JP6960076B2 - Array antenna for simultaneous transmission and reception - Google Patents

Description

The present invention relates to an array antenna for simultaneous transmission / reception that can improve signal reception sensitivity by suppressing self-interference, which is a problem in a full duplex system that transmits and receives radio waves simultaneously and at the same frequency, by using analog signal processing. ..

Currently, TDD (Time Division Duplex) schemes and FDD (Frequency Division Duplex) schemes are used in relay stations, but further high-speed communication schemes are required for fifth-generation communication systems (5G). However, due to the depletion of frequency resources, it is difficult to realize high-speed communication in a wide band. On the other hand, a full-duplex technology that performs simultaneous transmission and reception using the same frequency has appeared, and is expected as a technology that improves the channel capacity without using a new frequency band. Further, by using MIMO (Multiple-Input Multiple-Output) technology using a plurality of antennas for a transceiver, it is possible to improve the channel capacitance according to the number of antennas. A communication system that combines this MIMO technology and Full-duplex technology is defined as a MIMO Full-duplex communication system.

A problem with full-duplex communication is self-interference in which the receiver receives its own transmission signal. The receiver saturates or damages the RF (Radio Frequency) front end due to self-interference from a remote transmitter. Further, since the self-interference signal is 100 dB stronger than the noise floor, the desired signal is buried in the self-interference and demodulation becomes difficult.
The following techniques can be mentioned as a method of suppressing this self-interference.

First, there is a method of forming a null in the receiving antenna by devising the arrangement of the transmitting antenna (for example, Non-Patent Document 1). Specifically, it is a method in which a signal is intentionally circulated from a transmission to a reception circuit by an analog circuit and canceled immediately before being input to the receiver. However, this method assumes the case where there is one transmitting / receiving antenna, and it is difficult to form nulls in all receiving antennas when a plurality of receiving antennas are used. That is, in this method, it is necessary to individually prepare a cancel circuit for every combination of all transmitting antennas and all receiving antennas, which causes a problem that the circuit becomes complicated.

Further, as a method for suppressing self-interference in MIMO Full-duplex communication, an intrinsic beamforming method (eigen-beamforming method) can be mentioned (for example, Non-Patent Document 2). In this technique, as shown in FIG. 1, the spatial correlation in the LOS (Line of Sight) environment is increased by setting the antenna arrangement to the end fire. When the spatial correlation increases, only the first eigenvalue increases, and the other eigenvalues approach zero. Since the eigenvalue and the interference received power are in a proportional relationship, interference suppression can be achieved by performing transmission beamforming using the eigenvalues other than the first eigenvalue.
Further, there is a technique for performing digital signal processing in combination with the above-mentioned intrinsic beamforming method and subtraction processing (Non-Patent Document 3).

However, the technique using the eigenbeam forming method has a problem that the interference suppression is insufficient because the eigenvalues below the second eigenvalue do not become 0 in the actual environment. Further, in the technique of performing digital signal processing, there is a problem that a weak signal cannot be decoded because quantization noise is generated in the presence of interference having extremely strong intensity.

J. I. Choi, M. Jain, K. Srinivasan, P. Levis and S. Katti, “Achieving single channel, full duplex wireless communication,” in Proc. 2010ACM MobiCom., Pp. 1-12, Sept. 2010. M.Tsunezawa, N. Honma, K.Takahashi, Y.Tsunekawa, K.Murata and K.Nishimori, “Interference reduction between SDD linear array antennas using end-firearrangement,” 2015 IEEE International Symposium on Antennas and Propagation & USNC / URSI National Radio Science Meeting, pp. 2511-2512, Jul. 2015. Yoshiyuki Yamamoto, Ryota Takahashi, Masakuni Tsunezawa, NaokiHonma, and Kentaro Murata, “Experimental evaluation of interference reduction effect; Eigen-beamforminng and digital subtraction by using MIMO-OFDm signals” in IEICE Communications Express, vol.6, No, 2, 71- 76

The present invention is a weak signal in a MIMO Full-duplex communication system using a plurality of antennas, in which self-interference is suppressed even in a real environment as an array antenna for simultaneous transmission / reception to which a feeding circuit for realizing analog signal processing is added. It is an object of the present invention to provide an array antenna for simultaneous transmission / reception, which can be decrypted even if the antenna is used, and which has a low cost configuration and does not require a significant change in the repeater system.

The invention according to claim 1 of the present invention includes a transmitting array antenna and
A receiving array antenna consisting of multiple antenna elements arranged at equal intervals and linearly,
A simultaneous transmission / reception array antenna including an analog feeding circuit connected to the reception array antenna or the transmission antenna.
The transmitting antenna and the receiving array antenna are arranged in a positional relationship so as to be in the endfire direction with each other.
The analog power supply circuit input Ri output 2 ports der 2 port, which is configured in a multistage output phase difference by using a plurality of hybrid circuits is a directional coupler which is a predetermined value,
Each of the two input ports of the first-stage hybrid circuit is connected to two antenna element pairs constituting the array antenna, and one of the two output ports of each of the first-stage hybrid circuits is connected to the signal receiving means. And the other output port is connected to the second stage hybrid circuit,
Each of the two input ports of the second-stage hybrid circuit is connected to one of the output ports of each of the two first-stage hybrid circuits, and one of the output ports of each of the second-stage hybrid circuits. The output port is connected to the signal receiving means, and if there are a plurality of the second-stage hybrid circuits, the other output port is connected to the third-stage hybrid circuit.
The other output ports with one output port is connected to the signal receiving means of the two output ports of the hybrid circuit of the final stage After repeatedly multistage connection hybrid circuit as in the second stage signal termination It is an array antenna for simultaneous transmission / reception, which is characterized by being connected to a means.

According to the second aspect of the present invention, the antenna element spacing of the transmitting or receiving array antenna to which the analog feeding circuit is connected is an integral multiple of 1/2 wavelength, and the hybrid circuit constituting the analog feeding circuit . The array antenna for simultaneous transmission / reception according to claim 1, wherein the output phase difference is 180 degrees.

According to the array antenna for simultaneous transmission / reception according to claim 1 of the present invention, a null is formed in the endfire direction with a low-cost device configuration by using a power supply circuit that realizes analog signal processing in a full-duplex communication system. It has the effect of suppressing self-interference.

According to the array antenna for simultaneous transmission / reception according to claim 2 of the present invention, the antenna element spacing of the receiving array antenna is set to an integral multiple of 1/2 wavelength, and a null is formed in the endfire direction in a low-cost device configuration to cause self-interference. Has the effect of suppressing.

According to the present invention, in a full-duplex communication system using a plurality of antennas, by using a power feeding circuit that realizes analog signal processing, a null is formed in the endfire direction in a low-cost device configuration to suppress self-interference. It is possible to obtain an array antenna for simultaneous transmission and reception.

It is explanatory drawing which shows the end fire arrangement. It is a conceptual diagram which shows the desired directivity of a receiving antenna. It is a principle diagram of a hybrid circuit. It is a structural drawing which shows the transmission / reception antenna which concerns on embodiment of this invention. It is a block diagram of the interference suppression apparatus which concerns on embodiment of this invention. It is a graph which shows the decrease of the self-interference power which concerns on embodiment of this invention.

In the embodiment for carrying out the present invention, interference suppression of MIMO Full-duplex communication is realized. This embodiment utilizes the phase difference of the signal received by the receiving antenna, and as shown in FIG. 1, the transmitting array antenna 20 and the receiving array antenna 30 are arranged in an endfire arrangement. FIG. 2 shows the desired directivity of the receiving array antenna. As shown in FIG. 2, self-interference can be suppressed by forming a null in the end fire direction of the receiving array antenna. Connect a 180 degree hybrid circuit to the receiving antenna. In this embodiment, due to the input / output characteristics of the 180-degree hybrid circuit and the phase difference of the received signal, it is possible to form a null in the endfire direction only with the analog circuit.

The advantages of this embodiment include the following three points. The first point is that as long as the element spacing of the receiving array antenna is constant, it is not affected by the type of element antenna. The second point is that interference suppression is possible regardless of the distance between the transmitting and receiving antennas. The third point is that if the number of receiving antennas is 2 ^N (N is an integer), interference suppression is possible regardless of the number of antennas.

In order to explain this embodiment, the principle of the hybrid circuit will be described first.
The hybrid circuit is a directional coupler such that the output phase difference becomes a predetermined value. Mainly used in high frequency and microwave systems. In the 90 degree hybrid circuit, the output phase difference is 90 degrees, and in the 180 degree hybrid circuit, the output phase difference is 180 degrees.

Hereinafter, a 180-degree hybrid (hereinafter referred to as a hybrid) will be described as an example. The hybrid is a passive element composed of two inputs and two outputs, and FIG. 3 shows a schematic diagram of the hybrid. Ports 1 and 2 are input ports, and ports 3 and 4 are output ports. First, the output characteristics for the input of port 1 will be described. As shown in FIG. 3A, the signal input to the port 1 is output to the port 3 and the port 4 with the same amplitude, and the phases are in phase. Also, it is not output from port 2. As shown in FIG. 3B, the output characteristics for the input of the port 2 are output to the port 3 and the port 4 with the same amplitude, and the phases are out of phase. Also, it is not output from port 1. Therefore, the sum of the inputs from the port 1 and the port 2 is output to the port 3, and the difference between the inputs from the port 1 and the port 2 is output to the port 4. Therefore, port 3 is a Σ port and port 4 is a Δ port.

と４つの区分行列で表せる。入力および出力ポート数はそれぞれ ２ となるため各区分行列は ２ 次の正方行列となる。ここで （１） における各区分行列のインデックスｉ およびｏ はそれぞれ入力および出力ポートを表している。ここで区分行列Ｓ_{ｈｙｂ，ｉｉ}およびはＳ_{ｈｙｂ，ｏｏ}それぞれ入力部および出力部におけるポートでの反射およびポート間の相互結合を表す。理想的なハイブリッド回路であれば、入出力部の反射、結合はないため、

と表せる．ここでＯ_ｎはｎ次の正方零行列を表している。また区分行列Ｓ_{ｈｙｂ，ｏｉ}は入力ポートから出力ポートへの電力の伝達を表しており、

と表される。
またハイブリッド回路のＳパラメータは可逆性が成り立ち、かつＳ_{ｈｙｂ，ｉｏ}は対称行列であるため

となる。ここでA^Tは行列Aの転値を表す。 Next, the S-parameter characteristics of the hybrid will be described. The hybrid S-parameter _Shyb

Can be represented by four block matrices. Since the number of input and output ports is 2, each block matrix is a quadratic square matrix. Here, the indexes i and o of each block matrix in (1) represent input and output ports, respectively. Here, the _{block matrices Shyb, ii} and _{Shyb, oo} represent reflections at the ports and interconnections between the ports at the input and output sections, respectively. If it is an ideal hybrid circuit, there is no reflection or coupling of the input / output part, so

Can be expressed as. Where O _n represents the n-order square zero matrix. The _{block matrix Shyb and oi} represent the transfer of electric power from the input port to the output port.

It is expressed as.
Also, since the S-parameters of the hybrid circuit are reversible, and _{Shyb and io} are symmetric matrices.

Will be. Where A ^T represents the turning value of the matrix A.

FIG. 4 shows the arrangement relationship between the transmitting antenna and the receiving array antenna according to the embodiment of the present invention. In FIG. 4, the receiving array antenna has four elements (1, 2, 3, 4), and the transmitting is a point wave source (21). It is assumed that the point wave source 21 is in the end fire direction of the receiving array antenna 30. Spacing elements (1, 2, 3, 4) between the receiving array antennas 30 are all set to _{d element} = _{λ 0/2,} defines a transmission and reception antenna distance _{d TX-RX.}

と示すことができる． FIG. 5 shows a configuration diagram of an interference suppression device connected to the receiving array antenna. In this embodiment, when the number of receiving array antennas is 2 ^{N, the} number of hybrids required is (2 ^N- 1). In FIG. 4, since the receiving array antenna 30 has four elements, three hybrids are required. Since the intervals between the elements (1, 2, 3, 4) of the receiving array antennas are half wavelengths, the received power phases of the elements (1, 2, 3, 4) of each receiving array antenna are shifted by 180 degrees for reception. In the first-stage 180-degree hybrid shown in FIG. 5, the Σ port suppresses the interference from the transmitter, and the Δ port retains the interference. The Δ ports of the 180 degree hybrid are connected to the 180 degree hybrid of the second stage. Since the interference power of the same phase is input to the 180-degree hybrid of the second stage, the interference of the Δ port is suppressed, and the interference remains in the Σ port. The Σ port of the second stage hybrid where the interference remains is terminated. According to the present invention, it is possible to leave interference in one of the four ports and suppress the interference in the other three ports (# 1, # 2, # 3). The reception weight w _RX in this embodiment is

Can be shown as.

とする。
また、受信電力ｐ（ｎ）、自己干渉電力Ｐ_Ｒｘを、

と定義する。ここで、ｐ_ｎは給電回路の出力ｎポートの受信電力を表す。干渉が残留するポート４を含む全てのポートの受信電力を平均化した値が本発明を用いない参考例に係る自己干渉電力（実線）であり、ポート４を除くポートの受信電力を平均化した値が本発明の実施例に係る自己干渉電力（点線）である。 FIG. 6 shows the result of calculating the self-interference power when the transmission / reception antenna distance is changed for the model of FIG. 4 which is the embodiment of the present invention. In this calculation, the free space loss is taken into consideration, and the hybrid operates ideally. The frequency used is 2.29 GHz. Here, λ ₀ is the wavelength in vacuum, and the propagation path h _i of the _{receiving antenna Rx i is drawn from the point wave source.}

And.
Further, the received power p (n) and the self-interference power _PRx are set to

Is defined as. Here, p _n represents the received power of the output n ports of the feeder circuit. The value obtained by averaging the received powers of all the ports including the port 4 in which the interference remains is the self-interference power (solid line) according to the reference example in which the present invention is not used, and the received powers of the ports excluding the port 4 are averaged. The value is the self-interference power (dotted line) according to the embodiment of the present invention.

From FIG. 6, it can be seen that the embodiment (solid line) of the present invention can reduce the self-interference power as compared with the reference example. The greater the distance between the transmitting and receiving antennas, the greater the effect of the present invention. This is because the longer the distance between the transmitting and receiving antennas, the smaller the difference in free space loss between the antennas. If the hybrid performance is ideal and the amplitude of the received power for each receiving antenna is equal, the interference from the point wave source can be completely suppressed.

From the above results, this embodiment can suppress the interference signal in the end fire direction for the analog circuit using only the hybrid, and self-interference can be suppressed only by adding the circuit of this embodiment to the receiving array antenna. Was shown to be. Although the calculation result at 2.29 GHz is shown in this embodiment, the present invention can be used regardless of the frequency band. The higher the frequency, the smaller the element spacing, so miniaturization is possible. Moreover, even if the number of antennas increases, it can be adapted by increasing the number of hybrids accordingly.
In the above-mentioned example, a 180-degree hybrid circuit is used, but a 90-degree hybrid circuit may be used when the antenna element spacing is an integral multiple of the 1/4 wavelength. For example, a signal having a phase that causes interference suppression may be selected and input to the input ports 1 and 2. Further, a 90-degree hybrid and a 180-degree hybrid may be combined.
Further, in the above example, an example is shown in which 2 ^N / 2 hybrid circuits are used in the first stage and combined in multiple stages in sequence until the number of hybrid circuits in the final stage becomes 1, but the number of hybrid circuits is 1. The stage before becoming the final stage may be used as the final stage, and this case is also included in the scope of the present invention.
The type of circuit configuration of the hybrid circuit is not limited. For example, as a 180-degree hybrid circuit, for example, a rat race circuit may be used.

According to the present invention, in a Full-duplex communication system using a plurality of antennas, by using a power feeding circuit that realizes analog signal processing, a null is formed in the endfire direction in a low-cost device configuration to suppress self-interference. It is possible to obtain an array antenna for simultaneous transmission and reception, which contributes to the development of communication-related industries.

10 Simultaneous transmission / reception array antenna 20 Transmission array antenna 21 Transmission antenna 30 Reception array antenna 1, 2, 3, 4 Reception antenna elements A, B, C, D, E 180 degree hybrid circuit

Claims (2)

With the transmitting array antenna
A receiving array antenna consisting of multiple antenna elements arranged at equal intervals and linearly,
A simultaneous transmission / reception array antenna including an analog feeding circuit connected to the reception array antenna or the transmission antenna.
The transmitting antenna and the receiving array antenna are arranged in a positional relationship so as to be in the endfire direction with each other.
The analog power supply circuit input Ri output 2 ports der 2 port, which is configured in a multistage output phase difference by using a plurality of hybrid circuits is a directional coupler which is a predetermined value,
Each of the two input ports of the first-stage hybrid circuit is connected to two antenna element pairs constituting the array antenna, and one of the two output ports of each of the first-stage hybrid circuits is connected to the signal receiving means. And the other output port is connected to the second stage hybrid circuit,
Each of the two input ports of the second-stage hybrid circuit is connected to one of the output ports of each of the two first-stage hybrid circuits, and one of the output ports of each of the second-stage hybrid circuits. The output port is connected to the signal receiving means, and if there are a plurality of the second-stage hybrid circuits, the other output port is connected to the third-stage hybrid circuit.
The other output ports with one output port is connected to the signal receiving means of the two output ports of the hybrid circuit of the final stage After repeatedly multistage connection hybrid circuit as in the second stage signal termination An array antenna for simultaneous transmission and reception, which is characterized by being connected to a means. The antenna element spacing of the transmitting or receiving array antenna to which the analog feeding circuit is connected is an integral multiple of 1/2 wavelength, and the output phase difference of the hybrid circuit constituting the analog feeding circuit is 180 degrees. The array antenna for simultaneous transmission / reception according to claim 1.

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