WO2008054077A1

WO2008054077A1 - Transmission apparatus and method based on beam

Info

Publication number: WO2008054077A1
Application number: PCT/KR2007/005083
Authority: WO
Inventors: Young-Seog Song; Dong-Seung Kwon
Original assignee: Electronics And Telecommunications Research Institute; Samsung Electronics Co., Ltd.
Priority date: 2006-11-02
Filing date: 2007-10-17
Publication date: 2008-05-08
Also published as: KR20080040105A

Abstract

Disclosed is a beam-based transmission method and device. A multi-user MIMO system forms a spatial channel matrix including a precoding matrix by using a unitary matrix, estimates performance based on the spatial channel matrix to extract and store an optimized terminal set combination and an optimized beam, and performs a scheduling process by using the optimized terminal set combination. Therefore, the optimized multi-user MIMO system can be provided by scheduling various terminals and increasing the number of terminals applied to the MIMO system.

Description

TRANSMISSION APPARATUS AND METHOD BASED ON

BEAM

Technical Field

[1] The present invention relates to a beam-based transmission method and device, and in particular, it relates to a beam-based transmission method and device using a multiuser multi-input multi-output (MEMO) in an uplink.

[2]

Background Art

[3] Techniques for increasing sector throughput by using multiple antennas from among wireless transmission techniques have been researched. The smart antenna technique increases the signal-to-noise ratio (SNR) of signals by using beams generated by a plurality of antennas to transmit or receives signals, and acquires the gain.

[4] The diversity technique using multiple antennas multiplexes a signal path when the correlation of a channel is small, it reduces the received probability with a low SNR signal, and acquires the gain. When the SNR is high, the spatial multiplexing (SM) technique for transmitting different signals to a plurality of antennas and acquiring a multiplexing gain is used. The above-noted spatial multiplexing, diversity, and SNR techniques are important for increasing sector throughputs in the MIMO system.

[5] When the wireless transmission technique is used in the uplink, the number of transmit antennas is restricted by the power consumption and terminal size. Considering the contemporary standardization trends, the uplink MIMO technique in the IEEE 802. 16e supports two transmit antennas.

[6] However, the conventional uplink MIMO technique does not use the beam forming and precoding technique using a plurality of antennas. Also, the conventional uplink MIMO technique does not provide an integrated transmission method when the number of transmit antennas for a plurality of terminals is different.

[7] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. Disclosure of Invention Technical Problem [8] The present invention has been made in an effort to provide a beam-based transmission device and method using a multi-user MIMO scheme in the uplink. Technical Solution

[9] In one aspect of the present invention, a beam-based transmission method using a multi-user multi input multi output (MIMO) scheme includes: (a) selecting at least one terminal set combination within a base station's coverage area; (b) forming a spatial channel matrix including a precoding matrix based on the selected terminal set, and estimating performance; (c) forming a new spatial channel matrix to estimate performance while changing the precoding matrix combination, comparing performance estimates of the formed new spatial channel matrix and the stored existing spatial channel matrix to store an optimized performance value, and selecting a corresponding optimized terminal set; and (d) performing a scheduling process by using the selected optimized terminal set. In another aspect of the present invention, a beam-based transmitter using a multi-user multi-input multi-output (MIMO) scheme includes: a terminal selector for selecting at least one terminal set coirbination within a base station's coverage area; a precoding matrix selector for generating a spatial channel matrix including a precoding matrix of the selected terminal set, changing the precoding matrix combination, and forming a new spatial channel matrix including a new precoding matrix; a performance estimation calculator for calculating a performance estimation result based on the formed new spatial channel matrix; and a controller for comparing a performance estimate of the new spatial channel matrix with a performance estimate of the stored spatial channel matrix to store the optimized performance estimate, and performing a scheduling function by using a corresponding optimized terminal set. Advantageous Effects

[10] Accordingly, since the present invention can schedule various types of terminals by combining them, the number of terminals provided to the MIMO system is increased to thus configure the optimized multi-user MIMO system.

[11] The sector throughput can be increased since the number of terminals for the multiuser MIMO system can be increased. Brief Description of the Drawings

[12] FIG. 1 shows beam transmission for a multi-user MIMO system according to an exemplary embodiment of the present invention.

[13] FIG. 2 shows a block diagram for a beam-based transmitter according to an exemplary embodiment of the present invention.

[14] FIG. 3 shows a flowchart of a beam-based transmission method for a multi-user

MIMO system using a beam-based transmitter according to an exemplary embodiment of the present invention.

Best Mode for Carrying Out the Invention

[15] In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described erriodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

[16] Throughout this specification and the claims which follow, unless explicitly described to the contrary, the word "comprising" or variations such as "comprises" will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

[17] A beam-based transmission method and device according to an exemplary embodiment of the present invention will now be described with reference to drawings.

[18] FIG. 1 shows beam transmission for a multi-user MEMO system according to an exemplary embodiment of the present invention.

[19] A base station is assumed to know a spatial channel matrix generated by a transmit antenna of a terminal and a receive antenna of the base station through a pilot signal received from the terminal in the uplink. Also, the base station is assumed to allocate any conϋnations of predetermined beams to the respective terminals and use a predetermined precoding matrix.

[20] A terminal having one transmit antenna forms one beam, and a terminal having a plurality of transmit antennas can form various transmission beams by multiplying the transmission signal by a weight. Beam formation is a technique for allocating different weights to a plurality of antenna elements and providing a directional beam in the direction of the terminal so as to provide the maximum received power to the terminal.

[21] The number of beams generated by the transmit antenna can be the number of transmit antennas when the matrix is restricted to be a unitary matrix of the transmit antenna. Therefore, when N unitary matrix sets are assumed, the beams can be formed by the number of N * transmit antennas.

[22] However, the beams by the rank of a channel matrix of the terminal are important for the receiver so as to successfully receive the signal. Therefore, the number of beams that can be formed by the transmit antenna becomes the number of the channel rank.

[23] FIG. 1 shows an optimized terminal set and the beam of the terminal, ATI, AT2, and

AT3 respectively transmit 1, 2, and 1 data streams to the base station. Referring to FIG. 2 and FIG. 3, a scheduling process for finding an optimized terminal set and beams of the terminals will now be described.

[24] FIG. 2 shows a block diagram for a beam-based transmitter 100 according to an exemplary embodiment of the present invention.

[25] The beam-based transmitter 100 includes a terminal selector 102, a precoding matrix selector 104, a performance estimation calculator 106, a controller 108, and a data storage unit 109. The data storage unit 109 includes a terminal set combination storage unit 109a, a spatial channel matrix storage unit 109b, and an optimized terminal combination storage unit 109c.

[26] The terminal selector 102 selects at least one terminal set combination with the coverage area of the base station, and stores the same in the terminal set combination storage unit 109a.

[27] One example of selecting the terminal set (ATI, AT2, and AT3) is given in Table 1.

[28] [Table 1]

[29] As shown in FIG. 1, the numbers of the transmit antennas of the terminals (ATI,

AT2, and AT3) are respectively given as 1, 2, and 4, the channel ranks are respectively given as 1, 1, and 2, and the data streams indicate beam combinations when the data streams respectively have 1, 1, and 2 transmission data. The number of base station receive antennas is assumed to be 4. The channel matrix H is given as the number of receive antennas x the number of transmit antennas, and the precoding matrix P is given as the number of transmit antennas x the number of data streams.

[30] In this instance, when a base station received signal vector is given Y, the rela- tionship between the transmit signal vector X and the receive signal vector Y according to the three terminals is given in Equation 1.

[31] (Equation 1)

[33] where H_± and P_k are respectively a channel matrix and a precoding matrix of the terminal, and H is a spatial channel matrix including a precoding matrix. [34] The base station received signal vector is a product of a transmission signal vector by the terminal and the spatial channel matrix including a precoding matrix. Here, the precoding matrix is a matrix for multiplying the vector of the matrix for each data stream by using a unitary matrix.

[35] Referring to the precoding matrix of Table 1, ATI, AT2, and AT3 are respectively available for 1x1, 2x2, and 4x4 unitary matrixes. Assuming that one unitary matrix is used for precoding, the combinations of the unitary matrixes are given as Ix2x ₄C₂ = 12. In the case of AT3, 2 data streams are given, and hence 2 column vectors are selected from among 4 column vectors of the unitary matrix.

[36] The precoding matrix selector 104 selects one of the beam coπtanations available by the unitary matrixes according to the respective numbers of antennas of the terminals, and generates a spatial channel matrix including the precoding matrix of the selected terminal set.

[37] The performance estimation calculator 106 calculates the performance estimation result of the configured spatial channel matrix, and stores the result in the spatial channel matrix storage unit 109b. The performance estimation is variable by the receiving methods. Assuming a minimum mean squared error (MMSE) receiver, the performance estimation calculator 106 calculates the signal to interference and noise ratio (SINR) from the MMSE receiver, compares the SINR with the mapping table for indicating the data rate, and finds the data rate value. The performance estimation calculator 106 can show the performance estimation for the respective data streams with numbers. The general method for finding the performance estimates is well known to a skilled person, and hence no detailed description will be provided.

[38] The controller 108 compares the calculated performance estimated value with the existing performance estimate of the existing terminal combination stored in the spatial channel matrix storage unit 109b, extracts the optimized performance estimate with greater performance reference, and stores the extracted estimate and the optimized terminal set in the optimized terminal combination storage unit 109c. In this instance, the performance reference represents the entire data rate of the respective terminals.

[39] The controller 108 performs a scheduling function with the extracted optimized terminal set.

[40] The terminal set con±ination storage unit 109a stores the terminal set combination selected by the terminal selector 102. The spatial channel matrix storage unit 109b stores a performance estimate of the spatial channel matrix including the precoding matrix. The optimized terminal combination storage unit 109c stores the extracted optimized performance estimate and a corresponding optimized terminal set.

[41] FIG. 3 shows a flowchart of a beam-based transmission method for a multi-user

MEMO system using a beam-based transmitter 100 according to an exemplary embodiment of the present invention.

[42] The base station estimates a spatial channel matrix and a channel rank formed by the transmit antenna of the terminal and the receive antenna of the base station within the coverage area (SlOO). The terminal selector 102 selects a terminal set combination within the base station's coverage area (S 102).

[43] The precoding matrix selector 104 selects one of the precoding matrix combinations, and generates a spatial channel matrix including a new precoding matrix as expressed in Equation 1 (S 104). The performance estimation calculator 106 calculates the performance estimation result using the spatial channel matrix including the precoding matrix, and stores the calculated result in the spatial channel matrix storage unit 109b.

[44] The controller 108 compares the calculated performance estimate with the existing stored performance estimate and stores the optimized performance estimate with the greater performance reference, and stores the optimized terminal conϋnation corresponding to the optimized performance estimate in the optimized terminal combination storage unit 109c (S 106).

[45] The controller 108 changes the precoding matrix combinations expressed in Equation

1 to determine whether a new precoding matrix is formed (S 108). The controller 108 goes to the step of S 104 and repeats the subsequent steps when determining that not all the precoding matrix con±inations are tested.

[46] When all the precoding matrix combinations are tested, the controller 108 determines whether it has finished the performance estimation test for the spatial channel matrix of all the terminal set combinations within the base station's coverage area (S 110). Referring to Teble 1 again, the controller 108 selects the terminal set of ATI, AT2, and AT3 and estimates the performance based on the spatial channel matrix including the precoding matrix combination, and repeats the performance estimation tests of all the terminal sets within the coverage area while changing the terminal set combination, such as to AT3, AT7, and AT9.

[47] The controller 108 goes to the step of S 102 and repeats subsequent steps when determining that the performance estimation tests for the spatial channel matrix of all the terminal set combinations within the base station's coverage area are finished.

[48] When determining that the performance estimation tests for the spatial channel matrix of all the terminal set combinations within the base station's coverage area are finished, the controller 108 performs scheduling by using the optimized terminal combination for indicating the optimized performance value stored in the optimized terminal combination storage unit 109c (Sl 12).

[49] Equation 1 can be rewritten as Equation 2. [50] (Equation 2)

[52] where S is the number of terminals included in the multi-user MIMO system, D is all data streams provided to the base station, and H_k and P_k are respectively a channel matrix and a precoding matrix of the terminal.

[53] The base station can perform scheduling by selecting not the typical beam but the antenna when setting the precoding matrix to be 1 or 0, as expressed in Equation 3.

[54] (Equation 3)

[56] The controller 108 forms the new precoding matrixes of as many as the combinations of the unitary matrixes to repeat the performance estimation tests of the spatial channel matrix, and performs the performance estimation tests of the spatial channel matrix for all the terminal sets within the base station's coverage area.

[57] The controller 108 repeatedly changes the precoding matrix to form a new spatial channel matrix, and extracts the optimized performance estimate and a corresponding optimized terminal set by using the new terminal set combination selected by the terminal selector 102.

[58] While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[59] Accordingly, since the present invention can schedule various types of terminals by combining them, the number of terminals provided to the MIMO system is increased to thus configure the optimized multi-user MIMO system.

[60] The sector throughput can be increased since the number of terminals for the multiuser MIMO system can be increased.

Claims

[1] In a beam-based transmission method using a multi-user multi-input multi-output

(MIMO) scheme, a transmission method comprising:

(a) selecting at least one terminal set combination within a base station's coverage area;

(b) forming a spatial channel matrix including a precoding matrix based on the selected terminal set, and estimating performance;

(c) forming a new spatial channel matrix to estimate performance while changing the precoding matrix combination, comparing performance estimates of the formed new spatial channel matrix and the stored existing spatial channel matrix to store an optimized performance value, and selecting a corresponding optimized terminal set; and

(d) performing a scheduling process by using the selected optimized terminal set.

[2] The transmission method of claim 1, wherein in (C), the formed new spatial channel matrix is formed by selecting one of the unitary matrix combinations of the precoding matrix and forming a new precoding matrix.

[3] The transmission method of claim 1, further comprising, between (c) and (d): determining whether a new precoding matrix is formed while changing the unitary matrix combinations of the precoding matrix; and determining whether a performance estimation test is performed by using the spatial channel matrix of the terminal set combinations within the base station's coverage area when as many new precoding matrixes are formed as the unitary matrix combinations.

[4] The transmission method of claim 1, wherein a spatial channel matrix is formed according to an antenna selection method when the precoding matrix has 1 or 0.

[5] In a beam-based transmitter using a multi-user multi-input multi-output (MIMO) scheme, a transmitter comprising: a terminal selector for selecting at least one terminal set combination within a base station's coverage area; a precoding matrix selector for generating a spatial channel matrix including a precoding matrix of the selected terminal set, changing the precoding matrix combination, and forming a new spatial channel matrix including a new precoding matrix; a performance estimation calculator for calculating a performance estimation result based on the formed new spatial channel matrix; and a controller for comparing a performance estimate of the new spatial channel matrix with a performance estimate of the stored spatial channel matrix to store the optimized performance estimate, and performing a scheduling function by using a corresponding optimized terminal set.

[6] The transmitter of claim 5, wherein the precoding matrix selector selects one of the unitary matrix combinations of the precoding matrix to form the new precoding matrix.

[7] The transmitter of claim 5, wherein the controller compares the performance estimate of the formed new spatial channel matrix and the performance estimate of the stored spatial channel matrix with reference to the sum of the data rates of the terminals.