margin indicating a difference between a MER threshold value that indicates a modulation error ratio set in advance with respect to an error rate and a modulation error ratio after the transmission power is allocated in the MIMO eigenmode transmission system includes each eigenmode. Power distribution calculation means for calculating the power distribution of each eigenmode to be equal to each other, and for each combination pattern of the modulation scheme, using the power distribution of each eigenmode calculated by the power distribution calculation means MER margin calculating means for calculating the MER margin of each eigenmode after allocating the transmission power; Of the MER margins of the respective eigenmodes calculated by the ER margin calculating means, the modulation scheme and the power distribution that allocate the combination of the modulation schemes and the power distribution of the eigenmodes having the largest MER margin value to the eigenmodes. And a modulation method / power determination means for determining as follows.

  In the wireless communication apparatus according to the present invention, the modulation scheme / power distribution determination unit further acquires a modulation error ratio when the transmission power is equally distributed among the eigenmodes as an initial MER of each eigenmode. Initial MER acquisition means, wherein the power distribution calculation means for each of the modulation scheme combination patterns, the initial MER of each eigenmode acquired by the initial MER acquisition means, the number of eigenmodes, the MER threshold value, and The power distribution of each eigenmode is calculated so that the MER margin using the power distribution as a parameter is equal in each eigenmode.

とし、前記各固有モードの前記ＭＥＲマージンを

とする、ことを特徴とする。 The radio communication apparatus according to the present invention may be configured such that the number of the eigenmodes is K (positive integer), the number of the eigenmode is k (positive integer), the power distribution ratio of each eigenmode is p _k , The initial MER of each eigenmode acquired by the initial MER acquisition means is μ _k , the MER threshold value of each eigenmode is μ _k ^L, and the sum of the power distribution ratios p _k of each eigenmode is 1, The modulation error ratio of each eigenmode after the transmission power is allocated

And the MER margin for each eigenmode

It is characterized by that.

  Furthermore, the wireless communication method according to the present invention distributes the information bit sequence to be transmitted to each eigenmode, modulates the information bits of each eigenmode with a predetermined modulation scheme, and transmits the information bit transmission power with a predetermined power distribution. In a radio communication method of a MIMO eigenmode transmission system that allocates and transmits by a MIMO transmission method, a predetermined bit error rate is obtained for each combination pattern of modulation methods of each eigenmode and equal in transmission rate. MER margin indicating a difference between a MER threshold value indicating a modulation error ratio set in advance to the modulation error ratio after the transmission power is allocated in the MIMO eigenmode transmission system in each eigenmode. A first step of calculating the power distribution of each eigenmode to be equal, and a combination of the modulation schemes For each of the patterns, a second step of calculating a MER margin of each eigenmode after allocating the transmission power using the power distribution of each eigenmode calculated in the first step; Among the MER margins of the respective eigenmodes calculated in the step, the combination of the modulation schemes and power distribution of the eigenmodes having the largest MER margin value are determined as the modulation scheme and the power distribution to be allocated to each eigenmode. And a fourth step of modulating the information bits in which the information bit sequence is distributed to each eigenmode by the modulation scheme of each eigenmode determined in the third step, The transmission power of the information bits of each eigenmode after the modulation is the power of each eigenmode determined in the third step. A fifth step of allocating at min and having a.

  As described above, according to the present invention, in the MIMO eigenmode transmission system, the combination of the number of modulation bits allocated to each eigenmode and the transmission power in order to minimize the bit error rate under the condition that the transmission rate is constant. The distribution can be easily obtained with a small amount of calculation.

It is a block diagram which shows the structure of the transmission system containing the radio | wireless communication apparatus by embodiment of this invention. It is a block diagram which shows the structure of a bit and electric power distribution control part. It is a flowchart which shows the process of a bit and electric power distribution control part. It is a figure which shows the example of the combination of the modulation system which transmits a total of 8 bits per symbol. It is a figure which shows the example of the MER-BER characteristic in each modulation system. It is a diagram illustrating an example of MER threshold mu _k ^L of each modulation scheme. Is a diagram showing a power distribution ratio p _k and MER margin [Delta] [mu _k of each eigenmode for the combination of the modulation scheme.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a transmission system including a wireless communication device according to an embodiment of the present invention, and shows a functional configuration block of a general N × M-order MIMO system that realizes an eigenmode transmission scheme. In FIG. 1, it is assumed that eigenmodes of K channels are formed. The number of eigenmodes is K.

  The transmission system 1 includes both a wireless communication device 2 that transmits information bit sequences and receives channel information, and a wireless communication device 3 that receives information bit sequences and transmits channel information. Realize communication. FIG. 1 shows an antenna and a configuration for transmitting and receiving an information bit sequence, and an antenna and a configuration for transmitting and receiving channel information are omitted. Hereinafter, the wireless communication device 2 will be referred to as a transmission-side wireless communication device 2 and the wireless communication device 3 will be described as a reception-side wireless communication device 3.

  The wireless communication device 2 on the transmission side includes an S (serial) / P (parallel) conversion unit 21, a bit / power distribution control unit (modulation scheme / power distribution determination unit) 22, a modulation / power distribution unit 23, and a singular value decomposition unit. 26, a transmission weight unit 27, and N transmission antennas 28 are provided. The modulation / power distribution unit 23 includes modulation units 24-1 to 24-K and a power distribution unit 25. The radio communication device 3 on the reception side includes M reception antennas 31, a singular value decomposition unit 32, a reception weight unit 33, demodulation units 34-1 to 34-K, and a P / S conversion unit 35.

  Note that the wireless communication devices 2 and 3 of the actual transmission system 1 include components that implement an error correction function, an interleaving function, and the like, but these are not directly related to the present invention, so that the description is simplified. It is omitted.

[Sender]
First, the wireless communication device 2 on the transmission side will be described. When the transmitting-side radio communication apparatus 2 inputs an information bit sequence to be transmitted, the S / P converter 21 inputs the information bit sequence, converts the serial information bit sequence into information bits of a parallel substream, and The information bits of the K system substreams are output to the modulation units 24-1 to 24-K of the modulation / power distribution unit 23, respectively.

  Here, K is equal to the smaller of the numbers N and M, and K = min (N, M). In the MIMO eigenmode transmission scheme, the substream is synonymous with the eigenmode. Hereinafter, independent orthogonal substreams will be described as eigenmodes.

  Modulation sections 24-1 to 24-K each receive substream information bits (information bits of eigenmodes) from S / P conversion section 21, perform modulation processing independently, and use the modulated information bits as power. The data is output to the distribution unit 25.

  In this case, the modulation units 24-1 to 24-K input the modulation system combination pattern number from the bit / power distribution control unit 22 before performing the modulation process, for example, the modulation system combination pattern number and the modulation system. Are used to identify the modulation schemes corresponding to the modulation units 24-1 to 24-K indicated by the combination pattern numbers of the modulation schemes.

  For example, in FIG. 4 to be described later, when the modulation method combination pattern number b = 8, the modulation unit 24-1 specifies the modulation method as 16QAM, the modulation unit 24-2 specifies the modulation method as 8QAM, The modulation unit 24-3 specifies the modulation method as BPSK. The modulation units 24-1 to 24-K perform modulation processing on the information bits for each modulation bit number corresponding to the modulation method, using the specified modulation method.

  The power distribution unit 25 receives information bits after modulation processing for each eigenmode (for each system) from the modulation units 24-1 to 24-K, and uses the power distribution ratio determined by the bit / power distribution control unit 22. The information bits for each eigenmode are multiplied by a weight corresponding to the power distribution ratio. The power distribution unit 25 outputs information bits after multiplication for each eigenmode to the transmission weight unit 27. In this case, before performing the power distribution process, the power distribution unit 25 inputs the power distribution ratio assigned to each eigenmode from the bit / power distribution control unit 22 and specifies the power distribution ratio of each eigenmode.

  The bit / power distribution control unit 22 combines the optimum modulation schemes allocated to the respective eigenmodes in the modulation units 24-1 to 24-K, and the optimal transmission power allocation (power) allocated to the eigenmodes in the power distribution unit 25. In order to control the distribution ratio) according to a modulation error ratio (MER) in which the bit error rate is reflected, a combination of modulation schemes assigned to each eigenmode and a power distribution ratio are determined.

  Specifically, the bit / power allocation control unit 22 has the same MER margin after power allocation in each eigenmode under the condition that the transmission rate of the information bits transmitted from the wireless communication device 2 is constant (fixed). In addition, the modulation scheme and power distribution ratio at the maximum are determined as the modulation scheme and power distribution ratio of each eigenmode when the bit error rate is minimized. Details of the bit / power distribution control unit 22 will be described later.

  The MER margin indicates a difference between a MER threshold value that indicates a modulation error ratio set in advance for a predetermined bit error rate and an actual modulation error ratio in the transmission system 1. It means that the rate is low.

  Prior to the modulation processing in the modulation units 24-1 to 24-K, the bit / power distribution control unit 22 assigns pattern numbers (combination pattern combination pattern numbers) indicating the combinations of modulation methods determined to the modulation units 24-1 to 24-1. Output to 24-K. The bit / power distribution control unit 22 outputs the determined power distribution ratio to the power distribution unit 25 prior to the power distribution process in the power distribution unit 25.

When the power distribution ratio assigned to the k-th eigenmode determined by the bit / power distribution control unit 22 is p _k , the power distribution ratio p _k is expressed by the following equation. k is a positive integer of 1 to K.

  When the modulation scheme to be assigned to each eigenmode is determined, the number of modulation bits to be assigned to each eigenmode is also uniquely determined. The bit / power distribution control unit 22 may determine a combination of the number of modulation bits instead of the modulation scheme assigned to each eigenmode. In this case, the modulation units 24-1 to 24-K input the combination pattern number of the number of modulation bits from the bit / power distribution control unit 22 before performing the modulation process. Using the table in which the modulation method is defined, the modulation method corresponding to the modulation units 24-1 to 24-K indicated by the combination pattern number of the modulation bit number is specified.

  The singular value decomposition unit 26 acquires channel information of a transmission path formed between the N transmission antennas 28 and the M reception antennas 31. Then, the singular value decomposition unit 26 obtains the right singular matrix V by singular value decomposition of the channel matrix H representing the channel information as shown in the equation (1), and obtains the right singular matrix V as shown in the equation (2). The transmission weight F is output to the transmission weight unit 27.

  The singular value decomposition unit 26 transmits channel information of the transmission path estimated by the reception-side wireless communication apparatus 3 described later via a separate transmission path (wireless communication path or wired communication path). It shall be acquired from the communication device 3. On the other hand, in the bidirectional communication system using the TDD (Time Division Duplex) method, the transmission path from the wireless communication apparatus 2 to the wireless communication apparatus 3 and the transmission path from the wireless communication apparatus 3 to the wireless communication apparatus 2 are considered to be the same. Then, the channel information of the transmission path may be estimated by the wireless communication device 2 on the transmission side, and this information may be directly acquired and used by the singular value decomposition unit 26.

  The transmission weight unit 27 receives the information bits of each eigenmode from the power distribution unit 25, receives the transmission weight F from the singular value decomposition unit 26, multiplies the information bits by the transmission weight F, and generates N transmission antennas. A signal for each transmission antenna system corresponding to each of the 28 is generated. Thereby, eigen beams orthogonal to each eigen mode are generated. The broadcast wave of the signal generated by the transmission weight unit 27 is transmitted from the transmission antenna 28 for each transmission antenna system.

  In this way, the eigenmodes when the bit error rate is minimized by the modulation scheme and the power distribution ratio when the MER margin after power distribution in each eigenmode is equal and maximum by the bit / power distribution control unit 22 are as follows. Modulation scheme and power distribution ratio. Then, modulation processing and power distribution processing are performed with these modulation schemes and power distribution ratios, and broadcast waves are transmitted from the transmission antenna 28.

〔Receiver〕
Next, the receiving-side wireless communication device 3 will be described. When the reception-side wireless communication device 3 receives a broadcast wave transmitted by the transmission-side wireless communication device 2, the reception weight unit 33 of the wireless communication device 3 receives M receptions via the M reception antennas 31. A signal for each reception antenna system corresponding to each of the antennas 31 is input, and a reception weight G is input from the singular value decomposition unit 32. Then, the reception weight unit 33 multiplies the signal for each reception antenna system by the reception weight G, and generates information bits for each eigenmode. As a result, the signal transmitted for each eigenmode is detected without receiving interference ideally. Then, the reception weight unit 33 outputs information bits of each eigenmode to the demodulation units 34-1 to 34-K.

  The singular value decomposition unit 32 acquires channel information of a transmission path estimated by a transmission path estimation unit (not shown) in the wireless communication device 3 of FIG. Then, the singular value decomposition unit 32 obtains the left singular matrix U by performing singular value decomposition on the channel matrix H representing the channel information as in the equation (1). The complex conjugate transpose is set as a reception weight G, and the reception weight G is output to the reception weight unit 33.

  The demodulating units 34-1 to 34-K each receive the corresponding eigenmode information bits from the reception weight unit 33, and independently perform demodulation processing in the same modulation scheme as the corresponding modulating units 24-1 to 24-K. Then, the demodulated information bits are output to the P / S converter 35.

  Note that the demodulation units 34-1 to 34-K have received the modulation schemes used in the modulation units 24-1 to 24-K included in the transmission-side wireless communication device 2 from the transmission-side wireless communication device 2. It is assumed that it is obtained from control information such as a header and retained.

  The P / S conversion unit 35 receives eigenmode information bits from the demodulation units 34-1 to 34-K, converts the K system information bits into a serial information bit sequence, and outputs it as the original information bit sequence. To do.

  In this way, the broadcast wave transmitted from the radio communication device 2 on the transmission side is received by the reception antenna 31, restored to the substream of each eigenmode, and restored to the original information bit sequence.

[Bit / Power Distribution Control Unit 22]
Next, the bit / power distribution control unit 22 provided in the transmission-side wireless communication device 2 shown in FIG. 1 will be described in detail. As described above, the bit / power distribution control unit 22 determines the MER margin after power distribution in each eigenmode under the condition that the transmission rate of information bits transmitted from the wireless communication device 2 on the transmission side is constant (fixed). The modulation scheme and power distribution ratio when equal and maximum are determined as the modulation scheme and power distribution ratio of each eigenmode when the bit error rate is minimized.

  FIG. 2 is a block diagram showing a configuration of the bit / power distribution control unit 22, and FIG. 3 is a flowchart showing processing of the bit / power distribution control unit 22. As shown in FIG. 2, the bit / power distribution control unit 22 includes an initial MER acquisition unit 11, a power distribution calculation unit 12, a MER margin calculation unit 13, and a modulation scheme / power determination unit 14.

Hereinafter, a description will be given with reference to FIGS. First, the initial MER acquisition unit 11 of the bit / power distribution control unit 22 transmits the signal of each eigenmode with the same power distribution when the wireless communication device 2 transmits the transmission power equally between the eigenmodes. ), The initial MER μ _k (= μ ₁ ,..., Μ _K ) of each eigenmode is acquired (step S301). For example, when the number of transmission antennas 28 is N = 4 and the number of reception antennas 31 is M = 8, the initial MER acquisition unit 11 calculates K = min (N, M) = 4, and K = 4 is unique. The initial MER μ _k (= μ ₁ , μ ₂ , μ ₃ , μ ₄ ) is acquired for each mode. Then, the initial MER acquisition unit 11 outputs the initial MER μ _k (= μ ₁ ,..., Μ _K ) to the power distribution calculation unit 12.

As a method for obtaining the initial MER, for example, it is used that the square of the singular value of the channel matrix H obtained by the equation (1) represents the channel gain of each eigenmode in eigenmode transmission. That is, the initial MER acquisition unit 11 calculates the singular value of the channel matrix H, divides the square of the singular value by the Gaussian noise power estimated separately, and converts the value of the division result into MER, thereby initial MER μ _k (= Μ ₁ ,..., Μ _K ) is acquired.

In addition, as another example of the technique for acquiring the initial MER, there is also a technique of actually measuring the MER at the time of equal power allocation during communication using a training signal. That is, the initial MER acquisition unit 11 outputs the same power distribution ratio for each eigenmode to the power distribution unit 25, and causes the power distribution unit 25 to distribute the transmission power of each eigenmode to equal power. At this time, the broadcast wave of the training signal transmitted from the radio communication device 2 on the transmission side is received by the radio communication device 3 on the reception side, and the radio communication device 3 measures the MER in each eigenmode. Then, the wireless communication device 2 receives the MER of each eigenmode from the wireless communication device 3 via a separate transmission line, and the initial MER acquisition unit 11 converts the received MER of each eigenmode to the initial value of each eigenmode. Acquired as MER μ _k (= μ ₁ ,..., Μ _K ).

  Here, it is assumed that there are B types of combinations of modulation schemes that realize a fixed transmission rate. FIG. 4 is a diagram illustrating an example of combinations of modulation schemes that transmit a total of 8 bits per symbol, and illustrates a case where the number of eigenmodes is K = 3. Assuming that a 1-bit modulation scheme from BPSK to 256QAM is used as the modulation scheme, combinations of modulation schemes with equal transmission rates are discrete, and there are 10 parameters B = 10. Here, the combination pattern numbers b = 1,.

  When the modulation method is 256QAM, the number of modulation bits is 8, when the modulation method is 128QAM, the number of modulation bits is 7, and when the modulation method is 64QAM, 32QAM, 16QAM, and 8QAM, the number of modulation bits is 6, respectively. 5,4,3. When the modulation scheme is QPSK or BPSK, the number of modulation bits is 2 or 1, respectively.

  It is assumed that the k-th eigenmode (k-th eigenmode) has a channel gain that is greater than or equal to the (k + 1) -th eigenmode. Further, it is assumed that the number of modulation bits in the k-th eigenmode is always greater than or equal to the number of modulation bits in the (k + 1) -th eigenmode. In FIG. 4, “-” indicates that there is no assignment. That is, the eigenmode indicates that it is not used for data transmission. Specifically, the modulation scheme / power determination unit 14 described later sets the power distribution ratio of the eigenmode to 0 and outputs it to the power distribution unit 25 so that data transmission in the eigenmode is not performed. To do.

2 and 3, the bit / power distribution control unit 22 sets the modulation scheme combination pattern number b = 1, which is an initial value. Then, the bit / power distribution control unit 22 performs processing of steps S303 to S306 described later for each of the modulation scheme combination pattern numbers b (b = 1,..., 10 in the example of FIG. 4). Thus, the power distribution ratio p _k and the MER margin Δμ _k are calculated.

The bit / power distribution control unit 22 determines whether or not the combination pattern number b of the modulation scheme is equal to or less than the parameter B (step S302). If the bit / power distribution control unit 22 determines in step S302 that the combination pattern number b of the modulation scheme is equal to or less than the parameter B (b = 1,..., B), the bit / power distribution control unit 22 performs steps S303 to S306 described later. By processing, the power distribution ratio p _k and the MER margin Δμ _k for the modulation scheme combination pattern number b are calculated.

を設定する（ステップＳ３０３）。ここで、

は、電力配分後のＭＥＲを示し、μ_k ^Lは、ＭＥＲ閾値を示す。つまり、ＭＥＲマージンΔμ_kは、電力配分後のＭＥＲからＭＥＲ閾値を減算した減算結果（電力配分後のＭＥＲとＭＥＲ閾値との間の差）で定義される。 The power distribution calculation means 12 and the MER margin calculation means 13 of the bit / power distribution control unit 22

Is set (step S303). here,

Indicates MER after power distribution, and μ _k ^L indicates the MER threshold. That is, the MER margin Δμ _k is _defined by a subtraction result obtained by subtracting the MER threshold value from the MER after power distribution (difference between the MER after power distribution and the MER threshold value).

は、初期ＭＥＲμ_kと電力配分後に増減した電力分１０ｌｏｇＫｐ_kとを加算した結果であり、次式で表される。

ここで、第ｋ固有モードの電力配分比率ｐ_kは、前記式（１０）を満たす。 MER after power distribution shown in step S303

Is a result of adding the power component 10LogKp _k which increases or decreases the initial MERmyu _k and power after allocation is expressed by the following equation.

Here, the power distribution ratio p _k of the k-th eigenmode satisfies the formula (10).

The MER threshold μ _k ^L shown in step S303 is a modulation error ratio (MER) indicating a certain bit error rate (BER) under an additive white Gaussian noise (AWGN). FIG. 5 is a diagram illustrating an example of the MER-BER characteristic in each modulation scheme, and FIG. 6 is a diagram illustrating an example of the MER threshold value μ _k ^{L in} each modulation scheme.

In FIG. 5, the vertical axis represents the bit error rate (BER), and the horizontal axis represents the modulation error ratio (MER) [dB]. The modulation error rate (MER) corresponding to BER = 1 × 10 ⁻⁴ shown in FIG. 5 is used as the MER threshold μ _k ^L , and FIG. 6 shows each modulation when BER = 1 × 10 ⁻⁴ is set. The MER threshold μ _k ^{L for the} scheme is shown.

Therefore, the MER threshold μ _k ^L is a modulation error value (MER) obtained from the example of the MER-BER characteristic shown in FIG. 5, and is a preset value in the modulation scheme assigned to the k-th eigenmode. Used.

In the above example, the modulation error rate (MER) corresponding to BER = 1 × 10 ⁻⁴ in the example of the MER-BER characteristic shown in FIG. 5 is used as the MER threshold μ _k ^L. A modulation error rate (MER) corresponding to a predetermined BER in a section (for example, a section of 1 × 10 ⁻⁵ <BER <1 × 10 ⁻² ) in which the curves of the respective modulation schemes in the example of the BER characteristic are substantially parallel is used. You may do it. In this case, regardless of which MER threshold value μ _k ^L is used, the modulation scheme combination pattern number b and the power distribution ratio p _k determined in step S307 described later are the same.

Returning to FIG. 2 and FIG. 3, the power distribution calculating means 12 of the bit and power allocation control unit 22 inputs the initial MERmyu _k from an initial MER acquisition unit 11 inputs the MER threshold mu _k ^L set in advance .

Here, assuming an equation in which the equation (11) is substituted into the MER margin Δμ _k set in step S303, the parameters for calculating the MER margin Δμ _k are the MER threshold μ _k ^L , the initial MER μ _k , The number of eigenmodes K and the power distribution ratio p _k . Among these parameters, the MER threshold μ _k ^L , the initial MER μ _k and the number K of eigenmodes are constants. Therefore, the MER margin Δμ _k is expressed by an expression using only the power distribution ratio p _k as a variable.

Power allocation calculating means 12, the formula to obtained by substituting the equation (11) in MER margin [Delta] [mu _k set in step S303, by substituting the MER threshold mu _k ^L, initial MERmyu _k and the number K of eigenmodes Thus, an expression of the MER margin Δμ _k expressed by a variable of only the power distribution ratio p _k is obtained.

The power distribution calculating unit 12 calculates the power distribution ratio p _k by solving the simultaneous equations shown in the following equations so that the K MER margins Δμ _k are equal in each eigenmode (step S304). i and j are positive integers of 1 to K. The power distribution calculating unit 12 outputs the calculated power distribution ratio p _k to the MER margin calculating unit 13 and the modulation scheme / power determining unit 14.

The MER margin calculation unit 13 of the bit / power distribution control unit 22 receives the power distribution ratio p _k calculated by the power distribution calculation unit 12 and uses the input power distribution ratio p _k as a variable only for the power distribution ratio p _k. MER margin Δμ _k is calculated by substituting it into the equation of MER margin Δμ _k expressed by (Step S305). Then, the MER margin calculating unit 13 outputs the calculated MER margin Δμ _k to the modulation method / power determining unit 14.

In the example shown in FIG. 4, when the modulation method combination pattern number b = 1, it indicates that only the first eigenmode is used, and the second eigenmode and the third eigenmode are not used. In this case, the power distribution calculation unit 12 calculates the power distribution ratio p ₁ = 1 assuming that all power is distributed to the first eigenmode. The MER margin calculation means 13 has a MER threshold value of 256 QAM μ ₁ ^L = 30.3 [dB] (FIG. 6, the modulation method of the first eigenmode is 256 QAM (FIG. 4)), the initial MER μ ₁ and the number of eigenmodes K = 3 and the MER margin Δμ ₁ is calculated from the power distribution ratio p ₁ = 1.

  The bit / power distribution control unit 22 increments the combination pattern number b of the modulation method (step S306), and proceeds to step S302. Then, as long as the modulation scheme combination pattern number b is equal to or smaller than the parameter B (b = 1,..., B), the processing of the above-described steps S303 to S306 is performed.

Thus, for each of the modulation scheme combination pattern numbers b = 1,..., B, the power distribution ratio p _k of each eigenmode is calculated in step S304, and the MER margin Δμ of each eigenmode in step S305. _k is calculated.

FIG. 7 is a diagram showing the power distribution ratio p _k and MER margin Δμ _k of each eigenmode for a combination of modulation schemes, and shows an example when the number of eigenmodes is K = 3. This data group includes power distribution ratios p ₁ , p ₂ , p ₂ , p ₂ , p ₂ , p ₂ , p ₂ , p ₂ , p ₂ , p ₂ , p ₂ , p ₂ ,. p ₃ and the MER margin Δμ ₁ , Δμ ₂ , Δμ _{3 of} each eigenmode calculated by the MER margin calculating unit 13 in step S 305.

“-” Indicates that no modulation scheme is assigned and the calculation is not performed by the power distribution calculating unit 12 and the MER margin calculating unit 13. For example, when the modulation scheme combination pattern number b = 1, as shown in FIG. 4, there is no modulation scheme assignment in the second eigenmode and the third eigenmode, so the power distribution ratio p ₂ of the second eigenmode, The power distribution ratio p ₃ of the _third eigenmode, the MER margin Δμ ₂ of the second eigenmode, and the MER margin Δμ ₃ of the third eigenmode are not calculation targets. Also, in the combination pattern numbers b = 2 and 3 of the modulation scheme, as shown in FIG. 4, since there is no modulation scheme assignment in the third eigenmode, the power distribution ratio p ₃ of the third eigenmode and the third eigenmode The mode MER margin Δμ ₃ is not subject to calculation. In this case, the power distribution calculation unit 12 sets 0 to the power distribution ratio p _k that is not a calculation target, and outputs it to the modulation scheme / power determination unit 14. As a result, the power distribution unit 25 multiplies the information bits by 0 in the eigenmode in which the power distribution ratio p _k = 0 is input, so that data transmission in the eigenmode is not performed.

  2 and 3, when the bit / power distribution control unit 22 determines that the combination pattern number b of the modulation scheme exceeds the parameter B in step S302 (step S302: b> B), the step The process proceeds to S307.

The modulation method / power determination unit 14 of the bit / power distribution control unit 22 inputs the power distribution ratio p _k of each eigenmode calculated by the power distribution calculation unit 12 for each combination pattern number b of the modulation method, and enter the MER margin [Delta] [mu _k of each eigenmode that is calculated by the MER margin calculating unit 13, and stores in the memory (not shown). Thereby, for example, the data group shown in FIG. 7 is stored in the memory.

Modulation scheme and power determination unit 14, from the memory, the combination pattern number b = 1 modulation scheme, reads the MER margin [Delta] [mu _k of · · · B, among the read MER margin [Delta] [mu _k, has the largest MER margin value The modulation system combination pattern number b is specified, and the power distribution ratio p _k of each eigenmode for the specified modulation system combination pattern number b is specified.

  Here, since the bit error rate becomes lower as the MER margin value is larger, by using the modulation method of the combination pattern number b of the modulation method having the largest MER margin value, the modulation method of the other combination pattern number b is changed. The bit error rate can be reduced as compared with the case of using it. That is, the bit error rate can be minimized in the modulation schemes of all the combination pattern numbers b.

The modulation scheme / power determination means 14 determines the combination pattern number b of the identified modulation scheme and the power distribution ratio p _k of each eigenmode as the optimum transmission control parameters (step S307). Then, the modulation scheme / power determination means 14 outputs the combination pattern number b of the specified modulation scheme to the modulation sections 24-1 to 24-K, and outputs the power distribution ratio p _k of each identified eigenmode to the power distribution section. To 25.

As a result, the modulation units 24-1 to 24-K define a table in which, for example, the combination pattern number b of the modulation scheme shown in FIG. Can be used to specify the modulation scheme indicated by the combination pattern number b of the modulation scheme. Further, the power distribution unit 25 can identify the power distribution ratio p _k of each eigenmode before performing the power distribution process.

As described above, according to the wireless communication device 2 on the transmission side according to the embodiment of the present invention, the initial MER acquisition unit 11 assumes that each eigenmode is assumed to have been transmitted with equal power distribution. The initial MERμ _k was obtained. Then, the power distribution calculation means 12 sets the initial MER μ _k and the number K of eigenmodes as constants for each combination pattern having the same transmission rate between the modulation scheme combination patterns, and also the MER corresponding to the modulation scheme combination pattern. Using the threshold μ _k ^L as a constant, an expression of the MER margin Δμ _k after power distribution represented by a variable of only the power distribution ratio p _k is obtained, and in each eigenmode, the K MER margins Δμ _k are equal. The power distribution ratio p _k is calculated. The MER margin calculation unit 13 converts the power distribution ratio p _k calculated by the power distribution calculation unit 12 for each combination pattern of the modulation scheme into an expression of a MER margin Δμ _k that is represented by a variable of only the power distribution ratio p _k. By substituting, the MER margin Δμ _k is calculated.

Then, the modulation scheme / power determination unit 14 specifies the combination pattern of the modulation scheme having the largest MER margin value among the MER margins Δμ _k for each of the modulation scheme combination patterns calculated by the MER margin calculation unit 13. Then, for the combination pattern of the specified modulation scheme, the power distribution ratio p _k of each eigenmode calculated by the power distribution calculating unit 12 is specified, and the combination pattern of the specified modulation scheme and the power distribution ratio p _k of each eigenmode Are determined as the optimum transmission control parameters.

The modulation units 24-1 to 24-K perform modulation processing for each eigenmode in the modulation scheme indicated by the modulation scheme combination pattern determined by the modulation scheme / power determination unit 14, and the power distribution unit 25 performs modulation. Transmission power is distributed for each eigenmode at the power distribution ratio p _k determined by the scheme / power determination means 14.

As a result, the power distribution ratio p _k is determined on condition that the MER margin Δμ _k after power distribution becomes equal between the eigenmodes. Therefore, the power distribution ratio p _k is uniquely determined to reduce the calculation load. Can do. Further, since the combination of modulation schemes for each eigenmode that maximizes the MER margin Δμ _k after power distribution is specified, transmission processing is performed using the modulation scheme and power distribution ratio p _k for each specified eigenmode. In this case, the bit error rate on the receiving side is the smallest among the combination patterns of the modulation schemes. This is because transmission quality with the same bit error rate can be realized in all eigenmodes, and the bit error rate decreases as the MER margin value increases, so that the MER margin Δμ _k after power distribution is maximized. by using the modulation scheme and power distribution ratio p _k when made, as a result, because the bit error rate of the information bit sequence transmission and reception target is minimized.

  Further, since the method of Patent Document 1 described above is based on an application control method based on the water injection theorem, when the number of modulation bits has only a discrete combination as in an actual system, the viewpoint of transmission characteristics and hardware In view of the ease of hardware implementation. In contrast, the embodiment of the present invention is effective in that the processing load is reduced when the number of modulation bits is a discrete combination, and is an adaptive control that is intended for a real system and suitable for hardware implementation. Can be realized. Further, in the methods of Patent Document 2 and Non-Patent Document 1 described above, it is necessary to perform calculations using complex bit error rate approximation formulas, calculations of total throughput, etc., by changing the power distribution ratio little by little. Therefore, complicated operations were necessary. On the other hand, in the embodiment of the present invention, the power distribution ratio can be uniquely determined, and the processes shown in FIG. 3 such as the four arithmetic operations such as the formulas (11) and (12) and the substitution process may be performed. Since no calculation is required, the amount of calculation is small and the processing load is low.

  Therefore, in the MIMO eigenmode transmission scheme, the combination of the number of modulation bits that minimizes the bit error rate and the transmission power distribution are combinations in which the MER margin after power distribution in each eigenmode is equal and maximized. Can do. That is, the combination of the number of modulation bits to be allocated to each eigenmode and the distribution of transmission power for minimizing the bit error rate can be easily obtained with a small amount of calculation.

The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the technical idea thereof. In the above-described embodiment, the initial MER acquisition unit 11 of the bit / power distribution control unit 22 included in the wireless communication device 2 on the transmission side assumes that each eigenmode signal is transmitted with equal power distribution. In order to obtain the initial MER μ _k (= μ ₁ ,..., Μ _K ) of the mode, for example, the square of the singular values of the channel matrix H obtained by the above equation (1) is the eigenmode transmission in the eigenmode transmission. A method using the channel gain is used, or a method of actually measuring the MER at the time of equal power allocation using a training signal during communication. The present invention does not limit the method of acquiring the initial MER μ _k (μ ₁ ,..., Μ _K ), and other methods may be used.

DESCRIPTION OF SYMBOLS 1 Transmission system 2 and 3 Wireless communication apparatus 11 Initial MER acquisition means 12 Power distribution calculation means 13 MER margin calculation means 14 Modulation method / power determination means 21 S / P conversion section 22 Bit / power distribution control section 23 Modulation / power distribution section 24-1 to 24-K Modulation unit 25 Power distribution unit 26, 32 Singular value decomposition unit 27 Transmission weight unit 28 Transmission antenna 31 Reception antenna 33 Reception weight unit 34-1 to 34-K Demodulation unit 35 P / S conversion unit

Claims (4)

The information bit sequence to be transmitted is allocated to each eigenmode, the information bits of each eigenmode are modulated by a predetermined modulation scheme, the transmission power of the information bits is allocated by a predetermined power allocation, and the MIMO transmission scheme is used. In the wireless communication device of the MIMO eigenmode transmission system to transmit,
A modulation scheme and a power allocation determination unit for determining the modulation scheme and the power allocation to be assigned to each eigenmode;
A modulation unit that modulates the information bits in which the information bit sequence is allocated to each eigenmode, using the modulation scheme of each eigenmode determined by the modulation scheme / power distribution determination unit;
A power distribution unit that distributes the transmission power of information bits of each eigenmode modulated by the modulation unit in the power distribution of each eigenmode determined by the modulation scheme / power distribution determination unit, and
The modulation method / power distribution determination unit
A MER threshold indicating a modulation error ratio set in advance with respect to a predetermined bit error rate for each combination pattern of modulation schemes of each eigenmode and having the same transmission rate, and the MIMO eigenmode transmission system Power distribution calculating means for calculating the power distribution of each eigenmode so that the MER margin indicating the difference between the modulation error ratio after allocating the transmission power in FIG.
MER margin calculating means for calculating the MER margin of each eigenmode after allocating the transmission power, using the power distribution of each eigenmode calculated by the power distribution calculating means for each of the combination patterns of the modulation schemes. When,
Of the MER margin of each eigenmode calculated by the MER margin calculating means, the modulation scheme and the power for allocating the combination and power distribution of each eigenmode having the largest MER margin value to each eigenmode. A wireless communication apparatus comprising: a modulation method / power determination means for determining distribution. The wireless communication device according to claim 1,
The modulation method / power distribution determination unit
Furthermore, it comprises an initial MER acquisition means for acquiring a modulation error ratio when the transmission power is equally distributed among the eigenmodes as an initial MER of each eigenmode,
The power distribution calculating means includes
For each combination pattern of the modulation scheme, the initial MER of each eigenmode acquired by the initial MER acquisition unit, the number of eigenmodes, the MER threshold, and the MER margin using the power distribution as parameters are respectively A wireless communication apparatus that calculates power distribution of each eigenmode so as to be equal in each mode. The wireless communication device according to claim 2,
The number of the eigenmodes is K (positive integer), the eigenmode number is k (positive integer), the power distribution ratio of each eigenmode is p _k , and each eigenmode acquired by the initial MER acquisition unit The initial MER of the mode is μ _k , the MER threshold value of each eigenmode is μ _k ^L , the total power distribution ratio p _k of each eigenmode is 1, and each eigen after the transmission power is allocated Modulation error ratio of mode

And the MER margin for each eigenmode

A wireless communication device characterized by that. The information bit sequence to be transmitted is allocated to each eigenmode, the information bits of each eigenmode are modulated by a predetermined modulation scheme, the information bit transmission power is allocated by a predetermined power distribution, and transmitted by a MIMO transmission scheme In the wireless communication method of the MIMO eigenmode transmission system,
A MER threshold indicating a modulation error ratio set in advance with respect to a predetermined bit error rate for each combination pattern of modulation schemes of each eigenmode and having the same transmission rate, and the MIMO eigenmode transmission system A first step of calculating a power distribution of each eigenmode so that a MER margin indicating a difference between the modulation error ratio after the transmission power is allocated in the eigenmode is equal in each eigenmode;
Second step of calculating the MER margin of each eigenmode after allocating the transmission power using the power distribution of each eigenmode calculated in the first step for each of the combination patterns of the modulation schemes. When,
Among the MER margins of the respective eigenmodes calculated in the second step, the modulation scheme and the power for allocating the combination and power distribution of the modulation modes of each eigenmode having the largest MER margin value to each eigenmode. A third step to determine the distribution;
A fourth step of modulating the information bits in which the information bit sequence is assigned to each eigenmode, respectively, with the modulation scheme of each eigenmode determined in the third step;
A fifth step of allocating the transmission power of information bits of each eigenmode after modulation in the power distribution of each eigenmode determined in the third step;
A wireless communication method comprising:

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