JP2020048001A - Electronic device and antenna installation method - Google Patents

Abstract

To provide an electronic device and a method for installing an antenna thereof, which can simply remove interference when full-duplex communication is performed using LOS-MIMO.SOLUTION: An electronic device includes a transmission array antenna unit and a reception array antenna unit. The transmission array antenna unit includes a plurality of first antenna elements that transmit transmission signals. The reception array antenna unit includes the same number of second antenna elements as the first antenna elements, which receive a reception signal in a reception frequency band at least partially overlapping the transmission signal in a reception period at least partially overlapping a transmission period of the transmission signal. The first antenna elements are arranged in a wavelength corresponding to the band of the reception frequency and at an interval based on the transmission array antenna unit and the reception array antenna unit.SELECTED DRAWING: Figure 8

Description

  Embodiments described herein relate generally to an electronic device that performs full-duplex communication wirelessly, and an antenna installation method thereof.

  In a 5G backhaul line, high-speed communication of several tens of Gbps or more is required. In order to improve the transmission speed in backhaul scenarios, LOS-MIMO, which is MIMO (Multiple-input and Multiple-output) transmission that maintains orthogonality even in line-of-sight environments, unlike conventional MIMO transmission that utilizes multipath, is proposed. Have been. In LOS-MIMO, a plurality of streams can be transmitted without interference by effectively utilizing a deterministic path difference (phase relationship) between transmission and reception. On the other hand, full-duplex communication, which is a technique for performing two-way communication at the same time, has attracted attention. Using these two techniques theoretically quadruples the frequency utilization efficiency over SISO.

  Conventionally, there is no known example in which the LOS-MIMO mechanism for backhaul is effectively used for both an inter-transmission / reception channel and an interference channel. For example, Patent Literature 1 proposes a technique for reducing inter-stream interference by arranging antennas between short-range electronic devices in the same way as in LOS-MIMO, focusing on the path difference between channels. The full-duplex communication in Patent Document 1 is frequency division duplex (FDD). Patent Document 1 focuses on only the channel between transmission and reception, and does not consider the interference channel.

Japanese Patent No. 5672683

  In full-duplex communication, the influence of self-interference is large on a received signal. Several techniques are known for eliminating the effect of the self-interference of the full-duplex communication. However, when performing full-duplex communication in a multi-antenna system such as MIMO, interference cancellation is likely to be complicated because the number of combinations of interference channels increases.

  The embodiment provides an electronic device and a method of installing an antenna thereof, which can easily remove interference when performing full-duplex communication by LOS-MIMO.

The electronic device according to the embodiment includes a first antenna unit and a second antenna unit. The first antenna unit has a plurality of first antenna elements for transmitting a transmission signal. The second antenna unit receives the received signal in a reception frequency band at least partially overlapping a transmission frequency band of the transmission signal and in a reception period at least partially overlapped with the transmission period of the transmission signal. And the same number of second antenna elements. An interval s between at least two second antenna elements of the plurality of second antenna elements is λ, a wavelength corresponding to the reception frequency band, and D is a distance between the first antenna unit and the second antenna unit.
It is.

FIG. 1 is a diagram illustrating a configuration example of an electronic device according to an embodiment. FIG. 2 is a diagram for describing LOS-MIMO. FIG. 3 is a diagram for explaining full-duplex communication. FIG. 4 is a diagram for explaining full-duplex communication. FIG. 5 is a diagram for explaining interference removal in full-duplex communication. FIG. 6 is a diagram for explaining simplification of interference removal in full-duplex communication. FIG. 7 is a diagram illustrating an example of an antenna arrangement of LOS-MIMO. FIG. 8 is a diagram illustrating an example of an element arrangement of full-duplex communication in the embodiment. FIG. 9 is a diagram illustrating a configuration example of an antenna unit of the electronic device according to the embodiment. FIG. 10 is a diagram illustrating an example of a method of arranging the elements of the transmission array antenna unit. FIG. 11 is a diagram illustrating an example of a method of arranging elements of the transmission array antenna unit. FIG. 12 is a diagram illustrating candidates for element positions of the transmission array antenna unit. FIG. 13 is a diagram illustrating candidates for element positions of the transmission array antenna unit. FIG. 14 is a diagram illustrating candidates for element positions of the transmission array antenna unit. FIG. 15 is a diagram illustrating a modification of the method of arranging the elements of the transmission array antenna unit and the reception array antenna unit. FIG. 16 is a diagram illustrating a modification of the method of arranging the elements of the transmission array antenna unit and the reception array antenna unit. FIG. 17 is a diagram showing an example of a method of arranging elements of the transmission array antenna unit and the reception array antenna unit in the case of full-duplex communication of the n × n element MIMO. FIG. 18 is a diagram showing an image of calculation of equation (2) in the case of 3 × 3 element MIMO. FIG. 19 is a diagram for describing simplification of interference removal in full-duplex communication in the case of an n × n element MIMO. FIG. 20 is a diagram for describing a modification of the channel estimation of the first channel information holding unit. FIG. 21 is a diagram for describing a modified example of the channel estimation of the second channel information holding unit. FIG. 22 is a diagram for explaining the interference signal removal processing of the interference signal removal unit in a state where interference removal is simplified. FIG. 23 is a diagram showing a comparison between bit error rates. FIG. 24 is a diagram illustrating an example of a communication system with full-duplex communication. FIG. 25 is a diagram illustrating an example of a communication system without full-duplex communication.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration example of an electronic device according to an embodiment. The electronic device includes a transmission array antenna unit 101, a transmission unit 102, a transmission signal information holding unit 103, a first channel information holding unit 104, a second channel information holding unit 105, a weight calculation unit 106, an interference signal It has a removing unit 107, a receiving unit 108, a receiving array antenna unit 109, and a processing unit 110. This electronic device is various electronic devices that perform full-duplex communication by LOS-MIMO. In the full-duplex communication described below, at least part of the transmission frequency band of the transmission signal and at least part of the reception frequency band of the reception signal overlap, and further, at least part of the transmission period of the transmission signal and the reception period of the reception signal. Refers to overlapping communications.

  The transmission array antenna unit 101 has an array of two or more first antenna elements for transmitting a transmission signal. Each antenna element is not limited as long as it can transmit a radio signal.

  Transmitting section 102 generates a transmission signal based on the data transmitted from processing section 110, and outputs the generated transmission signal to each first antenna element of transmission array antenna section 101. Processing for generating a transmission signal includes modulation processing, filtering processing, amplification processing, and the like. The transmission unit 102 may be configured to perform modulation processing, filter processing, amplification processing, and the like by software processing, or may have a dedicated circuit that performs modulation processing, filter processing, amplification processing, and the like. Good.

  The transmission signal information holding unit 103 holds information of the transmission signal generated by the transmission unit 102. The transmission signal information holding unit 103 includes a memory such as a RAM, for example. Here, the transmission signal information holding unit 103 separately holds information of a transmission signal for each first antenna element. The information of these transmission signals is used for specifying an interference signal with respect to the reception signal of the own station as described later.

  The first channel information holding unit 104 is a channel based on a reception signal transmitted from the transmission array antenna unit of the wireless station (the other station) of the communication partner and received by the reception array antenna unit 109 of the target station (the own station). Information on the channel between transmission and reception is held as first channel information. The first channel information holding unit 104 includes a memory such as a RAM, for example. The first channel information may be, for example, channel information obtained as a result of performing channel estimation. The channel estimation is performed in, for example, the processing unit 110.

  Second channel information holding section 105 uses, as second channel information, information on an interference channel, which is a channel based on a reception signal transmitted from transmission array antenna section 101 of the own station and received by reception array antenna section 109 of the own station. Hold. The second channel information holding unit 105 includes a memory such as a RAM, for example. The second channel information may be, for example, channel information obtained as a result of performing channel estimation. The channel estimation is performed in, for example, the processing unit 110.

  Weight calculation section 106 calculates the weight by calculating the inverse matrix of the channel matrix, and performs weight calculation to multiply the calculated weight by the reception signal received by reception section 108. The weight calculation unit 106 may be configured to perform weight calculation by software processing, or may have a dedicated circuit for performing weight calculation. Multiplying the weights before the interference removal has the effect of facilitating the later-described interference removal. Weight calculation section 106 may be omitted.

  The interference signal elimination section 107 eliminates an interference signal based on the information of the transmission signal held in the transmission signal information holding section 103 from the weighted reception signal. Then, the interference signal removing unit sends the data of the received signal from which the interference signal has been removed to the processing unit 110. The interference signal removal unit 107 may be configured to remove the interference signal by software processing, or may have a dedicated circuit for removing the interference signal.

  Receiving section 108 demodulates a received signal received from each second antenna element of receiving array antenna section 109. Further, receiving section 108 performs processing such as filter processing and amplification processing on the demodulated received signal. Then, receiving section 108 extracts data from the received signal, and sends the extracted data to first channel information holding section 104, weight calculating section 106, and interference signal removing section 107. The receiving unit 108 may be configured to perform demodulation processing, filter processing, amplification processing, and the like by software processing, or may have a dedicated circuit that performs demodulation processing, filter processing, amplification processing, and the like. Good.

  The reception array antenna unit 109 has an array of two or more second antenna elements for receiving a reception signal. Each antenna element is not limited as long as it can receive a radio signal.

  The processing unit 110 has a digital signal processor such as a CPU, an ASIC, an FPGA, or a DSP. The processing unit 110 may include a memory such as a ROM and a RAM. Further, the processing unit 110 may have a plurality of CPUs or the like, or may have a plurality of memories. Such a processing unit 110 processes data included in the transmission signal and data included in the reception signal. Further, the processing unit 110 performs various controls of the electronic device as needed.

  Hereinafter, a method of arranging the antenna elements in the embodiment will be described. First, LOS-MIMO will be described to describe a method for arranging antenna elements according to the present embodiment. FIG. 2 is a diagram for describing LOS-MIMO.

  MIMO is a technique for improving a transmission rate without expanding a frequency band by using a plurality of antennas for transmission and reception. In general MIMO transmission, transmission paths are made orthogonal by utilizing multipath (a plurality of reflected waves). On the other hand, LOS-MIMO is MIMO transmission that maintains orthogonality even in line-of-sight environments. In LOS-MIMO, since only direct waves are used, the transmission path between transmission and reception is deterministically modeled.

For example, as shown in FIG. 2, an array antenna composed of two antenna elements for transmission and reception is assumed. In FIG. 2, when the element interval between antenna elements is a and the transmission distance between transmission and reception is b, the transmission path length from the first antenna element # 1 of the target station to the second antenna element # 1 of the partner station is b. . Further, the transmission path length from the first antenna element # 1 of the target station to the second antenna element # 1 of the partner station is represented as follows.
In MIMO, a plurality of signals (a plurality of streams) can be transmitted without interference by effectively utilizing a path difference of a deterministic path between transmitting and receiving antenna elements, that is, a phase difference caused by a path difference described below.

For example, the orthogonality is satisfied when the phase difference is 90 degrees. If the transmission path (channel matrix) when the phase difference becomes 90 degrees is set to H, H is represented by the following equation (1).

One of the evaluation indexes of the MIMO transmission is a spatial correlation. This is an index indicating the similarity of the received signals at the two receiving elements. When the spatial correlation is low, that is, when the similarity of the signals is low, the signals can be easily separated. Based on the channel matrix H, the spatial correlation ρ _r is calculated according to the following equations (2) and (3).
By substituting equation (1) into equation (3), _r becomes zero. At this time, it can be seen that low correlation, that is, orthogonalization of the transmission path can be achieved. In LOS-MIMO, signals can be easily separated by adjusting the element spacing a of antenna elements and the transmission distance b between transmission and reception.

  Next, full-duplex communication will be described. Full-duplex communication is a technique for performing two-way communication simultaneously as shown in FIG. That is, the target station A transmits a signal from its own station and simultaneously receives a signal from the partner station B. When comparing full-duplex communication with time-division duplex (TDD) or frequency-division duplex (FDD), in full-duplex communication, an upstream signal and a downstream signal do not need to be divided and transmitted for time and frequency. Therefore, the frequency utilization efficiency is twice that of time division duplex (TDD) or frequency division duplex (FDD). However, in full-duplex communication, the transmission signal of the station A wraps around and is received by the station A as shown in FIG. The transmitted signal that has been wrapped around and becomes an interference signal with respect to the signal from the station B. Therefore, in order to correctly obtain the signal from the station B, it is necessary to remove the interference signal from the received signal of the station A.

The interference removal in full-duplex communication will be described. First, as shown in FIG. 4, it is assumed that both antennas # 1 and # 2 are used for both transmission and reception, and the impulse response of the transmission path (channel between transmission and reception) between station A and station B is h _ij , The transmission path (interference channel) of the interference signal between the transmitting and receiving antenna elements is _{defined as hI, ij} . i indicates a signal transmission destination. When i is 1, it indicates that the transmission destination of the signal is the second antenna element # 1, and when i is 2, it indicates that the transmission destination of the signal is the second antenna element # 2. j indicates the transmission source of the signal. When j is 1, it indicates that the signal transmission source is the first antenna element # 1, and when j is 2, it indicates that the signal transmission source is the first antenna element # 2. Here, for simplicity, noise is ignored. If the desired received signal from station B is s _i , the interference signal at station A is s _{I, i} , and the received signal at station A is y _j , then if there are two transmitting and receiving antenna elements, y _j is given by the equation ( It is represented by matrix operation as in 4).
Here, for the sake of simplicity, it is assumed that the information of the transmission path has been completely estimated, and the inverse matrix operation of the matrix (channel matrix) of the impulse response of the transmission path is performed on the received signal. Equation (5) is obtained.
Here, the first row of the matrix represents the impulse response of the second antenna element # 1, and the second row represents the impulse response of the second antenna element # 2. The interference signals sI _{, i} of the second antenna elements # 1 and # 2 can be removed because they are known signals at the station A. However, in the case of MIMO, as indicated by the second term on the right side of Equation (5), both of the second antenna element # 1 and the second antenna element # 2 are referred to as sI _{, 1} , sI _{, 2.} It is necessary to subtract two signal components related to the interference signal. That is, the interference signal removing unit 107, _s I, 1 for the second antenna element # 1 as shown in FIG. _{5, s I, 2} subtracts the interference components 501 and 502 by, for the second antenna element # 2 _{s I , 1} and s _{I, 2} are subtracted.

Here, when both the inter-transmission / reception channel and the interference channel are channels that satisfy the LOS-MIMO condition as in Expression (1), Expression (4) can be written as in Expression (6).
When the inverse matrix operation is similarly performed on Expression (6), the following Expression (7) can be calculated.
From the right side of Equation (7), it can be seen that if the interference channel is also orthogonalized under the condition of LOS-MIMO, the signal can be easily separated. In the second antenna element # 1, the interference signal is only _{sI, 1} , and in the second antenna element # 2, the interference signal is only _{sI, 2} . Since it is sufficient to remove one component of the interference signal for any of the second antenna elements, it can be seen that the simplification is made as compared with the equation (5). In other words, as shown in FIG. 6, the interference signal removing unit 107, for the second antenna element # 1 may be subtracted interference component 601 by _{s I, 1,} according to _{s I, 2} for the second antenna element # 2 The interference component 602 may be subtracted. Thus, the subtraction of the interference component of FIG. 6 is easier than the subtraction of the interference component of FIG.

  If the inter-transmission / reception channel and the interference channel are designed to satisfy the conditions of LOS-MIMO, the deduction of the interference component becomes easy. A method for installing the antenna element of the channel between transmission and reception for that purpose will be described. In the following description, λ is used wavelength and D is horizontal distance between transmission and reception. The used wavelength λ is the reciprocal of the used frequency of the transmission / reception signal. The frequency used for the transmission / reception signal may have a band. Further, the horizontal distance D between transmission and reception may be a distance between corresponding ones of the first antenna element and the second antenna element. At this time, the shortest D is the distance between near ones of the first and second antenna elements, and the longest D is the distance between far ones of the first and second antenna elements.

First, placing a respective d _y direct wave path length as shown in Figure 7. When the distance between the first antenna element and the second antenna element is sufficiently short with respect to the horizontal distance between transmission and reception, the amplitude change due to the difference between the elements can be ignored. At this time, the channel matrix H can be written as the following equation (8).
When the spatial correlation matrix of Expression (2) is calculated using Expression (8), the spatial correlation matrix can be expressed as Expression (9) below.
In Equation (9), if a condition that the non-diagonal element becomes 0 is set as a condition for orthogonalizing channels, a relational expression such as the following Equation (10) is derived.
Here, p represents an integer of 0 or more. Next, assuming that the transmission element interval is s ₁ and the reception element interval is s ₂ as shown in FIG. 7, d ₁₁ , d ₁₂ , d ₂₁ , and d ₂₂ are expressed by the following equations (11) to (14). It can be written.
By substituting the equations (11)-(14) into the equation (10) and transforming the equation, the following equation (15) is obtained.
Here, assuming that the intervals between the transmitting and receiving antenna elements are the same, s = s ₁ = s ₂ can be set. At this time, when Equation (15) is solved for s, Equation (15) is transformed into Equation (16).
Therefore, by arranging the respective antenna elements of the transmission array antenna unit 101 and the reception array antenna unit 109 at an element interval of the equation (16), orthogonalization of the transmission path is achieved.

In the channel between transmission and reception, consider an interference channel when p = 0 in Equation (16) and the element spacing s is set as follows.
Such setting of the element interval corresponds to a scenario as shown in FIG. _Assuming that each component of the channel is d ′ _ij as shown in FIG. 7, the condition of LOS-MIMO of Expression (10) is satisfied if the following Expressions (17) to (20) are satisfied.
Therefore, by arranging the first antenna element and the second antenna element as shown in FIG. 8, both the interference channel and the transmission / reception channel are orthogonalized. At this time, interference elimination in full-duplex communication is simplified as shown in FIG.

From Equations (17) to (20), d ₂₁ -d ₁₁ and d ₁₂ -d ₂₂ are constant values, and both are (λ / 4) (2p + 1) (p is an integer of 0 or more). Therefore, for example, by setting a point where the difference between the two receiving elements is an odd multiple of λ / 4 as shown in FIG. 10 as the position of the first antenna element, orthogonalization of the interference channel is achieved.

Based on Equations (17)-(20) and FIG. 10, the first antenna element with respect to the interference channel has a focal point on the curve where the difference in distance is constant, that is, as shown in FIG. It can be seen that it suffices to set them on a hyperbola. The general formula of the hyperbola is the following formula (21).
Further, the following equations (22) to (24) are obtained from the properties of the hyperbola.
By transforming equation (21) using equations (22)-(24), the following equation (25) is derived.
By solving the equation (25) for the x coordinate of the first antenna element, the following equation (26) is obtained. Also, assuming that the transmitting element is installed in parallel with the receiving element and that the element spacing is the same for transmitting and receiving, solving equation (25) for the y coordinate of the first antenna element gives the following equation (27). Can be
Note that, from b ² > 0, the range of p in Expressions (26) and (27) is represented by the following Expression (28).
In other words, the position of the first antenna element is determined by calculating the x coordinate and the y coordinate of the first antenna element within the range of p in equation (28) according to equations (26) and (27). Good.

  FIG. 12 is a diagram showing a candidate position 1202 of the first antenna element of the interference channel when the frequency is set to 80 GHz, the position of the second antenna element is fixed at the position 1201, and p is changed. As shown in FIG. 12, an infinite number of hyperbolas are drawn, and it can be seen that there are many candidate positions 1202 for the first antenna element. By installing the first antenna element on this candidate position 1202, both the interference channel and the transmission / reception channel are orthogonalized.

  As shown in FIG. 12, especially in the case of a millimeter wave, although there are many candidate positions of the first antenna element, if the position is slightly shifted, the phase changes and the orthogonality of the interference channel is broken. FIG. 13 is a diagram illustrating a candidate position 1302 of the first antenna element when the position of the second antenna element is changed to the position 1301 to reduce the element interval. FIG. 14 is a diagram showing candidate positions 1402 of the first antenna element when the position of the second antenna element is changed to the position 1401 to further reduce the element interval. 13 and 14 that when the element interval of the second antenna element is reduced, the hyperbolic interval increases from the position of the second antenna element to the position on the negative side. Therefore, by setting the position of the first antenna element on the hyperbola having the widened interval, the channel change with respect to the element position shift is reduced. That is, it becomes robust against the element displacement, and the orthogonality of the channels is easily maintained.

  As described above, according to the present embodiment, the first antenna element for transmitting the transmission signal and the second antenna element for receiving the reception signal are arranged such that the orthogonality of both the transmission / reception channel and the interference channel is maintained. Has been installed. This makes it possible to apply LOS-MIMO interference cancellation conditions in full-duplex communication, thereby simplifying interference cancellation.

  Here, the channel has reversibility. Therefore, in the above-described embodiment, the positions of the first antenna element and the second antenna element may be interchanged. That is, in the above-described embodiment, the position of the first antenna element is determined based on Equations (17) to (20) with reference to the second antenna element. On the other hand, the position of the second antenna element may be determined based on Equations (17) to (20) based on the first antenna element.

[Modification 1]
Hereinafter, modified examples will be described. The first antenna element and the second antenna element are arranged symmetrically with respect to an axis passing through the center C of the array, for example, as shown in FIG. However, as shown in FIG. 15, the element spacing of the first antenna element and the element spacing of the second antenna element do not have to be the same. When the element spacing of the first antenna element and the element spacing of the second antenna element are not the same, the channel matrix of the interference channel is expressed by the following equation (29).
When the spatial correlation matrix is calculated using Expression (29) in the same manner as Expression (9), the spatial correlation matrix is as shown in Expression (30) below.
Here, when the first antenna element and the second antenna element are arranged symmetrically with respect to an axis passing through the array center C, A ₁₁ = A ₂₂ = X and A ₁₂ = A ₂₁ = Y hold. By rearranging equation (30) using this relationship, the following equation (31) is obtained.
For example, when θ ₂₁ −θ ₁₂ = 90 °, that is, when the path difference is λ / 4, θ ₂₂ −θ ₁₁ = −90 ° due to channel symmetry. At this time, since the off-diagonal element of equation (31) disappears, the spatial correlation ρ _r of equation (3) becomes zero. Therefore, even if the first antenna element is arranged in a portion where the hyperbolic space in FIG. 14 is widened, that is, even if the first antenna element is arranged as shown in FIG. 15, the interference channels are orthogonal.

[Modification 2]
Modification 2 will be described. If there is a difference in the amplitude of each interference channel between the transmission array antenna unit 101 and the reception array antenna unit 109, for example, the processing unit 110 determines the directivity of the transmission array antenna unit of the partner station based on the ratio of these amplitudes. May be required to change. For example, when the ratio of X and Y in Expression (31) cannot be ignored, the processing unit 110 controls the directivity of the transmission array antenna unit so that the amplitude ratio of the channel between transmission and reception becomes X: Y as shown in FIG. To the partner station to adjust When the amplitude ratio of the channel between transmission and reception is X: Y, the following expression (32) is established from expression (4).

Considering that the transmission / reception channel and the interference channel shown in FIG. 16 are formed, the following equation (33) is established. However, in Equation (33), it is assumed that orthogonality is maintained for both the transmission / reception channel and the interference channel.
Here, for the sake of simplicity, assuming that the information on the transmission path has been completely estimated, multiplying the received signal by the inverse matrix of the channel matrix gives the following equations (34) and (35). .
In the second term on the right side of Expression (35), although it is necessary to multiply the interference signal by ej ^{(α-β) of the} diagonal element, the elimination of the interference signal can be simplified also in the configuration of FIG. .

  Here, in the above discussion, for simplicity, the amplitude of the interference channel and the amplitude of the channel between transmission and reception are assumed to be the same. The same argument can be made when the amplitude is different by measuring the ratio in advance or estimating it geometrically.

[Modification 3]
Modification 3 will be described. In the above-described embodiment, an example in which the number of antenna elements is two has been described. On the other hand, the number of antenna elements may be an arbitrary number of two or more elements. Here, simplification of interference signal removal when the number of antenna elements is n will be described. First, when the first antenna element and the second antenna element are each n elements as shown in FIG. 17, the received signal is represented by a matrix represented by the following equation (36) in the same manner as equation (4). .
Here, for the sake of simplicity, it is assumed that the information of the transmission path has been completely estimated, and when the inverse matrix operation of the channel matrix is performed on the received signal, the following equations (37) to (39) are obtained. .
Each element of the product of the matrix of the second term on the right side of Expression (37) is denoted as A _ij for simplicity. Comparing Expression (39) with Expression (5), it can be seen that the interference component of the second term on the right-hand side has increased to n. Therefore, it is necessary to remove n × n interference components in the total of the n elements. That is, the interference removal becomes complicated by the increase in the number of elements.

Here, consider a channel in which both the transmission / reception channel and the interference channel satisfy the condition of LOS-MIMO of Expression (1). Note that a channel matrix in the case of n × n MIMO can be generally set as in the following equation (40).
FIG. 18 is a diagram illustrating an image of calculation of Expression (2) in the case of 3 × 3 MIMO. Here, the angles of the arrows in FIG. 18 correspond to the phases of the elements of each matrix. The calculation of the product of the channel matrix and its inverse matrix in 3 × 3 MIMO is as shown on the right side of FIG. That is, the off-diagonal elements in the matrix resulting from the product are zero because they are the sum of vectors with different phases. On the other hand, the diagonal elements in the matrix obtained as a result of the product are real numbers. Therefore, the spatial correlation ρ _r of Expression (3) calculated based on the result of this product becomes zero.

Here, consider a case where the concept of FIG. 18 is extended to n × n MIMO. Expression (40) is used to represent a received signal in the same manner as Expression (4), and is expressed by Expression (41) below.
When the inverse matrix operation similar to the expression (9) is performed on the expression (41), the following expression (42) is obtained.
Comparing Expressions (42) and (39), it is necessary to remove n × n interference signals in Expression (39), whereas Expression (42) removes n interference signals. I just need. In other words, the effect of simplification of interference removal increases as the number of antenna elements increases.

  Therefore, by arranging the antenna elements such that both the transmission / reception channel and the interference channel satisfy Expression (40), it is possible to similarly perform simple interference cancellation in n × n MIMO.

[Modification 4]
In the embodiment described above, the first channel information and the second channel information are assumed to be channel information obtained as a result of performing channel estimation, for example. On the other hand, the first channel information and the second channel information may be obtained by other methods.

  For example, the first channel information and the second channel information may be information of a channel measured in a previous calibration process. For example, the initial value of the first channel information may be estimated by a calibration process as shown in FIG. That is, the channel information may be estimated by measuring the reception signal while the transmission signal is stopped. Further, the initial value of the second channel information may be estimated by a calibration process as shown in FIG. That is, channel information may be estimated by measuring an interference signal due to a transmission signal in a state where the reception signal is blocked.

  Further, the first channel information and the second channel information may be deterministically calculated channel information. When the direct wave is strong in the channel between transmission and reception, the channel is determined deterministically. Therefore, the information of the channel can be calculated geometrically. In addition, the interference channel is generally static because the transmission / reception distance is short, and can be calculated geometrically.

[Modification 5]
The method of calculating the weight in the weight calculation unit 106 is not limited to the calculation of the inverse matrix of the channel matrix. The weight calculation unit 106 may calculate the weight using, for example, a MIMO reception weight calculation technique of minimum mean square error (MMSE) and maximum likelihood detection (MLD).

[Modification 6]
As shown in FIG. 22, the interference signal removing unit 107 subtracts the interference signal from the first antenna element corresponding to each second antenna element from the reception signal from each second antenna element. For example, the interference signal removing section 107 may subtract the interference signal from only the first antenna element # 1 for the reception signal from the second antenna element # 1, and the first antenna element # 2 in the second antenna element # 2. It is sufficient to subtract the interference signal from only 2.

On the other hand, if the transmission is represented by the formula (35) array antenna unit 101 and the receiving array antenna unit 109, that is, when the amplitude ratio between the channels is large, the diagonal elements of the second term on the right side of formula (35) e ^{j (alpha-beta)} _is expressed by _{h I, 11 / h 11,} h I, 22 / h 22. For this reason, the interference signal removing section 107 may subtract the interference signal after multiplying the known interference signal by the ratio of the interference channel to the transmission / reception channel.

[Specific effects of the embodiment]
FIG. 23 shows the calculation of the bit error rate characteristics by the equivalent low-pass system simulation at 80 GHz. “LOS-MIMO with interface” in FIG. 23 is a configuration including the full-duplex communication system illustrated in FIG. 24, and illustrates a bit error rate characteristic in a configuration in which a received signal may include an interference component due to a transmission signal of the own station. Is shown. On the other hand, “LOS-MIMO” of FIG. 23 is a configuration of a communication system without full-duplex communication shown in FIG. 25, and is a configuration of a communication system in which a received signal cannot include an interference component due to a transmission signal of the own station. 5 shows the bit error rate characteristics at the time.

  As shown in FIG. 23, the bit error rate characteristic of “LOS-MIMO with interface” is almost the same as the bit error rate characteristic of “LOS-MIMO”. That is, as described in the embodiment, by appropriately setting the arrangement of the antenna elements, even if only the interference components 501 and 504 in FIG. 5 are removed, the characteristics are not substantially deteriorated. From this, the effectiveness of interference removal by simplification can be confirmed.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements in an implementation stage without departing from the scope of the invention. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Further, components of different embodiments may be appropriately combined.

  101 transmission array antenna section, 102 transmission section, 103 transmission signal information holding section, 104 first channel information holding section, 105 second channel information holding section, 106 weight calculation section, 107 interference signal removal section, 108 reception section, 109 reception Array antenna unit, 110 processing unit.

Claims (16)

A first antenna unit having a plurality of first antenna elements for transmitting a transmission signal;
The reception frequency band at least partially overlaps the transmission frequency band of the transmission signal, and receives a reception signal in a reception period at least partially overlaps the transmission period of the transmission signal, the same number as the number of the first antenna elements A second antenna unit having a plurality of second antenna elements;
With
The interval s between at least two second antenna elements of the plurality of second antenna elements is λ for the wavelength corresponding to the reception frequency band, and D for the distance between the first antenna unit and the second antenna unit. When
An electronic device.   The electronic device according to claim 1, wherein each of the first antenna elements is installed such that a distance difference between each of the first antenna elements is an odd multiple of a quarter wavelength.   3. The electronic device according to claim 2, wherein each of the first antenna elements is provided on a hyperbola whose focal point is a position of each of the second antenna elements. 4.   4. The electronic device according to claim 3, wherein each of the first antenna elements is provided on the hyperbola whose distance is widened by reducing the distance between the second antenna elements. 5. A first antenna unit having a plurality of first antenna elements for transmitting a transmission signal;
A receiving frequency band that at least partially overlaps a transmission frequency band of the transmission signal, and a reception signal that is received in a reception period that at least partially overlaps a transmission period of the transmission signal; A second antenna unit having an array of antenna elements;
With
The distance s between at least two first antenna elements of the plurality of first antenna elements is λ, the wavelength corresponding to the reception frequency band, and D is the distance between the first antenna unit and the second antenna unit. When
An electronic device.   The electronic device according to claim 5, wherein each of the second antenna elements is installed such that a distance difference between each of the second antenna elements is an odd multiple of a quarter wavelength.   7. The electronic device according to claim 6, wherein each of the second antenna elements is provided on a hyperbola whose focal point is the position of each of the second antenna elements. 8.   The electronic device according to claim 7, wherein each of the second antenna elements is provided on the hyperbola whose interval is widened by reducing the interval between the second antenna elements.   The electronic device according to claim 1, wherein an element interval of the first antenna element and an element interval of the second antenna element are the same.   The electronic device according to claim 1, wherein an element interval of the first antenna element is different from an element interval of the second antenna element.   If there is a difference between the amplitudes of the respective channels between the first antenna unit and the second antenna unit, the radio station has a radio station that is a communication partner of the electronic device based on the amplitude ratio. The electronic device according to claim 1, further comprising a processing unit that requests to change the directivity of the first antenna unit. A transmission signal information holding unit that holds information of a transmission signal transmitted from the first antenna unit;
A first channel for holding first channel information between the electronic device and the wireless station based on a first reception signal transmitted from a wireless station of a communication partner of the electronic device and received by the second antenna unit; An information holding unit;
A second channel for holding second channel information between the first antenna unit and the second antenna unit based on a second reception signal transmitted from the first antenna unit and received by the second antenna unit An information holding unit;
A weight calculation unit that performs a weight calculation on the first received signal based on the first channel information and the second channel information;
An interference signal removal unit that removes an interference signal in the first reception signal based on the weighted first reception signal and the transmission signal held in the transmission signal information holding unit;
The electronic device according to claim 1, further comprising:   The first channel information and the second channel information may be channel information obtained as a result of channel estimation, channel information measured in a prior calibration process, or deterministically calculated channel information. The electronic device according to claim 12, which is:   The electronic device according to claim 12, wherein the interference signal removing unit removes the interference signal from only the corresponding first antenna element with respect to the first received signal from each of the second antenna elements. A first antenna unit having a plurality of first antenna elements for transmitting a transmission signal, a reception frequency band at least partially overlapping a transmission frequency band of the transmission signal, and at least partially overlapping a transmission period of the transmission signal; A second antenna unit having an array of the same number of second antenna elements as the first antenna element for receiving a reception signal during a reception period, comprising:
The distance between at least two second antenna elements of the plurality of second antenna elements is s, the wavelength corresponding to the reception frequency band is λ, and the distance between the first antenna unit and the second antenna unit is D. When
An antenna installation method for installing the second antenna element. A first antenna unit having a plurality of first antenna elements for transmitting a transmission signal, a reception frequency band at least partially overlapping a transmission frequency band of the transmission signal, and at least partially overlapping a transmission period of the transmission signal; A second antenna unit having an array of the same number of second antenna elements as the first antenna element for receiving a reception signal during a reception period, comprising:
An interval between at least two first antenna elements of the plurality of first antenna elements is s, a wavelength corresponding to the reception frequency band is λ, and a distance between the first antenna section and the second antenna section is D. When
An antenna installation method for installing the first antenna element.