JP5551121B2 - MIMO terminal measurement method and measurement system - Google Patents

Description

  The present invention relates to a technique for easily and cost-effectively performing terminal measurement of a multiple-input multiple-output communication method called MIMO (Multiple Input Multiple Output).

  The MIMO method uses a plurality of data at the same time and the same frequency between wireless communication devices (mainly mobile communication base stations such as mobile phones and portable wireless terminals) each having a plurality of antennas. In a 4 × 4 MIMO system in which the number of both antennas is four, the size of the system is determined by the number of antennas that both have, and the number of antennas in both is 1 The transmission speed (throughput) is ideally four times that of the communication system.

  In actual mobile communication, the propagation path between a plurality of M base station side antennas and a plurality of N terminal side antennas is a multipath propagation path in actual mobile communication, and each of them is a statistically independent transmission path. In other words, if the characteristics of each transmission path are known, the signal output from each antenna on the transmitting side can be separated from the combined signal received by each antenna on the receiving side.

  Here, the signals input to the antenna on the receiving side are signals that have been subjected to different fading and overlapped with each other, and in the MIMO scheme, information on the signals that have received this interference is obtained. The transmission side is fed back, and the transmission side obtains the characteristics of each transmission path from the transmission signal to each antenna and the fed back information, and each antenna receives the maximum throughput based on the characteristics. Processing the transmission signal to.

  Since such a MIMO system is a system in which a base station, a fading propagation path, and a terminal operate integrally, a system that simulates a base station and a fading propagation path is required as a system for evaluating terminal performance. However, in order to measure the characteristics closer to actuality of the terminal, so-called OTA (Over The Air) measurement in which radio waves are transmitted and received in space is required.

  A measurement system shown in FIG. 11 is known as a specific example of a system for performing OTA measurement on a MIMO terminal.

This measurement system is called a fading emulator type, has a function equivalent to that of a MIMO base station, and outputs a plurality of base stations signals RF1 to RF4 of M sequences (here, M = 4 is shown as an example). Upon receiving the base station apparatus 11 and base station signals RF1 to RF4 from the base station apparatus 11, each of these signals is assumed to be a virtual plurality of Ps (here P = In the fading emulator 12 for generating fading signals FRF1 to FRF8 obtained when passing through the fading propagation path (path) of FIG. 8, the radio wave non-reflection chamber 13, and the radio wave non-reflection chamber 13. placed in a particular position as a virtual scatterers around the MIMO terminal 1, a plurality of P fading signal FRF1~FRF8 are respectively supplied antennas 14 ₁ It is composed of a 14 _8.

  Various fading emulators 12 have been proposed so far, and the one shown in FIG. 12 is known as the MIMO system.

The fading emulator 12, the high frequency of the base station signal RF1～RF4, down each converter (D _{/ C)} 121 1 by to 121 ₄ into a predetermined intermediate frequency band, A / D converter (A / D) 122 converted by _{1-122 4} into a digital signal, and distributes the signal path of the connection matrix processing unit it (connection matrix) multiple P (8 in this case) by 123.

The distributed signals are input to delay devices 124 _{1 to} 124 ₈ , respectively, and after delays corresponding to the respective paths are given, D / A converters (D / A) 125 _{1 to} 125 _{8 are provided.} by being converted to an analog intermediate frequency band signals, is further converted into up-converter (U / C) 126 ₁ - 126 original high frequency band by ₈ (the frequency band used for the wireless communication with the terminal), the antennas 14 ₁ It is supplied to the to 14 _8.

  In FIG. 12, reference numeral 127 denotes a local signal generator for down-conversion and up-conversion, reference numeral 128 denotes a Doppler shift adder (frequency variable unit) that selectively gives a Doppler shift at the time of up-conversion, and reference numeral 129 denotes A parameter setting unit for setting a delay amount and a Doppler shift to be given to each path.

  This Doppler shift simulates the Doppler frequency that is generated when the distance between the terminal and a scatterer such as a surrounding building changes when a person carrying the terminal moves at high speed on a bus, car, train, etc. belongs to.

  When testing the MIMO terminal 1 via the fading emulator 12 as described above, arbitrary fading is given to the output signal of the base station apparatus 11 and input to the MIMO terminal 1, and the response from the MIMO terminal 1 is transmitted to the base station apparatus. Ascertained by 1, various performances of the MIMO terminal 1 with respect to the assigned fading are grasped.

  The fading emulator having the above configuration and the OTA measurement method using the fading emulator are disclosed in Non-Patent Document 1, for example.

Yoshio Karasawa, Kosako Kosa, Masahiko Shimizu, “A Simple Configuration Method for MIMO Fading Emulator-type OTA Systems” IEICE Tech. A / P 2010/131 (2010-12)

  As described above, the measurement system configured to arrange the antennas 14 according to the number P of virtual scatterers (paths) in the radio wave non-reflection chamber 13 so as to surround the MIMO terminal 1 can freely set the parameters of the fading environment. Although it is a large standard and can be said to be a standard OTA measurement for a MIMO terminal, a relatively large number of antennas 14 corresponding to the number of radio wave non-reflection chambers 13 and the number of virtual scatterers P are required, which increases the system cost and construction costs. There is a problem that becomes high.

  An object of the present invention is to provide a MIMO terminal measurement method and a measurement system that can solve the above-described problems and can be constructed at a low cost with a simpler configuration.

In order to achieve the above object, a MIMO terminal measurement method according to claim 1 of the present invention comprises:
Generating a plurality of M-sequence base station signals for transmission to a MIMO terminal (1) having a plurality of N terminal antennas (1a, 1b);
Assuming a plurality of M × N propagation paths from the plurality of M base station antennas to a plurality of N terminal antennas of the MIMO terminal, each of the plurality of M × N propagation paths is received by receiving the plurality of M base station signals. Generating a plurality of M × N sequences of fading signals to which fading according to each is given,
Combining the plurality of M × N-sequence fading signals for each incoming wave to the N terminal antennas to generate a plurality of N-sequence combined signals;
The MIMO terminal (1) is held such that the plurality of N terminal antennas are positioned in the vicinity of one focal point on the major axis of the elliptical sphere in an elliptical spherical space covered with a metal wall that reflects radio waves. In addition, a plurality of N measurement antennas (31 ₁ , 31 ₂ ) to which the plurality of N-sequence combined signals are respectively supplied are positioned in the vicinity of the other focal point on the long axis and the center of the long axis Each of the measurement antennas and each of the terminal antennas is selectively coupled in a one-to-one manner in the space, and the plurality of M Forming a state equivalent to a spatial coupling between the base station antenna and the plurality of N terminal antennas.

Further, the MIMO terminal measurement system according to claim 2 of the present invention is:
A MIMO system base station apparatus (11) for outputting a plurality of M-sequence base station signals to be transmitted to a MIMO terminal having a plurality of N terminal antennas;
Assuming a plurality of M × N propagation paths from the plurality of M base station antennas to a plurality of N terminal antennas of the MIMO terminal, each of the plurality of M × N propagation paths is received by receiving the plurality of M base station signals. A fading emulator (12) for generating and outputting fading signals of the plurality of M × N sequences to which fading corresponding to each of the fading is given,
A multiplexing unit (25) that multiplexes the fading signals output in the plurality of M × N sequences for each incoming wave to the N terminal antennas to generate a plurality of N-sequence combined signals;
The MIMO has an elliptical spherical space covered with a metal wall that reflects radio waves, and the plurality of N terminal antennas are positioned in the vicinity of one focal point on the major axis of the elliptical sphere in the space. While holding the terminal (1), a plurality of N measurement antennas (31 ₁ , 31 ₂ ) to which the plurality of N-sequence combined signals are respectively supplied are positioned near the other focal point on the major axis, In addition, each measurement antenna and each terminal antenna are selectively coupled on a one-to-one basis in the space while being held in a substantially point-symmetrical position with each terminal antenna with respect to the center of the major axis. And a coupler (30) for forming a state equivalent to a spatial coupling between the plurality of M base station antennas and the plurality of N terminal antennas.

A MIMO terminal measurement system according to claim 3 of the present invention is the MIMO terminal measurement system according to claim 2,
The coupler is provided with a moving mechanism (35, 36) for moving the MIMO terminal and the plurality of measurement antennas held in the coupler in a direction along the long axis. Features.

A MIMO terminal measurement system according to claim 4 of the present invention is the MIMO terminal measurement system according to claim 2 or 3,
The plurality of measurement antennas are covered with a radio wave absorber (40).

  As described above, the present invention assumes a simplified model in which a plurality of M base station antennas and a plurality of N terminal antennas of a MIMO terminal are coupled by a plurality of M × N propagation paths. The base station signal generates a fading signal of a plurality of M × N sequences to which fading is given according to each propagation path, and multiplexes them for each incoming wave to each terminal antenna. On the other hand, a plurality of terminal antennas of the MIMO terminal are held so as to be positioned in the vicinity of one focal point of the elliptical spherical coupler, and each terminal antenna is positioned in the vicinity of the other focal point and the major axis center of the elliptical sphere. Each of the measurement antennas is arranged at a substantially point-symmetrical position to form a state in which each terminal antenna and the measurement antenna are selectively coupled in a one-to-one relationship within the coupler. The combined signal is supplied to form an equivalent state to the spatial coupling between the base station antenna and each terminal antenna.

  This eliminates the need for a large radio wave non-reflective chamber and eliminates the need for a large number of antennas corresponding to the number of virtual scatterers, thus simplifying the system and realizing it at a low construction cost.

  In addition, in the case of having a moving mechanism for moving the MIMO terminal and a plurality of measurement antennas held in the coupler in the direction along the long axis, even if there is multiple reflection in the coupler, It can be set at a position where the degree of separation from the measurement antenna is high.

  In addition, when the antenna for measurement is covered with a radio wave absorber, the multiple reflection component can be greatly attenuated, and a large drop in the frequency characteristic can be suppressed to obtain a broadband characteristic.

The figure which shows an example of the spatial coupling model of a base station and a MIMO terminal Overall configuration diagram of an embodiment of M = N = 2 of the present invention Diagram showing a more specific configuration of the coupler The figure which shows the positional relationship of the antenna for a measurement in a coupler, and a terminal antenna Measurement results showing the change in degree of coupling (separation) when the distance between the antenna for measurement and the terminal antenna is changed The figure which shows the state which covered the antenna for measurement with the absorber Measurement results showing changes in the degree of coupling (separation) when the distance between the antenna for measurement and the terminal antenna is changed in the presence of an absorber Measurement results showing changes in the degree of coupling (separation) when the distance between the antennas for measurement and the distance between the terminal antennas is changed with the absorber Measurement results showing the change in degree of coupling (separation) with frequency change in the presence of an absorber Overall configuration diagram of an embodiment where M = N = 4 Configuration diagram of conventional measurement system Figure showing a configuration example of a fading emulator

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Before that, FIG. 1 shows an assumed spatial coupling model between a base station and a MIMO terminal which is a premise of the present invention.

  As shown in FIG. 1, radio waves Pa and Pb emitted from base station antennas 5 a and 5 b of a plurality M (here, M = 2) of the base station 5 are transmitted to a plurality N ( Here, the terminal antennas 1a and 1b of N = 2) are reached.

  Here, the radio wave Pa emitted from the base station antenna 5a receives inherent fading (delay, attenuation, and Doppler shift) Fa and Fb on the propagation path 6, and arrives at the terminal antennas 1a and 1b, respectively. The radio wave Pb emitted from the station antenna 5b also receives unique fading Fc and Fd on the propagation path 6 and arrives at the terminal antennas 1a and 1b, respectively.

  That is, the radio wave arriving at the terminal antenna 1a is represented by the sum of the radio wave Pa with the fading Fa [Pa * Fa] and the radio wave Pb with the fading Fc [Pb * Fc].

  Similarly, the radio wave arriving at the terminal antenna 1b is represented by the sum of [Pa * Fb] in which the fading Fb is added to the radio wave Pa and [Pb * Fd] in which the fading Fd is added to the radio wave Pb. .

  In order to realize this simplified model by OTA measurement, M × N sequence fading signals to which fading corresponding to M × N propagation paths are respectively added are generated from M sequence base station signals. May be synthesized for each incoming wave to the terminal antenna, and the synthesized wave may be selectively supplied to each terminal antenna.

  A measurement system that realizes this is shown in FIG. This measurement system includes a base station apparatus 11 that supports the MIMO system, a fading emulator 12, a multiplexing unit 25, and an elliptical spherical coupler 30 for spatial coupling.

  In FIG. 2, the base station apparatus 11 and the fading emulator 12 have the same structure as described above, and the base station apparatus 11 is a multiple M sequence (here, 2 × 2 MIMO example) for transmission to the MIMO terminal 1. The base station signals RF1 and RF2 of M = 2) are output to the fading emulator 12. Although not described in detail here, arbitrary fading by the fading emulator 12 is given to the signal output from the base station apparatus 11 and transmitted to the MIMO terminal 1, and the response from the MIMO terminal 1 is transmitted by the base station apparatus 11. By confirming, various performances of the MIMO terminal 1 with respect to the assigned fading will be grasped.

  The fading emulator 12 receives M-sequence base station signals RF1 and RF2, and receives 4 sequences of M × N (2 × 2 = 4 in this example) propagation paths assumed between the base station antenna and the terminal antenna. Fading signals FRF1 to FRF4 are generated and output. In terms of the internal processing of the fading emulator 12, the internal processing is divided into 4 series by branching each of the signals obtained by down-converting the base station signals RF 1 and RF 2 and A / D converting them into two by connection matrix processing. , And delay processing, D / A, and up-conversion, respectively, to obtain four series of fading signals FRF1 to FRF4. Here, the fading signal FRF1 corresponds to the propagation path between the base station antenna 5a and the terminal antenna 1a, and the fading signal FRF2 corresponds to the propagation path between the base station antenna 5a and the terminal antenna 1b. FRF3 corresponds to the propagation path between the base station antenna 5b and the terminal antenna 1a, and the fading signal FRF4 corresponds to the propagation path between the base station antenna 5b and the terminal antenna 1b.

  These fading signals FRF <b> 1 to FRF <b> 4 are input to the multiplexing unit 25. The multiplexing unit 25 multiplexes the four sequences of fading signals FRF1 to FRF4 for each incoming wave to the N terminal antennas 1a and 1b to generate a plurality of N sequences of combined signals Q1 and Q2. .

The multiplexing unit 25 in FIG. 2 corresponds to M = N = 2, and among the fading signals FRF1 to FRF4 output from the fading emulator 12, the signals FRF1 and FRF3 to be given to the terminal antenna 1a are combined in phase. enter the multiplexer 26 ₁ generates a multiplexed signal Q1, it applied to the terminal antenna 1b signal FRF2, to produce a type multiplexed signal Q2 to the multiplexer 26 _2-phase type the FRF4.

The combined signals Q1 and Q2 generated in this way are input to the coupler 30. The coupler 30 is formed by covering an ellipsoidal space obtained by rotating an ellipse around its major axis with a metal wall that reflects radio waves, and one focal point F2 on the major axis of the ellipse in the space. The MIMO terminal 1 is held so that the plurality of terminal antennas 1a and 1b are positioned in the vicinity of and a plurality of measurement antennas 31 _{1 to} 31 ₂ to which a plurality of N-sequence combined signals Q1 and Q2 are respectively supplied. The antennas for measurement 31 ₁ , 31 in the space are held in the vicinity of the other focal point F1 and in positions substantially symmetrical with the respective terminal antennas 1a, 1b with respect to the long axis center O of the ellipse. ₂ and each of the terminal antennas 1a and 1b are selectively coupled in a one-to-one manner to form an equivalent state with the assumed spatial coupling of the M base station antennas and the N terminal antennas.

  This elliptical spherical coupler 30 is formed by internally forming a hollow elliptical spherical space obtained by rotating an ellipse around its long axis by a metal plate (plate or film body) that reflects radio waves. The applicant of the present application uses an ellipse's geometrical properties, and uses an antenna arranged at one of the two focal points F1 and F2 on the major axis to reflect the radio wave reflected by the inner wall at the other focal point. It was applied to the characteristic test of a terminal having a single antenna or a terminal antenna.

  The applicants of the present application are that the elliptical space type coupler 30 has the antenna group disposed in the vicinity of one focal point and the antennas disposed in the vicinity of the other focal point at the center of the ellipse. In contrast, when they are arranged at points symmetrical to each other (strictly, a slight deviation is allowed), the points symmetrical with each other are selectively coupled on a one-to-one basis. .

  In geometric optics, light emitted from a light source that is slightly displaced from the focal point in a direction perpendicular to the major axis of the ellipse is reflected by the inner wall surface of the elliptical spherical space and then converges around a point-symmetric position. It is known that light is strongest at a point-symmetrical position, but it is spatially spread without being concentrated at one point, and has a Gaussian distribution. The same applies to radio waves, but radio waves are not emitted from a single point like light, and the size of the ellipsoidal space cannot be made large enough to be ignored with respect to wavelength. Since the distribution is wider than the case, the center of the distribution for each measurement antenna is at the position of the terminal antenna, and the distribution of the distribution is small, so that the measurement antenna and the terminal antenna have a one-to-one relationship. Will be selectively combined.

In the configuration example of FIG. 2, the terminal antennas 1a and 1b of the MIMO terminal 1 are arranged on a line perpendicular to the elliptical long axis with one focal position F2 of the coupler 30 interposed therebetween, and two measurements are made at point symmetric positions thereof. The antennas 31 ₁ and 31 ₂ are arranged, and the combined signals Q 1 and Q 2 generated by the multiplexer 25 are supplied to the measurement antennas 31 ₁ and 31 ₂ .

However, in consideration of such overlapping of the above-described distribution, the terminal antenna 1a, 1b distance measurement antenna ₃₁ 1 (in d 4 below) and two, 31 _second interval (d in FIG. 4 described later ') Are not necessarily the same. That is, it is important that the two terminal antennas receive the radio waves transmitted from one of the two measurement antennas with a sufficient degree of separation (selectively couple one-on-one).

  That is, while the actual distance d between the terminal antennas 1a and 1b is determined by the design of the portable terminal, the distance between the two measurement antennas can be arbitrarily selected. The interval d ′ may be changed so that the distribution of the aggregation points does not overlap (a sufficient degree of separation is obtained). In this case, the position of the measurement antenna with respect to each terminal antenna is deviated from the point-symmetrical position, but the amount of deviation is relative to the distance between the measurement antenna and the terminal antenna (approximately 1000 mm, for example, the distance between the focal points). Since it is confirmed that it is sufficiently small (λ / 4 = about 50 mm), in the present invention, the “substantially point-symmetrical position” is included including this deviation.

  In addition, the larger the elliptical sphere space compared to the wavelength, the smaller the spread of the distribution of the aggregation points, and even when the distance between the terminal antennas is narrow, the point symmetry position or the point symmetry position is very small. It is possible to selectively couple to a measurement antenna arranged at a shifted position.

Here, each of the terminal antennas 1a and 1b and the measurement antennas 31 ₁ and 31 ₂ is a dipole system (including a sleeve antenna), and the direction in which both are not directly coupled, that is, the length direction of each antenna is parallel to the major axis of the ellipse. Collinear arrangement.

As described above, the MIMO measurement method of the embodiment generates a plurality of M-sequence base station signals to be transmitted to the MIMO terminal 1 having the plurality of N terminal antennas 1a and 1b, and the MIMO terminal from the plurality of M base station antennas. A plurality of M × N sequences in which M × N propagation paths to a plurality of N terminal antennas are assumed, a plurality of M series base station signals are received, and fading corresponding to each of the plurality of M × N propagation paths is provided. The fading signal is generated. Then, the fading signals are combined for each incoming wave to the plurality N of terminal antennas 1a and 1b to generate a plurality of N series combined signals, and an elliptical spherical shape covered with a metal wall that reflects the radio waves. The MIMO terminal 1 is held so that a plurality of N terminal antennas 1a and 1b are positioned in the vicinity of one focal point on the major axis of the elliptical sphere in the space, and a plurality of N-sequence combined signals are respectively supplied. A plurality of N measuring antennas 31 ₁ and 31 ₂ are held in positions near the other focal point on the long axis and in positions substantially symmetrical with the terminal antennas 1a and 1b with respect to the long axis center. Then, each of the measurement antennas 31 ₁ and 31 ₂ and each of the terminal antennas 1a and 1b is selectively coupled in a one-to-one manner in the space, and a plurality of M base station antennas and a plurality of N terminal antennas are assumed. Spatial coupling with etc. To form a state.

Further, in terms of the system configuration, a MIMO system base station apparatus 11 that outputs a plurality of M-sequence base station signals to be transmitted to a MIMO terminal 1 having a plurality of N terminal antennas 1a and 1b, and a plurality of M base stations. Assuming an M × N propagation path from a station antenna to a plurality of N terminal antennas of a MIMO terminal, a plurality of M-sequence base station signals are received, and a plurality of fadings respectively assigned to each M × N propagation path are provided. A fading emulator 12 that generates and outputs M × N-sequence fading signals and a plurality of M × N-sequence fading signals are combined for each incoming wave to a plurality of N terminal antennas 1a and 1b to combine a plurality of N-sequences. A combining unit 25 that generates a signal and an elliptical spherical space covered with a metal wall that reflects radio waves, and a plurality of N are arranged in the vicinity of one focal point on the major axis of the elliptical sphere in the space. End antenna 1a, 1b holds a MIMO terminal 1 so as to position the measuring antenna 31 of a plurality N of multiplexing signals of a plurality of N series are _supplied, 31 _2, the other focal point on the long axis And each terminal antenna 1a, 1b is held in a substantially point-symmetrical position with respect to the center of the major axis, and each measurement antenna and each terminal antenna are selected on a one-to-one basis in space. And a coupler 30 that forms an equivalent state with the spatial coupling of a plurality of M base station antennas and a plurality of N terminal antennas.

According to such a measurement method and measurement system, one of the multiplexed signal Q1 generated by the multiplexing section 25 is supplied to the measuring antenna 31 _1, the radio wave that signal Q1 is one of MIMO terminal 1 terminal is selectively received by the antenna 1a, the other of the multiplexed signal Q2 is supplied to the measurement antenna _312, that radio waves of the signal Q2 is selectively received by the other terminal antenna 1b of MIMO terminal 1 Thus, a fading test corresponding to the simplified spatial coupling model can be performed.

  However, when the elliptical spherical coupler 30 is used, the radio wave emitted from one of the measurement antennas is not reflected by the inner wall and absorbed entirely by the one terminal antenna 1a. Multiple reflection modes that pass through, reflect on the inner wall again, return to the antenna for measurement, and exit to the inner wall again occur, and this interference of multiple reflected waves causes ripples in the frequency characteristics of the coupling between the antennas. In some cases, a high degree of coupling cannot be obtained at a frequency.

This state can be avoided by adjusting the distance between the MIMO terminal 1 and the measurement antennas 31 ₁ and 31 _{2. As} shown in FIG. 3, the MIMO terminal 1 and the measurement antenna are connected to each other. Provided are moving mechanisms 36 and 37 for moving the holding parts 33 and 34 for holding each of the holding parts (which are arbitrary in structure but not affecting the propagation of radio waves) along the major axis of the elliptic sphere, The test may be performed after symmetric movement with respect to the ellipse center O while maintaining the point-symmetric arrangement described above and positioning so that the degree of coupling between the two becomes maximum.

  As the moving mechanism, it is possible to employ a mechanism in which a part of the holding portions 33 and 34 protrudes outside the coupler 30 and is slid by hand or driven by a stepping motor or the like along the elliptical long axis.

  Various structures are conceivable for the coupler 30 itself. That is, the coupler 30 basically has a structure that covers the elliptical spherical space with a metal wall that reflects radio waves, so that the elliptical spherical space is formed inside in consideration of the ease of setting work of the MIMO terminal. It is preferable to obtain the maximum opening surface by dividing the partition member into two vertically divided by a plane along the major axis of the ellipse.

  In that case, a simple separation structure in which the lower partition member is used as a base portion and the upper partition member is placed on the lower partition member (positioning is required), or the upper partition member is attached to the lower partition member. Arbitrary structures can be employed, such as a freely openable structure connected by a hinge. The metal wall that reflects radio waves can be formed of a metal plate, a metal net, or a metal paint.

Next, simulation results regarding the degree of coupling and the degree of separation between the measurement antennas 31 ₁ and 31 ₂ and the terminal antennas 1a and 1b (actually pseudo antennas for simulation) in the coupler 30 will be described.

FIG. 4 shows an example of the coupler 30 and the antenna structure used in the simulation, and the length of the elliptic sphere space of the coupler 30 formed of a metal wall with conductivity σ = 2 × 10 ⁵ S / m. The shaft diameter 2a = 1200 mm, the short shaft diameter 2b = 1094 mm, the eccentricity = 0.41, and the frequency 1.47 GHz (wavelength λ204.1 mm). Each antenna is a half-wave dipole, and for convenience, # 1 and # 4 are provided for two antennas on one focal side (for measurement), and # 2 and # 3 are provided for two antennas (terminal antennas) on the other focal side. The number is attached. Also, the interval between antennas # 1 and # 4 is d ', and the interval between antennas # 2 and # 3 is d (it is difficult to make the distance between the antennas in the actual terminal and the distance between the antennas for measurement strictly coincide with each other). And ideally d = d ').

  FIG. 5 shows antenna # 1 to antenna # 2, # 3 when the center position of the antenna group for measurement and the center position of the terminal antenna group are symmetrically displaced from the reference position (focal position) on the elliptical long axis. It is the simulation result which measured the transmission coefficients S31 and S21 for. Here, the displacement Δz = 0 is the reference position, the + direction represents outward displacement, and the − direction represents inward displacement.

  FIG. 5A shows that when d = d ′ = 0.25λ, the difference between S31 and S21 at the position of Δz = 60 mm, that is, a maximum separation of 20 dB is obtained. FIG. 5B shows that when d = d ′ = 0.5λ, the degree of separation is maximum at a position of Δz = 80 mm, and a value close to 20 dB is obtained. Furthermore, in this case, a sufficient degree of separation of 10 dB or more is obtained even at a position of Δz = −20 mm. FIG. 5C shows that when d = 0.25λ and d ′ = 0.3λ, the degree of separation becomes maximum at a position of Δz = 60 mm, and a value close to 30 dB is obtained. From the example of d.noteq.d 'as shown in FIG. 5C, the symmetry between the terminal antenna and the measurement antenna is 20 percent {= 100.times. (0.3-0.25) / 0. It can be inferred that a sufficient degree of separation can be obtained even if it decreases by about 25}.

  In this way, by adjusting the distance between the two antenna groups while maintaining the above point symmetry, it is possible to obtain the degree of separation necessary for measurement without being affected by the ripple due to multiple reflection.

  In the above-described embodiment, measurement is performed by selecting a position where the influence of multiple reflection is small. However, this requires a mechanism for moving the antenna group, which is disadvantageous when performing broadband measurement quickly.

  As a method for improving this point, it is conceivable to reduce the multiple reflection itself, but it is practically difficult to selectively attenuate only the second and subsequent reflected waves.

  Therefore, the inventors of the present application have found that multiple reflected waves can be greatly attenuated by covering the periphery of antennas # 1 and # 4 (measuring antennas) with a radio wave absorber.

  In this case, attenuation of the first outgoing wave also occurs, but it is sufficient to increase the supply signal level in anticipation of the attenuation, and radio waves that have passed through the terminal antenna and returned to the position of the measurement antenna are absorbed. Attenuate by the body. Here, if the attenuation amount by the radio wave absorber is, for example, 6 dB, the first return wave can be attenuated to 1/4 power ratio, and the second return wave can be attenuated to 1/16 power ratio. Can ignore the reflected wave.

An experiment using this radio wave absorber will be described.
FIG. 6 shows the structure of the coupler 30 using the radio wave absorber 40. The structure of the coupler itself and the antenna are the same as those in FIG.

  As the radio wave absorber 40, two kinds of materials having different electrical constants, absorbers A and B, are used as shown in the following table (the material is carbon-impregnated urethane).

  Similarly to the above, d = d = 0.5λ (the interval is widened for convenience of covering with the radio wave absorber 40) and the transmittances S31 and S21 are measured, and the results are shown in FIGS. 7A and 7B. The separation degree of the transmittance difference is also indicated by a one-dot chain line.

  (A) of FIG. 7 is a result at the time of using the absorber A with a small absorptance, the level of S31 and S21 is comparatively high, the change is gradual, and a separation degree is a displacement range of -120 mm-+120 mm. Among them, 10 to 15 dB is obtained in the range of −30 mm to 0 mm.

  Moreover, (b) of FIG. 7 is a result at the time of using the absorber B with a comparatively large absorption rate, and the level of S31 and S21 has fallen about 15 dB compared with the case of the absorber A. The change is further gradual, and the separation degree is 10 to 11 dB in the range of −20 mm to −10 mm.

  FIG. 8 shows the results of measuring the transmittances S31 and S21 and the degree of separation when d = d ′ = 0.25λ, and the result of FIG. 8A using the absorber A is the result of FIG. As in the case of a), a separation degree of 10 to 16 dB is obtained in the range of −30 mm to 0 mm, and the result of FIG. 8B using the absorber B is the same as the case of FIG. Almost the same, a degree of separation of 10 to 16 dB is obtained in the range of −30 mm to 0 mm, and a degree of separation of 10 to 11 dB is obtained in the range of −20 mm to −5 mm.

  In principle, if the distance between the terminal antennas of the MIMO terminal 1 is short, the degree of separation decreases. In this case, the necessary degree of separation is ensured by finely adjusting the distance between the measurement antennas as described above. Make sure you can. The distance between the terminal antennas of the MIMO terminal 1 is a design matter of the terminal and is fixed. However, since the distance between the measurement antennas can be arbitrarily changed, the coupler 30 is provided with a measurement antenna interval adjustment mechanism. Thus, a test with a high degree of separation can be performed. This may be achieved by providing a measuring antenna interval adjusting section (not shown) in the holding section 34 described above.

  FIG. 9 shows the measurement of the frequency characteristics of the transmittances S31 and S21 and the degree of separation when the antenna interval is d = d ′ = 0.5λ and the centers of both antenna groups are at the reference position (focal position z = 0). The result is shown.

  Although a relatively large ripple remains in the frequency characteristic of FIG. 9A using the absorber A, the frequency characteristic of FIG. 9B using the absorber B having a higher absorption rate is flat. Therefore, it can be said that it is more suitable for measurement of a MIMO terminal that transmits a broadband signal.

In the above embodiment, an example of M = N = 2 is shown. However, when M = N = 4, four base station signals RF1 to RF4 are transmitted from the base station apparatus 1 as shown in FIG. Assuming a model that is input to the fading emulator 12 and the four base station antennas (not shown) and the four terminal antennas 1a to 1d are coupled by 16 (= 4 × 4) propagation paths, fading generates a fading signal FRF1-1~FRF4-4 of granted 16 sequence according to their respective propagation paths, the four multiplexers ₂₆ 1 to 26 ₄ of the multiplexing unit 25 four terminal antenna It multiplexes for every incoming wave of 1a-1d.

  Here, fading signals FRF1-1 to FRF1-4 correspond to four propagation paths respectively formed between the first base station antenna and the four terminal antennas 1a to 1d, and fading signals FRF1-1 to FRF1-1 to FRF1-4. FRF1-4 correspond to the four propagation paths formed between the first base station antenna and the four terminal antennas 1a-1d, respectively, and the fading signals FRF2-1 to FRF2-4 are the second base stations. The fading signals FRF3-1 to FRF3-4 correspond to the four propagation paths respectively formed between the station antenna and the four terminal antennas 1a to 1d, and the fading signals FRF3-1 to FRF3-4 are the third base station antenna and the four terminal antennas 1a. Correspond to the four propagation paths formed between -1d, and the fading signals FRF4-1 to FRF4-4 include the fourth base station antenna and the four terminal antennas. Correspond to the four propagation paths, each of which is formed between the burner 1 a to 1 d.

Then, the four terminal antennas 1a to 1d of the MIMO terminal 1 are held so as to be positioned in the vicinity of one focal point of the elliptic spherical coupler 30, and the major axis center of the elliptical sphere is positioned in the vicinity of the other focal point. for arranged four measurement antenna ₃₁ 1-31 ₄ each approximately point symmetrical positions with each terminal antenna, combiner 30 within the measuring antenna ₃₁ 1-31 ₄ cusps and each terminal antenna 1a~1d a state that selectively bind to one-to-one between those of symmetrically arranged to form, with respect to their measurement antenna 31 _{1-31 4} supplies a multiplexed signal Q1~Q4 respectively, were assumed 4 What is necessary is just to form an equivalent state with the spatial coupling of one base station antenna and four terminal antennas.

  Even in this case, the moving mechanisms 35 and 36 are used together or the influence of multiple reflections is suppressed so that each measurement antenna and each terminal antenna can be selectively coupled to each other with a higher degree of one-to-one. A radio wave absorber can be used.

DESCRIPTION OF SYMBOLS 1 ... MIMO terminal, 1a, 1b ... Terminal antenna, 11 ... Base station apparatus, 12 ... Fading emulator, 14 ... Antenna (virtual scatterer), 20 ... MIMO terminal measurement system, 25 ... Multiplexing , 30... Coupler, 31 ₁ , 31 ₂ ...... antenna for measurement, 33, 34 ...... holding part, 35, 36 ...... moving mechanism, 40 …… radio wave absorber

Claims (4)

Generating a plurality of M-sequence base station signals for transmission to a MIMO terminal (1) having a plurality of N terminal antennas (1a, 1b);
Assuming a plurality of M × N propagation paths from the plurality of M base station antennas to a plurality of N terminal antennas of the MIMO terminal, each of the plurality of M × N propagation paths is received by receiving the plurality of M base station signals. Generating a plurality of M × N sequences of fading signals to which fading according to each is given,
Combining the plurality of M × N-sequence fading signals for each incoming wave to the N terminal antennas to generate a plurality of N-sequence combined signals;
The MIMO terminal (1) is held such that the plurality of N terminal antennas are positioned in the vicinity of one focal point on the major axis of the elliptical sphere in an elliptical spherical space covered with a metal wall that reflects radio waves. In addition, a plurality of N measurement antennas (31 ₁ , 31 ₂ ) to which the plurality of N-sequence combined signals are respectively supplied are positioned in the vicinity of the other focal point on the long axis and the center of the long axis Each of the measurement antennas and each of the terminal antennas is selectively coupled in a one-to-one manner in the space, and the plurality of M Forming a state equivalent to a spatial coupling between a plurality of base station antennas and the plurality of N terminal antennas. A MIMO system base station apparatus (11) for outputting a plurality of M-sequence base station signals to be transmitted to a MIMO terminal having a plurality of N terminal antennas;
Assuming a plurality of M × N propagation paths from the plurality of M base station antennas to a plurality of N terminal antennas of the MIMO terminal, each of the plurality of M × N propagation paths is received by receiving the plurality of M base station signals. A fading emulator (12) for generating and outputting fading signals of the plurality of M × N sequences to which fading corresponding to each of the fading is given,
A multiplexing unit (25) that multiplexes the fading signals output in the plurality of M × N sequences for each incoming wave to the N terminal antennas to generate a plurality of N-sequence combined signals;
The MIMO has an elliptical spherical space covered with a metal wall that reflects radio waves, and the plurality of N terminal antennas are positioned in the vicinity of one focal point on the major axis of the elliptical sphere in the space. While holding the terminal (1), a plurality of N measurement antennas (31 ₁ , 31 ₂ ) to which the plurality of N-sequence combined signals are respectively supplied are positioned near the other focal point on the major axis, In addition, each measurement antenna and each terminal antenna are selectively coupled on a one-to-one basis in the space while being held in a substantially point-symmetrical position with each terminal antenna with respect to the center of the major axis. Then, a MIMO terminal measurement system comprising a coupler (30) that forms a state equivalent to a spatial coupling between the plurality of M base station antennas and the plurality of N terminal antennas.   The coupler is provided with a moving mechanism (35, 36) for moving the MIMO terminal and the plurality of measurement antennas held in the coupler in a direction along the long axis. The MIMO terminal measurement system according to claim 2, wherein:   The MIMO terminal measurement system according to claim 2 or 3, wherein the plurality of measurement antennas are covered with a radio wave absorber (40).

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