Wireless communication device, wireless communications system, communication control method, and communication control program

Abstract

To provide a wireless communication device that can suppress deterioration of communication quality.SOLUTION: A wireless communication device comprises: a demodulator that demodulates a plurality of uplink signals received from a plurality of user terminals, respectively; an estimation unit that estimates a propagation channel for each of a plurality of layers from a plurality of reference signals contained in the plurality of demodulated uplink signals; a weight calculation unit that calculates a precoding weight from an estimated result of the propagation channel; a precoding unit that applies the precoding weight to a transmission signal; and a modulator that modulates the transmission signal to which the precoding weight has been applied and transmits the signal toward the plurality of user terminals as a downlink signal. The weight calculation unit calculates the precoding weight such that a ratio between the plurality of layers of amplitudes of the downlink signals corresponding to the plurality of layers is adjusted to a prescribed ratio.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a wireless communication device, a wireless communication system, a communication control method, and a communication control program.

Background Art

[0002] In mobile communication using wireless communication, a method of improving frequency efficiency by spatially multiplexing communication signals by utilizing the correlation of radio wave propagation channels has begun to be adopted. As spatial multiplexing techniques, various methods have been proposed, and methods such as zero forcing (ZF) and minimum mean square error (MMSE) are widely used. Methods such as ZF and MMSE can improve the signal-to-noise ratio (SNR) of communication by forming a null with respect to the receiving terminal positions of layers other than the communication target using the inverse matrix of the estimated propagation channel matrix. Techniques related to wireless communication using spatial multiplexing techniques are disclosed in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, the propagation channel changes over time and there are errors in the estimation of the propagation channel. Therefore, the propagation channel estimated from the uplink signal is likely to be different from the actual propagation channel at the time of downlink signal transmission. Here, since the wireless communication device of the related art calculates the precoding weight to be applied to the downlink signal from the estimation result of the propagation channel different from the actual propagation channel, it cannot accurately form a null for the receiving terminal of the layer other than the communication target layer, and as a result, there is a possibility of causing interference between layers. That is, the wireless communication device of the related art has a problem that the communication quality deteriorates.

[0005] One object of the present disclosure is to provide a wireless communication device, a wireless communication system, a communication control method, and a communication control program that solve the above-described problems.

Means for Solving the Problems

[0006] A wireless communication device according to an aspect of the present disclosure includes a demodulator that demodulates a plurality of uplink signals corresponding to a plurality of layers received from each of a plurality of user terminals, and a plurality of reference signals included in each of the demodulated plurality of uplink signals. An estimation unit that estimates the propagation channel of each of the plurality of layers, a weight calculation unit that calculates a precoding weight from the estimation result of the propagation channel, and a precoding unit that applies the precoding weight to a transmission signal for each of the plurality of layers. And a modulator that modulates the transmission signal to which the precoding weight is applied and transmits it as a downlink signal to the plurality of user terminals. The weight calculation unit is configured to calculate the precoding weight such that the ratio between the amplitudes of the downlink signals corresponding to each of the plurality of layers is adjusted to a predetermined ratio.

[0007] A communication control method according to one aspect of the present disclosure includes a computer demodulating a plurality of uplink signals corresponding to a plurality of layers received from each of a plurality of user terminals, estimating a propagation channel of each of the plurality of layers from a plurality of reference signals included in each of the demodulated plurality of uplink signals, calculating a precoding weight from the estimation result of the propagation channel, applying the precoding weight to a transmission signal for each of the plurality of layers, modulating the transmission signal to which the precoding weight has been applied, and transmitting the modulated signal as a downlink signal to the plurality of user terminals. In the calculation of the precoding weight, the precoding weight is calculated such that a ratio of amplitudes of the downlink signals corresponding to the plurality of layers is adjusted to a predetermined ratio among the plurality of layers.

[0008] A communication control program according to one aspect of the present disclosure causes a computer to execute a process of demodulating a plurality of uplink signals corresponding to a plurality of layers received from each of a plurality of user terminals, a process of estimating a propagation channel of each of the plurality of layers from a plurality of reference signals included in each of the demodulated plurality of uplink signals, a process of calculating a precoding weight from the estimation result of the propagation channel, a process of applying the precoding weight to a transmission signal for each of the plurality of layers, and a process of modulating the transmission signal to which the precoding weight has been applied and transmitting the modulated signal as a downlink signal to the plurality of user terminals. In the process of calculating the precoding weight, the precoding weight is calculated such that a ratio of amplitudes of the downlink signals corresponding to the plurality of layers is adjusted to a predetermined ratio among the plurality of layers.

Advantages of the Invention

[0009] The present disclosure can provide a wireless communication device, a wireless communication system, a communication control method, and a communication control program capable of preventing deterioration of communication quality.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described with reference to the drawings. Note that since the drawings are simplified, the technical scope of the embodiments should not be narrowly interpreted based on the description of these drawings. Also, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] In the following embodiments, when necessary for convenience, they will be divided into multiple sections or embodiments for description. However, unless otherwise explicitly stated, they are not unrelated to each other, and one is related to the other as a partial or complete modification example, application example, detailed description, supplementary description, etc. Also, in the following embodiments, when referring to the number of elements, etc. (including the number, numerical value, quantity, range, etc.), unless otherwise explicitly stated and except for cases where it is clearly limited to a specific number in principle, it is not limited to that specific number, and it may be more than or less than the specific number.

[0013] Furthermore, in the following embodiments, the constituent elements (including operation steps, etc.) are not necessarily essential unless otherwise explicitly stated and except for cases where they are clearly considered essential in principle. Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of the constituent elements, unless otherwise explicitly stated and except for cases where it is clearly not the case in principle, it includes those that are substantially approximate or similar to the shape, etc. This also applies to the above-mentioned numbers, etc. (including the number, numerical value, quantity, range, etc.).

[0014] <Embodiment 1> FIG. 1 is a block diagram showing a configuration example of a wireless communication system 1 in which a base station apparatus according to the present disclosure is used. As shown in FIG. 1, the wireless communication system 1 includes a base station apparatus AP and K user terminals UE1 to UEK. Note that K is an integer of 2 or more. In the example of FIG. 1, K = 2, that is, two user terminals UE1 and UE2 are provided. The base station apparatus AP performs wireless communication with the user terminals UE1 and UE2 simultaneously and at the same frequency by using spatial multiplexing technology.

[0015] In the example of FIG. 1, the user terminal UE1 is located closer to the base station apparatus AP than the user terminal UE2. Also, in the example of FIG. 1, the user terminals UE1 and UE2 are each communicating using a different layer, one layer at a time. Therefore, the number of layers is K for K user terminals UE1 to UEK. Here, a layer is also called a stream and means a different data flow that is transmitted or received at the same time and in the same frequency band.

[0016] Each user terminal UE1 and UE2 transmits an uplink signal UL including a reference signal RS. The base station apparatus AP estimates the propagation channels of each user terminal UE1 and UE2 with reference to the reference signals RS from each user terminal UE1 and UE2. Then, the base station apparatus AP calculates a precoding weight from the estimated propagation channels using, for example, a zero-forcing (ZF) spatial multiplexing technique. ZF is an abbreviation for Zero Forcing. Then, the base station apparatus AP applies the calculated precoding weight to each of the transmission signals of the two layers corresponding to the user terminals UE1 and UE2. Specifically, the base station apparatus AP performs distribution, weighting, and synthesis according to the calculated precoding weight for each of the transmission signals of the two layers corresponding to the user terminals UE1 and UE2. Then, the base station apparatus AP up-converts the transmission signal to which the precoding weight has been applied to the carrier frequency and transmits it externally from a plurality of antennas as a downlink signal DL. Each user terminal UE1 and UE2 receives the downlink signal DL transmitted from the plurality of antennas of the base station apparatus AP. In this way, wireless communication is performed simultaneously and at the same frequency between the base station apparatus AP and the user terminals UE1 and UE2.

[0017] FIG. 2 is a block diagram showing an overview of the transceiver unit of the base station apparatus AP. The base station apparatus AP is a TDD (Time Division Duplex) wireless communication apparatus that supports the digital beamforming format. TDD is the abbreviation of Time Division Duplex. Specifically, the base station apparatus AP includes a precoding unit 11, M OFDM modulators 12, M OFDM demodulators 15, a channel estimation unit 16, and a weight calculation unit 17. M is an integer larger than K. OFDM is the abbreviation of Orthogonal Frequency Division Multiplexing. The M OFDM modulators 12 are also collectively referred to as the OFDM modulator 12. The M OFDM demodulators 15 are also collectively referred to as the OFDM demodulator 15.

[0018] The M OFDM demodulators 15 demodulate the uplink signals UL received from each of the user terminals UE1 and UE2 using the orthogonal frequency division multiplexing method. Each OFDM demodulator 15 demodulates the uplink signals UL corresponding to two layers corresponding to the user terminals UE1 and UE2. The channel estimation unit 16 estimates the propagation channels of each of the two layers corresponding to the user terminals UE1 and UE2 by referring to the reference signal RS included in the uplink signal UL demodulated by the M OFDM demodulators 15. The weight calculation unit 17 calculates the precoding weight from the estimated propagation channel using, for example, the zero-forcing (ZF) spatial multiplexing technique. The precoding unit 11 applies the calculated precoding weight to the transmission signals directed to each of the user terminals UE1 and UE2. The M OFDM modulators 12 modulate the transmission signal to which the precoding weight is applied using the orthogonal frequency division multiplexing method, and then up-convert it to the carrier frequency and transmit it as the downlink signal DL to the user terminals UE1 and UE2.

[0019] FIG. 3 is a block diagram showing a more specific configuration example of the transceiver unit of the base station apparatus AP. The base station apparatus AP is a TDD (Time Division Duplex) type wireless communication apparatus corresponding to the digital beamforming format. TDD is an abbreviation for Time Division Duplex. Specifically, the base station apparatus AP includes a precoding unit 11, M OFDM modulators 12, M switches 13, M antennas 14, M OFDM demodulators 15, a channel estimation unit 16, and a weight calculation unit 17. M is an integer greater than K. OFDM is an abbreviation for Orthogonal Frequency Division Multiplexing. The M OFDM modulators 12 are also collectively referred to as the OFDM modulator 12. The M OFDM demodulators 15 are also collectively referred to as the OFDM demodulator 15.

[0020] The M switches 13 switch between the path from the M OFDM modulators 12 to the M antennas 14 and the path from the M antennas 14 to the M OFDM demodulators 15. The M antennas 14 transmit the transmission signals up-converted to the carrier frequency by each of the M OFDM modulators 12 to the outside as the downlink signal DL, or receive the uplink signal UL from the outside wirelessly. The M OFDM demodulators 15 demodulate the uplink signal UL received via the M antennas 14 using the orthogonal frequency division multiplexing method. Each OFDM demodulator 15 demodulates the uplink signal UL corresponding to two layers corresponding to the user terminals UE1 and UE2. The channel estimation unit 16 estimates the propagation channels of each of the two layers corresponding to the user terminals UE1 and UE2 by referring to the reference signal RS included in the uplink signal UL demodulated by the M OFDM demodulators 15. The weight calculation unit 17 calculates the precoding weight from the estimated propagation channel using, for example, the zero-forcing (ZF) spatial multiplexing technique. The precoding unit 11 applies the calculated precoding weight to the transmission signals directed to each of the user terminals UE1 and UE2. The M OFDM modulators 12 modulate the transmission signal to which the precoding weight is applied using the orthogonal frequency division multiplexing method, then up-convert it to the carrier frequency, and transmit it to the outside from the M antennas 14 as the downlink signal DL.

[0021] Figure 4 is a block diagram showing a configuration example of the weight calculation unit 17. As shown in Figure 4, the weight calculation unit 17 includes an inverse matrix calculation unit 171, an amplitude normalization unit 172, and a scale adjustment unit 173. Details of the weight calculation unit 17 will be described later.

[0022] Subsequently, the operation of the wireless communication system 1 will be described with reference to Figure 5. Figure 5 is a flowchart showing the operation of the wireless communication system 1.

[0023] First, user terminals UE1 and UE2 each transmit an uplink signal UL including a reference signal RS (step S101). Note that both user terminals UE1 and UE2 transmit uplink signals UL in the same frequency band. However, for the reference signals RS included in their respective uplink signals UL, in order to avoid interference, the user terminals UE1 and UE2 perform frequency multiplexing by changing the subcarrier arrangement of OFDM modulation and then transmit. The resource elements where the user terminal UE1 arranges the reference signal RS are blank for the user terminal UE2, and the resource elements where the user terminal UE2 arranges the reference signal RS are blank for the user terminal UE1.

[0024] After that, the base station apparatus AP receives the uplink signals UL transmitted from each of the user terminals UE1 and UE2 via a plurality of antennas 14 (step S102).

[0025] After that, in the base station apparatus AP, the OFDM demodulator 15 OFDM-demodulates the uplink signals UL from each of the user terminals UE1 and UE2 received via each antenna 14 (step S103).

[0026] After that, in the base station apparatus AP, the channel estimation unit 16 estimates the propagation channels of each of the two layers corresponding to the user terminals UE1 and UE2 from the reference signals RS included in the uplink signals UL demodulated by the OFDM demodulator 15 (step S104). Note that the channel estimation unit 16 estimates the propagation channel for each resource block RB. The resource block RB is composed of 12 consecutive subcarriers.

[0027] After that, in the base station apparatus AP, the weight calculation unit 17 calculates a precoding weight from the estimated propagation channel using, for example, the spatial multiplexing technique of the ZF method (steps S105 to S107). Here, the weight calculation unit 17 is configured to calculate a precoding weight such that the amplitudes of the downlink signals DL for each of the plurality of layers are substantially the same among the plurality of layers.

[0028] In the present embodiment, a case will be described as an example in which the weight calculation unit 17 normalizes the precoding weight before normalization for each layer to an amplitude corresponding to the average value of the amplitudes of the precoding weight, but the present invention is not limited thereto. For example, the weight calculation unit 17 may normalize the amplitude of the precoding weight before normalization for each layer to an amplitude corresponding to the total value of the amplitudes. Alternatively, the weight calculation unit 17 may normalize the amplitude of the precoding weight before normalization for each layer to an amplitude corresponding to the total value or the average value of the squares of the amplitudes. Alternatively, the weight calculation unit 17 may normalize the amplitude of the precoding weight before normalization for each layer to an amplitude corresponding to the maximum value of the amplitudes.

[0029] Specifically, first, in the weight calculation unit 17, the inverse matrix calculation unit 171 calculates the inverse matrix of the propagation channel (step S105). For example, the inverse matrix Z of the propagation channel of the f-th resource block RB is represented by the following equation (1). f is represented as follows.

[0030]

Equation

[0031] Here, H f represents the propagation channel of the f-th resource block RB estimated by the channel estimation unit 16. Also, the " + " of H represents a general inverse matrix, and the " + " of Z represents a transposed matrix. Z T and the " T " of H f and Hf They are all complex matrices of M rows and K columns.

[0032] Next, in the weight calculation unit 17, the amplitude normalization unit 172 normalizes the amplitude of the inverse matrix Z f (step S106). In the present embodiment, a case where the precoding weight before normalization is normalized to an amplitude according to the average value of its amplitude will be described as an example. The reference amplitude a(k) of the k-th layer is expressed as in the following equation (2). Note that k is an arbitrary number among 1 to K.

[0033]

Equation

[0034] Here, z f [m, k] represents the element in the m-th row and k-th column of Z f , that is, the element of the k-th layer received via the m-th antenna 14. Note that m is an arbitrary number among 1 to M. N RB represents the total number of resource blocks RB in the band used for communication.

[0035] The precoding weight w f [m, k] of the m-th row and k-th column is expressed as in the following equation (3) by normalizing the element z f [m, k] of the inverse matrix Z f using the reference amplitude a(k) of the k-th layer.

[0036]

Equation

[0037] In equation (3), the inverse matrix Z f is normalized by a constant coefficient for each layer number k. The precoding weight W f is expressed as in the following equation (4) by matrixifying the precoding weight w f [m, k] of the m-th row and k-th column.

[0038]

Number

[0039] Next, in the weight calculation unit 17, the scale adjustment unit 173 performs scale adjustment so that the amplitude of the precoding weight W f between layers becomes a predetermined amplitude in the digital signal processing in the base station apparatus AP (step S107). The coefficient r used in the scale adjustment is expressed as in the following equation (6) using v(m) obtained by the following equation (5).

[0040]

Number

[0041]

Number

[0042] v(m) is a parameter related to the average value of the signal amplitude at the m-th antenna 14. Specifically, v(m) is the sum of the amplitudes of the precoding weights W f of all layers at the m-th antenna 14, averaged by the number of all resource blocks RB. V is a value related to the rated power output of an amplifier (not shown) that supplies signals to each antenna 14. When the average amplitude value of the band is set to V, a signal of the rated power is transmitted from the amplifier. In equation (6), the coefficient r is obtained by dividing the average amplitude value V of the band by the amplitude average value max[v(m)] indicating the maximum value among the amplitude average values v(m) of each of the M antennas 14. The scale-adjusted precoding weight W f ’ is expressed as in the following equation (7).

[0043]

Number

[0044] After that, in the base station apparatus AP, the precoding unit 11 multiplies the transmission signal s of each layer by the precoding weight W f ’ to generate a transmission signal x transmitted to the outside from each antenna 14 (step S108). The transmission signal x is represented by the following equation (8).

[0045]

Equation

[0046] s is a K-row and 1-column complex matrix, and x is an M-row and 1-column complex matrix. The precoding weight W f ’ has a value corresponding to the resource block RB number f of the transmission signal s.

[0047] In the base station apparatus AP, the OFDM modulator 12 modulates the transmission signal x of each antenna 14 using the orthogonal frequency division multiplexing method, and then up-converts it to the carrier frequency (step S109), and transmits it to the outside from each antenna 14 as a downlink signal DL (step S110). Then, the user terminals UE1 and UE2 receive the downlink signal DL transmitted from the plurality of antennas 14 of the base station apparatus AP, respectively (step S111).

[0048] FIG. 6 is a schematic diagram of the spatial signal electric field strength distribution when there is no error in the estimation of the propagation channel without normalizing the amplitude between layers. In the example of FIG. 6, the solid line represents the electric field strength distribution of the layer signal for the user terminal UE1 transmitted from the base station apparatus AP, and the dotted line represents the electric field strength distribution of the layer signal for the user terminal UE2 transmitted from the base station apparatus AP.

[0049] In the example of FIG. 6, the signal for user terminal UE2 becomes null at the position of user terminal UE1, and the signal for user terminal UE1 becomes null at the position of user terminal UE2. Thereby, in the example of FIG. 6, even when the amplitude normalization between layers is not performed, nulls are formed for the user terminals of the layers not being communicated with, so that the signal-to-noise ratio (SNR) of the communication is maintained at a high value. SNR is the abbreviation of Signal to Noise Ratio.

[0050] Here, in the inverse matrix calculation of Equation (1), the amplitude is adjusted so that the received power of each of user terminals UE1 and UE2 becomes equal. Therefore, when precoding is performed using a precoding weight in which the amplitude normalization between layers is not performed, among user terminals UE1 and UE2, the transmission power from base station apparatus AP to user terminal UE1 that is close to base station apparatus AP is low, and the transmission power from base station apparatus AP to user terminal UE2 that is far from base station apparatus AP is high.

[0051] When there is no error in the estimation of the propagation channel, even when precoding is performed using a precoding weight in which the amplitude normalization between layers is not performed, the SNR of the communication is maintained at a high value. However, in reality, the estimation of the propagation channel includes errors. Note that the estimation error of the propagation channel also includes the change in the propagation channel over time.

[0052] FIG. 7 is a schematic diagram of the spatial signal electric field strength distribution when there is an error in the estimation of the propagation channel without performing the amplitude normalization between layers. In the example of FIG. 7, due to the influence of the estimation error of the propagation channel, the beamforming of the transmission signal from base station apparatus AP to user terminal UE2 is shifted distantly.

[0053] In the example of Fig. 7, since the local peak portion of the transmission power distribution from the base station apparatus AP to the user terminal UE2 has a gentle shape, the received power of the user terminal UE2 is about the same as the case where there is no error in the estimation of the propagation channel. On the other hand, since the null has steep characteristics, even a slight shift in the propagation channel causes a large change. In the example of Fig. 7, due to the change in the null formation position, the interference of the signal for the user terminal UE2 to the user terminal UE1 increases significantly, and the SNR of the communication decreases. The decrease in SNR due to the influence of the estimation error of the propagation channel is more likely to occur as the carrier frequency increases.

[0054] Fig. 8 is a diagram showing the constellation of the downlink signal DL from the base station apparatus AP to each of the user terminals UE1 and UE2 when the amplitude normalization between layers is not performed. The left diagram of Fig. 8 shows the constellation of the downlink signal DL from the base station apparatus AP to the user terminal UE1, and the right diagram of Fig. 8 shows the constellation of the downlink signal DL from the base station apparatus AP to the user terminal UE2. This signal is modulated by Quadrature Phase Shift Keying (QPSK). Referring to Fig. 8, in the user terminal UE2 far from the base station apparatus AP, high modulation accuracy is obtained by concentrating on the symbol positions of QPSK, while in the user terminal UE1 close to the base station apparatus AP, the received symbols are dispersed due to the interference of the signal for the user terminal UE2, and the modulation accuracy is greatly deteriorated.

[0055] Fig. 9 is a schematic diagram of the spatial signal electric field strength distribution when the amplitude normalization between layers is performed. In the example of Fig. 9, similar to the case of the example of Fig. 7, it is assumed that there is an error in the estimation of the propagation channel. Also, Fig. 10 is a diagram showing the constellation of the downlink signal DL from the base station apparatus AP to each of the user terminals UE1 and UE2 when the amplitude normalization between layers is performed. The left diagram of Fig. 10 shows the constellation of the downlink signal DL from the base station apparatus AP to the user terminal UE1, and the right diagram of Fig. 10 shows the constellation of the downlink signal DL from the base station apparatus AP to the user terminal UE2.

[0056] When the amplitude between layers is normalized, the power of the transmission signals transmitted from the base station apparatus AP to each of the user terminals UE1 and UE2 becomes equal. Therefore, compared with the case where the amplitude between layers is not normalized, the reception power of the user terminal UE2 far from the base station apparatus AP decreases. On the other hand, the reception power of the user terminal UE1 close to the base station apparatus AP increases, and the interference of the signal for the user terminal UE2 also relatively decreases. Therefore, the modulation accuracy at the user terminal UE1 is greatly improved compared with the case where the amplitude between layers is not normalized.

[0057] Thus, the base station apparatus AP according to the present disclosure can prevent the degradation of the modulation accuracy for each of a plurality of spatially multiplexed user terminals in actual communication including errors in the estimation of the propagation channel by normalizing the amplitude between layers. That is, the base station apparatus AP according to the present disclosure can prevent the degradation of the communication quality.

[0058] <Embodiment 2> The base station apparatus AP according to the present disclosure is not limited to the case of normalizing the entire signal band at a certain ratio as in formula (3). For example, the base station apparatus AP may be configured to normalize the amplitude between layers for each of one or more resource blocks RB.

[0059] In a communication environment with many multipaths, etc., the frequency characteristics of the propagation channel may fluctuate violently. In such a situation, if the entire signal band is normalized at a certain ratio, the modulation accuracy may deteriorate at a specific frequency. Therefore, the base station apparatus AP according to the present disclosure can prevent the degradation of the modulation accuracy at a specific frequency by normalizing the amplitude between layers for each of one or more resource blocks RB.

[0060] <Embodiment 3> The base station apparatus AP according to the present disclosure is not limited to making the amplitudes of the downlink signals DL corresponding to the respective layers substantially the same among the plurality of layers, and may be configured such that the ratio of the amplitudes of the downlink signals DL corresponding to the respective layers among the plurality of layers can be adjusted to a predetermined ratio. That is, the weight calculation unit 17 may be configured to calculate a precoding weight such that the ratio of the amplitudes of the downlink signals DL corresponding to the respective layers among the plurality of layers is adjusted to a predetermined ratio. When adjusting the ratio of the amplitudes between layers, the precoding weight w f [m, k] is expressed as in the following formula (9).

[0061] [Equation]

[0062] However, α k is changed so as to satisfy the conditions of the following formula (10).

[0063] [Equation]

[0064] For example, when the base station apparatus AP and the user terminal UE1 communicate using the first layer and the base station apparatus AP and the user terminal UE2 communicate using the second layer, and when the user terminal UE1 requires more communication capacity than the user terminal UE2, in order to make the reception power of the downlink signal DL of the user terminal UE1 1.5 times that of the user terminal UE2, α1 = √1.5 and α2 = √0.5 are set. Thereby, the base station apparatus AP according to the present disclosure can improve the communication quality of a specific user terminal, for example, increase the communication capacity of a specific user terminal.

[0065] <Embodiment 4> The base station apparatus AP according to the present disclosure may be configured to adjust the amplitude ratio between layers using the bit efficiency as an index. The bit efficiency is obtained by dividing the throughput by the power consumption.

[0066] For example, when the base station apparatus AP communicates with the user terminal UE1 using the first layer and the base station apparatus AP communicates with the user terminal UE2 using the second layer, if the propagation loss of the signal of the user terminal UE1 close to the base station apparatus AP is small and the propagation loss of the signal of the user terminal UE2 far from the base station apparatus AP is large, the power of the transmission signal from the base station apparatus AP to the second layer is decreased and the power of the transmission signal from the base station apparatus AP to the first layer is increased, whereby the bit efficiency is improved. For adjusting the transmission power of each of the first layer and the second layer, for example, the method described in Embodiment 3 is used.

[0067] In this way, the base station apparatus AP according to the present disclosure can realize high-power-efficiency communication by adjusting the signal amplitude of each layer so that the bit efficiency estimated from the communication state with the user terminal is maximized.

[0068] (Configuration of hardware for realizing the communication control function of the base station apparatus AP) The communication control process realized by the base station apparatus AP can be realized by a general-purpose computer system. This will be briefly described below with reference to FIG. 11.

[0069] FIG. 11 is a block diagram showing an example of the hardware configuration for realizing the communication control function of the base station apparatus AP. The computer 300 includes, for example, a CPU (Central Processing Unit) 301 which is a control device, a RAM (Random Access Memory) 302, and a ROM (Read Only Memory) 303. The computer 300 further includes an IF (Inter Face) 304 which is an interface with the outside, and an HDD (Hard Disk Drive) 305 which is an example of a non-volatile storage device. Further, the computer 300 may include input devices such as a keyboard and a mouse, and display devices such as a display, as other configurations not shown in the figure.

[0070] The HDD 305 stores an OS (Operating System) not shown in the figure and a communication control program 306. The communication control program 306 is a computer program in which the communication control process of the base station apparatus AP is implemented.

[0071] The CPU 301 controls various processes in the computer 300, accesses to the RAM 302, the ROM 303, the IF 304, and the HDD 305. The computer 300 reads and executes the OS and the communication control program 306 stored in the HDD 305 by the CPU 301. Thereby, the computer 300 realizes the communication control function of the base station apparatus AP.

[0072] When the above program is loaded into a computer, it includes a set of instructions (or software code) for causing the computer to perform one or more functions described in this disclosure. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, a computer-readable medium or a tangible storage medium includes RAM, ROM, flash memory, SSD (Solid-State Drive) or other memory technologies, CD-ROM, DVD (Digital Versatile Disc), Blu-ray (registered trademark) disc or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may also be transmitted on a transitory computer-readable medium or a communication medium. By way of example and not limitation, a transitory computer-readable medium or a communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0073] The present disclosure has been described with reference to the embodiments above, but the present disclosure is not limited to the above-described embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. And each embodiment can be combined with other embodiments as appropriate.

[0074] Each drawing is merely an illustration for explaining one or more embodiments. Each drawing is not associated with only one specific embodiment, but may be associated with one or more other embodiments. As can be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with the features or steps shown in one or more other drawings to create, for example, embodiments not explicitly illustrated or described. Not all of the features or steps shown in any one drawing for explaining exemplary embodiments are necessarily essential, and some features or steps may be omitted. The order of the steps described in any drawing may be changed as appropriate.

[0075] Also, some or all of the above embodiments may be described as follows, but are not limited thereto.

[0076] (Appendix 1) A demodulator that demodulates a plurality of uplink signals corresponding to a plurality of layers received from each of a plurality of user terminals; An estimation unit that estimates a propagation channel of each of the plurality of layers from a plurality of reference signals included in each of the demodulated plurality of uplink signals; A weight calculation unit that calculates a precoding weight from an estimation result of the propagation channel; A precoding unit that applies the precoding weight to a transmission signal for each of the plurality of layers; A modulator that modulates the transmission signal to which the precoding weight has been applied and transmits it as a downlink signal to the plurality of user terminals; Comprising The weight calculation unit is configured to calculate the precoding weight such that a ratio between the amplitudes of the downlink signals corresponding to the plurality of layers is adjusted to a predetermined ratio. Wireless communication device.

[0077] (Appendix 2) The weight calculation unit is configured to calculate the precoding weight such that the amplitudes of the downlink signals corresponding to the plurality of layers are substantially the same among the plurality of layers. The wireless communication device according to Appendix 1.

[0078] (Appendix 3) The weight calculation unit is configured to calculate the precoding weight such that a ratio between the amplitudes of the downlink signals corresponding to the plurality of layers is adjusted to a predetermined ratio for each one or more resource blocks of the reference signals. The wireless communication device according to Appendix 1.

[0079] (Appendix 4) The weight calculation unit normalizes the amplitude of the precoding weight corresponding to each layer to an amplitude according to the total value or average value of the amplitudes. The wireless communication device according to Appendix 1.

[0080] (Appendix 5) The weight calculation unit normalizes the amplitude of the precoding weight corresponding to each layer to an amplitude according to the total value or average value of the squares of the amplitudes. The wireless communication device according to Appendix 1.

[0081] (Appendix 6) The weight calculation unit normalizes the amplitude of the precoding weight corresponding to each layer to an amplitude according to the maximum value of the amplitudes. The wireless communication device according to Appendix 1.

[0082] (Appendix 7) The weight calculation unit An inverse matrix calculation unit that calculates the inverse matrix of the estimated propagation channel, An amplitude normalization unit that normalizes the calculated inverse matrix of the propagation channel so that the ratio of the amplitudes of the downlink signals corresponding to each of the plurality of layers becomes a predetermined ratio, A scale adjustment unit that adjusts the scale of the amplitude of the normalized inverse matrix and outputs it as the precoding weight, and has The wireless communication device according to Appendix 1.

[0083] (Appendix 8) A base station device that is the wireless communication device according to Appendix 1, A plurality of user terminals that communicate using layers different from those of the base station device, and a wireless communication system including the same.

[0084] (Appendix 9) A computer demodulates a plurality of uplink signals corresponding to a plurality of layers received from each of the plurality of user terminals, estimates the propagation channel of each of the plurality of layers from a plurality of reference signals included in each of the demodulated plurality of uplink signals, calculates a precoding weight from the estimation result of the propagation channel, applies the precoding weight to a transmission signal for each of the plurality of layers, modulates the transmission signal to which the precoding weight is applied, and transmits it as a downlink signal to the plurality of user terminals. A communication control method, wherein in the calculation of the precoding weight, the precoding weight is calculated such that a ratio of amplitudes of the downlink signals corresponding to each of the plurality of layers among the plurality of layers is adjusted to a predetermined ratio. Communication control method.

[0085] (Appendix 10) a process of demodulating a plurality of uplink signals corresponding to a plurality of layers received from each of the plurality of user terminals, a process of estimating the propagation channel of each of the plurality of layers from a plurality of reference signals included in each of the demodulated plurality of uplink signals, a process of calculating a precoding weight from the estimation result of the propagation channel, a process of applying the precoding weight to a transmission signal for each of the plurality of layers, a process of modulating the transmission signal to which the precoding weight is applied and transmitting it as a downlink signal to the plurality of user terminals, A communication control program for causing a computer to execute, In the process of calculating the precoding weight, the precoding weight is calculated such that the ratio of the amplitudes of the downlink signals corresponding to each of the plurality of layers is adjusted to a predetermined ratio among the plurality of layers. Communication control program.

[0086] Some or all of the elements (for example, configurations and functions) described in Appendices 2 to 8 that are subordinate to Appendix 1 may be subordinate to each of Appendices 9 and 10 in the same subordinate relationship as Appendices 2 to 8. Some or all of the elements described in any appendix may be applied to various hardware, software, recording means for recording software, systems, and methods.

Explanation of symbols

[0087] 1 Wireless communication system 11 Precoding unit 12 OFDM modulator 13 Switch 14 Antenna 15 OFDM demodulator 16 Channel estimation unit 17 Weight calculation unit 171 Inverse matrix calculation unit 172 Amplitude normalization unit 173 Scale adjustment unit 300 Computer 301 CPU 302 RAM 303 ROM 304 IF 305 HDD 306 Communication control program AP Base station device UE1, UE2 User terminal

Claims

1. A demodulator that demodulates a plurality of uplink signals corresponding to a plurality of layers received from each of a plurality of user terminals; An estimator that estimates a propagation channel for each of the plurality of layers from a plurality of reference signals included in each of the plurality of demodulated uplink signals; A weight calculation unit that calculates a precoding weight from the estimation result of the propagation channel; A precoding unit that applies the precoding weight to a transmission signal for each of the plurality of layers; A modulator that modulates the transmission signal to which the precoding weight is applied and transmits it as a downlink signal to the plurality of user terminals; Comprising: The weight calculation unit is configured to calculate the precoding weight such that a ratio of amplitudes of the downlink signals corresponding to the plurality of layers is adjusted to a predetermined ratio; A wireless communication device.

2. The weight calculation unit is configured to calculate the precoding weight such that amplitudes of the downlink signals corresponding to the plurality of layers are substantially the same among the plurality of layers; The wireless communication device according to claim 1.

3. The weight calculation unit is configured to calculate the precoding weight such that a ratio of amplitudes of the downlink signals corresponding to the plurality of layers is adjusted to a predetermined ratio for each one or more resource blocks of the reference signals; The wireless communication device according to claim 1.

4. The weight calculation unit normalizes an amplitude of the precoding weight corresponding to each layer to an amplitude according to a total value or an average value of the amplitudes; The wireless communication device according to claim 1.

5. The weight calculation unit normalizes an amplitude of the precoding weight corresponding to each layer to an amplitude according to a total value or an average value of squares of the amplitudes; The wireless communication device according to claim 1.

6. The weight calculation unit normalizes an amplitude of the precoding weight corresponding to each layer to an amplitude according to a maximum value of the amplitudes; The wireless communication device according to claim 1.

7. The weight calculation unit: An inverse matrix calculation unit that calculates an inverse matrix of the estimated propagation channel; An amplitude normalization unit that normalizes the inverse matrix of the calculated propagation channel so that the ratio of the amplitudes of the downlink signals corresponding to each of the plurality of layers is a predetermined ratio among the plurality of layers; A scale adjustment unit that adjusts the scale of the amplitude of the normalized inverse matrix and outputs it as the precoding weight; having The wireless communication device according to claim 1.

8. A base station device that is the wireless communication device according to claim 1, A plurality of user terminals that communicate using layers different from those of the base station device, A wireless communication system comprising

9. A computer Demodulates a plurality of uplink signals corresponding to a plurality of layers received from each of the plurality of user terminals, Estimates the propagation channel of each of the plurality of layers from a plurality of reference signals included in each of the demodulated plurality of uplink signals, Calculates a precoding weight from the estimation result of the propagation channel, Applies the precoding weight to the transmission signal for each of the plurality of layers, Modulates the transmission signal to which the precoding weight is applied and transmits it as a downlink signal to the plurality of user terminals, A communication control method, In the calculation of the precoding weight, calculates the precoding weight such that the ratio of the amplitudes of the downlink signals corresponding to each of the plurality of layers is adjusted to a predetermined ratio among the plurality of layers, Communication control method.

10. A process of demodulating a plurality of uplink signals corresponding to a plurality of layers received from each of the plurality of user terminals, A process of estimating the propagation channel of each of the plurality of layers from a plurality of reference signals included in each of the demodulated plurality of uplink signals, A process of calculating a precoding weight from the estimation result of the propagation channel, A process of applying the precoding weight to the transmission signal for each of the plurality of layers, A process of modulating the transmission signal to which the precoding weight is applied and transmitting it as a downlink signal to the plurality of user terminals, A communication control program for causing a computer to execute In the process of calculating the precoding weight, the precoding weight is calculated such that the ratio of the amplitudes of the downlink signals corresponding to each of the plurality of layers is adjusted to a predetermined ratio among the plurality of layers. Communication control program.

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