JP5952731B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system, and more specifically, a technique for reducing delay waves caused by multiple reflections generated in a transmission path in short-range wireless communication utilizing direct wave propagation between direct transmission and reception antennas. About.

  In recent years, development and practical use of wireless communication systems in line-of-sight transmission paths have been promoted, as represented by download kiosk-type contactless high-speed wireless transmission and indoor millimeter-wave wireless communication. Conventionally, there is a MIMO (Multiple-Input Multiple-Output) transmission technique as one of high-speed transmission techniques using a limited frequency band. In MIMO transmission, different signals are transmitted from a plurality of transmitting antennas at the same time at the same frequency, and each signal is separated by signal processing on the receiving side by using a multipath environment between the transmitter and the receiver. And decrypt. As a result, the communication speed can be improved according to the number of transmission / reception antenna elements without widening the use frequency band.

  In general, MIMO transmission is premised on radio waves propagating in a multipath rich environment, but if the environment between the transmitter and the receiver is not a multipath environment, a plurality of signals to be transmitted and received are transmitted. Propagation paths are almost equal, and spatial correlation between antennas increases. For this reason, signal separation on the receiving side becomes difficult, and the channel capacity decreases. However, as shown in Non-Patent Document 1, the transmission antenna and the reception antenna are arranged close to each other, and the MIMO transmission technology can be applied even in short-range communication where the environment between the antennas is not a multipath environment. is there. Hereinafter, MIMO transmission in near field communication is referred to as near field MIMO transmission. According to the technique disclosed in Non-Patent Document 1, in short-range MIMO transmission, the element spacing of each array antenna is appropriately set according to the distance between the transmitter and the receiver, so that it is not a multipath environment. Even in this case, the spatial correlation between the antennas becomes low, and a high channel capacity can be achieved.

  Non-Patent Document 2 discloses a technique for simplifying the decoding process by optimizing the antenna element interval in the short-range MIMO transmission. Non-Patent Document 3 discusses multipath waves caused by multiple reflections that occur when wireless transmission is performed through a medium such as a building wall in short-distance MIMO transmission.

Honma, Nishimori, Seki, Mizoguchi, "Evaluation of transmission capacity in nearby MIMO communication", IEICE Technical Report, AP2008-125, Nov. 2008. Hiraga, Sakamoto, Nishimori, Seki, Nakagawa, Uehara, "Simple reception decoding of short-distance MIMO using microstrip antenna", 2012 UEC, B-1-211. Sakamoto, Hiraga, Seki, Nakagawa, Uehara, "Evaluation of Millimeter-Wave Short-Range MIMO Transmission in a Multipath Environment in a Wall", 2012 Shingaku Sodai, B-5-124. IEICE Transactions e95-b no.1 pp.87-96.

  As shown in Non-Patent Document 3, for example, when wireless transmission is performed through a wall of a building using a wall transmission repeater, the discontinuous surface of the medium on the surface of the structure such as the wall Multiple reflections of radio waves occur on the (dielectric constant boundary surface) and on the discontinuous surface of the medium existing inside the multi-layered wall. For this reason, not only a direct wave but also a delayed wave due to multiple reflections reaches the receiving antenna. In addition, the protective material (radome) installed on the front surface of the antenna and the housing of the wireless communication device are mainly composed of a dielectric, and the surface of this protective material forms a discontinuous surface of the medium as described above. Multiple reflection occurs. This delayed wave causes degradation of transmission quality and performance of decoding processing proposed in Non-Patent Document 2.

With reference to FIG. 17, the problem caused by the above-described delayed wave will be specifically described.
FIG. 17 is a diagram illustrating an example of a transmission path of a conventional short-range wireless communication system, and a dielectric DE such as a concrete wall exists on a transmission path between a transmitting antenna Tx and a receiving antenna Rx arranged to face each other. An example of a radio wave propagation path is shown. Here, FIG. 9A shows a case where the transmission antenna Tx and the reception antenna Rx are arranged apart from the dielectric DE, and FIG. 9B shows the case where the transmission antenna Tx and the reception antenna Rx are dielectric DE. (C) shows a case where the transmitting antenna Tx is arranged away from the dielectric DE and the receiving antenna Rx is arranged close to the dielectric DE. Yes. In any case, the radio wave incident on the dielectric DE from the transmission antenna Tx passes through the dielectric DE and reaches the reception antenna Rx as a direct wave WA, and a part of the radio wave incident on the dielectric DE is As viewed from the transmitting antenna Tx, multiple reflection is performed by the back surface ZA and the front surface ZB of the wall surface of the dielectric DE. Due to this multiple reflection, a delayed wave WB is generated and reaches the receiving antenna Rx.

  The delayed wave WB generated in this way may cause deterioration of transmission characteristics depending on its power level. In particular, in short-range MIMO transmission as shown in Non-Patent Document 2, a wireless transmission method that can obtain the highest transmission capacity in an environment where only the direct wave WA described above exists is used. Transmission capacity degradation can be a challenge for performance improvement in actual system design.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a wireless communication system capable of reducing frequency characteristics depending on multipath and improving transmission quality in short-range wireless communication. It is to provide.

A wireless communication system according to an aspect of the present invention includes a first wireless communication apparatus having a first directional antenna, and a second wireless communication apparatus having a second directional antenna, wherein the first and first A wireless communication system that performs wireless communication between the first wireless communication device and the second wireless communication device via two directional antennas, wherein the first directional antenna and the second directional antenna The directional antennas are arranged so as to face each other, and a path connecting the radiating portion of the first directional antenna and the radiating portion of the second directional antenna is a main path of the second directional antenna. and axis substantially coincides beam, among the radio waves emitted from the first directional antenna, a discontinuous surface of the transmission path between the first directional antenna and the second directional antenna Generated by reflection and refraction of light The first directional antenna and the second directivity are deviated from a path connecting the radiating portion of the first directional antenna and the radiating portion of the second directional antenna. And a radio communication system characterized in that a radio antenna is disposed.

In the wireless communication system, for example, an offset is provided along the discontinuous surface between the arrangement position of the first directional antenna and the arrangement position of the second directional antenna.
Prior Symbol wireless communication system, for example, the first directional antenna transmits a radio wave with a linear polarization, said second directional antenna, radio wave polarization and the same polarization by the linear polarization A polarizing plate having a polarization characteristic that receives a radio wave from the first directional antenna and transmits a radio wave having the same polarization plane as that of the linearly polarized wave into the transmission path. Has been placed.
In the wireless communication system, for example, the polarizing plate, the disposed on the front surface of one or both of the antennas of the first directional antenna and the second directional antenna, polarization of the both or one of the antennas It has a polarization characteristic that transmits a radio wave having a polarization plane in the same direction as the direction.
In the wireless communication system, for example, the first directional antenna transmits radio waves by circular polarization, and the second directional antenna has the same circular polarization as the first circular polarization. A radio wave is received from a directional antenna, and a first dielectric layer having a first refractive index and a second refractive index different from the first refractive index are provided in the transmission path. The dielectric layers are arranged so as to be in contact with each other.
In the wireless communication system, for example, the first wireless communication device and the second wireless communication device perform wireless communication using short-range MIMO (Multi-Input and Multi-Output) transmission.
In summary, the present invention relates to a main beam direction of a transmitting directional antenna in short-range wireless communication in which a transmitting directional antenna and a receiving directional antenna are opposed to each other across a medium boundary surface. Each directional antenna so that the geometric optical path of the electromagnetic wave radiated on the antenna coincides with the main beam direction of the directional antenna on the receiving side, and the angle formed by the geometric optical path and the medium boundary surface is non-perpendicular One of the features is that the geometric optical path of the multiple reflected wave of the electromagnetic wave radiated in the main beam direction of the transmitting directional antenna is offset from the main beam direction of the directional antenna on the receiving side. It is said.

The present invention can be paraphrased as follows.
A wireless communication system according to an aspect of the present invention is a wireless communication system in which a first wireless communication device and a second wireless communication device perform wireless communication, and the first wireless communication device and the second wireless communication. The radio transmitting / receiving antennas of each device are arranged so that they face each other, directional antennas are used as antenna elements, linear light is drawn in the same direction as the main beam direction of the transmitting antenna, and discontinuities in the radio wave transmission path The radio communication system has a configuration in which a geometric optical path of multiple reflected waves generated by reflection and refraction at a point has an offset from the main beam direction of the receiving antenna.
In the wireless communication system, for example, the first wireless communication apparatus transmits and receives radio waves with a single plane of polarization, and the second wireless communication apparatus transmits radio waves with the same plane of polarization as the single polarization plane. Is transmitted and received, and a polarizing plate having a polarization characteristic in the same direction as the linearly polarized wave is disposed in a transmission path between the antenna of the first wireless communication device and the antenna of the second wireless communication device. May be.
In the wireless communication system, for example, a polarizing plate having the same direction as the polarization direction of the antenna may be disposed in front of both or one of the antenna of the first wireless communication device and the second wireless communication device. .
In the wireless communication system, for example, the first wireless communication device transmits and receives radio waves with circular polarization, and the second wireless communication device transmits and receives radio waves with the same circular polarization as the circular polarization. A dielectric layer having a first refractive index in a transmission path between the antenna of the first wireless communication device and the antenna of the first wireless communication device is different from the first refractive index. A dielectric layer having a second refractive index may be disposed.
The wireless communication system may be, for example, a wireless communication system using short-range MIMO (Multi-Input and Multi-Output) transmission.

  According to the present invention, it is possible to reduce multiple reflections that occur on a transmission line. As a result, it is possible to reduce frequency characteristics depending on multipath and improve transmission quality in short-range wireless communication.

It is a figure for demonstrating arrangement | positioning of the transmission antenna with which the radio | wireless communications system by 1st Embodiment of this invention is equipped, and a receiving antenna, and is a figure which shows the 1st example of arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmission antenna with which the radio | wireless communications system by 1st Embodiment of this invention is equipped, and a receiving antenna, and is a figure which shows the 2nd example of arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmission antenna and reception antenna with which the radio | wireless communications system by 1st Embodiment of this invention is provided, and is a figure which shows the 3rd example of arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmission antenna with which the radio | wireless communications system by 1st Embodiment of this invention is equipped, and a receiving antenna, and is a figure which shows the 4th example of arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmission antenna with which the radio | wireless communications system by 2nd Embodiment of this invention is equipped, and a receiving antenna. It is a figure for demonstrating the modification of arrangement | positioning of the transmission antenna with which the radio | wireless communications system by 2nd Embodiment of this invention is equipped, and a receiving antenna. It is a figure for demonstrating the arrangement | positioning of the transmission antenna by the conventional structure corresponding to the radio | wireless communications system by 2nd Embodiment of this invention, and a receiving antenna. It is a figure for demonstrating arrangement | positioning of the transmission antenna with which the radio | wireless communications system by 3rd Embodiment of this invention is provided, and a receiving antenna. It is a figure for demonstrating the arrangement | positioning of the transmission antenna by the conventional structure corresponding to the radio | wireless communications system by 3rd Embodiment of this invention, and a receiving antenna. It is a figure for demonstrating the principle of arrangement | positioning of the transmission antenna by the conventional structure corresponding to the radio | wireless communications system by 4th Embodiment of this invention, and a receiving antenna. It is a figure for demonstrating arrangement | positioning of the transmission antenna and reception antenna with which the radio | wireless communications system by 4th Embodiment of this invention is provided, and is a figure which shows the 1st example of arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmitting antenna and receiving antenna with which the radio | wireless communications system by 4th Embodiment of this invention is provided, and is a figure which shows the 2nd example of arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmitting antenna and receiving antenna with which the radio | wireless communications system by 4th Embodiment of this invention is provided, and is a figure which shows the 3rd example of arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmission antenna with which the radio | wireless communications system by 4th Embodiment of this invention is equipped, and a receiving antenna, and is a figure which shows the example of 4th arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmission antenna and reception antenna with which the radio | wireless communications system by 4th Embodiment of this invention is provided, and is a figure which shows the 5th example of arrangement | positioning. It is a figure for demonstrating arrangement | positioning of the transmitting antenna and receiving antenna with which the radio | wireless communications system by 5th Embodiment of this invention is provided. It is a figure showing the example of the transmission line of the conventional near field communication system.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<First Embodiment>
In the first embodiment of the present invention, a case where the present invention is applied to SISO (Single Input Single Output) transmission will be described.

[Description of configuration]
FIG. 1 is a diagram for explaining the arrangement of first directional antennas Tx and second directional antennas Rx included in the wireless communication system according to the first embodiment of the present invention, and shows a first arrangement example of antennas. FIG. In the first arrangement example, the first directional antenna Tx and the second directional antenna Rx are arranged apart from the dielectric DE existing on the transmission path.

  The wireless communication system according to the present embodiment includes a first wireless communication device (not shown) and a second wireless communication device (not shown), and the first wireless communication device includes the first wireless communication device described above. The second wireless communication apparatus includes the directional antenna Tx, and includes the above-described second directional antenna Rx. In this embodiment, for simplification of description, the first directional antenna Tx included in the first wireless communication apparatus is a transmission antenna, and the second directional antenna Rx included in the second wireless communication apparatus is a reception. A case will be described as an example in which radio waves are transmitted from the first wireless communication device to the second wireless communication device via the first directional antenna Tx and the second directional antenna Rx. .

However, each of the first directional antenna Tx and the second directional antenna Rx may be a transmission / reception antenna capable of transmitting and receiving, and the wireless communication system according to the present embodiment includes the first directional antenna. Bidirectional wireless communication may be performed between the first wireless communication device and the second wireless communication device via Tx and the second directional antenna Rx.
Hereinafter, the first directional antenna Tx is referred to as “transmitting antenna Tx”, and the second directional antenna Rx is referred to as “receiving antenna Rx”.

  In the present embodiment, among radio waves radiated from the transmission antenna Tx, reflection and refraction at the discontinuous surfaces (boundary surfaces) ZA and ZB of the dielectric DE existing on the transmission path between the transmission antenna Tx and the reception antenna Rx. The transmission antenna Tx and the reception antenna Rx are arranged so that the path of the multiple reflected waves generated by the above deviates from the path connecting the radiation part of the transmission antenna Tx and the radiation part of the reception antenna Rx. Specifically, an offset doff is provided along the discontinuous surfaces ZA and ZB between the arrangement position of the transmission antenna Tx and the arrangement position of the reception antenna Rx. This offset doff is set so as to reduce the delayed wave WB as long as transmission / reception of radio waves is not hindered. Here, the dielectric DE is, for example, a wall of a building. In addition, the discontinuous surfaces ZA and ZB of the dielectric DE indicate portions where the dielectric constant of the medium through which the radio wave propagates changes discontinuously, for example, at the boundary surface of the medium through which the radio wave propagates, such as the surface of a building wall. is there.

  In the present embodiment, the transmission antenna Tx and the reception antenna Rx are arranged so as to face each other, and the path connecting the radiation part of the transmission antenna Tx and the radiation part of the reception antenna Rx is the main beam of the reception antenna Rx. It almost coincides with the direction axis. That is, the axial direction of the main beam of the transmission antenna Tx and the axial method of the main beam of the reception antenna Rx are such that the radio wave radiated from the transmission antenna Tx propagates along the direction axis of the main beam of the reception antenna Rx. Are facing each other.

[Description of operation / effect]
The radio wave radiated from the transmission antenna Tx propagates through the transmission path, passes through the dielectric DE on the transmission path, and reaches the reception antenna Rx as a direct wave WA. Further, a part of the radio wave incident on the dielectric DE from the transmitting antenna Tx is multiple-reflected by the discontinuous surface ZA and the discontinuous surface ZB inside the dielectric DE, and passes through the dielectric DE as a delayed wave WB.

  Here, in the present embodiment, as described above, the offset doff is provided along the discontinuous planes ZA and ZB between the arrangement position of the transmission antenna Tx and the arrangement position of the reception antenna Rx, and the transmission antenna Since Tx and receiving antenna Rx are arranged so as to face each other, the main beam directions of transmitting antenna Tx and receiving antenna Rx and discontinuous surfaces (medium boundary surfaces) ZA and ZB in the transmission path are orthogonal to each other. There is no relation, and the angle θ (an angle other than zero) is non-right angle.

  For this reason, the propagation path in which the power of the delayed wave WB, which is a multiple reflected wave, becomes maximum is shifted from the main beam direction of the receiving antenna Rx as shown by the dotted line in FIG. And deviate from the path connecting the radiating portion of the transmitting antenna Tx and the radiating portion of the receiving antenna Rx. As a result, the power level of the delayed wave WB reaching the receiving antenna Rx is reduced, and the component of the direct wave WA is relatively increased. As the angle θ between the direction axis of each main beam of the transmission antenna Tx and the reception antenna Rx and the discontinuous surfaces ZA and ZB in the transmission path is larger, the reception antenna Rx of the propagation path in which the power of the delayed wave WB becomes maximum. The amount of deviation from the main beam direction increases, and the power level of the delayed wave WB reaching the receiving antenna Rx decreases. However, if the angle θ is increased, the direct wave WA that reaches the receiving antenna Rx also decreases, so there is an upper limit for the angle θ.

Therefore, according to the present embodiment, the power level ratio of the direct wave WA and the delayed wave WB in the receiving antenna Rx can be improved according to the angle θ, and the multiplexing generated on the discontinuous surface (boundary surface) of the medium. The influence of reflection can be reduced. Therefore, radio transmission characteristics can be improved, and transmission quality in short-range radio communication can be improved.
Although omitted in FIG. 1, it is desirable to design the arrangement positions of the antenna elements of the transmission antenna Tx and the reception antenna Rx in consideration of refraction of radio waves on the discontinuous surface of the medium.

  FIG. 2 is a diagram illustrating a second arrangement example of the transmission antennas Tx and the reception antennas Rx included in the wireless communication system according to the first embodiment of the present invention. In the second arrangement example, both the transmission antenna Tx and the reception antenna Rx are arranged close to or in contact with the dielectric DE existing on the transmission path. Also in this case, as in the first arrangement example shown in FIG. 1 described above, the propagation path in which the power of the delayed wave WB, which is a multiple reflected wave, becomes maximum is the receiving antenna as shown by the dotted line in FIG. A deviation occurs from the main beam direction of Rx, and the path of the delayed wave WB deviates from the path connecting the radiating portion of the transmitting antenna Tx and the radiating portion of the receiving antenna Rx. As a result, the power level of the delayed wave WB reaching the receiving antenna Rx is reduced, and the component of the direct wave WA is relatively increased.

  FIG. 3 is a diagram illustrating a third arrangement example of the transmission antennas Tx and the reception antennas Rx included in the wireless communication system according to the first embodiment of the present invention. In the third arrangement example, the transmission antenna Tx is arranged away from the dielectric DE existing on the transmission path, and the reception antenna Rx is arranged close to or in contact with the dielectric DE. Also in this case, as in the arrangement example shown in FIG. 1 or FIG. 2 described above, the propagation path where the power of the delayed wave WB which is a multiple reflected wave is the maximum is the receiving antenna as shown by the dotted line in FIG. A deviation occurs from the main beam direction of Rx, and the path of the delayed wave WB deviates from the path connecting the radiating portion of the transmitting antenna Tx and the radiating portion of the receiving antenna Rx. As a result, the power level of the delayed wave WB reaching the receiving antenna Rx is reduced, and the component of the direct wave WA is relatively increased.

  FIG. 4 is a diagram illustrating a fourth arrangement example of the transmission antennas Tx and the reception antennas Rx included in the wireless communication system according to the first embodiment of the present invention. In the fourth arrangement example, the transmission antenna Tx is arranged close to or in contact with the dielectric DE existing on the transmission path, and the reception antenna Rx is arranged apart from the dielectric DE. Also in this case, like the arrangement examples shown in FIGS. 1 to 3, the propagation path in which the power of the delayed wave WB, which is a multiple reflected wave, is maximized is the receiving antenna as shown by the dotted line in FIG. A deviation occurs from the main beam direction of Rx, and the path of the delayed wave WB deviates from the path connecting the radiating portion of the transmitting antenna Tx and the radiating portion of the receiving antenna Rx. As a result, the power level of the delayed wave WB reaching the receiving antenna Rx is reduced, and the component of the direct wave WA is relatively increased.

  Thus, in the present embodiment, the transmission antenna Tx and the reception antenna Rx may be arranged away from the dielectric DE, or may be arranged close to or in contact with each other. This also applies to other embodiments described later.

Next, for reference, when the main beam directions of the transmission antenna Tx and the reception antenna Rx are orthogonal to the discontinuous surfaces (medium boundary surfaces) ZA and ZB in the transmission path, that is, the angle θ is zero. The case where it is is demonstrated.
The arrangement relationship of each antenna in this case corresponds to the conventional arrangement relationship shown in FIG. In this case, as will be described next, the delayed wave WB is not effectively reduced, and the wireless transmission characteristics are not effectively improved.

For example, in the antenna arrangement example shown in FIG. 17A, when radio waves are radiated from the transmission antenna Tx of the first radio communication device toward the reception antenna Rx of the second radio communication device, The delayed wave WB is generated due to the reflection at the discontinuous surfaces ZA and ZB of the dielectric DE constituting the medium existing in FIG. According to this arrangement example, since the angle θ between the direction axis of each main beam of the transmission antenna Tx and the reception antenna Rx and the discontinuous surfaces ZA and ZB in the transmission path is small, the power of the spread wave WB becomes maximum. The amount of deviation of the propagation path from the main beam direction of the receiving antenna Rx is reduced. For this reason, the power level of the delayed wave WB reaching the reception antenna Rx is hardly reduced, and the delay wave WB reaches the reception antenna Rx in addition to the direct wave WA. Therefore, for example, when a high-speed wireless transmission method using a single carrier having a wide band is used, the influence of the delayed wave WB on the deterioration of transmission characteristics is increased. As shown in FIGS. 17B and 17C, the same applies even when both or one of the transmission antenna Tx and the reception antenna Rx is in contact with the discontinuous surfaces ZA and ZB.
In this embodiment, not only SISO (Single-Input and Single-Output) transmission, but also MIMO (Multi-Input and Multi-Output) transmission, SIMO (Single-Input and Multi-Output) transmission, MISO (Multi-Input). and single-output) transmission.

Second Embodiment
Next, a second embodiment of the present invention will be described.
In the second embodiment of the present invention, a case where the present invention is applied to MIMO (Multiple Input Multiple Output) transmission will be described.
In the present embodiment, a plurality of transmission antennas Txj (j is a positive integer) configuring an array antenna included in the first wireless communication device on the transmission side and an array antenna included in the second wireless communication device on the reception side are configured. Of the receiving antennas Rxi (i is a positive integer), focusing on a pair of transmitting antennas and receiving antennas that correspond to each other, it is the same as in the first embodiment. That is, this embodiment is an application of the first embodiment described above to MIMO transmission.

  FIG. 5 is a diagram for explaining the arrangement of transmission antennas Tx1 and Tx2 and reception antennas Rx1 and Rx2 included in the wireless communication system according to the second embodiment of the present invention. As shown in FIG. 5, in this embodiment, as in the first embodiment, there is an offset doff between the disposition position of the transmission antenna Tx1 and the disposition position of the reception antenna Rx1 along the discontinuous surfaces ZA and ZB. In addition to being provided, an offset doff is also provided between the arrangement position of the transmission antenna Tx2 and the installation position of the reception antenna Rx2 along the discontinuous surfaces ZA and ZB.

  According to the present embodiment, the radio wave transmitted from the transmission antenna Tx1 propagates through the transmission path, passes through the dielectric DE on the transmission path, and reaches the reception antenna Rx1 as the direct wave WA1. Further, a part of the radio wave transmitted from the transmitting antenna Tx1 and incident on the dielectric DE is multiple-reflected by the discontinuous surface ZA and the discontinuous surface ZB inside the dielectric DE, and the dielectric DE is formed as a delayed wave WB1. To Penetrate.

  Here, as in the first embodiment, an offset doff is provided along the discontinuous planes ZA and ZB between the arrangement position of the transmission antenna Tx1 and the arrangement position of the reception antenna Rx1, and the transmission antenna Tx1 and the reception antenna are received. Since the antenna Rx1 is disposed so as to face each other, the main beam directions of the transmission antenna Tx1 and the reception antenna Rx1 and the discontinuous surfaces (medium boundary surfaces) ZA and ZB in the transmission path are not orthogonal to each other. An angle θ that is non-right angle (an angle other than zero) is formed.

For this reason, the propagation path in which the power of the delayed wave WB1 that is the multiple reflected wave is maximum is shifted from the main beam direction of the receiving antenna Rx1 as shown by the dotted line in FIG. 5, and the path of the delayed wave WB1 is , And deviates from the path connecting the radiating portion of the transmitting antenna Tx1 and the radiating portion of the receiving antenna Rx1. As a result, the power level of the delayed wave WB1 reaching the receiving antenna Rx1 is reduced, and the component of the direct wave WA1 is relatively increased.
The direct wave WA2 and the delayed wave WB2 based on the radio wave transmitted from the transmission antenna Tx2 toward the reception antenna Rx2 will be described in the same manner.
Therefore, according to the present embodiment, if attention is paid to a pair of transmission antennas and reception antennas corresponding to each other, the power level ratio of the direct wave and the delayed wave in the reception antenna can be improved as in the first embodiment. Wireless transmission characteristics can be improved.

  However, in order to maximize the transmission capacity in short-distance MIMO transmission, it is necessary to consider the transmission path matrix representing the communication environment of the transmission path, and therefore, the path connecting the transmission antenna Tx1 to the reception antenna Rx1 and the transmission antenna A necessary condition is that the difference between the path connecting Tx2 and the reception antenna Rx1 is equal to the difference between the path connecting the transmission antenna Tx2 and the reception antenna Rx2 and the path connecting the transmission antenna Tx1 and the reception antenna Rx2. This condition can be realized by providing an offset of the installation position of each antenna element of the transmission antenna and the reception antenna as shown in FIG.

  Here, FIG. 6 is a figure for demonstrating the modification of arrangement | positioning of the transmission antenna and receiving antenna with which the radio | wireless communications system by 2nd Embodiment of this invention is provided. As shown in FIG. 6, in order to satisfy the above-described requirements, a pair of transmission antennas Tx1 and a pair of reception antennas Rx1 and a pair of transmissions are based on an axis orthogonal to the discontinuous surfaces ZA and ZB of the dielectric DE. The antenna Tx2 and the receiving antenna Rx may be arranged line-symmetrically. Accordingly, in the example of FIG. 6, the receiving antenna Rx1 is disposed at a position moved by the offset doff downward along the discontinuous planes ZA and ZB with respect to the arrangement position of the transmitting antenna Tx1, and the receiving antenna Rx2 is With respect to the arrangement position of the transmitting antenna Tx2, it is arranged at a position moved by an offset doff upward along the discontinuous surfaces ZA and ZB.

As will be described later, when the short-range MIMO simple reception decoding scheme shown in Non-Patent Document 2 is used, suppression of the delayed waves WB1 and WB2 is particularly effective. According to the arrangement shown in FIG. 6, radio transmission characteristics can be effectively improved when such a short-range MIMO simple reception decoding system is used.
When an array antenna is used as in the present embodiment, the antenna element in each array antenna is set so that the propagation path in which the power of the delayed waves WB1 and WB2 is maximum does not overlap with the main beam direction of the nearby receiving antenna. It is desirable to design the offset and the offset doff of the arrangement position of the antenna.

For reference, in the present embodiment, when the main beam directions of the transmission antennas Tx1 and Tx2 and the reception antennas Rx1 and Rx2 and the discontinuous surfaces (medium boundary surfaces) ZA and ZB in the transmission path are orthogonal to each other, A case where the angle θ shown in FIG. 6 is zero will be described. The arrangement relationship of each antenna in this case is the conventional arrangement relationship shown in FIG.
FIG. 7 is a diagram for explaining the arrangement of transmission antennas and reception antennas according to a conventional configuration corresponding to the radio communication system according to the second embodiment of the present invention. In this case, similarly to the conventional arrangement example shown in FIG. 17 described above, the delayed waves WB1 and WB2 arrive in the main beam direction of the receiving antennas Rx1 and Rx2 between the antenna elements facing in front. For this reason, the delayed waves WB1 and WB2 received by the receiving antennas Rx1 and Rx2 are not effectively reduced, and the wireless transmission characteristics are not effectively improved.

<Third Embodiment>
Next, a third embodiment of the present invention will be described.
In the present embodiment, a case will be described in which the present invention is applied to a stem using a simple reception decoding scheme for short-range MIMO transmission. Here, a case of 2 × 2 MIMO transmission will be described as an example. The details of the simple reception decoding method for short-range MIMO transmission itself are described in Non-Patent Document 2.

Here, a simple reception decoding scheme for short-range MIMO transmission will be briefly described. According to the simple reception decoding system for short-range MIMO transmission, when the antenna elements of the transmission antennas Tx1 and Tx2 and the reception antennas Rx1 and Rx2 are optimally arranged, the transmission path matrix H is approximated by the equation (1). Here, in Expression (1), a is a real number depending on the antenna directivity. H ₁₁ is a complex number representing the amplitude and phase modulation of the signal in the channel.

At this time, the weighting matrix W _ZF for the receiving array antenna in the zero forcing (ZF) method, which is one of the MIMO transmission methods, is as shown in Equation (2).

  Therefore, as shown in Expression (3), the product of the transmission line matrix and the reception weighting matrix is represented by a diagonal matrix. This means that the signals transmitted from the respective transmitting antennas are separated by multiplying the reception weighting matrix in the receiver, and are received without causing interference with each other.

When the wireless transmission path does not change with time and always has the characteristic represented by the equation (1), the weighting matrix W _ZF of the equation (2) can be configured only by the RF circuit. This is disclosed in Non-Patent Document 2. Non-Patent Document 2 also discloses the case of 4 × 4 MIMO transmission.

FIG. 8 is a diagram for explaining the arrangement of the transmission antennas Tx1 and Tx2 and the reception antennas Rx1 and Rx2 included in the wireless communication system according to the third embodiment of the present invention. It is a figure which shows the structural example of the 2 * 2 MIMO radio | wireless communications system using the simple reception decoding system for radio | wireless.
The 2 × 2 MIMO wireless communication system shown in FIG. 8 has a configuration in which the weighting circuit 100 is connected to the receiving antennas Rx1 and Rx2 in the configuration shown in FIG.

  As shown in FIG. 8, the power levels of the delayed waves WB1 and WB2 reaching the reception antennas Rx1 and Rx2 are set by setting the offset doff of the arrangement positions of the antenna elements of the transmission antennas Tx1 and Tx2 and the reception antennas Rx1 and Rx2. To improve the power level ratio between the direct waves WA1 and WA2 and the delayed waves WB1 and WB2 in the receiving antennas Rx1 and Rx2, and the communication environment of the wireless transmission path viewed from the transmitting antennas Tx1 and Tx2 and the receiving antennas Rx1 and Rx2 It approaches the condition shown by Formula (1). As a result, it is possible to reduce radio transmission capacity deterioration in short-distance MIMO transmission caused by the delayed waves WB1 and WB2 due to reflection generated in the transmission path.

For reference, a conventional configuration in the case where the angle θ is set to zero and the offset doff is set to zero in the configuration of FIG. 8 described above will be described.
FIG. 9 is a diagram for explaining the arrangement of transmission antennas and reception antennas according to a conventional configuration corresponding to the wireless communication system according to the third embodiment of the present invention.

  In FIG. 9, the transmission RF signal S1 and the transmission RF signal S2 transmitted from the transmission antenna Tx1 and the transmission antenna Tx2, respectively, are mixed and received by the reception antenna Rx1 and the reception antenna Rx2. Here, when the antenna elements are optimally arranged as described above, and the delayed waves WB1 and WB2 do not occur in the transmission path and only the direct waves WA1 and WA2 exist, based on the above theory, By the action of the weighting circuit 100, the decoded RF signal S1 ′ and the decoded RF signal S2 ′ derived from the transmission RF signal S1 and the transmission RF signal S2, respectively, are output separately from the output terminal T1 and the output terminal T2. .

  However, as shown by the dotted line in FIG. 9, when the delayed waves WB1 and WB2 due to reflection on the discontinuous surfaces ZA and ZB are generated in the transmission line, the transmission line seems to have a large deviation from the condition of the expression (1). And the off-diagonal term of the portion of the matrix indicated by the unit matrix on the right side of Equation (3) becomes large. This means that the decoded RF signals S1 ′ and S2 ′ output to the output terminal T1 and the output terminal T2 of the weighting circuit 100 are mixed signals of the RF signal derived from the transmission RF signal S1 and the transmission RF signal S2. This means that the transmission capacity deteriorates in the simple reception decoding for short-distance MIMO transmission by the system shown in FIG.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described.
In the present embodiment, a radio wave with linear polarization is transmitted from the transmission antenna Tx, and the radio wave from the transmission antenna Tx is received by the reception antenna Rx with the same polarization plane as that of the radio wave with linear polarization. In the present embodiment, a polarizing plate having a polarization characteristic that transmits a radio wave having the same polarization plane as that of the linearly polarized wave is disposed in the transmission line.

  FIG. 10 is a diagram for explaining the principle of arrangement of transmission antennas and reception antennas according to a conventional configuration corresponding to the radio communication system according to the fourth embodiment of the present invention. It is a figure explaining the polarization direction in receiving point R1-R4 in which the electromagnetic wave transmitted from the vertically polarized antenna exists in the near field. It can be considered that the electromagnetic field propagates as a spherical wave in the near field of the reception point. As shown in FIG. 10, assuming that the transmission point T and the reception points R1 to R4 are assumed to have a rectangular parallelepiped positional relationship, a current wave source in the y-axis direction (that is, a vertically polarized transmission antenna) exists at the transmission point T. The direction of the electric field at each peripheral reception point will be described. The radio wave transmitted from the transmission point T is a vertically polarized plane wave when observed from a sufficiently long distance.

The electric field direction at each of the reception points R1 to R4, that is, the polarization direction is as follows.
Since the electric field direction at the reception point R1 is the y-axis direction, it has only the y component.
Since the electric field direction at the reception point R2 is the y-axis direction, it has only the y component.
Since the electric field direction at the reception point R3 is in the plane formed by the points T-R1-R3 and is orthogonal to the straight line formed by the points T-R3, the y component and the z component are Have.
Since the electric field direction at the reception point R4 is in the plane formed by T-R2-R4 and is orthogonal to the straight line formed by the point T-R4, the x component, the y component, and z With ingredients.

  That is, the electric field direction at the receiving point has an x component except for the point on the plane formed by the points T-R1-R3 and the point on the plane formed by the points T-R1-R2. That is, a horizontal polarization component appears. An actual example is shown in Non-Patent Document 4, and a horizontally polarized wave component is observed as XPD degradation in short-range MIMO communication.

  As described above, in short-range communication, linearly-polarized waves assumed by the transmission antenna at reception points other than the plane orthogonal to the transmission antenna aperture plane PA shown in FIG. 10 and parallel to the polarization direction (vertical direction). A polarization component perpendicular to the direction of appears. That is, a component that is reflected at a point other than a plane orthogonal to the transmission antenna aperture plane PA and parallel to the polarization direction always generates a crossed polarization component, even if the reception antenna is in front of the transmission antenna (point in FIG. 10). Even if it is arranged at R1), the reflection component arrives as a delayed wave. When antenna elements with a wide directivity are used, when two-dimensionally arranged array antennas or offset antenna elements are offset in the oblique direction, the amount of cross-polarized waves included in the delayed wave is large. I can say.

  FIG. 11 is a diagram for explaining the arrangement of the transmission antennas Tx and the reception antennas Rx included in the wireless communication system according to the fourth embodiment of the present invention, and shows a first arrangement example. As shown in FIG. 11, a polarizing plate PP that passes only polarized waves in the same direction as the direction of polarized waves transmitted from the transmitting antenna Tx outside a transmission path such as a plate-like dielectric DE in which multiple reflection occurs. Place. In FIG. 11, the solid line represents the direct wave WA, and the dotted line represents an example of the path of the delayed wave WB caused by the multiple reflected waves in which the rotation of the polarization plane as described above occurs. In the delayed wave WB whose polarization plane has been rotated, the power of the cross polarization component is suppressed by the polarizing plate PP disposed in front of the receiving antenna Rx. For this reason, the power of the delayed wave WB can be reduced by the polarizing plate PP.

FIG. 12 is a diagram for explaining the arrangement of the transmission antennas Tx1 and Tx2 and the reception antennas Rx1 and Rx2 included in the wireless communication system according to the fourth embodiment of the present invention. The arrangement of FIG. 11 described above is applied to the array antenna. It is a figure which shows the 2nd example of arrangement | positioning at the time of doing.
As shown in FIG. 12, when the present invention is applied to the configuration of an array antenna, for example, the delayed wave WB12 that reaches the receiving antenna Rx2 from the transmitting antenna Tx1 has a large polarization rotation, so that the effect of reducing the power can be expected.
In the above example, the polarizing plate PP is installed in the transmission line. However, the polarizing plate PP may be installed as a component of the array antenna included in the transmission antennas Tx1 and Tx2 or the reception antennas Rx1 and Rx2. For example, as illustrated in FIGS. 13 to 15, the polarizing plate PP may be provided on the front surface of each antenna as a radome of the transmission antennas Tx1 and Tx2 or the reception antennas Rx1 and Rx2.

Here, FIG. 13 is a diagram for explaining the arrangement of the transmission antennas Tx1 and Tx2 and the reception antennas Rx1 and Rx2 included in the wireless communication system according to the present embodiment, and the polarizing plate PP includes the reception antennas Rx1 and Rx2. It is a figure which shows the 3rd example of arrangement | positioning provided as a radome in the front surface of the array antenna ARR performed. FIG. 14 is a diagram for explaining the arrangement of the transmission antennas Tx1 and Tx2 and the reception antennas Rx1 and Rx2 included in the wireless communication system according to the present embodiment, and the polarizing plate PP is composed of the transmission antennas Tx1 and Tx2. It is a figure which shows the 4th example of arrangement | positioning provided as a radome in the front surface of the array antenna ART. FIG. 15 is a diagram for explaining the arrangement of the transmission antennas Tx1 and Tx2 and the reception antennas Rx1 and Rx2 included in the wireless communication system according to the present embodiment. The polarizing plates PPA and PPB are respectively provided to the reception antennas Rx1 and Rx1. It is a figure which shows the 5th example of arrangement | positioning provided as a radome in the front surface of the array antenna ARR comprised from Rx2, and the front surface of the radome of the array antenna ART comprised from transmitting antenna Tx1, Tx2.
As described above, in the present embodiment, the transmission antenna and the reception antenna have a polarization characteristic that transmits a radio wave having a polarization plane in the same direction as the polarization direction of the both antennas or one of the antennas. A polarizing plate is disposed.
This embodiment is applicable to SISO transmission, MIMO transmission, SIMO transmission, and MISO transmission.

<Fifth embodiment>
Next, a fifth embodiment of the present invention will be described.
FIG. 16 is a diagram for explaining the arrangement of the transmission antenna Tx and the reception antenna Rx included in the wireless communication system according to the fifth embodiment of the present invention.
In the present embodiment, as shown in FIG. 16, a radio wave with circular polarization is transmitted from the transmission antenna Tx, and the reception antenna Rx receives the radio wave from the transmission antenna Tx with the same circular polarization as the circular polarization. . In the present embodiment, the transmission line includes a dielectric plate having a two-layer structure including a dielectric DEA layer having a refractive index NA and a dielectric DEB layer having a refractive index NB different from the refractive index NA. (Dielectric layer) is installed in the air, and delayed waves WBA and WBB are generated by multiple reflection on the dielectric plate. Here, it is assumed that the refractive index NB of the dielectric DEB facing the transmitting antenna Tx is larger than the refractive index NA of the dielectric DEA facing the receiving antenna Rx.

When a radio frequency signal is transmitted from the transmitting antenna Tx with right-handed polarization, the direct wave WA reaches the receiving antenna Rx with right-handed polarization. On the other hand, the polarization characteristics of the delayed waves WBA and WBB due to multiple reflection on the double-layered dielectric layer made of the dielectrics DEA and DEB vary depending on the multiple reflection path as follows.
Here, the polarization characteristics of the delayed waves WBA and WBB due to multiple reflection will be described. Note the path of the delayed wave WBA shown in FIG. The delayed wave WBA is incident on the discontinuous surface (boundary surface) ZA from the left side of the figure and reflected, and thereafter, the delayed wave WBA is reflected on the discontinuous surface ZC, which is a boundary surface between the dielectric DEA and the dielectric DEB. The light enters from the right direction and is reflected, and then passes through the discontinuous surface ZA and reaches the receiving antenna Rx. Reflection of the radio wave incident on the discontinuous surface ZC from the right side of the figure is fixed-end reflection due to the magnitude relationship between the refractive indexes NA and NB of the dielectric DEA and the dielectric DEB.

  In addition, the reflection of the radio wave incident on the discontinuous surface ZA from the left in the figure is a free end reflection due to the magnitude relationship between the dielectric DEA and the refractive index in the air. Therefore, since the reflection of the delayed wave WBA includes one fixed-end reflection and one free-end reflection, the delayed wave WBA is reversed only once in the circular polarization. For this reason, when a radio frequency signal is transmitted from the transmitting antenna Tx with right-handed polarization, the polarization at the receiving antenna Rx is left-handed polarization. Therefore, if the polarization characteristic of the receiving antenna Rx is set to right-handed polarization, the reception level of the delayed wave WBA can be reduced. However, in the case of including two free-end reflections as in the delayed wave WBB shown in FIG. 16, since the polarization rotation changes in the opposite direction twice, the delayed wave WBB becomes a right-handed polarized wave. It will reach the receiving antenna.

If this embodiment is combined with the first to third embodiments described above, the effect of reducing the multiple reflection itself in this embodiment and the reception level of unwanted waves due to the multiple reflection in the first to third embodiments are reduced. The effect is superimposed and the reception level of the delayed wave due to multiple reflection can be further effectively suppressed.
This embodiment is applicable to SISO transmission, MIMO transmission, SIMO transmission, and MISO transmission.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be arbitrarily modified or modified without departing from the gist of the present invention.

ARR, ART ... Array antenna DE, DEA, DEB ... Dielectric PP, PPA, PPB ... Polarizing plate Rx, Rx1, Rx2 ... Reception antenna Tx, Tx1, Tx2 ... Transmission antenna ZA, ZB, ZC ... Discontinuous surface (boundary surface) )
100: Weighting circuit

Claims (6)

A first wireless communication device having a first directional antenna; and a second wireless communication device having a second directional antenna, wherein the first wireless communication device includes the first and second directional antennas. A wireless communication system for performing wireless communication between the wireless communication device and the second wireless communication device,
The first directional antenna and the second directional antenna are arranged to face each other,
The path connecting the radiation part of the first directional antenna and the radiation part of the second directional antenna substantially coincides with the direction axis of the main beam of the second directional antenna;
Of the radio wave radiated from said first directional antenna, multiple reflections caused by the reflection and refraction at discontinuities in the transmission path between the first directional antenna and the second directional antenna The first directional antenna and the second directivity are set such that a wave path deviates from a path connecting the radiating portion of the first directional antenna and the radiating portion of the second directional antenna. A wireless communication system, wherein an antenna is disposed.   2. The radio according to claim 1, wherein an offset is provided along the discontinuous surface between an arrangement position of the first directional antenna and an arrangement position of the second directional antenna. Communications system. The first directional antenna transmits radio waves by linearly polarized waves,
The second directional antenna receives a radio wave from the first directional antenna with a polarization plane identical to a plane of polarization of the radio wave by the linearly polarized wave,
To the transmission path, to claim 1 or 2 polarizing plate characterized in that it is arranged to have a polarization property of transmitting a radio wave having the same polarization and polarization of radio waves by the linearly polarized The wireless communication system described. The polarizing plate is disposed in front of both or one of the first directional antenna and the second directional antenna, and has a polarization plane in the same direction as the polarization direction of the both or one antenna. The wireless communication system according to claim 3 , wherein the wireless communication system has a polarization characteristic that allows a radio wave to pass therethrough. The first directional antenna transmits radio waves by circular polarization,
The second directional antenna receives radio waves from the first directional antenna with the same circular polarization as the circular polarization,
In the transmission line, a two-layer structure of a first dielectric layer having a first refractive index and a second dielectric layer having a second refractive index different from the first refractive index. The wireless communication system according to claim 1, wherein a dielectric layer is disposed. The first wireless communication device and the second wireless communication device, any of claims 1 to 5, characterized in that performs radio communication by using short range MIMO (Multi-Input and Multi- Output ) transmission A wireless communication system according to claim 1.

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