U.S. patent application number 16/737049 was filed with the patent office on 2020-05-07 for method for transmitting and receiving signal in wireless communication system, and apparatus therefor.
The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Jiwon Kang, Heejin Kim, Kitae Kim, Kilbom Lee, Kyungmin Park.
Application Number | 20200145074 16/737049 |
Document ID | / |
Family ID | 57884585 |
Filed Date | 2020-05-07 |
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United States Patent
Application |
20200145074 |
Kind Code |
A1 |
Kim; Heejin ; et
al. |
May 7, 2020 |
METHOD FOR TRANSMITTING AND RECEIVING SIGNAL IN WIRELESS
COMMUNICATION SYSTEM, AND APPARATUS THEREFOR
Abstract
The present invention relates to a method for receiving a signal
in a wireless communication system, and an apparatus therefor.
Particularly, the present invention relates to a method and an
apparatus therefor, the method comprising the steps: receiving
information associated with a preferred beam from another user
equipment (UE), wherein the information associated with the
preferred beam includes information indicating at least one
preferred beam for said another UE; determining at least one shared
beam on the basis of the received information associated with the
preferred beam; transmitting, to a base station, information
associated with the at least one determined shared beam;
determining a beam dedicated for a particular UE on the basis of
the at least one determined shared beam; transmitting, to the base
station, information associated with the determined dedicated beam;
and simultaneously receiving, from the base station, UE-common data
on the basis of the information associated with the at least one
shared beam, and UE-specific data on the basis of the information
associated with the dedicated beam.
Inventors: |
Kim; Heejin; (Seoul, KR)
; Kang; Jiwon; (Seoul, KR) ; Kim; Kitae;
(Seoul, KR) ; Lee; Kilbom; (Seoul, KR) ;
Park; Kyungmin; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Family ID: |
57884585 |
Appl. No.: |
16/737049 |
Filed: |
January 8, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15748408 |
Jan 29, 2018 |
10560167 |
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PCT/KR2016/006851 |
Jun 27, 2016 |
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16737049 |
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62199206 |
Jul 30, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 7/0417 20130101;
H04B 7/0639 20130101; H04B 7/0695 20130101; H04B 7/0617 20130101;
H04B 7/0626 20130101; H04B 7/0632 20130101 |
International
Class: |
H04B 7/06 20060101
H04B007/06; H04B 7/0417 20060101 H04B007/0417 |
Claims
1-10. (canceled)
11. A method performed by a user equipment (UE) in a wireless
communication system, the method comprising: receiving, from
another UE, information about at least one preferred beam for the
another UE; determining at least one shared beam based on the
received information about the at least one preferred beam for the
another UE; and transmitting, to the another UE, information about
the determined at least one shared beam.
12. The method of claim 11, wherein the UE is a representative UE
in a UE group comprising the UE and the another UE.
13. The method of claim 11, wherein the at least one shared beam is
determined from among beams overlapping between at least one
preferred beam for the UE and the at least one preferred beam for
the another UE.
14. The method of claim 11, wherein the information about the
determined at least one shared beam is transmitted to the another
UE in a broadcasting or multicasting manner.
15. The method of claim 11, wherein the information about the at
least one shared beam comprises precoding matrix index
information.
16. The method of claim 11, further comprising: transmitting, to a
base station, the information about the determined at least one
shared beam; and receiving, from the base station, UE-common data
based on the at least one shared beam.
17. The method of claim 11, further comprising: determining a
dedicated beam of the UE based on the determined at least one
shared beam; transmitting, to a base station, information about the
determined dedicated beam; and receiving, from the base station,
UE-specific data based on the dedicated beam.
18. The method of claim 17, wherein the dedicated beam is
determined from among beams other than the at least one shared
beam.
19. The method of claim 17, wherein the information about the
dedicated beam comprises precoding matrix index information.
20. A user equipment (UE) configured to operate in a wireless
communication system, the UE comprising: at least one distributed
antenna unit (DU) configured to transmit and receive a radio
signal; and a processor operatively connected to the DU and
configured to: receive, from another UE through the at least one
DU, information about at least one preferred beam for the another
UE; determine at least one shared beam based on the received
information about the at least one preferred beam for the another
UE; and transmit, to the another UE through the at least one DU,
information about the determined at least one shared beam.
21. The UE of claim 20, wherein the UE is a representative UE in a
UE group comprising the UE and the another UE.
22. The UE of claim 20, wherein the at least one shared beam is
determined from among beams overlapping between at least one
preferred beam for the UE and the at least one preferred beam for
the another UE.
23. The UE of claim 20, wherein the information about the
determined at least one shared beam is transmitted to the another
UE in a broadcasting or multicasting manner.
24. The UE of claim 20, wherein the information about the at least
one shared beam comprises precoding matrix index information.
25. The UE of claim 20, wherein the processor is further configured
to: transmit, to a base station through the at least one DU, the
information about the determined at least one shared beam; and
receive, from the base station through the at least one DU,
UE-common data based on the at least one shared beam.
26. The UE of claim 20, wherein the processor is further configured
to: determine a dedicated beam of the UE based on the determined at
least one shared beam; transmit, to a base station through the at
least one DU, information about the determined dedicated beam; and
receive, from the base station through the at least one DU,
UE-specific data based on the dedicated beam.
27. The UE of claim 26, wherein the dedicated beam is determined
from among beams other than the at least one shared beam.
28. The UE of claim 26, wherein the information about the dedicated
beam comprises precoding matrix index information.
29. An apparatus for a user equipment (UE) configured to operate in
a wireless communication system, the apparatus comprising: a
computer-readable memory comprising executable codes; and a
processor coupled to the computer-readable memory to implement the
executable codes to perform operations comprising: receiving, from
another UE, information about at least one preferred beam for the
another UE; determining at least one shared beam based on the
received information about the at least one preferred beam for the
another UE; and transmitting, to the another UE, information about
the determined at least one shared beam.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system, and more specifically, relates to a method and apparatus
for transmitting and receiving signals using a beam shared between
user equipments based on cooperation between the user
equipments.
BACKGROUND ART
[0002] MIMO (multiple-input multiple-output) used in a wireless
communication system is a scheme of increasing channel capacity and
enhancing transceiving efficiency using multiple transmitting
antennas and/or multiple receiving antennas. MIMO may be called a
multi-antenna.
[0003] In MIMO environment, it may be unnecessary for data to be
transmitted on a single antenna path. For instance, in MIMO
environment, a receiver can reconfigure data by aggregating data
fragments respectively received through a plurality of receiving
antennas. Comparing a single antenna environment and an MIMO
environment to each other, a data rate can be improved by
maintaining a cell area size or coverage can be increased by
maintaining a data rate, in MIMO environment.
[0004] A beamforming scheme in MIMO environment is widely used for
a base station, a user equipment, a relay or the like. The
beamforming scheme can be classified into a digital beamforming
scheme or an analog beamforming scheme depending on whether a
weight vector/matrix (or a precoding vector/matrix) is used for a
baseband or an RF band. And, the digital beamforming scheme is
applied to a precoding procedure of 3G/4G mobile communication
system. For instance, in a current mobile communication system, a
user equipment feds back a precoding matrix index (PMI) to a base
station for a closed-loop based digital beamforming and the base
station performs a beamforming based on the PMI.
DISCLOSURE
Technical Problem
[0005] An object of the present invention devised to solve the
problem lies in a method and device for effectively transmitting
and/or receiving data in a wireless communication system.
[0006] Another object of the present invention devised to solve the
problem lies in a method and device for effectively transmitting
and/or receiving data by sharing a beam between user equipments
(UEs) based on cooperation between UEs in a wireless communication
system.
[0007] Another object of the present invention devised to solve the
problem lies in a method and device for transmitting and/or
receiving control information for enhancing data transmission
efficiency by sharing a beam between UEs in a wireless
communication system.
[0008] It is to be understood that both the foregoing general
description and the following detailed description of the present
invention are exemplary and explanatory and are intended to provide
further explanation of the invention as claimed.
Technical Solution
[0009] In an aspect of the present invention, provided herein is a
method of receiving a signal by a specific user equipment (UE) in a
wireless communication system, the method comprising: receiving
information about a preferred beam from another UE, the information
about the preferred beam comprising information indicating at least
one preferred beam for the another UE; determining at least one
shared beam based on the received information about the preferred
beam; transmitting information about the determined at least one
shared beam to a base station (BS); determining a dedicated beam of
the specific UE based on the determined at least one shared beam;
transmitting information about the determined dedicated beam to the
BS; and simultaneously receiving UE-common data based on the
information about the at least one shared beam and UE-specific data
based on the information about the dedicated beam from the BS.
[0010] In another aspect of the present invention, provided herein
is a user equipment (UE) for transmitting precoding information in
a wireless communication system, the UE comprising: a radio
frequency (RF) unit configured to transmit and receive a radio
signal; and a processor connected to the RF unit while being
operated, wherein the processor is configured to receive
information about a preferred beam from another UE, the information
about the preferred beam comprising information indicating at least
one preferred beam for the another UE, to determine at least one
shared beam based on the received information about the preferred
beam, to transmit information about the determined at least one
shared beam to a base station (BS), to determine a dedicated beam
of the specific UE based on the determined at least one shared
beam, to transmit information about the determined dedicated beam
to the BS, and to simultaneously receive UE-common data based on
the information about the at least one shared beam and UE-specific
data based on the information about the dedicated beam, from the
BS.
[0011] Preferably, the method further comprises receiving group
information from the BS, wherein the group information comprises
information indicating a representative UE in a UE group and
information indicating one or more member UEs, and wherein the
specific UE corresponds the representative UE.
[0012] Preferably, the method further comprises determining at
least one preferred beam of the specific UE, wherein the at least
one shared beam is determined from among beams overlapping between
at least one preferred beam for the specific UE and the at least
one preferred beam for the another UE.
[0013] Preferably, the method further comprises receiving
information indicating a specific shared beam from the BS, wherein
the dedicated beam is determined from among beams other than the
specific shared beam.
[0014] Preferably, the information about the preferred beam further
comprises information about priority of at least one shared beam
candidate.
[0015] Preferably, each of the information about the shared beam
and the information about the dedicated beam comprises precoding
matrix index information.
[0016] Preferably, the UE-common data is received through a
physical broadcast channel (PBCH) and the UE-specific data is
received through a physical downlink shared channel (PDSCH).
[0017] Preferably, the UE-common data is received through a
physical multicast channel (PMCH) and the UE-specific data is
received through a physical downlink shared channel (PDSCH).
[0018] Preferably, the UE-common data and the UE-specific data are
received through different antenna ports.
Advantageous Effects
[0019] According to the present invention, data may be effectively
transmitted and/or received in a wireless communication system.
[0020] According to the present invention, data may be effectively
transmitted and/or received by sharing a beam between user
equipments (UEs) based on cooperation between UEs in a wireless
communication system.
[0021] According to the present invention, control information may
be transmitted and/or received to enhance data transmission
efficiency by sharing a beam between UEs in a wireless
communication system.
[0022] It will be appreciated by persons skilled in the art that
that the effects that could be achieved with the present invention
are not limited to what has been particularly described hereinabove
and other advantages of the present invention will be more clearly
understood from the following detailed description taken in
conjunction with the accompanying drawings.
DESCRIPTION OF DRAWINGS
[0023] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention.
[0024] FIG. 1 is a diagram of a MIMO environment.
[0025] FIG. 2 is a diagram of a massive MIMO environment.
[0026] FIG. 3 is a diagram illustrating a distributed antenna
system that may be considered in the present invention.
[0027] FIG. 4 is a diagram illustrating an example in which a
distributed antenna unit is selected in a multi-vehicle
situation.
[0028] FIG. 5 is a diagram illustrating a structure of PUCCH format
2/2a/2b in an LTE system.
[0029] FIG. 6 is a diagram showing a data transmission method
according to the present invention.
[0030] FIG. 7 is a flowchart according to the present
invention.
[0031] FIG. 8 is a diagram illustrating a BS and a UE to which the
present invention is applicable.
MODE FOR INVENTION
[0032] The following embodiments of the present invention may be
applied to a variety of wireless access technologies such as code
division multiple access (CDMA), frequency division multiple access
(FDMA), time division multiple access (TDMA), orthogonal frequency
division multiple access (OFDMA), single carrier frequency division
multiple access (SC-FDMA), and the like. CDMA may be embodied
through wireless (or radio) technology such as universal
terrestrial radio access (UTRA) or CDMA2000. TDMA may be embodied
through wireless (or radio) technology such as global system for
mobile communication (GSM)/general packet radio service
(GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA may be
implemented by wireless (or radio) technology such as Institute of
Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE
802.16 (WiMAX), IEEE 802-20, and evolved UTRA (E-UTRA). UTRA is a
part of universal mobile telecommunications system (UMTS). 3rd
generation partnership project (3GPP) long term evolution (LTE) is
a part of E-UMTS (Evolved UMTS), which uses E-UTRA. LTE-Advanced
(LTE-A) is an evolved version of 3GPP LTE.
[0033] For clarity of explanations, the following description
focuses on 3GPP LTE(-A) system. However, technical features of the
present invention are not limited thereto. Further, a particular
terminology is provided for better understanding of the present
invention. However, such a particular terminology may be changed
without departing from the technical scope of the present
invention. For example, the present invention may be applied to a
system in accordance with a 3GPP LTE/LTE-A system as well as a
system in accordance with another 3GPP standard, IEEE 802.xx
standard, or 3GPP2 standard.
[0034] In the present specification, a user equipment (UE) may be
fixed or mobile. The user equipment (UE) refers to one of various
apparatuses communicating with a base station (BS) to transmit and
receive data and/or control information. The UE may be referred to
as a terminal, a Mobile Station (MS), a Mobile Terminal (MT), a
User Terminal (UT), a Subscriber Station (SS), a wireless device, a
Personal Digital Assistant (PDA), a wireless modem, a handheld
device, etc. In the present specification, the term "UE" may be
interchangeably used with the term "terminal".
[0035] In the present specification, a base station (BS) generally
refers to a fixed station that performs communication with a UE
and/or another BS, and exchanges various kinds of data and control
information with the UE and another BS. The base station (BS) may
be referred to as an advanced base station (ABS), a node-B (NB), an
evolved node-B (eNB), a base transceiver system (BTS), an access
point (AP), a processing server (PS), a transmission point (TP),
etc. In the present invention, the term "BS" may be interchangeably
used with the term "eNB".
[0036] MIMO Environment
[0037] FIG. 1 is a diagram of a MIMO environment.
[0038] Referring to FIG. 1, N.sub.T transmitting antennas are
installed on a transmitting stage, while N.sub.R receiving antennas
are installed on a receiving stage. In case that each of the
transmitting and receiving stages uses a plurality of antennas,
theoretical channel transmission capacity is increased more than
that of a case that either the transmitting stage or the receiving
stage uses a plurality of antennas. The increase of the channel
transmission capacity is in proportion to the number of antennas.
Hence, a transmission rate is enhanced and frequency efficiency can
be raised. Assuming that a maximum transmission rate in case of
using a single antenna is set to R.sub.0, the transmission rate in
case of using multiple antennas may be theoretically raised by a
result from multiplying the maximum transmission rate R.sub.0 by a
rate increasing rate R.sub.i, as shown in Equation 1. In this case,
R.sub.i is a smaller one of N.sub.T and N.sub.R.
[0039] For instance, in an MIMO communication system, which uses 4
transmitting antennas and 4 receiving antennas, it may be able to
obtain a transmission rate 4 times higher than that of a single
antenna system.
[0040] In order to explain a communicating method in an MIMO system
in detail, mathematical modeling can be represented as follows.
Referring to FIG. 1, assume that N.sub.T transmitting antennas and
N.sub.R receiving antennas exist. First of all, regarding a
transmission signal, if there are N.sub.T transmitting antennas, a
maximum number of transmittable information is N.sub.T. Hence, the
transmitted information may be represented by N.sub.T.lamda.1
vector as shown in Equation 1.
s=[s.sub.1,s.sub.2, . . . ,s.sub.N.sub.T].sup.T [Equation 1]
[0041] Meanwhile, transmission powers can be set different from
each other for transmitted information s.sub.1, s.sub.2, . . . ,
s.sub.N.sub.T, respectively. If the transmission powers are set to
P.sub.1, P.sub.2, . . . , P.sub.N, respectively, the transmission
power adjusted transmission information can be represented by
N.sub.T.times.1 vector as shown in Equation 2.
s=[s.sub.1,s.sub.2, . . .
,s.sub.N.sub.T].sup.T=[P.sub.1s.sub.I,P.sub.2S.sub.2, . . .
,P.sub.N.sub.TS.sub.N.sub.T].sup.T [Equation 2]
[0042] And, S may be represented as Equation 3 using a diagonal
matrix P of the transmission power.
s ^ = [ P 1 0 P 2 0 P N T ] [ s 1 s 2 s N T ] = P s [ Equation 3 ]
##EQU00001##
[0043] Let us consider a case of configuring N.sub.T transmitted
signals which are actually transmitted, by applying a weight matrix
W to a transmission power adjusted information vector S. In this
case, the weight matrix plays a role in properly distributing each
transmitted information to each antenna according to a transmission
channel status and the like. The transmitted signals may be
represented by N.sub.T.times.1 vector as shown in Equation 4. In
Equation 4, W.sub.ij means a weight between an i.sup.th
transmitting antenna and a j.sup.th information. And, the W may be
called a weight matrix or a precoding matrix.
x = [ x 1 x 2 x i x N T ] = [ w 11 w 12 w 1 N T w 21 w 22 w 2 N T w
i 1 w i 2 w i N T w N T 1 w N T 2 w N T N T ] [ s ^ 1 s ^ 2 s ^ j s
^ N T ] = W s ^ = WPs [ Equation 4 ] ##EQU00002##
[0044] If there are N.sub.R receiving antennas, received signals
may be represented by N.sub.R.times.1 vector as shown in Equation
5.
y = [ y 1 , y 2 , , ? ] ? ? indicates text missing or illegible
when filed [ Equation 5 ] ##EQU00003##
[0045] When channels are modeled in a multiple antenna
communication system, they may be distinguished according to
indexes of transmitting and receiving antennas. The channel from a
j.sup.th transmitting antenna and an i.sup.th receiving antenna may
be represented as h.sub.ij. It is to be noted herein that the index
of the receiving antenna precedes that of the transmitting antenna
in h.sub.ij.
[0046] Channels from N.sub.T transmitting antennas to the i.sup.th
receiving antenna may be represented as h.sub.i, all channels from
the N.sub.T transmitting antennas to the N.sub.R receiving antennas
may be expressed by Equation 6.
H = [ h 1 T h 2 T h l T h N R T ] = [ h 11 h 12 h 1 N T h 12 h 12 h
2 N T h i 2 h i 2 h i N T h N R 1 h N R 2 h N R N T ] [ Equation 6
] ##EQU00004##
[0047] Actual channels experience the above channel matrix H and
then are added with Additive White Gaussian Noise (AWGN). The AWGN
added to the N.sub.R receiving antennas may be expressed as
N.sub.R.times.1 vector, and received signals are expressed by
Equation 7.
y = [ y 1 y 2 y i y N R ] = [ h 11 h 12 h 1 N T h 12 h 12 h 2 N T h
i 2 h i 2 h i N T h N R 1 h N R 2 h N R N T ] [ x 1 x 2 x j x N T ]
[ n 1 n 2 n i n N R ] = Hx + n [ Equation 7 ] ##EQU00005##
[0048] In the meantime, the numbers of rows and columns in the
channel matrix H representing channel states are determined
according to the numbers of Tx and Rx antennas. The number of rows
is identical to that of Rx antennas, N.sub.R and the number of
columns is identical to that of Tx antennas, N.sub.T. Thus, the
channel matrix H is of size N.sub.R.times.N.sub.T.
[0049] In general, the rank of a matrix is defined as the smaller
between the numbers of independent rows and columns. The rank of a
matrix may be defined as the number of non-zero Eigen values when
the matrix is Eigen-value-decomposed. Similarly, the rank of a
matrix may be defined as the number of non-zero singular values
when the matrix is singular-value-decomposed. Accordingly, the
physical meaning of the rank of a channel matrix can be a maximum
number of channels through which different pieces of information
can be transmitted.
[0050] Meanwhile, each different information sent by MIMO
technology may be defined as `transport stream` or `stream` simply.
This `stream` may be called a layer. If so, the number of transport
streams is unable to be greater than a channel rank, which is the
maximum number for sending different informations.
[0051] Various methods for making at least one stream correspond to
several antennas may exist. These methods may be described in
accordance with a type of MIMO technique as follows. First of all,
if one stream is transmitted via several antennas, it may be
regarded as spatial diversity. If several streams are transmitted
via several antennas, it may be regarded as spatial multiplexing.
Of course, such an intermediate type between spatial diversity and
spatial multiplexing as a hybrid type of spatial diversity and
spatial multiplexing may be possible.
[0052] FIG. 2 illustrates a massive MIMO environment. FIG. 2
diagrammatizes a system in which a base station or user equipment
has a plurality of transmitting/receiving antennas capable of an
active antenna system based 3D beamforming.
[0053] Referring to FIG. 2, if a 3D (3-dimensional) beam pattern is
utilized in a transmitting antenna aspect, it is able to perform a
quasi-static or dynamic beamforming in a vertical direction of a
beam as well as in a horizontal direction of the beam. And, it is
also able to consider application such as a sector forming in a
vertical direction or the like. Moreover, in a receiving antenna
aspect, when a receiving beam is formed using massive receiving
antennas, it is able to expect a signal power increasing effect in
accordance with an antenna array gain. Hence, in case of uplink, a
base station can receive a signal transmitted from a user equipment
through a plurality of of antennas. In doing so, it is advantageous
in that the user equipment can set its transmission power to a very
low power in consideration of a gain of the massive receiving
antennas in order to reduce interference influence.
[0054] Distributed Antenna System
[0055] FIG. 3 is a diagram illustrating a distributed antenna
system that may be considered in the present invention.
[0056] Referring to FIG. 3, antennas that have various shapes and
radiation patterns according to an installment position may be
distributed at a plurality of portions of a vehicle and a central
unit (CU) for integrally controlling transmission and receiving
signals through a distributed antenna unit (DU) may be installed.
Through a configuration illustrated in FIG. 3, reception diversity
gain may be maximized via use of an antenna array, and wireless
access between a base station and a vehicle reception end may be
prevented from being disconnected through cooperative reception
between antennas with different radiation patterns in a high speed
movement situation in which a communication environment is abruptly
changed.
[0057] FIG. 4 is a diagram illustrating an example in which a
distributed antenna unit is selected in a multi-vehicle
situation.
[0058] When vehicles are close to each other in a limited area, it
is difficult to separate and distinguish beams for users (e.g.,
vehicles) and distributed antenna arrays thereof due to an issue of
beam sharpness in a vehicular distributed antenna array. For
example, distributed antenna arrays positioned at very adjacent
distances receive signals passing through similar channel
environments, and thus the possibility that a plurality of DUs
receive the same beam or are blocked by obstacles or cannot receive
any beam is very high. Accordingly, in this case, as illustrated in
FIG. 2, when a method for selectively activating/deactivating a DU
of each vehicle is applied and each vehicle receives beams passing
through as much as possible independent paths that experience
different clusters from a beam that can be received by an adjacent
vehicle through an activated DU of the corresponding vehicle, it
may be more advantageous in terms of performance than in the case
in which all DUs arranged in each vehicle are activated and
used.
[0059] Channel State Information (CSI) Measurement and Report
[0060] In order to generate a beam appropriate for reception, a
transmitting end needs to recognize information about a channel and
to accurately measure the appropriate beam and a gain obtained by
using the beam based on the recognized channel information. The
channel information may be measured by transmitting a separate
pilot to the transmitting end by a receiving end, but in the case
of a current mobile communication system, the receiving end may
measure a channel and then provide the measured information to the
transmitting end in the form of CSI. When MIMO is implemented, a
channel may be defined by combining sub channels generated between
a plurality of transmission and reception antennas, and as the
number of antennas used to implement the MIMO increases, a more
complex structure may be obtained. According to a method for
measuring and reporting channel information, the method may be
divided into 1) an implicit CSI reporting method and 2) an explicit
CSI reporting method.
[0061] The implicit CSI reporting method may be a method for
interpreting measured channel information instead of information
about a channel measured by a receiving end and selectively
reporting only information that is materially required to generate
a beam at a transmitting end. Compared with the explicit CSI
reporting method, the implicit CSI reporting method is advantageous
in that signaling overhead consumed to report CSI is small, and
thus the implicit CSI reporting method has been used in a current
mobile communication system. For example, the implicit CSI feedback
information may include the following information. [0062] When the
implicit CSI feedback information has a limited number of precoder
candidates, precoder index feedback (e.g., precoding matrix index,
and PMI) [0063] Channel Quality Information (CQI) [0064] Rank
Information (RI)
[0065] The explicit CSI reporting method may be a method for
transmitting information that is as much as possible approximate
information to a measurement value without interpreting a channel
measured by the receiving end. Various methods for reducing
signaling overhead used for CSI report via quantization or singular
value decomposition (SVD) calculation of a MIMO channel expressed
in the form of a matrix may be used. For example, the explicit CSI
feedback information may have the following information. [0066]
Channel coefficient quantization & quantization index feedback
[0067] MIMO matrix or vector quantization & quantization index
feedback [0068] Channel covariance matrix feedback [0069]
Transmission of Eigen vector of Eigen matrix feedback or Channel
matrix and/or Eigen value
[0070] CSI in LTE System
[0071] In most cellular systems including a LTE system, a UE may
receive a pilot signal or reference signal for channel estimation
from a base station, calculate channel state information (CSI), and
report the CSI to the base station. The base station may transmit a
data signal based on CSI information that is fed back from the UE.
The CSI information that is fed back by the UE in the LTE system
may include channel quality information (CQI), precoding matrix
index (PMI), and rank indicator (RI).
[0072] CQI feedback may include radio channel quality information
that is provided to a base station for the purpose of providing a
guide about a modulation and coding scheme that is applied when the
base station transmits data (e.g., link adaptation). When link
quality between a base station and a UE is high, the UE may
feedback a high CQI value and the base station may apply a
relatively high modulation order and a low channel coding rate and
transmit data. When link quality between the base station and the
UE is low, the UE may feedback a low CQI value and the base station
may apply a relatively low modulation order and a high channel
coding rate and transmit data.
[0073] The PMI feedback may include preferred precoding matrix
information that is provided to a base station for the purpose of
providing a guide about a MIMO precoding scheme that is applied
when the base station is installed with multiple antennas. The UE
may estimate a downlink MIMO channel between the base station and
the UE from a pilot signal and recommend MIMO precoding to be used
by the base station through PMI feedback. An LTE system considers
linear MIMO precoding that can be expressed in the form of a matrix
for PMI configuration. The base station and the UE may share a
codebook configured with a plurality of precoding matrices and each
MIMO precoding matrix in the codebook may have a unique index.
Accordingly, the UE may feedback an index corresponding to a MIMO
precoding matrix that is most preferred in the codebook as PMI so
as to minimize the amount of feedback information of the UE.
[0074] The RI feedback may include information about the number of
preferred transmission layers that are provided to the base station
for the purpose of providing a guide about the number of
transmission layers preferred by the UE when the base station and
the UE are installed with multiple antennas so as to perform
multi-layer transmission through spatial multiplexing. The RI has a
very close relationship with the PMI. This is because the base
station can know precoding to be applied to each layer according to
the number of transmission layers. With regard to a PMI/RI feedback
configuration, a PMI codebook may be configured based on
transmission of a single layer and then PMI may be defined and fed
back for each layer, but this method is disadvantageous in that the
amount of PMI/RI feedback information is largely increased
according to increase in number of transmission layers.
Accordingly, a PMI codebook according to the number of transmission
layers may be defined in an LTE system. That is, N Nt.times.R
matrices (R is the number of layers, Nt is the number of
transmission antenna ports, and N is the size of a codebook) may be
defined in a codebook for R layer transmission. Accordingly, the
size of the PMI codebook may be defined irrespective of the number
of transmission layers in the LTE system. Since PMI/RI is defined
according to this structure, the transmission layer number R
corresponds to a rank number of the precoding matrix (Nt.times.R
matrix), and thus the transmission layer number R may be referred
to as a rank indicator RI.
[0075] The CSI information may be obtained from an entire system
frequency domain or obtained from a partial frequency domain. In
particular, it may be useful to obtain and feedback CSI information
about a partial frequency domain (e.g., subband) preferred by each
UE in a system using orthogonal frequency division multiple access
(OFDMA) technology.
[0076] The PMI/RI described in the specification is not limited to
indicating an index value of a precoding matrix represented by a
Nt.times.R matrix such as PMI/RI in the LTE system and a rank value
of a precoding matrix. The PMI described in the specification may
refer to preferred MIMO precoder information among MIMO precoders
applicable in a transmission end, and the form of the precoder may
not be limited to only a linear precoder that can be represented by
a matrix such as in the LTE system. In addition, the RI described
in the specification may include any feedback information that
refers to a preferred transmission layer number in a broader
meaning than in the LTE system.
[0077] The PMI information described in the specification is not
configured by only one index. In the LTE-A system, a final PMI is
divided into W1 as long term and/or wideband (WB) PMI and W2 as
short term and/or sub-band (SB) PMI such that PMI with a dual
structure is used. For example, the final PMI W may be defined as
W=W1*W2 or W=W2*W1. For example, when the number of transmission
antenna ports in the LTE-A is 8 or
alternativeCodeBookEnabledFor4TX-r12=TRUE is configured via RRC
signaling while the number of transmission antenna ports is 4, a
final MIMO precoding matrix may be derived by only combining two
indexes (WB PMI(W1) and SB PMI(W2)).
[0078] CSI Feedback Using Uplink Channel
[0079] In the LTE system, CSI feedback may be performed through an
uplink channel. Periodic CSI feedback may be performed through a
physical uplink control channel (PUCCH) and aperiodic CSI feedback
may be performed through a physical uplink shared channel (PUSCH)
as an uplink data channel. However, an information payload size in
a reporting type may be defined according to a reporting mode and a
mode state in CSI feedback through PUCCH, and a payload size of
PUCCH format 2/2a/2b (PUCCH format 3 that can be used to apply
carrier aggregation is excluded) that is defined in the LTE system
may be very restrictive.
[0080] FIG. 5 is a diagram illustrating a structure of PUCCH format
2/2a/2b in an LTE system.
[0081] Cyclic shift (CS) of a sequence in each OFDM symbol may be
used as PUCCH format. The cyclic shifted sequence may be generated
by cyclic shifting a base sequence by as much as a specific CS
amount.
[0082] FIG. 5 illustrates a channel structure of PUCCH format
2/2a/2b of one slot in a normal CP. PUCCH format 2/2a/2b may be
generated through the following steps.
[0083] Step 1. 10 CQI information bits may be channel-coded at a
ratio of 1/2 to obtain 20 coded bits. For example, a Reed-Muller
(RM) code may be used in channel coding.
[0084] Step 2. A QPSK modulation symbol may be generated via
scrambling and then QPSK constellation mapping (d0 to d4 in slot
0).
[0085] Step 3. Each QPSK modulation symbol may be modulated via
cyclic shift of a base reference signal (RS) sequence with a length
of 12 and then transmitted in each of 10 single carrier frequency
division multiple access (SC-FDMAs) symbols in a subframe.
[0086] Step 4. 12 cyclic shifts that are uniformly spaced may be
configured in such a way that 12 different UEs are orthogonally
multiplexed in the same PUCCH resource block. A base RS sequence
with a length of 12 may be used for a demodulation reference signal
(DM RS) sequence applied to SC-FDMA symbols 1 and 5.
[0087] The 20 coded bits in Step 2 may be scrambled by a
UE-specific scrambling sequence and may be represented according to
Equation 8 below.
{tilde over (b)}=(b(i)+c(i)mod2 [Equation 8]
[0088] In Equation 8, b(i) denotes a control information (or CQI
information) bit sequence, c(i) denotes a scrambling sequence,
{tilde over (b)}(i) is a scrambled control information (or CQI
information) bit sequence, and mod refers to modulo calculation.
The scrambling sequence c(i) may be generated according to Equation
9 and initialized according to Equation 10 at every start of a
subframe. In Equation 9, Nc may be 1600, x.sub.1(0)=1, and
x.sub.i(n)=0, n=1, . . . , 30.
c(n)=(x.sub.1(n+N.sub.C)+x.sub.2(n+N.sub.C))mod2
x.sub.1(n+31)=(x.sub.1(n+3)+x.sub.1(n))mod2
x.sub.2(n+31)=(x.sub.2(n+3)+x.sub.2(n+2)+x.sub.2(n+1)+x.sub.2(n)mod2
[Equation 9]
c.sub.init=(.left brkt-bot.n.sub.s/2.right
brkt-bot.+1)(2N.sub.ID.sup.cell+1)2.sup.16+n.sub.RNTI [Equation
10]
[0089] In Equation 10, n.sub.RNTI may refer to identification
information of a corresponding UE and may be a cell-radio network
temporary identifier (C-RNTI). Accordingly, when control
information (or CQI information) is transmitted through a PUCCH,
the control information may be scrambled based on the
identification information of the corresponding UE, and another UE
cannot recognize the identification information of the
corresponding UE, and thus the another UE cannot acquire control
information transmitted from the corresponding UE.
[0090] Multiuser MIMO with Densely-Distributed Users
[0091] In general, in single user-MIMO (SU-MIMO), only data of a
single user may be scheduled in the same time/frequency domain. On
the other hand, in the case of multiuser-MIMO (MU-MIMO) in which a
single eNB intends to communicates with a plurality of UEs, data of
a plurality of users may be scheduled together in the same
time/frequency domain. A current communication system is operated
in such a way that, even if a plurality of users are present in a
cell, users are selectively scheduled to prevent performance from
being degraded due to influence of an interference signal between
users and, thus, as many interference signals as possible between
users may be avoided to enhance QoS of a served user.
[0092] However, channel information of a user needs to be pre-known
for user scheduling and, when numerous UEs are densely distributed
in a narrow area, the number of resources occupied by a UL
reference signal therefor needs to be remarkably increased and,
thus, resources to be used in data transmission may be
insufficient. In addition, it is known that user scheduling is
efficient when more users present in a cell are present than the
number of antennas of an eNB and, thus, an effect of enhancing
system transmission efficiency of a scheduling-based MU-MIMO
transmission scheme may be insignificant in a situation in which a
massive MIMO system is considered.
[0093] A time division multiple access (TDMA)/frequency division
multiple access (FDMA) method for scheduling data of a plurality of
users together has a limit in enhancing transmission efficiency
because only a single UE uses the same resource. Accordingly, a
multiuser method in which a multiuser shares the same
time/frequency resource and performs communication may be
considered. For example, a multiuser-MIMO (MU-MIMO) method in which
different UEs use as spatially separated beams as possible and
perform communication in the same time/frequency resource may be
considered. This method may include a method of dividing a spatial
resource via multiple beamforming and performing multiple access
and the method of dividing a spatial resource and performing
multiple access may also be referred to as space division multiple
access (SDMA).
[0094] An MU-MIMO technology such as SDMA may be performed via an
independent channel as possible so as to space a beam apart from a
multiuser (or device). When the multiuser has similar radio channel
characteristics (e.g., when a correlation is high), MU-MIMO
performance may be reduced and it may be difficult to apply the
MU-MIMO technology. An environment in which the multiuser has
similar radio channel characteristics may be generated when a
plurality of UEs are adjacently present to each other and, for
example, a problem may arise, in particular, when numerous UEs are
densely distributed in a narrow area, such as a stadium environment
or an environment of densely distributed vehicles.
[0095] Accordingly, a multiuser/multiple stream transmission scheme
via sharing a beam between users may be considered as an example of
resolution and, in more detail, a multiuser/multiple stream
transmission scheme via sharing a beam between users based on
cooperation between UEs may be considered. When the
multiuser/multiple stream transmission scheme via sharing a beam
between users is used, even if a plurality of UEs are densely
distributed to have similar radio channel characteristics, system
transmission efficiency may be enhanced.
[0096] As a scheme for enhancing transmission efficiency via
sharing a beam between users transmission efficiency, a NOMA scheme
and a broadcast/multicast scheme via a shared beam may be
considered. The shared beam may refer to a beam that is commonly
formed for a plurality of users to simultaneously transmit/receive
to a plurality of users and may refer to a UE-common beam. A signal
for a plurality of users may be simultaneously transmitted/received
via a shared beam. A UE-dedicated beam may refer to a beam formed
to transmit/receive a signal to a specific user and a signal for
the specific user may be transmitted/received through the
UE-dedicated beam.
[0097] Non-Orthogonal Multiple Access (NOMA)
[0098] When a plurality of UEs are densely distributed to have
similar radio channel characteristics, UE-dedicated symbols of
different users may be transmitted to one beam to be supposed on
each other, thereby enhancing transmission efficiency. In detail,
when it is difficult to apply a general SDMA technology like in a
situation in which a densely distributed multiuser needs to be
simultaneously supported, non-orthogonal multiple access (NOMA)
schemes such as hierarchical modulation and superposition coding
may be considered.
[0099] In an NOMA-based system, an eNB may transmit corresponding
data symbols to be superposed on each other with respect to a
plurality of UEs (e.g., a UE positioned in a cell-centered region
and a UE of a cell boundary) with a high difference between channel
qualities. In this case, for example, low power may be allocated to
a UE of a cell-centered region and high power may be allocated to a
UE of a cell boundary region. A cell-centered UE may decode and
cancel an interference signal of a cell boundary UE with high
signal intensity to successfully decode a signal thereof using a
successive interference cancellation (SIC) method and, an
interference signal of a cell-centered UE is weakly reached and,
thus, a cell boundary UE may decode a signal thereof while
considering the interference signal of the cell-centered UE as
interference.
[0100] Broadcast/Multicast by Shared Beam
[0101] When a plurality of UEs are densely distributed to have
similar radio channel characteristics, a common data symbol to a
plurality of users may be broadcast or multicast to a shared beam
between users to enhance transmission efficiency. A plurality of
users that share a beam may be UEs grouped as one UE group or
adjacent UEs.
[0102] In a current LTE/LTE-A system, an eNB may transmit data in
all directions without selection of a user preferred beam in a
broadcast transmission mode. On the other hand, according to a
broadcast/multicast scheme according to the present invention, the
eNB may transmit a UE-specific data symbol to a multiuser and,
simultaneously, may broadcast/multicast a UE-common data symbol to
a beam (or a shared beam) shared by a densely distributed
multiuser. Each user may receive a data symbol thereof from a
UE-dedicated beam and, simultaneously, may additionally receive a
UE-common data symbol from a shared beam, thereby enhancing data
transmission efficiency for each user.
[0103] FIG. 6 is a diagram showing a data transmission method
according to the present invention. In an example of FIG. 6, it may
be assumed that an eNB performs beamforming in 16 beam directions
to form at least one beam and transmits a signal (e.g., a data
signal or a symbol) through the formed beam. Accordingly, in the
example of FIG. 6, the eNB may simultaneously transmit a signal to
at least one beam direction among the 16 beam directions. The
number of the beam directions shown in FIG. 6 is merely an example
and, even if there are greater or fewer beam directions, the
present invention may be applied in the same/similar way. In the
example of FIG. 6, it may be assumed that a first UE (UE1) and a
second UE (UE2) each include multiple reception antennas.
[0104] Referring to FIG. 6, beam #5 may be commonly used to
transmit and receive a signal for the first UE (UE1) and the second
UE (UE2) and, thus, may correspond to a shared beam. On the other
hand, beam #4 may be used to transmit and receive a signal of the
first UE (UE1) but may not be used to transmit a signal for the
second UE (UE2) and, thus, may correspond to a UE-dedicated beam
for the first UE (UE1). Similarly, beam #11 may be used to transmit
and receive a signal for the second UE (UE2) but may not be used to
transmit and receive a signal for the first UE (UE1) and, thus, may
correspond to a UE-dedicated beam for the second UE (UE2).
[0105] The first UE (UE1) may have a multiple antenna, may receive
beam #5 (or a signal transmitted therethrough) through a first
antenna, and may receive beam #4 (or a signal transmitted
therethrough) through a second antenna. Similarly, the second UE
(UE2) may have a multiple antenna, may receive beam #5 (or a signal
transmitted therethrough) through a first antenna, and may receive
beam #11 (or a signal transmitted therethrough) through a second
antenna.
[0106] When an eNB simultaneously forms three beams (e.g., beam #4,
#5, and #11) through an antenna array, the eNB may broadcast common
data to the first UE and the second UE through a shared beam (e.g.,
beam #5), may transmit UE-specific data to the first UE through a
UE-dedicated beam (e.g., beam #4), and may transmit UE-specific
data to the second UE through a UE-specific beam (e.g., beam #11).
Accordingly, the eNB may transmit UE-common data to the first UE
(UE1) through a shared beam (e.g., beam #5) and, simultaneously,
may transmit UE-specific data through a UE-dedicated beam (e.g.,
beam #4), thereby enhancing data transmission efficiency.
Similarly, an UE may transmit UE-common data to the second UE (UE2)
through a shared beam (e.g., beam #5) and, simultaneously, may
transmit UE-specific data through a UE-dedicated beam (e.g., beam
#11), thereby enhancing data transmission efficiency.
[0107] Hereinafter, the present invention proposes a scheme of
selecting a direction of a shared beam between users in a group (or
adjacent users) or selecting a direction of a UE-dedicated beam
when data is (additionally) transmitted using a shared beam between
users in a group (or adjacent users). The beam direction may be
determined by a precoder and, thus, a beam (or a beam direction)
may have equivalent meaning as the precoder. Alternatively, a
precoder may apply a precoding matrix to form a beam and, thus, a
beam (or a beam direction) may have equivalent meaning to a
precoding matrix index. Alternatively, a specific beam may be
formed/transmitted through a specific antenna port and, thus, a
beam (or a beam direction) may have equivalent meaning to a
specific antenna port. For example, determination of a beam (or a
beam direction) may have equivalent meaning to determination of a
precoder for a corresponding beam and/or determination of a
precoding matrix index for a corresponding beam, and
transmission/reception of a signal through a beam (or a beam
direction) may have equivalent meaning to transmission/reception of
a signal through a specific antenna port to a corresponding
beam.
[0108] A method of designing a precoder based on cooperation
between users for multiuser/multiple stream downlink transmission
via sharing of a beam between UEs according to the present
invention may be performed via the following procedures.
[0109] Operation 1: Determine Shared Beam
[0110] UEs in a group or adjacent UEs may share preferred beam
information thereof, may determine a preferred shared beam via
cooperation between UEs and, then, may feedback the preferred
shared beam to an eNB. A UE group or adjacent UEs may be determined
by the eNB based on a beam direction and, then, the eNB may
transmit/share information about the UE group or adjacent UEs to
corresponding UEs. For example, the information about the UE group
or adjacent UEs may include information indicating a representative
UE or a header UE and/or information indicating a member UE. As
another example, the information about the UE group
transmitted/shared by the eNB may indicate a representative UE (or
a header UE) and/or a member UE through one piece of
information.
[0111] To share preferred beam information by UEs in a group or
adjacent UEs, each user may broadcast/multicast information about
preferred beam thereof (e.g., a preferred shared beam).
Alternatively, each UE may transmit information about preferred
beam thereof to a UE (e.g., a representative UE or a header UE)
determined by an eNB in a group or a specific type of UE (e.g., a
UE according to existing LTE/LTE-A standard).
[0112] Each user may share a plurality of preferred beam
information items thereof with an adjacent user and, when users
share a plurality of preferred beam directions, it may be possible
to share a preferred beam direction and priority thereof. In this
case, the information about the preferred beam that is
transmitted/broadcast/multicast by each user may include at least
one of information about the number of preferred beams, information
indicating a preferred beam direction, or information about
priority when there is a plurality of preferred beams.
[0113] The shared beam direction may be determined and/or fed back
by a specific UE among a UE group or adjacent UEs. For example, a
UE that determines and feeds back a shared beam direction may be
autonomously determined via cooperation between UEs, a UE (e.g., a
representative UE or a header UE) determined by an eNB, or a
specific type of UE (e.g., a UE according to existing LTE/LTE-A
standard).
[0114] The shared beam direction may be determined by a beam
direction selected by most UEs from shared preferred beam direction
information of each user.
[0115] Feedback of determined shared beam information may be set to
perform corresponding feedback by only some UEs (e.g., a
representative UE or a header UE) in a group, thereby reducing
overhead in terms of a system.
[0116] The determined shared beam information may be transmitted to
the eNB through a PUCCH signal (e.g., refer to FIG. 5). In this
case, UEs that do not feedback the determined shared beam
information may overhear a PUCCH signal between the eNB and a
representative UE or a header UE using lastly determined shared
beam information or the representative UE or the header UE may
broadcast/multicast the determined shared beam information to other
UEs to acquire the determined shared beam information.
[0117] In the present specification, overhearing may refer to
reception and/or acquisition of UE-specific information (e.g.,
uplink control information (UCI)) of another UE by a specific UE.
In more detail, overhearing may include acquiring scrambling
information for control information of another UE by a specific UE
and decoding and/or acquiring the control information of the other
UE using the acquired scrambling information. For example, a
specific UE may acquire identification information (e.g., C-RNTI)
of another UE via overhearing and, then, may decode and/or acquire
the control information (e.g., preferred beam information) of the
other UE using the acquired identification information (e.g.,
C-RNTI). In the present specification, scrambling information may
not be limited only to C-RNTI information and other information may
be used.
[0118] A plurality of candidate beam directions as a shared beam
direction may be inducted via cooperation between UEs and a lastly
shared beam direction may be determined by an eNB. In this case,
the eNB may or may not notify UEs in a group about information
about the determined shared beam thereof.
[0119] Referring back to FIG. 6, as an example of shared beam
determination and a feedback procedure in operation 1 according to
the present invention, the first UE (UE1) and the second UE (UE2)
may be determined as a UE group or adjacent UEs. In the example of
FIG. 6, the first UE (UE1) may select beam #1 to beam #5 as a
preferred beam (direction) and the second UE (UE2) may select beam
#5 to beam #16 as a preferred beam (direction). Each UE (UE1 and
UE2) may broadcast/multicast preferred beam information thereof or
transmit the preferred beam information thereof to a representative
UE. In this case, preferred beam information of a first UE may
include at least one of information about the number (e.g., 5) of
preferred beams, information indicating a preferred beam (e.g.,
beam #1 to beam #5), or information indicating priority between
preferred beams and preferred beam information of a second UE may
include at least one of information about the number (e.g., 12) of
preferred beams, information indicating a preferred beam (e.g.,
beam #5 to beam #16), or information indicating priority between
preferred beams.
[0120] In an example of FIG. 6, when the first UE (UE1) is
determined as a representative UE or a header UE, the first UE
(UE1) may broadcast/multicast preferred beam information thereof or
may not transmit the preferred beam information to the second UE
(UE2). The first UE (UE1) may receive preferred beam information
from the second UE (UE2), may recognize that the second UE (UE2)
prefers beam #5 to beam #16, may check whether the preferred beam
direction thereof overlaps the preferred beam information of the
second UE (UE2), and may lastly determine a shared beam direction
between two UEs as beam #5. This is merely an example of beam
direction selection and is not limited to a share beam selection
scheme.
[0121] In the example of FIG. 6, the first UE (UE1) may transmit
information about the determined beam (e.g., beam #5) to the eNB
through a PUCCH signal. In addition, the first UE (UE1) may
transmit information about the determined shared beam (e.g., beam
#5) to the second UE (UE2) that is not a representative UE or a
header UE to share information about the determined shared beam
(e.g., beam #5) or the second UE (UE2) may overhear a PUCCH signal
transmitted by the first UE to acquire information about the
determined shared beam (e.g., beam #5).
[0122] Although FIG. 6 illustrates that one beam (e.g., beam #5) is
a preferred beam common between the first UE (UE1) and the second
UE (UE2), a plurality of beams may be common. In this case, a
representative UE or a header UE (e.g., a first UE or UE1) may
transmit information about a plurality of candidate beams
corresponding to a plurality of common beams to an eNB. In this
case, a shared beam may be determined by the eNB among a plurality
of candidate beams or the determined shared beam may or may not be
shared by the first UE (UE1) and the second UE (UE2). An operation
when the determined shared beam is or is not shared by the first UE
(UE1) and the second UE (UE2) will be described below in detail. A
plurality of candidate beam information items may be induced by a
first UE (or a representative UE or a header) based on preferred
beam information received from a second UE or may be induced via
cooperation between the first UE and the second UE.
[0123] Alternatively, differently from the aforementioned case, the
first UE (UE1) and the second UE (UE2) may not share preferred beam
information and may transmit preferred beam information to the eNB
and, then, the eNB may determine a shared beam.
[0124] Operation 2: Determine UE-Dedicated Beam
[0125] Each UE may select a UE-dedicated beam direction preferred
thereby among remaining beam directions except for a shared beam
direction based on the shared beam information acquired in
operation 1 according to the present invention and may feedback
information about the UE-dedicated beam to the eNB. The information
about the UE-dedicated beam may be transmitted to the eNB through a
PUCCH signal (e.g., refer to FIG. 5) and may include precoder
information, precoding matrix index information, or the like
corresponding to the UE-dedicated beam.
[0126] A plurality of candidate beam directions as a shared beam
direction may be induced via cooperation between UEs and, when a
lastly shared beam direction is determined by the eNB, each UE may
determine a UE-dedicated beam direction using the following two
methods. [0127] When an eNB notifies UEs in a group about lastly
determined shared beam information by transmitting the information:
a UE may determine a UE-dedicated beam direction among all
remaining beam directions except for a lastly determined shared
beam direction. [0128] When an eNB does not notify UEs in a group
or adjacent UEs about lastly shared beam information: UEs knows
only a candidate set of a plurality of shared beams induced via
cooperation between the UEs and, thus, each UE may select a
UE-dedicated beam direction among remaining beam directions except
for all beam directions corresponding to a shared beam candidate
set from all beam directions.
[0129] The eNB may receive UE-dedicated beam information from each
UE and, then, may transmit UE-common data through a shared beam
and, simultaneously, may transmit UE-specific data through a
UE-dedicated beam. In the present specification, UE-common data
transmitted/received through a shared beam may refer to a signal
transmitted/received through a broadcast/multicast channel and, for
example, may be one of a physical broadcast channel (PBCH) and a
physical multicast channel (PMCH). The UE-specific data may refer
to a signal transmitted/received through a channel allocated for a
specific UE and, for example, a channel allocated for a specific UE
may be a physical downlink shared channel (PDSCH).
[0130] Referring back to FIG. 6, an example of UE-dedicated beam
determination and a feedback procedure in operation 2 according to
the present invention, the first UE (UE1) and the second UE (UE2)
may determine a UE-dedicated beam direction among preferred beam
directions thereof. Assuming that beam #5 is determined as a shared
beam in the above case, the first UE (UE1) may determine a
preferred UE-dedicated beam direction among remaining beam
directions (e.g., beam #1 to beam #4) except for a shared beam
(e.g., beam #5) from preferred beam directions thereof (e.g., beam
#1 to beam #5) and the second UE (UE2) may determine a preferred
UE-dedicated beam direction among remaining beam directions (e.g.,
beam #6 to beam #16) except for a shared beam (e.g., beam #5) from
preferred beam directions thereof (e.g., beam #5 to beam #16).
[0131] Referring back to FIG. 6, in operation 2, the first UE (UE1)
may determine beam #4 that is not a shared beam (e.g., beam #5) as
a preferred UE-dedicated beam thereof and may transmit information
indicating beam #4 to the eNB. The second UE (UE2) may determine
beam #11 that is not a shared beam (e.g., beam #5) as a preferred
UE-dedicated beam thereof and may transmit information indicating
beam #11 to the eNB. The eNB may unicast/broadcast/multicast common
data to the first UE (UE1) and the second UE (UE2) through the
shared beam received or determined in operation 1 and,
simultaneously, may unicast specific data to the first UE (UE1) or
the second UE (UE2) through the dedicated beam received in
operation 2.
[0132] According to the present invention, when a method of
designing a precoder based on cooperation between users for
multiuser/multiple stream downlink transmission via sharing of a
beam between users is applied, there is a difference from a
conventional method. [0133] An eNB may receive a plurality of
preferred beam information items with respect to respective
separate UEs. Accordingly, a preferred shared beam (transmission of
common information to UEs in a group) and preferred UE-dedicated
beam (transmission of UE-specific information) may be set for each
UE. In a conventional method, an eNB may receive one preferred beam
information item from each UE and may set one beam for a
corresponding UE based on the information. On the other hand,
according to the present invention, different types of information
items are capable of being simultaneously transmitted through a
plurality of UEs set for respective UEs and, accordingly,
transmission efficiency may be advantageously enhanced. [0134] When
each UE selects a preferred beam to transmit a data stream thereof,
a preferred beam direction thereof may be determined among
remaining beam directions except for the above shared beam
determined via cooperation between UEs. Accordingly, a UE-dedicated
beam and a shared beam for a corresponding UE may be prevented from
being set to be superposed and setting of different beams may be
ensured. When the shared beam and the UE-dedicated beam are set to
be superposed, interference may occur and data transmission
efficiency may also be lowered.
[0135] FIG. 7 is a flowchart according to the present invention.
The flowchart of FIG. 7 is a non-limited example, some operations
may be omitted, and other operations that are not shown in FIG. 7
may be added.
[0136] Referring to FIG. 7, in operation S702, a UE may acquire
information about a shared beam to be shared by UEs in a group and
adjacent UEs. Operation S702 may be performed by the operations of
a UE and/or an eNB described with regard to operation 1 according
to the present invention or may include performing the operations
of a UE and/or an eNB described with regard to operation 1.
[0137] For example, in operation S702, when a UE is a
representative UE or a header UE, the UE may receive information
about a preferred beam from UEs in a group or adjacent UEs and
determine at least one shared beam based on the received
information about the preferred beam. The received information
about the preferred beam may include at least one of information
about the number of preferred beam directions of UEs in a group or
adjacent UEs, information about at least one preferred beam of
another UE that is not the above UE, or information indicating
priority of the at least one preferred beam.
[0138] The information about the group to which the UE belongs or
the adjacent UEs may be received from the eNB and may include
information indicating a representative UE or a header UE among UEs
in a group or adjacent UEs and information indicating one or more
member UEs. In this case, the information may indicate that the UE
is a representative UE or a header UE.
[0139] In operation S702, when a UE is a representative UE or a
header UE, the UE may transmit information about the at least one
determined shared beam to the eNB. The information about the at
least one shared beam transmitted to the eNB may include precoding
matrix index (PMI) information. As described above, when the UE
determines a plurality of shared beams and transmits the determined
shared beams to the eNB, the shared beam may be determined by the
eNB and may or may not be shared by UEs.
[0140] As another example, in operation S702, when a UE is not a
representative UE or a header UE (or when the UE is a member UE),
the UE may determine at least one preferred beam thereof and
unicast or broadcast/multicast information about the determined at
least one preferred beam to a representative UE or a header UE. In
addition, the UE may overhear information about the determined at
least one shared beam by a representative UE or a header UE,
receive the information via direct communication (or D2D
communication) between UEs from a representative UE or a header UE,
or receive or acquire the information from the eNB.
[0141] Operations S704 and S706 may be performed by the operations
of a UE and/or an eNB described with regard to operation 2
according to the present invention or may include performing the
operations of a UE and/or an eNB described with regard to operation
2.
[0142] For example, in operation S704, the UE may determine a
dedicated beam thereof based on the information about at least one
shared beam acquired in operation S702 and transmit the determined
information about the dedicated beam to the eNB.
[0143] In operation S706, the eNB may transmit
(unicast/broadcast/multicast) UE-common data based on the
information about the at least one shared beam received in
operation S702 and transmit (unicast) specific data to a
corresponding UE based on the information about the dedicated beam
of a specific UE received in operation S704. In detail, the eNB may
transmit UE-common data corresponding to the shared beam
information and transmit UE-specific data in a beam direction
corresponding dedicated beam information. In this case, the eNB may
simultaneously transmit UE-common data and UE-specific data.
Simultaneous transmission may refer to transmission in the same
time interval (e.g., a subframe in the case of an LTE/LTE-A
system). Through a plurality of beamforming operations performed by
the eNB, the UE may simultaneously receive UE-common data that is
common to UEs in a group or adjacent UEs and UE-specific data
thereof.
[0144] In operation S706, the UE-common data may be
transmitted/received through a physical broadcast channel (PBCH) or
a physical multicast channel (PMCH) and the UE-specific data may be
transmitted/received through a physical downlink shared channel
(PDSCH). For beamforming in a wireless communication system, a
plurality of antenna ports (a physical antenna ports or a virtual
antenna port) may be determined, a first antenna port may be
dedicatedly determined to transmit a shared beam among the
plurality of antenna ports, and a second antenna port may be
dedicatedly determined to transmit a dedicated beam. In this case,
the UE-common data may be transmitted/received to and from the
first antenna port specific to a shared beam and the UE-specific
data may be transmitted/received to and from the second antenna
port specific to a dedicated beam.
[0145] In the specification, although the methods according to the
present invention have been described in terms of multi-vehicle
communication, the present invention is not limited thereto and may
be applied in the same way to a general multiuser multi antenna
system situation. Thus, the present invention may be applicable to
a UE other than a vehicle in the same or similar manner.
[0146] FIG. 8 is a diagram illustrating a BS 110 and a UE 120 to
which the present invention is applicable.
[0147] Referring to FIG. 8, a wireless communication system
includes the BS 110 and the UE 120. When the wireless communication
system includes a relay, the BS 110 or the UE 120 can be replaced
with the relay.
[0148] The BS 110 includes a processor 112, a memory 114, and a
radio frequency (RF) unit 116. The processor 112 may be configured
to embody the procedures and/or methods proposed by the present
invention. The memory 114 is connected to the processor 112 and
stores various pieces of information associated with an operation
of the processor 112. The RF unit 116 is connected to the processor
112 and transmits/receives a radio signal. The UE 120 includes a
process 122, a memory 124, and an RF unit 126. The processor 122
may be configured to embody the procedures and/or methods proposed
by the present invention. The memory 124 is connected to the
processor 122 and stores various pieces of information associated
with an operation of the processor 122. The RF unit 126 is
connected to the processor 122 and transmits/receives a radio
signal.
[0149] The embodiments of the present invention described above are
combinations of elements and features of the present invention. The
elements or features may be considered selective unless otherwise
mentioned. Each element or feature may be practiced without being
combined with other elements or features. Further, an embodiment of
the present invention may be constructed by combining parts of the
elements and/or features. Operation orders described in embodiments
of the present invention may be rearranged. Some constructions of
any one embodiment may be included in another embodiment and may be
replaced with corresponding constructions of another embodiment. It
is obvious to those skilled in the art that claims that are not
explicitly cited in each other in the appended claims may be
presented in combination as an embodiment of the present invention
or included as a new claim by a subsequent amendment after the
application is filed.
[0150] Specific operations to be conducted by the base station in
the present invention may also be conducted by an upper node of the
base station as necessary. In other words, it will be obvious to
those skilled in the art that various operations for enabling the
base station to communicate with the terminal in a network composed
of several network nodes including the base station will be
conducted by the base station or other network nodes other than the
base station. The term "base station (BS)" may be replaced with a
fixed station, Node-B, eNode-B (eNB), or an access point as
necessary. The term "terminal" may also be replaced with a user
equipment (UE), a mobile station (MS) or a mobile subscriber
station (MSS) as necessary.
[0151] The embodiments of the present invention may be achieved by
various means, for example, hardware, firmware, software, or a
combination thereof. In a hardware configuration, an embodiment of
the present invention may be achieved by one or more application
specific integrated circuits (ASICs), digital signal processors
(DSPs), digital signal processing devices (DSDPs), programmable
logic devices (PLDs), field programmable gate arrays (FPGAs),
processors, controllers, microcontrollers, microprocessors,
etc.
[0152] In a firmware or software configuration, an embodiment of
the present invention may be implemented in the form of a module, a
procedure, a function, etc. Software code may be stored in a memory
unit and executed by a processor. The memory unit is located at the
interior or exterior of the processor and may transmit and receive
data to and from the processor via various known means.
[0153] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the scope of the invention. Thus, it is
intended that the present invention cover the modifications and
variations of this invention provided they come within the scope of
the appended claims and their equivalents.
INDUSTRIAL APPLICABILITY
[0154] The present invention is applicable to a wireless
communication apparatus such as a user equipment (UE), a base
station (BS), etc.
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