JP2018148370A - Array antenna for simultaneous transmission/reception - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an array antenna for simultaneous transmission/reception capable of suppressing self interference by forming null in an end-fire direction with a low-cost device configuration by using a power feeding circuit for implementing analog signal processing in a Full-duplex communication system using a plurality of antennas.SOLUTION: An array antenna for simultaneous transmission/reception includes: a transmission array antenna 21 and a reception array antenna 30 configured using a reception antenna elements 1, 2, 3, 4, the antennas being arranged in positional relation in which the antennas are in an end-fire direction to each other; and an analog power feeding circuit configured using a plurality of hybrid circuits having two ports for input and two ports for output. Two input ports of each hybrid circuit at a first state are connected to an antenna element pair of two elements constituting an array antenna. One output port of two output ports of each hybrid circuit at the first state is connected to signal reception means; the other output port is connected to a hybrid circuit at a second stage.SELECTED DRAWING: Figure 4

Description

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

  Currently, TDD (Time Division Duplex) and FDD (Frequency Division Duplex) are used in relay stations, but further high-speed communication is required for the fifth generation communication system (5G). However, due to the depletion of frequency resources, it is difficult to realize high-speed communication with a wide band. On the other hand, Full-duplex technology that performs simultaneous transmission and reception using the same frequency has appeared, and is expected as a technology for improving channel capacity without using a new frequency band. Further, it is possible to improve the channel capacity according to the number of antennas by using MIMO (Multiple-Input Multiple-Output) technology using a plurality of antennas in the transceiver. A communication method combining the MIMO technology and the 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. In the receiver, the RF (Radio Frequency) front end is saturated or damaged by self-interference from a transmitter at a close distance. Further, since the self-interference signal is 100 dB stronger than the noise floor, the desired signal is buried in the self-interference and it is difficult to demodulate.
The following techniques can be cited as a method of suppressing this self-interference,

First, there is a method in which the arrangement of the transmission antenna is devised to form a null in the reception antenna (for example, Non-Patent Document 1). Specifically, it is a method in which an analog circuit intentionally wraps a signal from a transmission to a reception circuit and cancels it immediately before it is input to the receiver. However, this method assumes a case where one transmission / reception antenna is provided, and if a plurality of reception antennas are used, it is difficult to form nulls in all reception antennas. That is, in this method, it is necessary to individually prepare cancellation circuits for every possible combination of all transmitting antennas and all receiving antennas, and there is a problem that the circuit becomes complicated.

Further, as a method for suppressing self-interference in MIMO Full-duplex communication, there is an eigen-beamforming method (for example, Non-Patent Document 2). In this technique, as shown in FIG. 1, the spatial correlation in an LOS (Line of Sight) environment is increased by using an antenna arrangement as an endfire. As 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 performed by performing transmission beamforming using eigenvalues excluding the first eigenvalue.
Further, there is a technique for performing digital signal processing in combination with the eigen beam forming method and subtraction processing (Non-patent Document 3).

However, the technique using the eigen beamforming method has a problem that interference suppression is insufficient because an eigenvalue equal to or lower than the second eigenvalue does not become 0 in an actual environment. Further, the technique for performing digital signal processing has a problem in that weak signals cannot be decoded because quantization noise is generated in the presence of extremely strong interference.

J. I. Choi, M. Jain, K. Srinivasan, P. Levis and S. Katti, “Achieving single channel, full duplex wireless communication,” in Proc. 2010 ACM 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 MIMO full-duplex communication system using a plurality of antennas. However, an object of the present invention is to provide an array antenna for simultaneous transmission and reception that can be decoded and that does not require a significant change in the repeater system with a low-cost configuration.

The invention according to claim 1 of the present invention includes a transmission array antenna,
A receiving array antenna comprising a plurality of antenna elements arranged at equal intervals and linearly;
An array antenna for simultaneous transmission and reception comprising an analog power 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 that is in the endfire direction,
The analog power feeding circuit is configured in multiple stages using a plurality of hybrid circuits having two ports for input and two ports for output.
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 first-stage two 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 when there are a plurality of the second-stage hybrid circuits, the other output port is connected to the third-stage hybrid circuit,
As in the second stage, after connecting the hybrid circuits in multiple stages, one of the two output ports of the final stage hybrid circuit is connected to the signal receiving means and the other output port is connected to the signal terminating means. It is an array antenna for simultaneous transmission and reception characterized by being connected.

In the invention according to claim 2 of the present invention, the antenna element interval of the transmitting or receiving array antenna to which the analog power feeding circuit is connected is an integral multiple of ½ wavelength, and the hybrid circuit constituting the analog power feeding circuit is 2. The simultaneous transmission / reception array antenna according to claim 1, wherein the array antenna is a 180-degree hybrid.

According to the array antenna for simultaneous transmission and reception according to claim 1 of the present invention, in a full-duplex communication system, a null is formed in the endfire direction with a low-cost device configuration by using a feeding circuit that realizes analog signal processing. There is an effect that self-interference can be suppressed.

According to the array antenna for simultaneous transmission and reception according to claim 2 of the present invention, the antenna element interval of the receiving array antenna is an integral multiple of ½ wavelength, and a null is formed in the endfire direction with a low-cost device configuration, and self-interference There is an effect that can be suppressed.

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

It is explanatory drawing showing endfire arrangement | positioning It is a conceptual diagram which shows the desired directivity of a receiving antenna. It is a principle diagram of a hybrid circuit 1 is a structural diagram showing a transmission / reception antenna according to an embodiment of the present invention. 1 is a configuration circuit diagram of an interference suppression device according to an embodiment of the present invention. 4 is a graph showing a decrease in self-interference power according to an embodiment of the present invention.

In the form for implementing this invention, the interference suppression of MIMO Full-duplex communication is implement | achieved. In this embodiment, the phase difference of signals received by the receiving antenna is used, and the transmitting array antenna 20 and the receiving array antenna 30 are arranged in an endfire arrangement as shown in FIG. FIG. 2 shows the desired directivity of the receiving array antenna. As shown in FIG. 2, the receiving array antenna forms a null in the endfire direction, so that self-interference can be suppressed. A 180 degree hybrid circuit is connected to the receiving antenna. In this embodiment, it is possible to form a null in the endfire direction with only an analog circuit from the input / output characteristics of the 180-degree hybrid circuit and the phase difference between the received signals.

The following three points are listed as advantages of this embodiment. First, 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. Third, if the number of receiving antennas is 2 ^N (N is an integer), interference can be suppressed 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 whose output phase difference has a predetermined value. Mainly used in high frequency and microwave systems. The 90-degree hybrid circuit has an output phase difference of 90 degrees, and the 180-degree hybrid circuit has an output phase difference of 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 having 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, output characteristics with respect to the input of port 1 will be described. As shown in FIG. 3A, the signal input to port 1 is output to port 3 and port 4 with the same amplitude, and the phase is the same. Also, it is not output from port 2. As shown in FIG. 3B, the output characteristics with respect to the input of the port 2 are output to the ports 3 and 4 with the same amplitude, and the phases are reversed. Also, it is not output from port 1. Therefore, the sum of the inputs from port 1 and port 2 is output to port 3, and port 4 outputs the difference between the inputs from port 1 and port 2. 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 S parameter S _{hyb of the} hybrid is

And four piecewise matrices. Since the number of input and output ports is 2, each partition matrix is a quadratic square matrix. Here, the indices i and o of each partition matrix in (1) represent the input and output ports, respectively. Here, the partition matrices S _{hyb, ii} and S _{hyb, oo} represent the reflection at the port and the mutual coupling between the ports in the input part and the output part, respectively. In the case of an ideal hybrid circuit, there is no reflection or coupling at the input / output section.

It can be expressed as Where O _n represents the n-order square zero matrix. The partition matrix S _{hyb, oi} represents the transmission of power from the input port to the output port,

It is expressed.
In addition, the S parameter of the hybrid circuit is reversible, and _{Shyb and io} are symmetric matrices.

It becomes. Here, ^AT represents the transposed value of the matrix A.

FIG. 4 shows an arrangement relationship between the transmitting antenna and the receiving array antenna in the embodiment of the present invention. In FIG. 4, the receiving array antenna has four elements (1, 2, 3, 4), and transmission is a point wave source (21). It is assumed that there is a point wave source 21 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 apparatus connected to the receiving array antenna. In this embodiment, when there are 2 ^N reception array antennas, (2 ^N -1) hybrids are required. In FIG. 4, since the number of elements of the receiving array antenna 30 is four, three hybrids are required. Since the interval between the elements (1, 2, 3, 4) of the receiving array antenna is a half wavelength, the received power phase of the elements (1, 2, 3, 4) of each receiving array antenna is shifted by 180 degrees for reception. In the first-stage 180-degree hybrid shown in FIG. 5, the Σ port suppresses interference from the transmitter, and the Δ port remains with interference. The 180 degree hybrid Δ ports are connected to the second stage 180 degree hybrid. Since the in-phase interference power is input to the 180-degree hybrid at the second stage, the interference at the Δ port is suppressed and the interference remains at the Σ port. The Σ port of the second-stage hybrid where interference remains is terminated. According to the present invention, interference can remain in one of the four ports, and interference from the other three ports (# 1, # 2, # 3) can be suppressed. The reception weight w _RX in this embodiment is

Can be shown.

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 an embodiment of the present invention. In this calculation, it is assumed that the hybrid operates ideally in consideration of free space loss. 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 from the point wave source is

And
Also, the received power p (n) and the self-interference power _PRx are

It 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 power of all the ports including the port 4 where interference remains is the self-interference power (solid line) according to the reference example not using the present invention, and the received power of the ports excluding the port 4 is averaged. The value is the self-interference power (dotted line) according to the embodiment of the present invention.

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

From the above results, this form can suppress the interference signal in the endfire direction for analog circuits using only a hybrid, and can suppress self-interference simply by adding the form circuit to the receiving array antenna. It was shown that. In this embodiment, the calculation result at 2.29 GHz is shown, but the present invention can be used regardless of the frequency band. Further, the higher the frequency, the smaller the element spacing, and thus the miniaturization is possible. Moreover, even if the number of antennas increases, it can be adapted by increasing the number of hybrids accordingly.
In the example described above, the 180-degree hybrid circuit is used. However, if the antenna element interval is an integral multiple of a quarter wavelength, a 90-degree hybrid circuit may be used. For example, a signal having a phase that causes interference suppression may be selected and input to the input ports 1 and 2. Also, a 90-degree hybrid and a 180-degree hybrid may be combined.
In the above example, 2 ^N / 2 hybrid circuits are used in the first stage, and the number of hybrid circuits is sequentially combined until the number of hybrid circuits in the final stage becomes 1, but the number of hybrid circuits is 1 The last stage may be 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, a rat race circuit may be used as the 180-degree hybrid circuit, for example.

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

10 array antenna for simultaneous transmission / reception 20 transmitting array antenna 21 transmitting antenna 30 receiving array antenna 1, 2, 3, 4 receiving antenna elements A, B, C, D, E 180 degree hybrid circuit

Claims (2)

A transmitting array antenna;
A receiving array antenna comprising a plurality of antenna elements arranged at equal intervals and linearly;
An array antenna for simultaneous transmission and reception comprising an analog power 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 that is in the endfire direction,
The analog power feeding circuit is configured in multiple stages using a plurality of hybrid circuits having two ports for input and two ports for output.
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 first-stage two 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 when there are a plurality of the second-stage hybrid circuits, the other output port is connected to the third-stage hybrid circuit,
As in the second stage, after connecting the hybrid circuits in multiple stages, one of the two output ports of the final stage hybrid circuit is connected to the signal receiving means and the other output port is connected to the signal terminating means. An array antenna for simultaneous transmission and reception characterized by being connected. The antenna element interval of the transmitting or receiving array antenna to which the analog power feeding circuit is connected is an integral multiple of ½ wavelength, and the hybrid circuit constituting the analog power feeding circuit is a 180-degree hybrid. Item 9. An array antenna for simultaneous transmission and reception according to Item 1.

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