U.S. patent number RE47,338 [Application Number 14/832,839] was granted by the patent office on 2019-04-02 for multi-user mimo transmissions in wireless communication systems.
This patent grant is currently assigned to Samsung Electronics Co., Ltd.. The grantee listed for this patent is Samsung Electronics Co., Ltd.. Invention is credited to Young-Han Nam, Jianzhong Zhang.
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United States Patent |
RE47,338 |
Zhang , et al. |
April 2, 2019 |
Multi-user MIMO transmissions in wireless communication systems
Abstract
An apparatus and method for providing control information in a
Multi User-Multiple Input Multiple Output (MU-MIMO) wireless
communication system is provided. The method includes receiving a
plurality of Resource Elements (REs) including Downlink Control
Information (DCI), determining, using the DCI, a set of REs to
which a plurality of Downlink Reference Signals (DRSs) may be
mapped, determining remaining REs as REs to which data is mapped,
and demodulating the data using a precoding vector of a DRS
corresponding to the MS.
Inventors: |
Zhang; Jianzhong (Plano,
TX), Nam; Young-Han (Plano, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd. |
Suwon-si, Gyeonggi-do |
N/A |
KR |
|
|
Assignee: |
Samsung Electronics Co., Ltd.
(Suwon-si, KR)
|
Family
ID: |
42934304 |
Appl.
No.: |
14/832,839 |
Filed: |
August 21, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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14276750 |
May 13, 2014 |
RE46161 |
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61212659 |
Apr 14, 2009 |
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Reissue of: |
12753364 |
Apr 2, 2010 |
8369885 |
Feb 5, 2013 |
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Reissue of: |
12753364 |
Apr 2, 2010 |
8369885 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
52/346 (20130101); H04W 52/346 (20130101); H04W
52/325 (20130101); H04W 56/0015 (20130101); H04W
52/325 (20130101); H04W 72/0406 (20130101); H04W
52/242 (20130101); H04W 52/327 (20130101); H04W
52/146 (20130101); H04L 1/1812 (20130101); H04W
52/16 (20130101); H04W 52/16 (20130101); H04L
1/0025 (20130101); H04W 52/146 (20130101); H04L
1/0025 (20130101); H04L 1/1812 (20130101) |
Current International
Class: |
H04B
7/00 (20060101); H04W 56/00 (20090101); H04W
52/32 (20090101); H04W 52/34 (20090101); H04W
72/04 (20090101); H04W 52/24 (20090101); H04L
1/18 (20060101); H04W 52/14 (20090101); H04W
52/16 (20090101); H04L 1/00 (20060101) |
Field of
Search: |
;455/522 ;370/252,329
;375/130,267 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101287278 |
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Oct 2008 |
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CN |
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2013509739 |
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Mar 2013 |
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JP |
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20080054164 |
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Jun 2008 |
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KR |
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20090033001 |
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Apr 2009 |
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KR |
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2347320 |
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Feb 2009 |
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RU |
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2008/044882 |
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Apr 2008 |
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WO |
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2008/050964 |
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May 2008 |
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WO |
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2008072899 |
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Jun 2008 |
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WO |
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2008/115588 |
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Sep 2008 |
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WO |
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Other References
Office Action dated Jun. 20, 2016 in connection with Japanese
Application No. 2015-188766, 8 pages. cited by applicant .
NEC Group, Downlink Control Signalling Support for SU/MU-MIMO, 3GPP
TSG-RAN WG1 Meeting #69, R1-094730, Jeju, Korea, Nov. 9-13, 2009, 7
pages. cited by applicant .
Fujitsu, "Pseudo Transmission Timing Control Using Cyclic Shift for
Downlink CoMP Joint Transmission", 3GPP TSG-RAN1 #56bis, R1-091502,
Seoul, Korea, Feb. 23-27, 2009, 8 pages. cited by applicant .
Motorola, "Control Signaling for Enhanced DL Transmission for LTE",
3GPP TSG RAN WG1 #58bis, R1-091339, Seoul, Korea, Mar. 23-27, 2009,
10 pages. cited by applicant .
Motorola, et al., "DRS EPRE", 3GPP TSG-RAN WG1#54, R1-083247, Jeju,
Korea, Aug. 18-22, 2008, 2 pages. cited by applicant .
Office Action dated Feb. 5, 2016 in connection with Korean Patent
Application No. 10-2011-7027023. cited by applicant .
Chinese Office Action for Chinese Application No. 201510032514.X,
dated Sep. 4, 2017. (13 pages). cited by applicant.
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Primary Examiner: Heneghan; Matthew E
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
.Iadd.Notice: More than one reissue application has been filed for
the reissue of U.S. Pat. No. 8,369,885. The reissue applications
are the present application, which is a divisional reissue of U.S.
Pat. No. 8,369,885, and U.S. patent application Ser. No.
14/276,750, which is an original reissue of U.S. Pat. No. 8,369,885
and which issued as U.S. Pat. No. RE46,161. .Iaddend.This
application .Iadd.is a reissue divisional of U.S. patent
application Ser. No. 14/276,750 filed May 13, 2014, which is an
application for reissue of U.S. Pat. No. 8,369,885 issued Feb. 5,
2013 on U.S. patent application Ser. No. 12/753,364 filed Apr. 2,
2010, and .Iaddend.claims the benefit under 35 U.S.C.
.[..sctn.119(e).]. .Iadd..sctn. 119(e) .Iaddend.of U.S. Provisional
Application No. 61/212,659 filed in the U.S. Patent and Trademark
Office on Apr. 14, 2009, the entire disclosure of which is hereby
incorporated by reference.
Claims
What is claimed is:
.[.1. A method for determining a power ratio of Resource Elements
(REs) transmitted by a Mobile Station (MS), the method comprising:
determining a type of multiplexing used for multiplexing the
Dedicated Reference Signals (DRS) REs; if the type of multiplexing
is determined to be one of Time Division Multiplexing (TDM) and
Frequency Division Multiplexing (FDM), determining if the number of
DRSs transmitted by the BS is known; if the number of transmitted
DRSs is known, setting the Physical Downlink Shared Channel (PDSCH)
data to DRS power ratio to correspond to the number of transmitted
DRSs; and if the number of transmitted DRSs is not known,
determining if the maximum number of DRSs that may be transmitted
is known; if the maximum number of DRSs that may be transmitted is
known: setting the power ratio to correspond to a maximum number of
DRSs that may be transmitted; and otherwise setting the power ratio
to 0 dB..].
.[.2. The method of claim 1, wherein the setting of the power ratio
to correspond to the number of transmitted DRSs comprises using the
equation: .gamma.[dB]=-10log.sub.10(N_DRS), where .gamma.[dB]
comprises the power ratio and N_DRS comprises the number of
transmitted DRSs..].
.[.3. The method of claim 1, wherein the setting of the power ratio
to correspond to the maximum number of DRSs that may be transmitted
comprises using the equation: .gamma.[dB]=-10 log.sub.10(M), where
.gamma.[dB] comprises the power ratio and M comprises the maximum
number of DRSs that may be transmitted..].
.[.4. The method of claim 1, wherein, if the type of modulation is
determined to be Code Division Multiplexing (CDM), setting the
power ratio to 0 dB..].
.[.5. A method for determining a power ratio of Resource Elements
(REs) transmitted by a Mobile Station (MS), the method comprising:
determining a type of multiplexing used for multiplexing Dedicated
Reference Signal (DRS) REs; if the type of multiplexing is
determined to be one of Time Division Multiplexing (TDM) and
Frequency Division Multiplexing (FDM), determining if the number of
DRSs transmitted by a Base Station (BS) is known; if the number of
transmitted DRSs is known, setting Physical Downlink Shared Chanel
(PDSCH) data to DRS power ratio to correspond to the number of
transmitted DRSs; if the number of transmitted DRSs is not known,
determining if the maximum number of DRSs that may be transmitted
is known; if the type of multiplexing is determined to be a hybrid
of CDM and one of FDM and TDM, determining if the number of DRSs
transmitted by the BS is known; and if the number of transmitted
DRSs is known, setting the power ratio to correspond to the number
of transmitted DRSs and a spreading length used for the CDM..].
.[.6. The method of claim 5, wherein, if the total number of DRS
sets that are transmitted is known: setting the power ratio to
correspond to the total number of DRS sets that are transmitted;
and otherwise setting the power ratio to 0 dB..].
.[.7. The method of claim 6, wherein the setting of the power ratio
to correspond to the number of transmitted DRSs and a spreading
length used for the CDM comprises using the equation:
.gamma.[dB]=-10 log.sub.10(N_DRS)+10 log.sub.10(N_SF), where
.gamma.[dB] comprises the power ratio, N_DRS comprises the number
of transmitted DRSs, and N_SF comprises the spreading length used
for the CDM..].
.[.8. The method of claim 5, wherein, if the type of multiplexing
is determined to be a hybrid of CDM and one of FDM and TDM,
determining if the number of CDMed DRS sets and the number of DRSs
transmitted by the BS are known, and determining if the number of
total transmission layers is an odd number and that is greater than
1; and if the number of total transmission layers is an odd number
and the transmission layers are split into two CDMed DRS sets,
applying different power ratios to the layers in the two CDMed DRS
sets..].
.[.9. The method of claim 8, wherein, if it is determined that
three transmission layers are split into two CDMed DRS sets,
applying the power ratio to the set with 2 layers as:
.gamma.[dB]=-10 log.sub.10(N_DRS)+10 log.sub.10(N_SF), and applying
the power ratio to the set with 1 layer as: .gamma.[dB]=10
log.sub.10(N_SET)..].
.[.10. A method for determining a power ratio of Resource Elements
(REs) transmitted by a Mobile Station (MS), the method comprising:
determining a type of multiplexing used for multiplexing Dedicated
Reference Signal (DRS) REs; if the type of multiplexing is
determined to be one of Time Division Multiplexing (TDM) and
Frequency Division Multiplexing (FDM), determining if the number of
DRSs transmitted by a Base Station (BS) is known; if the number of
transmitted DRSs is known, setting Physical Downlink Shared Chanel
(PDSCH) data to DRS power ratio to correspond to the number of
transmitted DRSs; if the number of transmitted DRSs is not known,
determining if the maximum number of DRSs that may be transmitted
is known; if the type of multiplexing is determined to be a hybrid
of CDM and one of FDM and TDM, determining if the number of CDMed
DRS sets transmitted by the BS is known; and if the number of CDMed
DRS sets is known, setting the power ratio to correspond to the
number of CDMed DRS sets..].
.[.11. The method of claim 10, wherein the setting of the power
ratio to correspond to the total number of DRS sets that are
transmitted comprises using the equation: .gamma.[dB]=-10
log.sub.10(N_SET), where .gamma.[dB] comprises the power ratio and
N_SET comprises the total number of DRS sets that are
transmitted..].
.Iadd.12. A method for transmitting a signal in a communication
system, the method comprising: determining a ratio of physical
downlink shared channel (PDSCH) energy per resource element (EPRE)
to mobile specific reference signal EPRE based on a number of
layers; transmitting downlink control information including Hybrid
Automatic Repeat reQuest (HARQ) information, mobile specific
reference signal information, modulation and coding scheme
information per a transport block, and new data indicator
information per the transport block; and transmitting data on the
PDSCH according to the determined ratio and based on the downlink
control information. .Iaddend.
.Iadd.13. The method of claim 12, wherein the number of layers is
equal to a number of mobile specific reference signals.
.Iaddend.
.Iadd.14. The method of claim 12, wherein indices of mobile
specific reference signals indicated by the mobile specific
reference signal information are consecutive. .Iaddend.
.Iadd.15. The method of claim 12, wherein an L.sup.th layer is
associated with an index of mobile specific reference signal,
i_DRS+L-1. .Iaddend.
.Iadd.16. The method of claim 12, wherein a mobile specific
reference signal is defined by applying code division multiplexing
and frequency division multiplexing. .Iaddend.
.Iadd.17. The method of claim 12, wherein the data is mapped onto
resource elements other than cell specific reference signal
resource elements and mobile specific reference signal resource
elements. .Iaddend.
.Iadd.18. An apparatus for transmitting a signal in a communication
system, the apparatus comprising: control circuitry configured to
determine a ratio of physical downlink shared channel (PDSCH)
energy per resource element (EPRE) to mobile specific reference
signal EPRE based on a number of layers; and a transmitter
configured to transmit downlink control information including
Hybrid Automatic Repeat reQuest (HARQ) information, mobile specific
reference signal information, modulation and coding scheme
information per a transport block, new data indicator information
per the transport block, and to transmit data on the PDSCH
according to the determined ratio and based on the downlink control
information. .Iaddend.
.Iadd.19. The apparatus of claim 18, wherein the number of layers
is equal to a number of mobile specific reference signals.
.Iaddend.
.Iadd.20. The apparatus of claim 18, wherein indices of multiple
mobile specific reference signals indicated by the mobile specific
reference signal information are consecutive. .Iaddend.
.Iadd.21. The apparatus of claim 18, wherein a L.sup.th layer is
associated with an index of mobile specific reference signal,
i_DRS+L-1. .Iaddend.
.Iadd.22. The apparatus of claim 18, wherein a mobile specific
reference signal is defined by applying code division multiplexing
and frequency division multiplexing. .Iaddend.
.Iadd.23. The apparatus of claim 18, wherein the data is mapped
onto resource elements other than cell specific reference signal
resource elements and mobile specific reference signal resource
elements. .Iaddend.
.Iadd.24. A method for receiving a signal in a communication
system, the method comprising: receiving downlink control
information including Hybrid Automatic Repeat reQuest (HARQ)
information, mobile specific reference signal information,
modulation and coding scheme information per a transport block, new
data indicator information per the transport block; obtaining a
ratio of physical downlink shared channel (PDSCH) energy per
resource element (EPRE) to mobile specific reference signal EPRE
based on a number of layers; and receiving data that has been
transmitted on the PDSCH according to the obtained ratio and based
on the downlink control information. .Iaddend.
.Iadd.25. The method of claim 24, wherein the number of layers is
equal to a number of mobile specific reference signals.
.Iaddend.
.Iadd.26. The method of claim 24, wherein indices of mobile
specific reference signals indicated by the mobile specific
reference signal information are consecutive. .Iaddend.
.Iadd.27. The method of claim 24, wherein an L.sup.th layer is
associated with an index of mobile specific reference signal,
i_DRS+L-1. .Iaddend.
.Iadd.28. The method of claim 24, wherein a mobile specific
reference signal is defined by applying code division multiplexing
and frequency division multiplexing. .Iaddend.
.Iadd.29. The method of claim 24 wherein the data is mapped onto
resource elements other than cell specific reference signal
resource elements and mobile specific reference signal resource
elements. .Iaddend.
.Iadd.30. An apparatus for receiving a signal in a communication
system, the apparatus comprising: a receiver configured to receive
downlink control information including Hybrid Automatic Repeat
reQuest (HARQ) information, mobile specific reference signal
information, modulation and coding scheme information per a
transport block, new data indicator information per the transport
block; and control circuitry configured to obtain a ratio of
physical downlink shared channel (PDSCH) energy per resource
element (EPRE) to mobile specific reference signals (RSs) based on
a number of layers, wherein the receiver is configured to receive
data that has been transmitted on the PDSCH according to the
obtained ratio and based on the downlink control information.
.Iaddend.
.Iadd.31. The apparatus of claim 30, wherein the number of layers
is equal to a number of mobile specific reference signals.
.Iaddend.
.Iadd.32. The apparatus of claim 30, wherein indices of multiple
mobile specific reference signals indicated by the mobile specific
reference signal information are consecutive. .Iaddend.
.Iadd.33. The apparatus of claim 30, wherein a L.sup.th layer is
associated with an index of mobile specific reference signal,
i_DRS+L-1. .Iaddend.
.Iadd.34. The apparatus of claim 30, wherein a mobile specific
reference signal is defined by applying code division multiplexing
and frequency division multiplexing. .Iaddend.
.Iadd.35. The apparatus of claim 30, wherein the data is mapped
onto resource elements other than cell specific reference signal
resource elements and mobile specific reference signal resource
elements. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to signaling in a Multi User-Multiple
Input Multiple Output (MU-MIMO) wireless communication system. More
particularly, the present invention relates to an apparatus and
method for providing Downlink Control Information (DCI) in a
MU-MIMO wireless communication system.
2. Description of the Related Art
The rapid growth of the wireless mobile communication market has
resulted in a greater demand for various multimedia services in a
wireless environment. Recently, to provide such multimedia
services, which include a large amount of transmit data and
increased data delivery rate, research is being conducted on
Multiple Input Multiple Output (MIMO) wireless communication
systems that provide a more efficient use of limited
frequencies.
A MIMO wireless communication system can transmit a signal over
independent channels per antenna and thus increase transmission
reliability and data throughput without the use of an additional
frequency or need for additional transmit power, as compared to a
single-input single-output system. Furthermore, the MIMO wireless
communication system can be extended to a MIMO system in a Multi
User (MU) environment supporting a plurality of users. Such an
MU-MIMO system enables the plurality of users to share spatial
resources ensured by the multiple antennas, thus further improving
the spectral efficiency.
In the next generation communication system employing MU-MIMO,
research is actively in progress to provide a variety of Quality of
Services (QoS) with a data transfer speed of about 100 Mbps.
Representative examples of such communication systems include the
Institute of Electrical and Electronics Engineers (IEEE) 802.16
system and the 3.sup.rd Generation Partnership Project (3GPP) Long
Term Evolution (LTE) standard. Both the IEEE 802.16 system and the
LTE standard employ Orthogonal Frequency Division Multiplexing
(OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme
so that a broadband network can be supported in a physical
channel.
FIGS. 1A and 1B illustrate a generic downlink frame structure used
in a wireless communication system employing OFDM according to the
related art.
Referring to FIG. 1A, the generic frame structure used in OFDM
downlink includes a 10 ms radio frame 101 divided into 20 equal
slots 103 of 0.5 ms. A sub-frame 105 consists of two consecutive
slots such that one frame includes 10 sub-frames.
Referring to FIG. 1B, a generic structure of a resource grid for
the duration of one downlink slot 103 is illustrated. The available
downlink bandwidth consists of N.sub.BW.sup.DL sub-carriers with a
spacing of 15 kHz. The value of N.sub.BW.sup.DL can vary in order
to allow for scalable bandwidth operation up to 20 MHz. One
downlink slot also consists of N.sub.Symb.sup.DL symbols, each
symbol including a Cyclic Prefix (CP) added as a guard time such
that the value of N.sub.Symb.sup.DL depends on the length of the
CP. As illustrated in FIG. 1, the generic frame structure with
normal CP length has N.sub.Symb.sup.DL=7 symbols.
In a wireless communication system employing OFDM technology, data
is allocated to a Mobile Station (MS) using Resource Elements (REs)
107 of a resource block 109. As illustrated in FIG. 1B, a resource
block 109 consists of 12 consecutive sub-carriers in the frequency
domain and N.sub.Symb.sup.DL consecutive symbols in the time
domain. Depending on the required data rate, each MS can be
assigned one or more resource blocks in each transmission interval
of 1 ms (i.e., 2 slots or 1 sub-frame), the resource assignment
being performed by a Base Station (BS). The user data is carried on
a Physical Downlink Shared Channel (PDSCH) and the downlink control
signaling, used to convey scheduling decisions to individual MSs,
is carried on the Physical Downlink Control Channel (PDCCH). The
PDCCH is located in the first OFDM symbols of a slot.
An aspect of the OFDM technology is the use of reference signals
that are provided within the resource blocks for each MS. The
reference signals are used by an MS for cell search, channel
estimation, neighbor cell monitoring, mobility measurements, and
the like. Moreover, the types of reference signals include a
Cell-specific Reference Signal (CRS) and an MS specific reference
signal, also known as a Dedicated Reference Signal (DRS).
FIGS. 2A through 2G illustrate downlink CRSs used in 1-antenna,
2-antenna and 4-antenna configurations according to the related
art.
Referring to FIGS. 2A through 2G, pre-defined REs are used to carry
the CRS sequences depending on the number of antennas. In the
single antenna system illustrated in FIG. 2A, a CRS is placed in
the RE associated with the #0 and #4 symbols of each slot in the
time domain. In the frequency domain, the CRS is placed in the RE
associated with each 6.sup.th subcarrier, there being a staggering
of 3 subcarriers between symbols. In the two and four antenna
systems of FIGS. 2B through 2G, CRSs are placed in REs in a fashion
similar to that of the single antenna system, there being an offset
of 3 subcarriers between CRSs for the different antennas. Moreover,
with reference to the 2-antenna system (FIGS. 2B and 2C) and
4-antenna system (FIGS. 2D through 2G), REs used for CRS
transmission of one antenna are not used for transmission on the
other antenna(s).
FIG. 3 illustrates a downlink DRS for use in a wireless
communication system employing OFDM technology according to the
related art.
Referring to FIG. 3, a DRS pattern, indicated by elements
(R.sub.5), is illustrated in a pair of resource blocks along with
unnumbered CRSs of a 4-antenna system. In contrast to the CRS,
which uses 8 REs per resource block pair, the DRS uses 12 REs
within the pair of resource blocks. The DRSs are supported for
1-antenna transmission of PDSCH and the MS is informed by a higher
layer as to whether the DRS is present. Moreover, the DRS is
transmitted only on the resource blocks upon which the
corresponding PDSCH is mapped, the PDSCH and antenna port using the
same pre-coding.
The downlink control signaling, used to convey scheduling decisions
to individual MSs, is carried on the PDCCH, which is located in the
first OFDM symbols of a slot. The information carried on the PDCCH
is referred to as Downlink Control Information (DCI). Depending on
the purpose of the control message, different formats of DCI are
defined. More specifically, the 3GPP Technical Specification (TS)
36.212 defines various formats of DCI based on different needs of
the communication system at the time of scheduling. For example,
DCI Format 0 is used for the scheduling of a Physical Uplink Shared
Channel (PUSCH), and DCI Format 1 is used for the scheduling of one
PDSCH codeword. In TS 36.212, there are 10 DCI formats (i.e.,
formats 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 3 and 3A), each DCI format
including various information that may be used in conjunction with
the reference signals for receiving data transmitted by the BS.
As the technology regarding wireless communication systems continue
to advance, improvements are being made regarding transmission and
reception of greater amounts of data. These improvements often
require additional or different control information to be
transmitted from a BS to an MS. Accordingly, there is a need for an
improved apparatus and method for providing and using control
information in a wireless communication system.
SUMMARY OF THE INVENTION
An aspect of the present invention is to address at least the
above-mentioned problems and/or disadvantages and to provide at
least the advantages described below. Accordingly, an aspect of the
present the present invention is to provide an improved apparatus
and method for providing and using control information in a Multi
User-Multiple Input Multiple Output (MU-MIMO) mobile communication
system.
According to an aspect of the present invention, a method for
receiving a wireless communication signal by a Mobile Station (MS)
is provided. The method includes receiving a plurality of Resource
Elements (REs) including Downlink Control Information (DCI),
determining, using the DCI, a set of REs to which a plurality of
Downlink Reference Signals (DRSs) may be mapped, determining
remaining REs as REs to which data is mapped, and demodulating the
data using a precoding vector of a DRS corresponding to the MS.
According to yet another aspect of the present invention, a method
for transmitting a wireless communication signal by a Base Station
(BS) is provided. The method includes code division multiplexing a
plurality of Dedicated Reference Signals (DRS) and mapping the
multiplexed DRSs to one or more respective sets of Resource
Elements (REs), mapping data to REs other than the one or more sets
of REs, and transmitting a plurality of REs including the one or
more sets of REs, the data REs, and REs comprising Downlink Control
Information (DCI), wherein the DCI includes a spreading code used
for the multiplexing of the DRSs.
According to still another aspect of the present invention, a
method for receiving a wireless communication signal by a MS. The
method including receiving a plurality of Resource Elements (REs)
including Downlink Control Information (DCI), determining, using
the DCI, one or more sets of REs to which a plurality of Downlink
Reference Signals (DRSs) are mapped, determining remaining REs as
REs to which data is mapped, despreading the data using a spreading
index included in the DCI, and demodulating the data using a
precoding vector of a DRS corresponding to the MS.
According to another aspect of the present invention, a method for
receiving a wireless communication signal by an MS is provided. The
method includes receiving a plurality of Resource Elements (REs)
including Downlink Control Information (DCI), determining, using a
downlink power offset field in the DCI, the number of Downlink
Reference Signals (DRSs) mapped to respective REs, determining
remaining REs as REs to which data is mapped, and demodulating the
data using a precoding vector of a DRS corresponding to the MS.
According to another aspect of the present invention, a method for
transmitting a wireless communication signal by a BS is provided.
The method includes mapping a plurality of Dedicated Reference
Signals (DRS) to respective Resource Elements (REs), mapping data
to REs other than REs mapped to respective DRSs, and transmitting a
plurality of REs including the REs mapped to respective DRSs, the
data REs, and REs comprising Downlink Control Information (DCI),
wherein the DCI includes a downlink power offset field indicating
the number of DRSs mapped to respective REs.
According to still another aspect of the present invention, a
method for controlling downlink power of a wireless communication
signal by a BS is provided. The method includes determining a
number of Dedicated Reference Signals (DRSs) transmitted by the BS,
and determining a value of power offset using the determined number
of DRSs.
According to yet another aspect of the present invention, a method
for determining a power ratio of Resource Elements (REs)
transmitted by an MS is provided. The method includes determining a
type of modulation used for modulating the REs, if the type of
modulation is determined to be one of Time Division Multiplexing
(TDM) and Frequency Division Multiplexing (FDM), determining if the
number of Dedicated Reference Signals (DRSs) transmitted by the BS
is known, if the number of transmitted DRSs is known, setting the
power ratio to correspond to the number of transmitted DRSs, and if
the number of transmitted DRSs is not known, determining if the
maximum number of DRSs that may be transmitted is known.
Other aspects, advantages, and salient features of the invention
will become apparent to those skilled in the art from the following
detailed description, which, taken in conjunction with the annexed
drawings, discloses exemplary embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and advantages of certain
exemplary embodiments of the present invention will be more
apparent from the following detailed description in conjunction
with the accompanying drawings, in which:
FIGS. 1A and 1B illustrate a generic downlink frame structure used
in a wireless communication system employing Orthogonal Frequency
Division Multiplexing (OFDM) according to the related art;
FIGS. 2A through 2G illustrate downlink Cell-specific Reference
Signals (CRSs) used in 1-antenna, 2-antenna and 4-antenna
configurations according to the related art;
FIG. 3 illustrates a downlink Dedicated Reference Signal (DRS) for
use in a wireless communication system employing OFDM technology
according to the related art;
FIGS. 4A and 4B illustrate a comparison between format 1D of
3.sup.rd Generation Partnership Project (3GPP) Technical
Specification (TS) 36.212 and a first proposed format for Downlink
Control Information (DCI) according to the related art;
FIG. 5 illustrates the use of two downlink DRSs in a wireless
communication system employing 2-antennas and using the proposed
DCI format 1E according to the related art;
FIGS. 6A and 6B illustrate individual Mobile Station (MS) behavior
upon receipt of the proposed DCI format 1E according to the related
art;
FIGS. 7A and B illustrate a comparison between format 1D of 3GPP TS
36.212 and a second proposed format for DCI according to the
related art;
FIGS. 8A and B illustrate individual MS behavior upon receipt of
the proposed DCI format 1F according to the related art;
FIGS. 9A and B illustrate a comparison between format 1D of 3GPP TS
36.212 and a third proposed format for DCI according to the related
art;
FIG. 10 illustrates a fourth proposed format for DCI according to
the related art;
FIGS. 11A and B illustrate a comparison between format 1D of 3GPP
TS 36.212 and a fifth proposed format for DCI according to the
related art;
FIG. 12 illustrates a sixth proposed format for DCI according to
the related art;
FIGS. 13A through 13C illustrate dual layer RS patterns for systems
using Frequency Division Multiplexing (FDM), Time Division
Multiplexing (TDM) and Code Division Multiplexing (CDM) according
to an exemplary embodiment of the present invention;
FIGS. 14A and B illustrate a downlink DRS pattern in a wireless
communication system according to an exemplary embodiment of the
present invention;
FIG. 15 illustrates a hybrid CDM/FDM DRS pattern according to an
exemplary embodiment of the present invention;
FIGS. 16A and B illustrate a DCI format according to an exemplary
embodiment of the present invention;
FIGS. 17A and B illustrate a DCI format according to an exemplary
embodiment of the present invention;
FIG. 18 is a flowchart illustrating a method of determining a power
ratio .gamma. according to an exemplary embodiment of the present
invention; and
FIGS. 19A through 19C illustrate a combination of two downlink
power control equations for a rank-3 transmission according to an
exemplary embodiment of the present invention.
Throughout the drawings, it should be noted that like reference
numbers are used to depict the same or similar elements, features,
and structures.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The following description with reference to the accompanying
drawings is provided to assist in a comprehensive understanding of
exemplary embodiments of the invention as defined by the claims and
their equivalents. It includes various specific details to assist
in that understanding but these are to be regarded as merely
exemplary. Accordingly, those of ordinary skill in the art will
recognize that various changes and modifications of the embodiments
described herein can be made without departing from the scope and
spirit of the invention. In addition, descriptions of well-known
functions and constructions are omitted for clarity and
conciseness.
The terms and words used in the following description and claims
are not limited to the bibliographical meanings, but, are merely
used by the inventor to enable a clear and consistent understanding
of the invention. Accordingly, it should be apparent to those
skilled in the art that the following description of exemplary
embodiments of the present invention are provided for illustration
purpose only and not for the purpose of limiting the invention as
defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a," "an," and "the"
include plural referents unless the context clearly dictates
otherwise. Thus, for example, reference to "a component surface"
includes reference to one or more of such surfaces.
Exemplary embodiments of the present invention provide an apparatus
and method for controlling operations of a Mobile Station (MS) when
control information is received from a Base Station (BS).
Additional exemplary embodiments of the present invention provide
an improved format for control information provided by a BS to an
MS. Yet further exemplary embodiments of the present invention
provide an apparatus and method by a BS for controlling the power
level used for transmitting control information to an MS.
The following description may refer to terminology that is specific
to a certain mobile communication technology. However, this is not
to be construed as limiting the application of the invention to
that specific technology. For example, although terms such as User
Equipment (UE) and evolved Node B (eNB), which are terms associated
with the Long Term Evolution (LTE) communication standard, may be
used in the following description, it is to be understood that
these are merely specific terms for the generic concepts of an MS
and a BS. That is, the present invention may be applied not only to
systems employing the LTE standard, but equally to any
communication system, such as a communication system employing the
Institute of Electrical and Electronics Engineers (IEEE) 802.16m
standard as well as the Worldwide Interoperability for Microwave
Access (WiMAX) forum technologies.
Before an explanation is provided regarding exemplary embodiments
of the present invention, a description of related art will be
provided to assist in understanding various aspects of the present
invention.
To facilitate Dedicated Reference Signal (DRS) based Multi
User-Multiple Input Multiple Output (MU-MIMO) with single-layer
data transmission, revised formats for Downlink Control Information
(DCI) have been suggested. Specifically, U.S. provisional patent
application 61/206,597, filed on Feb. 2, 2009, entitled "Multi-User
Multi-Cell MIMO Transmissions in Wireless Communication Systems"
and assigned to the assignee of the current application, the entire
disclosure of which is hereby incorporated by reference, discloses
therein a DCI format to address DRS based MU-MIMO single-layer
transmission. As will be illustrated below, the proposed DCI format
includes changes relative to DCI format 1D which is described in
3.sup.rd Generation Partnership Project (3GPP) Technical
Specification (TS) 36.212.
FIGS. 4A and B illustrate a comparison between format 1D of 3GPP TS
36.212 and a first proposed format for DCI according to the related
art.
Referring to FIG. 4A, DCI format 1D includes a Hybrid Automatic
Repeat reQuest (HARQ) field 403, a Modulation and Coding Scheme
(MCS) field 405, a Transmitted Precoding Matrix Indicator (TPMI)
field 407, and other fields 401. Referring to FIG. 4B, the DCI
format proposed in provisional application 61/206,597, which is
here designated as DCI format 1E, includes an HARQ field 411, an
MCS field 413, and other fields 409. In distinction from DCI format
1D, DCI format 1E does not include a TPMI field and introduces a
field regarding the index of the DRS (i_DRS) 415 used in the
relevant transmission. The i_DRS field 415 indicates which DRS in
the system is to be used by the MS receiving the DCI. The bitwidth
of the i_DRS field depends on the maximum number of DRSs allowed in
the MU-MIMO system. This maximum allowed DRS number is denoted by
M, such that the bitwidth of i_DRS is .left brkt-top. log.sub.2
M.right brkt-bot.. The value of M is either fixed in the standard
or signaled by the BS as a cell-specific value. In an exemplary
implementation, the value of M may be provided in a broadcast
channel.
Use of the proposed DCI format 1E results in the following actions
by the BS and the MS. If the DCI format 1E is used by the BS during
a Scheduling Assignment (SA) for MU-MIMO transmission, in the data
to Resource Element (RE) mapping step performed by the BS, the BS
transmits data on REs other than the set of DRS REs indicated by
the index i_DRS. Upon receipt of the DCI format 1E, the MS will
assume that the set of DRS REs indicated by i_DRS are precoded
using the same precoding vector as the data layer, and therefore
may be used as a demodulation pilot for the data layer. The MS will
also assume that the BS data is mapped to the REs other than the
set of DRS REs indicated by the index i_DRS. Furthermore, the MS
will assume that the BS data is mapped to REs other than any
Cell-specific Reference Signals (CRSs) used in the transmission.
The following example assists in understanding use of the DCI
format 1E with DRS patterns defined by a system.
FIG. 5 illustrates the use of two downlink DRSs in a wireless
communication system employing 2-antennas and using the proposed
DCI format 1E according to the related art. FIGS. 6A and 6B
illustrate individual MS behavior upon receipt of the proposed DCI
format 1E according to the related art.
Referring to FIG. 5, it is assumed that M=2 (i.e., there are 2 DRS
patterns specified in the system) and that there are two CRSs
(i.e., CRS1 and CRS2) in the Resource Block (RB). Furthermore, it
is assumed that two MSs are schedule in a sub-frame (e.g., MS#1 and
MS#2) such that for MS#1, i_DRS=1 meaning that the first DRS
pattern, DRS(1), is used for MS#1. Similarly, for MS#2, i_DRS=2
meaning that the second DRS pattern, DRS(2), is used for MS#2.
Referring to FIGS. 6A and 6B, FIG. 6A illustrates the observations
of MS#1 while FIG. 6B illustrates the observations of MS#2. As
illustrated in FIG. 6A, MS#1 only recognizes DRS(1) as a pilot RE
and recognizes other REs (other than CRS1, CRS2 and DRS(1)) as data
REs. Similarly, MS#2 as illustrated in FIG. 6B only recognizes
DRS(2) as a pilot RE and recognizes other REs (other than CRS1,
CRS2 and DRS(2)) as data REs. The drawback of this approach is that
MS#1 will transmit data on the REs where DRS(2) occurs. Similarly,
MS#2 will transmit data on the REs where DRS(1) occurs. Such
transmissions by the MSs will create interference between the data
REs of one MS and the DRS of the other MS.
FIGS. 7A and 7B illustrate a comparison between format 1D of 3GPP
TS 36.212 and a second proposed format for DCI according to the
related art.
Referring to FIGS. 7A and 7B, FIG. 7A illustrates DCI format 1D
which includes an HARQ field 703, an MCS field 705, a TPMI field
707, and other fields 701. Referring to FIG. 7B, a second DCI
format proposed in provisional application 61/206,597 and here
designated as DCI format 1F, includes an HARQ field 711, an MCS
field 713, and other fields 709. In distinction from DCI format 1D,
DCI format 1F does not include a TPMI field and introduces two
fields. Similar to the proposed DCI format 1E, DCI format 1F
introduces a field indicating the index of the DRS (i_DRS) 717 used
in this transmission. The i_DRS field 717 indicates which DRS in
the system is to be used by the MS receiving the DCI. The bitwidth
of the i_DRS field depends on the maximum number of DRSs allowed in
the MU-MIMO system. This maximum allowed DRS number is denoted by
M, such that the bitwidth of i_DRS is .left brkt-top. log.sub.2
M.right brkt-bot.. The value of M is either fixed in the standard
or signaled by the BS as a cell-specific value. In an exemplary
implementation, the value of M may be provided in a broadcast
channel.
The proposed DCI format 1F also introduces a field that indicates
the total number of DRSs (N_DRS) 715 in the scheduled band. More
specifically, the field N_DRS indicates the total number of DRSs in
the scheduled band which includes the DRSs used for this MS and
other MSs scheduled in the same band in this particular sub-frame.
The bitwidth of the N_DRS field is also .left brkt-top. log.sub.2
M.right brkt-bot., and the value range of N_DRS is
1.ltoreq.N_DRS.ltoreq.M.
Once an MS receives N_DRS and i_DRS, it expects that the set of
DRSs (i.e., DRS(1), DRS(2) . . . DRS(N_DRS)) is used for
transmitting data to multiple users in this sub-frame. In addition,
the MS expects DRS(i_DRS) is used as a reference signal to
demodulate its own data.
More specifically, use of the prolonged DCI format 1F results in
the following actions by the BS and the MS. The MS assumes that the
DRS RE indicated by i_DRS is precoded using the same precoding
vector as the data layer and can therefore be used as a
demodulation pilot for the data layer. In addition, if the DCI
format 1F is used by the BS during an SA for MU-MIMO transmission,
in terms of avoiding DRS REs in the data to RE mapping step of BS
transmission, there are at least three alternatives.
In alternative 1, the BS transmits data on REs other than the sets
of DRS REs indicated by (DRS(1), . . . , DRS(N_DRS)). At the MS,
the MS will assume the BS data is mapped to the REs other than the
set of DRS REs indicated by the set (DRS(1), . . . DRS(N_DRS)).
In alternative 2, similar to the actions regarding transmission of
DCI format 1D, the BS transmits data on REs other than the set of
DRS REs indicated by the index i_DRS. At the MS, the MS will assume
the BS data is mapped to the REs other than the set of DRS REs
indicated by the index i_DRS.
In alternative 3, the MS receives a cell-specific or MS-specific
switch, configured by the BS using higher layers, denoted by
DRS_region_switch. In this case, if DRS_region_switch=0, then the
MS assumes that the BS data is mapped to the REs other than the set
of DRS REs indicated by the set (DRS(1), . . . DRS(N_DRS)). On the
other hand, if DRS_region_switch=1, then the MS assumes that the BS
data is mapped to the REs other than the set of DRS REs indicated
by the index DRS(i_DRS). An example is provided to assist in
understanding use of the DCI format 1F.
FIGS. 8A and 8B illustrate individual MS behavior upon receipt of
the proposed DCI format 1F according to the related art.
Referring again to FIG. 5, it is assumed that M=2, and that 2 DRS
patterns and two CRS patterns are used in the RB. It is also
assumed that alternative 1 of data to RE mapping approach is use by
the BS. Furthermore, it is assumed that two MSs are scheduled in a
sub-frame (i.e., MS#1 and MS#2) such that for MS#1, N_DRS=2 and
i_DRS=1, meaning that the first DRS patterns, DRS(1), is used for
MS#1. Also, for MS#2, N_DRS=2 and i_DRS=2, meaning that the second
DRS pattern, DRS(2), is used for MS#2.
Referring to FIG. 8A, MS#1 only recognizes DRS(1) as a pilot RE and
recognizes other REs (other than CRS1, CRS2, DRS(1), and DRS(2)) as
data REs. Referring to FIG. 8B, MS#2 only recognizes DRS(2) as a
pilot RE and recognizes other REs (other than CRS1, CRS2, DRS(1),
and DRS(2)) as data REs. Compared to the approach illustrated in
FIGS. 6A and 6B, this approach does not suffer from the
interference caused by one MS's DRS and another MS's data.
FIGS. 9A and 9B illustrate a comparison between format 1D of 3GPP
TS 36.212 and a third proposed format for DCI according to the
related art. FIG. 10 illustrates a fourth proposed format for DCI
according to the related art.
Referring to FIG. 9A, DCI format 1D includes an HARQ field 903, an
MCS field 905, a TPMI field 907, and other fields 901. Referring to
FIG. 9B, the third DCI format proposed in provisional application
61/206,597 and here designated as DCI format 1G includes an HARQ
field 911, an MCS field 913, and other fields 909. In distinction
from DCI format 1D, DCI format 1G does not include a TPMI field and
introduces two fields. Similar to the proposed DCI formats 1E and
1F, DCI format 1G introduces a field indicating the index of the
DRS (i_DRS) 917 used in the relevant transmission. The i_DRS field
917 indicates which DRS in the system is to be used by the MS
receiving the DCI. The bitwidth of the i_DRS field depends on the
maximum number of DRSs allowed in the MU-MIMO system. This maximum
allowed DRS number is denoted by M, such that the bitwidth of i_DRS
is .left brkt-top. log.sub.2 M.right brkt-bot.. The value of M is
either fixed in the standard or signaled by the BS as a
cell-specific value. In an exemplary implementation, the value of M
may be provided in a broadcast channel.
The proposed DCI format 1G also introduces a field that indicates
the Number of Layers (N_L) 915 in the relevant transmission to the
MS. Accordingly, by using the proposed format 1G, the BS conveys
(1) how many layers are used for data transmission, and (2) the
corresponding DRSs for these layers. Furthermore, in DCI format 1G,
it is assumed that one codeword is transmitted from the BS to the
MS, regardless of the number of layers used in the
transmission.
If the DCI format 1G is used by the BS during an SA for MU-MIMO
transmission, in the data to RE mapping step, the BS transmits data
on REs other than the set of DRS REs indicated by the set of
consecutive DRS patterns (DRS (i_DRS), . . . , DRS(i_DRS+N_L)).
Upon receipt of this transmission, the MS will assume that the set
of REs indicated by DRS(i_DRS) is precoded using the same precoding
vector as the data layer #1, and therefore can be used as a
demodulation pilot for data layer #1. Similarly, DRS(i_DRS+1) is
used to demodulate layer #2, . . . , DRS(i_DRS+N_L) is used to
demodulate layer #N_L. The MS will also assume that the BS data is
mapped to the REs other than the set of DRS REs indicated by the
index (DRS(i_DRS), . . . DRS(i_DRS+N_L)).
Referring to FIG. 10, as a variation of format 1G, if up to two
codewords are used in the MU-MIMO, DCI format 2G is also proposed
in provisional application 61/206,597. As illustrated in FIG. 10,
the proposed DCI format 2G includes an HARQ field 1003, an N_L
field 1009, an i_DRS field 1011 and other fields 1001. The N_L
field 1009 and i_DRS field 1011 are substantially the same as those
proposed in DCI format 1G. However, as illustrated in FIG. 10,
there are two sets of MCS fields 1005 and 1007, each corresponding
to a given Transport Block (TB), respectively related to the two
codewords.
FIGS. 11A and 11B illustrate a comparison between format 1D of 3GPP
TS 36.212 and a fifth proposed format for DCI according to the
related art. FIG. 12 illustrates a sixth proposed format for DCI
according to the related art.
Referring to FIG. 11A, DCI format 1D includes an HARQ field 1103,
an MCS field 1105, a TPMI field 1107, and other fields 1101.
Referring to FIG. 11B, the fifth DCI format proposed in provisional
application 61/206,597 and here designated as DCI format 1H,
includes an HARQ field 1111, an MCS field 1113, and other fields
1109. In distinction from DCI format 1D, DCI format 1H does not
include a TPMI field and introduces three fields. Similar to the
proposed DCI formats 1E, 1F, and 1G, DCI format 1H introduces a
field indicating the index of the DRS (i_DRS) 1119 used in this
transmission. The i_DRS field 1119 indicates which DRS in the
system is to be used by the MS receiving the DCI. The bitwidth of
the i_DRS field 1119 depends on the maximum number of DRSs allowed
in the MU-MIMO system. This maximum allowed DRS number is denoted
by M, such that the bitwidth of i_DRS is .left brkt-top. log.sub.2
M.right brkt-bot.. The value of M is either fixed in the standard
or signaled by the BS as a cell-specific value. In an exemplary
implementation, the value of M may be provided in a broadcast
channel.
The proposed DCI format 1H also introduces a field that indicates
the number of layers (N_L) 1115 in the transmission to this MS and
introduces a field that indicates the total number of DRSs (N_DRS)
1117 in the scheduled band. More specifically, the field N_DRS 1117
indicates the total number of DRSs in the scheduled band which
includes the DRSs used for this MS and other MSs scheduled in the
same band in this particular sub-frame. The bitwidth of the N_DRS
field 1117 is also .left brkt-top. log.sub.2 M.right brkt-bot., and
the value range of N_DRS is 1.ltoreq.N_DRS.ltoreq.M.
In DCI format 1H, it is assumed that one codeword is transmitted
from the BS to the MS, regardless of number of layers used in the
transmission.
If the DCI format 1H is used by the BS during an SA for MU-MIMO
transmission, the MS shall assume that the set of REs indicated by
DRS(i_DRS) is precoded using the same precoding vector as the data
layer #1, and can therefore be used as a demodulation pilot for
data layer #1. Similarly, DRS(i_DRS+1) can be used to demodulate
layer #2, . . . , DRS(i_DRS+N_L) can be used to demodulate layer
#N_L. In addition, in terms of avoiding DRS REs in the data to RE
mapping step during BS transmission, there are at least three
alternatives.
In alternative 1, the BS transmits data on REs other than the sets
of DRS REs indicated by the set (DRS(1), . . . , DRS(N_DRS)). The
MS will assume the BS data is mapped to the REs other than the set
of DRS REs indicated by the set (DRS(1), . . . DRS(N_DRS)).
In alternative 2, similar to the case in DCI format 1G, the BS
transmits data on REs other than the set of DRS REs indicated by
the set (DRS(i_DRS), . . . , DRS(i_DRS+N_L)). The MS will assume
that the BS data is mapped to the REs other than the set of DRS REs
indicated by the set (DRS(i_DRS), . . . , DRS(i_DRS+N_L)).
In alternative 3, the MS receives a cell-specific or MS-specific
switch configured by the BS using higher layers and denoted as
DRS_region_switch. If DRS_region_switch=0, then the MS assumes that
BS data is mapped to the REs other than the set of DRS REs
indicated by the set (DRS(1), . . . DRS(N_DRS)). On the other hand,
if DRS_region_switch=1, then the MS assumes that BS data is mapped
to the REs other than the set of DRS REs indicated by the index set
(DRS(i_DRS), . . . , DRS(i_DRS+N_L)).
Referring to FIG. 12, as a variation of format 1H, if up to two
codewords are used in the MU-MIMO, DCI format 2H is also proposed
in provisional application 61/206,597. As illustrated in FIG. 12,
the proposed DCI format 2H includes an HARQ field 1203, an N_L
field 1209, an N_DRS field 1211, an i_DRS field 1213 and other
fields 1201. The N_L field 1209, N_DRS field 1211 and i_DRS field
1213 are substantially the same as those proposed in DCI format 1H.
However, as illustrated in FIG. 12, there are two sets of MCS
fields 1205 and 1207, each corresponding to a given TB.
First Exemplary Embodiment
In a first exemplary embodiment of the present invention, an
alternative method is provided for use of DCI format 1E. More
specifically, an alternative BS-MS behavior for the case in which
the BS uses the DCI format 1E for SA when the MSs are configured in
MU-MIMO transmission mode is provided. In an exemplary
implementation, Frequency Division Multiplexing (FDM) or Time
Division Multiplexing (TDM) is used for the DRS pattern in a
wireless communication system. In another exemplary implementation,
Code Division Multiplexing (CDM) is used for the DRS pattern.
FIGS. 13A through 13C illustrate dual layer RS patterns for systems
using FDM, TDM, and CDM according to an exemplary embodiment of the
present invention.
Referring to FIG. 13A, RS patterns for a system using TDM signals
is illustrated. Referring to FIG. 13B, RS patterns for a system
using TDM/FDM signals are illustrated. Referring to FIG. 13C, RS
patterns for a system using CDM signals are illustrated.
If the DCI format 1E is used by the BS during SA for MU-MIMO
transmission, in the data to RE mapping step performed by the BS,
the BS transmits data on REs other than the set of all M DRS REs.
Upon receipt of the transmission, the MS assumes that the set of
DRS REs indicated by i_DRS are precoded using the same precoding
vector as the data layer, and therefore may be used as a
demodulation pilot for the data layer. The MS also assumes that the
BS data is mapped to the REs other than those used by all M DRSs,
where M is the maximum number of DRSs indicated by the higher layer
semi-statically. An exemplary implementation of this method is
illustrated below.
FIGS. 14A and 14B illustrate a downlink DRS pattern in a wireless
communication system according to an exemplary embodiment of the
present invention.
Referring to FIG. 14A, an MS#1 only sees DRS(1) as a pilot RE.
However, the data REs seen by MS#1 will exclude both DRS(1) and
DRS(2). Referring to FIG. 14B, MS#2 only sees DRS(2) as a pilot RE.
However, the data REs seen by MS#2 will exclude both DRS(1) and
DRS(2), as well as any CRS. In the illustrated example of FIGS. 14A
and 14B, the maximum number of DRSs (M) is 2 so that the results
are similar to those illustrated in the related art of FIG. 8.
However, the exemplary implementation of FIGS. 14A and 14B
illustrates use of DCI format 1E, rather than proposed DCI format
1F of FIGS. 8A and 8B. As shown above, DCI format 1E does not
include the field N_DRS as required in DCI format 1F and thus does
not require the additional overhead of DCI format 1F. Moreover, by
assuming that data is mapped to all REs other than those used by
the maximum number M of DRS REs, the MS is able to more efficiently
receive and demodulate the data.
In an exemplary implementation, the wireless communication system
may employ a CDM DRS pattern similar to that illustrated in FIG.
13C. If such a CDM pattern is applied, then both DRS(1) and DRS(2)
occupy the same set of REs. In this example, since M=2, both DRSs
are CDMed together. Therefore, the MS and BS behavior are
substantially the same as above, except that the MS needs to
process the additional step of de-spreading to determine a channel
estimate. To accomplish this, it is noted that in the DCI format
1E, the field i_DRS continues to indicate the index of DRS, while
in the case of CDM DRS (or hybrid CDM/FDM(DRS)) the i_DRS also
indicates the spreading Walsh code being used by the BS. Notably,
using i_DRS to indicate both DRS location and spreading code is
applicable for any of DCI formats 1E, 1F, 1G, 2G, 1H and 2H, as
long as a CDM or a hybrid CDM/FDM scheme is used.
As an example of the present invention, it is assumed that the DCI
format 1E is used by the BS during SA for MU-MIMO transmission, and
all M DRSs are using a CDM pattern as shown in FIG. 13C. In the
data to RE mapping performed by the BS during transmission, the BS
transmits data on REs other than the entire set of DRS REs. In
response, the MS assumes that the DRS is precoded using the same
precoding vector as the data layer, and spread onto the resources
according to the Walsh index indicated by i_DRS. Furthermore, the
MS will assume the BS data is mapped to the REs other than those
used by the entire set of M DRSs, where M is the maximum number of
DRS indicated by a higher layer semi-statically.
Second Exemplary Embodiment
In a second exemplary embodiment of the present invention, an
alternative method is provided for use of DCI format 1F in the case
of a hybrid CDM/FDM DRS pattern.
FIG. 15 illustrates a hybrid CDM/FDM DRS pattern according to an
exemplary embodiment of the present invention.
Referring to FIG. 15, DRS(1) and DRS(2) share the same first set of
REs using length 2 Walsh spreading, while DRS(3) and DRS(4) share
the same second set of REs also using length 2 Walsh spreading.
In an exemplary method according to the present invention, the MS
assumes that the DRS RE indicated by i_DRS is precoded using the
same precoding vector as the data layer, and therefore may be used
as a demodulation pilot for the data layer. In addition, in terms
of avoiding DRS RE in the data to RE mapping step performed by the
BS during transmission, the BS transmits data on REs other than the
sets of DRS REs indicated by (DRS(1), . . . , DRS(N_DRS)). Upon
receipt of the transmission from the BS, the MS will assume that
the BS data is mapped to the REs other than the DRS REs indicated
by the set (DRS(1), . . . DRS(N_DRS)).
Furthermore, since a hybrid CDM/FDM is assumed, the i_DRS in DCI
format 1F also indicates the spreading Walsh code used by the BS to
spread the i_DRS.
As another example, it is considered that four MSs are scheduled by
the BS, and that each MS has a rank-1 transmission. It is also
assumed that the DRS pattern in FIG. 15 is used by the system. In
this case, the MS#1-MS#4 have the following behavior: 1) Each MS
will assume that data REs do not include CRS or DRS REs; 2) For
MS#1 and MS#2, the first set of DRSs is used for demodulation,
whereas MS#1 will use Walsh code [1,1] to de-spread the first set
of DRS, while the MS#2 will use Walsh code [1,-1] to de-spread the
first set of DRS; and 3) For MS#3 and MS#4, the second set of DRS
is used for demodulation, whereas MS#3 will use Walsh code [1,1] to
de-spread the second set of DRS, while the MS#4 will use Walsh code
[1,-1] to de-spread the second set of DRS. Third Exemplary
Embodiment
FIGS. 16A and 16B illustrate a DCI format according to an exemplary
embodiment of the present invention.
Referring to FIG. 16A, DCI format 1F which includes an HARQ field
1603, an MCS field 1605, an N_DRS field 1607, an i_DRS field 1609,
and other fields 1601 is illustrated. Referring to FIG. 16B, a DCI
format according to an exemplary embodiment of the present
invention and here designated as DCI format 1F_a, includes an HARQ
field 1613, an MCS field 1615, an i_DRS field 1619 and other fields
1611. In distinction from DCI format 1F, DCI format 1F_a does not
include an N_DRS field and introduces a new field. More
specifically, in DCI format 1F_a, the N_DRS field proposed in DCI
format 1F, is replaced with a field that indicates the total number
of DRS sets (N_SET) 1617 used in the transmission of a
sub-frame.
According to an exemplary implementation using DCI format 1F_a, in
each set, CDM is used to multiplex N_SF DRSs, where N_SF denotes
the spreading length. For a hybrid CDM/FDM DRS pattern such as
illustrated in FIG. 15, using the N_SET field reduces the number of
bits used in the DCI format 1F_a as compared to use of the N_DRS
field. For example, as illustrated FIG. 15, only two states of
N_SET are needed. That is, N_SET may have a state in which N_SET=1
(indicating only the first set of DRSs is used) or N_SET=2
(indicating both sets of DRSs are used). Because there are only two
states, the state status can be reflected with only a single bit in
DCI format 1F_a. In contrast, the N_DRS field of DCI format 1F must
reflect four possible states (i.e., N_DRS=1, 2, 3, 4), which
requires 2 bits to reflect the N_DRS state status in DCI format 1F.
Accordingly, use of DCI format 1F_a reduces overhead when
transmitting control information.
In alternative exemplary embodiments, other DCI formats, such as 1H
and 2H, may replace the N_DRS field with the N_SET field of the
present invention.
Fourth Exemplary Embodiment
FIGS. 17A and 17B illustrate a DCI format according to an exemplary
embodiment of the present invention.
Referring to FIG. 17A, DCI format 1D which includes an MCS field
1703, a Transmitted Precoding Matrix Indicator (TPMI) field 1705, a
Downlink power offset field 1707, and other fields 1701 is
illustrated. Referring to FIG. 17B, the DCI format according to an
exemplary embodiment of the present invention and here designated
as DCI format 1F_b, includes an MCS field 1711, a Downlink power
offset field 1715, and other fields 1709. In distinction from DCI
format 1D, DCI format 1F_b does not include a TPMI field and
introduces a field regarding the index of the DRS (i_DRS) 1713 used
in this transmission. The i_DRS field 1713 is similar to the i_DRS
field illustrated as above with reference to proposed DCI formats
1E, 1F, and 1G. The bitwidth of the i_DRS field 1713 depends on the
maximum number of DRSs allowed in MU-MIMO. This maximum allowed DRS
number, denoted by M, is either fixed in the standard or signaled
by the base station as a cell-specific value. Therefore, the
bitwidth of the i_DRS field 1713 is .left brkt-top. log.sub.2
M.right brkt-bot..
Referring to FIG. 17B, the DCI format 1F_b is designed for
supporting up to two MSs in MU-MIMO mode. More specifically, DCI
format 1F_b uses the field of "Downlink Power Offset" found in DCI
format 1D to also represent the total number of DRS used in the
transmission. That is, the DCI format 1F_b uses the field of
"Downlink Power Offset" to remove the necessity of using the N_DRS
field in DCI Format 1F.
Table 1 illustrates use of the existing "Downlink Power Offset"
field to indicate both the power offset and the number of DRSs in
format 1F_b.
TABLE-US-00001 TABLE 1 Downlink Power Number of DRSs used in Offset
field this sub-frame (N_DRS) .delta..sub.power-offset [dB] 0 2
-10log.sub.10(2) 1 1 0
According to an exemplary implementation, the BS and MS behavior
when using DCI format 1F_b remains substantially the same as when
using DCI format 1F, except for the additional step that the BS and
MS both use the "Downlink Power Offset" field to jointly indicate
the number of DRS and the power offset.
More specifically, once an MS receives Downlink Power Offset and
i_DRS, it determines an associated number of DRSs (i.e., N_DRS)
used in the subframe based on the Downlink Power Offset value. The
MS expects that the set of DRSs (i.e., DRS(1), DRS(2) . . .
DRS(N_DRS)) is used for transmitting data to multiple users in this
sub-frame. In addition, the MS expects DRS(i_DRS) is used as a
reference signal to demodulate its own data. The MS also assumes
that the DRS RE indicated by i_DRS is precoded using the same
precoding vector as the data layer and can therefore be used as a
demodulation pilot for the data layer.
Using the Downlink Power Offset field, the BS also determines an
associated number of DRSs (i.e., N_DRS) used in the subframe based
on the Downlink Power Offset value. Once the N_DRS is determined
based on the Downlink Power Offset field, during an SA for MU-MIMO
transmission, in terms of avoiding DRS REs in the data to RE
mapping step of BS transmission, there are at least three
alternatives.
In alternative 1, the BS transmits data on REs other than the sets
of DRS REs indicated by (DRS(1), . . . , DRS(N_DRS)). At the MS,
the MS will assume the BS data is mapped to the REs other than the
set of DRS REs indicated by the set (DRS(1), . . . DRS(N_DRS)).
In alternative 2, similar to the actions regarding transmission of
DCI format 1D, the BS transmits data on REs other than the set of
DRS REs indicated by the index i_DRS. At the MS, the MS will assume
the BS data is mapped to the REs other than the set of DRS REs
indicated by the index i_DRS.
In alternative 3, the MS receives a cell-specific or MS-specific
switch, configured by the BS using higher layers, denoted by
DRS_region_switch. In this case, if DRS_region_switch=0, then the
MS assumes that the BS data is mapped to the REs other than the set
of DRS REs indicated by the set (DRS(1), . . . DRS(N_DRS)). On the
other hand, if DRS_region_switch=1, then the MS assumes that the BS
data is mapped to the REs other than the set of DRS REs indicated
by the index DRS(i_DRS).
Fifth Exemplary Embodiment
In an exemplary embodiment of the present invention, an improved
method for controlling downlink power is provided.
Section 5.2 of 3GPP TS 36.213 addresses downlink power allocation
for physical layers in an evolved wireless communication system.
This section is noted herein as providing background to assist in
understanding exemplary aspects of the present invention.
As stated in section 5.2, the BS determines the downlink transmit
energy per RE. An MS may assume that downlink cell-specific RS
Energy Per Resource Element (EPRE) is constant across the downlink
system bandwidth and constant across all sub-frames until different
CRS power information is received. The downlink reference-signal
EPRE can be derived from the downlink reference-signal transmit
power given by the parameter Reference-Signal-Power provided by
higher layers. The downlink reference-signal transmit power is
defined as the linear average over the power contributions (in [W])
of all resource elements that carry CRSs within the operating
system bandwidth.
The ratio of PDSCH EPRE to CRS EPRE among PDSCH REs (not applicable
to PDSCH REs with zero EPRE) for each OFDM symbol is denoted by
either .rho..sub.A or .rho..sub.B according to the OFDM symbol
index as given by Table 5.2-2 [reproduced here as Table 2]. In
addition, .rho..sub.A and .rho..sub.B are MS-specific.
TABLE-US-00002 TABLE 2 OFDM symbol OFDM symbol indices within a
slot indices within a slot where the ratio of the where the ratio
of the corresponding PDSCH corresponding PDSCH EPRE to the CRS EPRE
to the CRS EPRE is denoted by .rho..sub.A EPRE is denoted by
.rho..sub.B Number of Normal Extended Normal Extended Antenna
Cyclic Cyclic Cyclic Cyclic Ports Prefix Prefix Prefix Prefix One
or Two 1, 2, 3, 5, 6 1, 2, 4, 5 0, 4 0, 3 Four 2, 3, 5, 6 2, 4, 5
0, 1, 4 0, 1, 3
The MS may assume that, for 16 Quadrature Amplitude Modulation
(QAM), 64 QAM, spatial multiplexing with more than one layer, or
for PDSCH transmissions associated with the MU-MIMO transmission
scheme, .rho..sub.A is equal to .delta..sub.power-offset+P.sub.A+10
log.sub.10(2) [dB] when the MS receives a PDSCH data transmission
using precoding for transmit diversity with 4 cell-specific antenna
ports according to Section 6.3.4.3 of 3GPP TS 36.211, and
.rho..sub.A is equal to .delta..sub.power-offset+P.sub.A [dB]
otherwise, where .delta..sub.power-offset is 0 dB for all PDSCH
transmission schemes except MU-MIMO and where P.sub.A is an MS
specific parameter provided by higher layers.
If DRSs are present in an RB, the ratio of PDSCH EPRE to DRS EPRE
for each OFDM symbol is equal. In addition, the MS may assume that
for 16QAM or 64QAM, this ratio is 0 dB.
The cell-specific ratio .rho..sub.B/.rho..sub.A is given by Table
5.2-1 [reproduced here as Table 3] according to cell-specific
parameter P.sub.B signaled by higher layers and the number of
configured BS cell specific antenna ports.
TABLE-US-00003 TABLE 3 .rho..sub.B/.rho..sub.A P.sub.B One Antenna
Port Two and Four Antenna Ports 0 1 5/4 1 4/5 1 2 3/5 3/4 3 1/2
For PMCH with 16QAM or 64QAM, the MS may assume that the ratio of
PMCH EPRE to Multicast Broadcast Single Frequency Network (MBSFN)
RS EPRE is equal to 0 dB.
Section 7.1.5 of 3GPP TS 36.213 addresses a procedure for receiving
the PDSCH in a system using a MU-MIMO scheme.
As stated in section 7.1.5, for the multi-user MIMO transmission
scheme of the PDSCH, the MS may assume that a BS transmission on
the PDSCH would be performed on one layer and according to Section
6.3.4.2.1 of 3GPP TS 36.211. The .delta..sub.power-offset dB value
signaled on PDCCH with DCI format 1D using the downlink power
offset field is given in Table 7.1.5-1 (reproduced here as Table
4).
TABLE-US-00004 TABLE 4 Downlink Power Offset field
.delta..sub.power-offset [dB] 0 -10log.sub.10(2) 1 0
As illustrated in the above discussion regarding sections 5.2 and
7.1.5 of 3GPP TS 36.213, the value of .delta..sub.power-offset is
determined as either 0 or -10 log.sub.10(2) depending on the value
of the "Downlink Power Offset" field. In the fifth exemplary
embodiment of the present invention, an alternative method for
determining the value of .delta..sub.power-offset is provided. More
specifically, the value of .delta..sub.power-offset is determined
as: .delta..sub.power-offset[dB]=-10 log.sub.10(N_DRS) Eq. (1)
In Equation (1), N_DRS indicates the total number of DRSs in the
scheduled band. By using Eq. (1), the value of
.delta..sub.power-offset will more accurately reflect situations in
which there are three or more DRSs in a scheduled band. In an
exemplary implementation, Eq. (1) may be used for any DCI format
for MU-MIMO in which the total number of DRSs (which corresponds to
total number of layers) is included. For example, Eq. (1) may be
used with any of DCI format 1F, 1H, 2H, etc. where the field N_DRS
or N_L is provided.
Sixth Exemplary Embodiment
In an exemplary embodiment of the present invention, a relationship
for the power ratio between the data RE (per layer) and the DRS RE
(per-layer), denoted as .gamma., is provided. As will be evidenced
below, while the power ratio .gamma. is applicable to all
modulations, it is particularly applicable for 16QAM and 64QAM
modulations. Moreover, the power ratio .gamma. is applicable to
both Single User (SU)-MIMO and MU-MIMO operations.
FIG. 18 is a flowchart illustrating a method of determining a power
ratio .gamma. according to an exemplary embodiment of the present
invention.
Referring to FIG. 18, in step 1801, the MS determines the
multiplexing that is used for DRS signaling. That is, the MS
determines if either TDM or FDM, CDM, or a hybrid of CDM with TDM
or FDM is used. If it is determined in step 1801 that either TDM or
FDM is used for DRS signaling, the MS proceeds to step 1803 and
determines if N_DRS is known. That is, the MS determines if the
field N_DRS is provided in signaling received from the BS. If the
MS determines in step 1803 that the field N_DRS is known, then the
MS proceeds to step 1805 and sets the power ratio .gamma.[dB]=-10
log.sub.10(N_DRS). On the other hand, if the MS determines in step
1803 that the value of N_DRS is not known, then the MS proceeds to
step 1807 and determines if M is known. That is, the MS determines
if a value of M is provided from the BS in the DCI signaling or
otherwise. If it is determined in step 1807 that the value of M is
known, then the MS proceeds to step 1809 and sets the power ratio
.gamma.[dB]=-10 log.sub.10(M). Alternatively, if it is determined
in step 1807 that the value of M is not known by the MS, the MS
proceeds to step 1811 and sets the power ratio .gamma.[dB]=0 dB. In
an alternative exemplary implementation, the BS may set the power
ratio of .gamma.[dB]=0 dB despite that the values of N_DRS and M
are known. In that case, the BS would provide information regarding
the power ratio .gamma.[dB]=0 dB to the MS.
If it is determined in step 1801 that DRS signaling is made using
pure CDM, that is, all DRS are CDMed together in the same set of
REs, then the MS proceeds to step 1811 and sets the power ratio
.gamma.[dB]=0 dB.
Lastly, if it is determined in step 1801 that DRS signaling is made
using a hybrid of CDM and either FDM or TDM, for example as
illustrated in FIG. 15, the MS proceeds to step 1813 and determines
if N_DRS is known. That is, the MS determines if the field N_DRS is
provided in signaling received from the BS. If it is determined in
step 1813 that the value of N_DRS is known, the MS sets the power
ratio .gamma.[dB]=-10 log.sub.10(N_DRS)+10 log.sub.10(N_SF),
wherein N_SF is the Walsh code spreading length. On the other hand,
if it is determined in step 1813 that the value of N_DRS is not
known, the MS proceeds to step 1817 and determines if the value of
N_SET is known. If the value of N_SET is known to the MS, the MS
proceeds to step 1809 and sets the power ratio .gamma.[dB]=-10
log.sub.10(N_SET), wherein N_SET is number of CDMed set as
discussed above. On the other hand, if the value of N_SET is not
known, the MS proceeds to step 1811 and sets the power ratio
.gamma.[dB]=0 dB. In an alternative exemplary implementation, the
BS may set the power ratio of .gamma.[dB]=0 dB despite that the
values of N_DRS and N_SET are known. In that case, the BS would
provide information regarding the power ratio .gamma.[dB]=0 dB to
the MS. In yet another exemplary implementation as illustrated
below, for a transmission with odd rank, a combination of two
equations can be used to determine the power ratio .gamma.[dB].
FIGS. 19A through 19C illustrate a combination of two downlink
power control equations for a rank-3 transmission according to an
exemplary embodiment of the present invention
Referring to FIG. 19A, a first CDM DRS set that is allocated two
layers (L0 and L1) and a second CDM DRS that is allocated one layer
(L2) is illustrated. The use of different numbers of layers allows
for different power assignments for the CDM DRS of each level which
in turn allows for unequal error protection. For example, as
illustrated in FIG. 19A, each layer (L0 and L1) of the first CDM
DRS is allocated an EPRE value of P/2 whereas the layer (L2) of the
second CDM DRS is allocated an EPRE value of P. In an exemplary
implementation, the two layers (L0 and L1) of the first CDM DRS are
allocated power according to the equation .gamma.[dB]=-10
log.sub.10 (N_DRS)+10 log.sub.10(N_SF), whereas the single layer
(L2) of the second CDM DRS set uses the equation .gamma.[dB]=-10
log.sub.10 (N_SET). As illustrated in FIG. 19B, a first CDM DRS may
include a single layer (L0) which is allocated an EPRE of P, while
a second CDM DRS may include two layers (L1 and L2) which are
allocated an EPRE of P/2. Similarly to the example of FIG. 19A, the
two layers (L1 and L2) of the second CDM DRS may be allocated power
according to the equation .gamma.[dB]=-10 log.sub.10(N_DRS)+10
log.sub.10(N_SF), whereas the single layer (L)) of the first CDM
DRS may use the equation .gamma.[dB]=-10 log.sub.10(N_SET).
Finally, as illustrated in FIG. 19C, a CDM DRS may be allocated
three layers (L0, L1, and L2) such that each layer is allocated an
EPRE value of P/3.
In addition, if either N_DRS or N_SET in the DCI format is also
used for the purpose of indicting power offset, then the existing
field "Downlink Power Offset" may be removed.
While the invention has been shown and described with reference to
certain exemplary embodiments thereof, it will be understood by
those skilled in the art that various changes in form and details
may be made therein without departing from the spirit and scope of
the invention as defined by the appended claims and their
equivalents.
* * * * *