WO2016035857A1 - Digital wireless communication device and digital wireless communication system - Google Patents

Abstract

In the present invention, a composite cable (4) houses a plurality of leaky coaxial cables (2a, 2b) having different emission characteristics. The leaky coaxial cables (2a, 2b) include in their respective interiors an internal conductor and an external conductor, and the cables are provided with a plurality of leakage slots. The plurality of leakage slots have a different pitch or are arranged in different patterns in the slot axial direction. The digital wireless communication device supplies a high-frequency signal from the end part of the composite cable (4) to execute multiple-input, multiple-output (MIMO) communication.

Description

Digital radio communication apparatus and digital radio communication system

The present invention relates to a configuration of a radio communication technique for performing digital communication between a mobile station and a ground station installed on the ground.

Mobile communication terminals such as smartphones are now a daily necessities, and the amount of communication by buses, trains, airplanes, etc. is increasing.

On the other hand, leaky coaxial cable (LCX: Leaky Coaxial Cable) is used as an antenna for dead zone countermeasures such as tunnels and underground malls due to its features such as stable connectivity, and further the communication range along the cable Since it can be configured, it is expected to be expanded to a “linear cell”.

That is, a stable wireless network connection is required on long and narrow locations called “linear cells”, such as areas along railways, tunnels, underground malls, shopping malls, airplanes or trains. May be. For linear cell environments, leaky coaxial cables can be used for wireless communications as antennas in such environments because leaky coaxial cables have several potential advantages. That is, when a leaky coaxial cable is used for a linear cell, for example, the area covered by the leaky coaxial cable is constant, and the installation may be simpler than other methods.

On the other hand, even in a system using LCX, application of MIMO (multiple-input multiple-output) technology is being studied to improve frequency utilization efficiency (see Non-Patent Document 1 described later). ).

However, in the method disclosed in Non-Patent Document 1, it is necessary to install a plurality of LCXs so as to have a sufficiently low correlation with each other, resulting in an increase in laying and maintenance costs.

In order to deal with such a problem, there is also a proposal for a 2 × 2 MIMO system using a single LCX (see Non-Patent Document 2 and Non-Patent Document 3 below). In this method, it is necessary to input signals from both sides of the LCX, and it is necessary to lay so that both ends of the LCX are substantially at the same position, or to lay a coaxial cable or the like separately to the opposite end of the LCX. Therefore, when the length of the LCX becomes long, the laying cost increases.

Further, in Patent Document 1 described later, in a bundled leaky coaxial cable, each outer conductor of the first leaky coaxial cable, the second leaky coaxial cable, and the third leaky coaxial cable has a predetermined size. The first to third leaky coaxial cables are formed so that the directions of the slits in the predetermined direction on the outer circumference are different between the leaky coaxial cables so that the correlation is reduced. Alternatively, a leaky coaxial cable in which the angle of the slit is set so that the interval between the leaky coaxial cables is more than half of the wavelength or the direction of the polarization plane is different between the leaky coaxial cables. A configuration that binds and realizes MIMO communication is disclosed.

JP 2011-199760 A

Kawai et al., "A study of intra-train MIMO throughput characteristics using LCX", IEICE Technical Report, AP2011-172 (2012-01), pp147-152. Tsukamoto Seiji, Ano Susumu, Maeda Takahiro, Ban Koji, Kobayashi Kiyoshi, “A Study of 2 × 2 MIMO System Using Single Leakage Coaxial Cable”, 2013 IEICE General Conference Proceedings, B-1-220 S. Tsukamoto, T. Maeda and Y. Hou, et al. "Performance evaluation of 2x2 MIMO system with single leaky coaxial cable," in Proc.VJISAP (Vietnam-Japan International Symposium on 2014 264, Jan. 2014.

However, for a system that can accommodate more communication traffic, it is necessary to further improve spectral efficiency.

Also, when realizing such an improvement in spectral efficiency with a leaky coaxial cable, it is also necessary to reduce the cost for installation.

On the other hand, although the technique described in Patent Document 1 has the disclosure as described above, when a plurality of leaky coaxial cables are arranged close to each other, a configuration for actually realizing good MIMO characteristics is sufficient. It cannot be said that it has been studied.

The present invention has been made to solve the above problems, and one object of the present invention is to accommodate more communication traffic by using a leaky coaxial cable for a linear cell. It is to provide a digital wireless communication apparatus and a digital wireless communication system capable of performing the above.

Another object of the present invention is to provide a digital radio communication apparatus and a digital radio communication system that can accommodate more communication traffic while suppressing the cost of installing a leaky coaxial cable.

According to one aspect of the present invention, a digital wireless communication device includes a composite cable that houses a plurality of leaky coaxial cables having different radiation characteristics, each leaky coaxial cable including an inner conductor and an outer conductor, When a radiation angle is an angle formed by a peak direction of radiation in a plane including the axial direction and the normal direction with respect to the normal direction in the axial direction of the leaky coaxial cable, Each of the leaky coaxial cables further has a transmission angle for supplying a high-frequency signal from at least one end of the composite cable and performing MIMO (multiple-input multiple-output) communication.

Preferably, the plurality of leaky coaxial cables have different leakage slot arrangement cycles so that each has a different radiation angle.

Preferably, the plurality of leaky coaxial cables have different dielectric constants or diameters of the inner conductors between the inner conductor and the outer conductor so as to have different radiation angles.

Preferably, the difference between the different radiation angles is at least 11 degrees or more.

Preferably, in the plurality of leaky coaxial cables, the angles of the leak slots with respect to the axial direction of the leaky coaxial are further different.

Preferably, the transmission means supplies a high-frequency signal to each of the leaky coaxial cables from both ends of the composite cable.

Preferably, the plurality of leaky coaxial cables are housed in a single covering structure.

According to another aspect of the present invention, a first digital wireless device is provided that is fixedly installed, and the first digital wireless communication device includes a composite cable that houses a plurality of leaky coaxial cables having different radiation characteristics. Each leaky coaxial cable includes an inner conductor and an outer conductor and is provided with a plurality of leak slots, and the peak direction of radiation is axial and normal with respect to the axial normal direction of the leaky coaxial cable. A plurality of leaky coaxial cables each having a different radiation angle, supplying a high-frequency signal from at least one end of the composite cable, and performing MIMO communication. The mobile terminal further includes a transmission means, and further includes a second digital wireless communication apparatus that performs MIMO communication with the first digital wireless communication apparatus.

Preferably, the plurality of leaky coaxial cables have different leakage slot arrangement cycles so that each has a different radiation angle.

Preferably, the plurality of leaky coaxial cables have different dielectric constants or diameters of the inner conductors between the inner conductor and the outer conductor so as to have different radiation angles.

Preferably, the difference between the different radiation angles is at least 11 degrees or more.

Preferably, in the plurality of leaky coaxial cables, the angles of the leak slots with respect to the axial direction of the leaky coaxial are further different.

Preferably, the transmission means supplies a high-frequency signal to each of the leaky coaxial cables from both ends of the composite cable.

Preferably, the plurality of leaky coaxial cables are housed in a single covering structure.

According to the digital wireless communication apparatus and the digital wireless communication system of the present invention, it is possible to accommodate more communication traffic using a leaky coaxial cable for a linear cell.

Furthermore, according to the digital radio communication apparatus and the digital radio communication system of the present invention, it is possible to accommodate more communication traffic while suppressing the cost of installing the leaky coaxial cable.

It is a conceptual diagram for demonstrating the aspect of the linear cell of this Embodiment. It is a conceptual diagram for demonstrating the MIMO system using the conventional LCX. It is a conceptual diagram for demonstrating the MIMO communication by the composite type LCX cable of this Embodiment. It is a figure for demonstrating the structure of LCX for making a radiation characteristic different. 2 is a functional block diagram for explaining the configuration of a digital wireless communication apparatus 1000 that supplies an RF signal to a composite cable 4. FIG. It is a conceptual diagram which shows a measurement system. It is a figure which shows the cumulative distribution function of CN value with respect to each measured area. It is a conceptual diagram for demonstrating the radiation principle and radiation angle from LCX. It is a figure which shows the structure of the MIMO system which uses single LCX as 2 antenna equivalent. It is a figure for demonstrating the structure which implement | achieves 2x2 MIMO by two adjacent LCX. It is a radiation pattern measurement result of a cable with a radiation angle of 11 degrees when one end of LCX is terminated at 50Ω. It is a radiation pattern measurement result of a cable with a radiation angle of 18 degrees when one end of LCX is terminated at 50Ω. It is a radiation pattern measurement result of a cable with a radiation angle of 26 degrees when one end of LCX is terminated at 50Ω. It is a radiation pattern measurement result of a cable with a radiation angle of 35 degrees when one end of LCX is terminated at 50Ω. It is a radiation pattern measurement result of a cable with a radiation angle of 44 degrees when one end of LCX is terminated at 50Ω. It is a radiation pattern measurement result of a cable with a radiation angle of 55 degrees when one end of LCX is terminated at 50Ω. It is a radiation pattern measurement result of a cable with a radiation angle of 71 degrees when one end of LCX is terminated at 50Ω. It is a figure for demonstrating the arrangement | positioning which measured the characteristic of 2x2 MIMO. It is a figure which shows the measurement result of the throughput at the time of feeding both sides to LCX of a zigzag slot with a radiation angle of 18 degrees. It is a figure which shows the measurement result of the throughput at the time of feeding both sides to LCX of the zigzag type slot with a radiation angle of 26 degrees. It is a figure which shows the measurement result of the throughput at the time of feeding both sides to LCX of the zigzag type slot with a radiation angle of 35 degrees. It is a figure which shows the measurement result of the throughput at the time of feeding both sides to LCX of the zigzag type slot with a radiation angle of 44 degrees. It is a figure which shows the measurement result of the throughput at the time of feeding both sides to LCX of a zigzag slot with a radiation angle of 55 degrees. It is a figure which shows the throughput at the time of supplying electric power from two sides to two adjacent LCXs having a radiation angle of 18 degrees and 55 degrees. It is a figure which shows the throughput at the time of supplying electric power from two sides to two adjacent LCXs having radiation angles of 26 degrees and 55 degrees. It is a figure which shows the throughput at the time of supplying electric power from two sides to two adjacent LCXs having a radiation angle of 44 degrees and 55 degrees. It is a figure which shows the throughput at the time of supplying electric power from two sides to two adjacent LCXs having radiation angles of 26 degrees and 71 degrees. It is a figure which shows the throughput at the time of supplying electric power to two LCX of 35 degree | times and 55 degree | times of radiation angles which adjoined from one side. It is a figure which shows the throughput at the time of supplying electric power from two sides to two LCXs with close radiation angles of 35 degrees and 71 degrees. It is a figure for demonstrating the peak direction and radiation angle of radiation.

Hereinafter, a radio communication system according to an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, components and processing steps with the same reference numerals are the same or equivalent, and the description thereof will not be repeated unless necessary.

(Embodiment 1)
(Outline of wireless communication system)
FIG. 1 is a conceptual diagram for explaining an aspect of the linear cell of the present embodiment.

As shown in FIG. 1A, for example, when wireless communication is realized in an environment such as a train home, conventionally, one wireless base station is arranged per picocell, and the user moves around the home. When a terminal held by the mobile terminal straddles between pico cells, it is necessary to perform a handover process.

On the other hand, as shown in FIG. 1B, when the leaky coaxial cable 2 is used as an antenna, it is possible to avoid a handover process and interference between cells.

Further, as will be described later, in FIG. 1 (b), in order to improve the frequency utilization efficiency in the LCX system in an environment where a mobile terminal exists at a high density that causes communication congestion, MIMO technology is used. Use to improve communication capacity in wireless communication.

FIG. 2 is a conceptual diagram for explaining a MIMO scheme using a conventional LCX.

As shown in FIG. 2 (a), conventionally, a MIMO system is configured assuming that one LCX is simply used as one antenna.

When the transmission directions of the input RF signal A and the signal B are the same, the radiation characteristics have a high correlation.

Therefore, in order to form a MIMO system, a plurality of (two in the figure) LCXs 2a and 2b are required, and the interval between the LCXs needs to be a certain distance or more. In this way, the signal A and the signal B are supplied from one end to the spaced LCX, respectively, and the terminal UE is positioned between the LCX, thereby realizing MIMO communication.

On the other hand, as described in Non-Patent Document 2 described above, the signals A and B are supplied from both ends of a single LCX as shown in FIG. Different directions occur in the directivity pattern, and the correlation becomes low. Therefore, a 2 × 2 MIMO system can be realized by using a single LCX as two antennas (antennas having two directivities).

3 is a conceptual diagram for explaining MIMO communication using the composite LCX cable according to the present embodiment.

By combining two LCXs 2a and 2b having different radiation characteristics into one composite cable 4, a 4 × 4 MIMO system can be realized. That is, the composite cable 4 contains two LCXs 2a and 2b having different radiation characteristics in one covering structure. The RF signal A and the signal C are transmitted from one end side, and the RF signal B is transmitted from the other end side. And the signal D are supplied to the LCXs 2a and 2b, respectively.

In FIG. 3A, the radiation characteristics are different depending on the interval P (see FIG. 2) of slots through which radio waves leak in LCX. As shown in FIG. 3B, the radiation characteristics such as radiation intensity and polarization can be changed by changing the angle at which the slot is inclined with respect to the axial direction of the leaky coaxial axis while keeping the opening area of the slot constant. . Further, in order to make the radiation characteristics different in different LCXs, in addition to the interval of the slots, the angle at which the slots are inclined with respect to the axial direction of the leaky coaxial may be changed. Note that the number of LCXs having different radiation characteristics stored in one covering structure is not limited to two and may be larger.

FIG. 4 is a diagram for explaining the structure of the LCX for making the radiation characteristics different. In FIG. 4, the structure is removed in order from the outside of the LCX, and the internal structure is sequentially displayed so as to appear.

An insulating layer 202 having a relative dielectric constant εr is provided around the inner conductor 200 on the central axis of the LCX. Slots 206 are provided at intervals P in the outer conductor 204 provided on the outer periphery of the insulating layer 202. A covering structure 208 is further provided on the outer periphery of the outer conductor 204.

In the configuration shown in FIG. 4, the angle θ _m formed by the direction of the peak of radiation with respect to the normal direction to the axial direction of LCX is expressed by the following equation.

　ここで、ｍは、高調波の次数に関するパラメータであり、その絶対値が次数を表す。λ_ＲＦは、ＲＦ波の波長であり、Ｐは、スロットの間隔である。ＬＣＸでは、通常は、高調波の放射を抑制し安定した伝搬路を形成するために、ｍ＝－１となるように設計される。

Here, m is a parameter related to the order of the harmonic, and its absolute value represents the order. λ _RF is the wavelength of the RF wave, and P is the slot spacing. The LCX is usually designed so that m = −1 in order to suppress harmonic radiation and form a stable propagation path.

FIG. 5 is a functional block diagram for explaining the configuration of the digital wireless communication apparatus 1000 that supplies an RF signal to the composite cable 4 (see FIG. 3). Digital wireless communication apparatus 1000 is installed in a ground station (for example, a base station) and generates a signal radiated from a composite cable. With regard to the reception structure, basically, it is only necessary to provide a configuration for performing processing in the reverse direction of the transmission configuration.

Referring to FIG. 5, digital wireless communication apparatus 1000 includes nodes 10.1 to 10 for transmitting signals to composite cable 4. n is provided. Although not particularly limited, for example, the nodes 10.1 to 10. It is assumed that n is four and that the nodes 10.1 to 10.4 transmit the signals A to D in FIG. In order to operate as 4 × 4 MIMO, it is necessary to transmit signals A to D from both sides of the composite cable 4 as shown in FIG. However, for example, if it is assumed to operate as 2 × 2 MIMO, signals A and C (or signals B and D) are transmitted from one end side of the composite cable 4 and a termination device is provided on the other end side. It is good. In the following description, the operation is performed as 4 × 4 MIMO.

Digital wireless communication apparatus 1000 further encodes data to be transmitted, further performs encoding unit 312 that performs error correction encoding, modulation unit 310 that modulates a signal from encoding unit 312, and modulation unit 310 A transmission signal weight control unit 308 that applies a transmission weight to the signal, a D / A conversion unit 302 that performs D / A conversion on the transmission weighted signal, and upconverts and amplifies the analog-converted signal. . 1 to 10.4, respectively. Note that the operation of the transmission signal weight control unit 308 is a general operation for MIMO signal processing, and thus description thereof is omitted.

As shown in FIG. 3 and FIG. 4, the LCX accommodated in one composite cable 4 adjusts the slot direction and the slot period (interval) P so that each LCX has different radiation characteristics. 4x4 MIMO channel can be realized.

In this way, since different propagation characteristics generate different propagation paths, an efficient 4 × 4 MIMO channel can be realized.

(4x4 LCX MIMO system measurement system configuration)
Hereinafter, experimentally evaluated characteristics of the MIMO system according to the above-described embodiment will be described.

For the measurement system provided in the anechoic chamber, the composite cable 4 is placed at the end of the polystyrene foam placed on the wave absorber.

Two types of LCX (hereinafter referred to as V-type LCX and M-type LCX) are combined as one composite cable.

FIG. 6 is a conceptual diagram showing the measurement system. As shown in FIG. 6, in this measurement system, the propagation path matrix between the composite cable and the four receiving antennas (monopole antennas are arranged at 1/2 wavelength intervals) is a plurality of 4 × 4 propagation paths. Configure. The characteristics of such a propagation path matrix are measured by a multiport vector network analyzer 2000 as shown in FIG. In FIG. 6, the symbol “LCX-Y” is used to represent the distance between two LCXs.

Since there is no reflection path and the propagation path is static in the anechoic chamber, the shape of the cell formed by LCX is assumed to be symmetric with respect to the Y axis at a position of 5 m, which is half the total length of LCX.

Fig. 6 also shows the measurement points in the area. Twelve (12) positions including two positions outside the end of the LCX are selected as measurement points. These positions are divided into two areas labeled area 1 and area 2. Region 1 represents the position where the terminal UE (user terminal) is inside the LCX. Region 2 represents a position where the terminal UE is outside the end of the LCX.

Measured at a center frequency of 2.452 GHz with a setting for sampling 401 frequency points in the measurement bandwidth of 125 MHz.

(Channel characteristics of 4 × 4 LCX MIMO)
In order to confirm that LCX-MIMO can realize a 4 × 4 channel, a condition number (CN) γ is used as a metric of the MIMO system. That is, as shown in Non-Patent Document 2, it is known that it can be easily evaluated by an index called the condition number, as indicating that 4 × 4 MIMO can achieve a quadruple multiplicity.

The smaller the condition number, the better the MIMO propagation path. In a MIMO propagation path with a large condition number, a high S / N ratio (signal-to-noise ratio) is used to increase the degree of separation between signal sequences when separating signal sequences. ) And transmission characteristics deteriorate. That is, the “condition number” is obtained from the ratio between the maximum singular value and the minimum singular value of the MIMO channel matrix. When only a small error occurs in decoding a signal from the MIMO transmission path due to a small estimation error of the propagation path matrix coefficient, it can be said to be a “conditional system”. System conditions are not good if small coefficient errors can have a large impact on signal decoding. The condition number is an index of the condition of such a system, and is usually represented by a numerical value in dB unit.

More specifically, the measured 4 × 4 matrix H is decomposed by singular value decomposition as follows:

　ここで、Ｕ，Ｖはユニタリ行列である。さらに、行列Σは特異値を対角成分に持つ対角成分が非負の実対角行列であり、行列Ｈが正規行列の場合には、特異値は固有値の絶対値に等しいことから、固有値がすべて非負の実数であるとすると、以下のような関係がある。

Here, U and V are unitary matrices. Furthermore, the matrix Σ is a real diagonal matrix with a diagonal component having a singular value as a diagonal component, and when the matrix H is a normal matrix, the singular value is equal to the absolute value of the eigenvalue. If all are non-negative real numbers, there is the following relationship.

ここで、λ_iは行列Ｈのｉ番目の固有値である。
条件数（ＣＮ）γ［ｄＢ］は４つの固有値のうち最大のものをλ_ｍａｘ、最小のものをλ_ｍｉｎとした場合に、以下の式のように計算される。

Here, λ _i is the i-th eigenvalue of the matrix H.
The condition number (CN) γ [dB] is calculated as in the following equation, where λ _{max is the} maximum among the four eigenvalues and λ _min is the minimum.

　低いＣＮを有する行列は、「良条件な（ｗｅｌｌ－ｃｏｎｄｉｔｉｏｎｅｄ）」行列であると言われている。それは、伝搬路が、トラッフィクを増大させるキャパシティに対してよい条件を持っていることを意味する。したがって、ＣＮの分布はそのチャネル特性を示すことができる。

A matrix with a low CN is said to be a “well-conditioned” matrix. That means that the propagation path has good conditions for capacity to increase traffic. Therefore, the CN distribution can show its channel characteristics.

FIG. 7 is a diagram showing a cumulative distribution function (CDF: Cumulative Distribution Function) of CN values for each measured area. In FIG. 7, the value of “LCX-Y” is changed to 1 cm, 2 cm, 3 cm and 6 cm.

The small “LCX-Y” reduces the thickness or width of the composite cable and is desirable for cable design.

As shown in FIG. 7, the LCX cable with “LCX-Y” of 1 cm, 2 cm, 3 cm and 6 cm in the area 1 assumed as the assumed service area of the linear cell has a better channel condition for MIMO transmission. In particular, when “LCX-Y” is set as 1 cm, a better state is shown.

This result indicates that the system according to the present embodiment can reduce the necessary space for installing the system.

Furthermore, the measurement results generally indicate that the smaller “LCX-Y” in region 1 can have better conditions for MIMO transmission than the larger “LCX-Y”.

Further, in FIG. 7, i.e. i. d. It shows the CDF of the CN value for a 4 × 4 MIMO channel (independent and uniquely distributed channel; the propagation characteristics having the same statistical characteristics of propagation characteristics between transmitting and receiving antenna elements, independent and uncorrelated).

The proposed LCX-MIMO CN value for an anechoic chamber with no reflection path is i. i. d. It is larger than the MIMO channel, but it is close to that of the outdoor environment.

Therefore, if the system using the LCX configured as in the present embodiment is placed in an actual environment having more reflection paths, the CN value is expected to decrease and the communication path state is improved. it can.

As described above, according to the digital radio communication apparatus and the digital radio communication system of the present embodiment, more MIMO communication is realized by using leaky coaxial cables having different radiation characteristics for linear cells. Communication traffic can be accommodated.

In addition, according to the digital wireless communication apparatus and the digital wireless communication system of the present embodiment, since a plurality of LCXs are stored together in one covering structure, more communication traffic can be stored in the leaky coaxial. This can be realized while suppressing the cable laying cost.

(Embodiment 2)
In the second embodiment, a configuration for satisfactorily realizing MIMO communication will be described in more detail with respect to a leaky coaxial cable having a configuration in which a plurality of LCXs are collectively stored in one covering structure described in the first embodiment.

As described with reference to FIG. 4, the insulating layer 202 having a relative dielectric constant εr is provided around the inner conductor 200 on the central axis of the LCX. Slots 206 are provided at intervals P in the outer conductor 204 provided on the outer periphery of the insulating layer 202, and a covering structure 208 is further provided on the outer periphery of the outer conductor 204.

As the covering structure, for example, a plastic resin sheath can be used. The outer conductor 204 is perforated with long holes called periodically arranged slots, through which electromagnetic wave signals are transmitted and received inside and around the LCX.

(Radiation principle and radiation angle)
FIG. 8 is a conceptual diagram for explaining a radiation principle and a radiation angle from LCX.

As shown in FIG. 8, the electromagnetic waves from the LCX are propagated by synthesizing waves emitted from the slots on the outer conductor as wave sources. In FIG. 8, the coordinates are set such that the length direction of LCX is X, the circumferential direction around LCX is φ, and the normal direction from LCX is r.

Slots S ₁ , S ₂ , S ₃ ,... Are slots located on the outer conductor and are arranged at regular intervals in the X direction. An interval between slots having the same inclination is indicated by a pitch P. There is a slot inclined in the middle in the slot. Such a pattern in which slots having different inclinations are called “zigzag type” is used for LCX that radiates vertically polarized waves.

On the other hand, there is an LCX that emits horizontally polarized waves that adopts a “vertical” pattern in which slots with no inclination are arranged at regular intervals. The term “vertically polarized wave” used herein refers to the direction in which the electric field is perpendicular to the ground when the LCX is stretched horizontally, that is, parallel to the ground. This is the direction.

The basic properties of LCX are the same as those of coaxial cables, and electromagnetic energy is transmitted by TEM waves. Inside the cable, an electric field exists perpendicularly from the surface of the central conductor to the outer conductor, and the magnetic field rotates around the central conductor. A current flows in the X direction on the inner surface of the outer conductor.

The lower side of FIG. 8 shows an image of an electric field generated in the slot portion by a current having a very low frequency compared to the slot pitch. If the electric field E is generated in the slot inclined by the current in the X direction, this indicates that it can be decomposed into the electric field Eφ in the φ direction and the electric field Ex in the X direction.

For example, here, if the slot pitch is set to be substantially the same as the wavelength in the cable of the high-frequency signal, instantaneous current flows in the slot S ₂ in the opposite direction to the slots S ₁ and S ₃ . As a result, the electric field Ex of the slot S ₂ in FIG cancel each other becomes field in the opposite direction from both sides.

On the other hand, since the electric field Eφ in the φ direction is in phase in these slots, vertical polarization is radiated.

(Radiation angle)
The radiation angle has been described above with reference to FIG. 4, but the principle will be described in more detail below.

Suppose that the normal direction of LCX is 0 degree, the termination side is + θ, and the feeding side is -θ. The synthetic electromagnetic wave from each slot radiates in the θ direction, and this θ is called a radiation angle. That is, the radiation angle here is an angle formed by the peak direction of the radiation in a plane including the axial direction and the normal direction with respect to the normal direction of the axial direction of LCX.

This point will be described in more detail with reference to FIG. The direction along the LCX is defined as the X direction, the direction in which a plurality of (two in FIG. 30) LCXs are arranged is defined as the Y direction, and the direction perpendicular to the XY direction is defined as the Z direction. The above-described peak direction of radiation means, for example, the peak direction on the XZ plane including the X axis. The direction of this peak is not limited to the direction on the XZ plane including the X axis, but may be the direction on the XY plane, for example. However, in the case of the direction on the XY plane, the performance may be slightly deteriorated due to the presence of the adjacent LCX. Therefore, the peak direction of radiation is preferably the peak direction on the XZ plane. Note that the peak direction of radiation is not limited to the XZ plane or the XY plane as long as the plane includes both the X axis and the normal direction to the X axis.

Referring to FIG. 8 again, the radiation conditions at this time are as follows: the phase at slot S ₁ is φ _S1 , the phase at slot S ₂ is φ _S2 , the phase at position A is φ _A , and slot S ₁ and slot S _{2 Assuming} that the phase between them is φ _S1S2 and the phase between the slots S ₁ and A is φ _S1A , the following equation (1) is obtained.

　ただし、ｎ＝０，±１，±２，…である。
ここで、λ₀およびλ_gをそれぞれ自由空間波長とケーブル内波長とすると、自由空間の伝搬定数ｋ₀とケーブル内の伝搬定数β_gはそれぞれ式（２）、（３）となる。

However, n = 0, ± 1, ± 2,.
Here, assuming that λ ₀ and λ _g are a free space wavelength and an in-cable wavelength, respectively, the free space propagation constant k ₀ and the propagation constant β _g in the cable are expressed by equations (2) and (3), respectively.

　ただし、ε_rは絶縁体の比誘電率である。

Where ε _r is the relative dielectric constant of the insulator.

Since the electric field component in the φ direction that generates the Eφ polarized wave is inverted in the adjacent slots from FIG. 8, π is added to the phase in the slot S ₂ , and the equation (4 ) Is obtained.

From equation (4), sin θφ, m (φ, m are subscripts, the same applies hereinafter) becomes the following equation (5).

　ここで、放射波である為にはθφ，ｍは実数の必要があるので（２ｎ＋１）は負でなければならず、式（５）の右辺は１以下となり、放射角θφ，ｍは次の式（６）となる。

Here, since θφ, m must be a real number in order to be a radiated wave, (2n + 1) must be negative, the right side of Equation (5) is 1 or less, and the radiation angle θφ, m is Equation (6) is obtained.

　ただし、ｍ＝２ｎ＋１＝－１，－３，…である。

However, m = 2n + 1 = −1, −3,...

This shows that the radiation angle can be adjusted by selecting an appropriate insulator material or slot pitch. That is, the radiation angle can be adjusted by changing the propagation speed in the cable according to the dielectric constant of the insulator and the diameter of the core wire (inner conductor) in addition to the period in which the slots are provided. .

Usually, only the so-called −1st order mode with n = −1 is often used. Since the electromagnetic waves radiated from a plurality of angles including the −1st order mode interfere with each other at the frequency at which the higher order mode after the −2nd order mode occurs, a standing wave is generated. This is because it becomes difficult to achieve the above.

For example, if the slot pitch of the zigzag slot is shortened, the higher-order mode does not occur and the -1st order single mode can be obtained. Further, not only the zigzag type but also the vertical type slot, the inclined type slot, the round type slot, and the square type slot can be set to only the −1st order mode depending on the pitch.

(Coupling loss)
The radiation and reception efficiency of LCX can be expressed in terms of coupling loss (Lc). The coupling loss is calculated by the equation (7) from the actual measurement value with Pin as the input to the LCX and Pout as the output from the antenna.

Further, the coupling loss Lcr at an arbitrary position r can be calculated from the equation (8) by using the distance r ₀ from the LCX as a reference.

Since this coupling loss can be adjusted by changing the opening area of the slot, the cell width corresponding to the short axis direction of the linear cell can be set by a method different from the power supplied to the LCX.

(Two types of MIMO configurations using LCX)
(2 × 2 MIMO with single LCX)
FIG. 9 is a diagram showing a configuration of a MIMO system that uses a single LCX equivalent to two antennas.

In the configuration of FIG. 9, 2 × 2 MIMO is realized by the directivity of the radio waves radiated from the LCX due to the difference in the feeding direction into the LCX as described above.

The signal fed from the left side (port 1) by the transmitter Tx to the LCX in the center of FIG. 9 is radiated, for example, in the directions of arrows h31 and h41. The signal from the right side (port 2) is radiated in the direction of arrows h32 and h42 in the opposite direction. In addition, since a phase is generated by propagation in the LCX to each radiating slot, as a result, different propagation paths can be generated and received by the receiver Rx.

(2 × 2 MIMO with two adjacent LCXs)
FIG. 10 is a diagram for explaining a configuration for realizing 2 × 2 MIMO by using two adjacent LCXs.

In MIMO with close LCX, the combination of LCX with different radiation characteristics is used to realize MIMO with LCX close to 1/2 wavelength or less. A signal fed from the left side (port 2) by the transmitter Tx to the LCX on the upper side of FIG. 10 is radiated in the directions of arrows h32 and h42. The signal from the lower side (port 1) is radiated in the direction of arrows h31 and h41 different from this. As a result, different propagation paths can be generated and received by the receiver Rx. In FIG. 10, it is assumed that the opposite sides of the two LCX feeding sides are terminated by a terminator.

Similarly, MIMO is also possible by combining LCXs with different polarizations. For this purpose, for example, the LCX of the “zigzag” slot and the LCX of the “vertical” slot may be combined.

Further, by combining the above-described methods as follows, 4 × 4 MIMO by two adjacent LCXs or 8 × 8 MIMO by four can be realized.
i) Two-sided feeding is performed with two adjacent LCXs having the same polarization characteristic, or two-sided feeding is performed with four adjacent LCXs having the same polarization characteristic.
ii) Two-sided feeding with two adjacent LCXs having different polarization characteristics, or two-sided feeding with LCX having different polarization characteristics in two sets of two adjacent sets and two sets And

In addition, since such a method is an independent method only for the antenna portion, it is possible to further improve the performance by using a signal processing technique such as nonlinear multi-user MIMO.

(Radiation pattern of LCX)
Hereinafter, the measurement result of the radiation pattern of LCX will be described.

¡A radio wave absorber is placed on a measurement turntable, and the LCX of a zigzag type slot having a length of 3 m is horizontally placed on the XY plane. The longitudinal direction of the LCX is defined as the X axis. The radiation pattern was considered rotationally symmetric with respect to the X axis, and vertical polarization and horizontal polarization on the XY plane were measured. The measurement frequency was 5.15 GHz, and the display was normalized with the maximum value being 0 dB.

FIGS. 11 to 17 show the radiation pattern measurement results of the cables with radiation angles R degrees (R = 11, 18, 26, 35, 44, 55, 71) when one end of the LCX is terminated at 50Ω, respectively.

FIGS. 11 (a) to 17 (a) show the radiation pattern measurement results of the cable with the radiation angle R degrees when one end of the LCX is terminated at 50Ω as forward feeding. It can be seen from the measurement results that the radiation from the LCX is strongest not in the Y-axis direction, which is directly beside the LCX, but in the direction of about R degrees before the feeding direction. The same applies to the case where the feeding direction is reversed (rear feeding) as shown in FIGS. Here, “radiation angle R degrees” means an LCX cable adjusted by adjusting the slot pitch so that the radiation angle becomes R degrees by Equation (6).

Since the radiation direction differs depending on the feeding end from these radiation patterns, MIMO can be realized by both-side feeding even with a single LCX. MIMO can also be realized by two LCXs having different radiation angles in close proximity.

(Measurement experiment)
FIG. 18 is a diagram for explaining an arrangement in which 2 × 2 MIMO characteristics are measured.

LCX is assumed to be 10 m, and a normal coaxial cable is connected to both sides thereof. Starting from the center of LCX, the throughput was measured from 0 m to 6 m while moving the terminal sequentially in the X-axis direction on a line parallel to LCX 1.5 m away from LCX in the Y-axis direction. Therefore, the last 1 m from 0 m to 6 m, that is, the section from 5 m to 6 m is outside the end of the LCX.

The measurement was performed by supplying power to port 1 to port 4 of FIG. 9 or 10 and in an anechoic chamber. In MIMO, an environment where reflected waves from the surroundings can be used is considered advantageous. Therefore, a wave absorber is intentionally arranged on the bottom surface and the back surface, and the viewing condition is unfavorable for MIMO in which direct waves from LCX are dominant.

The element spacing of the terminal antenna was ½ wavelength, and dummy antennas were also installed on both sides of the element with a ½ wavelength separation.

Also, the MCS representing a combination of modulation, coding rate, and MIMO multiplicity is set such that the conditions from 0 to 4 and the conditions from 8 to 12 are appropriately selected by the adaptive rate selection function.

(2 × 2 MIMO with single LCX: both sides feeding)
FIG. 19 is a diagram showing a measurement result of throughput when feeding both sides to the LCX of a zigzag slot with a radiation angle of 18 degrees.

FIG. 20 is a diagram showing a measurement result of the throughput when feeding both sides to the LCX of a zigzag slot with a radiation angle of 26 degrees.

FIG. 21 is a diagram showing the measurement results of the throughput when feeding both sides to the LCX of a zigzag slot with a radiation angle of 35 degrees.

FIG. 22 is a diagram showing a measurement result of throughput when feeding both sides to the LCX of a zigzag slot with a radiation angle of 44 degrees.

FIG. 23 is a diagram showing a measurement result of throughput when both sides are fed to the LCX of a zigzag slot with a radiation angle of 55 degrees.

In any of FIGS. 19 to 23, it can be seen that in the vicinity of the center part of the LCX, the throughput is larger than that in the case of the single stream, corresponding to the fact that 2 × 2 MIMO communication is realized.

However, the throughput decreases near the end of the LCX, and the region where this decrease occurs depends on the radiation angle.

From the LCX radiation characteristics, it can be seen that the location where MIMO is possible, that is, the cell edge substantially coincides with the line drawn in the radiation angle direction from the position of the LCX edge (X = 5 m, Y = 0 m). Therefore, as the distance from the center of the LCX increases, a section with lower throughput occurs. The throughput is relatively stable at a location closer to the center of the LCX than this line.

(2 × 2 MIMO with two adjacent LCXs: one-sided power supply)
Below, the measurement result of the throughput when power is supplied from two sides to two adjacent LCXs having different radiation angles will be described. The arrangement for measuring 2 × 2 MIMO characteristics in this case is the same as that shown in FIG.

FIG. 24 is a diagram showing the throughput when power is supplied from two sides to two LCXs having adjacent radiation angles of 18 degrees and 55 degrees.

FIG. 25 is a diagram showing the throughput when power is supplied from two sides to two LCXs having adjacent radiation angles of 26 degrees and 55 degrees.

FIG. 26 is a diagram showing the throughput when power is supplied from two sides to two LCXs having close radiation angles of 44 degrees and 55 degrees.

FIG. 27 is a diagram showing the throughput when power is supplied from two sides to two adjacent LCXs having radiation angles of 26 degrees and 71 degrees.

FIG. 28 is a diagram showing the throughput when power is supplied from two sides to two LCXs having adjacent radiation angles of 35 degrees and 55 degrees.

FIG. 29 is a diagram showing the throughput when power is supplied from two sides to two adjacent LCXs having radiation angles of 35 degrees and 71 degrees.

First, referring to FIG. 24, Type 1 indicates a case where power is supplied from only one side to LCX having a radiation angle of 18 degrees, and Type 2 is a case where power is supplied from only one side to LCX having a radiation angle of 55 degrees. Indicates. “Type 1” and “Type 2” indicate that power is supplied from one side to both LCXs having a radiation angle of 18 degrees and a radiation angle of 55 degrees.

It can be seen that by simultaneously feeding power to two LCXs, approximately twice the throughput has been achieved, and 2 × 2 MIMO has been realized.

Hereinafter, FIGS. 25 to 28 show the case where power is supplied from one side to both LCXs.

It can be seen that MIMO communication is realized by the combination of two LCXs having a radiation angle of 44 degrees and 55 degrees shown in FIG. 26, which is the case where the difference in radiation angle between the two leaky coaxial cables is the smallest. However, in combinations other than the combination of two LCXs having a radiation angle of 44 degrees and 55 degrees, 2 × 2 MIMO can be realized more stably within a certain range. Moreover, it can be seen that 2 × 2 MIMO can be realized in a wide region extending beyond the end of the LCX.

Therefore, when two adjacent LCXs having different radiation angles are fed from one side, at least in order to perform MIMO communication, the difference in radiation angles is preferably 11 degrees or more, and the difference in radiation angles is 15 It can be seen that the degree of degree is more preferable, and that the optimal MIMO communication can be realized if the difference in radiation angle is 20 degrees or more.

As in Embodiment 1, since MIMO communication can be realized by a plurality of adjacent LCXs, the plurality of LCXs can be stored together in one covering structure.

Also, it is possible to supply power from both sides to a configuration in which a plurality of LCXs are stored together in one covering structure.

As described above, according to the digital radio communication apparatus and digital radio communication system of the present embodiment, MIMO communication is performed using a leaky coaxial cable having different radiation characteristics with respect to a linear cell formed by the leaky coaxial cable. By realizing this, more communication traffic can be accommodated.

In addition, according to the digital wireless communication apparatus and the digital wireless communication system of the present embodiment, since a plurality of LCXs can be stored together in one covering structure, more communication traffic can be accommodated. It is possible to reduce the cost of installing the leaky coaxial cable.

The embodiment disclosed this time is an example of a configuration for concretely implementing the present invention, and does not limit the technical scope of the present invention. The technical scope of the present invention is shown not by the description of the embodiment but by the scope of the claims, and includes modifications within the scope of the words and equivalents of the scope of the claims. Is intended.

According to the present invention, it is possible to provide a digital wireless communication apparatus and a digital wireless communication system that can form a linear cell using a leaky coaxial cable and can accommodate more communication traffic. Furthermore, according to the present invention, it is possible to provide a digital wireless communication apparatus and a digital wireless communication system that can accommodate more communication traffic while suppressing the installation cost of a leaky coaxial cable.

10.1-10. n node 20 signal transmission unit 30 digital signal processing unit 302 D / A conversion unit 308 transmission signal weight control unit 310 modulation unit 312 encoding unit 1000 digital wireless communication apparatus

Claims (14)

Equipped with a composite cable containing multiple leaky coaxial cables with different radiation characteristics,
Each of the leaky coaxial cables includes an inner conductor and an outer conductor, and is provided with a plurality of leaky slots,
When the peak direction of radiation with respect to the normal direction of the axial direction of the leaky coaxial cable is an angle formed in a plane including the axial direction and the normal direction, the plurality of leaky coaxial cables are respectively Have different radiation angles,
A digital wireless communication apparatus further comprising a transmission means for supplying a high-frequency signal from at least one end of the composite cable and executing MIMO (multiple-input multiple-output) communication. The digital wireless communication apparatus according to claim 1, wherein the plurality of leaky coaxial cables have different arrangement periods of the leaky slots so as to have the different radiation angles. 2. The digital according to claim 1, wherein each of the plurality of leaky coaxial cables has a different dielectric constant of an insulator or a diameter of the inner conductor between the inner conductor and the outer conductor so as to have the different radiation angles. Wireless communication device. The digital wireless communication apparatus according to any one of claims 1 to 3, wherein the difference between the different radiation angles is at least 11 degrees or more. The digital wireless communication device according to claim 1, wherein the plurality of leaky coaxial cables further have different angles with respect to the axial direction of the leaky coaxial of the leaky slots. The digital wireless communication apparatus according to any one of claims 1 to 4, wherein the transmission means supplies a high-frequency signal to each of the leaky coaxial cables from both ends of the composite cable. The digital wireless communication device according to any one of claims 1 to 4, wherein the plurality of leaky coaxial cables are housed in a single covering structure. A first digital wireless device installed in a fixed manner, wherein the first digital wireless communication device comprises:
Includes a composite cable containing multiple leaky coaxial cables with different radiation characteristics,
Each of the leaky coaxial cables includes an inner conductor and an outer conductor, and is provided with a plurality of leaky slots,
When the peak direction of radiation with respect to the normal direction of the axial direction of the leaky coaxial cable is an angle formed in a plane including the axial direction and the normal direction, the plurality of leaky coaxial cables are respectively Have different radiation angles,
A transmission means for supplying a high-frequency signal from at least one end of the composite cable and performing MIMO communication;
A digital wireless communication system, further comprising a second digital wireless communication device that is a mobile terminal and performs the MIMO communication with the first digital wireless communication device. The digital wireless communication system according to claim 8, wherein the plurality of leaky coaxial cables have different arrangement periods of the leak slots so as to have the different radiation angles. 9. The digital according to claim 8, wherein each of the plurality of leaky coaxial cables has a different dielectric constant or a diameter of the inner conductor between the inner conductor and the outer conductor so as to have the different radiation angles. Wireless communication system. The digital wireless communication system according to any one of claims 8 to 10, wherein the difference between the different radiation angles is at least 11 degrees or more. The digital wireless communication system according to claim 8, wherein each of the plurality of leaky coaxial cables further has different angles with respect to the axial direction of the leaky coaxial of the leaky slots. The digital wireless communication system according to any one of claims 8 to 11, wherein the transmission means supplies a high-frequency signal to each of the leaky coaxial cables from both ends of the composite cable. The digital wireless communication system according to any one of claims 8 to 11, wherein the plurality of leaky coaxial cables are housed in a single covering structure.

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