# US 2014/0192761 A1 · Radio communication system, radio base station apparatus, user terminal and radio communication method

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- Number: US 2014/0192761 A1
- Document ID: US20140192761A1
- Status: Published application
- Kind: A1
- Application number: 14/238,264
- Filed: 2012-08-14
- Published: 2014-07-10
- Earliest claimed: 2011-08-15
- Assignees: Ntt Docomo, Inc.
- Inventors: Yuki Inoue; Tetsushi Abe
- Web page: https://patentgrep.com/patent/US20140192761A1

## CPC

- H04B 7/0417: Feedback systems
- H04B 7/024: Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
- H04B 7/0456: Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
- H04B 7/0473: {taking constraints in layer or codeword to antenna mapping into account}
- H04B 7/0626: {Channel coefficients, e.g. channel state information [CSI]}
- H04B 7/063: {Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection}
- H04B 7/0632: {Channel quality parameters, e.g. channel quality indicator [CQI]}
- H04B 7/0639: {Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection}
- H04W 16/28: using beam steering
- H04W 72/21: in the uplink direction of a wireless link, i.e. towards the network
- H04B 7/10: Polarisation diversity; Directional diversity
- H04W 24/10: Scheduling measurement reports {; Arrangements for measurement reports}
- H04B: TRANSMISSION
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

The present invention is designed to reduce the space to install antennas and still increase the system capacity despite the state of the distribution of user terminals in cells. According to the radio communication method of the present invention, a radio base station apparatus selects precoding vectors from a codebook that is set in advance to be uneven with respect to the direction of the arrangement of antenna elements, based on communication quality information of the user terminals in the cell, multiplies signals to supply to each antenna element by the selected precoding vectors, and transmits the signals multiplied by the precoding vectors to the user terminals, and the user terminal receives a signal from the radio base station apparatus, extracts a reference signal from the received signal and measures channel quality; and feeds back a communication quality feedback signal, including the measured channel quality, to the radio base station apparatus, via the uplink.

## Claims

### Claim 1

A radio communication system comprising a radio base station apparatus to form a cell and user terminals to establish radio connection with the radio base station apparatus, wherein:
the radio base station apparatus comprises:
an array antenna having a plurality of antenna elements that are arranged in one direction;
a selection section configured to select precoding vectors from a codebook that is set in advance to be uneven with respect to the direction of the arrangement of the antenna elements, based on communication quality information that is fed back from the user terminals in the cell;
a precoding multiplication section configured to multiply signals to supply to each antenna element by the selected precoding vectors; and
a transmission section configured to transmit the signals multiplied by the precoding vectors to the user terminals; and
the user terminals comprise:
a receiving section configured to receive a signal from the radio base station apparatus;
a channel quality measurement section configured to extract a reference signal from the received signal and measure channel quality; and
a transmission section configured to feed back a communication quality feedback signal, including the measured channel quality, to the radio base station apparatus, via an uplink.

### Claim 2 (depends on 1)

The radio communication system according to claim 1, wherein the codebook is formed with precoding vectors that make a reciprocal of a density of the user terminals uniform.

### Claim 3 (depends on 1, 2)

The radio communication system according to claim 1 and claim 2, wherein, when p(L) is a distribution function of the user terminals with respect to a distance from the radio base station apparatus and L[m] is the distance from the radio base station apparatus, the codebook is &limed with precoding vectors that are determined from the following equation:
CODEBOOKV[0, 1, . . . M−1]=exp(2πd·j cos(α+π/2)·[0, 1, 2, . . . , N−1]) α=a tan(h/(σ(L·[0, 1, . . . M−1])))
where h is a height of the radio base station apparatus, d is an interval of branches, which are groups of a plurality of antenna elements, a is a tilt angle of transmission beams directed to the user terminals UE with respect to a horizontal direction, and N is the number of branches.

### Claim 4 (depends on 3)

The radio communication system according to claim 3, wherein, when the user terminals are distributed evenly with respect to the distance from the radio base station apparatus, the codebook is formed with precoding vectors that are determined by the following equation:
CODEBOOKV[0, 1, . . . M−1]=exp(2πd·j cos(α+π/2)·[0, 1, 2, . . . , N−1]) α=a tan(h/(Lmax/M)·[0, 1, . . . M−1])))

### Claim 5 (depends on 3)

The radio communication system according to claim 3, wherein, when the user terminals are distributed squarefold with respect to the distance from the radio base station apparatus, the codebook is formed with precoding vectors that are determined from the following equation:
CODEBOOKV[0, 1, . . . M−1]=exp(2πd·j cos(α+π/2)·[0, 1, 2, . . . , N−1]) α=a tan(h/(Lmax/sqrt(2)̂[M−1, . . . 1, 0]))

### Claim 6

A radio base station apparatus in a radio communication system comprising the radio base station apparatus to than a cell and user terminals to establish radio connection with the radio base station apparatus, the radio base station apparatus comprising:
an array antenna having a plurality of antenna elements that are arranged in one direction;
a selection section configured to select precoding vectors from a codebook that is set in advance to be uneven with respect to the direction of the arrangement of the antenna elements, based on communication quality information of the user terminals in the cell;
a precoding multiplication section configured to multiply signals to supply to each antenna element by the selected precoding vectors; and
a transmission section configured to transmit the signals multiplied by the precoding vectors to the user terminals.

### Claim 7

A user terminal in a radio communication system comprising a radio base station apparatus to form a cell and user terminals to establish radio connection with the radio base station apparatus, the user terminal comprising:
a receiving section configured to receive a signal transmitted from the radio base station apparatus using a codebook that is set in advance in the radio base station apparatus to be uneven with respect to a direction of arrangement of antenna elements based on communication quality information of the user terminals in the cell;
a channel quality measurement section configured to extract a reference signal from the received signal and measure channel quality; and
a transmission section configured to feed back a communication quality feedback signal, including the measured channel quality, to the radio base station apparatus, via an uplink.

### Claim 8

A radio communication method in a radio communication system comprising a radio base station apparatus to form a cell and user terminals to establish radio connection with the radio base station apparatus, the radio communication method comprising the steps of:
at the radio base station apparatus:
selecting precoding vectors from a codebook that is set in advance to be uneven with respect to the direction of arrangement of antenna elements, based on communication quality information of the user terminals in the cell;
multiplying signals to supply to each antenna element by the selected precoding vectors; and
transmitting the signals multiplied by the precoding vectors to the user terminals, at the user terminal:
receiving a signal from the radio base station apparatus;
extracting a reference signal from the received signal and measuring channel quality; and
feeding back a communication quality feedback signal, including the measured channel quality, to the radio base station apparatus, via an uplink.

### Claim 9 (depends on 2)

The radio communication system according to claim 2, wherein, when p(L) is a distribution function of the user terminals with respect to a distance from the radio base station apparatus and L[m] is the distance from the radio base station apparatus, the codebook is formed with precoding vectors that are determined from the following equation:
CODEBOOKV[0, 1, . . . M−1]=exp(2πd·j cos(α+π/2)·[0, 1, 2, . . . , N−1]) α=a tan(h/(σ(L·[0, 1, . . . M−1])))
where h is a height of the radio base station apparatus, d is an interval of branches, which are groups of a plurality of antenna elements, a is a tilt angle of transmission beams directed to the user terminals UE with respect to a horizontal direction, and N is the number of branches.