WO2020183670A1

WO2020183670A1 - Calibration device and terminal device

Info

Publication number: WO2020183670A1
Application number: PCT/JP2019/010368
Authority: WO
Inventors: 石岡　和明
Original assignee: 三菱電機株式会社
Priority date: 2019-03-13
Filing date: 2019-03-13
Publication date: 2020-09-17
Also published as: JPWO2020183670A1; JP6929482B2

Abstract

A calibration device (3) that is characterized: by estimating the characteristics of a plurality of transmission amplifiers and the characteristics of a plurality of reception amplifiers by performing a canonical polyadic decomposition on an error function that is represented using uplink and downlink transmission path information that has been estimated on the basis of a reception signal and transmission path information that is calculated using the characteristics of the plurality of transmission amplifiers and the plurality of reception amplifiers; and by using the estimated values to calculate a calibration coefficient.

Description

Calibration device and terminal device

The present invention relates to a calibration device and a terminal device for calculating a calibration coefficient used for estimating a transmission line matrix.

In recent years, wireless terminals represented by smartphones have become widespread, and along with this, there is an increasing demand for increasing the capacity of wireless communication and increasing the transmission speed of wireless communication. As a technology for increasing the transmission speed of wireless communication, there is a MIMO (Multiple Input Multiple Output) transmission technology that spatially multiplexes using a plurality of transmitting antennas and a plurality of receiving antennas. In MIMO transmission technology, the transmission speed of wireless communication is improved by performing precoding using singular value decomposition of the transmission line matrix on the transmission side. In order to perform precoding, the transmitter needs to acquire the transmission line matrix. Patent Document 1 discloses a method in which a base station having a function of a transmission device acquires a transmission line matrix using transmission line reversibility.

Here, in a TDD (Time Division Duplex) system, a method of acquiring a transmission line matrix using transmission line reversibility will be described. First, a reference signal is transmitted in the uplink communication transmitted from the wireless terminal to the base station, and the transmission path matrix of the downlink communication is estimated using the reference signal acquired by the base station in the uplink communication. This method utilizes transmission line reversibility, which is the same property of uplink communication and downlink communication in a wireless transmission line.

When the transmission amplifier and the reception amplifier of the wireless device provided in the wireless terminal and the base station are the same, the transmission path reversibility is established in the wireless transmission path. However, when the transmission amplifier and the reception amplifier of the wireless device are different, the transmission path is different and the transmission path reversibility cannot be established. Therefore, reversible calibration that corrects the characteristics of the transmitting amplifier and the receiving amplifier is required.

JP-A-2017-38197

However, according to the above-mentioned conventional technique, when reversible calibration is performed with one reference antenna, the influence of the transmission line such as the difference in polarization between the reference antenna and the antenna of the radio device to be calibrated The level of transmission and reception is greatly reduced, and the calibration accuracy is reduced due to the influence of noise and the like. For example, if the reference antenna is made vertical and the antenna of the wireless device to be calibrated is made horizontal, the polarizations do not match and radio waves cannot be transmitted / received between the antennas. Therefore, when calibration is performed using one reference antenna, there is a problem that the accuracy of calibration deteriorates.

The present invention has been made in view of the above, and an object of the present invention is to obtain a calibration device capable of suppressing deterioration of calibration accuracy.

In order to solve the above-mentioned problems and achieve the object, the calibration apparatus according to the present invention has uplink and downlink transmission line information estimated based on received signals, and characteristics of a plurality of transmission amplifiers. , And the error function expressed using the transmission line information calculated using the characteristics of multiple receiving amplifiers is decomposed by Canonical Polyadic to estimate the characteristics of each of multiple transmitting amplifiers and multiple receiving amplifiers. It is characterized in that the calibration coefficient is calculated using the estimated value.

The calibration device according to the present invention has the effect of suppressing deterioration of calibration accuracy.

The figure which shows the structure of the wireless communication system which concerns on embodiment The figure which shows the control circuit which concerns on embodiment A flowchart showing the operation of the wireless communication system according to the embodiment. The figure which shows the description of the reversible calibration which concerns on embodiment

The calibration device and the terminal device according to the embodiment of the present invention will be described in detail below with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment.
FIG. 1 is a diagram showing a configuration of a wireless communication system according to an embodiment. The wireless communication system 300 includes a base station device 1, a measuring device 2, and a calibration device 3. The base station device 1 and the measuring device 2 communicate with each other by the TDD method. In the present embodiment, the wireless communication system 300 will be described as a system to which the TDD (Time Division Duplex) method is applied, but the reversibility of the transmission line is high even when the frequencies are different between the transmission and reception. If it holds, the wireless communication system 300 may be a system to which the FDD (Frequency Division Duplex) system is applied. The calibration device 3 includes a calibration coefficient calculation unit 31. The calibration coefficient calculation unit 31 calculates a calibration coefficient that corrects the difference in the characteristics of the plurality of antennas included in the base station device 1 and the measurement device 2. The calibration device 3 and the base station device 1 may communicate with each other by wire or wirelessly. The calibration device 3 and the measuring device 2 may communicate with each other by wire or wirelessly. Uplink is uplink communication from the measuring device 2 to the base station device 1. The downlink is downlink communication from the base station device 1 to the measuring device 2. The measuring device 2 may be a dedicated measuring device for calibration or a normal terminal device. In FIG. 1, the calibration device 3 is a device different from the base station device 1 and the measuring device 2, but the calibration device 3 may be built in the measuring device 2 or built in the base station device 1. May be good. Further, the base station device 1 may include the measuring device 2 and the calibration device 3.

The base station device 1 includes antennas 111 and 112, transmission /

reception selector switches

121 and 122, transmission

high power amplifiers

131 and 132 for each antenna,

reception amplifiers

141 and 142, downlink transmission line estimation unit 15, and a precoder. A 16 and a first transmission line estimation unit 17 are provided.

The measuring device 2 includes an antenna 211,212, a transmission / reception changeover switch 221,222, a transmission high power amplifier 231,232, a reception amplifier 241,242, and a second transmission line estimation unit 27. In this embodiment, an example is shown in which the base station device 1 is provided with two antennas of the antenna 111 and the antenna 112, and the measuring device 2 is provided with the two antennas of the antenna 211 and the antenna 212. The device 1 and the measuring device 2 may each include three or more antennas. The transmission line information of the transmission line between the antenna 111 and the antenna 211 is h ₁₁ . Further, the transmission line information of the transmission line between the antenna 111 and the antenna 212 is h ₂₁ . Furthermore, transmission path information of the transmission path between the antenna 112 and the antenna 211 is _{h 12.} Further, the transmission line information of the transmission line between the antenna 112 and the antenna 212 is h ₂₂ . The

antennas

111, 112, 211 and 212 are also referred to as reference antennas, respectively.

When downlink communication is performed, the transmission / reception changeover switch 121 connects the antenna 111 and the transmission high power amplifier 131, and the transmission / reception changeover switch 122 connects the antenna 112 and the transmission high power amplifier 132. Further, when downlink communication is performed, the transmission / reception changeover switch 221 connects the antenna 211 and the reception amplifier 241, and the transmission / reception changeover switch 222 connects the antenna 212 and the reception amplifier 242. When uplink communication is performed, the transmission / reception changeover switch 121 connects the antenna 111 and the reception amplifier 141, and the transmission / reception changeover switch 122 connects the antenna 112 and the reception amplifier 142. Further, when uplink communication is performed, the transmission / reception changeover switch 221 connects the antenna 211 and the transmission high power amplifier 231, and the transmission / reception changeover switch 222 connects the antenna 212 and the transmission high power amplifier 232. .. In this way, the transmission /

reception changeover switches

121, 122, 221, 222 switch between uplink communication and downlink communication. The transmission signal T _m1 is input to the transmission high power amplifier 231. The transmission signal T _m2 is input to the transmission high power amplifier 232. The transmission signal T _m1 and the transmission signal T _m2 are transmission signals generated by the measuring device 2. Further, the transmission signal T _m1 and the transmission signal T _m2 are known signals used when the base station apparatus 1 estimates the information of the uplink transmission line at the time of calibration. Further, the transmission signal T _m1 and the transmission signal T _m2 are reference signals defined by, for example, 3GPP (Third Generation Partnership Project).

The downlink transmission line estimation unit 15, the first transmission line estimation unit 17, the second transmission line estimation unit 27, and the calibration coefficient calculation unit 31 are realized by a processing circuit which is an electronic circuit that performs each processing.

The processing circuit may be dedicated hardware or a control circuit including a memory and a CPU (Central Processing Unit) that executes a program stored in the memory. Here, the memory corresponds to, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), or a flash memory, a magnetic disk, an optical disk, or the like. FIG. 2 is a diagram showing a control circuit according to the embodiment. When the processing circuit is a control circuit including a CPU, the control circuit is, for example, a control circuit 400 having the configuration shown in FIG.

As shown in FIG. 2, the control circuit 400 includes a processor 400a which is a CPU and a memory 400b. When it is realized by the control circuit 400 shown in FIG. 2, it is realized by the processor 400a reading and executing the program corresponding to each process stored in the memory 400b. The memory 400b is also used as a temporary memory in each process performed by the processor 400a.

The outline of the operation of the wireless communication system 300 will be described. The calibration device 3 calculates the calibration coefficient. The base station apparatus 1 calculates the downlink transmission line information using the calibration coefficient and the uplink transmission line information. The operation flow of the wireless communication system 300 will be described. FIG. 3 is a flowchart showing the operation of the wireless communication system 300 according to the embodiment. The base station apparatus 1 transmits a downlink reference signal (step S1). The measuring device 2 receives the downlink reference signal (step S2). The second transmission line estimation unit 27 estimates the downlink transmission line information using the received downlink reference signal (step S3).

The second transmission line estimation unit 27 transmits the estimated downlink transmission line information to the calibration coefficient calculation unit 31 (step S4). The measuring device 2 transmits an uplink reference signal (step S5). The base station apparatus 1 receives the uplink reference signal (step S6). The first transmission line estimation unit 17 estimates the uplink transmission line information using the received uplink reference signal (step S7). The first transmission line estimation unit 17 transmits the estimated uplink transmission line information to the calibration coefficient calculation unit 31 (step S8).

The calibration coefficient calculation unit 31 calculates the calibration coefficient using the downlink transmission line information received in step S4 and the uplink transmission line information received in step S8 (step S9). The calibration device 3 transmits the calculated calibration coefficient to the base station device 1 (step S10). This is the operation of calibration by the calibration device 3. Next, the flow of operation in which the base station device 1 transmits data to the measuring device 2 will be described. The base station apparatus 1 estimates the downlink transmission line information using the calibration coefficient and the uplink transmission line information estimated in step S7 (step S11). The base station apparatus 1 performs precoding using the estimated downlink transmission line information and generates a transmission signal (step S12).

Next, the details of the operation of the wireless communication system 300 will be described. At the time of data transmission in step S12, the base station apparatus 1 precodes the transmission stream signals S ₁ and S ₂ using the precoder 16 to generate the transmission signals T ₁ and T ₂ for each antenna. The transmission stream signals S ₁ and S ₂ are signals before precoding. The transmission signals T ₁ and T ₂ are precoded signals in which the transmission stream signals S ₁ and S ₂ are mixed. The precoding requires channel matrix h _d downlink, the value singular value decomposition of the channel matrix h _d can be expressed, for example, equation (1).
U ・ D ・ V ^H = SVD (h _d ) ・・・ (1)

In equation (1), the superscript H of V represents the conjugated transpose. When _hd is an N × M matrix, U is an N × N unitary matrix, V is an M × M unitary matrix, and D is an N × M diagonal matrix, and singular values are arranged in diagonal elements. N and M indicate rows and columns, respectively, and are arbitrary integers. SVD (Singular Value Decomposition) indicates that singular value decomposition is performed. Then, the precoder 16 performs a calculation of Equation (2) the unitary matrix V obtained by SVD of the _{h d} a precoding matrix.

In equation (2), S ₁ and S ₂ represent transmission stream signals. In equation (2), T ₁ and T ₂ represent transmission signals. Downlink channel estimation unit 15, by the equation (3) using the uplink transmission path R _1, R _2, calculates the channel matrix h _d downlink is the transmission path information of the downlink shown in the step S11 To do.
h _d = (C ₁ R ₁ C ₂ R ₂ ) ... (3)

In the equation (3), R ₁ is an uplink transmission line acquired from the antenna 111, and R ₂ is an uplink transmission line estimated by the first transmission line estimation unit 17 from the received signal of the antenna 112. Since the corresponding antennas of R ₁ and R ₂ are different information and the transmission lines are also different, the contents of R ₁ and R ₂ are different from each other. R ₁ and R ₂ are vertical vectors. C ₁ and C ₂ are calibration coefficients calculated by the calibration coefficient calculation unit 31 of the calibration before the start of communication shown in step S9, and the calibration coefficient is a complex number scalar per frequency. In the wireless communication system 300 applied to this embodiment, it is assumed that the reference signal is transmitted by the uplink communication, and the first transmission line estimation unit 17 uses the reference signal to transmit the uplink transmission line. Estimate the information.

At the time of calibration, the base station device 1 transmits the downlink reference signal, and the measuring device 2 receives the downlink reference signal. In the measuring device 2, the second transmission line estimation unit 27 estimates the downlink transmission line information using the received downlink reference signal. At the time of calibration, the second transmission line estimation unit 27 transmits the estimated downlink transmission line information to the calibration coefficient calculation unit 31. The measuring device 2 transmits the uplink reference signal, and the base station device 1 receives the uplink reference signal. In the base station apparatus 1, the first transmission line estimation unit 17 estimates the uplink transmission line information using the received uplink reference signal. Further, the first transmission line estimation unit 17 transmits the uplink transmission line information to the calibration coefficient calculation unit 31.

The calibration coefficient calculation unit 31 receives the uplink transmission line information and the downlink transmission line information from the first transmission line estimation unit 17 and the second transmission line estimation unit 27, respectively, and receives the calibration coefficient. Calculate C ₁ and C ₂ . Further, the calibration coefficient calculation unit 31 transmits the calibration coefficients C ₁ and C ₂ to the downlink transmission line estimation unit 15. In the above description, the operation of only one carrier frequency has been described, but in the OFDM (Orthogonal Frequency Division Multiplexing) signal, the above calculation is performed for each subcarrier.

The calibration coefficient calculation unit 31 calculates the calibration coefficient using CP decomposition (Canonical Polyadic Decomposition). The transmission lines of the plurality of reference antennas are different for each antenna to be calibrated. Further, the characteristics of the transmission amplifier and the reception amplifier connected to the reference antenna also differ for each reference antenna. Further, when the calibration measurement is measured a plurality of times at different times, the carrier phases of the transmission line and the transmission / reception are different from each other. The combined value of the characteristics of the reference antenna cannot be calculated by simply adding complex numbers, but the combined value of the characteristics of a plurality of reference antennas can be calculated by using CP decomposition. FIG. 4 is a diagram showing a description of the reversible calibration according to the embodiment. i is the number of the antenna included in the base station apparatus 1. The base station apparatus 1 includes n antennas, and the antenna numbers of the base station apparatus 1 are 0 to n-1. That is, i takes a value from 0 to n-1. j is the number of the antenna included in the measuring device 2. The measuring device 2 includes m antennas, and the antenna numbers of the measuring devices 2 are 0 to m-1. That is, j takes a value from 0 to m-1. _EBTi (f) is a value indicating the characteristics of the transmission amplifier of the base station apparatus 1 connected to the antenna number i. FIG. 4 shows _EBTi (f) having antenna numbers 0 and n-1. _EBRi (f) is a value indicating the characteristics of the receiving amplifier of the base station apparatus 1 connected to the antenna number i. FIG. 4 shows _EBRi (f) having antenna numbers 0 and n-1. E _UTj (f) is a value indicating the characteristics of the transmission amplifier of the measuring device 2 connected to the antenna number j. FIG. 4 shows _EUTj (f) having antenna numbers of 0 and m-1.

E _URj (f) is a value indicating the characteristics of the receiving amplifier of the measuring device 2 connected to the antenna number j. FIG. 4 shows _EURj (f) having antenna numbers of 0 and m-1. h _{i, j} (f) indicate a transmission path when the antenna number of the base station device 1 is i and the antenna number of the measuring device 2 is j, and the antenna number of the base station device 1 is 0 and the measuring device 2 is used. When the antenna number of is 0, the transmission line is _h0,0 (f). T _Bi (f) indicates a signal transmitted by the antenna of the antenna number i of the base station apparatus 1. R _Bi (f) indicates a signal received by the antenna of the antenna number i of the base station apparatus 1. _TUj (f) indicates a signal transmitted by the antenna of the antenna number j of the measuring device 2. _RUj (f) indicates a signal received by the antenna of the antenna number j of the measuring device 2.

The signal R _uji (f) received by the antenna of the antenna number j of the measuring device 2 is represented by the following equation (4). It is assumed that f represents CC (Component Carrier) and RB (Resource Block).

The downlink transmission lines h _{Di, j} (f) are represented as follows.

The signal R _Bi (f) received by the antenna of the antenna number i of the base station apparatus 1 is represented as follows.

The uplink transmission lines h _{Ui and j} (f) are represented as follows.

Calibration coefficients C _{i (f)} is expressed as follows.

In precoding, g (f) may be arbitrary. Downlink channel estimation unit 15, the transmission path _{h Ui uplink,} j transmission path h (with _hat) in the downlink by using the calibration coefficient _C i (f) from (f) _Di, j and (f) presume.

Equation (9) is a value k times that of Equation (5), but it does not affect the ratio between base station antennas. k is the value of equation (10).

h _{Di, j} (f) and h _{Ui, j} (f) are measured values including noise, and the error | e | ² is defined as follows.

_{Estimate hi} _{, j} (f), _EBTi (f), _EURj (f), _EBRi (f), and _EUTj (f) that minimize the error, and use Eq. (8) to estimate the calibration coefficient C. _i (f) is calculated.

The _{estimation of hi} _{, j} (f), _EBTi (f), _EURj (f), _EBRj (f), and _EUTj (f) is a CP decomposition that decomposes the tensor into multiple vectors with lower dimensions. Equivalent. Gradient descent is used for CP decomposition to minimize the error of CP decomposition. By using the gradient descent method for CP decomposition, the calculation accuracy of CP decomposition can be improved.

The partial differential of equation (11), which is an error function due to each variable, is expressed as equation (12). In equation (12), * indicates the complex conjugate.

The CP decomposition by the gradient descent method requires iteration (repetition) and the calculation scale is large. In this case, the calculation scale can be reduced by reducing the frequency resolution, reducing the amount of data, and improving the S / N (Signal / Noise) ratio. Further, if the frequency resolution is lowered to reduce the amount of data and improve the S / N ratio, the possibility of being supplemented by the local minimum is reduced and the performance is improved. When the frequency resolution is increased with the value obtained here as the initial value and CP decomposition is further performed, the initial value is close to the convergence value, so that the value converges to the optimum value with less iteration. In addition, CP decomposition using the gradient descent method is performed, the result of the first CP decomposition is calculated, the frequency resolution is higher than that of the gradient descent method used for the first CP decomposition, and the result of the first CP decomposition is performed. May be performed for the second CP decomposition with the initial value of.

As described above, in the present embodiment, the calibration coefficient calculation unit 31 estimates the characteristics of the transmission line, the transmission amplifier, and the reception amplifier, which are different for each antenna, by using the equation (12) using CP decomposition. Then, using these estimated values, the calibration coefficient is calculated using the equation (8). Therefore, it is possible to calculate the error of the value affected by different conditions for each antenna, and it is possible to calculate the calibration coefficient that minimizes the error due to the difference between these conditions. Therefore, it is possible to suppress a decrease in calibration accuracy. Further, the calibration coefficient calculation unit 31 may calculate the calibration coefficient by treating the transmission line information at different times as different antennas and CP-decomposing the transmission line information. Further, the calibration coefficient calculation unit 31 may calculate the calibration coefficient by CP-decomposing the information of the transmission lines of the plurality of uplinks of the antenna.

The configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1 base station device, 2 measuring device, 3 calibration device, 15 downlink transmission line estimation unit, 16 precoder, 17 first transmission line estimation unit, 27 second transmission line estimation unit, 31 calibration coefficient calculation unit, 111,112,211,212 antenna, 121,122,221,222 changeover switch, 131,132,231,232 transmission high power amplifier, 141,142,241,242 reception amplifier, 300 wireless communication system, 400 control circuit, 400a processor, 400b memory.

Claims

It is expressed using the uplink and downlink transmission line information estimated based on the received signal, the characteristics of multiple transmitting amplifiers, and the transmission line information calculated using the characteristics of multiple receiving amplifiers. A calibration device characterized in that the characteristics of each of the plurality of transmission amplifiers and the plurality of reception amplifiers are estimated by decomposing the error function into Canonical Polyadic, and the calibration coefficient is calculated using the estimated values. ..
The calibration device according to claim 1, wherein the calibration coefficient is calculated by decomposing the information of a plurality of uplink transmission lines having different times into Canonical Polyadic.
The calibration device according to claim 1 or 2, wherein the Canonical Polyadic decomposition is performed using a gradient descent method.
A terminal device comprising the calibration device according to any one of claims 1 to 3.