JP2010166316A - Mimo communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a MIMO (Multi Input Multi Output) communication system capable of achieving eigenmode transmission in a stable propagation path state without recognizing propagation path characteristics or a change in the propagation path characteristics between transmission and reception. <P>SOLUTION: An eigenmode transmission model 2 converts the transmission signal of transmission symbol sequences 1 to N(Sn) input from a left side in the figure into a plurality of paths with known transmission weight Φ to transmit the plurality of signals to a propagation path, and inversely converts a signal propagating on a known propagation path into the received signal of reception symbol sequences 1 to N(Sn') with known reception weight Φ<SP>H</SP>after receiving the signal. Here, in the case of the (N×N) MIMO of the number N of transmission antennas and the number N of reception antennas, a plane of polarization of the (n+1)-th antenna is rotated such that the plane of polarization of the antenna is a rotation amount (π/N)×n from a reference plane (n=0), and the N antennas are used at transmitting and receiving sides, respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless communication system, and more particularly to a high-frequency point-to-point line-of-sight MIMO (Multi Input Multi Output) communication system.

  In recent years, with the increase in broadband communication users, the cost of cable laying can be reduced by using a wireless line between the subscriber and the carrier. Fixed wireless access (FWA) is attracting attention.

  For fixed wireless access, a point-to-point (P-P) system in which base stations and users are connected one-to-one with directional radio waves, and one base station and a plurality of users communicate simultaneously. There is a P-MP (Point to Multiple Point) system. In the PP system, there is a technique using a MIMO (Multi Input Multi Output) system using a plurality of transmission / reception channels as a technique for realizing large-capacity transmission in a limited frequency band. The MIMO system performs parallel transmission by space division multiplexing (SDM) by transmitting independent signal sequences at the same time and the same frequency band by a plurality of transmission antennas, and further transmitted. A signal is received by a plurality of antennas and then separated into each signal series and demodulated.

  When a certain signal sequence is transmitted from a plurality of transmission antennas, a transmission beam can be formed by multiplying a predetermined transmission weight. Furthermore, a plurality of orthogonal beams can be formed between the transceivers by appropriately setting the transmission weight and the reception weight. Using this property, instead of transmitting a transmission signal independent from each transmission antenna, a plurality of transmission signal sequences (streams) are transmitted using a plurality of transmission signal sequences using these orthogonal beams. There is an EDM (Eigen Beam SDM) system.

FIG. 7 shows the configuration of a conventional eigenmode transmission model 100. Here, a case where the number of transmission antennas is equal to the number of reception antennas will be described. In general eigenmode transmission, a transmission / reception signal is acquired by some method, and a propagation path matrix (channel response matrix) H that is propagation path information CSI (Channel State Information) is calculated. The eigendecomposition of the propagation path matrix H is performed, and the unitary matrix Φ composed of the eigenvalue A and the eigenvector is calculated. In some way, the unitary matrix Φ is taught to the transmitting side and the receiving side. In the figure, a transmission vector composed of transmission symbol sequences 1 to N (Sn) input from the left side is multiplied by the acquired unitary matrix Φ as a transmission weight matrix Φ. On the reception side, a transmission vector of reception symbol sequences 1 to N (Sn ′) is multiplied by Hermitian transpose of the acquired unitary matrix Φ as a reception weight matrix Φ ^H to acquire transmission symbol sequences 1 to N (Sn). Can do. In this way, eigenmode transmission is realized.

  Patent Document 1 discloses a technique for updating an eigenvalue mode of a propagation path in eigenmode transmission by iterative calculation at regular intervals in order to follow a communication environment that changes every moment.

Special table 2007-534271 gazette

  However, in line-of-sight communication in a high frequency band such as millimeter wave, it is difficult to be affected by multipath, so there may not be a situation where the rank, which is the number of non-zero eigenvalues of the propagation path matrix, is full. The rank may be 1.

  Thus, in MIMO communication, a stable data transmission rate cannot be maintained in a state where the rank is unstable and the eigenvalue also fluctuates. Further, in order to realize eigenmode transmission, it is necessary to acquire the propagation path state by a method as in Patent Document 1, and to transmit the information to the transmission / reception side, and it is necessary to process enormous calculations.

  Accordingly, an object of the present invention is to provide a MIMO communication system capable of realizing eigenmode transmission without knowing propagation path characteristics or a change in propagation path characteristics between transmission and reception and in a stable propagation path state. To do.

  In order to achieve the above object, a MIMO communication system according to the present invention is a high-frequency point-to-point line-of-sight MIMO communication system in which a MIMO antenna is combined with a plurality of polarization antennas each having a different polarization plane. A MIMO antenna provided in each of the transceivers and connected to the transceiver has a plurality of polarization antennas inclined at equal division angles from a reference polarization plane.

  Also, in the MIMO communication system according to the present invention, the communication service of the transmitter / receiver is a known service required for line-of-sight communication with less multipath reflection by a plurality of polarization antennas inclined at equal division angles from the reference polarization plane. It is characterized by fixed wireless access communication using weighting.

  In the MIMO communication system according to the present invention, the propagation path formed by the MIMO antenna has a propagation path matrix that is a cyclic matrix.

  Further, in the MIMO communication system according to the present invention, the propagation path is estimated by using n polarization antennas obtained by rotating the polarization plane of the polarization antenna by π / n (n is a natural number of 3 or more). N × n MIMO eigenmode communication is enabled.

  By using the MIMO antenna according to the present invention, if the propagation path matrix has a full rank eigenvalue and an ideal line-of-sight propagation environment, the maximum communication capacity can be secured by MIMO without knowing the propagation path characteristics on the transmitting and receiving sides. There is an effect.

  In addition, when four polarization antennas are used, not only can the frequency efficiency be four times that of one antenna, but there is an effect that the same transmission / reception unit can be combined to use the same frequency band.

It is explanatory drawing explaining the structure of the eigenmode transmission model of the MIMO communication system which concerns on embodiment of this invention. It is explanatory drawing explaining the structure of the transmission antenna of the MIMO communication system which concerns on embodiment of this invention, and a receiving antenna. It is explanatory drawing explaining the polarization direction of the transmitting antenna which concerns on embodiment of this invention, and a receiving antenna. It is explanatory drawing explaining the structure of the waveguide slot array antenna which concerns on embodiment of this invention. It is explanatory drawing explaining the content of the calculation process of the weighting coefficient in the MIMO communication system which concerns on embodiment of this invention. It is a block diagram which shows the specific structural example of the MIMO communication system which concerns on embodiment of this invention. It is explanatory drawing explaining the structure of the conventional eigenmode transmission model.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings.

  FIG. 1 shows the configuration of an eigenmode transmission model 2 of a MIMO communication system. One of the features in the present embodiment is that by using a MIMO antenna having a plurality of polarization antennas inclined at equal division angles from the reference polarization plane without using propagation path information as in the prior art, This is to realize eigenmode transmission with known transmission weights and known reception weights based on known propagation path characteristics.

In the eigenmode transmission model 2, the transmission signals of the transmission symbol sequences 1 to N (Sn) input from the left side in the figure are converted into a plurality of paths by the known transmission weight matrix Φ and transmitted to the propagation path. After the propagated signal is received, it is inversely converted into received signals of received symbol sequences 1 to N (Sn ′) by a known received weight matrix Φ ^H. Here, in the case of (N × N) MIMO with the number of transmitting antennas N and the number of receiving antennas N, the polarization plane of the (n + 1) th antenna is the amount of rotation (π / N) · n from the reference plane (n = 0). The plane of polarization is rotated so that N antennas are used on the transmitting and receiving sides.

  FIG. 2 shows the configuration of the transmission antenna 16 and the reception antenna 20 of the MIMO communication system, and shows a 4 × 4 MIMO antenna using a linear antenna for linear polarization. In the figure, antenna A is a reference antenna, and B, C, and D have their polarization planes rotated by π / 4, π / 2, and 3π / 4, respectively, with respect to reference antenna A. The transmitting antenna 16 and the receiving antenna 20 are arranged to face each other, and the antenna A of the transmitting antenna 16 and the antenna A of the receiving antenna 20 face each other and have the same polarization plane.

  FIG. 3 shows the polarization directions of the transmission antenna and the reception antenna, and shows signal components corresponding to leakage to other antennas rotated δ from the main polarization plane of the reference antenna A. The leakage from the main polarization plane can be expressed by cos δ. At this time, in the case of line-of-sight communication with no reflected wave such as a multipath wave, a propagation path matrix H of a transmission path composed of N transmission antennas and N reception antennas is expressed by Equation 1.

However, the i matrix j column component H _ij of H is as shown in Equation 2.

H _ij shown in Expression 2 indicates a transmission path when the transmission signal from the j-th transmission antenna is received by the i-th reception antenna.

  Here, the propagation path matrix of Expression 1 has the same characteristics for each of the transmission and reception antennas, and the propagation path loss and the antenna gain are normalized to 1 without impairing generality.

  Next, the channel matrix shown in Equation 1 is a circulant matrix (Circulant Matrix), and can be diagonalized as shown in Equation 3.

Where Λ is a diagonal matrix having positive eigenvalues as elements, Φ is represented by a DFT matrix, and each column vector Φ _i is an eigenvector (HΦ _i = √λ _i Φ _i ) with respect to its eigenvalue √λ _i . (ΦΦ ^H = I). Further, (Φ) _mn represents an m-row n-column element of the matrix Φ.

  FIG. 4 shows the configuration of the transmission antenna 16 that is a waveguide slot array antenna. The antennas 16b, 16c, and 16d rotate their planes of polarization by π / 4, π / 2, and 3π / 4, respectively, with respect to the reference antenna 16a. ing. Note that the polarization angle of each antenna shown in FIG. 4 is important, and in the case of a MIMO antenna separated by a predetermined distance, some parallel movement between the polarization antennas is allowed.

Here, if the transmission vector is X and the reception vector is Y, there is a relationship of Y = HX. Here, transmission is performed after Φ weight is applied to the transmission data on the transmission side, and on the reception side, when the number of receptions is inversely converted to the received signal with Φ ^H weight, Y = HX is expressed by Equation 4, and eigenmode in parallel transmission Transmission is possible.

  Next, considering (3 × 3) MIMO communication with three transmission antennas and three reception antennas, the propagation path matrix H from Equation 1 becomes Equation 5.

  When formula 5 is diagonalized, formula 6 is obtained.

  However, Φ in Equation 6 is as shown in Equation 7.

  As a similar example, when considering (4 × 4) MIMO communication with four transmission antennas and four reception antennas, the propagation path matrix H from Equation 1 is as shown in Equation 8.

  However, α is α = 1 / √2. Since diagonalization is possible, formula 9 is obtained by diagonalizing formula 8.

  However, Φ in Equation 9 is as shown in Equation 10.

FIG. 5 shows the calculation processing of the weighting factor in the 4 × 4 eigenmode transmission MIMO communication system, and shows a specific configuration example of the transmission model 31 with the weight of Expression 10. In the transmission model 31, each stream is decomposed into Φ _ij by the fixed beam former 11, the four transmission antennas 16, the adder 17 connected to each of the four transmission antennas 16, the propagation path 30, and 4. Each receiving antenna 20 and an adder 27 for inputting the signals of the receiving antennas 20 to the respective fixed beam formers 25 and adding the outputs of the respective fixed beam formers 25. A stream is output from each adder 27. Will be. Here, the weight coefficient and each stream to be output are as shown in Expression 11.

  FIG. 6 shows a specific configuration example of the MIMO communication system 1. The MIMO communication system 1 includes a transmission system and a reception system. The transmission system includes a modulator 10 that modulates each stream, a fixed beam former 11 that performs transmission power control and fixed beam forming, a D / A converter 12, a quadrature modulator 13, an up converter 14, and an amplifier. 15 and four transmitting antennas 16 (0, π / 4, π / 2, 3π / 4). The modulated radio signal is transmitted to the reception system via the propagation path 30.

  The reception system includes four reception antennas 20 arranged to face the transmission antenna 16, an amplifier 21, a down converter 22, a quadrature demodulator 23, an A / D converter 24, and a fixed beam former 25. And a demodulator 26 that demodulates each stream.

  Here, the eigenvalue decomposition of the propagation path matrix is as shown in Equation 12.

  Here, the coefficient α and the eigenvalue √λ are as shown in Equation 13.

  The present invention relates to a high-frequency wireless communication system such as a microwave band and a millimeter-wave band, and can be used particularly for a high-frequency wireless communication system such as a high-frequency point-to-point line-of-sight MIMO communication system.

  DESCRIPTION OF SYMBOLS 1 MIMO communication system, 2 Eigenmode transmission model, 10 Modulator, 11, 25 Fixed beam former, 12 D / A converter, 13 Quadrature modulator, 14 Up converter, 15, 21 Amplifier, 16 Transmitting antenna, 16a- 16b Waveguide slot array antenna, 17, 27 adder, 20 receiving antenna, 22 down converter, 23 quadrature demodulator, 24 A / D converter, 26 demodulator, 30 propagation path, 31 transmission model, 100 eigenmode transmission Model, CSI channel information, H channel matrix, N number of transmitting or receiving antennas, Sn transmitted symbol, Sn ′ received symbol.

Claims (2)

High-frequency point-to-point prospects In MIMO communication systems,
A MIMO communication system comprising a transmitter and a receiver each having a MIMO antenna in which a plurality of polarization antennas having different polarization planes are combined. The MIMO communication system according to claim 1, wherein
By using n polarization antennas whose polarization planes are rotated every π / n (n is a natural number of 3 or more), n × n MIMO eigenmode communication is possible without estimating the propagation path. A MIMO communication system characterized by the above.

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