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Description
Title of Invention: METHOD FOR INDICATING A DM-RS
ANTENNA PORT IN A WIRELESS COMMUNICATION
SYSTEM
Technical Field
Hi The present invention relates generally to wireless communications
and, in particular,
to a method for transmitting a Channel State Information Reference Signal (CSI-
RS)
for a User Equipment (UE) to measure channel quality in a wireless
communication
system based on a multi-carrier multiple access scheme such as Orthogonal
Frequency
Division Multiple Access (OFDMA).
Background Art
[2] Mobile communication systems, which were originally designed for
providing voice-
based services, have developed to wireless packet data communication systems
that
provide high speed, high quality wireless data and multimedia services.
Technology
standardization organizations such as 3rd Generation Project Partnership
(3GPP),
3GPP2, and Institute of Electrical and Electronics Engineers (IEEE) are
working to
improve the beyond-3G communication technologies based on various multi-
carrier
multiple access schemes. For example, 3GPP Long Term Evolution (LTE), the
3GPP2
Ultra Mobile Broadband (UMB), and the IEEE 802.16m are mobile communication
technology standards based on the multi-carrier multiple access schemes for
supporting
high speed high quality wireless packet data transmission services.
1131 Evolved 3G communication systems, such as LTE, UMB, and 802.16m, based
on the
multi-carrier multiple access scheme various techniques including Multiple
Input
Multiple Output (MIMO) beamforming, Adaptive Modulation and Coding (AMC), and
channel sensitive scheduling for improving transmission efficiency. These
techniques
improve system throughput by concentrating the transmit power of multiple
antenna or
adjusting the transmit data amount and transmitting data first to the user
having good
channel quality. Because these techniques operate based on channel quality in-
formation between a base station (i.e., evolved Node B (eNB)) and a mobile
station
(i.e., User Equipment (UE)), the eNB or the UE measures the channel quality,
and a
CSI-RS is used for this purpose.
[4] Time, frequency, and power resources are limited in a mobile
communication
system. Accordingly, as resources allocated for a reference signal increase, a
traffic
channel resource decreases, thereby reducing the amount of data that can be
transmitted. In such a case, channel measurement and estimation performance is
improved, but the system throughput decreases.
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1151 Accordingly, there is a for efficient resource allocation for
transmission of the
reference signals and traffic channels in order to secure optimum performance
in view
of system throughput.
[6] In the evolved 3rd generation mobile communication system standards,
reference
signals are categorized into two categories: Common Reference Signal (CRS) and
Dedicated Reference Signal (DRS). A CRS is often referred to as a cell-
specific RS or
a Common RS in a 3GPP LTE system, and is received by all the UEs within the
cell of
an eNB. In order to support channel estimation and measurement for
transmission with
multiple transmit antennas, several reference signal patterns are defined for
distinction
between antenna ports.
1171 A DRS is an additional reference signal that is transmitted separately
from the CRS
and is transmitted to a specific UE selected by the eNB. The DRS is also
referred to as
a UE-specific RS in the 3GPP LTE system and is used for supporting the data
traffic
channel transmission with non-codebook based precoding.
1181 In LTE-Advanced (LTE-A), which evolved from LTE, a DeModulation
Reference
Signal (DM-RS) is used for supporting channel estimation of up to 8 layers, in
addition
to the CRS and DRS. Similar to the DRS, the DM-RS is transmitted in a UE-
specific
manner, apart from the transmission of CRS.
1191 In the LTE-A system, the downlink signal is transmitted with OFDMA
transmission
scheme utilizing both frequency and time domains. The downlink frequency band
is
divided into a plurality of Resource Blocks (RBs), each including 12
subcarriers in a
frequency domain, and subframes of which, each including 14 OFDM symbols in a
time domain. The eNB performs transmission in a unit of radio resources
composed of
one or more RBs in a frequency domain and in a subframe in time domain. The
resource unit defined by one subcarrier for one OFDM symbol duration is
referred to
as a Resource Element (RE).
[10] In a Single User-Multiple Input Multiple Output (SU-MIMO) mode or a
Multi User-
Multiple Input Multiple Output (MU-MIMO) mode, transmission can be performed
using multiple layers. For multi-layer transmission, the DM-RS resource is
allocated
for each layer. The DM-RS resource allocated for channel estimation of one
layer is
referred to as a DM-RS port in the LTE-A system. Herein, the term DM-RS
resource is
used interchangeably with DM-RS port.
[11] FIG. 1 illustrates DM-RS patterns designed for use in an LTE-A system.
[12] Referring to FIG. 1, reference number 100 denotes a rank 2 DM-RS
pattern in which
an eNB transmits DM-RSs for two layers. When transmitting two DM-RSs in the
rank
2 DM-RS pattern as illustrated in FIG. 1, the DM-RSs are orthogonally spread
with
spread factor 2 at positions 101 and 102 and then transmitted in a Code
Division Mul-
tiplexing (CDM) group. In a similar manner, the orthogonally spread DM-RSs are
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transmitted at positions 103 and 104. In FIG. 1, the consecutive blue-colored
REs carry
the DM-RSs. Accordingly, the DM-RSs of two DM-RS antenna ports are Code-
Division Multiplexed (CDMed) on the same frequency and time resource.
[13] In FIG. 1, reference number 110 denotes a rank 4 DM-RS pattern in
which the eNB
transmits DM-RSs for four layers. The rank 4 DM-RS pattern is also spread the
DM-
RSs with the same spread factor 2 as the rank 2 DM-RS pattern 100, except that
ad-
ditional REs are used for the four DM-RS antenna ports. Accordingly, the rank
4 DM-
RS pattern 110 has twice as many REs for DM-RSs as compared to the rank 2 DM-
RS
pattern 100.
[14] In FIG. 1, reference number 120 denotes a rank 8 DM-RS pattern in
which the eNB
transmits DM-RSs for eight layers. The rank 8 DM-RS pattern 120 uses the same
number of REs as the rank 4 DM-RS pattern 110 for DM-RS transmission. In order
to
transmit the DM-RSs for eight DM-RS antenna ports with the number of REs same
as
the rank 4 DM-RS pattern 110, the rank 8 DM-RS pattern 120 orthogonally
spreads the
DM-RSs with a spread factor 4 at the positions 105, 106, 107, and 108.
Disclosure of Invention
Technical Problem
[15] In an LTE-A system, the rank of the signal transmitted by the eNB
varies depending
on a state of the downlink channel. Because the rank of the transmit signal of
the eNB
varies, the DM-RS pattern also changes depending on the signal rank. That is,
the eNB
can use the rank 8 DM-RS pattern 120 for the layers having a large number of
channels
and the rank 2 DM-RS pattern 100 for the layers having a small number of
channels.
As described above, because the DM-RS pattern is time-varying and the DM-RS
port
allocated to a UE may also vary, the eNB should notify the corresponding UE of
the
DM-RS pattern and the DM-RS antenna port to modulate the correct downlink
traffic
channel.
[16] When the three DM-RS patterns of FIG. 1 are available and a maximum of
8 DM-RS
antenna ports are supported, the eNB can notify the UE of DM-RS information
using
two bits indicating the DM-RS pattern and eight bits indicating the DM-RS
antenna
port in the form of bit map. That is, in order to notify a UE of the DM-RS
resource, a
total of 10 bits are used. Assuming that a rank 2 DM-RS pattern, a rank 4 DM-
RS
pattern, and a rank 8 DM-RS pattern are indicated by 00, 01, and 02,
respectively, the
eNB can notify the UE that DM-RS antenna ports 1 and 2 are allocated in the
rank 4
DM-RS pattern by transmitting the information of 01 and 01100000.
[17] However, using 10 bits of information to notify the UE of the
allocated DM-RS
resource is relatively redundant, thereby reducing downlink system throughput.
[18] Another problem of the above-described method is that the UE cannot
acquire the
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DM-RS antenna port information for other UEs. That is, the UE can only acquire
its
own DM-RS antenna port information.
[19] In a wireless communication system supporting MU-MIMO downlink
transmission
such as an LTE-A system, if transmissions for other UEs on a same
time/frequency
resource allocated to a specific UE are known, it is possible to implement
efficient
reception algorithm for the UE. For a receiver operating based on a Minimum
Mean
Square Error (MMSE), the received determines strength of interference for
achieving
optimum performance. Further, in order to measure the strength of the
interference ac-
curately, the receiver first determines whether or not there is interference.
However,
the above-described DM-RS resource notification does not provide the UE with
any in-
terference-related information.
[20] Accordingly, there is a need to provide a UE with information on
whether other UE
transmissions are causing interference, in addition to efficient DM-RS
resource noti-
fication.
[21] In an LTE-A system, an eNB can assign up to 8 DM-RS antenna ports to a
single
UE. Each antenna port allows channel estimation for one of multiple layers of
MIMO
transmission of the eNB. The eNB notifies the UE of the allocated DM-RS
antenna
port using Physical Downlink Control Channel (PDCCH) designed to transmit
control
information. Because the DM-RS antenna port allocation is required for each
layer
when the eNB performs MIMO transmission, it is closely related to the MIMO
transmission scheme of the eNB. That is, for MIMO transmission for three
layers, the
eNB transmits the control information on the three DM-RS antenna ports to one
or
more UEs.
Solution to Problem
[22] The present invention has been made in view of at least the above-
described
problems, and provides a method for transmitting, to a UE, DM-RS resource in-
formation for receiving downlink traffic in an LTE-A system that informs the
UE of
DM-RS resources allocated for other UEs in a same frequency/time resource.
[23] In accordance with an aspect of the present invention, a control
information inter-
pretation method of a terminal in a mobile communication system is provided.
The
method includes receiving control information including transport block
information
and DM-RS antenna port allocation indication information, checking a number of
transport blocks allocated to the terminal, based on the transport block
information,
and interpreting the DM-RS antenna port allocation indication information
according
to the number of transport blocks.
[24] In accordance with another aspect of the present invention, a control
information
transmission method of a base station in a mobile communication system is
provided.
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The method includes checking a number of transport blocks allocated to a
terminal, selecting
DM-RS antenna port allocation indication information according to the number
of transport
blocks, generating control information including transport block information
and selected
DM-RS antenna port allocation indication information, and transmitting the
control
5 information to the terminal.
[25] In accordance with another aspect of the present invention, a terminal
for interpreting
control information received from a base station in a mobile communication
system is
provided. The terminal includes a radio communication unit that receives
control information
including transport block information and DM-RS antenna port allocation
indication
information, and a controller that checks a number of transport blocks
allocated to the
terminal based on the transport block information, and interprets the DM-RS
antenna port
allocation indication information according to the number of transport blocks.
[26] In accordance with another aspect of the present invention, a base
station for
transmitting control information in a mobile communication system is provided.
The base
station includes a controller that checks a number of transport blocks
allocated to a terminal,
selects DM-RS antenna port allocation indication information according to the
number of
transport bocks, and generates control information including transport block
information and
selected DM-RS antenna port allocation indication information. The base
station also
includes a radio communication unit that transmits the control information to
the terminal.
[26a] According to one aspect of the present invention, there is provided a
method of a
terminal in a mobile communication system, the method comprising: receiving,
by the
terminal, control information including transport block information and
Reference Signal (RS)
antenna port allocation indication information that indicates up to eight
antenna ports;
checking a number of transport blocks allocated to the terminal based on the
transport block
information; and determining at least one RS antenna port, scrambling identity
and a number
of layers by interpreting the RS antenna port allocation indication
information according to
the number of transport blocks allocated to the terminal, wherein the RS
antenna port
allocation indication information is used for data demodulation.
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[26b] According to another aspect of the present invention, there is provided
a control
information transmission method of a base station in a mobile communication
system, the
method comprising: checking, by the base station, a number of transport blocks
allocated to a
terminal; selecting Reference Signal (RS) antenna port allocation indication
information that
indicates up to eight antenna ports according to the number of transport
blocks allocated to the
terminal; generating control information including transport block information
indicating the
number of transport blocks and the RS antenna port allocation indication
information; and
transmitting the control information to the terminal, wherein the RS antenna
port allocation
indication information is used for data demodulation.
[26c] According to still another aspect of the present invention, there is
provided a terminal
in a mobile communication system, the terminal comprising: a radio
communication unit that
receives control information including transport block information and
Reference Signal (RS)
antenna port allocation indication information that indicates up to eight
antenna ports; and a
controller that checks a number of transport blocks allocated to the terminal
based on
transport block information, and determines at least one RS antenna port,
scrambling identity
and a number of layers by interpreting the RS antenna port allocation
indication information
according to the number of transport blocks allocated to the terminal, wherein
the RS antenna
port allocation indication information is used for data demodulation.
[26d] According to yet another aspect of the present invention, there is
provided a base
station for transmitting control information in a mobile communication system,
the base
station comprising: a controller that checks a number of transport blocks
allocated to a
terminal, selects-Reference Signal (RS) antenna port allocation indication
information that
indicates up to eight antenna ports according to the number of transport
blocks allocated to the
terminal, and generates control information including transport block
information indicating
the number of transport blocks and the RS antenna port allocation indication
information; and
a radio communication unit that transmits the control information to the
terminal, wherein the
RS antenna port allocation indication information is used for data
demodulation.
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Advantageous Effects of Invention
[27] The DM-RS antenna port indication method of the present invention is
capable of
efficiently notifying a UE of the DM-RS resource allocation information for
receiving the
downlink traffic signal along with the information on the DM-RS resources
allocated for other
UEs in a same frequency/time resources in an LTE-A system, thereby improving
system
performance.
Brief Description of Drawings
[28] The above and other aspects, features, and advantages of certain
embodiments of the
present invention will be more apparent from the following detailed
description in conjunction
with the accompanying drawings, in which:
[29] FIG. 1 is a diagram illustrating conventional DM-RS patterns designed for
use in an
LTE-A system;
[30] FIG. 2 is a diagram illustrating control information carried on a PDCCH
for use in an
LTE-A system according to an embodiment of the present invention;
[31] FIG. 3 is a flowchart illustrating a method for an eNB to notify a UE of
DM-RS
antenna ports allocated to the UE and other UEs scheduled in a same
frequency/time
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resource according to an embodiment of the present invention;
[32] FIG. 4 is a flowchart illustrating a method for a UE to determine DM-
RS antenna
ports allocated to the UE and other UEs scheduled in a same frequency/time
resource
based on a DM-RS antenna port allocation index transmitted by an eNB according
to
an embodiment of the present invention;
[33] FIG. 5 is a diagram illustrating a DM-RS pattern designed for
distinguishing among
DM-RS antenna ports in an MU-MIMO transmission using 3 or 4 transmission
layers
by using two scrambling sequences according to an embodiment of the present
invention;
[34] FIG. 6 is diagram illustrating control information carried on a PDCCH
for use in an
LTE-A system according to an embodiment of the present invention;
[35] FIGs. 7A and 7B are a flowchart illustrating a method for an eNB to
notify a UE of
DM-RS antenna port allocation and interference-related information according
to an
embodiment of the present invention;
[36] FIGs. 8A and 8B are a flowchart illustrating a method for a UE to
determine DM-RS
antenna ports allocated to the UE and other UEs scheduled in a same
frequency/time
resource based on a DM-RS antenna port allocation index and an SU/MU-MIMO
indicator transmitted by an eNB according to an embodiment of the present
invention;
[37] FIG. 9 is a flowchart illustrating a method for allocating DM-RS
antenna ports
according to an embodiment of the present invention;
[38] FIG. 10 is a flowchart illustrating a method for acquiring information
on allocated
DM-RS antenna ports according to an embodiment of the present invention;
[39] FIG. 11 is a diagram illustrating control information carried on a
PDCCH for use in
an LTE-A system according to an embodiment of the present invention;
[40] FIG. 12 is a flowchart illustrating a procedure for notifying of
whether transmit
diversity is applied with a New Data Indicator (NDI) bit for a transport block
according to an embodiment of the present invention;
[41] FIG. 13 is a flowchart illustrating a procedure for notifying of
whether a current
transmission is an initial transmission or a retransmission and whether
transmit
diversity is applied or not with an NDI bit for a transport block according to
an em-
bodiment of the present invention; and
[42] FIG. 14 is a flowchart illustrating a procedure for notifying of
whether synchronous
HARQ is applied or not with an NDI bit for a transport block according to an
em-
bodiment of the present invention.
Mode for the Invention
[43] Various embodiments of the present invention are described with
reference to the ac-
companying drawings in detail. The same reference numbers are used throughout
the
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drawings to refer to the same or like parts. Additionally, detailed
descriptions of well-
known functions and structures incorporated herein may be omitted to avoid
obscuring
the subject matter of the present invention.
[44]
[45] In an LTE-A system, there are two MIMO cases: (1) an SU-MIMO case in
which an
eNB allocates transmission layers to a single UE; and (2) an MU-MIMO case in
which
the eNB allocates the transmission layers to two or more UEs. In the SU-MIMO
case,
a UE can be allocated 1, 2, 3, 4, 5, 6, 7, or 8 transmission layers. That is,
the eNB can
allocate up to 8 DM-RS antenna ports according to its determination in the SU-
MIMO
case.
[46]
[47] However, the MU-MIMO case is implemented under the restrictions in
consideration
of implementation complexity.
[48] 1. The MU-MIMO can support transmission to up to four UEs on the same
frequency/time resource
[49] 2. The MU-MIMO can allocate up to 2 layers to a single UE.
[50] 3. The MU-MIMO can support transmission for up to 4 layers on the same
frequency/time resource. That is, it is possible for allocating one layer for
each of four
UEs or two layers for each of two UEs but two layers for each of three UEs.
[51] The SU-MIMO and MU-MIMO can change per frequency bandwidth in units of
a
subframe (1 msec) according to the determination of the eNB. In the LTE-A
system,
the restriction of up to 4 layers for eNB transmission can be substituted for
4
composite ranks of MU-MIMO.
[52]
[53] One of the restrictions relevant to MIMO transmission shared by the
LTE-A and LTE
systems is that only one transport block can be transmitted on a layer. Here,
the
transport block in a unit of the transmitted traffic information is
transferred from the
upper layer of the LTE or LTE-A system to the physical layer so as to be
encoded and
modulated. In the LTE or LTE-A system, the eNB can transmit up to two
transport
blocks to one UE using a same frequency/time resource. When transmitting one
transport block, the transport block is transmitted to the corresponding UE on
a single
layer; however, at least two layers are used to transmit two transport blocks.
[54]
[55] Considering restrictive conditions for allocating layers in MU-MIMO
and SU-MIMO
cases and the fact that the two transport blocks are transmitted on two or
more layers,
in accordance with an embodiment of the present invention, a method is
proposed for
minimizing control information used to notify a UE of DM-RS antenna ports
allocated
to the UE. Also, in accordance with another embodiment of the present
invention, a
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method is proposed for an eNB to notify a UE as to whether a signal received
by the
UE is a part of the MU-MIMO signal or the SU-MIMO signal dedicated to the UE.
When the received signal is a part of the MU-MIMO signal, information on DM-RS
antenna ports allocated to other UEs are notified such that the UE can measure
and
cancel interference components.
[56]
[57] In accordance with an embodiment of the present invention, DM-RS
antenna port no-
tification is performed using information on a DM-RS antenna port and
transport
blocks that are already used in the LTE and LTE-A systems. As described above,
two
transport blocks can always be transmitted on two or more layers. Also, one
transport
block is always transmitted on a single layer. When the eNB transmits the
traffic
channel, i.e. a PDSCH, in the LTE and LTE-A system, the PDCCH is configured to
carry control information notifying a UE as to whether a number of transport
blocks is
1 or 2. In accordance with an embodiment of the present invention, a UE is
notified of
DM-RS antenna ports using minimum control information by using transport block
in-
formation and DM-RS antenna port allocation information.
[58]
[59] FIG. 2 is a diagram illustrating control information carried on a
PDCCH for use in an
LTE-A system according to an embodiment of the present invention.
[60]
[61] Referring to FIG. 2, reference number 230 denotes DM-RS antenna port
indication
information (hereinafter, interchangeably referred to as a DM-RS resource
indicator),
which is a part of the control information transmitted on the PDCCH. When the
PDCCH is received, the UE analyzes the DM-RS antenna port indication control
in-
formation 230 by referencing the transport block 0 control information 210 and
the
transport block 1 control information 220. The transport block 0 control
information
210 includes information on whether the corresponding transport block is
transmitted
and, if it is, the size of the transport block. The transport block 1 control
information
220 includes information on whether the corresponding transport block is
transmitted
and, if it is, the size of the transport block. An eNB can notify the UE of
the transport
blocks to be transmitted, i.e., one or both of the transport block 0 and
transport block 1.
The control information on transport blocks 0 and 1, as denoted by reference
number
210 and 220 of FIG. 2, which has been used in the legacy LTE system, is also
used in
the LTE-A system. In accordance with an embodiment of the present invention, a
method is proposed for indicating DM-RS antenna port with a minimum number of
bits by using the transport block control information 210 and 220 and the DM-
RS
resource indication information 230.
[62]
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[63] Table 1, below, shows indices indicating DM-RS antenna port allocation
and
messages describing the meanings of the indices according to an embodiment of
the
present invention.
[64]
[65] The DM-RS antenna port allocation for MIMO transmission is notified as
follows:
[66]
[67] <system characteristics 1>
[68] 1. SU-MIMO transmission for 1-8 layers
[69] 2. MU-MIMO transmission for up to 2 layers allocated to a UE
[70] 3. MU-MIMO transmission to up to 4 UEs
[71] 4. MU-MIMO transmission for up to 4 layers (maximum composite rank of
MU-
MIMO is 4).
[72]
[73] When an eNB notifies a scheduled UE of an allocated DM-RS antenna port
for use in
an MU-MIMO transmission, the eNB also provides information on DM-RS antenna
ports allocated to other UEs that may transmit signals causing interference on
a same
time/frequency resource.
[74]
[75] According to an embodiment of the present invention, an eNB determines
different
DM-RS resource allocation schemes with DM-RS resource indicators according to
the
transport block(s) to be used, as shown in Table 1.
[76]
[77] Accordingly, the UE interprets the index transmitted by the UE
depending on the
transport block to be transmitted, i.e., transport block 0, transport block 1,
or transport
blocks 0 and 1. For example, if the eNB transmits an index value of 3 to a UE,
the
meaning of the index value can be interpreted by the UE differently depending
on the
settings of the transport block control information 210 and 220. Assuming that
the
transport block control information 210 and 220 are set such that only the
transport
block 1 is transmitted, the UE recognizes that the DM-RS antenna port 3 in the
rank 4
DM-RS pattern 110 of FIG. 1 is allocated to the UE and the DM-RS antenna ports
0, 1,
and 2 are allocated to other UEs for MU-MIMO transmission. That is, the UE can
acquire the information on the DM-RS antenna ports allocated to other UEs that
are
potentially causing interference, as well as the information on the DM-RS
antenna port
allocated to the UE itself, thereby efficiently mitigating interference.
[78]
[79] In order to allocate DM-RS antenna ports based on Table 1, 4 bits are
used for
identifying up to 10 indices of each transport block transmission, as shown in
Table 1.
When using Table 1, the DM-RS antenna port allocation and interference-related
in-
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formation of the 4 bits is carried in the information field 230 as illustrated
in FIG. 2.
[80] Table 1
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[Table 11
Transport Block 0 Transport Block 0 Transport Block 0
Enabled and Transport Disabled and Transport Enabled and Transport
Block 1 Disabled Block 1 Enabled Block 1 Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 0 with port 1 with S port 0, 1
SCO SCO with SCO
allocated,DM allocated,DM allocated,DM
RS port 1 with RS port 0 with RS port 0, 1
SCO and SCO used by with SC1 not
DMRS port 0, other used
1 with SC1 not UEs,DMRS
used port 0, 1 with
SC1 not used
1 Rank 2 1 Rank 2 1 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 0 with port 0 with S port 0, 1
SCO SC1 with SCO
allocated,DM allocated,DM allocated,DM
RS port 1 with RS port 0, 1 RS port 0
SCO used by with SCO used with SC1
other by other used by other
UEs,DMRS UEs,DMRS UEs,DMRS
port 0, 1 with port 1 with port 1 with
SC1 not used SC1 not used SC1 not used
2 Rank 2 2 Rank 2 2 Rank 4
pattern,DMRS pattern,DMRS pattern,DMR
port 0 with port 0 with S port 0, 1, 2
SCO SC1 with SCO
allocated,DM allocated,DM allocated,DM
RS port 1 with RS port 0, 1 RS port 3
SCO and with SCO and with SCO not
DMRS port 0 DMRS port 1 used,DMRS
with SC1 used with SC1 used with SC1 not
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by other by other UEs used
UEs ,DMRS
port 1 with
SC1 not used
3 Rank 2 3 Rank 2 3 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 1 with port 1 with S port 0, 1
SCO SC1 with SCO
allocated,DM allocated,DM allocated,DM
RS port 0 with RS port 0, 1 RS port 0, 1
SCO and with SCO and with SC1
DMRS port 0 DMRS port 0 used by other
with SC1 used with SC1 used UEs
by other by other UEs
UEs ,DMRS
port 1 with
SC1 not used
4 Rank 2 4 reserved 4 Rank 2
pattern,DMRS pattern,DMR
port 0 with S port 0, 1
SCO with SC1
allocated,DM allocated,DM
RS port 1 with RS port 0, 1
SCO and with SCO
DMRS port 0, used by other
1 with SC1 UEs
used by other
UEs
Rank 2 5 reserved 5 Rank 4
pattern,DMRS pattern,DMR
port 1 with S port 0, 1,
2,
SCO 3 with SCO
allocated,DM allocated,DM
RS port 0 with RS with SC1
SCO and not used
DMRS port 0,
1 with SC1
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used by other
UEs
6 reserved 6 reserved 6 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4 with SCO
allocated,DM
RS port 5, 6,
7 with SCO
not
usedDMRS
with SC1 not
used
7 reserved 7 reserved 7 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5 with
SCO
allocated,DM
RS port 6, 7
with SCO not
usedDMRS
with SC1 not
used
8 reserved 8 reserved 8 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5, 6 with
SCO
allocated,DM
RS port 7
with SCO not
usedDMRS
with SC1 not
used
9 reserved 9 reserved 9 Rank 8
pattern,DMR
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S port 0, 1,2,
3, 4, 5, 6, 7
with SCO
allocated,DM
RS with SC1
not used
[81] <Table 1: DM-RS antenna port allocation and interference notification
in SU-MIMO
transmission for up to 8 layers per UE and MU-MIMO transmission for up to 2
layers
per UE with maximum composite rank 4 (up to 4 co-scheduled UEs)>
[82]
[83] The DM-RS antenna port 0 indicates a first antenna port to which the
DM-RS is
allocated among all of the Reference Signals (RSs). That is, an arbitrary DM-
RS
antenna port n is indexed in ascending order from the DM-RS antenna port 0.
[84]
[85] More specifically, RSs for use in LTE and LTE-A systems include CRSs,
MBMS
broadcast reference signals, DRSs, Positioning Reference Signals (PRSs), and
DM-
RSs.
[86]
[87] In this case, antenna ports 0 to 3 are allocated for the CRS, antenna
port 4 is allocated
for the MBMS broadcast reference signal, antenna port 5 is allocated for the
DRS,
antenna port 6 is allocated for the PRS, and antenna ports 7 to 14 are
allocated for DM-
RS. In accordance with an embodiment of the present invention, the DM-RS
antenna
port 0 corresponds to the antenna port 7 and the DM-RS antenna port 1
corresponds to
the antenna port 8, and it is assumed that the principle is applied to the
following de-
scription.
[88]
[89] FIG. 3 is a flowchart illustrating a method for an eNB to notify a UE
of DM-RS
antenna ports allocated to the UE and other UEs scheduled in a same
frequency/time
resource according to an embodiment of the present invention.
[90]
[91] Referring to FIG. 3, the eNB performs scheduling in a specific
time/frequency
resource in step 310. In the scheduling process, the eNB determines a
time/frequency
resource to the UE(s) and a data transmission rate for each UE. In step 310 of
FIG. 3,
the eNB set a number of co-scheduled UEs to N. N=1 indicates an SU-MIMO
transmission, and N=2, 3, or 4 indicates an MU-MIMO transmission.
[92]
[93] In step 320, the eNB sets an index indicating a DM-RS antenna port
allocated to a jth
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UE. The j is a variable for distinguishing between UEs. The eNB checks a
number of
transport blocks for the jth UE among the co-scheduled UEs. The number of
transport
blocks available for a UE is 1 or 2. When transmitting one transport block,
the
transport block 0 or the transport block 1 can be transmitted.
[94]
[95] If it is determined that only the transport block 0 is transmitted, in
step 340, the eNB
selects the index for notifying the jth UE of the allocated DM-RS port from
the index
column wherein only transport block 0 is enabled in Table 1. The index column
wherein only the transport block 0 is enabled shows the indices for indicating
DM-RS
antenna ports allocated to the jth UE and other UEs scheduled in a same time/
frequency resource when the transport block 0 is enabled and the transport
block 1 is
disabled.
[96]
[97] If it is determined that only the transport block 1 is transmitted, in
step 350, the eNB
selects the index for notifying the jth UE of the allocated DM-RS port from
the index
column in Table 1 wherein only transport block 1 is enabled. The index column
wherein only transport block 1 is enabled shows the indices for indicating DM-
RS
antenna ports allocated to the jth UE and other UEs scheduled in a same time/
frequency resource when the transport block 1 is enabled and the transport
block 1 is
disabled.
[98]
[99] If it is determined that both the transport blocks 0 and 1 are
transmitted, in step 360,
the eNB selects the index for notifying the jth UE of the allocated DM-RS port
from
the index column in Table wherein both the transport blocks are enabled. The
index
column of Table 1 wherein the both transport blocks are enabled shows the
indices for
indicating DM-RS antenna ports allocated to the jth UE and other UEs scheduled
in a
same time/frequency resource when both the transport blocks 0 and 1 are
enabled.
[100]
[101] In step 370, the eNB determines whether all of the co-scheduled UEs
are allocated
the respective DM-RS antenna port allocation indices, i.e., j = N. If j is
equal to N, all
the co-scheduled UEs are assigned the respective DM-RS antenna port allocation
indices. If all the co-scheduled UEs are assigned the DM-RS antenna port
allocations
indices, the eNB transmits the DM-RS antenna port allocation indices to
corresponding
co-scheduled UEs on a PDCCH in step 390. However, if there is a UE that is not
assigned a DM-RS antenna port allocation index, i.e., j<N, the eNB increments
j by 1
in step 380 and repeats step 330 to the next co-scheduled UE.
[102]
[103] FIG. 4 is a flowchart illustrating a method for a UE to determine DM-
RS antenna
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ports allocated to the UE and other UEs scheduled in a same frequency/time
resource
based on a DM-RS antenna port allocation index transmitted by an eNB according
to
an embodiment of the present invention.
[104]
[105] Referring to FIG. 4, the UE performs PDCCH blind decoding in step
405. The blind
decoding is performed on the PDCCH candidates because the UE is not aware of
the
time/frequency resource on which the PDCCH specific to the UE is transmitted,
such
that the UE determines the PDCCH candidate decoded without CRC error as the
PDCCH carrying its own control information, in the LTE and LTE-A systems.
[106]
[107] While performing the blind decoding, the UE determines whether the
downlink
scheduling PDCCH specific to the UE is received in step 410. If no downlink
scheduling PDCCH specific to the UE is received, the UE returns repeats PDCCH
blind decoding in step 405. However, when the downlink scheduling PDCCH
specific
to the UE is received, the UE checks the Downlink Control Information (DCI) in
the
PDCCH in step 415. The DCI includes control information on transport blocks 0
and 1,
DM-RS antenna port allocation information, and other control information.
[108]
[109] In step 420, the UE determines whether any or both of the transport
block 0 and the
transport block 1 are transmitted, based on the transport block 0 control
information
210 and the transport block 1 control information 220 as illustrated in FIG.
2.
[110]
[111] When only the transport block 0 is transmitted, in step 425, the UE
searches the
index column of Table 1 wherein only transport block 0 is enabled for the
index
indicated by the DM-RS antenna allocation control information 230 of FIG. 2
and
checks the information on the allocated DM-RS antenna port through the message
detailing the index. Also, the UE can check whether the transmission is MU-
MIMO
transmission in which multiple UEs are involved and, if so, which DM-RS
antenna
ports are allocated to other UEs.
[112]
[113] When only the transport block 1 is transmitted at step 420, in step
430, the UE
searches the index column of Table 1 wherein only transport block 1 is enabled
for the
index indicated by the DM-RS antenna allocation control information 230 of
FIG. 2
and checks the information on the allocated DM-RS antenna port through the
message
detailing the index. Also, the UE can check whether the transmission is MU-
MIMO
transmission in which multiple UEs are involved and, if so, which DM-RS
antenna
ports are allocated to other UEs.
[114]
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[115] When both the transport block 0 and transport block 1 are
transmitted, in step 435,
the UE searches the index column of Table 1 wherein both transport blocks are
enabled
for the index indicated by the DM-RS antenna allocation control information
230 of
FIG. 2. Also, the UE can check whether the transmission is MU-MIMO
transmission
in which multiple UEs are involved and, if so, which DM-RS antenna ports are
allocated to other UEs.
[116]
[117] In step 440, the UE receives the corresponding transport block, i.e.,
transport block 0
or transport block 1, transmitted by the eNB, and estimates a channel for the
one
transmission layer using the single allocated DM-RS antenna port.
[118]
[119] In step 445, the UE receives both the transport blocks 0 and 1
transmitted by the
eNB, and estimates a channel for the multiple transmission layers using the
multiple
allocated DM-RS antenna ports.
[120]
[121] In step 450, the UE determines whether other UEs are co-scheduled on
a same time/
frequency resource along with the UE. That is, the UE determines whether the
signal
destined to the UE is received in an SU-MIMO transmission or an MU-MIMO
transmission. Whether the signal is received in the SU-MIMO transmission or
the MU-
MIMO transmission can be determined based on the information about the other
UEs
and the DM-RS antenna port allocated to the other UEs that are checked along
with the
DM-RS antenna port allocation information in steps 425, 430, and 435.
[122]
[123] When the UE-specific signal is transmitted in the MU-MIMO
transmission, in step
455, the UE detects the signal transmitted through the DM-RS antenna ports
allocated
to the other UEs and uses this information for improving its own signal
reception per-
formance. For example, to improve reception performance, the UE can measure
signal
strengths of DM-RSs transmitted to the other UEs and use the measurement in
the
MMSE receiver.
[124]
[125] When the UE-specific signal is transmitted in the SU-MIMO
transmission, in step
460, the UE processes the received signal according to the SU-MIMO reception
scheme under the assumption that there is no other UE co-scheduled in the same
time/
frequency resource.
[126]
[127] After receiving the signal in one of steps 455 and 460, the UE
returns to PDCCH
blind decoding in step 405.
[128]
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[129] Table 1 is used to support SU-MIMO and MU-MIMO transmissions having
the char-
acteristics as listed under <system characteristics 1> above. In a real LTE-A
system,
however, an eNB can perform SU-MIMO and MU-MIMO transmissions different
from the types in <system characteristics l>.
[130]
[131] Table 2, below, is used for supporting SU-MIMO and MU-MIMO
transmissions
having characteristics as listed in the following <system characteristics 2>,
according
to an embodiment of the present invention:
[132]
[133] <system characteristics 2>
[134] 1. SU-MIMO transmission for 1-8 layers
[135] 2. MU-MIMO transmission for up to 2 layers allocated to a UE
[136] 3. MU-MIMO transmission to up to 2 UEs
[137] 4. MU-MIMO transmission for up to 4 layers (maximum composite rank of
MU-
MIMO is 4)
[138]
[139] When up to 2 UEs are co-scheduled under the restrictive conditions of
the system
characteristics 2, the number of cases of DM-RS antenna port allocation and in-
terference-related information reduces, as compared to Table 1. The reduction
of the
number of cases can be observed by comparing the index columns of Table 2
wherein
only the transport block 0 is enabled and wherein only the transport block 1
is enabled
with the corresponding index columns of Table 1.
[140]
[141] When allocating DM-RS antenna ports using Table 2, 4 bits of
information amount
are used for identifying up to 10 indices of each transport block transmission
case.
That is, when using Table 2, DM-RS antenna port allocation and interference-
related
information of 4 bits is carried in the field 230 of FIG. 2.
[142]
[143] Table 2
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[Table 2]
Transport Block 0 Transport Block 0 Transport Block 0
Enabled and Transport Disabled and Transport Enabled and Transport
Block 1 Disabled Block 1 Enabled Block 1 Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 0 port 1 S port 0, 1
allocated, allocated, allocated
DMRS port 1 DMRS port 0
not used used by other
UE
1 Rank 2 1 Rank 4 1 Rank 4
pattern,DMRS pattern,DMRS pattern,DMR
port 0 port 2 Sport 0, 1
allocated, allocated,DM allocated,DM
DMRS port 1 RS port 0, 1 RS port 2
used by other used by other used by other
UE UEs,DMRS UEs,DMRS
port 3 not port 3 not
used used
2 Rank 4 2 reserved 2 Rank 4
pattern,DMRS pattern,DMR
port 0 Sport 0, 1
allocated,DM allocated,DM
RS port 2,3 RS port 2,3
used by other used by other
UEs,DMRS UEs
port 1 not
used
3 reserved 3 reserved 3 Rank 4
pattern,DMR
Sport 2,3
allocated,DM
RS port 0
used by other
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UEs ,DMRS
port 1 not
used
4 reserved 4 reserved 4 Rank 4
pattern,DMR
S port 0, 1,2
allocated,DM
RS port 3 not
used
reserved 5 reserved 5 Rank 4
pattern,DMR
S port 0, 1,2,
3 allocated
6 reserved 6 reserved 6 Rank 8
pattern,DMR
S port 0, 1,2,
3,4
allocated,DM
RS port 5, 6,
7 not used
7 reserved 7 reserved 7 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5 allo-
catedDMRS
port 6, 7 not
used
8 reserved 8 reserved 8 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5, 6 al-
locatedDMR
S port 7 not
used
9 reserved 9 reserved 9 Rank 8
pattern,DMR
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S port 0, 1,2,
3, 4, 5, 6, 7
allocated
[144] <Table 2 : DM-RS antenna port allocation and interference
notification in SU-MIMO
transmission for up to 8 layers per UE and in MU-MIMO transmission for up to 2
layers per UE with a maximum composite rank 4 (up to 2 co-scheduled UEs)>
[145]
[146] The method for an eNB to determine a DM-RS antenna port allocation
index using
Table 2 is identical with that described with reference to Table 1 and FIG. 3.
Also, the
method for a UE to receive and interpret a DM-RS antenna port allocation index
is
identical with that described with reference to Table 1 and FIG. 4.
Accordingly, a
repetitive description of the methods using Table 2 will not be provided.
[147]
[148] Table 3 shows indices for indicating DM-RS antenna port allocation
modes and
messages describing the meanings of the indices according to an embodiment of
the
present invention. Specifically, Table 3 is used to notify DM-RS antenna port
al-
location for MIMO transmissions as listed in <system characteristics l>.
However,
Table 3 differs from Table 2 in the method for distinguishing between the DM-
RS
patterns and DM-RSs per DM-RS antenna port used for transmitting the DM-RSs.
More specifically, the DM-RS patterns and DM-RS per DM-RS antenna port are
identified based on scrambling sequence in Table 3, as will be described
below.
[149]
[150] When the number of layers for an MU-MIMO transmission is 3 or 4, an
eNB maps
DM-RSs which are Frequency Division Multiplexed (FDMed) and Code Division
Multiplexed (CDMed) to the respective DM-RS antenna ports as illustrated in
the rank
4 DM-RS pattern 110 of FIG. 1. That is, the DM-RS antenna port 0 is
transmitted with
Walsh code 0 (+1, +1) of length 2 in blue REs, whereas DM-RS antenna port 3 is
transmitted with Walsh code 1 (+1, -1) of length 2 in red REs. Table 3
corresponds to
the case where the number of layers for the MU-MIMO transmission is 3 or 4 and
the
DM-RSs of the individual DM-RS antenna ports are distinguished in the manner
using
the scrambling sequence.
[151]
[152] Another method for identifying the DM-RS antenna ports, when the
number of layers
for the MU-MIMO transmission is 3 or 4, is to use two scrambling sequences.
That is,
when the number of layers for the MU-MIMO transmission is 3 or 4, up to 4 DM-
RS
antenna ports are allocated for the MU-MIMO transmission using the additional
scramble sequence at the blue REs without allocating additional REs, i.e. the
red REs
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as shown in the rank 4 DM-RS pattern 110 of FIG. 1. As a result, this method
has the
same effect to use the rank 2 DM-RS pattern with two scrambling sequences and
define both the DM-RS antenna port 0 and DM-RS antenna port 1 per scrambling
sequence. That is, for MU-MIMO transmission with 3 or 4 transmission layers,
the
DM-RS antenna ports can be identified as follows:
[153] 1. DM-RS antenna port 0 using Walsh code 0 with scrambling sequence 0
(SCO)
[154] 2. DM-RS antenna port 1 using Walsh code 1 with scrambling sequence 0
(SCO)
[155] 3. DM-RS antenna port 0 using Walsh code 0 with scrambling sequence 1
(SC1)
[156] 4. DM-RS antenna port 1 using Walsh code 1 with scrambling sequence 1
(SC1)
[157]
[158] In the MU-MIMO transmission using 3 or 4 transmission layers, the DM-
RS antenna
port 0 and DM-RS antenna port 1 are defined per scrambling sequence in order
to dis-
tinguish among the DM-RS antenna ports. Also, the same effect can be expected
when
the four cases can be referred to as DM-RS antenna port 0, DM-RS antenna port
1,
DM-RS antenna port 2, and DM-RS antenna port 3, respectively.
[159]
[160] FIG. 5 is a diagram illustrating a DM-RS pattern designed for
distinguishing among
DM-RS antenna ports in an MU-MIMO transmission using 3 or 4 transmission
layers
by using two scrambling sequences according to an embodiment of the present
invention.
[161]
[162] Referring to FIG. 5, the DM-RSs of the 4 DM-RS antenna ports are
transmitted on
the same REs using two scrambling sequences.
[163]
[164] Table 3, below, shows indices for use in DM-RS antenna port
information noti-
fication and messages describing the meanings of the indices when the DM-RS
pattern
utilizing the two scrambling sequences is used in the MU-MIMO transmission of
the
composite rank 3 or 4. In Table 3, it is assumed that the SCrambling sequence
(SC) is
always 0 in an SU-MIMO transmission.
[165]
[166] The theory on the indices for use in the DM-RS antenna port
information notification
and the messages describing the meanings of the indices in Table 3 is
identical with
that of Table 1, except that an MU-MIMO transmission of Table 3 uses
additional
scrambling sequences when the composite rank is 3 and 4, and distinguishes
among the
DM-RS antenna port signals with the pattern 110 of FIG. 1 only in an SU-MIMO
transmission, unlike Table 1, which distinguishes the DM-RS antenna port
signals with
the pattern 110 of FIG. 1 when the composite rank is 3 or 4, irrespective of
whether the
transmission is an SU-MIMO or MU-MIMO transmission.
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[167]
[168] The method for an eNB to determine the DM-RS antenna port allocation
index using
Table 3 is identical with the method illustrated in FIG. 3 in which Table 1 is
used.
Also, the method for a UE to receive and interpret the DM-RS antenna port
allocation
index is identical with the method depicted in FIG. 4 in which Table 1 is
used. Ac-
cordingly, a repetitive description of the same methods using Table 3 will not
be
provided.
[169]
[170] Table 3
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[Table 3]
Transport Block 0 Transport Block 0 Transport Block 0
Enabled and Transport Disabled and Transport Enabled and Transport
Block 1 Disabled Block 1 Enabled Block 1 Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 0 with port 1 with S port 0, 1
SCO SCO with SCO
allocated,DM allocated,DM allocated,DM
RS port 1 with RS port 0 with RS port 0, 1
SCO and SCO used by with SC1 not
DMRS port 0, other used
1 with SC1 UEs,DMRS
not used port 0, 1 with
SC1 not used
1 Rank 2 1 Rank 2 1 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 0 with port 0 with S port 0, 1
SCO SC1 with SCO
allocated,DM allocated,DM allocated,DM
RS port 1 with RS port 0, 1 RS port 0
SCO used by with SCO used with SC1
other by other used by other
UEs,DMRS UEs,DMRS UEs,DMRS
port 0, 1 with port 1 with port 1 with
SC1 not used SC1 not used SC1 not
used
2 Rank 2 2 Rank 2 2 Rank 4
pattern,DMRS pattern,DMRS pattern,DMR
port 0 with port 0 with S port 0, 1, 2
SCO SC1 with SCO
allocated,DM allocated,DM allocated,DM
RS port 1 with RS port 0, 1 RS port 3
SCO and with SCO and with SCO not
DMRS port 0 DMRS port 1 used,DMRS
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with SC1 used with SC1 used with SC1 not
by other by other UEs used
UEs,DMRS
port 1 with
SC1 not used
3 Rank 2 3 Rank 2 3 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 1 with port 1 with S port 0, 1
SCO SC1 with SCO
allocated,DM allocated,DM allocated,DM
RS port 0 with RS port 0, 1 RS port 0, 1
SCO and with SCO and with SC1
DMRS port 0 DMRS port 0 used by other
with SC1 used with SC1 used UEs
by other by other UEs
UEs,DMRS
port 1 with
SC1 not used
4 Rank 2 4 reserved 4 Rank 2
pattern,DMRS pattern,DMR
port 0 with S port 0, 1
SCO with SC1
allocated,DM allocated,DM
RS port 1 with RS port 0, 1
SCO and with SCO
DMRS port 0, used by other
1 with SC1 UEs
used by other
UEs
Rank 2 5 reserved 5 Rank 4
pattern,DMRS pattern,DMR
port 1 with S port 0, 1,
2,
SCO 3 with SCO
allocated,DM allocated,DM
RS port 0 with RS with SC1
SCO and not used
DMRS port 0,
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1 with SC1
used by other
UEs
6 reserved 6 reserved 6 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4 with SCO
allocated,DM
RS port 5, 6,
7 with SCO
not
usedDMRS
with SC1 not
used
7 reserved 7 reserved 7 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5 with
SCO
allocated,DM
RS port 6, 7
with SCO not
usedDMRS
with SC1 not
used
8 reserved 8 reserved 8 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5, 6 with
SCO
allocated,DM
RS port 7
with SCO not
usedDMRS
with SC1 not
used
9 reserved 9 reserved 9 Rank 8
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pattern,DMR
S port 0, 1,2,
3, 4, 5, 6, 7
with SCO
allocated,DM
RS with SC1
not used
[171] <Table 3 : DM-RS antenna port allocation and interference
notification in an SU-
MIMO transmission for up to 8 layers per UE and MU-MIMO transmission for up to
2
layers per UE with a maximum composite rank 4 (up to 4 co-scheduled UEs)>
[172]
[173] Referring to Table 3, for an MU-MIMO transmission of composite rank 3
and 4, 4
DM-RS antenna port signals are distinguished from each other using the rank 2
DM-
RS pattern with scrambling sequences. Another method for distinguishing among
the 4
DM-RS antenna port signals is to apply orthogonal codes of length 4 to the
rank 2 DM-
RS pattern. That is, in the MU-MIMO transmission of composite rank 3 and 4,
the or-
thogonal codes of length 4 are assigned to the DM-RS antenna ports in the rank
2 DM-
RS pattern. In this case, the definitions of Tables 1 and 3 can be used.
[174]
[175] For DM-RS antenna port allocation using Table 3, 4 bits of
information amount are
used for identifying up to 10 indices of each transport block transmission
case. That is,
when using Table 3, the DM-RS antenna port allocation information and
interference-
related information of 4 bits are carried in field 230 of FIG. 2.
[176]
[177] Tables 1, 2, and 3 show cases where an eNB notifies a UE of an SU-
MIMO or MU-
MIMO transmission along with DM-RS antenna port allocation information. In ac-
cordance with an embodiment of the present invention, a method is provided for
the
eNB to efficiently notify the UE of the transmission mode, i.e., SU-MIMO or MU-
MIMO, with additional information in the LTE-A system while the DM-RS antenna
port allocation information and interference-related information are notified
to the UE
separately.
[178]
[179] FIG. 6 is diagram illustrating control information carried on a PDCCH
for use in an
LTE-A system according to an embodiment of the present invention. In addition
to
transport block 0 control information 610 and transport block 1 control
information
620, which are similar to the transport block 0 control information 210 and
the
transport block 1 control information 220, as illustrated in FIG. 2, the
control in-
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formation on the PDCCH includes an SU/MU-MIMO indicator 630 of 1 bit for
distin-
guishing between SU-MIMO and MU-MIMO transmissions and a DM-RS antenna
port allocation information 640.
[180]
[181] When using the SU/MU-MIMO Indicator 630, an eNB sends the scheduled
UE the
SU/MIMO Indicator 630 set to 0 for the SU-MIMO transmission and the co-
scheduled
UEs the SU/MU-MIMO indicator set to 1 for the MU-MIMO transmission. If the SU/
MU-MIMO Indicator 630 is set to 0, i.e., SU-MIMO transmission is used, and
only
one transmission layer is allocated, this means that the transport block 0 is
transmitted.
That is, for an SU-MIMO transmission with 1 layer, a fixed transport block is
transmitted in order to reduce the amount of control information for DM-RS
antenna
port allocation. For an SU-MIMO transmission with 2, 3, 4, 5, 6, 7, or 8
layers, two
transport blocks are transmitted, and the transport block 0 is fixed to be
transmitted in
order to reduce the amount of control information for DM-RS antenna port
allocation.
[182]
[183] Additionally, two tables can be used, depending on the value of the
SU/MU-MIMO
Indicator 630, in order for the eNB to transmit and for the UE to receive the
DM-RS
antenna port allocation and interference information.
[184]
[185] Table 4, below, shows indices indicating DM-RS antenna port
allocation modes and
messages describing the meanings of the indices in an SU-MIMO transmission
using
an SU/MU-MIMO Indicator. Specifically, Table 4 includes two columns
representing
where the transport block 0 is fixedly enabled, and each column of these
columns
includes two sub-columns representing an index and a message. As compared to
Tables 1, 2, and 3, in Table 4, there is no case where transport block 1 is
transmitted
but the transport block 0 is not.
[186]
[187] Because Table 4 is configured to show the DM-RS antenna port
allocation in-
formation for the SU-MIMO transmission but not the MU-MIMO transmission, no in-
terference-related information is included.
[188]
[189] Table 5 shows indices for indicating DM-RS antenna port allocation
modes and
messages describing the meanings of the indices in an MU-MIMO transmission
when
using an SU/MU-MIMO Indicator. Specifically, Table 5 includes interference-
related
information and DM-RS antenna port allocation information.
[190]
[191] Tables 4 and 5 are configured in consideration of <system
characteristics 1>, as
described above.
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[192]
[193] Table 4
[Table 4]
Transport Block 0 Enabled and Transport Block 0 Enabled and
Transport Block 1 Disabled Transport Block 1 Enabled
Index Message Index Message
0 Rank 2 0 Rank 2
pattern,DMRS port 0 pattern,DMRS port 0,
with SCO allocated 1 allocated
1 reserved 1 Rank 4
pattern,DMRS port 0,
1, 2 allocated
2 reserved 2 Rank 4
pattern,DMRS port 0,
1, 2, 3 allocated
3 reserved 3 Rank 8
pattern,DMRS port 0,
1, 2, 3, 4 allocated
4 reserved 4 Rank 8
pattern,DMRS port 0,
1, 2, 3, 4, 5 allocated
reserved 5 Rank 8
pattern,DMRS port 0,
1, 2, 3, 4, 5, 6
allocated
6 reserved 6 Rank 8
pattern,DMRS port 0,
1, 2, 3, 4, 5, 6, 7
allocated
[194] <Table 4 : DM-RS antenna port allocation and interference
notification with an SU/
MIMO Indicator (for SU-MIMO)>
[195]
[196] Table 5
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[Table 51
Transport Block 0 Transport Block 0 Transport Block 0
Enabled and Transport Disabled and Transport Enabled and Transport
Block 1 Disabled Block 1 Enabled Block 1 Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 4
pattern,DMRS pattern,DMRS pattern,DMR
port 0 port 1 S port 0, 1
allocated, allocated, allocated,DM
DMRS port 1 DMRS port 0 RS port 2
used by other used by other used by other
UE UE UEs,DMRS
port 3 not
used
1 Rank 4 1 Rank 4 1 Rank 4
pattern,DMRS pattern,DMRS pattern,DMR
port 0 port 2 Sport 0, 1
allocated,DM allocated,DM allocated,DM
RS port 1, 2 RS port 0, 1 RS port 2, 3
used by other used by other used by other
UEs,DMRS UEs,DMRS UEs
port 3 not port 3 not
used used
2 Rank 4 2 Rank 4 2 Rank 4
pattern,DMRS pattern,DMRS pattern,DMR
port 1 port 2 S port 2, 3
allocated,DM allocated,DM allocated,DM
RS port 0, 2 RS port 0, 1, 3 RS port 0, 1
used by other used by other used by other
UEs,DMRS UEs UEs
port 4 not
used
3 Rank 4 3 Rank 4 3 reserved
pattern,DMRS pattern,DMRS
port 0 port 3
allocated,DM allocated,DM
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RS port 1, 2, 3 RS port 0, 1, 2
used by other used by other
UEs UEs
4 Rank 4 4 reserved 4 reserved
pattern,DMRS
port 1
allocated,DM
RS port 0, 2, 3
used by other
UEs
[197] <Table 5 : DM-RS antenna port allocation and interference
notification with SU/
MU-MIMO Indicator (for MU-MIMO)>
[198]
[199] When using Table 4 for DM-RS antenna port allocation, 4 bits of
information
amount are used, i.e., 3 bits for identifying up to 7 indices and 1 bit for
the SU/
MU-MIMO indicator. That is, when using Table 5, the control information
illustrated
in FIG. 6 has the SU/MU-MIMO Indicator 630 of 1 bit and the DM-RS antenna port
allocation and interference-related control information 640 of 3 bits.
[200]
[201] FIGs. 7A and 7B are a flowchart illustrating a method for an eNB to
notify a UE of
DM-RS antenna port allocation and interference-related information according
to an
embodiment of the present invention. With the DM-RS antenna port allocation
and in-
terference-related information, the UE can check the DM-RS antenna ports
allocated to
other UEs that are co-scheduled in a same frequency/time resource.
[202]
[203] Referring to FIGs. 7A and 7B, the eNB performs scheduling in a
specific time/
frequency resource in step 705. In the scheduling process, the eNB determines
the
time/frequency resource to the UE(s) and a data transmission rate for each UE.
Further,
the eNB sets the number of co-scheduled UEs to N.
[204]
[205] After scheduling the UEs, the eNB determines whether the number of
scheduled UEs
is 1, i.e., if N=1, in step 710. If N=1, SU-MIMO is used; and if N>l, MU-MIMO
is
used. If N=1 (i.e., SU-MIMO transmission is used), the eNB sets the SU/MU-MIMO
indicator to 0 in step 715. In step 720, the eNB determines whether the number
of
transport blocks to be transmitted in the SU-MIMO mode is 2. If the number of
transport blocks is 1, the eNB selects a DM-RS transmission mode index from
the
index column of the first case of Table 4 in step 725. Otherwise, if the
number of
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transport blocks is 2, the eNB selects a DM-RS transmission mode index from
the
index column of the second case of Table 4 in step 730. In steps 735, the eNB
transmits the DM-RS antenna port allocation index and the SU/MU-MIMO indicator
on a PDCCH along with other control information. Because the SU-MIMO
transmission is determined by the eNB, the SU/MU-MIMO indicator is set to 0.
[206]
[207] When N is greater than 1 in step 710 (i.e., MU-MIMO transmission is
necessary), the
eNB sets the SU/MU-MIMO indicator to 1 in step 740. Because steps 750 to 770
are
identical to step 320 to 370 of FIG. 3, which were already described above, a
repetitive
detailed description of steps 750 to 770 will not be provided.
[208]
[209] Even though 750 to 770 are identical to step 320 to 370 of FIG. 3,
step 780 of FIG. 7
is unique in that an SU/MU-MIMO indicator on the PDCCH transmitted to each UE
is
set to 1. At step 390 of FIG. 3, the SU/MU-MIMO indicator is not used, and
therefore,
this indication value is not transmitted.
[210]
[211] FIGs. 8A and 8B are a flowchart illustrating a method for a UE to
determine DM-RS
antenna ports allocated to the UE and other UEs scheduled in a same
frequency/time
resource based on a DM-RS antenna port allocation index and a SU/MU-MIMO
indicator transmitted by an eNB according to an embodiment of the present
invention.
[212]
[213] Referring to FIG. 8A, the UE performs PDCCH blind decoding in step
805. As
described above, blind decoding is performed on the PDCCH candidates because
the
UE is not aware of the time/frequency resource on which the PDCCH specific to
the
UE is transmitted such that the UE determines the PDCCH candidate decoded
without
a CRC error as the PDCCH carrying its own control information, in the LTE and
LTE-
A systems.
[214]
[215] While performing the blind decoding, the UE determines whether the
downlink
scheduling PDCCH specific to the UE is received in step 810. If no downlink
scheduling PDCCH specific to the UE is received, the UE repeats PDCCH blinding
decoding in step 805. However, if the downlink scheduling PDCCH specific to
the UE
is received, the UE checks the DCI in the PDCCH in step 815. The DCI includes
control information of transport block 0 and transport block 1, an SU/MU-MIMO
indicator, DM-RS antenna port allocation control information, and other
control in-
formation, as illustrated in FIG. 6.
[216]
[217] In step 820, the UE determines whether the SU/MU-MIMO indicator of
the control
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information carried on the PDCCH is set to 0 or 1. When the SU/MU-MIMO
indicator
is set to 0, this indicates an SU-MIMO transmission, and thus the UE
determines
whether the eNB transmits only the transport block 0 or both the transport
blocks 0 and
1 in step 825. When only the transport block 0 is transmitted, in step 830,
the UE
searches the index column of the first SU-MIMO case of Table 4 for the index
contained in the DM-RS antenna port allocation control information field 640
of FIG.
6 . The DM-RS antenna port allocation index is used for channel estimation.
[218]
[219] In step 835, the UE performs channel estimation for the layer
transmitted using the
DM-RS antenna port, and in step 840, the UE processes the received signal with
the
SU-MIMO reception method.
[220]
[221] When both the transport blocks 0 and 1 are transmitted at step 825,
in step 845, the
UE searches the index column of the second SU-MIMO case of Table 4 for the
index
contained in the DM-RS antenna port allocation control information field 640
of FIG.
6. The DM-RS antenna port allocation index is used for channel estimation.
[222]
[223] In step 850, the UE performs channel estimation for the multiple
layers transmitted
using the DM-RS antenna port and then processes the received signal with the
SU-
MIMO reception method in step 840.
[224]
[225] When the SU/MU-MIMO indicator is set to 1 in step 820, this indicates
an MU-
MIMO transmission, and thus, the UE determines whether the eNB transmits the
transport block 0, the transport block 1, or both the transport blocks 0 and 1
in step
855.
[226]
[227] When the eNB transmits only the transport block 0, in step 860, the
UE searches the
index column of the first MU-MIMO case of Table 5 for the index contained in
the
DM-RS antenna port allocation control information field 640 of FIG. 6. In step
865,
the UE performs channel estimation for the single layer transmitted through
the corre-
sponding DM-RS antenna port. In step 870, the UE detects the other DM-RS
antenna
ports signals, under the assumption that the received signal is a part of the
MU-MIMO
transmission, and improves the signal reception performance by using the
detected
other DM-RS antenna ports signals.
[228]
[229] When the eNB transmits only the transport block 1 in step 855, in
step 875, the UE
searches the index column of the second MU-MIMO case of Table 5 for the index
contained in the DM-RS antenna port allocation control information field 640
of FIG.
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6. Thereafter, UE performs steps 865 and 870.
[230]
[231] When the eNB transmits both transport blocks 0 and 1 in step 855, in
step 880, the
UE searches the index column of the third MU-MIMO case of Table 5 for the
index
contained in the DM-RS antenna port allocation control information field 640
of FIG.
6. In step 885, the UE performs channel estimation for the multiple layers
transmitted
through corresponding DM-RS antenna ports. Thereafter, UE performs step 870..
[232]
[233] After completing signal reception at step 840 or 870, the UE repeats
PDCCH blind
decoding in step 805.
[234]
[235] As described above, Tables 1, 2, 3, 4, and 5 provide information on a
transmission
mode (i.e., SU-MIMO transmission or MU-MIMO transmission) and DM-RS antenna
ports allocated other UEs that can cause interference in the MU-MIMO
transmission as
well as the information on the DM-RS antenna port allocated to the UE,
scheduled by
the eNB. The information on the DM-RS antenna ports allocated to other UEs
advan-
tageously improves reception performance of the scheduled UE and also
increases
control information overhead efficiency.
[236]
[237] An embodiment of the present invention proposes a DM-RS antenna port
allocation
in consideration of whether the transport block 0 and/or transport block 1
are/is
transmitted to one UE, without interference-related information. In this case,
no in-
terference-related information is transmitted, thereby reducing the amount of
control
information.
[238]
[239] Table 6, below, shows indices for indicating DM-RS antenna port
allocation modes
and messages describing the meanings of the indices according to an embodiment
of
the present invention. Specifically, Table 6 is designed for an eNB to notify
a target
UE of only information on the DM-RS antenna ports allocated to the UE, unlike
Tables 1, 2, 3, 4, and 5. When using Table 6, the eNB does not provide the UE
with the
additional information related to interference, even in an MU-MIMO
transmission.
[240]
[241] Table 6 is also designed in consideration of <system characteristics
1>, under an as-
sumption that the rank 4 DM-RS pattern is used for composite rank 3 or 4.
[242]
[243] Because the method for an eNB to notify a UE of an allocated DM-RS
using Table 6
is similar to the method described with reference FIG. 3, detailed description
is omitted
herein. Basically, the method using Table 6 differs from the method described
with
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reference to FIG. 3 only in that the eNB notifies the UE of the DM-RS antenna
port
without consideration of interference.
[244]
[245] In Table 6, 9 DM-RS antenna port allocation indices are provided for
each
transmission mode, unlike table 1 in which 10 DM-RS antenna port allocation
indices
are provided for each transmission mode. The reduction of the number of the
indices
means that the amount of information to be transmitted is reduced due to the
negation
of the interference-related information.
[246]
[247] Table 6
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[Table 6]
Transport Block 0 Transport Block 0 Transport Block 0
Enabled and Transport Disabled and Transport Enabled and Transport
Block 1 Disabled Block 1 Enabled Block 1 Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 0 port 1 S port 0, 1
allocated allocated allocated
1 Rank 4 1 Rank 4 1 Rank 4
pattern,DMRS pattern,DMRS pattern,DMR
port 0 port 2 Sport 0, 1
allocated allocated allocated
2 Rank 4 2 Rank 4 2 Rank 4
pattern,DMRS pattern,DMRS pattern,DMR
port 1 port 3 S port 2, 3
allocated allocated allocated
3 reserved 3 reserved 3 Rank 4
pattern,DMR
S port 0, 1,2
allocated
4 reserved 4 reserved 4 Rank 4
pattern,DMR
S port 0, 1,2,
3 allocated
reserved 5 reserved 5 Rank 8
pattern,DMR
S port 0, 1,2,
3,4
allocated
6 reserved 6 reserved 6 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5
allocated
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7 reserved 7 reserved 7 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5, 6
allocated
8 reserved 8 reserved 8 Rank 8
pattern,DMR
S port 0, 1,2,
3, 4, 5, 6, 7
allocated
[248] <Table 6 : DM-RS antenna port indication method in an SU-MIMO
transmission for
up to 8 layers per UE and an MU-MIMO transmission for up to 2 layers per UE
with a
maximum composite rank 4 (up to 4 co-scheduled UEs)>
[249]
[250] Table 7, below, shows indices for indicating DM-RS antenna port
allocation modes
and messages describing the meanings of the indices according to another
embodiment
of the present invention. Unlike Tables 1, 2, 3, 4, and 5, Table 7 is designed
such that
an eNB notifies a UE of only the information on a DM-RS antenna port allocated
to
the corresponding UE. Accordingly, when using Table 7, similar to Table 6, the
eNB
does not provide the UE with the interference-related information, even in the
MU-
MIMO transmission.
[251]
[252] Table 7 is also designed in consideration of <system characteristics
1> under an as-
sumption that rank 2 DM-RS patterns and two scrambling sequences are used for
the
composite rank 3 or 4. This is similar to Table 3.
[253]
[254] Because the method for the eNB to notify the UE of the allocated DM-
RS using
Table 7 is similar to the method described with reference FIG. 3, detailed
description is
omitted herein. Basically, the method using Table 7 differs from the method
described
with reference to FIG. 3 only in that an eNB notifies a UE of the DM-RS
antenna port,
without consideration of interference from other UEs.
[255]
[256] In Table 7, 8 DM-RS antenna port allocation indices are provided for
each
transmission mode, unlike table 1 in which 10 DM-RS antenna port allocation
indices
are provided for each transmission mode. The reduction of the number of the
indices
means that the amount of information to be transmitted is reduced due to the
negation
of the interference-related information.
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PCT/KR2011/000939
[257]
[258] In view of the number of bits, 3 bits are used for notifying the UE
of the DM-RS
antenna port allocation information and interference-related information when
using
table 7, as compared to using Table 1, in which 4 bits are used.
[259]
[260] Table 7
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[Table 7]
Transport Block 0 Enabled Transport Block 0 Transport Block 0
and Transport Block 1 Disabled and Transport Enabled and Transport
Disabled Block 1 Enabled Block 1 Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMR
port 0 with port 1 with S port 0, 1
SCO allocated SCO allocated with SCO
allocated
1 reserved 1 Rank 2 1 Rank 4
pattern,DMRS pattern,DMR
port 0 with S port 0, 1, 2
SC1 allocated with SCO
allocated
2 reserved 2 Rank 2 2 Rank 2
pattern,DMRS pattern,DMR
port 1 with S port 0, 1
SC1 allocated with SC1
allocated
3 reserved 3 reserved 3 Rank 4
pattern,DMR
Sport 0, 1,
2, 3 with
SCO
allocated
4 reserved 4 reserved 4 Rank 8
pattern,DMR
Sport 0, 1,
2, 3, 4 with
SCO
allocated
reserved 5 reserved 5 Rank 8
pattern,DMR
Sport 0,1,
2, 3, 4, 5
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with SCO
allocated
6 reserved 6 reserved 6 Rank 8
pattern,DMR
Sport 0, 1,
2, 3, 4, 5, 6
with SCO
allocated
7 reserved 7 reserved 7 Rank 8
pattern,DMR
Sport 0, 1,
2, 3, 4, 5, 6,
7 with SCO
allocated
[261] <Table 7 : DM-RS antenna port indication method in an SU-MIMO
transmission for
up to 8 layers per UE and MU-MIMO transmission for up to 2 layers per UE with
a
maximum composite rank 4 (up to 4 co-scheduled UEs)>
[262]
[263] When using Tables 1 to 7, an eNB notifies a DM-RS antenna port in an
initial
transmission of Hybrid Automatic Repeat reQuest (HARQ).
[264]
[265] In association with a HARQ process, it is required to notify of a
case other than the
DM-RS antenna port allocations listed in Tables 1 to 7 for retransmission.
[266]
[267] In the initial transmission, when one transport block is to be
transmitted, the transport
block is transmitted on a single layer. However, in the retransmission, when
one
transport block is transmitted, the transport block can be retransmitted on
multiple
layers according to an eNB's decision. In order to notify the UE of the DM-RS
antenna
port allocation for retransmission, in accordance with an embodiment of
present
invention, additional allocation information is defined with an index that is
not used in
Tables 1, 2, 3, 4, 5, 6, and 7.
[268]
[269] Like Table 7, Table 8, below, is designed in consideration of <system
characteristics
1>, under the assumptions that the rank 2 DM-RS patterns and two scrambling
sequences are used for the composite rank 3 and 4. Specifically, Table 8 is
designed
such that an eNB notifies a UE only of the DM-RS antenna port, unlike Table 1,
2, 3,
4, and 5. Accordingly, when using Table 8, the eNB does not provide the UE
with the
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interference-related information, even in an MU-MIMO transmission.
[270]
[271] Table 8 differs from Table 7 as follows:
[272] 1. In Table 8, it is possible to freely allocate one of 4
combinations of DM-RS
antenna ports and scrambling codes even when one of the transport blocks 0 and
1 is
transmitted to the UE. That is, when transmitting one transport block, one of
the DM-
RS antenna port 0 and scrambling sequence 0 combination, DM-RS antenna port 0
and
scrambling sequence 1 combination, DM-RS antenna port 1 and scrambling
sequence
0, and DM-RS antenna port 1 and scrambling sequence 1. The indices 0, 1, 2,
and 3 of
the index columns of the first and second transmission modes of Table 8 are
the cases.
[273] 2. In Table 8, the indices for additional DM-RS antenna port
allocation that can be
applied for retransmission is defined. The indices 4, 5, 6, and 7 of the index
columns of
the first and second transmission modes of Table 8.
[274]
[275] Table 8
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[Table 8]
Transport Block 0 Enabled Transport Block 0 Disabled Transport Block 0 Enabled
and Transport Block 1 and Transport Block 1 and Transport Block 1
Disabled Enabled Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMRS
port 0 with SCO port 0 with SCO port 0, 1 with
allocated allocated SCO allocated
1 Rank 2 1 Rank 2 1 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 1 with SCO port 1 with SCO port 0, 1, 2
with
allocated allocated SCO allocated
2 Rank 2 2 Rank 2 2 Rank 2
pattern,DMRS pattern,DMRS pattern,DMRS
port 0 with SC1 port 0 with SC1 port 0, 1 with
allocated allocated SC1 allocated
3 Rank 2 3 Rank 2 3 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 1 with SC1 port 1 with SC1 port 0, 1, 2, 3
allocated allocated with SCO
allocated
4 Rank 2 4 Rank 2 4 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1 with port 0, 1 with port 0, 1, 2,
3, 4
SCO allocated SCO allocated with SCO
allocated
Rank 2 5 Rank 2 5 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1 with port 0, 1 with port 0, 1, 2,
3,
SC1 allocated SC1 allocated 4, 5 with SCO
allocated
6 Rank 4 6 Rank 4 6 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1, 2 with port 0, 1, 2 with port 0, 1, 2,
3,
SCO allocated SCO allocated 4, 5, 6 with
SCO
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allocated
7 Rank 4 7 Rank 4 7 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1, 2, 3 port 0, 1, 2, 3 port 0, 1, 2,
3,
with SCO with SCO 4, 5, 6, 7 with
allocated allocated SCO allocated
[276] <Table 8 : DM-RS antenna port indication method in an SU-MIMO
transmission for
up to 8 layers per UE and an MU-MIMO transmission for up to 2 layers per UE
with a
maximum composite rank 4 (up to 4 co-scheduled UEs)>
[277]
[278] In Table 8, the index column of each of two transmission modes has 8
indices, unlike
Table 1 in which the index column of each transmission mode has 10 indices.
The
index column of the each transmission mode in Table 8 has 8 indices,
irrespective of
the number of transport blocks to be transmitted. Accordingly, when using
Table 8, 3
bits are used for DM-RS antenna port allocation. Table 8 can be used for DM-RS
antenna port allocation for an initial transmission and a retransmission in
HARQ
process only with 3 bits, unlike Table 7 that also uses 3 bits but does not
support re-
transmission.
[279]
[280] The DM-RS antenna port allocation information corresponding to the
indices 4, 5, 6,
and 7 of the index columns of the first and second transmission modes of Table
8 are
available only when one transport block is transmitted and the transport block
is re-
transmitted. In contrast, the DM-RS antenna port allocation information
corresponding
to the indices 4, 5, 6, and 7 of the index columns of the first and second
transmission
modes of table 8 are available for an initial transmission and a
retransmission.
[281]
[282] The first and second transmission modes are identical with each
other. Accordingly,
Table 8 can be expressed as shown in Table 9.
[283]
[284] In Table 9, the first and second transmission modes are unified into
one transmission
mode, but provide the same results. Additionally, the indices listed in Table
9 are
provided as an example, and it is not necessary to use all the indices shown
therein. For
example, some of the indices can be omitted according to the implementation
method.
[285]
[286] Table 9
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[Table 9]
One of Transport Block 0 or Transport Transport Block 0 Enabled and
Transport
Block 1 Enabled Block 1 Enabled
Index Message Index Message
0 Rank 2 pattern,DMRS 0 Rank 2 pattern,DMRS
port 0 with SCO port 0, 1 with SCO
allocated allocated
1 Rank 2 pattern,DMRS 1 Rank 4 pattern,DMRS
port 1 with SCO port 0, 1, 2 with SCO
allocated allocated
2 Rank 2 pattern,DMRS 2 Rank 2 pattern,DMRS
port 0 with SC1 port 0, 1 with SC1
allocated allocated
3 Rank 2 pattern,DMRS 3 Rank 4 pattern,DMRS
port 1 with SC1 port 0, 1, 2, 3 with
SCO
allocated allocated
4 Rank 2 pattern,DMRS 4 Rank 8 pattern,DMRS
port 0, 1 with SCO port 0, 1, 2, 3, 4 with
SCO
allocated allocated
Rank 2 pattern,DMRS 5 Rank 8 pattern,DMRS
port 0, 1 with SC1 port 0, 1, 2, 3, 4, 5
with
allocated SCO allocated
6 Rank 4 pattern,DMRS 6 Rank 8 pattern,DMRS
port 0, 1, 2 with SCO port 0, 1, 2, 3, 4, 5,
6 with
allocated SCO allocated
7 Rank 4 pattern,DMRS 7 Rank 8 pattern,DMRS
port 0, 1, 2, 3 with SCO port 0, 1, 2, 3, 4, 5,
6, 7
allocated with SCO allocated
[287] <Table 9 : DM-RS antenna port indication method in an SU-MIMO
transmission for
up to 8 layers per UE and an MU-MIMO transmission for up to 2 layers per UE
with
maximum composite rank 4 (up to 4 co-scheduled UEs)>
[288]
[289] As shown in Table 9, when one transport block is transmitted, a
maximum rank is 4,
and the scrambling sequence (SC) is 0 or 1 when the rank is 1 or 2, and is 0
when the
rank is 3 or above. Similarly, when two transport blocks are transmitted, a
maximum
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rank is 8, and the scrambling sequence is 0 or 1 when the rank is 1 or 2, and
is 0 when
the rank is 3 or above.
[290]
[291] In Table 9, when one transport block is transmitted at an initial
transmission, DM-RS
antenna port allocation indication information is interpreted only for rank 1.
When one
transport block is transmitted at a retransmission, the DM-RS antenna port
allocation
indication information is interpreted for all ranks. When two transport blocks
are
transmitted, at either initial transmission or retransmission, the DM-RS
antenna port al-
location indication information is interpreted for all ranks.
[292]
[293] FIG. 9 is a flowchart illustrating a method for allocating DM-RS
antenna ports using
Table 8, according to an embodiment of the present invention. Basically, the
eNB
checks a number of transport blocks assigned to a UE, selects DM-RS antenna
port al-
location indication information according to the number of transport blocks,
generates
control information including information on the number of transport blocks
and the
selected DM-RS antenna port allocation indication information, and transmits
the
generated control information to the UE.
[294]
[295] More specifically, referring to FIG. 9, the eNB performs scheduling
in a subframe in
step 900. In step 910, the eNB determines whether to transmit one or two
transport
blocks to the scheduled UE. According to the number of transport blocks, a
different
index is selected from Table 8. If is the eNB determines to transmit two
transport
blocks, the eNB selects the proper index for the DM-RS antenna port allocation
in-
formation from the index column of the third transmission mode in Table 8 in
step 950.
When transmitting two transport blocks, the index of the DM-RS antenna port al-
location information is selected from the index column of the third
transmission mode
in Table 8, irrespective of whether the transmission is an initial
transmission or a re-
transmission.
[296]
[297] When one transport block is transmitted, the eNB can select different
index from
table 8 depending on whether the current transmission is an initial
transmission or a re-
transmission of the transport block. Accordingly, when the eNB determines to
transmit
one transport block in step 910, the eNB determines whether the transmission
is the
initial transmission or the retransmission of the transport block in step 920.
[298]
[299] When the current transmission is the initial transmission, the eNB
selects an index
from the index column of the first or second transmission modes except the
indices 4,
5, 6, and 7 in step 940. However, when the current transmission is the
retransmission,
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the eNB selects anyone from the index column of the first or second
transmission
modes in step 930.
[300] FIG. 10 is a flowchart illustrating a method for acquiring
information on allocated
DM-RS antenna ports using Table 8, according to an embodiment of the present
invention. Basically, the UE receives control information including transport
block in-
formation and DM-RS antenna port allocation indication information, checks a
number
of transport blocks allocated to the UE based on the transport block
information, and
interprets the DM-RS antenna port allocation indication information according
to the
number of transport blocks.
[301]
[302] More specifically, referring to FIG. 10, the UE performs PDCCH blind
decoding on
the received signal in step 1000. In step 1010, the UE determines whether its
own
downlink scheduling PDCCH is received. When the downlink scheduling PDCCH is
received, the UE checks the DCI carried on the PDCCH in step 1020. In step
1030, the
UE determines whether the number of transport blocks transmitted is 1 or 2.
When the
number of transport blocks is 1, the UE determines whether the transmission is
an
initial transmission or a retransmission of the transport block in step 1040.
When the
transmission is the retransmission of the transport block, in step 1050, the
UE checks
the DM-RS antenna port allocated to the UE itself, based on the index of the
column of
the first and second transmission modes of Table 8 and the DM-RS antenna port
al-
location information corresponding to the index. However, when the
transmission is
the initial transmission of the transport block, in step 1060, the UE checks
the DM-RS
antenna port allocated to the UE itself, based on the index of the column of
the first
and second transmission modes of Table 8, excluding the indices 4, 5, 6, and
7, and the
DM-RS antenna port allocation information corresponding to the index.
[303] When the number of transport blocks is 2, in step 1070, the UE checks
the DM-RS
antenna port allocated to the UE itself, based on the index of the index
column of the
third transmission mode in Table 8 and the DM-RS antenna allocation
information cor-
responding to the index. When two transport blocks are transmitted, it is
possible to
determine the DM-RS antenna port allocated to the UE, irrespective of whether
the
transmission is an initial transmission or a retransmission.
[304]
[305] An example of how to determine whether a transmission is an initial
transmission or
a retransmission in the methods of FIGs. 9 and 10 is to reference an NDI bit
of the
control information transmitted by the eNB, as the NDI bit is toggled for a
new initial
transmission. That is, if a new initial transmission occurs at (n+l)th
transmission, the
NDI bit set to 0 at the nth transmission is toggled so as to be set to 1.
Otherwise, if the
transmission is the retransmission, the value of the NDI bit is maintained.
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[306]
[307] Each of Tables 8 and 9 can be used to notify a UE of DM-RS antenna
port allocation
information in an initial transmission and a retransmission. Another method
for ex-
pressing Tables 8 and 9 is to decompose each table into a table for an initial
transmission and a table for a retransmission. For example, Table 9 can be
divided into
Table 10 and Table 11 for an initial transmission and a retransmission,
respectively.
[308]
[309] Table 10
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[Table 10]
One of Transport Block 0 or Transport Transport Block 0 Enabled and
Transport
Block 1 Enabled Block 1 Enabled
Index Message Index Message
0 Rank 2 pattern,DMRS 0 Rank 2 pattern,DMRS
port 0 with SCO port 0, 1 with SCO
allocated allocated
1 Rank 2 pattern,DMRS 1 Rank 4 pattern,DMRS
port 1 with SCO port 0, 1, 2 with SCO
allocated allocated
2 Rank 2 pattern,DMRS 2 Rank 2 pattern,DMRS
port 0 with SC1 port 0, 1 with SC1
allocated allocated
3 Rank 2 pattern,DMRS 3 Rank 4 pattern,DMRS
port 1 with SC1 port 0, 1, 2, 3 with
SCO
allocated allocated
4 4 Rank 8 pattern,DMRS
port 0, 1,2, 3, 4 with SCO
allocated
5 Rank 8 pattern,DMRS
port 0, 1, 2, 3, 4, 5 with
SCO allocated
6 6 Rank 8 pattern,DMRS
port 0, 1, 2, 3, 4, 5, 6 with
SCO allocated
7 7 Rank 8 pattern,DMRS
port 0, 1, 2, 3, 4, 5, 6, 7
with SCO allocated
[310] <Table 10 : DM-RS antenna port indication method (for an initial
transmission) in an
SU-MIMO transmission for up to 8 layers per UE and an MU-MIMO transmission for
up to 2 layers per UE with a maximum composite rank 3 (up to 4 co-scheduled
UEs)>
[311]
[312] Table 11
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[Table 11]
One of Transport Block 0 or Transport Transport Block 0 Enabled and
Transport
Block 1 Enabled Block 1 Enabled
Index Message Index Message
0 Rank 2 pattern,DMRS 0 Rank 2 pattern,DMRS
port 0 with SCO port 0, 1 with SCO
allocated allocated
1 Rank 2 pattern,DMRS 1 Rank 4 pattern,DMRS
port 1 with SCO port 0, 1, 2 with SCO
allocated allocated
2 Rank 2 pattern,DMRS 2 Rank 2 pattern,DMRS
port 0 with SC1 port 0, 1 with SC1
allocated allocated
3 Rank 2 pattern,DMRS 3 Rank 4 pattern,DMRS
port 1 with SC1 port 0, 1, 2, 3 with
SCO
allocated allocated
4 Rank 2 pattern,DMRS 4 Rank 8 pattern,DMRS
port 0, 1 with SCO port 0, 1, 2, 3, 4 with
SCO
allocated allocated
Rank 2 pattern,DMRS 5 Rank 8 pattern,DMRS
port 0, 1 with SC1 port 0, 1, 2, 3, 4, 5
with
allocated SCO allocated
6 Rank 4 pattern,DMRS 6 Rank 8 pattern,DMRS
port 0, 1, 2 with SCO port 0, 1, 2, 3, 4, 5,
6 with
allocated SCO allocated
7 Rank 4 pattern,DMRS 7 Rank 8 pattern,DMRS
port 0, 1, 2, 3 with SCO port 0, 1, 2, 3, 4, 5,
6, 7
allocated with SCO allocated
[313] <Table 11: DM-RS antenna port indication method (for a
retransmission) in an SU-
MIMO transmission for up to 8 layers per UE and an MU-MIMO transmission for up
to 2 layers per UE with a maximum composite rank 4 (up to 4 co-scheduled UEs)>
[314]
[315] Tables 8, 9, 10, 10, and 11 are designed in consideration of <system
information 1>,
under an assumption that the rank 2 DM-RS pattern and two scrambling sequences
are
used for the composite rank 3 or 4. The rank 4 DM-RS pattern is used with the
same
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<system information 1> characteristics and composite rank 3 or 4, the indices
for
notifying the DM-RS antenna port information and the messages describing the
indices
can be proposed as shown in Table 12.
[316]
[317] Table 12
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[Table 12]
Transport Block 0 Enabled Transport Block 0 Disabled Transport Block 0 Enabled
and Transport Block 1 and Transport Block 1 and Transport Block 1
Disabled Enabled Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMRS
port 0 with port 0 with port 0, 1
allocated allocated allocated
1 Rank 2 1 Rank 2 1 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 1 with port 1 with port 0, 1
allocated allocated allocated
2 Rank 4 2 Rank 4 2 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 0 with port 0 with port 2, 3
allocated allocated allocated
3 Rank 4 3 Rank 4 3 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 1 with port 1 with port 0, 1, 2
allocated allocated allocated
4 Rank 4 4 Rank 4 4 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 2 with port 2 with port 0, 1, 2, 3
allocated allocated allocated
Rank 4 5 Rank 4 5 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 3 with port 3 with port 0, 1, 2,
3, 4
allocated allocated allocated
6 Rank 4 6 Rank 4 6 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1 with port 0, 1 with port 0, 1, 2,
3,
allocated allocated 4, 5 allocated
7 Rank 4 7 Rank 4 7 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
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port 2, 3 with port 2, 3 with port 0, 1, 2,
3,
allocated allocated 4, 5, 6
allocated
8 Rank 4 8 Rank 4 8 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1, 2 with port 0, 1, 2 with port 0, 1, 2,
3,
allocated allocated 4, 5, 6, 7
allocated
9 Rank 4 9 Rank 4 9
pattern,DMRS pattern,DMRS
port 0, 1, 2, 3 port 0, 1, 2, 3
with allocated with allocated
[318] <Table 12 : DM-RS antenna port indication method in an SU-MIMO
transmission
for up to 8 layers per UE and an MU-MIMO transmission for up to 2 layers per
UE
with a maximum composite rank 4 (up to 4 co-scheduled UEs)>
[319]
[320] In Table 12, indices 6, 7, 8, and 9 of the index columns of the first
and second
transmission modes and the DM-RS antenna port allocation messages
corresponding to
the indices are used only for the retransmission. For an initial transmission,
the DM-RS
antenna port allocation is notified with the indices of the index columns of
the first and
second transmission mode, excluding indices 6, 7, 8, and 9, and the messages
corre-
sponding to the indices.
[321]
[322] Table 12 can be expressed as a table having two transmission modes,
like Table 9,
and can also be divided into two separate tables for an initial transmission
and a re-
transmission, respectively, like Tables 10 and 11.
[323]
[324] Table 12 can be used for an eNB to determine DM-RS antenna port
allocation in-
formation to be transmitted and for a UE to interpret received DM-RS
allocation in-
formation, like as illustrated FIGs. 8A, 8B, 9, and 10.
[325]
[326] Table 13 shows indices for notifying a UE of DM-RS antenna port
information and
messages describing the meanings of the indices according to an embodiment of
the
present invention. Unlike Tables 1, 2, 3, 4, 5, 6, and 7, Table 13 is designed
such that
an eNB notifies of the DM-RS antenna port allocation information and
interference-
related information when one transport block is transmitted. Table 13 can be
used to
notify of the DM-RS antenna port allocation for MIMO transmission.
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[327]
[328] <system characteristics 3>
[329] 1. SU-MIMO transmission for 1 layer
[330] 2. MU-MIMO transmission for 1 layer to UE
[331] 3. MU-MIMO transmission to up to 4 UEs
[332] 4. MU-MIMO transmission for up to 4 layers (maximum composite rank 4
of MU-
MIMO)
[333]
[334] Table 13
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[Table 13]
Transport Block 0 Enabled and Transport Block 0 Disabled and
Transport Block 1 Disabled Transport Block 1 Enabled
Index Message Index Message
0 Rank 2 0 Rank 2
pattern,DMRS port 0 pattern,DMRS port 1
allocated,DMRS port allocated,DMRS port
1 not used 1 used by other UE
1 Rank 2 1 Rank 4
pattern,DMRS port 0 pattern,DMRS port 2
allocated,DMRS port allocated,DMRS port
1 used by other UE 0, 1 used by other
UE,DMRS port 3 not
used
2 Rank 4 2 Rank 4
pattern,DMRS port 0 pattern,DMRS port 2
allocated,DMRS port allocated,DMRS port
1, 2 used by other 0, 1, 3 used by
other
UE,DMRS port 3 not UE
used
3 Rank 4 3 Rank 4
pattern,DMRS port 1 pattern,DMRS port 3
allocated,DMRS port allocated,DMRS port
0, 2 used by other 0, 1, 2 used by
other
UE,DMRS port 3 not UE
used
4 Rank 4 4 reserved
pattern,DMRS port 0
allocated,DMRS port
1, 2, 3 used by other
UE
Rank 4 5 reserved
pattern,DMRS port 1
allocated,DMRS port
0, 2, 3 used by other
UE
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[335] <Table 13 : DM-RS antenna port and interference indication method in
SU and MU-
MIMO modes transmitting one transport block per UE with a maximum composite
rank 4>
[336]
[337] In Table 13, each index column has 6 indices, unlike Table 1 of which
each index
column has 10 indices. The number of indices in each index column is reduced
by re-
stricting the number of transport blocks per UE to 1. In view of the number of
bits,
Table 13 allows the eNB to notify the UE of the DM-RS antenna port allocation
and
interference-related information using only 3 bits, as opposed to Table 1
which uses 4
bits.
[338]
[339] Table 14, below, shows indices for notifying a UE of DM-RS antenna
port in-
formation and messages describing the meanings of the indices according to an
em-
bodiment of the present invention. Unlike Tables 1, 2, 3, 4, 5, 6, and 7,
Table 14 is
designed such that an eNB notifies of the DM-RS antenna port allocation
information
and interference-related information when one transport block is transmitted.
Table 14
is used for notifying of the DM-RS antenna port allocation for MIMO
transmission
such as <system characteristics 3>. Further, Table 14 is designed under
assumptions
that the rank 2 DM-RS pattern and two scrambling sequences are used in
composite
rank 3 or 4. This is similar to Table 3.
[340]
[341] In Table 14, the number of indices in each index column is 6, unlike
Table 1 in
which each index column has 10 indices. The number of indices in each index
column
is reduced by restricting the number of transport blocks per UE to 1. In view
of the
number of bits, Table 14 allows the eNB to notify the UE of the DM-RS antenna
port
allocation and interference-related information with only 3 bits as opposed to
Table 1,
uses 4 bits.
[342]
[343] Table 14
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[Table 14]
Transport Block 0 Enabled and Transport Block 0 Disabled and
Transport Block 1 Disabled Transport Block 1 Enabled
Index Message Index Message
0 Rank 2 0 Rank 2
pattern,DMRS port 0 pattern,DMRS port 1
with SCO with SCO
allocated,DMRS port allocated,DMRS port
1 with SCO and 0 with SCO used by
DMRS port 0, 1 with other UE
SC1 not used
1 Rank 2 1 Rank 2
pattern,DMRS port 0 pattern,DMRS port 0
with SCO with SC1
allocated,DMRS port allocated,DMRS port
1 with SCO used by 0, 1 with SCO used
by
other UE,DMRS port other UE,DMRS port
0, 1 with SC1 not 1 with SC1 not used
used
2 Rank 2 2 Rank 2
pattern,DMRS port 0 pattern,DMRS port 0
with SCO with SC1
allocated,DMRS port allocated,DMRS port
1 with SCO and 0, 1 with SCO and
DMRS port 0 with DMRS port 1 with
SC1 used by other SC1 used by other
UE,DMRS port 1 UE
with SC1 not used
3 Rank 2 3 Rank 2
pattern,DMRS port 1 pattern,DMRS port 1
with SCO with SC1
allocated,DMRS port allocated,DMRS port
0 with SCO and 0, 1 with SCO and
DMRS port 0 with DMRS port 0 with
SC1 used by other SC1 used by other
UE,DMRS port 1 UE
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with SC1 not used
4 Rank 2 4 reserved
pattern,DMRS port 0
allocated with
SCO,DMRS port 1
with SCO and DMRS
port 0, 1 with SC1
used by other UE
Rank 2 5 reserved
pattern,DMRS port 1
allocated with
SCO,DMRS port 0
with SCO and DMRS
port 0, 1 with SC1
used by other UE
[344] <Table 14 : DM-RS antenna port and interference indication method in
SU and MU-
MIMO modes transmitting one transport block per UE with a maximum composite
rank 4>
[345]
[346] In the above DM-RS antenna port allocation method, a specific DM-RS
antenna port
has been mentioned. For example, when the transport blocks 0 and 1 are
transmitted in
Table 7, the index 5 indicates the allocation of DM-RS antenna ports 0, 1, 2,
3, 4, and 5
with scrambling code 0. However, the present invention can be applied to the
DM-RS
antenna port combination other than the DM-RS antenna port combination as
described above. According to an embodiment of the present invention, when the
transport blocks 0 and 1 are transmitted simultaneously in Table 7, the index
5 can be
identically applied to the case where the scrambling code 0 is used and the DM-
RS
antenna ports 0, 1, 2, 5, 6, and 7 are allocated, rather than the DM-RS
antenna ports 0,
1, 2, 3, 4, and 5.
[347]
[348] FIG. 11 is a diagram illustrating control information carried on a
PDCCH for use in
an LTE-A system according to an embodiment of the present invention.
[349]
[350] Referring to FIG. 11, control information carried on a PDCCH is
identical with that
illustrated in FIG. 2, except that the control information on each transport
block is
divided into an NDI bit and other control information. The fields 1110 and
1120 carry
the control information on the transport block 0, and the fields 1130 and 1140
carry the
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control information on the transport block 1. More specifically, the NDI
fields 1120
and 1140 carry the control information indicating whether the transport blocks
0 and 1
are initial transmissions in the HARQ process. When the transport block 0 is
not
transmitted, the NDI 0 bit can be used for another purpose, rather than a
notification of
HARQ initial transmission or retransmission.
[351]
[352] Table 15 shows indices for indicating a DM-RS antenna port allocation
and
transmission mode with an NDI bit for a transport block that is not
transmitted
according to an embodiment of the present invention.
[353]
[354] Table 15
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[Table 151
One of Transport Block 0 or Transport Block 1 Enabled Transport Block 0
Enabled
and Transport Block 1
Enabled
NDIx=0 NDI x = 1
Index Message Index Message Index Message
0 Transmit 0 Rank 2 0 Rank 2
Diversity with pattern,DMRS pattern,DMRS
CRS port 0 with SCO port 0, 1 with
allocated SCO
allocated
1 Reserved 1 Rank 2 1 Rank 4
pattern,DMRS pattern,DMRS
port 1 with SCO port 0, 1, 2
allocated with SCO
allocated
2 Reserved 2 Rank 2 2 Rank 2
pattern,DMRS pattern,DMRS
port 0 with SC1 port 0, 1 with
allocated SC1
allocated
3 Reserved 3 Rank 2 3 Rank 4
pattern,DMRS pattern,DMRS
port 1 with SC1 port 0, 1, 2, 3
allocated with SCO
allocated
4 Reserved 4 Rank 2 4 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1 with
port 0, 1, 2, 3,
SCO allocated 4 with SCO
allocated
Reserved 5 Rank 2 5 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1 with
port 0, 1, 2, 3,
SC1 allocated 4, 5 with SCO
allocated
6 Reserved 6 Rank 4 6 Rank 8
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pattern,DMRS pattern,DMRS
port 0, 1, 2 with port 0, 1, 2,
3,
SCO allocated 4, 5, 6 with
SCO allocated
7 Reserved 7 Rank 4 7 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1, 2, 3 port 0, 1, 2,
3,
with SCO 4, 5, 6, 7 with
allocated SCO allocated
[355] <Table 15 : DM-RS antenna port and transmit diversity indication
method in an SU-
MIMO transmission for up to 8 layers per UE and an MU-MIMO transmission for up
to 2 layers per UE with a maximum composite rank 4 (maximum 4 co-scheduled
UEs)>
[356]
[357] In Table 15, NDI x is an NDI bit for the transport block which is not
transmitted and
can be used to notify the UE of the transmission mode in one transport block.
In Tables
1 to 14, only the transmission mode, i.e., SU-MIMO or MU-MIMO, can be notified
to
the UE. In Table 15, it is possible to notify the UE of the further
information, such as
whether transmit diversity is used, by using an NDI bit for a transport block
which is
not transmitted, when only one transport block is transmitted. The transmit
diversity is
available when a CRS is used, and it is possible to use only the Space
Frequency Block
Code (SFBC) or both the Frequency Selective Transmit Diversity (FSTD) and SFBC
depending on the number of CRS antenna ports. That is, when the CRS for two
antenna ports are transmitted, the transmit diversity is automatically
configured with
SFBC, and when the CRS for four antenna ports are transmitted, the transmit
diversity
is automatically configured with FSTC+SFBC. In contrast, if the CRS for a
signal
antenna port is transmitted, the transmit diversity is unavailable and thus
the single port
transmitted is automatically configured.
[358]
[359] Table 15 is designed for cases where an SFBC is used or both an FSTD
and an SFBC
are used. In an LTE-A system, it is possible to use transmit diversity based
on a DM-
RS as well as transmit diversity based on a CRS. When using a DM-RS, transmit
diversity can be implemented as follows:
[360] 1. SFBC with DM-RS antenna ports 0 and 1; and
[361] 2. FSTD+SFBC with DM-RS antenna ports 0, 1, 3, and 3.
[362]
[363] Table 16 shows indices indicating a DM-RS port and transmission mode
with an
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NDI bit for a transport block which is not transmitted and messages describing
the
meanings of the indices according to an embodiment of the present invention.
[364]
[365] Table 16
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[Table 16]
One of Transport Block 0 or Transport Block 1 Enabled Transport Block 0
Enabled
and Transport Block 1
Enabled
NDIx=0 NDI x = 1
Index Message Index Message Index Message
0 No Transmit 0 Rank 2 0 Rank 2
Diversity with pattern,DMRS pattern,DMRS
DMRS port 0 port 0 with SCO port 0, 1 with
with SCO allocated SCO allocated
1 Transmit 1 Rank 2 1 Rank 4
Diversity with pattern,DMRS pattern,DMRS
DMRS port 0,1 port 1 with SCO port 0, 1, 2
with
with SCO allocated SCO allocated
2 Transmit 2 Rank 2 2 Rank 2
Diversity with pattern,DMRS pattern,DMRS
DMRS port port 0 with SC1 port 0, 1 with
0,1,2,3 with allocated SC1 allocated
SCO
3 Reserved 3 Rank 2 3 Rank 4
pattern,DMRS pattern,DMRS
port 1 with SC1 port 0, 1, 2, 3
allocated with SCO
allocated
4 Reserved 4 Rank 2 4 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1 with port 0, 1, 2,
3, 4
SCO allocated with SCO
allocated
Reserved 5 Rank 2 5 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1 with port 0, 1, 2,
3,
SC1 allocated 4, 5 with SCO
allocated
6 Reserved 6 Rank 4 6 Rank 8
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pattern,DMRS pattern,DMRS
port 0, 1, 2 with port 0, 1, 2,
3,
SCO allocated 4, 5, 6 with
SCO allocated
7 Reserved 7 Rank 4 7 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1, 2, 3 port 0, 1, 2,
3,
with SCO 4, 5, 6, 7 with
allocated SCO allocated
[366] <Table 16 : DM-RS antenna port and transmit diversity indication
method in an SU-
MIMO for up to 8 layers per UE and an MU-MIMO for up to 2 layers per UE with a
maximum composite rank 4 (maximum 4 co-scheduled UE)>
[367]
[368] When using Table 16, it is possible to notify the UE of the
information on whether
the transport block is transmitted with transmit diversity and which transmit
diversity
scheme is used, by using an NDI bit for a transport block that is not
transmitted.
[369]
[370] Specifically, Table 15 is designed to notify of the transmit
diversity scheme with a
CRS, and Table 16 is designed to notify of the transmit diversity scheme with
a DM-
RS. In accordance with another embodiment of the present invention, both the
CRS-
based transmit diversity and the DM-RS-based transmit diversity are supported.
In
order to support both the CRS-based transmit diversity and DM-RS-based
transmit
diversity, Tables 15 and 16 are modified into one table.
[371]
[372] Table 17 shows indices indicating a DM-RS port and a transmission
mode with an
NDI bit for a transport block that is not transmitted according to an
embodiment of the
present invention.
[373]
[374] When using Table 17, an eNB to notifies a UE of information on
whether a
transmission is a retransmission and whether transmit diversity is applied and
the DM-
RS antenna port allocation with an NDI bit for a transport block which is not
transmitted. When only one transmit block is transmitted, if the NDI bit for
the
transport block which is not transmitted is set to 0, this NDI bit can be used
for
notifying the UE of the use of transmit diversity or the retransmission of the
transport
block. When using Table 17, if the NDI x for the transport block that is not
transmitted
is set to 0 and the index is 0, transmit diversity is notified to the UE. The
transmit
diversity can be applied to both the HARQ initial transmission and
retransmission. In
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order to simplify the system design, it is possible to configure design such
that transmit
diversity can applied to one of the HARQ initial transmission or
retransmission. When
the transmit diversity is applied to only HARQ retransmission, the NDI x
becomes the
value for determining whether the transmission is HARQ retransmission.
[375]
[376] Table 17
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[Table 17]
One of Transport Block 0 or Transport Block 1 Enabled Transport Block 0
Enabled
NDI x = 0 NDI x = 1 and Transport Block 1
Enabled
Index Message Index Message Index Message
0 Transmit 0 Rank 2 0 Rank 2
Diversity with pattern,DMRS pattern,DMRS
CRS (Initial Tx port 0 with SCO port 0, 1 with
or ReTx) allocated SCO allocated
1 Rank 2 1 Rank 2 1 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1 with port 1 with SCO port 0, 1, 2
with
SCO allocated allocated SCO allocated
(Retx)
2 Rank 2 2 Rank 2 2 Rank 2
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1 with port 0 with SC1 port 0, 1 with
SC1 allocated allocated SC1 allocated
(Retx)
3 Rank 4 3 Rank 2 3 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1, 2 with port 1 with SC1 port 0, 1, 2, 3
SCO allocated allocated with SCO
(Retx) allocated
4 Rank 4 4 Reserved 4 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1, 2, 3 port 0, 1, 2,
3, 4
with SCO with SCO
allocated (Retx) allocated
Reserved 5 Reserved 5 Rank 8
pattern,DMRS
port 0, 1, 2, 3,
4, 5 with SCO
allocated
6 Reserved 6 Reserved 6 Rank 8
pattern,DMRS
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port 0, 1, 2, 3,
4, 5, 6 with
SCO allocated
7 Reserved 7 Reserved 7 Rank 8
pattern,DMRS
port 0, 1, 2, 3,
4, 5, 6, 7 with
SCO allocated
[377] <Table 17 : DM-RS antenna port and transmit diversity indication
method in an SU-
MIMO for up to 8 layers per UE and an MU-MIMO for up to 2 layers per UE with a
maximum composite rank 4 (maximum 4 co-scheduled UEs)>
[378]
[379] Using Tables 15, 16, and 17, it is possible to notify a UE of one of
the SU-MIMO,
MU-MIMO, and transmit diversity along with the DM-RS port allocation
information
with the NDI bit. According to an embodiment of the present invention, another
usage
of an NDI bit for a transmit block that is not transmitted is for notifying of
syn-
chronous HARQ.
[380]
[381] Table 18 shows indices indicating a DM-RS port allocation and
synchronous HARQ
transmission with an NDI bit for a transport block that is not transmitted and
messages
describing the meanings of the indices.
[382]
[383] Table 18
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[Table 18]
One of Transport Block 0 or Transport Block 1 Enabled Transport Block 0
Enabled
and Transport Block 1
Enabled
NDIx=0 NDI x = 1
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMRS
port 0 with SCO port 0 with SCO port 0, 1 with
allocated allocated SCO allocated
(Synchronous
HARQ)
1 Rank 2 1 Rank 2 1 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 1 with SCO port 1 with SCO port 0, 1, 2
allocated allocated with SCO
(Synchronous allocated
HARQ)
2 Rank 2 2 Rank 2 2 Rank 2
pattern,DMRS pattern,DMRS pattern,DMRS
port 0 with SC1 port 0 with SC1 port 0, 1 with
allocated allocated SC1 allocated
(Synchronous
HARQ)
3 Rank 2 3 Rank 2 3 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 1 with SC1 port 1 with SC1 port 0, 1, 2, 3
allocated allocated with SCO
(Synchronous allocated
HARQ)
4 Rank 2 4 Rank 2 4 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1 with port 0, 1 with port 0, 1, 2,
3,
SCO allocated SCO allocated 4 with SCO
(Synchronous allocated
HARQ)
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Rank 2 5 Rank 2 5 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1 with port 0, 1 with port 0, 1, 2,
3,
SC1 allocated SC1 allocated 4, 5 with SCO
(Synchronous allocated
HARQ)
6 Rank 4 6 Rank 4 6 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1, 2 with port 0, 1, 2 with port 0, 1, 2,
3,
SCO allocated SCO allocated 4, 5, 6 with
(Synchronous SCO allocated
HARQ)
7 Rank 4 7 Rank 4 7 Rank 8
pattern,DMRS pattern,DMRS pattern,DMRS
port 0, 1, 2, 3 port 0, 1, 2, 3 port 0, 1, 2,
3,
with SCO with SCO 4, 5, 6, 7 with
allocated allocated SCO allocated
(Synchronous
HARQ)
[384] <Table 18 : DM-RS antenna port and synchronous HARQ indication method
in an
SU-MIMO transmission for up to 8 layers per UE and an MU-MIMO transmission for
up to 2 layers per UE with a maximum composite rank 4 (maximum 4 co-scheduled
UEs)>
[385]
[386] Using Table 18, it is possible to notify a UE of information on
whether a transport
block is transmitted in synchronous HARQ by using an NDI bit for a transport
block
that is not transmitted. Because the synchronous HARQ retransmission occurs
peri-
odically, there is no need to transmit additional PDCCH for the
retransmission.
However, the synchronous HARQ has a drawback in that it does not dynamically
adapt
to a time-varying radio channel. By designing Table 18 to support the
synchronous
HARQ in the single codeword transmission, it is possible to perform
notification with
Table 17, when the radio channel environment becomes proper for the
synchronous
HARQ, resulting in performance optimization.
[387]
[388] Table 19 shows indices indicating a DM-RS port and synchronous HARQ
transmission with an NDI bit for a transport block that is not transmitted and
messages
describing the meanings of the indices according to an embodiment of the
present
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PCT/KR2011/000939
invention.
[389]
[390] Table 19
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[Table 19]
One of Transport Block 0 or Transport Block 1 Enabled Transport Block 0
Enabled
NDI x = 0 NDI x = 1 and Transport Block 1
Enabled
Index Message Index Message Index Message
0 Rank 2 0 Rank 2 0 Rank 2
pattern,DMRS pattern,DMRS pattern,DMRS
port 0 with SCO port 0 with SCO port 0, 1 with
allocated allocated SCO allocated
(Synchronous
HARQ)
1 Rank 2 1 Rank 2 1 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 1 with SCO port 1 with SCO port 0, 1, 2
allocated allocated with SCO
(Synchronous allocated
HARQ)
2 Rank 2 2 Rank 2 2 Rank 2
pattern,DMRS pattern,DMRS pattern,DMRS
port 0 with SC1 port 0 with SC1 port 0, 1 with
allocated allocated SC1 allocated
(Synchronous
HARQ)
3 Rank 2 3 Rank 2 3 Rank 4
pattern,DMRS pattern,DMRS pattern,DMRS
port 1 with SC1 port 1 with SC1 port 0, 1, 2, 3
allocated allocated with SCO
(Synchronous allocated
HARQ)
4 Synchronous 4 Rank 2 4 Rank 8
Transmit pattern,DMRS pattern,DMRS
Diversity port 0, 1 with port 0, 1, 2,
3, 4
SCO allocated with SCO
allocated
Asynchronous 5 Rank 2 5 Rank 8
Transmit pattern,DMRS pattern,DMRS
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Diversity port 0, 1 with port 0, 1, 2,
3,
SC1 allocated 4, 5 with SCO
allocated
6 Reserved 6 Rank 4 6 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1, 2 with port 0, 1, 2,
3,
SCO allocated 4, 5, 6 with
SCO allocated
7 Reserved 7 Rank 4 7 Rank 8
pattern,DMRS pattern,DMRS
port 0, 1, 2, 3 port 0, 1, 2,
3,
with SCO 4, 5, 6, 7 with
allocated SCO allocated
[391] <Table 19 : DM-RS antenna port and synchronous HARQ indication method
in an
SU-MIMO transmission for up to 8 layers per UE and an MU-MIMO transmission for
up to 2 layers per UE with a maximum composite rank 4 (maximum 4 co-scheduled
UEs)>
[392]
[393] Using Table 19, it is possible to notify a UE of an synchronous HARQ
transmission
and whether transmit diversity is applied or not by using an NDI bit for a
transport
block that is not transmitted. In Table 19, when the NDI bit for the transport
block that
is not transmitted is set to 0, the index value can be used to notify the UE
of the syn-
chronous SU/MU-MIMO or the transmit diversity. Table 19 is designed such that
the
synchronous HARQ in SU/MU-MIMO is available for the initial transmission. This
is
the result of selecting the most significant transmission modes in
consideration of the
limited number of index.
[394]
[395] FIG. 12 is a flowchart illustrating a procedure for notifying a UE as
to whether
transmit diversity is applied by using an NDI bit for a transport block that
is not
transmitted in Tables 15 and 16, according to an embodiment of the present
invention.
[396]
[397] Referring to FIG. 12, the UE receives PDCCH and checks the DCI
carried on the
PDCCH in step 1200. In step 1210, the UE determines whether the number of
transport
blocks transmitted is 1 or 2. When 2 transport blocks are transmitted, the UE
de-
termines the DM-RS antenna port allocated to itself based on the DM-RS antenna
port
indication information 1150 of the control information on the PDCCH (see FIG.
11) in
step 1250. Otherwise, when 1 transport block is transmitted, in step 1220, the
UE de-
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termines whether the NDI for the transport block that is not transmitted is
set to 0 or 1.
[398] If the NDI for the transport block that is not transmitted is set to
0, in step 1230, the
UE determines that the transmit diversity is applied. Otherwise, if the NDI
for the
transport block that is not transmitted in set to 1, the UE determines that
the SU-MIMO
or MU-MIMO transmission is performed in step 1240. The detailed information
notified to the UE in FIG. 12 is determined by referencing Tables 15 and 16.
[399]
[400] FIG. 13 is a flowchart illustrating a procedure for notifying a UE as
to whether a
current transmission is an initial transmission or a retransmission and
whether transmit
diversity is applied or not by using an NDI bit for a transport block that is
not
transmitted in Table 17, according to an embodiment of the present invention.
[401]
[402] Referring to FIG. 13, the UE checks the DCI carried on the PDCCH in
step 1300. In
step 1310, the UE determines whether the number of transport blocks
transmitted is 1
or 2. When 2 transport blocks are transmitted, the UE determines the DM-RS
antenna
port allocated to the UE itself, based on the DM-RS antenna port indication in-
formation 1150 of the control information on the PDCCH (see FIG. 11) in step
1350.
Otherwise, when 1 transport block is transmitted at step 1310, in step 1320,
the UE de-
termines whether the NDI for the transport block which is not transmitted is
set to 0 or
1.
[403]
[404] If the NDI for the transport block that is not transmitted is set to
0, the UE determines
that the current transmission is retransmission in step 1330. Otherwise, if
the NDI for
the transport block that is not transmitted is set to 1, the UE determines
that the current
transmission is initial transmission in step 1340. Also, if it is determined
that one
transport block is transmitted and the NDI bit for the transport block which
is not
transmitted is set to 0, the UE determines whether the transmit diversity is
applied
based on the DM-RS antenna port indication information 1150. The detailed in-
formation notified to the UE in FIG. 13 is determined by referencing Table 17.
[405]
[406] FIG. 14 is a flowchart illustrating a procedure for notifying a UE as
to whether syn-
chronous HARQ is applied by using an NDI bit for a transport block that is not
transmitted in Table 18, according to an embodiment of the present invention.
[407]
[408] Referring to FIG. 14, the UE checks the DCI carried on a PDCCH in
step 1400. In
step 1410, the UE determines whether the number of transport blocks
transmitted is 1
or 2. When 2 transport blocks are transmitted, the UE determines the DM-RS
antenna
port allocated to the UE itself, based on the DM-RS antenna port indication in-
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formation 1150 of the control information on the PDCCH (see FIG. 11) in step
1450.
Otherwise, when 1 transport block is transmitted, the UE determines whether
the NDI
for the transport block that is not transmitted is set to 0 or 1 in step 1420.
[409]
[410] If the NDI for the transport block that is not transmitted is set to
0, the UE determines
that synchronous HARQ is applied in step 1430. Otherwise, if the NDI for the
transport block that is not transmitted is set to 1, the UE determines that
the asyn-
chronous HARQ is applied in step 1440. The detailed information notified to
the UE in
FIG. 14 is determined by referencing Table 18.
[411]
[412] The aforementioned synchronous HARQ transmission notification method
is directed
to the downlink transmission, i.e., from the eNB to the UE. However, the
synchronous
HARQ transmission notification method can also be applied to the uplink
transmission,
i.e., from the UE to the eNB.
[413]
[414] As described above, the DM-RS antenna port indication method of the
present
invention is capable of efficiently notifying a UE of the DM-RS resource
allocation in-
formation for receiving the downlink traffic signal along with the information
on the
DM-RS resources allocated for other UEs in a same frequency/time resources in
an
LTE-A system, thereby improving system performance.
[415]
[416] Although not illustrated in the drawings, the methods according to
the above-
described embodiments of the present invention can performed by a UE or an
eNB,
which includes a radio communication unit, i.e., transmitter and receiver, and
a
controller.
[417]
[418] For example, a UE can include a radio communication unit for
receiving the control
information including transport block information and DM-RS antenna port
allocation
indication information and a controller for checking a number of transport
blocks
allocated to the terminal using the transport block information and
interpreting the
DM-RS antenna port allocation indication information according to the number
of
transport blocks.
[419]
[420] Additionally, an eNB can include a controller for checking a number
of transport
blocks allocated to a UE, selecting DM-RS antenna port allocation information
according to the number of the transport blocks, generating control
information
including transport block information and selected DM-RS antenna port
allocation in-
dication information, and a radio communication unit for transmitting the
generated
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control information to the UE.
[421]
[422] Although certain embodiments of the present invention have been
described in detail
hereinabove, it should be clearly understood that many variations and/or
modifications
of the basic inventive concepts herein taught, which may appear to those
skilled in the
present art will still fall within the spirit and scope of the present
invention, as defined
in the appended claims and any equivalents thereof.
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