JP2011199506A - Radio repeater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio repeater by which spatial multiplexing with satisfactory characteristics is attained even when repeaters are installed in visible positions in MIMO transmission.SOLUTION: From a base station 30, signals transmitted by vertically polarized waves which are linearly-polarized waves from two antennas 31a, 31b are transmitted. On the other hand, the signals are received by an antenna 21a of rightward circularly polarized waves in a repeater 10a and received by an antenna 21b of leftward circularly polarized waves in a repeater 10b. Then the signals are amplified by the repeater 10a and transmitted again by the vertically polarized waves from antennas 22a, 22b.

Description

  The present invention relates to a radio relay apparatus used in a radio communication system that enables large-capacity transmission using a spatial multiplexing scheme such as MIMO.

  In the case of a wireless communication system such as a mobile phone, a system is configured by a base station and a mobile station installed at a high position. As a simple configuration, one base station is in charge of a service area with a radius of 1000 m, etc. There is a method in which the mobile station communicates. However, since the radio is straight, it is difficult to reach the shielded area, and there is propagation attenuation at a long distance, so it becomes an incommunicable area (so-called out-of-service area). Also called a booster).

  Non-Patent Document 1 describes a repeater installed in an outdoor area with low traffic such as a mountainous area. FIG. 10 is a diagram illustrating an example of a conventional repeater station described in Non-Patent Document 1. In FIG. In this figure, the signal from the base station 101 is received by the antenna for base station 103 of the repeater 102, the signal is amplified, and the radio wave is emitted from the antenna for mobile station 104 to the mountainous area outside the service area. The mobile station 105, which is a mobile phone, receives and secures a service area. In FIG. 10, transmission from the base station 101 is described, but when transmitted from the mobile station 105, the base station 101 receives it through the reverse route.

NTT Docomo Journal Vol15 No. 1 P31

  In recent years, a MIMO (Multi Input Multi Output) technique has been proposed to increase the transmission speed. The MIMO technology is a technology for transmitting and receiving using a plurality of transmission / reception antennas, and utilizes a difference in propagation path characteristics, and can perform spatial multiplexing of signals.

  FIG. 11 shows the model. In this figure, spatial multiplexing by two antennas each of the base station 121, the repeater 122, and the mobile station 123 is shown, and only one direction is shown. Become.

  In the MIMO scheme, spatial multiplexing transmission becomes possible by using a plurality of antennas. This is a technique for separating the multiplexed transmissions by utilizing the fact that the propagation functions between the antennas are different, and may be referred to as spatial multiplexing, SDM, or MIMO transmission as it is. In the case of spatial multiplexing with MIMO (hereinafter referred to as MIMO-SDM for distinction), since the difference in spatial transfer function is used, the number of repeaters that relay MIMO-SDM transmission is the same as the number of spatial multiplexing. Amplifier system is required. In FIG. 11, the repeater 122 is provided with two systems 122a and 122b. Each is independent, and the input signals arriving at the two antennas of the respective repeaters 122a and 122b can also be considered independent.

Further, when considering the characteristics of the propagation path, since the difference in the propagation path is used for the separation, there is a problem that the separation performance deteriorates when the correlation of the antenna becomes high.
An example is shown in FIG. This shows the characteristics of a MIMO-SDM with a spatial multiplexing number of 2 for two transmissions and two receptions. This example is a characteristic when transmitted from the base station 121 to the mobile station 123, and no repeater is used. FIG. 12 shows the error rate characteristics when the correlation between the two receiving antennas is changed. The horizontal axis represents S / N, and the vertical axis represents the bit error rate. As correlation, four types of 0 (no correlation) and 0.3, 0.6, and 0.9 are shown. When the reception antenna correlation is 0.3, 0.6, and 0.9 when the reception antenna correlation is zero, the bit error increases and the characteristics deteriorate.

  In a normal receiving mobile station, an environment that does not become a `` line of sight '' with no obstacles is common and the correlation is low, and since it is often used in a mobile environment, even if there is a state where the correlation is high, The situation is unlikely to continue. However, in the repeater 102 installed in the installation environment as shown in FIG. 10, it is assumed that the base station 101 and the repeater station 102 have a line-of-sight and fixed installation environment. Correlation may be high.

In FIG. 10, two propagation paths exist independently between the base station and the repeater and between the repeater and the base station. When the correlation between one (base station and the repeater) increases, the other (between the repeater and the mobile station). Even if the correlation is low, the overall correlation becomes high, so that the multiplexing performance of spatial multiplexing deteriorates. Such a correlation problem is expected to be a problem when the repeater is made MIMO.
In addition, even in use without spatial multiplexing (diversity use with a plurality of antennas), it goes without saying that the characteristics deteriorate as the spatial correlation increases.

  Therefore, an object of the present invention is to provide a radio relay apparatus that can realize spatial multiplexing or diversity communication with good characteristics even when a repeater is installed at a line-of-sight position in MIMO transmission.

The present invention relates to a plurality of antennas for a base station for transmitting / receiving to / from a radio base station having a plurality of antennas and a plurality of mobile stations for transmitting / receiving to / from a radio mobile station having a plurality of antennas A multi-antenna input multi-antenna output radio system that amplifies a communication signal between a radio base station and a radio mobile station between a pair of antennas for a base station and a transmit antenna for a mobile station In the relay device,
At least one pair of the antennas for the base station has a polarization characteristic different from that of the antenna for the radio base station, and the pair of antennas for the base station has the same bias as the antenna of the base station. It is characterized by using a polarization method that is lower than that of the wave method.

Here, all the antennas for mobile stations have the same polarization characteristics as the antennas of the radio mobile stations.
Alternatively, at least a pair of the mobile station antennas have polarization characteristics different from those of the radio mobile station antennas, and the pair of mobile station antennas has a correlation between the antennas and the mobile station antennas. It is characterized by using a polarization system that is lower than the case of the same polarization system.

In the present invention, the polarization method for reducing the correlation between the antenna for the base station or the antenna for the mobile station is a pair of orthogonally polarized waves.
Here, the pair of orthogonally polarized waves may be a right-handed circularly polarized wave or a left-handed circularly polarized wave when the antennas of the radio base station and the radio mobile station are linearly polarized waves. When the antennas of the base station and the radio mobile station are linearly polarized waves, they may be linearly polarized waves that are inclined with respect to the linearly polarized waves and are orthogonal to each other.

Further, the present invention has means for exchanging control information regarding the gain characteristics of the polarization of the antenna in each amplification system between the antenna for the base station and the antenna for the mobile station, and based on the control information The amplification degree between the amplification systems is controlled so that constant transmission power or reception power can be obtained.
Here, when the antenna is a transmission antenna, the transmission output is further controlled.
The control information includes information on the directivity gain in consideration of the polarization of the antenna, and based on the directivity gain, the degree of amplification between the amplification systems is controlled and the transmission output is controlled. It is characterized by.

  As described above, according to the present invention, by using the present invention for a MIMO-compatible multi-input / multi-output compatible repeater, even when a wireless repeater is installed at the line-of-sight position, good spatial multiplexing is realized. Will be able to.

It is a block diagram which shows the Example of the radio relay apparatus (repeater) which concerns on this invention. It is a figure explaining the polarization relationship of the antenna of the base station of 1st Example, a repeater, and a mobile station. It is a figure which shows the relationship between the electric field and magnetic field of each polarization, (a) shows linear polarization (vertical polarization), (b) shows right-handed polarization, and (c) shows right-handed polarization. It is a figure which shows the polarization system of the antenna of each apparatus at the time of transmitting to a mobile station via a repeater from a base station, (a) shows 1st, 2nd Example, (b) is 3rd implementation. An example is shown. It is a figure which shows the polarization system of the antenna of each apparatus in 4th Example at the time of transmitting to a mobile station via a repeater from a base station. It is a figure which shows the polarization system of the antenna of each apparatus in 5th Example at the time of transmitting to a base station via a repeater from a mobile station. It is a block diagram which shows the radio relay apparatus (repeater) in 6th Example. It is a figure explaining the polarization relation of the antenna of the 7th example. It is a figure which shows the polarization system of the antenna of each apparatus in 7th Example at the time of transmitting / receiving between a mobile station and a base station via a repeater. It is a figure which shows the conventional radio | wireless communications system using the repeater in a MIMO system. It is a figure explaining the polarization relationship of the antenna of the conventional base station, a repeater, and a mobile station. It is a figure which shows the relationship between an error rate characteristic and S / N with respect to the correlation of an antenna.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an embodiment of a wireless relay device (repeater) according to the present invention. This repeater has a two-system amplifier system, and is a MIMO radio relay apparatus using antennas 21a and 21b for base stations and antennas 22a and 22b for mobile stations. It consists of two amplification system repeaters 10a and 10b that connect two mobile station antennas as a pair.

  The repeaters 10a and 10b include duplexers 11a, 11b, 15a, and 15b, LNA (Low Noise Amp) 12a, 12b, 16a, and 16b, RF processing units 13a, 13b, 17a, and 17b, and HPA (High Power Amp). 14a, 14b, 18a, 18b.

  In the repeater 10a, a signal arriving from the base station enters from the antenna 21a for the base station, and enters the downstream system by the duplexer 11a. The input signal is amplified by the LNA 12a, and then processing such as suppression (removal) of unnecessary sneak waves is performed in the RF processing unit 13a. Thereafter, the signal is amplified to a high output by the HPA 14a and emitted from the antenna for mobile station 21a through the duplexer 15a. By such processing, the signal input from the antenna for base station 21a is amplified by several tens of dB. The signal transmitted from the antenna for mobile station 22a is received by the mobile station.

On the other hand, the signal transmitted from the mobile station enters from the antenna for mobile station 22a and enters the upstream system by the duplexer 15a. The input signal is amplified by the LNA 16a, and then processing such as suppression (removal) of unnecessary sneak waves is performed in the RF processing unit 17a. Thereafter, the signal is amplified to a high output by the HPA 18a, and is emitted from the antenna 21a for the base station through the duplexer 11a. As a result, the signal transmitted from the antenna for base station 21a is received by the base station.
A similar operation is performed in repeater 10b.

  Thus, the antennas for base stations 21a and 21b and the antennas for mobile stations 22a and 22b function as a transmission antenna and a reception antenna, respectively.

(First embodiment)
FIG. 2 shows the polarization relationship of the antenna of the first embodiment.
In the first embodiment, the base station 30 sends signals transmitted with vertical polarization, which is linearly polarized, from the two antennas 31a and 31b. On the other hand, the repeater 10a receives a right-handed circularly polarized antenna 21a, and the repeater 10b receives a left-handed circularly polarized antenna 21b. Thereafter, the signal is amplified by the repeater 10a and transmitted again from the antennas 22a and 22b with vertical polarization.

FIG. 3 shows the relationship between the electric field and magnetic field of each polarization, where (a) shows linearly polarized waves (vertically polarized waves), (b) shows right-handed polarized waves, and (c) shows right-handed polarized waves. Yes.
The circularly polarized waves in FIGS. 3B and 3C are a right-handed polarized wave and a left-handed polarized wave, and are in an orthogonal relationship because the magnetic field and the electric field are rotated in the opposite directions. How to use the polarized wave of the first embodiment is shown as type 1 in FIG.

Characteristics of circularly polarized antennas are as follows: (1) Circularly polarized antennas receive linearly polarized radio waves 3 dB down.
(2) Since left rotation and right rotation are orthogonal, the reception correlation is low. (Ideally zero)

  As shown in FIG. 2, the repeaters 10a and 10b are installed in a place where the base station 30 can be seen to increase the reception sensitivity, and the antennas 21a and 21b are installed even for the base station. By using circularly polarized waves for the reception antennas 21a and 21b of the repeaters 10a and 10b as in the configuration of the example, the reception gain is somewhat lowered (3 dB), but the propagation path is set so that the two antennas 21a and 21b are orthogonal to each other. It becomes possible to make it independent, and the correlation becomes low. As a result, even if the MIMO signal is repeated, the propagation path correlation is low, so that a good propagation path can be prepared.

  On the other hand, the transmitting antennas 22a and 22b of the repeaters 10a and 10b transmit using the polarization transmitted by the base station 30. On the mobile station 40 side, the antennas 41a and 41b are designed on the premise of linearly polarized waves. Therefore, transmission loss between the repeater and the mobile station can be minimized by transmitting using the matched polarization method.

As described above, in this embodiment, (1) the antenna for the base station of the repeater that is installed in the line of sight and can expect high signal reception power is different from the base station transmission polarization (circular polarization), and for the base station The antenna uses a polarization method that lowers the correlation between the antennas as compared with the case of the same polarization method (vertical polarization) as the antenna of the base station. In particular, a polarization system having an orthogonal relationship is used.
(2) For communication between a repeater and a mobile station having various propagation environments, a polarization system that has the highest gain on the mobile station side, that is, the same polarization system as that of the base station is used as a repeater transmission antenna.
As described above, stable mobile station received power with low correlation can be obtained, and MIMO-SDM transmission characteristics can be improved.

(Second embodiment)
Further, as a second embodiment, another usage of polarization is shown in type 2 of FIG.
A vertically polarized signal from the base station is received by a pair of linearly polarized antennas whose polarization planes are tilted 45 degrees to the left and right. Then, the property is as follows: (1) When the polarization plane is inclined 45 degrees with respect to the vertical polarization, the receiving antenna receives the signal by 3 dB down from the vertical polarization.
(2) A pair of linearly polarized antennas whose polarization planes are tilted 45 degrees to the left and right are orthogonal to each other and have a low correlation.

  Therefore, instead of the two circularly polarized waves in the first embodiment, a linearly polarized antenna inclined 45 degrees to the right and left with respect to the vertical polarization of the base station may be used as the repeater receiving antenna. The same effects as in the first embodiment can be obtained. Note that the transmission antenna of the repeater uses vertically polarized waves as in the first embodiment.

(Third embodiment)
FIG. 4B shows a third embodiment in the case of 4 × 4 MIMO.
Four different propagation functions can be formed by combining circularly polarized waves and vertically polarized waves inclined by 45 degrees. In this example, [45 degrees vertical, right-handed, left-handed, -45 degrees vertical] are arranged from the end, but this order is not limited to this, and circularly polarized waves are separated from each other or arranged alternately. You can also.

  Although the circularly polarized wave and the vertically polarized wave are orthogonal to each other, the circularly polarized wave and the 45 degree vertical polarized wave are not orthogonally, and there is a certain degree of correlation. In this case, the present invention can be extended to three or more MIMOs by installing them while allowing the correlation. Similarly, four antennas on the transmission side of the repeater are installed with vertically polarized waves.

(Fourth embodiment)
The fourth embodiment is a case where the number of antennas for base stations is further increased, and FIG. 5 shows a case of 6 × 6. In this case, the same vertical polarization as that of the base station is increased by two (antennas 1 and 6 in repeater reception for the base station). For these two lines, the received power is the highest, but the correlation between the circularly polarized waves of other repeater receiving antennas and the vertically polarized waves inclined by 45 degrees can be lowered. Note that the antenna 1 and the antenna 6 having the same polarization are likely to have a high correlation, and therefore, a configuration separated from each other is illustrated.

(5th Example)
FIG. 6 shows an example of polarization of the uplink (mobile station → repeater → base station) as the fifth embodiment. 6A shows a case where the repeater antenna is 2 × 2, and FIG. 6B shows a case where the repeater reception antenna is 4 × 4. In FIG. 6A, type 1 of repeater transmission is a case of circular polarization, and type 2 is a case of vertical polarization inclined by 45 degrees.

There is a high possibility that the propagation environment of the uplink is as follows.
(1) [Between base station and repeater] has high correlation in line of sight (2) [Between repeater and mobile station] has low correlation in line of sight and low

  Therefore, in the uplink, the repeater antenna for mobile stations uses the same polarization antenna as the mobile station (vertical polarization), whereas the repeater antenna for base stations differs from the base station receive antenna. An antenna with polarization is used. In type 1 of FIG. 6A, antenna 1 is right-handed polarized wave and antenna 2 is left-handed polarized wave. In type 2 of FIG. 6A, the antenna 1 is a linearly polarized wave inclined 45 degrees to the right, and the antenna 2 is a linearly polarized wave inclined 45 degrees to the left. Further, in FIG. 6B, the antenna 1 is linearly polarized with 45 degrees tilted to the right, the antenna 2 is clockwise polarized, the antenna 3 is counterclockwise polarized, and the antenna 4 is tilted 45 degrees to the left with linear polarization. It is a wave.

  Thus, in the uplink as well, in the same way as in the first to fourth embodiments, the same polarization antenna as that of the mobile station is used as the reception antenna for the mobile station of the repeater, so that [between the repeater and the mobile station] is out of line of sight. Since the correlation is low, the received power is the highest. The repeater antenna for the base station uses an antenna having a polarization different from that of the base station reception antenna, thereby keeping the correlation as low as possible.

(Sixth embodiment)
In the first to fifth embodiments, the repeater of the block diagram of FIG. 1 is used, but in the sixth embodiment, the repeater of the block diagram of FIG. 7 is used.
In this block diagram, the same reference numerals are given to the common parts with FIG. The difference is the RF processing units 53a, 53b, 57a, 57b of the repeaters 50a, 50b, and control information is exchanged between the RF processing units 53a, 53b on the receiving side and the transmitting side, and between the RF processing units 57a, 57b. The output to be transmitted is adjusted between the amplification systems.

  In circularly polarized waves, linearly polarized waves are received by right-handed rotation and left-handed rotation, and therefore the received power at the repeater receiving antenna end is not always equivalent. Furthermore, depending on the number of antennas as described above, antennas with various polarization characteristics including linearly polarized waves inclined by 45 degrees may be additionally used. For example, when there is linearly polarized waves as shown in FIG. The received power increases, and the received power difference increases.

  However, since the transmission antenna ends of the repeaters 50a and 50b all transmit with the same linear polarization, the transmission power transmitted from the repeaters 50a and 50b is preferably equal. Therefore, control information is exchanged between the repeaters 50a and 50b, so that the reception characteristic difference between the reception antennas is absorbed and transmitted with the same power.

If the base station antenna and the multiple receive antennas of the repeater have the same polarization as in the past, the received power between the multiple antennas is statistically averaged even if there is an instantaneous difference in received power. It becomes almost constant power.
However, in the present invention, the purpose of the invention is to lower the correlation by intentionally shifting the polarization method, and as a result, the received power varies between the receiving antennas of the repeater. In other words, since variations in received power are caused by the antenna characteristics of the receiving system, it is preferable to correct them as the receiving system.

Although not shown in the figure, when transmitting from the repeater, the transmission output may be adjusted in view of the receiving antenna characteristics of the base station.
For example, if the receiving antenna of the base station is vertically polarized and the transmitting antenna of the repeater is a mixture of circular and vertically polarized waves, the transmission output of the circularly polarized antenna needs to be increased by 3 dB. Adjust to.

  More specifically, since the antenna has a directivity gain, the gain adjustment of each RF processing unit is performed in view of this. In this case, the control information includes information regarding the directivity gain of the antenna. In the figure, the mutual control signals are sent only to the RF processing unit, but the HPA related to the output may naturally be the control target.

  It is also conceivable to increase the directivity gain itself. If the radiation gain of the vertically polarized wave is x dBi, the directivity may be taken so that the radiation gain of the circularly polarized wave is (× + 3) dBi.

(Seventh embodiment)
A seventh embodiment is shown in FIGS. This may be either the repeater of FIG. 1 or FIG.

The examples so far are
(1) [Between base station and repeater] The polarization method is different.
(2) [Between repeater and mobile station] The polarization method is the same.
As

  However, in the case of a repeater that is placed indoors, the repeater may be attached to the ceiling, and [between the repeater and the mobile station] may also be used almost in line of sight. In this case, it may happen that the received power of the mobile station is large but the antenna correlation is high.

  Therefore, the present embodiment is characterized in that the polarization system is changed also in [between repeater and mobile station]. As a result, the correlation can be lowered also in [between repeater and mobile station]. That is, circularly polarized waves (right-handed polarization and left-handed polarization) are also used in the mobile station transmission antennas 22a and 22b in FIG. Of course, circularly polarized waves are used in the repeater antennas 21a, 21b, 22a, and 22b even in the uplink. Further, instead of circularly polarized waves, linearly polarized waves inclined by 45 degrees may be used. FIG. 9 shows how to use this polarization.

  In this way, even when the mobile station is in a line-of-sight state, the spatial correlation between the repeater antenna and the mobile station can be realized by reducing the correlation between the repeater antennas.

  In a system where the reception power is likely to be enough, such as the present invention, the polarization system of the repeater and the antenna gain and amplifier gain control are optimally performed to achieve low reception and stable reception. A system capable of obtaining power can be provided, and the number of mobile stations capable of spatial multiplexing can be increased.

  In the above description, the plurality of antennas of the base station and the mobile station have all been shown with the same polarization, but this need not be the same. In other words, even if different polarization schemes are used for multiple antennas at the base station and mobile station, at least a pair of the opposing antennas of the repeater have different polarization schemes that lower the received power compared to the case of the same polarization scheme. By using it, the present invention can exert an effect. For example, this is the case when the base station transmits two horizontally polarized waves and two vertically polarized waves, and the repeater receives two pairs of right-handed and left-handed polarized waves.

10a, 10b Repeaters 11a, 11b, 15a, 15b Duplexers 13a, 13b, 17a, 17b RF processor 21a, 21b Antenna for base station 22a, 22b Antenna for mobile station 30 Base station 31a, 31b Antenna 40 Mobile station 41a , 41b Antennas 50a, 50b Repeaters 53a, 53b, 57a, 57b RF processing unit

Claims (9)

A plurality of antennas for base stations for transmitting / receiving to / from a radio base station having a plurality of antennas, and a plurality of transmitting antennas for mobile stations to transmit / receive to / from a radio mobile station having a plurality of antennas A multi-antenna input multi-antenna output radio relay apparatus that amplifies a communication signal between a radio base station and a radio mobile station between a pair of base station antennas and a mobile station transmission antenna.
At least one pair of the antennas for the base station has a polarization characteristic different from that of the antenna for the radio base station, and the pair of antennas for the base station has the same bias as the antenna of the base station. A radio repeater using a polarization method that is lower than that of a wave method.   The radio relay apparatus according to claim 1, wherein all the antennas for mobile stations have the same polarization characteristics as the antennas of the radio mobile stations.   At least a pair of the mobile station antennas have polarization characteristics different from those of the radio mobile station antenna, and the pair of mobile station antennas has the same correlation between the antennas as the mobile station antennas. The radio relay apparatus according to claim 1, wherein a polarization system that is lower than a polarization system is used.   The radio relay according to any one of claims 1 to 3, wherein the polarization system that lowers the correlation between the antenna for the base station or the antenna for the mobile station is a pair of orthogonally polarized waves. apparatus.   5. The pair of orthogonally polarized waves is a right-handed circularly polarized wave or a left-handed circularly polarized wave when antennas of a radio base station and a radio mobile station are linearly polarized waves. The wireless relay device described.   The pair of orthogonally polarized waves is a linearly polarized wave whose plane of polarization is inclined and orthogonal to the linearly polarized wave when the antennas of the radio base station and the radio mobile station are linearly polarized waves. The wireless relay device according to claim 4, wherein: Each amplification system between the antenna for the base station and the antenna for the mobile station has means for exchanging control information regarding the gain characteristics of the polarization of the antenna,
The radio relay apparatus according to any one of claims 1 to 6, wherein an amplification degree between the amplification systems is controlled based on the control information so that constant transmission power or reception power can be obtained.   The radio relay apparatus according to claim 7, wherein when the antenna is a transmission antenna, the transmission output is further controlled. The control information includes information on directivity gain in consideration of the polarization of the antenna,
9. The radio relay apparatus according to claim 8, wherein an amplification degree between amplification systems is controlled based on the directivity gain to control a transmission output.

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