JP2013090055A - Mimo channel capacity calculation device, mimo channel capacity calculation method, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of channel capacity calculation by using a difference in reception power per transmitting antenna and a correlation value between the transmitting antennas when the channel capacity of a 2×2 MIMO system is calculated.SOLUTION: An MIMO channel capacity calculation device comprises: a reception electric field calculation unit 2 which calculates, for each pair of transmitting and receiving antenna, a received electric field from the transmitting antenna to the receiving antenna; a received power difference calculation unit 3 which calculates a difference in received power by using the received electric field; an antenna corrections calculation unit 5 which calculates a correlation value between the transmitting antennas by using the received electric field; a characteristic value ratio estimation unit 6 which, by using the difference in received power and the correlation value between the transmitting antennas, estimates a ratio between two characteristic values obtained by a singular value decomposition of the channel response matrix of a 2×2 MIMO system; and a channel capacity calculation unit 7 which calculates a channel capacity by using the ratio of characteristic values and an average SNR.

Description

  The present invention relates to a MIMO channel capacity calculation device, a MIMO channel capacity calculation method, and a computer program.

  In recent years, a MIMO (Multiple Input Multiple Output) transmission technique is known as one technique for increasing the transmission speed in a wireless communication system. In the MIMO transmission technique, a plurality of streams are simultaneously transmitted on the same frequency from a plurality of transmission antennas to a plurality of reception antennas. In a wireless communication system using a MIMO transmission technique (hereinafter referred to as a MIMO system), a transmitter (for example, a base station) transmits a plurality of streams from a plurality of transmission antennas on the same frequency. Then, a receiver (for example, a mobile terminal) receives a plurality of streams transmitted from the transmitter with a plurality of reception antennas, and performs a process of separating the plurality of streams from the received signal.

  When evaluating a MIMO system area in a conventional radio wave propagation simulator, first, for example, based on the ray tracing method, the rays transmitted from a plurality of antennas installed in the MIMO system are traced, and the rays reaching the reception point are complex. The channel matrix of the MIMO system is obtained from the received electric field strength for each pair of transmitting antenna and receiving antenna obtained by adding the amplitude. Next, the eigenvalue is calculated by performing singular value decomposition on the channel matrix, and the channel capacity of the MIMO system is obtained from the Shannon equation using the calculated eigenvalue (see, for example, Non-Patent Document 1).

The channel capacity (C [bps / Hz]) in a MIMO system (hereinafter referred to as n _T × n _R MIMO system) in which the number of transmitting antennas is n _T and the number of receiving antennas is n _R is based on Shannon's theorem. Thus, it can be expressed by the following formula (1) (see, for example, Non-Patent Document 2).

γ is an average SNR (signal-to-noise-ratio) of the receiving antenna. H is a channel response matrix in the n _T × n _R MIMO system. _InR is a unit matrix of the number of reception antennas × the number of reception antennas. n _T is the number of transmitting antennas. n _R is the number of receive antennas.

  Formula (1) becomes Formula (2) by deformation | transformation of Formula.

Here, λ _i is the i-th eigenvalue obtained by singular value decomposition of the channel response matrix H.

Therefore, when the channel capacity C of the n _T × n _R MIMO system is calculated using Equation (2), it is necessary to perform eigenvalue calculation.

  On the other hand, Non-Patent Document 3 discloses a technique for calculating a channel capacity of a 2 × 2 MIMO system using a received power difference for each transmission antenna. In the prior art described in Non-Patent Document 3, using the received power difference (ΔG [dB]) between the transmitting antennas, a relational expression “10 × LOG (k) ) = − ΔG [dB] ”, the eigenvalue ratio is estimated from the power difference. Then, using the obtained eigenvalue ratio (k) and the average SNR (γ [dB]) of the receiving antenna, the channel capacity (C [bps / Hz]) of the 2 × 2 MIMO system is calculated by Equation (3). .

  According to the prior art described in Non-Patent Document 3, it is not necessary to perform eigenvalue calculation.

Junichi Ogawa, Satoru Tenri, Atsushi Yamamoto, "Transmission capacity analysis of terminal MIMO antenna with received power difference between branches", IEICE, Vol.J91-B No.9, pp.948-959. G. J. Foschini and M. J. Gans, "On Limits of Wireless Communications in a Fading Environment When Using Multiple Antennas", Wireless Personal Communications. Vol. 6, No. 3, March 1998, p. 311-335 S. Nanba, Y. Hirota, and Y. Kishi, “Estimation of 2x2 MIMO Capacity with Dual-Polarized Antennas Under Received Power Imbalance Through Propagation Measurements,” in Proc. IEEE EuCAP 2011, pp. 2309-2312, April. 2011.

  However, the above-described prior arts of Non-Patent Documents 1 and 2 require eigenvalue calculation, which causes a problem of a large amount of calculation.

  Further, the above-described prior art of Non-Patent Document 3 has a problem that the accuracy of calculation of channel capacity deteriorates in a radio wave propagation environment where the correlation between transmission antennas is high. This is because the eigenvalue ratio depends not only on the received power difference but also on the correlation between the transmitting antennas. For this reason, in the radio wave propagation environment in which the correlation between the transmission antennas greatly varies, when the conventional technique of Non-Patent Document 3 is applied, the estimation error of the eigenvalue ratio increases, and the accuracy of the calculated channel capacity also deteriorates as a result. There is a problem.

  The present invention has been made in view of such circumstances, and when calculating the channel capacity of the 2 × 2 MIMO system, by using the received power difference for each transmission antenna and the correlation value between the transmission antennas, It is an object of the present invention to provide a MIMO channel capacity calculation device, a MIMO channel capacity calculation method, and a computer program that can improve the calculation accuracy of channel capacity.

  In order to solve the above problems, a MIMO channel capacity calculation apparatus according to the present invention is a MIMO channel capacity calculation apparatus that calculates channel capacity in a MIMO system in which the number of transmission antennas is two and the number of reception antennas is two. A reception electric field calculation unit that calculates a reception electric field from the transmission antenna to the reception antenna for each pair of transmission antenna and reception antenna, and a reception power difference calculation that calculates a reception power difference using the reception electric field calculated by the reception electric field calculation unit An inter-antenna correlation calculation unit that calculates a correlation value between transmission antennas using the received electric field calculated by the received electric field calculation unit, and a received power difference calculated by the received power difference calculation unit and the inter-antenna correlation calculation unit 2 is obtained by performing singular value decomposition on the channel response matrix of the MIMO system using the correlation value between transmit antennas calculated by An eigenvalue ratio estimator that estimates the ratio of eigenvalues, a channel capacity calculator that calculates a channel capacity using the eigenvalue ratio calculated by the eigenvalue ratio estimator and the average SNR of the MIMO system. It is characterized by that.

  In the MIMO channel capacity calculation apparatus according to the present invention, the eigenvalue ratio estimation unit includes an approximate expression of a correlation value between transmission antennas and an eigenvalue ratio corresponding to each received power difference, and the eigenvalue ratio estimation unit calculates the received power difference. The eigenvalue ratio corresponding to the correlation value between the transmission antennas calculated by the inter-antenna correlation calculation unit is calculated using the approximate expression corresponding to the received power difference calculated by the unit.

  The MIMO channel capacity calculation apparatus according to the present invention includes an average SNR calculation unit that calculates an average SNR using the reception electric field calculated by the reception electric field calculation unit.

  The MIMO channel capacity calculation method according to the present invention is a MIMO channel capacity calculation method for calculating a channel capacity in a MIMO system in which the number of transmission antennas is two and the number of reception antennas is two, for each pair of transmission antenna and reception antenna. A reception electric field calculation step of calculating a reception electric field from the transmission antenna to the reception antenna, a reception power difference calculation step of calculating a reception power difference using the reception electric field calculated in the reception electric field calculation step, and the reception electric field calculation step An inter-antenna correlation calculation step for calculating a correlation value between transmission antennas using the calculated received electric field, a reception power difference calculated in the reception power difference calculation step, and a transmission antenna correlation value calculated in the inter-antenna correlation calculation step Singular value decomposition of the channel response matrix of the MIMO system using Eigenvalue ratio estimation step for estimating the ratio of two eigenvalues obtained in the above, channel capacity calculation step for calculating channel capacity using the eigenvalue ratio calculated in the eigenvalue ratio estimation step, and the average SNR of the MIMO system It is characterized by including these.

A computer program according to the present invention is a computer program for performing a MIMO channel capacity calculation process for calculating a channel capacity in a MIMO system having two transmission antennas and two reception antennas. A reception electric field calculation step of calculating a reception electric field from the transmission antenna to the reception antenna for each pair of antennas; a reception power difference calculation step of calculating a reception power difference using the reception electric field calculated in the reception electric field calculation step; Inter-antenna correlation calculation step for calculating a correlation value between transmission antennas using the reception electric field calculated in the reception electric field calculation step, and the reception power difference calculated in the reception power difference calculation step and the transmission calculated in the inter-antenna correlation calculation step Using the correlation value between the antennas, Using the eigenvalue ratio estimation step for estimating the ratio of two eigenvalues obtained by singular value decomposition of the channel response matrix, the eigenvalue ratio calculated in the eigenvalue ratio estimation step, and the average SNR of the MIMO system, It is a computer program for causing a computer to execute a channel capacity calculating step for calculating capacity.
As a result, the MIMO channel capacity calculation apparatus described above can be realized using a computer.

  According to the present invention, by calculating the channel capacity of the 2 × 2 MIMO system using the reception power difference for each transmission antenna and the correlation value between the transmission antennas, it is possible to improve the calculation accuracy of the channel capacity. In addition, since it is not necessary to perform eigenvalue calculation, the amount of calculation can be reduced.

It is a block diagram which shows the structure of the MIMO channel capacity calculation apparatus 1 which concerns on one Embodiment of this invention. It is an example of the relationship between a transmission antenna correlation value (ρ), a received power difference (ΔG [dB]), and an eigenvalue ratio (k). It is an example of the relationship between the transmission antenna correlation value (ρ) and the eigenvalue ratio (k: true value) in each received power difference (ΔG [dB]). It is a table | surface for demonstrating the effect which concerns on this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a MIMO channel capacity calculation apparatus 1 according to an embodiment of the present invention. The MIMO channel capacity calculation apparatus 1 is an apparatus that calculates the channel capacity of a 2 × 2 MIMO system.

  In FIG. 1, a MIMO channel capacity calculation device 1 includes a received electric field calculation unit 2, a received power difference calculation unit 3, an average SNR calculation unit 4, an inter-antenna correlation calculation unit 5, an eigenvalue ratio estimation unit 6, and a channel capacity calculation unit 7. Have

  The reception electric field calculation unit 2 calculates the reception electric field from the transmission antenna to the reception antenna for each pair of the transmission antenna and the reception antenna. A known method can be used to calculate the received electric field. As a known received electric field calculation method, for example, ray tracing simulation is known. When using the ray trace simulation, the reception electric field calculation unit 2 includes, as input data necessary for the ray trace simulation, information on buildings around the 2 × 2 MIMO system, information on the installation positions of the transmission antenna and the reception antenna, and an antenna. Antenna parameters such as patterns, transmission output information, and noise level are input.

  The received power difference calculation unit 3 uses the received electric field calculated by the received electric field calculation unit 2 to calculate the received power difference (ΔG [dB]) using Equation (4).

Here, h _1,1 is a reception electric field from the first transmission antenna to the first reception antenna. h _{1 and 2} are received electric fields from the second transmitting antenna to the first receiving antenna. h _2,1 is a received electric field from the first transmitting antenna to the second receiving antenna. h _{2 and 2} are received electric fields from the second transmitting antenna to the second receiving antenna.

  The average SNR calculation unit 4 calculates the average SNR (γ [dB]) by the equation (5) using the reception electric field calculated by the reception electric field calculation unit 2.

  Where N is the thermal noise power.

  In this embodiment, the average SNR calculation unit 4 is provided to calculate the average SNR of the 2 × 2 MIMO system, but the average SNR of the 2 × 2 MIMO system is separately obtained and input to the MIMO channel capacity calculation apparatus 1. Good.

  The inter-antenna correlation calculation unit 5 uses the received electric field calculated by the received electric field calculation unit 2 to calculate the correlation value (ρ) between the transmission antennas using Equation (6).

The eigenvalue ratio estimation unit 6 uses the received power difference (ΔG [dB]) calculated by the received power difference calculation unit 3 and the transmission antenna correlation value (ρ) calculated by the inter-antenna correlation calculation unit 5 to use the eigenvalue. Estimate the ratio (k). A method for estimating the eigenvalue ratio (k) will be described later. The eigenvalue ratio (k) is a ratio of two eigenvalues (λ ₁ , λ ₂ ) obtained by singular value decomposition of the channel response matrix H of the 2 × 2 MIMO system.

The channel capacity calculation unit 7 uses the eigenvalue ratio (k) calculated by the eigenvalue ratio estimation unit 6 and the average SNR (γ [dB]) calculated by the average SNR calculation unit 4 to The capacity (C [bps / Hz]) is calculated. However, the eigenvalue ratio (k) is a ratio of the second eigenvalue (λ ₂ ) to the _first eigenvalue (λ ₁ ) (λ ₁ ≧ λ ₂ ).

  The channel capacity calculation unit 7 outputs the calculated channel capacity (C [bps / Hz]).

  Next, a method for estimating the eigenvalue ratio (k) according to the present embodiment will be described. The eigenvalue ratio estimation unit 6 has a calculation formula for calculating the eigenvalue ratio (k) using the correlation value (ρ) between the transmitting antennas. This eigenvalue ratio calculation formula is prepared in advance according to the received power difference (ΔG [dB]).

  The eigenvalue ratio estimation unit 6 selects a corresponding eigenvalue ratio calculation formula according to the received power difference (ΔG [dB]) calculated by the received electric field calculation unit 2. Next, the eigenvalue ratio estimation unit 6 calculates the eigenvalue ratio (k) using the selected eigenvalue ratio calculation formula and the inter-antenna correlation value (ρ) calculated by the inter-antenna correlation calculation unit 5.

Next, a method for creating an eigenvalue ratio calculation formula will be described. First, transmission measurement of a 2 × 2 MIMO system is performed to obtain a relationship between a transmission antenna correlation value (ρ), a received power difference (ΔG [dB]), and an eigenvalue ratio (k). The transmission measurement method of the 2 × 2 MIMO system is an experiment or a computer simulation. FIG. 2 is an example of the relationship between the transmission antenna correlation value (ρ), the reception power difference (ΔG [dB]), and the eigenvalue ratio (k) obtained from the experimental values. Here, the eigenvalue ratio (k [dB]) is obtained by calculating _two eigenvalues (λ ₁ , λ ₂ ) from the channel response matrix H of the 2 × 2 MIMO system and calculating the _second eigenvalue ratio (λ ₁ ) with respect to the second eigenvalue (λ ₁ ). It is a ratio of eigenvalues (λ ₂ ) (λ ₁ ≧ λ ₂ ).

  In FIG. 2, the portion indicated by ◯ is the relationship between the received power difference (ΔG [dB]) and the eigenvalue ratio (k) when the correlation value (ρ) between the transmitting antennas is 0. In the other portions, when the correlation value (ρ) between the transmission antennas is “0 <ρ ≦ 0.3”, the correlation value (ρ) between the transmission antennas is “0.3 <ρ ≦ 0.6”. If the correlation value (ρ) between the transmission antennas is “0.6 <ρ ≦ 0.8”, the correlation value (ρ) between the transmission antennas is “0.8 <ρ”. This is the relationship between the power difference (ΔG [dB]) and the eigenvalue ratio (k).

  As shown in FIG. 2, the eigenvalue ratio (k) deteriorates as the correlation value (ρ) between the transmitting antennas increases.

  Next, “relationship between correlation value (ρ) between transmission antennas, reception power difference (ΔG [dB]) and eigenvalue ratio (k)” obtained from transmission measurement of 2 × 2 MIMO system, for example, from the relationship shown in FIG. For each received power difference (ΔG [dB]), the relationship between the correlation value (ρ) between the transmitting antennas and the eigenvalue ratio (k: true value) is obtained. FIG. 3 is an example of the relationship between the transmission antenna correlation value (ρ) and the eigenvalue ratio (k: true value) in each received power difference (ΔG [dB]).

  Next, for each received power difference (ΔG [dB]), an approximate expression representing the approximate relationship between the transmission antenna correlation value (ρ) and the eigenvalue ratio (k: true value) is obtained.

In the example of FIG. 3, an example of an approximate expression of the correlation value (ρ) between the transmission antennas and the eigenvalue ratio (k: true value) in each received power difference (ΔG [dB]) is shown below.
When the received power difference (ΔG [dB]) is 0, the approximate expression is
k = 0.4204ρ ² −1.2835ρ + 0.8658
It is.
When the received power difference (ΔG [dB]) is 10, the approximate expression is
k = −0.0586ρ ² −0.0668ρ + 0.1254
It is.
When the received power difference (ΔG [dB]) is 15, the approximate expression is
k = −0.0338ρ ² −0.0011ρ + 0.0344
It is.

  The “approximate expression of the correlation value (ρ) between the transmission antennas and the eigenvalue ratio (k; true value) corresponding to each received power difference (ΔG [dB])” obtained in advance in this way is estimated as the eigenvalue ratio. Part 6 is provided. The eigenvalue ratio estimation unit 6 calculates the eigenvalue ratio (k) using the approximate expression.

  FIG. 4 is a table for explaining the effects according to the present invention. FIG. 4 shows the theoretical value calculated using the eigenvalue calculation as the channel capacity [bps / Hz] of the 2 × 2 MIMO system, the value calculated using the conventional technique described in Non-Patent Document 3, and the present embodiment. Values calculated using the form are shown. FIG. 4 shows each value in the range where the received power difference [dB] is 9 to 10 and 14 to 15. As is apparent from FIG. 4, the present invention improves the calculation accuracy of the channel capacity as compared with the prior art.

  As described above, according to this embodiment, the channel capacity of the 2 × 2 MIMO system is calculated using the received power difference for each transmission antenna and the correlation value between the transmission antennas, thereby improving the calculation accuracy of the channel capacity. Can be planned. Thereby, it is possible to prevent the calculation accuracy of the channel capacity from being deteriorated due to the influence of the radio wave propagation path. In addition, since it is not necessary to perform eigenvalue calculation, the amount of calculation can be reduced.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

Also, a program for realizing the function of the MIMO channel capacity calculation apparatus 1 shown in FIG. 1 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed. Thus, the MIMO channel capacity calculation process may be performed. Here, the “computer system” may include an OS and hardware such as peripheral devices.
Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
“Computer-readable recording medium” refers to a flexible disk, a magneto-optical disk, a ROM, a writable nonvolatile memory such as a flash memory, a portable medium such as a DVD (Digital Versatile Disk), and a built-in computer system. A storage device such as a hard disk.

Further, the “computer-readable recording medium” means a volatile memory (for example, DRAM (Dynamic DRAM) in a computer system that becomes a server or a client when a program is transmitted through a network such as the Internet or a communication line such as a telephone line. Random Access Memory)), etc., which hold programs for a certain period of time.
The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.
The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

DESCRIPTION OF SYMBOLS 1 ... MIMO channel capacity calculation apparatus, 2 ... Received electric field calculation part, 3 ... Received power difference calculation part, 4 ... Average SNR calculation part, 5 ... Inter-antenna correlation calculation part, 6 ... Eigenvalue ratio estimation part, 7 ... Channel capacity calculation Part

Claims (5)

In a MIMO channel capacity calculating apparatus for calculating a channel capacity in a MIMO system having two transmitting antennas and two receiving antennas,
A reception electric field calculation unit for calculating a reception electric field from the transmission antenna to the reception antenna for each pair of the transmission antenna and the reception antenna;
A received power difference calculating unit that calculates a received power difference using the received electric field calculated by the received electric field calculating unit;
An inter-antenna correlation calculator that calculates a correlation value between transmitting antennas using the received electric field calculated by the received electric field calculator;
Using the received power difference calculated by the received power difference calculation unit and the correlation value between the transmission antennas calculated by the inter-antenna correlation calculation unit, two channel values obtained by singular value decomposition of the channel response matrix of the MIMO system are obtained. An eigenvalue ratio estimator for estimating the ratio of eigenvalues;
A channel capacity calculator that calculates a channel capacity using the eigenvalue ratio calculated by the eigenvalue ratio estimator and the average SNR of the MIMO system;
A MIMO channel capacity calculation apparatus comprising: The eigenvalue ratio estimator includes an approximate expression of a correlation value between transmission antennas corresponding to each received power difference and an eigenvalue ratio,
The eigenvalue ratio estimation unit calculates an eigenvalue ratio corresponding to the transmission antenna correlation value calculated by the inter-antenna correlation calculation unit, using the approximate expression corresponding to the reception power difference calculated by the reception power difference calculation unit. To
The MIMO channel capacity calculation apparatus according to claim 1.   The MIMO channel capacity calculation apparatus according to claim 1, further comprising an average SNR calculation unit that calculates an average SNR using the reception electric field calculated by the reception electric field calculation unit. In a MIMO channel capacity calculation method for calculating a channel capacity in a MIMO system in which the number of transmitting antennas is 2 and the number of receiving antennas is 2,
A reception electric field calculation step for calculating a reception electric field from the transmission antenna to the reception antenna for each pair of the transmission antenna and the reception antenna;
A received power difference calculating step of calculating a received power difference using the received electric field calculated in the received electric field calculating step;
Inter-antenna correlation calculation step of calculating a correlation value between transmission antennas using the reception electric field calculated in the reception electric field calculation step;
Using the received power difference calculated in the received power difference calculating step and the transmission antenna correlation value calculated in the inter-antenna correlation calculating step, two channel values obtained by singular value decomposition of the channel response matrix of the MIMO system are obtained. An eigenvalue ratio estimation step for estimating an eigenvalue ratio;
A channel capacity calculation step of calculating a channel capacity using the eigenvalue ratio calculated in the eigenvalue ratio estimation step and the average SNR of the MIMO system;
A MIMO channel capacity calculation method comprising: A computer program for performing a MIMO channel capacity calculation process for calculating a channel capacity in a MIMO system having two transmit antennas and two receive antennas,
A reception electric field calculation step for calculating a reception electric field from the transmission antenna to the reception antenna for each pair of the transmission antenna and the reception antenna;
A received power difference calculating step of calculating a received power difference using the received electric field calculated in the received electric field calculating step;
Inter-antenna correlation calculation step of calculating a correlation value between transmission antennas using the reception electric field calculated in the reception electric field calculation step;
Using the received power difference calculated in the received power difference calculating step and the transmission antenna correlation value calculated in the inter-antenna correlation calculating step, two channel values obtained by singular value decomposition of the channel response matrix of the MIMO system are obtained. An eigenvalue ratio estimation step for estimating an eigenvalue ratio;
A channel capacity calculation step of calculating a channel capacity using the eigenvalue ratio calculated in the eigenvalue ratio estimation step and the average SNR of the MIMO system;
A computer program for causing a computer to execute.

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